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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.

Effective diffusion coefficient in cell immobilization matrices

Itamunoala, G. F. January 1985 (has links)
No description available.

Determination of diffusion coefficient for unsaturated soils

Sood, Eeshani 29 August 2005 (has links)
The structures constructed on unsaturated soils are damaged by the movement of the soil underneath. The movement is basically due to the flow of moisture in and out of the soil. This change in moisture also affects the strength of the soil, thus resulting in failure of slopes of embankments constructed with these soils. Therefore, it is very important to study the diffusion properties of unsaturated soils. Study of the diffusion properties requires the determination of the diffusion coefficient (/). In this thesis improvements in the drying test, originally proposed by Mitchell (1979), have been discussed. The study also involves defining the evaporation coefficient (he) which has been ill-defined in previous research work. The flow through unsaturated soils is non-linear but due to the complexity involved it has been simplified to a linear problem. The nonlinear behavior has been studied during this research. Therefore, certain refinements have been applied in the determination of the diffusion coefficient. The laboratory procedure followed involves measuring the soil suction along the length of the sample and at different times using thermocouple psychrometers. The evaluation of the evaporation coefficient (he) has been made an integral part of the procedure. The diffusion coefficient is determined using the curve fitting procedure of Aubeny and Lytton, 2003.

A determination of diffusion coefficients for gaseous systems at various temperatures

Strehlow, Roger A. January 1950 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1950. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 94-95).

A Monte Carlo simulation of percolation diffusion above the threshold in disordered lattices

Poole, Owen John January 1996 (has links)
No description available.

Laboratorní a počítačové modelování difúze nízkomolekulových látek v gelových nosičích. / Experimental and computer modeling diffusion of low-molecular solutes in gel – based carriers

Masár, Lukáš January 2011 (has links)
This diploma thesis is focused on combination of experimental study and computer modelling of diffusion processes in gel phases. The aim of experimental part of the diploma thesis was to test and optimize the setting of the diffusion coefficient in gel medium by using the method of horizontal diffusion cells, commonly used for study of diffusion processes through membranes. Specific description of experiments was to determinate the impact of presence of reactive component in inert hydro-gel carrier on final value of diffusion coefficient of low-molecular model diffusion probe. The defined dependencies were subsequently combined with computer simulation of diffusion process in a properly designed model in order to determinate the experimentally unavailable system parameters. The stated combination of both approaches was proved to be an appropriate instrument for studying of hydro-gels with a wide potential especially in the field of preparation of hydro-gel carriers with controlled release of active substances.


Shafikhani, Mehdi January 2019 (has links)
For concrete, a sustainable design requires considering both mechanical properties and durability. One of the major deterioration modes of reinforced concrete structures is the entry of chloride ions and corrosion of embedded metals, which is mainly controlled by diffusion as the mass transport mechanism. Therefore, it is pivotal to quantify the chloride diffusion coefficient of concrete, which controls the rate of chloride ingress. Several testing methods exist for quantifying diffusivity of concrete. However, the current test methods are time consuming and demanding. The primary goal of this study is to develop models for quantifying the chloride diffusion coefficient of concrete. As such, initially, the most recent and prevailing analytical models proposed in the scientific literature were critically reviewed and the parameters controlling the chloride diffusion coefficient of concrete were identified. Then, the cement degree of hydration of concrete – as a key parameter which controls the properties of concrete – its measurement methods, and the uncertainties associated with different quantification methods were scrutinized. Finally, three models were developed to quantify the chloride diffusivity of concrete. The first model quantifies the chloride diffusivity of concrete in terms of its electrical resistivity based on the modified Nernst-Einstein equation. The model accounts for the ionic concentration of the pore solution through the alkalis released due to hydration of cementing materials and the alkali uptake of hydration products, the pore solution conductivity, and the interaction between the ions in the pore solution. The second model, which provides a phenomenological relationship for chloride diffusivity of concrete in terms of its compressive strength, accounts for the tortuosity factor of the mixture, aggregate volume fraction, porosity, compressive strength, and cementing materials content and composition. The third model is developed based on the mixture constituents and the cement degree of hydration of concrete. The model accounts for tortuosity factor through the volume fraction of aggregate particles, the interfacial transition zone thickness and diffusivity, cementing materials type and chemical composition, bulk cement paste transport properties through water to cementing materials ratio, cement degree of hydration, supplementary cementing materials type and replacement levels. In order to assess the accuracy and precision of the proposed models, an experimental program was developed and conducted. The following variables were considered for the experimental program: the volume fraction of coarse aggregate, water to cementing materials ratio, total cementing materials content, and supplementary cementing materials type and replacement levels. The experimental results along with the reported data in the scientific literature were used to validate the proposed models. The results revealed the capability of the models to capture the documented observations, as well as the high accuracy and precision of the proposed models for quantifying the chloride diffusivity of concrete in a wide range of concrete mixtures composition and age. The developed models provide designers, practicing engineers and standard/code developers with accurate, precise and consistent models for quantifying the chloride diffusion coefficient of concrete as a direct measure of its durability. / Thesis / Doctor of Philosophy (PhD)

Development of non-adherent single cell culturing and analysis techniques on microfluidic devices

Viberg, Pernilla January 1900 (has links)
Doctor of Philosophy / Department of Chemistry / Christopher T. Culbertson / Microfluidic devices have a wide variety of biological applications. My Ph.D. dissertation focuses on three major projects. A) culturing a non-adherent immortal cell line within a microfluidic device under static and dynamic media flow conditions; B) designing and fabricating novel microfluidic devices for electrokinetic injecting analytes from a hydrodynamic fluid; and C) using this novel injection method to lyse single non-adherent cells by applying a high electric field across the cell at a microfluidic channel intersection. There are several potential advantages to the use of microfluidic devices for the analysis of single cells: First, cells can be handled with care and precision while being transported in the microfluidic channels. Second, cell culturing, handling, and analysis can be integrated together in a single, compact microfluidic device. Third, cell culturing and analysis in microfluidic devices uses only extremely small volumes of culturing media and analysis buffer. In this dissertation a non-adherent immortal cell line was studied under static media flow conditions inside a CO[subscript]2 incubator and under dynamic media flow conditions in a novel portable cell culture chamber. To culture cells they must first be trapped on a microfluidic device. To attempt to successfully trap cells, three different types of cellular traps were designed, fabricated and tested in polydimethylsiloxane (PDMS)-based microfluidic devices. In the first generation device, cubic-shaped traps were used. After 48 h of culturing in these devices the cell viability of 79 [plus or minus] 6 % (n = 3). In the second generation device, circular wells with narrow connecting channels were employed. However, after 12 h of culturing, no viable cells were found. While the second generation device was not capable of successfully culturing cells, it did demonstrate the importance of culturing under dynamic conditions which lead to next design. The third generation microfluidic device consisted of hydrodynamic shaped traps that were used to culture the cells in a less confined environment. The cell viability after 12 h in this design was 29 [plus or minus] 41% (n = 3). In addition to cell trapping, a novel electrokinetic injection method was developed for injecting analytes from a hydrodynamic flow into a separation channel that was followed by an electrokinetic separation. As the hydrodynamic flow could introduce some excess band broadening in the separation, the actual band broadening of an analyte was measured for different channel depths and hydrodynamic fluid flow rates. The results consistently showed that the separations performed on these devices were diffusion limited. Finally, using this novel injection method, single cell lysis was performed by applying a high voltage at the microfluidic channel intersection. The results of these studies may eventually be applied to help answer some fundamental questions in the areas of biochemistry and pharmaceutical science.

Synthetic strategies for denatured cytochrome-c analogues towards analytical reporting of NOx species

Farao, Al Cerillio January 2019 (has links)
Philosophiae Doctor - PhD / Nitric oxide (NO) plays a key role as biological messenger in the biological system, however detection and quantification thereof has always posed significant problems. NOx is a principal constituent of air pollutants. There are seven oxides of nitrogen of which N2O, NO and NO2 are most important. NO is a free radical and reacts extremely fast with oxygen, peroxides and superoxides. It’s these reactions which are responsible for NO’s fleeting existence. The specific detection and quantification of NO still remains challenging. Most techniques rely on the measurements of secondary nitrite and nitrate species. Electrochemical techniques using ultra micro-electrode systems presented the possibility of direct detection of NO, offering a range of favourable characteristics; good selectivity towards NO, good sensitivity, fast response, long-term stability and ease of handling. Electrochemical detection of NO relies on the modification of electrode surfaces and exploiting the redox properties of NO. NO can either be oxidized or reduced electrochemically depending on the nature of the solution. Under cathodic current NO is reduced to nitrosyl, a highly unstable derivative of NO. These nitrosyls are subject to a serious of chemical reactions to eventually form nitrous oxide. Due to the interferences presented by the electrochemical reduction of NO, the electro oxidation of NO is therefore the methodology of choice for NO detection. The electrochemical oxidation of NO occurs at positive potentials around 800 mV vs. Ag/AgCl. However this potential range is not only favourable to NO oxidation but can lead to the oxidation of several other biological species. These interfering species are biologically present at concentrations higher than NO therefore selectivity is of the highest order when designing these electrode systems. Some nitric oxide sensors are limited in their sensitivity, stability and reproducibility. Direct electron transfer between redox proteins and conductive membrane layers has been scrutinized for years in an attempt to reproduce the mechanistic charge transfer processes for sensor application. However, literature reports have presented many arguments on the complexities associated with depositing these enzymes on electrode surfaces for the purpose of reproducing direct electron transfer at metalloprotein centres. The study sets out to design a material which could mimic the electrochemistry of denatured cytochrome-c. To achieve this it was imperative to design a polymer which could reproduce the electrochemistry of the ligands coordinated to the metal centre of the metalloprotein. A novel Schiff base was synthesized by cross-linking naphthalene to pyrrole to produce the monomer, N,N-bis((1H-pyrrol-2-yl)methylene)naphthalene-2,3-diamine). The monomer was electrodeposited on a screen print carbon electrode (SPCE) vs. Ag/AgCl and served as a supporting layer for denatured cytochrome-c. Cytochrome-c is classified as a metalloprotein. These metalloproteins possess metal centres which when denatured unfolds and allows access to the metal centre. Cytochrome-c was subjected to thermal denaturation which opened up the iron centre. The denatured metalloprotein was cross-linked to the ligand to reconstruct the heme centre environment. This was believed to facilitate the electrochemical activity of the system and allow for electrochemical analysis of these metalloproteins for sensor application. The redox behaviour of the sensors were modelled in phosphate buffer solution (PBS) with cyclic voltammetry. Electrochemical analysis reported the sensors to possess reversible electrochemistry with diffusion control characteristics. The sensor recorded a redox system in the negative potentials range. Following the establishment of the electrochemical profile of the sensor an attempt was made to produce a synthetic analogue of denatured cytochrome-c. Iron (II) was chelated to the monomer N,N-bis((1H-pyrrol-2-yl)methylene)naphthalene-2,3-diamine) to form an iron ligand complex. The complex was subjected to a series of characterization techniques which confirmed coordination to the metal centre. The iron ligand complex was electrodeposited on a SPCE over the potential window of -1 V and 1 V to model the electrochemical behaviour of the sensor. The material was found to be electroactive. Subsequent electrochemical analysis revealed the system to have electrochemical properties, analogous to that of the denatured cytochrome-c system. The sensor was applied in NO and NO2 studies and displayed an affinity towards NO. Based on extrapolated values it was postulated that the lower limit range for NO detection was in the range of 30 to 40 nM. The potentials recorded were lower than the reported oxidation potentials for nitric oxide. The sensor displayed stability and selectivity towards nitric oxide within a complex matrix. The complex matrix employed in this study was synthetic urine that was synthesised in the lab. The sensor displayed the capacity for linear range of NO detection with very low error margins. / 2021-09-01

Measurements of moisture suction in hot mix asphalt mixes

Kassem, Emad Abdel-Rahman 30 October 2006 (has links)
The presence of moisture in hot mix asphalt (HMA) causes loss of strength and durability of the mix, which is referred to as moisture damage. This study deals with the development of experimental methods for measuring total suction in HMA, which can be defined as the free energy state of water in HMA mixes. The total suction is related to the ability of moisture to get into the mix under unsaturated conditions; it is also related to the ability of the mix to retain moisture. Soil suction has been studied extensively. However, suction in HMA as a porous material and its relationship to moisture damage have not been studied. The development of a procedure to measure the total suction in HMA mixes is the first objective of this research. The second objective is to relate suction measurements to physical and chemical properties of the mixtures. The objectives were achieved in two phases. In the first phase, the total suction was measured in HMA specimens with different types of aggregates (limestone and granite), and with different air void distributions and aggregate gradations. The results of this phase showed that the drying test using a 60 oC temperature-controlled room is the proper setup for measuring the total suction in HMA using thermocouple psychrometers. The characteristics of suction-moisture content curves were found to be related to the air void distribution in HMA. In the second phase, total suction was measured in sand asphalt specimens. These specimens had different combinations of aggregates and binders with different bond energies and exhibited different field performance in terms of resistance to moisture damage. The suction measurements in sand asphalt specimens were used to calculate the moisture diffusion coefficient. The results revealed that water diffused into sand asphalt specimens that are known to have poor resistance to moisture damage faster than those that are known to have good resistance to moisture damage

Determination of diffusion coefficient through laboratory tests and analytically validating it using empirical relations for unsaturated soils

Thakur, Anshuman Bramhanand 01 November 2005 (has links)
Soil suction is one of the most important physical variables affecting the soil engineering behavior, moisture content. Suction has a major controlling influence on soil shear strength. The moisture diffusivity properties of unsaturated properties of soils exert a critical influence on the depth to which seasonal variations of moisture and suction at the ground surface extend into the soil mass. Hence, a study of moisture diffusion coefficient is pivotal. In this research the drying test originally proposed by Mitchell (1979) has been validated by back calculating the moisture diffusion values using the empirical relation established by Lytton (2003). The non-linear flow through unsaturated soils has been simplified to a linear problem for simplicity in this study. Owing to this simplification, certain refinements have therefore been applied in the determination of diffusion coefficient. Thermocouple psychrometer was used to measure the soil suction along the length of the sample and at different times in the laboratory. Initial suction measurements were done using the filter paper test. Curve fitting procedure established by (Aubeny and Lytton, 2003), has been used for the determination of the diffusion coefficient. Analytical validation of the moisture diffusion coefficient, required coefficient of permeability, ??k??, slope of suction water characteristic curve ??S?? and air entry value ??ho?? as the major input parameters. Mitchell (1979) assumed the value of ??ho?? to be 100 cm. In this research air entry value, ??ho?? has been re-evaluated and it comes out to be higher than the pre estimated value. The value of slope of suction water characteristic curve, ??S?? obtained from pressure plate tests, compares well to the empirical equation of Lytton (2003). The results of moisture diffusion coefficient obtained from the empirical equation come out in the same range as obtained from the refined Mitchell??s (1979) drying test. The refinements includes introduction of constant temperature environment. Owing to the least variation in temperature, more reliable and reproducible data was obtained. The range of moisture diffusion coefficient, ??-values obtained from empirical equation, comes out to be coherent with the laboratory data. Hence, it can be concluded that the research was successful.

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