A measurement invariance analysis of selected Opioid Overdose Knowledge Scale (OOKS) items among bystanders and first responders

The Opioid Overdose Knowledge Scale (OOKS) is widely used as an adjunct to opioid education and naloxone distribution (OEND) for assessing pre- and post-training knowledge. However, the extent to which the OOKS performs comparably for bystander and first responder groups has not been well determined. We used exploratory structural equation modeling (ESEM) to assess the measurement invariance of an OOKS item subset when used as an OEND training pre-test. We used secondary analysis of pre-test data collected from 446 first responders and 1,349 bystanders (N = 1,795) attending OEND trainings conducted by two county public health departments. Twenty-four items were selected by practitioner/trainer consensus from the original 45-item OOKS instrument with an additional 2 removed owing to low response variation. We used exploratory factor analysis (EFA) followed by ESEM to identify a factor structure, which we assessed for configural, metric, and scalar measurement invariance by participant group using the 22 dichotomous items (correct/incorrect) as factor indicators. EFA identified a 3-factor model consisting of items assessing: basic overdose risk information, signs of an overdose, and rescue procedures/ advanced overdose risk information. Model fit by ESEM estimation versus confirmatory factor analysis showed the ESEM model afforded a better fit. Measurement invariance analyses indicated the 3-factor model fit the data across all levels of invariance per standard fit statistic metrics. The reduced set of 22 OOKS items appears to offer comparable measurement of pre-training knowledge on opioid overdose risks, signs of an overdose, and rescue procedures for both bystanders and first responders

Implications of water medium for the evolution of rolling contact fatigue under rail surface defect conditions

With existing rail surface defects, third body mediums play an important role in the evolution of Rolling Contact Fatigue (RCF). This study investigates the effect of water mediums on the evolution process of RCF behavior on defective rails. Conical artificial defects were created using an indentation apparatus and wheel-rail rolling contact tests were conducted on a twin-disc test machine. Results indicate that rolling test preparation procedures can affect the development of RCF behavior of the rail material with surface defect under water condition. The morphology from cross-section views under water condition can be divided into four regions due to various RCF behavior evolution based on relative locations from surface defects. However, in all regions, average crack depths, densities and damage degrees increased first and then decreased with the progress of the tests. Damage in areas with and without pre-existing defects under water and dry conditions were compared and discussed. Results also show that the ratio between the remained defect depth and the RCF crack depth would determine whether the existence of defect influence the RCF behavior on the rail material

Experimental study on wheel-rail rolling contact fatigue damage starting from surface defects under various operational conditions

Surface defects in different railway lines experience different wheel-rail rolling contact actions owing to various railway line characteristics and vehicle operation parameters. This study focused on the evolution of defective wheel-rail rolling contact fatigue (RCF) behaviour under different operation conditions. Conical defects were created using an indentation apparatus. Wheel-rail RCF tests were performed using a twin-disc testing machine. Various operational conditions were simulated considering different slip ratios and wheel linear velocities on uphill and flat lines, as well as different vehicle axle loads and train configurations. The results indicate that surface damage, crack depths, and wear debris size increased only with decreasing wheel linear velocities, whereas the crack angles increased only with decreasing slip ratio. Meanwhile, both the wear rate and oxidation degree of wear debris were simultaneously affected by the slip ratio and wheel linear velocities. Under rolling conditions on flat lines, vehicle axle loads had a negligible influence on the wheel-rail RCF behaviour