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591.
Large-eddy simulation of turbulent flow above and within a forest 总被引:10,自引:22,他引:10
A large-eddy simulation has been performed of an atmospheric surface layer in which the lower third of the domain is occupied by a drag layer and heat sources to represent a forest. Subgridscale processes are treated using second-order closure techniques. Lateral boundaries are periodic, while the upper boundary is a frictionless fixed lid. Mean vertical profiles of wind velocity derived from the output are realistic in their shape and response to forest density. Similarly, vertical profiles of Reynolds stress, turbulent kinetic energy and velocity skewness match observations, at least in a qualitative sense. The limited vertical extent of the domain and the artificial upper boundary, however, cause some departures from measured turbulence profiles in real forests. Instantaneous turbulent velocity and scalar fields are presented which show some of the features obtained by tower instrumentation in the field and in wind tunnels, such as the vertical coherence of vertical velocity and the slope of structures revealed by temperature patterns. 相似文献
592.
Ulrich Jürgens 《GeoJournal》1993,30(3):309-316
Even before the definite scrapping of the Group Areas Act in July 1991, mixed racial residential areas developed in South African cities. Against the Apartheid laws, this mainly occurred in central areas of the cities, which the white population had left during the process of suburbanization. Thus the moving of non-white, middle-class population groups into these areas became possible (so-called grey areas).The objective of this paper is to present and analyse one example for this development from the Johannesburg area. The following questions are examined by own investigations: the process of immigration and the succession of different groups of immigrants; the demographic and social characteristics of the inhabitants, esp. in comparison to the white population; small-scale concentration of different ethnic groups; conflicts between whites and non-whites; the consequences of the ethnic changes on neighbouring residential areas. The results lead to several hypotheses concerning the future development of South African cities. 相似文献
593.
594.
Silcretes from Queensland (Australia) were dated by means of the electron spin resonance dating technique. The results range from 1.5 to 10.8 million years; therefore, these silcretes were formed between the upper Miocene and the early Pleistocene. For a conclusive interpretation of the data geochemical and thin section analyses were also carried out. ESR dating of silcretes for the first time offers a direct approach to a chronostratigraphic framework of the genesis of these duricrusts, and of the palaeoclimatic events attributed to them. 相似文献
595.
The Quaternary Herchenberg composite tephra cone (East Eifel, FR Germany) with an original bulk volume of 1.17·107 m3 (DRE of 8.2·106 m3) and dimensions of ca. 900·600·90 m (length·width·height) erupted in three main stages: (a) Initial eruptions along a NW-trending, 500-m-long fissure were dominantly Vulcanian in the northwest and Strombolian in the southeast. Removal of the unstable, underlying 20-m-thick Tertiary clays resulted in major collapse and repeated lateral caving of the crater. The northwestern Lower Cone 1 (LC1) was constructed by alternating Vulcanian and Strombolian eruptions. (b) Cone-building, mainly Strombolian eruptions resulted in two major scoria cones beginning initially in the northwest (Cone 1) and terminating in the southeast (Cones 2 and 3) following a period of simultaneous activity of cones 1 and 2. Lapilli deposits are subdivided by thin phreatomagmatic marker beds rich in Tertiary clays in the early stages and Devonian clasts in the later stages. Three dikes intruded radially into the flanks of cone 1. (c) The eruption and deposition of fine-grained uppermost layers (phreatomagmatic tuffs, accretionary lapilli, and Strombolian fallout lapilli) presumably from the northwestern center (cone 1) terminated the activity of Herchenberg volcano. The Herchenberg volcano is distinguished from most Strombolian scoria cones in the Eifel by (1) small volume of agglutinates in central craters, (2) scarcity of scoria bomb breccias, (3) well-bedded tephra deposits even in the proximal facies, (4) moderate fragmentation of tephra (small proportions of both ash and coarse lapilli/bomb-size fraction), (5) abundance of dense ellipsoidal juvenile lapilli, and (6) characteristic depositional cycles in the early eruptive stages beginning with laterally emplaced, fine-grained, xenolith-rich tephra and ending with fallout scoria lapilli. Herchenberg tephra is distinguished from maar deposits by (1) paucity of xenoliths, (2) higher depositional temperatures, (3) coarser grain size and thicker bedding, (4) absence of glassy quenched clasts except in the initial stages and late phreatomagmatic marker beds, and (5) predominance of Strombolian, cone-building activity. The characteristics of Herchenberg deposits are interpreted as due to a high proportion of magmatic volatiles (dominantly CO2) relative to low-viscosity magma during most of the eruptive activity. 相似文献
596.
597.
Hans Ulrich Roll 《Ocean Dynamics》1951,4(4-6):172-174
Ohne Zusammenfassung 相似文献
598.
Die Matrix der Fische VII. Essentielle Aminosäuren inAbramis undSalmo (Pisces) sowieTubifex (Vermes)
Ulrich A. Corti 《Aquatic Sciences - Research Across Boundaries》1950,12(1):94-98
Summary The amount of 10 and 11 amino acids respectively has been estimated in (a) a complete specimen ofAbramis brama; (b) muscles ofSalmo irideus; (c) Tubifex sp.
6. Mitteilung (im Druck) siehe C. r. XXIIe Congr. Chimie industr. (Barcelona) 1949. 5. Mitteilung (im Druck) siehe Verh. Schweiz. naturf. Ges. (Lausanne), 1949. 相似文献
6. Mitteilung (im Druck) siehe C. r. XXIIe Congr. Chimie industr. (Barcelona) 1949. 5. Mitteilung (im Druck) siehe Verh. Schweiz. naturf. Ges. (Lausanne), 1949. 相似文献
599.
Ulrich A. Corti 《Aquatic Sciences - Research Across Boundaries》1953,15(1):152-157
Summary The protein component of activated sludge is constituted by numerous aminoacids. The amino-acid content of 1 lb. of activated
sludge solids (produced by the purification of about 1000 gal. of sewage) may be quantitatively and qualitatively compared
with that of 0·50 gal. of fresh cow milk.
相似文献
600.
Hans Ulrich Roll 《Ocean Dynamics》1952,5(2-3):141-143
Summary This paper deals with the results obtained from temperature measurements within a range of 50 cm above and about 6 cm below the water surface. These observations were carried out on small pools in the tide lands around the island of Neuwerk in summer 1950 with the so called pan or knitting needle thermometer, a thermometer whose mercury bulb is replaced by a long and very thin-walled tube allowing the mercury to quickly adapt to fluctuations of temperature.
Mesures de la température effectuées près de la surface de l'eau
Résumè On expose les résultats des mesures de la température effectuées entre l'altitude de 50 cm au dessus de la surface d'une part et la profondeur de 6 cm environ au dessous de la surface d'autre part. Ces observations qui ont été faites dans des flaques de marée des bas fonds aux alentours de l'île de Neuwerk en été 1950 furent exécutées avec un thermomètre à aiguille à tricoter. L'originalité de cet instrument réside dans la forme de la cuvette de mercure, tube long à paroi mince qui assure une vite adaptation du mercure à la température du milieu environnant.相似文献