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  • American Institute of Physics (AIP)  (6)
  • 1995-1999  (6)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Conformational dynamics of a low temperature protein: Free base cytochrome-c (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 3229-3234 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Spectral diffusion waiting time experiments at 100 mK combined with aging time experiments are used to shed light on the features of the energy landscape of a cytochrome c-type protein and the respective conformational dynamics. The energy landscape shows features of a hierarchical organization. The time law which governs the dynamics in conformational phase space is a power law. The respective processes seem to be related to generalized diffusive-like motions. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477845
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  • 2
    Electronic Resource
    Electronic Resource
    Nonequilibrium phenomena in spectral diffusion physics of organic glasses (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 1798-1806 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We performed two different types of spectral diffusion experiments on persistent spectral holes. In all cases, we measured the holewidth as a function of time. The two experiments differed in their initial conditions: In the type 1 experiment (the "aging experiment''), the sample was cooled from room temperature to the final temperatures which were 100 and 800 mK, respectively. Holes were burnt at various time intervals after the final temperature was reached. In the type 2 experiment (the "cycling experiment''), the sample was allowed to relax for a period of about 10 days. Then, a hole was burnt and subjected to a temperature cycle. In all cases, the time dependence of the holewidths was strongly nonlogarithmic. The temperature cycled hole showed a narrowing regime which prevailed for the whole observation period of roughly one week. We will show that the deviation from the logarithmic time dependences is a nonequilibrium phenomenon. All features observed could be modelled within the standard tunneling model. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472055
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  • 3
    Electronic Resource
    Electronic Resource
    Rotational tunneling of partially deuterated methyl groups: Optical studies of dimethyl-s-tetrazine in different crystalline matrices (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 9762-9770 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rotational tunneling of monodeuterated methyl groups of dimethyl-s-tetrazine guest molecules in n-octane and tetramethylbenzene crystalline matrices is characterized by optical spectroscopy including hole burning methods. An analysis of the level structure shows that the asymmetric substitution leads to a partial localization of one of the methyl groups in n-octane, while in the tetramethylbenzene host both groups are equivalent and are strongly localized. The relaxation, by incoherent tunneling, between different orientations proceeds on a time scale of 〉107 s−1 in n-octane at temperatures below 2 K. The coupling of the orientation of the methyl group with the environment is estimated from information on inhomogeneous broadening attributed to random strain fields in the crystal. The strength of this coupling is related to the observed relaxation behavior. The origin of the asymmetry of the rotational potential is discussed in terms of static and dynamic contributions which are due to changes of bond length upon isotopic substitution and the dependence of vibrational frequencies on orientation. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472846
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  • 4
    Electronic Resource
    Electronic Resource
    Optical spectroscopy and ground state dynamics of methyl groups (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 942-949 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigated dimethyl-s-tetrazine (-h6 and -d6) in a n-heptane (-h16 and -d16) lattice with hole burning techniques. Stark experiments definitely show that the two methyl groups in dimethyl-s-tetrazine (DMST) are inequivalent. Hence, the respective rotational tunneling dynamics can be different. This is clearly seen in the behavior of DMST-d6 in both lattices n-heptane-h16 and -d16: Hole burning produces three pairs of sideholes symmetrically shifted from the laser frequency. The tunneling dynamics of the central hole as well as of the sideholes is governed by two relaxation times which differ by about one order of magnitude. Due to the narrow temperature range accessible, an unambiguous assignment of the microscopic tunneling relaxation process is not possible. On the other hand, DMST-h6 relaxes via a Raman process above 3 K and via a direct process below. In the Raman-active regime the tunneling rates for both host lattices fall on top of each other in agreement with theory. There are, however, features in the tunneling dynamics which are not yet understood. For instance, in the temperature regime where the direct process prevails, host deuteration speeds up the tunneling relaxation by an order of magnitude. In addition, the sidehole pattern of DMST-h6 is quite different from DMST-d6: Only one pair is observed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470817
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  • 5
    Electronic Resource
    Electronic Resource
    Experimental and numerical study of Rayleigh-Bénard convection affected by a rotating magnetic field (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 853-861 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the present paper we experimentally study the effects of a rotating magnetic field (RMF) on the fluid flow in an electrically conducting melt (Gallium), kept in a cylindrical container heated from below (Rayleigh-Bénard configuration). The experimental data are compared to results obtained from three-dimensional, time-dependent numerical calculations. The paper presents the influence of the magnetic induction B, the frequency of the RMF Ω, and the temperature difference ΔT between the hot bottom and cold top of the melt on heat transport and fluid flow, respectively. The results can be summarized in terms of the parameter Nrot, which is defined as the ratio of magnetic Taylor number (∝B2⋅Ω) to Grashof number (∝ΔT). It is shown that for 0.003〈Nrot〈0.1 large-scale regular thermal waves exist, which travel azimuthally in the same direction as the rotation direction of the RMF. These thermal waves are connected with large-scale temperature fluctuations (amplitude 6%–10% of ΔT). The amplitude decreases with increasing Nrot, whereas the mean frequency increases from 0.001 Hz up to 0.1 Hz for 0.003〈Nrot〈0.1. For Nrot〉0.1 temperature fluctuations with amplitudes smaller than 1%–2% of ΔT and frequencies greater than 0.1 Hz are observed. These oscillations can be attributed to Taylor vortices generated at the vertical cylinder walls. The regions of the different oscillation modes within the parameter space are shown in a stability diagram. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869957
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  • 6
    Electronic Resource
    Electronic Resource
    Scanning microscopy of magnetic domains using the Fe 3p core level transverse magneto-optical Kerr effect (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 4610-4612 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate the feasibility of the vacuum ultraviolet analog to visible-light magneto-optical imaging of magnetic structures using the resonantly enhanced transverse magneto-optical Kerr effect at core level thresholds with incident p-polarized radiation. The advantages are element specificity and a variable information depth. We used the scanning x-ray microscope at HASYLAB capable of obtaining about 1 μm resolution by means of its focusing ellipsoidal ring mirror. The p-polarized component of the reflected light was selected using multilayer reflection at an additional plane mirror downstream to the sample. Micrographs of the optical reflectivity were taken in the vicinity of the Fe 3p core level threshold at 53.7 and 56.5 eV photon energy where the magneto-optical effect is of opposite sign. Magnetic domains are visible in the difference of both recorded images. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370424
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