All-optical attosecond time domain interferometry

Interferometry, a key technique in modern precision measurements, has been used for length measurement in engineering metrology and astronomy. An analogous time-domain interferometric technique would represent a significant complement to spatial domain applications and require the manipulation of interference on extreme time and energy scales. Here, we report an all-optical interferometer using laser-driven high order harmonics as attosecond temporal slits. By controlling the phase of the temporal slits with an external field, a time domain interferometer that preserves both attosecond temporal resolution and hundreds of meV energy resolution is implemented. We apply this exceptional temporal resolution to reconstruct the waveform of an arbitrarily polarized optical pulse, and utilize the provided energy resolution to interrogate the abnormal character of the transition dipole near the Cooper minimum in argon. This novel attosecond interferometry paves the way for high precision measurements in the time-energy domain using all-optical approaches.     

社会感知驱动下的用户画像时空数据研究进展

【目的/意义】社会感知是借助海量时空数据研究人类时空间行为特征,进而揭示社会经济现象的时空分布、联系及过程的理论与方法。用户画像旨在通过挖掘用户属性特征和行为模式,以揭示群体、领域乃至社会现象的内在规律。用户画像是实现社会感知的重要手段。【方法/过程】紧密围绕社会感知数据涉及的情感认知、行为习惯和社交网络关系三个维度梳理与之映射的用户画像内容维度,更深层次地,对其三个维度中与用户画像息息相关的应用情境进行分类描述,以期总结其应用价值。【结果/结论】研究发现：当前用户画像的数据源拓展到多源异构时空数据;研究内容集中在情感及场所语义、空间交互以及社交网络挖掘等方面;时空语义推理等研究是该领域的拓展;应用情境可以在跨地域空间信息服务、城市人地交互关系挖掘、政府高效治理、领域事件时空关联趋势预测等主题领域加以展开。【创新/局限】社会感知数据的利用可以在多任务场景下实现态势感知和知识推理。通过融合多源异构时空数据和集成多种用户画像维度,能够实现多场景的精准知识服务。     

Array misalignment angle value estimation for OAM-based communication system

Orbit Angular Momentum (OAM) is a potential candidate for next-generation short-distance line-of-sight wireless communication, it is assumed that the channels associated with different OAM modes are orthogonal. When there are misalignments between transmitter and receiver arrays, the assumption is incorrect. In this paper, we propose the methods to estimate the array misalignment values in the OAM-based communication system for Uniform Circular Array (UCA) in transmitter and receiver. It is shown that, when the pilot signals are transmitted in a single or all OAM modes, the absolute value of the received signal can be approximated by the polynomial functions of misalignment angle. By solving these functions, the misalignment angle can be estimated. The proposed methods are theoretically analyzed and tested for OAM Index Modulation (OAM-IM)-based communication system, The obtained results indicate that the proposed methods improve the OAM-IM based communication system in the presence of array misalignments problem.     

混合层中四涡合并过程的数值研究

用拟谱方法对混合层四涡合并的规律进行了数值研究。分析了其波和次谐波之间相位差对涡合并过程的影响,并引入旋转点和拉伸点的概念对种影响进行了解释。计算结果表明：四涡的合并存在６种形式,因此,可以通过施加多级次谐波并改变它们之间的相位差主动控制拟序涡的发展和演变。     

微分干涉相称显微镜在棉麻检测上的应用

普通光学显微镜只能传递光波的振幅信息而丢失相位信息,因此用普通光学显微镜对透明和半透明的物体观察会丢失一些特征信息。植物纤维基本介于透明体与半透明体的状态,而透明物体对光只产生相位的移动而不能显著地改变光的振幅,所以在普通光学显微镜中难以观察到棉麻纤维的局部细节特征信息。而微分干涉相衬显微镜所观察的物体是位相物体,因此应用微分干涉显微镜可以明显改善这种情况。     

Fluent在城市街区大气环境中的一个应用

利用CFD软件Fluent建立了一个三维街道十字路口模型 ,模拟了 2种风向条件下街区风速分布和CO质量浓度分布的情况 .结果表明 ,十字路口的建筑物布局与风向共同作用 ,会对街区的风速和CO质量浓度分布产生很大影响 .模拟结果表明 ,CFD对所建模型模拟结果合理 ,用于街区大气环境问题研究有着良好前景 .     

激励介质的非线性波型动力学

以刻划著名的Belousov Zhabotinsky化学反应的俄勒冈振子为数学模型 ,研究解决了激励介质中一些悬而未决的理论问题 (如波的存在性和稳定性等 ) ,进一步完善了激励介质的非线性波型动力学的理论体系 .通过Painlev啨分析 ,B¨acklund变换和奇异摄动方法 ,分析地给出了一些常见的波型解 (如行波 ,螺旋波 ,靶型波 ,V 型波 ,涡卷波等 ) .在波前的邻域内 ,通过引进新的运动坐标系 ,获得了波在直角坐标下的运动方程 .特别是定量地给出了刻划小幅波的组织中心沿轴向和径向运动的规律 ,并由此可判定波的组织中心何时沿径向呈现膨胀或收缩 ,何时沿轴向有正向或反向漂移 .这一结果很好地与实验和数值模拟结果相吻合 .此外 ,研究了耦合的俄勒冈振子 ,解决了Tyson于 1 979年提出的一个猜想 (即对耦合的俄勒冈振子 ,稳定的回声波可以和稳定的正定态共存 ) ,提出了一套解决类似问题的一般方法 .     

轴对称射流中涡运动的三维涡丝模拟

用三维涡丝法对轴对称不可压射流进行了数值模拟 ,描述了轴对称射流在外加扰动下产生的拟序结构随时间的发展 .文中应用了涡丝的增加与合并技术 ,模拟了在基波扰动作用下涡的卷起 ,以及在扰动中加入次谐波后涡的配对 .通过对不同时刻涡量图的比较与分析 ,说明扰动中的基波导致涡的卷起 ,次谐波控制着涡的配对 ,所得结论与理论和实验结果相一致     

图像的增强与分割方法研究

以图像增强与分割这两个计算机视觉中最具基础性质的研究方向为内容,深入研究了红外序列图像的增强,以及一般图像的分割问题.在图像增强方面,提出了一种基于模型的远红外序列图像自适应增强算法(ASTHF).该算法保持了原有算法的良好效果和计算效率,从而达到了视觉效果和运算速度的良好统一.在图像分割方面,提出了一种综合利用边缘和区域信息的图像分割方法--基于尺度空间的区域竞争一般框架(GSRC).通过将被误标记可能性小的像素作为种子,GSRC首先自动确定初始分割(粗分割),然后以能量泛函为工具,通过综合运用轮廊平滑、概率模型和区域竞争来确定最终的分割(精细分割).GSRC不仅能有效地利用图像特征,还为特征的知觉组织提供了一条简单的计算途径.     

Bacterial aggregation and biofilm formation in a vortical flow

Bacterial aggregation and patchiness play an important role in a variety of ecological processes such as competition, adaptation, epidemics, and succession. Here, we demonstrate that hydrodynamics of their environment can lead to their aggregation. This is specially important since microbial habitats are rarely at rest (e.g., ocean, blood stream, flow in porous media, and flow through membrane filtration processes). In order to study the dynamics of bacterial collection in a vortical flow, we utilize a microfluidic system to mimic some of the important microbial conditions at ecologically relevant spatiotemporal scales. We experimentally demonstrate the formation of “ring”-shaped bacterial collection patterns and subsequently the formation of biofilm streamers in a microfluidic system. Acoustic streaming of a microbubble is used to generate a vortical flow in a microchannel. Due to bacteria''s finite-size, the microorganisms are directed to closed streamlines and trapped in the vortical flow. The collection of bacteria in the vortices occurs in a matter of seconds, and unexpectedly, triggers the formation of biofilm streamers within minutes. Swimming bacteria have a competitive advantage to respond to their environmental conditions. In order to investigate the role of bacterial motility on the rate of collection, two strains of Escherichia coli bacteria with different motilities are used. We show that the bacterial collection in a vortical flow is strongly pronounced for high motile bacteria.     

Control of PDE-ODE cascades with Neumann interconnections

We extend several recent results on full-state feedback stabilization and state estimation of PDE-ODE cascades, where the PDEs are either of heat type or of wave type, from the previously considered cases where the interconnections are of Dirichlet type, to interconnections of Neumann type. The Neumann type interconnections constrain the PDE state to be subject to a Dirichlet boundary condition at the PDE-ODE interface, and employ the boundary value of the first spatial derivative of the PDE state to be the input to the ODE. In addition to considering heat-ODE and wave-ODE cascades, we also consider a cascade of a diffusion-convection PDE with an ODE, where the convection direction is “away” from the ODE. We refer to this case as a PDE-ODE cascade with “counter-convection.” This case is not only interesting because the PDE subsystem is unstable, but because the control signal is subject to competing effects of diffusion, which is in both directions in the one-dimensional domain, and counter-convection, which is in the direction that is opposite from the propagation direction of the standard delay (transport PDE) process. We rely on the diffusion process to propagate the control signal through the PDE towards the ODE, to stabilize the ODE.     

酒石酸和甘油醛的构型与旋光性关系的分析

运用螺旋理论分析酒石酸和甘油醛的构型与旋光方向间的关系表明 ,即使对于这两个可形成多种氢键的化合物 ,其立体结构和旋光性间的关系同样是密切的     

非Kolmogorov湍流情况下低阶校正自适应光学系统的性能分析

系统地研究了非Kolmogorov湍流情况下低阶校正自适应光学系统的性能.从理论上分析了非Kolmogorov湍流情况下相位扰动的空间特性和时间特性,推导了相位扰动的空间结构函数、时间结构函数以及时间功率谱.基于哈特曼-夏克波前传感器,提出了一些测量大气参数的新方法.引入模式时间校正因子和模式非等晕因子,分析了低阶校正自适应光学系统的波前残余误差,并首次对扩展目标情况时低阶校正自适应光学系统的非等晕误差进行了研究.此外还根据实际采集的太阳表面米粒结构图像,采用事后处理的方法研究了倾斜校正自适应光学系统的性能.     

Predictive control of uncertain systems over networks with redundant link

Networked systems using redundant channels to transmit data can effectively reduce the probability of data loss and improve system reliability and control margin. However, the structural complexity and economic cost of the system are also increased. To balance the redundancy and feasibility, the ratio of attraction domain to packet loss rate is defined as a balanced feasibility index. In this paper, single-channel packet loss is considered as Bernoulli distribution and a bounded packet loss network system control model is constructed as the arbitrary bounded packet loss control problem for redundant channel transmission network system. Therefore, the robust conditions of the closed-loop system and the constraints of the input and state are established under the framework of robust predictive control to construct the linear matrix inequality (LMI) optimization problem. Finally, to verify the effectiveness of the design method proposed in this paper, the discrete time-varying linear system and the main steam control system with redundant channels are used as study cases.     

小波包分解在迎角传感器信号预处理中的应用

针对基于四象限压力传感器阵列的迎角测量方法中传感器信号受到干扰的问题,讨论了在其预处理中应用小波包变换进行信号分离提取的方法。根据小波包分解理论,对信号进行小波包分解,信号中频率不同的部分落在不同的尺度上,剔除反映干扰的变换尺度,提取出有用信息。结果表明,该方法可很好地提取信号的主要特征信息,也有效地去除了确定性干扰和随机噪声,与传统的信号滤波方法相比较具有明显的优点,同时为后续的信号处理奠定了基础。     

联苯衍生物及其类似物结构和旋光方向的关系(Ⅰ)

每种光学活性的联苯衍生物都是两种构象的混合物．在利用笔者所提出的螺旋理论［１～３］分析其旋光方向与结构间的关系时,必须确定它们的优势构象,比较取代基的可极化性大小及在优势和非优势构象中各种不同螺旋的扭曲角度（螺距的大小）．在全面考虑了这三种影响旋光性的因素条件下,可根据构型、构象推测它们的旋光方向和大小．反之,知道了它们的旋光方向和大小,也可推断它们的绝对构型和构象     

“丝绸之路经济带”沿线主要国家气候变化特征

基于美国国家气候中心发布的全球气象站点日数据,利用克里金插值、线性趋势法、累计距平曲线法、Mann-Kendall显著性检验和多尺度区域统计等方法,系统阐述了“丝绸之路经济带”主要国家1980-2014年气温和降水的变化趋势和空间分布特征。结果表明,研究区近35 年以0.4℃/10a的速率呈现明显升温态势,30.1%的区域升温显著,0.03%的区域降温显著。各国普遍在20世纪末进入偏暖阶段。降水以减少为主,却仅有0.19%的区域减少显著,零星分布于沙特阿拉伯和中国的西部。南亚1991年后进入降水偏多阶段,其余地区多在1999年后进入降水偏少阶段。该成果能够为相关国家在“一带一路”战略的统领下解决和应对气候变化问题提供科学依据和有益参考。     

突发医暴事件舆论情感能量域空间模型构建

[目的/意义]医暴舆论空间积聚的情感能量推动观点衍化并深刻影响事件发展趋势,识别不同维度的情感认知且关注能量特征可有效循迹医患冲突的情感焦点。[方法/过程]以情感维度为能量源、情感能量特征为能量波构建医暴舆论情感能量域空间模型,能量源基于关键词云划分为自我认知、民生民意、社会发展三大维度,能量波以各认知维度的情感倾向、情感强度与扩散速度综合刻画能量趋势,最终依据能量域模型立体剖析突发医暴事件舆论空间。[结果/结论]结果显示,能量域空间模型能够真实反映医暴舆论情感演化趋势;各能量源均持续积聚负向情感能量;民生民意为医暴舆论的情感焦点。     

Two-dimensional spatial manipulation of microparticles in continuous flows in acoustofluidic systems

We report a modeling and experimental study of techniques to acoustically focus particles flowing through a microfluidic channel. Our theoretical model differs from prior works in that we solve an approximate 2-D wave transmission model that accounts for wave propagation in both the solid and fluid phases. Our simulations indicate that particles can be effectively focused at driving frequencies as high as 10% off of the resonant condition. This conclusion is supported by experiments on the acoustic focusing of particles in nearly square microchannels, which are studied for different flow rates, driving frequencies and placements of the lead zirconate titanate transducer, either underneath the microchannel or underneath a parallel trough. The relative acoustic potential energy and the resultant velocity fields for particles with positive acoustic contrast coefficients are estimated in the 2-D limit. Confocal microscopy was used to observe the spatial distribution of the flowing microparticles in three dimensions. Through these studies, we show that a single driving frequency from a single piezoelectric actuator can induce the 2-D concentration of particles in a microchannel with a nearly square cross section, and we correlate these behaviors with theoretical predictions. We also show that it is possible to control the extent of focusing of the microparticles, and that it is possible to decouple the focusing of microparticles in the vertical direction from the lateral direction in rectangular channels with anisotropic cross sections. This study provides guidelines to design and operate microchip-based acoustofluidic devices for precise control over the spatial arrangement of microparticles for applications such as flow cytometry and cellular sorting.     

中国太阳辐射时空变化及不同时间尺度Ångström-Prescott模型校正参数适用性比较

逐日太阳辐射是作物模型的关键输入变量,被广泛用于计算太阳辐射的Ångström-Prescott模型（A-P公式）校正工作主要建立在月尺度数据上,开展不同区域日尺度及更大时间尺度校正及参数适用性研究有助于提高太阳辐射计算和作物模型模拟准确性,指导区域农业生产。本文基于中国九大农业区划和104个辐射站点的1981—2016年逐日太阳辐射实测资料,分析了中国年太阳辐射时空分布特征;在此基础上,分别在日尺度和月尺度校正A-P公式,并对其校正参数（a_s和b_s）的适用性进行检验评价。结果表明：①中国年太阳辐射在1990年前后经历了由“变暗”到“变亮”的转变,总体呈增加趋势（7.32±30.31 MJ/m²/a）,空间上呈西高东低的分布特征;②日尺度A-P公式校正拟合效果优于月尺度,且月尺度的校正参数存在明显的空间异质性;参数a_s的空间分布存在地带性,呈东南低西北高的特征,而b_s与海拔正相关;③日尺度和月尺度校正参数可互换,但在年尺度上线性A-P公式不再适用。本文对提高太阳辐射计算精度和指导区域农业生产具有一定的参考价值。