421 research outputs found
Electrostatic attraction between cationic-anionic assemblies with surface compositional heterogeneities
Electrostatics plays a key role in biomolecular assembly. Oppositely charged
biomolecules, for instance, can co-assembled into functional units, such as DNA
and histone proteins into nucleosomes and actin-binding protein complexes into
cytoskeleton components, at appropriate ionic conditions. These
cationic-anionic co-assemblies often have surface charge heterogeneities that
result from the delicate balance between electrostatics and packing
constraints. Despite their importance, the precise role of surface charge
heterogeneities in the organization of cationic-anionic co-assemblies is not
well understood. We show here that co-assemblies with charge heterogeneities
strongly interact through polarization of the domains. We find that this leads
to symmetry breaking, which is important for functional capabilities, and
structural changes, which is crucial in the organization of co-assemblies. We
determine the range and strength of the attraction as a function of the
competition between the steric and hydrophobic constraints and electrostatic
interactions.Comment: JCP June/200
Simulation of boron diffusion during low-temperature annealing of implanted silicon
Modeling of ion-implanted boron redistribution in silicon crystals during
low-temperature annealing with a small thermal budget has been carried out. It
was shown that formation of "tails"' in the low-concentration region of
impurity profiles occurs due to the long-range migration of boron interstitialsComment: 16 pages, 3 figure
Unusual features in the nonlinear microwave surface impedance of Y-Ba-Cu-O thin films
Striking features have been found in the nonlinear microwave (8 GHz) surface
impedance of high-quality YBaCuO thin films with comparable
low power characteristics [ and ]. The surface resistance is found to increase,
decrease, or remain independent of the microwave field (up to 60 mT)
at different temperatures and for different samples. However, the surface
reactance always follows the same functional form. Mechanisms which may
be responsible for the observed variations in and are briefly
discussed.Comment: 4 pages, 4 figure
On the determination of the quasiparticle scattering rate in unconventional superconductors by microwave surface impedance
In the approximation of validity of the Drude expression for quasiparticle
conductivity and the assumption that all electrons at T = 0 transform into a
superfluide condensate, the expression for the quasiparticle scattering rate
tau -1 in terms of the real and imaginary parts of the microwave surface
impedance has been obtained. The resulting expression is a generalization of
the well-known expression for tau^-1, valid for omega x tau is much less 1, to
an arbitrary value of omega x tau, where omega is the frequency of the
microwave field. From experimental Ka-band impedance measurements, temperature
dependence of tau^-1 in superconducting single crystal pnictides
Ba(Fe1-xCox)2As2 is obtained using the generalized expression. It is shown that
under condition of the given work, the approximation omega x tau is much less 1
gives the considerable error in determination of tau^-1.Comment: 3 pages, 1 figur
Pattern formation on the surface of cationic-anionic cylindrical aggregates
Charged pattern formation on the surfaces of self--assembled cylindrical
micelles formed from oppositely charged heterogeneous molecules such as
cationic and anionic peptide amphiphiles is investigated. The net
incompatibility among different components results in the formation of
segregated domains, whose growth is inhibited by electrostatics. The transition
to striped phases proceeds through an intermediate structure governed by
fluctuations, followed by states with various lamellar orientations, which
depend on cylinder radius and . We analyze the specific heat,
susceptibility , domain size and morphology as a
function of and .Comment: Sent to PRL 11Jan05 Transferred from PRL to PRE 10Jun0
Leukocytes phagocytic activity under moderate hypotension conditions in some representatives of bony fish, amphibians and reptiles
The leukocytes phagocytic activity against Bacillus subtilis and agromerulated latex particles in representatives of bony fish, amphibians and reptiles under reduced medium osmolarity conditions was studied. It was found that in moderate hypotension compared with isotonia, the white blood cells absorption capacity of the fish was not changed, but it was reduced for amphibians and reptile
Mechanisms of arsenic clustering in silicon
A model of arsenic clustering in silicon is proposed and analyzed. The main
feature of the proposed model is the assumption that negatively charged arsenic
complexes play a dominant role in the clustering process. To confirm this
assumption, electron density and concentration of impurity atoms incorporated
into the clusters are calculated as functions of the total arsenic
concentration. A number of the negatively charged clusters incorporating a
point defect and one or more arsenic atoms are investigated. It is shown that
for the doubly negatively charged clusters or for clusters incorporating more
than one arsenic atom the electron density reaches a maximum value and then
monotonically and slowly decreases as total arsenic concentration increases. In
the case of doubly negatively charged cluster incorporating two arsenic atoms,
the calculated electron density agrees well with the experimental data.
Agreement with the experiment confirms the conclusion that two arsenic atoms
participate in the cluster formation. Among all present models, the proposed
model of clustering by formation of doubly negatively charged cluster
incorporating two arsenic atoms gives the best fit to the experimental data and
can be used in simulation of high concentration arsenic diffusion.Comment: 13 pages, 4 figures. Revised and shortened version of the paper has
been published in Phys. Rev. B, Vol.74 (3), art. no. 035205 (2006
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