Institution
National Institute of Standards and Technology
Government•Gaithersburg, Maryland, United States•
About: National Institute of Standards and Technology is a government organization based out in Gaithersburg, Maryland, United States. It is known for research contribution in the topics: Laser & Scattering. The organization has 26667 authors who have published 60661 publications receiving 2215547 citations. The organization is also known as: National Bureau of Standards & NIST.
Topics: Laser, Scattering, Neutron scattering, NIST, Spectroscopy
Papers published on a yearly basis
Papers
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TL;DR: The role of magnetism in the superconductivity that occurs when mobile 'electrons' or 'holes' are doped into the antiferromagnetic parent compounds of rare-earth iron-based oxide systems was investigated in this paper.
Abstract: Following the discovery of long-range antiferromagnetic order in the parent compounds of high-transition-temperature (high-T(c)) copper oxides, there have been efforts to understand the role of magnetism in the superconductivity that occurs when mobile 'electrons' or 'holes' are doped into the antiferromagnetic parent compounds. Superconductivity in the newly discovered rare-earth iron-based oxide systems ROFeAs (R, rare-earth metal) also arises from either electron or hole doping of their non-superconducting parent compounds. The parent material LaOFeAs is metallic but shows anomalies near 150 K in both resistivity and d.c. magnetic susceptibility. Although optical conductivity and theoretical calculations suggest that LaOFeAs exhibits a spin-density-wave (SDW) instability that is suppressed by doping with electrons to induce superconductivity, there has been no direct evidence of SDW order. Here we report neutron-scattering experiments that demonstrate that LaOFeAs undergoes an abrupt structural distortion below 155 K, changing the symmetry from tetragonal (space group P4/nmm) to monoclinic (space group P112/n) at low temperatures, and then, at approximately 137 K, develops long-range SDW-type antiferromagnetic order with a small moment but simple magnetic structure. Doping the system with fluorine suppresses both the magnetic order and the structural distortion in favour of superconductivity. Therefore, like high-T(c) copper oxides, the superconducting regime in these iron-based materials occurs in close proximity to a long-range-ordered antiferromagnetic ground state.
1,441 citations
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TL;DR: The current state of knowledge of cement hydration mechanisms is reviewed, including the origin of the period of slow reaction in alite and cement, the nature of the acceleration period, the role of calcium sulfate in modifying the reaction rate of tricalcium aluminate, the interactions of silicates and aluminates, and the kinetics of the deceleration period as mentioned in this paper.
1,437 citations
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TL;DR: In this article, a necessary criterion for brittle fracture in crystals is established, in terms of the spontaneous emission of dislocations from an atomically sharp cleavage crack, and the stability of a sharp crack against emission of a blunting dislocation for a number of crystals and crystal types in two dimensions and the energy to form a stable loop of dislocation from the crack tip in three dimensions.
Abstract: A necessary criterion for brittle fracture in crystals is established, in terms of the spontaneous emission of dislocations from an atomically sharp cleavage crack. We have calculated the stability of a sharp crack against emission of a blunting dislocation for a number of crystals and crystal types in two dimensions and the energy to form a stable loop of dislocation from the crack tip in three dimensions. We find that contrary to previous expectations, an atomically sharp cleavage crack is stable in a wide range of crystal types, but that in the face centred cubic metals investigated, blunting reactions occur spontaneously. Of the body centred metals investigated, iron is an intermediate case between the brittle and ductile cases, and the ionic and covalent crystals investigated are all stable against dislocation emission. Qualitatively, we find that crystals whose dislocations have wide cores, and small values of the parameter μb/γ (μb/γ⋦7·5 to 10) are ductile while crystals with narrow cores ...
1,413 citations
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26 Oct 2006TL;DR: An introduction to information retrieval (IR) evaluation from both a user and a system perspective is given, high-lighting that system evaluation is by far the most prevalent type of evaluation carried out.
Abstract: The TREC Video Retrieval Evaluation (TRECVid)is an international benchmarking activity to encourage research in video information retrieval by providing a large test collection, uniform scoring procedures, and a forum for organizations 1 interested in comparing their results. TRECVid completed its fifth annual cycle at the end of 2005 and in 2006 TRECVid will involve almost 70 research organizations, universities and other consortia. Throughout its existence, TRECVid has benchmarked both interactive and automatic/manual searching for shots from within a video corpus,automatic detection of a variety of semantic and low-level video features, shot boundary detection and the detection of story boundaries in broadcast TV news. This paper will give an introduction to information retrieval (IR) evaluation from both a user and a system perspective, high-lighting that system evaluation is by far the most prevalent type of evaluation carried out. We also include a summary of TRECVid as an example of a system evaluation bench-marking campaign and this allows us to discuss whether such campaigns are a good thing or a bad thing. There are arguments for and against these campaigns and we present some of them in the paper concluding that on balance they have had a very positive impact on research progress.
1,395 citations
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TL;DR: In this article, the authors review the spectacular accuracy and stability gains that can be obtained when working with laser cooled ions or neutral atoms and discuss some important applications of these optical clocks, from geodesy to tests of fundamental theories to many body physics.
Abstract: Since 1967 the primary time standard is the cesium atomic clock, based on a hyperfine transition in the microwave domain The development of ultrastable laser sources now allows one to operate on electronic transitions in the optical domain, corresponding to a 5-order-of-magnitude increase in the clock frequency This article reviews the spectacular accuracy and stability gains that can be obtained when working with laser cooled ions or neutral atoms It also discusses some important applications of these optical clocks, from geodesy to tests of fundamental theories to many-body physics
1,393 citations
Authors
Showing all 26760 results
Name | H-index | Papers | Citations |
---|---|---|---|
Zhong Lin Wang | 245 | 2529 | 259003 |
John A. Rogers | 177 | 1341 | 127390 |
J. N. Butler | 172 | 2525 | 175561 |
Yury Gogotsi | 171 | 956 | 144520 |
Zhenan Bao | 169 | 865 | 106571 |
Gang Chen | 167 | 3372 | 149819 |
Michel C. Nussenzweig | 165 | 516 | 87665 |
Donald G. Truhlar | 165 | 1518 | 157965 |
Tobin J. Marks | 159 | 1621 | 111604 |
Jongmin Lee | 150 | 2257 | 134772 |
Galen D. Stucky | 144 | 958 | 101796 |
Thomas P. Russell | 141 | 1012 | 80055 |
William D. Travis | 137 | 605 | 93286 |
Peter Zoller | 134 | 734 | 76093 |
Anthony G. Evans | 130 | 576 | 65803 |