Occupational exposure to volatile organic compounds and aldehydes in the U.S. trucking industry

Diesel exhaust is a complex chemical mixture that has been linked to lung cancer mortality in a number of epidemiologic studies. However, the dose-response relationship remains largely undefined, and the specific components responsible for carcinogenicity have not been identified. Although previous focus has been on the particulate phase, diesel exhaust includes a vapor phase of numerous volatile organic compounds (VOCs) and aldehydes that are either known or suspected carcinogens, such as 1,3-butadiene, benzene, and formaldehyde. However, there are relatively few studies that quantify exposure to VOCs and aldehydes in diesel-heavy and other exhaust-related microenvironments. As part of a nationwide assessment of exposure to diesel exhaust in the trucking industry, we collected measurements of VOCs and aldehydes at 15 different U.S. trucking terminals and in city truck drivers (with 6 repeat site visits), observing average shift concentrations in truck cabs and at multiple background and work area locations within each terminal. In this paper, we characterize occupational exposure to 18 different VOCs and aldehydes, as well as relationships with particulate mass (elemental carbon in PM < 1 microm and PM2.5) across locations to determine source characteristics. Our results show that occupational exposure to VOCs and aldehydes varies significantly across the different sampling locations within each terminal, with significantly higher exposures noted in the work environments over background levels (p < 0.01). A structural equation model performed well in predicting terminal exposures to VOCs and aldehydes as a function of job, background levels, weather conditions, proximity to a major road, and geographic location (R2 = 0.2-0.4 work area; R2 = 0.5-0.9 background).     

Effects of stress from electrical dehorning on feed intake, growth, and blood constituents of Holstein heifer calves

Eighteen Holstein heifer calves were allotted to two groups. Calves in one group were dehorned electrically at 8 wk of age whereas the control group remained horned through 12 wk of age. Feed intake and growth rate did not differ between the two groups. Blood constituents varied with age, nutrition of calf, and dehorning. Dehorning influenced cortisol in blood plasma with high concentrations (25 versus 6 ng/ml) measured for 1 h after dehorning. Electrical dehorning at 8 wk of age presents no long-term stress to calves.     

Frictional characteristics of Al–SiC composite brake discs

The use of light materials such as aluminium matrix composites reinforced with silicon carbide (SiC) in railway braking devices is considered. Four quarter‐scale discs were produced by the vortex method with two distinct matrices and a SiC reinforcement with two different shapes and rates. Continuous braking tests (120 s) were run with organic pads in a dry environment. The 390.0 matrix discs exhibited a higher wear resistance than one produced from a 514.0 matrix. The use of a spherical SiC, instead of an angular one, very markedly improved the wear resistance of the antagonist materials. During the braking tests, the wear fragments become oxidized and their presence in tribocontact increases friction and pad wear but decreases the disc wear. This revised version was published online in July 2006 with corrections to the Cover Date.     

High thermal diffusivity materials for railway brakediscs

Two high thermal diffusivity brake discs have been worn againsta metallic pad, a composite pad and a new ceramic pad. Thesediscs are composed of a friction track made of molybdenum orCu-2.5% Be alloy. Molybdenum was used in the form of a coatingsprayed on an aluminum-based disc or as a thin solid disc mechanically clamped onto an aluminum-based stand disc. Coatingadherence, friction coefficient, surface temperature and wearthickness loss were determined for a set of reduced-scale steelbrake discs during a continuous braking simulation. It is shownthat the solid molybdenum disc tested against the composite padinduces significant surface temperature decreases as opposed tosliding against the bare steel disc. The friction coefficient isstable and wear damage acceptable. However, the molydenumcoating performs unsatisfactorily as the large difference inthermal expansion coefficient between molybdenum and aluminuminduces disbonding and crazing of the coating. The aluminumtitanate pad/Cu-2.5Be disc brake system has demonstrated remarkable tribological performance, with a steady frictioncoefficient, a pad surface temperature about 60°C lower thanthat of a steel disc and low pad wear.