Diffusion of Active Particles in Convective Flows

Soft Matter ◽  
2020 ◽  
Author(s):  
Pulak Kumar Ghosh ◽  
Debajyoti Debnath ◽  
Yunyun Li ◽  
Fabio Marchesoni
Keyword(s):  
Janus Particle ◽  
Convective Flows ◽  
Rotating Convection ◽  
Periodic Arrays ◽  
Active Particles ◽  
Convection Patterns ◽  
Convection Rolls

We numerically investigated the diffusion of an active Janus particle in periodic arrays of planar counter-rotating convection rolls at high P\'eclet numbers. We considered convection patterns with distinct longitudinal and...

scholarly journals Spatio-temporal patterns in inclined layer convection

2016 ◽  
Vol 794 ◽  
pp. 719-745 ◽  
Author(s):  
Priya Subramanian ◽  
Oliver Brausch ◽  
Karen E. Daniels ◽  
Eberhard Bodenschatz ◽  
Tobias M. Schneider ◽  
...  
Keyword(s):  
Boussinesq Equations ◽  
Temporal Patterns ◽  
Resonant Interaction ◽  
Onset Of Convection ◽  
Inclined Layer ◽  
Spatio Temporal ◽  
The Rich ◽  
Convection Patterns ◽  
Oriented Parallel ◽  
Convection Rolls

This paper reports on a theoretical analysis of the rich variety of spatio-temporal patterns observed recently in inclined layer convection at medium Prandtl number when varying the inclination angle ${\it\gamma}$ and the Rayleigh number $R$. The present numerical investigation of the inclined layer convection system is based on the standard Oberbeck–Boussinesq equations. The patterns are shown to originate from a complicated competition of buoyancy driven and shear-flow driven pattern forming mechanisms. The former are expressed as longitudinal convection rolls with their axes oriented parallel to the incline, the latter as perpendicular transverse rolls. Along with conventional methods to study roll patterns and their stability, we employ direct numerical simulations in large spatial domains, comparable with the experimental ones. As a result, we determine the phase diagram of the characteristic complex 3-D convection patterns above onset of convection in the ${\it\gamma}{-}R$ plane, and find that it compares very well with the experiments. In particular we demonstrate that interactions of specific Fourier modes, characterized by a resonant interaction of their wavevectors in the layer plane, are key to understanding the pattern morphologies.

scholarly journals An active particle in a complex fluid

2017 ◽  
Vol 823 ◽  
pp. 675-688 ◽  
Author(s):  
Charu Datt ◽  
Giovanniantonio Natale ◽  
Savvas G. Hatzikiriakos ◽  
Gwynn J. Elfring
Keyword(s):  
Newtonian Fluid ◽  
Slip Velocity ◽  
Shear Thinning ◽  
Reciprocal Theorem ◽  
Janus Particle ◽  
Active Particles ◽  
Complex Fluid ◽  
The Reciprocal Theorem ◽  
Fluid Rheology ◽  
Shear Thinning Fluid

In this work, we study active particles with prescribed surface velocities in non-Newtonian fluids. We employ the reciprocal theorem to obtain the velocity of an active spherical particle with an arbitrary axisymmetric slip velocity in an otherwise quiescent second-order fluid. We then determine how the motion of a diffusiophoretic Janus particle is affected by complex fluid rheology, namely viscoelasticity and shear-thinning viscosity, compared to a Newtonian fluid, assuming a fixed slip velocity. We find that a Janus particle may go faster or slower in a viscoelastic fluid, but is always slower in a shear-thinning fluid as compared to a Newtonian fluid.

Generation of Mean Flows in a Rotating Convection Layer

1982 ◽  
Vol 37 (8) ◽  
pp. 752-758 ◽  
Author(s):  
F. H. Busse
Keyword(s):  
Numerical Experiments ◽  
Fluid Layer ◽  
Horizontal Component ◽  
Rotation Vector ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Rotating Convection ◽  
Convection Layer ◽  
The Mean ◽  
Convection Rolls

The instability of convection rolls in a fluid layer heatet from below is studied in the case where the layer rotates about an axis slightly inclined with respect to the vertical. The inclination destroys the horizontal isotropy of the layer, but the instability of rolls found by Küppers and Lortz [1] is little affected as long as the angle of inclination is small. A new effect is the generation of mean Reynolds stresses by rolls not aligned with the horizontal component of the rotation vector. The mean flow exhibits a vorticity of the same sign as the horizontal component of rotation and agrees qualitatively with the mean flow found in the numerical experiments of Hathaway and Somerville [2]

scholarly journals Active particles as mobile microelectrodes for selective bacteria electroporation and transport

2020 ◽  
Vol 6 (5) ◽  
pp. eaay4412 ◽  
Author(s):  
Yue Wu ◽  
Afu Fu ◽  
Gilad Yossifon
Keyword(s):  
Electric Field ◽  
Single Cell ◽  
Targeted Delivery ◽  
Single Cell Analysis ◽  
Cell Types ◽  
Cell Analysis ◽  
Janus Particle ◽  
Field Gradients ◽  
Active Particles ◽  
Wide Range

Self-propelling micromotors are emerging as a promising micro- and nanoscale tool for single-cell analysis. We have recently shown that the field gradients necessary to manipulate matter via dielectrophoresis can be induced at the surface of a polarizable active (“self-propelling”) metallodielectric Janus particle (JP) under an externally applied electric field, acting essentially as a mobile floating microelectrode. Here, we successfully demonstrated that the application of an external electric field can singularly trap and transport bacteria and can selectively electroporate the trapped bacteria. Selective electroporation, enabled by the local intensification of the electric field induced by the JP, was obtained under both continuous alternating current and pulsed signal conditions. This approach is generic and applicable to bacteria and JP, as well as a wide range of cell types and micromotor designs. Hence, it constitutes an important and novel experimental tool for single-cell analysis and targeted delivery.

scholarly journals Enhanced buoyancy of active particles in convective flows

2021 ◽  
Vol 3 (3) ◽  
Author(s):  
Yunyun Li ◽  
Pulak K. Ghosh ◽  
Fabio Marchesoni
Keyword(s):  
Convective Flows ◽  
Active Particles

scholarly journals Anisotropic Diffusion in Driven Convection Arrays

Entropy ◽  
2021 ◽  
Vol 23 (3) ◽  
pp. 343
Author(s):  
Yunyun Li ◽  
Vyacheslav R. Misko ◽  
Fabio Marchesoni ◽  
Pulak K. Ghosh
Keyword(s):  
Laminar Flow ◽  
External Force ◽  
Anisotropic Diffusion ◽  
Nonlinear Response ◽  
Colloidal Particle ◽  
Diffusion Constant ◽  
Sharp Contrast ◽  
Rotating Convection ◽  
Convection Rolls ◽  
Square Array

We numerically investigate the transport of a Brownian colloidal particle in a square array of planar counter-rotating convection rolls at high Péclet numbers. We show that an external force produces huge excess peaks of the particle’s diffusion constant with a height that depends on the force orientation and intensity. In sharp contrast, the particle’s mobility is isotropic and force independent. We relate such a nonlinear response of the system to the advection properties of the laminar flow in the suspension fluid.

Empirical pseudo-balanced model reduction and feedback control of weakly nonlinear convection patterns

2010 ◽  
Vol 662 ◽  
pp. 36-65 ◽  
Author(s):  
A. C. OR ◽  
J. L. SPEYER
Keyword(s):  
Feedback Control ◽  
Model Reduction ◽  
Large Scale ◽  
Open Loop ◽  
Nonlinear Convection ◽  
Weakly Nonlinear ◽  
Reduced Order ◽  
Convection Patterns ◽  
Balanced Model ◽  
Convection Rolls

An empirical model reduction method is performed on nonlinear transient convection patterns near the threshold, using a pseudo-inverse-based projective method called the pseudo-balanced proper orthogonal decomposition (PBPOD). These transient patterns are large-scale amplitude/phase modulations in convection rolls, obtained by prescribing selected spatial input-shape functions. For the nonlinear convection patterns modelled, PBPOD appears to be very effective. Using the nonlinear front example, PBPOD is compared with other existing methods, such as POD and linearized BPOD. The limitations of the methods are discussed. Using a complex prescribed input, complex disturbances are generated and the outputs of the open-loop responses are compared between the original and the reduced-order models. The agreement is good. A feedback-control study is performed using the nonlinear front example. The controller is built by the pseudo-balanced reduced-order model, with a low-order nonlinear estimator. Closed-loop simulations show that the nonlinear travelling fronts can be effectively damped out by the feedback-control actions.

High-resolution x-ray analysis of dislocation networks nn tilt boundaries

1988 ◽  
Vol 46 ◽  
pp. 612-613
Author(s):  
J. R. Michael ◽  
C. H. Lin ◽  
S. L. Sass
Keyword(s):  
Grain Boundaries ◽  
Analytical Electron Microscopy ◽  
Solute Segregation ◽  
X Ray ◽  
Periodic Arrays ◽  
Analytical Electron ◽  
Primary Dislocation ◽  
Tilt Boundaries ◽  
Polycrystalline Solids ◽  
Twist Boundaries

The segregation of solute atoms to grain boundaries in polycrystalline solids can be responsible for embrittlement of the grain boundaries. Although Auger electron spectroscopy (AES) and analytical electron microscopy (AEM) have verified the occurrence of solute segregation to grain boundaries, there has been little experimental evidence concerning the distribution of the solute within the plane of the interface. Sickafus and Sass showed that Au segregation causes a change in the primary dislocation structure of small angle [001] twist boundaries in Fe. The bicrystal specimens used in their work, which contain periodic arrays of dislocations to which Au is segregated, provide an excellent opportunity to study the distribution of Au within the boundary by AEM.The thin film Fe-0.8 at% Au bicrystals (composition determined by Rutherford backscattering spectroscopy), ∼60 nm thick, containing [001] twist boundaries were prepared as described previously. The bicrystals were analyzed in a Vacuum Generators HB-501 AEM with a field emission electron source and a Link Analytical windowless x-ray detector.

Quasiperiodic interfaces: HREM observations of grain and phase boundaries

1990 ◽  
Vol 48 (4) ◽  
pp. 332-333
Author(s):  
K. L. Merkle
Keyword(s):  
Atomic Structure ◽  
Direct Determination ◽  
Lattice Parameter ◽  
Atomic Scale ◽  
Misfit Dislocations ◽  
Oxide Systems ◽  
Atomic Structures ◽  
Periodic Arrays ◽  
Parameter Ratio ◽  
Metal Metal

The atomic structures of internal interfaces have recently received considerable attention, not only because of their importance in determining many materials properties, but also because the atomic structure of many interfaces has become accessible to direct atomic-scale observation by modem HREM instruments. In this communication, several interface structures are examined by HREM in terms of their structural periodicities along the interface.It is well known that heterophase boundaries are generally formed by two low-index planes. Often, as is the case in many fcc metal/metal and metal/metal-oxide systems, low energy boundaries form in the cube-on-cube orientation on (111). Since the lattice parameter ratio between the two materials generally is not a rational number, such boundaries are incommensurate. Therefore, even though periodic arrays of misfit dislocations have been observed by TEM techniques for numerous heterophase systems, such interfaces are quasiperiodic on an atomic scale. Interfaces with misfit dislocations are semicoherent, where atomically well-matched regions alternate with regions of misfit. When the misfit is large, misfit localization is often difficult to detect, and direct determination of the atomic structure of the interface from HREM alone, may not be possible.

Electron Microscope study of commensurate-incommensurate phase transition in BaZnGeO4

1990 ◽  
Vol 48 (4) ◽  
pp. 172-173
Author(s):  
Naoki Yamamoto ◽  
Makoto Kikuchi ◽  
Tooru Atake ◽  
Akihiro Hamano ◽  
Yasutoshi Saito
Keyword(s):  
Phase Transition ◽  
Electron Microscope Study ◽  
Room Temperature ◽  
Hexagonal Lattice ◽  
Ferroelectric Materials ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Periodic Arrays ◽  
Modulation Wave Vector

BaZnGeO4 undergoes many phase transitions from I to V phase. The highest temperature phase I has a BaAl2O4 type structure with a hexagonal lattice. Recent X-ray diffraction study showed that the incommensurate (IC) lattice modulation appears along the c axis in the III and IV phases with a period of about 4c, and a commensurate (C) phase with a modulated period of 4c exists between the III and IV phases in the narrow temperature region (—58°C to —47°C on cooling), called the III' phase. The modulations in the IC phases are considered displacive type, but the detailed structures have not been studied. It is also not clear whether the modulation changes into periodic arrays of discommensurations (DC’s) near the III-III' and IV-V phase transition temperature as found in the ferroelectric materials such as Rb2ZnCl4.At room temperature (III phase) satellite reflections were seen around the fundamental reflections in a diffraction pattern (Fig.1) and they aligned along a certain direction deviated from the c* direction, which indicates that the modulation wave vector q tilts from the c* axis. The tilt angle is about 2 degree at room temperature and depends on temperature.

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