3,074 research outputs found
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
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
Multiple interfaces between a serine recombinase and an enhancer control site-specific DNA inversion.
Serine recombinases are often tightly controlled by elaborate, topologically-defined, nucleoprotein complexes. Hin is a member of the DNA invertase subclass of serine recombinases that are regulated by a remote recombinational enhancer element containing two binding sites for the protein Fis. Two Hin dimers bound to specific recombination sites associate with the Fis-bound enhancer by DNA looping where they are remodeled into a synaptic tetramer competent for DNA chemistry and exchange. Here we show that the flexible beta-hairpin arms of the Fis dimers contact the DNA binding domain of one subunit of each Hin dimer. These contacts sandwich the Hin dimers to promote remodeling into the tetramer. A basic region on the Hin catalytic domain then contacts enhancer DNA to complete assembly of the active Hin tetramer. Our results reveal how the enhancer generates the recombination complex that specifies DNA inversion and regulates DNA exchange by the subunit rotation mechanism. DOI:http://dx.doi.org/10.7554/eLife.01211.001
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
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
Assembly of a Tightly Interwound DNA Recombination Complex Poised for Deletion
In a recent issue of Molecular Cell, Mouw et al. (2008) report a crystal structure of a serine recombinase bound to a regulatory DNA site in an unexpected synaptic complex configuration, which forms the framework for a new model of the entire 12 subunit, 186 bp deletion complex
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
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
Coplanar stripline antenna design for optically detected magnetic resonance on semiconductor quantum dots
We report on the development and testing of a coplanar stripline antenna that
is designed for integration in a magneto-photoluminescence experiment to allow
coherent control of individual electron spins confined in single self-assembled
semiconductor quantum dots. We discuss the design criteria for such a structure
which is multi-functional in the sense that it serves not only as microwave
delivery but also as electrical top gate and shadow mask for the single quantum
dot spectroscopy. We present test measurements on hydrogenated amorphous
silicon, demonstrating electrically detected magnetic resonance using the
in-plane component of the oscillating magnetic field created by the coplanar
stripline antenna necessary due to the particular geometry of the quantum dot
spectroscopy. From reference measurements using a commercial electron spin
resonance setup in combination with finite element calculations simulating the
field distribution in the structure, we obtain an average magnetic field of
~0.2mT at the position where the quantum dots would be integrated into the
device. The corresponding pi-pulse time of ~0.3us fully meets the requirements
set by the high sensitivity optical spin read-out scheme developed for the
quantum dot
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