7,258 research outputs found
Nuclear Masses, Chaos, and the Residual Interaction
We interpret the discrepancy between semiempirical nuclear mass formulas and
actual nuclear masses in terms of the residual interaction. We show that
correlations exist among all binding energies and all separation energies
throughout the valley of stability. We relate our approach to chaotic motion in
nuclei.Comment: 9 page
Randomness in nuclei and in the quark-gluon plasma
The issue of averaging randomness is addressed, mostly in nuclear physics,
but shortly also in QCD. The Feshbach approach, so successful in dealing with
the continuum spectrum of the atomic nuclei ("optical model"), is extended to
encompass bound states as well ("shell model"). Its relationship with the
random-matrix theory is discussed and the bearing of the latter on QCD,
especially in connection with the spectrum of the Dirac operator, is briefly
touched upon. Finally the question of whether Feshbach's theory can cope with
the averaging required by QCD is considered.Comment: 24 pages, 6 figures; to appear in the Proceedings of the Workshop
"Quark-Gluon Plasma and Relativistic Heavy Ions", Frascati, 14-18 January
200
Complexity of ITL model checking: some well-behaved fragments of the interval logic HS
Model checking has been successfully used in many computer science fields,
including artificial intelligence, theoretical computer science, and databases.
Most of the proposed solutions make use of classical, point-based temporal
logics, while little work has been done in the interval temporal logic setting.
Recently, a non-elementary model checking algorithm for Halpern and Shoham's
modal logic of time intervals HS over finite Kripke structures (under the
homogeneity assumption) and an EXPSPACE model checking procedure for two
meaningful fragments of it have been proposed. In this paper, we show that more
efficient model checking procedures can be developed for some expressive enough
fragments of HS
Fundamental structure of steady plastic shock waves in metals
The propagation of steady plane shock waves in metallic materials is considered. Following the constitutive framework adopted by R. J. Clifton [Shock Waves and the Mechanical Properties of Solids, edited by J. J. Burke and V. Weiss (Syracuse University Press, Syracuse, N.Y., 1971), p. 73] for analyzing elastic–plastic transient waves, an analytical solution of the steady state propagation of plastic shocks is proposed. The problem is formulated in a Lagrangian setting appropriate for large deformations. The material response is characterized by a quasistatic tensile (compression) test (providing the isothermal strain hardening law). In addition the elastic response is determined up to second order elastic constants by ultrasonic measurements. Based on this simple information, it is shown that the shock kinetics can be quite well described for moderate shocks in aluminum with stress amplitude up to 10 GPa. Under the later assumption, the elastic response is assumed to be isentropic, and thermomechanical coupling is neglected. The model material considered here is aluminum, but the analysis is general and can be applied to any viscoplastic material subjected to moderate amplitude shocks. Comparisons with experimental data are made for the shock velocity, the particle velocity and the shock structure. The shock structure is obtained by quadrature of a first order differential equation, which provides analytical results under certain simplifying assumptions. The effects of material parameters and loading conditions on the shock kinetics and shock structure are discussed. The shock width is characterized by assuming an overstress formulation for the viscoplastic response. The effects on the shock structure of strain rate sensitivity are analyzed and the rationale for the J. W. Swegle and D. E. Grady [J. Appl. Phys. 58, 692 (1985)] universal scaling law for homogeneous materials is explored. Finally, the ability to deduce information on the viscoplastic response of materials subjected to very high strain rates from shock wave experiments is discussed
Source extraction and photometry for the far-infrared and sub-millimeter continuum in the presence of complex backgrounds
(Abridged) We present a new method for detecting and measuring compact
sources in conditions of intense, and highly variable, fore/background. While
all most commonly used packages carry out the source detection over the signal
image, our proposed method builds from the measured image a "curvature" image
by double-differentiation in four different directions. In this way point-like
as well as resolved, yet relatively compact, objects are easily revealed while
the slower varying fore/background is greatly diminished. Candidate sources are
then identified by looking for pixels where the curvature exceeds, in absolute
terms, a given threshold; the methodology easily allows us to pinpoint
breakpoints in the source brightness profile and then derive reliable guesses
for the sources extent. Identified peaks are fit with 2D elliptical Gaussians
plus an underlying planar inclined plateau, with mild constraints on size and
orientation. Mutually contaminating sources are fit with multiple Gaussians
simultaneously using flexible constraints. We ran our method on simulated
large-scale fields with 1000 sources of different peak flux overlaid on a
realistic realization of diffuse background. We find detection rates in excess
of 90% for sources with peak fluxes above the 3-sigma signal noise limit; for
about 80% of the sources the recovered peak fluxes are within 30% of their
input values.Comment: Accepted on A&
Spreading Widths of Doorway States
As a function of energy E, the average strength function S(E) of a doorway
state is commonly assumed to be Lorentzian in shape and characterized by two
parameters, the peak energy E_0 and the spreading width Gamma. The simple
picture is modified when the density of background states that couple to the
doorway state changes significantly in an energy interval of size Gamma. For
that case we derive an approximate analytical expression for S(E). We test our
result successfully against numerical simulations. Our result may have
important implications for shell--model calculations.Comment: 13 pages, 7 figure
Interaction of Regular and Chaotic States
Modelling the chaotic states in terms of the Gaussian Orthogonal Ensemble of
random matrices (GOE), we investigate the interaction of the GOE with regular
bound states. The eigenvalues of the latter may or may not be embedded in the
GOE spectrum. We derive a generalized form of the Pastur equation for the
average Green's function. We use that equation to study the average and the
variance of the shift of the regular states, their spreading width, and the
deformation of the GOE spectrum non-perturbatively. We compare our results with
various perturbative approaches.Comment: 26 pages, 9 figure
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