16 research outputs found
Constraining a possible time variation of the gravitational constant G with terrestrial nuclear laboratory data
Testing the constancy of the gravitational constant G has been a longstanding
fundamental question in natural science. As first suggested by Jofr\'{e},
Reisenegger and Fern\'{a}ndez [1], Dirac's hypothesis of a decreasing
gravitational constant with time due to the expansion of the Universe would
induce changes in the composition of neutron stars, causing dissipation and
internal heating. Eventually, neutron stars reach their quasi-stationary states
where cooling due to neutrino and photon emissions balances the internal
heating. The correlation of surface temperatures and radii of some old neutron
stars may thus carry useful information about the changing rate of G. Using the
density dependence of the nuclear symmetry energy constrained by recent
terrestrial laboratory data on isospin diffusion in heavy-ion reactions at
intermediate energies and the size of neutron skin in within the
gravitochemical heating formalism, we obtain an upper limit of the relative
changing rate of consistent with the
best available estimates in the literature.Comment: 27 pages, 11 figures, and 2 tables. Accepted version to appear in PRC
(2007
Constraining a possible time-variation of the gravitational constant through "gravitochemical heating" of neutron stars
A hypothetical time-variation of the gravitational constant would cause
neutron star matter to depart from beta equilibrium, due to the changing
hydrostatic equilibrium. This forces non-equilibrium beta processes to occur,
which release energy that is invested partly in neutrino emission and partly in
heating the stellar interior. Eventually, the star arrives at a stationary
state in which the temperature remains nearly constant, as the forcing through
the change of is balanced by the ongoing reactions. Comparing the surface
temperature of the nearest millisecond pulsar, PSR J0437-4715, inferred from
ultraviolet observations, with our predicted stationary temperature, we
estimate two upper limits for this variation: (1) yr, if we allow direct Urca reactions operating in the neutron
star core, and (2) yr, considering only
modified Urca reactions. Both results are competitive with those obtained by
other methods, with (2) being among the most restrictive.Comment: 4 pages, including 2 figures. Accepted for publication in Phys. Rev.
Lett. Revised version includes minor changes in the wording, and more
substantial changes in the last 2 paragraphs (Discussion and Conclusions).
Equations, figures, and results are unchange
Anisotropy in the Distribution of Galactic Radio Polarizations
Radiation traversing the observable universe provides powerful ways to probe
anisotropy of electromagnetic propagation. A controversial recent study claimed
a signal of dipole character. Here we test a new and independent data set of
361 points under the null proposal of {\it statistical independence} of linear
polarization alignments relative to galaxy axes, versus angular positions. The
null hypothesis is tested via maximum likelihood analysis of best fits among
numerous independent types of factored distributions. We also examine
single-number correlations which are parameter free, invariant under coordinate
transformations, and distributed very robustly. The statistics are shown
explicitly not to depend on the uneven distribution of sources on the sky.
We find that the null proposal is not supported at the level of less than 5%
to less than 0.1% by several independent statistics. The signal of correlation
violates parity, that is, symmetry under spatial inversion, and requires a
statistic which transforms properly. The data indicate an axis of correlation,
on the basis of likelihood determined to be , .Comment: 10 pages, Late
Internal heating and thermal emission from old neutron stars: Constraints on dense-matter and gravitational physics
The equilibrium composition of neutron star matter is achieved through weak
interactions (direct and inverse beta decays), which proceed on relatively long
time scales. If the density of a matter element is perturbed, it will relax to
the new chemical equilibrium through non-equilibrium reactions, which produce
entropy that is partly released through neutrino emission, while a similar
fraction heats the matter and is eventually radiated as thermal photons. We
examined two possible mechanisms causing such density perturbations: 1) the
reduction in centrifugal force caused by spin-down (particularly in millisecond
pulsars), leading to "rotochemical heating", and 2) a hypothetical
time-variation of the gravitational constant, as predicted by some theories of
gravity and current cosmological models, leading to "gravitochemical heating".
If only slow weak interactions are allowed in the neutron star (modified Urca
reactions, with or without Cooper pairing), rotochemical heating can account
for the observed ultraviolet emission from the closest millisecond pulsar, PSR
J0437-4715, which also provides a constraint on |dG/dt| of the same order as
the best available in the literature.Comment: 6 pages, 7 figures. To appear in the proceedings of "Isolated Neutron
Stars: from the Interior to the Surface", a conference held in London in
April 2006 (special issue of Astrophysics and Space Science, edited by Dany
Page, Roberto Turolla, & Silvia Zane
An HST Survey of the mid-UV Morphology of Nearby Galaxies
(Abbreviated) We present an imaging survey of 37 nearby galaxies observed
with HST/WFPC2 in the mid-UV F300W filter and in F814W. 11 galaxies were also
imaged in F255W. These galaxies were selected to be detectable with WFPC2 in
one orbit, and cover a wide range of Hubble types and inclinations. The mid-UV
spans the gap between our groundbased optical/NIR images and far-UV images
available from the Astro/UIT missions. Our first qualitative results are:
(1) Early-type galaxies show a significant decrease in surface brightness
going from the red to the mid-UV, and in some cases the presence of dust lanes.
Some galaxies would be classified different when viewed in the mid-UV, some
become dominated by a blue nuclear feature or point source.
(2) Half of the mid-type spiral and star-forming galaxies appear as a later
morphological type in the mid-UV, as Astro/UIT also found in the far-UV. Some-
times these differences are dramatic. The mid-UV images show a considerable
range in the scale and surface brightness of individual star-forming regions.
Almost all mid-type spirals have their small bulges bi-sected by a dust-lane.
(3) Most of the heterogeneous subset of late-type, irregular, peculiar, and
merging galaxies display F300W morphologies that are similar to those seen in
F814W, but with differences due to recognizable dust features absorbing the
bluer light, and due to UV-bright hot stars, star-clusters, and star-forming
ridges.
In the rest-frame mid-UV, early- to mid-type galaxies are more likely to be
misclassified as later types than vice versa. This morphological K-correction
explains only part of the excess faint blue galaxies seen in deep HST fields.Comment: 30 pages, LateX (AASTeX5.0), 2 figures and 3 tables included, mid-UV
atlas and pan-chromatic atlas provided as 63 JPG figures. Full resolution PS
version (~100Mb) available upon request. Accepted for publication in ApJ
Vision zero: from accident prevention to the promotion of health, safety and well-being at work
There is growing attention in industry for the Vision Zero strategy, which in terms of work-related health and safety is often labelled as Zero Accident Vision or Zero Harm. The consequences of a genuine commitment to Vision Zero for addressing health, safety and well-being and their synergies are discussed. The Vision Zero for work-related health, safety and well-being is based on the assumption that all accidents, harm and work-related diseases are preventable. Vision Zero for health, safety and well-being is then the ambition and commitment to create and ensure safe and healthy work and to prevent all accidents, harm and work-related diseases in order to achieve excellence in health, safety and well-being. Implementation of Vision Zero is a process – rather than a target, and healthy organizations make use of a wide range of options to facilitate this process. There is sufficient evidence that fatigue, stress and work organization factors are important determinants of safety behaviour and safety performance. Even with a focus on preventing accidents these additional factors should also be addressed. A relevant challenge is the integration of the Vision Zero into broader business policy and practice. There is a continued need more empirical research in this area
UV, Optical and IR Observations of the Cepheid R Muscae
Ultraviolet IUE spectra, optical 12A mm-1 red and blue spectra, optical BV photometry and infrared JHKL photometry of the 7.5-d classical Cepheid R Muscae = HD 110 311 is presented and discussed together with some earlier photometric and radial velocity data.
Using the CORS method, a newly derived radius is given, as well as new values for T.tT and log g. The UV spectra confirrned the predicted trend to increasing amplitudes with decreasing wavelength and indicate that R Mus has a shallow chromosphere, while no transition region lines could
be detected.
From all our data from 1200 A to 5 μm we conclude that R Mus
does not have a companion detectable with the sensitivity given,
contrary to earlier results