3,232 research outputs found
Shell Structures and Chaos in Deformed Nuclei and Large Metallic Clusters
A reflection-asymmetric deformed oscillator potential is analysed from the
classical and quantum mechanical point of view. The connection between
occurrence of shell structures and classical periodic orbits is studied using
the ''removal of resonances method'' in a classical analysis. In this
approximation, the effective single particle potential becomes separable and
the frequencies of the classical trajectories are easily determined. It turns
out that the winding numbers calculated in this way are in good agreement with
the ones found from the corresponding quantum mechanical spectrum using the
particle number dependence of the fluctuating part of the total energy. When
the octupole term is switched on it is found that prolate shapes are stable
against chaos whereas spherical and oblate cases become chaotic. An attempt is
made to explain this difference in the quantum mechanical context by looking at
the distribution of exceptional points which results from the matrix structure
of the respective Hamiltonians. In a similar way we analyse the modified
Nilsson model and discuss its consequences for nuclei and metallic clusters.Comment: to appear in Physica Scripta., CNLS-94-02, a talk given at the Nobel
sponsored conference SELMA 94 "New Nuclear Phenomena in the Vicinity of
Closed Shell" (Stockholm and Uppsala, 29 Aug.- 3 Sept. 1994
Resonance scattering and singularities of the scattering function
Recent studies of transport phenomena with complex potentials are explained
by generic square root singularities of spectrum and eigenfunctions of
non-Hermitian Hamiltonians. Using a two channel problem we demonstrate that
such singularities produce a significant effect upon the pole behaviour of the
scattering matrix, and more significantly upon the associated residues. This
mechanism explains why by proper choice of the system parameters the resonance
cross section is increased drastically in one channel and suppressed in the
other channel.Comment: 4 pages, 3 figure
Chaos in Axially Symmetric Potentials with Octupole Deformation
Classical and quantum mechanical results are reported for the single particle
motion in a harmonic oscillator potential which is characterized by a
quadrupole deformation and an additional octupole deformation. The chaotic
character of the motion is srongly dependent on the quadrupole deformation in
that for a prolate deformation virtually no chaos is discernible while for the
oblate case the motion shows strong chaos when the octupole term is turned on.Comment: 6 pages LaTex plus 4 figures available by contacting the authors
directly, published in PHYS.REV.LETT. 72(1994) 235
Deformation of Quantum Dots in the Coulomb Blockade Regime
We extend the theory of Coulomb blockade oscillations to quantum dots which
are deformed by the confining potential. We show that shape deformations can
generate sequences of conductance resonances which carry the same internal
wavefunction. This fact may cause strong correlations of neighboring
conductance peaks. We demonstrate the relevance of our results for the
interpretation of recent experiments on semiconductor quantum dots.Comment: 4 pages, Revtex, 4 postscript figure
Towards an empirical vulnerability function for use in debris flow risk assessment
In quantitative risk assessment, risk is expressed as a function of the hazard, the elements at risk and the vulnerability. From a natural sciences perspective, vulnerability is defined as the expected degree of loss for an element at risk as a consequence of a certain event. The resulting value is dependent on the impacting process intensity and the susceptibility of the elements at risk, and ranges from 0 (no damage) to 1 (complete destruction). With respect to debris flows, the concept of vulnerability &ndash; though widely acknowledged &ndash; did not result in any sound quantitative relationship between process intensities and vulnerability values so far, even if considerable loss occurred during recent years. <br><br> To close this gap and establish this relationship, data from a well-documented debris flow event in the Austrian Alps was used to derive a quantitative vulnerability function applicable to buildings located on the fan of the torrent. The results suggest a second order polynomial function to fit best to the observed damage pattern. Vulnerability is highly dependent on the construction material used for exposed elements at risk. The buildings studied within the test site were constructed by using brick masonry and concrete, a typical design in post-1950s building craft in alpine countries. Consequently, the presented intensity-vulnerability relationship is applicable to this construction type within European mountains. However, a wider application of the presented method to additional test sites would allow for further improvement of the results and would support an enhanced standardisation of the vulnerability function
Orbital Magnetism in Small Quantum Dots with Closed Shells
It is found that various kind of shell structure which occurs at specific
values of the magnetic field leads to the disappearance of the orbital
magnetization for particular magic numbers of small quantum dots with an
electron number .Comment: 4 pages, latex file, four figures as postscript files, to appear at
JETP Letters, December 199
Tri-axial Octupole Deformations and Shell Structure
Manifestations of pronounced shell effects are discovered when adding
nonaxial octupole deformations to a harmonic oscillator model. The degeneracies
of the quantum spectra are in a good agreement with the corresponding main
periodic orbits and winding number ratios which are found by classical
analysis.Comment: 10 pages, Latex, 4 postscript figures, to appear in JETP Letter
Statistical Fluctuations of Electromagnetic Transition Intensities in pf-Shell Nuclei
We study the fluctuation properties of E2 and M1 transition intensities among
T=0,1 states of A = 60 nuclei in the framework of the interacting shell model,
using a realistic effective interaction for pf-shell nuclei with a Ni56 as a
core. It is found that the B(E2) distributions are well described by the
Gaussian orthogonal ensemble of random matrices (Porter-Thomas distribution)
independently of the isobaric quantum number T_z. However, the statistics of
the B(M1) transitions is sensitive to T_z: T_z=1 nuclei exhibit a Porter-Thomas
distribution, while a significant deviation from the GOE statistics is observed
for self-conjugate nuclei (T_z=0).Comment: 8 pages, latex, 3 figures (ps format
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