74,511 research outputs found
A study of the electronic properties of liquid alkali metals. A self--consistent approach
We study the electronic properties (density of states, conductivity and
thermopower) of some nearly--free--electron systems: the liquid alkali metals
and two liquid alloys, Li-Na and Na-K. The study has been performed within the
self-consistent second order Renormalized Propagator Perturbation Expansion
(RPE) for the self-energy. The input ionic pseudopotentials and static
correlation functions are derived from the neutral pseudoatom method and the
modified hypernetted chain theory of liquids, respectively. Reasonable
agreement with experiment is found for Na, K, Rb and Na-K, whereas for Li and
Cs and Li-Na the agreement is less satisfactoryComment: 14 pages, Latex, 1 figure, 1 tabl
Interplay between the ionic and electronic density profiles in liquid metal surfaces
First principles molecular dynamics simulations have been performed for the
liquid-vapor interfaces of liquid Li, Mg, Al and Si. We analize the oscillatory
ionic and valence electronic density profiles obtained, their wavelengths and
the mechanisms behind their relative phase-shift.Comment: Accepted for publication in Journal of Chemical Physic
R-Band Imaging of Fields Around 1<z<2 Radiogalaxies
We have taken deep -band images of fields around five radiogalaxies:
0956+47, 1217+36, 3C256, 3C324 and 3C294 with . 0956+47 is found to
show a double nucleus. Our data on 1217+36 suggest the revision of its
classification as a radiogalaxy. We found a statistically significant excess of
bright () galaxies on scales of 2 arcmin around the radiogalaxies
(which have ) in our sample. The excess has been determined
empirically to be at level. It is remarkable that this excess
is not present for galaxies within the same area, suggesting that
the excess is not physically associated to the galaxies but due to intervening
groups and then related to gravitational lensing.Comment: 20 pages, uuencoded compressed PostScript including tables. Figures
available upon request. To appear in the March 1995 issue of The Astronomical
Journa
Developing Consistency in Enamel Etching by CO\u3csub\u3e2\u3c/sub\u3e Laser
It has been reported that CO2 laser energy can be utilized to etch enamel. However, consistency of etching has been a significant problem. This research was designed to ascertain which exposure parameters result in consistent etching of enamel. Fourteen non.carious teeth were selected and a 2x4 gridwork was cut into the buccal surfaces creating eight discrete windows for laser exposures. Four teeth served for the initial pilot project. Two windows were lased at each combination of exposure parameters. Laser exposures were at .01, .02, .05, or .10 sec. at 2, 5, 10, or 15 Watts (W) with a model 20C Pfizer CO2 laser. A 1.0mm focal spot was used throughout. Following SEM examinations, it became clear that etching occurred only at .05 and .10 sec. at 10 and 15W. Ten teeth were used for the main project at .05 and .10 sec. exposures at 10 and 15W. Ten windows were lased for each combination of exposure parameters. SEM analysis was accomplished at 100X and 1,200X. 10/10 laser exposures at .05 sec./15W, .10 sec./10W and .10 sec./15W resulted in etched enamel. Statistical analysis showed a significant difference in etching between the .05 sec.10W group and the higher exposure parameters (p= .003). The results indicate that CO2 laser energy can consistently etch enamel at .10 sec. at 10 or 15W and at .05 sec. at 15W with a 1.0mm focal spot
Length-weight relationships of coral reef fishes from the Alacran Reef, Yucatan, Mexico
Length-weight relationships were computed for 42 species of coral reef fishes from 14 families from the Alacran Reef (Yucatan, Mexico). A total of 1 892 individuals was used for this purpose. The fish species were caught by different fishing techniques such as fishhooks, harpoons, gill and trawl nets. The sampling period was from March 1998 to January 2000
Cosmological Implications of a Possible Class of Particles Able to Travel Faster than Light
We discuss the possible cosmological implications of a class of superluminal
particles, in a scenario where: a) Lorentz invariance is only an approximate
property of the equations of a sector of matter; b) several critical speeds of
matter in vacuum exist. The Big Bang scenario and the evolution of the very
early universe, as well as large scale structure, can be strongly influenced by
the new particles.Comment: 5 pages, to be published in the Proceedings of the Fourth
International Workshop on Theoretical and Phenomenological Aspects of
Underground Physics, Toledo (Spain) September 17-21 199
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