797 research outputs found
Ice Dynamics and Morphological Changes During Proglacial Lake Development at Exploradores Glacier, Patagonia
Proglacial lakes are ubiquitous features formed during deglaciarization and are currently increasing in number in Patagonia and elsewhere. Proglacial lakes can affect glacier dynamics, catchment hydrology and have the potential to cause glacial lake outburst floods. Therefore, monitoring the onset and development of proglacial lake formation is relevant to understand glacial processes and anticipate glacier response to climate change. In this study, we integrate geomorphological and ice-dynamic information to assess proglacial lake development in Exploradores Glacier, Chilean Patagonia. We monitor recent spatial and temporal changes in the lower trunk of Exploradores Glacier (10 km2) to provide a 20-year observation record by combining eight uncrewed aerial vehicles (UAV) surveys between 2019 and 2020, with high-medium resolution satellite imagery (Rapid Eye and Landsat) between 2000 and 2018. We use feature tracking techniques, digital surface elevation model analysis and field data to create a multi-temporal scale (inter-annual and seasonal) and a multi-spatial (cm to km) data set. Our analysis shows that surface velocity overall trend has not changed over the last 20 years and that surface velocity near the terminus is significant (>10 m a−1). Moreover, an exceptional advance over moraine deposits was detected. We also found low downwasting rates (<0.5 m a−1) close to the glacier terminus which are attributed to sufficient ice flux and the insulation effect of the debris-covered surface. However, hundreds of supraglacial ponds were observed and are currently coalescing and expanding by ice-cliff backwasting favoring glacier disintegration. Lastly, it was found that calving losses at the east marginal lake equaled ice-flux input into the lake for the UAV monitored period. This study contributes to a better understanding of glacial lake dynamics during proglacial lake development, and our results may help ice modelling efforts to predict glacier response to future climate scenarios
Following the crumbs: Statistical effects of ram pressure in galaxies
We analyse the presence of dust around galaxy group members through the reddening of background quasars. By taking into account quasar colour and their dependence on redshift and angular position, we derive mean quasar colours excess in projected regions around member galaxies and infer the associated dust mass. For disc-like galaxies perpendicular to the plane of the sky, and at groupcentric distances of the order of the virial radius, thus likely to reside in the infall regions of groups,we find systematic colour excess values e~0.009±0.004 for g - r colour. Under the hypothesis of MilkyWay dust properties, we derive dust masses of 5.8 ± 2.5 × 108M⊙ h-1, implying that a large fraction of dust is being stripped from galaxies in their path to groups. We also studied the photometry of member galaxies to derive a colour asymmetry relative to the group centre direction from a given galaxy. We conclude that the regions of galaxies facing the centre are bluer, consistent with the effects of gas compression and star formation. We also combine these two procedures finding that galaxies with a small colour asymmetry show the largest amounts of dust towards the external regions compared to a control sample. We conclude that dust removal is very efficient in galaxies on infall. The fact that galaxies redder towards groups centres are associated with the strongest reddening of background quasars suggest that gas removal induced by ram pressure stripping plays a key role in galaxy evolution and dust content.Fil: Rodríguez, S.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Garcia Lambas, Diego Rodolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Padilla, Nelson David. Pontificia Universidad Católica de Chile; Chile. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Troncoso-Iribarren, P.. Pontificia Universidad Católica de Chile; Chil
Electronic structure of crystalline binary and ternary Cd-Te-O compounds
The electronic structure of crystalline CdTe, CdO, -TeO,
CdTeO and CdTeO is studied by means of first principles
calculations. The band structure, total and partial density of states, and
charge densities are presented. For -TeO and CdTeO, Density
Functional Theory within the Local Density Approximation (LDA) correctly
describes the insulating character of these compounds. In the first four
compounds, LDA underestimates the optical bandgap by roughly 1 eV. Based on
this trend, we predict an optical bandgap of 1.7 eV for CdTeO. This
material shows an isolated conduction band with a low effective mass, thus
explaining its semiconducting character observed recently. In all these oxides,
the top valence bands are formed mainly from the O 2p electrons. On the other
hand, the binding energy of the Cd 4d band, relative to the valence band
maximum, in the ternary compounds is smaller than in CdTe and CdO.Comment: 13 pages, 15 figures, 2 tables. Accepted in Phys Rev
Random Walks on Stochastic Temporal Networks
In the study of dynamical processes on networks, there has been intense focus
on network structure -- i.e., the arrangement of edges and their associated
weights -- but the effects of the temporal patterns of edges remains poorly
understood. In this chapter, we develop a mathematical framework for random
walks on temporal networks using an approach that provides a compromise between
abstract but unrealistic models and data-driven but non-mathematical
approaches. To do this, we introduce a stochastic model for temporal networks
in which we summarize the temporal and structural organization of a system
using a matrix of waiting-time distributions. We show that random walks on
stochastic temporal networks can be described exactly by an
integro-differential master equation and derive an analytical expression for
its asymptotic steady state. We also discuss how our work might be useful to
help build centrality measures for temporal networks.Comment: Chapter in Temporal Networks (Petter Holme and Jari Saramaki
editors). Springer. Berlin, Heidelberg 2013. The book chapter contains minor
corrections and modifications. This chapter is based on arXiv:1112.3324,
which contains additional calculations and numerical simulation
Moraine-dammed lake failures in Patagonia and assessment of outburst susceptibility in the Baker Basin
Glacier retreat since the Little Ice Age has resulted in the development or
expansion of hundreds of glacial lakes in Patagonia. Some of these lakes
have produced large (≥ 106 m3) Glacial Lake Outburst Floods
(GLOFs) damaging inhabited areas. GLOF hazard studies in Patagonia have been
mainly based on the analysis of short-term series (≤ 50 years) of flood
data and until now no attempt has been made to identify the relative
susceptibility of lakes to failure. Power schemes and associated
infrastructure are planned for Patagonian basins that have historically been
affected by GLOFs, and we now require a thorough understanding of the
characteristics of dangerous lakes in order to assist with hazard assessment
and planning. In this paper, the conditioning factors of 16 outbursts from
moraine-dammed lakes in Patagonia were analysed. These data were used to
develop a classification scheme designed to assess outburst susceptibility,
based on image classification techniques, flow routine algorithms and the
Analytical Hierarchy Process. This scheme was applied to the Baker Basin,
Chile, where at least seven moraine-dammed lakes have failed in historic time.
We identified 386 moraine-dammed lakes in the Baker Basin of which 28 were
classified with high or very high outburst susceptibility. Commonly, lakes
with high outburst susceptibility are in contact with glaciers and have
moderate (> 8°) to steep (> 15°)
dam outlet slopes, akin to failed lakes in Patagonia. The proposed
classification scheme is suitable for first-order GLOF hazard assessments in
this region. However, rapidly changing glaciers in Patagonia make detailed
analysis and monitoring of hazardous lakes and glaciated areas upstream from
inhabited areas or critical infrastructure necessary, in order to better
prepare for hazards emerging from an evolving cryosphere
The evolution of Balmer jump selected galaxies in the ALHAMBRA survey
We present a new color-selection technique, based on the Bruzual & Charlot
models convolved with the bands of the ALHAMBRA survey, and the redshifted
position of the Balmer jump to select star-forming galaxies in the redshift
range 0.5 < z < 1.5. These galaxies are dubbed Balmer jump Galaxies BJGs. We
apply the iSEDfit Bayesian approach to fit each detailed SED and determine
star-formation rate (SFR), stellar mass, age and absolute magnitudes. The mass
of the haloes where these samples reside are found via a clustering analysis.
Five volume-limited BJG sub-samples with different mean redshifts are found to
reside in haloes of median masses slightly
increasing toward z=0.5. This increment is similar to numerical simulations
results which suggests that we are tracing the evolution of an evolving
population of haloes as they grow to reach a mass of at z=0.5. The likely progenitors of our samples at z3 are Lyman
Break Galaxies, which at z2 would evolve into star-forming BzK galaxies,
and their descendants in the local Universe are elliptical galaxies.Hence, this
allows us to follow the putative evolution of the SFR, stellar mass and age of
these galaxies. From z1.0 to z0.5, the stellar mass of the volume
limited BJG samples nearly does not change with redshift, suggesting that major
mergers play a minor role on the evolution of these galaxies. The SFR evolution
accounts for the small variations of stellar mass, suggesting that star
formation and possible minor mergers are the main channels of mass assembly.Comment: 14 pages, 10 figures. Submitted to A&A. It includes first referee's
comments. Abstract abridged due to arXiv requirement
Young Galaxy Candidates in the Hubble Frontier Fields - III. MACSJ0717.5+3745
In this paper we present the results of our search for and study of galaxy candidates behind the third Frontier Fields (FF) cluster,
MACSJ0717.5+3745, and its parallel field, combining data from Hubble and
Spitzer. We select 39 candidates using the Lyman Break technique, for which the
clear non-detection in optical make the extreme mid- interlopers hypothesis
unlikely. We also take benefit from samples selected using
previous Frontier Fields datasets of Abell 2744 and MACS0416 to improve the
constraints on the properties of very high-redshift objects. We compute the
redshift and the physical properties, such emission lines properties, star
formation rate, reddening, and stellar mass for all Frontier Fields objects
from their spectral energy distribution using templates including nebular
emission lines. We study the relationship between several physical properties
and confirm the trend already observed in previous surveys for evolution of
star formation rate with galaxy mass, and between the size and the UV
luminosity of our candidates. The analysis of the evolution of the UV
Luminosity Function with redshift seems more compatible with an evolution of
density. Moreover, no robust 8.5 object is selected behind the cluster
field, and few 9 candidates have been selected in the two previous
datasets from this legacy survey, suggesting a strong evolution in the number
density of galaxies between 8 and 9. Thanks to the use of the lensing
cluster, we study the evolution of the star formation rate density produced by
galaxies with L0.03L, and confirm the strong decrease observed
between 8 and 9.Comment: 21 pages - Accepted for publication in ApJ - v2: small correction
The 2015 Chileno Valley glacial lake outburst flood, Patagonia
Glacial Lake Outburst Floods (GLOFs) have become increasingly common over the past century in response to climate change, posing risks for human activities in many mountain regions. In this paper we document and reconstruct the sequence of events and impact of a large GLOF that took place in December 2015 in the Chileno Valley, Patagonia. Hydrograph data suggests that the flood continued for around eight days with an estimated total discharge of 105.6 × 106 m3 of water. The sequence of events was as follows: (1) A large debris flow entered the lake from two steep and largely non-vegetated mountain gullies located northeast of the Chileno Glacier terminus. (2) Water displaced in the lake by the debris flow increased the discharge through the Chileno Lake outflow. (3) Lake and moraine sediments were eroded by the flood. (4) Eroded sediments were redistributed downstream by the GLOF. The post-GLOF channel at the lake outlet widened in some places by >130 m and the surface elevation of the terrain lowered by a maximum of 38.8 ± 1.5 m. Farther downstream, large amounts of entrained sediment were deposited at the head of an alluvial plain and these sediments produced an ~340 m wide fan with an average increase in surface elevation over the pre-GLOF surface of 4.6 ± 1.5 m. We estimate that around 3.5 million m3 of material was eroded from the flood-affected area whilst over 0.5 million m3 of material was deposited in the downstream GLOF fan. The large debris flow that triggered the GLOF was probably a paraglacial response to glacier recession from its Little Ice Age limits. We suggest that GLOFs will continue to occur in these settings in the future as glaciers further recede in response to global warming and produce potentially unstable lakes. Detailed studies of GLOF events are currently limited in Patagonia and the information presented here will therefore help to inform future glacial hazard assessments in this region
The impact of SHS exposure on health status and exacerbations among patients with COPD
Secondhand smoke (SHS) is a major contributor to indoor air pollution. Because it contains respiratory irritants, it may adversely influence the clinical course of persons with chronic obstructive pulmonary disease (COPD). We used data from nonsmoking members of the FLOW cohort of COPD (n = 809) to elucidate the impact of SHS exposure on health status and exacerbations (requiring emergency department visits or hospitalization). SHS exposure was measured by a validated survey instrument (hours of exposure during the past week). Physical health status was measured by the SF-12 Physical Component Summary Score and disease-specific health-related quality of life (HRQL) by the Airways Questionnaire 20-R. Health care utilization for COPD was determined from Kaiser Permanente Northern California computerized databases. Compared to no SHS exposure, higher level SHS exposure was associated with poorer physical health status (mean score decrement −1.78 points; 95% confidence interval [CI] −3.48 to −0.074 points) after controlling for potential confounders. Higher level SHS exposure was also related to poorer disease-specific HRQL (mean score increment 0.63; 95% CI 0.016 to 1.25) and less distance walked during the Six-Minute Walk test (mean decrement −50 feet; 95% CI −102 to 1.9). Both lower level and higher level SHS exposure was related to increased risk of emergency department (ED) visits (hazard ratio [HR] 1.40; 95% CI 0.96 to 2.05 and HR 1.41; 95% CI 0.94 to 2.13). Lower level and higher level SHS exposure were associated with a greater risk of hospital-based care for COPD, which was a composite endpoint of either ED visits or hospitalizations for COPD (HR 1.52; 95% CI 1.06 to 2.18 and HR 1.40; 95% CI 0.94 to 2.10, respectively). In conclusion, SHS was associated with poorer health status and a greater risk of COPD exacerbation. COPD patients may comprise a vulnerable population for the health effects of SHS
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