Guiding the Way to Gamma-Ray Sources: X-ray Studies of Supernova Remnants

Supernova remnants have long been suggested as a class of potential counterparts to unidentified gamma-ray sources. The mechanisms by which such gamma-rays can arise may include emission from a pulsar associated with a remnant, or a variety of processes associated with energetic particles accelerated by the SNR shock. Imaging and spectral observations in the X-ray band can be used to identify properties of the remnants that lead to gamma-ray emission, including the presence of pulsar-driven nebulae, nonthermal X-ray emission from the SNR shells, and the interaction of SNRs with dense surrounding material.Comment: 16 pages, 11 figures, To appear in the proceedings of the workshop: "The Nature of the Unidentified Galactic Gamma-Ray Sources" held at INAOE, Mexico, October 2000, (A.Carraminana, O. Reiner and D. Thompson, eds.

Class of correlated random networks with hidden variables

We study a class models of correlated random networks in which vertices are characterized by \textit{hidden variables} controlling the establishment of edges between pairs of vertices. We find analytical expressions for the main topological properties of these models as a function of the distribution of hidden variables and the probability of connecting vertices. The expressions obtained are checked by means of numerical simulations in a particular example. The general model is extended to describe a practical algorithm to generate random networks with an \textit{a priori} specified correlation structure. We also present an extension of the class, to map non-equilibrium growing networks to networks with hidden variables that represent the time at which each vertex was introduced in the system

A generalized definition of reactivity for ecological systems and the problem of transient species dynamics

1. Perturbations to an ecosystem's steady state can trigger transient responses of great ecological relevance. Asymptotic stability determines whether a generic perturbation will fade out in the long run, but falls short of characterizing the dynamics immediately after an equilibrium has been perturbed. Reactivity, traditionally defined as the maximum instantaneous growth rate of small perturbations to a stable steady state, is a simple yet powerful measure of the short-term instability of a system as a whole. In many ecological applications, however, it could be important to focus on the reactivity properties of just some specific, problem-dependent state variables, such as the abundance of a focal species engaged in interspecific competition, either predators or preys in a trophic community, or infectious individuals in disease transmission. 2. We propose a generalized definition of reactivity (g-reactivity) that allows to evaluate the differential contribution of the state space components to the transient behaviour of an ecological system following a perturbation. Our definition is based on the dynamic analysis of a system output, corresponding to an ecologically motivated linear transformation of the relevant state variables. We demonstrate that the g-reactivity properties of an equilibrium are determined by the dominant eigenvalue of a Hermitian matrix that can be easily obtained from the Jacobian associated with the equilibrium and the system output transformation. 3. As a testbed for our methodological framework, we analyse the g-reactivity properties of simple spatially implicit metapopulation models of some prototypical ecological interactions, namely competition, predation and transmission of an infectious disease. We identify conditions for the temporary coexistence of an invader with a (possibly competitively superior) resident species, for transitory invasion of either prey or predator in otherwise predator- or prey-dominated ecosystems, and for transient epidemic outbreaks. 4. Through suitable examples, we show that characterizing the transient dynamics associated with an ecosystem's steady state can be, in some cases, as important as determining its asymptotic behaviour, from both theoretical and management perspective. Because g-reactivity analysis can be performed for systems of any complexity in a relatively straightforward way, we conclude that it may represent a useful addition to the toolbox of quantitative ecologists

Topology and correlations in structured scale-free networks

We study a recently introduced class of scale-free networks showing a high clustering coefficient and non-trivial connectivity correlations. We find that the connectivity probability distribution strongly depends on the fine details of the model. We solve exactly the case of low average connectivity, providing also exact expressions for the clustering and degree correlation functions. The model also exhibits a lack of small world properties in the whole parameters range. We discuss the physical properties of these networks in the light of the present detailed analysis.Comment: 10 pages, 9 figure

Familial hemiplegic migraine locus on 19p13 is involved in the common forms of migraine with and without aura

Migraine is a common neurological disease of two main types: migraine with aura and migraine without aura. Familial clustering suggests that genetic factors are involved in the etiology of migraine. Recently, a gene for familial hemiplegic migraine, a rare autosomal dominant subtype of migraine with aura, was mapped to chromosome 19p13. We tested the involvement of this chromosomal region in 28 unrelated families with the common forms of migraine with and without aura, by following the transmission of the highly informative marker D19S394. Sibpair analysis showed that affected sibs shared the same marker allele more frequently than expected by chance. Our findings thus also suggest the involvement of a gene on 19p13 in the etiology of the common forms of migraine

ARCTIC: Durvalumab + tremelimumab and durvalumab monotherapy vs SoC in ≥ 3L advanced NSCLC treatment

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Spatial updating in narratives.

Across two experiments we investigated spatial updating in environments encoded through narratives. In Experiment 1, in which participants were given visualization instructions to imagine the protagonist’s movement, they formed an initial representation during learning but did not update it during subsequent described movement. In Experiment 2, in which participants were instructed to physically move in space towards the directions of the described objects prior to testing, there was evidence for spatial updating. Overall, findings indicate that physical movement can cause participants to link a spatial representation of a remote environment to a sensorimotor framework and update the locations of remote objects while they move

Kaon-Nucleon Scattering Amplitudes and Z∗^*-Enhancements from Quark Born Diagrams

We derive closed form kaon-nucleon scattering amplitudes using the ``quark Born diagram" formalism, which describes the scattering as a single interaction (here the OGE spin-spin term) followed by quark line rearrangement. The low energy I=0 and I=1 S-wave KN phase shifts are in reasonably good agreement with experiment given conventional quark model parameters. For $k_{lab}> 0.7$ Gev however the I=1 elastic phase shift is larger than predicted by Gaussian wavefunctions, and we suggest possible reasons for this discrepancy. Equivalent low energy KN potentials for S-wave scattering are also derived. Finally we consider OGE forces in the related channels K$\Delta$, K$^*$N and K$^*\Delta$, and determine which have attractive interactions and might therefore exhibit strong threshold enhancements or ``Z$^*$-molecule" meson-baryon bound states. We find that the minimum-spin, minimum-isospin channels and two additional K$^*\Delta$ channels are most conducive to the formation of bound states. Related interesting topics for future experimental and theoretical studies of KN interactions are also discussed.Comment: 34 pages, figures available from the authors, revte

Sensitivity analysis of reactive ecological dynamics

Author Posting. © Springer, 2008. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Bulletin of Mathematical Biology 70 (2008): 1634-1659, doi:10.1007/s11538-008-9312-7.Ecological systems with asymptotically stable equilibria may exhibit significant transient dynamics following perturbations. In some cases, these transient dynamics include the possibility of excursions away from the equilibrium before the eventual return; systems that exhibit such amplification of perturbations are called reactive. Reactivity is a common property of ecological systems, and the amplification can be large and long-lasting. The transient response of a reactive ecosystem depends on the parameters of the underlying model. To investigate this dependence, we develop sensitivity analyses for indices of transient dynamics (reactivity, the amplification envelope, and the optimal perturbation) in both continuous- and discrete-time models written in matrix form. The sensitivity calculations require expressions, some of them new, for the derivatives of equilibria, eigenvalues, singular values, and singular vectors, obtained using matrix calculus. Sensitivity analysis provides a quantitative framework for investigating the mechanisms leading to transient growth. We apply the methodology to a predator-prey model and a size-structured food web model. The results suggest predator-driven and prey-driven mechanisms for transient amplification resulting from multispecies interactions.Financial support provided by NSF grant DEB-0343820, NOAA grant NA03-NMF4720491, the Ocean Life Institute of the Woods Hole Oceanographic Institution, and the Academic Programs Office of the MIT-WHOI Joint Program in Oceanography

MMN and Differential Waveform

A mismatch negativity response (MMN) and a new differential waveform were derived in an effort to evaluate a neural refractory or recovery effect in adult listeners. The MMN was elicited using oddball test runs in which the standard and deviant stimuli differed in frequency. To derive the differential waveform, the same standard and deviant stimuli were presented alone. MMN responses were obtained by subtracting the averaged responses to standards from the deviants. The differential waveforms were obtained by subtracting the averaged responses to standards presented alone from deviants presented alone. Scalp topography for the MMN and differential waveforms were similar. A significant (p < .05) positive and negative correlation was found between the earlier and later components of the bimodal MMN and the N1 and P2 component of the differential waveform, respectively. Further, N1 and P2 of the differential waveform were significant (p < .05) predictor variables of early and late peak amplitudes of the MMN. These results suggest that refractory effects may overlay/modify the morphology of the MMN waveform