20,671 research outputs found
Neuronal oxidative injury in the development of the epileptic disease : a potential target for novel therapeutic approaches
Epileptic diseases affect about 50 million people in the world and approximately 30% of patients diagnosed with epilepsy are unresponsive to current medications. For these reasons, primary prevention of epilepsy represents one of the priorities in epilepsy research. Intracellular oxido-reductive (redox) state is well known to play a crucial role, contributing to the maintenance of the proper function of biomolecules. Therefore, oxidative stress results in functional cellular disruption and cellular damage and may cause subsequent cell death via oxidation of proteins, lipids, and nucleotides. Recently, the role of oxidative stress in the early stage and in the progression of epileptic disorders has begun to be recognized. The early molecular response to oxidative stress represents a short-term reversible phenomenon that precedes higher and irreversible forms of oxidation. This article reviews the current understanding of the epileptogenic phenomena related to seizure-induced oxidative injury as potential “critical period” therapeutic targets for the prevention of chronic epileptic disorder.peer-reviewe
A data driven equivariant approach to constrained Gaussian mixture modeling
Maximum likelihood estimation of Gaussian mixture models with different
class-specific covariance matrices is known to be problematic. This is due to
the unboundedness of the likelihood, together with the presence of spurious
maximizers. Existing methods to bypass this obstacle are based on the fact that
unboundedness is avoided if the eigenvalues of the covariance matrices are
bounded away from zero. This can be done imposing some constraints on the
covariance matrices, i.e. by incorporating a priori information on the
covariance structure of the mixture components. The present work introduces a
constrained equivariant approach, where the class conditional covariance
matrices are shrunk towards a pre-specified matrix Psi. Data-driven choices of
the matrix Psi, when a priori information is not available, and the optimal
amount of shrinkage are investigated. The effectiveness of the proposal is
evaluated on the basis of a simulation study and an empirical example
Fermion Tunneling from Dynamical Horizons
The instability against emission of fermionic particles by the trapping
horizon of an evolving black hole is analyzed using the Hamilton-Jacobi
tunneling method. This method automatically selects one special expression for
the surface gravity of a changing horizon. The results also apply to point
masses embedded in an expanding universe. As a bonus of the tunneling method,
we gain the insight that the surface gravity still defines a temperature
parameter as long as the evolution is sufficiently slow that the black hole
pass through a sequence of quasi-equilibrium states, and that black holes
should be semi-classically unstable even in a hypothetical world without
bosonic fields.Comment: 8 pages, standard Latex document, few references adde
Stochastic Hydrodynamic Synchronization in Rotating Energy Landscapes
Hydrodynamic synchronization provides a general mechanism for the spontaneous
emergence of coherent beating states in independently driven mesoscopic
oscillators. A complete physical picture of those phenomena is of definite
importance to the understanding of biological cooperative motions of cilia and
flagella. Moreover, it can potentially suggest novel routes to exploit
synchronization in technological applications of soft matter. We demonstrate
that driving colloidal particles in rotating energy landscapes results in a
strong tendency towards synchronization, favouring states where all beads
rotate in phase. The resulting dynamics can be described in terms of activated
jumps with transition rates that are strongly affected by hydrodynamics leading
to an increased probability and lifetime of the synchronous states. Using
holographic optical tweezers we quantitatively verify our predictions in a
variety of spatial configurations of rotors.Comment: Copyright (2013) by the American Physical Societ
CONCISE: Compressed 'n' Composable Integer Set
Bit arrays, or bitmaps, are used to significantly speed up set operations in
several areas, such as data warehousing, information retrieval, and data
mining, to cite a few. However, bitmaps usually use a large storage space, thus
requiring compression. Nevertheless, there is a space-time tradeoff among
compression schemes. The Word Aligned Hybrid (WAH) bitmap compression trades
some space to allow for bitwise operations without first decompressing bitmaps.
WAH has been recognized as the most efficient scheme in terms of computation
time. In this paper we present CONCISE (Compressed 'n' Composable Integer Set),
a new scheme that enjoys significatively better performances than those of WAH.
In particular, when compared to WAH, our algorithm is able to reduce the
required memory up to 50%, by having similar or better performance in terms of
computation time. Further, we show that CONCISE can be efficiently used to
manipulate bitmaps representing sets of integral numbers in lieu of well-known
data structures such as arrays, lists, hashtables, and self-balancing binary
search trees. Extensive experiments over synthetic data show the effectiveness
of our approach.Comment: Preprint submitted to Information Processing Letters, 7 page
- …