Computer simulation of cerebrovascular circulation : assessment of intracranial hemodynamics during induction of anesthesia

The purpose of this project was to develop a computer model of cerebrovascular hemodynamics interacting with a pharmacokinetic drug model to examine the effects of various stimuli during anesthesia on cerebral blood flow and intracranial pressure. The mathematical model of intracranial hemodynamics is a seven compartment constant volume system. A series of resistances relate blood and cerebrospinal fluid fluxes to pressure gradients between compartments. Arterial, venous, and tissue compliance are also included. Autoregulation is modeled by transmural pressure dependent arterial-arteriolar resistance. The effect of a drug (thiopental) on cerebrovascular circulation was simulated by a variable arteriolar-capillary resistance. Thiopental concentration, in turn, was predicted by a three-compartment pharmacokinetic model. The effect site compartment was included to account for a disequilibrium between drug plasma and biophase concentrations. The model was validated by comparing simulation results with available experimental observations. The simulation program is written in VisSiM® dynamic simulation language for an IBM-compatible PC. The model developed was used to calculate cerebral blood flow and intracranial pressure changes which occur during the induction phase of general anesthesia. Responses to laryngoscopy and intubation were predicted for simulated patients with elevated intracranial pressure and nonautoregulated cerebral circulation. Simulation shows that the induction dose of thiopental reduces intracranial pressure up to 15%. The duration of this effect is limited to less than three minutes by rapid redistribution of thiopental and cerebral autoregulation. Subsequent laryngoscopy causes acute intracranial hypertension exceeding the initial intracranial pressure. Further simulation predicts that this untoward effect can be minimized by an additional dose of thiopental administered immediately prior to intubation. The presented simulation allows comparison of various drug administration schedules to control intracranial pressure and preserve cerebral blood flow during induction of anesthesia. The model developed can be extended to analyze more complex intraoperative events by adding new submodels

The construction of a social studies vocabulary test for teachers in training.

Thesis (Ed.M.)--Boston Universit

Novel types of anti-ecloud surfaces

In high power RF devices for space, secondary electron emission appears as the main parameter governing the multipactor effect and as well as the e-cloud in large accelerators. Critical experimental activities included development of coatings with low secondary electron emission yield (SEY) for steel (large accelerators) and aluminium (space applications). Coatings with surface roughness of high aspect ratio producing the so-call secondary emission suppression effect appear as the selected strategy. In this work a detailed study of the SEY of these technological coatings and also the experimental deposition methods (PVD and electrochemical) are presented. The coating-design approach selected for new low SEY coatings include rough metals (Ag, Au, Al), rough alloys (NEG), particulated and magnetized surfaces, and also graphene like coatings. It was found that surface roughness also mitigate the SEY deterioration due to aging processes.Comment: 4 pages, contribution to the Joint INFN-CERN-EuCARD-AccNet Workshop on Electron-Cloud Effects: ECLOUD'12; 5-9 Jun 2012, La Biodola, Isola d'Elba, Italy; CERN Yellow Report CERN-2013-002, pp.153-15

And then there were four: a study of UK market concentration - causes, consequences and the scope for market adjustment

While concentration measures are a good indicator of market structure, the link with competitiveness is more complex than often assumed. In particular, the modern theory of industrial organisation makes no clear statement regarding the impact of concentration on competition - the focus of this paper is concentration and no inferences are made about competitive aspects of the market. The extent and nature of concentration within the UK listed company audit market as at April, 2002 and, pro forma, after the collapse of Andersen is documented and analysed in detail (by firm, market segment and industry sector). The largest four firms held 90 per cent of the market (based on audit fees) in 2002, rising to 96 per cent with the demise of Andersen. A single firm, Pricewaterhouse-Coopers, held 70 per cent or more of the share of six out of 38 industry sectors, with a share of 50 per cent up to 70 per cent in a further seven sectors. The provision of non-audit services (NAS) by incumbent auditors is also considered. As at April 2002, the average ratio of non-audit fees (paid to auditor) to audit fees was 208 per cent, and exceeded 300 per cent in seven sectors. It is likely, however, that disposals by firms of their management consultancy and outsource firms, combined with the impact of the Smith Report on audit committees will serve to reduce these ratios. Another finding is that audit firms with expertise in a particular sector appeared to earn significantly higher nonaudit fees from their audit clients in that sector. The paper thus provides a solid empirical basis for debate. The subsequent discussion considers the implications for companies and audit firms of the high level of concentration in the current regulatory climate, where no direct regulatory intervention is planned

Experimental analysis of passive intermodulation at waveguide flange bolted connections

[EN] In this paper, the generation of passive intermodulation at rectangular waveguide flange bolted connections is investigated. An exhaustive series of tests has been performed in order to provide understanding on the physics lying behind such a phenomenon. In particular, the intermodulation response of the system has been studied as a function of the applied torque to the flange screws. It has been found that, in some situations, the intermodulation response differs from its expected behavior. An interpretation of such discrepancies is given, and practical guidelines for the design of waveguide flanges free of passive intermodulation are provided as well.This work was supported by the European Space Agency under the Surface Treatment and Coating for the Reduction of Multipactor and Passive Intermodulation Effects in RF Components Project, by the European Space Research and Technology Centre under Contract 17025/03/NL/EC, by the Generalitat Valenciana (Spain) under PREDECTOR Project IIARC0/2004/020, and by the Spanish Government (MEC) under a Juan de la Cierva Program Fellowship.Vicente, C.; Wolk, D.; Hartnagel, H.; Gimeno, B.; Boria Esbert, VE.; Raboso, D. (2007). Experimental analysis of passive intermodulation at waveguide flange bolted connections. IEEE Transactions on Microwave Theory and Techniques. 55(5):1018-1028. https://doi.org/10.1109/TMTT.2007.895400S1018102855