Transport properties of compact clays. II. Diffusion.

An experimental system was constructed in order to measure the diffusion coefficient in three types of porous media, namely mica, sodic montmorillonite, and natural compact clay. Several salts at various concentrations were used for the measurements in order to investigate the influence of these factors. Influence of porosity was also studied. In a first approximation, all the results can be summarized by a simple Archie's law independent of the clay and of the solute. The diffusion and electric formation factors have also been systematically compared; they generally agree for large porosities, while they disagree for small porosities for clay and montmorillonite.

Transport Properties of Compact Clays.

Conductivity and permeability of model and natural clays have been studied experimentally. Local properties such as porosity and zeta potentials were measured as functions of the electrolyte solutions. Whenever possible, experimental data were compared to numerical data obtained for random packings of grains of arbitrary shape, and a good agreement was found between them. Copyright 2001 Academic Press.

Topology of slightly polydisperse real foams.

The topology of slightly polydisperse, (meta-)stable, real foams was investigated by means of optical tomography associated with a numerical reconstruction procedure. The values of the mean numbers of faces per bubble and edges per face were very close to Matzke's data (1946). The real foams were essentially disordered and possessed a noncentered symmetry, and ideal structures also could not be observed. The disorder was quantified by the second moment of the edge per face and face per bubble distributions, and also by a statistical correlation coefficient between the numbers of edges of adjacent faces. It was found that the edge distributions of the internal bubbles, and not of the external ones, were significantly anticorrelated even during foam aging, which provided a measure of the disorder in the foam. No obvious relationship could be deduced between the isoperimetric quotient and the face combination in an individual bubble. Eventually, it was shown that the physical boundaries of the foam sample had no influence on the foam topology beyond a single bubble layer.

Racial differences in vaginal douching knowledge, attitude, and practices among sexually active adolescents.

STUDY OBJECTIVE: The study sought to assess knowledge of, attitude toward, and practices of vaginal douching among adolescent females attending a public family planning clinic, in order to better understand racial influences on douching. DESIGN, SETTING, PARTICIPANTS: In this descriptive, cross-sectional study, a one-page questionnaire was administered to all adolescent females (< or=19 years) presenting to a public family planning clinic in a small southern city between March 1 and May 31, 1999. RESULTS: Of the 169 participants, the mean age was 17.0 years (+/-1.5 years), 53% were Caucasian, and 47% were African-American. Sixty-nine percent of participants reported vaginal douching, mostly for hygienic reasons (68%). Those reporting vaginal douching were more likely to have a history of sexual intercourse (P < 0.01) and a history of one or more sexually transmitted diseases (P < 0.05). Age of first douche correlated positively with age of first sexual intercourse (r = 0.34, P < 0.001). African-Americans did not douche to a greater degree than Caucasians. However, racial differences were noted in knowledge of and attitude toward vaginal douching. CONCLUSIONS: Vaginal douching was a common practice among adolescent females attending a public family planning clinic in a small southern city. Culturally appropriate educational strategies for African-American and Caucasian adolescent females should improve awareness of adverse events associated with vaginal douching, despite family and personal beliefs about this practice.

Vaginal douching in adolescents attending a family planning clinic

Background: One of the variables most consistently associated with vaginal douching is race, with African-American women douching more regularly. Sparse data exists in the medical literature about the practice of vaginal douching among adolescents. The purpose of this study was to assess the prevalence, knowledge, attitude, and practices of vaginal douching among adolescent females attending a public family planning clinic, and determine whether African-American (AA) females douche to a greater degree than Caucasian females.Methods: In this cross-sectional study, a one-page questionnaire was administered to all adolescent females (

Influence of Dynamic Surface Tension on the Spreading of Surfactant Solution Droplets Impacting onto a Low-Surface-Energy Solid Substrate

We have investigated the impact of single droplets of various surfactant solutions on a low-surface-energy solid substrate using a high-frequency visualization technique (one picture every 100 µs). Whatever the surfactant, the drop spreads and retracts in about 1 s under the action of inertia and capillarity, respectively. During retraction, the capillary waves can be amplified and, in some cases, even yield droplet bouncing. Then, the droplet may slowly spread again due to gravity and the unbalanced capillary forces at the contact line between the droplet and the substrate. During the fast spreading process (2-3 ms), the droplet surface increases by almost one order of magnitude since its shape changes from a sphere to a flat pancake; this causes a strong deviation from thermodynamic equilibrium. The relevant surface property is therefore the dynamic surface tension which we have evaluated using a maximum bubble pressure apparatus. We have shown that droplet retraction is drastically influenced by the adsorption kinetics of the surfactant which limits the return to equilibrium surface tension.

Colonization with antibiotic-resistant Streptococcus pneumoniae in children with sickle cell disease.

OBJECTIVE: Because of susceptibility to severe pneumococcal infection, children with sickle cell disease (SCD) routinely receive penicillin prophylaxis. Increasing rates of penicillin resistance have been reported throughout the world. Our objective was to assess the prevalence of nasopharyngeal colonization with Streptococcus pneumoniae and to assess the antimicrobial susceptibility of the organisms in children with SCD. STUDY DESIGN: Nasopharyngeal cultures for S. pneumoniae were obtained from all children with SCD attending clinics in a statewide university-based network. Background colonization rates were determined in children attending day care centers in some of the same locations. All recovered S. pneumoniae organisms were tested for susceptibility to penicillin, and all resistant strains were examined for susceptibility to other antibiotics. RESULTS: Overall nasopharyngeal pneumococcal colonization rates among children with SCD were 12%. Colonization was associated with age less than 2 years (p <0.001) and day care attendance for more than 20 hr/wk (p = 0.00005). More than half of these strains (62%) were resistant to penicillin, 33% having intermediate resistance (minimal inhibitory concentration 0.06 to 1 microgram/ml) and 29%, high level resistance (minimal inhibitory concentration > or = 2.0 microgram/ml). Penicillin resistance was associated with penicillin prophylaxis (p <0.01). Many of these organisms were also resistant to other classes of antibiotics. CONCLUSIONS: Although penicillin prophylaxis and pneumococcal vaccine for patients with SCD have reduced overall nasopharyngeal colonization and disease caused by S. pneumoniae (p <0.001), a higher percentage of colonizing strains are now resistant both to penicillin and to other antimicrobial agents (p <0.01). Newer strategies for preventing disease and early management of suspected pneumococcal infection in these children must be developed.