1,904 research outputs found
Sigtuna Think Piece 5: Climate Change within Education for Sustainable Development- Ethical Tendency Discourse Analysis as a Tool
This think piece describes a way of including climate change within education for sustainable development (ESD), with a specific ambition to illuminate the moral dimension in a locally relevant way in the teaching. A method – ethical tendency discourse analysis – for creating a locally relevant teaching content that illuminates the moral dimension of climate change is described. This method has the potential to also, through an international collaboration, incorporate the global dimension in the teaching content
Cislunar Trajectory Generation with Sun-Exclusion Zone Constraints Using a Genetic Algorithm and Direct Method Hybridization
Space missions to the Moon have received renewed interest in recent decades. Science missions continue to be sent to the Moon, and several space agencies have aspirations of establishing a human presence on the Moon. With the increased number of artificial objects in cislunar space, the problem of tracking these objects arises. Optical sensors are able to track these objects in deep space. However, optical sensors cannot track objects that are close to the Sun as viewed from the observer. This unobservable region is the Sun-exclusion zone (SEZ). This research attempts to create optimal Moon-Earth transfers which are completely in the SEZ using a genetic algorithm-direct method hybridization. Such transfers demonstrate how much the SEZ can limit optical sensors from maintaining custody of a satellite. Transfers from L1 and L2 Lyapunov orbits to geosynchronous orbit are generated while optimizing fuel and time of flight. Remaining inside of the SEZ is shown to significantly increase the fuel required to make the transfer
Bolted Timber Connections. Part I. a Wafer Technique to Model Wood Deformation Around Bolts
An experimental technique to model wood material behavior in the plane perpendicular to the axes of bolts in joint members is described. In this technique, 0.8-mm-thick wood wafers sandwiched between glass plates, with a steel pin representing a bolt passing through them, are loaded in tension. Wood deformation and failure around the pin, visible through the glass plates as loading proceeds, are photographed, and load-slip curves are also recorded. Reported tests were limited to steel pins of 12.5-mm diameter; preliminary findings suggest that information can be gained that sheds light on the effects of growth-ring orientation, wood defects, bolt end-distance, and multiple-bolt positions. The technique may be used directly, to indicate the sensitivity of joints to design factors such as those above, or indirectly, when results are combined with bolt bending data obtained with X-ray scanning
Looking at quasars through galaxies
Observations of quasars (QSOs) shining through or close to galaxies offer a
way to probe the properties of the foreground matter through dust extinction
and gravitational lensing. In this paper the feasibility of measuring the dust
extinction properties is investigated using the backlitting of QSOs. We test
our method to search for QSOs affected by intervening extinction, by matching
the coordinates in the SDSS QSO DR3 catalogue with the New York University
Value-Added Galaxy Catalog. In total, 164 QSO-galaxy pairs were found with a
distance of less than 30 kpc between the galaxy centre and the QSO
line-of-sight at the galaxy redshift. Investigating the QSO colours with
multiband SDSS photometry, two pairs with galaxy redshifts z < 0.08 were found
to be particularly interesting in that the QSOs show evidence of heavy Galactic
type extinction with R_v ~ 3.1 at very large optical radii in the foreground
spiral galaxies. With the available data, it remains inconclusive whether the
two pairs can be explained as statistical colour outliers, by host extinction
or if they provide evidence of dust in the outskirts of spiral galaxies. Deeper
galaxy catalogues and/or higher resolution follow-up QSO spectra would help in
resolving this problem. We also analyse five QSOs reported in the literature
with spectroscopic absorption features originating from an intervening system.
These systems are at higher redshifts than the other two and we find in most
cases significantly lower best fit values of R_v. The wide range of preferred
values of R_v found, although affected by substantial uncertainties, already
indicates that the dust properties in other galaxies may be different from the
Milky Way. Furthermore, the available data suggests a possible evolution in the
dust properties with redshift, with lower R_v at high z.Comment: 7 pages, 7 figures. Matches version accepted by A&
Bolted Timber Connections: Part II. Bolt Bending and Associated Wood Deformation
Complete double-shear joints with a single bolt were tested in tension. Approximately 10 X-ray scans were made of each joint as it was progressively loaded to failure; in this way, bending and overall displacement of the bolts within the members could be quantified. Combining the above data with measured joint-slip values enables the penetration of the bolt into the surrounding wood to be calculated for all positions along the length of the bolt. In a preceding related study, the authors observed the mechanisms of deformation that occur in thin wood wafers around a round steel pin of a diameter identical to that of the bolts used in the present work. By combining this information on behavior mechanisms in the plane at right angles to the pin axis with the X-ray data for whole joints, wood behavior throughout the joint and reactions against the bolt along its length can be estimated. The above analysis is applied principally to joints with 75- x 75-mm wood main members, 75- x 37.5-mm wood side members, and a single 12.5-mm diameter bolt an an end-distance of seven diameters. Representative X-ray scans of joints manufactured with a range of steel side-member thicknesses and bolt diameters are also included. The techniques presented complement theoretical model predictions and thus may be used to aid in optimizing joint design
URLLC with Massive MIMO: Analysis and Design at Finite Blocklength
The fast adoption of Massive MIMO for high-throughput communications was enabled by many research contributions mostly relying on infinite-blocklength information-theoretic bounds. This makes it hard to assess the suitability of Massive MIMO for ultra-reliable low-latency communications (URLLC) operating with short-blocklength codes. This paper provides a rigorous framework for the characterization and numerical evaluation (using the saddlepoint approximation) of the error probability achievable in the uplink and downlink of Massive MIMO at finite blocklength. The framework encompasses imperfect channel state information, pilot contamination, spatially correlated channels, and arbitrary linear spatial processing. In line with previous results based on infinite-blocklength bounds, we prove that, with minimum mean-square error (MMSE) processing and spatially correlated channels, the error probability at finite blocklength goes to zero as the number M of antennas grows to infinity, even under pilot contamination. However, numerical results for a practical URLLC network setup involving a base station with M-100 antennas, show that a target error probability of 10^¿5 can be achieved with MMSE processing, uniformly over each cell, only if orthogonal pilot sequences are assigned to all the users in the network. Maximum ratio processing does not suffice.The work of Johan Östman, Alejandro Lancho, and Giuseppe Durisi was supported in part by the Swedish Research Council under grant 2016-03293 and in part by the Wallenberg AI, Autonomous Systems, and Software Program. The work of Luca Sanguinetti was supported in part by the Italian Ministry of Education and Research (MIUR) in the framework of the CrossLab Project (Departments of Excellence)
Type Ia supernova Hubble diagram with near-infrared and optical observations
We main goal of this paper is to test whether the NIR peak magnitudes of SNe
Ia could be accurately estimated with only a single observation obtained close
to maximum light, provided the time of B band maximum and the optical stretch
parameter are known. We obtained multi-epoch UBVRI and single-epoch J and H
photometric observations of 16 SNe Ia in the redshift range z=0.037-0.183,
doubling the leverage of the current SN Ia NIR Hubble diagram and the number of
SNe beyond redshift 0.04. This sample was analyzed together with 102 NIR and
458 optical light curves (LCs) of normal SNe Ia from the literature. The
analysis of 45 well-sampled NIR LCs shows that a single template accurately
describes them if its time axis is stretched with the optical stretch
parameter. This allows us to estimate the NIR peak magnitudes even with one
observation obtained within 10 days from B-band maximum. We find that the NIR
Hubble residuals show weak correlation with DM_15 and E(B-V), and for the first
time we report a possible dependence on the J_max-H_max color. The intrinsic
NIR luminosity scatter of SNe Ia is estimated to be around 0.10 mag, which is
smaller than what can be derived for a similarly heterogeneous sample at
optical wavelengths. In conclusion, we find that SNe Ia are at least as good
standard candles in the NIR as in the optical. We showed that it is feasible to
extended the NIR SN Ia Hubble diagram to z=0.2 with very modest sampling of the
NIR LCs, if complemented by well-sampled optical LCs. Our results suggest that
the most efficient way to extend the NIR Hubble diagram to high redshift would
be to obtain a single observation close to the NIR maximum. (abridged)Comment: 39 pages, 15 figures, accepted by A&
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Development of techniques to study the behavior of bolted wood joints
The design of bolted wood joints has, to date, been
primarily based on empirical work. Much of this has been
on single bolted joints. The extrapolation of this data to
cover multiple bolted and large diameter bolted joints is
questionable. There appears to be a lack of basic
understanding of the behavior of bolted wood joints as they
are loaded to failure. This thesis is concerned with the
development of two techniques that may be used to gain a
better understanding of bolted joint behavior.
The first technique involves the use of wood wafers or
lamina which provide a two dimensional representation of a
bolted joint during loading. It involves mounting a
specially cut thin section of wood between two glass plates
with a steel pin representing a bolt passing through the
resultant wood glass sandwich. The approach is used to
observe the wood deformation around the bolt in a plane
normal to the bolt axis. It may also be used to simulate multiple bolted joints.
The third dimension of the joint (in the axial
direction of the bolt) is added by the second technique.
This consists of taking x-ray scans of complete joints as
they are loaded to failure. The bending behavior of bolts
and associated wood deformation as they are effected by a
range of joint parameters may be quantified in this way.
The development and numerical integration of these two
techniques will, it is hoped provide means to obtain a
clearer three dimensional understanding of the behavior of
bolted wood joints
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