Acoustic streaming in Maxwell fluids generated by standing waves in two-dimensional microchannels

In this work, a semianalytic solution for the acoustic streaming phenomenon, generated by standing waves in Maxwell fluids through a two-dimensional microchannel (resonator), is derived. The mathematical model is non-dimensionalized and several dimensionless parameters that characterize the phenomenon arise: the ratio between the oscillation amplitude of the resonator and the half-wavelength ( $\eta =2A/\lambda _{a}$ ); the product of the fluid relaxation time times the angular frequency known as the Deborah number ( $De=\lambda _{1}\omega$ ); the aspect ratio between the microchannel height and the wavelength ( $\epsilon =2 H_{0}/\lambda _{a}$ ); and the ratio between half the height of the microchannel and the thickness of the viscous boundary layer ( $\alpha =H_{0}/\delta _{\nu }$ ). In the limit when $\eta \ll 1$ , we obtain the hydrodynamic behaviour of the system using a regular perturbation method. In the present work, we show that the acoustic streaming speed is proportional to $\alpha ^{2.65}De^{1.9}$ , and the acoustic pressure varies as $\alpha ^{6/5}De^{1/2}$ . Also, we have found that the growth of inner vortex is due to convective terms in the Maxwell rheological equation. Furthermore, the velocity antinodes show a high dependency on the Deborah number, highlighting the fluid's viscoelastic properties and the appearance of resonance points. Due to the limitations of perturbation methods, we will only analyse narrow microchannels.

TO THE QUESTION OF ANALYSIS OF EQUATIONS OF MOTION OF A RIGID BODY DURING THE MECHANICAL OSCILATIONS

Depending on the current position of the mass in different areas of the spring deformation during the oscillation process the values that determines the natural frequency of free continuous oscillations have opposite signs. It is defined by the change in the direction of acceleration of the mass in these areas, which makes it possible to determine a single inhomogeneous differential equation of the oscillation process in different areas of the movement of the mass. When the oscillation amplitude is much less than the static position of the mass, this inhomogeneous differential equation represents a homogeneous differential equation of free undamped oscillations.

Structural and functional abnormalities of cell membranes in the end-stage chronic kidney disease

Background: Chronic kidney disease (CKD) is associated with abnormalities in all functions of the body systems including changes in intracellular processes. Assessment of erythrocyte electrophoretic mobility (EEM) in patients with CKD stage 5 on dialysis (5d) has becoming increasingly relevant, since this method characterizes the pathophysiological state of the patient and gives the possibility to modify treatment.Aim: To identify EEM characteristics in patients on programmed hemodialysis and their association with clinical and laboratory parameters.Materials and methods: We performed a cross-sectional observational study in 220 patients with confirmed CKD 5d. The average age of the patients was 56.5±1.4 years (26 to 85 years) and the duration of dialysis therapy was 3.7±0.4 years. The Kt/V urea adequacy index was 1.54±0.08. The control group included 60 healthy blood donors, comparable for their age and sex. EEM was assessed with Cyto-Expert kit (Axion Holding, Izhevsk, 2010) and the WT-Cell program (LLC Westtrade LTD, 2019). Statistical analysis was performed with BioStat 2019 software.Results: The patients on the programmed hemodialysis had lower values of oscillation amplitude (10.2±0.5 μm and 21.2±2.1 μm, p<0.001) and lower proportion of mobile red blood cells (69.5±1.8%, 89.7±9.9%, p<0.001), compared to the control group. Lower values of the oscillation amplitude were found in the age group of 25 to 44 years (9.0±1.0 μm, p<0.05). There was a weak positive correlation between age and amplitude of erythrocyte oscillation (R=0.20, p<0.05). There were differences in the oscillation amplitude values in the patients with various dialysis experience: 1 to 2 years, 11.3±0.8 μm, 2 to 5 years, 9.9±0.7 μm, 6 to 10 years, 9.4±1.3 μm, and over 11 years, 7.4±0.9 μm (p<0.05). The duration of dialysis therapy demonstrated a weak negative correlation with the amplitude of erythrocyte oscillation (R=-0.24, p<0.01). The erythrocyte oscillation amplitude was associated with systolic blood pressure before hemodialysis procedure (R=0.34, p<0.05) and with pulse pressure before hemodialysis (R=0.37, p<0.05). The proportion of mobile erythrocytes correlated with parathyroid hormone level (R=0.32, p<0.05).Conclusion: EEM in the patients receiving programmed hemodialysis have their specific characteristics related to a significant decrease in the oscillation amplitude proportional to the effective cell charge and lower proportions of mobile erythrocytes compared to those in the healthy control. The erythrocyte oscillation amplitude is negatively correlated with age and duration of dialysis therapy and is associated with blood pressure parameters and mineral bone indices.

Numerical Investigation Into the Effects of CoFlow Air on a Self-Excited Helium Jet

A numerical investigation is carried out on a helium jet having Reynolds number 150, and Richardson number 6.11. The effect of air co-flow on a self-excited helium jet is studied in the near field using commercial software ANSYS Fluent V18.1. The co-flow velocity ratio varied in the range of 0.17–0.87. The contours of the helium mole fraction along with the streamlines show the interaction of the toroidal vortex with the jet. The suppression of toroidal vortex is observed as the air co-flow velocity induced to the jet flow. Due to the suppression of vortices, radial spread/diffusion is limited, resulting in large gradients at the shear layer. The flickering frequency increases with the air co-flow. The amplitude of the oscillation at axial locations of higher z/d increases up to a certain co-flow velocity and then drops significantly at high co-flow velocity ratios. However, at upstream (near jet exit plane), oscillation amplitude decrease with increase in air co-flow. The velocity difference in the shear layer to the ambient elucidates the stabilization mechanism of the self-excited helium jet.

Convergence of undulatory swimming kinematics across a diversity of fishes

Fishes exhibit an astounding diversity of locomotor behaviors from classic swimming with their body and fins to jumping, flying, walking, and burrowing. Fishes that use their body and caudal fin (BCF) during undulatory swimming have been traditionally divided into modes based on the length of the propulsive body wave and the ratio of head:tail oscillation amplitude: anguilliform, subcarangiform, carangiform, and thunniform. This classification was first proposed based on key morphological traits, such as body stiffness and elongation, to group fishes based on their expected swimming mechanics. Here, we present a comparative study of 44 diverse species quantifying the kinematics and morphology of BCF-swimming fishes. Our results reveal that most species we studied share similar oscillation amplitude during steady locomotion that can be modeled using a second-degree order polynomial. The length of the propulsive body wave was shorter for species classified as anguilliform and longer for those classified as thunniform, although substantial variability existed both within and among species. Moreover, there was no decrease in head:tail amplitude from the anguilliform to thunniform mode of locomotion as we expected from the traditional classification. While the expected swimming modes correlated with morphological traits, they did not accurately represent the kinematics of BCF locomotion. These results indicate that even fish species differing as substantially in morphology as tuna and eel exhibit statistically similar two-dimensional midline kinematics and point toward unifying locomotor hydrodynamic mechanisms that can serve as the basis for understanding aquatic locomotion and controlling biomimetic aquatic robots.

The experimental study of the influence of the string length and the position of the electromagnetic excitation coil on the metrological characteristics of the strain sensors of the intelligent monitoring system

The article is devoted to the study of the influence of changes in the string length of string converters and the position of the electromagnetic excitation coil relative to the points of attachment of the string on the amplitude of its vibrations. The re-search was carried out on a prototype of a string converter made under the patent for the invention of the Russian Federation No. 2685803 and having a constant string tension force. The results of theoretical and experimental studies showing the influence of the highest harmonics on the amplitude of string vibrations are presented. The factors determining the composition of harmonics are considered. The contribution of the harmonics to the resulting string oscillation amplitude and the measurement error of the controlled parameter of the stress-strain state is considered. The ranges of the measurements with the help of string converters with a constant string tension force and the ways of their expansion are justified.

Research on Efficient Reinforcement Learning for Adaptive Frequency-Agility Radar

Modern radar jamming scenarios are complex and changeable. In order to improve the adaptability of frequency-agile radar under complex environmental conditions, reinforcement learning (RL) is introduced into the radar anti-jamming research. There are two aspects of the radar system that do not obey with the Markov decision process (MDP), which is the basic theory of RL: Firstly, the radar cannot confirm the interference rules of the jammer in advance, resulting in unclear environmental boundaries; secondly, the radar has frequency-agility characteristics, which does not meet the sequence change requirements of the MDP. As the existing RL algorithm is directly applied to the radar system, there would be problems, such as low sample utilization rate, poor computational efficiency and large error oscillation amplitude. In this paper, an adaptive frequency agile radar anti-jamming efficient RL model is proposed. First, a radar-jammer system model based on Markov game (MG) established, and the Nash equilibrium point determined and set as a dynamic environment boundary. Subsequently, the state and behavioral structure of RL model is improved to be suitable for processing frequency-agile data. Experiments that our proposal effectively the anti-jamming performance and efficiency of frequency-agile radar.

Tuning of Friction Oscillation Amplitude in Halloysite, Montmorillonite, and Wollastonite Filled Friction Composites: Load, Speed, and Temperature Sensitivity

The influence of clay mineral silicate types, such as halloysite, montmorillonite, and wollastonite with tubular, plate like, and acicular morphologies respectively, on frictional oscillation of composite materials have been evaluated on Chase type dynamometer and optimised following the combination of Taguchi's L9 design of experiment and regression analysis approaches. The coefficient of friction of ~0.35-0.45 and cumulative wear at &lt; 10 % remained well within the acceptable range. The optimal tuning of friction oscillation to reduce braking induced noise and vibration propensity has been achieved by montmorillonite clay with platelet type morphology or by combination of MgO and wollastonite clay with acicular morphology. The extent of Fe- content in wear debris close to ~ 80 % on the composite surface led to an optimal level of friction oscillation amplitude (Aamp). The hierarchical ranking of the clay based composites by TOPSIS based operation research approach lead to the understanding of design ideology optimization for composites to ensure minimal friction oscillations.

Theoretical study on the sensitivity of dynamic acoustic force measurement through monomodal and bimodal excitations of rectangular micro-cantilever

We present a detailed analysis on measurement sensitivity of dynamic acoustic forces via numerical simulation of the micro-cantilever responses. The rectangular micro-cantilever is regarded as a point mass in the dynamic model of forced and damped harmonic oscillator. We use single- and bimodal-frequency excitation schemes for actuation of the micro-cantilever in the presence of dynamic acoustic forces. In bimodal-frequency excitation scheme, the micro-cantilever is excited at its first two eigenmode frequencies simultaneously as opposed to single-frequency excitation. First, we numerically obtain micro-cantilever deflections by solving the Equations of Motions (EOMs) constructed for the first two eigenmodes. Then, we determine oscillation amplitude and phase shift as a function of acoustic force strength within different frequency regions. Moreover, we relate amplitude and phase shift to virial and energy dissipation in order to explore the interaction between flexural modes in multifrequency excitation. The simulation results point out that bimodal-frequency excitation improves the measurement sensitivity of dynamic acoustic forces at particular frequencies. Herein, simultaneous application of driving forces enables higher sensitivities of observables and energy quantities as acoustic force frequencies become around the eigenmode frequencies. For our case, we obtain the highest phase shift (approximately 178 degrees) for the acoustic force strength of 100 pN at the frequency of around 307.2 kHz. Therefore, this method can be easily adapted to improve measurement sensitivity of dynamic acoustic forces in a wider frequency window.

Performance Simulation of a 5 kW hall Thruster

Hall thruster is a kind of plasma optics device, which is used mainly in space propulsion. To simulate the discharge process of plasma and the performance of a 5 kW hall thruster, a two-dimensional PIC-MCC model in the R-Z plane is built. In the model, the anomalous diffusion of the electrons including Bohm diffusion and near-wall conduction is modeled. The Bohm diffusion is modeled by using a Brownian motion instead of the Bohm collision method and the near-wall conduction is modeled by a secondary electron emission model. In addition to the elastic, excitation, and ionization collisions between electrons and neutral atoms, the Coulomb collisions are included. The plasma discharge process including the transient oscillation and steady state oscillation is well reproduced. First, the influence of the discharge voltage and magnetic field on the steady state oscillation is simulated. The oscillation amplitude increases as the discharge voltage gets larger at first, and then decreases. While the oscillation amplitude decreases as the magnetic field gets stronger at first, and then increases. Later, the influence of the discharge voltage and mass flow rate on the performance of the thruster is simulated. When the mass flow rate is constant, the total efficiency initially increases with the discharge voltage, reaches the maximum at 600 V, and then declined. When the discharge voltage is constant, the total efficiency increases as the mass flow rate rises from 10 to 15 mg/s. Finally, a comparison between simulated and experimental performance reveals that the largest deviation is within 15%, thereby indirectly validating the accuracy of the model.