Tunable Hydrogen Storage in Magnesium - Transition Metal Compounds

Magnesium dihydride (\mgh) stores 7.7 weight % hydrogen, but it suffers from a high thermodynamic stability and slow (de)hydrogenation kinetics. Alloying Mg with lightweight transition metals (TM = Sc, Ti, V, Cr) aims at improving the thermodynamic and kinetic properties. We study the structure and stability of Mg$_x$TM$_{1-x}$H$_2$ compounds, $x=[0$-1], by first-principles calculations at the level of density functional theory. We find that the experimentally observed sharp decrease in hydrogenation rates for $x\gtrsim0.8$ correlates with a phase transition of Mg$_x$TM$_{1-x}$H$_2$ from a fluorite to a rutile phase. The stability of these compounds decreases along the series Sc, Ti, V, Cr. Varying the transition metal (TM) and the composition $x$, the formation enthalpy of Mg$_x$TM$_{1-x}$H$_2$ can be tuned over the substantial range 0-2 eV/f.u. Assuming however that the alloy Mg$_x$TM$_{1-x}$ does not decompose upon dehydrogenation, the enthalpy associated with reversible hydrogenation of compounds with a high magnesium content ($x=0.75$) is close to that of pure Mg.Comment: 8 pages, 5 figure

Relativity and EPR Entanglement: Comments

Recent experiment by Zhinden et al (Phys. Rev {\bf A} 63 02111, 2001) purports to test compatibility between relativity and quantum mechanics in the classic EPR setting. We argue that relativity has no role in the EPR argument based solely on non-relativistic quantum formalism. It is suggested that this interesting experiment may have significance to address fundamental questions on quantum probability.Comment: 6 pages, no figure; Submitted to Phys. Rev.

Radiative and non-radiative effects of a substrate on localized plasmon resonance of particles

Experiments have shown strong effects of some substrates on the localized plasmons of metallic nano particles but they are inconclusive on the affecting parameters. Here we have used Discrete Dipole Approximation in conjunction with Sommerfeld integral relations to explain the effect of the substrates as a function of the parameters of incident radiation. The radiative coupling can both quench and enhance the resonance and its dependence on the angle and polarization of incident radiation with respect to the surface is shown. Non-radiative interaction with the substrate enhances the plasmon resonance of the particles and can shift the resonances from their free-space energies significantly. The non-radiative interaction of the substrate is sensitive to the shape of particles and polarization of incident radiation with respect to substrate. Our results show that plasmon resonances in coupled and single particles can be significantly altered from their free-space resonances and are quenched or enhanced by the choice of substrate and polarization of incident radiation.Comment: 14 pages, 4 figure

Investigation of radiative interactions in supersonic internal flows

Analyses and numerical procedures are presented to study the radiative interactions of absorbing emitting species in chemically reacting supersonic flow in various ducts. The 2-D time dependent Navier-Stokes equations in conjunction with radiative flux equation are used to study supersonic flows undergoing finite rate chemical reaction in a hydrogen air system. The specific problem considered is the flow of premixed radiating gas between parallel plates. Specific attention was directed toward studying the radiative contribution of H2O, OH, and NO under realistic physical and flow conditions. Results are presented for the radiative flux obtained for different gases and for various combination of these gases. The problem of chemically reacting and radiating flows was solved for the flow of premixed hydrogen-air through a 10 deg compression ramp. Results demonstrate that the radiative interaction increases with an increase in pressure, temperature, amount of participating species, plate spacing, and Mach number. Most of the energy, however, is transferred by convection in the flow direction. In general the results indicate that radiation can have a significant effect on the entire flow field

Classical Electron Model with Negative Energy Density in Einstein-Cartan Theory of Gravitation

Experimental result regarding the maximum limit of the radius of the electron \sim 10^{-16} cm and a few of the theoretical works suggest that the gravitational mass which is a priori a positive quantity in Newtonian mechanics may become negative in general theory of relativity. It is argued that such a negative gravitational mass and hence negative energy density also can be obtained with a better physical interpretation in the framework of Einstein-Cartan theory.Comment: 12 Latex pages, added refs and conclusion

Defence Expenditure and Economic Growth: Evidence from India

This thesis work presents both mathematical models and a simulation approach to get more insight to the R&D Project Portfolio Execution problem. It gives special care to finding the optimal number of projects to run simultaneously in a portfolio in order to get the maximum monetary gain, and give the factors that affect the most this number. This report tries as well to give the best simulation of resources behaviour inside an R&D department, and takes a stage-gate model for the projects. The proposed mathematical model is a Non-Linear Mixed Integer Program that is hard to solve. A simplification lead to a less complicated Mixed Integer Program that is easier to solve. But in order to have an insight of the whole complexity of the problem, a simulation platform has been implemented. Thanks to its low computation cost, it allowed to have a big number of simulations and draw some conclusions about the initial question. The simulation platform also allows to see the influence of different factors on the number of projects that should be executed in parallel in R &D departments, which was hard to do using the mathematical models.  Detta examensarbete presenterar både matematiska modeller och en simuleringsplattform för att få mer insikt i R & D Project Portfolio Execution problem. Målet är att beräkna det optimala antalet projekt att köra samtidigt i en portfölj och hitta de faktorer som har störst påverkan på detta. Rapporten försöker också att ge den bästa simuleringen av resursersbeteende i R & D avdelningar. Den föreslagna matematiska modellen är ett icke-linjärt Mixed Integer Program som är svårt att lösa. En simplifiering leder till en mindre komplicerad Mixed Integer Program som är lättare att lösa, men för att få en inblick i hela problemets komplexitet har en simuleringsplattform implementerats. Tack vare dess låga beräkningskostnad, är det möjligt att köra ett stort antal simuleringar och dra vissa slutsatser om den inledande frågan. Användandet av en simuleringsplattform gör det också möjligt att se påverkan av olika faktorer på antalet projekt som ska köras parallellt i R & D -avdelningar, som hade varit svårt att göra med matematisk modellering