43 research outputs found
IDENTIFYING COST-EFFECTIVE SOURCES FOR WATER TRANSFERS FROM AGRICULTURE TO ENDANGERED SPECIES PRESERVATION IN THE PLATTE RIVER BASIN
Resource /Energy Economics and Policy,
BENEFITS OF CONTROLLING SALINE WATER IN COLORADO
The Arkansas River in Colorado is confronted with a salinity issue; the majority of this salinity problem is due to agricultural runoff caused by irrigation. Reducing applications of irrigation water through adoption of more technically efficient irrigation systems is one means of improving water quality in the Arkansas River basin. This research uses positive mathematical programming to model the cropping practices of the farms along the Arkansas River. It examines the affect of acreage and profit levels of these farms given the choice of changing their irrigation technologies.Environmental Economics and Policy,
HD 101088, An Accreting 14 AU Binary in Lower Centaurus Crux With Very Little Circumstellar Dust
We present high resolution (R=55,000) optical spectra obtained with MIKE on
the 6.5 m Magellan Clay Telescope as well as Spitzer MIPS photometry and IRS
low resolution (R~60) spectroscopy of the close (14 AU separation) binary, HD
101088, a member of the ~12 Myr old southern region of the Lower Centaurus Crux
(LCC) subgroup of the Scorpius-Centaurus OB association. We find that the
primary and/or secondary is accreting from a tenuous circumprimary and/or
circumsecondary disk despite the apparent lack of a massive circumbinary disk.
We estimate a lower limit to the accretion rate of > 1x10^-9 solar masses per
year, which our multiple observation epochs show varies over a timescale of
months. The upper limit on the 70 micron flux allows us to place an upper limit
on the mass of dust grains smaller than several microns present in a
circumbinary disk of 0.16 moon masses. We conclude that the classification of
disks into either protoplanetary or debris disks based on fractional infrared
luminosity alone may be misleading.Comment: 8 pages, 2 figures, ApJ accepte
A Revised Age for Upper Scorpius and The Star-Formation History Among the F-Type Members of the Scorpius-Centaurus OB Association
We present an analysis of the ages and star-formation history of the F-type
stars in the Upper Scorpius (US), Upper Centaurus-Lupus (UCL) and Lower
Centaurus-Crux (LCC) subgroups of Scorpius-Centaurus. We find that 1) our
empirical isochrones are consistent with the previously published age-rank of
the Sco-Cen subgroups, 2) LCC and UCL appear to reach the main sequence turn-on
at spectral types ~F4 and ~F2, respectively. An analysis of the A-type stars
shows US reaching the main sequence at about spectral type ~A3. 3) The median
ages for the pre-main sequence members of UCL and LCC are 16 Myr and 17 Myr,
respectively, in agreement with previous studies, however we find that 4) Upper
Sco is much older than previously thought. The luminosities of the F-type stars
in US are typically a factor of ~2.5 less luminous than predicted for a 5 Myr
old population for four sets of evolutionary tracks. We reexamine the
evolutionary state and isochronal ages for the B-, A-, and G-type Upper Sco
members, and the evolved M supergiant Antares, and estimate a revised mean age
for Upper Sco of 11+/-1+/-2 Myr (statistical, systematic). Using radial
velocities and Hipparcos parallaxes we calculate a lower limit on the kinematic
expansion age for Upper Sco of >10.5 Myr (99% confidence). However, the data
are statistically consistent with no expansion. We reevaluate the inferred
masses for the known substellar companions in Upper Sco using the revised age.
Specifically, we estimate the mass of 1RXS J1609-2105b to be 14^{+2}_{-3} Mjup,
suggesting that it is a brown dwarf rather than a planet. Finally, we find the
fraction of F-type stars exhibiting Ha emission and/or a K-band excess
consistent with accretion to be 0/17 (<19%; 95% C.L.) in US at ~11 Myr, while
UCL has 1/41 (2^{+5}_{-1}%; 68% C.L.) accretors and LCC has 1/50 (2^{+4}_{-1}%;
68% C.L.) accretors at ~16 Myr and ~17 Myr, respectively. [Abridged]Comment: Accepted for publication in ApJ. Formatted with emulateapj, 28 pages,
16 figures, 14 table
Determination of an optimal response cut-off able to predict progression-free survival in patients with well-differentiated advanced pancreatic neuroendocrine tumours treated with sunitinib: an alternative to the current RECIST-defined response.
BACKGROUND: Sunitinib prolongs progression-free survival (PFS) in patients with advanced pancreatic neuroendocrine tumours (pNET). Response Evaluation Criteria in Solid Tumors (RECIST)-defined partial responses (PR; classically defined as ⩾30% size decrease from baseline) are infrequent.
METHODS: Individual data of pNET patients from the phase II [NCT00056693] and pivotal phase III [NCT00428597] trials of sunitinib were analysed in this investigator-initiated, post hoc study. The primary objective was to determine the optimal RECIST (v.1.0) response cut-off value to identify patients who were progression-free at 11 months (median PFS in phase III trial); and the most informative time-point (highest area under the curve (AUC) by receiver operating characteristic (ROC) analysis and logistic regression) for prediction of benefit (PFS) from sunitinib.
RESULTS: Data for 237 patients (85 placebo; 152 sunitinib (n=66.50 mg \u274-weeks on/2-weeks off\u27 schedule; n=86 \u2737.5 mg continuous daily dosing (CDD)\u27)) and 788 scans were analysed. The median PFS for sunitinib and placebo were 9.3 months (95% CI 7.6-12.2) and 5.4 months (95% CI 3.5-6.01), respectively (hazard ratio (HR) 0.43 (95% CI 0.29-0.62); P
CONCLUSIONS: A 10% reduction within marker lesions identifies pNET patients benefiting from sunitinib treatment with implications for maintenance of dose intensity and future trial design
Debris Disks in the Upper Scorpius OB Association
We present MIPS 24um and 70um photometry for 205 members of the Upper
Scorpius OB Association. These data are combined with published MIPS photometry
for 15 additional association members to assess the frequency of circumstellar
disks around 5 Myr old stars with spectral types between B0 and M5. Twelve
stars have a detectable 70um excess, each of which also has a detectable 24um
excess. A total of 54 stars are identified with a 24um excess more than 32%
above the stellar photosphere. The MIPS observations reveal 19 excess sources
-- 8 A/F/G stars and 11 K/M stars -- that were not previously identified with
an 8um or 16um excess. The lack of short-wavelength emission and the weak 24um
excess suggests that these sources are debris systems or the remnants of
optically thick primordial disks with inner holes. Despite the wide range of
luminosities of the stars hosting apparent debris systems, the excess
characteristics are consistent with all stars having dust at similar orbital
radii after factoring in variations in the radiation blowout particle size with
spectral type. The results for Upper Sco are compared to similar photometric
surveys from the literature to re-evaluate the evolution of debris emission.
After considering the completeness limits of published surveys and the effects
of stellar evolution on the debris luminosity, we find that the magnitude of
the 24um excess around F-type stars increases between ages of 5 and 17 Myr as
found by previous studies, but at < 2.6 sigma confidence. For B7-A9 and G0-K5
stars, any variations in the observed 24um excess emission over this age range
are significant at less than 2 sigma confidence.Comment: 34 pages, 9 figures, 4 tables, accepted by Ap
Ancient Lowland Maya neighborhoods: Average Nearest Neighbor analysis and kernel density models, environments, and urban scale
Many humans live in large, complex political centers, composed of multi-scalar communities including neighborhoods and districts. Both today and in the past, neighborhoods form a fundamental part of cities and are defined by their spatial, architectural, and material elements. Neighborhoods existed in ancient centers of various scales, and multiple methods have been employed to identify ancient neighborhoods in archaeological contexts. However, the use of different methods for neighborhood identification within the same spatiotemporal setting results in challenges for comparisons within and between ancient societies. Here, we focus on using a single method—combining Average Nearest Neighbor (ANN) and Kernel Density (KD) analyses of household groups—to identify potential neighborhoods based on clusters of households at 23 ancient centers across the Maya Lowlands. While a one-size-fits all model does not work for neighborhood identification everywhere, the ANN/KD method provides quantifiable data on the clustering of ancient households, which can be linked to environmental zones and urban scale. We found that centers in river valleys exhibited greater household clustering compared to centers in upland and escarpment environments. Settlement patterns on flat plains were more dispersed, with little discrete spatial clustering of households. Furthermore, we categorized the ancient Maya centers into discrete urban scales, finding that larger centers had greater variation in household spacing compared to medium-sized and smaller centers. Many larger political centers possess heterogeneity in household clustering between their civic-ceremonial cores, immediate hinterlands, and far peripheries. Smaller centers exhibit greater household clustering compared to larger ones. This paper quantitatively assesses household clustering among nearly two dozen centers across the Maya Lowlands, linking environment and urban scale to settlement patterns. The findings are applicable to ancient societies and modern cities alike; understanding how humans form multi-scalar social groupings, such as neighborhoods, is fundamental to human experience and social organization
MagAO Imaging of Long-period Objects (MILO). II. A Puzzling White Dwarf around the Sun-like Star HD 11112
The version of record, Rodigas, T. J. et al, 'MagAO Imaging of long-period objects (MILO). II. A puzzling white dwarf around the sun-like star HD 11112', The Astrophysical Journal, 831:177, November 2016, is available online via doi: 10.3847/0004-637X/831/2/177 © 2016. The American Astronomical Society. All rights reserved.HD 11112 is an old, Sun-like star that has a long-term radial velocity (RV) trend indicative of a massive companion on a wide orbit. Here we present direct images of the source responsible for the trend using the Magellan Adaptive Optics system. We detect the object (HD 11112B) at a separation of 2\fasec 2 (100 AU) at multiple wavelengths spanning 0.6-4 \microns ~and show that it is most likely a gravitationally-bound cool white dwarf. Modeling its spectral energy distribution (SED) suggests that its mass is 0.9-1.1 \msun, which corresponds to very high-eccentricity, near edge-on orbits from Markov chain Monte Carlo analysis of the RV and imaging data together. The total age of the white dwarf is discrepant with that of the primary star under most assumptions. The problem can be resolved if the white dwarf progenitor was initially a double white dwarf binary that then merged into the observed high-mass white dwarf. HD 11112B is a unique and intriguing benchmark object that can be used to calibrate atmospheric and evolutionary models of cool white dwarfs and should thus continue to be monitored by RV and direct imaging over the coming years.Peer reviewedFinal Published versio
Estimating residential water demand in the absence of volumetric water pricing
Rapid population growth has significantly increased the magnitude of water shortages in California. Although water shortages already exist, some of the state's utility systems are still not providing their residents with financial incentives for water conservation. Instead of using water meters to charge households according to their actual water usage, they are charging a flat fee for unlimited water service. When flat fees are charged for unlimited water service, the per-unit cost for additional water is zero and the decision to consume more water is determined by other factors. This study estimates the factors that influence residential water demand in a city that is currently charging flat fees for unlimited water service. The results indicate that the number of home occupants and the square footage of grass landscaping significantly affect water usage and the relationships between these variables are quantified.economics; residential water demand; water meters; water price; volumetric water pricing; California; water shortages; financial incentives; water conservation; water usage; flat fees; unlimited water service; USA; United States.