277 research outputs found
On the density profile of the globular cluster M92
We present new number density and surface brightness profiles for the
globular cluster M92 (NGC 6341). These profiles are calculated from optical
images collected with the CCD mosaic camera MegaCam at the
Canada-France-Hawaii-Telescope and with the Advanced Camera for Surveys on the
Hubble Space Telescope. The ground-based data were supplemented with the Sloan
Digital Sky Survey photometric catalog. Special care was taken to discriminate
candidate cluster stars from field stars and to subtract the background
contamination from both profiles. By examining the contour levels of the number
density, we found that the stellar distribution becomes clumpy at radial
distances larger than about 13 arcminutes, and there is no preferred
orientation of contours in space. We performed detailed fits of King and Wilson
models to the observed profiles. The best-fit models underestimate the number
density inside the core radius. Wilson models better represent the
observations, in particular in the outermost cluster regions: the good global
agreement of these models with the observations suggests that there is no need
to introduce an extra-tidal halo to explain the radial distribution of stars at
large radial distances. The best-fit models for the number density and the
surface brightness profiles are different, even though they are based on the
same observations. Additional tests support the evidence that this fact
reflects the difference in the radial distribution of the stellar tracers that
determine the observed profiles (main sequence stars for the number density,
bright evolved stars for the surface brightness).Comment: 18 pages, 10 figures, Accepted by A
Barrier properties of films of pea starch associated with xanthan gum and glycerol
O objetivo do trabalho foi avaliar as propriedades de barreira e a solubilidade de biofilmes obtidos a partir de amido de ervilha de alto teor de amilose em associação à goma xantana e glicerol. Soluções filmogênicas (SF) com diferentes teores de amido de ervilha (3, 4 e 5%), goma xantana (0, 0,05 e 0,1%) e glicerol (proporção glicerol-amido de 1:5 P/P) foram estudadas. As SF foram obtidas por ebulição (5 minutos), seguida de autoclavagem por 1 hora a 120 ºC e os filmes foram preparados por casting. O aumento da concentração de amido e de glicerol na composição causou aumento da espessura e da solubilidade dos filmes em água. O plastificante gerou ainda elevação dos coeficientes de permeabilidade ao vapor d'água e ao oxigênio. O aumento da concentração da goma xantana não interferiu nas propriedades estudadas. Os biofilmes obtidos a partir de amido de ervilha verde, associado ou não à goma xantana e glicerol, se comparados com filmes de amido de ervilha amarelas e outras fontes de amido, apresentaram boa barreira ao oxigênio e ao vapor d'água e baixa solubilidade em água.The aim of this work was to evaluate the barrier properties and solubility of biofilms made from wrinkled pea starch with high amylose content in association with xanthan gum and glycerol. Filmogenic solution (FS) with different levels of pea starch (3, 4 and 5%), xanthan gum (0, 0.05 and 0.1%) and glycerol (glycerol-starch 1:5 W/W) were tested. FS was obtained by boiling (5 minutes), autoclaving for 1 hour at 120 ºC and the films were prepared by casting. The increased concentration of starch and glycerol in the composition caused increases in thickness of the films and in their solubility in water. The plasticizer also generated higher coefficients of water vapor and oxygen permeabilities to water vapor and to oxygen. The increasing concentration of xanthan gum did not interfere in the properties studied. Biofilms produced with wrinkled pea starch, with or without xanthan gum and glycerol, showed better barrier to oxygen and water vapor and low solubility in water, in comparison with films of yellow pea starch and other starch sources.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP
Mass modelling globular clusters in the Gaia era: a method comparison using mock data from an N-body simulation of M 4
As we enter a golden age for studies of internal kinematics and dynamics of Galactic globular clusters (GCs), it is timely to assess the performance of modelling techniques in recovering the mass, mass profile, and other dynamical properties of GCs. Here, we compare different mass-modelling techniques (distribution function (DF)-based models, Jeans models, and a grid of N-body models) by applying them to mock observations from a star-by-star N-body simulation of the GC M 4 by Heggie. The mocks mimic existing and anticipated data for GCs: surface brightness or number density profiles, local stellar mass functions, line-of-sight velocities, and Hubble Space Telescope-and Gaia-like proper motions. We discuss the successes and limitations of the methods. We find that multimass DF-based models, Jeans, and N-body models provide more accurate mass profiles compared to single-mass DF-based models. We highlight complications in fitting the kinematics in the outskirts due to energetically unbound stars associated with the cluster ('potential escapers', captured neither by truncated DF models nor by N-body models of clusters in isolation), which can be avoided with DF-based models including potential escapers, or with Jeans models. We discuss ways to account for mass segregation. For example, three-component DF-based models with freedom in their mass function are a simple alternative to avoid the biases of single-mass models (which systematically underestimate the total mass, half-mass radius, and central density), while more realistic multimass DF-based models with freedom in the remnant content represent a promising avenue to infer the total mass and the mass function of remnants
Collisionless dynamics in Globular Clusters
Since globular clusters (GCs) are old, low-N systems their dynamics is widely
believed to be fully dominated by collisional two-body processes, and their
surface brightness profiles are fit by King models. However, for many GCs,
especially those with HST-resolved central regions, and `extra-tidal' features,
King models provide poor fits. We suggest that this is partly because
collisionless dynamics is also important and contribute to shaping the cluster
properties. We show using time-scale and length-scale arguments that except for
the very centers of clusters, collisionless dynamics should be more important
than collisional. We then fit 38 GCs analyzed by Noyola and Gebhardt (2006)
with (collisional) King and (collisionless) DARKexp models over the full
available radial range, and find that the latter provide a better fit to 29
GCs; for six of these the fit is at least ~5x better in term of rms. DARKexp
models are theoretically derived maximum entropy equilibrium states of
self-gravitating collisionless systems and have already been shown to fit the
results of dark matter N-body simulations. (We do not attempt fits with ad hoc
fitting functions.)Comment: 27 pages, 18 figures; accepted to MNRA
Streamer Propagation as a Pattern Formation Problem: Planar Fronts
Streamers often constitute the first stage of dielectric breakdown in strong
electric fields: a nonlinear ionization wave transforms a non-ionized medium
into a weakly ionized nonequilibrium plasma. New understanding of this old
phenomenon can be gained through modern concepts of (interfacial) pattern
formation. As a first step towards an effective interface description, we
determine the front width, solve the selection problem for planar fronts and
calculate their properties. Our results are in good agreement with many
features of recent three-dimensional numerical simulations.Comment: 4 pages, revtex, 3 ps file
The energy budget in Rayleigh-Benard convection
It is shown using three series of Rayleigh number simulations of varying
aspect ratio AR and Prandtl number Pr that the normalized dissipation at the
wall, while significantly greater than 1, approaches a constant dependent upon
AR and Pr. It is also found that the peak velocity, not the mean square
velocity, obeys the experimental scaling of Ra^{0.5}. The scaling of the mean
square velocity is closer to Ra^{0.46}, which is shown to be consistent with
experimental measurements and the numerical results for the scaling of Nu and
the temperature if there are strong correlations between the velocity and
temperature.Comment: 5 pages, 3 figures, new version 13 Mar, 200
Bubble dynamics in DNA
The formation of local denaturation zones (bubbles) in double-stranded DNA is
an important example for conformational changes of biological macromolecules.
We study the dynamics of bubble formation in terms of a Fokker-Planck equation
for the probability density to find a bubble of size n base pairs at time t, on
the basis of the free energy in the Poland-Scheraga model. Characteristic
bubble closing and opening times can be determined from the corresponding first
passage time problem, and are sensitive to the specific parameters entering the
model. A multistate unzipping model with constant rates recently applied to DNA
breathing dynamics [G. Altan-Bonnet et al, Phys. Rev. Lett. 90, 138101 (2003)]
emerges as a limiting case.Comment: 9 pages, 2 figure
Bottleneck effects in turbulence: Scaling phenomena in r- versus p-space
We (analytically) calculate the energy spectrum corresponding to various
experimental and numerical turbulence data analyzed by Benzi et al.. We find
two bottleneck phenomena: While the local scaling exponent of the
structure function decreases monotonically, the local scaling exponent
of the corresponding spectrum has a minimum of
at and a maximum
of at . A physical
argument starting from the constant energy flux in p--space reveals the general
mechanism underlying the energy pileups at both ends of the p--space scaling
range. In the case studied here, they are induced by viscous dissipation and
the reduced spectral strength on the scale of the system size, respectively.Comment: 9 pages, 3figures on reques
Transitions and Probes in Turbulent Helium
Previous analysis of a Paris turbulence experiment \cite{zoc94,tab95} shows a
transition at the Taylor Reynolds number \rel \approx 700. Here correlation
function data is analyzed which gives further evidence for this transition. It
is seen in both the power spectrum and in structure function measurements. Two
possible explanations may be offered for this observed transition: that it is
intrinsic to the turbulence flow in this closed box experiment or that it is an
effect of a change in the flow around the anemometer. We particularly examine a
pair of ``probe effects''. The first is a thermal boundary layer which does
exist about the probe and does limit the probe response, particularly at high
frequencies. Arguments based on simulations of the response and upon
observations of dissipation suggests that this effect is only crucial beyond
\rel\approx 2000. The second effect is produced by vortex shedding behind the
probe. This has been seen to produce a large modification in some of the power
spectra for large \rel. It might also complicate the interpretation of the
experimental results. However, there seems to be a remaining range of data for
\rel < 1300 uncomplicated by these effects, and which are thus suggestive of
an intrinsic transition.Comment: uuencoded .ps files. submitted to PRE. 12 figures are sent upon
request to jane wang ([email protected]
Defective Expression and Function of the Leukocyte Associated Ig-like Receptor 1 in B Lymphocytes from Systemic Lupus Erythematosus Patients
Systemic lupus erythematosus (SLE) is characterized by the production of a wide array of autoantibodies and dysregulation of B cell function. The leukocyte associated Immunoglobulin (Ig)-like receptor (LAIR)1 is a transmembrane molecule belonging to Ig superfamily which binds to different types of collagen. Herein, we have determined the expression and function of LAIR1 on B lymphocyte from SLE patients. LAIR1 expression in peripheral blood B lymphocytes from 54 SLE, 24 mixed connective tissue disease (MCTD), 20 systemic sclerosis (SSc) patients, 14 rheumatoid arthritis (RA) and 40 sex and age matched healthy donors (HD) have been analyzed by immunofluorescence. The effect of LAIR1 ligation by specific monoclonal antibodies, collagen or collagen producing mesenchymal stromal cells from reactive lymph nodes or bone marrow on Ig production by pokeweed mitogen and B cell receptor (BCR)-mediated NF-kB activation was assessed by ELISA and TransAM assay. The percentage of CD20+ B lymphocytes lacking or showing reduced expression of LAIR1 was markedly increased in SLE and MCTD but not in SSc or RA patients compared to HD. The downregulation of LAIR1 expression was not dependent on corticosteroid therapy. Interestingly, LAIR1 engagement by collagen or collagen-producing mesenchymal stromal cells in SLE patients with low LAIR1 expression on B cells delivered a lower inhibiting signal on Ig production. In addition, NF-kB p65 subunit activation upon BCR and LAIR1 co-engagement was less inhibited in SLE patients than in HD. Our findings indicate defective LAIR1 expression and function in SLE B lymphocytes, possible contributing to an altered control of B lymphocytes behavior
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