Δ\Delta-scaling and heat capacity in relativistic ion collisions

The $\Delta$-scaling method has been applied to the total multiplicity distribution of the relativistic ion collisions of p+p, C+C and Pb+Pb which were simulated by a Monte Carlo package, LUCIAE 3.0. It is found that the $\Delta$-scaling parameter decreases with the increasing of the system size. Moreover, the heat capacities of different mesons and baryons have been extracted from the event-by-event temperature fluctuation in the region of low transverse mass and they show the dropping trend with the increasing of impact parameter.Comment: version 2: major change: 4 pages, 3 figures; Proceeding of International Conference on "Strangeness in Quark Matter" (SQM2004), Cape Town, South Africa, Spet. 2004 (Submitted to J. Phys. G.

Dynamics of ferroelectric nano cluster in BaTiO3 observed as a real time correlation between two soft X-ray laser pulses

We carry out a theoretical investigation to clarify the dynamic property of photo-created nano-sized ferroelectric cluster observed in the paraelectric BaTiO3 as a real time correlation of speckle pattern between two soft X-ray laser pulses, at just above the paraelectric-ferroelectric phase transition temperature. Based on a model with coupled soft X-ray photon and ferroelectric phonon mode, we study the time dependence of scattering probability by using a perturbative expansion approach. The cluster-associated phonon softening as well as central peak effects are well reproduced in the phonon spectral function via quantum Monte Carlo simulation. Besides, it is found that the time dependence of speckle correlation is determined by the relaxation dynamics of ferroelectric clusters. Near the transition point, cluster excitation is stable, leading to a long relaxation time. While, at high temperature, cluster structure is subject to the thermal fluctuation, ending up with a short relaxation time.Comment: 9 pages, 3 figure

Pseudo-unitary symmetry and the Gaussian pseudo-unitary ensemble of random matrices

Employing the currently discussed notion of pseudo-Hermiticity, we define a pseudo-unitary group. Further, we develop a random matrix theory which is invariant under such a group and call this ensemble of pseudo-Hermitian random matrices as the pseudo-unitary ensemble. We obtain exact results for the nearest-neighbour level spacing distribution for (2 X 2) PT-symmetric Hamiltonian matrices which has a novel form, s log (1/s) near zero spacing. This shows a level repulsion in marked distinction with an algebraic form in the Wigner surmise. We believe that this paves way for a description of varied phenomena in two-dimensional statistical mechanics, quantum chromodynamics, and so on.Comment: 9 pages, 2 figures, LaTeX, submitted to the Physical Review Letters on August 20, 200

Recording advances for neural prosthetics

An important challenge for neural prosthetics research is to record from populations of neurons over long periods of time, ideally for the lifetime of the patient. Two new advances toward this goal are described, the use of local field potentials (LFPs) and autonomously positioned recording electrodes. LFPs are the composite extracellular potential field from several hundreds of neurons around the electrode tip. LFP recordings can be maintained for longer periods of time than single cell recordings. We find that similar information can be decoded from LFP and spike recordings, with better performance for state decodes with LFPs and, depending on the area, equivalent or slightly less than equivalent performance for signaling the direction of planned movements. Movable electrodes in microdrives can be adjusted in the tissue to optimize recordings, but their movements must be automated to be a practical benefit to patients. We have developed automation algorithms and a meso-scale autonomous electrode testbed, and demonstrated that this system can autonomously isolate and maintain the recorded signal quality of single cells in the cortex of awake, behaving monkeys. These two advances show promise for developing very long term recording for neural prosthetic applications

Δ\Delta-scaling and Information Entropy in Ultra-Relativistic Nucleus-Nucleus Collisions

The $\Delta$-scaling method has been applied to ultra-relativistic p+p, C+C and Pb+Pb collision data simulated using a high energy Monte Carlo package, LUCIAE 3.0. The $\Delta$-scaling is found to be valid for some physical variables, such as charged particle multiplicity, strange particle multiplicity and number of binary nucleon-nucleon collisions from these simulated nucleus-nucleus collisions over an extended energy ranging from $E_{lab}$ = 20 to 200 A GeV. In addition we derived information entropy from the multiplicity distribution as a function of beam energy for these collisions.Comment: 4 pages, 4 figures, 1 table; to appear in the July Issue of Chin. Phys. Lett.. Web Page: http://www.iop.org/EJ/journal/CP

Parton energy loss in an expanding quark-gluon plasma: Radiative vs collisional

We perform a comparison of the radiative and collisional parton energy losses in an expanding quark-gluon plasma. The radiative energy loss is calculated within the light-cone path integral approach. The collisional energy loss is calculated using the Bjorken method with an accurate treatment of the binary collision kinematics. Our numerical results demonstrate that for RHIC and LHC conditions the collisional energy loss is relatively small in comparison to the radiative one. We find an enhancement of the heavy quark radiative energy loss as compared to that of the light quarks at high energies.Comment: 13 pages, 3 figure

An SU(2) Formulation of the t-J model: Application to Underdoped Cuprates

We develop a slave-boson theory for the t-J model at finite doping which respect a SU(2) symmetry -- a symmetry previously known to be important at half filling. The mean field phase diagram is found to be consistent with the phases observed in the cuprate superconductors, which contains d-wave superconductor, spin gap, strange metal, and Fermi liquid phases. The spin gap phase is best understood as the staggered flux phase, which is nevertheless translationally invariant for physical quantities. The physical electron spectral function shows small Fermi segments at low doping which continuously evolve into the large Fermi surface at high doping concentrations. The close relation between the SU(2) and the U(1) slave-boson theory is discussed. The low energy effective theory for the low lying fluctuations is derived, and new lying modes (which were over looked in the U(1) theory) are identified.Comment: 28 pages, 8 figures, RevTe

Static and vibration analysis of functionally graded beams using refined shear deformation theory

Static and vibration analysis of functionally graded beams using refined shear deformation theory is presented. The developed theory, which does not require shear correction factor, accounts for shear deformation effect and coupling coming from the material anisotropy. Governing equations of motion are derived from the Hamilton's principle. The resulting coupling is referred to as triply coupled axial-flexural response. A two-noded Hermite-cubic element with five degree-of-freedom per node is developed to solve the problem. Numerical results are obtained for functionally graded beams with simply-supported, cantilever-free and clamped-clamped boundary conditions to investigate effects of the power-law exponent and modulus ratio on the displacements, natural frequencies and corresponding mode shapes

Interior regularity criteria for suitable weak solutions of the Navier-Stokes equations

We present new interior regularity criteria for suitable weak solutions of the 3-D Navier-Stokes equations: a suitable weak solution is regular near an interior point $z$ if either the scaled $L^{p,q}_{x,t}$-norm of the velocity with $3/p+2/q\leq 2$, $1\leq q\leq \infty$, or the $L^{p,q}_{x,t}$-norm of the vorticity with $3/p+2/q\leq 3$, $1 \leq q < \infty$, or the $L^{p,q}_{x,t}$-norm of the gradient of the vorticity with $3/p+2/q\leq 4$, $1 \leq q$, $1 \leq p$, is sufficiently small near $z$

Angular Dependence of X-ray Absorption Spectrum for Field-aligned Fe-based Superconductors

Anisotropic Fe K-edge and As K-edge X-ray absorption near edge spectrum (XANES) measurements on superconducting (T_c = 52 K) (Sm_{0.95}La_{0.05})FeAs(O_{0.85}F_{0.15}) field-aligned microcrystalline powder are presented. The angular dependence of Fe pre-edge peak (dipole transition of Fe-1s electrons to Fe-3d/As-4p hybrid bands) relative to the tetragonal ab-plane of aligned powder indicates larger density of state (DOS) along the c-axis, and is consistent with the LDA band structure calculation. The anisotropic Fe K-edge spectra exhibit a chemical shift to lower energy compared to FeO which are closely related to the itinerant character of Fe^{2+}-3d^6 orbitals. The anisotropic As K-edge spectra are more or less the mirror images of Fe K-edge due to the symmetrical Fe-As hybridiztion in the FeAs layer. Angular dependence of As main peak (dipole transition of As-1s electrons to higher energy hybrid bands) was observed suggesting character of As-4d e_g orbitals.Comment: 4 pages, 6 figures, accepted 9/11/2009 Physical Review B (B15