Error detection: a study in anaesthesia

Although error has been shown as the main cause of accidents in complex systems, little attention has been paid to error detection. However, reducing the consequences of error depends largely on error detection. The goal of this paper is to synthesize the existing scientific knowledge on error detection, mostly based on studies conducted in laboratory or self reporting and to further knowledge through the analysis of a corpus of cases collected in a complex system, anaesthesia. By doing this, this paper is better able to describe how this knowledge can be used to improve understanding of error detection modes. An anaesthesia accident reporting system developed and organized at two Belgian University Hospitals was used in order to collect information about the error detection patterns. Results show that detection of errors principally occurred through the standard check (routine monitoring of the environment). Significant relationships were found between the type of error and the error detection mode, and between the type of error and the training level of the anaesthetist who committed the error.     

Potentials Produced by Arbitrary Current Sources in an Infinite-and Finite-Length Circular Conducting Cylinder

In electrophysiology, the analytical expression of the potentials at the outer surface of a cylinder, caused by an embedded current source distribution, is useful in studies where measured potentials have to be related to unknown generators. The solutions found in the literature for different types of current sources are unfortunately contradictory. This paper rederives the solution to the general case of an arbitrary monopolar or dipolar current source and discloses where and how an error arose in earlier work. The problems encountered during the numerical implementation of the new equations are extensively discussed.     

The effect of 2D and 3D visual modes on surgical task performance: role of expertise and adaptation processes

The aim of this paper is to analyze how novices and experts are able to safely adapt and transfer their skills to new technology in medical domain. In order to answer this question, we compared the performance of 12 novices (medical students) with the performance of 12 laparoscopic surgeons (using a 2D view) and 4 robotic surgeons, using a new robotic system that allows 2D and 3D view. Our results showed a trivial effect of expertise (surgeons generally performed better than novices). Moreover, they revealed that experts have adaptive transfer capacities and are able to transfer their skills independently of the human–machine system. However, even if we observe transfer of skills, we showed that expert’s performance may be disturbed by changes in their usual environment. In a safety perspective but also for novice and expert training, this study emphasizes the necessity to take into account the impact of these environmental changes and the expert’s adaptive capacities but also the limits of expert’s adaptive capacities.     

Using Landmarks to Establish a Point-to-Point Correspondence between Signatures

This paper introduces a new approach for point-to-point correspondence finding, which can be used as pre-processing stage of a handwritten signature verification procedure. This approach provides a solid basis for comparing function features of two handwritten signatures. Corner points of the signatures are first extracted based on velocity information. The characteristics of curvilinear velocity and angular velocity are combined successfully by functions based on membership criteria. The signatures to be compared are then segmented at landmarks obtained by corner matching based on similarity measures. In the last step, the corresponding pairs of segments are mapped by a point-to-point matching algorithm, minimising a curve deformation energy. The techniques described were applied to a set of 188 signatures from 19 volunteers. The resulting point-to-point matching of signature pairs was satisfactory in all cases where there was a visual agreement between the signatures. Received: 01 February 1999, Received in revised form: 05 May 1999, Accepted: 24 May 1999     

A system to acquire and process scanning transmission electron microscope images

The numerical processing of electron microscope images is becoming important as more investigators need quantitative data on size and density of objects visualized by means of a STEM system [1–3]. We describe the hard- and software of a system for acquisition and processing of such images. Traditionally, the processed negatives of electromicrographs are scanned by a microdensitometer to provide a digital image [4,5]. We decided upon direct digitization of the transmission detector's output without intermediate optical or photochemical steps. The system's performance was tested on latex spheres.     

Single line CCD camera to improve positioning

This article describes an opto-electronic device that allows on-line visualization of the optical intensity function along a strip. The use of a linear optical charge-coupled device (CCD) array eliminates all moving parts. This makes adaptation to a standard microscope possible without modifications. The setup described here is essential where precise positioning of a reference graticule on diffuse lines must be performed.     

Assessing spatio-temporal rainfall variability in a tropical mountain area (Ethiopia) using NOAA’s rainfall estimates

Seasonal and interannual variation in rainfall can cause massive economic loss for farmers and pastoralists, not only because of deficient total rainfall amounts but also because of long dry spells within the rainy season. The semi-arid to sub-humid mountain climate of the North Ethiopian Highlands is especially vulnerable to rainfall anomalies. In this article, spatio-temporal rainfall patterns are analysed on a regional scale in the North Ethiopian Highlands using satellite-derived rainfall estimates (RFEs). To counter the weak correlation in the dry season, only the rainy season rainfall from March till September is used, responsible for approximately 91% of the annual rainfall. Validation analysis demonstrates that the RFEs are well correlated with the meteorological station (MS) rainfall data, i.e. 85% for RFE 1.0 (1996–2000) and 80% for RFE 2.0 (2001–2006). However, discrepancies indicate that RFEs generally underestimate MS rainfall and the scatter around the trendlines indicates that the estimation by RFEs can be in gross error. A local calibration of RFE with rain gauge information is validated as a technique to improve RFEs for a regional mountainous study area. Slope gradient, slope aspect, and elevation have no added value in the calibration of the RFEs. The estimation of monthly rainfall using this calibration model improved on average by 8%. Based upon the calibration model, annual rainfall maps and an average isohyet map for the period 1996–2006 were constructed. The maps show a general northeast–southwest gradient of increasing rainfall in the study area and a sharp east–west gradient in its northern part. Slope gradient, slope aspect, elevation, easting, and northing were evaluated as explanatory factors for the spatial variability of annual rainfall in a stepwise multiple regression with the calibrated average of RFE 1.0 as dependent variable. Easting and northing are the only significant contributing variables (R² = 0.86), of which easting has proved to be the most important factor (R² = 0.72). The scatter around the individual trendlines of easting and northing corresponds to an increase in rainfall variability in the drier regions. Despite the remaining underestimation of rainfall in the southern part of the study area, the improved estimation of spatio-temporal rainfall variability in a mountainous region by RFEs is valuable as input to a wide range of scientific models.     

Desertification? Northern Ethiopia re-photographed after 140 years

A collection of sepia photographs, taken during Great Britain's military expedition to Abyssinia in 1868, are the oldest landscape photographs from northern Ethiopia, and have been used to compare the status of vegetation and land management 140 years ago with that of contemporary times. Thirteen repeat landscape photographs, taken during the dry seasons of 1868 and 2008, were analyzed for various environmental indicators and show a significant improvement of vegetation cover. New eucalypt woodlands, introduced since the 1950s are visible and have provided a valuable alternative for house construction and fuel-wood, but more importantly there has also been locally important natural regeneration of indigenous trees and shrubs. The situation in respect to soil and water conservation measures in farmlands has also improved. According to both historical information and measured climatic data, rainfall conditions around 1868 and in the late 19th century were similar to those of the late 20th/early 21st century. Furthermore, despite a ten-fold increase in population density, land rehabilitation has been accomplished over extensive areas by large-scale implementation of reforestation and terracing activities, especially in the last two decades. In some cases repeat photography shows however that riparian vegetation has been washed away. This is related to river widening in recent degradation periods, particularly in the 1970s-1980s. More recently, riverbeds have become stabilized, and indicate a decreased runoff response. Environmental recovery programmes could not heal all scars, but this study shows that overall there has been a remarkable recovery of vegetation and also improved soil protection over the last 140 years, thereby invalidating hypotheses of the irreversibility of land degradation in semi-arid areas. In a highly degraded environment with high pressure on the land, rural communities were left with no alternative but to improve land husbandry: in northern Ethiopia such interventions have been demonstrably successful.     

A Multi-stage Online Signature Verification System

: This paper presents a new three-stage verification system which is based on three types of features: global features; local features of the corner points; and function features that contain information of each point of the signatures. The first verification stage implements a parameter-based method, in which the Mahalanobis distance is used as a dissimilarity measure between the signatures. The second verification stage involves corner extraction and corner matching. It also performs signature segmentation. The third verification stage implements a function-based method, which is based on an elastic matching algorithm establishing a point-to-point correspondence between the compared signatures. By combining the three different types of verification, a high security level can be reached. According to our experiments, the rates of false rejection and false acceptance are, respectively, 5.8% and 0%. Received: 12 Febuary 2001, Received in revised form: 24 May 2001, Accepted: 03 July 2001     

Pre- and post-degradation analysis of composite materials with different moduli in tension and compression

An isoparametric finite element tor the analysis of multi-layer composite materials is presented. Several linear and nonlinear stress-strain relations are discussed. Special attention is given to the composite materials with different moduli in tension and compression, for which a new mathematical model is presented and tested.Different failure criteria for the matrix degradation are incorporated in the element and several post-degradation behaviors are also considered.Finally we discuss the role of the Newton-Raphson method in composite materials, especially in the presence of geometrical nonlinearities.