4,788 research outputs found
Decaying grid turbulence in a rotating stratified fluid
Rotating grid turbulence experiments have been carried out in a stably stratified fluid for relatively large Reynolds numbers (mesh Reynolds numbers up to 18000). Under the combined effects of rotation and stratification the flow degenerates into quasihorizontal motions. This regime is investigated using a scanning imaging velocimetry technique which provides time-resolved velocity fields in a volume. The most obvious effect of rotation is the inhibition of the kinetic energy decay, in agreement with the quasi-geostrophic model which predicts the absence of a direct energy cascade, as found in two-dimensional turbulence. In the regime of small Froude and Rossby numbers, the dynamics is found to be non-dissipative and associated with a symmetric and highly intermittent vertical vorticity field, that displays k(h)(-3) energy spectra. For higher Rossby numbers, fundamental differences with the quasi-geostrophic model are found. A significant decay of kinetic energy, which does not depend on the stratification, is observed. Moreover, in this regime, although both cyclones and anticyclones are initially produced, the intense vortices are only cyclones. For late times the flow consists of an assembly of coherent interacting Structures. Under the influence of both rotation and stratification, they take the form of lens-like eddies with aspect ratio proportional to f/N
Four-fold Massey products in Galois cohomology
In this paper, we develop a new necessary and sufficient condition for the
vanishing of 4-Massey products of elements in the mod-2 Galois cohomology of a
field. This new description allows us to define a splitting variety for
4-Massey products, which is shown in the Appendix to satisfy a local-to-global
principle over number fields. As a consequence, we prove that, for a number
field, all such 4-Massey products vanish whenever they are defined. This
provides new explicit restrictions on the structure of absolute Galois groups
of number fields.Comment: Final version: several corrections made throughout the paper; some
sections reorganized; will appear in Compositio Mathematic
Male sperm whale acoustic behavior observed from multipaths at a single hydrophone
Sperm whales generate transient sounds (clicks) when foraging. These clicks have been described as echolocation sounds, a result of having measured the source level and the directionality of these signals and having extrapolated results from biosonar tests made on some small odontocetes. The authors propose a passive acoustic technique requiring only one hydrophone to investigate the acoustic behavior of free-ranging sperm whales. They estimate whale pitch angles from the multipath distribution of click energy. They emphasize the close bond between the sperm whale’s physical and acoustic activity, leading to the hypothesis that sperm whales might, like some small odontocetes, control click level and rhythm. An echolocation model estimating the range of the sperm whale’s targets from the interclick interval is computed and tested during different stages of the whale’s dive. Such a hypothesis on the echolocation process would indicate that sperm whales echolocate their prey layer when initiating their dives and follow a methodic technique when foraging
Interactive image manipulation for surgical planning
The Australian e-Health Research Centre in collaboration with the Queensland University of Technology's Paediatric Spine Research Group is developing software for visualisation and manipulation of large three-dimensional (3D) medical image data sets. The software allows the extraction of anatomical data from individual patients for use in preoperative planning. State-of-the-art computer technology makes it possible to slice through the image dataset at any angle, or manipulate 3D representations of the data instantly. Although the software was initially developed to support planning for scoliosis surgery, it can be applied to any dataset whether obtained from computed tomography, magnetic resonance imaging or any other imaging modality
Bi-class classification of humpback whale sound units against complex background noise with Deep Convolution Neural Network
Automatically detecting sound units of humpback whales in complex
time-varying background noises is a current challenge for scientists. In this
paper, we explore the applicability of Convolution Neural Network (CNN) method
for this task. In the evaluation stage, we present 6 bi-class classification
experimentations of whale sound detection against different background noise
types (e.g., rain, wind). In comparison to classical FFT-based representation
like spectrograms, we showed that the use of image-based pretrained CNN
features brought higher performance to classify whale sounds and background
noise.Comment: arXiv admin note: text overlap with arXiv:1702.02741 by other author
A Semi-Analytical Model of Visible-Wavelength Phase Curves of Exoplanets and Applications to Kepler-7 b and Kepler-10 b
Kepler has detected numerous exoplanet transits by precise measurements of
stellar light in a single visible-wavelength band. In addition to detection,
the precise photometry provides phase curves of exoplanets, which can be used
to study the dynamic processes on these planets. However, the interpretation of
these observations can be complicated by the fact that visible-wavelength phase
curves can represent both thermal emission and scattering from the planets.
Here we present a semi-analytical model framework that can be applied to study
Kepler and future visible-wavelength phase curve observations of exoplanets.
The model efficiently computes reflection and thermal emission components for
both rocky and gaseous planets, considering both homogeneous and inhomogeneous
surfaces or atmospheres. We analyze the phase curves of the gaseous planet
Kepler-7 b and the rocky planet Kepler-10 b using the model. In general, we
find that a hot exoplanet's visible-wavelength phase curve having a significant
phase offset can usually be explained by two classes of solutions: one class
requires a thermal hot spot shifted to one side of the substellar point, and
the other class requires reflective clouds concentrated on the same side of the
substellar point. The two solutions would require very different Bond albedos
to fit the same phase curve; atmospheric circulation models or eclipse
observations at longer wavelengths can effectively rule out one class of
solutions, and thus pinpoint the albedo of the planet, allowing decomposition
of the reflection and the thermal emission components in the phase curve.
Particularly for Kepler-7 b, reflective clouds located on the west side of the
substellar point can best explain its phase curve. We further derive that the
reflectivity of the clear part of the atmosphere should be less than 7% and
that of the cloudy part should be greater than 80% (abridged)Comment: 16 pages, 7 figures, accepted for publication in Ap
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Systemic and Intra-Habenular Activation of the Orphan G Protein-Coupled Receptor GPR139 Decreases Compulsive-Like Alcohol Drinking and Hyperalgesia in Alcohol-Dependent Rats.
GPR139 is an orphan G protein-coupled receptor (GPCR) that is expressed mainly in the brain, with the highest expression in the medial habenula. The modulation of GPR139 receptor function has been hypothesized to be beneficial in the treatment of some mental disorders, but behavioral studies have not yet provided causal evidence of the role of GPR139 in brain dysfunction. Because of the high expression of GPR139 in the habenula, a critical brain region in addiction, we hypothesized that GPR139 may play role in alcohol dependence. Thus, we tested the effect of GPR139 receptor activation using the selective, brain-penetrant receptor agonist JNJ-63533054 on addiction-like behaviors in alcohol-dependent male rats. Systemic administration of JNJ-63533054 (30 mg/kg but not 10 mg/kg, p.o.) reversed the escalation of alcohol self-administration in alcohol-dependent rats, without affecting water or saccharin intake in dependent rats or alcohol intake in nondependent rats. Moreover, systemic JNJ-63533054 administration decreased withdrawal-induced hyperalgesia, without affecting somatic signs of alcohol withdrawal. Further analysis demonstrated that JNJ-63533054 was effective only in a subgroup of dependent rats that exhibited compulsive-like alcohol drinking. Finally, site-specific microinjection of JNJ-63533054 in the habenula but not interpeduncular nucleus (IPN) reduced both alcohol self-administration and withdrawal-induced hyperalgesia in dependent rats. These results provide robust preclinical evidence that GPR139 receptor activation reverses key addiction-like behaviors in dependent animals, suggest that GPR139 may be a novel target for the treatment of alcohol use disorder, and demonstrate that GPR139 is functionally relevant in regulating mammalian behavior
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