171 research outputs found
Dating the Kawakawa/Oruanui eruption: Comment on "Optical luminescence dating of a loess section containing a critical tephra marker horizon, SW North Island of New Zealand" by R. Grapes et al.
An IRSL age of 17.0 ± 2.2 ka (and a “mean age” of ca. 19 ka) reported by Grapes et al. [Grapes, R., Rieser, U., Wang, N. Optical luminescence dating of a loess section containing a critical tephra marker horizon, SW North Island of New Zealand. Quaternary Geochronology 5(2-3), 164–169.] for the Kawakawa/Oruanui tephra, and other ages associated with a loess section in New Zealand are untenable: age data presented are inconsistent, no formal statistical treatments or error determinations were undertaken in age analysis, and the ages proposed are seriously at odds with multiple radiocarbon age determinations on tephra sequences bracketing the Kawakawa/Oruanui tephra and with palaeoenvironmental evidence elsewhere for the time period concerned. We suggest that the bulk polymineral IRSL ages on the tephra and encapsulating loess deposits were underestimated in part because of contamination of the loess by the integration of younger materials during slow deposition and continuous modification by upbuilding pedogenesis. Single-grain luminescence assays may reveal such contamination. A 14C-based age of ca. 27 ± 1 ka cal BP (2σ), reported in 2008, currently remains the best estimate for the age of eruption of the Kawakawa/Oruanui tephra
Geomagnetically Induced Currents in the Irish Power Network during Geomagnetic Storms
Geomagnetically induced currents (GICs) are a well-known terrestrial space
weather hazard. They occur in power transmission networks and are known to have
adverse effects in both high and mid-latitude countries. Here, we study GICs in
the Irish power transmission network (geomagnetic latitude 54.7--58.5
N) during five geomagnetic storms (06-07 March 2016, 20-21 December 2015, 17-18
March 2015, 29-31 October 2003 and 13-14 March 1989). We simulate electric
fields using a plane wave method together with two ground resistivity models,
one of which is derived from magnetotelluric measurements (MT model). We then
calculate GICs in the 220, 275 and 400~kV transmission network. During the
largest of the storm periods studied, the peak electric field was calculated to
be as large as 3.8~V~km\textsuperscript{-1}, with associated GICs of up to 23~A
using our MT model. Using our homogenous resistivity model, those peak values
were 1.46~V~km\textsuperscript{-1} and 25.8~A. We find that three 400 and
275~kV substations are the most likely locations for the Irish transformers to
experience large GICs.Comment: 14 pages, 11 Figures, 4 Table
Nested quantum search and NP-complete problems
A quantum algorithm is known that solves an unstructured search problem in a
number of iterations of order , where is the dimension of the
search space, whereas any classical algorithm necessarily scales as . It
is shown here that an improved quantum search algorithm can be devised that
exploits the structure of a tree search problem by nesting this standard search
algorithm. The number of iterations required to find the solution of an average
instance of a constraint satisfaction problem scales as , with
a constant depending on the nesting depth and the problem
considered. When applying a single nesting level to a problem with constraints
of size 2 such as the graph coloring problem, this constant is
estimated to be around 0.62 for average instances of maximum difficulty. This
corresponds to a square-root speedup over a classical nested search algorithm,
of which our presented algorithm is the quantum counterpart.Comment: 18 pages RevTeX, 3 Postscript figure
Counts-in-Cylinders in the Sloan Digital Sky Survey with Comparisons to N-body Simulations
Environmental statistics provide a necessary means of comparing the
properties of galaxies in different environments and a vital test of models of
galaxy formation within the prevailing, hierarchical cosmological model. We
explore counts-in-cylinders, a common statistic defined as the number of
companions of a particular galaxy found within a given projected radius and
redshift interval. Galaxy distributions with the same two-point correlation
functions do not necessarily have the same companion count distributions. We
use this statistic to examine the environments of galaxies in the Sloan Digital
Sky Survey, Data Release 4. We also make preliminary comparisons to four models
for the spatial distributions of galaxies, based on N-body simulations, and
data from SDSS DR4 to study the utility of the counts-in-cylinders statistic.
There is a very large scatter between the number of companions a galaxy has and
the mass of its parent dark matter halo and the halo occupation, limiting the
utility of this statistic for certain kinds of environmental studies. We also
show that prevalent, empirical models of galaxy clustering that match observed
two- and three-point clustering statistics well fail to reproduce some aspects
of the observed distribution of counts-in-cylinders on 1, 3 and 6-Mpc/h scales.
All models that we explore underpredict the fraction of galaxies with few or no
companions in 3 and 6-Mpc/h cylinders. Roughly 7% of galaxies in the real
universe are significantly more isolated within a 6 Mpc/h cylinder than the
galaxies in any of the models we use. Simple, phenomenological models that map
galaxies to dark matter halos fail to reproduce high-order clustering
statistics in low-density environments.Comment: 17 pages, 10 figures. Accepted, Ap
Geomagnetic conditions in Ireland During the St. Patrick's Day 2015 Storm
<p>Poster at UK National Astronomy Meeting in Llandudno, Wales on July 5-9, 2015 (www.nam2015.org)</p>
<p>Abstract:</p>
<p>Two coronal mass ejections were launched in quick succession from the Sun on March 15, 2015. They impacted the Earth's magnetosphere two days later on St. Patrick's Day (March 17), resulting in a geomagnetic storm with a planetary K-Index of 8.</p>
<p>Magnetic variations were measured across a recently deployed magnetometer network in Ireland and geoelectric fields were measured at a site in Co. Leitrim (magnetic latitude 57.08°). A local K-index maximum of 7 was calculated at Birr, Co. Offaly (magnetic latitude 55.97), while the aurora</p>
<p>borealis accompanying the geomagnetic storm was visible as far south as Co. Waterford (magnetic latitude 55.13°).</p>
<p>The British Geological Survey thin-sheet surface electric field model was used together with our magnetometer measurements to calculate electric fields and geomagnetically induced currents (GICs) in the Irish power grid.</p>
<p>Although it was one of the most magnetically disturbed days in a decade, with dB/dt reaching ~50 nT/min, the peak GIC level estimated in the Irish power grid was ~10 Amps. Note, no adverse effects were reported in the Irish power grid demonstrating its resilience to geomagnetic storms of this magnitude.</p
Novel approaches to the development and assessment of an ovine model of polycystic ovary syndrome
Polycystic ovary syndrome (PCOS) is a common reproductive, endocrine and metabolic
disorder present in women of reproductive age. Despite the widespread prevalence and
heritability of PCOS, the heterogeneous and polygenic traits have made the successful
identification of candidate genes difficult. Animal models have been developed on the
premise that early exposure to sex steroids can programme epigenetic changes that
predispose the fetus to the adult features of PCOS. Past research has modelled ovarian
dysfunction, endocrine abnormalities and metabolic perturbances in rodent, non-human
primate and sheep PCOS models, through the enhanced neonatal or prenatal exposure to the
male sex hormone, testosterone.
The modelling of PCOS in a large domestic species such as the sheep is advantageous due to
similar biological reproductive function as the human. In this regard the sheep has been
extensively used to model PCOS by the treatment of pregnant ewes from early to midgestation
with androgens such as testosterone propionate (TP). These experiments have
demonstrated the fetal programming effects of androgens on offspring that go on to develop
PCOS-like characteristics in adulthood. One of the caveats of assessing steroid effects in this
way is the effect of the placenta in mediating the transfer of these hormones. TP is an
aromatisable androgen and thus some of its effects in the fetus may be attributable to
placental by-products such as estrogens.
This thesis describes the development and assessment of a novel model of prenatal
androgenisation. Two models were compared: the indirect maternal exposure to TP (the
current model) and the direct fetal injection of TP. In directly treating the fetus this allowed
control over the dose of TP administered and avoidance of secondary effects that androgens
may exert in the mother that could be transferred to the fetus. For the maternal model,
pregnant Scottish Greyface ewes were administered TP twice weekly from day (d)62-102 of
a 147 day gestation. For the fetal model, fetuses were injected twice while the ewe was
anaesthetised with graded doses of TP during the same period of treatment as the maternal
model.
The effects of prenatal androgenisation were assessed in the female fetus shortly after
treatment and also in young adult sheep. Fetal ovarian and adrenal steroidogenic gene expression was monitored and found to be altered in response to elevated levels of sex
steroids. At d90 the morphology of the developing ovary was not changed by prenatal
androgens. In the adult a detailed ovarian and endocrine assessment was undertaken, by
examination of ovarian morphology, hormone levels, ovulatory cycles, hypothalamic
pituitary ovarian function and follicle steroidogenesis, during the first breeding season. In
addition, the metabolic effects of prenatal androgens were monitored by measuring body fat,
insulin and glucose homeostasis and liver function. Neither maternal nor fetal prenatal
androgenisation during mid-gestation resulted in a perturbed hormonal milieu or polycystic
ovaries in young adults. These treatments did however programme a clear ovarian phenotype
demonstrated by the increased capacity of follicles to secrete androgens, independently of an
abnormal endocrine environment and disordered folliculogenesis. Furthermore, animals that
were exposed maternally to TP developed fatty liver and had increased insulin secretion in
response to glucose load. A major outcome of this study was the finding that the fetally
injected control animals were phenotypically different than the maternal control animals. In
fact, some of the reproductive and metabolic features of maternal TP exposure were found in
the fetal control group. This unexpected finding has raised the possibility that it is the fetal
exposure to stress, that is secondary to elevated maternal androgens, rather than androgens
per se that is responsible for at least some of the multitude of anomalies encountered in
PCOS
Inhibitor of Differentiation (Id) Genes Are Expressed in the Steroidogenic Cells of the Ovine Ovary and Are Differentially Regulated by Members of the Transforming Growth Factor-beta Family
Inhibitor of Differentiation (Id) proteins act during embryogenesis and development to repress gene transcription required for lineage commitment, whilst promoting cell growth. Growth factors belonging to the transforming growth factor beta (TGFβ) superfamily of signaling molecules, notably the bone morphogenetic proteins (BMPs) and activin, can regulate Id expression in these tissues. Id expression and function in adult physiology is less well determined and we hypothesized a role for Id proteins in the adult mammalian ovary. Immunohistochemistry for Id1, Id2, Id3 and Id4 in the sheep ovary revealed consistent expression in granulosa and thecal cells of ovarian follicles throughout development. In atretic follicles Id proteins were selectively down-regulated in thecal cells (P<0.0001). Additionally Id1 was universally up-regulated in the cumulus cells adjacent to the oocyte. Immunohistochemistry for phospho (p)-smad 1/5/8 signalling components (stimulated by BMPs) showed a punctate pattern of expression whereas p-smad 2/3 (stimulated by activin) was ubiquitously expressed in follicles. Neither pathway however displayed differential staining in line with Id1 cumulus specific expression, suggesting a more complex relationship between Id1 expression and TGFβ signaling in these cells. Nevertheless, in vitro, stimulation of ovine granulosa cells with BMP6 or activin A led to a respective increase and decrease in Id1 (P<0.0001), Id2 (P<0.0001), Id3 (P<0.0001) and Id4 (P<0.05) transcripts and Id1 gene expression was further manipulated by the oocyte-secreted factors BMP15 and GDF9 (P<0.001). These data confirm that TGFβ signaling can regulate Id gene expression in the sheep ovarian follicle and suggest a functional role for the Id family in the mammalian ovary
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