2012 DETAILS
A detailed non-linear analysis of the deformation and breakup of a
perfect dielectric (PD) drop, suspended in another perfect dielectric
fluid, in the presence of a quadrupole electric field is presented
using analytical (asymptotic) and numerical (Boundary Integral)
methods. The quadrupole field is the simplest kind of an axisymmetric
non-uniform electric field. Several novel features are observed when
compared to that of a drop under a uniform electric field. The first
order analysis predicts oblate deformation for a PD-PD system when the
dielectric constant of the suspending medium is larger than that of
the drop. This is in contrast to uniform electric fields where oblate
shapes are observed only in leaky dielectric (LD-LD) systems. Prolate
shapes are observed when the drop is more polarisable, and the
deformation is larger than that for uniform fields for similar
electric capillary numbers. The steady state shapes are defined by
several higher harmonics as compared to the uniform field. The second
order analysis predicts larger prolate deformations but saturation of
oblate shapes. At large capillary numbers, prolate deformations show
breakup at all ratios of dielectric constants unlike uniform fields.
Positive and negative dielectrophoresis is observed when the drop is
placed off-center, and its translation and simultaneous deformation
under quadrupole fields is also investigated. The electro-hydrostatics
is unaffected by the viscosity ratio. However, the break-up of the
drop and the dielectrophoretic motion and deformation strongly depend
upon the viscosity ratio.
The superabsorbent polymers (SAPs) are crosslinked three-dimensional
network structures of hydrophilic polymers with an ability to absorb and
retain liquids more than 100 times of their own weight. The extremely high
liquid adsorption and retention properties of the SAPs make them suitable
for personal hygiene products such as diapers, sanitary napkins, and adult
incontinence products. The SAPs could be anionic, cationic, or amphoteric
depending on the nature and the net amount of the ionic repeat units. In
the present study we report the swelling, dye adsorption and degradation
characteristics of the anionic, cationic and amphoteric SAPs.
The effect of acrylamide content, concentration of the salt in swelling
medium, particle size on the swelling of anionic SAPs, and the effect of
crosslinking agent concentration on the swelling of the cationic SAPs has
been investigated. The effect of anionic to cationic repeat unit on the
swelling characteristics of amphoteric SAPs has also been studied.
The adsorption of cationic dyes on the anionic SAPs was carried out in the
dry as well as equilibrium swollen state of the SAPs. The cationic SAP was
employed to adsorb anionic dyes of different classes and the adsorption was
found to depend on the molecular sizes of the dyes. The amphoteric SAPs
were used to study the adsorption of an anionic and a cationic dye from the
individual dye solution as well as from the mixture of the two dyes. The
adsorption of the dyes depended on the nature and the amount of the net
charge on the amphoteric SAPs.
The degradation of the anionic and cationic SAPs was carried out in the dry
as well as in the equilibrium swollen state. The dry SAPs were subjected to
thermogravimetric analysis (TGA), while the equilibrium swollen SAPs were
subjected to photo degradation. The equilibrium swelling capacity and the
residual weight fraction of the SAPs were monitored during the photo
degradation. The SAPs degraded in two stages, wherein the swelling capacity
increased to a maximum and then subsequently decreased. The effect of
comonomer and crosslinker content on the photo degradation of the SAPs was
also investigated.
Thus, in this study, we have shown that the swelling, adsorption and
degradation characteristics can be controlled by varying the composition of
the monomers, crosslinker content and the nature of the charge on the SAPs,
Recently, the ability to create structures on micron and smaller length scales has led to the
utilization of microfluidic devices in a variety of applications. Multiphase flows provide several
mechanisms for enhancing and extending the performance of single phase microfluidic systems. The
properties of multiphase fluids are strongly dependent on their morphology, which is generated by a
combination of droplet breakup, deformation, relaxation and coalescence. When transporting complex
two-phasic fluids in microdevices, deviations from bulk behaviour can be expected if the dimensions
of the channel become comparable to the size of the dispersed phase. In order to fully understand
the underlying physics, confined shear flow is often chosen as a model flow condition for studying
morphology development. In the present work, we focus on the effects of geometrical confinement on
droplet breakup and coalescence in shear flow. The droplet dynamics have been visualized by means
of a home-built counter rotating parallel plate shear flow cell with a microscopy setup. It was
found that the effects of geometrical confinement on the critical conditions for droplet breakup
are governed by material parameters such as viscosity ratio and component viscoelasticity. In
addition, the breakup mode and resulting amount of daughter droplets are affected by these
parameters. The experimental data on droplet breakup have been used to validate phenomenological
models for droplet dynamics. In addition, numerical simulations with the Volume-Of-Fluid method
have been used to interpret the observations in blends with viscoelastic components, showing that
the viscoelastic stresses are significantly larger in confined as compared to bulk conditions. In
addition to droplet breakup, also the critical conditions for droplet coalescence are affected by
geometrical confinement. In this case, the relative position of the droplets with respect to each
other, rather than the viscosity ratio, is essential for the effects of geometrical confinement. In
order to obtain a better understanding of the forces and fluid dynamics that govern the
interactions between sheared droplets, the droplet trajectories, the time-dependent orientation
angles of the droplet doublets and the droplet deformation during the interaction process have
systematically been studied.
Classical reaction engineering has long set the foundation for a wide range of industrial processes. With the widespread application of
genomics-based analytical tools and the increasing complexity of biological information, a systems approach incorporating reaction
engineering principles has become pivotal in providing insights to biological problems. In the past decade, protein therapeutics
produced by recombinant mammalian cells has emerged as a major class of medicine. In the decades to come systems biology is poised to
drive medical innovations. This presentation will illustrate how classical reaction engineering analysis plays key roles in advancing
cellular bioprocessing and medical discovery.
Emulsions, which are drops of one liquid dispersed in another immiscible liquid, have a very
broad range of applications, including cosmetics, the food industry, and drug delivery.
Microfluidics offers a promising route to fabricate these systems. In this talk, I will discuss a
novel microfluidic technique that we developed based on electrospray in coflow geometries, to
generate drops with an average size that can be tuned in an unprecedented range, from well above
to well below the smallest geometric feature of the device. The method relies on coupling
electric and hydrodynamic forces. Using optical microscopy and high-speed imaging techniques, we
demonstrated that the device can be operated in various regimes: dripping, electro-dripping, and
an electrically controlled regime. These various regimes allow generation of drops in various
sizes compared to the tip diameter. Using the device, we also made fundamental studies on the
electric current behavior of electrospray processes and on droplet generation mechanism in
microfluidics.
Among the prominent applications of emulsions is also their use as templates for synthesis of
particles that act as drug delivery vehicles. The graft rejection problem usually encountered in
drug delivery applications is typically overcome through cell microencapsulation. Alginate, with
its excellent biocompatibility and biodegradability properties, is one of the most commonly used
biomaterials in drug delivery and tissue engineering applications. In this talk, I will focus on
a robust microfluidic platform we developed for generation of alginate micro particles and the
subsequent encapsulation of yeast cells. The technique allows for generation of surface
encapsulated alginate particles with precise control over both the particle size and yeast cell
content. The liquid core opens the possibility for encapsulation of multiple types of cells into
the alginate particles and for controlled drug delivery.
Abstract: Three of the four forces of Nature are described by
quantum YangâMills theories with remarkable precision. The fourth
force, gravity is described classically by the Einstein-Hilbert
theory. There appears to be an inherent incompatibility between
quantum mechanics and the Einstein-Hilbert theory that prevents
us from developing a consistent quantum theory of gravitation.
This talk will focus on some aspects of this incompatibility.
Although not known or appropriately recognized even 25 years ago, the natural geochemical arsenic contamination of groundwater
has now emerged as a global crisis threatening the quality of drinking water in over 50 countries. Of them, countries in South
and Southeast Asia, namely, Bangladesh, Nepal, Cambodia, Thailand, Laos, Myanmar and the eastern part of India are truly the
worst affected. Statistics abound in regard to the sufferings and deaths of thousands of human lives caused by drinking of
arsenic-contaminated water. Over 200 million people in this region with less than $2 per day earning are directly threatened
by arsenic contamination. Nearly no concerted effort has been undertaken to mitigate the arsenic crisis that has been
described as the worst natural calamity by the New York Times. This fact suggests that first, water related crisis is a
regional issue and second, crisis affecting resource-poor people is always slow to be resolved.
During the last 20 years, we, at Lehigh University in Pennsylvania, USA, have undertaken research and/or development effort
both in the laboratory and also in the field to mitigate arsenic crisis by collaborating with universities and NGOs in other
countries, namely, Cambodia, Argentina and obviously, India. Specific questions we attempted to answer are:
Can we create technologies that will economically treat arsenic-contaminated groundwater?
Is the treatment process sustainable in remote villages?
Can we safely dispose of arsenic removed in an environmentally safe manner?
Does the withdrawal of arsenic-contaminated groundwater pose any threat?
Our work has led to the development of the first reusable, polymer-based arsenic selective adsorbent that has the potential to
provide safe water at a significantly lower cost.We have validated a simple-to-operate technology to safely contain
arsenic-laden sludge in an environmentally sustainable manner. Also, use of appropriate technology has transformed arsenic
crisis into an engine for economic growth in many affected areas. Details will be presented.The work is currently underway to
address fluoride contaminated groundwater in Asia and Africa.
Multifunctional supramolecular polymer networks and gels are employed in several areas including biotechnology,
nanotechnology and microelectronics. For example, self-healing polymers composed of di- and tri-functional groups
(Cordier et al., 2008) find applications in construction, cosmetics, electronics and medicine. Furthermore, block
copolymer lithography has applications in semiconductor design (Tang et al., 2008).
This talk will present a field-theoretic model of polymer networks and gels composed of reactive multifunctional
monomeric units. Two examples are presented to illustrate the application of self-consistent field theory in
determining equilibrium structures arising from reactions among multifunctional monomers. In the first case, network
formation and gelation in a confined system of single-component multifunctional monomers is considered. In the second
case, microstructures arising from copolymerization reactions in a binary system of multifunctional monomers are
investigated. Morphologies arising from copolymerization may range from homogeneous disordered morphologies to
ordered microstructures such as lamellae, wherein the distinct constituents assemble into alternating layers. The
goal of this work is to enable the rational design of polymer materials with desirable properties, based the a priori
prediction of microstructures resulting from selected monomeric constituents.
Towards accelerating the pace of tissue engineering research, we are
developing combinatorial and high-throughput (CHT) technologies to
identify optimal biomaterial properties to maximize tissue generation.
Previously-developed CHT methods utilize a 2D planar cell culture format
that is not representative of the 3D tissue environment in vivo and cells
are sensitive to topographical differences between 2D surfaces and 3D
scaffolds. Thus, we have designed CHT platforms to prepare tissue scaffold
libraries where cells are presented to biomaterials in 3D format.
Specifically, we have measured osteoblast and bone marrow-derived
mesenchymal stem cell response to physical and chemical properties of
hydrogel and plastic scaffolds for bone tissue generation. These methods
enable systematic measurement of cell response to biomaterials in a
physiologically-relevant 3D format.
Atomization characteristics of liquid fuel sprays are known to
significantly impact efficiency and emission formation in
combustion devices used in the aerospace, automotive and energy
sectors. The work presented in this talk is motivated by the need
to study the atomization and spray structure of high viscosity
biofuels. Laser-based diagnostic techniques such as laser
shadowgraphy, Particle/Droplet Image Analysis (PDIA) and Laser
Sheet Dropsizing (LSD) are utilized to study the atomization
characteristics, tip penetration, droplet size and fuel
concentration of pure plant oils and their blends with diesel.
Various atomization strategies such as effervescent, impinging
jet and air blast methods are explored. A constant volume high
pressure spray chamber with optical access capable of high gas
pressures and temperatures is utilized to study transient sprays
used in automotive systems. The spray characterization under
atmospheric gas pressure shows a marked difference between
conventional diesel fuel and plant oil biofuels. An interesting
and counter-intuitive observation concerning the behaviour of the
conventional plant oil spray is the presence of an intact liquid
core even at injection pressures as high as 1600 bar. This is
attributed to the very high viscosity and possible non-Newtonian
behaviour of the oil at high pressure. A new method of
simultaneously obtaining planar droplet size and quantitative
liquid fraction data indicates a higher concentration of liquid
fraction at the spray central axis for the plant oil compared to
diesel indicating potentially poor air-fuel mixing. Effervescent
atomization is shown to be very effective for such biofuels. A
novel atomization method involving impinging liquid jets along
with air blast is proposed, and is shown to yield low Sauter Mean
Diameter (SMD) values over a range of liquid viscosities
A two-component mesoscopic lattice Boltzmann (LB) model with competing
short-range attractive and mid-range repulsive interactions is presented. The
rsulting competition is shown to give rise to a very rich dynamics of the density
configuration, which exhibits several distinctive features of soft-flowing materials,
such as long-time relaxation, anomalous enhanced viscosity, ageing effects
and non-linear Herschel-Bulkley rheology[1,2]. Such kind of complex behaviour
s found to associate with a regime whereby surface tension is allowed to attain
negative values within the interface, while still preserving a small, yet positive,
global value across the entire interface [3]. In this talk, we shall present results
from numerical simulations of frustrated LB models and associated Ginzburg-
Landau phase-field equations, which help elucidating the role of a sign-changing
surface tension on the complex rheology of soft flowing materials
Binary nanoparticle superlattices or BNSL's have been a major area of research in nanotechnology for the last decade.
Conventional
lithographic techniques are limited to fabricate features only within a plane while these self-assembled structures are formed
within a given volume. Potential applications of self-assembly leading to crystalline structures include nanoelectronics,
photonics
and improving the fundamental understanding of the bottom-up approach. The present work deals with the self-assembly from a
suspension of binary nanoparticles leading to formation of crystalline structures. In particular this study looks at the
formation
of BSNL. Our goal is to generate phase diagrams for binary nanoparticle suspensions with varying charge ratios between the two
particles. Monte Carlo molecular simulations in various equilibrium ensembles are the basis for the generation of equations of
state
and calculation of free energies of the two coexisting phases. Coexistence here implies the solid-fluid thermodynamic
equilibrium
and consequently the equivalence of free energies.
The calculation framework is pretty standard for pure substances but advanced techniques need to be used for mixtures. Focal
point
of this work is the effect of charge asymmetry on the formation and stability of BNSL's from the binary suspension. There are
six
phase diagrams for charge ratios of 0, - 0.2, -0.4, -0.6, -0.8 and -1.0. The variables are the reduced pressure and the mole
fraction. From the results, it is clear that symmetric mixtures are favorable for the formation of superlattice structures while
charge asymmetry gives rise to solid solutions
A brief overview on process modeling concepts is presented with four examples. Two examples are given for modeling for
understanding the processes. These include (i) the analysis of catalyst deactivation kinetics and (ii) prediction of both the
radial and axial concentration of catalyst in a bubble column slurry contactor. The experimental study is given for the second
problem. The basics of modeling for controller design are given for a fast breeder nuclear reactor and for a pH process. The
steps involved are presented for the development of bilinear model and Wiener model. The results of experimental implementation
of the linear PI and nonlinear PI controllers are provided for a pH process
Metal-organic coordination frameworks (MOFs) are a new class of storage materials with low density
and high specific
area and have promising applications in gas (H2, CH4, CO2) storage properties.1 Hydrogen is a very
small molecule
with a low polarizability and the corresponding van der Walls interaction is not so effective for
large amount of
storage via physisorption in the porous frameworks.2 To maintain high capacity hydrogen or carbon
dioxide storage in
a porous material at ambient condition, one needs strong interactions (heat of adsorption (Delta
H)) between the pore
surfaces and hydrogen or carbon dioxide molecules. For this purpose we have adopted different
strategies, like MOFs
with unsaturated metal sites, introduction of alkali metal sites or polar hetero-atoms on the pore
surface and
framework interpenetration to increase the heat of adsorption.2-5 My presentation will be focussed
on different
aspects of gas storage in porous metal-organic frameworks.
(1) J. L. C. Rowsell, O. M. Yaghi, Angew. Chem. Int. Ed. 2005, 44, 4670
(2) P. Kanoo, K. L. Gurunatha, T. K. Maji, J. Mater. Chem. 2010, 20, 1322.
(3) P. Kanoo, R. Matsuda, M. Higuchi, S. Kitagawa, T. K. Maji, Chem. Mater. 2009, 21, 5860.
(4) S. Mohapatra, K. P. S. S. Hembram, U. Waghmare, T. K. Maji, Chem. Mater. 2009, 21, 5406.
(5) A. Hazra, P. Kanoo, T. K. Maji, Chem. Commun., 2011, 47, 538
Replicating "life-like" characteristics in man-made systems is a great challenge in science and
engineering. Through
the careful integration of soft materials and chemistry, researchers have recently devised
chemo-responsive polymer
gels that autonomously oscillate in the absence of any external stimuli. The soft polymeric
material of the gel
allows it to bend, stretch and change its shape in a manner analogous to living creatures. The
chemistry, on the
other hand, makes these gels self-powered by virtue of the oscillatory Belousov-Zhabotinsky (BZ)
chemical reaction.
Driven by the periodic oxidation and reduction of the ruthenium (Ru) catalyst, which is grafted to
the polymer
network, these BZ gels swell and de-swell and thereby, transduce chemical energy into mechanical
response. The BZ
reaction, however, is photo-sensitive with light of a certain wavelength suppressing the
oscillations within the gel.
We demonstrate that the interplay between the chemo-responsive gels and the photosensitive reaction
can cause mm
sized BZ gels to exhibit autonomous, directed motion or reorientation away from the light. Using
our recently
developed three-dimensional gel lattice spring model we show that these synthetic BZ "worms"
display a fundamental
biomimetic behavior: movement away from an adverse environmental condition, which in the context of
the BZ reaction
is the presence of light. Furthermore, we exploit this property to control the self-sustained
motion of macroscopic
BZ gel "worms". By tailoring the arrangement of illuminated and non-illuminated regions, we direct
the movement of
these worms along complex paths, guiding them to bend, reorient and turn. In particular, these gels
can make both 900
and U-turns. Moreover, the path and the direction of the gel's motion can be dynamically and
remotely reconfigured
(as opposed to being fixed, for example, by a pattern on an underlying surface). We also perform
stability analysis
to establish broad guidelines that would yield the desired motion of the gel. Our findings can be
utilized to design
intelligent, autonomously moving "soft robots" that can be reprogrammed "on demand" to move to a
specific target
location and to remain at this location for a chosen period of time.
A dominant dogma in neuroscience literature is that the cellular basis for learning and memory resides in the synaptic
junctions that connect ne
urons. However, recent research into single neuron function has made it abundantly clear that there is more to learning
and memory than modifica
tions to synaptic junctions. Specifically, proteins called voltage-gated ion channels present on neuronal membrane have
also been shown to under
go modifications in response to learning-induced activity patterns, and contribute to how information is stored and
processed in neurons and the
ir networks. This talk will provide an introduction to this fascinating field of intrinsic plasticity, as it is
referred to as, and explore cert
ain theoretical and experimental questions related to the way forward.
Surface modification has wide ranging implications in lubrication,
microelectromechanical
systems (MEMS), colloidal systems and biological membranes.
Surface modification plays an important role in stabilizing gold nanoparticles, which
have
applications in targeted drug delivery, and catalysis. A variety of surface modification
techniques are used for controlling corrosion and wettability, as well as used
extensively
to understand the nature of interactions between surfaces. This thesis is mainly focused
on
understanding the kinetics, film growth and surface modification by long chain molecules
physisorbed on a surface.
The time evolution of the growth and domain formation of octadecylamine film on a mica
surface is studied using ex-situ AFM and reflectance FTIR. A novel technique of
interface
creation is developed to measure the height of the adsorbed film. The results show three
distinct regions of film growth mechanism. Region I, corresponds to the thin film and
the
interface height is in the monolayer regime. The transient regime (II) consists of a
sharp
increase in the film thickness where the film thickness increases from 1.5 nm to 25 nm
within a time span of 180 s. In the final stage of film growth the film thickness is
invariant with time, during which domain coarsening is observed. Domain evolution
reveals a
non-monotonic variation in the domain size as a function of adsorption time. A three
stage
mechanism is proposed to explain the domain evolution on the surface.
In order to explain the observed film thickness data, we have developed a model to
explain
the thin to thick film transition observed in the AFM experiments. The 1D diffusion
equation
across a thin liquid film adjacent to the planar mica surface is solved to obtain the
evolution of the adsorbed film. The model with a two-site adsorption isotherm
quantitatively
captures the thin to thick film transition observed in the AFM experiments. The
statistical
thermodynamics of adsorption of long chain molecules on a surface has been studied using
a
lattice model. The molecules are characterized by backbone chain either lying parallel
or
perpendicular to the surface. A square lattice with nearest neighbour interactions and a
mean field approximation are used to generate the adsorption isotherms for different
molecules as a function of chain length. The molecules change their orientation from a
surface parallel to an upright configuration with an increase in chemical potential. A
similar transition (with time) in the molecular orientation has been observed in the AFM
experiments. The transition between these two orientations is accompanied by an entropy
maximum.
The last part of the thesis is concerned with carbon-carbon interactions. More
specifically,
we are interested in the interactions between graphite surfaces and their modification
in
the presence of a lubricant or base oil. Diamond like carbon (DLC) AFM tips and highly
oriented pyrolitic graphite (HOPG) has been used for this study. Experiments were
carried
out by treating HOPG graphite in hexadecane oil at different temperatures. It is
observed
that pull-off forces on bare graphite are smaller when compared to the treated surface.
The
magnitude of the pull-off forces increases with the temperature of the hexadecane oil
bath.
Presence of charged patches responsible for the higher adhesion has been confirmed using
surface potential microscopy. Results also confirm the presence of a thin liquid-like
hexadecane film at room temperature.
In this work, a model for friction between a block of an elastomer, and a hard surface is
proposed. The model uses population balance of the bonds between the hard surface and the
polymer
chains of the soft solid, to estimate the frictional stress. Although the basic premises of
the
present model are the same as those of the Schallamach model for dynamic friction (Wear,
1963),
the present formulation is a clearer representation of the phenomena involved. It also allows
us
to point out an error in the expression for the steady dynamic friction stress in the
Schallamach
model. We also show that our expression is equivalent to that obtained by Chernyak and Leonov
(Wear, 1986) model which is based on the ergodic hypothesis. The model is further modified to
account for both the non-Hookean extension of the bonded chains and the viscous retardation
effect. The model is validated using the experimental data of Vorvolakos and Chaudhury
(Langmuir,
2003) on sliding of crosslinked PDMS solid on silane coated glass surface. From this
analysis,
scaling laws, which relate the model parameters to the molecular weight of the polymer chains
and
the temperature, are derived and justified.
The model has also been extended for estimating the force required to initiate sliding of a
soft
solid on a hard surface. The model predicts that under certain range of the pulling velocity,
shear strength varies as the logarithm of the pulling velocity, as well as the logarithm of
the
aging time. These results are in confirmation with the experiments.
Some results of the work initiated in our laboratory on friction between gelatin hydrogel and
glass surface have been presented. Especially, the results on stress relaxation after sudden
stoppage of a steadily sliding solid block have been discussed in the light of the present
model.
After a general introduction on the subject, we discuss the
different models of the literature concerning rheology of
microswimmer suspensions: a new class of complex fluid. We
evaluate these models results and compare them to experiments done
in our lab on suspensions of chlamidomonas: a green alga. We show
the pecularities of these algae in a shear flow and we elaborate a
new model.
Chemical Engineers make critical contributions in discovery and
development of life-saving medicines. Process engineers develop
safe, scalable, environmentally friendly, and economical processes
of molecules with high degree of complexity. Formulation
engineers study material properties and their impact on processes
to produce drug products with high degree of content uniformity.
Understanding of material properties and how they impact drug
product performance is critical for development of robust
processes. One of the important facets of material properties is
polymorphism, that is, same chemical entities packing in different
crystal forms. This talk will highlight broad areas of
contributions by chemical engineers in the pharmaceutical industry
and through a case study elaborate on how understanding of
thermodynamics and kinetics of crystal forms impacts drug
development.
Trace the evolutionary path of process control from simple On/Off
control
to Multivariable Predictive control.Outline how the developments
that took
place in control system hardware facilitated the development of
Process
control technology.
Drying colloidal dispersions exhibit fascinating arrays of cracks.
The tensile stress induced by the capillary pressure is
responsible for the cracking. Presence of flaws or defects in the particle bed
determines its ultimate strength under such circumstances.
Here, we present the asymptotic stress distribution around a flaw in a two dimensional colloidal
packing
saturated with liquid and compare the results
with those obtained from the full numerical solution of the
problem. These predictions are complimented by experiments where
the stress required to fracture a colloidal packing saturated with
solvent under axial tension varies inversely with the three-half
powers of the size of the packing. The predicted critical stress required to initiate cracks from
flaws shows the same scaling with flaw size. Close inspection of
the failed sections of the packing revealed flaws entrapped during the drying process
and of size that varied linearly with diameter. Interestingly,
the maximum capillary pressure sets the maximum possible tensile
stress and therefore a critical flaw size below which the crack will not nucleate, thereby giving the
ultimate strength of the colloidal packing.
The experiments show that if the flaw size can be restricted below the critical
value, large colloidal packings free of cracks can be synthesized.
Micron-sized polymeric particles find a variety of
applications in biotechnology and novel materials. Microfluidic
methods to synthesize such polymeric particles have recently gained
wide prominence. These methods provide the ability to design
microparticles with particular shapes, sizes and asymmetrical chemical
compositions. I will present one prominent method called Stop Flow
Lithography. It enables the synthesis of particles with any 2-D
extruded shape and containing up to 7 different chemical moieties.
The inhibition of free radical reactions in ambient conditions is
responsible for the ease of fabrication and particle recovery in this
method. A transport model that predicts particle height in such
conditions is presented. At Achira Labs, my current company, we are
using such particles for developing a low-cost platform for medical
diagnostics. Some features of this platform will also be presented.
High-resolution implicit discretization schemes which consider as
unknowns, at each discretization point, not only the value of a
function, but also those of its first or higher derivatives have
recently attracted much attention due to their ability to resolve
a wide range of length scales at relatively low computational
expense. However, their application to practical fluid flow
problems has been limited to low orders of accuracy due to the
instability of high-order boundary closures. A novel approach of
alleviating the instability associated with the high-order
boundary closures, through their use on a non-uniform grid, with
clustering of nodes at the boundary of the computational domain
will be presented. The stability and accuracy of this technique
will be demonstrated through simulations of compressible and
incompressible viscous flows in three dimensions. Extension of
this technique to simulate multi-dimensional flows in complex
geometries using domain decomposition will be discussed.
Graphene, a single layer of carbon atoms arranged in a honeycomb lattice, has been the
focus of recent research, due to its unique zero-gap electronic structure, which leads to
massless charge carriers. Functionalization offers a novel way to modify the electronic
and magnetic properties of graphene. Specific topology is essential to achieve devices
with the desired features. Using density functional theory, we demonstrate stability of
several such configurations, (in single and double sided functionalized graphene) and
analyze their electronic and magnetic properties. We show that "nanoroads" and "quantum
dots" of pristine graphene can be carved in the electrically insulating matrix of fully
hydrogenated carbon sheet (graphane). Designing magnetic, metallic, and semiconducting
elements within the same mechanically intact sheet of graphene presents a new opportunity
for applications. Furthermore, owing to their ability to bind hydrogen both by
physisorption and chemisorption, graphitic structures can satisfy the required binding
energy criterion for a cost-effective, safe, and efficient storage medium.
Efforts towards understanding the size-structure-property correlation for nanoscale entities
have gained importance in recent years. In case of nano-sized features, large surface area and
differences in the atomic coordination and chemistry of surfaces significantly alters the
surface energy of a system. The changes in surface energy produce substantial differences in
properties between nanoparticles and their bulk counterparts for similar compositions. One
interesting structural change at nanoscale is the formation of solid-solution between elements
which at bulk scale show miscibility gap. The tendency towards retaining a single phase
microstructure can be due to two different effects that must be understood precisely. They are;
(a) high surface curvature at smaller sizes enhancing the solid solubility through
Gibbs-Thompson effect and (b) decrease in the driving force for the nucleation and growth of
second phase within a small sized particle. This talk will focus on the diminishing miscibility
gap in Ag-Ni nanoparticles. Ag-Ni system is characterized by large difference in atomic sizes
(14%) and a positive heat of mixing (+23KJ/mol). The binary equilibrium diagram for this system,
therefore, exhibits a large miscibility gap both in solid and liquid state. This work explores
the size dependent changes in microstructure and the suppression of miscibility gap that occurs
when free alloy particles of nanometer size are synthesized by co-reduction of Ag and Ni metal
precursors. Complete mixing between Ag and Ni atoms could be achieved for smaller size
nanoparticles (size less than 7 nm). These particles exhibit a single phase solid solution with
fcc structure. With increase in size, the nanoparticles revealed two distinct regions. One of
the regions is composed of pure Ag. This region partially surrounds a region of fcc solid
solution at early stage of decomposition. In this work, experimental observations were compared
with the results obtained from the thermodynamic calculations which compared the free energies
corresponding to a physical mixture of pure Ag and Ni phases and a fcc Ag-Ni solid solution for
different particle sizes. Results from the theoretical calculations revealed that for Ag-Ni
system, solid solution was energetically preferred over the physical mixture configuration for
particle sizes of 7 nm and below. The experimentally observed two phase microstructure for
larger particles was thus primarily due to the growth of Ag rich regions epitaxially on
initially formed small sized fcc Ag-Ni nanoparticles.
The molecular sieving of isotopes has for long been considered impossible, as they are of
essentially identical size and shape; however, in recent years this perspective has been
modified with respect to hydrogen and its isotopes. It is now recognized that, because of their
low mass, quantum effects can lead to sufficiently large differences in their de Broglie
wavelengths at cryogenic conditions to make their molecular sieving possible in nanoporous
materials having pores of molecular dimension. Whilst the majority of the attention has focused
on their adsorption equilibrium, our recent theoretical work, based on molecular dynamics
simulations employing the Feynman-Hibbs path integral formulation, has shown even more
remarkable effects on diffusion, with the heavier isotope deuterium diffusing faster than
hydrogen at sufficiently low temperatures in microporous zeolite rho as well as
alumino-phosphate AlPO4-25. Here we will report the first microscopic experimental verification
of this interesting effect, as well as our extensive theoretical studies employing both the
Feynman-Hibbs and more accurate path integral approaches.
Microscopic Quasi-Elastic Neutron Scattering experiments have been conducted to determine the
diffusivities of hydrogen and deuterium over a wide temperature range in a microporous carbon
having sufficiently narrow nanopores. These measurements clearly demonstrate cross-over of the
diffusivities at about 100 K, with deuterium showing larger broadening of the energy spectrum
and diffusing faster below this temperature. This value is in remarkable accord with that from
the simulations with other materials discussed above, despite the approximation inherent to the
Feynman-Hibbs approach. The molecular mechanism for this phenomenon is also examined by
simulation of the self-diffusivity of H2 and D2 in various carbon models using equilibrium
molecular dynamics incorporating quantum effects. Equilibrium calculations using path integral
Monte Carlo simulations have also been conducted for this carbon, and together with our
molecular dynamics simulations provide the necessary ingredients for analyzing the feasibility
of kinetic molecular sieving in this carbon. The results of these studies will be reported.
Photo-initiated reactions involve the use of ultraviolet (UV) or visible radiation as sources
of energy to effect chemical transformations. The present research work deals with both the UV
and visible light initiated reactions like the degradation of hazardous organic compounds like
dyes and phenolic compounds, reduction of toxic metal ions to their non-toxic states, selective
synthesis of cyclohexanone by the partial oxidation of cyclohexane, polymerization and
degradation of synthetic polymers. The main emphasis of all the above works was to develop
mechanistic models, based on experimental evidences, for a better understanding of the process.
Photopolymerization is an attractive route to polymerization as it involves lesser energy
compared to the conventional thermal polymerization and offers an excellent way to control the
rate of polymerization by switching on/off the UV light. This part of my talk deals with the
photopolymerization of alkyl methacrylates initiated by benzoyl peroxide in presence of
toluene. The effects of initial initiator and monomer concentrations on the time evolution of
polymer concentration, number average molecular weight (Mn) and polydispersity (PDI) were
examined. Based on the experimental observations, the mechanism of photopolymerization was
proposed, which includes the decomposition of the initiator, chain initiation, chain
propagation, intermolecular hydrogen abstraction, reversible chain addition and ?-scission, and
primary radical termination. The rate equations were derived using continuous distribution
kinetics and solved numerically to fit the experimental data. The regressed rate coefficients
were validated by comparing them with the literature data. The model predicted all the salient
features of the photopolymerization including the instantaneous increase of Mn and PDI to
steady state values.
The second part of my talk will focus on the dye sensitized degradation of phenolic compounds
like phenol, 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol in presence of
visible light using nano-TiO2 as the catalyst. A mechanism for sensitized degradation was
proposed in the form of a pyramidal network and the kinetic model for the rate of degradation
of the phenolic compound was derived using the network reduction technique. An important
outcome of the kinetic analysis employed in this work shows that the degradation rate of the
phenolic compound is first order with respect to the concentration of the phenolic compound at
sufficiently high concentrations of the dye, while the degradation rate is first order with
respect to the concentration of the dye at sufficiently high concentrations of the phenolic
compound. The intermediates that were formed during the degradation of the phenolic compounds
were traced by mass spectroscopy and a plausible pathway of degradation was established. In
totality, the encouraging results of this work show that the dye sensitized systems are
potential candidates for the effective mineralization of organic contaminants under
solar/visible radiation.
While specific-ion effects on proteins are ubiquitous in nature their underlying mechanisms
remain elusive. In dilute (<0.1 M) salt solutions, ion-protein interactions are thought to be
governed predominantly by non-specific electrostatic screening. However, using first-principles
based charge and calorimetric measurements, we provide direct evidence for preferential and
selective accumulation of anions at the protein surface even under dilute salt conditions.
Employing this framework and several case studies, we show that seemingly different
manifestations of protein insolubility, reversible self-association, and aggregation can be
caused by similar underlying ion-protein interactions.
Speaker bio-sketch
Yatin is a chemical engineer (B. Chem. Eng. UDCT; MS University of New Hampshire (UNH)) and a
biophysical chemist (MS & PhD, UNH) by academic training. Having worked with leading
pharmaceutical companies, Pfizer, Amgen, and Genentech, for the past thirteen years, Yatin has
broad exposure & expertise in protein formulation science and process development. He presently
works as an Associate Director in Late-Stage Pharmaceutical Development at Genentech. His
research interests include mechanisms of protein aggregation, thermodynamics of protein
stability & interactions, protein-co-solute interactions, and thermostable formulations.
In his free time, he enjoys spending time with his family, listening to Hindustani classical
music, cooking, and reading non-fiction.
Frontal polymerization is a technique where the front propagates in an unstirred vessel via
localized reaction zone. It propagates primarily through thermal diffusion and follows
Arrhenius reaction kinetics. It was first "discovered" by Chechilo and Enikolopyan. Frontal
polymerization resembles self propagating high temperature synthesis (SHS), a methodology
developed in ceramics. Mechanism of these processes are not well understood. In both cases
reaction is triggered by igniting the reactants at one end of the reactor and the reaction
self-propagates as a front. This presentation will deal with synthesis of homo- and copolymers
with linear as well as crosslinked structures. An accidental identification of new sub-branch,
triggered by mere addition of water, will also be discussed. The linear polymerization front
spirals forward, leaving a rich variety of patterns. These too will be presented.
Excess fluoride (F-) in drinking water poses a health threat to
millions of people around the world. In the present work, activated
alumina (AA) has been used as an adsorbent. Data obtained from batch
experiments were fitted to the (i) pseudo-first order, (ii) pseudo-second
order, and (iii) Langmuir kinetic model. Model (ii) performed better than
the other models, and fitted the data well. However, the rate constant for
adsorption k_a had to be varied as a function of the initial concentration
of F- in the liquid phase c_0. A more satisfactory approach is provided by
Langmuir model, which fitted the data reasonably even though k_a was
independent of c_0. Shreyas (2008) developed a model for the batch
adsorption of F- onto porous pellets of AA. Some errors detected in his
computer program were corrected. The parameters of the model were
estimated by fitting predictions to data. The parameter values suggest
that the adsorption process is likely to be diffusion-limited.
Column experiments were conducted as follows. The pellets were
soaked in deionized water for a time t_s before they were loaded
into columns. A feed solution having a fluoride concentration c_f = 3 mg/L
was fed to column and the concentration of F- in the exit stream c_e was
measured at regular intervals. Breakthrough was deemed to have occurred
when c_e exceeded the permissible limit (= 1 mg/L). Constant values of the bed
height H, and the empty bed contact time t_c were used in the experiments.
The volume of treated water V, scaled by the volume of the bed V_b, varied
strongly with the soaking time t_s, with a maximum at t_s = 24 h. To
understand the possible reasons for this behaviour, XRD, FESEM, and FTIR
were used to characterize the surface of AA. Though the concentrations of
the surface hydroxyl groups may influence the adsorption of F-, FTIR
studies show there is no direct correlation between V/V_b and the
concentrations of these groups. The FESEM and XRD studies indicate that
fresh AA consists mainly of boehmite, which is gradually converted to
gibbsite during soaking.
For fixed values of H and t_c, the dimensionless volume of treated
water V/V_b showed a maximum at a bed diameter D = 45 mm. This behaviour
may be caused by wall effects for small values of D and by occurrence of
quasi-static regions near the wall for large values of D. The cost of
treated of water was Rs. 0.42/L. It decreased slightly to Rs. 0.37/L after
one regeneration cycle, but increased to Rs. 0.41/L after two cycles. The
volume of treated water after two cycles was 595 L/kg of AA. The
concentration of Al3+ ions c_a in the treated water increased and exceeded
the permissible limit of 0.2 mg/L as the number of regeneration cycles
increased. The concentration of F- in regeneration effluent was in the
range 32-70 mg/L. The effluent was subjected to solar distillation,
leading to a distillate whose fluoride concentration was in the range
9-12 mg/L. The distillate can then be discharged into the public
sewers, as the permissible limit is 15 mg/L.
The visualization of the dynamic behaviour of and interactions between
immune cells using time-lapse video microscopy has an important role
in modern immunology. To draw robust conclusions, quantification of
such cell migration is required. This is far from trivial because
imaging experiments are associated with various artefacts that can
affect the estimated positions of the immune cells under analysis,
which form the basis of any subsequent analysis. We construct
spatially explicit models of T cell and DC migration in LNs and show
that several dynamical properties of T cells are a consequence of the
densely packed LN environment. Our three-dimensional simulations
suggest that the initial decrease in T-cell motility after antigen
appearance is due to "stop signals" transmitted by activated DCs to T
cells. Because imaging is typically restricted to experiments lasting
1 h, and because T cell-DC conjugates frequently move into and out of
the imaged volume, it is difficult to estimate the true duration of
interactions from contact data. We propose a method to properly make
such an estimate of the average of the contact durations. The method
is validated by testing it to our spatially explicit computer
simulations. We use these techniques to analyze the migration of
antigen specific CD8 T cells in the skin after localized infection
with herpes simplex virus.
In this I will talk about the experiments that the Physics world
magazine has chosen in a survey conducted on its readers in the year
2002. The same has been published in its magazine in one of the 2002
issues. These experiments spread from 3rd century BC to as recent as the
year1961. Most of these experiments took place on tabletops and none of
them required more computational power than that of a slide rule or
calculator. The winners were largely solo performers, involving at most
a few assistants. These experiments not only explains the fundamentals
of physics, but also opens avenues for further improvements and
investigations in developing low cost experimental tools. This talk is
aimed at creating interest in science experiments.
Amphiphilic bilayers with hydrophilic polymer chains grafted onto the
head groups are used for the stabilization of liposomes designed for
targeted drug delivery, synthesis of supported membranes, surface
modification of implanted medical devices and development of cosmetic
formulations. Understanding the influence of grafted polymers on the
phase behaviour and mechanical properties of the membrane forms the
central focus of this thesis. Using dissipative particle dynamics we
investigate the effect of polymer grafting on the melting transition
and elastic moduli of bilayers composed of single as well as two tailed
lipid molecules. A specially modified Andersen barostat is used to
maintain the bilayer at zero tension. The bilayer shows a sharp gel
to liquid crystal transition in the absence of the grafted
polymer. For single tail lipids, increasing the grafting density is
found to induce an additional interdigitated phase in the gel to
liquid crystalline transition. The occurrence of the interdigitated phase
is accompanied by an increase in the area per head group of the lipid and
grafting was found to broaden the temperature range for the gel to liquid
crystalline transition. However interdigitation was not observed in the
two tailed lipid systems. Our study shows that the grafting density can
be used to control the temperature range and occurrence of a given bilayer
phase. Changes in the area per head group and the melting transition as
a function of the polymer grafting density were found to follow the
scaling predicted by self consistent mean field theories for both single
and two tailed lipid systems. Using a parameter free representation of
the bilayer surface with Delanuay triangulation the quadratic dependence
of the bending modulus of the liquid crystalline phase with the membrane
thickness is successfully captured. Additionally we also compute the
bending modulus for the gel phase. Using a continuum theory the bending
modulus is related to the area stretch modulus of the bilayer. The bilayer
bending modulus was found to increase with an increase in the polymer
grafting density.
The talk will be review of our attempts, carried out some time ago, to look for
molecules which may exhibit interesting mechanical behavior. We have been
interested in using fluxionality to design such molecules. We use density
functional calculations to explore this possibility. We have investigated designs
for molecular wheel, rollers, rockers and rattles. Our first example is a
molecular roller, which would remain attached (chemisorbed) to a surface, but can
move on the surface rather easily by rolling. We suggest that hypostrophene
adsorbed on Al(100) surface can undergo a 'Cope like' rearrangement on the metal
surface resulting in a rolling motion of the molecule. The activation energy for
rolling is found to be low. We find that syn-tricyclooctadiene on Al(100) has a
similar activation energy. Our next example is a 'molecular wheel', on a surface.
Cyclopentadienyl, co-adsorbed with hydrogen on M(111) surface is predicted to
undergo fluxional wheel like motion. We also present results of theoretical
calculations for some [Ring]-Li+ compounds. Our results predict
[cyclononatetraenyl]- Li+ to be a molecular rattle, where the Li moves to and fro
through the nine membered anionic ring. The activation energy for such to and fro
motion is found to be very low (11.50 kcal/mol). We also present designs for a
light driven molecular motor and a new type of fluxionality.
Polymer electrolyte membrane fuel cell (PEMFC) is an electrochemical cell
that converts chemical energy of the fuel into electrical energy. The
PEMFC
consists of an anodic and cathodic catalyst layer and gas diffusion
layers
(GDL), which sandwich the proton exchange membrane (Nafion). The whole
assembly, termed as the Membrane Electrode Assembly (MEA), is the ?heart?
of
PEMFC. The performance of a fuel cell is reported in the form of
polarization curve. The current state of the art fuel cell has
catalystloading of 0.3?0.4
mg Pt/cm2 and Pt-specific power density of 0.85?1.1 gmPt/kW. The present
cost of PEMFC is Rs 13,000/kW at production rate of 500,000 units/yr. In
order to compete with the Internal Combustion engine market the PEMFC
cost
should be lowered to Rs 1500/kW. In order to address this issue the
target Pt-specific
power density should be less than or equal to 0.2 gmPt/kW and future Pt
loading in MEA should be reduced to 0.15 mg Pt/cm2MEA while maintaining
high power densities. The present work attempts to achieve the above goals by
devising a novel, nanoporous, conducting, and electro catalytically
active
membrane electrode assembly for PEMFC.
Reference:
1. Zeis, R.; Mathur, A.; Fritz, G.; Lee, J.; Erlebacher, J.
Platinum-plated nanoporous gold: An efficient, low Pt loading
electrocatalyst for PEM fuel cells, Journal of Power Sources, 165,
(2007).*
2. Santhanam, V.; Liu, J.; Agarwal, R.; Andres, R. P. Self-Assembly of
Uniform Monolayer Arrays of Nanoparticles, Langmuir 2003, 19,
7881-7887.
Patterning of materials is important in device fabrication. The growth of
science of patterning is essentially centred on some challenging issues, namely
fineness and density of the patterns, their uniformity over large area,
site-specific patterning of different materials, number of process steps,
reproducibility and stability of the patterns and so on. Several lithography
techniques have emerged in recent times, to deal with the above issues. Among
them, soft lithography techniques have become popular for large area patterning
involving minimal number of steps. During the last one decade, the technique
has been improved to produce patterns down to 0.5 µm. However, the resolution
achievable with soft lithography is still far below compared to serial
techniques such electron beam lithography or scanning probe lithography, with
which sub 10 nm patterns have been realised.
The presentation will give an overview of nanolithography with emphasis on
direct patterning involving only one or two process steps. New recipes will be
presented which essentially make use of the known chemistry of metal-organics,
but in context of electron beam and soft lithography techniques. Single source
precursors not only enable direct patterning down to 30 nm, but lead to
functional patterns important in device fabrication. The performance of some of
the fabricated devices such as Raman biochip, hydrogen sensor and CNT fuse,
will be discussed.
I will talk about recent work in our group in developing various
optical sensing systems based on low cost materials. Examples include an
all polymer optical reflectance based biosensor, measurement of angular
displacement and polarization rotation using plasmons in regular optical
compact discs and so on
The design and scale-up of chemical reactors is a problem of continuing
interest to chemical and process engineers. In spite of more than 150
years of organized effort in the chemical and petroleum industry, and the
corresponding advancements in academia and the research community, this
continues to be more of an "art" rather than a "science". Part reason for
this state of affairs is the complexities of industrial geometries that
which make scaling up of experimental observations from laboratory scale
units non-trivial. However, arguably an equally important challenge to
scale-up is the fact that while the intrinsic kinetics of the reactions is
generally scale-independent, the flow patterns and associated transport
effects (particularly in turbulent, dispersed multiphase flows) are highly
scale-dependent. In recent years, advancements in computational fluid
dynamics (CFD), particularly those related to multiphase reactors, have
opened up possibilities of making scale-up more systematic (more or less
eliminating the challenges posed by complexities in system geometry).
However, CFD does not eliminate the need for rigorous fluid mechanical
theory and experiments in the laboratory or the pilot plant, rather it
merely offers a platform where the information collected from various
scales may be integrated in a scientific manner through appropriate
closures and spatially filtered or time-averaged models. Clearly then,
there is a need to establish fluid mechanical measurement tools that have
acceptable accuracy both in the laboratory, as well as pilot plants,
demonstration plants and eventually large scale process plants. In other
words, while one may visualize a “suite” of fluid mechanical models
spanning various scales (analytical, semi-analytical and numerical models
in small laboratory scale units, as well as fine-scale CFD and perhaps
even spatially filtered CFD models for larger units), a similar suite of
experimental techniques need to be established which would allow us to
span the multi-scale fluid flow in multiphase reactors. In the
presentation, the latest developments in a measurement technique for
multiphase reactors, called Radioactive Particle Tracking (RPT), will be
discussed. The first part of the talk will discuss the technical details
leading to development of this technique, whose hardware and software has
been developed and assembled in-house in IIT Delhi. Following this,
selected case studies will be presented from gas-liquid and gas-solid
flows, including our recent attempts to push this technique to industrial
scales without sacrificing the accuracy and resolution of the technique.
Finally, some attempts for validation of this technique with discrete
element CFD modeling (DEM) will be presented.
My group is interested in how cells attain and maintain the temporarily
arrested or quiescent state typical of adult stem cells.By contrast to
proliferating cells, where the dynamic drama of DNA replication and
chromosome segregation play out, or differentiated cells, which
permanently eschew proliferation in favor of tissue-specific functions,
these "interrupted" or quiescent cells epitomise a conservative
lifestyle. The quiescence program benefits the organism in that a
reserve stem cell pool is available for future unpredictable bouts of
tissue repair, but the mechanisms by which quiescent cells prevent the
expression of tissue-specific genes are not well defined.Quiescent cells
must deploymemory mechanisms if they are to fulfil their regenerative
role- when activated, these previously dormant cells must remember their
identity as cell type-specific progenitors. Mechano-chemical signalling
pathways appear to be linked with those that control the cell cycle and
tissue-specific genes. My talk will discuss the concept of active
regulation by a multiplicity of mechanisms induced in quiescence
topromote stem cell function, with a focus on signaling regulators.
We will discuss some examples of two-person games where quantum strategies
can give better payoffs than purely classical strategies (even if the
latter are probabilistic). The examples are as follows.
(i) a coin flipping game where two people, Q and C, play in the order
Q, C, Q. It turns out that Q has a quantum strategy which always
wins regardless of the classical strategy followed by C.
(ii) a game with two questions with yes/no answers and some payoffs for
the four possible answers. The best classical strategy has a success
rate of 3/4 in the long run, but there is a quantum strategy which
has a success rate of about 0.854.
(iii) the prisoner's dilemma: this is a famous game in which one strategy
is at a Nash equilibrium while the other three strategies are Pareto
optimal. A quantum version of this game has a Nash equilibrium which
coincides with one of the Pareto optimal strategies and has a better
payoff for both players compared to the Nash equilibrium of the
classical game.
Finally, I will mention some quantum games which have been played in
Prof. Anil Kumar's lab using NMR.
I will assume some elementary knowledge of quantum mechanics
(two-state systems), but no knowledge of game theory.
References:
1. Meyer, Phys. Rev. Lett. 82, 1052 (1999)
2. Eisert, Wilkens, and Lewenstein, Phys. Rev. Lett. 83, 3077 (1999)
3. Cleve, Hoyer, Toner, and Watrous, arXiv:quant-ph/0404076
4. Landsburg, Notices of the AMS 51, 394 (2004);
available at http://www.ams.org/notices/200404/fea-landsburg.pdf
(this is a simple introduction to quantum game theory written by
an economist)
When a homogeneous binary mixture (A+B) is quenched into the de-mixing
region, the system separates into A-rich and B-rich co-existing phases
divided by interface. In this lecture, while discussing about how to
estimate the boundary of such miscibility gap, primary focus will be on
the calculation of various interfacial properties in bulk as well as
confined systems, via Monte Carlo simulation.
Photocatalysis using semiconductor catalyst such as TiO2 has emerged as a
promising technology for the removal of organic pollutants from water. The
TiO2 in anatase is found to be superior to its rutile form. Commercially
available Degussa TiO2 has been widely used as a photocatalyst. A novel
combustion synthesis technique for the synthesis of anatase TiO2 has been
developed by Prof. Hegde and coworkers (Material research center, IISc). The
catalyst synthesized by Combustion synthesis method have been shown superior
to commercial Degussa catalyst for the degradation of various organic water
pollutants.
Apart from organic pollutants, microbial contaminants are also a source of
major water contamination. Our study focuses on the potential application of
photocatalysis for the inactivation of various microorganisms using
combustion synthesized TiO2 catalysts. In this talk I will discuss the
effect of various parameters on inactivation. Immobilization of catalyst by
a simple layer by layer (LbL) technique and application of immobilized
catalyst for inactivation of *E. coli* will also be discussed.
Graphene is a new promising material for active component in flexible
electronics, with many advantages in the form of high carrier
mobility, robustness, and miniaturization. There remain however many
challanges - absence of a band gap, large scale production etc are few
of them. The nature of disorder in graphene, which scatters charge and
degrades its mobility, is still a debated topic of research. One needs
to understand the sources disorder in graphene quantitatively not only
to accelerate its application in electronics, but also to realize many
of the exotic physics of Dirac Fermions. Disorder in electronic
systems often reflets in the low-frequency noise, or the flicker
noise, that may limit the performance of a graphene-based field-effect
transistor. This is particularly important in view of the emerging
methods of realizing graphene - ranging from mechanical exfoliation
to chemical and epitaxial routes. In this talk I shall present some
recent advances in understanding electronic properties of graphene
field-effect transistors. The electrical noise in these devices not
only indicates a strong influence of the underlying substrate, but
also casts valuable insight on the quantum interference effects in
graphene at low temperatures. I shall also discuss how this could
actually reflect the band structure related properties of graphene
with increasing number of layers.
This talk will report on the behaviour of sands and sand-fine mixtures through
elemental triaxial tests. The testing programme aims to understand the stress-strain
response of sands with small percentages of fines. With this objective in sight, the
testing program involved delineating the effect of four variables: density of the
sand, percentage of fines in the sand matrix, plasticity of the fines, and the mode of
deformation only under isotropically consolidated, and static loading triaxial
conditions. Four characteristic states were identified viz. the undrained instability
state, quasi-steady state, phase transformation state and critical state.
The experimental data was analyzed in the context of the critical-state framework. The
critical state was found to be independent of the initial fabric and of the pre-shear
stress history of the sand. The critical-state friction angle increased slightly with
the addition of small percentages of angular fine-grained particles (silt). The effect
of platy particles (clays) on the sand is also studied here. This experimental program
aims to provide a well designed and complete data set for systematic understanding of
the static behavior of sands and sand-fine mixtures. This data set was also used to
calibrate a constitutive model.
This talk gives an overview of the research work being done in our lab
focusing on using "traditional" chemical engineering tools applied to
developing research areas in reaction engineering and process control.
The talk will first show the "hierarchical" framework, where
information from several models of varying complexities is used to
gain insights into operation of small-scale microreactors for
combustion and fuel processing. Computational Fluid Dynamics (CFD)
simulations are coupled with simpler models to delineate flow,
reaction and thermal effects in gas phase catalytic systems. The
scaling arguments are employed to obtain low dimensional high fidelity
models to use for control applications. Finally, the talk ends with
demonstrating the application of Approximate Dynamic Programming (ADP)
framework for control of fixed bed reactors.
The continuing trend in the electronics industry to increase the operating
speed and packing density of integrated circuits results in the need for
improved materials and fabrication processes. There are certainly many
issues and problems still to be solved for current and short-term future
technology using the conventional inorganic elemental and compound
semiconductors. An alternative to conventional electronic materials is
organic semiconductors. In particular, classes of organic materials known
as inherently conducting polymers have been investigated for electronic
device applications; and even though these materials have great promise,
many scientific and technological issues have not been sufficiently
addressed or understood. For the full exploitation of this class of
electronic materials in integrated circuits, structure-property relationship
of the polymer in addition to fabrication of high quality
electrode/conducting polymer junctions is crucial. The electronic structure
and transport properties of an ICP can be reversibly controlled. In addition
electroactive polymer nanocomposites materials as precursor to electronic
devices will also be evaluated.
Biological processes at the cellular level typically take place in highly heterogeneous environments, and
usually involve no more than a few molecules at a time; they are inherently stochastic, as a result, and
usually cannot be described by simple deterministic laws. This talk is a survey of a selected set of
problems of relevance to biology in which randomness and heterogeneity play an important part, and suggests
how the stochasticity that is intrinsic to their dynamics can be characterized and treated mathematically.
Among the problems considered are the following: dynamic disorder in single enzyme kinetics, intermittent
strand separation in DNA, anomalous escape kinetics of trapped DNA, fractional viscoelasticity in crowded
polymeric environments, and anomalous gel degradation kinetics.
We have looked at the effect of the chemical bonding structure on mean-squared optical anisotropy of
chains by statistical mechanical theory for a certain class of macromolecules in dilute solution
under unperturbed conditions, by introducing different molecular groups and atomic species at
various positions on the backbone, with a motivation to reduce the birefringence. We present
results of recent calculations on some real systems as well as some preliminary studies on model
(bead-spring coarse grained chain) homopolymers. The principal components of the optical
polarizability tensor, the number and dihedral angle values of the conformational states at single
bond and at two successive bonds, have been varied in order to mimic a wider range of conditions as
compared to our earlier studies. The longer term plan via generalized simulations using is to map
the entire range of polymeric structures encompassing homopolymers, copolymers (via Monte Carlo
using discrete states) such as alternating and statistically random, graft copolymers including
side-chains (groups). 1
Next we present our recent work in looking at aggregation and adsorption of polymers and surfactants
in solution containing surfaces, using Lattice Monte Carlo simulations. The effect of
intermolecular energies for surfactant head-group, tails and polymer chain, have been studied at
different levels of overall solution concentration in this preliminary investigation using a model
system. 2
Next, we present our recent work in which we have devised a simple new method to predict the
optical birefringence on polymer surfaces via molecular simulations. The approach was implemented
for first to amorphous polyethylene and polyethylene oxide melts as classical examples using
united-atom and atomistic models, by configurational-bias Monte Carlo (CBMC) simulations.
Structure, surface energy, and optical birefringence were estimated using a classical approach
containing bond and group polarizability tensors. 3
Acknowledgements:
1. M.L.N. Pavani (currently: graduate school, Univ. of Minnesota)
2. S. Siddharth (currently: graduate school, MIT)
3. Abhijith S. Nayak (currently: Citicorp. Inc. Financial research group, Mumbai)
A large body of work exists where the hydrodynamics of solid-gas systems is
modelled using a two-fluid model based on the kinetic-collision theory. Recent
works, aimed to validate traditional models, have shown poor agreement with
experiments when dealing with dense flow such as the flow observed in bubbling
beds. It has been shown that predictions, by employing the kinetic-collisional
theory, overestimate the bubbling bed expansion detected experimentally. This
can be attributed to the fact that kinetic-collisional models only account for
the kinetic-collisional stresses with no account of other possible contact
forces such as inter-particle cohesive or frictional forces.
In this study, experimental data obtained in a bubbling bed using Electrical
Capacitance Tomography (ECT) are compared with the predictions from a
kinetic-collisional model. Subsequently, the model is generalised, by taking
into account the effect of cohesive and frictional forces; their effect on the
flow behaviour is discussed.
Lithium based batteries are of current interest for high rate applications. Battery performance is commonly studied
using porous electrode models, and this involves a pseudo two-dimensional approach to solve the electrochemical set
of equations. In order to facilitate a one-dimensional solution, approximate solution methods for solid state
diffusion have been developed specifically for phase change electrode materials. In this work, the isotropic
shell-core model with a moving interface is used to describe the diffusion phenomenon coupled with phase change. The
asymmetric behavior between charge and discharge for cathode materials like lithium iron phosphate, which may be
attributed in part to the solid state transport, is seen to be captured reasonably well by the solid state diffusion
models at a single particle level. The effect of both transport and thermodynamic properties on the charge-discharge
behavior has been considered.
Why is it that India is unable to be the source of major industrial
innovations on a sustained basis even though it has skilled talent and a
penchant for/ jugaad/ (creative improvisation)?
I will draw on social, cultural, political, economic and managerial
arguments to explain this paradox:
Firms are the primary agents of industrial innovation. While the incentive
for innovation by firms in India has increased after economic liberalisation
began in 1991, the inputs (funding, trained people and basic research and
development) for innovation by firms have not kept pace with firms needs.
Nor has the capacity of firms to innovate.
Governments efforts to enhance the availability of inputs to the innovation
process have been ineffective because of the lack of a strategic and
integrative vision, inadequate resources, and poor implementation. I will
explain the governments shortcomings in this respect in terms of the
political economy of Indias innovation policy.
Firms have failed to build an innovation capacity because of issues of
ownership and control, and a number of deeply embedded social and cultural
barriers to innovation. These include poor teamwork, the enduring
importance of upward hierarchical progression, and a weak systems and
strategic orientation.
To overcome these problems, India needs to move from a paradigm of/ Jugaad/
one of systematic innovation. Specifically, India needs to (1) create a
critical mass of new, innovative, technology-driven firms, (2) enhance the
technological capability of existing micro, small, and medium enterprises,
(3) transform large enterprises, (4) create a new incentive system for
institutions of higher education, (5) continue and enhance the process of
dynamic reform of public R&D organisations, (6) change the structure of
government involvement in supporting industrial R&D, and (7) create
supportive societal conditions for industrial innovation.
Understanding and controlling interactions between colloids, surfactants, polymers and
their mixtures is important to design new materials and to tailor many formulations that
are used in day-to-day life. In many formulations containing two-incompatible fluids,
usually a third component, such as surfactants or particles, is added to render
compatibility. The use of colloidal particles for emulsion stabilization has been known
since the famous work of Pickering in 1907. In Pickering emulsions, particles confined to
fluid-fluid interface prevent coalescence of droplets. In this talk, effect of particle shape
on emulsion stabilization will be discussed. We show that above a critical aspect ratio,
ellipsoid stabilized emulsions formed readily, while lower aspect ratio particles of same
surface chemistry did not produce stable emulsions. To understand this effect, the
structure and rheology of two dimensional (2D) suspensions of ellipsoids is studied. The
results shed some light on the role of surface rheology of the particle film in emulsion
stabilization.
A part of the talk would also focus on surfactants, which are active ingredients in many
personal care products. Self-assembly of surfactants in solutions can lead to a number of
structures such as spherical/warm-like micelles, vesicles, planar bilayers. Vesicles are
formed as a result of self-organization of curved surfactant bi-layers into a closed soft
core-shell particle comprising fluid-core and bi-layer shell. We create metastable
nanovesicles and develop a novel methodology to characterize their properties. A
combination of techniques (SANS, viscometry, Cryo-TEM, densitometry, DLS, and SAXS)
is used to characterize the nanostructure of well-defined surfactant nano-vesicles (~ 15
nm in diameter). The method presented is demonstrated to completely characterize
metastable dispersions of paucidisperse nanovesicles, which is of considerable
importance in the quantitative estimation of nanovesicle performance in various
applications.
A fluid heated to above the critical temperature and compressed to
above the critical pressure is known as a supercritical fluid. The
densities of supercritical fluids are comparable to that of liquids,
while the viscosities and diffusion coefficients are comparable to
that of gases. This enhances the rates for diffusion controlled
reactions. The low water activity environment shifts the thermodynamic
equilibrium of hydrolytic reactions to favor synthesis. Also,
reactions in which water is a product can be driven to completion.
Since enzymes are insoluble in supercritical fluids, recovery is
straightforward. The product fractionation and purification from the
reaction mixture are accomplished by reducing the pressure in a
sequence of separators. Further, traces of the supercritical fluid on
the system will not lead to adverse effects and thus the synthesis of
food products and pharmaceuticals in supercritical fluids is
considered green. Thus enzymatic reactions in supercritical carbon
dioxide combine the advantage of biocatalysis (substrate specifity
under mild reaction conditions) and supercritical fluids (high
mass-transfer rate, easy separation of reaction products from the
solvents and environmentally benign).
Abstract- The laminar-turbulent transition in channel and pipe flows is
one of the central ideas in fluid mechanics since its discovery by
Reynolds[1]. The transition from a laminar to a turbulent flow occurs
when the Reynolds number (ρDV/μ) exceeds a critical value
(about 2100 for pipe flows). Here, ρ and μ are the fluid density
and viscosity, D is the characteristic length (pipe diameter) and
V is the average flow velocity. In microfluidic applications, where
the Reynolds number is low because the channel/pipe diameter is
small, the flow is usually in the laminar regime. In a laminar flow
with smooth streamlines, mixing occurs only by molecular diffusion,
which is much slower than turbulent diffusion. Therefore, one
encounters the engineering limitation that the rates of mass and
heat transfer are much lower than that in a turbulent flow. It has
been proposed that if the wall of the tube is made soft enough, the
transition could occur at a Reynolds number lower than the flow
through a rigid pipe. However, this has been considered infeasible
so far, because the elasticity modulus of the wall material required
(0.1 − 1kPa) is too low to be realised in practice. We report the
first experimental realisation of the instability in a flow through a
tube with flexible walls. For soft walls with elasticity modulus of
about 17 kPa, the transition Reynolds number in a flexible tube
decreases in a to less than half that for rigid tubes. This has significant
implications for flow and mixing in microchannels, as well
as for the flow dynamics in physiological flows.
The Ramdas layer or the lifted temperature minimum (LTM) refers to the preferential cooling of
near-surface air layers on calm cloudless nights. The phenomenon is counter-intuitive, and its
occurrence goes against the traditional wisdom of a night-time inversion layer close to the
ground. The typical intensity of the LTM is about 5 K, and its height ranges from 30-50 cm.
The prevailing theoretical explanation for the LTM, the VSN model, is based on an infra-red
gray flux-emissivity formulation, and predicts a large near-surface cooling due to radiative
exchanges in a homogeneous nocturnal atmosphere. We show that the model is fundamentally
inconsistent, and that the predicted cooling is spurious. The error, in fact, occurs in a wide
class of radiative models of which the VSN model is a prominent example. We propose, for the
first time, the correct flux-emissivity formulation for non-black surfaces that eliminates the
spurious cooling. An immediate consequence is that LTM can only occur in an atmosphere that is
heterogeneous on the same scales. The steep near-surface concentration gradient of aerosols
appears a likely candidate for such a heterogeneity. Preliminary evidence from lab experiments
is presented to support this hypothesis.
The beginning of last century brought in fundamental understanding of the
physical and chemical world through advances in chemistry and physics.
These advances led to technologies and products that we see around today,
including computers, communication, aircraft and satellite technologies
etc. Whereas the field of biology was mainly descriptive, with elaborate
description of the layout of cells and tissue brought about by dissection
of living system. The extensive molecular biological studies in the last
four decades have elaborated on the molecular connectivity at genetic,
protein and metabolic levels. This has resulted in the description of
complex networks in the cells which connects genotype to phenotype through
proteins, RNA and metabolites. A recent editorial in the Journal of Cell
Biology clearly enumerates the need for mathematical and quantitative
analysis of these networks for obtaining insights into the design
principles prevailing in these networks. Engineered and Physical systems
have been quantified to the level that they can be designed, operated,
controlled, optimized and diagnose faults. We can see several examples in
real life around us, such as an aircraft, World Wide Web, space travel etc
wherein robust complex systems have been designed and operated. Better
designs emerge so that the limitations and faults of the previous designs
are eliminated leading to optimization of system behavior. Biological
systems also go through such an evolution, however through the
environmental pressures for survival as proposed by Darwin. Systems
Biology attempts to decipher inherent design principles in biological
networks in an attempt to connect the genotype to phenotype. The talk will
discuss some examples studied by our group, in the metabolic, genetic and
signaling pathways.
Modeling has never been easier - or more powerful- than what COMSOL
Multiphysics offers you today. This demonstration shows you why. Your
COMSOL Multiphysics modeling guide will lead you through the work
flow, and within minutes, bring designs to life with multiphysics
simulations. Applications include fluid-structural interactions,
thermal expansion, electromagnetic-structural interactions, and more.
In addition, a hands on demonstration on PDE based modeling approach
shall be carried out addressing different features from
preprocessing, mesh generation, solving and postprocessing in COMSOL
Multiphysics.
A solid can be perfect in only one way, but imperfect in an infinite number
of ways. Add stress and the number of combinations increases even further.
The current day SiGe based computer chips are an example of how simultaneous
stress and defect control in materials can be exploited to yield improved
products. Following a brief overview of the research being done planned in
Srinivasan Raghavan's group, the talk will use GaN (GaN is the material
used in white LEDs) to illustrate stress and defect control during thin film
growth of these materials.
Abstract- The reduction in size of materials and structures imparts unique physical properties to it.
Some of these properties are used to design ultrasensitive micro and nanoscale analytical systems. For
example, reduction in size (and appropriate material properties) is responsible for the optical
properties of quantum dots; small magnetic particles provide fast diffusion kinetics, small cantilever
mass imparts high quality factor and ultrasensitive mass sensitivity, and many more. In this regard,
fabrication techniques also bring it own advantages in terms of small feature size- controlled volume
handling in nano/picoliter (or even smaller), integration to optical systems, mimicking complex
repeatable structures, and integration to lab-on-a-chip. In my research, I am exploiting such properties
of materials and fabricated structures to develop optical, electrochemical and mass based biosensors for
a variety of application ranging from food, medical, environment, to biosafety. Some of the specific
projects that I have undertaken are using MEMS based resonators for mass sensing applied to detect prion
protein (causative factor of mad-cow disease in cattles and Creutzfeldt-Jakob disease in humans),
prostate specific antigen (for prostate cancer), avian influenza virus, plant pathogens, and other
disease markers; single molecule spectroscopy for epigenetic studies; magnetic particle based diagnostic
tools for nucleic acid and antibody based assays, and fluidic channels based optical and impedance based
sensors for pathogens detection.
Water-gas shift reaction is an industrially used reaction for the
purification of syn-gas and for enriching it with hydrogen. It involves
the reaction of carbon monoxide with steam over a catalyst to give carbon
dioxide and hydrogen. Recently, much attention has been focused on this
reaction as it is one of the reactions directly involved in the generation
and purification of hydrogen. With the advent of the fuel cell technology
and increasing demands of pure hydrogen, it becomes important to explore
new catalysts which can show high conversions at low temperatures. We have
synthesized a series of noble metal-substituted compounds and tested their
activity for the water-gas shift reaction.
To have an insight into the mechanism of the water-gas shift reaction over
the synthesized catalysts, the use of spectroscopic studies was made. The
various surface species were found using X-ray photoelectron spectroscopy
and the changes in the surface composition were traced to propose the
elementary surface processes. The changes in the lattice parameters and
crystal structures along with the changes in the oxidation states of the
metal and the support were determined for proposing the mechanisms. Noble
metal impregnated catalysts were also synthesized and tested. The
spectroscopic studies showed the difference in the mechanism of the
supported catalysts depending upon the ~Qmetal-in~R and ~Qmetal-on~R support
state. For the reaction over ionically-substituted catalysts, the rate
expressions were derived and the rate parameters were estimated.
Since 65 million years ago (Ma), Earth's climate has undergone a significant
and complex evolution, the finer details of which are now known through
investigations of deep-sea sediment cores, ice core, and variety of other
proxies. This evolution includes gradual trends of warming and cooling driven
by tectonic and orbital processes. Stable isotope ratios of the life science
elements carbon, hydrogen, oxygen and nitrogen vary slightly, but
significantly in major compartments of the earth enable us to investigate the
climate of past times in order to understand how the Earth~Rs climatic system
works and how it can react to external forcing. The objective of this
presentation is to discuss our ability to reconstruct past climate owing to
the development of new sampling and measurement technologies. Key ingredients
to this progress include high precision determination of trace gas
concentrations and stable isotope ratios in samples of air, water,
rocks and soils using chromatographic and mass spectrometric techniques.
This presentation will concentrate on two problems in complex fluids,
namely collective dynamics of suspensions of self propelled particles
and the rheology of dry granular materials. In both systems,
interaction between the particles is of utmost importance.
Self propelled particles such as micro-organisms propel themselves
by using waving, undulating, or rotating motion of their flagella or cilia.
Swimming speeds range up to 250 μ ms-1 and their size lies
in the range of 1 to 200 μm. The Reynolds number based on swimming
speed and diameter of the swimmers is usually very small. We have
proposed a model for self propulsion, and incorporated the full
hydrodynamic interactions between the particles. The motion of every
particleas a function of time is tracked, and the relevant statistical
and micro structural properties is extracted. We found
interesting and unexpected aspects of the collective dynamics
reflected in the distribution of particle velocity, and the
position and orientation correlations.
The other problem is the flow of slow dense granular materials.
In this regime of flow the particles are in enduring contacts which
occur during sliding and rolling of particles relative to each other.
Such flows are quite abundant in nature (e.g. avalanches, debris flows)
and in industrial processes (flow though hoppers and bins).
The stress profiles in a static and sheared granular bed were
measured using a multi-axis force transducer. A modified Couette
device with an arrangement to fix the transducer at any vertical
position on outer cylinder, was used to study the variation of
stress with respect to height in a sheared granular material.
Our results show a dramatic change in the stress profile in the
granular bed when the material is sheared at constant rate.
The behavior differs qualitatively from that of a static granular bed,
a sheared fluid, and the predictions of all available theories for
slow granular flows. Thus, this study reveals a fundamental behavior
of sheared granular materials, which has so far not been reported
in literature
The tear film is a thin film that protects the surface of the eye. It is a multi-faceted, complex fluid consisting of a 4-6
m aqueous layer nearest the surface of the eye (containing mucins and proteins) and a 100 nm lipid layer interfaced with the
air. Meibomian lipids, secreted by Meibomian glands, are the major component of the lipid layer and consist primarily of long
chain, non-polar species such as wax esters, fatty acids and cholesterol esters. A functional lipid layer is considered one
of the major factors in promoting tear film stability and dysfunctions, such as changes in composition or excretion levels,
of this layer make the film unstable resulting in dry eye disease. At this point the physical and chemical properties that
are required for stability in the tear film are unknown. We have used a variety of techniques to explore the basic mechanical
and structural properties of Meibomian lipids. Monolayers of lipids from a number of animal models (known to have different
compositions) were studied as a function of surface pressure using an interfacial stress rheometer (ISR) and Brewster angle
microscopy (BAM) at room temperature. The lipids were quite fluid at low surface pressures and exhibited classic gel behavior
upon compression; this transition corresponded to the disappearance of hundred-micron-scale holes in the monolayer
(visualized by BAM). Overall the lipids from the different animal models behaved similarly, showing that the strong
mechanical properties of Meibum at room temperature are not necessarily sensitive to composition.
Further studies have focused on the properties of human lipids within the range of their melt transition temperature. ISR
measurements have shown the mechanical properties of Meibomian lipid monolayers to be quite responsive to temperature with
modulus values dropping by up to four orders of magnitude as the lipids are heated from 20°C to 35°C. At 37°C and high
surface pressures, BAM images of the monolayer showed inhomogeneities that were not present at room temperature; presumably
due to the inability of the lipids to pack efficiently. On the molecular scale, small angle x-ray scattering at 25°C revealed
bulk Meibum to have a high degree of crystallinity with first and second order peaks indicating order ~50 Ĺ (corresponding
with the average length of the lipid molecules). As the samples were heated the intensity of these peaks decreased and the
centers shifted to larger length scales. By 45°C the peaks disappeared. The sensitivity of these samples to temperature could
have number of interesting clinical implications. In some forms of dry eye disease the composition of Meibum is different
than in asymptomatic individuals. If the melt temperature changes significantly compared to body temperature, the expression
of lipids from the gland to the surface of the tear film and the mechanical properties of the lipid layer itself may be
modified in such a way that the film becomes unstable. Ultimately we hope to fundamentally understand these differences so
that dry eye treatments can be improved.
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