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  • 1
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study theoretically the generation of coherent, anharmonic phonon-polariton responses through impulsive stimulated Raman scattering with intense, crossed ultrafast excitation pulses. We find that the refractive index appears modulated at the stimulated scattering wave vector and the corresponding phonon-polariton frequency, and, due to anharmonicity, at stimulated scattering wave vector overtones and their corresponding frequencies. A realistic model of the soft lattice vibrational mode of the ferroelectric crystal lithium tantalate is considered in detail. Specific predictions for the magnitudes of different wave vector overtone contributions to the lattice displacement are made compared to experimental observations of anharmonic lattice responses. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 1443-1446 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Coherent optical control in both spatial and temporal dimensions is demonstrated. Lattice waves are generated by femtosecond pulses at one region of a crystal, monitored through spatiotemporal imaging which captures their propagation at lightlike speeds, and manipulated by additional pulses at other regions of the crystal distinct from the first. The capabilities demonstrated here enable terahertz polaritonics through enhanced optical control over propagating lattice excitations and ultrahigh-bandwidth, terahertz-frequency signals. © 2001 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 1317-1320 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The propagation of collective lattice vibrational wave packets that move at lightlike speeds through their crystalline hosts has been monitored through a real-space imaging method based on Fresnel diffraction and phase-contrast microscopy. Coherent optic phonon–polaritons generated through impulsive stimulated Raman scattering in a ferroelectric crystal are imaged with 5 μm spatial resolution and 35 fs time resolution as they propagate out of the excitation region and into other parts of the crystal. The "spatiotemporal" imaging method will permit direct examination of nonlinear lattice dynamics and will provide feedback in coherent control systems that use spatiotemporal femtosecond pulse shaping to manipulate propagating excitations with ultrashort light pulses directed to specified sample locations at specified times. The method will also permit the examination of defects and fabricated structures in bulk or thin film crystals using visible light. © 1999 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 9540-9549 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An optimization protocol for modeling protein structures on lattice is proposed which is based on self-consistent mean field (SCMF) theory. In this procedure, the protein residues are supposed to be independent, and their possible positions are given by a list of lattice sites. To do this, an effective larger system is considered, in which each residue i is supposed to occupy all possible sites j, each with a weight V(i,j) stored in the so-called lattice probability matrix V. The effective energy of the system is computed, and iteratively minimized with respect to the weights V, the lattice sites being fixed in space. The final self-consistent V matrix describes the conformational space available to the protein, based on the energy function implemented. This energy function contains two types of terms, namely simple geometric terms which ensure bond connectivity and prevent chain intersection, and energy terms specific to the problem of interest. The application of the above protocol to building a lattice model of a protein, given its three dimensional structure, is discussed and compared with other lattice fitting procedures. © 1998 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 4768-4775 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An analytic formula is developed for calculating the generalized NMR order parameters in a protein from the normal mode analysis (NMA). The generalized order parameter, S˜2, is given as thermal ensemble average of a Taylor series in powers of Δ, the displacement of internuclear vector from its mean. Henry and Szabo developed a method to calculate the ensemble average based on the NMA carried out in the Cartesian coordinate space (CCS). However, atomic motions in each individual CCS normal modes are linear in the three-dimensional space, which may cause interatomic distances even between covalently bonded atoms to change significantly. In this situation Henry and Szabo proposed to use a special formula for S˜2 which includes a trick to compensate such changes. We showed that by carrying out the NMA in the dihedral angle space (DAS) and by interpreting each DAS normal mode into curved atomic motions, S˜2 can be calculated reliably for spin pairs separated up to about 10 intervening covalent bonds by a natural formula without any trick. © 1996 American Institute of Physics.
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