Janice DuBien

Dynamic mechanical analysis and optimization of vapor-grown carbon nanofiber/vinyl ester nanocomposites using design of experiments

A design of experiments approach demonstrated how four formulation and processing factors (i.e., nanofiber type, use of dispersing agent, mixing method, and nanofiber weight fraction) affected the dynamic mechanical properties of carbon nanofiber/vinyl ester nanocomposites. Only <0.50 parts of nanofiber per hundred parts resin produced a 20% increase in the storage modulus vs. that of the neat cured resin. Statistical response surface models predicted nanocomposite storage and loss moduli as a function of the four factors and their interactions. Nanofiber type and weight fraction were the key interacting factors influencing the mean storage modulus. Nanofiber weight fraction, mixing method, and dispersing agent had coupled effects on the mean loss modulus. Employing this methodology, optimized nanocomposite properties can be predicted as a function of nanocomposite formulation and processing.

A comparison of agglomerative clustering methods with respect to noise

This article delineates the important considerations in any extensive, systematic comparison of clustering methods, and then it presents an empirical investigation of the effect of correlated variables on the “retrieval” ability of a particular class of agglomerative clustering methods. The empirical investigation re- sulted in two major observations; namely, that there are many agglomerative clustering methods, which have never been applied, that are “better” than any of the commonly used agglomerative clus- tering methods, and that correlated variables affect the “retrieval” ability of different agglomerative clustering methods differ- ently.

A Proposed Relationship between Time and Load to Quantify Fatigue

Research has shown that both workload and time are associated with fatigue; however, a functional rela-tionship does not exist. This study observed sixteen participants in their workplace (computer programming and simulation) to quantify the workload-time-fatigue relationship for sedentary tasks. Equal numbers of participants were observed in the morning and afternoon sessions. Workload was measured both subjec-tively and objectively; while fatigue was measured using the Swedish Occupational Fatigue Inventory (SOFI) and a modified Borg scale. Forward selection stepwise regression analysis was performed to deter-mine the underlying mathematical relationship between workload, time, and fatigue. Results indicate that for sedentary tasks, fatigue is a hyperbolic function of workload and time; meaning an inherent interaction-only relationship between workload, time, and fatigue exists. Therefore, an individual can work for longer periods of time if the workload is minimal, and vice versa.

Evaluating pedestrian behavior at crosswalks: Validation of a pedestrian behavior questionnaire for the U.S. population

The aim of this study was to develop and validate a self-reporting Pedestrian Behavior Questionnaire (PBQ) for the U.S. population to measure frequency of risky behaviors among pedestrians. The PBQ includes 50 survey items that allow respondents to rate the frequency with which they engage in different types of road-using behaviors as pedestrians. The validation study was conducted on 425 participants (228 males and 197 females) between the ages of 18 and 71. Confirmatory factor analysis differentiated pedestrian behaviors into five factor categories: violations, errors, lapses, aggressive behaviors, and positive behaviors. A short version of the PBQ with 20 items was also created by selecting four items with high factor loadings from each of the five factor categories. Regression analyses investigated associations with scenario-based survey behavioral responses to validate the five-factor PBQ subscale scores and composite score. For both long and short versions, each of these five individual factor scales were found to be reliable (0.7<Cronbachs alpha (α)<0.9) and valid (significant association with p<0.0001), except in the case of positive behaviors (α<0.6) which requires further expansion. The effects of gender and age on the PBQ scores were investigated and found to be consistent with previous research. This PBQ can serve as an instrument of pedestrian self-assessment in educational and training contexts as well as can be useful to all researchers investigating pedestrian safety for all age groups.