分类: 物理学 >> 核物理学 提交时间: 2023-06-25
摘要: The Cooling Storage Ring external-target experiment (CEE) spectrometer is used to study the nuclear matter created in heavy-ion collisions atsNN= 2.1-2.4 GeV with the aim to reveal the quantum chromodynamics phase structure in the high-baryon density region. Collective flow is considered an effective probe for evaluating the properties of media during high-energy nuclear collisions. One of the main functions of the zero-degree calorimeter (ZDC), a subdetector system in the CEE, is to determine the reaction plane in heavy-ion collisions. This step is crucial for measuring the collective flow and other reaction-plane-related analyses. In this paper, we illustrate the procedures for event-plane determination using the ZDC. Finally, isospin-dependent quantum molecular dynamics model-based predictions of the rapidity dependence of the directed and elliptical flows forp,d,t,3He, and4He, produced in 2.1 GeV U+U collisions, are presented.
分类: 物理学 >> 核物理学 提交时间: 2023-10-24
摘要: The Zero Degree Calorimeter (ZDC) plays a crucial role in determining centrality at the Cooling-Storage-Ring External-target Experiment (CEE) in the Heavy Ion Research Facility in Lanzhou (HIRFL). A Boosted Decision Trees (BDT) multi-classification algorithm is employed to classify the centrality of the collision events based on the raw features from ZDC such as the number of fired channels and deposited energy. The data from simulated $ rm ^{238}U$ + $ rm ^{238}U$ collisions at 500 $ rm MeV/u$, generated by the IQMD event generator and subsequently modeled through the GEANT4 package, is employed to train and test the BDT model. The results showed the high accuracy of the multi-classification model adopted in ZDC for centrality determination, which is robust against variations in different factors of detector geometry and response. The study demonstrates a good performance of the CEE-ZDC for determining the centrality in nucleus-nucleus collisions.
分类: 核科学技术 >> 核探测技术与核电子学 分类: 核科学技术 >> 核仪器、仪表 提交时间: 2024-02-07
摘要: A new measurement method for the spatial distribution of neutron beam flux in boron neutron capture therapy (BNCT) is being developed based on the two-dimensional Micromegas detector. To address the issue of long processing time in traditional offline position reconstruction methods, this paper proposes an FPGA-based online position reconstruction method, grounded in the micro time projection chamber principle. This method encapsulates key technical aspects: self-adaptive serial link technique built upon the dynamical adjustment of delay chain length, fast sorting and coordinate matching technique based on the mapping between signal timestamps and random access memory (RAM) addresses, and precise start point merging technique utilizing a circular combined RAM. The performance test of the self-adaptive serial link shows the bit error rate of the link is better than 10^-12 at a confidence level of 99%, ensuring reliable data transmission. The combined experiment of the readout electronics and the Micromegas detector shows a spatial resolution of approximately 1.4 mm, surpassing the current method's resolution level of 5 mm. The beam experiment confirms that the readout electronics system can obtain the flux spatial distribution of neutron beam online, thus validating the feasibility of the position reconstruction method. The online position reconstruction method avoids traditional methods such as bubble sorting and traversal searching, simplifying the design of logic firmware and reducing the time complexity from O(n^2) to O(n). This study contributes to the advancement in measuring neutron beam flux for BNCT.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: In this work, six convolutional neural networks (CNNs) have been trained based on %different feature images and arrays from the database including 15,638 superflare candidates on solar-type stars, which are collected from the three-years observations of Transiting Exoplanet Survey Satellite ({\em TESS}). These networks are used to replace the artificially visual inspection, which was a direct way to search for superflares, and exclude false positive events in recent years. Unlike other methods, which only used stellar light curves to search superflare signals, we try to identify superflares through {\em TESS} pixel-level data with lower risks of mixing false positive events, and give more reliable identification results for statistical analysis. The evaluated accuracy of each network is around 95.57\%. After applying ensemble learning to these networks, stacking method promotes accuracy to 97.62\% with 100\% classification rate, and voting method promotes accuracy to 99.42\% with relatively lower classification rate at 92.19\%. We find that superflare candidates with short duration and low peak amplitude have lower identification precision, as their superflare-features are hard to be identified. The database including 71,732 solar-type stars and 15,638 superflare candidates from {\em TESS} with corresponding feature images and arrays, and trained CNNs in this work are public available.
分类: 物理学 >> 核物理学 提交时间: 2023-11-15
摘要: Macromolecular crystallography beamline BL17U1 at the Shanghai Synchrotron Radiation Facility hasbeenrelocated, upgraded, and given a newID (BL02U1). It now deliversX-rays intheenergyrangeof616 keV, withafocusedbeamof11.6m 4.8 m andphotonfluxgreater than 10^12phs/s. Thehighcredibilityandstabilityofthebeamandgoodtimingsynchronizationof the equipmentsignificantly improvetheexperimentalefficiency. SinceJune2021, whenitofficially openedtousers, over4200 hofbeamtimehavebeenprovidedto over200 researchgroupstocollectdataatthebeamline. Its goodperformanceandstableoperationhave led to the resolution of several structuresbasedondatacollectedatthebeamline.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: Femtosecond laser ablation has been demonstrated to be a versatile tool to produce micro/nanoscale features with high precision and accuracy. However, the use of high laser fluence to increase the ablation efficiency usually results in unwanted effects, such as redeposition of debris, formation of recast layer and heat-affected zone in or around the ablation craters. Here we circumvent this limitation by exploiting a thin frost layer with a thickness of tens of microns, which can be directly formed by the condensation of water vapor from the air onto the exposed surface whose temperature is below the freezing point. When femtosecond laser beam is focused onto the target surface covered with a thin frost layer, only the local frost layer around the laser-irradiated spot melts into water, helping to boost ablation efficiency, suppress the recast layer and reduce the heat-affect zone, while the remaining frost layer can prevent ablation debris from adhering to the target surface. By this frost-assisted strategy, high-quality surface micro/nano-structures are successfully achieved on both plane and curved surfaces at high laser fluences, and the mechanism behind the formation of high-spatial-frequency (HSF) laser induced periodic surface structures (LIPSSs) on silicon is discussed.
分类: 物理学 >> 地球物理学、天文学和天体物理学 提交时间: 2023-12-15 合作期刊: 《Research in Astronomy and Astrophysics》
摘要: Jet precession has previously been proposed to explain the apparently repeating features in the light curves of a few gamma-ray bursts (GRBs). In this paper, we further apply the precession model to a bright GRB 220408B by examining both its temporal and spectral consistency with the predictions of the model. As one of the recently confirmed GRBs observed by our GRID CubeSat mission, GRB 220408B is noteworthy as it exhibits three apparently similar emission episodes. Furthermore, the similarities are reinforced by their strong temporal correlations and similar features in terms of spectral evolution and spectral lags. Our analysis demonstrates that these features can be well explained by the modulated emission of a Fast-Rise-Exponential-Decay (FRED) shape light curve intrinsically produced by a precessing jet with a precession period of s, a nutation period of s and viewed off-axis. This study provides a straightforward explanation for the complex yet similar multi-episode GRB light curves.
分类: 物理学 >> 核物理学 提交时间: 2023-11-22
摘要: BL10U2 is an undulator-based macromolecular crystallography (MX) beamline located at the 3.5-GeV Shanghai Synchrotron Radiation Facility. BL10U2 is specifically designed for conducting routine and bio safety level-2 (BSL-2) MX experiments utilizing high-flux tunable X-rays with energies from 7 to 18 keV, providing a beam spot size of 20 m (horizontal) 10 m (vertical) at the sample point. Certification by the Shanghai Pudong Municipal Health Commission confirmed the capability to perform BSL-2 MX experiments. The beamline is currently equipped with an Eiger X 16M detector and two newly developed in-house high-precision diffractometers that can be switched to perform conventional or in situ crystal diffraction experiments. An automatic sample changer developed in-house allows fast sample exchange in less than 30s, supporting high-throughput MX experimentation and rapid crystal screening. Data collection from both the diffractometer and detector was controlled by an in-house developed data collection software (Finback) with a user-friendly interface for convenient operation. This study presents a comprehensive overview of the facilities, experimental methods, and performance characteristics of the BL10U2 beamline.