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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

Studies On Selective Adsorption Of Aqueous Glucose Or Fructose On Various Cationic Forms Of Zeolite Y

Yesiltepe, Suat Bora 01 August 2006 (has links) (PDF)
The equilibria of adsorption on calcium and hydrogen forms of zeolite Y by equimolar solutions of 12.5 %, 20%, 25%, 30% and 35% w/v of mixtures of glucose, G and fructose, F / also the non-equimolar mixtures of 20% w/v glucose - 30% w/v fructose, 30% w/v glucose - 20% w/v fructose, 25% w/v glucose &ndash / 35% w/v fructose, and 35% w/v glucose-25% w/v fructose solutions, which were prepared 24 hours in advance at the experimental temperature, have been studied batch wise at 50&ordm / C. Glucose adsorption, in solutions that had adsorption differences, was fast on both zeolites, on the contrary of slow adsorption of fructose with the stable dynamics. Both adsorptions had small amounts of adsorption changes after minute 30. The treatments made under the same conditions with the same mixtures showed Ca-Y zeolite had better separation capacity compared to H-Y zeolite. Some trials were repeated with CaCl2 added to the solutions. The slowed down affection of fructose adsorption in spite of the small change of glucose adsorption led to better separation. Samples were analyzed by classical methods, not HPLC. All the data were considered with various models and their convergence numbers were tested for their closeness to reality. The models were analyzed by response surface methodology and some of those models had correlation factors as high as 88% at the equilibrium points at 30th minutes. Besides, time dependent models have been considering the lag times with a time dependent variable included all the data of all treated solutions with correlation as high as 79.5%.
2

The Effect Of Mechanical Forces On Adipogenic Differentiation

Sharafi, Parisa 01 January 2008 (has links) (PDF)
Numerous intra and extra cellular factors take role in differentiation of cell towards a given lineage. These factors have crucial role in cell-cell and cell-environment interactions. In this study, the aim is to investigate the effect of mechanical forces on the adipogenic differentiation of preadipocytes and mesenchymal stem cells in an in vitro model. Human preadipocytes and mesenchymal stem cells were embedded in 2 % agarose discs. According to the stress-relaxation test results it was observed that initial mechanical properties of agarose-mesenchymal stem cell (MSC) discs did not change compared to acellular agarose whereas those of preadipocytes decreased significantly. The discs with cells were exposed to compression under different weights (1.4 &plusmn / 0.2 g, 7.5 &plusmn / 0.2 g, and 14.6 &plusmn / 0.3 g.) continuously in differentiation medium for 21 days. The control discs were treated with differentiation medium without any compressive weight on top of them. After 21 days, total ribonucleic acids (RNA) have been isolated. Adipogenic differentiation was investigated via reverse transcription coupled quantitative polymerase chain reaction (PCR). The expression of peroxisome proliferators-activated receptors (PPAR-gamma), CCAAT-enhancer binding protein (C/EBP-Beta), leptin, adiponectin, adipophilin and human stearoyl-CoA desaturase (hSCD) have been assessed as adipogenic markers. Differentiation to adipocytes has been further investigated by histochemical Sudan IV staining and immunochemistry and compared to control group. Decrease in the expression of adipogenic factors, size and number of lipid droplets were observed for both MSCs and preadipocytes subjected to compression in agarose discs. The decreases were correlated with the level of mechanical stress. The highest depletion of gene expression was observed in leptin and C/EBP&amp / #61538 / . From our results, it was shown for the first time that mechanical stress impaired the adipogenic differentiation of MSCs and preadipocytes in agarose discs. However, the differentiation pathways should be further investigated.
3

Preparation Of Sericin Based Wound Dressing And Investigation Of Its Biomaterial Properties

Akturk, Omer 01 February 2009 (has links) (PDF)
In this study, it was aimed to produce sericine/collagen composite membranes and to investigate their properties as a wound dressing. Different membrane compositions were prepared by casting and solvent evaporation method. After initial studies for optimization of ratios, membrane groups at two different thicknesses were prepared for each selected ratio and cross-linked with 3 % (w/v) glutaraldehyde (GTA). Considering the wound dressing requirements, equilibrium degree of swelling (EDS), water vapor transmission rate (WVTR), oxygen permeability, mechanical properties, in situ degradation, microbial penetration and cytotoxicity of membranes were examined. The EDS of membranes had a range of 14.91 to 4.37 (g/g) and increased significantly with the presence of sericin. There was no obvious relationship between the sericin ratio of membranes and WVTR, but the increase in membrane thickness decreased WVTR significantly. Thin and sericin containing membranes had statistically better oxygen permeabilities. Sericin deteriorated the tensile strength and elongation of membranes statistically. Cross-linked groups were resistant to hydrolytic degradation through 4 weeks of incubations. None of the membranes were penetrable to bacteria owing to their dense structure. For cytotoxicity studies, 3T3 fibroblasts and keratinocytes were seeded on membranes separately, and analyzed with MTT assays, and light microscopy and scanning electron microscopy (SEM). As regards to MTT assay, keratinocytes proliferated significantly on membranes and reached to high confluence within 7 days. Similarly, fibroblasts also showed high proliferation on membranes. Light microscopy and SEM analysis showed that both cells could attach, grow and spread on membranes. Also, cells gained their characteristic morphology after 1 day and formed flattened structure within 7 days.
4

An Investigation Of Microstructure, Microhardness And Biocompatibility Characteristics Of Yttrium Hydroxyapatite Doped With Fluoride

Toker, Sidika Mine 01 January 2010 (has links) (PDF)
The aim of this study was to investigate the microstructure, microhardness and biocompatibility properties of nano hydroxyapatite (HA) doped with a constant yttrium (Y3+) and varying fluoride (F-) compositions. HA was synthesized via precipitation method and sintered at 1100&amp / #61616 / C for 1 hour. Increased densities were achieved upon Y3+ doping while F- doping led to a decrease in densities. For structural analysis, XRD, SEM and FTIR spectroscopy examinations were performed. No secondary phases were observed in XRD studies upon doping. Lattice parameters decreased due to substitutions of ions. In SEM analysis, addition of doping ions was observed to result in smaller grains. In FTIR analysis, in addition to the characteristic bands of HA, novel bands indicating the substitution of F- ions were observed in F- ion doped samples. The highest microhardness value was obtained for the sample doped with 2.5%Y3+, 1%F-. Increased F- ion contents resulted in decreased microhardness values. For biocompatibility evaluation, in vitro tests were applied to the materials. MTT assay was performed for Saos-2 cell proliferation analysis. Y3+ and F- ion incorporation was found to improve cell proliferation on HA discs. Cells were found to attach and proliferate on disc surfaces in SEM analysis. ALP assay showed differentiation of cells on the discs can be improved by doping HA with an optimum amount of F- ion. Dissolution tests in DMEM revealed that structural stability of HA was improved with F- ion incorporation. The material exhibiting optimum structural, mechanical and biocompatibility properties was HA doped with 2.5%Y3+, 1%F-.
5

Scale Up Of Panel Photobioreactors For Hydrogen Production By Pns Bacteria

Avcioglu, Sevler Gokce 01 September 2010 (has links) (PDF)
Production of hydrogen from biomass through the use of dark and photofermentative bacteria will be applicable in the future and a promising route. The aim of this study is to develop and to scale-up solar panel photobioreactors for the biological hydrogen production by photosynthetic purple non sulfur (PNS) bacteria on artificial substrates and on real dark fermentation effluent of molasses. The parameters studied are light intensity, temperature, feed stock, feed rate, pH, cell density, light and dark cycle and carbon to nitrogen ratio on hydrogen production. Continuous hydrogen production has been achieved on artificial medium and dark fermentor effluent of molasses containing acetate and lactate by Rhodobacter capsulatus wild type and (hup-) mutant strains in panel photobioreactors in indoor and outdoor conditions by fed batch operation. Laboratory (from 4 to 8 liters) and large scale (20 L) panel photobioreactors by using various designs and construction materials were developed. In this photobioreactors continuous hydrogen production was achieved by feeding. Na2CO3 can be used as buffer to keep the pH stable during long term operation on molasses dark fermentor effluent. The adjustment of the feedstock by dilution and buffer addition were found to be essential for the long term stability of pH, biomass and H2 production for both in indoor and outdoor applications.
6

Hemicellulose Extraction From Agro-food Industrial Wastes And Its Apllication In Foods

Yilmaz, Hilal 01 September 2012 (has links) (PDF)
Hemicellulose is a valuable component of agro-food industrial wastes. Although there are some potential usage areas of hemicelluloses such as drug manufacture, encapsulation, and emulsification in food processing plants, they are not extensively utilized. In this study, effective extraction methods of the hemicelluloses from agro-food industrial wastes (corn peels and sugar beet pulp) and their application as coating material for banana fruits were investigated. Firstly, the effects of raw material type, particle size, and extraction conditions (alkaline concentration, temperature, time) and methods (direct alkaline extraction, alkaline extraction after component removal, and acidic extraction method) on hemicellulose yields were investigated. Sugar beet pulp and corn wastes were used as raw material. Alkali extraction resulted in 40.2% pure extracts while acidic hydrolysis gave only 27.4% purity in the same extraction conditions. The optimal extraction conditions were found as 30&deg / C temperature, 10% NaOH, and 24 h time (64.3%). It was also observed that removal of constituents such as fat, protein, starch, and soluble sugar increased the purity of hemicellulose from 40.2 to 58.2% at the same conditions. After finding optimum hemicellulose yield for practicle use, it was used as edible coating material to prevent darkening of banana fruits and any quality losses. On the fourth day of storage at 4 &ordm / C, there was no detected fungal decay of coated bananas / however, 20% of uncoated bananas (control) were infected. Moreover, the control group lost 5.1% of total weight but coated samples with 1%, 1.5%, and 2% hemicellulose (HC) lost 3.6%, 3.3%, and 3.1% of their total weight, respectively. Hemicellulose coating also protected firmness of bananas (701.1 gf for coated and 509.6 gf for uncoated samples at the end of 4th day). Color was another important quality parameter and it was showed that lightness and yellowness of coated bananas were preserved with very little losses at the end of storage period while control samples turned brown at an unacceptable level. The results indicated that using both low alkaline concentration and low temperature allows to recover higher quality extracts. In addition, hemicellulose showed a characteristic of a good edible coating material for banana in order to preserve their visual acceptance and other quality parameters.
7

Integrated Biomimetic Scaffolds For Soft Tissue Engineering

Guven, Sinan 01 July 2006 (has links) (PDF)
Tissue engineering has the potential to create new tissue and organs from cultured cells for transplantation. Biodegradable and biocompatible scaffolds play a vital role in the transfer of the cultured cells to a new tissue. Various scaffolds for soft tissue engineering have been developed, however there is not any structure totally mimicking the natural extracellular matrix (ECM), ready to use. In this study biodegradable and biocompatible scaffolds were developed from natural polymers by tissue engineering approach and tested in vitro. Scaffolds (SCAF) were prepared with freeze drying and composed of chitosan, gelatin and dermatan sulfate. Polymer solutions were treated with different stirring rates (500 rpm and 2000 rpm), freezing temperatures (-20 &deg / C and -80 &deg / C) and molding (cylindrical mold and petri dish) to achieve porous structure in order to provide sufficient space for cell growth and extracellular matrix production. Among the prepared scaffolds at different conditions, the scaffolds prepared at 500 rpm and frozen at -80 &deg / C, (SCAF-1), was chosen for further studies. These scaffolds achieved 0.512 MPa tensile strength, with 9.165 MPa tension modulus and 3.428 MPa compression modulus. Besides in lysozyme containing degradation medium they conserved their integrity and lost about 30 % of their initial weight in 30 days period. Mechanical and enzymatic degradation tests showed that scaffolds have physical integrity for the tissue engineering applications. To mimic the natural tissue and enhance cell growth, biologically active arginine &amp / #8211 / glycine - aspartic acid - serine (RGDS) peptides and platelet derived growth factor-BB (PDGF-BB) were immobilized on the SCAF-1. Fibroblast cells were seeded on the scaffolds containing RGDS, (SCAF-1-RGDS), and PDGF-BB, (SCAF-1-RGDS-PDGF), and incubated in media either free of serum or containing serum. Scaffolds immobilized with RGDS and PDGF-BB had the highest attached cell number by the day 15. Florescence microscopy studies also indicated that RGDS and RGDS-PDGF modified scaffolds were more suitable than controls, (SCAF-1), for cell growth and proliferation. According to scanning electron microscopy (SEM) results, modified scaffolds demonstrated better cell morphology and attachment of cells. Based on the obtained results, it can be concluded that RGDS-PDGF immobilized chitosan-gelatin-dermatan sulfate systems have a great potential to be used as a scaffold for soft tissue engineering applications.
8

Finite Element Investigation Of Mechanical Interaction Of Dental Implants With Bone

Eser, Atilim 01 July 2007 (has links) (PDF)
During the last years, biomechaniccs, the understanding of the very complex mechanical behavior of living tissue, becomes a very important field of research of the wide bravch of mechanichs. Thia study is very important, for instance , to improve the design of implants, with the important social and economical impact. one of important challenges in implant design is to model the complex material behavior of the bone. Remodeling of the bone due to the lodaing is one of the essential behaviors of the bone which can cause for the dental implants, marginal bone loss accuring particallary in the first years of function. On the other hand the finite element method(FEM) has become the most extended tool for engineers to analyse the mechanical behavior of the products which usualy have a complex material behavior and complicated geometries. The aim of this study is to model the remodeling behavior of the bone using FEM and to use the new bone material method to evaluate the implant performance for some commercial implants, taking account of the bone adaptation.
9

Structural, Mechanical, And Biocompatibility Investigations Of Yttrium And Fluoride Doped Nano Hydroxyapatite

Basar, Burcin 01 January 2009 (has links) (PDF)
In this study, it was aimed to investigate the structural, mechanical and biological properties of nano hydroxyapatite (HA) doped with yttrium and fluoride with different compositions. HAs were synthesized by precipitation method. After sintering at 900oC, 1100oC or 1300oC for 1 hour, the structural properties of HAs were investigated by XRD, FTIR spectroscopy and SEM. High relative densities (above 88 % of relative density) were achieved after sintering. No second phases were observed in XRD measurements. Hexagonal lattice parameters and unit cell volumes of doped HAs decreased indicating the substitutions of ions. Characteristics absorbtion bands of HA and additional bands due to fluoride substitutions were observed in FTIR patterns. SEM images showed that grain sizes decreased with increasing doping amounts and decreasing sintering temperatures. Discs prepared by cold pressing were sintered at 900oC, 1100oC and 1300oC for 1 hour to determine mechanical properties. Mechanical properties of HAs were found to be directly related to the sintering temperatures and amount of dopings. Biocompatibility of pure and doped HA discs was assessed with in vitro cytotoxicity studies. Cell attachment, proliferation and differentiation state of cells were studied using MTT, ALP and calcium assays and SEM. Cell attachment and proliferation were enhanced with dopings and increasing sintering temperatures. The highest ALP production and calcium deposition were observed on HAs sintered at 1100oC. In vitro studies revealed that 1100oC was the sintering temperature for best cell responses. Specifically, 2.5YFHA seemed to be promising as an alternative for pure HA among all doped HAs.
10

Simulated Fmri Toolbox

Turkay, Kemal Dogus 01 December 2009 (has links) (PDF)
In this thesis a simulated fMRI toolbox is developed in order to generate simulated data to compare and benchmark different functional magnetic resonance image analysis methods. This toolbox is capable of loading a high resolution anatomic brain volume, generating 4D fMRI data in the same data space with the anatomic image, and allowing the user to create block and event-related design paradigms. Common fMRI artifacts such as scanner drift, cardiac pulsation, habituation and task related or spontaneous head movement can be incorporated into the 4D fMRI data. Input to the toolbox is possible through MINC 2.0 file format, and output is provided in ANALYZE format. The major contribution of this toolbox is its facilitation of comparison of fMRI analysis methods by generating several different fMRI data under varying noise and experiment parameters.

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