2,927 research outputs found
Curvature and Acoustic Instabilities in Rotating Fluid Disks
The stability of a rotating fluid disk to the formation of spiral arms is
studied in the tightwinding approximation in the linear regime. The dispersion
relation for spirals that was derived by Bertin et al. is shown to contain a
new, acoustic instability beyond the Lindblad resonances that depends only on
pressure and rotation. In this regime, pressure and gravity exchange roles as
drivers and inhibitors of spiral wave structures. Other instabilities that are
enhanced by pressure are also found in the general dispersion relation by
including higher order terms in the small parameter 1/kr for wavenumber k and
radius r. These instabilities are present even for large values of Toomre's
parameter Q. Unstable growth rates are determined in four cases: a
self-gravitating disk with a flat rotation curve, a self-gravitating disk with
solid body rotation, a non-self-gravitating disk with solid body rotation, and
a non-self-gravitating disk with Keplerian rotation. The most important
application appears to be as a source of spiral structure, possibly leading to
accretion in non-self-gravitating disks, such as some galactic nuclear disks,
disks around black holes, and proto-planetary disks. All of these examples have
short orbital times so the unstable growth time can be small.Comment: 30 pages, 5 figures, scheduled for ApJ 520, August 1, 199
Cognitive behaviour analysis based on facial information using depth sensors
Cognitive behaviour analysis is considered of high impor- tance with many innovative applications in a range of sectors including healthcare, education, robotics and entertainment. In healthcare, cogni- tive and emotional behaviour analysis helps to improve the quality of life of patients and their families. Amongst all the different approaches for cognitive behaviour analysis, significant work has been focused on emo- tion analysis through facial expressions using depth and EEG data. Our work introduces an emotion recognition approach using facial expres- sions based on depth data and landmarks. A novel dataset was created that triggers emotions from long or short term memories. This work uses novel features based on a non-linear dimensionality reduction, t-SNE, applied on facial landmarks and depth data. Its performance was eval- uated in a comparative study, proving that our approach outperforms other state-of-the-art features
Symmetric eikonal model for projectile-electron excitation and loss in relativistic ion-atom collisions
At impact energies GeV/u the projectile-electron
excitation and loss occurring in collisions between highly charged ions and
neutral atoms is already strongly influenced by the presence of atomic
electrons. In order to treat these processes in collisions with heavy atoms we
generalize the symmetric eikonal model, used earlier for considerations of
electron transitions in ion-atom collisions within the scope of a three-body
Coulomb problem. We show that at asymptotically high collision energies this
model leads to an exact transition amplitude and is very well suited to
describe the projectile-electron excitation and loss at energies above a few
GeV/u. In particular, by considering a number of examples we demonstrate
advantages of this model over the first Born approximation at impact energies
--30 GeV/u, which are of special interest for atomic physics
experiments at the future GSI facilities.Comment: 14 pages, 5 figure
Quantum state tomography of photons polarization and path degrees of freedom
Quantum state tomography (QST), the process through which the density matrix
of a quantum system is characterized from measurements of specific observables,
is a fundamental pillar in the fields of quantum information and computation.
We propose a simple QST method to reconstruct the density matrix of two qubits
encoded in the polarization and path degrees of freedom of a single photon,
which can be realized with a single linear-optical setup. We demonstrate that
the density matrix can be fully described in terms of the one-point Stokes
parameters related to the two possibles paths of the photon, together with a
quantum version of the two-point Stokes parameters introduced here.Comment: 5 pages, 2 figure
Manual versus automatic identification of black-capped chickadee (Poecile atricapillus) vocalizations
One time-consuming aspect of bioacoustic research is identifying vocalizations from long audio recordings. SongScope (version 4.1.5. Wildlife Acoustics, Inc.) is a computer program capable of developing acoustic recognizers that can identify wildlife vocalizations. The goal of the current study was to compare the effectiveness of manual identification of black-capped chickadee vocalizations to identification by SongScope recognizers. A recognizer was developed for each main chickadee vocalization by providing previously annotated audio of chickadees. Six chickadees (three male, three female) were recorded in one-hour intervals with and without anthropogenic (i.e., man-made) noise to provide a variety of samples to test the recognizer. These recordings were analyzed via the recognizer and two human coders, with an additional third coder reviewing a random subset of recordings for reliability. Strong agreement was found between the human coders, Îș = 0.76, p < 0.00. Agreement between human coders and the recognizer was moderate for fee songs, Îș = 0.46, p < 0.00, and strong for fee-bee songs, Îș = 0.77, p < 0.00, as well as for chick-a-dee calls, Îș = 0.82, p < 0.00. Results showed that male chickadees produced more tseet calls in silence and females produced more gargle calls during noise. No differences were found in vocalizations based on time of day. Our observations also suggest that the chick-a-dee recognizer was capable of identifying gargle and tseet calls along with the intended chick-a-dee calls. Overall, SongScope was effective at identifying fee-bee songs and chick-a-dee calls, but not as effective for identifying fee songs. These recognizers can allow for faster acoustic analyses (by approximately four times) and be continuously improved for greater accuracy
The cellular interactions of PEGylated gold nanoparticles : effect of PEGylation on cellular uptake and cytotoxicity
Poly(ethylene glycol) (PEG) is frequently used to coat various medical nanoparticles (NPs). As PEG is known to minimize NP interactions with biological specimens, the question remains whether PEGylated NPs are intrinsically less toxic or whether this is caused by reduced NP uptake. In the present work, the effect of gold NP PEGylation on uptake by three cell types is compared and evaluated the effect on cell viability, oxidative stress, cell morphology, and functionality using a multiparametric methodology. The data reveal that PEGylation affects cellular NP uptake in a cell-type-dependent manner and influences toxicity by different mechanisms. At similar intracellular NP numbers, PEGylated NPs are found to yield higher levels of cell death, mostly by induction of oxidative stress. These findings reveal that PEGylation significantly reduces NP uptake, but that at similar functional (= cell-associated) NP levels, non-PEGylated NPs are better tolerated by the cells
The HI Content of Compact Groups of Galaxies
The HI content of Hickson Compact Groups in the southern hemisphere is
measured using data from the HI Parkes All Sky Survey (HIPASS), and dedicated
observations using the narrowband filter on the Multibeam instrument on the
Parkes telescope. The expected HI mass of these groups was estimated using the
luminosity, diameter and morphological types of the member galaxies, calibrated
from published data. Taking careful account of non-detection limits, the
results show that the compact group population that has been detected by these
observations has an HI content similar to that of galaxies in the reference
field sample. The upper limits for the undetected groups lie within the normal
range; improvement of these limits will require a large increase in
sensitivity.Comment: 27 pages, 5 figures. Accepted for publication in PAS
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