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1.
Summary Theoretical considerations are put forward for identifying the Dynamic and Static Methods of Diffusion measurements of aerosol particles. On the basic of this equality the Exhaustion Method of Diffusion developed byPollak andMetnieks for the size-frequency resolution of a heterogeneous aerosol by Dynamic Diffusion Methods should be applicable to Static Methods. This hypothesis is tested using a Pollak-Nolan nucleus counter as decay vessel. It is shown that turbulence in the counter is the most serious obstacle against this type of approach to finding the size components of an aerosol. The time involved, the high humidity in the counter and a hypothetical nucleus-free zone are other major difficulties for relatively large Aitken nuclei. It is established, however, that for particles whose diffusion coefficient is of the order of 10–3 cm2 sec–1, the proposed method should be quite workable. 相似文献
2.
Ronald Osinga Arjen J. Kop Gerard C. A. Duineveld Rudolf A. Prins Fleur C. Van Duyl 《Journal of Sea Research》1996,36(3-4)
Benthic oxygen uptake, sulphate reduction and benthic bacterial production were measured at two contrasting locations in the southern North Sea: the shallow and turbulent Broad Fourteens area in the Southern Bight, and the deeper Oyster Grounds, a deposition area, where thermohaline stratification occurs during summer. Oxygen uptake and sulphate reduction showed a clear seasonal pattern in the Broad Fourteens area, indicating a supply of carbon to the benthic system that is closely related to the standing stock of carbon in the water column. This close benthic-pelagic coupling is probably due to the influence of the tide in this part of the North Sea, which keeps the water column permanently mixed. At the Oyster Grounds, no seasonal pattern was observed. Peaks in oxygen uptake and sulphate reduction were found in winter. Irregularly occurring events, such as storms and fishery-related activities, are likely to affect the benthic mineralization patterns in this area. Annual benthic carbon mineralization rates estimated from oxygen uptake rates were 44 gC·m−2 at the Broad Fourteens, and 131 gC·m−2 at the Oyster Grounds, of which 26 and 28%, respectively, could be attributed to sulphate reduction (assuming an annual sulphide reoxidation rate of 100%). Although sulphate reduction rates in the southern North Sea are higher than previously suggested, aerobic respiration is the most important pathway for benthic carbon mineralization at the stations visited. Production rates of benthic bacterial carbon measured with labelled leucine were much higher than carbon mineralization rates based on oxygen uptake or sulphate reduction. This may either imply a very high bacterial carbon conversion efficiency, or point to shortcomings in the accuracy of the techniques. A critical evaluation of the techniques is recommended. 相似文献
3.
In turbidites, homogeneous and pelagic deposits of the Zaire Fan Th, La, Sm, and Rb and to a lesser extent Yb and Ta correlate strongly. La, Sm, Yb, Rb, Ta, and Th increase two-fold in Te3 turbidite intervals relative to Te 1 due to an increase in clay fraction with which these elements occur associated preferentially.Hf and Zr are anomalously high in Tel and Tel intervals which is probably a result of mineral separation. Zr is absent in Te3 intervals and the homogenous and pelagic deposits. Ba, Br. and U are lowest in turbidites and highest in homogenous continental slope deposits which is probably caused by upwelling. Cc anomalies may be related to the crystallinity of smectite. 相似文献
4.
Genetic Relationships Among One Non-Endemic and Two Endemic Mediterranean Triplefin Blennies (Pisces, Blennioidei) 总被引:1,自引:0,他引:1
Gerard J. Geertjes Albert Kamping Wilke van Delden & John J. Videler 《Marine Ecology》2001,22(3):255-265
Abstract. Three triplefin blennies occur sympatrically in the Mediterranean Sea; Tripterygion tripteronotus and T. melanurus are endemic, whereas T. delaisi is also found in the Eastern Atlantic. Although very similar in morphology, ecology and behaviour, some striking differences exist among reproductive strategies. Several authors proposed hypotheses on the evolution of these species. In order to enhance insight into the genetic structure of this genus, an enzyme electrophoretic survey was performed. Samples of 40 to 45 specimens of each species were collected near Calvi (Corsica, France). Twenty-four enzyme loci were analysed, of which 17 appeared polymorphic. T. delaisi showed a high level of average observed heterozygosity (Ho ) of 0.140, as opposed to very low levels of 0.009 and 0.021 in T. tripteronotus and T. melanurus , respectively. Nei's genetic distance was 0.21 between T. delaisi and T. tripteronotus , 0.35 between T. delaisi and T. melanurus and 0.45 between T. tripteronotus and T. melanurus . We hypothesise that divergence of these species started before the Pleistocene and that the endemic species survived the Pleistocene glaciations in refugia within the Mediterranean. The possibility that T. tripteronotus and T. delaisi diverged through sympatric speciation is discussed. 相似文献
5.
Results concerning the concentration of cadmium and lead in Mediterranean waters collected during the 2nd PHYCEMED cruise (Oct. 1983) are discussed. Sampling has been performed at seven stations in the Western Mediterranean Basin, two in the Strait of Gibraltar and the near Atlantic, two in the Sicily Strait and the Eastern Basin.In the Western Basin the observations are in fair agreement with those of PHYCEMED 1. Cadmium has a fairly homogeneous distribution vertically as well as from one station to another, with an average concentration of 8 ng l−1; while lead shows a slight but continuous decrease in concentrations with depth (from at least 50 ng l−1 in surface waters to 20 or 25 ng l−1 at depth). On the other hand, at the basin boundaries, where waters from different origins are present, vertical distributions appear very different. On the basis of calculated water budgets it can be estimated that the Mediterranean Sea discharges about 200 t y−1 of cadmium and about 250 t y−1 of lead into the Atlantic Ocean while 1000 t y−1 of lead are transferred from the Western to the Eastern Basin. 相似文献
6.
Florent Domin Roda Bounaceur Gerard Scacchi Paul-Marie Marquaire Daniel Dessort Bernard Pradier Olivier Brevart 《Organic Geochemistry》2002,33(12)
The discovery of crude oils and condensates at ever higher temperatures casts doubt on the validity of the usual geochemical modelling approach, that uses empirical reactions and rate constants. The solution used to account for such a high thermal stability is presently to adjust the rate parameters, but the physical meaning and scientific value of such a strategy can be questioned. We have developed a mechanistic model consisting of 5200 lumped free radical reactions to describe the thermal evolution of a mixture of 52 organic species meant to represent light petroleum. Rate constants used are those available in the literature or estimated using well established thermochemistry-reactivity correlations. Chemical structures included in the model are linear, branched and cyclic hydrocarbons, hydro- and alkyl-aromatics, PAHs, and three heteroatomic compounds. Reactions include cracking and alkylation chains and inhibiting and accelerating reactions from the various reactants. This model has been applied to several mixtures with various proportions of reaction inhibitors and accelerators, and to a composition representing a light mature oil. From the results obtained, we conclude that mature oils will be stable up to 240–260 °C, depending on their composition, and that the thermal cracking of oil to gas is not possible under reasonable basin conditions. The kinetics of petroleum cracking are thus much slower than generally recognized. 相似文献
7.
Gerard T. Schuster 《Geophysical Journal International》1996,127(2):427-440
8.
Olivier Planchon Norbert Silvera Raphael Gimenez David Favis‐Mortlock John Wainwright Yves Le Bissonnais Gerard Govers 《地球表面变化过程与地形》2005,30(7):833-844
This article introduces the SVG (salt‐velocity gauge), a novel automated technique for measuring flow velocity by means of salt tracing. SVG allows a high measuring rate (up to one every 2 seconds), short control section length (down to 10 cm), high accuracy (+[sol ]?1·5 cm s?1), and unbiased calculation of the mean velocity in experimental conditions with turbulent, supercritical flow. A few cubic centimetres of saturated salt solution (NaCl) are injected into the flow at regular time intervals using a programmable solenoid valve. The tracer successively passes two conductivity probes placed a short distance downstream. The transformation of the signal between the two probes is modelled as a one‐dimensional diffusion wave equation. Model calibration gives an estimation of the mean velocity and the diffusion for each salt plume. Two implementations of the SVG technique are described. The first was an outdoors simulated rainfall experiment in Senegal (conductivity probes at 40 cm apart, 8 Hz measurement rate, salt injections at 10 second intervals). Mean velocity was estimated to range between 0·1 and 0·3 m s?1. The second was a laboratory‐based flume experiment (conductivity probes at 10 cm apart, 32 Hz, salt injections at 2 second intervals). Another SVG with probes at 34 cm apart was used for comparison. An acoustic Doppler velocimeter (ADV) was also used to give an independent assessment of velocity. Using the 10 cm salt gauge, estimated mean velocity ranged from 0·6 to 0·9 m s?1 with a standard deviation of 1·5 cm s?1. Comparisons between ADV, 10 cm SVG and 34 cm SVG were consistent and demonstrated that the salt‐tracing results were unbiased and independent of distance between probes. Most peaks were modelled with r2 > 90 per cent. The SVG technology offers an alternative to the dye‐tracing technique, which has been severely criticized in the literature because of the wide interval of recommended values for the correction factor α to be applied to the timings. This article demonstrates that a fixed value of α is inappropriate, since the correction factor varies with velocity, diffusion and the length of the control section. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
9.
The outer slope of the eastern reefs of Mauritius shows: from 0 to 15 m depth, a spurs-and-grooves zone of coral morphogenesis, sometimes replaced by a flagstone of coral morphogenesis (down to 20 m) or a spurs-and-grooves zone of volcanic morphogenesis; from 20 to 50 m, a volcanic flagstone with a thin coral-built layer and a buttresses-and-valleys zone of volcanic morphogenesis. The living cover of the upper part (0–15 m) is also quite similar to the cover of the leeward side. On the contrary, the volcanic basement in the lower part is poorly covered by reef-building organisms, while soft or slightly calcified algae are of widespread occurrence. 相似文献
10.
Mulamba Teddy Bacopoulos Peter Kubatko Ethan J. Pinto Gerard F. 《Climatic change》2019,152(3-4):533-550
Climatic Change - Salinity response to sea-level rise is evaluated for a low-gradient, tidally active estuary, the lower St. Johns River, Florida. A high-resolution numerical model is forced by... 相似文献