Occurrence, Repetition and Matching of Patterns in the Low-temperature Ising Model

We continue our study of the exponential law for occurrences and returns of patterns in the context of Gibbsian random fields. For the low-temperature plus-phase of the Ising model, we prove exponential laws with error bounds for occurrence, return, waiting and matching times. Moreover we obtain a Poisson law for the number of occurrences of large cylindrical events and a Gumbel law for the maximal overlap between two independent copies. As a by-product, we derive precise fluctuation results for the logarithm of waiting and return times. The main technical tool we use, in order to control mixing, is disagreement percolation     

Large scale silver nanowires network fabricated by MeV hydrogen(H~+) ion beam irradiation

A random two-dimensional large scale nano-network of silver nanowires(Ag-NWs) is fabricated by MeV hydrogen(H~+) ion beam irradiation. Ag-NWs are irradiated under H~+ion beam at different ion fluences at room temperature. The Ag-NW network is fabricated by H~+ion beam-induced welding of Ag-NWs at intersecting positions. H~+ion beam induced welding is confirmed by transmission electron microscopy(TEM) and scanning electron microscopy(SEM). Moreover, the structure of Ag NWs remains stable under H~+ion beam, and networks are optically transparent. Morphology also remains stable under H~+ion beam irradiation. No slicings or cuttings of Ag-NWs are observed under MeV H~+ion beam irradiation.The results exhibit that the formation of Ag-NW network proceeds through three steps: ion beam induced thermal spikes lead to the local heating of Ag-NWs, the formation of simple junctions on small scale, and the formation of a large scale network. This observation is useful for using Ag-NWs based devices in upper space where protons are abandoned in an energy range from MeV to GeV. This high-quality Ag-NW network can also be used as a transparent electrode for optoelectronics devices.     

气管支气管树内气流和颗粒运动的大涡模拟

为更精确地描述真实人体呼吸道内的空气流动,明晰颗粒的运动沉积规律,本文从直接医学CT扫描得到的原始数据出发,利用图像辨识技术,重构了一个男性真人气管支气管树前三级的三维几何模型.采用大涡模拟的方法计算了非规则几何曲面结构内的气体流动现象,并在拉格朗日框架下跟踪颗粒的运动规律.数值计算得到了气流场的三维分布,以及颗粒的运动轨迹情况,结果表明现有基于Weibel的对称模型与真实人体的几何结构有较大的差异,而几何结构对流动影响较大;受非对称复杂结构影响,在不同截面的二次气流速度的分布规律不同;分叉后颗粒进入左右支气管的数量有明显的不同.     

Fermionic Zero Modes in Self-dual Vortex Background on a Torus

We study fermionic zero modes in the self-dual vortex background on an extra two-dimensional Riemann surface in （5＋1） dimensions. Using the generalized Abelian-Higgs model, we obtain the inner topological structure of the self-dual vortex and establish the exact self-duality equation with topological term. Then we analyze the Dirac operator on an extra torus and the effective Lagrangian of four-dimensional fermions with the self-dual vortex background. Solving the Dirac equation, the fermionic zero modes on a torus with the self-dual vortex background in two simple cases are obtained.     

A facile method for the synthesis of large‐size Ag nanoparticles as efficient SERS substrates

Silver nanoparticles (Ag NPs) enjoy a reputation as an ultrasensitive substrate for surface‐enhanced Raman spectroscopy (SERS). However, large‐scale synthesis of Ag NPs in a controlled manner is a challenging task for a long period of time. Here, we reported a simple seed‐mediated method to synthesize Ag NPs with controllable sizes from 50 to 300 nm, which were characterized by scanning electron microscopy (SEM) and UV–Vis spectroscopy. SERS spectra of Rhodamine 6G (R6G) from the as‐prepared Ag NPs substrates indicate that the enhancement capability of Ag NPs varies with different excitation wavelengths. The Ag NPs with average sizes of ~150, ~175, and ~225 nm show the highest SERS activities for 532, 633, and 785‐nm excitation, respectively. Significantly, 150‐nm Ag NPs exhibit an enhancement factor exceeding 10⁸ for pyridine (Py) molecules in electrochemical SERS (EC‐SERS) measurements. Furthermore, finite‐difference time‐domain (FDTD) calculation is employed to explain the size‐dependent SERS activity. Finally, the potential of the as‐prepared SERS substrates is demonstrated with the detection of malachite green. Copyright © 2016 John Wiley & Sons, Ltd.     

H基于模糊观测器参数摄动的耦合时空混沌H跟踪控制

由于子系统的时空耦合作用及参数的摄动性，实现参数摄动的耦合时空混沌的跟踪控制非常困难。然而模型未知的耦合时空混沌的每个子系统可由一系列模糊逻辑模型逼近，每个模糊逻辑模型代表子系统在特定运行点的局部线性化模型，同时考虑子系统状态的不可测性，采用模糊观测器来估计子系统的状态。基于模糊模型及状态观测器，计及混沌参数的摄动性，提出一种模糊跟踪控制方案，实现了参数摄动的耦合时空混沌的鲁棒跟踪控制，并将模糊跟踪控制表征为线性矩阵不等式问题，用线性矩阵不等式的凸优化方法求解控制器参数，确保系统的全局渐近稳定性。仿真验证了方案的有效性。     

圆形射流湍流场的大涡模拟研究

使用发展的大涡模拟并行程序,数值模拟了圆形射流湍流场,与实验值进行详细比较,对大涡模拟程序进行检验,并分析网格尺度对计算结果的影响。结果表明,大涡模拟计算的平均速度场和雷诺应力场与实验值符合得非常好,验证了该大涡模拟计算程序的可靠性和精确度。同时发现一阶统计矩受网格尺度影响不大,二阶及高阶矩与网格尺度有较大的关系,因此使用大涡模拟方法计算湍流及湍流燃烧问题应对网格依赖性进行必要分析,至少保证二阶统计矩具有较好的精度。     

大口径非球面主反射镜的装调方法研究

针对大口径非球面主反射镜（简称主镜）的装调要求,对比分析常用大口径非球面面形检测方法,提出该类主镜检测面形的最佳方案。在主镜的装调过程中,通过对主镜的固定方式和主镜变形补偿这2个关键环节的阐述,总结主镜固定的难点及主镜变形的原因,提出一套全新的装调方案,以旋转消重力法进行检测,并用专用工装实时定心调节,再用辅料焊接法固定主镜与中心轴,最后采用辅助支撑对主镜组件进行最终固定修正。装调结果表明:对于大口径非球面反射镜,装调完成后的主镜面形精度Rms0.03（＝632.8 nm）。     

Minimum SNR and acquisition for bias-free estimation of fractional anisotropy in diffusion tensor imaging - a comparison of two analytical techniques and field strengths

Although it is known that low signal-to-noise ratio (SNR) can affect tensor metrics, few studies reporting disease or treatment effects on fractional anisotropy (FA) report SNR; the implicit assumption is that SNR is adequate. However, the level at which low SNR causes bias in FA may vary with tissue FA, field strength and analytical methodology. We determined the SNR thresholds at 1.5 T vs. 3 T in regions of white matter (WM) with different FA and compared FA derived using manual region-of-interest (ROI) analysis to tract-based spatial statistics (TBSS), an operator-independent whole-brain analysis tool. Using ROI analysis, SNR thresholds on our hardware-software magnetic resonance platforms were 25 at 1.5 T and 20 at 3 T in the callosal genu (CG), 40 at 1.5 and 3 T in the anterior corona radiata (ACR), and 50 at 1.5 T and 70 at 3 T in the putamen (PUT). Using TBSS, SNR thresholds were 20 at 1.5 T and 3 T in the CG, and 35 at 1.5 T and 40 at 3 T in the ACR. Below these thresholds, the mean FA increased logarithmically, and the standard deviations widened. Achieving bias-free SNR in the PUT required at least nine acquisitions at 1.5 T and six acquisitions at 3 T. In the CG and ACR, bias-free SNR was achieved with at least three acquisitions at 1.5 T and one acquisition at 3 T. Using diffusion tensor imaging (DTI) to study regions of low FA, e.g., basal ganglia, cerebral cortex, and WM in the abnormal brain, SNR should be documented. SNR thresholds below which FA is biased varied with the analytical technique, inherent tissue FA and field strength. Studies using DTI to study WM injury should document that bias-free SNR has been achieved in the region of the brain being studied as part of quality control.     

基于区域生长重心的大型多阵列圆标定板基准点的提取技术

针对视觉测量在轨道交通隧道大范围轮廓测量上的问题,研究设计一种大型多阵列圆标定板进行系统标定工作,提出区域生长重心法实现对标定图像上基准点的提取。即将区域生长法和灰度重心法相结合,通过粗定位寻找每个基准圆的种子点,考虑种子点像素的4邻域像素进行区域生长,然后利用灰度重心法提取生长区域的重心作为基准点。将非线性变化的基准点替代线性提取的基准圆的种子点,消除了图像畸变的影响,保证了特征检测过程的可靠性和鲁棒性,达到对于多阵列圆大型标定板基准点的提取。通过搭载鱼眼镜头拍摄6m的模拟隧道横断面轮廓,进行轮廓测量与还原。实验表明该方法提取的基准点像素坐标误差可达到2pixel以内,系统测量精度能够达到±5mm以内,完全满足轨道交通隧道横断面轮廓测量误差标准。