The specific surface area and chemical composition of diamond dust near Barrow, Alaska

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95687/1/jgrd17349.pd

Les fièvres dans un centre PMI d'Abidjan : étiologies et pratiques thérapeutiques

Les auteurs ont étudié les caractéristiques clinicobiologiques de tous les enfants consultant pour fièvre dans un centre de Protection Maternelle et Infantile d'un quartier populaire d'Abidjan; soit du 01.02.1987 au 30.04.1987, 354 enfants avec plus de 37°8 C de température rectale. Le diagnostic le plus fréquent est celui de rougeole (184) suivi des infections respiratoires aiguës (90). Seuls 11 cas de paludisme ont été diagnostiqués cliniquement mais 29 enfants sont porteurs de plasmodium dont 4 #P. malariae$ et 26 avec une parasitémie supérieure à 1000 GR parasités par mm3. Il semble que la stratégie de chimiothérapie présomptive des accès fébriles continue à se justifier, les infirmiers se montrant capables de suspecter les causes d'hyperthermie autres que palustres. (Résumé d'auteur

Prurit après prise de chloroquine et filarioses

Une étude des rapports entre le prurit après prise de chloroquine et l'infection par #Mansonella perstans filaire sanguine fréquente dans certaines régions mais passant inaperçue car peu pathogène et par #Onchocerca volvulus filaire dermique fréquente et aux conséquences pathologiques parfois graves a été menée dans deux villages de Côte d'Ivoire. Il n'est pas possible de mettre en évidence un rapport entre l'existence de ce prurit et l'infection par ces deux filaires. (Résumé d'auteur

L'infection par le VIH chez les femmes en âge de procréer à Sassandra (Côte d'Ivoire)

Le travail, réalisé en 1988-1989, a consisté à comparer les caractéristiques socio-démographiques des femmes en âge de procréer (15-49 ans) d'une sous-préfecture rurale de Côte d'Ivoire (Sassandra) avec leur statut sérologique VIH afin de dégager des variables explicatives de cette séropositivité. Il n'a pas été possible de tester que 521 femmes sur les 1084 qui constituaient la population de départ, mais les deux sous-populations ne diffèrent que par les lieux de naissance et de résidence. La séropositivité tréponémique est élevée, de façon homogène. Pour la séropositivité du VIH, le taux global de séropositivité est de 6,1 plus ou moins 0,02 %, soit un taux intermédiaire (différences non significatives) entre ceux trouvés lors de l'enquête nationale en zone rurale (4,9 %) et en zone urbaine (7,3 %). Ce taux de séropositivité est lié au lieu de naissance (même après ajustement sur le taux de présentation); les femmes nées dans la région sont plus souvent positives que les autres et les femmes nées dans les villages plus souvent que celles nées en ville (p = 0,005 et 0,02). En revanche, les femmes mariées sont moins souvent positives que les femmes non mariées et que celles vivant en union libre (p = 0,02 et 0,0005); la polygamie semble apporter une certaine protection envers le VIH par rapport à la monogamie. Enfin les femmes séropositives ont eu plus souvent des enfants mort-nés et moins souvent des enfants décédés que les femmes séronégatives (p = 0,02 et 0,03). Il est proposé de renforcer les activités de surveillance prénatale et de les renforcer surtout en zone rurale pour prévenir de nouvelles infections par le VIH. (Résumé d'auteur

A Fluorescent Probe for Diacetyl Detection

A water-soluble fluorescent probe, rhodamine B hydrazide (RBH), was prepared and its properties for recognition of diacetyl were studied. The method employs the reaction of diacetyl with RBH, a colorless and non-fluorescent rhodamine B spiro form derivative to give a pink-colored fluorescent substance. In weakly acidic media, RBH reacts more selectively with diacetyl than with other carbonyls, causing a large increase in fluorescence intensity and thereby providing an easy assay for the determination of diacetyl

Thermodynamics of the Formaldehyde−Water and Formaldehyde−Ice Systems for Atmospheric Applications

International audienceFormaldehyde (HCHO) is a species involved in numerous key atmospheric chemistry processes that can significantly impact the oxidative capacity of the atmosphere. Since gaseous HCHO is soluble in water, the water droplets of clouds and the ice crystals of snow exchange HCHO with the gas phase and the partitioning of HCHO between the air, water, and ice phases must be known to understand its chemistry. This study proposes thermodynamic formulations for the partitioning of HCHO between the gas phase and the ice and liquid water phases. A reanalysis of existing data on the vapor−liquid equilibrium has shown the inadequacy of the Henry's law formulation, and we instead propose the following equation to predict the mole fraction of HCHO in liquid water at equilibrium, XHCHO,liq, as a function of the partial pressure PHCHO (Pa) and temperature T (K): XHCHO,liq = 1.700 × 10−15 e(8014/T)(PHCHO)1.105. Given the paucity of data on the gas−ice equilibrium, the solubility of HCHO and the diffusion coefficient (DHCHO) in ice were measured by exposing large single ice crystals to low PHCHO. Our recommended value for DHCHO over the temperature range 243−266 K is DHCHO = 6 × 10−12 cm2 s−1. The solubility of HCHO in ice follows the relationship XHCHO,ice = 9.898 × 10−13 e(4072/T)(PHCHO)0.803. Extrapolation of these data yields the PHCHO versus 1/T phase diagram for the H2O−HCHO system. The comparison of our results to existing data on the partitioning of HCHO between the snow and the atmosphere in the high arctic highlights the interplay between thermodynamic equilibrium and kinetics processes in natural systems

Acetaldehyde in the Alaskan subarctic snowpack

International audienceAcetaldehyde is a reactive intermediate in hydrocarbon oxidation. It is both emitted and taken up by snowpacks and photochemical and physical processes are probably involved. Understanding the reactivity of acetaldehyde in snow and its processes of physical and chemical exchanges requires the knowledge of its incorporation mechanism in snow crystals. We have performed a season-long study of the evolution of acetaldehyde concentrations in the subarctic snowpack near Fairbanks (65° N), central Alaska, which is subjected to a vigorous metamorphism due to persistent elevated temperature gradients in the snowpack, between 20 and 200° C m−1. The snowpack therefore almost entirely transforms into depth hoar. We have also analyzed acetaldehyde in a manipulated snowpack where temperature gradients were suppressed. Snow crystals there transformed much more slowly and their original shapes remained recognizable for months. The specific surface area of snow layers in both types of snowpacks was also measured. We deduce that acetaldehyde is not adsorbed onto the surface of snow crystals and that most of the acetaldehyde is probably not dissolved in the ice lattice of the snow crystals. We propose that most of the acetaldehyde measured is either trapped or dissolved within organic aerosol particles trapped in snow, or that acetaldehyde is formed by the hydrolysis of organic precursors contained in organic aerosols trapped in the snow, when the snow is melted for analysis. These precursors are probably aldehyde polymers formed within the aerosol particles by acid catalysis, but might also be biological molecules. In a laboratory experiment, acetaldehyde-di-n-hexyl acetal, representing a potential acetaldehyde precursor, was subjected to our analytical procedure and reacted to form acetaldehyde. This confirms our suggestion that acetaldehyde detected in snow could be produced during the melting of snow for analysis

Application of a data-processing model to determine the optimal sampling conditions for liquid phase trapping of atmospheric carbonyl compounds

International audienceThe reactivity of two fluorescent derivatization reagents, 2-diphenyl-1,3-indandione-1-hydrazone (DIH) and 2-aminooxy-N-[3-(5-dimethylamino-naphtalene-1-sulfonamino)-propyl]-acetamide (dansylacetamidooxyamine, DNSAOA), was studied towards selected atmospheric carbonyl compounds. The results were compared to those obtained using the 2,4-dinitrophenylhydrazine (2,4-DNPH) UV–vis reagent, a standard well-established technique used to detect atmospheric carbonyl compounds. The experimental rate constant were integrated into a data-processing model developed in the laboratory to simulate the trapping efficiencies of a mist chamber device as a function of temperature, reagent and solvent type among others. The results showed that in an aqueous solution, DNSAOA exhibits a higher reactivity towards carbonyl compounds without the addition of an acidic catalyst than 2,4-DNPH. It was observed that DNSAOA can trap efficiently water-soluble gaseous compounds (for example formaldehyde). However, because of a high initial contamination of the reagent caused by the synthesis procedure used in this work, DNSAOA cannot be used in high concentrations. As a result, very low trapping efficiencies of less reactive water-insoluble gaseous compounds (acetone) using DNSAOA are observed. However, the use of an organic solvent such as acetonitrile improved the trapping efficiencies of the carbonyl compounds. In this case, using DIH as the derivatization reagent (DNSAOA is not soluble in acetonitrile), trapping efficiencies greater than 95% were obtained, similar to 2,4-DNPH. Moreover, fluorescence associated with DIH derivatives (detection limits 3.33 × 10−8 M and 1.72 × 10−8 M for formaldehyde and acetone, respectively) is further advantage of this method for the determination of carbonyl compounds in complex matrix compared to the classical UV–vis detection method (detection limits 3.20 × 10−8 M and 2.9 × 10−8 M for formaldehyde and acetone, respectively)