Toward high-performance two-dimensional black phosphorus electronic and optoelectronic devices

Recently, black phosphorus(BP) has joined the two-dimensional material family as a promising candidate for electronic and photonic applications due to its moderate bandgap, high carrier mobility, and unusual in-plane anisotropy. Here,we review recent progress in BP-based devices, such as field-effect transistors, contact resistance, quantum transport, stability, photodetector, heterostructure, and in-plane anisotropy. We also give our perspectives on future BP research directions.     

Stability and Quasi Normal Modes of Charged Born–Infeld Black Holes

The static charged Born–Infeld black hole is stable. We compare its stability to the linear counterpart Reissner–Nordstrom black hole stability. We use the WKB method to compute how its quasi-normal modes vary with the non-linear parameter, temperature, mass of the scalar field and the spherical index.     

Conventionality of Simultaneity and the Tippe Top Paradox in Relativity

In this paper we critically examine a recently posed paradox (tippe top paradox in relativity) and its suggested resolution. A tippe top when spun on a table, tips over after a few rotations and eventually stands spinning on its stem. The ability of the top to demonstrate this charming feat depends on its geometry (all tops are not tippe tops). To a rocket-bound observer the top geometry should change because of the Lorentz contraction. This gives rise to the possibility that for a sufficiently fast observer the geometry of the top may get altered to such an extent that the top may not tip over! This is certainly paradoxical since a mere change of the observer cannot alter the fact that the top tips over on the table. In an effort to resolve the issue the authors of the paradox compare the equations of motion of the particles of the top from the perspective of the inertial frames of the rocket and the table and observe among other things that (1) the relativity of simultaneity plays an essential role in resolving the paradox and (2) the puzzle in some way is connected with one of the corrolaries of special relativity that the notion of rigidity is inconsistent with the theory. We show here that the question of the incompatibility of the notion of rigidity with special relativity has nothing to do with the current paradox and the role of the lack of synchronization of clocks in the context of the paradox is grossly over-emphasized. The conventionality of simultaneity of special relativity and the notion of the standard (Einstein) synchrony in the Galilean world have been used to throw light on some subtle issues concerning the paradox.     

Stability of modified electroweak strings

We discuss the stability of an electroweak string with axions in its core, which give to the configuration a quasi-topological property, and compare it with other modifications using instantons in the thin-wall approximation.     

Control of pattern formation by time-delay feedback with global and local contributions

We consider the suppression of spatiotemporal chaos in the complex Ginzburg-Landau equation by a combined global and local time-delay feedback. Feedback terms are implemented as a control scheme, i.e., they are proportional to the difference between the time-delayed state of the system and its current state. We perform a linear stability analysis of uniform oscillations with respect to space-dependent perturbations and compare with numerical simulations. Similarly, for the fixed-point solution that corresponds to amplitude death in the spatially extended system, a linear stability analysis with respect to space-dependent perturbations is performed and complemented by numerical simulations.     

Dynamics of an elastic L-shaped ring coupled to an internal frame

Analyzed is the dynamics of an elastic L-shaped ring coupled to an elastic frame joined at discrete locations of the ring perimeter. The approximate ring model is evaluated adopting a two-dimensional model of a short shell joined to a narrow annular disk along one of its boundaries thus forming the L-shaped cross-section. Coupling the ring to an internal frame is accomplished by segmenting the ring. The frame impedance matrix relating forces and displacements at terminations is then applied at junctions of ring segments corresponding to these terminations.     

Stability of ionically bonded surfaces in ionizing environments

We present criteria for the stability of ionic materials in ionizing environments, confining ourselves to cases where the core hole Auger decay mechanism of Knotek and Feibelman is applicable. The main result is that Auger induced decomposition will not occur unless the cation species in the solid is ionized down to a relatively deep filled shell. This shell must be sufficiently deep that an Auger decay starting from it will release the energy necessary for decomposition. The degree to which covalency in bonding affects stability is discussed. We show how these concepts can be applied by examination of the periodic table and a table of electron binding energies.     

一种新型双势和周期势模型的构造及其精确解

提出了一种构造并精确求解新型势函数的方法.采用这种方法.讨论了一维二次型函数的通解,将这种二次型函数分段连接构造出一种新型一维双势阱模型和新型一维周期势模型,在此基础上得出了这两种新型势模型的精确解.     

A local level-set method using a hash table data structure

We present a local level-set method based on the hash table data structure, which allows the storage of only a band of grid points adjacent to the interface while providing an O(1) access to the data. We discuss the details of the construction of the hash table data structure as well as the advection and reinitialization schemes used for our implementation of the level-set method. We propose two dimensional numerical examples and compare the results to those obtained with a quadtree data structure. Our study indicates that the method is straightforward to implement but suffers from limitations that make it less efficient than the quadtree data structure.     

Collective motion of active Brownian particles in one dimension

We analyze a model of active Brownian particles with non-linear friction and velocity coupling in one spatial dimension. The model exhibits two modes of motion observed in biological swarms: A disordered phase with vanishing mean velocity and an ordered phase with finite mean velocity. Starting from the microscopic Langevin equations, we derive mean-field equations of the collective dynamics. We identify the fixed points of the mean-field equations corresponding to the two modes and analyze their stability with respect to the model parameters. Finally, we compare our analytical findings with numerical simulations of the microscopic model.     

神光Ⅱ装置中空间滤波器系统的稳定性设计与分析

 考虑到空间滤波器系统在激光装置中的稳定性要求，分析了影响稳定性的各种因素。对现行装置中的SF4空间滤波器系统进行振动模态测试，初步确定系统的工作状况，并结合振动理论明确系统稳定性的设计参数。利用有限元软件ANSYS对空间滤波器系统及相关的设计进行仿真验证计算。结果表明：SF4系统的一阶固有频率达到83 Hz，与实验结果相符合，满足系统稳定性的要求；在系统中引入支撑不但能有效增加系统的刚度，同时能转移系统的振型；系统基础支撑平台的选择要求平台独立，并且选择较低的高度以便于控制上层光学元件的变形；在系统中的引入波纹管这种弹性连接，能降低系统变形量，并且通过改变波纹管的厚度能实现连接刚度的改变。上述设计可在神光装置其它系统结构中应用。     

Monte Carlo study of the step flow to island nucleation transition for close packed structures

Using joined super-lattice Kinetic Monte Carlo and continuous simulations we study the transition between step flow and two-dimensional island nucleation growth on stepped surfaces for close packed crystalline structures. The numerical analysis is performed in terms of misorientation cut, deposition rate and temperature. We compare the results of the atomistic approach with the predictions of the standard and generalized Burton-Cabrera-Frank (BCF) continuous model. The generalization consists in the explicit inclusion in the theory of the formation and dissolution of mobile dimers on the terraces. We show that the BCF-like continuous theories break down for low temperatures, large off-angle cuts and high deposition rates. In view of these results we critically discuss the basic assumptions of the continuous models.     

Strong Levinson theorem for the Dirac equation

We consider the Dirac equation in one space dimension in the presence of a symmetric potential well. We connect the scattering phase shifts at E= +m and E= -m to the number of states that have left the positive energy continuum or joined the negative energy continuum, respectively, as the potential is turned on from zero.     

History of the New York University Physics Department

We trace the history of physics at New York University after its founding in 1831, focusing especially on its relatively recent history, which can be divided into five periods: the Gregory Breit period from 1929 to 1934; the prewar period from 1935 to 1941; the wartime period from 1942 to 1945; the postwar period from around 1961 to 1973 when several semiautonomous physics departments were united into a single all-university department under a single head; and after 1973 when the University Heights campus was sold to New York City and its physics department joined the one at the Washington Square campus. For each of these periods we comment on the careers and work of prominent members of the physics faculty and on some of the outstanding graduate students who later went on to distinguished careers at NYU and elsewhere.     

Dynamics and Thermodynamics of Layered Neural Network

We consider the dynamics of overlaps in a layered network with tanhβ(χ) as its threshold transfer function. The analysis of dynamical stability shows that when the external stimulus is close enough to one of the stored patterns the retrieval state becomes globally stable. The statistical mechanics of the same model, in which the parameter β is introduced as thermal noise, is also studied. We find that the thermodynamical stability is equivalent to the dynamical stability.     

非自治混沌系统的脉冲同步

研究两个非自治混沌系统之间的脉冲同步的实用稳定性,将问题转化为同步误差系统的原点的实用稳定性．利用脉冲微分方程的相关理论,给出了同步误差系统原点实用稳定的相关判据,并给出了误差范围的理论表达式．计算机仿真实验的结果验证了理论结果 关键词：     

Collisions of strings with Y junctions

We study the dynamics of Nambu-Goto strings with junctions at which three strings meet. In particular, we exhibit one simple exact solution and examine the process of intercommuting of two straight strings in which they exchange partners but become joined by a third string. We show that there are important kinematical constraints on this process. The exchange cannot occur if the strings meet with very large relative velocity. This may have important implications for the evolution of cosmic superstring networks and non-Abelian string networks.     

A study of magnetism in disordered Pt-Mn, Pd-Mn and Ni-Mn alloys: an augmented space recursion approach

In this paper we shall study three binary alloy systems, one constituent of which is Mn. The other constituents are chosen from a particular column of the periodic table: Ni(3d), Pt (4d) and Pd (5d). As we go down the column, the d-bands become wider, discouraging spin-polarization. In a disordered alloy, the situation becomes more complicated, as the exchange interaction between two atoms is environment dependent. We shall compare and contrast their magnetic behaviour using robust electronic structure techniques. In all three alloy systems conjectures are made to explain experimental data. In this paper we shall examine whether there is any basis to these conjectures.     

The stability of the inert gas A(2)B(8) compounds

We analyse the stability of the hypothetical crystalline compounds of inert gases B⁽⁸⁾ with metals A⁽²⁾ of the second group of the periodic table. Compounds stable within wide temperature limits, and possessing specific optical properties are predicted.     

Nonlinear waves in the nonequilibrium systems of the oscillatory type. Part II

The paper is the continuation of the preceding one (Part I). In the part II we consider the inhomogeneous quasistationary wave patterns which result from collisions of the travelling waves with close wave-vectors, and which may be regarded as narrow stationary spectral packages consisting of the quasimonochromatic travelling waves. Then we consider the long-wave oscillatory system. It is well known that in the absence of dispersion this system possesses the potential which makes it possible to compare the absolute stability of different quasistationary states. We make an attempt to construct an analogous quantity for the dispersive system. We argue that this quantity should be of the type of the potential production (an analogue of the entropy production in the nonequilibrium thermodynamics) rather than a generalization of the potential itself. Though we have no rigorous proof that our quantity indeed determines the absolute stability, we demonstrate that this hypothesis is verisimilar.