905 research outputs found
Study on determining stability domains for nonlinear dynamical systems Quarterly progress report, 1 May - 1 Aug. 1966
Procedure for formulating problem of estimating domain of attraction of equilibrium solution of nonlinear dynamical system and development of numerical algorith
Parameterization of the set of positive- definite matrices and an algorithm for its generation
Numerical analysis on set elements for positive definite symmetric matrices by parameterizatio
Study on determining stability domains for nonlinear dynamical systems Final report 1 May 1966 - 1 Feb. 1967
Numerical procedure for determining stability domains in nonlinear dynamical system
Algorithm for Liapunov stability analysis
Development of algorithm provides automatic computation of quadratic estimate of domain of stability for stable equilibrium states of nonlinear systems of ordinary differential equations
Study on determining stability domains for nonlinear dynamical systems, II Quarterly progress report, 1 Aug. - 31 Oct. 1966
Stability domain determination for nonlinear dynamical syste
Further development of an algorithm for the nonlinear stability analysis of the orbiting astronomical observatory paired-tracker control system Final report
Algorithm development for estimating domain of attraction of OAO paired-tracker equilibrium state with Liapunov function
Isotopic Composition of Solar Wind Calcium: First in Situ Measurement by CELIAS/MTOF on Board SOHO
We present first results on the Ca isotopic abundances derived from the high
resolution Mass Time-of-Flight (MTOF) spectrometer of the charge, element, and
isotope analysis system (CELIAS) experiment on board the Solar and Heliospheric
Observatory (SOHO). We obtain isotopic ratios 40Ca/42Ca = (128+-47) and
40Ca/44Ca = (50+-8), consistent with terrestrial values. This is the first in
situ determination of the solar wind calcium isotopic composition and is
important for studies of stellar modeling and solar system formation since the
present-day solar Ca isotopic abundances are unchanged from their original
isotopic composition in the solar nebula.Comment: 14 pages, 3 figure
What is the benefit of ceilometers for aerosol remote sensing? An answer from EARLINET
With the establishment of ceilometer networks by national weather services, a discussion commenced to which extent these simple backscatter lidars can be used for aerosol research. Though primarily designed for the detection of clouds it was shown that at least observations of the vertical structure of the boundary layer might be possible. However, an assessment of the potential of ceilometers for the quantitative retrieval of aerosol properties is still missing. In this paper we discuss different retrieval methods to derive the aerosol backscatter coefficient beta(p),with special focus on the calibration of the ceilometers. Different options based on forward and backward integration methods are compared with respect to their accuracy and applicability. It is shown that advanced lidar systems such as those being operated in the framework of the European Aerosol Research Lidar Network (EARLINET) are excellent tools for the calibration, and thus beta(p) retrievals based on forward integration can readily be implemented and used for real-time applications. Furthermore, we discuss uncertainties introduced by incomplete overlap, the unknown lidar ratio, and water vapor absorption. The latter is relevant for the very large number of ceilometers operating in the spectral range around lambda = 905-910 nm. The accuracy of the retrieved beta(p) mainly depends on the accuracy of the calibration and the long-term stability of the ceilometer. Under favorable conditions, a relative error of beta(p) on the order of 10% seems feasible. In the case of water vapor absorption, corrections assuming a realistic water vapor distribution and laser spectrum are indispensable;otherwise errors on the order of 20% could occur. From case studies it is shown that ceilometers can be used for the reliable detection of elevated aerosol layers below 5 km, and can contribute to the validation of chemistry transport models, e. g.,the height of the boundary layer. However, the exploitation of ceilometer measurements is still in its infancy, so more studies are urgently needed to consolidate the present state of knowledge, which is based on a limited number of case studies
Cosmic ray neon, Wolf-Rayet stars, and the superbubble origin of galactic cosmic rays
The abundances of neon isotopes in the galactic cosmic rays (GCRs) are
reported using data from the Cosmic Ray Isotope Spectrometer (CRIS) aboard the
Advanced Composition Explorer (ACE). We compare our ACE-CRIS data for neon and
refractory isotope ratios, and data from other experiments, with recent results
from two-component Wolf-Rayet (WR) models. The three largest deviations of GCR
isotope ratios from solar-system ratios predicted by these models are indeed
present in the GCRs. Since WR stars are evolutionary products of OB stars, and
most OB stars exist in OB associations that form superbubbles, the good
agreement of these data with WR models suggests that superbubbles are the
likely source of at least a substantial fraction of GCRs.Comment: 22 pages, 6 figures Accepted for publication by Ap
Origin and evolution of the light nuclides
After a short historical (and highly subjective) introduction to the field, I
discuss our current understanding of the origin and evolution of the light
nuclides D, He-3, He-4, Li-6, Li-7, Be-9, B-10 and B-11. Despite considerable
observational and theoretical progress, important uncertainties still persist
for each and every one of those nuclides. The present-day abundance of D in the
local interstellar medium is currently uncertain, making it difficult to infer
the recent chemical evolution of the solar neighborhood. To account for the
observed quasi-constancy of He-3 abundance from the Big Bang to our days, the
stellar production of that nuclide must be negligible; however, the scarce
observations of its abundance in planetary nebulae seem to contradict this
idea. The observed Be and B evolution as primaries suggests that the source
composition of cosmic rays has remained quasi-constant since the early days of
the Galaxy, a suggestion with far reaching implications for the origin of
cosmic rays; however, the main idea proposed to account for that constancy,
namely that superbubbles are at the source of cosmic rays, encounters some
serious difficulties. The best explanation for the mismatch between primordial
Li and the observed "Spite-plateau" in halo stars appears to be depletion of Li
in stellar envelopes, by some yet poorly understood mechanism. But this
explanation impacts on the level of the recently discovered early ``Li-6
plateau'', which (if confirmed), seriously challenges current ideas of cosmic
ray nucleosynthesis.Comment: 18 pages, 9 figs. Invited Review in "Symposium on the Composition of
Matter", honoring Johannes Geiss on the occasion of his 80th birthday
(Grindelwald, Switzerland, Sept. 2006), to be published in Space Science
Series of ISS
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