Length estimation of extended targets based on bistatic high resolution range profile

The approach to estimate the length of extended targets by using the bistatic high resolution range profile（ H RRP） is analyzed in this paper. The relationship between the bistatic H RRP and the monostatic H RRP of extended targets are investigated. It is demonstrated by simulations that the target length measured by the bistatic H RRP is more meaningful and accurate than that by the monostatic HRRP,though the monostatic H RRP has been well developed and widely used in target recognizing and classification. The estimation results of a cone shaped target are present and compared at the end of the paper. To assure the reliability of the simulation,the bistatic H RRP is obtained through the scattering field data calculated by a fullwave numerical method,FE-BI-MLFMA.

Mathematical model of determination of die bearing length in design of aluminum profile extrusion die

Based on the finite element simulation of profile extrusion process, the effect of local extrusion ratio, die bearing area and the distance between extrusion cylindrical center and local die orfice center on mental flow velocity was investigated. The laws of deformed metal flow on profile extrusion process were obtained. The smaller the local extrusion ratio, the faster the metal flow velocity; the smaller the area of die bearing, the faster the metal flow velocity; the smaller the distance of position of local die orifice(the closer the distance of position of local die orifice from extrusion cylindrical axis), the faster the metal flow velocity. The effect of main parameters of die structure on metal flow velocity was integrated and the mathematical model of determination of die bearing length in design of aluminum profile extrusion die was proposed. The calculated results with proposed model were well compared with the experimental results. The proposed model can be applied to determine die bearing length in design of aluminum profile extrusion die.

The Planck Length and the Constancy of the Speed of Light in Five Dimensional Spacetime Parametrized with Two Time Coordinates

In relativity and quantum field theory, the vacuum speed of light is assumed to be constant;the range of validity of general relativity is determined by the Planck length. However, there has been no convincing theory explaining the constancy of the light speed. In this paper, we assume a five dimensional spacetime with three spatial dimensions and two local time coordinates giving us a hint about the constancy of the speed of light. By decomposing the five dimensional spacetime vector into four-dimensional vectors for each time dimension and by minimizing the resulting action, for a certain class of additional time dimensions, we observe the existence of a minimal length scale, which we identify as the Planck scale. We derive an expression for the speed of light as a function of space and time and observe the constancy of the vacuum speed of light in the observable universe.

Fractal features of soil profiles under different land use patterns on the Loess Plateau, China

Fractal theory is becoming an increasingly useful tool to describe soil structure dynamics for a better understanding of the performance of soil systems. Changes in land use patterns significantly affect soil physical, chemical and biological properties. However, limited information is available on the fractal characteristics of deep soil layers under different land use patterns. In this study, the fractal dimensions of particle size distribution（PSD） and micro-aggregates in the 0–500 cm soil profile and soil anti-erodibility in the 0–10 cm soil profile for 10 typical land use patterns were investigated in the Zhifanggou Watershed on the Loess Plateau, China. The 10 typical land use patterns were： slope cropland, two terraced croplands, check-dam cropland, woodland, two shrublands, orchard, artificial and natural grasslands. The results showed that the fractal dimensions of PSD and micro-aggregates were all significantly influenced by soil depths, land use patterns and their interaction. The plantations of shrubland, woodland and natural grassland increased the amount of larger micro-aggregates, and decreased the fractal dimensions of micro-aggregates in the 0–40 cm soil profile. And they also improved the aggregate state and aggregate degree and decreased dispersion rate in the 0–10 cm soil profile. The results indicated that fractal theory can be used to characterize soil structure under different land use patterns and fractal dimensions of micro-aggregates were more effective in this regard. The natural grassland may be the best choice for improving soil structure in the study area.

Study on the double-logarithmic profile of tidal flow velocity in the near-bed layers

Tidal current velocity profile in the near-bed layers has been widely studied. The results showed that velocity profile in the near-bed layer obviously departure from the traditional logarithmic profile, due to the acceleration or deceleration. Although the logarithmic linear profile can reduce the rate of deviation from this, only it is a lower-order approximate solution. In this paper, considering the unsteady and non-linear features of tidal motion, the double logarithmic profile near-bed layers in estuarine and coastal waters is established on the assumption that the turbulent shear stress along the water depth was parabolic distribution, and on the basis of Prandtl＇s mixing length theory and yon Karman＇s self-similar theory. Having been verified the data observed at the West Solent in the south of England, and comparison of the logarithmic linear profile, it found that the double logarithmic profile is more precious than the latter. At last, the discussed results showed that： （1） The parabolic distribution of the tidal shear stresses verified good by the field data and experimental data, can be better reflected the basic features of the tidal shear stress deviating from linear distribution that is downward when to accelerate, upward when to decelerate. （2） The traditional logarithmic velocity profile is the zero-order approximation solution of the double logarithmic profile, the logarithmic linear profile is the first order, and the logarithmic parabolic profile is the second order. （3） Ignoring the conditions of diffusion and convection in the tida movement, the double logarithmic profile can reflect the tidal properties of acceleration or deceleration, so that the calculation of the friction velocity and roughness length are more reasonable. When the acceleration or the deceleration is about zero, the double logarithmic profile becomes the logarithmic profile.

Three-Dimensional Tidal Model and Its Application to Numerical Simulation of Water Quality in Coastal Waters

The turbulence mechanism plays an important part in the mixing process and momentum transfer of turbulence. A three-dimensional Prandtl mixing length tidal model has been developed to simulate tidal flows and water quality. The eddy viscosities and diffusivities are computed from the Prandtl mixing length model. In order to model the water quality of an estuary or coastal area many interdependent processes need to be simulated. These may be conveniently separated into three main groups: transport and mixing processes, biochemical interaction of water quality variables and the utilization and re-cycling of nutrients by living matter. The model simulates full oxygen and nutrient balance, primary productivity and the transport, reaction mechanism and fate of pollutants over tidal time-scales. The model is applied to numerical simulation of tidal flows and water quality in Dalian Bay. The model has been calibrated against a limited data set of historical water quality observations and in general demonstrates excellent agreement with all available data.

A STUDY OF NEAR SURFACE WIND PROFILES IN THE HEBEI COASTAL AREA BASED ON OBSERVATIONAL EXPERIMENTS

In order to provide wind profiles for the microscale numerical simulation of wind farm with complex terrain,using the 100 m tower atmospheric turbulence observation experiment data in 2010 in Hebei Province offered by National Climate Center, the variation characteristics of wind profile under the different atmospheric stability conditions are analyzed, and the wind profile expression based on the local similarity theory is established. The results show that:(1) In spring, the occurrence probability of unstable stratification in the Hebei coastal area is as high as 28%, and the probability of stable stratification is more than 43% while, in summer, the probability of occurrence of unstable stratification is as high as 80% with a lower probability for stable stratification; and(2) for stable stratification, the characteristics of atmosphere change is dramatic in terms of the vertical direction, which need to be treated layer by layer.According to the atmospheric turbulence observation experiment data above, under stable stratification, the relationship between the dimensionless velocity gradient and the stability ζ can be expressed as 1 +βmζ, with βm changing with the height: βm takes 4.1-4.3 under 30 m, βm takes 4.6-4.7 between 30-50 m, and βm takes 6.3-6.7 over 50 m.

基于Matrix Profile的时间序列变长模体挖掘

已有的变长模体发现算法存在速度慢、可扩展性较差,且结果中包含过短、过长和平凡匹配等无意义模体的问题。本文提出一种基于Matrix Profile的时间序列变长模体挖掘算法。该算法使用STOMP算法作为子程序,使用结合了增量计算的下界距离来加速候选模体提取过程;采用长度相似性条件和模体分组等价类方法踢除过短、过长和平凡匹配等无意义的模体。在数据集UCR上的实验表明,提出的算法在发现变长模体时,能够有效地过滤无意义模体,且具有较高的效率和准确率。

A Method for Calculating Fractal Dimension of Amicrons and Fractal Simulation of Boundary Micro-Topography

A simple and practical method to calculate the fractal dimension （FD） of amicron＇s projective surface profile based on fractal theory is proposed. Taking AI（OH）3 material particles as an example, the scanning electron microscope （SEM） photos of particles were processed using an image.processing software （IPS） Photoshop. Taking the pixel as a fixed yardstick with the enlargement of the size of the particle image, the box-dimension and circumference-area （C-S） methods were used to calculate the FD of the surface profile of the particle. The FD of 1.2623 of the classic Koch curve is obtained, which approximates the true value of 1.2628. The complexities of the object＇s boundary and surface micro-topography are simulated successfully by a generator method.

Chinese Standards on Refractories Dimensions of Refractory Bricks-Part 1:Specification for General Bricks

1 Scope This standard specifies the terms, definition, di-mension series, size designation representation, dimen-sion standard representation, brick dimension, and di- mension characteristics of general refractory bricks.

A Solution to the Cosmological Constant Problem in Two Time Dimensions

For the last hundred years, the existence and the value of the cosmological constant Λ has been a great enigma. So far, any theoretical model has failed to predict the value of Λ by several orders of magnitude. We here offer a solution to the cosmological constant problem by extending the Einstein-Friedmann equations by one additional time dimension. Solving these equations, we find that the Universe is flat on a global scale and that the cosmological constant lies between 10-90 m-2 and 10-51 m-2 which is in range observed by experiments. It also proposes a mean to explain the Planck length and to mitigate the singularity at the Big Bang.

Efficient Method to Achieve Enhanced Thermal Dimensional Stability and Desired Dimensions of Hollow Polyester Fiber

This study has developed an efficient method to achieve excellent thermal dimensional stability and desired dimensions of hollow polyester fiber. Firstly,the influence of thermal treatment temperate( 140-180 ℃) on the degree of shrinkage of fiber was investigated. The influence was also analyzed with a 2nd heating to simulate the application situation. It was discovered that the heat treatment at a temperature which was above the application temperature( 2nd heating) would efficiently remove the internal stress in the fiber and improve the thermal dimensional stability.Secondly,the impact of heat treatment temperature on the fiber diameter and the degree of hollowness were studied. The results implied that with a fixed fiber length, higher treatment temperature led to thinner fiber and a lower degree of hollowness.Last but not least,key parameters that could further influence the fiber dimensions were investigated. The results suggested that the fiber diameters and the degree of hollowness could be further controlled by tuning the drawing speed,the spinning meter pump output and cooling status while the spinneret parameters were fixed.

Joint Rock Coefficient Estimation Based on Hausdorff Dimension

The strength of rock structures strongly depends inter alia on surface irregularities of rock joints. These irregularities are characterized by a coefficient of joint roughness. For its estimation, visual comparison is often used. This is rather a subjective method, therefore, fully computerized image recognition procedures were proposed. However, many of them contain imperfections, some of them even mathematical nonsenses and their application can be very dangerous in technical practice. In this paper, we recommend mathematically correct method of fully automatic estimation of the joint roughness coefficient. This method requires only the Barton profiles as a standard.

宽带复合双基地雷达舰船目标长度估计方法

舰船目标长度特征对舰船目标识别具有重要作用,该文提出一种基于宽带复合双基地雷达联合观测的舰船目标长度估计方法。该方法综合利用单/双基地雷达高分辨距离像(HRRPs)长度,结合双基地雷达-舰船之间的空间关系求解,实现了单次测量估计舰船目标的实际长度,并分析了各种误差因素和几何构型条件下的估计误差。典型场景动态仿真证明了所提方法的有效性,结果表明在高分辨距离像长度误差小于5%条件下,舰船目标长度估计误差小于5%,为舰船目标特征提取与识别提供了新思路。

面向星地激光通信的大气湍流预报研究进展(特邀)

激光通信系统在大气环境下应用的性能受到严重制约,当激光在大气湍流中传输时,其波面会发生畸变。在激光通信系统中,对大气湍流相关参数进行预报可以提前对星地数据传输链路进行调度,避免建立无效的通信任务。此外,大气湍流预报在天文选址、光学遥感等领域也有重要价值。随着国内外相关工作的长期积累以及算力、观测设备等硬件的能力提升,当前科研人员已经提出了一些大气湍流预报方案。文中主要综述了国内外学者在大气湍流预报方面的研究进展,首先详细介绍了目前应用比较广泛的中尺度数值预报技术,列举了使用中尺度数值预报方法对国内外典型区域的大气湍流进行预报的相关工作;然后介绍了深度学习方法在大气湍流预报中的应用情况,对其优势与局限性进行了讨论;最后介绍了一种面向星地激光通信的大气相干长度短时预报方法。

工程陶瓷圆弧成形磨削力预测与实验研究

圆弧成形磨削是难加工零件复杂型面的加工方法,对其磨削力的研究有利于改善工程陶瓷的表面质量。基于圆弧砂轮的结构特点及尺寸趋近思想对陶瓷材料圆弧成形磨削力进行预测。通过研究磨粒对工程陶瓷的去除机制,提出建立单颗磨粒滑擦、塑性及脆性去除磨削力模型。基于砂轮磨粒尺寸与分布差异,利用概率统计方法对磨削中不同去除方式的有效磨粒数进行探讨,进而实现圆弧成形磨削力理论模型的构建。最后通过磨削力实验对理论模型进行验证。结果表明:法向磨削力和切向磨削力理论值与实验值平均误差分别为8.793%和9.986%;磨削力随着磨削深度及进给速度的增加而增加,随着砂轮速度的增加而减小。

基于ClickHouse数据库实现加能站大数据客户画像分析

以石油销售行业为例,传统的客户画像分析方法在数据存储和计算时效率低、处理过程复杂,提出了一种高效精准的客户画像分析方法——ClickHouse列式存储数据库。介绍了该数据库的优点及数据采集和清洗、存储和管理、分析和计算以及精细化营销应用,针对客户群体的基本属性和交易行为,设计多维度层面的不同类别标签,并应用条件标签的组合,快速而准确地筛选出特定的客户群体,实际应用表明:该数据库可以为精细化的营销和个性化的服务提供依据和支持。

基于有限长线接触理论的齿轨列车齿轮齿条接触分析及齿形优化设计

为了探究齿轨列车曲线行驶时驱动齿轮与齿条轨道啮合中心距误差和轴线不平行度误差对接触应力分布的影响,基于有限长线接触理论,建立了综合考虑两种误差的齿轮齿条接触应力分析模型;通过与误差条件下的齿轮齿条接触有限元仿真进行对比,证明建立的模型具有良好的计算精度。基于该模型,研究了不同误差水平和综合两类误差作用下的接触应力响应,揭示了两类误差对接触应力分布的影响机理,并据此提出应对措施。研究结果表明,提出的接触应力分析模型能准确反映啮合中心距误差和轴线不平行度误差综合作用下齿轮齿条的接触情况;接触应力水平随啮合中心距误差的增大而增大,接触应力轴向不均匀程度随轴线不平行度误差的增大而增大;啮合中心距误差会加剧轴线不平行度误差引起的轴向接触应力不均匀性,轴线不平行度误差对啮合中心距误差的作用效果有轻微的抑制作用;啮合中心距误差的内在作用机理是减小了相同载荷水平处的承载面积,轴线不平行误差的内在作用机理是曲线内侧的齿轮齿条率先接触,产生了更大的变形;齿轮挖根可消除轴线不平行误差的影响,齿轮螺旋线修形可降低轴线不平行误差的影响。

基于数学形态学理论的旋转机械故障诊断方法研究

在数学形态学理论的基础上运用局部特征长度域(LCD)算法和区间估计分形维数对传统诊断方法进行改进,利用LCD算法对信号进行处理,同时利用区间估计对形态谱进行故障分析。实验结果表明,基于LCD算法的故障诊断研究方法可以准确判断不同故障类型,区间估计分形维数方法的故障判断精度为95%,而且不同故障类型的形态谱特征与实际相符合。

基于用户画像的智慧学科服务之时空特征研究

学科服务是高校图书馆重点服务内容之一。研究用户信息需求的时间、空间变化特征,对提升学科服务效果意义重大。文章以高校教师、科研人员和学生为研究对象,利用调查法、场景化方法研究了不同类型的用户在时间和空间维度下的信息需求特征,构建了智慧学科服务模型,探讨了时空维度下智慧学科服务的应用场景。实践表明,利用用户信息需求的时空特征能够提高学科服务的满意度。