Initial stage of the 2D-3D transition of a strained SiGe layer on a pit-patterned Si(001) template

We investigate the initial stage of the 2D-3D transition of strained Ge layers deposited on pit-patterned Si(001) templates. Within the pits, which assume the shape of inverted, truncated pyramids after optimized growth of a Si buffer layer, the Ge wetting layer develops a complex morphology consisting exclusively of {105} and (001) facets. These results are attributed to a strain-driven step-meandering instability on the facetted side-walls of the pits, and a step-bunching instability at the sharp concave intersections of these facets. Although both instabilities are strain-driven, their coexistence becomes mainly possible by the geometrical restrictions in the pits. It is shown that the morphological transformation of the pit surface into low-energy facets has strong influence on the preferential nucleation of Ge islands at the flat bottom of the pits.Comment: 19 pages, 7 figure

Time to Smile: How Onset Asynchronies Between Reciprocal Facial Expressions Influence the Experience of Responsiveness of a Virtual Agent

Human social interactions are highly coordinated in time and involve the reciprocal exchange of facial emotional expressions. While timing has been identified as an important factor in social communication via gaze or speech, so far there has been no systematic investigation on how the temporal delays in the exchange of facial emotional expressions between interactive partners influence the experience of responsiveness. In the present study, 40 participants were cued to direct a facial emotional expression (angry or happy) towards a virtual agent in front of them and the virtual agent would then react with a congruent facial expression. The temporal delay between the cue and the reaction was manipulated as an independent variable. Exact delays between facial expressions were determined based on the onset latencies of participants’ facial expressions measured via facial EMG (M. Zygomaticus and M. Corrugator). Ratings of experienced responsiveness of the virtual agent were collected as a dependent measure. Using a linear mixed effect model in a growth curve analysis revealed that experienced responsiveness peaked at delays around 700 ms. Moreover, experienced responsiveness at shorter temporal delays was higher when happy versus angry facial expressions were exchanged, while the reversed pattern was found at longer delays. Our results demonstrate a crucial role of timing in non-verbal communication, suggesting that temporal relations between facial expressions are processed as social information. Furthermore, our results can inform the implementation of virtual social interactions

Valley splitting of Si/SiGe heterostructures in tilted magnetic fields

We have investigated the valley splitting of two-dimensional electrons in high quality Si/Si$_{1-x}$Ge$_x$ heterostructures under tilted magnetic fields. For all the samples in our study, the valley splitting at filling factor $\nu=3$ ($\Delta_3$) is significantly different before and after the coincidence angle, at which energy levels cross at the Fermi level. On both sides of the coincidence, a linear density dependence of $\Delta_3$ on the electron density was observed, while the slope of these two configurations differs by more than a factor of two. We argue that screening of the Coulomb interaction from the low-lying filled levels, which also explains the observed spin-dependent resistivity, is responsible for the large difference of $\Delta_3$ before and after the coincidence.Comment: REVTEX 4 pages, 4 figure

Public speaking training in front of a supportive audience in Virtual Reality improves performance in real-life

Public speaking is a challenging task that requires practice. Virtual Reality allows to present realistic public speaking scenarios in this regard, however, the role of the virtual audience during practice remains unknown. In the present study, 73 participants completed a Virtual Reality practice session while audience was manipulated to be supportive or unsupportive or presentations were practiced without audience. Importantly, following the virtual practice, participants held the presentation during a real university course via Zoom. We measured emotional experience, self-efficacy, and the subjective evaluation of performance at baseline, after VR practice, and after the real presentation. Additionally, participants’ performance in the real presentation was evaluated by instructors (blinded to condition). Supportive in contrast to unsupportive audiences led to more positive believes about one’s own performance, while there were no changes in beliefs in the group without audience. Importantly, practice in front of a supportive compared to unsupportive audience resulted in a more positive evaluation of speaker confidence in real-life public speaking as rated by the instructors. These results demonstrate an impact of virtual social feedback during public speaking on subsequent subjective performance evaluation. This may increase self-confidence resulting in actual improved public speaking performance in real-life

Transient-Enhanced Surface Diffusion on Natural-Oxide-Covered Si(001) Templates during Vacuum Annealing

We report on the transient-enhanced shape transformation of nano-structured Si(001) surfaces upon in vacuo annealing at relatively low temperatures of 900 -950 °C for a few minutes. We find dramatic surface mass transport concomitant with the development of low-energy facets on surfaces that are covered by native oxide. The enhanced surface mass transport ceases after the oxide is completely desorbed, and it is not observed on surfaces where the native oxide had been removed by HF before annealing

Face masks reduce interpersonal distance in virtual reality

During the COVID-19 pandemic several behavioral measures have been implemented to reduce viral transmission. While these measures reduce the risk of infections, they may also increase risk behavior. Here, we experimentally investigate the influence of face masks on physical distancing. Eighty-four participants with or without face masks passed virtual agents in a supermarket environment to reach a target while interpersonal distance was recorded. Agents differed in wearing face masks and age (young, elderly). In addition, situational constraints varied in whether keeping a distance of 1.5 m required an effortful detour or not. Wearing face masks (both self and other) reduced physical distancing. This reduction was most prominent when keeping the recommended distance was effortful, suggesting an influence of situational constraints. Similarly, increased distances to elderly were only observed when keeping a recommended distance was effortless. These findings highlight contextual constraints in compensation behavior and have important implications for safety policies

Dependent self-employment: workers between employment and self-employment in the UK

Analysing the British Labour Force Survey, we highlight that dependent self-employed workers constitute a group distinct from both employees and independent self-employed workers in the labour market group. Dependent self-employed workers show characteristics of a more volatile labour market attachment than employed or self-employed workers. We provide empirical evidence that dependent self-employed workers are rather pushed than pulled into this labour market status, making dependent self-employment an example of 'necessity' rather than 'opportunity' entrepreneurship. Although data limitations only allow a limited longitudinal analysis, we provide evidence that the majority of dependent self-employed workers remain in the labour market in the short run - either as self-employed or employed - and that only few leave the labour market. In addition, dependent self-employment does not create jobs for others; in our data, dependent self-employed individuals stop being dependent and self-employed because they increase their customer base or return to paid employment

The Society for Microelectronics -Annual Report 2003 Spin Relaxation in Si Quantum Wells Suppressed by an Applied Magnetic Field

We investigate spin properties of the two-dimensional electron gas in Si quantum wells defined by SiGe barriers. We find, in contrast to predictions of the classical model of D'yakonov-Perel, a strong anisotropy of spin relaxation and a decrease of the spin relaxation rate with increasing electron mobility. We show that for high electron mobility the cyclotron motion causes an additional modulation of spin-orbit coupling which leads to an effective suppression of spin relaxation rate. In spintronics, the aim is to make use of the spin degrees of freedom in addition to the electronic ones. Therefore, spintronic devices based on spins of carriers in semiconductors appear particularly promising. In such elements carriers can be easily moved by applying external voltages, the well known tool of classical electronics. The utilization of spin properties, however, usually is limited by the fast spin relaxation of conduction electrons. Therefore analysis of the spin relaxation mechanisms and the search for a suitable material and optimum conditions are of primary interest in this field. In III-V compounds the spin relaxation time is below one nanosecond [1]. Silicon based devices, due to much weaker spin-orbit coupling, appear much more promising. 2D Si layers in Si/SiGe structures exhibit a spin relaxation time of the order of a few microseconds by measurements of electron spin resonance (ESR) [2] - The effect of BR coupling on spin, σ, of a conduction electron can be described by an effective magnetic field, B BR . This field is oriented in-plane and perpendicular to electron momentum, ħk. The resulting zero field splitting is given by: The direction of the BR field depends on the direction of electron k-vector, and therefore the spread of k-vectors results in a spread of the BR field. Consequently, the ESR resonance is shifted and broadened. Momentum scattering, described by a rate 1/τ k , causes a modulation of the BR field in time which leads to the so called D'yakonovPerel (DP) spin relaxatio

Interpersonal Distance During Real-Time Social Interaction: Insights From Subjective Experience, Behavior, and Physiology

Physical distance is a prominent feature in face-to-face social interactions and allows regulating social encounters. Close interpersonal distance (IPD) increases emotional responses during interaction and has been related to avoidance behavior in social anxiety. However, a systematic investigation of the effects of IPD on subjective experience combined with measures of physiological arousal and behavioral responses during real-time social interaction has been missing. Virtual Reality allows for a controlled manipulation of IPD while maintaining naturalistic social encounters. The present study investigates IPD in social interaction using a novel paradigm in Virtual Reality. Thirty-six participants approached virtual agents and engaged in short interactions. IPD was varied between 3.5 and 1 m by manipulating the distance at which agents reacted to the participant's approach. Closer distances were rated as more arousing, less pleasant, and less natural than longer distances and this effect was significantly modulated by social anxiety scores. Skin conductance responses were also increased at short distances compared to longer distances. Finally, an interaction of IPD and social anxiety was observed for avoidance behavior, measured as participants' backward motion during interaction, with stronger avoidance related to close distances and high values of social anxiety. These results highlight the influence of IPD on experience, physiological response, and behavior during social interaction. The interaction of social anxiety and IPD suggests including the manipulation of IPD in behavioral tests in Virtual Reality as a promising tool for the treatment of social anxiety disorder

Look at the Audience? A Randomized Controlled Study of Shifting Attention From Self-Focus to Nonsocial vs. Social External Stimuli During Virtual Reality Exposure to Public Speaking in Social Anxiety

Background: Enhanced self-focused attention plays a central role in the maintenance and treatment of Social Anxiety and is targeted in contemporary cognitive behavioral therapy. Actual developments use Virtual Reality (VR) for behavioral training. However, no VR attention training combining exposure to public speaking with shifting attention from self-focus to external focus has been investigated, and no experimental evidence exists on different kinds of external cues as targets of attention. Therefore, we investigated the effects of an attention training during public speaking in VR and examined differential effects of an external focus on nonsocial vs. social stimuli. Methods: In this randomized controlled study, highly socially anxious participants were instructed to focus on either objects or the audience within a virtual speech task. We assessed the pre-post effects on affective reactions, self-perception, and attentional processes during public speaking as well as general Social Anxiety using subjective, physiological, and eye-tracking measures. Repeated-measures analyses of variance (ANOVAs) were calculated to detect changes from pretest to posttest over both groups, and time × group interaction effects. Results: Within the analysis sample (n = 41), anxiety during public speaking and fear of negative evaluation significantly decreased, with no significant differences between groups. No significant time effect, but a significant time × group effect, was found for the looking time proportion on the audience members' heads. Follow-up tests confirmed a significant increase in the social-focus group and a significant decrease in the nonsocial-focus group. For all other variables, except external focus and fear of public speaking, significant improvements were found over both groups. Further significant time x group effects were found for positive affect during public speaking, with a significant increase in the social focus, and no significant change in the nonsocial-focus group. Conclusion: Our findings suggest that attention training to reduce self-focus can be successfully conducted in VR. Both training versions showed positive short-term effects in the highly socially anxious, with particular advantages of an external social focus concerning eye contact to the audience and positive affect. Further research should investigate whether social focus is even more advantageous long term and if reinterpretations of dysfunctional beliefs could be achieved by not avoiding social cues