6,202 research outputs found
Cellular Models of Aggregation-Dependent Template-Directed Proteolysis to Characterize Tau Aggregation Inhibitors for Treatment of Alzheimer's Disease
Copyright © 2015, The American Society for Biochemistry and Molecular Biology. Acknowledgements-We thank Drs Timo Rager and Rolf Hilfiker (Solvias, Switzerland) for polymorph analyses.Peer reviewedPublisher PD
K-band Spectroscopy of Clusters in NGC 4038/4039
Integral field spectroscopy in the K-band (1.9-2.4um) was performed on four
IR-bright star clusters and the two nuclei in NGC 4038/4039 (``The Antennae'').
Two of the clusters are located in the overlap region of the two galaxies, and
together comprise ~25% of the total 15um and ~10% of the total 4.8 GHz emission
from this pair of merging galaxies. The other two clusters, each of them
spatially resolved into two components, are located in the northern galaxy, one
in the western and one in the eastern loop of blue clusters. Comparing our
analysis of Brgamma, CO band-heads, He I (2.058um), Halpha (from archival HST
data), and V-K colors with stellar population synthesis models indicates that
the clusters are extincted (A_V ~ 0.7 - 4.3 mags) and young, displaying a
significant age spread (4-13 Myrs). The starbursts in the nuclei are much older
(65 Myrs), with the nucleus of NGC 4038 displaying a region of recent star
formation northward of its K-band peak. Using our derived age estimates and
assuming the parameters of the IMF (Salpeter slope, upper mass cut-off of 100
M_sun, Miller-Scalo between 1 M_sun and 0.1 M_sun), we find that the clusters
have masses between 0.5 and 5 * 10^6M_sun.Comment: 10 pages, 3 figures, ApJ accepte
Wolf-Rayet Galaxies in the Sloan Digital Sky Survey: the metallicity dependence of the initial mass function
We use a large sample of 174 Wolf-Rayet (WR) galaxies drawn from the Sloan
Digital Sky Survey to study whether and how the slope of the stellar initial
mass function depends on metallicity. We calculate for each object its oxygen
abundance according to which we divide our sample into four metallicity
subsamples. For each subsample, we then measure three quantities: the
equivalent width of \hb emission line, the equivalent width of WR bump around
4650\AA, and the WR bump-to-\hb intensity ratio, and compare to the predictions
of the same quantities by evolutionary synthesis models of Schaerer & Vacca.
Such comparisons lead to a clear dependence of the slope of initial mass
function () on metallicity in that galaxies at higher metallicities
tend to have steeper initial mass functions, with the slope index ranging from
1.00 for the lowest metallicity of to 3.30
for the highest metallicity . We have carefully examined the possible
sources of systematic error either in models or in our observational
measurements and shown that these sources do not change this result.Comment: 12 pages, 6 figures, ApJ accepte
Thinking about growth : a cognitive mapping approach to understanding small business development
School of Managemen
Spitzer IRS Observations of the Galactic Center: Shocked Gas in the Radio Arc Bubble
We present Spitzer IRS spectra (R ~600, 10 - 38 micron) of 38 positions in
the Galactic Center (GC), all at the same Galactic longitude and spanning
plus/minus 0.3 degrees in latitude. Our positions include the Arches Cluster,
the Arched Filaments, regions near the Quintuplet Cluster, the ``Bubble'' lying
along the same line-of-sight as the molecular cloud G0.11-0.11, and the diffuse
interstellar gas along the line-of-sight at higher Galactic latitudes. From
measurements of the [O IV], [Ne II], [Ne III], [Si II], [S III], [S IV], [Fe
II], [Fe III], and H_2 S(0), S(1), and S(2) lines we determine the gas
excitation and ionic abundance ratios. The Ne/H and S/H abundance ratios are ~
1.6 times that of the Orion Nebula. The main source of excitation is
photoionization, with the Arches Cluster ionizing the Arched Filaments and the
Quintuplet Cluster ionizing the gas nearby and at lower Galactic latitudes
including the far side of the Bubble. In addition, strong shocks ionize gas to
O^{+3} and destroy dust grains, releasing iron into the gas phase (Fe/H ~ 1.3
times 10^{-6} in the Arched Filaments and Fe/H ~ 8.8 times 10^{-6} in the
Bubble). The shock effects are particularly noticeable in the center of the
Bubble, but O is present in all positions. We suggest that the shocks
are due to the winds from the Quintuplet Cluster Wolf-Rayet stars. On the other
hand, the H_2 line ratios can be explained with multi-component models of warm
molecular gas in photodissociation regions without the need for H_2 production
in shocks.Comment: 51 pages, 17 figures To be published in the Astrophysical Journa
Meteorologic parameters analysis above Dome C made with ECMWF data
In this paper we present the characterization of all the principal
meteorological parameters (wind speed and direction, pressure, absolute and
potential temperature) extended over 25 km from the ground and over two years
(2003 and 2004) above the Antarctic site of Dome C. The data set is composed by
'analyses' provided by the General Circulation Model (GCM) of the European
Center for Medium Weather Forecasts (ECMWF) and they are part of the catalog
MARS. A monthly and seasonal (summer and winter time) statistical analysis of
the results is presented. The Richardson number is calculated for each month of
the year over 25 km to study the stability/instability of the atmosphere. This
permits us to trace a map indicating where and when the optical turbulence has
the highest probability to be triggered on the whole troposphere, tropopause
and stratosphere. We finally try to predict the best expected isoplanatic angle
and wavefront coherence time employing the Richardson number maps, the wind
speed profiles and simple analytical models of CN2 vertical profiles.Comment: 28 pages, 14 figures, pdf file, to be published on July 2006 - PASP,
see also http://www.arcetri.astro.it/~masciad
Time on a Rotating Platform
Traditional clock synchronisation on a rotating platform is shown to be
incompatible with the experimentally established transformation of time. The
latter transformation leads directly to solve this problem through noninvariant
one-way speed of light. The conventionality of some features of relativity
theory allows full compatibility with existing experimental evidence.Comment: 12 pages, Latex, no figure. Copies available at [email protected]
accepted for publication in Found. Phys. Let
The [CII] 158 um Line Deficit in Ultraluminous Infrared Galaxies Revisited
We present a study of the [CII] 157.74 um fine-structure line in a sample of
15 ultraluminous infrared (IR) galaxies (L_IR>10^12 Lsun; ULIRGs) using the
Long Wavelength Spectrometer (LWS) on the Infrared Space Observatory (ISO). We
confirm the observed order of magnitude deficit (compared to normal and
starburst galaxies) in the strength of the [CII] line relative to the far-IR
dust continuum emission found in our initial report (Luhman et al. 1998), but
here with a sample that is twice as large. This result suggests that the
deficit is a general phenomenon affecting 4/5 ULIRGs. We present an analysis
using observations of generally acknowledged photodissociation region (PDR)
tracers ([CII], [OI] 63 and 145 um, and FIR continuum emission), which suggests
that a high UV flux G_o incident on a moderate density n PDR could explain the
deficit. However, comparisons with other ULIRG observations, including CO
(1-0), [CI] (1-0), and 6.2 um polycyclic aromatic hydrocarbon (PAH) emission,
suggest that high G_o/n PDRs alone cannot produce a self-consistent solution
that is compatible with all of the observations. We propose that non-PDR
contributions to the FIR continuum can explain the apparent [CII] deficiency.
Here, unusually high G_o and/or n physical conditions in ULIRGs as compared to
those in normal and starburst galaxies are not required to explain the [CII]
deficit. Dust-bounded photoionization regions, which generate much of the FIR
emission but do not contribute significant [CII] emission, offer one possible
physical origin for this additional non-PDR component. Such environments may
also contribute to the observed suppression of FIR fine-structure emission from
ionized gas and PAHs, as well as the warmer FIR colors found in ULIRGs. The
implications for observations at higher redshifts are also revisited.Comment: to be published in The Astrophysical Journal, 58 page
Momentum transfer for momentum transfer-free which-path experiments
We analyze the origin of interference disappearance in which-path double
aperture experiments. We show that we can unambiguously define an observable
momentum transfer between the quantum particle and the path detector and we
prove in particular that the so called ``momentum transfer free'' experiments
can be in fact logically interpreted in term of momentum transfer.Comment: to appear in Phys. Rev . A (2006). (7 pages, 2 figures
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