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Aiesh, Basel. "Measurement of dispersion barriers through SEM images." Thesis, Uppsala universitet, Centrum för bildanalys, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-252764.
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In this thesis digital image analysis is applied to Scanning Electron Microscope imagesof dispersion barriers to measure specific properties. The thin barriers are used asprotection for paperboard packaging and are made of polymers and fillers. The orientation, area, length and density distributions of the fillers determine the functionality and quality of the barrier. Methods built on image analysis tools are developed with the objective to measure these quantities. Input for the methods are Scanning Electron Microscope images showing the cross-section of the barriers. To make the images relevant for the methods they are preprocessed by reducing noise and distinguishing fillers from the background. For measuring the orientation distribution of the fillers two different methods are implemented and compared. The first one is based on a structure tensor and the other one applies a covariance matrix. The structure tensor is preferable because of its flexibility and better performance for complex images. The area and length distributions are measured by applying mathematical morphology together withsoft-clipping. The density distribution is obtained by filtering the underlying image twice with a uniform filter which creates a heat map. The developed methods are evaluated by applying them on fabricated binary test images with known properties. The methods are very accurate when applied on simple test images but for more complex test images with greater variation the accuracy decreases. However, for most applications the results are still on an acceptable level.
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Myslivets, Yauheni. "Spatially resolved measurement in fibers with arbitrary chromatic dispersion." Diss., [La Jolla] : University of California, San Diego, 2010. http://wwwlib.umi.com/cr/ucsd/fullcit?p3391413.
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Thesis (Ph. D.)--University of California, San Diego, 2010.Title from first page of PDF file (viewed February 25, 2010). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 128-135).
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O'Leary, Michael Boyer 1969. "Geographic dispersion in teams : its history, experience, measurement, and change." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/16883.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Sloan School of Management, 2002.Vita.
Includes bibliographical references.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
This thesis begins with the simple argument that geographic dispersion has gone surprisingly unexamined despite its role as the domain-defining construct for geographically dispersed teams (a.k.a. "virtual teams"). The last few years have seen slow but steady growth in field studies of such teams, but our understanding of geographic dispersion and the role it plays in work is stillquite limited. The thesis attempts to open the "black box" of geographic dispersion, show that it is far from a new phenomenon in organizations, understand the ways in which it is experienced, propose ways in which it can be measured, and understand the effects of doing work at increasing degrees of dispersion. It does so through three studies which combine qualitative and quantitative methods, and draw on archival, survey, observational, and interview data. Study 1 uses rich archival data covering more than two centuries (1670-1950) of the life of one firm - i.e., the Hudson's Bay Company - to understand its far-flung managers' experience of dispersion. It shows that the managers experienced their dispersion through a combination of coordination, communication, isolation, and control challenges. It also serves as a "typifier," showing that modem "virtual" teams have deep historical roots. Study 2 proposes a multi-dimensional definition of dispersion, including spatial-temporal distance and configuration, as well as a series of new measures to capture those dimensions. It explores the measures and their relationship to communications frequency in a sample of 115 dispersed project teams from a Fortune 500 company.
(cont.) Study 3 is based on field research with nine geographically dispersed internal consulting teams in a large, national humanitarian aid organization. It follows them from the inception to the completion of their work and compares two teams in detail. One team was moderately dispersed and one was a pilot for a more fully dispersed approach to the internal consulting projects. It finds that perceptions about timing and dispersion differ from more objective measures like those in Study 2. It also shows how dispersion is a challenge for team boundaries and calls for more attention to the weighting of different team effectiveness criteria. Keywords: geographic dispersion, teams, virtual teams, effectiveness, communications, history.
by Michael Boyer O'Leary.
Ph.D.
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Pathak, Prashant, Olivier Guyon, Nemanja Jovanovic, Julien Lozi, F. Martinache, Y. Minowa, T. Kudo, H. Takami, Y. Hayano, and N. Narita. "First on-sky closed loop measurement and correction of atmospheric dispersion." SPIE-INT SOC OPTICAL ENGINEERING, 2016. http://hdl.handle.net/10150/622049.
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In the field of exoplanetary sciences, high contrast imaging is crucial for the direct detection of, and answering questions about habitability of exoplanets. For the direct imaging of habitable exoplanets, it is important to employ low inner working angle (IWA) coronagraphs, which can image exoplanets close to the PSF. To achieve the full performance of such coronagraphs, it is crucial to correct for atmospheric dispersion to the highest degree, as any leakage will limit the contrast. To achieve the highest contrast with the state-of-the-art coronagraphs in the SCExAO instrument, the spread in the point-spread function due to residual atmospheric dispersion should not be more than 1 mas in the science band. In a traditional approach, atmospheric dispersion is compensated by an atmospheric dispersion compensator (ADC), which is simply based on model which only takes into account the elevation of telescope and hence results in imperfect correction of dispersion. In this paper we present the first on-sky closed-loop measurement and correction of residual atmospheric dispersion. Exploiting the elongated nature of chromatic speckles, we can precisely measure the presence of atmospheric dispersion and by driving the ADC, we can do real-time correction. With the above approach, in broadband operation (y-H band) we achieved a residual of 4.2 mas from an initial 18.8 mas and as low as 1.4 mas in H-band only after correction, which is close to our science requirement. This work will be valuable in the field of high contrast imaging of habitable exoplanets in the era of the ELTs.
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Júnior, Reinaldo Borges. "Desenvolvimento de método de medição das espessuras de núcleos e revestimentos de placas combustíveis." Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-03022014-162505/.
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Um dos componentes mais importantes de um Reator Nuclear é o Combustível Nuclear. Atualmente, o mais avançado combustível comercial, cuja aplicabilidade nos reatores brasileiros vem sendo desenvolvida pelo IPEN desde 1985, é o siliceto de urânio U3Si2. Este é formado por placas combustíveis com núcleos de dispersão (onde o material físsil (U3Si2) é disperso homogeneamente em uma matriz de alumínio) revestidos por alumínio. Tal combustível é produzido no Brasil com tecnologia totalmente nacional, resultado do esforço realizado pelo grupo de fabricação de combustíveis nucleares (CCN Centro do Combustível Nuclear) do IPEN. Diante da necessidade do aumento da potência do reator IEA-R1 e da construção do Reator Multipropósito Brasileiro (RMB), para a produção de radioisótopos principalmente para fins na área da medicina , haverá significativo aumento na produção deste combustível nuclear no IPEN. Em face desta conjuntura, faz-se necessário o desenvolvimento de técnicas de qualificação mais modernas e automatizadas. Visando a este objetivo, neste trabalho foi desenvolvido um novo método computacional de medição de espessuras de núcleos e revestimentos de placas combustíveis, o qual é capaz de realizar tais medidas em tempo menor e com dados estatísticos mais significativos, quando comparado com o método atual de medição.One of the most important components of a nuclear reactor is the Nuclear Fuel. Currently, the most advanced commercial fuel, whose applicability in Brazilian reactors has been developed by IPEN since 1985, is the silicide U3Si2. This is formed by fuel plates with nuclei dispersion (where the fissile material (U3Si2) is homogeneously dispersed in a matrix of aluminum) coated aluminum. This fuel is produced in Brazil with developed technology, the result of the efforts made by the group of manufacturing nuclear fuel (CCN - Center of Nuclear Fuel) of IPEN. Considering the necessity of increasing the power of the IEA- R1 and Brazilian Multipurpose Reactor Building (RMB), for the production of radioisotopes - mainly for the area of medicine - there will be significant increase in the production of nuclear fuel at IPEN. Given this situation, if necessary, make the development of more modern and automated classification techniques. Aiming at this goal, this work developed a new computational method for measuring thickness of core and cladding of fuel plates, which are able to perform such measurements in less time and with more meaningful statistical data when compared with the current method of measurement.
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Molyneux, Joseph B. "Laboratory measurement of elastic-wave velocity, associated dispersion, attenuation and particle resonance." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0010/NQ60005.pdf.
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Eun, Sangho. "HYDROGEN SULFIDE FLUX MEASUREMENTS AND DISPERSION MODELING FROM CONSTR." Master's thesis, University of Central Florida, 2004. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3234.
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Odor problems are a common complaint from residents living near landfills. Many compounds can cause malodorous conditions. However, hydrogen sulfide (h2s) has been identified as a principal odorous component from construction and demolition (c&d)debris landfills. Although several studies have reported the ambient concentrations of h2s near c&d landfills, few studies have quantified emission rates of h2s. The most widely used and proven technique for measuring gas emission rates from landfills is the flux chamber method. Typically the flux chamber is a cylindrical enclosure device with a spherical top which limits the gas emission area. Pure zero grade air is introduced into the chamber, allowed to mix with emitting gases captured from the landfill surface, and then transported to the exit port where concentrations can be measured. Flux measurements using the flux chamber were performed at five different c&d landfills from june to august, 2003. The flux rates of h2s measured in this research were three to six orders of magnitude lower than the flux rates of methane reported in the literature. In addition to the h2s flux measurements, dispersion modeling was conducted, using the epa dispersion model, industrial source complex short term (iscst3), in order to evaluate impacts on landfill workers and communities around the landfills. The modeling results were analyzed to estimate the potential ground level maximum h2s concentrations for 1-hr and 3-min periods and the frequency (occurrences per year) above the h2s odor detection threshold for each landfill. Odor complaints could be expected from four among five landfills selected for this study, based on 0.5-ppb odor detection threshold.M.S.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Environmental Engineering
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O'Connor, Caleb S. "Measurement of Dispersion and Attenuation in Granular Media using a Filter-Correlation Method." Thesis, University of Louisiana at Lafayette, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1592420.
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A wideband technique for measuring sound dispersion and frequency-dependent attenuation in granular media is presented. The measurements were done on a mono-disperse medium of 2-cm solid polypropylene balls, over the frequency range of 500 Hz-20 kHz, enough to cover both weak and strong scattering regimes. A horn driver was used to launch sound into a foam-lined bucket containing the granular medium. The latter was mechanically isolated from the driver so as to minimize direct-contact coupling. The foam isolation was not enough, especially at resonances of the bucket-granular system. In the effort to simulate a free-granular medium, the bucket was replaced with a mesh bag hanging in free space. The frequency-dependent wavenumber of the granular is obtained by a filter-correlation method. After successive bandpass filtering, the phase speed and attenuation are obtained within each band, respectively, by signal alignment and amplitude log ratio. The attenuation coefficient yielded reasonable results, illustrating the transition from ``piston-like" dynamics to the strong scattering regime, as the frequency increased. The phase speed results where more sporadic, qualitatively there is a decrease in sound speed as the frequency increases.
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BARROS, FABRICIO JOSE BRITO. "MEASUREMENT AND ANALYZE OF UWB INDOOR CHANNEL TEMPORAL DISPERSION IN SEVERAL ENVIRONMENT TYPES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2005. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=7585@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOREste trabalho apresenta a análise das características de dispersão temporal do canal de propagação banda ultra larga (UWB) feitas a partir da técnica de sondagem em freqüência na banda de 850MHz em sete diferentes ambientes Indoor. Nestes ambientes os parâmetros de dispersão temporal dados pelo retardo médio, retardo RMS e banda de coerência são obtidos. Uma análise adicional sobre a perda de propagação e sobre a robustez do sinal UWB a desvanecimento de pequena escala é também realizada.
This work presents an analysis of the ultra wideband (UWB) channel temporal dispersion characteristics evaluated from the frequency sounding technique over a bandwidth of 850MHz at seven different indoor environment. In each environment, the channel temporal dispersions parameters were assessed in terms of mean delay, delay spread and coherence bandwidth. An additional analysis related to path loss and UWB robustness was also evaluated.
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Trubko, Raisa, and Raisa Trubko. "Tune-out Wavelength Measurement and Gyroscope Using Dispersion Compensation in an Atom Interferometer." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/625677.
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This Dissertation describes how I used a three nanograting Mach-Zehnder atom beam interferometer to precisely measure a wavelength of light, known as a tune-out wavelength, that causes zero energy shift for an atom. I also describe how such measurements can be remarkably sensitive to rotation rates. It is well known that atom interferometry can be used to measure accelerations and rotations, but it was a surprise to find out that tune-out wavelength measurements can under certain conditions be used to report the absolute rotation rate of the laboratory with respect to an inertial frame of reference. I also describe how we created conditions which improve the accuracy of tune out wavelength measurements. These measurements are important because they serve as a benchmark test for atomic structure calculations of line strengths, oscillator strengths, and dipole matrix elements. I present a new measurement of the longest tune-out wavelength in potassium, λzero = 768.9701(4) nm. To reach sub-picometer precision, an optical cavity surrounding the atom beam paths of the interferometer was used. Although this improved the precision of our experiment by increasing the light-induced phase shifts, the cavity also brought several systematic errors to our attentions. For example, I found that large ±200 pm shifts in tune-out wavelengths can occur due to the Earth's rotation rate. To solve this problem, I demonstrated that controlling the optical polarization, the magnetic field, and the atom beam velocity distribution can either suppress or enhance these systematic shifts. Suppressing these systemic shifts in tune-out wavelengths is useful for precision measurements used to test atomic structure calculations. By enhancing these systematic shifts, the interferometer can be a gyroscope that utilizes tune-out wavelengths.
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Yuen, Chi-king, and 阮志敬. "Feasibility of using neural network for air dispersion modelling." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1995. http://hub.hku.hk/bib/B31253325.
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Egorov, Roman V. "High resolution measurement of telecommunication component polarization mode dispersion by means of quantum interferometry." Thesis, Boston University, 2012. https://hdl.handle.net/2144/31544.
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Thesis (Ph.D.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.
As optical transport networks migrate towards supporting optical channel (or superchannel) bitrates of 100Gbps, 400Gbps, or even 1 Tbps, it becomes more important to conduct careful analysis, precise characterization, and optimized mitigation of polarization mode dispersion (PMD) in order to deliver optimal performance in fiber-optic communication systems. Telecommunication service providers need their system vendors to match the performance of their platforms to the overall system PMD accumulation, including both fiber and component PMD. The fiber PMD is a characteristic of the optical fiber plant and is very heterogeneous in both its design and time of installation. Today all installed fiber plants require mitigation solutions for PMD-induced impairments when transporting optical channels with bitrates of 40Gbps and higher. The component PMD is due to discrete components present in the optical path of a lightwave channel, such as Wavelength Selective Switches (WSS), amplifiers, Dispersion Compensating Modules (DCM), and multiplexer/demultiplexer structures. The proliferation of components, especially WSSs, has rapidly accelerated recently with the introduction of Reconfigurable Optical Add Drop Multiplexers (ROADM). Each component contributes a relatively small value to the overall system PMD. Until recently, these components were not considered to be important contributors to the total. The significance of component PMD suddenly became very apparent because ROADM introduction into the fiber-optic network fabric increased the number of components at least ten-fold. Depending on the Link Design Value (LDV) of network fabric, the component PMD can now contribute an amount similar to or even greater than the PMD penalty incurred in the fiber. Today's state of the art tedmiques in PMD measurement focus solely on characterizing fiber PMD. In our research we have developed a new method to measure very small values of PMD (or Differential Group Delay (DOD)) in discrete components of optical fiber communication systems based on the utilization of quantum interferometry. We designed a polarization counterpart of the Hong-Ou-Mandel (HOM) interferometer with entangled photons operating in the telecommunication region of the optical spectrum. Using this setup we were able to demonstrate close to 1 fs resolution while measuring DGD values of a 1x9 port Wavelength Selective Switch (WSS), based on Micro Electro Mechanical System (MEMS). We used a specially designed source of broadband polarization entangled photon pairs generated in the process of collinear type-II Spontaneous Parametric Down Conversion (SPDC). Our result paves the way for building future test and measurement devices that will be capable of resolving even smaller PMD values in discrete components of future optical communication systems, ultimately with atto-second resolution.
2031-01-01
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Gething, Bryce A. "The effect of security return dispersion on performance measurement in a South African context." Master's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/13123.
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Includes bibliographical references.This work replicates a similar study performed by de Silva et al. (2001). Our study was performed on the South African market. De Silva et al. (2001) studied the effect of cross-sectional volatility (CSV) on fund managerial skill measurement. This lead to the conjecture that increased fund performance dispersion was primarily due to higher CSV, and not changes in informational efficiency or ranges in managerial talent. In this dissertation we firstly critique the CSV-adjusted alpha as a measure of fund performance and show that it can only be used as a means of normalising fund performance, yet reveals very little with regard to managerial talent. Since fund performance is intrinsically linked to CSV, we find it difficult to disentangle the effects of CSV and managerial talent dispersion. Adjusting for CSV therefore also implies adjustment for managerial talent, and we conclude with ideas for how a CSV-adjusted alpha may be used to assess manager talent.
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Gustafsson, Stefan. "Electromagnetic dispersion modeling and analysis for HVDC power cables." Licentiate thesis, Linnéuniversitetet, Institutionen för datavetenskap, fysik och matematik, DFM, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-32525.
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Derivation of an electromagnetic model, regarding the wave propagation in a very long (10 km or more) High Voltage Direct Current (HVDC) power cable, is the central part of this thesis. With an existing “perfect” electromagnetic model there are potentially a wide range of applications.The electromagnetic model is focused on frequencies between 0 and 100 kHz since higher frequencies essentially will be attenuated. An exact dispersion relation is formulated and the propagation constant is computed numerically. The dominating mode is the first Transversal Magnetic (TM) mode of order zero, denoted TM01, which is also referred to as the quasi-TEM mode. A comparison is made with the second propagating TM mode of order zero denoted TM02. The electromagnetic model is verified against real time data from Time Domain Reflection (TDR) measurements on a HVDC power cable. A mismatch calibration procedure is performed due to matching difficulties between the TDR measurement equipment and the power cable regarding the single-mode transmission line model.An example of power cable length measurements is addressed, which reveals that with a “perfect” model the length of an 80 km long power cable could be estimated to an accuracy of a few centimeters. With the present model the accuracy can be estimated to approximately 100 m.In order to understand the low-frequency wave propagation characteristics, an exact asymptotic analysis is performed. It is shown that the behavior of the propagation constant is governed by a square root of the complex frequency in the lowfrequency domain. This thesis also focuses on an analysis regarding the sensitivity of the propagation constant with respect to some of the electric parameters in the model. Variables of interest when performing the parameter sensitivity study are the real relative permittivityand the conductivity.
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Elliott, Timothy John. "Chromatic dispersion measurement in single-mode optical fibers by acousto-optic modulation and phase detection." Thesis, Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/101274.
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A system to measure chromatic dispersion in single-mode optical fibers with near point wavelength resolution is described. Differential propagation constant data for the test fiber is collected by using an acousto-optic modulator to frequency-shift laser light passed to an optical heterodyne. Theoretical developments include a frequency-domain calculation technique for interpreting empirical results. The system is proven infeasible, however, due to inherent noise sensitivityM.S.
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KOSA, NADHIR BAHJAT. "NEW INTERFEROMETRIC METHOD FOR MEASURING CHROMATIC DISPERSION IN SINGLE MODE FIBERS (FOURIER TRANSFORM)." Diss., The University of Arizona, 1987. http://hdl.handle.net/10150/184171.
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A new interferometric method which indirectly measures the total chromatic dispersion of a single mode fiber is demonstrated. The technique utilizes a short length of fiber, an unmodulated broadband source, simple low frequency electronics, and a standard interferometer. The concept of this measurement is based on the behavior of the uncorrelated individual bursts of light from the elemental emitters that constitute a thermal source. Their propagation through a dispersive media, e.g., silica fiber, which is placed in one arm of the interferometer, is delayed and broadened. They will interfere with their counterpart from the other arm, generating a train of time-varying fringes as one mirror of the interferometer is uniformly translated. The local frequency of the fringes at a given position of the moving mirror is a direct measure of the instantaneous wavelength, while the mirror position itself demarks the corresponding relative delay. A colinearly launched HeNe laser beam is used as a reference to calibrate the other source's fringe width and location of the mirror. In this experiment, an edge-emitting LED of λo = 830 nm and Δλ = 60 nm was used. The tested fibers had a length of 27.9 cm and 38.3 cm, which made the width of the crosscorrelation function approximately 100 times greater than the source's coherence length. The speed of the mechanically driven mirror set the frequency of the HeNe fringes to approximately 800 Hz with an r.m.s. fluctuation around the mean of 0.2%. The SNR of the HeNe fringes was four times larger than the LED's. Ten different runs for each fiber were executed. Data from the two sets of simultaneous measurements of delay versus wavelength were used to fit the best linear and quadratic polynomials with a minimum residual mean error square. The derivative of this function with respect to wavelength gave the dispersion relation. The accuracy of measured delay and wavelength were 0.1 ps and 6 nm, respectively. The dispersion value and its standard error for the best linear fit was approximately 117 ∓ 2 ps/km nm. The standard error for the quadratic fit was much larger due to the high noise level accompanying signal. A thorough investigation of the noise sources, accuracies, standard error of the polynomial's coefficient, and SNR analysis is conducted. This measurement is simple and has the potential of achieving substantially higher accuracy--especially for the longer wavelength region where dispersion is minute.
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Thompson, Michael Thomas. "Fast amplitude and delay measurement for characterization of optical devices." Texas A&M University, 2006. http://hdl.handle.net/1969.1/4440.
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A fast measurement technique based on the modulation phase-shift technique is
developed to measure the wavelength-dependent magnitude and phase responses of
optical devices. The measured phase response is in the form of group delay, which is
used to determine the chromatic dispersion in the device under test by taking the
derivative of the group delay with respect to optical wavelength. The measurement
setup allows both step-tunable and sweeping laser sources. A modulation frequency of
up to 2.7 GHz is accommodated. An alternate method for the phase measurement that
overcomes non-linearities in the measurement setup is also presented. The speed of the
measurement setup is limited by the sweeping speed of the laser source, which for the
Agilent 81682A is 40 nm/sec. The magnitude accuracy is determined by taking a
comparison to the commercially available Micron Finisar measurement system, where
an error of 0.125 dB is noted. The phase accuracy of the measurement setup is tested
by taking the Hilbert transform of the measured magnitude response of an Acetylene
gas cell and comparing it to the integral of the measured group delay. The average
deviation between the two methods is 0.1 radians. An Acetylene gas cell, fiber Bragg
grating, and chirped Bragg grating are tested with the measurement setup and the
Agilent 8168The characterization of the setup leads to the conclusion that the measurement setup
developed in this paper is fast and accurate. The speed of the technique is on the order
of microseconds for a single measurement and excels beyond the speed of the standard
modulation phase-shift technique, which includes measurement times on the order of
minutes. The accuracy of the technique is within 0.125 dB for magnitude
measurements and 0.1 radians for phase measurements when compared to
commercially available measurement systems.2A laser source at 40 nm/sec and the measurement plots are presented.
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廖俊豪 and Chun-ho Liu. "Numerical modelling of atmospheric boundary layer with application to air pollutant dispersion." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1998. http://hub.hku.hk/bib/B31239018.
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Newhall, William George. "Wideband Propagation Measurement Results, Simulation Models, and Processing Techniques for a Sliding Correlator Measurement System." Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/35678.
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Radio wave propagation measurements provide a way to accurately and reliably characterize environments to assist in the development and optimization of wireless communication systems. As digital radio systems occupy wider bandwidths and use multipath signal combining to enhance quality of service, knowledge of time dispersion and the multipath structure of radio channels become increasingly important. The wideband measurement system presented herein provides a practical means to precisely measure the delays and strengths of individual multipath components which arrive at a radio receiver.
Presented in this Thesis are fundamental theory, practical implementation, and simulation models for a sliding correlator measurement system. The sliding correlator technique is explained in detail and large-scale measurement survey is presented. Techniques for statistically quantifying the characteristics of propagation using the sliding correlator measurements are presented and compared. The development of simulations of the sliding correlator system is described, and simulation results are used to test conventional and newly developed post-processing algorithms.
This Thesis presents a practical view of the sliding correlator measurement system, but its foundations are rooted in the theoretical results which are explained and derived herein. Propagation researchers and students in the wireless communication field may find this work and the cited references useful for continued study of wideband propagation measurements or for application of the sliding correlator system as a wideband measurement solution.
Master of Science
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Clark, Leah. "Measurement of the time dispersion due to multiple path trajectories in the shallow underwater acoustic channel." Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/15487.
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Bell, Matthew Richard. "Versatile high resolution dispersion measurements in semiconductor photonic nanostructures using ultrashort pulses." Thesis, St Andrews, 2007. http://hdl.handle.net/10023/339.
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Swantek, Steven David. "An Optical Method of Strain Measurement in the Split Hopkinson Pressure Bar." Thesis, Virginia Tech, 2000. http://hdl.handle.net/10919/34711.
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The split Hopkinson pressure bar (SHPB) continues to be one of the most common methods of testing materials at medium rates of strain. Elevated rates of strain, such as those found in impact and explosive applications, have been shown to induce phenomena such as strain hardening and phase transitions that can significantly affect the strength of most materials [14]. Due to its relative simplicity and robustness, the SHPB remains one of the preferred platforms for evaluating mechanical properties of materials at rates of strain up to approximately 104 in/in-s (s-1). At the Naval Surface Warfare Center Dahlgren Division (NSWCDD), research has been conducted in which a semiconductor laser diode has been used to measure the radial strain of a plastically deforming cylindrical test specimen in the SHPB.
The SHPB consists of two long, slender cylindrical bars, denoted input and output bars, that "sandwich" a cylindrical test specimen. Utilizing a high-pressure gas gun, a third cylindrical steel bar, known as the striker bar, is fired at the input bar, causing a compressive stress wave to travel through the input bar to the input bar - test specimen interface. At this interface, a portion of the stress wave propagates through the test specimen while the remainder of the pulse reflects back through the input bar as a tensile stress wave. The non-reflected portion of the stress pulse transmits through the test specimen and into the output bar causing the specimen to deform both elastically and plastically. Strain gages mounted to the input and output pressure bars measure both the incident, transmitted and reflected pulses. Specimen stress can be calculated using the transmitted strain signal while specimen strain and strain rate can be computed using the reflected strain pulse.
In order to measure the specimen strain directly, a 670-nm wavelength semiconductor laser diode was affixed to the SHPB such that a vertical line of light approximately 250 micrometer (µm) wide was generated across the diameter of the test specimen. A collector lens located aft of the specimen was positioned to collate the light not occluded by the diameter of the specimen and refocus the light to be collected by a 25 MHz photodetector. Thus, changes in specimen diameter due to the impact event would result in more light being occluded by the specimen and less spectral energy being collected by the photodetector. The light collected by the photodetector is then converted to a voltage output before being recorded by a digital storage oscilloscope. With a known voltage-to-diameter calibration relationship, medium strain rate compressive tests were conducted to compare the optically measured strain results with the data gathered with the existing strain gages.
It was found that the optical measurement system provided increased bandwidth and greater resolution than the conventional strain gage instrumentation while generating strain and strain rate results within 6.7% of corresponding strain gage data. This increased bandwidth and resolution allows the identification of both the elastic and plastic behavior of the specimen. In addition, the loading and unloading of the specimen can be clearly seen in the optical strain signal. These phenomena are evident in the peak diameter and strain achieved by the specimen, data not previously available with strain gage instrumentation. The plastic modulus, the theoretical relationship between the stress and strain in the plastic regime, also exhibits a significant increase in magnitude due to this ability to measure peak rather than average strain. Finally, by ridding the experiment of the input bar strain gage, input bar dispersion and the electrical and mechanical errors associated with the input bar strain gage were nullified. These conclusions will be validated through the presentation of several sets of experimental data correlated to data gathered previously.Master of Science
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So, Shuk-pan Ellen, and 蘇淑彬. "Large eddy simulations of wind flow and pollution dispersion in an urban street canyon." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2003. http://hub.hku.hk/bib/B29332710.
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Yoon, Sungsoo. "Array-Based Measurements of Surface Wave Dispersion and Attenuation Using Frequency-Wavenumber Analysis." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7246.
Full textAbstract:
Surface wave methods have been used to determine dynamic properties of near-surface soils in geotechnical engineering for the past 50 years. Although the capabilities of engineering surface wave methods have improved in recent years due to several advances, several issues including (1) near-field effects, (2) combined active and passive measurements, and (3) accurate measurements of surface wave attenuation still require study to further improve the capabilities of modern surface wave methods.
Near-field effects have been studied for traditional surface wave methods with two receivers and several filtering criteria to mitigate the effects have been recommended. However, these filtering criteria are not applicable to surface wave methods with multiple receivers. Moreover, the criteria are not quantitatively based and do not account for different types of soil profiles, which strongly influence near-field effects. A new study of near-field effects on surface wave methods with multiple receivers was conducted with numerical and experimental methods. Two normalized parameters were developed to capture near-field effects. Quantitatively based near-field effect criteria for an ideal homogeneous half-space and three typical soil profiles are presented.
Combining active and passive surface wave measurements allows developing a shear wave velocity profile to greater depth without sacrificing the near-surface resolution offered by active measurements. Generally, active and passive measurements overlap in the frequency range from approximately 4 to 10 Hz, and there are often systematic differences between the two measurements. The systematic errors in active and passive surface wave methods were explored to explain and resolve the differences, allowing for a more accurate composite dispersion curve.
The accuracy of measured surface wave attenuation is improved by properly accounting for (1) geometric spreading, (2) near-field effects, and (3) ambient noise. In this study, a traditional estimation method and a frequency-wavenumber method utilizing sub-arrays were investigated using displacement data from numerical simulations, focusing on near-field and ambient noise effects. Detailed procedures for the frequency-wavenumber estimation method are developed based on a study of the primary factors affecting attenuation estimates. The two methods are also evaluated using experimental displacement data obtained from surface wave field measurements with three different arrays.
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Gibson, Millan-John. "Fibre Length Distribution and Dispersion during the Injection Moulding Process: An experimental study evaluating fibre length attrition and dispersion during processing of long glass fibre reinforced polymer composites in injection moulding including an evaluation of long glass fibre measurement techniques." Thesis, University of Bradford, 2018. http://hdl.handle.net/10454/17360.
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This project evaluates fibre length dispersion and distribution within the injection moulding process of long glass fibre reinforced polypropylene, sponsored by Autodesk Simulation.
The primary material used in this investigation was a 15 mm long glass fibre reinforced polypropylene consisting of two fibre content levels, 20 wt. % and 40 wt. %.
A review of previous research was compiled in this study to evaluate various glass fibre measurement methods and fibre breakage studies to establish where along the injection moulding process fibre breakage predominantly occurs and which process parameters have the greatest influence on fibre length distribution along the screw.
Based on literature findings, a manual fibre length measurement method was developed and applied in this study and benchmarked against existing commercially available automated software programs and found to be more accurate in obtaining a reliable fibre length distribution within a glass fibre reinforced sample.
Fibre length measurements from the nozzle confirmed that the majority of fibre breakage had already occurred in the screw. Measurements taken along the screw showed a drastic decrease in weighted average glass fibre length from initial pellet form to the end of the metering zone with sudden transitions to lower weighted average values seen at the beginning of the feeding zone and along the compression zone.
Fibre dispersion results from the nozzle and along the screw through the use of a μ-CT scanner showed a complex fibre flow and orientation of fibres with the preservation of fibre clusters being seen all along the injection moulding process but chiefly in the feeding and compression zones of the screw.
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Gamatham, Romeo Reginald Gunther. "Investigation of polarization mode dispersion measurement perfomance in optical fibre with a focus on the fixed analyzer technique." Thesis, Nelson Mandela Metropolitan University, 2008. http://hdl.handle.net/10948/957.
Full textAbstract:
The work presented in this dissertation is a comparative study of polarization mode dispersion (PMD) measurement performance where the fixed analyzer (FA) technique was built and tested for the first time in South Africa. Techniques involved in the study are: the Jones matrix eigenanalysis (JME), generalised interferometric technique (GINTY) and the FA technique, with a particular focus on the FA technique. The FA PMD measurement technique determines the average differential group delay (DGD) from the transmitted intensity spectrum through a polarizer and has three analysis methods (extrema counting, mean level crossing and Fourier analysis) which were all evaluated. PMD measurements were performed in the laboratory on several different fibre types and in the field on buried deployed Telkom fibre links (28.8 km). The techniques showed good agreement in the measured PMD value, both in the laboratory and field measurements. In particular very good agreement was found between the JME average DGD and the extrema counting analysis PMD value. The GINTY and FA Fourier analysis method also gave very similar PMD values. It was found that the fibre birefringence and the mode coupling manifest in different ways on the intensity spectrum. By using the FA ratio method, the length regimes of the different fibre types were determined. Three characteristics of the FA technique were investigated, namely: wavelength window variation, sampling and input SOP scrambling. It was found that the wavelength window and the PMD are inversely proportional. Correct sampling plays a significant role in determining the correct measured PMD value. Lastly an average PMD value over the PMD values for different input SOPs serves as a better representation of the true PMD value. An additional study showed that the FA technique and a developed Poincaré sphere analysis method agree very well regarding the PMD value.
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Červenka, Dušan. "Metody řešení vlivu optické disperze na stávajících optických sítích." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2011. http://www.nusl.cz/ntk/nusl-218841.
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Polarization mode dispersion, PMD influence of fibres. Next includes optic dispersion measurement and compensation of optics dispersion follows. In the end thesis analyze measure of existing fibres, simulating and suggest optimal solutions.
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Kováč, Filip. "Reprodukovatelnost a přesnost měření polarizační vidové disperze." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2015. http://www.nusl.cz/ntk/nusl-221392.
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Thesis is divided into two parts. The first part is written rather in theoretical way. It deals with general formation of the dispersion mathematically and verbally. It focuses on the chromatic and polarization mode dispersion. Different types of optical fibers for category G.65X are mentioned as well in connection with the ITU-T. Further attention is drawn first to compensation and then the measurement both of the mentioned dispersions. The thesis describes also analyzers and their main features. The second part is devoted to practical measurements of polarization mode dispersion. In the beginning there are described the components used for construction of the optical measurements and topologies. It is followed by an analysis of an each optical link. The results of these measurement methods and their mutual comparisons are at the end of this section. Measurements in temperature chamber is the subject of a further practical part, which from the beginning captures the essential features of the temperature chamber. This is followed by a description of the measurements, analyses and final valuation depending on the amount of polarization mode dispersion versus the temperature.
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Patwari, Neal. "Measured and Modeled Time and Angle Dispersion Characteristics of the 1.8 GHz Peer-to-Peer Radio Channel." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/32201.
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In an extensive outdoor propagation study, low antenna heights of
1.7 m are used at both the transmitter and the receiver to measure
over 3500 wideband power-delay profiles (PDPs) of the channel for
a peer-to-peer communications system. Rural and urban areas are
studied in 22 different transmitter-receiver links. The results
are used to characterize the narrowband path loss, mean delay,
root-mean-square (RMS) delay spread, and timing jitter of the
peer-to-peer wideband channel. Small-scale fading characteristics are
measured in detail by measuring and analyzing 160 PDPs within each
local area. This thesis shows the measurement setup for the
calculation of fading rate variance and angular spread and reports
the first known attempt to calculate angular spread from track
power measurements. New analysis presented in this thesis shows
the effect of measurement error in the calculation of angular
spread. The expected characteristics of angular spread are
derived using two different angle-of-arrival (AOA) models from the
literature. Measurement results show initial validation of
Durgin's angular spread theory. A new measurement-based algorithm
for simulating wideband fading processes is developed and
implemented. This simulation technique shows promise in the
simulation of high-bit rate peer-to-peer radio communication
systems.Master of Science
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Baselt, Tobias, Christopher Taudt, Bryan Nelsen, Andrés Fabián Lasagni, and Peter Hartmann. "Experimental measurement and numerical analysis of group velocity dispersion in cladding modes of an endlessly single-mode photonic crystal fiber." SPIE, 2017. https://tud.qucosa.de/id/qucosa%3A35152.
Full textAbstract:
The optical properties of the guided modes in the core of photonic crystal fibers (PCFs) can be easily manipulated by changing the air-hole structure in the cladding. Special properties can be achieved in this case such as endless singlemode operation. Endlessly single-mode fibers, which enable single-mode guidance over a wide spectral range, are indispensable in the field of fiber technology. A two-dimensional photonic crystal with a silica central core and a micrometer-spaced hexagonal array of air holes is an established method to achieve endless single-mode properties. In addition to the guidance of light in the core, different cladding modes occur. The coupling between the core and the cladding modes can affect the endlessly single-mode guides. There are two possible ways to determine the dispersion: measurement and calculation.
We calculate the group velocity dispersion (GVD) of different cladding modes based on the measurement of the fiber structure parameters, the hole diameter and the pitch of a presumed homogeneous hexagonal array. Based on the scanning electron image, a calculation was made of the optical guiding properties of the microstructured cladding. We compare the calculation with a method to measure the wavelength-dependent time delay. We measure the time delay of defined cladding modes with a homemade supercontinuum light source in a white light interferometric setup. To measure the dispersion of cladding modes of optical fibers with high accuracy, a time-domain white-light interferometer based on a Mach-Zehnder interferometer is used. The experimental setup allows the determination of the wavelengthdependent differential group delay of light travelling through a thirty centimeter piece of test fiber in the wavelength range from VIS to NIR. The determination of the GVD using different methods enables the evaluation of the individual methods for characterizing the cladding modes of an endlessly single-mode fiber.
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Rydefalk, Staffan. "Particle Measurements Using Fluctuations in the Regular Transmittance of Light Through a Particle Dispersion : Concentration and Particles size - Theory, Measurement Principles and Applications for Pulp and Paper Production." Doctoral thesis, KTH, Industriell produktion, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10639.
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The regular transmittance of light or similar radiation through a flowing suspension of particles fluctuates because of the random occurrence of particles in the beam.In the work presented here, a theory for this fluctuating behaviour with the emphasison dispersions of mm-length slender cylindrical particles having circular crosssections is given. The particles in question are wood pulp fibres, which as a first approximation are considered to have a cylinder shape. Four possible measurementprinciples are described theoretically and experimentally. The four principles are for the measurement of concentration, length distribution characterized as lengthclasses, mean length, and mean width. The usefulness in industrial process monitoring of two of these principles is exemplified with pulp measurements. In order to estimate model errors, numerical simulations were used. Although other techniques such as image analysis may compete, the technique presented here is attractive because of the simplicity of the measurement device used.QC 20100806
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Correa, Loup. "Measurement of the generalized polarizabilities of the proton by virtual Compton scattering at MAMI and Q² = 0.2 GeV²." Thesis, Clermont-Ferrand 2, 2016. http://www.theses.fr/2016CLF22727/document.
Full textAbstract:
Ce travail présente la mesure des polarisabilités généralisées (GPs) électrique αE(Q2) et magnétique βM(Q2) du proton à Q2 =0.2 GeV 2. Les GPs sont définies dans le contexte de la diffusion Compton virtuelle (VCS), γ*p → γp, où Q2 est le quadri-moment de transfert du photon virtuel. Les GPs sont la généralisation des polarisabilités mesurées en diffusion Compton réel (RCS) en considérant leur dépendance en Q2. Ce sont des propriétés dynamiques du proton définissant sa déformation lorsqu'un champ électromagnétique lui est appliqué. αE(Q2) (ou βM(Q2)) donne accès à la densité de polarisation (magnétisation) locale du proton déformé. L'effet des GPs ne contribuant qu'à 1 – 15 % de la section efficace ep → epγ une mesure de haute précision est requise. Ce travail s'inscrit dans le cadre d'une expérience conduite par la collaboration A1 de MAMI à trois valeurs inédites de Q2 : 0.1,0.2 et 0.45 GeV 2. L'analyse de premier niveau comporte une calibration détaillée des données expérimentales et l'utilisation d'une simulation de l'expérience. L'extraction des GPs requiert la mesure et la renormalisation des sections efficaces ep → epγ et la correction des effets radiatifs. Les résultats obtenus par le fit « LEX » et « DR » sont en très bon accordThis work presents the measurement of the generalized electric αE(Q2) and magnetic βM(Q2) polarisabilities (GPs) of the proton. The GPs are defined in the Virtual Compton Scattering (VCS) context, i.e. the reaction γ*p → γp where Q2 is the four-momentum transfer of the virtual photon. The GPs are a generalization of polarizabilities measured in real Compton scattering (RCS) by taking into account the Q2-dependency. They are dynamical properties of the proton when it is deformed by an applied electromagnetic fiels. αE(Q2) (or βM(Q2)) gives access to the local polarization (or magnetization) density of the deformed proton. The studied VCS process is accessible by the photon-electroproduction reaction (ep → epγ). The GP effect is a 1 – 15 % contribution to the ep → epγ cross section, requiring a high-precision mleasurement. The present work is a part of an experiment conducted by the A1 collaboration at MAMI at three new Q2 values : 0.1,0.2 and 0.45 GeV 2. This thesis details the extraction at 0.2 GeV 2. The experiment uses the 1 GeV electron beam, the 5 cm liquid hydrogen target and spectrometers A (B) to detect the final electron (proton). The first-level analysis includes a detailed calibration of experimental data, and the use of a simulation of the experiment. The measurement of the unpolarized ep → epγ cross section is described with two of its important features : the correction of the radiative effects and the renormalization. Two differents frameworks are used to extract the GPs : the Low Energy Theorem (LET) and the dispersion relation model (DR). The two extractions lead to results in good argument. The world data still raises question about the Q2-behavior of the Gps
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Masey, Nicola. "Development and evaluation of portable passive and real-time measurement systems, and dispersion models, to estimate exposure to traffic-related air pollutants." Thesis, University of Strathclyde, 2018. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=29435.
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This research developed efficient applications of portable measurement systems to assess human exposure to traffic-related air pollution through direct measurement, and evaluation of exposure models. Passive NO2 samplers are deployed at large numbers of sites in epidemiological studies to estimate typical concentrations over 1-4 weeks. I found that deployment time could be reduced to 2 days with limited impact on the accuracy and precision of exposure estimates. This shorter measurement time enabled observation of wind-speed effects leading to overestimation of ambient concentrations by passive samplers. Through development of a post-processing technique and/or inclusion of a membrane I improved sampler accuracy. Portable sensors can provide detailed estimates of personal exposures to air pollution. Many sensor-based monitors have not been subject to rigorous testing procedures to quantify their accuracy. I observed that the most accurate estimates of concentrations from NO2 and O3 sensor-based monitors required regular, intermittent calibration against reference analysers under similar environmental conditions to field measurements. I also found deterioration in BC monitor accuracy and precison when the attenuation of the collection filter exceeded 40 and no improvement in monitor accuracy was observed when filter darkness correction algorithms were applied. Portable sensors can be used to identify locations with higher concentrations, which may require more detailed monitoring. I established that repeated 6-minute measurements of BC and particle number concentrations estimated similar spatial trends to 1-week NO2 measurements using passive samplers. Dispersion models can be used to estimate pollution exposure at multiple locations over a study area. I found that initial user parameterisation in a weather model had limited effect on pollution estimates from a dispersion model. I evaluated a new GIS-based dispersion model (5 x 5 m NO2 estimates for a 3,500 km2 area, with model run times of under 10 minutes). I demonstrated that inclusion of discrete street canyon models and geospatial surrogates (accounting for urban morphology) improved model accuracy. The measurement and modelling evaluation research in this thesis complimented each other by providing efficient ways to directly measure population exposures.
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Prášil, Jiří. "Metody řešení vlivu optické disperze na stávajících optických sítích." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2009. http://www.nusl.cz/ntk/nusl-218200.
Full textAbstract:
This diploma thesis deals with analysis of current diagnostic methods of optical networks, and it is focused on optical fiber dispersion in singlemode fibers. The work starts with a describtion chromatic dispersion and polarization mode dispersion, causes of and thein influence on the transmitted signal at the beginning. There are set out principles and their appropriate use in the list of measuring methods. Furthermore, the work are given the current possibilities for compensation above dispersions. The sixth chapter deals with the measurements and simulations of real routes in the OptiSystem. There are given appropriate compensation methods for the selected route speeds in the last chapter. The simulation is performed for the bit rate 2.5 Gbit / s, 10 Gbit / s and 40 Gbit / s.
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Kyselák, Martin. "Disperzní vlivy optických vláken na multiplexní přenosy." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2009. http://www.nusl.cz/ntk/nusl-233474.
Full textAbstract:
This doctoral thesis deals with present trend to turn up the bit rate of the optical fibres making use of wavelenght multiplex systems. There are new theoretical and practical problems caused by the new technologies. Except the known modal dispersion there exist problems caused by chromatical and polarization mode dispersion. In the opening of the thesis the known effects, which influence the payload signal, are introduced. The polarization mode dispersion has the main attention. Within the scope of this thesis there has been programmed the statistical calculator which can analyses the measured values of differential group delay by Monte Carlo calculation. Next meaningful output is the designating application of the optical routes. It is possible to mathematicaly unambiguously define the polarization mode dispersion by Jones, Stokes and Poynting vectors. This complicated calculations are mechanized and in the simulation application make possible to simulate the signification of the PMD influence at different input parameters. The thesis includes the study of the PMD modulation format impact with the results of simulations and confrontation with other scientists results. The significant output are the final practical results examinations, which can be implemented thanks to the possibility of using the FTB-5500B measuring device.
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Zhang, Runtong. "Measurement of effective diffusivity : chromatographic method (pellets & monoliths)." Thesis, University of Bath, 2013. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608352.
Full textAbstract:
This thesis aims to find out the effective diffusivity (Deff) of a porous material – γ-alumina, using an unsteady state method with two inert gases at ambient condition with no reactions. For porous materials, Deff is important because it determines the amount of reactants that transfers to the surface of pores. When Deff is known, the apparent tortuosity factor of γ-alumina is calculated using the parallel pore model. The apparent tortuosity factor is important because: (a) it can be used to back-calculate Deff at reacting conditions; (b) once Deff with reactions is known, the Thiele modulus can be calculated and hence the global reaction rate can be found; (c) apparent tortuosity factor is also important for modelling purposes (e.g. modelling a packed-bed column or a catalytic combustion reactor packed with porous γ-alumina in various shapes and monoliths). Experimental measurements were performed to determine the effective diffusivity of a binary pair of non-reacting gases (He in N2, and N2 in He) in spherical γ-alumina pellets (1 mm diameter), and in γ-alumina washcoated monoliths (washcoat thickness 20 to 60 µm, on 400 cpsi (cells per square inch) cordierite support). The method used is based on the chromatographic technique, where a gas flows through a tube, which is packed with the sample to be tested. A pulse of tracer gas is injected (e.g. using sample loops: 0.1, 0.2, 0.5 ml) and by using an on-line mass spectrometer the response in the outlet of the packed bed is monitored over time. For the spherical pellets, the tube i.d. = 13.8 mm and the packed bed depths were 200 and 400 mm. For monoliths the tube i.d. = 7 mm and the packed lengths were 500 and 1000 mm. When the chromatographic technique was applied to the monoliths, it was observed that experimental errors can be significant, and it is very difficult to interpret the data. However, the technique worked well with the spherical pellets, and the effective diffusivity of He in N2 was 0.75 – 1.38 × 10-7 m2 s-1, and for N2 in He was 1.81 – 3.10 × 10-7 m2 s-1. Using the parallel pore model to back-calculate the apparent tortuosity factor, then a value between 5 to 9.5 was found for the pellets.
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Barbosa, Itamar Magno. "Estudo das dispersões metrológicas em redes neurais artificiais do tipo Multilayer Perceptrons através da aplicação em curvas de calibração." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/3/3142/tde-12082010-113757/.
Full textAbstract:
Este trabalho é um estudo das dispersões metrológicas em aproximações de funções tidas como não conhecidas ou não totalmente conhecidas. A metodologia alternativa para esse fim são as redes neurais artificiais do tipo Multilayer Perceptrons (MLP), aqui utilizadas como aproximadoras de funções. As funções aproximadas são curvas de calibração decorrentes de indicações de instrumentos ou sistemas de medição numa calibração. Essas curvas levam consigo propriedades metrológicas e possuem, neste trabalho, papel de ponte entre os elementos considerados da teoria metrológica e os elementos considerados da teoria da Inteligência Computacional: as Multilayer Perceptrons (MLPs). Uma balança externa de medição de esforços aerodinâmicos e uma Língua Eletrônica (LE), aplicada na medição da concentração de cátions, foram os meios de aplicação dos conceitos dessa metodologia alternativa. As proposições desta tese visam implementar melhorias na exatidão do ajuste das curvas de calibração por meio da consideração dos seguintes fatores: grandezas de influências, incertezas nos Valores Objetivos (VOs), tendência de medição de erros sistemáticos ocultos ou não solvidos e indicadores de desempenho metrológicos. A indicação da qualidade na medição ou a indicação da competência metrológica de um laboratório de calibração é estabelecida pelos valores das incertezas, e a curva de calibração é o ponto de partida para os cálculos desses valores. Visto que o estabelecimento dessa curva é uma das dificuldades para o cálculo das incertezas e a própria curva é uma fonte de incerteza, sua aproximação requer uma a cuidadosa e meticulosa metodologia, daí a importância estratégica deste trabalho. As dispersões metrológicas possuem conotação de incertezas nas medições e elas são a base para a determinação de seu valor numérico; assim, os indicadores de desempenho podem representar essas dispersões e a recíproca também é verdadeira: a incerteza padrão pode ser um dos indicadores de desempenho. Sintetizando, nesta tese é mostrado de que forma a teoria da inteligência computacional adentra na teoria da metrologia e vice versa, nas esferas dos elementos aqui considerados.The present study investigates metrological dispersions in fitting partially or totally unknown functions. An alternative method is the application of a multilayer perceptron neural network used here to fit functions. The fitting functions are calibration curves from calibration indications of measurement systems or instruments. These curves hold metrological properties and establish a link between elements of Metrological theory and elements of Computing Intelligence theory: the Multilayer Perceptrons. An external balance of aerodynamic forces and moments and an electronic tongue applied in the measurement of cation concentrations were the measurement systems used to apply the concepts of this alternative methodology. This thesis proposes improvements in the accuracy of fitting calibration curves considering the following factors: influence quantities, uncertainties about target values, tendency of hidden or not solved systematic errors and metrological performance functions. The measurement quality indicator or the laboratory metrological competence indicator is established by uncertainty values and the calibration curve is the starting point for the calculation of these values. The establishment of this curve is one of the difficulties in assessing uncertainties and the curve itself is an uncertainty source. Therefore, a careful and meticulous methodology is necessary in curve approximation, which explains the strategic importance of this work. Metrological dispersions have connotation of uncertainty in measurements and are the basis for calculating their numerical values, the performance functions can represent metrological dispersions and the opposite is also true: the standard uncertainty can be a performance function. Making a synthesis, this thesis demonstrates how computing intelligence theory takes into account the metrological theory and vice versa, in the elements of these theories that were discussed in the present study.
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Taudt, Ch, T. Baselt, B. Nelsen, H. Aßmann, A. Greiner, E. Koch, and P. Hartmann. "Measurement of surface topographies in the nm-range for power chip technologies by a modified low-coherence interferometer." SPIE, 2016. https://tud.qucosa.de/id/qucosa%3A35098.
Full textAbstract:
This work introduces a modified low-coherence interferometry approach for nanometer surface-profilometry. The key component of the interferometer is an element with known dispersion which defines the measurement range as well as the resolution. This dispersive element delivers a controlled phase variation which can be detected in the spectral domain and used to reconstruct height differences on a sample. In the chosen setup, both axial resolution and measurement range are tunable by the choice of the dispersive element.
The basic working principle was demonstrated by a laboratory setup equipped with a supercontinuum light source (Δλ = 400 ̶ 1700 nm). Initial experiments were carried out to characterize steps of 101 nm on a silicon height standard. The results showed that the system delivers an accuracy of about 11.8 nm. These measurements also served as a calibration for the second set of measurements. The second experiment consisted of the measurement of the bevel of a silicon wafer. The modified low-coherence interferometer could be utilized to reproduce the slope on the edge within the previously estimated accuracy. The main advantage of the proposed measurement approach is the possibility to collect data without the need for mechanically moving parts.
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Mazzaro, Irineu. "Medidas de dispersão anômala de raios-x." Universidade de São Paulo, 1989. http://www.teses.usp.br/teses/disponiveis/54/54132/tde-30042009-102653/.
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Com a crescente disponibilidade de luz síncrotron tem-se utilizado cada vez mais a dispersão anômala (f´) no estudo de materiais. Apesar dos vários métodos já empregados na medida do fator de espalhamento atômico, ainda é pequeno o número de elementos abrangidos. Este trabalho apresenta uma contribuição à ampliação da gama de elementos mensuráveis através de um método interferométrico diferencial para a determinação experimental de f´. A sua demonstração é feita através de medidas em Selênio obtendo-se o mesmo nível de precisão do método Υ-Υ/2 usado em trabalhos anteriores. Esses dois métodos são criticados quanto ao limite de erro atingível devido à sua natureza não-absoluta. Uma técnica de preparação de amostras para materiais de baixo ponto de fusão é explorada, permitindo determinar f´absolutamente, com erro de 0,03 elétron. A medida do fator de espalhamento atômico através do desvio angular entre as reflexões de Bragg e Laue é proposta e testada com resultados de qualidade bastante inferior às técnicas interferométricas. A construção de interferômetros de raios X estáveis e de alto contraste é estudada quanto à seleção dos monocristais de silício e tratamento após o corte do dispositivo, atingindo-se contraste de 80% com estabilidade de uma milifranja por hora.The use of anomalous dispersion (f\') in the study of materials has been increasing with the availability of synchrotron radiation. Although many methods have been designed for the measurement of the atomic scattering factor, the number of elements the cover is still small. This work presents a contribution to the widening of the range of measurable elements through a Differential interferometric method for the determination of f´. Its demonstration is achieved by measurements on Selenium, reaching the same level of accuracy obtained by the Υ-Υ/2 method used in previous work. These two methods are criticized in terms of the achievable errors due to its non-absolute nature. A technique for the preparation of samples with low melting point materials is developed, allowing the determination of f´ absolutely, with an error of 0,03 electron. The measurement of atomic scattering factor through the angular offset between Bragg and Laue reflections is proposed and tested, with low quality results compared to interferometric methods. The construction of high stability and good contrast X-ray interferometers is studied in terms of silicon single crystal selection and its treatment after device cutting. 80% contrast was achieved with a stability of one milifringe per hour.
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Westafer, Ryan S. "Investigation of phononic crystals for dispersive surface acoustic wave ozone sensors." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41165.
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The object of this research was to investigate dispersion in surface phononic crystals (PnCs) for application to a newly developed passive surface acoustic wave (SAW) ozone sensor. Frequency band gaps and slow sound already have been reported for PnC lattice structures. Such engineered structures are often advertised to reduce loss, increase sensitivity, and reduce device size. However, these advances have not yet been realized in the context of surface acoustic wave sensors. In early work, we computed SAW dispersion in patterned surface structures and we confirmed that our finite element computations of SAW dispersion in thin films and in one dimensional surface PnC structures agree with experimental results obtained by laser probe techniques. We analyzed the computations to guide device design in terms of sensitivity and joint spectral operating point. Next we conducted simulations and experiments to determine sensitivity and limit of detection for more conventional dispersive SAW devices and PnC sensors. Finally, we conducted extensive ozone detection trials on passive reflection mode SAW devices, using distinct components of the time dispersed response to compensate for the effect of temperature. The experimental work revealed that the devices may be used for dosimetry applications over periods of several days.
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Allam, Nadine. "Estimation des émissions surfaciques du biogaz dans une installation de stockage des déchets non dangereux." Thesis, Nantes, Ecole des Mines, 2015. http://www.theses.fr/2015EMNA0187/document.
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Les ISDND produisent du biogaz par fermentation des déchets organiques. Le biogaz principalement composé de CH4 et CO2 représente un enjeu environnemental majeur. Cette étude propose un outil d’estimation des émissions surfaciques de biogaz d’une ISDND par modélisation de la dispersion atmosphérique d’un gaz traceur, en l’occurrence, le méthane. Les dynamiques spatiales et temporelles des concentrations en CH4 et en COV ont été suivies sur et dans l’entourage de l’ISDND d’étude (Séché Environnement) en fonction des conditions météorologiques. Les résultats montrent des faibles teneurs atmosphériques en COV et en CH4 sur le site d’étude validant une faible émission de ces espèces. Les COV mesurés sont émis par différentes sources dont la contribution est plus importante que celle de l’ISDND et aucun COV ne constitue un traceur de biogaz émis par le site. En revanche, l’ISDND apparait comme source principale du CH4 détecté. Deux méthodes sont proposées pour estimer les émissions surfaciques de méthane en utilisant un modèle de dispersion atmosphérique Gaussien ADMS, validé par comparaison des teneurs atmosphériques en méthane mesurées et modélisées et leur dynamique temporelle. La première méthode repose sur une approche inverse et la deuxième est une approche statistique par régression. Les émissions de CH4 sont estimées pour la période d’exposition de la diode laser aux émissions du site pour 4 scénarios météorologiques types identifiés par une classification hiérarchique. Les résultats valident l’influence des paramètres météorologiques, surtout de la stabilité de l’atmosphère, sur la dispersion atmosphérique et les émissions surfaciques en méthaneLandfill sites produce biogas by degradation of biodegradable organic matter. Biogas mainly composed of CH4 and CO2 represents a major environmental challenge. This study propose a method to estimate biogas surface emissions in landfill sites using atmospheric dispersion modeling of a tracer gas, in this case, methane. The spatial and temporal dynamics of CH4 and VOC concentrations have been followed on the studied landfill site (Séché Environnement) for several weather conditions. Measurement results show low atmospheric VOC and CH4 concentrations on the studied landfill site which validates low emissions of these compounds. Detected VOC are emitted by different sources, excluding the landfill site. The contribution of these sources on VOC concentrations is more important than that of the landfill site and no VOC could be identified as tracer of biogas emitted by landfill site. However, CH4 is emitted by the landfill site, its principal source. Two methods are proposed to estimate methane surface emissions using a Gaussian atmospheric dispersion model ADMS. Gaussian model is validated by comparison of the temporal dynamics and atmospheric concentrations of methane measured on the site and those modeled. The first method is based on an inverse approach and the second one is a statistical regression approach. CH4 emissions are estimated for the exposure period of the laser diode to the site emissions and for 4 weather scenarios identified by a hierarchical classification. Results validate the influence of meteorological parameters, especially the stability of the atmosphere, on the atmospheric dispersion and methane surface emissions
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Lawrence, Cameron Eoin. "Measurement of 222Rn Exhalation Rates and 210Pb Deposition Rates in a Tropical Environment." Queensland University of Technology, 2006. http://eprints.qut.edu.au/16291/.
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This thesis provides the measurements of 222Rn exhalation rates, 210Pb deposition rates and excess 210Pb inventories for locations in and around Ranger Uranium Mine and Jabiru located within Kakadu National Park, Australia. Radon-222 is part of the natural 238U series decay chain and the only gas to be found in the series under normal conditions. Part of the natural redistribution of 222Rn in the environment is a portion exhales from the ground and disperses into the atmosphere. Here it decays via a series of short-lived progeny, that attach themselves to aerosol particles, to the long lived isotope 210Pb (T1/2 = 22.3 y). Attached and unattached 210Pb is removed from the atmosphere through wet and dry deposition and deposited on the surface of the earth, the fraction deposited on soils is gradually transported through the soil and can create a depth profile of 210Pb. Here it decays to the stable isotope 206Pb completing the 238U series. Measurements of 222Rn exhalation rates and 210Pb deposition rates were performed over complete seasonal cycles, August 2002 - July 2003 and May 2003 - May 2004 respectively. The area is categorised as wet and dry tropics and it experiences two distinct seasonal patterns, a dry season (May-October) with little or no precipitation events and a wet season (December-March) with almost daily precipitation and monsoonal troughs. November and April are regarded as transitional months. As the natural processes of 222Rn exhalation and 210Pb deposition are heavily influenced by soil moisture and precipitation respectively, seasonal variations in the exhalation and deposition rates were expected. It was observed that 222Rn exhalation rates decreased throughout the wet season when the increase in soil moisture retarded exhalation. Lead-210 deposition peaked throughout the wet season as precipitation is the major scavenging process of this isotope from the atmosphere. Radon-222 is influenced by other parameters such as 226Ra activity concentration and distribution, soil porosity and grain size. With the removal of the influence of soil moisture during the dry season it was possible to examine the effect of these other variables in a more comprehensive manner. This resulted in categorisation of geomorphic landscapes from which the 222Rn exhalation rate to 226Ra activity concentration ratios were similar during the dry season. These results can be extended to estimate dry season 222Rn exhalation rates from tropical locations from a measurement of 226Ra activity concentration. Through modelling the 210Pb budget on local and regional scales it was observed that there is a net loss of 210Pb from the region, the majority of which occurs during the dry season. This has been attributed to the fact that 210Pb attached to aerosols is transported great distance with the prevailing trade winds created by a Hadley Circulation cell predominant during the dry season (winter) months. By including the influence of factors such as water inundation and natural 210Pb redistribution in the soil wet season budgeting of 210Pb on local and regional scales gave very good results.
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Neri, Quiroz José Antonio. "Développement d’un lab-on-chip pour la mesure d’acidité libre de solutions chargées en cations hydrolysables." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE1247/document.
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Une étude conjointe du CEA et d'AREVA la Hague a montré qu'une des voies d'amélioration majeure des usines de traitement/recyclage du combustible nucléaire usagé, actuelles et futures, concerné le domaine de l'analyse. En effet, le suivi et le pilotage des procédés déployés dans ces usines nécessitent de nombreuses analyses générant de grandes quantités d'effluents radioactifs. Réduire les volumes mis en jeu lors de ces analyses permettrait donc de réduire la nocivité des échantillons et des effluents et donc d'accroitre la sureté pour le personnel et de réduire l'impact sur l'environnement et le coût de fonctionnement des usines. Parmi toutes les analyses effectuées, la mesure d'acidité libre est la plus fréquente, car c'est un paramètre indispensable pour pouvoir piloter correctement le procédé. C'est pourquoi, ces travaux de thèse ont abouti à l'amélioration de la méthode de mesure via une réduction d'échelle de l'analyse et une automatisation du protocole de mesure. Deux voies ont été étudiées : - le titrage par injection séquentielle (SIA), qui est un dispositif de 25 L de volume et qui par rapport à la méthode d'analyse de référence, réduit 1000 fois le volume d'échantillon nécessaire à l'analyse, 8 fois le temps d'analyse et 40 fois le volume d'effluents générés. - le titrage ballist-mix emploie un dispositif microfluidique qui, après intégration et réduction des composants, peut atteindre un volume de 25 mL et offre des performances analytiques comparables à celles obtenues en SIA. La méthode par SIA a été validée sur des solutions chargées en uranium alors que la technologie utilisée pour développer les titrages ballist-mix est en cours de validation. Cependant le principe opératoire du titrage ballist-mix est plus avantageux puisqu'il simplifie le travail de développement analytique du fait de la possibilité de simuler en avance les phénomènes physicochimiques ayant lieu lors du titrageA joint study between the CEA and Areva La Hague has shown that chemical analysis is a crucial parameter for achieving a better performance in present and future spent nuclear fuel reprocessing plants. In fact, each plant’s process monitoring and control require a significant amount of laboratory analysis leading in overall to a considerable amount of nuclear waste. Hence, reducing the sample’s required volume for analysis would reduce its toxicity and subsequent waste, therefore increasing personnel safety, decreasing the environmental impact and the plant’s operation cost. Among the process control analytical workload, the free acidity measurement has been identified as a key analysis due to its measurement frequency. For this reason, the main objective of this research has been focused in the improvement of a reference method for free acidity measurement. The following work has been divided in two main studies seeking for the reduction of the sample volume and the automation of the analytical method protocol: - Sequential Injection Analysis (SIA) titration, whose application requires the employment of a device occupying a 25 L space, and which reduces 1000 fold the sample volume per analysis, 8 times the analysis time and 40 fold the amount of waste generated when compared to the reference analytical method. - Ballist-mix titration, whose analytical performance is equivalent to the SIA titration, but whose implementation is done inside a microfluidic device occupying a volume as low as 25 mL after integration of all of the elements needed for analysis. At the present time, the SIA titration has been validated using nitric acid samples containing uranyl cations, whereas the ballist-mix titration is being validated with the same sample conditions. However, this last analytical technique features a simplified operating principle which allows the user to shorten the analytical development process by opening the possibility to simulate the process before any experimentation
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Taudt, Ch, T. Baselt, B. Nelsen, H. Aßmann, A. Greiner, E. Koch, and P. Hartmann. "Two-dimensional low-coherence interferometry for the characterization of nanometer wafer topographies." SPIE, 2016. https://tud.qucosa.de/id/qucosa%3A35105.
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Within this work a scan-free, low-coherence interferometry approach for surface profilometry with nm-precision is presented. The basic setup consist of a Michelson-type interferometer which is powered by a supercontinuum light-source (Δλ = 400 - 1700 nm). The introduction of an element with known dispersion delivers a controlled phase variation which can be detected in the spectral domain and used to reconstruct height differences on a sample. In order to enable scan-free measurements, the interference signal is spectrally decomposed with a grating and imaged onto a two-dimensional detector. One dimension of this detector records spectral, and therefore height information, while the other dimension stores the spatial position of the corresponding height values.
In experiments on a height standard, it could be shown that the setup is capable of recording multiple height steps of 101 nm over a range of 500 µm with an accuracy of about 11.5 nm. Further experiments on conductive paths of a micro-electro-mechanical systems (MEMS) pressure sensor demonstrated that the approach is also suitable to precisely characterize nanometer-sized structures on production-relevant components. The main advantage of the proposed measurement approach is the possibility to collect precise height information over a line on a surface without the need for scanning. This feature makes it interesting for a production-accompanying metrology.
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Bachtiar, Vera Surtia. "Improving air quality dispersion models using lidar measurements." Thesis, University of Salford, 2011. http://usir.salford.ac.uk/26558/.
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Atmospheric boundary layer height is one of the most important parameters in atmospheric dispersion modelling because it has a large effect on predicted air quality. Comparisons between Atmospheric Dispersion Modelling System, version 4 (ADMS 4) and lidar data were carried out on boundary layer height data from central London. The comparison showed that the boundary layer height predicted by the ADMS 4 was, on average, lower than lidar for the subset of data taken. ADMS 4 has a very simple surface scheme which is not representative of complex urban environments and the results from this research imply that there is not sufficient surface roughness within the model to produce a large enough boundary layer height. This research aims to create an improved urban surface scheme to better forecast the growth of the daytime urban boundary layer in air quality dispersion models using lidar measurements. Improved performance of ADMS in an urban area was achieved by a number of steps carried out in this study. They were: establishing the weaknesses of ADMS, developing a combined model for atmospheric boundary layer height, sensitivity analysis and validation. The combined model was developed by combining a surface model and the atmospheric boundary layer height model. Measurements of the atmospheric boundary layer height by lidar used backscatter and vertical velocity variance. However, vertical velocity variance was chosen for comparison with the combined model. Statistically, the combined model was better than ADMS. Sensitivity analysis, which used reasonable ranges of meteorological data for the UK, encompassed surface roughness, friction velocity, sensible heat flux and potential temperature gradient above the atmospheric boundary layer and the atmospheric boundary layer height. A good agreement was observed between the combined model and lidar measurement using data collected at a site in Greater Manchester. The overall conclusion was that the combined model improved the performance of ADMS in urban areas.
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Louka, Petroula. "Measurements of airflow in an urban environment." Thesis, University of Reading, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312298.
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Gomit, Guillaume. "Développement de techniques de mesure de surfaces libres par moyens optiques : Application à l'analyse de l'écoulement généré par un modèle de bateau en bassin des carènes." Phd thesis, Université de Poitiers, 2013. http://tel.archives-ouvertes.fr/tel-01062934.
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Le développement de techniques de mesure optiques de surfaces libres permettant la mesure des ondes générées par un modèle de navire en bassin des carènes est proposé dans ce mémoire. Trois méthodes, toutes basées sur un système de prises de vues stéréoscopiques, sont présentées. La première repose sur l'emploi de procédures d'inter-corrélation des images des caméras composant le système de stéréovision. La seconde s'appuie sur la théorie de la réfraction de la lumière au travers de l'interface air/eau. La troisième méthode est basée sur l'identification des projections de faisceaux laser sur la surface libre vue par un système stéréoscopique. Ces méthodes sont appliquées à la mesure du champ de vague autour d'un modèle de navire tracté dans le bassin des carène de l'Institut Pprime et dans un bassin des carènes de grande taille (B600 de la DGA Techniques hydrodynamique) et permettent la reconstruction et l'analyse du sillage. Les principales caractéristiques des champs de vagues et leurs dépendances au nombre de Froude sont étudiées en détail. Afin de compléter l'étude de l'écoulement généré par le modèle de navire, des mesures de PIV stéréoscopique autour de la carène, des mesures spécifiques de la vague d'étrave et des simulations numériques sont réalisées. L'ensemble de ces données permettent l'analyse de champs de vitesse tridimensionnelle proche de la coque et l'identification des caractéristiques du champ de vague de l'étrave jusqu'au champ lointain.
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Taudt, Ch, T. Baselt, B. Nelsen, H. Assmann, A. Greiner, E. Koch, and P. Hartmann. "Evaluation of the thermal stability of a low-coherence interferometer for precision surface profilometry." SPIE, 2017. https://tud.qucosa.de/id/qucosa%3A34883.
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Manufacturing of precise structures in MEMS, semiconductors, optics and other fields requires high standards in manufacturing and quality control. Appropriate surface topography measurement technologies should therefore deliver nm accuracy in the axial dimension under typical industrial conditions. This work shows the characterization of a dispersion-encoded low-coherence interferometer for the purpose of fast and robust surface topography measurements. The key component of the interferometer is an element with known dispersion. This dispersive element delivers a controlled phase variation in relation to the surface height variation which can be detected in the spectral domain. A laboratory setup equipped with a broadband light source (200 - 1100 nm) was established. Experiments have been carried out on a silicon-based standard with height steps of 100 nm under different thermal conditions such as 293.15 K and 303.15 K. Additionally, the stability of the setup was studied over periods of 5 hours (with constant temperature) and 15 hours (with linear increasing temperature). The analyzed data showed that a height measurement of 97.99 ± 4:9nm for 293.15 K and of 101.43 ± 3:3nm for 303.15 K was possible. The time-resolved measurements revealed that the developed setup is highly stable against small thermal uctuations and shows a linear behaviour under increasing thermal load. Calibration data for the mathmatical corrections under different thermal conditions was obtained.
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Benvegnù, Agostino. "Trapping and Reliability investigations in GaN-based HEMTs." Thesis, Limoges, 2016. http://www.theses.fr/2016LIMO0064/document.
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Les transistors à haute mobilité d’électrons (HEMTs) en nitrure de gallium (GaN) s’affirment comme les candidats prometteurs pour les futurs équipements à micro-ondes - tels que les amplificateurs de puissance à état solide (SSPA), grâce à leurs excellentes performances. Une première démonstration d'émetteur en technologie GaN-MMIC a été développée et embarquée dans la mission spatiale PROBA-V. Mais cette technologie souffre encore des effets de pièges par des défauts présents au sein de la structure. L’objectif de ce travail est donc l'étude d’effets de pièges et des aspects de fiabilité des transistors de puissance GH50 pour des applications en bande C. Un protocole d’investigation des phénomènes de pièges est présenté, qui permet l’étude des dynamiques des effets de pièges du mode de fonctionnement DC au mode de fonctionnement radiofréquence, basé sur la combinaison des mesures IV impulsionnelles, des mesures de transitoires du courant de drain avec des impulsions DC et RF et des mesures de paramètres [S] en basse fréquence. Un modèle de HEMT AlGaN/GaN non-linéaire électrothermique est présenté, incluant un nouveau modèle thermique de pièges restituant le comportement dynamique de ces pièges et leurs variations en température afin de prédire correctement les performances en conditions réelles de fonctionnement RF. Enfin, une méthodologie temporelle pour l’évaluation de la fiabilité et de limites réelles d'utilisation de transistors dans l'amplificateur de puissance RF en régime d’overdrive (très forte compression), basée sur la mesure monitorée de Formes d'Onde Temporelles (FOT), est proposéeGaN-based high electron mobility transistors (HEMTs) are promising candidates for future microwave equipment, such as new solid state power amplifiers (SSPAs), thanks to their excellent performance. A first demonstration of GaN-MMIC transmitter has been developed and put on board the PROBA-V mission. But this technology still suffers from the trapping phenomena, principally due to lattice defects. Thus, the aim of this research is to investigate the trapping effects and the reliability aspects of the GH50 power transistors for C-band applications. A new trap investigation protocol to obtain a complete overview of trap behavior from DC to radio-frequency operation modes, based on combined pulsed I/V measurements, DC and RF drain current measurements, and low-frequency dispersion measurements, is proposed. Furthermore, a nonlinear electro-thermal AlGaN/GaN model with a new additive thermal-trap model including the dynamic behavior of these trap states and their associated temperature variations is presented, in order to correctly predict the RF performance during real RF operating conditions. Finally, an advanced time-domain methodology is presented in order to investigate the device’s reliability and to determine its safe operating area. This methodology is based on the continual monitoring of the RF waveforms and DC parameters under overdrive conditions in order to assess the degradation of the transistor characteristics in the RF power amplifier
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Shah, Hassan. "Construction of a setup for dispersion measurements on multilayer structures." Thesis, KTH, Tillämpad fysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-103007.
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Dispersion is a rather unavoidable phenomenon that occurs when using semiconductor, multilayer mirrors for experiments with mode-locked lasers. Due to unknown dispersion, the laser pulses may not be stable which results in unwanted laser pulse properties. This is especially the case when the light source is of a broadband characteristic, consisting of several wavelengths. However, if the dispersion of a semiconductor multilayer mirror is known, these unwanted effects can be considered, making the experiment efficient and the results more analysable. The goal of this Bachelor thesis has been to construct a setup for dispersion measurements of semiconductor multilayer mirrors, and to perform analysis to determine the dispersion. The setup constructed is a Michelson-interferometer with a white light source to analyse the mirrors in a broadband spectrum, and the analysis is done by using a Windowed Fourier Transform procedure.