Microscopic Calculation of in-Medium Proton-Proton Cross Sections

We derive in-medium PROTON-PROTON cross sections in a microscopic model based upon the Bonn nucleon-nucleon potential and the Dirac-Brueckner approach for nuclear matter. We demonstrate the difference between proton-proton and neutron-proton cross sections and point out the need to distinguish carefully between the two cases. We also find substantial differences between our in-medium cross sections and phenomenological parametrizations that are commonly used in heavy-ion reactions.Comment: 9 pages of RevTex and 4 figures (postscript in separate uuencoded file), UI-NTH-930

Space Alignment Based on Regularized Inversion Precoding in Cognitive Transmission

For a two-tier Multiple-Input Multiple-Output (MIMO) cognitive network with common receiver, the precoding matrix has a compact relationship with the capacity performance in the unlicensed secondary system. To increase the capacity of secondary system, an improved precoder based on the idea of regularized inversion for secondary transmitter is proposed. An iterative space alignment algorithm is also presented to ensure the Quality of Service (QoS) for primary system. The simulations reveal that, on the premise of achieving QoS for primary system, our proposed algorithm can get larger capacity in secondary system at low Signal-to-Noise Ratio (SNR), which proves the effectiveness of the algorithm

Space Charge Behaviour in Oil-Paper Insulation with Different Aging Condition

Oil-paper insulation system is widely used in power transformers and cables. The dielectric properties of oilpaper insulation play an important role in the reliable operation of power equipment. Oil-paper insulation degrades under a combined stress of thermal (the most important factor), electrical, mechanical, and chemical stresses during routine operations, which has great effect on the dielectric properties of oil-paper insulation [1]. Space charge in oil-paper insulation has a close relation to its electrical performance [1]. In this paper, space charge behaviour of oil-paper insulation sample with three different ageing conditions (aged for 0, 35 and 77 days) was investigated using the pulsed electroacoustic (PEA) technique. The influence of aging on the space charge dynamics behaviour was analysed. Results show that aging has great effect on the space charge dynamics of oil-paper insulation. The homocharge injection takes place under all three aging conditions above. Positive charges tend to accumulate in the sample, and increase with the oil-paper insulation sample deterioration. The time to achieve the maximum injection charge density is 30s, 2min and 10min for oil-paper insulation sample aged for 0, 35 and 77 days, respectively. The maximum charge density injected in the sample aged for 77 days is more than two times larger than the initial sample. In addition, the charge decay speed becomes much slower with the aging time increase. There is an exponential relationship between the total charge amount and the decay time. The decay time constant ? increases with the increasing deterioration condition of the oil-paper insulation sample. The ? value may be used to reflect the aging status of oil-paper insulation

Early Time Dynamics of Gluon Fields in High Energy Nuclear Collisions

Nuclei colliding at very high energy create a strong, quasi-classical gluon field during the initial phase of their interaction. We present an analytic calculation of the initial space-time evolution of this field in the limit of very high energies using a formal recursive solution of the Yang-Mills equations. We provide analytic expressions for the initial chromo-electric and chromo-magnetic fields and for their energy-momentum tensor. In particular, we discuss event-averaged results for energy density and energy flow as well as for longitudinal and transverse pressure of this system. For example, we find that the ratio of longitudinal to transverse pressure very early in the system behaves as $p_L/p_T = -[1-\frac{3}{2a}(Q\tau)^2]/[1-\frac{1}{a}(Q\tau)^2]+\mathcal{O}(Q\tau)^4$ where $\tau$ is the longitudinal proper time, $Q$ is related to the saturation scales $Q_s$ of the two nuclei, and $a = \ln (Q^2/\hat{m}^2)$ with $\hat m$ a scale to be defined later. Our results are generally applicable if $\tau \lesssim 1/Q$. As already discussed in a previous paper, the transverse energy flow $S^i$ of the gluon field exhibits hydrodynamic-like contributions that follow transverse gradients of the energy density $\nabla^i \varepsilon$. In addition, a rapidity-odd energy flow also emerges from the non-abelian analog of Gauss' Law and generates non-vanishing angular momentum of the field. We will discuss the space-time picture that emerges from our analysis and its implications for observables in heavy ion collisions.Comment: 26 pages, 9 figure

An improved closed-loop stability related measure for finite-precision digital controller realizations

The pole-sensitivity approach is employed to investigate the stability issue of the discrete-time control system, where a digital controller, implemented with finite word length (FWL), is used. A new stability related measure is derived, which is more accurate in estimating the closed-loop stability robustness of an FWL implemented controller than some existing measures for the pole-sensitivity analysis. This improved stability measure thus provides a better criterion to find the optimal realizations for a generic controller structure that includes output-feedback and observer-based controllers. A numerical example is used to verify the theoretical analysis and to illustrate the design procedure

An improved closed-loop stability related measure for finite-precision digital controller realizations

The pole-sensitivity approach is employed to investigate the stability issue of the discrete-time control system, where a digital controller, implemented with finite word length (FWL), is used. A new stability related measure is derived, which is more accurate in estimating the closed-loop stability robustness of an FWL implemented controller than some existing measures for the pole-sensitivity analysis. This improved stability measure thus provides a better criterion to find the optimal realizations for a generic controller structure that includes output-feedback and observer-based controllers. A numerical example is used to verify the theoretical analysis and to illustrate the design procedure

Medium Dependence of the Vector-Meson Mass: Dynamical and/or Brown-Rho Scaling?

We discuss the similarities and differences for the theories of Rapp, Wambach and collaborators (called R/W in short) and those based on Brown-Rho scaling (called B/R), as applied to reproduce the dileptons measured by the CERES collaboration in the CERN experiments. In both theories the large number of dileptons at invariant masses $\sim$~$m_\rho/2$ are shown to be chiefly produced by a density-dependent $\rho$-meson mass. In R/W the medium dependence is dynamically calculated using hadronic variables defined in the matter-free vacuum. In B/R scaling it follows from movement towards chiral symmetry restoration due to medium-induced vacuum change, and is described in terms of constituent (or quasiparticle) quarks. We argue that the R/W description should be reliable up to densities somewhat beyond nuclear density, where hadrons are the effective variables. At higher density there should be a crossover to constituent quarks as effective variables scaling according to B/R. In the crossover region, the two descriptions must be ``dual''.Comment: 13 pages LaTeX, incl. 5 eps-figures and appb.sty; Talk given at the Workshop on 'The Structure of Mesons, Baryons and Nuclei', Cracow, May 1998, in honor of J. Speth's 60th birthday, to be published in Acta Physica Polonica

First principles lattice dynamics of NaCoO2_2

We report first principles linear response calculations on NaCoO$_2$. Phonon frequencies and eigenvectors are obtained throughout the Brillouin zone for two geometries with different Na site occupancies. While most of the phonon modes are found to be unsensitive to the Na site occupancy, there are two modes dominated by out-of-plane vibrations of Na giving very different frequencies for different geometries. One of these two modes, the A$_{2u}$ mode, is infrared-active, and can be used as a suitable sensor of Na distribution/ordering. The longitudinal-transverse splitting of the zone-center optical-mode frequencies, Born effective charges and the dielectric constants are also reported, showing considerable anisotropy. The calculated frequencies of Raman-active modes generally agree with the experimental values of corresponding Na de-intercalated and/or hydrated compounds, while it requires better experimental data to clarify the infrared-active mode frequencies.Comment: 12 pages, 2 figure

Momentum-Dependent Mean Field Based Upon the Dirac-Brueckner Approach for Nuclear Matter

A momentum-dependent mean field potential, suitable for application in the transport-model description of nucleus-nucleus collisions, is derived in a microscopic way. The derivation is based upon the Bonn meson-exchange model for the nucleon-nucleon interaction and the Dirac-Brueckner approach for nuclear matter. The properties of the microscopic mean field are examined and compared with phenomenological parametrizations which are commonly used in transport-model calculations.Comment: 15 pages text (RevTex) and 4 figures (postscript in a separate uuencoded file), UI-NTH-930

The quantum Casimir operators of \Uq and their eigenvalues

We show that the quantum Casimir operators of the quantum linear group constructed in early work of Bracken, Gould and Zhang together with one extra central element generate the entire center of \Uq. As a by product of the proof, we obtain intriguing new formulae for eigenvalues of these quantum Casimir operators, which are expressed in terms of the characters of a class of finite dimensional irreducible representations of the classical general linear algebra.Comment: 10 page