Asymmetric Colliding Nuclear Matter Approach in Heavy Ion Collisions

The early stage of a heavy ion collision is governed by local non-equilibrium momentum distributions which have been approximated by colliding nuclear matter configurations, i.e. by two Lorentz elongated Fermi ellipsoids. This approach has been extended from the previous assumption of symmetric systems to asymmetric 2-Fermi sphere configurations, i.e. to different densities. This provides a smoother transition from the limiting situation of two interpenetrating currents to an equilibrated system. The model is applied to the dynamical situations of heavy ion collisions at intermediate energies within the framework of relativistic transport (RBUU) calculations. We find that the extended colliding nuclear matter approach is more appropriate to describe collective reaction dynamics in terms of flow observables, in particular, for the elliptic flow at low energies.Comment: 21 pages, 8 figures, accepted for publication in Nuclear Physics

Preparation of highly visible-light active N-doped TiO₂ photocatalyst

A series of N-doped anatase TiO2 samples have been prepared using a solvothermal method in an organic amine/ethanol–water reaction system. The effects of different starting N:Ti atomic ratios on the catalysts structure, surface property and catalytic activity have been investigated. The photocatalytic activity and stability of the N-doped TiO2 samples were evaluated through using the decomposition of Methylene blue (MB) and Methyl orange (MO) as model reaction under visible light irradiation. Characterization results show that the nitrogen dopant has a significant effect on the crystallite size and optical absorption of TiO2. It was found that the N-doped TiO2 catalysts have enhanced absorption in the visible light region, and exhibit higher activity for photocatalytic degradation of model dyes (e.g. MB and MO). The catalyst with the highest performance was the one prepared using N:Ti molar ratio of 1.0. Electron paramagnetic resonance (EPR) measurement suggests the materials contain Ti3+ ions, with both the degree of N doping and oxygen vacancies make contributions to the visible light absorption of TON. The presence of superoxide radicals (O•-) and hydroxyl radicals (•OH) on the surface of TON were found to be responsible for MB and MO solution decoloration under visible light. Based on the results of the present study, a visible light induced photocatalytic mechanism has been proposed for N-doped anatase TiO2

Investigations of Near-Field Thermal-Hydrologic-Mechanical-Chemical Models for Radioactive Waste Disposal in Clay/Shale Rock

Clay/shale has been considered as potential host rock for geological disposal of high-level radioactive waste throughout the world, because of its low permeability, low diffusion coefficient, high retention capacity for radionuclides, and capability to self-seal fractures. For example, Callovo-Oxfordian argillites at the Bure site, France (Fouche et al., 2004), Toarcian argillites at the Tournemire site, France (Patriarche et al., 2004), Opalinus Clay at the Mont Terri site, Switzerland (Meier et al., 2000), and Boom clay at the Mol site, Belgium (Barnichon and Volckaert, 2003) have all been under intensive scientific investigation (at both field and laboratory scales) for understanding a variety of rock properties and their relationships to flow and transport processes associated with geological disposal of radioactive waste. Figure 1-1 presents the distribution of clay/shale formations within the USA

The fermi arc and fermi pocket in cuprates in a short-range diagonal stripe phase

In this paper we studied the fermi arc and the fermi pocket in cuprates in a short-range diagonal stripe phase with wave vectors $(7\pi/8, 7\pi/8)$, which reproduce with a high accuracy the positions and sizes of the fermi arc and fermi pocket and the superstructure in cuprates observed by Meng et al\cite{Meng}. The low-energy spectral function indicates that the fermi pocket results from the main band and the shadow band at the fermi energy. Above the fermi energy the shadow band gradually departs away from the main band, leaving a fermi arc. Thus we conclude that the fermi arc and fermi pocket can be fully attributed to the stripe phase but has nothing to do with pairing. Incorporating a d-wave pairing potential in the stripe phase the spectral weight in the antinodal region is removed, leaving a clean fermi pocket in the nodal region.Comment: 5 pages, 6 figure

Transformation elastodynamics and active exterior acoustic cloaking

This chapter consists of three parts. In the first part we recall the elastodynamic equations under coordinate transformations. The idea is to use coordinate transformations to manipulate waves propagating in an elastic material. Then we study the effect of transformations on a mass-spring network model. The transformed networks can be realized with "torque springs", which are introduced here and are springs with a force proportional to the displacement in a direction other than the direction of the spring terminals. Possible homogenizations of the transformed networks are presented, with potential applications to cloaking. In the second and third parts we present cloaking methods that are based on cancelling an incident field using active devices which are exterior to the cloaked region and that do not generate significant fields far away from the devices. In the second part, the exterior cloaking problem for the Laplace equation is reformulated as the problem of polynomial approximation of analytic functions. An explicit solution is given that allows to cloak larger objects at a fixed distance from the cloaking device, compared to previous explicit solutions. In the third part we consider the active exterior cloaking problem for the Helmholtz equation in 3D. Our method uses the Green's formula and an addition theorem for spherical outgoing waves to design devices that mimic the effect of the single and double layer potentials in Green's formula.Comment: Submitted as a chapter for the volume "Acoustic metamaterials: Negative refraction, imaging, lensing and cloaking", Craster and Guenneau ed., Springe

Free flux flow resistivity in strongly overdoped high-T_c cuprate; purely viscous motion of the vortices in semiclassical d-wave superconductor

We report the free flux flow (FFF) resistivity associated with a purely viscous motion of the vortices in moderately clean d-wave superconductor Bi:2201 in the strongly overdoped regime (T_c=16K) for a wide range of the magnetic field in the vortex state. The FFF resistivity is obtained by measuring the microwave surface impedance at different microwave frequencies. It is found that the FFF resistivity is remarkably different from that of conventional s-wave superconductors. At low fields (H<0.2H_c2) the FFF resistivity increases linearly with H with a coefficient which is far larger than that found in conventional s-wave superconductors. At higher fields, the FFF resistivity increases in proportion to \sqrt H up to H_c2. Based on these results, the energy dissipation mechanism associated with the viscous vortex motion in "semiclassical" d-wave superconductors with gap nodes is discussed. Two possible scenarios are put forth for these field dependence; the enhancement of the quasiparticle relaxation rate and the reduction of the number of the quasiparticles participating the energy dissipation in d-wave vortex state.Comment: 9 pages 7 figures, to appear in Phys. Rev.

Search for the Rare Decays J/Psi --> Ds- e+ nu_e, J/Psi --> D- e+ nu_e, and J/Psi --> D0bar e+ e-

We report on a search for the decays J/Psi --> Ds- e+ nu_e + c.c., J/Psi --> D- e+ nu_e + c.c., and J/Psi --> D0bar e+ e- + c.c. in a sample of 5.8 * 10^7 J/Psi events collected with the BESII detector at the BEPC. No excess of signal above background is observed, and 90% confidence level upper limits on the branching fractions are set: B(J/Psi --> Ds- e+ nu_e + c.c.)<4.8*10^-5, B(J/Psi --> D- e+ nu_e + c.c.) D0bar e+ e- + c.c.)<1.1*10^-5Comment: 10 pages, 4 figure

Measurements of J/psi Decays into 2(pi+pi-)eta and 3(pi+pi-)eta

Based on a sample of 5.8X 10^7 J/psi events taken with the BESII detector, the branching fractions of J/psi--> 2(pi+pi-)eta and J/psi-->3(pi+pi-)eta are measured for the first time to be (2.26+-0.08+-0.27)X10^{-3} and (7.24+-0.96+-1.11)X10^{-4}, respectively.Comment: 11 pages, 6 figure

BESII Detector Simulation

A Monte Carlo program based on Geant3 has been developed for BESII detector simulation. The organization of the program is outlined, and the digitization procedure for simulating the response of various sub-detectors is described. Comparisons with data show that the performance of the program is generally satisfactory.Comment: 17 pages, 14 figures, uses elsart.cls, to be submitted to NIM