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601.
• Introduction
Clay soils are typically rich in nutrients but are often compact and hard during summer increasing planting shock by limiting root development. Recycling farm manure in hybrid poplar plantations may offer additional benefits to mineral fertilizer as organic amendment can create better conditions for the early development of roots in addition to nutrient release. 相似文献602.
Bertrand G 《Science (New York, N.Y.)》2004,305(5685):783-785
603.
van de Koppel J Gascoigne JC Theraulaz G Rietkerk M Mooij WM Herman PM 《Science (New York, N.Y.)》2008,322(5902):739-742
Spatial self-organization is the main theoretical explanation for the global occurrence of regular or otherwise coherent spatial patterns in ecosystems. Using mussel beds as a model ecosystem, we provide an experimental demonstration of spatial self-organization. Under homogeneous laboratory conditions, mussels developed regular patterns, similar to those in the field. An individual-based model derived from our experiments showed that interactions between individuals explained the observed patterns. Furthermore, a field study showed that pattern formation affected ecosystem-level processes in terms of improved growth and resistance to wave action. Our results imply that spatial self-organization is an important determinant of the structure and functioning of ecosystems, and it needs to be considered in their conservation. 相似文献
604.
Schawinski K Justham S Wolf C Podsiadlowski P Sullivan M Steenbrugge KC Bell T Röser HJ Walker ES Astier P Balam D Balland C Carlberg R Conley A Fouchez D Guy J Hardin D Hook I Howell DA Pain R Perrett K Pritchet C Regnault N Yi SK 《Science (New York, N.Y.)》2008,321(5886):223-226
Massive stars undergo a violent death when the supply of nuclear fuel in their cores is exhausted, resulting in a catastrophic "core-collapse" supernova. Such events are usually only detected at least a few days after the star has exploded. Observations of the supernova SNLS-04D2dc with the Galaxy Evolution Explorer space telescope reveal a radiative precursor from the supernova shock before the shock reached the surface of the star and show the initial expansion of the star at the beginning of the explosion. Theoretical models of the ultraviolet light curve confirm that the progenitor was a red supergiant, as expected for this type of supernova. These observations provide a way to probe the physics of core-collapse supernovae and the internal structures of their progenitor stars. 相似文献
605.
Millar CB Guy J Sansom OJ Selfridge J MacDougall E Hendrich B Keightley PD Bishop SM Clarke AR Bird A 《Science (New York, N.Y.)》2002,297(5580):403-405
The mammalian protein MBD4 contains a methyl-CpG binding domain and can enzymatically remove thymine (T) or uracil (U) from a mismatched CpG site in vitro. These properties suggest that MBD4 might function in vivo to minimize the mutability of 5-methylcytosine by removing its deamination product from DNA. We tested this hypothesis by analyzing Mbd4-/- mice and found that the frequency of of C --> T transitions at CpG sites was increased by a factor of three. On a cancer-susceptible Apc(Min/+) background, Mbd4-/- mice showed accelerated tumor formation with CpG --> TpG mutations in the Apc gene. Thus MBD4 suppresses CpG mutability and tumorigenesis in vivo. 相似文献
606.
Nelissen K Luppino G Vanduffel W Rizzolatti G Orban GA 《Science (New York, N.Y.)》2005,310(5746):332-336
Observation of actions performed by others activates monkey ventral premotor cortex, where action meaning, but not object identity, is coded. In a functional MRI (fMRI) study, we investigated whether other monkey frontal areas respond to actions performed by others. Observation of a hand grasping objects activated four frontal areas: rostral F5 and areas 45B, 45A, and 46. Observation of an individual grasping an object also activated caudal F5, which indicates different degrees of action abstraction in F5. Observation of shapes activated area 45, but not premotor F5. Convergence of object and action information in area 45 may be important for full comprehension of actions. 相似文献
607.
Canfield DE Poulton SW Knoll AH Narbonne GM Ross G Goldberg T Strauss H 《Science (New York, N.Y.)》2008,321(5891):949-952
Earth's surface chemical environment has evolved from an early anoxic condition to the oxic state we have today. Transitional between an earlier Proterozoic world with widespread deep-water anoxia and a Phanerozoic world with large oxygen-utilizing animals, the Neoproterozoic Era [1000 to 542 million years ago (Ma)] plays a key role in this history. The details of Neoproterozoic Earth surface oxygenation, however, remain unclear. We report that through much of the later Neoproterozoic (<742 +/- 6 Ma), anoxia remained widespread beneath the mixed layer of the oceans; deeper water masses were sometimes sulfidic but were mainly Fe2+-enriched. These ferruginous conditions marked a return to ocean chemistry not seen for more than one billion years of Earth history. 相似文献
608.
Damsté JS Muyzer G Abbas B Rampen SW Massé G Allard WG Belt ST Robert JM Rowland SJ Moldowan JM Barbanti SM Fago FJ Denisevich P Dahl J Trindade LA Schouten S 《Science (New York, N.Y.)》2004,304(5670):584-587
The 18S ribosomal DNA molecular phylogeny and lipid composition of over 120 marine diatoms showed that the capability to biosynthesize highly branched isoprenoid (HBI) alkenes is restricted to two specific phylogenetic clusters, which independently evolved in centric and pennate diatoms. The molecular record of C25 HBI chemical fossils in a large suite of well-dated marine sediments and petroleum revealed that the older cluster, composed of rhizosolenid diatoms, evolved 91.5 +/- 1.5 million years ago (Upper Turonian), enabling an accurate dating of the pace of diatom evolution that is unprecedented. The rapid rise of the rhizosolenid diatoms probably resulted from a major reorganization of the nutrient budget in the mid-Cretaceous oceans, triggered by plate tectonics. 相似文献
609.
Purification of a Low Molecular Weight Fucoidan for SPECT Molecular Imaging of Myocardial Infarction
Pierre Saboural Frédéric Chaubet Francois Rouzet Faisal Al-Shoukr Rana Ben Azzouna Nadia Bouchemal Luc Picton Liliane Louedec Murielle Maire Lydia Rolland Guy Potier Dominique Le Guludec Didier Letourneur Cédric Chauvierre 《Marine drugs》2014,12(9):4851-4867
Fucoidans constitute a large family of sulfated polysaccharides with several biochemical properties. A commercial fucoidan from brown algae, containing low molecular weight polysaccharidic species constituted of l-fucose, uronic acids and sulfate groups, was simply treated here with calcium acetate solution. This treatment led to a purified fraction with a yield of 45%. The physicochemical characterizations of the purified fucoidan using colorimetric assay, MALLS, dRI, FT-IR, NMR, exhibited molecular weight distributions and chemical profiles similar for both fucoidans whereas the sulfate and l-fucose contents increased by 16% and 71%, respectively. The biodistribution study in rat of both compounds labeled with 99mTc evidenced a predominant renal elimination of the purified fucoidan, but the crude fucoidan was mainly retained in liver and spleen. In rat myocardial ischemia-reperfusion, we then demonstrated the better efficiency of the purified fucoidan. This purified sulfated polysaccharide appears promising for the development of molecular imaging in acute coronary syndrome. 相似文献
610.