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  • 1
    Electronic Resource
    Electronic Resource
    Intermittency of activated events in single molecules: The reaction diffusion description (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 4812-4819 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We generalize the reaction diffusion approach in order to calculate the higher moments of the distribution of the population which characterize intermittency and can be derived by statistical analysis of single molecule experiments. We show the way the usual Poisson statistics is asymptotically approached with increasing barrier height for a reaction dependent on diffusing up an activation free energy barrier to a critical configuration. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478369
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  • 2
    Electronic Resource
    Electronic Resource
    Kinetics in a globally connected, correlated random energy model (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 11276-11284 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study the dynamics on a biased globally connected energy landscape with correlations, using the generalized random energy model. Though the kinetic model has many applications, we discuss the model in the context of protein folding kinetics. Restricting the hierarchy to just two tiers, we find that the time scale of the overall folding coincides with that predicted by the random energy model at temperatures above the transition to partial freezing. At intermediate temperatures below the partial freezing transition, the search time is reduced due to the correlation effects. The dispersion of the relaxation time from sample to sample is also discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472869
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  • 3
    Electronic Resource
    Electronic Resource
    Statistical mechanics of a correlated energy landscape model for protein folding funnels (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 2932-2948 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In heteropolymers, energetic correlations exist due to polymeric constraints and the locality of interactions. Pair correlations in conjunction with the a priori specification of the existence of a particularly low energy state provide a method of introducing the aspect of minimal frustration to the energy landscapes of random heteropolymers. The resulting funneled landscape exhibits both a phase transition from a molten globule to a folded state, and the heteropolymeric glass transition in the globular state. We model the folding transition in the self-averaging regime, which together with a simple theory of collapse allows us to depict folding as a double-well free energy surface in terms of suitable reaction coordinates. Observed trends in barrier positions and heights with protein sequence length and thermodynamic conditions are discussed within the context of the model. We also discuss the new physics which arises from the introduction of explicitly cooperative many-body interactions, as might arise from sidechain packing and nonadditive hydrophobic forces. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473355
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetocrystalline anisotropy of Pr2(Fe1−xCox)17−yGay compounds with a Th2Zn17-type structure (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 5326-5331 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The structure and magnetic properties of Pr2(Fe1−xCox)17−yGay compounds with 0≤x≤1 and 0≤y≤3 have been investigated using x-ray diffraction (XRD) and magnetization measurements. XRD patterns demonstrate that all samples were single phase with the rhombohedral Th2Zn17-type structure, except for Pr2Fe16.5Ga0.5 with some impurity phases. The replacement of (Fe, Co) by Ga results in an approximately linear increase in the unit cell volume, and decrease in the Curie temperature and saturation magnetization. The substitution of Co for Fe leads to a nonlinear variation in the unit cell volume, the Curie temperature and the saturation magnetization. The magnetic anisotropy phase diagrams of Pr2(Fe1−xCox)16.5Ga0.5 (0≤x≤1) and Pr2(Fe0.4Co0.6)17−yGay (0≤y≤3) compounds have been determined from the temperature dependence of magnetization and the XRD patterns of magnetically oriented powder samples. Most of the samples exhibit easy plane anisotropy. A small range exists in the magnetic anisotropy phase diagrams of Pr2(Fe1−xCox)17−yGay compounds at 300 K, in which the c axis is the easy magnetization direction, however, small amounts of Ga close the easy c-axis region at y=1.5. The spin-reorientation temperature was found to increase with Co and Ga content for Pr2(Fe1−xCox)16.5Ga0.5 (0.5≤x≤1) and Pr2(Fe0.4Co0.6)17−yGay (0≤y≤1.5) compounds, respectively. The relationship of the magnetocrystalline anisotropy with the lattice parameters and other magnetic properties were analyzed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367359
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  • 5
    Electronic Resource
    Electronic Resource
    X-ray standing waves as probes of surface structure: Incident beam energy effects (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 2311-2322 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The sensitivity to x-ray beam energy of structure measurements using x-ray standing waves (XSW) generated under conditions of total external reflection has been determined. To this end, the optical properties of the system were examined in a theoretical analysis to identify possible energy-dependent components such as surface roughness. The analysis shows that, provided surface roughness is small (Debye–Waller factor less than 10 A(ring)) and the energy range covered in the XSW measurements lies within several keV, its contribution can be accounted for satisfactorily by a simple Debye–Waller factor. In addition, a series of XSW measurements were made on Langmuir–Blodgett films of manganese arachidate (C20:0) on a gold mirror surface at three incident x-ray beam energies in the 7–11.2 keV range. The XSW data were analyzed to account for the Debye–Waller factor. No obvious dependence on incident x-ray energy was found. These results demonstrate that the contribution of surface roughness to the x-ray fluorescence yield profile is minimal under these conditions. Thus, mirrors of the type and quality used in these experiments are useful in XSW measurements where multiple element types are incorporated as structural labels in organic thin films and at surfaces. We also demonstrate that the resolving power of the XSW method is sufficient to distinguish and to locate two separate probe atom layers in a single Langmuir–Blodgett film. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360759
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  • 6
    Electronic Resource
    Electronic Resource
    Determination of the complex refractive index of individual quantum wells from distributed reflectance (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 3056-3059 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigate the measurement of the complex refractive index of individual quantum wells by reflectance spectroscopy. Placing the wells at half-wavelength spacing to cause resonant feedback produces an order-of-magnitude increase in measurement sensitivity over that of nonresonant structures. Quantum well dispersive and absorptive effects on reflectance can be differentiated in certain spectral regions. Experimental data confirm a theoretical model of refractive index and absorption for quantum wells of GaAs in Al0.2Ga0.8As in the region of the well band gap.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356153
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  • 7
    Electronic Resource
    Electronic Resource
    Speed response analysis of an electron-transfer multiple-quantum-well waveguide modulator (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 4669-4679 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A numerical model is presented for the electronic properties of a novel InxGa1−xAs/In1−yAlyAs multiple-quantum-well waveguide modulator and a theoretical analysis of electron and hole escape mechanisms from the quantum well is developed. The influence of carriers and dopant ion charges on the band structure is simulated with a self-consistent Poisson–Schrödinger solver. The different escape mechanisms for both electrons and holes are: direct tunneling, phonon-assisted sequential tunneling, and thermionic emission. At high forward biases, the electron escape time limits the device speed, while at high reverse biases, heavy holes take a longer time than electrons for escaping the quantum well. For both particles, phonon-assisted sequential tunneling is a key mechanism in determining the device speed operation. The calculated escape times are in good agreement with the experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352762
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  • 8
    Electronic Resource
    Electronic Resource
    Thickness vibrations of thin piezoelectric plates and the determination of the electro-elastic constants of Al0.88Ga0.12PO4 crystal (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 1696-1700 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thickness vibrations of thin piezoelectric plates excited by perpendicular or parallel fields have been investigated. In the analyses of the resonances of the thin plates, both the stress boundary and the electrical conditions have been considered. The theory has been applied to the determination of the electro-elastic constants of a newly developed piezoelectric crystal, Al0.88Ga0.12PO4. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360956
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  • 9
    Electronic Resource
    Electronic Resource
    Wave breaking in cold plasma (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 1432-1440 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Strongly nonlinear plasma oscillations in a cold plasma are investigated in the wave breaking regime using the two-fluid model. The electrons are described in Lagrangian coordinates; the ions are described by the usual Eulerian coordinates. The model is extended to describe the motion after wave breaking has occurred. Numerical solutions are followed up to and beyond wave breaking for both driven and undriven cases. In a driven cold plasma, the plasma waves are excited from fluctuations by the modulational instability, growing to very large amplitudes, which leads to wave breaking. For the undriven cold plasma, large initial perturbations are assumed, which also lead to wave breaking. Multistreams and the generation of fast electrons are observed for both cases after wave breaking.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860105
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  • 10
    Electronic Resource
    Electronic Resource
    The influence of temperature and surface conditions on surface absorptivity in laser surface treatment (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 3245-3253 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A one-dimensional, transient, inverse heat conduction problem is implemented to investigate the influence of temperature and surface conditions on surface absorptivity in the laser surface heating process. Analysis includes the utilization of the conjugate gradient method (CGM), with temperatures measured near the heated surface. To increase efficiency and accuracy of the calculation, the result retrieved from the least-square method is used as an initial guess for the CGM. Results show that absorptivity decreases when the temperature exceeds a certain value. This decrease is related to structural transformation during the temperature rise. As the surface temperature nears the melting point, the decreasing trend inverts and absorptivity increases. This final abrupt rise is caused by the phase transformation from order to disorder. Additionally, absorptivity is related to surface conditions such as absorption-enhancing coatings and surface roughness. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372331
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