Depletion of nonlinearity in magnetohydrodynamic turbulence: Insights from analysis and simulations

It is shown how suitably scaled, order-m moments, D-m(+/-), of the Elsasser vorticity fields in three-dimensional magnetohydrodynamics (MHD) can be used to identify three possible regimes for solutions of the MHD equations with magnetic Prandtl number P-M = 1. These vorticity fields are defined by omega(+/-) = curl z(+/-) = omega +/- j, where z(+/-) are Elsasser variables, and where omega and j are, respectively, the fluid vorticity and current density. This study follows recent developments in the study of three-dimensional Navier-Stokes fluid turbulence Gibbon et al., Nonlinearity 27, 2605 (2014)]. Our mathematical results are then compared with those from a variety of direct numerical simulations, which demonstrate that all solutions that have been investigated remain in only one of these regimes which has depleted nonlinearity. The exponents q(+/-) that characterize the inertial range power-law dependencies of the z(+/-) energy spectra, epsilon(+/-)(k), are then examined, and bounds are obtained. Comments are also made on (a) the generalization of our results to the case P-M not equal 1 and (b) the relation between D-m(+/-) and the order-m moments of gradients of magnetohydrodynamic fields, which are used to characterize intermittency in turbulent flows.

Making consistent contacts to graphene: effect of architecture and growth induced defects

The effects of contact architecture, graphene defect density and metal-semiconductor work function difference on the resistivity of metal-graphene contacts have been investigated. An architecture with metal on the bottom of graphene is found to yield resistivities that are lower, by a factor of four, and most consistent as compared to metal on top of graphene. Growth defects in graphene film were found to further reduce resistivity by a factor of two. Using a combination of method and metal used, the contact resistivity of graphene has been decreased by a factor of 10 to 1200. +/-. 250 Omega mu m using palladium as the contact metal. While the improved consistency is due to the metal being able to contact uncontaminated graphene in the metal on the bottom architecture, lower contact resistivities observed on defective graphene with the same metal are attributed to the increased number of modes of quantum transport in the channel.

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.

Infrared Magnitude-Redshift Relations for Luminous Radio Galaxies

Infrared magnitude-redshift relations for the 3CR and 6C samples of radio galaxies are presented for a wide range of plausible cosmological models, including those with non-zero cosmological constant OmegaLambda. Variations in the galaxy formation redshift, metallicity and star formation history are also considered. The results of the modelling are displayed in terms of magnitude differences between the models and no-evolution tracks, illustrating the amount of K-band evolution necessary to account for the observational data. Given a number of plausible assumptions, the results of these analyses suggest that: (i) cosmologies which predict T_0xH_0>1 (where T_0 denotes the current age of the universe) can be excluded; (ii) the star formation redshift should lie in the redshift interval 5OmegaLambda can provide good agreement with the observations only if appropriate adjustments of other parameters such as the galaxy metallicities and star-formation histories are made. Without such modifications, even after accounting for stellar evolution, the high redshift radio galaxies are more luminous (ie. more massive) than those nearby in models with finite OmegaLambda, including the favoured model with Omega=0.3, OmegaLambda=0.7. For cosmological models with larger values of T_0xH_0, the conclusions are the same regardless of whether any adjustments are made or not. The implications of these results for cosmology and models of galaxy formation are discussed.

Finite Element Solutions for Plane Strain Mode I Crack with Strain Grading Effect

In this paper, a new phenomenological theory with strain gradient effects is proposed to account for the size dependence of plastic deformation at micro- and submicro-length scales. The theory fits within the framework of general couple stress theory and three rotational degrees of freedom omega(i) are introduced in addition to the conventional three translational degrees of freedom mu(i). omega(i) is called micro-rotation and is the sum of material rotation plus the particles' relative rotation. While the new theory is used to analyze the crack tip field or the indentation problems, the stretch gradient is considered through a new hardening law. The key features of the theory are that the rotation gradient influences the material character through the interaction between the Cauchy stresses and the couple stresses; the term of stretch gradient is represented as an internal variable to increase the tangent modulus. In fact the present new strain gradient theory is the combination of the strain gradient theory proposed by Chen and Wang (Int. J. Plast., in press) and the hardening law given by Chen and Wang (Acta Mater. 48 (2000a) 3997). In this paper we focus on the finite element method to investigate material fracture for an elastic-power law hardening solid. With remotely imposed classical K fields, the full field solutions are obtained numerically. It is found that the size of the strain gradient dominance zone is characterized by the intrinsic material length l(1). Outside the strain gradient dominance zone, the computed stress field tends to be a classical plasticity field and then K field. The singularity of stresses ahead of the crack tip is higher than that of the classical field and tends to the square root singularity, which has important consequences for crack growth in materials by decohesion at the atomic scale. (C) 2002 Elsevier Science Ltd. All rights reserved.

A New Deformation Theory with Strain Gradient Effects

A new phenomenological deformation theory with strain gradient effects is proposed. This theory, which belongs to nonlinear elasticity, fits within the framework of general couple stress theory and involves a single material length scale l. In the present theory three rotational degrees of freedom omega(i) are introduced in addition to the conventional three translational degrees of freedom u(i). omega(i) has no direct dependence upon ui and is called the micro-rotation, i.e. the material rotation theta(i) plus the particle relative rotation. The strain energy density is assumed to only be a function of the strain tensor and the overall curvature tensor, which results in symmetric Cauchy stresses. Minimum potential principle is developed for the strain gradient deformation theory version. In the limit of vanishing 1, it reduces to the conventional counterparts: J(2) deformation theory. Equilibrium equations, constitutive relations and boundary conditions are given in details. Comparisons between the present theory and the theory proposed by Shizawa and Zbib (Shizawa, K., Zbib, H.M., 1999. A thermodynamical theory gradient elastoplasticity with dislocation density Censor: fundamentals. Int. J. Plast. 15, 899) are given. With the same hardening law as Fleck et al. (Fleck, N.A., Muller, G.H., Ashby, M.F., Hutchinson, JW., 1994 Strain gradient plasticity: theory and experiment. Acta Metall. Mater 42, 475), the new strain gradient deformation theory is used to investigate two typical examples, i.e. thin metallic wire torsion and ultra-thin metallic beam bend. The results are compared with those given by Fleck et al, 1994 and Stolken and Evans (Stolken, J.S., Evans, A.G., 1998. A microbend test method for measuring the plasticity length scale. Acta Mater. 46, 5109). In addition, it is explained for a unit cell that the overall curvature tensor produced by the overall rotation vector is the work conjugate of the overall couple stress tensor. (C) 2002 Elsevier Science Ltd. All rights reserved.

An in vitro transposon system for highly regulated gene expression: construction of Escherichia coli strains with arabinose-dependent growth at low temperatures.

Placing a gene of interest under the control of an inducible promoter greatly aids the purification, localization and functional analysis of proteins but usually requires the sub-cloning of the gene of interest into an appropriate expression vector. Here, we describe an alternative approach employing in vitro transposition of Tn Omega P(BAD) to place the highly regulable, arabinose inducible P(BAD) promoter upstream of the gene to be expressed. The method is rapid, simple and facilitates the optimization of expression by producing constructs with variable distances between the P(BAD) promoter and the gene. To illustrate the use of this approach, we describe the construction of a strain of Escherichia coli in which growth at low temperatures on solid media is dependent on threshold levels of arabinose. Other uses of the transposable promoter are also discussed.

微重力流体力学

目录

前言
第一章 微重力流体科学概论
一、微重力科学与微重力流体科学
1、微重力环境
2、重力的影响
3、微重力流体科学的发展
二、微重力流体力学概述
1、对流
2、扩散及输运现象
3、液滴和气泡动力学
4、多相流过程
5、残余重力效应
6、其他流体力学问题
三、微重力物理化学概述
1、临界现象
2、燃烧
3、分散体悬浮系统
4、晶体生长的物理化学问题
四、微重力流体科学的研究途径
1、微重力研究的一般途径
2、微重力实验手段
参考文献
第二章 基本方程组和流体运动特性
一、引言
二、连续性方程和迁移方程
三、动量方程
1、流体的粘性——Reynolds应力
2、动量守恒定律
3、Navier-Stokes方程
四、能量方程
1、总能量方程
2、动能方程
3、内能方程
4、粘性耗散函数
5、Fourier定律及另外二种形式的能量方程
6、不可压流体的导热方程
五、Newton流体的运动方程组及定解条件
1、基本方程组和适定性
2、定解条件
六、Boussinesq近似及适用范围
七、相似律和无量纲参数
1、利用Buckinghan〓定理导出相似参数
2、微重力流体力学的有关物理量和无量纲参数
参考文献
第三章 毛细现象以及界面的平衡和稳定
一、引言
二、表面张力的物理描述
三、液体射流的表面不稳定
1、基本方程组和基态
2、小扰动的线性化方程
3、本征值方程及其解
四、等温条件下液桥的平衡位型和稳定
1、表面张力作用下的平衡条件
2、毛细稳定性
3、旋转稳定性
第五章 液桥的流体动力学稳定理论
1、基本假设和液桥的平衡条件
2、稳定问题的数学提法
3、液桥的Liapunov稳定理论
4、特殊情形（Ω〓=μ=0）以及纯半波不稳定（n=1，m=1）
5、小扰动方程的变分方程
6、小Weber数和大Reynolds数情形的不稳定发展率
7、液桥微重力实验的结果的分析
8、讨论和结论
参考文献
第四章 对流和扩散
一、Pearson对流
1、自由面不变形时的小扰动分析
2、自由面可变形情形
3、非线性理论
4、多层不混溶液体系统
二、热毛细对流
1、矩形容器中的热毛细对流
2、柱形液桥的热毛细对流
3、半浮区液桥热毛细对流的数值模拟
4、薄层液体的热毛细对流
三、热毛细振荡对流的实验研究
1、液桥内部的温度振荡
2、热毛细对流的表面振荡
3、综合测量
四、热毛细对流的振荡机理
1、热流体波不稳定性
2、表面波不稳定性
3、有限高度液桥的线性不稳定性
4、三维不定常数值模拟
5、重力的影响
6、一种非稳定性理论
7、关于振荡的激发机制
参考文献
第五章 液滴动力学
一、等温液滴动力学
1、球形液滴的振荡
2、不混溶液体中球形液滴的振荡
3、弱非线性理论
4、实验模拟
二、非等温液滴的Marangoni迁移
1、定常线性化理论（小Reynolds数，小Marangoni数）
2、非线性理论
3、实验结果
三、液滴和气泡的相互作用
1、双气泡的轴对称理论
2、多液滴的轴对称理论
四、旋转液滴的演化序列和分叉理论
1、旋转液滴的演化
2、旋转液滴的Thomson-Tait稳定准则
3、长期稳定性和动力稳定性
4、长期稳定性真实性的实验证明
5、结论
参考文献
第六章 微重力材料流体力学
一、晶体生长过程
二、纯扩散过程
1、一维扩散过程
2、二维扩散过程
3、固-液界面弯曲对径向分凝的影响
三、浮区晶体生长
1、浮区的热毛细对流
2、浮区的熔质毛细对流
3、浮区对流的振荡特征（小Prandtl数对流）
4、耦合过程
四、溶液晶体生长
1、溶液晶体生长的相变界面过程
2、一维纯扩散过程
3、准定常溶液晶体生长过程
4、不定常溶液生长过程
五、气相晶体生长
1、气相晶体生长过程
2、一维模型
3、物理气相输运中的对流效应
4、化学气相沉积（CVD）过程
参考文献

Proximate composition and fatty acid and cholesterol content of 22 species of northwest Atlantic finfish

The moisture, fat, ash, fatty acid profile, and cholesterol content are reported for cooked and raw fillets from 22 species of finfish found in the Northwest Atlantic. All but nine species had 1%or less fat. Ocean perch and a spring sampling of mackerel and wolffiSh had about 2% fat, followed by yellowfin tuna, whiting, silver hake, butterfish, and a summer -sampling of mackerel and wolffish with a range of 3-7% fat. Herring had a range of 5-12% fat representing a winter sampling on the low end and summer sampling on the high end of the range. Bluefin tuna (a summer sampling) contained the most fat with a high of 23% fat. Omega-3 fatty acids were present in excess of omega-6 fatty acids. The fattier fISh supplied the most omega-3 fatty acids per gram of tissue. The mean cholesterol content for all species was 57 ± 16 mg/l00 g raw tissue. Finfish from the Northwest Atlantic would appear to fit into the regime for a healthy heart, being low in fat and cholesterol and rich in omega-3 fatty acids.(PDF file contains 42 pages.)

Identification and estimation of size from the beaks of 18 species of cephalopods from the Pacific Ocean

A method of identifying the beaks and estimating body weight and mantle length of 18 species of cephalopods from the Pacific Ocean is presented. Twenty specimens were selected from each of the following cephalopod species: Symplectoteuthis oualaniensis, Dosidicus gigas, Ommastrephes bartramii, S. luminosa, Todarodes pacificus, Nototodarus hawaiiensis, Ornithoteuthis volalilis, Hyaloteuthis pelagica, Onychoteuthis banksii, Pterygioteuthis giardi, Abraliopsis affinis, A. felis, Liocranchia reinhardti, Leachia danae, Histioteuthis heteropsis, H. dofleini, Gonalus onyx, and Loligo opalescens. Dimensions measured on the upper and lower beak are converted to ratios and compared individually among the species using an analysis of variance procedure with Tukey's omega and Duncan's multiple range tests. Significant differences (P =0.05) observed among the species' beak ratio means and structural characteristics are used to construct artificial keys for the upper and lower beaks of the 18 species. Upper and lower beak dimensions are used as independent variables in a linear regression model with mantle length and body weight (log transformed). (PDF file contains 56 pages.)

Nanostructured giant magneto-impedance multilayers deposited onto flexible substrates for low pressure sensing

Nanostructured FeNi-based multilayers are very suitable for use as magnetic sensors using the giant magneto-impedance effect. New fields of application can be opened with these materials deposited onto flexible substrates. In this work, we compare the performance of samples prepared onto a rigid glass substrate and onto a cyclo olefin copolymer flexible one. Although a significant reduction of the field sensitivity is found due to the increased effect of the stresses generated during preparation, the results are still satisfactory for use as magnetic field sensors in special applications. Moreover, we take advantage of the flexible nature of the substrate to evaluate the pressure dependence of the giant magneto-impedance effect. Sensitivities up to 1 Omega/Pa are found for pressures in the range of 0 to 1 Pa, demostrating the suitability of these nanostructured materials deposited onto flexible substrates to build sensitive pressure sensors.

Effect of Molecular Flexibility on the Nematic-to-Isotropic Phase Transition for Highly Biaxial Molecular Non-Symmetric Liquid Crystal Dimers

In this work, a study of the nematic (N)-isotropic (I) phase transition has been made in a series of odd non-symmetric liquid crystal dimers, the alpha-(4-cyanobiphenyl-4'-yloxy)-omega-(1-pyrenimine-benzylidene-4'-oxy) alkanes, by means of accurate calorimetric and dielectric measurements. These materials are potential candidates to present the elusive biaxial nematic (N-B) phase, as they exhibit both molecular biaxiality and flexibility. According to the theory, the uniaxial nematic (N-U)-isotropic (I) phase transition is first-order in nature, whereas the N-B-I phase transition is second-order. Thus, a fine analysis of the critical behavior of the N-I phase transition would allow us to determine the presence or not of the biaxial nematic phase and understand how the molecular biaxiality and flexibility of these compounds influences the critical behavior of the N-I phase transition.

Ein neues Messgerät zur Kontrolle der Maschenöffnung in der Fischerei

At present both the wedge gauge and the ICES mesh gauge are used to examine the mesh opening of trawl cod-ends. A thorough investigation of both instruments by an EU project (MESH) has revealed a number of deficiencies. This has lead to the conclusions to not further recommend the use of both devices but to go for the development of a complete new measurement tool. This is presently progressing in a further EU project named OMEGA. Prototypes of the new device have been produced and a number of introductory tests have already been made. This contribution reports on further laboratory tests carried out at the Institute for Fishing technology and Fish Quality with special emphasis on netting yarn diameters below 4 mm. The results demonstrate further yarn size depending inaccuracies of the wedge gauge and support the rapid introduction of the newly developed measurement instrument.

Short-pulse laser absorption via J x B heating in ultrahigh intensity laser plasma interaction

An analytical fluid model for JxB heating during the normal incidence by a short ultraintense linearly polarized laser on a solid-density plasma is proposed. The steepening of an originally smooth electron density profile as the electrons are pushed inward by the laser is included self-consistently. It is shown that the JxB heating includes two distinct coupling processes depending on the initial laser and plasma conditions: for a moderate intensity (a <= 1), the ponderomotive force of the laser light can drive a large plasma wave at the point n(e)=4 gamma(0)n(c) resonantly. When this plasma wave is damped, the energy is transferred to the plasma. At higher intensity, the electron density is steepened to a high level by the time-independent ponderomotive force, n(e)> 4 gamma(0)n(c), so that no 2 omega resonance will occur, but the longitudinal component of the oscillating ponderomotive field can lead to an absorption mechanism similar to "vacuum heating." (c) 2006 American Institute of Physics.

High energy photoproduction of neutral mesons

Cross sections for the photoproduction of neutral pi, eta, rho and phi mesons on hydrogen have been measured at the Stanford Linear Accelerator Center using a missing mass spectrometer technique. The data cover photon energies between 5.0 and 17.8 GeV and four momentum transfer squared t between -.12 and -1.38 (GeV/c)².

Pion differential cross sections at lower energies show a peak at low momentum transfers, a distinctive dip and secondary maximum for t in the region -.4 to -.9 (GeV /c)², and a smooth decrease at higher momentum transfers. As photon energy increases, the dip becomes less pronounced, in contradiction to the expectations of simple Regge theories based on the exchange of omega and B trajectories only.

Eta photoproduction was measured only below 10 GeV. The cross section has about the same magnitude as the pion production cross section, but decreases exponentially with t, showing no dip.

Rho mesons appear to be diffractively produced. The differential cross section varies approximately as exp(8.5t + 2t²). It falls slowly with energy, decreasing about 35 percent from 6 GeV to 17.8 GeV. A simple quark model relation appears to describe the data well.

Phi meson cross sections are also consistent with diffraction production. The differential cross section varies approximately as exp(4t). The cross section tends to decrease slightly with photon energy.