664 research outputs found
Some observations on the renormalization of membrane rigidity by long-range interactions
We consider the renormalization of the bending and Gaussian rigidity of model
membranes induced by long-range interactions between the components making up
the membrane. In particular we analyze the effect of a finite membrane
thickness on the renormalization of the bending and Gaussian rigidity by
long-range interactions. Particular attention is paid to the case where the
interactions are of a van der Waals type.Comment: 11 pages RexTex, no figure
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
Extraction Characteristics of Alumina from Gujrat Bauxites
ALUMINIUM has been termed the versatile metal of the 20th century since it finds applications right from the kitchen to the spaceship. The growing popularity of this metal has been attributed to its outstanding physical and chemical properties, viz. lightness, high strength of its alloys, high electrical and thermal conductivity, good workability and the most important of all-its resistance to corrosion.
Aluminium and its alloys find extensive applications
in road transport, railways and aviation due to their
good strength for relatively low weight. Aluminium also finds applications in chemical & food processing plants. Owing to its good electrical conductivity it finds use in electrical industries . Its strength, brightness, durab-ility and capacity to take anodic coatings and colours are the most important properties for its use for archite-ctural purposes
Non-monotoic fluctuation-induced interactions between dielectric slabs carrying charge disorder
We investigate the effect of monopolar charge disorder on the classical
fluctuation-induced interactions between randomly charged net-neutral
dielectric slabs and discuss various generalizations of recent results (A. Naji
et al., Phys. Rev. Lett. 104, 060601 (2010)) to highly inhomogeneous dielectric
systems with and without statistical disorder correlations. We shall focus on
the specific case of two generally dissimilar plane-parallel slabs, which
interact across vacuum or an arbitrary intervening dielectric medium. Monopolar
charge disorder is considered to be present on the bounding surfaces and/or in
the bulk of the slabs, may be in general quenched or annealed and may possess a
finite lateral correlation length reflecting possible `patchiness' of the
random charge distribution. In the case of quenched disorder, the bulk disorder
is shown to give rise to an additive long-range contribution to the total
force, which decays as the inverse distance between the slabs and may be
attractive or repulsive depending on the dielectric constants of the slabs. We
show that in the case of two dissimilar slabs the net effect due to the
interplay between the disorder-induced and the pure van der Waals interactions
can lead to a variety of unusual non-monotonic interaction profiles between the
dielectric slabs. In particular, when the intervening medium has a larger
dielectric constant than the two slabs, we find that the net interaction can
become repulsive and exhibit a potential barrier, while the underlying van der
Waals force is attractive. On the contrary, when the intervening medium has a
dielectric constant in between that of the two slabs, the net interaction can
become attractive and exhibit a free energy minimum, while the pure van der
Waals force is repulsive. Therefore, the charge disorder, if present, can
drastically alter the effective interaction between net-neutral objects.Comment: 13 pages, 8 figure
Dependences of the Casimir-Polder interaction between an atom and a cavity wall on atomic and material properties
The Casimir-Polder and van der Waals interactions between an atom and a flat
cavity wall are investigated under the influence of real conditions including
the dynamic polarizability of the atom, actual conductivity of the wall
material and nonzero temperature of the wall. The cases of different atoms near
metal and dielectric walls are considered. It is shown that to obtain accurate
results for the atom-wall interaction at short separations, one should use the
complete tabulated optical data for the complex refractive index of the wall
material and the accurate dynamic polarizability of an atom. At relatively
large separations in the case of a metal wall, one may use the plasma model
dielectric function to describe the dielectric properties of wall material. The
obtained results are important for the theoretical interpretation of
experiments on quantum reflection and Bose-Einstein condensation.Comment: 5 pages, 1 figure, iopart.cls is used, to appear in J. Phys. A
(special issue: Proceedings of QFEXT05, Barcelona, Sept. 5-9, 2005
Body-assisted van der Waals interaction between two atoms
Using fourth-order perturbation theory, a general formula for the van der
Waals potential of two neutral, unpolarized, ground-state atoms in the presence
of an arbitrary arrangement of dispersing and absorbing magnetodielectric
bodies is derived. The theory is applied to two atoms in bulk material and in
front of a planar multilayer system, with special emphasis on the cases of a
perfectly reflecting plate and a semi-infinite half space. It is demonstrated
that the enhancement and reduction of the two-atom interaction due to the
presence of a perfectly reflecting plate can be understood, at least in the
nonretarded limit, by using the method of image charges. For the semi-infinite
half space, both analytical and numerical results are presented.Comment: 17 pages, 9 figure
Universal behavior of dispersion forces between two dielectric plates in the low-temperature limit
The universal analytic expressions in the limit of low temperatures (short
separations) are obtained for the free energy, entropy and pressure between the
two parallel plates made of any dielectric. The analytical proof of the Nernst
heat theorem in the case of dispersion forces acting between dielectrics is
provided. This permitted us to formulate the stringent thermodynamical
requirement that must be satisfied in all models used in the Casimir physics.Comment: 6 pages, iopart.cls is used, to appear in J. Phys. A (special issue:
Proceedings of QFEXT05, Barcelona, Sept. 5-9, 2005
The lamellar-to-isotropic transition in ternary amphiphilic systems
We study the dependence of the phase behavior of ternary amphiphilic systems
on composition and temperature. Our analysis is based on a curvature elastic
model of the surfactant film with sufficiently large spontaneous curvature and
sufficiently negative saddle-splay modulus that the stable phases are the
lamellar phase and a droplet microemulsion. In addition to the curvature
energy, we consider the contributions to the free energy of the long-ranged van
der Waals interaction and of the undulation modes. We find that for bending
rigidities of order k_B T, the lamellar phase extends further and further into
the water apex of the phase diagram as the phase inversion temperature is
approached, in good agreement with experimental results.Comment: LaTeX2e, 11 pages with references and 2 eps figures included,
submitted to Europhys. Let
Field theoretic calculation of the surface tension for a model electrolyte system
We carry out the calculation of the surface tension for a model electrolyte
to first order in a cumulant expansion about a free field theory equivalent to
the Debye-H\"uckel approximation. In contrast with previous calculations, the
surface tension is calculated directly without recourse to integrating
thermodynamic relations. The system considered is a monovalent electrolyte with
a region at the interface, of width h, from which the ionic species are
excluded. In the case where the external dielectric constant epsilon_0 is
smaller than the electrolyte solution's dielectric constant epsilon we show
that the calculation at this order can be fully regularized. In the case where
h is taken to be zero the Onsager-Samaras limiting law for the excess surface
tension of dilute electrolyte solutions is recovered, with corrections coming
from a non-zero value of epsilon_0/epsilon.Comment: LaTeX, 14 pages, 3 figures, 1 tabl
Van der Waals interaction between microparticle and uniaxial crystal with application to hydrogen atoms and multiwall carbon nanotubes
The Lifshitz theory of the van der Waals force is extended for the case of an
atom (molecule) interacting with a plane surface of an uniaxial crystal or with
a long solid cylinder or cylindrical shell made of isotropic material or
uniaxial crystal. For a microparticle near a semispace or flat plate made of an
uniaxial crystal the exact expressions for the free energy of the van der Waals
and Casimir-Polder interaction are presented. An approximate expression for the
free energy of microparticle- cylinder interaction is obtained which becomes
precise for microparticle-cylinder separations much smaller than cylinder
radius. The obtained expressions are used to investigate the van der Waals
interaction between hydrogen atoms (molecules) and graphite plates or multiwall
carbon nanotubes. To accomplish this the behavior of graphite dielectric
permittivities along the imaginary frequency axis is found using the optical
data for the complex refractive index of graphite for the ordinary and
extraordinary rays. It is shown that the position of hydrogen atoms inside
multiwall carbon nanotubes is energetically preferable compared with outside.Comment: 23 pages, 8 figures, 2 tables. Minor corrections are made and new
references added. Accepted for publication in Phys. Rev.
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