1,721,666 research outputs found
A New Model for Indoor Propagation Prediction Using Genetic Algorithm
No full textIn this study, a new, simple and accurate computation of the received signal strength (RSS) level for indoor environment is performed. The genetic algorithm (GA) approach is used for prediction of the RSS. The proposed model is formed on the knowledge of measurements without requiring any detail of the environment. The model provides a time efficient method to estimate RSS dynamically at any location in the test environment. The accuracy of the measurement results and the genetic algorithm approach are presented for three distinct transmitters located at different positions.Scientific and Technological Research Council of Turkey (TUBITAK) [ID 105E130]This work is partially supported in the scope of project ID 105E130 by the Scientific and Technological Research Council of Turkey (TUBITAK). The author also would like to thank all colleagues for measurements and for fruitful discussions
Performance of the Yb/<i>n< Tunneling Barriers
No full textQasrawi, Atef Fayez/0000-0001-8193-6975In this article, the design and performance of the CdSe which are deposited onto thin films of Yb metal is reported and discussed. The thin films of CdSe which are deposited by the physical vapor deposition technique are observed to exhibit slightly deformed hexagonal polycrystalline nature with excess amount of Cd as confirmed by the X-ray, energy dispersive X-ray spectroscopy and scanning electron microscopy techniques. The n-type CdSe is also found to form a Schottky barrier of tunneling type when sandwiched between Yb and carbon. The quantum mechanical tunneling mechanism in this device which was tested and modeled in the frequency domain of 10-150 MHz is found to exhibit average intersite separations of similar to 5 nm. The tunneling device exhibited a widening in the depletion region associated with significantly large capacitance tunability in the studied frequency domain. On the other hand, as an optoelectronic device, the Yb/n-CdSe/C Schottky diode exhibited a responsivity of similar to 0.10 NW, photosensitivity of 6.5 x 10(4) and external quantum efficiency of 54% when biased with 1.0 V and exposed to laser light of wavelength of 406 nm.Arab American University, Jenin, Palestine; DSRThis project was funded by the Deanship of Scientific Research at Arab American University, Jenin, Palestine. The author, therefore, acknowledge with thanks the DSR for technical and financial support
Three Phase Grid-Connected Photovoltaic System using Three Level H-bridge Inverter under Partial Shading
Get PDFThis paper deals with three-phase three level H bridge inverter for a photovoltaic power plant interconnected to grid under variable irradiation conditions, that features a maximum power point tracking scheme based on the Perturb and Observe (P&O) method. With the aid of the sinusoidal pulse-width modulation control technique, proportional-integral controllers, and Park transformation, the inverter control system managed to convert photovoltaic power to ac power, stabilize the output voltage and current of a grid connected photovoltaic system. The photovoltaic module has been modelled, the maximum power point tracking algorithm and a three level inverter has been validated by simulation analysis. The simulation results show the detailed model of this grid-connected multi-level inverter and the control strategy used in the photovoltaic generation system
Gd and Tb Doping Effects on the Physical Properties of Nd<sub>2</Sub>sn<sub>2<
No full textKhanfar, Hazem k./0000-0002-3015-4049; Qasrawi, Atef Fayez/0000-0001-8193-6975; Yumusak, Gorkem/0000-0002-5047-4357In the current study, we report the light doping effects of the gadolinium and the terbium on the structural, morphological, optical and electrical properties of Nd2Sn2O7 pyrochlore ceramics. The pyrochlore which is prepared by the conventional solid state reaction technique is analyzed by means of scanning electron microscopy, energy dispersive X-ray analyzer, X-ray diffraction, ultraviolet- visible light spectrophotometry and temperature dependent current -voltage characteristics techniques. It is found that even though the doping content of both metals is low (2%), they significantly alter the physical properties of the pyrochlore. Particularly, it is observed that, these two doping agents increases the lattice parameter and strain and reduces the crystallite size and dislocation density. Optically, the effect of Gd doping on shrinking the energy band gap value of the Nd(2)Sn(2)O(7 )pyrochlore ceramic is more pronounced than that of Tb. On the other hand, the electrical investigations have shown that while the Gd make the pyrochlore exhibit p-type conductivity through forming shallow acceptor levels, the Tb forces n-type conductivity by forming deep donor levels below the conduction band edge. Such acceptor and donor impurity levels increases the electrical conductivity of the Nd(2)Sn(2)O(7 )pyrochlore ceramics by 390 and 58 times, respectively.Scientific Research Council of the Arab American University (AAUJ) of Palestine; Scientific and Technological Research Council of Turkey (TUBITAK); TUBITAK [FEN-E-120613-0266]; AAUJThe authors would like to thank the Scientific Research Council of the Arab American University (AAUJ) of Palestine and the Scientific and Technological Research Council of Turkey (TUBITAK) for the financial support. The work was supported by the TUBITAK under the Project FEN-E-120613-0266 and by the AAUJ under the Project Code (2017-2018 Cycle I)
Vibrational modes in (TlGaS2)(x)-(TlGaSe2)(1-x)mixed crystals by Raman measurements: compositional dependence of the mode frequencies and line-shapes
No full textTlGaS(2)and TlGaSe(2)ternary semiconducting compounds have been of scientific interest due to their large ultrafast optical nonlinearity characteristics. These remarkable properties make them promising semiconducting materials in photonic applications. A series of (TlGaS2)(x)-(TlGaSe2)(1-x)layered mixed crystals grown by Bridgman method were investigated from the standpoint of their Raman spectroscopy characteristics. Experimental Raman scattering study of crystals were reported in the frequency range of 80-400 cm(-1)for compositions ofx = 0, 0.25, 0.50, 0.75 and 1.0. The effects of crystal disorder on the line-width broadening of Raman-active modes were studied in detail. The asymmetry in the Raman line-shape was analyzed for two highest-frequency intralayer mode presenting two-mode behavior. It was shown that mixed crystal disorder effect is the major source for change of Raman line-shape with composition
Nonlinear optical absorption characteristics of PbMoO4 single crystal for optical limiter applications
No full text© 2022 Elsevier B.V.Molybdate materials take great interest due to their photocatalytic and optoelectronic applications. In this report, PbMoO4 single crystal, one of the member of molybdate materials, is grown by Czochralski technique and the change of nonlinear absorption characteristic depending on the input intensity was reported. Linear absorption analysis revealed the band gap energy and Urbach energy as to be 3.12 and 0.52 eV, respectively. Nonlinear absorption characteristics of the PbMoO4 single crystal was examined with the open aperture (OA) Z-scan experiments at 532 nm excitation wavelength under various input intensities. Fitting results of the OA Z-scan experiments indicated that PbMoO4 single crystal has nonlinear absorption (NA) behavior, and NA coefficient (βeff) increased from 7.11 × 10−8 to 1.96 × 10−7 m/W with increasing input intensity. This observation was associated with the increase of the contribution of the free carrier absorption to the NA with the generation of more excited electrons with increasing input intensity. At the 532 nm excitation wavelength (2.32 eV), the dominant mechanisms were revealed as one photon and free carrier absorptions. The optical limiting threshold of the PbMoO4 single crystal was obtained to be 4.91 mJ/cm2. The reported results indicated that PbMoO4 single crystal can be a good optical limiter in the visible wavelength region due to its effective NA behavior
A Practical Distributed Lightweight Multi-Hop Time Synchronization Algorithm for Linear Wireless Sensor Networks Implemented on a PIC Based System with Realistic Experimental Analysis
No full textTime synchronization is fundamental in the distributed networked systems, especially in Wireless Sensor Networks where a global time is essential to make sense of the events like collection of data and scheduled sleep/wake-up of nodes. There exists numerous time synchronization algorithms and techniques in the literature. Nonetheless, these proposed methods lack realistic experimentation of the synchronization process which is vital from the realization point of view. This study aims to bridge that gap by presenting a distributed lightweight time synchronization protocol implemented on an inexpensive PIC platform. Furthermore, PIC-based systems hadn’t been investigated before and gives an idea of the simplicity of the algorithm. Experimental analysis was done to see the performance of the protocol. The core motivation of the experiments was to the study the impact of the environment (e.g. indoor, outdoors, temperature variations and interference) on the synchronization. Our findings show that temperature indeed impedes the synchronization accuracy. © 2020, Sakarya University. All rights reserved
Thermoluminescence properties of Tl2Ga2S3Se layered single crystals
No full textThe trap center(s) in Tl2Ga2S3Se single crystals has been investigated from thermoluminescence (TL) measurements in the temperature range of 10-300 K. Curve fitting, initial rise, and peak shape methods were applied to observed TL glow curve to evaluate the activation energy, capture cross section, and attempt-to-escape frequency of the trap center. One trapping center has been revealed with activation energy of 16 meV. Moreover, the characteristics of trap distribution have been studied using an experimental technique based on different illumination temperature. An increase of activation energy from 16 to 58 meV was revealed for the applied illumination temperature range of 10-25K. (C) 2013 AIP Publishing LLC
FABRICATION AND CHARACTERIZATION OF TiO<sub>2</sub> THIN FILM FOR DEVICE APPLICATIONS
Get PDF Titanium oxide (TiO2) film was deposited by rectification factor (RF) magnetron sputtering technique on glass substrates and p-Si (111) wafers to fabricate n-TiO2/p-Si heterojunction devices for the investigation of material and device properties, respectively. The structural, surface morphology, optical and electrical properties of TiO2 film were characterized by means of scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), UV–visual (UV–Vis) spectral and dark current-voltage (I–V) measurement analyses. The deposited film layer was found to be homogeneous structure with crack-free surface. The bandgap value of TiO2 film was determined as 3.6[Formula: see text]eV and transmission was around 65–85% in the spectral range of 320–1100[Formula: see text]nm. The conductivity type of the deposited film was determined as n-type by hot probe method. These values make TiO2 film a suitable candidate as the n-type window layer in possible diode applications. TiO2 film was also deposited on p-Si (111) wafer to obtain Al/n-TiO2/p-Si/Al heterojunction device structure. The dark I–V characteristic was studied to determine the possible conduction mechanisms and diode parameters. </jats:p
Analysis of Temperature-Dependent Transmittance Spectra of Zn<sub>0.5</Sub>in<sub>0.5< (zis) Thin Films
No full textGasanly, Nizami/0000-0002-3199-6686; Delice, Serdar/0000-0001-5409-6528; parlak, mehmet/0000-0001-9542-5121; Gasanly, Nizami/0000-0002-3199-6686;Temperature-dependent transmission experiments of ZnInSe thin films deposited by thermal evaporation method were performed in the spectral range of 550-950nm and in temperature range of 10-300K. Transmission spectra shifted towards higher wavelengths (lower energies) with increasing temperature. Transmission data were analyzed using Tauc relation and derivative spectroscopy. Analysis with Tauc relation was resulted in three different energy levels for the room temperature band gap values of material as 1.594, 1.735 and 1.830eV. The spectrum of first wavelength derivative of transmittance exhibited two maxima positions at 1.632 and 1.814eV and one minima around 1.741eV. The determined energies from both methods were in good agreement with each other. The presence of three band gap energy levels were associated to valence band splitting due to crystal-field and spin-orbit splitting. Temperature dependence of the band gap energies were also analyzed using Varshni relation and gap energy value at absolute zero and the rate of change of gap energy with temperature were determined
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