57,772 research outputs found
Response of A356 to warm rotary forming and subsequent T6 heat treatment
The through-process microstructural effects in A356 subjected to rotary
forming at elevated temperatures have been investigated. Macro and
micro-hardness testing have been used extensively to track changes in the
material from the as-cast state to as-formed, and T6 heat treated. Targeted
thermal treatments have been used to isolate the effects of mechanical
deformation through comparative measurements. These measurements include macro
and micro hardness measurements, Energy-dispersive X-ray analysis and
examination of eutectic-Si particle size and morphology. The results indicate
that the as-cast material is stable up to approximately 144{\deg}C, with the
rotary formed material exhibiting decreased macrohardness in-line with the time
spent at elevated temperature. Post heat treatment, there was a significant
decrease in hardness with increased levels of deformation. Results indicate
that precipitation hardening is not appreciably affected by rotary forming, and
the principal cause for the drop in hardness with deformation is due to the
condition of Al-Si eutectic phase.Comment: 26 pages, 13 figure
Analysis and modelling of a rotary forming process for cast aluminum alloy A356
Spinning of a common aluminum automotive casting alloy A356 (Al-7Si-0.3 Mg)
at elevated temperatures has been investigated experimentally with a novel
industrial-scale apparatus. This has permitted the implementation of a fully
coupled thermomechanical finite element model aimed at quantifying the
processing history (stress, strain, strain-rate and temperature) and predicting
the final geometry. The geometric predictions of this model have been compared
directly to the geometry of the workpieces obtained experimentally. This study
is novel in regards to both the size and shape of the component as well as the
constitutive material representation employed. The model predictions are in
reasonable agreement with experimental results for small deformations, but
errors increase for large deformation conditions. The model has also enabled
the characterization of the mechanical state which leads to a common spinning
defect. Suggestions for improving the accuracy and robustness of the model to
provide a predictive tool for industry are discussed
Isolation and characterisation of two chymotrypsins from Allocyttus niger (black oreo dory) viscera
Two serine proteases from the viscera of deep-sea fish, black oreo dory (Allocyttus niger),were purified by hydrophobic, affinity, and cation exchange chromatography. They were designated as chymotrypsins on the basis of substrate specificity and susceptibility to inhibitors. The pH optima of chymotrypsin I and II were 8.6 and 10, respectively. Chymotrypsin II retained a remarkable 80% activity at pH 12.5. Thermal stability of both enzymes was enhanced in the presence of calcium ions. Both chymotrypsins were inhibited by high concentrations of substrate Suc-AAPF-NA
Supersymmetric lepton flavour violation in a linear collider: the role of charginos
The occurrence of a significant amount of supersymmetric lepton flavour
violation at laboratory energies, through
mixing, has become a realistic possibility in the wake of the super-Kamiokande
atmospheric neutrino result. This effect can be observed in an e+e- linear
collider with the distinct final state tau+mu+ jets+E_T. We show that the pair
production of charginos can make an important contribution to this process and
has to be taken into account in addition to that of sneutrinos or charged
sleptons. Some case studies are presented with CM energies of 500 and 800 GeV
and integrated luminosities of 50, 500 and 1000 fb-1.Comment: 15 pages, latex, including 2 figure
MODELING OF AGRICULTURAL SYSTEMS
The authors present an overview of agricultural systems models. Beginning with why systems are modeled and for what purposes, the paper examines types of agricultural systems and associated model types. The broad categories range from pictorial (iconic) models to descriptive analogue models to symbolic (usually mathematical) models. The uses of optimization versus non-optimizing mechanistic models are reviewed, as are the scale and aggregation challenges associated with scaling up from the plant cell to the landscape or from a farm enterprise to a world market supply-demand equilibrium Recent modeling developments include the integration of formerly stand-alone biophysical simulation models, increasingly with a unifying spatial database and often for the purpose of supporting management decisions. Current modeling innovations are estimating and incorporating environmental values and other system interactions. At the community and regional scale, sociological and economic models of rural community structure are being developed to evaluate long-term community viability. The information revolution is bringing new challenges in delivering agricultural systems models over the internet, as well as integrating decision support systems with the new precision agriculture technologies.Farm Management,
Trade deficits: causes and consequences
According to conventional wisdom, trade balances reflect a country's competitive strength-the lower the trade deficit, the stronger the country's industries and the higher its rate of economic growth. In this article, David Gould and Roy Ruffin review the history of the conventional wisdom and empirically examine whether large overall trade deficits or bilateral trade imbalances are associated with lower rates of economic growth. They find that, once the fundamental determinants of growth have been accounted for, trade imbalances have little effect on rates of economic growth.Deficit financing ; Free trade
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