Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8651
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Article Citation - WoS: 5Citation - Scopus: 3Intensity Fluctuations of Higher-Order Laser Modes in Jet Engine Exhaust Turbulence(Optica Publishing Group, 2025) Baykal, Yahya KemalIntensity fluctuations quantified by the scintillation index are evaluated in jet engine exhaust turbulence when higher-order laser modes are used in optical wireless communication links. The jet engine exhaust turbulence power spectrum, modified by low-pass and high-pass filters, is employed. Intensity fluctuations are evaluated against the link length, structure constant, wave number (inverse of wavelength) (i.e., against turbulence strength), source size, and jet engine exhaust turbulence parameters. It is found that higher-order laser modes are better at mitigating the scintillations. Jet engine exhaust turbulence parameters are found to affect scintillations substantially. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.Article Citation - WoS: 2Citation - Scopus: 1Propagation of Higher-Order Annular Gaussian Beams in Biological Tissues(Optica Publishing Group, 2025) Arpali, Serap Altay; Baykal, Yahya KemalThe propagation characteristics of a higher-order annular Gaussian (HOAG) beam in biological tissue turbulence are investigated. Average intensity at the receiver plane is found when the HOAG source field is used as excitation. The effects of the HOAG beam on different tissue types of the upper dermis (human), liver parenchyma (mouse), intestinal epithelium (mouse), and deep dermis (mouse) are studied. Variations of the average intensity versus the source and medium parameters such as the strength coefficient of the refractive-index fluctuations, propagation distance, wavelength, and beam size are presented. The results show that all modes of the HOAG beam can successively transmit beam energy at different levels of turbulence for all tissue types. At the same turbulence strength, HOAG beams having larger mode numbers transmit higher intensity to receivers than the modes with smaller mode orders, which is valid for all the examined tissue types. As the strength of tissue turbulence increases, the HOAG beam slowly turns into a pure Gaussian beam. For the different tissue types, the highest beam intensity at the receiver was observed for the deep dermis (mouse) tissue type. Despite the change in wavelength, refractive-index fluctuations, and source beam size, the highest beam transmission through the tissue in a turbulent environment was also observed for this same tissue type. This research may be useful in understanding the fundamentals of lighttissue interaction of HOAG laser beams, which may improve noninvasive disease detection and therapy methods through tissue in biophotonic technologies. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.Article Citation - WoS: 5Citation - Scopus: 6Bit Error Rate of M-Pulse Position Modulated Laser Beams for Vertical Links Operating in Weak Oceanic Turbulence(Iop Publishing Ltd, 2024) Gercekcioglu, Hamza; Baykal, YahyaThe on-axis scintillation index of laser beams is investigated by employing the Rytov method in a weakly turbulent oceanic medium for up/downlink coupling of laser communication between any underwater vehicles or divers. For vertical links, the formulation of the on-axis scintillation index of laser beams is derived analytically and evaluated for plane, collimated Gaussian and spherical beams in specific mediums, including the Atlantic Ocean at mid and low latitudes associating temperature and salinity changes at low latitudes, at mid latitude-summer and at mid latitude-winter. Using the scintillation index, bit error rate (BER) performance of M-pulse position modulation is investigated for these types of laser beams. The variations of the scintillation index against the uplink/downlink propagation distances, source size and zenith angle are examined, and BER variations versus the Kolmogorov microscale and the symbol orders, and results are compared. It is noted that the behavior of the scintillation index that depends on the relative strength of temperature and salinity fluctuations which changes in depth, is different for uplink/downlink and for each latitude due to its distinct characteristics. The source size that minimizes the scintillation index values is in the range of about 0.1 cm-0.2 cm for all latitudes.Article Citation - WoS: 4Citation - Scopus: 6Scintillation of Laser Beams in Weak Atmospheric Turbulence for Aerial Vehicle in the Use of Lidar(Ieee-inst Electrical Electronics Engineers inc, 2022) Baykal, Yahya; Gercekcioglu, HamzaFormulation of on-axis scintillation of laser beams is found in weak atmospheric turbulence for aerial vehicle in the use of light detection and ranging (LIDAR) systems by employing the Rytov method. The formulation derived for collimated Gaussian, plane and spherical beams is evaluated in vertical link involving up/down link. In this medium, the behavior of these beams in terms of deterioration is examined. In this context, the on-axis scintillation index values are plotted versus normalized target size parameter, target size, source size, propagation distance and zenith angle, and the results are obtained for LIDAR systems operating for aerial vehicle in vertical atmospheric link by using ground/space transceiver. The degradation is greater in operating with ground transceiver than in operating with space transceiver. Additionally, while the on-axis scintillation index is minimized in the smaller target size in use of ground transceiver than in use of space transceiver, that is, it can also be minimized in the larger target size in use of space transceiver. The values of source size and the normalized target size parameter minimizing the obtained scintillation index, are 1.2 cm, 10, and 6 cm and 5 for ground transceiver and space transceiver, respectively.Article Citation - WoS: 16Citation - Scopus: 17Flow Structure and Fish Passage Performance of a Brush-Type Fish Way: a Field Study in the Yidere River, Turkey(Csiro Publishing, 2019) Kucukali, Serhat; Verep, Bulent; Alp, Ahmet; Turan, Davut; Mutlu, Tanju; Kaya, Cuneyt; Ozelci, DursunThe fish passage performance and flow structure of a brush fish pass were investigated at the ncirli Small Hydropower Plant on the yidere River, located in the East Black Sea region of Turkey. The spatial distributions of velocity vectors, power velocity, Froude number and turbulent kinetic energy are presented. The flow is quasi-uniform and subcritical, which provides different migration corridors with favourable hydraulic conditions; importantly for the fish, these corridors continue through the complete fish pass. The flow-bristle interaction creates a reduced velocity and low-turbulence resting zones. In addition, the passage efficiency of the brush fish pass was assessed using passive integrated transponder telemetry. The results clearly showed that upstream passage efficiency differs between fish species: Salmo coruhensis performed better than Alburnoides fasciatus on the same fish passage. The passage efficiency for the target fish species S. coruhensis was calculated to be 82.4%. The data revealed that the brush fish passage provides passage for small-bodied fish (total body length <15 cm) in a high-gradient channel with a slope of 10%. The monitoring data revealed that bristles as flexible hydraulic elements are beneficial for migrating fish.Article Citation - WoS: 7Citation - Scopus: 5Tissue Turbulence and Its Effects on Optical Waves: a Review(Elsevier, 2023) Ata, Yalcin; Baykal, Yahya; Gokce, Muhsin CanerTissue turbulence and the effects of tissue turbulence on the propagation of optical waves are reviewed. After the introduction of a survey on the reported research in this area, various topics are elaborated. These topics include the spectrum of tissue turbulence, propagation of light in the tissue, average intensity, beam spread that occur at the receiver plane in the tissue. Other entities examined are the signal to noise ratio (SNR), intensity correlation, beam wander, mutual coherence function and the spectral degree of coherence. Furthermore, spectral change, cross spectral density, spectral correlation function, scintillation, bit error rate (BER), coupling efficiency in tissue turbulence are investigated. The refractive index structure of tissues, imaging in the presence of turbulence in the tissue, scattering, absorption and polarization aspects in tissues are reported. Finally, optical coherence tomography applications in turbulent tissues are reviewed.Article Citation - WoS: 8Citation - Scopus: 8M-Ary Pulse Position Modulation Performance With Adaptive Optics Corrections in Atmospheric Turbulence(Taylor & Francis Ltd, 2020) Gokce, Muhsin C.; Baykal, Yahya; Ata, YalcinThe performance of M-ary pulse position modulated (PPM) optical wireless communication (OWC) systems in atmospheric weak turbulence medium is evaluated by using adaptive optics corrections. Piston, tilt, defocus and coma components of adaptive optics corrections are applied to the avalanche photodetector (APD) type of receiver and the results are obtained depending on various turbulence and receiver parameters. The lognormal channel distribution is used to model the weak atmospheric turbulence conditions. Adaptive optics correction increases the bit-error-rate (BER) performance of an OWC system operating in atmospheric turbulence conditions. Piston component yields the highest BER performance, followed by the tilt, defocus and coma adaptive optics correction components respectively.Article Citation - WoS: 32Citation - Scopus: 31Wind Energy Resource Assessment of Izmit in the West Black Sea Coastal Region of Turkey(Pergamon-elsevier Science Ltd, 2014) Kucukali, Serhat; Dinckal, CigdemThe wind energy potential of Izmit (41.19 N, 30.30 E), which is located in the West Black Sea Coastal Region of Turkey, is assessed with the statistical analysis of the gathered wind data at the 50-m height measurement mast covering the period of 06/2008-06/2009. The annual average wind speed is calculated as 6 m/s and the prevailing wind direction is ENE (60 degrees). The Weibull distribution parameters of shape and scale factor are found as 2.03 and 6.73 m/s, respectively. The measured wind speed data are compared with the data of nearby meteorological stations and the results show that there is a considerable difference between the onsite measurements and the measurements of the meteorological stations. Moreover, a turbulence analysis is carried out and the turbulence intensity is negatively correlated with the normalized height from ground level with canopy height. The energy generation performances of three different wind turbines are evaluated by using the onsite wind speed measurements and the assessment shows that the capacity factor increase by a factor of two from 17% to 34% depending on the type of the turbine. Furthermore, an economic analysis is carried out for a 50 MW wind energy project for the potential site and the proposed project benefit/cost ratio is calculated as 8. (C) 2013 Elsevier Ltd. All rights reserved.Conference Object Citation - WoS: 3Citation - Scopus: 3About Metafluid Dynamics(inst Physics Acad Sci Czech Republic, 2004) Baleanu, DThe analog of Maxwell electromagnetism for hydrodynamic turbulence, the metafluid dynamics, is investigated as a constrained system within fractional Riemann-Liouville derivatives.Article Citation - WoS: 81Citation - Scopus: 86Propagation of Hermite-Cosh Laser Beams in Turbulent Atmosphere(Elsevier, 2005) Eyyuboglu, HTThe propagation characteristics of Hermite-cosh-Gaussian (HCG) beams in turbulence are studied. To this end, from a HCG source plane excitation, the average intensity of the receiver plane is developed analytically. This formulation is verified against the existing solution of HCG beams in free space. The results indicate that upon traveling in turbulent atmosphere, the HCG beam will undergo three stages of evolution. Initially, it will preserve the original profile. Then, with source parameters of right choice, this beam will turn into a sine shape if the sum of mode indices is odd, and into a cos shape if the sum of mode indices is even. Eventually however, HCG originated beam will become a pure Gassian beam. The dependence of these stages on source and propagation conditions is investigated. (C) 2004 Elsevier B.V. All rights reserved.