13 research outputs found
Phase transitions and non-equilibrium relaxation in kinetic models of opinion formation
We review in details some recently proposed kinetic models of opinion
dynamics. We discuss the several variants including a generalised model. We
provide mean field estimates for the critical points, which are numerically
supported with reasonable accuracy. Using non-equilibrium relaxation
techniques, we also investigate the nature of phase transitions observed in
these models. We study the nature of correlations as the critical points are
approached, and comment on the universality of the phase transitions observed.Comment: 11 pages, 8 eps figures, 1 table. Contribution for proceedings of
Statphys-Kolkata-VII 26-30 November, 201
Continuous transition of social efficiencies in the stochastic strategy Minority Game
We show that in a variant of the Minority Game problem, the agents can reach
a state of maximum social efficiency, where the fluctuation between the two
choices is minimum, by following a simple stochastic strategy. By imagining a
social scenario where the agents can only guess about the number of excess
people in the majority, we show that as long as the guess value is sufficiently
close to the reality, the system can reach a state of full efficiency or
minimum fluctuation. A continuous transition to less efficient condition is
observed when the guess value becomes worse. Hence, people can optimize their
guess value for excess population to optimize the period of being in the
majority state. We also consider the situation where a finite fraction of
agents always decide completely randomly (random trader) as opposed to the rest
of the population that follow a certain strategy (chartist). For a single
random trader the system becomes fully efficient with majority-minority
crossover occurring every two-days interval on average. For just two random
traders, all the agents have equal gain with arbitrarily small fluctuations.Comment: 8 pages, 6 fig
Disorder induced phase transition in kinetic models of opinion dynamics
We propose a model of continuous opinion dynamics, where mutual interactions
can be both positive and negative. Different types of distributions for the
interactions, all characterized by a single parameter denoting the fraction
of negative interactions, are considered. Results from exact calculation of a
discrete version and numerical simulations of the continuous version of the
model indicate the existence of a universal continuous phase transition at
p=p_c below which a consensus is reached. Although the order-disorder
transition is analogous to a ferromagnetic-paramagnetic phase transition with
comparable critical exponents, the model is characterized by some distinctive
features relevant to a social system.Comment: 10 pages, 5 eps fig
Preparation of Macroporous Scaffolds with Holes in Pore Walls and Pressure Driven Flows through them
Fire-Retardant, Self-Extinguishing Inorganic/Polymer Composite Memory Foams
Polymeric
foams used in furniture and automotive and aircraft seating applications
rely on the incorporation of environmentally hazardous fire-retardant
additives to meet fire safety norms. This has occasioned significant
interest in novel approaches to the elimination of fire-retardant
additives. Foams based on polymer nanocomposites or based on fire-retardant
coatings show compromised mechanical performance and require additional
processing steps. Here, we demonstrate a one-step preparation of a
fire-retardant ice-templated inorganic/polymer hybrid that does not
incorporate fire-retardant additives. The hybrid foams exhibit excellent
mechanical properties. They are elastic to large compressional strain,
despite the high inorganic content. They also exhibit tunable mechanical
recovery, including viscoelastic “memory”. These hybrid
foams are prepared using ice-templating that relies on a green solvent,
water, as a porogen. Because these foams are predominantly comprised
of inorganic components, they exhibit exceptional fire retardance
in torch burn tests and are self-extinguishing. After being subjected
to a flame, the foam retains its porous structure and does not drip
or collapse. In micro-combustion calorimetry, the hybrid foams show
a peak heat release rate that is only 25% that of a commercial fire-retardant
polyurethanes. Finally, we demonstrate that we can use ice-templating
to prepare hybrid foams with different inorganic colloids, including
cheap commercial materials. We also demonstrate that ice-templating
is amenable to scale up, without loss of mechanical performance or
fire-retardant properties
Fire-Retardant, Self-Extinguishing Inorganic/Polymer Composite Memory Foams
Polymeric
foams used in furniture and automotive and aircraft seating applications
rely on the incorporation of environmentally hazardous fire-retardant
additives to meet fire safety norms. This has occasioned significant
interest in novel approaches to the elimination of fire-retardant
additives. Foams based on polymer nanocomposites or based on fire-retardant
coatings show compromised mechanical performance and require additional
processing steps. Here, we demonstrate a one-step preparation of a
fire-retardant ice-templated inorganic/polymer hybrid that does not
incorporate fire-retardant additives. The hybrid foams exhibit excellent
mechanical properties. They are elastic to large compressional strain,
despite the high inorganic content. They also exhibit tunable mechanical
recovery, including viscoelastic “memory”. These hybrid
foams are prepared using ice-templating that relies on a green solvent,
water, as a porogen. Because these foams are predominantly comprised
of inorganic components, they exhibit exceptional fire retardance
in torch burn tests and are self-extinguishing. After being subjected
to a flame, the foam retains its porous structure and does not drip
or collapse. In micro-combustion calorimetry, the hybrid foams show
a peak heat release rate that is only 25% that of a commercial fire-retardant
polyurethanes. Finally, we demonstrate that we can use ice-templating
to prepare hybrid foams with different inorganic colloids, including
cheap commercial materials. We also demonstrate that ice-templating
is amenable to scale up, without loss of mechanical performance or
fire-retardant properties
Omniphilic Polymeric Sponges by Ice Templating
Sponges that absorb a large quantity
of solvent relative to their
weight, independent of the solvent polarity, represent useful universal
absorbents for laboratory and industrial spills. We report the preparation
of macroporous polymer sponges by ice templating of polyethylenimine
aqueous solutions and their cross-linking in the frozen state. The
as-prepared monolith is hydrophilic and absorbs over 30-fold its weight
in water. Modification of this sponge using valeroyl chloride renders
it omniphilic; viz., a modified sponge absorbs over 10-fold its dry
weight of either water or hexane. Modification using palmitoyl chloride
that has a longer chain length results in the preparation of a hydrophobic
sponge with a water contact angle around 130°, which retains
its oleophilicity underwater. The solvent absorbed in these sponges
can be simply squeezed out, and the sponges are stable to several
hundred cycles of compression. The large pore sizes of these sponges
allow rapid absorption of even high viscosity solvents such as pump
oil. Finally, we demonstrate that these sponges are also able to separate
apolar oils that are emulsified in water using surfactants. These
high porosity sponges with controllable solvophilicity represent inexpensive,
high performance universal absorbents for general solvent spills
Elastic Compressible Energy Storage Devices from Ice Templated Polymer Gels treated with Polyphenols
Design
and fabrication of rechargeable energy storage devices that
are robust to mechanical deformation is essential for wearable electronics.
We report the preparation of compressible supercapacitors that retain
their specific capacitance after large compression and that recover
elastically after at least a hundred compression–expansion
cycles. Compressible supercapacitors are prepared using a facile,
scalable method that readily yields centimeter-scale macroporous objects.
We ice template a solution of polyethylenimine in green tea extract
to prepare a macroporous cross-linked polymer gel (PG) whose walls
are impregnated with green tea derived polyphenols. As the PG is insulating,
we impart conductivity by deposition of gold on it. Gold deposition
is done in two steps: first, silver nanoparticles are formed on the
PG walls by in situ reduction by polyphenols and then gold films are
deposited on these walls. Gold coated PGs (GPGs) were used as electrodes
to deposit poly(3,4-ethylenedioxythiophene) as a pseudocapacitive
material. The specific capacitance of PEDOT coated GPGs (PGPG) was
found to be 253 F/g at 1 A/g. PGPG could be compressed and expanded
over a hundred cycles without any suffering mechanical failure or
loss of capacitative performance. The capacitance was found to be
243 F/g upon compressing the device to 25% of its original size (viz.
compressive strain = 75%). Thus, even large compression does not affect
the device performance. This device shows power and energy densities
of 2715 W/kg and 22 Wh/kg, respectively, in the uncompressed state.
The macroporous nature of PGPG makes it possible to fill the PGPG
pores with gel electrolyte. We report that the gel electrolyte filled
supercapacitor exhibited a specific capacitance of 200 F/g, which
increased by 4% upon 75% compression