分类: 地球科学 >> 空间物理学 提交时间: 2016-12-22
摘要: In a recent paper, arXiv:1309.4877, a holographic p-wave model has been proposed in an Einstein Maxwell-complex vector field theory with a negative cosmological constant. The model exhibits rich phase structure depending on the mass and the charge of the vector field. We investigate the behavior of the entanglement entropy of dual field theory in this model. When the above two model parameters change, we observe the second order, first order and zeroth order phase transitions from the behavior of the entanglement entropy at some intermediate temperatures. These imply that the entanglement entropy can indicate not only the occurrence of the phase transition, but also the order of the phase transition. The entanglement entropy is indeed a good probe to phase transition. Furthermore, the "retrograde condensation" which is a sub-dominated phase is also reflected on the entanglement entropy. (C) 2015 The Authors. Published by Elsevier B.V.
分类: 其他 >> 综合 提交时间: 2023-03-12 合作期刊: 《Art & Design Research》
摘要: Terrace is a farming way for human beings to adapt to nature and comply with the trend. In recent years, with the development of economy and tourism, the protection of terrace cultural landscape has gradually come into people's field of vision, this paper retrieves the relevant literature from CNKI and selects the highly relevant literature, and extracts the hot keywords through Citespace to the author organization and key words in the research field. This paper summarizes the research and comments on the number of articles in the protection for terrace cultural landscape, summarizes it from the aspects of policy, science and technology, tourism and so on, and puts forward the protection policy of terrace cultural landscape in the future.
分类: 物理学 >> 核物理学 提交时间: 2016-09-02
摘要: In this paper, we study the properties of the twist-3 distribution amplitude (DA) of the heavy pseudo-scalars such as ηc, Bc and ηb. New sum rules for the twist-3 DA moments ⟨ξnP⟩HP and ⟨ξnσ⟩HP up to sixth orders and up to dimension-six condensates are deduced under the framework of the background field theory. Based on the sum rules for the twist-3 DA moments, we construct a new model for the two twist-3 DAs of the heavy pseudo-scalar with the help of the Brodsky-Huang-Lepage prescription. Furthermore, we apply them to the Bc→ηc transition form factor (fBc→ηc+(q2)) within the light-cone sum rules approach, and the results are comparable with other approaches. It has been found that the twist-3 DAs ϕP3;ηc and ϕσ3;ηc are important for a reliable prediction of fBc→ηc+(q2). For example, at the maximum recoil region, we have fBc→ηc+(0)=0.674±0.066, in which those two twist-3 terms provide ∼33% and ∼22% contributions. Also we calculate the branching ratio of the semi-leptonic decay Bc→ηclν as Br(Bc→ηclν)=(9.31+2.27−2.01)×10−3.
分类: 物理学 >> 核物理学 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: We report our recent work on mean-field potential effects on the elliptic flows of matters and antimatters in heavy ion collisions leading to the production of a baryon-rich matter. Within the framework of a multiphase transport (AMPT) model that includes both initial partonic and final hadronic interactions, we have found that including mean-field potentials in the hadronic phase leads to a splitting of the elliptic flows of particles and their antiparticles, providing thus a plausible explanation of the different elliptic flows between p and anti-p, K+ and K, and + and observed by the STAR Collaboration in the Beam Energy Scan (BES) program at the Relativistic Heavy Ion Collider (RHIC). Using a partonic transport model based on the Nambu-Jona-Lasinio (NJL) model, we have also studied the effect of scalar and vector mean fields on the elliptic flows of quarks and antiquarks in these collisions. Converting quarks and antiquarks at hadronization to hadrons via the quark coalescence model, we have found that the elliptic flow differences between particles and antiparticles also depend on the strength of the quark vector coupling in baryon-rich quark-gluon plasma, providing thus the possibility of extracting information on the latters properties from the BES program at RHIC.
分类: 物理学 >> 核物理学 提交时间: 2023-05-16
摘要: N/A
分类: 天文学 >> 天文学 提交时间: 2017-10-20 合作期刊: 《天文研究与技术》
摘要: With long-term hard X-ray monitoring,observations on high mass X-ray binary GX 301-2 from 2003一2011 performed by INTEGRAL/IBIS,we first systematically studied its spectral properties in different accreting luminosities and orbital phases. The cyclotron resonant scattering feature(CRSF) at energies from 35一47 keV was detected in the hard X-ray spectra,suggesting the magnetic field of Sx10}Z Gs. The variations of the CRSF show no relation to the X-ray luminosity while the line centroid energy of the CRSF has a positive correlation to the photon index and spectral cutoff energy,and there also exists a weak correlation between the absorption depth and cutoff energy. These relations support the idea that the spectral cutoff in accreting X-ray pulsars is strongly affected by the cyclotron resonant scattering. The correlation between the ratio of the line width to the centroid energy and absorption depth implies a tall cylindrical accreting column on the surface of the neutron star in GX 301-2. The explanation of the long spin period in GX 301-2 requires a strong surface magnetic field at least higher than 2x 1014 Gs which is contradict with the measured value based on the cyclotron line energy. The line-forming region with a height at least larger than two neutron star radii is proposed to resolve the contradiction. This scenario is supported by the tall cylindrical accreting column on the neutron star surface in GX 301-2 according to the variation patterns of the CRSF. In addition,the possible evolution scenario of accreting magnetars like GX 301-2 is briefly discussed,and GX 301-2 would he an accreting magnetar in the equivalence phase.
分类: 地球科学 >> 空间物理学 提交时间: 2016-05-13
摘要: We investigate equilibrium height of a flux rope, and its internal equilibrium in a realistic plasma environment by carrying out numerical simulations of the evolution of systems including a current-carrying flux rope. We find that the equilibrium height of a flux rope is approximately described by a power-law function of the relative strength of the background field. Our simulations indicate that the flux rope can escape more easily from a weaker background field. This further confirms that a catastrophe in the magnetic configuration of interest can be triggered by a decrease in strength of the background field. Our results show that it takes some time to reach internal equilibrium depending on the initial state of the flux rope. The plasma flow inside the flux rope due to the adjustment for the internal equilibrium of the flux rope remains small and does not last very long when the initial state of the flux rope commences from the stable branch of the theoretical equilibrium curve. This work also confirms the influence of the initial radius of the flux rope in its evolution;the results indicate that a flux rope with a larger initial radius erupts more easily. In addition, by using a realistic plasma environment and a much higher resolution in our simulations, we notice some different characteristics compared to previous studies in Forbes.
分类: 地球科学 >> 空间物理学 提交时间: 2016-05-12
摘要: We present high-resolution observations of a quiescent solar prominence that consists of a vertical and a horizontal foot encircled by an overlying spine and has ubiquitous counter-streaming mass flows. While the horizontal foot and the spine were connected to the solar surface, the vertical foot was suspended above the solar surface and was supported by a semicircular bubble structure. The bubble first collapsed, then reformed at a similar height, and finally started to oscillate for a long time. We find that the collapse and oscillation of the bubble boundary were tightly associated with a flare-like feature located at the bottom of the bubble. Based on the observational results, we propose that the prominence should be composed of an overlying horizontal spine encircling a low-lying horizontal and vertical foot, in which the horizontal foot consists of shorter field lines running partially along the spine and has ends connected to the solar surface, while the vertical foot consists of piling-up dips due to the sagging of the spine fields and is supported by a bipolar magnetic system formed by parasitic polarities (i.e., the bubble). The upflows in the vertical foot were possibly caused by the magnetic reconnection at the separator between the bubble and the overlying dips, which intruded into the persistent downflow field and formed the picture of counter-streaming mass flows. In addition, the counter-streaming flows in the horizontal foot were possibly caused by the imbalanced pressure at the both ends.
分类: 地球科学 >> 空间物理学 提交时间: 2016-05-12
摘要: We study the role of the coronal magnetic field configuration of an active region (AR) in determining the propagation direction of a coronal mass ejection (CME). The CME occurred in the AR 11944 (S09W01) near the disk center on 2014 January 7 and was associated with an X1.2 flare. A new CME reconstruction procedure based on a polarimetric technique is adopted, which shows that the CME changed its propagation direction by around 28 degrees in latitude within 2.5 R-circle dot and 43 degrees in longitude within 6.5 R-circle dot with respect to the CME source region. This significant non-radial motion is consistent with the finding of Mostl et al. We use nonlinear force-free field and potential field source surface extrapolation methods to determine the configurations of the coronal magnetic field. We also calculate the magnetic energy density distributions at different heights based on the extrapolations. Our results show that the AR coronal magnetic field has a strong influence on the CME propagation direction. This is consistent with the "channeling" by the AR coronal magnetic field itself, rather than deflection by nearby structures. These results indicate that the AR coronal magnetic field configuration has to be taken into account in order to determine CME propagation direction correctly.
分类: 地球科学 >> 空间物理学 提交时间: 2016-05-12
摘要: Standing sausage modes in flare loops are important for interpreting quasi-periodic pulsations(QPPs) in solar flare light curves. We propose an inversion scheme that consistently uses their periods P and damping times tau to diagnose flare loop parameters. We derive a generic dispersion relation governing linear sausage waves in pressure-less straight tubes, for which the transverse density inhomogeneity takes place in a layer of arbitrary width l and is of arbitrary form. We find that P and tau depend on the combination of [R/nu(Ai), L/R, l/R, rho(i)/rho(e)], where R is the loop radius, L is the looplength, nu(Ai) is the internal Alfven speed, and rho(i)/rho(e) is the density contrast. For all the density profiles examined, P and tau experience saturation when L/R >> 1, yielding an inversion curve in the [R/nu(Ai), l/R, rho(i)/rho(e)] space with a specific density profile when L/R is sufficiently large. When applied to a spatially unresolved QPP event, the scheme yields that R/nu(Ai) is the best constrained, whereas l/R corresponds to the other extreme. For spatially resolved QPPs, while L/R >> 1 cannot be assumed beforehand, an inversion curve remains possible due to additional geometrical constraints. When a spatially resolved QPP event involves another mode, as is the case for a recent event, the full set of [nu(Ai), l, rho(i)/rho(e)] can be inferred. We conclude that the proposed scheme provides a useful tool for magneto-seismologically exploiting QPPs.
分类: 地球科学 >> 空间物理学 提交时间: 2016-05-12
摘要: The solar wind is observed to display high speeds in high heliolatitude coronal holes and low speeds near the ecliptic plane. The heliospheric magnetic field associated with the solar wind plays a very important role in the transport and modulation of charged energetic particles, including galactic cosmic rays (GCRs) and solar energetic particles (SEPs), in the three-dimensional heliosphere. In previous studies, a constant solar wind speed, which is independent of heliolatitude, was assumed and commonly used in modulation modeling of cosmic rays. In this work, we investigate the realistic latitudinally dependent solar wind speed and utilize the theoretical models in hyperbolic and piecewise polynomial forms to explore the important effects on the heliospheric magnetic field and the diffusion coefficients (parallel, perpendicular, and drift scale) of cosmic rays in the presence of adiabatic focusing. Comparisons of the diffusion coefficients derived from standard Parker field and modified magnetic fields are presented. Since the structures and properties of different solar wind sources (coronal streamer belt, polar coronal hole, and transition region between them) differ from each other in essence, we suggest that the latitudinally dependent solar wind speed and the corresponding heliospheric magnetic field and diffusion coefficients with adiabatic focusing should be employed in the global modeling studies of GCRs and SEPs in the heliosphere.
分类: 物理学 >> 核物理学 提交时间: 2016-09-13
摘要: We model the evolution of the spin frequency's second derivative ν¨ and the braking index n of radio pulsars with simulations within the phenomenological model of their surface magnetic field evolution, which contains a long-term power-law decay modulated by short-term oscillations. For the pulsar PSR B0329+54, a model with three oscillation components can reproduce its ν¨ variation. We show that the "averaged" n is different from the instantaneous n, and its oscillation magnitude decreases abruptly as the time span increases, due to the "averaging" effect. The simulated timing residuals agree with the main features of the reported data. Our model predicts that the averaged ν¨ of PSR B0329+54 will start to decrease rapidly with newer data beyond those used in Hobbs et al.. We further perform Monte Carlo simulations for the distribution of the reported data in |ν¨| and |n| versus characteristic age τc diagrams. It is found that the magnetic field oscillation model with decay index α=0 can reproduce the distributions quite well. Compared with magnetic field decay due to the ambipolar diffusion (α=0.5) and the Hall cascade (α=1.0), the model with no long term decay (α=0) is clearly preferred for old pulsars by the p-values of the two-dimensional Kolmogorov-Smirnov test.
分类: 地球科学 >> 空间物理学 提交时间: 2016-12-26
摘要: We study the solar energetic particle (SEP) event associated with the 2012 July 23 extreme solar storm, for which Solar Terrestrial Relations Observatory (STEREO) and the spacecraft at L1 provide multi-point remote sensing and in situ observations. The extreme solar storm, with a superfast shock and extremely enhanced ejecta magnetic fields observed near 1 au at STEREO A, was caused by the combination of successive coronal mass ejections (CMEs). Meanwhile, energetic particles were observed by STEREO and near-Earth spacecraft such as the Advanced Composition Explorer and SOlar and Heliospheric Observatory, suggesting a wide longitudinal spread of the particles at 1 au. Combining the SEP observations with in situ plasma and magnetic field measurements, we investigate the longitudinal distribution of the SEP event in connection with the associated shock and CMEs. Our results underscore the complex magnetic configuration of the inner heliosphere formed by solar eruptions. Examination of particle intensities, proton anisotropy distributions, element abundance ratios, magnetic connectivity, and spectra also gives important clues for particle acceleration, transport, and distribution.
分类: 地球科学 >> 空间物理学 提交时间: 2016-05-12
摘要: We numerically study the detailed evolutionary features of the wave-like disturbance and its propagation in the eruption. This work is a follow-up to Wang et al., using significantly upgraded new simulations. We focus on the contribution of the velocity vortices and the fast shock reflection and refraction in the solar corona to the formation of the EUV waves. Following the loss of equilibrium in the coronal magnetic structure, the flux rope exhibits rapid motions and invokes the fast-mode shock at the front of the rope, which then produces a type II radio burst. The expansion of the fast shock, which is associated with outward motion, takes place in various directions, and the downward expansion shows the reflection and the refraction as a result of the non-uniform background plasma. The reflected component of the fast shock propagates upward and the refracted component propagates downward. As the refracted component reaches the boundary surface, a weak echo is excited. The Moreton wave is invoked as the fast shock touches the bottom boundary, so the Moreton wave lags the type II burst. A secondary echo occurs in the area where reflection of the fast shock encounters the slow-mode shock, and the nearby magnetic field lines are further distorted because of the interaction between the secondary echo and the velocity vortices. Our results indicate that the EUV wave may arise from various processes that are revealed in the new simulations.
分类: 物理学 >> 核物理学 提交时间: 2016-08-31
摘要: In this article we study spontaneous chiral symmetry breaking for quark matter in the background of static and homogeneous parallel electric field $\bm E$ and magnetic field $\bm B$. We use a Nambu-Jona-Lasinio model with a local kernel interaction to compute the relevant quantities to describe chiral symmetry breaking at finite temperature for a wide range of E and B. We study the effect of this background on inverse catalysis of chiral symmetry breaking for E and B of the same order of magnitude. We then focus on the effect of equilibration of chiral density, n5, produced dynamically by axial anomaly on the critical temperature. The equilibration of n5, a consequence of chirality flipping processes in the thermal bath, allows for the introduction of the chiral chemical potential, μ5, which is computed self-consistently as a function of temperature and field strength by coupling the number equation to the gap equation, and solving the two within an expansion in E/T2, B/T2 and μ25/T2. We find that even if chirality is produced and equilibrates within a relaxation time τM, it does not change drastically the thermodynamics, with particular reference to the inverse catalysis induced by the external fields, as long as the average μ5 at equilibrium is not too large.
分类: 地球科学 >> 空间物理学 提交时间: 2016-05-12
摘要: This paper investigates the onset time of solar energetic particle (SEP) events with numerical simulations and analyzes the accuracy of the velocity dispersion analysis (VDA) method. Using a three-dimensional focused transport model, we calculate the fluxes of protons observed in the ecliptic at 1 AU in the energy range between 10 MeV and 80 MeV. In particular, three models are used to describe different SEP sources produced by flare or coronal shock, and the effects of particle perpendicular diffusion in the interplanetary space are also studied. We have the following findings. When the observer is disconnected from the source, the effects of perpendicular diffusion in the interplanetary space and particles propagating in the solar atmosphere have a significant influence on the VDA results. As a result, although the VDA method is valid with impulsive source duration, low background, and weak scattering in the interplanetary space or fast diffusion in the solar atmosphere, the method is not valid with gradual source duration, high background, or strong scattering.
分类: 生物学 >> 生物物理学 提交时间: 2016-05-11
摘要: Luminance and contrast are two major attributes of objects in the visual scene. Luminance and contrast information received by visual neurons are often updated simultaneously. We examined the temporal response properties of neurons in the primary visual cortex (V1) to stimuli whose luminance and contrast were simultaneously changed by 50 Hz. We found that response tuning to luminance changes precedes tuning to contrast changes in V1. For most V1 neurons, the onset time of response tuning to luminance changes was shorter than that to contrast changes. Most neurons carried luminance information in the early response stage, while all neurons carried both contrast and luminance information in the late response stage. The early luminance response suggests that cortical processing for luminance is not as slow as previously thought.
分类: 物理学 >> 交叉学科物理及相关领域的科学与技术 提交时间: 2016-05-03
摘要: Inherited the advantages of inorganic salts and organic solvents, ionic liquids (ILs) exhibit many superior properties allowing them promising green solvents for the future. Although it has been widely acknowledged that the unique features of ILs originate from their dual ionic and organic nature, its microscopic physical origin still remains blurry. In this work, by comparing the ion/molecule cage structures obtained from molecular dynamics simulations for seven prototypic liquids-a molten inorganic salt, four ILs, a strongly polar organic solvent, and a weakly polar organic solvent, we have revealed that the depth of the cage energy landscape characterizes the ionic nature of ILs, whereas the slope and curvature of its mimimum determine the organic nature of ILs. This finding advances our understanding of ILs and thus will help their efficient utilization as well as the systematic design of novel functionalized ILs.