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991.
A One-Equation Turbulence Model for Geophysical Applications: Comparison with Data and the k−ε Model
A one-equation turbulence model is presented, in which the turbulent kinetic energy k is calculated with a transport equation whereas the turbulent length scale l is calculated with an algebraic expression. The value of l depends on the local stratification and reduces to the classical |z| scaling for unstratified flows near a wall, where |z| is the distance to the wall. The length scale decreases during stable stratification, and increases for unstable stratification compared to the neutral case. In the limit of strong stable stratification, the so-called buoyancy length scale proportional to k
1/2
N
–1 is obtained, where N is the buoyancy frequency. The length scale formulation introduces a single model parameter which is calibrated against experimental data. The model is verified extensively against laboratory measurements and oceanic data, and comparisons are made with the two-equation k- model. It is shown that the performance of the proposed k model is almost identical to that of the k- model. In addition, the stability functions of Launder are revisited and adjusted to obtain better agreement with recent data. 相似文献
992.
Caglar G Caglar S Ergin O Yarim M 《Journal of environmental biology / Academy of Environmental Biology, India》2005,26(3):479-485
The objectives of this study were to examine the effect of TDZ and BAP on shoot proliferation and to develop a satisfactory rooting procedure for in vitro propagation of caper (Capparis spinosa L). TDZ was found to be more effective than BAP in shoot production. The highest shoot number per explant (45.7) was achieved on the media that contained 4.54 microM TDZ in the absence of IAA. TDZ at 4.54 microM alone or in combination with 0.57 microM IAA did not inhibit shoot elongation, although they produced the most shoots. Dipping the caper shoots in the solution of IBA at 24.6 microM for 10 minutes before planting on MS media, improved the rooting percentage up to 80.5% under a 16 hr photoperiod. 相似文献
993.
Sean O’Donnell 《Behavioral ecology and sociobiology》1996,38(2):83-88
Genetic variability within insect societies may provide a mechanism for increasing behavioral diversity among workers, thereby
augmenting colony efficiency or flexibility. In order to assess the possibility that division of labor has a genetic component
in the eusocial wasp Polybia aequatorialis, I asked whether the genotypes of workers within colonies correlated with behavioral specialization. Workers specialized
by foraging for one of the four materials (wood pulp, insect prey, nectar, or water) gathered by their colonies. I collected
foragers on 2 days from each of three colonies and identified the material the foragers were carrying when collected. I produced
random amplified polymorphic DNA (RAPD) markers from the genomic DNA of these foragers and estimated genotypic similarity
of foragers based on sharing of variable RAPD marker bands. Contingency tests on 20 variable loci per colony showed statistically
significant (P <0.05) biases in RAPD marker frequencies among forager types in the three colonies. Patterns of association of RAPD marker
bands with specializations were constant in two colonies, but changed between collection days in one colony. RAPD marker biases
suggest that division of labor among workers includes a genetic component in P. aequatorialis. Colony-level selection on variation in division of labor is a possible factor favoring the evolutionary maintenance of high
genotypic variability (low relatedness) in epiponine wasp colonies and in other eusocial insects.
Received: 18 July 1995/Accepted after revision: 1 October 1995 相似文献
994.
Eugene P Seskin Robert J Anderson Robert O Reid 《Journal of Environmental Economics and Management》1983,10(2):112-124
In evaluating current environmental protection policy, economists often note that current regulations are more costly than necessary to meet environmental quality standards. While the a priori case is strong that current regulatory approaches are resulting in higher-than-necessary costs to attain environmental standards, there is relatively little empirical evidence to support this claim. The purpose of this paper is to supply some of the missing evidence by presenting the results of one study that assesses some of the potential savings associated with implementing economic, rather than command-and-control, regulatory approaches to abate one type of air pollution in one region of the country. Specifically, the paper examines the costs of meeting a prospective short-term standard for nitrogen dioxide under a range of alternative emissions control strategies for stationary sources of nitrogen oxide emissions in the Chicago Air Quality Control Region. The alternative strategies that are considered range from those that might result under current regulatory policy to those that economic policy approaches (such as emissions charges or marketable permits) are designed to implement. The analysis shows that the most efficient program of emissions controls may be more than an order of magnitude less costly than current regulatory strategies, and that economic approaches have additional advantages over more conventional regulatory approaches. 相似文献
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998.
E. -A. Müller A. Gr?ser P. Kuhbier O. Lawaczeck G. B?hme et al. 《Die Naturwissenschaften》1995,82(12):579-580
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1000.