8,143 research outputs found
Radiation from a charged particle-in-flight from a laminated medium to vacuum
The radiation from a charged particle-in-flight from a semi-infinite
laminated medium to vacuum and back,- from vacuum to the laminated medium, has
been investigated. Expressions for the spectral-angular distribution of
radiation energy in vacuum (at large distances from the boundary of laminated
medium) were obtained for both the cases with no limitations on the amplitude
and variation profile of the laminated medium permittivity. The results of
appropriate numerical calculations are presented and possible applications of
the obtained results are discussed.Comment: 8 pages, 6 figures, contribution to Proceedings of International
Symposium RREPS-2009, 07-11 September, 2009, Zvenigorod, Russi
Exact Casimir Interaction Between Semitransparent Spheres and Cylinders
A multiple scattering formulation is used to calculate the force, arising
from fluctuating scalar fields, between distinct bodies described by
-function potentials, so-called semitransparent bodies. (In the limit
of strong coupling, a semitransparent boundary becomes a Dirichlet one.) We
obtain expressions for the Casimir energies between disjoint parallel
semitransparent cylinders and between disjoint semitransparent spheres. In the
limit of weak coupling, we derive power series expansions for the energy, which
can be exactly summed, so that explicit, very simple, closed-form expressions
are obtained in both cases. The proximity force theorem holds when the objects
are almost touching, but is subject to large corrections as the bodies are
moved further apart.Comment: 5 pages, 4 eps figures; expanded discussion of previous work and
additional references added, minor typos correcte
Self-Reported And Objectively Recorded Colorectal Cancer Screening Participation In England
Objective To compare self-reported with objectively recorded participation in Faecal Occult Blood testing (FOBt) colorectal cancer (CRC) screening in a national programme.
Methods Survey respondents living in England who were eligible for screening were asked in face-to-face interviews if they had ever been invited to do a CRC screening test, how many times they had been invited, and how many times they had participated. National Health Service (NHS) Bowel Cancer Screening Programme (BCSP) records were consulted for respondents who had consented to a record check. The outcome measures were ‘ever uptake’ (responded to ≥1 invitation), ‘repeat uptake’ (responded to ≥2 invitations), and ‘consistent uptake’ (responded to all invitations).
Results In the verified group, self-reported ever uptake was highly consistent with recorded ever uptake (87.0% vs. 87.8%). Among those who indicated that they had been invited more than once, self-reported repeat uptake was 89.8% compared with 84.8% recorded repeat uptake. Among those with more than one recorded invitation, self-reported repeat uptake was 72.7% compared with 77.2% recorded repeat uptake, and self-reported consistent uptake was 81.6% compared with 65.6% recorded consistent uptake.
Conclusion Our results suggest that people can accurately report whether they have ever taken part in CRC screening. The vast majority of those whose records were verified could also accurately report whether they had taken part in screening at least twice. They were somewhat less accurate in reporting whether they had responded to all screening invitations
Maladaptation and the paradox of robustness in evolution
Background. Organisms use a variety of mechanisms to protect themselves
against perturbations. For example, repair mechanisms fix damage, feedback
loops keep homeostatic systems at their setpoints, and biochemical filters
distinguish signal from noise. Such buffering mechanisms are often discussed in
terms of robustness, which may be measured by reduced sensitivity of
performance to perturbations. Methodology/Principal Findings. I use a
mathematical model to analyze the evolutionary dynamics of robustness in order
to understand aspects of organismal design by natural selection. I focus on two
characters: one character performs an adaptive task; the other character
buffers the performance of the first character against perturbations. Increased
perturbations favor enhanced buffering and robustness, which in turn decreases
sensitivity and reduces the intensity of natural selection on the adaptive
character. Reduced selective pressure on the adaptive character often leads to
a less costly, lower performance trait. Conclusions/Significance. The paradox
of robustness arises from evolutionary dynamics: enhanced robustness causes an
evolutionary reduction in the adaptive performance of the target character,
leading to a degree of maladaptation compared to what could be achieved by
natural selection in the absence of robustness mechanisms. Over evolutionary
time, buffering traits may become layered on top of each other, while the
underlying adaptive traits become replaced by cheaper, lower performance
components. The paradox of robustness has widespread implications for
understanding organismal design
Self-amplified Cherenkov radiation from a relativistic electron in a waveguide partially filled with a laminated material
The radiation from a relativistic electron uniformly moving along the axis of
cylindrical waveguide filled with laminated material of finite length is
investigated. Expressions for the spectral distribution of radiation passing
throw the transverse section of waveguide at large distances from the laminated
material are derived with no limitations on the amplitude and variation profile
of the layered medium permittivity and permeability. Numerical results for
layered material consisting of dielectric plates alternated with vacuum gaps
are given. It is shown that at a special choice of problem parameters,
Cherenkov radiation generated by the relativistic electron inside the plates is
self-amplified. The visual explanation of this effect is given and a possible
application is discussed.Comment: 8 pages, 4 figures,1 table, the paper is accepted for publication in
the Journal of Physics: Conference Serie
Channeling radiation on quartz stimulated by acoustic waves
The stimulation of channeling radiation by acoustic waves excited in the single crystal has been predicted in early works of the 1980’s. Based on quantum calculations, the described experiment aimed at verification of theoretical
considerations. Making use of the reverse piezoelectric effect, hypersonic waves of frequency 12GHz, which corresponds to a dedicated transition between bound states of planar channelled relativistic electrons, were excited in a single-Crystal quartz plate. The spectrum of channeling radiation measured under the influence of acoustic waves reveals enhanced radiation intensity. The obtained results are discussed and may be phenomenologically understood assuming electron diffraction
on an acoustic superlattice
Micro actions in colorectal cancer screening participation: a population-based survey study.
Low uptake of colorectal cancer (CRC) screening is a cause for concern. This study explored people's anticipated response to receiving the test kit to shed light on past screening uptake and help inform future interventions to increase participation
Distinct dynamics of social motivation drive differential social behavior in laboratory rat and mouse strains
Mice and rats are widely used to explore mechanisms of mammalian social behavior in health and disease, raising the question whether they actually differ in their social behavior. Here we address this question by directly comparing social investigation behavior between two mouse and rat strains used most frequently for behavioral studies and as models of neuropathological conditions: C57BL/6 J mice and Sprague Dawley (SD) rats. Employing novel experimental systems for behavioral analysis of both subjects and stimuli during the social preference test, we reveal marked differences in behavioral dynamics between the strains, suggesting stronger and faster induction of social motivation in SD rats. These different behavioral patterns, which correlate with distinctive c-Fos expression in social motivation-related brain areas, are modified by competition with non-social rewarding stimuli, in a strain-specific manner. Thus, these two strains differ in their social behavior, which should be taken into consideration when selecting an appropriate model organism
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