Modeling of impulse electric discharge propagation in a condensed dielectric

In the present paper, special features of electric discharge propagation in a condensed dielectric are considered. A mathematical model of growth of the discharge structure and operation of a high-voltage generator is described based on the stochastic-deterministic approach. Numerical realization of the model is used to describe quantitatively the space-time and current discharge characteristics. Results of computer modeling of the discharge propagation in a condensed dielectric are presented for the tip-plane electrode geometry. Current and field discharge characteristics are analyzed. The voltage-current characteristic of technical water breakdown is obtained. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 11–17, March, 2006.     

μs振荡脉冲电源激励下同轴电极介质阻挡放电特性

 采用μs振荡脉冲电源激励同轴电极结构产生空气中介质阻挡放电(DBD),通过电压-电流波形的测量及发光图像拍摄研究了放电特性,计算得到了放电功率及传输电荷量等重要放电参量,研究了电压幅值、气隙距离对放电特性及放电参量的影响,在分析放电机理的基础上对实验结果进行了解释。结果表明:μs振荡脉冲电源激励下,DBD平均放电功率可达上百W,传输电荷量可达几千nC;增大电压幅值和减小放电气隙距离能获得更剧烈的放电,平均放电功率和传输电荷量均增加。     

The effect of carrier concentration in the semiconductor on the voltage-current characteristics of Schottky barrier diodes at low temperatures

We report the results of a study of voltage-current characteristics of gallium arsenide metal-semiconductor Schottky barrier structures, in which palladium and W-Ni alloy were electrochemically deposited in SiO₂ windows to form the barrier. It is demonstrated that the voltage-current characteristics are significantly distorted at low temperatures. The observed behavior of the voltage-current characteristics at low temperatures —the appearance of excess current and the increase in the ideality factor with carrier concentration in the excess current regime —is explained by a model in which peripheral mechanical stresses in the contacts lower the potential barrier height on the periphery of the contacts.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No, 10, pp. 87–93, October, 1986.     

介质阻挡放电点燃大气压直流均匀放电的光谱研究

由于大气压均匀放电等离子体在工业领域具有广泛的应用前景,为了获得大尺寸的大气压均匀等离子体,采用氩气作为工作气体,在大气压空气环境中利用同轴介质阻挡放电点燃了针-板电极间的大气隙(气隙宽度达到5 cm)直流均匀放电。研究发现,同轴介质阻挡放电能够有效降低针-板电极间的击穿电压。该均匀放电由等离子体柱、等离子体羽、阴极暗区和阴极辉区组成。其中等离子体柱和阴极辉区都是连续放电。而等离子体羽不同位置的放电是不同时的。事实上,等离子体羽放电是由从阴极向着等离子体柱移动的发光光层(即等离子体子弹)叠加而成。利用电学方法测量了放电的伏安特性曲线,发现其与低气压正常辉光放电类似,均具有负斜率。采集了放电的发射光谱,发现存在N₂第二正带系、氩原子和氧原子谱线。通过Boltzmann plot方法对放电等离子体电子激发温度进行了空间分辨测量,发现等离子体柱的电子激发温度比等离子体羽的电子激发温度低。通过分析放电机制,对以上现象进行了定性解释。这些研究结果对大气压均匀放电等离子体源的研制和工业应用具有重要意义。     

Effects of the Noise on Voltage-Current Characteristics of Josephson Effect

In the case of T >> hω/k, by expanding the quasiparticle current power spectrum up to the third order term of hω/2kT, two noises are obtained: one is a white noise, the other is an O-U noise. We find that the two noises are the negative correlated noises, and correlation parameter λ is equal to -√6/3. Effects of the correlated noises on voltage-current characteristics curve are studied. The numerical computations show that the correlation parameter λ has very large effects on the voltage-current characteristics, but the correlation time τ of the O-U noise has a little effect.     

From strong to fragile glass- forming systems: A temperature modulated differential scanning calorimetry investigation

The capacity of temperature modulated differential scanning calorimetry (TMDSC) technique to determine dynamical parameters is tested on several glass-formers of different fragility. We show that both the fragility index m and the stretching exponent β deduced from TMDSC are consistent with results from other spectroscopic analyses. In particular, we are interested in the coherency and complementarity with the dielectric measurements. When the dielectric analysis is prevented by conductivity effects or when the molecules are non-polar, TMDSC appears as a very powerful tool to study low frequency relaxation.     

Search for a sliding charge density wave in layered compounds

Non-linear voltage-current behavior is observed in the quasi one dimensional compound NbSe₃, due to the contribution of a sliding Charge Density Wave (CDW) to the conductivity. We have looked for a non-linear voltage-current characteristics in the incommensurate CDW state of the layered compounds 2H-TaSe₂ and 1T-TaS₂ and find no evidence for such up to $\text{1.0V}\text{cm}$ and $\text{10V}\text{cm}$, respectively. These values are several orders of magnitude higher than the minimum depinning field observed in NbSe₃.     

Nonuniform self-organized dynamical states in superconductors with periodic pinning

We consider magnetic flux moving in superconductors with periodic pinning arrays. We show that sample heating by moving vortices produces negative differential resistivity (NDR) of both N and S type (i.e., N- and S-shaped) in the voltage-current characteristic (VI curve). The uniform flux flow state is unstable in the NDR region of the VI curve. Domain structures appear during the NDR part of the VI curve of an N type, while a filamentary instability is observed for the NDR of an S type. The simultaneous existence of the NDR of both types gives rise to the appearance of striking self-organized (both stationary and nonstationary) two-dimensional dynamical structures.     

Two-δ- Function Generalized Plasma Pole Model for First Principle Calculations of Quasiparticle Energies in Many-Electron Systems

To evaluate the dynamical effects of the screened interaction in the calculations of quasiparticle energies in many-electron systems a two-δ-function generalized plasma pole model (GPP) is introduced to simulate the dynamical dielectric function. The usual single δ-function GPP model has the drawback of over simplifications and for the crystals without.the center of symmetry is inappropriate to describe the finite frequency behavior for dielectric function matrices. The discrete frequency summation method requires too much computation to achieve converged results since ab initio calculations of dielectric function matrices are to be carried out for many different frequencies. The two-δ GPP model is an op timization of the two approaches. We analyze the two-δ GPP model and propose a method to determine from the first principle calculations the amplitudes and effective frequencies of these δ functions. Analytical solutions are found for the second order equations for the parameter matrices entering the model. This enables realistic applications of the method to the first principle quasiparticle calculations and makes the calculations truly adjustable parameter free.     

Dynamical Casimir–Polder force on a partially dressed atom in a cavity comprising a dielectric

We put a two-level atom into a cavity comprising a dielectric with output coupling. An analytical expression of the dynamical Casimir–Polder force in such a system is obtained when the system starts from a partially dressed state. And the effects of several relevant parameters of the system on the time-dependent force are also discussed.     

荷控忆阻器等效电路分析模型及其电路特性研究

忆阻器是物理上新实现的具有记忆特性的基本二端电路元件. 根据φ-q关系式的泰勒级数形式构建了荷控忆阻器等效电路分析模型, 以三次非线性荷控忆阻器模型为例, 对不同参数条件下的荷控忆阻器进行了伏安关系、有无源性等电路特性的理论分析. 结果表明: 荷控忆阻器的伏安关系具有斜体“8”字形紧磁滞回线特性, 随其参数符号的不同, 荷控忆阻器呈现出无源性和有源性, 导致其电路特性发生相应的变化; 相比无源荷控忆阻器, 有源荷控忆阻器更适用于作为二次谐波信号产生电路使用. 制作了荷控忆阻器特性分析等效电路的实验电路, 实验测量结果很好地验证了理论分析结果. 关键词： 荷控忆阻器 等效电路 伏安关系 电路特性     

升华外延碳化硅p-n结的性质

本工作测量了升华外延碳化硅p-n结的电流-电压特性和空间电荷电容。通过对正向电流-电压特性及电容-电压特性的分析,表明:随着外延生长条件的不同,这种p-n结的结构可以在相当宽的范围内变化,从近于线性梯度结直到典型的p-i-n结,而大多数p-n结则介于这两者之间。文中就外延生长条件对p-n结结构的影响进行了简略的讨论。此外,还给出了升华外延碳化硅p-n结正向电发光的亮度-电流关系、光谱分布以及脉冲和交流激励的测量结果。 关键词：     

Tunneling through the space charge region in a metal-amorphous silicon contact

By solving for the potential barrier profile in metal-amorphous silicon contacts using an exponential distribution of the density of states in the energy spectrum mobility gap, we compute the voltage-current characteristics of such contacts taking into account tunneling through the space charge region. We demonstrate that as the density of states in the middle of the mobility gap increases, such tunneling leads to significant changes in the rectifying properties of a metal-amorphous silicon contact.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 3–7, November, 1986.     

Dynamical exchange effects in the dielectric function of the two-dimensional electron gas

Dynamical exchange interactions can be introduced in the dielectric function via a dynamic local field factor. We study the effects of this inclusion on both the static and the frequency dependent dielectric function of a two-dimensional electron gas, using the dynamic local field factor that we derived recently via the dynamical exchange decoupling method. The results are compared with the dielectric function in the Random Phase Approximation and with different dynamic and static approximations of the local field factor.Received: 7 May 2003, Published online: 22 September 2003PACS: 71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons - 77.22.Ch Permittivity (dielectric function) - 77.55.+f Dielectric thin filmsJ.T. Devreese: , jtd@uia.ua.ac.be     

Specific heats of the charge density wave compounds o-TaS and (TaSe ) I

Specific heats of the charge-density-wave compounds o-TaS₃ and (TaSe₄)₂I have been measured over the wide temperature interval 10 K-300 K. Both systems exhibit strong non-Debye behavior. Very weak and broad anomalies are observed at the Peierls transition temperatures. For o-TaS₃, the change in the curvature of the specific heat occurs at temperature of 40 K where glass transition has been deduced from dielectric measurements, and an extended scaling analysis suggests that the glass transition is associated with a dynamical cross over in length scales. We briefly discuss the characteristics and physical origins of the anomalies at both the Peierls and glass transitions. Received 5 April 2002 / Received in final form 28 June 2002 Published online 17 September 2002     

Dynamical van der Waals atom–surface interaction

We obtained new nonrelativistic expression for the dynamical van der Waals atom–surface interaction energy of a very convenient form for different applications. It is shown that classical result (Ferrell and Ritchie, 1980) holds only for a very slowly moving atom. In general case, the van der Waals atom–surface interaction energy manifests strong nonlinear dependence on the velocity and distance. In close vicinity of metal and dielectric surfaces and velocities ranging from 1 to 10 bohr units the dynamical van der Waals potential proves to be several times lower than in the static case and goes to the static values with increasing the distance and (or) decreasing the velocity.     

Plasmon modes in 3-layer graphene structures: Inhomogeneity effects

We calculate the plasmon frequency and damping rate in a 3-layer graphene system made of parallel monolayer and bilayer graphene sheets using the random-phase-approximation dielectric function and taking into account the inhomogeneity of the dielectric background of the system. Numerical results show that two out-of-phase acoustic and one in-phase optical plasmon modes can be found from the zeroes of dynamical dielectric function of the structure. Plasmon frequencies and damping rate of plasma oscillations depend significantly on the inhomogeneity of environment, so plasmon curves become more distinctive from each other in single-particle excitation region, compared to the case of homogeneous medium. Finally, Plasmon dispersion patterns depend remarkably on the number (but not order) of bilayer graphene sheet constructing to the system.     

Study of the Nitrogen Arc under Reduced Pressure

The paper presents a model of arc in a d.c. vortex plasma torch which allows to determine distributions of temperature and plasma electron density in conditions of reduced pressure. The model makes it possible to elucidate voltage-current characteristics of the arc at different pressures and its dynamic behaviour connected with the phenomenon of the electric arc root displacement. The experimental research also determined voltage-current characteristics for different flow rates and pressures. The fluctuations of the arc current and the arc voltage were measured. The corresponding wave shapes were analysed by Fast Fourier Transform. The frequency variations with flow rate, arc current and pressure were studied and discussed.     

Magnetic field tuning of polaron losses in Fe doped BaTiO(3) single crystals

Artificial tuning of dielectric parameters can result from interface conductivity in polycrystalline materials. In ferroelectric single crystals, it has already been shown that ferroelectric domain walls can be the source of such artificial coupling. We show here that low-temperature dielectric losses can be tuned by a dc magnetic field. Since such losses were previously ascribed to polaron relaxation we suggest this results from the interaction of hopping polarons with the magnetic field. The fact that this loss alteration has no counterpart in the real part of the dielectric permittivity confirms that no interface is involved in this purely dynamical effect. The contribution of mobile charges hopping among Fe-related centers was confirmed by ESR spectroscopy, showing a maximum intensity at ca T?～?40?K.     

Photosensitive n-Ox/p-CuIn3Se5 heterostructures

We have created photosensitive heterostructures n-Ox/p-CuIn₃Se₅ for the first time. The synthesis process is based on thermal reaction of the ternary compound with atmospheric oxygen. We have studied the voltage-current characteristics and the photoconversion quantum efficiency spectra of the indicated structures. We discuss charge transport mechanisms and photosensitivity of the created structures. We show that n-Ox/p-CuIn₃Se₅ heterostructures can be used in designing solar cells and photoanalyzers for linearly polarized radiation. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 782–785, November–December, 2006.