Arrival Time Statistics in Global Disease Spread

Metapopulation models describing cities with different populations coupled by the travel of individuals are of great importance in the understanding of disease spread on a large scale. An important example is the Rvachev-Longini model [{\it Math. Biosci.} {\bf 75}, 3-22 (1985)] which is widely used in computational epidemiology. Few analytical results are however available and in particular little is known about paths followed by epidemics and disease arrival times. We study the arrival time of a disease in a city as a function of the starting seed of the epidemics. We propose an analytical Ansatz, test it in the case of a spreading on the world wide air transportation network, and show that it predicts accurately the arrival order of a disease in world-wide cities

Using CliftonStrengthsTM for Professional Development: Recommendations for Practice

This article explores how a culture of strengths-based leadership can positively impact professional development for school site administrators. The strengths of school district administrators were measured through the administration of CliftonStrengths™ assessment. Themes that emerged were determined through the assessment and qualitative analysis of responses. A sample of convenience 50 principals and assistant principals from a public school district in Southern California participated in this research. The findings revealed that the common talent themes among school site administrators were relationship building, executing, influencer, and learner. This study supports future practices to enable human resources personnel to design targeted professional development for school site administrators. An analysis of a school administrator\u27s strengths and personality traits is unique to each school district. The results support human resource professionals\u27 efforts to determine personnel\u27s future needs, including hiring and developing school leaders

Singular shell embedded into a cosmological model

We generalize Israel's formalism to cover singular shells embedded in a non-vacuum Universe. That is, we deduce the relativistic equation of motion for a thin shell embedded in a Schwarzschild/Friedmann-Lemaitre-Robertson-Walker spacetime. Also, we review the embedding of a Schwarzschild mass into a cosmological model using "curvature" coordinates and give solutions with (Sch/FLRW) and without the embedded mass (FLRW).Comment: 25 pages, 2 figure

Axially symmetric Einstein-Straus models

The existence of static and axially symmetric regions in a Friedman-Lemaitre cosmology is investigated under the only assumption that the cosmic time and the static time match properly on the boundary hypersurface. It turns out that the most general form for the static region is a two-sphere with arbitrarily changing radius which moves along the axis of symmetry in a determined way. The geometry of the interior region is completely determined in terms of background objects. When any of the most widely used energy-momentum contents for the interior region is imposed, both the interior geometry and the shape of the static region must become exactly spherically symmetric. This shows that the Einstein-Straus model, which is the generally accepted answer for the null influence of the cosmic expansion on the local physics, is not a robust model and it is rather an exceptional and isolated situation. Hence, its suitability for solving the interplay between cosmic expansion and local physics is doubtful and more adequate models should be investigated.Comment: Latex, no figure

Microdynamics in stationary complex networks

Many complex systems, including networks, are not static but can display strong fluctuations at various time scales. Characterizing the dynamics in complex networks is thus of the utmost importance in the understanding of these networks and of the dynamical processes taking place on them. In this article, we study the example of the US airport network in the time period 1990-2000. We show that even if the statistical distributions of most indicators are stationary, an intense activity takes place at the local (`microscopic') level, with many disappearing/appearing connections (links) between airports. We find that connections have a very broad distribution of lifetimes, and we introduce a set of metrics to characterize the links' dynamics. We observe in particular that the links which disappear have essentially the same properties as the ones which appear, and that links which connect airports with very different traffic are very volatile. Motivated by this empirical study, we propose a model of dynamical networks, inspired from previous studies on firm growth, which reproduces most of the empirical observations both for the stationary statistical distributions and for the dynamical properties.Comment: 8 pages, 7 figure

MiRNA let-7g regulates skeletal myoblast motility via Pinch-2

AbstractPost-transcriptional regulation of gene expression by RNA-binding proteins and by small non-coding RNAs plays an important role in cell biology. Our previous results show that in murine skeletal myoblasts, the expression of Pinch-2, a focal adhesion remodeling factor that regulates cell motility, is repressed by an RNA-binding protein IMP-2/Igf2bp2. We now show that the expression of Pinch-2 is also regulated by the miRNA let-7g. Let-7g and IMP-2 repress Pinch-2 expression independently of each other. A knock-down of let-7g leads to an increase in Pinch-2 expression, and to a decrease of cell motility, which can be reversed by a simultaneous knock-down of Pinch-2. We conclude that let-7g controls the motility of mouse myoblasts in cell culture by post-transcriptionally regulating the expression of Pinch-2

Consensus formation on coevolving networks: groups' formation and structure

We study the effect of adaptivity on a social model of opinion dynamics and consensus formation. We analyze how the adaptivity of the network of contacts between agents to the underlying social dynamics affects the size and topological properties of groups and the convergence time to the stable final state. We find that, while on static networks these properties are determined by percolation phenomena, on adaptive networks the rewiring process leads to different behaviors: Adaptive rewiring fosters group formation by enhancing communication between agents of similar opinion, though it also makes possible the division of clusters. We show how the convergence time is determined by the characteristic time of link rearrangement. We finally investigate how the adaptivity yields nontrivial correlations between the internal topology and the size of the groups of agreeing agents.Comment: 10 pages, 3 figures,to appear in a special proceedings issue of J. Phys. A covering the "Complex Networks: from Biology to Information Technology" conference (Pula, Italy, 2007

A class of exact solutions of Einstein's field equations in higher dimensional spacetimes, d≥4{\bm\geq 4}: Majumdar-Papapetrou solutions

The Newtonian theory of gravitation and electrostatics admit equilibrium configurations of charged fluids where the charge density can be equal to the mass density, in appropriate units. The general relativistic analog for charged dust stars was discovered by Majumdar and by Papapetrou. In the present work we consider Einstein-Maxwell solutions in d-dimensional spacetimes and show that there are Majumdar-Papapetrou type solutions for all ${\rm d} \geq 4$. It is verified that the equilibrium is independent of the shape of the distribution of the charged matter. It is also showed that for perfect fluid solutions satisfying the Majumdar-Papapetrou condition with a boundary where the pressure is zero, the pressure vanishes everywhere, and that the $({\rm d}-1)$-dimensional spatial section of the spacetime is conformal to a Ricci-flat space. The Weyl d-dimensional axisymmetric solutions are generalized to include electric field and charged matter.Comment: 26 pages, no figure

Classical Electron Model with Negative Energy Density in Einstein-Cartan Theory of Gravitation

Experimental result regarding the maximum limit of the radius of the electron \sim 10^{-16} cm and a few of the theoretical works suggest that the gravitational mass which is a priori a positive quantity in Newtonian mechanics may become negative in general theory of relativity. It is argued that such a negative gravitational mass and hence negative energy density also can be obtained with a better physical interpretation in the framework of Einstein-Cartan theory.Comment: 12 Latex pages, added refs and conclusion