Stimulated Raman scattering in hydrogen-filled hollow-core photonic crystal fiber     

Benabid F  Knight JC  Antonopoulos G  Russell PS 《Science (New York, N.Y.)》2002,298(5592):399-402

We report on stimulated Raman scattering in an approximately 1-meter-long hollow-core photonic crystal fiber filled with hydrogen gas under pressure. Light was guided and confined in the 15-micrometer-diameter hollow core by a two-dimensional photonic bandgap. Using a pulsed laser source (pulse duration, 6 nanoseconds; wavelength, 532 nanometers), the threshold for Stokes (longer wavelength) generation was observed at pulse energies as low as 800 +/- 200 nanojoules, followed by a coherent anti-Stokes (shorter wavelength) generation threshold at 3.4 +/- 0.7 microjoules. The pump-to-Stokes conversion efficiency was 30 +/- 3% at a pulse energy of only 4.5 microjoules. These energies are almost two orders of magnitude lower than any other reported energy, moving gas-based nonlinear optics to previously inaccessible parameter regimes of high intensity and long interaction length.  相似文献   

Soliton self-frequency shift cancellation in photonic crystal fibers     

Skryabin DV  Luan F  Knight JC  Russell PS 《Science (New York, N.Y.)》2003,301(5640):1705-1708

We report the cancellation of the soliton self-frequency shift in a silica-core photonic crystal fiber with a negative dispersion slope. Numerical and experimental results show that stabilization of the soliton wavelength is accompanied by exponential amplification of the red-shifted Cherenkov radiation emitted by the soliton. The spectral recoil from the radiation acts on the soliton to compensate for the Raman frequency shift. This phenomenon may find applications in the development of a family of optical parametric amplifiers.  相似文献   

Cooperation, control, and concession in meerkat groups     

Clutton-Brock TH  Brotherton PN  Russell AF  O'Riain MJ  Gaynor D  Kansky R  Griffin A  Manser M  Sharpe L  McIlrath GM  Small T  Moss A  Monfort S 《Science (New York, N.Y.)》2001,291(5503):478-481

"Limited control" models of reproductive skew in cooperative societies suggest that the frequency of breeding by subordinates is determined by the outcome of power struggles with dominants. In contrast, "optimal skew" models suggest that dominants have full control of subordinate reproduction and allow subordinates to breed only when this serves to retain subordinates' assistance with rearing dominants' own litters. The results of our 7-year field study of cooperative meerkats, Suricata suricatta, support the predictions of limited control models and provide no indication that dominant females grant reproductive concessions to subordinates to retain their assistance with future breeding attempts.  相似文献   

South Korea. Radical reforms would shake up leading science institute     

Russell M 《Science (New York, N.Y.)》2005,307(5713):1181

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A new type of meteoritic diamond in the enstatite chondrite abee     

Russell SS  Pillinger CT  Arden JW  Lee MR  Ott U 《Science (New York, N.Y.)》1992,256(5054):206-209

Diamonds with delta(13)C values of -2 per mil and less than 50 parts per million (by mass) nitrogen have been isolated from the Abee enstatite chondrite by the same procedure used for concentrating Cdelta, the putative interstellar diamond found ubiquitously in primitive meteorites and characterized by delta(13)C values of -32 to -38 per mil, nitrogen concentrations of 2,000 to 12,500 parts per million, and delta(15)N values of -340 per mil. Because the Abee diamonds have typical solar system isotopic compositions for carbon, nitrogen, and xenon, they are presumably nebular in origin rather than presolar. Their discovery in an unshocked meteorite eliminates the possibility of origins normally invoked to account for diamonds in ureilites and iron meteorites and suggests a low-pressure synthesis. The diamond crystals are approximately 100 nanometers in size, are of an unusual lath shape, and represent approximately 100 parts per million of Abee by mass.  相似文献   

Recent Recession of Tropical Cliffy Coasts: Elevated benches and other coastal forms give evidence of eustatic changes in sea level     

Russell RJ 《Science (New York, N.Y.)》1963,139(3549):9-15

My fieldwork in various parts of the world leads me to the conclusion that the retreat of cliffy coasts through abrasion and solutional erosion during Recent times has produced a whole complex of forms, including conspicuous benches well above sea level where bedrock conditions are favorable. In addition, flats of other origin are being developed at various levels. Broad exposures of beach rock are a marine phenomenon only in that such exposure is a result of beach recession and of the uncovering of materials that had been cemented, under freshwater conditions, along water tables, in some places 6 or more feet above sea level (24, 25). Contemporary coral and algal flats are forming in some instances several feet above the level of the highest tides.  相似文献   

Identifying autism loci and genes by tracing recent shared ancestry   总被引：2，自引：0，他引：2  

Morrow EM  Yoo SY  Flavell SW  Kim TK  Lin Y  Hill RS  Mukaddes NM  Balkhy S  Gascon G  Hashmi A  Al-Saad S  Ware J  Joseph RM  Greenblatt R  Gleason D  Ertelt JA  Apse KA  Bodell A  Partlow JN  Barry B  Yao H  Markianos K  Ferland RJ  Greenberg ME  Walsh CA 《Science (New York, N.Y.)》2008,321(5886):218-223

To find inherited causes of autism-spectrum disorders, we studied families in which parents share ancestors, enhancing the role of inherited factors. We mapped several loci, some containing large, inherited, homozygous deletions that are likely mutations. The largest deletions implicated genes, including PCDH10 (protocadherin 10) and DIA1 (deleted in autism1, or c3orf58), whose level of expression changes in response to neuronal activity, a marker of genes involved in synaptic changes that underlie learning. A subset of genes, including NHE9 (Na+/H+ exchanger 9), showed additional potential mutations in patients with unrelated parents. Our findings highlight the utility of "homozygosity mapping" in heterogeneous disorders like autism but also suggest that defective regulation of gene expression after neural activity may be a mechanism common to seemingly diverse autism mutations.  相似文献   

PATENT REFORM PROSPECTS     

Russell B  Jewett HJ 《Science (New York, N.Y.)》1917,46(1200):629-631

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A new astrophysical setting for chondrule formation     

Krot AN  Meibom A  Russell SS  Alexander CM  Jeffries TE  Keil K 《Science (New York, N.Y.)》2001,291(5509):1776-1779

Chondrules in the metal-rich meteorites Hammadah al Hamra 237 and QUE 94411 have recorded highly energetic thermal events that resulted in complete vaporization of a dusty region of the solar nebula (dust/gas ratio of about 10 to 50 times solar). These chondrules formed under oxidizing conditions before condensation of iron-nickel metal, at temperatures greater than or equal to 1500 K, and were isolated from the cooling gas before condensation of moderately volatile elements such as manganese, sodium, potassium, and sulfur. This astrophysical environment is fundamentally different from conventional models for chondrule formation by localized, brief, repetitive heating events that resulted in incomplete melting of solid precursors initially residing at ambient temperatures below approximately 650 K.  相似文献   

Debating whale sanctuaries     

Papastavrou V  Leaper R 《Science (New York, N.Y.)》2005,309(5731):51-2; author reply 51-2

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