High-Resolution Selective Excitation of Resonance-Enhanced Multiphoton-Ionization Photoelectron Spectroscopy by Shaping Femtosecond Laser Pulses

Femtosecond laser-induced resonance-enhanced multiphoton-ionization photoelectron spectroscopy （REMPI-PS） is faced with two drawbacks of low spectral resolution and poor selective excitation due to the broad spectral bandwidth. We propose a scheme to obtain a high-resolution selective excitation of （2＋1） REMPI-PS by com- bining 7r and cosinusoidal phase modulation. Our theoretical results indicate that the （2＋1） REMPI-PS signals related to neighboring excited states can be differentiated from their indistinguishable photoelectron spectra by the 7r phase modulation, and then their selective excitation can be realized by supplementally adding the cosi- nusoidal phase modulation. Furthermore, the physical mechanism of the high-resolution selective excitation of （2＋1） REMPI-PS is explained by considering the two-photon power spectrum.     

Prototype studies on the forward MWDC tracking array of the external target experiment at HIRFL-CSR

A prototype of the forward tracking array consisting of three multiwire drift chambers (MWDC) for the external target experiment (CEE) at the Heavy Ion Research Facility at the Lanzhou -Cooling Storage Ring (HIRFL-CSR) has been assembled and tested using cosmic rays. The signals from the anode wires are amplified and fed to a Flash-ADC to deliver the drift time and charge integration. The performances of the array prototype are investigated under various high voltages. For the tracking performances, after the space-time relation (STR) calibration and the detector displacement correction, the standard deviation of 223 μm of the residue is obtained. The performances of the forward MWDCs tracking array meets the requirements of CEE in design.     

Simulating resonance-mediated two-photon absorption enhancement in rare-earth ions by a rectangle phase modulation

Improving the up-conversion luminescence efficiency of rare-earth ions via the multi-photon absorption process is crucial in several related application areas. In this work, we theoretically propose a feasible scheme to enhance the resonance-mediated two-photon absorption in Er~(3+) ions by shaping the femtosecond laser field with a rectangle phase modulation. Our theoretical results show that the resonance-mediated two-photon absorption can be decomposed into the on-resonant and near-resonant parts, and the on-resonant part mainly comes from the contribution of laser central frequency components, while the near-resonant part mainly results from the excitation of low and high laser frequency components.So, the rectangle phase modulation can induce a constructive interference between the two parts by properly designing the modulation depth and width, and finally realizes the resonance-mediated two-photon absorption enhancement. Moreover, our results also show that the enhancement efficiency of resonance-mediated two-photon absorption depends on the laser pulse width(or laser spectral bandwidth), final state transition frequency, and intermediate and final state absorption bandwidths. The enhancement efficiency modulation can be attributed to the relative weight manipulation of on-resonant and near-resonant two-photon absorption in the whole excitation process. This study presents a clear physical insight for the quantum control of resonance-mediated two-photon absorption in the rare-earth ions, and there will be an important significance for improving the up-conversion luminescence efficiency of rare-earthions.     

负相依误差下随机设计的半参数回归模型的渐近正态性

考虑了误差为负相依误差的随机设计半参数回归模型.利用权函数和最小二乘估计的方法给出了参数和非参数的最小二乘估计和加权最小二乘估计,并在较弱的条件下得到了它们的渐近正态性.     

Flat Band and Z2 Topology of Kagome Metal CsTi3Bi5

The simple kagome-lattice band structure possesses Dirac cones, flat band, and saddle point with van Hove singularities in the electronic density of states, facilitating the emergence of various electronic orders. Here we report a titanium-based kagome metal CsTi₃Bi₅ where titanium atoms form a kagome network, resembling its isostructural compound CsV₃Sb₅. Thermodynamic properties including the magnetization, resistance, and heat capacity reveal the co...     

数据挖掘技术在控制器局域网总线中的应用研究

提出了数据挖掘技术在汽车控制器局域网（CAN）总线通信数据中的应用。汽车中的各种电子控制系统通过CAN总线相互连接通信,其中产生的大量报文被存储在日志文件中。首先对CAN总线日志文件的中大量通信数据做预处理,再扩展使用关联分析、分类及聚类分析等方法对处理过的数据进行挖掘,从而找到各条报文之间及报文内部各位或字节之间可能存在的新规律或者关系,为进一步研究CAN总线系统连接的各个控制系统之间的通信提供了帮助。     

Polarization control of multi-photon absorption under intermediate femtosecond laser field

It has been shown that the femtosecond laser polarization modulation is a very simple and well-established method to control the multi-photon absorption process by the light–matter interaction. Previous studies mainly focused on the multiphoton absorption control in the weak field. In this paper, we further explore the polarization control behavior of multiphoton absorption process in the intermediate femtosecond laser field. In the weak femtosecond laser field, the secondorder perturbation theory can well describe the non-resonant two-photon absorption process. However, the higher order nonlinear effect(e.g., four-photon absorption) can occur in the intermediate femtosecond laser field, and thus it is necessary to establish new theoretical model to describe the multi-photon absorption process, which includes the two-photon and four-photon transitions. Here, we construct a fourth-order perturbation theory to study the polarization control behavior of this multi-photon absorption under the intermediate femtosecond laser field excitation, and our theoretical results show that the two-photon and four-photon excitation pathways can induce a coherent interference, while the coherent interference is constructive or destructive that depends on the femtosecond laser center frequency. Moreover, the two-photon and fourphoton transitions have the different polarization control efficiency, and the four-photon absorption can obtain the higher polarization control efficiency. Thus, the polarization control efficiency of the whole excitation process can be increased or decreased by properly designing the femtosecond laser field intensity and laser center frequency. These studies can provide a clear physical picture for understanding and controlling the multi-photon absorption process in the intermediate femtosecond laser field, and also can provide a theoretical guidance for the future experimental realization.     

Simulation of Intermediate State Absorption Enhancement in Rare-Earth Ions by Polarization Modulated Femtosecond Laser Field

We extend the third perturbation theory to study the polarization control behavior of the intermediate state absorption in Nd~(3+)ions. The results show that coherent interference can occur between the single-photon and three-photon excitation pathways, and depends on the central frequency of the femtosecond laser field. Moreover,single-photon and three-photon absorptions have different polarization control efficiencies, and the relative weight of three-photon absorption in the whole excitation processes can increase with increasing the laser intensity.Therefore, the enhancement or suppression of the intermediate state absorption can be realized and manipulated by properly designing the intensity and central frequency of the polarization modulated femtosecond laser field.This research can not only enrich theoretical research methods for the up-conversion luminescence manipulation of rare-earth ions, but also can provide a clear physical picture for understanding and controlling multi-photon absorption in a multiple energy level system.     

发掘疾病和其风险因素关系的图像方法探析

该文介绍了一种医学数据分类研究中的图像分析方法,它把概念模型,数据和分类方法有效地整合在了一起,涵盖了完整的分类操作并采用了一系列图形图像和计算组件。通过案例研究展示了如何使用该系统寻找癌症死亡率和一些可能存在的危险因素之间的关系。