Interaction induced mergence of Dirac points in Non-Abelian optical lattices

We study the properties of an ultracold Fermi gas loaded in a square optical lattice and subjected to an external and classical non-Abelian gauge field. We calculate the energy spectrum of the system and show that the Dirac points in the energy spectrum will remain quite stable under onsite interaction of certain strength. Once the on-site interaction grows stronger than a critical value, the Dirac points will no longer be stable and merge into a single hybrid point. This mergence implies a quantum phase transition from a semimetallic phase to a band insulator. The on-site interaction between ultracold fermions could be conveniently controlled by Feshbach resonances in current experiments. We proposed that this remarkable interaction induced mergence of Dirac points may be observed in the ultracold fermi gas experiments

Experiments on thermal relaxation of copper films for nano-calorimetry

Hot-electron calorimeter is a device used to detect a small package of energy utilizing thermal effect. For detection, the incoming energy is converted to temperature changes by the absorber of the calorimeter and then it is detected by a thermometer. Normal metal is one of the candidates to function as the absorber of hot-electron calorimeter due to the decoupling of electrons from its phonons at low temperatures, which provides the natural thermal isolation for electrons in the normal metal. To improve the performance of a normal-metal based calorimeter, one needs to understand the thermal relaxation mechanism in the device. In this dissertation, we experimentally investigate thermal relaxation in evaporated copper films at sub-kelvin temperatures. We characterize the thermal transport properties of the copper film in both steady-state and dynamic regime.  First, we give a short introduction to the nano-calorimeter and theoretically describe the relevant thermal properties explored in the dissertation. We describe the working principle of proximity Josephson junction thermometer used in the experiments to measure the electron temperature of copper films.  Next, we show the steady-state measurement results where then thermal conductance between film electrons and the environment is measured. Electron-phonon and thermal boundary conductance limit to thermal relaxation are identified in the experiments. We report the crossover of the thermal relaxation mechanism as changing film thickness and temperature. The impact of reduced phonon dimensionality on thermal conductance is discussed.  Finally, we show the dynamic thermal relaxation of copper films. In contrary to what is expected, we find that the process shows several relaxation times for copper films. Experiments are explained with a thermal model considering an additional thermal reservoir coupled to the film electrons. One possible origin of the thermal reservoir is the electrically isolated grains in the film with a different texture, and the electron-phonon coupling strength varies for grains with different orientations

Double Graphs Regularized Multi-view Subspace Clustering

Recent years have witnessed a growing academic interest in multi-view subspace clustering. In this paper, we propose a novel Double Graphs Regularized Multi-view Subspace Clustering (DGRMSC) method, which aims to harness both global and local structural information of multi-view data in a unified framework. Specifically, DGRMSC firstly learns a latent representation to exploit the global complementary information of multiple views. Based on the learned latent representation, we learn a self-representation to explore its global cluster structure. Further, Double Graphs Regularization (DGR) is performed on both latent representation and self-representation to take advantage of their local manifold structures simultaneously. Then, we design an iterative algorithm to solve the optimization problem effectively. Extensive experimental results on real-world datasets demonstrate the effectiveness of the proposed method

Modal analysis of the triple-tower twin-span suspension bridge in deck unit erection stage

Modal analysis of large span suspension bridge in different construction stages has to be carried out for the aerodynamic instability analysis. Based on the finite element (FE) model of a triple-tower twin-span (TTTS) suspension bridge in the completed stage, the FE models of the tower-cable-deck system corresponding to 0 %, 5 %, 10 %, 20 %, 30 %, and 40 % deck units erection stage are established respectively by a backward dismantling method. Then, the dynamic characteristics of each of the tower-cable-deck systems are analyzed to study the modal properties of TTTS suspension bridge in various deck erection stages. The results demonstrate that the natural frequencies of each erection stage are closely distributed in the low-order range. In the beginning of the deck units erection stage, the tower-cable-dominated modes are the primary modes and the deck-dominated modes come to next. Due to the strong interactions between deck unites and the cables, both the in-plane and out-of-plane vibrations of cables would excite the swing, lifting or torsional modes of the deck units. Both the in-plane and out-of-plane modes including in-phase and out-of-phase modes of the two main cables in the same span or symmetry and anti-symmetry modes of the neighboring-span cables as well as their corresponding combinations can be classified into groups. With more deck unites erected, the main girder is built up gradually, and thus the frequencies of deck-dominated mode would arise. The different frequency variations result in the modal crossover phenomena, which reflect the instability of the dynamic characteristics during the long deck erection period. At last, the aerodynamic stability of the suspension bridge is checked at each early erection stage, and a wind ropes application for the aerodynamic stability enhancement is investigated. The study of dynamic characteristics provides a reference for the wind-resistance analysis of the TTTS suspension bridge during the deck units erection stage