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 94 (1991), S. 2176-2186 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present an analysis of crystal growth of a pure material from its melt, using a phase field model. This model for a first-order phase transition couples nonconserved order parameter kinetics to thermal diffusion. It has been shown to give unique one-dimensional solutions, with velocity selection. We demonstrate that these steady-state solutions cease to exist for the thermal diffusivity above a critical value, which depends on the parameter coupling the kinetics to the temperature. We suggest a scaling which leads to agreement between numerical integration of the time-dependent equations and a perturbation analysis of the coupling. For small velocity, our model reduces to a standard model commonly applied to dendritic growth, which replaces the kinetic equation with one of interfacial equilibrium. Because the velocity vanishes at the critical point, the thermal diffusion length and dendritic wavelength diverge at this point. We relate this critical point to bifurcations in the phase space of a mechanical equivalent to the steady-state growth equations. We conclude that solutions cease because thermal diffusion drives the system to local kinetic equilibrium, and we discuss experimental accessibility and means of avoiding equilibrium.
    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 100 (1994), S. 350-356 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a model calculation for the determination of quantum microcanonical average reaction rates for isolated molecules. The model system consists of two coupled electronic states, reactant and product, each with many nuclear motion eigenstates. The reaction rate is evaluated via a resummed perturbation expansion in the electronic coupling. From this we obtain an electronic adiabaticity criterion which depends on the probability to remain at or return to the transition region. We evaluate this survival probability using a global random matrix model for the nuclear Hamiltonian. This leads to an equation for the reaction rate which interpolates between the golden rule electronic crossing rate and the electronically adiabatic rate. We discuss the classical limit and make connection with thermal rate theory.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 5685-5692 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The growth of a crystal into an undercooled liquid is studied within a phase field model. In contrast to the usual Landau–Ginzburg approach, the free energy as a function of the order parameter is taken to be a pair of intersecting parabolas. This model is completely solvable and shows a transition from heat-diffusion allowed to disallowed steady-state crystal growth. Analytical expressions for the interface velocity and for the order parameter and temperature profiles are obtained and extensively discussed. In comparison with the Landau–Ginzburg model, most qualitative and quantitative features are the same. However, the solution of the present model is more general, avoiding perturbation theory, and gives a clearcut picture of the underlying transition.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 2753-2763 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , 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 105 (1996), S. 940-952 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We statistically analyze the dynamics of vibrational energy flow in a model system of anharmonic oscillators which are nonlinearly coupled, with a local topology. The spectra of many basis states of similar energy are computed, for different values of the magnitude of the coupling in the Hamiltonian between these states. From individual spectra of zero order basis states at each coupling strength the individual survival probabilities are determined, which are then used in computing statistical averages. When the average fluctuation of the survival probability is small, in the strongly coupled limit, the average survival probability closely follows a semiclassical diffusion prediction and reflects a predicted linear dependence of the rate of energy flow on coupling strength. When the average fluctuation is large, in the weakly coupled limit, the average survival probability closely follows a power law decay of t−1, in agreement with a quantum extension of the diffusion picture. In this regime, individual survival probabilities show strong quantum beats. We conclude that these large variations reflect a strong influence of quantum interference in the weakly coupled limit. © 1996 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 106 (1997), S. 7047-7054 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We continue a study in which we statistically analyze the dynamics of vibrational energy flow in a model system of anharmonic oscillators which are nonlinearly coupled, with a local topology. Average spectra are obtained from individual spectra of many basis states of similar energy, for different values of the magnitude of the coupling between states. The survival probabilities of the density are then determined from the average spectra. When the average fluctuation in spectral intensities is small then the density survival probability closely follows the average survival probability presented in our earlier paper for short times. For longer times, when the average survival probability shows a power law decay, this decay does not appear in the density survival probability. In addition, when spectral fluctuations are large, the two survival probabilities differ strongly. © 1997 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 98 (1993), S. 1123-1131 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present an analysis of quantum energy flow and localization in molecules from the point of view of a scaling approach. This scaling approach is based on earlier scaling theories of Anderson localization in disordered metals. The picture provides a simple general framework for describing both energy flow and the localization of eigenstates. This framework can be applied to molecules whose Hamiltonians are described by local random matrices, in which transitions between states nearby in quantum space occur more easily than those between distant states. In this theory the central quantity of interest is the survival probability. It is the squared overlap of a wave function at a later time with its initial condition. Its long time behavior varies depending on whether the eigenstates are localized or not. In the scaling description the survival probability approaches its long time limit varying inversely with time raised to some power. Different power laws are valid in different time regimes, depending on the degree of localization and the size of the molecule's phase space. Near the localization transition we find that the survival probability decays as t−1. This decay is much slower than when energy flows easily, for a large number of dimensions participating in the energy flow.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 7898-7902 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Recrossings of the transition state are normally thought of as modifying the dynamical prefactor (transmission coefficient) which corrects the Rice–Ramsperger–Kassel–Marcus (RRKM) theory. Here, a semiclassical path analysis is used to show that recurrences to parts of phase space from which reactive transitions can occur also lead to fluctuations of the reaction rate about its microcanonical average. This result leads to a simple formula for the power spectrum of the rates.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Publication Date: 1995-05-08
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Publication Date: 1995-03-01
    Print ISSN: 0022-3654
    Electronic ISSN: 1541-5740
    Topics: Chemistry and Pharmacology , Physics
    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...