Theoretical investigation on radiation tolerance of M_(n+1)AX_n phases

Ternary M_(n+1)AX_n phases with layered hexagonal structures, as candidate materials used for next-generation nuclear reactors, have shown great potential in tolerating radiation damage due to their unique combination of ceramic and metallic properties. However, M_(n+1)AX_n materials behave differently in amorphization when exposed to energetic neutron and ion irradiations in experiment. We first analyze the irradiation tolerances of different M_(n+1)AX_n(MAX) phases in terms of electronic structure, including the density of states(DOS) and charge density map. Then a new method based on the Bader analysis with the first-principle calculation is used to estimate the stabilities of MAX phases under irradiation. Our calculations show that the substitution of Cr/V/Ta/Nb by Ti and Si/Ge/Ga by Al can increase the ionicities of the bonds,thus strengthening the radiation tolerance. It is also shown that there is no obvious difference in radiation tolerance between M_(n+1)AC_n and M_(n+1)AN_n due to the similar charge transfer values of C and N atoms. In addition, the improved radiation tolerance from Ti_3AlC_2 to Ti_2AlC (Ti_3AlC_2 and Ti_2AlC have the same chemical elements), can be understood in terms of the increased Al/TiC layer ratio. Criteria based on the quantified charge transfer can be further used to explore other M_(n+1)AX_n phases with respect to their radiation tolerance, playing a critical role in choosing appropriate MAX phases before they are subjected to irradiation in experimental test for future nuclear reactors.     

Low energy excitation and scaling in Bi(2)Sr(2)Ca(n-1)Cu(n)O(2n+4) (n=1-3): angle-resolved photoemission spectroscopy

Angle-resolved photoemission spectroscopy (ARPES) has been performed on the single- to triple-layered Bi-family high-T (c) superconductors (Bi(2)Sr(2)Ca(n-1)Cu(n)O(2n+4), n=1-3). We found a sharp coherent peak as well as a pseudogap at the Fermi level in the triple-layered compound. Comparison among three compounds has revealed a universal rule that the characteristic energies of superconducting and pseudogap behaviors are scaled with the maximum T (c).     

V_nB_(8(n+1))~-(n=1-3)团簇的几何结构、电子和光谱特性

基于密度泛函理论和卡里普索结构预测方法,系统研究了V_nB_(8(n+1))~-(n=1-3)团簇的几何结构、电子和光谱特性.首先,利用卡里普索结构预测方法确定了VB_(16)~-的基态结构为高对称性的C_(2v)点群对称结构.在此基态结构基础上,通过堆积的方式优化得到了V_2B_(24)~-和V_3B_(32)~-团簇的基态结构.结果显示,V_2B_(24)~-和V_3B~(32)~-团簇分别拥有高对称性的C_(4h)和D_(8d)点群对称结构.基于上述基态结构,系统分析了不同尺寸团簇的自然布局分布和自然电子组态、Mayer键级和电子局域函数.最后,讨论了不同团簇的红外、拉曼光谱等光谱特性,为过渡金属钒掺杂硼基纳米材料的研究提供理论参考.     

(n+1)-Dimensional Gravity Duals to Quantum Criticalities with Spontaneous Symmetry Breaking

We reexamine the charged AdS domain wall solution to the Einstein-Abelian-Higgs model proposed by Gubser et al. as holographic superconductors at quantum critical points and comment on their statement about the uniqueness of gravity solutions. We generalize their explorations from (3+1)-dimensions to arbitrary n+1Ds and find that the n+1≥qslant5D charged AdS domain walls are unstable against electric perturbations.     

Accurate prediction of large antiferromagnetic interactions in high- T(c) HgBa2Ca(n-1)Cu(n)O(2n+2+delta) ( n = 2,3) superconductor parent compounds

The in-plane nearest-neighbor Heisenberg magnetic coupling constant, J, of La2CuO4, Nd2CuO4, Sr2CuO2Cl2, YBa2Cu3O6, and undoped HgBa(2)Ca(n-1)Cu(n)O(2n+2+delta) ( n = 1,2,3) is calculated from accurate ab initio configuration interaction calculations. For the first four compounds, the theoretical J values are in quantitative agreement with experiment. For the Hg-based compounds the predicted values are -135 meV ( n = 1) and approximately -160 meV ( n = 2,3), the latter being much larger than in previous cases and, for n = 3, increasing with pressure. Nevertheless, the physics governing J in all these layered cuprates appears to be the same. Moreover, calculations suggest a possible relationship between J and T(c).     

An (n+1)-Dimensional Integrable Model: Painlevé Test

A (3+1)-dimensional model is proposed at first. The integrability of the model is proved by using the standard Painlevk analysis. Then the model is extended to (n + 1)-dimensional case. The model is space-isotropic and is a type of the modified KdV extension in higher dimensions.     

LETTER: BTZ Black Hole from (3+1) Gravity

We propose an approach for constructing spatial slices of (3+1) spacetimes with cosmological constant but without a matter content, which yields (2+1) vacuum with solutions. The reduction mechanism from (3+1) to (2+1) gravity is supported on a criterion in which the Weyl tensor components are required to vanish together with a dimensional reduction via an appropriate foliation. By using an adequate reduction mechanism from the Plebaski–Carter[A] solution in (3+1) gravity, the (2+1) BTZ solution can be obtained.     

Interplay of self-doping and disorder in epitaxial Bi2Sr2Ca(n-1)Cu(n)O(2n+4+x) (n = 1,2) thin films under heavy-Ion irradiation

We propose a novel mechanism for the modification of T(c) in Bi(2)Sr(2)Ca(n-1)Cu(n)O(2n+4+x) epitaxial thin films (2212 and 2201) under energetic heavy-ion irradiation. By irradiating films with various oxygen content, we show from the temperature dependence of the resistance that irradiation always produces a doping effect superimposed on the damage caused to the sample. The effect is larger in 2201 than in 2212 thin films. The T(c) decrease observed by irradiating optimally doped films is partially due to this doping effect. Irradiation of semiconducting samples restores metallic superconducting behavior.     

The Embedding of Quantum Algebra U(gl(n+1)) in Irreducible Representations of U(gl(n+1))

Using a formula derived by Jimbo, we express the generators of U(gl(n+1)), the q-analogue of U(gl(n+1)) in an irreducible representation with Gel'fand basis, as functions of the generators of U(gl(n+1)).     

Quantum Teleportation of One-to-Many Using （n ＋ 1）-Particle Entanglement

In this paper, quantum teleportatlon of one-to-many using （n ＋1）-particle entanglement is presented. If the sender （Alice） wants to transmit an unknown quantum state to a distant receiver （Bob）, similar to the previous schemes, Alice performs Bell-state measurement on particles belonging to herself and informs the receiver the results through the classical channel. After that, it needs to perform the Hadamard operation on the other （n - 1） particles and measure them as well. With the aid of the measurement results, Bob can operate a corresponding unitary transformation on his particle to reconstruct the original state. Of course, the reconstruction may realize at either location of n, but it cannot realize at all locations at the same time.     

High-Resolution Fourier Transform Spectra of HDSe: The Interacting States (v(1) v(2) v(3))/(v(1) +/- 1 v(2) -/+ 2 v(3)) with 2v(1) + v(2) = 1, 2, 3, and 4

For the first time, high-resolution Fourier transform spectra of HDSe in the region of the three polyads, nu(1)/2nu(2), nu(1) + nu(2)/3nu(2), and 2nu(1)/nu(1) + 2nu(2)/nu(2) + nu(3), have been recorded and analyzed. Combined with an earlier investigation of the nu(2) band, and including estimates for the unobserved "dark" 4nu(2) band, these levels were subjected to a "Global Fit," which makes use of relations between parameters within the different polyads. Since there are five isotopic species present in natural HD(M)Se (M = 82, 80, 78, 77, 76), altogether 34 vibration-rotation bands have been studied in the present contribution. The parameters determined by the Global Fit reproduce upper vibrational-rotational energies of all these bands with accuracies close to experimental precision. Copyright 2000 Academic Press.     

A New Class of Stable (2+1) Dimensional Thin Shell Wormhole

Few years ago, Bañados, Teitelboim and Zanelli (BTZ) (in Phys. Rev. Lett. 69:1849 (1992)) has discovered an explicit vacuum solution of (2+1)-dimensional gravity with negative cosmological constant. It has been argued that the existence of such physical systems with an event horizon and thermodynamic properties similar to (3+1) dimensional black holes. These vacuum solutions of (2+1)-dimensional gravity are asymptotically anti-de Sitter and are known as BTZ black holes. We provide a new type of thin-shell stable wormhole from the BTZ black holes. This is the first example of stable thin shell wormhole in (2+1)-dimension. Several characteristics of this thin-shell wormhole have been discussed.     

锰原子的二步多光子与三步三光子共振电离研究

激光共振电离技术是痕量分析中的重要手段之一。文章以速率方程理论为基础,对锰原子的激光共振电离过程进行了分析,讨论了电离过程中各级激发光功率密度及激光作用时间对电离效率的影响;提出了根据所要求的电离效率和激光作用时间计算所需要的各激发光或电离激光的功率密度的方法;得到了饱和激发或饱和电离的规律及阈值条件。研究发现,在激光作用时间为10 ns时,锰原子饱和电离的激光强度阈值基本都在108 W·cm-2的量级,只有“1+1”双色双共振低三个量级;而“1+1”和“1+1+1”饱和激发的激光强度阈值则在102～103 W·cm-2量级;并且随着激光作用时间的增加,各过程的饱和激发和饱和电离的激光强度阈值将单调减少。     

The Dynamics of Relativistic Strings Moving in the Minkowski Space $$\mathbb{R}^{1+n}$$

In this paper we investigate the dynamics of relativistic (in particular, closed) strings moving in the Minkowski space . We first derive a system with n nonlinear wave equations of Born-Infeld type which governs the motion of the string. This system can also be used to describe the extremal surfaces in . We then show that this system enjoys some interesting geometric properties. Based on this, we give a sufficient and necessary condition for the global existence of extremal surfaces without space-like point in with given initial data. This result corresponds to the global propagation of nonlinear waves for the system describing the motion of the string in . We also present an explicit exact representation of the general solution for such a system. Moreover, a great deal of numerical analyses are investigated, and the numerical results show that, in phase space, various topological singularities develop in finite time in the motion of the string. Finally, some important discussions related to the theory of extremal surfaces of mixed type in are given.     

Form-preserving Transformations for the Time-dependent Schrödinger Equation in (n + 1) Dimensions

We define a form-preserving transformation (also called point canonical transformation) for the time-dependent Schrödinger equation (TDSE) in (n+1) dimensions. The form-preserving transformation is shown to be invertible and to preserve L ²-normalizability. We give a class of time-dependent TDSEs that can be mapped onto stationary Schrödinger equations by our form-preserving transformation. As an example, we generate a solvable, time-dependent potential of Coulombic ring-shaped type together with the corresponding exact solution of the TDSE in (3+1) dimensions. We further consider TDSEs with position-dependent (effective) masses and show that there is no form-preserving transformation between them and the conventional TDSEs, if the spatial dimension of the system is higher than one.     

Letter: O(d + 1, d + n + 1)-Invariant Formulation of Stationary Heterotic String Theory

We present a pair of symmetric formulations of the matter sector of the stationary effective action of heterotic string theory that arises after the toroidal compactification of d dimensions. The first formulation is written in terms of a pair of matrix potentials Z ₁ and Z ₂ which exhibits a clear symmetry between them and can be used to generate new families of solutions on the basis of either Z ₁ or Z ₂; the second one is an O(d + 1, d + n + 1)-invariant formulation which is written in terms of a matrix vector W endowed with an O(d + 1, d + n + 1)-invariant scalar product which linearizes the action of the O(d + 1, d + n + 1)symmetry group on the coset space O(d + 1, d + n + 1)/[O(d + 1) × O(d + n + 1)]; this fact opens as well a simple solution-generating technique which can be applied on the basis of known solutions.     

Restitution in mapping models with an arbitrary amount of memory

Restitution, the characteristic shortening of action potential duration (APD) with increased heart rate, has been studied extensively because of its purported link to the onset of fibrillation. Restitution is often represented in the form of mapping models where APD is a function of previous diastolic intervals (DIs) and/or APDs, A(n+1)=F(D(n),A(n),D(n-1),A(n-1),...), where A(n+1) is the APD following a DI given by D(n). The number of variables previous to D(n) determines the degree of memory in the mapping model. Recent experiments have shown that mapping models should contain at least three variables (D(n),A(n),D(n-1)) to reproduce a restitution portrait (RP) that is qualitatively similar to that seen experimentally, where the RP shows three different types of restitution curves (RCs) [dynamic, S1-S2, and constant-basic cycle length (BCL)] simultaneously. However, an interpretation of the different RCs has only been presented in detail for mapping models of one and two variables. Here we present an analysis of the different RCs in the RP for mapping models with an arbitrary amount of memory. We determine the number of variables necessary to represent the different RCs in the RP. We also present a graphical visualization of these RCs. Our analysis reveals that the dynamic and S1-S2 RCs reside on two-dimensional surfaces, and therefore provide limited information for mapping models with more than two variables. However, constant-BCL restitution is a feature of the RP that depends on higher dimensions and can possibly be used to determine a lower bound on the dimensionality of cardiac dynamics.     

Electronic structure of charge- and spin-controlled Sr(1-(x+y))La(x+y)Ti(1-x)Cr(x)O3

We present the electronic structure of Sr(1-(x+y))La(x+y)Ti(1-x)Cr(x)O3 investigated by high-resolution photoemission spectroscopy. In the vicinity of the Fermi level, it was found that the electronic structure was composed of a Cr 3d local state with the t(2g)3 configuration and a Ti 3d itinerant state. The energy levels of these Cr and Ti 3d states are well interpreted by the difference of the charge-transfer energy of both ions. The spectral weight of the Cr 3d state is completely proportional to the spin concentration x irrespective of the carrier concentration y, indicating that the spin density can be controlled by x as desired. In contrast, the spectral weight of the Ti 3d state is not proportional to y, depending on the amount of Cr doping.