TC2M2δ.5钛板冷热翻边成形极限及非对称化研究

TC2Mδ2.5mm钛板室温圆孔翻边成形试验结果表明,除翻边底孔尺寸小于极限值时在唇口边缘发生破裂的正常失效方式之外,冷翻边卸载后制件还出现凸缘平面翘曲、翻边孔口部椭圆化、唇口边缘高度不一致、壁厚分布不均匀等非对称化现象。600℃高温热翻边成形可以有效地提高成形极限,并消除了凸缘平面翘曲和口部椭圆化,但口部高度差以及壁厚不均等非对称化现象依然存在。本文在给出极限翻边系数的同时,对这种非轴对称化程度进行了定量描述,并给出了理论上的分析与解释。

基于改进型自适应非对称联合对角化双基地MIMO雷达多目标跟踪算法研究

针对双基地MIMO雷达自适应非对称联合对角化(AAJD)跟踪算法性能低的问题,该文提出一种改进AAJD双基地MIMO雷达多目标跟踪算法。AAJD算法角度估计时重复利用上一时刻的角度信息,导致跟踪性能的下降。通过证明AAJD算法求出的特征矢量每一列都对应着一个目标,改进AAJD算法直接求解目标的收发角度,提高了跟踪性能,更加适用于大机动目标跟踪,并对ESPRIT算法进行改进,实现了目标角度的自动配对与关联。仿真结果表明改进AAJD算法跟踪性能高于AAJD算法,特别是跟踪大机动目标时改进AAJD算法性能更优,验证了理论分析的有效性。

基于检测增强型YOLOv3-tiny的道路场景行人检测

为了给驾驶员提供实时准确的行人信息、减少交通事故的发生,提出一种检测增强型YOLOv3-tiny(detection of enhanced YOLOv3-tiny,DOEYT)行人检测算法.创建鲁棒的特征提取网络,首先使用非对称最大池化进行下采样,防止随着感受野增大行人横向特征的丢失;其次使用Hardswish作为卷积层的激活函数优化网络性能;最后使用GC(globe context)自注意力机制获得全文特征信息.在分类回归网络部分,采用三尺度检测策略,提升小尺度行人目标的检测精度;使用k-means++算法重新生成数据集锚框,提高网络收敛速度.构建行人检测数据集并分为训练集和测试集,对DOEYT算法的性能进行试验验证.结果表明,非对称最大池化、Hardswish函数、GC自注意力机制分别使平均准确率AP提高14.4%、7.9%、10.8%;DOEYT算法在测试集上检测的平均准确率高达91.2%,检测速度为103帧/s,可见该算法可快速准确地检测行人,降低交通事故发生的风险.

基于有限元法的钢轨硌伤模拟及其应力状态研究

为研究诱发局部滚动接触疲劳的钢轨硌伤现象,需精确模拟其应力应变场。基于显式有限元法建立钢轨动态硌伤有限元时域分析模型,考虑车轮滚滑、真实接触几何、率相关弹塑性本构等因素,轮-轨-异物间瞬态接触采用基于罚函数的“面-面”接触算法求解。针对摩擦系数为0.3,车轮运行速度为300 km/h,直径4 mm的刚性球形异物造成的硌伤进行模拟。结果表明:模型能捕捉到异物在硌伤过程中的复杂空间运动轨迹,以及连续体振动造成的应力波动;硌伤几何、残余应力、应变场具有明显的空间非对称性;车速从100 km/h增加至350 km/h,硌伤坑变浅,表层残余应力、等效塑性应变在200 km/h时出现极值;摩擦系数由0.5降至0.1,硌伤截面形状、残余应力应变非对称化加剧。

近20 a新疆天然草地NPP时空分析

基于MOD17A3HGF NPP(Net primary productivity)与气温、降水量等数据,采用趋势分析与偏相关分析,在多个尺度(全疆、北疆与南疆、各地州市与11种草地类型)探讨了2000-2018年新疆天然草地NPP时空动态及其对气候变化的响应。结果表明:近20 a新疆草地NPP呈波动递增,多年均值为0.103 kg C·m^(-2),由准噶尔西部山地、伊犁河谷、天山、阿尔泰山向准噶尔盆地、塔里木盆地逐渐降低;北疆草地多年平均NPP(0.149 kg C·m^(-2))高于南疆(0.055 kg C·m^(-2)),北疆、南疆草地NPP均表现为增加趋势;各地、州、市草地NPP总体为增加,但年际变化分异明显;11种天然草地类型(除高寒荒漠类)NPP表现为递增趋势,但不同草地类型存在差异。2000年后,新疆气候暖湿化有利于草地植被生长,但降水年际变化增强导致草地NPP年际波动剧烈。研究结果为新疆天然草地碳收支评估提供基础数据,能够促进天然草地健康评价以及可持续利用。

双基地MIMO雷达收发角和径向速度联合估计

在双基地MIMO雷达信号模型基础上,提出一种新的目标收发角和径向速度联合估计方法。该方法首先将三参数估计问题转化为非对称联合对角化问题,然后采用最小二乘循环算法对其求解,估计收发导向矩阵和速度矩阵,最后利用谱分析算法恢复收发角和径向速度。同时采用截断高阶奇异值分解(THOSVD)对数据进行压缩处理,减小运算量。该方法充分利用匹配滤波输出的所有信息,无需二维谱峰搜索,每次循环均可得到精确的闭式解。与基于并行因子(PARAFAC)分析的方法相比,该方法可获得更高的参数估计精度,且三参数自动配对。仿真表明了方法的有效性。

Etching Behavior of GaN/GaAs(001) Epilayers Grown by MOVPE

Wet etching characteristics of cubic GaN (c GaN) thin films grown on GaAs(001) by metalorganic vapor phase epitaxy (MOVPE) are investigated.The samples are etched in HCl,H 3PO 4,KOH aqueous solutions,and molten KOH at temperatures in the range of 90～300℃.It is found that different solution produces different etch figure on the surfaces of a sample.KOH based solutions produce rectangular pits rather than square pits.The etch pits elongate in 1 0] direction,indicating asymmetric etching behavior in the two orthogonal <110> directions.An explanation based on relative reactivity of the various crystallographic planes is employed to interpret qualitatively the asymmetric etching behavior.In addition,it is found that KOH aqueous solution would be more suitable than molten KOH and the two acids for the evaluation of stacking faults in c GaN epilayers. direction,indicating asymmetric etching behavior in the two orthogonal <110> directions.An explanation based on relative reactivity of the various crystallographic planes is employed to interpret qualitatively the asymmetric etching behavior.In addition,it is found that KOH aqueous solution would be more suitable than molten KOH and the two acids for the evaluation of stacking faults in c GaN epilayers.

Annealing hardening and deformation behavior of layered gradient Zr–Ti composite

To investigate potential strengthening approaches,multi-layered zirconium–titanium(Zr-Ti)composites were fabricated by hot-rolling bonding and annealing.The microstructures of these composites were characterized using scanning electron microscopy with energy dispersive spectroscopy(SEM-EDS)and electron backscatter diffractometry(EBSD).Their mechanical properties were evaluated by uniaxial tension and compression measurements.It was found that the fabricated Zr–Ti composites are composed of alternating Zr/diffusion/Ti layers,and chemical compositions of Zr and Ti showed a gradient distribution in the diffusion layer.Compared with as-rolled samples,annealing can strengthen the layered gradient Zr–Ti composite,and this is mainly caused by solid-solution strengthening and microstructure refinement-induced strengthening.Compared with the raw materials,a synergistic improvement of strength and ductility is achieved in the Zr–Ti composite as a result of the layered gradient microstructure.Tension–compression asymmetry is observed in the Zr–Ti composites,which may be attributed to twinning and microvoids induced by unbalanced diffusion.

Identification of LPV Models with Non-uniformly Spaced Operating Points by Using Asymmetric Gaussian Weights

In this paper, asymmetric Gaussian weighting functions are introduced for the identification of linear parameter varying systems by utilizing an input-output multi-model structure. It is not required to select operating points with uniform spacing and more flexibility is achieved. To verify the effectiveness of the proposed approach, several weighting functions, including linear, Gaussian and asymmetric Gaussian weighting functions, are evaluated and compared. It is demonstrated through simulations with a continuous stirred tank reactor model that the oroposed aonroach nrovides more satisfactory aonroximation.

Hamiltonian Systems and Darboux Transformation Associated with a 3 × 3 Matrix Spectral Problem

Starting from a 3 × 3 matrix spectral problem, we derive a hierarchy of nonlinear equations. It is shown that the hierarchy possesses bi-Hamiltonian structure. Under the symmetry constraints between the potentials and the eigenfunctions, Lax pair and adjoint Lax pairs including partial part and temporal part are nonlinearied into two finitedimensional Hamiltonian systems （FDHS） in Liouville sense. Moreover, an explicit N-fold Darboux transformation for CDNS equation is constructed with the help of a gauge transformation of the spectral problem.

Some Magnetized Bulk Viscous String Cosmological Models in Cylindrically Symmetric Inhomogeneous Universe with Variable Λ-Term

Some cylindrically symmetric inhomogeneous viscous fluid string cosmological models with magnetic field and cosmological term A varying with time are investigated. To get the deterministic solution, it has been assumed that the expansion （θ） in the model is proportional to the eigen value σ^11 of the shear tensor σ^ij. The value of cosmological constant for the model is found to be small and positive, which is supported by the results from recent supernovae Ia observations. The effect of bulk viscosity is to produce a change in perfect fluid and hence exhibits essential influence on the character of the solution. The physical and geometric properties of the models are also discussed in presence and absence of magnetic field.

Exclusive Semileptonic Rare Decays B→K()(?)+(?)^- in a Top Quark Two-Higgs-Doublet Model

Employing improved calculations of the decay form factors from light-cone sum rules, we evaluate the invariant mass spectrum, forward-backward asymmetry, and lepton polarizations of the exclusive processes B → K^（＊）e＋e- in the SM and T2HDM. From the recent measurements of their branching ratios, we find that these processes do provide additional bounds on the new parameters in the model considered here. After the inclusion of the new physics contributions, the large enhancement of FBA, which is unobservably small within the SM and of the lepton polarization at large tan β, may precisely test the SM or reveal new physics in forthcoming accurate experiments.

Conductivity of Oxalic Acid in Aqueous Solution at Low Concentration

Oxalic acid is a weak and unsymmetrical bi-basic acid. There exist dissociation and association equilibria among the species in aqueous solution. The molar conductivity of the solution is the sum of the ionic contributions.Based on this idea, a new prediction equation of ionic conductivity was proposed at low concentration. The molar conductivities of the solution and its relevant ions were calculated respectively. The results obtained were in good agreement with those from experiments and the Quint-Viallard equation.

Vibration Spectra of Quasi-confined Optical Phonon Modes in an Asymmetric Wurtzite AlxGa1-xN/GaN/AlyGa1-yN Quantum Well

Based on the dielectric continuum model and Loudon＇s uniaxial crystal model, the properties of the quasi. confined （QC） optical phonon dispersions and the electron-QC phonons coupling functions in an asymmetric wurtzite quantum well （QW） are deduced via the method of electrostatic .potential expanding. The present theoretical scheme can naturally reduce to the results in symmetric wurtzite QW once a set of symmetric structural parameters are chosen. Numerical calculations on an asymmetric AlN/GaN/AIo,15 Gao.85N Wurtzite Q W are performed. A detailed comparison with the symmetric wurtzite QW was also performed. The results show that the structural asymmetry of wurtzite QW changes greatly the dispersion frequencies and the electrostatic potential distributions of the QC optical phonon modes.

THE SYNTHESIS OF TWO KINDS OF POLYMER-SUPPORTED ASYMMETRIC PHASE TRANSFERCATALYSTS(PS-PTCS)AND THE COMPARISON OFTHEIR CATALYTIC ACTIVITIES

In this paper,two kinds of PS-PTCs were synthesized using different methods byintroducing cinchonine and quinine to the polymer support. Their catalytic properties forthe alkylation of N-diphenylmethylene glycine t-butyl ester were also compared

Non-interior Continuation Algorithm for Solving System of Inequalities over Symmetric Cones

As a basic mathematical structure,the system of inequalities over symmetric cones and its solution can provide an effective method for solving the startup problem of interior point method which is used to solve many optimization problems.In this paper,a non-interior continuation algorithm is proposed for solving the system of inequalities under the order induced by a symmetric cone.It is shown that the proposed algorithm is globally convergent and well-defined.Moreover,it can start from any point and only needs to solve one system of linear equations at most at each iteration.Under suitable assumptions,global linear and local quadratic convergence is established with Euclidean Jordan algebras.Numerical results indicate that the algorithm is efficient.The systems of random linear inequalities were tested over the second-order cones with sizes of 10,100,,1 000 respectively and the problems of each size were generated randomly for 10 times.The average iterative numbers show that the proposed algorithm can generate a solution at one step for solving the given linear class of problems with random initializations.It seems possible that the continuation algorithm can solve larger scale systems of linear inequalities over the secondorder cones quickly.Moreover,a system of nonlinear inequalities was also tested over Cartesian product of two simple second-order cones,and numerical results indicate that the proposed algorithm can deal with the nonlinear cases.

Enantioselective Hydrogenation of β-keto Esters Using Homogeneous and Heterogeneous Catalysts, a Case Study for Comparison of Different Catalytic Methodologies

The asymmetric reduction of β-keto esters to their corresponding hydroxy alcohols can be performed by employing homogeneous and heterogeneous chemo- and bio-catalysis. This review covers the scope and limitations of different catalysts and methodologies that were employed for the reaction and compare between them on the basis of catalytic performance, product separation and catalyst recycling procedure. In general, heterogeneous catalytic systems are advantageous from industrial point of views as they can be easily separated by filtration and re-used. Nickel modified with tartaric acid and sodium bromide was found to be suitable heterogeneous catalyst for the enantioselective hydrogenation, yet its performance is lower than this of homogeneous chiral metal catalysts such as Ru-BINAP. Heterogenization of the chiral complex via immobilization or entrapment using organic and inorganic supports was thus tested. However, though the resulted heterogeneous analogues were highly enantioselective and could be re-used, the activity of the system is often very low compared to homogeneous system due to mass transfer limitations. Alternatively, performing liquid phase hydrogenation under homogeneous conditions, using Ru-BINAP soluble derivatives, yielded high activit5＇ and enantioselectivity. Product separation and catalysts recycling were facilitated by either extraction of the product with solvent that does not dissolve the complex or by selective filtration of the product. Alternatively, precipitation of the complex at the end of the reaction was also reported.

Inconsistence of Non-Singular Spherically Symmetric Solution and a Satisfactory Energy-Momentum Complex

Two spherically symmetric non-singular black hole solutions in Moiler tetrad theory of gravitation have been obtained. Although the two solutions have the same form of metric （spherically symmetric nonsingular black hole）, their energy contents are different. We use another method given by Gibbons and Hawking to calculate the energy content of these solutions. We also obtained different value of energy. Study the requirements of a satisfactory energymomentum complex given by Moiler we find that the second solution, which behaves as 1/√r, is not transformed as a four-vector under Lorentz transformation.