1,135 research outputs found
Detection of arcs in Saturn's F ring during the 1995 Sun ring-plane crossing
Observations of the November 1995 Sun crossing of the Saturn's ring-plane
made with the 3.6m CFH telescope, using the UHAO adaptive optics system, are
presented here. We report the detection of four arcs located in the vicinity of
the F ring. They can be seen one day later in HST images. The combination of
both data sets gives accurate determinations of their orbits. Semi-major axes
range from 140020 km to 140080 km, with a mean of 140060 +- 60 km. This is
about 150 km smaller than previous estimates of the F ring radius from Voyager
1 and 2 data, but close to the orbit of another arc observed at the same epoch
in HST images.Comment: 8 pages, 3 figures, 1 table, To appear in A&A, for comments :
[email protected]
A Survey for Outer Satellites of Mars: Limits to Completeness
We surveyed the Hill sphere of Mars for irregular satellites. Our search
covered nearly the entire Hill Sphere, but scattered light from Mars excluded
the inner few arcminutes where the satellites Phobos and Deimos reside. No new
satellites were found to an apparent limiting red magnitude of 23.5, which
corresponds to radii of about 0.09 km using an albedo of 0.07.Comment: 5 figures (1 color), 2 Tables, to appear in AJ Nov. 200
On the Integrability, B\"Acklund Transformation and Symmetry Aspects of a Generalized Fisher Type Nonlinear Reaction-Diffusion Equation
The dynamics of nonlinear reaction-diffusion systems is dominated by the
onset of patterns and Fisher equation is considered to be a prototype of such
diffusive equations. Here we investigate the integrability properties of a
generalized Fisher equation in both (1+1) and (2+1) dimensions. A Painlev\'e
singularity structure analysis singles out a special case () as
integrable. More interestingly, a B\"acklund transformation is shown to give
rise to a linearizing transformation for the integrable case. A Lie symmetry
analysis again separates out the same case as the integrable one and
hence we report several physically interesting solutions via similarity
reductions. Thus we give a group theoretical interpretation for the system
under study. Explicit and numerical solutions for specific cases of
nonintegrable systems are also given. In particular, the system is found to
exhibit different types of travelling wave solutions and patterns, static
structures and localized structures. Besides the Lie symmetry analysis,
nonclassical and generalized conditional symmetry analysis are also carried
out.Comment: 30 pages, 10 figures, to appear in Int. J. Bifur. Chaos (2004
Accuracy of Cancer Information on the Internet: A Comparison of a Wiki with a Professionally Maintained Database
Background: A Wiki is a website which can be directly, openly edited; Wikipedia, a collaborative encyclopedia, is a well-known example. Due to Wiki’s lack of editorial control and formal structure, we hypothesized that the content would be less complete and less accurate than that presented on a formal, peer-reviewed web site. Our goal was to compare the coverage, accuracy, and readability of cancer information from a Wiki (Wikipedia) with a peer-reviewed web site, the patientoriented National Cancer Institute’s Physician Data Query (PDQ) comprehensive cancer database.
American Society of Clinical Oncology (ASCO) 46th Annual Meeting June 4-8, Chicago, IL
Homogenization of Biomechanical Models for Plant Tissues
In this paper homogenization of a mathematical model for plant tissue
biomechanics is presented. The microscopic model constitutes a strongly coupled
system of reaction-diffusion-convection equations for chemical processes in
plant cells, the equations of poroelasticity for elastic deformations of plant
cell walls and middle lamella, and Stokes equations for fluid flow inside the
cells. The chemical process in cells and the elastic properties of cell walls
and middle lamella are coupled because elastic moduli depend on densities
involved in chemical reactions, whereas chemical reactions depend on mechanical
stresses. Using homogenization techniques we derive rigorously a macroscopic
model for plant biomechanics. To pass to the limit in the nonlinear reaction
terms, which depend on elastic strain, we prove the strong two-scale
convergence of the displacement gradient and velocity field
- …