19,783 research outputs found
On the Optical -- X-ray correlation from outburst to quiescence in Low Mass X-ray Binaries: the representative cases of V404 Cyg and Cen X-4
Low mass X-ray binaries (LMXBs) show evidence of a global correlation of
debated origin between X-ray and optical luminosity. We study for the first
time this correlation in two transient LMXBs, the black hole V404 Cyg and the
neutron star Cen X-4, over 6 orders of magnitude in X-ray luminosity, from
outburst to quiescence. After subtracting the contribution from the companion
star, the Cen X-4 data can be described by a single power law correlation of
the form , consistent with disk reprocessing. We
find a similar correlation slope for V404 Cyg in quiescence (0.46) and a
steeper one (0.56) in the outburst hard state of 1989. However, V404 Cyg is
about times optically brighter, at a given keV X-ray
luminosity, compared to Cen X-4. This ratio is a factor of 10 smaller in
quiescence, where the normalization of the V404 Cyg correlation also changes.
We show that once the bolometric X-ray emission is considered and the known
main differences between V404 Cyg and Cen X-4 are taken into account (a larger
compact object mass, accretion disk size, and the presence of a strong jet
contribution in the hard state for the black hole system) the two systems lie
on the same correlation. In V404 Cyg, the jet dominates spectrally at
optical-infrared frequencies during the hard state, but makes a negligible
contribution in quiescence, which may account for the change in its correlation
slope and normalization. These results provide a benchmark to compare with data
from the 2015 outburst of V404 Cyg and, potentially, other transient LMXBs as
well.Comment: Accepted on ApJ, 12 pages, 4 figures, 4 table
Sinuosity and the affect grid: A method for adjusting repeated mood scores
Copyright @ 2012 Ammons Scientific. The article can be accessed from the links below.This article has been made available through the Brunel Open Access Publishing Fund.Sinuosity is a measure of how much a travelled pathway deviates from a straight line. In this paper, sinuosity is applied to the measurement of mood. The Affect Grid is a mood scale that requires participants to place a mark on a 9 x 9 grid to indicate their current mood. The grid has two dimensions: pleasure-displeasure (horizontal) and arousal-sleepiness (vertical). In studies where repeated measurements are required, some participants may exaggerate their mood shifts due to faulty interpretation of the scale or a feeling of social obligation to the experimenter. A new equation is proposed, based on the sinuosity measure in hydrology, a measure of the meandering of rivers. The equation takes into account an individual's presumed tendency to exaggerate and meander to correct the score and reduce outliers. The usefulness of the equation is demonstrated by applying it to Affect Grid data from another study.This article is made available through the Brunel Open Access Publishing Fund
Noise-induced dynamical transition in systems with symmetric absorbing states
We investigate the effect of noise strength on the macroscopic ordering
dynamics of systems with symmetric absorbing states. Using an explicit
stochastic microscopic model, we present evidence for a phase transition in the
coarsening dynamics, from an Ising-like to a voter-like behavior, as the noise
strength is increased past a nontrivial critical value. By mapping to a thermal
diffusion process, we argue that the transition arises due to locally-absorbing
states being entered more readily in the high-noise regime, which in turn
prevents surface tension from driving the ordering process.Comment: v2 with improved introduction and figures, to appear in PRL. 4 pages,
4 figure
Flat-top oscillons in an expanding universe
Oscillons are extremely long lived, oscillatory, spatially localized field
configurations that arise from generic initial conditions in a large number of
non-linear field theories. With an eye towards their cosmological implications,
we investigate their properties in an expanding universe. We (1) provide an
analytic solution for one dimensional oscillons (for the models under
consideration) and discuss their generalization to 3 dimensions, (2) discuss
their stability against long wavelength perturbations and (3) estimate the
effects of expansion on their shapes and life-times. In particular, we discuss
a new, extended class of oscillons with surprisingly flat tops. We show that
these flat topped oscillons are more robust against collapse instabilities in
(3+1) dimensions than their usual counterparts. Unlike the solutions found in
the small amplitude analysis, the width of these configurations is a
non-monotonic function of their amplitudes.Comment: v2-matches version published in Phys. Rev D. Updated references and
minor modification to section 4.
Comment on "Control landscapes are almost always trap free: a geometric assessment"
We analyze a recent claim that almost all closed, finite dimensional quantum
systems have trap-free (i.e., free from local optima) landscapes (B. Russell
et.al. J. Phys. A: Math. Theor. 50, 205302 (2017)). We point out several errors
in the proof which compromise the authors' conclusion.
Interested readers are highly encouraged to take a look at the "rebuttal"
(see Ref. [1]) of this comment published by the authors of the criticized work.
This "rebuttal" is a showcase of the way the erroneous and misleading
statements under discussion will be wrapped up and injected in their future
works, such as R. L. Kosut et.al, arXiv:1810.04362 [quant-ph] (2018).Comment: 6 pages, 1 figur
Conceptual mechanization studies for a horizon definition spacecraft structures and thermal subsystem
Conceptual mechanization for horizon definition spacecraft structures and thermal subsystem - spin-stabilized, hexagonal cylinder for launch of two-stage Improved Delta /DSV-3N
Results of the Mariner 6 and 7 Mars occultation experiments
Final profiles of temperature, pressure, and electron density on Mars were obtained for the Mariner 6 and 7 entry and exit cases, and results are presented for both the lower atmosphere and ionosphere. The results of an analysis of the systematic and formal errors introduced at each stage of the data-reduction process are also included. At all four occulation points, the lapse rate of temperature was subdadiabatic up to altitudes in excess of 20 km. A pronounced temperature inversion was present above the surface at the Mariner 6 exit point. All four profiles exhibit a sharp, superadiabatic drop in temperature at high altitudes, with temperatures falling below the frost point of CO2. These results give a strong indication of frozen CO2 in the middle atmosphere of Mars
Pyrophosphate: a key inhibitor of mineralisation
Inorganic pyrophosphate has long been known as a by-product of many intracellular biosynthetic reactions, and was first identified as a key endogenous inhibitor of biomineralisation in the 1960s. The major source of pyrophosphate appears to be extracellular ATP, which is released from cells in a controlled manner. Once released, ATP can be rapidly hydrolysed by ecto-nucleotide pyrophosphatase/phosphodiesterases to produce pyrophosphate. The main action of pyrophosphate is to directly inhibit hydroxyapatite formation thereby acting as a physiological 'water-softener'. Evidence suggests pyrophosphate may also act as a signalling molecule to influence gene expression and regulate its own production and breakdown. This review will summarise our current understanding of pyrophosphate metabolism and how it regulates bone mineralisation and prevents harmful soft tissue calcification
Multi-Wavelength Implications of the Companion Star in Eta Carinae
Eta Carinae is considered to be a massive colliding wind binary system with a
highly eccentric (e \sim 0.9), 5.54-yr orbit. However, the companion star
continues to evade direct detection as the primary dwarfs its emission at most
wavelengths. Using three-dimensional (3-D) SPH simulations of Eta Car's
colliding winds and radiative transfer codes, we are able to compute synthetic
observables across multiple wavebands for comparison to the observations. The
models show that the presence of a companion star has a profound influence on
the observed HST/STIS UV spectrum and H-alpha line profiles, as well as the
ground-based photometric monitoring. Here, we focus on the Bore Hole effect,
wherein the fast wind from the hot secondary star carves a cavity in the dense
primary wind, allowing increased escape of radiation from the hotter/deeper
layers of the primary's extended wind photosphere. The results have important
implications for interpretations of Eta Car's observables at multiple
wavelengths.Comment: 5 pages, 4 figures, To be published in the proceedings of the meeting
'Four Decades of Research on Massive Stars' in honor of Tony Moffat, 11-15
July 2011, Saint-Michel-des-Saints, Quebe
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