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  • American Institute of Physics (AIP)
  • 11
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 36 (1995), S. 4138-4161 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: We obtain a classification of infinitesimal symmetries of an autonomous higher-order Lagrangian system by using the theory of lifts of vector fields to tangent bundles. Also, a classification of infinitesimal symmetries of a time-dependent higher-order Lagrangian system is obtained. The relationship between infinitesimal symmetries and constants of the motion is investigated. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 12
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 37 (1996), S. 3389-3414 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: We present a geometric framework for non-holonomic Lagrangian systems in terms of distributions on the configuration manifold. If the constrained system is regular, an almost product structure on the phase space of velocities is constructed such that the constrained dynamics is obtained by projecting the free dynamics. If the constrained system is singular, we develop a constraint algorithm which is very similar to that developed by Dirac and Bergmann, and later globalized by Gotay and Nester. Special attention to the case of constrained systems given by connections is paid. In particular, we extend the results of Koiller for Caplygin systems. An application to the so-called non-holonomic geometry is given. © 1996 American Institute of Physics.
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  • 13
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 29 (1988), S. 332-335 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: It is demonstrated, via recent global estimates for the heat kernel found by Li and Yau [Acta Matematica 156, 153 (1986)], that the covariance of the mass m free field decays exponentially, at a rate m, with the geodesic distance on any complete, noncompact Riemannian manifold with non-negative Ricci curvature. The rate of the exponential decay is larger than m on simply connected manifolds with negative sectional curvature.
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  • 14
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 7984-7994 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ionization and dissociation processes occurring after two-photon excitation of the d 1Σ+ state of NH have been investigated using one- and two-color multiphoton ionization spectroscopy in combination with mass-resolved ion and kinetic energy-resolved electron detection. The photoelectron spectra obtained for ionization of the molecule via the d 1Σ+ state (v'=0,1) reveal a one-photon ionization process to all energetically accessible vibrational levels of the X 2Π ground ionic state, at variance with a one-configuration description of the two states. Moreover, electrons are observed that derive from a one-photon ionization of excited neutral nitrogen and hydrogen atoms. Two-color excitation experiments of the d 1Σ+ state show that the influence of discrete states at the overall three-photon level on the dissociation dynamics is insignificant. Using the results of ab initio calculations it is concluded that these experimental observations can be interpreted consistently if two competing processes are assumed to take place from the d 1Σ+ excited state: a molecular one-photon ionization which is forbidden in zeroth order, and a two-photon nonresonance enhanced excitation to neutral (pre)dissociative states.
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  • 15
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3722-3724 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An optical microphone configuration is experimentally demonstrated. It is based on the deflection of a He-Ne laser beam from a thin reflective pellicle bound on one edge over the duct of a conventional photoacoustic cell. Possible applications of this kind of photoacoustic detection are discussed.
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  • 16
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3282-3286 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Based on the grain barrier model of Levinson an expression of the off-current Ioff of a thin-film transistor is derived.The dependence of Ioff on the donor concentration ND and the semiconductor thickness ds is discussed and compared to experimental data. It is shown that NDds has to be smaller than the grain-boundary trap concentration in order to obtain enhancement thin-film transistors completely turned off at VG=0.
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  • 17
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigated the influence of the presence of oxygen during the deposition of the calcium cathode on the structure and on the performance of polymeric light emitting diodes (pLEDs). The oxygen background pressure during deposition of the calcium cathode of polymeric LEDs was varied. Subsequently, the oxygen depth distribution was measured and correlated with the performance of the pLEDs. The devices have been fabricated in a recently built ultraclean setup. The polymer layers of the pLEDs have been spincoated in a dry nitrogen atmosphere and transported directly into an ultrahigh vacuum chamber where the metal electrodes have been deposited by evaporation. We used indium–tin–oxide as anode, OC1C10 PPV as electroluminescent polymer, calcium as cathode, and aluminum as protecting layer. We achieved reproducibility of about 15% in current and brightness for devices fabricated in an oxygen atmosphere of (very-much-less-than)10−9 mbar. For further investigations the calcium deposition was carried out in an oxygen atmosphere from 10−8 to 10−5 mbar. We determined the amount of oxygen in the different layers of the current–voltage-light characterized pLEDs with elastic recoil detection analysis and correlated it with the characteristics of the devices. The external efficiency of the pLEDs decreases continuously with increasing oxygen pressure, the current shows a pronounced minimum. The brightness mostly decreases with increasing oxygen with an indication of a slight minimum. PLEDs with completely oxidized calcium are not operational. The first contact of the pLEDs with the dry glove box environment leads to an immediate reduction of current and brightness which is caused by the cooling of the devices by several degrees. Determining reproducible characteristics of pLEDs in the vacuum requires the measurement of their temperature. © 2001 American Institute of Physics.
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  • 18
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Progress in fusion research shows an increasing demand for diagnostics with high temporal and spatial resolution in order to study small and fast phenomena in fusion plasmas. Therefore, a new ten-channel pulsed radar reflectometer is under development for the TEXTOR Tokamak, to measure electron density profiles in the range of 0.4–4×1019 m−3 at a high repetition rate of 2 MHz. An additional feature of this diagnostic is the possibility to perform correlation measurements at 10 MHz repetition rate to investigate density fluctuations. The reflectometer will scan the plasma with 1-ns-long radar pulses in the 18–57 GHz range. In spite of the long flight time of the pulses of about 100 ns, the above mentioned high repetition rates could be achieved by time multiplexing the generation and reception of the radar pulses. Temporal selection of the received pulses is performed by fast switching of the local oscillators inputs of the heterodyne receiver, to generate time windows in which the reception of the reflected pulses is expected. An embedded VME controller will manage the system and store the data with a speed of 20 Msamples/s, up to a maximum of 64 Mbyte data per plasma shot. In order to facilitate the handling of such a huge amount of data, an advanced data reduction scheme is being developed. Remote operation with a fast data link from FZ Jülich (Germany) to FOM Nieuwegein (The Netherlands) will be possible. © 1999 American Institute of Physics.
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  • 19
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 714-716 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured rotationally resolved photoelectron spectra of the OH radical using (2+1) resonance enhanced multiphoton ionization spectroscopy via the D 2Σ−(3pσ) and 3 2Σ−(4sσ) Rydberg states. For the D 2Σ−(3pσ) state, we observe primarily ΔN=even distributions of ionic rotational states, in contrast to the ΔN=odd distribution expected for ionization of a 3pσ Rydberg electron. The observations are described quantitatively by ab initio calculations which predict a Cooper minimum in the 3pσ→kπ(l=2) channel, whose occurrence determines the ΔN=even ion rotational distribution. In contrast, the 3 2Σ−(4sσ) photoelectron spectra reveal a broad distribution in rotational levels, arising from greater l mixing in the higher Rydberg orbital and much weaker Cooper minima in the continuum.
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  • 20
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetization curves have been calculated for single crystals of ferrimagnetic rare-earth transition-metal compounds that are free to rotate in the applied magnetic field. The calculations have been performed taking into account the magnetic-anisotropy constants of the rare-earth and transition-metal sublattices up to the fourth order. Seven different types of rotation processes can be distinguished.
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