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在四阳极直流放电装置上,测量并分析了辉光放电的电流-电压和发光特征随气压的变化关系。结果表明,采用稳流放电模式比稳压放电具有更宽的稳定放电气压和电流范围,能在从1~800Pa的较宽气压范围内实现氦气辉光放电,放电电流可达到500mA左右。随着电极表面亮斑的变化,对于同一气压,在低电流区,放电电压几乎成指数增长;随电流增大,电压的增长速度变缓;对于高的气压,碰撞频率的增大使得电压随电流升高的速率变小。分析表明,放电处于异常辉光区。从放电管的CCD图像可以看出,对于同一放电电流,随气压的升高,等离子体往阴极收缩。 相似文献
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We present a linear rational pseudospectral (collocation) method with preassigned poles for solving boundary value problems. It consists in attaching poles to the trial polynomial so as to make it a rational interpolant. Its convergence is proved by transforming the problem into an associated boundary value problem. Numerical examples demonstrate that the rational pseudospectral method is often more efficient than the polynomial method. 相似文献
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Sebastiaan van Dijken Xavier Fain Steven M. Watts Kentaro Nakajima J. M. D. Coey 《Journal of magnetism and magnetic materials》2004,280(2-3):322-326
A detailed study of the in-plane magnetotransport properties of spin valves with one and two Fe3O4 electrodes is presented. Fe3O4/Au/Fe3O4 spin valves exhibit a clear anisotropic magnetoresistance in small magnetic fields but no giant magnetoresistance (GMR). The absence of GMR in these structures is due to simultaneous magnetization reversal in the two Fe3O4 layers. By contrast, a negative GMR effect is measured on Fe3O4/Au/Fe spin valves. The negative GMR is attributed to an electron spin scattering asymmetry at the Fe3O4/Au interface or an induced spin scattering asymmetry in the Au interfacial layers. 相似文献
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对于Bellman最优性原理,本文举出实例表明:(1)策略不一定有(合理的)子策略;(2)子策略不一定存在最优子策略;(3)最优策略不一定有最优子策略;(4)用最短路与反证法来论述最优性原理的正确性,不能肯定成立;(5)Bellman最优性原理与其递推公式并不等价。 讨论四类最优策略之后,给出最优性原理与递推公式等价的一个充分性定理。 相似文献
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Flow injection spectrofluorimetry with in-line Winklers procedure was developed for the dissolved oxygen (DO) determination. 2-Thionaphthol reacted with iodine produced by Winkler’s method to form fluorescence inactive disulfide compound. To automate the process completely, a 5-channel flow system with a newly designed 16-way valve was assembled. The system consisted of a dispersion coil (DC), a precipitate formation coil (PFC), a precipitate dissolving coil (PDC), and extraction coil (EC). A calibration can be constructed by using a standard iodine solution for dissolved oxygen. The calibration graph was linear over the range 1.2×10−4∼6.0×10−4 mol l−1 iodine (1.96∼9.80 mg O l−1)). The relative standard deviation (n=6) was below 0.3% for the 4×10−4 mol l−1 iodine (6.27 mg O l−1) determination. The sample throughput was 12/h. 相似文献
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A novel flow-injection system is proposed for the rapid measurement of the fish freshness indices K1 and K2: K1=[([HxR+[Hx])×100/([IMP]+[HxR]+[Hx])] and K2=[[Hx]×100/([HxR]+[Hx])], where [IMP], [HxR] and [Hx] are inosine-5′-monophosphate, inosine and hypoxanthine concentrations, respectively. For the estimation of index K1, 5′-nucleotidase immobilized reactor and nucleoside phosphorylase (NP)/xanthine oxidase (XO) coimmobilized reactor were incorporated in series in the flow-injection line made up by a 16-way switching valve with two sample loops. For the estimation of index K2, NP and XO immobilized reactors were also incorporated in the similar flow-line. Two sample portions passed through the flow-line with different residence times so that two peaks were obtained. The first and second peaks obtained in the K1-determining system corresponded to the total of HxR and Hx and the total of Hx, HxR and IMP, respectively. Similarly, the first and second peaks obtained in the K2-determining system corresponded to Hx and the total of Hx and HxR, respectively. Therefore, the indices K1 and K2 can be estimated by where i1 and i2 present the peak current of the first and second peaks, respectively, and f the ratio of the peak currents of the first and second peaks for a Hx standard solution. A sea bream was selected as a model fish and it was stored at 4 °C after death. A good correlation was found between the index K1 and the storage time over a period of 400 h, with a correlation coefficient of 0.992, but no correlation between the index K2 and the storage time. The measurements could be performed at a rate of 22 samples per hour with satisfactory precision (0.6–1.2% R.S.D.), without calibration for each species, accurate weighing of fish meat and any interferences in fish meat. 相似文献