A continuous time version and a generalization of a Markovrecapture model for trapping experiments

Wileyto et al. [E.P. Wileyto, W.J. Ewens, M.A. Mullen, Markov-recapture population estimates: a tool for improving interpretation of trapping experiments, Ecology 75 (1994) 1109] propose a four-state discrete time Markov process, which describes the structure of a marking-capture experiment as a method of population estimation. They propose this method primarily for estimation of closed insect populations. Their method provides a mark-recapture estimate from a single trap observation by allowing subjects to mark themselves. The estimate of the unknown population size is based on the assumption of a closed population and a simple Markov model in which the rates of marking, capture, and recapture are assumed to be equal. Using the one step transition probability matrix of their model, we illustrate how to go from an embedded discrete time Markov process to a continuous time Markov process assuming exponentially distributed holding times. We also compute the transition probabilities after time t for the continuous time case and compare the limiting behavior of the continuous and discrete time processes. Finally, we generalize their model by relaxing the assumption of equal per capita rates for marking, capture, and recapture. Other questions about how their results change when using a continuous time Markov process are examined. © 2008 Elsevier Inc. All rights reserved

Investigation of in vivo measurement of cerebral cytochrome-c-oxidase redox changes using near-infrared spectroscopy in patients with orthostatic hypotension

We have previously used a continuous four wavelength near infrared spectrometer to measure changes in the cerebral concentrations of oxy- (Δ[HbO2] and deoxy- haemoglobin (Δ[HHb]) during head-up tilt in patients with primary autonomic failure. The measured changes in light attenuation also allow calculation of changes in the concentration of oxidised cytochrome c oxidase (Δ[oxCCO]), and this paper analyses the Δ[oxCCO] during the severe episodes of orthostatic hypotension produced by this experimental protocol. We studied 12 patients during a passive change in position from supine to a 60º head-up tilt. The challenge caused a reduction in mean blood pressure of 59.93 (±26.12) mmHg (Mean (±SD), p<0.0001), which was associated with a reduction in the total concentration of haemoglobin (Δ[HbT]= Δ[HbO2]+Δ[HHb]) of 5.02 (±3.81) μM (p<0.0001) and a reduction in the haemoglobin difference concentration (Δ[Hbdiff]= Δ[HbO2]-Δ[HHb]) of 14.4 (±6.73) μM (p<0.0001). We observed a wide range of responses in Δ[oxCCO]. 6 patients demonstrated a drop in Δ[oxCCO] (0.17 ±0.15μM ); 4 patients demonstrated no change (0.01 ±0.12 μM ) and 2 patients showed an increase in Δ[oxCCO] (0.21 ±0.01 μM ). Investigation of the association between the changes in concentrations of haemoglobin species and the Δ[oxCCO] for each patient show a range of relationships. This suggests that a simple mechanism for crosstalk, which might produce artefactual changes in [oxCCO], is not present between the haemoglobin and the oxCCO NIRS signals. Further investigation is required to determine the clinical significance of the changes in [oxCCO]

Adaptive, cautious, predictive control with Gaussian process priors

Nonparametric Gaussian Process models, a Bayesian statistics approach, are used to implement a nonlinear adaptive control law. Predictions, including propagation of the state uncertainty are made over a k-step horizon. The expected value of a quadratic cost function is minimised, over this prediction horizon, without ignoring the variance of the model predictions. The general method and its main features are illustrated on a simulation example

Carrier-mediated transport of norepinephrine transporter substrates.

An overview of the noradrenergic system, including the identification of norepinephrine (NE) in animal tissue, its synthesis and metabolism, adrenoceptor classification, peripheral and central actions, uptake and storage, and mechanisms of NE release are presented. After characterizing the kinetic, ion dependence and inhibitor sensitivity of the norepinephrine transporter (NET) expressed in a recombinant cell line (LLC-NET cells), the influence of catecholamine (CA) metabolizing enzymes on studies of transport was assessed. Inhibitors of catechol-O-methyltransferase (COMT) potentiated the apparent uptake and retention of [3H]NE and [3H]DA. COMT inhibition had a greater influence on [3H]DA than [3H]NE uptake and retention, which corresponds to the higher spontaneous loss of radiolabel from cells exposed to [3H]DA than [3H]NE ([3H]methoxytyramine, is more lipophilic than [3H]normetanephrine). The monoamine oxidase inhibitor, pargyline, had no augmentary action on [3H]CA uptake, but actually inhibited substrate influx by blocking the NET. [3H]substrate specific differences were demonstrated for [3H]NE, [3H]DA and [3H]MPP+. For a given length of exposure to low Na+ or tyramine, [3H]NE release was the lowest, but most sensitive to NET inhibitors. Disparities in the kinetics of each [3H]substrate for the inwardly facing NET may account for this. Inhibitors of the NET were found to stimulate the efflux of [3H]substrates from preloaded cells incubated in a physiological HEPES buffer. Efflux was NET-dependent and differed greatly for each [3H]substrate. Inhibitor-induced release was greatest for [3H]MPP+ and least for [3H]NE. Finally, a functional model of carrier-mediated NE release in myocardial ischemia, was developed in this study. Release of [3H]MPP+ was stimulated by Na+-H+ exchanger (NHE) activation and modulated by inhibitors of the NET, NHE, Na+,K+-ATPase, and via a receptor-operated pathway. Excessive NE release contributes to severe myocardial arrhythmias, therefore an improved understanding of the carrier-mediated NE release process will ultimately enhance our ability to intervene and prevent the deleterious effects of excessive NE release

Investigation of stratiform sulphide mineralisation at Meall Mor, South Knapdale, Argyll

A co-ordinated geochemical-geophysical-geological investigation of copper mineralisation in the Meal1 ?46r area, South Knapdale, Argyll was carried 0th in 1976 and followed by a drilling programme of 3 shallow holes in early 1977. The mineralisation occursin a zone of weak stratiform sulphide mineralisation (the pyrite zone) with a strike length of 1Okm in the Upper &ins Quartz&e of the Middle Dalradian. The geochemical drainage survey showed the existence of a strongly anomalous distribution of Cu and Sb in the Abhainn Srathain draining south from . Meal1 M&- and detailed soil sampling over the pyrite zone outlined a broad area enriched in copper. Deeper soil sampling confirmed the anomalously high copper values and a coincident IP anomaly was found stretching from Meal1 M& south to the old mine workings on Abhainn Srathain, and is probably caused by a local enrichment of pyrite and chalcopyrite within the pyrite zone. Three boreholes were drilled; two on coincident geochemical and geophysical anomalies, and the third beneath the old mines at Abhainn Srathain. Copper values in the first two holes range up to 0.24% Cu over 4.27m, but up to 1.06% Cu over 2.67m in the third and this enrichment may be related to a later remobilisation of the disseminated chalcopyrite. The results of subsequent drilling at two other sites are given in Appendix III

Formula for success: Multilevel modelling of Formula One Driver and Constructor performance, 1950-2014

This paper uses random-coefficient models and (a) finds rankings of who are the best formula 1 (F1) drivers of all time, conditional on team performance; (b) quantifies how much teams and drivers matter; and (c) quantifies how team and driver effects vary over time and under different racing conditions. The points scored by drivers in a race (standardised across seasons and Normalised) is used as the response variable in a cross-classified multilevel model that partitions variance into team, team-year and driver levels. These effects are then allowed to vary by year, track type and weather conditions using complex variance functions. Juan Manuel Fangio is found to be the greatest driver of all time. Team effects are shown to be more important than driver effects (and increasingly so over time), although their importance may be reduced in wet weather and on street tracks. A sensitivity analysis was undertaken with various forms of the dependent variable; this did not lead to substantively different conclusions. We argue that the approach can be applied more widely across the social sciences, to examine individual and team performance under changing conditions

Computationally efficient velocity profile solutions for cardiac haemodynamics

DOI: 10.1109/IEMBS.2004.1403316This paper reformulates the non-linear differential equations associated with time varying resistance in minimal cardio-vascular system models into a system of linear equations with an analytical solution. The importance of including time varying resistance is shown for a single chamber model where there is a 17.5% difference in cardiac output when compared with a constant resistance model. However, the increased complexity has significant extra computational cost. This new formulation provides a significant computational saving of 15x over the previous method. This improvement enables more physiological accuracy with minimal cost in computational time. As a result, the model can be used in clinical situations to aid diagnosis and therapy selection without compromising on physiological accuracy

Pressure, Temperature and Dwell Time Effects on Fatigue Life in 304 Stainless Steel Using a R5-based Mechanistic Fatigue Model

AbstractThis paper aims to evaluate the effects of pressure, temperature, pipe wall thickness and dwell time on fatigue life in 304 stainless steel. For a given dwell time and temperature-internal pressure combination, fatigue life is calculated using the mechanistic fatigue model (MFM) presented. In addition, the influence of pipe wall thickness is also examined. The MFM uses Tresca strain range for initiation and Rankine strain range to account for crack growth rate up to a crack limiting length. The results showed that fatigue life was generally lower for a given load combination in the thinner pipe considered given its smaller surface area compared to the thicker pipe. This led to higher plastic strains and consequently, faster crack growth rates. Also, dwell time influences fatigue life with longer dwell times found to be more damaging. However, the influence of dwell time is tightly coupled with pipe wall thickness as it determines the nature of the thermal gradients developed

Adjunctive therapy in epilepsy: a cost-effectiveness comparison of two AEDs

AbstractThe objective of this study was to compare the relative cost-effectiveness of two AEDs by a prospective clinical audit. Patients starting on the adjunctive therapies lamotrigine and topiramate were recruited from the out-patient epilepsy clinics at Queen Square. Three interview were scheduled: baseline; three months follow-up and six months from baseline. Of the 81 patients recruited, a total of 73 patients completed all three interviews. An intention to treat analysis was performed on the data. Seizure severity and frequency were assessed using the National Hospital Seizure Severity Scale. Side-effects, adverse events and reasons for stopping medication were also recorded.At the third interview, a total of 47/73 (64%) were still on the prescribed adjunctive drug. Outcome was assessed by two methods: the >50% seizure reduction cited in the literature and a more stringent assessment of patient ‘satisfaction’ which we defined operationally on clinical criteria. Using this definition, a total of 10/73 (14%) patients were ‘satisfied’. The relative costs of starting patients on each of the two AEDs were calculated, both drug costs and the costs of adverse events (the latter were defined as events requiring urgent medical attention). The costs of the two drugs were compared. A number of methodological issues relating to cost comparison are discussed. Outcome and pharmaco-economic studies need to assess more than reduction in number of seizures. They should take into account variables important for quality of life including side-effects and adverse events