Analysis of the booster DC to DC converter with feedback

The field effect power transistors are used in many applications in electromechanical systems. Control of the field effect power transistors requires isolated 5V control signals and isolated 12V DC sources. The first problem is resolved by using optical pairs: light emitting diodes with phototransistors. The second problem can be resolved by using impulse voltage sources. The primary coil of a transformer is connected to the battery by a transistor switch. In the first period of operation of this voltage source, the energy is stored in the magnetic field of transformer’s inductance. In the second period, the energy is delivered to the output voltage source. Energy is delivered from the secondary transformer’s coil to the output capacitor through a diode. As a rule, one separate voltage source has a small power, that is why one impulse voltage source can have the necessary number of isolated output voltage sources, i.e., 3, 6, 9, 12, etc So, we can design an impulse DC to DC voltage source with multiple isolated output voltage sources. By changing the charge time of the inductor, we can control the output voltage by using negative feedback proportional to the output voltage and / or a current. In the report, different variants of impulse voltage sources are considered, with analog base elements and on the base of microprocessors. Analyses operation of these impulse voltage sources enable us to determine the period (frequency) of internal operation with ordered maximum transformer efficiency values. The concept of controlled impulse voltage sources is very important because these sources are very simple. They are reliable and have high level of electrical isolation

Elastic and inelastic collisions of interfacial solitons and integrability of two-layer fluid system subject to horizontal vibrations

We study interfacial waves in a system of two horizontal layers of immiscible inviscid fluids involved into horizontal vibrational motion. We analyze the linear and nonlinear stability properties of the solitons in the system and consider two-soliton collision scenarios. We describe the events of explosive formation of sharp peaks on the interface, which may presumably lead to the layer rapture, and find that beyond the vicinity of this peaks the system dynamics can be represented as a kinetics of a soliton gas.Comment: 6 pages, 6 figures, to appear in Europhys. Let

Auto-Surprise: An Automated Recommender-System (AutoRecSys) Library with Tree of Parzens Estimator (TPE) Optimization

We introduce Auto-Surprise, an Automated Recommender System library. Auto-Surprise is an extension of the Surprise recommender system library and eases the algorithm selection and configuration process. Compared to out-of-the-box Surprise library, Auto-Surprise performs better when evaluated with MovieLens, Book Crossing and Jester Datasets. It may also result in the selection of an algorithm with significantly lower runtime. Compared to Surprise's grid search, Auto-Surprise performs equally well or slightly better in terms of RMSE, and is notably faster in finding the optimum hyperparameters.Comment: To be presented at RecSys '20 Fourteenth ACM Conference on Recommender Systems, September 21-26, 2020, Virtual Even

Thermosolutal convection in a horizontal porous layer heated from below in the presence of a horizontal through flow

In this paper, we study the effect of a homogeneous longitudinal through flow on the onset of convection in a horizontal porous layer saturated by a binary fluid and heated from below or above. The layer boundaries are subjected to a constant heat flux. The investigation is made by taking the Soret effect into account. It is found that in the case of positive separation ratio when the denser component moves toward the cooler wall, through flow has no effect on the stability threshold but exerts an orientating effect on the convective patterns. For negative separation ratio, a strong destabilization occurs of the spatially homogeneous state with respect to long-wave disturbances. The stability range for long-wavelength convective rolls is defined

On the Mathematical Simulation of the Measuring of the Intraocular Pressure by Maklakov Method

Maklakov’s method for measurement of the intraocular pressure (IOP) is based on approach, in which an eyeball is modeled as a thin-walled spherical liquid-filled shell. Measuring the IOP one estimates the diameter of the circular contact area of the cornea and the tonometer. In the clinic special tables are used to estimate the IOP relating to the measured diameter. However nowadays the calculating of such tables is based on the empirical values of the IOP. In the present paper the mathematical simulation of the measuring of the intraocular pressure by Maklakov method is considered

Variations of cosmic rays according to the data of interplanetary probes Zond-3 and Venus-2

Cosmic ray intensity variation measured by Zond 3 and Venus 2 interplanetary probe

Capture of particles of dust by convective flow

Interaction of particles of dust with vortex convective flows is under theoretical consideration. It is assumed that the volume fraction of solid phase is small, variations of density due to nonuniform distribution of particles and those caused by temperature nonisothermality of medium are comparable. Equations for the description of thermal buoyancy convection of a dusty medium are developed in the framework of the generalized Boussinesq approximation taking into account finite velocity of particle sedimentation. The capture of a cloud of dust particles by a vortex convective flow is considered, general criterion for the formation of such a cloud is obtained. The peculiarities of a steady state in the form of a dust cloud and backward influence of the solid phase on the carrier flow are studied in detail for a vertical layer heated from the sidewalls. It is shown that in the case, when this backward influence is essential, a hysteresis behavior is possible. The stability analysis of the steady state is performed. It turns out that there is a narrow range of governing parameters, in which such a steady state is stable.Comment: 14 pages, 10 figures, published in Physics of Fluid

Stability of Plane-Parallel Vibrational Flow In a Two-Layer System

The stability of the interface separating two immiscible incompressible fluids of different densities and viscosities is considered in the case of fluids filling a cavity which performs horizontal harmonic oscillation. There exists a simple basic state which corresponds to the unperturbed interface and plane-parallel unsteady counter flows; the properties of this state are examined. A linear stability problem for the interface is formulated and solved a) for both inviscid and b) for both viscous fluids. A transformation is found which reduces the linear stability problem under inviscid approximation to the Mathieu equation. The parametric resonant regions of instability associated with the intensification of capillary-gravity waves at the interface are examined and the results are compared to those found in the viscous case in a fully numerical investigation.Comment: 15 pages, 6 figures; soon to appear in European Journal of Fluid Mechanic

Flow and Noise Predictions of Coaxial Jets using LES and RANS Methods

Flow and noise solutions of the two Large Eddy Simulation (LES) approaches are evaluated for the jet flow conditions corresponding to a benchmark co-axial jet case from the EU CoJeN (Computation of Coaxial Jet Noise) experiment. The jet is heated and issues for a short-cowl axi-symmetric nozzle with a central body at a transonic speed. The first LES method is based on the Compact Accurately Boundary-Adjusting high-REsolution Technique (CABARET) scheme, for which implementation features include asynchronous time stepping at an optimal Courant–Friedrichs–Lewy (CFL) number, a wall model, and a synthetic turbulence inflow boundary condition. The CABARET LES is implemented on Graphics Processing Units (GPUs). The second LES approach is based on the hybrid Reynolds Averaged Navier-Stokes (RANS)/ Implicit LES method that uses a mixture of high-order Roe and WENO scheme and a wall distance model of the Improved Delayed Detached Eddy Simulation (IDDES) type. The RANS/ILES method is run on an MPI cluster. Two grid generation approaches are considered: the unstructured grid using OpenFOAM utility “snappyHexMesh” (sHM) and the conventional structured multiblock body-fitted curvilinear grid. The LES flow solutions are compared with the experiment and also with solutions obtained from the standard axi-symmetric RANS method using the k- turbulence model. For noise predictions, The LES solutions are coupled with the penetrable surface formation of the Ffowcs Williams –Hawkings method. The results of noise predictions are compared with the experiment and the effect of different LES grids and acoustic integration surfaces is discussed