Hidden vortices in a Bose-Einstein condensate in a rotating double-well potential

We study vortex formation in a Bose-Einstein condensate in a rotating double-well potential. Besides the ordinary quantized vortices and elusive ghost vortices, "hidden" vortices are found distributing along the central barrier. These hidden vortices are invisible like ghost vortex but carry angular momentum. Moreover, their core size is not given by the healing length, but is strongly influenced by the external potential. We find that the Feynman's rule can be well satisfied only after including the hidden vortices. There is no critical rotating frequency for the formation of hidden vortex while there is one for the formation of ordinary visible vortices. Hidden vortices can be revealed in the free expansion of the Bose-Einstein condensates. In addition, the hidden vortices in a Bose-Einstein condensate can appear in other external potentials, such as a rotating anisotropic toroidal trap.Comment: 6pages,5figure

A Maxwell-vector p-wave holographic superconductor in a particular background AdS black hole metric

We study the p-wave holographic superconductor for AdS black holes with planar event horizon topology for a particular Lovelock gravity, in which the action is characterized by a self-interacting scalar field nonminimally coupled to the gravity theory which is labeled by an integer $k$. As the Lovelock theory of gravity is the most general metric theory of gravity based on the fundamental assumptions of general relativity, it is a desirable theory to describe the higher dimensional spacetime geometry. The present work is devoted to studying the properties of the p-wave holographic superconductor by including a Maxwell field which nonminimally couples to a complex vector field in a higher dimensional background metric. In the probe limit, we find that the critical temperature decreases with the increase of the index $k$ of the background black hole metric, which shows that a larger $k$ makes it harder for the condensation to form. We also observe that the index $k$ affects the conductivity and the gap frequency of the holographic superconductors.Comment: 14 pages, 6 figure

Overview of 2015 International Symposium on Animal Environment and Welfare held in Chongqing, China

On October 24-25, 2015 International Symposium on Animal Environment and Welfare (ISAEW2015), jointly sponsored by the International Research Center for Animal Environment and Welfare (IRCAEW) and the Chinese Society of Agricultural Engineering, was convened in Chongqing Academy of Animal Sciences (CAAS), Chongqing, China. Prof. Baoming Li from China Agricultural University (CAU) and Distinguished Prof. Hongwei Xin from Iowa State University were the Co-Chairs of ISAEW2015, and Prof. Zuohua Liu from CAAS chaired the Organizing Committee. Prof. Jun Bao, President of Northeast Agriculture University, China, presided over the opening ceremony. Prof. Xiwen Luo, an Academician of Chinese Academy of Engineering, presented the challenges and shared his thoughts on the sustainable development of animal production industry in China in the opening remarks

Thermal performance analysis of a solar energy storage unit encapsulated with HITEC salt/copper foam/nanoparticles composite

HITEC salt (40 wt. % NaNO2, 7 wt. % NaNO3, 53 wt. % KNO3) with a melting temperature of about 142 °C is a typical phase change material (PCM) for solar energy storage. Both aluminum oxide (Al2O3) nanopowder and metal foam were used to enhance pure HITEC salt, so as to retrieve the limitation of composite PCMs with single enhancement. The morphologies and thermo-physical properties of the composites were firstly characterized with Scanning Electron Microscope, Fourier-transform Infrared spectroscopy and Differential Scanning Calorimeter, respectively. A pilot test rig with a heater of 380 W located in the inner pipe was built, which was encapsulated with HITEC salt, nano-salt (HITEC salt seeded with 2 wt. % Al2O3 nanopowder) and salt/copper foam composite seeded with 2 wt. % Al2O3 nanopowder as storage media. Then heat storage and retrieval tests of the energy storage system were conducted both for pure HITEC salt and composite PCMs at various heating temperatures. The temperature evolutions and distributions of the PCMs at different locations were measured, including radial, angular, and axial locations, and the energy and volumetric mean powers during heat storage/retrieval processes were calculated subsequently. The results show that metal foam is generally compatible with the nano-salt. The maximum deviation of the melting/freezing phase change temperatures of the nano-salt/copper foam composite is 3.54 °C, whereas that of the nano-salt/nickel foam composite is 3.80 °C. The specific heats of the nano-salt are apparently enhanced with the addition of Al2O3 nanopowder both in solid and liquid states. The system encapsulated with the nano-salt/copper foam composite can be considerably enhanced, e.g. the time-duration of heat storage process at the heating temperature of 160 °C can be reduced by about 58.5%, compared to that of pure salt. The volumetric mean power of heat storage for the nano-salt/copper foam composite at the heating temperature of 180 °C increases to 109.32 kW/m3, compared with 53.01 kW/m3 of pure HITEC salt. The information will be helpful for solar system design, construction and application using molten salt for solar energy storage

Stabilization of highly polar BiFeO3_3-like structure: a new interface design route for enhanced ferroelectricity in artificial perovskite superlattices

In ABO3 perovskites, oxygen octahedron rotations are common structural distortions that can promote large ferroelectricity in BiFeO3 with an R3c structure [1], but suppress ferroelectricity in CaTiO3 with a Pbnm symmetry [2]. For many CaTiO3-like perovskites, the BiFeO3 structure is a metastable phase. Here, we report the stabilization of the highly-polar BiFeO3-like phase of CaTiO3 in a BaTiO3/CaTiO3 superlattice grown on a SrTiO3 substrate. The stabilization is realized by a reconstruction of oxygen octahedron rotations at the interface from the pattern of nonpolar bulk CaTiO3 to a different pattern that is characteristic of a BiFeO3 phase. The reconstruction is interpreted through a combination of amplitude-contrast sub 0.1nm high-resolution transmission electron microscopy and first-principles theories of the structure, energetics, and polarization of the superlattice and its constituents. We further predict a number of new artificial ferroelectric materials demonstrating that nonpolar perovskites can be turned into ferroelectrics via this interface mechanism. Therefore, a large number of perovskites with the CaTiO3 structure type, which include many magnetic representatives, are now good candidates as novel highly-polar multiferroic materials [3].Comment: Phys. Rev. X, in productio