The influence of hubs in the structure of a neuronal network during an epileptic seizure

In this work, we propose changes in the structure of a neuronal network with the intention to provoke strong synchronization to simulate episodes of epileptic seizure. Starting with a network of Izhikevich neurons we slowly increase the number of connections in selected nodes in a controlled way, to produce (or not) hubs. We study how these structures alter the synchronization on the spike firings interval, on individual neurons as well as on mean values, as a function of the concentration of connections for random and non-random (hubs) distribution. We also analyze how the post-ictal signal varies for the different distributions. We conclude that a network with hubs is more appropriate to represent an epileptic state.     

Antennal morphology, structure and sensilla distribution in Microplitis pallidipes (Hymenoptera: Braconidae)

Microplitis pallidipes (Hymenoptera: Braconidae) is an important larval parasitoid of noctuid larval pests. In this study, we describe the morphology, ultrastructure and distribution of sensilla on the antennae of both male and female adults using scanning electron microscopy; complemented with transmission electron microscopy. Observations determined that the antennae of M. pallidipes were threadlike and the flagella were composed of 16 sub-segments. Totally, there were six types of sensilla found on the antennae. They were identified as Sensilla trichodea, Sensilla chaetica, Sensilla basiconica type I, S. basiconica type II, Sensilla coeloconicum, and elongated Sensilla placodea, respectively. The S. trichodea were the most abundant sensilla and distributed over the entire antennae, while S. basiconica I and II, S. coeloconicum, and elongated S. placodea were limited to the flagellum. S. chaetica were found on the scape and pedicle in very low numbers. The S. basiconica II and elongated S. placodea walls were full of pores as evident in transmission electron micrographs. Though the shape and structure of antennae between male and female adults were not basically different, the length and width of the antennae on male wasps were significantly greater than that of females. Also, the number, size and density of S. placodea of the male were significantly greater than those of females. The morphology and structure of these sensilla were compared with that found in other braconid wasps. Their possible functions are discussed in light of previously published literature.     

On a hierarchical error estimator combined with a stabilized method for the Navier–Stokes equations

This work combines two complementary strategies for solving the steady incompressible Navier–Stokes model with a zeroth‐order term, namely, a stabilized finite element method and a mesh–refinement approach based on an error estimator. First, equal order interpolation spaces are adopted to approximate both the velocity and the pressure while stability is recovered within the stabilization approach. Also designed to handle advection dominated flows under zeroth‐order term influence, the stabilized method incorporates a new parameter with a threefold asymptotic behavior. Mesh adaptivity driven by a new hierarchical error estimator and built on the stabilized method is the second ingredient. The estimator construction process circumvents the saturation assumption by using an enhancing space strategy which is shown to be equivalent to the error. Several numerical tests validate the methodology. © 2011 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2011     

A novel derivative for the assessment of urinary and salivary nitrate using gas chromatography/mass spectrometry

Previous gas chromatography/mass spectrometry (GC/MS) methods for determining nitrate in biological samples involve either hazardous chemicals or produce multiple isomers that can be difficult to quantitate. Modification of these methods, by the nitration of mesitylene instead of benzene and in the presence of trifluoroacetic anhydride rather than sulphuric acid, should enable simple isotopic quantitation for use in tracer studies, for example, in the measurement of nitric oxide production. Desiccated urine and saliva samples, in addition to aqueous labelled and unlabelled nitrate standards, were treated with trifluoroacetic anhydride and mesitylene at 70°C for 1 h, cooled, then sequentially washed with deionised water and aqueous sodium bicarbonate. The solution of nitromesitylene in mesitylene was separated, dried and analysed by GC/MS. The full mass spectra exhibited abundant ions at m/z 165 and 166 corresponding to the unlabelled and labelled molecular species of nitromesitylene, respectively. Selected ion monitoring of these masses for a series of gravimetrically prepared standards indicated good agreement with isotopic enrichments in the range 0.0625–5 mole % excess, and at nitrate concentrations within the physiological range of 0.078–2 mmol/L. Derivatised samples were stable with respect to isotopic enrichments and nitrate concentrations at −20°C for up to 21 days and exhibited excellent repeatability. Nitration of mesitylene proved to be a simple and rapid method for the measurement of isotope ratios in aqueous nitrates by GC/MS, which has applications in tracer studies and in concentration determinations by isotope dilution techniques for nitric oxide production. Copyright © 2008 John Wiley & Sons, Ltd.     

An Analysis of Stapp’s “A Bell-Type Theorem without Hidden Variables”

H.P. Stapp has proposed a number of demonstrations of a Bell-type theorem which dispensed with an assumption of hidden variables, but relied only upon locality together with an assumption that experimenters can choose freely which of several incompatible observables to measure. In recent papers his strategy has centered upon counterfactual conditionals. Stapp’s paper in American Journal of Physics, 2004, replies to objections raised against earlier expositions of this strategy and proposes a simplified demonstration. The new demonstration is criticized, several subtleties in the logic of counterfactuals are pointed out, and the proofs of J.S. Bell and his followers are advocated.Dedicated to the memory of my dear friend Asher Peres.     

Electronic structure of Sr2FeMoO6

We have used electron spectroscopies to investigate the electronic structure of the double perovskite Sr₂FeMoO₆. The valence-band photoemission spectra present a well-defined cut-off at the Fermi level, indicative of the metallic character of the material. The O 1s X-ray absorption spectrum presents three peaks, which are in good correspondence with the main structures in the unoccupied density-of-states of DF-LDA calculations. The electron energy-loss spectra present two structures which are also interpreted in terms of transitions between the bands obtained in the DF-LDA calculations.     

Synchronization structure of evolving epileptic networks using cross-entropy

In this paper we present connectivity patterns of evolving large scale epileptic networks. We employed a cross-entropy measure in the frequency domain on EEG signals to infer the networks, before and during episodes of epileptic seizures. This measure allowed us to make a richer portrait about the node interactions on the graph and to identify emergent structures associated with the synchronization of brain activity. Our results points to a more complex scenario of network organization than the synchronized/unsynchronized dichotomy, with two main results: first, showing regions with unsynchronized (or independent) behavior, even during absence seizures, contradicting the concept of hypersynchrony. Furthermore, we explore the cross-entropy fluctuations along the seizure: a group of nodes became more similar over time while another group became more different, showing a complementary behaviour and different local brain activities. These results bring new questions about the spreading and the sustenance of the epileptic seizures and others synchronization phenomena in living systems.