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Soft Materials meet Active Matter: Sticky Colloids in a Bacterial Bath
Get PDFThis thesis is an experimental work, investigating how active matter can control the assembly of soft materials. We design a novel experimental system, combining sticky colloids sedimented on the bottom surface of a glass capillary with a bath of motile {\it E. coli}. The colloids diffuse and stick together, assembling into large, quasi - 2D aggregates. Motile {\it E. coli} generate forces and flows in the surrounding media: an active bath which injects energy into the system through mechanical work. In the active bath, aggregates exhibit a a persistent clockwise rotation, leading to a non-conventional aggregation mechanism. These aggregates form structures which are not accessible via conventional aggregation in a thermal bath. Aided by numerical simulation of spinning, sticky beads, we elucidate that the rotation and folding of aggregates is the salient feature driving the structural differences, and the activity of the bath controls the phase diagram of aggregation. Further experiments indicate that the bacteria collide with and then swim through the aggregates; additionally, the direction of rotation of the aggregates is correlated with the direction of the circular trajectories made by the {\it E. coli} bacteria. Based on these insights, we propose a simple model for the swimmer-aggregate interactions, and propose further experiments to test its validity. As a whole, this work constitutes a proof of concept that active matter can be harnessed to direct the assembly of soft materials. The experiments presented in this thesis lay the groundwork for the development of a new class active, soft materials, whose structure and mechanical properties are dictated by their assembly in an active bath
Indigenous Peoples and Litigation:Strategies for Legal Empowerment
Get PDFAcross the globe indigenous peoples are increasingly using litigation to seek remedies for violation of their fundamental human rights. The rise of litigation is to be placed in the larger issue of increased land grabbing, natural resources exploitation and the general lack of recognition of their rights at the national level. This lack of legal rights is usually coupled with a lack of political will to address the issues faced by indigenous peoples, often leading to serious human rights violations, leaving indigenous advocates with few options but to turn to courts as a last resort to seek remedies. This article examines some of the issues faced by indigenous peoples and their advocates when engaging in human rights litigation. The goal is to offer a practice-based reflection on the encounter between courts and indigenous peoples with a specific focus on analysing strategies to ensure their legal empowerment. This is particularly important knowing the technicality, externalities and complexities of the process of litigation, and the fact that many decisions do not get implemented. In this context this article explores how the process of litigation in itself can support legal empowerment and the wider fight for justice. © 2020, The Author(s). The attached document (embargoed until 10/10/2022) is an author produced version of a paper published in JOURNAL OF HUMAN RIGHTS PRACTICE uploaded in accordance with the publisher’s self-archiving policy. The final published version (version of record) is available online at the link. Some minor differences between this version and the final published version may remain. We suggest you refer to the final published version should you wish to cite from it.<br/
3-D geological and petrophysical models with synthetic geophysics based on data from the Hamersley region (Western Australia)
No full text3-D geological and petrophysical models with synthetic geophysics based on data from the Hamersley region (Western Australia)
M. Jessell 1,2, J. Giraud 1,2, M. Lindsay 1,2
1 Centre for Exploration Targeting (School of Earth Sciences), University of Western Australia, 35 Stirling Highway, 6009 Crawley, Australia
2 Mineral Exploration Cooperative Research Centre, School of Earth Sciences, University of Western Australia, 35 Stirling Highway, WA Crawley 6009, Australia
Contact author: Jeremie Giraud ([email protected])
Companion dataset to the paper:
Structural, petrophysical and geological constraints in potential field inversion using the Tomofast-x open-source code, J. Giraud, V. Ogarko, R. Martin, M. Lindsay, M. Jessell, Geoscientific Model Development Discussions.
This dataset contains models and data shown in the paper, in both 2D and 3D:
1. Geological model
Reference lithology voxet:
The reference geological model was obtained using public data from the Geological Survey of Western Australia and modified subsequently (stretched vertically and flattened at surface level) for the purpose of this study.
Probability voxet
The lithology probability voxet was derived using Monte Carlo simulations for uncertainty estimation as mentioned in the paper.
2. True and inverted models for density and magnetic susceptibility
Derivation is detailed in the paper; it uses fictitious density and magnetic susceptibility values.
3. Bouguer and total magnetic field anomaly
Calculation is detailed in the paper.
The authors are supported, in part, by Loop – Enabling Stochastic 3D Geological Modelling (LP170100985) and the Mineral Exploration Cooperative Research Centre (MinEx CRC) whose activities are funded by the Australian Government's Cooperative Research Centre Program. This is MinEx CRC Document 2021/3. Mark Lindsay acknowledges funding from the ARC and DECRA DE190100431.
It is a companion dataset to:
Vitaliy Ogarko, Jeremie Giraud, & Roland. (2021, February 5). Tomofast-x v1.0 source code (Version 1.0). Zenodo. http://doi.org/10.5281/zenodo.445262
Rotation Control, Interlocking and Self-positioning of Active Cogwheels
Get PDFGears and cogwheels restrain degrees of freedom and channel power into a
specified motion. They are fundamental components of macroscopic machines.
Interlocking microrotors similarly constitute key elements toward feasible
micromachinery. Their assembly, positioning and control is a challenge at
microscale, where noise is ubiquituous. Here, we show the assembly and control
of a family of self-spinning cogwheels with varying teeth numbers and study
interlocking mechanisms in systems of multiple cogwheels. The cogwheels are
autonomous and active, with teeth formed by colloidal microswimmers that power
the structure, and control its rotation rate. Leveraging the angular momentum
of light with optical vortices, we control the direction of rotation of the
cogwheels. We study pairs of interlocking cogwheels, that roll over each other
in a random walk and curvature-dependent mobility. We leverage this feature to
achieve self-positioning of cogwheels on structures with variable curvature and
program microbots, notably demonstrating the ability to pick up, displace and
release a load. This work highlights untapped opportunities of manufacturing at
microscale using self-positioning components and constitutes an important step
towards autonomous and programmable microbots.Comment: 4 Figures. arXiv admin note: text overlap with arXiv:2111.0868
Activity-controlled annealing of colloidal monolayers
Get PDFMolecular motors are essential to the living, generating fluctuations that boost transport and assist assembly. Active colloids, that consume energy to move, hold similar potential for man-made materials controlled by forces generated from within. Yet, their use as a powerhouse in materials science lacks. Here we show a massive acceleration of the annealing of a monolayer of passive beads by moderate addition of self-propelled microparticles. We rationalize our observations with a model of collisions that drive active fluctuations and activate the annealing. The experiment is quantitatively compared with Brownian dynamic simulations that further unveil a dynamical transition in the mechanism of annealing. Active dopants travel uniformly in the system or co-localize at the grain boundaries as a result of the persistence of their motion. Our findings uncover the potential of internal activity to control materials and lay the groundwork for the rise of materials science beyond equilibrium
A parametric study of vestibular stimulation during centrifugation
Get PDFThesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2006.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections."February 2006."Includes bibliographical references (p. 155-160).Artificial Gravity (AG) provided by short-radius centrifugation is a promising countermeasure to the health problems associated with long duration human spaceflight. Head-turns performed during centrifugation, however, trigger a disturbing vestibular response that is only qualitatively understood. In order to design an efficient incremental adaptation procedure, the present study investigates the quantitative aspect of the vestibular side effects associated with AG, in particular, the relationship among crosscoupled stimulation, vestibular response, and adaptation. We tested 20 young adults with supine right-quadrant yaw head-turns performed in a dark environment during short-radius centrifugation. We studied the changes in vestibular response and adaptation to head-turns at different levels of cross-coupled stimulation. Nine combinations of head-turn angle (20°, 40° or 80°) with centrifugevelocity (12, 19 or 30 rpm) were tested over two consecutive days.(cont.) There were four key findings: 1. All measures, except the slow-phase velocity (SPV) peak amplitude of the vestibulo-ocular reflex, decrease significantly between the two experimental days, which demonstrates that significant adaptation is achieved. 2. Large head-angles lead to longer vertical vestibulo-ocular reflex time-constants than smaller angles do, but do not lead to greater adaptation. 3. In the nose-up position, the perceived body-tilt is highly correlated with the true tilt of the gravito-inertial force at mid-chest level. 4. The SPV-peak amplitude and all subjective ratings except body-tilt show significant correlation with the intensity of the cross-coupled stimulus (CCS): the larger the CCS, the stronger the vestibular response.by Jeremie M. Pouly.S.M
Metamachines of pluripotent colloids
Get PDFMobile micromachines have the potential to probe and manipulate matter at small scales emulating the biological machinery of living organisms. Here, the authors take advantage of the anisotropy of self-propelled colloidal heterodimers to control anisotropic and reprogrammable interactions between particles
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