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  • 1
    Electronic Resource
    Electronic Resource
    Bifurcation analysis of chemical reaction mechanisms. I. Steady state bifurcation structure (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3083-3095 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vocabulary and techniques of numerical bifurcation analysis are described, with an emphasis on steady state bifurcations of codimension one and two. The direct computation of bifurcation sets is shown to be of considerable utility in analyzing and comparing complex chemical reaction mechanisms. The systems chosen for analysis are the chlorite–iodide and the mixed Landolt reactions. The calculation of a simple hysteresis loop for a mechanism of the chlorite–iodide reaction using both numerical bifurcation analysis and numerical integration begins an extended comparison between the methods advocated in this paper and more familiar methods. The systematic identification of the existence of isolated branches of steady states is described for a second mechanism of the chlorite–iodide reaction. Two mechanisms for the mixed Landolt system are contrasted. It is found that the alternative negative feedback pathway mechanism, which reproduces the periodic behavior more successfully at a selected point in parameter space, is less satisfactory than the EOE mechanism in describing the overall bifurcation behavior of the system in the parameter plane for which experimental data are available. Finally, we examine another mechanism for the chlorite–iodide reaction. This mechanism was designed with the intent of suppressing oscillatory behavior on a subset of parameter space. Numerical integration revealed only bistability of steady states, as desired, but numerical bifurcation analysis reveals a sizeable region in the previously investigated subset of parameter space on which oscillatory behavior exists.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459831
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  • 2
    Electronic Resource
    Electronic Resource
    Differential delay equations in chemical kinetics: Some simple linear model systems (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 1702-1712 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reasons for and the effects of incorporating time lags into the differential equations of chemical kinetics are investigated for some simple model systems. Complex networks of first-order reactions may, in the limit of long times, be described by relatively simple systems of differential delay (differential difference) equations, in which the effects of intermediates are replaced by time lags. Explicit inclusion of time lags affords a more physically realistic description of nucleation in certain solid state reactions. An electrochemical cell with lagged feedback gives rise to a particularly simple and instructive delay equation. A two-chamber system in which molecules diffuse with a time lag through a membrane shows unexpected oscillatory, and seemingly nonconservative behavior, which is explained in terms of the number of molecules in passage through the membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458052
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  • 3
    Electronic Resource
    Electronic Resource
    Comment on: Projection operator formalism for the characterization of molecular eigenstates: Application to a 3:4 resonant system (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5358-5358 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459659
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  • 4
    Electronic Resource
    Electronic Resource
    Differential delay equations in chemical kinetics. Nonlinear models: The cross-shaped phase diagram and the Oregonator (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 244-254 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Delayed feedback plays a key role in most, if not all chemical oscillators. We derive general results useful in the linear stability analysis of models that explicitly incorporate delay by using differential delay equations. Two models of nonlinear chemical oscillators, the cross-shaped phase diagram model of Boissonade and De Kepper and the Oregonator, are modified by deleting a feedback species and mimicking its effect by a delay in the kinetics of another variable. With an appropriate choice of the delay time, the reduced models behave very much like the full systems. It should be possible to carry out similar reductions on more complex mechanisms of oscillating reactions, thereby providing insight into the role of delayed feedback in these systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461481
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  • 5
    Electronic Resource
    Electronic Resource
    Ferromagnetic behavior of decamethylchromocenium tetracyanoethanide [CrCp2*][TCNE] : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5476-5478 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Studies on the magnetic properties of decamethylchromocenium tetracyanoethanide, [CrCp*2][TCNE] are reported herein. Near-zero field (H=150 mG) data indicates a ferromagnetic transition with Tc=3.65 K. The temperature dependence below Tc can be fit to a mean-field result M=M0(1−T/Tc)1/2, and the data above Tc gives a critical exponent γ=1.2 for the dc magnetic susceptibility. Data at higher temperature indicates a strong 1-D ferromagnetic behavior. Magnetizations at different H and T at low temperature can be scaled to a universal function with M=f(H/T3.2). The reduction in Tc in [CrCp*2][TCNE] compared with [FeCp*2][TCNE] indicates a competition between the coupling constants and the residing spins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353671
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  • 6
    Electronic Resource
    Electronic Resource
    Anomalous charge transport phenomena in molecular-based magnet V(TCNE)x⋅y(solvent) : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6566-6568 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present charge transport studies on recently developed molecular-based magnets V(TCNE)x⋅y(solvent) (TCNE=tetracyanoethylene) which show local magnetic ordering at temperatures, T, as high as 400 K. V(TCNE)x⋅y(solvent) prepared from the solvent CH2Cl2 has σ(300 K)∼10−3 S/cm, and that prepared from the solvent CH3CN has σ(300 K)∼10−5 S/cm. The σ(T) of both materials follows the Mott 3D variable range hopping [log(T1/2σ)∝T−1/4] behavior. An anomalously strong T-dependent ac conductivity is likely caused by the short-range ferrimagnetic correlations. Cole–Cole analysis of the ac complex dielectric constant suggests there are two relaxation mechanisms, with an Arrhenius relation fitted to both. The microwave frequency response is consistent with audio frequency data and yields a localization length of ∼ 5 A(ring), comparable with the dimensions of a [TCNE]−. group.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352565
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  • 7
    Electronic Resource
    Electronic Resource
    Spin frustration and metamagnetic behavior in a molecular-based quasi-1D ferrimagnetic chain: (MnTPP)(TCNE) : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6569-6571 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report an experimental observation of spin frustration and metamagnetic behavior in a quasi-1D ferrimagnetic chain, (MnTPP)+(TCNE)−. Metastability, hysteresis effects, and irreversibility of thermal and magnetic histories are observed in magnetization measurements. The "memory'' phenomenon is seen in the temperature dependence of the thermoremanent and isothermal remanent magnetization. This system may be relevant to the magnetic behavior of the quantum/classical spin chains. The isothermal M(H) at T=2.25 K supports a first order transition which may be related to effects of local anisotropy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352566
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  • 8
    Electronic Resource
    Electronic Resource
    Electromagnetic radiation shielding by intrinsically conducting polymers (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2278-2280 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The shielding efficiency of various intrinsically conducting polymers (ICPs) as a function of their intrinsic properties (conductivity and dielectric constant), thickness, and temperature is determined. Two types of shielding, reflection and absorption, by ICPs are discussed. The high shielding efficiencies of highly conducting doped polyaniline, polypyrrole, and polyacetylene are reported and compared to that of copper. The easy tuning of intrinsic properties by chemical processing suggests the wide applications of ICPs, especially polyaniline for shielding. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112717
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  • 9
    Electronic Resource
    Electronic Resource
    Molecular magnets V(tetracyanoethylene)x⋅y(solvent): Applications to magnetic shielding : 38th Annual Confrerence on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5782-5784 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The specific advantages and limitations of a new class of polymer based magnets [exemplified by V(TCNE)x⋅y(solvent) (TCNE=tetracyanoethylene)] for static and low frequency magnetic shielding and inductive applications are evaluated using results of dc superconducting quantum interference device magnetization and ac permeability measurements. Present materials have very low density (ρ∼1 g/cm3), relatively high resistivity (∼104 Ω cm), and low power loss (as low as ∼2 erg cm−3 cycle−1). The highest initial room temperature permeability observed to date (for solvent=CH2Cl2) of μi=13 is modest for practical applications. Flexible processing methods are suggested for optimization of magnetic properties important for shielding applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355561
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  • 10
    Electronic Resource
    Electronic Resource
    Complex ac susceptibility studies of the disordered molecular based magnets V(TCNE)x: Role of spinless solvent : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5648-5650 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of different spinless solvents on the magnetism of V(TCNE)x⋅y(solvent) (TCNE=tetracyanoethylene) is studied by temperature (T) dependent ac susceptibility above 2.3 K. Though V(TCNE)x⋅y(CH2Cl2) has a critical temperature Tc ∼400 K, for V(TCNE)x⋅y(C4H8O), Tc ∼205 K and the coercive field is reduced, while for V(TCNE)x⋅y(CH3CN), Tc ∼140 K or below and a spin glass phase exists below a spin freezing temperature of Tf∼7–15 K. The variations with solvent are suggested to be due to spin dilution and random anisotropy introduced by the spinless solvents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353627
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