A formally verified application-level framework for real-time scheduling on POSIX real-time operating systems

We present a framework, called meta scheduler, for implementing real-time scheduling algorithms. The meta scheduler is a portable middleware layer component designed for implementations over POSIX-compliant operating systems. It accommodates pluggable real-time scheduling algorithms while offering the flexibility of platform independence - the singular underlying OS requirement is the now nearly ubiquitous POSIX compliance. The versatility of pluggable schedulers positions the meta scheduler for deployment in an interoperable heterogeneous real-time environment. We present the design of the meta scheduler and outline its implementation. Furthermore, we present a mechanized correctness verification using the UPPAAL model checker. Prototype implementation of the meta scheduler over QNX Neutrino real-time operating system demonstrates high performance and a small footprint.     

Algorithm for converting a forest of quadtrees to a binary array

An algorithm for reconstructing a binary array of size N sx N from its forest of quadtree representation is presented. The algorithm traverses each tree of the forest in preorder and maps each ‘black’ node into the spatial domain. The time complexity in mapping is O(log N × B_n + B_p), where B_n is the number of black nodes in the forest and B_p is the number of black pixels in the N × N array. The algorithm has been implemented on an Apple II.     

Effect of Melt Cleanliness on the Mechanical Properties and Microstructure on AZ91E Mg Alloy Castings

The current study examines various filter configurations, argon bubbling, and degasser addition to improve melt cleanliness of AZ91E permanent mold castings. The unfiltered castings had an average yield strength, ultimate tensile strength, and elongation of 93.3, 153.3 MPa, and 2.2% respectively. Using a fine mesh filter within the well of the mold, the ultimate tensile strength and elongation increased by 9 and 41%, respectively, compared to the unfiltered samples. A combination of a fine filter and argon bubbling resulted in an average increase in ultimate tensile strength and elongation of 29 and 123%, respectively, that matched the performance of the C₂Cl₆-based degassed castings with 95.8, 194.3, and 4.9% for yield strength, ultimate tensile strength, and elongation, respectively. The addition of the C₂Cl₆-based degasser released harmful vapors that can be avoided using the fine filter with argon bubbling. In all cases, the removal of MgO-based inclusions improved mechanical properties.     

Improvements in Mechanical Properties of 319 Al Alloy Engine Blocks Through Cost-Effective Solution Heat Treatment

The use of Al engine blocks has increased significantly to improve vehicle fuel efficiency. However, the gray cast iron cylinder liners cause the development of large tensile residual stress along the cylinder bores which necessitates the optimization of mechanical properties in this region to prevent premature engine failure. This study compared the microstructure of T4-treated Al billet castings of varying cooling rate to that of the cylinder region of T4-treated (current production schedule) Al engine blocks. The aim of this study was to develop a cost-effective small scale heat treatment optimization method for engine block production. Comparisons in microstructure between the engine block and the billet castings were carried out using optical and scanning electron microscopy. The results suggest that the microstructure and hardness at the top, middle, and bottom of the cylinder were similar to those of each representative billet casting, indicating that heat treatment resulted in successful replication of the engine block locations. In addition, tensile testing revealed that the YS and UTS increased slightly following T4 treatment for all billet castings, which was also observed at the middle of the engine block cylinder bridge. As such, this method can be an effective forerunner for future heat treatment optimization in Al engine block production.     

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.     

3D finite element simulation of temperature distribution,residual stress and distortion on 304 stainless steel plates using GTA welding

In the present study, the distortion induced in rectangular plate of AISI 304 SS during autogenous GTA welding process is measured experimentally and further validated using Finite element (FE) analysis. The thermal histories are measured at fixed locations over the surface of the plate and the results are compared with FE analysis. The Gaussian surface and Volumetric heat source models are simulated and transient heat transfer analysis is performed. The heat source models have been tested with two different speeds. The effectiveness of change in thermal histories of the heat sources have been studied and reported. In FE analysis, the sequentially coupled thermomechanical analysis is performed using the thermal histories as input and the distortion of the plates are predicted and compared with experimental measurements. The large and small displacement theories are employed for the above purpose and the effectiveness of the theories are reported. The edge deformation of the plates have been measured and validated for both the theories. The residual stress and distortion at the mid span are predicted and discussed. The results predicted using large displacement theory is in good agreement with measured values.