Do bacteria-sized marine eukaryotes consume significant bacterial production?     

Fuhrman JA  McManus GB 《Science (New York, N.Y.)》1984,224(4654):1257-1260

Up to 60 percent of the total marine primary production (or about one-fourth of the total global carbon dioxide fixation) passes through the free-living bacterioplankton. Grazing by bacteriovores is probably the predominant fate of the bacteria, although data are scarce. Evidence is presented that previously uncharacterized, small eukaryotes that are able to pass even 0.6-micrometer filters may be responsible for a large fraction (more than 50 percent) of the total grazing in coastal waters. These organisms have not yet been observed microscopically.  相似文献   

Effects of pretreatment conditions on ammonium and nitrate uptake by Douglas-fir seedlings     

Rygiewicz PT  Bledsoe CS 《Tree physiology》1986,1(2):145-150

Effects of pretreatment solutions containing varying concentrations of calcium, potassium, ammonium and nitrate were evaluated by measuring fluxes of the same ions during a subsequent 4-hour uptake by Douglas-fir seedlings. Maximal rate of ammonium uptake (11 microeq g(-1) root dry weight h(-1)) was about 5 times faster than that of nitrate (2 microeq g(-1) root dry weight h(-1)). Ammonium uptake was most rapid after pretreatment with low potassium levels and was unaffected by ammonium pretreatment. Nitrate uptake was most rapid after pretreatment with high levels of nitrate and low levels of potassium. Calcium uptake was greater when nitrate replaced ammonium as the N source. High calcium pretreatment levels depressed subsequent calcium uptake or resulted in calcium release in both ammonium and nitrate experiments. Potassium efflux occurred with both N sources, but the release was less during nitrate uptake than during ammonium uptake. Efflux of potassium is probably associated with the high potassium status of the seedlings and the exchange between potassium and other cations. High levels of potassium in the pretreatment solutions enhanced potassium efflux and caused a reduction in the subsequent rates of uptake of both ammonium and nitrate. Length of pretreatment and seedling size generally did not affect uptake rates.  相似文献   

Validation of liquid chromatographic method for assay of calcitriol and alfacalcidol in capsule formulations     

B C Flann  B A Lodge 《Journal of the Association of Official Analytical Chemists》1986,69(6):1026-1030

The validation of a liquid chromatographic procedure suitable for the determination of calcitriol and alfacalcidol in their respective formulations labeled to contain at least 0.25 micrograms drug per unit is described. The capsule content is diluted and chromatographed in 15-20 min on silica columns (5 micron) with a mobile phase of hexane-tetrahydrofuran-methylene dichloride-isopropanol (72 + 12 + 12 + 4, v/v) with detection at 254 nm. The calibration curve is linear. Recoveries of "spikes" averaged 101% with a standard deviation of 2%. Precision was better than 1.5%.  相似文献   

Riverine mammals: otters     

Estes JA 《Science (New York, N.Y.)》1986,233(4770):1333-1334

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Venus: detailed mapping of maxwell montes region     

Alexandrov YN  Crymov AA  Kotelnikov VA  Petrov GM  Rzhiga ON  Sidorenko AI  Sinilo VP  Zakharov AI  Akim EL  Basilevski AT  Kadnichanski SA  Tjuflin YS 《Science (New York, N.Y.)》1986,231(4743):1271-1273

From October 1983 to July 1984, the north hemisphere of Venus, from latitude 30 degrees to latitude 90 degrees , was mapped by means of the radar imagers and altimeters of the spacecraft Venera 15 and Venera 16. This report presents the results of the radar mapping of the Maxwell Montes region, one of the most interesting features of Venus' surface. A radar mosaic map and contour map have been compiled.  相似文献   

Book reviews     

P. A. L. Wight  G. C. Perry 《British poultry science》1986,27(3):511-514

Birds Their Structure and Function, By A. S. King and J. McLelland, 1984. 2nd ed. 334 pp. illustrated. London, Baillière Tindall. £9.50. ISBN 0 7020 0872 9.

Proceedings of the 2nd European Symposium on Poultry Welfare, 1985. 360 pp. illustrated. German Branch of the World's Poultry Science Association, Celle, Institut für Kleintierzucht.  相似文献   

Optical experiments and weak interactions     

Bouchiat MA  Pottier L 《Science (New York, N.Y.)》1986,234(4781):1203-1210

Recent optical experiments have demonstrated cases in which mirror symmetry in stable atoms is broken during absorption of light. These results, which are in contradiction with quantum electrodynamics, support the theory of unification of the electromagnetic and weak forces. The interpretation of these experimental results is based on exchanges of weak neutral Z(0) bosons between the electrons and the nucleus of the atom. The information obtained from low-energy experiments is different from, but complementary to, the results of high-energy experiments. Sensitive measurements in a simple, reliably computable atom are in quantitative agreement with the standard electroweak theory and put stringent constraints on alternative models. Attaining sufficient accuracy in the experiments and the computations for the electroweak radiative corrections to manifest themselves is now the challenge for experimenters and theorists.  相似文献   

Changing climate: geothermal evidence from permafrost in the alaskan arctic   总被引：2，自引：0，他引：2  

Lachenbruch AH  Marshall BV 《Science (New York, N.Y.)》1986,234(4777):689-696

Temperature profiles measured in permafrost in northernmost Alaska usually have anomalous curvature in the upper 100 meters or so. When analyzed by heat-conduction theory, the profiles indicate a variable but widespread secular warming of the permafrost surface, generally in the range of 2 to 4 Celsius degrees during the last few decades to a century. Although details of the climatic change cannot be resolved with existing data, there is little doubt of its general magnitude and timing; alternative explanations are limited by the fact that heat transfer in cold permafrost is exclusively by conduction. Since models of greenhouse warming predict climatic change will be greatest in the Arctic and might already be in progress, it is prudent to attempt to understand the rapidly changing thermal regime in this region.  相似文献   

Sinking Slabs Puncture Layered Mantle Model: Seismologists are finding that oceanic plates sinking into the mantle plunge right through the supposedly impenetrable boundary between the upper and lower mantle     

Kerr RA 《Science (New York, N.Y.)》1986,231(4738):548-549

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Cliff swallow colonies as information centers     

Brown CR 《Science (New York, N.Y.)》1986,234(4772):83-85

Colonies of cliff swallows (Aves: Hirundo pyrrhonota) appear to be information centers in which colony residents acquire information on the location of food sources. Individuals that have been unsuccessful on a foraging trip return to the colony, locate a successful forager, and follow that individual to a food source. Individuals often follow, and are followed by, their neighbors within the colony, possibly because neighbors can observe foraging success through food brought back to nestlings. All individuals are equally likely to follow others or be followed, and thus all individuals benefit from opportunities to receive information.  相似文献