分类: 动力与电气工程 >> 工程热物理学 提交时间: 2017-03-31 合作期刊: 《热科学学报》
摘要: This paper presents effects of heating directions on heat transfer performance of R134a flow boiling in mi- cro-channel heat sink. The heat sink has 30 parallel rectangular channels with cross-sectional dimensions of 500m width 500m depth and 30mm length. The experimental operation condition ranges of the heat flux and the mass flux were 13.48 to 82.25 W/cm2 and 373.3 to 1244.4 kg/m2s respectively. The vapor quality ranged from 0.07 to 0.93. The heat transfer coefficients of top heating and bottom heating both were up to 25 kW/m2 K. Two dominate transfer mechanisms of nucleate boiling and convection boiling were observed according to boiling curves. The experimental results indicated that the heat transfer coefficient of bottom heating was 13.9% higher than top heating in low heat flux, while in high heat flux, the heat transfer coefficient of bottom heating was 9.9%.higher than the top heating, because bubbles were harder to divorce the heating wall. And a modified corre- lation was provided to predict heat transfer of top heating.
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: 2023-02-19
摘要: Low surface brightness (LSB) galaxies are galaxies with central surface brightness fainter than the night sky. Due to the faint nature of LSB galaxies and the comparable sky background, it is difficult to search LSB galaxies automatically and efficiently from large sky survey. In this study, we established the Low Surface Brightness Galaxies Auto Detect model (LSBG-AD), which is a data-driven model for end-to-end detection of LSB galaxies from Sloan Digital Sky Survey (SDSS) images. Object detection techniques based on deep learning are applied to the SDSS field images to identify LSB galaxies and estimate their coordinates at the same time. Applying LSBG-AD to 1120 SDSS images, we detected 1197 LSB galaxy candidates, of which 1081 samples are already known and 116 samples are newly found candidates. The B-band central surface brightness of the candidates searched by the model ranges from 22 mag arcsec $^ {- 2} $ to 24 mag arcsec $^ {- 2} $, quite consistent with the surface brightness distribution of the standard sample. 96.46\% of LSB galaxy candidates have an axis ratio ($b/a$) greater than 0.3, and 92.04\% of them have $fracDev\_r$\textless 0.4, which is also consistent with the standard sample. The results show that the LSBG-AD model learns the features of LSB galaxies of the training samples well, and can be used to search LSB galaxies without using photometric parameters. Next, this method will be used to develop efficient algorithms to detect LSB galaxies from massive images of the next generation observatories.
分类: 物理学 >> 地球物理学、天文学和天体物理学 提交时间: 2024-02-01 合作期刊: 《Research in Astronomy and Astrophysics》
摘要: Cross-matching is a key technique to achieve fusion of multi-band astronomical catalogs. Due to different equipment such as various astronomical telescopes, the existence of measurement errors, and proper motions of the celestial bodies, the same celestial object will have different positions in different catalogs, making it difficult to integrate multi-band or full-band astronomical data. In this study, we propose an online cross-matching method based on pseudo-spherical indexing techniques and develop a service combining with high performance computing system (Taurus) to improve cross-matching efficiency, which is designed for the Data Center of Xinjiang Astronomical Observatory. Specifically, we use Quad Tree Cube to divide the spherical blocks of the celestial object and map the 2D space composed of R.A. and decl. to 1D space and achieve correspondence between real celestial objects and spherical patches. Finally, we verify the performance of the service using Gaia 3 and PPMXL catalogs. Meanwhile, we send the matching results to VO tools-Topcat and Aladin respectively to get visual results. The experimental results show that the service effectively solves the speed bottleneck problem of cross-matching caused by frequent I/O, and significantly improves the retrieval and matching speed of massive astronomical data.
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: Uranium removal efficacy of fullerence multi-macrocyclic polyamine derivatives (C60-MMP), a novel chelating agent, was evaluated in mice. C60-MMP was administrated intravenously into mice at 30 min after the uranium contamination. The molar ratio of chelating ligand/uranium was about 1:1. The results indicate that C60-MMP can effectively prevent accumulation of uranium in liver at 8 h after C60-MMP injection. At 48 h after the last injection, uranium deposition in liver of C60-MMP treated mice is approximately 65% less than that of the control group. C60-MMP reacted positively in promoting the removal of uranium from kidney, and the urinary uranium excretion increased significantly, compared with the control and DTPA-treated mice. However, repeated administration of C60-MMP, and combined injection of DTPA and C60-MMP, did not show desirable effects on uranium removal from mice. It implies that more investigations are needed for the treatment protocols and clinical applications of C60-MMP.
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: To develop a microbe-based bioremediation strategy for cleaning up thorium-contaminated sites, we have investigated the biosorption behavior and mechanism of thorium on Bacillus sp. dwc-2, one of the dominant species of bacterial groups isolated from soils in Southwest China. Thorium biosorption depended on the pH of environment, and its rapid biosorption reached a maximum of up to 10.75 mg Th per gram of the bacteria (wet wt.) at pH 3.0. The biosorption agreed bettter with Langmuir isotherm model than Freundlich model, indicating that thorium biosorption was a monolayer adsorption. The thermodynamic parameters, negative change in Gibbs free energy and positive value in enthalpy and entropy, suggested that the biosorption was spontaneous, more favorable at higher temperature and endothermic process with an increase of entropy. Scanning electron microscopy (SEM) indicated that thorium initially binded with the cell surface, while transmission electron microscopy (TEM) revealed that Th deposited in the cytoplasm and served as cores for growth of element precipitation (e.g., phosphate minerals) or by self-precipitation of hydroxides, which is probably controlled by ion-exchange, as evidenced by particle induced X-ray emission (PIXE) and enhanced proton backscattering spectrometry (EPBS). Fourier Transform Infrared (FTIR) further indicated that thorium biosorption involved carboxyl and phosphate groups and protein in complexation or electrostatic interaction. Overall results indicated that a combined electrostatic interaction-complexation-ion exchange mechanism could be involved in thorium biosorption by Bacillus sp. dwc-2.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We propose to develop a wide-field and ultra-high-precision photometric survey mission, temporarily named "Earth 2.0 (ET)". This mission is designed to measure, for the first time, the occurrence rate and the orbital distributions of Earth-sized planets. ET consists of seven 30cm telescopes, to be launched to the Earth-Sun's L2 point. Six of these are transit telescopes with a field of view of 500 square degrees. Staring in the direction that encompasses the original Kepler field for four continuous years, this monitoring will return tens of thousands of transiting planets, including the elusive Earth twins orbiting solar-type stars. The seventh telescope is a 30cm microlensing telescope that will monitor an area of 4 square degrees toward the galactic bulge. This, combined with simultaneous ground-based KMTNet observations, will measure masses for hundreds of long-period and free-floating planets. Together, the transit and the microlensing telescopes will revolutionize our understandings of terrestrial planets across a large swath of orbital distances and free space. In addition, the survey data will also facilitate studies in the fields of asteroseismology, Galactic archeology, time-domain sciences, and black holes in binaries.