417 research outputs found
Modeling of the Terminal Velocities of the Dust Ejected Material by the Impact
We compute the distribution of velocities of the particles ejected by the
impact of the projectile released from NASA Deep Impact spacecraft on the
nucleus of comet 9P/Tempel 1 on the successive 20 hours following the
collision. This is performed by the development and use of an ill-conditioned
inverse problem approach, whose main ingredients are a set of observations
taken by the Narrow Angle Camera (NAC) of OSIRIS onboard the Rosetta
spacecraft, and a set of simple models of the expansion of the dust ejecta
plume for different velocities. Terminal velocities are derived using a maximum
likelihood estimator.
We compare our results with published estimates of the expansion velocity of
the dust cloud. Our approach and models reproduce well the velocity
distribution of the ejected particles. We consider these successful comparisons
of the velocities as an evidence for the appropriateness of the approach. This
analysis provides a more thorough understanding of the properties of the Deep
Impact dust cloud.Comment: Comments: 6 pages, 2 Postscript figures, To appear in the proceedings
of "Deep Impact as a World Observatory Event - Synergies in Space, Time", ed.
Hans Ulrich Kaeufl and Chris Sterken, Springer-Verla
Sungrazing comets: Properties of nuclei and in-situ detectability of cometary ions at 1 AU
A one dimensional sublimation model for cometary nuclei is used to derive
size limits for the nuclei of sungrazing comets, and to estimate oxygen ion
fluxes at 1 AU from their evaporation. Given that none of the ~300 sungrazers
detected by the SOlar and Heliospheric Observatory (SOHO) was observed after
disappearing behind the sun, and that small nuclei with a radius of ~3.5m could
be observed, it is assumed that all SOHO sungrazers were completely destroyed.
For the case that sublimation alone is sufficient for destruction, the model
yields an upper size limit as a function of nuclear density, albedo and
perihelion distance. If the density of the nuclei is that typical of porous ice
(600kg/m^3), the maximum size is 63m. These results confirm similar model
calculations by Weissman (1983). An analytical expression is derived that
approximates the model results well. We discuss possible modifications of our
results by different disruption mechanisms. While disruption by thermal stress
does not change the upper size limits significantly, they may be somewhat
increased by tidal disruption (up to 100m for a density of 600kg/m^3) dependent
on the isotropy of the sublimation process and the tensile strength of the
comet. Implications for the Kreutz family of sungrazers are discussed.
Oxygen ions from the sublimation of sungrazing comets form a tail. Fluxes
from this tail are sufficiently high to be measured at 1 AU by particle
detectors on spacecraft, but the duration of a tail crossing is only about half
an hour. Therefore the probability of a spacecraft actually encountering a tail
of an evaporating sungrazer is only of the order of two percent per year.Comment: 32 pages, 11 figures, accepted for publication in Icaru
Physical Properties of OSIRIS-REx Target Asteroid (101955) 1999 RQ36 derived from Herschel, ESO-VISIR and Spitzer observations
In September 2011, the Herschel Space Observatory performed an observation
campaign with the PACS photometer observing the asteroid (101955) 1999 RQ36 in
the far infrared. The Herschel observations were analysed, together with ESO
VLT-VISIR and Spitzer-IRS data, by means of a thermophysical model in order to
derive the physical properties of 1999 RQ36. We find the asteroid has an
effective diameter in the range 480 to 511 m, a slightly elongated shape with a
semi-major axis ratio of a/b=1.04, a geometric albedo of 0.045 +0.015/-0.012,
and a retrograde rotation with a spin vector between -70 and -90 deg ecliptic
latitude. The thermal emission at wavelengths below 12 micron -originating in
the hot sub-solar region- shows that there may be large variations in roughness
on the surface along the equatorial zone of 1999 RQ36, but further measurements
are required for final proof. We determine that the asteroid has a
disk-averaged thermal inertia of Gamma = 650 Jm-2s-0.5K-1 with a 3-sigma
confidence range of 350 to 950 Jm-2s-0.5K-1, equivalent to what is observed for
25143 Itokawa and suggestive that 1999 RQ36 has a similar surface texture and
may also be a rubble-pile in nature. The low albedo indicates that 1999 RQ36
very likely contains primitive volatile-rich material, consistent with its
spectral type, and that it is an ideal target for the OSIRIS-REx sample return
mission.Comment: Accepted for publication in Astronomy & Astrophysics, 9 pages, 7
figure
Floating stones off El Hierro, Canary Islands: xenoliths of pre-island sedimentary origin in the early products of the October 2011 eruption
The eruption that started off the south coast of El Hierro, Canary Islands, in October 2011 has emitted intriguing eruption products found floating in the sea. These specimens appeared as floating volcanic "bombs" that have in the meantime been termed "restingolites" (after the close-by village of La Restinga) and exhibit cores of white and porous pumice-like material. Currently the nature and origin of these "floating stones" is vigorously debated among researchers, with important implications for the interpretation of the hazard potential of the ongoing eruption. The "restingolites" have been proposed to be either (i) juvenile high-silica magma (e.g. rhyolite), (ii) remelted magmatic material (trachyte), (iii) altered volcanic rock, or (iv) reheated hyaloclastites or zeolite from the submarine slopes of El Hierro. Here, we provide evidence that supports yet a different conclusion. We have collected and analysed the structure and composition of samples and compared the results to previous work on similar rocks found in the archipelago. Based on their high silica content, the lack of igneous trace element signatures, and the presence of remnant quartz crystals, jasper fragments and carbonate relicts, we conclude that "restingolites" are in fact xenoliths from pre-island sedimentary rocks that were picked up and heated by the ascending magma causing them to partially melt and vesiculate. They hence represent messengers from depth that help us to understand the interaction between ascending magma and crustal lithologies in the Canary Islands as well as in similar Atlantic islands that rest on sediment/covered ocean crust (e.g. Cape Verdes, Azores). The occurrence of these "restingolites" does therefore not indicate the presence of an explosive high-silica magma that is involved in the ongoing eruption
Liver Transplantation for Advanced Liver Disease with Alpha-1antitrypsin Deficiency
ALPHA-1-antitrypsin deficiency associated with chronic obstructive airway disease was recognized in 1963 by Laurell and Ericksson.1 In 1969, Sharp2 described the first cases of alpha-1-antitrypsin-deficiency disease in children with cirrhosis. Since then, this inborn error has been recognized as one of the more common factors in cirrhosis of infancy and childhood,3 including “neonatal hepatitis.”4 Alpha-1-antitrypsin is a glycoprotein that accounts for a major portion of the alpha-1 globulin fraction of the serum.5 It is responsible for approximately 90 per cent of the antitrypsin activity6 of the serum, and it also inhibits several other plasma enzymes, including plasmin,7 elastase,8 collagenase,9 and. © 1980, Massachusetts Medical Society. All rights reserved
Representing winter wheat in the Community Land Model (version 4.5)
Winter wheat is a staple crop for global food security, and is the
dominant vegetation cover for a significant fraction of Earth's croplands. As
such, it plays an important role in carbon cycling and land–atmosphere
interactions in these key regions. Accurate simulation of winter wheat growth
is not only crucial for future yield prediction under a changing climate, but
also for accurately predicting the energy and water cycles for winter wheat
dominated regions. We modified the winter wheat model in the Community Land
Model (CLM) to better simulate winter wheat leaf area index, latent heat
flux, net ecosystem exchange of CO2, and grain yield. These included
schemes to represent vernalization as well as frost tolerance and damage. We
calibrated three key parameters (minimum planting temperature, maximum crop
growth days, and initial value of leaf carbon allocation coefficient) and
modified the grain carbon allocation algorithm for simulations at the US
Southern Great Plains ARM site (US-ARM), and validated the model performance
at eight additional sites across North America. We found that the new winter
wheat model improved the prediction of monthly variation in leaf area index,
reduced latent heat flux, and net
ecosystem exchange root mean square error (RMSE) by 41 and 35 % during the
spring growing season. The model accurately simulated the interannual
variation in yield at the US-ARM site, but underestimated yield at sites and
in regions (northwestern and southeastern US) with historically greater
yields by 35 %
From wellness to medical diagnostic apps: the Parkinson's Disease case
This paper presents the design and development of the CloudUPDRS app and supporting system developed as a Class I medical device to assess the severity of motor symptoms for Parkinson’s Disease. We report on lessons learnt towards meeting fidelity and regulatory requirements; effective procedures employed to structure user context and ensure data quality; a robust service provision architecture; a dependable analytics toolkit; and provisions to meet mobility and social needs of people with Parkinson’s
Identification of key parameters controlling demographically structured vegetation dynamics in a land surface model: CLM4.5(FATES)
Vegetation plays an important role in regulating global carbon cycles and is a key component of the Earth system models (ESMs) that aim to project Earth\u27s future climate. In the last decade, the vegetation component within ESMs has witnessed great progress from simple “big-leaf” approaches to demographically structured approaches, which have a better representation of plant size, canopy structure, and disturbances. These demographically structured vegetation models typically have a large number of input parameters, and sensitivity analysis is needed to quantify the impact of each parameter on the model outputs for a better understanding of model behavior. In this study, we conducted a comprehensive sensitivity analysis to diagnose the Community Land Model coupled to the Functionally Assembled Terrestrial Simulator, or CLM4.5(FATES). Specifically, we quantified the first- and second-order sensitivities of the model parameters to outputs that represent simulated growth and mortality as well as carbon fluxes and stocks for a tropical site with an extent of 1×1∘. While the photosynthetic capacity parameter (Vc,max25) is found to be important for simulated carbon stocks and fluxes, we also show the importance of carbon storage and allometry parameters, which determine survival and growth strategies within the model. The parameter sensitivity changes with different sizes of trees and climate conditions. The results of this study highlight the importance of understanding the dynamics of the next generation of demographically enabled vegetation models within ESMs to improve model parameterization and structure for better model fidelity
Assessing climate change impacts on live fuel moisture and wildfire risk using a hydrodynamic vegetation model
Live fuel moisture content (LFMC) plays a critical role in wildfire dynamics, but little is known about responses of LFMC to multivariate climate change, e.g., warming temperature, CO2 fertilization, and altered precipitation patterns, leading to a limited prediction ability of future wildfire risks. Here, we use a hydrodynamic demographic vegetation model to estimate LFMC dynamics of chaparral shrubs, a dominant vegetation type in fire-prone southern California. We parameterize the model based on observed shrub allometry and hydraulic traits and evaluate the model\u27s accuracy through comparisons between observed and simulated LFMC of three plant functional types (PFTs) under current climate conditions. Moreover, we estimate the number of days per year of LFMC below 79 % (which is a critical threshold for wildfire danger rating of southern California chaparral shrubs) from 1960 to 2099 for each PFT and compare the number of days below the threshold for medium and high greenhouse gas emission scenarios (RCP4.5 and 8.5). We find that climate change could lead to more days per year (5.2 %–14.8 % increase) with LFMC below 79 % between the historical (1960–1999) and future (2080–2099) periods, implying an increase in wildfire danger for chaparral shrubs in southern California. Under the high greenhouse gas emission scenario during the dry season, we find that the future LFMC reductions mainly result from a warming temperature, which leads to 9.1 %–18.6 % reduction in LFMC. Lower precipitation in the spring leads to a 6.3 %–8.1 % reduction in LFMC. The combined impacts of warming and precipitation change on fire season length are equal to the additive impacts of warming and precipitation change individually. Our results show that the CO2 fertilization will mitigate fire risk by causing a 3.5 %–4.8 % increase in LFMC. Our results suggest that multivariate climate change could cause a significant net reduction in LFMC and thus exacerbate future wildfire danger in chaparral shrub systems
Protecting climate with forests
Policies for climate mitigation on land rarely acknowledge biophysical factors, such as reflectivity, evaporation, and surface roughness. Yet such factors can alter temperatures much more than carbon sequestration does, and often in a conflicting way. We outline a framework for examining biophysical factors in mitigation policies and provide some best-practice recommendations based on that framework. Tropical projects-avoided deforestation, forest restoration, and afforestation-provide the greatest climate value, because carbon storage and biophysics align to cool the Earth. In contrast, the climate benefits of carbon storage are often counteracted in boreal and other snow-covered regions, where darker trees trap more heat than snow does. Managers can increase the climate benefit of some forest projects by using more reflective and deciduous species and through urban forestry projects that reduce energy use. Ignoring biophysical interactions could result in millions of dollars being invested in some mitigation projects that provide little climate benefit or, worse, are counter-productive
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