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匹配条件: “Yahya S. Masrahi” ,找到相关结果约324649条。
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Crassulacean Acid Metabolism Permutation and Survival of Caralluma Species (Apocynaceae) in Arid Habitats
Yahya S. Masrahi,Turki A. Al-Turki,Osama H. Sayed
Ecologia Balkanica , 2012,
Abstract: Several species of the stem succulent Caralluma (Apocynaceae) are abundant perennials in arid regions of the Arabian Peninsula. These arid regions have a short wet season with erratic rainfall and are characterized by harsh climatic conditions of high temperature, high evaporation and sand storms. Work presented in this paper aimed at investigating importance of Crassulacean Acid Metabolism (CAM) for survival of three Caralluma species in their natural habitat. Investigations involved studying stomatal characteristics, stomatal diffusive conductance, chlorophyll fluorescence, and CAM in three species of Caralluma, namely C. acutangula (Decne.) N.E.Br., C. edulis (Edgew.) Benth. ex Hook.f., and C. subulata (Forssk.) Decne. Microscopic examination revealed a pattern of stomatal characteristics typical of CAM plants in these three Caralluma species. Results showed that these three Caralluma species were obligate CAM plants exhibiting this mode of photosynthesis during both the wet and the dry seasons. Under protracted water stress during the long dry season very low values of stomatal diffusive conductance and dampening of CAM acidification-deacidification cycles denoted the tendency of these three Caralluma species to shift from the obligate CAM physiotype to CAM-idling mode. Chlorophyll fluorescence measurements indicated that protracted water stress induced a reduction in Photosystem II (PSII) antenna efficiency and quantum yield in the three studied Caralluma species. This reduction of PSII activity occurred in concomitance with a marked rise in non-photochemical quenching of chlorophyll fluorescence denoting operation of non-photochemical energy dissipating mechanisms known to be important for photoprotection of the photosynthetic apparatus.
A Conservative Pressure-Correction Method on Collocated Grid for Low Mach Number Flows  [PDF]
S. M. Yahya, S. F. Anwer, S. Sanghi
World Journal of Mechanics (WJM) , 2012, DOI: 10.4236/wjm.2012.25031
Abstract: A novel extension to SMAC scheme is proposed for variable density flows under low Mach number approximation. The algorithm is based on a predictor—corrector time integration scheme that employs a projection method for the momentum equation. A constant-coefficient Poisson equation is solved for the pressure following both the predictor and corrector steps to satisfy the continuity equation at each time step. The proposed algorithm has second order centrally differenced convective fluxes with upwinding based on Cell Peclet number while diffusive flux are viscous fourth order accurate. Spatial discretization is performed on a collocated grid system that offers computational simplicity and straight forward extension to curvilinear coordinate systems. The algorithm is kinetic energy preserving. Further in this paper robustness and accuracy are demonstrated by performing test on channel flow with non-Boussinesq condition on different temperature ratios.
Design of 4 Elements Rectangular Microstrip Patch Antenna with High Gain for 2.4 GHz applications
Yahya S. H. khraisat
Modern Applied Science , 2011, DOI: 10.5539/mas.v6n1p68
Abstract: In the recent years the development in communication systems requires the development of low cost, minimal weight and low profile antennas that are capable of maintaining high performance over a wide spectrum of frequencies. This technological trend has focused much effort into the design of a microstrip patch antenna. The objective of this paper is to design, and fabricate an inset fed rectangular microstrip patch antenna. Therefore, a novel particle swarm optimization method based on IE3D was used to design an inset feed linearly polarized rectangular microstrip patch antenna with four element array. The length of the antenna is nearly half wavelength in the dielectric; it’s a very critical parameter, which governs the resonant frequency of the antenna. In view of design, selection of the patch width and length are the major parameters along with the feed line depth. Desired patch antenna design was simulated by IE3D simulator program. Initially we set our antenna as a single patch and after evaluating the outcomes of antenna features, operation frequency, radiation patterns, reflected loss, efficiency and antenna gain, and then we transformed it to a 2x1 linear array. Then we analyzed the 4x1 linear antenna array to increase directivity, gain, efficiency, and have better radiation patterns.
Simulation the Hybrid Combinations of 24GHz and 77GHz Automotive Radar
Yahya S. H. Khraisat
Applied Physics Research , 2012, DOI: 10.5539/apr.v4n1p193
Abstract: In this paper we used MATLAB simulation to simulate the hybrid combinations of short range automotive radar (SRR) operating at frequency 24 GHz and long range automotive radar (LRR) operating at frequency 77 GHz. We obtained the velocity, the range and the time of scanning target. The objective of this work is to get the advantage of both SRR and LRR covering short and long distance with high resolution from 1m to 200m range.
Analysis of the Parameters of Symmetrical Multi – Fed Full – Wave Dipole Antenna
Yahya S. H. Khraisat
Computer and Information Science , 2012, DOI: 10.5539/cis.v5n2p69
Abstract: This paper demonstrates the analysis of the parameters of symmetrical full-wave dipole antenna based on multi – fed techniques. The current distributions were measured, followed by the measurement of parameters of antenna like gain, radiation patterns and input impedance. Based on these observations four equations for current distribution were eventually formulated. These equations were then used to compute the values of the same parameters of the antenna. Finally, the values of parameters obtained practically and theoretically were compared to analyse the validity of the developed equation.
Design a Wireless Meteorological Station in Jordan
Yahya S. H. Khraisat
Computer and Information Science , 2011, DOI: 10.5539/cis.v5n1p87
Abstract: This paper demonstrates a low-cost, yet reliable, weather monitoring system. The proposed system has three sensors that measure the temperature, wind speed and wind direction, respectively. The analogue outputs of the sensors converted to digital signals and further processed by a microcontroller. Using easily-available components and simple circuitry, the system should be beneficial in providing a portable and low-cost weather monitoring using wireless communication system. Until now these parameters in the meteorological department in Jordan are transmitted by telephone. In this system we developed an automated system which continuously measures weather parameter and transmit them to the main meteorological station. In future we are planning to have more substations which can interact with main station.
The Effect of the pH of Ammonum Nitrate Solution on the Susceptability of Mild Steel to Stress Corrosion Cracking (SCC) and General Corrosion  [PDF]
Fathia S. Mohammed, Alyaa G. Elramady, Salheddin E. Abu Yahya
Materials Sciences and Applications (MSA) , 2010, DOI: 10.4236/msa.2010.14030
Abstract: This work investigates the relative aggressiveness of nitrate solutions at different pH values on mild steel towards stress corrosion cracking (SCC) and general corrosion. Electrochemical behavior and stress corrosion cracking sus-ceptibility measurements were carried out in 52 Wt% ammonium nitrate solutions at 368° K and various pH values ranging from 0.77 to 9.64. Constant load stress corrosion test at 90% yield stress was conducted. Tested specimens were prepared and examined using the scanning electron microscope (SEM). The potentiodynamic polarization curves for different pH values again emphasized the validity of the gravimetric measurements and hence the mechanism of cracking was attributed to the stress that assisted the dissolution process.
Design of Integrated Triple Band Notched for Ultra-Wide Band Microstrip Antenna  [PDF]
Yahya S. H. Khraisat, Ahmad Bataineh, Malak Angor
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2015, DOI: 10.4236/jemaa.2015.73011
Abstract: Ultra-wideband (UWB) is one of the recent topics that received a great concern from academia and industry. However, UWB found many difficulties to be standardized due to the overlay working that made UWB an important potential interference source to many licensed and unlicensed spectrum throughout the band 3.1 to 10.6 GHz. This paper demonstrates the design of integrated triple band notched for UWB Microstrip antenna. We simulated UWB short range systems which require low power and these are built using inexpensive digital components. We proposed a compact triple band notched CPW (Co-planar Waveguide) fed Micro strip Antenna (MSA) for UWB. This band-notched antenna has rejection characteristics at 3.2 GHz (for Wi-MAX band 3.16 to 3.32 GHz), at 5.5 GHz (for WLAN 2 band—5.3 to 5.72 GHz) and at 7.9 GHz (for ITU band 7.72 GHz to 8.13 GHz). The simulation was done using IE3D simulator.
Joint Polling and Contention Based Feedback Algorithm to Exploit Multiuser Diversity
Yahya S. Al-Harthi
Journal of Communications , 2009, DOI: 10.4304/jcm.4.5.348-356
Abstract: One of the most promising approaches to boost the communication efficiency in wireless systems is the use of multiuser diversity (MUDiv), where the fading of channels is exploited. The mechanism of scheduling the user with the best channel condition is called opportunistic scheduling (OS). In this paper we propose a joint polling and contention based feedback (JPCF) algorithm that exploits MUDiv while reducing the feedback load. The guard time, which is between bursts, is divided into minislots that alternate between polling-based feedback minislot (p-minislot) and contention-based feedback minislot (c-minislot). During the minislot, users feedback their channel qualities if above a predetermined threshold. We analyze the scheduling algorithm under slow Rayleigh fading assumption and derive the closed-form expressions of the feedback load as well as the system capacity. We also consider the delay resulting from the time needed to schedule a user and derive the system throughput. The scheduling algorithm is compared with other scheduling algorithms.
Tiered Instruction: An Effective Strategy to Differentiation of Instruction
Yahya BELER,Süleyman AVCI
Journal of Kirsehir Education Faculty , 2011,
Abstract: This study aimed to examine the effects of a tiered instructional design on classroom management, attitude and the learning level of students. The instructional program was prepared for an introductory science course for 3rd grade students. The case study research method was used. Observation form, teacher and student interview forms were used to collect data. The teaching program was planned using a tiered instruction method for nine subjects of the “Yesterday, Today, Tomorrow” curriculum theme. The teacher made a short presentation and then students were classified into ability groups. Finally, each group completed learning activity via individual and group tasks based on activities appropriate to their abilities. The results indicate that tiered instruction had positive effects on the learning outcomes of students. All groups completed the classroom activities easily, which increased their motivation. Students participated in activities voluntarily and enthusiastically.
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