摘要： The research achievements of China's higher vocational art and design professional project course include: first, it demonstrates the role and significance of China's higher vocational art and design professional program courses from multiple perspectives; second, it introduces China's higher vocational art and design professional program courses in detail. The third is to clearly point out the problems existing in the development of China's higher vocational art and design professional project courses; the fourth is to condense the construction strategy of China's higher vocational art and design professional project courses. Looking forward to the future, we still need to do: first, strengthen theoretical research and improve the accuracy of research; second, carry out systematic research and broaden research directions; third, enrich research methods and attach importance to empirical research.
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： The study of hyperon decays at the Beijing Electron Spectrometer III (BESIII) is proposed to investigate the events of J/ψ decay into hyperon pairs, which provide a pristine experimental environment at the Beijing Electron–Positron Collider II. About 106–108 hyperons, i.e., Λ, Σ, Ξ, and Ω, will be produced in the J/ψ and ψ(2S) decays with the proposed data samples at BESIII. Based on these samples, the measurement sensitivity of the branching fractions of the hyperon decays is in the range of 10−5–10−8. In addition, with the known center-of-mass energy and “tag technique,” rare decays and decays with invisible final states can be probed.
分类： 生物学 >> 植物学 >> 植物生态学和植物地理学 提交时间： 2016-05-04
摘要： Environmental or ecological footprints have been widely used in recent years as indicators of resource consumption and waste absorption presented in terms of biologically productive land area [in global hectares (gha)] required per capita with prevailing technology. In contrast, carbon footprints are the amount of carbon (or carbon dioxide equivalent) emissions for such activities in units of mass or weight (like kilograms per functional unit), but can be translated into a component of the environmental footprint (on a gha basis). The carbon and environmental footprints associated with the world production of liquid biofuels have been computed for the period 20102050. Estimates of future global biofuel production were adopted from the 2011 International Energy Agency (IEA) technology roadmap for transport biofuels. This suggests that, although first generation biofuels will dominate the market up to 2020, advanced or second generation biofuels might constitute some 75% of biofuel production by 2050. The overall environmental footprint was estimated to be 0.29 billion (bn) gha in 2010 and is likely to grow to around 2.57 bn gha by 2050. It was then disaggregated into various components: bioproductive land, built land, carbon emissions, embodied energy, materials and waste, transport, and water consumption. This component-based approach has enabled the examination of the Manufactured and Natural Capital elements of the four capitals model of sustainability quite broadly, along with specific issues (such as the linkages associated with the so-called energylandwater nexus). Bioproductive land use was found to exhibit the largest footprint component (a 48% share in 2050), followed by the carbon footprint (23%), embodied energy (16%), and then the water footprint (9%). Footprint components related to built land, transport and waste arisings were all found to account for an insignificant proportion to the overall environmental footprint, together amounting to only about 2%
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Sausage modes are one leading mechanism for interpreting short period quasi-periodic pulsations (QPPs) of solar flares. Forward modeling their radio emission is crucial for identifying sausage modes observationally and for understanding their connections with QPPs. Using the numerical output from three-dimensional magnetohydrodynamic (MHD) simulations, we forward model the gyrosynchrotron (GS) emission of flare loops modulated by sausage modes and examine the influence of loop fine structures. The temporal evolution of the emission intensity is analyzed for an oblique line of sight crossing the loop center. We find that the low- and high-frequency intensities oscillate in-phase at the period of sausage modes for models with or without fine structures. For low-frequency emissions where the optically thick regime arises, the modulation magnitude of the intensity is dramatically reduced by the fine structures at some viewing angles. On the contrary, for high-frequency emissions where the optically thin regime holds, the effect of fine structures or viewing angle is marginal. Our results show that the periodic intensity variations of sausage modes are not wiped out by the fine structures, and sausage modes remains a promising candidate mechanism for QPPs even when flare loops are fine-structured.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Fast sausage modes (FSMs) in flare loops have long been invoked to account for rapid quasi-periodic pulsations (QPPs) with periods of order seconds in flare lightcurves. However, most theories of FSMs in solar coronal cylinders assume a perfectly axisymmetric equilibrium, an idealized configuration apparently far from reality. In particular, it remains to examine whether FSMs exist in coronal cylinders with fine structures. Working in the framework of ideal magnetohydrodynamics (MHD), we numerically follow the response to an axisymmetric perturbation of a coronal cylinder for which a considerable number of randomly distributed fine structures are superposed on an axisymmetric background. The parameters for the background component are largely motivated by the recent IRIS identification of a candidate FSM in Fe XXI 1354 \AA~observations. We find that the composite cylinder rapidly settles to an oscillatory behavior largely compatible with a canonical trapped FSM. This happens despite that kink-like motions develop in the fine structures. We further synthesize the Fe XXI 1354 \AA~emissions, finding that the transverse Alfv\'en time characterizes the periodicities in the intensity, Doppler shift, and Doppler width signals. Distinct from the case without fine structuring, a non-vanishing Doppler shift is seen even at the apex. We conclude that density-enhanced equilibria need not be strictly axisymmetric to host FSM-like motions in general, and FSMs remain a candidate interpretation for rapid QPPs in solar flares.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We examine resonantly damped kink modes in straight coronal slabs, paying special attention to the effects of the formulation for the transverse density distribution ("profile"). We work in the framework of pressure-less, gravity-free, resistive magnetohydrodynamics, and we adopt the dissipative-eigenmode perspective. The density profile is restricted to be one-dimensional, but nonetheless allowed to take a generic form characterized by a continuous transition layer connecting a uniform interior to a uniform exterior. A dispersion relation (DR) is derived in the thin-boundary limit, yielding analytical expressions for the eigenfrequencies that generalize known results in various aspects. We find that the analytical rather than the numerical solutions to the thin-boundary DR serve better the purpose for validating our self-consistent resistive solutions. More importantly, the eigenfrequencies are found to be sensitive to profile specifications, the ratio of the imaginary to the real part readily varying by a factor of two when one profile is used in place of another. Our eigenmode computations are also examined in the context of impulsively excited kink waves, suggesting the importance of resonant absorption for sufficiently oblique components when the spatial scale of the exciter is comparable to the slab half-width.
分类： 光学 >> 量子光学 提交时间： 2023-02-25
摘要： We study the open XXZ spin chain with a PT-symmetric non-Hermitian boundary field. We find an interaction-induced scale-free non-Hermitian skin effect by using the coordinate Bethe ansatz. The steady state and the ground state in the PT broken phase are constructed, and the formulas of their eigen-energies in the thermodynamic limit are obtained. The differences between the many-body scale-free states and the boundary string states are explored, and the transition between the two at isotropic point is investigated. We also discuss an experimental scheme to verify our results.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We numerically follow the response of density-enhanced slabs to impulsive, localized, transverse velocity perturbations by working in the framework of ideal magnetohydrodynamics (MHD). Both linear and nonlinear regimes are addressed. Kink wave trains are seen to develop along the examined slabs, sharing the characteristics that more oscillatory patterns emerge with time and that the apparent wavelength increases with distance at a given instant. Two features nonetheless arise due to nonlinearity, one being a density cavity close to the exciter and the other being the appearance of shocks both outside and inside the nominal slab. These features may be relevant for understanding the interaction between magnetic structures and such explosive events as coronal mass ejections. Our numerical findings on kink wave trains in solar coronal slabs are discussed in connection with typical measurements of streamer waves.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We simulate transverse oscillations in radiatively cooling coronal loops and forward-model their spectroscopic and imaging signatures, paying attention to the influence of background emission. The transverse oscillations are driven at one footpoint by a periodic velocity driver. A standing kink wave is subsequently formed and the loop cross-section is deformed due to the Kelvin-Helmholtz instability, resulting in energy dissipation and heating at small scales. Besides the transverse motions, a long-period longitudinal flow is also generated due to the ponderomotive force induced slow wave. We then transform the simulated straight loop to a semi-torus loop and forward-model their spectrometer and imaging emissions, mimicking observations of Hinode/EIS and SDO/AIA. We find that the oscillation amplitudes of the intensity are different at different slit positions, but are roughly the same in different spectral lines or channels. X-t diagrams of both the Doppler velocity and the Doppler width show periodic signals. We also find that the background emission dramatically decreases the Doppler velocity, making the estimated kinetic energy two orders of magnitude smaller than the real value. Our results show that background subtraction can help recover the real oscillation velocity. These results are helpful for further understanding transverse oscillations in coronal loops and their observational signatures. However, they cast doubt on the spectroscopically estimated energy content of transverse waves using the Doppler velocity.
分类： 物理学 >> 核物理学 提交时间： 2016-09-14
摘要： The charged lepton flavor violation process is a clean and sensitive probe of new physics beyond the Standard Model. A sensitivity study is performed to the process τ−→γμ− based on a 3~fb−1 inclusive Monte Carlo sample of e+e− collisions at a center-of-mass energy of 4.26 or 4.6~GeV, in the framework of the BESIII software system. The 90\% confidence level upper limits on $\BR(\tau^- \to \gamma \mu^-)$ are estimated assuming no signal is produced. We also obtain the sensitivity on $\BR(\tau^- \to \gamma \mu^-)$ as a function of the integrated luminosity, to serve as a reference for the HIEPA being proposed in China. It is found that 6.34~ab−1 are needed to reach the current best upper limit of 4.4×10−8 and about 2510~ab−1 are needed to reach a sensitivity of 10−9 if the detector design is similar to that of BESIII.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The lack of observed sausage perturbations in solar active region loops is customarily attributed to the relevance of cutoff axial wavenumbers and the consequent absence of trapped modes (called ``evanescent eigenmodes'' here). However, some recent eigenvalue problem studies yield that cutoff wavenumbers may disappear for those equilibria where the external density varies sufficiently slowly, thereby casting doubt on the rarity of candidate sausage perturbations. We examine the responses of straight, transversely structured, coronal slabs to small-amplitude sausage-type perturbations that excite axial fundamentals by solving the pertinent initial value problem with eigensolutions for a closed domain. The density variation in the slab exterior is dictated by some steepness parameter $\mu$, and cutoff wavenumbers are theoretically expected to be present (absent) when $\mu \ge 2$ ($\mu < 2$). However, our numerical results show no qualitative difference in the system evolution when $\mu$ varies, despite the differences in the modal behavior. Only oscillatory eigenmodes are permitted when $\mu \ge 2$. Our discrete eigenspectrum becomes increasingly closely spaced when the domain broadens, and an oscillatory continuum results for a truly open system. Oscillatory eigenmodes remain allowed and dominate the system evolution when $\mu <2$. We show that the irrelevance of cutoff wavenumbers does not mean that all fast waves are evanescent. Rather, it means that an increasing number of evanescent eigenmodes emerge when the domain size increases. We conclude that sausage perturbations remain difficult to detect even for the waveguide formulated here.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Working in pressureless magnetohydrodynamics, we examine the consequences of some peculiar dispersive properties of linear fast sausage modes (FSMs) in one-dimensional cylindrical equilibria with a continuous radial density profile ($\rho_0(r)$). As recognized recently on solid mathematical grounds, cutoff axial wavenumbers may be absent for FSMs when $\rho_0(r)$ varies sufficiently slowly outside the nominal cylinder. Trapped modes may therefore exist for arbitrary axial wavenumbers and density contrasts, their axial phase speeds in the long-wavelength regime differing little from the external Alfv$\acute{\rm e}$n speed. If these trapped modes indeed show up in the solutions to the associated initial value problem (IVP), then FSMs have a much better chance to be observed than expected with classical theory, and can be invoked to account for a considerably broader range of periodicities than practiced. However, with axial fundamentals in active region loops as an example, we show that this long-wavelength expectation is not seen in our finite-difference solutions to the IVP, the reason for which is then explored by superposing the necessary eigenmodes to re-solve the IVP. At least for the parameters we examine, the eigenfunctions of trapped modes are characterized by a spatial extent well exceeding the observationally reasonable range of the spatial extent of initial perturbations, meaning a negligible fraction of energy that a trapped mode can receive. We conclude that the absence of cutoff wavenumbers for FSMs in the examined equilibrium does not guarantee a distinct temporal behavior.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The lack of observed sausage perturbations in solar active region loops is customarily attributed to the relevance of cutoff axial wavenumbers and the consequent absence of trapped modes (called ``evanescent eigenmodes'' here). However, some recent eigenvalue problem studies yield that cutoff wavenumbers may disappear for those equilibria where the external density varies sufficiently slowly, thereby casting doubt on the rarity of candidate sausage perturbations. We examine the responses of straight, transversely structured, coronal slabs to small-amplitude sausage-type perturbations that excite axial fundamentals by solving the pertinent initial value problem with eigensolutions for a closed domain. The density variation in the slab exterior is dictated by some steepness parameter $\mu$, and cutoff wavenumbers are theoretically expected to be present (absent) when $\mu \ge 2$ ($\mu < 2$). However, our numerical results show no qualitative difference in the system evolution when $\mu$ varies, despite the differences in the modal behavior. Only oscillatory eigenmodes are permitted when $\mu \ge 2$. Our discrete eigenspectrum becomes increasingly closely spaced when the domain broadens, and an oscillatory continuum results for a truly open system. Oscillatory eigenmodes remain allowed and dominate the system evolution when $\mu <2$. We show that the irrelevance of cutoff wavenumbers does not mean that all fast waves are evanescent. Rather, it means that an increasing number of evanescent eigenmodes emerge when the domain size increases. We conclude that sausage perturbations remain difficult to detect even for the waveguide formulated here.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： We show that a local non-Hermitian perturbation in a Hermitian lattice system generically induces scale-free localization for the continuous-spectrum eigenstates. Furthermore, when the local non-Hermitian perturbation enjoys parity-time (PT) symmetry, the PT symmetry breaking of continuous spectrum is always accompanied by the emergence of scale-free localization. This type of PT symmetry breaking is highly sensitive to boundary conditions: The continuous spectrum of a periodic system undergoes a PT symmetry breaking as long as the non-Hermitian perturbation is strong enough; however, the counterpart under open boundary condition allows PT symmetry breaking only when the band structure satisfies certain condition that we unveil here. We also obtain the precise energy window in which the PT symmetry breaking is possible. Our results uncover a generic boundary-induced non-Hermitian phenomenon, which has unexpected interplay with PT symmetry.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Magnetohydrodynamic (MHD) waves are often invoked to interpret quasi-periodic pulsations (QPPs) in solar flares. We study the response of a straight flare loop to a kink-like velocity perturbation using three-dimensional MHD simulations and forward model the microwave emissions using the fast gyrosynchrotron code. Kink motions with two periodicities are simultaneously generated,with the long-period component P_L = 57s being attributed to the radial fundamental kink mode and the short-period component P_S=5.8s to the first leaky kink mode. Forward modeling results show that the two-periodic oscillations are detectable in the microwave intensities for some lines of sight. Increasing the beam size to (1")^2 does not wipe out the microwave oscillations. We propose that the first leaky kink mode is a promising candidate mechanism to account for short-period QPPs. Radio telescopes with high spatial resolutions can help distinguish between this new mechanism with such customary interpretations as sausage modes.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： There has been considerable interest in magnetoacoustic waves in static, straight, field-aligned, one-dimensional equilibria where the exteriors of a magnetic slab are different between the two sides. We focus on trapped, transverse fundamental, oblique quasi-kink modes in pressureless setups where the density varies continuously from a uniform interior (with density $\rho_{\rm i}$) to a uniform exterior on either side (with density $\rho_{\rm L}$ or $\rho_{\rm R}$), assuming $\rho_{\rm L}\le\rho_{\rm R}\le\rho_{\rm i}$. The continuous structuring and oblique propagation make our study new relative to pertinent studies, and lead to wave damping via the Alfv$\acute{\rm e}$n resonance. We compute resonantly damped quasi-kink modes as resistive eigenmodes, and isolate the effects of system asymmetry by varying $\rho_{\rm i}/\rho_{\rm R}$ from the ``Fully Symmetric'' ($\rho_{\rm i}/\rho_{\rm R}=\rho_{\rm i}/\rho_{\rm L}$) to the ``Fully Asymmetric'' limit ($\rho_{\rm i}/\rho_{\rm R}=1$). We find that the damping rates possess a nonmonotonic $\rho_{\rm i}/\rho_{\rm R}$-dependence as a result of the difference between the two Alfv$\acute{\rm e}$n continua, and resonant absorption occurs only in one continuum when $\rho_{\rm i}/\rho_{\rm R}$ is below some threshold. We also find that the system asymmetry results in two qualitatively different regimes for the phase and group diagrams. The phase and group trajectories lie essentially on the same side (different sides) relative to the equilibrium magnetic field when the configuration is not far from a ``Fully Asymmetric'' (``Fully Symmetric'') one. Our numerical results are understood by making analytical progress in the thin-boundary limit, and discussed for imaging observations of axial standing modes and impulsively excited wavetrains.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Impulsively excited wave trains are of considerable interest in solar coronal seismology. To our knowledge, however, it remains to examine the three-dimensional (3D) dispersive propagation of impulsive kink waves in straight, field-aligned, symmetric, low-beta, slab equilibria that are structured only in one transverse direction. We offer a study here, starting with an analysis of linear oblique kink modes from an eigenvalue problem perspective. Two features are numerically found for continuous and step structuring alike, one being that the group and phase velocities may lie on opposite sides of the equilibrium magnetic field ($\vec{B}_0$), and the other being that the group trajectories extend only to a limited angle from $\vec{B}_0$. We justify these features by making analytical progress for the step structuring. More importantly, we demonstrate by a 3D time-dependent simulation that these features show up in the intricate interference patterns of kink wave trains that arise from a localized initial perturbation. In a plane perpendicular to the direction of inhomogeneity, the large-time slab-guided patterns are confined to a narrow sector about $\vec{B}_0$, with some wavefronts propagating toward $\vec{B}_0$. We conclude that the phase and group diagrams lay the necessary framework for understanding the complicated time-dependent behavior of impulsive waves.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Impulsively excited wave trains are of considerable interest in solar coronal seismology. To our knowledge, however, it remains to examine the three-dimensional (3D) dispersive propagation of impulsive kink waves in straight, field-aligned, symmetric, low-beta, slab equilibria that are structured only in one transverse direction. We offer a study here, starting with an analysis of linear oblique kink modes from an eigenvalue problem perspective. Two features are numerically found for continuous and step structuring alike, one being that the group and phase velocities may lie on opposite sides of the equilibrium magnetic field ($\vec{B}_0$), and the other being that the group trajectories extend only to a limited angle from $\vec{B}_0$. We justify these features by making analytical progress for the step structuring. More importantly, we demonstrate by a 3D time-dependent simulation that these features show up in the intricate interference patterns of kink wave trains that arise from a localized initial perturbation. In a plane perpendicular to the direction of inhomogeneity, the large-time slab-guided patterns are confined to a narrow sector about $\vec{B}_0$, with some wavefronts propagating toward $\vec{B}_0$. We conclude that the phase and group diagrams lay the necessary framework for understanding the complicated time-dependent behavior of impulsive waves.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： There has been considerable interest in magnetoacoustic waves in static, straight, field-aligned, one-dimensional equilibria where the exteriors of a magnetic slab are different between the two sides. We focus on trapped, transverse fundamental, oblique quasi-kink modes in pressureless setups where the density varies continuously from a uniform interior (with density $\rho_{\rm i}$) to a uniform exterior on either side (with density $\rho_{\rm L}$ or $\rho_{\rm R}$), assuming $\rho_{\rm L}\le\rho_{\rm R}\le\rho_{\rm i}$. The continuous structuring and oblique propagation make our study new relative to pertinent studies, and lead to wave damping via the Alfv$\acute{\rm e}$n resonance. We compute resonantly damped quasi-kink modes as resistive eigenmodes, and isolate the effects of system asymmetry by varying $\rho_{\rm i}/\rho_{\rm R}$ from the ``Fully Symmetric'' ($\rho_{\rm i}/\rho_{\rm R}=\rho_{\rm i}/\rho_{\rm L}$) to the ``Fully Asymmetric'' limit ($\rho_{\rm i}/\rho_{\rm R}=1$). We find that the damping rates possess a nonmonotonic $\rho_{\rm i}/\rho_{\rm R}$-dependence as a result of the difference between the two Alfv$\acute{\rm e}$n continua, and resonant absorption occurs only in one continuum when $\rho_{\rm i}/\rho_{\rm R}$ is below some threshold. We also find that the system asymmetry results in two qualitatively different regimes for the phase and group diagrams. The phase and group trajectories lie essentially on the same side (different sides) relative to the equilibrium magnetic field when the configuration is not far from a ``Fully Asymmetric'' (``Fully Symmetric'') one. Our numerical results are understood by making analytical progress in the thin-boundary limit, and discussed for imaging observations of axial standing modes and impulsively excited wavetrains.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Magnetohydrodynamic (MHD) waves are often invoked to interpret quasi-periodic pulsations (QPPs) in solar flares. We study the response of a straight flare loop to a kink-like velocity perturbation using three-dimensional MHD simulations and forward model the microwave emissions using the fast gyrosynchrotron code. Kink motions with two periodicities are simultaneously generated,with the long-period component P_L = 57s being attributed to the radial fundamental kink mode and the short-period component P_S=5.8s to the first leaky kink mode. Forward modeling results show that the two-periodic oscillations are detectable in the microwave intensities for some lines of sight. Increasing the beam size to (1")^2 does not wipe out the microwave oscillations. We propose that the first leaky kink mode is a promising candidate mechanism to account for short-period QPPs. Radio telescopes with high spatial resolutions can help distinguish between this new mechanism with such customary interpretations as sausage modes.
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