2,551 research outputs found
Structural analysis of ultra-high speed aircraft structural components
The buckling characteristics of a hypersonic beaded skin panel were investigated under pure compression with boundary conditions similar to those found in a wing mounted condition. The primary phases of analysis reported include: (1) experimental testing of the panel to failure; (2) finite element structural analysis of the beaded panel with the computer program NASTRAN; and (3) summary of the semiclassical buckling equations for the beaded panel under purely compressive loads. A comparison of each of the analysis methods is also included
First NACO observations of the Brown Dwarf LHS 2397aB
Observations of the standard late type M8 star LHS 2397aA were obtained at
the ESO-VLT 8m telescope ``Yepun'' using the NAOS/CONICA Adaptive Optics
facility. The observations were taken during the NACO commissioning, and the
infrared standard star LHS 2397aA was observed in the H, and Ks broad band
filters. In both bands the brown dwarf companion LHS2397aB was detected. Using
a program recently developed (Bouy et al., 2003) for the detection of stellar
binaries we calculated the principal astrometric parameters (angular binary
separation and position angle P.A.) and the photometry of LHS 2397aA and LHS
2397aB. Our study largely confirms previous results obtained with the
AO-Hokupa'a facility at Gemini-North (Freed et al., 2003); however a few
discrepancies are observed.Comment: 5 page
VLT Diffraction Limited Imaging and Spectroscopy in the NIR: Weighing the black hole in Centaurus A with NACO
We present high spatial resolution near-infrared spectra and images of the
nucleus of Centaurus A (NGC 5128) obtained with NAOS-CONICA at the VLT. The
adaptive optics corrected data have a spatial resolution of 0.06" (FWHM) in K-
and 0.11" in H-band, four times higher than previous studies. The observed gas
motions suggest a kinematically hot disk which is orbiting a central object and
is oriented nearly perpendicular to the nuclear jet. We model the central
rotation and velocity dispersion curves of the [FeII] gas orbiting in the
combined potential of the stellar mass and the (dominant) black hole. Our
physically most plausible model, a dynamically hot and geometrically thin gas
disk, yields a black hole mass of M_bh = (6.1 +0.6/-0.8) 10^7 M_sun. As the
physical state of the gas is not well understood, we also consider two limiting
cases: first a cold disk model, which completely neglects the velocity
dispersion; it yields an M_bh estimate that is almost two times lower. The
other extreme case is to model a spherical gas distribution in hydrostatic
equilibrium through Jeans equation. Compared to the hot disk model the best-fit
black hole mass increases by a factor of 1.5. This wide mass range spanned by
the limiting cases shows how important the gas physics is even for high
resolution data. Our overall best-fitting black hole mass is a factor of 2-4
lower than previous measurements. With our revised M_bh estimate, Cen A's
offset from the M_bh-sigma relation is significantly reduced; it falls above
this relation by a factor of ~2, which is close to the intrinsic scatter of
this relation. (Abridged)Comment: 12 pages, 14 figures, including minor changes following the referee
report; accepted for publication in The Astrophysical Journa
Applying consumer responsibility principle in evaluating environmental load of carbon emissions
There is a need for a proper indicator in order to assess the environmental impact of international
trade, therefore using the carbon footprint as an indicator can be relevant and useful. The aim of this
study is to show from a methodological perspective how the carbon footprint, combined with input-
output models can be used for analysing the impacts of international trade on the sustainable use
of national resources in a country. The use of the input-output approach has the essential advantage
of being able to track the transformation of goods through the economy. The study examines the environmental
impact of consumption related to international trade, using the consumer responsibility
principle. In this study the use of the carbon footprint and input-output methodology is shown on the
example of the Hungarian consumption and the impact of international trade. Moving from a production-
based approach in climate policy to a consumption-perspective principle and allocation,
would also help to increase the efficiency of emission reduction targets and the evaluation of the
ecological impacts of international trade
Crystal Structure of the Hexamerization Domain of N-ethylmaleimide–Sensitive Fusion Protein
AbstractN-ethylmaleimide–sensitive fusion protein (NSF) is a cytosolic ATPase required for many intracellular vesicle fusion reactions. NSF consists of an amino-terminal region that interacts with other components of the vesicle trafficking machinery, followed by two homologous ATP-binding cassettes, designated D1 and D2, that possess essential ATPase and hexamerization activities, respectively. The crystal structure of D2 bound to Mg2PLUSPUSSIGN-AMPPNP has been determined at 1.75 Å resolution. The structure consists of a nucleotide-binding and a helical domain, and it is unexpectedly similar to the first two domains of the clamp-loading subunit δ′ of E. coli DNA polymerase III. The structure suggests several regions responsible for coupling of ATP hydrolysis to structural changes in full-length NSF
A direct and differential imaging search for sub-stellar companions to epsilon Indi A
We have carried out a direct and differential imaging search for sub-stellar
companions to eps Indi A using the adaptive optics system NACO at the ESO VLT.
The observations were carried out in September 2004 with NACO/SDI as well as
with NACO's S27 camera in the H and Ks filters. The SDI data cover an area of
\~2.8" around eps Indi A. No detection was achieved in the inner neighbourhood
down to 53 Mj (5 sigma confidence level) at a separation > 0.4" (1.45 AU) and
down to 21 Mj for separations > 1.3" (4.7 AU). To cover a wider field of view,
observations with the S27 camera and a coronagraphic mask were obtained. We
detected a faint source at a separation of (7.3 +/- 0.1)" and a position angle
of (302.9 +/- 0.8) degree. The photometry for the candidate companion yields
m(H)=(16.45 +/- 0.04)mag and m(Ks) = (15.41 +/- 0.06)mag, respectively. Those
magnitudes and the resulting color (H-Ks) = (1.04 +/- 0.07)mag fit best to a
spectral type of L5 - L9.5 if it is bound. Observations done with HST/NICMOS by
M. Endl have shown the source to be a background object.Comment: 6 pages, 5 figures, accepted by A&
The Variable Reflection Nebula Cepheus A East
We report K'-band imaging observations of the reflection nebula associated
with Cepheus A East covering the time interval from 1990 to 2004. Over this
time the reflection nebula shows variations of flux distribution, which we
interpret as the effect of inhomogeneous and varying extinction in the light
path from the illuminating source HW2 to the reflection nebula. The obscuring
material is located within typical distances of approximately 10 AU from the
illuminating source.Comment: 22 pages, including 6 figures, accepted for publication in The
Astronomical Journa
Improved age constraints for the AB Dor quadruple system - The binary nature of AB Dor B
We present resolved NACO photometry of the close binary AB Dor B in H- and
Ks-band. AB Dor B is itself known to be a wide binary companion to AB Dor A,
which in turn has a very low-mass close companion named AB Dor C. These four
known components make up the young and dynamically interesting system AB Dor,
which will likely become a benchmark system for calibrating theoretical
pre-main sequence evolutionary mass tracks for low-mass stars. However, for
this purpose the actual age has to be known, and this subject has been a matter
of discussion in the recent scientific literature. We compare our resolved
photometry of AB Dor Ba and Bb with theoretical and empirical isochrones in
order to constrain the age of the system. This leads to an age estimate of
about 50 to 100 Myr. We discuss the implications of such an age range for the
case of AB Dor C, and compare with other results in the literature.Comment: 7 pages, 6 figures, accepted for publication in A&
Constraints on Extrasolar Planet Populations from VLT NACO/SDI and MMT SDI and Direct Adaptive Optics Imaging Surveys: Giant Planets are Rare at Large Separations
We examine the implications for the distribution of extrasolar planets based
on the null results from two of the largest direct imaging surveys published to
date. Combining the measured contrast curves from 22 of the stars observed with
the VLT NACO adaptive optics system by Masciadri et al. (2005), and 48 of the
stars observed with the VLT NACO SDI and MMT SDI devices by Biller et al.
(2007) (for a total of 60 unique stars; the median star for our survey is a 30
Myr K2 star at 25 pc), we consider what distributions of planet masses and
semi-major axes can be ruled out by these data, based on Monte Carlo
simulations of planet populations. We can set this upper limit with 95%
confidence: the fraction of stars with planets with semi-major axis from 20 to
100 AU, and mass >4 M_Jup, is 20% or less. Also, with a distribution of planet
mass of dN/dM ~ M^-1.16 between 0.5-13 M_Jup, we can rule out a power-law
distribution for semi-major axis (dN/da ~ a^alpha) with index 0 and upper
cut-off of 18 AU, and index -0.5 with an upper cut-off of 48 AU. For the
distribution suggested by Cumming et al. (2007), a power-law of index -0.61, we
can place an upper limit of 75 AU on the semi-major axis distribution. At the
68% confidence level, these upper limits state that fewer than 8% of stars have
a planet of mass >4 M_Jup between 20 and 100 AU, and a power-law distribution
for semi-major axis with index 0, -0.5, and -0.61 cannot have giant planets
beyond 12, 23, and 29 AU, respectively. In general, we find that even null
results from direct imaging surveys are very powerful in constraining the
distributions of giant planets (0.5-13 M_Jup) at large separations, but more
work needs to be done to close the gap between planets that can be detected by
direct imaging, and those to which the radial velocity method is sensitive.Comment: 46 pages, 17 figures, accepted to Ap
Gas-phase CO2 emission toward Cepheus A East: the result of shock activity?
We report the first detection of gas-phase CO2 emission in the star-forming
region Cepheus A East, obtained by spectral line mapping of the v2 bending mode
at 14.98 micron with the Infrared Spectrograph (IRS) instrument onboard the
Spitzer Space Telescope. The gaseous CO2 emission covers a region about 35'' x
25'' in extent, and results from radiative pumping by 15 micron continuum
photons emanating predominantly from the HW2 protostellar region. The gaseous
CO2 exhibits a temperature distribution ranging from 50 K to 200 K. A
correlation between the gas-phase CO2 distribution and that of H2 S(2), a
tracer of shock activity, indicates that the CO2 molecules originate in a cool
post-shock gas component associated with the outflow powered by HW2. The
presence of CO2 ice absorption features at 15.20 micron toward this region and
the lack of correlation between the IR continuum emission and the CO2 gas
emission distribution further suggest that the gaseous CO2 molecules are mainly
sputtered off grain mantles -- by the passage of slow non-dissociative shocks
with velocities of 15-30 km/s -- rather than sublimated through grain heating.Comment: 11 pages, 6 figures, accepted for publication in ApJ
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