890 research outputs found
Structure of trajectories of complex matrix eigenvalues in the Hermitian-non-Hermitian transition
The statistical properties of trajectories of eigenvalues of Gaussian complex
matrices whose Hermitian condition is progressively broken are investigated. It
is shown how the ordering on the real axis of the real eigenvalues is reflected
in the structure of the trajectories and also in the final distribution of the
eigenvalues in the complex plane.Comment: 12 pages, 3 figure
Symmetry Breaking Study with Deformed Ensembles
A random matrix model to describe the coupling of m-fold symmetry in
constructed. The particular threefold case is used to analyze data on
eigenfrequencies of elastomechanical vibration of an anisotropic quartz block.
It is suggested that such experimental/theoretical study may supply powerful
means to discern intrinsic symmetries in physical systems.Comment: 12 pages, 5 figure
Evaluation of Effective Astrophysical S factor for Non-Resonant Reactions
We derived analytic formulas of the effective S astrophysical S factor,S^eff
for a non-resonant reaction of charged particles using a Taylor expension of
the astrophysical S factor and a uniform approximation.The formulas will be
able to generate generate more accurate approximation to S^eff than previous
ones
Causal Classical Theory of Radiation Damping
It is shown how initial conditions can be appropriately defined for the
integration of Lorentz-Dirac equations of motion. The integration is performed
\QTR{it}{forward} in time. The theory is applied to the case of the motion of
an electron in an intense laser pulse, relevant to nonlinear Compton
scattering.Comment: 8 pages, 2 figure
Addendum: Attenuation of the intensity within a superdeformed band
We investigate a random matrix model [Phys. Rev. C {\bf 65} 024302 (2002] for
the decay-out of a superdeformed band as a function of the parameters:
, , and . Here
is the spreading width for the mixing of an SD state
with a normally deformed (ND) doorway state , and
are the electromagnetic widths of the the SD and ND states respectively, is
the mean level spacing of the compound ND states and is the energy
difference between and . The maximum possible effect of an
order-chaos transition is inferred from analytical and numerical calculations
of the decay intensity in the limiting cases for which the ND states obey
Poisson and GOE statistics. Our results show that the sharp attenuation of the
decay intensity cannot be explained solely by an order-chaos transition.Comment: 4 pages, 4 figures, submitted to Physical Review
Energy averages over regular and chaotic states in the decay out of superdeformed bands
We describe the decay out of a superdeformed band using the methods of
reaction theory. Assuming that decay-out occurs due to equal coupling (on
average) to a sea of equivalent chaotic normally deformed (ND) states, we
calculate the average intraband decay intensity and show that it can be written
as an ``optical'' background term plus a fluctuation term, in total analogy
with average nuclear cross sections. We also calculate the variance in closed
form. We investigate how these objects are modified when the decay to the ND
states occurs via an ND doorway and the ND states' statistical properties are
changed from chaotic to regular. We show that the average decay intensity
depends on two dimensionless variables in the first case while in the second
case, four variables enter the picture.Comment: 8 pages, 1 figure, presented at FUSION03, Matsushima, Miyagi, Japan,
Nov 12-15, 2003, to appear in Progress of Theoretical Physics; corrected
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Symmetry Breaking Study with Random Matrix Ensembles
A random matrix model to describe the coupling of -fold symmetry is
constructed. The particular threefold case is used to analyze data on
eigenfrequencies of elastomechanical vibration of an anisotropic quartz block.
It is suggested that such experimental/theoretical study may supply a powerful
means to discern intrinsic symmetry of physical systems.Comment: 12 pages, 3 figures Contribution to the International Workshop on
Nuclei and Mesoscopic Physics (WNM07), 20-22 October, Michigan Sate
University, East Lansing, Michigan. To appear in a AIP Proceeding (Pawel
Danielewicz, Editor
Level density for deformations of the Gaussian orthogonal ensemble
Formulas are derived for the average level density of deformed, or
transition, Gaussian orthogonal random matrix ensembles. After some general
considerations about Gaussian ensembles we derive formulas for the average
level density for (i) the transition from the Gaussian orthogonal ensemble
(GOE) to the Poisson ensemble and (ii) the transition from the GOE to GOEs.Comment: 7 pages revtex4, 5 eps figures, submitted to Phys. Rev.
Implicit 2D surface flow models performance assessment: Shallow Water Equations vs. Zero-Inertia Model
Zero-Inertia (ZI) models are used in overland flow simulation due to their mathematical simplicity, compared to more complex formulations such as Shallow Water (SW) models. The main hypothesis in ZI models is that the flow is driven by water surface and friction gradients, neglecting local accelerations. On the other hand, SW models are a complete dynamical formulation that provide more information at the cost of a higher level of complexity. In realistic problems, the usually huge number of cells required to ensure accurate spatial representation implies a large amount of computing effort and time. This is particularly true in 2D models. Hence, there is an interest in developing efficient numerical methods. In general terms, numerical schemes used to solve time dependent problems can be classified in two groups, attending to the time evaluation of the unknowns: explicit and implicit methods. Explicit schemes offer the possibility to update the solution at every cell from the known values but are restricted by numerical stability reasons. This can lead to very slow simulations in case of using fine meshes. Implicit schemes avoid this restriction at the cost of generating a system of as many equations as computational cells multiplied by the number of variables to solve. In this work, an implicit finite volume numerical scheme has been used to solve the 2D equations in both ZI and SW models. The scheme is formulated so that both quadrilateral and triangular meshes can be used. A conservative linearization is done for the flux terms, leading to a non-structured matrix for unstructured meshes thus requiring iterative methods for solving the system. A comparison between 2D SW and 2D ZI is done in terms of performance, efficiency and mesh requirements, in which both models benefit of an implicit temporal discretization in steady and nearly-steady situations
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