4,257 research outputs found
Fluctuations of Quantum Radiation Pressure in Dissipative Fluid
Using the generalized Langevin equations involving the stress tensor
approach, we study the dynamics of a perfectly reflecting mirror which is
exposed to the electromagnetic radiation pressure by a laser beam in a fluid at
finite temperature. Based on the fluctuation-dissipation theorem, the minimum
uncertainty of the mirror's position measurement from both quantum and thermal
noises effects including the photon counting error in the laser interferometer
is obtained in the small time limit as compared with the "standard quantum
limit".
The result of the large time behavior of fluctuations of the mirror's
velocity in a dissipative environment can be applied to the laser
interferometer of the ground-based gravitational wave detector.Comment: 8 pages. Version published in Physics Letters
A model of population dynamics - further investigations
The population is composed of individuals characterised by their genetic
strings, phenotypes and ages. We discuss the influence of probabilities of
survival of the individuals on the dynamics and phenotypic variability of the
population.
We show that constant survival probabilities of individuals are propitious
for preserving phenotypic variability of the population. For constant survival
probabilities oscillations of 'the average fitness' of the population and
normal distributions of the phenotypes are observed. When the probabilities of
survival are directly proportinal to the individuals' adaptations the
population can reach the maximum possible average adaptation, but the
phenotypic variability of the population is completely lost and oscillations of
'the average fitness' of the population do not occur.
We also investigate the behaviour of the population caused by the
probabilities of survival that partly depend on the individuals' adaptations.
The role of the length of the individuals' genetic strings is considered here.Comment: 17 pages, 6 figure
The Dwarf Spheroidal Companions to M31: Variable Stars in Andromeda VI
We have surveyed Andromeda VI, a dwarf spheroidal galaxy companion to M31,
for variable stars using F450W and F555W observations obtained with the Hubble
Space Telescope. A total of 118 variables were found, with 111 being RR Lyrae,
6 anomalous Cepheids, and 1 variable we were unable to classify. We find that
the Andromeda VI anomalous Cepheids have properties consistent with those of
anomalous Cepheids in other dwarf spheroidal galaxies. We revise the existing
period-luminosity relations for these variables. Further, using these and other
available data, we show that there is no clear difference between fundamental
and first-overtone anomalous Cepheids in a period-amplitude diagram at shorter
periods, unlike the RR Lyrae. For the Andromeda VI RR Lyrae, we find that they
lie close to the Oosterhoff type I Galactic globular clusters in the
period-amplitude diagram, although the mean period of the RRab stars, =
0.588 d, is slightly longer than the typical Oosterhoff type I cluster. The
mean V magnitude of the RR Lyrae in Andromeda VI is 25.29+/-0.03, resulting in
a distance 815+/-25 kpc on the Lee, Demarque, & Zinn distance scale. This is
consistent with the distance derived from the I magnitude of the tip of the red
giant branch. Similarly, the properties of the RR Lyrae indicate a mean
abundance for Andromeda VI which is consistent with that derived from the mean
red giant branch color.Comment: 23 pages, including 13 figures and 6 tables, emulateapj5/apjfonts
style. Accepted by the Astronomical Journal. We recommend the interested
reader to download the preprint with full-resolution figures, which can be
found at http://www.noao.edu/noao/staff/pritzl/M31dwarfs.htm
The development of a new measure of quality of life in the management of gastro-oesophageal reflux disease: the Reflux Questionnaire.
INTRODUCTION
This paper reports on the development of a new measure of health-related quality of life for use among patients with gastro-oesophageal reflux disease (GORD), funded as part of the REFLUX trial. This is a large UK multi centre trial that aims to compare the clinical and cost effectiveness of minimal access surgery with best medical treatment for patients with GORD within the NHS.
Method Potential items were identified via a series of interviews and focus groups carried out with patients who were receiving/had received medical or surgical treatment for GORD. The final measure consisted of 31 items covering 7 categories (Heartburn; Acid reflux; Wind; Eating and swallowing; Bowel movements; Sleep; Work, physical and social activities). The measure produced two outputs: a quality of life score (RQLS) and five Reflux symptom scores. Reliability (internal consistency), criterion validity with the SF-36 and, sensitivity to change in terms of relationship with reported change in prescribed medication were assessed amongst a sample of 794 patients recruited into the trial.
RESULTS
The measure was shown to be internally consistent, to show criterion validity with the SF-36 and sensitive to changes in patients use of prescribed medication at baseline and 3 month follow-up.
DISCUSSION
The Reflux questionnaire is a new self-administered questionnaire for use amongst patients with GORD. Initial findings suggest that the new measure is valid, reliable, acceptable to respondents and simple to administer in both a clinical and research context
Physical oceanography of the western Iberia ecosystem: latest views and challenges.
The present review is focused on the mesoscale physical processes recognized in the Western Iberia Ecosystem, complementing earlier reviews dedicated to larger scales. Recent studies support the idea that the mesoscale processes, superimposed on the larger scale variability, are the major factor controlling the ecosystem functioning in the region. A complex structure of interleaved alongshore slope, shelf and coastal currents that interact with eddies, buoyant plumes, upwelling filaments and fronts, surface layer expressions of the subsurface circulation and internal waves is revealed by the latest research. All of these contribute in different ways to have an effect on the ecosystem. The supposedly less variable winter circulation also exhibits significant mesoscale activity, in the form of eddy shedding from the poleward slope current, intermittent upwelling events and transient nearshore poleward flows. The present incomplete knowledge of this complex system presents a number of challenges and questions that must be addressed if we are to arrive at a satisfactory understanding and predictive capability for the system as a whole
High-order 3D Voronoi tessellation for identifying Isolated galaxies, Pairs and Triplets
Geometric method based on the high-order 3D Voronoi tessellation is proposed
for identifying the single galaxies, pairs and triplets. This approach allows
to select small galaxy groups and isolated galaxies in different environment
and find the isolated systems. The volume-limited sample of galaxies from the
SDSS DR5 spectroscopic survey was used. We conclude that in such small groups
as pairs and triplets the segregation by luminosity is clearly observed:
galaxies in the isolated pairs and triplets are on average two times more
luminous than isolated galaxies. We consider the dark matter content in
different systems. The median values of mass-to-luminosity ratio are 12
M_sol/L_sol for the isolated pairs and 44 M_sol/L_sol for the isolated
triplets; 7 (8) M_sol/L_sol for the most compact pairs (triplets). We found
also that systems in the denser environment have greater rms velocity and
mass-to-luminosity ratio.Comment: 11 pages, 7 figures, Accepted 2008 October 25 in MNRA
A thick shell Casimir effect
We consider the Casimir energy of a thick dielectric-diamagnetic shell under
a uniform velocity light condition, as a function of the radii and the
permeabilities. We show that there is a range of parameters in which the stress
on the outer shell is inward, and a range where the stress on the outer shell
is outward. We examine the possibility of obtaining an energetically stable
configuration of a thick shell made of a material with a fixed volume
- …