35 research outputs found
Synchronization Based Approach for Estimating All Model Parameters of Chaotic Systems
The problem of dynamic estimation of all parameters of a model representing
chaotic and hyperchaotic systems using information from a scalar measured
output is solved. The variational calculus based method is robust in the
presence of noise, enables online estimation of the parameters and is also able
to rapidly track changes in operating parameters of the experimental system.
The method is demonstrated using the Lorenz, Rossler chaos and hyperchaos
models. Its possible application in decoding communications using chaos is
discussed.Comment: 13 pages, 4 figure
Templeting of Thin Films Induced by Dewetting on Patterned Surfaces
The instability, dynamics and morphological transitions of patterns in thin
liquid films on periodic striped surfaces (consisting of alternating less and
more wettable stripes) are investigated based on 3-D nonlinear simulations that
account for the inter-site hydrodynamic and surface-energetic interactions. The
film breakup is suppressed on some potentially destabilizing nonwettable sites
when their spacing is below a characteristic lengthscale of the instability,
the upper bound for which is close to the spinodal lengthscale. The thin film
pattern replicates the substrate surface energy pattern closely only when, (a)
the periodicity of substrate pattern matches closely with the characteristic
lengthscale, and (b) the stripe-width is within a range bounded by a lower
critical length, below which no heterogeneous rupture occurs, and an upper
transition length above which complex morphological features bearing little
resemblance to the substrate pattern are formed.Comment: 5 pages TeX (REVTeX 4), other comments: submitted to Phys. Rev.Let
Dewetting of thin films on heterogeneous substrates: Pinning vs. coarsening
We study a model for a thin liquid film dewetting from a periodic
heterogeneous substrate (template). The amplitude and periodicity of a striped
template heterogeneity necessary to obtain a stable periodic stripe pattern,
i.e. pinning, are computed. This requires a stabilization of the longitudinal
and transversal modes driving the typical coarsening dynamics during dewetting
of a thin film on a homogeneous substrate. If the heterogeneity has a larger
spatial period than the critical dewetting mode, weak heterogeneities are
sufficient for pinning. A large region of coexistence between coarsening
dynamics and pinning is found.Comment: 4 pages, 4 figure
Submicrometer Pattern Fabrication by Intensification of Instability in Ultrathin Polymer Films under a Water-Solvent Mix
Dewetting of ultrathin (< 100 nm) polymer films, by heating above the glass
transition, produces droplets of sizes of the order of microns and mean
separations between droplets of the order of tens of microns. These relatively
large length scales are because of the weak destabilizing van der Waals forces
and the high surface energy penalty required for deformations on small scales.
We show a simple, one-step versatile method to fabricate sub-micron (>~100 nm)
droplets and their ordered arrays by room temperature dewetting of ultrathin
polystyrene (PS) films by minimizing these limitations. This is achieved by
controlled room temperature dewetting under an optimal mixture of water,
acetone and methyl-ethyl ketone (MEK). Diffusion of organic solvents in the
film greatly reduces its glass transition temperature and the interfacial
tension, but enhances the destabilizing field by introduction of electrostatic
force. The latter is reflected in a change in the exponent, n of the
instability length scale, {\lambda} ~h^n, where h is the film thickness and n =
1.51 \pm 0.06 in the case of water-solvent mix, as opposed to its value of 2.19
\pm 0.07 for dewetting in air. The net outcome is more than one order of
magnitude reduction in the droplet size as well as their mean separation and
also a much faster dynamics of dewetting. We also demonstrate the use of this
technique for controlled dewetting on topographically patterned substrates with
submicrometer features where dewetting in air is either arrested, incomplete or
unable to produce ordered patterns
pH-Sensitive Mebeverine Microspheres for Colon Delivery
Mebeverine hydrochloride is known to suffer from extensive first pass effect. In an attempt to improve its oral bioavailability and possibility to restrict its absorption only to the colon, mebeverine microspheres were prepared by emulsion solvent evaporation method. Four formulations were prepared with varying drug and polymer ratio. These formulations were subjected to various evaluation parameters like percent practical yield, entrapment efficiency, particle size, in vitro drug release, in vivo activity. Practical yield of the microspheres was up to 89.59% with encapsulation efficiency up to 79.4%. Scanning electron microscopy confirmed that the microsphere structures were smooth, spherical, and discrete and the particles were of the size range 200 to 300 μm. In vitro release of the drug showed biphasic release pattern with non-Fickian diffusion release in 12 h. On the basis of drug content, particle size, in vitro release and in vivo studies, formulation F-3 was found to be optimal. Antiirritable bowel syndrome activity was performed in colorectal distention in rat, which is a model for constipation-induced irritable bowel syndrome. The formulations F-2 and F-3 showed significant effect in fecal output when compared to the control as well as the marketed preparation in the constipation-induced irritable bowel syndrome in rats