3,610 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
Magnetic Anomaly Mapping for Navigation
Magnetic navigation (MagNav) has the potential to provide a global form of navigation that uses magnetic measurements of the Earth’s anomaly magnetic field and compares those measurements to a magnetic anomaly map in order to determine the user’s position. Widespread use of MagNav will require a database of fully-sampled, low-altitude magnetic anomaly maps. Existing magnetic anomaly map databases usually come from under- or poorly-sampled surveys. In this work, we provide an easy to follow MagNav anomaly map generation framework and set of survey collection metrics/requirements in an effort to help facilitate and standardize the creation of such a database. We further explore the necessary equipment, sensors, and software algorithms required to conduct a magnetic anomaly survey and generate a map for use with MagNav by generating maps from both simulated and real-world aeromagnetic surveys
A Direct Detection of Gas Accretion: The Lyman Limit System in 3C 232
The gas added and removed from galaxies over cosmic time greatly affects
their stellar populations and star formation rates. QSO absorption studies in
close QSO/galaxy pairs create a unique opportunity to study the physical
conditions and kinematics of this gas. Here we present new Hubble Space
Telescope (HST) images of the QSO/galaxy pair 3C 232/NGC 3067. The quasar
spectrum contains a Lyman-limit absorption system (LLS) due to NGC 3067 at cz =
1421 km/s that is associated with the nearby SAB galaxy NGC 3067. Previous work
identifies this absorber as a high-velocity cloud (HVC) in NGC 3067 but the
kinematics of the absorbing gas, infalling or outflowing, were uncertain. The
HST images presented here establish the orientation of NGC 3067 and so
establish that the LLS/HVC is infalling. Using this system as a prototype, we
extend these results to higher-z Mg II/LLS to suggest that Mg II/LLSs are a
sight line sampling of the so-called "cold mode accretion" (CMA) infalling onto
luminous galaxies. But to match the observed Mg II absorber statistics, the CMA
must be more highly ionized at higher redshifts. The key observations needed to
further the study of low-z LLSs is HST/UV spectroscopy, for which a new
instrument, the Cosmic Origins Spectrograph, has just been installed greatly
enhancing our observational capabilities.Comment: 9 pages, 5 figures, accepted by PAS
L’emploi de modèles intersectoriels rectangulaires à coefficients modifiables pour simuler la propagation de la demande pour les fins de la planification du développement industriel
This article presents a methodology which draws heavily on the philosophy of the Input-Output models and having been made completely operational has already been used on three occasions in two countries for the purposes of regional development of construction materials industries.This methodology, or more precisely the strictly formalized part of it is an extension of that of rectangular Input-Output models with modifiable coefficients. Thus, not surprisingly, it resembles fairly closely the approach by simulation, although the proposed model contains some simple optimizing sub-models. While obviously normative, these sub-models play a descriptive rôle in the model as a whole.It is to be noted that the approach presented here can be applied to only one sector of the economy at a time. What is more, although capable of various extensions it will never be more than an auxiliary instrument destined to be used jointly with other analysis and planning instruments.It is vital for any valid regional analysis not to restrict its investigations exclusively to what goes on in the region directly concerned. Even if the objective of the analysis is limited to a single region, one must take into account the interrelations between regions within the national economy and with foreign economies: important feedbacks affecting the region concerned may on occasion travel far beyond its limits before returning. The type of a model presented here, thanks to a great number of interrelations of which it can systematically keep track may turn out to be particularly useful here
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
Spectroscopic analysis of DA white dwarfs from the McCook & Sion catalog
For some years now, we have been gathering optical spectra of DA white dwarfs
in an effort to study and define the empirical ZZ Ceti instability strip.
However, we have recently expanded this survey to include all the DA white
dwarfs in the McCook & Sion catalog down to a limiting visual magnitude of
V=17.5. We present here a spectroscopic analysis of over 1000 DA white dwarfs
from this ongoing survey. We have several specific areas of interest most
notably the hot DAO white dwarfs, the ZZ Ceti instability strip, and the DA+dM
binary systems. Furthermore, we present a comparison of the ensemble properties
of our sample with those of other large surveys of DA white dwarfs, paying
particular attention to the distribution of mass as a function of effective
temperature.Comment: 8 pages, 7 figures, to appear in Journal of Physics Conference
Proceedings for the 16th European White Dwarf Worksho
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
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