Real-time dynamics of open quantum spin systems driven by dissipative processes

We study the real-time evolution of large open quantum spin systems in two spatial dimensions, whose dynamics is entirely driven by a dissipative coupling to the environment. We consider different dissipative processes and investigate the real-time evolution from an ordered phase of the Heisenberg or XY model towards a disordered phase at late times, disregarding unitary Hamiltonian dynamics. The corresponding Kossakowski-Lindblad equation is solved via an efficient cluster algorithm. We find that the symmetry of the dissipative process determines the time scales, which govern the approach towards a new equilibrium phase at late times. Most notably, we find a slow equilibration if the dissipative process conserves any of the magnetization Fourier modes. In these cases, the dynamics can be interpreted as a diffusion process of the conserved quantity.

Cancer's positive flip side: posttraumatic growth after childhood cancer.

BACKGROUND Surviving childhood cancer may result in positive psychological changes called posttraumatic growth (PTG). Knowing about the possibility of positive changes may facilitate survivors' reintegration in daily life. We aimed to (1) describe PTG in Swiss childhood cancer survivors including the most and the least common PTG phenomena on the subscale and item levels and (2) determine factors associated with PTG. METHOD Within the Swiss Childhood Cancer Survivor Study (SCCSS), we sent two questionnaires to childhood cancer survivors registered in the Swiss Childhood Cancer Registry (SCCR). Eligible survivors were diagnosed after 1990 at age ≤16 years, survived ≥5 years, and were aged ≥18 years at the time the second questionnaire was sent. We included the Posttraumatic Growth Inventory (PTGI) to assess five areas of PTG. We investigated the association of PTG with socio-demographic characteristics, self-reported late effects, and psychological distress, which were assessed in the SCCSS and clinical variables extracted from the SCCR. We used descriptive statistics to describe PTG and linear regressions to investigate factors associated with PTG. RESULTS We assessed PTG in 309 childhood cancer survivors. Most individuals reported to have experienced some PTG. The most endorsed change occurred in "relation with others," the least in "spiritual change." PTG was significantly higher in survivors with older age at diagnosis (p = 0.001) and those with a longer duration of treatment (p = 0.042), while it was lower in male survivors (p = 0.003). CONCLUSIONS Supporting experiences of PTG during follow-up may help survivors successfully return to daily life.

Street crossing behavior in younger and older pedestrians: an eye- and head-tracking study

BACKGROUND: Crossing a street can be a very difficult task for older pedestrians. With increased age and potential cognitive decline, older people take the decision to cross a street primarily based on vehicles' distance, and not on their speed. Furthermore, older pedestrians tend to overestimate their own walking speed, and could not adapt it according to the traffic conditions. Pedestrians' behavior is often tested using virtual reality. Virtual reality presents the advantage of being safe, cost-effective, and allows using standardized test conditions. METHODS: This paper describes an observational study with older and younger adults. Street crossing behavior was investigated in 18 healthy, younger and 18 older subjects by using a virtual reality setting. The aim of the study was to measure behavioral data (such as eye and head movements) and to assess how the two age groups differ in terms of number of safe street crossings, virtual crashes, and missed street crossing opportunities. Street crossing behavior, eye and head movements, in older and younger subjects, were compared with non-parametric tests. RESULTS: The results showed that younger pedestrians behaved in a more secure manner while crossing a street, as compared to older people. The eye and head movements analysis revealed that older people looked more at the ground and less at the other side of the street to cross. CONCLUSIONS: The less secure behavior in street crossing found in older pedestrians could be explained by their reduced cognitive and visual abilities, which, in turn, resulted in difficulties in the decision-making process, especially under time pressure. Decisions to cross a street are based on the distance of the oncoming cars, rather than their speed, for both groups. Older pedestrians look more at their feet, probably because of their need of more time to plan precise stepping movement and, in turn, pay less attention to the traffic. This might help to set up guidelines for improving senior pedestrians' safety, in terms of speed limits, road design, and mixed physical-cognitive trainings.