Modulation of AMPA receptor surface diffusion restores hippocampal plasticity and memory in Huntington’s disease models

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Physical properties underlying observed kinematics of satellite galaxies

We study the kinematics of satellites around isolated galaxies selected from the Sloan Digital Sky Survey (SDSS) spectroscopic catalog. Using a model of the phase-space density previously measured for the halos of LCDM dark matter cosmological simulations, we determine the properties of the halo mass distribution and the orbital anisotropy of the satellites as a function of the colour-based morphological type and the stellar mass of the central host galaxy. We place constraints on the halo mass and the concentration parameter of dark matter and the satellite number density profiles. We obtain a concentration-mass relation for galactic dark matter haloes that is consistent with predictions of a standard LCDM cosmological model. At given halo or stellar mass, red galaxies have more concentrated halos than their blue counterparts. The fraction of dark matter within a few effective radii is minimal for 11.25<log M_star<11.5. The number density profile of the satellites appears to be shallower than of dark matter, with the scale radius typically 60 per cent larger than of dark matter. The orbital anisotropy around red hosts exhibits a mild excess of radial motions, in agreement with the typical anisotropy profiles found in cosmological simulations, whereas blue galaxies are found to be consistent with an isotropic velocity distribution. Our new constraints on the halo masses of galaxies are used to provide analytic approximations of the halo-to-stellar mass relation for red and blue galaxies.Comment: 12 pages, 11 figures; accepted for publication in MNRAS (updated references

The non-evolving internal structure of early-type galaxies: the case study SDSS J0728+3835 at z = 0.206

We study the internal dynamical structure of the early-type lens galaxy SDSS J0728+3835 at z = 0.206. The analysis is based on two-dimensional kinematic maps extending out to 1.7 effective radii obtained from Keck spectroscopy, on lensing geometry and on stellar mass estimates obtained from multiband Hubble Space Telescope imaging. The data are modelled under the assumptions of axial symmetry supported by a two-integral distribution function (DF), by applying the combined gravitational lensing and stellar dynamics code CAULDRON, and yielding high-quality constraints for an early-type galaxy at cosmological redshifts. Modelling the total density profile as a power-law of the form rho_tot ~ 1/r^{gamma}, we find that it is nearly isothermal (logarithmic slope gamma = 2.08^{+0.04}_{-0.02}), and quite flattened (axial ratio q = 0.60^{+0.08}_{-0.03}). The galaxy is mildly anisotropic (delta = 0.08 +/- 0.02) and shows a fair amount of rotational support, in particular towards the outer regions. We determine a dark matter fraction lower limit of 28 per cent within the effective radius. The stellar contribution to the total mass distribution is close to maximal for a Chabrier initial mass function (IMF), whereas for a Salpeter IMF the stellar mass exceeds the total mass within the galaxy inner regions. We find that the combination of a NFW dark matter halo with the maximally rescaled luminous profile provides a remarkably good fit to the total mass distribution over a broad radial range. Our results confirm and expand the findings of the SLACS survey for early-type galaxies of comparable velocity dispersion (sigma_SDSS = 214 +/- 11 km/s). The internal structure of J0728 is consistent with that of local early-type galaxies of comparable velocity dispersion as measured by the SAURON project, suggesting lack of evolution in the past two billion years.Comment: 13 pages, 10 figures. MNRAS in press. Revised to match accepted versio

Using NMAGIC to probe the dark matter halo and orbital structure of the X-ray bright, massive elliptical galaxy, NGC 4649

We create dynamical models of the massive elliptical galaxy, NGC 4649, using the N-body made-to-measure code, NMAGIC, and kinematic constraints from long-slit and planetary nebula (PN) data. We explore a range of potentials based on previous determinations from X-ray observations and a dynamical model fitting globular cluster (GC) velocities and a stellar density profile. The X-ray mass distributions are similar in the central region but have varying outer slopes, while the GC mass profile is higher in the central region and on the upper end of the range further out. Our models cannot differentiate between the potentials in the central region, and therefore if non-thermal pressures or multi-phase components are present in the hot gas, they must be smaller than previously inferred. In the halo, we find that the PN velocities are sensitive tracers of the mass, preferring a less massive halo than that derived from the GC mass profile, but similar to one of the mass distributions derived from X-rays. Our results show that the GCs may form a dynamically distinct system, and that the properties of the hot gas derived from X-rays in the outer halo have considerable uncertainties that need to be better understood. Estimating the mass in stars using photometric information and a stellar population mass-to-light ratio, we infer a dark matter mass fraction in NGC 4649 of ~0.39 at 1Re (10.5 kpc) and ~0.78 at 4Re. We find that the stellar orbits are isotropic to mildly radial in the central ~6 kpc depending on the potential assumed. Further out, the orbital structure becomes slightly more radial along R and more isotropic along z, regardless of the potential assumed. In the equatorial plane, azimuthal velocity dispersions dominate over meridional velocity dispersions, implying that meridional velocity anisotropy is the mechanism for flattening the stellar system.Comment: 17 pages, 15 figures, accepted in MNRA

The stellar and sub-stellar IMF of simple and composite populations

The current knowledge on the stellar IMF is documented. It appears to become top-heavy when the star-formation rate density surpasses about 0.1Msun/(yr pc^3) on a pc scale and it may become increasingly bottom-heavy with increasing metallicity and in increasingly massive early-type galaxies. It declines quite steeply below about 0.07Msun with brown dwarfs (BDs) and very low mass stars having their own IMF. The most massive star of mass mmax formed in an embedded cluster with stellar mass Mecl correlates strongly with Mecl being a result of gravitation-driven but resource-limited growth and fragmentation induced starvation. There is no convincing evidence whatsoever that massive stars do form in isolation. Various methods of discretising a stellar population are introduced: optimal sampling leads to a mass distribution that perfectly represents the exact form of the desired IMF and the mmax-to-Mecl relation, while random sampling results in statistical variations of the shape of the IMF. The observed mmax-to-Mecl correlation and the small spread of IMF power-law indices together suggest that optimally sampling the IMF may be the more realistic description of star formation than random sampling from a universal IMF with a constant upper mass limit. Composite populations on galaxy scales, which are formed from many pc scale star formation events, need to be described by the integrated galactic IMF. This IGIMF varies systematically from top-light to top-heavy in dependence of galaxy type and star formation rate, with dramatic implications for theories of galaxy formation and evolution.Comment: 167 pages, 37 figures, 3 tables, published in Stellar Systems and Galactic Structure, Vol.5, Springer. This revised version is consistent with the published version and includes additional references and minor additions to the text as well as a recomputed Table 1. ISBN 978-90-481-8817-

Selenomethionine Incorporation into Amyloid Sequences Regulates Fibrillogenesis and Toxicity

The capacity of a polypeptide chain to engage in an amyloid formation process and cause a conformational disease is contained in its sequence. Some of the sequences undergoing fibrillation contain critical methionine (Met) residues which in vivo can be synthetically substituted by selenomethionine (SeM) and alter their properties

The Physics of the B Factories

This work is on the Physics of the B Factories. Part A of this book contains a brief description of the SLAC and KEK B Factories as well as their detectors, BaBar and Belle, and data taking related issues. Part B discusses tools and methods used by the experiments in order to obtain results. The results themselves can be found in Part C

Bidirectional fluxes of spermine across the mitochondrial membrane.

The polyamine spermine is transported into the mitochondrial matrix by an electrophoretic mechanism having as driving force the negative electrical membrane potential (DW). The presence of phosphate increases spermine uptake by reducingDpH and enhancingDW. The transport system is a specific uniporter constituted by a protein channel exhibiting two asymmetric energy barriers with the spermine binding site located in the energy well between the two barriers. Although spermine transport is electrophoretic in origin, its accumulation does not follow the Nernst equation for the presence of an efflux pathway. Spermine efflux may be induced by different agents, such as FCCP, antimycin A and mersalyl, able to completely or partially reduce theDWvalue and, consequently, suppress or weaken the force necessary to maintain spermine in the matrix. However this efflux may also take place in normal conditions when the electrophoretic accumulation of the polycationic polyamine induces a sufficient drop inDWable to trigger the efflux pathway. The release of the polyamine is most probably electroneutral in origin and can take place in exchange with protons or in symport with phosphate anion. The activity of both the uptake and efflux pathways induces a continuous cycling of spermine across the mitochondrial membrane, the rate of which may be prominent in imposing the concentrations of spermine in the inner and outer compartment. Thus, this event has a significant role on mitochondrial permeability transition modulation and consequently on the triggering of intrinsic apoptosis