Strain dependence of the acoustic properties of amorphous metals below 1K: Evidence for the interaction between tunneling states

We have conducted a thorough study of the acoustic properties between 10^-4 and 1 Kelvin for the amorphous metal Zr_x Cu_1-x (x=0.3 and x=0.4), by measuring the relative change of sound velocity dv/v and internal friction Q^-1 as a function of temperature and also of the applied strain, in both superconducting and normal state. We have found that when plotted versus the ratio of strain energy to thermal energy, all measurements display the same behavior: a crossover from a linear regime of ``independent'' tunneling systems at very low strains and/or high enough temperatures to a nonlinear regime where dv/v and Q^-1 depend on applied strain and the tunneling systems cannot be considered as independent.Comment: 4 pages, 4 figures (submitted to PRL

Cavitation of Electrons Bubbles in Liquid Helium Below saturation Pressure

We have used a Hartree-type electron-helium potential together with a density functional description of liquid $^4$He and $^3$He to study the explosion of electron bubbles submitted to a negative pressure. The critical pressure at which bubbles explode has been determined as a function of temperature. It has been found that this critical pressure is very close to the pressure at which liquid helium becomes globally unstable in the presence of electrons. It is shown that at high temperatures the capillary model overestimates the critical pressures. We have checked that a commonly used and rather simple electron-helium interaction yields results very similar to those obtained using the more accurate Hartree-type interaction. We have estimated that the crossover temperature for thermal to quantum nucleation of electron bubbles is very low, of the order of 6 mK for $^4$He.Comment: 22 pages, 9 figure

Passung zwischen Kompetenzen der Mitarbeiter und Anforderungen des Arbeitsplatzes als Prädiktor für Leistung über das Arbeitsleben

In modern work environments, employees need to flexibly adjust their abilities to an increasing complexity of their work place demands. We assumed that a fit between demands and individual abilities might positively influence work ability, job-related self-efficacy, and job satisfaction as important indicators of job performance. A misfit on the contrary, might have adverse effects and interfere with job performance measures. Linking to the demographic change, it is even more important to analyze if age has an impact on the association between fit or misfit and performance outcomes to reveal evidence for age specific intervention strategies. We asked 103 employees and 15 supervisors of a production company to rate individual abilities and work-place demands in the sensory, motor, and cognitive fields to identify associations between a fit/misfit and outcomes that influence job performance. Our analyses showed that a fit/misfit between subjectively perceived demands and abilities in motor control influenced job-related self-efficacy. This was particularly true for blue collar workers and for older employees. A fit/misfit between the supervisor- and employee-rated abilities to learn new tasks had a high impact on work ability. Both white and blue collar workers as well as middle aged and older employees were sensitive to this effect. A fit/misfit between employee- and supervisor rated ability to deal with high task complexity was not associated with job satisfaction over the entire group, but in white collar workers and older employees. We conclude that a fit/misfit between work abilities and demands as well as between self and supervisor ratings of the employees' abilities has to be constantly evaluated with regard to age and work type to maintain healthy and productive employees

Electron cyclotron heating can drastically alter reversed shear Alfvén eigenmode activity in DIII-D through finite pressure effects

A recent DIII-D experiment investigating the impact of electron cyclotron heating (ECH) on neutral beam driven reversed shear Alfvén eigenmode (RSAE) activity is presented. The experiment includes variations of ECH injection location and timing, current ramp rate, beam injection geometry (on/off-axis), and neutral beam power. Essentially all variations carried out in this experiment were observed to change the impact of ECH on AE activity significantly. In some cases, RSAEs were observed to be enhanced with ECH near the off-axis minimum in magnetic safety factor (), in contrast to the original DIII-D experiments where the modes were absent when ECH was deposited near . It is found that during intervals when the geodesic acoustic mode (GAM) frequency at is elevated and the calculated RSAE minimum frequency, including contributions from thermal plasma gradients, is very near or above the nominal TAE frequency (f TAE), RSAE activity is not observed or RSAEs with a much reduced frequency sweep range are found. This condition is primarily brought about by ECH modification of the local electron temperature (T e) which can raise both the local T e at as well as its gradient. A q-evolution model that incorporates this reduction in RSAE frequency sweep range is in agreement with the observed spectra and appears to capture the relative balance of TAE or RSAE-like modes throughout the current ramp phase of over 38 DIII-D discharges. Detailed ideal MHD calculations using the NOVA code show both modification of plasma pressure and pressure gradient at play an important role in modifying the RSAE activity. Analysis of the ECH injection near the case where no frequency sweeping RSAEs are observed shows the typical RSAE is no longer an eigenmode of the system. What remains is an eigenmode with poloidal harmonic content reminiscent of the standard RSAE, but absent of the typical frequency sweeping behavior. The remaining eigenmode is also often strongly coupled to gap TAEs. Analysis with the non-perturbative gyro fluid code TAEFL confirms this change in RSAE activity and also shows a large drop in the resultant mode growth rates