Nonequilibrium Magnetization Dynamics of Nickel

Ultrafast magnetization dynamics of nickel has been studied for different degrees of electronic excitation, using pump-probe second-harmonic generation with 150 fs/800 nm laser pulses of various fluences. Information about the electronic and magnetic response to laser irradiation is obtained from sums and differences of the SHG intensity for opposite magnetization directions. The classical M(T)-curve can be reproduced for delay times larger than the electron thermalization time of about 280 fs, even when electrons and lattice have not reached thermal equilibrium. Further we show that the transient magnetization reaches its minimum approx. 50 fs before electron thermalization is completed.Comment: 8 pages, 5 figures, revte

Social Media Behaviors and Experiences During the COVID-19 Pandemic: Associations With Anxiety, Depression, and Stress

The majority of research concerning public health crises and social media platforms has focused on analyzing the accuracy of information within social media posts. The current exploratory study explored social media users’ specific social media behaviors and experiences during the early weeks of the COVID-19 pandemic and whether these behaviors and experiences related to anxiety, depression, and stress. Data were collected March 21–31, 2020 from adults in the United States (N = 564) through snowball sampling on social media sites and Prime Panels. Online surveys included questions regarding social media use during the pandemic and the Depression Anxiety and Stress Scales (DASS). Forward stepwise modeling procedures were used to build three models for anxiety, stress, and depression. Participants who actively engaged with COVID-19 social media content were more likely to experience higher anxiety. Those who had emotional experiences via social media and used social media to connect during the pandemic were susceptible to higher levels of stress and depression. The current study suggests that during the pandemic specific behaviors and experiences via social media were related to anxiety, stress, and depression. Thus, limiting time spent on social media during public health crises may protect the mental health of individuals

Understanding Cultural Perceptions of Health in Middle School Females for Obesity Prevention: A Case Study

The purpose of this study was to understand acculturation and race/ethnicity influences in the home and school environment that affect physical activity and nutrition in female adolescents attending middle school. A convenience sample of eight female adolescents (n = 2 Asian American, n = 2 Black, n =2 Latinx/Hispanic, and n = 2 White) was interviewed individually via Zoom. Responses regarding acculturation, physical activity, and nutrition in the home and school environment were analyzed using qualitative case study analysis. Three themes were identified: 1) experiences related to home, health, and culture, 2) the intersection between school meals and personal culture, and 3) the intersection between school physical activity and personal culture. Study findings can inform policies on school nutrition and physical activity and lead to opportunities for students and families to collaborate with schools to improve adolescent health

Simple theory for spin-lattice relaxation in metallic rare earth ferromagnets

The spin-lattice relaxation time $\tau_{SL}$ is a key quantity both for the dynamical response of ferromagnets excited by laser pulses and as the speed limit of magneto-optical recording. Extending the theory for the electron paramagnetic resonance of magnetic impurities to spin-lattice relaxation in ferromagnetic rare earths we calculate $\tau_{SL}$ for Gd and find a value of 48 ps in very good agreement with time-resolved spin-polarized photoemission experiments. We argue that the time scale for $\tau_{SL}$ in metals is essentially given by the spin-orbit induced magnetocrystalline anisotropy energy.Comment: 18 pages revtex, 5 uuencoded figure

Ultrafast Spin Dynamics in Nickel

The spin dynamics in Ni is studied by an exact diagonalization method on the ultrafast time scale. It is shown that the femtosecond relaxation of the magneto-optical response results from exchange interaction and spin-orbit coupling. Each of the two mechanisms affects the relaxation process differently. We find that the intrinsic spin dynamics occurs during about 10 fs while extrinsic effects such as laser-pulse duration and spectral width can slow down the observed dynamics considerably. Thus, our theory indicates that there is still room to accelerate the spin dynamics in experiments.Comment: 4 pages, Latex, 4 postscript figure

Nonlinear Magneto-Optical Response of ss- and dd-Wave Superconductors

The nonlinear magneto-optical response of $s$- and $d$-wave superconductors is discussed. We carry out the symmetry analysis of the nonlinear magneto-optical susceptibility in the superconducting state. Due to the surface sensitivity of the nonlinear optical response for systems with bulk inversion symmetry, we perform a group theoretical classification of the superconducting order parameter close to a surface. For the first time, the mixing of singlet and triplet pairing states induced by spin-orbit coupling is systematically taken into account. We show that the interference of singlet and triplet pairing states leads to an observable contribution of the nonlinear magneto-optical Kerr effect. This effect is not only sensitive to the anisotropy of the gap function but also to the symmetry itself. In view of the current discussion of the order parameter symmetry of High-T$_c$ superconductors, results for a tetragonal system with bulk singlet pairing for various pairing symmetries are discussed.Comment: 21 pages (REVTeX) with 8 figures (Postscript

Ultrafast spin dynamics and critical behavior in half-metallic ferromagnet : Sr_2FeMoO_6

Ultrafast spin dynamics in ferromagnetic half-metallic compound Sr_2FeMoO_6 is investigated by pump-probe measurements of magneto-optical Kerr effect. Half-metallic nature of this material gives rise to anomalous thermal insulation between spins and electrons, and allows us to pursue the spin dynamics from a few to several hundred picoseconds after the optical excitation. The optically detected magnetization dynamics clearly shows the crossover from microscopic photoinduced demagnetization to macroscopic critical behavior with universal power law divergence of relaxation time for wide dynamical critical region.Comment: 14 pages, 4 figures. Abstract and Figures 1 & 3 are correcte

Active children through individual vouchers – evaluation (ACTIVE): protocol for a mixed method randomised control trial to increase physical activity levels in teenagers

BackgroundMany teenagers are insufficiently active despite the health benefits of physical activity (PA). There is strong evidence to show that inactivity and low fitness levels increase the risk of non-communicable diseases such as coronary heart disease (CHD), type 2 diabetes and breast and colon cancers (Lee et al. Lancet 380:219–29, 2012). A major barrier facing adolescents is accessibility (e.g. cost and lack of local facilities). The ACTIVE project aims to tackle this barrier through a multi-faceted intervention, giving teenagers vouchers to spend on activities of their choice and empowering young people to improve their fitness and PA levels.DesignACTIVE is a mixed methods randomised control trial in 7 secondary schools in Swansea, South Wales. Quantitative and qualitative measures including PA (cooper run test (CRT), accelerometery over 7 days), cardiovascular (CV) measures (blood pressure, pulse wave analysis) and focus groups will be undertaken at 4 separate time points (baseline, 6 months,12 months and follow-up at 18 months). Intervention schools will receive a multi-component intervention involving 12 months of £20 vouchers to spend on physical activities of their choice, a peer mentor scheme and opportunities to attend advocacy meetings. Control schools are encouraged to continue usual practice. The primary aim is to examine the effect of the intervention in improving cardiovascular fitness.DiscussionThis paper describes the protocol for the ACTIVE randomised control trial, which aims to increase fitness, physical activity and socialisation of teenagers in Swansea, UK via a voucher scheme combined with peer mentoring. Results can contribute to the evidence base on teenage physical activity and, if effective, the intervention has the potential to inform future physical activity interventions and policy

Social media for health promotion and weight management: A critical debate

© 2018 The Author(s). Background: In 2016 an estimated 1.9 billion adults world-wide were either overweight or obese. The health consequences of obesity are responsible for 2.8 million preventable deaths per year. The WHO now considers obesity as a global epidemic and recommends population-wide health promotion strategies to address this issue. Weight gain is caused by increased energy intake and physical inactivity, so treatment should focus on changes to behaviour regarding diet and physical activity. Discussion: The WHO has also recognised the importance of social resources as a valuable agent for behaviour change in health promotion. Social resources are translated at the community level as support provided by significant others such as family, partners and peers, in the form of information, material aid and encouragement. Social support has been shown to improve health and well-being, whereas social isolation has been shown to have a negative impact on health outcomes. Social support provided by peers has been shown to be a useful strategy to employ in weight management programmes. The documented increased use of ICT and social media has presented health promoters with a potentially useful medium to increase social support for weight management. Conclusion: While the use of social media for health promotion is an emerging field of investigation, preliminary research suggests that it increases participant engagement, and may provide a cost-effective tool to provide social support for individuals participating in weight management programmes. With stringent privacy protocols in place, social media may be a useful, cost-effective accompaniment to multifactorial weight management programmes. However more research is needed to identify how to make the best use of social media as health promotion tool