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1.
Phys Rev Lett ; 131(17): 176101, 2023 Oct 27.
Artigo em Inglês | MEDLINE | ID: mdl-37955491

RESUMO

Dispersion relations govern wave behaviors, and tailoring them is a grand challenge in wave manipulation. We demonstrate the inverse design of phononic dispersion using nonlocal interactions on one-dimensional spring-mass chains. For both single-band and double-band cases, we can achieve any valid dispersion curves with analytical precision. We further employ our method to design phononic crystals with multiple ordinary (roton or maxon) and higher-order (undulation) critical points and investigate their wave packet dynamics.

2.
Phys Rev Lett ; 116(19): 198101, 2016 May 13.
Artigo em Inglês | MEDLINE | ID: mdl-27232048

RESUMO

Helicobacter pylori swims through mucus gel by generating ammonia that locally neutralizes the acidic gastric environment, turning nearby gel into a fluid pocket. The size of the fluid zone is important for determining the physics of the motility: in a large zone swimming occurs as in a fluid through hydrodynamic principles, while in a very small zone the motility could be strongly influenced by nonhydrodynamic cell-mucus interactions including chemistry and adhesion. Here, we calculate the size of the fluid pocket. We model how swimming depends on the de-gelation range using a Taylor sheet swimming through a layer of Newtonian fluid bounded by a Brinkman fluid. Then, we model how the de-gelation range depends on the swimming speed by considering the advection-diffusion of ammonia exuded from a translating sphere. Self-consistency between both models determines the values of the swimming speed and the de-gelation range. We find that H. pylori swims through mucus as if unconfined, in a large pocket of Newtonian fluid.


Assuntos
Helicobacter pylori/fisiologia , Muco , Difusão , Helicobacter pylori/química , Hidrodinâmica , Concentração de Íons de Hidrogênio , Movimento
3.
J R Soc Interface ; 21(212): 20230706, 2024 03.
Artigo em Inglês | MEDLINE | ID: mdl-38471535

RESUMO

The feeding performance of zooplankton influences their evolution and can explain their behaviour. A commonly used metric for feeding performance is the volume of fluid that flows through a filtering surface and is scanned for food. Here, we show that such a metric may give incorrect results for organisms that produce recirculatory flows, so that fluid flowing through the filter may have been already filtered of food. In a numerical model, we construct a feeding metric that correctly accounts for recirculation in a sessile model organism inspired by our experimental observations of Vorticella and its flow field. Our metric tracks the history of current-borne particles to determine if they have already been filtered by the filtering surface. Examining the pathlines of food particles reveals that the capture of fresh particles preferentially involves the tips of cilia, which we corroborate in observations of feeding Vorticella. We compare the amount of fresh nutrient particles carried to the organism with other metrics of feeding, and show that metrics that do not take into account the history of particles cannot correctly compute the volume of freshly scanned fluid.


Assuntos
Comportamento Alimentar , Zooplâncton , Animais , Nutrientes
4.
Phys Rev E ; 102(3-1): 033115, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-33076012

RESUMO

Hook dynamics are important in the motility of singly flagellated bacteria during flick motility. Although the hook is relatively short, during reorientation events it may undergo large deformations, leading to nonlinear behavior. Here, we explore when these nonlinear and large deformations are important for the swimming dynamics in different ranges of hook flexibilities and flagellar motor torques. For this purpose, we investigate progressively more faithful models for the hook, starting with linear springs, then models that incorporate nonlinearities due to larger hook deformations. We also employ these models both with and without hydrodynamic interactions between the flagellum and cell body to test the importance of those hydrodynamic interactions. We show that for stiff hooks, bacteria swim with a flagellum rotating on-axis in orbits and hydrodynamic interactions between the cell body and flagellum change swimming speeds by about 40%. As the hook stiffness decreases, there is a critical hook stiffness that predicts the initiation of the dynamic instability causing flicks. We compare the transition value of stiffnesses predicted by our models to experiments and show that nonlinearity and large deflections do not significantly affect critical transition values, while hydrodynamic interactions can change transition values by up to 13%. Below the transition value, we observe precession of the flagellum, in which it deflects off-axis to undergo nearly circular stable trajectories. However, only slightly below the transition stiffness, nonlinearity in hook response destabilizes precession, leading to unstable deflections of the flagellum. We conclude that while the linear hook response can qualitatively predict transition stiffnesses, nonlinear models are necessary to capture the behavior of hooks for stiffnesses below transition. Furthermore, we show that for the lower range of hook stiffnesses observed in actual bacteria, models which capture the full deformations of hooks are necessary. Inclusion of the hydrodynamic interactions of the cell body, hook, and flagellum is required to quantitatively simulate nonlinear dynamics of soft hooks during flick motility.


Assuntos
Fenômenos Fisiológicos Bacterianos , Flagelos/metabolismo , Modelos Biológicos , Movimento , Bactérias/citologia , Natação
5.
Phys Rev E ; 97(1-1): 012402, 2018 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-29448321

RESUMO

Dynamical bending, buckling, and polymorphic transformations of the flagellum are known to affect bacterial motility, but run-reverse-flick motility of monotrichous bacteria also involves the even more flexible hook connecting the flagellum to its rotary motor. Although flick initiation has been hypothesized to involve either static Euler buckling or dynamic bending of the hook, the precise mechanism of flick initiation remains unknown. Here, we find that flicks initiate via a dynamic instability requiring flexibility in both the hook and flagellum. We obtain accurate estimates of forces and torques on the hook that suggest that flicks occur for stresses below the (static) Euler buckling criterion, then provide a mechanistic model for flick initiation that requires combined bending of the hook and flagellum. We calculate the triggering torque-stiffness ratio and find that our predicted onset of dynamic instability corresponds well with experimental observations.


Assuntos
Flagelos/fisiologia , Modelos Biológicos , Fenômenos Biomecânicos , Elasticidade , Hidrodinâmica , Movimento , Rotação , Torque , Vibrio alginolyticus/fisiologia
6.
Phys Rev E ; 95(6-2): 069904, 2017 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-28709356

RESUMO

This corrects the article DOI: 10.1103/PhysRevE.90.063006.

7.
Sci Rep ; 6: 30472, 2016 07 28.
Artigo em Inglês | MEDLINE | ID: mdl-27464852

RESUMO

The realization of reconfigurable modular microrobots could aid drug delivery and microsurgery by allowing a single system to navigate diverse environments and perform multiple tasks. So far, microrobotic systems are limited by insufficient versatility; for instance, helical shapes commonly used for magnetic swimmers cannot effectively assemble and disassemble into different size and shapes. Here by using microswimmers with simple geometries constructed of spherical particles, we show how magnetohydrodynamics can be used to assemble and disassemble modular microrobots with different physical characteristics. We develop a mechanistic physical model that we use to improve assembly strategies. Furthermore, we experimentally demonstrate the feasibility of dynamically changing the physical properties of microswimmers through assembly and disassembly in a controlled fluidic environment. Finally, we show that different configurations have different swimming properties by examining swimming speed dependence on configuration size.

8.
Artigo em Inglês | MEDLINE | ID: mdl-25615186

RESUMO

Magnetically actuated microswimmers have recently attracted attention due to many possible biomedical applications. In this study we investigate the dynamics of rigid magnetically rotated microswimmers with permanent magnetic dipoles. Our approach uses a boundary element method to calculate a mobility matrix, accurate for arbitrary geometries, which is then used to identify the steady periodically rotating orbits in a co-rotating body-fixed frame. We evaluate the stability of each of these orbits. We map the magnetoviscous behavior as a function of dimensionless Mason number and as a function of the angle that the magnetic field makes with its rotation axis. We describe the wobbling motion of these swimmers by investigating how the rotation axis changes as a function of experimental parameters. We show that for a given magnetic field strength and rotation frequency, swimmers can have more than one stable periodic orbit with different rotation axes. Finally, we demonstrate that one can improve the controllability of these types of microswimmers by adjusting the relative angle between the magnetic field and its axis of rotation.

9.
Artigo em Inglês | MEDLINE | ID: mdl-25314529

RESUMO

Controllable propulsion of microscale and nanoscale devices enhanced with additional functionality would enable the realization of miniaturized robotic swimmers applicable to transport and assembly, actuators, and drug delivery systems. Following biological examples, existing magnetically actuated microswimmers have been designed to use flexibility or chirality, presenting fabrication challenges. Here we show that, contrary to biomimetic expectations, magnetically actuated geometries with neither flexibility nor chirality can produce propulsion, through both experimental demonstration and a theoretical analysis, which elucidates the fundamental constraints on micropropulsion via magnetetic rotation. Our results advance existing paradigms of low-Reynolds-number propulsion, possibly enabling simpler fabrication and design of microswimmers and nanoswimmers.


Assuntos
Fenômenos Magnéticos , Rotação , Algoritmos , Elasticidade , Modelos Lineares , Imãs , Modelos Teóricos , Nanoestruturas , Robótica , Natação , Torque
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