169 research outputs found
Geophysical characterization of derelict coalmine workings and mineshaft detection: a case study from Shrewsbury, United Kingdom
A study site of derelict coalmine workings near Shrewsbury, United Kingdom was the focus for multi‐phase, near‐surface geophysical investigations. Investigation objectives were: 1) site characterization for remaining relict infrastructure foundations, 2) locate an abandoned coalmine shaft, 3) determine if the shaft was open, filled or partially filled and 4) determine if the shaft was capped (and if possible characterize the capping material).
Phase one included a desktop study and 3D microgravity modelling of the relict coalmine shaft thought to be on site. In phase two, electrical and electromagnetic surveys to determine site resistivity and conductivity were acquired together with fluxgate gradiometry and an initial microgravity survey. Phase three targeted the phase two geophysical anomalies and acquired high‐resolution self potential and ground penetrating radar datasets. The phased‐survey approach minimised site activity and survey costs.
Geophysical results were compared and interpreted to characterize the site, the microgravity models were used to validate interpretations. Relict buildings, railway track remains with associated gravel and a partially filled coalmine shaft were located. Microgravity proved optimal to locate the mineshaft with radar profiles showing ‘side‐swipe’ effects from the mineshaft that did not directly underlie survey lines.
Geophysical interpretations were then verified with subsequent geotechnical intrusive investigations. Comparisons of historical map records with intrusive geotechnical site investigations show care must be taken using map data alone, as the latter mineshaft locations was found to be inaccurate
Accretion-ejection instability in magnetized disks: Feeding the corona with Alfven waves
We present a detailed calculation of the mechanism by which the
Accretion-Ejection Instability can extract accretion energy and angular
momentum from a magnetized disk, and redirect them to its corona. In a disk
threaded by a poloidal magnetic field of the order of equipartition with the
gas pressure, the instability is composed of a spiral wave (analogous to
galactic ones) and a Rossby vortex. The mechanism detailed here describes how
the vortex, twisting the footpoints of field lines threading the disk,
generates Alfven waves propagating to the corona. We find that this is a very
efficient mechanism, providing to the corona (where it could feed a jet or a
wind) a substantial fraction of the accretion energy.Comment: accepted by A&
Using automated imaging to interrogate gonadotrophin-releasing hormone receptor trafficking and function
Gonadotrophin-releasing hormone (GnRH) acts via seven transmembrane receptors on gonadotrophs to stimulate gonadotrophin synthesis and secretion, and thereby mediates central control of reproduction. Type I mammalian GnRHR are unique, in that they lack C-terminal tails. This is thought to underlie their resistance to rapid homologous desensitisation as well as their slow rate of internalisation and inability to provoke G-protein-independent (arrestin-mediated) signalling. More recently it has been discovered that the vast majority of human GnRHR are actually intracellular, in spite of the fact that they are activated at the cell surface by a membrane impermeant peptide hormone. This apparently reflects inefficient exit from the endoplasmic reticulum and again, the absence of the C-tail likely contributes to their intracellular localisation. This review is intended to cover some of these novel aspects of GnRHR biology, focusing on ways that we have used automated fluorescence microscopy (high content imaging) to explore GnRHR localisation and trafficking as well as spatial and temporal aspects of GnRH signalling via the Ca(2+)/calmodulin/calcineurin/NFAT and Raf/MEK/ERK pathways
Local models of stellar convection II: Rotation dependence of the mixing length relations
We study the mixing length concept in comparison to three-dimensional
numerical calculations of convection with rotation. In a limited range, the
velocity and temperature fluctuations are linearly proportional to the
superadiabaticity, as predicted by the mixing length concept and in accordance
with published results. The effects of rotation are investigated by varying the
Coriolis number, Co = 2 Omega tau, from zero to roughly ten, and by calculating
models at different latitudes. We find that \alpha decreases monotonically as a
function of the Coriolis number. This can be explained by the decreased spatial
scale of convection and the diminished efficiency of the convective energy
transport, the latter of which leads to a large increase of the
superadibaticity, \delta = \nabla - \nabla_ad as function of Co. Applying a
decreased mixing length parameter in a solar model yields very small
differences in comparison to the standard model within the convection zone. The
main difference is the reduction of the overshooting depth, and thus the depth
of the convection zone, when a non-local version of the mixing length concept
is used. Reduction of \alpha by a factor of roughly 2.5 is sufficient to
reconcile the difference between the model and helioseismic results. The
numerical results indicate reduction of \alpha by this order of magnitude.Comment: Final published version, 8 pages, 9 figure
A microquasar classification from a disk instability perspective
The spectacular variability of microquasars has led to a long string of
efforts in order to classify their observed behaviors in a few states. The
progress made in the understanding of the Quasi-Periodic Oscillations observed
in these objects now makes it possible to develop a new way to find order in
their behavior, based on the theorized physical processes associated with these
oscillations. This will also have the interest of reuniting microquasars in a
single classification based on the physical processes at work and therefore
independent of their specificities (mass, variation timescale, outburst
history, etc.). This classification is aimed to be a tool to further our
understanding of microquasars behavior and not to replace phenomenological
states. We start by considering three instabilities that can cause accretion in
the disk. We compare the conditions for their development, and the
Quasi-Periodic Oscillations they can be expected to produce, with the spectral
states in which these Quasi-Periodic Oscillations are observed and sometimes
coexist. From the three instabilities that we proposed to explain the three
states of GRS 1915+105 we actually found the theoretical existence of four
states. We compared those four states with observations and also how those four
states can be seen in a model-independent fashion. Those four state can be used
to find an order in microquasar observations, based on the properties of the
Quasi-Periodic Oscillations and the physics of the associated instabilities.Comment: accepted by A&
Local models of stellar convection: Reynolds stresses and turbulent heat transport
We study stellar convection using a local three-dimensional MHD model, with
which we investigate the influence of rotation and large-scale magnetic fields
on the turbulent momentum and heat transport. The former is studied by
computing the Reynolds stresses, the latter by calculating the correlation of
velocity and temperature fluctuations, both as functions of rotation and
latitude. We find that the horisontal correlation, Q_(theta phi), capable of
generating horisontal differential rotation, is mostly negative in the southern
hemisphere for Coriolis numbers exceeding unity, corresponding to equatorward
flux of angular momentum in accordance with solar observations. The radial
component Q_(r phi) is negative for slow and intermediate rotation indicating
inward transport of angular momentum, while for rapid rotation, the transport
occurs outwards. Parametrisation in terms of the mean-field Lambda-effect shows
qualitative agreement with the turbulence model of Kichatinov & R\"udiger
(1993) for the horisontal part H \propto Q_(theta phi)/cos(theta), whereas for
the vertical part, V \propto Q_(r phi)/sin(theta), agreement only for
intermediate rotation exists. The Lambda-coefficients become suppressed in the
limit of rapid rotation, this rotational quenching being stronger for the V
component than for H. We find that the stresses are enhanced by the presence of
the magnetic field for field strengths up to and above the equipartition value,
without significant quenching. Concerning the turbulent heat transport, our
calculations show that the transport in the radial direction is most efficient
at the equatorial regions, obtains a minimum at midlatitudes, and shows a
slight increase towards the poles. The latitudinal heat transport does not show
a systematic trend as function of latitude or rotation.Comment: 26 pages, 20 figures, final published version. For a version with
higher resolution figures, see http://cc.oulu.fi/~pkapyla/publ.htm
Dust in Brown Dwarfs IV. Dust formation and driven turbulence on mesoscopic scales
Dust formation in brown dwarf atmospheres is studied by utilising a model for
driven turbulence in the mesoscopic scale regime. We apply a pseudo-spectral
method where waves are created and superimposed within a limited wavenumber
interval. The turbulent kinetic energy distribution follows the Kolmogoroff
spectrum which is assumed to be the most likely value. Such superimposed,
stochastic waves may occur in a convectively active environment. They cause
nucleation fronts and nucleation events and thereby initiate the dust formation
process which continues until all condensible material is consumed. Small
disturbances are found to have a large impact on the dust forming system. An
initially dust-hostile region, which may originally be optically thin, becomes
optically thick in a patchy way showing considerable variations in the dust
properties during the formation process. The dust appears in lanes and curls as
a result of the interaction with waves, i.e. turbulence, which form larger and
larger structures with time. Aiming on a physical understanding of the
variability of brown dwarfs, related to structure formation in substellar
atmospheres, we work out first necessary criteria for small-scale closure
models to be applied in macroscopic simulations of dust forming astrophysical
systems.Comment: A&A accepted, 20 page
Accretion-ejection instability and QPO in black-hole binaries.II. Relativistic effects
The Accretion-Ejection Instability has been proposed to explain the low
frequency Quasi-Periodic Oscillation (QPO) observed in low-mass X-Ray Binaries,
in particular Black-Hole candidates. Its frequency, typically a fraction of the
Keplerian frequency at the disk inner radius, is exactly in the range indicated
by observations. The variations of the frequency with the disk inner radius
(extracted from spectral fits of the X-ray emission) might thus be a useful
test. In this paper we discuss how changes in the rotation curve, due to
relativistic effects when the disk approaches the central object, affect the
physics of the instability, and thus this frequency-inner radius relation. We
find that the relationship between the frequency of the mode and the Keplerian
frequency at the inner disk radius () departs from the one obtained in
a Keplerian disk, when approaches the last stable orbit. This might
agree with the recently published results, showing a discrepancy between the
behavior of the QPO in the micro quasar GRO J1655, compared to other sources
such as XTE J1550 and GRS 1915.
In a companion paper (Rodriguez et al., 2002, hereafter Paper I) we have
presented detailed observational results for GRO J1655 and GRS 1915. We show
how the opposite correlations found in these sources between the disk color
radius (assumed to be close to its inner radius) and the QPO frequency could
indeed be explained by our theoretical result.Comment: accepted by A&
Suppression of mutant Kirsten-RAS (KRASG12D)-driven pancreatic carcinogenesis by dual-specificity MAP kinase phosphatases 5 and 6
The cytoplasmic phosphatase DUSP6 and its nuclear counterpart DUSP5 are negative regulators of RAS/ERK signalling. Here we use deletion of either Dusp5 or Dusp6 to explore the roles of these phosphatases in a murine model of KRASG12D-driven pancreatic cancer. By 56-days, loss of either DUSP5 or DUSP6 causes a significant increase in KRASG12D-driven pancreatic hyperplasia. This is accompanied by increased pancreatic acinar to ductal metaplasia (ADM) and the development of pre-neoplastic pancreatic intraepithelial neoplasia (PanINs). In contrast, by 100-days, pancreatic hyperplasia is reversed with significant atrophy of pancreatic tissue and weight loss observed in animals lacking either DUSP5 or DUSP6. On further ageing, Dusp6−/− mice display accelerated development of metastatic pancreatic ductal adenocarcinoma (PDAC), while in Dusp5−/− animals, although PDAC development is increased this process is attenuated by atrophy of pancreatic acinar tissue and severe weight loss in some animals before cancer could progress. Our data suggest that despite a common target in the ERK MAP kinase, DUSP5 and DUSP6 play partially non-redundant roles in suppressing oncogenic KRASG12D signalling, thus retarding both tumour initiation and progression. Our data suggest that loss of either DUSP5 or DUSP6, as observed in certain human tumours, including the pancreas, could promote carcinogenesis
Magnetoconvection and dynamo coefficients III: alpha-effect and magnetic pumping in the rapid rotation regime
Aims. The alpha- and gamma-effects, which are responsible for the generation
and turbulent pumping of large scale magnetic fields, respectively, due to
passive advection by convection are determined in the rapid rotation regime
corresponding to the deep layers of the solar convection zone.
Methods. A 3D rectangular local model is used for solving the full set of MHD
equations in order to compute the electromotive force (emf), E = ,
generated by the interaction of imposed weak gradient-free magnetic fields and
turbulent convection with varying rotational influence and latitude. By
expanding the emf in terms of the mean magnetic field, E_i = a_ij , all
nine components of a_ij are computed. The diagonal elements of a_ij describe
the alpha-effect, whereas the off-diagonals represent magnetic pumping. The
latter is essentially the advection of magnetic fields by means other than the
underlying large-scale velocity field. Comparisons are made to analytical
expressions of the coefficients derived under the first-order smoothing
approximation (FOSA).
Results. In the rapid rotation regime the latitudinal dependence of the
alpha-components responsible for the generation of the azimuthal and radial
fields does not exhibit a peak at the poles, as is the case for slow rotation,
but at a latitude of about 30 degrees. The magnetic pumping is predominantly
radially down- and latitudinally equatorward as in earlier studies. The
numerical results compare surprisingly well with analytical expressions derived
under first-order smoothing, although the present calculations are expected to
lie near the limits of the validity range of FOSA.Comment: 14 pages, 12 figures, accepted for publication in Astronomy &
Astrophysic
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