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  • 11
    Electronic Resource
    Electronic Resource
    The rotational spectrum and molecular properties of bromine dioxide, OBrO (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 8292-8302 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rotational spectrum of the OBrO radical has been observed in the gas phase over the solid products of the O+Br2 reaction. Spectra have been measured for both O79BrO and O81BrO in their (000), (010), and (020) vibrational states in selected regions between 88 and 627 GHz spanning the quantum numbers 1≤N≤61 and 0≤Ka≤14. The spectra are well described by a Hamiltonian which includes centrifugal distortion effects for fine and hyperfine terms. The molecular structure, the dipole moment, and the harmonic force field have been derived, and they, as well as fine and hyperfine structure constants, are compared with data of related molecules and electron spin resonance data from OBrO isolated in cryogenic salt matrices. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475030
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  • 12
    Electronic Resource
    Electronic Resource
    Pressure dependence and metastable state formation in the photolysis of dichlorine monoxide (Cl2O) (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 2857-2868 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation of dichlorine monoxide (Cl2O) was studied using broadband flash photolysis to investigate the influence of variations in the photolysis wavelength domain, bath gas pressure and bath gas identity on the yield and temporal dependence of the ClO product. ClO yields were independent of bath gas pressure when the photolysis spectral band extended to 200 nm (quartz cutoff) but for photolysis restricted to wavelengths longer than about 250 nm, ClO yields decreased with increasing bath gas pressure and there was a pressure-dependent delay in the formation of ClO. Under these conditions, a weak, highly structured absorption spectrum was observed in the range 16 600–26 000 cm−1 with a lifetime on the order of 500 ms. A portion of the spectrum could be analyzed (22 000–26 000 cm−1) which showed progressions having differences of 283, 443, and 505 cm−1. Ab initio calculations were performed to evaluate vertical excitation energies and oscillator strengths from the lowest-energy singlet (X 1A1) or triplet (1 3B1) states to various excited states. The calculations indicated that the 2 3A2←1 3B1 transition has an unusually large oscillator strength. The transition energy, 3.05 eV, is consistent with the observed metastable spectrum. The observed pressure dependence of ClO formation could be modeled using a mechanism which assumed that Cl2O excitation at wavelengths longer than about 300 nm leads to rapid intersystem crossing to two metastable states in the triplet manifold. These states undergo competitive dissociation to ClO+Cl and collisional relaxation to the ground state. The dynamics of Cl2O may serve as a model for other molecules of importance in the earth's lower stratosphere such as ClONO2 where filtering of the solar spectrum by ozone restricts photolysis to the weak tail of the absorption continuum. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471109
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  • 13
    Electronic Resource
    Electronic Resource
    Single trapped vortices induced in a superconducting film by laser switching (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 2419-2423 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Light pulses from an infrared laser can momentarily drive a superconducting strip of niobium normal. Under certain conditions, a single vortex may be trapped while the strip returns to the superconducting state. It was determined that the speckle pattern due to modal interference in the incident light is the most probable cause of vortex trapping. By changing the relative contrast of the speckle pattern, we can change the trapping probability from 0% to about 5% per pulse.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353096
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  • 14
    Electronic Resource
    Electronic Resource
    Photothermal description of polymer ablation: Absorption behavior and degradation time scales (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 5172-5178 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A photothermal model of ablation is used to investigate the time scales for polymer degradation by UV laser light. In the absence of a significant incubation effect, strong absorbers (e.g., polyimide) are expected to decompose roughly three orders of magnitude faster than weak absorbers (e.g., polymethylmethacrylate), owing to the higher surface temperature attained during the absorption. This difference in the time scales reflects processes taking place at significantly different temperatures and should extrapolate to the overall ablation process. The very short calculated time scales (femtoseconds for polyimide and picoseconds for polymethylmethacrylate) indicate that polymer decomposition occurs rapidly compared to the actual ejection of material. For multipulsed ablation experiments, significant incubation modification tends to increase the absorbance of weak absorbers, making the effect less marked than in the ideal case. Incubation effects are attributed to nonablative decomposition that occurs at cooler temperatures (〈1000 K).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351997
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  • 15
    Electronic Resource
    Electronic Resource
    Silicon photodiode detector for fluorescence EXAFS (1987)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 58 (1987), S. 1891-1894 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A large-area silicon diode is used as a fluorescence detector for extended x-ray absorption fine-structure (EXAFS) measurements. A direct comparison of this diode detector relative to a gas ionization fluorescence detector is made. Advantages of the diode detector include: higher signal for a given photon flux (due to higher quantum efficiency), vacuum and cryogenic compatibility, freedom from microphonic noise, good linearity, extremely wide dynamic range, operation without high voltage or gas connections, very simple electronics, and low cost. A brief comparison with other detection methods for fluorescence EXAFS is given. Use of photodiodes for transmission EXAFS is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139538
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  • 16
    Electronic Resource
    Electronic Resource
    The dispersion functional for multidimensional equilibria (1985)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 28 (1985), S. 3546-3556 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerical study of the linear stability of plasmas is very difficult when one or more of the plasma species is collisionless and the equilibrium is multidimensional, that is, characterized by two or more nonignorable spatial coordinates. The problem arises, for example, in evaluating kinetic stabilizing effects on the internal tilting mode (an n=1 ballooning mode) in field-reversed configurations. In this paper, the Laplace transform of the perturbation distribution function for a collisionless species is derived for all classes of phase-space trajectories and used to construct the dispersion functional for multidimensional equilibria. The kinetic part of the dispersion functional is expressed in terms of the Laplace transform of autocorrelation functions with respect to a certain delay time. It is shown how to obtain the same result formally by using Liouville eigenfunctions. For the case of the Vlasov-fluid model, the dispersion functional is transformed in a way that is particularly appropriate for computation of the kinetic stability of field-reversed configurations to the internal tilting mode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865309
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  • 17
    Electronic Resource
    Electronic Resource
    Particle and fluid simulations of resistive current-driven electrostatic ion cyclotron waves (1987)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 3113-3128 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The results from 1-D numerical simulations of electrostatic ion cyclotron waves (EIC) are presented for a model in which the electrons are a resistive (collisional) fluid. Simulations of both the kinetic and fluid descriptions are performed and compared in order to assess the fundamental limitations of fluid theory for EIC waves. The effect of ion–neutral collisions is also included using a simple Monte Carlo technique. It is found that a small ion–neutral collision frequency destroys the frequency harmonic coupling of kinetic EIC waves and tends to validate the fluid description. The saturation amplitude of the current driven EIC instability is in agreement with recent laboratory experiments. The coherent nature (extremely narrow spectral width) and phase velocity agree with ground based (coherent backscatter radars) and in situ observations of current-driven EIC waves in the high latitude ionosphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866487
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  • 18
    Electronic Resource
    Electronic Resource
    Results of an experimental study of the properties of ion-beam modes found in a double plasma device containing a hemispherical separating screen (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 3455-3464 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ion-beam modes have been generated in a double plasma device containing argon in which the driver and target plasmas were separated by a hemispherical screen biased negatively with respect to both plasmas. Making the driver plasma positive with respect to the target plasma resulted in the formation of an ion beam flowing from the driver plasma to the target plasma and causing the formation of a focal region in the target plasma. Both single pulses and pulse trains were excited in the target plasma by application of positive voltage pulses and/or sine waves to the hemispherical grid. Detection of these modes was accomplished using a positively biased spherical probe capable of axial and rotational movement. The wave amplitude and the phase velocity along the axis of the target plasma were measured over a distance of more than two hemispherical grid radii. Since no theoretical treatments have as yet been published for the hemispherical case, the measured values have been compared with theoretical values for a spherical separating screen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860873
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  • 19
    Electronic Resource
    Electronic Resource
    Kinetic tilting stability of field-reversed configurations (1986)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 29 (1986), S. 2616-2629 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Stability of the internal tilting mode in an elongated prolate field-reversed configuration (FRC) is investigated numerically. Eigenfrequencies are calculated from a Vlasov-fluid dispersion functional that is separated into fluid and kinetic portions. The latter are evaluated by a Monte Carlo method following a sample of the equilibrium orbits. An innovative Fourier transform technique is developed to reduce the operation count of the algorithm. Kinetic growth rates obtained for an experimentally relevant equilibrium indicate essential stabilization of internal tilting in an FRC with s¯(approximately-less-than)2, where s¯ measures the number of thermal gyroradii in the configuration. For s¯→∞ the kinetic growth rates approach previous magnetohydrodynamic (MHD) values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.865503
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  • 20
    Electronic Resource
    Electronic Resource
    Resolution in surface plasmon microscopy (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 2829-2836 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this article we demonstrate how to obtain the ultimate lateral resolution in surface plasmon microscopy (SPM) (diffraction limited by the objective). Surface plasmon decay lengths are determined theoretically and experimentally, for wavelengths ranging from 531 to 676 nm, and are in good agreement. Using these values we can determine for each particular situation which wavelength should be used to obtain an optimal lateral resolution, i.e., where the plasmon decay length does not limit the resolution anymore. However, there is a trade-off between thickness resolution and lateral resolution in SPM. Because of the non-optimal thickness resolution, we use several techniques to enhance the image acquisition and processing. Without these techniques the use of short wavelengths results in images where the contrast has vanished almost completely. In an example given, a 2.5 nm SiO2 layer on a gold layer is imaged with a lateral resolution of 2 μm, and local reflectance curves are measured to determine the layer thickness. The SPM image is compared with an atomic force microscopy image of the same object. We obtain a 3 μm resolution when thickness differences within a lipid monolayer are imaged and measured.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144623
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