The limiting state of bodies during separation in the case of the general plane problem

Работа посвящена решению общей плоской задачи, связанной с определением предельного состояния тел при отрыве. Уравнения, определяющие условия предельного состояния принимаются функциями, зависящими от среднего давления и направлений отрыва. В результате вычислений были получены характеристические уравнения для двух случаев: при достижении предельных значений отрыва двумя главными напряжениями и при достижении предельного значения отрыва одним главным напряжением. Для двух рассмотренных случаев были получены уравнения характеристик и соотношения вдоль них. The work is devoted to the solution of the general plane problem related to the determination of the limiting state of bodies during separation. The equations defining the conditions for the limiting state are taken as functions that depend on the average pressure and directions of separation. As a result of calculations, the characteristic equations were determined for two cases: when the limiting values of separation by two main stresses are reached and when the limiting value of separation by one main stress is reached. For the two considered cases, equations of characteristics and relations along them were obtained.

New mathematical model of sunflower productivity depending on area plant nutrition

The article provides a brief analysis of the results of plot and field experiments to study the productivity (yield) of sunflower, depending on the area of plant nutrition, performed at VNIIMK. Based on the analysis of the experimental dependencies that determine the change in yield, the following statement is applied: yield (y) and its increase rise with an increase in the amount of growth factor (x) and are proportional to the amount of yield (A - y) that does not reach the maximum the limiting value (A), and the possible yield value (B + y), is higher than a certain minimum (initial) value (B) of the yield. The analytic formulas for the quantitative determination of yield value (у), maximum limiting yield (A), amount of nutrients in soil, a rate of action of growth factors, etc. are present for the first time. These formulas allow studying many problems of soil management in certain hydro-temperature conditions and landscape. The samples of accounts due to the new methodology which showed good correspondence between test and theme data are presented.

Fracture of Protective Structures from Heavy Reinforcing Cement During Interaction with High-velocity Impactor

In this work, the fracture of a reinforced concrete barrier made of heavy reinforced ce- ment is numerically simulated during normal interaction with a high-velocity titanium projectile. The projectile has the initial velocity 750 m/s. The problem of impact interaction is numerically solved by the finite element method in a three-dimensional formulation within a phenomenological framework of solid mechanics. Numerical modeling is carried out using an original EFES 2.0 software, which al- lows a straightforward parallelization of the numerical algorithm. Fracture of concrete is described by the Johnson-Holmquist model that includes the strain rate dependence of the compressive and tensile strengths of concrete. The computational algorithm takes into account the formation of discontinuities in the material and the fragmentation of bodies with the formation of new contact and free surfaces. The behavior of the projectile material is described by an elastoplastic medium. The limiting value of the plastic strain intensity is taken as a local fracture criterion for the projectile material. A detailed numerical analysis was performed to study the stress and strain dynamics of the reinforced concrete target and the effect of shock-wave processes on its fracture. The influence of reinforcement on the resistance of a heavy cement target to the penetration of a projectile has been investigated

METHOD FOR DETERMINING TIPPING STABILITY OF A LARGE-LOADED VEHICLE IN CURVED MOVEMENT

The overturning of the vehicle corresponds to such a rise of the propeller above the support-ing surface, at which the roll angle of the frame reaches a limiting value and its further movement in the direction of roll under the action of gravity and inertia becomes irreversible. The main criteria for the stability of vehicles (V) against overturning are the characteristics of its geometric parame-ters and the location of the center of mass, relative to the propeller, which determine the boundaries of its static stability.

Stability features of steady-state solutions for a diode with electron and ion counter-streams

Stability features of steady-state solutions for a diode with counter-streaming electron and ion flows are studied. For this purpose, the time-dependent problem for an exponential potential perturbation with complex frequency is considered. By linearization of the Poisson equation and electron and ion densities integrodifferential equation for the potential perturbation amplitude is derived. In the case of uniform unperturbed potential distribution an explicit solution of this equation is obtained. Eigen modes of the perturbation are studied. The limiting value of the diode length above which steady state solutions in question are unstable is found. The obtained analytical Eigen modes coincide with the result of numerical simulation of the potential perturbation evolution.

Determination of the limiting state of bodies during separation in the case of the general plane problem

The paper considers the general plane problem of determining the limiting state of bodies during separation. The conditions for reaching the limiting state are considered to depend on the average pressure and the direction of separation. The paper defines the characteristic equations for two cases of separation: equality of two principal stresses to the limiting value of separation and equality of one principal stress to the limiting value of separation. Equations of characteristics’ lines and relations along them are determined.

Influence of the reagents’ ratio on photoelectric and optical properties of perovskite films for photovoltaics

The properties of the synthesized films of organic-inorganic perovskites CH3NH3PbI3 obtained at various ratios of starting reagents (PbI2 and CH3NH3I) have been studied. As a solvent, we used chemically pure dried dimethylformamide (DMF). Organic-inorganic perovskites are promising for photovoltaic applications. It has been shown that regardless of the ratio of the starting reagents, single-phase perovskites are formed, at the same time the microstructure of the films changes significantly. It has been reported photoelectric and optical properties of synthesized films, namely: experimental and theoretical spectral dependences of the low-signal surface photovoltage and transmission. The band gap and the Urbach parameter dependence on the ratio of precursors were determined. It has been found that the materials’ band gap depends on the ratio of precursors and equals to 1.59, 1.62 and 1.57 eV, while the characteristic Urbach energy equals to 18, 19 and 22 meV for the PbI2:CH3NH3I films with PbI2 ratio of 1:1, 1:2 and 1:3, respectively. It has been ascertained that the spectral dependences of the low-signal surface photovoltage are much more sensitive to the material microstructure and its electronic structure close to the absorption edge, while the optical transmission spectra are not so sensitive. The limiting value of the short-circuit current density for the films with different PbI2 and CH3NH3I ratios has been determined.

Reasonable Limiting of 7-Day Incidence per Hundred Thousand and Herd Immunization in Germany and Other Countries

Based on hospital capacities, facts from past experience with the coronavirus disease 2019 (COVID-19) virus and the number of dark infections during the second wave (DII=2D2), a reasonable limiting value of 140/D2 for the 7-day incidence per 100,000 persons (MSDIHT) and a second wave herd immunization threshold fraction value of 0.26 in Germany were calculated. If the MSDIHT is held below this limiting value, the German hospital system can cope with the number of new seriously infected persons without any triage decisions. On the basis of the SIRV epidemics model, the classical threshold values for herd immunization were calculated for 18 countries. For these countries, the dates regarding when herd immunization against the second COVID-19 wave will be reached were estimated.

An Alternative Approach to Obtain a New Gain in Step-Size of LMS Filters Dealing with Periodic Signals

Partial updates (PU) of adaptive filters have been successfully applied in different contexts to lower the computational costs of many control systems. In a PU adaptive algorithm, only a fraction of the coefficients is updated per iteration. Particularly, this idea has been proved as a valid strategy in the active control of periodic noise consisting of a sum of harmonics. The convergence analysis carried out here is based on the periodic nature of the input signal, which makes it possible to formulate the adaptive process with a matrix-based approach, the periodic least-mean-square (P-LMS) algorithm In this paper, we obtain the upper bound that limits the step-size parameter of the sequential PU P-LMS algorithm and compare it to the bound of the full-update P-LMS algorithm. Thus, the limiting value for the step-size parameter is expressed in terms of the step-size gain of the PU algorithm. This gain in step-size is the quotient between the upper bounds ensuring convergence in the following two scenarios: first, when PU are carried out and, second, when every coefficient is updated during every cycle. This step-size gain gives the factor by which the step-size can be multiplied so as to compensate for the convergence speed reduction of the sequential PU algorithm, which is an inherently slower strategy. Results are compared with previous results based on the standard sequential PU LMS formulation. Frequency-dependent notches in the step-size gain are not present with the matrix-based formulation of the P-LMS. Simulated results confirm the expected behavior.

Non-singular black holes with a zero-shear S-brane

We propose a construction with which to resolve the black hole singularity and enable an anisotropic cosmology to emerge from the inside of the hole. The model relies on the addition of an S-brane to the effective action which describes the geometry of space-time. This space-like defect is located inside of the horizon on a surface where the Weyl curvature reaches a limiting value. We study how metric fluctuations evolve from the outside of the black hole to the beginning of the cosmological phase to the future of the S-brane. Our setup addresses i) the black hole singularity problem, ii) the cosmological singularity problem and iii) the information loss paradox since the outgoing Hawking radiation is entangled with the state inside the black hole which becomes the new universe.