Steiner's formula in the Heisenberg group

Steiner's tube formula states that the volume of an ∈-neighborhood of a smooth regular domain in ℝn is a polynomial of degree n in the variable ∈ whose coefficients are curvature integrals (also called quermassintegrals). We prove a similar result in the sub-Riemannian setting of the first Heisenberg group. In contrast to the Euclidean setting, we find that the volume of an ∈-neighborhood with respect to the Heisenberg metric is an analytic function of ∈ that is generally not a polynomial. The coefficients of the series expansion can be explicitly written in terms of integrals of iteratively defined canonical polynomials of just five curvature terms

Risk-taking and decision-making in youth: Relationships to addiction vulnerability

Background: Decision-making and risk-taking behavior undergo developmental changes during adolescence. Disadvantageous decision-making and increased risk-taking may lead to problematic behaviors such as substance use and abuse, pathological gambling and excessive internet use. Methods: Based on MEDLINE searches, this article reviews the literature on decision-making and risk-taking and their relationships to addiction vulnerability in youth. Results: Decision-making and risk-taking behaviors involve brain areas that undergo developmental changes during puberty and young adulthood. Individual differences and peer pressure also relate importantly to decision-making and risk-taking. Conclusions: Brain-based changes in emotional, motivational and cognitive processing may underlie risk-taking and decision-making propensities in adolescence, making this period a time of heightened vulnerability for engagement in addictive behaviors

Population size estimation for the Warren root collar weevil, Hylobius warreni Wood (Coleoptera: Curculionidae), a pest of regenerating lodgepole pine plantations

The Warren root collar weevil, Hylobius warreni Wood (Coleoptera: Curculionidae), is an endemic pest species of conifers, particularly lodgepole pine (Pinus contorta var. latifolia) (Pinaceae), in British Columbia. Larvae feed on the roots and root collars of young trees, resulting in girdling damage and mortality or growth reductions. Population sizes of adult H. warreni have historically been difficult to assess due to a lack of operational sampling methods or chemical attractants for the species. Therefore, most previous population estimates have relied on indirect or incomplete measures of damage by immature individuals. In this study, we tested the Björklund funnel trap to assess its efficacy as a method to estimate H. warreni populations. Funnel traps were placed on all 182 trees in half of a small (~1 ha) lodgepole pine stand over four days and remained in place for 13 days after the last traps were installed. Adult weevils were captured, marked, and released on the bole of the tree on which they had been caught. It is likely that most of the adult weevils in the plot, which was isolated from any nearby lodgepole pine stands, were caught at least once and many were caught multiple times. Population sizes were estimated using both the Schnabel method and the Schumacher and Eschmeyer method, resulting in population estimates of 1.83-2.19 weevils/tree and 731-875 weevils/ha. These measures are within the range of population sizes estimated by previous studies. The results suggest the Björklund funnel trap may be an effective operational tool for population monitoring for this species and may also be an effective tactic in population reduction strategies

On the relationship between cooling flows and bubbles

A common feature of the X-ray bubbles observed in Chandra images of some cooling flow clusters is that they appear to be surrounded by bright, cool shells. Temperature maps of a few nearby luminous clusters reveal that the shells consist of the coolest gas in the clusters—much cooler than the surrounding medium. Using simple models, we study the effects of this cool emission on the inferred cooling flow properties of clusters. We find that the introduction of bubbles into model clusters that do not have cooling flows results in temperature and surface brightness profiles that resemble those seen in nearby cooling flow clusters. They also approximately reproduce the recent XMM-Newton and Chandra observations of a high minimum temperature of ~1-3 keV. Hence, bubbles, if present, must be taken into account when inferring the physical properties of the intracluster medium. In the case of some clusters, bubbles may account entirely for these observed features, calling into question their designation as clusters with cooling flows. However, since not all nearby cooling flow clusters show bubble-like features, we suggest that there may be a diverse range of physical phenomena that give rise to the same observed features

Város és reprezentáció = City, urbanity and representation

A 2004-ben induló, több önálló projektet magában foglaló kutatás középpontjában annak vizsgálata állt, hogy miképpen fonódik egybe egy város fizikai valósága kulturális képekkel, képzetekkel, történetekkel és társadalmi imaginációkkal. Azt vizsgáltuk meg, hogyan jelennek meg a városi terek irodalmi szövegekben, élettörténetekben, emlékezési rítusokban, a térhasználatban, különböző performance-okban. Elemeztük a térhasználat, azaz a terek kulturális jelentéssel telítésének folyamatait. Vizsgáltuk, hogy milyen térhasználati módok léteznek, ezek milyen összefüggéseket mutatnak konkrét történeti, társadalmi időszakokkal, a kollektív, vagy a személyes emlékezet síkjaival, az egyéni, vagy a közösségi identitás gyakorlataival. Célkitűzésünk kettős volt. Egyrészt azoknak az általános szimbolikus mechanizmusoknak és reprezentációs stratégiáknak a megmutatására törekedtünk, amelyek révén egy adott földrajzi térből belakott, bejárt, használt, leírt, eljátszott, emlékezett, azaz kulturálisan létrehozott tér, város lesz. Másrészt azt térképeztük föl, hogy milyen az a konkrét kulturális kontextus, melyek azok a sajátos tartalmak, képek és mítoszok, társadalmi és szimbolikus gyakorlatok, amelyek a szimbolikus értelemben vett Pécset megalkotják. Ez a kettős perspektíva az egyes projekteken belül, de azok egymásraépülésén, a különböző témák, módszerek és nézőpontok között létrejövő "dialógusban" is érvényesült. A támogatott időszakban a kutatómunka eredményeit konferenciákon, tanulmányokban, tanulmánykötetekben, és kiállítások létrehozásával prezentáltuk. | This project has been started in 2004. The project has focused on the issue of relationship between physical reality of cities and its cultural images, imaginations, histories. We have investigated how urban spaces appear in literary texts, biographies, rites of memories and in different performances. We analysed different processes of use of urban space, and of its cultural meanings. We dissect the different forms of use of urban space, and its relationships to given historical and social periods, to different aspects of collective and personal memory, to practices of collective and individual identity. The project had a double aim. We were going to describe those symbolic mechanisms and strategies of representations which turned geographical space into lived, used, memorized cultural space, into a city. At the same time we analysed and described the cultural context of contents, images, and myths, which create symbolically the city of Pécs. This double perspective in each parts of the project, its interconnection, the relationship between different themes, methods, and approaches has been expressed in "dialogs" between the projects. During this time we presented the products of our research on conferences, in volumes, books, and exhibitions

Our changing Sun

Stellar astronomy tells us much about the long-term evolution of our Sun while forensic evidence (for example, cosmic-ray products in ice cores) gives us indications of its fluctuations over the last millennium. However, such studies do not give us a sufficiently detailed understanding of solar change over the last century to allow us to detect and quantify any role that the Sun might have played in the observed rise in average surface temperatures on Earth. This paper describes recent research that has filled this gap by applying advances in our understanding of the effects and structure of the solar wind to historical data on the Earth's magnetic field

On Bootstrap Percolation in Living Neural Networks

Recent experimental studies of living neural networks reveal that their global activation induced by electrical stimulation can be explained using the concept of bootstrap percolation on a directed random network. The experiment consists in activating externally an initial random fraction of the neurons and observe the process of firing until its equilibrium. The final portion of neurons that are active depends in a non linear way on the initial fraction. The main result of this paper is a theorem which enables us to find the asymptotic of final proportion of the fired neurons in the case of random directed graphs with given node degrees as the model for interacting network. This gives a rigorous mathematical proof of a phenomena observed by physicists in neural networks

Galaxy interactions II: High density environments

With the aim to assess the role of dense environments in galaxy interactions, properties we present an analysis of close galaxy pairs in groups and clusters, obtained from the Sloan Digital Sky Survey Data Release 7 (SDSS-DR7). We identified pairs that reside in groups by cross-correlating the total galaxy pair catalogue with the SDSS-DR7 group catalogue from Zapata et al. (2009). We classify pair galaxies according to the intensity of interaction. We analysed the effect of high density environments on different classes of galaxy-galaxy interactions and we have also studied the impact of the group global environment on pair galaxies. We find that galaxy pairs are more concentrated towards the group centres with respect to the other group galaxy members, and disturbed pairs show a preference to contain the brightest galaxy in the groups. The color-magnitude relation exhibits significant differences between pair galaxies and the control sample, consisting in color tails with a clear excess of extremely blue and red galaxies for merging systems. In addition, pair galaxies show a significant excess of young stellar populations with respect to galaxies in the control sample; this finding suggests that, in dense environments, strong interactions produce an important effect in modifying galaxy properties. We find that the fraction of star forming galaxies decreases toward the group centre; however, galaxy pairs show a more efficient star formation activity than galaxies without a close companion. We have also found that pair galaxies prefer groups with low density global environments with respect to galaxies of the corresponding control sample. Blue, young stellar population galaxies prefer groups within low density global environments.Comment: 10 pages, 11 figures, accepted for publication in A&