Avoidance of Catastrophic Structural Failure as an Evolutionary Constraint: Biomechanics of the Acorn Weevil Rostrum.

The acorn weevil (Curculio Linnaeus, 1758) rostrum (snout) exhibits remarkable flexibility and toughness derived from the microarchitecture of its exoskeleton. Modifications to the composite profile of the rostral cuticle that simultaneously enhance the flexibility and toughness of the distal portion of the snout are characterized. Using classical laminate plate theory, the effect of these modifications on the elastic behavior of the exoskeleton is estimated. It is shown that the tensile behavior of the rostrum across six Curculio species with high morphological variation correlates with changes in the relative layer thicknesses and orientation angles of layers in the exoskeleton. Accordingly, increased endocuticle thickness is strongly correlated with increased tensile strength. Rostrum stiffness is shown to be inversely correlated with work of fracture; thus allowing a highly curved rostrum to completely straighten without structural damage. Finally, exocuticle rich invaginations of the occipital sutures are identified both as a likely site of crack initiation in tensile failure and as a source of morphological constraint on the evolution of the rostrum in Curculio weevils. It is concluded that avoidance of catastrophic structural failure, as initiated in these sutures under tension, is the driving selective pressure in the evolution of the female Curculio rostrum.

Heterosexual anal sex reported by women receiving HIV prevention services in Los Angeles County.

BACKGROUND: This study examined reported heterosexual receptive anal intercourse (HRAI) in a sample of women recruited from HIV prevention providers in Los Angeles County. METHODS: The majority of women surveyed were Latina and the modal age was 19 years. Women reporting HRAI were more likely to use both injected and non injected drugs and to have sexual partners who injected drugs. RESULTS: Factors associated with HRAI in a multivariate regression model included use of methamphetamine; use of alcohol before, during, or after sex; and use of dental services at the interview agency. Factors inversely associated with heterosexual anal sex were being African American (compared with Latina) and endorsing the use of condoms for episodes of vaginal sex from start to finish. CONCLUSION: HIV prevention providers in Los Angeles County should be aware of the need for basic prevention messages concerning condom use and injection behavior in young Latina women.

Evolving neural network optimization of cholesteryl ester separation by reversed-phase HPLC.

Cholesteryl esters have antimicrobial activity and likely contribute to the innate immunity system. Improved separation techniques are needed to characterize these compounds. In this study, optimization of the reversed-phase high-performance liquid chromatography separation of six analyte standards (four cholesteryl esters plus cholesterol and tri-palmitin) was accomplished by modeling with an artificial neural network-genetic algorithm (ANN-GA) approach. A fractional factorial design was employed to examine the significance of four experimental factors: organic component in the mobile phase (ethanol and methanol), column temperature, and flow rate. Three separation parameters were then merged into geometric means using Derringer's desirability function and used as input sources for model training and testing. The use of genetic operators proved valuable for the determination of an effective neural network structure. Implementation of the optimized method resulted in complete separation of all six analytes, including the resolution of two previously co-eluting peaks. Model validation was performed with experimental responses in good agreement with model-predicted responses. Improved separation was also realized in a complex biological fluid, human milk. Thus, the first known use of ANN-GA modeling for improving the chromatographic separation of cholesteryl esters in biological fluids is presented and will likely prove valuable for future investigators involved in studying complex biological samples.