[1] While the ability of subaquatic vegetation to attenuate wave energy is well recognized in general, there is a paucity of data from the field to describe the rate and mechanisms of wave decay, particularly with respect to the relative motion of the vegetation. The purpose of this study was to quantify the attenuation of incident wave height through a seagrass meadow and characterize the blade movement under oscillatory flow under the low-energy conditions characteristic of fetch-limited and sheltered environments. The horizontal motion of the seagrass blades and the velocity just above the seagrass canopy were measured using a digital video camera and an acoustic Doppler velicometer (ADV) respectively in order to refine the estimates of the drag coefficient based on the relative velocity. Significant wave heights (H s ) were observed to increase by $0.02 m ($20%) through the first 5 m of the seagrass bed but subsequently decrease exponentially over the remainder of the bed. The exponential decay coefficient varied in response to the Reynolds number calculated using blade width (as the length scale) and the oscillatory velocity measured immediately above the canopy. The ability of the seagrass to attenuate wave energy decreases as incident wave heights increase and conditions become more turbulent. Estimates of the time-averaged canopy height and the calculated hydraulic roughness suggest that, as the oscillatory velocity increases, the seagrass becomes fully extended and leans in the direction of flow for a longer part of the wave cycle. The relationship between the drag coefficient and the Reynolds number further suggests that the vegetation is swaying (going with the flow) at low-energy conditions but becomes increasingly rigid as oscillatory velocities increase over the limited range of the conditions observed (200 < Re < 800). In addition to the changing behavior of the seagrass motion, the attenuation was not uniform with wave frequency, and waves at a secondary frequency of 0.38 Hz (2.6 s) appeared to be unaffected by the seagrass. Cospectral analysis between the oscillatory and blade velocity suggests that the seagrass was moving in phase with the current at the (lower) secondary frequency and out of phase at the (higher) peak frequency. In this respect, seagrass is not only an attenuator of wave energy but also serves as a low-pass filter; higher frequencies in the spectra tend to be more attenuated.Citation: Bradley, K., and C. Houser (2009), Relative velocity of seagrass blades: Implications for wave attenuation in low-energy environments,

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Advanced automobile technology, developed infrastructure, and changing economic markets have resulted in increasing commute times. Traffic is a major source of harmful pollutants and consequently daily peak exposures tend to occur near roadways or while traveling on them. The objective of this study was to measure simultaneous real-time particulate matter (particle numbers, lung-deposited surface area, PM2.5, particle number size distributions) and CO concentrations outside and in-cabin of an on-road car during regular commutes to and from work. Data was collected for different ventilation parameters (windows open or closed, fan on, AC on), whilst traveling along different road-types with varying traffic densities. Multiple predictor variables were examined using linear mixed-effects models. Ambient pollutants (NOx, PM2.5, CO) and meteorological variables (wind speed, temperature, relative humidity, dew point) explained 5–44% of outdoor pollutant variability, while the time spent travelling behind a bus was statistically significant for PM2.5, lung-deposited SA, and CO (adj-R2 values = 0.12, 0.10, 0.13). The geometric mean diameter (GMD) for outdoor aerosol was 34 nm. Larger cabin GMDs were observed when windows were closed compared to open (b = 4.3, p-value = <0.01). When windows were open, cabin total aerosol concentrations tracked those outdoors. With windows closed, the pollutants took longer to enter the vehicle cabin, but also longer to exit it. Concentrations of pollutants in cabin were influenced by outdoor concentrations, ambient temperature, and the window/ventilation parameters. As expected, particle number concentrations were impacted the most by changes to window position / ventilation, and PM2.5 the least. Car drivers can expect their highest exposures when driving with windows open or the fan on, and their lowest exposures during windows closed or the AC on. Final linear mixed-effects models could explain between 88–97% of cabin pollutant concentration variability. An individual may control their commuting exposure by applying dynamic behavior modification to adapt to changing pollutant scenarios.

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any ether aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate AFRL-HE-WP-TR-2001-0130 SUPPLEMENTARY NOTES 12a. DISTRIBUTION AVAILABILITY STATEMENTApproved for public release; distribution is unlimited. 12b. DISTRIBUTION CODE ABSTRACT (Maximum 200 words)This report presents the results of the third in a proposed sequence of studies to investigate human annoyance to noise from low-altitude military training route (MTR) flight operations. The sequence ranges from laboratory studies, in which the physical and social parameters are well controlled, but highly artificial, to field attitudinal surveys, in which these parameters are largely uncontrolled, but the setting is natural. In this third study, subjects were exposed to both real and recorded MTR noise events in their own homes for a period of four weeks. In the laboratory study it was found that MTR sounds having onset rates faster than 30 dB/second caused annoyance beyond what would be expected from the corresponding sound exposure level (SEL). The best fit to the data was found to be an onset rate adjustment to SEL, which has the form of a linear relation on a dB versus log (rate) scale, from 0 dB at a rate of 30 dB/second to 11 dB at 150 dB/second. The rented home study confirmed the laboratory onset rate adjustment, although the adjustment was found to begin at 15 dB/second rather than at 30 dB/second. The present study continued to confirm the existence of an onset rate effect. It also confirmed the equal energy principle. However, it did not show any dependence of annoyance on the sporadicity of the events.