Viscosity and Stokes-Einstein relation in deeply supercooled water under pressure

We report measurements of the shear viscosity $\eta$ in water up to $150\,\mathrm{MPa}$ and down to $229.5\,\mathrm{K}$. This corresponds to more than $30\,\mathrm{K}$ supercooling below the melting line. The temperature dependence is non-Arrhenius at all pressures, but its functional form at $0.1\,\mathrm{MPa}$ is qualitatively different from that at all pressures above $20\,\mathrm{MPa}$. The pressure dependence is non-monotonic, with a pressure-induced decrease of viscosity by more than 50 % at low temperature. Combining our data with literature data on the self-diffusion coefficient $D_\mathrm{s}$ of water, we check the Stokes-Einstein relation which, based on hydrodynamics, predicts constancy of $D_\mathrm{s} \eta/T$, where $T$ is the temperature. The observed temperature and pressure dependence of $D_\mathrm{s} \eta/T$ is analogous to that obtained in simulations of a realistic water model. This analogy suggests that our data are compatible with the existence of a liquid-liquid critical point at positive pressure in water.Comment: 11 pages, 8 figures, 7 tables, 1 supplementary figure. Summary of main changes: the abstract and conclusion were modified, minor edits were made to all figures for clarity, one table and the supplementary figure were adde

Prevalence of trachoma in the Afar Region of Ethiopia: results of seven population-based surveys from the Global Trachoma Mapping Project.

PURPOSE: Trachoma is to be eliminated as a public health problem by 2020. To help the process of planning interventions where needed, and to provide a baseline for later comparison, we set out to complete the map of trachoma in Afar, Ethiopia, by estimating trachoma prevalence in evaluation units (EUs) of grouped districts ("woredas"). METHODS: We conducted seven community-based surveys from August to October 2013, using standardised Global Trachoma Mapping Project (GTMP) survey methodologies. RESULTS: We enumerated 5065 households and 18,177 individuals in seven EUs covering 19 of Afar's 29 woredas; the other ten were not accessible. 16,905 individuals (93.0%) were examined, of whom 9410 (55.7%) were female. One EU incorporating four woredas (Telalak, Dalefage, Dewe, Hadele Ele) was shown to require full implementation of the SAFE strategy for three years before impact survey, with a trachomatous inflammation-follicular (TF) prevalence in 1-9-year-olds of 17.1% (95%CI 9.4-25.5), and a trichiasis prevalence in adults aged ≥15 years of 1.2% (95%CI 0.6-2.0). Five EUs, covering 13 woredas (Berahle, Aba'ala, Dupti, Kurri, Elidihare, Ayesayeta, Afamboo, Bure Mudaitu, Gewane, Amibara, Dulecho, Dalolo, and Konebo), had TF prevalences in children of 5-9.9% and need one round of azithromycin mass treatment and implementation of the F and E components of SAFE before re-survey; three of these EUs had trichiasis prevalences in adults ≥0.2%. The final EU (Mile, Ada'ar) had a sub-threshold TF prevalence and a trichiasis prevalence in adults just >0.2%. CONCLUSION: Trachoma is a public health problem in Afar, and implementation of the SAFE strategy is required

Internal ocean dynamics contribution to North Atlantic interdecadal variability strengthened by ocean-atmosphere thermal coupling

Identifying the primary drivers of North Atlantic interdecadal climate variability is crucial for improving climatic prediction over the coming decades. Here the effect of thermal coupling on the leading energy sources of the interdecadal variability of the ocean-atmosphere system is examined by means of a stochastically-forced idealized coupled model. The effect of coupling is quantified from a comparison of the buoyancy variance budget of coupled and uncoupled model configurations. The simplicity of the model allows us to contrast the effect of coupling between a super-critical regime where the deterministic ocean dynamics drive the variability and a damped regime where noise forcing is central to its existence. The results show that changes in surface buoyancy fluxes act as a sink of temperature variance in the super-critical regime, and only become a source in the strongly damped regime. By contrast, internal ocean dynamics associated with the interaction of transient buoyancy fluxes with mean buoyancy gradients always act as a source of interdecadal variability. In addition to the reduced thermal damping effect in coupled integrations, thermal coupling with the atmosphere is shown to significantly increase the role of internal ocean dynamics in the variability, in particular in the regime where interdecadal modes are damped. Only for oceanic background states in the strongly damped regime do changes in surface buoyancy fluxes play a leading role in the upper ocean variability. A stochastically-forced coupled box model is proposed that captures the basic effect of thermal coupling on atmospheric and oceanic energy sources of variability

Internal ocean dynamics contribution to North Atlantic interdecadal variability strengthened by ocean-atmosphere thermal coupling

International audienceAbstract Identifying the primary drivers of North Atlantic interdecadal climate variability is crucial for improving climatic prediction over the coming decades. Here the effect of thermal coupling on the leading energy sources of the interdecadal variability of the ocean-atmosphere system is examined by means of a stochastically-forced idealized coupled model. The effect of coupling is quantified from a comparison of the buoyancy variance budget of coupled and uncoupled model configurations. The simplicity of the model allows us to contrast the effect of coupling between a super-critical regime where the deterministic ocean dynamics drive the variability and a damped regime where noise forcing is central to its existence. The results show that changes in surface buoyancy fluxes act as a sink of temperature variance in the super-critical regime, and only become a source in the strongly damped regime. By contrast, internal ocean dynamics associated with the interaction of transient buoyancy fluxes with mean buoyancy gradients always act as a source of interdecadal variability. In addition to the reduced thermal damping effect in coupled integrations, thermal coupling with the atmosphere is shown to significantly increase the role of internal ocean dynamics in the variability, in particular in the regime where interdecadal modes are damped. Only for oceanic background states in the strongly damped regime do changes in surface buoyancy fluxes play a leading role in the upper ocean variability. A stochastically-forced coupled box model is proposed that captures the basic effect of thermal coupling on atmospheric and oceanic energy sources of variability

Prevalence of trachoma in the Afar Region of Ethiopia: results of seven population-based surveys from the Global Trachoma Mapping Project.

PurposeTrachoma is to be eliminated as a public health problem by 2020. To help the process of planning interventions where needed, and to provide a baseline for later comparison, we set out to complete the map of trachoma in Afar, Ethiopia, by estimating trachoma prevalence in evaluation units (EUs) of grouped districts ("woredas").MethodsWe conducted seven community-based surveys from August to October 2013, using standardised Global Trachoma Mapping Project (GTMP) survey methodologies.ResultsWe enumerated 5065 households and 18,177 individuals in seven EUs covering 19 of Afar's 29 woredas; the other ten were not accessible. 16,905 individuals (93.0%) were examined, of whom 9410 (55.7%) were female. One EU incorporating four woredas (Telalak, Dalefage, Dewe, Hadele Ele) was shown to require full implementation of the SAFE strategy for three years before impact survey, with a trachomatous inflammation-follicular (TF) prevalence in 1-9-year-olds of 17.1% (95%CI 9.4-25.5), and a trichiasis prevalence in adults aged ≥15 years of 1.2% (95%CI 0.6-2.0). Five EUs, covering 13 woredas (Berahle, Aba'ala, Dupti, Kurri, Elidihare, Ayesayeta, Afamboo, Bure Mudaitu, Gewane, Amibara, Dulecho, Dalolo, and Konebo), had TF prevalences in children of 5-9.9% and need one round of azithromycin mass treatment and implementation of the F and E components of SAFE before re-survey; three of these EUs had trichiasis prevalences in adults ≥0.2%. The final EU (Mile, Ada'ar) had a sub-threshold TF prevalence and a trichiasis prevalence in adults just >0.2%.ConclusionTrachoma is a public health problem in Afar, and implementation of the SAFE strategy is required