17 research outputs found
Diffusion Limited Aggregation with Power-Law Pinning
Using stochastic conformal mapping techniques we study the patterns emerging
from Laplacian growth with a power-law decaying threshold for growth
(where is the radius of the particle cluster). For
the growth pattern is in the same universality class as diffusion
limited aggregation (DLA) growth, while for the resulting patterns
have a lower fractal dimension than a DLA cluster due to the
enhancement of growth at the hot tips of the developing pattern. Our results
indicate that a pinning transition occurs at , significantly
smaller than might be expected from the lower bound
of multifractal spectrum of DLA. This limiting case shows that the most
singular tips in the pruned cluster now correspond to those expected for a
purely one-dimensional line. Using multifractal analysis, analytic expressions
are established for both close to the breakdown of DLA universality
class, i.e., , and close to the pinning transition, i.e.,
.Comment: 5 pages, e figures, submitted to Phys. Rev.
Synthesis of Nanocomposites Using Glasses and Mica as Templates
Various nanocomposites were synthesized using either a silica-based glass or mica crystallites as
the medium. In some cases by an oxidation or a sulfidation treatment a core-shell nanostructure could be generated.
Iron–iron oxide core-shell structured nanocomposites exhibited excellent humidity sensing behaviour.
Gold–gold sulfide core-shell nanorods exhibited a number of optical absorption peaks which arose because of
their structural characteristics. Nanoparticles of silver and silver oxide could be aligned in a polymethylmethacrylate
film by an a.c. electric field of 1 MHz frequency. The composites showed large sensitivity to relative
humidity. Lead sulfide nanowires of diameter, 1â‹…2 nm, were grown within the nanochannels of Na-4 mica.
These exhibited a semiconductor to metal transition at around 300 K. This arose because of high pressure
generated on the nanowires. Copper sulfide nanowires grown within the Na-4 mica channels showed metallic
behaviour. Silver core–silver orthosilicate shell nanostructures developed within a silicate glass medium
showed discontinuous changes in resistivity at some specific temperatures. This was explained as arising due
to excitation of Lamb modes at certain pressures generated because of thermal expansion mismatch of the
core and the shell phases. Optical properties of iron core–iron oxide shell nanocomposites when analysed by
effective medium theory led to the result of a metal non-metal transition for particle diameters below a critical
value. Similar results were obtained from optical absorption data of silver nanoparticles grown in a tetrapeptide
solution