237 research outputs found
Moisture Diffusion Analysis of Composite Strength Degradation
Moisture diffusion analysis (MDA) has been developed as a new non-destructive evaluation methodology to monitor the strength degradation of graphite-epoxy composite materials. Studies of composite strength degradation due to high moisture identify reversible strength loss due to current moisture content and irreversible strength loss related to prior moisture exposure with microstructure damage. MDA measures current moisture content, directional diffusion coefficients, and moisture concentration profiles. MDA measurement utilizes an electrolytic cell to concurrently record cumulative moisture content and moisture effusion rate. Extension of the diffusion analysis of Shen and Springer isolates directional diffusion coefficients and indicates a high sensitivity of MDA to moisture degradation of the fiber-matrix interface. Extension of the methodology to analyze non-Fickian diffusion shows that MDA can be applied to locate regions of composite strength degradation related to hydrothermal cycling effects. Studies which correlate MDA with ultrasonic response, and interlaminar shear strength of composite laminates subjected to localized moisture damage, show that MDA can be applied to map and locate low strength regions of a composite structure
Study program for encapsulation materials interface for low-cost solar array
The service integrity of the bonded interface in solar cell modules used in solar arrays is addressed. The development of AC impedance as a nondestructive evaluation (NDE) methodology for solar arrays is reported along with development of corrosion models and materials selection criteria for corrosion resistant interfaces
Study program for encapsulation materials interface for low cost silicon solar array
An atmospheric corrosion model was developed and verified by five months of corrosion rate and climatology data acquired at the Mead, Nebraska LSA test site. Atmospheric corrosion rate monitors (ACM) show that moisture condensation probability and ionic conduction at the corroding surface or interface are controlling factors in corrosion rate. Protection of the corroding surface by encapsulant was shown by the ACM recordings to be maintained, independent of climatology, over the five months outdoor exposure period. The macroscopic corrosion processes which occur at Mead are shown to be reproduced in the climatology simulator. Controlled experiments with identical moisture and temperature aging cycles show that UV radiation causes corrosion while UV shielding inhibits LSA corrosion
High Velocity Rain: The Terminal Velocity of Model of Galactic Infall
A model is proposed for determining the distances to falling interstellar
clouds in the galactic halo by measuring the cloud velocity and column density
and assuming a model for the vertical density distribution of the Galactic
interstellar medium. It is shown that falling clouds with may be decelerated to a terminal velocity which increases with
increasing height above the Galactic plane. This terminal velocity model
correctly predicts the distance to high velocity cloud Complex M and several
other interstellar structures of previously determined distance. It is
demonstrated how interstellar absorption spectra alone may be used to predict
the distances of the clouds producing the absorption. If the distances to the
clouds are already known, we demonstrate how the model may be used to determine
the vertical density structure of the ISM. The derived density distribution is
consistent with the expected density distribution of the warm ionized medium,
characterized by Reynolds. There is also evidence that for
one or more of the following occurs: (1) the neutral fraction of the cloud
decreases to , (2) the density drops off faster than
characterized by Reynolds, or (3) there is a systematic decrease in drag
coefficient with increasing z.Comment: ApJ, in pres
The Farm, the city, and the emergence of social security
We study the social, demographic and economic origins of social security. The data for the U.S. and for a cross section of countries suggest that urbanization and industrialization are associated with the rise of social insurance. We describe an OLG model in which demographics, technology, and social security are linked together in a political economy equilibrium. In the model economy, there are two locations (sectors), the farm (agricultural) and the city (industrial) and the decision to migrate from rural to urban locations is endogenous and linked to productivity differences between the two locations and survival probabilities. Farmers rely on land inheritance for their old age and do not support a pay-as-you-go social security system. With structural change, people migrate to the city, the land loses its importance and support for social security arises. We show that a calibrated version of this economy, where social security taxes are determined by majority voting, is consistent with the historical transformation in the United States
Surfactants at the design limit
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Langmuir, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.langmuir.5b00336This article analyzes how the individual structural elements of surfactant molecules affect surface properties, in particular, the point of reference defined by the limiting surface tension at the aqueous cmc, γcmc. Particular emphasis is given to how the chemical nature and structure of the hydrophobic tails influence γcmc. By comparing the three different classes of surfactants, fluorocarbon, silicone, and hydrocarbon, a generalized surface packing index is introduced which is independent of the chemical nature of the surfactants. This parameter ϕcmc represents the volume fraction of surfactant chain fragments in a surface film at the aqueous cmc. It is shown that ϕcmc is a useful index for understanding the limiting surface tension of surfactants and can be useful for designing new superefficient surfactants
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Robust image analysis with sparse representation on quantized visual features
10.1109/TIP.2012.2219543IEEE Transactions on Image Processing223860-871IIPR
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