Derivation of Cahn-Hilliard equations from Ginzburg-Landau models

The generalized Cahn-Hilliard equation is obtained as the hydrodynamic limit from a stochastic Ginzburg-Landau model. The associated large-deviation principle is also proved. In the one-dimensional case, we prove a related result about the scaling limit of conservative Langevin dynamics of an SOS surface.     

A vector radiative transfer model for coupled atmosphere and ocean systems with a rough interface

We report on an exact vector (polarized) radiative transfer (VRT) model for coupled atmosphere and ocean systems. This VRT model is based on the successive order of scattering (SOS) method, which virtually takes all the multiple scattering processes into account, including atmospheric scattering, oceanic scattering, reflection and transmission through the rough ocean surface. The isotropic Cox–Munk wave model is used to derive the ref and transmission matrices for the rough ocean surface. Shadowing effects are included by the shadowing function. We validated the SOS results by comparing them with those calculated by two independent codes based on the doubling/adding and Monte Carlo methods. Two error analyses related to the ocean color remote sensing are performed in the coupled atmosphere and ocean systems. One is the scalar error caused by ignoring the polarization in the whole system. The other is the error introduced by ignoring the polarization of the light transmitted through the ocean interface. Both errors are significant for the cases studied. This code fits for the next generation of ocean color study because it converges fast for absorbing medium as, for instance, ocean.     

The dependence of time-domain speed-of-sound measurements on center frequency, bandwidth, and transit-time marker in human calcaneus in vitro

Time-domain speed-of-sound (SOS) measurements in calcaneus are effective predictors of osteoporotic fracture risk. High attenuation and dispersion in bone, however, produce severe distortion of transmitted pulses that leads to ambiguity of time-domain SOS measurements. An equation to predict the effects of system parameters (center frequency and bandwidth), algorithm parameters (pulse arrival-time marker), and bone properties (attenuation coefficient and thickness) on time-domain SOS estimates is derived for media with attenuation that varies linearly with frequency. The equation is validated using data from a bone-mimicking phantom and from 30 human calcaneus samples in vitro. The data suggest that the effects of dispersion are small compared with the effects of frequency-dependent attenuation. The equation can be used to retroactively compensate data. System-related variations in SOS are shown to decrease as the pulse-arrival-time marker is moved toward the pulse center. Therefore, compared with other time-domain measures of SOS, group velocity exhibits the minimum system dependence.     

半导体断路开关数值模拟

 为了研究半导体断路开关(SOS)的截断过程及其在脉冲功率系统中的工作特性,建立了半导体断路开关的电流控制模型,对p⁺-p-n-n⁺掺杂结构的半导体断路开关进行了数值模拟研究。通过数值模拟,给出了p⁺-p-n-n⁺型半导体断路开关在正、反向泵浦过程中的载流子及电场分布,并获得了电流截断效应。计算结果表明,半导体断路开关的截断过程首先发生在p区。     

Analytic Approximations for the Velocity of Field-Driven Ising Interfaces

We present analytic approximations for the field, temperature, and orientation dependences of the interface velocity in a two-dimensional kinetic Ising model in a nonzero field. The model, which has nonconserved order parameter, is useful for ferromagnets, ferroelectrics, and other systems undergoing order–disorder phase transformations driven by a bulk free-energy difference. The solid-on-solid (SOS) approximation for the microscopic surface structure is used to estimate mean spin-class populations, from which the mean interface velocity can be obtained for any specific single-spin-flip dynamic. This linear-response approximation remains accurate for higher temperatures than the single-step and polynuclear growth models, while it reduces to these in the appropriate low-temperature limits. The equilibrium SOS approximation is generalized by mean-field arguments to obtain field-dependent spin-class populations for moving interfaces, and thereby a nonlinear-response approximation for the velocity. The analytic results for the interface velocity and the spin-class populations are compared with Monte Carlo simulations. Excellent agreement is found in a wide range of field, temperature, and interface orientation.     

基于SOS和LTD技术的高重复频率脉冲发生器

提出了磁饱和直线变压器驱动源(LTD)泵浦半导体断路开关(SOS)产生高重复频率短脉冲的技术路线。利用LTD初次级线圈为单匝同轴结构和磁芯可饱和的特点,实现快速反向泵浦SOS,通过多级LTD模块叠加获得高电压输出。采用射频金属氧化物场效应晶体管(RF MOSFET)作为LTD初级电路的主开关,将SOS正向泵浦电流脉冲时间降至数十ns,泵浦电流脉冲重复频率最高可达MHz。最终研制出一台基于SOS的10级磁饱和LTD型脉冲发生器,输出电压约11kV,电流220A,脉冲宽度约2ns,重复频率为20kHz。实验验证了磁饱和直线脉冲变压器泵浦SOS产生高重复频率短脉冲的技术路线可行。     

Conservative Langevin dynamics of solid-on-solid interfaces

We study the dynamics of an interface between two phases in interaction with a wall in the case when the evolution is dominated by surface diffusion. For this, we use an SOS model governed by a conservative Langevin equation and suitable boundary conditions. In the partial wetting case, we study various scaling regimes and show oscillatory behavior in the relaxation of the interface toward its equilibrium shape. We also consider complete wetting and the structure of the precursor film.     

The Influence of Boundary Conditions on Solid-on-Solid Models

We investigate various 1D solid-on-solid (SOS) models using the transfer matrix method. The main results of the paper concern SOS interfaces near an attracting wall (line) when the end points of the interface are fixed away from the wall (line). We obtain typical interface shapes in the macroscopic scale. If attraction of the wall is strong enough, then a part of the interface is pinned to the wall (line) and the remaining parts of the interface form angles with the wall (line)—the contact angles. Explicit expressions for the contact angles are derived. We show also that for a certain range of parameters the models exhibit reentrant wetting and drying. As a result the free energy of the SOS model as a function of temperature can have up to three points of nonanalyticity. The fluctuations of the SOS interface are investigated in detail. Quite unusual fluctuations are observed at the contact points—the points where unpinned and pinned parts of the interface meet.     

基于半导体断路开关的8 MW,10 kHz脉冲发生器

 功率器件半导体断路开关具有高重复频率工作能力。采用高速绝缘栅双极晶体管组件作为初级充电回路的主开关,建立了一台工作频率为10 kHz的脉冲发生器。脉冲发生器采用磁饱和脉冲变压器、磁开关及高压脉冲电容器组等固态器件进行两级脉冲压缩,产生小于100 ns的电流脉冲,对半导体断路开关进行泵浦,半导体断路开关反向截断泵浦电流在负载上产生高压脉冲输出。实验装置在电阻负载上得到了脉冲输出功率约为8.6 MW,脉冲宽度约10 ns,重复频率10 kHz的高压脉冲输出。     

Investigation of silicon-on-sapphire structures by means of TEM

The initial stages of the molecular beam epitaxy (MBE) growth of silicon-on-sapphire (SOS) are investigated via transmission electron microscopy (TEM). The sample preparation procedure is improved to study SOS structures by TEM. It is shown that silicon in the shape of 3D islets can form on a continuous silicon layer grown on sapphire.     

Optical and DC-electric poling on AgX (X = Cl, I)-Doped chalcohalide glasses

The influence of the simultaneous polarized optical treatment (10-ns Nd:YAG lasers with a poser density of 3.6 GW/cm²) together with an electrostatic DC-electric field (up to 8 kV/cm) on GeS₂-Ga₂S₃-AgX (X = Cl, I) and GeS₂-Ga₂S₃-KBr chalcohalide glasses is explored. The maximal second-order susceptibility (SOS) was achieved for the AgI-doped specimen. In samples without silver halides, however, the SOS was below 0.25 pm/V. This fact may indicate the principal role of the high polarizability of Ag⁺ ions in the enhanced SOS. A common feature for all three glasses is that the SOS achieves maximal values after one minute of simultaneous DC-electrical optical treatment. Further treatment will not enhance the SOS values and can even lead to its decrease by several times. The independent measurement of the local temperature shows that local heating does not excess 5°–7°.     

Correlations between acoustic properties and bone density in bovine cancellous bone from 0.5 to 2 MHz

Correlations between acoustic properties and bone density were investigated in the 12 defatted bovine cancellous bone specimens in vitro. Speed of sound (SOS) and broadband ultrasonic attenuation (BUA) were measured in three different frequency bandwidths from 0.5 to 2 MHz using three matched pairs of transducers with the center frequencies of 1, 2.25, and 3.5 MHz. The relative orientation between ultrasonic beam and bone specimen was the mediolateral (ML) direction of the bovine tibia. SOS shows significant linear positive correlation with apparent density for all three pairs of transducers. However, BUA shows relatively weak correlation with apparent density. SOS and BUA are only weakly correlated with each other. The linear combination of SOS and BUA in a multiple regression model leads to a significant improvement in predicting apparent density. The correlations among SOS, BUA, and bone density can be effectively and clearly represented in the three-dimensional space by the multiple regression model. These results suggest that the frequency range up to 1.5 MHz and the multiple regression model in the three-dimensional space can be useful in the osteoporosis diagnosis.     

A numerical method to predict the effects of frequency-dependent attenuation and dispersion on speed of sound estimates in cancellous bone

Many studies have demonstrated that time-domain speed-of-sound (SOS) measurements in calcaneus are predictive of osteoporotic fracture risk. However, there is a lack of standardization for this measurement. Consequently, different investigators using different measurement systems and analysis algorithms obtain disparate quantitative values for calcaneal SOS, impairing and often precluding meaningful comparison and/or pooling of measurements. A numerical method has been developed to model the effects of frequency-dependent attenuation and dispersion on transit-time-based SOS estimates. The numerical technique is based on a previously developed linear system analytic model for Gaussian pulses propagating through linearly attenuating, weakly dispersive media. The numerical approach is somewhat more general in that it can be used to predict the effects of arbitrary pulse shapes and dispersion relationships. The numerical technique, however, utilizes several additional assumptions (compared with the analytic model) which would be required for the practical task of correcting existing clinical databases. These include a single dispersion relationship for all calcaneus samples, a simple linear model relating phase velocity to broadband ultrasonic attenuation, and a constant calcaneal thickness. Measurements on a polycarbonate plate and 30 human calcaneus samples were in good quantitative agreement with numerical predictions. In addition, the numerical approach predicts that in cancellous bone, frequency-dependent attenuation tends to be a greater contributor to variations in transit-time-based SOS estimates than dispersion. This approach may be used to adjust previously acquired individual measurements so that SOS data recorded with different devices using different algorithms may be compared in a meaningful fashion.     

近十年中国东北森林植被物候遥感监测

基于归一化差值植被指数(normalized difference vegetation index, NDVI),提出了一种新的物候遥感监测方法,基于森林植被的年NDVI时间累积曲线,利用Logistic模型对NDVI累积曲线进行拟合,依据曲率极值方法提取森林植被物候期的关键参数(生长季开始日期, SOS; 生长季结束日期, EOS),并对森林植被的生长季长度(length of season, LOS)进行分析,探讨近10年东北森林物候的时空变化。主要结论为：(1)2001年～2010年间,东北森林生长季开始日期集中在110～140天但在10年间没有明显变化;(2)第260～290天,森林逐渐停止生长,生长季结束日期从北向南逐渐推迟,但在十年间几乎没变化;(3)与生长季开始和结束日期相对应,东北森林生长季长度集中在120～160天之间,但存在空间差异,大兴安岭地区森林生长季长度较短,集中在120～140天之间,小兴安岭、长白山、辽东半岛地区的森林生长季长度可达到160天,对整个研究区来讲,近10年间变化的区域仅占研究区的14.9%,变化趋势集中在1d/10年。研究结果与物候观测数据及已有的研究具有较好的一致性,说明利用遥感数据动态监测东北森林植被物候期具有一定的可靠性。     

Exact solution of the discrete (1+1)-dimensional SOS model with field and surface interactions

We present the solution of a linear solid-on-solid (SOS) model. Configurations are partially directed walks on a two-dimensional square lattice and we include a linear surface tension, a magnetic field, and surface interaction terms in the Hamiltonian. There is a wetting transition at zero field and, as expected, the behavior is similar to a continuous model solved previously. The solution is in terms ofq-series most closely related to theq-hypergeometric functions_{1 1}.     

On the insulating properties of the interfacial layer between ion bombarded-amorphous and crystalline silicon

After bombarding silicon single crystals with heavy neon ion doses, the resulting amorphous surface layer has been found to be electrically insulated from the underlying bulk material. Current-voltage characteristics indicate the formation of a junction between the crystalline and the damaged layer. As a consequence, the electrical properties of the amorphous layer can be measured at low temperatures up to about 230 K and considerably beyond room temperature, if thick crystal wafers and silicon-on-sapphire (SOS) samples, respectively, are used.     

A semi-analytic technique to speed up successive order of scattering model for optically thick media

A semi-analytic technique has been developed to speed up the integration of radiative transfer over optically thick media for the successive order of scattering (SOS) method. Based on the characteristics of the internal distribution of scattering intensity, this technique uses piecewise analytic eigenfunctions to fit internal scattering intensities and integrates them analytically over optical depth. This semi-analytic approach greatly reduces the number of sub-layers required for accurate radiative transfer calculation based on the SOS method. Results show that an accuracy of 1% for both flux and radiance (polar angle less than 67^°) can be achieved with a significantly small number of layers. This technique is accurate and efficient and makes the SOS method applicable for optically thick scattering media.