229 research outputs found
Temperature-dependent resistivity of suspended graphene
In this paper we investigate the electron-phonon contribution to the
resistivity of suspended single layer graphene. In-plane as well as flexural
phonons are addressed in different temperature regimes. We focus on the
intrinsic electron-phonon coupling due to the interaction of electrons with
elastic deformations in the graphene membrane. The competition between screened
deformation potential vs fictitious gauge field coupling is discussed, together
with the role of tension in the suspended flake. In the absence of tension,
flexural phonons dominate the phonon contribution to the resistivity at any
temperature with a and dependence at low and high
temperatures, respectively. Sample-specific tension suppresses the contribution
due to flexural phonons, yielding a linear temperature dependence due to
in-plane modes. We compare our results with recent experiments.Comment: 11 pages, 3 figure
Flexural phonons in free-standing graphene
Rotation and reflection symmetries impose that out-of-plane (flexural)
phonons of free-standing graphene membranes have a quadratic dispersion at long
wavelength and can be excited by charge carriers in pairs only. As a result, we
find that flexural phonons dominate the phonon contribution to the resistivity
below a crossover temperature T_x where we obtain an anomalous
temperature dependence . The logarithmic factor
arises from renormalizations of the flexural phonon dispersion due to coupling
between bending and stretching degrees of freedom of the membrane.Comment: 4 pages, 2 figure
Trends in diabetic retinopathy screening attendance and associations with vision impairment attributable to diabetes in a large nationwide cohort
AIMS: To investigate diabetic retinopathy screening attendance and trends in certified vision impairment caused by diabetic eye disease. METHODS: This was a retrospective study of attendance in three urban UK diabetic eye screening programmes in England. A survival analysis was performed to investigate time from diagnosis to first screen by age and sex. Logistic regression analysis of factors influencing screening attendance during a 15-month reporting period was conducted, as well as analysis of new vision impairment certifications (Certificate of Vision Impairment) in England and Wales from 2009 to 2019. RESULTS: Of those newly registered in the Routine Digital Screening pathway (n = 97 048), 80% attended screening within the first 12 months and 88% by 36 months. Time from registration to first eye screening was longer for people aged 18-34 years, and 20% were unscreened after 3 years. Delay in first screen was associated with increased risk of referable retinopathy. Although 95% of participants (n = 291 296) attended during the 15-month reporting period, uptake varied considerably. Younger age, social deprivation, ethnicity and duration of diabetes were independent predictors of non-attendance and referable retinopathy. Although the last 10 years has seen an overall reduction in vision impairment certification attributable to diabetic eye disease, the incidence of vision impairment in those aged <35 years was unchanged. CONCLUSIONS: Whilst the majority of participants are screened in a timely manner, there is considerable variation in uptake. Young adults, have sub-optimal attendance, and levels of vision impairment in this population have not changed over the last 10 years. There is an urgent need to explore barriers to/enablers of attendance in this group to inform policy initiatives and tailored interventions to address this issue
Trends in diabetic retinopathy screening attendance and associations with vision impairment attributable to diabetes in a large nationwide cohort
AIMS: To investigate diabetic retinopathy screening attendance and trends in certified vision impairment caused by diabetic eye disease. METHODS: This was a retrospective study of attendance in three urban UK diabetic eye screening programmes in England. A survival analysis was performed to investigate time from diagnosis to first screen by age and sex. Logistic regression analysis of factors influencing screening attendance during a 15-month reporting period was conducted, as well as analysis of new vision impairment certifications (Certificate of Vision Impairment) in England and Wales from 2009 to 2019. RESULTS: Of those newly registered in the Routine Digital Screening pathway (n = 97 048), 80% attended screening within the first 12 months and 88% by 36 months. Time from registration to first eye screening was longer for people aged 18-34 years, and 20% were unscreened after 3 years. Delay in first screen was associated with increased risk of referable retinopathy. Although 95% of participants (n = 291 296) attended during the 15-month reporting period, uptake varied considerably. Younger age, social deprivation, ethnicity and duration of diabetes were independent predictors of non-attendance and referable retinopathy. Although the last 10 years has seen an overall reduction in vision impairment certification attributable to diabetic eye disease, the incidence of vision impairment in those aged <35 years was unchanged. CONCLUSIONS: Whilst the majority of participants are screened in a timely manner, there is considerable variation in uptake. Young adults, have sub-optimal attendance, and levels of vision impairment in this population have not changed over the last 10 years. There is an urgent need to explore barriers to/enablers of attendance in this group to inform policy initiatives and tailored interventions to address this issue
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