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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 2627-2636 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A novel technique is described to measure weaker long range forces between a single colloidal particle and a flat surface as a function of separation distance. The technique uses a three-dimensional optical trap as a force transducer and evanescent wave light scattering to measure the particle-surface separation distance. The three-dimensional optical trap allows direct manipulation of the particle near the surface, and the measured displacement of the particle from the center of the optical trap determines the force of interaction between the particle and the surface. The particle position is determined by measuring the scattered light from the particle in an evanescent wave created by total internal reflection of a laser beam on the surface. This combination of optical techniques allows forces to be directly measured for smaller particles (∼0.25–5.0 μm) and over a range of forces (∼10−14–10−11 N) than has been previously reported for similar force measurement techniques such as atomic force microscopy and total internal reflection microscopy. The experimental results have been compared with DLVO theory predictions for 1.5 μm silica microspheres interacting with glass in NaCl solutions of known ionic strength. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Design features of a proposed high-resolution, high-speed powder diffractometer for operation at a synchrotron source are described. A key feature of the design is the use of imaging plates to record an almost complete range of data including both the high-angle and the small-angle scattering regime. The x-ray optics involve the use of a condensing-collimating channel-cut monochromator (CCCC) to achieve narrow parallel beams with cross sections of the order of 50 μm in the plane of diffraction, so that geometrical aberrations are very low and the beam cross section is well matched to the spatial resolution of the imaging plate detector. Angular resolution in 2θ of the diffractometer is easily variable, and designed to range from 0.01° upwards. Optional translation of the detector perpendicular to the incident-beam direction makes it possible to obtain time-resolved data. Applications of the instrument include high-resolution powder data collection for Rietveld analysis, studies of dynamic phenomena such as chemical reactions and phase transformations, particle-size determination, texture analysis, residual-stress measurements, single-crystal studies of the truncation-rod effect and surface scattering, microdiffraction, combined high-angle and small-angle scattering measurements, and studies of multilayer structures. As an illustration of the sort of results attainable with the proposed system, we present an oscillation photograph of the crystal-truncation rod effect for a Si wafer which was recorded at a synchrotron source using an imaging plate as the detector.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 226-234 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Propagation of medium energy electrons (10–20 keV) in carbon dioxide is studied for application to using the Electron Beam Fluorescence (EBF) technique with CO2 as a rarefied gas dynamic diagnostic tool. A collimated (1 mm nominal diameter) electron beam at energies of 10, 15, and 20 keV was injected into a vacuum chamber containing ambient CO2 maintained at pressures of 50, 100, 200, 400, 600, and 800 mTorr. Through deconvolution of recorded two-dimensional images of the emitted fluorescence, the growth of the root-mean-square (rms) radius of the beam was obtained as a function of axial distance. An empirical form of the differential scattering cross section which includes the contributions of both elastic and inelastic collisions between fast electrons and CO2 molecules is used in single scattering, multiple scattering, and scattering envelope models developed for describing the electron distribution along the electron beam. Using these models, the rms radius of the electron beam is calculated and compared with experimental results obtained from imaging of the electron beam fluorescence. It is found that the multiple scattering and envelope models significantly overestimate experimental rms radius data. The single scattering model underestimates radius data at target thickness higher than ∼2 and 4 Torr cm for the 10 and 15 keV beams, respectively. The single scattering model matches well with the 20 keV beam data. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 2212-2220 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Acoustic emission (AE) signals emanating from various deformation processes in materials are of a broadband nature. It is also well established that the ultrasonic attenuation caused by grain boundary scattering in polycrystalline materials is strongly frequency dependent. It is worth noting that distortions of AE signals due to grain boundary scattering (Rayleigh or stochastic type) have been inadequately treated in some previous quantitative AE studies. We propose a quantitative approach to estimating AE source parameters with proper care taken of the frequency-dependent media attenuation. Without getting involved in the complete measurement of media attenuation, the present approach is designed to find some characteristic quantities in both the frequency and time domains that are least sensitive to attenuation. The node frequency in the amplitude spectra and the peak time in real-time signals are found to be the most suitable for the purpose. They can be used to infer the source parameters such as the final size and the average velocity of source expansion.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 792-795 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous ribbons of Nb79Si21 were formed using the melt spinning technique. These were then implanted with nitrogen ions to form uniform surface layers of 1 and 2 at. % N. The A15 phase formed between annealing temperatures of 650–750 °C. The lattice parameter was 0.514 nm and the superconducting transition temperature was 6 K. To our knowledge, previous attempts to synthesize A15 Nb3Si from amorphous solids have required the application of very high pressures.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 2384-2388 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Alloys of Nb75Ge24.5B0.5 were rapidly solidified into amorphous ribbons using the melt-spinning technique. After annealing continuous Al5 tapes were obtained with an average grain size of 30 nm. It was not possible to form a continuous tape by melt spinning directly into the Al5 structure since only brittle fragments were obtained. The amorphous annealed Al5 phase was close to stoichiometry with a lattice parameter of 0.514 nm and a superconducting transition temperature of 18 K. The critical current densities were 5×1010 and 8×108 A/m2 at magnetic fields of 0 and 15 T, respectively. This processing technique could be the initial step in the fabrication of multifilamentary Nb3Ge superconducting composites.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 4672-4677 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The melt spinning technique was used to rapidly solidify superconducting materials. In the Ti3Nb6Mo3Si4 alloy system, it was possible to form metastable A-15 and amorphous ribbons as the quenching rate was increased. The liquid-quenched A-15 ribbons were extremely brittle, which is typical of this crystal structure. The metastable A-15 phase could also be formed by annealing the amorphous ribbons. These, however, were far more flexible, their percent elongation being up to 30 times greater than that of the liquid quenched A-15's. The flexibility appeared to depend on grain size, and increased as the grain size decreased. This is consistent with behavior observed in other brittle materials of a brittle to ductile transition as a function of grain size.
    Type of Medium: Electronic Resource
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