12,671 research outputs found
Hydrogen storage in pillared Li-dispersed boron carbide nanotubes
Ab initio density-functional theory study suggests that pillared Li-dispersed
boron carbide nanotubes is capable of storing hydrogen with a mass density
higher than 6.0 weight% and a volumetric density higher than 45 g/L. The boron
substitution in carbon nanotube greatly enhances the binding energy of Li atom
to the nanotube, and this binding energy (~ 2.7 eV) is greater than the
cohesive energy of lithium metal (~1.7 eV), preventing lithium from aggregation
(or segregation) at high lithium doping concentration. The adsorption energy of
hydrogen on the Li-dispersed boron carbide nanotube is in the range of 10 ~24
kJ/mol, suitable for reversible H2 adsorption/desorption at room temperature
and near ambient pressure.Comment: 17 pages, 4 figure
General stationary charged black holes as charged particle accelerators
We study the possibility of getting infinite energy in the center of mass
frame of colliding charged particles in a general stationary charged black
hole. For black holes with two-fold degenerate horizon, it is found that
arbitrary high center-of-mass energy can be attained, provided that one of the
particle has critical angular momentum or critical charge, and the remained
parameters of particles and black holes satisfy certain restriction. For black
holes with multiple-fold degenerate event horizons, the restriction is
released. For non-degenerate black holes, the ultra-high center-of-mass is
possible to be reached by invoking the multiple scattering mechanism. We obtain
a condition for the existence of innermost stable circular orbit with critical
angular momentum or charge on any-fold degenerate horizons, which is essential
to get ultra-high center-of-mass energy without fine-tuning problem. We also
discuss the proper time spending by the particle to reach the horizon and the
duality between frame dragging effect and electromagnetic interaction. Some of
these general results are applied to braneworld small black holes.Comment: 23 pages, no figures, revised version accepted for publication in
Phys. Rev.
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