21 research outputs found

### Closed form representation for a projection onto infinitely dimensional subspace spanned by Coulomb bound states

The closed form integral representation for the projection onto the subspace
spanned by bound states of the two-body Coulomb Hamiltonian is obtained. The
projection operator onto the $n^2$ dimensional subspace corresponding to the
$n$-th eigenvalue in the Coulomb discrete spectrum is also represented as the
combination of Laguerre polynomials of $n$-th and $(n-1)$-th order. The latter
allows us to derive an analog of the Christoffel-Darboux summation formula for
the Laguerre polynomials. The representations obtained are believed to be
helpful in solving the breakup problem in a system of three charged particles
where the correct treatment of infinitely many bound states in two body
subsystems is one of the most difficult technical problems.Comment: 7 page

### Collective excitations of degenerate Fermi gases in anisotropic parabolic traps

The hydrodynamic low-frequency oscillations of highly degenerate Fermi gases
trapped in anisotropic harmonic potentials are investigated. Despite the lack
of an obvious spatial symmetry the wave-equation turns out to be separable in
elliptical coordinates, similar to a corresponding result established earlier
for Bose-condensates. This result is used to give the analytical solution of
the anisotropic wave equation for the hydrodynamic modes.Comment: 11 pages, Revte

### Statistical Mechanics of Elastica on Plane as a Model of Supercoiled DNA-Origin of the MKdV hierarchy-

In this article, I have investigated statistical mechanics of a non-stretched
elastica in two dimensional space using path integral method. In the
calculation, the MKdV hierarchy naturally appeared as the equations including
the temperature fluctuation.I have classified the moduli of the closed elastica
in heat bath and summed the Boltzmann weight with the thermalfluctuation over
the moduli. Due to the bilinearity of the energy functional,I have obtained its
exact partition function.By investigation of the system,I conjectured that an
expectation value at a critical point of this system obeys the Painlev\'e
equation of the first kind and its related equations extended by the KdV
hierarchy.Furthermore I also commented onthe relation between the MKdV
hierarchy and BRS transformationin this system.Comment: AMS-Tex Us

### QED on Curved Background and on Manifolds with Boundaries: Unitarity versus Covariance

Some recent results show that the covariant path integral and the integral
over physical degrees of freedom give contradicting results on curved
background and on manifolds with boundaries. This looks like a conflict between
unitarity and covariance. We argue that this effect is due to the use of
non-covariant measure on the space of physical degrees of freedom. Starting
with the reduced phase space path integral and using covariant measure
throughout computations we recover standard path integral in the Lorentz gauge
and the Moss and Poletti BRST-invariant boundary conditions. We also
demonstrate by direct calculations that in the approach based on Gaussian path
integral on the space of physical degrees of freedom some basic symmetries are
broken.Comment: 29 pages, LaTEX, no figure

### Crossover from strong to weak confinement for excitons in shallow or narrow quantum wells

We present a theoretical study of the crossover from the two-dimensional (2D, separate confinement of the carriers) to the three-dimensional (3D, center-of-mass confinement) behavior of excitons in shallow or narrow quantum wells (QW's). Exciton binding energies and oscillator strengths are calculated by diagonalizing the Hamiltonian on a large nonorthogonal basis set. We prove that the oscillator strength per unit area has a minimum at the crossover, in analogy with the similar phenomenon occurring for the QW to thin-film crossover on increasing the well thickness, and in agreement with the analytic results of a simplified ÎŽ-potential model. Numerical results are obtained for GaAs/Alx Ga1-xAs and InxGa1-xAs/GaAs systems. Our approach can also be applied to obtain an accurate description of excitons in QW's with arbitrary values of the offsets (positive or negative) and also for very narrow wells. In particular, the crossover from 2D to 3D behavior in narrow GaAs/AlxGa1-xAs QW's is investigated: the maximum binding energy of the direct exciton in GaAs/AlAs QW's is found to be âŒ26 meV and to occur between one and two monolayers

### Signals for Bidirectional Nucleocytoplasmic Transport in the Duck Hepatitis B Virus Capsid Protein

Hepadnavirus genome replication involves cytoplasmic and nuclear stages, requiring balanced targeting of cytoplasmic nucleocapsids to the nuclear compartment. In this study, we analyze the signals determining capsid compartmentalization in the duck hepatitis B virus (DHBV) animal model, as this system also allows us to study hepadnavirus infection of cultured primary hepatocytes. Using fusions to the green fluorescent protein as a functional assay, we have identified a nuclear localization signal (NLS) that mediates nuclear pore association of the DHBV nucleocapsid and nuclear import of DHBV core protein (DHBc)-derived polypeptides. The DHBc NLS mapped is unique. It bears homology to repetitive NLS elements previously identified near the carboxy terminus of the capsid protein of hepatitis B virus, the human prototype of the hepadnavirus family, but it maps to a more internal position. In further contrast to the hepatitis B virus core protein NLS, the DHBc NLS is not positioned near phosphorylation target sites that are generally assumed to modulate nucleocytoplasmic transport. In functional assays with a knockout mutant, the DHBc NLS was found to be essential for nuclear pore association of the nucleocapsid. The NLS was found to be also essential for virus production from the full-length DHBV genome in transfected cells and from hepatocytes infected with transcomplemented mutant virus. Finally, the DHBc additionally displayed activity indicative of a nuclear export signal, presumably counterbalancing NLS function in the productive state of the infected cell and thereby preventing nucleoplasmic accumulation of nucleocapsids