Stabilization of unbounded bilinear control systems in Hilbert space

We consider bilinear control systems of the form y^′(t)=Ay(t)+u(t)By(t) where A generates a strongly continuous semigroup of contraction (etA)_t?0 on an infinite-dimensional Hilbert space Y whose scalar product is denoted by 〈.,.〉. We suppose that this system is unbounded in the sense that the linear operator B is unbounded from the state Y into itself. Tacking into account eventual control saturation, we study the problem of stabilization by (possibly nonquadratic) feedback of the form u(t)=−f(〈By(t),y(t)〉). Applications to the heat equation is considered.     

电子初始能量对双向流二极管空间电荷限制流密度的影响

从理论上研究了阴极发射电子初始能量对一维平面非相对论性双向流二极管内空间电荷限制电子、离子流密度的影响,并与阴极发射电子初始能量为0情况下的空间电荷限制电子、离子流密度进行了比较。     

动力飞行体电磁脉冲效应数值分析

 利用时域有限差分方法模拟了在不考虑等离子体高温尾焰情况下,电磁脉冲与动力飞行体的相互作用。计算结果表明：在入射电磁脉冲的作用下, 飞行体蒙皮上将感应很大的皮电流; 感应电流密度的波形为衰减振铃信号波形,振铃周期等于电流波在整个飞行体长度上流动两次的时间;感应皮电流密度分布的特点是飞行体两端电流密度小,中部大。     

A new tuning procedure for the DTL RF field pattern

The DTL tank is a multi-cell cavity.In a fabricated tank,the measured average axial field E0 for each cell may obviously deviate from the designed value.It is generally thought the deviation is due to the errors in fabrication and assembly.But it is not always true.In this paper,it is shown that the deviation may already exist before fabrication in some cases.It is partly due to the imperfection of the current design procedures.A new design method is introduced to reduce the deviation in the design stage.     

Effect of the Noise Correlation Time on the Stationary Current of Brownian Particle in a Spatially Symmetric Periodic Potential

We investigate the noise-induced transport of Brownian particle in a deterministic spatial symmetrical periodic potential driven by colored cross correlation between a multiplicative white noise and an additive white noise. We derive the general formula of the stationary current. Based on numerical computation, we found that directed motion of the Brownian particles can be induced by the correlation time τ of cross correlation between the multiplicative noise and the additive noise and the current reversal and the direction of the current is controlled by the τ.     

Direct model-based predictive control scheme without cost function for voltage source inverters with reduced common-mode voltage

This paper presents a direct model-based predictive control scheme for voltage source inverters (VSIs) with reduced common-mode voltages (CMVs). The developed method directly finds optimal vectors without using repetitive calculation of a cost function. To adjust output currents with the CMVs in the range of –V_dc/6 to +V_dc/6, the developed method uses voltage vectors, as finite control resources, excluding zero voltage vectors which produce the CMVs in the VSI within ±V_dc/2. In a model-based predictive control (MPC), not using zero voltage vectors increases the output current ripples and the current errors. To alleviate these problems, the developed method uses two non-zero voltage vectors in one sampling step. In addition, the voltage vectors scheduled to be used are directly selected at every sampling step once the developed method calculates the future reference voltage vector, saving the efforts of repeatedly calculating the cost function. And the two non-zero voltage vectors are optimally allocated to make the output current approach the reference current as close as possible. Thus, low CMV, rapid current-following capability and sufficient output current ripple performance are attained by the developed method. The results of a simulation and an experiment verify the effectiveness of the developed method.     

Current-voltage characteristics of radiating Josephson sandwich

Josephson sandwich is considered, along which the radiating chain of vortices travels. Uniform movement of the chain is supported by bias current. The current-voltage characteristic connecting this current with the voltage at the Josephson junction is found. It is shown that when the current increases, generation of electromagnetic waves with frequency weakly dependent on the current is possible.     

Uniqueness of the standard model neutral current predictions

In view of an excellent agreement between the recently determinedv _μ-hadron couplings and predictions of the standard model, the basic question discussed is how far its neutral current predictions can be mimiced in going either from the isodoublet to an isotriplet (or an even higher isospin) left-handed representation or from SU _L (2) × U(1) toG × U(1), whereG is a simple group of rank two. This question is addressed with reference to a sufficiently broad class of schemes. Their most distinctive properties are: in the higher isospin scheme, neutrino couplings are precisely in the form obtainable with standard l.h. representation; the higher g.g. scheme isL+R type in which, to each light fermion of evenRU parity, a superheavy fermion of the same charge and oddRU parity is associated, parity conservation forbidding their mixing. Reasons for excluding theL-type andG ₂ higher g.g. schemes are given. Their neutral current predictions are compared with those of the standard model. A higher isospin representation can mimic the predictions of the standard model in inclusive and semi-inclusivev _μ-hadron reactions but is conclusively discriminated from the isodoublet representation by elasticv _μ ⁽⁻ p scattering. TheG × U(1) scheme can mimic standard model neutrino sector but is conclusively discriminated from minimal scheme by parity violating effects.     

Crystal field effects on the saturation magnetic moment of Sm3+ ion in ferronagnetic samarium compounds

The effects of cubic crystal fields on the saturation magnetic moment of Sm³⁺ ion in ferromagnetic compounds have been investigated. In samarium compounds with magnetic elements, the exchange fieldH _ex acting on Sm³⁺ ion is taken to be proportional to the sublattice magnetization of the magnetic element, while in compounds with nonmagnetic elementsH _ex is taken to be proportional to the spin average of the Sm³⁺ ion and is determined self-consistently. In both types of compoundsH _ex is assumed to be along [001] direction. The saturation magnetic moment is calculated by taking into account the admixture of excited (J=7/2 andJ=9/2) levels into the ground (J=5/2) level of Sm³⁺ ion by crystal fields and exchange fields. It is shown that depending upon the strength, the crystal fields quench or enhance the magnetic moment from the free ion value, and in some cases force Sm³⁺ ion to behave effectively like an (L+S) ion rather than an (L−S)ion. The crystal fields may have important bearing on the performance of samarium compounds as permanent magnet materials.     

ITER高温超导电流引线的高安全分流器研究

电流引线是室温电源电缆与低温磁体之间的电连接部件.高温超导材料在液氮温度下具有零电阻率和低热导率的特性,用它做成的电流引线可以大大减小低温系统的热负荷,从而减少制冷设备投资及系统运行费.高温超导电流引线可以分为阻性换热器段和高温超导段两部分(其中还包括各部件间的连接部分).高温超导段的分流器设计关系到冷端热负荷大小以及超导段失超后的安全问题.为了研究国际热核聚变试验堆(ITER)电流引线高安全性能,专门设计、试验了68kA引线的1/90实验样品.本文通过对比全CuBe(cu-2%Be)分流器、全不锈钢分流器和二元分流器的失冷故障(LOFA)实验结果,证明二元分流器能够克服安全性和冷端漏热矛盾,可以满足ITER高安全性的要求.