This study investigated the available and utilized friction during non-slip gait in level walking, and determined the limit which human starts to walk carefully to adapt to slippery surface. Sixteen floor–footwear-contaminant conditions with different slipperiness (dynamic coefficient of friction, DCOF, from 0.11 to 1.06) were employed. Fifteen harnessed Chinese male performed ten self-paced walking trials in each condition without slips. The utilized friction (COFu) was obtained from the maximum value of shear to normal ground reaction force ratio during the first 25% stance. ANOVA and Tukey tests showed three subsets with similar COFu, and confirmed the hypothesis that the utilized friction drops gradually when the available friction drops below a certain critical limit. Non-linear regression models were applied to the data to determine the COFu to be 0.20 and the limit of available ground friction which human starts to walk carefully to adapt to slippery surface (DCOFlimit) to be 0.41. 相似文献
Objective: Suboptimal child restraint use includes incorrect and/or inappropriate restraint use and increases the risk of injury. Comfort has been suggested as an important factor impacting on optimal use of restraints by children. This article aims to examine the relationships between parent reported comfort and restraint misuse and age-appropriate restraint choice.
Methods: This is an analysis of data from a cross sectional observation study of child restraint use in New South Wales. Logistic regression was used to model the relationship between parent-reported comfort and restraint misuse and age-appropriate restraint choice.
Results: There was no significant relationship between either parent-reported comfort and restraint misuse or parent-reported comfort and age-appropriate restraint choice.
Conclusions: Parent perceptions of comfort of children in child restraints do not appear to be associated with incorrect child restraint use or age appropriate restraint choice. It is possible that the actual comfort of the child may be related to incorrect use but this remains to be tested. Further investigation of the relationship between parent-perceived comfort and the actual comfort of the child, as well as the impact of child comfort on optimal child restraint use is warranted. 相似文献
Macroalgal dominance of some tropical reef communities in the Eastern Pacific after coral mortality during the 1997-1998 El Ni?o Southern Oscillation (ENSO) was facilitated by protection from herbivory by epiphytic cyanobacteria. Our results do not support that reduction in number of herbivores was a necessary precursor to coral reef decline and shifts to algal reefs in this system. Rather, macroalgae dominated the community for several years after this pulse disturbance with no concurrent change in herbivore populations. While results of microcosm experiments identified the importance of nutrients, especially phosphorus, in stimulating macroalgal growth, nutrient supply alone could not sustain macroalgal dominance as nutrient-stimulated growth rates in our in situ experiments never exceeded consumption rates of unprotected thalli. In addition, thalli with nutrient-enriched tissue were preferentially consumed, possibly negating the positive effects of nutrients on growth. These tropical reefs may be ideal systems to conduct experimental tests distinguishing phase shifts from alternative stable states. Shifts were initiated by a large-scale disturbance with no evidence of a changing environment except, perhaps, dilution in herbivory pressure due to increased algal cover. Community establishment was most likely stochastic, and the community was likely maintained by strongly positive interaction between macroalgal hosts and cyanobacterial epiphytes that uncoupled consumer control of community structure. 相似文献
Metropolitan residents are concerned about their exposure to airborne pollutants. But establishing these exposures is challenging. A compact personal exposure kit (PEK) was developed to evaluate personal integrated exposure (PIE) from time-resolved data to particulate matter with aerodynamic diameter less than 2.5 μm (PM2.5) in five microenvironments, including office, home, commuting, other indoor activities (other than home and office), and outdoor activities experienced both on weekdays and weekends. The study was conducted in Hong Kong. The PEK measured PM2.5, reported location and several other factors, stored collected data, as well as reported the data back to the investigators using global system for mobile communication (GSM) telemetry. Generally, PM2.5 concentrations in office microenvironment were found to be the smallest (13.0 μg/m3), whereas the largest PM2.5 concentration microenvironments were experienced during outdoor activities (54.4 μg/m3). Participants spent more than 85% of their time indoors, including in offices, homes, and other public indoor venues. On average, 42% and 81% of the time were spent in homes, which contributed 52% and 79% of PIE (during weekdays and weekends, respectively), suggesting that improvement of air quality in homes may reduce overall exposures and indicating the need for actions to mitigate possible public health burdens in Hong Kong. This study also found that various indoor/outdoor microenvironments experienced by urban office workers cannot be accurately represented by general urban air quality data reported from the regulatory monitoring. Such personalized air quality information, especially while in transit or in offices and homes, may provide improved information on population exposures to air pollution.
Implications: A newly developed personal exposure kit (PEK) was used to monitor PM2.5 exposure of metropolitan citizens in their daily life. Different microenvironments and time durations caused various personal integrated exposure (PIE). The stationary monitoring method for PIE was also compared and evaluated with PEK. Positive protection actions can be taken after understanding the major contribution to PM2.5 exposure. 相似文献
The Tropospheric Ozone Pollution Project (TOPP) launched >220 ozonesondes in Houston (July 2004–June 2008) providing examples of pollution transported into, re-circulated within, and exported from the Houston area. Fifty-one launches occurred during the Texas Air Quality Study (TexAQS) II and the summer portion of IONS-06 (INTEX [Intercontinental Transport Experiment] Ozonesonde Network Study). On 11 days during TexAQS II and on 8 other occasions, ozonesondes were launched both at dawn and in the afternoon. Analysis of these “intensive” launch sequences shows that morning residual layer (RL) ozone concentrations ([O3]) explained 60–70% of the variability found in the afternoon mixed layer (ML). Furthermore, maximum RL [O3] is nearly identical to the mean ML [O3] from the previous afternoon (morning minus afternoon = ?1.6 ± 8.4 ppbv). During TexAQS II, mean [O3] below 1.3 km (the mean ML height from ozonesonde data) increased from 37 ± 22 ppbv in the morning to 74 ± 18 ppbv in the afternoon, suggesting an average net local daily O3 production of ~500–900 tons over the metropolitan Houston area. 相似文献
This paper describes, compares and evaluates selected Oxidant Prediction Relationships {OPRs) in terms of projections of hydrocarbon emission reductions required for attainment of the former 0.08 ppm standard and the new 0.12 ppm standard in the San Francisco Bay Area in 1985. The OPRs analyzed are the LIRAQ physicochemical model, EPA’s Empirical Kinetic Modeling Approach (EKMA), linear and Appendix J rollback, and an empirical OPR based on local observations. LIRAQ simulations indicated that to achieve the 0.12 ppm ozone standard, 1985 hydrocarbon emissions must be reduced by 27% from projected levels. The equivalent reductions derived from simple linear rollback, linear rollback with 0.04 ppm background, and the local empirical OPR were 32%, 45% and 37%, respectively. The LIRAQ simulations also showed that reduction of both hydrocarbon and NOx emissions is less effective than reduction of hydrocarbons only. The attempt to apply EKMA failed because the Bay Area’s low hydrocarbon/NOx ratios and observed ozone levels are not consistent with the standard EKMA isopleth curves. For planning, proper OPR selection is important because the wide range in the projections of various OPRs translates into a correspondingly wide range in control costs. Physicochemical OPRs are preferred because they are verifiable; they account for complex topography, meteorology, and source distributions; and because they can treat a variety of control strategies. In the future, the uncertainties associated with the projections can be resolved by assessing trends in air quality on a regular basis and by upgrading and reapplying the prediction methodologies as new information becomes available. 相似文献
Environmental and Ecological Statistics - We introduce a new type of threshold regression models called upper hinge models. Under this type of threshold models, there only exists an association... 相似文献
The atmospheric haze over the Pearl River Delta (PRD) was investigated by using the Models-3 Community Multi-scale Air Quality
modeling system with meteorological fields simulated by the Fifth-generation National Center for Atmospheric Research/Penn
State University Mesoscale Model (MM5) from September 26th to September 30th, 2004. The model-simulated meteorological elements
and particulate matter with aerodynamic diameter less than 10 μm (PM10) were compared with observations at four air quality-monitoring stations. The results showed that MM5 successfully reproduced
the diurnal variations of temperature, wind speed, and wind directions at these stations. The temporal variations of the simulated
values were consistent with those of the observed (such as temperature, wind speed, and wind direction). The correlation coefficient
was 0.91 for temperature and 0.56 for wind speed. The modeling results show that the spatial distributions of simulated PM10 were closely related to the source emissions indicating three maxima of PM10 over the PRD. The sea–land breezes diurnal cycle played a significant role in the redistribution and transport of PM10. Nighttime land breeze could transport PM10 to the coast and the sea, while daytime sea breeze (SB) could carry the accumulated PM10 offshore back to the inland cities. PM10 could also be transported vertically to a height of up to about 1000 m because of strong turbulence in the SB front. Process
analyses indicated that the emission sources and the vertical diffusion were the major processes to influence the concentrations
of particulate matter with aerodynamic diameter less than 2.5 μm (PM2.5). 相似文献