Strain path change effects in the local necking of aluminum sheet and in the tension of internally pressurized tubes

It is possible to increase significantly the uniform elongation achieved in the uniaxial tension of commercial purity aluminum by accelerating the testing rate. This effect is linked to a significant rate sensitivity of strain hardening. However, very little increase in the strains associated with the final stages of localization in sheet specimens were achieved by this means. The importance of the change in strain rate and path on local necking has been investigated by introducing path changes of appropriate magnitudes in tubular tensile specimens by internal pressurization. The path change led to a decrease in strain-hardening rate which was not compensated for by an increase in strain rate. The potential consequences of this effect upon ductility in sheets are significant and limit the potential usefulness of any rate sensitivity of strain hardening in increasing formability.     

Algebraic properties of BCH codes useful for decoding

In this paper theorems are presented which allow the simplified decoding of (n, k, δ) BCH codes in certain cases of practical interest. Such results are in a way implicit in the theory of BCH codes, but so far have not appeared explicitly in the literature. It is shown that any t₀ errors, 1 ? t₀ ? δ-1, can be detected by using any set of only t₀ consecutive coefficients of the syndrome polynomial. The correction of any t₀ errors, 1 ? t₀ ? [(δ-1)/2], can be performed by using any set of 2t₀ consecutive coefficients of the syndrome polynomial, where [x] means the integer part of x. Similar results are derived for punctured BCH codes. In this case sets of t₀ or 2t₀ consecutive coefficients, respectively, for detecting or correcting t₀ errors, are selected from the δ-1-p higher-order coefficients of the modified syndrome polynomial, where p is the number of digits punctured from a code word. These results hold true even when the punctured digits are not consecutive.     

An Integrated Approach to Scheduling in Safety-Critical Embedded Control Systems

This paper describes an approach that has been developed over a number of years for the job of scheduling systems and providing evidence that timing requirements are met. The approach has been targeted at the safety-critical systems domain, and more specifically the development of control systems for jet engines. The work provides a usable computational model that supports the reuse of legacy systems. In addition, timing analysis has been developed that features low pessimism, low computational complexity and that is robust to change. The contributions of this paper are to show how standard timing analysis is often insufficient for real systems, presenting extensions to the standard analysis to give an integrated approach to verification, and providing a case study that demonstrates the appropriateness and benefits of the overall technique.     

Texture development in the cold rolling of IF steel

The development of deformation texture in ferrite has been measured in cold rolled IF steel. This has been compared, in a quantitative way, to the predictions of Taylor models—including those with relaxed constraints—and a finite element model with crystal plasticity constitutive laws. The finite element model gave much better prediction of the overall levels of orientation density but failed to predict the relatively high level of {0 0 1}1 1 0 texture which occurred at strains greater than about unity. That feature was predicted by relaxed constraint Taylor models. It is argued that that prediction is a coincidence, and either the finite element model cannot readily deal with the intragranular inhomogeneity of deformation in an adequate way, or that factors such as high-angle boundary migration may be important in the development of deformation texture.     

Evaluation of Potential Risks from Ash Disposal Site Leachate

A risk-based approach is used to evaluate potential human health risks associated with a discharge from an ash disposal site into a small stream. The RIVRISK model was used to estimate downstream concentrations and corresponding risks. The modeling and risk analyses focus on boron, the constituent of greatest potential concern to public health at the site investigated, in Riddle Run, Pennsylvania. Prior to performing the risk assessment, the model is validated by comparing observed and predicted results. The comparison is good and an uncertainty analysis is provided to explain the comparison. The hazard quotient (HQ) for boron is predicted to be greater than 1 at presently regulated compliance points over a range of flow rates. The reference dose (RfD) currently recommended by the United States Environmental Protection Agency (U.S. EPA) was used for the analyses. However, the toxicity of boron as expressed by the RfD is now under review by both the U.S. EPA and the World Health Organization. Alternative reference doses being examined would produce predicted boron hazard quotients of less than 1 at nearly all flow conditions.     

Footprinting of the spinach nitrite reductase gene promoter reveals the preservation of nitrate regulatory elements between fungi and higher plants

Similar neurochemical events appear to be involved in the development of myopia in chicks and mammals. The rapid post-hatching development of the chick is ideal for studying experimental myopia. In this investigation, one eye of 2-day-old chicks was deprived of form vision for 2 weeks and then compared to the fellow, non-deprived eye by immunohistochemistry and light and electron microscopy. All deprived eyes showed a high refractive error and ocular enlargement. In deprived eyes, the posterior cartilaginous sclera was thicker and the fibrous sclera of the same section was thinner than the control. Scleral morphological changes were restricted to a central button 6-7 mm in diameter (the posterior pole) within the posterior hemisphere, further divided into posterotemporal and posteronasal parts. The most enlarged, posterior cartilaginous structure of deprived sclera could be divided into an inner and an outer zone. The inner zone had many unevenly-arranged chondrocytes, each having a well-developed granular endoplasmic reticulum and Golgi complex and a very irregular cell surface. Numerous S-phase cells and isogenous groups were detected in the outer zone. Hypertrophic chondrocytes were often observed in the innermost region of the outer zone and the outermost region of the inner zone. The boundary between the outer fibrous sclera and the cartilaginous sclera was irregular and obscured in myopic eyes. Spindle-shaped chondrocytes were seen to be in contact with each other. Thick collagen fibrils, usually seen only in the outer fibrous sclera, were present among the chondrocytes. Results of this morphological study suggest an increased proliferation of chondrocytes and active synthesis of extracellular matrix in visually deprived eyes. The elongation of the ocular axis that accompanies myopia is caused primarily by an active remodeling and differentiation in a restricted section of the posterior scleral cartilage. These facts indicate the posterior scleral cartilage may be more immature than cartilage in anterior and lateral segments.     

The differentiation between neuroglia and connective tissue sheath in insect ganglia revisited: the neural lamella and perineurial sheath cells are absent in a mesodermless mutant of Drosophila

Two morphogenetic mutations, twist and Delta, that affect the embryonic development of Drosophila in known ways were used to examine the derivation and function of the outer layers of the central nervous system (CNS). Both the extracellular neural lamella, which ensheaths the CNS, and its source, the underlying perineurial sheath cell layer, fail to develop in Drosophila embryos that are homozygous for a loss of function mutation in the twist gene, and which thus lack mesodermal derivatives. The cell layer immediately below the perineurial sheath cells, here termed barrier glial cells, constitute the ion permeability barrier in wild-type embryos. They are present in twist mutant embryos, appear to be normal at the ultrastructural level, and function as a blood-brain ion barrier. The apparent derivation of perineurial sheath cells from mesodermal precursors distinguishes them from neurons, glia and other nonneural components of the CNS, such as tracheae, all of which are of ectodermal origin. We confirm Scharrer's interpretation of the relationship between the perineurium and underlying neuroglia. In embryos homozygous for the neurogenic mutant Delta, an embryonic lethal in which excess ventral blastoderm gives rise to neuroblasts, the CNS forms as an amorphous cell mass, with discontinuous perineurial sheath and barrier glial cell layers. We propose that the cell mass is permeable to lanthanum ions and fails to form a blood-brain barrier because volume growth prevents the formation of continuous surface cell layers.     

Blowouts in coastal foredunes

Foredune blowouts within many embayments along the south coast of South Africa are traditionally believed to be caused by human activities and the result of onshore winds reducing vegetation cover and developing landward migrating patches of bare sand. These bare areas are not blowouts sensu strictu, however, and are more likely the elongated horns of barchan dunes formed across the direction of the dominant winds. Blowouts of this type have been present on the foreshore of Algoa Bay for more than 100 years and long before present-day human pressures could be the possible causal factor. They are not likely to present major management problems provided buildings are not constructed within them or closely behind them. Where necessary, vegetation cover should be maintained either by keeping people out of the dunes or by implementing revegetation options. Some mechanical sand relocation may occasionally be a helpful short-term management solution.