Modelling of fatigue damage progression and life of CFRP laminates

A progressive fatigue damage model has been developed for predicting damage accumulation and life of carbon fibre‐reinforced plastics (CFRP) laminates with arbitrary geometry and stacking sequence subjected to constant amplitude cyclic loading. The model comprises the components of stress analysis, fatigue failure analysis and fatigue material property degradation. Stress analysis of the composite laminate was performed by creating a three‐dimensional finite element model in the ANSYS FE code. Fatigue failure analysis was performed by using a set of Hashin‐type failure criteria and the Ye‐delamination criterion. Two types of material property degradations on the basis of element stiffness and strength were applied: a sudden degradation because of sudden failure detected by the fatigue failure criteria and a gradual degradation because of the nature of cyclic loading, which is driven by the increased number of cycles. The gradual degradation of the composite material was modelled by using functions relating the residual stiffness and residual strength of the laminate to the number of cycles. All model components have been programmed in the ANSYS FE code in order to create a user‐friendly macro‐routine. The model has been applied in two different quasi‐isotropic CFRP laminates subjected to tension–compression (T–C) fatigue and the predictions of fatigue life and damage accumulation as a function of the number of cycles were compared with experimental data available in the literature. A very good agreement was obtained.     

Role of IL-4 and IFN-gamma in modulation of immunity to Borrelia burgdorferi in mice

Because T cells appear to modulate the severity of murine Borrelia burgdorferi infections, we decided to examine the possible involvement of T cell-associated cytokines in disease outcome. Comparison of in vitro B. burgdorferi Ag-induced cytokine production in disease-susceptible and -resistant strains revealed striking differences; spleen cells from susceptible C3H mice produced significantly higher levels of IL-2 and IFN-gamma and lower levels of IL-4 than spleen cells from resistant BALB/c mice. Lymph node responses were even more divergent, with C3H mice producing high levels of IFN-gamma, and BALB/c mice producing little or none. This apparent Th1/Th2 cytokine imbalance was also reflected in vivo, since serum from C3H had significantly higher levels of B. burgdorferi-specific IgG2a Ab and lower levels of IgG1 Ab than serum from BALB/c mice. In vivo studies confirmed the importance of IL-4 in early control of spirochete growth, since treatment of either strain with neutralizing anti-IL-4 mAb led to increased joint swelling and higher spirochete burdens in joints compared with those in control mAb-treated mice. In contrast, IFN-gamma may hinder early control of spirochete growth in susceptible C3H mice, since treatment of mice with neutralizing anti-IFN-gamma mAb reduced both joint swelling and joint spirochete burdens compared with those in control mAb-treated mice. These studies indicate opposing roles for IL-4 and IFN-gamma in the modulation of spirochete growth and disease development in B. burgdorferi-infected mice and suggest that differential cytokine production early in infection may contribute to strain-related differences in susceptibility.     

Risk factors associated with incisor injury in elementary school children

This study examined risk factors associated with incisor injury in 3396 third and fourth grade school children in Alachua County, Florida. One of six orthodontists completed a standardized examination form for each child to assess severity of incisor injury, gender, age, race, skeletal relationships, morphologic malocclusion, incisor exposure, interlabial gap, TMJ sounds, chin trauma, and history of lower facial trauma. One in five (19.2%) exhibited some degree of incisor injury. This was limited to a single tooth in 73.1% of those with injury, while enamel injury predominated (89.4%). The majority of the injuries (75.4%) were localized in the maxillary arch, with central incisors the most frequently traumatized. Chi-square tests of association indicated that gender, race, school, orthodontist, history of lower facial trauma, chin trauma, profile, and maxillary and mandibular horizontal positions were associated with incisor injury (P < 0.05). Wilcoxon rank sum tests identified differences in age, overjet, time of screening, and interlabial gap between those with and without injury (P < 0.05). Results of logistic regression analyses indicated risk of incisor injury was greater for children who had a prognathic maxilla, a history of trauma, were older, were male, and had greater overjet and mandibular anterior spacing.     

High-risk sexual behavior at a midwestern university: a confirmatory survey

According to a 1991 study of sexual behavior based on a random sample of heterosexual undergraduates at a Midwestern university, 80% of the males and 73% of the females had experienced vaginal or anal intercourse. The average age at first vaginal intercourse was 17.2 years for both sexes. Seventeen percent of the sexually experienced males and 18% of the sexually experienced females had engaged in heterosexual anal intercourse; among these respondents, the average age at first anal intercourse was 20.3 for males and 19.1 for females. Although less than four years, on average, had elapsed since the respondents had first had vaginal intercourse, males reported an average of 8.0 lifetime vaginal-sex partners and females reported an average of 6.1. Overall, the findings from this random sample of students are similar to those from a 1988 convenience sample of the same college population.     

Multiplexed biochemical assays with biological chips

High density peptide and oligonucleotide chips are fabricated using semiconductor-based technologies. These chips have a variety of biological applications.