We consider a nonlinear control system with periodic coefficients. We study the problem of asymptotic stabilization of the equilibrium x=0 of the closed-loop system by state feedback. We assume that ...the free dynamic system possesses a periodic Lyapunov function ensuring Lyapunov stability of the equilibrium x=0. We have developed a method for constructing a damping control for affine systems with periodic coefficients based on a generalization of weak Jurdjevic–Quinn conditions, using an extension of the notion of the commutator to non-stationary vector fields. Using this approach, we obtain sufficient conditions for uniform local and global asymptotic stabilization of general nonlinear systems, in particular, affine control systems, with periodic coefficients. Stabilization results generalize known results for time-invariant systems to time-varying periodic systems.
A device for controlling a two-winding polarized electromagnet is considered, and its disadvantages are noted. A circuit for the control of a single-winding polarized electromagnet is proposed in ...which the disadvantages of the existing control circuit are eliminated. Transient processes of charge/discharge of a capacitor to ensure actuation and reset of a polarized electromagnet are considered. The operability of the proposed circuit based on a composite transistor has been experimentally confirmed.
The 'nut-and-bolt' mechanism of a bacteriophage-bacteria flagellum translocation motion is modelled by numerically integrating the 3D Stokes equations using a Finite-Element Method (FEM). Following ...the works by Katsamba and Lauga (Phys Rev Fluids 4(1): 013101, 2019), two mechanical models of the flagellum-phage complex are considered. In the first model, the phage fiber wraps around the smooth flagellum surface separated by some distance. In the second model, the phage fiber is partly immersed in the flagellum volume via a helical groove imprinted in the flagellum and replicating the fiber shape. In both cases, the results of the Stokes solution for the translocation speed are compared with the Resistive Force Theory (RFT) solutions (obtained in Katsamba and Lauga Phys Rev Fluids 4(1): 013101, 2019) and the asymptotic theory in a limiting case. The previous RFT solutions of the same mechanical models of the flagellum-phage complex showed opposite trends for how the phage translocation speed depends on the phage tail length. The current work uses complete hydrodynamics solutions, which are free from the RFT assumptions to understand the divergence of the two mechanical models of the same biological system. A parametric investigation is performed by changing pertinent geometrical parameters of the flagellum-phage complex and computing the resulting phage translocation speed. The FEM solutions are compared with the RFT results using insights provided from the velocity field visualisation in the fluid domain.
Epilepsy is a group of neurological disorders commonly associated with the neuronal malfunction leading to generation of seizures. Recent reports point to a possible contribution of astrocytes into ...this pathology. We used the lithium-pilocarpine model of status epilepticus (SE) in rats to monitor changes in astrocytes. Experiments were performed in acute hippocampal slices two to four weeks after SE induction. Nissl staining revealed significant neurodegeneration in the pyramidal cell layers of hippocampal CA1, CA3 areas, and the hilus, but not in the granular cell layer of the dentate gyrus. A significant increase in the density of astrocytes stained with an astrocyte-specific marker, sulforhodamine 101, was observed in CA1 stratum (str.) radiatum. Astrocytes in this area were also whole-cell loaded with a morphological tracer, Alexa Fluor 594, for two-photon excitation imaging. Sholl analyses showed no changes in the size of the astrocytic domain or in the number of primary astrocytic branches, but a significant reduction in the number of distal branches that are resolved with diffraction-limited light microscopy (and are thought to contain Ca2+ stores, such as mitochondria and endoplasmic reticulum). The atrophy of astrocytic branches correlated with the reduced size, but not overall frequency of Ca2+ events. The volume tissue fraction of nanoscopic (beyond the diffraction limit) astrocytic leaflets showed no difference between control and SE animals. The results of spatial entropy-complexity spectrum analysis were also consistent with changes in ratio of astrocytic branches vs. leaflets. In addition, we observed uncoupling of astrocytes through the gap-junctions, which was suggested as a mechanism for reduced K+ buffering. However, no significant difference in time-course of synaptically induced K+ currents in patch-clamped astrocytes argued against possible alterations in K+ clearance by astrocytes. The magnitude of long-term-potentiation (LTP) was reduced after SE. Exogenous D serine, a co-agonist of NMDA receptors, has rescued the initial phase of LTP. This suggests that the reduced Ca2+-dependent release of D-serine by astrocytes impairs initiation of synaptic plasticity. However, it does not explain the failure of LTP maintenance which may be responsible for cognitive decline associated with epilepsy.
Antibiotics are widely used to treat infectious diseases. This leads to the presence of antibiotics and their metabolic products in the ecosystem, especially in aquatic environments. In many ...countries, the growth of pathogen resistance to antibiotics is considered a threat to national security. Therefore, methods for determining the sensitivity/resistance of bacteria to antimicrobial drugs are important. This review discusses the mechanisms of the formation of antibacterial resistance and the various methods and sensor systems available for analyzing antibiotic effects on bacteria. Particular attention is paid to acoustic biosensors with active immobilized layers and to sensors that analyze antibiotics directly in liquids. It is shown that sensors of the second type allow analysis to be done within a short period, which is important for timely treatment.
The paper presents a program for simulating electron scattering in layered materials
. Calculations show that the absorbed energy density is three-dimensional, while the contribution of the ...forward-scattered electrons is better described by a power function rather than the commonly used Gaussian. It is shown that for the practical correction of the proximity effect, it is possible, nevertheless, to use the classical two-dimensional proximity function containing three parameters: α, β, η. A method for determining the parameters α, β, η from three-dimensional calculations based on MC simulation and development consideration is proposed. A good agreement of the obtained parameters and experimental data for various substrates and electron energies is shown. Thus, a method for calculating the parameters of the classical proximity function for arbitrary layered substrates based on the Monte Carlo simulation has been developed.
Febrile seizures (FSs) in early life are significant risk factors of neurological disorders and cognitive impairment in later life. However, existing data about the impact of FSs on the developing ...brain are conflicting. We aimed to investigate morphological and functional changes in the hippocampus of young rats exposed to hyperthermia-induced seizures at postnatal day 10. We found that FSs led to a slight morphological disturbance. The cell numbers decreased by 10% in the CA1 and hilus but did not reduce in the CA3 or dentate gyrus areas. In contrast, functional impairments were robust. Long-term potentiation (LTP) in CA3-CA1 synapses was strongly reduced, which we attribute to the insufficient activity of N-methyl-D-aspartate receptors (NMDARs). Using whole-cell recordings, we found higher desensitization of NMDAR currents in the FS group. Since the desensitization of NMDARs depends on subunit composition, we analyzed NMDAR current decays and gene expression of subunits, which revealed no differences between control and FS rats. We suggest that an increased desensitization is due to insufficient activation of the glycine site of NMDARs, as the application of D-serine, the glycine site agonist, allows the restoration of LTP to a control value. Our results reveal a new molecular mechanism of FS impact on the developing brain.
•Compact analyzer for measuring electrical and mechanical properties of liquid was developed.•Compact analyzer includes lateral electric field excited resonator and small impedance meter.•Method for ...determination of viscosity, permittivity and elastic module of liquid was developed.•This method based on electromechanical equivalent scheme was tested on water solutions of glycerol.
A compact hardware-software complex for measuring the electrical and mechanical parameters of a liquid based on a piezoelectric resonator with a lateral exciting electric field has been developed. It is shown that the modulus of the electrical impedance of the resonator near the resonant frequency decreases monotonically with an increase in conductivity of the contacting liquid. The obtained dependences can be used as calibration curves for measuring conductivity in the range of 100–10,000 μS/cm. A method for the simultaneous determination of the modulus of elasticity, viscosity, and permittivity of a liquid using the electromechanical equivalent scheme was developed and tested on a mixture “water - glycerol” with the different glycerol content.
Atrial fibrillation (AF) commonly associates with atrial dilatation by poorly understood mechanisms. We hypothesized that elevation of intra-atrial pressure elicits high-frequency and ...spatio-temporally organized left atrial (LA) sources emanating from the superior pulmonary veins.
We used a stretch-related AF model in the sheep heart to induce stable episodes of AF (>40 minutes) in 9 animals. Video movies of the LA free wall (LAFW) and LA superior pulmonary vein junction (JPV) were obtained by using di-4-ANEPPS. Electrograms from the right atrium were recorded. At intra-atrial pressures >10 cm H2O, the maximum dominant frequency (DFMax) was significantly higher in the JPV than in the LAFW (12.0+/-0.2 and 10.5+/-0.2 Hz, respectively mean+/-SEM; P<0.001). Below 10 cm H2O, DFMax was similar in the JPV and LAFW (10.8+/-0.3 versus 10.2+/-0.3 Hz; P=0.6); DFMax in both JPV and LAFW was significantly higher than in the right atrium (7.8+/-0.3 Hz; P<0.001). Analysis of excitation direction in JPV showed positive correlation between intra-atrial pressure and the number of waves emanating from the left superior pulmonary vein (r=0.79, P=0.02) but not from the LAFW (r=0.54, P=0.09). The number of spatio-temporally periodic waves in the JPV correlated with pressure (r=0.92, P=0.002). In 3 cases, JPV rotors were identified with a cycle length equal to 1/DFMax.
We demonstrate for the first time that an increase in intra-atrial pressure increases the rate and organization of waves emanating from the superior pulmonary veins underlying stretch-related AF.
We consider activation of a solar prominence by sharp increase in electric current in the frame of the Kuperus-Raadu model. The dynamics of the prominence is described in terms of the Ampère force, ...gravity, and the drag force. We suggest that the drag force is determined by the ion viscosity of ambient plasma. The upward Ampère force acting on the filament increases with the electric current in the filament, which results in the increase in the height of the filament. As a result of the dynamical process, a new equilibrium state corresponding to the new value of the electric current is reached. The maximum height and velocity of the prominence are estimated using the nonlinear equation for prominence dynamics. A sharp increase in the electric current can be due to the magnetic Rayleigh-Taylor instability in the chromospheric footpoints of the filament. Two examples of solar active filaments are analyzed in the context of the proposed model. Failed or two-stage eruption of the prominences is also discussed.
•Prominence activation by electric current in the Kuperus-Raadu model is studied.•Prominence dynamics is described by Ampère force, gravity, and the drag force.•Drag force is due to ion viscosity of ambient plasma.•Analysis of equation describing of the filament evolution are presented.•Two-stage prominence eruption and CME core formation are explained.
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