29,796 research outputs found
A Census of the Carina Nebula -- II. Energy Budget and Global Properties of the Nebulosity
The first paper in this series took a direct census of energy input from the
known OB stars in the Carina Nebula, and in this paper we study the global
properties of the surrounding nebulosity. We find that the total IR luminosity
of Carina is about 1.2E7 Lsun, accounting for only about 50-60% of the known
stellar luminosity from Paper I. Similarly, the ionizing photon luminosity --
(abridged; many important details omitted). Synchronized star formation around
the periphery of Carina provides a strong case that star formation here was
indeed triggered by stellar winds and UV radiation. This second generation
appears to involve a cascade toward preferentially intermediate- and low-mass
stars, but this may soon change when eta Car and its siblings explode. If the
current reservoir of atomic and molecular gas can be tapped at that time,
massive star formation may be rejuvinated around the periphery of Carina much
as if it were a young version of Gould's Belt. Also, when these multiple SNe
occur, the triggered second generation will be pelted repeatedly with SN ejecta
bearing short-lived radioactive nuclides. Carina may therefore represent the
most observable analog to the cradle of our own Solar System.Comment: MNRAS accepted, 14 pages, fig 1 in colo
Mathematical Properties of a Class of Four-dimensional Neutral Signature Metrics
While the Lorenzian and Riemanian metrics for which all polynomial scalar
curvature invariants vanish (the VSI property) are well-studied, less is known
about the four-dimensional neutral signature metrics with the VSI property.
Recently it was shown that the neutral signature metrics belong to two distinct
subclasses: the Walker and Kundt metrics. In this paper we have chosen an
example from each of the two subcases of the Ricci-flat VSI Walker metrics
respectively.
To investigate the difference between the metrics we determine the existence
of a null, geodesic, expansion-free, shear-free and vorticity-free vector, and
classify these spaces using their infinitesimal holonomy algebras. The
geometric implications of the holonomy algebras are further studied by
identifying the recurrent or covariantly constant null vectors, whose existence
is required by the holonomy structure in each example. We conclude the paper
with a simple example of the equivalence algorithm for these pseudo-Riemannian
manifolds, which is the only approach to classification that provides all
necessary information to determine equivalence.Comment: 18 page
Loran-C performance assurance assessment program
The Federal Aviation Administration (FAA) has accepted the Loran-C navigation system as a supplemental navigation aid for enroute use. Extension of Loran-C utilization to instrument approaches requires establishment of a process by which the current level of performance of the system is always known by the pilot. This system 'integrity' translates into confidence that, if the system is made available to the pilot, the guidance will be correct. Early in the consideration of Loran-C for instrument approaches, the Loran-C Planning Work-Group (LPW) was formed with membership from the FAA, the US Coast Guard, various state governments, aviation users, equipment manufacturers and technical experts. The group was hosted and co-chaired by the National Association of State Aviation Officials (NASAO). This forum was ideal for identification of system integrity issues and for finding the correct process for their resolution. Additionally, the Wild Goose Association (WGA), which is the international Loran-C technical and user forum, regularly brings together members of the FAA, Coast Guard, and the scientific community. Papers and discussions from WGA meetings have been helpful. Given here is a collection of the issues in which Ohio University became involved. Issues definition and resolution are included along with the recommendations in those areas where resolution is not yet complete
An Unusual Case of Tertiary Syphilis Behaving Like Tongue Squamous Cell Carcinoma.
Syphilis may present with a myriad of oral manifestations in the primary, secondary, and tertiary stages, and may be confused with malignancy. Despite a rise in the incidence of syphilis, tertiary syphilis is exceedingly rare. Tertiary syphilis gummas usually affect the hard palate, while tongue involvement is very rare. A 55-year-old male with extensive smoking and alcohol use was referred for malignancy evaluation with an ulcerative mass creating a tongue cleft, and a positron emission tomography scan suggestive for malignancy. Biopsy results demonstrated no carcinoma but histology demonstrated granulomatous inflammation. Further laboratory results demonstrated elevated rapid plasma reagin titers with Treponema pallidum immunoglobulin G antibodies present. The patient was diagnosed with tertiary syphilis, received appropriate antibiotic therapy, and had healing of the tongue with a persistent cleft. Syphilis may mimic many disease processes. As such, it is important to include this disease in the differential of an unusual tongue lesion. An oral lesion may be the first sign of infection
Stock assessment of protogynous fish: evaluating measures of spawning biomass used to estimate biological reference points
In stock assessments, recruitment is typically modeled as a function of females only. For protogynous stocks, however, disproportionate fishing on males increases the possibility of reduced fertilization rates. To incorporate the importance of males in protogynous stocks, assessment models have been used to predict recruitment not just from female spawning biomass (Sf), but also from that of males (Sm) or both sexes (Sb). We conducted a simulation study to evaluate the ability of these three measures to estimate biological reference points used in fishery management. Of the three, Sf provides best estimates if the potential for decreased fertilization is weak, whereas Sm is best only if the potential is very strong. In general, Sb estimates the true reference points most closely, which indicates that if the potential for decreased fertilization is moderate or unknown, Sb should be used in assessments of protogynous stocks. Moreover, for a broad range of scenarios, relative errors from Sf and Sb occur in opposite directions, indicating that estimates from these measures could be used to bound uncertainty
AGROFORESTRY POLICIES CONTRIBUTE TO SUSTAINABLE LAND USE
Resource /Energy Economics and Policy,
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