8,139 research outputs found
Detailed state model of CaMKII activation and autophosphorylation
By combining biochemical experiments with computer modelling of biochemical reactions we elucidated some of the currently unresolved aspects of calcium-calmodulin-dependent protein kinase II (CaMKII) activation and autophosphorylation that might be relevant for its physiological function and provided a model that incorporates in detail the mechanism of CaMKII activation and autophosphorylation at T286 that is based on experimentally determined binding constants and phosphorylation rates. To this end, we developed a detailed state model of CaMKII activation and autophosphorylation based on the currently available literature, and constrained it with data from CaMKII autophosphorylation essays. Our model takes exact phosphorylation patterns of CaMKII holoenzymes into account, and is valid at physiologically relevant conditions where the concentrations of calcium and calmodulin are not saturating. Our results strongly suggest that even when bound to less than fully calcium-bound calmodulin, CaMKII is in the active state, and indicate that the autophosphorylation of T286 by an active non-phosphorylated CaMKII subunit is significantly faster than by an autophosphorylated CaMKII subunit. These results imply that CaMKII can be efficiently activated at significantly lower calcium concentrations than previously thought, which may explain how CaMKII gets activated at calcium concentrations existing at synapses in vivo. We also investigated the significance of CaMKII holoenzyme structure on CaMKII autophosphorylation and obtained estimates of previously unknown binding constants
The Economic Effects of Unions in Latin America: Their Impact on Wages and the Economic Performance of Firms in Uruguay
This study examines the impact of unionization and the level of centralization in bargaining, at the level of the industry or the firm, on wages and on the economic performance of firms within the manufacturing sector in Uruguay, using a panel of establishments for the period 1988 to 1995. In doing so, we control for the degree of exposure to international and regional competition as well as for industry and firm characteristics. The main findings suggest that unionization increases wages and employment and promotes investment due to firms substituting labor by capital. Unions tend to organize in those plants with highest rates of profits, but promote increases in productivity and prevent profitability increases. The mechanism at work seems to be that firms moved to more capital-intensive technologies, hence increasing the rate of growth of labor productivity and reducing that of profitability. Given the negative effect of unionization at the industry level on the rate of growth of profitability of firms, results also suggest that unions tended to organize and to be stronger in those sectors in which extra rents were higher due to monopoly power. The evidence also suggests that firm-level negotiations take into account the interests of both parties, so that enhanced productivity and probably survival were achieved together with lower rates of substitution between labor and capital and/or lower profits.
An exact formalism to study the thermodynamic properties of hard-sphere systems under spherical confinement
This paper presents a modified grand canonical ensemble which provides a new
simple and efficient scheme to study few-body fluid-like inhomogeneous systems
under confinement. The new formalism is implemented to investigate the exact
thermodynamic properties of a hard sphere (HS) fluid-like system with up to
three particles confined in a spherical cavity. In addition, the partition
function of this system was used to analyze the surface thermodynamic
properties of the many-HS system and to derive the exact curvature dependence
of both the surface tension and adsorption in powers of the density. The
expressions for the surface tension and the adsorption were also obtained for
the many- HS system outside of a fixed hard spherical object. We used these
results to derive the dependence of the fluid-substrate Tolman length up to
first order in density.Comment: 6 figures. The paper includes new exact results about hard spheres
fluid-like system
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Shape Morphing Using PDE Surfaces
NoA methodology for shape morphing using partial differential
equation (PDE) surfaces is presented in this work.
The use of the PDE formulation shows how shape morphing
can be based on a boundary-value approach by which
intermediate shapes can be created. Furthermore, the
mathematical properties of the method give rise to several
alternatives in which morphing one shape into another
can be achieved. Three of these alternatives are presented
here. The first one is based on the gradual variation of
the weighted sum of the boundary conditions for each
surface, the second one consists of varying the Fourier
mode for which the PDE is solved whilst the third results
from a combination of the first two. Examples showing the
efficiency of these methodologies are presented. Thus, it is
shown that the PDE based approach for morphing, when
combined with a parametric variation of the boundary
conditions, is capable of obtaining smooth intermediate
surfaces automatically
Spectroscopy of Close Companions to QSOs and the Ages of Interaction-Induced Starbursts
We present low-resolution absorption-line spectra of three candidate close (
< 3 arcsec) companions to the low redshift QSOs 3CR 323.1, PG 1700+518, and PKS
2135-147. The spectra were obtained with LRIS on the Keck telescopes and with
the Faint Object Spectrograph on the University of Hawaii 2.2 m telescope. For
3CR 323.1 and PG 1700+518, we measure relative velocities that are consistent
with an association between the QSOs and their companion galaxies. The spectral
features of the companion galaxy to 3CR 323.1 indicate a stellar population of
intermediate age (approx. 2.3 Gyr). In contrast, the spectrum of the companion
object to PG 1700+518 shows strong Balmer absorption lines from a relatively
young stellar population, along with the Mg Ib absorption feature and the 4000
A break from an older population. By modeling the two stellar components of
this spectrum, it is possible to estimate the time that has elapsed since the
end of the most recent major starburst event: we obtain approx. 0.1 Gyr. This
event may have coincided with an interaction that triggered the QSO activity.
Finally, our spectroscopy shows conclusively that the supposed companion to PKS
2135-147 is actually a projected Galactic G star.Comment: 10 pages, 5 Postscript figures. Latex (AASTEX). To appear in ApJ.
Letters, Volume 480 (1997
Non-thermal radiation from Cygnus X-1 corona
Cygnus X-1 was the first X-ray source widely accepted to be a black hole
candidate and remains among the most studied astronomical objects in its class.
The detection of non-thermal radio, hard X-rays and gamma rays reveals the fact
that this kind of objects are capable of accelerating particles up to very high
energies.
In order to explain the electromagnetic emission from Cygnus X-1 in the
low-hard state we present a model of a black hole corona with both relativistic
lepton and hadron content. We characterize the corona as a two-temperature hot
plasma plus a mixed non-thermal population in which energetic particles
interact with magnetic, photon and matter fields. Our calculations include the
radiation emitted by secondary particles (pions, muons and electron/positron
pairs). Finally, we take into account the effects of photon absorption. We
compare the results obtained from our model with data of Cygnus X-1 obtained by
the COMPTEL instrument.Comment: 6 pages, 10 figures, presented as a poster in HEPRO II, Buenos Aires,
Argentina, October 26-30 2009 / accepted for publication in Int. Jour. Mod.
Phys.
Neutrino oscillation probabilities through the looking glass
In this paper we review different expansions for neutrino oscillation
probabilities in matter in the context of long-baseline neutrino experiments.
We examine the accuracy and computational efficiency of different exact and
approximate expressions. We find that many of the expressions used in the
literature are not precise enough for the next generation of long-baseline
experiments, but several of them are while maintaining comparable simplicity.
The results of this paper can be used as guidance to both phenomenologists and
experimentalists when implementing the various oscillation expressions into
their analysis tools.Comment: 32 pages, 6 figure
DNA meets the SVD
This paper introduces an important area of computational cell biology where complex, publicly available genomic data is being examined by linear algebra methods, with the aim of revealing biological and medical insights
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