High-order, Dispersionless "Fast-Hybrid" Wave Equation Solver. Part I: O(1)\mathcal{O}(1) Sampling Cost via Incident-Field Windowing and Recentering

This paper proposes a frequency/time hybrid integral-equation method for the time dependent wave equation in two and three-dimensional spatial domains. Relying on Fourier Transformation in time, the method utilizes a fixed (time-independent) number of frequency-domain integral-equation solutions to evaluate, with superalgebraically-small errors, time domain solutions for arbitrarily long times. The approach relies on two main elements, namely, 1) A smooth time-windowing methodology that enables accurate band-limited representations for arbitrarily-long time signals, and 2) A novel Fourier transform approach which, in a time-parallel manner and without causing spurious periodicity effects, delivers numerically dispersionless spectrally-accurate solutions. A similar hybrid technique can be obtained on the basis of Laplace transforms instead of Fourier transforms, but we do not consider the Laplace-based method in the present contribution. The algorithm can handle dispersive media, it can tackle complex physical structures, it enables parallelization in time in a straightforward manner, and it allows for time leaping---that is, solution sampling at any given time $T$ at $\mathcal{O}(1)$-bounded sampling cost, for arbitrarily large values of $T$, and without requirement of evaluation of the solution at intermediate times. The proposed frequency-time hybridization strategy, which generalizes to any linear partial differential equation in the time domain for which frequency-domain solutions can be obtained (including e.g. the time-domain Maxwell equations), and which is applicable in a wide range of scientific and engineering contexts, provides significant advantages over other available alternatives such as volumetric discretization, time-domain integral equations, and convolution-quadrature approaches.Comment: 33 pages, 8 figures, revised and extended manuscript (and now including direct comparisons to existing CQ and TDIE solver implementations) (Part I of II

Windowed Green Function method for layered-media scattering

This paper introduces a new Windowed Green Function (WGF) method for the numerical integral-equation solution of problems of electromagnetic scattering by obstacles in presence of dielectric or conducting half-planes. The WGF method, which is based on use of smooth windowing functions and integral kernels that can be expressed directly in terms of the free-space Green function, does not require evaluation of expensive Sommerfeld integrals. The proposed approach is fast, accurate, flexible and easy to implement. In particular, straightforward modifications of existing (accelerated or unaccelerated) solvers suffice to incorporate the WGF capability. The mathematical basis of the method is simple: the method relies on a certain integral equation posed on the union of the boundary of the obstacle and a small flat section of the interface between the penetrable media. Numerical experiments demonstrate that both the near- and far-field errors resulting from the proposed approach decrease faster than any negative power of the window size. In the examples considered in this paper the proposed method is up to thousands of times faster, for a given accuracy, than a corresponding method based on the layer-Green-function.Comment: 17 page

Temperature post out-of-hospital cardiac arrest: the TOPCAT study

INTRODUCTION Out-of-hospital cardiac arrest (OHCA) is a significant cause of death and severe neurological disability in Scotland. Optimal pre-hospital resuscitation is required for the patient to achieve return of spontaneous circulation (ROSC). The only post-ROSC therapy shown to increase survival is mild therapeutic hypothermia (MTH), but its mechanism of action and optimal application are still unknown. The quality of pre-hospital resuscitation in Scotland is unmeasured. The relationship between body temperature post-OHCA, systemic inflammation, markers of brain injury and outcome are still poorly defined. This study examines two aspects of OHCA; firstly, the clinical practice of resuscitation in the pre¬ hospital and Emergency Department (ED) setting and, secondly, the post-ROSC physiological changes of body temperature, systemic inflammation and serum markers of brain injury.METHODS Prospective observational study of all OHCA patients admitted to a single centre for a 14- month period (1/08/2008 to 1/02/2010). Oesophageal temperature was measured, blood samples assayed for markers of systemic inflammation (TNF-a, IL-ip, 1L-6, IL-8, IL-10, 1L12, elastase, cell surface markers of neutrophil activation) and markers of brain injury (neuron-specific enolase [NSE], SI00b, glial fibrillary acidic protein [GFAP]) in the ED and Intensive Care Unit (ICU). Selected patients had pre-hospital temperature monitoring and blood sampling. Routine physiological variables were recorded. Patients who survived to ICU had repeat blood samples taken at 24-,48-,72- and 120-hours post-ROSC. Patients were followed up for 6-months. We conducted qualitative analysis of the effect of having a doctor on-scene at an OHCA and performed a Scottish national survey on the ED management of post-OHCA patientsRESULTS 236 OHCA patients were included in the study. 161 (68%) were pronounced dead at the scene or in the ED. 75 (32%) were admitted to ICU for cooling; 49 (21%) died in ICU and 27 (11%) survived to hospital discharge. We have characterised the natural progression of core body temperature post-OHCA. Patients who achieved ROSC and had oesophageal temperature measured pre-hospital all had temperatures below normal. Quality of pre¬ hospital resuscitation performed by ambulance crews was observed to be highly variable. Standard ED care of post-OHCA patients varied across Scotland. All patients arriving in the ED post-OHCA had a relatively low temperature (34.3°C, 95% CI 34.1-34.5). Patients surviving to hospital discharge were warmer on admission to ICU than patients who died in hospital (35.6°C vs. 34.4°C, p<0.01). Patients surviving to hospital discharge also took longer to reach target therapeutic hypothermia level than non-survivors (222 vs. 313 min, p<0.05). Cell surface markers of neutrophil activation, IL-6, IL-8, IL-10 and elastase were all significantly raised in the early post-ROSC period. The degree of cytokinaemia at 24- hours was related to survival outcome. In the context of MTH, SI00b at 24-hours was superior to NSE and GFAP at predicting in-hospital death following OHCA, with an AUCROC of 0.90 (95% CI 0.82-0.98).CONCLUSIONS The quality of pre-hospital and in-hospital resuscitation in Scotland is variable. Both prehospital and ED management of OHCA patients varied on a local and national scale.Following OHCA all patients have oesophageal temperatures below normal in the pre¬ hospital phase and on arrival in the ED. Patients who achieve ROSC following OHCA and survive to hospital discharge are warmer on arrival in ICU and take longer to reach target MTH temperatures compared to patients who die in hospital.A systemic inflammatory response occurs earlier in the post-ROSC phase than previously anticipated. SI00b is a more reliable predictor of outcome following OHCA than NSE or GFAP. The mechanisms of action underlying changes in oesophageal temperature and survival from OHCA remain unclear. This study adds to the information around oesophageal temperature post-OHCA and MTH further studies are warranted to clarify the mechanism of action of MTH post-OHCA and the role of inflammatory response in determining survival

A novel method of non-clinical dispatch is associated with a higher rate of critical Helicopter Emergency Medical Service intervention

Background - Helicopter Emergency Medical Services (HEMS) are a scarce resource that can provide advanced emergency medical care to unwell or injured patients. Accurate tasking of HEMS is required to incidents where advanced pre-hospital clinical care is needed. We sought to evaluate any association between non-clinically trained dispatchers, following a bespoke algorithm, compared with HEMS paramedic dispatchers with respect to incidents requiring a critical HEMS intervention. Methods - Retrospective analysis of prospectively collected data from two 12-month periods was performed (Period one: 1st April 2014 – 1st April 2015; Period two: 1st April 2016 – 1st April 2017). Period 1 was a Paramedic-led dispatch process. Period 2 was a non-clinical HEMS dispatcher assisted by a bespoke algorithm. Kent, Surrey & Sussex HEMS (KSS HEMS) is tasked to approximately 2500 cases annually and operates 24/7 across south-east England. The primary outcome measure was incidence of a HEMS intervention.Results - A total of 4703 incidents were included; 2510 in period one and 2184 in period two. Variation in tasking was reduced by introducing non-clinical dispatchers. There was no difference in median time from 999 call to HEMS activation between period one and two (period one; median 7 min (IQR 4–17) vs period two; median 7 min (IQR 4–18). Non-clinical dispatch improved accuracy of HEMS tasking to a mission where a critical care intervention was required (OR 1.25, 95% CI 1.04–1.51, p = 0.02).Conclusion - The introduction of non-clinical, HEMS-specific dispatch, aided by a bespoke algorithm improved accuracy of HEMS tasking. Further research is warranted to explore where this model could be effective in other HEMS services.Peer reviewedFinal Published versio

Space Telescope Sensitivity and Controls for Exoplanet Imaging

Herein we address design considerations and outline requirements for space telescopes with capabilities for high contrast imaging of exoplanets. The approach taken is to identify the span of potentially detectable Earth-sized terrestrial planets in the habitable zone of the nearest stars within 30 parsecs and estimate their inner working angles, flux ratios, SNR, sensitivities, wavefront error requirements and sensing and control times parametrically versus aperture size. We consider 1, 2, 4, 8 and 16-meter diameter telescope apertures. The achievable science, range of telescope architectures, and the coronagraphic approach are all active areas of research and are all subject to change in a rapidly evolving field. Thus, presented is a snapshot of our current understanding with the goal of limiting the choices to those that appear currently technically feasible. We describe the top-level metrics of inner working angle, contrast and photometric throughput and explore how they are related to the range of target stars. A critical point is that for each telescope architecture and coronagraphic choice the telescope stability requirements have differing impacts on the design for open versus closed-loop sensing and control