Subjective rating scales as a workload

A multidimensional bipolar-adjective rating scale is employed as a subjective measure of operator workload in the performance of a one-axis tracking task. The rating scale addressed several dimensions of workload, including cognitive, physical, and perceptual task loading as well as fatigue and stress effects. Eight subjects performed a one-axis tracking task (with six levels of difficulty) and rated these tasks on several workload dimensions. Performance measures were tracking error RMS (root-mean square) and the standard deviation of control stick output. Significant relationships were observed between these performance measures and skill required, task complexity, attention level, task difficulty, task demands, and stress level

Early increases in plasminogen activator activity following partial hepatectomy in humans

Background Increases in urokinase-like plasminogen activator (uPA) activity are reported to be amongst the earliest events occurring in remnant liver following partial hepatectomy in rats, and have been proposed as a key component of the regenerative response. Remodelling of the extracellular matrix, conversion of single chain hepatocyte growth factor to the active two-chain form and a possible activation of a mitogenic signalling pathway have all been ascribed to the increased uPA activity. The present study aimed to determine whether similar early increases in uPA activity could be detected in the remnant liver following resection of metastatic tumours in surgical patients. Results Eighteen patients undergoing partial hepatectomy for the removal of hepatic metastases secondary to primary colonic tumours were studied. Increased plasminogen activator activity was found in the final liver samples for the group of patients in whom the resection size was at least 50%. For smaller resections, the increased activity was not observed. The increased activity did not correlate with the age of the patient or with the time between the start of resection and the end of the operation. There was, however, a negative correlation between plasminogen activator activity and the time for which blood supply to the liver was clamped. Conclusions Our findings are in accordance with those from experimental animal models and show, for the first time, that rapid increases in plasminogen activator activity can occur following similarly large liver resection in humans. Thus, increases in plasminogen activator activity are an early event in the remnant liver following major liver resection in man. Our observations provide support for the contention that increases in plasminogen activators play a key role in the initiation of hepatic regeneration in man

Statistics of Bubble Rearrangements in a Slowly Sheared Two-dimensional Foam

Many physical systems exhibit plastic flow when subjected to slow steady shear. A unified picture of plastic flow is still lacking; however, there is an emerging theoretical understanding of such flows based on irreversible motions of the constituent ``particles'' of the material. Depending on the specific system, various irreversible events have been studied, such as T1 events in foam and shear transformation zones (STZ's) in amorphous solids. This paper presents an experimental study of the T1 events in a model, two-dimensional foam: bubble rafts. In particular, I report on the connection between the distribution of T1 events and the behavior of the average stress and average velocity profiles during both the initial elastic response of the bubble raft and the subsequent plastic flow at sufficiently high strains

Decoupling control technology for medium STOL transports

The advanced control technology is considered that is necessary to cope with the medium STOL transport landing problem and, in particular, the necessity to decouple with active control techniques. It is shown that the need to decouple is independent of the powered lift concept but that the provisioning for decoupling is most greatly dependent on the preassumed piloting technique. The implications of decoupling and active control techniques with respect to pilot technique options, handling quality criteria, flight control mechanization, and the use of piloted simulation as a design tool, are also discussed

Quantifying the Infilling of Mekong Floodplains in Cambodia using DEM Differencing

Global sand and gravel (aggregate) extraction is changing landscapes, with 29,375x106m3 to 36,875x106m3 globally mined each year (Steinberger et al, 2010). Rapid economic development in South East Asia has markedly driven demand for sand in the Mekong River basin (Hackney et al, 2019). The Mekong River, a convenient source of high-quality aggregate, is the main source of sediment in the region (Kondolf, 1994; Bravard et al, 2013). Aggregate is used in the burgeoning construction industry, reclamation projects, and infilling of land along the Mekong’s low-lying floodplains (Pierdet, 2008; Doyle, 2012; Mailhe et al, 2019). Questionnaire-based research found all countries that the Mekong flows through extracted material during 2010-11, of these Cambodia extracted the largest volume of at least 21x106m3yr-1 of Mekong River sediment (Bravard et al, 2013). However, the study timeframe was limited, and specific destinations of this sand were not mapped or quantified with field measurements. This research develops differencing methods that tie the datasets together to facilitate direct comparisons between the 2000 (NASADEM) and 2013 (TanDEM-X) global elevation DEMs, a promising new approach that could be applied globally. For the Cambodia study area over 183±18 x106 m3 of floodplain infill (FPI) occurred, identifying FPI the likely biggest demand for sand along the Cambodian Mekong River. Timing of FPI can be determined with annual high-resolution imagery, with peak infill activity occurring between 2010 and 2011. FPI volumes measured in this period were over 4±2x106m3 greater than estimates of sediment extraction from the Mekong during 2011 (Bravard et al, 2013). FPI decreases flood risk, bringing economic and social advantages to property owners in the basin (Pierdet, 2008). But rising demand for sand in the basin has caused local channel changes and a sediment deficit being supplied to the delta, causing delta retreat and flooding, which has displaced people (Orr et al, 2012; Jordan et al, 2019). The timing and enormous scale of FPI quantified in this paper can inform future frameworks and policies, and the novel techniques provide a pathway to expanding this research elsewhere

Direct simulation for a homogenous gas

A probabilistic analysis of the direct simulation of a homogeneous gas is given. A hierarchy of equations similar to the BBGKY hierarchy for the reduced probability densities is derived. By invoking the molecular chaos assumption, an equation similar to the Boltzmann equation for the single particle probability density and the corresponding H-theorem is derived

Interfacial friction between semiflexible polymers and crystalline surfaces

The results obtained from molecular dynamics simulations of the friction at an interface between polymer melts and weakly attractive crystalline surfaces are reported. We consider a coarse-grained bead-spring model of linear chains with adjustable intrinsic stiffness. The structure and relaxation dynamics of polymer chains near interfaces are quantified by the radius of gyration and decay of the time autocorrelation function of the first normal mode. We found that the friction coefficient at small slip velocities exhibits a distinct maximum which appears due to shear-induced alignment of semiflexible chain segments in contact with solid walls. At large slip velocities the decay of the friction coefficient is independent of the chain stiffness. The data for the friction coefficient and shear viscosity are used to elucidate main trends in the nonlinear shear rate dependence of the slip length. The influence of chain stiffness on the relationship between the friction coefficient and the structure factor in the first fluid layer is discussed.Comment: 31 pages, 12 figure