3,063 research outputs found
Atomic resolution STM imaging of a twisted single-wall carbon nanotube
We present atomically-resolved STM images of single-wall carbon nanotubes
(SWNTs) embedded in a crystalline nanotube rope. Although they may be
interpreted as of a chiral nanotube, the images are more consistently explained
a an achiral armchair tube with a quenched twist distortion. The existence of
quenched twists in SWNTs in ropes might explain the fact that both as-grown
bulk nanotube material and individual ropes have insulator-like conductivity at
low temperature.Comment: preprint, 4 pages, and 4 gif figure
Disappearances
Disappearances is a coming of age novel that includes science fiction and magical elements. It focuses on a young man named Leo who awakes on morning to find that everyone on the planet has disappeared. He travels around the empty United State for six months, grappling with memories and loneliness until he meets a shaman who helps him come to terms with the major events of his life
XMM observations of the narrow-line QSO PHL 1092: Detection of a high and variable soft component
We present results based on an XMM-Newton observation of the high luminosity
narrow-line QSO PHL 1092 performed in 2003 January. The 0.3 - 10 keV spectrum
is well described by a model which includes a power-law (Gamma ~ 2.1) and two
blackbody components (kT ~ 130 eV and kT ~ 50 eV). The soft X-ray excess
emission is featureless and contributes ~ 80% to the total X-ray emission in
the 0.3 - 10 keV band. The most remarkable feature of the present observation
is the detection of X-ray variability at very short time scale: the X-ray
emission varied by 35% in about 5000 s. We find that this variability can be
explained by assuming that only the overall normalization varied during the
observation. There was no evidence for any short term spectral variability and
the spectral shape was similar even during the ASCA observation carried out in
1997. Considering the high intrinsic luminosity (~ 2x10^45 erg/s) and the large
inferred mass of the putative black hole (~ 1.6x10^8 M_sun), the observed time
scale of variability indicates emission at close to Eddington luminosity
arising from very close to the black hole. We suggest that PHL 1092 in
particular (and narrow line Seyfert galaxies in general) is a fast rotating
black hole emitting close to its Eddington luminosity and the X-ray emission
corresponds to the high-soft state seen in Galactic black hole sources.Comment: 7 figures, 8 pages, emulateapj style, ApJ in pres
A NLTE model atmosphere analysis of the pulsating sdO star SDSS J1600+0748
We started a program to construct several grids of suitable model atmospheres
and synthetic spectra for hot subdwarf O stars computed, for comparative
purposes, in LTE, NLTE, with and without metals. For the moment, we use our
grids to perform fits on our spectrum of SDSS J160043.6+074802.9 (J1600+0748
for short), this unique pulsating sdO star. Our best fit is currently obtained
with NLTE model atmospheres including carbon, nitrogen and oxygen in solar
abundances, which leads to the following parameters for SDSS J1600+0748 : Teff
= 69 060 +/- 2080 K, log g = 6.00 +/- 0.09 and log N(He)/N(H) = -0.61 +/- 0.06.
Improvements are needed, however, particularly for fitting the available He II
lines. It is hoped that the inclusion of Fe will help remedy the situation.Comment: 4 pages, 4 figures, accepted in Astrophysics and Space Science
(24/02/2010), Special issue Hot sudbwarf star
Micro-displacement sensors based on plastic photonic bandgap Bragg fibers
We demonstrate an amplitude-based micro-displacement sensor that uses a
plastic photonic bandgap Bragg fiber with one end coated with a silver layer.
The reflection intensity of the Bragg fiber is characterized in response to
different displacements (or bending curvatures). We note that the Bragg
reflector of the fiber acts as an efficient mode stripper for the wavelengths
near the edge of the fiber bandgap, which makes the sensor extremely sensitive
to bending or displacements at these wavelengths. Besides, by comparison of the
Bragg fiber sensor to a sensor based on a regular multimode fiber with similar
outer diameter and length, we find that the Bragg fiber sensor is more
sensitive to bending due to presence of mode stripper in the form of the
multilayer reflector. Experimental results show that the minimum detection
limit of the Bragg fiber sensor can be smaller than 5 um for displacement
sensing
Model atmosphere analysis of the extreme DQ white dwarf GSC2U J131147.2+292348
A new model atmosphere analysis for the peculiar DQ white dwarf discovered by
Carollo et al. (2002) is presented. The effective temperature and carbon
abundance have been estimated by fitting both the photometric data
(UBJ,VRF,IN,JHK) and a low resolution spectrum (3500<lambda<7500 A) with a new
model grid for helium-rich white dwarfs with traces of carbon (DQ stars). We
estimate Teff ~ 5120 +/- 200 K and log[C/He] ~ -5.8 +/- 0.5, which make GSC2U
J131147.2+292348 the coolest DQ star ever observed. This result indicates that
the hypothetical transition from C2 to C2H molecules around Teff = 6000 K,
which was inferred to explain the absence of DQ stars at lower temperatures,
needs to be reconsidered.Comment: 4 pages, 2 figures, accepted for publication in Astronomy and
Astrophysics Letter
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