183 research outputs found
Semiclassical treatment of logarithmic perturbation theory
The explicit semiclassical treatment of logarithmic perturbation theory for
the nonrelativistic bound states problem is developed. Based upon
-expansions and suitable quantization conditions a new procedure for
deriving perturbation expansions for the one-dimensional anharmonic oscillator
is offered. Avoiding disadvantages of the standard approach, new handy
recursion formulae with the same simple form both for ground and exited states
have been obtained. As an example, the perturbation expansions for the energy
eigenvalues of the harmonic oscillator perturbed by are
considered.Comment: 6 pages, LATEX 2.09 using IOP style
Evidence for a long-lived superheavy nucleus with atomic mass number A=292 and atomic number Z=~122 in natural Th
Evidence for the existence of a superheavy nucleus with atomic mass number
A=292 and abundance (1-10)x10^(-12) relative to 232Th has been found in a study
of natural Th using inductively coupled plasma-sector field mass spectrometry.
The measured mass matches the predictions [1,2] for the mass of an isotope with
atomic number Z=122 or a nearby element. Its estimated half-life of t1/2 >=
10^8 y suggests that a long-lived isomeric state exists in this isotope. The
possibility that it might belong to a new class of long-lived high spin super-
and hyperdeformed isomeric states is discussed.[3-6]Comment: 14 pages, 5 figure
Logarithmic perturbation theory for quasinormal modes
Logarithmic perturbation theory (LPT) is developed and applied to quasinormal
modes (QNMs) in open systems. QNMs often do not form a complete set, so LPT is
especially convenient because summation over a complete set of unperturbed
states is not required. Attention is paid to potentials with exponential tails,
and the example of a Poschl-Teller potential is briefly discussed. A numerical
method is developed that handles the exponentially large wavefunctions which
appear in dealing with QNMs.Comment: 24 pages, 4 Postscript figures, uses ioplppt.sty and epsfig.st
Shell closure effects studied via cluster decay in heavy nuclei
The effects of shell closure in nuclei via the cluster decay is studied. In
this context, we have made use of the Preformed Cluster Model () of Gupta
and collaborators based on the Quantum Mechanical Fragmentation Theory. The key
point in the cluster radioactivity is that it involves the interplay of close
shell effects of parent and daughter. Small half life for a parent indicates
shell stabilized daughter and long half life indicates the stability of the
parent against the decay. In the cluster decay of trans lead nuclei observed so
far, the end product is doubly magic lead or its neighbors. With this in our
mind we have extended the idea of cluster radioactivity. We investigated decay
of different nuclei where Zirconium is always taken as a daughter nucleus,
which is very well known deformed nucleus. The branching ratio of cluster decay
and -decay is also studied for various nuclei, leading to magic or
almost doubly magic daughter nuclei. The calculated cluster decay half-life are
in well agreement with the observed data. First time a possibility of cluster
decay in nucleus is predicted
Theoretical analysis of the role of chromatin interactions in long-range action of enhancers and insulators
Long-distance regulatory interactions between enhancers and their target
genes are commonplace in higher eukaryotes. Interposed boundaries or insulators
are able to block these long distance regulatory interactions. The mechanistic
basis for insulator activity and how it relates to enhancer
action-at-a-distance remains unclear. Here we explore the idea that topological
loops could simultaneously account for regulatory interactions of distal
enhancers and the insulating activity of boundary elements. We show that while
loop formation is not in itself sufficient to explain action at a distance,
incorporating transient non-specific and moderate attractive interactions
between the chromatin fibers strongly enhances long-distance regulatory
interactions and is sufficient to generate a euchromatin-like state. Under
these same conditions, the subdivision of the loop into two topologically
independent loops by insulators inhibits inter-domain interactions. The
underlying cause of this effect is a suppression of crossings in the contact
map at intermediate distances. Thus our model simultaneously accounts for
regulatory interactions at a distance and the insulator activity of boundary
elements. This unified model of the regulatory roles of chromatin loops makes
several testable predictions that could be confronted with \emph{in vitro}
experiments, as well as genomic chromatin conformation capture and fluorescent
microscopic approaches.Comment: 10 pages, originally submitted to an (undisclosed) journal in May
201
High orders of the perturbation theory for hydrogen atom in magnetic field
The states of hydrogen atom with principal quantum number and zero
magnetic quantum number in constant homogeneous magnetic field are
considered. The coefficients of energy eigenvalues expansion up to 75th order
in powers of are obtained for these states. The series for energy
eigenvalues and wave functions are summed up to values of the order
of atomic magnetic field. The calculations are based on generalization of the
moment method, which may be used in other cases of the hydrogen atom
perturbation by a polynomial in coordinates potential.Comment: 16 pages, LaTeX, 6 figures (ps, eps
Perturbative Approach to the Quasinormal Modes of Dirty Black Holes
Using a recently developed perturbation theory for uasinormal modes (QNM's),
we evaluate the shifts in the real and imaginary parts of the QNM frequencies
due to a quasi-static perturbation of the black hole spacetime. We show the
perturbed QNM spectrum of a black hole can have interesting features using a
simple model based on the scalar wave equation.Comment: Published in PR
Systematics of Fission Barriers in Superheavy Elements
We investigate the systematics of fission barriers in superheavy elements in
the range Z = 108-120 and N = 166-182. Results from two self-consistent models
for nuclear structure, the relativistic mean-field (RMF) model as well as the
non-relativistic Skyrme-Hartree-Fock approach are compared and discussed. We
restrict ourselves to axially symmetric shapes, which provides an upper bound
on static fission barriers. We benchmark the predictive power of the models
examining the barriers and fission isomers of selected heavy actinide nuclei
for which data are available. For both actinides and superheavy nuclei, the RMF
model systematically predicts lower barriers than most Skyrme interactions. In
particular the fission isomers are predicted too low by the RMF, which casts
some doubt on recent predictions about superdeformed ground states of some
superheavy nuclei. For the superheavy nuclei under investigation, fission
barriers drop to small values around Z = 110, N = 180 and increase again for
heavier systems. For most of the forces, there is no fission isomer for
superheavy nuclei, as superdeformed states are in most cases found to be
unstable with respect to octupole distortions.Comment: 17 pages REVTEX, 12 embedded eps figures. corrected abstrac
Scaling Laws and Transient Times in 3He Induced Nuclear Fission
Fission excitation functions of compound nuclei in a mass region where shell
effects are expected to be very strong are shown to scale exactly according to
the transition state prediction once these shell effects are accounted for. The
fact that no deviations from the transition state method have been observed
within the experimentally investigated excitation energy regime allows one to
assign an upper limit for the transient time of 10 zs.Comment: 7 pages, TeX type, psfig, submitted to Phys. Rev. C, also available
at http://csa5.lbl.gov/moretto/ps/he3_paper.p
Shell structure and orbit bifurcations in finite fermion systems
We first give an overview of the shell-correction method which was developed
by V. M. Strutinsky as a practicable and efficient approximation to the general
selfconsistent theory of finite fermion systems suggested by A. B. Migdal and
collaborators. Then we present in more detail a semiclassical theory of shell
effects, also developed by Strutinsky following original ideas of M.
Gutzwiller. We emphasize, in particular, the influence of orbit bifurcations on
shell structure. We first give a short overview of semiclassical trace
formulae, which connect the shell oscillations of a quantum system with a sum
over periodic orbits of the corresponding classical system, in what is usually
called the "periodic orbit theory". We then present a case study in which the
gross features of a typical double-humped nuclear fission barrier, including
the effects of mass asymmetry, can be obtained in terms of the shortest
periodic orbits of a cavity model with realistic deformations relevant for
nuclear fission. Next we investigate shell structures in a spheroidal cavity
model which is integrable and allows for far-going analytical computation. We
show, in particular, how period-doubling bifurcations are closely connected to
the existence of the so-called "superdeformed" energy minimum which corresponds
to the fission isomer of actinide nuclei. Finally, we present a general class
of radial power-law potentials which approximate well the shape of a
Woods-Saxon potential in the bound region, give analytical trace formulae for
it and discuss various limits (including the harmonic oscillator and the
spherical box potentials).Comment: LaTeX, 67 pp., 30 figures; revised version (missing part at end of
3.1 implemented; order of references corrected
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