32,223 research outputs found
Comparison of data on Mutation Frequencies of Mice Caused by Radiation - Low Dose Model -
We propose LD(Low Dose) model, the extension of LDM model which was proposed
in the previous paper [Y. Manabe et al.: J. Phys. Soc. Jpn. 81 (2012) 104004]
to estimate biological damage caused by irradiation. LD model takes account of
all the considerable effects including cell death effect as well as
proliferation, apoptosis, repair. As a typical example of estimation, we apply
LD model to the experiment of mutation frequency on the responses induced by
the exposure to low levels of ionizing radiation. The most famous and extensive
experiments are those summarized by Russell and Kelly [Russell, W. L. & Kelly,
E. M: Proc. Natl Acad. Sci. USA 79 (1982) 539-541], which are known as
'Mega-mouse project'. This provides us with important information of the
frequencies of transmitted specific-locus mutations induced in mouse
spermatogonia stem-cells. It is found that the numerical results of the
mutation frequency of mice are in reasonable agreement with the experimental
data: the LD model reproduces the total dose and dose rate dependence of data
reasonably. In order to see such dose-rate dependence more explicitly, we
introduce the dose-rate effectiveness factor (DREF). This represents a sort of
preventable effects such as repair, apoptosis and death of broken cells, which
are to be competitive with proliferation effect of broken cells induced by
irradiation.Comment: subimitting to J. Phys. Soc. Jpn, 32 pages, 8 figure
Hydrodynamic and Brownian Fluctuations in Sedimenting Suspensions
We use a mesoscopic computer simulation method to study the interplay between
hydrodynamic and Brownian fluctuations during steady-state sedimentation of
hard sphere particles for Peclet numbers (Pe) ranging from 0.1 to 15. Even when
the hydrodynamic interactions are an order of magnitude weaker than Brownian
forces, they still induce backflow effects that dominate the reduction of the
average sedimentation velocity with increasing particle packing fraction.
Velocity fluctuations, on the other hand, begin to show nonequilibrium
hydrodynamic character for Pe > 1Comment: 4 pages 4 figures, RevTex, to appear in Phys. Rev. Lett. New version
with some minor correction
Spurious Eccentricities of Distorted Binary Components
I discuss the effect of physical distortion on the velocities of close binary
components and how we may use the resulting distortion of velocity curves to
constrain some properties of binary systems, such as inclination and mass
ratio. Precise new velocities for 5 Cet convincingly detect these distortions
with their theoretically predicted phase dependence. We can even use such
distortions of velocity curves to test Lucy's theory of convective gravity
darkening. The observed distortions for TT Hya and 5 Cet require the contact
components of those systems to be gravity darkened, probably somewhat more than
predicted by Lucy's theory but clearly not as much as expected for a radiative
star. These results imply there is no credible evidence for eccentric orbits in
binaries with contact components. I also present some speculative analyses of
the observed properties of a binary encased in a non-rotating common envelope,
if such an object could actually exist, and discuss how the limb darkening of
some recently calculated model atmospheres for giant stars may bias my resuts
for velocity-curve distortions, as well as other results from a wide range of
analyses of binary stars.Comment: 14 pp, 2 tables, 12 fig; under review by Ap
Determining land use patterns through man-machine analysis of LANDSAT data: A tutorial simulation
There are no author-identified significant results in this report
On resonances and bound states of the 't Hooft-Polyakov monopole
We present a systematic approach to the linearised Yang-Mills-Higgs equations
in the background of a 't Hooft-Polyakov monopole and use it to unify and
extend previous studies of their spectral properties. We show that a
quaternionic formulation allows for a compact and efficient treatment of the
linearised equations in the BPS limit of vanishing Higgs self-coupling, and use
it to study both scattering and bound states. We focus on the sector of
vanishing generalised angular momentum and analyse it numerically, putting
zero-energy bound states, Coulomb bound states and infinitely many Feshbach
resonances into a coherent picture. We also consider the linearised
Yang-Mills-Higgs equations with non-vanishing Higgs self-coupling and confirm
the occurrence of Feshbach resonances in this situation.Comment: 33 pages, 7 figure
Intrinsic and extrinsic factors drive ontogeny of early-life at-sea behaviour in a marine top predator
Young animals must learn to forage effectively to survive the transition from parental provisioning to independent feeding. Rapid development of successful foraging strategies is particularly important for capital breeders that do not receive parental guidance after weaning. The intrinsic and extrinsic drivers of variation in ontogeny of foraging are poorly understood for many species. Grey seals (Halichoerus grypus) are typical capital breeders; pups are abandoned on the natal site after a brief suckling phase, and must develop foraging skills without external input. We collected location and dive data from recently-weaned grey seal pups from two regions of the United Kingdom (the North Sea and the Celtic and Irish Seas) using animal-borne telemetry devices during their first months of independence at sea. Dive duration, depth, bottom time, and benthic diving increased over the first 40 days. The shape and magnitude of changes differed between regions. Females consistently had longer bottom times, and in the Celtic and Irish Seas they used shallower water than males. Regional sex differences suggest that extrinsic factors, such as water depth, contribute to behavioural sexual segregation. We recommend that conservation strategies consider movements of young naïve animals in addition to those of adults to account for developmental behavioural changes
Ground-Based Coronagraphy with High Order Adaptive Optics
We summarize the theory of coronagraphic optics, and identify a dimensionless
fine-tuning parameter, F, which we use to describe the Lyot stop size in the
natural units of the coronagraphic optical train and the observing wavelength.
We then present simulations of coronagraphs matched to adaptive optics (AO)
systems on the Calypso 1.2m, Palomar Hale 5m and Gemini 8m telescopes under
various atmospheric conditions, and identify useful parameter ranges for AO
coronagraphy on these telescopes. Our simulations employ a tapered, high-pass
filter in spatial frequency space to mimic the action of adaptive wavefront
correction. We test the validity of this representation of AO correction by
comparing our simulations with recent K-band data from the 241-channel Palomar
Hale AO system and its dedicated PHARO science camera in coronagraphic mode.Comment: To appear in ApJ, May 2001 (28 pages, 10 figs
Probing the Evolution of the Galaxy Interaction/Merger Rate Using Collisional Ring Galaxies
We present the results from our program to determine the evolution of the
galaxy interaction/merger rate with redshift using the unique star-forming
characteristics of collisional ring galaxies. We have identified 25 distant
collisional ring galaxy candidates (CRGCs) in a total of 162 deep Hubble Space
Telescope Wide Field/Planetary Camera-2 images obtained from the HST Archives.
Based on measured and estimated redshifts, these 25 CRGCs all lie in the
redshift interval of 0.1 < z < 1. Using the local collisional ring galaxy
volume density and the new ``standard'' cosmology, we find that in order to
account for the number of identified CRGCs in our surveyed fields, the galaxy
interaction/merger rate, parameterized as (1 + z)^m, must increase steeply with
redshift.We determine a minimum value of m = 5.2 0.7, though m could be
as high as 7 or 8. We can rule out a non-evolving (m = 0) and weakly evolving
(m = 1-2) galaxy interaction/merger rate at greater than the 4 sigma level of
confidence.Comment: Accepted in the Astrophysical Journal (11 pages, 4 figures). Higher
resolution version of the figures is available at
http://www.astro.cornell.edu/~vassilis/papers
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