Elastic Wave Scattering by Two-Dimensional Periodical Array of Cylinders

We extend the multiple-scattering theory (MST) for elastic wave scattering and propagating in two-dimensional composite. The formalism for the band structure calculation is presented by taking into account the full vector character of the elastic wave. As a demonstration of application of the formalism we calculate the band structure of elastic wave propagating in a two-dimensional periodic arrangement of cylinders. The results manifest that the MST shows great promise in complementing the plane-wave (PW) approach for the study of elastic wave.

USING TWO-DIMENSIONAL TIME RESOLVED LIGHT SCATTERING TO STUDY THE CURE REACTION INDUCED PHASE SEPARATION PROCESS OF EPOXY-AMINE-POLYETHERSULFONE BLEND WITH SECONDARY PHASE SEPARATION

The generalized two-dimensional correlation analysis based on time-resolved light scattering patterns （2D TRLS） has been employed to study the phase separation process of an epoxy-amine-polyethersulfone blend in which the secondary phase separation takes place. The results of the 2D TRLS provided more detailed information that was not readily observed in the 1D TRLS patterns. （i） During the first process of phase separation, the sequential order of coarsening in size of the domains among the larger and smaller ones has been reversed between the diffusion regime and the hydrodynamic regime. （ii） The change of the larger domains in size, due to the hydrodynamic flow in the late stage of the first phase separation process, keeps on taking place earlier than that of the new domains appeared in the secondary phase separation process. （iii） During the secondary phase separation process the size growth of the smaller domains takes place earlier than that of the larger ones, probably due to the assumption that the coarsening mode could decrease the interface tension more quickly.

Scattering Relations for Two-Dimensional Electromagnetic Waves in Chiral Media

We consider the scattering of time-harmonic plane waves by an infinitely long penetrable chiral cylinder. The electromagnetic scattering problem is reduced to a transmission problem for a system of two-dimensional Helmholtz equations. We prove the classical reciprocity principle, a general scattering theorem and an optical theorem in R2. Using Herglotz wave functions we define the corresponding far field operator. Applying the general scattering theorem useful relations are proved for the reconstruction of the scatterer. We also prove that for real chirality measure of the penetrable scatterer the far field operator has a countable number of eigenvalues which lie on a circle.

Raman scattering study of two-dimensional magnetic van der Waals compound VI3

The layered magnetic van der Waals materials have generated tremendous interest due to their potential applications and importance in fundamental research.Previous x-ray diffraction(XRD)studies on the magnetic van der Waals compound VI3,revealed a structural transition above the magnetic transition but output controversial analysis on symmetry.In this paper we carried out polarized Raman scattering measurements on VI3 from 10 K to 300 K,with focus on the two Ag phonon modes at^71.1 cm^-1 and 128.4 cm-1.Our careful symmetry analysis based on the angle-dependent spectra demonstrates that the crystal symmetry can be well described by C2h rather than D3d both above and below structural phase transition.We further performed temperature-dependent Raman experiments to study the magnetism in VI3.Fano asymmetry and anomalous linewidth drop of two Ag phonon modes at low temperatures,point to a significant spin-phonon coupling.This is also supported by the softening of 71.1-cm^-1 mode above the magnetic transition.The study provides the fundamental information on lattice dynamics and clarifies the symmetry in VI3.And spin-phonon coupling existing in a wide temperature range revealed here may be meaningful in applications.

Solution of two-dimensional scattering problem in piezoelectric/piezomagnetic media using a polarization method

Using a polarization method, the scattering problem for a two-dimensional inclusion embedded in infinite piezoelectric/piezomagnetic matrices is investigated. To achieve the purpose, the polarization method for a two-dimensional piezoelectric/piezomagnetic ＂comparison body＂ is formulated. For simple harmonic motion, kernel of the polarization method reduces to a 2-D time-harmonic Green＇s function, which is obtained using the Radon transform. The expression is further simplified under conditions of low frequency of the incident wave and small diameter of the inclusion. Some analytical expressions are obtained. The analytical solutions for generalized piezoelectric/piezomagnetic anisotropic composites are given followed by simplified results for piezoelectric composites. Based on the latter results, two numerical results are provided for an elliptical cylindrical inclusion in a PZT-5H-matrix, showing the effect of different factors including size, shape, material properties, and piezoelectricity on the scattering cross-section.

Refractive Features and Diffraction Scattering Patterns Observed in the Elastic Scattering of ¹²C from ¹²C at Various Energies

We have measured the angular distributions for 12C ion beam elastically scattered from 12C target of thickness 17.4 μg/cm2 at energies 15, 18 and 21 MeV which is close to the Coulomb barrier energy for 12C + 12C nuclear system. The elastic scattering of 12C beam on 12C was analysed also at different energies (139.5, 158.8, 180, 240, 288.6, 300, 360 and 420 MeV) from literature in order to obtain the global optical potential parameters, which could fairly reproduce the experimental data. The experimental results were analysed within the framework of both the optical model and the double folding potential obtained with different density-dependent NN interactions which give the corresponding values of the nuclear incompressibility K in the Hartree-Fock calculation of nuclear matter. The agreement between the experimental results and the theoretical predictions in the whole angular range is fairly good.

Polarization characteristics and controllability mechanism of passive scattering elements

Polarization feature is one of the important features of radar targets,which has been used in many fields.In this paper,the grid models of some typical foreign moving targets are constructed on the simulation platform,such as glider,cruiser,fixed wing aircraft,and rotorcraft.The electromagnetic scattering characteristics of the moving platforms under the incidence of circular polarization waves are calculated.The typical polarization characteristics which the orthogonal and in-phase components have in the echoes are analyzed and proved.Based on the polarization scattering matrix(PSM)theory,from the point of view of the physical reproduction,the technical status quo that the existing technical approaches are difficult to realize the passive simulation of polarization characteristic of the target is summarized.To solve this problem,combined with the vector synthesis law,the realization mechanism of controllable polarization characteristic of target echoes is proposed,the analytical expressions of polarization control matrix and polarization ratio are deduced,and the controllability of polarization ratio feature in the case of circular polarization is verified by simulation calculation.

Numerical Study on Microwave Scattering by Various Plasma Objects

The scattering features of microwave（MW） by planar plasma layer, plasma column and plasma-column array under different parameters have been numerically studied by the finitedifference time-domain（FDTD） method. The effects of the plasma frequency and electron collision rate on MW＇s reflectance, transmittance and absorptance are examined. The results show that for the planar plasma layer, the electron collision plays an important role in MW absorption and the reduction of wave reflection. In the plasma column condition, strong scattering occurs in certain directions. The scattering pattern depends on the plasma frequency, electron collision rate and column radius. A collisional, non-planar shaped plasma object like the plasma-column array can reduce significantly the wave reflection comparing with the planar plasma layer.

HIGH RESOLUTION PARAMETRIC MODELLING FOR TWO-DIMENSIONAL RADAR TARGET USING PRONY ALGORITHM

On the conditions of low-resolution radar, a parametric model for two-dimensional radar target is described here according to the theory of electromagnetic scattering and the geometrical theory of diffraction. A high resolution estimation algorithm to extract the model parameters is also developed by building the relation of the scattering model and Prony model. The analysis of Cramer-Rao bound and simulation show that the method here has better statistical performance. The simulated analysis also indicates that the accurate extraction of the diffraction coefficient of scattering center is restricted by signal to noise ratio, radar center frequency and radar bandwidth.

Raman scattering study of magnetic layered MPS_3 crystals(M = Mn, Fe, Ni)

We report a comprehensive Raman scattering study on layered MPS_3(M = Mn, Fe, Ni), a two-dimensional magnetic compound with weak van der Waals interlayer coupling. The observed Raman phonon modes have been well assigned by the combination of first-principles calculations and the polarization-resolved spectra. Careful symmetry analysis on the angle-dependent spectra demonstrates that the crystal symmetry is strictly described by C_(2h)but can be simplified to D_(3d) with good accuracy. Interestingly, the three compounds share exactly the same lattice structure but show distinct magnetic structures. This provides us with a unique opportunity to study the effect of different magnetic orders on lattice dynamics in MPS_3. Our results reveal that the in-plane Nel antiferromagnetic(AF) order in MnPS_3 favors a spin–phonon coupling compared to the in-plane zig-zag AF in NiPS_3 and FePS_3. We have discussed the mechanism in terms of the folding of magnetic Brillouin zones. Our results provide insights into the relation between lattice dynamics and magnetism in the layered MPX_3(M = transition metal, X = S, Se) family and shed light on the magnetism of monolayer MPX_3 materials.

Electron mobility anisotropy in (Al,Ga)Sb/InAs two-dimensional electron gases epitaxied on GaAs (001) substrates

The electron mobility anisotropy in (Al,Ga)Sb/InAs two-dimensional electron gases with different surface morphology has been investigated.Large electron mobility anisotropy is found for the sample with anisotropic morphology,which is mainly induced by the threading dislocations in the InAs layer.For the samples with isotropic morphology,the electron mobility is also anisotropic and could be attributed to the piezoelectric scattering.At low temperature (below transition temperature),the piezoelectric scattering is enhanced with the increase of temperature,leading to the increase of electron mobility anisotropy.At high temperature (above transition temperature),the phonon scattering becomes dominant.Because the phonon scattering is isotropic,the electron mobility anisotropy in all the samples would be reduced.Our results provide useful information for the comprehensive understanding of electron mobility anisotropy in the (Al,Ga)Sb/InAs system.

Direct observation of melted Mott state evidenced from Raman scattering in 1T-TaS_2 single crystal

The evolution of electron correlation and charge density wave （CDW） in 1T-TaS2 single crystal has been investi- gated by temperature-dependent Raman scattering, which undergoes two obvious peaks of Aig modes about 70.8 cm-t and 78.7 cm I at 80 K, respectively. The former peak at 70.8 cm-t is accordant with the lower Hubbard band, resulting in the electron-correlation-driven Mott transition. Strikingly, the latter peak at 78.7 cm-1 shifts toward low energy with increasing the temperature, demonstrating the occurrence of nearly commensurate CDW phase （melted Mott phase）. In this case, phonon transmission could be strongly coupled to commensurate CDW lattice via Coulomb interaction, which likely induces appearance of hexagonal domains suspended in an interdomain phase, composing the melted Mott phase characterized by a shallow electron pocket. Combining electronic structure, atomic structure, transport properties with Ra- man scattering, these findings provide a novel dimension in understanding the relationship between electronic correlation, charge order, and phonon dynamics.

Influence of the channel electric field distribution on the polarization Coulomb field scattering in In_(0.18) Al_(0.82) N/AlN/GaN heterostructure field-effect transistors

By making use of the quasi-two-dimensional （quasi-2D） model, the current-voltage （l-V） characteristics of In0AsA10.82N/A1N/GaN heterostructure field-effect transistors （HFETs） with different gate lengths are simulated based on the measured capacitance-voltage （C-V） characteristics and I-V characteristics. By analyzing the variation of the electron mobility for the two-dimensional electron gas （2DEG） with electric field, it is found that the different polarization charge distributions generated by the different channel electric field distributions can result in different polarization Coulomb field scatterings. The difference between the electron mobilities primarily caused by the polarization Coulomb field scatterings can reach up to 1522.9 cm2/V.s for the prepared In0.38AI0.82N/A1N/GaN HFETs. In addition, when the 2DEG sheet density is modulated by the drain-source bias, the electron mobility presents a peak with the variation of the 2DEG sheet density, the gate length is smaller, and the 2DEG sheet density corresponding to the peak point is higher.

On the Far Field Pattern for Acoustic Scattering by a Piecewise Homogeneous Obstacle in Two Dimensions

A time-harmonic plane acoustic wave is scattered by a piecewise homogeneous obstacle with a penetrable or impenetrable core. We construct in the close form an integral representation for the far field pattern in which we have incorporated the physical and geometrical characteristics of the scatterer. Through this representation, we obtain the far field pattern for this scatterer. We prove scattering relations between the far field patterns of two scattering problems due to two distinct incident waves on the same scatterer. In particular, we prove reciprocity and general scattering theorems. The optical theorem, connecting the total power that the scatterer extracts from the incident plane wave either by radiation or by absorption with the corresponding far field pattern of an incident plane wave, is recovered as a corollary of the general scattering theorem. Moreover, if we consider incident waves to be both a plane and a spherical, we derive a mixed reciprocity theorem. We define the corresponding far field operators and using these relations, we prove some properties that can be used for solving inverse scattering problems.

Geometric Feature Extraction and Model Reconstruction Based on Scattered Data

A method of 3D model reconstruction based on scattered point data in reverse engineering is presented here. The topological relationship of scattered points was established firstly, then the data set was triangulated to reconstruct the mesh surface model. The curvatures of cloud data were calculated based on the mesh surface, and the point data were segmented by edge-based method; Every patch of data was fitted by quadric surface of freeform surface, and the type of quadric surface was decided by parameters automatically, at last the whole CAD model was created. An example of mouse model was employed to confirm the effect of the algorithm.

小角中子散射物理模型自动化筛选

小角中子散射(SANS)实验数据的分析过程需要科研人员选择样品对应的物理模型进行迭代拟合来表征样品的结构和属性。目前选择物理模型的方法大多是基于人工经验,分析门槛高、准确率较低。基于标准神经网络模型的小角中子散射实验样品物理模型自动化筛选方法面临着图像缺乏局部特征、类内差异大、类间差异小等问题。设计双模态特征融合卷积神经网络(BFF-CNN)模型,先引入物理感知的傅里叶-贝塞尔变换(FBT)来提取散射图像的全局结构信息,再将原始图像与FBT变换图像通过两个子网络分别进行特征提取与特征融合,以提升神经网络整体的特征表达能力。提出受限Softmax(R-Softmax)损失函数,通过在原生Softmax损失函数的基础上添加惩罚项来限制输入样本被分配到非本真类的概率,可在Softmax损失接近0时缓解梯度的消失问题,进而提高收敛速度。在自建的小角中子散射图像数据集上的实验结果表明,BFF-CNN的预测准确率和平均召回率相比于ResNet-18、PMG等模型提升幅度较大,采用R-Softmax与中心损失函数的联合学习策略后的预测准确率和召回率相比只采用Softmax损失函数提升了5.4和10.5个百分点,具有较好的小角中子散射图像分类效果。

用于不平衡类癌症数据的非标记检测和识别的SERS分析新策略

SERS技术与机器学习结合的策略在检测和识别不平衡类癌症中发挥着极其重要的作用.为了解决类不平衡问题给分类精度造成的影响,设计了一种SERS技术结合APS-SMOTE-PCA-KNN(synthetic minority oversampling method with adaptive priority selection(APS-SMOTE)-principal component analysis(PCA)-k-nearest neighbors(KNN))的癌症诊断新策略,实现快速、灵敏、非标记地检测和识别癌症.结果显示:新策略能够测得健康人和癌症患者血清的特征光谱,很好地解决了类不平衡问题给分类精度造成的影响,准确率可以达到85.0%.SERS技术结合APS-SMOTE-PCA-KNN对于未来癌症诊断具有积极的借鉴意义.

旋翼无人机与直升机二次曲面散射中心提取与重建方法

采用快速物理光学(FPO)方法模拟二次曲面片剖分后的旋翼无人机目标散射场,该方法考虑了目标的物理机理,可采用大尺寸比例细分和属性散射中心(ASC)模型提取目标的散射中心。为解决ASC参数估计中的不适定问题,减少计算时间和精度误差,提出一种正交匹配追踪(OMP)与基于成功历史记录的自适应参数差分进化(SHADE)相结合的稀疏方法。数值算例表明,文中方法能够有效准确地提取复杂目标的散射中心,同时在10 GHz频段时,面片数目减少了两到三个数量级。根据散射中心提取结果,得到了旋翼无人机的多个小散射中心围绕中央散射中心呈中心对称分布,而直升机的多个散射中心呈近似平行分布的结论,为利用雷达目标电磁散射特性差异进行低慢小目标精准识别提供可靠仿真依据与理论基础。

一种雷达成像匹配算法分析及应用

针对雷达成像后的场景定位,提出了一种基于强散射点目标几何位置关系的特征匹配新算法,首先根据灰度特性提取图像上强散射点,再连接各候选点形成不规则多边形,通过分析该形状各顶点之间的几何位置关系特征实现匹配定位。实测数据仿真结果表明该方法运算量小、匹配精度高,并且可靠性和鲁棒性强,是具有较高实用价值的雷达图像匹配工程应用方法。

100例急性早幼粒细胞白血病临床特征和血常规及散点图分析

目的通过100例APL的临床特征和血常规及散点图分析,警示血常规报告审核人员及时进行显微镜复检,保证异常早幼粒细胞报告的准确性与及时性。方法回顾性分析100例APL患者的临床特征、血常规及散点图特征。根据白细胞计数不同,分析散点图特征。结果APL男女发病率相当,男性略多于女性。以出血、发热、乏力为主诉就诊的占比分别为46%、20%、15%,其次为体检发现血细胞减少和肿瘤术后复查发现血常规异常,分别占比8%和5%。APL患者就诊时,82%患者白细胞异常,82%患者存在不同程度的贫血,95%患者血小板降低,仅3%患者就诊时未在外周血发现异常早幼粒细胞。白细胞相近的APL患者,血常规散点图较一致。结论通过患者就诊的主诉、血常规结果和散点图指导检验人员镜检时寻找异常早幼粒细胞,为APL的快速诊断提供技巧。