319 research outputs found
Estimation of dynamic load demand on a ground support scheme due to a large structurally controlled violent failure – a case study
© 2015 Institute of Materials, Minerals and Mining and The AusIMM Published by Maney on behalf of the Institute and The AusIMM. In the future a larger proportion of underground mines will operate in deep, high stress environments where excavations may be exposed to very high loading demands. This case study has examined a violent structurally controlled failure occurring in a deep hardrock underground mine at a depth of 1055 metres below surface. On the basis of the damage observations the back analysis of this event concludes that the surface support system was ejected from the wall of the excavation with an initial velocity of 10.7 m s-1. Estimates of the mechanical demand imparted to the ground support scheme during failure were also calculated. These estimates carry several assumptions in order to simplify complex uncertainties concerning the loading mass of rock and transfer of kinetic energy between the rock and ground support. However, the demand may be conservatively assumed to be at least 150 kJ m-2. These results may reflect future mining conditions at great depth
A four year longitudinal sero-epidemiological study of bovine herpesvirus type-1 (BHV-1) in adult cattle in 107 unvaccinated herds in south west England
Background: Bovine herpesvirus type-1 (BHV-1) is an important pathogen of cattle that presents with a
variety of clinical signs, including the upper respiratory tract infection infectious bovine rhinotracheitis
(IBR). A seroepidemiological study of BHV-1 antibodies was conducted in England from 2002 – 2004: 29,782 blood samples were taken from 15,736 cattle from 114 herds which were visited on up to three occasions. Antibody concentration was measured using a commercial ELISA. Farm management
information was collected using an interview questionnaire, and herd size and cattle movements were obtained from the cattle tuberculosis testing database and the British Cattle Movement Service. Hierarchical statistical models were used to investigate associations between cattle and herd variables and the continuous outcome percentage positive (PP) values from the ELISA test in unvaccinated herds.
Results: There were 7 vaccinated herds, all with at least one seropositive bovine. In unvaccinated herds 83.2% had at least one BHV-1 seropositive bovine, and the mean cattle and herd BHV-1 seroprevalence were 42.5% and 43.1% respectively. There were positive associations between PP value, age, herd size, presence of dairy cattle. Adult cattle in herds with grower cattle had lower PP values than those in herds without grower cattle. Purchased cattle had significantly lower PP values than homebred cattle, whereas
cattle in herds that were totally restocked after the foot-and-mouth epidemic in 2001 had significantly higher PP values than those in continuously stocked herds. Samples taken in spring and summer had significantly lower PP values than those taken in winter, whereas those taken in autumn had significantly higher PP values than those taken in winter. The risks estimated from a logistic regression model with a binary outcome (seropositive yes/no) were similar.
Conclusion: The prevalence of BHV-1 seropositivity in cattle and herds has increased since the 1970s.
Although the study population prevalence of BHV-1 was temporally stable during study period, the
associations between serological status and cattle age, herd size, herd type, presence of young stock and
restocked versus continuously stocked herds indicate that there is heterogeneity between herds and so
potential for further spread of BHV-1 within and between herds
A four year longitudinal sero-epidemiology study of Neospora caninum in adult cattle from 114 cattle herds in south west England : associations with age, herd and dam-offspring pairs
Background: Neosporosis caused by the protozoan parasite Neospora caninum, is an economically
important cause of abortion, stillbirth, low milk yield, reduced weight gain and premature culling in
cattle. Consequently, a seroepidemiological study of N. caninum antibodies was conducted in
England with 29,782 samples of blood taken from 15,736 cattle from 114 herds visited on three
occasions at yearly intervals. Herds were categorised into lower (< 10%) and higher (≥ 10%)
median herd seroprevalence. Hierarchical models were run to investigate associations between the
sample to positive (S/P) ratio and herd and cattle factors.
Results: Ninety-four percent of herds had at least one seropositive cow; 12.9% of adult cattle had
at least one seropositive test. Approximately 90% of herds were seropositive at all visits; 9 herds
(8%) changed serological status between visits. The median N. caninum seroprevalence in positive
herds was 10% (range 0.4% to 58.8%). There was a positive association between the serostatus of
offspring and dams that were ever seropositive. In the hierarchical model of low seroprevalence
herds there was no significant association between S/P ratio and cattle age. There was a significantly
lower S/P ratio in cattle in herds that were totally restocked after the foot-and-mouth epidemic of
2001 compared with those from continuously stocked herds and cattle purchased into these herds
had a higher S/P ratio than homebred cattle. In the model of high seroprevalence herds the S/P ratio
increased with cattle age, but was not associated with restocking or cattle origin.
Conclusion: There were no strong temporal changes in herd seroprevalence of N. caninum but
90% of herds had some seropositive cattle over this time period. Vertical transmission from
seropositive dams appeared to occur in all herds. In herds with a high seroprevalence the increasing
S/P ratio in 2–4 year old cattle is suggestive of exposure to N. caninum: horizontal transmission
between adult cattle, infection from a local source or recrudescence and abortions. Between-herd
movements of infected cattle enhance the spread of N. caninum, particularly into low
seroprevalence herds. Some restocked herds had little exposure to N. caninum, while in others
infection had spread in the time since restocking
Studying the Warm Hot Intergalactic Medium in emission: a reprise
The Warm-Hot Intergalactic Medium (WHIM) is believed to host a significant
fraction of the ``missing baryons'' in the nearby Universe. Its signature has
been detected in the X-ray absorption spectra of distant quasars. However, its
detection in emission, that would allow us to study the WHIM in a systematic
way, is still lacking. Motivated by the possibility to perform these studies
with next generation integral field spectrometers, and thanks to the
availability of a large suite of state-of-the-art hydrodynamic simulations --
the CAMELS suite -- we study here in detail the emission properties of the WHIM
and the possibility to infer its physical properties with upcoming X-ray
missions like Athena. We focused on the two most prominent WHIM emission lines,
the OVII triplet and the OVIII singlet, and build line surface brightness maps
in a lightcone, mimicking a data cube generated through integral field
spectroscopy. We confirm that detectable WHIM emission, even with next
generation instruments, is largely associated to galaxy-size dark matter halos
and that the WHIM properties evolve little from to now. Some
characteristics of the WHIM, like the line number counts as a function of their
brightness, depend on the specific hydrodynamic simulation used, while others,
like the WHIM clustering properties, are robust to this aspect. The large
number of simulations available in the CAMELS datasets allows us to assess the
sensitivity of the WHIM properties to the background cosmology and to the
energy feedback mechanisms regulated by AGN and stellar activity. [ABRIDGED]Comment: 23 pages, 17 figures, 3 table
Cosmic degeneracies - I. Joint N-body simulations of modified gravity and massive neutrinos
We present the first suite of cosmological N-body simulations that simultaneously include the effects of two different and theoretically independent extensions of the standard Lambda cold dark matter (Lambda CDM) cosmological scenario - namely an f (R) theory of modified gravity and a cosmological background of massive neutrinos - with the aim to investigate their possible observational degeneracies. We focus on three basic statistics of the large-scale matter distribution, more specifically the non-linear matter power spectrum, the halo mass function, and the halo bias. Our results show that while these two extended models separately determine very prominent and potentially detectable features in all the three statistics, when we allow them to be simultaneously at work these features are strongly suppressed. In particular, when an f (R) gravity model with f(R0) = -1 x 10(-4) is combined with a total neutrino mass of Sigma(i)m(nu i) = 0.4 eV, the resulting matter power spectrum, halo mass function, and bias at z = 0 are found to be consistent with the standard model's predictions at the less than or similar to 10, less than or similar to 20, and less than or similar to 5 per cent accuracy levels, respectively. Therefore, our results imply an intrinsic theoretical limit to the effective discriminating power of present and future observational data sets with respect to these widely considered extensions of the standard cosmological scenario
The GIGANTES dataset: precision cosmology from voids in the machine learning era
We present GIGANTES, the most extensive and realistic void catalog suite ever
released -- containing over 1 billion cosmic voids covering a volume larger
than the observable Universe, more than 20 TB of data, and created by running
the void finder VIDE on QUIJOTE's halo simulations. The expansive and detailed
GIGANTES suite, spanning thousands of cosmological models, opens up the study
of voids, answering compelling questions: Do voids carry unique cosmological
information? How is this information correlated with galaxy information?
Leveraging the large number of voids in the GIGANTES suite, our Fisher
constraints demonstrate voids contain additional information, critically
tightening constraints on cosmological parameters. We use traditional void
summary statistics (void size function, void density profile) and the void
auto-correlation function, which independently yields an error of
on for a 1
simulation, without CMB priors. Combining halos and voids we forecast an error
of from the same volume. Extrapolating to next generation
multi-Gpc surveys such as DESI, Euclid, SPHEREx, and the Roman Space
Telescope, we expect voids should yield an independent determination of
neutrino mass. Crucially, GIGANTES is the first void catalog suite expressly
built for intensive machine learning exploration. We illustrate this by
training a neural network to perform likelihood-free inference on the void size
function. Cosmology problems provide an impetus to develop novel deep learning
techniques, leveraging the symmetries embedded throughout the universe from
physical laws, interpreting models, and accurately predicting errors. With
GIGANTES, machine learning gains an impressive dataset, offering unique
problems that will stimulate new techniques.Comment: references added, typos corrected, version submitted to Ap
Maritime antarctic lakes as sentinels of climate change
Remote lakes, such as lakes from the Maritime Antarctica, can be used as sentinels of climate change, because
they are mostly free of direct anthropogenic pressures, and they experience climate change as a main stressor
capable of modifying the ecosystem structure and function. In this paper, the content of a lecture that has been
presented at the First Conference of Lake Sustainability, which has been centred in our studies on lakes from
Byers Peninsula (Maritime Antarctica), are summarized. These included physical, chemical and biological
studies of these lakes and other freshwater ecosystems, which highlighted the relevance of biotic interactions
for these ecosystems and its sensibility to temperature variations and to biological invasions, which is of rel-
evance given the acute regional warming occurring during the last decades in the area, concomitant with the
enhancement of dispersion of alien species linked to the increased presence of humans
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