737 research outputs found
Lorentzian compact manifolds: isometries and geodesics
In this work we investigate families of compact Lorentzian manifolds in
dimension four. We show that every lightlike geodesic on such spaces is
periodic, while there are closed and non-closed spacelike and timelike
geodesics. Their isometry groups are computed. We also show that there is a non
trivial action by isometries of \Heis_3(\RR) on the nilmanifold S^1\times
(\Gamma_k \bsh \Heis_3(\RR)) for a lattice of \Heis_3(\RR).Comment: 17 page
Computational Approach to Anaphora Resolution in Spanish Dialogues
This paper presents an algorithm for identifying noun-phrase antecedents of
pronouns and adjectival anaphors in Spanish dialogues. We believe that anaphora
resolution requires numerous sources of information in order to find the
correct antecedent of the anaphor. These sources can be of different kinds,
e.g., linguistic information, discourse/dialogue structure information, or
topic information. For this reason, our algorithm uses various different kinds
of information (hybrid information). The algorithm is based on linguistic
constraints and preferences and uses an anaphoric accessibility space within
which the algorithm finds the noun phrase. We present some experiments related
to this algorithm and this space using a corpus of 204 dialogues. The algorithm
is implemented in Prolog. According to this study, 95.9% of antecedents were
located in the proposed space, a precision of 81.3% was obtained for pronominal
anaphora resolution, and 81.5% for adjectival anaphora
Selective Boosting of Transcriptional and Behavioral Responses to Drugs of Abuse by Histone Deacetylase Inhibition
Histone acetylation and other modifications of the chromatin are important regulators of gene expression and, consequently, may contribute to drug-induced behaviors and neuroplasticity. Earlier studies have shown that a reduction in histone deacetylase (HDAC) activity results in the enhancement of some psychostimulant-induced behaviors. In this study, we extend those seminal findings by showing that the administration of the HDAC inhibitor sodium butyrate enhances morphine-induced locomotor sensitization and conditioned place preference. In contrast, this compound has no effects on the development of morphine tolerance and dependence. Similar effects were observed for cocaine and ethanol-induced behaviors. These behavioral changes were accompanied by a selective boosting of a component of the transcriptional program activated by chronic morphine administration that included circadian clock genes and other genes relevant to addictive behavior. Our results support a specific function for histone acetylation and the epigenetic modulation of transcription at a reduced number of biologically relevant loci on non-homeostatic, long-lasting, drug-induced behavioral plasticity
Millikelvin magnetic relaxation measurements of alpha-Fe2O3 antiferromagnetic particles
In this paper we report magnetic relaxation data for antiferromagnetic
alpha-Fe2O3 particles of 5 nm mean diameter in the temperature range 0.1 K to
25 K. The average spin value of these particles S=124 and the uniaxial
anisotropy constant D=1.6x10^-2 K have been estimated from the experimental
values of the blocking temperature and anisotropy field. The observed plateau
in the magnetic viscosity from 3 K down to 100 mK agrees with the occurrence of
spin tunneling from the ground state Sz = S. However, the scaling M vs Tln(nu
t) is broken below 5 K, suggesting the occurrence of tunneling from excited
states below this temperature.Comment: 4 pages (two columns), 4 figure
Magnetic qubits as hardware for quantum computers
We propose two potential realisations for quantum bits based on nanometre
scale magnetic particles of large spin S and high anisotropy molecular
clusters. In case (1) the bit-value basis states |0> and |1> are the ground and
first excited spin states Sz = S and S-1, separated by an energy gap given by
the ferromagnetic resonance (FMR) frequency. In case (2), when there is
significant tunnelling through the anisotropy barrier, the qubit states
correspond to the symmetric, |0>, and antisymmetric, |1>, combinations of the
two-fold degenerate ground state Sz = +- S. In each case the temperature of
operation must be low compared to the energy gap, \Delta, between the states
|0> and |1>. The gap \Delta in case (2) can be controlled with an external
magnetic field perpendicular to the easy axis of the molecular cluster. The
states of different molecular clusters and magnetic particles may be entangled
by connecting them by superconducting lines with Josephson switches, leading to
the potential for quantum computing hardware.Comment: 17 pages, 3 figure
Electron Paramagnetic Resonance Linewidths and Lineshapes for the Molecular Magnets Fe8 and Mn12
We study theoretically Electron Paramagentic Resonance (EPR) linewidths for
single crystals of the molecular magnets Fe and Mn as functions of
energy eigenstates , frequency, and temperature when a magnetic field
along the easy axis is swept at fixed excitation frequency. This work was
motivated by recent EPR experiments. To calculate the linewidths, we use
density-matrix equations, including dipolar interactions and distributions of
the uniaxial anisotropy parameter and the Land\'{e} factor. Our
calculated linewidths agree well with the experimental data. We also examine
the lineshapes of the EPR spectra due to local rotations of the magnetic
anisotropy axes caused by defects in samples. Our preliminary results predict
that this effect leads to asymmetry in the EPR spectra.Comment: 2001 MMM conferenc
Syndromic features and mild cognitive impairment in mice with genetic reduction on p300 activity: Differential contribution of p300 and CBP to Rubinstein-Taybi syndrome etiology
Rubinstein-Taybi syndrome (RSTS) is a complex autosomal-dominant disease characterized by mental and growth retardation and skeletal abnormalities. A majority of the individuals diagnosed with RSTS carry heterozygous mutation in the gene CREBBP, but a small percentage of cases are caused by mutations in EP300. To investigate the contribution of p300 to RSTS pathoetiology, we carried out a comprehensive and multidisciplinary characterization of p300+/- mice. These mice exhibited facial abnormalities and impaired growth, two traits associated to RSTS in humans. We also observed abnormal gait, reduced swimming speed, enhanced anxiety in the elevated plus maze, and mild cognitive impairment during the transfer task in the water maze. These analyses demonstrate that p300+/- mice exhibit phenotypes that are reminiscent of neurological traits observed in RSTS patients, but their comparison with previous studies on CBP deficient strains also indicates that, in agreement with the most recent findings in human patients, the activity of p300 in cognition is likely less relevant or more susceptible to compensation than the activity of CBP. © 2009 Elsevier Inc. All rights reserved.This work was supported by the European Commission grant MEXT-CT-2003-509550, the Spanish Ministry of Science and Innovation Grants CSD2007-00023 and SAF2008-00611, and a grant from Fundación Ramón Areces. J.V. holds a fellowship from the Generalitat Valenciana and J.P.L.-A. a Juan de la Cierva contract supported by the Spanish Ministry of Science and Innovation.Peer Reviewe
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