124 research outputs found
Massive scalar field instability in Kerr spacetime
We study the Klein-Gordon equation for a massive scalar field in Kerr
spacetime in the time-domain. We demonstrate that under conditions of
super-radiance, the scalar field becomes unstable and its amplitude grows
without bound. We also estimate the growth rate of this instability.Comment: 10 pages, 5 figure
AFFDEX 2.0: A Real-Time Facial Expression Analysis Toolkit
In this paper we introduce AFFDEX 2.0 - a toolkit for analyzing facial
expressions in the wild, that is, it is intended for users aiming to; a)
estimate the 3D head pose, b) detect facial Action Units (AUs), c) recognize
basic emotions and 2 new emotional states (sentimentality and confusion), and
d) detect high-level expressive metrics like blink and attention. AFFDEX 2.0
models are mainly based on Deep Learning, and are trained using a large-scale
naturalistic dataset consisting of thousands of participants from different
demographic groups. AFFDEX 2.0 is an enhanced version of our previous toolkit
[1], that is capable of tracking efficiently faces at more challenging
conditions, detecting more accurately facial expressions, and recognizing new
emotional states (sentimentality and confusion). AFFDEX 2.0 can process
multiple faces in real time, and is working across the Windows and Linux
platforms.Comment: Accepted at the FG2023 conferenc
Superradiant instability of charged massive scalar field in Kerr-Newman-anti-de Sitter black hole
We study the superradiance instability of charged massive scalar field in the
background of Kerr-Newman-anti-de Sitter black hole. By employing the
asymptotic matching technique to solve Klein-Gordon equation analytically, the
complex parts of quasinormal frequencies are shown to be positive in the regime
of superradiance. Because the calculation is performed in the approximation of
small black hole, the result indicates that small Kerr-Newman-anti-de Sitter
black hole is unstable against the massive scalar field perturbation with small
charge.Comment: 13 pages, no figure, comments are welcome! Revised version accepted
by PL
New instability for rotating black branes and strings
The evolution of small perturbations around rotating black branes and
strings, which are low energy solutions of string theory, are investigated. For
simplicity, we concentrate on the Kerr solution times transverse flat extra
dimensions, possibly compactified, but one can also treat other branes composed
of any rotating black hole and extra transverse dimensions, as well as analogue
black hole models and rotating bodies in fluid mechanics systems. It is shown
that such a rotating black brane is unstable against any massless (scalar,
vectorial, tensorial or other) field perturbation for a wide range of
wavelengths and frequencies in the transverse dimensions. Since it holds for
any massless field it can be considered, in this sense, a stronger instability
than the one studied by Gregory and Laflamme. Accordingly, it has also a
totally different physical origin. The perturbations can be stabilized if the
extra dimensions are compactified to a length smaller than the minimum
wavelength for which the instability settles in, resembling in this connection
the Gregory-Laflamme case. Likewise, this instability will have no effect for
astrophysical black holes. However, in the large extra dimensions scenario,
where TeV scale black holes can be produced, this instability should be
important. It seems plausible that the endpoint of this instability is a
static, or very slowly rotating, black brane and some outgoing radiation at
infinity.Comment: 4 pages, ReVTeX4. v2: minor improvement
Stability study of a model for the Klein-Gordon equation in Kerr spacetime
The current early stage in the investigation of the stability of the Kerr
metric is characterized by the study of appropriate model problems.
Particularly interesting is the problem of the stability of the solutions of
the Klein-Gordon equation, describing the propagation of a scalar field of mass
in the background of a rotating black hole. Rigorous results proof the
stability of the reduced, by separation in the azimuth angle in Boyer-Lindquist
coordinates, field for sufficiently large masses. Some, but not all, numerical
investigations find instability of the reduced field for rotational parameters
extremely close to 1. Among others, the paper derives a model problem for
the equation which supports the instability of the field down to .Comment: Updated version, after minor change
Comparisons among computed tomographic features of adipose masses in dogs and cats
A better understanding of the CT features of different forms of canine and feline adipose tumors would be valuable for improving patient management and treatment. The purpose of this retrospective, cross-sectional study was to describe and compare the CT features of pathologically confirmed lipomas, infiltrative lipomas, and liposarcomas in a sample of canine and feline patients. A total of 50 animals (46 dogs, four cats) and a total of 60 lesions (23 lipomas, 20 infiltrative lipomas, and 17 liposarcomas) were included in the study. Lipomas appeared as round to oval-shaped (n = 21), well-marginated (n = 20) fat-attenuating lesions. Infiltrative lipomas appeared as homogeneous, fat-attenuating masses but, unlike lipomas, they were most commonly characterized by an irregular shape (75%; P < 0.001), and linear components, hyperattenuating relative to the surrounding fat (100%; P < 0.05). Liposarcomas were represented exclusively by heterogeneous lesions with soft tissue attenuating components with a multinodular appearance (76.5%; P < 0.05). Regional lymphadenopathy (n = 10) and amorphous mineralization (n = 4) were also observed in association with liposarcomas. Computed tomography can provide useful information regarding disease location, extent, and involvement of the adjacent structures. Tumor definition and shape were the most useful parameters to differentiate between lipomas and infiltrative lipomas. The presence of a heterogeneous mass, with a multinodular soft tissue component and associated regional lymphadenopathy and mineralization, were features favoring a diagnosis of liposarcoma
Morphological characterization and immunohistochemical detection of the proinflammatory cytokines IL-1β, IL-17A, and TNF-α in lung lesions associated with contagious bovine pleuropneumonia
Further studies on the site and mechanism of action of s-(1,2 dichlorovinyl)-l-cysteine and s-(1,2 dichlorovinyl)-3-mercaptopropionic acid in rat liver
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