Classical generalized constant coupling model for geometrically frustrated antiferromagnets

A generalized constant coupling approximation for classical geometrically frustrated antiferromagnets is presented. Starting from a frustrated unit we introduce the interactions with the surrounding units in terms of an internal effective field which is fixed by a self consistency condition. Results for the magnetic susceptibility and specific heat are compared with Monte Carlo data for the classical Heisenberg model for the pyrochlore and kagome lattices. The predictions for the susceptibility are found to be essentially exact, and the corresponding predictions for the specific heat are found to be in very good agreement with the Monte Carlo results.Comment: 4 pages, 3 figures, 2 columns. Discussion about the zero T value of the pyrochlore specific heat correcte

Effect of large-scale intermittency and mean shear on scaling-range exponents in a turbulent jet

The present study investigates the combined impact of the intermittency associated with the turbulent-nonturbulent interface and the mean shear rate in an axisymmetric jet on the structure of turbulence in the scaling range, where the spectrum exhibits a power-law behavior. Second-order structure functions, autocorrelations of the dissipation rate, and spectra of both the longitudinal velocity fluctuation and the passive temperature fluctuation are measured at a distance of 40 diameter downstream from the nozzle exit. All the scaling range exponents are influenced by the large-scale intermittency and the mean shear. The scalar fluctuation is much more sensitive to the variation in large-scale intermittency than the velocity fluctuation.J. Mi and R. A. Antoni

Effect of cylinder deactivation on tribological performance of piston compression ring and connecting rod bearing

Thermo-mixed-hydrodynamics of compression rings and big-end bearings are presented. Frictional losses under normal engine operating conditions for a gasoline engine and those with cylinder deactivation (CDA) are predicted. With CDA, the combustion chamber pressure increases in the active cylinders, whilst some residual pressure remains in the deactivated ones. For the former, the increased in-cylinder temperatures reduce viscous friction, whilst reducing the load carrying capacity, promoting increased boundary interactions. In deactivated cylinders, lower contact temperatures yield increased viscous friction. Overall, a 5% improvement in expended fuel is expected with the application of CDA. However, 10% of these gains are expended due to increased friction. The study demonstrates the need to consider total system effects when introducing new technologies such as CDA

Optimization of the cavity size for AM1-SCRF calculations of electrode potentials in aqueous solution

A procedure for optimization of the cavity size for AM1-SCRF calculations of the electrode potentials in aqueous solution is presented. Comparison between the calculated electrode potentials of some benzoquinones and naphthoquinones obtained using the scaled cavity size and the experimental values suggests that the optimum cavity is placed at 1.4 times the van der Waals radii. Also, the electrode potentials of [2,5-bis(1-aziridinyl)-1,4-benzoquinones] with a wide range of substituents were calculated using the AM1-SCRF method. The calculated electrode potentials of these compounds using the optimum cavities give an r.m.s. error of 28 mV compared with an r.m.s. of 49 mV for the values obtained using the recommended radii for SCRF calculation

Theoretical studies of electrode potentials in aqueous solution. Investigation of individual contributions from electrostatic, cavity and dispersion interactions to redox potentials

Electrode potentials of some benzoquinones and naphthoquinones were calculated using ab-initio and AM1 methods. The effect of individual contributions from electrostatic, cavity and dispersion interactions were analyzed for polar and nonpolar molecules. Up to 7% of variation in the electrode potentials of quinones studied in this work is due to cavitation and 15% to the dispersion term. Both SCRF and FEP methods give reasonable agreement when 6-31G* basis set is used at the Hartree-Fock level. Comparison of the AM1 calculated electrode potentials with the AM1-COSMO results shows the superiority of the SCRF model and the importance of the inclusion of the cavity and dispersion terms

Fuel Preprocessor (FPP) for a Solid Oxide Fuel Cell Auxiliary Power Unit

Auxiliary Power Units (APUs), driven by truck engines, consume over 800 million gallon of diesel fuel while idling. Use of separate SOFC based APUs are an excellent choice to reduce the cost and pollution associated with producing auxiliary power. However, diesel fuel is a challenging fuel to use in fuel cell systems because it has heavy hydrocarbons that can transform into carbon deposits and gums that can block passages and deactivate fuel reformer and fuel cell reactor elements. The work reported herein addresses the challenges associated with the diesel fuel sulfur and carbon producing contaminants in a Fuel Preprocessor (FPP). FPP processes the diesel fuel onboard and ahead of the reformer to reduce its carbon deposition tendency and its sulfur content, thus producing a fuel suitable for SOFC APU systems. The goal of this DOE supported Invention and Innovation program was to design, develop and test a prototype Fuel Preprocessor (FPP) that efficiently and safely converts the diesel fuel into a clean fuel suitable for a SOFC APU system. The goals were achieved. A 5 kWe FPP was designed, developed and tested. It was demonstrated that FPP removes over 80% of the fuel sulfur and over 90% of its carbon residues and it was demonstrated that FPP performance exceeds the original project goals