3,060 research outputs found
Implementing the Gaia Astrometric Global Iterative Solution (AGIS) in Java
This paper provides a description of the Java software framework which has
been constructed to run the Astrometric Global Iterative Solution for the Gaia
mission. This is the mathematical framework to provide the rigid reference
frame for Gaia observations from the Gaia data itself. This process makes Gaia
a self calibrated, and input catalogue independent, mission. The framework is
highly distributed typically running on a cluster of machines with a database
back end. All code is written in the Java language. We describe the overall
architecture and some of the details of the implementation.Comment: Accepted for Experimental Astronom
Improving distances to nearby bright stars: Combining astrometric data from Hipparcos, Nano-JASMINE and Gaia
Starting in 2013, Gaia will deliver highly accurate astrometric data, which
eventually will supersede most other stellar catalogues in accuracy and
completeness. It is, however, lim- ited to observations from magnitude 6 to 20
and will therefore not include the brightest stars. Nano-JASMINE, an ultrasmall
Japanese astrometry satellite, will observe these bright stars, but with much
lower accuracy. Hence, the Hipparcos catalogue from 1997 will likely remain the
main source of accurate distances to bright nearby stars. We are investigating
how this might be improved by optimally combining data from all three missions
in a joint astrometric solu- tion. This would take advantage of the unique
features of each mission: the historic bright-star measurements of Hipparcos,
the updated bright-star observations of Nano-JASMINE, and the very accurate
reference frame of Gaia. The long temporal baseline between the missions pro-
vides additional benefits for the determination of proper motions and binary
detection, which indirectly improve the parallax determination further. We
present a quantitative analysis of the expected gains based on simulated data
for all three missions.Comment: Final draft for the proceedings of the IAU Symposium 289: Advancing
the physics of cosmic distances, held in Beijing, China, August 2012, eds.
Richard de Grijs and Giuseppe Bono, Cambridge Univ. Pres
Largeâscale hydroâclimatology of the terrestrial Arctic drainage system
The largeâscale hydroâclimatology of the terrestrial Arctic drainage system is examined, focusing on the period 1960 onward. Special attention is paid to the Ob, Yenisey, Lena, and Mackenzie watersheds, which provide the bulk of freshwater discharge to the Arctic Ocean. Station data are used to compile monthly gridded time series of gaugeâcorrected precipitation (P). Gridded time series of precipitation minus evapotranspiration (PâET) are calculated from the moisture flux convergence using NCEP reanalysis data. Estimates of ET are obtained as a residual. Runoff (R) is obtained from available discharge records. For longâterm waterâyear means, PâET for the Yenisey, Lena, and Mackenzie watersheds is 16â20% lower than the observed runoff. In the Ob watershed, the two values agree within 9%. Given the uncertainties in PâET, we consider the atmospheric and surface water budgets to be reasonably closed. Compared to the other three basins, the mean runoff ratio (R/P) is lower in the Ob watershed, consistent with the high fraction of annual precipitation lost through ET. All basins exhibit summer maxima in P and minima in PâET. Summer PâET in the Ob watershed is negative due to high ET rates. For large domains in northern Eurasia, about 25% of July precipitation is associated with the recycling of water vapor evapotranspirated within each domain. This points to a significant effect of the land surface on the hydrologic regime. Variability in P and PâET has generally clear associations with the regional atmospheric circulation. A strong link with the Urals trough is documented for the Ob. Relationships with indices of the Arctic Oscillation and other teleconnections are generally weak. Waterâyear time series of runoff and PâET are strongly correlated in the Lena watershed only, reflecting extensive permafrost. Coldâseason runoff has increased in the Yenisey and Lena watersheds. This is most pronounced in the Yenisey watershed, where runoff has also increased sharply in spring, decreased in summer, but has increased for the year as a whole. The mechanisms for these changes are not entirely clear. While they fundamentally relate to higher air temperatures, increased winter precipitation, and strong summer drying, we speculate links with changes in active layer thickness and thawing permafrost
Growth and Carcass Characteristics of Market Pigs Fed Reduced Lysine Diets in Bedded Hoop Barns
This study compared growth performance and carcass characteristicsof finishing pigsfed reduced lysine diets in bedded hoop barns. The purpose of this study was to compare growth performance and carcass characteristics of market pigs fed reduced lysine diets in bedded hoop barns with the intended goal of improving intramuscular fat. Pens of finishing pigs housed in hoop barns at the ISU Western Research Farm,Castana,IA,were randomly assigned one of two dietary treatments. The first dietary treatment was a corn-soybean meal based finishing pig diet formulated to meet or exceed recommended standardized ileal digestible (SID) Lysine concentration. The second dietary treatment was also a corn-soybean meal based diet that was formulated to deliver 24% less SID Lysine. Pigs were fed for 80â110 days, with pig weight and feed disappearancebeing measured every 28d.Pigs were scanned using real time ultrasound at the end of the trial. Following harvest, a subset of loins were analyzed for quality attributes. Overall,pigs underfed lysine grew slower and less efficiently. There were no differences in loin quality caused by dietary treatment,although there was a trend for pigs underfed lysine to produce smaller loin muscles. Matching diet formulation with genetic potential is a sound strategy for maximizing lean growth in pigs. Underfeeding lysine to pigs with the genetic potential for high levels of lean-growth didnot result in improved loin quality
Researchers explore Arctic freshwater\u27s role in ocean circulation
A critical, but insufficiently understood, component of global change is the influence of Arctic freshwater input on water mass exchange between the Arctic Ocean and Atlantic and Pacific Oceans. Four of the Earth\u27s 10 largest river systems, the Mackenzie, Ob,Yenisei, and Lena, contribute water to the Arctic shore (Figure 1) from a vast watershed that drains continental interiors. This river discharge flows into the world\u27s largest contiguous continental shelf and supplies over 50% (1823 km3 ) of the riverine input to the Arctic Ocean
The Niche Pork Production Handbook
Niche pork markets grew rapidly in the late 1990âs and have continued to expand. There are currently at least 35 pork niche markets active in Iowa. These range from direct sales to consumers by individual farmers to organized marketing groups. Marketers consistently report more demand for pork than the existing supply of pigs that meet the niche market criteria. They also consistently report a shortage of producers and the expectation that the niche markets will continue to grow.
The lifestyle and financial opportunities offered by niche pork markets are attractive to many individuals. These individuals may have little or no experience with raising pigs. Much of the existing pig production resources are not appropriate for this audience. To address these needs, a Niche Pork Production handbook was developed in 2007. The handbook is a collection of 30 individual leaflets addressing practical issues of niche pork production. The handbook is available for download from the Iowa Pork Industry Center website: http://www.ipic.iastate.edu/publications.html.
This handbook was written to serve as an introduction to pig production with a focus on the practical issues facing niche market pig producers. Although perhaps most valuable to the novice, the information in this handbook is also useful to the more experienced pig producer considering niche pork production as well as the seasoned niche pork producer
Combining and comparing astrometric data from different epochs: A case study with Hipparcos and Nano-JASMINE
The Hipparcos mission (1989-1993) resulted in the first space-based stellar
catalogue including measurements of positions, parallaxes and annual proper
motions accurate to about one milli-arcsecond. More space astrometry missions
will follow in the near future. The ultra-small Japanese mission Nano-JASMINE
(launch in late 2013) will determine positions and annual proper motions with
some milli-arcsecond accuracy. In mid 2013 the next-generation ESA mission Gaia
will deliver some tens of micro-arcsecond accurate astrometric parameters.
Until the final Gaia catalogue is published in early 2020 the best way of
improving proper motion values is the combination of positions from different
missions separated by long time intervals. Rather than comparing positions from
separately reduced catalogues, we propose an optimal method to combine the
information from the different data sets by making a joint astrometric
solution. This allows to obtain good results even when each data set alone is
insufficient for an accurate reduction. We demonstrate our method by combining
Hipparcos and simulated Nano-JASMINE data in a joint solution. We show a
significant improvement over the conventional catalogue combination.Comment: 4 pages, 1 figure, 1 table; proceedings of ADASS XXI (Paris, 2011),
ASP Conference Serie
Diabetes, intracranial stenosis and microemboli in asymptomatic carotid stenosis
Background: The risk of stroke in patients with asymptomatic carotid stenosis (ACS) is now so low that it is important to have methods to identify those patients most likely to benefit from intervention, or who may require special consideration in choice of medical therapy. We studied the prediction of stroke, death or transient ischemic attacks (stroke/death/TIA) in patients with ACS by intracranial arterial stenosis, and microemboli on transcranial Doppler (TCD), and the effect of diabetes mellitus on microemboli, intracranial stenosis and risk of events. Methods: Patients with ACS \u3e 60% by Doppler ultrasound were recruited from the Stroke Prevention Clinic of University Hospital, London, Canada. All 339 participants underwent TCD for detection of intracranial stenosis and detection of microemboli, and carotid ultrasound to measure extracranial stenosis and total carotid plaque area. Participants were followed for three years, to determine the risk of stroke/death/TIA. Results: Stroke/death/TIA occurred in 38% of patients with microemboli versus 10% without (p=0.0001), and in 18% of patients with intracranial stenosis, versus 10% without (p=0.042). Diabetics were significantly more likely to have intracranial stenosis (45% vs. 29%, p =0.014), microemboli (38% vs. 10%, p \u3c0.0001), and had significantly higher risk of stroke/death/TIA over three years (21% vs. 11% without; p=0.024). Survival free of stroke, TIA or death was significantly better without microemboli or intracranial stenosis (p\u3c0.0001). Conclusions: Diabetes, microemboli and intracranial stenosis predicted higher risk of stroke, death or TIA than did extracranial stenosis or total plaque area; diabetics may need more intensive therapy
Joint astrometric solution of Hipparcos and Gaia: A recipe for the Hundred Thousand Proper Motions project
The first release of astrometric data from Gaia is expected in 2016. It will
contain the mean stellar positions and magnitudes from the first year of
observations. For more than 100 000 stars in common with the Hipparcos
Catalogue it will be possible to compute very accurate proper motions due to
the time difference of about 24 years between the two missions. This Hundred
Thousand Proper Motions (HTPM) project will be part of the first release. Our
aim is to investigate how early Gaia data can be optimally combined with
information from the Hipparcos Catalogue in order to provide the most accurate
and reliable results for HTPM. The Astrometric Global Iterative Solution (AGIS)
was developed to compute the astrometric core solution based on the Gaia
observations and will be used for all releases of astrometric data from Gaia.
We adapt AGIS to process Hipparcos data in addition to Gaia observations, and
use simulations to verify and study the joint solution method. For the HTPM
stars we predict proper motion accuracies between 14 and 134 muas/yr, depending
on stellar magnitude and amount of Gaia data available. Perspective effects
will be important for a significant number of HTPM stars, and in order to treat
these effects accurately we introduce a scaled model of kinematics. We define a
goodness-of-fit statistic which is sensitive to deviations from uniform space
motion, caused for example by binaries with periods of 10-50 years. HTPM will
significantly improve the proper motions of the Hipparcos Catalogue well before
highly accurate Gaia- only results become available. Also, HTPM will allow us
to detect long period binary and exoplanetary candidates which would be
impossible to detect from Gaia data alone. The full sensitivity will not be
reached with the first Gaia release but with subsequent data releases.
Therefore HTPM should be repeated when more Gaia data become available.Comment: Revised manuscript following referee report. Accepted for publication
in A&
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