ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 5378-5386 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of charge carrier trapping and recombination are measured as a function of ZnO cluster diameter by ultrafast pump–probe absorption spectroscopy. A finite spherical potential well model which shows good agreement with previous experimental work is employed to predict ZnO cluster diameters from absorption onsets. The rate of electron trapping is measured for clusters of 3.2 and 6.2 nm, and is found to increase with increasing cluster size. This increase in trapping rate for increasing cluster size is not consistent with either a diffusional or quantum mechanical picture of electron trapping. A mechanism for electron trapping involving trap-to-trap hopping is discussed whereby the number density of optically accessible deep traps must increase with increasing cluster size. Differences in the dynamics and in the ratio of interior to exterior atoms on the cluster are correlated and discussed. The time-resolved absorption data of the subsequent electron–hole recombination shows the appearance of an early time signal which increases as the cluster size grows. The early time species decays away within the first 50 ps to a diameter-independent plateau value via second-order recombination, and is assigned to electrons trapped in the interior of the cluster. The electron–hole recombination is found to occur faster and to a greater extent in the largest nanoclusters. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 9025-9033 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A grand canonical ensemble molecular dynamics (GMD) simulation method has been adapted to examine the thermodynamics of clay-mineral hydration. In the GMD method, the number of water molecules in the system is treated as a continuous variable for which an equation of motion is established. Fluctuations in the water content at constant chemical potential are investigated using trajectories of this particle number variable. A bias potential may be used to modify the free energy contour along the particle number coordinate. This catalyzes particle fluctuations and greatly improves simulation convergence. Adaptation of the GMD method to treat hydrated clay minerals included the introduction of a local-control technique that fixes the water chemical potential in the clay interlayer region. In addition, a bias-potential feedback algorithm was implemented to improve particle fluctuation efficiency. Information pertaining to the free energy contour, generated during the course of the simulation, was used periodically to enhance the bias potential. This allowed for the utilization of a single input bias potential under a broad range of simulation conditions. The method was used to investigate swelling of a cesium–montmorillonite clay. Measured disjoining pressures showed oscillations that are indicative of crystalline-swelling phase transitions. Integration of the disjoining pressures yielded a swelling free energy profile with distinct free-energy minima for the one- and two-layer hydrates. The results may be compared qualitatively with both clay swelling and surface force apparatus experiments, and with previous simulation studies of simple fluids in slit pores. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4866-4868 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Elongated metal particles have been prepared by depositing transition metals into the pore channels of anodic aluminum oxide (alumite), with well-defined pores that build up into uniform and parallel channels. The highest coercivity for freshly prepared α-Fe particles in the alumite substrate reached 2700 Oe in the easy direction. The remanance curves of alumite films containing electrodeposited metals (Fe and Co) were measured to study the magnetostatic interaction of the particles. The possible reversal mechanisms of the metal particles in the alumite substrates were examined by the rotational hysteresis integral and the angular variation of the coercivity. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4869-4871 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: To increase the coercivity of α-Fe particles, needlelike goethite crystals were first coated with different Ln3+ ions (Ln=La,Nd,Sm,Gd,Dy,Eu) plus B3+, then reduced to α-Fe under H2. The magnetic moment of the particles depends upon the Ln and B contents and temperature. Both powder x-ray diffraction and Mössbauer spectra indicate the existence of a crystalline FeO phase; the FeO content decreased as the reduction temperature increased. A phase with no hyperfine splitting was also detected in the Mössbauer spectra, which may be superparamagnetic α-Fe or amorphous iron oxide; the amount of this phase decreased as the reduction temperature increased. The temperature dependence of the coercivity of these B- and Ln-coated particles was steeper than for particles coated with silica: this suggests a coercivity mechanism other than shape anisotropy. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 8295-8302 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An extended Hamiltonian technique for performing grand canonical ensemble molecular dynamics simulations has been reformulated to include umbrella sampling, thus improving the efficiency of particle creation and annihilation processes. This was accomplished through incorporation of a bias potential in the Hamiltonian that modifies the free energy contour between integer particle number states. The extended Hamiltonian includes a continuous particle number variable that is the sum of the integer particle number and a coupling parameter, the latter being used in a scaling function for a fractional molecule's interactions with the rest of the system. Equations of motion for the coupling parameter, derived from the Hamiltonian, integrate to yield density fluctuations at constant chemical potential. This new method may be adapted to a wide range of potential scaling functions. The technique was applied to calculations of extended simple point charge water density versus chemical potential, using both linear and nonlinear scaling. For each scaling function, a bias potential was constructed using a thermodynamic integration technique. Grand canonical ensemble simulations then yielded results in agreement with independent calculations. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 4377-4384 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dispersion of particles in a stratified medium with a flow normal to the stratification is studied for the case when the transition rates between the various strata are random variables. One- and two-dimensional stratified systems are considered. The effective diffusion coefficient in the flow direction is computed numerically. The numerical results are compared with the predictions of a mean-field theory known as the effective (or coherent) medium approximation. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 5331-5340 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electron-spin resonance studies of laser-ablated titanium metal isolated in neon and argon display an intense feature which exhibits a symmetric, narrow line and a large matrix-dependent g shift. On the basis of a number of experiments, this is assigned to a matrix isolated 3d3,4F Ti+ ion in an octahedral matrix environment. Although the ground state of the gas-phase Ti+ ion is 3d24s1,4F, the assignment to the 3d3,4F state is supported by the small hyperfine structure which is observed. The neon magnetic parameters are: g=1.934(1) and A(47Ti)=64(1) MHz; for argon, g=1.972(1) and A=56(1) MHz. This unusual stabilization of an excited atomic state by a rare gas matrix is consistent with ab initio studies, and has been previously found for atomic nickel. A crystal-field study of the expected behavior of a d3,4F ion isolated in a tetrahedral, octahedral, or cuboctahedral environment supports the assignment to an octahedral Ti+(Rg)6 species, and using the atomic spin–orbit parameter, ζ permits accurate values of Dq to be derived from the measured g values. Finally, it is also noted that for small values of Dq/(Dq+ζ), or for a d3,4F ion in a tetrahedral environment, an as yet unobserved, unequal Zeeman splitting of the fourfold degeneracy occurs, causing a departure of the Zeeman energies from the standard formula of EZeeman=βeH0gM, with M=±3/2, ±1/2. For these situations it becomes necessary to define two values of g, corresponding to the more strongly (g3/2) and less strongly (g1/2) affected Zeeman levels, respectively. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This communication describes dynamic light scattering measurements on three low molar mass symmetric polystyrene–polybutadiene diblock copolymer melts. Above but close to the order–disorder transition, four modes contribute to the time-dependent correlation function. In the depolarized geometry there is a very fast, broad relaxation typifying the segmental reorientational dynamics and a slower, single-exponential mode related to chain orientation and stretching. In the polarized experiments two additional processes are seen: the heterogeneity mode related to the self-diffusion of individual copolymer molecules and a slow mode representing the translational diffusion of large ((approximately-equal-to)100 nm) clusters. Just below the order–disorder transition (ODT), the slowest mode is shifted to very long times. The heterogeneity mode gives rise to depolarized scattering below the ODT because of the anisotropy induced by the lamellar structure. With the lowest molar mass copolymer above the ODT, it could be seen that the amplitude of the mode related to chain orientation and stretching decreases the deeper the sample is in the disordered state. A new subtraction technique was used for data analysis. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 7397-7401 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The monomer–monomer surface reaction model with an adsorbate interaction term is studied. An epidemic analysis of the poisoning times (tp) for small square lattices as a function of lattice edge length L and interaction strength α at the point of equal adsorption rates yields a dynamic scaling relation which describes the crossover between log-power-law and exponential behavior in L, and is able to fit the entire dependence of tp upon α and L. The phase transition is further explored by varying adsorption rates and is found to follow second-order kinetics. A mean-field approximation is introduced as a comparison for the numerical results. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 9 (1997), S. 57-66 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Three-dimensional interactions between an elliptic vortex ring and two no-slip parallel walls are visualized in a numerical simulation and an experiment. The vortex ring induces a surface vorticity layer on the wall which reconnects with the vortex ring. During the interaction core-area-varying axial waves are generated and carry the surface layer away from the wall. The vortex ring then becomes two tornado-like structures with strong upward helical flows near the wall surface, which provides entrainment of the surface fluid into the vortex structure. Similarities between the entrainment mechanisms of vorticity in the simulation and dye in the experiment from the surface layer are identified. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...