241 research outputs found
Collapse of Flux Tubes
The dynamics of an idealized, infinite, MIT-type flux tube is followed in
time as the interior evolves from a pure gluon field to a
plasma. We work in color U(1). pair formation is evaluated
according to the Schwinger mechanism using the results of Brink and Pavel. The
motion of the quarks toward the tube endcaps is calculated by a Boltzmann
equation including collisions. The tube undergoes damped radial oscillations
until the electric field settles down to zero. The electric field stabilizes
the tube against pinch instabilities; when the field vanishes, the tube
disintegrates into mesons. There is only one free parameter in the problem,
namely the initial flux tube radius, to which the results are very sensitive.
Among various quantities calculated is the mean energy of the emitted pions.Comment: 16 pages plus 12 figures. RevTex3. DOE/ER/40427-160N9
Quantum Energies of Interfaces
We present a method for computing the one-loop, renormalized quantum energies
of symmetrical interfaces of arbitrary dimension and codimension using
elementary scattering data. Internal consistency requires finite-energy sum
rules relating phase shifts to bound state energies.Comment: 8 pages, 1 figure, minor changes, Phys. Rev. Lett., in prin
Beyond the Thomas-Fermi approximation for a trapped condensed Bose-Einstein gas
Corrections to the zero-temperature Thomas-Fermi description of a dilute
interacting condensed Bose-Einstein gas confined in an isotropic harmonic trap
arise due to the presence of a boundary layer near the condensate surface.
Within the Bogoliubov approximation, the various contributions to the
ground-state condensate energy all have terms of order R^{-4}ln R and R^{-4},
where R is the number-dependent dimensionless condensate radius in units of the
oscillator length. The zero-order hydrodynamic density-fluctuation amplitudes
are extended beyond the Thomas-Fermi radius through the boundary layer to
provide a uniform description throughout all space. The first-order correction
to the excitation frequencies is shown to be of order R^{-4}.Comment: 12 pages, 2 figures, revtex. Completely revised discussion of the
boundary-layer corrections to collective excitations, and two new figures
added. To appear in Phys. Rev. A (October, 1998
Hygienisation, gentrification, and urban displacement in Brazil
This article engages recent debates over gentrification and urban displacement in the global South. While researchers increasingly suggest that gentrification is becoming widespread in “Southern” cities, others argue that such analyses overlook important differences in empirical context and privilege EuroAmerican theoretical frameworks. To respond to this debate, in this article, we outline the concept of higienização (hygienisation), arguing that it captures important contextual factors missed by gentrification. Hygienisation is a Brazilian term that describes a particular form of urban displacement, and is directly informed by legacies of colonialism, racial and class stigma, informality, and state violence. Our objective is to show how “Southern” concepts like hygienisation help urban researchers gain better insight into processes of urban displacement, while also responding to recent calls to decentre and provincialise urban theory
Non-Metabolic Membrane Tubulation and Permeability Induced by Bioactive Peptides
BACKGROUND: Basic cell-penetrating peptides are potential vectors for therapeutic molecules and display antimicrobial activity. The peptide-membrane contact is the first step of the sequential processes leading to peptide internalization and cell activity. However, the molecular mechanisms involved in peptide-membrane interaction are not well understood and are frequently controversial. Herein, we compared the membrane activities of six basic peptides with different size, charge density and amphipaticity: Two cell-penetrating peptides (penetratin and R9), three amphipathic peptides and the neuromodulator substance P. METHODOLOGY/PRINCIPAL FINDINGS: Experiments of X ray diffraction, video-microscopy of giant vesicles, fluorescence spectroscopy, turbidimetry and calcein leakage from large vesicles are reported. Permeability and toxicity experiments were performed on cultured cells. The peptides showed differences in bilayer thickness perturbations, vesicles aggregation and local bending properties which form lipidic tubular structures. These structures invade the vesicle lumen in the absence of exogenous energy. CONCLUSIONS/SIGNIFICANCE: We showed that the degree of membrane permeabilization with amphipathic peptides is dependent on both peptide size and hydrophobic nature of the residues. We propose a model for peptide-induced membrane perturbations that explains the differences in peptide membrane activities and suggests the existence of a facilitated “physical endocytosis,” which represents a new pathway for peptide cellular internalization
Rift Valley fever virus detection in susceptible hosts with special emphasis in insects
Rift Valley fever phlebovirus (RVFV, Phenuiviridae) is an emerging arbovirus that can cause potentially fatal disease in many host species including ruminants and humans. Thus, tools to detect this pathogen within tissue samples from routine diagnostic investigations or for research purposes are of major interest. This study compares the immunohistological usefulness of several mono- and polyclonal antibodies against RVFV epitopes in tissue samples derived from natural hosts of epidemiologic importance (sheep), potentially virus transmitting insect species (Culex quinquefasciatus, Aedes aegypti) as well as scientific infection models (mouse, Drosophila melanogaster, C6/36 cell pellet). While the nucleoprotein was the epitope most prominently detected in mammal and mosquito tissue samples, fruit fly tissues showed expression of glycoproteins only. Antibodies against non-structural proteins exhibited single cell reactions in salivary glands of mosquitoes and the C6/36 cell pellet. However, as single antibodies exhibited a cross reactivity of varying degree in non-infected specimens, a careful interpretation of positive reactions and consideration of adequate controls remains of critical importance. The results suggest that primary antibodies directed against viral nucleoproteins and glycoproteins can facilitate RVFV detection in mammals and insects, respectively, and therefore will allow RVFV detection for diagnostic and research purposes
A idéia de cultura teuto-brasileira: literatura, identidade e os significados da etnicidade
Systematics, taxonomy and floristics of Brazilian Rubiaceae: an overview about the current status and future challenges
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