Rapid field-cycling MRI using fast spin-echo

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Inference of epidemiological parameters from household stratified data

We consider a continuous-time Markov chain model of SIR disease dynamics with two levels of mixing. For this so-called stochastic households model, we provide two methods for inferring the model parameters---governing within-household transmission, recovery, and between-household transmission---from data of the day upon which each individual became infectious and the household in which each infection occurred, as would be available from first few hundred studies. Each method is a form of Bayesian Markov Chain Monte Carlo that allows us to calculate a joint posterior distribution for all parameters and hence the household reproduction number and the early growth rate of the epidemic. The first method performs exact Bayesian inference using a standard data-augmentation approach; the second performs approximate Bayesian inference based on a likelihood approximation derived from branching processes. These methods are compared for computational efficiency and posteriors from each are compared. The branching process is shown to be an excellent approximation and remains computationally efficient as the amount of data is increased

Recovery of Punitive Damages in Ohio Wrongful Death Actions: A Preferred Approach

Punitive damages in tort law, awarded to the plaintiff in addition to full compensation for injuries, are said to punish the defendant, to restrain him from committing the same act again, and to deter others from following his example. Nevertheless, “[s]omething more than the mere commission of a tort is always required for punitive damages. There must be circumstances of aggravation or outrage … or such a conscious and deliberate disregard of the interests of others that [the defendant’s] conduct may be called willful or wanton.” An anomalous area exists in the awarding of punitive damages. Under the general rule, punitive damages cannot be awarded in a wrongful death action unless the governing provision expressly or by clear implication confers the right to such damages. The reason given for this rule is that punitive damages are mere incidents to the cause of action, a windfall to the decedent’s representative who suffered no personal injury. American courts have universally accepted the rule that a civil action for wrongful death was not recognized at common law and that no such cause of action may be maintained except under statute. Furthermore, the statutes creating such a cause of action have been construed as not authorizing the imposition of exemplary damages. As a result of this construction, it may be cheaper for the defendant to kill, rather than injure, the victim. A defendant who willfully or wantonly injures a victim may be forced to pay punitive damages in addition to compensating the victim for any injury incurred; whereas, a defendant who kills a victim while engaged in the same willful or wanton act will not be required to pay punitive damages. This anomaly will be examined by focusing specifically upon Ohio law. The historical setting of wrongful death actions must first be analyzed, however, because the present status of punitive damages in wrongful death actions can be properly understood only in light of past developments. An explanation of the Ohio approach to this area will follow. Additionally, current trends in this area will be examined in order to compare and contrast the Ohio position and to develop grounds for liberalization and reform. Finally, a preferred approach to the area will be offered: an approach that appears more logical considering the purposes behind an award of punitive damages

A continuum model for the dynamics of the phase transition from slow-wave sleep to REM sleep

Previous studies have shown that activated cortical states (awake and rapid eye-movement (REM) sleep), are associated with increased cholinergic input into the cerebral cortex. However, the mechanisms that underlie the detailed dynamics of the cortical transition from slow-wave to REM sleep have not been quantitatively modeled. How does the sequence of abrupt changes in the cortical dynamics (as detected in the electrocorticogram) result from the more gradual change in subcortical cholinergic input? We compare the output from a continuum model of cortical neuronal dynamics with experimentally-derived rat electrocorticogram data. The output from the computer model was consistent with experimental observations. In slow-wave sleep, 0.5–2-Hz oscillations arise from the cortex jumping between “up” and “down” states on the stationary-state manifold. As cholinergic input increases, the upper state undergoes a bifurcation to an 8-Hz oscillation. The coexistence of both oscillations is similar to that found in the intermediate stage of sleep of the rat. Further cholinergic input moves the trajectory to a point where the lower part of the manifold in not available, and thus the slow oscillation abruptly ceases (REM sleep). The model provides a natural basis to explain neuromodulator-induced changes in cortical activity, and indicates that a cortical phase change, rather than a brainstem “flip-flop”, may describe the transition from slow-wave sleep to REM

Simple algorithm for the correction of MRI image artefacts due to random phase fluctuations

Grant support: This work was supported by EPSRC [grant numbers EP/E036775/1, EP/K020293/1] and received funding from the European Union's Horizon 2020 research and innovation programme [grant agreement No 668119, project “IDentIFY”]Peer reviewedPublisher PD

What can a mean-field model tell us about the dynamics of the cortex?

In this chapter we examine the dynamical behavior of a spatially homogeneous two-dimensional model of the cortex that incorporates membrane potential, synaptic flux rates and long- and short-range synaptic input, in two spatial dimensions, using parameter sets broadly realistic of humans and rats. When synaptic dynamics are included, the steady states may not be stable. The bifurcation structure for the spatially symmetric case is explored, identifying the positions of saddle–node and sub- and supercritical Hopf instabilities. We go beyond consideration of small-amplitude perturbations to look at nonlinear dynamics. Spatially-symmetric (breathing mode) limit cycles are described, as well as the response to spatially-localized impulses. When close to Hopf and saddle–node bifurcations, such impulses can cause traveling waves with similarities to the slow oscillation of slow-wave sleep. Spiral waves can also be induced. We compare model dynamics with the known behavior of the cortex during natural and anesthetic-induced sleep, commenting on the physiological significance of the limit cycles and impulse responses

Rapid Fast Field-Cycling Imaging using the Keyhole Technique

Peer reviewedPublisher PD

Rapid Fast Field-Cycling MRI using Keyhole Imaging

Abstract published in the Proceedings of the 23rd ISMRM Annual MeetingPeer reviewedPublisher PD