6,314 research outputs found
Optical properties of 4 A single-walled carbon nanotubes inside the zeolite channels studied from first principles calculations
The structural, electronic, and optical properties of 4 A single-walled
carbon nanotubes (SWNTs) contained inside the zeolite channels have been
studied based upon the density-functional theory in the local-density
approximation (LDA). Our calculated results indicate that the relaxed
geometrical structures for the smallest SWNTs in the zeolite channels are much
different from those of the ideal isolated SWNTs, producing a great effect on
their physical properties. It is found that all three kinds of 4 A SWNTs can
possibly exist inside the Zeolite channels. Especially, as an example, we have
also studied the coupling effect between the ALPO_4-5 zeolite and the tube
(5,0) inside it, and found that the zeolite has real effects on the electronic
structure and optical properties of the inside (5,0) tube.Comment: 9 pages, 6figure
Microscopic origin of local moments in a zinc-doped high- superconductor
The formation of a local moment around a zinc impurity in the high-
cuprate superconductors is studied within the framework of the bosonic
resonating-valence-bond (RVB) description of the model. A topological
origin of the local moment has been shown based on the phase string effect in
the bosonic RVB theory. It is found that such an moment distributes
near the zinc in a form of staggered magnetic moments at the copper sites. The
corresponding magnetic properties, including NMR spin relaxation rate, uniform
spin susceptibility, and dynamic spin susceptibility, etc., calculated based on
the theory, are consistent with the experimental measurements. Our work
suggests that the zinc substitution in the cuprates provide an important
experimental evidence for the RVB nature of local physics in the original (zinc
free) state.Comment: The topological reason of local moment formation is given. One figure
is adde
Bethe-Salpeter equation for doubly heavy baryons in the covariant instantaneous approximation
In the heavy quark limit, a doubly heavy baryon is regarded as composed of a
heavy diquark and a light quark. We establish the Bethe-Salpeter (BS) equations
for the heavy diquarks and the doubly heavy baryons, respectively, to leading
order in a expansion. The BS equations are solved numerically under
the covariant instantaneous approximation with the kernels containing scalar
confinement and one-gluon-exchange terms. The masses for the heavy diquarks and
the doubly heavy baryons are obtained and the non-leptonic decay widths for the
doubly heavy baryons emitting a pseudo-scalar meson are calculated within the
model.Comment: Corrections to the text, two references added, version accepted for
publication in Physical Review
Cafeato de metilo butilado: un nuevo antioxidante
A novel caffeic acid derivative, butylated methyl caffeate (BMC), was synthesized via esterification between butylated caffeic acid (BCA) and methanol. Its antioxidant activity was investigated and compared to TBHQ, caffeic acid (CA), methyl caffeate (MC) and BCA through deep-frying, an oven test in oil-in-water emulsions and DPPH radical scavenging. BMC showed the strongest antioxidant activity among the five antiÂoxidants in emulsions and its antioxidant activity was almost as strong as BCA in frying. Its soybean oil-water partition coefficient was 9.18 due to its ester and tert-butyl groups, far greater than those of MC (4.82), BCA (2.41), CA (0.84) and TBHQ (3.22). This meant that it was much more soluble in the lipid phase than the other four antioxidants in emulsions. The DPPH radical scavenging activity of BMC was near TBHQ, lower than the other three because of its steric hindrance and less functional phenolic hydroxyl groups compared to others when their masses were the same.Un novedoso derivado del ácido cafeico, el cafeato de metilo butilado (BMC), fue sintetizado mediante esterificación entre el ácido cafeico butilado (BCA) y el metanol. Se investigó su actividad antioxidante y se comparó con TBHQ, ácido cafeico (CA), cafeato de metilo (MC) y BCA mediante pruebas de fritura, pruebas en horno, en emulsiones de aceite en agua y mediante eliminación de radicales DPPH. BMC mostró la mayor actividad antioxidante entre los cinco antioxidantes en emulsiones y tenÃa una actividad antioxidante casi tan fuerte como la del BCA en fritura. Su coeficiente de partición aceite de soja-agua es de 9.18 debido a sus grupos éster y terc-butilo, mucho mayores que los de MC (4.82), BCA (2.41), CA (0.84) y TBHQ (3.22). Esto significa que es mucho más soluble en la fase lipÃdica que los otros cuatro antioxidantes cuando está en emulsiones. La actividad de captación de radicales DPPH de BMC fue cercana a la del TBHQ, más baja que las otras tres debido a su impedimento estérico y grupos hidroxilo fenólicos, menos funcionales en comparación con los otros cuando sus masas son iguales
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