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  • 1
    Electronic Resource
    Electronic Resource
    Nonlinear effect of an oscillating electric field on membrane proteins (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4891-4901 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The nonlinear response of a two-state chemical transition to an oscillating electric field is examined. A reaction for which this analysis is particularly relevant is a conformational transition of a membrane protein exposed to an ac electric field. Even a modest externally applied field leads to a very large local field within the membrane. This gives rise to nonlinear behavior. The applied ac field causes harmonics in the polarization and can cause a dc shift in the state occupancy, both of which can be observed and used to determine kinetic parameters. Fourier coefficients are calculated for the enzyme state probability in the ac field, exactly for infinite frequency, and in powers of the field for finite frequency. Kramers–Kronig relations are proved and response functions are given for the leading terms of the harmonics. The results are extended to the spherical symmetry relevant to suspensions of spherical cells, vesicles, or colloidal particles. If the protein catalyzes a reaction, free energy is transduced from the electric field to the output reaction, even if that reaction is electrically silent. Many transport enzymes are ideal examples. The ac field can cause the enzyme to pump ions or molecules through the membrane against an (electro)chemical potential. The efficiency of this energy transduction can be as high as 25%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456728
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  • 2
    Electronic Resource
    Electronic Resource
    Xenon excited state density measurements in electron beam pumped XeCl laser mixtures (1987)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 1986-1988 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Time-dependent density measurements of the lowest xenon excited states (5p56s) in electron beam (e-beam) pumped XeCl laser mixtures (nonlasing) are performed using pulsed hook interferometry. The e-beam pulse length is ≈0.45 μs (full width at half-maximum) with an average excitation rate of ≈250 kW/cm3. Density differences (ΔN*) of transitions at 823.2 nm (6s[3/2]02 –6p[3/2]2), 828.0 nm (6s[3/2]01 –6p[1/2]0), and 840.9 nm (6s[3/2]02 –6p[3/2]1) are obtained for various HCl and Xe concentrations. For a 98.3% Ne/1.5% Xe/0.16% HCl mixture at 3000 Torr, ΔN* (823.2 nm) and ΔN*(828.0 nm) are relatively constant at ≈3×1014 and ≈1.7×1014 cm−3, respectively. At lower initial HCl concentrations, the ΔN*(823.2 nm) density starts out similar to the 0.16% HCl case, but tends to increase dramatically during the e-beam pulse. For a 0.04% HCl mixture, a ΔN*(840.9 nm) density of ≈4.5×1015 cm−3 is measured at the end of the e-beam pulse. Preliminary comparisons of the data with a computer model show good agreement for HCl concentrations ≥0.16%, but disagreements at leaner concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.98319
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  • 3
    Electronic Resource
    Electronic Resource
    Narrowband, single line, 1 μs XeF laser (1987)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 1063-1065 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A narrowband (5 GHz) electron beam pumped XeF oscillator/amplifier, lasing at 353.2 nm over a 1-μs pulse duration, has been demonstrated. Line selection, bandwidth narrowing, and near-diffraction-limited output are achieved by using an echelle grating and an intracavity solid étalon in a stable oscillator configuration. The amplifier features an off-axis design and yields output energies (approximately-greater-than)0.8 J. The oscillator and amplifier are located in the same gas chamber and are transversely pumped by the same electron beam. A Fabry–Perot interferometer together with a streak camera is used to verify narrowband operation over the entire pulse duration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.98792
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  • 4
    Electronic Resource
    Electronic Resource
    Xenon excited-state densities in electron-beam pumped XeCl and XeF (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 507-515 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Understanding of the neutral channel formation kinetics in excimer laser gas mixtures has been limited by the lack of data on the pertinent excited-state populations in these mixtures. Presented are time-dependent measurements of the lower level xenon excited-state densities in electron-beam (e-beam) pumped XeCl and XeF laser mixtures (neon diluent). Measurements are obtained using hook interferometry under nonlasing conditions at an average excitation rate of ≈250 kW/cm3 and e-beam pulse lengths of 0.4 and 1 μs. The population differences, ΔN*, between four different electronic transitions [three in the Xe*(6s)-Xe**(6p) manifold, and one in the Xe**(6s')-Xe***(6p') manifold] are examined as a function of halogen concentration. For both XeCl and XeF at high initial halogen concentrations (〉4 Torr), the ΔN* densities of the Xe*(6s) and Xe**(6s') transitions are relatively constant during the 0.4-μs e-beam pulse [for ΔN*(6s-6p): ≈4×1014 cm−3 for XeCl, and ≈1.5×1014 cm−3 for XeF]. At lower initial halogen concentrations, the ΔN* densities of 6s-6p and 6s'-6p' start at the beginning of the pulse at approximately the same densities as the richer halogen mixtures, but at a certain point during the pulse, the ΔN* densities abruptly increase. This increase can be 〉10 times for very lean halogen mixtures (1–2 Torr), and occurs at earlier times as the initial halogen concentration is reduced. From other measurements, this increase appears related to the depletion of the halogen. The observed lifetime of the Xe*(6s) densities is ≈2 μs for the low initital halogen concentration mixtures. Additional density data for halogen-free Ne/Xe and Ar/Xe mixtures are also presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341989
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  • 5
    Electronic Resource
    Electronic Resource
    Dissociation rates for individual eigenstates of S0 formaldehyde: Fluctuations and barrier height (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 6519-6521 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Spectra of S0 D2CO rovibronic states near the dissociation threshold have been taken with a new method by monitoring S1 lifetime while Stark shifting an S1 level through the S0 manifold. An order of magnitude variation in the unimolecular dissociation rate and in the S1–S0 vibronic coupling matrix element is observed among S0 levels within a 0.2 cm−1 energy range. These individual molecular eigenstates exhibit distinctive chemical properties. Dissociation rates averaged over an energy range of a few cm−1 vary smoothly with energy and give a barrier height of 78.0–81.1 kcal/mol for H2CO→H2+CO.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450750
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