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Taha Toros Arşivi, Dosya No: 142-Zekeriya-Yıldız-Sabiha Sertel. Not: Gazetenin "Arada Bir" köşesinde yayımlanmıştır

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Taha Toros Arşivi, Dosya No: 142-Zekeriya-Yıldız-Sabiha Serte

The use and characterization of composite alumina-titania-zirconia-silica-ceramic membranes for gas separation

Thesis (Master)--Izmir Institute of Technology, Materials Science and Engineering, Izmir, 2002Includes bibliographical references (leaves: 120-124)Text in English; Abstract: Turkish and Englishx, 124 leavesThe preparation, characterization and pure gas permeation of sol-gel derived alumina and silica membranes were investigated in this work. The effects of various parameters on sol particle size and unsupported membranes pore structure were investigated by laser light scattering particle size and N2 adsorption-desorption analysis .-alumina membranes were prepared on ZrO2 supports by successive dipping into boehmite sols. Almost proportional decreases in sol particle size and membrane pore diameter were determined with increasing acid content during the boehmite sol preparation. Increasing the H+/Al3+ mole ratio from 0.1 to 0.25 caused the hydrodynamic particle size and BJH pore size to decrease from 65 to 30 nm and 3.6 to 2.9 nm, respectively. The pore size increased from 2.8 nm to 3 nm upon increasing the calcination temperature from 500 to 600oC. Unsupported membranes were heat treated in the 200 to 1200 oC range for the characterization of the phase structure. Boehmite was the dominant phase below 500 oC, gamma being the dominant phase up to 900 oC and pure .-Al2O3 phase was obtained upon heat treatment at 1200oC. Pinhole and crack free alumina membranes about 3 .m (double layer) in thickness were observed from SEM pictures with insignificant infiltration. The CO2 permeability through the double layer .-Al2O3 membrane calcined at 600 oC was about 2.25*10-7 mol/m2.s.Pa, and had a slight pressure dependence which may indicate Knudsen Diffusion and Laminar Flow as the effective transport mechanisms. Upon the calcination of a similar double layer alumina membrane at 500oC, the CO2 permeability decreased to 1.51*10-8 mol/m2.s.Pa and was independent of pressure. Silica membranes were prepared by a sol-gel technique. These sols were prepared by acid catalysed hydrolysis and condensation of tetraethylorthosilicate in the presence of a solvent. The effects of processing parameters like the acid type and amount utilized during sol preparation, sol aging, heat treatment conditions, dipping time on the membrane pore structure and the permeation of pure gases were investigated. The supported membranes were heat treated in the 50-400 oC range. The N2 and CO2 permeabilities of silica membranes varied in the 2.2 * 10-10 . 2.7 * 10-8 mol / m2.s.Pa and 1.2*10-9 . 6.95*10-8 mol / m2.s.Pa range for single layer membranes dipped for 10 seconds into the sol. The sols became viscous and gelled in 16 hours at 50 oC. The O2 permeability increased with aging time. The optimum dipping time during processing was determined to be 10 seconds. The permeabilities of these membranes increased significantly with the sol acid content. The thickness of the silica membranes were determined to be about 2.m and significant infiltration into the support was observed from the SEM pictures

Gas permeation through sol-gel derived alumina and silica based membranes

Thesis (Doctoral)--Izmir Institute of Technology, Chemical Engineering, Izmir, 2009Includes bibliographical references (leaves: 201-214)Text in English; Abstract: Turkish and Englishxix, 214 leavesThe scope of this thesis is to design defect-free microporous and mesoporous ceramic membranes having micro-engineered pore network that would contribute to the enhancement of pore control abilities as well as the thermal stability.In this study, mono-dispersed silica sols having well-defined silica spheres ranging in size from 5 to 700 nm were prepared through sol-gel methods and thin membrane layers were consolidated on either y-alumina support or unsupported form.The packing of 5 nm silica spheres resulted in micropores of 0.87 nm in 400 oC treatedmembranes with the porosity of 0.32 which are in well aggrement with the porosity level of random loose packing. Silica spheres with varying concentration and size were incorporated into polymeric network to complement the percolative structure of sphere packing with interpenetrated polymeric silica network in order to design well-defined thermally stable transport pathway. Low shrinkage value was obtained for sphere incorporated system providing the high thermal stability by affecting the thermally induced microcrack formation as well as the structural relaxation during consolidation.The resulting hybrid structure enabled the detailed transport properties that support to be able to control the pore structure but N2/CO2 separation properties are needed to be improved.Stable polymeric alumina sols having particle sizes smaller than 2 nm could be obtained when the hydrolysis conditions were accurately controlled. The mixture of prepared polymeric silica and alumina sols in mullite compositions (3:2) provided to the crystallization of mullite with homogeneously mixed stable oxide network upon heat treatment at 775 oC

Birbiriyle Karıştırılan Üç Kavram: Alevilik, Bektaşilik, Şiilik

Untersucht man die islamische Geschichte, sticht die „Schia“ als ein zentraler Begriff hervor. Dieser wird von vielen Personen und sogar von vielen Forschern fälschlicherweise mit dem Alevitentum und dem Bektaschitentum gleichgesetzt. In dieser Studie werden diese drei Konzepte in allen Aspekten analysiert, und es wird der Versuch unternommen, die Ähnlichkeiten und Unterschiede zwischen ihnen verständlicher zu darzustellen. Was sind die Gemeinsamkeiten und Unterschiede zwischen Alevitentum, Bektaschitentum und Schiitentum in Bezug auf Glauben, Praxis, Quellen und Kultur? Sind diese drei Gruppen miteinander identisch oder nicht? Worin unterscheiden sie sich? Die Antworten auf all diese Fragen, denen diese Arbeit hauptsächlich nachgeht, werden am Ende des Artikels in einer einfachen Grafik dargestellt. In methodologischer Hinsicht wurden die wichtigsten Quellen und Forschungsarbeiten in dem Gebiet auf Grundlage eines vergleichenden, thematischen und ganzheitlichen Ansatzes untersucht.When Islamic history is analyzed, it is seen that the concept of “Shia” is one of the most striking concepts. However, it is also known that this concept is wrongly used in the same way as Alevism and Bektashism by many people and even many researchers. In this study, all these three concepts will be analyzed in all aspects. And the similarities and differences between them will be tried to be explained in a more understandable way. What are the similarities and differences between Alevism, Bektashism and Shiism in terms of belief, practice, sources and culture? Are these three groups the same with each other or not? If they have differences, what are these differences? The answers to all these questions, which exist the main questions of the study, will be given in a simple graphic at the end of the study. The methodology of this study will be a comparative, thematic and holistic approach to the main sources and studies.İslam tarihi araştırmalarında, “Şii” kavramı en dikkat çekici kavramlardan biridir. Ancak bu kavram, Alevilik ve Bektaşilik kavramları gibi birçok kişi ve hatta birçok araştırmacı tarafından yanlış bir şekilde kullanılmaktadır. Bu çalışmada söz konusu üç kavram tüm yönleriyle incelenecek ve aralarındaki benzerlikler/farklılıklar daha anlaşılır bir şekilde açıklanmaya çalışılacaktır. İnanç, uygulama, kaynak ve kültür bakımından Alevilik, Bektaşilik ve Şiilik arasındaki benzerlikler ve farklılıklar nelerdir? Bu üç topluluk birbiriyle aynı mıdır, değil midir? Farklılıkları varsa, bu farklılıklar nelerdir? Çalışmanın ana meselesini oluşturan tüm bu soruların cevapları, çalışmanın sonunda bir grafik halinde verilecektir. Bu çalışmada ana kaynakların ve araştırmaların karşılaştırmalı, tematik ve bütüncül bir yaklaşımla incelendiği bir metodooji kullanılacaktır

Development of a static analysis tool to find securty vulnerabilities in java applications

Thesis (Master)--Izmir Institute of Technology, Computer Engineering, Izmir, 2010Includes bibliographical references (leaves: 57-60)Text in English Abstract: Turkish and Englishix, 77 leavesThe scope of this thesis is to enhance a static analysis tool in order to find security limitations in java applications. This will contribute to the removal of some of the existing limitations related with the lack of java source codes. The generally used tools for a static analysis are FindBugs, Jlint, PMD, ESC/Java2, Checkstyle. In this study, it is aimed to utilize PMD static analysis tool which already has been developed to find defects Possible bugs (empty try/catch/finally/switch statements), Dead code (unused local variables, parameters and private methods), Suboptimal code (wasteful String/StringBuffer usage), Overcomplicated expressions (unnecessary if statements for loops that could be while loops), Duplicate code (copied/pasted code means copied/pasted bugs). On the other hand, faults possible unexpected exception, length may be less than zero, division by zero, stream not closed on all paths and should be a static inner class cases were not implemented by PMD static analysis tool. PMD performs syntactic checks and dataflow analysis on program source code.In addition to some detection of clearly erroneous code, many of the .bugs. PMD looks for are stylistic conventions whose violation might be suspicious under some circumstances. For example, having a try statement with an empty catch block might indicate that the caught error is incorrectly discarded. Because PMD includes many detectors for bugs that depend on programming style, PMD includes support for selecting which detectors or groups of detectors should be run. While PMD.s main structure was conserved, boundary overflow vulnerability rules have been implemented to PMD

Efficiency and performance of real estate investment trusts (REITs): An empirical examination

This study has a threefold purpose. Its first objective is to investigate input and output efficiencies in the Real Estate Investment Trust (REIT) industry. Its second objective is to understand the impact of size, property share, loan production, debt ratio, property and geographic diversification, control and governance variables, overall risk, capital risk, growth rate, and management type on a number of efficiency measures, including profit, cost, allocative, technical, pure technical and scale efficiency. The third objective is to assess the impact of structural and regulatory changes in the industry on REITs\u27 productivity, technology, and efficiency changes. I have estimated the REITs\u27 efficiency in the period 1989–1999 by employing a nonparametric approach, namely Data Envelopment Analysis (DEA), along with a parametric approach, the Stochastic Frontier Approach (SFA). Results suggest that the average efficiency for all indexes is very low, implying waste of REIT resources and potential profits. Results also indicate that the dominant source of inefficiency in REIT industry is due to technical inefficiency rather than allocative inefficiency. Pure technical inefficiency is generally larger than the scale inefficiency, suggesting that the dominant source of overall technical inefficiency is mainly due to pure technical inefficiency. Several conclusions emerge from second stage regression analysis, which examines the efficiency variations. First, robust capitalization and higher loan production bear a positive relation to REITs\u27 efficiency. Second, the growth rate in their assets impacts positively on cost, technical, pure technical, and scale efficiencies, but negatively on profit efficiency. Third, REITs with more market power (higher property share) experience lower cost, technical, scale, and profit efficiencies. In addition, REIT efficiency decreases with higher debt. Finally, those REITs having separate management (decision) and board (control) structures are more efficient than those REITs with the same management and board. I also examined the REITs\u27 productivity change relative to both fixed reference technology and successive reference technology. The results suggest that REIT efficiency increases due to both scale efficiencies and better management practices; whereas their productivity generally decreases because of experiencing technical regress. I conclude that greater efficiency and technical improvement could both be achieved by the adoption of appropriate regulations