The Innermost Stable Circular Orbit of Binary Black Holes

We introduce a new method to construct solutions to the constraint equations of general relativity describing binary black holes in quasicircular orbit. Black hole pairs with arbitrary momenta can be constructed with a simple method recently suggested by Brandt and Bruegmann, and quasicircular orbits can then be found by locating a minimum in the binding energy along sequences of constant horizon area. This approach produces binary black holes in a "three-sheeted" manifold structure, as opposed to the "two-sheeted" structure in the conformal-imaging approach adopted earlier by Cook. We focus on locating the innermost stable circular orbit and compare with earlier calculations. Our results confirm those of Cook and imply that the underlying manifold structure has a very small effect on the location of the innermost stable circular orbit.Comment: 8 pages, 3 figures, RevTex, submitted to PR

Kinetic vs. Thermal-Field-Theory Approach to Cosmological Perturbations

A closed set of equations for the evolution of linear perturbations of homogeneous, isotropic cosmological models can be obtained in various ways. The simplest approach is to assume a macroscopic equation of state, e.g.\ that of a perfect fluid. For a more refined description of the early universe, a microscopic treatment is required. The purpose of this paper is to compare the approach based on classical kinetic theory to the more recent thermal-field-theory approach. It is shown that in the high-temperature limit the latter describes cosmological perturbations supported by collisionless, massless matter, wherein it is equivalent to the kinetic theory approach. The dependence of the perturbations in a system of a collisionless gas and a perfect fluid on the initial data is discussed in some detail. All singular and regular solutions are found analytically.Comment: 31 pages, 10 figures (uu encoded ps-file appended), REVTEX 3.0, DESY 94-040 / TUW-93-2

Estimating yield potential in temperate high-yielding, direct-seeded US rice production systems

Accurate estimation of a crop’s yield potential (Yp) is critical to addressing long-term food security via identification of the exploitable yield gap. Due to lack of field data, efforts to quantify crop yield potential typically rely on crop models. Using the ORYZA rice crop model, we sought to estimate Yp of irrigated rice for two widely used rice varieties (M-206 and CXL745) in three major US rice-producing regions that together represent some of the highest yielding rice regions of the world. Three major issues with the crop model had to be addressed to achieve acceptable simulation of Yp; first, the model simulated leaf area index (LAI) and biomass agreed poorly for all direct-seeded systems using default settings;second, cold-induced sterility and associated yield losses were poorly simulated for environments with a large diurnal temperature variation; lastly, simulated Yp was sensitive to the specified definition of physiological maturity. Except for the simulation of cold-induced sterility, all issues could be remedied within the existing model structure. In contrast, simulation of cold-induced sterility posed a continuing challenge to accurate simulation—one that will likely require changes to ORYZA’s formulation. Estimates of Yp from the modified model were validated against large multi-year data sets of experimental yields covering the majority of US rice production areas. Validation showed the adjusted model simulated Yp well, with most top yields falling within 85% of Yp for both varieties (77% and 78% observed yields within15% of Yp for CXL745 and M-206 respectively). Maximum estimated Yp was 14.3 (range of 8.2–14.5) and14.5 (range of 8.7–15.3) t ha−1for the Southern US and CA, respectively

Water quality investigations in the Upper Serpent River 1980 - 1984

Because the Provincial Water Quality Objectives for ammonia are exceeded for the length of the upper Serpent River downstream of the industrial effluents during certain periods of the year, it is inappropriate to define mixing zones. Due to the periodic presence of ammonia concentrations potentially lethal to fish, the immediate rehabilitation of the upper Serpent River is not a viable option with the existing process technology. It is recommended that the investigation of an alternate process technology that would significantly reduce in-stream ammonia concentrations be initiated. Realizing that stress to fish communities exists periodically in the upper Serpent River from the interaction of ammonia and pH, it is recommended that a feasibility study into effluent pH control be initiated. This study should determine the effect of effluent pH maintenance in the 6.5 to 7.5 range, recognizing the implications to downstream ammonia oxidation and the mobilization of metals from tailings areas. A study to define the cause of elevated river pH values during the winter months should also be initiated

In Depth Characterization of Repetitive DNA in 23 Plant Genomes Reveals Sources of Genome Size Variation in the Legume Tribe Fabeae

The differential accumulation and elimination of repetitive DNA are key drivers of genome size variation in flowering plants, yet there have been few studies which have analysed how different types of repeats in related species contribute to genome size evolution within a phylogenetic context. This question is addressed here by conducting large-scale comparative analysis of repeats in 23 species from four genera of the monophyletic legume tribe Fabeae, representing a 7.6-fold variation in genome size. Phylogenetic analysis and genome size reconstruction revealed that this diversity arose from genome size expansions and contractions in different lineages during the evolution of Fabeae. Employing a combination of low-pass genome sequencing with novel bioinformatic approaches resulted in identification and quantification of repeats making up 55-83% of the investigated genomes. In turn, this enabled an analysis of how each major repeat type contributed to the genome size variation encountered. Differential accumulation of repetitive DNA was found to account for 85% of the genome size differences between the species, and most (57%) of this variation was found to be driven by a single lineage of Ty3/gypsy LTR-retrotransposons, the Ogre elements. Although the amounts of several other lineages of LTR-retrotransposons and the total amount of satellite DNA were also positively correlated with genome size, their contributions to genome size variation were much smaller (up to 6%). Repeat analysis within a phylogenetic framework also revealed profound differences in the extent of sequence conservation between different repeat types across Fabeae. In addition to these findings, the study has provided a proof of concept for the approach combining recent developments in sequencing and bioinformatics to perform comparative analyses of repetitive DNAs in a large number of non-model species without the need to assemble their genomes

Water balances and evapotranspiration in water- and dry-seeded rice systems

Rice is a crop that is usually grown under flooded conditions and can require large amounts of water. The objective of this 3-year study was to quantify water use in water- (WS) and dry-seeded (DS) systems. In WS systems, the field is continuously flooded, while in DS systems the field is flush irrigated for the first month and then flooded. Research was conducted on commercial rice fields where the residual of the energy balance method using a sonic anemometer and the eddy covariance method were used to determine crop evapotranspiration (ETc) and crop coefficient (Kc) values. In addition, inlet irrigation water and tailwater drainage were determined. Across years, there was no difference in ETc (averaged 862 mm), seasonal Kc (averaged 1.07), irrigation water delivery (averaged 1839 mm) and calculated percolation and seepage losses (averaged 269 mm) between systems. An analysis of the first month of the season, when the water management between these two practices was different, indicated that Kc and water use were lower in DS systems relative to WS systems when there was only one irrigation flush during this period, while two or three irrigation flushes resulted in similar values between the two systems

Switchgrass is a promising, high-yielding crop for California biofuel

Ethanol use in California is expected to rise to 1.62 billion gallons per year in 2012, more than 90% of which will be trucked or shipped into the state. Switchgrass, a nonnative grass common in other states, has been identified as a possible high-yielding biomass crop for the production of cellulosic ethanol. The productivity of the two main ecotypes of switchgrass, lowland and upland, was evaluated under irrigated conditions across four diverse California ecozones - from Tulelake in the cool north to warm Imperial Valley in the south. In the first full year of production, the lowland varieties yielded up to 17 tons per acre of biomass, roughly double the biomass yields of California rice or maize. The yield response to nitrogen fertilization was statistically insignificant in the first year of production, except for in the Central Valley plots that were harvested twice a year. The biomass yields in our study indicate that switchgrass is a promising biofuel crop for California

Whispering to the Deaf: Communication by a Frog without External Vocal Sac or Tympanum in Noisy Environments

Atelopus franciscus is a diurnal bufonid frog that lives in South-American tropical rain forests. As in many other frogs, males produce calls to defend their territories and attract females. However, this species is a so-called “earless” frog lacking an external tympanum and is thus anatomically deaf. Moreover, A. franciscus has no external vocal sac and lives in a sound constraining environment along river banks where it competes with other calling frogs. Despite these constraints, male A. franciscus reply acoustically to the calls of conspecifics in the field. To resolve this apparent paradox, we studied the vocal apparatus and middle-ear, analysed signal content of the calls, examined sound and signal content propagation in its natural habitat, and performed playback experiments. We show that A. franciscus males can produce only low intensity calls that propagate a short distance (<8 m) as a result of the lack of an external vocal sac. The species-specific coding of the signal is based on the pulse duration, providing a simple coding that is efficient as it allows discrimination from calls of sympatric frogs. Moreover, the signal is redundant and consequently adapted to noisy environments. As such a coding system can be efficient only at short-range, territory holders established themselves at short distances from each other. Finally, we show that the middle-ear of A. franciscus does not present any particular adaptations to compensate for the lack of an external tympanum, suggesting the existence of extra-tympanic pathways for sound propagation