135 research outputs found
On the Production of Flux Vortices and Magnetic Monopoles in Phase Transitions
We examine the basic assumptions underlying a scenario due to Kibble that is
widely used to estimate the production of topological defects. We argue that
one of the crucial assumptions, namely the geodesic rule, although completely
valid for global defects, becomes ill defined for the case of gauged defects.
We address the issues involved in formulating a suitable geodesic rule for this
case and argue that the dynamics plays an important role in the production of
gauge defects.Comment: 9 pages, in LATEX, UMN-TH-1028/92, TPI-MINN-92/20-
Probing shapes of microbes using liquid crystal textures
Topological defects in nematic liquid crystals are routinely investigated
using a cross-polarizer set-up in optical microscopes. Characteristic signature
of topology and structure of the defect is contained in the structure of dark
brushes emanating from the core of topological defects. Even with defect core
of size of few tens of nanometers, simple optical microscopy is able to
identify the defects using these brushes. We propose to use this property to
identify shapes of microbes embedded in a nematic liquid crystal (NLC) sample.
Assuming certain anchoring conditions for the NLC director at the surface of
the microbe, we determine the resulting shapes of brushes using numerical
simulations. Our results suggest that for asymmetrical microbes (such as
cylindrical shaped bacteria/viruses), resulting brushes may carry the imprints
of this asymmetry (e.g. the aspect ratio of cylindrical shape) at relatively
large distances to be able to be seen using simple optical microscopy, even for
microbe sizes in few tens to few hundred nanometer range. For more complicated
shapes, such as spiral shape bacterias or Filovirus such as Ebola virus, even
the topology of brushes may be non-trivial depending on the spiral
nature/folding of the virus along its length. For roughly spherical microbes,
such as the corona virus, complete symmetry of brushes can help distinguishing
from general asymmetric impurities/microbes. Further, information about the
size of a spherical microbe may possibly be probed using brush deformations
near the core in the presence of external electric/magnetic field.Comment: 12 pages, 7 figures, Electric field interaction term corrected,
discussion improved/corrected, e.g. for intensity of light in the
cross-polarizer setu
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