How specific is synchronous neuronal firing? : Poster presentation

Background Synchronous neuronal firing has been discussed as a potential neuronal code. For testing first, if synchronous firing exists, second if it is modulated by the behaviour, and third if it is not by chance, a large set of tools has been developed. However, to test whether synchronous neuronal firing is really involved in information processing one needs a direct comparison of the amount of synchronous firing for different factors like experimental or behavioural conditions. To this end we present an extended version of a previously published method NeuroXidence [1], which tests, based on a bi- and multivariate test design, whether the amount of synchronous firing above the chance level is different for different factors

Detection of task-related synchronous firing patterns

Poster presentation: Background To test the importance of synchronous neuronal firing for information processing in the brain, one has to investigate if synchronous firing strength is correlated to the experimental subjects. This requires a tool that can compare the strength of the synchronous firing across different conditions, while at the same time it should correct for other features of neuronal firing such as spike rate modulation or the auto-structure of the spike trains that might co-occur with synchronous firing. Here we present the bi- and multivariate extension of previously developed method NeuroXidence [1,2], which allows for comparing the amount of synchronous firing between different conditions. ..

Fast Spinning Pulsars as Probes of Massive Black Holes' Gravity

Dwarf galaxies and globular clusters may contain intermediate mass black holes ($10^{3}$ to $10^{5}$ solar masses) in their cores. Estimates of ~$10^{3}$ neutron stars in the central parsec of the Galaxy and similar numbers in small elliptical galaxies and globular clusters along with an estimated high probability of ms-pulsar formation in those environments has led many workers to propose the use of ms-pulsar timing to measure the mass and spin of intermediate mass black holes. Models of pulsar motion around a rotating black hole generally assume geodesic motion of a "test" particle in the Kerr metric. These approaches account for well-known effects like de Sitter precession and the Lense-Thirring effect but they do not account for the non-linear effect of the pulsar's stress-energy tensor on the space-time metric. Here we model the motion of a pulsar near a black hole with the Mathisson-Papapetrou-Dixon (MPD) equations. Numerical integration of the MPD equations for black holes of mass 2 X $10^{6}$, $10^{5}$ and $10^{3}$ solar masses shows that the pulsar will not remain in an orbital plane with motion vertical to the plane being largest relative to the orbit's radial dimensions for the lower mass black holes. The pulsar's out of plane motion will lead to timing variations that are up to ~10 microseconds different from those predicted by planar orbit models. Such variations might be detectable in long term observations of millisecond pulsars. If pulsar signals are used to measure the mass and spin of intermediate mass black holes on the basis of dynamical models of the received pulsar signal then the out of plane motion of the pulsar should be part of that model.Comment: Accepted by MNRAS March 27, 201

Multivariate characterization of hydrogen Balmer emission in cataclysmic variables

The ratios of hydrogen Balmer emission line intensities in cataclysmic variables are signatures of the physical processes that produce them. To quantify those signatures relative to classifications of cataclysmic variable types, we applied the multivariate statistical analysis methods of principal components analysis and discriminant function analysis to the spectroscopic emission data set of Williams (1983). The two analysis methods reveal two different sources of variation in the ratios of the emission lines. The source of variation seen in the principal components analysis was shown to be correlated with the binary orbital period. The source of variation seen in the discriminant function analysis was shown to be correlated with the equivalent width of the H$\beta$ line. Comparison of the data scatterplot with scatterplots of theoretical models shows that Balmer line emission from T CrB systems is consistent with the photoionization of a surrounding nebula. Otherwise, models that we considered do not reproduce the wide range of Balmer decrements, including "inverted" decrements, seen in the data.Comment: Accepted by PAS

Knots with unknotting number 1 and essential Conway spheres

For a knot K in S^3, let T(K) be the characteristic toric sub-orbifold of the orbifold (S^3,K) as defined by Bonahon and Siebenmann. If K has unknotting number one, we show that an unknotting arc for K can always be found which is disjoint from T(K), unless either K is an EM-knot (of Eudave-Munoz) or (S^3,K) contains an EM-tangle after cutting along T(K). As a consequence, we describe exactly which large algebraic knots (ie algebraic in the sense of Conway and containing an essential Conway sphere) have unknotting number one and give a practical procedure for deciding this (as well as determining an unknotting crossing). Among the knots up to 11 crossings in Conway's table which are obviously large algebraic by virtue of their description in the Conway notation, we determine which have unknotting number one. Combined with the work of Ozsvath-Szabo, this determines the knots with 10 or fewer crossings that have unknotting number one. We show that an alternating, large algebraic knot with unknotting number one can always be unknotted in an alternating diagram. As part of the above work, we determine the hyperbolic knots in a solid torus which admit a non-integral, toroidal Dehn surgery. Finally, we show that having unknotting number one is invariant under mutation.Comment: This is the version published by Algebraic & Geometric Topology on 19 November 200