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  • American Institute of Physics (AIP)  (10)
  • Wiley-Blackwell  (5)
  • 2000-2004  (4)
  • 1995-1999  (11)
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  • 1
    Electronic Resource
    Electronic Resource
    Protein dynamics at low temperatures (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 3045-3050 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The low temperature conformational dynamics of the heme type protein mesoporphyrin-IX-substituted horseradish peroxidase is investigated by spectral diffusion waiting time/aging experiments. Spectral diffusion broadening is governed by a power law in time. There is a small but significant aging effect. It is assumed that the conformational dynamics of the protein which leads to the spectral broadening of the burnt-in holes is governed by a diffusion type equation. In this case the shape of the spectral diffusion kernel is Gaussian. This model is contrasted with spectral diffusion phenomena as described by the TLS-model (TLS, two level system). © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480879
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  • 2
    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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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    Early stages of mechanical crystallization of amorphous FeZrBCu soft magnetic material (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 2464-2468 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nanocrystalline Fe-base soft magnetic materials with high saturation magnetization have been obtained by crystallization of FeZrBCu amorphous precursors. In contrast to the conventional thermal crystallization, mechanical crystallization provides an alternative route for the generation of nanocrystalline materials using a high energy ball mill. Special emphasis is put here on the early stages of the transformation. X-ray diffraction, Mössbauer spectroscopy, and magnetization measurements are used to characterize the material. We find a continuous increase of the saturation magnetization accompanied by an increase of the crystalline fraction. The coercivity shows a different behavior with a large increase after very short milling within the amorphous state and a decrease for long milling duration. The influence of the deformation process on the magnetic anisotropy and the coercivity is discussed in terms of stresses and shear band formation. The results are compared with the phase formation and magnetic properties of thermally crystallized FeZrBCu samples and mechanical crystallization studies of other materials. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372203
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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    Glasses and proteins: Similarities and differences in their spectral diffusion dynamics (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 8718-8721 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We compare the spectral diffusion dynamics of resorufin doped glycerol/H2O- and glycerol/D2O-glass with the respective dynamics of a chromoprotein in the same glass at 4.2 K. Spectral diffusion broadening of photochemical holes is measured over almost four orders of magnitude in time. In all samples there are strong aging phenomena. Resorufin in deuterated water/glycerol is reasonably well-described by the two level system (TLS) model. In the protonated glass, the TLS model does not seem to describe the experiments reasonably well. In the protein sample it totally fails. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1367382
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  • 7
    Electronic Resource
    Electronic Resource
    Influence of isotopic substitution on the conformational dynamics of frozen proteins (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 9638-9644 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The spectral diffusion dynamics was measured over 3 orders of magnitude in time of a myoglobin-type protein with the heme group substituted by Zn-pheophorbid a. After burning a photochemical hole at 4.2 K, the width of the spectral diffusion kernel is well described by a power law in waiting time with an exponent of 0.24. Spectral diffusion broadening is subject to "aging," viz., to the equilibration time at 4.2 K before hole burning. It decays with a power law in aging time. Deuteration of the solvent has a significant effect on the dynamics of the protein. Spectral diffusion broadening is smaller in the deuterated sample, however, the respective power law is not changed. The aging dynamics, on the other hand, does not seem to be influenced significantly by deuteration. The conclusion is that deuteration influences the fluctuations but not the relaxation. In addition to spectral diffusion, we also measured the recovery dynamics of the hole. It is slowed down tremendously by deuteration, confirming that the photoreaction is based on a light-induced proton transfer. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1369137
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  • 8
    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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  • 9
    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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  • 10
    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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