9,124 research outputs found
A wide family of singularity-free cosmological models
In this paper a family of non-singular cylindrical perfect fluid cosmologies
is derived. The equation of state corresponds to a stiff fluid. The family
depends on two independent functions under very simple conditions. A sufficient
condition for geodesic completeness is provided.Comment: 7 pages, RevTeX
Lubrication of DLC Coatings with Two Tris(pentafluoroethyl)trifluorophosphate Anion-Based Ionic Liquids
The lubrication of a Cr-DLC coating with ethyl-dimethyl-2-methoxyethylammonium tris(pentafluoroethyl)trifluoropho-sphate [(NEMM)MOE][FAP] and 1-butyl-1-methylpyrro-lidinium tris(pentafluoroethyl)trifluorophosphate [BMP] [FAP] ionic liquids (ILs) as 1 wt% additives to a polyalphaolefin (PAO 6) was studied. Zinc dialkyldithiophosphate (ZDDP) was also used as reference in order to evaluate the effectiveness of the ILs. Reciprocating ball-on-plate tribological tests at loads of 20 and 40 N were performed. The results showed that both ILs exhibited a friction reduction, especially at the lowest load tested. Antiwear properties were also improved; the PAO 6 + 1% [BMP][FAP] mixture was slightly better, close to the values for PAO 6 + 1% ZDDP. Scanning electron microscopy (SEM) images and X-ray photoelectron spectroscopy (XPS) analysis indicated that the additive–surface interaction was responsible for the tribological improvement
Papiloma de plexo coroideo del cuarto ventrículo cerebral : diagnóstico y tratamiento quirúrgico
Se trata de una perra mestiza, de ocho años de edad y unos 30 kg de peso, con hemiparesis e inclinación de la cabeza hacia el lado izquierdo. Tras realizar una resonancia magnética nuclear (RMN) se identificó la lesión, compatible con una neoplasia, en fosa posterior a nivel del cuarto ventrículo cerebral. El tratamiento quirúrgico consistió en una craneotomía suboccipital que permitió el acceso a la fosa posterior, para poder así extraer el tumor. El resultado obtenido tras la cirugía se puede considerar satisfactorio, si tenemos en cuenta el alto grado de morbilidad que supone trabajar en esta regiónHerein, we report the case of an eight-year-old, 30 kg, female mixed-breed dog, with hemiparesis and left head tilt. Magnetic resonance imaging led to identify the lession as a tumor in the caudal fossa of the fourth ventricle. The surgical treatment consisted of a suboccipital craniotomy, which allowed the access to the caudal fossa, and the xtirpation of the tumor. A satisfactory result was achieved after the surgery, if we consider the high sick rate involved when working in this region
Non-singular radiation cosmological models
In this paper we analyse the possibility of constructing singularity-free
inhomogeneous cosmological models with a pure radiation field as matter
content. It is shown that the conditions for regularity are very easy to
implement and therefore there is a huge number of such spacetimes.Comment: 13 pages, LaTex, ws-mpla, to appear in Modern Physics Letters
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