# Physical Review E

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### Stability criterion for the magnetic separation of rare-earth ions

Author(s): Zhe Lei, Barbara Fritzsche, and Kerstin Eckert

The stability criterion for the magnetic separation of rare-earth ions is studied, taking dysprosium Dy(iii) ions as an example. Emphasis is placed on quantifying the factors that limit the desired high enrichment. During magnetic separation, a layer enriched in Dy(iii) ions is generated via the sur...

[Phys. Rev. E 101, 013109] Published Fri Jan 17, 2020

### Acoustic streaming outside and inside a fluid particle undergoing monopole and dipole oscillations

Author(s): Thierry Baasch, Alexander A. Doinikov, and Jürg Dual

An analytical theory is developed for acoustic streaming induced by an acoustic wave field inside and outside a spherical fluid particle, which can be a liquid droplet or a gas bubble. The particle is assumed to undergo the monopole (pulsation) and the dipole (translation) oscillation modes. The dis...

[Phys. Rev. E 101, 013108] Published Wed Jan 15, 2020

### Mode-locked rotating detonation waves: Experiments and a model equation

Author(s): James Koch, Mitsuru Kurosaka, Carl Knowlen, and J. Nathan Kutz

Direct observation of a rotating detonation engine combustion chamber has enabled the extraction of the kinematics of its detonation waves. These records exhibit a rich set of instabilities and bifurcations arising from the interaction of coherent wave fronts and global gain dynamics. We develop a m...

[Phys. Rev. E 101, 013106] Published Fri Jan 10, 2020

### Multifidelity kinematic parameter optimization of a flapping airfoil

Author(s): Hongyu Zheng, Fangfang Xie, Tingwei Ji, Zaoxu Zhu, and Yao Zheng

We construct a multifidelity framework for the kinematic parameter optimization of flapping airfoil. We employ multifidelity Gaussian process regression and Bayesian optimization to effectively synthesize the aerodynamic performance of the flapping airfoil with the kinematic parameters under multire...

[Phys. Rev. E 101, 013107] Published Fri Jan 10, 2020

### Influence of the viscosity and charge mobility on the shape deformation of critically charged droplets

Author(s): E. Giglio, J. Rangama, S. Guillous, and T. Le Cornu

In this work, we model and simulate the shape evolution of critically charged droplets, from the initial spherical shape to the charge emission and back to the spherical shape. The shape deformation is described using the viscous correction for viscous potential flow model, which is a potential flow...

[Phys. Rev. E 101, 013105] Published Thu Jan 09, 2020

### Drag forces on nanoparticles in the free-molecule regime: Effect of the particle temperature

Author(s): Jun Wang, Junjie Su, and Guodong Xia

In the present paper, we theoretically study the drag force on nanoparticles in the free-molecule regime. It has been widely assumed that the particle temperature is equal to the gas media temperature in the open literature. However, this assumption can be invalid in some real applications. Based on...

[Phys. Rev. E 101, 013103] Published Wed Jan 08, 2020

### Study of the Hopf functional equation for turbulence: Duhamel principle and dynamical scaling

Author(s): Koji Ohkitani

We consider a formulation for the Hopf functional differential equation which governs statistical solutions of the Navier-Stokes equations. By introducing an exponential operator with a functional derivative, we recast the Hopf equation as an integro-differential functional equation by the Duhamel p...

[Phys. Rev. E 101, 013104] Published Wed Jan 08, 2020

### Input-output system identification of a thermoacoustic oscillator near a Hopf bifurcation using only fixed-point data

Author(s): Minwoo Lee, Yu Guan, Vikrant Gupta, and Larry K. B. Li

We present a framework for performing input-output system identification near a Hopf bifurcation using data from only the fixed-point branch, prior to the Hopf point itself. The framework models the system with a van der Pol–type equation perturbed by additive noise, and identifies the system parame...

[Phys. Rev. E 101, 013102] Published Mon Jan 06, 2020

### Application of the Schwarz-Christoffel map to the Laplacian growth of needles and fingers

Author(s): N. R. McDonald

A numerical procedure based on the Schwarz-Christoffel map suitable for the study of the Laplacian growth of thin two-dimensional protrusions is presented. The protrusions take the form of either straight needles or curved fingers satisfying Loewner's equation, and are represented by slits in the co...

[Phys. Rev. E 101, 013101] Published Fri Jan 03, 2020

### Numerical study on electrohydrodynamic multiple droplet interactions

Author(s): P. S. Casas, M. Garzon, L. J. Gray, and J. A. Sethian

We present a numerical study of inviscid multiple droplet coalescence and break-up under the action of electric forces. Using an embedded potential flow model for the droplet hydrodynamics, coupled with an unbounded exterior electrostatic problem, we are able to perform computations through various ...

[Phys. Rev. E 100, 063111] Published Mon Dec 30, 2019

### Flagellated bacteria swim in circles near a rigid wall

Author(s): Yunyoung Park, Yongsam Kim, and Sookkyung Lim

The rotation of bacterial flagella driven by rotary motors enables the cell to swim through fluid. Bacteria run and reorient by changing the rotational direction of the motor for survival. Fluid environmental conditions also change the course of swimming; for example, cells near a solid boundary dra...

[Phys. Rev. E 100, 063112] Published Mon Dec 30, 2019

### Solute transport in porous media studied by lattice Boltzmann simulations at pore scale and x-ray tomography experiments

Author(s): Chunwei Zhang, Tetsuya Suekane, Kosuke Minokawa, Yingxue Hu, and Anindityo Patmonoaji

With the aid of nondestructive microfocus x-ray computed tomography (CT), we performed three-dimensional (3D) tracer dispersion experiments on randomly unconsolidated packed beds. Plumes of nonreactive sodium iodide solution were point injected into a sodium chloride solvent as a tracer for the eval...

[Phys. Rev. E 100, 063110] Published Thu Dec 26, 2019

### Upper bound on angular momentum transport in Taylor-Couette flow

Author(s): Zijing Ding and Elena Marensi

We investigate the upper bound on angular momentum transport in Taylor-Couette flow theoretically and numerically by a one-dimensional background field method. The flow is bounded between a rotating inner cylinder of radius Ri and a fixed outer cylinder of radius Ro. A variational problem is formula...

[Phys. Rev. E 100, 063109] Published Tue Dec 24, 2019

### Acoustic radiation force acting on a heavy particle in a standing wave can be dominated by the acoustic microstreaming

Author(s): Thierry Baasch, Alen Pavlic, and Jürg Dual

We numerically investigate the contribution of the microstreaming to the acoustic radiation force acting on a small elastic spherical particle placed into an ultrasonic standing wave. When an acoustic wave scatters on a particle the acoustic radiation force and the microstreaming appear as nonlinear...

[Phys. Rev. E 100, 061102(R)] Published Mon Dec 23, 2019

### Flow-induced buckling dynamics of sperm flagella

Author(s): Manish Kumar, Derek M. Walkama, Jeffrey S. Guasto, and Arezoo M. Ardekani

The swimming sperm of many external fertilizing marine organisms face complex fluid flows during their search for egg cells. Aided by chemotaxis, relatively weak flows are known to enhance sperm-egg fertilization rates through hydrodynamic guidance. However, strong flows have the potential to mechan...

[Phys. Rev. E 100, 063107] Published Fri Dec 20, 2019

### Clustering of floating tracers in weakly divergent velocity fields

Author(s): Konstantin V. Koshel, Dmitry V. Stepanov, Eugene A. Ryzhov, Pavel Berloff, and V. I. Klyatskin

This work deals with buoyant tracers floating at the ocean surface, where the geostrophic velocity component is two dimensional and rotational (nondivergent) and the ageostrophic component can contain rotational and potential (divergent) contributions that are comparable in size. We consider a rando...

[Phys. Rev. E 100, 063108] Published Fri Dec 20, 2019

### Active pitching of short splitters past a cylinder: Drag increase and wake

Author(s): Yaqing Jin, Shyuan Cheng, and Leonardo P. Chamorro

The flow and drag induced by active pitching of plates in the wake of a cylinder of diameter d were experimentally studied for various plate lengths L as well as pitching frequencies fp and amplitudes A0 at Reynolds number Re=1.6×104. Planar particle image velocimetry and a load cell were used to ch...

[Phys. Rev. E 100, 063106] Published Thu Dec 19, 2019

### Application of the stochastic closure theory to the Townsend-Perry constants

Author(s): John Kaminsky, Joe Klewicki, and Björn Birnir

We compare the stochastic closure theory (SCT) to the Townsend-Perry constants as estimated from measurements in the Flow Physic Facility (FPF) at the University of New Hampshire. First, we explain the derivation of the Townsend-Perry constants, which were originally formulated by Meneveau and Marus...

[Phys. Rev. E 100, 061101(R)] Published Mon Dec 16, 2019

### Jet direction in bubble collapse within rectangular and triangular channels

Author(s): Lebo Molefe and Ivo R. Peters

A vapor bubble collapsing near a solid boundary in a liquid produces a liquid jet that points toward the boundary. The direction of this jet has been studied for boundaries such as flat planes and parallel walls enclosing a channel. Extending these investigations to enclosed polygonal boundaries, we...

[Phys. Rev. E 100, 063105] Published Fri Dec 13, 2019

### Stability boundaries for the Rayleigh-Taylor instability in accelerated elastic-plastic solid slabs

Author(s): A. R. Piriz, S. A. Piriz, and N. A. Tahir

The linear theory of the incompressible Rayleigh-Taylor instability in elastic-plastic solid slabs is developed on the basis of the simplest constitutive model consisting in a linear elastic (Hookean) initial stage followed by a rigid-plastic phase. The slab is under the action of a constant acceler...

[Phys. Rev. E 100, 063104] Published Thu Dec 12, 2019