Design and implementation of end-pumped Neodymium: YAG lasers

Ankara : Department of Electrical and Electronics Engineering and Institute of Engineering and Sciences, Bilkent Univ., 1996.Thesis (Master's) -- Bilkent University, 1996.Includes bibliographical references leaves 63-66.In this stud}·, we implemented end-pumped Fabry-Perot and ring NeodymiumiYAC lasers operating at 1064 nm. Intracavity frequency doubling of these lasers to 532nm was also achieved. A 4W diode laser was used as a pump source. Diode light was transferred to the Nd:YAG crystal via various optics. 2.5 W pump power was incident on the NdiYAG crystal. Various FabryPerot resonator configurations were implemented and evaluated. A maximum output power of 780 m\\ was obtained. This corresponds to 31% optical conversion efficiency. A strong relationship between the laser performance and the radius of the laser mode was observed. It is also noted that the wavelength of the diode light is a very important parameter for laser performance. In addition to Fabry-Perot lasers, a ring laser was implemented, yielding a maximum output power of 230 mW. With these two types of lasers, intracavity frequency doubling experiments were carried out using a KTP crystal. 165 mW and 85rnW maximum output powers at 532 nm were obtained from intracavity frequency doubled Fabry-Perot and ring lasers, respectivelyUğur, SalihM.S

Novel methods for SAR imaging problems

Ankara : The Department of Electrical and Electronics Engineering and the Graduate School of Engineering and Science of Bilkent University, 2013.Thesis (Ph. D.) -- Bilkent University, 2013.Includes bibliographical references leaves 62-70.Synthetic Aperture Radar (SAR) provides high resolution images of terrain reflectivity. SAR systems are indispensable in many remote sensing applications. High resolution imaging of terrain requires precise position information of the radar platform on its flight path. In target detection and identification applications, imaging of sparse reflectivity scenes is a requirement. In this thesis, novel SAR image reconstruction techniques for sparse target scenes are developed. These techniques differ from earlier approaches in their ability of simultaneous image reconstruction and motion compensation. It is shown that if the residual phase error after INS/GPS corrected platform motion is captured in the signal model, then the optimal autofocused image formation can be formulated as a sparse reconstruction problem. In the first proposed technique, Non-Linear Conjugate Gradient Descent algorithm is used to obtain the optimum reconstruction. To increase robustness in the reconstruction, Total Variation penalty is introduced into the cost function of the optimization. To reduce the rate of A/D conversion and memory requirements, a specific under sampling pattern is introduced. In the second proposed technique, Expectation Maximization Based Matching Pursuit (EMMP) algorithm is utilized to obtain the optimum sparse SAR reconstruction. EMMP algorithm is greedy and computationally less complex resulting in fast SAR image reconstructions. Based on a variety of metrics, performances of the proposed techniques are compared. It is observed that the EMMP algorithm has an additional advantage of reconstructing off-grid targets by perturbing on-grid basis vectors on a finer grid.Uğur, SalihPh.D

Effects of Extremely Low Frequency Magnetic Field on the Lens of the Rats

The present aim of the study is to evaluate the effects of extremely low frequency magnetic field (ELF MF) on lens epithelial cells. Twenty adult female Spraque Dawley rats were divided into two groups, each containing 10 rats. The experimental group received magnetic field 2 hours/day for 7 days. The second group receiving standard laboratory care, was used as a control. The specimens were evaluated for cataractogenesis alteretion of lens and histological changes in lens epithelial cells.On biomicroscopic examination, no pathological damage to the lens was detected. In addition, on microscopic examination of materials in the controls, there were also no changes in lens fibrils and lens epithelial cells. In experimental group, however, only a slight pleomorphism was determined at the surface of epithelial cells.In the study, it is cocluded that ELF MF exposure do might not lead to histopathological alterations of the lens fibrils and lens epithelial cells

Inflammatory pseudotumor of the lung

Pulmoner inflamatuar psödotümör nadir görülen, etiyolojisi bilinmeyen proliferatif bir lezyondur ve tüm pulmoner tümörlerin % 0.7-1'ini olusturmaktadır. Öksürük, dispne ve hemoptizi yakınmalarıyla basvuran 65 erkek hastanın PA ve sag yan akciger grafilerinde sag hemitoraks üst zonda düzensiz sınırlı konsolidasyon saptanmıstır. Kontrastlı toraks BT'de sag akciger üst lob posterior segmentinde, periferik yerlesim gösteren, 9x8x4 cm boyutlarında, düzensiz kenar yapısı gösteren, kavitasyon içeren, periferik tarzda kontrast tutulumu gösteren heterojen dansitede kitle ve minimal plevral efüzyon saptanmıstır. Tanımlanan lezyonun radyografik olarak düzensiz kenar yapısı gösteren konsolidasyon alanı seklinde olması ve BT incelemesinde kavitasyon ve minimal düzeyde plevral efüzyon saptanması pulmoner inflamatuar psödotümör için sık olmayan bulgulardır.Pulmonary inflammatory pseutumor is a rare proliferative lesion with unknown etiology and constitutes 0.7-1% of all pulmonary tumors. Posteroanterior and right lateral chest radiographies of a 65 year old male patient presenting with complaints of cough, dyspnea and hemoptysis revealed an ill-defined consoldation in the superior zone of the right hemithorax. On contrast-enhanced thorax CT, an ill-defined, heterogenous lesion located peripherally at the posterior segment of the right upper lobe with dimensions of 9x8x4 cm, having cavitation and peripheral contrast enhancement and minimal pleural effusion were detected. The finding of a consolidation area with irregular margins at radiography and the detection of cavitation as well as minimal pleural effusion are infrequent for pulmonary inflammatory pseudotumor

A rare tumor of the thorax: synovial sarcoma case report and review of the literature

Toraksın primer sinovyal sarkomu oldukça nadirdir. Akciger, plevra veya gögüs duvarı tutulumu görülebildigi gibi bu bölgelerin birden fazlası da tutulabilir. Gögüs duvarında kitle saptanması nedeniyle opere edilen ve operasyon materyaline ait doku tanısı monofazik sinovyal sarkom olarak raporlanan, 55 yasındaki erkek hastanın operasyon öncesindeki PA akciger grafisinde sag hemitoraks alt zonda, diyafragmadan net olarak sınırlandırılamayan kitle görünümü izlendi. Toraks BT incelemesinde sag akciger orta lob komsulugunda, plevraya genis tabanla oturan, interkostal alanlardan gögüs duvarına uzanan, 97x72 mm boyutlarında düzgün sınırlı kitle saptandı. Tanımlanan görüntüleme bulguları özgül olmamakla birlikte, ayırıcı tanıda toraksın primer malign neoplazmları içerisinde nadir görülen sinovyal sarkom da göz önünde bulundurulmalıdır.Primary synovial sarcoma of the thorax is extremely rare. The involvement of lung, pleura or chest wall may be seen and sometimes more than one of these structures may be effected. The preoperative chest radiography of a 55-year-old male patient operated for a mass lesion detected on chest wall revealed a mass lesion at the inferior zone of the right hemithorax which was not discernible from the diaphragma. Thorax CT examination revealed a sharply marginated mass lesion with dimensions of 97x72 mm, located adjacent to the right middle lobe, having a wide pleural base and extending through the intercostal space to the chest wall. Rare synovial sarcoma of the thorax should be considered in the diferential diagnosis of the primary malignant neoplasms of the thorax, though the imaging findings are non-specific

Length-weight relationships of 28 fish species caught from demersal trawl survey in the Middle Black Sea, Turkey

This study provides updated the length-weight relationships and Fulton's condition factor of 28 fish species belonging to 23 families from the Black Sea. Samples were collected along the depths between 0-100 meters by demersal trawl surveys conducted seasonally from May 2017 to September 2019. A total of 83,885 specimens were collected. The length-weight relationships and Fulton's condition factor, minimum, maximum and mean lengths, total weights, descriptive statistics, and growth type were provided for all the species. The results indicate that LWR parameters of b varied from 2.2039 to 3.737 and Fulton's condition factor varied between 0.004 and 1.18. These findings could be useful for monitoring and management of sustainable fisheries and habitat health

The Relationship Between Public External Debt And Economic Growth: An Empirical Application On Turkey (1975-2016)

Bu çalışmanın temel amacı, kamu dış borçlanması ve ekonomik büyüme arasındaki ilişkiyi Türkiye ekonomisinde 1975-2016 döneminde incelemektir. Değişkenlerin birim kök özelliklerin belirlenmesinde ADF, PP ve Ng-Perron testi kullanılmıştır. Daha sonra değişkenler arasındaki eşbütünleşmenin varlığı Engle-Granger eşbütünleşme testi ile araştırılmıştır. Son olarak uzun dönem katsayılarının analiz edilmesinde DOLS tahmin tekniği uygulanmıştır. Ampirik bulgular i) değişkenlerin birinci farkında durağan olduğu, ii) değişkenlerin eşbütünleşik olduğu, iii) uzun dönemde kamu dış borçlanmasının ekonomik büyümeyi arttırdığı, iv) bazı politika eğilimleri sunabileceği ortaya koymaktadır.The main purpose of this study is to the relationship between external debt and economic growth in Turkey over the period 1975-2016. ADF, PP and Ng-Perron tests were used in determining the unit root properties of the variables. The existence of cointegration between the variables was then investigated by the Engle-Granger cointegration test. Finally, DOLS estimation technique was applied in analyzing long term coefficients. Empirical findings i) the variables are firts difference stationary, ii) the variables are cointegrated, iii) long-term public debt increases economic growth, iv) some policy implications can be preseted

The Addition of Graphite in Battery Waste to a Ceramic Soft Plastic Body

Bu çalışmada piyasadan toplanan atık kuru pillerdeki grafitin, seramik plastik çamurunda kullanılabilirliği araştırılmıştır. Bu amaçla kuru pilin içindeki grafit çıkarılmıştır. Elde edilen grafit az miktarda su ile karıştırılmış ve plastik çamura katılarak homojen bir şekilde yoğrulmuştur. Hazırlanan plastik çamurdan şekillendirilen parçalar, oda sıcaklığında kurutulmuş ve 900 oC'de pişirilmiştir. Elde edilen bisküvilerin kuru ve pişme küçülmesi, mukavemet ve su emme testleri yapılmıştır.In this study, graphite which was found in the battery waste was investigated as an addition of ceramic soft plastic body. In this purpose, graphite was taken out from battery waste. This graphite was added to ceramic raw materials and kneaded with some water. Plastic prepared parts were shaped by hand and shaped parts were dried in the ambient temperature. Dried bodies were fired at 900 oC temperature. Drying and fired shrinkage, water absorption and fired strength of these bodies were studied

Low-frequency Breakdown of the Potential Integral Equations and Its Remedy

Potential integral equations (PIEs) introduced recently also have a low-frequency breakdown that becomes visible when considering the electric charge density and near-zone electric field intensity values. As opposed to the well-known low-frequency breakdown of the electric-field integral equation (EFIE), which shows itself as both inaccuracy and ill-conditioning, the low-frequency breakdown of PIEs is not related to the conditioning properties of the related matrix equations. Therefore, we clearly distinguish the low-frequency breakdowns of EFIE and PIEs by categorizing the underlying mechanisms as field imbalance and source imbalance. Numerical examples are presented to provide a complete picture of these integral equations at low-frequencies, besides an effective post-processing method to mitigate the inaccuracies in PIEs