Calculations of field ionization in the field ion microscope

The ionization of a gas atom as it occurs in the field ion microscope is discussed. A wide range of values for the electric field intensity at the metal surface are considered in calculating the ionization occurring both far away from and close to the tip. Ionization distribution curves are calculated and electric fields strengths are determined at points where the distributions peak. Calculations of ionization zone widths and best image conditions are made and a new interpretation of best image conditions is considered. A new field calibration method is suggested.     

脉冲场励磁YBCO块材俘获磁通特性

研究了熔融织构法制备的单畴高温超导YBaCuO块材在脉冲场下的俘获磁通特性。分别测试了YBCO块材在不同强度脉冲场下的俘获磁场,并对实验结果进行了分析。实验发现:YBCO块材在脉冲场输入电压小于300V时的俘获磁场,随着外加脉冲场强度的增加而增加;而脉冲输入电压大于300V时,俘获磁场并没有继续增加。实验获得的超导块材俘获磁场图形呈现出明显的十字结构,这是由于块材采用顶部籽晶熔融织构生长技术、存在五个生长区域、不同生长区域及边界处临界电流密度的不同而导致的。     

虚光场对玻色-爱因斯坦凝聚体与二项式光场相互作用系统中光场压缩性质的影响

在二项式光场和二能级原子玻色-爱因斯坦凝聚体相互作用系统中, 应用全量子理论, 分别在旋波近似和非旋波近似下, 研究了光场的压缩特性以及原子本征频率、原子-光场的耦合系数、光场参数以及虚光场对系统光场压缩特性的影响. 研究表明, 光场的两个正交分量均被周期性压缩, 光场压缩持续时间与原子的本征频率有关, 压缩深度与二项式光场概率分布参数和虚光场有关, 光场与原子的耦合系数决定了光场涨落的崩塌-回复频率. 关键词： 量子光学 玻色-爱因斯坦凝聚 虚光场 光场压缩     

Frequency dependence of the coercive field and the internal bias field in ferroelectric thin films

The dependences of the coercive field and the internal bias field on the switching field frequency for lead zirconate titanate and lead titanate thin films are experimentally studied over a wide temperature range. It is shown that, as the frequency increases, the coercive field and the bias field in these films increase at the rate dependent on the temperature and the substrate used.     

恒定流速场与静电场、静磁场的类比

本文将“物理类比法”引入大学物理电磁学部分的教学,将恒定流速场与静电场和静磁场在特征量、场的分布及其描述等方面进行了类比,使学生对电磁场有一个较清晰和全面的认识,对电磁学的理论有一个较深刻的理解和掌握,收到了较理想的教学效果.     

Enhancement of the electric field threshold for microwave breakdown by crossed magnetic field

The enhancement of breakdown threshold is of benefit to the high power microwave transmission. We propose a magnetic field in the transverse direction to the electric field to enhance the breakdown threshold. A theory of electric field threshold with crossed magnetic field for short pulse is developed, and verified by particle-in-cell/Monte Carlo collision (PIC/MCC) simulations. The result shows that the crossed magnetic field can enhance the breakdown threshold significantly.     

The effect of the crystal structure of the field emitter on field ion energy distributions

The field ionization probability of an atom as a function of distance from the field emitter is discussed in terms of the atomic arrangement and the electron scattering properties of the ion cores of the emitter in the immediate neighborhood of the atom to be ionized, and the electron transmission properties of the potential barrier between the emitter and that atom. This approach to field ionization calculations is somewhat similar to field ionization calculations based on low energy electron diffraction (LEED) procedure in that it takes into account electron scattering from the first few atomic layers of the emitter. It differs from LEED type calculations, because it considers the highly localized nature of the ionization near a surface atom. This localization makes the ionization probability relatively insensitive to the two-dimensional periodicity of the emitter surface. A one-dimensional calculation, in which only the potential barrier and three ion core scatterers in line with the field are considered, shows secondary structure in the predicted field ion energy distributions near the critical energy deficit, as well as the well known, primary field induced resonance peaks. The surface orientation dependence of these distributions arises naturally from this model because the secondary structure depends strongly upon the crystal parameter along a line parallel to the field. This one-dimensional calculation can be no more than an approximation to a complete calculation. It is interesting, however, that such a simple physical model, in which scattering from the image potential and only two or three ion cores is considered, rather than scattering from a complete crystal, can give prodicted field ion onergy distributions which are similar to those experimentally observed.     

New field equations in the 5-dimensional projective unified field theory

New field equations of the Projective Unified Field Theory are presented which avoid potential difficulties of former versions with respect to the equivalence principle. The physical interpretation of this new version remains unchanged: constancy of the “gravitational constant”, electromagnetic polarization of the vacuum, definiteness of the energy of the stationary scalaric field, etc. Furthermore, the Klein-Gordon field and the Dirac field are treated.     

耦合二能级原子与光场相互作用系统中场熵的演化

利用T-C模型研究了耦合二能级原子与相干态光场相互作用系统中场熵的演化规律,数值计算结果表明:场熵的演化受原子间耦合强度和光场初始平均光子数的变化的影响.     

似稳场中的涡旋电场和电流源的关系

推导了涡旋电场与它的电流源之间的关系，利用此关系和磁场矢势计算了球形线圈内外的磁感应强度，并证明了两个闭合回路之间的互感系数相符。     

Numerical simulation of graphene in a magnetic field within the effective field theory

Monte Carlo simulation of graphene in an external magnetic field perpendicular to the plane of graphene has been reported. The calculations have been performed using the effective quantum field theory with a noncompact (3 + 1)-dimensional Abelian gauge field and (2 + 1)-dimensional Kogut-Susskind fermions. It has been revealed that the external magnetic field shifts the semimetal-insulator phase transition point toward higher dielectric constants of the substrate. The phase diagram of the semimetal-insulator phase transition has been plotted in the (dielectric constant of the substrate-magnetic field) plane.     

Classical theory of the octonian field

We develop a nonassociative classical theory of the octonion spinor field. We construct the Lagrange function, the field equations, the solutions, the energymomentum tensor, the spin, and the associator, which is a new quantum characteristic. We consider the interaction of the octonion spinor field with the electromagnetic field. We show that, in the case of a massless field, the energy, the spin, and the associator can be measured simultaneously, while in the case of a field with rest mass, only either spin and energy or spin and associator can be measured simultaneously.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 58–62, December, 1986.     

Influence of field evaporation treatment on the field emission properties of carbon nanotubes array

Field evaporation was used in the post-fabrication treatment of a carbon nanotubes (CNTs) array and effectively modified the CNTs morphology in favor of the field emission under a moderate field. After the field evaporation treatment, the uniformity of the emission site distribution improved but the onset voltage rose. Using the Fowler-Nordheim theory, the actual onset field and the evaporation field around the CNT were calculated to be −4.6-5 and 9-12 V/nm, respectively. These values are close to those obtained from the individual CNT samples. The above results have provided an alternative to modify the configuration of an array sample and demonstrated the feasibility of tackling the problem of the disparity in the field emission capability of different CNTs in an array.     

Conformal field theory and the symmetries of string field theory

The two-dimensional conformal field theory representation of Witten's bosonic string field theory is discussed. The basic overlap equations, K_n symmetry and BRST invariance are proved directly, without the usual expansion in oscillators. The conformal field theory approach naturally provides local overlap identities which (when integrated over half the string) can be used to verify properties of the cubic action. In particular, a recently proposed diffeomorphism invariance is shown to be free of anomalies. Finally, a new class of symmetries, including generalizations of the K_n symmetries which are local in spacetime, are presented.     

Theoretical limit of the minimal magnetization switching field and the optimal field pulse for Stoner particles

The theoretical limit of the minimal magnetization switching field and the optimal field pulse design for uniaxial Stoner particles are investigated. Two results are obtained. One is the existence of a theoretical limit of the smallest magnetic field out of all possible designs. It is shown that the limit is proportional to the damping constant in the weak damping regime and approaches the Stoner-Wohlfarth (SW) limit at large damping. For a realistic damping constant, this limit is more than 10 times smaller than that of so-called precessional magnetization reversal under a noncollinear static field. The other is on the optimal field pulse design: if the magnitude of a magnetic field does not change, but its direction can vary during a reversal process, there is an optimal design that gives the shortest switching time. The switching time depends on the field magnitude, damping constant, and magnetic anisotropy.     

Magnetic properties of the bond and crystal field dilution Blume-Emery-Griffiths model in the presence of magnetic field

The magnetic properties of the spin-1 bond and crystal field dilution Blume-Emery-Griffiths (BEG) model in the presence of magnetic field are investigated on a simple cubic lattice by using effective field theory (EFT). In the M-H plane, the common action of bond and crystal field dilution leads to the exhibition of an irregular initial magnetization curve and slows down the magnetization process. The peak of the susceptibility curve has an explicit decline and shows a distinct shift toward the direction of increase of magnetic field. On the other hand, in the M-T plane, the magnetization curves show a discontinuity and a vertical leap in the small range of magnetic field when the negative crystal field is larger and the ratio of biquadratic and exchange interaction is positive (α>0). These results have not been revealed in previous works.     

Generalized equations of the gravitoinertial field

Generalized equations of the gravitoinertial field which contain quasi-Maxwellian field equations are obtained.     

非均匀弱直流偏置磁场中CoFe-基非晶态合金丝的静磁化分布和退磁场分布

当前从事非晶态合金丝巨磁阻抗效应的理论研究均以忽略其内部退磁场为前提,该前提对于小尺寸非晶态合金丝不适用.本文提出一种用于计算Co Fe-基非晶态合金丝内部静磁化强度、退磁场分布的模型.该模型将非晶态合金丝内部划分成同轴、等宽、等厚、半径不同的相邻无交圆环,计算各圆环内磁化强度对场点r处退磁场冲激响应,得到冲激响应矩阵.利用该矩阵求解均匀/非均匀直流偏置磁场中非晶态合金丝内静磁化强度、退磁场分布.     

On the field penetration into semiconductors in the field ion microscope

The calculation of field penetration in semiconductors and consequent band bending during field ionization/evaporation is discussed. The shielding by surface states is also taken into account. The Si(111) face example demonstrates that neglection of surface states may give unrealistic high band bending values. Because of the lack of reliable data for the density of surface states, a possible maximal band bending has been calculated for GaAs. Its value in the case of an external applied field of $\text{1}\text{V}\text{A}\text{?}$ may be such smaller as formerly assumed in recent works.     

具有广义协变的包含重力场贡献的重力场方程

利用半度规λ^(α)_μ表象的数学工具定义一个对广义坐标具有协变形式的重力场矢势函数ω^(α)_μ≡-cλ^(α)_μ，给出一个具有广义协变的包含重力场贡献的重力场方程R_μν-g_μνR/2+Λg_μν=8πG(T^(Ⅰ)_μν+T^(Ⅱ)_μν) 关键词： 重力场方程 协变形式 能量-动量张量 量子化