分类: 生物学 >> 生物物理学 >> 生物物理、生物化学与分子生物学 提交时间: 2016-05-12
摘要: The architecture and structural details of chromatin assembler, chromatin modifier, and chromatin remodeler, and their complexes with nucleosome and chromatin, are critical for revealing the molecular mechanisms for the establishment, maintenance and regulation of epigenetic information. The fast-developing cryo-electron microscopy (cryo-EM) provides an indispensible tool for the structure determiantion of the huge, multi-subunits, and flexible epigenetic regulation related macromolecular assemblies. In this review, we summarized the recent progresses on EM structural studies of macromolecules and complexes relating to epigenetic regulation.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-09
摘要: We investigate the cosmic age problem associated with 9 extremely old globular clusters in M31 galaxy and 1 very old high-z quasar automatic plate-measuring machine 08279 + 5255 at z = 3.91. These 9 globular clusters have not been used to study the cosmic age problem in the previous literature. By evaluating the age of the Universe in the Lambda cold dark matter model with the observational constraints from the Type Ia supernovae, the baryon acoustic oscillations, the cosmic microwave background, and the independent H-0 measurements, we find that the existence of 5 globular clusters and 1 high-z quasar are in tension (over 2 sigma confidence level) with the current cosmological observations. So if the age estimates of these objects are correct, the cosmic age puzzle still remains in the standard cosmology. Moreover, we extend our investigations to the cases of the interacting dark energy models. It is found that although the introduction of the interaction between dark sectors can give a larger cosmic age, the interacting dark energy models still have difficulty to pass the cosmic age test.
分类: 生物学 >> 生物物理学 提交时间: 2016-05-12
摘要: Purpose: To investigate the longitudinal brain regional homogeneity (ReHo) changes in nonhuman primate after spinal cord injury (SCI) by resting-state functional magnetic resonance imaging (fMRI). Methods: Three adult female rhesus monkeys underwent unilateral thoracic cord injury. A resting-state fMRI examination was performed in the healthy stage and 4, 8, and 12 weeks after the injury. The ReHo value of each voxel in the monkey brain was calculated and compared between pre- and post-SCI monkeys with paired t test. The regions of interest (ROIs) in the significantly changed ReHo regions were set. The correlations between the ReHo change and the time after injury were also determined. Results: Compared with those in healthy period, the ReHo values of the left premotor cortex and the anterior cingulate cortex (ACC) in post-SCI rhesus monkeys significantly increased in 4-week follow-up examinations. The ReHo values of posterior cingulate cortex, left precuneus, left temporal parietooccipital area, and bilateral superior parietal lobules decreased at 8-week follow-up examinations. In 12-week follow-up examinations, the ReHo values of the left postcentral gyrus, right caudate nucleus, and superior temporal gyrus increased. Correlation analysis showed positive correlations between left ACC and the postoperative time. Conclusion: SCI can change the regional synchronism of brain activity in sensorimotor system and the default mode network. These findings may help us to understand the potential pathophysiological changes in the central nervous system after SCI. (C) 2015 Elsevier Inc. All rights reserved.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-09
摘要: The possibility of reconstructing a spherically symmetric inhomogeneous Lemaitre-Tolman-Bondi (LTB) model with Lambda CDM observations has drawn much attention. Recently, an inhomogeneous LTB model having the same luminosity-distance and light-cone mass density of the homogeneous Lambda CDM model was reconstructed. From the Wilkinson microwave anisotropy probe 7-year measurements together with other cosmological observations, we calculate the cosmic age at our position in this LTB model, and obtain a constraint t(LTB) < 11.7 Gyr at 1 sigma confidence level. We find that this result is, although 2 Gyr younger compared with the age of the homogeneous Lambda CDM model, still within 1 sigma agreement with the constraint of cosmic age given by current astronomical measurements. We expect that in the future, with the help of more advanced observations, we can distinguish the reconstructed inhomogeneous LTB model from the homogeneous Lambda CDM model.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-09
摘要: In this paper we investigate the possible direct, non-gravitational interaction between holographic dark energy (HDE) and dark matter. Firstly, we start with two simple models with the interaction terms Q proportional to rho(dm) and Q proportional to rho(de), and then we move on to the general form Q proportional to rho(alpha)(m)rho(beta)(de). The cosmological constraints of the models are obtained from the joint analysis of the present Union 2.1+BAO+CMB+H-0 data. We find that the data slightly favor an energy flow from dark matter to dark energy, although the original HDE model still lies in the 95.4% confidence level (CL) region. For all models we find c -1. We show that this solution cannot be accomplished in the two simple models, while for the general model such a solution can be achieved with a large beta, and the big rip may be avoided at the 95.4% CL.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-05-08
摘要: Self-questioning mechanism which is similar to single spin-flip of Ising model in statistical physics is introduced into spatial evolutionary game model. We propose a game model with altruistic to spiteful preferences via weighted sums of own and opponent’s payoffs. This game model can be transformed into Ising model with an external field. Both interaction between spins and the external field are determined by the elements of payoff matrix and the preference parameter. In the case of perfect rationality at zero social temperature , this game model has three different phases which are entirely cooperative phase, entirely non-cooperative phase and mixed phase. In the investigations of the game model with Monte Carlo simulation, two paths of payoff and preference parameters are taken. In one path, the system undergos a discontinuous transition from cooperative phase to non-cooperative phase with the change of preference parameter. In another path, two continuous transitions appear one after another when system changes from cooperative phase to non-cooperative phase with the prefenrence parameter. The critical exponents and of two continuous phase transitions are estimated by the finite-size scaling analysis. Both continuous phase transitions have the same critical exponents and they belong to the same universality class as the two-dimensional Ising model.
分类: 工程与技术科学 >> 工程物理学 分类: 核科学技术 >> 粒子加速器 提交时间: 2023-12-13
摘要: The China Spallation Neutron Source (CSNS) upgrade project (CSNS-II) aims to enhance the beam power from 100 to 500 kW. A dual-harmonic accelerating method has been adopted to alleviate the stronger space-charge effect in rapid-cycling synchrotrons owing to the increased beam intensity. To satisfy the requirements of dual-harmonic acceleration, a new radiofrequency (RF) system based on a magnetic alloy-loaded cavity is proposed . This paper presents design considerations and experimental results regarding the performance evaluation of the proposed RF system through high-power tests and beam commissioning. The test results demonstrate that the RF system satisfies the desired specifications and affords significant benefits for CSNS-II .
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: One novel phenoxyacetamide derivative (C22H28N2O3, Mr = 368.47) has been synthesized and determined by means of NMR spectroscopy, high resolution mass spectra and single-crystal X-ray diffraction. The single crystal belongs to the monoclinic system, space group Cc with a = 14.910(3), b = 14.592(3), c = 38.683(8) Å, β = 100.37(3)°, V = 8279(3) Å3, Z = 16, Dc = 1.183 g/cm3, F(000) = 3168, μ = 0.079 mm-1, MoKα radiation (λ = 0.71073 Å), the final R = 0.0508 and wR = 0.0666 for 4120 observed reflections with I > 2σ(I). There are four independent molecules in an asymmetric unit cell. The four symmetry-independent molecules have a variety of different conformations indicating considerable conformational freedom. The bioassay results indicated that the title compound displayed effective activities against glutamine-induced neurotoxicity in PC12 cells and significantly prolonged the survival time of mice subjected to acute cerebral ischemia.
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: Orthorhombic AgInS2 nanoplate and nanoparticle were synthesized using pyridine and 1-dodecanethiol as the solvent. The obtained products were characterized by X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), field-emission transmission electron microscope (FETEM), and the possible growth mechanism of AgInS2 was also proposed by the exploration of reaction temperature and time. Meanwhile, the bandgap of AgInS2 was calculated by the UV-Vis diffuse reflectance spectrum, and the photocatalytic activity was also investigated. Those experimental results indicate that the reaction temperature, reaction time and solvent have an influence on phase and morphology of AgInS2, and both AgInS2 nanoplate and nanoparticle have some ability on photocatalytic degradation of organic dyes under UV-Vis light irradiation.
分类: 核科学技术 >> 粒子加速器 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: Microstructure and oxidation behavior of modified Ni-16Mo-7Cr-4Fe alloys by yttrium microalloying were investigated by scanning electron microscopy, transmission electron microscopy, grazing incident X-ray diffraction and synchrotron radiation X-ray fluorescence. M6C and Ni17Y2 phases were observed and the amount of Ni17Y2 increased with yttrium concentration. When the yttrium concentration increased to 0.43wt.%, some Ni17Y2 chains and multi phase regions containing Ni17Y2, M6C and phase appeared, which is harmful for the oxidation resistance. The alloy containing 0.05wt.% yttrium showed the best oxidation resistance, which derives its oxidation resistance from the adequate concentration of yttrium in the solid-solution ( phase), the formation of the protective layer of YCrO3 and chromia oxide and the strengthening effect of yttrium on oxide boundaries.
分类: 核科学技术 >> 粒子加速器 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: Beamline BL16B1 at Shanghai Synchrotron Radiation Facility (SSRF) is dedicated to small angle X-ray scattering (SAXS) study. It aims at probing microstructure and dynamic processes of polymers, nanomaterials, mesoporous materials, colloids, liquid crystals, metal materials, etc. At present, SAXS, wide angle X-ray scattering (WAXS), simultaneous SAXS/WAXS, grazing incident SAXS, and anomalous SAXS techniques are available. The sample-to-detector distance is adjustable from 0.2 m to 5 m. For conventional SAXS, the practicable q-range is from 0.033.6 nm-1 at incident X-ray of 10 keV. A continuous q-region of 0.0633 nm-1 can be achieved in simultaneous SAXS/WAXS mode. Time-resolved SAXS measurements in sub-second level can be performed. Detailed descriptions about status, performance and application of the SAXS beamline are given in this paper.
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: 核科学技术 >> 粒子加速器 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: The X-ray diffraction beamline developed at Shanghai Synchrotron Radiation Facility (SSRF)is located at the BL14B1 bending magnet port of the 3.5 GeV storage ring. The beamline optics is based on a collimating mirror, a sagittally focused double crystal monochromator and a focusing mirror. Photon flux of 4.43�1011 phs/s at 10 keV is obtained. The primary instrument equipped in the experimental end-station is a Huber 5021 six-cycle diffractometer. BL14B1 is a general purpose X-ray diffraction beamline and focused on material science, condensed matter physics and other relevant fields looking for structural information.
分类: 物理学 >> 核物理学 提交时间: 2016-09-13
摘要: The neutrino detector of the Jiangmen Underground Neutrino Observatory (JUNO) is designed to use 20 kilotons of liquid scintillator and approximately 16,000 20-inch photomultipliers (PMTs).One of the options is to use the 20-inch R12860 PMT with high quantum efficiency which has recently been developed by Hamamatsu Photonics. The performance of the newly developed PMT preproduction samples is evaluated. The results show that its quantum efficiency is�0%燼t�00nm. Its Peak/Valley (P/V) ratio for the single photoelectron is 4.75 and the dark count rate is�7kHz燼t the threshold of 3 mV while the gain is at��07. The transit time spread of a single photoelectron is2.86ns. Generally the performances of this new 20-inch PMT are improved over the old one of R3600.
提交时间: 2017-05-02
摘要: Two types of flexible terahertz metamaterials were fabricated on polyethylene naphthalate [PEN] substrates. The unit cell of one type consists of two identical split-ring resonators [SRRs] that are arranged face-to-face [i.e., FlexMetaF]; the unit cell of