917 research outputs found
New Singularity in Anisotropic, Time-Dependent Solutions to Maximally Gauss-Bonnet Extended Gravity
Among the solutions for anisotropic, time-dependent, maximally Gauss-Bonnet extended gravity, we find a class of curvature singularities for which the metric components remain finite. These new singularities therefore differ in type from the standard Kasner-like divergences expected for this class of theories. We study perturbative solutions near the singularity and show that there exist solutions with timelike paths that reach the singularity in finite proper time. Solving the equation of geodesic deviation in the same approximation, we show that the comoving coordinate system does not break down at the singularity. A brief classification of the corresponding singularity types in Robertson-Walker cosmologies is also provided
The cross-frequency mediation mechanism of intracortical information transactions
In a seminal paper by von Stein and Sarnthein (2000), it was hypothesized
that "bottom-up" information processing of "content" elicits local, high
frequency (beta-gamma) oscillations, whereas "top-down" processing is
"contextual", characterized by large scale integration spanning distant
cortical regions, and implemented by slower frequency (theta-alpha)
oscillations. This corresponds to a mechanism of cortical information
transactions, where synchronization of beta-gamma oscillations between distant
cortical regions is mediated by widespread theta-alpha oscillations. It is the
aim of this paper to express this hypothesis quantitatively, in terms of a
model that will allow testing this type of information transaction mechanism.
The basic methodology used here corresponds to statistical mediation analysis,
originally developed by (Baron and Kenny 1986). We generalize the classical
mediator model to the case of multivariate complex-valued data, consisting of
the discrete Fourier transform coefficients of signals of electric neuronal
activity, at different frequencies, and at different cortical locations. The
"mediation effect" is quantified here in a novel way, as the product of "dual
frequency RV-coupling coefficients", that were introduced in (Pascual-Marqui et
al 2016, http://arxiv.org/abs/1603.05343). Relevant statistical procedures are
presented for testing the cross-frequency mediation mechanism in general, and
in particular for testing the von Stein & Sarnthein hypothesis.Comment: https://doi.org/10.1101/119362 licensed as CC-BY-NC-ND 4.0
International license: http://creativecommons.org/licenses/by-nc-nd/4.0
Optical anisotropy and electronic structures of CdMoO4 and CdWO4 crystals: Polarized reflection measurements, x-ray photoelectron spectroscopy, and electronic structure calculations
Copyright (c) 2008 American Physical SocietyArticlePHYSICAL REVIEW B. 77(15): 155118 (2008)journal articl
Is a soft nuclear equation of state extracted from heavy-ion data incompatible with pulsar data?
We discuss the recent constraints on the nuclear equation of state from
pulsar mass measurements and from subthreshold production of kaons in heavy-ion
collisions. While recent pulsar data points towards a hard equation of state,
the analysis of the heavy-ion data allows only for soft equations of state. We
resolve the apparent contradiction by considering the different density regimes
probed. We argue that future measurements of global properties of low-mass
pulsars can serve as an excellent cross-check to heavy-ion data.Comment: 8 pages, 1 figure, contribution to the proceedings of the
international conference on 'Nuclear Physics in Astrophysics III', Dresden,
Germany, March 26-31, 2007, minor corrections to match published version, JPG
in pres
Interaction and Localization of One-electron Orbitals in an Organic Molecule: Fictitious Parameter Analysis for Multi-physics Simulations
We present a new methodology to analyze complicated multi-physics simulations
by introducing a fictitious parameter. Using the method, we study quantum
mechanical aspects of an organic molecule in water. The simulation is
variationally constructed from the ab initio molecular orbital method and the
classical statistical mechanics with the fictitious parameter representing the
coupling strength between solute and solvent. We obtain a number of
one-electron orbital energies of the solute molecule derived from the
Hartree-Fock approximation, and eigenvalue-statistical analysis developed in
the study of nonintegrable systems is applied to them. Based on the results, we
analyze localization properties of the electronic wavefunctions under the
influence of the solvent.Comment: 4 pages, 5 figures, the revised version will appear in J. Phys. Soc.
Jpn. Vol.76 (No.1
The dual frequency RV-coupling coefficient: a novel measure for quantifying cross-frequency information transactions in the brain
Identifying dynamic transactions between brain regions has become
increasingly important. Measurements within and across brain structures,
demonstrating the occurrence of bursts of beta/gamma oscillations only during
one specific phase of each theta/alpha cycle, have motivated the need to
advance beyond linear and stationary time series models. Here we offer a novel
measure, namely, the "dual frequency RV-coupling coefficient", for assessing
different types of frequency-frequency interactions that subserve information
flow in the brain. This is a measure of coherence between two complex-valued
vectors, consisting of the set of Fourier coefficients for two different
frequency bands, within or across two brain regions. RV-coupling is expressed
in terms of instantaneous and lagged components. Furthermore, by using
normalized Fourier coefficients (unit modulus), phase-type couplings can also
be measured. The dual frequency RV-coupling coefficient is based on previous
work: the second order bispectrum, i.e. the dual-frequency coherence (Thomson
1982; Haykin & Thomson 1998); the RV-coefficient (Escoufier 1973); Gorrostieta
et al (2012); and Pascual-Marqui et al (2011). This paper presents the new
measure, and outlines relevant statistical tests. The novel aspects of the
"dual frequency RV-coupling coefficient" are: (1) it can be applied to two
multivariate time series; (2) the method is not limited to single discrete
frequencies, and in addition, the frequency bands are treated by means of
appropriate multivariate statistical methodology; (3) the method makes use of a
novel generalization of the RV-coefficient for complex-valued multivariate
data; (4) real and imaginary covariance contributions to the RV-coherence are
obtained, allowing the definition of a "lagged-coupling" measure that is
minimally affected by the low spatial resolution of estimated cortical electric
neuronal activity.Comment: technical report, pre-print, 2016-03-1
Self-trapped states and the related luminescence in PbCl crystals
We have comprehensively investigated localized states of photoinduced
electron-hole pairs with electron-spin-resonance technique and
photoluminescence (PL) in a wide temperature range of 5-200 K. At low
temperatures below 70 K, holes localize on Pb ions and form
self-trapping hole centers of Pb. The holes transfer to other trapping
centers above 70 K. On the other hand, electrons localize on two Pb ions
at higher than 50 K and form self-trapping electron centers of Pb.
From the thermal stability of the localized states and PL, we clarify that
blue-green PL band at 2.50 eV is closely related to the self-trapped holes.Comment: 8 pages (10 figures), ReVTEX; removal of one figure, Fig. 3 in the
version
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