Mousterian cultures in European Russia     

Klein RG 《Science (New York, N.Y.)》1969,165(3890):257-265

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A thiosulfate shunt in the sulfur cycle of marine sediments   总被引：1，自引：0，他引：1  

Jørgensen BB 《Science (New York, N.Y.)》1990,249(4965):152-154

The oxidation of sulfide, generated by bacterial sulfate reduction, is a key process in the biogeochemistry of marine sediments, yet the pathways and oxidants are poorly known. By the use of (35)S-tracer studies of the S cycle in marine and freshwater sediments, a novel shunt function of thiosulfate (S(2)O(3)(2-)) was identified. The S(2)O(3)(2-) constituted 68 to 78 percent of the immediate HS(-)-oxidation products and was concurrently (i) reduced back to HS(-), (ii) oxidized to SO(4)(2-), and (iii) disproportionated to HS(-) + SO(4)(2-). The small thiosulfate pool is thus involved in a dynamic HS(-) - S(2)O(3)(2-) cycle in anoxic sediments. The disproportionation of thiosulfate may help account for the large difference in isotopic composition ((34)S/(32)S) of sulfate and sulfides in sediments and sedimentary rocks.  相似文献   

SURFACE SCIENCE: How to Power a Nanomotor     

Besenbacher F  Nørskov JK 《Science (New York, N.Y.)》2000,290(5496):1520

A successful nanotechnology will require nanomotors that can perform functions from switches to pumps and actuators. In their Perspective, Besenbacher and N?rskov discuss the study by Schmid et al., who show that tin islands on a copper surfaces propel themselves forward on the surface, drawing energy from alloy formation with the surface below. The system has about the same power-to-weight ratio as a car and may provide a paradigm for future nanomotors.  相似文献   

The interdiffision of polymers     

Klein J 《Science (New York, N.Y.)》1990,250(4981):640-646

In contrast to interdiffusion in simple liquids, interdiffusion of polymeric chains is dominated by their intertanglement and their large size. These properties profoundly reduce both the molecular mobilities and the role of entropy in driving the mixing. The resulting diffusional processes have only recently been studied. Such studies reveal a wide spectrum of behavior ranging from accelerated interdiffusion (for strongly compatible chains) to its suppression below the critical point for phase separation. Effects that are still poorly understood include the initial disposition at interfaces of the chains' ends (through which diffusion proceeds by reptation) and the need for cooperative motion, which can strongly magnify local friction.  相似文献   

Potassium induced improvement of yield response in barley exposed to soil water stress     

C. R. Jensen  H. Tophøj 《Irrigation Science》1985,6(2):117-129

Summary The interaction of different K status of barley plants (Hordeum vulgare, L.) and water stress on yield and water relations was studied. The plants which were cultivated outdoor in pots and supplied with 0.8, 5.0, 8.5 or 12.0 g K per pot, as KCl, were subjected to increased soil water stress during the early grain filling stage.The water content of the flag leaf tissue was significantly increased from 3.1 to 4.1 g H₂O/g D.M. (dry matter) by K application resulting in maintenance of similar leaf osmotic potentials (–1.5 MPa) at all K levels prior to onset of water stress (Table 2). At the lowest K level Ca contributed essentially to maintenance of the cell osmotic potential (Fig. 2).In fully watered plants grain yield at the lowest K level was reduced 20% (Fig. 5 a) due to a decrease in the number of tillers with ears per plant (Fig. 5 b) and to early commencement of maturity processes (Table 3).Water stress caused grain yield reductions between 15 and 50%. However, by increase of K application yield was maintained to the greatest degree in high K plants (Fig. 5 a) due to improved water status in these plants during the drying cycle (Fig. 4). The production of above ground dry matter (top D.M.) during the grain filling period and the grain yield were highly correlated with the leaf water content at the end of the drying cycles (Fig. 6). The greater yield in high K plants was associated with prolongation of the grain filling period by up to 7 days (Table 3) and with an increase in grain weight by up to 20% (Fig. 5 b) as compared with low K plants. Preanthesis reserves contributed up to 52% of grain yield at low K levels (Fig. 5 c) reducing differences in grain yield between the K levels.Abbreviations RWC predawn relative water content - predawn leaf osmotic potential - WUE water use efficiency - R preanthesis reserves - ear D.M. increase in ear D.M. during the grain filling period - top D.M. increase in top D.M. during the grain filling period - SD standard deviation - LSD least significant difference  相似文献   

Carotene, tocopherol, and ascorbate contents in subspecies of Brassica oleracea   总被引：1，自引：0，他引：1  

Kurilich AC  Tsau GJ  Brown A  Howard L  Klein BP  Jeffery EH  Kushad M  Wallig MA  Juvik JA 《Journal of agricultural and food chemistry》1999,47(4):1576-1581

Cruciferous vegetables contain high levels of vitamins that can act as antioxidants, compounds that may protect against several degenerative diseases. The edible portions of 50 broccoli and 13 cabbage, kale, cauliflower, and Brussels sprouts accessions were assayed to determine variation in alpha-carotene, beta-carotene, alpha-tocopherol, gamma-tocopherol, and ascorbate contents within and between subspecies of Brassica oleracea. Ascorbate content was estimated in fresh samples using HPLC. Tissues for carotene and tocopherol analysis were lyophilized prior to extraction. Carotene and tocopherol concentrations were simultaneously measured using a reverse phase HPLC system. Results indicate that there is substantial variation both within and between subspecies. Kale had the highest levels of vitamins, followed by broccoli and Brussels sprouts with intermediate levels and then by cabbage and cauliflower, with comparatively low concentrations. Variability in vitamin content among the broccoli accessions suggests that potential health benefits that accrue with consumption are genotype dependent.  相似文献   

Forthcoming Papers-JSS No. 4, 2004 (October issue)     

Ute Feiler  Ilona Kirchesch  Peter Heininger  J?rg R?mbke  Mónica Amorim  Gobi Muthukaruppan  Suman Janardhanan  Ganesan S. Vijayalakshmi 《Journal of Soils and Sediments》2004,4(3):212

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The diatoms: Applications for the environmental and earth sciences     

Susanne Raphael  Jörg Matschullat  Franz D. Oeste 《Journal of Soils and Sediments》2002,2(2):103-104

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Behaviour of sulphur and nitrogen compounds measured at marine stations Lista and Säby in Scandinavia     

J. Isakson  E. A. Selin Lindgren  V. L. Foltescu  J. M. Pacyna  K. Tørseth 《Water, air, and soil pollution》1995,85(4):2039-2044

Long distance transport of various air pollutants has been studied at two Scandinavian coastal sites. The measuring period has covered one year divided into 4 campaigns. Seasonal variations for sulphur and nitrogen compounds as well as anthropogenically emitted metals are reported. Concentrations of Pb and Zn as well as the ratio of V/Ni concentrations have been used to trace sulphuric episodes. Covariation of anthropogenic pollutants for the two sites is demonstrated.  相似文献   

The concentrations of K,Rb and Cs in spruce needles (Picea abies Karst.) and in the associated soils     

Armin Wyttenbach  Sixto Bajo  Jürg Bucher  Verena Furrer  Patrick Schleppi  Leonhard Tobler 《植物养料与土壤学杂志》1995,158(5):499-504

The elemental concentrations of K, Rb and Cs were determined in needles from individual spruce trees as a function of the needle age class. The concentrations are highest in current year's needles and decrease smoothly in older needles, approaching a constant value. Rb and Cs show similar behaviour, whereas that of K differs in so far as its relative decrease with time is less pronounced. Intra- and intersite variation of the needle concentrations are largest for Cs and smallest for K. Individual trees show a highly significant correlation between the log (Cs) and log (Rb) values. Total soil concentrations were determined at 9 sites with different parent material. Intra- and intersite variations of K are comparable for soils and for needles, whereas those for Rb and Cs are much smaller for soils than for needles. All three elements are correlated in soil samples. There is no close connection between soil and needle concentrations at the various sites. However, the results suggest that needle concentrations of Rb and Cs, but not of K, are strongly dependent on the sorption properties of the associated soils.  相似文献