Prospective study on observations of γ-ray sources in the Galaxy using the HADAR experiment

The High Altitude Detection of Astronomical Radiation (HADAR) experiment is a refracting terrestrial telescope array based on the atmospheric Cherenkov imaging technique. It focuses the Cherenkov light emitted by extensive air showers through a large aperture water-lens system for observing very-high-energy γ-rays and cosmic rays. With the advantages of a large field-of-view (FOV) and low energy threshold, the HADAR experiment operates in a large-scale sky scanning mode to observe galactic sources. This study presents the prospects of using the HADAR experiment for the sky survey of TeV γ-ray sources from TeVCat and provids a one-year survey of statistical significance. Results from the simulation show that a total of 23 galactic point sources, including five supernova remnant sources and superbubbles, four pulsar wind nebula sources, and 14 unidentified sources, were detected in the HADAR FOV with a significance greater than 5 standard deviations (σ). The statistical significance for the Crab Nebula during one year of operation reached 346.0 σ and the one-year integral sensitivity of HADAR above 1 TeV was ~1.3%–2.4% of the flux from the Crab Nebula.     

Synthesizing Red Fluorescent Carbon Dots from Rigid Polycyclic Conjugated Molecules: Dual-Mode Sensing and Bioimaging in Biochemical Applications

Red fluorescent carbon dots (R-CDs) are special desirable for biochemical analysis due to good biological compatibility and deep penetration; however, they remain as bottlenecks due to difficulties in expanding the sp² domain, especially those are fused from rigid polycyclic conjugated molecules (RPCMs) with heteroatom substituents due to huge steric hindrance and heteroatom blockage toward graphic lattice. Here, an RPCM with heteroatom substituents, 1,5-diamino-4,8-dihydroxyanthraquinone (DDAQ), based self-doped R-CDs with PL emission at 635 nm is reported. Further investigations reveal that the expanding, hybrid sp² domain with indanthrone tannin structure from DDAQ is mainly responsible for the obtained red fluorescence of R-CDs. Taking advantage of optical properties, R-CDs are considered to construct a colorimetric/fluorescent dual mode sensing array for quantifying trace levels of Fe³⁺ and glyphosate based on the static quenching, and a biomarker for cell imaging. The CD-based sensors exhibit outstanding recovery, high selectivity, and sensitivity, also facilitated dual-mode detection with the naked-eye. The R-CDs have low cytotoxicity, good cell membrane penetration for rapid cell entry, and high resolution, demonstrating their potential for biolabeling and bioanalytic applications.     

Automated Spleen Injury Detection Using 3D Active Contours and Machine Learning

The spleen is one of the most frequently injured organs in blunt abdominal trauma. Computed tomography (CT) is the imaging modality of choice to assess patients with blunt spleen trauma, which may include lacerations, subcapsular or parenchymal hematomas, active hemorrhage, and vascular injuries. While computer-assisted diagnosis systems exist for other conditions assessed using CT scans, the current method to detect spleen injuries involves the manual review of scans by radiologists, which is a time-consuming and repetitive process. In this study, we propose an automated spleen injury detection method using machine learning. CT scans from patients experiencing traumatic injuries were collected from Michigan Medicine and the Crash Injury Research Engineering Network (CIREN) dataset. Ninety-nine scans of healthy and lacerated spleens were split into disjoint training and test sets, with random forest (RF), naive Bayes, SVM, k-nearest neighbors (k-NN) ensemble, and subspace discriminant ensemble models trained via 5-fold cross validation. Of these models, random forest performed the best, achieving an Area Under the receiver operating characteristic Curve (AUC) of 0.91 and an F1 score of 0.80 on the test set. These results suggest that an automated, quantitative assessment of traumatic spleen injury has the potential to enable faster triage and improve patient outcomes.     

Negative thermal expansion: Mechanisms and materials

Negative thermal expansion (NTE) of materials is an intriguing phenomenon challenging the concept of traditional lattice dynamics and of importance for a variety of applications. Progresses in this field develop markedly and update continuously our knowledge on the NTE behavior of materials. In this article, we review the most recent understandings on the underlying mechanisms (anharmonic phonon vibration, magnetovolume effect, ferroelectrorestriction and charge transfer) of thermal shrinkage and the development of NTE materials under each mechanism from both the theoretical and experimental aspects. Besides the low frequency optical phonons which are usually accepted as the origins of NTE in framework structures, NTE driven by acoustic phonons and the interplay between anisotropic elasticity and phonons are stressed. Based on the data documented, some problems affecting applications of NTE materials are discussed and strategies for discovering and design novel framework structured NET materials are also presented.     

晚期HEMP作用下铁路牵引供电系统GIC算法研究

高空核爆电磁脉冲晚期效应（E₃）会引起地磁场剧烈变化并形成地面感应电场。感应电场等效为激励源与地面长距离导体和大地构成回路,产生地磁感应电流 （GIC）。GIC可引起牵引供电系统中变压器直流偏磁,从而严重威胁牵引供电系统的安全运行。本文基于平面波理论、分层大地电导率模型并结合牵引供电系统的电路模型,提出E₃作用下的牵引供电系统GIC算法,并以带回流线的直接供电方式的铁路牵引供电系统为例,首次计算了系统GIC情况。结果表明,该供电方式下牵引供电系统中的GIC远大于系统中变压器等设备的耐受值,为进一步研究E₃作用下牵引供电系统效应及我国铁路设备选型、灾害防治等提供支撑。     

数字束流位置探测器通道自动增益校准方法的研究与实现

在现有硬件基础上,基于BPM测量准确度的需求,在自制的电子学FPGA芯片内,通过Verilog语言实现了一种数字BPM采样数据增益自动校准的设计。首先介绍了自动增益校准模块的系统总体设计;然后对模块的实现方法做了详细说明,设计并搭建了ADC数据自动增益校准测试平台以验证自动增益较准模块的功能;最后介绍了该设计在BPM通道标定中的应用。实验结果表明,该方法可以实现4通道增益一致,使ADC采样后的数据幅度相同,有效解决了由通道增益不一致引起的测量偏差,以及工程应用中ADC数据幅度校准工作量大且难于操作的问题,将在BPM系统通道自动标定中发挥重要作用。     

基于维纳滤波的同轴电缆脉冲信号传输畸变补偿研究

由于同轴电缆的低通传输特性,脉冲信号在同轴电缆中传输时不可避免地会出现畸变,并且畸变程度会随着脉冲信号频率、带宽以及传输距离的增加而增大。创新性地将图像处理领域中的一种图像复原方法——维纳滤波法应用于脉冲信号同轴电缆传输畸变补偿,仅利用同轴电缆的S参数和输出信号即可完成输入信号的重构。并以10 m同轴电缆为对象,采用该方法分别对双指数脉冲信号、高斯调制脉冲信号、调制方波信号进行传输畸变补偿。结果表明：对于不同样式的信号,该方法均具有优异的补偿性能;并且,与工程上常用的衰减补偿法相比,该方法不仅补偿精度高,还具有高的计算效率,在同轴电缆脉冲信号传输畸变补偿中具有很好的实用价值。     

Universality of entropy principle for a general diffeomorphism-covariant purely gravitational theory

Thermodynamics plays an important role in gravitational theories. It is a principle that is independent of gravitational dynamics, and there is still no rigorous proof to show that it is consistent with the dynamical principle. We consider a self-gravitating perfect fluid system with the general diffeomorphism-covariant purely gravitational theory. Based on the Noether charge method proposed by Iyer and Wald, considering static off/on-shell variational configurations, which satisfy the gravitational constraint equation, we rigorously prove that the extrema of the total entropy of a perfect fluid inside a compact region for a fixed total particle number demands that the static configuration is an on-shell solution after we introduce some appropriate boundary conditions, i.e., it also satisfies the spatial gravitational equations. This means that the entropy principle of the fluid stores the same information as the gravitational equation in a static configuration. Our proof is universal and holds for any diffeomorphism-covariant purely gravitational theories, such as Einstein gravity, \begin{document}$ f(R)$\end{document} gravity, Lovelock gravity, f(Gauss-Bonnet) gravity and Einstein-Weyl gravity. Our result indicates the consistency between ordinary thermodynamics and gravitational dynamics.     

金属磁记忆效应的第一性原理计算与实验研究

为研究铁磁材料应力集中区域金属磁记忆信号的产生机理及其变化规律, 采用基于密度泛函理论的第一性原理平面波赝势法, 建立了磁记忆效应的磁力学模型; 计算分析了力与磁记忆自发漏磁信号的定量变化关系. 研究结果表明:力作用导致晶格畸变是磁记忆自发漏磁信号产生的根本原因; 常温下, 磁记忆信号随应力近似线性变化的规律与X70钢管水压爆破实验结果具有很好的一致性. 研究结果有助于金属磁记忆检测机理的研究. 关键词： 金属磁记忆 第一性原理 漏磁信号     

两相流有限穿越可视图演化动力学研究

针对小管径两相流流动特性, 全新优化设计弧形对壁式电导传感器. 通过动态实验在获取传感器测量信号的基础上, 采用有限穿越可视图理论构建对应于不同流型的两相流复杂网络. 通过分析发现, 有限穿越可视图网络异速生长指数和网络平均度值的联合分布可实现对小管径两相流的流型辨识; 有限穿越可视图度分布曲线峰值可有效刻画与泡径大小分布相关的流动物理结构细节特征; 网络平均度值可表征流动结构的宏观特性; 网络异速生长指数对流体动力学复杂性十分敏感, 可揭示不同流型演化过程中的细节演化动力学特性. 两相流测量信号的有限穿越可视图分析为揭示两相流流型的形成及演化动力学机理提供了新途径. 关键词： 两相流 复杂网络 有限穿越可视图 网络异速生长指数