Accountability of work activity in high-consequence work systems: human error in context

Organizational context is now accepted as a central concept in attempts to understand error in human–machine systems. However, accounts which emphasize the processes of everyday organizing, such as accountability and work activity, are needed in order to establish organizational requirements for design. In this article, we provide a framework for the consideration of organizational contexts of human error in high-consequence work systems, with a view to integrating empirical insights and supporting practical design work. We draw on computer-supported cooperative work conceptualizations of the process of everyday organizing, particularly the notion of “accountability for work activity” which is pivotal to our organizational account of error. The conceptual framework is characterized here as a set of dimensions which are expressive concerning the relationship between accountability and work activity in different contexts: (1) explicit–implicit; (2) global–local; (3) stable–transient and (4) dependent–independent. The framework is demonstrated with respect to everyday work practices in a radiology department and its analytical utility validated with respect to two documented aviation system failures. Applying the framework has enabled us to identify and define, in terms of the dimensions, a number of contexts for vulnerability in high-consequence systems: contexts for collusion, violation, deference, loss of control, buck passing and complacency. These are discussed in terms of requirements for error-tolerant design. In the final section of the article, links between the various contexts for vulnerability and the design process are explored.     

THE ADVENT OF CRYPTOLOGY IN THE GAME OF BRIDGE

The surprising discovery that information can be passed both covertly and legally between bridge partners has added a new dimension to the theory of this popular game. In this paper some of the methods are sketched and their cryptologic foundation is described.     

State estimation of dynamical systems with nonlinearities by using proportional-integral observer

In this paper the application of a PI observer technique to dynamical systems with nonlinearities is proposed. The PI observer has two feedback loops, a proportional loop and an integral loop of the estimation error. In this way the PI observer combines the structures of the practical orientated nonlinearity observer developed by the third author and the classical Luenberger observer. The structure and the estimation performance of the PI observer are discussed and analysed. The results show that the PI observer can estimate the states not only of linear systems, but also, more significantly, of systems with any arbitrary external input which appear as unknown input, nonlinearity or unmodelled dynamics. It is shown that the PI observer works with weak assumptions, which can be fulfilled by many classes of systems to be observed. Owing to the weak assumptions it can improve many observer-based technical solutions as diagnosis or control based on observers. In the paper the conditions are given and proved. The design method is declared and carried out with illustrative examples of a linear system and of a nonlinear system of a link manipulator with flexible joints. The results are good and they show the efficiency of the PI observer. In the case of nonlinear systems the advantages of ‘robustness’ and the model independency of the proposed observer scheme can be shown clearly.     

The reflectance factors of a rough ocean with foam—comment on ‘Remote sensing of the sea state using the 0·8-1·1 μm spectral band’ by L. Wald and J. M. Monget

Reflectance factors of a rough ocean surface with and without foam are presented. They are calculated from the Cox-Munk model for an ocean without foam. The isotropic reflectance of oceanic foam is added as function of the wind speed. The effective reflectance of foam patches is taken into account     

On-line Animated Visualization of Huge Graphs using a Modified Spring Algorithm

On-line graph drawing deals with huge graphs which are partially unknown. At any time, a tiny part of the graph is displayed on the screen. Examples include web graphs and graphs of links in distributed file systems. This paper discusses issues arising in the presentation of such graphs. The paper describes a system for dealing with web graphs using on-line graph drawing.     

Assimilate transport in grapevines -effect of phloem disruption

Assimilate translocation in mature grapevines (cv. Gewürztraminer and cv. Harslevelü) under field conditions was investigated during the growth season by quantifying individual sugars and organic acids in mature leaves, shoot bark and berries, as affected by girdling the shoot just above the bunches. Tissue was sampled at berry set, pea size, veraison and ripeness stages of the vine. Invertase activity was determined in the shoot bark at ripeness. In the leaves, malic acid concentrations reached lowest levels at pea size, but increased thereafter. Tartaric acid decreased after peaking at pea size stage. Tartaric acid concentrations increased with girdling. Despite the increase in leaf age, sucrose concentrations remained virtually stable during the season, emphasising the importance of mature leaves for nourishing bunches. Girdling resulted in a build‐up of sucrose in the leaves. In the bark, malic and tartaric acid stayed more or less the same during the growth period, but increased above the girdle. As a result of phloem disruption, sucrose also increased. The increase in glucose and tartaric acid is believed to result from catabolic cleavage of sucrose by invertase. Invertase activity was evident in the bark (of mature Harslevelü vines) at ripeness, which may indicate involvement in osmotic adjustments and gradients in the bark/phloem structure. In the berries, malic and tartaric acids reached peak concentrations at pea size. The volume increase during the ripening period, and in the case of malic acid also respiratory loss, resulted in a decrease in organic acid concentration. Malic acid continued to decrease after the initial decline, whereas tartaric acid stayed virtually stable. Girdling had no marked effect on organic acid accumulation in the berries. Sucrose concentrations were low during the first part of the season, but increased thereafter. Sucrose concentrations during ripening increased with girdling, which may represent a concentration effect and/or import from the rest of the vine. Sucrose concentrations (in mature Harslevelü vines) were indeed lower below than above the girdle. Comparison of sucrose concentrations in the leaves, bark and berries showed the existence of a decreasing concentration gradient, in line with the source:sink transport concept. An equally prominent decrease in sucrose:glucose ratio in the berries from the start of the ripening period indicates that vacuolar integrity (compartmentation) was affected in the ripening berry, most probably allowing hydrolysis of sucrose by invertase and decreasing osmotic potential within the berry. The results provide further evidence for the hypothesis of an osmotic gradient driven transport to the berry.     

MICROORGANISMS AS POTENTIAL SOURCES OF NOVEL DIPHENOL OXIDASE INHIBITORS

Culture filtrates and mycelial homogenates from over 100 microorganisms were tested for their ability to inhibit catecholase and laccase (o- and p-diphenol oxidase) activity using simple, rapid, colorimetric assays in microtiter plates or polarographic assays using an O₂-electrode. Of the organisms screened, 56 produced inhibition of catecholase activity and 34 gave rise to laccase inhibition, with most of the latter group showing inhibition of both enzymes. The role of this enzyme inhibitor system in plant pathogenicity is also discussed.