989 research outputs found
Direct solar energy conversion for large scale terrestrial use
Various techniques to increase the open circuit voltage are being explored. It had been previously observed that cells made on CdS deposited from a single source gave a consistently higher V sub oc. Further tests have now shown that this effect may in fact relate to differences in source and substrate temperatures. The resulting differences in CdS structure and crystallinity are being documented. Deposits of mixed CdS and ZnS are being produced and will be initially made into cells using the conventional barriering technique. Analysis of I-V characteristics at temperatures between 25 and 110 C is being perfected to provide nondestructive analysis of the Cu2S. Changes due to vacuum heat treatments and exposure to oxygen are also being monitored by the same technique. Detailed spectral response measurements are being made
Modeling the effect of variation in sagittal curvature on the force required to produce a follower load in the lumbar spine
Peer reviewedPreprin
Phase transitions in diluted negative-weight percolation models
We investigate the geometric properties of loops on two-dimensional lattice
graphs, where edge weights are drawn from a distribution that allows for
positive and negative weights. We are interested in the appearance of spanning
loops of total negative weight. The resulting percolation problem is
fundamentally different from conventional percolation, as we have seen in a
previous study of this model for the undiluted case.
Here, we investigate how the percolation transition is affected by additional
dilution. We consider two types of dilution: either a certain fraction of edges
exhibit zero weight, or a fraction of edges is even absent. We study these
systems numerically using exact combinatorial optimization techniques based on
suitable transformations of the graphs and applying matching algorithms. We
perform a finite-size scaling analysis to obtain the phase diagram and
determine the critical properties of the phase boundary.
We find that the first type of dilution does not change the universality
class compared to the undiluted case whereas the second type of dilution leads
to a change of the universality class.Comment: 8 pages, 7 figure
No self-similar aggregates with sedimentation
Two-dimensional cluster-cluster aggregation is studied when clusters move
both diffusively and sediment with a size dependent velocity. Sedimentation
breaks the rotational symmetry and the ensuing clusters are not self-similar
fractals: the mean cluster width perpendicular to the field direction grows
faster than the height. The mean width exhibits power-law scaling with respect
to the cluster size, ~ s^{l_x}, l_x = 0.61 +- 0.01, but the mean height
does not. The clusters tend to become elongated in the sedimentation direction
and the ratio of the single particle sedimentation velocity to single particle
diffusivity controls the degree of orientation. These results are obtained
using a simulation method, which becomes the more efficient the larger the
moving clusters are.Comment: 10 pages, 10 figure
Computer-aided detection in musculoskeletal projection radiography: A systematic review
This is the author accepted manuscript. The final version is available from WB Saunders via the DOI in this record.Objectives
To investigated the accuracy of computer-aided detection (CAD) software in musculoskeletal projection radiography via a systematic review.
Key findings
Following selection screening, eligible studies were assessed for bias, and had their study characteristics extracted resulting in 22 studies being included. Of these 22 three studies had tested their CAD software in a clinical setting; the first study investigated vertebral fractures, reporting a sensitivity score of 69.3% with CAD, compared to 59.8% sensitivity without CAD. The second study tested dental caries diagnosis producing a sensitivity score of 68.8% and specificity of 94.1% with CAD, compared to sensitivity of 39.3% and specificity of 96.7% without CAD. The third indicated osteoporotic cases based on CAD, resulting in 100% sensitivity and 81.3% specificity.
Conclusion
The current evidence reported shows a lack of development into the clinical testing phase; however the research does show future promise in the variation of different CAD systems
Do investigator meetings improve recruitment rates in clinical trials? A retrospective before-and-after study of data from nine multi-centre clinical trials
© 2020 The Author(s). Background: Poor recruitment in clinical trials is well-documented. In large, multi-centre trials, communication between the coordinating centre and trial sites is essential. A commonly used communication tool is the hosting of an investigator/collaborator meeting, which offers an opportunity for sites to re-train and receive trial updates, learn from each other, share best practice and troubleshoot issues. Anecdotally, there is a perception that recruitment rates may increase after holding such a meeting. The aim of this before-and-after study was to examine any changes in recruitment after an investigator meeting. Methods: We conducted a retrospective study of nine trials at the Nottingham Clinical Trials Unit (NCTU) that were open to recruitment between 2014 and 2018. In the 8 weeks prior to the date of the investigator meeting, 82 sites (across nine trials) were open to recruitment; 60 of which attended the meeting, 22 who did not. Using meeting attendance data available in Trial Master Files (TMF) and recruitment data from randomisation datasets, we examined recruitment rates in the 8 weeks prior to and following the date of the investigator meeting. Results: For the 82 sites included, 284 participants were recruited in the 8 weeks prior to the meeting, with a further 300 participants recruited in the 8 weeks post meeting. This gives a mean change in weekly recruitment of 0.073 (- 0.129, 0.275) per site, demonstrating no statistically significant increase in recruitment after the investigator meeting. For the 60 attending sites, recruitment increased from 254 participants prior to the meeting to 271 post meeting, giving a 0.100 (- 0.160, 0.360) mean change in weekly recruitment per site, providing no evidence that recruitment rates increase following an investigator meeting. Conclusion: There is no statistical evidence to conclude that holding an investigator meeting increases recruitment in the 8 weeks following the meeting. Thus, if the meeting has been held in the belief that it will have a positive impact upon recruitment, trialists may wish to consider other evidence-based strategies known to increase recruitment rates. However, since there are a variety of reasons why an investigator meeting may be held, trialists should continue to consider this as a communication strategy with sites
Multidimensional supernova simulations with approximative neutrino transport. II. Convection and the advective-acoustic cycle in the supernova core
By 2D hydrodynamic simulations including a detailed equation of state and
neutrino transport, we investigate the interplay between different non-radial
hydrodynamic instabilities that play a role during the postbounce accretion
phase of collapsing stellar cores. The convective mode of instability, which is
driven by negative entropy gradients caused by neutrino heating or by time
variations of the shock strength, can be identified clearly by the development
of typical Rayleigh-Taylor mushrooms. However, in cases where the gas in the
postshock region is rapidly advected towards the gain radius, the growth of
such a buoyancy instability can be suppressed. In such a situation the shocked
flow nevertheless can develop non-radial asymmetry with an oscillatory growth
of the amplitude. This phenomenon has been termed ``standing accretion shock
instability'' (SASI). It is shown here that the SASI oscillations can trigger
convective instability and like the latter they lead to an increase of the
average shock radius and of the mass in the gain layer. Both hydrodynamic
instabilities in combination stretch the advection time of matter through the
neutrino-heating layer and thus enhance the neutrino energy deposition in
support of the neutrino-driven explosion mechanism. A rapidly contracting and
more compact nascent NS turns out to be favorable for explosions, because the
accretion luminosity and neutrino heating are larger and the growth rate of the
SASI is higher. Moreover, we show that the oscillation period of the SASI and a
variety of other features in our simulations agree with estimates for the
advective-acoustic cycle (AAC), in which perturbations are carried by the
accretion flow from the shock to the neutron star and pressure waves close an
amplifying global feedback loop. (abridged)Comment: 23 pages, 20 figures; revised version with extended Sect.5, accepted
by Astronomy & Astrophysics; high-resolution images can be obtained upon
reques
Particle Survival and Polydispersity in Aggregation
We study the probability, , of a cluster to remain intact in
one-dimensional cluster-cluster aggregation when the cluster diffusion
coefficient scales with size as . exhibits a
stretched exponential decay for and the power-laws for
, and for . A random walk picture
explains the discontinuous and non-monotonic behavior of the exponent. The
decay of determines the polydispersity exponent, , which
describes the size distribution for small clusters. Surprisingly,
is a constant for .Comment: submitted to Europhysics Letter
Ballistic deposition patterns beneath a growing KPZ interface
We consider a (1+1)-dimensional ballistic deposition process with
next-nearest neighbor interaction, which belongs to the KPZ universality class,
and introduce for this discrete model a variational formulation similar to that
for the randomly forced continuous Burgers equation. This allows to identify
the characteristic structures in the bulk of a growing aggregate ("clusters"
and "crevices") with minimizers and shocks in the Burgers turbulence, and to
introduce a new kind of equipped Airy process for ballistic growth. We dub it
the "hairy Airy process" and investigate its statistics numerically. We also
identify scaling laws that characterize the ballistic deposition patterns in
the bulk: the law of "thinning" of the forest of clusters with increasing
height, the law of transversal fluctuations of cluster boundaries, and the size
distribution of clusters. The corresponding critical exponents are determined
exactly based on the analogy with the Burgers turbulence and simple scaling
considerations.Comment: 10 pages, 5 figures. Minor edits: typo corrected, added explanation
of two acronyms. The text is essentially equivalent to version
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