Mercury's Rotation Period: Photographic Confirmation     

Smith BA  Reese EJ 《Science (New York, N.Y.)》1968,162(3859):1275-1277

Photographic measures of surface features on Mercury have led to a rotation period of 58.663 +/- 0.021 days, which is in good agreement with the 58.646-day period required by a predicted 2:3 resonance between the axial and orbital periods. The incorrect interpretation of earlier visual and photographic observations which supported an 88-day rotation period appears to be partially explained by peculiar characteristics associated with the observability of various hermo-graphic longitudes. The apparent contrast of most of the recorded surface features is marginal for visual observation when viewed through the terrestrial daytime sky. The intrinsic contrast of a relatively conspicuous feature was measured as 0.20, a value lower than that of typical markings observed on the moon and Mars.  相似文献   

Experimental Diabetes and Diet     

Houssay BA  Martínez C 《Science (New York, N.Y.)》1947,105(2734):548-549

In the experiments described the following observations have been made: (1) The toxic and diabetogenic action of alloxan increases in rats fed a low protein diet and even more so in the case of a high lard or ox fat diet. (2) The action of these fat diets was corrected by the addition of methionine, thiouracil, or coconut oil, but there was no modification either by addition of choline or sulfonamide or by increase in the protein proportion. (3) In rats fed other high fat diets (olive oil, butter) the actions of alloxan were not modified, but there was a slight diminution when high oleomargarine or corn oil diets were fed. However, complete protection was observed when a high coconut oil diet was administered. (4) The unfavorable effect of the high lard diet was observed also on the initiation and evolution of diabetes due to subtotal pancreatectomy. Contrarily, feeding a high protein diet and especially treatment with thiouracil had a favorable effect. (5) Diabetes appeared first in subtotal pancreatectomized rats which were overfed, then in those which ate ad libitum, and finally in those which were underfed. Diabetes appeared in rats fed a single meal before it did in those eating the same amount of food divided into three meals.  相似文献   

Control of synapse number by glia   总被引：1，自引：0，他引：1  

Ullian EM  Sapperstein SK  Christopherson KS  Barres BA 《Science (New York, N.Y.)》2001,291(5504):657-661

Although astrocytes constitute nearly half of the cells in our brain, their function is a long-standing neurobiological mystery. Here we show by quantal analyses, FM1-43 imaging, immunostaining, and electron microscopy that few synapses form in the absence of glial cells and that the few synapses that do form are functionally immature. Astrocytes increase the number of mature, functional synapses on central nervous system (CNS) neurons by sevenfold and are required for synaptic maintenance in vitro. We also show that most synapses are generated concurrently with the development of glia in vivo. These data demonstrate a previously unknown function for glia in inducing and stabilizing CNS synapses, show that CNS synapse number can be profoundly regulated by nonneuronal signals, and raise the possibility that glia may actively participate in synaptic plasticity.  相似文献   

The Fiske Range-Finder     

Fiske BA 《Science (New York, N.Y.)》1890,15(368):134-135

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Mechanism of Na+/H+ antiporting     

Arkin IT  Xu H  Jensen MØ  Arbely E  Bennett ER  Bowers KJ  Chow E  Dror RO  Eastwood MP  Flitman-Tene R  Gregersen BA  Klepeis JL  Kolossváry I  Shan Y  Shaw DE 《Science (New York, N.Y.)》2007,317(5839):799-803

Na+/H+ antiporters are central to cellular salt and pH homeostasis. The structure of Escherichia coli NhaA was recently determined, but its mechanisms of transport and pH regulation remain elusive. We performed molecular dynamics simulations of NhaA that, with existing experimental data, enabled us to propose an atomically detailed model of antiporter function. Three conserved aspartates are key to our proposed mechanism: Asp164 (D164) is the Na+-binding site, D163 controls the alternating accessibility of this binding site to the cytoplasm or periplasm, and D133 is crucial for pH regulation. Consistent with experimental stoichiometry, two protons are required to transport a single Na+ ion: D163 protonates to reveal the Na+-binding site to the periplasm, and subsequent protonation of D164 releases Na+. Additional mutagenesis experiments further validated the model.  相似文献   

Materials science. Nanosprings take shape     

Korgel BA 《Science (New York, N.Y.)》2005,309(5741):1683-1684

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Localization of wheat germ agglutinin--like lectins in various species of the gramineae     

Mishkind ML  Palevitz BA  Raikhel NV  Keegstra K 《Science (New York, N.Y.)》1983,220(4603):1290-1292

Antigenically similar chitin-binding lectins are present in the embryos of wheat, barley, and rye, members of the Triticeae tribe of the grass family (Gramineae). However, the lectins display different localization patterns in these embryos. Lectin is absent from the coleoptile of barley but is present in the outer surface cells of this organ in wheat and in both inner and outer surface cells of rye coleoptiles. All three cereals contain lectin at the periphery of embryonic roots. Similar lectins were not detected in oats and pearl millet, members of other tribes of the Gramineae. Rice, a species only distantty related to wheat, contains a lectin that is antigenically similar to the other cereal lectins and located at the periphery of embryonic roots and throughut the coleoptile.  相似文献   

Mawson "tillite" in antarctica: preliminary report of a volcanic deposit of jurassic age     

Borns HW  Hall BA 《Science (New York, N.Y.)》1969,166(3907):870-872

Reexamination of the Mawson "Tillite" (Jurassic) of Antarctica indicates that the deposit is of volcanic origin and consists largely of both primary and reworked volcanic materials. No evidence diagnostic of a glacial origin was found.  相似文献   

Origin of lead in andean calc-alkaline lavas, southern peru     

Tilton GR  Barreiro BA 《Science (New York, N.Y.)》1980,210(4475):1245-1247

Lead isotope data from Quaternary andesitic lavas of the Arequipa and Barroso groups of southern Peru and from regional Precambrian granulitic gneisses reveal a lead component in the lavas from the gneisses. The lava leads can be accounted for by two-component mixtures of lead from mantle and lower crustal sources, although the mixing process need not have occurred in the lower crust.  相似文献   

Emergence of anoxia in the California current large marine ecosystem     

Chan F  Barth JA  Lubchenco J  Kirincich A  Weeks H  Peterson WT  Menge BA 《Science (New York, N.Y.)》2008,319(5865):920

Eastern boundary current systems are among the world's most productive large marine ecosystems. Because upwelling currents transport nutrient-rich but oxygen-depleted water onto shallow seas, large expanses of productive continental shelves can be vulnerable to the risk of extreme low-oxygen events. Here, we report the novel rise of water-column shelf anoxia in the northern California Current system, a large marine ecosystem with no previous record of such extreme oxygen deficits. The expansion of anoxia highlights the potential for rapid and discontinuous ecosystem change in productive coastal systems that sustain a major portion of the world's fisheries.  相似文献