分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： An explanation for superluminal phenomena based on wave-particle duality of photons is suggested. A single photon may be regarded as a wave packet, whose spatial extension is its coherence volume. As a photon propagates as a wave train in vacuum, its velocity is just the speed of light. When it tunnels through a barrier as a particle, its wave function collapses and it will travel faster than light. Superluminal propagation can occur only within the coherence length and the time constrained by uncertainty principle. A massive particle cannot be superluminal during the tunneling process. So superluminality does not violate causality. As for the superluminal and negative group velocities in anomalously dispersive medium, they are merely reshaping effect of the pulse, and they will become subluminal at large distances. A couple of experiments are proposed to test the superluminal phenomena.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The energy spectrum of gravitational waves (GWs), which depicts the energy of GWs per unit volume of space per logarithmic frequency interval normalized to the critical density of the Universe, is a widely used way for quantifying the sensitivity of GW detectors and the strength of GWs, since it has the advantage of having a clear physical meaning. It was found that the energy spectrum of GWs depends on the gauge when the GWs beyond the linear order perturbations are considered. We show that this gauge dependence issue originates from the inappropriate description for the energy of GWs. With the proper description for the energy of GWs, we give a well-defined energy spectrum of GWs, in which the gauge issue disappears naturally.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The energy of gravitational waves is a fundamental problem in gravity theory. The existing descriptions for the energy of gravitational waves, such as the well-known Isaacson energy-momentum tensor, suffer from several defects. Due to the equivalence principle, the gravitational energy-momentum can only be defined quasilocally, being associated with a closed spacelike 2-surface bounding a region. We propose a new approach to derive the energy of gravitational waves $directly$ from the quasilocal gravitational energy. Such an approach is natural and consistent with the quasilocality of gravitational energy-momentum.
分类： 物理学 >> 核物理学 提交时间： 2023-09-13
摘要： Abstract: In this experimental study, involving deuteriumdeuterium fusion neutron emission spectroscopy (NES) measurement on the experimental advanced superconducting tokamak (EAST), a liquid scintillator detector (BC501A) was employed. This decision was based on the detector's superior sensitivity, optimal time-response, and its exceptional n- discrimination capability. This detector emits fast pulse signals that are as narrow as 100 ns, with high count rates that can peak at several Mcps. However, conventional nuclear circuits faced challenges in performing pulse height analysis, n pulse shape discrimination (PSD), and in recording the entire pulse waveform under such high-count-rate conditions. To address these challenges, a high-speed digital pulse signal acquisition and processing system was designed. The system was developed around a micro-telecommunications computing architecture (MTCA). Within this structure, a signal acquisition and processing (SAQP) module communicated through PCI Express (PCIe) links, achieving a bandwidth of up to 1.6 GB/s. To accurately capture the detailed shape of the pulses, four channels of analog-to-digital converters (ADCs) were used, each with a 500-MSPS sampling rate and a 14-bit resolution, ensuring an accuracy that surpassed 11 bits. An n- discrimination algorithm, based on the two-gate integral method, was also developed. Implemented within field programmable gate arrays (FPGA), this algorithm provided a real-time n- discrimination spectrum for pulse height analysis. The system underwent rigorous testing in a laboratory setting and during an EAST experiment. The results confirmed that the innovative SAQP system can satisfy the demanding requirements of high-parameter experiments, manage count rates of up to 2 Mcps, execute real-time n- discrimination algorithms, and record entire pulse waveforms without any data loss.
分类： 核科学技术 >> 核仪器、仪表 提交时间： 2023-06-01
Shi-Xing Liu
Wei Zhang
Zi-Han Zhang
Shuang Lin
Hong-Rui Cao
Cheng-Xin Song
Jin-Long Zhao
Guo-Qiang Zhong
摘要： 核安全防护通常需要同时探测中子和伽马射线，探测器的实时中子/伽马脉冲分辨是其关键性能参数。近年来，采用Cs2LiLaBr6 (CLLB)晶体的双读出探测器引起了广泛关注，论文研究电荷比较法、幅度比较法、时间比较法和脉冲梯度法的甄别性能，以及Sallen-Key滤波器的甄别效果。实验结果表明，通过合适的滤波，四种方法的品质因数(FOM)都有所提高。其中，电荷比较法抗噪声性能最佳，最适合CLLB探测器实时甄别中子/伽马脉冲。其甄别性能取决于参数、和。在对应脉冲峰值10%的时刻，，仅需延迟640-740 ns，此刻对应3.1-3.3 MeV的电荷比较方法最优FOM大于1.46。所提出的最大分辨差模型( MDDM)计算值与最优FOM的差异小于3.9%，表明该模型可以很好地指导电荷比较法的参数选择。
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