30,641 research outputs found
An empirical way to correct some drawbacks of mulliken population analysis
Indexación: ScieloThe problem of negative electronic populations and of occupation numbers greater than 2 has plagued Mulliken Population Analysis since the very beginning. Through the analysis of three model molecular systems, several basis sets and the relevant literature, we conclude that there is not enough evidence to assign the origin of these errors to the self-consistent scheme, to Mulliken's partition, to the basis set structure or to a combination of these. As Mulliken Population Analysis is still widely used, we have developed an empirical method to eliminate negative electronic populations and occupation numbers greater than 2. This method can be used for any partition of the electron density (not only Mulliken's), for any basis set and for any LCAO-MO methodology (semiempirical or ab initio). Finally, the method does not produce any change in the original atomic net charges.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000400036&lng=es&nrm=is
Cosmological solutions in F(R) Horava-Lifshitz gravity
At the present work, it is studied the extension of F (R) gravities to the
new recently proposed theory of gravity, the so-called Horava-Lifshitz gravity,
which provides a way to make the theory power counting renormalizable by
breaking Lorentz invariance. It is showed that dark energy can be well
explained in the frame of this extension, just in terms of gravity. It is also
explored the possibility to unify inflation and late-time acceleration under
the same mechanism, providing a natural explanation the accelerated expansion.Comment: 4 pages. Contribution to the Proceedings of the Spanish Relativity
Meeting (ERE) 2010, Granada, Spai
Gravitational waveforms with controlled accuracy
A partially first-order form of the characteristic formulation is introduced
to control the accuracy in the computation of gravitational waveforms produced
by highly distorted single black hole spacetimes. Our approach is to reduce the
system of equations to first-order differential form on the angular
derivatives, while retaining the proven radial and time integration schemes of
the standard characteristic formulation. This results in significantly improved
accuracy over the standard mixed-order approach in the extremely nonlinear
post-merger regime of binary black hole collisions.Comment: Revised version, published in Phys. Rev. D, RevTeX, 16 pages, 4
figure
Energy consumption, income and CO2 emissions in Latin America
I describe and compare the environment policies of European Union and of 12 Latin Americans economies. For this, I use common statistical methods, such as non-parametric tests, convergence analysis (Beta and Sigma) and panel data, in order to verify the hypothesis that emissions and energy use in Latin America has been increasing since the mid-20th century. The statistical tests used confirm the proposed hypothesis. I also rely upon the Environmental Kuznets Curve- whereby economies that are at the growth stage are more focused on achieving the latter than they are on environmental concerns and those which have already achieved growth focus more on environmental concerns-to take an alternative approach by introducing the role of economic growth in the evolution of energy consumption and emissions. This chapter reaches the conclusion that energy consumption and pollutant emissions in LA, in per capita terms, are converging. This suggests that the initial levels of the variables help to explain why some countries have increased emissions (in this case, energy consumption) to a greater extent than other economies in the region. Evidence of convergence is also found, as well as a monotonic relationship between the level of pollution and the level of development (consistent with the Environmental Kuznets Curve).Energy Consumption, emissions, Latin America, Convergence
Cauchy-characteristic Evolution of Einstein-Klein-Gordon Systems: The Black Hole Regime
The Cauchy+characteristic matching (CCM) problem for the scalar wave equation
is investigated in the background geometry of a Schwarzschild black hole.
Previously reported work developed the CCM framework for the coupled
Einstein-Klein-Gordon system of equations, assuming a regular center of
symmetry. Here, the time evolution after the formation of a black hole is
pursued, using a CCM formulation of the governing equations perturbed around
the Schwarzschild background. An extension of the matching scheme allows for
arbitrary matching boundary motion across the coordinate grid. As a proof of
concept, the late time behavior of the dynamics of the scalar field is
explored. The power-law tails in both the time-like and null infinity limits
are verified.Comment: To appear in Phys. Rev. D, 9 pages, revtex, 5 figures available at
http://www.astro.psu.edu/users/nr/preprints.htm
Symmetries of Discrete Dynamical Systems Involving Two Species
The Lie point symmetries of a coupled system of two nonlinear
differential-difference equations are investigated. It is shown that in special
cases the symmetry group can be infinite dimensional, in other cases up to 10
dimensional. The equations can describe the interaction of two long molecular
chains, each involving one type of atoms.Comment: 40 pages, no figures, typed in AMS-LaTe
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