分类： 地球科学 >> 空间物理学 提交时间： 2017-03-10
摘要： A passive sub-millimeter precipitation retrievals algorithm is provided based on Microwave Humidity and Temperature Sounder (MWHTS) onboard the Chinese Feng Yun 3C (FY-3C) satellite. Using the validated global reference physical model NCEP/WRF/ VDISORT), NCEP data per 6 hours are downloaded to run the Weather Research and Forecast model WRF, and derive the typical precipitation data from the whole world. The precipitation retrieval algorithm can operate either on land or on seawater for global. To simply the calculation procedure and save the training time, principle component analysis (PCA) was adapted to filter out the redundancy caused by scanning angle and surface effects, as well as system noise. According to the comparison and validation combing with other precipitation sources, it is demonstrated that the retrievals are reliable for surface precipitation rate higher than 0.1 mm/h at 15km resolution.
分类： 核科学技术 >> 裂变堆工程技术 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： In this work, we developed a numerical analysis-associated experiment method to determine the effective multiplication factor keff, which is difficult to obtain directly from conventional neutron source multiplication (NSM) method. The method is based on the relationship between keff, subcritical multiplication factor ks and external neutron source efficiency in the subcritical system. On basis of the theoretical analysis, the dependence of ks and on subcriticality and source position was investigated at the Chinese Fast Burst Reactor-II (CFBR-II). A series of ks were measured by NSM experiments at four subcritical states (keff = 0.996; 0.994; 0.991; 0.986) with the 252Cf neutron source located at different positions (from the system center to outside) at each subcritical states. The was obtained by Monte-Carlo simulation for each condition. With the measured ks and calculated , keff of the subcritical system was evaluated with a relative difference of <1% between values obtained by the improved method and by positive period method. Especially, the relative difference of <0.18% with the source located at the system center.
分类： 核科学技术 >> 核材料与工艺技术 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： Graphene oxide (GO) nanosheets possess several advantages, such as a large surface, outstanding bio-compatibility, and straightforward chemical modification capability. They also have great potential as a drug-carrier. In this article, we radiolabeled GO nanosheets with 99mTc, which satisfies the potential needs of micro-SPECT imaging probes in pre-clinical and clinical research. GO nanosheets were synthesized through the modified Hummers method, then GO nanosheets with azide group covalently functionalized in two steps were conjugated to DOTA (1,4,7,10-tetraazacyclododecane-N,N,N,N -tetraacetic acid) and functionalized with an alkynyl group by means of click chemistry. Then through the addition and reduction of technetium-99m, the 99mTc-DOTA-GO were attained. DOTA-conjugated GOs with lateral dimensions of 500600 nm were synthesized. Both atomic force microscopy (AFM) and FT-IR were performed to characterize the GO-DOTA. Labeling efficiency of GO-DOTA with 99mTc was >90% and radiochemical purities were >96% with purification. We successfully synthesized graphene oxide derivatives, DOTA-conjugated GOs, via Click Chemistry, and it was labeled with 99mTc for SPECT imaging. High radiolabeling efficiency makes GO nanosheets suitable platforms for future molecular imaging research.
分类： 天文学 >> 天文学 提交时间： 2024-02-28 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： We conduct a statistical analysis of the hardness ratio (HR) for bright sources in the 4 yr Galactic Plane Scanning Survey catalog of Insight-HXMT. Depending on the stable (variable) flux Fs (Fv) or spectrum Ss(Sv) of each source, the bright sources are classified into three groups: Fv&Sv, Fv&Ss, and Fs&Ss. Our study of the HR characteristics in different types of sources reveals that accretion-powered neutron star (NS) low-mass X-ray binaries (LMXBs) exhibit softer energy spectra than NS high-mass X-ray binaries (HMXBs), but harder energy spectra than black hole binaries in most cases. This difference is probably due to their different magnetic field strengths. Additionally, Fv&Sv LMXBs tend to be harder than Fv&Ss LMXBs below 7 keV, while the opposite is true for HMXBs. Our results suggest that LMXBs may dominate unclassified sources, and NS binaries are likely to be the primary type of X-ray binaries with ambiguous compact stars. By comparing the HR of transient sources in their outburst and low-flux states, it is found that the averaged HR of four sources in the two states are roughly comparable within uncertainties. We also investigate the spatial properties of the three groups and find that Fv&Sv sources are mainly located in the longitude of −20° < l < 9°, Fv&Ss sources cross the Galactic Plane, and Fs&Ss sources are predominantly concentrated in 19° < l < 42°. In addition, analyzing the HR spatial distributions shows the absorption of soft X-rays (primarily below 2 keV) in the Galactic Plane.
分类： 物理学 >> 核物理学 提交时间： 2024-03-09
Xin-Tong Du
Xiao-Bao Wei
Shao-Bo Ma
Li-Na Sheng
Xue-Heng Zhang
Shi-Tao Wang
Kai-Long Wang
Chun-Wang Ma
Hool-Jin Ong
Zhi-Yu Sun
Shu-Wen Tang
Yu-Hong Yu
摘要： The study of nuclide production and its properties in the N=126 neutron-rich region is the frontier and hot topic in nuclear physics and astrophysics research. The upcoming High energy FRagment Separator (HFRS) at the High Intensity heavy-ion Accelerator Facility (HIAF), an in-flight separator at relativistic energies, is characterized by high beam intensity, large ion-optical acceptance, high magnetic rigidity, and high momentum resolution power. It provides an opportunity for the study of the production and properties of neutron-rich nuclei around N=126. In this paper, an experimental scheme is proposed to produce the neutron-rich nuclei around N=126 and simultaneously measure their mass and lifetime based on the HFRS separator, and the feasibility of this scheme is evaluated by the simulations. The results show that under the high resolution optical mode many new neutron-rich nuclei approaching the r-process abundance peak around A=195 can be produced for the first time, and many nuclei with unknown mass and lifetime can be produced with high statistics. Using the time-of-flight corrected by the measured dispersive position and the energy loss information, the cocktails produced from the 208Pb fragmentation can be unambiguously identified. Moreover, the masses of some neutron-rich nuclei in the vicinity of N=126 can be measured with high precision using the time-of-flight magnetic rigidity technique. This indicates that the HIAF-HFRS facility has potential for the production and property research of neutron-rich nuclei around N=126, which is of great significance for expanding chart of nuclides, developing nuclear theories, and understanding the origin of heavy elements in the universe.
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