The formation of aerosols proceeds through nucleation, growth and aging stages. The understanding of nucleation and droplet growth is essential for handling the more complex atmospheric condensation processes. To achieve this goal, measurements of the nucleation rate of various systems are performed in an expansion chamber. In this manner nucleation and growth are decoupled by applying a short nucleation pulse of about 1 ms during which the nuclei are formed. The subsequent droplet growth is quantitatively monitored by Mie-scattering. To this end, the Mie-maxima and -minima are detected as a function of time and compared to theoretical Mie-scattering calculations for increasing radii. In this fashion, a wealth of growth curves for pure water depending on supersaturations, number densities of droplets, and temperatures were obtained. Following the approach of Fuchs and Sutugin [Fuchs, N.A., Sutugin, A.G., 1970. Highly Dispersed Aerosols. Ann Arbor Science Publishers, Ann Arbor; Fuchs, N.A., Sutugin, A.G., 1971. In: Hidy, G.M., Brock, J.R. (Eds.), International Reviews in Aerosol Physics and Chemistry: Topics in Current Aerosol Research (Part 2), Pergamon, New York, p. 1], we calculated theoretical growth curves taking into account the depletion of water vapor, the increase of droplet- and system-temperature, temperature-dependent functions of the diffusion coefficient, surface tension, liquid density and latent heat of condensation. The calculated growth curves and experimental data for 230, 240 and 250 K with number densities of droplets between 5×102 and 2×106 droplets/cm3 yield quantitative agreement between theory and experiment. This is remarkable in so far as the theory contains no adjustable parameters and assumes the sticking probability of the vapor molecules to be unity. Using a sticking probability smaller than 0.8 in the calculation leads to growth functions already outside the experimental error. 相似文献
Life history, habitat utilisation, and biomass of benthic and pelagic opossum shrimp (Mysis relicta) were studied in the oligotrophic Lake Jonsvatn, central Norway. Sampling in the pelagic zone was done by means of a closing zooplankton net; in the benthic zone by means of a benthic beam trawl.
M. relicta had a mixed one or two year life cycle. In the autumn, the proportion of mature females and males were larger in the pelagic than in the benthic habitat. Copulation took place in late autumn, and the first females with eggs occurred in November. In February, the first juvenile M. relicta were released in the benthic habitat. In May and July, however, juveniles were found in large numbers in all parts of the lake. The length distribution of M. relicta indicates that juveniles partly segregate between benthic and pelagic habitats.
Both juvenile and adult M. relicta performed vertical diel migrations in the pelagic habitat. In the benthic habitat, diel vertical migrations along the bottom were not as pronounced as vertical migrations in the pelagic habitat. In the benthic habitat, major migrations were performed only by adults in the autumn. Our results indicate that the light intensity in the green part of the spectrum gives the proximate cue for regulation of vertical distribution of M. relicta.
The mean total biomass varied between 288 and 1576 kg dry weight, corresponding to 23.2–127.1 mg dry weight m−2 surface area. M. relicta had smallest biomass during late spring/early summer and largest biomass during autumn and early winter. Estimated pelagic biomasses were largest in February, August, October and November, while benthic biomasses were largest in May and July. Estimated biomass of pelagic M. relicta during autumn was approximately 1/10 of the estimated biomass of zooplankton in this lake. 相似文献
The peculiar rainfall pattern in Indiarenders the country highly vulnerable to floods. Forty million hectares of land, roughlyone-eighth of the country's geographical area, is prone to floods. Each year, floods cause extensive damage to life and property, losses being exacerbated by rapid population growth, unplanned development and unchecked environmental degradation. The country has been tackling the problem through structural and non-structural measures. While non-structural measures like flood forecasting aim at improving the preparedness to floods by seeking to keep people away from floodwaters, structural measures involve the construction of physical structures like embankments, dams, drainage channels, and reservoirs that prevent floodwaters from reaching potential damage centres. Almost 48% of the vulnerable area has been provided with reasonable protection, though floods continue to cause widespread losses year after year. This paper examines the incidence of floods and the trends in consequent losses in the eastern region of the country – one of the most vulnerable – with the objective of studying the efficacy of flood protection measures in the region. Based on a simple regression exercise for three highly vulnerable states in the region, the paper argues that flood protection measures have been inadequate in controlling losses and reducing vulnerability. Regressions for the three states over the period 1971 to 1996 indicate that the level of protection is an insignificant explanatory variable in explaining the number of people (adjusted for increases in density) affected by floods; while area affected, as an indicator of the intensity of floods remains the main loss-determining factor. 相似文献
