842 research outputs found
Clustering and Triaxial Deformations of Ca
We have studied the positive-parity states of Ca using antisymmetrized
molecular dynamics (AMD) and the generator coordinate method (GCM). Imposing
two different kinds of constraints on the variational calculation, we have
found various kinds of structures such as a deformed-shell
structure, as well as -Ar and C-Si cluster
structures. After the GCM calculation, we obtained a normal-deformed band and a
superdeformed band together with their side bands associated with triaxial
deformation. The calculated values agreed well with empirical data. It
was also found that the normal-deformed and superdeformed bands have a
non-negligible -Ar cluster component and C-Si
cluster component, respectively. This leads to the presence of an
-Ar higher-nodal band occurring above the normal-deformed band.Comment: 11pages, 9 figure
nature of the superdeformed band of and the evolution of the molecular structure
The relation between the superdeformed band of and molecular bands is studied by the deformed-base
antisymmetrized molecular dynamics with the Gogny D1S force. It is found that
the obtained superdeformed band members of have considerable
amount of the component. Above the superdeformed
band, we have obtained two excited rotational bands which have more prominent
character of the molecular band. These three
rotational bands are regarded as a series of
molecular bands which were predicted by using the unique
- optical potentil. As the excitation energy and principal
quantum number of the relative motion increase, the cluster structure becomes more prominent but at the same time, the band
members are fragmented into several states
Breakdown of `phase rigidity' and variations of the Fano effect in closed Aharonov-Bohm interferometers
Although the conductance of a closed Aharonov-Bohm interferometer, with a
quantum dot on one branch, obeys the Onsager symmetry under magnetic field
reversal, it needs not be a periodic function of this field: the conductance
maxima move with both the field and the gate voltage on the dot, in an apparent
breakdown of `phase rigidity'. These experimental findings are explained
theoretically as resulting from multiple electronic paths around the
interferometer ring. Data containing several Coulomb blockade peaks, whose
shapes change with the magnetic flux, are fitted to a simple model, in which
each resonant level on the dot couples to a different path around the ring
Observation of "Partial Coherence" in an Aharonov-Bohm Interferometer with a Quantum Dot
We report experiments on the interference through spin states of electrons in
a quantum dot (QD) embedded in an Aharonov-Bohm (AB) interferometer. We have
picked up a spin-pair state, for which the environmental conditions are ideally
similar and have traced the AB amplitude in the range of the gate voltage that
covers the pair. The behavior of the asymmetry in the amplitude around the two
Coulomb peaks agrees with the theoretical prediction that relates a spin-flip
process in a QD to the quantum dephasing of electrons. These results consist
evidence of "partial coherence" due to an entanglement of spins in the QD and
the interferometer.Comment: 4 pages, 3 figures, RevTe
Internal One-Particle Density Matrix for Bose-Einstein Condensates with Finite Number of Particles in a Harmonic Potential
Investigations on the internal one-particle density matrix in the case of
Bose-Einstein condensates with a finite number () of particles in a harmonic
potential are performed. We solve the eigenvalue problem of the
Pethick-Pitaevskii-type internal density matrix and find a fragmented
condensate. On the contrary the condensate Jacobi-type internal density matrix
gives complete condensation into a single state. The internal one-particle
density matrix is, therefore, shown to be different in general for different
choices of the internal coordinate system. We propose two physically motivated
criteria for the choice of the adequate coordinate systems which give us a
unique answer for the internal one-particle density matrix. One criterion is
that in the infinite particle number limit () the internal
one-particle density matrix should have the same eigenvalues and eigenfunctions
as those of the corresponding ideal Bose-Einstein condensate in the laboratory
frame. The other criterion is that the coordinate of the internal one-particle
density matrix should be orthogonal to the remaining internal
coordinates. This second criterion is shown to imply the first criterion. It is
shown that the internal Jacobi coordinate system satisfies these two criteria
while the internal coordinate system adopted by Pethick and Pitaevskii for the
construction of the internal one-particle density matrix does not. It is
demonstrated that these two criteria uniquely determine the internal
one-particle density matrix which is identical to that calculated with the
Jacobi coordinates. The relevance of this work concerning -particle
condensates in nuclei, as well as bosonic atoms in traps, is pointed out.Comment: revised version, to appear in Phys. Rev.
Off-pump coronary bypass grafting is safe and efficient in patients with left main disease and higher EuroScore
Background: Summary Left main disease (LMD) and associated cardiac risk factors are often perceived as a limiting factor for the outcome of off-pump coronary artery bypass (OPCAB) grafting. In this study, we assess whether the outcome of OPCAB surgery is affected in such patients. Methods: We retrospectively compared perioperative parameters in 66 OPCAB patients (group A) with LMD and 216 OPCAB patients without (group B) LMD. The patients were operated in the time frame between 2002 and 2007. LMD was defined as a stenosis >50%. Results: Patients in group A had a higher EuroSCORE (logistic: 3.7 ± 0.1 vs 6.3 ± 0.3, p = 0.027), increased coronary artery disease (CAD) family history (p = 0.015) and cerebrovascular accidents (p = 0.027), increased history of congestive heart failure (p = 0.013), more urgent surgery (p = 0.008), previous percutaneous transluminal coronary angioplasties (PTCAs) (p = 0.05) and previous stent implantation (p = 0.023). An intra-aortic balloon pump (IABP) was inserted more frequently in the LMD group preoperatively (p = 0.004). There were two conversions to on-pump during OPCAB surgery. There were no differences in the postoperative outcomes in the LMD group A versus group B, such as cardiac-related events, neurological deficits, cardiac enzyme course, arrhythmias, blood loss, infections and renal failure. Conclusions: The presence of LMD and higher EuroSCORE does not yield adverse outcomes in OPCAB patient
Antisymmetrized molecular dynamics of wave packets with stochastic incorporation of Vlasov equation
On the basis of the antisymmetrized molecular dynamics (AMD) of wave packets
for the quantum system, a novel model (called AMD-V) is constructed by the
stochastic incorporation of the diffusion and the deformation of wave packets
which is calculated by Vlasov equation without any restriction on the one-body
distribution. In other words, the stochastic branching process in molecular
dynamics is formulated so that the instantaneous time evolution of the averaged
one-body distribution is essentially equivalent to the solution of Vlasov
equation. Furthermore, as usual molecular dynamics, AMD-V keeps the many-body
correlation and can naturally describe the fluctuation among many channels of
the reaction. It is demonstrated that the newly introduced process of AMD-V has
drastic effects in heavy ion collisions of 40Ca + 40Ca at 35 MeV/nucleon,
especially on the fragmentation mechanism, and AMD-V reproduces the
fragmentation data very well. Discussions are given on the interrelation among
the frameworks of AMD, AMD-V and other microscopic models developed for the
nuclear dynamics.Comment: 26 pages, LaTeX with revtex and epsf, embedded postscript figure
Universal bound to the amplitude of the vortex Nernst signal in superconductors
A liquid of superconducting vortices generates a transverse thermoelectric
response. This Nernst signal has a tail deep in the normal state due to
superconducting fluctuations. Here, we present a study of the Nernst effect in
two-dimensional hetero-structures of Nb-doped strontium titanate (STO) and in
amorphous MoGe. The Nernst signal generated by ephemeral Cooper pairs above the
critical temperature has the magnitude expected by theory in STO. On the other
hand, the peak amplitude of the vortex Nernst signal below is comparable
in both and in numerous other superconductors despite the large distribution of
the critical temperature and the critical magnetic fields. In four
superconductors belonging to different families, the maximum Nernst signal
corresponds to an entropy per vortex per layer of k.Comment: Accepted for publication in Phys. Rev. Let
A detailed study of quasinormal frequencies of the Kerr black hole
We compute the quasinormal frequencies of the Kerr black hole using a
continued fraction method. The continued fraction method first proposed by
Leaver is still the only known method stable and accurate for the numerical
determination of the Kerr quasinormal frequencies. We numerically obtain not
only the slowly but also the rapidly damped quasinormal frequencies and analyze
the peculiar behavior of these frequencies at the Kerr limit. We also calculate
the algebraically special frequency first identified by Chandrasekhar and
confirm that it coincide with the quasinormal frequency only at the
Schwarzschild limit.Comment: REVTEX, 15 pages, 7 eps figure
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