318 research outputs found
The CR structure of minimal orbits in complex flag manifolds
Let \^G be a complex semisimple Lie group, Q a parabolic subgroup and G a
real form of \^G. The flag manifold \^G/Q decomposes into finitely many
G-orbits; among them there is exactly one orbit of minimal dimension, which is
compact. We study these minimal orbits from the point of view of CR geometry.
In particular we characterize those minimal orbits that are of finite type and
satisfy various nondegeneracy conditions, compute their fundamental group and
describe the space of their global CR functions. Our main tool are parabolic CR
algebras, which give an infinitesimal description of the CR structure of
minimal orbits.Comment: AMS-TeX, 44 pages v2: minor revisio
On the topology of minimal orbits in complex flag manifolds
We compute the Euler-Poincar\'e characteristic of the homogeneous compact
manifolds that can be described as minimal orbits for the action of a real form
in a complex flag manifold.Comment: 21 pages v2: Major revisio
Low-frequency noise spectroscopy as an effective tool for electric transport analysis
2016 - 2017In this work, several experiments and analyses performed by means of noise spectroscopy, on a broad typology of materials and compounds, are presented. Structural, DC electrical transport and noise properties are exposed for each investigated sample, and theoretical models and possible explanations of the experimental results are given to unravel physical phenomena. In particular, two distinct types of iron-chalcogenide superconductors are investigated, in their pristine and aged state, suggesting the more likely mechanism which generates the resistance fluctuations and resorting to Weak Localization theory. In the case of the polymer/carbon nanotubes composites, the fluctuation-induced tunneling model is introduced to explain the measured temperature dependence of the electrical conductance and the I-V curve behaviors. Then, noise measurements prove the existence of a structural phase transition occurring around 160 K within the perovskite compound and highlight the correlation between electronic defect states distribution and device performance.
The variety of investigated devices and materials validates the soundness of the noise spectroscopy as an effective tool for electric transport analysis. [edited by author]XXX cicl
Steady-state pattern electroretinogram and frequency doubling technology in anisometropic amblyopia
Background: Steady-state pattern electroretinogram (PERG) and frequency doubling technology (FDT) perimetry can be used to selectively investigate the activity of the M-Y ganglion cells in adult anisometropic amblyopes.
Methods: Fifteen normal subjects (mean 27.8\ub14.1 years) and 15 adults with anisometropic amblyopia (mean 28.7\ub15.9 years) were analyzed using steady-state PERG and FDT.
Results: The amplitude of steady-state PERG was significantly different not only among the control group and both the amblyopic eye (P=0.0001) and the sound eye group (P=0.0001), but also between the latter two groups (P=0.006). The difference in FDT mean deviation was statistically significant not only between the control group and amblyopic eye group (P=0.0002), but also between the control group and the sound eye group (P=0.0009). The FDT pattern standard deviation was significantly higher in the control group rather than in the amblyopic eye (P=0.0001) or the sound eye group (P=0.0001). A correlation was found between the reduction in PERG amplitude and the increase in FDT-pattern standard deviation index not only in amblyopic (P=0.0025) and sound (P=0.0023) eyes, but also in the healthy control group (P=0.0001).
Conclusion: These data demonstrate that in anisometropic amblyopia, there is an abnormal functionality of a subgroup of the magnocellular ganglion cells (M-Y), and the involvement of these cells, together with the parvocellular pathway, may play a key role in the clinical expression of the disease
Vocero Buenos Aires : Producción y edición de una publicación gráfica sobre comunicación institucional para el ámbito de la provincia de Buenos Aires
Facultad de Periodismo y Comunicación Socia
Slow slip detection with deep learning in multi-station raw geodetic time series validated against tremors in Cascadia
Slow slip events (SSEs) originate from a slow slippage on faults that lasts
from a few days to years. A systematic and complete mapping of SSEs is key to
characterizing the slip spectrum and understanding its link with coeval
seismological signals. Yet, SSE catalogues are sparse and usually remain
limited to the largest events, because the deformation transients are often
concealed in the noise of the geodetic data. Here we present the first
multi-station deep learning SSE detector applied blindly to multiple raw
geodetic time series. Its power lies in an ultra-realistic synthetic training
set, and in the combination of convolutional and attention-based neural
networks. Applied to real data in Cascadia over the period 2007-2022, it
detects 78 SSEs, that compare well to existing independent benchmarks: 87.5% of
previously catalogued SSEs are retrieved, each detection falling within a peak
of tremor activity. Our method also provides useful proxies on the SSE duration
and may help illuminate relationships between tremor chatter and the nucleation
of the slow rupture. We find an average day-long time lag between the slow
deformation and the tremor chatter both at a global- and local-temporal scale,
suggesting that slow slip may drive the rupture of nearby small asperities
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