arXiv subjects

Marina Chugunova

Publications and source records attributed to Marina Chugunova.

At least 19 recordsLinked to original sources

arXiv2024

Analysis of a Radiotherapy Model for Brain Tumors

In this work, we focus on the analytical and numerical study of a mathematical model for brain tumors with radiotherapy influence. Under certain assumptions on the given data in the model, we prove existence and uniqueness of a weak nonnegative (biological relevant) solution. Then, assuming only more regular initial data, we obtain the extra regularity of this solution. Besides, we analyze the optimal control of the advection coefficient responding for the radiotherapy effect on the tumor cell population. Finally, we provide numerical illustration to all obtained analytical results.

math.AP↗

arXiv2024

Data Clustering and Visualization with Recursive Goemans-Williamson MaxCut Algorithm

In this article, we introduce a novel recursive modification to the classical Goemans-Williamson MaxCut algorithm, offering improved performance in vectorized data clustering tasks. Focusing on the clustering of medical publications, we employ recursive iterations in conjunction with a dimension relaxation method to significantly enhance density of clustering results. Furthermore, we propose a unique vectorization technique for articles, leveraging conditional probabilities for more effective clustering. Our methods provide advantages in both computational efficiency and clustering accuracy, substantiated through comprehensive experiments.

math.OC↗

arXiv2024

Data Clustering and Visualization with Recursive Max k-Cut Algorithm

In this article, we continue our analysis for a novel recursive modification to the Max $k$-Cut algorithm using semidefinite programming as its basis, offering an improved performance in vectorized data clustering tasks. Using a dimension relaxation method, we use a recursion method to enhance density of clustering results. Our methods provide advantages in both computational efficiency and clustering accuracy for grouping datasets into three clusters, substantiated through comprehensive experiments.

math.OC↗

arXiv2024

Modeling Ion-Specific Effects in Polyelectrolyte Brushes: A Modified Poisson-Nernst-Planck Model

Polyelectrolyte brushes consist of a set of charged linear macromolecules each tethered at one end to a surface. An example is the glycocalyx which refers to hair-like negatively charged sugar molecules that coat the outside membrane of all cells. We consider the transport and equilibrium distribution of ions, and the resulting electrical potential, when such a brush is immersed in a salt buffer containing monovalent cations (sodium and/or potassium). The Gouy-Chapman model for ion screening at a charged surface captures the effects of the Coulombic force that drives ion electrophoresis and diffusion, but neglects non-Coulombic forces and ion pairing. By including the distinct binding affinities of these counter-ions with the brush, and their so-called Born radii, which account for Born forces acting on them when the permittivity is non-uniform, we propose modified Poisson-Nernst-Planck continuum models that show the distinct profiles that may result depending on those ion-specific properties.

physics.bio-ph↗

arXiv2024

On weak solutions of a control-volume model for liquid films flowing down a fibre

This paper presents an analytical investigation of the solutions to a control volume model for liquid films flowing down a vertical fibre. The evolution of the free surface is governed by a coupled system of degenerate nonlinear partial differential equations, which describe the fluid film's radius and axial velocity. We demonstrate the existence of weak solutions to this coupled system by applying a priori estimates derived from energy-entropy functionals. Additionally, we establish the existence of traveling wave solutions for the system. To illustrate our analytical findings, we present numerical studies that showcase the dynamic solutions of the partial differential equations as well as the traveling wave solutions.

math.AP↗

arXiv2022

Qualitative analysis of solutions for a degenerate PDE model of epidemic dynamics

Compartmental models are widely used in mathematical epidemiology to describe dynamics of infection disease. A new SIS-PDE model, recently derived by Chalub and Souza, is based on a diffusion-drift approximation of probability density in a well-known discrete - time Markov chain SIS-DTMC model. This new SIS-PDE model is conservative due to degeneracy of the diffusion term at the origin. We analyze a class of degenerate PDE models and obtain sufficient conditions for existence of classical solutions with certain regularity properties. Also, we show that under some additional assumptions about coefficients and initial data classical solutions vanish at the origin at any finite time. Vanishing at the origin of solutions is consistent with the conservation property of the model. The main results of this article are: sufficient conditions for existence of weak solutions, analysis of their asymptotic behavior at the origin, and the proof of existence of weak solutions convergent to Dirac delta function. Moreover, we study long-time behavior of solutions and confirm our analysis by numerical computations.

math.AP↗

arXiv2022

Mathematical Modeling of Microscale Biology: Ion Pairing, Dielectric Decrement, and Born Energy in Glycosaminoglycan Brushes

Biological macromolecules including nucleic acids, proteins, and glycosaminoglycans are typically anionic and can span domains of up to hundreds of nanometers and even micron length scales. The structures exist in crowded environments that are dominated by weak multivalent electrostatic interactions that can be modeled using mean field continuum approaches that represent underlying molecular nanoscale biophysics. We develop such models for glycosaminoglycan brushes using both steady state modified Poisson-Boltzmann models and transient Poisson-Nernst-Planck models that incorporate important ion-specific (Hofmeister) effects. The results quantify how electroneutrality is attained through ion electrophoresis, dielectric decrement hydration forces, and ion-specific pairing. Brush-Salt interfacial profiles of the electrostatic potential as well as bound and unbound ions are characterized for imposed jump conditions across the interface. The models should be applicable to many intrinsically-disordered biophysical environments and are anticipated to provide insight into the design and development of therapeutics and drug-delivery vehicles to improve human health.

physics.bio-ph↗

arXiv2021

On travelling wave solutions of a model of a liquid film flowing down a fibre

Existence of non-negative weak solutions is shown for a full curvature thin-film model of a liquid thin film flowing down a vertical fibre. The proof is based on the application of a priori estimates derived for energy-entropy functionals. Long-time behaviour of these weak solutions is analysed and, under some additional constraints for the model parameters and initial values, convergence towards a travelling wave solution is obtained. Numerical studies of energy minimizers and travelling waves are presented to illustrate analytical results.

math.AP↗

arXiv2019

Thin liquid film resulting from a distributed source on a vertical wall

We examine the dynamics of a thin film formed by a distributed liquid source on a vertical solid wall. The model is derived using the lubrication approximation and includes the effects of gravity, upward airflow and surface tension. When surface tension is neglected, a critical source strength is found below which the film flows entirely upward due to the airflow, and above which some of the flow is carried downward by gravity. In both cases, a steady state is established over the region where the finite source is located. Shock waves that propagate in both directions away from the source region are analyzed. Numerical simulations are included to validate the analytical results. For models including surface tension, numerical simulations are carried out. The presence of surface tension, even when small, causes a dramatic change in the film profiles and the speed and structure of the shock waves. These are studied in more detail by examining the traveling wave solutions away from the source region.

physics.flu-dyn↗

arXiv2019

Existence and stability analysis of solutions for a ultradian glucocorticoid rhythmicity and acute stress model

The hypothalamic pituitary adrenal (HPA) axis responds to physical and mental challenge to maintain homeostasis in part by controlling the body's cortisol level. Dysregulation of the HPA axis is implicated in numerous stress-related diseases. For a structured model of the HPA axis that includes the glucocorticoid receptor but does not take into account the system response delay, we analyze linear and non-linear stability of stationary solutions. For a second mathematical model that describes the mechanism of the HPA axis self-regulatory activities and takes into account a delay of system response, we prove existence of periodic solutions under certain assumptions on ranges of parameter values and analyze stability of these solutions with respect to the time delay value.

math.DS↗

arXiv2018

Thin film flow dynamics on fiber nets

We analyze existence and qualitative behavior of non-negative weak solutions for fourth order degenerate parabolic equations on graph domains with Kirchhoff's boundary conditions at the inner nodes and Neumann boundary conditions at the boundary nodes. The problem is originated from industrial constructions of spray coated meshes which are used in water collection and in oil-water separation processes. For a certain range of parameter values we prove convergence toward a constant steady state that corresponds to the uniform distribution of coating on a fiber net.

math.AP↗

arXiv2017

Marangoni effects on a thin liquid film coating a sphere with axial or radial thermal gradients

We study the time evolution of a thin liquid film coating the outer surface of a sphere in the presence of gravity, surface tension and thermal gradients. We derive the fourth-order nonlinear partial differential equation that models the thin film dynamics, including Marangoni terms arising from the dependence of surface tension on temperature. We consider two different imposed temperature distributions with axial or radial thermal gradients. We analyze the stability of a uniform coating under small perturbations and carry out numerical simulations in COMSOL for a range of parameter values. In the case of an axial temperature gradient, we find steady states with either uniform film thickness, or with the fluid accumulating at the bottom or near the top of the sphere, depending on the total volume of liquid in the film, dictating whether gravity or Marangoni effects dominate. In the case of a radial temperature gradient, a stability analysis reveals the most unstable non-axisymmetric modes on an initially uniform coating film.

cond-mat.soft↗

arXiv2011

Convergence to equilibrium for a thin film equation on a cylindrical surface

The degenerate parabolic equation u_t + [u^3(u_xxx + u_x - sin x)]_x=0 models the evolution of a thin liquid film on a stationary horizontal cylinder. It is shown here that for each given mass there is a unique steady state, given by a droplet hanging from the bottom of the cylinder that meets the dry region at the top with zero contact angle. The droplet minimizes the energy and attracts all strong solutions that satisfy certain energy and entropy inequalities. The distance of any solution from the steady state decays no faster than a power law.

math.AP↗

arXiv2011

Asymptotic behavior of regularized shock solutions in coating flows

We consider a model for thin liquid films in a rotating cylinder in the small surface tension limit. Using dynamical system methods, we show that the continuum of increasing shock solutions persists in the small surface tension limit, whereas the continuum of decreasing shock solutions terminates at the limit. Using delicate numerical computations, we show that the existence curves of regularized shock solutions on the mass-flux diagram exhibit loops. The number of loops increases and their locations move to infinity as the surface tension parameter decreases to zero. If $n$ is the number of loops in the mass-flux diagram with $2n+1$ solution branches, we show that $n+1$ solution branches are stable with respect to small perturbations.

physics.flu-dyn↗

arXiv2010

On the energy-minimizing steady states of a thin film equation

Steady states of the thin film equation $u_t+[u^3 (u_xxx + α^2 u_x -\sin(x) )]_x=0$ are considered on the periodic domain $Ω= (-π,π)$. The equation defines a generalized gradient flow for an energy functional that controls the $H^1$-norm. The main result establishes that there exists for each given mass a unique nonnegative function of minimal energy. This minimizer is symmetric decreasing about $x=0$. For $α<1$ there is a critical value for the mass at which the minimizer has a touchdown zero. If the mass exceeds this value, the minimizer is strictly positive. Otherwise, it is supported on a proper subinterval of the domain and meets the dry region at zero contact angle. A second result explores the relation between strict positivity and exponential convergence for steady states. It is shown that positive minimizers are locally exponentially attractive, while the distance from a steady state with a dry region cannot decay faster than a power law.

math.AP↗

arXiv2010

Research Announcement: Finite-time Blow Up and Long-wave Unstable Thin Film Equations

We study short--time existence, long--time existence, finite speed of propagation, and finite--time blow--up of nonnegative solutions for long-wave unstable thin film equations $h_t = -a_0(h^n h_{xxx})_x - a_1(h^m h_x)_x$ with $n>0$, $a_0 > 0$, and $a_1 >0$. The existence and finite speed of propagation results extend those of [Comm Pure Appl Math 51:625--661, 1998]. For $0<n<2$ we prove the existence of a nonnegative, compactly--supported, strong solution on the line that blows up in finite time. The construction requires that the initial data be nonnegative, compactly supported in $\R^1$, be in $H^1(\R^1)$, and have negative energy. The blow-up is proven for a large range of $(n,m)$ exponents and extends the results of [Indiana Univ Math J 49:1323--1366, 2000].

math-ph↗

arXiv2010

New dissipated energy for nonnegative weak solution of unstable thin-film equations

The fluid thin film equation $h_t = - (h^n h_{xxx})_x - a_1\,(h^m h_x)_x$ is known to conserve mass $\int\,h \, dx$, and in the case of $a_1 \leq 0$, to dissipate entropy $\int\,h^{3/2 - n}\,dx$ (see [8]) and the $L^2$-norm of the gradient $\int\,h_x^2\,dx$ (see [3]). For the special case of $a_1 = 0$ a new dissipated quantity $\int\, h^α\,h_x^2\,dx $ was recently discovered for positive classical solutions by Laugesen (see [15]). We extend it in two ways. First, we prove that Laugesen's functional dissipates strong nonnegative generalized solutions. Second, we prove the full $α$-energy $\int\,\bigl(\frac{1}{2} \,h^α\, h_x^2\, - \frac{a_1\,h^{α+ m - n + 2}}{(α+ m - n + 1)(α+ m - n + 2)} \bigr)\, dx $ dissipation for strong nonnegative generalized solutions in the case of the unstable porous media perturbation $a_1> 0$ and the critical exponent $m = n+2$.

math.AP↗

arXiv2009

Nonnegative solutions for a long-wave unstable thin film equation with convection

We consider a nonlinear 4th-order degenerate parabolic partial differential equation that arises in modelling the dynamics of an incompressible thin liquid film on the outer surface of a rotating horizontal cylinder in the presence of gravity. The parameters involved determine a rich variety of qualitatively different flows. Depending on the initial data and the parameter values, we prove the existence of nonnegative periodic weak solutions. In addition, we prove that these solutions and their gradients cannot grow any faster than linearly in time; there cannot be a finite-time blow-up. Finally, we present numerical simulations of solutions.

math.AP↗