2,053 research outputs found
Conformational transformations induced by the charge-curvature interaction at finite temperature
The role of thermal fluctuations on the conformational dynamics of a single
closed filament is studied. It is shown that, due to the interaction between
charges and bending degrees of freedom, initially circular aggregates may
undergo transformation to polygonal shape. The transition occurs both in the
case of hardening and softening charge-bending interaction. In the former case
the charge and curvature are smoothly distributed along the chain while in the
latter spontaneous kink formation is initiated. The transition to a
non-circular conformation is analogous to the phase transition of the second
kind.Comment: 23 pages (Latex), 10 figures (Postscript), 2 biblio file (bib-file
and bbl-file
Elementary derivation of Spitzer's asymptotic law for Brownian windings and some of its physical applications
A simple derivation of Spitzer'z asymptotic law for Brownian windings
[Trans.Am.Math.Soc.87,187 (1958)]is presented along with its generalizations
>.These include the cases of planar Brownian walks interacting with a single
puncture and Brownian walks on a single truncated cone with variable conical
angle interacting with the truncated conical tip.Such situations are typical in
the theories of quantum Hall effect and 2+1 quantum gravity, respectively .They
also have some applications in polymer physic
The role of long-chain acyl-CoA in the damage of oxidative phosphorylation in heart mitochondria
AbstractThe aim of this investigation was to study the effect of intramitochondrial acyl-CoA on the respiration of rabbit heart mitochondria over the whole range of stationary respiratory rates between States 4 and 3. The creatine phosphokinase system was used for stabilization of extramitochondrial adenine nucleotide concentration. It was shown that acyl-CoA depressed respiration more effectively in the intermediate range of respiration between States 4 and 3. The effect of acyl-CoA was negligible near State 4 and in State 3. These data are in line with our previous results concerning the dependence of the adenine nucleotide translocator control coefficient on the rate of mitochondrial respiration. Thus, our data suggest that long-chain acyl-CoA may regulate oxidative phosphorylation in heart mitochondria in vivo
Veneziano Amplitudes, Spin Chains and String Models
In a series of recently published papers we reanalyzed the existing
treatments of Veneziano and Veneziano-like amplitudes and the models associated
with these amplitudes. In this work we demonstrate that the already obtained
new partition function for these amplitudes can be exactly mapped into that for
the Polychronakos-Frahm (P-F) spin chain model. This observation allows us to
recover many of the existing string-theoretic models, including the most recent
ones.Comment: 38 page
Entropically driven transition to a liquid-crystalline polymer globule
A self-consistent-field theory (SCFT) in the grand canonical ensemble
formulation is used to study transitions in a helix-coil multiblock copolymer
globule. The helices are modeled as stiff rods. In addition to the established
coil-globule transition we show for the first time that, even without explicit
rod-rod alignment interaction, the system undergoes a transition to a nematic
liquid-crystalline (LC) globular state. The LC-globule formation is driven by
the hydrophobic helical segment attraction and the anisotropy of the globule
surface energy. The full phase diagram of the copolymer was calculated. It
discriminates between an open chain, amorphous globule and LC-globule. This
model provides a relatively simple example of the interplay between secondary
and tertiary structures in homopolypeptides. Moreover, it gives a simple
explanation for the formation of helix bundles in certain globular proteins.Comment: 5 pages, 5 figures, submitted to Europhys. Let
A transfer matrix approach to the enumeration of plane meanders
A closed plane meander of order is a closed self-avoiding curve
intersecting an infinite line times. Meanders are considered distinct up
to any smooth deformation leaving the line fixed. We have developed an improved
algorithm, based on transfer matrix methods, for the enumeration of plane
meanders. While the algorithm has exponential complexity, its rate of growth is
much smaller than that of previous algorithms. The algorithm is easily modified
to enumerate various systems of closed meanders, semi-meanders, open meanders
and many other geometries.Comment: 13 pages, 9 eps figures, to appear in J. Phys.
Positional Information Generated by Spatially Distributed Signaling Cascades
The temporal and stationary behavior of protein modification cascades has been extensively studied, yet little is known about the spatial aspects of signal propagation. We have previously shown that the spatial separation of opposing enzymes, such as a kinase and a phosphatase, creates signaling activity gradients. Here we show under what conditions signals stall in the space or robustly propagate through spatially distributed signaling cascades. Robust signal propagation results in activity gradients with long plateaus, which abruptly decay at successive spatial locations. We derive an approximate analytical solution that relates the maximal amplitude and propagation length of each activation profile with the cascade level, protein diffusivity, and the ratio of the opposing enzyme activities. The control of the spatial signal propagation appears to be very different from the control of transient temporal responses for spatially homogenous cascades. For spatially distributed cascades where activating and deactivating enzymes operate far from saturation, the ratio of the opposing enzyme activities is shown to be a key parameter controlling signal propagation. The signaling gradients characteristic for robust signal propagation exemplify a pattern formation mechanism that generates precise spatial guidance for multiple cellular processes and conveys information about the cell size to the nucleus
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