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

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 $1/m_{Q}$ 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

Spectral Analyses of the Nearest Persistent Ultraluminous X-Ray Source M33 X-8

We provide a detailed analysis of 12 XMM observations of the nearest persistent extragalactic ultraluminous X-ray source (ULX), M33 X-8. No significant spectral evolution is detected between the observations, therefore we combine the individual observations to increase the signal-to-noise ratio for spectral fitting. The combined spectra are best fitted by the self-consistent p-free disk plus power-law component model with p = 0.571_{-0.030}^{+0.032}, kT_{in} = 1.38_{-0.08}^{+0.09} keV, and the flux ratio of the p-free disk component to the power-law component being 0.63:0.37 in the 0.3 -- 10 keV band. The fitting indicates that the black hole in M33 X-8 is of \sim 10 M_{\odot} and accretes at a super-Eddington rate (\sim 1.5 L_{Edd}), and the phase of the accretion disk is close to a slim disk (p = 0.5). We report, for the first time, that an extra power-law component is required in addition to the p-free disk model for ULXs. In super-Eddington cases, the power-law component may possibly result from the optically thin inner region f the disk or a comptonized corona similar to that of a standard thin disk.Comment: 11 pages, 1 table, 2 figures, accepted by PAS

Un nuevo antioxidante: 6,6'-(butano-1,1-diil)bis(4-metil-benceno-1,2-diol)

A novel compound, 6,6'-(butane-1,1-diyl)bis(4-methylbenzene-1,2-diol) (BMB), was synthesized through an acid-catalyzed condensation reaction between 4-methylcatechol (HPC) and butyraldehyde. When evaluated by the Rancimat and deep frying methods, BMB exhibited a stronger antioxidant activity than TBHQ. Its DPPH radical scavenging activity was also fairly higher than TBHQ, but lower compared to its mother phenol, HPC, due to its relative ease of binding DPPH•. BMB had the strongest scavenging ability of the 4-methylcatechol analogues reported to date. It could be used effectively to retard lipid peroxidation in both moderate and high temperature food preparations.Un nuevo compuesto, 6,6'-(butano-1,1-diil)bis(4-metilbenceno-1,2-diol) (BMB) fue sintetizado mediante una reacción de condensación catalizada por ácido entre el 4-metilcatecol (HPC) y el butiraldehído. Cuando se evaluó mediante los métodos Rancimat y de fritura, el BMB mostró una actividad antioxidante más fuerte que el TBHQ. Su actividad de eliminación de radicales DPPH también fue bastante mayor que la del TBHQ, pero menor en comparación con el fenol de partida, HPC, debido a su relativa facilidad para unirse a DPPH•. BMB tiene una actividad de eliminación más fuerte que los análogos de 4-metilcatecol reportados hasta la fecha. Podría usarse eficazmente para retardar la peroxidación de lípidos en la preparación de alimentos a temperatura moderada y alta