Stochastic processes with distributed delays: chemical Langevin equation and linear-noise approximation

We develop a systematic approach to the linear-noise approximation for stochastic reaction systems with distributed delays. Unlike most existing work our formalism does not rely on a master equation, instead it is based upon a dynamical generating functional describing the probability measure over all possible paths of the dynamics. We derive general expressions for the chemical Langevin equation for a broad class of non-Markovian systems with distributed delay. Exemplars of a model of gene regulation with delayed auto-inhibition and a model of epidemic spread with delayed recovery provide evidence of the applicability of our results.Comment: 21 pages, 7 figure

Generating functionals and Gaussian approximations for interruptible delay reactions

We develop a generating functional description of the dynamics of non-Markovian individual-based systems, in which delay reactions can be terminated before completion. This generalises previous work in which a path-integral approach was applied to dynamics in which delay reactions complete with certainty. We construct a more widely applicable theory, and from it we derive Gaussian approximations of the dynamics, valid in the limit of large, but finite population sizes. As an application of our theory we study predator-prey models with delay dynamics due to gestation or lag periods to reach the reproductive age. In particular we focus on the effects of delay on noise-induced cycles.Comment: 18 pages, 4 figure

Gaussian approximations for stochastic systems with delay: chemical Langevin equation and application to a Brusselator system

We present a heuristic derivation of Gaussian approximations for stochastic chemical reaction systems with distributed delay. In particular we derive the corresponding chemical Langevin equation. Due to the non-Markovian character of the underlying dynamics these equations are integro-differential equations, and the noise in the Gaussian approximation is coloured. Following on from the chemical Langevin equation a further reduction leads to the linear-noise approximation. We apply the formalism to a delay variant of the celebrated Brusselator model, and show how it can be used to characterise noise-driven quasi-cycles, as well as noise-triggered spiking. We find surprisingly intricate dependence of the typical frequency of quasi-cycles on the delay period.Comment: 14 pages, 9 figure

A multichannel frequency response analyser for impedance spectroscopy on power sources

A low-cost multi-channel frequency response analyser (FRA) has been developed based on a DAQ (data acquisition)/LabVIEW interface. The system has been tested for electric and electrochemical impedance measurements. This novel association of hardware and software demonstrated performance comparable to a commercial potentiostat / FRA for passive electric circuits. The software has multichannel capabilities with minimal phase shift for 5 channels when operated below 3 kHz. When applied in active (galvanostatic) mode in conjunction with a commercial electronic load (by discharging a lead acid battery at 1.5 A) the performance was fit for purpose, providing electrochemical information to characterize the performance of the power source

Fault diagnosis of PEMFC based on the AC voltage response and 1D convolutional neural network

Real-time diagnosis is required to ensure the safety, reliability, and durability of the polymer electrolyte membrane fuel cell (PEMFC) system. Two categories of methods are (1) intrusive, time consuming, or require alterations to the cell architecture but provide detailed information about the system or (2) rapid and benign but low-information-yielding. A strategy based on alternating current (AC) voltage response and one-dimensional (1D) convolutional neural network (CNN) is proposed as a methodology for detailed and rapid fuel cell diagnosis. AC voltage response signals contain within them the convoluted information that is also available via electrochemical impedance spectroscopy (EIS), such as capacitive, inductive, and diffusion processes, and direct use of time-domain signals can avoid time-frequency conversion. It also overcomes the disadvantage that EIS can only be measured under steady-state conditions. The utilization of multi-frequency excitation can make the proposed approach an ideal real-time diagnostic/characterization tool for fuel cells and other electrochemical power systems

A study of the effect of water management and electrode flooding on the dimensional change of polymer electrolyte fuel cells

AbstractWater management and flooding play an important role in the performance and durability of polymer electrolyte fuel cells (PEFCs). In this study, a dynamic electro-mechanical analysis is performed to examine the performance of a working PEFC during hydration transients and flooding events. Cell resistance is measured using electrochemical impedance spectroscopy (EIS), and the stress/strain characteristics – cell compression and membrane electrode assembly (MEA) dimensional change – are studied using a controlled compression unit (CCU).Ex-situ measurements of membrane thickness as a function of hydration level provide a direct correlation between ionic conductivity and thickness. During initial hydration of Nafion membranes there is a direct relationship between membrane conductivity and dimensional change (swelling) of MEAs. Electrode flooding is found to result in membrane hydration and an increase in stress or strain, depending on the compression mode of the fuel cell. Results suggest that hydration cycles and flooding events can lead to cell degradation due to the stresses imposed

Could rebel child soldiers prolong civil wars?

While we know why rebels may recruit children for their cause, our understanding of the consequences of child soldiering by non-state armed groups remains limited. The following research contributes to addressing this by examining how rebels? child recruitment practice affects the duration of internal armed conflicts. We advance the argument that child soldiering increases the strength of rebel organizations vis-�-vis the government. This, in turn, lowers the capability asymmetry between these nonstate actors and the incumbent, allowing the former to sustain in dispute. Ultimately, the duration of armed conflicts is likely to be prolonged. We analyze this relationship with quantitative data on child soldier recruitment by rebel groups in the post-1989 period. The results confirm our main hypothesis: disputes are substantially longer when rebels recruit children. This work has important implications for the study of armed conflicts, conflict duration, and our understanding of child soldiering

Pancreatogastrostomy versus pancreatojejunostomy for RECOnstruction after partial PANCreatoduodenectomy (RECOPANC): study protocol of a randomized controlled trial UTN U1111-1117-9588

BACKGROUND: Pancreatoduodenectomy is one of the most complex abdominal operations, usually performed for tumors of the periampullary region and chronic pancreatitis. Leakage of pancreatic juice from the pancreatoenteric anastomosis, called postoperative pancreatic fistula, is the most prominent postoperative complication. Retrospective studies show a significant reduction of fistula rates with pancreatogastrostomy as compared to pancreatojejunostomy, the most frequently employed method of pancreatoenterostomy. Most single-center prospective trials, however, have not validated this finding. A large multicenter trial is needed for clarification. METHODS/DESIGN: RECOPANC is a prospective, randomized, controlled multicenter trial with two treatment arms, pancreatogastrostomy versus pancreatojejunostomy. The trial hypothesis is that postoperative pancreatic fistula rate is lower after pancreatogastrostomy when compared to pancreatojejunostomy. Fourteen academic centers for pancreatic surgery will participate to allocate 360 patients to the trial. The duration of the entire trial is four years including prearrangement and analyses. DISCUSSION: Postoperative pancreatic fistula is the main reason for clinically important postoperative morbidity after pancreatoduodenectomy. The primary goal of the chosen reconstruction technique for pancreatoenteric anastomosis is to minimize postoperative fistula rate. A randomized trial performed at multiple high-volume centers for pancreatic surgery is the best opportunity to investigate one of the most crucial issues in pancreatic surgery. TRIAL REGISTRATION: German Clinical Trials Register DRKS00000767 (2011/03/23), FSI 2011/05/31. Universal Trial Number U1111-1117-9588

Declining human pressure and opportunities for rewilding in the steppes of Eurasia

Large and ecologically functioning steppe complexes have been lost historically across the globe, but recent land‐use changes may allow the reversal of this trend in some regions. We aimed to develop and map indicators of changing human influence using satellite imagery and historical maps, and to use these indicators to identify areas for broad‐scale steppe rewilding.Peer Reviewe