310 research outputs found
Supercritical water (SCW): a new medium to generate novel materials for solar energy applications
Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.We present here developments and results from a multidisciplinary experimental program focused on the use of supercritical water (SCW) for energy applications and hydrothermal processing. We highlight our findings from investigating the interaction of organic and inorganic materials with SCW, and also comment on progress with advanced measurement systems. Supercritical water (SCW) possesses unique properties, which have prompted investigation into its usage in a plethora of energy and chemical applications. Beyond its critical point (374 °C and 22.1 MPa), water exhibits unconventional solubility and heat transfer characteristics, which are potentially advantageous. In this paper, we present an overview of our progress in experimental studies of the interaction of SCW with a variety of materials, both organic and inorganic. Our most notable progress has been in the development of several novel materials, designs and experimental techniques for small-scale research, and the use of these designs and techniques for detailed experimental study. The work shown highlights the potential of SCW as a useful medium for solar energy applications, and identifies some intriguing features of SCW research.cf201
A Bayesian Approach to Calibrating Period-Luminosity Relations of RR Lyrae Stars in the Mid-Infrared
A Bayesian approach to calibrating period-luminosity (PL) relations has
substantial benefits over generic least-squares fits. In particular, the
Bayesian approach takes into account the full prior distribution of the model
parameters, such as the a priori distances, and refits these parameters as part
of the process of settling on the most highly-constrained final fit.
Additionally, the Bayesian approach can naturally ingest data from multiple
wavebands and simultaneously fit the parameters of PL relations for each
waveband in a procedure that constrains the parameter posterior distributions
so as to minimize the scatter of the final fits appropriately in all wavebands.
Here we describe the generalized approach to Bayesian model fitting and then
specialize to a detailed description of applying Bayesian linear model fitting
to the mid-infrared PL relations of RR Lyrae variable stars. For this example
application we quantify the improvement afforded by using a Bayesian model fit.
We also compare distances previously predicted in our example application to
recently published parallax distances measured with the Hubble Space Telescope
and find their agreement to be a vindication of our methodology. Our intent
with this article is to spread awareness of the benefits and applicability of
this Bayesian approach and encourage future PL relation investigations to
consider employing this powerful analysis method.Comment: 6 pages, 1 figure. Accepted for publication in Astrophysics & Space
Science. Following a presentation at the conference The Fundamental Cosmic
Distance Scale: State of the Art and the Gaia Perspective, Naples, May 201
On the Normalization of the Neutrino-Deuteron Cross Section
As is well-known, comparison of the solar neutrino fluxes measured in
SuperKamiokande (SK) by and in the Sudbury Neutrino
Observatory (SNO) by can provide a ``smoking gun''
signature for neutrino oscillations as the solution to the solar neutrino
puzzle. This occurs because SK has some sensitivity to all active neutrino
flavors whereas SNO can isolate electron neutrinos. This comparison depends
crucially on the normalization and uncertainty of the theoretical
charged-current neutrino-deuteron cross section. We address a number of effects
which are significant enough to change the interpretation of the SK--SNO
comparison.Comment: 4 pages, 1 figure, submitted to PR
Tevatron Beam Halo Collimation System: Design, Operational Experience and New Methods
Collimation of proton and antiproton beams in the Tevatron collider is
required to protect CDF and D0 detectors and minimize their background rates,
to keep irradiation of superconducting magnets under control, to maintain
long-term operational reliability, and to reduce the impact of beam-induced
radiation on the environment. In this article we briefly describe the design,
practical implementation and performance of the collider collimation system,
methods to control transverse and longitudinal beam halo and two novel
collimation techniques tested in the Tevatron.Comment: 25 p
Nuclear Octupole Correlations and the Enhancement of Atomic Time-Reversal Violation
We examine the time-reversal-violating nuclear ``Schiff moment'' that induces
electric dipole moments in atoms. After presenting a self-contained derivation
of the form of the Schiff operator, we show that the distribution of Schiff
strength, an important ingredient in the ground-state Schiff moment, is very
different from the electric-dipole-strength distribution, with the Schiff
moment receiving no strength from the giant dipole resonance in the
Goldhaber-Teller model. We then present shell-model calculations in light
nuclei that confirm the negligible role of the dipole resonance and show the
Schiff strength to be strongly correlated with low-lying octupole strength.
Next, we turn to heavy nuclei, examining recent arguments for the strong
enhancement of Schiff moments in octupole-deformed nuclei over that of 199Hg,
for example. We concur that there is a significant enhancement while pointing
to effects neglected in previous work (both in the octupole-deformed nuclides
and 199Hg) that may reduce it somewhat, and emphasizing the need for
microscopic calculations to resolve the issue. Finally, we show that static
octupole deformation is not essential for the development of collective Schiff
moments; nuclei with strong octupole vibrations have them as well, and some
could be exploited by experiment.Comment: 25 pages, 4 figures embedded in tex
Enhanced T-odd P-odd Electromagnetic Moments in Reflection Asymmetric Nuclei
Collective P- and T- odd moments produced by parity and time invariance
violating forces in reflection asymmetric nuclei are considered. The enhanced
collective Schiff, electric dipole and octupole moments appear due to the
mixing of rotational levels of opposite parity. These moments can exceed
single-particle moments by more than two orders of magnitude. The enhancement
is due to the collective nature of the intrinsic moments and the small energy
separation between members of parity doublets. In turn these nuclear moments
induce enhanced T- and P- odd effects in atoms and molecules. First a simple
estimate is given and then a detailed theoretical treatment of the collective
T-, P- odd electric moments in reflection asymmetric, odd-mass nuclei is
presented and various corrections evaluated. Calculations are performed for
octupole deformed long-lived odd-mass isotopes of Rn, Fr, Ra, Ac and Pa and the
corresponding atoms. Experiments with such atoms may improve substantially the
limits on time reversal violation.Comment: 28 pages, Revte
Detector Description and Performance for the First Coincidence Observations between LIGO and GEO
For 17 days in August and September 2002, the LIGO and GEO interferometer
gravitational wave detectors were operated in coincidence to produce their
first data for scientific analysis. Although the detectors were still far from
their design sensitivity levels, the data can be used to place better upper
limits on the flux of gravitational waves incident on the earth than previous
direct measurements. This paper describes the instruments and the data in some
detail, as a companion to analysis papers based on the first data.Comment: 41 pages, 9 figures 17 Sept 03: author list amended, minor editorial
change
The Theory of Brown Dwarfs and Extrasolar Giant Planets
Straddling the traditional realms of the planets and the stars, objects below
the edge of the main sequence have such unique properties, and are being
discovered in such quantities, that one can rightly claim that a new field at
the interface of planetary science and and astronomy is being born. In this
review, we explore the essential elements of the theory of brown dwarfs and
giant planets, as well as of the new spectroscopic classes L and T. To this
end, we describe their evolution, spectra, atmospheric compositions, chemistry,
physics, and nuclear phases and explain the basic systematics of
substellar-mass objects across three orders of magnitude in both mass and age
and a factor of 30 in effective temperature. Moreover, we discuss the
distinctive features of those extrasolar giant planets that are irradiated by a
central primary, in particular their reflection spectra, albedos, and transits.
Aspects of the latest theory of Jupiter and Saturn are also presented.
Throughout, we highlight the effects of condensates, clouds, molecular
abundances, and molecular/atomic opacities in brown dwarf and giant planet
atmospheres and summarize the resulting spectral diagnostics. Where possible,
the theory is put in its current observational context.Comment: 67 pages (including 36 figures), RMP RevTeX LaTeX, accepted for
publication in the Reviews of Modern Physics. 30 figures are color. Most of
the figures are in GIF format to reduce the overall size. The full version
with figures can also be found at:
http://jupiter.as.arizona.edu/~burrows/papers/rm
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