arXiv subjects

Jānis Cīmurs

Publications and source records attributed to Jānis Cīmurs.

4 recordsLinked to original sources

arXiv2024

Physical model of serum supplemented medium flow in organ-on-a-chip systems

Creating a physiologically relevant shear stress in organ-on-a-chip (OOC) devices requires careful tailoring of microfluidic flow parameters. It is currently fairly common to use a simple approximation assuming a constant viscosity, even for serum-based media. Here, we show that a popular nutrient solution (Dulbecco's Modified Eagle Medium supplemented with Fetal Bovine Serum) requires a more complex treatment (i.e., is a non-Newtonian fluid), with observed shear stress values significantly greater than reported in literature. We measure the rheology of the solutions and combine it with a 3-dimensional flow field measurement to derive shear stress at the channel surface. We verify the experiments with numerical simulations, finding good agreement and deriving flow properties. Finally, we provide relevant expressions for shear stress approximation, suitable for development of OOC devices with various geometries.

physics.flu-dyn↗

arXiv2023

Macroscopic emulation of microscopic magnetic particle systems

In this work we show that macroscopic experiments can be used to investigate microscopic systems. Such macroscopic experiments enable testing the assumptions and results obtained by theoretical considerations or simulations that can not be obtained under microscope (e.g., the orientation of a spherical particle). To emulate the dynamics of a single hematite cube immersed in water and subjected to a rotating magnetic field, a cubic magnet is firmly positioned in a 3D printed superball shell. The dimensionless parameters of the microscopic and macroscopic systems can be equalized by using a glycerol-water mixture instead of water as well as by the material and infill of the 3D printed shell. The pose of the superball is tracked using ArUco stickers which act as fiducial markers. It was found that there is a qualitative agreement between the macroscopic experiments and theoretical predictions. However, the reduced thermal effects in the macroscopic experiments lead to an increase in friction between the superball and the surface, thus shifting the critical frequency of the system. Since the shell is 3D printed, the given method can be extended to any shape and magnetization orientation.

cond-mat.soft↗

arXiv2022

Adaptively compressed exchange in LAPW

We present an implementation of the adaptively compressed exchange (ACE) operator in the LAPW formalism. ACE is a low-rank representation of the Fock exchange that avoids any loss of precision for the total energy. Our study shows that this property remains in the all-electron case, as we apply this method in non-relativistic total-energy calculations with a hybrid exchange-correlation functional PBE0. The obtained data for light atoms and molecules are within a few $μ$Ha off the precise multi-resolution-analysis calculations. Aside from ACE, another key ingredient to achieve such a high precision with Fock exchange was the use of high-energy local orbitals. Finally, we use this implementation to calculate PBE0 gaps in solids and compare the results to other all-electron results.

cond-mat.mtrl-sci↗

arXiv2018

Stability of paramagnetic spheroid in precessing field

Stability analysis of paramagnetic prolate and oblate spheroidal particle in precessing magnetic field is studied. Bifurcation diagram is calculated analytically in dependence of magnetic field frequency and precession angle. The direction of particle in synchronous regime is calculated. Rotational dynamics and mean rotational frequency in asynchronous regime is found. Obtained theoretical model gives possibility to calculate analytically dynamics of the particle in limiting case (when motion is periodic). Theoretically obtained models were compared with experimental results of rod like particle dynamics in precessing magnetic field. Experimental results are in good agreement with proposed theory.

cond-mat.soft↗