Time-of-flight imaging of invisibility cloaks

As invisibility cloaking has recently become experimental reality, it is interesting to explore ways to reveal remaining imperfections. In essence, the idea of most invisibility cloaks is to recover the optical path lengths without an object (to be made invisible) by a suitable arrangement around that object. Optical path length is proportional to the time of flight of a light ray or to the optical phase accumulated by a light wave. Thus, time-of-flight images provide a direct and intuitive tool for probing imperfections. Indeed, recent phase-sensitive experiments on the carpet cloak have already made early steps in this direction. In the macroscopic world, time-of-flight images could be measured directly by light detection and ranging (LIDAR). Here, we show calculated time-of-flight images of the conformal Gaussian carpet cloak, the conformal grating cloak, the cylindrical free-space cloak, and of the invisible sphere. All results are obtained by using a ray-velocity equation of motion derived from Fermat's principle.Comment: 11 pages, 6 figures, journal pape

Bazı Sosyoekonomik Etmenlerin Türkiye’de Yükseköğretime Katılım Üzerindeki Etkileri

The purpose of this study is to determine the impact of some socio-economic factors (household income, parents’ education, and parents’ residential status such that of urban or rural) on higher education participation through the comparison of the socio-economic status of the students with the same status of the related population in Turkey. The data of the study were obtained through the administration of a questionnaire to 4910 first year university-level students at Cumhuriyet, Erciyes and Hacettepe universities and a thorough literature review. General results of the study are as follows: (1) Distribution of household income of Turkey and students’ annual disposable income by quintiles are similar and household income is not a direct factor on higher education participation. (2) Educational status of parents is a determining factor in higher education participation. (3) Students whose parents are graduates of higher levels of education and income are over-represented in the programs that are assumed to be prestigious and high income generating. (4) Higher education institutions serve to students coming from urban areas to a great extent (92%).Bu çalışmanın amacı, yükseköğretimden yararlanan öğrencilerin bazı sosyoekonomik özelliklerinin (hanehalkı geliri, anne-babanın eğitim durumu, yerleşim yeri) dağılımı ile Türkiye’deki nüfusun aynı özelliklerinin dağılımının karşılaştırılması yoluyla bu etmenlerin yükseköğretimden yararlanma üzerindeki etkilerini belirlemektir. Araştırmanın verileri Cumhuriyet, Erciyes ve Hacettepe üniversitelerinde öğrenim gören 4910 öğrenciye uygulanan anket ve alanyazın taramasına dayalı olarak elde edilmiştir.Araştırma betimsel bir çalışmadır. Bu çalışmada şu sonuçlara ulaşılmıştır: (1) Gelire göre sıralı %20’lik Türkiye ve üniversite öğrencileri hanehalkı gruplarının yıllık kullanılabilir gelirlerinin yüzdelik dağılımları birbirine benzerdir ve yükseköğretime girişte gelir doğrudan belirleyici etkiye sahip değildir. (2) Yükseköğretimden yararlanmada anne-babanın eğitim düzeyi belirleyici bir etkendir. (3) Daha yüksek gelirli ve eğitimli ailelerin çocukları daha prestijli ve daha yüksek getirisi olduğu varsayılan alanlarda daha yüksek oranda temsil edilmektedirler. (4) Yükseköğretim sistemi çok büyük ölçüde kentsel yerleşim birimlerinden gelen öğrencilere (%92) hizmet etmektedir

Optical Microscopy of 3D Carpet Cloaks : Ray-Tracing Calculations

In a recent publication (T. Ergin et al., Science 328, 337 (2010)), three-dimensional broadband dielectric carpet cloaks have been fabricated and experimentally characterized by optical bright-field and dark-field microscopy using unpolarized light from an incandescent lamp. A direct comparison with theory has not been provided so far. In the present work, we treat the carpet cloak as well as the entire optical microscope within the ray-optics approximation and the cloak within the effective-medium approximation. We find good qualitative agreement between experimental results and our calculations

Photorespiration in Eelgrass (\u3ci\u3eZostera marina\u3c/i\u3e L.): A Photoprotection Mechanism for Survival in a CO₂-Limited World

Photorespiration, commonly viewed as a loss in photosynthetic productivity of C3 plants, is expected to decline with increasing atmospheric CO2, even though photorespiration plays an important role in the oxidative stress responses. This study aimed to quantify the role of photorespiration and alternative photoprotection mechanisms in Zostera marina L. (eelgrass), a carbon-limited marine C3 plant, in response to ocean acidification. Plants were grown in controlled outdoor aquaria at different [CO2]aq ranging from ~55 (ambient) to ~2121 μM for 13 months and compared for differences in leaf photochemistry by simultaneous measurements of O2 flux and variable fluorescence. At ambient [CO2], photosynthesis was carbon limited and the excess photon absorption was diverted both to photorespiration and non-photochemical quenching (NPQ). The dynamic range of NPQ regulation in ambient grown plants, in response to instantaneous changes in [CO2]aq, suggested considerable tolerance for fluctuating environmental conditions. However, 60 to 80% of maximum photosynthetic capacity of ambient plants was diverted to photorespiration resulting in limited carbon fixation. The photosynthesis to respiration ratio (PE : RD) of ambient grown plants increased 6-fold when measured under high CO2 because photorespiration was virtually suppressed. Plants acclimated to high CO2 maintained 4-fold higher PE : RD than ambient grown plants as a result of a 60% reduction in photorespiration. The O2 production efficiency per unit chlorophyll was not affected by the CO2 environment in which the plants were grown. Yet, CO2 enrichment decreased the light level to initiate NPQ activity and downregulated the biomass specific pigment content by 50% and area specific pigment content by 30%. Thus, phenotypic acclimation to ocean carbonation in eelgrass, indicating the coupling between the regulation of photosynthetic structure and metabolic carbon demands, involved the downregulation of light harvesting by the photosynthetic apparatus, a reduction in the role of photorespiration and an increase in the role of NPQ in photoprotection. The quasi-mechanistic model developed in this study permits integration of photosynthetic and morphological acclimation to ocean carbonation into seagrass productivity models, by adjusting the limits of the photosynthetic parameters based on substrate availability and physiological capacity

Türkiye’de Yükseköğretimde Öğrenci Harcama ve Maliyetleri

The purpose of this study is to determine individual (private), public and total unit costs of higher education and their components within three universities in Turkey. The sample of the study has consisted of 3330 first grade undergraduate students of Hacettepe, Cumhuriyet and Erciyes universities in 2007-2008 academic year. The data related to individual expenditures of the students were obtained through the administration of the questionnaire to the students in the sample. The data related to public expenditures and foregone earnings and taxes were obtained from official records. The study revealed that almost all students within the scope of the study have spent a significant amount of money (4.475 TL) for the purpose of university entrance preparations compared to the incomes of the households, and in general, the share of the private cost (8.692 TL) is greater than the share of the public cost (6.647 TL) in annual unit cost (15.339 TL).Bu çalışmanın amacı, Türkiye’deki üç üniversitede bireysel, kamusal ve toplam birim öğrenci maliyetlerini belirlemek ve bu maliyetleri oluşturan bileşenleri ortaya koymaktır. Araştırmanın örneklemini 2007-2008 öğretim yılında Hacettepe, Cumhuriyet ve Erciyes üniversitelerinde öğrenim gören 3330 birinci sınıf öğrencisi oluşturmaktadır. Araştırmanın bireysel harcamalara ilişkin verileri, araştırmacı tarafından geliştirilen anketin örnekleme uygulanması ile elde edilmiştir. Kamusal harcamalara ve vazgeçilen maliyetlere ilişkin veriler yasal ve yönetsel kayıtlardan elde edilmiştir. Araştırma ile (1) araştırma kapsamındaki öğrencilerin neredeyse tamamının üniversiteye hazırlık harcaması yaptığı ve bu harcamaların hanehalkı gelirleriyle karşılaştırıldığında önemli miktarlara (4.475 TL) ulaştığı ve (2) toplam birim öğrenci maliyeti (15.339 TL) içinde, genel olarak bireysel öğrenci maliyetinin (8.692 TL) payının kamusal öğrenci maliyetinden (6.647 TL) daha yüksek olduğu belirlenmiştir

Luneburg lens in silicon photonics

The Luneburg lens is an aberration-free lens that focuses light from all directions equally well. We fabricated and tested a Luneburg lens in silicon photonics. Such fully-integrated lenses may become the building blocks of compact Fourier optics on chips. Furthermore, our fabrication technique is sufficiently versatile for making perfect imaging devices on silicon platforms. (C) 2011 Optical Society of AmericaPublisher PDFPeer reviewe

Blood transfusion improves renal oxygenation and renal function in sepsis-induced acute kidney injury in rats

Background: The effects of blood transfusion on renal microcirculation during sepsis are unknown. This study aimed to investigate the effect of blood transfusion on renal microvascular oxygenation and renal function during sepsis-induced acute kidney injury. Methods: Twenty-seven Wistar albino rats were randomized into four groups: a sham group (n = 6), a lipopolysaccharide (LPS) group (n = 7), a LPS group that received fluid resuscitation (n = 7), and a LPS group that received blood transfusion (n = 7). The mean arterial blood pressure, renal blood flow, and renal microvascular oxygenation within the kidney cortex were recorded. Acute kidney injury was assessed using the serum creatinine levels, metabolic cost, and histopathological lesions. Nitrosative stress (expression of endothelial (eNOS) and inducible nitric oxide synthase (iNOS)) within the kidney was assessed by immunohistochemistry. Hemoglobin levels, pH, serum lactate levels, and liver enzymes were measured. Results: Fluid resuscitation and blood transfusion both significantly improved the mean arterial pressure and renal blood flow after LPS infusion. Renal microvascular oxygenation, serum creatinine levels, and tubular damage significantly improved in the LPS group that received blood transfusion compared to the group that received fluids. Moreover, the renal expression of eNOS was markedly suppressed under endotoxin challenge. Blood transfusion, but not fluid resuscitation, was able to restore the renal expression of eNOS. However, there were no significant differences in lactic acidosis or liver function between the two groups. Conclusions: Blood transfusion significantly improved renal function in endotoxemic rats. The specific beneficial effect of blood transfusion on the kidney could have been mediated in part by the improvements in r

Organizational silence behaviors of faculty members, their causes and consequencesÖğretim elemanlarında örgütsel sessizlik davranışı, nedenleri ve sonuçları

Purpose: The purpose of this study is to investigate faculty members’ organizational silence behaviors, the effects of reasons leading to silence, the consequences of silence behaviors and their relationships with some variables of gender and academic titles. Method: The study was conducted as a quantitative descriptive research. The sample of the study is comprised of 554 faculty members. The data of the study were collected through the administration of three questionnaires developed by the researchers to the sample group. In data analysis, descriptive statistics, t-test for independent groups, one-way variance analysis (ANOVA) were employed. Results: The major results of the study are: (1) The faculty members exhibit the silence behavior in three problem areas to a great extent (non-ethical behaviors and practices, administrative functioning and practices and academic structure and functioning) (2) Both the individual factors and factors related to administrative practices are effective over a moderate level in the faculty members’ exhibiting the silence behavior. (3) The faculty members are of the opinions that their organizational silence behaviors result in problems that can considerably affect individual and organizational efficiency. (4) Among all staff, the research assistants show the most silence behavior and observe the consequences of the silence behavior the most. In short, organizational silence is an important managerial proble.Extended English summary is in the end of Full Text PDF (TURKISH) file. ÖzetAmaç: Bu çalışmanın amacı öğretim elemanlarının örgütsel sessizlik davranışına yol açan sorunları, nedenlerini ve sonuçlarını belirlemek ve cinsiyet ve akademik unvan değişkenleri ile ilişkisini incelemektir. Yöntem: Tarama modelinde betimsel bir çalışma olan araştırmanın örneklemini 554 öğretim elemanı oluşturmaktadır. Araştırmanın verileri araştırmacılar tarafından geliştirilen üç ölçeğin örnekleme uygulanmasıyla elde edilmiştir. Araştırma verilerinin çözümlenmesinde betimsel istatistikler, karşılaştırmalarda t-testi ve varyans analizi (ANOVA) kullanılmıştır. Sonuçlar: Araştırmada şu temel sonuçlara ulaşılmıştır: (1) Öğretim elemanları üç sorun alanında (etik olamayan davranış ve uygulamalar, yönetsel işleyiş ve uygulamalar, akademik yapı ve işleyiş) önemli ölçüde sessizlik davranışı göstermektedirler. (2) Öğretim elemanlarının sessizlik davranışı göstermelerinde hem bireysel etmenler hem de yönetsel uygulamalarla ilgili etmenler orta düzeyin üstünde etkili olmaktadır. (3) Öğretim elemanları örgütsel sessizlik davranışlarının bireysel ve kurumsal etkililiği etkileyebilecek sorunlara yol açtığı düşüncesine oldukça yüksek düzeyde sahiptirler. (3) Araştırma görevlileri en fazla sessizlik gösteren ve sonuçlarından en fazla etkilenen akademik unvan grubu olarak görünmektedir. Kısaca örgütsel sessizlik üniversiteler için üstesinden gelmek için çaba gösterilmesi gereken önemli bir yönetsel sorun alandır

Öğretmenlerin Yapısal ve Psikolojik Güçlendirilmeleri ile Örgütsel Vatandaşlık Davranışları Arasındaki İlişki

The purpose of this study is to determine the relationships between structural and psychological empowerment of teachers and their organizational citizenship behaviors. The sample of this descriptive study consists of 384 teachers employed in the province of Muğla. The data of the study were collected through the administration of the questionnaires (namely Conditions of Work Effectiveness Questionnaire, Psychological Empowerment Scale and Organizational Citizenship Behavior Scale) to the teachers in the sample. In the analysis of the data, descriptive statistics, t test, ANOVA and hierarchical multiple regression analysis were conducted. The study revealed that that the level of teachers’ organizational citizenship behaviors (OCB) is higher than the medium level. Besides, teachers’ organizational citizenship behaviors differed significantly in terms of the variables of gender, school type and school location (urban or rural) whereas there was no significant difference in terms of the variable of seniority. The level of teachers’ structural empowerment (SE) was determined to be medium. Moreover, in terms of school type and school location variables, some dimensions of teachers’ SE differed significantly, however no significant difference was found in terms of gender and seniority variables. On the other hand, the level of teachers’ psychological empowerment (PE) was high. In terms of gender and school type variables, some dimensions of teachers’ (PE) differed significantly, yet it did not differ significantly according to the variables of seniority and school location. In addition, teachers’ psychological and SE explained one third of the OCB. According to the results of regression analysis, both the dimensions of knowledge and opportunity and the dimension of individual oriented empowerment were identified to be significant predictors of OCB. In addition, some recommendations were developed in the study in order to increase teachers’ structural and psychological empowerment.Bu çalışmanın amacı, öğretmenlerin yapısal ve psikolojik güçlendirilmeleri ile örgütsel vatandaşlık davranışları arasındaki ilişkinin belirlenmesidir. Tarama modelindeki araştırmanın örneklemini, Muğla il merkezinde görev yapan 384 öğretmen oluşturmaktadır. Araştırmanın verileri, “Çalışma Etkililiği Koşulları Ölçeği, Psikolojik Güçlendirme Ölçeği ve Örgütsel Vatandaşlık Davranışı Ölçeği” ile toplanmıştır. Verilerin analizinde betimsel istatistikler, t testi, ANOVA ve hiyerarşik çoklu regresyon analizi kullanılmıştır. Araştırma sonuçlarına göre, öğretmenlerin örgütsel vatandaşlık davranışları orta düzeyin üzerindedir. Öğretmenlerin örgütsel vatandaşlık davranışları, cinsiyet, okul türü ve okulun bulunduğu yer değişkenlerine göre anlamlı düzeyde farklılaşmakta; hizmet süresi değişkenine göre farklılaşmamaktadır. Öğretmenlerin yapısal güçlendirilmeleri orta düzeydedir. Öğretmenlerin yapısal güçlendirilmeleri, okul türü ve okul bulunduğu yer değişkenine göre bazı boyutlarda anlamlı düzeyde farklılaşmakta; cinsiyet ve hizmet süresi değişkenlerine göre farklılaşmamaktadır. Öğretmenlerin psikolojik güçlendirilmeleri yüksek düzeydedir. Öğretmenlerin psikolojik güçlendirilmeleri cinsiyet ve okul türü değişkenlerine göre bazı boyutlarda anlamlı düzeyde farklılaşmakta; hizmet süresi ve okulun bulunduğu yer değişkenlerine göre farklılaşmamaktadır. Öğretmenlerin psikolojik ve yapısal güçlendirilmeleri, örgütsel vatandaşlık davranışlarının yaklaşık üçte birini açıklamaktadır. Regresyon analizi sonuçlarına göre, yapısal güçlendirmenin bilgi ve fırsat boyutu ile psikolojik güçlendirmenin birey merkezli güçlendirme boyutu öğretmenlerin örgütsel vatandaşlık davranışlarının önemli yordayıcılarıdır. Araştırmada, öğretmenlerin yapısal ve psikolojik güçlendirmelerini artırmaya yönelik çeşitli öneriler geliştirilmiştir

One Loop Beta Functions in Topologically Massive Gravity

We calculate the running of the three coupling constants in cosmological, topologically massive 3d gravity. We find that \nu, the dimensionless coefficient of the Chern-Simons term, has vanishing beta function. The flow of the cosmological constant and Newton's constant depends on \nu, and for any positive \nu there exist both a trivial and a nontrivial fixed point.Comment: 44 pages, 16 figure