Compression failure mechanisms in unidirectional composites

Compression failure mechanisms in unidirectional composites were examined. Possible failure modes of constituent materials are summarized and analytical models for fiber microbuckling are reviewed from a unified viewpoint. Due to deficiencies in available models, a failure model based on nonlinear properties and initial fiber curvature is proposed. The effect of constituent properties on composite compression behavior was experimentally investigated using two different graphite fibers and four different epoxy resins. The predominant microscopic scale failure mode was found to be shear crippling. In a soft resin, shear crippling was in the form of buckling of fibers on a microscopic scale. However, stiff resins failure was characterized by the formation of a kink band. For unidirectional laminates, compressive strength, and compressive modulus to a less extent, were found to increase with increasing magnitude of resin modulus. The change in compressive strength with resin modulus was predicted using the proposed nonlinear model

Cloud information for FIRE from surface weather reports

Surface weather observations of clouds were analyzed to obtain a global cloud climatology (Warren et al, 1986; 1988). The form of the synoptic weather code limits the types of cloud information which are available from these reports. Comparison of surface weather reports with instrumental observations during the FIRE field experiments can help to clarify the operational definitions which were made in the climatology because of the nature of the synoptic code. The long-term climatology from surface weather observations is also useful background for planning the location and timing of intensive field experiments

The effect of resin toughness and modulus on compressive failure modes of quasi-isotropic graphite/epoxy laminates

Compressive failure mechanisms in quasi-isotropic graphite/epoxy laminates were characterized for both unnotched and notched specimens and also following damage by impact. Two types of fibers (Thornel 300 and 700) and four resin systems (Narmco 5208, American Cyanamid BP907, and Union Carbide 4901/MDA and 4901/mPDA) were studied. For all material combinations, failure of unnotched specimens was initiated by kinking of fibers in the 0-degree plies. A major difference was observed, however, in the mode of failure propagation after the 0-degree ply failure. The strength of quasi-isotropic laminates in general increased with increasing resin tensile modulus. The laminates made with Thornel 700 fibers exhibited slightly lower compressive strengths than did the laminates made with Thornel 300 fibers. The notch sensitivity as measured by the hole strength was lowest for the BP907 resin and highest for the 5208 resin. For the materials studied, however, the type of fiber had no effect on the notch sensitivity

U.S. Demand for Source–Differentiated Shrimp: A Differential Approach

Estimates of price and scale elasticities for U.S. consumed shrimp are derived using aggregate shrimp data differentiated by source country. Own-price elasticities for all countries had the expected negative signs, were statistically significant, and inelastic. The scale elasticities for all countries were positive and statistically significant at the 1% level with only the United States and Ecuador having scale elasticities of less than one. For the most part, the compensated demand effects showed that most of the cross-price effects were positive. Our results also suggest that despite the countervailing duties imposed by the United States, shrimp demand was fairly stable.CBS, conditional demand, countervailing duty, imports, scale elasticity, shrimp, Agribusiness, Farm Management, Food Consumption/Nutrition/Food Safety, Production Economics, C32, D12, Q13, Q22,

Livestock production system management responses to thermal challenges

The adaptive capabilities of animals and livestock production systems have been emphasized in this report. Biometeorology has a key role in rational management to meet the challenges of thermal environments. While the focus is primarily on cattle in warm or hot climates, the importance of dynamic animal responses to environmental challenges applies to all species and climates. Methods used to mitigate environmental challenges focus on heat loss/heat production balance. Under cold stress, reduction of heat loss is the key. Under heat stress, reduction of heat load or increasing heat loss are the primary management tools, although heat-tolerant animals are also available. In general, livestock with health problems and the most productive animals (e.g., highest growth rate or milk production) are at greatest risk of heat stress, thereby requiring the most attention. Risk management, by considering perceived thermal challenges, then assessing the potential consequences and acting accordingly, will reduce the impact of such challenges. Appropriate actions include: shade, sprinkling, air movement, or active cooling. Summarizing, the most important element of proactive environmental management to reduce risk is preparation: be informed, develop a strategic plan, observe and recognize animals in distress, and take appropriate tactical action

Fast Evaluation of Feynman Diagrams

We develop a new representation for the integrals associated with Feynman diagrams. This leads directly to a novel method for the numerical evaluation of these integrals, which avoids the use of Monte Carlo techniques. Our approach is based on based on the theory of generalized sinc ($\sin(x)/x$) functions, from which we derive an approximation to the propagator that is expressed as an infinite sum. When the propagators in the Feynman integrals are replaced with the approximate form all integrals over internal momenta and vertices are converted into Gaussians, which can be evaluated analytically. Performing the Gaussians yields a multi-dimensional infinite sum which approximates the corresponding Feynman integral. The difference between the exact result and this approximation is set by an adjustable parameter, and can be made arbitrarily small. We discuss the extraction of regularization independent quantities and demonstrate, both in theory and practice, that these sums can be evaluated quickly, even for third or fourth order diagrams. Lastly, we survey strategies for numerically evaluating the multi-dimensional sums. We illustrate the method with specific examples, including the the second order sunset diagram from quartic scalar field theory, and several higher-order diagrams. In this initial paper we focus upon scalar field theories in Euclidean spacetime, but expect that this approach can be generalized to fields with spin.Comment: uses feynmp macros; v2 contains improved description of renormalization, plus other minor change

CP violating asymmetry in H±→W±h1H^\pm\to W^\pm h_1 decays

The CP violating asymmetry from the decay rates $H^\pm\to W^\pm h_1$ of charged Higgs bosons into the lightest neutral Higgs boson and a $W^\pm$ boson is calculated and discussed in the complex MSSM. The contributions from all complex phases are considered, especially from the top-squark trilinear coupling, which induces a large contribution to the CP asymmetry.Comment: 19 pages, 10 figures, version published in JHE

CP Asymmetry in Charged Higgs Decays in MSSM

We discuss and compare the charge-parity (CP) asymmetry in the charged Higgs boson decays H -> \bar{u}_i d_j for the second and third generation quarks in the minimal supersymmetric standard model. As part of the analysis, we derive some general analytical formulas for the imaginary parts of two-point and three-point scalar one-loop integrals and use them for calculating vectorial and tensorial type integrals needed for the problem under consideration. We find that, even though each decay mode has a potential to yield a CP asymmetry larger than 10%, further analysis based on the number of required charged Higgs events at colliders favors the \bar{t}b, \bar{c}b, and \bar{c}s channels, whose asymmetry could reach 10-15% in certain parts of the parameter space.Comment: 25 pages, 9 figures. Discussion about charged Higgs observability added, typos corrected, accepted for publication in PR

Organic diets with alfalfa silage for laying hens: Egg quality

Laying hens were fed with organic diets containing chopped, extruded or pelleted alfalfa silage and the quality of the eggs was evaluated. Four groups were conformed: a control group (A) fed with a complete feed mixture (CFM) and three silage groups (B, C and D) fed with a supplementary feed mixture (SFM). The SFM was formulated based on an assumed ingestion of 20 % silage and rapeseed oil was used as energy source. Before ensiling, the alfalfa was chopped (B) and additionally extruded (C). One half of the extruded silage was pelleted together with the SFM to produce the pelletized silage (D). Eggs from hens fed with silage (B, C and D) contained 2.4 times more n-3 fatty acids than A. The thermally treated silage (C and D) produced higher concentrations of saturated fatty acids. B and C (high rapeseed oil intakes) showed the highest monounsaturated fatty acids. In spite of the high fat intake, their cholesterol levels were similar to A (A: 12.4; B: 12.3; C: 12.6 mg/g yolk; p > 0.05) due to the anti-cholesterolemic effect of the alfalfa. D consumed the lowest amount of fat but the highest amount of silage, corresponding to the lowest cholesterol level. The fat consumed was essential in the absorption of carotenoids. Thus, yolks from the silage groups showed decreasing values for the intensity of red and yellow colour as the intake in terms of the amount of fat/silage decreased