Perfect matchings on a type of lattices with toroidal boundary

Enumeration of perfect matchings on graphs has a longstanding interest in combinatorial mathematics. In this paper, we obtain some explicit expressions of the number of perfect matchings for a type of Archimedean lattices with toroidal boundary by applying Tesler's crossing orientations to obtain some Pfaffan orientations and enumerating their Pfaffans.

Matching Boundary Conditions for a Heterogeneous Atomic Chain

We propose accurate boundary treatments for a heterogeneous atomic chain, in terms of matching boundary conditions （MBCs）. The main challenge lies in reproducing the physical reflection across the boundary to a correct amount. With reflection coefficients we demonstrate that the accuracy is improved when more atoms are used under the boundary condition. The inclusion of an atom in the embedded sublattice B may considerably enhance the performance. Numerical testing illustrates the effectiveness of the proposed MBCs.

Fast Multi-Pattern Matching Algorithm on Compressed Network Traffic

Pattern matching is a fundamental approach to detect malicious behaviors and information over Internet, which has been gradually used in high-speed network traffic analysis. However, there is a performance bottleneck for multi-pattern matching on online compressed network traffic(CNT), this is because malicious and intrusion codes are often embedded into compressed network traffic. In this paper, we propose an online fast and multi-pattern matching algorithm on compressed network traffic(FMMCN). FMMCN employs two types of jumping, i.e. jumping during sliding window and a string jump scanning strategy to skip unnecessary compressed bytes. Moreover, FMMCN has the ability to efficiently process multiple large volume of networks such as HTTP traffic, vehicles traffic, and other Internet-based services. The experimental results show that FMMCN can ignore more than 89.5% of bytes, and its maximum speed reaches 176.470MB/s in a midrange switches device, which is faster than the current fastest algorithm ACCH by almost 73.15 MB/s.

Improved Parallel Processing Function for High-Performance Large-Scale Astronomical Cross-Matching

Astronomical cross-matching is a basic method for aggregating the observational data of different wavelengths. By data aggregation, the properties of astronomical objects can be understood comprehensively. Aiming at decreasing the time consumed on I/O operations, several improved methods are introduced, including a processing flow based on the boundary growing model, which can reduce the database query operations; a concept of the biggest growing block and its determination which can improve the performance of task partition and resolve data-sparse problem; and a fast bitwise algorithm to compute the index numbers of the neighboring blocks, which is a significant efficiency guarantee. Experiments show that the methods can effectively speed up cross-matching on both sparse datasets and high-density datasets.

Comparison of perfectly matched layer and multi-transmitting formula artificial boundary condition based on hybrid finite element formulation

The theory of perfectly matched layer （PML） artificial boundary condition （ABC）, which is characterized by absorption any wave motions with arbitrary frequency and arbitrarily incident angle, is introduced. The construction process of PML boundary based on elastodynamic partial differential equation （PDE） system is developed. Combining with velocity-stress hybrid finite element formulation, the applicability of PML boundary is investigated and the numerical reflection of PML boundary is estimated. The reflectivity of PML and multi-transmitting formula （MTF） boundary is then compared based on body wave and surface wave simulations. The results show that although PML boundary yields some reflection, its absorption performance is superior to MTF boundary in the numerical simulations of near-fault wave propagation, especially in comer and large angle grazing incidence situations. The PML boundary does not arise any unstable phenomenon and the stability of PML boundary is better than MTF boundary in hybrid finite element method. For a specified problem and analysis tolerance, the computational efficiency of PML boundary is only a little lower than MTF boundary.

基于模板匹配的法兰盘位姿估计研究

针对工业机器人自动分拣中当工件有较大的旋转角度时,普通的模板匹配法无法准确地得到抓取和放置工件正确位置的问题,提出一种基于内边界追踪粗定位和基于模板匹配精定位的两步视觉定位方法。针对谐波减速器输出法兰盘,采用八邻域内边界追踪法对工件旋转角度进行粗定位,通过霍夫圆检测技术得到工件的中心位置,并通过一种改进的模板匹配法得到工件精确的旋转角度。实验结果表明,位姿检测的平均误差不大于0.1°,该定位方法在合适条件下可以满足精度要求。

发展方程的完美匹配边界层模型

在有界区域上使用数值方法模拟无界区域上的偏微分方程时,要求在有界区域边界上添加人工边界条件。构造的人工边界条件必须能消除边界上不必要的反射,完美匹配边界层是非常有效的人工吸收边界条件之一。本研究采用复值坐标拉伸的方法,在不分离变量的前提下对发展方程推导出了完美匹配边界层模型。通过平面波分析可知,波在初始求解区域边界上无反射,且在有界的完美匹配边界层上振幅是指数衰减的。

毫瓦级电磁式振动能量收集中低功耗变换技术

能量收集是保障分布式传感器持续供电的关键。电磁式能量收集为交流输出,且幅值低,输出阻抗高。为了实现能量高效传输和变换,需要高升压比的低功耗AC/DC变换器,并通过阻抗匹配提高传输效率。然而,现有微能量变换的电路效率仅为60%;且无法实现与输出和输入电压解耦的阻抗匹配,功率传输效率低。为了解决以上问题,这里提出采用临界导通模式(BCM)使变换器输入阻抗仅受导通时间控制,利用固定开通时间的控制方法实现阻抗匹配,并给出了在低压、毫瓦级变换下高效功率器件选型标准。构建了基于氮化镓(GaN)HEMT的双Boost单级AC/DC功率变换器,峰值开环变换效率达74.5%,峰值闭环效率达72.3%。

An improved convolution perfectly matched layer for elastic second-order wave equation

A convolution perfectly matched layer(CPML)can efficiently absorb boundary reflection in numerical simulation.However,the CPML is suitable for the first-order elastic wave equation and is difficult to apply directly to the second-order elastic wave equation.In view of this,based on the first-order CPML absorbing boundary condition,we propose a new CPML(NCPML)boundary which can be directly applied to the second-order wave equation.We first systematically extend the first-order CPML technique into second-order wave equations,neglecting the space-varying characteristics of the partial damping coefficient in the complex-frequency domain,avoiding the generation of convolution in the time domain.We then transform the technique back to the time domain through the inverse Fourier transform.Numerical simulation indicates that the space-varying characteristics of the attenuation factor have little influence on the absorption effect and increase the memory at the same time.A number of numerical examples show that the NCPML proposed in this study is effective in simulating elastic wave propagation,and this algorithm is more efficient and requires less memory allocation than the conventional PML absorbing boundary.

New artificial boundary condition for saturated soil foundations

Anew artificial boundary model based on multi-directional transmitting and viscous-spring artificial boundary theories is proposed to absorb stress waves in a saturated soil foundation in dynamic analysis. Since shear waves （S-waves） are the same in a saturated soil foundation and a single-phase medium foundation, a tangential visco-elastic boundary condition for a single-phase medium foundation can also be used for saturated soil foundations. Thus, the purpose of the artificial boundary proposed in this paper is primarily to absorb two types of P-waves in a saturated soil foundation. The main idea is that the stress of the P-waves in the saturated soil foundation is decomposed into two types. The first type of stress, δra＇ is absorbed by the first artificial boundary. The second type of stress, δrb, is balanced by the stress generated by the second artificial boundary. Ultimately, both types of P-waves （fast-P-waves and slow-P-waves） are absorbed by the artificial boundary model proposed in this paper. In particular, note that the fast-P-waves and slow-P-waves are absorbed at the position of the first boundary. Thus, the artificial boundary model proposed herein can simultaneously absorb P-fast waves, P-slow waves and shear waves. Finally, a numerical example is given to examine the proposed artificial boundary model, and the results show that it is very accurate.

DIFFRACTION OF A SOLITARY WAVE BY A THIN WEDGE PART 2. EFFECTS OF VISCOUS BOUNDARY LAYERS

Based on the study on the Mach reflection of a solitary wave in [3] , we continue to investi- gate effects of the boundary layers on the bottom and the vertical side wall. By using matched asymptotic methods, the two-dimensional KdV equation is modified to account for effects of viscosity. Numerical simulation of the problem shows that the effects of side wall are important while the effects of the bottom can be neglected. The results including the side wall's effects agree satisfactorily with those of Melville's experiments. Finally, we establish the simplified concept of the side wall effect and conclude that it repre- sents the physical reason for the discrepancy between the experiments and the previous calculations based on the inviscid fluid flow theory.

APPLICATION OF THE PML ABSORBING BOUNDARY CONDITION TO FD-TD SIMULATION

The key problem of finite-difference time-domain (FD-TD) method is the skillful application of special conditions on the boundaries of the computational domain. A new technique named Perfectly Matched Layer(PML) yields a robust Absorbing Boundary Condition(ABC) independent of the angle of incidence and the frequency of outgoing waves. In this paper, the principle of the PML technique is briefly presented. Then some problems in the application and their settlements are discussed emphatically. Finally three numerical tests and a measured result are devoted to examine the accuracy and effectiveness of this approach.

数智化使能企业跨界搜索提升创新绩效的模式匹配与选择——基于知识治理机制视角

随着数字智能技术的蓬勃发展,如何通过外部创新知识搜寻与配置提高创新能力,成为企业应对当前极度不确定性环境的关键。基于知识治理机制视角,选取4家典型企业进行多案例比较研究,探寻数智化使能企业跨界搜索提升创新绩效的动态过程。研究发现:①在数智化使能企业跨界搜索过程中,存在网络拓扑模式、全景互动模式两种跨界搜索模式以及技术内生风险、知识基础风险两种过程风险;②知识治理机制中的正式知识治理与非正式知识治理可以有效防范数智技术大规模应用中带来的过程风险,因此在数智化跨界搜索转化为创新绩效的过程中,需要对不同知识治理机制进行权衡考量;③在数智化使能作用下,企业能够基于自身知识治理机制的不同,创造性地匹配高拓扑—低互动、高拓扑—高互动、低拓扑—高互动跨界搜索模式,提高企业创新绩效。基于上述分析,构建并阐释了数智化使能企业跨界搜索提升创新绩效的整合模型,为后续跨界搜索影响企业创新绩效的研究提供了新理论视角,并为企业创新实践提供指导。

CO_(2)地质封存源汇匹配及安全性评价进展

CCUS是实现碳中和目标的重要技术手段,目前中国正处于“双碳”目标的落实阶段,在CO_(2)地质封存的经济界限评价、源汇优化和安全监测方面还缺乏成熟的技术体系。从封存技术经济界限、源汇匹配技术、封存安全性及监测3个方面总结了中国CO_(2)地质封存技术发展历程。回顾了CCUS技术在捕集、运输、注入封存阶段的经济成本,进一步总结了目前各阶段的技术经济界限及其影响因素。此外,通过总结国内外CCUS源汇匹配技术发展现状,明确了中国源汇特征及其分布,提出了进一步开展源汇匹配优化技术的发展方向。最后,通过总结CO_(2)地质封存安全风险评价及封存监测技术,明确了经济高效、有效、定量的监测方法是未来的研究重点。

球-柱-球复合壳体结构声辐射建模及特性分析

针对典型复合材料轴对称结构的外部声辐射问题,本文建立了基于结构完整边界的广义谱-配点边界元法的结构声辐射分析模型。从一阶剪切层合壳理论出发,推导了复合材料结构振动能量方程,引入广义谱方法和边界元方法的思想,将Helmholtz积分方程转化为边界积分方程,再将位移、声学变量和Green函数等展开为周向Fourier多项式和轴向Chebyshev多项式的形式,经化简得到一维半解析声振耦合求解的声场方程。对于浸没在轻质和重质流体中的壳体结构,均采用强耦合的处理方式对结构声问题进行求解。通过数值结果验证了本文方法的正确性,分析了各向同性均匀材料和正交各向异性球-柱-球复合壳体的声辐射问题,并讨论了不同载荷方式、铺层角度等因素对复合壳体结构声辐射的影响。结果表明:对于铺层为[90°/±θ/0°]S的玻璃纤维材料复合壳体结构,随着铺层角的增大,组合结构的轴向拉伸和弯曲刚度逐渐减小,周向的刚度得到加强,并在结构弯曲-扭转耦合效应的作用下,壳体结构的辐射声功率级响应曲线的峰值频率向高频发生偏移。

面向旋转爆轰燃烧室的涡轮气动性能数值研究

为研究旋转爆轰燃烧室出口流场对涡轮气动性能的影响,基于指数函数的非线性特征简化了燃烧室出口的流场分布,采用求解三维SST k-ω湍流模型的方法对涡轮全流场开展数值计算。讨论了不同来流脉动特性对叶栅瞬态流场的作用机制,分析了涡轮叶片对燃烧室出口压力振荡峰值的抑制作用,并在此基础上探究了不同工况下涡轮流动特性的变化。计算结果表明:脉动来流使涡轮瞬时流场呈现复杂的周期性变化;单级轴流式涡轮使得压力振荡峰值最高降低73.49%,其中静子叶栅对双波模态下压力峰值的抑制效果最优,最多可降低49.9%,转子叶栅对压力峰值的二次抑制具有补偿效应,压力峰值平均减小46.95%;涡轮虽然会增强来流的总压脉动特性,但本身具有一定自适应能力,此外总压脉动与流动均匀性有较为密切的关系。

基于改进边界匹配网络的鱼群摄食动作时序检测方法研究

集约化水产养殖中,实时监测鱼群摄食状态是制定科学投喂策略的重要依据之一。为实现鱼群摄食和非摄食状态的时序探测,解决现有方法在探测摄食状态切换时误差较高的问题,提出了基于改进边界匹配网络(Boundary Matching Network,BMN)的鱼群状态检测网络BMN-Fish。该网络在BMN的基础上,引入高效深度模块,包含高效通道注意力模块(Efficient Channel Attention Module Net,ECANet)和基础残差模块(Base Residual Module,BRM)。高效通道注意力模块可扩大时序维度特征的感受野,提高了模型提取局部信息的能力;基础残差模块可关注特征图中感兴趣的区域,增强算法的全局感知能力。结果显示,相比于原始的鱼群时序摄食动作检测网络BMN,BMN-Fish的AUC和AR@100指标达93.32%和95.28%,分别提高2.17%和1.95%。研究表明,该方法可以高效检测鱼群时序摄食动作,为集约化水产养殖制定智能投饲策略提供参考。

边界跨越对科学论文引文量的影响:基于因果推断的分析

[目的/意义]知识的分化、重组、融合是激发科学创新、促进科学发展的重要动力。基于知识重组视角,揭示知识边界跨越特征与被引量的因果机制对知识扩散研究具有重要意义。[研究设计/方法]通过倾向值匹配的方法,基于科学计量学领域5本期刊2011-2015年的论文及双向引用数据,从知识主题的层面检验边界跨越论文对其被引数量的影响。[结论/发现]边界跨越对论文的被引量有积极效应,边界跨越程度高的论文平均比跨越程度低的论文超出9次左右的被引量。平衡性及共同区间表明了匹配结果的有效性和可靠性。[创新/价值]揭示科学论文边界跨越特征与引文量的内在关系,为解构交叉科学知识流动、解析知识演化提供必要的实证支撑。

几何特征约束的SIFT特征匹配改进算法

图像配准精度直接影响机器视觉尺度检测的精度,针对尺寸不变特征变换(SIFT)特征匹配未考虑特征点之间的几何关系,对于小插件等灰度变化较平滑的图像易产生误匹配点的问题,提出了几何特征约束的SIFT特征匹配改进算法。首先,用基于边界拓扑分析的图像跟踪算法提取目标轮廓;然后,用轮廓特征对SIFT算法进行约束并利用随机抽样一致(RANSAC)算法去除“离群点对”;最后,估计变换矩阵并完成图像精确配准。基于高分辨率工业相机和高性能计算机构建精密尺度检测系统,以手机USB接口插件为对象进行实验,实验结果表明:该算法图像配准精准度可达95.31%,与SIFT算法、SIFT+RANSAC算法相比较,配准精准度得到了较大提高,该算法已应用于某检测设备研制中。

基于单红外光与单白光的双光谱测距方法

为了克服红外光与白光成像机理不同引起的图像信息无法同步、无法同时使用红白光双光谱系统实现测距的问题,以待测目标的边界作共性特征,采用红白光相机对同一目标的共性特征进行采集,将采集到的图像通过高斯算子进行平滑处理,再运用Laplace扩展算子进行边界特征检测,将不同距离下目标边界像素位置数据进行线性拟合并建立测距误差模型,从而生成边界特征匹配算法。研究结果表明边界特征匹配算法可以使红白光双目系统克服成像机理不同这一问题实现测距功能,测距范围可达到40 m,最大相对误差是0.975%。