1,323 research outputs found
Hematological response in sheep given protracted exposures to Co 60 gamma radiation
Leukocyte count changes in sheep after prolonged exposure to gamma irradiation at rate of 1.9 R/h
Information theoretic approach to interactive learning
The principles of statistical mechanics and information theory play an
important role in learning and have inspired both theory and the design of
numerous machine learning algorithms. The new aspect in this paper is a focus
on integrating feedback from the learner. A quantitative approach to
interactive learning and adaptive behavior is proposed, integrating model- and
decision-making into one theoretical framework. This paper follows simple
principles by requiring that the observer's world model and action policy
should result in maximal predictive power at minimal complexity. Classes of
optimal action policies and of optimal models are derived from an objective
function that reflects this trade-off between prediction and complexity. The
resulting optimal models then summarize, at different levels of abstraction,
the process's causal organization in the presence of the learner's actions. A
fundamental consequence of the proposed principle is that the learner's optimal
action policies balance exploration and control as an emerging property.
Interestingly, the explorative component is present in the absence of policy
randomness, i.e. in the optimal deterministic behavior. This is a direct result
of requiring maximal predictive power in the presence of feedback.Comment: 6 page
Measurements of the effect of collisions on transverse beam halo diffusion in the Tevatron and in the LHC
Beam-beam forces and collision optics can strongly affect beam lifetime,
dynamic aperture, and halo formation in particle colliders. Extensive
analytical and numerical simulations are carried out in the design and
operational stage of a machine to quantify these effects, but experimental data
is scarce. The technique of small-step collimator scans was applied to the
Fermilab Tevatron collider and to the CERN Large Hadron Collider to study the
effect of collisions on transverse beam halo dynamics. We describe the
technique and present a summary of the first results on the dependence of the
halo diffusion coefficient on betatron amplitude in the Tevatron and in the
LHC.Comment: 4 pages, 2 figures. Submitted to the Proceedings of the ICFA
Mini-Workshop on Beam-beam Effects in Hadron Colliders (BB2013), Geneva,
Switzerland, 18-22 March 201
FUSE Observations of a Full Orbit of Hercules X-1: Signatures of Disk, Star, and Wind
We observed an entire 1.7 day orbit of the X-ray binary Hercules X-1 with the
Far Ultraviolet Spectroscopic Explorer (FUSE). Changes in the O VI 1032,1037
line profiles through eclipse ingress and egress indicate a Keplerian accretion
disk spinning prograde with the orbit. These observations may show the first
double-peaked accretion disk line profile to be seen in the Hercules X-1
system. Doppler tomograms of the emission lines show a bright spot offset from
the Roche lobe of the companion star HZ Her, but no obvious signs of the
accretion disk. Simulations show that the bright spot is too far offset from
the Roche lobe to result from uneven X-ray heating of its surface. The absence
of disk signatures in the tomogram can be reproduced in simulations which
include absorption from a stellar wind. We attempt to diagnose the state of the
emitting gas from the C III 977, C III 1175, and N III 991 emission lines. The
latter may be enhanced through Bowen fluorescence.Comment: Accepted for publication in The Astrophysical Journa
The Origin of Soft X-rays in DQ Herculis
DQ Herculis (Nova Herculis 1934) is a deeply eclipsing cataclysmic variable
containing a magnetic white dwarf primary. The accretion disk is thought to
block our line of sight to the white dwarf at all orbital phases due to its
extreme inclination angle. Nevertheless, soft X-rays were detected from DQ Her
with ROSAT PSPC. To probe the origin of these soft X-rays, we have performed
Chandra ACIS observations. We confirm that DQ Her is an X-ray source. The bulk
of the X-rays are from a point-like source and exhibit a shallow partial
eclipse. We interpret this as due to scattering of the unseen central X-ray
source, probably in an accretion disk wind. At the same time, we observe what
appear to be weak extended X-ray features around DQ Her, which we interpret as
an X-ray emitting knot in the nova shell.Comment: 18 pages including 4 figures, accepted for publication in
Astrphyisical Journa
Secondary-Structure Design of Proteins by a Backbone Torsion Energy
We propose a new backbone-torsion-energy term in the force field for protein
systems. This torsion-energy term is represented by a double Fourier series in
two variables, the backbone dihedral angles phi and psi. It gives a natural
representation of the torsion energy in the Ramachandran space in the sense
that any two-dimensional energy surface periodic in both phi and psi can be
expanded by the double Fourier series. We can then easily control
secondary-structure-forming tendencies by modifying the torsion-energy surface.
For instance, we can increase/decrease the alpha-helix-forming-tendencies by
lowering/raising the torsion-energy surface in the alpha-helix region and
likewise increase/decrease the beta-sheet-forming tendencies by
lowering/raising the surface in the beta-sheet region in the Ramachandran
space. We applied our approach to AMBER parm94 and AMBER parm96 force fields
and demonstrated that our modifications of the torsion-energy terms resulted in
the expected changes of secondary-structure-forming-tendencies by performing
folding simulations of alpha-helical and beta-hairpin peptides.Comment: 13 pages, (Revtex4), 5 figure
Mycotoxins and Other Secondary Metabolites Produced in vitro by Penicillium paneum Frisvad and Penicillium roqueforti Thom Isolated from Baled Grass Silage in Ireland
Characterizing two solar-type Kepler subgiants with asteroseismology: KIC10920273 and KIC11395018
Determining fundamental properties of stars through stellar modeling has
improved substantially due to recent advances in asteroseismology. Thanks to
the unprecedented data quality obtained by space missions, particularly CoRoT
and Kepler, invaluable information is extracted from the high-precision stellar
oscillation frequencies, which provide very strong constraints on possible
stellar models for a given set of classical observations. In this work, we have
characterized two relatively faint stars, KIC10920273 and KIC11395018, using
oscillation data from Kepler photometry and atmospheric constraints from
ground-based spectroscopy. Both stars have very similar atmospheric properties;
however, using the individual frequencies extracted from the Kepler data, we
have determined quite distinct global properties, with increased precision
compared to that of earlier results. We found that both stars have left the
main sequence and characterized them as follows: KIC10920273 is a
one-solar-mass star (M=1.00 +/- 0.04 M_sun), but much older than our Sun
(t=7.12 +/- 0.47 Gyr), while KIC11395018 is significantly more massive than the
Sun (M=1.27 +/- 0.04 M_sun) with an age close to that of the Sun (t=4.57 +/-
0.23 Gyr). We confirm that the high lithium abundance reported for these stars
should not be considered to represent young ages, as we precisely determined
them to be evolved subgiants. We discuss the use of surface lithium abundance,
rotation and activity relations as potential age diagnostics.Comment: 12 pages, 3 figures, 5 tables. Accepted by Ap
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