149 research outputs found
TREM2 deficiency attenuates neuroinflammation and protects against neurodegeneration in a mouse model of tauopathy
Significance
Alzheimer’s disease (AD) is the most common cause of dementia and is a major public health problem for which there is currently no disease-modifying treatment. There is an urgent need for greater understanding of the molecular mechanisms underlying neurodegeneration in patients to create better therapeutic options. Recently, genetic studies uncovered novel AD risk variants in the microglial receptor, triggering receptor expressed on myeloid cells 2 (TREM2). Previous studies suggested that loss of TREM2 function worsens amyloid-β (Aβ) plaque-related toxicity. In contrast, we observe TREM2 deficiency mitigates neuroinflammation and protects against brain atrophy in the context of tau pathology. These findings indicate dual roles for TREM2 and microglia in the context of amyloid versus tau pathology, which are important to consider for potential treatments targeting TREM2.</jats:p
Stellar Subsystems of the Galaxy NGC 2366
Hubble Space Telescope archive data are used to perform photometry of stars
in seven fields at the center and periphery of the galaxy NGC2366. The
variation of the number density of stars of various ages with galactocentric
radius and along the minor axis of the galaxy are determined. The boundaries of
the thin and thick disks of the galaxy are found. The inferred sizes of the
subsystems of NGC2366 ( kpc and kpc for the thin
and thick disks, respectively) are more typical for spiral galaxies. Evidence
for a stellar halo is found at the periphery of NGC2366 beyond the thick disk
of the galaxy.Comment: 16 pages, 4 figures, Astronomy Reports, 2008,v. 52, n.1, p. 1
Bose condensates in a harmonic trap near the critical temperature
The mean-field properties of finite-temperature Bose-Einstein gases confined
in spherically symmetric harmonic traps are surveyed numerically. The solutions
of the Gross-Pitaevskii (GP) and Hartree-Fock-Bogoliubov (HFB) equations for
the condensate and low-lying quasiparticle excitations are calculated
self-consistently using the discrete variable representation, while the most
high-lying states are obtained with a local density approximation. Consistency
of the theory for temperatures through the Bose condensation point requires
that the thermodynamic chemical potential differ from the eigenvalue of the GP
equation; the appropriate modifications lead to results that are continuous as
a function of the particle interactions. The HFB equations are made gapless
either by invoking the Popov approximation or by renormalizing the particle
interactions. The latter approach effectively reduces the strength of the
effective scattering length, increases the number of condensate atoms at each
temperature, and raises the value of the transition temperature relative to the
Popov approximation. The renormalization effect increases approximately with
the log of the atom number, and is most pronounced at temperatures near the
transition. Comparisons with the results of quantum Monte Carlo calculations
and various local density approximations are presented, and experimental
consequences are discussed.Comment: 15 pages, 11 embedded figures, revte
Broadband Observations of the Afterglow of GRB 000926: Observing the Effect of Inverse Compton Scattering and Evidence for a High-Density Environment
GRB 000926 has one of the best-studied afterglows to-date, with multiple
X-ray observations, as well as extensive multi-frequency optical and radio
coverage. Broadband afterglow observations, spanning from X-ray to radio
frequencies, provide a probe of the density structure of the circumburst
medium, as well as of the ejecta energetics, geometry, and the physical
parameters of the relativistic blastwave resulting from the explosion. We
present an analysis of {\em Chandra X-ray Observatory} observations of this
event, along with {\em Hubble Space Telescope} and radio monitoring. We combine
these data with ground-based optical and IR observations and fit the
synthesized afterglow lightcurve using models where collimated ejecta expand
into a surrounding medium. We find that we can explain the broadband lightcurve
with reasonable physical parameters only if the cooling is dominated by inverse
Compton scattering. Excess X-ray emission in the broadband spectrum indicates
that we are directly observing a contribution from inverse Compton scattering.
It is the first time this has been observed in a GRB afterglow, and it implies
that the GRB exploded in a reasonably dense (n~30 cm^{-3}) medium, consistent
with a diffuse interstellar cloud environment.Comment: 16 pages, 5 figures Accepted for publication in the Astrophysical
Journa
Stellar disks and halos of the edge-on spiral galaxies: NGC 891, NGC 4144 and NGC 4244
The results of the stellar photometry of the images ACS/WFC and WFPC2 of the
HST are used to study stellar population and spatial distribution of stars in
three edge-on galaxies: NGC 891, NGC 4144 and NGC 4244. The measuring of the
number density of the old stars revealed two stellar substructures in these
galaxies: thick disk and halo. The borders of these substructures consisting
mainly of red giants, are determined by the change of number density gradient
of the old stars. The revealed halos have flattened shapes and extend up to 25
kpc from the galaxy planes. The obtained results of number density
distributions of different type stars perpendicular to the galaxy planes allow
us to verify our stellar model of spiral galaxies. Using the determination of
the tip of red giant branch (TRGB method) we have derived the following
distances: D = 9.82 Mpc (NGC 891), D = 7.24 Mpc (NGC 4144), D = 4.29 Mpc (NGC
4244).Comment: 18 pages, 9 figures. accepted to Astrofizic
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