热容型板条激光器的感应折射率计算

高平均功率固体激光器的增益介质由于受热而容易发生畸变,如常用材料YAG,波前畸变和去偏振现象会同时发生,高热负载固体激光介质的热效应已成为制约激光器输出功率进一步提高的严重障碍。给出一种计算热容型板条激光器热感生折射率的方法。把YAG晶体的四阶压光张量从晶胞坐标系转换到实验室坐标系,采用经过坐标转换后的新的张量,可以分析在YAG激光器中任意应力分布引起的热感应双折射。进一步的计算表明,在zigzag板条激光器中,应力双折射率与板条从晶体毛胚上切割成材的角度有关。同时也对热容板条激光器的热效应和应力特性进行了二维的理论性概述。

On the invariant representation of spin tensors with applications

The invariant representation of the spin tensor defined as the rotation rate of a principal triad for a symmetric and non-degenerate tensor is derived on the basis of the general solution of a linear tensorial equation. The result can be naturally specified to study the. spin of the stretch tensors and to investigate the relations between various rotation rate tensors encountered frequently in modern continuum mechanics. A remarkable formula which relates the generalized stress conjugate to the generalized strain in Hill's sense. to Cauchy stress, is obtained in invariant form through the work conjugate principle. Particularly, a detailed discussion on the time rate of logarithmic strain and its conjugate stress is made as the principal axes of strain arc not fixed during deformation.

Strain gradient theory with couple stress for crystalline solids

A new phenomenological strain gradient theory for crystalline solid is proposed. It fits within the framework of general couple stress theory and involves a single material length scale Ics. In the present theory three rotational degrees of freedom omega (i) are introduced, which denote part of the material angular displacement theta (i) and are induced accompanying the plastic deformation. omega (i) has no direct dependence upon u(i) while theta = (1 /2) curl u. The strain energy density omega is assumed to consist of two parts: one is a function of the strain tensor epsilon (ij) and the curvature tensor chi (ij), where chi (ij) = omega (i,j); the other is a function of the relative rotation tensor alpha (ij). alpha (ij) = e(ijk) (omega (k) - theta (k)) plays the role of elastic rotation reason The anti-symmetric part of Cauchy stress tau (ij) is only the function of alpha (ij) and alpha (ij) has no effect on the symmetric part of Cauchy stress sigma (ij) and the couple stress m(ij). A minimum potential principle is developed for the strain gradient deformation theory. In the limit of vanishing l(cs), it reduces to the conventional counterparts: J(2) deformation theory. Equilibrium equations, constitutive relations and boundary conditions are given in detail. For simplicity, the elastic relation between the anti-symmetric part of Cauchy stress tau (ij), and alpha (ij) is established and only one elastic constant exists between the two tensors. Combining the same hardening law as that used in previously by other groups, the present theory is used to investigate two typical examples, i.e., thin metallic wire torsion and ultra-thin metallic beam bend, the analytical results agree well with the experiment results. While considering the, stretching gradient, a new hardening law is presented and used to analyze the two typical problems. The flow theory version of the present theory is also given.

Moment Tensor Analysis of the Acoustic Emission Source in the Rock Damage Process

To further investigate the mechanism of acoustic emission (AE) in the rock fracture experiment, moment tensor analysis was carried out. The AE sources characterized by crack sizes, orientations and fracture modes, are represented by a time-dependent momen

An incremental micromechanical scheme for nonlinear particulate composites

A general incremental micromechanical scheme for the nonlinear behavior of particulate composites is presented in this paper. The advantage of this scheme is that it can reflect partly the effects of the third invariant of the stress on the overall mechanical behavior of nonlinear composites. The difficulty involved is the determination of the effective compliance tensors of the anisotropic multiphase composites. This is completed by making use of the generalized self-consistent Mori-Tanaka method which was recently developed by Dai et al. (Polymer Composites 19(1998) 506-513; Acta Mechanica Solida 18 (1998) 199-208). Comparison with existing theoretical and numerical results demonstrates that the present incremental scheme is quite satisfactory. Based on this incremental scheme, the overall mechanical behavior of a hard-particle reinforced metal matrix composite with progressive particle debonding damage is investigated.

A second-order dynamic subgrid-scale stress model

A second-order dynamic model based on the general relation between the subgrid-scale stress and the velocity gradient tensors was proposed. A priori test of the second-order model was made using moderate resolution direct numerical simulation date at high Reynolds number ( Taylor microscale Reynolds number R-lambda = 102 similar to 216) for homogeneous, isotropic forced flow, decaying flow, and homogeneous rotating flow. Numerical testing shows that the second-order dynamic model significantly improves the correlation coefficient when compared to the first-order dynamic models.

Orientation-Dependent Adhesion Strength Of A Rigid Cylinder In Non-Slipping Contact With A Transversely Isotropic Half-Space

Recently, Chen and Gao [Chen, S., Gao, H., 2007. Bio-inspired mechanics of reversible adhesion: orientation-dependent adhesion strength for non-slipping adhesive contact with transversely isotropic elastic materials. J. Mech. Phys. solids 55, 1001-1015] studied the problem of a rigid cylinder in non-slipping adhesive contact with a transversely isotropic solid subjected to an inclined pulling force. An implicit assumption made in their study was that the contact region remains symmetric with respect to the center of the cylinder. This assumption is, however, not self-consistent because the resulting energy release rates at two contact edges, which are supposed to be identical, actually differ from each other. Here we revisit the original problem of Chen and Gao and derive the correct solution by removing this problematic assumption. The corrected solution provides a proper insight into the concept of orientation-dependent adhesion strength in anisotropic elastic solids. (c) 2008 Elsevier Ltd. All rights reserved.

A kinematic subgrid scale model for large-eddy simulation of turbulence generated sound

In the hybrid approach of large-eddy simulation (LES) and Lighthill’s acoustic analogy for turbulence-generated sound, the turbulence source fields are obtained using an LES and the turbulence-generated sound at far fields is calculated from Lighthill’s acoustic analogy. As only the velocity fields at resolved scales are available from the LES, the Lighthill stress tensor, serving as a source term in Lighthill’s acoustic equation, has to be evaluated from the resolved velocity fields. As a result, the contribution from the unresolved velocity fields is missing in the conventional LES. The sound of missing scales is shown to be important and hence needs to be modeled. The present study proposes a kinematic subgrid-scale (SGS) model which recasts the unresolved velocity fields into Lighthill’s stress tensors. A kinematic simulation is used to construct the unresolved velocity fields with the imposed temporal statistics, which is consistent with the random sweeping hypothesis. The kinematic SGS model is used to calculate sound power spectra from isotropic turbulence and yields an improved result: the missing portion of the sound power spectra is approximately recovered in the LES.

Polarized Raman scattering studies of nonpolar a-plane GaN films grown on r-plane sapphire substrates by MOCVD

Nonpolar (1120) a-plane GaN thin films were grown on r-plane (1102) sapphire substrates by low-pressure metal organic chemical vapor deposition (MOCVD). The stress characteristics of the a-plane GaN films were investigated by means of polarized Raman scattering spectra in backscattering configurations. The experimental results show that there are strong anisotropic in-plane stresses within the epitaxial a-plane GaN films by calculating the corresponding stress tensors. The temperature dependence of Raman scattering spectra was studied in the range from 100 K to 550 K. The measurements reveal that the Raman phonon frequencies decrease with increasing temperature. The temperature at which nonpolar a-plane GaN films are strain free is discussed. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Biologically Inspired Tensor Features

According to the research results reported in the past decades, it is well acknowledged that face recognition is not a trivial task. With the development of electronic devices, we are gradually revealing the secret of object recognition in the primate's visual cortex. Therefore, it is time to reconsider face recognition by using biologically inspired features. In this paper, we represent face images by utilizing the C1 units, which correspond to complex cells in the visual cortex, and pool over S1 units by using a maximum operation to reserve only the maximum response of each local area of S1 units. The new representation is termed C1 Face. Because C1 Face is naturally a third-order tensor (or a three dimensional array), we propose three-way discriminative locality alignment (TWDLA), an extension of the discriminative locality alignment, which is a top-level discriminate manifold learning-based subspace learning algorithm. TWDLA has the following advantages: (1) it takes third-order tensors as input directly so the structure information can be well preserved; (2) it models the local geometry over every modality of the input tensors so the spatial relations of input tensors within a class can be preserved; (3) it maximizes the margin between a tensor and tensors from other classes over each modality so it performs well for recognition tasks and (4) it has no under sampling problem. Extensive experiments on YALE and FERET datasets show (1) the proposed C1Face representation can better represent face images than raw pixels and (2) TWDLA can duly preserve both the local geometry and the discriminative information over every modality for recognition.

海底金属矿床充水条件及矿坑突水的断层效应研究

The Xinli mine area of Sanshandao mine is adjacent to the Bohai Sea and its main exploitable ore deposit occurs in the undersea rock mass. The mine is the biggest undersea gold mine of China after production. The mine area faces a latent danger of water bursting, even sudden seawater inrush. There is no mature experience in undersea mining in China so far. The vein ore deposit is located in the lower wall of a fault; its possible groundwater sources mainly include bittern, Quaternary pore water and modern seawater. To ensure the safety of undersea mining, to survey the flooding conditions of the ore deposit using proper measures and study the potential seawater inrush pattern are the key technical problems. With the Xinli mine area as a case study, the engineering geological conditions of the Xinli mine area are surveyed in situ, the regional structural pattern and rock mass framework characteristics are found out, the distribution of the structural planes are modeled by a Monte Carlo method and the connectivity coefficients of rock mass structural planes are calculated. The regional hydro-geological conditions are analyzed and the in-situ hydro-geological investigation and sampling are performed in detail, the hydrochemistry and isotopes testing and groundwater dynamic monitoring are conducted, the recharge, runoff, discharge conditions are specified and the sources of flooding are distinguished. Some indices are selected from the testing results to calculate the proportion of each source in some water discharge points and in the whole water discharge of the Xinli mine area. The temporal and spatial variations of each water source of the whole ore deposit flooding are analyzed. According to the special project conditions in the Xinli mine area, the permeability coefficient tensors of the rock mass in Xinli mine area are calculated based on a fracture geometry measurement method, in terms of the connectivity and a few hydraulic testing results, a modified synthetic permeability coefficient are calculated. The hydro-geological conceptual and mathematical model are established，the water yield of mine is predicted using Visual Modflow code. The spreading law of surrounding rock mass deformation and secondary stress are studied by numerical analysis; the intrinsic mechanism of the faults slip caused by the excavation of ore deposit is analyzed. The results show that the development of surrounding rock mass deformation and secondary stress of vein ore deposit in the lower wall of a fault, is different from that in a thick-big ore deposit. The secondary stress caused by the excavation of vein ore deposit in the lower wall of a fault, is mainly distributed in the upper wall of the fault, one surface subsidence center will occur. The influences of fault on the rock mass movement, secondary stress and hydro-geological structures are analyzed; the secondary stress is blocked by the fault and the tensile stress concentration occurs in the rock mass near the fault, the original water blocking structure is destructed and the permeable structure is reconstructed, the primary structural planes begin to expand and newborn fissures occur, so the permeability of the original permeable structure is greatly enhanced, so the water bursting will probably occur. Based on this knowledge, the possible water inrush pattern and position of the Xinli mine area are predicted. Some computer programs are developed using object-oriented design method under the development platform Visual Studio.Net. These programs include a Monte Carlo simulation procedure, a joint diagrammatizing procedure, a structural planes connectivity coefficient calculating procedure, a permeability tensor calculating procedure, a water chemical formula edit and water source fixture conditions calculating procedure. A new computer mapping algorithm of joint iso-density diagram is raised. Based on the powerful spatial data management and icon functions of Geographic Information System, the pit water discharge dynamic monitoring data management information systems are established with ArcView.