40,213 research outputs found
Pharmacological and neurophysiological aspects of space/motion sickness
A motorized motion testing device modeled after a Ferris wheel was constructed to perform motion sickness tests on cats. Details of the testing are presented, and some of the topics covered include the following: xylazine-induced emesis; analysis of the constituents of the cerebrospinal fluid (CSF) during motion sickness; evaluation of serotonin-1A (5-HT sub 1A) agonists; other 5HT receptors; antimuscarinic mechanisms; and antihistaminergic mechanisms. The ability of the following drugs to reduce motion sickness in the cats was examined: amphetamines, adenosinergic drugs, opioid antagonists, peptides, cannabinoids, cognitive enhancers (nootropics), dextromethorphan/sigma ligands, scopolamine, and diphenhydramine
Parallel structurally-symmetric sparse matrix-vector products on multi-core processors
We consider the problem of developing an efficient multi-threaded
implementation of the matrix-vector multiplication algorithm for sparse
matrices with structural symmetry. Matrices are stored using the compressed
sparse row-column format (CSRC), designed for profiting from the symmetric
non-zero pattern observed in global finite element matrices. Unlike classical
compressed storage formats, performing the sparse matrix-vector product using
the CSRC requires thread-safe access to the destination vector. To avoid race
conditions, we have implemented two partitioning strategies. In the first one,
each thread allocates an array for storing its contributions, which are later
combined in an accumulation step. We analyze how to perform this accumulation
in four different ways. The second strategy employs a coloring algorithm for
grouping rows that can be concurrently processed by threads. Our results
indicate that, although incurring an increase in the working set size, the
former approach leads to the best performance improvements for most matrices.Comment: 17 pages, 17 figures, reviewed related work section, fixed typo
First record of an Odontaspidid shark in Ascension Island waters
The occurrence of the poorly understood shark species Odontapsis ferox is reported at an oceanic seamount in the central south Atlantic, within the Exclusive Economic Zone of Ascension Island. The presence of the species at this location is confirmed by the discovery of a tooth embedded in scientific equipment, and footage of at least one animal on autonomous underwater video. The new record of this shark species at this location demonstrates the knowledge gaps which still exist at many remote, oceanic structures and their candidacy for status as important conservation areas.info:eu-repo/semantics/publishedVersio
Illumination uniformity in endoscopic imaging
Standardised endoscopic digital images were taken and analysed using an image analysis software (National Instruments Vision Assistant version 7.1.1). The luminance plane was extracted and the pixel intensity distribution was determined along a horizontal line at the position of highest average intensity (centroid). The data was exported to MS Excel and the pixel intensity (y-axis) was plotted against pixel position (x-axis). A trendline using a 2nd order polynomial curve was fitted to each data set. The resultant equation for each curve was compared with equations obtained from other images taken under various illumination conditions and settings
Magnification Ratio of the Fluctuating Light in Gravitational Lens 0957+561
Radio observations establish the B/A magnification ratio of gravitational
lens 0957+561 at about 0.75. Yet, for more than 15 years, the optical
magnfication ratio has been between 0.9 and 1.12. The accepted explanation is
microlensing of the optical source. However, this explanation is mildly
discordant with (i) the relative constancy of the optical ratio, and (ii)
recent data indicating possible non-achromaticity in the ratio. To study these
issues, we develop a statistical formalism for separately measuring, in a
unified manner, the magnification ratio of the fluctuating and constant parts
of the light curve. Applying the formalism to the published data of Kundi\'c et
al. (1997), we find that the magnification ratios of fluctuating parts in both
the g and r colors agrees with the magnification ratio of the constant part in
g-band, and tends to disagree with the r-band value. One explanation could be
about 0.1 mag of consistently unsubtracted r light from the lensing galaxy G1,
which seems unlikely. Another could be that 0957+561 is approaching a caustic
in the microlensing pattern.Comment: 12 pages including 1 PostScript figur
From Classical to Quantum Mechanics: "How to translate physical ideas into mathematical language"
In this paper, we investigate the connection between Classical and Quantum
Mechanics by dividing Quantum Theory in two parts: - General Quantum Axiomatics
(a system is described by a state in a Hilbert space, observables are
self-adjoint operators and so on) - Quantum Mechanics properly that specifies
the Hilbert space, the Heisenberg rule, the free Hamiltonian... We show that
General Quantum Axiomatics (up to a supplementary "axiom of classicity") can be
used as a non-standard mathematical ground to formulate all the ideas and
equations of ordinary Classical Statistical Mechanics. So the question of a
"true quantization" with "h" must be seen as an independent problem not
directly related with quantum formalism. Moreover, this non-standard
formulation of Classical Mechanics exhibits a new kind of operation with no
classical counterpart: this operation is related to the "quantization process",
and we show why quantization physically depends on group theory (Galileo
group). This analytical procedure of quantization replaces the "correspondence
principle" (or canonical quantization) and allows to map Classical Mechanics
into Quantum Mechanics, giving all operators of Quantum Mechanics and
Schrodinger equation. Moreover spins for particles are naturally generated,
including an approximation of their interaction with magnetic fields. We find
also that this approach gives a natural semi-classical formalism: some exact
quantum results are obtained only using classical-like formula. So this
procedure has the nice property of enlightening in a more comprehensible way
both logical and analytical connection between classical and quantum pictures.Comment: 47 page
Forest disturbance and recovery: A general review in the context of spaceborne remote sensing of impacts on aboveground biomass and canopy structure
Abrupt forest disturbances generating gaps \u3e0.001 km2 impact roughly 0.4–0.7 million km2a−1. Fire, windstorms, logging, and shifting cultivation are dominant disturbances; minor contributors are land conversion, flooding, landslides, and avalanches. All can have substantial impacts on canopy biomass and structure. Quantifying disturbance location, extent, severity, and the fate of disturbed biomass will improve carbon budget estimates and lead to better initialization, parameterization, and/or testing of forest carbon cycle models. Spaceborne remote sensing maps large-scale forest disturbance occurrence, location, and extent, particularly with moderate- and fine-scale resolution passive optical/near-infrared (NIR) instruments. High-resolution remote sensing (e.g., ∼1 m passive optical/NIR, or small footprint lidar) can map crown geometry and gaps, but has rarely been systematically applied to study small-scale disturbance and natural mortality gap dynamics over large regions. Reducing uncertainty in disturbance and recovery impacts on global forest carbon balance requires quantification of (1) predisturbance forest biomass; (2) disturbance impact on standing biomass and its fate; and (3) rate of biomass accumulation during recovery. Active remote sensing data (e.g., lidar, radar) are more directly indicative of canopy biomass and many structural properties than passive instrument data; a new generation of instruments designed to generate global coverage/sampling of canopy biomass and structure can improve our ability to quantify the carbon balance of Earth\u27s forests. Generating a high-quality quantitative assessment of disturbance impacts on canopy biomass and structure with spaceborne remote sensing requires comprehensive, well designed, and well coordinated field programs collecting high-quality ground-based data and linkages to dynamical models that can use this information
Do Trustees and Administrators Matter? Diversifying the Faculty Across Gender Lines
Our paper focuses on the role that the gender composition of the leaders of American colleges and universities – trustees, presidents/chancellors, and provosts/academic vice presidents – plays in influencing the rate at which academic institutions diversify their faculty across gender lines. Our analyses make use of institutional level panel data that we have collected for a large sample of American academic institutions.
We find, other factors held constant including our estimate of the “expected” share of new hires that should be female, that institutions with female presidents/chancellors and female provosts/academic vice presidents, as well as those with a greater share of female trustees, increase their shares of female faculty at a more rapid rate. The magnitudes of the effects of these leaders are larger at smaller institutions, where central administrators may play a larger role in faculty hiring decisions. A critical share of female trustees must be reached before the gender composition of the board matters
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