X-Ray Source Classification Using Machine Learning:A Study with EP-WXT Pathfinder LEIA

X-ray observations play a crucial role in time-domain astronomy.The Einstein Probe(EP),a recently launched X-ray astronomical satellite,emerges as a forefront player in the field of time-domain astronomy and high-energy astrophysics.With a focus on systematic surveys in the soft X-ray band,EP aims to discover high-energy transients and monitor variable sources in the universe.To achieve these objectives,a quick and reliable classification of observed sources is essential.In this study,we developed a machine learning classifier for autonomous source classification using data from the EP-WXT Pathfinder—Lobster Eye Imager for Astronomy(LEIA)and EP-WXT simulations.The proposed Random Forest classifier,built on selected features derived from light curves,energy spectra,and location information,achieves an accuracy of approximately 95%on EP simulation data and 98%on LEIA observational data.The classifier is integrated into the LEIA data processing pipeline,serving as a tool for manual validation and rapid classification during observations.This paper presents an efficient method for the classification of X-ray sources based on single observations,along with implications of most effective features for the task.This work facilitates rapid source classification for the EP mission and also provides valuable insights into feature selection and classification techniques for enhancing the efficiency and accuracy of X-ray source classification that can be adapted to other X-ray telescope data.

Real-time Abnormal Detection of GWAC Light Curve based on Wavelet Transform Combined with GRU-Attention

Nowadays, astronomy has entered the era of Time-Domain Astronomy, and the study of the time-varying light curves of various types of objects is of great significance in revealing the physical properties and evolutionary history of celestial bodies. The Ground-based Wide Angle Cameras telescope, on which this paper is based, has observed more than 10 million light curves, and the detection of anomalies in the light curves can be used to rapidly detect transient rare phenomena such as microgravity lensing events from the massive data. However, the traditional statistically based anomaly detection methods cannot realize the fast processing of massive data. In this paper, we propose a Discrete Wavelet(DW)-Gate Recurrent Unit-Attention(GRU-Attention) light curve warning model. Wavelet transform has good effect on data noise reduction processing and feature extraction, which can provide richer and more stable input features for a neural network, and the neural network can provide more flexible and powerful output model for wavelet transform. Comparison experiments show an average improvement of 61% compared to the previous pure long-short-term memory unit(LSTM) model, and an average improvement of 53.5% compared to the previous GRU model. The efficiency and accuracy of anomaly detection in previous paper work are not good enough, the method proposed in this paper possesses higher efficiency and accuracy,which incorporates the Attention mechanism to find out the key parts of the light curve that determine the anomalies. These parts are assigned higher weights, and in the actual anomaly detection, the star is detected with83.35% anomalies on average, and the DW-GRU-Attention model is compared with the DW-LSTM model, and the detection result f1 is improved by 5.75% on average, while having less training time, thus providing valuable information and guidance for astronomical observation and research.

Phase-locked single-mode terahertz quantum cascade lasers array

We demonstrated a scheme of phase-locked terahertz quantum cascade lasers(THz QCLs)array,with a single-mode pulse power of 108 mW at 13 K.The device utilizes a Talbot cavity to achieve phase locking among five ridge lasers with first-order buried distributed feedback(DFB)grating,resulting in nearly five times amplification of the single-mode power.Due to the optimum length of Talbot cavity depends on wavelength,the combination of Talbot cavity with the DFB grating leads to better power amplification than the combination with multimode Fabry-Perot(F-P)cavities.The Talbot cavity facet reflects light back to the ridge array direction and achieves self-imaging in the array,enabling phase-locked operation of ridges.We set the spacing between adjacent elements to be 220μm,much larger than the free-space wavelength,ensuring the operation of the fundamental supermode throughout the laser's dynamic range and obtaining a high-brightness far-field distribution.This scheme provides a new approach for enhancing the single-mode power of THz QCLs.

Molecular chaperones in stroke-induced immunosuppression

Stroke-induced immunosuppression is a process that leads to peripheral suppression of the immune system after a stroke and belongs to the central nervous system injury-induced immunosuppressive syndrome.Stroke-induced immunosuppression leads to increased susceptibility to post-stroke infections,such as urinary tract infections and stroke-associated pneumonia,worsening prognosis.Molecular chaperones are a large class of proteins that are able to maintain proteostasis by directing the folding of nascent polypeptide chains,refolding misfolded proteins,and targeting misfolded proteins for degradation.Various molecular chaperones have been shown to play roles in stroke-induced immunosuppression by modulating the activity of other molecular chaperones,cochaperones,and their associated pathways.This review summarizes the role of molecular chaperones in stroke-induced immunosuppression and discusses new approaches to restore host immune defense after stroke.

Dynamic phasor-based hybrid simulation for multi-inverter grid-connected system

To realize the efficient transient simulation of a grid-connected power generation system based on multiple inverters, this paper proposes a hybrid simulation method integrating the models of electromagnetic transient and dynamic phasors. Based on a demonstration of the concepts and properties of dynamic phasors, the models of single-phase and three-phase inverters described by dynamic phasors are established first. Considering the numerical compatibility problem between dynamic phasors and instantaneous values, an interface scheme between dynamic phasors and instantaneous values is designed, and the efficiency and precision differences of various transformation methods are compared in detail.Finally, by utilizing MATLAB/Simulink, a hybrid simulation platform of a multi-inverter grid-connected system is built, and the efficiency and accuracy of the hybrid simulation are validated via comparison with the full electromagnetic transient simulation.

An Area Optimization Based Cooperative Localization Algorithm with Node Selection

In recent years,position information has become a key feature to drive location and context aware services in mobile communication.Researchers from all over the world have proposed many solu-tions for indoor positioning over the past several years.However,due to weak signals,multipath or non-line-of-sight signal propagation,accurately and efficiently localizing targets in harsh indoor environments re-mains a challenging problem.To improve the perfor-mance in harsh environment with insufficient anchors,cooperative localization has emerged.In this paper,a novel cooperative localization algorithm,named area optimization and node selection based sum-product al-gorithm over a wireless network(AN-SPAWN),is de-scribed and analyzed.To alleviate the high compu-tational complexity and build optimized cooperative cluster,a node selection method is designed for the cooperative localization algorithm.Numerical experi-ment results indicate that our proposed algorithm has a higher accuracy and is less impacted by NLOS errors than other conventional cooperative localization algo-rithms in the harsh indoor environments.

DFF-EDR:An Indoor Fingerprint Location Technology Using Dynamic Fusion Features of Channel State Information and Improved Edit Distance on Real Sequence

Positioning technology based on wireless network signals in indoor environments has developed rapidly in recent years as the demand for locationbased services continues to increase.Channel state information(CSI)can be used as location feature information in fingerprint-based positioning systems because it can reflect the characteristics of the signal on multiple subcarriers.However,the random noise contained in the raw CSI information increases the likelihood of confusion when matching fingerprint data.In this paper,the Dynamic Fusion Feature(DFF)is proposed as a new fingerprint formation method to remove the noise and improve the feature resolution of the system,which combines the pre-processed amplitude and phase data.Then,the improved edit distance on real sequence(IEDR)is used as a similarity metric for fingerprint matching.Based on the above studies,we propose a new indoor fingerprint positioning method,named DFF-EDR,for improving positioning performance.During the experimental stage,data were collected and analyzed in two typical indoor environments.The results show that the proposed localization method in this paper effectively improves the feature resolution of the system in terms of both fingerprint features and similarity measures,has good anti-noise capability,and effectively reduces the localization errors.

A Simplified Model for Buckling and Post-Buckling Analysis of Cu Nanobeam Under Compression

Both of Buckling and post-buckling are fundamental problems of geometric nonlinearity in solid mechanics.With the rapid development of nanotechnology in recent years,buckling behaviors in nanobeams receive more attention due to its applications in sensors,actuators,transistors,probes,and resonators in nanoelectromechanical systems(NEMS)and biotechnology.In this work,buckling and post-buckling of copper nanobeam under uniaxial compression are investigated with theoretical analysis and atomistic simulations.Different cross sections are explored for the consideration of surface effects.To avoid complicated high order buckling modes,a stressbased simplified model is proposed to analyze the critical strain for buckling,maximum deflection,and nominal failure strain for post-buckling.Surface effects should be considered regarding critical buckling strain and the maximum post-buckling deflection.The critical strain increases with increasing nanobeam cross section,while themaximumdeflection increases with increasing loading strain but stays nearly the same for different cross sections,and the underlying mechanisms are revealed by our model.The maximum deflection is also influenced by surface effects.The nominal failure strains are captured by our simulations,and they are in good agreement with the simplified model.Our results can be used for helping design strain gauge sensors and nanodevices with self-detecting ability.

从电子垃圾到生态恢复:全球视角下的电子垃圾不平等处理模式与景观干预方法研究

电子技术的飞速发展导致了每年大量电子垃圾(废弃电气和电子设备)的产生,在发达国家尤其如此。在经济全球化的背景下,发展中国家和欠发达国家由于缺乏相关环境法律和政策的保护且劳动力成本较低,导致发达国家将数量庞大的电子垃圾出口至这些国家。在低技拆解这些电子垃圾的过程中,产生的有害化学物质进入空气、土壤和深层地下水,污染饮用水和食物,并最终进入人体。由于经济和政策发展不均衡,产生电子垃圾最少的国家和地区(例如中国、印度、加纳等)反而遭受最大的损失。本文研究了全球范围内电子垃圾的生产、分布和流动情况,及其不平等的分布和处理模式;随后分析了不同国家和国际电子垃圾回收政策,并讨论了非正规拆解行为对经济、社会和环境造成的影响;最后,以中国贵屿为例,重点关注农田、河流和城市用地三种用地类型,从关键景观问题中总结出景观干预策略和方法,并将其实施划分为三个不同的恢复和发展阶段。本文旨在从景观干预的角度,为全球电子垃圾污染地区的生态、健康和生计恢复提供研究和干预建议。

Crystal facet-dependent CO_(2) cycloaddition to epoxides over ZnO catalysts

With regard to green chemistry and sustainable development,the fixation of CO_(2) into epoxides to form cyclic carbonates is an attractive and promising pathway for CO_(2) utilization.Metal oxides,renowned as promising eco-friendly catalysts for industrial production,are often undervalued in terms of their impact on the CO_(2)addition reaction.In this work,we successfully developed ZnO nanoplates with(002)surfaces and ZnO nanorods with(100)surfaces via morphology-oriented regulation to explore the effect of crystal faces on CO_(2) cycloaddition.The quantitative data obtained from electron paramagnetic resonance spectroscopy indicated that the concentration of oxygen vacancies on the ZnO nanoplate surfaces was more than twice that on the ZnO nanorod surfaces.Density functional theory calculations suggested that the(002)surfaces have lower adsorption energies for CO_(2) and epichlorohydrin than the(100)surfaces.As a result,the yield of cyclochloropropene carbonate on the ZnO nanoplates(64.7%)was much greater than that on the ZnO nanorods(42.3%).Further evaluation of the reused catalysts revealed that the decrease in the oxygen vacancy concentration was the primary factor contributing to the decrease in catalytic performance.Based on these findings,a possible catalytic mechanism for CO_(2) cycloaddition with epichlorohydrin was proposed.This work provides a new idea for the controllable preparation of high-performance ZnO catalysts for the synthesis of cyclic carbonates from CO_(2) and epoxides.

Fully Decoupled Branch Energy Balancing Control Method for Modular Multilevel Matrix Converter Based on Sequence Circulating Components

The modular multilevel matrix converter(M3C)is a potential frequency converter for low-frequency AC transmission.However,capacitor voltage control of high-voltage and largecapacity M3C is more difficult,especially for voltage balancing between branches.To solve this problem,this paper defines sequence circulating components and theoretically analyzes the influence mechanism of different sequence circulating components on branch capacitor voltage.A fully decoupled branch energy balancing control method based on four groups of sequence circulating components is proposed.This method can control capacitor voltages of nine branches in horizontal,vertical and diagonal directions.Considering influences of both circulating current and voltage,a cross decoupled control is designed to improve control precision.Simulation results are taken from a low-frequency transmission system based on PSCAD/EMTDC,and effectiveness and precision of the proposed branch energy balancing control method are verified in the case of nonuniform parameters and an unbalanced power system.

High brightness terahertz quantum cascade laser with near-diffraction-limited Gaussian beam

High-power terahertz(THz)quantum cascade laser,as an emerging THz solid-state radiation source,is attracting attention for numerous applications including medicine,sensing,and communication.However,due to the subwavelength confinement of the waveguide structure,direct beam brightness upscaling with device area remains elusive due to several mode competition and external optical lens is normally used to enhance the THz beam brightness.Here,we propose a metallic THz photonic crystal resonator with a phase-engineered design for single mode surface emission over a broad area.The quantum cascade surface-emitting laser is capable of delivering an output peak power over 185 mW with a narrow beam divergence of 4.4°×4.4°at 3.88 THz.A high beam brightness of 1.6×10^(7)W sr^(-1)m^(-2)with near-diffraction-limited M2 factors of 1.4 in both vertical and lateral directions is achieved from a large device area of 1.6×1.6 mm^(2)without using any optical lenses.The adjustable phase shift between the lattices enables a stable and high-intensity surface emission over a broad device area,which makes it an ideal light extractor for large-scale THz emitters.Our research paves the way to high brightness solid-state THz lasers and facilitates new applications in standoff THz imaging,detection,and diagnosis.

High-power distributed feedback lasers based on InP corrugated sidewalls atλ~2μm

We report a high-power single-mode InP-based 2μm distributed feedback(DFB)laser with a second-order buried grating and corrugated sidewalls.A second-order semiconductor grating is used for in-plane feedback and vertical out-coupling.The corrugated sidewalls are used to eliminate higher-order transverse modes.For the DFB laser with a 2 mm long cavity and 15μm wide ridge,the maximum continuous-wave edge-emitting and surface-emitting single-mode powers at 300 K are up to 81 and 42 m W,respectively.A single-lobed far-field radiation pattern with a low divergence angle of approximately 8.6°is achieved by a device with a ridge width of 15μm.The single-longitudinal-mode emission wavelength of the fabricated laser can be adjusted from2003.8 nm at 288 K to 2006.9 nm at 313 K without any mode hopping.Robust single-mode emission with a side-mode suppression ratio of 30 dB is achieved under all injection currents and temperature conditions.

Periodic atomization characteristics of simplex swirl injector induced by klystron effect

The atomization dynamic characteristics of a simplex swirl injector was investigated experimentally by using a hydrodynamic mechanical pulsator and the shadow photography technique. The frequency response characteristics of the fluid film and atomization fluctuations and their correlations with pressure fluctuations were obtained by using an in-house code of image processing. It is demonstrated that the klystron effect induced by periodic pressure fluctuations results in periodic liquid film fluctuation with large amplitudes, periodic superposition of droplets and reduction of the breakup length. It was found that the atomization of the simplex swirl injector only responds to the pressure fluctuation in frequency range approximately from 0 to 300 Hz, and it is particularly sensitive to pressure fluctuations at frequencies from 100 to 200 Hz. According to this experiment, the responsive frequency limitation is merely affected by injector configuration, rather than the supply line.

Voltage sag compensation strategy for unified power quality conditioner with simultaneous reactive power injection

Unified power quality conditioner(UPQC)holds the capability of solving power quality problems,especially shows good performance in the voltage sag compensation. In this paper, a compensation strategy based on simultaneous reactive power injection for UPQC(namely UPQC-SRI) is proposed to address the issue of voltage sag. The proposed UPQC-SRI determines the injection angle of compensation voltage with consideration of optimal configuration of UPQC current-carrying.Moreover, the compensation strategy also considers the current-carrying limit of UPQC, and then the zero active power injection region of UPQC-SRI(also called UPQCSRI region) is obtained. Under the conditions which exceed the UPQC-SRI region, the limit value of shunt current is determined by this proposed strategy. Finally, the proposed strategy and the corresponding algorithm are verified under the PSCAD/EMTDC platform. The result indicates the proposed UPQC-SRI strategy in this paper can provide more persistent voltage sag compensation than the previous strategies for the sensitive load.

Periodic atomization characteristics of an impinging jet injector element modulated by Klystron effect

An experimental study on the Klystron effect of periodic injection modulated by pressure drop fluctuations on subsequent atomization is conducted. Time-resolved atomization backlit images and atomization Mie scatter images are captured by using the high speed camera. It is found that periodicity of forced atomization relies on pressure drop fluctuation amplitude and phase differences between atomization and pressure drop fluctuations relate to fluctuation frequencies. This feature of periodic atomization induced by Klystron effect corresponds to periodicities and high amplitudes of pressure fluctuations in unstable combustion chambers and chaos and low amplitudes of pressure fluctuations in stable combustions chambers. Drastically periodic varying of gross surface area of droplets with time was shown in Mie scatter images. The importance of periodic impinging jet atomization modulated by pressure drop fluctuations for acoustic liquid propellant combustion instabilities is illustrated.

A Three-phase Integrated Power Electronic Transformer with the Capability of DC Fault Clearance

This paper presents a three-phase integrated power electronic transformer(PET)topology with the capability of DC fault clearance based on the investigation of PET topology.The proposed PET has three ports of high-voltage AC,high-voltage DC and low-voltage DC,which can achieve the flexible access of distributed energy resources・The power unit of the PET adopts a three-phase integrated topology,and the single-phase fluctuating power in the DC-link capacitor is reduced by a 4-port DC/DC converter,thereby reducing the capacitance of the DC-link capacitor;Meanwhile,the power unit uses the clamp double sub-module(CDSM)to allow for self-clearing of the short-circuit fault on the high-voltage DC side.Finally,this paper verifies the proposed PET through an EMT simulation and experimental prototype.

Simultaneous electromagnetically induced transparency and absorption in thermal atomic medium

A three-level lambda system driven by multicolor control, pump, and probe fields is investigated. The pump and probe fields are derived from the same laser with opposite propagating directions. Due to the Doppler effect, the zero group-velocity atoms face bichromatic fields, while other atoms face trichromatic fields. The atomic medium shows distinct characteristics and exhibits simultaneous electromagnetically induced transparency（EIT） and electromagnetically induced absorption（EIA） at two frequencies. EIT and EIA peaks have a fixed relationship with frequency, which is determined by the Doppler shifts.

Continuous-wave single-mode quantum cascade laser at 5.1 THz based on graded sampled grating design

We report on the terahertz(THz)quantum cascade lasers in continuous-wave(CW)operation with an emitting frequency above 5 THz.Excellent performance with a smaller leakage current and higher population inversion efficiency is obtained by one-well bridged bound-to-continuum hybrid quantum design at 5 THz.By designing and fabricating a graded metallic sampled distributed feedback grating in the waveguide,the first single-mode THz quantum cascade laser at 5.13 THz in CW operation mode is achieved.The maximum single-mode optical power of~48 mW is achieved at 15 K with a side-mode suppression ratio above 24 dB.This will draw great interest in the spectroscopy applications above the 5 THz range for THz quantum cascade lasers.

Recent advances in emerging techniques for non-destructive detection of seed viability: A review

Over the past decades,imaging and spectroscopy techniques have been developed rapidly with widespread applications in non-destructive agro-food quality determination.Seeds are one of themost fundamental elements of agriculture and forestry.Seed viability is of great significance in seed quality characteristics reflecting potential seed germination,and there is a great need for a quick and effective method to determine the germination condition and viability of seeds prior to cultivate,sale and plant.Some researches based on spectra and/or image processing and analysis have been explored in terms of the external and internal quality of a variety of seeds.Many attempts have been made in image segmentation and spectra correction methods to predict seed quality using various traditional and novel methods.This review focuses on the comparative introduction,development and applications of emerging techniques in the analysis of seed viability,in particular,near infrared spectroscopy,hyperspectral and multispectral imaging,Raman spectroscopy,infrared thermography,and soft X-ray imaging methods.The basic theories,principle components,relative chemometric processing,analytical methods and prediction accuracies are reported and compared.Additionally,on the foundation of the observed applications,the technical challenges and future outlook for these emerging techniques are also discussed.