Çil, Celal Zaim
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Elektronik ve Haberleşme Mühendisliği
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Scholarly Output
14
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20
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110
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0
14 results
Scholarly Output Search Results
Now showing 1 - 10 of 14
Article Beam wander of J (0)- and I (0)-Bessel Gaussian beams propagating in turbulent atmosphere(Springer, 2010) Çil, Celal Zaim; Eyyuboğlu, Halil T.; Baykal, Yahya; Korotkova, Olga; Cai, Yangjian; 7688; 7812; Elektronik ve Haberleşme MühendisliğiRoot mean square (rms) beam wander of J (0)-Bessel Gaussian and I (0)-Bessel Gaussian beams, normalized by the rms beam wander of the fundamental Gaussian beam, is evaluated in atmospheric turbulence. Our formulation is based on the first and the second statistical moments obtained from the Rytov series. It is found that after propagating in atmospheric turbulence, the collimated J (0)-Bessel Gaussian and the I (0)-Bessel Gaussian beams have smaller rms beam wander than that of the Gaussian beam, regardless of the choice of Bessel width parameter. However, the extent of such an advantage depends on the chosen width parameter, Gaussian source size, propagation distance and the wavelength. Focusing at finite distances of the considered beams causes the rms beam wander to decrease sharply at the propagation distances equal to the focusing parameterArticle Citation - WoS: 8Citation - Scopus: 8Intensity fluctuations of partially coherent cos Gaussian and cosh Gaussian beams in atmospheric turbulence(Iop Publishing Ltd, 2011) Baykal, Yahya; Çil, Celal Zaim; Eyyuboglu, Halil T.; Cil, Celal Z.; Cai, Yangjian; Korotkova, Olga; 7812; 7688; Elektronik ve Haberleşme MühendisliğiOn-axis and off-axis scintillation indices of partially coherent collimated cos Gaussian and cosh Gaussian beams are evaluated on their propagation in a weakly turbulent atmosphere. In the coherent limits, our results are in quite good agreement with those for the existing Rytov scintillation index of coherent cos Gaussian and cosh Gaussian beams, especially for very small and very large sized beams and at weaker turbulence levels. The on-axis scintillation index becomes lower as the degree of source coherence decreases for both cos Gaussian and cosh Gaussian beams. Comparing to the partially coherent Gaussian beam on-axis scintillations, partially coherent cos Gaussian beam scintillations are generally lower and partially coherent cosh Gaussian beam scintillations are higher. Scintillations of Gaussian beams are very close to the scintillations of equal-power cos Gaussian and are quite similar to the scintillations of equal-power cosh Gaussian beams. Off-axis evaluations yield that the scintillations of both cos Gaussian and cosh Gaussian beams increase as the diagonal distance from the origin increases, being valid for all degrees of partial coherence.Conference Object LED’lerin Spektrofotometride Kullanımı(2011) Çil, Celal Zaim; Özdumanlar, Sercan; Cambaz Büke, Göknur; Çil, Celal Zaim; Kamışlı, Özcan; Ertuğ, A. Mithat; Elektronik ve Haberleşme MühendisliğiIşık yayan diyotların (Light Emitting Diode-LED) ışık yayma modunda verici olduğu, fotodiyot veya güneş pili modunda alıcı olduğu bir düzenek oluşturularak LED’lerin çeşitli ışık şiddetleri altında ürettikleri fotoakım değerleri ölçülmüştür. Bu fotoakım değerleri verici ve alıcı LED’lerin yaydıkları ve hassas oldukları dalgaboylarına ve ışık şiddetlerine göre karşılaştırılmıştır. Bu çalışmada yapılan ölçümler değerlendirildiğinde, LED’lerin düşük maliyetli spektrometrelerde ve spektrofotometri uygulamalarında kullanılabileceği gösterilmiştir.Article Citation - WoS: 26Citation - Scopus: 26Beam wander characteristics of cos and cosh-Gaussian beams(Springer, 2009) Cil, C. Z.; Çil, Celal Zaim; Eyyuboglu, H. T.; Baykal, Y.; Cai, Y.; 7688; 7812; Elektronik ve Haberleşme MühendisliğiWithin the context of a general beam formulation, beam wander characteristics of cos and cosh-Gaussian beams are derived and numerically evaluated. In our graphs, the fundamental Gaussian beam is used as a benchmark for comparisons. The associated plots reveal that at small source sizes, a cos-Gaussian beam has the lowest beam wander, while this property is enhanced with increasing values of the displacement parameter. At large source sizes however, this advantage is taken over by cosh-Gaussian beam. Joint examination against the changing source sizes and propagation lengths shows that the range of source sizes, where the beam wander of cos-Gaussian beam remains lower, is enlarged as we go toward higher propagation lengths. Asymmetric beams tend to exhibit higher beam wanders both at small and large source sizes, but for the intermediate source size ranges, the beam wanders of asymmetric beams will fall below those of the symmetric beams. Explanations concerning these behaviors are offered. A historical account of beam wander formulation is also included.Article Citation - WoS: 1Literature Review on Cyber Security Investment Decisions(Gazi Univ, 2016) Senturk, Hakan; Çil, Celal Zaim; Cil, Celal Zaim; Sagiroglu, Seref; Elektronik ve Haberleşme MühendisliğiSevere financial losses incurred by cyber security attacks with increasing complexity and frequency, as well as booming cyber security sector offering variety of products as investment options have led the focus of the research in the field to the economic dimension of cyber security. The need for determination of methods to be used when making cyber security investment decisions under budget constraints have become prominent. In five sections as the cyber security investment strategies, risk identification and measurement, attack costs and impacts calculation, measurement of technology effectiveness and determination of optimum level of cyber security investments, this study reviews and evaluates the academic literature on economic aspects of cyber security for the last fifteen years and aims to provide research directions by pinpointing literature gaps.Article Beam wander of J (0)- and I (0)-Bessel Gaussian beams propagating in turbulent atmosphere(2010) Çil, Celal Zaim; Baykal, Yahya Kemal; Baykal, Yahya Kemal; Korotkova, O.; Cai, Y.; 7812; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik MühendisliğiRoot mean square (rms) beam wander of J (0)-Bessel Gaussian and I (0)-Bessel Gaussian beams, normalized by the rms beam wander of the fundamental Gaussian beam, is evaluated in atmospheric turbulence. Our formulation is based on the first and the second statistical moments obtained from the Rytov series. It is found that after propagating in atmospheric turbulence, the collimated J (0)-Bessel Gaussian and the I (0)-Bessel Gaussian beams have smaller rms beam wander than that of the Gaussian beam, regardless of the choice of Bessel width parameter. However, the extent of such an advantage depends on the chosen width parameter, Gaussian source size, propagation distance and the wavelength. Focusing at finite distances of the considered beams causes the rms beam wander to decrease sharply at the propagation distances equal to the focusing parameter.Article Siber Güvenlik Yatırım Kararları Üzerine Literatür İncelemesi(2016) Çil, Celal Zaim; Şentürk, Hakan; Çil, Celal Zaim; Sagıroglu, Seref; Elektronik ve Haberleşme MühendisliğiKarmaşıklığı ve sıklığı her geçen gün artan siber saldırıların yol açtığı yüksek ekonomik zararlar ile bu saldırılara karşı korumasağlayan çok sayıda siber güvenlik teknolojisi ürünlerinin yatırım alternatifi olarak sunulduğu güvenlik sektörü, alanda yapılançalışmaların odak noktasını siber güvenliğin ekonomik boyutuna yöneltmiştir. Kısıtlı kaynak şartları altında siber güvenlikyatırım kararlarının verilebilmesine yönelik kullanılabilecek yöntemlerin belirlenmesi ihtiyacı öne çıkmıştır.Bu çalışmada siber güvenlik yatırım kararlarının verilmesi sürecinde uygulanabilecek yatırım stratejileri, siber güvenlikrisklerinin belirlenmesi ve ölçülmesi, güvenlik saldırılarının maliyet ve etkisinin ölçülmesi, güvenlik teknolojilerinin etkinliğininölçülmesi ve güvenlik yatırımlarının en uygun seviyesinin belirlenmesi olmak üzere beş kategoride alanda son onbeş yıldayapılan akademik çalışmalar incelenmiş, literatürdeki boşluklar ortaya konularak sonraki araştırmalara yön verilmesiamaçlanmıştır.Article Citation - WoS: 26Citation - Scopus: 27Beam Wander of J (0)- and I (0)-Bessel Gaussian Beams Propagating In Turbulent Atmosphere(Springer, 2010) Cil, C. Z.; Çil, Celal Zaim; Eyyuboglu, H. T.; Baykal, Y.; Korotkova, O.; Cai, Y.; 7812; 7688; Elektronik ve Haberleşme MühendisliğiRoot mean square (rms) beam wander of J (0)-Bessel Gaussian and I (0)-Bessel Gaussian beams, normalized by the rms beam wander of the fundamental Gaussian beam, is evaluated in atmospheric turbulence. Our formulation is based on the first and the second statistical moments obtained from the Rytov series. It is found that after propagating in atmospheric turbulence, the collimated J (0)-Bessel Gaussian and the I (0)-Bessel Gaussian beams have smaller rms beam wander than that of the Gaussian beam, regardless of the choice of Bessel width parameter. However, the extent of such an advantage depends on the chosen width parameter, Gaussian source size, propagation distance and the wavelength. Focusing at finite distances of the considered beams causes the rms beam wander to decrease sharply at the propagation distances equal to the focusing parameter.Article Citation - WoS: 12Citation - Scopus: 14Partially coherent elegant Hermite-Gaussian beams(Springer Heidelberg, 2010) Wang, F.; Çil, Celal Zaim; Cai, Y.; Eyyuboglu, H. T.; Baykal, Y.; Cil, C. Z.; 7688; 7812; Elektronik ve Haberleşme MühendisliğiElegant Hermite-Gaussian beams (EHGBs) are extended to the partially coherent case. An explicit and analytical formula is derived for the cross-spectral density of a partially coherent EHGB propagating through an aligned or misaligned paraxial ABCD optical system. The propagation properties of a partially coherent EHGB in free space and its focusing properties through a thin lens are studied numerically, and are compared to those of a partially coherent standard Hermite-Gaussian beam (SHGB). It is found that the propagation and focusing properties of a partially coherent EHGB are closely related to its initial coherence. A partially coherent EHGB spreads slower than a partially coherent SHGB in free-space propagation. A partially coherent EHGB can be focused more tightly than a partially coherent SHGB.Article Desıgnıng an off-road workıng lamp wıth leds(2011) Çil, Celal Zaim; Yakışır, Burcu; Elektronik ve Haberleşme MühendisliğiIn this study a working lamp used on the offroad working machines and vehicles is designed by using the LED diodes instead of a halogen bulb. In the design, firs tly a LED array is determined and a proper driver circuit that can provid e the required optical power is designed, and the working lamp developed is tested under various conditions. The luminous output values of the designed LED working lamp are compared with those of a commercial working lamp, which uses a halogen bulb. It is evaluated that in automotive applications lamps using LEDs could be successfully utilized depending on the optical efficacy of the LED used, the designs of the LED driver and the reflecto
