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  • 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
    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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  • 3
    Electronic Resource
    Electronic Resource
    Thermal recovery and spectral diffusion of photochemical holes in polymorphic systems (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 9262-9270 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present comparative investigations of doped benzophenone in its glass and crystal phases by using thermal cycling hole burning techniques. Chlorin and s-tetrazine were used as probe molecules. We measured the distribution of reactive barriers and the spectral diffusion behavior in both phases. The distribution in the glass is broad and is well described by a Gaussian. In the crystal, there are rather well-defined barriers, yet they are different for different sites. The respective kinetics is exponential and its temperature dependence is Arrhenius-like in contrast to the glass phase. Thermally induced spectral diffusion broadening in the glass phase is strong and shows the pattern well known from other organic glasses. In the crystal, it is much weaker, yet it is not completely absent. The experiments seem to indicate a threshold temperature ∼40 K. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468018
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Proton implantation into GaAs: Transmission electron microscopy results (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 2206-2210 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Semi-insulating liquid-encapsulated Czochralski grown GaAs wafers were implanted at room temperature with protons at energies of 2, 4, and 30 keV at doses up to 1×1018 cm−2. Without using further annealing treatments the samples were inspected, also using cross-sectional techniques, by transmission electron microscopy. Surface amorphization of the bombarded GaAs was found. Excess hydrogen precipitates in the form of large bubbles in the amorphous layer. Nearly spherical hydrogen bubbles were detected in the crystalline layer below the amorphous zone. At 30 keV, pressurized bubble rafts, where a certain number of bubbles are located in the plane of a microcrack, were detected. The recent observations of similar bubble rafts by Neethling and Snyman [J. Mater. Sci. 23, 2697 (1988)] and the present rafts are discussed in the light of the theoretical treatment by d'Olieslaeger et al. [Philos. Mag. B 63, 1321 (1991)]. The bubble rafts have presumably been produced by the collapse of pressurized hydrogen-filled microcracks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351118
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  • 6
    Electronic Resource
    Electronic Resource
    Hot implantation of protons into GaAs: Transmission electron microscopy (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4371-4374 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Implantation of hydrogen at 600 °C into GaAs at 8 keV and at high doses resulted in the formation of a two-layer structure. The topmost layer roughly extended in depth to the range of the protons and exhibited a high concentration of loops, hydrogen bubbles, decorated dislocations, and faults. Occasional microsplits on {110} were observed. The deeper layer contained pressurized hydrogen platelets on {111}. These results are critically compared with previous results obtained with cold implanted and subsequently annealed GaAs. The present observations are also discussed in relation to the theoretical treatment by d'Olieslaeger [J. Mater. Sci. 23, 2697 (1988)]. Estimates of the importance of arsine production are also presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354404
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    Structural disorder and spin-lattice relaxation (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 605-609 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We measured the spin-lattice relaxation of the photoexcited triplet state of quinoxaline in variety of organic glasses and polymers as a function of temperature. The experiment covered the temperature range from a few K close to the glass transition. The remarkable thing is that the temperature dependence of the spin-lattice relaxation seems to be uniform for the various glassy and polymeric materials within the whole temperature range and seems to follow a quadratic temperature dependence. The only exception in polyethylene. There, the temperature dependence is much steeper but levels off above 40 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465732
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  • 9
    Electronic Resource
    Electronic Resource
    A comparative pressure tuning hole burning study of protoporphyrin IX in myoglobin and in a glassy host (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 2478-2486 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We measured the behavior of spectral holes under isotropic pressure changes as a function of burn frequency. We compared a protein sample, namely protoporphyrin IX substituted myoglobin in a glycerol/water glass with a sample where the protoporphyrin IX was directly dissolved in a host glass. The differences are remarkable—holes in the pure glass behave as expected for a homogeneous isotropic material. It is the nonlinear frequency dependence of the pressure shift where the deviation of the protein sample is most obvious. These observations signal a correlation between the structures of the dye probe and the structures of the apoprotein. They further show that global parameters of the apoprotein, such as the isothermal compressibility, depend strongly on the associated conformational substates and are subject to unexpected large variations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465210
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  • 10
    Electronic Resource
    Electronic Resource
    Spin-conversion relaxation in dimethyl-s-tetrazine doped n-octane: Deuteration and symmetry breaking (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 1-6 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Spectral hole burning is used to measure spin-conversion relaxation of methyl groups attached to a dye probe. The dye is dimethyl-s-tetrazine, the host is n-octane, which is, at low temperatures, a Shpol'skii-matrix. The temperature dependence of the spin-conversion relaxation follows the same pattern for the protonated and the perdeuterated methyl-rotor. However, the relaxation rates of the perdeuterated rotor are higher by almost two orders of magnitude. Partial deuteration destroys the rotor symmetry and leads to a breakdown of the correlation between nuclear spin and rotational wave function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465798
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