30,930 research outputs found
Simple equation of state for hard disks on the hyperbolic plane
A simple equation of state for hard disks on the hyperbolic plane is
proposed. It yields the exact second virial coefficient and contains a pole at
the highest possible packing. A comparison with another very recent theoretical
proposal and simulation data is presented.Comment: 3 pages, 1 figur
On the radial distribution function of a hard-sphere fluid
Two related approaches, one fairly recent [A. Trokhymchuk et al., J. Chem.
Phys. 123, 024501 (2005)] and the other one introduced fifteen years ago [S. B.
Yuste and A. Santos, Phys. Rev. A 43, 5418 (1991)], for the derivation of
analytical forms of the radial distribution function of a fluid of hard spheres
are compared. While they share similar starting philosophy, the first one
involves the determination of eleven parameters while the second is a simple
extension of the solution of the Percus-Yevick equation. It is found that the
{second} approach has a better global accuracy and the further asset of
counting already with a successful generalization to mixtures of hard spheres
and other related systems.Comment: 3 pages, 1 figure; v2: slightly shortened, figure changed, to be
published in JC
Modeling the spectrum of gravitational waves in the primordial Universe
Recent observations from type Ia Supernovae and from cosmic microwave
background (CMB) anisotropies have revealed that most of the matter of the
Universe interacts in a repulsive manner, composing the so-called dark energy
constituent of the Universe. The analysis of cosmic gravitational waves (GW)
represents, besides the CMB temperature and polarization anisotropies, an
additional approach in the determination of parameters that may constrain the
dark energy models and their consistence. In recent work, a generalized
Chaplygin gas model was considered in a flat universe and the corresponding
spectrum of gravitational waves was obtained. The present work adds a massless
gas component to that model and the new spectrum is compared to the previous
one. The Chaplygin gas is also used to simulate a -CDM model by means
of a particular combination of parameters so that the Chaplygin gas and the
-CDM models can be easily distinguished in the theoretical scenarios
here established. The lack of direct observational data is partialy solved when
the signature of the GW on the CMB spectra is determined.Comment: Proc. of the Conference on Magnetic Fields in the Universe: from
laboratories and stars to primordial structures, AIP(NY), eds. E. M. de
Gouveia Dal Pino, G. Lugones & A. Lazarian (2005), in press. (8 pages, 11
figures
Comment on "Theory and computer simulation for the equation of state of additive hard-disk fluid mixtures"
A flaw in the comparison between two different theoretical equations of state
for a binary mixture of additive hard disks and Monte Carlo results, as
recently reported in C. Barrio and J. R. Solana, Phys. Rev. E 63, 011201
(2001), is pointed out. It is found that both proposals, which require the
equation of state of the single component system as input, lead to comparable
accuracy but the one advocated by us [A. Santos, S. B. Yuste, and M. L\'{o}pez
de Haro, Mol. Phys. 96, 1 (1999)] is simpler and complies with the exact limit
in which the small disks are point particles.Comment: 4 pages, including 1 figur
Caracterização e avaliação de acessos de coqueiro-anão.
O presente trabalho teve como objetivo caracterizar e avaliar acessos de coqueiro-anão, validando os descritores mÃnimos da lista proposta pela UPOV e identificar cultivares exemplo. O trabalho foi realizado no Campo Experimental de Itaporanga d’Ajuda, no Banco de Germoplasma de Coco, avaliando os acessos anão-verde-do-Brasil-de-Jiqui (AVeBrJ), anão-vermelho-de-Gramame (AVG) e anão-amarelo-de-Gramame (AAG) por meio de descritores morfológicos e agronômicos. Os acessos foram implantados em 2003, no delineamento experimental em blocos casualizados, com cinco repetições, com parcela composta por 16 plantas, no espaçamento de 7,5 x 7,5 x7,5 m. Os acessos foram avaliados utilizando a lista descritiva proposta pela UPOV, em comparação com a lista do (IPGRI, 1995) utilizando os seguintes descritores: altura do estipe (AE), circunferência do estipe a 20cm (CE20), comprimento da folha (CPE), largura da folha (LPE), espessura do pecÃolo (EPE), comprimento da ráquis (CF) e número total de folÃolos (NFOL). Foi possÃvel avaliar, de forma preliminar, os descritores propostos. Observou-se valores diferenciais entre os acessos mas, ainda não é possÃvel estabelecer diferenciação e identificação de cultivares exemplos apenas com base nos descritores relatados
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