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  • 1
    Electronic Resource
    Electronic Resource
    Analysis of a four-variable model of coupled chemical oscillators (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3071-3080 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A simple model for the coupling of two chemical oscillators is proposed. The model consists of twotwo-variable subsystems, each of which gives rise to a "cross-shaped phase diagram'' containing two different steady states plus regions of bistability and of oscillation. The subsystems are coupled by diffusion of both species. Extensive numerical simulations reveal that when one subsystem is in the bistable and the other in the oscillatory region of the parameter space, coupling can result in birhythmicity, period doubling, and chaos. When both subsystems are in the oscillatory region, the coupled behavior is even richer, including quasiperiodicity, entrainment, chaos, and phase death (cessation of oscillations), with various hysteresis phenomena between these modes of behavior. The relation of these observations to behavior found experimentally in coupled chemical oscillators is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455910
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  • 2
    Electronic Resource
    Electronic Resource
    Stochastic behavior and stirring rate effects in the chlorite–iodide reaction (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 6925-6928 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The autocatalytic reaction between chlorite and iodide ions in a closed system is a clock reaction, showing a sudden appearance of brown I2 followed by a rapid disappearance of the color. Under certain conditions, the reaction time displays a striking irreproducibility. This stochastic behavior is studied potentiometrically and spectrophotometrically as a function of initial [I− ], stirring rate and solution volume. The results imply that the irreproducibility is an inherent feature of the reaction generated by fluctuations in the solution after it is "well mixed.'' The key contributors to the stochasticity are local concentration inhomogeneities resulting from imperfect stirring and the "supercatalytic'' reaction kinetics. A qualitative explanation is given that incorporates these aspects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455316
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  • 3
    Electronic Resource
    Electronic Resource
    Ambipolar diffusion length measurements in hydrogenated amorphous silicon (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 2461-2463 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Many studies have been devoted in recent years to the experimental determination of the diffusion length of the minority carriers in hydrogenated amorphous silicon. The most popular method for this purpose was the surface photovoltage technique while the most novel method is the photocarrier grating technique. In the present work we report the first experimental comparison of the two methods. It is found that the first method yields values which are typically twice as large as those of the second method. This disagreement can be explained by the recent theoretical studies of the two methods. On the other hand, the present results seem to indicate how some more information on the electronic structure of the above material can be derived by future comparisons between theoretical and experimental results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101072
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  • 4
    Electronic Resource
    Electronic Resource
    Thermal transport studies of 351-nm laser-produced plasmas using extreme ultraviolet spectroscopy (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 674-680 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spectra from an extreme ultraviolet (XUV) grazing incidence spectrograph have been used in the study of thermal transport in laser plasmas. These measurements with XUV lines allowed a diagnosis of much lower temperatures in the heating front than had been previously measured. The OMEGA (24-beam, 351-nm) laser system at the University of Rochester was used to produce plasmas from glass microballoons coated with Al or Ti substrates and overcoated with a plastic ablator. Thermal transport was investigated by measuring the intensity of x-ray and XUV lines as a function of the thickness of the plastic overcoat. These measurements were then compared to the 1D hydrodynamic code lilac. Agreement between the hydrodynamic code and experiment could not be obtained with a reasonable value for the flux limiter ( f≤0.65). Consistent results were reached if nonuniform irradiation and flux inhibition is assumed. The measured burnthrough depths of around 9 μm are similar to previous measurements made with x-ray lines at fluxes below 1015 W/cm2. No evidence of preheat in the heat front was observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340056
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  • 5
    Electronic Resource
    Electronic Resource
    Experimental and numerical study of thermal transport in 24-beam ultraviolet irradiation of spherical targets (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 969-977 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of thermal transport experiments using spectral-line signature and ion expansion measurements has been performed in spherical geometry using the 24 UV-converted beams of the Omega laser system at the Laboratory for Laser Energetics of the University of Rochester. Comparison with previous experiments employing only six beams shows a much better agreement in the mass ablation rate, when using 24 beams, between experimental results obtained from charge collectors and code simulations using a flux limiter of 0.1. The influence of nonuniformities in the irradiation, x-ray line reabsorption, and ionization time lag (non-LTE effects) were studied with the help of a collisional-radiative model. These processes were found to alter the falloff rates (determined mainly by the radical profile of the temperature) of the relative x-ray line intensity with overcoat thickness. With these effects included, agreement between calculated and measured burnthrough curves is greatly improved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343000
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  • 6
    Electronic Resource
    Electronic Resource
    Ferromagnetism in molecular materials: Decamethylferrocenium tetracyanoethanide (DMeFc) (TCNE) (invited) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 2952-2956 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ferromagnetism has only recently been observed in molecular materials. We present here a summary of the ferromagnetic phenomena observed in the molecular charge transfer salt, decamethylferrocenium tetracyanoethanide (DMeFc)(TCNE), and related compounds. A spontaneous magnetization is observed in this material for T〈4.8 K, with a saturation moment in agreement with alignment of individual spins localized on the DMeFc+⋅ and TCNE−⋅ ions. A comparison of these results with analogous charge transfer salts is presented. Models for the magnetic interaction in the charge transfer salts and the preparation of other molecular and/or polymeric materials with ferromagnetic exchange are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340914
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  • 7
    Electronic Resource
    Electronic Resource
    The quest for a polymeric ferromagnet: A new polymorph of 1,4-bis(2,2,6,6-tetramethyl-4-oxy-4-piperidyl-1-oxy)butadiyne (invited) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 2949-2951 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new polymorph of 1,4-bis(2,2,6,6-tetramethyl-4-oxy-4-piperidyl-1-oxy)butadiyne has been prepared and characterized by x-ray diffraction, infrared and Raman spectroscopies, and magnetic susceptibility. Unlike the Pccn-α phase, the β phase belongs to the Pca21 space group [a=14.265(1) A(ring), b=8.079 (3) A(ring), and c=18.865(2) A(ring), V=2174.1 A(ring)3, Z=4, T=−100 °C, Ru=4.8%, Rw=5.0%). The C 3/4 C, CC–CC, and NO distances are 1.201, 1.391, and 1.293 A(ring), respectively. The only intermolecular interactions are 1.844-A(ring)–OH ⋅ ⋅ ⋅ ON hydrogen bonding interactions. The vibrations νOH,NH =3289, 3070, 3021, νNO(IR) =1341, and νC 3/4 C (Raman) =2236 cm−1 are present. The solid-state motif is that of pleated sheets. UV, electron beam, and γ-ray induced polymerization has not been achieved; however, thermal treatment turns the crystals black. Thermogravimetric analysis under nitrogen reveals an explosive decomposition at ∼140 °C. Between 2 and 300 K the susceptibility obeys the Curie–Weiss expression with aitch-theta=−2.75 K. The effective moment is 2.47μB per molecule which is consistent with two independent S= 1/2 spins per molecule. Upon thermal treatment (17 h at 90 °C) the resultant black material exhibits a reduced Curie–Weiss susceptibility of 1.12μB and aitch-theta=−2.87 K. Unlike the α phase evidence for ferromagnetic behavior has not been observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340913
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  • 8
    Electronic Resource
    Electronic Resource
    High-speed electrometer for use in voltage-mode xerographic time-of-flight measurements (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 1396-1398 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have constructed a compact, inexpensive, high-speed electrometer for use in xerographic voltage measurements. The device consists of a single operational amplifier stage. The type of amplifier is selected to fit the particular experiment. Amplifiers with frequency responses from dc to 100 MHz and input resistances of up to 10+13 Ω are available. Measurements on amorphous selenium have shown this type of electrometer to be more versatile than commercially available units.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138608
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  • 9
    Electronic Resource
    Electronic Resource
    X-ray diagnosis of high-density compression of Ar-filled polymer shell targets (abstract) (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1851-1851 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Time-resolved x-ray diagnosis is the only practical approach at present to examining the change of fuel and shell conditions during the final stages of compression of laser fusion targets. Time-resolved spectroscopy of lines emitted by the fuel or shell elements can provide information about the time history of the density, temperature, and integrity of the target. We report on time-integrated and time-resolved x-ray measurements of compressed polymer shell targets filled with Ar, or mixtures of Ar/Kr, directly irradiated by the 24-beam 2-kJ, UV (351-nm) OMEGA laser. These include x-ray photography, time-resolved and spaced-resolved x-ray spectroscopy, and x-ray diode measurements. Picosecond x-ray spectroscopy of the K shell emission from Ar has been studied, and detailed modeling and Spark Broadening analysis of the H-like and He-like line emission made. The results are compared with predictions of hydrodynamics code simulations of the implosions. From this analysis, a consistent history of the density and temperature of the compressed target is inferred. This work was supported by the U.S. DOE Office of Inertial Fusion under agreement No. DE-FC08-85DP40200 and the Sponsors of the Laser Fusion Feasibility Project at the Laboratory for Laser Energetics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140083
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  • 10
    Electronic Resource
    Electronic Resource
    High-frequency response heat-flux gauge (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 639-649 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A double-sided, high-frequency response heat-flux gauge has been developed which allows measurement of heat flux from dc to 100 kHz. The instrument is designed for heat-flux magnitudes ranging from one to several hundred kW/m2 at temperatures up to 400 °C and is independent of the test article material. The gauges consist of a metal film (1500 A(ring)) resistance thermometers sputtered on both sides of a thin (25 μm) polyimide sheet. The sheet, which can contain many gauges, is then adhesively bonded to a test article. The temperature difference across the polyimide is a direct measure of the heat flux at low frequencies, while a quasi-1D analysis is used to infer the high-frequency heat flux from the upper surface temperature history. The design criteria, construction and application techniques, and a novel, ratiometric calibration procedure are discussed in detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138882
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