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  • 1
    Electronic Resource
    Electronic Resource
    Dynamic friction on rigid and flexible bonds (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5084-5095 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A wide variety of problems involving molecular motion in liquids can be formulated in terms of the generalized Langevin equation (GLE). The friction coefficient on a molecular bond or on some more complicated reaction coordinate is then required. An often used approximation is to set the dynamic friction constant equal to the autocorrelation function of the fluctuating force exerted on the frozen bond by the remaining unfrozen coordinates. The true friction involves projection operators and should differ from this approximation. In this paper we derive various identities and show that the rigid bond approximation is the high frequency limit of the true dynamic friction coefficient. We compute the "true'' dynamic friction and the friction approximated on the basis of the rigid or frozen bond and show that the asymptotic limit is very accurate even for frequencies not much larger than the peak frequency of the solvent spectral density. Two different dynamical systems are studied using MD simulations with our newly devised NAPA integrator for systems with disparate time scales. In one the molecule is not allowed to rotate and in the other it is allowed to rotate. Interestingly, even for very long rotational reorientation times, small but significant differences in the long time decay of the bond dynamic friction are observed for rotational and nonrotational molecules—differences, however, that do not produce large differences in the static friction constants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458647
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Theory of size distribution of associating polymer aggregates. I. Spherical aggregates (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 1824-1833 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We examine the stability of spherical, micellelike aggregates composed of long-chain, polymeric surfactants in dilute solution. The associating polymers consist of long, unbranched hydrophobic chains with one polar end-group per chain and are in a good solvent for the chains. Although the head groups prefer to aggregate in the nonpolar solvent and thus stabilize the spherical structure, the energy associated with the chain repulsions tends to destabilize the aggregates as the chain length increases. For a liquid-drop model of the head interactions, the average aggregation number evolves smoothly towards zero as the chain length increases. An alternate model of the head region, which assumes a preferred head-packing geometry, results in the ultimate destabilization of the spherical aggregate as the chain length is increased beyond a certain threshold. Both models yield a critical micelle concentration (CMC) at low values of the polymer concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453195
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Insulin binding and insulin action in rat fat cells after adrenalectomy (1980)
    Springer
    Diabetologia 19 (1980), S. 379-385 
    Details
    ISSN: 1432-0428
    Keywords: Adrenalectomy ; insulin receptor ; cortisol ; insulin effect ; glucose transport ; glucose oxidation ; lipogenesis ; antilipolysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Insulin binding and the effect of insulin on the transport of 3-O-methylglucose, lipogenesis from glucose, glucose oxidation and lipolysis was studied in fat cells of adrenalectomised rats and of a control group of sham-operated rats. The serum insulin level of the adrenalectomised rats (0.7 ng/ml) was lower than that of the controls (1.6 ng/ml). In adrenalectomised rats as compared to sham-operated rats the insulin concentrations causing half-maximal effect were reduced by 50% in lipogenesis and antilipolysis and by 30% in glucose transport. The increase in sensitivity to submaximal insulin concentrations was not observed in glucose oxidation. The maximal responsiveness was unchanged in all test systems. The increase in sensitivity in three of the four studied insulin effects may be related to the 37% increase in the binding capacity of fat cells from adrenalectomised compared with sham-operated rats. The unchanged sensitivity with respect to glucose oxidation indicates possible post-receptor modulation. When adrenalectomised rats were substituted with either insulin or cortisol serum insulin levels were elevated above normal; however, the changes in the receptor were prevented in the cortisol supplemented rats and only partially in the insulin supplemented rats. The observation suggests, that the insulin receptor is regulated not only by the serum insulin level but also by cortisol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00280524
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  • 4
    Electronic Resource
    Electronic Resource
    Lennard-Jones fluids in cavities (1989)
    Springer
    International journal of thermophysics 10 (1989), S. 469-478 
    Details
    ISSN: 1572-9567
    Keywords: dimer ; Lennard-Jones ; molecular dynamics ; porous media ; rotational relaxation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Static and dynamic properties of Lennard-Jones particles in spherical cavities of molecular dimension are studied by molecular dynamics (MD) simulation. The local density is a function of the radial coordinate; a layered density profile is reproduced by the iterative solution of an approximate BGY equation. The pair correlation function exhibits a broadened first-neighbor peak and a second-neighbor peak which is shifted inward from its location in the homogeneous fluid. The viscosity, as measured by the relaxation of a rotor in the cavity, is a function of the cavity radius and may actually decrease as the cavity radius decreases. This qualitative trend is reversed when the smooth cavity is replaced by a cavity with rough, molecular walls.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01133543
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    Paper (German National Licenses)
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