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Lu Z.,University of Massachusetts Amherst | Mo H.J.,Anhui Science and Technology University
Astrophysical Journal | Year: 2015

The empirical model of Lu et al. for the relation between star formation rate and halo mass growth is adopted to predict the classical bulge mass (Mcb)-total stellar mass (M∗) relation for central galaxies. The assumption that the supermassive black hole (SMBH) mass (MBH) is directly proportional to the classical bulge mass, with the proportionality given by that for massive galaxies, predicts a MBH-M∗relation that matches well the observed relation for different types of galaxies. In particular, the model reproduces the strong transition at M∗= 1010.5-1011 Me⊙, below which MBH drops rapidly with decreasing M∗. Our model predicts a new sequence at M∗< 1010.5 M⊙, where MBH ∝ M∗but the amplitude is a factor of ∼50 lower than the amplitude of the sequence at M∗> 1011 M⊙. If all SMBHs grow through similar quasar modes with a feedback efficiency of a few percent, then the energy produced in low-mass galaxies at redshift z ≳ 2 can heat the circumgalactic medium up to a specific entropy level that is required to prevent excessive star formation in low-mass dark matter halos. © 2015. The American Astronomical Society. All rights reserved. Source


Wang J.,Anhui Science and Technology University
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

Gapless nodal quasiparticles emerge at a low-energy regime of high-T c cuprate superconductors due to the dx2-y2 gap symmetry. We study the unusual renormalizations of the Fermi velocity vF and gap velocity vΔ of these quasiparticles close to various quantum critical points in a superconducting dome. Special attention is paid to the behavior of the velocity ratio, vΔ/vF, since it determines a number of observable quantities. We perform a renormalization-group analysis and show that the velocity ratio may vanish, approach unity, or diverge at different quantum critical points. The corresponding superfluid densities and critical temperatures are suppressed, slightly increased, or significantly enhanced. The effects of three types of static disorders, namely, random mass, random gauge potential, and random chemical potential, on the stability of the system are also addressed. An analogous analysis reveals that both random mass and random gauge potential are irrelevant. This implies that these fixed points of the velocity ratio are stable, and hence observable effects ignited by them are unchanged. However, the random chemical potential is marginal. As a result, these fixed points are broken, and thus, the instabilities of quantum phase transitions are triggered. © 2013 American Physical Society. Source


Chen S.,Anhui Science and Technology University | Chen S.,Huaibei Normal University | Hu Y.,Huaibei Normal University | Meng S.,Huaibei Normal University | Fu X.,Huaibei Normal University
Applied Catalysis B: Environmental | Year: 2014

The separation mechanisms of photogenerated electrons and holes for composite photocatalysts have been a research focus. In this paper, the composite g-C3N4-WO3 photocatalysts with different main parts of C3N4 or WO3 were prepared by ball milling and heat treatment methods. The photocatalytic performance was evaluated by degradation of methylene blue (MB) and fuchsin (BF) under visible light illumination. The photocatalyst was characterized by X-ray powder diffraction (XRD), UV-vis diffuse reflection spectroscopy (DRS), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET) methods. The separation mechanisms of photogenerated electrons and holes of the g-C3N4-WO3 photocatalysts were investigated by electron spin resonance technology (ESR), photoluminescence technique (PL), and determination of reactive species in the photocatalytic reactions. When the main part of the g-C3N4-WO3 photocatalyst is WO3 (namely g-C3N4/WO3), the transport process of the photogenerated electrons and holes adopts the generic band-band transfer. Meanwhile, g-C3N4 is covered by WO3 powder, and the role of g-C3N4 can not be played fully. The photocatalytic activity of the photocatalyst is not obviously increased. However, when the primary part of the WO3-g-C3N4 photocatalyst is g-C3N4 (namely WO3/g-C3N4), the migration of photogenerated electrons and holes exhibits a typical characteristic of Z-scheme photocatalyst, and the photocatalytic activity of the photocatalyst is increased greatly. © 2014 Elsevier B.V. Source


Qi X.,Anhui Science and Technology University
Ocean Engineering | Year: 2015

This paper investigates path following problem of underactuated underwater vehicle (UUV) which follows desired spatial path with constraint control inputs. Three dimensional path following error dynamics in Serret-Frenet coordinate frame is set up. The virtual target point on the desired spatial path is not the nearest point to UUV, which relaxes the restrictions on the initial conditions of controller. Considering speed of UUV and introducing the line-of-sight navigation, path following errors can converge rapidly. Hyperbolic tangent functions are employed to design path following controller which generates amplitude-limited control signals to prevent the actuators from the saturation. This improves the transient performance for large initial tracking errors in path following problem. Moreover, Nussbaum gains are incorporated into the control laws in order to estimate unknown parameters. This makes the controller realizable. The control method was proposed based on Lyapunov theory and backstepping technique. Theoretical proof and simulation experiment showed that the proposed method is effective to deal with path following problem of UUV. © 2015 Elsevier Ltd. All rights reserved. Source


Qi X.,Anhui Science and Technology University
Ocean Engineering | Year: 2014

A practical design method is developed for cooperative tracking control of multiple autonomous underwater vehicles (AUVs). Each AUV is modeled by a system with time-varying parameters, unknown nonlinear dynamics and unknown disturbance. A robust adaptive distributed controller is designed for each AUV such that all AUVs ultimately synchronize to the desired paths with required formation. Moreover, these controllers are distributed in the sense that the controller design for each AUV only requires relative state in formation between itself and its neighbors. Finally, a simulation example demonstrates the effectiveness of the control method. © 2014 Elsevier Ltd. Source

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