153 research outputs found
The 1979 outburst of U Scorpii
Optical and ultraviolet observations are presented of the 1979 outburst of the recurrent nova U Sco. For the first time the evolution through outburst is documented photometrically and spectroscopically. Lines of the following ions are identified: H I, He II, C IV, N III, N IV, N V, O IV, O VI and Si IV. No forbidden lines were observed. Mg I was seen in absorption at a late stage in the decline. The Balmer lines have broad and narrow components which change with time. There is evidence that nitrogen is overabundant with respect to carbon and the helium to hydrogen number ratio is about 2
Rheophysics of dense granular materials : Discrete simulation of plane shear flows
We study the steady plane shear flow of a dense assembly of frictional,
inelastic disks using discrete simulation and prescribing the pressure and the
shear rate. We show that, in the limit of rigid grains, the shear state is
determined by a single dimensionless number, called inertial number I, which
describes the ratio of inertial to pressure forces. Small values of I
correspond to the quasi-static regime of soil mechanics, while large values of
I correspond to the collisional regime of the kinetic theory. Those shear
states are homogeneous, and become intermittent in the quasi-static regime.
When I increases in the intermediate regime, we measure an approximately linear
decrease of the solid fraction from the maximum packing value, and an
approximately linear increase of the effective friction coefficient from the
static internal friction value. From those dilatancy and friction laws, we
deduce the constitutive law for dense granular flows, with a plastic Coulomb
term and a viscous Bagnold term. We also show that the relative velocity
fluctuations follow a scaling law as a function of I. The mechanical
characteristics of the grains (restitution, friction and elasticity) have a
very small influence in this intermediate regime. Then, we explain how the
friction law is related to the angular distribution of contact forces, and why
the local frictional forces have a small contribution to the macroscopic
friction. At the end, as an example of heterogeneous stress distribution, we
describe the shear localization when gravity is added.Comment: 24 pages, 19 figure
Dual task interference during gait in patients with unilateral vestibular disorders
<p>Abstract</p> <p>Background</p> <p>Vestibular patients show slower and unsteady gait; they have also been shown to need greater cognitive resources when carrying out balance and cognitive dual tasks (DT). This study investigated DT interference during gait in a middle-aged group of subjects with dizziness and unsteadiness after unilateral vestibular neuronitis and in a healthy control group.</p> <p>Methods</p> <p>Fourteen individuals with subacute unilateral vestibular impairment after neuronitis and seventeen healthy subjects performed gait and cognitive tasks in single and DT conditions. A statistical gait analysis system was used and spatio-temporal parameters were considered. The cognitive task, consisting of backward counting by three, was tape recorded and the number of right figures was then calculated.</p> <p>Results</p> <p>Both patients and controls showed a more conservative gait during DT and between groups significant differences were not found. A significant decrease in cognitive performance during DT was found only in the vestibular group.</p> <p>Conclusions</p> <p>Results suggest that less attentional resources are available during gait in vestibular patients compared to controls, and that a priority is given in keeping up the motor task to the detriment of a decrease of the cognitive performance during DT.</p
The Relationships Among Compact Stellar Systems: A Fresh View of Ultra Compact Dwarfs
We use a combined imaging and spectroscopic survey of the nearby central
cluster galaxy, M87, to assemble a sample of 34 confirmed ultra compact dwarfs
(UCDs) with half-light radii of >~ 10 pc measured from Hubble Space Telescope
images. This doubles the existing sample in M87, making it the largest such
sample for any galaxy, while extending the detection of UCDs to unprecedentedly
low luminosities (MV = -9). With this expanded sample, we find no correlation
between size and luminosity, in contrast to previous suggestions, and no
general correlation between size and galactocentric distance. We explore the
relationships between UCDs, less luminous extended clusters (including faint
fuzzies), globular clusters (GCs), as well as early-type galaxies and their
nuclei, assembling an extensive new catalog of sizes and luminosities for
stellar systems. Most of the M87 UCDs follow a tight color-magnitude relation,
offset from the metal-poor GCs. This, along with kinematical differences,
demonstrates that most UCDs are a distinct population from normal GCs, and not
simply a continuation to larger sizes and higher luminosities. The UCD
color-magnitude trend couples closely with that for Virgo dwarf elliptical
nuclei. We conclude that the M87 UCDs are predominantly stripped nuclei. The
brightest and reddest UCDs may be the remnant nuclei of more massive galaxies
while a subset of the faintest UCDs may be tidally limited and related to more
compact star clusters. In the broader context of galaxy assembly, blue UCDs may
trace halo build-up by accretion of low-mass satellites, while red UCDs may be
markers of metal-rich bulge formation in larger galaxies.Comment: Re-submitted to the Astronomical Journal after minor revisions. 19
pages, 9 figures, 2 table
Stochastic analysis of the GAL genetic switch in Saccharomyces cerevisiae: Modeling and experiments reveal hierarchy in glucose repression
<p>Abstract</p> <p>Background</p> <p>Transcriptional regulation involves protein-DNA and protein-protein interactions. Protein-DNA interactions involve reactants that are present in low concentrations, leading to stochastic behavior. In addition, multiple regulatory mechanisms are typically involved in transcriptional regulation. In the <it>GAL </it>regulatory system of <it>Saccharomyces cerevisiae</it>, the inhibition of glucose is accomplished through two regulatory mechanisms: one through the transcriptional repressor Mig1p, and the other through regulating the amount of transcriptional activator Gal4p. However, the impact of stochasticity in gene expression and hierarchy in regulatory mechanisms on the phenotypic level is not clearly understood.</p> <p>Results</p> <p>We address the question of quantifying the effect of stochasticity inherent in these regulatory mechanisms on the performance of various genes under the regulation of Mig1p and Gal4p using a dynamic stochastic model. The stochastic analysis reveals the importance of both the mechanisms of regulation for tight expression of genes in the <it>GAL </it>network. The mechanism involving Gal4p is the dominant mechanism, yielding low variability in the expression of <it>GAL </it>genes. The mechanism involving Mig1p is necessary to maintain the switch-like response of certain <it>GAL </it>genes. The number of binding sites for Mig1p and Gal4p further influences the expression of the genes, with extra binding sites lowering the variability of expression. Our experiments involving growth on various substrates show that the trends predicted in mean expression and its variability are transmitted to the phenotypic level.</p> <p>Conclusion</p> <p>The mechanisms involved in the transcriptional regulation and their variability set up a hierarchy in the phenotypic response to growth on various substrates. Structural motifs, such as the number of binding sites and the mechanism of regulation, determine the level of stochasticity and eventually, the phenotypic response.</p
VIII SeminĂĄrio de Pesquisas em Andamento e IV Encontro de Egressos (PGET/UFSC) : Caderno de Resumos e Artigos
Editoria: FlorianĂłpolis: Universidade Federal de Santa Catarina, 2015. PĂĄginas: 262 p. LĂngua da publicação: PortuguĂȘs ReferĂȘncia ABNT: Guerini, AndrĂ©ia; Andrade, Adriana Aikawa da Silveira; Sousa, AĂda Carla Rangel de; Riconi, AndrĂ©ia; Marini, Clarissa Prado; Gonçalves, Davi; Bignardi, Ingrid; Abreu, Juliana de; Sales, Kall; Gonzalez, Mara; Cherobin, Nicoletta; Costa, PatrĂcia Rodrigues; Silva, Rodrigo DâĂvila Braga; Santos, Saionara Figuereido; Hanes, Vanessa Lopes Lourenço (Orgs.). VIII SeminĂĄrio de Pesquisas em Andamento e IV Encontro de Egressos (PGET/UFSC) : Caderno de Resumos e Artigos. FlorianĂłpolis: Universidade Federal de Santa Catarina, 2015. 262 p
Transgenic Expression of Entire Hepatitis B Virus in Mice Induces Hepatocarcinogenesis Independent of Chronic Liver Injury
Hepatocellular carcinoma (HCC), the third leading cause of cancer deaths worldwide, is most commonly caused by chronic hepatitis B virus (HBV) infection. However, whether HBV plays any direct role in carcinogenesis, other than indirectly causing chronic liver injury by inciting the host immune response, remains unclear. We have established two independent transgenic mouse lines expressing the complete genome of a mutant HBV (âpreS2 mutantâ) that is found at much higher frequencies in people with HCC than those without. The transgenic mice show evidence of stress in the endoplasmic reticulum (ER) and overexpression of cyclin D1 in hepatocytes. These mice do not show any evidence of chronic liver injury, but by 2 years of age a majority of the male mice develop hepatocellular neoplasms, including HCC. Unexpectedly, we also found a significant increase in hepatocarcinogenesis independent of necroinflammation in a transgenic line expressing the entire wildtype HBV. As in the mutant HBV mice, HCC was found only in agedâ2-year-oldâmice of the wildtype HBV line. The karyotype in all the three transgenic lines appears normal and none of the integration sites of the HBV transgene in the mice is near an oncogene or tumor suppressor gene. The significant increase of HCC incidence in all the three transgenic linesâexpressing either mutant or wildtype HBVâtherefore argues strongly that in absence of chronic necroinflammation, HBV can contribute directly to the development of HCC
Wide-Field Precision Kinematics of the M87 Globular Cluster System
We present the most extensive combined photometric and spectroscopic study to
date of the enormous globular cluster (GC) system around M87, the central giant
elliptical galaxy in the nearby Virgo cluster. Using observations from DEIMOS
and LRIS at Keck, and Hectospec on the MMT, we derive new, precise radial
velocities for 451 GCs around M87, with projected radii from ~ 5 to 185 kpc. We
combine these measurements with literature data for a total sample of 737
objects, which we use for a re-examination of the kinematics of the GC system
of M87. The velocities are analyzed in the context of archival wide-field
photometry and a novel Hubble Space Telescope catalog of half-light radii,
which includes sizes for 344 spectroscopically confirmed clusters. We use this
unique catalog to identify 18 new candidate ultra-compact dwarfs, and to help
clarify the relationship between these objects and true GCs.
We find much lower values for the outer velocity dispersion and rotation of
the GC system than in earlier papers, and also differ from previous work in
seeing no evidence for a transition in the inner halo to a potential dominated
by the Virgo cluster, nor for a truncation of the stellar halo. We find little
kinematical evidence for an intergalactic GC population. Aided by the precision
of the new velocity measurements, we see significant evidence for kinematical
substructure over a wide range of radii, indicating that M87 is in active
assembly. A simple, scale-free analysis finds less dark matter within ~85 kpc
than in other recent work, reducing the tension between X-ray and optical
results. In general, out to a projected radius of ~ 150 kpc, our data are
consistent with the notion that M87 is not dynamically coupled to the Virgo
cluster; the core of Virgo may be in the earliest stages of assembly.Comment: 47 pages, ApJS in press. Redacted long data tables available on
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A competitive integration model of exogenous and endogenous eye movements
We present a model of the eye movement system in which the programming of an eye movement is the result of the competitive integration of information in the superior colliculi (SC). This brain area receives input from occipital cortex, the frontal eye fields, and the dorsolateral prefrontal cortex, on the basis of which it computes the location of the next saccadic target. Two critical assumptions in the model are that cortical inputs are not only excitatory, but can also inhibit saccades to specific locations, and that the SC continue to influence the trajectory of a saccade while it is being executed. With these assumptions, we account for many neurophysiological and behavioral findings from eye movement research. Interactions within the saccade map are shown to account for effects of distractors on saccadic reaction time (SRT) and saccade trajectory, including the global effect and oculomotor capture. In addition, the model accounts for express saccades, the gap effect, saccadic reaction times for antisaccades, and recorded responses from neurons in the SC and frontal eye fields in these tasks. © The Author(s) 2010
A Role for Non-Antimicrobial Actions of Tetracyclines in Combating Oxidative Stress in Periodontal and Metabolic Diseases: A Literature Review
This review addresses the role of adjunctive tetracycline therapy in the management of periodontal diseases and its efficacy in reducing inflammatory burden, oxidative stress and its sequelae in patients with coexisting features of metabolic syndrome. Removal of the dimethylamine group at C4 of the tetracycline molecule reduces its antibiotic properties, enhancing its non-antimicrobial actions; this strategy has aided the development of several chemically modified tetracyclines such as minocycline and doxycycline, by altering different regions of the molecule for focused action on biological targets. Tetracyclines are effective in reducing inflammation by inhibiting matrix metalloproteinases, preventing excessive angiogenesis, inhibiting apoptosis and stimulating bone formation. There are important applications for tetracyclines in the management of diabetic, dyslipidaemic periodontal patients who smoke. The diverse mechanisms of action of tetracyclines in overcoming oxidative stress and enhancing matrix synthesis are discussed in this review
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