22,034 research outputs found
The beryllium atom and beryllium positive ion in strong magnetic fields
The ground and a few excited states of the beryllium atom in external uniform
magnetic fields are calculated by means of our 2D mesh Hartree-Fock method for
field strengths ranging from zero up to 2.35*10^9T. With changing field
strength the ground state of the Be atom undergoes three transitions involving
four different electronic configurations which belong to three groups with
different spin projections S_z=0,-1,-2. For weak fields the ground state
configuration arises from the 1s^2 2s^2, S_z=0 configuration. With increasing
field strength the ground state evolves into the two S_z=-1 configurations
1s^22s 2p_{-1} and 1s^2 2p_{-1}3d_{-2}, followed by the fully spin polarised
S_z=-2 configuration 1s2p_{-1}3d_{-2}4f_{-3}. The latter configuration forms
the ground state of the beryllium atom in the high field regime \gamma>4.567.
The analogous calculations for the Be^+ ion provide the sequence of the three
following ground state configurations: 1s^22s and 1s^22p_{-1} (S_z=-1/2) and
1s2p_{-1}3d_{-2} (S_z=-3/2).Comment: 15 pages, 7 figure
Impurity center in a semiconductor quantum ring in the presence of a radial electric field
The problem of an impurity electron in a quantum ring (QR) in the presence of
a radially directed strong external electric field is investigated in detail.
Both an analytical and a numerical approach to the problem are developed. The
analytical investigation focuses on the regime of a strong wire-electric field
compared to the electric field due to the impurity. An adiabatic and
quasiclassical approximation is employed. The explicit dependencies of the
binding energy of the impurity electron on the electric field strength,
parameters of the QR and position of the impurity within the QR are obtained.
Numerical calculations of the binding energy based on a finite-difference
method in two and three dimensions are performed for arbitrary strengths of the
electric field. It is shown that the binding energy of the impurity electron
exhibits a maximum as a function of the radial position of the impurity that
can be shifted arbitrarily by applying a corresponding wire-electric field. The
maximal binding energy monotonically increases with increasing electric field
strength. The inversion effect of the electric field is found to occur. An
increase of the longitudinal displacement of the impurity typically leads to a
decrease of the binding energy. Results for both low- and high-quantum rings
are derived and discussed. Suggestions for an experimentally accessible set-up
associated with the GaAs/GaAlAs QR are provided.Comment: 16 pages, 8 figure
Exclusive diffractive electroproduction of dijets in collinear factorization
Exclusive electroproduction of hard dijets can be described within the
collinear factorization. This process has clear experimental signature and
provides one with an interesting alternative venue to test QCD description of
hard diffractive processes and extract information on generalized nucleon
parton distributions. In this work we present detailed leading-order QCD
calculations of the relevant cross sections, including longitudinal momentum
fraction distribution of the dijets and their azimuthal angle dependence.Comment: 11 pages, 14 Postscript figures, uses revtex4.st
Entropy Bounds, Holographic Principle and Uncertainty Relation
A simple derivation of the bound on entropy is given and the holographic
principle is discussed. We estimate the number of quantum states inside space
region on the base of uncertainty relation. The result is compared with the
Bekenstein formula for entropy bound, which was initially derived from the
generalized second law of thermodynamics for black holes. The holographic
principle states that the entropy inside a region is bounded by the area of the
boundary of that region. This principle can be called the kinematical
holographic principle. We argue that it can be derived from the dynamical
holographic principle which states that the dynamics of a system in a region
should be described by a system which lives on the boundary of the region. This
last principle can be valid in general relativity because the ADM hamiltonian
reduces to the surface term.Comment: LaTeX, 8 pages, no figure
Coulomb effects in a ballistic one-channel S-S-S device
We develop a theory of Coulomb oscillations in superconducting devices in the
limit of small charging energy . We consider a small
superconducting grain of finite capacity connected to two superconducting leads
by nearly ballistic single-channel quantum point contacts. The temperature is
supposed to be very low, so there are no single-particle excitations on the
grain. Then the behavior of the system may be described as quantum mechanics of
the superconducting phase on the island. The Josephson energy as a function of
this phase has two minima which become degenerate at the phase difference on
the leads equal to , the tunneling amplitude between them being controlled
by the gate voltage at the grain. We find the Josephson current and its
low-frequency fluctuations and predict their periodic dependence on the induced
charge with period .Comment: 11 pages, REVTeX, 10 figures, uses eps
Wavelets and their use
This review paper is intended to give a useful guide for those who want to
apply discrete wavelets in their practice. The notion of wavelets and their use
in practical computing and various applications are briefly described, but
rigorous proofs of mathematical statements are omitted, and the reader is just
referred to corresponding literature. The multiresolution analysis and fast
wavelet transform became a standard procedure for dealing with discrete
wavelets. The proper choice of a wavelet and use of nonstandard matrix
multiplication are often crucial for achievement of a goal. Analysis of various
functions with the help of wavelets allows to reveal fractal structures,
singularities etc. Wavelet transform of operator expressions helps solve some
equations. In practical applications one deals often with the discretized
functions, and the problem of stability of wavelet transform and corresponding
numerical algorithms becomes important. After discussing all these topics we
turn to practical applications of the wavelet machinery. They are so numerous
that we have to limit ourselves by some examples only. The authors would be
grateful for any comments which improve this review paper and move us closer to
the goal proclaimed in the first phrase of the abstract.Comment: 63 pages with 22 ps-figures, to be published in Physics-Uspekh
- …