Region-of-interest micro-focus computed tomography based on an all-optical inverse Compton scattering source

Micro-focus computed tomography(CT),which allows the hyperfine structure within objects to be reconstructed,is a powerful nondestructive testing tool in many fields.However,current x-ray sources for micro-focus CT are typically limited by their relatively low photon energy and low flux.An all-optical inverse Compton scattering source(AOCS)based on laser wakefield acceleration can generate intense quasi-monoenergetic x/gamma-ray pulses in the kilo-to megaelectronvolt range with micrometer-level source size,and its potential application for micro-focus CT has become very attractive in recent years because of the rapid progress made in laser wakefield acceleration.Reported here is a successful experimental demonstration of high-fidelity micro-focus CT using an AOCS(∼70 keV)by imaging and reconstructing a test object with complex inner structures.A region-of-interest CT method is adopted to utilize the relatively small field of view of the AOCS to ensure high spatial resolution.This demonstration of AOCS-based region-of-interest micro-focus CT is a key step toward its application in the field of hyperfine nondestructive testing.

Scattering of Solitons of Modified KdV Equation with Self-consistent Sources

这篇论文详细与前後一致的来源一起调查修改 KdV 方程的动力学，包括 one-soliton 的特征，散布条件和二 solitons，二 solitons 的退化案例和“鬼”的阶段移动 solitons，等等。合作行动并列框架在 asymptotic 分析被采用。

Solving Non-Isospectral mKdV Equation and Sine-Gordon Equation Hierarchies with Self-Consistent Sources via Inverse Scattering Transform

N-soliton solutions of the hierarchy of non-isospectral mKdV equation with self-consistent sources andthe hierarchy of non-isospectral sine-Gordon equation with self-consistent sources are obtained via the inverse scatteringtransform.

Numerical simulation for all-optical Thomson scattering X-ray source

Energy spectra, angular distributions, and temporal profiles of the photons produced by an all-optical Thomson scat- tering X-ray source are explored through numerical simulations based on the parameters of the SILEX-I laser system （800 nm, 30 fs, 300 TW） and the previous wakefield acceleration experimental results. The simulation results show that X-ray pulses with a duration of 30 fs and an emission angle of 50 mrad can be produced from such a source. Using the optimized electron parameters, X-ray pulses with better directivity and narrower energy spectra can be obtained. Besides the electron parameters, the laser parameters such as the wavelength, pulse duration, and spot size also affect the X-ray yield, the angular distribution, and the maximum photon energy, except the X-ray pulse duration which is slightly changed for the case of ultrafast laser-electron interaction.

Blind Source Separation based on Time-Frequency Morphological Characteristics for Rigid Acoustic Scattering by Underwater Objects

僵硬声学的散布由的部件的分离在水下目标在获得如此的目标的结构的特征是必要的。克服看起来有一样的僵硬结构的问题光谱在时间领域的结构，时间频率窗帘来源分离(BSS ) 能与图象形态学在联合被使用分开不同目标的僵硬散布部件。基于一个热点模型，有时间频率分发的目标的僵硬散布结构的分离被推出。用一个词法过滤器，在 Wigner-Ville 分布(WVD ) 的不同特征观察到术语能被简化移开任何跨术语的干扰单个汽车术语和十字。由选择术语表明的汽车的时间和频率点， BSS 的精确性能被改进。试验性的模拟被使用了，与在播送信号，相对振幅和时间延期参数的脉搏宽度的变化，以便分析这个新方法的可行性。模拟结果证明新方法不仅能分开僵硬散布当有弹性的散布并且僵硬散布时，部件，而且罐头也分开部件同时存在。试验性的结果证实新方法能在分开僵硬散布结构被使用在水下目标。

Reconstruction Parameters of Local Scattering Sources of a Metallic Strip from the Backscattering Pattern

In this paper, it is proved the ability of quantity reconstruction, amplitudes and coordinates of metallic strip local scattering sources from the backscattering pattern. They are performed as the results of numerical solution for the infinite perfect conducting strip in case of E-polarization of the incident plane electromagnetic wave. In this case it is necessary to fulfill the following conditions. The local sources amplitudes should be the same order, in transverse and longitudinal directions the local sources should be separated into distances more than apparatus resolution, and the object maximum size does not have to be more than approximately 50λ. It was shown the limit and ability of the further development of the offered method.

High-brightness photo-injector with standing-wave buncher-based ballistic bunching scheme for inverse Compton scattering light source

We report our recent progress in the design and simulation of a high-brightness S-band photo-injector with a ballistic bunching scheme aimed at driving an inverse Compton scattering(ICS)X-ray source.By adding a short standing-wave buncher between the RF gun and first booster in a conventional S-band photo-injector,electron bunches with a 500 pC charge can be compressed to the sub-picosecond level with very limited input RF power and an unchanged basic layout of the photo-injector.Beam dynamics analysis indicates that fine tuning of the focusing strength of the gun and linac solenoid can well balance additional focusing provided by the standing wave buncher and generate a well-compensated transverse emittance.Thorough bunching dynamics simulations with different operating conditions of the buncher show that a buncher with more cells and a moderate gradient is suitable for simultaneously obtaining a short bunch duration and low emittance.In a typical case of a 9-cell buncher with a 38 MV/m gradient,an ultrashort bunch duration of 0.5 ps(corresponding to a compression ratio of>5)and a low emittance of<1 mm mrad can be readily obtained for a 500 pC electron pulse.This feasible ballistic bunching scheme will facilitate the implementation of an ultrashort pulse mode inverse Compton scattering X-ray source on most existing S-band photo-injectors.

INVERSE SCATTERING PROBLEMS BY SINGULAR SOURCE METHODS

The inverse scattering problems are to detect the property of obstacles from the measurements outside the obstacles. One of important research areas in this topic is the recovery of boundary property for impenetrable obstacles. In this paper, we would like to give a brief review about the recently developed singular source methods. There are three different methods in this category, namely, linear sampling method, pointsource method and probe method. We also present some recent new results about the probe method.

ANALYSIS OF THE FIELDS SCATTERED FROM A TWO－DIMENSIONAL CYLINDER ILLUMINATED BY A POINT SOURCE

ＡＮＡＬＹＳＩＳＯＦＴＨＥＦＩＥＬＤＳＳＣＡＴＴＥＲＥＤＦＲＯＭＡＴＷＯ－ＤＩＭＥＮＳＩＯＮＡＬＣＹＬＩＮＤＥＲＩＬＬＵＭＩＮＡＴＥＤＢＹＡＰＯＩＮＴＳＯＵＲＣＥＣｈｅｎｇＣｈｏｎｇｈｕ（程崇虎）ＺｈａｎｇＷｅｎｘｕｎ（章文勋）（ＳｔａｔｅＫｅｙＬａ...

A whole-space transform formula of cylindrical wave functions for scattering problems

The theory of elastic wave scattering is a fundamental concept in the study of elastic dynamics and wave motion,and the wave function expansion technique has been widely used in many subjects.To supply the essential tools for solving wave scattering problems induced by an eccentric source or multi-sources as well as multi-scatters,a whole-space transform formula of cylindrical wave functions is presented and its applicability to some simple cases is demonstrated in this study.The transforms of wave functions in cylindrical coordinates can be classifi ed into two basic types: interior transform and exterior transform,and the existing Graf’s addition theorem is only suitable for the former.By performing a new replacement between the two coordinates,the exterior transform formula is fi rst deduced.It is then combined with Graf’s addition theorem to establish a whole-space transform formula.By using the whole-space transform formula,the scattering solutions by the sources outside and inside a cylindrical cavity are constructed as examples of its application.The effectiveness and advantages of the whole-space transform formula is illustrated by comparison with the approximate model based on a large cycle method.The whole-space transform formula presented herein can be used to perform the transform between two different cylindrical coordinates in the whole space.In addition,its concept and principle are universal and can be further extended to establish the coordinate transform formula of wave functions in other coordinate systems.

Numerical study of scattering Legendre moments and effect of anisotropic scattering on S_N shielding calculation

In neutron and photon transport problems,anisotropic scattering is of great importance for the particle flux,especially when the angular flux has a strong forward peak in shielding analyses.The conventional Legendre expansion is widely used in discrete ordinates transport codes because of algebraic simplifications with spherical harmonics for the scattering source.However,negative cross sections caused by the finitely truncated expansion may give rise to a negative source and flux.A simple method is adopted,based on integrating functions of scattering moments,to evaluate anisotropy and convergence of expanded functions.A series of problems were designed with angular fluxes of different anisotropy,and numerical simulations were performed using the ARES transport code to study different treatments and algorithms for scattering.Results show that the diagonal transport approximation is more stable and obtains a similar accuracy with the extended approximation.A conservative fixup for the negative source could ensure particle balance and improve computational accuracy significantly for photon transport.The effect of anisotropic scattering is problem-dependent,and no distinct differences among various methods are observed for volume source problems with a continuous energy source.For beam source problems,flux results are sensitive to negative scattering functions,and strictly nonnegative cross sections need to be implemented.

Seismoelectric waves in a borehole excited by an external explosive source

The conversion of energy between seismic and electromagnetic wave fields has been described by Pride's coupled equations in porous media. In this paper, the seismoelectric field excited by the explosive point source located at the outside of the borehole is studied. The scattering fields inside and outside a borehole are analyzed and deduced under the boundary conditions at the interface between fluid and porous media. The influences of the distance of the point source, multipole components of the eccentric explosive source, and the receiving position along the axis of vertical borehole, on the converted waves inside the borehole are all investigated. When the distance from the acoustic source to the axis of a borehole is far enough, the longitudinal and coseismic longitudinal wave packets dominate the acoustic and electric field, respectively. The three components of both electric field and magnetic field can be detected, and the radial electric field is mainly excited and converted by the dipole component. Owing to the existence of borehole, the electric fields and magnetic fields in the borehole are azimuthal. The distance from the point where the maximum amplitude of the axial components of electric field is recorded, to the origin of coordinate indicates the horizontal distance from the explosive source to the axis of vertical borehole.

Numerical Investigation of a UCN Source Based on Solid Deuterium by Combining a Simulation Code with an Analytical Approach

At thermal ultra-cold neutron (UCN) sources (neutrons in thermal equilibrium with the moderator) only a very small fraction of neutrons have velocities ~6 m/s. Therefore, the UCN production rate cannot be substantially increased by simply lowering the temperature of the moderator. The new approach is to use the super-thermal principle, i.e., neutrons not in thermal equilibrium with the converter. We want to investigate scattering kernels for a super-thermal UCN source based on a two-layer arrangement of D2O and solid D2. The solid D2 (sD2) at temperature 8 K is kept in close contact with D2O moderator at room temperature. Using the MCNP code, the fast neutron flux on the spallation target, the thermal flux in the D2O near the sD2, and the cold flux in the sD2 are simulated. For a given cold flux, neutron transport equations are calculated. In order to obtain precise neutron scattering kernels, and consequently UCN flux and density, 330 neutron energy groups have been taken. The coupled energy dependent transport equations have been solved by combining MCNPX code with an analytical approach and using implicit method in MATLAB. We have obtained an optimal dimension for the UCN source. A suitable space step has been taken for the numerical stability.

Parasitic source resistance at different temperatures for AlGaN/AlN/GaN heterostructure field-effect transistors

The parasitic source resistance（RS） of AlGaN/AlN/GaN heterostructure field-effect transistors（HFETs） is studied in the temperature range 300–500 K. By using the measured RSand both capacitance–voltage（C–V） and current–voltage（I–V） characteristics for the fabricated device at 300, 350, 400, 450, and 500 K, it is found that the polarization Coulomb field（PCF） scattering exhibits a significant impact on RSat the above-mentioned different temperatures. Furthermore, in the AlGaN/AlN/GaN HFETs, the interaction between the additional positive polarization charges underneath the gate contact and the additional negative polarization charges near the source Ohmic contact, which is related to the PCF scattering, is verified during the variable-temperature study of RS.

Experimental investigation of the stimulated Raman scattering effect in high-power nanosecond superfluorescent fiber source

In this work,we experimentally investigate the dependence of the stimulated Raman scattering(SRS)effect on the seed linewidth of a high-power nanosecond superfluorescent fiber source(ns-SFS).The results reveal that the SRS in the ns-SFS amplifier is significantly influenced by the full width at half maximum(FWHM)of the ns-SFS seed,and there is an optimal FWHM linewidth of 2 nm to achieve the lowest SRS in our case.The first-order SRS power ratio increases rapidly when the seed’s linewidth deviates from the optimal FWHM linewidth.By power scaling the ns-SFS seed with the optimal FWHM linewidth,a narrowband all-fiberized ns-SFS amplifier is achieved with a maximum average power of 602 W,pulse energy of 24.1 mJ and corresponding peak power of 422.5 kW.This is the highest average power and pulse energy achieved for all-fiberized ns-SFS amplifiers to the best of our knowledge.

Proposal for a high brightness γ-ray source at the SXFEL

High brightness γ-rays produced by laser Compton scattering(LCS) are ideal probes for the study of nucleon and nuclear structure. We propose such a γ-ray source using the backscattering of a laser from the bright electron beam produced by the linac of the Shanghai Soft X-ray Free-electron Laser(SXFEL) test facility at the Shanghai Institute of Applied Physics(SINAP). The performance is optimized through theoretical analysis and benchmarked with 4D Monte-Carlo simulations. The peak brightness of the source is expected to be larger than2 × 1022photons/(mm2mrad2s 0.1%BW) and photon energy ranges from 3.7 Me V to 38.9 Me V. Its performance, compared to Extreme Light Infrastructure-Nuclear Physics(ELI-NP), and the Shanghai Laser-Electron Gamma-ray Source(SLEGS), is given. The potential for basic and applied research is also briefly outlined.

基于机器学习的深圳大气颗粒物消光来源识别

利用浊度计于2021年11月~2021年12月在深圳市开展颗粒物光散射在线观测,并同步利用相关在线仪器开展PM_(2.5)及其化学组分观测,结合受体模型和可解释性机器学习模型探究深圳市秋冬季颗粒物散射的主要来源.结果显示,深圳市颗粒物525nm散射系数在观测期间平均值为119.61/Mm.相关性分析表明,颗粒物散射系数与相对湿度相关性低,与PM_(2.5)相关性高(R^(2)>0.8),其中,与PM_(2.5)中NH4+、NO_(3)-、m/z 44、OM、SO_(4)^(2-)、黑碳的相关性在0.55~0.83,表明PM_(2.5)中二次组分及黑碳是影响深圳市颗粒物散射的重要因素.基于相对湿度和受体模型识别的污染源,利用XGBoost模型建立了颗粒物散射系数预测模型并利用SHAP模型识别其主要来源,研究表明二次硝酸盐、二次硫酸盐、机动车排放和二次有机气溶胶是影响深圳市颗粒物散射系数的主要源类,燃煤和相对湿度也有一定贡献,生物质燃烧、船舶排放、工业排放、扬尘和建筑尘的影响小.

飞行器典型结构雷达成像诊断与分析

隐身飞行器逐步受到各国青睐,评估目标隐身能力并明确隐身性能改善的方向在飞行器隐身设计工作中至为关键。在雷达高频区,飞行器目标的散射特性呈现“稀疏性”,散射场遵循局部性原理,目标的散射分布能够等效为由一系列离散分布的孤立散射中心组成。鉴于逆合成孔径雷达(inverse synthetic aperture radar,ISAR)图像具有分辨率高、能够准确精细反映散射点空间位置等优势,本文以仿真成像的形式展现了典型结构对应的ISAR图像,分析了散射点形态与散射机理之间的关联关系,提炼得到了球体、圆柱体、三棱柱、圆锥、直筒式腔体、S弯腔体等6类典型飞行器结构对应的主要散射路径,并针对两种不同类型的隐身无人机,开展了基于雷达成像的强散射点诊断与评估,得出了两类无人机的主要散射源集中在进气道的结论。

基于同步辐射光源X射线散射对聚乙醇酸挤出棒材退火条件的优化

文中用同步辐射光源对聚乙醇酸(PGA)挤出棒材的切片进行广角X射线散射(WAXS)和小角X射线散射(SAXS)表征,研究聚乙醇酸棒材在挤出成型后优选的退火条件,以尽可能消除内应力,改善棒材后续的机械加工性。WAXS结果表明,高温更有利于微观应变的减小,但较高温时晶粒尺寸会随退火时间的延长而减小。SAXS结果表明,高温更有利于取向程度的减小,退火时间对取向程度的影响明显弱于退火温度。综合各数据建立目标函数,并利用响应面分析法进行分析。结果表明,在实验范围内,PGA棒材的优选退火条件为200℃退火2h。

High-precision RCS measurement of aircraft's weak scattering source

The radar cross section （RCS） of weak scattering source on the surface of an aircraft is usually less than -40 dBsm. How to accurately measure the RCS characteristics of weak scattering source is a technical challenge for the aircraft＇s RCS measurement. This paper proposes separating and extracting the two-dimensional （2D） reflectivity distribution of the weak scattering source with the microwave imaging algorithm and spectral transform so as to enhance its measurement preci- sion. Firstly, we performed the 2D microwave imaging of the target and then used the 2D gating function to separate and extract the reflectivity distribution of the weak scattering source. Secondly, we carried out the spectral transform of the reflectivity distribution and eventually obtained the RCS of the weak scattering source through calibration. The prototype experimental results and their analysis show that the measurement method is effective. The experiments on an aircraft＇s low-scattering conformal antenna verify that the measurement method can eliminate the clutter on the surface of aircraft. The precision of measuring a -40 dBsm target is 3 5 dB better than the existing RCS measurement methods. The measurement method can more accurately obtain the weak scattering source＇s RCS characteristics.