Formation of three kinds of hard domains by low-bias-field method

The formation of three kinds of hard domains (HDs) at low bias field was studied experimentally. Low-bias-field method provides a simple way to produce the three kinds of HDs in different proportions. Also, the relationship between the shape of the multi-branched domains (MBDs) and the different kinds of domains was studied. Most branches of the MBDs correspond to the first kind of dumbbell domains or the second kind of dumbbell domains; in contrast, few branches of the MBDs correspond to the hard bubbles or soft bubbles.     

脉冲偏场作用下石榴石磁泡薄膜中布洛赫线的形成

实验研究了石榴石磁泡薄膜中不同脉冲宽度下产生的硬磁畴的动态特性.结果表明：由零偏场下产生的枝状畴收缩而成的哑铃畴均逆时针转动,与产生枝状畴时所用的脉冲偏场的脉冲宽度无关.而固定直流偏场下由软畴段硬化而成的哑铃畴的转动状态,则与所用的硬化脉冲偏场的脉冲宽度有关.低脉冲宽度下硬化成的哑铃畴均逆时针转动,随硬化脉冲宽度的升高,出现混合转动向顺时针转动的过渡.由此揭示了直流偏场和脉冲偏场在石榴石磁泡薄膜中形成正、负垂直布洛赫线的作用. 关键词： 磁畴 磁泡 垂直布洛赫线     

Influence of Temperature on Equilibrium Separation Between Vertical Bloch Lines in OHBs in Garnet Bubble Films

The diameters of the ordinary hard bubbles （OHBs） and soft bubbles in epitaxial garnet films are measured under the microscope at various temperatures. It is found that the bubble diameters of OHBs increase with temperature, and it is concluded that the equilibrium separation between two neighbouring vertical Bloch lines （VBLs） Seq is widened with increasing temperature. At the same time, the results can be understood simply as that there are more VBLs in the domain walls of the first dumbbell domains （IDs） than those in walls of OHBs at the same temperature.     

用弛豫法探寻新的双开口膜泡

基于面积差弹性模型, 用弛豫法探寻满足开口膜泡边界条件的欧拉-拉格朗日方程组的新解, 得到了双开口的哑铃形分支解, 并结合以前得到的单开口哑铃形及闭合哑铃形, 对它们之间的相变进行了深入的研究. 为了探究实验上是否可能发现这些形状, 与以往实验上观察到的较小约化弛豫面积差的杯形、管形、烟囱形开口形状的能量进行了比较, 发现这些新形状在较大的约化弛豫面积差值时, 在某些线张力区间比以往发现的形状能量更低. 另外为了对比, 本文对于实验上已知的杯形、管形、烟囱形及球形之间的相变行进行了探讨, 并对两者之间的不同特点进行了对比.     

系列脉冲偏磁场作用下硬磁泡的形成

实验研究了系列脉冲偏场作用下外延石榴石薄膜的硬磁泡(包括哑铃畴)的形成规律。发现系列脉冲对畴段的作用不是单次脉冲作用(软畴段硬化的物理过程)的简单迭加,而有其特有的规律性,存在着硬畴段进一步硬化及硬畴段软化的另两个物理过程。运用上述三个物理过程对实验结果作了解释。 关键词：     

Mixtures of polar and nonpolar molecules

The site-site Ornstein-Zernike (SSOZ) equation with mean spherical approximation closure is solved analytically for a mixture of hard dumbbells and polar hard dumbbells. The solution reduces to that of the pure polar hard dumbbell fluid at the polar species density rather than the total density. The thermodynamic properties of the mixture are obtained using the zero-pole approximation (ZPA) to the free energy. The mixture is shown to separate into two mixed phases, one rich in the nonpolar species and the other rich in the polar species. This phase separation terminates in an upper critical solution temperature. The excess thermodynamic functions are presented and the mixture exhibits both positive and negative values of the excess volume. The negative values of the excess volume occur in mixtures rich in the polar component.     

The stability limit of the fluid phase of polydisperse sticky spheres

It has been shown by Stell (1991, J. statist. Phys., 63, 1203) that at low temperature mono-disperse sticky spheres collapse to form coexisting close-packed solid and infinitely dilute gases. We show that polydisperse sticky spheres also collapse and calculate the collapse temperature. The polydisperse spheres separate into fractions with narrower polydispersities which can then solidify. This is perhaps the first example of a single-peaked polydisperse mixture phase solidifying and separating. It implies that a mixture of polydisperse large hard spheres with much smaller hard spheres does not show fluid—fluid coexistence.     

Spontaneous patterning of quantum dots at the air-water interface

Nanoparticles deposited at the air-water interface are observed to form circular domains at low density and stripes at higher density. We interpret these patterns as equilibrium phenomena produced by a competition between an attraction and a longer-ranged repulsion. Computer simulations of a generic pair potential with attractive and repulsive parts of this kind, reproduce both the circular and stripe patterns. Such patterns have a potential use in nanoelectronic applications.     

甲烷微尺度催化燃烧的数值模拟

本文联合使用计算流体力学软件FLUENT和可以计算表面反应的化学反应动力学软件DETCHEM对有逆流换热的微尺度燃烧器进行了数值计算。计算中忽略空间反应。燃料-空气混合物的当量比为0.4,反应器壁面采用等温边界条件。计算结果表明,采用催化燃烧可以实现微尺度下通常情况下无法实现的甲烷稳定燃烧。通过适当设置催化表面,可以实现燃料低温、高效转变。甲烷的总转变率受流动状态、反应温度和催化表面的大小等因素的影响。     

Memory effects in the diffusion of an interacting polydisperse suspension: II. Hard spheres at low density

We consider the diffusion of a low density suspension of polydisperse hard spheres. In a previous article (I) we have obtained at long wavelength a general expression to first order in density for the memory matrix appropriate to such a system. In the present article we evaluate the memory matrix in closed form using a certain approximations for the hydrodynamic interaction and for the 2-body propagator. We find that memory effects convert the exponential decay of density correlation functions to long time power law decay of the form $\text{t}{}^{\mathrm{<mtext>-</mtext><mtext>5</mtext><mtext>2</mtext>}}$. We consider the so-called long time self-diffusion constant and show that memory effects to first order in density are negligible compared to the first cumulant contribution. Our treatment shows that for hard sphere systems it is essential to treat the short distance hydrodynamic forces accurately.     

Lyapunov instability of two-dimensional fluids: Hard dumbbells

We generalize Benettin's classical algorithm for the computation of the full Lyapunov spectrum to the case of a two-dimensional fluid composed of linear molecules modeled as hard dumbbells. Each dumbbell, two hard disks of diameter sigma with centers separated by a fixed distance d, may translate and rotate in the plane. We study the mixing between these qualitatively different degrees of freedom and its influence on the full set of Lyapunov exponents. The phase flow consists of smooth streaming interrupted by hard elastic collisions. We apply the exact collision rules for the differential offset vectors in tangent space to the computation of the Lyapunov exponents, and of time-averaged offset-vector projections into various subspaces of the phase space. For the case of a homogeneous mass distribution within a dumbbell we find that for small enough d/sigma, depending on the density, the translational part of the Lyapunov spectrum is decoupled from the rotational part and converges to the spectrum of hard disks. (c) 1998 American Institute of Physics.     

Effect of vacancies and interstitials in the dumbbell configuration on the shear modulus and vibrational density of states of copper

It has been shown by the molecular dynamics method that the introduction of interstitials in the dumbbell configuration into the copper crystal leads to a significantly stronger shear modulus reduction than the vacancy introduction. Specific low-frequency modes appear in the spectrum of vibrational states of “defect” atoms. The vacancy formation enthalpy weakly depends on their concentration, and the interstitial dumbbell formation enthalpy at high concentrations can decrease by a factor of 8. In this case, the radial distribution function takes the form characteristic of noncrystalline materials. The results obtained confirm the interstitial theory of the condensed state.     

Cu60Zr30Ti10非晶合金弛豫和晶化过程的小角X射线散射研究

应用小角X射线散射技术研究了Cu₆₀Zr₃₀Ti₁₀非晶合金从300到813 K之间微结构的演化情况.发现在淬火状态下Cu₆₀Zr₃₀Ti₁₀非晶合金中存在直径30 nm左右的富Cu区.非晶的结构弛豫包括573 K之前的低温结构弛豫和573 K到玻璃转变温度的高温结构弛豫，弛豫的结果是产生含有有序原子团簇的富Cu区，这些有序原子团簇的富Cu区是随后晶化过程中晶核产生的基础.Porod曲线分析表明，晶化生成的纳米体心立方CuZr相和基体之间有明锐的界面. 关键词： 小角X射线散射 非晶合金 结构弛豫 晶化     

铁磁/反铁磁双层膜中交换偏置及矫顽场的温度特性研究

讨论了铁磁-反铁磁双层膜中交换偏置和矫顽场随温度变化的关系。在本模型中,温度的依赖性来源于系统态的热激发以及相关磁学参量的温度依赖性。数值结果显示:低温下,交换偏置和矫顽场随温度的升高而减少,但是随着界面的交换耦合的增强或铁磁层各向异性的减少,其交换偏置变得平坦。随着温度的升高,交换偏置减少直至零;而矫顽场却达到峰值后再减为零。这些结果与实验结果定性一致。根据数值计算结果,可以预见软的铁磁层耦合上硬的反铁磁层,在恰当的交换耦合强度下,可构建具有大的交换偏置、小矫顽场;并在某温度区几乎不随温度变化的磁存贮器件.     

Modeling the self-assembly of copolymer-nanoparticle mixtures confined between solid surfaces

Using numerical calculations, we undertake the first morphological studies of mixtures of AB diblocks and nanoparticles that are confined between two hard walls. A complex interplay of entropic and enthalpic interactions drives the nonselective particles to localize at the hard walls and A/B interfaces, causing the mixture to spontaneously self-assemble into particle-decorated lamellae that are oriented perpendicular to the surfaces. The film reveals a periodic array of particle "nanowires" that are separated by the nanoscale polymer domains, yielding a vital material for nanodevice fabrication.     

The influence of high pressure on the structural and magnetic properties of Y2Fe17?xMx (M=Si, Al; x=1.7) compounds

The influence of high pressure on the crystal structure of the hexagonal intermetallic compounds Y₂Fe₁₇, Y₂Fe_15.3Al_1.7, and Y₂Fe_15.3Si_1.7 is investigated by neutron diffraction for the first time. It is shown that, under high pressure, the crystal lattice undergoes an isotropic contraction. A correlation of the changes in the Curie temperature with the distance between iron atoms in the dumbbell positions under pressure is revealed. The effect of pressure on the Y₂Fe₁₇ compound is examined at low temperatures. It is found that the magnetostriction in this compound is suppressed under high pressure. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 2, 2004, pp. 299–304. Original Russian Text Copyright ? 2004 by Voronin, Kuchin, Glazkov, Kozlenko, Savenko.     

温度对普通硬磁泡的影响

实验研究了温度对外延石榴石磁泡薄膜中硬磁泡及其相应硬条畴的影响。发现了一个与材料参量有关的临界温度T₀当试验温度T0时,硬条畴畴壁中的VBL链在升降温后不变;而当T>T₀时,VBL链消失,所有硬磁泡都软化为正常磁泡。当畴壁中的VBL处于压缩态时,较硬的硬磁泡在较低的温度下软化。软化时,VBL消失的方式是整个VBL链的解体。 关键词：     

Contribution of interstitial defects and anharmonicity to the premelting increase in the heat capacity of single-crystal aluminum

With the use of experimental data on the temperature dependence of the concentration of interstitial atoms, it has been shown within the interstitial theory that the premelting nonlinear increase in the heat capacity of aluminum can be caused by the intense generation of interstitial defects in a dumbbell configuration.     

Untersuchungen zum photokapazitiven Effekt von Phosphoren

Capacitance and loss angle of several phosphors are measured as a function of exciting irradiation intensity at different temperatures and different frequencies. Furthermore, the decay of the photocapacitive effect after shutting off the radiation is observed. Criteria are developed for deciding whether the photocapacitive effect is due to conduction band electrons (photoconductive effect of first kind), to impurity band electrons (photoconductive effect of second kind), or to polarization of filled traps (photodielectric effect). These are based on the decay behavior at low temperature (fast, slow, slow, respectively) and the dispersion at low frequencies (strong, strong, weak, respectively). It is shown that even for the photoconductive effect of first kind the interplay of conduction band and shallow traps is essential but that, nevertheless, conductivity data can be obtained from capacitance measurements.     

基于光纤中交叉相位调制的波长转换器研究

波长转换器在未来的全光网络中将起到重要的作用.通过大量的数值仿真,研究了利用色散位移光纤中的自相位调制效应的波长转换器,首次对各参量,包括输入光信号脉冲的峰值功率,连续波的功率,两束光信号的频率间隔,光纤的色散,光纤的长度以及输入信号的比特率对此波长转换器的性能影响进行了数值研究.结果表明,光纤的色散和输入光信号脉冲的功率在这种波长转换器中起重要作用,而且这种波长转换器可以对高达200Gb/s的信号进行转换.