Spatial targeted vector control is able to reduce malaria prevalence in the highlands of Burundi.

In a highland province of Burundi, indoor residual spraying and long-lasting insecticidal net distribution were targeted in the valley, aiming also to protect the population living on the hilltops. The impact on malaria indicators was assessed, and the potential additional effect of nets evaluated. After the intervention--and compared with the control valleys--children 1-9 years old in the treated valleys had lower risks of malaria infection (odds ratio, OR: 0.55), high parasite density (OR: 0.48), and clinical malaria (OR: 0.57). The impact on malaria prevalence was even higher in infants (OR: 0.14). Using nets did not confer an additional protective effect to spraying. Targeted vector control had a major impact on malaria in the high-risk valleys but not in the less-exposed hilltops. Investment in targeted and regular control measures associated with effective case management should be able to control malaria in the highlands

Advances in Characterization of Gas Transport in Concrete: Determination of Oxygen Diffusion Coefficient from Permeability Coefficient and Porosity

One of the most relevant mechanisms that influence the life service of concrete (carbonation, compactness, alkaline protection) is gas diffusion through its mass. However, determination of gas diffusion coefficient in concrete is not a simple task. There is not a general standard which determines the test procedure. Other approaches or alternative parameters could be used in order to obtain the gas diffusion coefficient, including the use of permeability coefficient. Both parameters are dependent on material porosity and moisture content. The literature already proposes generic correlations for these parameters, but these correlations do not support the direct derivation of the gas diffusion coefficient. This paper presents the results of research carried out to analyse these generic correlations and to propose specific expressions that support the derivation of a value for the oxygen diffusion coefficient, based on the porosity and permeability coefficients. The research was centred on a experimentation process to obtain these parameters. A diffusion chamber was designed and built for use with two types of concrete mix, two distinct concrete curing processes and three separate values for humidity. Each test case sought to derive values for oxygen diffusion and permeability coefficients

Porosity and electrical resistivity-based empirical calculation of the oxygen diffusion coefficient in concrete

Concrete carbonation induced by gas transport has an adverse effect on the service life of the steel-reinforced material. Gas tightness is crucial where concrete is used to contain radioactive materials and of utmost importance where acting as a radon barrier. Since as a rule gas travel inside concrete is governed either by diffusion or permeability, the material’s performance in that respect is assessed by analysing those two parameters. The gas diffusion coefficient in concrete is not readily found, however, due to the practical difficulties involved in preventing gas from leaking out of standard diffusion cells. An alternative approach is to measure permeability at high gas concentration and pressure. The existence of a relationship between the oxygen diffusion coefficient and permeability in OPC concrete was established by the authors in a previous paper. Diffusion has also been shown to be related to porosity and, in solutions, to electrical resistivity. Little is known, however, about the relationship between gas diffusion and resistivity where the pores may be filled not with a liquid, but with air. Inasmuch as resistivity is a non-destructive technique and porosity a property that can be readily measured, these two parameters could be used to directly assess concrete durability, its performance in nuclear facilities and its suitability as a radon barrier. This paper describes a study conducted to formulate equations from which to analytically determine the oxygen diffusion coefficient. These equations are derived from empirical measurements of oxygen diffusion coefficient, concrete porosity and electrical resistivity. The findings, which corroborate the existence of such relationships, were used to formulate an equation to calculate the diffusion coefficient directly from the experimental values of concrete porosity and resistivity. Since porosity depends primarily on concrete batching, curing and moisture content, two OPC concrete mixes were prepared using different water/cement ratios and two curing conditions. The combination resulted in four types of concrete. Pre-conditioning at three values of relative humidity was subsequently deployed

Concrete as a radon barrier and its chracterization

Resumen del trabajo presentado en el Second International Conference on Concrete Sustanability (ICCS16), celebrado en Madrid (España), del 13 al 15 de junio de 201

Porosity and electrical resistivity-based empirical calculation of the oxygen diffusion coefficient in concrete

Concrete carbonation induced by gas transport has an adverse effect on the service life of the steel-reinforced material. Gas tightness is crucial where concrete is used to contain radioactive materials and of utmost importance where acting as a radon barrier. Since as a rule gas travel inside concrete is governed either by diffusion or permeability, the material’s performance in that respect is assessed by analysing those two parameters. The gas diffusion coefficient in concrete is not readily found, however, due to the practical difficulties involved in preventing gas from leaking out of standard diffusion cells. An alternative approach is to measure permeability at high gas concentration and pressure. The existence of a relationship between the oxygen diffusion coefficient and permeability in OPC concrete was established by the authors in a previous paper. Diffusion has also been shown to be related to porosity and, in solutions, to electrical resistivity. Little is known, however, about the relationship between gas diffusion and resistivity where the pores may be filled not with a liquid, but with air. Inasmuch as resistivity is a non-destructive technique and porosity a property that can be readily measured, these two parameters could be used to directly assess concrete durability, its performance in nuclear facilities and its suitability as a radon barrier. This paper describes a study conducted to formulate equations from which to analytically determine the oxygen diffusion coefficient. These equations are derived from empirical measurements of oxygen diffusion coefficient, concrete porosity and electrical resistivity. The findings, which corroborate the existence of such relationships, were used to formulate an equation to calculate the diffusion coefficient directly from the experimental values of concrete porosity and resistivity. Since porosity depends primarily on concrete batching, curing and moisture content, two OPC concrete mixes were prepared using different water/cement ratios and two curing conditions. The combination resulted in four types of concrete. Pre-conditioning at three values of relative humidity was subsequently deployed.This study was funded exclusively by the three authors’ employer, the Spanish National Research Council.Peer reviewe

Bases para la estimación del coeficiente de difusión del radón en el hormigón a partir del coeficiente de difusión del oxígeno

Trabajo presentado en las Jornadas Internacionales Conmemorativas del 80 Aniversario del IETCC : Conservar, rehabilitar, innovar, celebradas en Madrid (España), del 12 al 14 de noviembre de 2014Es ya ampliamente conocido que la exposición a altas concentraciones de radón supone un riesgo de desarrollar cáncer de pulmón. El radón que se encuentra en los edifi cios proviene principalmente del terreno. Por ello, es de gran importancia conocer las soluciones constructivas que supongan una barrera a la entrada de radón del terreno en los edifi cios. Una envolvente de hormigón que separe el ambiente interior del edifi cio del terreno circundante puede funcionar como barrera frente al radón, siempre y cuando reúna una serie de características de entre la que destaca su bajo coefi ciente de difusión. La determinación de este coefi ciente de difusión se realiza por medios sofi sticados y altamente especializados utilizando fuentes radiactivas, con lo que implica en cuanto a seguridad radiológica. En este artículo se presenta la posibilidad de estimar el coefi ciente de difusión del radón en el hormigón utilizando para ello los resultados obtenidos experimentalmente del coefi ciente de difusión de otros gases no radioactivos

Dissolution of portlandite

Resumen del trabajo presentado en el XIII International Congress on the Chemistry of Cement, celebrado en Madrid (España), del 3 al 8 de julio de 2011Portlandite, one of the main products of cement hydration and which normally comprises about 25% of the paste, is a principal buffer responsible for maintaining the high pH in response to interactions between the paste and its service environment. The kinetics of these environmentally - conditioned reactions are often important. However the present approach to kinetics is handicapped by lack of fundamental data. For example, we lack data on the kinetics of dissolution of portlandite. Portlandite is congruently soluble and its dissolution rate and mechanism are reported. Single crystals of portlandite have been grown and their effective surface area measured. Dissolution rates are reported into initially pure water as functions of calcium hydroxide concentration. The impacts of low concentration of other ions, e.g., chloride, on congruent dissolution kinetics are reported

Interaction of active droplets with director gradients in nematic liquid crystal

https://kent-islandora.s3.us-east-2.amazonaws.com/node/14386/83891-thumbnail.jpgNematic liquid crystal environment enables directional propulsion of spherical droplets representing aqueous dispersion of bacterial microswimmers[1]. Here we explore how the dynamics of active droplets can be controlled by patterning the nematic environment with singular and nonsingular director field. We use the plasmonic metamasks technique to pattern the director the form of non-singular disclinations. We demonstrate that interactions of the active droplet with the director gradients of the environment can be used to control propagation direction, speed, and locations of traps that stop propulsion. Rajabi, M., Baza, H., Turiv, T. &amp; Lavrentovich, O. D. Directional self-locomotion of active droplets enabled by nematic environment. Nat. Phys., doi:https://doi.org/10.1038/s41567-020-01055-5 (2020). </ol