18,941 research outputs found
Strong vertical light output from thin silicon rich oxide/SiO₂ multilayers via in-plane modulation of photonic crystal patterns
Three-dimensional-confined structures with triangular-lattice air-hole photonic crystal patterns were fabricated to enhance the light output from silicon rich oxide/SiO₂multilayer stack. The intensity and profile of spontaneous emission were found to be efficiently modulated by controlling the optical modes of the periodic arrays via varying their structural parameters. With lattice constant/radius of 700nm∕280nm, the photoluminescence intensity was found to be enhanced by nearly nine times in the vertical direction. The mechanisms for different enhancement features have been theoretically analyzed based on coherent scattering and quantum electrodynamic effects, well supporting the experimental observation
Warm-Hot Gas in and around the Milky Way: Detection and Implications of OVII Absorption toward LMC X-3
X-ray absorption lines of highly-ionized species such as OVII at about zero
redshift have been firmly detected in the spectra of several active galactic
nuclei. However, the location of the absorbing gas remains a subject of debate.
To separate the Galactic and extragalactic contributions to the absorption, we
have obtained Chandra LETG-HRC and FUSE observations of the black hole X-ray
binary LMC X--3. A joint analysis of the detected OVII and Ne IX Kalpha lines,
together with the non-detection of the OVII Kbeta and OVIII Kalpha lines, gives
the measurements of the temperature, velocity dispersion, and hot oxygen column
density. The X-ray data also allow us to place a 95% confidence lower limit to
the Ne/O ratio as 0.14. The OVII line centroid and its relative shift from the
Galactic OI Kalpha absorption line, detected in the same observations, are
inconsistent with the systemic velocity of LMC X--3 ().
The far-UV spectrum shows OVI absorption at Galactic velocities, but no OVI
absorption is detected at the LMC velocity at significance. Both
the nonthermal broadening and the decreasing scale height with the increasing
ionization state further suggest an origin of the highly-ionized gas in a
supernova-driven galactic fountain. In addition, we estimate the warm and hot
electron column densities from our detected OVII Kalpha line in the LMC X--3
X-ray spectra and from the dispersion measure of a pulsar in the LMC vicinity.
We then infer the O/H ratio of the gas to be ,
consistent with the chemically-enriched galactic fountain scenario. We conclude
that the Galactic hot interstellar medium should in general substantially
contribute to zero-redshift X-ray absorption lines in extragalactic sources.Comment: 11 pages, accepted for publication in Ap
A Comparison of Quintessence and Nonlinear Born-Infeld Scalar Field Using Gold Supernova data
We study the Non-Linear Born-Infeld(NLBI) scalar field model and quintessence
model with two different potentials( and ). We
investigate the differences between those two models. We explore the equation
of state parameter w and the evolution of scale factor in both NLBI
scalar field and quintessence model. The present age of universe and the
transition redshift are also obtained. We use the Gold dataset of 157 SN-Ia to
constrain the parameters of the two models. All the results show that NLBI
model is slightly superior to quintessence model.Comment: 17 pages, 10 figures, some references adde
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