Jia L.-B.,Southwest University of Science and Technology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015
The recent astronomical observation of GeV gamma-ray excess from the Galactic center was suggested due to a bb¯ mode in the tens GeV of weakly interacting massive particle (WIMP) pair annihilations, and this mode was also explored by the new dwarf galaxy observation. Considering the case where the WIMP pair mass is below the top quark mass, a pseudoscalar φ is studied in this article, which mediates the interactions between the standard model fermions and fermionic WIMPs and the neutral flavor-changing interactions in standard model fermion sectors. The bb¯ mode is favored in WIMP pair annihilations, while the WIMP-nucleus scattering is highly suppressed in direct detection. Alternative schemes of t→c decay and single top production are employed to search the WIMPs. Assuming the mass of the WIMPs is around 5-60 GeV and with reasonable inputs by the constraints, the branching ratio Bt→cχ¯χ of a top quark decaying into a charm quark and a WIMP pair is derived of order 10-8-10-5; thus, careful studies in the future on top physics may help to gain a better understanding of WIMPs. © 2015 American Physical Society.
Fan X.-Y.,Southwest University of Science and Technology
Yantu Lixue/Rock and Soil Mechanics | Year: 2011
Based on systematic analysis of the landslide displacements and its evolvement characteristics, a detailed research is performed on the features of the complexity, catastrophe and nonlinearity in terms of the basic principle of multifractal. The single fractals are deficiencies in prediction of evolvement trend of landslide displacement. The evolvement of landslide displacement is determined by the multifractal dimensions. Firstly, taking the typical landslides-The Xintan landslide, Danba landslide and Huanglashi landslide as the practical examples, the evolvement of multifractal dimensions of the displacement-time are calculated. Secondly, the correlation between the displacement evolvement and multifractal dimensions is studied. It is found that the landslides are stable when the multifractal dimensions are D1 > D2 > ⋯ > D∞ and the landslides are unstable when the multifractal dimensions are D1 < D2 < ⋯ < D∞. Moreover, if there were inflexions in the multifractal dimensions of landslide displacements-time the landslide stability would change. For example, they are from D1 > D2 > ⋯ > D∞, through D1 > ⋯ > Dn < Dn+1 < ⋯ < D∞ to D1 < D2 < ⋯ < D∞, the landslides are unstable gradually. On the contrary, when they were from D1 < D2 < ⋯ < D∞, through D1 > ⋯ > Dn < Dn+1 < ⋯ < D∞ to D1 > D2 > ⋯ > D∞, the landslides are stable gradually. The study results show that the multifractal dimensions of displacement are an effective method to evaluate and predict landslide displacement evolvement.
Ren X.,Southwest Institute of Applied Magnetics |
Xu G.,Southwest University of Science and Technology
Journal of Magnetism and Magnetic Materials | Year: 2014
NiCoZn-ferrites doped with La3+ ions, Ni0.35Co 0.15Zn0.5LaxFe2O4(x=0, 0.02, 0.04, 0.06), were prepared by sol-gel method. The effect of the La 3+ ions doping on the microstructure, complex permeability, permittivity and microwave absorption of the samples was investigated. The results show that all samples exhibited a well defined spinel phase when x≤0.04 with the sintering temperature of 1000 C. With the increase of the substitution ratio of La3+ ions from 0 to 0.06, the lattice parameters increased gradually, which resulted in the change of the particle shape and size. The data of magnetism showed that the addition of La 3+ ions result in the decrease of saturation magnetization (M s) and coercivity (Hc). The La3+ ions doped in the ferrite not only improved complex permittivity, but also microwave absorbency. The minimum reflection loss of -34 dB was obtained for x=0.02 sample for thickness t=4 mm and its bandwidth under -10 dB reaches 5.5 GHz. © 2013 Elsevier B.V.
Zhou L.,Southwest University of Science and Technology
IEEE Transactions on Fuzzy Systems | Year: 2016
In this paper, we propose a method to construct homeomorphisms from the interior of intuitionistic fuzzy interpretation triangle to the complex plane. Based on such homeomorphisms, we define concepts of pure intuitionistic fuzzy sets and pure intuitionistic fuzzy numbers, and obtain some properties of these new concepts. In addition, we prove that all the pure intuitionistic fuzzy numbers form a field, whose arithmetic operations are given. Finally, we use two numerical examples to show computational skills in such field. © 1993-2012 IEEE.
Xiang W.,Southwest Jiaotong University |
Xiao J.,Southwest University of Science and Technology
International Journal of Robust and Nonlinear Control | Year: 2012
In this paper, we investigate the stability analysis problem of switched impulsive nonlinear systems and several stabilization problems of switched discrete-time linear systems are studied. First, sufficient conditions ensuring globally uniformly asymptotically stability of switched nonlinear impulsive system under arbitrary and DDT (dynamical dwell time which defines the length of the time interval between two successive switchings) switching are derived, respectively. In the DDT switching case, we first consider the switched system composed by stable subsystems, then we extend the results to the case where not all subsystems are stable. The stabilizations of switched discrete-time linear system under arbitrary switching, DDT switching and asynchronous switching are investigated respectively. Based on the stability analysis results, the control synthesis consists of controller design for each subsystem and state impulsive jumping generators design at switching instant. With the aid of the state impulsive jumping generators at switching instant, the 'energy' produced by switching can be minimized, which leads to less conservative results. Several numerical examples are given to illustrate the proposed results within this paper. Copyright © 2011 John Wiley & Sons, Ltd. Copyright © 2011 John Wiley & Sons, Ltd.