23,112 research outputs found
A new intermediate for the production of flexible stable polymers
Method of incorporating ether linkages into perfluoroalkylene segment of a dianydride intermediate yields intermediate that may be used in synthesis of flexible, stable polyimides for use as high-temperature, solvent-resistant sealants
Development of improved potting and conformal coating compounds
Improved organic potting and conformal coating materials protect fragile electronic components and circuitry from mechanical shock and vibration, moisture, and corrosion. These materials meet specifications covering resistance to cycling, radiation, flammability, and sterilizing agents for certain space applications
Cereal Leaf Beetle (Coleoptera: Chrysomelidae) Influence of Seeding Rate of Oats on Populations
In field and greenhouse studies, more cereal leaf beetle [Oulema melanopus (Lin- naeus)] eggs and larvae were found per unit area on spring oats, Avena sativa L., planted either at intermediate (54 kg/ha) or high (136 kg/ha) seeding rates, than when planted at a lower seeding rate (14 kg/ha). However, there were fewer eggs and larvae per stem in plantings of the high or intermediate rates than in those of the lower rate. Oats should not be planted at less than the recommended rates in beetle-infested areas
Quasar-galaxy associations
There is controversy about the measurement of statistical associations
between bright quasars and faint, presumably foreground galaxies. We look at
the distribution of galaxies around an unbiased sample of 63 bright, moderate
redshift quasars using a new statistic based on the separation of the quasar
and its nearest neighbour galaxy. We find a significant excess of close
neighbours at separations less than about 10 arcsec which we attribute to the
magnification by gravitational lensing of quasars which would otherwise be too
faint to be included in our sample. About one quarter to one third of the
quasars are so affected although the allowed error in this fraction is large.Comment: uuencoded Postscript file (including figures and tables), SUSSEX-AST
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Multi-stage models for the failure of complex systems, cascading disasters, and the onset of disease
Complex systems can fail through different routes, often progressing through
a series of (rate-limiting) steps and modified by environmental exposures. The
onset of disease, cancer in particular, is no different. Multi-stage models
provide a simple but very general mathematical framework for studying the
failure of complex systems, or equivalently, the onset of disease. They include
the Armitage Doll multi-stage cancer model as a particular case, and have
potential to provide new insights into how failures and disease, arise and
progress. A method described by E.T. Jaynes is developed to provide an
analytical solution for a large class of these models, and highlights
connections between the convolution of Laplace transforms, sums of random
variables, and Schwinger/Feynman parameterisations. Examples include: exact
solutions to the Armitage-Doll model, the sum of Gamma-distributed variables
with integer-valued shape parameters, a clonal-growth cancer model, and a model
for cascading disasters. Applications and limitations of the approach are
discussed in the context of recent cancer research. The model is sufficiently
general to be used in many contexts, such as engineering, project management,
disease progression, and disaster risk for example, allowing the estimation of
failure rates in complex systems and projects. The intended result is a
mathematical toolkit for applying multi-stage models to the study of failure
rates in complex systems and to the onset of disease, cancer in particular
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