A generalized Chudley-Elliott vibration-jump model in activated atom surface diffusion

Here the authors provide a generalized Chudley-Elliott expression for activated atom surface diffusion which takes into account the coupling between both low-frequency vibrational motion (namely, the frustrated translational modes) and diffusion. This expression is derived within the Gaussian approximation framework for the intermediate scattering function at low coverage. Moreover, inelastic contributions (arising from creation and annihilation processes) to the full width at half maximum of the quasi-elastic peak are also obtained.Comment: (5 pages, 2 figures; revised version

Quantum Markovian activated surface diffusion of interacting adsorbates

A quantum Markovian activated atom-surface diffusion model with interacting adsorbates is proposed for the intermediate scattering function, which is shown to be complex-valued and factorizable into a classical-like and a quantum-mechanical factor. Applications to the diffusion of Na atoms on flat (weakly corrugated) and corrugated-Cu(001) surfaces at different coverages and surface temperatures are analyzed. Quantum effects are relevant to diffusion at low surface temperatures and coverages even for relatively heavy particles, such as Na atoms, where transport by tunneling is absent.Comment: 6 pages, 4 figure

Two-bath model for activated surface diffusion of interacting adsorbates

The diffusion and low vibrational motions of adsorbates on surfaces can be well described by a purely stochastic model, the so-called interacting single adsorbate model, for low-moderate coverages (\theta \lesssim 0.12). Within this model, the effects of thermal surface phonons and adsorbate-adsorbate collisions are accounted for by two uncorrelated noise functions which arise in a natural way from a two-bath model based on a generalization of the one-bath Caldeira-Leggett Hamiltonian. As an illustration, the model is applied to the diffusion of Na atoms on a Cu(001) surface with different coverages.Comment: 7 pages, 3 figure

The relationship between perceived social support and psychological distress in carers of older relatives: A longitudinal cross-lagged analysis

BACKGROUND AND OBJECTIVES: Although a large body of research has examined the relationship between social support and psychological health of family carers of frail older people, the exact nature and direction of this relationship is not well understood with most research to date being cross-sectional. This longitudinal study explored the relationship between perceived social support and psychological distress in carers of older relatives. METHODS: We used data from two longitudinal cohorts which included a total of 332 family carers of frail older people. We used cross-lagged panel analysis to investigate the longitudinal association between perceived social support and carer psychological distress controlling for a number of covariates over time. RESULTS: Fully-adjusted Generalised Estimating Equations (GEE) and cross-lagged models indicated that higher social support was significantly associated with lower carer psychological distress over time (regression coefficient [B] = -0.178, standard error [SE] = 0.028), with levels of perceived social support exerting an effect on psychological distress rather than vice versa (β = 0.03, p = 0.32). LIMITATIONS: All observations were based on self-report data, and there may be other variables that may explain the results that we did not account for. DISCUSSION AND IMPLICATIONS: Our study finds that the directionality of the relationship appears to be from perceived social support to carer psychological distress suggesting that social support directly affects carer psychological health but not vice versa. This finding has important implications for the provision of social support interventions for carers of frail older people at risk of experiencing psychological distress

Quantum Zeno and anti-Zeno effects in surface diffusion of interacting adsorbates

Surface diffusion of interacting adsorbates is here analyzed within the context of two fundamental phenomena of quantum dynamics, namely the quantum Zeno effect and the anti-Zeno effect. The physical implications of these effects are introduced here in a rather simple and general manner within the framework of non-selective measurements and for two (surface) temperature regimes: high and very low (including zero temperature). The quantum intermediate scattering function describing the adsorbate diffusion process is then evaluated for flat surfaces, since it is fully analytical in this case. Finally, a generalization to corrugated surfaces is also discussed. In this regard, it is found that, considering a Markovian framework and high surface temperatures, the anti-Zeno effect has already been observed, though not recognized as such.Comment: 17 pages, 1 figur

The mediating role of sense of coherence on mental health outcomes in carers of older dependent relatives: a longitudinal study

Background: Sense of coherence (SOC) is an important protective factor for carer well‐being but research to date remains cross‐sectional, focusing primarily on the direct effects of SOC on carers’ mental health. The study's aim was to investigate the mediating role of SOC in the longitudinal relationship between caregiver strain and carers’ psychological health, and its stability over time. / Methods: Prospective longitudinal study conducted in Jaén (Spain) with a probabilistic sample of 132 carers of older people, with data collected at baseline and at one‐year follow‐up. We measured SOC, caregiver strain, anxiety and depressive symptoms, and several care recipient characteristics and intensity of care provided. We used multiple linear regression modelling and the Sobel test to analyse mediation effects. / Results: SOC was significantly negatively longitudinally associated with both anxiety (β= ‐0.38, p= 0.001) and depressive symptoms (β= ‐0.28, p= 0.023), after controlling for several confounders. SOC mediated both the relationship between caregiver strain and anxiety and caregiver strain and depressive symptoms (Sobel test; p< 0.001 for anxiety and p< 0.001 for depressive symptoms). Differences between baseline and one‐year follow‐up SOC scores were not statistically significant (p= 0.617). / Conclusions: SOC appears to buffer the impact of caregiver strain on symptoms of depression and anxiety in informal carers of older people. Our data showed that SOC is an important psychological resource for carers that remained relatively stable under non‐experimental conditions over a period of one year in this sample. Findings suggest that interventions aimed at strengthening SOC may protect carer psychological well‐being

Subjective caregiver burden and anxiety in informal caregivers: a systematic review and meta-analysis

There is increasing evidence that subjective caregiver burden is an important determinant of clinically significant anxiety in family carers. This meta-analysis aims to synthesise this evidence and investigate the relationship between subjective caregiver burden and anxiety symptoms in informal caregivers. We searched PubMed, CINAHL and PsycINFO up to January 2020. Combined estimates were obtained using a random-effects model. After screening of 4,312 articles, 74 studies (with 75 independent samples) were included. There was a large, positive association between subjective caregiver burden and anxiety symptoms (r = 0.51; 95% CI = 0.47, 0.54; I2 = 0.0%). No differences were found in subgroup analyses by type of study design (cross-sectional vs. longitudinal), sampling, control of confounders or care-recipient characteristics. Subjective caregiver burden is an important risk factor for anxiety in informal caregivers. Targeting subjective caregiver burden could be beneficial in preventing clinically significant anxiety for the increasing number of family carers worldwide

Line Shape Broadening in Surface Diffusion of Interacting Adsorbates with Quasielastic He Atom Scattering

The experimental line shape broadening observed in adsorbate diffusion on metal surfaces with increasing coverage is usually related to the nature of the adsorbate-adsorbate interaction. Here we show that this broadening can also be understood in terms of a fully stochastic model just considering two noise sources: (i) a Gaussian white noise accounting for the surface friction, and (ii) a shot noise replacing the physical adsorbate-adsorbate interaction potential. Furthermore, contrary to what could be expected, for relatively weak adsorbate-substrate interactions the opposite effect is predicted: line shapes get narrower with increasing coverage.Comment: 4 pages, 2 figures (slightly revised version

A constitutive model for analyzing martensite formation in austenitic steels deforming at high strain rates

This study presents a constitutive model for steels exhibiting SIMT, based on previous sem inal works, and the corresponding methodology to estimate their parameters. The model includes temperature effects in the phase transformation kinetics, and in the softening of each solid phase through the use of a homogenization technique. The model was validated with experimental results of dynamic tensile tests on AISI 304 sheet steel specimens, and their predictions correlate well with the experimental evidence in terms of macroscopic stress strain curves and martensite volume fraction formed at high strain rates. The work shows the value of considering temperature effects in the modeling of metastable austen itic steels submitted to impact conditions. Regarding most of the works reported in the lit erature on SIMT, modeling of the martensitic transformation at high strain rates is the distinctive feature of the present paper.The researchers of the University Carlos III of Madrid are indebted to the Comunidad Autónoma de Madrid (Project CCG10 UC3M/DPI 5596)) and to the Ministerio de Ciencia e Innovación de España (Project DPI/2008 06408) for the financial support received which allowed conducting part of this work. The authors express their thanks to Mr. Philippe and Mr. Tobisch from the company Zwick for the facilities provided to perform the tensile tests at high strain rates.Publicad