32,903 research outputs found
USAF solar thermal applications overview
Process heat applications were compared to solar thermal technologies. The generic process heat applications were analyzed for solar thermal technology utilization, using SERI's PROSYS/ECONOMAT model in an end use matching analysis and a separate analysis was made for solar ponds. Solar technologies appear attractive in a large number of applications. Low temperature applications at sites with high insolation and high fuel costs were found to be most attractive. No one solar thermal technology emerges as a clearly universal or preferred technology, however,, solar ponds offer a potential high payoff in a few, selected applications. It was shown that troughs and flat plate systems are cost effective in a large number of applications
The cutoff-dependence of the Casimir force within an inhomogeneous medium
We consider the ground state energy of the electromagnetic field in a piston
geometry. In the idealised case, where the piston and the walls of the chamber
are taken as perfect mirrors, the Casimir pressure on the piston is finite and
independent of the small scale physics of the media that compose the mirrors;
the Casimir-energy of the system can be regularised and is cutoff-independent.
Yet we find that, when the body of the piston is filled with an inhomogeneous
dielectric medium, the Casimir energy is cutoff-dependent, and the value of the
pressure is thus inextricably dependent on the detailed behaviour of the mirror
and the medium at large wave-vectors. This result is inconsistent with recent
proposals for regularising Casimir forces in inhomogeneous media.Comment: 6 pages, 2 figure
CPD 1 - Embedding Epistemic Insight and Big Questions across a whole school curriculum
Professional development workshop.
Explanation of Epistemic Insight pedagogical approach, tools and resources to help embed Big questions into a school-wide curriculum
Determining the Dependence Structure of Multivariate Extremes
In multivariate extreme value analysis, the nature of the extremal dependence
between variables should be considered when selecting appropriate statistical
models. Interest often lies with determining which subsets of variables can
take their largest values simultaneously, while the others are of smaller
order. Our approach to this problem exploits hidden regular variation
properties on a collection of non-standard cones and provides a new set of
indices that reveal aspects of the extremal dependence structure not available
through existing measures of dependence. We derive theoretical properties of
these indices, demonstrate their value through a series of examples, and
develop methods of inference that also estimate the proportion of extremal mass
associated with each cone. We apply the methods to UK river flows, estimating
the probabilities of different subsets of sites being large simultaneously
Isospin-breaking interactions studied through mirror energy differences
Background: Information on charge-dependent (i.e., isospin-non-conserving) interactions is extracted from excited states of mirror nuclei.
Purpose: Specifically, the purpose of the study is to extract effective isovector (Vpp 12Vnn) interactions which, in general, can either be of Coulomb or nuclear origin.
Methods: A comprehensive shell-model description of isospin-breaking effects is used to fit data on mirror energy differences in the A = 42\u201354 region. The angular-momentum dependence of isospin-breaking interactions was determined from a systematic study of mirror energy differences.
Results: The results reveal a significant isovector term, with a very strong spin dependence, beyond that expected of a two-body Coulomb interaction.
Conclusions: The isospin-breaking terms that are extracted have a J dependence that is not consistent with the known CSB properties of the bare nucleon-nucleon interaction
Overview of the Main Propulsion System for a Nuclear Thermal Propulsion Flight Demonstrator
A demonstration of a Nuclear Thermal Propulsion (NTP) engine has not been conducted in over 50 years. Several tests were conducted during the NERVA program but no NTP engine was ever flown in space. In the last several years there has been a considerable amount of conceptual design work on NTP engines conducted. With the prospect of human Mars missions in the 2030s there has been a renewed interest in NTP engines. A concept design study was conducted with the intent to design 2 flight demonstrator vehicles that would buy down programmatic and technical risks associated with launching and operating nuclear reactors in space. The intent of the first demonstrator mission would be to employ a simplified NTP engine and buy down programmatic risks whereas the second demonstrator would buy down technical risks with a NTP engine designed to be similar to an operational NTP model. The results of the study showed that a simplified NTP engine demonstrator could be feasibly built and flown in the near term with mostly high TRL, commercial off-the-shelf components
Estimating the masses of extra-solar planets
All extra-solar planet masses that have been derived spectroscopically are
lower limits since the inclination of the orbit to our line-of-sight is unknown
except for transiting systems. It is, however, possible to determine the
inclination angle, i, between the rotation axis of a star and an observer's
line-of-sight from measurements of the projected equatorial velocity (v sin i),
the stellar rotation period (P_rot) and the stellar radius (R_star). This
allows the removal of the sin i dependency of spectroscopically derived
extra-solar planet masses under the assumption that the planetary orbits lie
perpendicular to the stellar rotation axis. We have carried out an extensive
literature search and present a catalogue of v sin i, P_rot, and R_star
estimates for exoplanet host stars. In addition, we have used Hipparcos
parallaxes and the Barnes-Evans relationship to further supplement the R_star
estimates obtained from the literature. Using this catalogue, we have obtained
sin i estimates using a Markov-chain Monte Carlo analysis. This allows proper
1-sigma two-tailed confidence limits to be placed on the derived sin i's along
with the transit probability for each planet to be determined. While a small
proportion of systems yield sin i's significantly greater than 1, most likely
due to poor P_rot estimations, the large majority are acceptable. We are
further encouraged by the cases where we have data on transiting systems, as
the technique indicates inclinations of ~90 degrees and high transit
probabilities. In total, we estimate the true masses of 133 extra-solar
planets. Of these, only 6 have revised masses that place them above the 13
Jupiter mass deuterium burning limit. Our work reveals a population of
high-mass planets with low eccentricities and we speculate that these may
represent the signature of different planetary formation mechanisms at work.Comment: 40 pages, 6 tables, 2 figures. Accepted for publication in the
Monthly Notices of the Royal Astronomical Society after editing of Tables 1 &
6 for electronic publication. Html abstract shortened for astro-ph submissio
An algorithm for determining program feasibility of a multi-mode PAM commutator telemetry system Technical report no. 10
Algorithm formulation for evaluation of strapping arrangement programs for PAM multimode commutation system of Saturn telemetry syste
Low-power radio galaxy environments in the Subaru/XMM-Newton Deep Field at z~0.5
We present multi-object spectroscopy of galaxies in the immediate (Mpc-scale)
environments of four low-power (L_1.4 GHz < 10^25 W/Hz) radio galaxies at
z~0.5, selected from the Subaru/XMM-Newton Deep Field. We use the spectra to
calculate velocity dispersions and central redshifts of the groups the radio
galaxies inhabit, and combined with XMM-Newton (0.3-10 keV) X-ray observations
investigate the L_X--sigma_v and T_X--sigma_v scaling relationships. All the
radio galaxies reside in moderately rich groups -- intermediate environments
between poor groups and rich clusters, with remarkably similar X-ray
properties. We concentrate our discussion on our best statistical example that
we interpret as a low-power (FRI) source triggered within a sub-group, which in
turn is interacting with a nearby group of galaxies, containing the bulk of the
X-ray emission for the system -- a basic scenario which can be compared to more
powerful radio sources at both high (z>4) and low (z<0.1) redshifts. This
suggests that galaxy-galaxy interactions triggered by group mergers may play an
important role in the life-cycle of radio galaxies at all epochs and
luminosities.Comment: 12 pages, 7 figures, accepted for publication in MNRAS. High
resolution version available upon reques
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