2,386 research outputs found
Two of the three actin-binding domains of gelsolin bind to the same subdomain of actin Implications for capping and severing mechanisms
AbstractGelsolin binds two monomers in the nucleating complex with G-actin in calcium and caps actin filaments. However, 3 actin-binding domains have been identified within its 6 repeating sequence segments corresponding to S1,S2–3 and S4–6, S1 and S4–6 bind only G-actin whereas S2–3 binds specifically to F-actin. Two of the three domains (S2–3 and S4–6) are required for nucleation and a different pair (S1 and S2–3) for severing. Here we show for the first time that the domains unique to nucleation (S4–6) or severing (S1) compete for the same region on subdomain 1 of G-actin. We further show that S2–3 binds actin monomers weakly in G-buffer conditions and that this interaction persists when S1 or S4–6 are also bound. Thus gelsolin associates with two distinct regions on actin. Since S2–3 does not bind monomeric actin in F-buffer, we suggest that its high affinity 1:1 stoichiometry for filament subunits reflects interaction with two adjacent subunits
Areas and entropies in BFSS/gravity duality
The BFSS matrix model provides an example of gauge-theory / gravity duality
where the gauge theory is a model of ordinary quantum mechanics with no spatial
subsystems. If there exists a general connection between areas and entropies in
this model similar to the Ryu-Takayanagi formula, the entropies must be more
general than the usual subsystem entanglement entropies. In this note, we first
investigate the extremal surfaces in the geometries dual to the BFSS model at
zero and finite temperature. We describe a method to associate regulated areas
to these surfaces and calculate the areas explicitly for a family of surfaces
preserving symmetry, both at zero and finite temperature. We then
discuss possible entropic quantities in the matrix model that could be dual to
these regulated areas.Comment: 29 pages, 3 figures. v2 Examples in section 6 moved to appendix.
Minor comments adde
X-ray Over-Luminous Elliptical Galaxies: A New Class of Mass Concentrations in the Universe?
We detect four isolated, X-ray over-luminous (Lx>2e43 [h/0.5]**-2 erg/s)
elliptical galaxies (OLEGs) in our 160 square degree ROSAT PSPC survey. The
extent of their X-ray emission, total X-ray luminosity, total mass, and mass of
the hot gas in these systems correspond to poor clusters, and the optical
luminosity of the central galaxies (M_R<-22.5 + 5 lg h) is comparable to that
of cluster cDs. However, there are no detectable fainter galaxy concentrations
around the central elliptical. The mass-to-light ratio within the radius of
detectable X-ray emission is in the range 250-450 Msun/Lsun, which is 2-3 times
higher than typically found in clusters or groups. These objects can be the
result of galaxy merging within a group. However, their high M/L values are
difficult to explain in this scenario. OLEGs must have been undisturbed for a
very long time, which makes them the ultimate examples of systmes in
hydrostatic equilibrium. The number density of OLEGs is n=2.4(+3.1-1.2}x10**-7
(h/0.5)**-3 Mpc**-3 at the 90% confidence. They comprise 20% of all clusters
and groups of comparable X-ray luminosity, and nearly all galaxies brighter
than M_R=-22.5. The estimated contirubution of OLEGs to the total mass density
in the Universe is close to that of T>7 keV clusters.Comment: 4 pages, 2 figures, uses emulateapj.sty, submitted to ApJ Letter
Novel Methods for Predicting Photometric Redshifts from Broad Band Photometry using Virtual Sensors
We calculate photometric redshifts from the Sloan Digital Sky Survey Main
Galaxy Sample, The Galaxy Evolution Explorer All Sky Survey, and The Two Micron
All Sky Survey using two new training-set methods. We utilize the broad-band
photometry from the three surveys alongside Sloan Digital Sky Survey measures
of photometric quality and galaxy morphology. Our first training-set method
draws from the theory of ensemble learning while the second employs Gaussian
process regression both of which allow for the estimation of redshift along
with a measure of uncertainty in the estimation. The Gaussian process models
the data very effectively with small training samples of approximately 1000
points or less. These two methods are compared to a well known Artificial
Neural Network training-set method and to simple linear and quadratic
regression. Our results show that robust photometric redshift errors as low as
0.02 RMS can regularly be obtained. We also demonstrate the need to provide
confidence bands on the error estimation made by both classes of models. Our
results indicate that variations due to the optimization procedure used for
almost all neural networks, combined with the variations due to the data
sample, can produce models with variations in accuracy that span an order of
magnitude. A key contribution of this paper is to quantify the variability in
the quality of results as a function of model and training sample. We show how
simply choosing the "best" model given a data set and model class can produce
misleading results.Comment: 36 pages, 12 figures, ApJ in Press, modified to reflect published
version and color figure
Recommended from our members
Preliminary Evidence That CD38 Moderates the Association of Neuroticism on Amygdala-Subgenual Cingulate Connectivity.
CD38 genetic variation has been associated with autism spectrum disorders and social anxiety disorder, which may result from CD38's regulation of oxytocin secretion. Converging evidence has found that the rs3796863 A-allele contributes to increased social sensitivity compared to the CC genotype. The current study examined the moderating role of CD38 genetic variants (rs3796863 and rs6449182) that have been associated with enhanced (or reduced) social sensitivity on neural activation related to neuroticism, which is commonly elevated in individuals with social anxiety and depression. Adults (n = 72) with varying levels of social anxiety and depression provided biological samples for DNA extraction, completed a measure of neuroticism, and participated in a standardized emotion processing task (affect matching) while undergoing fMRI. A significant interaction effect was found for rs3796863 x neuroticism that predicted right amygdala-subgenual anterior cingulate cortex (sgACC) functional connectivity. Simple slopes analyses showed a positive association between neuroticism and right amygdala-sgACC connectivity among rs3796863 A-allele carriers. Findings suggest that the more socially sensitive rs3796863 A-allele may partially explain the relationship between a known risk factor (i.e. neuroticism) and promising biomarker (i.e. amygdala-sgACC connectivity) in the development and maintenance of social anxiety and depression
Evidence for a role of the oxytocin system, indexed by genetic variation in CD38 , in the social bonding effects of expressed gratitude
Oxytocin is thought to play a central role in promoting close social bonds via influence on social interactions. The current investigation targeted interactions involving expressed gratitude between members of romantic relationships because recent evidence suggests gratitude and its expression provides behavioral and psychological ‘glue’ to bind individuals closer together. Specifically, we took a genetic approach to test the hypothesis that social interactions involving expressed gratitude would be associated with variation in a gene, CD38, which has been shown to affect oxytocin secretion. A polymorphism (rs6449182) that affects CD38 expression was significantly associated with global relationship satisfaction, perceived partner responsiveness and positive emotions (particularly love) after lab-based interactions, observed behavioral expression of gratitude toward a romantic partner in the lab, and frequency of expressed gratitude in daily life. A separate polymorphism in CD38 (rs3796863) previously associated with plasma oxytocin levels and social engagement was also associated with perceived responsiveness in the benefactor after an expression of gratitude. The combined influence of the two polymorphisms was associated with a broad range of gratitude-related behaviors and feelings. The consistent pattern of findings suggests that the oxytocin system is associated with solidifying the glue that binds adults into meaningful and important relationships
Tides on Other Earths: Implications for Exoplanet and Palaeo-Tidal Simulations
A key controller of a planet's rotational evolution, and hence habitability, is tidal dissipation, which on Earth is dominated by the ocean tides. Because exoplanet or deep‐time Earth topographies are unknown, a statistical ensemble is used to constrain possible tidal dissipation rates on an Earth‐like planet. A dedicated tidal model is used together with 120 random continental configurations to simulate Earth's semidiurnal lunar tide. The results show a possible ocean tidal dissipation range spanning 3 orders of magnitude, between 2.3 GWto 1.9 TW (1 TW=1012 W). When model resolution is considered, this compares well with theoretical limits derived for the energetics of Earth's present‐day deep ocean. Consequently, continents exert a fundamental control on tidal dissipation rates and we suggest that plate tectonics on a planet will induce a time‐varying dissipation analogous to Earth's. This will alter rotational periods over millions of years and further complicate the role of tides for planetary evolution. Plain Language Summary The daylength of a planet is key for habitability because it regulates the rate with which solar radiation is received and redistributed at the surface. A main controller of a planet's daylength is the ocean tide, because the dissipation of tidal energy works as a brake on the planet's spin, increasing the daylength. Tides are sensitive to the continental arrangement on a planet, but there are no details of the surface of any exoplanet and only limited information of what Earth looked like in the distant past. The change in Earth's daylength forces the Moon to recede into a higher orbit, but the present‐day recession rate is very high and does not fit our age models of the moon, implying that the tides must have been much weaker in the distant past. Here, we use a series of tidal predictions for random continental configurations of Earth to provide a range of tidal dissipation rates and thus an estimate of how the tides in the deep past may have evolved as Earth's continents grew more and more complex. This research also provides a range of dissipation rates that can be used for simulations of the rotational and orbital evolution of exoplanets
- …