330,479 research outputs found
Antikaon flow in heavy-ion collisions: the effects of absorption and mean fields
We study antikaon flow in heavy-ion collisions at SIS energies based on the
relativistic transport model (RVUU 1.0). The production of antikaons from both
baryon-baryon and pion-baryon collisions are included. Taking into account only
elastic and inelastic collisions of the antikaon with nucleons and neglecting
its mean-field potential as in the cascade model, a strong antiflow or
anti-correlation of antikaons with respect to nucleons is seen as a result of
the strong absorption of antikaons by nucleons. However, the antiflow of
antikaons disappears after including also their propagation in the attractive
mean-field potential. The experimental measurement of antikaon flow in
heavy-ion collision will be very useful in shedding lights on the relative
importance of antikaon absorption versus its mean-field potential.Comment: 12 pages, 2 postscript figures omitted in the original submission are
included, to appear in Phys. Rev.
Antiproton production in Ni+Ni collisions at 1.85 GeV/nucleon
Antiproton production in Ni+Ni collisions at 1.85 GeV/nucleon is studied in
the relativistic Vlasov-Uehling-Uhlenbeck model. The self-energies of the
antiproton are determined from the nucleon self-energies by the G-parity
transformation. Also, the final-state interactions of the antiproton including
both rescattering and annihilation are explicitly treated. With a soft nuclear
equation of state, the calculated antiproton momentum spectrum is in good
agreement with recent experimental data from the heavy-ion synchrotron at GSI.
The effect due to the reduced nucleon and antinucleon masses in a medium is
found to be more appreciable than in earlier Bevalac experiments with lighter
systems and at higher energies.Comment: 10 pages, 4 figures available upon request to [email protected].
TAMUNT-940
Accurate angle-of-arrival measurement using particle swarm optimization
As one of the major methods for location positioning, angle-of-arrival (AOA) estimation is a significant technology in radar, sonar, radio astronomy, and mobile communications. AOA measurements can be exploited to locate mobile units, enhance communication efficiency and network capacity, and support location-aided routing, dynamic network management, and many location-based services. In this paper, we propose an algorithm for AOA estimation in colored noise fields and harsh application scenarios. By modeling the unknown noise covariance as a linear combination of known weighting matrices, a maximum likelihood (ML) criterion is established, and a particle swarm optimization (PSO) paradigm is designed to optimize the cost function. Simulation results demonstrate that the paired estimator PSO-ML significantly outperforms other popular techniques and produces superior AOA estimates
Probability-dependent gain-scheduled filtering for stochastic systems with missing measurements
Copyright @ 2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.This brief addresses the gain-scheduled filtering problem for a class of discrete-time systems with missing measurements, nonlinear disturbances, and external stochastic noise. The missing-measurement phenomenon is assumed to occur in a random way, and the missing probability is time-varying with securable upper and lower bounds that can be measured in real time. The multiplicative noise is a state-dependent scalar Gaussian white-noise sequence with known variance. The addressed gain-scheduled filtering problem is concerned with the design of a filter such that, for the admissible random missing measurements, nonlinear parameters, and external noise disturbances, the error dynamics is exponentially mean-square stable. The desired filter is equipped with time-varying gains based primarily on the time-varying missing probability and is therefore less conservative than the traditional filter with fixed gains. It is shown that the filter parameters can be derived in terms of the measurable probability via the semidefinite program method.This work was supported in part by the Leverhulme Trust of the U.K., the Engineering and Physical Sciences Research Council (EPSRC) of the U.K. under Grant GR/S27658/01, the National Natural Science Foundation of China under Grants 61028008, 61074016 and 60974030, the Shanghai Natural
Science Foundation of China under Grant 10ZR1421200, and the Alexander von Humboldt Foundation of Germany
Probing the momentum dependence of medium modifications of the nucleon-nucleon elastic cross sections
The momentum dependence of the medium modifications on nucleon-nucleon
elastic cross sections is discussed with microscopic transport theories and
numerically investigated with an updated UrQMD microscopic transport model. The
semi-peripheral Au+Au reaction at beam energy MeV is adopted as an
example. It is found that the uncertainties of the momentum dependence on
medium modifications of cross sections influence the yields of free nucleons
and their collective flows as functions of their transverse momentum and
rapidity. Among these observables, the elliptic flow is sensitively dependent
on detailed forms of the momentum dependence and more attention should be paid.
The elliptic flow is hardly influenced by the probable splitting effect of the
neutron-neutron and proton-proton cross sections so that one might pin down the
mass splitting effect of the mean-field level at high beam energies and high
nuclear densities by exploring the elliptic flow of nucleons or light clusters.Comment: 13 pages, 6 figures, 1 tabl
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