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Short-Range Spectroscopic Ruler Based on a Single-Molecule Optical Switch

Physical Review Letters 2005年第10期94卷 108101-108101页

作者： Mark Bates Timothy R. Blosser Xiaowei Zhuang Division of Engineering and Applied Sciences Harvard University Cambridge Massachusetts 02138 USA Graduate Program in Biophysics Harvard University Cambridge Massachusetts 02138 USA Department of Chemistry Harvard University Cambridge Massachusetts 02138 USA Department of Physics Harvard University Cambridge Massachusetts 02138 USA

We demonstrate a novel all-optical switch consisting of two molecules: a primary fluorophore (Cy5) that can be switched between a fluorescent and a dark state by light of different wavelengths, and a secondary chromophore (Cy3) that facilitates switching. The interaction between the two molecules exhibits a distance dependence much steeper than that of conventional Förster resonance energy transfer. This enables the switch to act as a ruler with the capability to probe distances difficult to access by other spectroscopic methods, thus presenting a new tool for the study of biomolecules at the single-molecule level.

关键词： Optical switches

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Exactly Sparse Delayed-State Filters

Exactly Sparse Delayed-State Filters

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IEEE International Conference on Robotics and Automation (ICRA)

作者： R.M. Eustice H. Singh J.J. Leonard MIT/WHOI Joint Program in Applied Ocean Science and Engineering Woods Hole Oceanographic Institution Woods Hole MA USA Department of Applied Ocean Physics and Engineering Woods Hole Oceanographic Institution Woods Hole MA USA Department of Ocean Engineering Massachusetts Institute of Technology Cambridge MA USA

This paper presents the novel insight that the SLAM information matrix is exactly sparse in a delayed-state framework. Such a framework is used in view-based representations of the environment which rely upon scan-matching raw sensor data. Scan-matching raw data results in virtual observations of robot motion with respect to a place its previously been. The exact sparseness of the delayed-state information matrix is in contrast to other recent feature based SLAM information algorithms like Sparse Extended Information Filters or Thin Junction Tree Filters. These methods have to make approximations in order to force the feature-based SLAM information matrix to be sparse. The benefit of the exact sparseness of the delayed-state framework is that it allows one to take advantage of the information space parameterization without having to make any approximations. Therefore, it can produce equivalent results to the “full-covariance” solution.

关键词： Delay Simultaneous localization and mapping Navigation Cameras Oceans Information filters Sparse matrices Information filtering Remotely operated vehicles Robot vision systems

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Recent development of patterned structure light-emitting diodes

Recent development of patterned structure light-emitting dio...

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Fifth International Conference on Solid State Lighting

作者： Cho, Jaehee Lee, Jeong Wook Im, Jin Seo Sone, Cheolsoo Park, Yongjo Kim, Dongho Jeon, Heonsu Yoon, Euijoon Leem, Dong-Seok Seong, Tae-Yeon Photonics Program Team Samsung Advanced Institute of Technology Suwon 440-600 Korea Republic of School of Physics Inter-university Semiconductor Research Center Seoul National Univ. Seoul 151-747 Korea Republic of School of Materials Science and Engineering Inter-university Semiconductor Research Center Seoul National Univ. Seoul 151-742 Korea Republic of Gwangju 500-712 Korea Republic of

The efficiency of a conventional light emitting diode (LED) is limited by coupling of light into guided modes in the structure. Several methods to increase the extraction efficiency of nitride-based LEDs are studied from the perspective of the patterned structures in LEDs. The patterned structures are made in the interface between a semiconductor and a sapphire substrate and on the surface of a semiconductor or an indium tin oxide electrode. All of these approaches show an increased light output compared to that of reference samples, which means these kinds of scattering sources are inevitable to make a highly efficient light emitter in nitride-based semiconductor system.

关键词： Light emitting diodes

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Sensing cellular function and molecular activity in vivo using fluorescence lifetime imaging microscopy (FLIM)

Sensing cellular function and molecular activity in vivo usi...

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Novel Optical Instrumentation for Biomedical Applications II

作者： Zhong, Wei Sud, Dhruv Wu, Mei Merrick, Karl A. Merajver, Sofia D. Beer, David G. Mycek, Mary-Ann Dept. of Biomedical Engineering University of Michigan Ann Arbor MI 48109 Department of Internal Medicine Medical School University of Michigan Ann Arbor MI 48109 Comprehensive Cancer Center University of Michigan Medical School Ann Arbor MI 48109 Department of Surgery Medical School University of Michigan Ann Arbor MI 48109 Applied Physics Program University of Michigan Ann Arbor MI 48109

In contrast to intensity-based fluorescence microscopy, fluorescence lifetime imaging microscopy (FLIM) bases image contrast on fluorophore excited-state lifetime. This technique is sensitive to the fluorophore's local environment (temperature, ion concentration, dissolved gas concentration, and molecular associations), while being independent of factors impacting fluorescence intensity (fluorophore concentration, photobleaching, scattering, and absorption). We present design features of a novel UV-visible-NIR wide-field time-domain FLIM system with optical sectioning (10 μm), high temporal discrimination (50 ps), and large temporal dynamic range (750 ps - 1 μs), and apply the system to probe cellular metabolic function and detect molecular activity in vivo. © 2005 SPIE and OSA.

关键词： Image processing

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Editorial

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Surface and Coatings Technology 2005年第1-3 SPEC. ISS.期198卷 1-1页

作者： Zhang, Sam Teixeira, Vasco Thin Film Technology Strategic Research Program School of Mechanical and Aerospace Engineering Nanyang Technological University 50 Nanyang Avenue Singapore 639798 Singapore GRF-Functional Coatings Group Physics Department University of Minho Campus de Azurém P-4800-058 Guimarães Portugal

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Hydrostatic pressure control of the magnetostructural phase transition in Gd5Si2Ge2 single crystals

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Physical Review B 2005年第2期72卷 024416-024416页

作者： C. Magen L. Morellon P. A. Algarabel M. R. Ibarra Z. Arnold J. Kamarad T. A. Lograsso D. L. Schlagel V. K. Pecharsky A. O. Tsokol K. A. Gschneidner, Jr. Departamento de Física de la Materia Condensada and Instituto de Ciencia de Materiales de Aragón Universidad de Zaragoza and Consejo Superior de Investigaciones Científicas 50009 Zaragoza Spain Institute of Physics AS CR Na Slovance 2 182 21 Prague 8 Czech Republic Materials and Engineering Physics Program Ames Laboratory Iowa State University Ames Iowa 50011-3020 USA Department of Materials Science and Engineering Iowa State University Ames Iowa 50011-2300 USA

Magnetic and structural properties of single crystalline Gd5Si2Ge2 under hydrostatic pressure have been characterized by using magnetization, linear thermal expansion, and compressibility measurements. A strong dependence of Curie temperature on pressure, dTC∕dP=+4.8K∕kbar, is observed in contrast with the smaller values of about 3K∕kbar found in polycrystalline specimens. This difference reflects the role the microstructure may play in pressure-induced magnetic-crystallographic phase changes, likely related to stress relaxation at the grain boundaries, domain pinning and/or nucleation of defects. The pressure dependence of the critical magnetic field, d(dHC∕dT)∕dP, drops at the rate −0.122(5)kOe∕Kkbar, which points to an enhancement of the magnetoelastic coupling with pressure. The latter affects the magnetocaloric behavior of the material at the rate d(ΔSM)∕dP≅1.8J∕kgKkbar. The linear thermal expansion confirms the strongly anisotropic change of the lattice parameters through the orthorhombic to monoclinic crystallographic transformation with Δa∕a=+0.94%, Δb∕b=−0.13%, and Δc∕c=−0.22%. The structural transition temperature varies with pressure synchronously with the Curie temperature, and the size and shape of the strain anomalies remain nearly unaffected by the hydrostatic pressure, indicating, respectively, that the structural and magnetic transformations remain coupled, and the anisotropic behavior of the lattice is preserved as pressure increases. The room temperature linear compressibility data show that the magnetostructural transformation can be triggered isothermally at ∼6kbar and that the compressibility is anisotropic.

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Molecular dynamics simulations of the mechanical strength of Si∕Si3N4 interfaces

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Physical Review B 2005年第9期72卷 094115-094115页

作者： Martina E. Bachlechner Jennifer Zhang Ye Wang Jarrod Schiffbauer Steven R. Knudsen Dimitris Korakakis Physics Department West Virginia University Morgantown West Virginia 26506 USA NASA Independent Verification and Validation Facility Science and Engineering Apprenticeship Program—Morgantown High School Morgantown West Virginia 26501 USA Institute for Scientific Research Inc. Fairmont West Virginia 26555 USA Lane Department for Computer Science and Electrical Engineering West Virginia University Morgantown West Virginia 26506 USA

Molecular dynamics simulations are performed on parallel computers to investigate the crystalline Si(111)∕Si3N4(0001) interface that is modeled as an eight-component system. The average total energy per particle and the average kinetic energy per particle of the subsystems are monitored during the preparation of the system. The Young’s modulus of the interface is compared with that of the silicon part alone and that of the silicon-nitride film, respectively. The results for one extended simulation feature a crack in the silicon-nitride film and dislocated atoms in silicon below the crack. Simulations at rates of strain ranging from 0.00125to0.05ps−1 show that for lower strain rates, the systems stretched faster reach their ultimate strength at a higher strain value than those that were stretched more slowly. At the highest strain rates, however, the failure mechanisms change qualitatively indicative of a more ductile behavior.

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Carbon nanotubes: Anomalous photo-galvanic effect, electromechanical instability, and IR detection

Carbon nanotubes: Anomalous photo-galvanic effect, electrome...

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Frontiers in Optics, FiO 2005

作者： Rakitin, A. Meĺnikov, I.V. Haus, J.W. Aitchison, J.S. Department of Physics and Astronomy York University 4700 Keele Street North York Ontario M3P 1P3 Canada Comtex Consulting Inc 162 Princess Margaret Boulevard Etobicoke Ontario M9B 2Z5 Canada Electro-Optics Program School of Engineering University of Dayton 300 College Park Dayton Ohio 45469-0245 United States The E. S. Rogers Sr. Department of Electrical and Computer Engineering University of Toronto 10 King's College Road Toronto. Ontario M5S 3G4 Canada

ISBN: (纸本)1557527970

Carbon nanotubes (CNTs) are hollow cylinders composed of one or more concentric layers of carbon atoms arranged in a honeycomb lattice. CNTs are widely considered as an elemental material for a future nanoelectronic technology. This is not simply due to their small size but rather to their overall properties: CNTs are known to exhibit either metallic or semiconducting behaviour, with the band gap being dependent on the nanotube diameter. Both active devices (transistors) and interconnects can be made out of semiconducting and metallic nanotubes, respectively. The key nanotube dimension, their diameter, is controlled by chemistry, not conventional fabrication. The strong covalent bonding gives the CNTs high mechanical and thermal stability and ability to sustain current densities as high as 10 A/cm2.

关键词： Atoms Carbon nanotubes Chemistry Curvature Infrared detection Scattering

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Stalactite Growth as a Free-Boundary Problem: A Geometric Law and Its Platonic Ideal

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Physical Review Letters 2005年第1期94卷 018501-018501页

作者： Martin B. Short James C. Baygents J. Warren Beck David A. Stone Rickard S. Toomey, III Raymond E. Goldstein Department of Physics University of Arizona Tucson Arizona 85721 USA Department of Chemical and Environmental Engineering University of Arizona Tucson Arizona 85721 USA Program in Applied Mathematics University of Arizona Tucson Arizona 85721 USA Accelerator Mass Spectrometry Facility University of Arizona Tucson Arizona 85721 USA Department of Soil Water and Environmental Science University of Arizona Tucson Arizona 85721 USA Kartchner Caverns State Park P.O. Box 1849 Benson Arizona 85602 USA

The chemical mechanisms underlying the growth of cave formations such as stalactites are well known, yet no theory has yet been proposed which successfully accounts for the dynamic evolution of their shapes. Here we consider the interplay of thin-film fluid dynamics, calcium carbonate chemistry, and CO2 transport in the cave to show that stalactites evolve according to a novel local geometric growth law which exhibits extreme amplification at the tip as a consequence of the locally-varying fluid layer thickness. Studies of this model show that a broad class of initial conditions is attracted to an ideal shape which is strikingly close to a statistical average of natural stalactites.

关键词： Limestone

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Residual stress measurements in welded and plastically deformed target structural materials

Journal of ASTM International

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Journal of ASTM International 2005年第6期2卷 67-79页

作者： Roy, Ajit K. Venkatesh, Anand Dronavalli, Satish Marthandam, Vikram Wells, Douglas Selim, Farida Rogge, Ronald Department of Mechanical Engineering University of Nevada Las Vegas Box 454027 4505 Maryland Parkway Las Vegas NV 89154 Department of Physics Idaho State University Campus Box 8106 785 S. 8th Ave. Pocatello ID 83209 Department of Physics Idaho State University Campus Box 8263 785 S. 8th Ave. Pocatello ID 83209 National Research Council Neutron Program for Materials Research Chalk River Laboratories Chalk River Ont. KOJ 1JO Canada

Transmutation of spent nuclear fuels (SNF) is currently being considered to transform long-lived isotopes to species with relatively short half-lives and reduced radioactivity through capture and decay of minor actinides and fission products. This process is intended for geologic disposal of SNF for shorter durations in the proposed repository at the Yucca Mountain site. The structural material (Type 304L stainless steel/Alloy EP-823) surrounding the transmutation target will be subjected to welding operation and plastic deformation during fabrication, which could induce residual stresses in it. Destructive ring-core, and nondestructive x-ray diffraction, neutron diffraction, and positron annihilation spectroscopic techniques were used to evaluate residual stresses in welded and cold-worked specimens of both materials. The results indicate that, in general, for a welded specimen consisting of Alloy EP-823 and Type 304L stainless steel on opposite sides, compressive and tensile residual stresses were observed in the former and latter materials, respectively. However, a welded specimen consisting of only Alloy EP-823 on both sides showed tensile residual stresses. The extent of residual stresses in cold-worked specimens was enhanced with increased level of cold-reduction. In case of a bent specimen, compressive and tensile residual stresses were noticed in the convex and concave sides, respectively. Copyright © 2005 by ASTM International.

关键词： Residual stresses

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