274 research outputs found
Geoacoustic Inversion of Ship Radiated Noise in Shallow Water Using Data From a Single Hydrophone
The Centre for Maritime Research and Experimentation conducted a geoacoustic inverse experiment in the Mediterranean Sea in the summer of 2012. Among the objectives was to employ an autono- mous underwater vehicle to collect acoustic data to invert for properties of the seafloor. Inversion results for the compression wave speed in the bottom and the source spectrum of the R/V Alliance during a close approach to the bottom moored vehicle are presented. The estimated wave speed was 1529 m/s (r ΒΌ 10). The source spectrum of the Alliance was estimated across more than six octaves of frequency
Limit on UHE Neutrino Flux from the Parkes Lunar Radio Cherenkov Experiment
The first search for ultra-high energy (UHE) neutrinos using a radio
telescope was conducted by Hankins, Ekers and O'Sullivan (1996). This was a
search for nanosecond duration radio Cherenkov pulses from electromagnetic
cascades initiated by ultra-high energy (UHE) neutrino interactions in the
lunar regolith, and was made using a broad-bandwidth receiver fitted to the
Parkes radio telescope, Australia. At the time, no simulations were available
to convert the null result into a neutrino flux limit. Since then, similar
experiments at Goldstone, USA, and Kalyazin, Russia, have also recorded null
results, and computer simulations have been used to model the experimental
sensitivities of these two experiments and put useful limits on the UHE
neutrino flux.
Proposed future experiments include the use of broad-bandwidth receivers,
making the sensitivity achieved by the Parkes experiment highly relevant to the
future prospects of this field. We have therefore calculated the effective
aperture for the Parkes experiment and found that when pointing at the lunar
limb, the effective aperture at all neutrino energies was superior to
single-antenna, narrow-bandwidth experiments, and that the detection threshold
was comparable to that of the double-antenna experiment at Goldstone. However,
because only a small fraction of the observing time was spent pointing the
limb, the Parkes experiment places only comparatively weak limits on the UHE
neutrino flux. Future efforts should use multiple telescopes and
broad-bandwidth receivers.Comment: 6 pages, 2 figures, accepted for publication in MNRA
Abrasive water jet drilling of advanced sustainable bio-fibre-reinforced polymer/hybrid composites : a comprehensive analysis of machining-induced damage responses
This paper aims at investigating the effects of variable traverse speeds on machining-induced damage of fibre-reinforced composites, using the abrasive water jet (AWJ) drilling. Three different types of epoxy-based composites laminates fabricated by vacuum bagging technique containing unidirectional (UD) flax, hybrid carbon-flax and carbon fibre-reinforced composite were used. The drilling parameters used were traverse speeds of 20, 40, 60 and 80 mm/min, constant water jet pressure of 300 MPa and a hole diameter of 10 mm. The results obtained depict that the traverse speed had a significant effect with respect to both surface roughness and delamination drilling-induced damage responses. Evidently, an increase in water jet traverse speed caused an increase in both damage responses of the three samples. Significantly, the CFRP composite sample recorded the lowest surface roughness damage response, followed by C-FFRP, while FFRP exhibited the highest. However, samples of FFRP and hybrid C-FFRP recorded lowest and highest delamination damage responses, respectively. The discrepancy in both damage responses, as further validated with micrographs of colour video microscopy (CVM), scanning electron microscopy (SEM) and X-ray micro-computed tomography (X-ray ΞΌCT), is attributed to the different mechanical properties of the reinforced fibres, fibre orientation/ply stacking and hybridisation of the samples.Peer reviewe
The First Hour of Extra-galactic Data of the Sloan Digital Sky Survey Spectroscopic Commissioning: The Coma Cluster
On 26 May 1999, one of the Sloan Digital Sky Survey (SDSS) fiber-fed
spectrographs saw astronomical first light. This was followed by the first
spectroscopic commissioning run during the dark period of June 1999. We present
here the first hour of extra-galactic spectroscopy taken during these early
commissioning stages: an observation of the Coma cluster of galaxies. Our data
samples the Southern part of this cluster, out to a radius of 1.5degrees and
thus fully covers the NGC 4839 group. We outline in this paper the main
characteristics of the SDSS spectroscopic systems and provide redshifts and
spectral classifications for 196 Coma galaxies, of which 45 redshifts are new.
For the 151 galaxies in common with the literature, we find excellent agreement
between our redshift determinations and the published values. As part of our
analysis, we have investigated four different spectral classification
algorithms: spectral line strengths, a principal component decomposition, a
wavelet analysis and the fitting of spectral synthesis models to the data. We
find that a significant fraction (25%) of our observed Coma galaxies show signs
of recent star-formation activity and that the velocity dispersion of these
active galaxies (emission-line and post-starburst galaxies) is 30% larger than
the absorption-line galaxies. We also find no active galaxies within the
central (projected) 200 h-1 Kpc of the cluster. The spatial distribution of our
Coma active galaxies is consistent with that found at higher redshift for the
CNOC1 cluster survey. Beyond the core region, the fraction of bright active
galaxies appears to rise slowly out to the virial radius and are randomly
distributed within the cluster with no apparent correlation with the potential
merger of the NGC 4839 group. [ABRIDGED]Comment: Accepted in AJ, 65 pages, 20 figures, 5 table
Improving well-being in Higher Education: Adopting a compassionate approach
Β© Springer Nature Switzerland AG 2019. This is a post-peer-review, pre-copyedit version of a chapter published in the 'Values of the University in a Time of Uncertainty'. The final authenticated version is available online at: https://doi.org/10.1007/978-3-030-15970-2_18Peer reviewe
Colors of 2625 Quasars at 0<z<5 Measured in the Sloan Digital Sky Survey Photometric System
We present an empirical investigation of the colors of quasars in the Sloan
Digital Sky Survey (SDSS) photometric system. The sample studied includes 2625
quasars with SDSS photometry. The quasars are distributed in a 2.5 degree wide
stripe centered on the Celestial Equator covering square degrees.
Positions and SDSS magnitudes are given for the 898 quasars known prior to SDSS
spectroscopic commissioning. New SDSS quasars represent an increase of over
200% in the number of known quasars in this area of the sky. The ensemble
average of the observed colors of quasars in the SDSS passbands are well
represented by a power-law continuum with (). However, the contributions of the bump
and other strong emission lines have a significant effect upon the colors. The
color-redshift relation exhibits considerable structure, which may be of use in
determining photometric redshifts for quasars. The range of colors can be
accounted for by a range in the optical spectral index with a distribution
(95% confidence), but there is a red tail in the
distribution. This tail may be a sign of internal reddening. Finally, we show
that there is a continuum of properties between quasars and Seyfert galaxies
and we test the validity of the traditional division between the two classes of
AGN.Comment: 66 pages, 15 figures (3 color), accepted by A
Pathway to the Square Kilometre Array - The German White Paper -
The Square Kilometre Array (SKA) is the most ambitious radio telescope ever
planned. With a collecting area of about a square kilometre, the SKA will be
far superior in sensitivity and observing speed to all current radio
facilities. The scientific capability promised by the SKA and its technological
challenges provide an ideal base for interdisciplinary research, technology
transfer, and collaboration between universities, research centres and
industry. The SKA in the radio regime and the European Extreme Large Telescope
(E-ELT) in the optical band are on the roadmap of the European Strategy Forum
for Research Infrastructures (ESFRI) and have been recognised as the essential
facilities for European research in astronomy.
This "White Paper" outlines the German science and R&D interests in the SKA
project and will provide the basis for future funding applications to secure
German involvement in the Square Kilometre Array.Comment: Editors: H. R. Kl\"ockner, M. Kramer, H. Falcke, D.J. Schwarz, A.
Eckart, G. Kauffmann, A. Zensus; 150 pages (low resolution- and colour-scale
images), published in July 2012, language English (including a foreword and
an executive summary in German), the original file is available via the MPIfR
homepag
Mapping the cold dust temperatures and masses of nearby Kingfish galaxies with Herschel
Taking advantage of the sensitivity and angular resolution of the Herschel
Space Observatory at far-infrared and submm wavelengths, we aim to characterize
the physical properties of cold dust within nearby galaxies and study the
robustness of the parameters we derive using different modified blackbody
models. For a pilot subsample of the KINGFISH program, we perform 2 temperature
fits of the Spitzer and Herschel photometric data (24 to 500um), with a warm
and a cold component, globally and in each resolution element.At global scales,
we observe ranges of values for beta_c(0.8 to 2.5) and Tc(19.1 to 25.1K).We
compute maps of our parameters with beta fixed or free to test the robustness
of the temperature and dust surface density maps we deduce. When the emissivity
is fixed, we observe temperature gradients as a function of radius.When the
emissivity is fitted as a free parameter, barred galaxies tend to have uniform
fitted emissivities.Gathering resolved elements in a Tc-beta_c diagram
underlines an anti-correlation between the two parameters.It remains difficult
to assess whether the dominant effect is the physics of dust grains, noise, or
mixing along the line of sight and in the beam. We finally observe in both
cases that the dust column density peaks in central regions of galaxies and bar
ends (coinciding with molecular gas density enhancements usually found in these
locations).We also quantify how the total dust mass varies with our assumptions
about the emissivity index as well as the influence of the wavelength coverage
used in the fits. We show that modified blackbody fits using a shallow
emissivity (beta_c < 2.0) lead to significantly lower dust masses compared to
the beta_c < 2.0 case, with dust masses lower by up to 50% if beta_c=1.5 for
instance.The working resolution affects our total dust mass estimates: masses
increase from global fits to spatially-resolved fits.Comment: 26 pages, 12 figures, 4 tables, accepted for publication in MNRAS,
2012 June 2
Dietary Modulation of Drosophila Sleep-Wake Behaviour
Background
A complex relationship exists between diet and sleep but despite its impact on human health, this relationship remains uncharacterized and poorly understood. Drosophila melanogaster is an important model for the study of metabolism and behaviour, however the effect of diet upon Drosophila sleep remains largely unaddressed.
Methodology/Principal Findings
Using automated behavioural monitoring, a capillary feeding assay and pharmacological treatments, we examined the effect of dietary yeast and sucrose upon Drosophila sleep-wake behaviour for three consecutive days. We found that dietary yeast deconsolidated the sleep-wake behaviour of flies by promoting arousal from sleep in males and shortening periods of locomotor activity in females. We also demonstrate that arousal from nocturnal sleep exhibits a significant ultradian rhythmicity with a periodicity of 85 minutes. Increasing the dietary sucrose concentration from 5% to 35% had no effect on total sucrose ingestion per day nor any affect on arousal, however it did lengthen the time that males and females remained active. Higher dietary sucrose led to reduced total sleep by male but not female flies. Locomotor activity was reduced by feeding flies Metformin, a drug that inhibits oxidative phosphorylation, however Metformin did not affect any aspects of sleep.
Conclusions
We conclude that arousal from sleep is under ultradian control and regulated in a sex-dependent manner by dietary yeast and that dietary sucrose regulates the length of time that flies sustain periods of wakefulness. These findings highlight Drosophila as an important model with which to understand how diet impacts upon sleep and wakefulness in mammals and humans
Having a lot of a good thing: multiple important group memberships as a source of self-esteem.
Copyright: Β© 2015 Jetten et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are creditedMembership in important social groups can promote a positive identity. We propose and test an identity resource model in which personal self-esteem is boosted by membership in additional important social groups. Belonging to multiple important group memberships predicts personal self-esteem in children (Study 1a), older adults (Study 1b), and former residents of a homeless shelter (Study 1c). Study 2 shows that the effects of multiple important group memberships on personal self-esteem are not reducible to number of interpersonal ties. Studies 3a and 3b provide longitudinal evidence that multiple important group memberships predict personal self-esteem over time. Studies 4 and 5 show that collective self-esteem mediates this effect, suggesting that membership in multiple important groups boosts personal self-esteem because people take pride in, and derive meaning from, important group memberships. Discussion focuses on when and why important group memberships act as a social resource that fuels personal self-esteem.This study was supported by 1. Australian Research Council Future Fellowship (FT110100238) awarded to Jolanda Jetten (see http://www.arc.gov.au) 2. Australian Research Council Linkage Grant (LP110200437) to Jolanda Jetten and Genevieve Dingle (see http://www.arc.gov.au) 3. support from the Canadian Institute for Advanced Research Social Interactions, Identity and Well-Being Program to Nyla Branscombe, S. Alexander Haslam, and Catherine Haslam (see http://www.cifar.ca)
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