Temperature dependence of tunneling in intrinsic Josephson junctions of high temperature superconductors

Thesis (Master)--Izmir Institute of Technology, Physics, Izmir, 2008Includes bibliographical references (leaves: 73-79)Text in English; Abstract: Turkish and Englishxi, 79 leavesThe lack of coherent, continuous and tunable compact solid-state sources of electromagnetic radiations at terahertz (THz) frequency range (0.3-30 THz) can be solved by high temperature superconductors (HTS) which are better candidates for generation of THz radiation. THz sources have potential application areas in materials characterization, biology, communication, medicine and security. The HTSs have large energy gap intervals which are available for radiations at THz frequency range, so recently, they were used as better converters from DC-voltage to high frequency radiation in junction technologies. Bi2Sr2CaCu2O8+8 (Bi2212) HTS single crystals include natural superconductor-insulator-superconductor multi-junctions called intrinsic Josephson junctions. For generation of coherent continuous and powerful THz radiations, we have fabricated large and tall mesas on Ca rich Bi2212, although mesas with small planar and lateral dimensions were preferred in recent studies because of the heating effect. We have used under-doped Bi2212 to control the heating problem. The mesas with size of 100x300 .m2 have been fabricated by vacuum evaporation, photolithography analyzed by Atomic Force Microscopy. We have investigated temperature dependence of c-axis resistivity and current-voltage (I-V) tunneling characteristics of under-doped Bi2212 which exhibit exponentially increases in resistivity from 300 K to Tc. The influences of heating effect were analyzed at temperature evolution of I-V measurements. Finally, bolometric detections of emission from long edges of mesas were done

Caries Risk Assessment in Children with Different Rates of Vitamin D Deficiency, Using Cariogram Model

Objective: Vitamin D plays a very important role in improving oral and dental health as well as general health. The present study aims to evaluate the risk of caries development risk of children with and without vitamin D deficiency using the Cariogram model. Methods: This study included a total of 75 healthy children aged 6-12 years, of which 50 (35 girls and 15 boys) had different levels of vitamin D deficiency, and 25 (12 girls and 13 boys) had none. Their risk of developing new dental caries was assessed with Cariogram. SPSS v21.0 (IBM, USA) was used for analyzing the study data. In the statistical tests, a p-value less than 0.05 was considered statistically significant. Results: Mean chronological and dental ages of the participants were obtained as 9±2.32 and 8±2.36, respectively. The distribution of salivary flow rate, buffering capacities, and distributions of Lactobacilli and S. mutans counts between the groups were found to be similar. There was a significant difference between Group I and Group II and between Group I and Group III in regard to the Cariogram green percentage (percentage of chances to avoid caries), p=0.002 and p<0.001, respectively. Conclusion: In the present study, we observed a decrease in the Cariogram green sector percentage with low levels of vitamin D and an increase with normal vitamin D levels. Therefore, chances to avoid new dental caries were increased in sufficient levels of vitamin D

Van’da Konut Üretim Faaliyetlerinin Kentsel Gelişmeye Etkileri (1927-2020)

Bu çalışmanın amacı, Van’da kentsel gelişim sürecinde yaşanan kritik eşiklerin kentte ortaya çıkardığı konut sorununa yönelik yapılan gecekondu, kooperatif, özel ve kamu konut üretimlerinin kentin mekânsal gelişim sürecine etkilerini ortaya koymaktır. 1990’lı yıllarda artan zorunlu göçlerin sebep olduğu konut ihtiyacına yönelik yapılan gecekonduların ortaya çıkardığı yeni mahalleler, 2011 depremleri sonrası yapılan TOKİ konutlarının yapıldığı mahalleler ve yeni açılan mahalleler kentin gelişim istikametine yön vermiş, yeni aksların ortaya çıkmasını sağlamıştır. Ayrıca 2012 yılında Van’ın Büyükşehir Belediyesi statüsüne getirilmesi ile birlikte il merkezine bağlı bütün köylerin ilin merkez mahallesi olması kentsel alan sınırını değiştirmiş ve genişletmiştir. Sadece demografik anlamda gerçekleşen bu değişim hareketi ile kentin kırsal karakteri daha da güçlendirilmiş ancak kentsel anlamda bir gelişme söz konusu olamamıştır. Çalışma nitel araştırma yöntemi kullanılarak yapılmış ve varılan sonuçlara göre: Van kentinin mekânsal gelişim sürecine etki eden göçler, depremler ve büyükşehir olma gibi faktörlerle beraber gelişen konut üretim faaliyetleri neticesinde kentsel alan sınırı değişime uğramıştır. Bu bağlamında çalışmada kentin değişen sosyal, ekonomik ve fiziki özellikleri ele alınarak değerlendirilmiştir

The fabrication of THz emitting mesas by reactive ion-beam etching of superconducting Bi2212 with multilayer masks

Generation of powerful THz radiation from intrinsic Josephson Junctions (IJJs) of Bi2Sr2CaCu2O8+δ (Bi2212) may require mesas with large lateral dimensions. However, there are difficulties in fabrication of perfect rectangular mesas. The lateral angles of mesas should be close to 90 degrees to obtain IJJs with same planar dimensions for synchronization of IJJs. We patterned Ta/photoresist and photoresist/Ta/photoresist masks on Bi2212 and used selectiveionetchingtoovercomethethickphotoresistlayershading on the lateral dimension of mesa during the ion-beam etching. The reactive ion-beam etchings have been done with ion beams of Ar, N2 and O2, and we have obtained mesas about 1 µm with lateral angle of approximately 50 to 75°, which is better than the mesas fabricated with photoresist mask.TUBITAK (Scientific and Technical Council of Turkey) project No. 108T238

Towards prioritizing vulnerability testing

Vulnerability assessment is the process of identifying and prioritizing the vulnerabilities in a system. Vulnerability scanners can, for example, scan a website for known vulnerabilities by running a repository of security tests, each of which is designed to reveal a known vulnerability. As the security tests need to be executed on each and every web page encountered, it may take quite a while for these scanners to report vulnerabilities. In this work, we present an approach for revealing the vulnerabilities faster by prioritizing the executions of the security tests on a per web page basis. The approach is based on a simple conjecture that 'similar' web pages may possess 'similar' vulnerabilities and that identifying these similarities can help prioritize the security tests. The results of the experiments we carried out by using 2927 distinct web pages (collected from 80 web sites), support our basic hypothesis; the percentages of the times the actual vulnerabilities appear in the top 8 and 15 predicted vulnerabilities were 86.9% and 98.4%, respectively

Performance of Some Forages Species (\u3cem\u3eFestuca arundinacea\u3c/em\u3e L., \u3cem\u3eChloris gayana\u3c/em\u3e var. Katambora, \u3cem\u3eLotus corniculatus\u3c/em\u3e L. and \u3cem\u3eMedicago sativa\u3c/em\u3e L.) in Saline Soil

Salinity is a soil degradation process which reduces plant diversity and agricultural productivity, decreases fertility and devalues the land in regions with arid and semi-arid climate. This process inhibits water and nutrient intake of plants from soil due to changeable nitrogen percentage and/or the intensity of soluble salt concentration. When the fact that agricultural lands are limited around the world and that the need for nutrition increases incrementally is taken into consideration, it is obvious that available lands should be used more effectively. Hence, it is quite crucial to reclaim saline soil and utilize it more economically (Woods 1996)

Analysis approach to finite monoids

In a previous paper by the authors, a new approach between algebra and analysis has been recently developed. In detail, it has been generally described how one can express some algebraic properties in terms of special generating functions. To continue the study of this approach, in here, we state and prove that the presentation which has the minimal number of generators of the split extension of two finite monogenic monoids has different sets of generating functions (such that the number of these functions is equal to the number of generators) that represent the exponent sums of the generating pictures of this presentation. This study can be thought of as a mixture of pure analysis, topology and geometry within the purposes of this journal.Selçuk ÜniversitesiAkdeniz Üniversites

New families of special numbers and polynomials arising from applications of p-adic q-integrals

In this manuscript, generating functions are constructed for the new special families of polynomials and numbers using the p-adic q-integral technique. Partial derivative equations, functional equations and other properties of these generating functions are given. With the help of these equations, many interesting and useful identities, relations, and formulas are derived. We also give p-adic q-integral representations of these numbers and polynomials. The results we have obtained for these special numbers and polynomials are closely related to well-known families of polynomials and numbers including the Bernoulli numbers, the Apostol-type Bernoulli numbers and polynomials and the Frobenius-Euler numbers, the Stirling numbers, and the Daehee numbers. We give some remarks and observations on the results of this paper.Akdeniz Üniversites