Articles

Lifecycle architectures for rental fleets couple pricing, vehicle assignment, maintenance scheduling and disposal timing, and the profit they add over revenue-based scoring has two sources that behave differently. Mileage steering changes the odometer reading at which a vehicle reaches disposal, and decision-focused forecast training reduces ranking regret at that point. Both sources matter only where the cost-optimal disposal mileage lies within a band around an odometer mark at which wholesale prices drop. The band half-width equals the residual-value forecast error divided by the slope of the retention margin. On realized retirements of midsize sedans at one enterprise rental operator, 28.2% of vehicles fall inside the band. Coupling adds $206 to $228 per vehicle there and $7 to $13 elsewhere, differences indistinguishable from zero. Mileage steering supplies 60.7% of the premium and survives a step-aware forecaster; the decision-focused component falls from $67.60 to $8.20 once the forecaster learns the price drops. Richer telematics raise profit by $86 to $118 per vehicle in every cell, so architecture and data are separable contributions. Operators can restrict the cost of coupling to vehicles inside the band.

Silver nanoparticles (Ag⁺NPs) contamination in the environment is a serious concern. This study investigated selected heavy metal (Ag⁺, Cd^2+, Cr²⁺ and Pb²⁺) concentrations at different sampling points to assess the risk to human health (infants, children, and adults). To do this, an enclosed area (laboratory) of 12.6 m X 8.5 m (107.1 m²) was clearly marked at different coded distances of S1, S2, S3, and S4 representing 2, 4, 6, and 8 m, while unpolluted atmosphere at 50 m away without Ag⁺NPs served as the control (S5). The silver fireworks were allowed to burn for an approximate 00h03m30s at each sampling points using a high-volume air sampler mounted at the Environmental Engineering Departmental Laboratory, Rivers State University, with windows and doors closed to simulate indoor conditions. Samples were digested using a mixture of analytical-grade nitric acid, analytical-grade hydrochloric acid and analyzed to evaluate the levels of heavy metals by atomic absorption spectrophotometry. The Ag⁺ result at S1 shows 30,000 µg/cm³, S2 was 29,000 µg/cm³, while S3 was 28000 µg/cm³ and then S4 was 13,000 µg/cm³. These results exceeded the permissible values of the United States National Ambient Air Concentration for rural, urban and industrial areas (0.0005, 0.004 and 0.6 µg/cm³, respectively). The result for the control (S5) (0.037 µg/cm³) was within the maximum allowable value. Results from other heavy metals such as Cd were 1000, 743, 401, 153, 0.001 µg/cm³, Cr was 5000, 4000, 3729, 2960, 0.002 µg/cm³, Pb was 0.048, 0.041, 0.035, 0.034 and 0.01, µg/cm³, respectively. However, higher values of Ag⁺, Cd, and Cr indicated a higher propensity for the metals to be toxic (bioavailable). In addition, the assessment of the potential health risk posed by these metals proved contaminated and harmful. Visitors recorded high values in exposure concentration (EC) and low values in average daily dose (ADD).