A New Constitutive Strain-Dependent Garofalo Equation to Describe the High-Temperature Processing of Materials—Application to the AZ31 Magnesium Alloy

A new strain-dependent equation derived from that of Garofalo is developed in this work. This equation describes mathematically the deformation behavior of materials as a function of strain, strain rate, and temperature and is valid over a wide range of strain with good statistical accuracy. An explicit expression s( e) = f( e,T,[(e)\dot] ) \sigma \left( \varepsilon \right) = f\left( {\varepsilon ,T,\dot{\varepsilon }} \right) is introduced that reproduces stress-strain curves. Statistical tools for determining the validity of the equation have been applied. Predictions from this expression were compared with torsion data obtained in AZ31 magnesium alloy that was deformed at various temperatures and strain rates. Analysis of the strain dependence of the Garofalo parameters allowed us to establish a steady state at strains of about 0.6. It also allows drawing conclusions about the microstructural changes that occur during deformation of the alloy. In addition, the characteristic points in the evolution with strain of the parameters of the equation are related to the most significant values that characterize the microstructural processes occurring during deformation of the AZ31 alloy. The observed decrease of Q and n as a function of strain is attributed first to a softening process due to dynamic recrystallization and grain size refinement and finally to flow localization. The predicted values obtained with the new constitutive equation and the experimental values for the AZ31 alloy are in good agreement with an average relative error of about 6.5 pct.     

Adaptive discrete harmonic grid generation

We present a new adaptive-harmonic structured grid generation method. It is based on a functional that shares a common set of minimizers with Ivanenko’s harmonic functional [A.A. Charakhch’yan, S.A. Ivanenko, Curvilinear grids of convex quadrilaterals, Comput. Maths. Math. Phys. 28(2) (1988) 126–133.]. An unconstrained optimization process related to a continuation parameter is used to guarantee the convexity of the grid cells. Several numerical examples of grids generated on quite irregular 2D$2D$regions, show the effective performance of the proposed method and its robustness when preset monitor functions are given.     

Synthesis,reactivity, and properties of new diaryliodonium salts as photoinitiators for the cationic polymerization of epoxy silicones

Diaryliodonium tetrakis (pentafluorophenyl) borate salts generate a higher reactivity than any other known diaryliodonium salt. The photochemical properties of diaryliodonium tetrakis (pentafluorophenyl) borate salts were compared to those of the diaryliodonium hexafluoroantimonate salt. The results show that these new salts are the most reactive photoinitiators in this family. In addition, diaryliodonium tetrakis (pentafluorophenyl) borate salts are soluble in low polarity media, such as epoxy silicone oils, which are rich in epoxy groups and insensitive to humidity. These salts have the advantage not to contain a heavy metal (such as antimony). The new properties generated by the use of the tetrakis (pentafluoropheyl) borate anion make the future of the cationic photopolymerization promising. © 1996 John Wiley & Sons, Inc.     

Intestinal invagination in the adult

Idiopathic intestinal invagination is a relatively frequent process in children in comparison with cases of intestinal obstruction/subocclusion by invagination secondary to a tumor in adults which is unusual and more often observed in patients over the age of 60 years. Two clinical cases of intestinal obstruction in young adult males due to intestinal invagination by a tumor of the small intestine are presented. One case was due to a submucosal lipoma which lead to ileo-ileal intussusception and an ileo-cecal invagination by a terminal ileum lymphoma. The clinical and diagnostic aspects of this infrequent disease are discussed.     

Quantitative brain magnetic resonance imaging in attention-deficit hyperactivity disorder

BACKGROUND: Anatomic magnetic resonance imaging (MRI) studies of attention-deficit hyperactivity disorder (ADHD) have been limited by small samples or measurement of single brain regions. Since the neuropsychological deficits in ADHD implicate a network linking basal ganglia and frontal regions, 12 subcortical and cortical regions and their symmetries were measured to determine if these structures best distinguished ADHD. METHODS: Anatomic brain MRIs for 57 boys with ADHD and 55 healthy matched controls, aged 5 to 18 years, were obtained using a 1.5-T scanner with contiguous 2-mm sections. Volumetric measures of the cerebrum, caudate nucleus, putamen, globus pallidus, amygdala, hippocampus, temporal lobe, cerebellum; a measure of prefrontal cortex; and related right-left asymmetries were examined along with midsagittal area measures of the cerebellum and corpus callosum. Interrater reliabilities were .82 or greater for all MRI measures. RESULTS: Subjects with ADHD had a 4.7% smaller total cerebral volume (P = .02). Analysis of covariance for total cerebral volume demonstrated a significant loss of normal right > left asymmetry in the caudate (P = .006), smaller right globus pallidus (P = .005), smaller right anterior frontal region (P = .02), smaller cerebellum (P = .05), and reversal of normal lateral ventricular asymmetry (P = .03) in the ADHD group. The normal age-related decrease in caudate volume was not seen, and increases in lateral ventricular volumes were significantly diminished in ADHD. CONCLUSION: This first comprehensive morphometric analysis is consistent with hypothesized dysfunction of right-sided prefrontal-striatal systems in ADHD.     

Interactive Effects of Fly Ash and CNI on Corrosion of Reinforced High-Performance Concrete

The interactive effects of fly ash and CNI in corrosion of reinforced concrete were investigated. A 3⁴ full factorial design was developed considering water to cement ratio, fly ash percent, CNI and cracked condition as factors. The response factors were the weight loss calculated from Linear Polarization Resistance measurements and the pit depth of the steel bars embedded in concrete. Small-scale concrete slabs containing steel reinforcement with a cover depth of 20 mm were cast for this purpose. The slabs were subjected to a simulated marine environment with two cycles of wetting and drying per day during one year; after the exposure, the slabs were broken, the bars were cleaned and the pith depth measured by using SEM. Under the studied conditions, it was found that CNI alone does not provide corrosion protection of the steel reinforcement even for uncracked silica fume concrete in a 0.45 w/c ratio; however, the combination of CNI and fly ash can be useful to overcome this problem. The results indicate that low w/c ratio concrete in its crack state creates conditions suitable for the development of pitting corrosion.     

Global overview of industrial energy intensity

Given the need to reduce the CO₂ emissions coming from the manufacturing sector, it is important, for planning purposes, to know which countries and which manufacturing sub-sectors have the greatest potential for reducing energy use. Using data from the International Atomic Energy Agency and the United Nations Industrial Development Organization, the authors estimate trends in global decoupling of energy use and manufacturing value added, compare energy-use intensity in six country groups and estimate the potential for reducing energy use and CO₂ emissions under two scenarios and compare selected sub-sector energy intensity and estimate the potential for reducing energy use CO₂ emissions. The comparison of energy intensities across country groups and among countries suggests that there still remains significant potential to reduce energy use and associated CO₂ emissions. The analysis of four sub-sectors in developing and transition economies also shows similar but varied potential for reducing energy use and associated CO₂ emissions.