9,413 research outputs found
Recent results on graphs with convex quadratic stability number
The main results about graphs with convex quadratic stability number (that is, graphs for which the stability number can be determined by convex quadratic programming) are surveyed including the most recently obtained. Furthermore, a few algorithmic techniques for the recognition of this type of graphs in particular families are presented
Reconhecimento de grafos com número de estabilidade quadrático convexo
São apresentados os principais e mais recentes resultados sobre grafos com número de estabilidade quadrático convexo (que são grafos cujo número de estabilidade pode ser determinado através de técnicas de programação quadrática convexa) e descritas algumas estratégias algorÃtmicas para o reconhecimento de grafos deste tipo em famÃlias particulares
Kinetic energy of protons in ice Ih and water: a path integral study
The kinetic energy of H and O nuclei has been studied by path integral
molecular dynamics simulations of ice Ih and water at ambient pressure. The
simulations were performed by using the q-TIP4P/F model, a point charge
empirical potential that includes molecular flexibility and anharmonicity in
the OH stretch of the water molecule. Ice Ih was studied in a temperature range
between 210-290 K, and water between 230-320 K. Simulations of an isolated
water molecule were performed in the range 210-320 K to estimate the
contribution of the intramolecular vibrational modes to the kinetic energy. Our
results for the proton kinetic energy, K_H, in water and ice Ih show both
agreement and discrepancies with different published data based on deep
inelastic neutron scattering experiments. Agreement is found for water at the
experimental melting point and in the range 290-300 K. Discrepancies arise
because data derived from the scattering experiments predict in water two
maxima of K_H around 270 K and 277 K, and that K_H is lower in ice than in
water at 269 K. As a check of the validity of the employed water potential, we
show that our simulations are consistent with other experimental thermodynamic
properties related to K_H, as the temperature dependence of the liquid density,
the heat capacity of water and ice at constant pressure, and the isotopic shift
in the melting temperature of ice upon isotopic substitution of either H or O
atoms. Moreover, the temperature dependence of K_H predicted by the q-TIP4P/F
model for ice Ih is found to be in good agreement to results of path integral
simulations using ab initio density functional theory.Comment: 11 pages, 6 figures, 2 table
The Distance to the M31 Globular Cluster System
The distance to the centroid of the M31 globular cluster system is determined
by fitting theoretical isochrones to the observed red-giant branches of
fourteen globular clusters in M31. The mean true distance modulus of the M31
globular clusters is found to be 24.47 +/- 0.07 mag. This is consistent with
distance modulii for M31 that have been obtained using other distance
indicators.Comment: 11 pages, 2 postscript figures, uses aaspp4.sty, to be published in
the May 1998 Astronomical Journa
- …