Comparison of shear banding in BMGs due to thermal-softening and free volume creation

This paper reports a comparative study of shear banding in BMGs resulting from thermal softening and free volume creation. Firstly, the effects of thermal softening and free volume creation on shear instability are discussed. It is known that thermal softening governs thermal shear banding, hence it is essentially energy related. However, compound free volume creation is the key factor to the other instability, though void-induced softening seems to be the counterpart of thermal softening. So, the driving force for shear instability owing to free volume creation is very different from the thermally assisted one. In particular, long wave perturbations are always unstable owing to compound free volume creation. Therefore, the shear instability resulting from coupled compound free volume creation and thermal softening may start more like that due to free volume creation. Also, the compound free volume creation implies a specific and intrinsic characteristic growth time of shear instability. Finally, the mature shear band width is governed by the corresponding diffusions (thermal or void diffusion) within the band. As a rough guide, the dimensionless numbers: Thermal softening related number B, Deborah number (denoting the relation of instability growth rate owing to compound free volume and loading time) and Lewis number (denoting the competition of different diffusions) show us their relative importance of thermal softening and free volume creation in shear banding. All these results are of particular significance in understanding the mechanism of shear banding in bulk metallic glasses (BMGs). Supported by the Chinese Academy of Sciences under the project “Multi-Scale Complex System” (Grant No. KJCX-SW-L08), the National Natural Science Foundation of China (Grant Nos. 10725211 and 10721202), and the Doctorial Start-up Fund of Hunan University of Science and Technology (Grant No. E50840)     

Quantum theory of transition radiation and transition pair creation

A theory of the transition radiation and the transition pair creation is developed in the frame of QED. The spectral-angular distributions of probability of the transition radiation and of the transition pair creation are found. The total energy losses of an electron and the total probability of pair creation by a photon are calculated and analyzed. Features of radiation and pair creation processes in a superdense medium (typical for white dwarfs) are discussed.     

Thermodynamics of the Bulk Viscous Cosmological Fluid in Presence of the Particle Creation Pressure

In the present work, we consider FRW metric and investigate some cosmological quantities in presence of bulk viscosity and particle creation pressure. The obtained results for a viscous cosmological fluid with particle creation show that the Hubble expansion parameter, energy density, bulk viscosity pressure, creation pressure and temperature depend on the particle creation rate and increase with increasing particle creation coefficient. It is found that the bulk viscosity and particle creation pressure seem to play important roles in the evolution of the early Universe.     

Degree distributions of growing networks

The in-degree and out-degree distributions of a growing network model are determined. The in-degree is the number of incoming links to a given node (and vice versa for out-degree). The network is built by (i) creation of new nodes which each immediately attach to a preexisting node, and (ii) creation of new links between preexisting nodes. This process naturally generates correlated in-degree and out-degree distributions. When the node and link creation rates are linear functions of node degree, these distributions exhibit distinct power-law forms. By tuning the parameters in these rates to reasonable values, exponents which agree with those of the web graph are obtained.     

大学物理实验中的创新设计方法及应用研究

大学物理实验运用原理应用设计法、联想类比设计法、改进设计法、变异设计法、组合设计法等创新设计方法。掌握这些方法可以提升大学生的创新设计能力,为后续课程的学习和将来的工作打下良好基础。     

O(3)-invariant tunneling in general relativity

We derived a general formula for the action for any O(3)-invariant tunneling processes in false vacuum decay in general relativity. The general classification of the bubble euclidean trajectories is elaborated and explicit expressions for bounces for some processes like the vacuum creation of a double bubble in particular in the vicinity of a black hole, the subbarrier creation of the Einstein-Rosen bridge, creation from nothing of two Minkowski worlds connected by a shell, etc., are given.     

共轭高分子中激子形成的非绝热动力学研究

有机共轭高分子被光激发后,其电子结构会发生明显的变化,通过非绝热数值计算的方法模拟了受光激发后有机高分子中激子生成的动力学过程.结果表明,激子的生成一般需要数十飞秒时间,激子的生成周期随分子链长度的增大而增大.高激发态激子可以根据生成周期分为两类,第一类激子的生成周期在数十到上百飞秒之间,第二类激子的生成周期可达上千飞秒.对于超过200个碳原子的高分子,第二类激子的生成周期可达5000飞秒以上.这个计算结果说明,相比于有机高分子,有机小分子中更容易观测到激子.     

Nitric oxide flow tagging in unseeded air

A scheme for molecular tagging velocimetry is presented that can be used in air flows without any kind of seeding. The method is based on the local and instantaneous creation of nitric oxide (NO) molecules from N(2) and O(2) in the waist region of a focused ArF excimer laser beam. This NO distribution is advected by the flow and can be visualized any time later by laser-induced fluorescence in the gamma bands. The creation of NO is confirmed by use of an excitation spectrum. Two examples of the application of the new scheme for air-flow velocimetry are given in which single laser pulses are used for creation and visualization of NO.     

A new creation cosmology

A new conformal creation field cosmology is considered and it is found that a negative energy scalar field nonminimally coupled to the gravitational field gives rise to creation and, in contrast to Hoyle-Narlikar theory, no a priori assumption about the rate of creation is required to solve the field equations.     

Photon energy dependence of SW effect in a-Si:H films

In order to explore the creation process of Staebler-Wronski (SW) defect in a-Si: H films. We investigated the effect of monochromatic light exposure with different photon energies: 2.54, 1.96, 1.17 and 0.95 eV. The experimental results show that threshold energy for SW defect creation is around 1.17 eV.     

Bethe Vectors of the osp(1|2) Gaudin Model

The eigenvectors of the osp(1|2) invariant Gaudin Hamiltonians are found using explicitly constructed creation operators. Commutation relations between the creation operators and the generators of the loop superalgebra are calculated. The coordinate representation of the Bethe states is presented. The relation between the Bethe vectors and solutions to the Knizhnik–Zamolodchikov equation yields the norm of the eigenvectors.     

Quark pair creation in color electric fields and effects of magnetic fields

The time evolution of a system where a uniform and classical SU(3) color electric field and quantum fields of quarks interact with each other is studied focusing on non-perturbative pair creation and its back reaction. We characterize a color direction of an electric field in a gauge invariant way, and investigate its dependence. Momentum distributions of created quarks show plasma oscillation as well as quantum effects such as the Pauli blocking and interference. Pressure of the system is also calculated, and we show that pair creation moderates degree of anisotropy of pressure. Furthermore, enhancement of pair creation and induction of chiral charge under a color magnetic field which is parallel to an electric field are discussed.     

Some remarks on spinor particle pair creation in alternating homogeneous external field

It is shown that the dynamical symmetry group of the problem of spinor particle pair creation in alternating homogeneous external field is the SO (5) group. The probability of pair creation is given by the modulus square of the matrix element of spinor representation of this group.     

Switched wave packets: a route to nonperturbative quantum control

The dynamic Stark effect due to a strong nonresonant but nonionizing laser field provides a route to quantum control via the creation of novel superposition states. We consider the creation of a field-free "switched" wave packet through adiabatic turn-on and sudden turn-off of a strong dynamic Stark interaction. There are two limiting cases for such wave packets. The first is a Raman-type coupling, illustrated by the creation of field-free molecular axis alignment. An experimental demonstration is given. The second case is that of dipole-type coupling, illustrated by the creation of charge localization in an array of quantum wells.     

Scale-covariant gravitation and electromagnetism

The theory of scale-covariant gravity is extended to include charged matter and electromagnetism at the classical level. The possibility of charge creation exists and the creation rate of charge differs from the creation rate of matter. A variational principle for scale-covariant gravity and electromagnetism coupled to a charged perfect fluid is given.Supported by a grant from the National Research Council of Canada.     

Formation of the 1∶2∶3 structure in Y-Ba-Cu(Fe)-O system studied by Mössbauer spectroscopy

Annealing time and temperature dependence of Y, Ba, Cu, Fe nitrade mixture towards new phases creation was revealed by Mössbauer spectroscopy. The observed changes can be assigned to chemical decomposition of corresponding nitrades and creation of intermedial and final Y₁Baz(Cuo.o3Feo. o3)3Ox phase.     

The supersymmetric Casimir effect and quantum creation of the universe with nontrivial topology

We estimate the probability of quantum creation of the universe, having the spatial topology (S¹)³, and filled with the fields of minimal N = 1 supergravity, in the semiclassical approximation. After creation, inflation of the universe occurs due to the topological Casimir effect. Creation of the universe with an isotropic topology is found to be the most preferable.     

Fock-type representation of the Lie superalgebraA(0, 1)

A Fock space of two pairs of generalized creation and annihilation operators is constructed. These operators belong to the odd part of the Lie superalgebraA(0, 1) and generate the whole algebra. The creation and annihilation operators define in the Fock space an infinite-dimensional irreducible representation of the algebraA(0, 1).     

Dynamically assisted Schwinger mechanism

We study electron-positron pair creation from the Dirac vacuum induced by a strong and slowly varying electric field (Schwinger effect) which is superimposed by a weak and rapidly changing electromagnetic field (dynamical pair creation). In the subcritical regime where both mechanisms separately are strongly suppressed, their combined impact yields a pair creation rate which is dramatically enhanced. Intuitively speaking, the strong electric field lowers the threshold for dynamical particle creation--or, alternatively, the fast electromagnetic field generates additional seeds for the Schwinger mechanism. These findings could be relevant for planned ultrahigh intensity lasers.     

Creation of vector bosons by an electric field in curved spacetime

We investigate the creation rate of massive spin-1 bosons in the de Sitter universe by a time-dependent electric field via the Duffin–Kemmer–Petiau (DKP) equation. Complete solutions are given by the Whittaker functions and particle creation rate is computed by using the Bogoliubov transformation technique. We analyze the influence of the electric field on the particle creation rate for the strong and vanishing electric fields. We show that the electric field amplifies the creation rate of charged, massive spin-1 particles. This effect is analyzed by considering similar calculations performed for scalar and spin-1/2$1/2$ particles.