A framework for statistical modelling of plastic yielding initiated cleavage fracture of structural steels

The well established consensus that cleavage fracture is preceded by plastic deformation in structural steels implies that plastic yielding is the threshold stress state for a volume element to incur cleavage fracture. An accurate compliance with this consensus underlies the normalisation of cumulative cleavage fracture probability and the justification of constraint effect on cleavage fracture. These understandings lead to the proposal of a framework for statistical modelling of cleavage fracture in structural steels. The framework takes the spatial microcrack distribution into account to formulate the cumulative failure probability model that allows for a pertinent physical interpretation of Weibull statistics, and derives the fracture probability of an elemental volume in conformity with the yielding condition from a set of commonly adopted microcrack size or strength distributions. Alternative approaches to calibrating model parameters are suggested based on frequency analysis of brittle particles as cleavage initiators and on statistical analysis of cleavage fracture stress. The strict adherence to plastic yielding as a prerequisite to cleavage fracture also reveals the probabilistic nature of notch brittleness and ductile-to-brittle transition behaviour.     

Parton distribution functions and nuclear EMC effect in a statistical model

A new and simple statistical approach is performed to calculate the parton distribution functions (PDFs) of the nucleon in terms of light-front kinematic variables.Analytic expressions of x-dependent PDFs are obtained in the whole x region.And thereafter,we treat the temperature T as a parameter of the atomic number A to explain the nuclear EMC effect in the region x ∈ [0.2,0.7].We give the predictions of PDF ratios,and they are very different from those by other models,thus experiments aiming at measuring PDF ratios are suggested to provide a discrimination of different models.     

Parton distribution functions and nuclear EMC effect in a statistical model

A new and simple statistical approach is performed to calculate the parton distribution functions （PDFs） of the nucleon in terms of light-front kinematic variables.Analytic expressions of x-dependent PDFs are obtained in the whole x region.And thereafter,we treat the temperature T as a parameter of the atomic number A to explain the nuclear EMC effect in the region x ∈ [0.2,0.7].We give the predictions of PDF ratios,and they are very different from those by other models,thus experiments aiming at measuring PDF ratios are suggested to provide a discrimination of different models.     

Extraction of temperature dependences of small-signal model parameters in SiGe HBT HICUM model

In this work, temperature dependences of small-signal model parameters in the SiGe HBT HICUM model are presented. Electrical elements in the small-signal equivalent circuit are first extracted at each temperature, then the temperature dependences are determined by the series of extracted temperature coefficients, based on the established temperature formulas for corresponding model parameters. The proposed method is validated by a 1 × 0.2 × 16 μm~2 SiGe HBT over a wide temperature range(from 218 K to 473 K), and good matching is obtained between the extracted and modeled results. Therefore, we believe that the proposed extraction flow of model parameter temperature dependence is reliable for characterizing the transistor performance and guiding the circuit design over a wide temperature range.     

修正的混响多普勒扩展非对称统计模型

运动声源探测低速目标时,混响谱呈现的非对称性导致正负速度目标的回波具有不同的信混比,需要准确估计双边谱的扩展程度来分别设计检测策略,而传统的对称模型不能描述这种非对称性。基于双边指数分布对称模型,修正的非对称统计模型可用来描述由平台运动、海面运动等引起的混响谱非对称扩展现象。文中推导了非对称模型的数学表达式,并阐述了模型各参数的物理意义。运动声呐平台的湖试实验分析结果验证了该模型对平台在不同速度运动时引起的非对称混响谱都有较高的拟合度,证明混响谱负向多普勒扩展程度随平台运动速度提高而加剧,且非对称模型参数具有量化描述混响谱非对称扩展程度的能力。     

On the dependence of the critical temperature on pressure in the bisoliton model of high temperature superconductors

Abstract

In the framework of the bisoliton model we have studied the critical temperature T _c, as a function of the pressure P and of the hole concentration δ for the high temperature superconductors YBa₂Cu₃O_x and (La_1-xM_x)₂CuO₄. Our results for δ ln T_c/δ ln V as a function of T _c describe quite satisfactorily the general trend of the experimental data. Furthermore we show that in the bisoliton model the energy gap δ (in units of Jg³/3, where J is the nearest-neighbour exchange integral and g is the nonlinearity parameter) is an universal function of δ/g. An analogous property is valid for T _c By fitting the maximum value of T _c we are able also to reproduce the experimental data for T _c(δ).     

Isospin dependence of nuclear multifragmentation in statistical model

The evolution of nuclear disintegration mechanisms with increasing excitation energy, from com- pound nucleus to multifragmentation, has been studied by using the Statistical Multifragmentation Model (SMM) within a micro-canonical ensemble. We discuss the observable characteristics as functions of excitation energy in multifragmentation, concentrating on the isospin dependence of the model in its decaying mechanism and break-up fragment configuration by comparing the A<,0> = 200, Z<,0> = 78 and A<,0> = 200, Z<,0> = 100 systems. The calculations indicate that the neutron-rich system (Z<,0> = 78) translates to a fission-like process from evaporation later than the symmetric nucleus at a lower excitation energy, but gets a larger average multiplicity as the excitation energy increases above 1.0 MeV/u.     

Isospin dependence of nuclear multifragmentation in statistical model

The evolution of nuclear disintegration mechanisms with increasing excitation energy, from compound nucleus to multifragmentation, has been studied by using the Statistical Multifragmentation Model (SMM) within a micro-canonical ensemble. We discuss the observable characteristics as functions of excitation energy in multifragmentation, concentrating on the isospin dependence of the model in its decaying mechanism and break-up fragment configuration by comparing the A₀=200, Z₀=78 and A₀=200, Z₀=100 systems. The calculations indicate that the neutron-rich system (Z₀=78) translates to a fission-like process from evaporation later than the symmetric nucleus at a lower excitation energy, but gets a larger average multiplicity as the excitation energy increases above 1.0 MeV/u.     

氧化锌发光中心的统计力学模型

根据ZnO结构的两种空隙(四面体和多面体),提出了一种发光模型.用统计系综求得了上述两种填隙锌的数量计算公式.     

Continuity of the temperature and derivation of the Gibbs canonical distribution in classical statistical mechanics

For a classical system of interacting particles we prove, in the microcanonical ensemble formalism of statistical mechanics, that the thermodynamic-limit entropy density is a differentiable function of the energy density and that its derivative, the thermodynamic-limit inverse temperature, is a continuous function of the energy density. We also prove that the inverse temperature of a finite system approaches the thermodynamic-limit inverse temperature as the volume of the system increases indefinitely. Finally, we show that the probability distribution for a system of fixed size in thermal contact with a large system approaches the Gibbs canonical distribution as the size of the large system increases indefinitely, if the composite system is distributed microcanonically.Supported by The British Council and the Universidad Nacional Autónoma de México.     

考虑通孔效应和边缘传热效应的纳米级互连线温度分布模型

提出了同时考虑通孔效应和边缘传热效应的互连线温度分布模型,获得了适用于单层互连线和多层互连线温度分布的解析模型,并基于65 nm互补金属氧化物半导体（CMOS）工艺参数计算了不同长度单层互连线和多层互连线的温度分布.对于单层互连线,考虑通孔效应后中低层互连线的温升非常低,而全局互连线几乎不受通孔效应的影响,温升仍然很高.对于多层互连线,最上层互连线的温升最高,温升和互连介质层厚度近似成正比,而且互连介质材料热导率越低,温升越高.所提出的互连线温度分布模型,能应用于纳米级CMOS计算机辅助设计. 关键词： 通孔效应 边缘传热效应 纳米级互连线 温度分布模型     

Continuum model for dislocation dynamics in a slip plane

In this paper, we present a continuum model for dislocation dynamics in a slip plane, which accurately incorporates both the long-range interaction and the local line tension effect of dislocations. Unlike the continuum models in the literature using dislocation densities, we use the disregistry across the slip plane to represent the continuous distribution of dislocations in the slip plane, which has the advantage of including the orientation dependence of dislocations in a very simple way. The continuum dislocation dynamics model is validated by linear instability analysis of a uniform dislocation array to small perturbations and comparisons of the results with those of the discrete dislocation dynamics model. Numerical examples for the evolution of distributions of dislocations and plastic slips in a slip plane are presented.     

Upper bounds on the critical temperature for the two-dimensional Blume-Emery-Griffiths model

We obtain rigorous upper bounds for the critical temperature associated with second-order phase transitions of the two-dimensional spin-1 BEG model for real values ofK andD coupling constants and forJ0. We use some correlation equalities and inequalities to show the exponential decay of the two-point function characterizing the disordered phase.     

On the structure and chemistry of complex oxide nanofeatures in nanostructured ferritic alloy U14YWT

The remarkable radiation damage resistance of nanostructured ferritic alloys (NFAs) is attributed to the large numbers of matrix nanofeatures (NFs) of various types, which can enhance the recombination of displacement defects and trap transmutant helium in fine scale bubbles. Characterizing the chemistry, crystallographic structure and orientation relationships of the NFs is critical to understanding how they enhance the radiation damage resistance of NFAs. Conventional and high-resolution transmission electron microscopy and energy-dispersive spectroscopy were used to characterize the various types of NF and larger oxide phases in a model 14Cr–3?W–0.4Ti–0.25Y₂O₃ NFA (14YWT) hot isostatic pressed (HIP-ed) at 1150°C. Large CrTiO₃ precipitates (50–300?nm) and small diffracting NFs (<5?nm) were found in this alloy. One major new result is the observation of an additional type of nanofeature (10–50?nm), orthorhombic in structure, with a square center cross-section, which constitutes a new kind of Y–Ti-oxide phase with lattice parameters different from those of known Y and Ti complex oxides. The interfaces of these particles seem to be semicoherent, while manifesting a possible orientation relationship with the BCC matrix. The ratio of Y to Ti varies between <1 and 2 for these larger NFs.     

Bayes-optimal solution to inverse halftoning based on statistical mechanics of the Q-Ising model

On the basis of statistical mechanics of the Q-Ising model, we formulate the Bayesian inference to the problem of inverse halftoning, which is the inverse process of representing gray-scales in images by means of black and white dots. Using Monte Carlo simulations, we investigate statistical properties of the inverse process, especially, we reveal the condition of the Bayes-optimal solution for which the mean-square error takes its minimum. The numerical result is qualitatively confirmed by analysis of the infinite-range model. As demonstrations of our approach, we apply the method to retrieve a grayscale image, such as standard image Lena, from the halftoned version. We find that the Bayes-optimal solution gives a fine restored grayscale image which is very close to the original. In addition, based on statistical mechanics of the Q-Ising model, we are sucessful in constructing a practically useful method of inverse halftoning using the Bethe approximation.      

140A MeV~(40,48)Ca和~(58,64)Ni炮弹碎裂反应产物的统计擦碎模型计算

用统计擦碎模型计算了140AMeV40,48Ca+9Be和58,64Ni+9Be弹核碎裂反应产物的截面.通过对碎片截面计算结果和实验测量结果的比较发现,采用自由空间的核子-核子反应截面计算时,对非中心反应产物的截面拟合很好,而对中心反应产物的截面有较大高估,而采用饱和密度相关的核子-核子反应截面计算时,对非周边反应产物的截面拟合较好,而对周边反应产物的截面有一定程度的低估.在统计擦碎模型中,对核子-核子反应截面进行细致的介质密度关联,可能会改进计算值与实验值的符合程度.     

Deformation parameter changes in fission mass yields within the systematic statistical scission-point model

The fission fragment mass-yields are evaluated for pre-actinide and actinide isotopes using a systematic statistical scission point model. The total potential energy of the fissioning systems at the scission point is presented in approximate relations as functions of mass numbers,deformation parameters and the temperature of complementary fission fragments. The collective temperature, Tcoll, and the temperature of fission fragments, Ti, are separated and the effect of collective temperature on mass yields results is investigated. The fragment temperature has been calculated with the generalized superfluid model. The sum of deformation parameters of complementary fission fragments has been obtained by fitting the calculated results with the experimental data. To investigate the transitions between symmetric and asymmetric modes mass yields for pre-actinide and heavy actinides are calculated with this model. The transition from asymmetric to symmetric fission is well reproduced using this systematic statistical scission point model. The calculated results are in good agreement with the experimental data with Tcoll= 2 Me V at intermediate excitation energy and with T_(coll)= 1MeV for spontaneous fission.Despite the Langevin model, in the scission point model, a constraint on the deformation parameters of fission fragments has little effect on the results of the mass yield.     

On the temperature dependence of the mean number of clusters

The random variable number of cluster defined on the configurations of a ferromagnetic Ising model at zero field and inverse temperature on a graphG is considered. The Gibbs average at=0 is proved to be greater than the one at>0 if the degree ofG is not greater than 3.     

简单体系温度涨落的发散问题

平衡体系热力学推导涨落的前提是涨落必须很小，如果得到一个发散的结果说明这一涨落是不可靠的.对一些体系温度涨落的热力学结果，在温度趋于绝对零度时是发散的，这时必须用统计物理来处理.对这些体系进行统计物理处理的结果表明，涨落在温度趋于绝对零度时是趋于零的. 关键词： 热力学与统计物理 涨落