469 research outputs found
Topological defect launches 3D mound in the active nematic sheet of neural progenitors
Cultured stem cells have become a standard platform not only for regenerative
medicine and developmental biology but also for biophysical studies. Yet, the
characterization of cultured stem cells at the level of morphology and
macroscopic patterns resulting from cell-to-cell interactions remain largely
qualitative, even though they are the simplest features observed in everyday
experiments. Here we report that neural progenitor cells (NPCs), which are
multipotent stem cells that give rise to cells in the central nervous system,
rapidly glide and stochastically reverse its velocity while locally aligning
with neighboring cells, thus showing features of an active nematic system.
Within the two-dimensional nematic pattern, we find interspaced topological
defects with +1/2 and -1/2 charges. Remarkably, we identified rapid cell
accumulation leading to three-dimensional mounds at the +1/2 topological
defects. Single-cell level imaging around the defects allowed quantification of
the evolving cell density, clarifying that not only cells concentrate at +1/2
defects, but also escape from -1/2 defects. We propose the mechanism of
instability around the defects as the interplay between the anisotropic
friction and the active force field, thus addressing a novel universal
mechanism for local cell density control.Comment: 4 pages, 4 figures + Supplementary Information (4 pages, 9 figures
A Note on Aspiration in English and its Counterpart in Japanese
It is widely known that in English, the voiceless stops /p/, /t/, and /k/ are aspirated in certain environments. According to Kahn (1976=1980), who argues for syllable-based analyses of various phonological phenomena, ..
Active Motion of Janus Particle by Self-thermophoresis in Defocused Laser Beam
We study self-propulsion of a half-metal coated colloidal particle under
laser irradiation. The motion is caused by self-thermophoresis: i.e. absorption
of laser at the metal-coated side of the particle creates local temperature
gradient which in turn drives the particle by thermophoresis. To clarify the
mechanism, temperature distribution and a thermal slip flow field around a
micro-scale Janus particle are measured for the first time. With measured
temperature drop across the particle, the speed of self-propulsion is
corroborated with the prediction based on accessible parameters. As an
application for driving micro-machine, a micro-rotor heat engine is
demonstrated
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