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1.
针对目标声源在复杂声场环境下进行声场重建易受到其它声源干扰的问题,提出存在干扰源声场、散射声场及目标声源声场的混合声场环境下基于单面声场分离技术的目标声源声场分离及重建方法。首先,通过理论分析和公式推导,清除干扰源声场及散射声场的影响;然后,利用传递函数性质对声场分离及重建误差进行分析,并对计算公式中存在的奇异性问题予以消除,得到高分辨率的声场重建图像。数值仿真表明:利用常规的单面声场分离技术很难重建混合声场环境下目标声源的声场,而利用本文研究的声场分离及重建方法能够很好反映目标声源声场的实际情况,提高声场重建的精度。 相似文献
2.
静电场对熔融结晶聚丙烯薄膜显微形态的影响 总被引:1,自引:0,他引:1
用偏光显微镜研究了聚丙烯薄膜在静电场作用下的熔融结晶过程。结果表明,聚合物在熔融状态下易受静电场的作用而产生极化,随着电场强度的增加极化现象加剧,结晶时与未经电场作用的分子链有不同的构象。静电场使聚合物球晶沿电场方向被拉长,趋于定向结晶。在外场的“牵引”下,环状消光环消失,表明球晶的辐射状片晶由扭曲生长转变为伸直生长。静电场对晶棱生长有促进作用,使其晶体尺寸增大。 相似文献
3.
Development of a 4‐node hybrid stress tetrahedral element using a node‐based smoothed finite element method 下载免费PDF全文
J.H. Choi B.C. Lee 《International journal for numerical methods in engineering》2018,113(11):1711-1728
In this paper, a new 4‐node hybrid stress element is proposed using a node‐based smoothing technique of tetrahedral mesh. The conditions for hybrid stress field required are summarized, and the field should be continuous for better performance of a constant‐strain tetrahedral element. Nodal stress is approximated by the node‐based smoothing technique, and the stress field is interpolated with standard shape functions. This stress field is linear within each element and continuous across elements. The stress field is expressed by nodal displacements and no additional variables. The element stiffness matrix is calculated using the Hellinger‐Reissner functional, which guarantees the strain field from displacement field to be equal to that from the stress field in a weak sense. The performance of the proposed element is verified by through several numerical examples. 相似文献
4.
针对目前国内还没有在环境监测中广泛使用的对工频电场探头进行计量的检定规程或者校准规范,设计了一套工频电场探头校准装置,根据理论推导,确定所产生标准电场强度。通过高压源控制器来控制升压实现高压输出。校准所采用的电板满足所有工频电场测量仪校准需求,产生的电场强度范围从10 V/m到100 kV/m。最后,对溯源后的HI-3604分别进行电场强度测试与分析,实验数据表明:该校准装置可以用于工频电场探头校准,并给出了校准不确定度。 相似文献
5.
A simplified analysis method based on micromagnetic simulation is proposed to investigate effects of nonmagnetic particles on the demagnetizing field of a permanent magnet. By applying the additivity law of the demagnetizing field, the complicated demagnetizing field of the real magnet could be analyzed by only focusing on the stray field of the reserved magnet. For a magnet with nonmagnetic particles inside, the particle size has no significant effect on the maximum value of the demagnetization field, but the area of the affected region by the particle is proportional to the particle size. A large particle produces a large affected area overlapped with those influenced by other particles, which leads to the large demagnetization field. With increasing the length of the particle along the magnetization direction, the demagnetization field on the pole surface increases. The pole surface with a convex shape will increase the demagnetization field. The demagnetizing field near the nonmagnetic particle will be further increased by the large macroscopic demagnetizing field near the pole surface. This work suggests some practical approaches to optimize the microstructure of permanent magnets. 相似文献
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Y. K. Zhang J. Gao Y. L. Zhou D. M. Herlach J. C. He 《Journal of Materials Science》2010,45(6):1648-1654
The influence of gradient magnetic field on the undercooling behavior of glass-fluxed pure Sb melts was investigated using
a superconducting magnet. It was found that under a positive gradient magnetic field, the mean undercooling of pure Sb melts
increased with increasing magnetic field intensity. However, under a negative gradient magnetic field, the mean undercooling
showed a decreasing tendency following an initial increase with increasing magnetic field intensity. The results were discussed
by considering the Lorentz force and the magnetization force imposed by the gradient magnetic field. 相似文献
8.
D. Shaltiel H.-A. Krug von Nidda B. Y. Shapiro B. Rosenstein A. Loidl B. Bogoslavsky I. Shapiro T. Fujii T. Watanabe T. Tamegai 《Journal of Superconductivity and Novel Magnetism》2009,22(4):387-399
The Josephson Vortex dynamics in high anisotropy superconductors Bi2212 and Bi2223 induced by AC magnetic field collinear
to DC magnetic field and parallel to the layers is studied via their interaction with microwave field. Experimental results
as function of DC magnetic field, AC magnetic field and temperature are presented. The AC induced microwave dissipation is
larger than dissipation without AC field. The results are explained by the theoretical interpretation reported recently due
to shaking by the AC field that depins the JV (Shaltiel et al., Phys. Rev. B 77, 014508, 2008). Similar behavior in these two compounds as a function of the variables involved discloses that the shaking effect should
be observed in any high anisotropy superconductors. It shows that the AC field interacting with JV has an active and not the
usual passive modulating role of the DC field in EPR dissipation experiments. The technique can be used to investigate JV
dynamics and JV phase diagram. 相似文献
9.
K. Sakaue Y. Uchiyama H. Tanaka S. Yoneyama M. Takashi 《Engineering Fracture Mechanics》2008,75(14):4140-4150
The crack tip strain and stress fields in a viscoelastic material under nonproportional loading conditions are evaluated. In order to evaluate the strain field, the crack tip displacement field is measured by using the digital image correlation (DIC) technique. This displacement field is then approximated by using the theoretically obtained crack tip displacement field in viscoelastic materials. The result shows that the approximation method can smoothly reconstruct the experimentally obtained displacement field. From the approximated displacement field, the crack tip strain field can be precisely obtained by using the differential form of the theoretical displacement. On the other hand, the crack tip stress field is analyzed by using the stress function. This suggests that the strain and stress fields can be independently evaluated. In addition, different time dependencies between stress and strain fields near the crack tip are observed. Based on this experiment, we can discuss the several criteria for the crack propagation directions in viscoelastic materials. 相似文献
10.
Jianing Chen Pablo Albella Zhaleh Pirzadeh Pablo Alonso‐González Florian Huth Stefano Bonetti Valentina Bonanni Johan Åkerman Josep Nogués Paolo Vavassori Alexandre Dmitriev Javier Aizpurua Rainer Hillenbrand 《Small (Weinheim an der Bergstrasse, Germany)》2011,7(16):2341-2347
The fundamental optical properties of pure nickel nanostructures are studied by far‐field extinction spectroscopy and optical near‐field microscopy, providing direct experimental evidence of the existence of particle plasmon resonances predicted by theory. Experimental and calculated near‐field maps allow for unambiguous identification of dipolar plasmon modes. By comparing calculated near‐field and far‐field spectra, dramatic shifts are found between the near‐field and far‐field plasmon resonances, which are much stronger than in gold nanoantennas. Based on a simple damped harmonic oscillator model to describe plasmonic resonances, it is possible to explain these shifts as due to plasmon damping. 相似文献
11.
Yoshikazu Miyahara Ken Takayama Gen'ichi Horikoshi 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1988,270(2-3):217-225
Transport properties of trapped ions in an electron storage ring were studied analytically and by a computer simulation with a particular regard to the fringe field of bending magnets. It has been found that the fringe field works as a potential barrier for the longitudinal motion of trapped ions because of its field gradient. The ions are reflected by the fringe field or transmitted through the bending field depending on initial conditions. Analytical results including reflection condition are confirmed by the simulation, and compared with experimental results. 相似文献
12.
S. V. Loginov 《Technical Physics Letters》2007,33(10):805-808
It is shown that the process of magnetic field penetration into the plasma bridge in a plasma opening switch is determined by the field diffusion near the magnetic piston, followed by the convective transport of magnetic field in the bridge. This transport is due to the field being “frozen in” to the flow of plasma behind the front of a shock wave, which is formed in the plasma accelerated by the magnetic field pressure. 相似文献
13.
外源波动问题数值模拟的一种实现方式 总被引:9,自引:1,他引:9
将人工边界上的波动场分解为无局部场地效应影响的自由场与局部场地效应引起的散射场两部分,无限域地基中的波动传播对人工边界的影响通过将位移场、速度场转化为应力场施加到人工边界节点上来反映,其中散射波场的模拟采用了杜修力等提出的一种远场近似解。在此基础上,利用通用有限元软件实现了斜入射条件下瞬态平面地震波作用引起的局部场地效应的时域数值模拟,为计算二维、三维局部不规则、非均匀场地的地震局部场地效应以及土结动力相互作用等外源波动问题提供了一种有效、实用的实现方式。建议方法的优点是可直接借助通用有限元软件强大的求解器和前后处理功能来计算和分析近场波动反应,且实现简便。实际上,由于通用有限元软件强大的求解功能,可方便地用于局部场地存在不均匀、非线性的情况。 相似文献
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16.
James Chen Xianqiao Wang Huachuan Wang James D. Lee 《Engineering Fracture Mechanics》2010,77(4):736-743
A multiscale approach is employed to investigate a center-cracked specimen with the purpose to redefine fracture toughness from the atomistic perspective and to simulate different modes of crack propagation. The specimen is divided into three regions: (1) far field, modeled by classical fracture mechanics, (2) near field, modeled by a multiscale field theory and analyzed by a generalized finite element method, and (3) crack tip atomic region, modeled by molecular dynamics (MD). The exact and analytical solution of the far field is utilized to specify boundary conditions at the interface between the far field and the near field. The interaction between the near field and the crack tip region is described by full-blown interatomic forces. In this work, crystals of perovskite (Barium Titanate) and rocksalt (Magnesia) have been studied. Fracture toughness is defined as a material property associated with instability of the MD simulation. Mode I, Mode II, and mixed mode fracture have been investigated and numerical results will be presented and discussed. 相似文献
17.
The influence of high magnetic field with different strength on the proeutectoid ferrite transformation in high purity Fe-0.36 wt% C during diffusional γ→α phase transformation was studied.It was found that the formation of acicular ferrite(i.e.Widmanst¨atten ferrite) was obviously suppressed by the applied high magnetic field.The stronger the magnetic field is,the more the ferrite grains elongating and aligning along the field direction will be.This is attributed to additional driving force for phase transformation and demagnetization effect introduced by the applied magnetic field.This is also considered to be related to the preferential growth of proeutectoid ferrite nuclei along field direction caused by magnetic dipolar interaction. 相似文献
18.
Danhong Huang Alsing P.M. Cardimona D.A. Gumbs G.A. 《Nanotechnology, IEEE Transactions on》2008,7(2):151-164
Some possibilities for coherent optical amplification of a normally incident and weak radiation field are reviewed based on various physical mechanisms, such as electronic quantum interference induced by a coupling laser field in a three-level system, field enhancement through the cavity confinement of a radiation field in a photonic crystal and field concentration seen in a transmitted near field through a metallic surface grating due to excitation of surface-plasmon-polariton modes. Numerical results are presented and discussed to demonstrate these interesting effects. The modification to the spontaneous emission inside a photonic crystal is also studied. The important role played by a longitudinal field resulting from the absorption by an induced three-dimensional plasma wave inside a doped semiconductor is analyzed using a nonlocal and nonadiabatic model. Moreover, the coupling between two-dimensional plasmons and surface plasmon modes in the nonretardation limit is explored. 相似文献
19.
Olofsson J Levin M Strömberg A Weber SG Ryttsén F Orwar O 《Analytical chemistry》2005,77(14):4667-4672
We here report on a concept for creating well-defined electric field gradients between the boundaries of capillary electrode (a capillary of a nonconducting material equipped with an interior metal electrode) outlets, and dielectric surfaces. By keeping a capillary electrode opening close to a boundary between a conducting solution and a nonconducting medium, a high electric field can be created close to the interface by field focusing effects. By varying the inner and outer diameters of the capillary, the span of electric field strengths and the field gradient obtained can be controlled, and by varying the slit height between the capillary rim and the surface, or the applied current, the average field strength and gradient can be varied. Field focusing effects and generation of electric field patterns were analyzed using finite element method simulations. We experimentally verified the method by electroporation of a fluorescent dye (fluorescein diphosphate) into adherent, monolayered cells (PC-12 and WSS-1) and obtained a pattern of fluorescent cells corresponding to the focused electric field. 相似文献
20.
《Probabilistic Engineering Mechanics》1999,14(1-2):63-72
The problem of the arbitrary choice of variables for random field modelling in structural mechanics or in soil mechanics is treated. For example, it is relevant to ask the question of whether it is best to choose a stiffness field along a beam element or to choose its reciprocal field, the flexibility field, as the input to the stochastic finite element model. To answer this question the focus should be on the error of the output of the mechanical model rather than on the input field itself when discretizing the field through replacing it by a field defined in terms of a finite number of random variables. Several reported discretization methods define these random variables as integrals of the product of the field and some suitable weight functions. In particular, the weight functions can be Dirac delta functions whereby the random variables become the field values at a finite set of given points. The replacement field is often defined as the linear regression of the original field on the considered vector of the weighted integrals of the field. For example, this holds for discretizations obtained by truncation of the Karhunen–Loéve expansion of the field, but only approximately so for truncations of expansions given in terms of any other complete orthogonal function basis. Solely discretizations based on the linear regression method are considered herein. The solution to the problem of best choice of the vector of weight functions is not universal but depends on the mechanical problem under consideration as well as on the choice of the input field. Obviously it makes a difference whether it is the stiffness field or its reciprocal field that is chosen to be represented by a vector of weighted averages of the field. As a test example a lognormal stiffness field along the axis of a linear-elastic Bernoulli–Euler column is considered. Then the exact one-to-one conversion from the stiffness field to the flexibility field is directly obtained. From the form of two functionals that have similarity to the potential energy functional and the complementary energy functional, respectively, both derived from the differential equation of the column displacement and the relevant boundary conditions, it can be expected that the discretization of the flexibility field is preferable over the discretization of the stiffness field. Direct mechanical considerations support this expectation. 相似文献