Modulating proactive cognitive control by reward:Differential anticipatory effects of performance contingent and non-contingent rewards

The present study investigated the influences of two different forms of reward presentation in modulating cognitive control. In three experiments, participants performed a flanker task for which one-third of trials were precued for a chance of obtaining a reward (reward trials). In Experiment 1, a reward was provided if participants made the correct response on reward trials, but a penalty was given if they made an incorrect response on these trials. The anticipation of this performance-contingent reward increased response speed and reduced the flanker effect, but had little influence on the sequential modulation of the flanker effect after incompatible trials. In Experiment 2, participants obtained a reward randomly on two-thirds of the precued reward trials and were given a penalty on the remaining one-third, regardless of their performance. The anticipation of this non-contingent reward had little influence on the overall response speed or flanker effect, but reduced the sequential modulation of the flanker effect after incompatible trials. Experiment 3 also used performance non-contingent rewards, but participants were randomly penalized more often than they were rewarded; non-contingent penalty had little influence on the sequential modulation of the flanker effect. None of the three experiments showed a reliable influence of the actual acquisition of rewards on task performance. These results indicate anticipatory effects of performance-contingent and non-contingent rewards on cognitive control with little evidence of aftereffects

Controlled low-temperature growth of carbon nanofibres by plasma deposition

Vertically aligned carbon nanofibres were grown at temperatures as low as 120degreesC by plasma-enhanced chemical vapour deposition (PECVD). A systematic study of the temperature dependence of the growth rate found an activation energy of 0.23 eV, much less than that for thermal chemical vapour deposition (1.2-1.5 eV). This suggests that growth occurs by surface diffusion of carbon on nickel. Vertically aligned carbon nanofibres were grown by PECVD on to flexible plastic substrates. We show that individual lines and dots of free-standing 20-50 nm diameter nanotubes can be grown on to chromium-covered polyimide foil. The scalable deposition method allows large-area coverage without damaging or bending the sensitive substrate material. Field-emission cathodes were made for the purpose of demonstration

Low-temperature growth of carbon nanotubes by plasma-enhanced chemical vapor deposition

Vertically aligned carbon nanotubes were grown at temperatures as low as 120degreesC by plasma-enhanced chemical vapor deposition. A systematic study of the temperature dependence of the growth rate and the structure of the as-grown nanotubes is presented using a C2H2/NH3 system and nickel as the catalyst. The activation energy for the growth rate was found to be 0.23 eV, much less than for thermal chemical vapor deposition (1.2-1.5 eV). This suggests growth occurs by surface diffusion of carbon on nickel. The result could allow direct growth of nanotubes onto low-temperature substrates like plastics, and facilitate the integration in sensitive nanoelectronic devices. (C) 2003 American Institute of Physics