10,691 research outputs found
Estimates for the dilatation of -harmonic mappings
We consider planar -harmonic mappings, that is mappings whose
components and solve a divergence structure elliptic equation , for . We investigate whether a locally
invertible -harmonic mapping is also quasiconformal. Under mild
regularity assumptions, only involving and the antisymmetric part
of , we prove quantitative bounds which imply quasiconformality.Comment: 8 pages, to appear on Rendiconti di Matematica e delle sue
applicazion
Quantitative estimates on Jacobians for hybrid inverse problems
We consider -harmonic mappings, that is mappings whose components
solve a divergence structure elliptic equation , for . We investigate whether, with suitably prescribed
Dirichlet data, the Jacobian determinant can be bounded away from zero. Results
of this sort are required in the treatment of the so-called hybrid inverse
problems, and also in the field of homogenization studying bounds for the
effective properties of composite materials.Comment: 15 pages, submitte
Invertible harmonic mappings, beyond Kneser
We prove necessary and sufficient criteria of invertibility for planar
harmonic mappings which generalize a classical result of H. Kneser, also known
as the Rad\'{o}-Kneser-Choquet theorem.Comment: One section added. 15 page
Noise Estimate of Pendular Fabry-Perot through Reflectivity Change
A key issue in developing pendular Fabry-Perot interferometers as very
accurate displacement measurement devices, is the noise level. The Fabry-Perot
pendulums are the most promising device to detect gravitational waves, and
therefore the background and the internal noise should be accurately measured
and reduced. In fact terminal masses generates additional internal noise mainly
due to thermal fluctuations and vibrations. We propose to exploit the
reflectivity change, that occurs in some special points, to monitor the
pendulums free oscillations and possibly estimate the noise level. We find that
in spite of long transients, it is an effective method for noise estimate. We
also prove that to only retain the sequence of escapes, rather than the whole
time dependent dynamics, entails the main characteristics of the phenomenon.
Escape times could also be relevant for future gravitational wave detector
developments.Comment: PREPRINT Metrology for Aerospace (MetroAeroSpace), 2014 IEEE
Publication Year: 2014, Page(s): 468 - 47
Spin connection as Lorentz gauge field: propagating torsion
We propose a modified gravitational action containing besides the
Einstein-Cartan term some quadratic contributions resembling the Yang-Mills
lagrangian for the Lorentz spin connections. We outline how a propagating
torsion arises and we solve explicitly the linearised equations of motion on a
Minkowski background. We identify among torsion components six degrees of
freedom: one is carried by a pseudo-scalar particle, five by a tachyon field.
By adding spinor fields and neglecting backreaction on the geometry, we point
out how only the pseudo-scalar particle couples directly with fermions, but the
resulting coupling constant is suppressed by the ratio between fermion and
Planck masses. Including backreaction, we demonstrate how the tachyon field
provides causality violation in the matter sector, via an interaction mediated
by gravitational waves.Comment: 7 pages, no figures, new section adde
Pathophysiological role of extrasynaptic GABAA receptors in typical absence epilepsy
GABA is the principal inhibitory neurotransmitter in the mammalian CNS. It acts via two classes of receptors, the GABAA, a ligand gated ion channel (ionotropic receptor) and the metabotropic G-protein coupled GABAB receptor. While synaptic GABAA receptors underlie classical ‘phasic’ GABAA receptor-mediated inhibition, extrasynaptic GABAA receptors (eGABAAR) mediate a new form of inhibition, termed ‘tonic’ GABAA inhibition. The subunit composition of eGABAARs differs from those present at the synapse, resulting in pharmacologically and functionally distinct properties. In this mini-review the findings presented at the 2nd Neuroscience Day meeting held last July in Malta will be summarised. Particular emphasis will be given to the important pathophysiological role of eGABAAR within thalamocortical circuits as a major player in nonconvulsive absence epilepsy. The new findings presented at the conference suggest that enhanced tonic inhibition is a common cause of seizures in several animal models of absence epilepsy and may provide new targets for therapeutic intervention.peer-reviewe
Nonlinear equations involving the square root of the Laplacian
In this paper we discuss the existence and non-existence of weak solutions to
parametric fractional equations involving the square root of the Laplacian
in a smooth bounded domain ()
and with zero Dirichlet boundary conditions. Namely, our simple model is the
following equation \begin{equation*} \left\{ \begin{array}{ll} A_{1/2}u=\lambda
f(u) & \mbox{ in } \Omega\\ u=0 & \mbox{ on } \partial\Omega.
\end{array}\right. \end{equation*} The existence of at least two non-trivial
-bounded weak solutions is established for large value of the
parameter requiring that the nonlinear term is continuous,
superlinear at zero and sublinear at infinity. Our approach is based on
variational arguments and a suitable variant of the Caffarelli-Silvestre
extension method
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