960 research outputs found
A self-healable fluorescence active hydrogel based on ionic block copolymers prepared via ring opening polymerization and xanthate mediated RAFT polymerization
YesIn this work we report a facile method to prepare a fluorescence active self-healable hydrogel via incorporation of fluorescence responsive ionic block copolymers (BCPs). Ionic block copolymers were prepared via a combined effect of ring opening polymerization (ROP) of Δ-caprolactone and xanthate mediated reversible additionâfragmentation chain transfer (RAFT) polymerization. Here polycaprolactone (PCL) was modified with xanthate to prepare a PCL based macro-RAFT agent and then it was utilized to prepare block copolymers with cationic poly(2-(methacryloyloxy)ethyltrimethyl ammonium chloride) (PCL-b-PMTAC) and anionic poly(sodium 4-vinylbenzenesulfonate) (PCL-b-PSS). During the block formation, the cationic segments were randomly copolymerized with a trace amount of fluorescein O-acrylate (FA) (acceptor) whereas the anionic segments were randomly copolymerized with a trace amount of 9-anthryl methylmethacrylate (AMMA) (donor) to make both the segments fluorescent. The block copolymers form micelles in a DMFâ:âwater mixture (1â:â4 volume ratio). The ionic interaction of two BCPs was monitored via Förster resonance energy transfer (FRET) and zeta potential measurements. The oppositely charged BCPs were incorporated into a polyacrylamide (PAAm) based hydrogel that demonstrated self-healing behavior and is also highly fluorescent.IIT Kharagpur and MRC (MR/N501888/2
Role of Initial Data in Higher Dimensional Quasi-Spherical Gravitational Collapse
We study the gravitational collapse in ()-D quasi-spherical Szekeres
space-time (which possess no killing vectors) with dust as the matter
distribution. Instead of choosing the radial coordinate `' as the initial
value for the scale factor , we consider a power function of as the
initial scale for the radius . We examine the influence of initial data on
the formation of singularity in gravitational collapse.Comment: 7 Latex Pages, RevTex Style, No figure
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A muscle mimetic polyelectrolyteânanoclay organicâinorganic hybrid hydrogel: its self-healing, shape-memory and actuation properties
yesHere in, we describe a non-covalent (ionic interlocking and hydrogen bonding) strategy of self-healing in a covalently crosslinked organic-inorganic hybrid 15 nanocomposite hydrogel, with special emphasize on it's improved mechanical stability. The hydrogel was prepared via in-situ free radical polymerization of sodium acrylate (SA) and successive crosslinking in the presence of poly(2-(methacryloyloxy)ethyl trimethyl ammonium chloride) (PMTAC) grafted cationically armed starch and organically modified montmorillonite (OMMT). This hydrogel shows stimuli triggered self-healing following damage in both neutral and acidic solutions (pH=7.4 and pH=1.2). This was elucidated by tensile strength and rheological analyses of the hydrogel segments joined at their fractured points. Interestingly this hydrogel can show water based shape memory effects. It was observed that the ultimate tensile strength (UTS) of the self-healed hydrogel at pH = 7.4 was comparable to extensor digitorum longus (EDL) muscle of the New Zealand white rabbit. The as synthesized self-healable hydrogel was found to be non-cytotoxic against NIH 3T3 fibroblast cells.Medical Research Council (MRC (MR/N501888/2)
Failure due to fatigue in fiber bundles and solids
We consider first a homogeneous fiber bundle model where all the fibers have
got the same stress threshold beyond which all fail simultaneously in absence
of noise. At finite noise, the bundle acquires a fatigue behavior due to the
noise-induced failure probability at any stress. We solve this dynamics of
failure analytically and show that the average failure time of the bundle
decreases exponentially as the stress increases. We also determine the
avalanche size distribution during such failure and find a power law decay. We
compare this fatigue behavior with that obtained phenomenologically for the
nucleation of Griffith cracks. Next we study numerically the fatigue behavior
of random fiber bundles having simple distributions of individual fiber
strengths, at stress less than the bundle's strength (beyond which it fails
instantly). The average failure time is again seen to decrease exponentially as
the stress increases and the avalanche size distribution shows similar power
law decay. These results are also in broad agreement with experimental
observations on fatigue in solids. We believe, these observations regarding the
failure time are useful for quantum breakdown phenomena in disordered systems.Comment: 13 pages, 4 figures, figures added and the text is revise
On spin-1 massive particles coupled to a Chern-Simons field
We study spin one particles interacting through a Chern-Simons field. In the
Born approximation, we calculate the two body scattering amplitude considering
three possible ways to introduce the interaction: (a) a Proca like model
minimally coupled to a Chern-Simons field, (b) the model obtained from (a) by
replacing the Proca's mass by a Chern-Simons term and (c) a complex
Maxwell-Chern-Simons model minimally coupled to a Chern-Simons field. In the
low energy regime the results show similarities with the Aharonov-Bohm
scattering for spin 1/2 particles. We discuss the one loop renormalization
program for the Proca's model. In spite of the bad ultraviolet behavior of the
matter field propagator, we show that, up to one loop the model is power
counting renormalizable thanks to the Ward identities satisfied by the
interaction vertices.Comment: 14 pages, 5 figures, revte
Tachyon Kinks in Boundary String Field Theory
We study tachyon kinks with and without electromagnetic fields in the context
of boundary string field theory. For the case of pure tachyon only an array of
kink-antikink is obtained. In the presence of electromagnetic coupling, all
possible static codimension-one soliton solutions such as array of
kink-antikink, single topological BPS kink, bounce, half kink, as well as
nonBPS topological kink are found, and their properties including the
interpretation as branes are analyzed in detail. Spectrum of the obtained kinks
coincides with that of Dirac-Born-Infeld type effective theory.Comment: LaTex, 29 pages, 17 Figure
Elementary excitations of trapped Bose gas in the large-gas-parameter regime
We study the effect of going beyond the Gross-Pitaevskii theory on the
frequencies of collective oscillations of a trapped Bose gas in the large gas
parameter regime. We go beyond the Gross-Pitaevskii regime by including a
higher-order term in the interatomic correlation energy. To calculate the
frequencies we employ the sum-rule approach of many-body response theory
coupled with a variational method for the determination of ground-state
properties. We show that going beyond the Gross-Pitaevskii approximation
introduces significant corrections to the collective frequencies of the
compressional mode.Comment: 17 pages with 4 figures. To be published in Phys. Rev.
Natural Orbitals and BEC in traps, a diffusion Monte Carlo analysis
We investigate the properties of hard core Bosons in harmonic traps over a
wide range of densities. Bose-Einstein condensation is formulated using the
one-body Density Matrix (OBDM) which is equally valid at low and high
densities. The OBDM is calculated using diffusion Monte Carlo methods and it is
diagonalized to obtain the "natural" single particle orbitals and their
occupation, including the condensate fraction. At low Boson density, , where and is the hard core diameter, the condensate is
localized at the center of the trap. As increases, the condensate moves
to the edges of the trap. At high density it is localized at the edges of the
trap. At the Gross-Pitaevskii theory of the condensate
describes the whole system within 1%. At corrections are
3% to the GP energy but 30% to the Bogoliubov prediction of the condensate
depletion. At , mean field theory fails. At , the Bosons behave more like a liquid He droplet than a trapped Boson
gas.Comment: 13 pages, 14 figures, submitted Phys. Rev.
Effects of columnar disorder on flux-lattice melting in high-temperature superconductors
The effect of columnar pins on the flux-lines melting transition in
high-temperature superconductors is studied using Path Integral Monte Carlo
simulations. We highlight the similarities and differences in the effects of
columnar disorder on the melting transition in YBaCuO
(YBCO) and the highly anisotropic BiSrCaCuO (BSCCO) at
magnetic fields such that the mean separation between flux-lines is smaller
than the penetration length. For pure systems, a first order transition from a
flux-line solid to a liquid phase is seen as the temperature is increased. When
adding columnar defects to the system, the transition temperature is not
affected in both materials as long as the strength of an individual columnar
defect (expressed as a flux-line defect interaction) is less than a certain
threshold for a given density of randomly distributed columnar pins. This
threshold strength is lower for YBCO than for BSCCO. For higher strengths the
transition line is shifted for both materials towards higher temperatures, and
the sharp jump in energy, characteristic of a first order transition, gives way
to a smoother and gradual rise of the energy, characteristic of a second order
transition. Also, when columnar defects are present, the vortex solid phase is
replaced by a pinned Bose glass phase and this is manifested by a marked
decrease in translational order and orientational order as measured by the
appropriate structure factors. For BSCCO, we report an unusual rise of the
translational order and the hexatic order just before the melting transition.
No such rise is observed in YBCO.Comment: 32 pages, 13 figures, revte
Direct construction of the effective action of chiral gauge fermions in the anomalous sector
The anomaly implies an obstruction to a fully chiral covariant calculation of
the effective action in the abnormal parity sector of chiral theories. The
standard approach then is to reconstruct the anomalous effective action from
its covariant current. In this work we use a recently introduced formulation
which allows to directly construct the non trivial chiral invariant part of the
effective action within a fully covariant formalism. To this end we develop an
appropriate version of Chan's approach to carry out the calculation within the
derivative expansion. The result to four derivatives, i.e., to leading order in
two and four dimensions and next-to-leading order in two dimensions, is
explicitly worked out. Fairly compact expressions are found for these terms.Comment: 19 pages, revtex, no figures. Writing improved. (Refers to
arXiv:0807.1696.
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