热声制冷机回热器的构形优化

用构形理论对热声制冷机平板型回热器进行了优化,导出了最优平板间距及最优平板数的解析式,讨论了运行频率、温度梯度、以及平板厚度对最优平板间距的影响,所得结论对实际热声制冷机的设计工作具有一定的理论指导意义。     

Vibration analysis and design optimization of viscoelastic sandwich cylindrical shell

Damping properties of viscoelastic sandwich structure can be improved by changing some parameters such as thickness of the layers, distribution of partial treatments, slippage between layers at the interfaces, cutting and its distribution at the top and core layers. Since the optimization problem may result in a thick core layer, for achieving more accuracy a new higher-order Taylor's expansion of transverse and in-plane displacement fields is developed for the core layer of sandwich cylindrical shell in which the displacement fields at the core layer are compatibly described in terms of the displacement fields at the elastic faces. The presented model includes fewer parameters than the previously developed models and therefore decreases the number of degree of freedom in the finite element modeling. The transverse normal stress in the core layer is also considered. The formulations are developed to consider the slippage between layers at the interfaces. Finally, by combining the finite element method and the optimization algorithms based on the genetic algorithm and sequential quadratic programming technique, a design optimization methodology has been formulated to maximize the damping characteristics using the optimal number and location of cuts and partial treatments with optimal thicknesses of top and core layers.     

Optimization of the Hartmann-Shack microlens array

In this work we propose to optimize the microlens-array geometry for a Hartmann-Shack wavefront sensor. The optimization makes possible that regular microlens arrays with a larger number of microlenses are replaced by arrays with fewer microlenses located at optimal sampling positions, with no increase in the reconstruction error. The goal is to propose a straightforward and widely accessible numerical method to calculate an optimized microlens array for a known aberration statistics. The optimization comprises the minimization of the wavefront reconstruction error and/or the number of necessary microlenses in the array. We numerically generate, sample and reconstruct the wavefront, and use a genetic algorithm to discover the optimal array geometry. Within an ophthalmological context, as a case study, we demonstrate that an array with only 10 suitably located microlenses can be used to produce reconstruction errors as small as those of a 36-microlens regular array. The same optimization procedure can be employed for any application where the wavefront statistics is known.     

Fast simulation of the forward tracking detector of HPLUS

The necessity of installing a forward tracking detector stack is discussed for the Hadron Physics LanzhoU Spectrometer(HPLUS).A local tracker is developed to solve the multi-track finding problem.The track candidates are searched iteratively via Hough Transform.The fake tracks are removed by a least square fitting process.With this tracker we have studied the feasibility of pp→pp + φ(→K+K-),a typical physical channel proposed on HPLUS.The single track momentum resolution due to the uncertainty of the positioning in FTD is 1.3%.The multiple scattering effect contributes about 20% to the momentum resolution in the FTD coverage.The width and the signal-to-background ratio of the reconstructed φ are 1.51 MeV and 4.36,respectively,taking into account the direct Kaon channel pp→pp+K+K- as background.The geometry coverage of FTD for φ events is about 85.4%.Based on the current fast simulation and estimation,the geometrical configuration of FTD meets the physical requirement of HPLUS under the current luminosity and multiplicity conditions.The tracker is applicable in the full simulation coming next and is extendable to other tracking component of HPLUS.     

Surface layer relaxation on Mo(111) measured by low energy alkali ion scattering

The surface of clean Mo(111) has been studied using Li⁺ ion scattering at 1000 eV. The dependence of single scattering intensity was measured as a function of incident polar angle in the [12̄1] and the [21̄1̄] azimuths for various total scattering angles. Very pronounced intensity cut-offs are observed and are readily assignable to shadowing and blocking effects in scattering from first, second or third layer atoms. After taking certain precautions to avoid interference from deeper layers, the measured positions of the features yield the first-second layer spacing which is found to be strongly contracted by (18 ± 2)% compared to the bulk spacing. The method also indicates that the second-third layer spacing is possibly expanded (4 ± 4)%, but this result is uncertain due to possible contributions from deeper layers which make this value an upper limit of the layer spacing. The physical implications of these results and the uncertainties in the technique are discussed.     

Maximal potential energy transport: a variational principle for solidification problems

We analyze numerically the mechanisms controlling the spacing of chimneys--channels devoid of solid--in two-dimensional mushy layers formed by solidifying a binary alloy. Chimneys are the principal conduits through which buoyancy effects material transport out of the mushy layer and into the liquid from which it formed. Experiments show a coarsening of chimney spacing; we pursue the hypothesis that the spacing adjusts to optimize material transport and hence maximize the rate of removal of potential energy stored in the mushy layer. The optimal solute flux increases approximately linearly with the mush Rayleigh number. However, for spacings below a critical value, the chimneys collapse and solute fluxes cease, revealing a hysteresis between chimney convection and no flow. The results are consistent with a variational principle controlling the dynamics of this dissipative system.     

Structure of Cu(100) from low energy electron diffraction: II. Nonspecular beam

A large number of nonspecular LEED intensity profiles from the clean (100) surface of copper have been measured. The geometrical structures resulting from application of data averaging methods to both experimental and theoretical intensity profiles are presented and compared with earlier work. The present results indicate that the upper layer spacing of the Cu (100) surface is within 1% of the bulk layer spacing, but that the surface registry vector of the layer is 8% larger in magnitude than the bulk registry vector. The results obtained from grand-averaged model calculations indicate that averaging does not give accurate results for surface layer registries. In general, it seems that the data-averaging technique is much more useful for determination of surface layer spacing (which is most sensitive to the momentum spacing between kinematic peaks) than for finding surface registry (which is most dependent upon absolute peak positions).     

Thin multilayers characterization by grazing X-ray reflectometry and use of Fourier transform

Grazing X-ray reflectometry is used in order to characterize thin layer stacks, in particular periodic multilayers. The specular reflectivity depends on the thickness, the complex refractive index of each layer and on the roughness of the interfaces. By a trial and error method, the experimental reflectivity curve can be fitted with a theoretical one, and so, the parameters of the stack can be obtained. This numerical method needs usually initial guess of the kind of results.Fourier transform method allows to obtain directly the values of distances between interfaces, with a good approximation depending on the maximum angular scan of the measure. It can also reveal some particularity of the multilayer, i.e. periodic multilayered structures with more than two layers per period. As an illustration of this characterization method, some examples in XUV optical domain will be shown. This method can also be used for the characterization of many kinds of multilayer stacks, in particular semi-conductor heterostructures ones, under the condition that adjacent layers have sufficient contrast index at the wavelength of the X-ray source.     

步进扫描投影光刻机剂量控制参量优化新算法研究

提出了一种以生产率、剂量精度与激光器使用成本三者最佳匹配为优化目标的步进扫描投影光刻机剂量控制参量优化新算法及其数学模型,通过将激光器重复频率作为可调参量并引入有效脉冲个数的概念,获得了有效剂量区间内任意给定剂量所应采取的优化策略并给出了剂量控制参量的具体计算方法。理论推导和模拟计算结果表明,新算法既保持了原算法在生产率和剂量精度优化方面的优势,又改进了原算法在激光器成本优化目标上的缺陷。随着准分子激光器及其剂量控制技术的进一步发展,新算法可望更能显示出其优越性并具有更广阔的应用前景。     

Solid-perforated panel layout optimization by topology optimization based on unified transfer matrix

This paper presents a numerical method for the optimization of the sequencing of solid panels, perforated panels and air gaps and their respective thickness for maximizing sound transmission loss and/or absorption. For the optimization, a method based on the topology optimization formulation is proposed. It is difficult to employ only the commonly-used material interpolation technique because the involved layers exhibit fundamentally different acoustic behavior. Thus, an optimization method formulation using a so-called unified transfer matrix is newly proposed. The key idea is to form elements of the transfer matrix such that interpolated elements by the layer design variables can be those of air, perforated and solid panel layers. The problem related to the interpolation is addressed and bench mark-type problems such as sound transmission or absorption maximization problems are solved to check the efficiency of the developed method.     

Local to global normalization dynamic by nonlinear local interactions

Here, I present a novel method for normalizing a finite set of numbers, which is studied by the domain of biological vision. Normalizing in this context means searching the maximum and minimum number in a set and then rescaling all numbers such that they fit into a numerical interval. My method computes the minimum and maximum number by two pseudo-diffusion processes in separate diffusion layers. Activity of these layers feed into a third layer for performing the rescaling operation. The dynamic of the network is richer than merely performing a rescaling of its input, and reveals phenomena like contrast detection, contrast enhancement and a transient compression of the numerical range of the input. Apart from presenting computer simulations, some properties of the diffusion operators and the network are analysed mathematically. Furthermore, a method is proposed for to freeze the model’s state when adaptation is observed.     

The effect of turbulence damping on acoustic wave propagation in tubes

The attenuation of sound due to the interaction between a low Mach number turbulent boundary layer and acoustic waves can be significant at low frequencies or in narrow tubes. In a recent publication by the present authors the acoustics of charge air coolers for passenger cars has been identified as an interesting application where turbulence attenuation can be of importance. Favourable low-frequency damping has been observed that could be used for control of the in-duct sound that is created by the engine gas exchange process. Analytical frequency-dependent models for the eddy viscosity that controls the momentum and thermal boundary layers are available but are restricted to thin acoustic boundary layers. For cases with cross-sections of a few millimetres a model based on thin acoustic boundary layers will not be applicable in the frequency range of interest.In the present paper a frequency-dependent axis-symmetric numerical model for interaction between turbulence and acoustic waves is proposed. A finite element scheme is used to formulate the time harmonic linearized convective equations for conservation of mass, momentum and energy into one coupled system of equations. The turbulence is introduced with a linear model for the eddy viscosity that is added to the shear viscosity. The proposed model is validated by comparison with experimental data from the literature.     

Characteristics of filament induced Dammann gratings fabricated using femtosecond laser

To establish optimal processing conditions for direct write fabrication of diffractive optical elements such as gratings, waveguides, lenses, we have investigated the effect of process parameters such as scan speed, numerical aperture (NA) of objective lens, pulse energy on the characteristics of the filament induced inside fused silica with a femtosecond Ti:sapphire laser. The optimum process parameters were used to fabricate a number of Dammann gratings, 6×6 array, having different thicknesses and number of layers. The performance of these optical elements was evaluated by measuring their diffraction efficiencies. All gratings fabricated were strongly birefringent, the zero order spot with high intensity was not separated from the spot array, and the intensity distribution of 6×6 spot array exhibited some degree of nonuniformity. The single layer Dammann grating fabricated with a thickness of 80 μm attained a maximum diffraction efficiency of 38.8%.     

Propagation of gaseous detonation across inert layers

In rotating detonation engines and explosion accidents, detonation may propagate in an inhomogeneous mixture with inert layers. This study focuses on detonation propagation in a stoichiometric H₂/O₂/N₂ mixture with multiple inert layers normal to the detonation propagation direction. One- and two-dimensional simulations considering detailed chemistry are conducted. The emphasis is placed on assessing the effects of inert layer on detonation reinitiation/failure, detonation propagation speed, detonation cell structure and cell size. Specifically, the inert layer thickness and the spacing between two consecutive inert layers are varied. Either detonation reinitiation or failure across the inert layers is observed. It is found that successful detonation reinitiation occurs only at relatively small values of the inert layer thickness and spacing. For each given value of the inert layer spacing, there is a critical inert layer thickness above which detonation fails after crossing the inert layers. This critical inert layer thickness is found to decrease as the inert layer spacing increases. The detailed process of detonation reinitiation across the inert layers is analyzed. The interaction between the transverse shock waves is shown to induce local autoignition/explosion and eventually over-driven detonation development in the reactive layer. The averaged detonation propagation speed in the inhomogeneous mixture is compared to the CJ speed and very good agreement is achieved. This indicates that the inert layer does not affect the detonation propagation speed once successful detonation reinitiation happens. Unlike the detonation speed, the detonation cell structure and cell size are greatly affected by the inert layer results. For the first time, large cellular structure with size linearly proportional to the inert layer spacing is observed for detonation propagation across inert layers. Besides, a double cellular structure is observed for relatively large spacing between inert layers. The formation of double cellular structure is interpreted.     

广义Schwarzschild几何的引力微扰

利用Regge和Wheeler提出的方法,导出了广义Schwarzschild几何的轴扰动方程.对给定角动量L和λ参数,通过数值计算,得到了拟正则模的值.数值结果与不稳定性的解析证明相一致. 关键词：     

Fold amplification rates and dominant wavelength selection in multilayer stacks

A combination of thin- and thick-plate theories, and finite element models is used to systematically analyze folding in multilayer stacks. We show that if the interlayer spacing is large, individual layers fold as single layers, if the spacing is small the entire stack folds as one effective single layer. In between, a third folding mode exists that is characterised by a dominant wavelength that scales with n ^1/3, irrespective of total number of layers, n. The maximum growth rates in the true multilayer-folding mode are higher than the corresponding single layer growth rates, increase with n and are bounded by a saturation value that is directly proportional to the viscosity contrast. This growth rate saturation as well as the applicability of the true multilayer-folding mode with respect to interlayer spacing can be explained by the normal and inverse contact strain theory. The true multilayer-folding mode is expected to be the most frequent mode in nature, because it exhibits the highest growth rates and has a relatively large applicability range with respect to interlayer spacing. The increased growth rates in multilayer folding are especially important for systems where the corresponding single layer values are not sufficient to drive the folding instability, such as folding in low-viscosity contrast layers and detachment folding.     

A field expansions method for scattering by periodic multilayered media

The interaction of acoustic and electromagnetic waves with periodic structures plays an important role in a wide range of problems of scientific and technological interest. This contribution focuses upon the robust and high-order numerical simulation of a model for the interaction of pressure waves generated within the earth incident upon layers of sediment near the surface. Herein described is a boundary perturbation method for the numerical simulation of scattering returns from irregularly shaped periodic layered media. The method requires only the discretization of the layer interfaces (so that the number of unknowns is an order of magnitude smaller than finite difference and finite element simulations), while it avoids not only the need for specialized quadrature rules but also the dense linear systems characteristic of boundary integral/element methods. The approach is a generalization to multiple layers of Bruno and Reitich's "Method of Field Expansions" for dielectric structures with two layers. By simply considering the entire structure simultaneously, rather than solving in individual layers separately, the full field can be recovered in time proportional to the number of interfaces. As with the original field expansions method, this approach is extremely efficient and spectrally accurate.     

Optimal poroelastic layer sequencing for sound transmission loss maximization by topology optimization method

Optimal layer sequencing of a multilayered acoustical foam is solved to maximize its sound transmission loss. A foam consisting of air and poroelastic layers can be optimized when a limited amount of a poroelastic material is allowed. By formulating the sound transmission loss maximization problem as a one-dimensional topology optimization problem, optimal layer sequencing and thickness were systematically found for several single and ranges of frequencies. For optimization, the transmission losses of air and poroelastic layers were calculated by the transfer matrix derived from Biot's theory. By interpolating five intrinsic parameters among several poroelastic material parameters, distinct air-poroelastic layer distributions were obtained; no filtering or postprocessing was necessary. The optimized foam layouts by the proposed method were shown to differ depending on the frequency bands of interest.     

渐变折射率薄膜的分层评价探讨

首先阐述了将渐变折射率薄膜细分为多层均匀薄膜的分层介质理论,接着给出了一种获得最佳分层数目的分层评价方法,最后以线性变化渐变折射率薄膜为例说明了如何优化获得渐变折射率薄膜的分层数目.研究发现：渐变折射率薄膜的分层数目与薄膜的厚度和薄膜的折射率变化快慢有关,在一定的折射率变化范围内,渐变折射率薄膜的分层数目随着薄膜厚度的增加先减小后增大. 关键词： 渐变折射率 分层介质理论 分层评价     

Magnetization dynamics due to pure spin currents in magnetic double layers

The magnetization dynamics in magnetic double layers is affected by spin-pump and spin-sink effects. So far, only the spin pumping and its effect on the magnetic damping has been studied. However, due to conservation of angular momentum this spin current also leads to magnetic excitation of the layer dissipating this angular momentum. In this Letter we use time resolved magneto-optic Kerr effect to directly show the excitation due to the pure spin current. In particular, we observe magnetization dynamics due to transfer of angular momentum in magnetic double layers. In contrast to other experiments where a spin polarized charge current is passed through a nanomagnet, the effects discussed in this Letter are based on pure spin currents without net transfer of electric charge.