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1.
Attar A. Nakhai M.R. Aghvami A.H. 《Wireless Communications, IEEE Transactions on》2008,7(4):1157-1162
In this paper, we propose a cognitive cellular system based on DS MC-CDMA to coexist with a number of narrow-band legacy systems in the same frequency range. If the bandwidth and the frequency location of each narrow-band system are known to this cognitive MC-CDMA, it is possible to mitigate their interfering effect in the cognitive receivers by adaptive transmission. We will develop an algorithm for calculating the adaptive transmission parameters and show that it combats interference in the channel effectively. 相似文献
2.
3.
Khaled Chahine Mark Ballico John Reizes Jafar Madadnia 《International Journal of Thermophysics》2007,28(6):2118-2127
A simple quasi-2D model for the temperature distribution in a graphite tube furnace is presented. The model is used to estimate
the temperature gradients in the furnace at temperatures above which contact sensors can be used, and to assist in the redesign
of the furnace heater element to improve the temperature gradients. The Thermogage graphite tube furnace is commonly used
in many NMIs as a blackbody source for radiation thermometer calibration and as a spectral irradiance standard. Although the
design is robust, easy to operate and can change temperature rapidly, it is limited by its effective emissivity of typically
99.5–99.8%. At NMIA, the temperature gradient along the tube is assessed using thermocouples up to about 1,500°C, and the
blackbody emissivity is calculated from this. However, at higher operating temperatures (up to 2,900°C), it is impractical
to measure the gradient, and we propose to numerically model the temperature distributions used to calculate emissivity. In
another paper at this conference, the model is used to design an optimized heater tube with improved temperature gradients.
In the model presented here, the 2-D temperature distribution is simplified to separate the axial and radial temperature distributions
within the heater tube and the surrounding insulation. Literature data for the temperature dependence of the electrical and
thermal conductivities of the graphite tube were coupled to models for the thermal conductivity of the felt insulation, particularly
including the effects of allowing for a gas mixture in the insulation. Experimental measurements of the temperature profile
up to 1,500°C and radial heat fluxes up to 2,200°C were compared to the theoretical predictions of the model and good agreement
was obtained. 相似文献
4.
In this article, we consider the project critical path problem in an environment with hybrid uncertainty. In this environment, the duration of activities are considered as random fuzzy variables that have probability and fuzzy natures, simultaneously. To obtain a robust critical path with this kind of uncertainty a chance constraints programming model is used. This model is converted to a deterministic model in two stages. In the first stage, the uncertain model is converted to a model with interval parameters by alpha-cut method and distribution function concepts. In the second stage, the interval model is converted to a deterministic model by robust optimization and min-max regret criterion and ultimately a genetic algorithm with a proposed exact algorithm are applied to solve the final model. Finally, some numerical examples are given to show the efficiency of the solution procedure. 相似文献
5.
Mohammad Mizanur Rahman Md. Hasan Zahir Md. Eyasin Arafat Mohammad Abu Jafar Mazumder Rami Suleiman A. Madhan Kumar 《应用聚合物科学杂志》2021,138(9):49904
A waste material called oil fly ash (OFA) was acid-functionalized, yielding f-OFA-COOH, which was then reacted with cerium oxide (CeO2) to make CeO2-functionalized OFA, or f-OFA-CeO2. Pristine OFA and f-OFA-CeO2 were used to make waterborne polyurethane (WBPU) dispersions, referred to as WBPU/OFA and WBPU/f-OFA-CeO2, respectively, with defined OFA and f-OFA-CeO2 content. All the dispersions were applied to mild steel as organic coatings to evaluate their protective properties, such as their hydrophobicity, adhesive strength and UV-shielding resistance. These protective properties varied based on the OFA and f-OFA-CeO2 content. The highest water contact angle, minimum water swelling and maximum adhesive strength were found using WBPU/f-OFA-CeO2-20 coating (using 2.00 wt% f-OFA-CeO2), which also showed the maximum ultraviolet (UV) absorption via UV–vis spectroscopy analysis. This UV shielding result also matched field test results, as that coating was found to exhibit the lowest UV degradation near a marine atmosphere, as shown by X-ray photoelectron spectroscopy (XPS) analysis. The least affected hydrophobicity was also recorded for the sample with the WBPU/f-OFA-CeO2-20 coating. 相似文献
6.
Force-driven liquid argon flows both in nanoscale periodic domains and in gold nano-channels are simulated using non-equilibrium molecular dynamics to investigate the scale and wall force field effects. We examined variations in liquid density, viscosity, velocity profile, slip length, shear stress and mass flow rate in different sized periodic domains and nano-channels at a fixed thermodynamic state. In the absence of walls, liquid argon obeys Newton’s law of viscosity with the desired absolute viscosity in domains as small as 4 molecular diameters in height. Results prove that deviations from continuum solution are solely due to wall effects. Simulations in nano-channels with heights varying from 3.26 to 36 nm exhibit parabolic velocity profiles with constant slip length modeled by Navier-type slip boundary condition. Both channel averaged density and “apparent viscosity” decrease with reduced channel height, which has competing effects in determination of the mass flow rate. Density layering and wall force field induce deviations from Newton’s law of viscosity in the near-wall region, while constant “apparent viscosity” with the deformation rate from a parabolic velocity profile successfully predicts shear stress in the bulk flow region. 相似文献
7.
Mahdikhah V. Ataie A. Akbari Moayyer H. Molaei Mohammad Jafar Babaei A. 《Journal of Electroceramics》2022,48(1):51-66
Journal of Electroceramics - In this research, hard/soft CoFe2O4/Ni magnetic nanocomposite samples with different concentrations of Ni were successfully produced by a two-step mechanical alloying... 相似文献
8.
One of the most important assumptions in production scheduling is that the machines are permanently available without any breakdown. In the real world of scheduling, machines can be made unavailable due to various reasons such as preventive maintenance and unpredicted breakdown. In this paper, we explore flowshop configuration under the assumption of condition-based maintenance to minimize expected makespan. Furthermore, we consider a condition-based maintenance (CBM) strategy which could be used in most industrial settings. The proposed algorithm is designed for non-resumable flowshop state where the processing of jobs after preventive maintenance is restarted from the beginning. We propose a hybrid algorithm based on genetic algorithm and simulated annealing. Additionally, we conduct an extensive parameter calibration with the utilization of Taguchi method and select the optimal levels of the algorithm’s performance influential factors. The preliminary results indicate that the proposed method provides significantly better results compared with other high performing algorithms in the literature. 相似文献
9.
Jafar Biazar Behzad Ghanbari Mehdi Gholami Porshokouhi Mohammad Gholami Porshokouhi 《Computers & Mathematics with Applications》2011,61(4):1016-1023
In this paper, He’s homotopy perturbation method is applied to solve non-linear systems of mixed Volterra–Fredholm integral equations. Two examples are presented to illustrate the ability of the method. Also comparisons are made between the Adomian decomposition method and the homotopy perturbation method. The results reveal that He’s homotopy perturbation method is very effective and simple and in these examples leads to the exact solutions. 相似文献
10.
In this paper, a new homotopy perturbation method (NHPM) is introduced for obtaining solutions of systems of non-linear partial differential equations. Theoretical considerations are discussed. To illustrate the capability and reliability of the method three examples are provided. Comparison of the results of applying NHPM with those of applying HPM reveal the effectiveness and convenience of the new technique. 相似文献