PubMed · 10244352
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E A Cox. 1979-11-12. The night we worked through hell.. https://pubmed.ncbi.nlm.nih.gov/10244352/
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Resolved computation of two dimensional insect hovering shows for the first time that a two dimensional hovering motion can generate enough lift to support a typical insect weight. The computation reveals a two dimensional mechanism of creating a downward dipole jet of counterrotating vortices, which are formed from leading and trailing edge vortices. The vortex dynamics further elucidates the role of the phase relation between the wing translation and rotation in lift generation and explains why the instantaneous forces can reach a periodic state after only a few strokes. The model predicts the lower limits in Reynolds number and amplitude above which the averaged forces are sufficient.
The impact of oxides of nitrogen (NO(x)) emissions from motor vehicles to the air quality in city-state Singapore is analyzed using AIRVIRO, a regional scale dispersion model developed by the Swedish Meteorological and Hydrological Institute. In a predominantly urban location like Singapore, it is difficult to separate out the contribution of pollutants from mobile and point sources at different locations. In this work, a new approach is used by first modeling only the impact of point and area sources and then overlaying the traffic impact on air quality at different locations. Monthly scenario simulations are run with point, area and traffic sources of emissions for the Gaussian model validation. Street Canyon modeling is used for street segments surrounded by buildings on either side. A simplified photochemical model, which takes into account NO(x) undergoing chemical transformations in the urban atmosphere, is used to account for variations in NO(x) and ozone levels with respect to traffic data. The diurnal variation of NO(x) concentration levels is studied as a function of ozone levels at site, hourly traffic counts and meteorological parameters. The impact on ambient air quality within the breathing zone of the public from mobile sources, is found to be about 40% at urban stations although overall emissions from mobile sources is only 24%. The proposed approach appears to predict the variations in NO(x) as a function of traffic and meteorological conditions.
The investigation of settled dust is a proven and simple screening-method for considering indoor contamination for semivolatile compounds. Here we investigate the correlation of PCP concentrations in air and freshly settled dust from floors. Air and dust samples were taken from 75 rooms in 30 buildings with suspicion of an application of PCP-containing wood preservatives. Sampling was repeated four times within 18 months. PCP air concentrations were found in the range of <0.3-576 ng m-3 (mean value 25.3 ng m-3, median 2.5 ng m-3). PCP dust concentrations were found in the range of 0.083-79 microg g-1 (mean value 3.5 microg g-1, median 1.1 microg g-1. A weak highly significant correlation (P < 0.0001) with a correlation coefficient of R2 = 0.433, of the PCP concentration in dust with the PCP concentration in air, was observed. Measurement of PCP concentrations in dust, therefore, is a suitable screening method for the evaluation of indoor contamination with PCP. Due to the high dispersion of the data it is not possible to calculate PCP concentrations in air from concentrations in dust although a highly significant correlation of the PCP concentrations in air and dust was found.