A cluster of tuberculosis associated with use of a marijuana water pipe

SETTING: New cases of pulmonary tuberculosis (TB) were noted in a cluster of young Caucasian males, an unusual ethnic group for this disease in Queensland, Australia. It was noted that marijuana water pipe ('bong') smoking was common amongst cases and contacts. OBJECTIVE: To report this cluster of TB and to investigate whether shared use of a marijuana water pipe was associated with transmission of TB. DESIGN: All contacts were identified and screened according to standard protocols. Cases were asked to list contacts with whom they had shared a marijuana water pipe. RESULTS: Five cases of open pulmonary TB were identified clinically and on sputum culture, and all isolates of Mycobacterium tuberculosis were identical on typing. Of 149 contacts identified, 114 (77%) completed screening, and 57 (50%) had significant tuberculin skin test (TST) reactions on follow-up. Of 45 contacts who had shared a marijuana water pipe with a case, 29 (64%) had a significant TST reaction. CONCLUSION: Sharing a marijuana water pipe with a case of pulmonary TB was associated with transmission of TB (OR 2.22, 95% CI 0.96-5.17), although the most important risk factor for acquiring TB infection in this cluster was close household contact with a case (OR 4.91, 95% CI 1.13-20.70).

Friction factors and rheological behavior of Australian honey in a straight pipe

The pumping characteristics of four Australian honey samples were investigated in a straight pipe. Six flow rates (100-500 kg h(-1)) were studied at three temperatures (35-50degreesC). The pressure loss increased with an increase in the length of the pipe, as the low rate was increased and as the temperature was reduced. In the 25.4 mm-pipe, the Reynolds number ranged from 0.2-32.0 and are substantially less than the critica value (2040-2180) for laminar condition in the system. The relationship between the wall shear stress and shear rate approximated power-law behaviour, and the power-law index was not significantly (p>0.05) different from 1.0. The honey samples exhibited Newtonian behaviour at all the temperatures and this was confirmed by rheometric studies using Couette geometry. A friction chart was generated independent of temperature and the type of honey. An equation was developed to predict the pressure loss of the honey in a typical pipeline at any temperature once the viscosity-temperature relationship had been established.

Mode II delamination testing in uniaxially oriented PVC pipes

The mode II fracture toughness of an oriented PVC pipe was measured using an End Notched Flexure test geometry. A relatively low value of G(IIC) was found of 1.07 kJ m(-2) and this indicates that it is energetically more favorable for a crack to propagate in the tangential direction rather than radially through the wall of the pipe. Examination of the mechanism of crack advanced showed that although the crack was propagating globally in mode II, micro-cracks were opening ahead of the crack in mode I or in mixed mode. Growth of the crack occurred by linking up of these micro-cracks. This is similar to the mechanism found for mode II cracking in carbon fibre epoxy composites. (C) 2004 Kluwer Academic Publishers.

A review of ACI recommendations for prevention of plastic cracking

The ACI recommendations for the prevention of cracking of plastic concrete attempt to eliminate such cracking by ensuring that the rate of evaporation from unprotected concrete surfaces does not exceed the estimated rate of bleed water production. The current recommendations, however do not account for the large scatter of the underlying experimental evaporation data nor the effect of altitude on evaporation rate. Ignoring the scatter of the evaporation data frequently leads to an unacceptably high probability that the evaporation rate will exceed the bleed rate. Ignoring the effect of altitude leads to similar high probabilities, but in only a comparatively small number of cases. Simple modifications of the ACI recommendations are suggested that can account for both effects. However; insufficient data on the variability of bleed rates are currently available to allow the scatter of the evaporation data to be accounted for completely.

Suctions, fracture energy, and plastic cracking of cement mortar and concrete

Plastic cracking of cement mortar and concrete is primarily attributable to desiccation by evaporation from unprotected surfaces. This causes high suctions (negative pressures) to develop in the pore water adjacent to these surfaces. Dissolved salts in the pore water can also contribute significantly to suctions. Quantitative expressions are available for all of the components of the total suction. The development of suctions over time is illustrated by the results of desiccation tests conducted on cement mortars, supplemented by data from the literature. It is shown that ambient conditions conducive to plastic cracking can arise almost anywhere, but that the extremely high suctions that develop in mature cement mortar and concrete do not imply that compression failures should occur A high value of fracture energy is derived from data from the desiccation tests that implies that plastic cracking is characterized by a significant zone of plastic straining or microcracking.

Crack depths in desiccating plastic concrete

The depths of cracks in desiccating plastic concrete are estimated by considering the effects of the suction (negative pore pressure) associated with desiccation and applying five failure models derived from fracture, theories combined with theories drawn from geotechnical engineering under the assumption that plastic concrete is a frictional particulate material. The estimated crack depths vary with the depth of desiccation, the suction profile, and a small number of material parameters that depend on the model adopted and are comparatively easy to estimate accurately. Four of the models predict excessively large crack depths. The fifth, however, predicts shallower crack depths that increase with the age of the concrete and are consistent with those of analogous desiccation cracks in coal mine tailings. It thus offers a relatively robust method of estimating the depth of desiccation cracks. Confirmation of this with data for plastic concrete is clearly desirable but not possible at present.