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941.
Abraham Debebe Woldeyohannes Mohd Amin Abd Majid 《能源与动力工程:英文版》2009,(12):29-38
Simulation has proven to be an effective tool for analyzing pipeline network systems (PNS) in order to determine the design and operational variables which are essential for evaluating the performance of the system. This paper discusses the use of simulation for performance analysis of transmission PNS. A simulation model was developed for determining flow and pressure variables for different configuration of PNS. The mathematical formulation for the simulation model was derived based on the principles of energy conservation, mass balance, and compressor characteristics. For the determination of the pressure and flow variables, solution procedure was developed based on iterative Newton Raphson scheme and implemented using visual C++6. Evaluations of the simulation model with the existing pipeline network system showed that the model enabled to determine the operational variables with less than ten iterations. The performances of the compressor working in the pipeline network system xvhich includes energy consumption, compression ratio and discharge pressure were evaluated to meet pressure requirements ranging from 4000-5000 kPa at various speed. Results of the analyses from the simulation indicated that the model could be used for performance analysis to assist decisions regarding the design and optimal operations of transmission PNS. 相似文献
942.
The reactivity feedback coefficients of a material test research reactor fueled with high-density U3Si2 dispersion fuels were calculated. For this purpose, the low-density LEU fuel of an MTR was replaced with high-density U3Si2 LEU fuels currently being developed under the RERTR program. Calculations were carried out to find the fuel temperature reactivity coefficient, moderator temperature reactivity coefficient and moderator density reactivity coefficient. Nuclear reactor analysis codes including WIMS-D4 and CITATION were employed to carry out these calculations. It is observed that the average values of fuel temperature reactivity feedback coefficient, moderator temperature reactivity coefficient and moderator density reactivity coefficient from 20 °C to 100 °C, at the beginning of life, followed the relationships (in units of Δk/k × 10−5 K−1) −2.116 − 0.118 ρU, 0.713 − 37.309/ρU and −12.765 − 34.309/ρU, respectively for 4.0 ≤ ρU (g/cm3) ≤ 6.0. 相似文献
943.
Hashem M. A. Al-Mattarneh Deepak K. Ghodgaonkar Wan Mahmood B. W. A. Majid 《Subsurface Sensing Technologies and Applications》2001,2(4):377-390
The existence of moisture in concrete is a major cause of damage to the concrete structure, so there is an increasing need for nondestructive detection and monitoring of moisture content in concrete. Microwave nondestructive testing (MNDT) techniques have advantages over other NDT methods (such as radiography, ultrasonic, and eddy current) regarding low cost, good penetration in nonmetallic materials, good resolution and requirement of only one face of material for testing. In this paper, microwave open-ended rectangular waveguide was used to measure the electromagnetic properties of Portland cement concrete (PCC) over a frequency range of 7.0 to 13.0 GHz. PCC specimens of six different water cement ratio (w/c) were prepared. PCC dielectric properties were evaluated at different moisture content ranges from saturated to oven dry. The results show reflection coefficients, dielectric constants and loss factors increase with increasing moisture content of PCC. At the same values of moisture content, the reflection coefficients, dielectric constants and loss factors of PCC increase with decreasing w/c ratio. The measured values of reflection coefficients, dielectric constants and loss factors can be used to determine the moisture content of PCC. 相似文献
944.
945.
Majid Zandian J. D. Garnett R. E. Dewames M. Carmody J. G. Pasko M. Farris C. A. Cabelli D. E. Cooper G. Hildebrandt J. Chow J. M. Arias K. Vural Donald N. B. Hall 《Journal of Electronic Materials》2003,32(7):803-809
We report on Hg1−xCdxTe mid-wavelength infrared (MWIR) detectors grown by molecular-beam epitaxy (MBE) on CdZnTe substrates. Current-voltage (I-V)
characteristics of HgCdTe-MWIR devices and temperature dependence of focal-plane array (FPA) dark current have been investigated
and compared with the most recent InSb published data. These MWIR p-on-n Hg1−xCdxTe/CdZnTe heterostructure detectors give outstanding performance, and at 68 K, they are limited by diffusion currents. For
temperatures lower than 68 K, in the near small-bias region, another current is dominant. This current has lower sensitivity
to temperature and most likely is of tunneling origin. High-performance MWIR devices and arrays were fabricated with median
RoA values of 3.96 × 1010 Ω-cm2 at 78 K and 1.27 × 1012 Ω-cm2 at 60 K; the quantum efficiency (QE) without an antireflection (AR) coating was 73% for a cutoff wavelength of 5.3 μm at
78 K. The QE measurement was performed with a narrow pass filter centered at 3.5 μm. Many large-format MWIR 1024 × 1024 FPAs
were fabricated and tested as a function of temperature to confirm the ultra-low dark currents observed in individual devices.
For these MWIR FPAs, dark current as low as 0.01 e−/pixel/sec at 58 K for 18 × 18 μm pixels was measured. The 1024 × 1024 array operability and AR-coated QE at 78 K were 99.48%
and 88.3%, respectively. A comparison of these results with the state-of-the-art InSb-detector data suggests MWIR-HgCdTe devices
have significantly higher performance in the 30–120 K temperature range. The InSb detectors are dominated by generation-recombination
(G-R) currents in the 60–120 K temperature range because of a defect center in the energy gap, whereas MWIR-HgCdTe detectors
do not exhibit G-R-type currents in this temperature range and are limited by diffusion currents. 相似文献
946.
In many applications, one is interested to detect certain patterns in random process signals. We consider a class of random process signals which contain sub-similarities at random positions representing the texture of an object. Those repetitive parts may occur in speech, musical pieces and sonar signals. We suggest a warped time-resolved spectrum kernel for extracting the subsequence similarity in time series in general, and as an example in biosonar signals. Having a set of those kernels for similarity extraction in different size of subsequences, we propose a new method to find an optimal linear combination of those kernels. We formulate the optimal kernel selection via maximizing the kernel Fisher discriminant (KFD) criterion and use Mesh Adaptive Direct Search (MADS) method to solve the optimization problem. Our method is used for biosonar landmark classification with promising results. 相似文献
947.
In this study, a reconfigurable triple‐band triple‐mode substrate integrated waveguide filter is designed and fabricated in the C‐band spectrum. A novel and simplified design procedure based on analytical equations is proposed. The filter design also benefits from a reconfigurable structure, using metallic via holes as perturbation, allowing wide‐band selectivity of the C‐band spectrum (from 4.4 to 6.9 GHz). Moreover, the filter benefits from a magnetic coupling solution between the resonators, which only couples the first three modes and rejects the next resonating modes. Therefore, a large bandgap in the spectrum is achieved. The proposed structure is fabricated and measured, and a high similarity between the simulation and fabrication is observed. The measured results show that the first band can be tuned in the frequency range of 4.4 to 7, the second band can be tuned in the range 5.8 to 7.7 GHz, and the third band from 5.8 to 7.7 GHz. The insertion loss 1.5 to 2.5 dB, 2 to 3 dB, and 2.5 to 3.5 dB for the first, second, and third bands, respectively. 相似文献
948.
Majid Khodier 《国际射频与微波计算机辅助工程杂志》2020,30(8)
This article presents a study of circular antenna array design and optimization using the cuckoo search (CS) algorithm. The goal of optimization is to minimize the maximum sidelobe level with and without null steering. The CS algorithm is used to determine the parameters of the array elements that produce the desired radiation pattern. We illustrated the effectiveness of the CS in the design and optimization of circular antenna arrays by means of extensive numerical simulations. We compared our results with other methods from the literature whenever possible. We presented numerous examples that show the excellent performance and robustness of the CS algorithm and the results reveal that the design of circular antenna arrays using the CS algorithm provides acceptable enhancement compared with the uniform array or the design obtained using other optimization methods. 相似文献
949.
Chong You Beh Ee Meng Cheng Nashrul Fazli Mohd Nasir Mohd Shukry Abdul Majid Shing Fhan Khor Mohd Ridzuan Mohd Jamir Emma Ziezie Mohd Tarmizi Kim Yee Lee 《International journal of molecular sciences》2022,23(10)
This paper aims to investigate the dielectric properties, i.e., dielectric constant (ε′), dielectric loss factor (ε″), dielectric tangent loss (tan δ), electrical conductivity (σ), and penetration depth (Dp), of the porous nanohydroxyapatite/starch composites in the function of starch proportion, pore size, and porosity over a broad band frequency range of 5 MHz–12 GHz. The porous nanohydroxyapatite/starch composites were fabricated using different starch proportions ranging from 30 to 90 wt%. The results reveal that the dielectric properties and the microstructural features of the porous nanohydroxyapatite/starch composites can be enhanced by the increment in the starch proportion. Nevertheless, the composite with 80 wt% of starch proportion exhibit low dielectric properties (ε′, ε″, tan δ, and σ) and a high penetration depth because of its highly interconnected porous microstructures. The dielectric properties of the porous nanohydroxyapatite/starch composites are highly dependent on starch proportion, average pore size, and porosity. The regression models are developed to express the dielectric properties of the porous nanohydroxyapatite/starch composites (R2 > 0.96) in the function of starch proportion, pore size, and porosity from 1 to 11 GHz. This dielectric study can facilitate the assessment of bone scaffold design in bone tissue engineering applications. 相似文献
950.
This paper summarises findings on road safety performance and bus-involved accidents in Melbourne along roads where bus priority measures had been applied. Results from an empirical analysis of the accident types revealed significant reduction in the proportion of accidents involving buses hitting stationary objects and vehicles, which suggests the effect of bus priority in addressing manoeuvrability issues for buses. A mixed-effects negative binomial (MENB) regression and back-propagation neural network (BPNN) modelling of bus accidents considering wider influences on accident rates at a route section level also revealed significant safety benefits when bus priority is provided. Sensitivity analyses done on the BPNN model showed general agreement in the predicted accident frequency between both models. The slightly better performance recorded by the MENB model results suggests merits in adopting a mixed effects modelling approach for accident count prediction in practice given its capability to account for unobserved location and time-specific factors. A major implication of this research is that bus priority in Melbourne's context acts to improve road safety and should be a major consideration for road management agencies when implementing bus priority and road schemes. 相似文献