1,161 research outputs found
Mutual information for examining correlations in DNA
This paper examines two methods for finding whether long-range correlations
exist in DNA: a fractal measure and a mutual information technique. We evaluate
the performance and implications of these methods in detail. In particular we
explore their use comparing DNA sequences from a variety of sources. Using
software for performing in silico mutations, we also consider evolutionary
events leading to long range correlations and analyse these correlations using
the techniques presented. Comparisons are made between these virtual sequences,
randomly generated sequences, and real sequences. We also explore correlations
in chromosomes from different species.Comment: 8 pages, 3 figure
Loosely bound hyperons in the SU(3) Skyrme model
Hyperon pairs bound in deuteron like states are obtained within the SU(3)
Skyrme model in agreement with general expectations from boson exchange models.
The central binding from the flavor symmetry breaking terms increases with the
strangeness contents of the interacting baryons whereas the kinetic non-linear
-model term fixes the spin and isospin of the bound pair. We give a
complete account of the interactions of octet baryons within the product
approximation to baryon number configurations.Comment: 35 pages REVTEX including 2 figs, with 3 further figs available on
request from [email protected] or from [email protected]
SI-94-TP3S2; STPHY-Th/94-
Some comments on -annihilation branching ratios into -, - and -channels
We give some remarks on the -partial branching ratios in flight at
low momenta of antineutron, measured by OBELIX collaboration. The comparison is
made to the known branching ratios from the -atomic states. The
branching ratio for the reaction is found to be
suppressed in comparison to what follows from the -data. It is also
shown, that there is no so called dynamic I=0-amplitude suppression for the
process .Comment: 8 pages, LaTeX, no figure
Monoenergetic proton beams accelerated by a radiation pressure driven shock
High energy ion beams (> MeV) generated by intense laser pulses promise to be
viable alternatives to conventional ion beam sources due to their unique
properties such as high charge, low emittance, compactness and ease of beam
delivery. Typically the acceleration is due to the rapid expansion of a laser
heated solid foil, but this usually leads to ion beams with large energy
spread. Until now, control of the energy spread has only been achieved at the
expense of reduced charge and increased complexity. Radiation pressure
acceleration (RPA) provides an alternative route to producing laser-driven
monoenergetic ion beams. In this paper, we show the interaction of an intense
infrared laser with a gaseous hydrogen target can produce proton spectra of
small energy spread (~ 4%), and low background. The scaling of proton energy
with the ratio of intensity over density (I/n) indicates that the acceleration
is due to the shock generated by radiation-pressure driven hole-boring of the
critical surface. These are the first high contrast mononenergetic beams that
have been theorised from RPA, and makes them highly desirable for numerous ion
beam applications
Rates for the reactions antiproton-proton --> pi phi and gamma phi
We study antiproton-proton annihilation at rest into and
. Rescattering by and
for states is sizable, of
order in the branching ratio, but
smaller than experiment. For the
rescattering contributions are negligible, but the channel is well
explained by a intermediate state combined with vector meson
dominance.Comment: 12 pages, plain latex, 2 postscript figures available upon request,
PSI-PR-93-2
Limits on \boldmath n {\bar n} oscillations from nuclear stability
The relationship between the lower limit on the nuclear stability lifetime as
derived from the non disappearance of `stable` nuclei
( yr), and the lower limit thus implied on
the oscillation time of a possibly underlying
neutron-antineutron oscillation process, is clarified by studying the time
evolution of the nuclear decay within a simple model which respects unitarity.
The order-of-magnitude result sec, where is a typical
nuclear annihilation width, agrees as expected with the limit on established by several detailed nuclear physics calculations, but sharply
disagreeing by 15 orders of magnitude with a claim published recently in Phys.
Rev. CRAP.Comment: 8 pages; this PRC version (accepted for publication, November 4 1999)
differs from the original version only by a few minor editorial change
Universal trend of the information entropy of a fermion in a mean field
We calculate the information entropy of single-particle states in
position-space and momentum-space for a nucleon in a nucleus, a
particle in a hypernucleus and an electron in an atomic cluster. It
is seen that and obey the same approximate functional form as
functions of the number of particles, ({\rm or}
in all of the above many-body systems in position- and momentum- space
separately. The net information content is a slowly varying
function of of the same form as above. The entropy sum is
invariant to uniform scaling of coordinates and a characteristic of the
single-particle states of a specific system. The order of single-particle
states according to is the same as their classification according to
energy keeping the quantum number constant. The spin-orbit splitting is
reproduced correctly. It is also seen that enhances with
excitation of a fermion in a quantum-mechanical system. Finally, we establish a
relationship of with the energy of the corresponding single-particle
state i.e. . This relation holds for all the
systems under consideration.Comment: 9 pages, latex, 6 figure
Hyperon-nucleon scattering and hyperon masses in the nuclear medium
We analyze low-energy hyperon-nucleon scattering using an effective field
theory in next-to-leading order. By fitting experimental cross sections for
laboratory hyperon momenta below 200 MeV/c and using information from the
hypertriton we determine twelve contact-interaction coefficients. Based on
these we discuss the low-density expansion of hyperon mass shifts in the
nuclear medium.Comment: 10 pages, 2 figure
Neutron Star Constraints on the H Dibaryon
We study the influence of a possible H dibaryon condensate on the equation of
state and the overall properties of neutron stars whose population otherwise
contains nucleons and hyperons. In particular, we are interested in the
question of whether neutron stars and their masses can be used to say anything
about the existence and properties of the H dibaryon. We find that the equation
of state is softened by the appearance of a dibaryon condensate and can result
in a mass plateau for neutron stars. If the limiting neutron star mass is about
that of the Hulse-Taylor pulsar a condensate of H dibaryons of vacuum mass 2.2
GeV and a moderately attractive potential in the medium could not be ruled out.
On the other hand, if the medium potential were even moderately repulsive, the
H, would not likely exist in neutron stars. If neutron stars of about 1.6 solar
mass were known to exist, attractive medium effects for the H could be ruled
out. Certain ranges of dibaryon mass and potential can be excluded by the mass
of the Hulse-Taylor pulsar which we illustrate graphically.Comment: Revised by the addition of a figure showing the region of dibaryon
mass and potential excluded by the Hulse-Taylor pulsar. 18 pages, 11 figures,
latex (submitted to Phys. Rev. C
Reliability of knee joint position sense measurement: a comparison between goniometry and image capture methods
Aims: Evaluate the intra-rater and inter-rater reliability of hand-held goniometry compared to image capture (IMC) in the assessment of joint position sense (JPS) in healthy participants. Methodology: Repeated-measures observational study design was undertaken with 36 asymptomatic university students of both genders aged between 18 to 45 years. JPS in the knee was assessed by two assessors over two sessions (one-week interval) using hand-held goniometry and IMC methods. Joint position sense was assessed at four target knee flexion angles. Intra- and inter-rater reliability was assessed with absolute error (AE), relative error (RE) and intra-class correlation coefficient. Findings: Inter-rater reliability for goniometry was poor to substantial (ICC: 0.00 to 0.64) and was poor to moderate (ICC: 0.00 to 0.47) for IMC. Intra-rater reliability for goniometry was poor to moderate (ICC: 0.00 to 0.42) and poor to moderate for IMC (ICC: 0.00 to 0.41). AE for goniometry ranged from 3.2° to 8.6°, with RE from 0.1°-8.3°. For IMC, AE for goniometry was 5.3° to 12.5°, with RE ranging from 0.1° to 11.1°. Principal Conclusions: Neither goniometry nor IMC appeared superior to the other in JPS assessment. Caution should be made when considering the reliability for goniometry and IMC before clinical assessment is made
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