Sandia National Laboratories

About: Sandia National Laboratories is a facility organization based out in Livermore, California, United States. It is known for research contribution in the topics: Laser & Thin film. The organization has 21501 authors who have published 46724 publications receiving 1484388 citations. The organization is also known as: SNL & Sandia National Labs.

Consistent structural properties for AlN, GaN, and InN.

Abstract: The plane-wave pseudopotential method is used to calculate structural properties for wurtzite and zinc-blende AlN and InN using large plane-wave basis sets and treating the indium 4[ital d] electrons as valence. These calculations, together with corresponding ones for GaN [A. F. Wright and J. S. Nelson, Phys. Rev. B 50, 2159 (1994)], yield a consistent set of well-converged structural properties for AlN, GaN, and InN. In particular, the measured lattice mismatch among these compounds---essential for an accurate description of alloy properties---is well reproduced.

Slip planes in bcc transition metals

Abstract: Slip in face centred cubic (fcc) metals is well documented to occur on {111} planes in 〈110〉 directions. In body centred cubic (bcc) metals, the slip direction is also well established to be 〈111〉, but it is much less clear as to the slip planes on which dislocations move. Since plasticity in metals is governed by the collective motion and interaction of dislocations, the nature of the relevant slip planes is of critical importance in understanding and modelling plasticity in bcc metals. This review attempts to address two fundamental questions regarding the slip planes in bcc metals. First, on what planes can slip, and thus crystallographic rotation, be observed to occur, i.e. what are the effective slip planes? Second, on what planes do kinks form along the dislocation lines, i.e. what are the fundamental slip planes? We review the available literature on direct and indirect characterisation of slip planes from experiments, and simulations using atomistic models. Given the technological importan...

The Depth/Breadth Tradeoff in Hierarchical Computer Menus

Abstract: Goal acquisition speed and accuracy were compared for subjects using four different menu configurations of a semantic hierarchy on an interactive computer terminal. Depth (the number of menu levels...

Potential of Thermal Stratification and Combustion Retard for Reducing Pressure-Rise Rates in HCCI Engines, Based on Multi-Zone Modeling and Experiments

Abstract: This work investigates the potential of in-cylinder thermal stratification for reducing the pressure-rise rate in HCCI engines, and the coupling between thermal stratification and combustion-phasing retard A combination of computational and experimental results is employed The computations were conducted using both a custom multi-zone version and the standard single-zone version of the Senkin application of the CHEMKIN III kinetics-rate code, and kinetic mechanisms for iso-octane This study shows that the potential for extending the high-load operating limit by adjusting the thermal stratification is very large With appropriate stratification, even a stoichiometric charge can be combusted with low pressure-rise rates, giving an output of 16 bar IMEPg for naturally aspirated operation For more typical HCCI fueling rates (Φ = 038 - 045), the optimal charge-temperature distribution is found to depend on both the amount of fuel and the combustion phasing For combustion phasing in the range of 7 - 10°CA after TDC, a linear thermal distribution is optimal since it produces a near-linear pressure rise For other combustion phasings, non-linear distributions are required to achieve a linear pressure rise Also, the total thermal width must be greater at higher fueling rates to avoid excessive pressure-rise rates The study also shows that increasing the natural thermal width of the charge by 50% would allow the equivalence ratio to be increased from 044 to 060, with an associated increase of the IMEPg from 524 to 695 kPa for naturally aspirated operation It was also found that the naturally occurring thermal stratification plays a major role in producing the experimentally observed benefit of combustion-timing retard for slowing the combustion rate Reduced chemical-kinetic rates with combustion retard are found to play a lesser role