4,115 research outputs found
Influence of boundary conditions and geometric imperfections on lateral–torsional buckling resistance of a pultruded FRP I-beam by FEA
Presented are results from geometric non-linear finite element analyses to examine the lateral torsional buckling (LTB) resistance of a Pultruded fibre reinforced polymer (FRP) I-beam when initial geometric imperfections associated with the LTB mode shape are introduced. A data reduction method is proposed to define the limiting buckling load and the method is used to present strength results for a range of beam slendernesses and geometric imperfections. Prior to reporting on these non-linear analyses, Eigenvalue FE analyses are used to establish the influence on resistance of changing load height or displacement boundary conditions. By comparing predictions for the beam with either FRP or steel elastic constants it is found that the former has a relatively larger effect on buckling strength with changes in load height and end warping fixity. The developed finite element modelling methodology will enable parametric studies to be performed for the development of closed form formulae that will be reliable for the design of FRP beams against LTB failure
Energetic radiation and the sulfur chemistry of protostellar envelopes: Submillimeter interferometry of AFGL 2591
CONTEXT: The chemistry in the inner few thousand AU of accreting envelopes
around young stellar objects is predicted to vary greatly with far-UV and X-ray
irradiation by the central star. Aim We search for molecular tracers of
high-energy irradiation by the protostar in the hot inner envelope. METHODS:
The Submillimeter Array (SMA) has observed the high-mass star forming region
AFGL 2591 in lines of CS, SO, HCN, HCN(v2=1), and HC15N with 0.6" resolution at
350 GHz probing radial scales of 600-3500 AU for an assumed distance of 1 kpc.
The SMA observations are compared with the predictions of a chemical model
fitted to previous single-dish observations. RESULTS: The CS and SO main peaks
are extended in space at the FWHM level, as predicted in the model assuming
protostellar X-rays. However, the main peak sizes are found smaller than
modeled by nearly a factor of 2. On the other hand, the lines of CS, HCN, and
HC15N, but not SO and HCN(v2=1), show pedestal emissions at radii of about 3500
AU that are not predicted. All lines except SO show a secondary peak within the
approaching outflow cone. A dip or null in the visibilities caused by a sharp
decrease in abundance with increasing radius is not observed in CS and only
tentatively in SO. CONCLUSIONS: The emission of protostellar X-rays is
supported by the good fit of the modeled SO and CS amplitude visibilities
including an extended main peak in CS. The broad pedestals can be interpreted
by far-UV irradiation in a spherically non-symmetric geometry, possibly
comprising outflow walls on scales of 3500 -- 7000 AU. The extended CS and SO
main peaks suggest sulfur evaporation near the 100 K temperature radius.Comment: Astronomy and Astrophysics, in pres
A 100-MIPS GaAs asynchronous microprocessor
The authors describe how they ported an asynchronous microprocessor previously implemented in CMOS to gallium arsenide, using a technology-independent asynchronous design technique. They introduce new circuits including a sense-amplifier, a completion detection circuit, and a general circuit structure for operators specified by production rules. The authors used and tested these circuits in a variety of designs
Residual stress development and evolution in two-phase crystalline material: a discrete dislocation study
Crystalline materials undergo heterogeneous deformation upon the application of external load, which results in the development of incompatible elastic strains in the material as soon as the load is removed. The presence of heterogeneous distribution of elastic strains in the absence of any form of external load results in the building up of stresses referred to as residual stresses. The heterogeneity of strain is attributed either to the presence of multiple phases or to the orientation gradients across the sample volume. This paper is an endeavour to model the presence of second phase in a two-dimensional discrete dislocation dynamics framework, which already contains constitutive rules to include three-dimensional mechanisms, such as line tension and dynamic junction formation. The model is used to investigate residual stress development in single crystals subjected to plane strain loading and then subsequently unloaded to study residual stresses. The dislocation accumulation around the second phase and its effect on the mechanical properties is studied. The orientation dependence of residual stresses as a function of the underlying defect substructure has also been explored. A variety of results are obtained. In particular, the development of stresses as a function of underlying defect substructure is also presented and found to depend upon the orientation of the crystal
Identifying Galaxy Mergers in Observations and Simulations with Deep Learning
Mergers are an important aspect of galaxy formation and evolution. We aim to
test whether deep learning techniques can be used to reproduce visual
classification of observations, physical classification of simulations and
highlight any differences between these two classifications. With one of the
main difficulties of merger studies being the lack of a truth sample, we can
use our method to test biases in visually identified merger catalogues. A
convolutional neural network architecture was developed and trained in two
ways: one with observations from SDSS and one with simulated galaxies from
EAGLE, processed to mimic the SDSS observations. The SDSS images were also
classified by the simulation trained network and the EAGLE images classified by
the observation trained network. The observationally trained network achieves
an accuracy of 91.5% while the simulation trained network achieves 65.2% on the
visually classified SDSS and physically classified EAGLE images respectively.
Classifying the SDSS images with the simulation trained network was less
successful, only achieving an accuracy of 64.6%, while classifying the EAGLE
images with the observation network was very poor, achieving an accuracy of
only 53.0% with preferential assignment to the non-merger classification. This
suggests that most of the simulated mergers do not have conspicuous merger
features and visually identified merger catalogues from observations are
incomplete and biased towards certain merger types. The networks trained and
tested with the same data perform the best, with observations performing better
than simulations, a result of the observational sample being biased towards
conspicuous mergers. Classifying SDSS observations with the simulation trained
network has proven to work, providing tantalizing prospects for using
simulation trained networks for galaxy identification in large surveys.Comment: Submitted to A&A, revised after first referee report. 20 pages, 22
figures, 14 tables, 1 appendi
A Parameter Study of the Dust and Gas Temperature in a Field of Young Stars
We model the thermal effect of young stars on their surrounding environment
in order to understand clustered star formation. We take radiative heating of
dust, dust-gas collisional heating, cosmic-ray heating, and molecular cooling
into account. Using Dusty, a spherical continuum radiative transfer code, we
model the dust temperature distribution around young stellar objects with
various luminosities and surrounding gas and dust density distributions. We
have created a grid of dust temperature models, based on our modeling with
Dusty, which we can use to calculate the dust temperature in a field of stars
with various parameters. We then determine the gas temperature assuming energy
balance. Our models can be used to make large-scale simulations of clustered
star formation more realistic.Comment: 29 pages, 19 figures. Submitted to Ap
Structure and Evolution of the Envelopes of Deeply Embedded Massive Young Stars
The physical structure of the envelopes around a sample of fourteen massive
(1000-100,000 solar L) young stars is investigated on 100- 100,000 AU scales
using maps and spectra in submillimeter continuum and lines of C17O, CS and
H2CO. The total column densities and the temperature profiles are obtained by
fitting self-consistent dust models to submillimeter photometry. Both the
molecular line and dust emission data indicate density gradients ~r^{-alpha},
with alpha=1.0-1.5, significantly flatter than the alpha=2.0 generally found
for low-mass objects. This flattening may indicate that in massive young
stellar objects, nonthermal pressure is more important for the support against
gravitational collapse, while thermal pressure dominates for low-mass sources.
We find alpha=2 for two hot core-type sources, but regard this as an upper
limit since in these objects, the CS abundance may be enhanced in the warm gas
close to the star.Comment: To be published in The Astrophysical Journal. 54 pages including 14
figures Revised version with references adde
Deep Learning for Galaxy Mergers in the Galaxy Main Sequence
Starburst galaxies are often found to be the result of galaxy mergers. As a
result, galaxy mergers are often believed to lie above the galaxy main
sequence: the tight correlation between stellar mass and star formation rate.
Here, we aim to test this claim. Deep learning techniques are applied to images
from the Sloan Digital Sky Survey to provide visual-like classifications for
over 340 000 objects between redshifts of 0.005 and 0.1. The aim of this
classification is to split the galaxy population into merger and non-merger
systems and we are currently achieving an accuracy of 91.5%. Stellar masses and
star formation rates are also estimated using panchromatic data for the entire
galaxy population. With these preliminary data, the mergers are placed onto the
full galaxy main sequence, where we find that merging systems lie across the
entire star formation rate - stellar mass plane.Comment: 4 pages, 1 figure. For Proceedings IAU Symposium No. 34
De-blending Deep Herschel Surveys: A Multi-wavelength Approach
Cosmological surveys in the far infrared are known to suffer from confusion.
The Bayesian de-blending tool, XID+, currently provides one of the best ways to
de-confuse deep Herschel SPIRE images, using a flat flux density prior. This
work is to demonstrate that existing multi-wavelength data sets can be
exploited to improve XID+ by providing an informed prior, resulting in more
accurate and precise extracted flux densities. Photometric data for galaxies in
the COSMOS field were used to constrain spectral energy distributions (SEDs)
using the fitting tool CIGALE. These SEDs were used to create Gaussian prior
estimates in the SPIRE bands for XID+. The multi-wavelength photometry and the
extracted SPIRE flux densities were run through CIGALE again to allow us to
compare the performance of the two priors. Inferred ALMA flux densities
(F), at 870m and 1250m, from the best fitting SEDs from the
second CIGALE run were compared with measured ALMA flux densities (F) as an
independent performance validation. Similar validations were conducted with the
SED modelling and fitting tool MAGPHYS and modified black body functions to
test for model dependency. We demonstrate a clear improvement in agreement
between the flux densities extracted with XID+ and existing data at other
wavelengths when using the new informed Gaussian prior over the original
uninformed prior. The residuals between F and F were calculated. For
the Gaussian prior, these residuals, expressed as a multiple of the ALMA error
(), have a smaller standard deviation, 7.95 for the Gaussian
prior compared to 12.21 for the flat prior, reduced mean, 1.83
compared to 3.44, and have reduced skew to positive values, 7.97
compared to 11.50. These results were determined to not be significantly model
dependent. This results in statistically more reliable SPIRE flux densities.Comment: 8 pages, 7 figures, 3 tables. Accepted for publication in A&
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