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51.
Kent R Bass CR Woods W Sherwood C Madeley NJ Salzar R Kitagawa Y 《Traffic injury prevention》2003,4(4):297-314
Thoracic deformation under an applied load is an established indicator of injury risk, but the force required to achieve an injurious level of deformation currently is not understood adequately. This article evaluates how two potentially important factors, loading condition and muscle tensing, affect the structural response of the dynamically loaded thorax. Structural models of two human cadaver thoraxes and two porcine thoraxes were used to quantify the effects. The human cadavers, which represent anthropometric extremes, were subjected to anterior loading from (1) a 5.1-cm-wide belt oriented diagonally (i.e., seatbelt-like loading), (2) a 15.2-cm-diameter rigid hub, and (3) a 20.3-cm-wide belt oriented laterally (i.e., a distributed load). A structural model having the mathematical formulation of a quasilinear viscoelastic material model was used to model the elastic and viscous response, with ramp-hold tests used to determine the model coefficients. The effect of thoracic musculature was assessed using similar ramp-hold tests on the porcine subjects, each with and without forced muscle contraction. Even maximally contracted thoracic musculature is shown to have a minimal effect on the response, with similar elastic and viscous characteristics exhibited by each subject regardless of muscle tone. The elastic response is shown to be approximately a factor of three stiffer for diagonal belt loading and for this distributed loading condition than for the hub loading, indicating that the response is influenced most by the particular anatomical structures that are engaged and, secondarily, by the area of load application. Specifically, shoulder involvement is shown to have a strong influence. The force relaxation is found to be pronounced, but insensitive to the loading condition, with long-time force relaxation coefficients (G( infinity )) in the range of 0.1 to 0.3. The findings of this study provide restraint-specific guidelines for the force-deflection characteristics of both physical and computational thoracic models. 相似文献
52.
The objective of this study was to quantify the importance of societal aging relative to other factors that are known to affect injury risk. An aging population's effect on Maximum Abbreviated Injury Scale (MAIS) 3+ injury trends for passenger car drivers in frontal crashes was projected and compared to the effects of projected changes in fleet composition, changes in seat belt usage, and changes in air bag availability. It was determined that increased frailty due to an aging population will result in 19,816 to 43,568 additional injuries to passenger car drivers in frontal crashes from 1996 to 2012. Aging was shown to have an effect similar to the increased presence of light trucks in the fleet (a cumulative increase of approximately 47,428 injuries). Aging and changing fleet composition were shown to have a smaller effect than the projected increases in seat belt use or air bag availability, though the effect of increased belt use is not much greater than the effect of aging. After 2012, however, air bag availability and seat belt use will plateau, while societal aging will continue. 相似文献
53.
Georgette L. Siparsky Kent J. Voorhees Fudu Miao 《Journal of Polymers and the Environment》1998,6(1):31-41
Polylactic acid (PLA) is a hydrolytically degradable aliphatic polyester. The rate of polymer hydrolysis increases with time, and that has been attributed to the high reactivity of the terminal ester and the kinetics of autocatalysis. Hydrolysis is carried out in an acetonitrile/water solution to eliminate any solid-state contributions such as diffusion and crystallinity to the degradation process. A kinetic equation is derived to describe the autocatalytic effect of the increasing carboxylic acid end-group concentration. The results of solution hydrolysis are examined and found to fit the derived equation. Hydrolysis was also carried out with polycaprolactone (PCL) in acetonitrile, where reaction kinetics were found to differ from those of PLA. The PCL polymer required external acid catalysis by the addition of HCl, whereas hydrolysis of PLA was selfcatalyzed by the carboxylic acid end-groups. 相似文献
54.
Regulations to implement the National Environmental Policy Act state that environmental impact statements shall be written in plain language. Federal land management agencies operate under this guideline when they prepare plans for their lands. We examined 23 agency plans, using the Flesch Reading Ease Scale, to determine if they met this criterion. The scores show that the plans are written for people with three to six years of college education, far beyond the reading ability of the average person. The results suggest that the plans may limit or bias who participates in agency planning. National policy on the readability of the plans needs to be clarified, and agencies need to evaluate, and defend or revise, their writing programs. 相似文献
55.
Kent M. McGregor Glen A. Marotz Donald O. Whittemore 《Journal of the American Water Resources Association》1988,24(1):43-48
ABSTRACT: Drought affects the quality of ground water in certain aquifers used by municipalities in Kansas. Water quality changes occur as a function of the amount of water available for recharge and hence to dilute more mineralized ground waters. Several measures of meteorological drought, including the Palmer Index and Eagleman Aridity Index, were correlated with water quality data to determine the degree of association. Several locations showed sharp delinces in water quality as the drought progressed. These relationships can be used to predict possible variations in present and future well-water supplies in locations subject to drought induced water quality deterioration. 相似文献
56.
Stefaniak AB Hoover MD Day GA Dickerson RM Peterson EJ Kent MS Schuler CR Breysse PN Scripsick RC 《Journal of environmental monitoring : JEM》2004,6(6):523-532
Little is known about the physicochemical properties of beryllium aerosols associated with increased risk of beryllium sensitization and chronic beryllium disease (CBD). Such information is needed to evaluate whether airborne mass of beryllium is the appropriate metric of exposure or alternatively to provide a scientific basis for using information on particle size, surface area, and chemistry to support an improved exposure limit based on bioavailability through the inhalation and dermal routes of exposure. Thus, we used a suite of analytical techniques to characterize aerodynamically size-fractionated beryllium particles and powders that have been associated in epidemiological studies with higher prevalence of CBD. Aerosol particles were sampled from the ventilation systems of production lines for powders of beryllium metal and beryllium oxide and for ingots of copper-beryllium alloy. End product powders from the metal and oxide production lines were also collected.Particles released during production of beryllium metal were found to be complex, having heterogeneous composition, including reactive species such as fluorine. Powders from beryllium metal production were of high purity with only a minor component of beryllium oxide. Both particles and powders from oxide production were high-purity oxide. Particles released during production of copper-beryllium alloy were heterogeneous, being predominantly copper oxides. Thus, all particles and powders contain at least some beryllium in the form of beryllium oxide.These data justify efforts to thoroughly characterize beryllium aerosol properties when performing exposure assessments. The data also suggest that differences in particle chemical composition, size, number, and surface area may influence bioavailability of beryllium and contribute to risk of CBD. However, a scientific basis does not yet exist to replace mass as the current metric of exposure. 相似文献
57.
Robert Kent Kenneth Belitz Carmen A. Burton 《Journal of the American Water Resources Association》2005,41(5):1109-1128
This study examined algal productivity and nitrate assimilation in a 2.85 km reach of Cucamonga Creek, California, a concrete lined channel receiving treated municipal wastewater. Stream nitrate concentrations observed at two stations indicated nearly continuous loss throughout the diel study. Nitrate loss in the reach was approximately 11 mg/L/d or 1.0 g/m2/d as N, most of which occurred during daylight. The peak rate of nitrate loss (1.13 mg/l/hr) occurred just prior to an afternoon total CO2 depletion. Gross primary productivity, as estimated by a model using the observed differences in dissolved oxygen between the two stations, was 228 mg/L/d, or 21 g/m2/d as O2. The observed diel variations in productivity, nitrate loss, pH, dissolved oxygen, and CO2 indicate that nitrate loss was primarily due to algal assimilation. The observed levels of productivity and nitrate assimilation were exceptionally high on a mass per volume basis compared to studies on other streams; these rates occurred because of the shallow stream depth. This study suggests that concrete‐lined channels can provide an important environmental service: lowering of nitrate concentrations similar to rates observed in biological treatment systems. 相似文献
58.
59.
Kovacs K Václavík T Haight RG Pang A Cunniffe NJ Gilligan CA Meentemeyer RK 《Journal of environmental management》2011,92(4):1292-1302
Phytophthora ramorum, cause of sudden oak death, is a quarantined, non-native, invasive forest pathogen resulting in substantial mortality in coastal live oak (Quercus agrifolia) and several other related tree species on the Pacific Coast of the United States. We estimate the discounted cost of oak treatment, removal, and replacement on developed land in California communities using simulations of P. ramorum spread and infection risk over the next decade (2010-2020). An estimated 734 thousand oak trees occur on developed land in communities in the analysis area. The simulations predict an expanding sudden oak death (SOD) infestation that will likely encompass most of northwestern California and warrant treatment, removal, and replacement of more than 10 thousand oak trees with discounted cost of $7.5 million. In addition, we estimate the discounted property losses to single family homes of $135 million. Expanding the land base to include developed land outside as well as inside communities doubles the estimates of the number of oak trees killed and the associated costs and losses. The predicted costs and property value losses are substantial, but many of the damages in urban areas (e.g. potential losses from increased fire and safety risks of the dead trees and the loss of ecosystem service values) are not included. 相似文献
60.