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A NOVEL INCREMENTAL BENDING PROCESS OF COMPLEX CURVED

Qiyang, Zuo; Kai, He; Zhigang, Sun; Hui, Xu; Wei, Li; Wei, Li; Xiaobing, Dang; Ruxu, DuSubjects: Mechanical Engineering >> Machinofacture Technique and Equipment

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。 |

submitted time
2018-03-14
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Insight-HXMT observations of the first binary neutron star merger GW170817

TiPei Li; ShaoLin Xiong; ShuangNan Zhang; FangJun Lu; LiMing Song; XueLei Cao; Zhi Chang; Gang Chen; Li Chen; TianXiang Chen; Yong Chen; YiBao Chen; YuPeng Chen; Wei Cui; WeiWei Cui; JingKang Deng; YongWei Dong; YuanYuan Du; MinXue Fu; GuanHua GaoSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Finding the electromagnetic (EM) counterpart of binary compact star merger, especially the binary neutron star (BNS) merger, is critically important for gravitational wave (GW) astronomy, osmology and fundamental physics. On Aug. 17, 2017, Advanced LIGO and Fermi/GBM independently triggered the first BNS merger, GW170817, and its high energy EM counterpart, GRB 170817A, respectively, resulting in a global observation campaign covering gamma-ray, X-ray, UV, optical, IR, radio as well as neutrinos. The High Energy X-ray telescope (HE) onboard Insight-HXMT (Hard X-ray Modulation Telescope) is the unique high-energy gamma-ray telescope that monitored the entire GW localization area and especially the optical counterpart (SSS17a/AT2017gfo) with very large collection area (~1000 cm2) and microsecond time resolution in 0.2-5 MeV. In addition, Insight-HXMT quickly implemented a Target of Opportunity (ToO) observation to scan the GW localization area for potential X-ray emission from the GW source. Although Insight-HXMT did not detect any significant high energy (0.2-5 MeV) radiation from GW170817, its observation helped to confirm the nexpected weak and soft nature of GRB 170817A. Meanwhile, Insight-HXMT/HE provides one of the most stringent constraints (~10-7 to 10-6 erg/cm2/s) for both GRB170817A and any other possible precursor or extended emissions in 0.2-5 MeV, which help us to better understand the properties of EM radiation from this BNS merger. Therefore the observation of Insight-HXMT constitutes an important chapter in the full context of multi-wavelength and multi-messenger observation of this historical GW event. |

Probing Primordial Gravitational Waves: Ali CMB Polarization Telescope

Hong Li; Si-Yu Li; Yang Liu; Yong-Ping Li; Yifu Cai; Mingzhe Li; Gong-Bo Zhao; Cong-Zhan Liu; Zheng-Wei Li; He Xu; Di Wu; Yong-Jie Zhang; Zu-Hui Fan; Yong-Qiang Yao; Chao-Lin Kuo; Fang-Jun Lu; Xinmin ZhangSubjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

In this paper, we will give a general introduction to the project of Ali CMB Polarization Tele-scope (AliCPT), which is a Sino-US joint project led by the Institute of High Energy Physics (IHEP) and has involved many di erent institutes in China. It is the rst ground-based cosmic microwave background (CMB) polarization experiment in China and an integral part of China's Gravitational Waves Program. The main scienti c goal of AliCPT project is to probe the primor-dial gravitational waves (PGWs) originated from the very early Universe. The AliCPT project includes two stages. The rst stage referred to as AliCPT-1, is to build a telescope in the Ali region of Tibet with an altitude of 5,250 meters. Once completed, it will be the worldwide highest ground-based CMB observatory and open a new window for probing PGWs in northern hemisphere. AliCPT-1 telescope is designed to have about 7,000 TES detectors at 90GHz and 150GHz. The second stage is to have a more sensitive telescope (AliCPT-2) with the number of detectors more than 20,000. Our simulations show that AliCPT will improve the current constraint on the tensor-to-scalar ratio r by one order of magnitude with 3 years' observation. Besides the PGWs, the AliCPT will also enable a precise measurement on the CMB rotation angle and provide a precise test on the CPT symmetry. We show 3 years' observation will improve the current limit by two order of magnitude. |

submitted time
2017-11-10
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Analytical result on the supercurrent through a superconductor/quantum-dot/superconductor junction

Wei Li, Yu Zhu, Tsung-han LinSubjects: Physics >> The Physics of Elementary Particles and Fields

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. |

Subjects: Physics >> The Physics of Elementary Particles and Fields

Using the nonequilibrium Green function, we show that microwave irradiation can reverse the supercurrent flowing through a superconductor / quantum-dot / superconductor structure. In contrast with the conventional sideband effect in normal-metal / quantum-dot / normal-metal junctions, the photon-assisted structures appear near E0=n2?ω(n=±1,±2...), where E0 is the resonant energy level of the quantum dot and ω is the frequency of microwave field. Each photon-assisted structure is composed of a negative and a positive peak, with an abrupt jump from the negative peak to the positive peak around E0=n2?ω. The microwave-induced π-junction transition is interpreted in the picture of photon-assisted Andreev bound states, which are formed due to multiple photon-assisted Andreev reflection between the two superconductors. Moreover, the main resonance located at E0=0 can also be reversed with proper microwave strength and frequency. |

ac Josephson effect in the resonant tunneling through mesoscopic superconducting junctions

Yu Zhu, Qing-feng Sun, Wei Li, Zhong-shui Ma, Tsung-han LinSubjects: Physics >> The Physics of Elementary Particles and Fields

We investigate ac Josephson effect in the resonant tunneling through mesoscopic superconducting junctions. In the presence of microwave irradiation, we show that the trajectory of multiple Andreev reflections can be closed by emitting or absorbing photons. Consequently, photon-assisted Andreev states are formed and play the role of carrying supercurrent. On the Shapiro steps, dc component appears when the resonant level is near a series of positions with spacing of half of the microwave frequency. Analytical result is derived in the limit of infinite superconducting gap, based on which new features of ac Josephson effect are revealed. |

Supersymmetric Probes in a Rotating 5D Attractor

Wei Li, Andrew StromingerSubjects: Physics >> The Physics of Elementary Particles and Fields

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. |

Non-Supersymmetric Attractor Flow in Symmetric Spaces

Davide Gaiotto, Wei Li, Megha PadiSubjects: Physics >> The Physics of Elementary Particles and Fields

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. |

Non-Supersymmetric Attractors in Symmetric Coset Spaces

Wei LiSubjects: Physics >> The Physics of Elementary Particles and Fields

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. |

Comment on "Cosmological Topological Massive Gravitons and Photons"

Wei Li, Wei Song, Andrew StromingerSubjects: Physics >> The Physics of Elementary Particles and Fields

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). |