分类： 核科学技术 >> 核科学与技术 提交时间： 2024-03-08
摘要： Various electromagnetic signals are excited by the beam in the acceleration and beam-diagnostic elements of a particle accelerator. It is important to obtain time-domain waveforms of these signals with high temporal resolution for research, such as the study of beam-cavity interactions and bunch-by-bunch parameter measure#2;ments. Therefore, a signal reconstruction algorithm with ultrahigh spatiotemporal resolution and bunch phase compensation based on equivalent sampling is proposed in this paper. Compared with traditional equivalent sampling, the use of phase compensation and setting the bunch signal zero-crossing point as the time reference can construct a more accurate reconstructed signal. The basic principles of the method, simulation, and experi#2;mental comparison are also introduced. Based on the beam test platform of the Shanghai Synchrotron Radiation Facility (SSRF) and the method of experimental verification, the factors that affect the reconstructed signal qual#2;ity are analyzed and discussed, including the depth of the sampled data, quantization noise of analog-to-digital converter (ADC), beam transverse oscillation, and longitudinal oscillation. The results of the beam experiments show that under the user operation conditions of the Shanghai Synchrotron Radiation Facility (SSRF), a beam excitation signal with an amplitude uncertainty of 2% can be reconstructed.
分类： 物理学 >> 核物理学 分类： 天文学 >> 天文仪器与技术 提交时间： 2023-08-29
Wan, Qiang
Guo, Jianhua
Xu, Xing
Wang, Shen
Zhang, Yongqiang
Hu, Yiming
Zhang, Yan
Pan, Xu
Li, Xiang
Yue, Chuan
Jiang, Wei
Cui, Yuxin
Chen, Dengyi
摘要： In the future, the Very Large Area gamma-ray Space Telescope (VLAST) is expected to observe high-energy electrons and gamma rays in the MeV to TeV range with unprecedented acceptance. As part of the detector suite, a high-energy imaging calorimeter (HEIC) is currently being developed as a homogeneous calorimeter that utilizes long bismuth germanate (BGO) scintillation crystals as both absorbers and detectors. To accurately measure the energy deposition in the BGO bar of HEIC, a high-dynamic-range readout method using a silicon photoMultiplier (SiPM) and multiphotodiode (PD) with different active areas has been proposed. A prototype readout system that adopts multichannel charge measurement ASICs was also developed to read out the combined system of SiPMs and PDs. Preliminary tests confirmed the feasibility of the readout scheme, which is expected to have a dynamic range close to 106.
分类： 核科学技术 >> 粒子加速器 提交时间： 2023-07-08
摘要： Radio-frequency (RF) breakdown analysis and location are critical for successful development of high-gradient traveling-wave (TW) accelerators, especially those expected to generate high-intensity, high-power beams. Compared with commonly used schemes involving dedicated devices or complicated techniques, a convenient approach for breakdown locating based on transmission line (TL) theory offers advantages in the typical constant-gradient TW-accelerating structure. To deliver such an approach, an equivalent TL model has been constructed to equate the TW-accelerating structure based on the fundamental theory of the TL transient response in the time domain. An equivalence relationship between the TW-accelerating structure and the TL model has been established via analytical derivations associated with grid charts and verified by TL circuit simulations. Furthermore, to validate the proposed fault-locating method in practical applications, an elaborate analysis via such a method has been conducted for the recoverable RF-breakdown phenomena observed at an existing prototype of a TW-accelerating-structure-based beam injector constructed at the Huazhong University of Science and Technology. In addition, further considerations and discussion for extending the applications of the proposed method have been given. This breakdown-locating approach involving the transient response in the framework of TL theory can be a conceivable supplement to existing methods, facilitating solution to construction problems at an affordable cost.
分类： 数学 >> 应用数学 提交时间： 2021-09-22
摘要： In the early days of the epidemic of coronavirus disease 2019 (COVID-19), due to insufficient knowledge of the pandemic, inadequate nucleic acid tests, lack of timely data reporting, etc., the origin time of the onset of COVID-19 is difficult to determine. Therefore, source tracing is crucial for infectious disease prevention and control. The purpose of this paper is to infer the origin time of pandemic of COVID-19 based on a data and model hybrid driven method. We model the testing positive rate to fit its actual trend, and use the least squares estimation to obtain the optimal model parameters. Further, the kernel density estimation is applied to infer the origin time of pandemic given the specific confidence probability. By selecting 12 representative regions in the United States for analysis, the dates of the first infected case with 50% confidence probability are mostly between August and October 2019, which are earlier than the officially announced date of the first confirmed case in the United States on January 20, 2020. The experimental results indicate that the COVID-19 pandemic in the United States starts to spread around September 2019 with a high confidence probability. In addition, the existing confirmed cases are also used in Wuhan City and Zhejiang Province in China to infer the origin time of COVID-19 and provide the confidence probability. The results show that the spread of COVID-19 pandemic in China is likely to begin in late December 2019.
分类： 生物学 >> 生物医药 提交时间： 2017-05-10
摘要： Signal transducer and activator of transcription (STAT) proteins play an important role in cytokine signaling pathways and regulation of immune responses. The balance of the phosphorylated (activated) STAT1 (pSTAT1) and STAT3 (pSTAT3) has been documented in cancer immunology. In this study, we investigated the dynamic balance of pSTAT1 and pSTAT3 in C57BL/6 mice infected with either a nonlethal (Py17XNL) or lethal (Py17XL) strain of Plasmodium yoelii. Both Py17XNL and Py17XL infections induced a maximum activation of STAT1 and STAT3 on the first day after parasite inoculation. Additionally, the Py17XNL infection induced a pSTAT1-dominant response in mice during the early stage of infection, with the resolution of parasitemia. In contrast, Py17XL infection induced a pSTAT3-dominant response during the early phase of infection, with the death of the animals. Our results indicated that maximum activation of STAT1 and STAT3 occurred much earlier than the peak levels of cytokines induced by Plasmodium yoelii infection based on previous reports and that infection with Py17XNL and Py17XL induced different dynamic patterns of pSTAT1 and pSTAT3 balance. Cellular & Molecular Immunology
分类： 生物学 >> 生物医药 提交时间： 2017-05-10
摘要： The genetic program of embryonic stem (ES) cells is orchestrated by a core of transcription factors that has OCT4, SOX2, and NANOG as master regulators. Protein levels of these core factors are tightly controlled by autoregulatory and feed-forward transcriptional mechanisms in order to prevent early differentiation. Recent studies have shown that knockdown of Esrrb (estrogen-related-receptor beta), a member of the nuclear orphan receptor family, induces differentiation of mouse ES cells cultured in the presence of leukemia inhibitory factor. It was however not known how knocking down Esrrb exerts this effect. Herein we have identified two ESRRB binding sites in the proximal 5'-untranslated region of the mouse Oct4 gene, one of which is in close proximity to a NANOG binding site. Both ESRRB and NANOG are necessary for maintaining the activity of this promoter in ES cell lines. We have also demonstrated that the two transcription factors interact through their DNA binding domains. This interaction reciprocally modulates their transcriptional activities and may be important to fine-tune ES cell pluripotency. Supporting all of these data, stable transfection of Esrrb in ES cell lines proved sufficient to sustain their characteristics in the absence of leukemia-inhibitory factor. In summary, our experiments help to understand how Esrrb coordinates with Nanog and Oct4 to activate the internal machinery of ES cells.
分类： 物理学 >> 核物理学 提交时间： 2016-09-14
Jingyu Tang
J. Scott Berg
Weiping Chai
Fusan Chen
Nian Chen
Weiren Chou
HaiyiDong
Jie Gao
Tao Han
Yongbin Leng
Guangrui Li
Ramesh Gupta
Peng Li
Zhihui Li
Baiqi Liu
Yudong Liu
Xinchou Lou
Qing Luo
Ernie Malamud
Lijun Mao
摘要： Following the discovery of the Higgs boson at LHC, new large colliders are being studied by the international high-energy community to explore Higgs physics in detail and new physics beyond the Standard Model. In China, a two-stage circular collider project CEPC-SPPC is proposed, with the first stage CEPC (Circular Electron Positron Collier, a so-called Higgs factory) focused on Higgs physics, and the second stage SPPC (Super Proton-Proton Collider) focused on new physics beyond the Standard Model. This paper discusses this second stage.
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