8,848 research outputs found
Existence and stability of regularized shock solutions, with applications to rimming flows
This paper is concerned with regularization of shock solutions of nonlinear hyperbolic equations, i.e.,
introduction of a smoothing term with a coefficient ε, then taking the limit ε → 0. In addition to the classical use
of regularization for eliminating physically meaningless solutions which always occur in non-regularized equa tions (e.g. waves of depression in gas dynamics), we show that it is also helpful for stability analysis. The general
approach is illustrated by applying it to rimming flows, i.e., flows of a thin film of viscous liquid on the inside of a
horizontal rotating cylinder, with or without surface tension (which plays the role of the regularizing effect). In the
latter case, the spectrum of available linear eigenmodes appears to be continuous, but in the former, it is discrete and,
most importantly, remains discrete in the limit of infinitesimally weak surface tension. The regularized (discrete)
spectrum is fully determined by the point where the velocity of small perturbations vanishes, with the rest of the
domain, including the shock region, being unimportant.info:eu-repo/semantics/publishedVersio
Measuring the Impact of Nextstep Career Advice in the North East of England
In September, 2007, the main contractors of the four nextstep networks in the North East (referred to in this paper as the ‘consortium’) successfully submitted a proposal to the Learning & Skills Council (LSC) for funding to develop a
framework for measuring the impact of career advice. It was agreed that the project would result in a practice-based ‘Impact Toolkit’ that would include:-
• a set of impact measures that should be used in the new adult careers service with a rationale for their inclusion;
• methodologies for each of the impact measures identified;
• approaches to obtaining information on progression in learning and work – with templates and case study material;
• approaches to measuring soft outcomes; and
• suggested Key Performance Indicators (KPIs)
The Case for Optically-Thick High Velocity Broad Line Region Gas in Active Galactic Nuclei
A combined analysis of the profiles of the main broad quasar emission lines
in both Hubble Space Telescope and optical spectra shows that while the
profiles of the strong UV lines are quite similar, there is frequently a strong
increase in the Ly-alpha/H-alpha ratio in the high-velocity gas. We show that
the suggestion that the high velocity gas is optically-thin presents many
problems. We show that the relative strengths of the high velocity wings arise
naturally in an optically-thick BLR component. An optically-thick model
successfully explains the equivalent widths of the lines, the Ly-alpha/H-alpha
ratios and flatter Balmer decrements in the line wings, the strengths of CIII]
and the lambda 1400 blend, and the strong variability of high-velocity,
high-ionization lines (especially HeII and HeI).Comment: 34 pages in AASTeX, including 10 pages of figures. Submitted to
Astrophysical Journa
Spin-dynamics of the low-dimensional magnet (CH3)2NH2CuCl3
Dimethylammonium copper (II) chloride (also known as DMACuCl3 or MCCL) is a
low dimensional S=1/2 quantum spin system proposed to be an alternating
ferro-antiferromagnetic chain with similar magnitude ferromagnetic (FM) and
antiferromagnetic (AFM) exchange interactions. Subsequently, it was shown that
the existing bulk measurements could be adequately modeled by considering
DMACuCl3 as independent AFM and FM dimer spin pairs. We present here new
inelastic neutron scattering measurements of the spin-excitations in single
crystals of DMACuCl3. These results show significant quasi-one-dimensional
coupling, however the magnetic excitations do not propagate along the expected
direction. We observe a band of excitations with a gap of 0.95 meV and a
bandwidth of 0.82 meV.Comment: 3 pages, 2 figures included in text, submitted to proceedings of
International Conference on Neutron Scattering, December 200
Testing the standard fireball model of GRBs using late X-ray afterglows measured by Swift
We show that all X-ray decay curves of GRBs measured by Swift can be fitted
using one or two components both of which have exactly the same functional form
comprised of an early falling exponential phase followed by a power law decay.
The 1st component contains the prompt gamma-ray emission and the initial X-ray
decay. The 2nd component appears later, has a much longer duration and is
present for ~80% of GRBs. It most likely arises from the external shock which
eventually develops into the X-ray afterglow. In the remaining ~20% of GRBs the
initial X-ray decay of the 1st component fades more slowly than the 2nd and
dominates at late times to form an afterglow but it is not clear what the
origin of this emission is.
The temporal decay parameters and gamma/X-ray spectral indices derived for
107 GRBs are compared to the expectations of the standard fireball model
including a search for possible "jet breaks". For ~50% of GRBs the observed
afterglow is in accord with the model but for the rest the temporal and
spectral indices do not conform to the expected closure relations and are
suggestive of continued, late, energy injection. We identify a few possible jet
breaks but there are many examples where such breaks are predicted but are
absent.
The time, T_a, at which the exponential phase of the 2nd component changes to
a final powerlaw decay afterglow is correlated with the peak of the gamma-ray
spectrum, E_peak. This is analogous to the Ghirlanda relation, indicating that
this time is in some way related to optically observed break times measured for
pre-Swift bursts.Comment: submitted to Ap
Is diversity good?
Prominent ethical and policy issues such as affirmative action and female
enrollment in science and engineering revolve around the idea that diversity is
good. However, even though diversity is an ambiguous concept, a precise
definition is seldom provided. We show that diversity may be construed as a
factual description, a craving for symmetry, an intrinsic good, an instrumental
good, a symptom, or a side effect. These acceptions differ vastly in their
nature and properties. The first one cannot lead to any action and the second
one is mistaken. Diversity as intrinsic good is a mere opinion, which cannot be
concretely applied; moreover, the most commonly invoked forms of diversity
(sexual and racial) are not intrinsically good. On the other hand, diversity as
instrumental good can be evaluated empirically and can give rise to policies,
but these may be very weak. Finally, symptoms and side effects are not actually
about diversity. We consider the example of female enrollment in science and
engineering, interpreting the various arguments found in the literature in
light of this polysemy.
Keywords: ethics, policy, higher education, female students, minority
students, affirmative actionComment: 7 page
Some New/Old Approaches to QCD
This is a talk delivered at the Meeting on Integrable Quantum Field Theories,
Villa Olmo and at STRINGS 1992, Rome, September 1992. I discuss some recent
attempts to revive two old ideas regarding an analytic approach to QCD-the
development of a string representation of the theory and the large N limit of
QCD.Comment: 20 page
Application of energy and angular momentum balance to gravitational radiation reaction for binary systems with spin-orbit coupling
We study gravitational radiation reaction in the equations of motion for
binary systems with spin-orbit coupling, at order (v/c)^7 beyond Newtonian
gravity, or O(v/c)^2 beyond the leading radiation reaction effects for
non-spinning bodies. We use expressions for the energy and angular momentum
flux at infinity that include spin-orbit corrections, together with an
assumption of energy and angular momentum balance, to derive equations of
motion that are valid for general orbits and for a class of coordinate gauges.
We show that the equations of motion are compatible with those derived earlier
by a direct calculation.Comment: 12 pages, submitted to General Relativity and Gravitatio
Photostatistics Reconstruction via Loop Detector Signatures
Photon-number resolving detectors are a fundamental building-block of optical
quantum information processing protocols. A loop detector, combined with
appropriate statistical processing, can be used to convert a binary on/off
photon counter into a photon-number-resolving detector. Here we describe the
idea of a signature of photon-counts, which may be used to more robustly
reconstruct the photon number distribution of a quantum state. The methodology
is applied experimentally in a 9-port loop detector operating at a
telecommunications wavelength and compared directly to the approach whereby
only the number of photon-counts is used to reconstruct the input distribution.
The signature approach is shown to be more robust against calibration errors,
exhibit reduced statistical uncertainty, and reduced reliance on a-priori
assumptions about the input state.Comment: 13 pages, 12 figure
Multiwavelength Monitoring of the Narrow-Line Seyfert 1 Galaxy Akn 564. II. Ultraviolet Continuum and Emission-line Variability
We present results of an intensive two-month campaign of approximately daily
spectrophotometric monitoring of the narrow-line Seyfert 1 galaxy Akn 564 with
HST. The fractional variability amplitude of the continuum variations between
1365-3000 A is ~6%, about a factor 3 less than that found in typical Seyfert 1
galaxies over a similar period of time. However, large amplitude, short
time-scale flaring behavior is evident, with trough-to-peak flux changes of
about 18% in approximately 3 days. We present evidence for wavelength-dependent
continuum time delays, with the variations at 3000 A lagging behind those at
1365 A by about 1 day. These delays may be interpreted as evidence for a
stratified continuum reprocessing region, possibly an accretion-disk structure.
The Lyman-alpha 1216 emission-line exhibits flux variations of about 1%
amplitude.Comment: 27 pages, 14 figures. Accepted by Astrophysical Journa
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