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  • 1
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 405-407 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A nonoptical phase-locked shear-force microscope utilizing a quartz crystal tuning fork acting as a voltage-controlled oscillator in a phase-locked loop has been implemented. A tapered optical fiber is rigidly mounted on one of the prongs of the fork to serve as both a shear-force pickup and a near-field optical probe. The crystal is driven at its resonance frequency through positive feedback of the monitored current through the crystal. This signal is used as the voltage-controlled oscillator in a phase-locked loop. The scheme allows for scan speeds far beyond the Q-limited amplitude sensor bandwidth and exhibits excellent sensitivity for a high-Q resonator. Furthermore, given the small vibration amplitude of the tip (〈0.5 nm) and the distance over which it is reduced (〉 6 nm), it is unlikely that the tip is making direct contact with the sample surface as has been suggested for the optical shear-force detection scheme. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 3859-3861 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Direct-write lithography on a 100 nm scale has been carried out using the near-field optical interaction between an uncoated tapered fiber tip and a layer of photoresist. This allows both lithography and shear force microscopic examination of the surface, which reveals morphological changes in the photoresist before development. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 1942-1944 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A technique to characterize the local nonlinearity of lead zirconate titanate piezoceramic (PZT) has been developed. Near-field optical microscopy has been used to image variations in local optical second harmonic generation from the PZT surface. Individual crystalline grains and grain boundaries are the main features visible in the images. The technique allows us to determine the local poling direction of individual submicrometer size crystalline grains of ceramic by near-field second harmonic imaging at different angles of incidence and polarization states of fundamental excitation light. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 4441-4450 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The complex dielectric constants of binary mixtures of water–methanol and water–ethanol in the frequency range from 45 MHz to 26.5 GHz, and binary mixtures of methanol–ethanol in the range from 200 MHz to 26.5 GHz have been measured with various volume fractions around room temperature by means of an open-ended coaxial sensor and a network analyzer. Methanol–ethanol mixtures display a near-Debye dispersion while water–alcohol mixtures show a Cole–Davidson dispersion. The logarithm of relaxation time log τ and dielectric decrement Δε for methanol–ethanol mixtures show a good linear relation with the volume fraction of methanol, while log τ and Δε extracted with the Debye function for water–alcohol mixtures display a near-linear relation with volume fraction of water. Two simple formulas are proposed for identifying the volume fractions of the components in binary mixtures of alcohol–alcohol and water–alcohol from a knowledge of τ and Δε for the pure liquids and the mixtures. The validity of these formulas has been demonstrated with three blind tests. The relation between the mole fraction of water and log τ for water–methanol and water–ethanol mixtures extracted by the use of a Cole–Davidson function clearly shows two linear regions, which implies a change of relaxation mechanism with mole fraction. © 1996 American Institute of Physics.
    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 67 (1990), S. 68-75 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An optical heterodyne technique has been used to make new measurements of the ultrasonic properties of aqueous solutions of biomolecules, dimethyl sulfoxide, and 1,4-butanediol. A LiNbO3 transducer provided acoustic excitation from 0.2 to 1.5 GHz. Acoustic velocity and attenuation were measured using angularly resolved detection of Bragg-scattered light from the liquid sample. A thermodynamic theory based on the heat of mixing was used to explain the concentration dependence of the liquid mixture properties. This paper contributes new data at high frequencies, a calculation of measurement sensitivity for this technique, and a complete treatment of a little known thermodynamic theory that describes these results.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-4994
    Keywords: Voltage-sensitive dye ; optical fiber ; fluorescence ; lobster axon ; frog heart ; laser
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract With the use of a single, implantable, optical fiber, to excite fluorescence and detect changes from voltage-sensitive dyes, transmembrane potential changes were measured without the need for a clear line-of-sight path between the excitation light, the tissue, and the detector. In a previous study, we were required to use signal averaging and could detect only cardiac action potentials from frog. In the present study we improved this system so that unaveraged cardiac action potentials were resolved with high fidelity, and action potentials from single nerve axons were detected. Endeavors to optimize the signal-to-noise ratio resulted in the selection of a larger core fiber with a rounded tip, styryl dyes, and filters based upon fluorescence spectra of the dyes when bound to membrane (rather than in solution). The frog gave signals nearly comparable in magnitude and signal-to-noise ratio to those seen with systems that use a fluorescence microscope. Action potential-induced signals could be detected in single lobster axons with the intracellular injection of a dye. The improvement in the signal-to-noise ratio allowed the use of a reduced-intensity excitation illumination which produced less bleaching of the dye.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The microwave absorption of aqueous solutions of DNA extracted from E. coli has been studied between 8 and 12 GHz by the use of an optical heterodyne technique. By measuring optically the temperature rise produced in an absorbing sample by pulsed microwave radiation, unambiguous, direct measurement of the microwave absorption is possible. Our results show that E. coli DNA absorbs microwaves in the 8-12-GHz region substantially more efficiently than water, which is itself an extremely efficient absorber. The observed absorption is featureless and decreases slightly with increasing frequency. These observations are consistent with an explanation involving direct absorption by longitudinal acoustic modes of the double helix.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Bioelectromagnetics 4 (1983), S. 21-42 
    ISSN: 0197-8462
    Keywords: biomolecules ; DNA ; microwave absorption ; optical method ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Direct determination of the microwave absorption characteristics of biological molecules in solution by an optical heterodyne technique is described. A visibly transparent sample is irradiated in a spatially nonuniform manner with pulsed microwaves, and the spatial variation in temperature increase measured by detecting the phase chirp impressed on a single-frequency He—Ne laser beam passing through the heated region. Results for several liquids and solutions such as water, methanol, various saline solutions, and solutions of DNA and DNA sodium salt in water are described. Where direct comparison is possible the results agree very well with published values. A significant increase in the absorption of DNA solutions compared with pure water has been observed that is consistent with microwave absorption by the longitudinal mode of the double helix.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0197-8462
    Keywords: 2450-MHz microwaves ; pulsed and continuous waves ; thermal effects ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: Normal human lymphocytes were isolated from the peripheral blood of healthy donors. One-ml samples containing (106) cells in chromosome medium 1A were exposed for 5 days to conventional heating or to continuous wave (CW) or pulsed wave (PW) 2450-MHz radiation at non-heating (37°C) and various heating levels (temperature increases of 0.5, 1.0, 1.5, and 2 °C). The pulsed exposures involved 1-μs pulses at pulse repetition frequencies from 100 to 1,000 pulses per second at the same average SAR levels as the CW exposures. Actual average SARs ranged to 12.3 W/kg. Following termination of the incubation period, spontaneous lymphoblastoid transformation was determined with an image analysis system. The results were compared among each of the experimental conditions and with sham-exposed cultures. At non-heating levels, CW exposure did not affect transformation. At heating levels both conventional and CW heating enhanced transformation to the same extent and correlate with the increases in incubation temperature. PW exposure enhanced transformation at non-heating levels. This finding is significant (P 〈 .002). At heating levels PW exposure enhanced transformation to a greater extent than did conventionalor CW heating. This finding is significant at the .02 level. We conclude that PW 2450-MHz radiation acts differently on the process of lymphoblastoid transformation in vitro compared with CW 2450-MHz radiation at the same average SARs. © 1992 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Bioelectromagnetics 18 (1997), S. 439-445 
    ISSN: 0197-8462
    Keywords: ELF ; magnetic fields ; calcium ; jurkat ; flow-cytometry ; Life and Medical Sciences ; Occupational Health and Environmental Toxicology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Physics
    Notes: To explore possible biochemical mechanisms whereby electromagnetic fields of around 0.1 mT might affect immune cells or developing cancer cells, we studied intracellular calcium signaling in the model system Jurkat E6-1 human T-leukemia cells during and following exposure to a 60 Hz magnetic field. Cells were labeled with the intracellular calcium-sensitive fluorescent dye Fluo-3, stimulated with a monoclonal antibody against the cell surface structure CD3 (associated with ligand-stimulated T-cell activation), and analyzed on a FACScan flow-cytometer for increases in intensity of emissions in the range of 515-545 nm. Cells were exposed during or before calcium signal-stimulation to 0.15 mTrms 60 Hz magnetic field. The total DC magnetic field of 78.2 μT was aligned 17.5° off the vertical axis. Experiments used both cells cultured at optimal conditions at 37 °C and cells grown under suboptimal conditions of 24 °C, lowered external calcium, or lowered anti-CD3 concentration. These experiments demonstrate that intracellular signaling in Jurkat E6-1 was not affected by a 60 Hz magnetic field when culture and calcium signal-stimulation were optimal or suboptimal. These results do not exclude field-induced calcium-related effects further down the calcium signaling pathway, such as on calmodulin or other calcium-sensitive enzymes. Bioelectromagnetics 18:439-445, 1997. © 1997 Wiley-Liss, Inc. This article is a US Government work and, as such, is in the public domain in the United States of America.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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