分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Ellerman bombs (EBs) and UV bursts are both small-scale solar activities that occur in active regions. They are now believed to form at different heights in the lower atmosphere. In this paper, we use one-dimensional radiative hydrodynamic simulations to calculate various line profiles in response to heating in different atmospheric layers. We confirm that heating in the upper photosphere to the lower chromosphere can generate spectral features of typical EBs, while heating in the mid to upper chromosphere can generate spectral features of typical UV bursts. The intensity evolution of the H$\alpha$ line wing in EBs shows a rise--plateau pattern, while that of the Si IV 1403 \r{A} line center in UV bursts shows a rise--fall pattern. However, the predicted enhancement of FUV continuum near 1400 \r{A} for EBs is rarely reported and requires further observations to check it. With two heating sources or an extended heating source in the atmosphere, both EB and UV burst features could be reproduced simultaneously.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ying Li
Qiao Li
De-Chao Song
Andrea Francesco Battaglia
Hualin Xiao
Säm Krucker
Udo Schühle
Hui Li
Weiqun Gan
M. D. Ding
摘要： The hydrogen Lyman-$\alpha$ (H {\sc i} Ly$\alpha$) emission during solar flares has rarely been studied in spatially resolved images and its physical origin has not been fully understood. In this paper, we present novel Ly$\alpha$ images for a C1.4 solar flare (SOL2021-08-20T22:00) from the Extreme Ultraviolet Imager aboard Solar Orbiter, together with multi-waveband and multi-perspective observations from the Solar Terrestrial Relations Observatory Ahead and the Solar Dynamics Observatory spacecraft. It is found that the Ly$\alpha$ emission has a good temporal correlation with the thermal emissions at 1--8 \AA\ and 5--7 keV, indicating that the flaring Ly$\alpha$ is mainly produced by a thermal process in this small event. However, nonthermal electrons play a minor role in generating Ly$\alpha$ at flare ribbons during the rise phase of the flare, as revealed by the hard X-ray imaging and spectral fitting. Besides originating from flare ribbons, the Ly$\alpha$ emission can come from flare loops, likely caused by plasma heating and also cooling that happen in different flare phases. It is also found that the Ly$\alpha$ emission shows fairly similar features with the He {\sc ii} 304 \AA\ emission in light curve and spatio-temporal variation along with small differences. These observational results improve our understanding of the Ly$\alpha$ emission in solar flares and also provide some insights for investigating the Ly$\alpha$ emission in stellar flares.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
Qifeng Ruan
Wang Zhang
Hao Wang
John You En Chan
Hongtao Wang
Hailong Liu
Dianyuan Fan
Ying Li
Cheng-Wei Qiu
Joel K. W. Yang
摘要： Colour changes can be achieved by straining photonic crystals or gratings embedded in stretchable materials. However, the multiple repeat units and the need for a volumetric assembly of nanostructures limit the density of information content. Inspired by surface reliefs on oracle bones and music records as means of information archival, here we endow surface-relief elastomers with multiple sets of information that are accessible by mechanical straining along in-plane axes. Distinct from Bragg diffraction effects from periodic structures, we report trenches that generate colour due to variations in trench depth, enabling individual trench segments to support a single colour. Using 3D printed cuboids, we replicated trenches of varying geometric parameters in elastomers. These parameters determine the initial colour (or lack thereof), the response to capillary forces, and the appearance when strained along or across the trenches. Strain induces modulation in trench depth or the opening and closure of a trench, resulting in surface reliefs with up to six distinct states, and an initially featureless surface that reveals two distinct images when stretched along different axes. The highly reversible structural colours are promising in optical data archival, anti-counterfeiting, and strain-sensing applications.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Quantum entanglement plays a key role in both understanding the fundamental aspects of quantum physics and realizing various quantum devices for practical applications. Here we propose how to achieve coherent switch of optomechanical entanglement in an optical whispering-gallery-mode resonator, by tuning the phase difference of the driving lasers. We find that the optomechanical entanglement and the associated two-mode quantum squeezing can be well tuned in a highly asymmetric way, providing an efficient way to protect and enhance quantum entanglement against optical backscattering, in comparison with conventional symmetric devices. Our findings shed a new light on improving the performance of various quantum devices in practical noisy environment, which is crucial in such a wide range of applications as noise-tolerant quantum processing and the backscattering-immune quantum metrology.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Entanglement between distant massive mechanical oscillators is of particular interest in quantum-enabled devices due to its potential applications in distributed quantum information processing. Here we propose how to achieve nonreciprocal remote entanglement between two spatially separated mechanical oscillators within a cascaded optomechanical configuration, where the two optomechanical resonators are indirectly coupled through a telecommunication fiber. We show that by selectively spinning the optomechanical resonators, one can break the time reversal symmetry of this compound system via Sagnac effect, and more excitingly, enhance the indirect couplings between the mechanical oscillators via the individual optimizations of light-motion interaction in each optomechanical resonator. This ability allows us to generate and manipulate nonreciprocal entanglement between distant mechanical oscillators, that is, the entanglement could be achieved only through driving the system from one specific input direction but not the other. Moreover, in the case of two frequency-mismatched mechanical oscillators, it is also found that the degree of the generated nonreciprocal entanglement is counterintuitively enhanced in comparison with its reciprocal counterparts, which are otherwise unattainable in static cascaded systems with a single-tone driving laser. Our work, which is well within the feasibility of current experimental capabilities, provides an enticing new opportunity to explore the nonclassical correlations between distant massive objects and facilitates a variety of emerging quantum technologies ranging from quantum information processing to quantum sensing.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Topological valley photonics has emerged as a new frontier in photonics with many promising applications. Previous valley boundary transport relies on kink states at internal boundaries between two topologically distinct domains. However, recent studies have revealed a novel class of topological chiral edge states (CESs) at external boundaries of valley materials, which have remained elusive in photonics. Here, we propose and experimentally demonstrate the topological CESs in valley photonic metamaterials (VPMMs) by accurately tuning on-site edge potentials. Moreover, the VPMMs work at deep-subwavelength scales. Thus, the supported CESs are highly confined and self-guiding without relying on a cladding layer to prevent leakage radiation. Via direct near-field measurements, we observe the bulk bandgap, the edge dispersions, and the robust edge transport passing through sharp corners, which are hallmarks of the CESs. Our work paves a way to explore novel topological edge states in valley photonics and sheds light on robust and miniaturized photonic devices.
分类： 管理学 >> 管理学其他学科 提交时间： 2022-11-21 合作期刊: 《Modern Law Research》
摘要： In order to prevent and defuse corporate debt risks, standardize the withdrawal mechanism of market subjects, and maintain the market operation order, it is necessary to establish a good company liquidation obligor system, and properly balance the interests of different subjects such as companies, minority shareholders and creditors.However, Article 70 of the General Provisions of the Civil Code has relatively general provisions on the liquidation obligations of minority shareholders, which are different from the relevant provisions of the Judicial Interpretation of the Company Law II, resulting in differences in how to coordinate the judgments of the two in practice.The theoretical circle has great differences on whether to list minority shareholders as liquidation agents, which are roughly divided into affirmative and negative.Minority shareholders shall be listed as liquidation agents, but a more palliative path may be adopted, that is, to endow them with defense reasons and exempt the minority shareholders from liquidation liability under certain conditions.
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： Within the factorization-assisted topological-amplitude approach, we studied the 33 charmless B(s) → VV decays, where V stands for a light vector meson. According to the flavor flows, the amplitude of each process can be decomposed into 8 different topologies. In contrast to the conventional flavor diagrammatic approach, we further factorize each topological amplitude into decay constant, form factors and unknown universal parameters. By χ2 fitting 46 experimental observables, we extracted 10 theoretical parameters with χ2 per degree of freedom around 2. Using the fitted parameters, we calculated the branching fractions, polarization fractions, CP asymmetries and relative phases between polarization amplitudes of each decay mode. The decay channels dominated by tree diagram have large branching fractions and large longitudinal polarization fraction. The branching fractions and longitudinal polarization fractions of color-suppressed decays become smaller. Current experimental data of large transverse polarization fractions in the penguin dominant decay channels can be explained by only one transverse amplitude of penguin annihilation dia-gram. Our predictions of those not yet measured channels can be tested in the ongoing LHCb experiment and the Belle-II experiment in future.
分类： 物理学 >> 核物理学 提交时间： 2016-09-14
摘要： Within the factorization-assisted topological-amplitude approach, we study the two-body charmed B meson decays Bu,d,s→D(∗)M, with M denoting a light pseudoscalar (or vector) meson. The meson decay constants and transition form factors are factorized out from the hadronic matrix element of topological diagrams. Therefore the effect of SU(3) symmetry breaking is retained, which is different from the conventional topological diagram approach. The number of free nonperturbative parameters to be fitted from experimental data is also much less. Only four universal nonperturbative parameters χC, ϕC, χE and ϕE are introduced to describe the contribution of the color suppressed tree and W-exchanged diagrams for all the decay channels. With the fitted parameters from 31 decay modes induced by b→c transition, we then predict the branching fractions of 120 decay modes induced by both b→c and b→u transitions. Our results are well consistent with the measured data or to be tested in the LHCb and Belle-II experiments in the future. Besides, the SU(3) symmetry breaking, isospin violation and CP asymmetry are also investigated.
分类： 物理学 >> 核物理学 提交时间： 2016-09-13
摘要： We calculate the tree and penguin amplitudes in the B0→π+π− decay channel employing the perturbative QCD factorization approach. Using the amplitudes as input with the theoretical uncertainties sufficiently considered, we constrain the UT angle γ to 53∘≤γ≤70∘, from the measurements of the CP violation parameters Cπ+π− and Sπ+π− in B0→π+π−. The U-spin breaking effect between B0→π+π− and B0s→K+K− is estimated to be around 30\%.
分类： 物理学 >> 核物理学 提交时间： 2016-09-13
摘要： By assuming that the scalar meson K∗0(1430) belongs to the first excited states or the lowest lying ground states, we study the pure annihilation-type decays B→K∗±0(1430)K(∗)∓ in the QCD factorization approach. Within the standard model, the branching fractions are at the order of 10−8−10−7, which is possible to be measured in the ongoing LHCb experiment or forthcoming Belle-II experiment. We also study these decays in the family non-universal Z′ model. The results show that if mZ′≈600GeV (ζ=0.02), both the branching fractions and CPasymmetries of B¯¯¯¯0→K∗+0(1430)K− could be changed remarkably, which provides us a place for probing the effect of new physics. These results could be used to constrain the parameters of Z′ model.
分类： 物理学 >> 核物理学 提交时间： 2016-09-13
摘要： Within the QCD factorization approach, we calculate the branching fractions and CP asymmetry parameters of 12 B→K∗0(1430)K(∗) decay modes under the assumption that the scalar meson K∗0(1430) is the first excited state or the lowest lying ground state in the quark model. We find that the decay modes with the scalar meson emitted, have large branching fractions due to the enhancement of large chiral factor rK∗0χ. The branching fractions of decays with the vector meson emitted, become much smaller owing to the smaller factor rK∗χ. Moreover, the annihilation type diagram will induce large uncertainties because of the extra free parameter dealing with the endpoint singularity. For the pure annihilation type decays, our predictions are smaller than that from PQCD approach by 2-3 orders of magnitudes. These results will be tested by the ongoing LHCb experiment, forthcoming Belle-II experiment and the proposing circular electron-positron collider.
分类： 物理学 >> 核物理学 提交时间： 2016-09-13
摘要： We reexamine the branching ratios, CP-asymmetries, and other observables in a large number of Bq→VV(q=u,d,s) decays in the perturbative QCD (PQCD) approach, where V denotes a light vector meson (ρ,K∗,ω,ϕ). The essential difference between this work and the earlier similar works is of parametric origin and in the estimates of the power corrections related to the ratio r2i=m2Vi/m2B(i=2,3) (mV and mB denote the masses of the vector and B meson, respectively). In particular, we use up-to-date distribution amplitudes for the final state mesons and keep the terms proportional to the ratio r2i in our calculations. Our updated calculations are in agreement with the experimental data, except for a limited number of decays which we discuss. We emphasize that the penguin annihilation and the hard-scattering emission contributions are essential to understand the polarization anomaly, such as in the B→ϕK∗ and Bs→ϕϕ decay modes. We also compare our results with those obtained in the QCD factorization (QCDF) approach and comment on the similarities and differences, which can be used to discriminate between these approaches in future experiments.
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