Generalized Symmetries in Supergravities and Superconformal Field Theories via String Theory

In this dissertation, we study the generalized symmetries in supergravities and superconformal field theories from the string theory perspective. Part one is devoted to the study of string universality in high spacetime dimensions. Answering this question requires us to combine the following two approaches. In the "top-down" approach, We focus on supergravity theories in 7, 8, and 9 dimensional spacetime with 16 supercharges. We emphasize two discrete aspects of these theories: generalized global symmetries and frozen singularities. We give an exhaustive classification of IIB supergravity theory in 8D, particularly emphasizing these two discrete aspects. In the "bottom-up" approach, we present a consistency condition of general 8D supergravity theories involving their higher-form symmetries use it to rule out many global structures of the gauge groups in 8D supergravity theories that do not admit string theory constructions. Part two studies the generalized global symmetries of geometrically-engineered quantum field theories via string theory. We examined branes wrapping on relative topological cycles that give heavy defects that are charged under generalized global symmetries, which can then be used to construct new lower-dimensional theories. By investigating the string theory origin of the topological operators, we provide a general construction of these topological operators in the context of geometric engineering as branes wrapped on the homological cycles in the asymptotic boundary of the internal geometry. We illustrate this proposal by determining non-invertible 2-form symmetries in 6D superconformal field theories. Furthermore, by wrapping type IIB 7-brane on the entire asymptotic boundary of the internal manifold, we explicitly give a unified string-theoretic construction of two different types of field-theoretic non-invertible duality defects.Comment: Ph.D. Dissertatio

Understanding the white-light flare on 2012 March 9 : Evidence of a two-step magnetic reconnection

We attempt to understand the white-light flare (WLF) that was observed on 2012 March 9 with a newly constructed multi-wavelength solar telescope called the Optical and Near-infrared Solar Eruption Tracer (ONSET). We analyzed WLF observations in radio, H-alpha, white-light, ultraviolet, and X-ray bands. We also studied the magnetic configuration of the flare via the nonlinear force-free field (NLFFF) extrapolation and the vector magnetic field observed by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). Continuum emission enhancement clearly appeared at the 3600 angstrom and 4250 angstrom bands, with peak contrasts of 25% and 12%, respectively. The continuum emission enhancement closely coincided with the impulsive increase in the hard X-ray emission and a microwave type III burst at 03:40 UT. We find that the WLF appeared at one end of either the sheared or twisted field lines or both. There was also a long-lasting phase in the H-alpha and soft X-ray bands after the white-light emission peak. In particular, a second, yet stronger, peak appeared at 03:56 UT in the microwave band. This event shows clear evidence that the white-light emission was caused by energetic particles bombarding the lower solar atmosphere. A two-step magnetic reconnection scenario is proposed to explain the entire process of flare evolution, i.e., the first-step magnetic reconnection between the field lines that are highly sheared or twisted or both, and the second-step one in the current sheet, which is stretched by the erupting flux rope. The WLF is supposed to be triggered in the first-step magnetic reconnection at a relatively low altitude.Comment: 4 pages, 4 figures, published in A&A Lette

Phase separation in the trapped spinor gases with anisotropic spin-spin interaction

We investigate the effect of the anisotropic spin-spin interaction on the ground state density distribution of the one dimensional spin-1 bosonic gases within a modified Gross-Pitaevskii theory both in the weakly interaction regime and in the Tonks-Girardeau (TG) regime. We find that for ferromagnetic spinor gas the phase separation occurs even for weak anisotropy of the spin-spin interaction, which becomes more and more obvious and the component of $m_F=0$ diminishes as the anisotropy increases. However, no phase separation is found for anti-ferromagnetic spinor gas in both regimes.Comment: 5pages, 4 figure

Atomic-scale identification of novel planar defect phases in heteroepitaxial YBa2_2Cu3_3O7−δ_{7-\delta} thin films

We have discovered two novel types of planar defects that appear in heteroepitaxial YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO123) thin films, grown by pulsed-laser deposition (PLD) either with or without a La$_{2/3}$Ca$_{1/3}$MnO$_3$ (LCMO) overlayer, using the combination of high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging and electron energy loss spectroscopy (EELS) mapping for unambiguous identification. These planar lattice defects are based on the intergrowth of either a BaO plane between two CuO chains or multiple Y-O layers between two CuO$_2$ planes, resulting in non-stoichiometric layer sequences that could directly impact the high-$T_c$ superconductivity

Time-domain structural damage identification: from a dictionary learning perspective

Structures inevitably deteriorate during their service lives. To accurately evaluate their structural condition, the methods capable of identifying and assessing damage in a structure timely and accurately have drawn increasing attention. Compared to widely-used frequency-domain methods, the processing of time-domain data is more efficient, but remains difficult since it is usually hard to discern signals from different conditions. In fact, the signal processing fields have observed the evolution of techniques, from such traditional fixed transforms as Fourier, to dictionary learning (DL). DL leads to better representation and hence can provide improved results in many practical applications. In this paper, an innovative time-domain damage identification algorithm is proposed from a DL perspective, using D-KSVD algorithm. The numerical simulated soil-pipe system is used for verifying the performance of the proposed method. The results demonstrate that this damage identification scheme is a promising tool for structural health monitoring

Numerical simulation of stress wave interaction in short-delay blasting with a single free surface

It is generally believed that stress wave superposition does occur and plays an important role in cutting blasting with a single free surface, in which explosive columns of several blast holes with short spacing are simultaneously initiated. However, considering the large scatter of pyrotechnic delay detonators that are used in most underground metal mines in China, the existence of stress wave superposition and the influence of this effect on rock fragmentation are questionable. In the present study, the stress wave interaction in short-delay blasting with a single free surface was studied through the use of the LS-DYNA code. Stress waves induced by two blast holes blasting with different delays were compared with the single blast hole case, and the effects of delay time, detonating location and spacing on stress wave superposition were investigated. The numerical results showed that for blast holes with a 1 m spacing, stress wave interaction only occurs when the delay time is 0 ms and does not occur for blasting with delays of more than 1 ms. An increase in the duration of a stress wave via optimizing the detonation location does not improve the stress wave interaction. For a 1 ms delay, stress wave superposition only occurs when the spacing is more than 4 m, which is a rare case in practice. The results indicated that the occurrence of stress wave superposition for blasting with a single free surface is strictly limited to conditions that would be difficult to achieve under the existing delay accuracy of detonators. Therefore, it is unrealistic to improve fragmentation via the stress wave interaction in field blasting. Furthermore, the numerical results of the stress wave interaction also show that there would be a great potential to reduce the hazardous vibrations induced by short-delay blasting by using electronic detonators with better control of delays in an order of several milliseconds

Simulating aerosol–radiation–cloud feedbacks on meteorology and air quality over eastern China under severe haze conditionsin winter

The aerosol-radiation-cloud feedbacks on meteorology and air quality over eastern China under severe winter haze conditions in January 2013 are simulated using the fully coupled online Weather Research and Forecasting/Chemistry (WRF-Chem) model. Three simulation scenarios including different aerosol configurations are undertaken to distinguish the aerosol's radiative (direct and semi-direct) and indirect effects. Simulated spatial and temporal variations of PM2.5 are generally consistent with surface observations, with a mean bias of −18.9 μg m−3 (−15.0%) averaged over 71 big cities in China. Comparisons between different scenarios reveal that aerosol radiative effects (direct effect and semi-direct effects) result in reductions of downward shortwave flux at the surface, 2 m temperature, 10 m wind speed and planetary boundary layer (PBL) height by up to 84.0 W m−2, 3.2°C, 0.8 m s−1, and 268 m, respectively. The simulated impact of the aerosol indirect effects is comparatively smaller. Through reducing the PBL height and stabilizing lower atmosphere, the aerosol effects lead to increases in surface concentrations of primary pollutants (CO and SO2). Surface O3 mixing ratio is reduced by up to 6.9 ppb (parts per billion) due to reduced incoming solar radiation and lower temperature, while the aerosol feedbacks on PM2.5 mass concentrations show some spatial variations. Comparisons of model results with observations show that inclusion of aerosol feedbacks in the model significantly improves model performance in simulating meteorological variables and improves simulations of PM2.5 temporal distributions over the North China Plain, the Yangtze River delta, the Pearl River delta, and central China. Although the aerosol–radiation–cloud feedbacks on aerosol mass concentrations are subject to uncertainties, this work demonstrates the significance of aerosol–radiation–cloud feedbacks for real-time air quality forecasting under haze conditions