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  • Institute of Physics  (17)
  • Nature Publishing Group  (13)
  • American Institute of Physics (AIP)  (8)
  • 1
    Digitale Medien
    Digitale Medien
    The diffusion coefficient of a reptating polymer (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3252-3257 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The dynamics of a polymer in a network of entanglements is studied. The viscosity has been examined for chains up to 50 links and is found to scale with chain length L as L3.41±0.14 in agreement with previous theoretical work, that attributes this anomalous exponent as a finite size effect because of the finite tube length. Numerical results for chains up to 100 links give that the diffusion coefficient D, scales as L−2.50±0.04. This result differs from theoretical predictions based on tube fluctuations which claim finite length effects are unimportant for diffusion and therefore imply a −2 power law dependence for D. The reason for this discrepancy is examined. Previous work used a one-dimensional rather than a three-dimensional diffusion coefficient as the starting point of analysis. By deriving the correct procedure for calculating the three-dimensional D, one sees that it has corrections to its asymptotic behavior which are quite large, of order L−1/2, rather than L−1 as was thought previously. This suggests that fluctuations in the tube length cannot provide an adequate explanation for the experimental data.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.456900
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  • 2
    Digitale Medien
    Digitale Medien
    Simulation of highly stretched chains using long-range Monte Carlo (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 2065-2071 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The behavior of highly stretched chains is not well described by computer simulations using the usual short-range Monte Carlo algorithms. Results from these have been shown to produce unphysical slowing down due to artificial energy barriers imposed by the dynamics. Furthermore, relaxation in the absence of a field from a highly stretched state is shown to be improperly described by the usual Monte Carlo algorithms. We propose a novel model employing long-range moves that should describe the motion in such situations more correctly. We implement this model on a square lattice to study gel electrophoresis. Using a highly efficient numerical code, the time for one long-range move scales as log(N), where N is the number of monomers in the chain. This allows us to conduct simulations of DNA molecules in a regime of molecular weights much greater than previously possible. Our results are in surprisingly good agreement with previous work for short chains using more realistic dynamics, and for longer chains, interesting data is obtained.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.461006
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  • 3
    Digitale Medien
    Digitale Medien
    Theoretical studies of DNA during gel electrophoresis (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2476-2485 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The dynamics of a long chain macromolecule in a gel is examined using numerical and analytical approaches. In contrast with previous conjectures, it is found that the chain does not move entirely in a "tube.'' For strong fields, an instability produced by the applied field causes the chain to frequently contract on itself. This is followed by it unwinding into an extended configuration. For lower fields, portions of the chain frequently double up on themselves and move through the gel thereby violating the tube constraint. The results can be explained by breaking down the motion into various stages, each of which can be further analyzed. The results of the simulation appear in accord with experiment and provide a more realistic description of DNA motion then tube models.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.455990
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  • 4
    Digitale Medien
    Digitale Medien
    Explanation of anomalous mobility and birefringence measurements found in pulsed field electrophoresis (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 7436-7441 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The study of DNA in a gel under the application of a time-dependent field has revealed some unexpected experimental features. These features are recovered by means of a detailed numerical simulation incorporating the many internal degrees of freedom of the DNA chain. These results can in turn be understood qualitatively by means of a model containing only four degrees of freedom.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.456223
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  • 5
    Digitale Medien
    Digitale Medien
    Simulation of forces on entangled polymers due to slippage (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 7251-7255 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We consider the force on the end of a polymer chain being pulled through a network at velocity v, using computer simulations. We develop algorithms for measuring the force on the end of the chain using lattice models of polymers. Our algorithm attaches a spring to the end being pulled and uses its average extension to calculate the force. General problems associated with the use of lattice models in obtaining forces are discussed. Variants of this method are used to obtain upper and lower bounds to the force. The results obtained are in agreement with recent analytical predictions and experiments. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.469036
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  • 6
    Digitale Medien
    Digitale Medien
    Dynamics of a polymer in the presence of permeable membranes (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 9090-9095 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We study the diffusion of a linear polymer in the presence of permeable membranes without excluded volume interactions, using scaling theory and Monte Carlo simulations. We find that the average time it takes for a chain with polymerization index N to cross a single isolated membrane varies with N as N5/2, giving its permeability proportional to N2. When the membranes are stacked with uniform spacing d in the unit of the monomer size, the dynamics of a polymer is shown to have three different regimes. In the limit of small d(very-much-less-than)N1/2, the chain diffuses through reptation and D∼N−2. When d is comparable to N1/2 the diffusion coefficients parallel and perpendicular to the membranes become different from each other. While the diffusion becomes Rouse-like, i.e. D∼N−1, in the parallel direction, the motion in the perpendicular direction is still hindered by the two-dimensional networks. The diffusion eventually becomes isotropic and Rouse-like for large d(very-much-greater-than)N. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.468857
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  • 7
    Digitale Medien
    Digitale Medien
    Macromolecular separation through a porous surface (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 9376-9381 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A new technique for the separation of macromolecules is proposed and investigated. A thin mesh with pores comparable to the radius of gyration of a free chain is used to filter chains according to their length. Without a field it has previously been shown that the permeability decays as a power law with chain length. However by applying particular configurations of pulsed fields, it is possible to have a permeability that decays as an exponential. This faster decay gives much higher resolution of separation. We also propose a modified screen containing an array of holes with barblike protrusions running parallel to the surface. When static friction is present between the macromolecule and the protrusion, some of the chains get trapped for long durations of time. By using this and a periodic modulation of an applied electric field, high resolution can be attained. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.474007
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  • 8
    Digitale Medien
    Digitale Medien
    Long range moves for high density polymer simulations (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 8849-8854 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Monte Carlo simulations of proteins are hindered by the system's high density which often makes local moves ineffective. Here we devise and test a set of long range moves that work well even when all sites in a lattice simulation are filled. We demonstrate that for a 27-mer cube, the ground state of random heteropolymers can quickly be reached. We discuss results for 48-mer systems where the ground state is known exactly. For ten sequences that were examined, the introduction of long range moves speeds up the search for the ground state by about one order of magnitude. The method is compared to a fast folding chain growth algorithm that had previously been used with much success. The new algorithm here appears to be more efficient. The point is illustrated by the folding of an 80-mer four-helix bundle considered previously. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.473943
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  • 9
    Digitale Medien
    Digitale Medien
    Bombesin—satiety or malaise? (1980)
    [s.l.] : Nature Publishing Group
    Nature 285 (1980), S. 592-592 
    Details
    ISSN: 1476-4687
    Quelle: Nature Archives 1869 - 2009
    Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik
    Notizen: [Auszug] IT has recently been claimed by Gibbs et al.1 that bombesin (BBS), like cholecystokinin (CCK), produces satiety in rats. However, their report ignores crucial evidence and lacks critical controls. First, there is good evidence that CCK suppresses feeding because it produces malaise. This has been ...
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1038/285592a0
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  • 10
    Digitale Medien
    Digitale Medien
    Cholecystokinin produces bait shyness in rats (1977)
    [s.l.] : Nature Publishing Group
    Nature 266 (1977), S. 196-196 
    Details
    ISSN: 1476-4687
    Quelle: Nature Archives 1869 - 2009
    Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik
    Notizen: [Auszug] BECAUSE an injection of cholecystokinin (CCK) (or of the synthetic C-terminal octapeptide of CCK1) reduces food intake in the fasted rat, it has been suggested by Gibbs, Smith and colleagues2,6 that CCK may be a satiety signal. We present here evidence against this conclusion. To quote from ref 4, ...
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1038/266196a0
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