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1
Zhan, Rongrong. "Structural investigation of complex surface interfaces by means of X-ray Photoelectron Diffraction." Doctoral thesis, Università degli studi di Trieste, 2012. http://hdl.handle.net/10077/7447.
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2010/2011<br>The goal of this dissertation is to explain how the X-ray photoelectron diffraction technique can be successfully employed in the structural investigation of complex surface interfaces of ultra-thin films. Local geometrical analysis, combined with other techniques that gain additional electronic and surface morphological information to the system investigated, shed light on those extremely complicated surface atomic systems. These studies are aimed to contribute to the many interesting applications in fields like nano-electronics, surface coating and magnetic storage devices.<br>XXIV Ciclo<br>1982
2
Islam, Md Khairul. "TRANSFORMED TESTS FOR HOMOGENEITY OF VARIANCES AND MEANS." Bowling Green State University / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1150727264.
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3
Fransson, Thomas. "X-ray absorption spectroscopy by means of Lanczos-chain driven damped coupled cluster response theory." Thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-72460.
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A novel method by which to calculate the near edge X-rayabsorption fine structure region of the X-ray absorption spectrum has been derived and implemented. By means of damped coupled cluster theory at coupled cluster levels CCS, CC2, CCSD and CCSDR(3), the spectra of neon and methane have been investigated. Using methods incorprating double excitations, the important relaxation effects maybe taken into account by simultaneous excitation of the core electron and relaxation of other electrons. An asymmetric Lanczos-chain driven approach has been utilized as a means to partially resolve the excitation space given by the coupled cluster Jacobian. The K-edge of the systems have been considered, and relativistic effects are estimated with use of the Douglas--Kroll scalar relativistic Hamiltonian. Comparisons have been made to results obtained with the four-component static-exchange approach and ionization potentials obtained by the {Delta}SCF-method. The appropriate basis sets by which to describe the core and excited states have been been determined. The addition of core-polarizing functions and diffuse or Rydberg functions is important for this description. Scalar relativistic effects accounts for an increase in excitation energies due to the contraction of the 1s-orbital, and this increase is seen to be 0.88 eV for neon. The coupled cluster hierachy shows a trend of convergence towards the experimental spectrum, with an 1s -> 3p excitation energy for neon of an accuracy of 0.40 eV at a relativistic CCSDR(3) level of theory. Results obtained at the damped coupled cluster and STEX levels of theory, respectively, are seen to be in agreement, with a mere relative energy shift.
4
Heldt, Georg. "Arrays of magnetic nanostructures : a dynamical and structural study by means of X-ray experiments." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/arrays-of-magneticnanostructuresa-dynamical-and-structuralstudy-by-means-of-xrayexperiments(99302e83-f625-4c43-99c1-02b2576f0175).html.
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The work in this PhD thesis covers two strands of x-ray experiments: firstly, the characterisation of large arrays of dense structures by means of x-ray scattering, and, secondly, the investigation of hybrid anisotropy square structures with x-ray microscopy. The ability to accurately characterise large arrays of nanoscale magnetic structures is a key requirement for both scientific understanding and technological advance such as bit patterned recording media (BPM). In this work small angle x-ray scattering (SAXS) was investigated as a characterisation technique for large arrays of patterned structures. Dense arrays of magnetic nanostructures were prepared on x-ray transparent membranes and measured. The SAXS data was then modelled to obtain structure parameters such as the mean structure diameter, the diameter distribution and the mean position variance with statistical significance. Arrays (500 x 500 μm2) of nominally uniform nanostructures with centre-to-centre distances between 250 nm-50 nm were structurally characterised and compared to structure diameters obtained by optical scanning electron microscopy measurements. The mean structure diameter was found to be between 39 nm-15nm and agree within the errors with the diameter obtained from SEM measurements. This work provides accurate data on the distribution (variance) of nanostructure sizes which is key for modelling these arrays for applicationin BPM. In the second part of the work, the static and dynamic properties of patterned hybrid anisotropy square structures ([Co/Pd]-Py) were investigated by using time-resolved scanning transmission X-ray microscopy (STXM). In these patterned structures the magnetisation in the layers change both in magnitude and direction and gives rise to interesting new domain configurations. The reciprocal interaction between magnetic vortices in the Py layer and locally circular stripe domains in the Co/Pd was investigated and a mutual domain imprint between the layer was observed. In dynamic excitation experiments the precession of the vortex core is studied and showed good agreement with micromagnetic simulations made by Hrkac and Bryan. As demonstrated patterned hybrid anisotropy square structures have promising magnetic properties with potential applications in data storage (vortex switching) or spintronics (vortex oscillators).
5
Sakildien, Muneer. "Plasma characterisation of an electron cyclotron resonance ion source by means of x-ray spectroscopy." Thesis, University of the Western Cape, 2012. http://hdl.handle.net/11394/5212.
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>Magister Scientiae - MSc<br>The ultimate aim of any multiply-charged ion source, like the Electron Cyclotron Resonance Ion Source, ECRIS, is the production of multiply-charged ions, in sufficiently large quantities. These multiplycharged ions, in the case of the ECRIS, are created by a step-by-step ionisation process, whereby neutral atoms are ionised by energetic electrons. The goal of this thesis was to gain an understanding of the relative importance of various ECRIS parameters on the production of these energetic electrons. This was done by measuring the bremsstrahlung continuum emitted by the mirror confined plasma of an ECR ion source. The focus of our study was to investigate the influence of neutral pressure, incident microwave power and magnetic field configuration on spectral temperature and electron density of the warm electron population of the ECRIS plasma. The thesis begins by familiarising the reader with various aspects of plasma physics as it relates to the measurements. The measurements were done with a high-purity germanium detector and processed with the DGF Pixie-4 module. Analyses of the measured spectra were done with subroutines written in Root. From the measured result, it was concluded that by increasing the incident microwave power from 50 W to 300 W, the spectral temperature increases by 14.01% for helium plasma and 7.88% for argon plasma. Evidence of saturation of spectral temperature and electron density with increasing microwave power was also noticed, as reported by other groups investigating plasma bremsstrahlung. The increase of spectral temperature with neutral pressure was found to be considerable, increasing by 20.23% as the neutral pressure in the plasma chamber of the ECRIS was decreased. This increase in spectral temperature was accompanied by a 40.33% decrease in electron density, which led us to conclude that the increase in spectral temperature was most likely due to an increase in the mean free path of the electrons.
The influence of the magnetic field configuration on both spectral temperature and electron density was also investigated. During this investigation, one of the solenoid coil currents was increased, whilst keeping the other constant. This amounts to moving the plasma volume around axially in the plasma chamber of the ECRIS. This was found to significantly enhance the spectral temperature and this effect was attributed to more efficient heating of the electrons near the resonance zone. The electron density on the other hand was found to remain relatively constant, if one excludes the electron density as a result of one particularly setting of the solenoid coils. The decrease of electron density as a result of this particular setting of the solenoid coils enhanced the electron losses through the magnetic bottle. This is evidenced by the increase in photon counts as measured by our detector. The influence of neutral pressure, incident microwave power and magnetic field configuration on the extracted ion beam intensities was also investigated. This investigation led us to conclude that the mean charge state extracted increases with spectral temperature. This result was in agreement with those measured by other groups.
6
Lalechos, Antonios V. "Evaluation of X-ray CT tomography as a means for investigating in-situ electrical contact interfaces." Thesis, University of Southampton, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.536365.
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7
Fournet, Steven P. "High Resolution X-ray Diffraction Analysis of CB1 Receptor Antagonists as a Means to Explore Binding Affinity." ScholarWorks@UNO, 2013. http://scholarworks.uno.edu/td/1737.
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Abstract
Charge density studies have been conducted on ten CB1 cannabinoid receptor antagonists via high resolution x-ray crystallography. Bond critical point values and various other properties derived from these studies including the electrostatic potential were analyzed in correlation to the affinity of each compound with the CB1 receptor. Correlation/anti-correlation was found between several properties and Ki. The data was also interpreted by principal component analysis with three principal components accounting for 85% of the data variation. Data mining was limit due to the low sample count and the requirements set for the inclusion of correlated/anti-correlated variables left fewer variables to analyze. The model presented is left for future interpretation.
8
Schmacke, Saskia [Verfasser]. "Investigations of Polyethylene Materials by Means of X-ray Diffraction : artificial ageing of polyethylene gas pipes / Saskia Schmacke." Dortmund : Universitätsbibliothek Technische Universität Dortmund, 2011. http://d-nb.info/1011568497/34.
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9
Mercurio, Giuseppe [Verfasser]. "Study of molecule-metal interfaces by means of the normal incidence x-ray standing wave technique / Giuseppe Mercurio." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2012. http://d-nb.info/1028084870/34.
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10
HAIDE, Robert Christian. "Characterization of Multi-Phase Fluid Displacement in Porous Media during Drying by means of X-Ray Micro Computed Tomography." Doctoral thesis, Università degli studi di Bergamo, 2021. http://hdl.handle.net/10446/189681.
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Lo spostamento del fluido in mezzi porosi durante la lenta essiccazione in atmosfera controllata viene esplorato a livello dei pori, utilizzando la tecnica della micro tomografia computerizzata a raggi X. A tal fine, un corpo campione regolare, poroso e di dimensioni micro-metriche, che presenta una struttura dei pori e una bagnabilità predefinite, è concepito e prodotto sulla base di una serie di esperimenti preliminari. Dopo l’infusione con acqua distillata, viene studiato il comportamento di essiccazione del campione in atmosfera controllata. Successivamente viene definita e condotta una serie di esperimenti tomografici e vengono valutati i dati risultanti.
Un punto focale principale è l’ottimizzazione dell’intera catena del processo di acquisizione dei dati tomografici ad alta risoluzione. Questo include la preparazione del campione, la definizione dei parametri di scansione, gli approcci di ricostruzione, così come l’elaborazione e la segmentazione delle immagini. Un approccio sistematico in tutti questi settori fornisce una visione d’insieme delle lacune esistenti e delle potenzialità ancora non sfruttate della tomografia micro computata a raggi X come strumento per studiare i processi di essiccazione a livello dei pori.
Il secondo punto focale principale è la segmentazione dei dati e il contenuto informativo dei dati segmentati relativi agli eventi di spostamento dei fluidi a livello dei pori durante l’essiccamento.
I modelli di rete dei pori vengono estratti e trasmessi, in combinazione con i dati valutati, a progetti di ricerca correlati sulla simulazione e la visualizzazione per ulteriori usi e scopi di validazione.<br>Fluid displacement in porous media during slow drying in controlled atmosphere is explored on the pore-level, by using the technique of X-ray micro computed tomography. To this end, a regular, porous sample body of micro-metric dimensions, which exhibits a predefined pore structure and wettabilty, is conceived and produced on basis of a set of preliminary experiments. After infusion with distilled water, the drying behavior of the sample in a controlled atmosphere is investigated. Subsequently a set of tomographic experiments is defined and conducted, and the resulting data is evaluated.
One main focus point is set on the optimization of the whole process chain of acquiring high-resolution tomographic data. This includes the sample preparation, definition of scanning parameters, reconstruction approaches, as well as image processing and segmentation. A systematic approach in all of those domains provides insight into the existing shortcomings and the existing, as well as the yet untapped potential of X-ray micro computed tomography as a tool to investigate drying processes on the pore-level.
The second main focus point is set onto the segmentation of the data and the information content of the segmented data regarding pore-level fluid displacement events during drying.
Pore network models are extracted and relayed in combination with the evaluated data to related research projects on simulation and visualization for further usage and validation purposes.
11
Larsson, Emanuel. "Quantitative Analysis of Bone Tissue Engineering Scaffolds and Skull Bones by means of Synchrotron and Conventional X-ray Computed Microtomography." Thesis, Linköpings universitet, Teknisk biologi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-63196.
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The study of internal structure of materials has always been an essential issue in a variety of application fields, from the medical radiology to the materials science. X-ray computed microtomography (with both conventional and synchrotron radiation sources) has a great potential for these purposes because its three-dimensional and non destructive nature as well as the fact that it does not require any sample preparation and it allows to study samples under stress or after consecutive treatments. The recent developments of new X-ray sources with innovative imaging techniques, as well as novel high resolution detectors, allow moving forward the maximum achievable resolution of this technique to a few micrometers or even less. This contributed to increase its application in biomedical purposes, but also to raise the need for quantitative analysis of the reconstructed data. Indeed in most of the cases a quantitative characterization of the samples microstructures is needed to better understand their physical and chemical behavior, the effects of manufacturing process or the response to stress. Dedicated software packages have been developed to perform a geometrical and morphological characterization of the samples texture and to evaluate some typical parameters commonly used to classify porous media such as porosity, cell size distribution, connectivity and anisotropy. In this work two case studies have been considered for the application of a quantitative analysis approach to microtomography datasets: the first concerns the characterization of bone ingrowth within tissue engineering scaffolds, while the second is related to the extraction of morphological descriptors for the architecture of human skull bones. It will be shown how suitable image processing and analysis techniques are able to effectively quantify significant parameters such as the trabecular thickness of the skull bones as well as the porosity and the degree of connectivity of bone tissue engineering scaffolds. Similar quantitative analysis methods applied to microtomography images have to be considered as an effective methodology for a comprehensive characterization of other biomedical samples.
12
PINTO, OLIVIA WOYAMES. "METROLOGICAL EVALUATION AND INTERLABORATORY COMPARISON OF THE MEASUREMENT TECHNIQUE OF SULFUR IN DIESEL OIL BY MEANS OF X-RAY FLUORESCENCE." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2003. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=4390@1.
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Os compostos de enxofre estão presentes em todos os
derivados de petróleo bruto. Para o meio ambiente, dois
poluentes resultantes da queima do óleo diesel são
considerados críticos, o material particulado (MP) e os
óxidos de nitrogênio. Sendo que o primeiro tem relação
direta com o teor de enxofre no óleo diesel e a presença do
segundo nos gases de escapamento tem relação primordial com
o projeto de motor. Daí a importância do monitoramento do
teor de enxofre em óleo diesel, cuja qualidade e a
rastreabilidade de medição foi verificada em seis
laboratórios do Rio de Janeiro através de uma participação
em um Programa de Comparação Interlaboratorial. Houve a
necessidade de enquadramento da técnica de medição de
enxofre por fluorescência de raios-x (FRX) baseado na norma
ASTM D 2622-98 em cumprimento aos requisitos da ABNT
ISO/IEC 17025, a qual especifica a competência para a
realização de ensaios e/ou calibrações. O objetivo deste
trabalho foi realizar uma análise metrológica do ensaio de
determinação do teor de enxofre em óleo diesel por
fluorescência de raios-x. Foram utilizados como parâmetros
de desempenho, a faixa de trabalho, a linearidade, o limite
de detecção e de quantificação, a exatidão, a
repetitividade, a reprodutibilidade e a incerteza de
medição. Nesta análise metrológica foi observado que o uso
de material de referência certificado e os parâmetros de
desempenho no limite de 95,45 por cento de confiança apresentaram
resultados compatíveis com a metodologia. Quanto ao
desempenho no ensaio de proficiência dos laboratórios
participantes, o programa orientou-os na identificação de
erros não detectados pelo próprio laboratório, propiciando
o aprimoramento das técnicas analíticas, melhoria na
qualidade das medições e maior confiabilidade dos
resultados obtidos.<br>Sulfur compounds are among the components of most crude
oils and their products. When burning diesel fuel, two main
pollutants are discharged into the atmosphere. Particulate
matter (PM) is directly related to the amount of the sulfur
content in the diesel fuel. Nitrogen oxides in the exhaust
gases are a direct function of the engine design and
operating conditions. It is therefore important to monitor
the sulfur content of the diesel fuel. In this
dissertation, its measurement quality and traceability
were determined when comparing the results obtained by six
laboratories, which are operating in the state of Rio de
Janeiro. The x-ray fluorescence (XRF) sulfur measurement
technique, as described by the ASTM D2622-98 standard, was
used by all the laboratories in this intercomparison
program, which was conducted following the ABNT ISO/IEC
17025 standard. The objective of this work is thus to
perform a metrological evaluation of the sulfur content in
the diesel fuel through the x-ray fluorescence technique.
Working range, linearity, resolution, accuracy,
repeatability, reproducibility and measurement uncertainty
are the parameters used for the performance evaluation, as
referred to the 95,45 percent confidence level. The metrological
evaluation showed that the use of a certified reference
material, together with the performance evaluation
parameters, produced results, which were compatible with
the used methodology. This intercomparison program also
helped the laboratories to identify nonpreviously detected
measurement errors, thus improving the measurement quality
and reliability in the analytical technique.
13
Boubnov, Alexey [Verfasser], and J. D. [Akademischer Betreuer] Grunwaldt. "Structural studies on iron-based exhaust gas catalysts by means of X-ray absorption spectroscopy / Alexey Boubnov. Betreuer: J.-D. Grunwaldt." Karlsruhe : KIT-Bibliothek, 2014. http://d-nb.info/1073204839/34.
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14
Syha, Melanie [Verfasser]. "Microstructure evolution in strontium titanate : investigated by means of grain growth simulations and x-ray diffraction contrast tomography experiments / Melanie Syha." Karlsruhe : KIT Scientific Publishing, 2014. http://www.ksp.kit.edu.
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15
Syha, Melanie [Verfasser], and P. [Akademischer Betreuer] Gumbsch. "Microstructure evolution in strontium titanate Investigated by means of grain growth simulations and x-ray diffraction contrast tomography experiments / Melanie Syha. Betreuer: P. Gumbsch." Karlsruhe : KIT-Bibliothek, 2014. http://d-nb.info/1050767578/34.
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16
Abdullahi, Sahra [Verfasser], Hans [Akademischer Betreuer] Pretzsch, Thomas [Gutachter] Knoke, Hans [Gutachter] Pretzsch, and Mathias [Gutachter] Schardt. "Detection and definition of forest structure types by means of radar remote sensing (TanDEM-X) / Sahra Abdullahi ; Gutachter: Thomas Knoke, Hans Pretzsch, Mathias Schardt ; Betreuer: Hans Pretzsch." München : Universitätsbibliothek der TU München, 2018. http://d-nb.info/1187443867/34.
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17
Bjurenfalk, Jonatan, and August Johnson. "Automated error matching system using machine learning and data clustering : Evaluating unsupervised learning methods for categorizing error types, capturing bugs, and detecting outliers." Thesis, Linköpings universitet, Programvara och system, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-177280.
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For large and complex software systems, it is a time-consuming process to manually inspect error logs produced from the test suites of such systems. Whether it is for identifyingabnormal faults, or finding bugs; it is a process that limits development progress, and requires experience. An automated solution for such processes could potentially lead to efficient fault identification and bug reporting, while also enabling developers to spend more time on improving system functionality. Three unsupervised clustering algorithms are evaluated for the task, HDBSCAN, DBSCAN, and X-Means. In addition, HDBSCAN, DBSCAN and an LSTM-based autoencoder are evaluated for outlier detection. The dataset consists of error logs produced from a robotic test system. These logs are cleaned and pre-processed using stopword removal, stemming, term frequency-inverse document frequency (tf-idf) and singular value decomposition (SVD). Two domain experts are tasked with evaluating the results produced from clustering and outlier detection. Results indicate that X-Means outperform the other clustering algorithms when tasked with automatically categorizing error types, and capturing bugs. Furthermore, none of the outlier detection methods yielded sufficient results. However, it was found that X-Means’s clusters with a size of one data point yielded an accurate representation of outliers occurring in the error log dataset. Conclusively, the domain experts deemed X-means to be a helpful tool for categorizing error types, capturing bugs, and detecting outliers.
18
Larsson, Emanuel. "Evaluation of the Dual-Modal usage of contrast agents by means of Synchrotron X-ray Computed Microtomography and Magnetic Resonance Imaging using Macrophages loaded with Barium Sulfate and Gadolinium Nanoparticles for Detection and Monitoring in Animal Disease Models." Doctoral thesis, Linköpings universitet, Molekylär ytfysik och nanovetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-122607.
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¨This thesis focuses on evaluating the dual-modal Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) capabilities of contrast agents. For such purposes a gadolinium based contrast agent is of high interest, due to its paramagnetic properties, which while present inside a magnetic field will hence interact with the protons spins of water (in tissue and fat) and shorten their the T1 relaxation time, thereby creating a positive image contrast in MRI. Furthermore, the X-ray Mass Attenuation Coefficient (MAC) of gadolinium is relatively high, thus suggesting its potential use, also as a CT contrast agent. Gadolinium nanoparticles (GdNPs) can be loaded into cells, such as macrophages, which offers the possibility to track cells inside entire organisms. In the first step the uptake of GdNPs inside cells was investigated, together with a test for toxicity. To show the potential of using GdNP loaded macrophages for functional imaging of inflammation, an acute allergic airway inflammation mouse model (mimicking asthma in humans) was used and analyzed by in-situ synchrotron phase contrast CT. In the first step this approach was evaluated using macrophages loaded with a clinical contrast agent containing barium sulphate (BaSO4), since this agent is known to provide high contrast in CT. In the ultimate step a combination of both BaSO4 and GdNP loaded macrophages was used in the same asthmatic mouse model and analyzed by dual modal Synchrotron phase contrast CT and Micro Magnetic Resonance Imaging (μ-MRI). Complementary results in terms of the biodistribution of injected macrophages could only be obtained by the combination of both synchrotron phase contrast CT and μ-MRI, where the first modality allows a detailed localization of clustered BaSO4 loaded macrophages, but fails to detect single macrophages, which could instead be indirectly observed by μ-MRI as an increase of the T1-contrast, coming from the soft tissue of mice injected with GdNP loaded macrophages.
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LARSSON, MARCUS EMANUEL. "Evaluation of the Dual-Modal usage of contrast agents by means of Synchrotron X-ray Computed Microtomography and Magnetic Resonance Imaging using Macrophages loaded with Barium Sulfate and Gadolinium Nanoparticles for Detection and Monitoring in Animal Disease Models." Doctoral thesis, Università degli Studi di Trieste, 2015. http://hdl.handle.net/11368/2908060.
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Technical improvements of imaging devices during the last two decades
have led to the development of so called hybrid imaging modalities,
containing at least two different imaging modalities in the same
machine. Hybrid imaging allows the combination of multi-modal images
and the extraction of both complementary and synergistic information,
which is useful for more accurate and reliable diagnosis.
Within this framework there was an increased need for multi-modal
contrast agents. During the last decade development of multi-modal
contrast agents have hence received further attention.
Recent developments of X-ray based imaging techniques now also offers
imaging in other regimes, than standard absorption based imaging,
e.g. phase contrast imaging, which exploits the refraction and
phase-shift of the incident X-ray beam at tissue-interfaces. It has been
shown that phase contrast imaging is more sensitive than classical
clinical radiography, especially in soft-tissue applications, such as
mammography.
This thesis focuses on evaluating the dual-modal Computed Tomography
(CT) and Magnetic Resonance Imaging (MRI) capabilities of contrast
agents. For such purposes a gadolinium based contrast agent
is of high interest, due to its paramagnetic properties, which while
present inside a magnetic field will hence interact with the protons
spins of water (in tissue and fat) and shorten their the T1 relaxation
time, thereby creating a positive image contrast in MRI. Furthermore,
the X-ray Mass Attenuation Coefficient (MAC) of gadolinium is relatively
high, thus suggesting its potential use, also as a CT contrast
agent.
Gadolinium nanoparticles can be loaded into cells, such as macrophages,
which offers the possibility to track cells inside entire organisms.
In the first step the uptake of gadolinium nanoparticles inside
cells was investigated, together with a test for toxicity. To show the
potential of using gadolinium nanoparticle loaded macrophages for
functional imaging of inflammation, an acute allergic airway inflammation
mouse model (mimicking asthma in humans) was used and
analyzed by in-situ synchrotron phase contrast CT. This animal model
was chosen, since macrophages are one of the main effector cells in
asthma, where especially their ability to migrate is of crucial interest,
which up until now was not possible to study in-situ.
In the first step this approach was evaluated using macrophages loaded
with a clinical contrast agent containing barium sulphate, since
this agent is known to provide high contrast in CT. In the ultimate step
a combination of both barium sulphate and gadolinium nanoparticle
loaded macrophages was used in the same mouse model (mimicking
human asthma) and analyzed by dual modal Synchrotron phase contrast
CT and Micro Magnetic Resonance Imaging (-MRI).
Complementary results in terms of the biodistribution of injected
macrophages could only be obtained by the combination of both
synchrotron phase contrast CT and -MRI, where the first modality
allows a detailed localization of clustered barium sulphate loaded
macrophages, but fails to detect single macrophages, which could
instead be indirectly observed by -MRI as an increase of the T1-
contrast, coming from the soft tissue of mice injected with gadolinium
nanoparticle loaded macrophages.
In conclusion, the results obtained on cells
20
Simán, Frans Filip. "Assessment of Machine Learning Applied to X-Ray Fluorescence Core Scan Data from the Zinkgruvan Zn-Pb-Ag Deposit, Bergslagen, Sweden." Thesis, Luleå tekniska universitet, Geovetenskap och miljöteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-82050.
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Lithological core logging is a subjective and time consuming endeavour which could possibly be automated, the question is if and to what extent this automation would affect the resulting core logs. This study presents a case from the Zinkgruvan Zn-Pb-Ag mine, Bergslagen, Sweden; in which Classification and Regression Trees and K-means Clustering on the Self Organising Map were applied to X-Ray Flourescence lithogeochemistry data derived from automated core scan technology. These two methods are assessed through comparison to manual core logging. It is found that the X-Ray Fluorescence data are not sufficiently accurate or precise for the purpose of automated full lithological classification since not all elements are successfully quantified. Furthermore, not all lithologies are possible to distinquish with lithogeochemsitry alone furter hindering the success of automated lithological classification. This study concludes that; 1) K-means on the Self Organising Map is the most successful approach, however; this may be influenced by the method of domain validation, 2) the choice of ground truth for learning is important for both supervised learning and the assessment of machine learning accuracy and 3) geology, data resolution and choice of elements are important parameters for machine learning. Both the supervised method of Classification and Regression Trees and the unsupervised method of K-means clustering applied to Self Organising Maps show potential to assist core logging procedures.
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Moldón, Vara Francisco Javier. "Structure and nature of gamma-ray binaries by means of VLBI observations." Doctoral thesis, Universitat de Barcelona, 2012. http://hdl.handle.net/10803/96996.
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Gamma-ray binaries are extreme systems that produce non-thermal emission from radio to very-high-energy (above TeV) gamma rays, with the energy output in the spectral energy distribution (SED) dominated by the MeV–GeV photons. Their broadband emission is usually modulated by the orbital cycle of the system, which suggests that the physical conditions are also periodic and reproducible. The diversity of systems, together with the reproducibility of the conditions within each system, makes gamma-ray binaries excellent physical laboratories in which high energy particle acceleration, diffusion, absorption, and radiation mechanisms can be explored. Nevertheless, the number of known gamma-ray binaries is still very limited, and only a six binary systems have been classified as gamma-ray binaries. These systems produce outflows of relativistic particles emitting synchrotron radio emission that extend up to several astronomical units, which correspond to projected angular scales of a few milliarcseconds (mas) at typical distances of 2-3 kpc. Very Long Baseline Interferometry (VLBI) provide mas resolution and therefore can be used to directly see this radio outflow. In this thesis we present VLBI observations of five of the six gamma-ray binaries known. We have revealed for the first time the radio structure of two gamma-ray binaries, and found periodic changes in the structure of other two. Based on these results, we have established the basic properties and behaviour of the radio emission of gamma-ray binaries on AU scales, and we have contributed to find characteristics that are common to all of them.<br>En los últimos años se ha producido una mejora significativa de los instrumentos que permiten observar fenómenos astrofísicos en rayos gamma de alta y muy alta energía. Gracias a estos avances, se ha podido detectar emisión de rayos gamma en sistemas binarios. Tan sólo seis sistemas binarios han sido clasificados como estrellas binarias de rayos gamma (tres de ellos aún son candidatos). Estos sistemas producen chorros de material relativista que a su vez producen grandes cantidades de energía en todo el espectro electromagnético, desde ondas radio hasta emisión de rayos gamma hasta energías del teraelectronvolt (TeV). Estos chorros se desplazan a alta velocidad produciendo estructuras en escalas de varias unidades astronómicas (UA). Estas estructuras pueden ser observadas directamente mediante técnicas de interferometría radio de muy larga línea de base (VLBI). En esta tesis nos centramos en el estudio de las propiedades morfológicas y astrométricas de binarias de rayos gamma observadas mediante VLBI. De las seis binarias conocidas, se han observado cinco de ellas. Los resultados principales son los siguientes. Se ha detectado estructura extendida en escalas de 120 UA en el sistema binario PSR B1259-63. Esta ha sido la primera evidencia observacional de que púlsares jóvenes no acretantes interaccionando con estrellas jóvenes pueden producir emisión radio extendida. Se ha descubierto que la emisión del sistema LS 5039 muestra cambios periódicos en su morfología, que son estables en escalas de varios años. También se ha determinado el movimiento propio de este sistema y se ha obtenido su trayectoria galáctica en el pasado. Se ha confirmado que el sistema LS I +61 303 muestra variabilidad orbital periódica, aunque presenta cambios significativos en ciertas fases orbitales. Se ha encontrado un desplazamiento del pico de la emisión a varias frecuencias, así como un cambio en sus posiciones relativas. Se ha descubierto emisión extendida procedente de la fuente de rayos gamma HESS J0632+057, y se ha confirmado inequívocamente su asociación con el sistema binario MWC 148. Por último, no se ha encontrado contrapartida radio a la fuente de rayos gamma AGL 2241+4454, cuya contrapartida óptica ha sido propuesta en el sistema MWC 656. Estos resultados permiten sentar las bases de la estructura en escalas de varias UA de los sistemas binarios de rayos gamma, así como su comportamiento en función de la fase orbital. Las características comunes halladas en estos sistemas ha permitido encontrar enlaces observacionales entre estos sistemas, dando consistencia a este particular grupo de estrellas que presentan emisión en rayos gamma.
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Perry, Scott E. "Multienergetic external-beam PIXE as a means of studying the surface enrichment effect in coins /." Diss., CLICK HERE for online access, 2003. http://contentdm.lib.byu.edu/ETD/image/etd233.pdf.
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Mullan, Lorna A. "Stimulation of intracellular proteolytic degradation as a means of reducing ER stress in a model of skeletal dysplasia." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/stimulation-of-intracellular-proteolytic-degradation-as-a-means-of-reducing-er-stress-in-a-model-of-skeletal-dysplasia(b2bb722a-4c5b-4cae-8624-c83aeddd3d2a).html.
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MCDS is an autosomal dominant skeletal dysplasia disorder caused by mutations in collagen X. In most cases, mutations in collagen X result in a misfolded protein which is retained within the ER of hypertrophic chondrocytes, causing increased ER stress. It has previously been demonstrated that increased ER stress causes hypertrophic chondrocytes to de-differentiate in an attempt to avoid the stress. The altered differentiation results in reduced cell hypertrophy and impaired vascular invasion accounting for reduced bone growth. The presence of increased ER stress in hypertrophic chondrocytes is sufficient to cause the MCDS pathology; therefore reducing ER stress may be beneficial in terms of improving the associated pathology. The autophagy enhancing drug carbamazepine (CBZ) has been shown to be capable of reducing ER stress in cells expressing the MCDS-causing p.N617K collagen X mutation. I show in this thesis that CBZ treatment reduced ER stress in HeLa cells transiently expressing a further 3 MCDS-causing collagen X mutations. I have also demonstrated that CBZ treatment induced the degradation of mutant collagen X proteins either through autophagy or proteasomal degradation depending on the nature of the mutation. The drug was tested in vivo using the p.N617K collagen X mouse model of MCDS. In MCDS mice, CBZ reduced the severity of the disease pathology based on histological analyses, restored hypertrophic chondrocyte differentiation toward normal, increased long bone growth rates and decreased the severity of the hip dysplasia. Gene expression analyses on RNA isolated from microdissected hypertrophic chondrocytes revealed that CBZ shifted the pattern of hypertrophic differentiation markers in MCDS mice toward the wild-type pattern, most likely through its stimulation of gene expression associated with intracellular proteolytic pathways. The results presented in this thesis have contributed to the identification of a potential treatment strategy for MCDS- the stimulation of intracellular proteolysis of mutant collagen X. CBZ is FDA approved for the use of epilepsy and bipolar disorder and has a strong safety record in humans. Therefore CBZ could be a potential treatment strategy for MCDS.
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Dudziak, Lukasz. "Mitigating autogenous shrinkage of Ultra-High Performance Concrete by means of internal curing using superabsorbent polymers." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-224382.
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Application of smart curing concept called internal curing (IC) is the most promising strategy for mitigating autogenous shrinkage and related early-age cracking in cement-based materials with low water-to-cement ratio. There are still many theoretical and practical questions that need to be answered before IC could become a standard method. Many of these questions concern the most appealing of water-regulating additives for IC called Superabsorbent Polymers (SAP). The clear linkage between SAP material properties, the moment of water release and the effect on autogenous shrinkage is still missing, which blocks formulating recommendations for use of particular potential IC agents in concrete construction. In this treatise various aspects that are decisive for effectiveness of IC in mitigating autogenous shrinkage were examined. The choice of materials was purposefully limited to two compositions of Ultra-High Performance Concrete (UHPC), one fine-grained and one coarse-grained mixture, and one particular, in-depth characterized SAP. The objectives of examination which shaped the final experimental programme were: assessment of IC agent absorption capacity, specification of periods of water migration from fresh concrete mixture into SAP and from SAP back into hardening concrete, determination of effect of SAP addition on cement hydration, evaluation of IC influence on and determination of start of effective autogenous shrinkage and, finally, assessment of autogenous shrinkage with selfsame IC agent but for different matrices. Ideally, description of the mechanisms behind the action of IC at different stages of concrete life and reasoning of differences observed for the UHPCs under investigation had to be provided. First, the main components of the system – UHPC and SAP material – were characterized as to their suitability for IC application. Special attention was paid to the material properties which affect water transport. Usage of different testing methods was necessary here and included: testing with ESEM, FT-IR, tea-bag test, sol fraction content examination and X-ray computed tomography (for SAP) as well as air content measurement and various methods for characterization of the porosity and other features of the microstructure. The observed delay in the start of pozzolanic reactions in case of fine-grained UHPC was rather surprising, but, under consideration of porosity, shed new light on permeability of young UHPC. The work at hand revealed numerous methods that can be used for studying the absorption capacity of polymers, but hardly representative for the behaviour of those polymers within concrete matrix. Because of its general availability and the relatively robust testing procedure, it was decided to focus on possibilities and limitations of using tea-bag test for evaluation of absorption capacity of SAP. New interpretation of tea-bag test results was deduced which enabled assessment of maximum absorption capacity of SAP from measurement of consistency of concrete before and after modification with IC. Influence of IC on hydration process was revealed by using two non-destructive methods, in particular ultrasonic measurement and concrete temperature record. It could be shown that the ionic polymer exhibits complex effects including retardation and acceleration of individual chemical processes. Additionally, X-ray computed tomography (CT) and instrumented ring tests were performed in order to understand scientific significance of the characteristic event appearing during shrinkage measurements, taken as time-zero (= starting point for evaluation of autogenous shrinkage data). Linkage of time-zero with certain phenomenon, e.g., changes of the SAP particles volume or specific value of yield stress, but not with final set, was suggested for the future investigations. By using two setups based on corrugated tube protocol it was possible to register and compare autogenous shrinkage of both UHPCs without and with modification by IC. The effectiveness of IC was shown to be dependent on the matrix in which IC was implemented. This was related to the observed changes in pore percolation that resulted from different absorption behaviour of SAP in the two UHPCs under investigation. Furthermore, the effect of fibres on effectiveness of IC was discussed. Description and discussion of mechanisms behind IC was supported by measurement of capillary pressure, total shrinkage tests with simultaneous mass loss measurement, free autogenous shrinkage tests and the CT measurement. Valuable source of information was furthermore the in-depth literature review. The most appealing finding of the work and the biggest paradox revealed was high efficiency of IC in mitigating autogenous shrinkage and simultaneously appearance of stage where very clear reverse in mode of polymer volume change was observed. This suggests partial reabsorption of water initially released. This puts interpretation of operative shrinkage mechanisms and ones standing behind IC effect in a new perspective<br>Die innere Nachbehandlung (Internal Curing – IC) ist die derzeit aussichtsreichste Strategie, um das in zementgebundenen Baustoffen mit niedrigen Wasser/Zement-Werten ausgeprägt auftretende autogene Schwinden wirksam zu verringern und die damit einhergehende Rissbildung in jungem Beton zu vermeiden. Vor einer breiten baupraktischen Anwendung des IC sind noch viele offene Fragen zu beantworten. Die meisten dieser Fragen betreffen die derzeit interessanteste Klasse von wasserregulierenden Stoffen für das IC – die superabsorbierenden Polymere (SAP). Von entscheidender Bedeutung ist hier der noch weitgehend unerforschte Zusammenhang zwischen den Materialeigenschaften der SAP, dem Zeitpunkt der Wasserabgabe und der Auswirkung auf das autogene Schwinden. In der vorliegenden Arbeit werden verschiedene Einflussfaktoren auf die Wirksamkeit von SAP zur Verringerung des autogenen Schwindens untersucht. Für die Experimente wurde ein feinkörniger und ein grobkörniger ultra-hochfester Beton (UHPC) sowie ein schon detailliert charakterisiertes SAP genutzt. Das experimentelle Programm wurde auf folgende Untersuchungsziele ausgerichtet: Absorptionsvermögen der SAP, Zeitfenster der Wassermigration aus dem Frischbeton in das SAP sowie vom SAP in den erhärtenden Beton, autogenes Schwindmaß sowie effektiver Beginn des autogenen Schwindens. Ziel der Arbeiten ist die Beschreibung der Mechanismen, die IC zugrundliegen – und dies zu verschiedenen Betonaltern und unter Berücksichtigung der an den untersuchten UHPC beobachteten Unterschiede. Bei der Charakterisierung der Hauptkomponenten des betrachteten Systems – UHPC und SAP – wurde auf die Materialeigenschaften fokussiert, die den Wassertransport beeinflussen. Dazu wurden u. a. folgende Untersuchungsmethoden angewendet: ESEM, FT-IR, Teebeuteltest, Sol-Fraction Test, Röntgentomographie (für SAP) sowie verschiedene Verfahren zur Charakterisierung der Poren im Beton. Im feinkörnigen UHPC wurde überraschenderweise ein verzögerter Beginn der puzzolanischen Reaktion festgestellt, der bei Berücksichtigung der vorliegenden Porosität zu einer Neubewertung der Permeabilität von UHPC in jungem Alter führte. In der vorliegenden Arbeit werden verschiedene Methoden zur Beschreibung des Wasserabsorptionsvermögens von SAP benannt, deren Aussagekraft bei Anwendung dieser Polymere im Beton aber sehr eingeschränkt ist. Aufgrund seiner einfachen Verfügbarkeit und Robustheit wurde daher der Teebeutetest zur Bestimmung der Wasserabsorption des SAP genutzt. Die Wasserabsorption der SAP im Beton wurde durch Gegenüberstellung von Konsistenzmessungen am Beton vor und nach Zugabe von SAP und Ergebnissen der Teebeuteltest abgeschätzt. Der Einfluss des IC auf die Hydratation wurde zerstörungsfrei mit Ultraschall- und Betontemperaturmessungen erfasst. Auf dieser Grundlage konnten Hypothesen zu den komplexen Wechselwirkungen zwischen ionischem Polymer und der Beschleunigung oder Verzögerung einzelner chemischer Prozesse formuliert werden. Mit Hilfe von instrumentierten Ringversuchen und X-ray Computertomographie wurden die Auswirkungen des IC mit SAP auf das autogene Schwinden, den Aufbau von Zwangsspannungen bei behindertem Schwinden und Time-Zero diskutiert. Dabei konnte ein Zusammenhang zwischen Time-Zero und verschiedenen Phänomenen, wie z. B. Volumenänderung des SAP oder der Fließgrenze des erhärtenden Betons, nicht aber zum Ende des Erstarrens aufgezeigt werden. Das autogene Schwinden beider untersuchter UHPC (jeweils mit und ohne IC) wurde mit Hilfe von Corrugated Tube-Versuchen gemessen. Es konnte gezeigt werden, dass wie Wirksamkeit des IC von der Betonzusammensetzung sowie der in den UHPC infolge Wechselwirkungen mit den SAP verschieden ausgebildeten Porenstruktur der Matrix abhängt. Weiterhin konnte ein Einfluss von Faserzugaben auf die Wirksamkeit des IC gezeigt werden. Die Beschreibung und Diskussion der Mechanismen des IC wurde durch Messungen des Kapillardrucks, des Gesamtschwindens, des freien autogenen Schwindens, des Masseverlustes und Computertomographie unterstützt. Eine wichtige Erkenntnisquelle war zudem die umfangreich gesichtete und diskutierte Literatur. Das interessanteste und zugleich paradoxe Ergebnis der Untersuchungen ist die Tatsache, dass die bei Einsatz von SAP beobachtete Verringerung des autogenen Schwindens eindeutig mit einer zeitgleichen Umkehr der Volumenänderung der SAP einhergeht: die bis dahin dominierende Wasserabgabe geht in eine erneute Wasseraufnahme über. Dies stellt die Interpretation der Triebkräfte des Schwindens und die dem IC zugrundliegenden Mechanismen in einen neuen Zusammenhang
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Mahmoodabadi, Majid. "KOREAN ANTHRACITE COAL CLEANING BY MEANS OF DRY AND WET BASED SEPARATION TECHNOLOGIES." UKnowledge, 2015. http://uknowledge.uky.edu/mng_etds/18.
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Korean coals are typically high rank anthracite characterized by high ash content and difficult cleaning characteristics. The main objective of the study was to evaluate the feasibility of treating various size fractions within the coal using an assortment of physical coal cleaning technologies. Dry cleaning is preferred due to the friability of the coal. As such, three pneumatic processes were tested including Ore Sorting for the plus 10 mm material, Air Table Separation for 10 x 1 mm fraction and Tribo-electric Separator for - 1 mm fraction. The Dense Medium Cyclone is known to be one of the most efficient separation processes and thus was evaluated for the cleaning of 10 x 1 mm coal.
To realize the optimum performances from the Air Table and Rotary Tribo-electric Separator, their operational variables were systematically studied using a parametric experimental design. In addition, the dense medium cyclone and X-ray Transmission Sorting trials were performed under various medium densities and separation settings, respectively. A comparison of the cleaning performance revealed that the Dense Medium Cyclone and X-ray Transmission Sorting proved to provide the most effective results with maximum ash rejection and combustible recovery. The tribo-electric separation process was ineffective while the air table provided modest ash reduction potential.
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Lovstedt, Stephan P. "Improving Performance of the Filtered-X Least Mean Square Algorithm for Active Control of Noise Contatining Multiple Quasi-Stationary Tones." Diss., CLICK HERE for online access, 2008. http://contentdm.lib.byu.edu/ETD/image/etd2290.pdf.
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Aleksandrovienė, Aušra. "Kineziterapijos priemonių efektyvumo nustatymas sergantiems juveniline stuburo osteochondropatija." Master's thesis, Lithuanian Academic Libraries Network (LABT), 2005. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2005~D_20050518_084859-84354.
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THEME: Kinesitherapy means effectiveness determination for ill with juvenile spinal column osteochondropathy.
THE WORK CARRIED OUT: Ausra Aleksandroviene.
THE WORK SUPERVISOR: ass. prof. Dr. P.Zachovajevas
THE AIM OF THE WORK: to determine the most effective kinesitherapy means out of those which were applied PC Silainiai polyclinic kinesiotherapy consulting-room visiting patients ill with juvenile spinal column osteochondropathy.
TASKS:
1. To determine kinesitherapy means impact on children's general
balance.
2. To determine kinesitherapy means impact on children's flexibility.
3. To determine kinesitherapy means impact on the abdomen, back,
waist muscles endurance power.
4. To determine kinesitherapy means impact on aerobic working
capacity .
SUMMARY:
Many people have back pains. The reasons of these pains are different, they are caused by various diseases. One of the most met diagnosis of late - juvenile spinal column osteochondropathy which has several names - they are juvenile ciphosis or Schojerman - Mau disease. This disease has a property to become chronic, to cause various complications, lasts more than one year. Due to early diagnostics the first symptoms of the disease are found out though many have no complaints. The inveteracy of the disease has impact on human self-feeling, cause muscles and nerves pain, decrease working capacity.
The spinal column injuries and diseases determination complexity is related to this that up till now practically there is no healthy... [to full text]
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Spencer, Benjamin. "On-line C-arm intrinsic calibration by means of an accurate method of line detection using the radon transform." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAS044/document.
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Les ``C-arm'' sont des systémes de radiologie interventionnelle fréquemment utilisés en salle d'opération ou au lit du patient. Des images 3D des structures anatomiques internes peuvent être calculées à partir de multiples radiographies acquises sur un ``C-arm mobile'' et isocentrique décrivant une trajectoire généralement circulaire autour du patient. Pour cela, la géométrie conique d'acquisition de chaque radiographie doit être précisément connue. Malheureusement, les C-arm se déforment en général au cours de la trajectoire. De plus leur motorisation engendre des oscillations non reproductibles. Ils doivent donc être calibrés au cours de l'acquisition. Ma thèse concerne la calibration intrinsèque d'un C-arm à partir de la détection de la projection du collimateur de la source dans les radiographies.Nous avons développé une méthode de détection de la projection des bords linéaires du collimateur. Elle surpasse les méthodes classiques comme le filtre de Canny sur données simulées ou réelles. La précision que nous obtenons sur l'angle et la position (phi,s) des droites est de l'ordre de: phi{RMS}=+/- 0.0045 degrees et s{RMS}=+/- 1.67 pixels. Nous avons évalué nos méthodes et les avons comparés à des méthodes classiques de calibration dans le cadre de la reconstruction 3D<br>Mobile isocentric x-ray C-arm systems are an imaging tool used during a variety of interventional and image guided procedures. Three-dimensional images can be produced from multiple projection images of a patient or object as the C-arm rotates around the isocenter provided the C-arm geometry is known. Due to gravity affects and mechanical instabilities the C-arm source and detector geometry undergo significant non-ideal and possibly non reproducible deformation which requires a process of geometric calibration. This research investigates the use of the projection of the slightly closed x-ray tube collimator edges in the image field of view to provide the online intrinsic calibration of C-arm systems.A method of thick straight edge detection has been developed which outperforms the commonly used Canny filter edge detection technique in both simulation and real data investigations. This edge detection technique has exhibited excellent precision in detection of the edge angles and positions, (phi,s), in the presence of simulated C-arm deformation and image noise: phi{RMS} = +/- 0.0045 degrees and s{RMS} = +/- 1.67 pixels. Following this, the C-arm intrinsic calibration, by means of accurate edge detection, has been evaluated in the framework of 3D image reconstruction
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Hall, Edward John. "The influence of occasion on consumer choice: an occasion based, value oriented investigation of wine purchase, using means-end chain analysis." Title page, contents and abstract only, 2003. http://web4.library.adelaide.edu.au/theses/09PH/09phh1756.pdf.
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Includes list of Supplementary refereed publications relating to thesis; and of Refereed conference papers, as appendix 1 Includes bibliograhical references (p. 316-343) Focusses particularly on the purchase of wine and the factors that influence consumer choice and the values that drive the decision process across different consumption occasions. The effectiveness of occasion as part of the theoretical model of means-end chain analysis is investigated, as well as the feasibility of occasion in the Olsen and Thach (2001) conceptual framework of consumer behavior relating to wine.
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Tant, Joseph. "The influence of second phases on the microstructural evolution and the mechanical properties of geological materials." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/the-influence-of-second-phases-on-the-microstructural-evolution-and-the-mechanical-properties-of-geological-materials(d51de894-09a3-413e-adf7-ca2dc7788ced).html.
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Polycrystalline geological materials are not normally single phase materials and commonly contain second phases which are known to influence the grain size and mechanical properties of bulk material. Despite the well documented significance of second phases, there are relatively few detailed systematic experimental studies of the effect of second phases on isostatic high temperature grain growth in geological materials. Grain growth is a process that is fundamental to our understanding of how rocks behave in the lower crust / upper mantle where grain size is considered to play an important role in the localization of deformation in addition to determining the strength of materials at these pressure and temperature conditions. Furthermore, the effect that the spatial distribution and grain size of the second phases have on the mechanical properties of rocks is generally acknowledged, but it is not well constrained. Spatial variation is particularly significant in geological systems where a strength contrast exists between phases. With these two things in mind, a two-part study is presented in which the influence of a pore second phase on the microstructural evolution of halite during grain growth (Part I), and the influence of a calcite second phase on the mechanical behaviour of two phase calcite + halite aggregates (Part II), is investigated. In Part I, high temperature (330 °-600 °C), high confining pressure (200 MPa) isostatic grain growth experiments were carried out on 38-125 μm reagent grade halite (99.5%+ NaCl) powder over durations of 10 secs up to 108 days. After hot-pressing, the halite displays a foam texture. Some porosity remained along the grain boundaries, the size and distribution of which appears to impact significantly on the resulting grain size, growth mechanism and kinetics of halite grain growth. Halite grain growth was found to be well described by the normal grain growth equation: d^(1/n)-d0^(1/n)=k0(t-t0)exp(-H/RT) where t is the duration of the growth period, t0 is the time at which normal growth begins, d is the grain size, d0 is the grain size at t0, k0 is a constant, H is the activation enthalpy for the growth controlling process, R is the universal gas constant,T is temperature and n is a growth constant. At 330 °-511 °C, the data is best described by n = 0.25 indicating growth controlled by surface diffusion around pores that lie on the grain boundaries. An activation enthalpy of 122±34 kJ/mol was obtained using the grain size data from these data sets. At 600 °C the data is best described by n = 0.5, suggesting that a transition to interface controlled growth takes place between 511 °C and 600 °C. To investigate the impact of porosity, the Zener parameter (Z = pore size/pore volume fraction) was determined for individual grains in 10 samples. A general trend of increasing with increasing halite grain size is observed, indicating pore elimination keeps pace with pore accumulation in the growing grains. In some samples, the largest grains display a decrease in the Zener parameter corresponding with an increase in pore volume fraction. These grains are interpreted as having experienced a short-lived, abnormal growth phase shortly after t0 during which pore accumulation outpaced pore elimination. A model of pore controlled grain growth is proposed with a view to explaining these observations. In Part II, calcite + halite aggregates of constant volume fraction (0.60 calcite : 0.40 halite) and varying calcite clast size (6 μm 361 μm) were axially deformed to <1% bulk strain at room temperature in a neutron diffraction beamline. Elastic strain and stress in each phase was determined as a function of load from the neutron diffraction data. The strain (and stress) behaviour correlates well with the microstructural parameters: 1) halite mean free path and 2) calcite contiguity. Both phases behaved elastically up to aggregate axial stresses of 20-37 MPa, above these stresses the halite yielded plastically while the calcite remained elastic. Once yielding began, the rate of enhanced load transfer from halite to calcite with increasing applied load decreased with halite mean free path and increased calcite with contiguity. A Hall-Petch relationship between halite mean free path and aggregate yield stress was observed.
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Ichikawa, Rodrigo Uchida. "Aplicações do método Warren-Averbach de análise de perfis de difração." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-10012014-103427/.
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O objetivo deste trabalho foi desenvolver e implementar uma metodologia envolvendo a análise de perfis de difração de raios X (X-ray Line Profile Analysis - XLPA) para o estudo e determinação do tamanho médio de cristalitos e microdeformação em materiais. Para isto houve o desenvolvimento de um programa computacional para facilitar o tratamento dos picos presentes em um difratograma e realizar a deconvolução de perfis através do Método de Stokes para se corrigir a contribuição instrumental nos perfis de difração. Os métodos de XLPA de espaço real estudados e aplicados neste trabalho foram os métodos de Scherrer, Williamson-Hall e Single-Line (ou Linha Única) e o método de Warren-Averbach de espaço de Fourier. Além disso, utilizando-se um modelamento matemático foi possível calcular a distribuição de tamanhos de cristalitos para um caso isotrópico, onde considerou-se a distribuição log-normal e cristalitos com forma esférica. Foi possível demonstrar que a teoria proposta pode ser considerada como uma boa aproximação avaliando-se uma razão de dispersão. As metodologias descritas acima foram aplicadas em dois materiais distintos: na liga metálica Zircaloy-4 e em ZnO.<br>The objective of this work was to develop and implement a methodology of X-ray Line Profile Analysis (XLPA) for the study and determination of the mean crystallite sizes and microstrains in materials. A computer program was developed to speed up the treatment of diffraction peaks and perform the deconvolution utilizing the Stokes method to correct the instrumental contribution in the X-ray diffraction measurements. The XLPA methods used were the Scherrer, Williamson-Hall and Single-Line methods, which can be called real space methods, and the Fourier space method of Warren-Averbach. Furthermore, considering a mathematical modelling it was possible to calculate the crystallite size distribution, considering the log-normal distribution and spherical crystallites. It was possible to demonstrate the proposed theory can provide reliable results evaluating a dispersion parameter. The methodologies described above were applied in two distinct materials: in the alloy Zircaloy-4 and in ZnO.
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Fuster, Criado Laura. "Linear and nonlinear room compensation of audio rendering systems." Doctoral thesis, Universitat Politècnica de València, 2016. http://hdl.handle.net/10251/59459.
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[EN] Common audio systems are designed with the intent of creating real and immersive scenarios that allow the user to experience a particular acoustic sensation that does not depend on the room he is perceiving the sound. However, acoustic devices and multichannel rendering systems working inside a room, can impair the global audio effect and thus the 3D spatial sound.
In order to preserve the spatial sound characteristics of multichannel rendering techniques, adaptive filtering schemes are presented in this dissertation to compensate these electroacoustic effects and to achieve the immersive sensation of the desired acoustic system. Adaptive filtering offers a solution to the room equalization problem that is doubly interesting. First of all, it iteratively solves the room inversion problem, which can become computationally complex to obtain when direct methods are used. Secondly, the use of adaptive filters allows to follow the time-varying room conditions.
In this regard, adaptive equalization (AE) filters try to cancel the echoes due to the room effects. In this work, we consider this problem and propose effective and robust linear schemes to solve this equalization problem by using adaptive filters. To do this, different adaptive filtering schemes are introduced in the AE context. These filtering schemes are based on three strategies previously introduced in the literature: the convex combination of filters, the biasing of the filter weights and the block-based filtering. More specifically, and motivated by the sparse nature of the acoustic impulse response and its corresponding optimal inverse filter, we introduce different adaptive equalization algorithms.
In addition, since audio immersive systems usually require the use of multiple transducers, the multichannel adaptive equalization problem should be also taken into account when new single-channel approaches are presented, in the sense that they can be straightforwardly extended to the multichannel case.
On the other hand, when dealing with audio devices, consideration must be given to the nonlinearities of the system in order to properly equalize the electroacoustic system. For that purpose, we propose a novel nonlinear filtered-x approach to compensate both room reverberation and nonlinear distortion with memory caused by the amplifier and loudspeaker devices.
Finally, it is important to validate the algorithms proposed in a real-time implementation. Thus, some initial research results demonstrate that an adaptive equalizer can be used to compensate room distortions.<br>[ES] Los sistemas de audio actuales están diseñados con la idea de crear escenarios reales e inmersivos que permitan al usuario experimentar determinadas sensaciones acústicas que no dependan de la sala o situación donde se esté percibiendo el sonido. Sin embargo, los dispositivos acústicos y los sistemas multicanal funcionando dentro de salas, pueden perjudicar el efecto global sonoro y de esta forma, el sonido espacial 3D.
Para poder preservar las características espaciales sonoras de los sistemas de reproducción multicanal, en esta tesis se presentan los esquemas de filtrado adaptativo para compensar dichos efectos electroacústicos y conseguir la sensación inmersiva del sistema sonoro deseado. El filtrado adaptativo ofrece una solución al problema de salas que es interesante por dos motivos. Por un lado, resuelve de forma iterativa el problema de inversión de salas, que puede llegar a ser computacionalmente costoso para los métodos de inversión directos existentes. Por otro lado, el uso de filtros adaptativos permite seguir las variaciones cambiantes de los efectos de la sala de escucha.
A este respecto, los filtros de ecualización adaptativa (AE) intentan cancelar los ecos introducidos por la sala de escucha. En esta tesis se considera este problema y se proponen esquemas lineales efectivos y robustos para resolver el problema de ecualización mediante filtros adaptativos. Para conseguirlo, se introducen diferentes esquemas de filtrado adaptativo para AE. Estos esquemas de filtrado se basan en tres estrategias ya usadas en la literatura: la combinación convexa de filtros, el sesgado de los coeficientes del filtro y el filtrado basado en bloques. Más especificamente y motivado por la naturaleza dispersiva de las respuestas al impulso acústicas y de sus correspondientes filtros inversos óptimos, se presentan diversos algoritmos adaptativos de ecualización específicos.
Además, ya que los sistemas de audio inmersivos requieren usar normalmente múltiples trasductores, se debe considerar también el problema de ecualización multicanal adaptativa cuando se diseñan nuevas estrategias de filtrado adaptativo para sistemas monocanal, ya que éstas deben ser fácilmente extrapolables al caso multicanal.
Por otro lado, cuando se utilizan dispositivos acústicos, se debe considerar la existencia de no linearidades en el sistema elactroacústico, para poder ecualizarlo correctamente. Por este motivo, se propone un nuevo modelo no lineal de filtrado-x que compense a la vez la reverberación introducida por la sala y la distorsión no lineal con memoria provocada por el amplificador y el altavoz.
Por último, es importante validar los algoritmos propuestos mediante implementaciones en tiempo real, para asegurarnos que pueden realizarse. Para ello, se presentan algunos resultados experimentales iniciales que muestran la idoneidad de la ecualización adaptativa en problemas de compensación de salas.<br>[CAT] Els sistemes d'àudio actuals es dissenyen amb l'objectiu de crear ambients reals i immersius que permeten a l'usuari experimentar una sensació acústica particular que no depèn de la sala on està percebent el so. No obstant això, els dispositius acústics i els sistemes de renderització multicanal treballant dins d'una sala poden arribar a modificar l'efecte global de l'àudio i per tant, l'efecte 3D del so a l'espai.
Amb l'objectiu de conservar les característiques espacials del so obtingut amb tècniques de renderització multicanal, aquesta tesi doctoral presenta esquemes de filtrat adaptatiu per a compensar aquests efectes electroacústics i aconseguir una sensació immersiva del sistema acústic desitjat.
El filtrat adaptatiu presenta una solució al problema d'equalització de sales que es interessant baix dos punts de vista. Per una banda, el filtrat adaptatiu resol de forma iterativa el problema inversió de sales, que pot arribar a ser molt complexe computacionalment quan s'utilitzen mètodes directes. Per altra banda, l'ús de filtres adaptatius permet fer un seguiment de les condicions canviants de la sala amb el temps.
Més concretament, els filtres d'equalització adaptatius (EA) intenten cancel·lar els ecos produïts per la sala. A aquesta tesi, considerem aquest problema i proposem esquemes lineals efectius i robustos per a resoldre aquest problema d'equalització mitjançant filtres adaptatius. Per aconseguir-ho, diferent esquemes de filtrat adaptatiu es presenten dins del context del problema d'EA. Aquests esquemes de filtrat es basen en tres estratègies ja presentades a l'estat de l'art: la combinació convexa de filtres, el sesgat dels pesos del filtre i el filtrat basat en blocs. Més concretament, i motivat per la naturalesa dispersa de la resposta a l'impuls acústica i el corresponent filtre òptim invers, presentem diferents algorismes d'equalització adaptativa.
A més a més, com que els sistemes d'àudio immersiu normalment requereixen l'ús de múltiples transductors, cal considerar també el problema d'equalització adaptativa multicanal quan es presenten noves solucions de canal simple, ja que aquestes s'han de poder estendre fàcilment al cas multicanal.
Un altre aspecte a considerar quan es treballa amb dispositius d'àudio és el de les no linealitats del sistema a l'hora d'equalitzar correctament el sistema electroacústic. Amb aquest objectiu, a aquesta tesi es proposa una nova tècnica basada en filtrat-x no lineal, per a compensar tant la reverberació de la sala com la distorsió no lineal amb memòria introduïda per l'amplificador i els altaveus.
Per últim, és important validar la implementació en temps real dels algorismes proposats. Amb aquest objectiu, alguns resultats inicials demostren la idoneïtat de l'equalització adaptativa en problemes de compensació de sales.<br>Fuster Criado, L. (2015). Linear and nonlinear room compensation of audio rendering systems [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/59459<br>TESIS
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Natori, Willian Massashi Hisano. "j = 3/2 Quantum spin-orbital liquids." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-25092018-161836/.
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Quantum spin liquids (QSLs) are strongly correlated systems displaying fascinating phenomena like long-range entanglement and fractionalized excitations. The research on these states has since its beginning followed trends generated by the synthesis of new compounds and the construction of new theoretical tools. In coherence with this history, a manifold of new results about QSLs were established during the past decade due to studies on the integrable Kitaev model on the honeycomb lattice. This j = 1/2 model displays bond-dependent and anisotropic exchanges that are essential to stabilize its QSL ground state with Majorana fermion excitations and emergent Z2 gauge field. Even more interestingly, this model is relevant to understand the magnetism of a certain class of 4/5d5 Mott insulators with specific lattice constraints, t2g orbital degeneracy and strong spin-orbit coupling (SOC). This mechanism defining these so-called Kitaev materials can be applied to similar compounds based on transition metal ions in different electronic configurations. In this thesis, I investigate minimal models for two types of 4/5d1 Mott insulators: the ones on the ordered double perovskite structure (ODP) and the ones isostructural to the Kitaev materials. Their effective models generically show bond-dependent and anisotropic interactions involving multipoles of an effective j = 3/2 angular momentum. Such degrees of freedom are conveniently written in terms of pseudospin s and pseudo-orbital τ operators resembling spin and orbital operators of Kugel-Khomskii models with twofold orbital degeneracy. Despite their anisotropy, the two realistic models display continuous global symmetries in the limit of vanishing Hund\'s coupling enhancing quantum fluctuations and possibly stabilizing a QSL phase. Parton mean-field theory was used to propose fermionic QSLs that will be called quantum spin-orbital liquids (QSOLs) due their dependence with s and τ. On ODPs, I studied a chiral QSOL with Majorana fermion excitations and a gapless spectrum characterized by nodal lines along the edges of the Brillouin zone. These nodal lines are topological defects of a non-Abelian Berry connection and the system exhibits dispersing surface states. Several experimental responses of the chiral QSOL within the mean-field approximation are compared with the experimental data available for the spin liquid candidate Ba2YMoO6. Moreover, based on a symmetry analysis, I discuss the operators involved in resonant inelastic X-ray scattering (RIXS) amplitudes for 4/5d1 Mott insulators and show that the RIXS cross sections allow one to selectively probe pseudospin and pseudo-orbital degrees of freedom. For the chiral spin-orbital liquid in particular, these cross sections provide information about the spectrum for different flavors of Majorana fermions. The model for materials isostructural to the Kitaev materials has an emergent SU(4) symmetry that is made explicit by means of a Klein transformation on pseudospin degrees of freedom. The model is known to stabilize a QSOL on the honeycomb lattice and instigated the investigation of QSOLs on a generalization of this lattice to three dimensions. Parton mean-field theory was used once again to propose the liquid states, and a variational Monte Carlo (VMC) method was used to compute the energies of the projected wave functions. The numerical results show that the lowest-energy QSOL corresponds to a zero-flux state with a Fermi surface of four-color fermionic partons. Further VMC computations also revealed that this state is stable against formation of plaquette ordering (tetramerization). The energy of this QSOL is highly competitive even when Hund\'s coupling induced perturbations are included, as shown by comparison with simple ordered states. Extensions and perspectives for future work are discussed in the end of this thesis.<br>Líquidos de spin quânticos (QSLs) são sistemas fortemente correlacionados que apresentam fenômenos fascinantes como emaranhamento de longo alcance e excitações fracionárias. A pesquisa a respeito destes estados seguiu tendências geradas pela síntese de novos compostos e construção de novas técnicas teóricas desde seu princípio. Coerentemente com essa história, uma variedade de novos resultados a respeito de líquidos de spin foram estabelecidos na última década graças a estudos feitos sobre o modelo integrável de Kitaev na rede colmeia. Este modelo de spins j = 1/2 apresenta interações de troca anisotrópicas e direcionalmente dependentes que são essenciais para estabilizar um estado fundamental do tipo QSL com férmions de Majorana e campo de gauge Z2 emergente. Ainda mais interessante, este modelo é relevante para se entender o magnetismo de uma certa classe de isolantes de Mott baseados em metais de transição na configuração 4/5d5 em redes específicas, degenerescência orbital t2g e acoplamento spin-órbita forte (SOC). Esse mecanismo que define os chamados materiais do tipo Kitaev podem ser aplicados a compostos baseados em metais de transição em configurações eletrônicas diferentes. Nesta tese, eu investigo modelos mínimos para dois tipos de isolantes de Mott do tipo 4/5d1: os que se apresentam na estrutura perovskita dupla ordenada (ODP) e os isostruturais aos materiais do tipo Kitaev. Seus modelos efetivos genericamente apresentam interações multipolares anisotrópicas e direcionalmente dependentes de um momento angular efetivo j = 3/2. Estes graus de liberdade são convenientemente escritos em termos de operadores de pseudospin s e pseudo-orbital τ semelhantes a operadores de spin e orbital de modelos do tipo Kugel-Khomskii com orbitais duplamente degenerados. A despeito da anisotropia, esses dois modelos realísticos apresentam simetrias globais contínuas no limite de acoplamento de Hund nulo que incrementam flutuações quânticas e possivelmente estabilizam uma fase do tipo QSL. A teoria de campo médio com partons foi usada para propor QSLs fermiônicos que serão chamados de líquidos spin-orbitais quânticos (QSOLs) devido à dependência deles com s e τ. Em ODPs, eu estudei um líquido de spin quiral com excitações do tipo férmion de Majorana e um espectro sem gap caracterizado por linhas nodais ao longo das arestas da zona de Brillouin. Essas linhas nodais são defeitos topológicos de uma conexão de Berry não-abeliana e o sistema apresenta estados de superfície dispersivos. Várias respostas experimentais foram calculadas para o QSOL quiral dentro da aproximação de campo médio e comparadas com os dados experimentais disponíveis para o candidato a líquido de spin Ba2YMoO6. Além disso, baseado em uma análise de simetria, discuto os operadores envolvidos nas amplitudes de espalhamento de raios-x ressonante para isolantes de Mott na configuração 4/5d1 e mostro que seções de choque de RIXS permitem estudar seletivamente os graus de liberdade de pseudospins e pseudo-orbitais. Para o caso particular do líquido spin-orbital quiral, essas seções de choque nos fornecem informações sobre o espectro de diferentes sabores de férmions de Majorana. Esse modelo possui uma simetria SU(4) emergente que é tornada explícita através de uma transformações de Klein nos graus de liberdade de pseudospin. Sabe-se que este modelo estabiliza um QSOL na rede colmeia, o que instigou uma investigação de QSOLs na generalização desta rede em três dimensões. A teoria de campo médio com partons foi usada novamente para propor estes líquidos quânticos, e o método de Monte Carlo Variacional (VMC) foi usado para calcular as energias das funções de onda projetadas. Os resultados numéricos mostraram que o QSOL de menor energia corresponde a um estado de fluxo-zero com superfície de Fermi envolvendo partons fermiônicos de quatro cores. Cálculos adicionais com VMC também demonstraram que este estado é estável à formação de ordem de plaquetas (tetramerização). A energia deste QSOL é altamente competitiva mesmo quando perturbações induzidas pelo acoplamento de Hund são incluídas, o que é mostrado através da comparação com estados ordenados simples. Extensões e perspectivas para trabalhos futuros são discutidas no final desta tese.
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Martins, Diego Schmaedech. "CLASSIFICAÇÃO DE FASES EM IMAGENS HIPERESPECTRAIS DE RAIOS X CARACTERÍSTICOS PELO MÉTODO DE AGRUPAMENTO POR DESLOCAMENTO PARA A MÉDIA." Universidade Federal de Santa Maria, 2012. http://repositorio.ufsm.br/handle/1/5390.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>In the present work we introduce the Mean Shift Clustering (MSC) algorithm as a
valuable alternative to perform materials phase classification from hyperspectral images.
As opposed to other multivariate statistical techniques, such as principal components analysis
(PCA), clustering techniques directly assign a class (phase) label to each pixel, so
that their outputs are phase segmented images, i.e. , there is no need for an additional segmentation
algorithm. On the other hand, as compared to other clustering procedures and
classification methods based on cluster analysis, MSC has the advantages of not requiring
previous knowledge of the number of data clusters and not assuming any shape of these
clusters, i.e., neither the number nor the composition of the phases must be previously
known. This makes MSC a particularly useful tool for exploratory research, allowing automatic
phase identification of unknown samples. Other advantages of this approach are
the possibility of multimodal image analysis, composed of different types of signals, and
estimate the uncertainties of the analysis. Finally, the visualization and interpretation of
results are also simplified, since the information content of the output image does not depend
on any arbitrary choice of the contents of the color channels. In this paper we apply
the PCA and MSC algorithms for the analysis of characteristic X-ray maps acquired in
Scanning Electron Microscopes (SEM) which is equipped with Energy Dispersive Detection
Systems (EDS). Our results indicate that MSC is capable of detecting minor phases,
not clearly identified when only three components obtained by PCA are used.<br>No presente trabalho será introduzido o algoritmo de Agrupamento por Deslocamento
para a Média (ADM) como uma alternativa para executar a classificação de fases em materiais
a partir de imagens hiperspectrais de mapas raios X característicos. Ao contrário
de outras técnicas estatísticas multivariadas, tal como Análise de Componentes Principais
(ACP), técnicas de agrupamentos atribuiem diretamente uma classe de rótulo (fase)
para cada pixel, de modo que suas saídas são imagens de fase segmentadas, i.e., não há
necessidade de algoritmos adicionais para segmentação. Por outro lado, em comparação
com outros procedimentos de agrupamento e métodos classificação baseados em análise
de agrupamentos, ADM tem a vantagem de não necessitar de conhecimento prévio do
número de fases, nem das formas dos agrupamentos, o que faz dele um instrumento particularmente
útil para a pesquisa exploratória, permitindo a identificação automática de
fase de amostras desconhecidas. Outras vantagens desta abordagem são a possibilidade
de análise de imagens multimodais, compostas por diferentes tipos de sinais, e de estimar
as incertezas das análises. Finalmente, a visualização e a interpretação dos resultados
também é simplificada, uma vez que o conteúdo de informação da imagem de saída não
depende de qualquer escolha arbitrária do conteúdo dos canais de cores. Neste trabalho
foram aplicados os algoritmos de ADM e ACP para a análise de mapas de raios X característicos
adquiridos em Microscópios de Varredura Eletrônica (MEV) que está equipado
com um Espectrômetro de Raios X por Dispersão em Energia (EDS). Nossos resultados
indicam que o método ADM é capaz de detectar as fases menores, não claramente identificadas
nas imagens compostas pelo três componentes mais significativos obtidos pelo
método ACP.
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Kuurstra, Alan. "HARDI Denoising using Non-local Means on the ℝ³ x 𝕊² Manifold". Thesis, 2011. http://hdl.handle.net/10012/6436.
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Magnetic resonance imaging (MRI) has long become one of the most powerful and accurate tools of medical diagnostic imaging. Central to the diagnostic capabilities of MRI is the notion of contrast, which is determined by the biochemical composition of examined tissue as well as by its morphology. Despite the importance of the prevalent T₁, T₂, and proton density contrast mechanisms to clinical diagnosis, none of them has demonstrated effectiveness in delineating the morphological structure of the white matter - the information which is known to be related to a wide spectrum of brain-related disorders. It is only with the recent advent of diffusion-weighted MRI that scientists have been able to perform quantitative measurements of the diffusivity of white matter, making possible the structural delineation of neural fibre tracts in the human brain. One diffusion imaging technique in particular, namely high angular resolution diffusion imaging (HARDI), has inspired a substantial number of processing methods capable of obtaining the orientational information of multiple fibres within a single voxel while boasting minimal acquisition requirements.
HARDI characterization of fibre morphology can be enhanced by increasing spatial and angular resolutions. However, doing so drastically reduces the signal-to-noise ratio. Since pronounced measurement noise tends to obscure and distort diagnostically relevant details of diffusion-weighted MR signals, increasing spatial or angular resolution necessitates application of the efficient and reliable tools of image denoising. The aim of this work is to develop an effective framework for the filtering of HARDI measurement noise which takes into account both the manifold to which the HARDI signal belongs and the statistical nature of MRI noise. These goals are accomplished using an approach rooted in non-local means (NLM) weighted averaging. The average includes samples, and therefore dependencies, from the entire manifold and the result of the average is used to deduce an estimate of the original signal value in accordance with MRI statistics. NLM averaging weights are determined adaptively based on a neighbourhood similarity measure. The novel neighbourhood comparison proposed in this thesis is one of spherical neighbourhoods, which assigns large weights to samples with similar local orientational diffusion characteristics. Moreover, the weights are designed to be invariant to both spatial rotations as well as to the particular sampling scheme in use. This thesis provides a detailed description of the proposed filtering procedure as well as experimental results with synthetic and real-life data. It is demonstrated that the proposed filter has substantially better denoising capabilities as compared to a number of alternative methods.
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洪在萬. "A study of economic design of X charts to control non-normal process means." Thesis, 1992. http://ndltd.ncl.edu.tw/handle/42658764304128250224.
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37
Schmid, Benjamin. "Surface preparation and Mn states of (Ga,Mn)As investigated by means of soft- and hard x-ray photoemission spectroscopy." Doctoral thesis, 2010. https://nbn-resolving.org/urn:nbn:de:bvb:20-opus-50057.
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The present thesis deals with surface treatment, material improvement, and the electronic structure of the diluted magnetic semiconductor (Ga,Mn)As. The two key issues are the preparation of clean surfaces and the observation of potential valence hybridizations in (Ga,Mn)As by means of photoemission spectroscopy. Several cleaning methods are applied individually to (Ga,Mn)As and their e ects are compared in detail by various methods. Based on the results of each method, a sophisticated recipe has been elaborated, which provides clean, stoichiometric, and reconstructed surfaces, even if the sample was exposed to air prior to preparation. Moreover, the recipe works equally well for intentionally oxidized surfaces. The individual advantages of ex-situ wet- chemical etching and in situ ion-milling and tempering can be combined in an unique way. In regard to the post-growth annealing in order to optimize the electronic and magnetic properties of (Ga,Mn)As, the effect of surface segregation of interstitial Mn was quantifed. It turns out that the Mn concentration at the surface increases by a factor 4.3 after annealing at 190 C for 150 h. The removal of the segregated and oxidized species by wet-chemical etching allows a tentative estimate of the content of interstitial Mn. 19-23% of the overall Mn content in as-grown samples resides on interstitial positions. The complementary results of core level photoemission spectroscopy and resonant photoemission spectroscopy give hints to the fact that a sizeable valence hybridization of Mn is present in (Ga,Mn)As. This outlines that the simple Mn 3d5-con guration is too naive to refect the true electronic structure of substitutional Mn in (Ga,Mn)As. Great similarities in the core level spectra are found to MnAs. The bonding is thus dominantly of covalent, not ionic, character. Transport measurements, in particular for very low temperatures (<10 K), are in agreement with previous results. This shows that at low temperature, the conduction is mainly governed by variable-range hopping which is in line with the presence of an impurity band formed by substitutional Mn. In the light of the presented results, it is therefore concluded that a double-exchange interaction is the dominant mechanism leading to ferromagnetic coupling in (Ga,Mn)As. The valence hybridization and the presents of an impurity band, both of which are inherent properties of substitutional Mn, are indications for a double-exchange scenario, being at variance to a RKKY-based explanation. Contributions from a RKKY-like mechanism cannot definitely be excluded, however, they are not dominant<br>Die vorliegende Arbeit befasst sich mit der Oberflächenbehandlung, der Materialoptimierung und der elektronischen Struktur des verdünnten magnetischen Halbleiters (Ga,Mn)As. Die beiden Hauptaspekte sind dabei die Präparation sauberer Oberflächen und die Identifikation einer möglichen Valenzhybridisierung in (Ga,Mn)As mithilfe von Photoemissionspektroskopie. Mehrere Reinigungsmethoden wurden einzeln auf (Ga,Mn)As Oberflächen angewandt und deren Wirkung anhand mehrerer Untersuchungsmethoden verglichen. Basierend auf den Einzelergebnissen wurde eine spezielle Reinigungsprozedur ausgearbeitet, welche stöchiometrische, reine und wohldefinierte Oberflächen liefert, selbst wenn die Proben Umgebungsluft ausgesetzt wurde. Die beschriebene Vorgehensweise funktioniert des Weiteren auch bei absichtlich oxidierten Proben. Hierbei werden die individuellen Vorteile von ex situ nass-chemischen Ätzen, in situ Ionenstrahlätzen und Erhitzen auf besondere Art und Weise kombiniert. Im Hinblick auf das Ausheilen nach dem Wachstum konnte die Oberflächensegregation von interstitiellem Mangan quantifiziert werden, wobei sich zeigte, dass die Mangankonzentration an der Oberfläche um einen Faktor 4.3 nach 150 Stunden Ausheilen an Luft zunahm. Ein Vergleich zwischen ausgeheilten und anschließend geätzen Proben lässt eine vorsichtige Abschätzung des Anteils an interstitiellem Mangan in nicht ausheilten Proben zu. Hierbei zeigt sich, dass sich 19-23% das Gesamtgehalts an Mangan auf interstitiellen Gitterplätzen befindet. Komplementäre Untersuchungen mit Photoemissionsmethoden an Rumpfniveaus und mithilfe resonanter Photoemission geben Hinweis darauf, dass für Mangan in (Ga,Mn)As eine Valenzhybridisierung vorliegt. Dies führt zu dem Schluss, dass die simple Annahme eines zweifach positiv geladenen Mn-Atoms in 3d5-Kon guration zu pauschal ist, um die tatsächliche elektronische Struktur von substitutionellem Mn in (Ga,Mn)As widerzuspiegeln. Die Spektren zeigen eine große Ähnlichkeit zu Manganarsenid, was beweißt, dass die Bindung vorherrschend kovalenter und nicht ionischer Natur ist. Darüber hinaus sind ebenfalls durchgeführte Transportmessungen im Einklang mit bereits veröffentlichten Ergebnissen aus der Literatur. Dabei zeigt sich, dass der Ladungstransport, vor allem bei tiefen Temperaturen unterhalb von 10 K, durch variable range hopping statt findet. Dieses Verhalten steht im Einklang mit dem Vorhandensein eines Störstellenbandes, welches von substitutionellem Mn gebildet wird. Angesichts der hier gezeigten Daten kann gefolgert werden, dass ein Doppelaustausch der ausschlaggebende Mechanismus für das Auftreten ferromagnetischer Kopplung in (Ga,Mn)As ist. Sowohl die Valenzhybridisierung substitutionellem Mn als auch die Ausbildung eines Störstellenbandes durch selbiges, deuten auf einen Doppelaustausch in, was im Gegensatz zu einer RKKY-basierten Erklärung steht. Hierbei kann ein gewisse Bedeutung des RKKY-Modells nicht vollständig ausgeschlossen werden, jedoch ist diese definitiv nicht dominant
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Lakomek, Kristina. "Structural characterization of the lysosomal 66.3 kDa protein and of the DNA repair enzyme Mth0212 by means of X-ray crystallography." Doctoral thesis, 2009. http://hdl.handle.net/11858/00-1735-0000-0006-AD5D-B.
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39
Schmid, Benjamin [Verfasser]. "Surface preparation and Mn states of (Ga,Mn)As investigated by means of soft and hard x-ray photoemission spectroscopy / vorgelegt von Benjamin Schmid." 2010. http://d-nb.info/1005666016/34.
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40
Lakomek, Kristina [Verfasser]. "Structural characterization of the lysosomal 66.3 kDa protein and of the DNA repair enzyme Mth0212 by means of X-ray crystallography / vorgelegt von Kristina Lakomek." 2009. http://d-nb.info/1003500234/34.
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41
Joshi, Siddharth [Verfasser]. "Fundamental studies of structure and crystallinity of low & high molecular weight poly(3-hexylthiophene) P3HT by means of synchrotron X-ray diffraction / vorgelegt von Siddharth Joshi." 2008. http://d-nb.info/994271093/34.
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42
Liu, Chi-Shuan, and 劉季旋. "Design of Single-Featured EWMA-X (SFEWMA-X) Control Chart Using Individual Observations for Detecting Process Mean Shifts and Standard Deviation Changes." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/xcs95k.
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博士<br>國立臺北科技大學<br>工商管理研究所<br>100<br>Quality control chart is an important tool for process monitoring and quality improvement. Several combined control charts have been proposed to enhance the detection ability in detecting small and large process parameter changes simultaneously. However, these control charts require calculating and monitoring two statistics along with two sets of control limits. This study propose a new control chart using individual observations, called a single featured EWMA-X (SFEWMA-X) control chart, to monitor both small and large process mean shifts and process standard deviation changes. The SFEWMA-X control chart is designed by a simple variable transformation that rescales the statistic of EWMA into the range of Shewhart-X so that only one statistic is required to be monitored. A pilot experiment demonstrates the detection ability of the proposed scheme. To facilitate the use of the proposed method on the shop floor, this study proposed the algorithm for deriving optimal chart design tables and implementing procedures. A comparison of the detection ability shows that the proposed control chart is superior to individual control chart when monitoring both small and large process parameter change. A SFEWMA-X diagnosis chart was extended from SFEWMA-X control chart. An example was given to show the application of the proposed diagnosis chart.
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Chiu, Shih-Chen, and 邱士珍. "Economical design of X-bar control charts under the mean shift and variance increasing." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/n46em2.
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碩士<br>國立屏東科技大學<br>工業管理系所<br>105<br>Dr. Duncan put forward economical Design of X-bar Control Charts in 1956. This model only considers the mean shift. However, the variation increasing in the process can also possibly occur. Therefore, this study makes the discussion in view of this part and the Duncan’s model was extended. Through the Visual Basic software to carry on a computerized system development and design that optimizes the quality control chart. Apart from considering the mean shift, the variance increases influences on sample size, interval between samples and width of control limits also be considered. Under the goal of minimizing the total unit cost, the optimal combination of n, h and k are found.
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Dudziak, Lukasz. "Mitigating autogenous shrinkage of Ultra-High Performance Concrete by means of internal curing using superabsorbent polymers." Doctoral thesis, 2016. https://tud.qucosa.de/id/qucosa%3A30316.
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Application of smart curing concept called internal curing (IC) is the most promising strategy for mitigating autogenous shrinkage and related early-age cracking in cement-based materials with low water-to-cement ratio. There are still many theoretical and practical questions that need to be answered before IC could become a standard method. Many of these questions concern the most appealing of water-regulating additives for IC called Superabsorbent Polymers (SAP). The clear linkage between SAP material properties, the moment of water release and the effect on autogenous shrinkage is still missing, which blocks formulating recommendations for use of particular potential IC agents in concrete construction.
In this treatise various aspects that are decisive for effectiveness of IC in mitigating autogenous shrinkage were examined. The choice of materials was purposefully limited to two compositions of Ultra-High Performance Concrete (UHPC), one fine-grained and one coarse-grained mixture, and one particular, in-depth characterized SAP. The objectives of examination which shaped the final experimental programme were: assessment of IC agent absorption capacity, specification of periods of water migration from fresh concrete mixture into SAP and from SAP back into hardening concrete, determination of effect of SAP addition on cement hydration, evaluation of IC influence on and determination of start of effective autogenous shrinkage and, finally, assessment of autogenous shrinkage with selfsame IC agent but for different matrices. Ideally, description of the mechanisms behind the action of IC at different stages of concrete life and reasoning of differences observed for the UHPCs under investigation had to be provided.
First, the main components of the system – UHPC and SAP material – were characterized as to their suitability for IC application. Special attention was paid to the material properties which affect water transport. Usage of different testing methods was necessary here and included: testing with ESEM, FT-IR, tea-bag test, sol fraction content examination and X-ray computed tomography (for SAP) as well as air content measurement and various methods for characterization of the porosity and other features of the microstructure. The observed delay in the start of pozzolanic reactions in case of fine-grained UHPC was rather surprising, but, under consideration of porosity, shed new light on permeability of young UHPC.
The work at hand revealed numerous methods that can be used for studying the absorption capacity of polymers, but hardly representative for the behaviour of those polymers within concrete matrix. Because of its general availability and the relatively robust testing procedure, it was decided to focus on possibilities and limitations of using tea-bag test for evaluation of absorption capacity of SAP. New interpretation of tea-bag test results was deduced which enabled assessment of maximum absorption capacity of SAP from measurement of consistency of concrete before and after modification with IC.
Influence of IC on hydration process was revealed by using two non-destructive methods, in particular ultrasonic measurement and concrete temperature record. It could be shown that the ionic polymer exhibits complex effects including retardation and acceleration of individual chemical processes. Additionally, X-ray computed tomography (CT) and instrumented ring tests were performed in order to understand scientific significance of the characteristic event appearing during shrinkage measurements, taken as time-zero (= starting point for evaluation of autogenous shrinkage data). Linkage of time-zero with certain phenomenon, e.g., changes of the SAP particles volume or specific value of yield stress, but not with final set, was suggested for the future investigations.
By using two setups based on corrugated tube protocol it was possible to register and compare autogenous shrinkage of both UHPCs without and with modification by IC. The effectiveness of IC was shown to be dependent on the matrix in which IC was implemented. This was related to the observed changes in pore percolation that resulted from different absorption behaviour of SAP in the two UHPCs under investigation. Furthermore, the effect of fibres on effectiveness of IC was discussed.
Description and discussion of mechanisms behind IC was supported by measurement of capillary pressure, total shrinkage tests with simultaneous mass loss measurement, free autogenous shrinkage tests and the CT measurement. Valuable source of information was furthermore the in-depth literature review. The most appealing finding of the work and the biggest paradox revealed was high efficiency of IC in mitigating autogenous shrinkage and simultaneously appearance of stage where very clear reverse in mode of polymer volume change was observed. This suggests partial reabsorption of water initially released. This puts interpretation of operative shrinkage mechanisms and ones standing behind IC effect in a new perspective.<br>Die innere Nachbehandlung (Internal Curing – IC) ist die derzeit aussichtsreichste Strategie, um das in zementgebundenen Baustoffen mit niedrigen Wasser/Zement-Werten ausgeprägt auftretende autogene Schwinden wirksam zu verringern und die damit einhergehende Rissbildung in jungem Beton zu vermeiden. Vor einer breiten baupraktischen Anwendung des IC sind noch viele offene Fragen zu beantworten. Die meisten dieser Fragen betreffen die derzeit interessanteste Klasse von wasserregulierenden Stoffen für das IC – die superabsorbierenden Polymere (SAP). Von entscheidender Bedeutung ist hier der noch weitgehend unerforschte Zusammenhang zwischen den Materialeigenschaften der SAP, dem Zeitpunkt der Wasserabgabe und der Auswirkung auf das autogene Schwinden.
In der vorliegenden Arbeit werden verschiedene Einflussfaktoren auf die Wirksamkeit von SAP zur Verringerung des autogenen Schwindens untersucht. Für die Experimente wurde ein feinkörniger und ein grobkörniger ultra-hochfester Beton (UHPC) sowie ein schon detailliert charakterisiertes SAP genutzt. Das experimentelle Programm wurde auf folgende Untersuchungsziele ausgerichtet: Absorptionsvermögen der SAP, Zeitfenster der Wassermigration aus dem Frischbeton in das SAP sowie vom SAP in den erhärtenden Beton, autogenes Schwindmaß sowie effektiver Beginn des autogenen Schwindens. Ziel der Arbeiten ist die Beschreibung der Mechanismen, die IC zugrundliegen – und dies zu verschiedenen Betonaltern und unter Berücksichtigung der an den untersuchten UHPC beobachteten Unterschiede.
Bei der Charakterisierung der Hauptkomponenten des betrachteten Systems – UHPC und SAP – wurde auf die Materialeigenschaften fokussiert, die den Wassertransport beeinflussen. Dazu wurden u. a. folgende Untersuchungsmethoden angewendet: ESEM, FT-IR, Teebeuteltest, Sol-Fraction Test, Röntgentomographie (für SAP) sowie verschiedene Verfahren zur Charakterisierung der Poren im Beton. Im feinkörnigen UHPC wurde überraschenderweise ein verzögerter Beginn der puzzolanischen Reaktion festgestellt, der bei Berücksichtigung der vorliegenden Porosität zu einer Neubewertung der Permeabilität von UHPC in jungem Alter führte.
In der vorliegenden Arbeit werden verschiedene Methoden zur Beschreibung des Wasserabsorptionsvermögens von SAP benannt, deren Aussagekraft bei Anwendung dieser Polymere im Beton aber sehr eingeschränkt ist. Aufgrund seiner einfachen Verfügbarkeit und Robustheit wurde daher der Teebeutetest zur Bestimmung der Wasserabsorption des SAP genutzt. Die Wasserabsorption der SAP im Beton wurde durch Gegenüberstellung von Konsistenzmessungen am Beton vor und nach Zugabe von SAP und Ergebnissen der Teebeuteltest abgeschätzt.
Der Einfluss des IC auf die Hydratation wurde zerstörungsfrei mit Ultraschall- und Betontemperaturmessungen erfasst. Auf dieser Grundlage konnten Hypothesen zu den komplexen Wechselwirkungen zwischen ionischem Polymer und der Beschleunigung oder Verzögerung einzelner chemischer Prozesse formuliert werden. Mit Hilfe von instrumentierten Ringversuchen und X-ray Computertomographie wurden die Auswirkungen des IC mit SAP auf das autogene Schwinden, den Aufbau von Zwangsspannungen bei behindertem Schwinden und Time-Zero diskutiert. Dabei konnte ein Zusammenhang zwischen Time-Zero und verschiedenen Phänomenen, wie z. B. Volumenänderung des SAP oder der Fließgrenze des erhärtenden Betons, nicht aber zum Ende des Erstarrens aufgezeigt werden.
Das autogene Schwinden beider untersuchter UHPC (jeweils mit und ohne IC) wurde mit Hilfe von Corrugated Tube-Versuchen gemessen. Es konnte gezeigt werden, dass wie Wirksamkeit des IC von der Betonzusammensetzung sowie der in den UHPC infolge Wechselwirkungen mit den SAP verschieden ausgebildeten Porenstruktur der Matrix abhängt. Weiterhin konnte ein Einfluss von Faserzugaben auf die Wirksamkeit des IC gezeigt werden.
Die Beschreibung und Diskussion der Mechanismen des IC wurde durch Messungen des Kapillardrucks, des Gesamtschwindens, des freien autogenen Schwindens, des Masseverlustes und Computertomographie unterstützt. Eine wichtige Erkenntnisquelle war zudem die umfangreich gesichtete und diskutierte Literatur.
Das interessanteste und zugleich paradoxe Ergebnis der Untersuchungen ist die Tatsache, dass die bei Einsatz von SAP beobachtete Verringerung des autogenen Schwindens eindeutig mit einer zeitgleichen Umkehr der Volumenänderung der SAP einhergeht: die bis dahin dominierende Wasserabgabe geht in eine erneute Wasseraufnahme über. Dies stellt die Interpretation der Triebkräfte des Schwindens und die dem IC zugrundliegenden Mechanismen in einen neuen Zusammenhang.
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Roeser, Frank [Verfasser]. "Non-parametric hypersurfaces of prescribed mean curvature in Hn x R / vorgelegt von Frank Roeser." 2010. http://d-nb.info/1007979771/34.
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Lee, Ping-Chung, and 李秉中. "Determination of Mean Diameter and Size Distribution of Nano-size Powder by X-ray Powder Diffraction." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/64294980009145925849.
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碩士<br>國立中央大學<br>物理研究所<br>91<br>Finite size X-ray diffraction theory was used to determine the mean particle diameter and size distribution of powders composed of nano-scale particles. The X-ray diffraction patterns were analyzed assuming a single size as well as multi sizes for the powder. Better fits were frequently obtained when a size distribution for the powder was assumed, as expected. Gaussian and Lognormal distributions were then considered. Through the process, we were able to determine the size distribution of the powder by using the x-ray diffraction pattern. Comparisons of the results to that obtained from the AFM images were also presented.
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GIACCO, DANIELA. "Design of Li-O2 cells and study of the electrodes reactivity by means of a multi-technique approach." Doctoral thesis, 2018. http://hdl.handle.net/11573/1209688.
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The PhD thesis work has been focused on aprotic Li-O2 cells assembled with different cathode materials in combination with the ether-based LiTFSI/TEGDME electrolyte. The performance of these promising energy storage systems have been investigated and related to the electrochemical and chemical processes at the triple O2/cathode/electrolyte interface and to the peculiar influence of each type of cathode material. These goals have been achieved by a powerful combination of techniques such as X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). The remarkable role of the TFSI- anion in the degradation process of a carbon-based cathode has been discussed in Chapter 4 on the basis of a post-mortem characterization of the positive electrode. Moreover, the fade of long-term stability of the cells has been related to the accumulation on the cathode surface of both insulating reaction products and byproducts, leading to the rise of overvoltages upon discharge and charge. A full electrochemical and chemical characterization of novel carbon-free Mn+-doped (Mn+=Cr3+ and Zn2+) NiCo2O4 nanomaterials grown on Ni foam (NCCr@Ni and NCZn@Ni) has been reported in Chapters 5 and 6. For the first time in the literature these materials have been tested as cathodes in Li-O2 cells and the beneficial effect of Cr(III)- and Zn(II)-doping of the NiCo2O4 spinel to boost the kinetics of both the ORR and the OER has been demonstrated. By means of in-house and synchrotron measurements the dopants role in the increase of the performance respect to the undoped material has been investigated. The preparation and characterization of novel composite Pd/PdO@NCCr@Ni cathodes made of Pd nanoparticles deposited on a nanostructured Cr(III)doped NiCo2O4 on Ni foam has been described in Chapter 7. The synergistic co-catalytic effect between the Pd NP and the doped nickel cobaltite has been proved to reduce both discharge and charge overvoltages and to improve the cell calendar life.
Overall, the general objectives of the PhD activity have been met, since three novel materials have been produced and demonstrated to be performing cathodes for Li-O2 cells. Moreover, this study allowed the acquisition of skills concerning laboratory practice and widely applicable electrochemical and chemical characterization techniques.
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Ye, Zi-yi, and 葉子以. "Feedforward Active Noise Control System With Leaky Filter-x Normalized Least-Mean-Square Algorithm for Kitchen Hood." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/54575317626764338416.
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碩士<br>逢甲大學<br>電聲碩士學位學程<br>104<br>This study used the Leaky Filter-x Normalized Least Mean Square (Leaky Filter-x NLMS) algorithm to develop a feed-forward active noise control (ANC) system for the active control of noise in kitchen hoods. It is hoped that the resulting ANC system can effectively reduce the noise in kitchen hoods.
With regard to hardware, a microphone amplifier was used to record and amplify the sound signal. In order to improve the ANC system, a low-pass filtered is developed. Additionally, this study presents a method how to choose a better placement point for noise reduction and placing the ANC system inside the bellows of kitchen hoods. This placement was tested for the function of noise reduction.
With regard to the noise cancelling software for kitchen hoods, this study differed from past studies in that the Leaky Least Mean Squares (LMS) and NLMS algorithms were integrated in the traditionally applied Filter-x LMS algorithm. Consideration of new influencing factors can allow for more flexible changes and adjustments, thus providing more improvement schemes for controlling the noise caused by the complex structures of kitchen hoods.
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Zharkova, Valentina V., and Mykola Gordovskyy. "The Effects of Return Current on Hard X-Ray Photon and Electron Spectra in Solar Flares." 2009. http://hdl.handle.net/10454/2657.
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No<br>The effect of a self-induced electric field is investigated analytically and numerically on differential and mean electron spectra produced by beam electrons during their precipitation into a flaring atmosphere as well as on the emitted hard X-ray (HXR) photon spectra. The induced electric field is found to be a constant in upper atmospheric layers and to fall sharply in the deeper atmosphere from some "turning point" occurring either in the corona (for intense and softer beams) or in the chromosphere (for weaker and harder beams). The stronger and softer the beam, the higher the electric field before the turning point and the steeper its decrease after it. Analytical solutions are presented for the electric fields, which are constant or decreasing with depth, and the characteristic "electric" stopping depths are compared with the "collisional" ones. A constant electric field is found to decelerate precipitating electrons and to significantly reduce their number in the upper atmospheric depth, resulting in their differential spectra flattening at lower energies (<100 keV). While a decreasing electric field slows down the electron deceleration, allowing them to precipitate into deeper atmospheric layers than for a constant electric field, the joint effect of electric and collisional energy losses increases the energy losses by lower energy electrons compared to pure collisions and results in maxima at energies of 40-80 keV in the differential electron spectra. This, in turn, leads to the maxima in the mean source electron spectra and to the "double power law" HXR photon spectra (with flattening at lower energies) similar to those reported from the RHESSI observations. The more intense and soft the beams are, the stronger is the lower energy flattening and the higher is the "break" energy where the flattening occurs.
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Pacheco, Marta Sofia Martins. "Análise da variabilidade e dispersão espacial elementar em solos e sedimentos por micro fluorescência de raios X – um caso de estudo." Master's thesis, 2020. http://hdl.handle.net/10362/113885.
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A presente tese tem como objectivo estabelecer um procedimento de análise de amostras
heterogéneas com o M4 TORNADO, através do estudo da variabilidade e distribuição espacial
dos elementos químicos constituintes de um grupo de amostras de solo e sedimentos, recolhidas
na área da antiga mina de São Domingos, localizada no concelho de Mértola (Portugal), em
plena Faixa Piritosa Ibérica (FPI).
Após a peneiração das amostras em quatro classes (≥ 2 mm, < 2 mm e ≥ 500 μm, < 500
μm e ≥ 250 μm e < 250 μm) no laboratório, as amostras foram analisadas sob a forma de
pastilhas no M4 TORNADO, um espectrómetro de micro fluorescência de raios X (μ-XRF) de
energia dispersiva, da Bruker Nano GmbH. Esta técnica, aplicada de forma semi-quantitativa,
permitiu identificar e quantificar elementos químicos presentes nas amostras, bem como obter a
sua distribuição espacial através do mapeamento individual de cada elemento nas amostras de
solo.
O principal desafio no estudo realizado consistiu no facto de as amostras serem
granulares e heterogéneas, o que dificulta a sua análise e conduz a variabilidades altas nos
resultados. É ainda de revelar a existente escassez de trabalhos desenvolvidos neste
equipamento com este tipo de amostras, tendo-se tornado necessário a verificação dos melhores
procedimentos possíveis a adoptar de modo a assegurar a obtenção de resultados
suficientemente fidedignos e representativos da realidade em estudo.
Neste sentido, os resultados obtidos foram tratados estatisticamente, permitindo
estabelecer a relação entre as concentrações dos elementos e a sua variabilidade e distribuição
nas amostras. As interpretações realizadas e a análise dos resultados em termos locais (análise
por ponto múltiplo) e espaciais (mapeamentos) permitiu desenvolver um procedimento que se
sugere para futuras análises de solos ou sedimentos, em que se recorre à técnica de μ-XRF de
energia dispersiva. Foi também possível verificar que as amostras demonstram a forte relação que os solos
e sedimentos nesta área têm para com a geologia local, refletindo os efeitos da anomalia
geoquímica regional em que se insere a antiga área mineira de São Domingos.