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  • Digitale Medien  (29)
  • 1995-1999  (19)
  • 1980-1984  (8)
  • 1955-1959  (2)
  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 1792-1795 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: We have built an apparatus to study the viscoelastic response and measure the complex shear moduli of Langmuir monolayers as functions of the frequency and amplitude of the applied sinusoidal shear strain. A rotor is placed in contact with the monolayer and suspended by a torsion wire; a coil attached to the rotor carries a direct current. The voltage induced in this coil by a high-frequency external magnetic field is used to measure the angle of rotation with an accuracy of ∼0.005°. A low-frequency external magnetic field is used to drive the rotor into forced oscillations at the desired frequency (1 mHz–1 Hz), or the rotor may oscillate freely with the "natural" frequency variable over the range 0.01–3 Hz using a static external magnetic field. The apparatus has a large dynamic range for shear modulus measurement (∼5×10−3–103 dyn/cm), achieved by using the free oscillation (ring-down) method for films with low shear moduli (∼5×10−3–1 dyn/cm), and the forced oscillation method for films with higher shear moduli (∼1–103 dyn/cm). We have found that the complex shear modulus G of heneicosanoic acid Langmuir monolayers depends on the applied strain except at very low amplitudes. We also present sample data showing the frequency dependence of G. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 6148-6154 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A study of the temporal response of a biased Fabry–Perot etalon with a nematic liquid crystal exposed to short (∼10 μs) voltage pulses is presented. It is found that the finesse is the crucial factor determining the achievable switching time. For a given maximum transmission the reflectivities of the Fabry–Perot mirrors are optimized to achieve minimum switching times. In particular, switching times of 0.5 μs with an initial transmission of 3% and a maximum value of 70% have been obtained. The experimental results are in good agreement with theory. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3020-3025 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A study of the temporal response of a biased planar nematic liquid crystal to short (∼10 μs) voltage pulses is presented. The resulting optical phase shift varies quadratically with time during the first 2 μs after switching the voltage on and then linearly. A theoretical model is developped starting from the Leslie-Ericksen theory which describes the investigated phase modulation in the microsecond time scale. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    BJOG 104 (1997), S. 0 
    ISSN: 1471-0528
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 196-198 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Metal–semiconductor–metal photodetectors were fabricated on an AlGaAs/GaAs/AlGaAs double heterostructure with no graded layers. Devices with photolithographically defined finger spacing and width of 1 μm ("1×1") exhibited a saturation bandwidth of greater than 20 GHz, for bias voltages between 3 and 4 V. We attribute this to minimal hole pileup, and propose a simple model for the energy of hot holes near the band offset at the cathode. Using this model, estimates of the bias required to reduce hole pileup in different material systems were derived. The model shows good agreement with results reported here and elsewhere. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 2863-2872 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A direct measurement of the transition dipole moment, μ3, of the degenerate v3 in-plane asymmetric C–H stretching vibration of the methyl radical has been made. The measurements were carried out in a flow reactor using laser-photolysis transient infrared absorption spectroscopy. Cyano (CN) radicals (and Cl atoms) were produced by laser photolysis of BrCN (or ClCN) at 193 nm and reacted with methane to give both CH3 and HCN (and HCl). The intensities of 18 rotational lines of the v3 fundamental band were measured relative to the R(8) line of the C–H stretching vibration (v3) of HCN(001←0). The best estimate of the transition dipole moment of the CH3 (00110←0) transition was provided by the measured line intensity for the CH3 (00110←0)rR(3,3) transition and was determined to be μ3=0.0327±0.0021 D. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 7966-7982 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The reaction of the cyano radical (CN) with ethane was studied using time-resolved infrared absorption spectroscopy to monitor individual rovibrational states of the HCN product. A method is described that can be used to determine the initial vibrational state distribution at pressures of several Torr. This technique was applied to the title reaction to determine that the vibrational states of HCN(v1,0,v3), where v1, v3=0, 1, and 2, were not directly populated in the title reaction to any significant extent. The initial vibrational energy content of the CN radical was also varied but did not influence the initial population in the HCN vibrational levels probed in this experiment. The time dependence of HCN(v1,0,v3) was followed and interpreted in terms of bimolecular rate constants for vibrational relaxation with ethane. The title reaction is mode specific in its energy disposal in that at least every HCN product appears to have at least one quantum of bending excitation, likely in combination with stretching vibrations. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Oxford : Blackwell Science Ltd, UK
    Anaesthesia 53 (1998), S. 0 
    ISSN: 1365-2044
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: All senior house officer posts in the Yorkshire Deanery have been assessed against five parameters. Posts in anaesthesia were among the best with excellent consultant support, good exposure to clinical practice and well-structured education and training. Anaesthetic posts were almost unique in satisfying the ‘New Deal’ on junior doctors hours though intensity of work was something of a problem for the on-call senior house officer. Appraisal is a new educational tool which is being used to a greater degree in anaesthetics than in any other specialty. The deficiencies found in anaesthetic posts could be corrected by the universal use of appraisal and solving the recruitment problems that have compromised the delivery of good training in some districts.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Anaesthesia 50 (1995), S. 0 
    ISSN: 1365-2044
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 4533-4549 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The reaction of the cyano radical (CN) with methane was studied by time-resolved infrared absorption spectroscopy by monitoring individual rovibrational states of the HCN and CH3 products. The initial vibrational level distribution of the bendless vibrational levels of HCN(v1,0,v3) was determined by plotting the time dependence of the fractional population of a vibrational level and extrapolating these curves to the origin of time. About 20% of the HCN products were observed to be initially produced in the HCN(v1,0,v3) vibrational levels, with v1 and v3=0,1,2. The CN radical was created by laser photolysis of three different precursors. Each photolyte provided a different initial vibrational level distribution of CN; however, similar initial HCN(v1,0,v3) vibrational level distributions were obtained independent of the CN radical precursor. This may indicate that the CN radical does not act as a spectator bond during the course of a reactive encounter for this system. The time dependence of the CH3 (00000) ground state was also followed using time-resolved infrared absorption spectroscopy. Preliminary data indicates that a large fraction, if not all, the CH3 radicals are produced in their ground state in the title reaction. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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