7,789 research outputs found
Accelerated Test Development for Coil-coated Steel Building Panels
This paper discusses the experimental design and the preliminary findings of an ongoing project designed to establish an accelerated laboratory test that would rank coating system performance the same as their performance in atmospheric exposure. A total of ten materials are included in the program: four substrates each with two coating systems and one substrate with two additional coating systems. Samples were installed at four atmospheric exposure sites: Middletown, OH, Daytona Beach, FL, Monroeville, PA, and Halifax, NS, Canada. Three different orientations were utilized at each of the exposure sites and a variety of building panel features were included on the test panels (roll formed bends, laps, cut drip edges, standing seam closures, and scribes). The work discussed in this paper includes the program design and implementation and preliminary correlation\u27s of the three-year atmospheric exposure results to several standard accelerated test methods including: ASTM B117, ASTM G85, ASTM G87, and GM 9540
A Search for Sub-Millisecond Pulsars
We have conducted a search of 19 southern Galactic globular clusters for
sub-millisecond pulsars at 660 MHz with the Parkes 64-m radio telescope. To
minimize dispersion smearing we used the CPSR baseband recorder, which samples
the 20 MHz observing band at the Nyquist rate. By possessing a complete
description of the signal we could synthesize an optimal filterbank in
software, and in the case of globular clusters of known dispersion measure,
much of the dispersion could be removed using coherent techniques. This allowed
for very high time resolution (25.6 us in most cases), making our searches in
general sensitive to sub-millisecond pulsars with flux densities greater than
about 3 mJy at 50 cm. No new pulsars were discovered, placing important
constraints on the proportion of pulsars with very short spin periods in these
clusters.Comment: 8 pages, 3 figures, to appear in Ap
CMB component separation by parameter estimation
We propose a solution to the CMB component separation problem based on
standard parameter estimation techniques. We assume a parametric spectral model
for each signal component, and fit the corresponding parameters pixel by pixel
in a two-stage process. First we fit for the full parameter set (e.g.,
component amplitudes and spectral indices) in low-resolution and high
signal-to-noise ratio maps using MCMC, obtaining both best-fit values for each
parameter, and the associated uncertainty. The goodness-of-fit is evaluated by
a chi^2 statistic. Then we fix all non-linear parameters at their
low-resolution best-fit values, and solve analytically for high-resolution
component amplitude maps. This likelihood approach has many advantages: The
fitted model may be chosen freely, and the method is therefore completely
general; all assumptions are transparent; no restrictions on spatial variations
of foreground properties are imposed; the results may be rigorously monitored
by goodness-of-fit tests; and, most importantly, we obtain reliable error
estimates on all estimated quantities. We apply the method to simulated Planck
and six-year WMAP data based on realistic models, and show that separation at
the muK level is indeed possible in these cases. We also outline how the
foreground uncertainties may be rigorously propagated through to the CMB power
spectrum and cosmological parameters using a Gibbs sampling technique.Comment: 20 pages, 10 figures, submitted to ApJ. For a high-resolution
version, see http://www.astro.uio.no/~hke/docs/eriksen_et_al_fgfit.p
Strong electron-phonon coupling in delta-phase stabilized Pu
Heat capacity measurements of the delta-phase stabilized alloy Pu-Al suggest
that strong electron-phonon coupling is required to explain the moderate
renormalization of the electronic density of states near the Fermi energy. We
calculate the heat capacity contributions from the lattice and electronic
degrees of freedom as well as from the electron-lattice coupling term and find
good overall agreement between experiment and theory assuming a dimensionless
electron-phonon coupling parameter of order unity, lambda ~ 0.8. This large
electron-phonon coupling parameter is comparable to reported values in other
superconducting metals with face-centered cubic crystal structure, for example,
Pd (lambda ~ 0.7) and Pb (lambda ~ 1.5). Further, our analysis shows evidence
of a sizable residual low-temperature entropy contribution, S_{res} ~ 0.4 k_B
(per atom). We can fit the residual specific heat to a two-level system.
Therefore, we speculate that the observed residual entropy originates from
crystal-electric field effects of the Pu atoms or from self-irradiation induced
defects frozen in at low temperatures.Comment: 9 pages, 11 figures, to appear in Phys. Rev.
Focusing of timelike worldsheets in a theory of strings
An analysis of the generalised Raychaudhuri equations for string world sheets
is shown to lead to the notion of focusing of timelike worldsheets in the
classical Nambu-Goto theory of strings. The conditions under which such effects
can occur are obtained . Explicit solutions as well as the Cauchy initial value
problem are discussed. The results closely resemble their counterparts in the
theory of point particles which were obtained in the context of the analysis of
spacetime singularities in General Relativity many years ago.Comment: 14 pages, RevTex, no figures, extended, to appear in Phys Rev
Symmetries of the Dirac operators associated with covariantly constant Killing-Yano tensors
The continuous and discrete symmetries of the Dirac-type operators produced
by particular Killing-Yano tensors are studied in manifolds of arbitrary
dimensions. The Killing-Yano tensors considered are covariantly constant and
realize certain square roots of the metric tensor. Such a Killing-Yano tensor
produces simultaneously a Dirac-type operator and the generator of a
one-parameter Lie group connecting this operator with the standard Dirac one.
The Dirac operators are related among themselves through continuous or discrete
transformations. It is shown that the groups of the continuous symmetry can be
only U(1) and SU(2), specific to (hyper-)Kahler spaces, but arising even in
cases when the requirements for these special geometries are not fulfilled. The
discrete symmetries are also studied obtaining the discrete groups Z_4 and Q.
The briefly presented examples are the Euclidean Taub-NUT space and the
Minkowski spacetime.Comment: 27 pages, latex, no figures, final version to be published in Class.
Quantum Gravit
The fall and rise of V854 Centauri: long-term ultraviolet spectroscopy of a highly-active R Coronae Borealis star
We examine long-term low-dispersion IUE, SWP and LWP spectroscopy of the R
Coronae Borealis (RCB) star V854 Cen, obtained across the deep 1991, 1992-1993
and 1994 declines. We also report the optical light curve for the star in the
interval 1987-1998, including multi-color photometry obtained during 1989-1998.
Analysis of the UV emission line spectra indicates most lines decay during
the deep declines on characteristic timescales comparable to that reported for
optical features. Fe, Mg and neutral C lines decay on timescales of typically
50-100 d. Other lines, notably ionized C lines, decay on longer timescales (>
200 d) or appear to be unaffected by the declines. The general nature of the UV
emission lines and other UV features during the declines is consistent with the
E1/E2/BL line-region model developed from the behavior of optical spectral
features during declines. However, the detailed line-behavior indicates large
intrinsic variability between decline events inconsistent with the simple
E1/E2/BL model. Limited temporal coverage prevents detailed examination of the
geometry of the emission line region or the obscuring dust. We also report the
first detection of the transition-region line C IV 1550 in the spectrum of an
RCB star.Comment: AJ in press (June), 7 figures, 4 table
A cardiovascular disease policy model:part 2-preparing for economic evaluation and to assess health inequalities
Objectives This is the second of two papers introducing a cardiovascular disease (CVD) policy model. The first paper described the structure and statistical underpinning of the state transition model, demonstrating how life expectancy estimates are generated for individuals defined by ASSIGN risk factors. This second paper describes how the model is prepared to undertake economic evaluation. Design To generate quality adjusted life expectancy (QALE), the Scottish Health Survey was used to estimate background morbidity (health utilities) and the impact of CVD events (utility decrements). The SF-6D algorithm generated utilities and decrements were modelled using ordinary least squares (OLS). To generate lifetime hospital costs the Scottish Heart Health Extended Cohort (SHHEC) was linked to the Scottish morbidity and death records (SMR) to cost each Continuous Inpatient Stay (CIS). OLS and restricted cubic splines estimated annual costs before and after each of the first four events. A Kaplan Meier Sample Average (KMSA) estimator was then used to weight expected health related quality of life and costs by the probability of survival. Results The policy model predicts the change in QALE and lifetime hospital costs as a result of an intervention(s) modifying risk factors. Cost effectiveness analysis and a full uncertainty analysis can be undertaken, including probabilistic sensitivity analysis. Notably, the impacts according to socioeconomic deprivation status can be made. Conclusions The policy model can conduct cost effectiveness analysis and decision analysis to inform approaches to primary prevention, including individually targeted and population interventions, and to assess impacts on health inequalities. </p
An Algebraic Pairing Model with Sp(4) Symmetry and its Deformation
A fermion realization of the compact symplectic sp(4) algebra provides a
natural framework for studying isovector pairing correlations in nuclei. While
these correlations manifest themselves most clearly in the binding energies of
0^+ ground states, they also have a large effect on the energies of excited
states, including especially excited 0^+ states. In this article we consider
non-deformed as well as deformed algebraic descriptions of pairing through the
reductions of sp_{(q)}(4) to different realizations of u_{(q)}(2) for single-j
and multi-j orbitals. The model yields a classification scheme for completely
paired 0^{+} states of even-even and odd-odd nuclei in the 1d_{3/2}, 1f_{7/2},
and 1f_{5/2}2p_{1/2}2p_{3/2}1g_{9/2} shells. Phenomenological non-deformed and
deformed isospin-breaking Hamiltonians are expressed in terms of the generators
of the dynamical symmetry groups Sp(4) and Sp_{q}(4). These Hamiltonians are
related to the most general microscopic pairing problem, including isovector
pairing and isoscalar proton-neutron interaction along with non-linear
interaction in the deformed extension. In both the non-deformed and deformed
cases the eigenvalues of the Hamiltonian are fit to the relevant Coulomb
corrected experimental 0^{+} energies and this, in turn, allows us to estimate
the interaction strength parameters, to investigate isovector-pairing
properties and symmetries breaking, and to predict the corresponding energies.
While the non-deformed theory yields results that are comparable to other
theories for light nuclei, the deformed extension, which takes into account
higher-order interactions between the particles, gives a better fit to the
data. The multi-shell applications of the model provide for reasonable
predictions of energies of exotic nuclei.Comment: 19 pages, 5 figures minor changes; improvements to achieve a better
and clearer presentation of our messages and idea
Feeling our way: academia, emotions and a politics of care
This paper aims to better understand the role of emotions in academia, and their part in producing, and challenging, an increasingly normalized neoliberal academy. It unfolds from two narratives that foreground emotions in and across academic spaces and practices, to critically explore how knowledges and positions are constructed and circulated. It then moves to consider these issues through the lens of care as a political stance towards being and becoming academics in neoliberal times. Our aim is to contribute to the burgeoning literature on emotional geographies, explicitly bringing this work into conversation with resurgent debates surrounding an ethic of care, as part of a politic of critiquing individualism and managerialism in (and beyond) the academy. We consider the ways in which neoliberal university structures circulate particular affects, prompting emotions such as desire and anxiety, and the internalisation of competition and audit as embodied scholars. Our narratives exemplify how attendant emotions and affect can reverberate and be further reproduced through university cultures, and diffuse across personal and professional lives. We argue that emotions in academia matter, mutually co-producing everyday social relations and practices at and across all levels. We are interested in their political implications, and how neoliberal norms can be shifted through practices of caring-with
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