Exopolymer‐producing bacteria can be used to modify soil profiles for enhanced oil recovery or bioremediation. Understanding the mechanisms associated with biomass plug development and propagation is needed for successful application of this technology. These mechanisms were determined from packed‐bed and micromodel experiments that simulate plugging in porous media. Leuconostoc mesenteroides was used, because production of dextran, a water‐insoluble exopolymer, can be controlled by using different carbon sources. As dextran was produced, the pressure drop across the porous media increased and began to oscillate. Three pressure phases were identified under exopolymer‐producing conditions: the exopolymer‐induction phase, the plugging phase, and the plug‐propagation phase. The exopolymer‐induction phase extended from the time that exopolymer‐producing conditions were induced until there was a measurable increase in pressure drop across the porous media. The plugging phase extended from the first increase in pressure drop until a maximum pressure drop was reached. Changes in pressure drop in these two phases were directly related to biomass distribution. Specifically, flow channels within the porous media filled with biomass creating a plugged region where convective flow occurred only in water channels within the biofilm. These water channels were more restrictive to flow causing the pressure drop to increase. At a maximum pressure drop across the porous media, the biomass yielded much like a Bingham plastic, and a flow channel was formed. This behavior marked the onset of the plug‐propagation phase which was characterized by sequential development and breakthrough of biomass plugs. This development and breakthrough propagated the biomass plug in the direction of nutrient flow. The dominant mechanism associated with all three phases of plugging in porous media was exopolymer production; yield stress is an additional mechanism in the plug‐propagation phase. © 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 72: 353–363, 2001.

Two experiments investigated the impact of DNA evidence in a child sexual assault (CSA) case involving a 6-year-old alleged victim. In Experiment 1, participants read criminal trial summaries of CSA cases in which only DNA evidence was presented, only the alleged child victim's testimony was presented, or both forms of evidence were presented. When DNA evidence was presented, there were more guilty verdicts and greater belief of the alleged victim than when only the alleged victim testified. In Experiment 2, DNA evidence was countered by an alibi witness testifying as to the defendant's whereabouts at the time of the alleged assault. The alibi witness reduced the influence of DNA evidence compared with when DNA evidence was presented without this witness. These results are discussed in terms of the comparative strengths of DNA evidence versus the testimony of the alleged victim.

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