Generation of spatially coherent light at extreme ultraviolet wavelengths     

Bartels RA  Paul A  Green H  Kapteyn HC  Murnane MM  Backus S  Christov IP  Liu Y  Attwood D  Jacobsen C 《Science (New York, N.Y.)》2002,297(5580):376-378

We present spatial coherence measurements of extreme ultraviolet (EUV) light generated through the process of high-harmonic up-conversion of a femtosecond laser. With a phase-matched hollow-fiber geometry, the generated beam was found to exhibit essentially full spatial coherence. The coherence of this laser-like EUV source was shown by recording Gabor holograms of small objects. This work demonstrates the capability to perform EUV holography with a tabletop experimental setup. Such an EUV source, with low divergence and high spatial coherence, can be used for experiments involving high-precision metrology, inspection of optical components for EUV lithography, and microscopy and holography with nanometer resolution. Furthermore, the short time duration of the EUV radiation (a few femtoseconds) will enable EUV microscopy and holography to be performed with ultrahigh time resolution.  相似文献   

High-Resolution Imaging by Fourier Transform X-ray Holography     

McNulty I  Kirz J  Jacobsen C  Anderson EH  Howells MR  Kern DP 《Science (New York, N.Y.)》1992,256(5059):1009-1012

Fourier transform x-ray holography has been used to image gold test objects with submicrometer structure, resolving features as small as 60 nanometers. The hologram-recording instrument uses coherent 3.4-nanometer radiation from the soft x-ray undulator beamline X1A at the National Synchrotron Light Source. The specimen to be imaged is placed near the first-order focal spot produced by a Fresnel zone plate; the other orders, chiefly the zeroth, illuminate the specimen. The wave scattered by the specimen interferes with the spherical reference wave from the focal spot, forming a hologram with fringes of low spatial frequency. The hologram is recorded in digital form by a charge-coupled device camera, and the specimen image is obtained by numerical reconstruction.  相似文献   

One-way control of FWA imprinting in Arabidopsis endosperm by DNA methylation   总被引：1，自引：0，他引：1  

Kinoshita T  Miura A  Choi Y  Kinoshita Y  Cao X  Jacobsen SE  Fischer RL  Kakutani T 《Science (New York, N.Y.)》2004,303(5657):521-523

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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   

Cancer risk and salmon intake     

Lund E  Engeset D  Alsaker E  Skeie G  Hjårtaker A  Lundebye AK  Niebor E 《Science (New York, N.Y.)》2004,305(5683):477-8; author reply 477-8

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RNA silencing genes control de novo DNA methylation   总被引：1，自引：0，他引：1  

Chan SW  Zilberman D  Xie Z  Johansen LK  Carrington JC  Jacobsen SE 《Science (New York, N.Y.)》2004,303(5662):1336

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Frequent long-distance plant colonization in the changing Arctic     

Alsos IG  Eidesen PB  Ehrich D  Skrede I  Westergaard K  Jacobsen GH  Landvik JY  Taberlet P  Brochmann C 《Science (New York, N.Y.)》2007,316(5831):1606-1609

The ability of species to track their ecological niche after climate change is a major source of uncertainty in predicting their future distribution. By analyzing DNA fingerprinting (amplified fragment-length polymorphism) of nine plant species, we show that long-distance colonization of a remote arctic archipelago, Svalbard, has occurred repeatedly and from several source regions. Propagules are likely carried by wind and drifting sea ice. The genetic effect of restricted colonization was strongly correlated with the temperature requirements of the species, indicating that establishment limits distribution more than dispersal. Thus, it may be appropriate to assume unlimited dispersal when predicting long-term range shifts in the Arctic.  相似文献   

Spin transition zone in Earth's lower mantle     

Lin JF  Vankó G  Jacobsen SD  Iota V  Struzhkin VV  Prakapenka VB  Kuznetsov A  Yoo CS 《Science (New York, N.Y.)》2007,317(5845):1740-1743

Mineral properties in Earth's lower mantle are affected by iron electronic states, but representative pressures and temperatures have not yet been probed. Spin states of iron in lower-mantle ferropericlase have been measured up to 95 gigapascals and 2000 kelvin with x-ray emission in a laser-heated diamond cell. A gradual spin transition of iron occurs over a pressure-temperature range extending from about 1000 kilometers in depth and 1900 kelvin to 2200 kilometers and 2300 kelvin in the lower mantle. Because low-spin ferropericlase exhibits higher density and faster sound velocities relative to the high-spin ferropericlase, the observed increase in low-spin (Mg,Fe)O at mid-lower mantle conditions would manifest seismically as a lower-mantle spin transition zone characterized by a steeper-than-normal density gradient.  相似文献   

Determination and depletion of residues of carbadox, tylosin, and virginiamycin in kidney, liver, and muscle of pigs in feeding experiments   总被引：1，自引：0，他引：1  

M G Lauridsen  C Lund  M Jacobsen 《Journal of the Association of Official Analytical Chemists》1988,71(5):921-925

The results of residue determinations of the growth promotors carbadox, tylosin, and virginiamycin in kidney, liver, and muscle from pigs in feeding experiments are described as well as the analytical methods used. Residues of the carbadox metabolite quinoxaline-2-carboxylic acid were found in liver from pigs fed 20 mg/kg in the diet with a withdrawal time of 30 days. No residues were detected in muscle with zero withdrawal time. The limit of determination was 0.01 mg/kg for both tissues. No residues of virginiamycin and tylosin were found in pigs fed 50 and 40 mg/kg, respectively, in the diet, even with zero withdrawal time. Residues of tylosin of 0.06 mg/kg and below were detected in liver and kidney from pigs fed 200 or 400 mg/kg and slaughtered within 3 h after the last feeding.  相似文献   

Effects of lactoferrin, phytic acid, and EDTA on oxidation in two food emulsions enriched with long-chain polyunsaturated fatty acids     

Nielsen NS  Petersen A  Meyer AS  Timm-Heinrich M  Jacobsen C 《Journal of agricultural and food chemistry》2004,52(25):7690-7699

The influence of the addition of metal chelators on oxidative stability was studied in a milk drink and in a mayonnaise system containing highly polyunsaturated lipids. Milk drinks containing 5% (w/w) of specific structured lipid were supplemented with lactoferrin (6-24 muM) and stored at 2 degrees C for up to 9 weeks. Mayonnaise samples with 16% fish oil and 64% rapeseed oil (w/w) were supplemented with either lactoferrin (8-32 muM), phytic acid (16-124 muM), or EDTA (16-64 muM) and were stored at 20 degrees C for up to 4 weeks. The effect of the metal chelators was evaluated by determination of peroxide values, secondary volatile oxidation products, and sensory analysis. Lactoferrin reduced the oxidation when added in concentrations of 12 muM in the milk drink and 8 muM in the mayonnaise, whereas it was a prooxidant at higher concentrations in both systems. In mayonnaise, EDTA was an effective metal chelator even at 16 muM, whereas phytic acid did not exert a distinct protective effect against oxidation. The differences in the equimolar effects of the metal chelators are proposed to be due to differences in their binding constants to iron and their different stabilities toward heat and low pH.  相似文献