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: 2017-11-10
摘要: We study the excited B mesons' contributions to the coupled-channel e ects under the framework of the 3P0 model for the bottomonium. Contrary to what has been widely accepted, the contributions of P wave B mesons are generally the largest, and to some extent, this result is independent of the potential parameters. We also push the calculation beyond B(1P) and carefully analyze the contributions of B(2S). A form factor is a key ingredient to suppress the contributions of B(2S) for low lying bottomonia. However, this suppression mechanism is not e cient for highly excited bottomonia, such as (5S) and (6S). We give explanations why this di culty happens to the 3P0 model and suggest analyzing the ux-tube breaking model for the full calculation of coupled-channel e ects.
分类: 物理学 >> 核物理学 提交时间: 2016-09-06
摘要: With Gaussian expansion method (GEM), realistic wave functions are used to calculate coupled-channel effects for the bottomonium under the framework of 3P0 model. The simplicity and accuracy of GEM are explained. We calculate the mass shifts, probabilities of the B meson continuum, S−D mixing angles, strong and dielectric decay widths. Our calculation shows that both S−D mixing and the B meson continuum can contribute to the suppression of the vector meson's dielectric decay width. We suggest more precise measurements on the radiative decays of Υ(10580) and Υ(11020) to distinguish these two effects. The above quantities are also calculated with simple harmonic oscillator (SHO) wave function approximation for comparison. The deviation between GEM and SHO indicates that it is essential to treat the wave functions accurately for near threshold states.
分类: 生物学 >> 生物物理学 提交时间: 2016-05-12
摘要: The prokaryotic mechanosensitive channel of large conductance (MscL) is a pressure-relief valve protecting the cell from lysing during acute osmotic downshock. When the membrane is stretched, MscL responds to the increase of membrane tension and opens a nonselective pore to about 30 angstrom wide, exhibiting a large unitary conductance of similar to 3 nS. A fundamental step toward understanding the gating mechanism of MscL is to decipher the molecular details of the conformational changes accompanying channel opening. By applying fusion-protein strategy and controlling detergent composition, we have solved the structures of an archaeal MscL homolog from Methanosarcina acetivorans trapped in the closed and expanded intermediate states. The comparative analysis of these two new structures reveals significant conformational rearrangements in the different domains of MscL. The large changes observed in the tilt angles of the two transmembrane helices (TM1 and TM2) fit well with the helix-pivoting model derived from the earlier geometric analyses based on the previous structures. Meanwhile, the periplasmic loop region transforms from a folded structure, containing an.-shaped loop and a short beta-hairpin, to an extended and partly disordered conformation during channel expansion. Moreover, a significant rotating and sliding of the N-terminal helix (N-helix) is coupled to the tilting movements of TM1 and TM2. The dynamic relationships between the N-helix and TM1/TM2 suggest that the N-helix serves as a membrane-anchored stopper that limits the tilts of TM1 and TM2 in the gating process. These results provide direct mechanistic insights into the highly coordinated movement of the different domains of the MscL channel when it expands.
分类: 生物学 >> 植物学 >> 植物细胞学与植物遗传学、植物形态学 提交时间: 2016-05-03
摘要: Jasmonates (JAs) are rapidly induced after wounding and act as key regulators for wound induced signaling pathway. However, what perceives the wound signal and how that triggers JA biosynthesis remains poorly understood. To identify components involved in Arabidopsis wound and JA signaling pathway, we screened for mutants with abnormal expression of a luciferase reporter, which is under the control of a wound-responsive promoter of an ethylene response factor (ERF) transcription factor gene, RAP2.6 (Related to APetala 2.6). The rea1 (R
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 control system of SSRF (Shanghai Synchrotron Radiation Facility) is based on EPICS (Experimental Physics and Industrial Control System). Operation data storage for synchrotron radiation facility is important for its status monitoring and analysis. At SSRF, operation data used to be index files recorded by traditional EPICS Channel Archiver. Nevertheless, index files are not suitable for long-term maintenance and difficult for data analysis. Now, RDB Channel Archiver and MySQL are used for SSRF beamline operation data archiving, so as to promote the data storage reliability and usability. By applying a new uploading mechanism to RDB Channel Archiver, its writing performance is improved. A web-based GUI (Graphics User Interface) is also developed to make it easier to access database.
分类: 生物学 >> 植物学 >> 植物生理学 提交时间: 2016-05-03
摘要: During photosynthesis, photosynthetic electron transport generates a proton motive force (pmf) across the thylakoid membrane, which is used for ATP biosynthesis via ATP synthase in the chloroplast. The pmf is composed of an electric potential () and an osmotic component (pH). Partitioning between these components in chloroplasts is strictly regulated in response to fluctuating environments. However, our knowledge of the molecular mechanisms that regulate pmf partitioning is limited. Here, we report a bestrophin-like protein (AtBest), which is critical for pmf partitioning. While the pH component was slightly reduced in atbest, the component was much greater in this mutant than in the wild type, resulting in less efficient activation of nonphotochemical quenching (NPQ) upon both illumination and a shift from low light to high light. Although no visible phenotype was observed in the atbest mutant in the greenhouse, this mutant exhibited stronger photoinhibition than the wild type when grown in the field. AtBest belongs to the bestrophin family proteins, which are believed to function as chloride (Cl) channels. Thus, our findings reveal an important Cl channel required for ion transport and homeostasis across the thylakoid membrane in higher plants. These processes are essential for fine-tuning photosynthesis under fluctuating environmental conditions.
分类: 物理学 >> 核物理学 提交时间: 2024-02-07
摘要: We report on using synthetic silicon for a high-precision X-ray polarimeter comprising a polarizer and an analyzer, each based on a monolithic channel-cut crystal used at multiple Brewster reflections with a Bragg angle very close to 45. Experiments were performed at the BL09B bending magnet beamline of the Shanghai Synchrotron Radiation Facility using a Si(800) crystal at an X-ray energy of 12.914 keV. A polarization purity of 8.410-9was measured. This result is encouraging, as the measured polarization purity is the best-reported value for the bending magnet source. Notably, this is the firstly systematic study on the hard X-ray polarimeter in China, which is crucial for exploring new physics, such as verifying vacuum birefringence.
分类: 物理学 >> 核物理学 提交时间: 2024-02-05
摘要: The feasibility of producing superheavy nuclei in proton evaporation channels was systematically studied within the dinuclear system (DNS) model. Due to the Z=114 proton-shell, one can synthesize Fl isotopes in proton evaporation channels. We only considered the case of evaporating one proton first and then n neutrons in this work, other cases were ignored due to the small cross-section. The production cross sections of unknown isotopes 290,291Fl in 38S+255Es reaction are the highest compared with 50Ti+243Np and 54Cr+239Pa reactions, and the maximum cross sections are 1.1 and 15.1 pb, respectively. 42S+254Es is a promising candidate to approach the island of stability as the radioactive beam facilities are upgraded in the future, and the production cross sections of 291294Fl in that reaction are estimated to be 3.2, 6.0, 4.0, and 0.1 pb, respectively.
分类: 生物学 >> 生态学 提交时间: 2017-11-17
摘要: Followed pharmacological evaluation exposed an extensive hepatic first pass effect within our recently disclosed DPP-IV inhibitors bearing thienopyrimidine scaffold. Through scaffold replacement with pyrrolopyrimidine, compound 1a had substantially improved the metabolic stability (from 6.6% to 65.07%), yet with severely poor absorptive property. Further modification by incorporation with varied substituents and structure conversion yielded both permeable and metabolic stable compounds. The whole pharmacokinetic- property based optimization had succeeded in balancing overall properties and resulted in the compound 1j, that with excellent efficacy to be a potential anti-diabetic candidate.
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: 2017-11-02 合作期刊: 《热科学学报》
摘要: The efficiency, robustness and reliability of recent numerical methods for finding solutions to flow problems have given rise to the implementation of computational fluid dynamics (CFD) as a broadly used analysis method for engineering problems like membrane separation system. The CFD modeling in this study observes steady and unsteady (transient) heat flux and temperature profiles in a polymeric (cellulose acetate) membrane. This study is novel due to the implementation of user defined scalar (LIDS) diffusion equation by using user-defined functions (UDFs) infinite volume method (FVM). Some details of the FVM used by the solver are carefully discussed when implementing terms in the governing equation and boundary conditions (BC). The contours of temperature due to high-temperature gradient are reported for steady and unsteady problems.
分类: 生物学 >> 生物物理学 >> 细胞生物学 提交时间: 2016-05-12
摘要: Mitochondrial calcium uniporter (MCU) is a conserved Ca2+ transporter at mitochondrial in eukaryotic cells. However, the role of MCU protein in oxidative stress-induced cell death remains unclear. Here, we showed that ectopically expressed MCU is mitochondrial localized in both HeLa and primary cerebellar granule neurons (CGNs). Knockdown of endogenous MCU decreases mitochondrial Ca2+ uptake following histamine stimulation and attenuates cell death induced by oxidative stress in both HeLa cells and CGNs. We also found MCU interacts with VDAC1 and mediates VDAC1 overexpression-induced cell death in CGNs. This finding demonstrates that MCU-VDAC1 complex regulates mitochondrial Ca2+ uptake and oxidative stress-induced apoptosis, which might represent therapeutic targets for oxidative stress related diseases.
分类: 物理学 分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-12-28
摘要: We evaluate the supersymmetric QCD corrections to single top quark production via qq?′→tb?qq?′→tb?q \bar q'\to t \bar b at the Fermilab Tevatron in the minimal supersymmetric model. We find that within the allowed range of squark and gluino masses the sup
分类: 物理学 分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-12-28
摘要: We have calculated the O(αewMt 2/MW 2)O(αewMt 2/MW 2)O(\alpha_{ew} M_t~2/M_W~2) supersymmetric electroweak corrections to single top quark production via qq?′→tb?qq?′→tb?q\bar q' \to t\bar b at the Fermilab Tevatron in the minimal supersymmetric model. Th
分类: 物理学 分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-12-28
摘要: We evaluate the top-quark FCNC productions induced by the topcolor assisted technicolor (TC2) model at the LHC. These productions proceed respectively through the parton-level processes g g -> t c_bar, c g->t, c g -> t g, c g -> t Z and c g -> t \gamma. W
分类: 物理学 分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-12-28
摘要: We investigate the ability of single top quark production via qq'-> squark->tb and q \bar q'->slepton->t\bar b at the LHC and Tevatron to probe the strength of R-parity violating couplings in the minimal supersymmetric model. We found that given the exist
分类: 物理学 分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-12-28
摘要: The light stop if produced in hadron colliders in the form of t ̃ t ̄ ̃ pair and decaying through the likely decay chain t ̃ →χ ̃+bfollowedbyχ ̃+ →χ ̃0ff ̄′,can mimic closely a 1 top quark event when the mass of the stop is close to that of the top quark. Because of the much lower production rate, the stop event can be buried under the top quark event sample. In order to uncover the stop event, specific selection cuts need to be applied. Through Monte Carlo simulation with suitable kinematic cuts, we found that such stop event can be extracted from the top quark sample and detected by the top counting experiments in the upcoming upgraded Tevatron and LHC. However, because of the small statistics of the Run 1 of the Tevatron, the stop signal remains hidden at Run 1.
分类: 物理学 分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-12-28
摘要: In the littlest Higgs model with T-parity, which predicts a pair of T-even and T-odd partners for the top quark, the top quark interactions are altered with respect to the Standard Model predictions and deviation will manifest in various top quark process
分类: 物理学 分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-12-28
摘要: In the minimal supersymmetric model the R-parity violating top quark interactions, which are so far weakly constrained, can induce various flavor-changing neutral-current (FCNC) productions for the top quark at the Large Hadron Collider (LHC). In this wor
分类: 物理学 分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-12-28
摘要: We examine the possibility of observing exotic top quark decays via R-violating SUSY interactions at the Fermilab Tevatron and CERN LHC. We present cross-sections for tt?tt?t\bar t production followed by the subsequent decay of either ttt or t?t?\bar t vi
分类: 物理学 分类: 物理学 >> 基本粒子与场物理学 提交时间: 2016-12-28
摘要: We examine the possibility of observing exotic top quark decays via RRR-Parity violating SUSY interactions in e+e?e+e?e^+e^- collisions at \sqrt{s = 500 GeV\sqrt{s = 500 GeV\sqrt{s = 500 GeV. We present cross-sections for tt?tt?t\bar t production followed