787 research outputs found
Analytical and experimental study of reentrant stream crossed-field amplifiers Final report
Computer simulation and noise measurements of reentrant stream crossed-field amplifier
The harmonic oscillator on Riemannian and Lorentzian configuration spaces of constant curvature
The harmonic oscillator as a distinguished dynamical system can be defined
not only on the Euclidean plane but also on the sphere and on the hyperbolic
plane, and more generally on any configuration space with constant curvature
and with a metric of any signature, either Riemannian (definite positive) or
Lorentzian (indefinite). In this paper we study the main properties of these
`curved' harmonic oscillators simultaneously on any such configuration space,
using a Cayley-Klein (CK) type approach, with two free parameters \ki, \kii
which altogether correspond to the possible values for curvature and signature
type: the generic Riemannian and Lorentzian spaces of constant curvature
(sphere , hyperbolic plane , AntiDeSitter sphere {\bf
AdS}^{\unomasuno} and DeSitter sphere {\bf dS}^{\unomasuno}) appear in this
family, with the Euclidean and Minkowski spaces as flat limits.
We solve the equations of motion for the `curved' harmonic oscillator and
obtain explicit expressions for the orbits by using three different methods:
first by direct integration, second by obtaining the general CK version of the
Binet's equation and third, as a consequence of its superintegrable character.
The orbits are conics with centre at the potential origin in any CK space,
thereby extending this well known Euclidean property to any constant curvature
configuration space. The final part of the article, that has a more geometric
character, presents those results of the theory of conics on spaces of constant
curvature which are pertinent.Comment: 29 pages, 6 figure
The Backgrounds Data Center
The Strategic Defense Initiative Organization has created data centers for midcourse, plumes, and backgrounds phenomenologies. The Backgrounds Data Center (BDC) has been designated as the prime archive for data collected by SDIO programs. The BDC maintains a Summary Catalog that contains 'metadata,' that is, information about data, such as when the data were obtained, what the spectral range of the data is, and what region of the Earth or sky was observed. Queries to this catalog result in a listing of all data sets (from all experiments in the Summary Catalog) that satisfy the specified criteria. Thus, the user can identify different experiments that made similar observations and order them from the BDC for analysis. On-site users can use the Science Analysis Facility (SAFE for this purpose. For some programs, the BDC maintains a Program Catalog, which can classify data in as many ways as desired (rather than just by position, time, and spectral range as in the Summary Catalog). For example, data sets could be tagged with such diverse parameters as solar illumination angle, signal level, or the value of a particular spectral ratio, as long as these quantities can be read from the digital record or calculated from it by the ingest program. All unclassified catalogs and unclassified data will be remotely accessible
Evaluation of Reclaimer Sludge Disposal from Post-combustion CO2 Capture
AbstractAn important environmental issue for amine-based post-combustion CO2 capture is the generation of reclaimer sludge containing degradation products and impurities that must be disposed. This paper evaluated the environmental fate of reclaimer wastes generated from three amine-based solvents (monoethanolamine, piperazine, and a methyldiethanolamine/piperazine blend) used for CO2 capture at a pulverized coal and a natural-gas combined cycle power plant (900 and 810 MWe, respectively) with typical flue gas compositions. The solvent loss and impurities and degradation accumulation in the CO2 capture units were modeled. A techno-economic analysis of different reclaiming technologies was conducted. The reclaimer sludge was classified based on US and EU regulations for hazardous waste, and alternative options for reclaimer sludge disposal were evaluated
Active and driven hydrodynamic crystals
Motivated by the experimental ability to produce monodisperse particles in
microfluidic devices, we study theoretically the hydrodynamic stability of
driven and active crystals. We first recall the theoretical tools allowing to
quantify the dynamics of elongated particles in a confined fluid. In this
regime hydrodynamic interactions between particles arise from a superposition
of potential dipolar singularities. We exploit this feature to derive the
equations of motion for the particle positions and orientations. After showing
that all five planar Bravais lattices are stationary solutions of the equations
of motion, we consider separately the case where the particles are passively
driven by an external force, and the situation where they are self-propelling.
We first demonstrate that phonon modes propagate in driven crystals, which are
always marginally stable. The spatial structure of the eigenmodes depend solely
on the symmetries of the lattices, and on the orientation of the driving force.
For active crystals, the stability of the particle positions and orientations
depends not only on the symmetry of the crystals but also on the perturbation
wavelengths and on the crystal density. Unlike unconfined fluids, the stability
of active crystals is independent of the nature of the propulsion mechanism at
the single particle level. The square and rectangular lattices are found to be
linearly unstable at short wavelengths provided the volume fraction of the
crystals is high enough. Differently, hexagonal, oblique, and face-centered
crystals are always unstable. Our work provides a theoretical basis for future
experimental work on flowing microfluidic crystals.Comment: 10 pages, 10 figure
The stroke ‘Act FAST’ campaign: Remembered but not understood?
Background: The stroke awareness raising campaign ‘Act FAST' (Face, Arms, Speech: Time to call Emergency Medical Services) has been rolled out in multiple waves in England, but impact on stroke recognition and response remains unclear. Purpose: The purpose of this study was to test whether providing knowledge of the FAST acronym through a standard Act FAST campaign leaflet increases accurate recognition and response in stroke-based scenario measures. Methods: This is a population-based, cross-sectional survey of adults in Newcastle upon Tyne, UK, sampled using the electoral register, with individuals randomized to receive a questionnaire and Act FAST leaflet (n = 2500) or a questionnaire only (n = 2500) in 2012. Campaign message retention, stroke recognition, and response measured through 16 scenario-based vignettes were assessed. Data were analyzed in 2013. Results: Questionnaire return rate was 32·3% (n = 1615). No differences were found between the leaflet and no-leaflet groups in return rate or demographics. Participants who received a leaflet showed better campaign recall (75·7% vs. 68·2%, P = 0·003) and recalled more FAST mnemonic elements (66·1% vs. 45·3% elements named correctly, P < 0·001). However, there were no between-group differences for stroke recognition and response to stroke-based scenarios (P > 0·05). Conclusions: Despite greater levels of recall of specific ‘Act FAST' elements among those receiving the Act FAST leaflet, there was no impact on stroke recognition and response measures
A Netrin-3 Like Protein is Secreted from \u3ci\u3eTetrahymena thermophila\u3c/i\u3e
Netrin proteins are a family of laminin-related secreted proteins that provide signals for axonal growth and cell migration during vertebrate development. Netrin homologs are expressed throughout the animal kingdom; however, some animals do not express a homolog of any known netrin receptors. We have previously found that the ciliated protozoan, Tetrahymena thermophila, responds to netrin-1 peptide by showing avoidance behavior. In addition, Tetrahymena secrete a protein that is immunologically similar to netrin-1 as detected by ELISA. Since netrin-3, like netrin-1, is a guidance molecule for axons and overlaps signaling pathways with netrin-1 in vertebrates, we hypothesized that netrin-3 may also act as a chemorepellent in Tetrahymena. While behavioral assays did not confirm this hypothesis, growth assays indicate that netrin-3 peptide inhibits cell division in Tetrahymena. In addition, ELISA and Western blots indicate that a netrin-3 like protein of approximately 48 kDa is secreted from Tetrahymena. Immunolocalization of this protein within the cell shows that it appears in widely distributed throughout the cell, and co-localizes with the netrin-1 like protein. Using ER tracker™, we found that some of the netrin-3-like protein co-localizes with the endoplasmic reticulum, as might be expected for a secreted protein. Further experimentation is necessary to determine the mechanism by which netrin-3 peptide inhibits growth in Tetrahymena
Stellar Rotation in Young Clusters. II. Evolution of Stellar Rotation and Surface Helium Abundance
We derive the effective temperatures and gravities of 461 OB stars in 19
young clusters by fitting the H-gamma profile in their spectra. We use
synthetic model profiles for rotating stars to develop a method to estimate the
polar gravity for these stars, which we argue is a useful indicator of their
evolutionary status. We combine these results with projected rotational
velocity measurements obtained in a previous paper on these same open clusters.
We find that the more massive B-stars experience a spin down as predicted by
the theories for the evolution of rotating stars. Furthermore, we find that the
members of binary stars also experience a marked spin down with advanced
evolutionary state due to tidal interactions. We also derive non-LTE-corrected
helium abundances for most of the sample by fitting the He I 4026, 4387, 4471
lines. A large number of helium peculiar stars are found among cooler stars
with Teff < 23000 K. The analysis of the high mass stars (8.5 solar masses < M
< 16 solar masses) shows that the helium enrichment process progresses through
the main sequence (MS) phase and is greater among the faster rotators. This
discovery supports the theoretical claim that rotationally induced internal
mixing is the main cause of surface chemical anomalies that appear during the
MS phase. The lower mass stars appear to have slower rotation rates among the
low gravity objects, and they have a large proportion of helium peculiar stars.
We suggest that both properties are due to their youth. The low gravity stars
are probably pre-main sequence objects that will spin up as they contract.
These young objects very likely host a remnant magnetic field from their natal
cloud, and these strong fields sculpt out surface regions with unusual chemical
abundances.Comment: 50 pages 18 figures, accepted by Ap
Witness Response at Acute Onset of Stroke: A Qualitative Theory-Guided Study
Background: Delay in calling emergency medical services following stroke limits access to early treatment that can reduce disability. Emergency medical services contact is mostly initiated by stroke witnesses (often relatives), rather than stroke patients. This study explored appraisal and behavioural factors that are potentially important in influencing witness behaviour in response to stroke. Methods and Findings: Semi-structured interviews with 26 stroke witnesses were transcribed and theory-guided content analysed was undertaken based on the Common Sense Self-Regulation Model (appraisal processes) and Theory Domains Framework (behavioural determinants). Response behaviours were often influenced by heuristics-guided appraisal (i.e. mental rules of thumb). Some witnesses described their responses to the situation as ‘automatic' and ‘instinctive', rather than products of deliberation. Potential behavioural influences included: environmental context and resources (e.g. time of day), social influence (e.g. prompts from patients) and beliefs about consequences (e.g. 999 accesses rapid help). Findings are based on retrospective accounts and need further verification in prospective studies. Conclusions: Witnesses play a key role in patient access to emergency medical services. Factors that potentially influence witnesses' responses to stroke were identified and could inform behavioural interventions and future research. Interventions might benefit from linking automatic/instinctive threat perceptions with deliberate appraisal of stroke symptoms, prompting action to call emergency medical services
Two-body quantum mechanical problem on spheres
The quantum mechanical two-body problem with a central interaction on the
sphere is considered. Using recent results in representation
theory an ordinary differential equation for some energy levels is found. For
several interactive potentials these energy levels are calculated in explicit
form.Comment: 41 pages, no figures, typos corrected; appendix D was adde
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