3,835 research outputs found
Evolution of the phase-space density and the Jeans scale for dark matter derived from the Vlasov-Einstein equation
We discuss solutions of Vlasov-Einstein equation for collisionless dark
matter particles in the context of a flat Friedmann universe. We show that,
after decoupling from the primordial plasma, the dark matter phase-space
density indicator Q remains constant during the expansion of the universe,
prior to structure formation. This well known result is valid for
non-relativistic particles and is not "observer dependent" as in solutions
derived from the Vlasov-Poisson system. In the linear regime, the inclusion of
velocity dispersion effects permits to define a physical Jeans length for
collisionless matter as function of the primordial phase-space density
indicator: \lambda_J = (5\pi/G)^(1/2)Q^(-1/3)\rho_dm^(-1/6). The comoving Jeans
wavenumber at matter-radiation equality is smaller by a factor of 2-3 than the
comoving wavenumber due to free-streaming, contributing to the cut-off of the
density fluctuation power spectrum at the lowest scales. We discuss the
physical differences between these two scales. For dark matter particles of
mass equal to 200 GeV, the derived Jeans mass is 4.3 x 10^(-6) solar masses.Comment: 18 pages, 2 figures. Accepted for publication in JCA
Questões acerca do coping: a propósito do estudo de adaptação do Brief Cope
O objectivo do presente estudo é investigar as propriedades psicométricas
da versão reduzida do questionário de coping desenvolvido por Carver a partir da
versão longa do mesmo questionário e, simultaneamente, discutir alguns aspectos de
coping que se colocam no virar do século. Participaram no estudo 364 indivÃduos,
41,5% do sexo masculino, com caracterÃsticas idênticas aos participantes do estudo de
Carver. O questionário Brief COPE foi submetido a tratamentos estatÃsticos idênticos
ao original e os resultados encontrados são também idênticos à versão original. A
versão encontrada em português é uma boa adaptação da versão original que sugere a
sua utilidade em estudos no Campo da saúde? ------ ABTRACT ------ The primary purpose of the present paper is to identify the
psychometric properties of the short form of the COPE scale named Brief-COPE.
Participants are 364 individuals, 41.5% males, with similar characteristics of the
participants in Carver’s study. The translation of the Brief-COPE followed standard
procedures (translation, back translation, reconciliation, cultural equivalence
verification of translation, identification of content validity, cognitive debriefing).
Statistical procedures followed the original model. Portuguese version that emerges
from the present study shows similar patterns to the original version. The Portuguese
version proposed seems to be a good adaptation of the original one, and a useful
instrument to be used in health psychology
Measuring Efflux and Permeability in Mycobacteria
Mycobacteria are intrinsically resistant to most antimicrobials, which is generally attributed to the impermeability of their cell wall that considerably limits drug uptake. Moreover, like in other pathogenic bacteria, active efflux systems have been widely characterized from diverse mycobacterial species in laboratory conditions, showing that they can promote resistance by extruding noxious compounds prior to their reaching their intended targets. Therefore, the intracellular concentration of a given compound is determined by the balance between permeability, influx, and efflux.
Given the urgent need to discover and develop novel antimycobacterial compounds in order to design effective therapeutic strategies, the contributions to drug resistance made by the controlled permeability of the cell wall and the increased activity of efflux pumps must be determined. In this chapter, we will describe a method that allows (1) the measuring of permeability and the quantification of general efflux activity of mycobacteria, by the study of the transport (influx and efflux) of fluorescent compounds, such as ethidium bromide; and (2) the screening of compounds in search of agents that increase the permeability of the cell wall and efflux inhibitors that could restore the effectiveness of antimicrobials that are subject to efflux
Photon bubble turbulence in cold atom gases
Turbulent radiation flow is commonplace in systems with strong, incoherent, light-matter interactions. In astrophysical contexts, photon bubble turbulence is considered a key mechanism behind enhanced radiation transport, and its importance has been widely asserted for a variety of high energy objects such as accretion disks and massive stars. Here, we show that analogous conditions to those of dense astrophysical objects can be obtained in large clouds of cold atoms, prepared in a laser-cooling experiment, driven close to a sharp electronic resonance. By accessing the spatially-resolved atom density, we are able to identify a photon bubble instability and the resulting regime of photon bubble turbulence. We also develop a theoretical model describing the coupled dynamics of both photon and atom gases, which accurately describes the statistical properties of the turbulent regime. This study thus opens the possibility of simulating radiation-dominated astrophysical systems in cold atom experiments.European Union's Horizon 2020 Research and Innovation programme 820392; Portuguese Foundation for Science and Technology PD/BD/135211/2017info:eu-repo/semantics/publishedVersio
An analytical solution for the analysis of zero-length-column experiments with heat effects
An analytical solution for the analysis of zero-length-column (ZLC) experiments with heat effects is developed. The model is an extension of the original one developed by Eic and Ruthven with the inclusion of the energy balance. Two additional parameters are obtained, beta = (DeltaH/C-p) (partial derivativeq/partial derivativeT)\ (c0),(T0) and alpha = (ha/C-p)(r(c)(2)/D-c). A criterion for negligible heat effects, 3L beta/alpha < 0.1, is derived from the analytical solution based on ZLC operating parameters. ZLC desorption curves in nonisothermal operation are discussed. The model reduces to the original solution of isothermal operation developed by Eic and Ruthven when heat effects are negligible. ZLC experiments with heat effects are analyzed, and trends are in good agreement with theory. Because of its simplicity, the model is a valuable tool for the analysis of ZLC experiments with heat effects
Development of a low-cost culture medium for biopolymer production by Rhizobium viscosum CECT 908 and its potential application in Microbial Enhanced Oil Recovery
Polymers are a versatile class of compounds that play an essential role in our society, being their production
estimated in more than 180 million tons per year. Nowadays, the world market is dominated by synthetic and
plant-derived polymers. Biopolymers of microbial origin are characterized by their better environmental
compatibility and biodegradability when compared with the synthetic ones, and their production is faster than
those obtained from plants. Microbial biopolymers usually exhibit excellent rheological properties, stability at
a wide range of temperatures, salinities and pH values, as well as a broad variety of chemical structures,
which results in different physicochemical and rheological properties. However, despite their outstanding
properties, their application is still limited by their high production costs. In this work, an alternative low-cost
culture medium was developed for biopolymer production by Rhizobium viscosum CECT 908, containing
sugarcane molasses (60 g/L) and corn steep liquor (1%, v/v) as carbon and nitrogen sources, respectively.
Using this low-cost medium, higher biopolymer production and apparent viscosity values (5.2 g/L and 6700
mPa s, respectively) were obtained comparing with the synthetic medium (2.3 g/L and 1100 mPa s), which
contained glucose and yeast extract. As a result, the cost of the culture medium necessary to produce 1 Kg
of biopolymer was reduced more than 20 times. The biopolymer produced in the alternative low-cost medium
exhibited better rheological properties as compared to xanthan gum, including higher viscosity at the same
concentration. Furthermore, it was found to be stable at temperatures up to 80ºC, NaCl concentrations as
high as 200 g/L, and high shear rates (300 s-1). Polymers are widely used by the oil industry to increase the
oil reservoirs productivity during the tertiary oil recovery processes. In sand-pack column assays performed
using a heavy crude oil (40ºC= 170 mPa s), this biopolymer produced using the low-cost medium
demonstrated a better performance than xanthan gum, recovering almost 50% of the entrapped oil. Results
herein obtained highlight that the R. viscosum biopolymer is a promising candidate for application in MEOR
as an alternative to the conventional microbial and synthetic polymers currently used.info:eu-repo/semantics/publishedVersio
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