580 research outputs found
Pre-Columbian Tuberculosis: An Epidemiological Approach
In this study we have combined both biological and cultural data in the investigation of resorptive pathology in Woodland and Mississippian skeletal series from west-central Illinois. Information concerning the types of lesions and their distribution confirms the presence of a previously unknown disease in Mississippian populations. Adults and adolescents from Yokem and Schild Mississippian components clearly display cystic vertebral pathology, which in association with other peripheral osseous lesions distinguishes them from earlier groups. This idea is supported indirectly by evidence from both infants and children of the Schild sample
Photometric Confirmation of MACHO Large Magellanic Cloud Microlensing Events
We present previously unpublished photometry of three Large Magellanic Cloud
(LMC) microlensing events and show that the new photometry confirms the
microlensing interpretation of these events. These events were discovered by
the MACHO Project alert system and were also recovered by the analysis of the
5.7 year MACHO data set. This new photometry provides a substantial increase in
the signal-to-noise ratio over the previously published photometry and in all
three cases, the gravitational microlensing interpretation of these events is
strengthened. The new data consist of MACHO-Global Microlensing Alert Network
(GMAN) follow-up images from the CTIO 0.9 telescope plus difference imaging
photometry of the original MACHO data from the 1.3m "Great Melbourne" telescope
at Mt. Stromlo. We also combine microlensing light curve fitting with
photometry from high resolution HST images of the source stars to provide
further confirmation of these events and to show that the microlensing
interpretation of event MACHO-LMC-23 is questionable. Finally, we compare our
results with the analysis of Belokurov, Evans & Le Du who have attempted to
classify candidate microlensing events with a neural network method, and we
find that their results are contradicted by the new data and more powerful
light curve fitting analysis for each of the four events considered in this
paper. The failure of the Belokurov, Evans & Le Du method is likely to be due
to their use of a set of insensitive statistics to feed their neural networks.Comment: 29 pages with 8 included postscript figures, accepted by the
Astrophysical Journa
The MACHO Project LMC Microlensing Results from the First Two Years and the Nature of the Galactic Dark Halo
The MACHO Project is a search for dark matter in the form of massive compact
halo objects (Machos). Photometric monitoring of millions of stars in the Large
Magellanic Cloud (LMC), Small Magellanic Cloud (SMC), and Galactic bulge is
used to search for gravitational microlensing events caused by these otherwise
invisible objects. Analysis of the first 2.1 years of photometry of 8.5 million
stars in the LMC reveals 8 candidate microlensing events. This is substantially
more than the number expected () from lensing by known stellar
populations. The timescales (\that) of the events range from 34 to 145 days.
We estimate the total microlensing optical depth towards the LMC from events
with 2 < \that < 200 days to be \tau_2^{200} = 2.9 ^{+1.4}_{-0.9} \ten{-7}
based upon our 8 event sample. This exceeds the optical depth, \tau_{\rm
backgnd} = 0.5 \ten{-7}, expected from known stars, and the difference is to
be compared with the optical depth predicted for a ``standard" halo composed
entirely of Machos: \tau_{halo} = 4.7\ten{-7}. Likelihood analysis gives a
fairly model independent estimate of the halo mass in Machos within 50 kpc of
2.0^{+1.2}_{-0.7} \ten{11} \msun, about half of the ``standard halo" value.
We also find a most probable Macho mass of 0.5^{+0.3}_{-0.2}\msun, although
this value is strongly model dependent. Additionally, the absence of short
duration events places stringent upper limits on the contribution of low-mass
Machos: objects from 10^{-4} \msun to 0.03 \msun contribute \simlt 20\%
of the ``standard" dark halo.Comment: Latex, 54 pages, uses aas2pp4.sty and astrobib.sty, with 24 out of 26
Postscript figures in gzipped tar file. 2 extra greyscale figures and/or full
paper available from ftp://igpp.llnl.gov/pub/macho/LMC2/ Submitted to ApJ,
June 199
Complementary Embryonic and Adult Cell Populations Enhance Myocardial Repair in Rat Myocardial Injury Model
We compared the functional outcome of Isl-1+ cardiac progenitors, CD90+ bone marrow-derived progenitor cells, and the combination of the two in a rat myocardial infarction (MI) model. Isl-1+ cells were isolated from embryonic day 12.5 (E12.5) rat hearts and expanded in vitro. Thy-1+/CD90+ cells were isolated from the bone marrow of adult Sprague-Dawley rats by immunomagnetic cell sorting. Six-week-old female Sprague-Dawley rats underwent permanent left anterior descending (LAD) coronary artery ligation and received intramyocardial injection of either saline, Isl-1+ cells, CD90+ cells, or a combination of Isl-1+ and CD90+ cells, at the time of infarction. Cells were delivered transepicardially to the peri-infarct zone. Left ventricular function was assessed by transthoracic echocardiography at 1- and 4-week post-MI and by Millar catheterization (-dP/dt and +dP/dt) at 4-week post-MI. Fluorescence in situ hybridization (Isl-1+cells) and monochrystalline iron oxide nanoparticles labeling (MION; CD90+ cells) were performed to assess biodistribution of transplanted cells. Only the combination of cells demonstrated a significant improvement of cardiac function as assessed by anterior wall contractility, dP/dt (max), and dP/dt (min), compared to Isl-1+ or CD90+ cell monotherapies. In the combination cell group, viable cells were detected at week 4 when anterior wall motion was completely restored. In conclusion, the combination of Isl-1+ cardiac progenitors and adult bone marrow-derived CD90+ cells shows prolonged and robust myocardial tissue repair and provides support for the use of complementary cell populations to enhance myocardial repair
Constraining the LyC escape fraction from LEGUS star clusters with SIGNALS HII region observations: A pilot study of NGC 628
The ionising radiation of young and massive stars is a crucial form of
stellar feedback. Most ionising (Lyman-continuum; LyC, )
photons are absorbed close to the stars that produce them, forming compact HII
regions, but some escape into the wider galaxy. Quantifying the fraction of LyC
photons that escape is an open problem. In this work, we present a semi-novel
method to estimate the escape fraction by combining broadband photometry of
star clusters from the Legacy ExtraGalactic UV Survey (LEGUS) with HII regions
observed by the Star formation, Ionized gas, and Nebular Abundances Legacy
Survey (SIGNALS) in the nearby spiral galaxy NGC 628. We first assess the
completeness of the combined catalogue, and find that 49\% of HII regions lack
corresponding star clusters as a result of a difference in the sensitivities of
the LEGUS and SIGNALS surveys. For HII regions that do have matching clusters,
we infer the escape fraction from the difference between the ionising power
required to produce the observed HII luminosity and the predicted ionising
photon output of their host star clusters; the latter is computed using a
combination of LEGUS photometric observations and a stochastic stellar
population synthesis code SLUG (Stochastically Lighting Up Galaxies). Overall,
we find an escape fraction of across our
sample of 42 HII regions; in particular, we find HII regions with high
are predominantly regions with low H-luminosity. We also
report possible correlation between and the emission lines [O ii]/[N
ii] and [O ii]/H.Comment: Accepted for publication at MNRA
Recommended from our members
Development of a wind gust model to estimate gust speeds and their return periods
Spatially dense observations of gust speeds are necessary for various applications, but their availability is limited in space and time. This work presents an approach to help to overcome this problem. The main objective is the generation of synthetic wind gust velocities. With this aim, theoretical wind and gust distributions are estimated from 10 yr of hourly observations collected at 123 synoptic weather stations provided by the German Weather Service. As pre-processing, an exposure correction is applied on measurements of the mean wind velocity to reduce the influence of local urban and topographic effects. The wind gust model is built as a transfer function between distribution parameters of wind and gust velocities. The aim of this procedure is to estimate the parameters of gusts at stations where only wind speed data is available. These parameters can be used to generate synthetic gusts, which can improve the accuracy of return periods at test sites with a lack of observations. The second objective is to determine return periods much longer than the nominal length of the original time series by considering extreme value statistics. Estimates for both local maximum return periods and average return periods for single historical events are provided. The comparison of maximum and average return periods shows that even storms with short average return periods may lead to local wind gusts with return periods of several decades. Despite uncertainties caused by the short length of the observational records, the method leads to consistent results, enabling a wide range of possible applications
H α morphologies of star clusters: a LEGUS study of H II region evolution time-scales and stochasticity in low-mass clusters
The morphology of H II regions around young star clusters provides insight into the time-scales and physical processes that clear a cluster’s natal gas. We study ∼700 young clusters (≤10 Myr) in three nearby spiral galaxies (NGC 7793, NGC 4395, and NGC 1313) using Hubble Space Telescope (HST) imaging from LEGUS (Legacy ExtraGalactic Ultraviolet Survey). Clusters are classified by their H α morphology (concentrated, partially exposed, no-emission) and whether they have neighbouring clusters (which could affect the clearing time-scales). Through visual inspection of the HST images, and analysis of ages, reddenings, and stellar masses from spectral energy distributions fitting, together with the (U− B), (V − I) colours, we find (1) the median ages indicate a progression from concentrated (∼3 Myr), to partially exposed (∼4 Myr), to no H α emission (>5 Myr), consistent with the expected temporal evolution of H II regions and previous results. However, (2) similarities in the age distributions for clusters with concentrated and partially exposed H α morphologies imply a short time-scale for gas clearing (≲1 Myr). Also, (3) our cluster sample’s median mass is ∼1000 M⊙, and a significant fraction (∼20 per cent) contain one or more bright red sources (presumably supergiants), which can mimic reddening effects. Finally, (4) the median E(B − V) values for clusters with concentrated H α and those without H α emission appear to be more similar than expected (∼0.18 versus ∼0.14, respectively), but when accounting for stochastic effects, clusters without H α emission are less reddened. To mitigate stochastic effects, we experiment with synthesizing more massive clusters by stacking fluxes of clusters within each H α morphological class. Composite isolated clusters also reveal a colour and age progression for H α morphological classes, consistent with analysis of the individual clusters
Measurement of the Depth of Maximum of Extensive Air Showers above 10^18 eV
We describe the measurement of the depth of maximum, Xmax, of the
longitudinal development of air showers induced by cosmic rays. Almost four
thousand events above 10^18 eV observed by the fluorescence detector of the
Pierre Auger Observatory in coincidence with at least one surface detector
station are selected for the analysis. The average shower maximum was found to
evolve with energy at a rate of (106 +35/-21) g/cm^2/decade below 10^(18.24 +/-
0.05) eV and (24 +/- 3) g/cm^2/decade above this energy. The measured
shower-to-shower fluctuations decrease from about 55 to 26 g/cm^2. The
interpretation of these results in terms of the cosmic ray mass composition is
briefly discussed.Comment: Accepted for publication by PR
Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC
The uncertainty on the calorimeter energy response to jets of particles is
derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the
calorimeter response to single isolated charged hadrons is measured and
compared to the Monte Carlo simulation using proton-proton collisions at
centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009
and 2010. Then, using the decay of K_s and Lambda particles, the calorimeter
response to specific types of particles (positively and negatively charged
pions, protons, and anti-protons) is measured and compared to the Monte Carlo
predictions. Finally, the jet energy scale uncertainty is determined by
propagating the response uncertainty for single charged and neutral particles
to jets. The response uncertainty is 2-5% for central isolated hadrons and 1-3%
for the final calorimeter jet energy scale.Comment: 24 pages plus author list (36 pages total), 23 figures, 1 table,
submitted to European Physical Journal
- …