Turbulent dynamo in the shell model and the Kazantsev-Kraichnan approach.

We investigate small-scale magnetic energy generation in a turbulent conducting flow using two different approaches. One is based on the Kazantsev-Kraichnan (KK) model, developed for a random velocity field with short time correlations, and the other uses the shell magnetohydrodynamic (MHD) method, which describes a turbulent energy cascade on a finite number of spectral shells. We consider only the kinematic (linear) regime and show an exponential growth of magnetic energy for sufficiently large magnetic Reynolds numbers (Rm) in both approaches.

Double-diffusive convection in a plane layer with low thermal conductivity boundaries.

This study examines double-diffusive convection in a horizontal fluid layer with low thermal conductivity boundaries, where the heat flux is fixed. Using linear stability analysis and nonlinear modeling, the behavior of the system is explored under different thermal and concentration gradients. Two instability modes are identified: monotonous and oscillatory.

Phase inversion of skin temperature oscillations under the influence of local heating.

The relationship between skin blood flow (SkBF) and skin temperature oscillations (STO) under local heating allows microvascular function and regulation to be assessed. The dynamics of STO during local heating are determined by both SkBF and the diverse mechanisms of heat transfer within biological tissues. The aim of this study is to investigate the changes in the phase and amplitude of STO resulting from local heating.

Influence of experimental conditions on apparent AFM tip-surface contact in air.

Accurate determination of the onset of the contact between the atomic force microscope (AFM) tip and the surface in force measurements is necessary both for calculating the constants of non-contact interactions and for determining the structural and mechanical properties of the materials. In an air environment the contact is preceded by a rapid jump of the tip to the surface due to attractive forces. If a surface is not deformed by a probe of a given stiffness, the end of the jump (minimum of the deflection of the cantilever) is taken as the onset of the contact.

Magnetoelectric PVDF-Cobalt Ferrite Films: Magnetostrictive and Magnetorotational Effects, Synergy, and Counteraction.

Numerical modeling of the direct magnetoelectric (ME) effect in a PVDF-cobalt ferrite (CFO) composite film has been performed. The problem is solved within the framework of the mesoscopic RVE approach, where each elementary cell contains three particles with varying mutual positions. Both modes of mechanical stress generation are taken into account: magnetostrictive and magnetorotational, i.

Improvement of Microvascular Function in Patients with Morbid Obesity After Bariatric Surgery Revealed by Imaging Photoplethysmography.

Background: Morbid obesity leads to serious complications such as diabetes mellitus, arterial hypertension, and atherosclerosis. Bariatric surgery aims to reduce body weight and correct metabolic disorders and associated macro- and microvascular dysfunction. Metabolic disturbances can be assessed by biochemical markers, whereas microvascular function can be assessed by the response to provocative stimuli.

Effect of magnetomechanical hysteresis on the field-induced oscillations of particles in a magnetoactive elastomer.

A model is proposed for mesoscopic dynamics of a magnetoactive elastomer (MAE). The elementary cell comprises two spherical linearly magnetizing particles embedded in an elastoviscous medium of the Kelvin type. The forced oscillations of this system induced by an ac field are studied.

Rare-reversal chaos in two-disk dynamo models.

A systematic comparative study of two-disk dynamo models without friction (the Rikitake model) and with friction has been carried out. It is shown that the sets of chaotic and periodic modes realized in both models are qualitatively similar. We introduce a simple measure of the complexity of a solution, which allows finding the chaotic mode characterized by long-lived quasistationary states with very weak oscillations of variables, ending with a sharp burst of oscillations with a possible transition to the attraction area of the other stationary solution.

Nonlinear bias of collective oscillation frequency induced by asymmetric Cauchy noise.

We report the effect of nonlinear bias of the frequency of collective oscillations of sin-coupled phase oscillators subject to individual asymmetric Cauchy noises. The noise asymmetry makes the Ott-Antonsen ansatz inapplicable. We argue that, for all stable non-Gaussian noises, the tail asymmetry is not only possible (in addition to the trivial shift of the distribution median) but also generic in many physical and biophysical setups.

Discrete Synaptic Events Induce Global Oscillations in Balanced Neural Networks.

Despite the fact that neural dynamics is triggered by discrete synaptic events, the neural response is usually obtained within the diffusion approximation representing the synaptic inputs as Gaussian noise. We derive a mean-field formalism encompassing synaptic shot noise for sparse balanced neural networks. For low (high) excitatory drive (inhibitory feedback) global oscillations emerge via continuous or hysteretic transitions, correctly predicted by our approach, but not from the diffusion approximation.

Contrasting thermodynamic and hydrodynamic entropy.

In this paper, using hydrodynamic entropy, we quantify multiscale disorder in Euler and hydrodynamic turbulence. These examples illustrate that the hydrodynamic entropy is not extensive because it is not proportional to the system size. Consequently, we cannot add hydrodynamic and thermodynamic entropies, which measure disorder at macroscopic and microscopic scales, respectively.

Mechanism of transition from subdiffusive transport to normal diffusion for passive tracers in a plane periodical flow induced by Gaussian noise.

The known analytical solution describing a two-dimensional viscous flow with vortices under a driving force is generalized. It is shown that a periodic pattern of asymmetric vortices arises when the force amplitude exceeds a critical value. The transport of an ensemble of passive particles through the resulting structure has been studied.

AFM Nanoindentation of Stiff Inhomogeneous Layer on Polymeric Substrate.

Analysis of indentation data of heterogeneous material, in particular, layer on an elastic substrate requires information about the contact area that is essential for calculating mechanical properties. The actual shape of the AFM-tip is not described by simple body of revolution. In this work, the indentation of a stiff layer on a hyperelastic substrate by a truncated conical tip is studied using finite element methods.

Newest Methods and Approaches to Enhance the Performance of Optical Frequency-Domain Reflectometers.

In this review, we summarize the latest advances in the design of optical frequency-domain reflectometers (OFDRs), digital signal processing, and sensors based on special optical fibers. We discuss state-of-the-art approaches to improving metrological characteristics, such as spatial resolution, SNR, dynamic range, and the accuracy of determining back reflection coefficients. We also analyze the latest achievements in the OFDR-based sensors: the accuracy of spatial localization of the impact, the error in detecting temperatures, deformation, and other quantities, and the features of separate measurement of various physical quantities.

Foreign Body Reaction to Ion-Beam-Treated Polyurethane Implant.

All artificial materials used for implantation into an organism cause a foreign body reaction. This is an obstacle for a number of medical technologies. In this work, we investigated the effect of high-energy ion bombardment on polyurethane for medical purposes and the reaction of body tissues to its insertion into the mouse organism.

Superparamagnetic effects in the linear magnetic response of polydisperse ensembles of nanoparticles suspended in a fluid.

Within a kinetic theory, the linear magnetic response of uniaxial single-domain particles suspended in a fluid is analyzed. The main qualitatively different types of frequency dependence of the longitudinal dynamic magnetic susceptibility of such particles are described. It is shown that superparamagnetic (related to orientation thermal fluctuations of the magnetic moment inside a particle) peculiarities of the response of a particle to a probing magnetic field are not fully determined by the ratio of anisotropy energy to thermal energy when a stationary bias field is applied.

Scaling of damage mechanism for additively manufactured alloys at very high cycle fatigue.

A comparative analysis of fracture mechanisms in high- and very high- cycle fatigue (HCF, VHCF) regimes was carried out based on the results of multifractal analysis of the fracture surfaces of additively manufactured 316L stainless steel samples. In terms of scale invariants, the morphology of fracture surfaces in HCF and VHCF regimes inside and outside the fine granular area is shown. The analysis demonstrated that chaotic patterns of relief formation prevail in the crack initiation zone of VHCF samples.

Attachment of Fibrinogen on Ion Beam Treated Polyurethane.

Protein-stable coverage of the artificial implant is a key problem for biocompatibility. In the present study, a protein layer was attached covalently to a polyurethane surface treated by an ion beam. A plasma system consisting of a vacuum chamber (0.

Piezoceramics Actuator with Attached Mass for Active Vibration Diagnostics of Reinforced Concrete Structures.

One of the effective methods of non-destructive testing of structures is active vibration diagnostics. This approach consists of the local dynamic impact of the actuator on the structure and the registration of the vibration response. Testing of massive reinforced concrete structures is carried out with the use of actuators, which are able to create sufficiently high-impact loads.

Does Magnetic Field Influence the Surface Tension of Ferrofluid?

Studying the physical properties of ferrofluids is a challenging task, especially when conventional experimental techniques are adapted to the presence of a magnetic field. To date, there has been no definitive understanding of how the magnetic field affects the surface energy of ferrofluid interfaces. In this study, we perform a direct experimental investigation to assess the effect of magnetic fields on the surface tension of ferrofluids.

Macroscopic behavior of populations of quadratic integrate-and-fire neurons subject to non-Gaussian white noise.

We study macroscopic behavior of populations of quadratic integrate-and-fire neurons subject to non-Gaussian noises; we argue that these noises must be α-stable whenever they are delta-correlated (white). For the case of additive-in-voltage noise, we derive the governing equation of the dynamics of the characteristic function of the membrane voltage distribution and construct a linear-in-noise perturbation theory. Specifically for the recurrent network with global synaptic coupling, we theoretically calculate the observables: population-mean membrane voltage and firing rate.

Mechanical Properties of the Carbonized Layer Formed by Ion Flow Orientated at Different Angles to the Polyurethane Surface.

Polymer materials are widely used in medicine due to their mechanical properties and biological inertness. When ion-plasma treatment is used on a polymer material, a carbonization process occurs in the surface nanolayer of the polymer sample. As a result, a surface carbonized nanolayer is formed, which has mechanical properties different from those of the substrate.

Circular cumulant reductions for macroscopic dynamics of oscillator populations with non-Gaussian noise.

We employ the circular cumulant approach to construct a low dimensional description of the macroscopic dynamics of populations of phase oscillators (elements) subject to non-Gaussian white noise. Two-cumulant reduction equations for α-stable noises are derived. The implementation of the approach is demonstrated for the case of the Kuramoto ensemble with non-Gaussian noise.

Challenges of reliable AFM-tip shape reconstruction and approximation.

Reliable reconstruction of AFM tip geometry is not an easy task. The shape of the tip can be (partially) reconstructed from the AFM image of a calibration sample using a blind reconstruction method. The result is a range of the tip shapes (from unrealistically sharp to blunt).