36 research outputs found
Cytoskeleton influence on normal and tangent fluctuation modes in the red blood cells
We argue that the paradoxal softness of the red blood cells (RBC) in
fluctuation spectra experiments is apparent. We show that the effective surface
shear modulus of the RBC obtained from fluctuation data and that
measured in static deformation experiments have the same order of magnitude. A
simple micromechanical model of the RBC developped for this purpose accounts
for the influence of a finite-thickness cytoskeleton on the fluctuations of the
composite membrane-cytoskeleton system. The spectrin network cytoskeleton with
the bulk shear modulus estimated as Pa contributes to
both normal and tangent fluctuations of the system and confines the
fluctuations of the lipid membrane. The ratio of mean square amplitudes of the
RBC normal and tangent fluctuations calculated in the frame
of the model is 2-3 orders of magnitude smaller that it is in the free membrane
with the same bending and shear moduliComment: 14 pages, 4 figure
Structures of Spherical Viral Capsids as Quasicrystalline Tilings
Spherical viral shells with icosahedral symmetry have been considered as
quasicrystalline tilings. Similarly to known Caspar-Klug quasi-equivalence
theory, the presented approach also minimizes the number of conformations
necessary for the protein molecule bonding with its neighbors in the shell, but
is based on different geometrical principles. It is assumed that protein
molecule centers are located at vertices of tiles with identical edges, and the
number of different tile types is minimal. Idealized coordinates of
nonequivalent by symmetry protein positions in six various capsid types are
obtained. The approach describes in a uniform way both the structures
satisfying the well-known Caspar-Klug geometrical model and the structures
contradicting this model.Comment: 8 pages, 2 figures; This version was published in Physics of the
Solid State, 2015, Vol. 57, No.4, pp. 810-81
Two-dimensional elasticity determines the low-frequency dynamics of single- and double-walled carbon nanotubes
We develop a continuous theory of low-frequency dynamics for nanotubes with
truly two-dimensional (2D) walls constituted by single-atom monolayer. In this
frame topological bending elasticity of the monolayer is not related to its
vanishing macroscopic thickness. The proposed approach predicts completely new
sound dispersions and radius dependences of non-resonant Raman-active modes
frequencies in single-walled carbon nanotubes (SWCNT). Resulting relations are
suitable for nanotubes identification and more complete or alternative
characterization. The theory is also applied to describe the low-frequency
dynamics of double-walled carbon nanotubes (DWCNT). It establishes a clear-cut
relation between the radial breathing mode in SWCNT and breathing-like modes in
DWCNT and fits the existing Raman data better than previously developed 3D
continuous or discrete models. The results obtained constitute the basis for
new quantitative studies of the low-frequency vibrational spectrum, heat
capacity and heat transfer properties of carbon nanotubes.Comment: 12 pages, 1 figur
Chiral Quasicrystalline Order and Dodecahedral Geometry in Exceptional Families of Viruses
On the example of exceptional families of viruses we i) show the existence of
a completely new type of matter organization in nanoparticles, in which the
regions with a chiral pentagonal quasicrystalline order of protein positions
are arranged in a structure commensurate with the spherical topology and
dodecahedral geometry, ii) generalize the classical theory of quasicrystals
(QCs) to explain this organization, and iii) establish the relation between
local chiral QC order and nonzero curvature of the dodecahedral capsid faces.Comment: 8 pages, 3 figure
Density waves theory of the capsid structure of small icosahedral viruses
We apply Landau theory of crystallization to explain and to classify the
capsid structures of small viruses with spherical topology and icosahedral
symmetry. We develop an explicit method which predicts the positions of centers
of mass for the proteins constituting viral capsid shell. Corresponding density
distribution function which generates the positions has universal form without
any fitting parameter. The theory describes in a uniform way both the
structures satisfying the well-known Caspar and Klug geometrical model for
capsid construction and those violating it. The quasiequivalence of protein
environments in viral capsid and peculiarities of the assembly thermodynamics
are also discussed.Comment: 8 pages, 3 figur
Flexoelectricity and piezoelectricity - reason for rich variety of phases in antiferroelectric liquid crystals
The free energy of antiferroelectric liquid crystal which takes into account
polar order explicitly is presented. Steric, van der Waals, piezoelectric and
flexoelectric interactions to the nearest layers and dipolar electrostatic
interactions to the nearest and to the next nearest layers induce indirect tilt
interactions with chiral and achiral properties, which extend to the third and
to the fourth nearest layers. Chiral indirect interactions between tilts can be
large and induce helicoidal modulations even in systems with negligible chiral
van der Waals interactions. If indirect chiral interactions compete with chiral
van der Waals interactions, the helix unwinding is possible. Although strength
of microscopic interactions change monotonically with decreasing temperature,
effective interlayer interactions change nonmonotonically and give rise to
nonmonotouous change of modulation period through various phases. Increased
enatiomeric excess i.e. increased chirality changes the phase sequence.Comment: 4 pages, 1 figur