• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1424
  • 1335
  • 530
  • 205
  • 37
  • 30
  • 22
  • 22
  • 18
  • 17
  • 10
  • 9
  • 8
  • 7
  • 5
  • Tagged with
  • 4181
  • 936
  • 624
  • 485
  • 361
  • 296
  • 284
  • 242
  • 235
  • 208
  • 187
  • 185
  • 183
  • 179
  • 173
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
241

Characterization of the High-Temperature Helium Facility in the Thermal Hydraulics Laboratory

Glosup, Richard Edwin 28 September 2011 (has links)
No description available.
242

Potent Broad-Spectrum Antibacterial Activity of Bismuth-Based NPs Prepared by a Top-Down Method

Pant, Bishnu Datt 22 September 2022 (has links)
No description available.
243

Characterization in Apuleius' Cupid and Psyche Episode

Elford, Juanita 04 1900 (has links)
<p>This dissertation is a careful study of characterization in the Cupid and Psyche episode (IV.28 - VI.24) in Apuleius’ <em>Metamorphoses</em>. In general, although the <em>Metamorphoses</em> has been the subject of a good deal of scholarly interest as of late, there has previously been minimal focused examination of characterization in the Cupid and Psyche section. This dissertation therefore represents an important contribution to current scholarship and uses a multi-faceted approach which includes investigation of the characters’ relationships to one another, roles, function, speech, intertextual connections, and questions of genre and authorial technique.</p> <p>After a brief discussion of preliminaries such as the scope of the study, methodology, and the isolation of the Cupid and Psyche narrative from the rest of the novel, Chapter One examines the minor characters of the episode. The minor characters are defined and then placed into five groups for analysis: the invisible servants, the personifications of the abstract concepts, the floral and faunal characters, the animate object, and the deities. Chapter Two addresses the role of Psyche’s family in the narrative, covering her parents’ small but important contribution and her sisters in their larger role as Psyche’s secondary adversaries. Chapters Three, Four, and Five investigate the characterization of Venus, Cupid, and Psyche respectively. The Conclusion summarizes the larger picture of Apuleius and his approach to characterization and reviews some of his favorite techniques of characterization, as well as his approach to the characterization of females.</p> / Doctor of Philosophy (PhD)
244

Identification and Characterization of Non-coding RNAs in Escherichia coli

Zhu, Rebecca 05 1900 (has links)
<p> Until a little over a decade ago, the regulatory roles of small RNAs (sRNAs) in prokaryotes were largely undetected. Since then, there has been an explosion in the discovery of novel sRNA sequences and we have begun to understand their functions and mechanisms of regulation. The identification and characterization of sRNAs from different organisms have largely been achieved through computational and experimental approaches that focus on sequence elements in intergenic regions. Based on these previously established techniques, we have developed and applied a new bioinformatics approach to search for highly conserved sequences in unannotated intergenic regions from several bacterial genomes, which may contain new sRNA sequences. Through this search, we have identified seven candidate sequences that are conserved at the primary sequence level, and some of the secondary structure motifs are also conserved among multiple bacteria genomes. When we examined those seven candidates experimentally, it was found that when the expression of one mutated candidate (rUIG0803 _ 4D) was induced at the RNA level, minor morphological changes and a delayed lethal phenotype was elicited. The expression of the RNA also may result in the altered expression of kanamycin kinase and glycerol kinase, as indicated by the mass spectrometry data. Experimental characterizations of eight previously identified sRNAs from literature with functions unknown have also been performed but no apparent phenotypic phenomenon was observed in this project, which indicated that all or some of those 8 sRNAs might not play any regulatory roles in cells, or their roles need to be characterized through other genetic screens. To further search for RNA sequences with regulatory functions, we created a library of random DNA transcript using the Lambda Phage genomic DNA. Preliminary screening efforts show that three of the 192 clones screened could trigger reduced cell growth when their RNA was overexpressed. This study marks the first use of a bioinformatics approach that uses primary sequence and secondary structure information to search for sRNAs in the unannotated intergenic region. Moreover it also marks the first time that the effects of introducing random lambda phage RNA in an E. coli host. </p> / Thesis / Master of Science (MSc)
245

Synthesis and Characterization of Environment-Responsive Membranes for Bioseparations / Environment-Responsive Membranes for Bioseparations

Huang, Ruixiang 08 1900 (has links)
Environment-responsive membranes were created by modification of a commerical polyvinylidene fluoride (PVDF) membrane support with a thermo-responsive hydrogel composed of poly N-vinyllactams cross-linked with bisacrylamide. The modified membranes were then characterized by their percentage mass gains as well as by their valve effect in response to changes in salt concentration. One set of membranes, with a large valve effect, was selected for highest retention of intermediately sized proteins was examined for ultrafiltration-based protein separation applications. A batch separation protocol featuring pulsed sample injection technique (PSIT) was then used to sieve single proteins and to fractionate a synthetic binary protein mixture and a synthetic ternary protein mixture with some success, demonstrating the potential of these environment-responsive membranes for use in multi-component separations. A second set of membranes, with a small valve effect, was selected for its ability to alter between hydrophobic and hydrophilic states under different environmental conditions and its potential in hydrophobic interaction membrane chromatography (HIMC) applications was successfully demonstrated by comparing against a benchmark membrane that is used successfully for HIMC applications in prior literature. / Thesis / Master of Applied Science (MASc)
246

Modification and Characterization of Alpha and Beta Nickel (II) Hydroxide

Safari, Reza 27 November 2018 (has links)
I have submitted another pdf file which is my permissions for figures used in my thesis. The name this file is Clearance. / Nickel Hydroxide is one of highly active materials used in various energy conversion applications. One of the key factors in the deposition of Ni(OH)2 is the active surface area which plays an important role in improving the efficiency of transformation reactions. There are various methods to enhance the active area. One method that can be used to modify the morphology of deposited Ni(OH)2 is to generate porous structures. Ni(OH)2 can be formed in two different phases namely alpha and beta. The main objective in our work is to optimize the synthesis conditions and characterize structures at the nanoscale, and also demonstrate unequivocally the presence of alpha and beta phases. For this work, a combination of electron microscopy and electrochemistry is needed to modify the morphology of nickel hydroxide and for detailed structural characterization. Various characterization techniques are used to investigate different electrochemical depositions conditions of Ni(OH)2 in alpha and beta phase forms using Direct and Indirect methods, respectively. Kinetically, alpha-Ni(OH)2 is easier and faster to be synthesized and can be deposited directly in one step. During cyclic voltammetry of alpha-Ni(OH)2 in KOH, the volume of material involved in the oxidation reaction increases in every cycle. Scanning Electron Microscopy and Transmission Electron Microscopy characterization shows that this may be due to microbubble formation that transform deposited sheets to particulate shapes. On the other hand, conversion of nickel metal to beta-Ni(OH)2 during cyclic voltammetry causes an expansion of particles. Effectively, nickel hydroxide is formed on the shell while nickel remains in the core. High Resolution Transmission Electron Microscopy is then used to identify the distribution of these phases. Another foremost feature for the beta phase is to make nickel metal in any desired shape, which can then be converted to beta-Ni(OH)2 through Cyclic Voltammetry in KOH. The presence of both phases is demonstrated with electron diffraction. Finally, as future work, all experiments will be performed in-situ TEM using liquid cell to observe structural changes in real time. / Thesis / Master of Science (MSc)
247

Microindentation for Characterization of Interactions in Liquid Metal Composites

Albacarys, Daniel Alexander 31 May 2024 (has links)
Liquid Metal (LM) Composites are a rapidly expanding field within function materials research. Composed of isolated LM droplets dispersed in an elastomer, these composites can exhibit properties that include electrical conductivity, thermal conductivity, and programmable and anisotropic mechanical properties. Microindentation is a material characterization technique that can be used to study the micron-scale droplet-droplet interactions between the inclusions in these composites. Because most microindentation systems are incapable of producing plastic/elastic deformation volumes large enough to measure the interaction between inclusion and matrix or inclusion and inclusion in these systems, a specialized microindenter is designed and detailed here. The indenter is then used to test various droplet size, spacings, and matrix material combinations to view the mechanical and electrical implications of these variables. These materials were analyzed with a basic fracture energy scaling formula. It was also found that resistivity can decrease by up to seven orders of magnitude after droplet rupture, with as little as a 20μm elastomer film separating droplets before rupture. Continued studies of these phenomena will allow us to exploit the properties of these materials in new and interesting ways. / Master of Science / When a metal which is a liquid at room temperature (eutectic gallium-indium) is dispersed inside a soft, stretchable material such as a silicone rubber, it creates a unique functional material. These materials go beyond their typical uses by having new and exciting properties such as the ability to conduct heat and electricity. Not only do these materials have these properties, but we can also control them through specific manufacturing steps. These materials are called liquid metal composites or liquid metal embedded elastomers. These materials can be used to create flexible wiring for soft electronics and robots which can bend and stretch to suit their environment. One component of the interactions that lead to these properties is the interaction between pairs of droplets of liquid metal inside of the silicone. To study these interactions, we utilize micro-indentation which produces very small and precise deformations in a material. By slowly pressing on the material, and measuring forces, displacements, and electrical resistance, we can gain a closer insight into how the interactions of droplets and rubber produce these properties. These materials can be modeled using an analysis of fracture energy, and pairs of droplets decrease electrical resistance by over 10 million times when droplets combine. By studying these interactions, we gain a greater sense of how to control the properties of these materials, and can create new wearable devices that can bend and stretch with the human body's movements.
248

Optimization Study of the Stripline Resonator Technique for Dielectric Characterization

El-Bakly, Ahmed Mostafa 24 February 1999 (has links)
To properly design the microwave components such as transmission lines, filters, capacitors, inductors, and many others, it is important to know the characteristics of the construction materials at microwave frequencies. One of the most reliable techniques in material characterization at microwave frequencies is the coplaner coupled stripline resonator technique. This technique is an enhancement to the classical stripline resonator technique. In this technique, the measured resonance frequency and quality factor of the resonator are used to determine the complex permitivity. One of the main problems in this technique is the proper modeling of the coupling gaps. In this dissertation we will introduce an accurate model of the coupling gap, which will shows that the capacitive behavior of the gap is not pure capacitive as known before, but it turns into more complex one at higher frequencies depending on the dimensions of the gap primarily. The second main problem is the limitation in the frequency range for accurate measurements. At higher frequencies, the coupling reaches its peak value for a given stripline resulting in excessive loading to the resonator and thus a lowered Q value. In this frequency range, measurement of the dielectric properties looses its accuracy because the lowered Q values which means inaccuracies in determining the resonant frequencies as well as great error in determining the Qc and Qd terms. In this dissertation, attempts to remedy this problem by introducing two different approaches to get an improved design for the coplaner coupled stripline resonator are presented. The first approach to optimize the design of the coplaner coupled stripline resonator is based on optimizing the dimensions of the coplaner coupled stripline resonator three sections (coplaner, transition region, and the center stripline). In the second approach, a reactive stub (via) is introduced in the coupling gap between the coplaner line and the center stripline. The added stub is designed to improve the Q values of the structure resonances. Simulations of different designs of the coplaner coupled stripline resonator using different stub dimensions are presented. Advantages and disadvantages of these designs as well as the solution to their resonance frequency shift problems are discussed as well. / Ph. D.
249

Synthesis, Characterization and Properties of Vinyl Ester Matrix Resins

Li, Hui III 28 May 1998 (has links)
Vinyl ester oligomers diluted with styrene are important matrix resins for thermosetting polymer composites. A major objective of this work has been to study the chemistry and kinetics of the cure reactions of vinyl ester resins at elevated curing temperatures, which are consistent with typical composite processing conditions. The crosslinking reaction of vinyl ester resins was studied by FTIR and the loss of the carbon-carbon double bonds of the methacrylate (943 cm-1) and styrene (910 cm-1) were followed independently. A small background absorbance overlapping the absorbance at 943 cm-1 was subtracted from all spectra collected as a function of reaction time to quantify conversions. Copolymerization reactivity ratios of styrene and terminal methacrylates on vinyl ester oligomers were calculated to be rs = 0.36 ± 0.05 and rm = 0.24 ± 0.1 from early conversion data obtained at 140°C on a series of resins with systematically increasing levels of styrene. The composition data were analyzed using the integrated form of the copolymerization equation and assuming a terminal reactivity model to predict copolymer compositions throughout the reactions. These curves agreed well with the experimental data even at high conversion levels. Another important part of this research was to study structure-property relationships of vinyl ester resins. Characteristics of vinyl ester resins and networks such as shrinkage, viscosity, crosslink density, glass transition temperature, gel swelling, and toughness have been studied. The shrinkage of vinyl ester resins during cure was calculated according to density measurements to be 4% - 10% depending on styrene content. It was found that the chain length of vinyl ester oligomers strongly affects the properties of the networks. For vinyl ester resins with longer lengths (Mn = 1000 g/mol), crosslinked networks have higher fracture toughness values and lower Tg's. Finally, the synthesis, cure reactions and toughness of a new low viscosity vinyl ester resin were also investigated in this work. The new oligomer has a structure with which the hydroxyl groups on the backbone are replaced by methyl groups. They could be processed without a diluent. The cure reactions of the new resin were studied by FTIR, DSC and 13C-NMR. / Ph. D.
250

The Development of Measurement and Characterization Techniques of Road Profiles

Kern, Joshua Victor 26 July 2007 (has links)
The principal excitation to a vehicle's chassis system is the road profile. Simulating a vehicle traversing long roads is impractical and a method to produce short roads with given characteristics must be developed. By understanding the characteristics of the road, a reduced set of models can be created from which appropriate representations of the terrain can be synthesized. Understanding the characteristics of the terrain requires the ability to accurately measure the terrain topology. It is only by increasing the fidelity and resolution of terrain topology data that application of these data can be advanced. The first part of this work presents the development of a high fidelity 3-D laser terrain measurement system. The system is developed for both on-highway and off-road measurement. It is capable of measuring terrain in three dimensions, whereas current systems measure separate 2-D profiles in each wheel path of the vehicle. The equipment setup and signal processing techniques are discussed, as well as future improvements and applications of this enabling technology. The second part of this work develops a method of characterizing non-stationary road profile data using ARIMA (Autoregressive Integrated Moving Average) modeling techniques. The first step is to consider the road to be a realization of an underlying stochastic process. The model identification techniques are demonstrated. Statistical techniques are developed and used to examine the distribution of the residual process and the results are demonstrated. The use of the ARIMA model parameters and residual distributions in classifying road profiles is also discussed. By classifying various road profiles according to given model parameters, any synthetic road realized from a given class of model parameters will represent all roads in that set, resulting in a timely and efficient simulation of a vehicle traversing any given type of road. / Master of Science

Page generated in 0.0395 seconds