4,629 research outputs found
A Treatise on Left Abomasal Displacement in Dairy Cattle
The modern dairy cow has become a refined biological machine. Hers is a background of production-oriented breeding and management practices that seek to maximize lactation capabilities. Such emphasis on these capabilities is not without consequence, however, and the dairy cow has acquired maladies that are uncommon in other members of the bovine species. This paper will review a problem that is more or less unique to dairy cows
A Planetary Companion to gamma Cephei A
We report on the detection of a planetary companion in orbit around the
primary star of the binary system Cephei. High precision radial
velocity measurements using 4 independent data sets spanning the time interval
1981--2002 reveal long-lived residual radial velocity variations superimposed
on the binary orbit that are coherent in phase and amplitude with a period or
2.48 years (906 days) and a semi-amplitude of 27.5 m s. We performed a
careful analysis of our Ca II H & K S-index measurements, spectral line
bisectors, and {\it Hipparcos} photometry. We found no significant variations
in these quantities with the 906-d period. We also re-analyzed the Ca II
8662 {\AA} measurements of Walker et al. (1992) which showed possible
periodic variations with the ``planet'' period when first published. This
analysis shows that periodic Ca II equivalent width variations were only
present during 1986.5 -- 1992 and absent during 1981--1986.5. Furthermore, a
refined period for the Ca II 8662 {\AA} variations is 2.14 yrs,
significantly less than residual radial velocity period. The most likely
explanation of the residual radial velocity variations is a planetary mass
companion with sin = 1.7 and an orbital semi-major axis
of 2.13 AU. This supports the planet hypothesis for the residual
radial velocity variations for Cep first suggested by Walker et al.
(1992). With an estimated binary orbital period of 57 years Cep is the
shortest period binary system in which an extrasolar planet has been found.
This system may provide insights into the relationship between planetary and
binary star formation.Comment: 19 pages, 15 figures, accepted in Ap. J. Includes additional data and
improved orbital solutio
Policy conformance in the corporate blog space
This paper describes part of a solution to the interpretation of human-readable policy documents into semi-automatic conformance checking. Using a socio-cognitively motivated representation of shared knowledge, and applying appropriate inference mechanisms from a normative perspective, a mechanism to automatically detect potentially non-conforming blog entries is detailed. Candidate non-conforming blog entries are flagged for a human to make a judgement on whether they should be published. Analysis of data from a public corporate blog is analysed and results suggest the methodology has merit
Minimal molecular building blocks for screening in quasi-two-dimensional organic–inorganic lead halide perovskites
Layered hybrid organic–inorganic lead halide perovskites have intriguing optoelectronic properties, but some of the most interesting perovskite systems, such as defective, disordered, or mixed perovskites, require multiple unit cells to describe and are not accessible within state-of-the-art ab initio theoretical approaches for computing excited states. The principal bottleneck is the calculation of the dielectric matrix, which scales formally as O(N4). We develop here a fully ab initio approximation for the dielectric matrix, known as IPSA-2C, in which we separate the polarizability of the organic/inorganic layers into minimal building blocks, thus circumventing the undesirable power-law scaling. The IPSA-2C method reproduces the quasi-particle band structures and absorption spectra for a series of Ruddlesden–Popper perovskites to high accuracy, by including critical nonlocal effects neglected in simpler models, and sheds light on the complicated interplay of screening between the organic and inorganic sublattices
Natural organic matter in sedimentary basins and its relation to arsenic in anoxic ground water: the example of West Bengal and its worldwide implications
In order to investigate the mechanism of As release to anoxic ground water in alluvial aquifers, the authors sampled ground waters from 3 piezometer nests, 79 shallow (80 m) wells, in an area 750 m by 450 m, just north of Barasat, near Kolkata (Calcutta), in southern West Bengal. High concentrations of As (200-1180 mug L-1) are accompanied by high concentrations of Fe (3-13.7 mgL(-1)) and PO4 (1-6.5 mg L-1). Ground water that is rich in Mn (1-5.3 mg L-1) contains <50 mug L-1 of As. The composition of shallow ground water varies at the 100-m scale laterally and the metre-scale vertically, with vertical gradients in As concentration reaching 200 mug L-1 m(-1). The As is supplied by reductive dissolution of FeOOH and release of the sorbed As to solution. The process is driven by natural organic matter in peaty strata both within the aquifer sands and in the overlying confining unit. In well waters, thermotolerant coliforms, a proxy for faecal contamination, are not present in high numbers (<10 cfu/100 ml in 85% of wells) showing that faecally-derived organic matter does not enter the aquifer, does not drive reduction of FeOOH, and so does not release As to ground water.Arsenic concentrations are high (much greater than50 mug L-1) where reduction of FeOOH is complete and its entire load of sorbed As is released to solution, at which point the aquifer sediments become grey in colour as FeOOH vanishes. Where reduction is incomplete, the sediments are brown in colour and resorption of As to residual FeOOH keeps As concentrations below 10 mug L-1 in the presence of dissolved Fe. Sorbed As released by reduction of Mn oxides does not increase As in ground water because the As resorbs to FeOOH. High concentrations of As are common in alluvial aquifers of the Bengal Basin arise because Himalayan erosion supplies immature sediments, with low surface-loadings of FeOOH on mineral grains, to a depositional environment that is rich in organic mater so that complete reduction of FeOOH is common. (C) 2004 Published by Elsevier Ltd
Origin and Dynamics of the Mutually Inclined Orbits of Upsilon Andromedae c and d
We evaluate the orbital evolution and several plausible origins scenarios for
the mutually inclined orbits of Upsilon Andromedae c and d. These two planets
have orbital elements that oscillate with large amplitudes and lie close to the
stability boundary. This configuration, and in particular the observed mutual
inclination, demands an explanation. The planetary system may be influenced by
a nearby low-mass star, Upsilon And B, which could perturb the planetary
orbits, but we find it cannot modify two coplanar orbits into the observed
mutual inclination of ~30 deg. However, it could incite ejections or collisions
between planetary companions that subsequently raise the mutual inclination to
>30 deg. Our simulated systems with large mutual inclinations tend to be
further from the stability boundary than Upsilon And, but we are able to
produce similar systems. We conclude that scattering is a plausible mechanism
to explain the observed orbits of Upsilon And c and d, but we cannot determine
whether the scattering was caused by instabilities among the planets themselves
or by perturbations from Upsilon And B. We also develop a procedure to
quantitatively compare numerous properties of the observed system to our
numerical models. Although we only implement this procedure to Upsilon And, it
may be applied to any exoplanetary system.Comment: 19 pages, 5 figures, accepted to Astrophysical Journa
Evidence for a Long-period Planet Orbiting Epsilon Eridani
High precision radial velocity (RV) measurements spanning the years
1980.8--2000.0 are presented for the nearby (3.22 pc) K2 V star Eri.
These data, which represent a combination of six independent data sets taken
with four different telescopes, show convincing variations with a period of
7 yrs. A least squares orbital solution using robust estimation
yields orbital parameters of period, = 6.9 yrs, velocity -amplitude
19 {\ms}, eccentricity 0.6, projected companion mass sin = 0.86
, and semi-major axis 3.3 AU. Ca II H&K S-index
measurements spanning the same time interval show significant variations with
periods of 3 and 20 yrs, yet none at the RV period. If magnetic activity were
responsible for the RV variations then it produces a significantly different
period than is seen in the Ca II data. Given the lack of Ca II variation with
the same period as that found in the RV measurements, the long-lived and
coherent nature of these variations, and the high eccentricity of the implied
orbit, Keplerian motion due to a planetary companion seems to be the most
likely explanation for the observed RV variations. The wide angular separation
of the planet from the star (approximately 1 arc-second) and the long orbital
period make this planet a prime candidate for both direct imaging and
space-based astrometric measurements.Comment: To appear in Astrophysical Journal Letters. 9 pages, 2 figure
Gravitational F-terms of N=1 Supersymmetric SU(N) Gauge Theories
We use the generalized Konishi anomaly equations and R-symmetry anomaly to
compute the exact perturbative and non-perturbative gravitational F-terms of
four-dimensional N=1 supersymmetric gauge theories. We formulate the general
procedure for computation and consider chiral and non-chiral SU(N) gauge
theories.Comment: 25 pages, v2: minor changes in section 4, references adde
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