Maxim Solovchuk | National Taiwan University (original) (raw)

Papers by Maxim Solovchuk

Acoustic hemostasis is a new field of ultrasound research in which high intensity focused ultraso... more Acoustic hemostasis is a new field of ultrasound research in which high intensity focused ultrasound (HIFU) is used to induce hemostasis. Although it was experimentally shown that focused ultrasound can be used to seal the bleeding site while leaving the vessel patent and to occlude the blood vessel, physical mechanisms of acoustic hemostasis are not fully understood. Quanti-* Speaker.

EAI/Springer Innovations in Communication and Computing, 2024

Social Science Research Network, 2020

Background: Case isolation and contact tracing are two essential parts of control measures to pre... more Background: Case isolation and contact tracing are two essential parts of control measures to prevent the spread of COVID-19. Recent studies have shown that asymptomatic and pre-symptomatic transmissions play an important role in the ongoing SARS-CoV-2 pandemic, which makes outbreak control only through contact tracing and case isolation very difficult. Additional interventions, such as mask wearing, are required. There are various approaches to mask usage during the epidemic and, correspondingly, their effects on disease transmission may differ. We modelled the effects of different interventions on the disease spread and showed that high mask wearing coverage can lead to a better control of the outbreak, even in the absence of a lockdown. Methods: A stochastic model of COVID-19 propagation was implemented in order to estimate the effectiveness of mask wearing in addition to case isolation and contact tracing. It is assumed that after isolation, an infected person cannot transmit the virus anymore. We varied the percentage of mask efficiency and the percentage of people wearing masks and investigated three different approaches towards mask usage: the mask prevents spreading of the infection, and an infected person only starts wearing it after the onset of symptoms; the mask prevents spreading and all people wear masks; all people wear masks, and the mask prevents spreading and protects healthy persons from getting infection. We estimated the effect of mask wearing together with other interventions on the basic reproduction number (R0) and calculated the effective reproduction number after implementation of interventions. We also simulated the possibility of controlling the outbreak. An outbreak was defined as being controlled if it did not exceed a total of 5000 cases over three months and no new cases were found in the following fourth month. Findings: For the 20 initial symptomatic cases, with 40% pre-symptomatic transmission and a R0 = 2·5 , the outbreak could not be controlled even with 100% contact tracing. Wearing of masks only after symptom onset added only a very small improvement on the pandemic situation and cannot be used to control the outbreak. When all people wear masks and it is assumed that a mask prevents spreading and protects healthy individuals, then there is almost 70% probability of outbreak control even without contact tracing. The probability of control increases with an increase in the number of traced contacts. As a result, with 60% efficiency of contact tracing, the outbreak can be controlled with almost 100% probability. When initial number of asymptomatic cases is equal to the number of symptomatic cases, then an almost completely controlled outbreak is achieved when 70% of all people wear masks and 60% of infected individuals (with symptoms) are traced. Similar results can be achieved for larger number of total initial cases. Interpretation: With a large proportion of infectiousness before the onset of symptoms (40%) and the presence of asymptomatic cases, three investigated interventions (isolation of cases, contact tracing, and mask wearing by all people) are sufficient to control the disease spread within three months. A high probability of mask wearing by both infected and healthy people, even in presence of asymptomatic individuals, significantly increased the probability of controlling the outbreak even with only modest effectiveness of contact tracing. This shows that a second wave of COVID-19 could be avoided by tracing contacts and through the use of masks. Funding Statement: This work was supported in part by NHRI (National Health Research Institutes, Taiwan, project number BN-106-PP-08) and MOST (Ministry of Science and Technology, Taiwan, project number MOST 106 2115 M 400 001). Declaration of Interests: The authors declare no comparing interests.

Nanoscale, 2022

Concentration profiles of sodium and chloride ions through the envelope (E) protein of SARS-CoV-2... more Concentration profiles of sodium and chloride ions through the envelope (E) protein of SARS-CoV-2 RNA virus.

Physical review, Nov 13, 2020

Ion flow inside an ion channel can be described through continuum based Born-Poisson-Nernst-Planc... more Ion flow inside an ion channel can be described through continuum based Born-Poisson-Nernst-Planck (BPNP) equations in conjunction with the Lennard-Jones potential. Keeping in mind the ongoing pandemic, in this study, an attempt has been made to understand the selectivity and the current voltage relation of the COVID-19 E protein pentameric ion channel. Two ionic species, namely Na + and Cl − , have been considered here. E protein is one of the smallest structural protein which is embedded in the outer membrane of the virus. Once the virus is inside the host cell, this protein is expressed abundantly and is responsible for activities such as replication and budding of the virus. In the literature, we can find a few experimental studies focusing on understanding the activity of the channel formed by E proteins of different viruses. Here, we attempt the same study for the COVID-19 E protein ion channel through mathematical modeling. The channel geometry is calculated from the protein data bank file which was provided by NARLabs, Taiwan, using the HOLE program. Further, it was used to obtain the charge distribution using the PDBTOPQR online program. The immersed boundary-lattice Boltzmann method (IB-LBM) has been implemented to numerically solve the system of equations in the channel generated by the protein data bank file. Further, an in-house code which operates on multiple GPUs and uses the CUDA platform has been developed to achieve the goal of performing the current investigation.

Journal of Clinical Medicine, Jun 23, 2021

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Computers & Fluids, Sep 1, 2018

A double-precision numerical solver to describe the propagation of high-intensity ultrasound fluc... more A double-precision numerical solver to describe the propagation of high-intensity ultrasound fluctuations using a novel finite-amplitude compressible acoustic model working in multiple processing units (GPUs) is presented. The present solver is based on a conservative hyperbolic formulation derived from a variational analysis of the compressible Navier-Stokes equations and is implemented using an explicit highorder finite difference strategy. In this work, a WENO-Z reconstruction scheme along with a high-order finite-difference stencil are used to approximate the contributions of convective and diffusive spatial operators, respectively. The spatial operators are then associated to a low-storage Runge-Kutta scheme to integrate the system explicitly in time. The present multi-GPU implementation aims to make the best use of every single GPU and gain optimal performance of the algorithm on the per-node basis. To assess the performance of the present solver, a typical mini-server computer with 4 Tesla K80 dual GPU accelerators is used. The results show that the present formulation scales linearly for large domain problems. Moreover, when compared to an OpenMP implementation running with an i7 processor of 4.2 GHz, this is outperformed by our MPI-GPU implementation by a factor of 99. In this work, the present multi-GPU solver is illustrated with a three-dimensional simulation of a highly-intense focused ultrasound propagation.

Social Science Research Network, 2022

International Journal of Heat and Mass Transfer, 2012

Computer Methods in Applied Mechanics and Engineering, Nov 1, 2019

Highlights • Free surface influences the time scale on which bioconvection patterns occur. • Conv... more Highlights • Free surface influences the time scale on which bioconvection patterns occur. • Convection patterns resemble to those characteristic for Bénard type convection. • Three-dimensional results show an excellent resemblance to real experiment.

International Journal of Heat and Mass Transfer, Aug 1, 2011

arXiv (Cornell University), Jan 7, 2022

An energy stable finite element scheme within arbitrary Lagrangian Eulerian (ALE) framework is de... more An energy stable finite element scheme within arbitrary Lagrangian Eulerian (ALE) framework is derived for simulating the dynamics of millimetric droplets in contact with solid surfaces. Supporting surfaces considered may exhibit non-homogeneous properties which are incorporated into system through generalized Navier boundary conditions (GNBC). Numerical scheme is constructed such that the counterpart of (continuous) energy balance holds on the discrete level. This ensures that no spurious energy is introduced into the discrete system, i.e. the discrete formulation is stable in the energy norm. The newly proposed scheme is numerically validated to confirm the theoretical predictions. Of a particular interest is the case of droplet on a non-homogeneous inclined surface. This case shows the capabilities of the scheme to capture the complex droplet dynamics (sliding and rolling) while maintaining stability during the long time simulation.

AIP Advances, 2023

Fluid-ion transport through a nanochannel is studied to understand the role and impact of differe... more Fluid-ion transport through a nanochannel is studied to understand the role and impact of different physical phenomena and medium properties on the flow. Mathematically, the system is described through coupled fourth order Poisson-Nernst-Planck-Bikerman and Navier-Stokes equations. The fourth order-Poisson-Nernst-Planck-Bikerman model accounts for ionic and nonionic interactions between particles, the effect of finite size of the particles, polarization of the medium, solvation of the ions, etc. Navier-Stokes equations are modified accordingly to include both electroviscous and viscoelectric effects and the velocity slip. The governing equations are discretized using the lattice Boltzmann method. The mathematical model is validated by comparing the analytical and experimental ion activity while the numerical model is validated by comparing the analytical and numerical velocity profiles for electro-osmotic flow through a microchannel. For a pressure driven flow, the electroviscous and viscoelectric effects decrease the fluid velocity while the velocity slip enhances it. The acidity of the medium also influences the fluid velocity by altering the ζ potential and ion concentration. The finite size of the particle limits the concentration of ionic species, thus, reducing electroviscous effects. As the external concentration decreases, the impact of finite size of particles also reduces. The inhomogeneous diffusion coefficient also influences electroviscous effects as it changes the concentration distribution. The variation in external pressure does not influence the impact of steric and viscoelectric effects significantly. The maximum impact is observed for ΔP = 0 (electro-osmotic flow).

Nucleation and Atmospheric Aerosols, 2012

The present study is aimed at predicting liver tumor temperature during a high-intensity focused ... more The present study is aimed at predicting liver tumor temperature during a high-intensity focused ultrasound (HIFU) thermal ablation in a patient-specific liver geometry. The model comprises the nonlinear Westervelt equation and bioheat equations in liver and blood vessel. The nonlinear hemodynamic equations are also taken into account with the convected cooling and acoustic streaming effects being taken into account. We found from this three-dimensional three-field coupling study that in large blood vessel both convective ...

Journal of Computational Surgery, Jan 10, 2014

High-intensity focused ultrasound (HIFU) is a rapidly developing medical technology that allows n... more High-intensity focused ultrasound (HIFU) is a rapidly developing medical technology that allows non-invasive thermal ablation of tumors. Thermal treatment of liver tumor, which is one of the most common malignancies worldwide, is problematic because large blood vessels act as a heat sink. Convective cooling protects the cancer cells from thermal destruction and decreases the necrosed volume. A major objective of the method development is to achieve a virtually complete necrosis of tumors close to major blood vessels and to avoid blood vessel damage and, hence, the needed treatment planning. The present study is aimed at predicting liver tumor temperature during HIFU thermal ablation in a patient-specific liver geometry. The model comprises the nonlinear Westervelt equation and bioheat equations in the liver and blood vessels. The nonlinear hemodynamic equations are also taken into account with the convected cooling and acoustic streaming effects being taken into account. We found from this three-dimensional three-field coupling study that in large blood vessels, both convective cooling and acoustic streaming may change the temperature considerably near the blood vessel. More precisely, acoustic streaming velocity magnitude can be several times larger than the blood vessel velocity. The results presented in the current work can be further used to construct a surgical planning platform.

Journal of Non-newtonian Fluid Mechanics, Sep 1, 2023

arXiv (Cornell University), Sep 18, 2018

The aim of this paper is to introduce a finite element formulation within Arbitrary Lagrangian Eu... more The aim of this paper is to introduce a finite element formulation within Arbitrary Lagrangian Eulerian framework with vanishing discrete Space Conservation Law (SCL) for differential equations on time dependent domains. The novelty of the formulation is the method for temporal integration which results in preserving the SCL property and retaining the higher order accuracy at the same time. Once the time derivative is discretized (based on integration or differentiation formula), the common approach for terms in differential equation which do not involve temporal derivative is classified to be a kind of "time averaging" between time steps. In the spirit of classical approaches, this involves evaluating these terms in several points in time between the current and the previous time step ([tn, t n+1 ]), and then averaging them in order to provide the satisfaction of discrete SCL. Here, we fully use the polynomial in time form of mapping through which evolution of domain is realized-the so called ALE map-in order to avoid the problematics arising due to the moving grids. We give a general recipe on temporal schemes that have to be employed once the discretization for the temporal derivative is chosen. Numerical investigations on stability, accuracy and convergence are performed and the simulated results are compared with benchmark problems set up by other authors.

Journal of the Acoustical Society of America, Nov 1, 2013

This study investigates the influence of blood flow on temperature distribution during high-inten... more This study investigates the influence of blood flow on temperature distribution during high-intensity focused ultrasound (HIFU) ablation of liver tumors. A three-dimensional acoustic-thermal-hydrodynamic coupling model is developed to compute the temperature field in the hepatic cancerous region. The model is based on the nonlinear Westervelt equation, bioheat equations for the perfused tissue and blood flow domains. The nonlinear Navier-Stokes equations are employed to describe the flow in large blood vessels. The effect of acoustic streaming is also taken into account in the present HIFU simulation study. A simulation of the Westervelt equation requires a prohibitively large amount of computer resources. Therefore a sixth-order accurate acoustic scheme in threepoint stencil was developed for effectively solving the nonlinear wave equation. Results show that focused ultrasound beam with the peak intensity 2470 W/cm 2 can induce acoustic streaming velocities up to 75 cm/s in the vessel with a diameter of 3 mm. The predicted temperature difference for the cases considered with and without acoustic streaming effect is 13.5 C or 81% on the blood vessel wall for the vein. Tumor necrosis was studied in a region close to major vessels. The theoretical feasibility to safely necrotize the tumors close to major hepatic arteries and veins was shown.

Computer Methods in Applied Mechanics and Engineering, Oct 1, 2022

Computer Methods in Applied Mechanics and Engineering, Dec 1, 2020

Abstract It is known that spurious non-physical velocities can occur when one employs the finite ... more Abstract It is known that spurious non-physical velocities can occur when one employs the finite element method for simulation of incompressible flows subjected to external forces. In presence of external body forces, the main reason for this is the incompressibility constraint that is satisfied only in a weak sense against test functions from the pressure function space. In case of the two-phase (incompressible) immiscible flow, a surface force, which is a function of the interface curvature, arises and introduces additional problematics to the finite element model. Due to discrete representation of the interface, the question arises on how to approximate the curvature. A particularly natural approach for the finite element method employs the Laplace–Beltrami operator which allows to express the mean curvature in a weak sense. However, once incorporated into the equations governing the fluid flow, Laplace–Beltrami-reconstructed curvature may introduce spurious non-physical forces at the interface if finite element spaces are chosen arbitrarily. The reason for this is that the test space used for curvature calculation is the test space associated with the velocity field. We show that it is necessary for the function space used for the geometry construction to be of the order equal to or higher than the order of the test space involved in curvature evaluation. This leaves two possibilities for practical fluid flow problems: use the same function spaces for the mesh geometry and the velocity field (isoparametric concept) or decouple the curvature calculation from the main problem.