Downward Flame Spread over PMMA Spheres

Experiments were conducted to measure downward flame spread over PMMA spheres, and an underpinning theoretical basis was developed to explain the relevant mechanisms governing flame spread over spherical geometries. Flame spread over a sphere was classified into two distinct regimes, that being spread over the upper and lower hemispheres. Experiments were conducted using cast PMMA spheres 40 and 50 mm in diameter. Samples were ignited at the top of the sphere and the progression of the flame front was determined using video analysis. The time resolved flame spread rate was found to increase nearly linearly in time while the flame spread across the upper hemisphere of the sample (at rates ranging from approximately 2.0–3.5 mm/min). Flame spread on the lower hemisphere was observed to accelerate nonlinearly reaching instantaneous flame spread rates greater than 15 mm/min. The flame spread rates were found to be unsteady (i.e., continuously increasing) throughout each experiment. A Stokes flow solution was found to adequately characterize the opposed flame spread rate over the upper hemisphere with respect to the induced buoyant flow. Flame spread rates in the lower hemisphere were found to be controlled by a combination of increasing velocity of the ambient flow and increased heat transfer through the interior of the solid. Flame spread rates for each diameter tested were normalized and presented as a function of the relative angle of inclination at the flame front, . Thus, the two regimes of flame spread identified in this work are largely independent across sphere size for the diameters used in this study. The study of flame spread over spheres provides a unique condition to observe the transition from spread dictated by a well-defined flow condition to one in which heat transfer effects through the solid become increasingly significant

Sexual behaviour and condom use among university students in Madagascar

Although the number of known HIV-infected students in Madagascar increased significantly between 1989 and 1995, very little is known about student behaviour with regard to AIDS. The study objectives were: to describe Malagasy students\' sexual behaviour and condom use; to document students\' perceptions about condoms; and to study the relationships between students\' socio-demographic characteristics, their perceptions about condoms, and their condom use. The survey used a cross-sectional design and was conducted at the Antananarivo\'s university campus sites. Anonymous questionnaires were self-administered to 320 randomly selected students. Descriptive statistics and 95% confidence intervals were calculated. Logistic regressions were performed to identify the predictors of condom use. Participants\' average age was 24 years. Approximately 80% of the participants reported sexual experiences, and the average age at sexual debut was 19 years. Only 5.7% reported consistent condom use. Common reasons for non-use were steady relationships (75.6%), the perception that condoms were useful only during ovulation periods (8.7%), and the decrease of pleasure (6.4%). The predictors of condom use were male gender, and the perception that condoms were useful during ovulation periods. Risky sexual behaviours with regard to AIDS were prevalent in this community. An HIV prevention programme is recommended. Bien que le nombre connu des étudiants malgaches infectés par le VIH ait largement augmenté entre 1989 et 1995, l\'information sur le comportement des étudiants par rapport au SIDA est très limitée. Les objectifs de cette étude furent: 1) décrire le comportement sexuel des étudiants malgaches et l\'utilisation du préservatif, 2) documenter les perceptions des étudiants envers les préservatifs, 3) examiner dans quelle mesure l\'utilisation du préservatif par les étudiants varie en fonction de leurs caractéristiques sociodémographiques et leurs perceptions envers les préservatifs. Cette étude a été menée dans les sites du campus universitaire d\'Antananarivo en utilisant un devis transversal. Un questionnaire anonyme a été auto-administré à 320 étudiants sélectionnés au hasard. Des statistiques descriptives et intervalles de confiance à 95% ont été calculés. La régression logistique a été utilisée pour identifier les déterminants de l\'utilisation du préservatif. La moyenne d\'âge des participants était de 24 ans. Environ 80% des répondants ont signalé avoir eu des rapports sexuels et l\'âge moyen de premiers rapports était de 19 ans. Seulement 5,7% ont rapporté l\'utilisation systématique du préservatif. Les raisons de non utilisation furent les suivantes : être dans une relation stable (75,6%), la perception que le préservatif est uniquement utile durant la période d\'ovulation (8,7%) et la réduction du plaisir (6,4%). Le genre masculin et l\'argument d\'ovulation ont été identifiés comme prédicteurs d\'utilisation de préservatifs. Les comportements sexuels à risque vis-à-vis du SIDA étaient prédominants dans cette communauté. Un programme de prévention du VIH est recommandé. Keywords: Sexual behaviour, condoms, HIV, students, Madagascar. SAHARA J Vol. 5 (1) 2008: pp. 28-3

Evaluation of pyrolysis processes and biochar quality in the operation of flame curtain pyrolysis kiln for sustainable biochar production

Please click Additional Files below to see the full abstrac

Cytological changes related to Brucella canis variants uptake in vitro

In this study, evidence for in vitro uptake, invasion, and cytopathogonomic effects of normal and variant strains of B. canis on tissue culture, is presented. B. canis L-phase were penicillin-induced and these microorganisms produced revertants on penicillin-free media. Tissue culture (LLC-MK 2 ) cells were divided into different normal and variant-infected groups (I–IV), including controls. Bright-field and electron microscopic observations indicated uptake of all the strains and recognizable host cell damage (CPE) to varying degrees. At 72 h after infection, the extent of damage by L-phase was the least (55.5% CPE). The L-phase-derived revertants resulted in 80% damage; this approximates the adverse effect of normal B. canis (85%). In addition to these gross changes, various structural abnormalities, including pyknosis, nuclear disorganization, vacuolation, and karyorrhexis, were apparent. The implications of these findings and the indirect role of the L-phase in brucellosis due to B. canis are discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47529/1/430_2005_Article_BF02123560.pd

Systematic evaluation of pyrolysis processes and biochar quality in the operation of low-cost flame curtain pyrolysis kiln for sustainable biochar production

Low-cost pyrolysis units such as flame curtain pyrolysis kilns are gaining popularity for biochar production. However, the processes that govern the working of such units are not well understood. Here, emissions, temperatures and mass loss are monitored in real-time during kiln operation, followed by extensive biochar sampling. We found that by adjusting the layering rates of feedstock during kiln operation, we can obtain a biochar yield (28 wt% with a fixed carbon content of 65 wt%) comparable to that produced from the same feedstock in a continuous-scale pyrolysis unit, highlighting the importance of systematic guidelines for optimal kiln operation