7,559 research outputs found
What can be learned from binding energy differences about nuclear structure: the example of delta V_{pn}
We perform an analysis of a binding energy difference called delta
V_{pn}(N,Z) =- 1/4(E(Z,N)-E(Z,N-2)-E(Z-2,N)+ E(Z-2,N-2) in the framework of a
realistic nuclear model. Using the angular-momentum and particle-number
projected generator coordinate method and the Skyrme interaction SLy4, we
analyze the contribution brought to delta V_{pn} by static deformation and
dynamic fluctuations around the mean-field ground state. Our method gives a
good overall description of delta V_{pn} throughout the chart of nuclei with
the exception of the anomaly related to the Wigner energy along the N=Z line.
The main conclusions of our analysis are that (i) the structures seen in the
systematics of delta V_{pn} throughout the chart of nuclei can be easily
explained combining a smooth background related to the symmetry energy and
correlation energies due to deformation and collective fluctuations; (ii) the
characteristic pattern of delta V_{pn} around a doubly-magic nucleus is a
trivial consequence of the asymmetric definition of delta V_{pn}, and not due
to a the different structure of these nuclei; (iii) delta V_{pn} does not
provide a very reliable indicator for structural changes; (iv) \delta V_{pn}
does not provide a reliable measure of the proton-neutron interaction in the
nuclear EDF, neither of that between the last filled orbits, nor of the one
summed over all orbits; (v) delta V_{pn} does not provide a conclusive
benchmark for nuclear EDF methods that is superior or complementary to other
mass filters such as two-nucleon separation energies or Q values.Comment: 19 pages and 12 figure
Asymptotic Analysis of the Boltzmann Equation for Dark Matter Relics
This paper presents an asymptotic analysis of the Boltzmann equations
(Riccati differential equations) that describe the physics of thermal
dark-matter-relic abundances. Two different asymptotic techniques are used,
boundary-layer theory, which makes use of asymptotic matching, and the delta
expansion, which is a powerful technique for solving nonlinear differential
equations. Two different Boltzmann equations are considered. The first is
derived from general relativistic considerations and the second arises in
dilatonic string cosmology. The global asymptotic analysis presented here is
used to find the long-time behavior of the solutions to these equations. In the
first case the nature of the so-called freeze-out region and the
post-freeze-out behavior is explored. In the second case the effect of the
dilaton on cold dark-matter abundances is calculated and it is shown that there
is a large-time power-law fall off of the dark-matter abundance. Corrections to
the power-law behavior are also calculated.Comment: 15 pages, no figure
A perturbative approach to the spectral zeta functions of strings, drums and quantum billiards
We have obtained an explicit expression for the spectral zeta functions and
for the heat kernel of strings, drums and quantum billiards working to third
order in perturbation theory, using a generalization of the binomial theorem to
operators. The perturbative parameter used in the expansion is either the small
deformation of a reference domain (for instance a square), or a small variation
of the density around a constant value (in two dimensions both cases can
apply). This expansion is well defined even in presence of degenerations of the
unperturbed spectrum. We have discussed several examples in one, two and three
dimensions, obtaining in some cases the analytic continuation of the series,
which we have then used to evaluate the corresponding Casimir energy. For the
case of a string with piecewise constant density, subject to different boundary
conditions, and of two concentric cylinders of very close radii, we have
reproduced results previously published, thus obtaining a useful check of our
method.Comment: 23 pages, 5 figures, 2 tables; version accepted on Journal of
Mathematical Physic
Advanced analog television study final report, 4 nov. - 19 dec. 1963
Information bandwidth reduction for analog television signals - Description of multiple interlace syste
sd-shell study with a multi-configuration mixing approach designed for large scale nuclear structure calculations
A systematic numerical investigation of a recently developed nuclear structure approach is presented which diagonalizes the Hamiltonian in the space of the symmetry-projected Hartree-Fock-Bogoliubov (HFB) vacuum and symmetry-projected quasiparticle excitations with respect to it. The underlying HFB transformation, which is assumed to be time-reversal and axially symmetric, is determined by variation after the projection. The model allows the use of large basis systems. It has been applied to the calculation of energy spectra of several even-even, odd-odd and odd mass nuclei in the sd shell with mass numbers reaching from A=20 to 30. The Chung-Wildenthal interaction has been used. Good agreement with the exact shell model diagonalization and a considerable improvement on a previous approach, where the HFB transformation was significantly more restricted, is obtained
PT-symmetry breaking in complex nonlinear wave equations and their deformations
We investigate complex versions of the Korteweg-deVries equations and an Ito
type nonlinear system with two coupled nonlinear fields. We systematically
construct rational, trigonometric/hyperbolic, elliptic and soliton solutions
for these models and focus in particular on physically feasible systems, that
is those with real energies. The reality of the energy is usually attributed to
different realisations of an antilinear symmetry, as for instance PT-symmetry.
It is shown that the symmetry can be spontaneously broken in two alternative
ways either by specific choices of the domain or by manipulating the parameters
in the solutions of the model, thus leading to complex energies. Surprisingly
the reality of the energies can be regained in some cases by a further breaking
of the symmetry on the level of the Hamiltonian. In many examples some of the
fixed points in the complex solution for the field undergo a Hopf bifurcation
in the PT-symmetry breaking process. By employing several different variants of
the symmetries we propose many classes of new invariant extensions of these
models and study their properties. The reduction of some of these models yields
complex quantum mechanical models previously studied.Comment: 50 pages, 39 figures (compressed in order to comply with arXiv
policy; higher resolutions maybe obtained from the authors upon request
Vacuum Stability of the wrong sign Scalar Field Theory
We apply the effective potential method to study the vacuum stability of the
bounded from above (unstable) quantum field potential. The
stability ( and the mass renormalization
( conditions force the effective
potential of this theory to be bounded from below (stable). Since bounded from
below potentials are always associated with localized wave functions, the
algorithm we use replaces the boundary condition applied to the wave functions
in the complex contour method by two stability conditions on the effective
potential obtained. To test the validity of our calculations, we show that our
variational predictions can reproduce exactly the results in the literature for
the -symmetric theory. We then extend the applications
of the algorithm to the unstudied stability problem of the bounded from above
scalar field theory where classical analysis prohibits the
existence of a stable spectrum. Concerning this, we calculated the effective
potential up to first order in the couplings in space-time dimensions. We
find that a Hermitian effective theory is instable while a non-Hermitian but
-symmetric effective theory characterized by a pure imaginary
vacuum condensate is stable (bounded from below) which is against the classical
predictions of the instability of the theory. We assert that the work presented
here represents the first calculations that advocates the stability of the
scalar potential.Comment: 21pages, 12 figures. In this version, we updated the text and added
some figure
Effective Operator Treatment of the Anharmonic Oscillator
We analyse the one dimensional quartic oscillator using the effective
operator methodology of Lee and Suzuki. We reproduce known results for low
lying energy eigenvalues.Comment: 9 Pages, Extended version with new references. To appear in
Phys.ReV.
Polymer-Chain Adsorption Transition at a Cylindrical Boundary
In a recent letter, a simple method was proposed to generate solvable models
that predict the critical properties of statistical systems in hyperspherical
geometries. To that end, it was shown how to reduce a random walk in
dimensions to an anisotropic one-dimensional random walk on concentric
hyperspheres. Here, I construct such a random walk to model the
adsorption-desorption transition of polymer chains growing near an attractive
cylindrical boundary such as that of a cell membrane. I find that the fraction
of adsorbed monomers on the boundary vanishes exponentially when the adsorption
energy decreases towards its critical value. When the adsorption energy rises
beyond a certain value above the critical point whose scale is set by the
radius of the cell, the adsorption fraction exhibits a crossover to a linear
increase characteristic to polymers growing near planar boundaries.Comment: latex, 12 pages, 3 ps-figures, uuencode
Trypanosoma brucei brucei: differences in the nuclear chromatin of bloodstream forms and procyclic culture forms
Nucleosome filaments of two stages of the life-cycle of Trypanosoma brucei brucei, namely bloodstream forms and procyclic culture forms, were investigated by electron microscopy. Chromatin of bloodstream forms showed a salt-dependent condensation. The level of condensation was higher than that shown by chromatin from procyclic culture forms, but 30 nm fibres as formed in rat liver chromatin preparations were not found. Analysis of histones provided new evidence for the existence of H1-like proteins, which comigrated in the region of the core histones in SDS-PAGE and in front of the core histones in Triton acid urea gels. Differences were found between the H1-like proteins of the two trypanosome stages as well as between the core histones in their amount, number of bands and banding pattern. It can be concluded that T. b. brucei contains a full set of histones, including H1-like proteins, and that the poor condensation of its chromatin is not due to the absence of H1, but most probably due to histone-DNA interaction being weak. It is obvious that structural and functional differences of the chromatin exist not only between T. b. brucei and higher eukaryotes, but also between various stages of the life-cycle of the parasite. It is therefore not adequate to investigate the chromatin only of the procyclic culture forms as a model for all stages of the life-cycle of T. b. bruce
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