压电驱动器布置对光栅拼接误差的影响

分析了两种光栅拼接调整机构（三角形和L形）,利用有限元分析软件对这两种光栅调整机构进行了模态分析和优化分析设计。相同光栅尺寸下（以口径为450 mm420 mm60 mm光栅为例）,驱动器三角形分布的固有频率与L形分布的固有频率相差无几,一阶频率分别为58.816 Hz和58.864 Hz。对两种驱动器布置方式引入的误差进行了分析比较,计算结果表明:三角形调整机构的最大误差比L形的大,同时三角形分布控制算法较L形的复杂。在主动控制中三角形模型误差迭代次数多,不利于控制。因此L形的压电驱动器布置方式优于三角形。     

Stress-based crystal analysis of yielding in rolled Mg AZ31B

A stress-based analysis is demonstrated that can be used to evaluate the effect of material orientation and loading conditions on the micro- and macro-scale yield response of strongly textured metals. This analysis is used to construct microscale yield surfaces for selected deformation mechanisms in rolled AZ31B. Two-dimensional projections of these surfaces are plotted along sample directions to quantify the relative activity of each mechanism for various loading conditions. By assigning each mechanism realistic strengths, the analysis is used to quantify the influence of each deformation mechanism on macroscale yield behaviour. Due to its simplicity, this analysis can be easily carried out to probe and visualize projections of material response in any part of stress space given the material’s texture, its relevant deformation mechanisms and realistic initial strengths of these mechanisms.     

Mechanisms of the strain-induced dissolution of phases in nanostructured metals

The possible mechanisms of the strain-induced dissolution of phases in metals subjected to severe plastic deformation have been investigated. The mechanisms of impurity absorption by new interphase and grain boundaries formed under severe plastic deformation and the high-temperature phase at its strain-induced nucleation are shown to be the most effective. The possible dislocation mechanisms of phase dissolution are low-efficient. In carbon steels, the strain-induced dissolution of cementite continues until the limiting nanostructure absorbs about 10–12 at % carbon from the mixture volume.     

Membrane potential detection with second-harmonic generation and two-photon excited fluorescence: A theoretical comparison

We theoretically compare the performance of TPEF and SHG microscopy for membrane potential imaging. We argue that electrochromic TPEF and SHG membrane potential responses are reflections of the same phenomenon, and can be described in a unified manner as resulting from the linear Stark effect. We also show that TPEF and SHG exhibit similar sensitivities in the case of both electrochromic and orientational response mechanisms. Despite their similar sensitivities, SHG nevertheless presents advantages over TPEF for membrane potential imaging because of its remarkable spatial and spectral contrast, and because of its insensitivity to non-radiative excited-state damping mechanisms.     

Microstructural peculiarities of copper and mechanisms of its hardening after mechanical activation and torsion in Bridgman anvils

The paper presents the results of complex research on microstructural peculiarities of copper and mechanisms of its hardening after mechanical activation in planetary ball mills, high-pressure torsion, and combined treatment which includes mechanical activation and subsequent consolidation under high-pressure torsion in Bridgman anvils. The main structural factors responsible for the hardening mechanisms are discussed depending on the pattern and degree of deformation.     

Supersymmetry breaking

We review the various mechanisms of supersymmetry breaking and its transmission to the observable sector. We argue that hybrid models where gauge dominates over gravity mediation, but gravity provides the main contributions to the Higgs sector masses and the neutralino mass, are able to combine the advantages and reduce the disadvantages of the two transmission mechanisms.      

Modeling complex diffusion mechanisms in L1 2 -structured compounds

We report on a procedure developed to create stochastic models of hyperfine interactions for complex diffusion mechanisms and demonstrate its application to simulate perturbed angular correlation spectra for the divacancy and 6-jump cycle diffusion mechanisms in L1₂-structured compounds.     

The relaxations of temporal bond polarizabilities of methylviologen adsorbed on the Ag electrode by 514.5 nm excitation: a Raman intensity study

An algorithm to elucidate the temporal bond polarizabilities from the surface enhanced Raman (SERS) intensities was employed to the case of methylviologen (MV) adsorbed on the Ag electrode. This enables us to obtain the properties of its SERS mechanisms and the effect of its adsorption. The analysis shows that the charge transfer and electromagnetic mechanisms involving in this MV SERS system possess different relaxation times for its various temporal bond polarizabilities. The physics is that the process involved in the charge transfer mechanism will take longer time than that involved in the electromagnetic mechanism since it needs more time to redistribute the charges during relaxation. The time division between these two mechanisms is figured out to be around 3 ps for this system. Adsorption also enhances the relaxation of the temporal bond polarizabilities, in general. The adsorption effect is indicated by the temporal bond polarizabilities close to the final stage of relaxation. They are, in fact, the quantities parallel to the bond electronic densities in the molecular orbital (MO) concept. For comparison, the case of MV solid was also analyzed. Copyright © 2008 John Wiley & Sons, Ltd.     

Universal behavior of the upper critical field in iron-based superconductors

The newly discovered iron-based high temperature superconductors have demonstrated rich physical properties. Here we give a brief review on the recent studies of the upper critical field and its anisotropy in a few typical series of the iron-based superconductors (FeSCs). In spite of their characters of a layered crystal structure, all the FeSCs possess an extremely large upper critical field and a weak anisotropy of superconductivity, being unique among the layered superconductors. These particular properties indicate potential applications of the FeSCs in the future. Based on the experimental facts of the FeSCs, we will discuss the possible mechanisms of pair breaking in high magnetic fields and its restrictions on the theoretical analysis of the superconducting pairing mechanisms.     

Review on ionization and quenching mechanisms of Trichel pulse

Trichel pulse is a kind of pulsed mode in negative DC corona discharge, which has attracted significant attention because of its considerable applications in industry. Over eighty years, plenty of effort including simulations and experiments has been spent to reveal the ionization and quenching mechanisms of Trichel pulse. By revisiting and summarizing the basic characteristics and well-accepted ionization and quenching mechanisms, this review provides a basic understanding and the current status of Trichel pulse.     

Structural fracture scales in shock-loaded epoxy composites

Shock fracture mechanisms of different scales were investigated on epoxy composite materials reinforced with silicon carbide microparticles of different concentrations. It is shown that the high heterogeneity of the epoxy composites at different structural scales is one of the factors responsible for their physical and mechanical properties. Under dynamic loading, the material reveals a developed structural scale hierarchy which provides self-consistent deformation and fracture of the material bulk with the lead of rotational deformation modes. As a result, microcracks develop due to low shear strain limited in addition by reinforcing particles. At the start of a main crack, microscale mechanisms dominate, whereas the propagation of its front is governed by macroscale fracture mechanisms.     

Influence of the isotopic constitution of the O2 −-center in alkali halides on its reorientation time

The theory of simple phonon induced reorientation of an O₂ ^?-center in alkali halides is refined to include the effect of the symmetry of its wave function. It is shown that the diagonal terms of the strain matrix and the off-diagonal ones lead to different coupling mechanisms between phonons and the impurity. For a rotation byπ/2 of a homonuclear molecule, either one or the other of the coupling mechanisms becomes ineffective, depending upon the isotopic constitution of the molecule and its nuclear spin state. Expressions for the reorientation time are obtained.     

Experimental Studies on Viscosity Reduction of Heavy Crude Oil by Ultrasonic Irradiation

Acoustical Physics - Viscosity reduction is one of the key issues for heavy oil reservoir development and its transportation. Up to now, the mechanisms for ultrasonic viscosity reduction still...     

磁绝缘线振荡器中模式竞争问题的数值模拟

为理解磁绝缘线振荡器(MILO)实验中频频出现的模式竞争问题,利用3维全电磁粒子模拟程序对C波段MILO的实验模型进行研究,探索各种非对称激励机制对产生微波模式的影响,结果显示:阴极电子随机发射、电压的慢上升前沿、较低的电压等因素都可导致非对称高阶模式的产生,并使输出微波功率大大降低。模拟计算得出MILO中存在频率为3.6 GHz左右的基模和频率分别为3.7,4.1,4.6 GHz左右的3种高阶模式,与Karat计算结果基本一致。     

Isospin violating mechanisms in quarkonium hadronic decays

We analyze the φ meson production in e+e-→ωπ0 as a probe for studying the isospin violation mechanisms.By clarifying the dynamic sources causing the isospin violation,we succeed in quantifying those mechanisms with the help of the recent KLOE data.Hence,the φ→ωπ0 branching ratio is extracted.We find that apart from the electromagnetic(EM)transitions,the strong transition via intermediate kaon loops plays an important role in understanding the cross section and its lineshape.     

Deep-elastic scattering and asymptotics

Deep-elastic scattering and its role in discrimination of the possible absorptive and reflective asymptotic scattering mechanisms are discussed with emphasis on the difference in the experimental signatures related to production processes.     

Localization of five-dimensional Elko spinors on dS/AdS thick branes

Owing to the special structure of a five-dimensional Elko spinor, its localization on a brane with codimension one becomes completely different from that of a Dirac spinor. By introducing the coupling between the Elko spinor and the scalar field that can generate the brane, we have two types of localization mechanism for the five-dimensional Elko spinor zero mode on a brane. One is the Yukawa-type coupling, and the other is the non-minimal coupling. In this study, we investigate the localization of the Elko zero mode on de Sitter and Anti-de Sitter thick branes with the two localization mechanisms, respectively. The results show that both the mechanisms can achieve localization. The forms of the scalar coupling function in both localization mechanisms have similar properties, and they play a similar role in localization.     

What do we know about self-similarity in fluid turbulence?

The evidence is reviewed on the statistical behavior of the small-scale fluctuations in high-Reynolds-number fluid turbulence. The qualitative phenomeno-logical information is summarized and the predictions of the 1941 Kolmogorov theory are reviewed. Then direct numerical simulation and its role in suggesting dynamical mechanisms are briefly discussed. Finally, the evidence on the multifractal structure of the dissipation field is reviewed. It is concluded that the experimental evidence for some kind of dynamical self-similarity is strong, but that there has been essentially no progress in fundamental theoretical understanding of the underlying mechanisms.     

Anchoring properties of substrate with a grating surface

The anchoring properties of substrate with a grating surface are investigated analytically. The alignment of nematic liquid crystal (NLC) in a grating surface originates from two mechanisms, thus the anchoring energy consists of two parts. One originates from the interaction potential between NLC molecules and the molecules on the substrate surface, and the other stems from the increased elastic strain energy. Based on the two mechanisms, the expression of anchoring energy per unit area of a projected plane of this grating surface is deduced and called the equivalent anchoring energy formula. Both the strength and the easy direction of equivalent anchoring energy are a function of the geometrical parameters (amplitude and pitch) of a grating surface. By using this formula, the grating surface can be replaced by its projected plane and its anchoring properties can be described by the equivalent anchoring energy formula.     

Optics-less smart sensors and a possible mechanism of cutaneous vision in nature

Although optics-less cutaneous (“skin”) vision is not uncommon among living organisms, its mechanisms and capabilities have not been thoroughly investigated. This paper demonstrates, using methods from statistical parameter estimation theory and numerical simulations, that arrays of bare radiation detectors arranged on a planar or curved surface have the ability to perform imaging tasks without any optics at all. The working principle of this type of optics-less sensors and the model developed here for determining their performance may be used to shed light on possible mechanisms, capabilities and evolution of cutaneous vision in nature.