Correlated evolution and dietary change in fossil stickleback     

Purnell MA  Bell MA  Baines DC  Hart PJ  Travis MP 《Science (New York, N.Y.)》2007,317(5846):1887

The importance of trophic ecology in adaptation and evolution is well known, yet direct evidence that feeding controls microevolution over extended evolutionary time scales, available only from the fossil record, is conspicuously lacking. Through quantitative analysis of tooth microwear, we show that rapid evolutionary change in Miocene stickleback was associated with shifts in feeding, providing direct evidence from the fossil record for changes in trophic niche and resource exploitation driving directional, microevolutionary change over thousands of years. These results demonstrate the potential for tooth microwear analysis to provide powerful insights into trophic ecology during aquatic adaptive radiations.  相似文献   

Age-associated inclusions in normal and transgenic mouse brain     

Wirak D  Bayney R  Ramabhadran TV  Fracasso RP  Hart JT  Hauer PE  Hsiau P  Pekar SK  Scangos GA  Trapp BD  Unterbeck AJ 《Science (New York, N.Y.)》1992,255(5050):1445

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Initial Analysis of OSTA-1 Ocean Color Experiment Imagery     

Kim HH  Hart WD  VAN DER Piepen H 《Science (New York, N.Y.)》1982,218(4576):1027-1031

Ocean images were obtained at three widely separated locations on the earth as part of NASA's ocean color experiment. Digital computer enhancement and band-ratioing techniques were applied to radiometrically corrected spectral data to emphasize patterns of chlorophyll distribution and, in one case, of bottom topography. The chlorophyll pattern in the Yellow Sea between China and Korea was evident in a scene produced from shuttle orbit 24. The effects of the discharge from the Yangtze and other rivers were also observed. Two scenes from orbits 30 and 32 revealed the movement of patches of plankton in the Gulf of Cádiz. Geometric corrections of these images permitted ocean current velocities in the vicinity to be deduced. The variability in water depth over the Grand Bahama Bank was estimated by using the blue-green channel of the instrument. The very clear water conditions in the area caused bottom-reflected sunlight to produce a sensor signal that was inversely related to the depth of the water.  相似文献   

THE ASSOCIATION OF TEACHERS OF MATHEMATICS IN THE MIDDLE STATES AND MARYLAND     

Hart HF 《Science (New York, N.Y.)》1911,33(836):40

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Epitaxial cuprate superconductor/ferroelectric heterostructures     

Ramesh R  Inam A  Chan WK  Wilkens B  Myers K  Remschnig K  Hart DL  Tarascon JM 《Science (New York, N.Y.)》1991,252(5008):944-946

Thin-film heterostructures of Bi(4)Ti(3)O(12)Bi(2)Sr(2)CuO(6+x), have been grown on single crystals of SrTiO(3), LaAlO(3), and MgAl(2)O(4) by pulsed laser deposition. X-ray diffraction studies show the presence of c-axis orientation only; Rutherford backscattering experiments show the composition to be close to the nominal stoichiometry. The films are ferroelectric and exhibit a symmetric hysteresis loop. The remanent polarization was 1.0 microcoulomb per square centimeter, and the coercive field was 2.0 x 10(5) volts per centimeter. Similar results were obtained with YBa(2)Cu(3)O(7-x) and Bi(2)Sr(2)CaCu(2)O(8+x), and single-crystal Bi(2)Sr(2)CuO(6+x)as the bottom electrodes. These films look promising for use as novel, lattice-matched, epitaxial ferroelectric film/electrode heterostructures in nonvolatile memory applications.  相似文献   

A specific, highly active malate dehydrogenase by redesign of a lactate dehydrogenase framework   总被引：19，自引：0，他引：19  

H M Wilks  K W Hart  R Feeney  C R Dunn  H Muirhead  W N Chia  D A Barstow  T Atkinson  A R Clarke  J J Holbrook 《Science (New York, N.Y.)》1988,242(4885):1541-1544

Three variations to the structure of the nicotinamide adenine dinucleotide (NAD)-dependent L-lactate dehydrogenase from Bacillus stearothermophilus were made to try to change the substrate specificity from lactate to malate: Asp197----Asn, Thr246----Gly, and Gln102----Arg). Each modification shifts the specificity from lactate to malate, although only the last (Gln102----Arg) provides an effective and highly specific catalyst for the new substrate. This synthetic enzyme has a ratio of catalytic rate (kcat) to Michaelis constant (Km) for oxaloacetate of 4.2 x 10(6)M-1 s-1, equal to that of native lactate dehydrogenase for its natural substrate, pyruvate, and a maximum velocity (250 s-1), which is double that reported for a natural malate dehydrogenase from B. stearothermophilus.  相似文献   

Thermohaline circulation, the achilles heel of our climate system: will man-made CO2 upset the current balance?   总被引：2，自引：0，他引：2  

WS Broecker 《Science (New York, N.Y.)》1997,278(5343):1582-1588

During the last glacial period, Earth's climate underwent frequent large and abrupt global changes. This behavior appears to reflect the ability of the ocean's thermohaline circulation to assume more than one mode of operation. The record in ancient sedimentary rocks suggests that similar abrupt changes plagued the Earth at other times. The trigger mechanism for these reorganizations may have been the antiphasing of polar insolation associated with orbital cycles. Were the ongoing increase in atmospheric CO2 levels to trigger another such reorganization, it would be bad news for a world striving to feed 11 to 16 billion people.  相似文献   

Free-radical carbon-carbon bond formation in organic synthesis     

Hart DJ 《Science (New York, N.Y.)》1984,223(4639):883-887

Organic chemists have begun to use intra- and intermolecular free-radical addition reactions to develop useful synthetic transformations. Carboncentered radicals can form bonds with electron-rich or electron-deficient alkenes, allenes, and acetylenes. Radical addition reactions can also be used to construct hindered carbon-carbon bonds. These characteristics, as well as the large number of functional groups that tolerate free-radical conditions contribute to the importance of such reactions in organic synthesis.  相似文献   

Effect of processing and storage on the ascorbic acid (vitamin C) content of some pineapple varieties grown in the Rivers State of Nigeria     

S. C. Achinewhu  A. D. Hart 《Plant foods for human nutrition (Dordrecht, Netherlands)》1994,46(4):335-337

Ascorbic acid contents of the juice of four different pineapples species grown in the Rivers State of Nigeria were determined before and after storage of whole pineapple and processing and storage of the juice for two months. Ascorbic acid of the fresh juice ranged from 22.5 mg to 33.5 mg/100 g sample. After storage at room temperature (30–32 °C) of whole pineapple for two weeks, ascorbic acid was reduced to between 59 and 65 percent of the fresh juice. Processing the juice by pasteurisation reduced the ascorbic acid to between 28 and 46 percent while storage in plastic bottles for two months further reduced the ascorbic acid content to between 10 and 21 percent.  相似文献   

Potato quality XIX: A preliminary study of the Browning reaction in potato chips using radiophosphorus     

Thomas G. Hart  Ora Smith 《American Journal of Potato Research》1963,40(12):421-429

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