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The vertical distribution of Cyclops strenuus and its prey, and the gut contents of C. strenuus were investigated at 3 h intervals over 24 h periods in the pelagic area of oligotrophic Lake Toya in May, August and October 1992. C. strenuus showed slight diel vertical migration (DVM) in May, but did not migrate and was always distributed below 15 m in August and October, the thermally stratified period. This suggests that the DVM is strongly influenced by the development of the thermocline, which the copepod may not be able to cross. Gut content analyses revealed that in Lake Toya it is omnivorous, and that the dominant prey are cladocerans and Filinia longiseta. The number of prey remains in the gut varied with time, and the diel changes did not follow changes in prey density that take the vertical overlap between predator and prey into account. We argue that very low prey density associated with the oligotrophic nature of the lake would mask the relationship between prey density and the number of prey in the gut of the predator. 相似文献
2.
The hydrodynamic forces acting on a circular cylinder and a rectangular cylinder undergoing slow drift oscillation in regular
waves were investigated experimentally and numerically. Forced oscillation tests with low frequency and large amplitude in
regular waves and forced two-harmonic oscillation with combined low and high frequencies were carried out in the experimental
study. In the numerical study a finite-difference method was used to simulate viscous flow around a two-dimensional oscillating
cylinder. The results of experiments showed that a horizontal rectangular cylinder oscillating slowly in waves has much higher
damping coefficients than one oscillating in two-harmonic mode, while the numerical study indicated that such differences
in the damping coefficient arise partly from the different effects of one-direction harmonic flow and rotating flow on the
vortex shedding caused by the slow drift oscillation. 相似文献
3.
Tran Hong Ha Osami Nishida Hirotsugu Fujita Harano Wataru 《Journal of Marine Science and Technology》2010,15(3):271-279
Marine diesel engines are major sources of air pollution. They emit a large amount of pollutants, including diesel particulate
matter (DPM), carbon oxide (CO
x
), unburned hydrocarbons (HC), nitrogen oxide (NO
x
), sulfur oxide (SO
x
), and other products of combustion. Among these, DPM may cause respiratory and mutagenic diseases in humans, including lung
and bladder cancer (see Donaldson et al. J Aerosol Sci 29:553–560, 1998). In this study, experiments were performed with an
electrostatic water-spraying scrubber (EWSS) to evaluate its effectiveness for the collection of mass- and number-based DPM
emissions from a marine diesel engine. The results show that the collection efficiency of the scrubber increases as the engine
load increases due to an increase in the large DPM concentration and an increase in the amount of DPM collected by the charged
droplets. The effect of water spraying performance on DPM collection at constant engine load was investigated experimentally.
The strength of the electrical attraction between the charged water droplets and the charged DPM within the scrubber led to
a significant increase in total DPM collection efficiency (up to 4–7 times). In addition, the total DPM collection efficiency
was found to be directly related to the corona power, the electrical properties of water, water spraying performance and engine
load. The EWSS appears to be a promising alternative method for controlling mass-based as well as number-based DPM emissions. 相似文献
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