3,656 research outputs found
Reduction of the Clavicles in the Mesoenatidae, with Some Remarks Concerning the Relationship of the Clavicle to Flight-Function in Birds
Author Institution: Blue Sea Lake Biological Laboratory, Messines, Quebec, and Division of Birds, U. S. National Museum, Washington, D. C
Cosmological Relativity: A General-Relativistic Theory for the Accelerating Expanding Universe
Recent observations of distant supernovae imply, in defiance of expectations,
that the universe growth is accelerating, contrary to what has always been
assumed that the expansion is slowing down due to gravity. In this paper a
general-relativistic cosmological theory that gives a direct relationship
between distances and redshifts in an expanding universe is presented. The
theory is actually a generalization of Hubble's law taking gravity into account
by means of Einstein's theory of general relativity. The theory predicts that
the universe can have three phases of expansion, decelerating, constant and
accelerating, but it is shown that at present the first two cases are excluded,
although in the past it had experienced them. Our theory shows that the
universe now is definitely in the stage of accelerating expansion, confirming
the recent experimental results
Classification of multifluid CP world models
Various classification schemes exist for homogeneous and isotropic (CP) world
models, which include pressureless matter (so-called dust) and Einstein's
cosmological constant Lambda. We here classify the solutions of more general
world models consisting of up to four non-interacting fluids, each with
pressure P, energy density epsilon and an equation of state P = (gamma - 1)
epsilon with 0 <= gamma <= 2.
In addition to repulsive fluids with negative pressure and positive energy
density, which generalize the classical repulsive (positive) Lambda component,
we consider fluids with negative energy density as well. The latter generalize
a negative Lambda component. This renders possible new types of models that do
not occur among the classical classifications of world models. Singularity-free
periodic solutions as well as further `hill-type', `hollow-type' and
`shifting-type' models are feasible.
However, if one only allows for three components (dust, radiation and one
repulsive component) in a spatially flat universe the repulsive classical
Lambda fluid (with Lambda > 0) tends to yield the smoothest fits of the
Supernova Ia data from Perlmutter et al. (1999). Adopting the SN Ia
constraints, exotic negative energy density components can be fittingly
included only if the universe consists of four or more fluids.Comment: 12 pages, 11 figures, latex, A&A in pres
Aeroelastic simulation of higher harmonic control
This report describes the development of an aeroelastic analysis of a helicopter rotor and its application to the simulation of helicopter vibration reduction through higher harmonic control (HHC). An improved finite-state, time-domain model of unsteady aerodynamics is developed to capture high frequency aerodynamic effects. An improved trim procedure is implemented which accounts for flap, lead-lag, and torsional deformations of the blade. The effect of unsteady aerodynamics is studied and it is found that its impact on blade aeroelastic stability and low frequency response is small, but it has a significant influence on rotor hub vibrations. Several different HHC algorithms are implemented on a hingeless rotor and their effectiveness in reducing hub vibratory shears is compared. All the controllers are found to be quite effective, but very differing HHC inputs are required depending on the aerodynamic model used. Effects of HHC on rotor stability and power requirements are found to be quite small. Simulations of roughly equivalent articulated and hingeless rotors are carried out, and it is found that hingeless rotors can require considerably larger HHC inputs to reduce vibratory shears. This implies that the practical implementation of HHC on hingeless rotors might be considerably more difficult than on articulated rotors
Radon and lung cancer: case-control studies versus ecologic studies
Problems in epidemiological studies in connection with the
determination of radon-caused lung cancer are discussed. Biasing and confounding effects have led to very divergent results in epidemiological studies and there is still doubt on the carcinogenic effect of radon progenies in the concentration range of usual indoor air (say below several hundred Bq/m3). Nevertheless, epidemiological
investigations seem to be the key tool to decide this question. Main advantages and disadvantages of case-control and ecologic studies are discussed and an overall
uncertainty estimation is given for both types of investigations
Report of Virtual Conference. BASICS Phase I - Achievements and Learnings Meeting. May 18-19, 2020
The Building an Economically Sustainable Integrated Cassava Seed System in Nigeria (BASICS) project began in 2016 and formally ends on 30 June 2020. The project has made progress in demonstrating that commercially viable production and sale of breeder, foundation and certified seed is possible. Furthermore, the project has established a strong basis for building a sustainable seed system by developing building blocks across the seed value chain. This meeting had the following objectives: 1. To identify the achievements and lessons learned in each of the project components; 2. To identify the shortcomings in each component (what would I do differently, knowing what I know now?), remaining challenges and ideas to overcome them; 3. To assess and discuss the challenges and progress made in integrating the components into an integrated seed system and identify ways integration can be improved; 4. To assess and discuss the commercial sustainability of the seed system and identify options to promote its sustainability and further scaling; and 5. To make plans for the publication of the findings and lessons learned during BASICS-
Entropic Accelerating Universe
To accommodate the observed accelerated expansion of the universe, one
popular idea is to invoke a driving term in the Friedmann-Lemaitre equation of
dark energy which must then comprise 70% of the present cosmological energy
density. We propose an alternative interpretation which takes into account the
entropy and temperature intrinsic to the horizon of the universe due to the
information holographically stored there. Dark energy is thereby obviated and
the acceleration is due to an entropic force naturally arising from the
information storage on the horizon surface screen. We consider an additional
quantitative approach inspired by surface terms in general relativity and show
that this leads to the entropic accelerating universe.Comment: 14 pages, 1 figure, extended and clarifie
1980 Ruby Yearbook
A digitized copy of the 1980 Ruby, the Ursinus College yearbook.https://digitalcommons.ursinus.edu/ruby/1083/thumbnail.jp
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