Surveillance of Transmitted Drug-Resistant HIV Among Young Pregnant Women in Ouagadougou, Burkina Faso

Burkina Faso began rapid antiretroviral therapy (ART) scale-up in 2003 and by December 2009, 26 448 individuals were on treatment. With rapid scale-up of ART, some degree of human immunodeficiency virus transmitted drug resistance (TDR) is inevitable. Following World Health Organization methods, between June 2008 and July 2009, Burkina Faso assessed TDR in primigravid pregnant women aged <25 years attending antenatal care clinics in Ouagadougou, Burkina Faso. TDR was classified as moderate (5%-15%) for both nucleoside reverse-transcriptase inhibitors and nonnucleoside reverse-transcriptase inhibitors. The observed moderate TDR in Ouagadougou is a cause for concern and calls for closer monitoring of Burkina Faso's ART progra

Physical-chemistry of silica/alkaline silicate interactions during consolidation. Part 1: Effect of cation size

International audienceThe purpose of this work is to identify the effect of the cation nature on mechanisms of the sand consolidation with alkaline silicate solution at low temperature (70 °C). Three diluted lithium, sodium and potassium silicate solutions with [Si] = 2.8 mol/l were used to agglomerate sand composed of grains which mean diameter is 340 μm. According to the cation, different behaviors were observed in terms of the drying time and the material cohesion. Essentially, the drying time increases with decreasing cation size. In contrast, the compressive strength raises when the cation size increases inducing intra-granular rupture highlighted by SEM observations. This could find an explanation in the cation hydration sphere of cations. The strength of the cation-water electrostatic interaction becomes less important as the size of the cations increase leading to more ionic bonds. Despite their strong consolidation, potassium-based materials have a high solubility in water. This result is consistent with the ionic nature of bond

Consolidation mechanism of materials obtained from sodium silicate solution and silica-based aggregates

International audienceA study based on the use of sodium silicate gels as binder for cold consolidation of silica-based aggregates has been investigated. The gels used as precursor of binder were synthesized by adding hydrochloric acid to a concentrated sodium silicate solution. Consolidated materials were obtained by mixing the previous solution before gelation with granular materials (fine silica powder and sand). The study of the gel-silica-sand ternary system shows that the existence domain of materials depends on the sand size distribution. The microstructure of gel-silica-sand ternary samples reveals the presence of the three components with a partial attack of grain surface. This was confirmed by FTIR experiments during the monitoring of the synthesis. Actually, the νasSisingle bondOsingle bondSi broad band resulting from the average of the contribution of the set of Q4, Q3 and Q2 units with a sharp peak located around 1078 cm− 1, firstly shifts to lower wavenumber until 21 days and then to higher wavenumber characteristic of dissolution/precipitation reactions. On the other hand, the consolidation of the material is strong when the amount of fine silica in the material is high leading to efficient mechanical properties. Therefore, consolidation could be explained by the dissolution of small particles of silica and their precipitation into the grain boundary of sand

Physico-chemistry of silica / Na silicate interactions during consolidation. Part 2: Effect of pH

International audienceThis work aims to study the effect of the pH of a sodium silicate solution on the consolidation of silica-based aggregates at low temperature (70 °C). A diluted solution obtained by adding 50 wt% of distilled water into a concentrated commercial solution was used as starting solution. Solutions with an increasing pH values were prepared by alkalinizing the diluted solution with solid NaOH. This leads to the depolymerization of silicate species present in solution. Consolidated materials were obtained by impregnating silica sand with the solution. In order to increase the surface reactivity, the sand was also functionalized by a prior basic attack. Results reveal that the increase in the pH value or the functionalization of the sand surface leads to improve mechanical properties of materials suggesting chemical reactions between the components confirmed by FTIR experiments. Actually, the ν asSi-O-Si broad band with a sharp peak located around 1015 cm -1, shifts firstly to lower and then to higher wavenumber characteristic of dissolution / precipitation reactions. Moreover, the enhancement of the pH value induces intra-granular break characterized by SEM observations confirming the best consolidation. However, these samples are more soluble in water related to the excess in sodium that induces more ionic bonds

Interactions between silica sand and sodium silicate solution during consolidation process

International audienceThis work is based on the knowledge of the consolidation of silica sand with an alkaline solution in order to determine the mechanisms that occur during the drying of sand and various alkaline solution mixtures. The investigations concern effects of sand distribution size, dilution of sodium silicate solutions and drying temperature of the mixtures on consolidation behaviour. The thermal analysis performed on fresh mixtures show a release of free-water from diluted silicate solution during the consolidation. SEM observations and compressive strength tests results indicate that interactions between sodium silicate binder and silica sand depend on drying temperature. Consequently two consolidation mechanisms are proposed: at low drying temperature (70 °C), sodium silicate acts as a thin layer of glue covering sand grains and bind them to each other, while at high temperature (150 °C), dissolution-precipitation reaction occurred in the mixture consolidating more strongly the granular system. The increase of Si/Na molar ratio in a sodium silicate solution containing silica sand is in accordance with the proposed mechanis