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Nie Jiawang | Nie M. | Nie Feiping | Nie Jundan | Nie Jia-Cai | Nie J. Y. | Nie Sian | Nie Liqiang | Nie Simin | Nie Zhaohu

W S. R. Juarez | W | W Aaron Sonabend | W B. | W Lee C. | W Lehnert. | W Medhat Shafaa. | W Rupert | W Shivaraj B | W Wei G.

X Nomaan | x | X Alex | X Waintal | X Zhang

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Scaling p_T distributions for p and \bar{p} produced in Au+Au collisions at RHIC

Zhang W. C., Zeng Y., Nie W. X., Zhu L. L., Yang C. B.
09 Apr 2007 nucl-th arxiv.org/abs/0704.1062

With the experimental data from STAR and PHENIX on the centrality dependence of the $p_T$ spectra of protons and anti-protons produced at mid-rapidity in Au+Au collisions at 200 GeV, we show that for protons and anti-protons there exists a scaling distribution independent of the colliding centrality. The scaling functions can also describe data from BRAHMS for both proton and anti-proton spectra at $y=2.2$ and 3.2. The scaling behaviors are shown to be incompatible with the usual string fragmentation scenario for particle production.

Nonperturbative Explanation of the Enhancement Factors in QCD Sum Rule for the rho Meson

Nie Shu-Quan, Kuang Yu-Ping, Wang Qing, Yi Yu-Ping
25 Mar 1997 hep-ph arxiv.org/abs/hep-ph/9703408

Taking the sum rule for the rho meson as an example, we study the possibility of explaining the phenomenological enhamcement factors for certain terms in the vacuum expectation value of the operator product expansion in the QCD sum rule. We take a QCD motivated extended Nambu-Jona-Lasinio (ENJL) model as the low energy effective Lagrangian for QCD with which we calculate the nonperturbative contributions to the vacuum condensate expansion to obtain the enhancement factors. Our result shows that such nonperturbative contributions can cause large enough enhancement factors which can be consistent with the phenomenological values.

Clustering Kinetics of Granular Media in Three Dimensions

Chen Shiyi, Deng Yuefan, Nie Xiaobo, Tu Yuhai
21 Apr 1998 cond-mat.mtrl-sci arxiv.org/abs/cond-mat/9804235

Three-dimensional molecular dynamics simulations of dissipative particles (~ 10^6) are carried out for studying the clustering kinetics of granular media during cooling. The inter-connected high particle density regions are identified, showing tube-like structures. The energy decay rates as functions of the particle density and the restitution coefficient are obtained. It is found that the probability density function of the particle density obeys an exponential distribution at late stages. Both the fluctuation of density and the mean cluster size of the particle density have power law relations against time during the inelastic coalescing process.

Nonsingular Surface-Quasi-Geostrophic Flow

Constantin Peter, Nie Qing, Schorghofer Norbert
06 May 1998 math.NA math.AP physics.ao-ph arxiv.org/abs/math/9805027

The dynamics of large eddies in the atmosphere and oceans is described by the surface quasi geostrophic equation, which is reminiscent of the Euler equations. Thermal fronts build up rapidly. Two different numerical methods combined with analytical criteria are used to show there are no singularities in finite time.

The Anomalous Magnetic Moment of the Muon and Higgs-Mediated Flavor Changing Neutral Currents

Nie Shuquan, Sher Marc
19 May 1998 hep-ph arxiv.org/abs/hep-ph/9805376

In the two-Higgs doublet extension of the standard model, flavor-changing neutral couplings arise naturally. In the lepton sector, the largest such coupling is expected to be $\mu-\tau-\phi#. We consider the effects of this coupling on the anomalous magnetic moment of the muon. The resulting bound on the coupling, unlike previous bounds, is independent of the value of other unknown couplings. It will be significantly improved by the upcoming E821 experiment at Brookhaven National Lab.

Lattice-Boltzmann Simulations of Fluid Flows in MEMS

Nie Xiaobo, Doolen Gary D., Chen Shiyi
11 Jun 1998 comp-gas nlin.CG arxiv.org/abs/comp-gas/9806001

The lattice Boltzmann model is a simplified kinetic method based on the particle distribution function. We use this method to simulate problems in MEMS, in which the velocity slip near the wall plays an important role. It is demonstrated that the lattice Boltzmann method can capture the fundamental behavior in micro-channel flow, including velocity slip and nonlinear pressure drop along the channel. The Knudsen number dependence of the position of the vortex center and the pressure contour in micro-cavity flows is also demonstrated.

The statistics of the gravitational field arising from an inhomogenous system of particles

Del Popolo A., Gambera M., x
27 Oct 1998 astro-ph arxiv.org/abs/astro-ph/9810435

In this paper we extend Chandrasekhar and von Neumann's analysis of the statistics of the gravitational field to systems in which particles (e.g. stars, galaxies) are not homogeneously distributed. We derive a distribution function W({F},dF/dt) giving the joint probability that a test particle is subject to a force F and an associated rate of change of F given by dF/dt. We calculate the first moment of dF/dt to study the effects of inhomogenity on dynamical friction.

Vacuum Stability Bounds in the Two-Higgs Doublet Model

Nie Shuquan, Sher Marc
03 Nov 1998 hep-ph arxiv.org/abs/hep-ph/9811234

In the standard model, the requirements of vacuum stability and the validity of perturbation theory up to the unification scale force the mass of the Higgs boson to be approximately between 130 GeV and 180 GeV. We re-examine these requirements in the (non-supersymmetric) two-Higgs doublet model, in the light of the large top quark mass, and constrain the masses of the Higgs bosons in this model. It is found that the mass of the charged Higgs boson must be lighter than 150 GeV. This bound is below the lower bound in the popular model-II two-Higgs doublet model, and thus we conclude that this model cannot be valid up to the unification scale. The bounds on the neutral Higgs scalars are also discussed.

Periodic Instanton and Phase Transition in Quantum Tunneling of Spin Systems

Zhang Y. -B., Nie Y. -H., Kou S. -P., Liang J. -Q., Mueller-Kirsten H. J. W., Pu F. -C.
28 Jan 1999 cond-mat.soft cond-mat.mes-hall arxiv.org/abs/cond-mat/9901325

The quantum-classical transitions of the escape rates in a uniaxial spin model relevant to the molecular magnet Mn$_{12}$Ac and a biaxial anisotropic ferromagnetic particle are investigated by applying the periodic instanton method. The effective free energies are expanded around the top of the potential barrier in analogy to Landau theory of phase transitions. We show that the first-order transitions occur below the critical external magnetic field $h_x = 1/4$ for the uniaxial spin model and beyond the critical anisotropy constant ratio $\lambda = 1/2$ for the biaxial ferromagnetic grains, which are in good agreement with earlier works.

Macroscopic Quantum Coherence in Small Antiferromagnetic Particle and the Quantum Interference Effects

Nie Y. -H., Zhang Y. -B., Liang J. -Q., Mueller-Kirsten H. J. W., Pu F. -C.
26 Sep 1999 cond-mat.mes-hall arxiv.org/abs/cond-mat/9909371

Starting from the Hamiltonian operator of the noncompensated two-sublattice model of a small antiferromagnetic particle, we derive the effective Lagrangian of a biaxial antiferromagnetic particle in an external magnetic field with the help of spin-coherent-state path integrals. Two unequal level-shifts induced by tunneling through two types of barriers are obtained using the instanton method. The energy spectrum is found from Bloch theory regarding the periodic potential as a superlattice. The external magnetic field indeed removes Kramers' degeneracy, however a new quenching of the energy splitting depending on the applied magnetic field is observed for both integer and half-integer spins due to the quantum interference between transitions through two types of barriers.