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1
Elm, Svensson Erik. "Nanomaterials for high-temperature catalytic combustion." Licentiate thesis, Stockholm : School of Chemical Science, KTH, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4360.
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Agnew, Rachel Elizabeth. "The Characterization and Size Distribution of Engineered Carbon Nanomaterials." University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1243362684.
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Lukawska, Anna Beata. "THERMAL PROPERTIES OF MAGNETIC NANOPARTICLES IN EXTERNAL AC MAGNETIC FIELD." Wright State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=wright1401441820.
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ZHU, SHUN. "SYNTHESIS OF SIZE, STRUCTURE AND SHAPE CONTROLLED IRON BASED MAGNETIC NANOMATERIALS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1322920113.
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Hos, James Pieter. "Mechanochemically synthesized nanomaterials for intermediate temperature solid oxide fuel cell membranes." University of Western Australia. School of Mechanical Engineering, 2005. http://theses.library.uwa.edu.au/adt-WU2006.0016.
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[Truncated abstract] In this dissertation an investigation into the utility of mechanochemically synthesized nanopowders for intermediate temperature solid oxide fuel cell components is reported. The results are presented in the following parts: the synthesis and characterisation of precursors for ceramic and cermet components for the fuel cell; the physical and electrical characterisation of the electrolyte and electrodes; and the fabrication, operation and analysis of the resulting fuel cells. Samarium-doped (20 mol%) ceria (SDC) nanopowder was fabricated by the solid-state mechanochemical reaction between SmCl3 with NaOH and Ce(OH)4 in 85 vol% dilution with NaCl. A milling time of 4 hours and heat treatment for 2 hours at 700°C yielded a material with equivalent particle and crystallite sizes of 17 nm. The existence of a complete solid solution was affirmed by electron energy loss spectroscopy and x-ray diffraction analysis. Doped-ceria compacts were sintered for 4 hours at 1350°C forming ceramics of 88% theoretical density. The ionic conductivity in flowing air was 0.009 S/cm, superior to commercially supplied nanoscale SDC. Anode precursor composite NiO-SDC nanopowder was synthesized by milling Ni(OH)2 with the previously defined SDC formulation ... Anode-supported fuel cells were fabricated on a substrate of at least 500 'm 55wt%NiO-SDC with 17vol% graphite pore formers. Suspensions of SDC were deposited by aerosol on the sintered bilayer at a thickness around 5 'm. A cathode of 10% SDC (SmSr)0.5CoO3 was deposited onto the sintered electrolyte and after firing had a thickness of around 25 'm. Operation of fuel cells in single-chamber mixtures of CH4 and air diluted in argon were successful and gave power outputs of 483 'W/cm2. Operation in undiluted 25 vol% CH4:air gave a power output of 5.5 mW/cm2. It was shown that a large polarisation resistance of 4.1 Ω.cm2 existed and this was assigned to losses in the anode, namely mass transport limitation associated with the catalytic combustion of methane and insufficient porosity. The large surface area of Ni appeared to allow more methane to combust and hence prevented its electrochemical reaction from occurring, thus limiting the performance of the cell. The synthesis procedures, ceramic processing and fabrication techniques and testing methods are discussed and contribute significant understanding to the fields of ceramic science and fuel cell technology.
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Elzey, Sherrie Renee. "Applications and physicochemical characterization of nanomaterials in environmental, health, and safety studies." Diss., University of Iowa, 2010. https://ir.uiowa.edu/etd/494.
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As commercially manufactured nanomaterials become more commonplace, they have the potential to enter ecological and biological environments sometime during their lifecycle of production, distribution, use or disposal. Despite rapid advances in the production and application of nanomaterials, little is known about how nanomaterials may interact with the environment or affect human health. This research investigates an environmental application of nanomaterials and characterizes the physicochemical properties of commonly manufactured nanomaterials in environmental health and safety studies.
Characterization of nanomaterials for applications and environmental health and safety studies is essential in order to understand how physicochemical properties correlate with chemical, ecological, or biological response or lack of response. Full characterization includes determining the bulk and surface properties of nanomaterials. Bulk characterization methods examine the shape, size, phase, electronic structure and crystallinity, and surface characterization methods include surface area, arrangement of surface atoms, surface electronic structure, surface composition and functionality.
This work investigates the selective catalytic reduction (SCR) of NO2 to N2 and O2 with ammonia on nanocrystalline NaY, Aldrich NaY and nanocrystalline CuY using in situ Fourier transform infrared (FTIR) spectroscopy. It was determined that the kinetics of SCR were 30% faster on nanocrystalline NaY compared to commercial NaY due to an increase in external surface area and external surface reactivity. Copper-cation exchanged nanocrystalline Y resulted in an additional increase in the rate of SCR as well as distinct NO2 and NH3 adsorption sites associated with the copper cation. These superior materials for reducing NOx could contribute to a cleaner environment.
This work consists of characterization of commonly manufactured or synthesized nanomaterials and studies of nanomaterials in specific environmental conditions. Bulk and surface characterization techniques were used to examine carbon nanotubes, titanium dioxide nanoparticles, bare silver nanoparticles and polymer-coated silver nanoparticles, and copper nanoparticles. Lithium titanate nanomaterial was collected from a manufacturing facility was also characterized to identify occupational health risks. Particle size distribution measurements and chemical composition data showed the lithium titanate nanomaterial forms larger micrometer agglomerates, while the nanoparticles present were due to incidental processes.
A unique approach was applied to study particle size during dissolution of nanoparticles in aqueous and acidic conditions. An electrospray coupled to a scanning mobility particle sizer (ES-SMPS) was used to determine the particle size distribution (PSD) of bare silver nanoparticles in nitric acid and copper nanoparticles in hydrochloric acid. The results show unique, size-dependent dissolution behavior for the nanoparticles relative to their micrometer sized counterparts.
This research shows size-dependent properties of nanomaterials can influence how they will be transported and transformed in specific environments, and the behavior of larger sized materials cannot be used to predict nanomaterial behavior. The type of nanomaterial and the media it enters are important factors for determining the fate of the nanomaterial. These studies will be important when considering measures for exposure control and environmental remediation of nanomaterials.
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Drake, Christina. "UNDERSTANDING THE LOW TEMPERATURE ELECTRICAL PROPERTIESOF NANOCRYSTALLINE SNO2 FOR GAS SENSOR APPLICATIONS." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3957.
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Nanocrystalline metal/metal oxide is an important class of transparent and electronic materials due to its potential use in many applications, including gas sensors. At the nanoscale, many of the phenomena observed that give nanocrystalline semiconducting oxide enhanced performance as a gas sensor material over other conventional engineering materials is still poorly understood. This study is aimed at understanding the low temperature electrical and chemical properties of nanocrystalline SnO2 that makes it suitable for room temperature gas detectors. Studies were carried out in order to understand how various synthesis methods affect the surfaces on the nano-oxides, interactions of a target gas (in this study hydrogen) with different surface species, and changes in the electrical properties as a function of dopants and grain size. A correlation between the surface reactions and the electrical response of doped nanocrystalline metal-oxide-semiconductors exposed to a reducing gas is established using Fourier Transform Infrared (FTIR) Spectroscopy attached to a specially built custom designed catalytic cell. First principle calculations of oxygen vacancy concentrations from absorbance spectra are presented. FTIR is used for effectively screening of these nanostructures for gas sensing applications. The effect of processing temperature on the microstructural evolution and on the electronic properties of nanocrystalline trivalent doped–SnO2 is also presented. This study includes the effect of dopants (In and Ce) on the growth of nano-SnO2, as well as their effects on the electronic properties and gas sensor behavior of the nanomaterial at room temperature. Band bending affects are also investigated for this system and are related to enhanced low temperature gas sensing. The role and importance of oxygen vacancies in the electronic and chemical behavior of surface modified nanocrystalline SnO2 are explored in this study. A generalized explanation for the low temperature gas sensor behavior of nanocrystalline oxide is presented that can be generalized to other nano-oxide systems and be useful in specific engineering of other nanomaterials. Deeper understanding of how nano-oxides react chemically and electronically would be extremely beneficial to issues present in current low cost, low temperature sensor technology. Ability to exactly monitor and then engineer the chemistry of nanostructures in the space charge region as well as the surface is also of great significance. Knowledge of the mechanisms responsible for enhanced sensor response in this material system could viably be applied to other material systems for sensor applications.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science & Engr PhD
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Reeve, Michael William. "Temperature, body size and life history in Drosophila melanogaster." Thesis, University College London (University of London), 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271338.
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Gabrielyan, Nare. "Low temperature fabrication of one-dimensional nanostructures and their potential application in gas sensors and biosensors." Thesis, De Montfort University, 2013. http://hdl.handle.net/2086/9607.
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Nanomaterials are the heart of nanoscience and nanotechnology. Research into nanostructures has been vastly expanding worldwide and their application spreading into numerous branches of science and technology. The incorporation of these materials in commercial products is revolutionising the current technological market. Nanomaterials have gained such enormous universal attention due to their unusual properties, arising from their size in comparison to their bulk counterparts. These nanosized structures have found applications in major devices currently under development including fuel cells, computer chips, memory devices, solar cells and sensors. Due to their aforementioned importance nanostructures of various materials and structures are being actively produced and investigated by numerous research groups around the world. In order to meet the market needs the commercialisation of nanomaterials requires nanomaterial fabrication mechanisms that will employ cheap, easy and low temperature fabrication methods combined with environmentally friendly technologies. This thesis investigates low temperature growth of various one-dimensional nanostructures for their potential application in chemical sensors. It proposes and demonstrates novel materials that can be applied as catalysts for nanomaterial growth. In the present work, zinc oxide (ZnO) and silicon (Si) based nanostructures have been fabricated using low temperature growth methods including hydrothermal growth for ZnO nanowires and plasma-enhanced chemical vapour deposition (PECVD) technique for Si nanostructures. The structural, optical and electrical properties of these materials have been investigated using various characterisation techniques. After optimising the growth of these nanostructures, gas and biosensors have been fabricated based on Si and ZnO nanostructures respectively in order to demonstrate their potential in chemical sensors. For the first time, in this thesis, a new group of materials have been investigated for the catalytic growth of Si nanostructures. Interesting growth observations have been made and theory of the growth mechanism proposed. The lowest growth temperature in the published literature is also demonstrated for the fabrication of Si nanowires via the PECVD technique. Systematic studies were carried out in order to optimise the growth conditions of ZnO and Si nanostructures for the production of uniformly shaped nanostructures with consistent distribution across the substrate. v The surface structure and distribution of the variously shaped nanostructures has been analysed via scanning electron microscopy. In addition, the crystallinity of these materials has been investigating using Raman and X-ray diffraction spectroscopies and transmission electron microscopy. In addition to the fabrication of these one-dimensional nanomaterials, their potential application in the chemical sensors has been tested via production of a glucose biosensor and an isopropyl alcohol vapour gas sensor based on ZnO and Si nanostructures respectively. The operation of the devices as sensors has been demonstrated and the mechanisms explored.
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Chen, Zongkun [Verfasser]. "Simple Preparation and Formation Mechanism of Two-Dimensional Nanomaterials at Room Temperature / Zongkun Chen." Konstanz : KOPS Universität Konstanz, 2020. http://d-nb.info/1213659221/34.
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Radwan, Islam Mohamed Othman. "Fate of Nanomaterials in the Environment: Effects of Particle Size,Capping agent and Surface Cleaning Products on the Stability of Silver Nanomaterials In Colloidal Consumer Products." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin15632953645698.
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Kopp, Bastian [Verfasser]. "Thermopower of Atomic-Size Contacts at Low Temperature / Bastian Kopp." Konstanz : Bibliothek der Universität Konstanz, 2016. http://d-nb.info/1115727486/34.
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Archer, Stephen D. "The effects of temperature and size on swimming in fish." Thesis, University of St Andrews, 1990. http://hdl.handle.net/10023/7097.
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This study examines swimming in fish as a function of the performance of the locomotor musculature. Aspects of evolutionary adaptation and scaling relevant to swimming performance in fish are introduced. The concepts of resistance and capacity adaptations are illustrated in relation to the evolution of the suborder Notothenioidei to the antarctic environment. Alterations in hydrodynamics, swimming performance and efficiency with growth/scaling are discussed.
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Forster, Jack. "Exploring the mechanism of how ectotherms change size with changing temperature." Thesis, Queen Mary, University of London, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610932.
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Reynolds, Bryan. "Electronic Transport Properties of Nanonstructured Semiconductors: Temperature Dependence and Size Effects." University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1463130513.
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Brandt, Josef. "Temperature Dependent Size Exclusion Chromatography for Investigating Thermoreversibly Bonding Polymer Systems." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-207589.
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Polymers capable of thermally controlled reversible bonding reactions are promising candidates for stimuli responsive materials, as required for self-healing or drug delivery materials. In order to investigate how the dynamic reactions can be controlled, effective analytical tools are demanded that are capable of analyzing not only the polymers but can also monitor the respective bonding reactions. Herein, we employ size exclusion chromatography in a newly developed temperature dependent mode (TD SEC) for the in situ characterization of polymers that undergo retro Diels-Alder (rDA) reaction at temperatures higher than 60 °C. Monitoring the evolution of the molar mass distribution of the polymers during the rDA reaction and evaluating the data quantitatively gives detailed information about the extent of the reaction and allows elucidating structural parameters that can be used for controlling the polymers debonding behavior.
In contrast to spectroscopic techniques, TD SEC analyzes only the size of the polymers, hence the polymers do not need to fulfill any particular requirements (e.g. presence of detectable functional groups) but only need to be soluble in the TD SEC, which makes the method universally applicable. Side effects that might bias the results are minimized by using a high temperature chromatograph that allows performing the analysis in a broad temperature range (60 – 200 °C) and in different solvents. Thus, the analysis can be performed under the exact conditions that are required for the bonding reactions and an in situ image is provided.
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Calboli, Federico Corrado Fulcieri. "Evolution and plasticity of body size of Drosophila in response to temperature." Thesis, University College London (University of London), 2004. http://discovery.ucl.ac.uk/1446582/.
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Ectotherm body size is positively correlated with latitude, giving rise to body size clines, found in different continents. Ectotherm body size also shows a developmental response to temperature, increasing at lower developmental temperatures. To investigate the effects of temperature in the evolution and plasticity of body size dines, I used two species of the genus Drosophila as model organisms. To investigate the cellular mechanism underlying the evolution of wing size clines the two newly established D. subobscura wing size clines in the Americas were compared with the ancestral European dine. Clinal differences in Europe and South America were due to changes in cell number, whereas clinal differences in North America are due to changes in cell area. These results suggest that the cellular mechanism underlying the establishment of wing size clines is contingent and not predictable. The genetic control of body size in the D. melanogaster South American body size cline was investigated by means of QTL mapping. The results found in South America were consistent with those previously found in Australia, and in both continents the inversion In(3R)P was associated QTL controlling wing area. Genes of the insulin signalling pathway, known to affect size, were characterized in their effects under different temperature and larval crowding regimes. The evolution of plasticity of body size traits was analysed using different thermal selection regimes. The phenotypic plasticity of wing size and its cellular components was examined by rearing flies, selected under fixed or variable thermal environments, at two different experimental temperatures. Plasticity of wing size did not vary among the different selection lines, however, plasticity of both cellular components of body size did. Costs and benefits of adaptation to cyclical thermal environments were assessed with larval competition assays and by assessing size when all lines were reared under cyclic thermal conditions.
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Legrand, William. "Crafting magnetic skyrmions at room temperature : size, stability and dynamics in multilayers." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS066/document.
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Les skyrmions magnétiques sont des enroulements bidimensionnels et nanométriques de la configuration de spin, pouvant être stabilisés dans certains matériaux magnétiques soumis à l’interaction d’échange antisymétrique Dzyaloshinskii-Moriya. Ils présentent une topologie non-triviale et s’annoncent peut-être comme étant les plus petites configurations magnétiques pouvant être réalisées. Très récemment, des skyrmions magnétiques ont pu être stabilisés à température ambiante grâce à la conception de multicouches magnétiques brisant la symétrie d’inversion selon la direction verticale. Suite à cette avancée, l’objectif central de cette thèse est la compréhension et la maîtrise des multiples propriétés physiques des skyrmions hébergés dans ces systèmes multicouches. Pour aborder cet objectif, un modèle original est décrit puis employé, permettant la prédiction des profils adoptés par les skyrmions multicouches. Ce modèle numérique est très générique, n’utilisant que la symétrie cylindrique des skyrmions afin de simplifier la détermination des interactions magnétostatiques. Ce modèle est ensuite étendu afin de pouvoir approximer la stabilité thermique des skyrmions, ce qui constitue un élément clé dans leur obtention expérimentale. Une seconde dimension de ce travail consiste en l’étude expérimentale de la manipulation électrique des skyrmions multicouches, démontrant la possibilité de trois fonctionnalités centrales que sont leur nucléation par courants locaux, leur déplacement sous courant de spin et leur détection électrique individuelle par tension transverse. Le troisième aspect de ma thèse est l’étude des propriétés physiques influençant le déplacement des skyrmions dans les multicouches magnétiques. Un comportement d’ancrage sur des défauts est mis en évidence expérimentalement et est analysé à l’aide d’une modélisation micromagnétique. Un des résultats importants de ce travail est aussi la prédiction d’une chiralité hybride dans les configurations magnétiques de certaines multicouches, qui est ensuite démontrée expérimentalement par des mesures au synchrotron. Les conséquences attendues de cette chiralité hybride sur le déplacement des skyrmions sont étudiées pour permettre l’optimisation des multicouches, aboutissant à l’observation expérimentale de la propagation de skyrmions de 50 nm de rayon à des vitesses atteignant environ 40 m/s. La dernière partie de cette thèse vise à mettre à profit ces avancées théoriques et expérimentales afin de parvenir à réduire la taille des skyrmions à température ambiante. Après avoir analysé l’impact des interactions dipolaires sur la stabilité des skyrmions, il est entrepris d’optimiser les matériaux et la périodicité des couches. Je m’intéresse aussi à la conception expérimentale de textures magnétiques dont l’aimantation est compensée au sein de structures multicouches appelées antiferromagnétiques synthétiques, dont je montre qu’elles peuvent héberger des skyrmions antiferromagnétiques à température ambiante. Ce résultat final ouvre de nouvelles perspectives vers l’obtention de skyrmions à la fois mesurant moins de 10 nm et très mobiles, qui pourraient être utilisés dans la conception de composants de calcul et de stockage d’information plus compacts et plus efficacesMagnetic skyrmions are nanoscale two-dimensional windings in the spin configuration of some magnetic materials subject to the Dzyaloshinskii-Moriya antisymmetric exchange interaction. They feature a non-trivial topology and show promise to be the smallest achievable magnetic textures. Very recently, magnetic skyrmions have been successfully stabilised up to room temperature by leveraging on the design of magnetic multilayer systems breaking the vertical inversion symmetry. Following up on this achievement, the main objective of this thesis is the understanding and the control of the various physical properties of skyrmions hosted by such multilayer systems. As a first approach to this objective, an original model allowing to predict the profiles adopted by multilayer skyrmions is described and then employed. This numerical model is very generic, as it exploits only the cylindrical symmetry of multilayer skyrmions, in order to determine the magnetostatic interactions with less effort. This model is further extended in order to approximate the thermal stability of multilayer skyrmions, which is key to their experimental realisation. The next aspect of this thesis consists in the experimental study of the electrical manipulation of multilayer skyrmions, demonstrating three main functionalities that are nucleation by local currents, displacement under spin currents and individual detection by transverse voltage. The third aspect of my thesis is the study of the physical properties influencing the current-induced motion of skyrmions in magnetic multilayers. A pinning behaviour is evidenced experimentally and analysed relying on micromagnetic modelling. One of the important results of this work is also the prediction of hybrid chirality for some multilayer magnetic configurations, which is then demonstrated experimentally using a synchrotron technique. The impact of hybrid chirality on current-induced skyrmion motion is discussed and leads to the optimisation of the multilayer design, resulting in the experimental observation of motion for skyrmions below 50 nm in radius at velocities reaching around 40 m/s. The last part of this thesis aims at leveraging on these theoretical and experimental advances in order to reduce the size of skyrmions at room temperature. After the analysis of the impact of dipolar interactions on skyrmion stability, the engineering of the materials and of the layers periodicity is attempted. I also investigate experimentally the conception of magnetic textures with compensated magnetization in multilayer structures known as synthetic antiferromagnets, and show that they can host antiferromagnetic skyrmions at room temperature. This last result opens up new prospects for achieving room-temperature skyrmions combining size in the single-digit nm range and high mobility, potentially allowing applications towards energy-efficient computation and storage devices with a very dense integration
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Liu, Chang. "Controlled Evaluation of Silver Nanoparticle Dissolution: Surface Coating, Size and Temperature Effects." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/97509.
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The environmental fate and transport of engineered nanomaterials have been broadly investigated and evaluated in many published studies. Silver nanoparticles (AgNPs) represent one of the most widely manufactured nanomaterials. They are currently being incorporated into a wide range of consumer products due to their purported antimicrobial properties. However, either the AgNPs themselves or dissolved Ag+ ions has a significant potential for the environmental release. The safety issues for nanoparticles are continuously being tested because of their potential danger to the environment and human health. Studies have explored the toxicity of AgNPs to a variety of organisms and have shown such toxicity is primarily driven by Ag+ ion release. Dissolution of nanoparticles is an important process that alters their properties and is a critical step in determining their safety. Therefore, studying nanoparticles' dissolution can help in the current move towards safer design and application of nanoparticles. This research endeavor sought to acquire comprehensive kinetic data of AgNP dissolution to aid in the development of quantitative risk assessments of AgNP fate.
To evaluate the dissolution process in the absence of nanoparticle aggregation, AgNP arrays were produced on glass substrates using nanosphere lithography (NSL). Changes in the size and shape of the prepared AgNP arrays were monitored during the dissolution process by atomic force microscopy (AFM). The dissolution of AgNP is affected by both internal and external factors. First, surface coating effects were investigated by using three different coating agents (BSA, PEG1000, and PEG5000). Capping agent effects nanoparticle transformation rate by blocking reactants from the nanoparticle surface. Coatings prevented dissolution to different extents due to the various way they were attached to the AgNP surface. Evidence for the existence of bonds between the coating agents and the AgNPs was obtained by surface enhanced Raman spectroscopy. Moreover, to study the size effects on AgNP dissolution, small, medium, and large sized AgNPs were used. The surrounding medium and temperature were the two variables that were included in the size effects study. Relationships were established between medium concentration and dissolution rate for three different sized AgNP samples. By using the Arrhenius equation to plot the reaction constant vs. reaction temperature, the activation energy of AgNPs of different sizes were obtained and compared.Doctor of Philosophy
Nanomaterials, defined as materials with at least one characteristic dimension less than 100 nm, often have useful attributes that are distinct from the bulk material. The novel physical, chemical, and biological properties enable the promising applications in various manufacturing industry. Silver nanoparticles (AgNPs) represent one of the most widely manufactured nanomaterials and has been used as the antimicrobial agent in a wide range of consumer products. However, either the AgNPs themselves or dissolved Ag+ ions has a significant potential for the environmental release. The environmental fate and transport of AgNPs drawn considerable attentions because of the potential danger to environment and human health. Dissolution of nanoparticles is an important process that alters their properties and is a critical step in determining their safety. Ag+ ions migrate from the nanoparticle surface to the bulk solution when an AgNP dissolves. Studying nanoparticles' dissolution can help in the current move towards safer design and application of nanoparticles. This research aimed to acquire comprehensive kinetic data of AgNP dissolution to aid in the development of quantitative risk assessments of AgNP fate. AgNP arrays were produced on glass substrates using nanosphere lithography (NSL) and changes in the size and shape during the dissolution process were monitored by atomic force microscopy (AFM). First, surface coating effects were investigated by using three different coating agents. Coatings prevented dissolution to different extents due to the various way they were attached to the AgNP surface. Moreover, small, medium, and large sized AgNPs were used to study the size effects on AgNP dissolution. The surrounding medium concentration and temperature were the two variables that were included in the size effects study.
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Stovern, Diana R., and Elizabeth A. Ritchie. "Simulated Sensitivity of Tropical Cyclone Size and Structure to the Atmospheric Temperature Profile." AMER METEOROLOGICAL SOC, 2016. http://hdl.handle.net/10150/622152.
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This study uses the WRF ARW to investigate how different atmospheric temperature environments impact the size and structure development of a simulated tropical cyclone (TC). In each simulation, the entire vertical virtual temperature profile is either warmed or cooled in 1 degrees C increments from an initial specified state while the initial relative humidity profile and sea surface temperature are held constant. This alters the initial amount of convective available potential energy (CAPE), specific humidity, and air-sea temperature difference such that, when the simulated atmosphere is cooled (warmed), the initial specific humidity and CAPE decrease (increase), but the surface energy fluxes from the ocean increase (decrease). It is found that the TCs that form in an initially cooler environment develop larger wind and precipitation fields with more active outer-core rainband formation. Consistent with previous studies, outer-core rainband formation is associated with high surface energy fluxes, which leads to increases in the outer-core wind field. A larger convective field develops despite initializing in a low CAPE environment, and the dynamics are linked to a wider field of surface radial inflow. As the TC matures and radial inflow expands, large imports of relative angular momentum in the boundary layer continue to drive expansion of the TC's overall size.
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Akalin, Suleyman. "Water temperature effect on sand transport by size fraction in the Lower Mississippi River." Access citation and abstract, 2002. http://wwwlib.umi.com/dissertations/fullcit/3075335.
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Gardiner, Benjamin Robert. "High temperature creep performance of alloy 800H." Thesis, University of Canterbury. Mechanical, 2014. http://hdl.handle.net/10092/9949.
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Investigations on post service material showed that Alloy 800H pigtails from methanol producer Methanex have service lives ranging from 3 to 18 years. Because of this variability in service life, Alloy 800H creep performance was assessed and a new criterion for its procurement developed. The current criterion recommends an ASTM grain size of 5 (72µm) or coarser with no consideration given to grain size distribution, grain boundary types, or grain boundary network topology. Results from the investigation showed that this current criterion may produce variations in steady state creep rates of an order of magnitude between ASTM grain size 1 and 5, and a 2.5 times variation in creep ductility.
The ability to accurately reveal grain boundaries and assess grain boundary types is fundamental to the identification and quantification of coherent twin boundaries, and the measurement of average grain size and grain size distribution. EBSD mapping has the ability to distinguish grain boundary types using crystal orientation measurement. Grain size measurement from optical micrographs relies on morphological indicators to identify coherent twins. However, it is shown that many of the boundaries observed as straight line morphology on 2D sections did not possess {111} (coherent) interfaces.
3D reconstructions of Alloy 800H revealed the deficiencies in classifying geometry from two-dimensional (2D) sections. Σ3 Crystal volumes can be categorized as lamellar or edge structures. Lamellar structures are characterized by the appearance of parallel Σ3 boundary planes while an edge structure contains a single Σ3 interface. Sectioning plane location alters the perception of morphology. For simple twin structures, the tradition 2D classifications of morphology (complete parallel, incomplete parallel and corner Σ3) may all appear on a section plane from a single lamellar structure.
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Tunnicliffe, M. C. "The fracture toughness of low carbon steels : the effects of grain size and temperature." Thesis, University of Canterbury. Mechanical Engineering, 1991. http://hdl.handle.net/10092/8327.
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For materials that exhibit a fracture mode transition as temperature is lowered one of the important criteria for material performance is the material's fracture mode transition temperature and not necessarily the specific fracture toughness at any temperature. Therefore, it is important to establish whether operating conditions place a structure below the selected material's transition temperature or that a material is selected with a transition below that of the structure's operating conditions.
Quantitative design processes, based on linear elastic (KIC) and elastic-plastic (CTOD) fracture mechanics using experimental fracture toughness data, allow the design of safer structures. In recent years standard procedures have been adopted for KIC and CTOD testing. Using the traditional Charpy V-notch impact test, detailed information on the effects of composition and grain size on the fracture mode transition temperature are known. The fracture mode transition temperature is not as equally well understood in CTOD or KIC testing, especially for low carbon steels.
The CTOD and Charpy impact tests have been used to determine the grain size dependence of the fracture mode transition temperature for two low carbon (structural) steels, one of low active nitrogen content and one of high active nitrogen content. Both the CTOD and Charpy tests show a fracture mode transition over a narrow temperature range. It was established from theoretical derivation and experimental observation that there is a linear dependence of the transition temperature TC on the reciprocal square root of grain size (d-½) for both the CTOD and Charpy tests i.e. Tc = B₀ + B₁d-½ where B₀ and B₁ are constants. When the results of the CTOD and Charpy tests are compared the magnitude of B₁ is significantly different for each test. It was concluded that the difference in B₁ between the two tests is due to the different strain rates of the tests and that the strain rate significantly affects the local yield stress around the crack tip or notch.
Micromechanical modelling of fracture toughness predicted a variation in transition temperature with variation of grain size but this did not show a linear dependence on d-½. The predicted transition temperature was a lower bound of the range in transition temperature.
The observed decrease in transition temperature with grain refinement when using the CTOD test is explained by the increase in crack initiation and crack propagation energy necessary to overcome grain boundary resistance to fracture. For example, at the fracture mode transition temperature for the low nitrogen steel, the proportion of energy required to overcome grain boundary resistance to fracture increased from 39% at d-½ = 4.218 mm-½ to 55% at d-½ = 9.939 mm-½ of the total critical energy released. Also, it is thought that grain refinement means a lower critical crack-tip strain is needed for transition.
Correlations between Charpy Impact Energy (Cv) and CTOD (δc) or KIC suggested a suitable relationship was δc (or KIC) = D(Cv)n. The constants D and n were independent of grain size but were composition dependent. The temperature shift showed a grain size dependence, given as ∆T = ∆B₀ + ∆B₁d-½ for the data available.
The CTOD measured from Clip Gauge Displacement was determined to be grain size and composition dependent. From a technique using silicone-rubber replicas of the crack tip the CTOD was found to be a function clip gauge displacement (Vg) and grain size (d). namely, δt = 0.121113 Vg + 0.034222 Vg²d ½, for the compact tension specimens tested.
For toughness calculations and determining the fracture mode transition the temperature and grain size dependence of the steels' yield stress (at constant strain rate) was determined. Using the Hall-Petch equation (σys = σi + kyd-½), a suitable model was found to be σys =A₁ + A₂T + A₃T² + A₄T³ + kyd-½ where the constants A₁, A₂, A₃, A₄ and ky were determined by multiple-linear regression analysis from experimental data over the temperature range -196 to +65°C.
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McCraith, Andrew D. (Andrew Douglas) 1976. "Material temperature effects on final product size for new profile ring mill forming technology." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/80512.
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Cromwell, Avery B. "Root kinematics in relation to temperature and genome size in wild and domesticated Zea." DigitalCommons@CalPoly, 2013. https://digitalcommons.calpoly.edu/theses/1086.
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We studied root kinematics in relation to temperature and genome size variation in teosinte (Zea mays subspecies parviglumis) and corn (Zea mays subspecies mays). Corn had significantly faster radicle growth than teosinte when grown at a constant temperature. Both species exhibited variation in seed size and for each species larger seeds had faster root growth. Genome size was not significantly correlated with faster radicle growth rates across multiple land races of corn. To examine temperature dependent growth in corn and teosinte, a germinated seedling was grown at multiple temperatures. Growth rates at these temperatures were used to fit a temperature response model for each species. Parameters of this model (maximum growth temperature and optimum growth temperature) were not significantly different between the species.
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Horne, Curtis Robert. "Major patterns of body size variation within arthropod species : exploring the impact of habitat, temperature, latitude, seasonality and altitude." Thesis, Queen Mary, University of London, 2017. http://qmro.qmul.ac.uk/xmlui/handle/123456789/25854.
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Body size affects rates of most biological and ecological processes, from individual performance to ecosystem function. Within species, emergent body size patterns have been formalised into prominent biogeographical and biological rules, including James' Rule (larger individuals are found at higher, colder latitudes), and the Temperature-Size Rule (individuals reared in warmer conditions grow to a smaller adult size). Body size also varies seasonally and with altitude. Yet, the patterns and drivers of these size gradients, and the degree to which they co-vary and share explanatory mechanisms, have never been systematically evaluated. We undertake the most comprehensive metaanalyses to date of temperature- and biogeographical-size clines within arthropod species. Aquatic species show greater reductions in body size with warming and decreasing latitude compared to terrestrial species, likely an adaptive response to deal with increased metabolic demand in the warm and the greater difficulty to uptake oxygen in water than in air. Voltinism explains variation in laboratory temperature- and latitudinal-size clines in terrestrial species. While size decreases with warming and with decreasing latitude in multivoltine terrestrial arthropods, size increases on average in univoltine species, consistent with predictions from size vs. season-length trade-offs. In the globally distributed sub-class Copepoda, seasonal temperature-size (T-S) gradients differ between current-feeding calanoids and ambush-feeding cyclopoids, suggesting that differences in the size- and temperature-dependence of alternative feeding strategies may influence the T-S response. Finally, through experimentation, we explore the progression of the T-S response of Copepoda during ontogeny. The T-S response is more strongly generated in particular life stages, and even reduced in some periods, providing evidence that the temperature-dependence of growth and developmental rates is modified during ontogeny. Ultimately, close similarities between T-S responses measured in controlled laboratory conditions, and seasonal and biogeographical size clines in the field across different arthropod taxa, suggests that these patterns share similar selective pressures.
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Elnitsky, Michael Adam. "THE EFFECTS OF TEMPERATURE, BODY SIZE, AND GROWTH ON THE LOCOMOTOR PERFORMANCE OF JUVENILE TURTLES." Miami University / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=miami1101827122.
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Kleinsmidt, Jacques N. "The effect of temperature and crystallite size on the growth and morphology of carbon nanotubes." Master's thesis, University of Cape Town, 2005. http://hdl.handle.net/11427/6695.
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The aim of the study was to synthesise iron oxide crystallites with different crystallite sizes supported on y-A120 3 using the reverse micelle technique. It was hypothesised that changing the crystallite size of the synthesised iron oxide crystallites could lead to the control of the external nanotube diameter. The effect of temperature on the external diameter and productivity was also investigated. It was found through titration and AAS that the iron loading was lower than the expected 15 wt.-%. Furthermore, it was observed that the loading was not consistent through different catalyst samples. This was attributed to incomplete precipitation of iron using the reverse micelle technique, the rigorous cleaning regime implemented and weak metal-support interaction. It was found through XRD and TEM that crystallites in the nanometre range were produced although they were not well distributed over the support. It was also found that the expected linear relationship between water to surfactant ratio and crystallite size was not achieved. Hence the obtained crystallite sizes were significantly different from those obtained in the work by Mabaso.
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Amod, Muhammad Ali. "Carbidization and size effects of unsupported nanosized iron in the low temperature Fischer-Tropsch process." Master's thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/10048.
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Includes abstract.Includes bibliographical references.
In the process of developing the most efficient production of fuels from coal or natural gas, there have been major advances in the development of the catalysts used. Previous work at the Centre for Catalysis Research, at the University of Cape Town, has shown great potential and provided a much deeper under- standing of the workings of the Fischer-Tropsch catalyst. The research has found that the catalyst crystallite size plays a crucial part in the product selectivity and requires strict control in order to obtain a certain desired product spectrum. The aim of this project is to provide insight on the behavior of various iron oxide crystallite sizes when placed in a CO concentrated environment during catalyst pretreatment. It will also clarify whether the sizes of the nano-crystallites will increase or decrease when the different phases form and which size carbides faster.
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Guenther, Gerrit [Verfasser], Olivier [Akademischer Betreuer] Guillon, and Horst [Akademischer Betreuer] Hahn. "Size-dependent High-Temperature Behavior of Bismuth Oxide Nanoparticles / Gerrit Guenther. Betreuer: Olivier Guillon ; Horst Hahn." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2012. http://d-nb.info/1106453921/34.
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Menyeh, Aboagye. "Domain observations, particle size and temperature dependent magnetic hysteresis properties and thermoremanent magnetization of monoclinic pyrrhotite." Thesis, University of Newcastle Upon Tyne, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261230.
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Nauyoks, Stephen Edwin. "Microstructure of nano and micron size diamond-SIC composites sintered under high pressure high temperature conditions." [Fort Worth, Tex.] : Texas Christian University, 2009. http://etd.tcu.edu/etdfiles/available/etd-10152009-102152/unrestricted/Nauyoks.pdf.
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Wang, Yachao. "Molecular Dynamics Simulation of Nano-Indentation Process of Silicon: Effects of Initial Temperature and Grain Size." Thesis, North Dakota State University, 2014. https://hdl.handle.net/10365/27338.
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In this study, a comprehensive investigation on nano-scale indentation of monocrystal and polycrystalline silicon is carried out by adopting molecular dynamic (MD) simulation. Five levels of initial temperature (30K, 100K, 300K, 500K and 700K) are configured in this study and the simulation results reveal the amount of bct-5 silicon atoms at the maximum indentation position is not significantly affected by the initial temperature, substantially less ?-silicon atoms are observed with higher temperatures. The temperature effect on the unloading process is also discussed. Meanwhile, indentation force curves for polycrystalline silicon (grain size ranging from 6.45 nm to 20.48 nm) and single crystalline silicon is compared. The result shows that the normal Hall-Petch effect is not seen in the nano-indentation process of silicon. The grain boundary increases local stress during the indentation process and results in less formation of ?-silicon phase, but it hardly affects the formation of bct-5 silicon.
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Clum, Carey G. III. "The Effects of Particle Size, Chemical Composition and Temperature on Deposition in an Impingement Cooling Scheme." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1367482108.
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Adhikari, Shishir. "World-wide body size patterns in freshwater fish by geography, size class, trophic level, and taxonomy." Wright State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=wright1441039840.
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Wood, Erin Leigh. "An Atomic Force Microscopy Nanoindentation Study of Size Effects in Face-Centered Cubic Metal and Bimetallic Nanowires." ScholarWorks @ UVM, 2014. http://scholarworks.uvm.edu/graddis/260.
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The enhancement of strength of nanoscale materials such as face-centered cubic metal nanowires is well known and arises largely from processes mediated by high energy surface atoms. This leads to strong size effects in nanoscale plasticity; ,smaller is stronger. Yet, other factors, such as crystalline defects also contribute greatly to the mechanical properties. In particular, twin boundaries, which are pervasive and energetically favorable defects in face-centered cubic metal nanowires, have been shown to greatly enhance the strength, furthermore this increase in strength has been shown to be directly influenced by the twin density. However, attempts to control the introduction of beneficial defects remains challenging. Additionally, even minor local variations in the crystalline structure or size of metal nanowires may have drastic effects on the yielding of metal nanowires, which are difficult to measure through tensile and bending tests.
In this study, atomic force microscopy based nanoindentation techniques are used to measure the local plasticity of Ni-Au bimetallic as well as Cu and Ag metallic nanowires. In the first part of the thesis the hardness of bimetallic nanowires synthesized through template-assisted electrodeposition is measured and found to show significant size-effects. It was found that the nanoindentation hardness was governed by materials properties, the observed indentation size effects were dependent on geometrical factors.
The second part of this thesis presents a methodology to control the crystal structure of Ag and Cu nanowires through direct electrodeposition techniques, which were tested directly as grown on the substrate to limit effects of pre-straining. Ag nanowires showed marked size-effects as well as two distinct modes of deformation which we attribute to the defects that arise during crystalline growth. We also show control of the surface microstructure in Cu nanowires which leads to strengths that are more than doubled compared to single crystalline Cu nanowires. Finally, we present support from classic crystal growth theory to justify that the observed plasticity in Ag and Cu nanowires is largely dependent on defects that are nucleated through changes in the growth environment.
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Mutinda, Samuel I. "Hydrothermal Synthesis of Shape/Size-Controlled Cerium-Based Oxides." Youngstown State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1378917332.
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Xiang, Yanqiao. "Capillary Liquid Chromatography Using Micro Size Particles." Diss., CLICK HERE for online access, 2004. http://contentdm.lib.byu.edu/ETD/image/etd531.pdf.
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Cheng, Xiaojin. "A study on indium joints for low-temperature microelectronics interconnections." Thesis, Loughborough University, 2011. https://dspace.lboro.ac.uk/2134/9093.
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For microelectronics used in the low-temperature applications, the understanding of their reliability and performance has become an important research subject characterised as electronics to serve under the severe or extreme service conditions. Along with the impact from the increased miniaturization of devices, the various properties and the relevant thermo-mechanical response of the interconnection materials to temperature excursion at micro-scale become a critical factor which can affect the reliable performance of microelectronics in various applications. Pure indium as an excellent interconnection material has been used in pixellated detector systems, which are required to be functional at cryogenic temperatures. This thesis presents an extensive investigation into the thermo-mechanical properties of indium joints as a function of microstructure, strain (loading histories-dependent) and temperature (service condition-sensitive), specifically in the areas as follows: (i) the interfacial reactions and evolution between indium and substrate during the reflow process (liquid-solid) and thermal aging (solid-solid) stages by taking low-temperature cycling into account; (ii) determination of the effects of joint thickness and the types of substrate (e.g. Cu or Ni) on the mechanical properties of indium joints, and the stress- and temperature-dependent creep behaviour of indium joints; (iii) the establishment of a constitutive relationship for indium interconnects under a wide range of homologous temperature changes that was subsequently implemented into an FE model to allow the analysis of the evolution of thermally-induced stresses and strains associated with a hybrid pixel detector.
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Orolínová, Zuzana, Annamária Mockovčiaková, Armin Feldhoff, and Dirk Menzel. "Influence of amount of iron oxide and temperature of synthesis on their particle size in composites with bentonite." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-188042.
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Kline, Richard Joseph. "Metabolic rate of the gag grouper (Mycteroperca microlepsis) in relation to swimming speed, body size, and seasonal temperature." [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0008925.
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Orolínová, Zuzana, Annamária Mockovčiaková, Armin Feldhoff, and Dirk Menzel. "Influence of amount of iron oxide and temperature of synthesis on their particle size in composites with bentonite." Diffusion fundamentals 12 (2010) 80, 2010. https://ul.qucosa.de/id/qucosa%3A13904.
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Lukhele, Obed Mooki. "Influence of incubation temperature on chorio-allantoic membrane vascularization heart size and ascites incidence in broilers (Gallus domesticus)." Diss., University of Pretoria, 2009. http://hdl.handle.net/2263/67777.
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Ascites or pulmonary arterial hypertension (PAH) syndrome is a significant cause of mortality in modern fast-growing broilers that are raised at high altitude. Damage caused by temperature to the cardio-vascular system during embryo development is often overlooked as an important predisposing factor to ascites experienced on the farm.
Eggs from a 38 week-old Ross 308 flock were exposed to three temperature treatments. One group was exposed to 36.8oC (cool), the second group to 37.5oC (control) and the third group to 38.2oC (hot). Relative humidity ranged from 55-59% in all groups. These treatments were used throughout the incubation period.
Vascularisation of the chorio-allantoic membrane (CAM) was used as an indirect measure of embryonic blood vessel reaction to temperature insult. Vascular fraction (VF), density and fractal dimension (FD) and branching of blood vessels were assessed using a stereo microscope. The control had significantly lower (p<0.001) VF and FD compared to both hot and cool groups suggesting that high and low temperatures in incubators and hatchers trigger vascular compensation.
High temperature during embryonic development resulted in significantly lower heart mass in both the control (p<0.002) and the hot (p<0.001) groups compared to the cool treatment. A smaller heart will limit the ability of the fast growing broiler to compensate for low oxygen levels at high altitude and thus be prone to ascites.
Formation of the embryo muscle mass was significantly reduced in hot (p<0.001) and the control (p<0.007) groups compared to the cool treatment. In this study embryo mass was reported as yolk-free body mass (YFBM). The hot treatment had significantly (p<0.001) lower (1 843g) body mass at 35 days of age when slaughtered compared to the cool and control groups that averaged 2 107g and 2 130, respectively.
There was, however, no statistical difference (p<0.178) on heart mass (HM) to YFBM ratio amongst all three temperature treatment groups.
Mortality due to ascites was double (53%) in the hot group compared to the control and cool treatments which were similar. The difference in mortality was significant at p<0.001. This very high mortality in the hot group is likely to have skewed the right ventricle to total ventricular (RV: TV) ratio which was the same to that of the cool treatment at 0.26. This falls within the range of a normal fowl. Birds in the control group had higher (0.28) RV: TV ratio which indicated susceptibility to ascites.
Feed conversion for the control group was 2.94% better (1.517) than the cool group (1.563) and 5.2% better than the hot treatment (1.601), the differences were not significant between the hot and control group and slaughter.
The combined farm performance variables expressed in terms of an efficiency factor (PEF) showed that the control group (292) performed 4.8% better than the cool group (278) and 47.6% better than the hot group (153). Bacterial growth in yolks from eggs in the hot treatments was recorded in 19.2% of the samples, with 12% being gram-negative bacteria. Only 3% and 3.7% of samples from the control and cool groups, respectively, had bacterial growth. Of the bacteria isolated in the cool treatment group, all were gram-negative isolates. As the incubation and setter temperature increased, so has the number of positive samples. Statistically, bacterial growth was significantly (p<0,024) higher in the hot treatment compared to the cool and control groups combined.Dissertation (MMedVet)--University of Pretoria, 2018.
Production Animal Studies
MMedVet
Unrestricted
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Ask, Per. "Invasion of top and intermediate consumers in a size structured fish community." Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-37995.
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In this thesis I have investigated the effects of invading top and intermediate consumers in a size-structured fish community, using a combination of field studies, a lake invasion experiment and smaller scale pond and aquaria experiments. The lake invasion experiment was based on introductions of an intermediate consumer, ninespine stickleback (Pungitius pungitius L.), in to allopatric populations of an omnivorous top predator, Arctic char (Salvelinus alpinus L.). The invasion experiment was performed in two tundra lakes and in two birch forest lakes to investigate the effect of climate on the invasion success. I found that the effect of sticklebacks on char was size dependent. Small char suffered reduced growth from resource competition with sticklebacks whereas the maximum size of adult char increased from the addition of a larger prey resource, stickleback. The negative effect of sticklebacks on the growth of small char suggests that sticklebacks may be a better resource competitor than char, which was also supported by the pond and aquaria experiments. The pond experiments also suggested that char were more efficient cannibals than interspecific predators on sticklebacks. Cannibalism in char may limit the recruitment of char and decrease both their predatory and competitive effect on coexisting species and thereby also promote the coexistence of char and sticklebacks. The successful invasion by sticklebacks and their subsequent increases in density suggest that the absence of sticklebacks in char lakes in this region is not caused by biotic interactions with char. Instead, it may be suggested that co-occurrence of sticklebacks and char in the region is limited by dispersal. The char – stickleback system resembles an intraguild predation system with char as the top consumer and stickleback as the intermediate consumer. The effects of the stickleback invasion is also contrasted with a field study of a northern pike (Esox lucius L.) invasion into a system with coexisting char and stickleback, where pike can be viewed as the top consumer and char as the intermediate consumer both feeding on sticklebacks. In this case pike excluded char. The identity of the invading species and the relative strength of the predatory and competitive interactions in the two contrasting systems are discussed in relation to coexistence in intraguild predation systems. I found that the identity of the invading species is of crucial importance for the response at the ecosystem level, and that the inherent size dependency of competitive and predatory interactions in fish communities is important for attaining a mechanistical understanding of the effects of invasive species in lake ecosystems.
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Wen, Xingshuo. "Creep Behavior of High Temperature Alloys for Generation IV Nuclear Energy Systems." University of Cincinnati / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1397468088.
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Jones, Simon Philip. "Influence of modifiers on Palladium based nanoparticles for room temperature formic acid decomposition." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:873277f2-c4f7-45b7-a16d-bba064e24bee.
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Heterogeneous catalysts form a highly important part of everyday life, ranging from the production of fertiliser enabling the growth of crops that sustain much of the world's population to the production of synthetic fuels. They constitute a key part of the chemical industry and contribute towards substantial economic and environmental benefits. Heterogeneous catalysts are also believed to have an important role to play in a future hydrogen economy, reducing our requirements for fossil fuels. To this end, formic acid has been proposed as a potential hydrogen storage material for small portable devices. Additionally, formic acid has historically been used as a probe molecule to study catalyst materials and recent developments in the knowledge of its decomposition pathways and the preferred sites of these reactions, establish a good foundation for further study. This work explores a range of novel modification techniques that alter the activity of Pd nanoparticles to decompose formic acid to H2 and CO2. The methods used are the addition of polymers, attaching various functional groups to the surface of the catalyst support and decoration of nanoparticles with sub-monolayer coverages of another metal. Using a range of characterisation methods including FTIR of an adsorbed CO probe, XRD and XPS coupled with computational modelling, it is found that these methods result in some significant electronic and/or geometric alterations to the Pd nanoparticles. For polymer modification, the nature of the pendent group is highly important in determining the effects of the polymer on the Pd particles, with all the tested polymers resulting in varying degrees of electronic donation to the Pd surface. The geometric modifications caused by the polymers also varied with pendent groups; with amine containing pendent groups found to selectively block low coordinate sites, preventing the undesired dehydration of formic acid which results in poisoning of the Pd catalyst by the resulting CO. Attachment of amine groups to the surface of metal oxide catalyst supports, is demonstrated to result in dramatic electronic promotional effects to the supported Pd nanoparticles, and when an amine polymer is attached to the support surface the geometric modification is again observed. Finally decoration of Pd nanoparticles with a sub-monolayer coverage of a second metal is examined, resulting in some similar electronic and geometric effects on Pd nanoparticle surfaces to those observed with polymer modification with corresponding changes in formic acid decomposition activity. Overall, a number of methods are displayed to tune the catalytic activity and selectivity of Pd nanoparticles for formic acid decomposition, resulting in catalysts with some of the highest reported TOF's at room temperature. These modification methods are believed to be potentially applicable to a wide range of other catalytic reactions that operate under mild conditions.
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Meier, Roland. "Curie temperature and magnetic phase transition of nanostructured ultrathin Fe/GaAs(001) size dependence and relevance of dipolar coupling." Berlin mbv, 2009. http://d-nb.info/100028090X/04.
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Sob, Peter Baonhe. "Modelling stain rate sensitive nanomaterials' mechanical properties: the effects of varying definitions." Thesis, 2016. http://hdl.handle.net/10352/332.
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M. Tech. (Mechanical Engineering, Faculty of Engineering and Technology): Vaal University of TechnologyPresently there exist a lot of controversies about the mechanical properties of nanomaterials. Several convincing reasons and justifications have been put forward for the controversies. Some of the reasons are varying processing routes, varying ways of defining equations, varying grain sizes, varying internal constituent structures, varying techniques of imposing strain on the specimen etc. It is therefore necessary for scientists, engineers and technologists to come up with a clearer way of defining and dealing with nanomaterials’ mechanical properties. The parameters of the internal constituent structures of nanomaterials are random in nature with random spatial patterns. So they can best be studied using random processes, specifically as stochastic processes. In this dissertation the tools of stochastic processes have been used as they offer a better approach to understand and analyse random processes. This research adopts the approach of ascertaining the correct mathematical models to be used for experimentation and modelling. After a thorough literature survey it was observed that size and temperature are two important parameters that must be considered in selecting the relevant mathematical definitions for nanomaterials’ mechanical properties. Temperature has a vital role to play during grain refinement since all severe plastic deformation involves thermomechanical processes. The second task performed in this research is to develop the mathematical formulations based on the experimental observation of 2-D grains and 3-D grains deformed by Accumulative Roll-Bonding and Equal Channel Angular Pressing. The experimental observations revealed that grains deformed by Accumulative Roll-Bonding and Equal Channel Angular Pressing are elongated when observed from the rolling direction, and transverse direction, and equiaxed when observed from the normal direction. In this dissertation, the different experimental observations for the grain size variants during grain refinement were established for 2-D and 3-D grains. This led to the development of a stochastic model of grain-elongation for 2-D and 3-D grains. The third task was experimentations and validation of proposed models. Accumulative Roll-Bonding, Equal Channel Angular Pressing and mechanical testing (tensile test) experiments were performed. The effect of size on elongation and material properties were studied to validate the developed models since size has a major effect on material’s properties. The fourth task was obtaining results and discussion of theoretical developed models and experimental results. The following facts were experimentally observed and also revealed by the models. Different approaches of measuring grain size reveal different strains that cannot be directly obtained from plots of the corresponding grain sizes. Grain elongation evolved as small values for larger grains, but became larger for smaller grains. Material properties increased with elongation reaching a maximum and started decreasing as is evident in the Hall-Petch to the Reverse Hall-Petch Relationship. This was alluded to the fact that extreme plastic straining led to distorted structures where grain boundaries and curvatures were in “non-equilibrium” states. Overall, this dissertation contributed new knowledge to the body of knowledge of nanomaterials’ mechanical properties in a number of ways. The major contributions to the body of knowledge by his study can be summarized as follows: (1) The study has contributed in developing a model of elongation for 2-D grain and 3-D grains. It has been generally reported by researchers that materials deformed by Accumulative Roll-Bonding and Equal Channel Angular Pressing are generally elongated but none of these researchers have developed a model of elongation. Elongation revealed more information about “size” during grain refinement. (2) The Transmission Electron Microscopy revealed the grain shape in three directions. The rolling direction or sliding direction, the normal direction and the transverse direction. Most developed models ignored the different approaches of measuring nanomaterials’ mechanical properties. Most existing models dealt only with the equivalent radius measurement during grain refinement. In this dissertation, the different approaches of measuring nanomaterials’ mechanical properties have been considered in the developed models. From this dissertation an accurate correlation can be made from microscopy results and theoretical results. (3) This research has shown that most of the published results on nanomaterials’ mechanical properties may be correct although controversies exist when comparing the different results. This research has also shown that researchers might have considered different approaches to measure nanomaterials’ mechanical properties. The reason for different results is due to different approaches of measuring nanomaterials’ mechanical properties as revealed in this research. Since different approaches of measuring nanomaterials’ mechanical properties led to different obtained results, this justify that most published results of nanomaterials’ mechanical properties may be correct. This dissertation revealed more properties of nanomaterials that are ignored by the models that considered only the equivalent length. (4) This research has contributed to the understanding of nanomaterials controversies when comparing results from different researchers.
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Huang, Chiao-Ting, and 黃巧婷. "Size and Shape-Controlled Synthesis of Cobalt Nanomaterials." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/13684612489667234223.
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碩士國立中正大學
化學暨生物化學研究所
99
Monodispersed magnetic nanoparticles ( NPs ) recently have been actively studied due to their potential applications in data storage and magnetic resonance imaging (MRI). Cobalt nanostructures were prepared by thermal decomposition of dicobalt octacarbonyl, Co2(CO)8, in o-xylene and n-decane in this study. Significantly monodiapersed Co nanoparticles were obtained by tuning the reaction conditions such as precursor : surfactant ( oleylamine : oleic acid ) mole ratio, the reaction temperature and reaction time. Interestingly, the crucial role of the precursor: surfactant ( oleylamine : oleic acid ) mole ratio on the shape of the nanoparticles was demonstrated by altering the ratio from 1:10:1 ( spherical particles ) to 1:10:2 at 175°C leading to rectangular particles. Besides the observations of spherical particles in the former case with precursor: surfactant mole ratio of 1:10:1, the lowering the reaction temperature to 165°C led to formation of rectangular particles. This observation was explained by the controlled growth of the nanocrystals at lower temperature lead to special structures. Further examination by tuning the mole ratio to 1:12:1.2 at 165°C led to elongated rectangular particles. Characterization of the cobalt nanoparticles was conducted by transmission electron microscope ( TEM ) and EDS. The crystal structures of the nanoparticles were analyzed by powder x-ray diffraction and electron diffraction from the HR-TEM images. Hysteresis curve was found in magnetism analysis of Co nanoparticles.
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Ho, Ming-Kang, and 何明鋼. "Study on the anisotropy of room temperature ferromagnetic nanomaterials." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/t88283.
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碩士國立東華大學
物理學系
107
This research work mainly focuses on the shape anisotropy of magnetic. The sample is mainly divided into the internal magnetic moment extension axis direction and the internal magnetic moment along the short axis direction, and is analyzed by various thicknesses. The thickness is divided into 0.7, 1.0, 1.3, 1.5. 1.7 (mm) five different thicknesses, the material is doped with nano-particles Fe3O4 using poly-L-lactic acid (PLLA). The large ferromagnetic material is composed of multiple magnetic domains, each of which is about 10μm. Therefore, the Fe3O4 we use can be regarded as the magnetic moment in one direction. Then we can use our self-made external magnetic field instrument to reheat and make us The direction of the magnetic moment inside the sample can be controlled. Then, using the characteristics of shape anisotropy, when the internal magnetic moment direction is parallel to the long axis, the applied magnetic field of the sample will be fully converted into the magnetization generated by the sample, and the internal magnetic moment will be affected by the demagnetizing field when it is perpendicular to the long axis. The magnetization is much lower than the applied magnetic field strength. Using this feature, we can use a superconducting quantum interferometer (SQUID) to observe whether our samples conform to shape anisotropy. Although in the study, when the data was found to be 1.0 mm thick, the sample with the internal magnetic moment extending the axial direction has a special phenomenon that the residual magnetic flux suddenly rises, but when compared with the sample with the internal magnetic moment along the short axis direction, It is still possible to see the data we originally expected, so we will not discuss it in depth in this study. The main purpose of this study is to test whether our homemade methods can make samples anisotropic and use this method to make biomedical micro-robots. Fortunately, in this study, we finally confirmed our The sample is indeed affected by magnetization, which in turn produces an anisotropic character. In the article, we will also mention how to make the instrument and how to use it. The main reason is to use the more convenient Arduino controller and write the code yourself, which can greatly reduce the budget of our homemade instruments, and can complete our various needs.