Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 1Citation - Scopus: 1An Improved Pointing Error Model for Mmwave and Thz Links: Antenna and Array Design Impact(IEEE-Inst Electrical Electronics Engineers inc, 2025) Ahrazoglu, Evla Safahan; Gul, Ahmet Caner; Akinci, Mehmet Nuri; Altunbas, Ibrahim; Erdogan, EylemPointing error has a significant impact on the performance of millimeter wave (mmWave) and terahertz (THz) communications due to directional transmission. Currently existing pointing error models are lacking in capturing the mmWave/THz radiation characteristics and/or the impact of antenna design and array design. Therefore, in this letter, a simple analytical pointing error model for highly directional mmWave/THz transmission is proposed. By utilizing the Gaussian beam approximation for both the array element radiation pattern and the array factor, the presented model incorporates antenna design parameters (maximum gain and 3 dB beamwidth) and array design parameters (number of array elements, element spacing, and 3 dB beamwidth). This approximation is validated via electromagnetic simulations in CST Microwave Studio. Afterwards, the statistics of the pointing error are derived according to the Gaussian beam approximation, and it is demonstrated that the pointing error follows a special case of the negative log-Gamma distribution with the shape parameter of 2 and the scale parameter depending on antenna/array design and jitter variance. It is shown that the proposed model aligns perfectly with the simulation results. Moreover, the outage performance of an aerial communication scenario is analyzed to examine the impact of pointing errors. The results have revealed that the antenna and array design parameters are as influential as the jitter variance, and they cannot be neglected.Conference Object Utilizing Modeling Approach Patterns in the Embedded Software Industry(Institute of Electrical and Electronics Engineers Inc., 2019) Akdur, Deniz; Demirörs, OnurTo cope with the growing complexity of software-intensive embedded system development, modeling is a widely used approach. The modeling approaches in the embedded software industry vary depending on many modeling characteristics (e.g., purpose, modeling rigor, medium type used, modeling stakeholder profile, etc.). In the light of our previous studies, we have identified modeling approach patterns of embedded software development projects and constructed a characterization model. This model not only identifies and defines modeling approach patterns of the stakeholder in embedded software development projects, but also gives recommendations for commonsense modeling practices. In this article, one of the application results of this characterization model, which was performed in Defense & Aerospace sector is presented. The model was successfully applied to the case, in which a series of both structured and semi-structured interviews with 17 embedded software professionals were conducted. The results show that identification of individual patterns provide insight for improvement both for individuals as well as larger units of operations such as projects and organizations.Article Citation - WoS: 23Citation - Scopus: 24Investigation of Kinetics of Supercritical Drying of Alginate Alcogel Particles(Elsevier Ltd., 2019) Şahin, İbrahim; Uzunlar, Erdal; Erkey, CanSpherical calcium alginate gel particles were synthesized by dripping method. The effects of temperature, pressure, particle size and CO2 flow rate on kinetics of supercritical drying of alginate gel particles in a packed bed were investigated. Increase in CO2 flow rate, increase in temperature and decrease in particle size increased the drying rate and decreased the drying time. A mathematical model based on (i) the diffusion of the solvent inside the pores of gel particles, (ii) external mass transfer of the solvent from the surface of the gel particles into the flowing fluid stream, and (iii) convection and axial dispersion of the solvent in the flowing fluid stream was developed. A correlation for predicting external mass transfer coefficients for supercritical drying of alcogel particles was developed by fitting the model to experimental data. A good agreement between the experimental data and model results was achieved using the developed correlation.Book Part Citation - Scopus: 21Short-Wave Ultraviolet Light Inactivation of Pathogens in Fruit Juices(Elsevier, 2018) Baysal, Ayşe HandanFruit juice processing techniques are continuously developing to conform to modern consumer demands for safe, nutritious, tasty, natural, and fresh-like products. Short-wave ultraviolet (UV-C) light has been proven to be a suitable alternative processing method because of its positive consumer image and low processing cost. The use of UV-C light at 253.7. nm for food processing is safe and has been approved as an alternative treatment to reduce pathogens and other microorganisms in the production, processing, and handling of foods. The bactericidal mechanism of UV-C is based on the absorption of UV-C light by microbial DNA or RNA structures and the formation of pyrimidine dimers, preventing replication, making pathogens inactive and unable to cause infection. Fruit juices have a range of optical and physical properties and diverse chemical compositions that influence UV-C efficacy. Thus, this chapter describes the effect of UV-C light applications on the inactivation of pathogens in fruit juice and critical factors to ensure efficient treatment. © 2018 Elsevier Inc. All rights reserved.Article Citation - WoS: 1Citation - Scopus: 1Modeling Pollutant Transport in Overland Flow Over Non-Planar and Non-Homogenous Infiltrating Surfaces(Zhejiang University Press, 2013) He, Zhi-guo; Tayfur, Gökmen; Ran, Qihua; Weng, HaoxuanPollutant transport in overland flow over surfaces with spatially varying microtopography, roughness, and infiltration was investigated using the diffusion wave equation and transport rate-based equation. The finite volume method in space and an implicit backward difference scheme in time were employed in the numerical solution of the 2D governing equations. The developed model was first tested against an analytical solution and an experimental study involving overland flow and the associated pollutant transport, subsequently a series of numerical tests were carried out. Non-point source pollution was investigated under spatially varying microtopography, roughness, and infiltration. The simulation results showed that microtopography and roughness were the dominant factors causing significant spatial variations in solute concentration. When the spatially varying microtopography was replaced by a smooth surface, the result was an overestimation of the solute rate at the outlet of the upland. On the other hand, when the spatially varying roughness was replaced by the average roughness and spatially varying infiltration rate by the average infiltration rate, the pollutant discharge at the outlet of the upland was not significantly affected. The numerical results further showed that one cannot ignore the spatial variations of slope and roughness when investigating the local pollutant concentration distribution.Article Citation - WoS: 70Citation - Scopus: 80Modeling of Coal Bed Methane (cbm) Production and Co2 Sequestration in Coal Seams(Elsevier Ltd., 2009) Özdemir, EkremA mathematical model was developed to predict the coal bed methane (CBM) production and carbon dioxide (CO2) sequestration in a coal seam accounting for the coal seam properties. The model predictions showed that, for a CBM production and dewatering process, the pressure could be reduced from 15.17 MPa to 1.56 MPa and the gas saturation increased up to 50% in 30 years for a 5.4 × 105 m2 of coal formation. For the CO2 sequestration process, the model prediction showed that the CO2 injection rate was first reduced and then slightly recovered over 3 to 13 years of injection, which was also evidenced by the actual in seam data. The model predictions indicated that the sweeping of the water in front of the CO2 flood in the cleat porosity could be important on the loss of injectivity. Further model predictions suggested that the injection rate of CO2 could be about 11 × 103 m3 per day; the injected CO2 would reach the production well, which was separated from the injection well by 826 m, in about 30 years. During this period, about 160 × 106 m3 of CO2 could be stored within a 21.4 × 105 m2 of coal seam with a thickness of 3 m.Article Citation - WoS: 91Citation - Scopus: 122Artificial Neural Networks To Predict Daylight Illuminance in Office Buildings(Elsevier Ltd., 2009) Kazanasmaz, Zehra Tuğçe; Günaydın, Hüsnü Murat; Binol, SelcenA prediction model was developed to determine daylight illuminance for the office buildings by using artificial neural networks (ANNs). Illuminance data were collected for 3 months by applying a field measuring method. Utilizing weather data from the local weather station and building parameters from the architectural drawings, a three-layer ANN model of feed-forward type (with one output node) was constructed. Two variables for time (date, hour), 5 weather determinants (outdoor temperature, solar radiation, humidity, UV index and UV dose) and 6 building parameters (distance to windows, number of windows, orientation of rooms, floor identification, room dimensions and point identification) were considered as input variables. Illuminance was used as the output variable. In ANN modeling, the data were divided into two groups; the first 80 of these data sets were used for training and the remaining 20 for testing. Microsoft Excel Solver used simplex optimization method for the optimal weights. The model's performance was then measured by using the illuminance percentage error. As the prediction power of the model was almost 98%, predicted data had close matches with the measured data. The prediction results were successful within the sample measurements. The model was then subjected to sensitivity analysis to determine the relationship between the input and output variables. NeuroSolutions Software by NeuroDimensions Inc., was adopted for this application. Researchers and designers will benefit from this model in daylighting performance assessment of buildings by making predictions and comparisons and in the daylighting design process by determining illuminance.Article Citation - WoS: 1Citation - Scopus: 2Kinetic Estimation of the Adsorbate Distribution on the Surface From Adsorbed Amounts(Elsevier Ltd., 2006) Polat, MehmetA phenomenological multilayer adsorption model for a well-dispersed, homogeneous, nonporous adsorbent and a molecular adsorbate is presented. The model provides explicit kinetic expressions associating the adsorbed amounts to the fraction of the surface occupied and reduces to the first- and second-order adsorption models for special cases. Parameters of the model are a pair of true rate constants related to the adsorbate-adsorbent and adsorbate-surface adsorbate affinities. A general graphical procedure and analytical equations for special cases are provided to estimate the rate constants from kinetic adsorption data. Data from the adsorption of sodium stearate onto α-alumina from water were used to test the model. The predicted values of the rate constants suggested that the stearate was distributed homogeneously on the alumina surface and essentially adsorbed as a monolayer before starting to form the second layer.Article Citation - WoS: 10Citation - Scopus: 10Multi-Zone Drying Schemes for Lowering the Residual Solvent Content During Multi-Component Drying of Semicrystalline Polymers(Taylor and Francis Ltd., 2007) Wong, Sim-Siong; Alsoy Altınkaya, Sacide; Mallapragada, Surya K.The development of a glassy skin in multicomponent semicrystalline polymer systems limits the diffusion of solvents out of the system and increases residual solvent levels. Based on the results of a mathematical model that we had previously developed, we have proposed a multi-zone drying scheme aimed at lowering the residual solvent levels by taking into account the effect of interactions between the various solvents as predicted by the model. This article focuses on the application of this model to develop optimal drying schemes and to verify the effectiveness of these predictions using experimental techniques. The mathematical model developed previously to study the diffusion of multiple solvents and changes in the crystallinity of semicrystalline polymer systems during drying incorporates many features including Vrentas-Duda diffusion theory, solvent-induced crystallization kinetics, as well as glass transition effects and skinning of the film. The multi-zone drying system was developed by varying the drying temperature in each zone as well as changing the partial pressure of individual solvents during the drying process. The effectiveness of the multi-zone drying schemes predicted by the model was validated experimentally using thermogravimetric methods. The polymer-solvent system chosen was a poly(vinyl alcohol)-water-methanol system. Our experimental data suggested that the multi-zone drying schemes were superior to a single-zone drying system through direct comparison. Further examination of the mathematical model yielded individual solvent profiles and these data reaffirmed our conclusions that a multi-zone drying scheme has the ability to reduce the effect of solvent trapping and thus lower the overall residual solvent content.