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多数大宗商品市场迎来暖春 004

多数大宗商品市场迎来暖春

DOA and Subarray-Interval Estimation for Arbitrarily Distributed UAV Swarm System

经济日报

作者：蒋华栋

2024年一季度，大宗商品市场终于“扬眉吐气”。虽然部分商品价格持续低迷，但多数商品在历经2023年的下跌后迎来了“暖春”。总体来看，一季度大宗商品市场呈现加速复苏态势。路透商品研究局指数（RJ/crb）在历经2023年5.01%的下跌... 详细信息

2024年一季度，大宗商品市场终于“扬眉吐气”。虽然部分商品价格持续低迷，但多数商品在历经2023年的下跌后迎来了“暖春”。总体来看，一季度大宗商品市场呈现加速复苏态势。路透商品研究局指数（RJ/crb）在历经2023年5.01%的下跌后，延续了2023年12月开始的上行态势。今年

关键词：大宗商品市场 crb 黄金储备世界黄金协会一季度大宗商品价格黄金投资黄金市场美联储净流出

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China Communications 2023年第4期20卷 102-117页

作者： Dian Fan Yue Zhu Jia You Zhe Wang Nan Zhong The China Academy of Information and Communications Technology Beijing 100191China The China Academy of Railway Sciences Corporation Limited Beijing 100081China

In this paper,DOA and subarray-interval estimation are considered and applied to arbitrarily distributed unmanned aerial vehicle(UAV)swarm system,in which multiple small UAVs containing uniform linear array(ULA)are divided by unknown intervals because of dynamic moving.Three parameters are taken to indicate the steering vector,namely,the direction of arrivals(DOAs)of target users,the intervals of UAVs,and the orientation angles of UAVs.The orientation angles are first estimated with an auxiliary user and the DOAs are obtained through a search free rooting method,despite the intervals among the UAVs.Afterwards,the intervals among UAVs can also be calculated via exhaustive when the number of target users are no less than three.We further develop a low-complex method to reduce the computational complexity during subarray-interval estimation.The deterministic Cramér-Rao bound(crb)of the DOA,orientation angle and subarray-interval can be inferred in a closed form.Eventually,numerical instances are cited to verify the research results.

关键词： distributed subarray DOA orientation angle subarray-interval crb

不同压力下crb的晶体结构、电子结构及力学性质的第一性原理研究

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稀有金属材料与工程 2023年第10期52卷 3399-3409页

作者：刘飞孙伟王丽贾斌天津中德应用技术大学机械工程学院天津300350

基于密度泛函理论第一性原理的方法,使用CALYPSO对crb进行晶体进行结构搜索,并对搜索出的结构进行了电子结构的分析及力学性质的预测。结果表明,采用1倍分子式搜索出的2种结构中,α-Cr B相为立方结构,空间群为Fm-3m(No.225),β-crb相为... 详细信息

基于密度泛函理论第一性原理的方法,使用CALYPSO对crb进行晶体进行结构搜索,并对搜索出的结构进行了电子结构的分析及力学性质的预测。结果表明,采用1倍分子式搜索出的2种结构中,α-Cr B相为立方结构,空间群为Fm-3m(No.225),β-crb相为四方结构,空间群为P4/mmm(No.123)。当压强超过90 GPa时,crb将会发生结构相变,由α-crb相转变为β-crb相。声子谱的计算结果及力学稳定性的判据结果表明,α-Cr B相及β-crb相均具有动力学及力学稳定性。β-crb相晶体中,B原子的s轨道、p轨道及Cr原子的d轨道发生杂化,形成共价键及离子键;α-crb相晶体,Cr的d轨道和B的p轨道发生轨道杂化,形成了离子键。β-crb相中态密度能量范围分布较大且峰值相对较低,能带色散较强,原子轨道相互作用较强。随着压力的增加,α-crb相的硬度值逐渐升高,在90 GPa时达到最大值28 GPa,并且韧性和硬度的匹配程度最好,即此时材料的综合力学性能最好。当压力超过90 GPa发生相变后,β-crb相的硬度值明显降低,低至9.3 GPa,此时B/G值增加至3.9,表现出明显的韧性特征。α-crb相晶体虽然原子间作用力较低且体积模量较小,但是由于晶体内部原子之间形成了化学键网络,体积模量的各向异性相对较低,这是其具有较高硬度的主要原因。

关键词：第一性原理晶体结构搜索 crb 电子结构超硬材料

Phase pure and well crystalline Cr2AlB2:A key precursor for two-dimensional crb

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Journal of Materials Science & Technology 2019年第8期35卷 1593-1600页

作者： Haiming Zhang Fu-Zhi Dai Huimin Xiang Xiaohui Wang Zhili Zhang Yanchun Zhou School of Mechanical Electronic and Control EngineeringBeijing Jiaotong UniversityBeijing 100044 China Science and Technology on Advanced Functional Composite Laboratory Aerospace Research Institute of Materials & Processing TechnologyNo. 1 South Dahongmen Road Beijing 100076 China Shenyang National Laboratory for Materials Sciences Institute of Metal ResearchChinese Academy of Sciences72 Wenhua Road Shenyang 110016 China

Phase pure and well crystalline Cr2AlB2 powders are synthesized by heating the mixtures of crb and Al powders at 900~℃.Cr2AlB2 exhibits nanolaminated morphology which transforms from flake-like crystallite to needle-like grain with the increase of holding time.The morphology-structure relationships of Cr2AlB2 are delicately discussed.Meanwhile,as the precursor for fabrication of Cr2AlB2,high purity crb powders are also prepared by high-temperature reaction of B and Cr elemental powders at 1800℃.crb grains grow into regular plate-like morphology.Through Rietveld structure refinement,new sets of diffraction data are presented for both crb and Cr2AlB2 and overlapped peak positions and intensities are revealed which make up for the deficiency of the existing data in ICDD PDF#32-0277(crb)and ICDD PDF#72-1847(Cr2AlB2).Moreover,since MAB phases are precursors for preparing MBenes,2D-crbnanosheets are successfully prepared by completely etching out Al atomic layers from Cr2AlB2.2D-crb crystalizes in crb structure with two-dimensional lamellar morphology.Simultaneously the formation mechanism of 2D-crb is vividly depicted.A system of materials preparation from crb to Cr2AlB2 and then to 2D-crb is well established.

关键词： Cr2AlB2 crb MAB phases 2D-crb Ultrahigh temperature ceramics

DSC modelling for predicting resilient modulus of crushed rock base as a road base material for Western Australia roads

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交通运输工程学报 2013年第2期13卷 10-16页

作者： KHOBKLANG Pakdee VIMONSATIT Vanissorn JITSANGIAM Peerapong NIKRAZ Hamid Department of Civil Engineering Curtin UniversityGPO Box U1987 Perth 6845Western AustraliaAustralia

In order to increase the applied efficiency of crushed rock base(crb) in pavement structure design for Western Australia roads,the material modelling based on the experimental results was investigated,and the disturbed state concept(DSC) was used to predict the resilient modulus of crb because of its simplicity and strong ability in capturing the elastic and inelastic responses of materials to loads.The actual deformation of DSC,at any loading state,was determined from its assumed relative intact(RI) state.The DSC equation of crb was constructed by using a set of experimental results of resilient modulus tests,and an idealized material model,namely the linear elastic model,of relative intact(RI) part was considered.Analysis results reveal that the resilient modulus-applied stress relationships back-predicted by using the DSC modelling are consistent with the experimental results,so,the DSC equation is suited for predicting the resilient modulus of crb specimen.However,the model and the equation coming from the test results are conducted in accordance with the Austroads standard,so further investigation and validation with respect to the field behaviours of pavement structure should be performed.

关键词： pavement engineering crb resilient modulus DSC RI triaxial test

Cramér-Rao bound for multiple parameters estimation using a polarization sensitive array

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The Journal of China Universities of Posts and Telecommunications 2012年第3期19卷 107-113页

作者： ZHENG Gui-mei CHEN Bai-xiao YANG Ming-lei National Laboratory of Radar Signal Processing Xidian UniversityXi'an 710071China

In this paper, new Cramér-Rao lower bounds （crb） of the estimates of frequencies, two-dimensional arrival angles and polarization parameters of multiple incident signals are derived for a polarization sensitive array. The incident sources have distinct carrier-frequencies, in contrast to the modeling of all sources to be at the same known carrier-frequency, which has been investigated in the existing research literature on the Cramér-Rao bounds （crb） for polarization sensitive direction finding. The derived crbs are compact closed-form expressions and applicable to an arbitrary array geometry. Numerical examples and analysis of some special cases provide insights into the fact that the estimation accuracy of all parameters is enhanced with the increasing signal-to-noise ratio （SNR） and number of snapshots. In addition, they are hardly influenced by the sampling frequency and independent of the initial phase of incident sources. These insights offer guidelines to the system engineer on how to improve parameters＇ estimation accuracy.

关键词： array signal processing polarization sensitive array crb direction of arrival estimation frequency estimation

Study on joint Bayesian model selection and parameter estimation method of GTD model

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Science in China(Series F) 2007年第2期50卷 261-272页

作者： SHI ZhiGuang ZHOU JianXiong ZHAO HongZhong FU Qiang ATR Laboratory National University of Defence Technoloqy Chanqsha 410073. China

The Bayesian method is applied to the joint model selection and parameter estimation problem of the GTD model. An algorithm based on RJ-MCMC is designed. This algorithm not only improves the model order selection and parameter estimation accuracy by exploiting the priori information of the GTD model, but also solves the mixed parameter estimation problem of the GTD model properly. Its performance is tested using numerical simulations and data generated by electromagnetic code. It is shown that it gives good model order selection and parameter estimation results, especially for low SNR, closely-spaced components and short data situations.

关键词： RJ-MCMC GTD model scattering centers parameter estimation model order selection ESPRIT crb

基于贝叶斯统计和MIMO雷达的心跳呼吸频率估计理论与方法研究

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基于贝叶斯统计和MIMO雷达的心跳呼吸频率估计理论与方法研究

作者：李浩正电子科技大学

学位级别：硕士

随着社会发展,人们对自身健康的重视程度与日俱增,开发一种能够便捷测量人体健康数据的技术显得尤为必要。作为无接触式测量的重要分支,基于雷达的生命体征测量技术应运而生。多输入多输出（Multiple-Input Multiple-Output,MIMO）雷达... 详细信息

随着社会发展,人们对自身健康的重视程度与日俱增,开发一种能够便捷测量人体健康数据的技术显得尤为必要。作为无接触式测量的重要分支,基于雷达的生命体征测量技术应运而生。多输入多输出（Multiple-Input Multiple-Output,MIMO）雷达能够获得高于传统雷达的优异性能,因此本文提出基于MIMO雷达的心跳呼吸频率测量理论与方法研究,旨在提高心跳和呼吸频率等生命体征参数的估计性能,为相应雷达系统的优化设计提供理论参考。雷达通过探测心肺运动引起的胸腔起伏来测量心跳呼吸频率。时频分析作为传统方法,利用信号的频域特性对心跳呼吸频率作出估计。本文给出包含生命体征信息的MIMO雷达信号模型,拓展复信号解调法（Complex Signal Demodulation,CSD）和反正切解调法（Arctangent Demodulation,AD）两种经典时频分析方法在MIMO体制下的应用。通过频谱特性的理论推导结合仿真分析,证实两种算法都能对呼吸频率作出较为准确的估计。由于谐波干扰问题的存在,CSD方法无法稳定地估计心率而AD方法在条件充分时则可以。两种方法都受到信噪比、观测时长、频谱精度的显著影响而限制了估计精度的进一步提升。为进一步提高性能,本文提出采用基于贝叶斯统计理论的极大似然（Maximum Likelihood,ML）估计方法,推导心跳呼吸频率的ML估计器和克拉美罗界（CramerRao Bound,crb）表达式。通过仿真实验,证明理论推导的正确性,说明crb能够作为可靠的指标评价心跳呼吸频率估计性能。在不同脉冲数下对CSD、AD、和ML三种估计方法的性能进行了对比。本文还利用crb分析心率估计困难的原因,以及载频、信号时宽、发射信号正交性和天线数等雷达系统参数对估计性能的影响。最后,本文通过模拟不同天线布置方式下的测量情况,说明合理的天线布置可以明显提高心跳呼吸频率的估计精度。

关键词： MIMO雷达生命体征心跳呼吸监测参数估计 crb

Analysis of crb;and VB;formation in molten Al-Cr-V-B alloy

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Transactions of Nonferrous Metals Society of China 2021年

作者： H.T.Ali A.Khaliq M.Yusuf DepartmentofMechanicalEngineering，CollegeofEngineering，TaifUniversity DepartmentofMechanicalEngineering，CollegeofEngineering，UniversityofHa'il SchoolofEngineering，RMITUniversity DepartmentofClinicalPharmacy，CollegeofPharmacy，TaifUniversity

Transition metal impurities such as chromium （Cr） and vanadium （V） in solution deteriorate electrical conductivity of smelter grade aluminium （Al）. These impurities can be removed from solution via boron treatment in which borides form upon their in-situ reaction with boron （B）-bearing substances. However，Cr removal from smelter grade Al solution is not well understood. A disagreement related to chromium boride （crb2）formation in molten Al in the presence of other transition metals （V， Ti， Zr， Fe） by adding Al-B master alloy has been reported in literature. This study presents an effort to understand the mechanism of Cr removal from Al-0.50% Cr-0.50% V alloy by adding Al-B （AlB12） master alloy at 750 ℃ in the Al alloy solution. Results indicate that Cr removal from molten Al-0.50% Cr-0.50% V alloy by forming stable borides cannot be achieved at 750 ℃. Whereas， excess of B in the solution preferentially forms aluminium boride （AlB2） over crb2 during boron treatment of molten Al. The underlying kinetics of V removal from molten Al-0.50% Cr-0.50% V alloy revealed that early reaction stage is controlled by [B]/[V] mass transfer through liquid phase and mass transfer coefficient （km） was measured as 9.6 x 10;m/s. The later reaction stage was controlled by [B]/[V] diffusion through boride ring （VB2）. This study， therefore advocates to investigate alternative ways to remove Cr from molten Al.

关键词： Boron treatment Al crb VB Thermodynamics Kinetics