Short-Range Spin Glasses and Random Overlap Structures

Properties of Random Overlap Structures (ROSt)’s constructed from the Edwards-Anderson (EA) Spin Glass model on ℤ ^d with periodic boundary conditions are studied. ROSt’s are ℕ×ℕ random matrices whose entries are the overlaps of spin configurations sampled from the Gibbs measure. Since the ROSt construction is the same for mean-field models (like the Sherrington-Kirkpatrick model) as for short-range ones (like the EA model), the setup is a good common ground to study the effect of dimensionality on the properties of the Gibbs measure. In this spirit, it is shown, using translation invariance, that the ROSt of the EA model possesses a local stability that is stronger than stochastic stability, a property known to hold at almost all temperatures in many spin glass models with Gaussian couplings. This fact is used to prove stochastic stability for the EA spin glass at all temperatures and for a wide range of coupling distributions. On the way, a theorem of Newman and Stein about the pure state decomposition of the EA model is recovered and extended.     

Exterior and interior metrics with quadrupole moment

We present the Ernst potential and the line element of an exact solution of Einstein’s vacuum field equations that contains as arbitrary parameters the total mass, the angular momentum, and the quadrupole moment of a rotating mass distribution. We show that in the limiting case of slowly rotating and slightly deformed configuration, there exists a coordinate transformation that relates the exact solution with the approximate Hartle solution. It is shown that this approximate solution can be smoothly matched with an interior perfect fluid solution with physically reasonable properties. This opens the possibility of considering the quadrupole moment as an additional physical degree of freedom that could be used to search for a realistic exact solution, representing both the interior and exterior gravitational field generated by a self-gravitating axisymmetric distribution of mass of perfect fluid in stationary rotation.     

How accurate is the cancelation of the first even zonal harmonic of the geopotential in the present and future LAGEOS-based Lense-Thirring tests?

The strategy followed so far in the performed or proposed tests of the general relativistic Lense-Thirring effect in the gravitational field of the Earth with laser-ranged satellites of LAGEOS type relies upon the cancelation of the disturbing huge precessions induced by the first even zonal harmonic coefficient J ₂ of the multipolar expansion of the Newtonian part of the terrestrial gravitational potential by means of suitably designed linear combinations of the nodes Ω of more than one spacecraft. Actually, such a removal does depend on the accuracy with which the coefficients of the combinations adopted can be realistically known. Uncertainties of the order of 2 cm in the semimajor axes a and 0.5 milliarcseconds in the inclinations I of LAGEOS and LAGEOS II, entering the expression of the coefficient c ₁ of the combination of their nodes used so far, yield an uncertainty δc ₁ = 1.30 × 10⁻⁸. It gives an imperfectly canceled J ₂ signal of 10.8 milliarcseconds per year corresponding to 23% of the Lense-Thirring signature. Uncertainties of the order of 10–30 microarcseconds in the inclinations yield δc ₁ = 7.9 × 10⁻⁹ which corresponds to an uncanceled J ₂ signature of 6.5 milliarcseconds per year, i.e. 14% of the Lense-Thirring signal. Concerning a future LAGEOS-LAGEOS II-LARES combination with coefficients k ₁ and k ₂, the same uncertainties in a and the less accurate uncertainties in I as before yield δk ₁ = 1.1 × 10⁻⁸, δk ₂ = 2 × 10⁻⁹; they imply a residual J ₂ combined precession of 14.7 milliarcseconds per year corresponding to 29% of the Lense-Thirring trend. Uncertainties in the inclinations at ≈ 10 microarcseconds level give δk ₁ = 5 × 10⁻⁹, δk ₂ = 2 × 10⁻⁹; the uncanceled J ₂ effect is 7.9 milliarcseconds per year, i.e. 16% of the relativistic effect.     

Thermodynamics of Lema$$\hat{i}$$ tre−Tolman−Bondi Model

Here we consider our universe as inhomogeneous spherically symmetric Lema [^(i)]{\hat{i}} tre−Tolman−Bondi Model and analyze the thermodynamics of this model of the universe. The trapping horizon is calculated and is found to coincide with the apparent horizon. The Einstein field equations are shown to be equivalent with the unified first law of thermodynamics. Finally assuming the first law of thermodynamics validity of the generalized second law of thermodynamics is examined at the apparent horizon for the perfect fluid and at the event horizon for holographic dark energy.     

基于GUI的阿贝-波特滤波实验的计算机仿真

介绍了阿贝-波特空间滤波的实验原理,在Matlab环境下建立了带有图形用户界面（GUI）的计算机仿真平台.不仅可以准确地完成针对不同输入图像、不同滤波要求的滤波过程,还可以通过调整滤波器参数观察滤波效果的差异,形象地展现光学空间滤波过程的物理本质,提高教学效果.     

LabVIEW与Matlab在信息光学教学中的应用

计算机仿真技术已经被广泛应用到教学和科研中.将LabVIEW和Matlab引入信息光学课程教学中,通过设计相关的程序,可使复杂的物理理论以形象直观的实验仿真表现出来.经过实践证明,该措施可提高学生的学习兴趣和教学质量.     

随机取向双层椭球粒子偏振散射特性研究

基于T矩阵方法,给出了随机取向、轴对称、含核椭球粒子的散射计算方法.散射体的核和外壳均可为非球形粒子,整个粒子具有轴对称性.以含核椭球粒子为模型,计算了含有吸收性内核(黑炭,black carbon)的水凝物气溶胶的散射特性,分析了核的大小、形状对消光系数、散射系数、吸收系数、不对称因子、单次散射反照率以及Muller矩阵等的影响. 关键词： 光散射 T矩阵 Muller矩阵 椭球粒子     

Neutron diffraction study on composite compound Nd2Co7

The crystallographic and the magnetic structures of the composite compound Nd₂Co₇ at 300 K are investigated by a combined refinement of X-ray diffraction data and high-resolution neutron diffraction data. The compound crystallizes into a hexagonal Ce₂Ni₇-type structure and consists of alternately stacking MgZn₂-type NdCo₂ and CaCu₅-type NdCo₅ structural blocks along the c axis. A magnetic structure model with the moments of all atoms aligning along the c axis provides a satisfactory fitting to the neutron diffraction data and coincides with the easy magnetization direction revealed by the X-ray diffraction experiments on magnetically pre-aligned fine particles. The refinement results show that the derived atomic moments of the Co atoms vary in a range of 0.7 μ_B-1.1 μ_B and the atomic moment of Nd in the NdCo₅ slab is close to the theoretical moment of a free trivalent Nd³⁺ ion, whereas the atomic moment of Nd in the NdCo₂ slab is much smaller than the theoretical value for a free Nd³⁺ ion. The remarkable difference in the atomic moment of Nd atoms between different structural slabs at room temperature is explained in terms of the magnetic characteristics of the NdCo₂ and NdCo₅ compounds and the local chemical environments of the Nd atoms in different structural slabs of the Nd₂Co₇ compound.     

Matrix theory of gravitation

A new classical theory of gravitation within the framework of general relativity is presented. It is based on a matrix formulation of four-dimensional Riemann-spaces and uses no artificial fields or adjustable parameters. The geometrical stress-energy tensor is derived from a matrix-trace Lagrangian, which is not equivalent to the curvature scalar R. To enable a direct comparison with the Einstein-theory a tetrad formalism is utilized, which shows similarities to teleparallel gravitation theories, but uses complex tetrads. Matrix theory might solve a 27-year-old, fundamental problem of those theories (Sect. 4.1). For the standard test cases (PPN scheme, Schwarz schild-solution) no differences to the Einstein-theory are found. However, the matrix theory exhibits novel, interesting vacuum solutions.     

Three-dimension direct writing TiO<Subscript>2</Subscript> crystalline patterns in Bi-free glass using femtosecond laser

Crystalline TiO₂ was induced three dimensionally inside Bi-free glass sample by an 800 nm, 250-kHz femtosecond laser irradiation. Micro-Raman spectra analysis indicated that the laser-induced crystals in the focal point of the laser beam were monophase TiO₂ rutile. Continuous crystalline lines were written through moving the focal point of the laser beam inside the glass. The results demonstrate that this technique is a convenient method to engrave three-dimensional patterns of crystals for fabricating integrated optical devices in transparent materials.