Color screening in a constituent quark model of hadronic matter

The effect of color screening on the formation of a heavy quark-antiquark ($Q\bar{Q}$) bound state--such as the $J/\psi$ meson--is studied using a constituent-quark model. The response of the nuclear medium to the addition of two color charges is simulated directly in terms of its quark constituents via a string-flip potential that allows for quark confinement within hadrons yet enables the hadrons to separate without generating unphysical long-range forces. Medium modifications to the properties of the heavy meson, such as its energy and its mean-square radius, are extracted by solving Schr\"odinger's equation for the $Q\bar{Q}$ pair in the presence of a (screened) density-dependent potential. The density dependence of the heavy-quark potential is in qualitative agreement with earlier studies of its temperature dependence extracted from lattice calculations at finite temperature. In the present model it is confirmed that abrupt changes in the properties of the $J/\psi$-meson in the hadronic medium ({\it plasma}), correlate strongly with the deconfining phase transition.Comment: 7 pages, 3 figures, submitted to PRC for publication, uses revtex

Soliton Stability in Systems of Two Real Scalar Fields

In this paper we consider a class of systems of two coupled real scalar fields in bidimensional spacetime, with the main motivation of studying classical or linear stability of soliton solutions. Firstly, we present the class of systems and comment on the topological profile of soliton solutions one can find from the first-order equations that solve the equations of motion. After doing that, we follow the standard approach to classical stability to introduce the main steps one needs to obtain the spectra of Schr\"odinger operators that appear in this class of systems. We consider a specific system, from which we illustrate the general calculations and present some analytical results. We also consider another system, more general, and we present another investigation, that introduces new results and offers a comparison with the former investigations.Comment: 16 pages, Revtex, 3 f igure

Lipid-modulated assembly of magnetized iron-filled carbon nanotubes in millimeter-scale structures

Biomolecule-functionalized carbon nanotubes (CNTs) combine the molecular recognition properties of biomaterials with the electrical properties of nanoscale solid state transducers. Application of this hybrid material in bioelectronic devices requires the development of methods for the reproducible self-assembly of CNTs into higher-order structures in an aqueous environment. To this end, we have studied pattern formation of lipid-coated Fe-filled CNTs, with lengths in the 1–5 µm range, by controlled evaporation of aqueous CNT-lipid suspensions. Novel diffusion limited aggregation structures composed of end-to-end oriented nanotubes were observed by optical and atomic force microscopy. Significantly, the lateral dimension of assemblies of magnetized Fe-filled CNTs was in the millimeter range. Control experiments in the absence of lipids and without magnetization indicated that the formation of these long linear nanotube patterns is driven by a subtle interplay between radial flow forces in the evaporating droplet, lipid-modulated van der Waals forces, and magnetic dipole–dipole interactions. Keywords

Caront : gestió flexible de grups d'alumnes en una assignatura i activitats sobre grups. Nova activitat de control

L'Espai Europeu d'Educació Superior promociona el plantejament de noves metodologies docents. Davant la demanda de realitzar més avaluacions als estudiants i poder formar grups de treball de forma més flexible, Caront pretén donar aquesta flexibilitat de forma electrónica. Caront permet definir diferents dinàmiques de grups de treball (teoria, pràctiques, problemes, ABP, etc.) on un alumne es pot inscriure en cadascuna d'elles amb companys diferents i entregar els treballs que faci en cada grup de forma diferenciada. En aquest article es presenta una de les principals aportacions de Caront, entorn basat en Moodle: la gestió flexible de grups d'alumnes dins una assignatura universitària. Entenem per grup universitari un conjunt d'alumnes que realitzen un treball, de forma que un d'ells pot fer efectiva l'activitat proposada (entrega, enquesta, etc.) en representació del grup. Un dels punts que hem treballat és en la confecció d'aquests grups. Quan els grups els formen els propis alumnes, apareixen problemes d'intromissió d'un alumne en un grup ja definit. Per evitar això, hem implementat un sistema d'inscripció de grup per contrassenya, que posa el primer que entra, per a compartirla amb els companys que han de formar el grup. Caront ofereix un conjunt d'activitats basades en aquest concepte de grup: enquestes, tasques (entrega de treballs o pràctiques), enquestes d'autoevaluació a nivell de grup i qüestionaris, entre les més importants. Basada en l'activitat de l'enquesta, hem definit una activitat de Control, que permet un cert feedback electrònic del professor sobre l'activitat del grup. Aquesta activitat de control consisteix en una enquesta definida pel professor, amb preguntes que avaluen l'activitat del grup. Així, el professor ha de contestar una enquesta dirigida als alumnes. Les respostes són vistes pels alumnes de forma privada. Finalment, es presenta un resum de les experiències d'us de Caronte sobre un conjunt d'assignatures de les titulacions d'Enginyeria Informàtica en el curs 2006-07, al no disposar encara dels resultats del 2007-08

Quantum entanglement of bound particles under free center of mass dispersion

On the basis of the full analytical solution of the overall unitary dynamics, the time evolution of entanglement is studied in a simple bipartite model system evolving unitarily from a pure initial state. The system consists of two particles in one spacial dimension bound by harmonic forces and having its free center of mass initially localized in space in a minimum uncertainty wave packet. The existence of such initial states in which the bound particles are not entangled is pointed out. The entanglement of the two particles is shown to be independent of the wavepacket mean momentum, and to increase monotonically in a time scale distinct from that of the spreading of the center of mass wavepacket.Comment: 17 pages, 5 figure

Population Density and Home Range Estimates of Black Rat (Rattus rattus) Populations in Southwestern Puerto Rico

Black rats are among the world’s most invasive rodent species and are responsible for considerable agricultural losses and risks to human health through zoonotic disease. In Puerto Rico, rats may also compete with the primary rabies reservoir (the small Indian mongoose) for baits during oral rabies vaccination (ORV) programs. We evaluated black rat population density and home range size on the Cabo Rojo National Wildlife Refuge, southwestern Puerto Rico. We fitted 10 rats with VHF transmitters and tracked them using radio telemetry for approximately 4 weeks. We entered locations into ArcGIS and obtained minimum convex polygon (MCP) home range estimates. We established two plots of 55 snap traps and performed removal for 5 consecutive days during January and July, to correspond roughly with wet and dry seasons for this region. To calculate abundance, we entered snap trap data using a removal model approach in Program MARK. We calculated the effective trapping area by creating a buffer around the trapping area based on the square root of mean home range estimate. We divided the abundance calculated in MARK by the effective trapping area to calculate the estimated population density. Mean MCP home range estimate was 0.28 ha (SE: 0.05, range: 0.07-0.50 ha). Population density estimates were 114.7 (SE: 201.80) and 19.3 (SE: 6.85) per ha for January and July, respectively. To reduce the potential for rat consumption of ORV baits, wildlife managers should consider conducting ORV activities in Puerto Rico during periods of lower rat abundance or density