20,754 research outputs found
Effects of fiber/matrix interactions on the properties of graphite/epoxy composites
A state-of-the-art literature review of the interactions between fibers and resin within graphite epoxy composite materials was performed. Emphasis centered on: adhesion theory; wetting characteristics of carbon fiber; load transfer mechanisms; methods to evaluate and measure interfacial bond strengths; environmental influence at the interface; and the effect of the interface/interphase on composite performance, with particular attention to impact toughness. In conjunction with the literature review, efforts were made to design experiments to study the wetting behavior of carbon fibers with various finish variants and their effect on adhesion joint strength. The properties of composites with various fiber finishes were measured and compared to the base-line properties of a control. It was shown that by tailoring the interphase properties, a 30% increase in impact toughness was achieved without loss of mechanical properties at both room and elevated temperatures
Metopolophium festucae cerealium (Hemiptera: Aphididae) : a new addition to the aphid fauna of North America
Metopolophium festucae cerealium (Stroyan) (Hemiptera: Aphididae) was found in wheat fields in the Pacific Northwest in 2011 and 2012. This is the first record of M. f. cerealium in North America. This subspecies can be a serious pest of cereal crops
Money, credit, and the cyclical behavior of household investment
This paper focuses on a monetary explanation of two business cycle regularities: (i) business and household investment are positively correlated and procyclical and (ii) household investment tends to lead business investment. We construct a general equilibrium framework that explicitly incorporates a credit sector where real resources are employed in the production of costly household and business credit services. Financial intermediaries provide interest bearing accounts to households and loanable funds for credit producers. It is shown that liquidity effects from asymmetric monetary injections to the financial sector increase the availability of consumer and business credit services. The relative strength of these liquidity effects on business and household spending can provide a mechanism which captures both the direction and timing of their corresponding investments expenditures over the cycle. Furthermore, explaining these observations with a household credit channel also resolves some problematic predictions of existing liquidity effect models.Investments
Modelling the spring ozone maximum and the interhemispheric asymmetry in the remote marine boundary layer 1. Comparison with surface and ozonesonde measurements
Here we report a modelling study of the spring ozone maximum and its
interhemispheric asymmetry in the remote marine boundary layer (MBL). The
modelled results are examined at the surface and on a series of time-height
cross sections at several locations spread over the Atlantic, the Indian, and
the Pacific Oceans. Comparison of model with surface measurements at remote MBL
stations indicate a close agreement. The most striking feature of the
hemispheric spring ozone maximum in the MBL can be most easily identified at
the NH sites of Westman Island, Bermuda, and Mauna Loa, and at the SH site of
Samoa. Modelled ozone vertical distributions in the troposphere are compared
with ozone profiles. For the Atlantic and the Indian sites, the model generally
produces a hemispheric spring ozone maximum close to those of the measurements.
The model also produces a spring ozone maximum in the northeastern and tropical
north Pacific close to those measurements, and at sites in the NH high
latitudes. The good agreement between model and measurements indicate that the
model can reproduce the proposed mechanisms responsible for producing the
spring ozone maximum in these regions of the MBL, lending confidence in the use
of the model to investigate MBL ozone chemistry (see part 2 and part 3). The
spring ozone maximum in the tropical central south Pacific and eastern
equatorial Pacific are less well reproduced by the model, indicating that both
the transport of precursors from biomass burning emissions taking place
in southeastern Asia, Australia, Oceania, southern Africa, and South America
are not well represented in the model in these regions. Overall, the model
produces a better simulation at sites where the stratosphere and biomass
burning emissions are the major contributors.Comment: 24 pages, 8 figure
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