Efficient excitation and control of integrated photonic circuits with virtual critical coupling.

Critical coupling in integrated photonic devices enables the efficient transfer of energy from a waveguide to a resonator, a key operation for many applications. This condition is achieved when the resonator loss rate is equal to the coupling rate to the bus waveguide. Carefully matching these quantities is challenging in practice, due to variations in the resonator properties resulting from fabrication and external conditions. Here, we demonstrate that efficient energy transfer to a non-critically coupled resonator can be achieved by tailoring the excitation signal in time. We rely on excitations oscillating at complex frequencies to load an otherwise overcoupled resonator, demonstrating that a virtual critical coupling condition is achieved if the imaginary part of the complex frequency equals the mismatch between loss and coupling rate. We probe a microring resonator with tailored pulses and observe a minimum intensity transmission T = 0.11 in contrast to a continuous-wave transmission T = 0.58 , corresponding to 8 times enhancement of intracavity intensity. Our technique opens opportunities for enhancing and controlling on-demand light-matter interactions for linear and nonlinear photonic platforms.

Electron-Transparent Thermoelectric Coolers Demonstrated with Nanoparticle and Condensation Thermometry.

More efficient thermoelectric devices would revolutionize refrigeration and energy production, and low-dimensional thermoelectric materials are predicted to be more efficient than their bulk counterparts. But nanoscale thermoelectric devices generate thermal gradients on length scales that are too small to resolve with traditional thermometry methods. Here we fabricate, using single-crystal bismuth telluride (Bi2Te3) and antimony/bismuth telluride (Sb2-xBixTe3) flakes exfoliated from commercially available bulk materials, functional thermoelectric coolers (TECs) that are only 100 nm thick. These devices are the smallest TECs ever demonstrated by a factor of 104. After depositing indium nanoparticles to serve as nanothermometers, we measure the heating and cooling produced by the devices with plasmon energy expansion thermometry (PEET), a high-spatial-resolution, transmission electron microscopy (TEM)-based thermometry technique, demonstrating a ΔT = -21 ± 4 K from room temperature. We also establish proof-of-concept for condensation thermometry, a quantitative temperature-change mapping technique with a spatial precision of ≲300 nm.

The relationship between collective efficacy and precompetitive affect in rugby players: testing Bandura's model of collective efficacy.

This study extended research examining Bandura's (1997) proposed model of collective efficacy. Specifically, it examined the relationships between groups' collective efficacy and the precompetitive anxiety and affect they experienced. Prior to a competitive match 66 male Rugby Union footballers from 6 teams (2 university teams and 4 county league teams) completed a single-item measure of confidence in their team winning the forthcoming match, a 10-item measure of confidence in their team performing well in the forthcoming match, the modified Competitive State Anxiety Inventory-2, and the Positive and Negative Affect Schedule. Stepwise (forward) multiple regression analyses indicated that scores for collective efficacy accounted for only 6.3% of the variance in the intensities of cognitive state anxiety and only 22% of the variance in the positive affect experienced prior to the rugby match. The results indicate that concerns with the team's ability to win a match were associated with high cognitive state anxiety and that doubts regarding the team's ability to perform well were related to low positive affect. Given the magnitude of predicted variances, the findings seem to give some support to Bandura's proposal that the beliefs in collective efficacy of individuals engaged in a team task are related to precompetitive affective reactions and the experience of state anxiety.

The impact of collective efficacy beliefs on effort and persistence in a group task.

Collective efficacy is an important determinant of the motivation of individuals within groups, with increases in collective efficacy producing more effort in a task and greater persistence when faced with failure. To test hypotheses concerning the impact of collective efficacy on effort and persistence, participants (n = 22) were assigned to triads (consisting of the participant and two confederates) and performed three time trials on cycle ergometers. After trial 1, the participants were assigned to either a high or low collective efficacy condition, receiving appropriate bogus performance feedback. All groups received failure feedback after trial 2. Effort was assessed by performance time and maximum heart rate (HRmax) achieved during performance. A 2 (collective efficacy condition) x 3 (trials) analysis of variance with repeated measures on trials revealed significant interaction effects for both performance time and HRmax. Fisher's least significant difference post-hoc tests indicated that, following efficacy manipulation, groups low in collective efficacy significantly reduced both their performance time and HRmax, whereas groups high in collective efficacy maintained performance and HRmax. However, predictions concerning the impact of failure on persistence were not supported. Our results provide partial support for the role of collective efficacy in team sports.