First-principles investigations of the MMgH3 (, Na, K, Rb, Cs) series

The structural stability of the MMgH₃ (M=Li, Na, K, Rb, Cs) series has been investigated using the density-functional projector-augmented-wave method within the generalized-gradient approximation. Among the 24 structural arrangements used as inputs for the structural optimization calculations, the experimentally known frameworks are successfully reproduced, and positional and unit-cell parameters are found to be in good agreement with the experimental findings. The crystal structure of LiMgH₃ has been predicted, the most stable arrangement being the trigonal LiTaO₃-type (R3c) structure, which contains highly distorted octahedra. The formation energy for all members of the MMgH₃ series is investigated along different reaction pathways. The electronic density of states reveals that the MMgH₃ compounds are wide-band-gap insulators. Analyses of chemical bonding in terms of charge density, charge transfer, electron-localization function, Born effective charge, and Mulliken population show that these hydrides are basically saline hydrides similar to the parent alkali-/alkaline-earth mono-/di-hydrides.     

Influence of grain refinement on hot tearing in B206 and A319 aluminum alloys

Aluminum-copper (Al-Cu) and aluminum-silicon-copper (Al-Si-Cu) alloys are among the most common aluminum casting alloys. Aluminum alloy B206 is a relatively new Al-Cu alloy with high strength and ductility at room and elevated temperatures, while A319 is an Al-Si-Cu alloy with good strength and excellent wear resistance. However, despite their advantages, when these alloys are cast via the permanent mold casting (PMC) process, they show a high susceptibility to hot tearing. Grain refinement has shown promise as a means to reducing hot tears in aluminum alloys. In this study, Ti-B grain refiner was used to investigate the effect of grain refinement on hot tearing in B206 and A319 aluminum alloys during permanent mold casting. The results suggest that Ti-B additions significantly reduced hot tearing in B206 and A319. Grain sizes were also seen to reduce significantly in both alloys with addition of Ti-B grain refiner. However, Ti-B grain refiner had a diverse effect on alloy grain morphology, as a dendritic morphology in B206 was transformed to a more globular one, while in A319, the grain structure remained dendritic.     

Experimental characterization of meso‐scale deformation mechanisms and the RVE size in plastically deformed carbon steel

The local deformation response of low carbon steel subjected to uniaxial tensile loading is investigated, and the local strain field at sub‐grain scale is obtained using high‐spatial‐resolution digital image correlation. The implemented digital image correlation method enables the observation and study of inhomogeneous deformation response at microstructural levels. Detailed local deformation mechanisms including mesoscopic slip bands are captured. Furthermore, the local information is used for the determination of representative volume element size in polycrystalline low carbon steel. To obtain the representative volume element size, we proposed and successfully implemented a strain variation method. Further, the influence of global strain on the local deformation mechanisms and representative volume element size is discussed. The challenges associated with the local strain measurement using digital image correlation are also discussed.     

Biopolymers as sustainable metal bio-adhesives

We describe the use of biopolymers, such as sodium alginate, as an sustainable adhesive binder for several metals and high-density polyethylene. A standard pull test and peel test was performed with disks, made of different material and size. Adhesive failure was investigated by varying the amount of applied alginate solution, drying time, drying temperature, effect of surface area, and the nature of the adherend. Alginate adhesion was remarkably strong, relatively general, and sensitive to the presence of water. A brief comparison with other biopolymers is also provided.     

Chemical-bonding and high-pressure studies on hydrogen-storage materials

From gradient-corrected, all-electron, full-potential, density-functional calculations, including structural relaxation, it is shown that the metal-hydride series RTInH_1.333 (R=La, Ce, Pr, or Nd; T=Ni, Pd, or Pt) violate the “2-Å” rule as well as the hole-size requirement. These hydrides possess unusually short H–H separations which in the most extreme case for LaPtInH_1.333 is as short as 1.454 Å. These findings have been analyzed in terms of charge density, charge transfer, electron-localization function, crystal-orbital Hamilton population, and density of states analyses. From high-pressure studies it is predicted several successive pressure-induced structural transitions in MgH₂ within the 20 GPa range. Calculations have also shown several pressure-induced structural transitions in alkali aluminum tetrahydrides with large volume reductions at the phase-transition points and small energy differences between the ambient-pressure and subsequent high-pressure phases.     

Electrical conductivity and magnetic susceptibility of rutile type CrVNbO6, FeVNbO6 and NiV2Nb2O10

Electrical conductivity (77–300K) and magnetic susceptibility (4.2–300K) of rutile type polycrystalline samples of CrVNbO₆, FeVNbO₆ and NiV₂Nb₂O₁₀ are reported. All three compounds are n-type semiconductors with room termperature resistivities of the order of 10²–10³ ohm-cm. CrVNbO₆ shows ferromagnetic coupling in the high temperature region and orders antiferromagnetically below 10K. FeVNbO₆ trans-forms to a spin glass state below 20K. NiV₂Nb₂O₁₀ shows evidence of weak antiferromagnetic interactions. The transport properties of the compounds are discussed in terms of structural properties and unpaired d electrons present on the respective transition metal ions.     

Production planning & scheduling: Computational feasibility of multi-criteria models of production, planning and scheduling

This paper surveys the applications of multi-criteria decision making (MCDM) methods to production planning, scheduling, and sequencing problems. The basic structure of the decision models are described by their objectives and the resulting models are classified by decision variables into the areas of Aggregate Production Planning, Disaggregate Production Planning, Production Scheduling, and Single Machine Sequencing. The problem sizes that have been solved are summarized to determine how practical it is to use MCDM.     

Acidification of weaner pig diets: A review

The potential of diet acidification to overcome the digestive insufficiency and postweaning lag in early weaned pigs is examined in the review. A survey of published data on various types of acidifiers reveal considerable variation in response to acidification of weaner diets. Several reasons may be proposed to explain the inconsistencies in response, these include differences in diet type, age of pigs, type and level of acidifier, and existing performance levels. Reducing the gastric pH does not appear to be the primary effect of acidifiers. Acidification, however, consistently suppressed pathogenic coliforms in the gastrointestinal tract. Future developments in the use of acidifiers would be intrinsically linked to the understanding of their mode(s) of action in the animal.     

Mechanized material handling systems design and routing

Tinker AFB (TAFB) is the prime Air Force rework facility for jet engine parts that support standard engines. The wear and tear on the engine parts of the various aircraft currently produces about 10 million individual requirements annually for part inspection and subsequent discard or rework. Past practices have resulted in extremely long flow times for rework and a burgeoning requirement for conveyor capacity.

A new concept, called the Modular Repair Center (MRC), is being implemented to correct the problem. The MRC's have most of the processes necessary to inspect and repair components of a given engine assembly. They have the advantage of reducing the number of long moves, giving more accountability for quality and better tracking. A large network model of TAFB facility has been developed to determine the required work-in-process storage, conveyor capacity, shortest routes for parts to flow from one MRC to another and the maximum flow along each conveyor section. The model was analyzed using Floyd's shortest route algorithm. It resulted in reducing the “bottlenecks” on certain conveyor sections by rerouting some of the flow along low density traffic links and thus reducing the need for extra conveyor capacity. Simple formulas were designed to estimate the number of pallets generated by disassembly and each MRC to provide the demand requirements for conveyor capacity.     

THE MEASUREMENT OF OXYGEN TRANSPORT PARAMETERS FOR ASPHALT/AGGREGATE AND ASPHALT/GLASS SYSTEMS USING AN ELECTRODYNAMIC BALANCE

A gravimetric method using an eledrodynamic balance was developed for the measurement of transport properties such as the diffusion coefficient, D, solubility, S, and permeability, P, for oxygen into thin layers of asphalt materials deposited on aggregate and glass particles. Glass spheres and aggregate particles in the 14 to 50 μm size range coated with asphalt materials (AAB1, AAG1, and AAK1) were suspended contactless in the balance to measure D, S, and P in the temperature range 21 to 61° C. Transport parameters were determined from the changes in the particle mass due to the uptake of oxygen by the asphalt coating on glass spheres and nonspherical aggregate particles.