分类: 地球科学 >> 空间物理学 提交时间: 2017-01-22
摘要: By use of the global PPMLR Magnetohydrodynamics(MHD) model, a serial of quasi-steady-state numerical simulations were conducted to examine the modulation property of the interplanetary magnetic field clock angle theta on the solar wind energy input into the magnetosphere. All the simulations can be divided into seven groups according to different criteria of solar wind conditions. For each group, 37 numerical examples are analyzed, with the clock angle varying from 0�to 360�with an interval of 10� keeping the other solar wind parameters(such as the solar wind number density, velocity, and the magnetic field magnitude) unchanged. As expected, the solar wind energy input into the magnetosphere is modulated by the IMF clock angle. The axisymmetrical bell-shaped curve peaks at the clock angle of 180� However, the modulation effect remains invariant with varying other solar wind conditions. The function form of such an invariant modulation is found to be sin(0/2)2.70 + 0.25.
分类: 物理学 >> 地球物理学、天文学和天体物理学 提交时间: 2023-12-15 合作期刊: 《Research in Astronomy and Astrophysics》
摘要: Machine learning has become a crucial technique for classifying the morphology of galaxies as a result of the meteoric development of galactic data. Unfortunately, traditional supervised learning has significant learning costs since it needs a lot of labeled data to be effective. FixMatch, a semi-supervised learning algorithm that serves as a good method, is now a key tool for using large amounts of unlabeled data. Nevertheless, the performance degrades significantly when dealing with large, imbalanced data sets since FixMatch relies on a fixed threshold to filter pseudo-labels. Therefore, this study proposes a dynamic threshold alignment algorithm based on the FixMatch model. First, the class with the highest amount has its reliable pseudo-label ratio determined, and the remaining classes' reliable pseudo-label ratios are approximated in accordance. Second, based on the predicted reliable pseudo-label ratio for each category, it dynamically calculates the threshold for choosing pseudo-labels. By employing this dynamic threshold, the accuracy bias of each category is decreased and the learning of classes with less samples is improved. Experimental results show that in galaxy morphology classification tasks, compared with supervised learning, the proposed algorithm significantly improves performance. When the amount of labeled data is 100, the accuracy and F1-score are improved by 12.8% and 12.6%, respectively. Compared with popular semi-supervised algorithms such as FixMatch and MixMatch, the proposed algorithm has better classification performance, greatly reducing the accuracy bias of each category. When the amount of labeled data is 1000, the accuracy of cigar-shaped smooth galaxies with the smallest sample is improved by 37.94% compared to FixMatch.
分类: 医学、药学 >> 临床医学 提交时间: 2023-11-10 合作期刊: 《中国全科医学》
摘要: none
分类: 化学 >> 物理化学 提交时间: 2017-11-05 合作期刊: 《结构化学》
摘要: A coordination polymer [Mn2(ctpt)2(aic)2]n (1, ctpt = 2-(4-chloro-phenyl)-1H-1,3,7,8- tetraaza-cyclopenta[l]phenanthrene, H2aic = 5-amino-isophthalic acid) was hydrothermally designed and synthesized. The complex was characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction, and thermogravimetric analysis (TGA). Each Mn(II) atom is linked by the aic ligands with neighbor Mn(II) atoms, forming an infinite one-dimensional (1D) double-chain structure. Complex 1 crystallizes in monoclinic, space group C2/c, with a = 18.23(1), b = 17.27(1), c = 16.69(1) Å, V = 4814.0(7) Å3, C27H16ClMnN5O4, Mr = 564.84, Dc = 1.559 g/cm3, μ(MoKα) = 0.706 mm-1, F(000) = 2296, Z = 8, the final R = 0.0487 and wR = 0.1269 (I > 2σ(I)). The 1D chain structure of complex 1 is stable below 458 ℃. In addition, to elucidate the essential electronic characters of this complex, theoretical calculation analysis of 1 was performed by the PBE0/LANL2DZ method in Gaussian 03 Program.
分类: 化学 >> 核化学 提交时间: 2023-06-06
摘要: N,N,N,N-Tetraoctyl diglycolamide (TODGA) is one of the most promising extractants tailored for high-level liquid radioactive waste treatment during nuclear fuel reprocessing. The -radiolysis of TODGA (0.2 mol/L) in n-dodecane (nDD) solution with and without pre-equilibrated 3.0 mol/L HNO3 was investigated using HPLC and UPLC-QTOF-MS and compared with the -radiolysis of neat TODGA in this study. With increased absorbed doses, the concentration of TODGA decreased exponentially for the studied systems. Moreover, pre-equilibration with HNO3 (3.0 mol/L) slightly influenced the -radiolysis of TODGA in nDD. Seven radiolytic products generated from the rupture of the C C, C O, and C N bonds in TODGA were identified in the studied extraction system. The influence of -radiation on TODGA/nDD for the extraction of Eu(III) was evaluated using the first combination of extraction experiments and density functional theory (DFT) calculations, in which the complexations of Eu(III) with TODGA and its radiolytic products were systematically compared. Based on the radiolysis kinetic model of TODGA, the slope curve of the distribution ratio of Eu(III) (DEu ) and the absorbed dose, and fluorescence titration analysis, the empirical equation of the absorbed dose and DEu was obtained successfully. Below 300 kGy, the experimental DEu agreed well with the obtained empirical equation for TODGA/nDD. Conversely, at a high absorbed dose, the experimental DEu was higher than the theoretical DEu based on the empirical equation because the radiolytic products of TODGA with similar coordination structures still possessed partial complexation toward Eu(III), which was confirmed by DFT calculations. This work provides a method to predict the extraction distribution ratio of an irradiated extractant system and to understand the complex extraction process.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: n this paper, nanoscale zero-valent iron (NZVI) immobilized on carbon nanotube (CNT) composite (NZVI/CNT) was prepared, characterized and used for the sequestration of Se(IV) in water. The structural analysis revealed that NZVI were uniformly immobilized on CNT surfaces, and thus the oxidation and aggregation of NZVI was obviously minimized. Compared to bare NZVI, the NZVI/CNT exhibited much higher efficiency on Se(IV) sequestration due to the good synergistic effect between CNT adsorption and NZVI reduction. The results from X-ray absorption fine structure (XAFS) revealed that Se(IV) could be almost completely reduced into Se(0)/Se(-II) by NZVI/CNT, while partial reduction occurred on NZVI with a trace of Se(IV) adsorbed on the corrosion products. Besides, the role of pH in Se(IV) sequestration on NZVI/CNT was lower than that on NZVI due to the buffering effect of CNT. Moreover, CNT immobilization could also weaken the inhibition effect of humic acid (HA) on the removal of Se(IV) by NZVI, since CNT showed strong adsorption for HA that blocks potential reactivity. The excellent performance of NZVI/CNT offer a promising material for detoxification of Se(IV) from wastewater.
分类: 生物学 >> 生物物理学 提交时间: 2016-05-11
摘要: Hippocampus-related topographic amnesia is the most common symptom of memory disorders in Alzheimer's disease (AD) patients. Recent studies have revealed that experience-mediated DNA methylation, which is regulated by enzymes with DNA methyltransferase (DNMT) activity, is required for the formation of recent memory as well as the maintenance of remote memory. Notably, overexpression of DNMT3a in the hippocampus can reverse spatial memory deficits in aged mice. However, a decline in global DNA methylation was found in the autopsied hippocampi of patients with AD. Exactly, what endogenous factors that affect DNA methylation still remain to be elucidated. Here, we report a marked increase in endogenous formaldehyde levels is associated with a decline in global DNA methylation in the autopsied hippocampus from AD patients. In vitro and in vivo results show that formaldehyde in excess of normal physiological levels reduced global DNA methylation by interfering DNMTs. Interestingly, intrahippocampal injection of excess formaldehyde before spatial learning in healthy adult rats can mimic the learning difficulty of early stage of AD. Moreover, injection of excess formaldehyde after spatial learning can mimic the loss of remote spatial memory observed in late stage of AD. These findings suggest that aging-associated formaldehyde contributes to topographic amnesia in AD patients. (C) 2015 Elsevier Inc. All rights reserved.