About the Importance of Nanometer-Thick Intergranular Penetration in the Analysis of Liquid Metal Embrittlement

Liquid metal embrittlement (LME) of copper by liquid bismuth is investigated at 300°C. It is shown that a very rapid damage is due to the synergy between the external stress and the phenomenon of intergranular penetration (IGP). Tests of IGP, i.e. without external stress, were done at 300°C and at 600°C and have resulted in strong intergranular embrittlement due to the formation of nanometer-thick intergranular films, as measured and quantified by Auger electron spectroscopy (AES). The formation of these films is discussed with respect to apparently non-zero dihedral angles at 600°C. A general procedure based on mechanical testing and AES measurements, to check whether IGP has occurred or not, is outlined. This procedure can be seen as an alternative way to determine the wetting transition temperature. The presence of nanometer-thick films due to IGP is discussed with respect to the LME mechanisms.     

Research on spatial economic structure for different economic sectors from a perspective of a complex network

The economy system is a complex system, and the complex network is a powerful tool to study its complexity. Here we calculate the economic distance matrices based on annual GDP of nine economic sectors from 1995–2010 in 31 Chinese provinces and autonomous regions,¹ then build several spatial economic networks through the threshold method and the Minimal Spanning Tree method. After the analysis on the structure of the networks and the influence of geographic distance, some conclusions are drawn. First, connectivity distribution of a spatial economic network does not follow the power law. Second, according to the network structure, nine economic sectors could be divided into two groups, and there is significant discrepancy of network structure between these two groups. Moreover, the influence of the geographic distance plays an important role on the structure of a spatial economic network, network parameters are changed with the influence of the geographic distance. At last, 2000 km is the critical value for geographic distance: for real estate and finance, the spearman’s rho with l<2000$l<2000$ is bigger than that with l>2000$l>2000$, and the case is opposite for other economic sectors.     

Comparison of spatial harmonics in infinite and finite Bragg stacks for metamaterial homogenization

Metamaterial homogenization may be based on the dominance of a single Floquet–Bloch spatial harmonic in an infinite periodic structure – with the dominance quantified in terms of the relative magnitude of the associated spatial harmonic Poynting vector. For the corresponding finite structure the field is not quasi-periodic and cannot be expanded in Floquet–Bloch spatial harmonics; however, a set of pseudo spatial harmonics can be defined and the dominance of a single such harmonic likewise be used to determine whether the structure can be homogenized. For three different lossless Bragg stack configurations (one of which is magneto-dielectric), we show, using spectral representation, that the field in the finite structure can be accurately expanded in terms of these pseudo spatial harmonics and that the distribution of these agrees very well with the distribution of Floquet–Bloch spatial harmonics of the corresponding infinite Bragg stack. This is even the case for finite Bragg stacks having only two unit cells; thus, the number of unit cells does not influence the homogenizability of this type of configuration.     

In-Situ HREM Studies of Grain Boundary Migration

Thermally activated grain boundary migration (GB) is important in grain growth and thermo-mechanical processing of materials, but very little is known about the atomic-scale mechanisms involved. The purpose of this paper is to identify atomic-scale GB migration mechanism and investigate their dependence on GB structure. High-angle tilt and general GBs are investigated at elevated temperatures by high-resolution transmission electron microscopy (HREM) in Au and Al bicrystalline thin films. Digital analysis of HREM video recordings is used to detect atomic-scale structural changes at migrating GBs. GB motion typically is not smooth, but involves sharply varying speeds and thermally activated spatial fluctuations. Collective effects in GB migration are shown to exist and several different migration mechanisms are identified. Atomic-scale GB migration is found to depend on the macroscopic GB geometry as well as details of the interatomic interactions.     

Self-deflection of steady-state bright spatial solitons in biased centrosymmetric photorefractive crystals

The effects of diffusion on self-deflection of steady-state bright spatial solitons in biased centrosymmetric photorefractive crystals are investigated systematically by both numerical and perturbation methods. The results show that the soliton propagates along a parabolic trajectory and the central spatial frequency component shifts linearly with the propagation distance. Both the deflection effects vary cubically with applied external bias field.     

Spatial arrangement of the structural elements ofvocal fold layers: An adjustment to the vibration process

It is well established that the multilayered structure of the vocal fold is highly adjusted to the requirements of the vibration process during phonation. There is also some partial data indicating that the spatial arrangement of each vocal fold layer corresponds to the functional requirements, and thus facilitate the phonation process. Nevertheless, all reports on the spatial arrangement of the vocal fold structures deal only with an individual element of the vocal fold histologic structure. The present study encompasses the spatial histologic analysis of all major elements of the vocal fold layers. It was demonstrated that the vocal fold epithelial cells, the connective and muscle fibers, and even the blood vessels run parallel to the vocal fold free edge, which indicates a high adjustment to the phonation requirements and the vibration process.     

空间频率域超声背散射参量用于骨质状况的评价*

在超声背散射骨质评价中,不同测量感兴趣区域(ROI)的超声背散射信号会有波动,致使诊断准确度降低。该文目的是研究超声背散射信号随测量区域的变化规律。采用空间扫描方法离体测量了35块骨样本,将超声背散射参数从空间域变换到空间频率域。结果表明,超声背散射参数的主要空间频率成分集中于低频部分;空间频率域超声背散射参量最大值(MASF)与骨矿密度等参数具有中高度显著相关性(R2=0.45~0.83,p0.001);空间频率域超声背散射参量衰减系数(AC)也与松质骨密度及结构特征有显著相关性(R2=0.41~0.72,p0.001)。研究表明空间频率域变换方法有助于明确超声背散射信号随测量ROI的变化规律,空间频率域的超声背散射相关新参量评价松质骨状况具有可行性。     

Study on the spatial coherence of vortex Gaussian beams passed atmospheric turbulence

In this paper, the spectral degree of coherence formula was derived by using the generalized Huygens–Fresnel principle and the method of Rytov phase structure function quadratic approximation. The spatial coherence of vortex Gaussian beams passed atmospheric turbulence was studied. It showed that the spatial coherence was mainly affected by the coherence of light source, the number of topological charges and the transmission distance. The distance of transmission was farther, the spatial coherence of beam was better. The number of topological charges were more, the spatial coherence of beam was better. In a certain transmission distance, the coherence of light source was better, the spatial coherence of beam was worse. In addition, there were coherent vortexes which spectral degree of coherence was zero after the partially coherent vortex beams getting through atmospheric turbulence transmission.     

Compton profile of tantalum

The Compton profile of tantalum (Ta) has been measured using IGP type coaxial photon detector. The target atoms were excited by means of 59.54 keV γ-rays from Am-241. The measurements were carried out on a high purity thin elemental foil. The data were recoreded in a 4 K multichannel analyzer. These data duly corrected for various effects are presented and compared with theoretical and measured values. Best agreement with experiment is found for the 5d³6s² electron configuration     

ICF用Kirkpatrick-Baez型显微镜光学设计

 提出了直接针对惯性约束聚变（ICF）诊断目标的X射线Kirkpatrick-Baez型显微镜的像差校正和光学设计方法。在校正掠入射细光束像散的基础上,推导了内爆压缩区全视场范围内的垂轴像差表达式,进而构建了系统的空间分辨率预测模型。基于对空间分辨率和集光立体角两个关键指标的分析,结合ICF的实验要求,得到了系统的初始结构参数确定原则和光学设计流程。实例表明,该方法克服了传统的轴上球差评价的不足,设计结果能够同时满足内爆压缩区的视场、分辨率和集光效率的要求。     

Global Migration Can Lead to Stronger Spatial Selection than Local Migration

The outcome of evolutionary processes depends on population structure. It is well known that mobility plays an important role in affecting evolutionary dynamics in group structured populations. But it is largely unknown whether global or local migration leads to stronger spatial selection and would therefore favor to a larger extent the evolution of cooperation. To address this issue, we quantify the impacts of these two migration patterns on the evolutionary competition of two strategies in a finite island model. Global migration means that individuals can migrate from any one island to any other island. Local migration means that individuals can only migrate between islands that are nearest neighbors; we study a simple geometry where islands are arranged on a one-dimensional, regular cycle. We derive general results for weak selection and large population size. Our key parameters are: the number of islands, the migration rate and the mutation rate. Surprisingly, our comparative analysis reveals that global migration can lead to stronger spatial selection than local migration for a wide range of parameter conditions. Our work provides useful insights into understanding how different mobility patterns affect evolutionary processes.     

Effect of spatial patterns on population size

We investigate the role of the spatial pattern and temporal dynamics on the population properties of a diffusive Gause–Lotka–Volterra system. The average total population size is insensitive to the temporal dynamics, whereas a significant decrease of the population size can be found as the spatial diffusion effect is increased, implying that the spatial pattern plays an important role. At large diffusion coefficients, a saturation of the spatial pattern variation is observed, which can be understood by a spatial scaling analysis of the system. The existence of multiple attractors can also indicate that spatial patterns play a more important role than temporal dynamics in dominating the population size.     

一种递归神经网络空间分集均衡器

水声信道中的衰变多途特性常引起难以克服的码间干扰(ISI)。为了降低误码率、改善系统性能,本文提出了一种递归神经网络空间分集均衡器。它在传统的空间分集结构中融入了多层感知器,该结构能够充分利用训练信号的信息,在可调权数较少的情况下,能够得到较好的均衡效果;针对该结构,采取了初始设定权值的办法,从而使该均衡器的收敛速度得到大大提高。仿真与湖试试验结果表明,该均衡器结构合理,对空间分集均衡性能有一定的改善。     

基于晶体旋光效应的近场光学空间滤波

 在激光传输与放大系统中，激光束的空间滤波是光束质量控制的重要环节。利用各向同性晶体的旋光性，采用偏振光检偏法选择不同空间频率光束的通过与阻挡，实现激光光束的近场空间滤波。用多个滤波器串接构成滤波器组，可提高光束空间窄带滤波性能。该方法有利于克服激光工程中采用4f滤波带来的空间滤波器体积庞大与抽空耗能的缺点。     

低山丘陵区可见光谱的分形特征

遥感影像记录的反射光谱特征主要来源于异质反射地物的光谱综合作用,了解其空间分布特征有助于影像解译和遥感模型的建立.该文以低山丘陵区10月底多光谱TM遥感影像为研究对象,采用统计学和多重分形相结合的手段分析其空间变异性.结果表明,研究区可见光谱(0.45～0.69μm)亮度值(digital number,DN)空间分布...     

Geometrical order-of-magnitude estimates for spatial curvature in realistic models of the Universe

The thoughts expressed in this article are based on remarks made by Jürgen Ehlers at the Albert-Einstein-Institut, Golm, Germany in July 2007. The main objective of this article is to demonstrate, in terms of plausible order-of-magnitude estimates for geometrical scalars, the relevance of spatial curvature in realistic models of the Universe that describe the dynamics of structure formation since the epoch of matter–radiation decoupling. We introduce these estimates with a commentary on the use of a quasi-Newtonian metric form in this context. In memoriam: Jürgen Ehlers (1929–2008).     

Generating mixtures of spatial qubits

In a recent letter [L. Neves, G. Lima, J.G. Aguirre Gómez, C.H. Monken, C. Saavedra, S. Pádua, Phys. Rev. Lett. 94 (2005) 100501], we presented a scheme for generating pure entangled states of spatial qudits (D-dimensional quantum systems) by using the momentum transverse correlation of the parametric down-converted photons. In this work, we discuss a generalization of this process to enable the creation of mixed states. With the technique proposed we experimentally generated a mixture of two spatial qubits.     

Transitions in spatial networks

Networks embedded in space can display all sorts of transitions when their structure is modified. The nature of these transitions (and in some cases crossovers) can differ from the usual appearance of a giant component as observed for the Erdös–Rényi graph, and spatial networks display a large variety of behaviors. We will discuss here some (mostly recent) results about topological transitions, ‘localization’ transitions seen in the shortest paths pattern, and also about the effect of congestion and fluctuations on the structure of optimal networks. The importance of spatial networks in real-world applications makes these transitions very relevant, and this review is meant as a step towards a deeper understanding of the effect of space on network structures.     

Scintillation and optical behavior of GaN nanowires in the presence of low-energy X-ray photons: A Geant4 simulation

GaN nanowires were studied as a possible candidate for use in the future development of X-ray scintillator detectors with high spatial resolution using a Monte Carlo simulation. The assessment was performed from the optical response perspective. The ability of such a nanowire to act as scintillating fibers was simulated using Geant4 code. The optimal dimensions of the nanowire (considering practical limitations) to achieve the best optical guiding effect were also determined. Moreover, the energy response of the nanowire was investigated for the design of a suitable external photodetector. To more accurately study the proposed structure, a scintillating screen containing approximately 2,000,000 nanowires was simulated in a porous anodized alumina membrane (PAAM) with a hexagonal arrangement. Using these specifications, the spatial resolution and efficiency of the detector were precisely calculated. The results showed that the spatial resolution and efficiency of the detector were <1 μm and ∼17%, respectively.     

First-order kernel density estimation of abdomen medical image intensity and spatial information and application to segmentation

Kernel density estimators (KDE) used for many medical image applications only consider the intensity information of each pixel or its neighbors without the ability of expressing the structure and shape of tissues and organs, and they suffer from boundary bias problem. In this paper, we propose a new first-order kernel density estimation (FOKDE) method for 1D intensity information and 2D spatial information of medical image in two steps. First, the FOKDE of intensity information is estimated and applied to medical image segmentation with the multi-thresholding algorithm. Second, we estimate the FOKDE of spatial information on the initial segmentation, which can express the structure and shape of organs and tissues. In order to evaluate the FOKDE and KDE of the 2D spatial information, we apply them to medical image segmentation with the hill-climbing strategy. Density estimation experiments and segmentation application results on the simulated dataset and real abdomen CT images show us that the FOKDE has smaller boundary bias than the KDE, and that it can estimate the structure and shape of tissues and organs with spatial information effectively.