3,786 research outputs found
Mobility of Power-law and Carreau Fluids through Fibrous Media
The flow of generalized Newtonian fluids with a rate-dependent viscosity
through fibrous media is studied with a focus on developing relationships for
evaluating the effective fluid mobility. Three different methods have been used
here: i) a numerical solution of the Cauchy momentum equation with the Carreau
or power-law constitutive equations for pressure-driven flow in a fiber bed
consisting of a periodic array of cylindrical fibers, ii) an analytical
solution for a unit cell model representing the flow characteristics of a
periodic fibrous medium, and iii) a scaling analysis of characteristic bulk
parameters such as the effective shear rate, the effective viscosity,
geometrical parameters of the system, and the fluid rheology. Our scaling
analysis yields simple expressions for evaluating the transverse mobility
functions for each model, which can be used for a wide range of medium porosity
and fluid rheological parameters. While the dimensionless mobility is, in
general, a function of the Carreau number and the medium porosity, our results
show that for porosities less than , the dimensionless
mobility becomes independent of the Carreau number and the mobility function
exhibits power-law characteristics as a result of high shear rates at the pore
scale. We derive a suitable criterion for determining the flow regime and the
transition from a constant viscosity Newtonian response to a power-law regime
in terms of a new Carreau number rescaled with a dimensionless function which
incorporates the medium porosity and the arrangement of fibers
Markers of automaticity in sleep-associated consolidation of novel words
Two experiments investigated effects of sleep on consolidation and integration of novel form-meaning mappings using size congruity and semantic distance paradigms. Both paradigms have been used in previous studies to measure automatic access to word meanings. When participants compare semantic or physical font size of written word-pairs (e.g. BEEāCOW), judgments are typically faster if relative sizes are congruent across both dimensions. Semantic distance effects are also found for wellestablished words, with semantic size judgements faster for pairs that differ substantially on this dimension. English-speaking participants learned novel form-meaning mappings with Mandarin (Experiment 1) or Malay (Experiment 2) words and were tested following overnight sleep or a similar duration awake. Judgements on English words controlled for circadian effects. The sleep group demonstrated selective stronger size congruity and semantic distance effects for novel word-pairs. This benefit occurred in Experiment 1 for semantic size comparisons of novel words, and in Experiment 2 on comparisons where novel pairs had large distances and font differences (for congruity effects) or in congruent trials (for semantic distance effects). Conversely, these effects were equivalent across sleep and wake for English words. Experiment 2 included polysomnography data and revealed that changes in the strength of semantic distance and congruity effects were positively correlated with slow-wave sleep and sleep spindles respectively. These findings support systems consolidation accounts of declarative learning and suggest that sleep plays an active role in integrating new words with existing knowledge, resulting in increased automatic access of the acquired knowledge
Estimating Quantile Families of Loss Distributions for Non-Life Insurance Modelling via L-moments
This paper discusses different classes of loss models in non-life insurance
settings. It then overviews the class Tukey transform loss models that have not
yet been widely considered in non-life insurance modelling, but offer
opportunities to produce flexible skewness and kurtosis features often required
in loss modelling. In addition, these loss models admit explicit quantile
specifications which make them directly relevant for quantile based risk
measure calculations. We detail various parameterizations and sub-families of
the Tukey transform based models, such as the g-and-h, g-and-k and g-and-j
models, including their properties of relevance to loss modelling.
One of the challenges with such models is to perform robust estimation for
the loss model parameters that will be amenable to practitioners when fitting
such models. In this paper we develop a novel, efficient and robust estimation
procedure for estimation of model parameters in this family Tukey transform
models, based on L-moments. It is shown to be more robust and efficient than
current state of the art methods of estimation for such families of loss models
and is simple to implement for practical purposes.Comment: 42 page
Bayesian sequential experimental design for binary response data with application to electromyographic experiments
We develop a sequential Monte Carlo approach for Bayesian analysis of the experimental design for binary response data. Our work is motivated by surface electromyographic (SEMG) experiments, which can be used to provide information about the functionality of subjects' motor units. These experiments involve a series of stimuli being applied to a motor unit, with whether or not the motor unit res for each stimulus being recorded. The aim is to learn about how the probability of ring depends on the applied stimulus (the so-called stimulus response curve); One such excitability parameter is an estimate of the stimulus level for which the motor unit has a 50% chance of ring. Within such an experiment we are able to choose the next stimulus level based on the past observations. We show how sequential Monte Carlo can be used to analyse such data in an online manner. We then use the current estimate of the posterior distribution in order to choose the next stimulus level. The aim is to select a stimulus level that mimimises the expected loss. We will apply this loss function to the estimates of target quantiles from the stimulus-response curve. Through simulation we show that this approach is more ecient than existing sequential design methods for choosing the stimulus values. If applied in practice, it could more than halve the length of SEMG experiments
Biallelic and Genome Wide Association Mapping of Germanium Tolerant Loci in Rice (Oryza sativa L.)
Funding: This project was partially funded by a Biotechnology and Biological Sciences Research Council (BBSRC) grant (BB/J003336/1) awarded to AHP. The work was also supported by a self-funded studentship (PT). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD
Visco-Elasto-Capillary Thinning and Break-Up of Complex Fluids
Submitted to Annual Rheology Reviews, 2005.The progressive break-up of an initially stable fluid column or thread into a
number of smaller droplets is an important dynamical process that impacts many
commercial operations from spraying and atomization of fertilizers and pesticides, to
paint application, roll-coating of adhesives and food processing operations such as
container- and bottle-filling. The progressive thinning of a fluid filament is driven by
capillarity and resisted by inertia, viscosity and additional stresses resulting from the
extensional deformation of the fluid microstructure within the thread. In many
processes of interest the fluid undergoing break-up is non-Newtonian and may contain
dissolved polymer, suspended particles, surfactants or other microstructural
constituents. In such cases the transient extensional viscosity of the fluid plays an
important role in controlling the dynamics of break-up. The intimate connection
between the degree of strain-hardening that develops during free extensional flow and
the dynamical evolution in the profile of a thin fluid thread is also manifested in
heuristic concepts such as Ć¢spinnabilityā, Ć¢tackinessā and Ć¢stringinessā. In this review
we survey recent experimental and theoretical developments in the field of capillarydriven
thinning and break-up with a special focus on how quantitative measurements
of the thinning and rupture processes can be used to quantify the material properties of
the fluid. As a result of the absence of external forcing the dynamics of the necking
process are often self-similar and observations of this Ć¢self-thinningā can be used to
extract qualitative, and even quantitative, measures of the transient extensional
viscosity of a complex fluid.NASA, NSF, Schlumberger Foundatio
Dimensionless Groups For Understanding Free Surface Flows of Complex Fluids
Submitted to Bulletin of the Society of Rheology, May 2005No abstrac
Health workforce governance and professions: a re-analysis of New Zealandās primary care workforce policy actors
Background: This article contributes to the health workforce planning literature by exploring the dynamics of health professions in New Zealandās Primary Care sector and deriving broad lessons for an international audience. Professions tend influence health policy and governance decisions and practices to retain their place, status and influence. Therefore, understanding their power dynamics and the positions that they have on workforce policies and issues assists workforce governance or health system reform plans. Methods: Using the infrequently reported health workforce policy tool, actor analysis, a reanalysis of previously collected data is undertaken using an actor-based framework for the study of professionalism. Two models were developed, (1) the frameworkās original four-actor model and (2) a five-actor model for the comparison of the Medical and Nurse professions. Existing workforce actor data were reclassified, formatted, and entered into actor analysis software to reveal the professionsā relative power, inter-relationships and strategic workforce issue positions. Results: In the four-actor model, the Organised user actor is found to be most influential, while the others are found to be dependent. In the five-actor model, the Medical and Nurse professions are individually more influential than their combined position in the four-actor model. Practicing professionals and Organised user actors have strong converging inter-relationships over workforce issues in both models, though in the five-actor model, the Nurse profession has weaker coherency than the Medical profession. The Medical and Nurse professions are found to be in opposition over the workforce issues labelled divisive. Conclusions: These results reflect the professionsā potential to influence New Zealandās Primary Care sector, indicating their power and influence over a range of policy and reform measures. As such, the four lessons that are derived from the case indicate to policy makers that they should be aware of situational contexts and actor power, take care when encountering divisive issues and try to achieve broad-based support for proposed policies
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