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Application of passive seismic to the detection of buried hollows
Pilot studies involving the use of passive seismic techniques in a range of geological settings and
applications, e.g., mapping bedrock, studies of soil erosion and Quaternary mapping have shown that it
is a versatile, non-invasive and economic technique. This paper presents the findings of three case studies
that trialled the use of passive seismic techniques for the detection and characterisation of buried hollows
in carbonate rocks, comprising: i) a buried hollow in the Cretaceous Chalk at Ashford Hill in the Kennet
Valley, a tributary of the River Thames, UK; ii) buried karst in the foundation excavations for wind turbines in Carboniferous Limestone at Brassington, Wirksworth, Derbyshire, UK, and iii) defining the extent of solution hollows that host terrestrial Miocene deposits, near Friden, Newhaven, Derbyshire, UK. Whilst case studies ii) and iii) are focused on areas of buried dolines, the geological context of the Ashford
Hill site is more complex; comprising a deformation hollow with an uplifted “pinnacle” of chalk bedrock at
the centre. The data were collected using a (Tromino), a three-component, broadband seismometer to measure background ambient noise (microtremors induced by wind, ocean waves, industrial machinery, road and rail traffic, etc.). The Tromino is small, portable with an operating range of 0.1 Hz to 1,024 Hz and interpreted using proprietary software (Grilla), which subjects the data to Fourier transformation and smoothing. Where possible, estimated shear wave velocities used in the
Grilla Software modelling, based on peaks identified on the H/V spectrum, have been calibrated using borehole data or parallel geophysical techniques. In each case, the karst features were defined by Nakamura’s
horizontal to vertical (H/V) spectral ratio technique, where microtremors are converted to show impedance
contrasts (velocity x density), or a pseudo layered seismic stratigraphy of the near surface along each
profile. An additional benefit of the use of this technique is its depth of penetration and potential for defining the
structural and lithological context of the hollows, thereby contributing to the process understanding associated with their formation. To this end the technique has helped define discontinuity (fault, joint or bedding) guidance of the hollows.S. Castellaro, Mrs J. Renwick, West Coast Energy Ltd (GDF Suez), Mr Roger Durrant (Raymond Brown Construction Ltd
Can a total knee arthroplasty be both rotationally unconstrained and anteroposteriorly stabilised? A pulsed fluoroscopic investigation
Objectives: Throughout the 20th Century, it has been postulated that the knee moves on the basis of a four-bar link mechanism composed of the cruciate ligaments, the femur and the tibia. As a consequence, the femur has been thought to roll back with flexion, and total knee arthroplasty (TKA) prostheses have been designed on this basis. Recent work, however, has proposed that at a position of between 0° and 120° the medial femoral condyle does not move anteroposteriorly whereas the lateral femoral condyle tends, but is not obliged, to roll back - a combination of movements which equates to tibial internal/femoral external rotation with flexion. The aim of this paper was to assess if the articular geometry of the GMK Sphere TKA could recreate the natural knee movements in situ/in vivo. Methods: The pattern of knee movement was studied in 15 patients (six male: nine female; one male with bilateral TKAs) with 16 GMK Sphere implants, at a mean age of 66 years (53 to 76) with a mean BMI of 30 kg/m2 (20 to 35). The motions of all 16 knees were observed using pulsed fluoroscopy during a number of weight-bearing and non-weight-bearing static and dynamic activities. Results: During maximally flexed kneeling and lunging activities, the mean tibial internal rotation was 8° (standard deviation (SD) 6). At a mean 112° flexion (SD 16) during lunging, the medial and lateral condyles were a mean of 2 mm (SD 3) and 8 mm (SD 4) posterior to a transverse line passing through the centre of the medial tibial concavity. With a mean flexion of 117° (SD 14) during kneeling, the medial and lateral condyles were a mean of 1 mm (SD 4) anterior and 6 mm (SD 4) posterior to the same line. During dynamic stair and pivoting activities, there was a mean anteroposterior translation of 0 mm to 2 mm of the medial femoral condyle. Backward lateral condylar translation occurred and was linearly related to tibial rotation. Conclusion: The GMK Sphere TKA in our study group shows movements similar in pattern, although reduced in magnitude, to those in recent reports relating to normal knees during several activities. Specifically, little or no translation of the medial femoral condyle was observed during flexion, but there was posterior roll-back of the lateral femoral condyle, equating to tibiofemoral rotation. We conclude that the GMK Sphere is anteroposteriorly stable medially and permits rotation about the medial compartment
Fragments of the earliest land plants
The earliest fossil evidence for land plants comes from microscopic dispersed spores. These microfossils are abundant and widely distributed in sediments, and the earliest generally accepted reports are from rocks of mid-Ordovician age (Llanvirn, 475 million years ago). Although distribution, morphology and ultrastructure of the spores indicate that they are derived from terrestrial plants, possibly early relatives of the bryophytes, this interpretation remains controversial as there is little in the way of direct evidence for the parent plants. An additional complicating factor is that there is a significant hiatus between the appearance of the first dispersed spores and fossils of relatively complete land plants (megafossils): spores predate the earliest megafossils (Late Silurian, 425 million year ago) by some 50 million years. Here we report the description of spore-containing plant fragments from Ordovician rocks of Oman. These fossils provide direct evidence for the nature of the spore-producing plants. They confirm that the earliest spores developed in large numbers within sporangia, providing strong evidence that they are the fossilized remains of bona fide land plants. Furthermore, analysis of spore wall ultrastructure supports liverwort affinities
The Regge Limit for Green Functions in Conformal Field Theory
We define a Regge limit for off-shell Green functions in quantum field
theory, and study it in the particular case of conformal field theories (CFT).
Our limit differs from that defined in arXiv:0801.3002, the latter being only a
particular corner of the Regge regime. By studying the limit for free CFTs, we
are able to reproduce the Low-Nussinov, BFKL approach to the pomeron at weak
coupling. The dominance of Feynman graphs where only two high momentum lines
are exchanged in the t-channel, follows simply from the free field analysis. We
can then define the BFKL kernel in terms of the two point function of a simple
light-like bilocal operator. We also include a brief discussion of the gravity
dual predictions for the Regge limit at strong coupling.Comment: 23 pages 2 figures, v2: Clarification of relation of the Regge limit
defined here and previous work in CFT. Clarification of causal orderings in
the limit. References adde
Does ligament balancing technique affect kinematics in rotating platform, PCL retaining knee arthroplasties?: A prospective randomized study
The goal of this prospective, randomized, blinded trial was to determine if ligament balancing techniques for rotating platform TKA affect postoperative knee kinematics. Sixteen patients with unilateral rotating platform TKA consented to participate in this institutional review board approved study. Eight patients were randomly selected to receive ligament balancing with an instrumented joint spreader device and eight patients received ligament balancing using fixed thickness spacer blocks. A single plane shape matching technique was used for kinematic analysis of static deep knee flexion and dynamic stair activities. There were no differences in knee kinematics between groups during static deep flexion activities. The spreader group demonstrated kinematics more similar to the normal knee during the ascending phase of the dynamic stair activity. Knee kinematics in static knee flexion were unaffected by ligament balancing technique, while knees balanced with the spreader demonstrated a medial pivot motion pattern during stair ascent. This medial pivot motion pattern may improve long-term results by more closely replicating normal knee kinematics
Incompressible Fluids of the de Sitter Horizon and Beyond
There are (at least) two surfaces of particular interest in eternal de Sitter
space. One is the timelike hypersurface constituting the lab wall of a static
patch observer and the other is the future boundary of global de Sitter space.
We study both linear and non-linear deformations of four-dimensional de Sitter
space which obey the Einstein equation. Our deformations leave the induced
conformal metric and trace of the extrinsic curvature unchanged for a fixed
hypersurface. This hypersurface is either timelike within the static patch or
spacelike in the future diamond. We require the deformations to be regular at
the future horizon of the static patch observer. For linearized perturbations
in the future diamond, this corresponds to imposing incoming flux solely from
the future horizon of a single static patch observer. When the slices are
arbitrarily close to the cosmological horizon, the finite deformations are
characterized by solutions to the incompressible Navier-Stokes equation for
both spacelike and timelike hypersurfaces. We then study, at the level of
linearized gravity, the change in the discrete dispersion relation as we push
the timelike hypersurface toward the worldline of the static patch. Finally, we
study the spectrum of linearized solutions as the spacelike slices are pushed
to future infinity and relate our calculations to analogous ones in the context
of massless topological black holes in AdS.Comment: 27 pages, 8 figure
Orbifold equivalence for finite density QCD and effective field theory
In the large N_c limit, some apparently different gauge theories turn out to
be equivalent due to large N_c orbifold equivalence. We use effective field
theory techniques to explore orbifold equivalence, focusing on the specific
case of a recently discovered relation between an SO(2N_c) gauge theory and
QCD. The equivalence to QCD has been argued to hold at finite baryon chemical
potential, \mu_B, so long as one deforms the SO(2N_c) theory by certain
"double-trace" terms. The deformed SO(2N_c) theory can be studied without a
sign problem in the chiral limit, in contrast to SU(N_c) QCD at finite \mu_B.
The purpose of the double-trace deformation in the SO(2N_c) theory is to
prevent baryon number symmetry from breaking spontaneously at finite density,
which is necessary for the equivalence to large N_c QCD to be valid. The
effective field theory analysis presented here clarifies the physical
significance of double-trace deformations, and strongly supports the proposed
equivalence between the deformed SO(2N_c) theory and large N_c QCD at finite
density.Comment: 39 pages, 5 figures, 2 tables. v2: Minor typo fixes and
clarification
Trajectories of self-rated health in people with diabetes: Associations with functioning in a prospective community sample
© 2013 Schmitz 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 credited.Background: Self-rated health (SRH) is a single-item measure that is one of the most widely used measures of general health in population health research. Relatively little is known about changes and the trajectories of SRH in people with chronic medical conditions. The aims of the present study were to identify and describe longitudinal trajectories of self-rated health (SRH) status in people with diabetes. Methods: A prospective community study was carried out between 2008 and 2011. SRH was assessed at baseline and yearly at follow-ups (n=1288). Analysis was carried out through trajectory modeling. The trajectory groups were subsequently compared at 4 years follow-up with respect to functioning. Results: Four distinct trajectories of SRH were identified: 1) 72.2% of the participants were assigned to a persistently good SRH trajectory; 2) 10.1% were assigned to a persistently poor SRH trajectory; 3) mean SRH scores changed from good to poor for one group (7.3%); while 4) mean SRH scores changed from poor to medium/good for another group (10.4%). Those with a persistently poor perception of health status were at higher risk for poor functioning at 4 years follow-up than those whose SRH scores decreased from good to poor. Conclusions: SRH is an important predictor for poor functioning in diabetes, but the trajectory of SRH seems to be even more important. Health professionals should pay attention to not only SRH per se, but also changes in SRH over time.This work was supported by Operating Grant MOP-84574 from the Canadian Institutes of Health Research (CIHR). GG was supported by a doctoral fellowship from the CIHR. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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