作者机构：
[Zhang, GP; Ming, H; Huang, ZM] Cent China Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Zhang, GP] C;Cent China Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
We propose a new method for optical trap in this paper. It is based on a tapered fibre probe with a tip size less than a Light wavelength. A three-dimension gradient optical field is formed within the optical near field of the fibre probe, and a particle approaching the fibre tip will be trapped. We calculate the evanescent electromagnetic field near the fibre tip and obtain the trapping force for a dielectric particle. The calculating results show the availability of this method.
通讯机构：
[Chen, XS] H;Hua Zhong Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.
关键词：
05.70.Jk Critical point phenomena;64.60.-i General studies of phase transitions
摘要：
Using φ field theory and Monte Carlo (MC) simulation we investigate the finite-size effects of the magnetization M for the three-dimensional Ising model in a finite cubic geometry with periodic boundary conditions. The field theory with infinite cutoff gives a scaling form of the equation of state h/Mδ = f(hLβδ/v,t/h1/βδ) where t = (T - TC)/Tc is the reduced temperature, h is the external field and L is the size of system. Below Tc and at Tc the theory predicts a nonmonotonic dependence of f(x,y) with respect to x ≡ hLβδ/v at fixed y ≡ t/h1/βδ and a crossover from nonmonotonic to monotonic behaviour when y is further increased. These results are confirmed by MC simulation. The scaling function f(x,y) obtained from the field theory is in good quantitative agreement with the finite-size MC data. Good agreement is also found for the bulk value f(∞,0) at Tc.
摘要：
We study the large-distance behavior of the bulk order-parameter correlation function
for T > T
c within the lattice version of the
theory including lattice effects. We also study the large-L behavior of the susceptibility
for T > T
c of the confined lattice system of linear size L with periodic boundary conditions. We find that the structure of the large-L behavior of
of the confined system is closely related to the structure of the large-distance behavior of
of the bulk system. Explicit results are derived in the spherical (large-n) limit and in one-loop order for general dimensions d > 2. For the lattice model with cubic symmetry we find that finite-size scaling must be formulated in terms of the anisotropic bulk correlation length (exponential correlation length) that governs the exponential decay of
for large r rather than in terms of the ordinary isotropic bulk correlation length
defined via the second moment of
. We show that it is the exponential bulk correlation length
in the direction of the cubic axes that determines the exponential finite-size scaling behavior of lattice systems in a rectangular geometry. This result modifies a recent interpretation concerning an apparent violation of finite-size scaling in terms of the second-moment correlation length
. Exact results for the one-dimensional Ising model illustrate our conclusions. Furthermore we show for general d>2 that a description of finite-size effects for finite n in the entire region
requires
different perturbative approaches that are applicable either to the region
or
, respectively. In particular we show that the exponential finite-size behavior for
above T
c is not captured by the standard perturbation approach that separates the homogeneous lowest mode from the inhomogeneous higher modes. Consequences for the theory of finite-size effects above four dimensions are discussed. We show that the two-variable finite-size scaling form predicts an exponential approach
to the bulk critical behavior above T
c whereas the reduction to a single-variable scaling form implies a power-law approach
.
作者机构：
[Zhou, DC; Wu, T] Huazhong Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Wu, T] H;Huazhong Normal Univ, Inst Particle Phys, Wuhan 430079, Peoples R China.
摘要：
Multiplicity distributions of negative binomial distribution (NBD) and modified NBD are obtained from it birth process model with an immigration. The ratio of factorial cumulant moment to factorial moment, i.e., H moment is calculated from different multiplicity distributions of NBD, modified NBD and the three fireball model, which shows an oscillatory behavior when there is a truncation of multiplicity. The oscillation of H moment is related to the common character of the truncated multiplicity distributions.
作者机构：
[Peng, JS] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.;Queens Univ Belfast, Dept Appl Math & Theoret Phys, Belfast BT7 1NN, Antrim, North Ireland.
通讯机构：
[Peng, JS] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
A cavity-modified master equation is derived for a coherently driven, V-type three-level atom coupled to a single-mode cavity in the bad-cavity limit. We show that population inversion in both the bare- and dressed-state bases may be achieved, originating from the enhancement of the atom-cavity interaction when the cavity is resonant with an atomic dressed-state transition. The atomic populations in the dressed-state representation are analyzed in terms of the cavity-modified transition rates. The atomic fluorescence spectrum and probe absorption spectrum are also investigated, and it is found that the spectral profiles may be controlled by adjusting the cavity frequency. Peak suppression and line narrowing occur under the appropriate conditions.
作者机构：
[Shen Guo-jin] Department of Physics, Wuhan University of Automobile Industry, Wuhan, China;[Wang Xin-min] Department of Physics, Xiaogan Teachers' College, Xiaogan, Hubei, China;[Huang Xin-tang] Department of Physics, Central China Normal University, Wuhan, China;[Wang You-qing] The State Key Lab of Laser Technology, Huazhong University of Science and Technology, Wuhan, China
摘要：
The energies and the magnetization of an electron in a piece of metal in the structure of Metal/Insulator/Metal/Insulator… (M/I/M/I…), in a magnetic field, at high temperature, and in range of quantum size thickness of the piece of metal layer have been obtained. The results show that when the thickness of the metal layer becomes smaller, the orbital magnetism of the charged particles which collide with the wall of the metal layer is to vary from diamagnetism to paramagnetism. The smaller the thickness of the metal layer becomes, the more particles will collide with the boundary of the metal layer, and then the paramagnetism becomes stronger. Finally, when the thickness of the metal layer becomes very small (<100 nm), all of the orbital diamagnetism will reverse to paramagnetism, and then the paramagnetization will be almost a maximum constant.
作者机构：
[Hu, XM; Peng, JS] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Hu, XM] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
We show that quantum interference from spontaneous decay in a three-level Λ-type system can be realized in the dressed-state picture of coherently driven systems. The physical realization relaxes the stringent conditions upon the level spacing and quantum numbers of the lower-level doublet. Since the physical realization means the equivalence between the Λsystems with quantum interference and the driven systems, the equivalence may be conveniently used to illustrate the physical pictures of some phenomena. We give two interesting examples. The first is the dynamically induced population inversion, which originates from quantum interference between dressed states. The second is the disappearance of a dark state in a bare Λsystem with quantum interference, which is due to a disparity in coupling intensities on two transitions of the equivalent V system.
摘要：
A FitzHugh Nagumo(FHN) neural model,which is double singular stochastic system, is studied.The effects of parameter β,which marks the singular degree of stochastic force at singular point, on the phase transition of the FHN model are discussed when β is non integer.It is shown that the parameter β plays an important role in phase transition of the system, and there is a locking phenomenon in the FHN model.
