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981.
Cocco S Marko JF Monasson R Sarkar A Yan J 《The European physical journal. E, Soft matter》2003,10(3):249-263
The elastic response of flexible polymers made of elements which can be either folded or unfolded, having different lengths
in these two states, is discussed. These situations are common for biopolymers as a result of folding interactions intrinsic
to the monomers, or as a result of binding of other smaller molecules along the polymer length. Using simple flexible-chain
models, we show that even when the energy ε associated with maintaining the folded state is comparable to k
B
T, the elastic response of such a chain can mimic usual polymer linear elasticity, but with a force scale enhanced above that
expected from the flexibility of the chain backbone. We discuss recent experiments on single-stranded DNA, chromatin fiber
and double-stranded DNA with proteins weakly absorbed along its length which show this effect. Effects of polymer semiflexiblity
and torsional stiffness relevant to experiments on proteins binding to dsDNA are analyzed. We finally discuss the competition
between electrostatic self-repulsion and folding interactions responsible for the complex elastic response of single-stranded
DNA.
Received 7 August 2002 and Received in final form 7 March 2003 / Published online: 15 April 2003
RID="a"
ID="a"e-mail: jmarko@uic.edu 相似文献
982.
One or more methoxy groups on the benzylic carbon at the ortho-position of tricarbonylchromium-complexed aryl aldehydes (2, 3 or 4) permit chelation-controlled addition of nucleophiles to the carbonyl function in the presence of Lewis acids. In the absence of a Lewis acid additive, a complementary set of diastereomeric products are obtained. 相似文献
983.
We propose a left-right model of quarks and leptons based on the gauge group SU(3)(C)xSU(2)(L)xSU(2)(R)xU(1)(B-L), where the scalar sector consists of only two doublets: (1,2,1,1) and (1,1,2,1). As a result, any fermion mass, whether it be Majorana or Dirac, must come from dimension-five operators. This allows us to have a common view of quark and lepton masses, including the smallness of Majorana neutrino masses as the consequence of a double seesaw mechanism. 相似文献
984.
M. C. Rath S. K. Sarkar V. K. Wadhawan R. Verma I. M. L. Das R. Dąbrowski M. Tykarska R. Dhar 《Opto-Electronics Review》2008,16(4):399-403
Electron beam irradiation studies on liquid crystal material 5CB have been carried out at a temperature where the compound
exists in the isotropic liquid phase. In situ time-resolved spectroscopic characterization was carried out during the irradiation.
Three different transients were observed during the 2-μs electron pulse. After about 50 μs, only one transient species was
found to be present, which has an absorption peak at 360 nm. Radiolysed sample exhibits a broad absorption at ∼400 nm. The
dielectric measurements show that even a low level of irradiation results in a dramatic increase in the component of dielectric
permittivity normal to the long axes of the molecules ε⊥′, and a corresponding decrease in the dielectric anisotropy (Δε′=ε∥′−ε⊥′ ). These studies show that 5CB is prone to substantial radiation damage on exposure to the beam of high-energy electrons. 相似文献
985.
Ataur Rahman Sarkar Mohammed Nazrul Islam Mohammad Golam Mostafa 《Optical and Quantum Electronics》2007,39(8):659-675
The performance of an optical wideband wavelength division multiplexed (WDM) communication system is analyzed considering
the effects of stimulated Raman scattering, fiber attenuation and chromatic dispersion. Improved models for the Raman gain
and the fiber attenuation constant are proposed, which yield better and reliable performance results of the WDM system. Effect
of fiber chromatic dispersion is also investigated and it is observed that dispersion can suitably be selected to overcome
the limitations imposed by the stimulated Raman scattering phenomenon. 相似文献
986.
We investigate energy localization and transport in the form of discrete breathers and their movability in two-dimensional
Fermi–Pasta–Ulam(FPU) lattices. We study the dynamics of the two-dimensional Fermi–Pasta–Ulam(FPU) lattice, incorporating
the complicated effects of geometry, long-range interactions as well as nonlinear dispersion. We obtain several exact discrete
breather(DB) solutions, such as the odd-parity and even-parity DBs, compact-like DBs and moving DBs for various geometries
of the two-dimensional FPU chain. We show that DBs also exist in the same lattice in presence of next-nearest neighbour interaction.
Large-amplitude exact subsonic travelling kink-soliton solutions are obtained in such a periodic chain in presence of long-range
nonlinear dispersive interaction in the long-wavelength and weakly nonlinear limit. Such a two-dimensional FPU lattice admits
finite amplitude nonlinear sinusoidal wave (NSW) solutions with short commensurate as well as incommensurate wavelengths for
different geometries of the chain. The usefulness of these solutions for energy localization and transport in various physical
systems are discussed. 相似文献
987.
We present a numerical investigation of the tunneling dynamics of a particle moving in a bistable potential with fluctuating
barrier which is coupled to a non-integrable classical system and study the interplay between classical chaos and barrier
fluctuation in the tunneling dynamics. We found that the coupling of the quantum system with the classical subsystem decreases
the tunneling rate irrespective of whether the classical subsystem is regular or chaotic and also irrespective of the fact
that whether the barrier fluctuates or not. Presence of classical chaos always enhances the tunneling rate constant. The effect
of barrier fluctuation on the tunneling rate in a mixed quantum-classical system is to suppress the tunneling rate. In contrast
to the case of regular subsystem, the suppression arising due to barrier fluctuation is more visible when the subsystem is
chaotic.
相似文献
988.
Hemanta K. Sarkar Pill-Soon Song Ta-Yan Leong† Winslow R. Briggs† 《Photochemistry and photobiology》1982,35(4):593-595
Abstract— The fluorescence lifetime of a partially-purified membrane fraction containing flavin and b-type cytochrome, presumably on the same protein, has been described. Possible implications of the blue light photoreactivity of the flavin as an assay, on the basis of its short fluorescence lifetime (about 1.37 ns), has been discussed. 相似文献
989.
990.