It is shown that the pressure and temperature of the radiating arc plasma can be determined from the measured values of the voltage on the plasma column, the discharge current and the photocurrent ...caused by the radiation flux of the entire volume of plasma to the photodetector. For the case of axially symmetric homogeneous arc plasma in a state of the local thermodynamic equilibrium, equations are formulated that connect the plasma parameters with the measurement results. The equation for the photocurrent is obtained from the solution of the radiation transfer equation in the arc plasma of the arbitrary optical density. The cases of electrode surfaces reflecting and absorbing electromagnetic radiation are considered. It is shown that the problem of determining the parameters of the arc plasma is reduced to solving a system of two non-linear equations with respect to pressure and temperature. The described method is used to determine plasma parameters of a high-current vacuum arc at the stage of the anode activity. The stability of the method with respect to the errors of the initial data is shown by the example of the vacuum arc plasma.
Abstract
The paper considers the possibility of using a pulsed discharge in cesium as an environmentally friendly high quality light source for lighting industrial premises of railway transport ...facilities. The use of cesium filling of standard sapphire burners of high-pressure sodium lamps and a pulsed mode of electric power supply of the discharge to create a light source has been substantiated. A mathematical model of a high-pressure pulsed discharge in cesium is formulated on the basis of the radiative gas dynamics equations. The discharge was simulated and it was shown that it is possible to create a plasma with a temperature 4000 -7000 K and a pressure of 0.5 - 1.5 at
m
with the power supplied to the discharge ∼ 100 W/cm in the steady-state combustion mode. The dependence of the discharge lighting characteristics on the amplitude of the current pulses and the amount of cesium in the gas discharge tube is analyzed. It is shown that in a wide range of currents and plasma densities, the color rendering index of the discharge radiation
Ra>
95 with luminous efficacy η
V
∼ 70lm/W and more. The average luminous flux emitted per unit length of the discharge column is ∼ 10
4
lm/cm. The color temperature of the discharge radiation can vary over a wide range of values
T
c
∼
3000÷4500 K. It is shown that the color coordinates X
c
,Y
c
of discharge radiation are close to the values X
c
,Y
c
of a blackbody. The use of such a source in conditions of a short daylight hours will make it possible to create practically solar illumination of large production areas.
It is shown that the forces acting on the points of the mechanical system may depend on their accelerations. The differential equations of a mechanical system motion prove to be implicit. It is not ...allowed with respect to higher derivatives. There are fundamental mathematical problems related to the possibility and the only solution of these equations with respect to higher derivatives. Implicit equations of motion are typical for mechanical systems with dry friction sliding and rolling. In the dynamics of material point such problems do not arise. But in more complex mechanical systems, including the study of the motion of a solid whole mass is concentrated at one point, as well as in systems with one degree of freedom, such a situation is very characteristic. The paper discusses four fairly simple examples of mechanical systems movement, which is described by implicit differential equations of motion.
Walking wheel Lapshin, V V
Journal of physics. Conference series,
12/2020, Letnik:
1705, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The dynamics of a 2D walking wheel motion down an inclined plane is analytically investigated in nonlinear formulation. It is the simplest model of a bipedal walking. The possible cases of the motion ...of the walking wheel are investigated at various values of the inclination of the support surface and the initial angular velocity of the wheel. It is shown that various modes of motion of the walking wheel are possible. The most interesting of which is the existence of a stable periodic solution (self-oscillations).
Missing observations in market data is a frequent problem in financial studies. The problem of missing data is often overlooked in practice. Missing data is mostly treated using ad hoc methods or ...just ignored. Our
goal
is to develop practical recommendations for treatment of missing observations in financial data. We illustrate the issue with an example of yield curve estimation on Russian bond market. We compare three
methods
of missing data imputation — last observation carried forward, Kalman filtering and EM–algorithm — with a simple strategy of ignoring missing observations. We
conclude
that the impact of data imputation on the quality of yield curve estimation depends on model sensitivity to the market data. For non-sensitive models, such as Nelson-Siegel yield curve model, final effect is insignificant. For more sensitive models, such as bootstrapping, missing data imputation allows to increase the quality of yield curve estimation. However, the
result
does not depend on the chosen data imputation method. Both simple last observation carried forward method and more advanced EM–algorithm lead to similar final results. Therefore, when estimating yield curves on the illiquid markets with missing market data, we
recommend
to use either simple non-sensitive to the data parametric models of yield curve or to impute missing data before using more advanced and sensitive yield curve models.
The viability, productivity and survival of higher plants under the adverse factors influence are largely determined by the functional activity of the antioxidant system. The aim of our work was to ...investigate changes in formation of high-molecular (superoxide dismutase and peroxidase) and low-molecular (phenolics, including flavanols and proanthocyanidins) antioxidants in callus culture of
under influence of phenolic precursors (L-phenylalanine-3 mM,
-cinnamic acid-1 mM, naringenin-0.5 mM). According to the data obtained, the effect of precursors on tea callus cultures did not lead to significant increasing of superoxide dismutase and peroxidase activity in most cases. However, it led to the increased accumulation of the total phenolics content, as well as flavanols and proanthocyanidins contents. For
callus cultures, the most promising regulator of phenolic compounds was L-phenylalanine, in the presence of which its content increased almost twice. Thus, the exogenous effect of various precursors is possible to use for the targeted regulation of certain phenolics classes accumulation in plant cells.
Tea plants (Camellia sinensis L.) are phenol-accumulating crops that are widely used for public health. The healing effect of tea leaf products is due to the biosynthesis of such phenolic compounds ...(PCs) as flavans, which have P-vitamin capillary-strengthening activity. Due to their limited habitat and the value of their specialized metabolites of a phenolic nature, a promising approach is to establish in vitro cultures from them that retain the ability to form PCs, which is characteristic of ex vivo tea plants. The aim of this study was to investigate the effect of exogenic H2O2 (0.01 mM; 0.1 mM; 1 mM) on the growth, morphology, degree of stress response, and accumulation of various phenolic compounds in tea plant callus cultures of different ages (24 or 36 days) grown under different cultivation conditions (darkness or light). According to the results obtained, the H2O2 effect on tea callus cultures of different ages did not cause changes in their morphophysiological characteristics, both after 2 h of exposure (rapid response of callus culture, RRCC) and after 48 h (delayed response of callus culture, DRCC). The determination of the malondialdehyde (MDA) content, which serves as an indicator of changes in the level of lipid peroxidation (LPO) and the presence of stress responses in plant cells, indicated either its maintenance at the control level, a decrease, or an increase. All these effects depended on the growth conditions of the tea callus cultures (darkness or light), their age, the duration of exposure (rapid or delayed response), and the H2O2 concentration. Similar trends were noted for the total content of PCs as well as the amount of flavans, proanthocyanidins (soluble and insoluble forms), and lignin. The plant cell responses reflected changes in its adaptation programs, when specialized metabolites act as a target for the action of H2O2, thereby contributing to an increase in their resistance.
Using the mechanorheological viscoelastic plastic model, the effect of impact velocity of a spherical body on rebound height after impact interaction was studied. With an increase in impact velocity, ...the energy losses of impact interaction increase. Under the elastic deformations, energy dissipation depends on the deformation rate and increases with increasing impact velocity. During plastic deformations, energy dissipation increases with increasing deformations. Plasticity of the material significantly reduces rebound height. The more ductile the material, the lower the rebound height due to large plastic deformations. In case of an elastic impact, a decrease in elasticity leads to a decrease in the rebound height, since the viscoelastic model becomes more viscous, and the viscous resistance to deformations increases compared to the elastic resistance. This increases energy losses and decreases the rebound height. For the elastic-plastic model, the relationship is reverse. A decrease in elasticity leads to an increase in the rebound height. This is due to the fact that an increase in elasticity of the material leads to an increase in its stiffness. Elastic deformation resistance increases. An increase in the force causes an increase in plastic deformations and an increase in energy losses. An increase in the viscous resistance to deformations leads to an increase in energy losses and a decrease in the rebound height. Thus, the rebound height depends on impact interaction velocity. To improve reliability of dynamic process simulation, it is necessary to take into account these factors when studying the operation of equipment in the conditions of impact interaction of structural elements.
Simulation of the pulse-periodic high pressure cesium discharge is performed on the basis of equations of radiative gas dynamics. It is shown that in the discharge it is possible to implement two ...different types of structure of the plasma channel. At the beginning of the current pulse, the plasma discharge channel has a centered structure. At the same time, most of the plasma is concentrated near the discharge axis. The concentration of charged particles decreases along the radius. Then, if the current amplitude is large enough, during the plasma heating process, a transformation from the centered to the shell structure of the channel occurs. In this case, most of the plasma is concentrated on the periphery of the discharge and its concentration increases along the radius from the axis to the walls of the tube. It is shown that the transition from one channel structure to another occurs at a time when the specific heat capacity of the plasma near the axis reaches a deep minimum corresponding to a completely single ionized
e
–
i
-plasma.
Abstract
The thermodynamic properties of alkali metal vapor plasma in the pressure range 0.25 - 3.0 atm and temperatures 1500 - 60000 K are considered. It is shown that a distinctive feature of this ...plasma is the existence of a relatively narrow critical temperature interval in which the plasma consists only of electrons and singly ionized atoms. The specific heat capacity of the plasma has a minimum value in the critical temperature range, corresponding to the heat capacity of a simple e-i plasma in which the second ionization of atoms has not begun. It has been shown that, due to this property, in gas discharge lamps filled with alkali metal vapors, it is possible to control the type of spatial distribution of the plasma. Under relatively low currents, when the temperature of the plasma doesn’t reach the critical range of the value, the traditional space distribution of the plasma is realized in the gas discharge tube. In this case, most of the plasma is concentrated in the axial region of the tube and its concentration decreases along the radius from the axis to the walls of the tube. With sufficiently high currents, when the plasma temperature on the axis exceeds the values from the critical interval, the opposite case is realized: the main part of the plasma is now concentrated on the periphery of the gas discharge volume. In this case, the plasma concentration increases along the radius from the axis to the tube walls. It is shown that the transformation of one type of spatial distribution of plasma into another occurs when the plasma temperature on the axis reaches values from the critical interval and the specific heat capacity approaches its minimum value, corresponding to a simple plasma consisting of electrons and single-charge ions.
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