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Here we introduce the use of transparent experimental models fabricated by stereolithography for studying the impacts of biomass accumulation, minerals precipitation, and physical configuration of flow paths on liquid flow in fracture apertures. The internal configuration of the models ranged in complexity from simple geometric shapes to those that incorporate replicated surfaces of natural fractures and computationally derived fracture surfaces. High-resolution digital time-lapse imaging was employed to qualitatively observe the migration of colloidal and soluble dyes through the flow models. In this study, a Sphingomonas sp. and Sporosarcina (Bacillus) pasteurii influenced the fluid dynamics by physically altering flow paths. Microbial colonization and calcite deposition enhanced the stagnant regions adjacent to solid boundaries. Microbial growth and calcite precipitation occurred to a greater extent in areas behind the fabricated obstacles and less in high-velocity orifices.

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We report the development of a prototype database that "maps" microbial diversity in the context of the geochemical and geological environment and geographic location. When it is fully implemented, scientists will be able to conduct database searches, construct maps containing the information of interest, download files, and enter data over the Internet.

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A fluorescence-labeled wheat germ agglutinin staining technique (R. K. Sizemore et al., Appl. Environ. Microbiol. 56:2245-2247, 1990) was modified and found to be effective for staining gram-positive, acidophilic mining bacteria. Bacteria identified by others as being gram positive through 16S rRNA sequence analyses, yet clustering near the divergence of that group, stained weakly. Gram-negative bacteria did not stain. Background staining of environmental samples was negligible, and pyrite and soil particles in the samples did not interfere with the staining procedure.

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This study demonstrates the efficacy of a direct 5S rRNA assay for the characterization of mixed microbial populations by using as an example the bacteria associated with acidic mining environments. The direct 5S rRNA assay described herein represents a nonselective, direct molecular method for monitoring and characterizing the predominant, metabolically active members of a microbial population. The foundation of the assay is high-resolution denaturing gradient gel electrophoresis (DGGE), which is used to separate 5S rRNA species extracted from collected biomass. Separation is based on the unique migration behavior of each 5S rRNA species during electrophoresis in denaturing gradient gels. With mixtures of RNA extracted from laboratory cultures, the upper practical limit for detection in the current experimental system has been estimated to be greater than 15 different species. With this method, the resolution was demonstrated to be effective at least to the species level. The strength of this approach was demonstrated by the ability to discriminate between Thiobacillus ferrooxidans ATCC 19859 and Thiobacillus thiooxidans ATCC 8085, two very closely related species. Migration patterns for the 5S rRNA from members of the genus Thiobacillus were readily distinguishable from those of the genera Acidiphilium and Leptospirillum. In conclusion, the 5S rRNA assay represents a powerful method by which the structure of a microbial population within acidic environments can be assessed.

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To study mechanisms by which microorganisms oxidize thiophenic sulfur in coal, we tested bacterial cultures for the ability to degrade dibenzothiophene (DBT), DBT-5-oxide, and DBT-sulfone and to modify water-soluble coal products derived from Illinois no. 6 and Ugljevik coals. In yeast extract medium, the majority of selected isolates degraded DBT and accumulated DBT-5-oxide in culture fluids; all but one of the cultures degraded DBT-5-oxide, and none of them degraded DBT-sulfone. Elemental analysis data indicated that the microbial cultures were able to decrease the amount of sulfur in soluble coal products derived from Illinois no. 6 and Ugljevik coals. However, these data suggested that microbially mediated sulfur removal from soluble Ugljevik coal occurred by nonspecific mechanisms. That is, extensive degradation of the carbon structure was concurrent with the loss of sulfur. This conclusion was supported by X-ray photoelectron spectroscopic data which indicated that the reduced sulfur forms in the soluble Ugljevik coal product was not oxidized by microbial treatment.

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Microbial communities in water from Baltimore Harbor and from the mainstem of Chesapeake Bay were examined for sensitivity to mercuric chloride, monomethyl mercury, stannic chloride, and tributyltin chloride. Acute toxicity was determined by measuring the effects of [3H]thymidine incorporation, [14C]glutamate incorporation and respiration, and viability as compared with those of controls. Minimum inhibitory concentrations were low for all metals (monomethyl mercury, less than 0.05 microgram liter-1; mercuric chloride, less than 1 microgram liter-1; tributyltin chloride, less than 5 micrograms liter-1) except stannic chloride (5 mg liter-1). In some cases, mercuric chloride and monomethyl mercury were equally toxic at comparable concentrations. The Chesapeake Bay community appeared to be slightly more sensitive to metal stress than the Baltimore Harbor community, but this was not true for all treatments or assays. For culturable bacteria the opposite result was found. Thymidine incorporation and glutamate metabolism were much more sensitive indicators of metal toxicity than was viability. To our knowledge, this is the first use of the thymidine incorporation method for ecotoxicology studies. We found it the easiest and fastest of the three methods; it is at least equal in sensitivity to metabolic measurements, and it likely measures the effects on greater portion of the natural community.

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The supportive properties of polyurethane foam wheelchair cushions change significantly during the first hours of use. Thus, cushions which initially appear to optimally distribute the patient's weight may not do so after a break-in period. To solve this problem, a cushion prestressing protocol has been devised which breaks-in the foam cushion prior to determination of the patient's pressure distribution. It was found that the useful life of these cushions is adversely affected by heavy static loading and high temperatures, and if allowed to rest, polyurethane foam cushions recover a portion of their original load-bearing properties.

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In the past, the only acceptable method for protecting hospital patients against the hazards of macroshock and microshock was equipotential grounding: a system whereby potential differences between conductive surfaces are minimized, and ground loops are eliminated, through use of a network of grounding conductors connected in a tree-branch configuration to a common reference point. Experience at a major medical facility involving attempts to create and maintain an equipotential grounding system has proven this method to be costly, impractical, and potentially hazardous. Recent improvements in the input circuitry of medical instrumentation and the rapid disappearance of explosive anesthetics from many hospital inventories now make it possible to suggest an alternative approach to electrical safety: the insulated environment.

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A preliminary model was prepared for the development of superficial burns which can result from the interaction of faulty defibrillator and other electrical operating room equipment. A thermal model previously used to predict retinal coagulation was adapted to give temperature rise history of the skin. Skin resistance is assumed to decrease rapidly due to the instability of a small volume near the surface. Heating due to dissipation of the defibrillator capacitor energy in this skin volume is shown to be high enough to cause burns. A sensitivity analysis is included to isolate the dominant input parameters. Recommendations are made for future research.

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The attachment of various types of electronic instrumentation to a patient can lead to hazardous interactions. Component malfunction in a single piece of equipment connected to a patient may be totally innocuous. However, the same fault occurring in an identical piece of equipment functioning as one component in a network of monitoring and electrosurgical equipment can result in severe burns or even electrocution. This paper describes interaction between a defective defibrillator paddle and an electrosurgical unit. Burns and ventricular fibrillation resulting from this malfunction and interaction are described in detail and the electrical circuits are analyzed.

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A case is presented and electrochemical theory is discussed in a situation in which a battery was produced between two dissimilar metals in a Finochietto rib spreader. The problem developed in the thorax of a patient undergoing transthoracic cervical sympathectomy and resection of the first rib. Caution is advised in the use of dissimilar metals in patients undergoing surgery.

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