基于System Generator的射频直接带通采样MRI信号接收方法

本文将软件无线电技术应用于磁共振成像（Magnetic Resonance Imaging，MRI）信号接收，提出了射频直接带通采样MRI信号接收的方法.基于此接收方法设计了一种MRI信号数字解调方法，该方法利用Xilinx公司推出的数字信号处理（Digital Signal Processing，DSP）设计开发工具——System Generator实现，同时设计验证了能够灵活实现数字下变频（Digital Down Conversion，DDC）功能的DDC系统.仿真与实验平台均验证了该接收方法的正确性和有效性.     

Subgraphs of Interest Social Networks for Diffusion Dynamics Prediction

Finding the building blocks of real-world networks contributes to the understanding of their formation process and related dynamical processes, which is related to prediction and control tasks. We explore different types of social networks, demonstrating high structural variability, and aim to extract and see their minimal building blocks, which are able to reproduce supergraph structural and dynamical properties, so as to be appropriate for diffusion prediction for the whole graph on the base of its small subgraph. For this purpose, we determine topological and functional formal criteria and explore sampling techniques. Using the method that provides the best correspondence to both criteria, we explore the building blocks of interest networks. The best sampling method allows one to extract subgraphs of optimal 30 nodes, which reproduce path lengths, clustering, and degree particularities of an initial graph. The extracted subgraphs are different for the considered interest networks, and provide interesting material for the global dynamics exploration on the mesoscale base.     

TDLAS波长调制压力测量法参数优化

使用TDLAS技术进行动态压力测量已经成为压力测量领域的研究热点。波长调制法实验装置较为复杂,需要对多个参数进行设置,选择出最优的预设参数能够取得更好的实验效果,获得更高的测量精度。目前波长调制法的实验参数设置基本凭借个人经验,使用Matlab程序仿真结合波长调制法的TDLAS测量技术,能够对实验中需要进行预设的重要参数进行了分析。通过计算4990cm-1波段和6330cm-1波段附近的多条吸收峰,发现4990.09cm-1波段处的吸收峰更适合作为波长调制法的测量波段。以4990.09cm-1处的吸收峰为研究对象,进行了波长调制法压力测量仿真建模,计算了调制度、调谐频率和调制频率对二次谐波幅值和对称性的影响并深入地分析了影响因素,总结了其变化规律。在综合考虑抗噪性能和测量精度的情况下,选择了调制度为2.5,调谐频率30Hz,调制频率5kHz为最佳实验参数。基于Matlab的仿真模型能够快速计算大量参数点,更加直观地分析出对参数的影响趋势,为实验仪器和预设参数的选择提供依据。     

Fast and efficient nested simulation for large variable annuity portfolios: A surrogate modeling approach

The nested-simulation is commonly used for calculating the predictive distribution of the total variable annuity (VA) liabilities of large VA portfolios. Due to the large numbers of policies, inner-loops and outer-loops, running the nested-simulation for a large VA portfolio is extremely time consuming and often prohibitive. In this paper, the use of surrogate models is incorporated into the nested-simulation algorithm so that the relationship between the inputs and the outputs of a simulation model is approximated by various statistical models. As a result, the nested-simulation algorithm can be run with much smaller numbers of different inputs. Specifically, a spline regression model is used to reduce the number of outer-loops and a model-assisted finite population estimation framework is adapted to reduce the number of policies in use for the nested-simulation. From simulation studies, our proposed algorithm is able to accurately approximate the predictive distribution of the total VA liability at a significantly reduced running time.     

Systematic coarse‐graining of semicrystalline polyethylene

In an effort to accelerate simulations exploring deformation mechanisms in semicrystalline polymers, we have created structure‐based coarse‐grained (CG) models of polyethylene and evaluated the extent to which they can simultaneously represent its amorphous and crystalline phases. Two CG models were calibrated from target data sampled from atomistic simulations of supercooled oligomer melts that differ in how accurately they represent the distribution of bond lengths between CG sites. Both models yield semicrystalline morphology when simulations are performed at ambient conditions, and both accurately predict the glass transition and melt temperatures. A thorough evaluation of the models was then conducted to assess how well they represent various properties of the amorphous and crystalline phases. We found that the model that more faithfully reproduces the target bond length distribution poorly represents the crystalline phase, which results from its inability to reproduce correlations in the structural distributions. The second model, which utilizes a harmonic bond potential and thus reproduces the target bond length distribution less accurately, represents the structure and chain mobility within the crystalline phase more realistically. Furthermore, the latter model more faithfully reproduces the vastly different relaxation timescales of the phases, a critical feature for modeling deformation mechanisms in semicrystalline polymers. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 331–342     

优良抽样设计下总体均值的比率估计

当研究目标的实际测量具有不可修复的破坏性或耗资巨大时,有效的抽样设计将是一项重要的研究课题.在统计推断方面,排序集抽样被视为一种更为有效的收集数据的方式.极值排序集抽样(ERSS)是一种改进的排序集抽样.文章在ERSS下研究了总体均值的比率估计.以正态分布为例,比较了简单随机抽样和ERSS下比率估计的相对效率.数值结果表明ERSS下的比率估计优于简单随机抽样下的比率估计.     

Efficient sampling for decision making in materials discovery

Accelerating materials discovery crucially relies on strategies that efficiently sample the search space to label a pool of unlabeled data. This is important if the available labeled data sets are relatively small compared to the unlabeled data pool. Active learning with efficient sampling methods provides the means to guide the decision making to minimize the number of experiments or iterations required to find targeted properties. We review here different sampling strategies and show how they are utilized within an active learning loop in materials science.     

Ambient ionisation mass spectrometry for in situ analysis of intact proteins

Ambient surface mass spectrometry is an emerging field which shows great promise for the analysis of biomolecules directly from their biological substrate. In this article, we describe ambient ionisation mass spectrometry techniques for the in situ analysis of intact proteins. As a broad approach, the analysis of intact proteins offers unique advantages for the determination of primary sequence variations and posttranslational modifications, as well as interrogation of tertiary and quaternary structure and protein‐protein/ligand interactions. In situ analysis of intact proteins offers the potential to couple these advantages with information relating to their biological environment, for example, their spatial distributions within healthy and diseased tissues. Here, we describe the techniques most commonly applied to in situ protein analysis (liquid extraction surface analysis, continuous flow liquid microjunction surface sampling, nano desorption electrospray ionisation, and desorption electrospray ionisation), their advantages, and limitations and describe their applications to date. We also discuss the incorporation of ion mobility spectrometry techniques (high field asymmetric waveform ion mobility spectrometry and travelling wave ion mobility spectrometry) into ambient workflows. Finally, future directions for the field are discussed.     

Cluster Structure of Optimal Solutions in Bipartitioning of Small Worlds

Using simulated annealing, we examine a bipartitioning of small worlds obtained by adding a fraction of randomly chosen links to a one-dimensional chain or a square lattice. Models defined on small worlds typically exhibit a mean-field behavior, regardless of the underlying lattice. Our work demonstrates that the bipartitioning of small worlds does depend on the underlying lattice. Simulations show that for one-dimensional small worlds, optimal partitions are finite size clusters for any fraction of additional links. In the two-dimensional case, we observe two regimes: when the fraction of additional links is sufficiently small, the optimal partitions have a stripe-like shape, which is lost for a larger number of additional links as optimal partitions become disordered. Some arguments, which interpret additional links as thermal excitations and refer to the thermodynamics of Ising models, suggest a qualitative explanation of such a behavior. The histogram of overlaps suggests that a replica symmetry is broken in a one-dimensional small world. In the two-dimensional case, the replica symmetry seems to hold, but with some additional degeneracy of stripe-like partitions.