United time-frequency spectroscopy for dynamics and global structure     

Marian A  Stowe MC  Lawall JR  Felinto D  Ye J 《Science (New York, N.Y.)》2004,306(5704):2063-2068

Ultrashort laser pulses have thus far been used in two distinct modes. In the time domain, the pulses have allowed probing and manipulation of dynamics on a subpicosecond time scale. More recently, phase stabilization has produced optical frequency combs with absolute frequency reference across a broad bandwidth. Here we combine these two applications in a spectroscopic study of rubidium atoms. A wide-bandwidth, phase-stabilized femtosecond laser is used to monitor the real-time dynamic evolution of population transfer. Coherent pulse accumulation and quantum interference effects are observed and well modeled by theory. At the same time, the narrow linewidth of individual comb lines permits a precise and efficient determination of the global energy-level structure, providing a direct connection among the optical, terahertz, and radio-frequency domains. The mechanical action of the optical frequency comb on the atomic sample is explored and controlled, leading to precision spectroscopy with an appreciable reduction in systematic errors.  相似文献   

Comment on "Role of NMDA receptor subtypes in governing the direction of hippocampal synaptic plasticity"     

Rusakov DA  Scimemi A  Walker MC  Kullmann DM 《Science (New York, N.Y.)》2004,305(5692):1912; author reply

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Cassini imaging of Jupiter's atmosphere,satellites, and rings     

Porco CC  West RA  McEwen A  Del Genio AD  Ingersoll AP  Thomas P  Squyres S  Dones L  Murray CD  Johnson TV  Burns JA  Brahic A  Neukum G  Veverka J  Barbara JM  Denk T  Evans M  Ferrier JJ  Geissler P  Helfenstein P  Roatsch T  Throop H  Tiscareno M  Vasavada AR 《Science (New York, N.Y.)》2003,299(5612):1541-1547

The Cassini Imaging Science Subsystem acquired about 26,000 images of the Jupiter system as the spacecraft encountered the giant planet en route to Saturn. We report findings on Jupiter's zonal winds, convective storms, low-latitude upper troposphere, polar stratosphere, and northern aurora. We also describe previously unseen emissions arising from Io and Europa in eclipse, a giant volcanic plume over Io's north pole, disk-resolved images of the satellite Himalia, circumstantial evidence for a causal relation between the satellites Metis and Adrastea and the main jovian ring, and information on the nature of the ring particles.  相似文献   

Comment on "Independent origins of middle ear bones in monotremes and therians" (I)     

Bever GS  Rowe T  Ekdale EG  Macrini TE  Colbert MW  Balanoff AM 《Science (New York, N.Y.)》2005,309(5740):1492; author reply 1492

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Reciprocal binding of PARP-1 and histone H1 at promoters specifies transcriptional outcomes   总被引：1，自引：0，他引：1  

Krishnakumar R  Gamble MJ  Frizzell KM  Berrocal JG  Kininis M  Kraus WL 《Science (New York, N.Y.)》2008,319(5864):819-821

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Sex-specific UV and fluorescence signals in jumping spiders     

Lim ML  Land MF  Li D 《Science (New York, N.Y.)》2007,315(5811):481

No animals are known to possess both ultraviolet (UV) reflectance and fluorescence that are sex-specific. We provide evidence for this separation in the jumping spider Cosmophasis umbratica, which has UV reflectance and UV-induced green fluorescence restricted to males and females, respectively. During courtship, many of the studied pairs failed to show typical display posturing when UV light was blocked. Occluding the UV component of sunlight to only one of each pair also caused atypical behavior: Females showed no interest in non-UV-reflective courting males, and males either ignored or were lackluster in courting nonfluorescing females. These results demonstrate the importance of both sex-specific hues as sexual signals for effective intraspecific communication.  相似文献   

Computer science. Technological networks and the spread of computer viruses     

Balthrop J  Forrest S  Newman ME  Williamson MM 《Science (New York, N.Y.)》2004,304(5670):527-529

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Targeting QseC signaling and virulence for antibiotic development     

Rasko DA  Moreira CG  Li de R  Reading NC  Ritchie JM  Waldor MK  Williams N  Taussig R  Wei S  Roth M  Hughes DT  Huntley JF  Fina MW  Falck JR  Sperandio V 《Science (New York, N.Y.)》2008,321(5892):1078-1080

Many bacterial pathogens rely on a conserved membrane histidine sensor kinase, QseC, to respond to host adrenergic signaling molecules and bacterial signals in order to promote the expression of virulence factors. Using a high-throughput screen, we identified a small molecule, LED209, that inhibits the binding of signals to QseC, preventing its autophosphorylation and consequently inhibiting QseC-mediated activation of virulence gene expression. LED209 is not toxic and does not inhibit pathogen growth; however, this compound markedly inhibits the virulence of several pathogens in vitro and in vivo in animals. Inhibition of signaling offers a strategy for the development of broad-spectrum antimicrobial drugs.  相似文献   

Phanerozoic trends in the global diversity of marine invertebrates     

Alroy J  Aberhan M  Bottjer DJ  Foote M  Fürsich FT  Harries PJ  Hendy AJ  Holland SM  Ivany LC  Kiessling W  Kosnik MA  Marshall CR  McGowan AJ  Miller AI  Olszewski TD  Patzkowsky ME  Peters SE  Villier L  Wagner PJ  Bonuso N  Borkow PS  Brenneis B  Clapham ME  Fall LM  Ferguson CA  Hanson VL  Krug AZ  Layou KM  Leckey EH  Nürnberg S  Powers CM  Sessa JA  Simpson C  Tomasovych A  Visaggi CC 《Science (New York, N.Y.)》2008,321(5885):97-100

It has previously been thought that there was a steep Cretaceous and Cenozoic radiation of marine invertebrates. This pattern can be replicated with a new data set of fossil occurrences representing 3.5 million specimens, but only when older analytical protocols are used. Moreover, analyses that employ sampling standardization and more robust counting methods show a modest rise in diversity with no clear trend after the mid-Cretaceous. Globally, locally, and at both high and low latitudes, diversity was less than twice as high in the Neogene as in the mid-Paleozoic. The ratio of global to local richness has changed little, and a latitudinal diversity gradient was present in the early Paleozoic.  相似文献   

Ancient biomolecules from deep ice cores reveal a forested southern Greenland   总被引：2，自引：0，他引：2  

Willerslev E  Cappellini E  Boomsma W  Nielsen R  Hebsgaard MB  Brand TB  Hofreiter M  Bunce M  Poinar HN  Dahl-Jensen D  Johnsen S  Steffensen JP  Bennike O  Schwenninger JL  Nathan R  Armitage S  de Hoog CJ  Alfimov V  Christl M  Beer J  Muscheler R  Barker J  Sharp M  Penkman KE  Haile J  Taberlet P  Gilbert MT  Casoli A  Campani E  Collins MJ 《Science (New York, N.Y.)》2007,317(5834):111-114

It is difficult to obtain fossil data from the 10% of Earth's terrestrial surface that is covered by thick glaciers and ice sheets, and hence, knowledge of the paleoenvironments of these regions has remained limited. We show that DNA and amino acids from buried organisms can be recovered from the basal sections of deep ice cores, enabling reconstructions of past flora and fauna. We show that high-altitude southern Greenland, currently lying below more than 2 kilometers of ice, was inhabited by a diverse array of conifer trees and insects within the past million years. The results provide direct evidence in support of a forested southern Greenland and suggest that many deep ice cores may contain genetic records of paleoenvironments in their basal sections.  相似文献