Emergence and competition of virus variants in respiratory viral infections.

The emergence of new variants of concern (VOCs) of the SARS-CoV-2 infection is one of the main factors of epidemic progression. Their development can be characterized by three critical stages: virus mutation leading to the appearance of new viable variants; the competition of different variants leading to the production of a sufficiently large number of copies; and infection transmission between individuals and its spreading in the population. The first two stages take place at the individual level (infected individual), while the third one takes place at the population level with possible competition between different variants.

Airway obstruction in respiratory viral infections due to impaired mucociliary clearance.

Respiratory viral infections, such as SARS-CoV-2 or influenza, can lead to impaired mucociliary clearance in the bronchial tree due to increased mucus viscosity and its hyper-secretion. We develop in this work a mathematical model to study the interplay between viral infection and mucus motion. The results of numerical simulations show that infection progression can be characterized by three main stages.

Mixed Electronic-Ionic Conductivity and Stability of Spark Plasma Sintered Graphene-Augmented Alumina Nanofibres Doped Yttria Stabilized Zirconia GAlN/YSZ Composites.

Graphene-doped ceramic composites with mixed electronic-ionic conductivity are currently attracting attention for their application in electrochemical devices, in particular membranes for solid electrolyte fuel cells with no necessity to use the current collector. In this work, composites of the YO-ZrO matrix with graphene-augmented γ-AlO nanofibres (GAlN) were spark plasma sintered. The conductivity and electrical stability in cyclic experiments were tested using electrical impedance spectroscopy.

Finite Element Modeling for Virtual Design to Miniaturize Medical Implants Manufactured of Nanostructured Titanium with Enhanced Mechanical Performance.

The study is aimed to virtually miniaturize medical implants produced of the biocompatible Ti with improved mechanical performance. The results on the simulation-driven design of medical implants fabricated of nanostructured commercially pure Ti with significantly enhanced mechanical properties are presented. The microstructure of initially coarse-grained Ti has been refined to ultrafine grain size by severe plastic deformation.

Mathematical modeling of respiratory viral infection and applications to SARS-CoV-2 progression.

Viral infection in cell culture and tissue is modeled with delay reaction-diffusion equations. It is shown that progression of viral infection can be characterized by the viral replication number, time-dependent viral load, and the speed of infection spreading. These three characteristics are determined through the original model parameters including the rates of cell infection and of virus production in the infected cells.

Stable in Biocompatible Buffers Silver Nanoisland Films for SERS.

We investigated the stability of silver nanoisland films, which were formed on glass surface by the method of out-diffusion, in biocompatible buffers and the applicability of the films in surface enhanced Raman scattering (SERS). We have shown that silver nanoisland films are stable in one of the most widespread in biological studies buffer-phosphate buffer saline (PBS), and in 1:100 water-diluted PBS, in the PBS-based buffer, in which NaCl is replaced by the same amount of NaClO, and in acidic phosphate buffer. At the same time, the replacement of NaCl in PBS by N(CH)Cl leads to the degradation of the nanoislands.

Energy and frequency ripple in devices with inertial excitation of oscillations.

We consider vibration devices that consist of softly vibration-isolated rigid bodies subjected to vibrations transmitted by means of inertial vibration exciters (unbalanced rotors) driven into rotation by electric motors. Typically, when designing such devices, it is assumed that the rotors rotate uniformly with a certain circular frequency and the body performs small harmonic oscillations with the same frequency. The present work, using a second-order approximation of their nonlinear coupled differential equations, shows that the rotor and the oscillating body keep exchanging energy.

Mode Localization and Eigenfrequency Curve Veerings of Two Overhanged Beams.

Overhang provides a simple but effective way of coupling (sub)structures, which has been widely adopted in the applications of optomechanics, electromechanics, mass sensing resonators, etc. Despite its simplicity, an overhanging structure demonstrates rich and complex dynamics such as mode splitting, localization and eigenfrequency veering. When an eigenfrequency veering occurs, two eigenfrequencies are very close to each other, and the error associated with the numerical discretization procedure can lead to wrong and unphysical computational results.

Rise of nations: Why do empires expand and fall?

We consider centralized networks composed of multiple satellites arranged around a few dominating super-egoistic centers. These so-called empires are organized using a divide and rule framework enforcing strong center-satellite interactions while keeping the pairwise interactions between the satellites sufficiently weak. We present a stochastic stability analysis, in which we consider these dynamical systems as stable if the centers have sufficient resources while the satellites have no value.

SERS-Active Pattern in Silver-Ion-Exchanged Glass Drawn by Infrared Nanosecond Laser.

The irradiation of silver-to-sodium ion-exchanged glass with 1.06-μm nanosecond laser pulses of mJ-range energy results in the formation of silver nanoparticles under the glass surface. Following chemical removal of ~25-nm glass layer reveals a pattern of nanoparticles capable of surface enhancement of Raman scattering (SERS).

Mathematical modeling reveals the factors involved in the phenomena of cancer stem cells stabilization.

Cancer Stem Cells (CSC), a subset of cancer cells resembling normal stem cells with self-renewal and asymmetric division capabilities, are present at various but low proportions in many tumors and are thought to be responsible for tumor relapses following conventional cancer therapies. In vitro, most intriguingly, isolated CSCs rapidly regenerate the original population of stem and non-stem cells (non-CSCs) as shown by various investigators. This phenomenon still remains to be explained.

Corrigendum: Spatial Lymphocyte Dynamics in Lymph Nodes Predicts the Cytotoxic T Cell Frequency Needed for HIV Infection Control.

[This corrects the article DOI: 10.3389/fimmu.2019.

Spatial Lymphocyte Dynamics in Lymph Nodes Predicts the Cytotoxic T Cell Frequency Needed for HIV Infection Control.

The surveillance of host body tissues by immune cells is central for mediating their defense function. imaging technologies have been used to quantitatively characterize target cell scanning and migration of lymphocytes within lymph nodes (LNs). The translation of these quantitative insights into a predictive understanding of immune system functioning in response to various perturbations critically depends on computational tools linking the individual immune cell properties with the emergent behavior of the immune system.

Interplay between reaction and diffusion processes in governing the dynamics of virus infections.

Spreading of viral infection in the tissues such as lymph nodes or spleen depends on virus multiplication in the host cells, their transport and on the immune response. Reaction-diffusion systems of equations with delays in cell proliferation and death by apoptosis represent an appropriate model to study this process. The properties of the cells of the immune system and the initial viral load determine the spatiotemporal regimes of infection spreading.

The Origin of Species by Means of Mathematical Modelling.

Darwin described biological species as groups of morphologically similar individuals. These groups of individuals can split into several subgroups due to natural selection, resulting in the emergence of new species. Some species can stay stable without the appearance of a new species, some others can disappear or evolve.

Grain Refinement Kinetics in a Low Alloyed Cu-Cr-Zr Alloy Subjected to Large Strain Deformation.

This paper investigates the microstructural evolution and grain refinement kinetics of a solution-treated Cu-0.1Cr-0.06Zr alloy during equal channel angular pressing (ECAP) at a temperature of 673 K via route B.

Fraction-exponential representation of the viscoelastic properties of dentin.

We propose the fraction-exponential description of the viscoelastic properties of dentin. Creep tests are performed on specimens cut from the molar coronal part. Four parameters determining instantaneous and long term Young's moduli as well as the relaxation time are extracted from the experimental data.

Neurofeedback learning modifies the incidence rate of alpha spindles, but not their duration and amplitude.

Although the first experiments on alpha-neurofeedback date back nearly six decades ago, when Joseph Kamiya reported successful operant conditioning of alpha-rhythm in humans, the effectiveness of this paradigm in various experimental and clinical settings is still a matter of debate. Here, we investigated the changes in EEG patterns during a continuously administered neurofeedback of P4 alpha activity. Two days of neurofeedback training were sufficient for a significant increase in the alpha power to occur.

Modelling non-equilibrium thermodynamic systems from the speed-gradient principle.

The application of the speed-gradient (SG) principle to the non-equilibrium distribution systems far away from thermodynamic equilibrium is investigated. The options for applying the SG principle to describe the non-equilibrium transport processes in real-world environments are discussed. Investigation of a non-equilibrium system's evolution at different scale levels via the SG principle allows for a fresh look at the thermodynamics problems associated with the behaviour of the system entropy.

Spatiotemporal Dynamics of Virus Infection Spreading in Tissues.

Virus spreading in tissues is determined by virus transport, virus multiplication in host cells and the virus-induced immune response. Cytotoxic T cells remove infected cells with a rate determined by the infection level. The intensity of the immune response has a bell-shaped dependence on the concentration of virus, i.

Network science on belief system dynamics under logic constraints.

Breakthroughs have been made in algorithmic approaches to understanding how individuals in a group influence each other to reach a consensus. However, what happens to the group consensus if it depends on several statements, one of which is proven false? Here, we show how the existence of logical constraints on beliefs affect the collective convergence to a shared belief system and, in contrast, how an idiosyncratic set of arbitrarily linked beliefs held by a few may become held by many.

Dynamics of non-stationary processes that follow the maximum of the Rényi entropy principle.

We propose dynamics equations which describe the behaviour of non-stationary processes that follow the maximum Rényi entropy principle. The equations are derived on the basis of the speed-gradient principle originated in the control theory. The maximum of the Rényi entropy principle is analysed for discrete and continuous cases, and both a discrete random variable and probability density function (PDF) are used.

Target morphology and cell memory: a model of regenerative pattern formation.

Despite the growing body of work on molecular components required for regenerative repair, we still lack a deep understanding of the ability of some animal species to regenerate their appropriate complex anatomical structure following damage. A key question is how regenerating systems know when to stop growth and remodeling - what mechanisms implement recognition of correct morphology that signals a stop condition? In this work, we review two conceptual models of pattern regeneration that implement a kind of pattern memory. In the first one, all cells communicate with each other and keep the value of the total signal received from the other cells.