23,973 research outputs found
Micro-Engineered Devices for Motion Energy Harvesting
Published versio
Overview of the Tevatron Collider Complex: Goals, Operations and Performance
For more than two decades the Tevatron proton-antiproton collider was the
centerpiece of the world's high energy physics program. The collider was
arguably one of the most complex research instruments ever to reach the
operation stage and is widely recognized for numerous physics discoveries and
for many technological breakthroughs. In this article we outline the historical
background that led to the construction of the Tevatron Collider, the strategy
applied to evolution of performance goals over the Tevatron's operational
history, and briefly describe operations of each accelerator in the chain and
achieved performance.Comment: Includes modifications suggested by reviewer
Glass transitions and shear thickening suspension rheology
We introduce a class of simple models for shear thickening and/ or `jamming'
in colloidal suspensions. These are based on schematic mode coupling theory
(MCT) of the glass transition, having a memory term that depends on a density
variable, and on both the shear stress and the shear rate. (Tensorial aspects
of the rheology, such as normal stresses, are ignored for simplicity.) We
calculate steady-state flow curves and correlation functions. Depending on
model parameters, we find a range of rheological behaviours, including
`S-shaped' flow curves, indicating discontinuous shear thickening, and
stress-induced transitions from a fluid to a nonergodic (jammed) state, showing
zero flow rate in an interval of applied stress. The shear thickening and
jamming scenarios that we explore appear broadly consistent with experiments on
dense colloids close to the glass transition, despite the fact that we ignore
hydrodynamic interactions. In particular, the jamming transition we propose is
conceptually quite different from various hydrodynamic mechanisms of shear
thickening in the literature, although the latter might remain pertinent at
lower colloid densities. Our jammed state is a stress-induced glass, but its
nonergodicity transitions have an analytical structure distinct from that of
the conventional MCT glass transition.Comment: 33 pages; 19 figure
The relevance of information and trading costs in explaining momentum profits: evidence from optioned and non-optioned stocks
Considerable evidence from many countries suggests momentum strategies generate profits. These have been difficult to rationalise and evidence on the sources of such profitability is inconclusive. We utilise a sample of optioned stocks, characterised by high liquidity, high market capitalisation and fewer short sales constraints and compare results with control samples of non optioned stocks chosen on the basis of market value, turnover and bid-ask spread. The sample characteristics, and the fact that derivatives improve the impounding of information into prices, enable us to draw conclusions about the causes of momentum profits. While we find that short sales constraints are not the major driver of profitability and that most momentum profits disappear using two transactions costs measures of the bid-ask spread, one not previously used, the persistence of some momentum profits indicates that the market underreacts even to the most publicly available information
Applicability of selected wheat remote sensing technology to corn and soybeans
There are no author-identified significant results in this report
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The multisensory attentional consequences of tool use : a functional magnetic resonance imaging study
Background: Tool use in humans requires that multisensory information is integrated across different locations, from objects
seen to be distant from the hand, but felt indirectly at the hand via the tool. We tested the hypothesis that using a simple tool
to perceive vibrotactile stimuli results in the enhanced processing of visual stimuli presented at the distal, functional part of the
tool. Such a finding would be consistent with a shift of spatial attention to the location where the tool is used.
Methodology/Principal Findings: We tested this hypothesis by scanning healthy human participants’ brains using
functional magnetic resonance imaging, while they used a simple tool to discriminate between target vibrations,
accompanied by congruent or incongruent visual distractors, on the same or opposite side to the tool. The attentional
hypothesis was supported: BOLD response in occipital cortex, particularly in the right hemisphere lingual gyrus, varied
significantly as a function of tool position, increasing contralaterally, and decreasing ipsilaterally to the tool. Furthermore,
these modulations occurred despite the fact that participants were repeatedly instructed to ignore the visual stimuli, to
respond only to the vibrotactile stimuli, and to maintain visual fixation centrally. In addition, the magnitude of multisensory
(visual-vibrotactile) interactions in participants’ behavioural responses significantly predicted the BOLD response in occipital
cortical areas that were also modulated as a function of both visual stimulus position and tool position.
Conclusions/Significance: These results show that using a simple tool to locate and to perceive vibrotactile stimuli is
accompanied by a shift of spatial attention to the location where the functional part of the tool is used, resulting in
enhanced processing of visual stimuli at that location, and decreased processing at other locations. This was most clearly
observed in the right hemisphere lingual gyrus. Such modulations of visual processing may reflect the functional
importance of visuospatial information during human tool use
Quantifying Spatiotemporal Chaos in Rayleigh-B\'enard Convection
Using large-scale parallel numerical simulations we explore spatiotemporal
chaos in Rayleigh-B\'enard convection in a cylindrical domain with
experimentally relevant boundary conditions. We use the variation of the
spectrum of Lyapunov exponents and the leading order Lyapunov vector with
system parameters to quantify states of high-dimensional chaos in fluid
convection. We explore the relationship between the time dynamics of the
spectrum of Lyapunov exponents and the pattern dynamics. For chaotic dynamics
we find that all of the Lyapunov exponents are positively correlated with the
leading order Lyapunov exponent and we quantify the details of their response
to the dynamics of defects. The leading order Lyapunov vector is used to
identify topological features of the fluid patterns that contribute
significantly to the chaotic dynamics. Our results show a transition from
boundary dominated dynamics to bulk dominated dynamics as the system size is
increased. The spectrum of Lyapunov exponents is used to compute the variation
of the fractal dimension with system parameters to quantify how the underlying
high-dimensional strange attractor accommodates a range of different chaotic
dynamics
Slow dynamics in a turbulent von K\'arm\'an swirling flow
We present an experimental study of a turbulent von K\'arm\'an flow produced
in a cylindrical container using two propellers. The mean flow is stationary up
to , where a bifurcation takes place. The new regime breaks some
symmetries of the problem, and is time-dependent. The axisymmetry is broken by
the presence of equatorial vortices with a precession movement, being the
velocity of the vortices proportional to the Reynolds number. The reflection
symmetry through the equatorial plane is broken, and the shear layer of the
mean flow appears displaced from the equator. These two facts appear
simultaneously. In the exact counterrotating case, a bistable regime appears
between both mirrored solutions and spontaneous reversals of the azimuthal
velocity are registered. This evolution can be explained using a three-well
potential model with additive noise. A regime of forced periodic response is
observed when a very weak input signal is applied.Comment: Improved model, additional results and figures, accepted in PR
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Capacity of English NHS hospitals to monitor quality in infection prevention and control using a new European framework: a multilevel qualitative analysis
Objective:(1) To assess the extent to which current English national regulations/policies/guidelines and local hospital practices align with indicators suggested by a European review of effective strategies for infection prevention and control (IPC); (2) to examine the capacity of local hospitals to report on the indicators and current use of data to inform IPC management and practice.
Design
A national and local-level analysis of the 27 indicators was conducted. At the national level, documentary review of regulations/policies/guidelines was conducted. At the local level data collection comprised: (a) review of documentary sources from 14 hospitals, to determine the capacity to report performance against these indicators; (b) qualitative interviews with 3 senior managers from 5 hospitals and direct observation of hospital wards to find out if these indicators are used to improve IPC management and practice.
Setting
2 acute English National Health Service (NHS) trusts and 1 NHS foundation trust (14 hospitals).
Participants
3 senior managers from 5 hospitals for qualitative interviews.
Primary and secondary outcome measures
As primary outcome measures, a ‘Red-Amber-Green’ (RAG) rating was developed reflecting how well the indicators were included in national documents or their availability at the local organisational level. The current use of the indicators to inform IPC management and practice was also assessed. The main secondary outcome measure is any inconsistency between national and local RAG rating results.
Results
National regulations/policies/guidelines largely cover the suggested European indicators. The ability of individual hospitals to report some of the indicators at ward level varies across staff groups, which may mask required improvements. A reactive use of staffing-related indicators was observed rather than the suggested prospective strategic approach for IPC management.
Conclusions
For effective patient safety and infection prevention in English hospitals, routine and proactive approaches need to be developed. Our approach to evaluation can be extended to other country settings
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