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  • 1
    Electronic Resource
    Electronic Resource
    Structure of polyacetylene–iodine complexes (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 2523-2530 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We confirm the existence of a 15 A(ring) period in iodine-doped polyacetylene and provide a new interpretation for this key feature as part of a general model for structural changes during iodine doping. The observed diffraction intensities for different samples suggest the existence of structures with two different types of dopant-containing layers: layers obtained by complete replacement of polyacetylene chains by iodine columns (F layers) and layers obtained by replacement of every other polyacetylene chain by an iodine column (P layers). The F layers in the heavily doped complex alternate with dopant-free layers of polyacetylene chains (U layers), corresponding to a (UF)n stacking sequence. The phase obtained at a lower dopant concentration, which provides the 15 A(ring) spacing, is attributed to a (UPUF)n stacking sequence. At still lower dopant concentrations, one obtains a (UP)n stacking sequence. This model, along with published Raman, Mössbauer, and photoelectron spectroscopy data, suggests that the ratio of I−5 to I−3 increases in going from P layers to F layers. Intense and monotonically decreasing, diffuse x-ray scattering suggests that vacancies of size ∼3 A(ring) are present, probably in iodine columns. A diffuse reflection at 3.1 A(ring), observed in all iodine-doped samples, is due to an average iodine–iodine distance in disordered columnar arrays. On the other hand, ordered arrays of iodine columns in oriented samples give rise to sharp meridional reflections. All ten observed reflections (down to 1.17 A(ring)) in one sample could be indexed based on a 33.8 A(ring) repeat corresponding to (–I−3–I−5–I−3–)n arrays. The observed diffraction pattern was calculated from this model without using any freely adjustable parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455046
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  • 2
    Electronic Resource
    Electronic Resource
    Detection of plasma equilibrium shifts with fiber-optic sensing of image currents (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1500-1502 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Plasma shifts generate opposite-polarity net shell image currents at diametrically opposed shell locations. In theory these image currents can be detected by Faraday rotation fiber-optic current sensors wound around the shell sections. In practice the validity of the measurement depends on the extent of suppression of the linear birefringence induced by the fiber coil bending and lateral pressure. Circular birefringence bias twist of 60 turns/m of 125-μm o.d. single-mode fiber is sufficient for 2-in. radii of curvature bends, in agreement with theory, while 100 turns/m of 80-μm o.d. fiber have not been successful with 1-in. radii of curvature, contrary to calculations. Different means for further suppression of linear birefringence are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140176
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  • 3
    Electronic Resource
    Electronic Resource
    Improved bolometry system for reversed field pinch research (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 700-708 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A bolometry system for time and spatially resolved energy-loss measurements on the ZT-40M reversed-field pinch is described. This system allows ∼100-μs time resolution with a radiation detection limit of ∼100 mW/cm2 , in particularly noisy electromagnetic environments. The bolometer element fabrication using evaporative techniques and photolithography is discussed. Increased noise rejection is realized by using an oscillator/FM receiver electronics system based on 5-MHz ac excitation of the resistor. An improved oscillator is described. Because resistive sensing is done at 5 MHz, pulsed heating currents may simultaneously be passed through the bolometer resistor and this allows for absolute in situ system calibration. We describe a new method of such calibration that is independent of the resistor geometry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139813
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  • 4
    Electronic Resource
    Electronic Resource
    Low-temperature growth of HgTe and HgCdTe using methylallyltelluride (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 137-139 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: HgTe and HgCdTe (MCT) layers have been grown by organometallic vapor phase epitaxy at low temperature by using methylallyltelluride (MATe), dimethylcadmium (DMCd), and elemental mercury. Use of MATe enabled the growth of layers in the 250–320 °C temperature range, which is 50 °C lower than the growth temperature when diisopropyltelluride is used as the tellurium alkyl, for the same growth rate. The layers were characterized by optical microscopy, double crystal x-ray diffraction, and Fourier transform infrared spectroscopy. Growth at 320 °C resulted in featureless surfaces for both HgTe and HgCdTe layers. The high quality of HgTe layers grown at 320 °C is demonstrated by the very narrow full width at half maximum of x-ray diffraction (29 arcsec), which is comparable to that of the CdTeZn substrates used in this study. MCT layers grown at 320 °C showed sharp interference fringes even for very thin layers, indicating the presence of a very sharp interface with the substrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102124
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  • 5
    Electronic Resource
    Electronic Resource
    A comparison of edge turbulence in tokamaks, stellarators, and reversed-field pinches* (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2491-2497 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Edge equilibrium, turbulence and transport related plasma parameters from the Advanced Toroidal Facility (ATF) [Fusion Technol. 10, 179 (1986)] torsatron, the ZT-40M [Fusion Technol. 8, 1571 (1985)] reversed-field pinch, the Phaedrus-T [Nucl. Fusion 32, 2040 (1992)] tokamak, the Texas Experimental Tokamak (TEXT) [Nucl. Technol. Fusion 1, 479 (1981)], and the Tokamak Fusion Test Reactor (TFTR) [in Plasma Physics and Controlled Nuclear Fusion Research, 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 1, p. 9] have been obtained using a standardized Langmuir probe array and a consistent set of data analysis packages. Additional data from some other devices have also been furnished via private communications and incorporated from published results. Experimental results over a wide range of parameters are compared and the turbulence contribution to edge transport are assessed. Certain physical properties that are relevant to the modeling of edge turbulence are identified: namely, shear decorrelation of turbulence, the role of resistive dissipation and electron parallel thermal conduction, radial mode structure in sheared magnetic field, and electromagnetic contribution to the parallel Ohm's law.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860734
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  • 6
    Electronic Resource
    Electronic Resource
    Oscillating field current drive experiments in a reversed field pinch (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 2285-2291 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Steady-state current sustainment by oscillating field current drive (OFCD) utilizes a technique in which the toroidal and poloidal magnetic fields at the plasma surface are modulated at audio frequencies in quadrature. Experiments on the ZT-40M reversed field pinch [Fusion Technol. 8, 1571 (1985)] have examined OFCD over a range of modulation amplitude, frequency, and phase. For all cases examined, the magnitude of the plasma current is dependent on the phase of the modulations as predicted by theory. However, evidence of current drive has only been observed at relatively low levels of injected power. For larger modulation amplitudes, the data suggest that substantial current drive is offset by increased plasma resistance as a result of modulation enhanced plasma–wall interactions. The initial experimental results and supporting theoretical interpretations of OFCD are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866629
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  • 7
    Electronic Resource
    Electronic Resource
    Phase dynamics of Kármán vortices in cylinder wakes (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 8 (1996), S. 91-96 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temporal evolution of Kármán vortex shedding patterns in the wake of a cylinder placed at right angles to a uniform flow is studied for Reynolds numbers (based on cylinder diameter) between 80 and 140. Focusing on the dynamics of the vortex shedding phase in the wake planview (the plane spanned by the free-stream direction and the cylinder axis) we study experimentally and model the response of shedding patterns to time-dependent boundary conditions imposed at the cylinder ends. By appropriate impulsive changes of end conditions, spanwise wave number "shocks'' can be produced that travel along the cylinder span. These shock experiments, together with data from steady oblique shedding patterns, are used to determine the parameters for the spanwise Ginzburg–Landau model, which has already been used successfully to describe many of the phenomena observed in cylinder wakes. We then demonstrate experimentally that, in analogy to gasdynamics, it is also possible to produce "expansion waves'' of the spanwise wave number, which are well described by the Ginzburg–Landau model without further adjustment of its parameters. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868817
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  • 8
    Electronic Resource
    Electronic Resource
    A rocking beam electrostatic balance for the measurement of small forces (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 705-709 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: There exists interest in the measurement of small forces for applications such as microtopography of semiconductor devices and atomic force microscopy. A new method is introduced here in which a small silicon beam, that is acted on by the external force of interest, has its position sensed by an rf phase shift technique. The position information in turn is fed back via electrostatic forces to continuously rebalance the beam about its central support. This force-feedback approach provides high sensitivity, submillisecond response, inherent force calibration, and electronically controlled stiffness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142071
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  • 9
    Electronic Resource
    Electronic Resource
    Resonant phase shift technique for the measurement of small changes in grounded capacitors (1990)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 61 (1990), S. 1267-1272 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A simple technique has been developed for the high resolution measurement of small changes in capacitors which have one grounded electrode. The capacitor is arranged to be the tuning element in a series resonant LC tank circuit that is driven by a transistor emitter follower. Signal information is provided by observing the phase shift in the transistor collector current that results from any small change in the capacitor value. Implementation is simple, readily analyzable, provides good diagnostics, is easily multiplexed into arrays, and has potential applications in a number of areas including high resolution proximity sensing, capacitive topography, atomic force microscopy, and capacitor microphones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1141224
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  • 10
    Electronic Resource
    Electronic Resource
    A simple, inexpensive, hyperthermal atomic oxygen sensor (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 3557-3562 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: With the increasing duration of space flights, the development of a permanent facility in space, and the increasing use of ground-based hyperthermal atomic oxygen sources there is a need for a simple instrument to provide long-term monitoring of the beam flux. Such an instrument can also be used as a diagnostic tool to investigate the material degradation process. Reliance on models of the upper atmosphere to determine the fluence of atomic oxygen is not only necessarily complex but also imprecise due to the strong dependence of oxygen concentration on day/night, latitude, and solar activity. Mass spectroscopy, the traditional method for determining the gas phase species densities at low pressure, is not only expensive but is limited in the area that it can monitor as well as subject to effects of material degradation. Our group has developed a simple and inexpensive dosimeter to measure the atomic oxygen fluence via the change in resistance as the sensor element is gradually oxidized. The sensors consist of thin-film circuit elements of selected material deposited on a suitable substrate. Four-point resistance measurements are used to monitor the change in sensor resistance with respect to time. Results obtained from silver and carbon dosimeters flown on STS-46 (CONCAP-II-01) indicate that such sensors are sensitive enough to monitor the diurnal variations in atomic oxygen distribution and sufficiently durable to last the lifetime of a mission. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148322
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