148 research outputs found
Vibron Self--trapped States in Biological Macromolecules: Comparison of Different Theoretical Approaches
A study of the applicability of the variational treatments based on using of
the modified Lang-Firsov unitary transformation (MLF method) in the
investigation of the vibron self-trapped states in biological macromolecular
chains are presented. We compare the values of the ground state energy
predicted by MLF methods with the values of the ground state energy predicted
by the standard small-polaron theory, for various values of the basic energy
parameters of the system. We obtain regions in system parameter space where MLF
approach gives better description of the vibron states.Comment: 8 pages, 4 figures, To appear in the Proceedings of Conference
Dubna-Nano2012 (July 9 - 14, 2012
Vibron transport in macromolecular chains
We study the hopping mechanism of the vibron excitation transport in the
simple 1D model of biological macromolecular chains. We supposed that the
vibron interaction with thermal oscillations of the macromolecular structural
elements will result in vibron self -trapping, and the formation of the partial
dressed vibron state. With use of the modified Holstein polaron model, we
calculate vibron diffusivity in dependence of the basic system parameters and
temperature. We obtain that the vibron diffusivity smoothly decreases in non
adiabatic limit when the strength of the vibron-phonon coupling grows. However
this dependence becomes by discontinuous one in case of growth of the
adiabaticity of the system. The value of the critical point depends of the
system temperature, and at room temperatures it belongs to the low or
intermediate coupling regime. We discuss an application of these results to
study of vibron transport to 3D bundles of such macromolecules chains
considering it as polymer nanorods and to 2D polymer films organized from such
macromolecules.Comment: 4 pages, 6 figures, contribution to the Proceedings of the Conference
"Physical mesomechanics of multi-level systems`2014", September 3-5 2014,
Tomsk, Russi
Two-vibron bound states in alpha-helix proteins : the interplay between the intramolecular anharmonicity and the strong vibron-phonon coupling
The influence of the intramolecular anharmonicity and the strong
vibron-phonon coupling on the two-vibron dynamics in an -helix protein
is studied within a modified Davydov model. The intramolecular anharmonicity of
each amide-I vibration is considered and the vibron dynamics is described
according to the small polaron approach. A unitary transformation is performed
to remove the intramolecular anharmonicity and a modified Lang-Firsov
transformation is applied to renormalize the vibron-phonon interaction. Then, a
mean field procedure is realized to obtain the dressed anharmonic vibron
Hamiltonian. It is shown that the anharmonicity modifies the vibron-phonon
interaction which results in an enhancement of the dressing effect. In
addition, both the anharmonicity and the dressing favor the occurrence of two
different bound states which the properties strongly depend on the interplay
between the anharmonicity and the dressing. Such a dependence was summarized in
a phase diagram which characterizes the number and the nature of the bound
states as a function of the relevant parameters of the problem. For a
significant anharmonicity, the low frequency bound states describe two vibrons
trapped onto the same amide-I vibration whereas the high frequency bound states
refer to the trapping of the two vibrons onto nearest neighbor amide-I
vibrations.Comment: may 2003 submitted to Phys. Rev.
From Davydov solitons to decoherence-free subspaces: self-consistent propagation of coherent-product states
The self-consistent propagation of generalized [coherent-product]
states and of a class of gaussian density matrix generalizations is examined,
at both zero and finite-temperature, for arbitrary interactions between the
localized lattice (electronic or vibronic) excitations and the phonon modes. It
is shown that in all legitimate cases, the evolution of states reduces
to the disentangled evolution of the component states. The
self-consistency conditions for the latter amount to conditions for
decoherence-free propagation, which complement the Davydov soliton
equations in such a way as to lift the nonlinearity of the evolution for the
on-site degrees of freedom. Although it cannot support Davydov solitons, the
coherent-product ansatz does provide a wide class of exact density-matrix
solutions for the joint evolution of the lattice and phonon bath in compatible
systems. Included are solutions for initial states given as a product of a
[largely arbitrary] lattice state and a thermal equilibrium state of the
phonons. It is also shown that external pumping can produce self-consistent
Frohlich-like effects. A few sample cases of coherent, albeit not solitonic,
propagation are briefly discussed.Comment: revtex3, latex2e; 22 pages, no figs.; to appear in Phys.Rev.E
(Nov.2001
Correlation between acoustic divergence and phylogenetic distance in soniferous European gobiids (Gobiidae; Gobius lineage)
In fish, species identity can be encoded by sounds, which have been thoroughly investigated
in European gobiids (Gobiidae, Gobius lineage). Recent evolutionary studies suggest
that deterministic and/or stochastic forces could generate acoustic differences among
related animal species, though this has not been investigated in any teleost group to date. In
the present comparative study, we analysed the sounds from nine soniferous gobiids and
quantitatively assessed their acoustic variability. Our interspecific acoustic study, incorporating
for the first time the representative acoustic signals from the majority of soniferous
gobiids, suggested that their sounds are truly species-specific (92% of sounds correctly
classified into exact species) and each taxon possesses a unique set of spectro-temporal
variables. In addition, we reconstructed phylogenetic relationships from a concatenated
molecular dataset consisting of multiple molecular markers to track the evolution of acoustic
signals in soniferous gobiids. The results of this study indicated that the genus Padogobius
is polyphyletic, since P. nigricans was nested within the Ponto-Caspian clade, while the congeneric
P. bonelli turned out to be a sister taxon to the remaining investigated soniferous
species. Lastly, by extracting the acoustic and genetic distance matrices, sound variability
and genetic distance were correlated for the first time to assess whether sound evolution follows
a similar phylogenetic pattern. The positive correlation between the sound variability
and genetic distance obtained here emphasizes that certain acoustic features from representative
sounds could carry the phylogenetic signal in soniferous gobiids. Our study was
the first attempt to evaluate the mutual relationship between acoustic variation and genetic
divergence in any teleost fish
Relaxation channels of two-vibron bound states in \alpha-helix proteins
Relaxation channels for two-vibron bound states in an anharmonic alpha-helix
protein are studied. It is pointed out that the relaxation originates in the
interaction between the dressed anharmonic vibrons and the remaining phonons.
This interaction is responsible for the occurrence of transitions between
two-vibron eigenstates mediated by both phonon absorption and phonon emission.
At biological temperature, it is shown that the relaxation rate does not
significantly depends on the nature of the two-vibron state involved in the
process. Therefore, the lifetime for both bound and free states is of the same
order of magnitude and ranges between 0.1 and 1.0 ps for realistic parameters.
By contrast, the relaxation channels strongly depend on the nature of the
two-vibron states which is a consequence of the breather-like behavior of the
two-vibron bound states.Comment: octobre 2003 - soumis Phys. Rev.
Long-term leukocyte reconstitution in NSG mice transplanted with human cord blood hematopoietic stem and progenitor cells
Abstract Background Humanized mice (hu mice) are based on the transplantation of hematopoietic stem and progenitor cells into immunodeficient mice and have become important pre-clinical models for biomedical research. However, data about their hematopoiesis over time are scarce. We therefore characterized leukocyte reconstitution in NSG mice, which were sublethally irradiated and transplanted with human cord blood-derived CD34+ cells at newborn age, longitudinally in peripheral blood and, for more detailed analyses, cross-sectionally in peripheral blood, spleen and bone marrow at different time points. Results Human cell chimerism and absolute human cell count decreased between week 16 and 24 in the peripheral blood of hu mice, but were stable thereafter as assessed up to 32 weeks. Human cell chimerism in spleen and bone marrow was maintained over time. Notably, human cell chimerism in peripheral blood and spleen as well as bone marrow positively correlated with each other. Percentage of B cells decreased between week 16 and 24, whereas percentage of T cells increased; subsequently, they levelled off with T cells clearly predominating at week 32. Natural killer cells, monocytes and plasmacytoid dendritic cells (DCs) as well as CD1c + and CD141+ myeloid DCs were all present in hu mice. Proliferative responses of splenic T cells to stimulation were preserved over time. Importantly, the percentage of more primitive hematopoietic stem cells (HSCs) in bone marrow was maintained over time. Conclusions Overall, leukocyte reconstitution was maintained up to 32 weeks post-transplantation in our hu NSG model, possibly explained by the maintenance of HSCs in the bone marrow. Notably, we observed great variation in multi-lineage hematopoietic reconstitution in hu mice that needs to be taken into account for the experimental design with hu mice
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