0000000000246546
AUTHOR
Kaspars ĒRglis
showing 12 related works from this author
Time-resolved velocity measurements in a magnetic micromixer
2015
Abstract Mixing efficiency is lower in passive micromixers due to viscous forces and substantial research effort is focused on designing high performance micromixers. Active micromixers make use of external forces to enhance mixing efficiency. Among these, magnetic forces are popular because they are non-contact and therefore the micromixer design can be kept simple. Laser-based diagnostic tools have great potential in providing multi-parameter information in microfluidics research on mixing. MicroPIV experiments are performed to investigate the transient flow field in a magnetic micromixer undergoing labyrinthine instability. Velocity and interface front information is extracted from a seq…
Magnetic field driven micro-convection in the Hele-Shaw cell: the Brinkman model and its comparison with experiment
2015
International audience; The micro-convection caused by the ponderomotive forces of the self-magnetic field in a magnetic fluid is studied here both numerically and experimentally. The theoretical approach based on the general Brinkman model substantially improves the description with respect to the previously proposed Darcy model. The predictions of both models are here compared to finely controlled experiments. The Brinkman model, in contrast to the Darcy model, allows us to describe the formation of mushrooms on the plumes of the micro-convective flow and the width of the fingers. In the Brinkman approach, excellent quantitative agreement is also obtained for the finger velocity dynamics …
Flexible ferromagnetic filaments and the interface with biology
2009
Flexible ferromagnetic filaments are studied both theoretically and experimentally. Two main deformation modes of the filament at magnetic field inversion are theoretically described and observed experimentally by using DNA-linked chains of ferromagnetic particles. Anomalous orientation of ferromagnetic filaments perpendicular to AC field with a frequency which is high enough is predicted and confirmed experimentally. By experimental studies of magnetotactic bacteria it is demonstrated how these properties of ferromagnetic filaments may be used to measure the flexibility of the chain of magnetosomes.
Gelation of semiflexible polyelectrolytes by multivalent counterions
2012
Filamentous polyelectrolytes in aqueous solution aggregate into bundles by interactions with multivalent counterions. These effects are well documented by experiment and theory. Theories also predict a gel phase in isotropic rodlike polyelectrolyte solutions caused by multivalent counterion concentrations much lower than those required for filament bundling. We report here the gelation of Pf1 virus, a model semiflexible polyelectrolyte, by the counterions Mg(2+), Mn(2+) and spermine(4+). Gelation can occur at 0.04% Pf1 volume fraction, which is far below the isotropic-nematic transition of 0.7% for Pf1 in monovalent salt. Unlike strongly crosslinked gels of semiflexible polymers, which stif…
Salmon fibrinogen and chitosan scaffold for tissue engineering: in vitro and in vivo evaluation
2018
3D fibrous scaffolds have received much recent attention in regenerative medicine. Use of fibrous scaffolds has shown promising results in tissue engineering and wound healing. Here we report the development and properties of a novel fibrous scaffold that is useful for promoting wound healing. A scaffold made of salmon fibrinogen and chitosan is produced by electrospinning, resulting in a biocompatible material mimicking the structure of the native extracellular matrix (ECM) with suitable biochemical and mechanical properties. The scaffold is produced without the need for enzymes, in particular thrombin, but is fully compatible with their addition if needed. Human dermal fibroblasts culture…
Magnetic microrods as a tool for microrheology
2015
International audience; Dynamics of superparamagnetic rods in crossed constant and alternating magnetic fields as a function of field frequency are studied and it is shown that above the critical value of the amplitude of the alternating field the rod oscillates around the direction of the alternating field. The fit of the experimentally measured time dependence of the mean orientation angle of the rod allows one to determine the ratio of magnetic and viscous torques which act on the rod. The protocol of microrheological measurements consists of recording the dynamics of the orientation of the rod when the magnetic field is applied at an angle to the rod and observing its relaxation due to …
Dynamics of Magnetotactic Bacteria in a Rotating Magnetic Field
2007
The dynamics of the motile magnetotactic bacterium Magnetospirillum gryphiswaldense in a rotating magnetic field is investigated experimentally and analyzed by a theoretical model. These elongated bacteria are propelled by single flagella at each bacterial end and contain a magnetic filament formed by a linear assembly of approximately 40 ferromagnetic nanoparticles. The movements of the bacteria in suspension are analyzed by consideration of the orientation of their magnetic dipoles in the field, the hydrodynamic resistance of the bacteria, and the propulsive force of the flagella. Several novel features found in experiments include a velocity reversal during motion in the rotating field a…
Stability analysis of a paramagnetic spheroid in a precessing field
2019
Abstract The stability of a paramagnetic prolate or oblate spheroidal particle in a precessing magnetic field is studied. The bifurcation diagram is calculated analytically as a function of the magnetic field frequency and the precession angle. The orientation of the particle in the synchronous regime is calculated. The rotational dynamics and the mean rotational frequency in the asynchronous regime are also obtained. The theoretical model we describe enables the analytic calculation of the dynamics of the particle in the limiting case when the motion is periodic. The theoretical models were also compared with experimental results of rod like particle dynamics in a precessing magnetic field…
Lokanu magnētisku stīgu īpašību un kustības eksperimentāli pētījumi
2010
Elektroniskā versija nesatur pielikumus
Three dimensional dynamics of ferromagnetic swimmer
2011
It is shown that a flexible ferromagnetic filament self-propels perpendicularly to the AC magnetic field during a limited period of time due to the instability of the planar motion with respect to three dimensional perturbations. The transition from the oscillating U-like shapes to the oscillating S-like shapes is characterized by the calculated Wr number.
Magnetic field driven micro-convection in the Hele-Shaw cell
2013
AbstractMicro-convection caused by ponderomotive forces of the self-magnetic field of a magnetic fluid in the Hele-Shaw cell under the action of a vertical homogeneous magnetic field is studied both experimentally and numerically. It is shown that a non-potential magnetic force at magnetic Rayleigh numbers greater than the critical value causes fingering at the interface between the miscible magnetic and non-magnetic fluids. The threshold value of the magnetic Rayleigh number depends on the smearing of the interface between fluids. Fingering with its subsequent decay due to diffusion of particles significantly increases the mixing at the interface. Velocity and vorticity fields at fingering…
Elastic properties of DNA linked flexible magnetic filaments.
2011
Elastic properties of magnetic filaments linked by DNA in solutions of univalent and bivalent salts with different pH values are investigated through their deformation in an external field. A strong dependence of the bending modulus in bivalent salt solution on the pH is shown. Experimental results are interpreted on the basis of the magnetic elastica.