7,134 research outputs found
Evidence for intermediate-age stellar populations in early-type galaxies from K-band spectroscopy
The study of stellar populations in early-type galaxies in different
environments is a powerful tool for constraining their star formation
histories. This study has been traditionally restricted to the optical range,
where dwarfs around the turn-off and stars at the base of the RGB dominate the
integrated light at all ages. The near-infrared spectral range is especially
interesting since in the presence of an intermediate-age population, AGB stars
are the main contributors. In this letter, we measure the near-infrared indices
NaI and D for a sample of 12 early-type galaxies in low density
environments and compare them with the Fornax galaxy sample presented by Silva
et al. (2008). The analysis of these indices in combination with Lick/IDS
indices in the optical range reveals i) the NaI index is a metallicity
indicator as good as C4668 in the optical range, and ii) D is a
tracer of intermediate-age stellar populations. We find that low-mass galaxies
in low density environments show higher NaI and D than those located
in Fornax cluster, which points towards a late stage of star formation for the
galaxies in less dense environments, in agreement with results from other
studies using independent methods.Comment: 7 pages, 3 figures, accepted for publication in ApJ
Seismic Damage Accumulation of Highway Bridges in Earthquake Prone Regions
Civil infrastructures, such as highway bridges, located in seismically active
regions are often subjected to multiple earthquakes, such as multiple main shocks
along their service life or main shock-aftershock sequences. Repeated seismic events
result in reduced structural capacity and may lead to bridge collapse causing
disruption in normal functioning of transportation networks. This study proposes a
framework to predict damage accumulation in structures under multiple shock
scenarios after developing damage index prediction models and accounting for the
probabilistic nature of the hazard. The versatility of the proposed framework is
demonstrated on a case study highway bridge located in California for two distinct
hazard scenarios: a) multiple main shocks along the service life, and b) multiple
aftershock earthquake occurrences following a single main shock. Results reveal that
in both cases there is a significant increase in damage index exceedance probabilities
due to repeated shocks within the time window of interest
Impact of an enhanced screening program on the detection of non-AIDS neoplasias in patients with human immunodeficiency virus infection
Background
The incidence of non-AIDS defining cancer (NADC) is higher in people living with HIV (PLWH) than in the general population, and it is already one of the leading causes of death in the HIV-infected population. It is estimated that the situation will be aggravated by the progressive aging of PLWH. Early diagnosis through intensive cancer screening may improve the ability for therapeutic interventions and could be critical in reducing mortality, but it might also increase expenditure and harms associated with adverse events. The aim of this study is to evaluate an enhanced screening program for early diagnosis of cancer in PLWH compared to standard practice. The specific objectives are (1) to compare the frequency of cancer diagnosed at an early stage, (2) to analyze safety of the enhanced program: adverse events and unnecessary interventions, (3) to analyze the cost-utility of the program, and (4) to estimate the overall and site-specific incidence of NADC in PLWH.
Methods
We will conduct a multicenter, non-blinded, randomized, controlled trial, comparing two parallel arms: conventional vs enhanced screening. Data will be recorded in an electronic data collection notebook. Conventional intervention group will follow the standard of care screening in the participating centers, according to the European AIDS Clinical Society recommendations, and the enhanced intervention group will follow an expanded screening aimed to early detection of lung, liver, anal, cervical, breast, prostate, colorectal, and skin cancer. The trial will be conducted within the framework of the Spanish AIDS Research Network Cohort (CoRIS).
Discussion
The trial will evaluate the efficacy, safety, and efficiency of an enhanced screening program for the early diagnosis of cancer in HIV patients compared to standard of care practice. The information provided will be relevant since there are currently no studies on expanded cancer screening strategies in patients with HIV, and available data estimating cost effectiveness or cost-utility of such as programs are scarce. An enhanced program for NADC screening in patients with HIV could lead to early diagnosis and improve the prognosis of these patients, with an acceptable rate of unnecessary interventions, but it is critical to demonstrate that the benefits clearly outweigh the harms, before the strategy could be implemented
Towards unified understanding of conductance of stretched monatomic contacts
When monatomic contacts are stretched, their conductance behaves in
qualitatively different ways depending on their constituent atomic elements.
Under a single assumption of resonance formation, we show that various
conductance behavior can be understood in a unified way in terms of the
response of the resonance to stretching. This analysis clarifies the crucial
roles played by the number of valence electrons, charge neutrality, and orbital
shapes.Comment: 2 figure
Dripping Faucet Dynamics Clarified by an Improved Mass-Spring Model
An improved mass-spring model for a dripping faucet is presented. The model
is constructed based on the numerical results which we recently obtained from
fluid dynamical calculations. Both the fluid dynamical calculations and the
present mass-spring model exhibit a variety of complex behavior including
transition to chaos in good agreement with experiments. Further, the
mass-spring model reveals fundamental dynamics inherent in the dripping faucet
system.Comment: 17 pages, 17 figure
Integrated K-band spectra of old and intermediate-age globular clusters in the Large Magellanic Cloud
Current stellar population models have arguably the largest uncertainties in
the near-IR wavelength range, partly due to a lack of large and well calibrated
empirical spectral libraries. In this paper we present a project, which aim it
is to provide the first library of luminosity weighted integrated near-IR
spectra of globular clusters to be used to test the current stellar population
models and serve as calibrators for the future ones. Our pilot study presents
spatially integrated K-band spectra of three old (>10 Gyr) and metal poor
([Fe/H]~-1.4), and three intermediate age (1-2 Gyr) and more metal rich
([Fe/H]~-0.4) globular clusters in the LMC. We measured the line strengths of
the Na I, Ca I and 12CO(2-0) absorption features. The Na I index decreases with
the increasing age and decreasing metallicity of the clusters. The Dco index,
used to measure the 12CO(2-0) line strength, is significantly reduced by the
presence of carbon-rich TP-AGB stars in the globular clusters with age ~1 Gyr.
This is in contradiction with the predictions of the stellar population models
of Maraston (2005). We find that this disagreement is due to the different CO
absorption strength of carbon-rich Milky Way TP-AGB stars used in the models
and the LMC carbon stars in our sample. For globular clusters with age >2 Gyr
we find Dco index measurements consistent with the model predictions.Comment: 15 pages, 11 figures, accepted for publication in A&
Reconstructing the impact of human activities in a NW Iberian Roman mining landscape for the last 2500 years
This article was made available through the Brunel Open Access Publishing Fund.Little is known about the impact of human activities during Roman times on NW Iberian mining landscapes beyond the geomorphological transformations brought about by the use of hydraulic power for gold extraction. We present the high-resolution pollen record of La Molina mire, located in an area intensely used for gold mining (Asturias, NW Spain), combined with other proxy data from the same peat core to identify different human activities, evaluate the strategies followed for the management of the resources and describe the landscape response to human disturbances. We reconstructed the timing and synchronicity of landscape changes of varying intensity and form occurred before, during and after Roman times. An open landscape was prevalent during the local Late Iron Age, a period of relatively environmental stability. During the Early Roman Empire more significant vegetation shifts took place, reflected by changes in both forest (Corylus and Quercus) and heathland cover, as mining/metallurgy peaked and grazing and cultivation increased. In the Late Roman Empire, the influence of mining/metallurgy on landscape change started to disappear. This decoupling was further consolidated in the Germanic period (i.e., Visigothic and Sueve domination of the region), with a sharp decrease in mining/metallurgy but continued grazing. Although human impact was intense in some periods, mostly during the Early Roman Empire, forest regeneration occurred afterwards: clearances were local and short-lived. However, the Roman mining landscape turned into an agrarian one at the onset of the Middle Ages, characterized by a profound deforestation at a regional level due to a myriad of human activities that resulted in an irreversible openness of the landscape. © 2014 The Authors
The Sunyaev-Zel'dovich effects from a cosmological hydrodynamical simulation: large-scale properties and correlation with the soft X-ray signal
Using the results of a cosmological hydrodynamical simulation of the
concordance LambdaCDM model, we study the global properties of the
Sunyaev-Zel'dovich (SZ) effects, both considering the thermal (tSZ) and the
kinetic (kSZ) component. The simulation follows gravitation and gas dynamics
and includes also several physical processes that affect the baryonic
component, like a simple reionization scenario, radiative cooling, star
formation and supernova feedback. Starting from the outputs of the simulation
we create mock maps of the SZ signals due to the large structures of the
Universe integrated in the range 0 < z < 6. We predict that the Compton
y-parameter has an average value of (1.19 +/- 0.32) 10^-6 and is lognormally
distributed in the sky; half of the whole signal comes from z < 1 and about 10
per cent from z > 2. The Doppler b-parameter shows approximately a normal
distribution with vanishing mean value and a standard deviation of 1.6 10^-6,
with a significant contribution from high-redshift (z > 3) gas. We find that
the tSZ effect is expected to dominate the primary CMB anisotropies for l >~
3000 in the Rayleigh-Jeans limit, while interestingly the kSZ effect dominates
at all frequencies at very high multipoles (l >~ 7 10^4). We also analyse the
cross-correlation between the two SZ effects and the soft (0.5-2 keV) X-ray
emission from the intergalactic medium and we obtain a strong correlation
between the three signals, especially between X-ray emission and tSZ effect
(r_l ~ 0.8-0.9) at all angular scales.Comment: 12 pages, 15 figures. Accepted for publication in MNRAS. Minor
changes, added reference
Performance Evaluation of HL-LHC Crab Cavity Prototypes in a CERN Vertical Test Cryostat
Three proof-of-principle compact crab cavity designs have been fabricated in bulk niobium and cold tested at their home labs, as a first validation step towards the High Luminosity LHC project. As a cross check, all three bare cavities have been retested at CERN, in order to cross check their performance, and cross-calibrate the CERN SRF cold test facilities. While achievable transverse deflecting voltage is the key performance indicator, secondary performance aspects derived from multiple cavity monitoring systems are also discussed. Temperature mapping profiles, quench detection, material properties, and trapped magnetic flux effects have been assessed, and the influence on performance discussed. The significant effort invested in developing expertise in preparation and testing of these crab cavities has already been fruitful for all partners, and more is to come within this ongoing program
- …