Quantifying the grain boundary resistance against slip transfer by experimental combination of geometric and stress approach using stage-I-fatigue cracks

In recent studies, many groups have investigated the interaction of dislocations and grain boundaries by bi-crystals and micro-specimen experiments. Partially, these experiments were combined with supplementary simulations by discrete dislocation dynamics, but quantitative data for the grain boundary resistance against slip transfer is still missing. In this feasibility study with first results, we use stage-I-fatigue cracks as highly localised sources for dislocations with well-known Burgers vectors to study the interaction between dislocations in the plastic zone in front of the crack tip and selected grain boundaries. The stress concentration at the grain boundary is calculated with the dislocation-free zone model of fracture using the dislocation density distribution in the plastic zone from slip trace height profile measurements by atomic force microscopy. The grain boundary resistance values calculated from common geometric models are compared to the local stress distribution at the grain boundaries. Hence, it is possible to quantify the grain boundary resistance and to combine geometric and stress approach for grain boundary resistance against slip transfer to a self-contained concept. As a result, the prediction of the grain boundary resistance effect based on a critical stress concept is possible with knowledge of the geometric parameters of the grain boundary only, namely the orientations of both participating grains and the orientation of the grain boundary plane.     

纳米器件电流噪声的散射理论统一模型研究

传统散射理论在研究器件噪声特性时,并没有考虑非相干输运和库仑作用对散粒噪声的抑制,而在实际纳米器件中这两种效应不可忽略.本文基于散射区等效接触端模型推导了考虑上述两种效应的电流噪声散射理论统一模型,该模型适用于从相干输运到非相干输运的整个输运区,并同时考虑了泡利不相容原理和库仑作用对散粒噪声的抑制.本文也提出了一种基于统一模型的电流噪声数值模拟方法,该方法所得散射区特性与散射区等效接触端模型特性一致. 关键词： 电流噪声 散射理论 统一模型     

Nonlinear phase field theory for fracture and twinning with analysis of simple shear

A phase field theory for coupled twinning and fracture in single crystal domains is developed. Distinct order parameters denote twinned and fractured domains, finite strains are addressed and elastic nonlinearity is included via a neo-Hookean strain energy potential. The governing equations and boundary conditions are derived; an incremental energy minimization approach is advocated for prediction of equilibrium microstructural morphologies under quasi-static loading protocols. Aspects of the theory are analysed in detail for a material element undergoing simple shear deformation. Exact analytical and/or one-dimensional numerical solutions are obtained in dimensionless form for stress states, stability criteria and order parameter profiles at localized fractures or twinning zones. For sufficient applied strain, the relative likelihood of localized twinning vs. localized fracture is found to depend only on the ratio of twin boundary surface energy to fracture surface energy. Predicted criteria for shear stress-driven fracture or twinning are often found to be in closer agreement with test data for several types of real crystals than those based on the concept of theoretical strength.     

A unified dynamic scaling property for the unified hybrid network theory framework

In this article, we present a new type of unified dynamic scaling property for synchronizability, which can describe the scaling relationship between dynamic synehronizability and four hybrid ratios under the unified hybrid network theory framework （UHNTF）. Our theory results can not only be applied to judge and analyze dynamic synehronizability for most of complex networks associated with the UHNTF, but also we can flexibly adjust and design different hybrid ratios and sealing exponent to meet actual requirement for the dynanfic characteristics of the UHNTF.     

A perturbation density functional theory for hydrogen bonding cyclic molecules

Using the framework of Wertheim's thermodynamic perturbation theory, a new polyatomic density functional theory is developed to account for the intermolecular association of cyclic molecules in interfacial systems. To test the theory, Monte Carlo simulations in the canonical ensemble were performed for the specific case of an associating triatomic ring with one association site next to a hard wall. The theory and simulation results were found to be in good agreement.     

A simplified shear and normal deformations nonlocal theory for bending of nanobeams in thermal environment

This article presents a simplified three-unknown shear and normal deformations nonlocal beam theory for the bending analysis of nanobeams in thermal environment. Eringen's nonlocal constitutive equations are considered in the analysis. Governing equations are derived according to the present refined theory using Hamilton's principle. Central deflections of nanobeams under uniform and point loads are given and compared with the available ones in the literature. Additional results of displacement and stresses are presented for future comparison. The effects of nonlocality, temperature parameters, length of beam, length-to-depth ratio as well as shear and normal strains are all investigated.     

对称型闪耀光栅的矢量模态理论

本文将满足均匀矢量亥姆霍兹方程的标准矢量波函数作为基矢对对称型闪耀光栅槽内、外的电磁场分别进行矢量模式和矢量平面波展开。然后通过在槽内外分界面上的场耦合条件得到一组振幅系数方程组。从方程组中求解出相应的振幅系数,就可研究光栅的衍射场分布。该方法适用于对称型闪耀光栅对任意入射方向、任意偏振态入射场衍射问题的研究。在K_2=0入射情况下,其振幅方程组与已发表的文献[6]相同。     

A numerical analytic method for electromagnetic radiation accompanying with fracture of rocks

This paper studies Rabinovitch’s compression experiments on granite and chalk and proposes an oscillating dipole model to analyse and simulate the electromagnetic radiation phenomenon caused by fracture of rocks. Our model assumes that the electromagnetic radiation pulses are initiated by vibrations of the charged rock grains on the tips of the crack. The vibrations of the rock grains are stimulated by the pulses of the cracks. Our simulations show comparable results with Rabinovitch’s compression experiments. From the simulation results, it verifies an assumption that the crack width is inversely proportional to the circular frequency electromagnetic radiation, which is presented by Rabinovitch et al. The simulation results also imply that, by using our oscillating dipole model together with Rabinovitch’s two equations about the crack length and crack width, we can quantitatively analyse and simulate the electromagnetic radiation phenomenon, which is induced from the fracture of the rocks.     

回旋行波管多模稳态理论及初步应用

建立了一种回旋行波管的多模稳态理论.利用该理论研究了输入功率和引导中心半径变化对回旋返波振荡的抑制作用,发现两者单独作用都在一定程度上可以减弱返波振荡,但两者的共同作用对改善工作模式输出性能和稳定性更有效.     

A new Cellular Automata Model including a decelerating damping effect to reproduce Kerner’s three-phase theory

Most of the conventional traffic Cellular Automaton (CA) models based on the Nagel-Schreckenberg model (NaSch model) have two problems: an unrealistic deceleration dynamics when a vehicle agent collides with a preceding vehicle in a stopping event, and the problem with reproducing the synchronized flow in Kerner’s three-phase theory. In this paper, a revised stochastic Nishinari-Fukui-Schadschneider (S-NFS) model, belonging to the class of NaSch models, is presented. The proposed CA model, where a random braking effect is improved by considering the dependency on the velocity difference and heading distance with a preceding vehicle, is confirmed to overcome the two above-mentioned drawbacks.     

Dilute-crack approximations for damage and fracture in disordered structures

Quenched disorder in local breaking thresholds within a two-dimensional lattice is studied, using dilute-crack approximations. Two different failure criteria are compared. Application of classical theory of strength, instead of fracture mechanics energy balance criterion, yields two times greater critical crack length, and two times greater amount of damage, in the case of failure threshold distributions without nonzero lower cutoff. Upper bounds of threshold distributions chosen correspondingly, critical voltages become similar. Normalized distribution of crack sizes appears to be independent of the applied mesoscopic failure criterion, as well as of the details of the distribution of the values for the failure threshold.     

Theoretical study on stability,mechanical properties and thermodynamic parameters of the orthorhombic-A2N2O (A=C,Si and Ge)

The structural stability, mechanical properties and thermodynamic parameters such as Debye temperature, minimum thermal conductivities of orthorhombic-A₂N₂O (A=C, Si and Ge) are calculated by first principles calculations based on density functional theory. The calculated lattice parameters, elastic constants of Si₂N₂O and Ge₂N₂O using PBEsol function are consisted with the experimental data and other calculated values. The full set elastic constants of the orthorhombic-A₂N₂O (A=C, Si and Ge) are calculated by stress–strain method. The mechanical moduli (bulk modulus, shear modulus and Young's modulus) are evaluated by the Voigt–Reuss–Hill approach. The orthorhombic-C₂N₂O exhibits larger mechanical moduli than the other two structures. The hardness of orthorhombic-A₂N₂O (A=C, Si and Ge) is evaluated according to the intrinsic hardness calculation theory of covalent crystal relying on Mulliken overlap population. The results indicate that the orthorhombic-C₂N₂O is a super hard material. Furthermore, the mechanical anisotropy, Debye temperature and minimum thermal conductivity of the orthorhombic-A₂N₂O (A=C, Si and Ge) have been estimated by empirical methods. The orthorhombic-Ge₂N₂O shows the lowest thermal conductivity, which may have useful applications as gas turbine engines and diesel engines.     

Why is nacre strong? Elastic theory and fracture mechanics for biocomposites with stratified structures

Nacre, stratified ceramic layers surrounded by organic matrix, is a tough material found inside certain seashells. We construct a coarse-grained elastic energy for such an anisotropic system and present an analytic solution for a notch crack normal to the stratified sheets. This analysis proves the reduction in stress concentration which was announced in our earlier work (P. G. de Gennes and K. Okumura, C. R. Acad. Sci. Paris 1, Ser. IV, 257 (2000)) and the related increase in toughness. Received 18 March 2000     

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.     

Quantum field theory analysis of polarizations correlations,entanglement and Bell's inequality: explicit processes

This paper provides explicit and detailed quantum field theory (QFT) computations of polarizations correlations of emerging particles in several processes in QED, Electroweak Theory, and even in particle productions from strings, and hence are based on dynamical theries. The novel properties observed in the computations of such polarizations correlations, as predicted by QFT, is that they depend on the speed of the colliding particles, and, in some cases, even on coupling parameters ratios as well as on mass ratios of the underlying theory. These investigations clearly show that arguments based simply on combining spins to generate probabilities of such polarization correlations are not reliable. The novel properties obtained, with details of derivations provided here, hopefully would call for experiments on polarizations correlations which would monitor speeds of colliding particles, and, would, in turn, lead to new tests of the fundamental interactions of QFT such as of QED and of the Electroweak Theory.     

Many‐body Green's function theory for thin ferromagnetic films: exact treatment of the single‐ion anisotropy

A theory for the magnetization of ferromagnetic films is formulated within the framework of many‐body Green's function theory which considers all components of the magnetization. The model Hamiltonian includes a Heisenberg term, an external magnetic field, a second‐ and fourth‐order uniaxial single‐ion anisotropy, and the magnetic dipole‐dipole coupling. The single‐ion anisotropy terms can be treated exactlyby introducing higher‐order Green's functions and subsequently taking advantage of relations between products of spin operators which leads to an automatic closure of the hierarchy of the equations of motion for the Green's functions with respect to the anisotropy terms. This is an improvement on the method of our previous work, which treated the corresponding terms only approximately by decoupling them at the level of the lowest‐order Green's functions. RPA‐like approximations are used to decouple the exchange interaction terms in both the low‐order and higher‐order Green's functions. As a first numerical example we apply the theory to a monolayer for spin S = 1 in order to demonstrate the superiority of the present treatment of the anisotropy terms over the previous approximate decouplings.     

Application of network theory for the description of nanocluster distributions in ion track electronics

The recently developed ion track-based electronic structures of the TEMPOS type have often been filled up with (semi)conducting nanoclusters (NCs) to optimize their operation. Network theory is applied here for the first time to describe the distribution of the ion tracks and the NC, and of the current paths followed by the latter ones. The presence of ion tracks makes the NC distribution deviate from the purely random distribution. The theory is used to calculate the electrical surface currents around a given contact. A radius of influence (ROI) around such a contact can be defined, beyond which the surface currents become negligible. ROI depends on track density, NC density and on the working point of the electronic device.     

First principles study of structural,electronic, mechanical and thermal properties of A15 intermetallic compounds Ti3X (X=Au,Pt, Ir)

The structural, electronic, elastic, mechanical and thermal properties of Ti₃Au, Ti₃Pt and Ti₃Ir intermetallic compounds crystallizing in A15 structure have been studied using density functional theory within generalized gradient approximation (GGA) for the exchange correlation potential. Elastic properties such as Young's modulus (E), rigidity modulus (G), bulk modulus (B), Poisson's ratio (σ) and elastic anisotropic factor (A) have been calculated. From the present study it is noted that Ti₃Ir is the hardest compound among the three materials studied due to its larger bulk modulus. Also, it is more ductile in nature.