On the role of initial velocities in pair dispersion in a microfluidic chaotic flow

Chaotic flows drive mixing and efficient transport in fluids, as well as the associated beautiful complex patterns familiar to us from our every day life experience. Generating such flows at small scales where viscosity takes over is highly challenging from both the theoretical and engineering perspectives. This can be overcome by introducing a minuscule amount of long flexible polymers, resulting in a chaotic flow dubbed \textit{elastic turbulence}. At the basis of the theoretical frameworks for its study lie the assumptions of a spatially smooth and random-in-time velocity field. Previous measurements of elastic turbulence have been limited to two-dimensions. Using a novel three-dimensional particle tracking method, we conduct a microfluidic experiment, allowing us to explore elastic turbulence from the perspective of particles moving with the flow. Our findings show that the smoothness assumption breaks already at scales smaller than a tenth of the system size. Moreover, we provide conclusive experimental evidence that \textit{ballistic} separation prevails in the dynamics of pairs of tracers over long times and distances, exhibiting a memory of the initial separation velocities. The ballistic dispersion is universal, yet it has been overlooked so far in the context of small scales chaotic flows.Comment: 28 pages (Main Article: 17 pages ; Supplementary Information: 11 pages), 5 Main Figures, 6 Supplementary Figures, 3 Supplementary Notes, Supplementary Reference

Characteristic spatial scale of vesicle pair interactions in a plane linear flow

We report the experimental studies on interaction of two vesicles trapped in a microfluidic analog of four-roll mill, where a plane linear flow is realized. We found that the dynamics of a single vesicle is significantly altered by the presence of another vesicle at separation distances up to about 3.2 \div 3.7 times of effective radius of the vesicles. This is supported by direct measurements of a single vesicle back-reaction on the velocity field. Thus, the experiment provides the lower bound for the interaction scale of vesicles and so the corresponding upper bound for the volume fraction \phi=0.08 \div 0.13 of non-interacting vesicle suspensions.Comment: 5 pages, 8 figures, PRE accepted for publicatio

Calcium signals are necessary to establish auxin transporter polarity in a plant stem cell niche

In plants mechanical signals pattern morphogenesis through the polar transport of the hormone auxin and through regulation of interphase microtubule (MT) orientation. To date, the mechanisms by which such signals induce changes in cell polarity remain unknown. Through a combination of time-lapse imaging, and chemical and mechanical perturbations, we show that mechanical stimulation of the SAM causes transient changes in cytoplasmic calcium ion concentration (Ca^(2+)) and that transient Ca^(2+) response is required for downstream changes in PIN-FORMED 1 (PIN1) polarity. We also find that dynamic changes in Ca^(2+) occur during development of the SAM and this Ca^(2+) response is required for changes in PIN1 polarity, though not sufficient. In contrast, we find that Ca^(2+) is not necessary for the response of MTs to mechanical perturbations revealing that Ca^(2+) specifically acts downstream of mechanics to regulate PIN1 polarity response

Calcium signals are necessary to establish auxin transporter polarity in a plant stem cell niche

In plants mechanical signals pattern morphogenesis through the polar transport of the hormone auxin and through regulation of interphase microtubule (MT) orientation. To date, the mechanisms by which such signals induce changes in cell polarity remain unknown. Through a combination of time-lapse imaging, and chemical and mechanical perturbations, we show that mechanical stimulation of the SAM causes transient changes in cytoplasmic calcium ion concentration (Ca^(2+)) and that transient Ca^(2+) response is required for downstream changes in PIN-FORMED 1 (PIN1) polarity. We also find that dynamic changes in Ca^(2+) occur during development of the SAM and this Ca^(2+) response is required for changes in PIN1 polarity, though not sufficient. In contrast, we find that Ca^(2+) is not necessary for the response of MTs to mechanical perturbations revealing that Ca^(2+) specifically acts downstream of mechanics to regulate PIN1 polarity response

Dynamical states of self-organised waves in a giant unicellular green alga

Associated manuscript:Afik, Liu and Meyerowitz (2023) : “Macroscopic waves, biological clocks and morphogenesis driven by light in a giant unicellular green alga.” bioRxiv. https://doi.org/10.1101/2023.02.22.529174.AbstractA hallmark of self-organisation in living systems is their capacity to stabilise their own dynamics, often appearing to anticipate and act upon potential outcomes. Caulerpa brachypus is a marine green alga consisting of differentiated organs resembling leaves, stems and roots. While an individual can exceed a metre in size, it is a single multinucleated giant cell. Thus Caulerpa presents the mystery of morphogenesis on macroscopic scales in the absence of cellularization.The experiments reported here reveal self-organised waves of greenness --- chloroplasts --- that propagate throughout the alga in anticipation of the day-night light cycle. Using dynamical systems analysis we show that these waves are coupled to a self-sustained oscillator, and demonstrate their entrainment to light. Under constant conditions light intensity affects the natural period and drives transition to temporal disorder. Moreover, we find distinct morphologies depending on light temporal patterns, suggesting waves of chlorophyll could link biological oscillators to metabolism and morphogenesis in this giant single-celled organism.Suggested setupDownload all files to one folder, and extract the compressed files.Environment setupDownload and install miniforge#mambaforge ; other conda based installations should work as well.Run in command line:mamba update -n base -c conda-forge condamamba create -n eaDataLab python=3.10mamba activate eaDataLabmamba install -n eaDataLab jupyterlab # optional : jupyterlab-gitmamba install -n eaDataLab hvplot pandas pyarrow ipympl # optional : zarr dask-image scikit-image scikit-learn napari pytables tabulate python-graphviz mamba install -n eaDataLab watermarkinit jupyter labjupyter lab EA_TJBL_EMM_2023_SI_Fig2.ipynb</pre

A Lagrangian approach to elastic turbulence in a curvilinear microfluidic channel

<b>A Lagrangian approach to elastic turbulence in a curvilinear microfluidic channel: <br>Particle dispersion in a dissipative chaotic flow</b><br><br>Elastic turbulence, a random in time flow which can drive efficient mixing in microfluidics, serves as a laboratory for non-linear and out-of-equilibrium classical physics. <br><br>The literature to date shows that previous measurements of elastic turbulence have been limited to two-dimensions. By means of a direct three-dimensional Lagrangian particle tracking technique [1], we have established an experimental database of about 10⁷ trajectories derived from passive tracers in elastic turbulence, generated in a curvilinear microfluidic tube.<br><br>This dataset has allowed us to study the dispersion of pairs in the chaotic flow. It has revealed that the smoothness assumption, which is at the basis of the theoretical frameworks commonly employed in the study of elastic turbulence, breaks at scales far smaller than previously believed, and that <i>ballistic pair dispersion</i> holds over much longer distances than expected. [2]<br><br>The experimental dataset is made available here as we are certain it would prove useful once applied further analysis, not only as reference to compare with new theoretical, numerical and experimental results, but also in addressing novel basic questions in the field.<br><br><br>[1] Afik, E. Robust and highly performant ring detection algorithm for 3d particle tracking using 2d microscope imaging. <i>Sci. Rep.</i> 5, 13584; doi: 10.1038/srep13584 (2015).<br><br>[2] Afik, E. & Steinberg V. On the role of initial velocities in pair dispersion in a microfluidic chaotic flow. <i>Nat. Commun.</i>; doi: 10.1038/s41467-017-00389-8 (2017). <br><br>************************************************<br><br>The original file was split using:<br><br> split --number=l/15 ET_Lagrangian_smoothing_splines_all_20130219-20130227.h5 ET_Lagrangian_smoothing_splines_20130219-20130227.h5.<br><br>to merge back can use:<br><br>[UNIX]<br><br><code> cat ET_Lagrangian_smoothing_splines_20130219-20130227.h5.a{a..o} > ET_Lagrangian_smoothing_splines_20130219-20130227.h5<br><br>[MS Windows]<br><br></code> copy /b ET_Lagrangian_smoothing_splines_20130219-20130227.h5.a* ET_Lagrangian_smoothing_splines_20130219-20130227.h5<br><br>To confirm integrity of the output file the MD5 checksum value is provided.<br><br><br>The attached Jupyter notebook <br> `A Lagrangian approach to elastic turbulence -- example notebook.ipynb` <br>is meant to provide a simple example of how to access information in the dataset; <br>ViTables (by PyTables) is another convenient way to explore the data.<br><br><br><br

Contribution a l'etude de la pliabilite des alliages Zn Cu Ti a basse temperature

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : TD 82171 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc