Control of structure and growth of polymorphic crystalline thin films of amphiphilic molecules on liquid surfaces     

Weinbach SP  Kjaer K  Bouwman WG  Grübel G  Legrand JF  Als-Nielsen J  Lahav M  Leiserowitz L 《Science (New York, N.Y.)》1994,264(5165):1566-1570

The spontaneous formation and coexistence of crystalline polymorphic trilayer domains in amphiphilic films at air-liquid interfaces is demonstrated by grazing incidence synchrotron x-ray diffraction. These polymorphic crystallites may serve as models for the early stages of crystal nucleation and growth, helping to elucidate the manner in which additives influence the progress of crystal nucleation, growth, and polymorphism and suggesting ways of selectively generating and controlling multilayers on liquid surfaces. Auxiliary molecules have been designed to selectively inhibit development of the polymorphs, leading primarily to a single phase monolayer.  相似文献   

Bias in Peer Review of Organic Farming Grant Applications     

Jesper Rasmussen  Vibeke Langer  Hugo Fjelsted Alrøe 《Agriculture and Human Values》2006,23(2):181-188

Peer reviews of 84 organic farming grant applications from Sweden were analyzed to determine whether the reviewers’ affiliation to one of two types of agriculture (i.e., organic and conventional) influenced their reviews. Fifteen reviewers were divided into three groups: (1) scientists with experience in organic farming research; (2) scientists with no experience in organic farming research; and (3) users of organic farming research. The two groups of scientists assessed the societal relevance and scientific quality of the grant applications based on three criteria (i.e., presentation, methodology, qualifications), whereas the user group only assessed societal relevance. The analysis showed that the two groups of scientists provided very different reviews. Scientist reviewers with experience in organic farming research agreed more with the user group on research relevance than did scientist reviewers without such experience, and the assessment of relevance was closely correlated to the assessment of scientific quality within both scientific groups. As both scientific groups did not clearly distinguish between societal relevance and scientific quality, the idea of an objective science is challenged. The contextual values associated with the norms of good agriculture were not clearly distinguished from the constitutive values of science associated with the traditional norms of good science. This raises the question of whether organic and conventional grant applications should be mixed for review regardless of the reviewers.  相似文献   

One thousand centuries of climatic record from cAMP century on the greenland ice sheet   总被引：1，自引：0，他引：1  

Dansgaard W  Johnsen SJ  Møller J  Langway CC 《Science (New York, N.Y.)》1969,166(3903):377-380

A correlation of time with depth has been evaluated for the Camp Century, Greenland, 1390 meter deep ice core. Oxygen isotopes in approximately 1600 samples throughout the core have been analyzed. Long-term variations in the isotopic composition of the ice reflect the climatic changes during the past nearly 100,000 years. Climatic oscillations with periods of 120, 940, and 13,000 years are observed.  相似文献   

Creation of liquid crystal waveguides with scanning force microscopy     

Rüetschi M  Grütter P  Fünfschilling J  Güntherodt HJ 《Science (New York, N.Y.)》1994,265(5171):512-514

The rubbing of a polymer layer, a commonly applied process, leads to an anisotropic surface morphology, aligning liquid crystal molecules. Scanning force microscopy can be used to intentionally create areas with a similar anisotropy by operating the instrument at loads in the range of 10(-7) to 10(-5) newtons. These areas have an orientation effect on liquid crystals indistinguishable from the rubbing process, which allows a systematic investigation of the orientation properties of an alignment layer as a function of its nanometer-scale morphology. Refractive index patterns can be tailored with this method by scratching a suitable area, as demonstrated by fabrication of an optical waveguide 6 micrometers wide and 5 millimeters long.  相似文献   

Enhanced modern heat transfer to the Arctic by warm Atlantic Water   总被引：3，自引：0，他引：3  

Spielhagen RF  Werner K  Sørensen SA  Zamelczyk K  Kandiano E  Budeus G  Husum K  Marchitto TM  Hald M 《Science (New York, N.Y.)》2011,331(6016):450-453

The Arctic is responding more rapidly to global warming than most other areas on our planet. Northward-flowing Atlantic Water is the major means of heat advection toward the Arctic and strongly affects the sea ice distribution. Records of its natural variability are critical for the understanding of feedback mechanisms and the future of the Arctic climate system, but continuous historical records reach back only ~150 years. Here, we present a multidecadal-scale record of ocean temperature variations during the past 2000 years, derived from marine sediments off Western Svalbard (79°N). We find that early-21st-century temperatures of Atlantic Water entering the Arctic Ocean are unprecedented over the past 2000 years and are presumably linked to the Arctic amplification of global warming.  相似文献   

Oldest knowii terrestrial arachnids     

Størmer L 《Science (New York, N.Y.)》1969,164(3885):1276-1277

New finds of nonscorpionid arachnids in the Lower Devonian Nellenk?pfchen Shale of Alken an der Mosel, Germany, give valuable iniformation on the first appearance of terrestrial arachnids.  相似文献   

Mechanism of the selective catalytic reduction of nitric oxide by ammonia elucidated by in situ on-line fourier transform infrared spectroscopy   总被引：1，自引：0，他引：1  

Topsøe NY 《Science (New York, N.Y.)》1994,265(5176):1217-1219

The selective catalytic reduction reaction of nitric oxide bv ammonia over vanadia-titania catalysts is one of the methods of removing NOx pollution. In the present study, it has been possible to identify the reaction mechanism and the nature of the active sites in these catalysts by combining transient or steady-state in situ (Fourier transform infrared spectroscopy) experiments directly with on-line activity studies. The results suggest a catalytic cycle that consists of both acid and redox reactions and involves both surface V-OH (Br?nsted acid sites) and V=O species. A fundamental microkinetic model is proposed, which accounts for the observed industrial kinetics performance.  相似文献   

Paleo-Eskimo mtDNA genome reveals matrilineal discontinuity in Greenland     

Gilbert MT  Kivisild T  Grønnow B  Andersen PK  Metspalu E  Reidla M  Tamm E  Axelsson E  Götherström A  Campos PF  Rasmussen M  Metspalu M  Higham TF  Schwenninger JL  Nathan R  De Hoog CJ  Koch A  Møller LN  Andreasen C  Meldgaard M  Villems R  Bendixen C  Willerslev E 《Science (New York, N.Y.)》2008,320(5884):1787-1789

The Paleo-Eskimo Saqqaq and Independence I cultures, documented from archaeological remains in Northern Canada and Greenland, represent the earliest human expansion into the New World's northern extremes. However, their origin and genetic relationship to later cultures are unknown. We sequenced a mitochondrial genome from a Paleo-Eskimo human by using 3400-to 4500-year-old frozen hair excavated from an early Greenlandic Saqqaq settlement. The sample is distinct from modern Native Americans and Neo-Eskimos, falling within haplogroup D2a1, a group previously observed among modern Aleuts and Siberian Sireniki Yuit. This result suggests that the earliest migrants into the New World's northern extremes derived from populations in the Bering Sea area and were not directly related to Native Americans or the later Neo-Eskimos that replaced them.  相似文献   

Ecology. Vole stranglers and lemming cycles     

Hudson PJ  Bjørnstad ON 《Science (New York, N.Y.)》2003,302(5646):797-798

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A maximum in the strength of nanocrystalline copper     

Schiøtz J  Jacobsen KW 《Science (New York, N.Y.)》2003,301(5638):1357-1359

We used molecular dynamics simulations with system sizes up to 100 million atoms to simulate plastic deformation of nanocrystalline copper. By varying the grain size between 5 and 50 nanometers, we show that the flow stress and thus the strength exhibit a maximum at a grain size of 10 to 15 nanometers. This maximum is because of a shift in the microscopic deformation mechanism from dislocation-mediated plasticity in the coarse-grained material to grain boundary sliding in the nanocrystalline region. The simulations allow us to observe the mechanisms behind the grain-size dependence of the strength of polycrystalline metals.  相似文献