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71.
72.
A numerical simulation is presented for investigating the effects of pressure ratio of D2 injector to supersonic nozzle on the population inversion in the DF chemical laser cavity, while a lasing concurrently takes place. The chemical laser is generally used for the industrial process and manufacturing as well as the military weapon system, which requires high power characteristic of laser system rather than the others. The population inversion is absolutely needed to generate the laser beam and is non-equilibrium process. The laser beam is generated between the mirrors in the cavity and it is important to obtain stronger population inversion and more uniform distribution of the excited molecules in the laser cavity in order to produce high-power laser beam with good quality. In this study, these phenomena are investigated by means of analyzing the distributions of the DF excited molecules and the F atom used as an oxidant, while simultaneously estimating the maximum small signal and saturated gains and power in the DF chemical laser cavity. For the numerical solution, a fully conservative implicit method and a second order total variation diminishing (TVD) scheme are used with the finite-volume method (FVM). An 11-species (including DF molecules in various excited states of energies), 32-step chemistry model is adopted for the chemical reaction of the DF chemical laser system. The results are discussed by comparison with two D2 injector pressure cases; 192 and 388.64 torr. Major results reveal that in the resonator, stronger population inversions occur in the all transitions except DF(1)-DF(0), when the D2 injection pressure is lower. But, the higher D2 injection pressure provides a favorable condition for DF(1)-DF(0) transition to generate the higher power laser beam. In other words, as the pressure of D2 injector increases, the maximum small signal gain in the v1-0 transition, which is in charge of generating most of laser power, becomes higher. Therefore, the total laser beam power becomes higher. 相似文献
73.
DF100型100KW短波发射机是电台的重要设备,为维护发射稳定,电路维护工作应受到高度重视.本文先分析了不良极间电容的影响,并给出了解决方法,然后选择中和电路,针对DF100型100KW短波发射机出现的问题进行了分析. 相似文献
74.
Application of best relay selection approach to cooperative DF IDMA systems over Rayleigh/Weibull fading channels
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This paper analyzes the performance of cooperative decode‐and‐forward (DF) interleave‐division multiple‐access (IDMA) networks with best relay selection over Rayleigh/Weibull fading environments. In the analysis, approximate outage probability (OP) and bit error probability (BEP) expressions are derived for the considered system. Further, a 2‐hop DF IDMA system is also designed to compare with cooperative one. We propose OP and BEP expression for 2‐hop DF IDMA systems. Numerical results are obtained by changing the number of relays and the value of fading parameter in the proposed expressions. Also, simulations are provided to corroborate the exactness of the derived approximate OP and BEP expressions. 相似文献
75.
Nenad Cakić Zoran Kadelburg Miloje Rajović 《Numerical Functional Analysis & Optimization》2013,34(1-2):37-45
This is an expository article devoted to the answers to the 10 open problems of the fundamental paper of Grothendieck (Summa Res. Math. 1954; 3:57–123), some of which were given in the recent years. 相似文献
76.
We carried out an experimental investigation of the frequency regime of generation of a holographic distributed feedback (DF) dye laser. We show that the convection induced in liquid by heating-up a solution in the excitation zone ensures self-pumping of the solution through this zone that is sufficient for stable operation of the laser in the regime of frequently repeating pulses without forced circulation of the solution through the cuvette. It is found that the main condition for the operation of a DF-laser in this regime is the sharp focusing of pumping radiation, which ensures transverse dimensions of the generation zone of less than 1 mm. In experiments, we produced stable generation of a holographic DF dye laser in the regime of self-pumping of a solution with a pulse repetition rate of up to 1 kHz with an efficiency of 10% and a spectral line width of 0.01 nm. 相似文献
77.
In this letter, a miniaturized log‐periodic dipole array (LPDA) antenna operating from 1 GHz to 6 GHz is proposed for portable direction finding applications. To reduce the lateral size of an LPDA antenna, bow‐tie elements and a top‐loading technique are utilized and spacing factor is decreased to reduce the spacing between the LPDA elements. The proposed miniaturized LPDA antenna has the measured gain and front‐to‐back ratio ranging from 1.2 dBi to 3 dBi and from 7 dB to 22 dB, respectively. 相似文献
78.
79.
80.
Wenbo Xu Jiaru Lin Kai Niu Zhiqiang He 《International Journal of Communication Systems》2010,23(8):1016-1040
This paper investigates the error performance of three relaying protocols with multiple decode‐and‐forward relays. In the first protocol, relays that can decode correctly will forward the signals from source. Nevertheless, selection cooperation (SC) and opportunistic relaying (OR) are adopted to select only a single relay to forward in the other two protocols, respectively. At sufficiently high signal‐to‐noise ratio, the upper bounds on bit error probability are derived for three protocols, where the developments apply for various channel fading models. Simulation results are provided to verify the tightness of the analytical bounds, and the performance comparisons among different relaying protocols are presented. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献