Measuring workload weak resilience signals at a rail control post

This paper describes an observational study at a rail control post to measure workload weak-resilience-signals (WRS). A weak resilience signal indicates a possible degradation of a system's resilience, which is defined as the ability of a complex socio-technical system to cope with unexpected and unforeseen disruptions. A method, based upon a WRS framework, introduces a new metric, Stretch, to measure the signals. Stretch is a subjective or an objective reaction of the system to an external cluster-event, and is an operationalization of variables in an earlier Stress-Strain model. The Stretch-ratio between the subjective and objective Stretch are used to identify workload WRS. WRSs identified during real-time operation revealed obstacles that influence the resilience state and enabled actions to anticipate and mitigate changes, to maintain the resilience of the system

Team reflection makes resilience-related knowledge explicit through collaborative sensemaking: observation study at a rail post

Resilience is defined as the ability to adaptively deal with system boundaries in the face of the unexpected and unforeseen (Branlat and Woods in AAAI Fall Sympoisum, 2010. http://www.aaai.org/ocs/index.php/FSS/FSS10/paper/viewPaper/2238). We hypothesize that drawing upon resilience-related knowledge is a prerequisite for such adaptivity. This paper proposes team reflection (Ellis et al. in Curr Dir Psychol Sci 23(1):67–72, 2014) as a macrocognitive function to make the resilience-related knowledge explicit. This knowledge is implicitly available with individual team members active at the sharp end but is never explicitly shared due to invisibility of goal-relevant constraints. To overcome this invisibility, we suggest an application that makes changes in the current rail socio-technical system visible in terms of the three system boundaries, a variation of the originally proposed by Rasmussen (Saf Sci 27(2/3):183–213, 1997): safety, performance and workload. This allows a team of rail signallers to analyse movements towards system boundaries and share knowledge on these movements. An observational study at a rail control post was conducted to assess the value of team reflection in making resilience-related knowledge explicit. For this purpose, we developed a first prototype of the application concerning the performance boundary only. Using naturalistic observations of a team during a week, we observed how they reflected at the end of their shift on salient system changes. A global content analysis was used to show the relevance of the content to resilience and to test the increase in the resilience-related knowledge throughout the observation period. A specific case of a human approaching the rail tracks, as a potential suicide, was analysed in detail. The results show the value of team reflection on system movements towards their boundaries, thus making goal-relevant constrained knowledge explicit within the operational rail environment

Developing resilience signals for the Dutch railway system

A resilience state model for a railway system is proposed consisting of three boundaries putting pressure on the operating state: Safety, Performance (Capacity & Punctuality) and Workload. In order to model the pressure of the boundaries, an additional dimension is added where the slope represents the pressure. By doing so, the model is able to differentiate between internal changes that keep the system in a resilient state or have it move towards brittleness. The resilience state model is also used to develop a quantitative signal model, indicating pressure change of the boundaries. A newly defined resilience signal (RS), a quantitative indication of change in system resilience, can be created with help of the signal model and be used for anticipation during operations. The resulting parametric functions will be evaluated and tuned by empirical testing in further research. Using data from governmental reports on responses to incidents, two empirical cases are worked out using the signal model. The first case shows the correlation between a safety RS and safety risk. The second case analyses a capacity RS and explains the results by the system adaptation process through a multi-layer hierarchy

MassFLOW-3D as a simulation tool for turbidity currents

Turbidity currents are the most important mechanism for the dispersal and deposition of sand in the deep-sea setting and thus the main phenomenon leading to the formation of oil and gas reservoirs in deep water deposits. The flow characteristics of turbidity currents are difficult to observe and study from the modern environment and their experimental approximations in the laboratory are typically limited by scaling issues, unrealistic flume geometries and short durations. Computational fluid dynamic (CFD) analysis, realised as numerical simulations, has been developed to fill the gap between the small and large scale, integrating data from theory, nature and experiments. CFD can also shed light on flow parameters which are so far impossible to deduce from experimental and field studies, such as detailed density and turbulent kinematic energy distributions. The deterministic process modelling CFD software MassFLOW-3D™ has been developed and used successfully to construct a three-dimensional model for the simulation of turbidity currents. All principal hydraulic properties of the flow (e.g. velocity, density, sediment concentration, apparent viscosity, turbulence intensity and bottom shear stress) and its responses to topography can be monitored continuously in three dimensions over the whole duration of the turbidity current. In this paper, comparisons made between the numerical output of MassFLOW-3DTM and the physical experiments are presented. In addition, the code is used to model the spatial characteristics, velocity structure and deposits of high-density turbidity currents and the flow dynamics of low-density turbidity currents in a sinuous channel. The numerical simulations show close fit to experimental sandy turbidity current dynamics for flows with sediment concentrations up to 27%. However, despite this initial success, on-going customisation and validation of these models, together with implementation of improved subroutines aimed at sediment transport and deposition, is essential in improving the computational code and our understanding of the natural phenomena

Can weak-resilience-signals (WRS) reveal obstacles compromising (rail-)system resilience?

Analysis of accidents in socio-technical systems frequently reveals unnoticed obstacles, which have grown to become the main cause of incubation and surprise at failure (Dekker, 2011). Thus far, it has proven to be a challenge to identify those unnoticed obstacles upfront among the tremendous number of events occurring during normal operations. In this article, we describe the usage of weak resilience signals (WRS)(Siegel & Schraagen, 2014), at a rail control post, to reveal obstacles compromising the resilience ..

Evaluation of a novel bioartificial liver in rats with complete liver ischemia: treatment efficacy and species-specific alpha-GST detection to monitor hepatocyte viability

BACKGROUND/AIMS: There is an urgent need for an effective bioartificial liver system to bridge patients with fulminant hepatic failure to liver transplantation or to regeneration of their own liver. Recently, we proposed a bioreactor with a novel design for use as a bioartificial liver (BAL). The reactor comprises a spirally wound nonwoven polyester fabric in which hepatocytes are cultured (40 x 10(6) cells/ml) as small aggregates and homogeneously distributed oxygenation tubing for decentralized oxygen supply and CO2 removal. The aims of this study were to evaluate the treatment efficacy of our original porcine hepatocyte-based BAL in rats with fulminant hepatic failure due to liver ischemia (LIS) and to monitor the viability of the porcine hepatocytes in the bioreactor during treatment. The latter aim is novel and was accomplished by applying a new species-specific enzyme immunoassay (EIA) for the determination of porcine alpha-glutathione S-transferase (alpha-GST), a marker for hepatocellular damage. METHODS: Three experimental groups were studied: the first control group (LIS Control, n = 13) received a glucose infusion only; a second control group (LIS No-Cell-BAL, n = 8) received BAL treatment without cells; and the treated group (LIS Cell-BAL, n = 8) was connected to our BAL which had been seeded with 4.4 x 10(8) viable primary porcine hepatocytes. RESULTS/CONCLUSIONS: In contrast to previous comparable studies, BAL treatment significantly improved survival time in recipients with LIS. In addition, the onset of hepatic encephalopathy was significantly delayed and the mean arterial blood pressure significantly improved. Significantly lower levels of ammonia and lactate in the LIS Cell-BAL group indicated that the porcine hepatocytes in the bioreactor were metabolically activity. Low pig alpha-GST levels suggested that our bioreactor was capable of maintaining hepatocyte viability during treatment. These results provide a rationale for a comparable study in LIS-pigs as a next step towards potential clinical application