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  • 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.
1

Symptoms of exercise-induced muscle damage in boys and men following eccentric exercise

Marginson, Vicky January 2003 (has links)
No description available.
2

Studies on volume change movements in high PI clays for better design of low volume pavements

Manosuthikij, Thammanoon. January 2008 (has links)
Thesis (Ph.D.) -- University of Texas at Arlington, 2008.
3

Life cycle assessment of bio-material stabilized expansive soils

Rosenberk, Ranjith Samuel. January 2008 (has links)
Thesis (Ph.D.) -- University of Texas at Arlington, 2008.
4

Effect of fabric on the swelling of highly plastic clays

Armstrong, Christian Philip 11 September 2014 (has links)
Expansive soils are extremely problematic in transportation projects, and significant research has been done into examining the effect of moisture content changes and index properties on the swelling of soils. However, little has been reported on the effect of soil structure, or fabric, on swelling. The purpose of this study is to examine the effect of the soil fabric on swelling while, at the same time, validating a new set-up for a centrifuge testing program developed over the course of the project to allow for testing of undisturbed specimens. Testing to examine fabric was performed using two methods at the same effective stress, the conventional swelling test, ASTM D4546, and a new double infiltration approach in a centrifuge, on specimens of the Cook Mountain clay which were either compacted in the testing set-up or trimmed into cutting rings from soil compacted via ASTM D698, the Standard Proctor test. Specimens were compacted either dry of optimum to create a flocculated soil structure or wet of optimum to create a dispersed soil structure. Specimens were tested at their as-compacted moisture content or at a moisture conditioned moisture content to remove the effect of the initial moisture content. The results show that soils with a dispersed structure tended to swell more, over a longer time frame, and with a higher amount of secondary swelling in relation to soils with a flocculated structure when tested using the same initial moisture content. The strong influence of the initial moisture content on swelling was also verified. Further, soil specimens prepared at a comparatively high dry density for a given fabric and initial moisture content were found to swell more than soils prepared at a comparatively low dry density. The new centrifuge set-up, involving submerged specimens, was validated and was found to produce similar swelling results as those obtained from the ASTM D4546 tests. In addition, the new centrifuge approach was found to be more expeditious and results in less secondary swelling than the conventional ASTM approach. / text
5

Swelling characteristics of some British mudrocks

Chuay, Ho-Yen January 1986 (has links)
One-dimensional swelling tests were conducted on seven undisturbed and remoulded heavily-overconsolidated clays and indurated mudstones. The samples cover a wide range of properties in terms of geological age, mineralogy, plasticity and diagenetic bonds. It is found that swelling proceeds faster than is predicted by Terzaghi's theory of swelling at low overconsolidation ratios (OCR), but it is slower at high OCR values, probably due to the prominence of secondary swelling. The results show that swelling is of a progressive nature, regardless of plasticity and diagenetic bonds. The coefficient of swelling decreases and the ratio of secondary to primary swelling increases with increasing OCR. At high OCR's, the former drops by more than an order of magnitude below the coefficient of consolidation; the latter can be as high as 0.6 within a log-cycle of time. Progressive softening and failure phenomena in mudrocks are considered to be due to the combined effects of progressive swelling and breakdown of diagenetic bonds. Swelling pressure is found to be indicative of in situ stress conditions. The average swelling index generally increases with pre-consolidation pressure in remoulded samples. Three types of diagenetic bonds are postulated: carbonate cements, viscous-adsorbed-water-type, and mechanical adhesion. Bonds tend to decrease the swelling index and so increase the coefficient of swelling. The fabric of the samples is far different from that assumed in the double-layer theory, which can qualitatively predict the physico-chemical forces involved in swelling. Dead volume, in which the double-layer force cannot operate, is shown to be large. The results of tests using n-decane as pore fluid to suppress osmotic swelling indicates that mechanical swelling is more than 50 to 60 per cent of total swelling in the samples. Both mechanical and total swelling indices are linearly correlated with liquid limit among remoulded samples, except for the Fuller's Earth clay which contains at least 65 per cent smectite (expandable clay).
6

Developments in geomechanics for unsaturated and swelling soils, with particular reference to the Australian environment /

Richards, B. G. January 1900 (has links) (PDF)
Thesis (D.E.)--University of Adelaide, 1991. / Includes bibliographical references.
7

Development of an anisotropic swelling hydrogel for tissue expansion: control over the degree, rate and direction of hydrogel swelling

Lee, Jinhyun 21 November 2008 (has links)
Hydrogels are polymeric materials with chemically, physically or topologically crosslinked networks which have a capacity to absorb and retain water. They have been frequently used for many medical applications because of their useful physical properties such as oxygen permeability and excellent compatibility with living tissue and blood. The long term goal of this research is to develop a hydrogel system for potential use in reconstructive and plastic surgeries such as the closure of cleft palate defects and syndactyly (congenitally fused fingers or toes) repair. The medical requirements for such systems are not only a high degree of swelling, but also slow swelling rate, preferred direction of swelling (anisotropic swelling), appropriate mechanical strength, in addition to being biocompatible. A large degree of swelling would limit the number of surgical procedures required thereby reducing the cost and risk of surgery. A slow swelling rate can avoid tissue necrosis and help tissue growth during the tissue expansion process. Anisotropic swelling is required for specific surgical applications such as cleft palate repairs. Known to be biocompatible hydrogel systems, of a neutral gel system consisting of N-vinyl-2-pyrrolidinone (VP) and 2-hydroxyethyl methacrylate (HEMA) copolymers and an ionizable gel system of VP and acrylic acid (AA) copolymers were prepared using thermal and controlled UV-initiated polymerization. Using these VP/HEMA and VP/AA gel systems, various approaches to control their degree and rate of swelling were studied as a function of key controllable parameters. Their mechanical properties and structural characteristics determining their swelling behavior and mechanical properties also were investigated. Through these studies, how to control the key parameters that affect such swelling behavior was understood in addition to optimizing the gel systems for large degree of swelling, slow swelling rate, and mechanical integrity. Investigations into a number of methods to control the swelling rate were also undertaken for different VP/HEMA based gel systems. Multilayers of alternating gels and elastomer films (polybutadiene (PB) or polydimethylsiloxane (PDMS)) as well as gels encapsulated with the elastomer films were prepared. In addition, gels were prepared with inclusion of either silver nanoparticles or methacrylates with increasing the length of hydrophobic groups for the studies of swelling rate. In this work, two novel methods to control swelling direction (anisotropic swelling) of hydrogels were investigated. One method induces anisotropic swelling through structural gradients within the VP/HEMA gels synthesized by UV polymerization using gradient photomasks. A more promising method used stress induced anisotropic swelling for compressed VP/AA gels. The morphology-gradient VP/HEMA hydrogel system did not show large scale anisotropic swelling. However, the compressed VP/AA gels produced significant anisotropic swelling due to the controlled anisotropy of network morphology. A systematic study as a function of compression temperature, stain and strain rate was performed to derive an understanding of the anisotropic swelling behavior. These compressed gel systems produced not only a large degree of swelling and slow swelling rates but also high anisotropic swelling and proper mechanical stiffness of hydrogels. These materials are believed to be ideal candidates for tissue or skin expansion.
8

Die Inhibition der Müllerzellschwellung unter hypotonen Bedingungen durch HB-EGF

Weuste, Malte 06 June 2011 (has links) (PDF)
Bibliographische Beschreibung: Weuste, Malte Die Inhibition der Müllerzellschwellung unter hypotonen Bedingungen durch Heparine binding epidermal growth factor-like growth factor (HB-EGF) Universität Leipzig, Dissertation 62 S., 135 Lit., 30 Abb., 2 Tab. Referat: Die Einleitung der Arbeit beschreibt die Müllerzelle als vorherrschende Gliazelle der Säugetiernetzhaut. Müllerzellen eignen sich dadurch als Modell für andere Makrogliazellen des Zentralen Nervensystems. Sie sind an der Regulation des Wasser- und Ionenhaushaltes der Netzhaut beteiligt. Müllerzellen postischämischer sowie mit Bariumionen behandelter Netzhäute schwellen unter hypotonen Bedingungen an. In vielen Versuchen der vorliegenden Arbeit wurde daher ein postischämischer Zustand der Netzhaut durch Zugabe von Bariumionen zu gesunden Netzhäuten simuliert. Die Arbeit untersucht die Rolle des Wachstumsfaktors HB-EGF in der postischämischen Netzhaut der Ratte. Dazu wurde der HB-EGF-Gehalt in postischämischen und in Kontrollnetzhäuten mit Western Blots und immunohistochemischer Färbung dargestellt. Der Einfluss von HB-EGF auf die Müllerzellschwellung wurde an vitalen Müllerzellen in vitro untersucht. Hierzu wurden Müllerzellen in Netzhäuten der Ratte mit einem Vitalfarbstoff angefärbt und über einen Zeitraum von 5 Minuten mit hypotoner extrazellulärer Lösung perfundiert. Die Perfusionslösung diente dabei auch als Träger verschiedener Testsubstanzen. Das Schwellungsverhalten der Müllerzellsomata wurde in diesem Zeitraum mit einem konfokalen laser-scanning Mikroskop aufgezeichnet und mit der zum Mikroskop gehörenden Software ausgewertet. Die Versuche der vorliegenden Arbeit zeigten, dass der HB-EGF-Gehalt der synaptischen Schichten der Netzhaut nach einer Ischämie ansteigt. Es zeigte sich auch, dass HB-EGF eine Müllerzellschwellung im hypotonen Milieu hemmt. Durch Perfusion der Netzhäute mit verschiedenen Rezeptoragonisten und Rezeptorantagonisten sowie Enzyminhibitoren und Ionenkanalblockern konnte das Bild einer möglichen Signalkaskade der Schwellungsinhibition durch HB-EGF gezeichnet werden. An dieser Signalkaskade sind verschiedene Proteinkinasen, ein Anstieg des freien intrazellulären Kalziums, die neuronale Freisetzung von Glutamat, die Aktivierung von glialen Adenosinrezeptoren sowie die Öffnung unterschiedlicher Ionenkanäle beteiligt. Verschiedene Hypothesen zur Ätiologie und Pathogenese der glialen Zellschwellung und zu deren Inhibition werden diskutiert. Abschließend wird die Rolle der glialen Zellschwellung als Teil der Pathogenese von Erkrankungen, die mit einem Hirn- und Netzhautödemen einhergehen, dargestellt. In Zukunft könnten solche Erkrankungen einmal spezifisch mit Substanzen wie dem HB-EGF therapiert werden.
9

Diffusion, Swelling and Mechanical Properties of Polymers

Ritums, Janis January 2004 (has links)
Polymers capability to withstand harmful interactions withdifferent environments can be determined by looking at thetransport and mechanical properties of the material exposed tothe medium. The diffusion of a penetrant in a polymer and itsswelling characteristics can be verified by a simplesorption-desorption experiment followed by methodical analysisof the data. Three different systems have been investigated andreported on using the sorption-desorption technique, tensiletesting, compression testing, stress-relaxation and curvefitting routines in Matlab. Fluoropolymers of different repeating unit structure andcrystallinities were exposed to tetrachloroethylene (TCE),water, hydrochloric acid (35%) and hydrobromic acid (47%) at70°C yielding solubility and diffusivity data. Thetransport properties were mostly controlled by the polarity ofthe polymer and to a less degree by the polymer crystallinity.Low solubilities were observed for the aqueous solutes andtheir diffusivities were best fitted using a dual sorption modeassuming no concentration dependent diffusivities. Thepolarisable non-polar TCE showed the highest solubility, andthe diffusivity was solute-concentration dependent. The rate atwhich the surface-concentration approached the saturation levelwas proportional to the product of the Young's modulus, thesquare of the dry polymer thickness and the logarithm of thesolute diffusivity. Data for water-hyperbranched polymer andlimonene-polyethylene confirmed the relationship. Low and high-density poly-ethylene (LDPE, HDPE), crosslinkedethylene vinyltrimetoxy silane (PEX), natural rubber (NR) andacrylonitrile-butadiene rubber were exposed to crude oilcomponents at 25 and 30°C. Solubility data indicated thatthe accessibility of the interfacial components decreased inthe order: cyclohexane, n-hexane/2,2-dimethylbutane andn-decane/n-tetradecane. The free-volume model describeddesorption data better than the semi-empirical exponentialmodel, but the numerical differences were for most practicalapplications negligibly small. The decrease in tensile modulus,yield stress and relaxation modulus for dry HDPE and PEXcompared to n-hexane, n-heptane, cyclohexane andtoluene-swollen samples was clearly caused by thepenetrant-induced plasticisation effect. LDPE and NR-sheets were exposed to limonene at 25°C.The limonene-NR displayed saddle-shape during sorption andcup-shape during desorption were most likely a consequence oflocal differences in limonene concentration that affected thestress state across the sheet thickness. The ratio in bulkmodulus between LDPE and NR was significantly smaller than thecorresponding ratio in tensile modulus and close to the ratioin the degree of anisotropy for the same polymers.Consequently, the bulk modulus is more accurate than thetensile modulus to use when predicting the degree of swellinganisotropy.
10

Diffusion, Swelling and Mechanical Properties of Polymers

Ritums, Janis January 2004 (has links)
<p>Polymers capability to withstand harmful interactions withdifferent environments can be determined by looking at thetransport and mechanical properties of the material exposed tothe medium. The diffusion of a penetrant in a polymer and itsswelling characteristics can be verified by a simplesorption-desorption experiment followed by methodical analysisof the data. Three different systems have been investigated andreported on using the sorption-desorption technique, tensiletesting, compression testing, stress-relaxation and curvefitting routines in Matlab.</p><p>Fluoropolymers of different repeating unit structure andcrystallinities were exposed to tetrachloroethylene (TCE),water, hydrochloric acid (35%) and hydrobromic acid (47%) at70°C yielding solubility and diffusivity data. Thetransport properties were mostly controlled by the polarity ofthe polymer and to a less degree by the polymer crystallinity.Low solubilities were observed for the aqueous solutes andtheir diffusivities were best fitted using a dual sorption modeassuming no concentration dependent diffusivities. Thepolarisable non-polar TCE showed the highest solubility, andthe diffusivity was solute-concentration dependent. The rate atwhich the surface-concentration approached the saturation levelwas proportional to the product of the Young's modulus, thesquare of the dry polymer thickness and the logarithm of thesolute diffusivity. Data for water-hyperbranched polymer andlimonene-polyethylene confirmed the relationship.</p><p>Low and high-density poly-ethylene (LDPE, HDPE), crosslinkedethylene vinyltrimetoxy silane (PEX), natural rubber (NR) andacrylonitrile-butadiene rubber were exposed to crude oilcomponents at 25 and 30°C. Solubility data indicated thatthe accessibility of the interfacial components decreased inthe order: cyclohexane, n-hexane/2,2-dimethylbutane andn-decane/n-tetradecane. The free-volume model describeddesorption data better than the semi-empirical exponentialmodel, but the numerical differences were for most practicalapplications negligibly small. The decrease in tensile modulus,yield stress and relaxation modulus for dry HDPE and PEXcompared to n-hexane, n-heptane, cyclohexane andtoluene-swollen samples was clearly caused by thepenetrant-induced plasticisation effect.</p><p>LDPE and NR-sheets were exposed to limonene at 25°C.The limonene-NR displayed saddle-shape during sorption andcup-shape during desorption were most likely a consequence oflocal differences in limonene concentration that affected thestress state across the sheet thickness. The ratio in bulkmodulus between LDPE and NR was significantly smaller than thecorresponding ratio in tensile modulus and close to the ratioin the degree of anisotropy for the same polymers.Consequently, the bulk modulus is more accurate than thetensile modulus to use when predicting the degree of swellinganisotropy.</p>

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