Exact Solution of a Jamming Transition: Closed Equations for a Bootstrap Percolation Problem

Jamming, or dynamical arrest, is a transition at which many particles stop moving in a collective manner. In nature it is brought about by, for example, increasing the packing density, changing the interactions between particles, or otherwise restricting the local motion of the elements of the system. The onset of collectivity occurs because, when one particle is blocked, it may lead to the blocking of a neighbor. That particle may then block one of its neighbors, these effects propagating across some typical domain of size named the dynamical correlation length. When this length diverges, the system becomes immobile. Even where it is finite but large the dynamics is dramatically slowed. Such phenomena lead to glasses, gels, and other very long-lived nonequilibrium solids. The bootstrap percolation models are the simplest examples describing these spatio-temporal correlations. We have been able to solve one such model in two dimensions exactly, exhibiting the precise evolution of the jamming correlations on approach to arrest. We believe that the nature of these correlations and the method we devise to solve the problem are quite general. Both should be of considerable help in further developing this field.Comment: 17 pages, 4 figure

Geometry of Empty Space is the Key to Near-Arrest Dynamics

We study several examples of kinetically constrained lattice models using dynamically accessible volume as an order parameter. Thereby we identify two distinct regimes exhibiting dynamical slowing, with a sharp threshold between them. These regimes are identified both by a new response function in dynamically available volume, as well as directly in the dynamics. Results for the selfdiffusion constant in terms of the connected hole density are presented, and some evidence is given for scaling in the limit of dynamical arrest.Comment: 11 page

The Carina Flare: What can fragments in the wall tell us?

$^{13}$CO(J=2--1) and C$^{18}$O(J=2--1) observations of the molecular cloud G285.90+4.53 (Cloud~16) in the Carina Flare supershell (GSH287+04-17) with the APEX telescope are presented. With an algorithm DENDROFIND we identify 51 fragments and compute their sizes and masses. We discuss their mass spectrum and interpret it as being the result of the shell fragmentation process described by the pressure assisted gravitational instability - PAGI. We conclude that the explanation of the clump mass function needs a combination of gravity with pressure external to the shell.Comment: 19 pages, 14 figures, accepted by A&

Plant hydraulic traits reveal islands as refugia from worsening drought.

Relatively mesic environments within arid regions may be important conservation targets as 'climate change refugia' for species persistence in the face of worsening drought conditions. Semi-arid southern California and the relatively mesic environments of California's Channel Islands provide a model system for examining drought responses of plants in potential climate change refugia. Most methods for detecting refugia are focused on 'exposure' of organisms to certain abiotic conditions, which fail to assess how local adaptation or acclimation of plant traits (i.e. 'sensitivity') contribute to or offset the benefits of reduced exposure. Here, we use a comparative plant hydraulics approach to characterize the vulnerability of plants to drought, providing a framework for identifying the locations and trait patterns that underlie functioning climate change refugia. Seasonal water relations, xylem hydraulic traits and remotely sensed vegetation indices of matched island and mainland field sites were used to compare the response of native plants from contrasting island and mainland sites to hotter droughts in the early 21st century. Island plants experienced more favorable water relations and resilience to recent drought. However, island plants displayed low plasticity/adaptation of hydraulic traits to local conditions, which indicates that relatively conserved traits of island plants underlie greater hydraulic safety and localized buffering from regional drought conditions. Our results provide an explanation for how California's Channel Islands function as a regional climate refugia during past and current climate change and demonstrate a physiology-based approach for detecting potential climate change refugia in other systems

Modifications to the Properties of the Higgs Boson

We explore the impact of new SU(3)XSU(2)XU(1) invariant interactions characterized by a scale of order a TeV on Higgs boson properties. The Higgs production rate and branching ratios can be very different from their standard model values. We also discuss the possibility that these new interactions contribute to acceptable unification of the gauge couplings.Comment: Minor typos fixed. 8 pages, 5 figure

Peaks of Otter Salamander (Plethodon hubrichti) Condition: Optimal Elevations for This Montane Species of Salamander

Undergraduate Basi

Self-determination in the constitutional future of the EU

This article analyses three prominent proposals for the functional and political transformation of the EU from a constitutional perspective. It argues that existing EU reform proposals, to varying degrees, entrench rather than reverse the challenges to individual and political self-determination brought about by the EU's response to its Euro crisis. As the article will conclude, challenging ‘authoritarian liberalism' in an EU context may require the development of a constitutional structure for the Union able to contest, rather than set in stone, the EU's existing economic and political goals

From balance to conflict: a new constitution for the EU

As the crisis (and the Union’s response to it) further develops, one thing appears clear: the European Union post-crisis will be a very different animal from the pre-crisis EU. This article offers an alternative model for the EU’s constitutional future. Its objective is to invert the Union’s current path-dependency: changes to the way in which the Union works should serve to question, rather than entrench, its future objectives and trajectory. The paper argues that the post-crisis EU requires a quite different normative, institutional and juridical framework. Such a framework must focus on reproducing the social and political cleavages that underlie the idea of authority on the national level, and that allow divisive political choices to be legitimised. This reform project implies reshaping the prerogatives of the European institutions. Rather than seeking to prevent or bracket political conflict, the division of institutional competences and tasks should be rethought in order to allow the EU institutions to internalize within their decision-making process the conflicts reproduced by social and political cleavages. Finally, a reformed legal order must play an active role as a facilitator and container of conflict over the ends of the integration project

NLO distributions for Higgs production at the LHC

We report on results for the NLO corrected differential distributions $d\sigma/dp_T$ and $d\sigma/dy$ for the process $p + p\to H + 'X'$, where $p_T$ and $y$ are the transverse momentum and rapidity of the Higgs-boson $H$ respectively and $X$ denotes the inclusive hadronic state. All QCD partonic subprocesses have been included. The computation is carried out in the limit that the top-quark mass $m_t \to \infty$. Our calculations reveal that the dominant subprocess is given by $g + g \to H + 'X'$ but the reaction $g + q(\bar q) \to H + 'X'$ is not negligible. Also the $K$-factor representing the ratio between the next-to-leading order and leading order differential distributions varies from 1.4 to 1.7 depending on the kinematic region and choice of parton densities.Comment: 4 pages, Latex, 4 postscript figures, Contribution to Radcor0