Fifty Years of Research and Development Coming to Fruition; Unraveling the Complex Interactions during Processing of Transparent Magnesium Aluminate (MgAl2O4) Spinel

The need for materials for demanding optical applications has engendered a resurgent interest in transparent ceramics. Transparent polycrystalline magnesium aluminate spinel is one especially promising and rapidly maturing technology that can fill this niche. Although it has been studied for over 50 yr, it is only recently that highly transparent components with acceptable mechanical properties have been reliably fabricated at reasonable cost. Development has been hindered by the inherent difficulty in sintering spinel to the near‐theoretical density required for transparency, a high sensitivity to powder and processing parameters, variable stoichiometry, and a lack of understanding of the synthesis–processing–property relationships. The driver of recent success is an emerging understanding of complex, multiscale, multivariable interactions that occur during green‐body formation and sintering. In particular, certain key variables play a decisive role in determining compact properties and their evolution must be controlled from synthesis to the finished product. This article features the interactions between these key variables during processing and gives an exposé of the state of the art in transparent polycrystalline spinel fabrication.     

Possibilities for the utilisation of marine by‐products

Fish industry by‐products can account for up to 75% of the catch depending on postharvest or industrial preparation processes. Different terms such as ‘fish waste’, ‘by‐product’ and ‘rest raw materials’ have been used. The review gives an overview of value‐added processes that provide an alternative to low‐profit uses such as silage, fish meal and mince. The preparation of different by‐product fractions such as fish blood, marine lipids, omega‐3 fatty acids, fish protein fractions and bioactive components with nutraceutical potential, i.e. antioxidants and bioactive peptides, is considered. There are several future opportunities for the preparation of high‐value by‐products such as enzymes, minerals and other bioactive substances including hydroxyapatite, phosphorus, taurine and creatine. Both regulatory status and future market potential need to be considered. In addition, there is a need for technologies that maintain good quality by‐products and ‘simple’ processes to produce bulk products for further refining.     

Cortical gray matter atrophy in healthy aging cannot be explained by undetected incipient cognitive disorders: A comment on Burgmans et al. (2009).

Burgmans, van Boxtel, Vuurman, et al. (2009) published an interesting study titled “The Prevalence of Cortical Gray Matter Atrophy May Be Overestimated in the Healthy Aging Brain” on how subclinical cognitive disorders may affect correlations between age and cortical volume. Correlations between cortical gray matter volume and age were found in 30 elderly with cognitive decline after 6 years, but not in 28 elderly without cognitive decline. This study is important, and demonstrates that preclinical cognitive disorders may affect cortical brain volumes before being detectable by neuropsychological tests. However, we are not convinced by the conclusions: “… gray matter atrophy… is to a lesser extent associated with the healthy aging process, but more likely with brain processes underlying significant cognitive decline” (p. 547) and “… cortical gray matter atrophy in the aging brain may be overestimated in a large number of studies on healthy aging” (p. 547). We analyzed the cross-sectional MR data (n = 1,037) as well as longitudinal data from a sample of very well-screened elderly followed by cognitive testing for 2 years. In the cross-sectional data, the correlations between age and brain volumes were generally not much reduced when the upper age limit was lowered. This would not be expected if age-related incipient cognitive disorders caused the correlations given that the incidence of cognitive decline increased with age. Longitudinally, 1-year atrophy was identified in all tested regions. It is likely that cortical brain atrophy is manifested in cognitively normal elderly without subclinical cognitive disorders. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fabrication of Graded Nickel–Alumina Composites with a Thermal-Behavior-Matching Process

Composites of nickel and Al₂O₃ with compositionally graded microstructures were fabricated from powders through an empirically determined thermal-behavior-matching process that was designed to minimize processing-induced stresses. Compositions ranged from pure Al₂O₃ to pure nickel. Specimen geometries included round disks 25 mm in diameter and 5–25 mm thick, as well as rectangular bars 25 mm × 25 mm in cross section and 75 mm long. Several different gradients were produced, including samples with single interlayers. Compacts were formed by cold uniaxial pressing in a die, followed by consolidation through sintering at 1 atm or hot isostatic pressing. Several different particle sizes of nickel and Al₂O₃ comprised the composite interlayers. The compaction behavior, sintering start temperature, sintering rate, and total linear shrinkage of each composition were evaluated. Careful data analysis, coupled with sintering theory, led to a layer configuration with matched green density and sintering behavior. Thermomechanically matched layers allowed large, crack-free, graded composites to be produced.     

Analysis of moiré data for near-interface cracks

The analysis of moiré data obtained in bimaterials with near-interface cracks is examined. To extract stress intensity factors, a collocation-type method is developed where Westergaard crack-tip expansions are used for displacements in the cracked portion of the bimaterial, expansions from the method of fundamental solutions are used for displacements in the uncracked portion of the bimaterial, and continuity conditions at the interface are used to couple the two expansions. Proof-of-principle numerical experiments performed on synthetic data from a boundary element analysis of a cracked bimaterial successfully demonstrated the analysis method. Mixed-mode stress intensity factors were then determined from actual moiré data obtained in a copper–tungsten specimen.     

够了，让我们实践吧！

众多的软件开发过程到底是为我们解决的问题多,还是造成的问题更多?它们是否真的能够为改进团队的工作方式提供深刻的见解和所需的指导?文中对当代软件开发过程所面临的问题做了深刻的分析,并指出为什么我们现在拥有如此多的过程。     

Comparative study of the buckling of steel beams in Eurocode 3 and the Russian code

Lateral torsional buckling is the main limit state that must be checked for steel beams. Design codes provide different models for the analysis of this complex phenomenon. The present paper describes a comparative study of the interpretation of beam buckling of symmetrical sections in EN 1993-1-1 (EC3), its preliminary ENV-version and a Russian steel structure design code. In order to choose the nationally determined parameters in EC3, the impact of parameters on the safety level and overall design results has to be carefully studied. Modification factors, introduced in EC3, have moved the resistance for certain load distribution from ENV-based values closer to the Russian code.