1,109 research outputs found
A Novel Method for the Synthesis of Core-shell Magnetic Nanoparticle
Core-shell type magnetic nanoparticles are finding attractive applications in biomedicine, from diagnostic to cancer therapy. Both for targeted drug delivery and hyperthermia, as well as a contrast agent used for external biomedical imaging systems, small (< 20 nm) superparamagnetic nanoparticles are desired. Some iron oxide nanoparticle formulations are already approved for human administration as contrast agent for magnetic resonance imaging. However, search continues for nanoparticles with higher saturation magnetisation. Metallic, bi-metallic and intermetallic magnetic nanoparticles are finding attention. Biocompatibility and optimal clearance are important criteria for the medical applications and therefore core-shell type particles are favored, where a biocompatible shell (e.g. polymer, Silica) can prevent inadvertent host reaction with the magnetic core. A recently developed novel synthesis method (electrochemical selective phase dissolution - ESPD), which can produce core-shell magnetic nanoparticles, is reviewed in this paper. ESPD, as the name suggests, uses electro-chemical separation of a phase from metallic alloys to synthesize nanoparticles. It is a versatile method and can be adopted to produce a wide range of nanostructures in addition to the core-shell magnetic nanoparticles
Unexpected crossover dynamics of single polymer in a corrugated tube
We present molecular dynamics study of a generic (coarse-grained) model for
single-polymer diffusion confined in a corrugated cylinder. For a narrow tube,
i.e., diameter of the cylinder , the axial diffusion coefficient
scales as , with chain length , up to then crosses over to Rouse scaling for the larger values. The
scaling is due to the large fluctuation of the polymer chain along
its fully stretched equilibrium conformation. The stronger scaling, namely
, is not observed for an atomistically smooth tube and/or for a
cylinder with larger diameter.Comment: 10 pages, 3 figures, LaTeX, version accepted by J. Chem. Phy
Reunion of random walkers with a long range interaction: applications to polymers and quantum mechanics
We use renormalization group to calculate the reunion and survival exponents
of a set of random walkers interacting with a long range and a short
range interaction. These exponents are used to study the binding-unbinding
transition of polymers and the behavior of several quantum problems.Comment: Revtex 3.1, 9 pages (two-column format), 3 figures. Published version
(PRE 63, 051103 (2001)). Reference corrections incorporated (PRE 64, 059902
(2001) (E
Shocks in asymmetric simple exclusion processes of interacting particles
In this paper, we study shocks and related transitions in asymmetric simple
exclusion processes of particles with nearest neighbor interactions. We
consider two kinds of inter-particle interactions. In one case, the
particle-hole symmetry is broken due to the interaction. In the other case,
particles have an effective repulsion due to which the particle-current-density
drops down near the half filling. These interacting particles move on a one
dimensional lattice which is open at both the ends with injection of particles
at one end and withdrawal of particles at the other. In addition to this, there
are possibilities of attachments or detachments of particles to or from the
lattice with certain rates. The hydrodynamic equation that involves the exact
particle current-density of the particle conserving system and additional terms
taking care of the attachment-detachment kinetics is studied using the
techniques of boundary layer analysis.Comment: 10 pages, 8 figure
Reunion of Vicious Walkers: Results from -Expansion -
The anomalous exponent, , for the decay of the reunion probability
of vicious walkers, each of length , in dimensions,
is shown to come from the multiplicative renormalization constant of a
directed polymer partition function. Using renormalization group(RG) we
evaluate to . The survival probability exponent is
. For , our RG is exact and stops at .
For , the log corrections are also determined. The number of walkers that
are sure to reunite is 2 and has no expansion.Comment: No of pages: 11, 1figure on request, Revtex3,IP/BBSR/929
Finite Size Correction In A Disordered System - A New Divergence
We show that the amplitude of the finite size correction term for the th
moment of the partition function, for randomly interacting directed polymers,
diverges (on the high temperature side) as , as a critical
moment is approached. The exponent is independent of temperature but
does depend on the effective dimensionality. There is no such divergence on the
low temperature side (.Comment: 8 pages, Revtex, 5 figures. For figs, send mail to [email protected]
Bulk and surface transitions in asymmetric simple exclusion process: Impact on boundary layers
In this paper, we study boundary-induced phase transitions in a particle
non-conserving asymmetric simple exclusion process with open boundaries. Using
boundary layer analysis, we show that the key signatures of various bulk phase
transitions are present in the boundary layers of the density profiles. In
addition, we also find possibilities of surface transitions in the low- and
high- density phases. The surface transition in the low-density phase provides
a more complete description of the non-equilibrium critical point found in this
system.Comment: 9 pages including figure
Multi-shocks in asymmetric simple exclusions processes: Insights from fixed-point analysis of the boundary-layers
The boundary-induced phase transitions in an asymmetric simple exclusion
process with inter-particle repulsion and bulk non-conservation are analyzed
through the fixed points of the boundary layers. This system is known to have
phases in which particle density profiles have different kinds of shocks. We
show how this boundary-layer fixed-point method allows us to gain physical
insights on the nature of the phases and also to obtain several quantitative
results on the density profiles especially on the nature of the boundary-layers
and shocks.Comment: 12 pages, 8 figure
Phase-plane analysis of driven multi-lane exclusion models
We show how a fixed point based boundary-layer analysis technique can be used
to obtain the steady-state particle density profiles of driven exclusion
processes on two-lane systems with open boundaries. We have considered two
distinct two-lane systems. In the first, particles hop on the lanes in one
direction obeying exclusion principle and there is no exchange of particles
between the lanes. The hopping on one lane is affected by the particle
occupancies on the other, which thereby introduces an indirect interaction
among the lanes. Through a phase plane analysis of the boundary layer equation,
we show why the bulk density undergoes a sharp change as the interaction
between the lanes is increased. The second system involves one lane with driven
exclusion process and the other with biased diffusion of particles. In contrast
to the previous model, here there is a direct interaction between the lanes due
to particle exchange between them. In this model, we have looked at two
possible scenarios with constant (flat) and non-constant bulk profiles. The
fixed point based boundary layer method provides a new perspective on several
aspects including those related to maximal/minimal current phases,
possibilities of shocks under very restricted boundary conditions for the flat
profile but over a wide range of boundary conditions for the non-constant
profile.Comment: 13 pages, 17 figure
Polymer collapse in miscible good solvents is a generic phenomenon driven by preferential adsorption
Water and alcohol, such as methanol or ethanol, are miscible and, individually, good solvents for poly(N-isopropylacrylamide) (PNIPAm), but this polymer precipitates in water–alcohol mixtures. The intriguing behaviour of solvent mixtures that cannot dissolve a given polymer or a given protein, while the same macromolecule dissolves well in each of the cosolvents, is called cononsolvency. It is a widespread phenomenon, relevant for many formulation steps in the physicochemical and pharmaceutical industry, that is usually explained by invoking specific chemical details of the mixtures: as such, it has so far eluded any generic explanation. Here, by using a combination of simulations and theory, we present a simple and universal treatment that requires only the preferential interaction of one of the cosolvents with the polymer. The results show striking quantitative agreement with experiments and chemically specific simulations, opening a new perspective towards an operational understanding of macromolecular solubility
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