3,542 research outputs found
A Third Planet Orbiting HIP 14810
We present new precision radial velocities and a three-planet Keplerian orbit
fit for the V = 8.5, G5 V star HIP 14810. We began observing this star at Keck
Observatory as part of the N2K Planet Search Project. Wright et al. (2007)
announced the inner two planets to this system, and subsequent observations
have revealed the outer planet planet and the proper orbital solution for the
middle planet. The planets have minimum masses of 3.9, 1.3, and 0.6 M_Jup and
orbital periods of 6.67, 147.7, and 952 d, respectively. We have numerically
integrated the family of orbital solutions consistent with the data and find
that they are stable for at least 10^6 yr. Our photometric search shows that
the inner planet does not transit.Comment: ApJL, accepte
Costing the ex situ conservation of genetic resources: maize and wheat at CIMMYT
Worldwide, the number of genebanks and the amount of seed stored in them has increased substantially over the past few decades. Most attention is focused on the likely benefits from conservation, but conserving germplasm involves costs whose nature and magnitude are largely unknown. In this paper we compile and use a set of cost data for wheat and maize stored in the CIMMYT genebank to address a number of questions. What is the cost of storing an accession of either crop for one more year, or, equivalently what is the benefit in terms of cost savings from eliminating duplicate accessions from the genebank? Relatedly, what is the cost from introducing a new accession into the genebank, given the decision to store it is revisited after one year? Does it make economic sense for CIMMYT to discard accessions that may be available elsewhere? As an extension of this line of inquiry it is possible to value the benefits from either consolidating genebanks or at least networking existing banks to reduce or eliminate duplicate holdings not needed for backup safety purposes. We present estimates of the size and scale economies evident in the CIMMYT operation as a basis for assessing the economics of consolidation. Genebanks represent a commitment to conserve seeds for the very long-run. In this study we report on these long-run costs for the CIMMYT genebank costs that are sensitive to the interest rate used and the protocols for periodically replenishing accessions that are shared with others or regenerating accessions whose viability gradually diminishes with age.Germplasm conservation., Gene banks, Plant., Maize Breeding., Wheat Breeding., Rate of return.,
Morphology of Anion-Conducting Ionenes Investigated by X-ray Scattering and Simulation
We have studied the morphology of a novel series of benzimidazole-based ionenes, methylated poly(hexamethyl-p-terphenylbenzimidazolium) (HMT-PMBI), in halide form. Materials with anion-exchange capacities ranging from 0 to 2.5 mequiv/g were studied. X-ray scattering reveals three length scales in the materials: ion–polymer spacing (4 Å), polymer–polymer interchain spacing (6 Å), and an intrachain repeat distance (20 Å). No long-range structure is apparent above the monomer length, which is rare in ion-conducting polymer membranes. In preliminary molecular dynamics simulations, water molecules were observed forming chains between ions, even at a modest level of hydration, providing an interpenetrating network where conductivity can occur
Improved Orbital Parameters And Transit Monitoring For HD 156846b
HD 156846b is a Jovian planet in a highly eccentric orbit (e = 0.85) with a period of 359.55 days. The pericenter passage at a distance of 0.16 AU is nearly aligned to our line of sight, offering an enhanced transit probability of 5.4% and a potentially rich probe of the dynamics of a cool planetary atmosphere impulsively heated during close approach to a bright star (V = 6.5). We present new radial velocity (RV) and photometric measurements of this star as part of the Transit Ephemeris Refinement and Monitoring Survey. The RV measurements from the Keck-High Resolution Echelle Spectrometer reduce the predicted transit time uncertainty to 20 minutes, an order of magnitude improvement over the ephemeris from the discovery paper. We photometrically monitored a predicted transit window under relatively poor photometric conditions, from which our non-detection does not rule out a transiting geometry. We also present photometry that demonstrates stability at the millimagnitude level over its rotational timescale
Gold as an inflation hedge?
This paper attempts to reconcile an apparent contradiction between short-run and long-run movements in the price of gold. The theoretical model suggests a set of conditions under which the price of gold rises over time at the general rate of inflation and hence be an effective hedge against inflation. The model also demonstrates that short-run changes in the gold lease rate, the real interest rate, convenience yield, default risk, the covariance of gold returns with other assets and the dollar/world exchange rate can disturb this equilibrium relationship and generate short-run price volatility. Using monthly gold price data (1976-1999), and cointegration regression techniques, an empirical analysis confirms the central hypotheses of the theoretical model
Ten New and Updated Multi-planet Systems, and a Survey of Exoplanetary Systems
We present the latest velocities for 10 multi-planet systems, including a
re-analysis of archival Keck and Lick data, resulting in improved velocities
that supersede our previously published measurements. We derive updated orbital
fits for ten Lick and Keck systems, including two systems (HD 11964, HD 183263)
for which we provide confirmation of second planets only tentatively identified
elsewhere, and two others (HD 187123, and HD 217107) for which we provide a
major revision of the outer planet's orbit. We compile orbital elements from
the literature to generate a catalog of the 28 published multiple-planet
systems around stars within 200 pc. From this catalog we find several
intriguing patterns emerging: - Including those systems with long-term radial
velocity trends, at least 28% of known planetary systems appear to contain
multiple planets. - Planets in multiple-planet systems have somewhat smaller
eccentricities than single planets. - The distribution of orbital distances of
planets in multi-planet systems and single planets are inconsistent:
single-planet systems show a pile-up at P ~ 3 days and a jump near 1 AU, while
multi-planet systems show a more uniform distribution in log-period. In
addition, among all planetary systems we find: - There may be an emerging,
positive correlation between stellar mass and giant-planet semi-major axis. -
Exoplanets more massive than Jupiter have eccentricities broadly distributed
across 0 < e < 0.5, while lower-mass exoplanets exhibit a distribution peaked
near e = 0.Comment: ApJ accepted. v.2 makes minor corrections to author list, citations,
and provides a stable set of orbital parameters for HD 183263 in Table 1. v.3
makes preprint consistent with ApJ version, minor changes to wording, orbital
parameters of HD 217107 and HD 187123c in Table
KELT-11b: A Highly Inflated Sub-Saturn Exoplanet Transiting the V=8 Subgiant HD 93396
We report the discovery of a transiting exoplanet, KELT-11b, orbiting the
bright () subgiant HD 93396. A global analysis of the system shows that
the host star is an evolved subgiant star with K,
, , log , and [Fe/H].
The planet is a low-mass gas giant in a day orbit,
with , , g cm, surface gravity log , and equilibrium temperature K. KELT-11 is the brightest known transiting exoplanet host
in the southern hemisphere by more than a magnitude, and is the 6th brightest
transit host to date. The planet is one of the most inflated planets known,
with an exceptionally large atmospheric scale height (2763 km), and an
associated size of the expected atmospheric transmission signal of 5.6%. These
attributes make the KELT-11 system a valuable target for follow-up and
atmospheric characterization, and it promises to become one of the benchmark
systems for the study of inflated exoplanets.Comment: 15 pages, Submitted to AAS Journal
The California Planet Survey III. A Possible 2:1 Resonance in the Exoplanetary Triple System HD 37124
We present new radial velocities from Keck Observatory and both Newtonian and
Keplerian solutions for the triple-planet system orbiting HD 37124. The orbital
solution for this system has improved dramatically since the third planet was
first reported in Vogt et al. 2005 with an ambiguous orbital period. We have
resolved this ambiguity, and the outer two planets have an apparent period
commensurability of 2:1. A dynamical analysis finds both resonant and
non-resonant configurations consistent with the radial velocity data, and
constrains the mutual inclinations of the planets to be less than about 30
degrees. We discuss HD 37124 in the context of the other 19 exoplanetary
systems with apparent period commenserabilities, which we summarize in a table.
We show that roughly one in three well-characterized multiplanet systems has a
apparent low-order period commensuribility, which is more than would naively be
expected if the periods of exoplanets in known multiplanet systems were drawn
randomly from the observed distribution of planetary orbital periods.Comment: 12 pp, emulateapj style, ApJ accepted. v2. Minor edits to update
numbers, fix garbled tex
Sexuality Generates Diversity in the Aflatoxin Gene Cluster: Evidence on a Global Scale
Aflatoxins are produced by Aspergillus flavus and A. parasiticus in oil-rich seed and grain crops and are a serious problem in agriculture, with aflatoxin B₁ being the most carcinogenic natural compound known. Sexual reproduction in these species occurs between individuals belonging to different vegetative compatibility groups (VCGs). We examined natural genetic variation in 758 isolates of A. flavus, A. parasiticus and A. minisclerotigenes sampled from single peanut fields in the United States (Georgia), Africa (Benin), Argentina (Córdoba), Australia (Queensland) and India (Karnataka). Analysis of DNA sequence variation across multiple intergenic regions in the aflatoxin gene clusters of A. flavus, A. parasiticus and A. minisclerotigenes revealed significant linkage disequilibrium (LD) organized into distinct blocks that are conserved across different localities, suggesting that genetic recombination is nonrandom and a global occurrence. To assess the contributions of asexual and sexual reproduction to fixation and maintenance of toxin chemotype diversity in populations from each locality/species, we tested the null hypothesis of an equal number of MAT1-1 and MAT1-2 mating-type individuals, which is indicative of a sexually recombining population. All samples were clone-corrected using multi-locus sequence typing which associates closely with VCG. For both A. flavus and A. parasiticus, when the proportions of MAT1-1 and MAT1-2 were significantly different, there was more extensive LD in the aflatoxin cluster and populations were fixed for specific toxin chemotype classes, either the non-aflatoxigenic class in A. flavus or the B₁-dominant and G₁-dominant classes in A. parasiticus. A mating type ratio close to 1∶1 in A. flavus, A. parasiticus and A. minisclerotigenes was associated with higher recombination rates in the aflatoxin cluster and less pronounced chemotype differences in populations. This work shows that the reproductive nature of the population (more sexual versus more asexual) is predictive of aflatoxin chemotype diversity in these agriculturally important fungi
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