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991.
Roadless space of the conterminous United States 总被引:1,自引:0,他引:1
Watts RD Compton RW McCammon JH Rich CL Wright SM Owens T Ouren DS 《Science (New York, N.Y.)》2007,316(5825):736-738
Roads encroaching into undeveloped areas generally degrade ecological and watershed conditions and simultaneously provide access to natural resources, land parcels for development, and recreation. A metric of roadless space is needed for monitoring the balance between these ecological costs and societal benefits. We introduce a metric, roadless volume (RV), which is derived from the calculated distance to the nearest road. RV is useful and integrable over scales ranging from local to national. The 2.1 million cubic kilometers of RV in the conterminous United States are distributed with extreme inhomogeneity among its counties. 相似文献
992.
Ané JM Kiss GB Riely BK Penmetsa RV Oldroyd GE Ayax C Lévy J Debellé F Baek JM Kalo P Rosenberg C Roe BA Long SR Dénarié J Cook DR 《Science (New York, N.Y.)》2004,303(5662):1364-1367
Legumes form symbiotic associations with both mycorrhizal fungi and nitrogen-fixing soil bacteria called rhizobia. Several of the plant genes required for transduction of rhizobial signals, the Nod factors, are also necessary for mycorrhizal symbiosis. Here, we describe the cloning and characterization of one such gene from the legume Medicago truncatula. The DMI1 (does not make infections) gene encodes a novel protein with low global similarity to a ligand-gated cation channel domain of archaea. The protein is highly conserved in angiosperms and ancestral to land plants. We suggest that DMI1 represents an ancient plant-specific innovation, potentially enabling mycorrhizal associations. 相似文献
993.
As a result of increasing frequency and intensity of tropical cyclones, an accurate forecasting of cyclone evolution and ocean response is becoming even more important to reduce threats to lives and property in coastal regions. To improve predictions, accurate evaluation of the air-sea momentum exchange is required. Using current observations recorded during a major tropical cyclone, we have estimated this momentum transfer from the ocean side of the air-sea interface, and we discuss it in terms of the drag coefficient. For winds between 20 and 48 meters per second, this coefficient initially increases and peaks at winds of about 32 meters per second before decreasing. 相似文献
994.
Hurricane Ivan, a category 4 storm, passed directly over six wave-tide gauges deployed by the Naval Research Laboratory on the outer continental shelf in the northeastern Gulf of Mexico. Waves were observed with significant wave heights reaching 17.9 meters and maximum crest-to-trough individual wave heights of 27.7 meters (91 feet). Analysis suggests that significant wave heights likely surpassed 21 meters (69 feet) and that maximum crest-to-trough individual wave heights exceeded 40 meters (132 feet) near the eyewall. 相似文献
995.
Antiallergic drug cromolyn may inhibit histamine secretion by regulating phosphorylation of a mast cell protein 总被引:8,自引:0,他引:8
Cromolyn inhibited histamine release from mast cells that was induced by a classic secretagogue and correspondingly increased incorporation of radioactive phosphate into a 78,000-dalton protein. These effects on histamine secretion and on protein phosphorylation were rapid in onset and both showed tachyphylaxis. Cromolyn may therefore act by altering the phosphorylation of a protein involved in the regulation of secretion. 相似文献
996.
Ramalho-Santos M Yoon S Matsuzaki Y Mulligan RC Melton DA 《Science (New York, N.Y.)》2002,298(5593):597-600
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999.
Multiple unrelated polymer systems have evolved to partition DNA molecules between daughter cells at division. To better understand polymer-driven DNA segregation, we reconstituted the three-component segregation system of the R1 plasmid from purified components. We found that the ParR/parC complex can construct a simple bipolar spindle by binding the ends of ParM filaments, inhibiting dynamic instability, and acting as a ratchet permitting incorporation of new monomers and riding on the elongating filament ends. Under steady-state conditions, the dynamic instability of unattached ParM filaments provides the energy required to drive DNA segregation. 相似文献
1000.
Lightfoot HD 《Science (New York, N.Y.)》2007,315(5810):328-30; author reply 328-30