Numerical simulations of phenomena observed at hot microelectrodes: Inlaid microdisk

In this paper we describe numerical simulations of a number of physico-chemical phenomena observed at disk microelectrodes polarized with a high frequency ac waveform. These phenomena include resistive heating of an electrolyte solution surrounding a microelectrode, electrothermal flow of the solution and electrochemical mass transport of dissolved redox species. The main purpose of doing these simulations was to provide the required theoretical background to the previously obtained experimental data. It is shown that the simulated linear flow rate of the solution is proportional to the voltage across the solution resistance in the power four and inversely proportional to the radius of the microelectrode. Thus this supports the idea that the convection at hot microelectrodes is driven primarily by the electrothermal flow. Simulations of the Faradaic current agree semi-quantitatively with the experimental observations. We have identified possible reasons for the observed discrepancy between the two sets of data.     

Fatigue, sleep loss, and confidence in judgment.

Sixty-four adults participated in a study examining the accuracy of metacognitive judgments during 28 hr of sleep deprivation (SD) and continuous cognitive work. Three tasks were studied (perceptual comparison, general knowledge, and mental addition), collectively spanning a range of cognitive abilities and levels of susceptibility to SD. Subjective and objective measures of sleepiness confirmed the expected patterns of increasing fatigue with SD. Participants displayed differing levels of metacognitive abilities across tasks, but traditional indices of the confidence-accuracy relation (i.e., calibration, resolution, over- and underconfidence), as well as the accuracy of pre- and posttask estimates of performance, remained stable over the SD period. The findings suggest that people can accurately assess their own cognitive performance when deprived of 1 night of sleep and that this ability need not be based on subjective estimates of sleepiness. The implications and limitations of the study are discussed and directions for future research are proposed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cyclic chronopotentiometry as a detection tool for flowing solution systems

Cyclic chronopotentiometry provides a very simple detection method, which may be particularly useful in capillary electrophoresis (CE) and microseparation systems. It has been shown that for disk microelectrodes it is possible to define safe reduction and oxidation currents that would never lead to the formation of H2 or O2 gas bubbles, even if they are applied for an indefinitely long time period. During end-column CE detection, currents passing through the working microelectrode can be completely controlled by the external electronic circuit and they are not affected by the separation current. Consequently, problems created by the offset potential in CE can be completely eliminated. The detection can be accomplished through a variety of different mechanisms; however, generation of the electrode response as a result of analyte adsorption seems to be most common. The method is applicable to many analytes, which do not have to be electroactive. The analytical signal is obtained by monitoring the change in the average electrode potential (calculated for either a cathodic or an anodic half-cycle) caused by an analyte interacting with the electrode. The analytical signal is proportional to the analyte concentration, within a concentration range extending over approximately 2 orders of magnitude.     

Dielectrophoretic and electrothermal effects at alternating current heated disk microelectrodes

When a disk microelectrode is polarized with an alternating potential of very high frequency (0.1-2 GHz) and a high amplitude (up to 2.8 V rms), the electrode is heated up, and at the same time, a very intense electric field is created around the electrode (>10(6) V/m for electrodes 1 microm in radius). This strong electric field gives rise to positive or negative dielectrophoretic effects. Positive dielectrophoretic effects can be used to assemble nanowires from nanoparticles at the electrode edge. On the other hand, a negative dielectrophoretic effect is probably responsible for "jet boiling" observed at overheated microelectrodes. In addition, a combination of a high temperature gradient and a high potential gradient generates an intense electrothermal flow of solution which very strongly enhances the mass transport and is responsible for intense convection in such systems. The electrothermal flow and dielectrophoretic forces can be generated directly on a microelectrode employed in electrochemical detection because the high frequency ac polarization of the electrode does not interfere with the acquisition of analytical signals.     

Testing architectures of the decision–confidence relation.

Two experiments examined the effect of rendering confidence judgments on the properties of the comparative decision process. In Exp 1, participants worked for 12 sessions that required 2-alternative perceptual, line-length comparisons. For sessions 1–4 and sessions 9–12, confidence judgments were not required. For sessions 5–8, participants provided confidence reports following each comparative judgment. The requirement of confidence judgments significantly increased decisional response time, suggesting that some confidence processing occurs in parallel with the primary decision process. Concomitantly, an examination of the properties of the time to determine confidence during sessions 5–8 revealed clear evidence of postdecisional confidence processing. These results were replicated in a 2nd experiment requiring 2 alternative comparative judgments of Canadian city populations. The authors conclude that confidence processing occurs both during the decision process and postdecisionally, and discuss the implications of the present findings for current theories of confidence in human judgment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adsorption-based electrochemical detection of nonelectrochemically active analytes for capillary electrophoresis

A sensitive electrochemical detection method (ECD) for capillary electrophoresis has been developed that is applicable to a much wider range of analytes than more conventional ECD methods. Using a modified Osteryoung square-wave voltammetry method, the adsorption of what are normally considered nonelectrochemically active analytes onto a platinum electrode was found to produce a concentration-proportional response. Although the mechanisms that cause this response may be complex, it appears that it is due to changes in the electrode/solution interface that accompany adsorption of the analyte onto the electrode rather than a simple redox process. Analytes that possess pi-electron density appeared to chemisorb rather than only physically adsorb onto the electrode and gave the best response with detection limits of < 10(-8) M while maintaining good linearity. Because this detection method requires only that the analyte adsorb onto the electrode, it has the advantage of much wider applicability than previously reported electrochemical detection methods. The applicability of this detection method was investigated for a variety of analytes and background electrolyte conditions (varied pH, ionic strength, buffer additives). Comparisons of the sensitivity of this method to UV detection showed that, even for analytes that have good UV chromophores, sensitivities greater than 1 order of magnitude were obtained using adsorption-based electrochemical detection.     

On the utility of experiential cross-training for team decision-making under time stress

This study investigated the effectiveness of experiential cross-training in a team context for team decision-making under time stress in a simulated naval surveillance task. It was hypothesized that teams whose members explicitly experience all team positions will perform better under time pressure due to a better shared Team Interaction Model (Cannon-Bowers et al. 1993). In addition, it was posited that experiential cross-training would reduce the negative effect of member reconfiguration that can occur in certain military situations. Three groups of teams participated in this study (cross-trained, reconfigured and control). The experiment involved three team training sessions, followed by three time-stressed exercise sessions. During training, one group of teams was cross-trained (CT) by asking each member to perform an entire session at each of the three team positions. Member reconfiguration (where each member was shifted to another's position) was unexpectedly introduced at the first of the exercise sessions for the CT group and for another group (reconfigured) that had not been cross-trained. A third (control) group was neither cross-trained nor reconfigured. During training, the performance of non-CT teams improved more quickly than that of CT teams. During the exercise, the CT group did not achieve the level of performance of the control teams. The immediate effect of team member reconfiguration was to degrade performance significantly for the non-CT teams, but not for CT teams. The findings are discussed in terms of the multiple mental models' view of team performance (Cannon-Bowers et al. 1993) and the authors discuss the relative utility of cross-training when overall training time is fixed.     

Options for liferaft entry after helicopter ditching

METHOD: Dry and wet evacuations were conducted by 24 male and 19 female subjects from the Nutec Super Puma Simulator into two different types of aviation liferaft. RESULTS: Dry evacuation on the windward side is the method of choice. The non-canopy raft is subjectively and objectively easier to enter both from the helicopter and the sea. CONCLUSIONS: The non-canopy raft is the raft of choice, the canopy raft needs a redesign to ensure that it always inflates the correct way and both rafts need a redesign of the painter anchor point. Aircrew should have special training in open water after traditional pool training. A helicopter ditching survival compass has been developed for training all who fly over water for a living.     

On the calibration of knowledge and perception

This study examined confidence judgements (i.e., calibration, resolution, and over/underconfidence) and response times in an intellectual knowledge task and a perceptual task requiring location comparisons. At each of four levels of judgement difficulty (i.e., Easy, Hard, Impossible and Misleading/Illusory), very similar properties were evident in the two tasks. The results are inconsistent with theories that assume a fundamentally different basis for confidence in human knowledge and perception.