分类: 物理学 >> 基本粒子与场物理学 提交时间: 2017-08-05
摘要: We present a method of constructing generic single-centered and multi-centered extremal black hole solutions in a large class of 4D N=2 supergravities coupled to vector-multiplets with cubic prepotentials. The method is applicable to models for which the 3D moduli spaces obtained via c*-map are symmetric coset spaces. The attractor solutions are generated by certain nilpotent elements in the coset algebra. We present explicit computations in 4D N=2 supergravity coupled to one vector-multiplet, whose 3D moduli space is the symmetric coset space G_{2(2)}/SL(2,R)^2. The non-supersymmetric multi-centered black holes in this model are found to lack the intricate moduli space of bound configurations that are typical of the supersymmetric case.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: This paper reports 209 O-type stars found with LAMOST. All 135 new O-type stars discovered so far with LAMOST so far are given. Among them, 94 stars are firstly presented in this sample. There are 1 Iafpe star, 5 Onfp stars, 12 Oe stars, 1 Ofc stars, 3 ON stars, 16 double-lined spectroscopic binaries, and 33 single-lined spectroscopic binaries. All O-type stars are determined based on LAMOST low-resolution spectra (R ~ 1800), with their LAMOST median-resolution spectra (R~7500) as supplements.
分类: 计算机科学 >> 计算机软件 提交时间: 2022-03-10
摘要: Distributed database system are widely used because of the rapid development of the Internet. With the ever-increasing demand, the boost performance and minimize resource and data contention are taken into consideration. A great distributed physical design, which determines where to place data, and which data item to replicate and partition, would help. This paper classification the development of physical design based on Michaels work and its references in research problems, research methods and measurement methods. Finally we put forward some suggestions for future research.
分类: 计算机科学 >> 自然语言理解与机器翻译 提交时间: 2022-03-04
摘要: The rise and application of neural network has successfully promoted the research of pattern recognition and data mining.In recent years, graph neural network has attracted more and more attention. It has some applications in text classification, sequence annotation, neural machine translation, relation extraction, image classification and other fields. This review mainly integrates the existing research on semi-supervised or unsupervised graph neural network. The research work of this paper is mainly classified in three aspects, one is based on the classification of research questions, the other is based on the classification of research methods, and the third is based on the classification of measures.The main research problems are the low-dimensional representation of nodes in graphs and the over-smooth problem in the process of message transfer. The research methods mainly focus on the graph embedding algorithm, such as the graph embedding algorithm based on probability graph and the method based on deep learning. The measurement methods mainly focus on the accuracy and efficiency of the algorithm and model.Finally, this paper also puts forward the feasible future research direction, which provides reference for readers.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2017-08-05
摘要: Supersymmetric zero-brane and one-brane probes in the squashed AdS2譙3 near-horizon geometry of the BMPV black hole are studied. Supersymmetric zero-brane probes stabilized by orbital angular momentum on the S3 are found and shown to saturate a BPS bound. We also find supersymmetric one-brane probes which have momentum and winding around a U(1)L譛(1)R torus in the S3 and in some cases are static.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2017-08-05
摘要: We propose a holographic correspondence of the flat spacetime based on the behavior of the entanglement entropy and the correlation functions. The holographic dual theory turns out to be highly non-local. We argue that after most part of the space is traced out, the reduced density matrix gives the maximal entropy and the correlation functions become trivial. We present a toy model for this holographic dual using a non-local scalar field theory that reproduces the same property of the entanglement entropy. Our conjecture is consistent with the entropy of Schwarzschild black holes in asymptotically flat spacetimes.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2017-08-05
摘要: We use the Chern-Simons formulation of higher spin theories in three dimensions to study aspects of holographic W-gravity. Concepts which were useful in studies of pure bulk gravity theories, such as the Fefferman-Graham gauge and the residual gauge transformations, which induce Weyl transformations in the boundary theory and their higher spin generalizations, are reformulated in the Chern-Simons language. Flat connections that correspond to conformal and lightcone gauges in the boundary theory are considered.
分类: 机械工程 >> 机械制造工艺与设备 提交时间: 2018-03-14
摘要: 由于水火弯板等传统成形工艺的一些固有缺陷,复杂曲面钢板的弯曲成形一直是造船厂面临的一个难题。本文提出了一种新的基于冲压的渐进成形弯板工艺,以获得复杂的弯曲钢板,以取代传统的船体成型过程。所提出的渐进成形弯板工艺是由一系列步进冲头进行的,因此也被定义为增量冲裁。通过这个过程,由柔性支承系统固定和保持的薄板可以按预定的刀具轨迹一步一步地被折弯成目标形状。同时,为了提高成形工件的几何精度,采用三维扫描反馈系统测量工件在成形过程中的变形。利用三维扫描反馈系统,可以对大量工件点云数据进行成像和重建,从而形成成形件的三维形状。然后获得成形工件模型与目标CAD模型之间的差异,必要时可用于成形精度的反馈控制。为了验证所提出的形成过程,原来的增量冲样机的设计和制造,其主要由三轴数控机床、柔性支撑体系和三维扫描反馈系统。利用该原型进行了渐变曲率钢板的成形试验,并对其进行了详细的讨论,以论证复杂弯钢板增量弯曲成形的可行性。
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: It is a common practice to evaluate probability density function or matter spatial density function from statistical samples. Kernel density estimation is a frequently used method, but to select an optimal bandwidth of kernel estimation, which is completely based on data samples, is a long-term issue that has not been well settled so far. There exist analytic formulae of optimal kernel bandwidth, but they cannot be applied directly to data samples, since they depend on the unknown underlying density functions from which the samples are drawn. In this work, we devise an approach to pick out the totally data-based optimal bandwidth. First, we derive correction formulae for the analytic formulae of optimal bandwidth to compute the roughness of the sample's density function. Then substitute the correction formulae into the analytic formulae for optimal bandwidth, and through iteration, we obtain the sample's optimal bandwidth. Compared with analytic formulae, our approach gives very good results, with relative differences from the analytic formulae being only 2%-3% for a sample size larger than 10^4. This approach can also be generalized easily to cases of variable kernel estimations.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2017-08-05
摘要: We derive extremal black hole solutions for a variety of four dimensional models which, after Kaluza-Klein reduction, admit a description in terms of 3D gravity coupled to a sigma model with symmetric target space. The solutions are in correspondence with certain nilpotent generators of the isometry group. In particular, we provide the exact solution for a non-BPS black hole with generic charges and asymptotic moduli in N=2 supergravity coupled to one vector multiplet. Multi-centered solutions can also be generated with this technique. It is shown that the non-supersymmetric solutions lack the intricate moduli space of bound configurations that are typical of the supersymmetric case.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2017-08-05
摘要: In a recent paper (arXiv: 0801.4566) it was shown that all global energy eigenstates of asymptotically AdS3 chiral gravity have non-negative energy at the linearized level. This result was questioned (arXiv: 0803.3998) by Carlip, Deser, Waldron and Wise (CDWW), who work on the Poincare patch. They exhibit a linearized solution of chiral gravity and claim that it has negative energy and is smooth at the boundary. We show that the solution of CDWW is smooth only on that part of the boundary of AdS3 included in the Poincare patch. Extended to global AdS3, it is divergent at the boundary point not included in the Poincare patch. Hence it is consistent with the results of (arXiv: 0801.4566).
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2017-08-05
摘要: Three dimensional Einstein gravity with negative cosmological constant -1/\ell^2 deformed by a gravitational Chern-Simons action with coefficient 1/\mu is studied in an asymptotically AdS_3 spacetime. It is argued to violate unitary or positivity for generic \mu due to negative-energy massive gravitons. However at the critical value \mu\ell=1, the massive gravitons disappear and BTZ black holes all have mass and angular momentum related by \ell M=J. The corresponding chiral quantum theory of gravity is conjectured to exist and be dual to a purely right-moving boundary CFT with central charges (c_L,c_R)=(0,3\ell /G).
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2017-08-05
摘要: We add fundamental matters to the N=6 Chern-Simons theory (ABJM theory), and show that D6-branes wrapped over AdS_4 x S^3/Z_2 in type IIA superstring theory on AdS_4 x CP^3 give its dual description with N=3 supersymmetry. We confirm this by the arguments based on R-symmetry, supersymmetry, and brane configuration of ABJM theory. We also analyze the fluctuations of the D6-brane and compute the conformal dimensions of dual operators. In the presence of fractional branes, the ABJM theory can model the fractional quantum Hall effect (FQHE), with RR-fields regarded as the external electric-magnetic field. We show that an addition of the flavor D6-brane describes a class of fractional quantum Hall plateau transition.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2017-08-05
摘要: We present type IIB supergravity solutions which are expected to be dual to certain Lifshitz-like fixed points with anisotropic scale invariance. They are expected to describe a class of D3-D7 systems and their finite temperature generalizations are straightforward. We show that there exist solutions that interpolate between these anisotropic solutions in the IR and the standard AdS5 solutions in the UV. This predicts anisotropic RG flows from familiar isotropic fixed points to anisotropic ones. In our case, these RG flows are triggered by a non-zero theta-angle in Yang-Mills theories that linearly depends on one of the spatial coordinates. We study the perturbations around these backgrounds and discuss the possibility of instability. We also holographically compute their thermal entropies, viscosities, and entanglement entropies.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2017-08-05
摘要: We study possibilities of string theory embeddings of the gravity duals for non-relativistic Lifshitz-like theories with anisotropic scale invariance. We search classical solutions in type IIA and eleven-dimensional supergravities which are expected to be dual to (2+1)-dimensional Lifshitz-like theories. Under reasonable ansaetze, we prove that such gravity duals in the supergravities are not possible. We also discuss a possible physical reason behind this.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2017-08-05
摘要: We present an analytical result for the supercurrent across a superconductor/quantum-dot/superconductor junction. By converting the current integration into a special contour integral, we can express the current as a sum of the residues of poles. These poles are real and give a natural definition of the Andreev bound states. We also use the exact result to explain some features of the supercurrent transport behavior.
分类: 物理学 >> 基本粒子与场物理学 提交时间: 2017-08-05
摘要: The holographic duals of higher spin theories on AdS_3 are described by the large N limit of a family of minimal model CFTs, whose symmetry algebra is equivalent to W(infinity)[lambda]. We study perturbations of these limit theories, and show that they possess a marginal symmetry-preserving perturbation that describes switching on the 1/N corrections. We also test our general results for the specific cases of lambda=0,1, where free field realisations are available.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We download the LAMOST DR8 low resolution catalog 6,478,063 AFGK tpye stars and plot the figures of effective temperature, gravitational acceleration, and metal abundance. Some small and medium mass stars are evolved from pre-main sequence or main sequence stage to planetary nebula stage or white dwarf stage by the stellar evolution code \texttt{MESA}. We analyze the observed statistical data and model calculation results, and then obtain some basic conclusions preliminarily. Most red giant and asymptotic giant stars with log$g$ less than 0.85 have poor metal abundance. Most hot A type main-sequence stars are metal rich stars with log$g$ from 3.5 to 4.5. The conclusions are reasonable within a certain error range. The theory of a gap area in the H-R diagram for stellar evolutions of medium mass stars is reflected in the statistical figures. The central core hydrogen burning stage and the central core helium burning stage correspond to the peak structures in the gravitational acceleration statistical figures respectively. The metal abundances among A, F, G, and K type stars have a wide distribution. We can not simply replace the metal abundances of these stars with the metal abundance of the Sun when doing a fine research work.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: The dipole blockade phenomenon is a direct consequence of strong dipole-dipole interaction, where only single atom can be excited because the doubly excited state is shifted out of resonance. The corresponding two-body entanglement with non-zero concurrence induced by the dipole blockade effect is an important resource for quantum information processing. Here, we propose a novel physical mechanism for realizing dipole blockade without the dipole-dipole interaction, where two qubits coupled to a cavity, are driven by a coherent field. By suitably chosen placements of the qubits in the cavity and by adjusting the relative decay strengths of the qubits and cavity field, we kill many unwanted excitation pathways. This leads to dipole blockade. In addition, we show that these two qubits are strongly entangled over a broad regime of the system parameters. We show that a strong signature of this dipole blockade is the bunching property of the cavity photons which thus provides a possible measurement of the dipole blockade. We present dynamical features of the dipole blockade without dipole-dipole interaction. The proposal presented in this work can be realized not only in traditional cavity QED, but also in non-cavity topological photonics involving edge modes.
分类: 光学 >> 量子光学 提交时间: 2023-02-19
摘要: Variational quantum circuits (VQCs) built upon noisy intermediate-scale quantum (NISQ) hardware, in conjunction with classical processing, constitute a promising architecture for quantum simulations, classical optimization, and machine learning. However, the required VQC depth to demonstrate a quantum advantage over classical schemes is beyond the reach of available NISQ devices. Supervised learning assisted by an entangled sensor network (SLAEN) is a distinct paradigm that harnesses VQCs trained by classical machine-learning algorithms to tailor multipartite entanglement shared by sensors for solving practically useful data-processing problems. Here, we report the first experimental demonstration of SLAEN and show an entanglement-enabled reduction in the error probability for classification of multidimensional radio-frequency signals. Our work paves a new route for quantum-enhanced data processing and its applications in the NISQ era.