Catalytic CO Oxidation on Nanoscale Pt Facets: Effect of Inter-Facet CO Diffusion on Bifurcation and Fluctuation Behavior

We present lattice-gas modeling of the steady-state behavior in CO oxidation on the facets of nanoscale metal clusters, with coupling via inter-facet CO diffusion. The model incorporates the key aspects of reaction process, such as rapid CO mobility within each facet, and strong nearest-neighbor repulsion between adsorbed O. The former justifies our use a "hybrid" simulation approach treating the CO coverage as a mean-field parameter. For an isolated facet, there is one bistable region where the system can exist in either a reactive state (with high oxygen coverage) or a (nearly CO-poisoned) inactive state. Diffusion between two facets is shown to induce complex multistability in the steady states of the system. The bifurcation diagram exhibits two regions with bistabilities due to the difference between adsorption properties of the facets. We explore the role of enhanced fluctuations in the proximity of a cusp bifurcation point associated with one facet in producing transitions between stable states on that facet, as well as their influence on fluctuations on the other facet. The results are expected to shed more light on the reaction kinetics for supported catalysts.Comment: 22 pages, RevTeX, to appear in Phys. Rev. E, 6 figures (eps format) are available at http://www.physik.tu-muenchen.de/~natali

Non-Arrhenius Behavior of Surface Diffusion Near a Phase Transition Boundary

We study the non-Arrhenius behavior of surface diffusion near the second-order phase transition boundary of an adsorbate layer. In contrast to expectations based on macroscopic thermodynamic effects, we show that this behavior can be related to the average microscopic jump rate which in turn is determined by the waiting-time distribution W(t) of single-particle jumps at short times. At long times, W(t) yields a barrier that corresponds to the rate-limiting step in diffusion. The microscopic information in W(t) should be accessible by STM measurements.Comment: 4 pages, Latex with RevTeX macro

Photoemission study of the metal-insulator transition in VO_2/TiO_2(001) : Evidence for strong electron-electron and electron-phonon interaction

We have made a detailed temperature-dependent photoemission study of VO_2/TiO_2(001) thin films, which show a metal-insulator transition at \sim 300 K. Clean surfaces were obtained by annealing the films in an oxygen atmosphere. Spectral weight transfer between the coherent and incoherent parts accompanying the metal-insulator transition was clearly observed. We also observed a hysteretic behavior of the spectra for heating-cooling cycles. We have derived the ``bulk'' spectrum of the metallic phase and found that it has a strong incoherent part. The width of the coherent part is comparable to that given by band-structure calculation in spite of its reduced spectral weight, indicating that the momentum dependence of the self-energy is significant. This is attributed to by ferromagnetic fluctuation arising from Hund's rule coupling between different d orbitals as originally proposed by Zylbersztejn and Mott. In the insulating phase, the width of the V 3d band shows strong temperature dependence. We attribute this to electron-phonon interaction and have reproduced it using the independent boson model with a very large coupling constant.Comment: 7 pages, 7 figures, submitted to Phys. Rev.

ARPES: A probe of electronic correlations

Angle-resolved photoemission spectroscopy (ARPES) is one of the most direct methods of studying the electronic structure of solids. By measuring the kinetic energy and angular distribution of the electrons photoemitted from a sample illuminated with sufficiently high-energy radiation, one can gain information on both the energy and momentum of the electrons propagating inside a material. This is of vital importance in elucidating the connection between electronic, magnetic, and chemical structure of solids, in particular for those complex systems which cannot be appropriately described within the independent-particle picture. Among the various classes of complex systems, of great interest are the transition metal oxides, which have been at the center stage in condensed matter physics for the last four decades. Following a general introduction to the topic, we will lay the theoretical basis needed to understand the pivotal role of ARPES in the study of such systems. After a brief overview on the state-of-the-art capabilities of the technique, we will review some of the most interesting and relevant case studies of the novel physics revealed by ARPES in 3d-, 4d- and 5d-based oxides.Comment: Chapter to appear in "Strongly Correlated Systems: Experimental Techniques", edited by A. Avella and F. Mancini, Springer Series in Solid-State Sciences (2013). A high-resolution version can be found at: http://www.phas.ubc.ca/~quantmat/ARPES/PUBLICATIONS/Reviews/ARPES_Springer.pdf. arXiv admin note: text overlap with arXiv:cond-mat/0307085, arXiv:cond-mat/020850

Nature of oxygen at rocksalt and spinel oxide surfaces

The chemical environment of oxygen in cobalt-containing metal oxides with compositions M xM′( x – 1) O and M xM′(3x – 1) O4 (M,M′ = Mn,Ni,Co) has been studied by Auger, x-ray and ultraviolet photoelectron, and high resolution electron energy loss spectroscopies. While there is a single type of lattice oxygen in the bulk structure of simple rocksalt and spinel oxides, the nature of oxygen at the surface of the spinel oxides is considerably more complex. Photoemission from core oxygen states in these materials often shows multiple peaks and satellite structure which have been attributed to a range of intrinsic and extrinsic oxygen states. All of these 3d transition metal oxides show a single, intense O 1s core photoemission peak at approximately 529.6 eV. In the spinel materials, a second state at 531.2 eV is also observed and is shown to be intrinsic to the spinel surface and not a result of hydroxylation or other surface contaminant. Similar photoemission features in Fe3O4 were previously attributed to final state effects; however, the nature of the multiple final states remains to be elucidated

Community Ageing Research 75+ (CARE75+) REMOTE study: a remote model of recruitment and assessment of the health, well-being and social circumstances of older people

Introduction: The Community Ageing Research 75+ (CARE75+) study is a longitudinal cohort study collecting extensive health and social data, with a focus on frailty, independence and quality of life in older age. CARE75+ was the first international experimental frailty research cohort designed using trial within cohorts (TwiCs) methodology, aligning epidemiological research with clinical trial evaluation of interventions to improve the health and well-being of older people. CARE75+ REMOTE is an extension of CARE75+ using a remote model that does not require face-to-face interactions for data collection in the current circumstances of a global pandemic and will provide an efficient, sustainable data collection model. Methods and analysis: Prospective cohort study using TwiCs. One thousand community-dwelling older people (≥75 years) will be recruited from UK general practices by telephone. Exclusions include: nursing home/care home residents; those with an estimated life expectancy of 3 months or less; and people receiving palliative care. Data collection: Assessments will be conducted by telephone, web-submission or postal questionnaire: baseline, 6 months, 12 months, 18 months, 24 months, 30 months and 36 months. Measures include activities of daily living, mood, health-related quality of life, comorbidities, medications, frailty, informal care, healthcare and social care service use. Consent will be sought for data linkage and invitations to additional studies (sub-studies). Ethics and dissemination: CARE75+ was approved by the National Research Ethics Service (NRES) Committee Yorkshire and the Humber—Bradford Leeds 10 October 2014 (14/YH/1120). CARE75+ REMOTE (amendment 13) was approved on the 18th November 2020. Consent is sought if an individual is willing to participate and has capacity to provide informed consent. Consultee assent is sought if an individual lacks capacity. Results will be disseminated in peer-reviewed scientific journals and conferences. Results will be summarised and disseminated to study participants via newsletters, local engagement events and on a bespoke website. Trial registration number: ISRCTN16588124

Community ageing research 75+ study (CARE75+): an experimental ageing and frailty research cohort

Introduction: The Community Ageing Research 75+ Study (CARE75+) is a longitudinal cohort study collecting an extensive range of health, social and economic data, with a focus on frailty, independence and quality of life in older age. CARE75+ is the first international experimental frailty research cohort designed using Trial within Cohorts (TwiCs) methodology, to align applied epidemiological research with clinical trial evaluation of interventions to improve the health and well-being of older people living with frailty. Methods and analysis: Prospective cohort study using a TwiCs design. One thousand community-dwelling older people (≥75 years) will be recruited from UK general practices. Nursing home residents, those with an estimated life expectancy of 3 months or less and people receiving palliative care will be excluded. Data collection assessments will be face to face in the person’s home at baseline, 6 months, 12 months, 24 months and 48 months, including assessments of frailty, cognition, mood, health-related quality of life, comorbidity, medications, resilience, loneliness, pain and self-efficacy. A modified protocol for follow-up by telephone or web based will be offered at 6 months. Consent will be sought for data linkage and invitations to additional studies, including intervention studies using the TwiCs design. A blood sample biobank will be established for future basic science studies. Ethics and dissemination: CARE75+ was approved by the NRES Committee Yorkshire and the Humber—Bradford Leeds 10 October 2014 (14/YH/1120). Formal written consent is sought if an individual is willing to participate and has capacity to provide informed consent. Consultee assent is sought if an individual lacks capacity. Study results will be disseminated in peer-reviewed scientific journals and scientific conferences. Key study results will be summarised and disseminated to all study participants via newsletters, local older people’s publications and local engagement events. Results will be reported on a bespoke CARE75+ website. Trial registration number: ISRCTN16588124;Results stag

Community based complex interventions to sustain independence in older people: systematic review and network meta-analysis

Objective To synthesise evidence of the effectiveness of community based complex interventions, grouped according to their intervention components, to sustain independence for older people. Design Systematic review and network meta-analysis. Data sources Medline, Embase, CINAHL, PsycINFO, CENTRAL, clinicaltrials.gov, and International Clinical Trials Registry Platform from inception to 9 August 2021 and reference lists of included studies. Eligibility criteria Randomised controlled trials or cluster randomised controlled trials with ≥24 weeks’ follow-up studying community based complex interventions for sustaining independence in older people (mean age ≥65 years) living at home, with usual care, placebo, or another complex intervention as comparators. Main outcomes Living at home, activities of daily living (personal/instrumental), care home placement, and service/economic outcomes at 12 months. Data synthesis Interventions were grouped according to a specifically developed typology. Random effects network meta-analysis estimated comparative effects; Cochrane’s revised tool (RoB 2) structured risk of bias assessment. Grading of recommendations assessment, development and evaluation (GRADE) network meta-analysis structured certainty assessment. Results The review included 129 studies (74 946 participants). Nineteen intervention components, including “multifactorial action from individualised care planning” (a process of multidomain assessment and management leading to tailored actions), were identified in 63 combinations. For living at home, compared with no intervention/placebo, evidence favoured multifactorial action from individualised care planning including medication review and regular follow-ups (routine review) (odds ratio 1.22, 95% confidence interval 0.93 to 1.59; moderate certainty); multifactorial action from individualised care planning including medication review without regular follow-ups (2.55, 0.61 to 10.60; low certainty); combined cognitive training, medication review, nutritional support, and exercise (1.93, 0.79 to 4.77; low certainty); and combined activities of daily living training, nutritional support, and exercise (1.79, 0.67 to 4.76; low certainty). Risk screening or the addition of education and self-management strategies to multifactorial action from individualised care planning and routine review with medication review may reduce odds of living at home. For instrumental activities of daily living, evidence favoured multifactorial action from individualised care planning and routine review with medication review (standardised mean difference 0.11, 95% confidence interval 0.00 to 0.21; moderate certainty). Two interventions may reduce instrumental activities of daily living: combined activities of daily living training, aids, and exercise; and combined activities of daily living training, aids, education, exercise, and multifactorial action from individualised care planning and routine review with medication review and self-management strategies. For personal activities of daily living, evidence favoured combined exercise, multifactorial action from individualised care planning, and routine review with medication review and self-management strategies (0.16, −0.51 to 0.82; low certainty). For homecare recipients, evidence favoured addition of multifactorial action from individualised care planning and routine review with medication review (0.60, 0.32 to 0.88; low certainty). High risk of bias and imprecise estimates meant that most evidence was low or very low certainty. Few studies contributed to each comparison, impeding evaluation of inconsistency and frailty. Conclusions The intervention most likely to sustain independence is individualised care planning including medicines optimisation and regular follow-up reviews resulting in multifactorial action. Homecare recipients may particularly benefit from this intervention. Unexpectedly, some combinations may reduce independence. Further research is needed to investigate which combinations of interventions work best for different participants and contexts. Registration PROSPERO CRD42019162195