85 research outputs found
Symmetry-breaking transition between defect-free and defect-laden turbulence in polar active matter
Coherent flows of self-propelled particles are characterized by vortices and
jets that sustain chaotic flows, referred to as active turbulence. Here, we
reveal a transition between defect-free active turbulence and active turbulence
laden with defects. Interestingly, we show that concurrent to the transition
from defect-free active turbulence to defect-laden turbulence is the
restoration of the previously broken -symmetry and fast decay of the
two-point correlations which suggests a symmetry-breaking transition. By
stability analyses of the topological charge density field, we provide an
analytical prediction of the activity threshold for the transition to the
defect-laden active turbulent state. Moreover, despite the distinct symmetry
features between the defect-free and defect-laden active turbulence, we
demonstrate universal behaviors for the self-similarity of the flow
fluctuations at large scales, and exponential decay of polarity power spectrum,
at small length scales compared to the active energy injection length. It is
further shown that increasing the self-propulsion of the active particles
results in exponential rarefaction of topological defects and a transition from
active defect-laden turbulence to a flocking state. These findings reveal new
dynamical transitions between distinct spatiotemporal organization patterns in
polar active mater
Spatiotemporal model of cellular mechanotransduction via Rho and YAP
How cells sense and respond to mechanical stimuli remains an open question.
Recent advances have identified the translocation of Yes-associated protein
(YAP) between nucleus and cytoplasm as a central mechanism for sensing
mechanical forces and regulating mechanotransduction. We formulate a
spatiotemporal model of the mechanotransduction signalling pathway that
includes coupling of YAP with the cell force-generation machinery through the
Rho family of GTPases. Considering the active and inactive forms of a single
Rho protein (GTP/GDP-bound) and of YAP (non-phosphorylated/phosphorylated), we
study the cross-talk between cell polarization due to active Rho and YAP
activation through its nuclear localization.
For fixed mechanical stimuli, our model predicts stationary
nuclear-to-cytoplasmic YAP ratios consistent with experimental data at varying
adhesive cell area. We further predict damped and even sustained oscillations
in the YAP nuclear-to-cytoplasmic ratio by accounting for recently reported
positive and negative YAP-Rho feedback. Extending the framework to time-varying
mechanical stimuli that simulate cyclic stretching and compression, we show
that the YAP nuclear-to-cytoplasmic ratio's time dependence follows that of the
cyclic mechanical stimulus. The model presents one of the first frameworks for
understanding spatiotemporal YAP mechanotransduction, providing several
predictions of possible YAP localization dynamics, and suggesting new
directions for experimental and theoretical studies
Driven Topological Transitions in Active Nematic Films
The topological properties of many materials are central to their behavior,
with the dynamics of topological defects being particularly important to
intrinsically out-of-equilibrium, active materials. In this paper, local
manipulation of the ordering, dynamics, and topological properties of
microtubule-based extensile active nematic films is demonstrated in a joint
experimental and simulation study. Hydrodynamic stresses created by
magnetically actuated rotation of disk-shaped colloids in proximity to the
films compete with internal stresses in the active nematic, enabling local
control of the motion of the +1/2 charge topological defects that are intrinsic
to spontaneously turbulent active films. Sufficiently large applied stresses
drive the formation of +1 charge topological vortices in the director field
through the merger of two +1/2 defects. The directed motion of the defects is
accompanied by ordering of the vorticity and velocity of the active flows
within the film that is qualitatively unlike the response of passive viscous
films. Many features of the film's response to the disk are captured by Lattice
Boltzmann simulations, leading to insight into the anomalous viscoelastic
nature of the active nematic. The topological vortex formation is accompanied
by a rheological instability in the film that leads to significant increase in
the flow velocities. Comparison of the velocity profile in vicinity of the
vortex with fluid-dynamics calculations provides an estimate of film viscosity
A growing bacterial colony in two dimensions as an active nematic
Rod-shaped bacteria are an example of active matter. Here the authors find that a growing bacterial colony harbours internal cellular flows affecting orientational ordering in its interior and at the boundary. Results suggest this system may belong to a new active matter universality class
IGAPS: the merged IPHAS and UVEX optical surveys of the Northern Galactic Plane
The INT Galactic Plane Survey (IGAPS) is the merger of the optical photometric surveys, IPHAS and UVEX, based on data from the Isaac Newton Telescope (INT) obtained between 2003 and 2018. Here, we present the IGAPS point source catalogue. It contains 295.4 million rows providing photometry in the filters, i, r, narrow-band Hα, g, and U_(RGO). The IGAPS footprint fills the Galactic coordinate range, |b| 5σ confidence)
IGAPS: the merged IPHAS and UVEX optical surveys of theNorthern Galactic Plane
The INT Galactic Plane Survey (IGAPS) is the merger of the optical
photometric surveys, IPHAS and UVEX, based on data from the Isaac Newton
Telescope (INT) obtained between 2003 and 2018. Here, we present the IGAPS
point source catalogue. It contains 295.4 million rows providing photometry in
the filters, i, r, narrow-band Halpha, g and U_RGO. The IGAPS footprint fills
the Galactic coordinate range, |b| < 5deg and 30deg < l < 215deg. A uniform
calibration, referred to the Pan-STARRS system, is applied to g, r and i, while
the Halpha calibration is linked to r and then is reconciled via field
overlaps. The astrometry in all 5 bands has been recalculated on the Gaia DR2
frame. Down to i ~ 20 mag (Vega system), most stars are also detected in g, r
and Halpha. As exposures in the r band were obtained within the IPHAS and UVEX
surveys a few years apart, typically, the catalogue includes two distinct r
measures, r_I and r_U. The r 10sigma limiting magnitude is ~21, with median
seeing 1.1 arcsec. Between ~13th and ~19th magnitudes in all bands, the
photometry is internally reproducible to within 0.02 magnitudes. Stars brighter
than r=19.5 have been tested for narrow-band Halpha excess signalling line
emission, and for variation exceeding |r_I-r_U| = 0.2 mag. We find and flag
8292 candidate emission line stars and over 53000 variables (both at >5sigma
confidence). The 174-column catalogue will be available via CDS Strasbourg.Comment: 28 pages, 22 figure
MicroMotility: State of the art, recent accomplishments and perspectives on the mathematical modeling of bio-motility at microscopic scales
Mathematical modeling and quantitative study of biological motility (in particular, of motility at microscopic scales) is producing new biophysical insight and is offering opportunities for new discoveries at the level of both fundamental science and technology. These range from the explanation of how complex behavior at the level of a single organism emerges from body architecture, to the understanding of collective phenomena in groups of organisms and tissues, and of how these forms of swarm intelligence can be controlled and harnessed in engineering applications, to the elucidation of processes of fundamental biological relevance at the cellular and sub-cellular level. In this paper, some of the most exciting new developments in the fields of locomotion of unicellular organisms, of soft adhesive locomotion across scales, of the study of pore translocation properties of knotted DNA, of the development of synthetic active solid sheets, of the mechanics of the unjamming transition in dense cell collectives, of the mechanics of cell sheet folding in volvocalean algae, and of the self-propulsion of topological defects in active matter are discussed. For each of these topics, we provide a brief state of the art, an example of recent achievements, and some directions for future research
BacHBerry: BACterial Hosts for production of Bioactive phenolics from bERRY fruits
BACterial Hosts for production of Bioactive phenolics from bERRY fruits (BacHBerry) was a 3-year project funded by the Seventh Framework Programme (FP7) of the European Union that ran between November 2013 and October 2016. The overall aim of the project was to establish a sustainable and economically-feasible strategy for the production of novel high-value phenolic compounds isolated from berry fruits using bacterial platforms. The project aimed at covering all stages of the discovery and pre-commercialization process, including berry collection, screening and characterization of their bioactive components, identification and functional characterization of the corresponding biosynthetic pathways, and construction of Gram-positive bacterial cell factories producing phenolic compounds. Further activities included optimization of polyphenol extraction methods from bacterial cultures, scale-up of production by fermentation up to pilot scale, as well as societal and economic analyses of the processes. This review article summarizes some of the key findings obtained throughout the duration of the project
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