Low-cost blast wave generator for studies of hearing loss and brain injury: blast wave effects in closed spaces.

BACKGROUND: Military personnel and civilians living in areas of armed conflict have increased risk of exposure to blast overpressures that can cause significant hearing loss and/or brain injury. The equipment used to simulate comparable blast overpressures in animal models within laboratory settings is typically very large and prohibitively expensive. NEW METHOD: To overcome the fiscal and space limitations introduced by previously reported blast wave generators, we developed a compact, low-cost blast wave generator to investigate the effects of blast exposures on the auditory system and brain. RESULTS: The blast wave generator was constructed largely from off the shelf components, and reliably produced blasts with peak sound pressures of up to 198dB SPL (159.3kPa) that were qualitatively similar to those produced from muzzle blasts or explosions. Exposure of adult rats to 3 blasts of 188dB peak SPL (50.4kPa) resulted in significant loss of cochlear hair cells, reduced outer hair cell function and a decrease in neurogenesis in the hippocampus. COMPARISON TO EXISTING METHODS: Existing blast wave generators are typically large, expensive, and are not commercially available. The blast wave generator reported here provides a low-cost method of generating blast waves in a typical laboratory setting. CONCLUSIONS: This compact blast wave generator provides scientists with a low cost device for investigating the biological mechanisms involved in blast wave injury to the rodent cochlea and brain that may model many of the damaging effects sustained by military personnel and civilians exposed to intense blasts.

Effect of swim suit design on passive drag.

INTRODUCTION: The drag (D) of seven (7) male swimmers wearing five (5) swimsuits was investigated. METHODS: The drag was measured during passive surface tows at speeds from 0.2 up to 2.2 m x s and during starts and push-offs. The swimsuits varied in body coverage from shoulder-to-ankle (SA), shoulder-to-knee (SK), waist-to-ankle (WA) and waist-to-knee (WK) and briefs (CS). RESULTS: Differences in total drag among the suits were small, but significant. In terms of least drag at 2.2 m x s, the swimsuits ranked: SK, SA, WA, WK and CS. The drag was decomposed into its pressure drag (DP), skin friction drag (DSF) and wave drag (DW) components using nonlinear regression and classical formulations for each drag component. The transition-to-turbulence Reynolds number and decreasing frontal area with speed were taken into account. The transition-to-turbulence Reynolds number location was found to be very close to the swimmers' "leading edge," i.e. the head. Flow was neither completely laminar, nor completely turbulent; but rather, it was transitional over most of the body. The DP contributed the most to drag at low speeds (<1.0 m x s) and DW the least at all speeds. DSF contributed the most at higher speeds for SA and SK suits, whereas DP and DW were reduced compared with the other suits. CONCLUSION: The decomposition of swimmer drag into DSF, DP and DW suggests that increasing DSF on the upper-body of a swimmer reduces DP and DW by tripping the boundary layer and attaching the flow to the body from the shoulder to the knees. It is possible that body suits that cover the torso and legs may reduce drag and improve performance of swimmers.

Size-dependent strength of dental adhesive systems.

OBJECTIVE: The aim of this study is to explain the influence of peripheral interface stress singularities on the testing of tensile bond strength. The relationships between these theoretically predicted singularities and the effect of specimen size on the measured bond strength are evaluated. METHODS: Finite element method (FEM) and boundary element method (BEM) analyses of microtensile bond strength test specimens were performed and the presence of localized high stress concentrations and singularities was analyzed. The specimen size effect predicted by the models was compared to previously published experimental data. RESULTS: FEM analysis of single-material trimmed hour-glass versus cast cylindrical specimens showed different theoretical stress distributions, with the dumbbell or cylindrical specimens showing a more homogeneous distribution of the stress on the critical symmetry plane. For multi-material specimens, mathematical singularities at the free edge of the bonded interface posed a computational challenge that resulted in mesh-dependence in the standard FEM analysis. A specialized weighted-traction BEM analysis, designed to eliminate mesh-dependence by capturing the effect of the singularity, predicted a specimen size effect that corresponds to that published previously in the literature. SIGNIFICANCE: The results presented here further support the attention to specimen dimensions that has already broadened the empirical use of the microtensile test methods. FEM and BEM analyses that identify stress concentrations and especially marginal stress singularities must be accounted for in reliable bonding strength assessments. Size-dependent strength variations generally attributed to the effects of flaw distributions throughout the interfacial region are not as relevant as the presence of singularities at bonded joint boundaries - as revealed by both FEM and BEM analyses, when interpreted from a generalized fracture mechanics perspective. Furthermore, this size-dependence must be considered when evaluating or designing dental adhesive systems.