32,898 research outputs found
Generalized MICZ-Kepler Problems and Unitary Highest Weight Modules
For each integer , we demonstrate that a -dimensional
generalized MICZ-Kepler problem has an \mr{Spin}(2, 2n+2) dynamical symmetry
which extends the manifest \mr{Spin}(2n+1) symmetry. The Hilbert space of
bound states is shown to form a unitary highest weight \mr{Spin}(2,
2n+2)-module which occurs at the first reduction point in the
Enright-Howe-Wallach classification diagram for the unitary highest weight
modules. As a byproduct, we get a simple geometric realization for such a
unitary highest weight \mr{Spin}(2, 2n+2)-module.Comment: 27 pages, Refs. update
Matter loops corrected modified gravity in Palatini formulation
Recently, corrections to the standard Einstein-Hilbert action are proposed to
explain the current cosmic acceleration in stead of introducing dark energy. In
the Palatini formulation of those modified gravity models, there is an
important observation due to Arkani-Hamed: matter loops will give rise to a
correction to the modified gravity action proportional to the Ricci scalar of
the metric. In the presence of such term, we show that the current forms of
modified gravity models in Palatini formulation, specifically, the 1/R gravity
and gravity, will have phantoms. Then we study the possible
instabilities due to the presence of phantom fields. We show that the strong
instability in the metric formulation of 1/R gravity indicated by Dolgov and
Kawasaki will not appear and the decay timescales for the phantom fields may be
long enough for the theories to make sense as effective field theory . On the
other hand, if we change the sign of the modification terms to eliminate the
phantoms, some other inconsistencies will arise for the various versions of the
modified gravity models. Finally, we comment on the universal property of the
Palatini formulation of the matter loops corrected modified gravity models and
its implications.Comment: 11 pages, 1 figures, References adde
Lambda and Anti-Lambda Hypernuclei in Relativistic Mean-field Theory
Several aspects about -hypernuclei in the relativistic mean field
theory, including the effective -nucleon coupling strengths based on
the successful effective nucleon-nucleon interaction PK1, hypernuclear magnetic
moment and -hypernuclei, have been presented. The effect of tensor
coupling in -hypernuclei and the impurity effect of to
nuclear structure have been discussed in detail.Comment: 8 pages, 2 figures, Proceedings of the Sendai International Symposium
"Strangeness in Nuclear and Hadronic Systems SENDAI08
Self-consistent relativistic quasiparticle random-phase approximation and its applications to charge-exchange excitations and -decay half-lives
The self-consistent quasiparticle random-phase approximation (QRPA) approach
is formulated in the canonical single-nucleon basis of the relativistic
Hatree-Fock-Bogoliubov (RHFB) theory. This approach is applied to study the
isobaric analog states (IAS) and Gamov-Teller resonances (GTR) by taking Sn
isotopes as examples. It is found that self-consistent treatment of the
particle-particle residual interaction is essential to concentrate the IAS in a
single peak for open-shell nuclei and the Coulomb exchange term is very
important to predict the IAS energies. For the GTR, the isovector pairing can
increase the calculated GTR energy, while the isoscalar pairing has an
important influence on the low-lying tail of the GT transition. Furthermore,
the QRPA approach is employed to predict nuclear -decay half-lives. With
an isospin-dependent pairing interaction in the isoscalar channel, the
RHFB+QRPA approach almost completely reproduces the experimental -decay
half-lives for nuclei up to the Sn isotopes with half-lives smaller than one
second. Large discrepancies are found for the Ni, Zn, and Ge isotopes with
neutron number smaller than , as well as the Sn isotopes with neutron
number smaller than . The potential reasons for these discrepancies are
discussed in detail.Comment: 34 pages, 14 figure
Cosmological Effects of Nonlinear Electrodynamics
It will be shown that a given realization of nonlinear electrodynamics, used
as source of Einstein's equations, generates a cosmological model with
interesting features, namely a phase of current cosmic acceleration, and the
absence of an initial singularity, thus pointing to a way to solve two
important problems in cosmology
Evaluating Response to High-Dose 13.3 mg/24 h Rivastigmine Patch in Patients with Severe Alzheimer's Disease
AIMS:
To identify factors predicting improvement/stabilization on the Alzheimer's Disease Cooperative Study-Clinical Global Impression of Change (ADCS-CGIC) and investigate whether early treatment responses can predict long-term outcomes, during a trial of 13.3 mg/24 h versus 4.6 mg/24 h rivastigmine patch in patients with severe Alzheimer's disease (AD).
METHODS:
Logistic regression was used to relate Week 24 ADCS-CGIC score to potential baseline predictors. Additional analyses based on receiver-operating characteristic curves were performed using Week 8/16 ADCS-CGIC scores to predict response (13.3 mg/24 h patch) at Week 24. ADCS-CGIC score of (1) 1-3 = "improvement," (2) 1-4 = "improvement or no change".
RESULTS:
"Treatment" (13.3 mg/24 h patch) and increased age were significant predictors of "improvement" (P = 0.01 and P = 0.003, respectively), and "treatment" (P = 0.001), increased age (P = 0.002), and prior AD treatment (P = 0.03) for "improvement or no change". At Week 8 and 16, ADCS-CGIC scores of 4 and 5 were optimal thresholds in predicting "improvement," and "improvement or no change," respectively, at Week 24.
CONCLUSIONS:
A significant therapeutic effect of high-dose rivastigmine patch on ADCS-CGIC response was observed. The 13.3 mg/24 h patch was identified as a predictor of "improvement" or "improvement or no change". Patients with minimal worsening/improvement/no change after treatment initiation may be more likely to respond following long-term therapy
A second-order class-D audio amplifier
Class-D audio amplifiers are particularly efficient, and this efficiency has led to their ubiquity in a wide range of modern electronic appliances. Their output takes the form of a high-frequency square wave whose duty cycle (ratio of on-time to off-time) is modulated at low frequency according to the audio signal. A mathematical model is developed here for a second-order class-D amplifier design (i.e., containing one second-order integrator) with negative feedback. We derive exact expressions for the dominant distortion terms, corresponding to a general audio input signal, and confirm these predictions with simulations. We also show how the observed phenomenon of “pulse skipping” arises from an instability of the analytical solution upon which the distortion calculations are based, and we provide predictions of the circumstances under which pulse skipping will take place, based on a stability analysis. These predictions are confirmed by simulations
Low-lying states in Mg: a beyond relativistic mean-field investigation
The recently developed model of three-dimensional angular momentum projection
plus generator coordinate method on top of triaxial relativistic mean-field
states has been applied to study the low-lying states of Mg. The effects
of triaxiality on the low-energy spectra and E0 and E2 transitions are
examined.Comment: 6 pages, 3 figures, 1 table, talk presented at the 17th nuclear
physics conference "Marie and Pierre Curie" Kazimierz Dolny, 22-26th
September 2010, Polan
Mean-field embedding of the dual fermion approach for correlated electron systems
To reduce the rapidly growing computational cost of the dual fermion lattice
calculation with increasing system size, we introduce two embedding schemes.
One is the real fermion embedding, and the other is the dual fermion embedding.
Our numerical tests show that the real fermion and dual fermion embedding
approaches converge to essentially the same result. The application on the
Anderson disorder and Hubbard models shows that these embedding algorithms
converge more quickly with system size as compared to the conventional dual
fermion method, for the calculation of both single-particle and two-particle
quantities.Comment: 10 pages, 10 figure
Dual Fermion Method for Disordered Electronic Systems
While the coherent potential approximation (CPA) is the prevalent method for
the study of disordered electronic systems, it fails to capture non-local
correlations and Anderson localization. To incorporate such effects, we extend
the dual fermion approach to disordered non-interacting systems using the
replica method. Results for single- and two- particle quantities show good
agreement with cluster extensions of the CPA; moreover, weak localization is
captured. As a natural extension of the CPA, our method presents an alternative
to the existing cluster theories. It can be used in various applications,
including the study of disordered interacting systems, or for the description
of non-local effects in electronic structure calculations.Comment: 5 pages, 4 figure
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