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661.
When organisms as diverse as yeast and rodents are subjected to a restricted diet, they live longer. The good news is, according to Vaupel, Carey, and Christensen in their Perspective, that switching to a restricted diet at any age can yield the benefit of increased longevity--at least in flies (Mair et al.). 相似文献
662.
Arvidson RE Anderson RC Bartlett P Bell JF Blaney D Christensen PR Chu P Crumpler L Davis K Ehlmann BL Fergason R Golombek MP Gorevan S Grant JA Greeley R Guinness EA Haldemann AF Herkenhoff K Johnson J Landis G Li R Lindemann R McSween H Ming DW Myrick T Richter L Seelos FP Squyres SW Sullivan RJ Wang A Wilson J 《Science (New York, N.Y.)》2004,305(5685):821-824
The precise location and relative elevation of Spirit during its traverses from the Columbia Memorial station to Bonneville crater were determined with bundle-adjusted retrievals from rover wheel turns, suspension and tilt angles, and overlapping images. Physical properties experiments show a decrease of 0.2% per Mars solar day in solar cell output resulting from deposition of airborne dust, cohesive soil-like deposits in plains and hollows, bright and dark rock coatings, and relatively weak volcanic rocks of basaltic composition. Volcanic, impact, aeolian, and water-related processes produced the encountered landforms and materials. 相似文献
663.
Studt F Abild-Pedersen F Bligaard T Sørensen RZ Christensen CH Nørskov JK 《Science (New York, N.Y.)》2008,320(5881):1320-1322
The removal of trace acetylene from ethylene is performed industrially by palladium hydrogenation catalysts (often modified with silver) that avoid the hydrogenation of ethylene to ethane. In an effort to identify catalysts based on less expensive and more available metals, density functional calculations were performed that identified relations in heats of adsorption of hydrocarbon molecules and fragments on metal surfaces. This analysis not only verified the facility of known catalysts but identified nickel-zinc alloys as alternatives. Experimental studies demonstrated that these alloys dispersed on an oxide support were selective for acetylene hydrogenation at low pressures. 相似文献
664.
Christensen PR Ruff SW Fergason RL Knudson AT Anwar S Arvidson RE Bandfield JL Blaney DL Budney C Calvin WM Glotch TD Golombek MP Gorelick N Graff TG Hamilton VE Hayes A Johnson JR McSween HY Mehall GL Mehall LK Moersch JE Morris RV Rogers AD Smith MD Squyres SW Wolff MJ Wyatt MB 《Science (New York, N.Y.)》2004,305(5685):837-842
The Miniature Thermal Emission Spectrometer (Mini-TES) on Spirit has studied the mineralogy and thermophysical properties at Gusev crater. Undisturbed soil spectra show evidence for minor carbonates and bound water. Rocks are olivinerich basalts with varying degrees of dust and other coatings. Dark-toned soils observed on disturbed surfaces may be derived from rocks and have derived mineralogy (+/-5 to 10%) of 45% pyroxene (20% Ca-rich pyroxene and 25% pigeonite), 40% sodic to intermediate plagioclase, and 15% olivine (forsterite 45% +/-5 to 10). Two spectrally distinct coatings are observed on rocks, a possible indicator of the interaction of water, rock, and airfall dust. Diurnal temperature data indicate particle sizes from 40 to 80 microm in hollows to approximately 0.5 to 3 mm in soils. 相似文献
665.
Tolson RH Duxbury TC Born GH Christensen EJ Diehl RE Farless D Hildebrand CE Mitchell RT Molko PM Morabito LA Palluconi FD Reichert RJ Taraji H Veverka J Neugebauer G Findlay JT 《Science (New York, N.Y.)》1978,199(4324):61-64
During the last 2 weeks of February 1977, an intensive scientific investigation of the martian satellite Phobos was conducted by the Viking Orbiter-1 (VO-1) spacecraft. More than 125 television pictures were obtained during this period and infrared observations were made. About 80 percent of the illuminated hemisphere was imaged at a resolution of about 30 meters. Higher resolution images of limited areas were also obtained. Flyby distances within 80 kilometers of the surface were achieved. An estimate of the mass of Phobos (GM) was obtained by observing the effect of Phobos's gravity on the orbit of VO-1 as sensed by Earth-based radiometric tracking. Preliminary results indicate a value of GM of 0.00066 +/- 0.00012 cubic kilometer per second squared (standard deviation of 3) and a mean density of about 1.9 +/- 0.6 gram per cubic centimeter (standard deviation of 3). This low density, together with the low albedo and the recently determined spectral reflectance, suggest that Phobos is compositionally similar to type I carbonaceous chondrites. Thus, either this object formed in the outer part of the asteroid belt or Lewis's theory that such material cannot condense at 1.5 astronomical units is incorrect. The data on Phobos obtained during this first encounter period are comparable in quantity to all of the data on Mars returned by Mariner flights 4, 6, and 7. 相似文献
666.
667.
Zini CA Augusto F Christensen E Caramão EB Pawliszyn J 《Journal of agricultural and food chemistry》2002,50(25):7199-7205
Headspace solid-phase microextraction coupled to gas chromatography/ion trap mass spectrometry-65 microm polydimethylsiloxane/divinylbenzene (PDMS/DVB) was used to identify and monitor the emission patterns of biogenic volatile organic compounds from leaves of Eucalyptus dunnii, Eucalyptus saligna, and Eucalyptus citriodora in situ. Short extractions (1 min) were performed every 30 min for periods of 8-10 h during 24 days taking advantage of the high capacity of this porous polymer coating. Forty-two compounds were detected and 20 identified in the headspace of E. saligna leaves, and 19 of 27 compounds were identified in the headspace of E. dunnii leaves. The emission pattern of (E)-beta-ocimene and rose oxide suggests that they may play a bioactive role in Eucalyptus. 相似文献
668.
Jesper Brandt Andreas Aagaard Christensen Stig Roar Svenningsen Esbern Holmes 《Landscape Ecology》2013,28(6):1125-1137
Conceptual frameworks which have seen man and nature as being an integrated whole were widespread before they became suppressed by developments within both capitalism and socialism. Therefore an idealistic use of such concepts in scientific work has often had limited practical value. At the same time, the practice behind such conceptual frameworks has survived in many land use systems, being a fundamental source of inspiration for the modern challenge of landscape sustainability. Here, the concept and practice of carrying capacity is used as an example. We provide a modern interpretation and relate it to an empirical study of sustainable tourism in eight protected areas and their regions in the Baltic. They are subject to large differences in human pressure. The political commitment to the related EU Natura 2000 networks has been taken as our point of departure for a more detailed analysis of accessibility and its related conflicts, and opportunities for a sustainable development of tourism in and around the protected areas. It is concluded that the concept of carrying capacity cannot meaningfully be used for sustainability studies at an abstract conceptual level, but proves its relevance through a detailed context specific analyses of visitor related conflicts. 相似文献
669.
Langkilde S Schrøder M Stewart D Meyer O Conner S Davies H Poulsen M 《Journal of agricultural and food chemistry》2008,56(18):8753-8760
Sprouted, stressed, or spoiled potato tubers have reportedly led to human acute intoxication, coma, and death when consumed in high amounts. These effects have been attributed to glycoalkaloids (GAs), primarily alpha-solanine and alpha-chaconine, naturally present in all potatoes. The level of GAs in potato tubers has previously been shown to increase substantially as a result of improper handling and postharvest storage. A short-term study was performed to investigate the dose-response profile of alpha-solanine and alpha-chaconine alone or in combination, administered daily by oral gavage to Syrian Golden hamsters. Daily doses of 100 mg of alpha-solanine [kg body weight (BW)] (-1) induced death in two of four hamsters within 4 days, when administered by gavage to female Syrian hamsters. Doses of 100 mg of alpha-chaconine alone or alpha-solanine and alpha-chaconine combined in a ratio of 1:2.5, in doses of 75 or 100 mg (kg BW) (-1), induced death in one of four hamsters within the same period. Animals dosed with alpha-solanine alone or in combination with alpha-chaconine suffered from fluid-filled and dilated small intestines. The GA administration had no effect on acetyl cholinesterase (AChE) or butyryl cholinesterase (BuChE) activity in plasma or brain. Liquid chromatography-mass spectrometry-based metabolomics showed that there was a specific accumulation of alpha-chaconine in the liver tissues. In addition, metabolomics gave direct evidence of glycolytic metabolism of the GA with the beta 1, beta 2, and gamma-GAs detected in the urine and, to a lesser extent, the feces. Doses from 75 mg (kg BW) (-1) of alpha-chaconine, alpha-solanine, or the two compounds combined were potentially lethal within 4-5 days in the Syrian Golden hamster. However, the cause of death in these studies could not be established. No synergistic effects of alpha-solanine combined with alpha-chaconine were evident. 相似文献
670.
Polycyclic Aromatic Hydrocarbons in the Sediments of the Milwaukee Harbor Estuary, Wisconsin, U.S.A.
An Li Irwan A. Ab Razak Fan Ni Michael F. Gin Erik R. Christensen 《Water, air, and soil pollution》1998,101(1-4):417-434
From 1990 to 1994, a total of 21 sediment cores and 37 grab sediment samples were collected from the Milwaukee Harbor Estuary. Each sediment core was sectioned and dated using 210Pb and137 Cs radioisotope techniques. A total of 305 samples were analyzed for sixteen polycyclic aromatic compounds (PAHs). Grain size distribution, porosity, and total organic carbon content as measured by loss on ignition were also determined. The results provide a historical overview of the impact of industrialization in the Milwaukee area. Although highly variable, the concentration profile of PAHs show, in general, peaks in the 1950's through 1980's. The PAH concentrations have declined since then for most sediment cores. The current levels of total PAHs in most surface sediment samples range from 25 to 200 ppm. A few cores, some of which were collected in 1994, have an elevated PAH concentration at the surface. Toxicity of the surface sediments was evaluated by comparing with the benchmark values developed by the United States National Oceanic and Atmospheric Administration (NOAA). The most heavily contaminated area was found in the Kinnickinnic River between the Becher Street Bridge and the Wisconsin Wrecking Company Wharf. The highest total PAH concentration determined from seven vibra cores collected in this area ranges from 380 to 1000 ppm. The former Wisconsin Solvay Coke Company may have been a major point source of PAHs until the 1970's. Highway traffic and various industrial discharges also contribute to the sediment PAHs in this area. 相似文献