Three-phase inverter with a variable control algorithm

The paper presents the construction of a three-phase frequency converter with the possibility of choosing the type of PWM modulation and a smooth change of the frequency of the modulated signal. In a practical way, various inverter control algorithms were implemented in the same hardware system using the STM ARM Cortex M3 processor. The use of THIPWM modulation allowed to reduce the harmonic content in the output signal and effectively use the possibilities of the power source. The system can choose one of two scalar control algorithms, with the option of compensation for the influence of the stator resistance on the motor shaft torque in the initial range of the linear control characteristic at a constant voltage to frequency ratio. The research confirmed that the most advantageous type of PWM in this system is unipolar double-edge modulation. The use of the THIPWM method resulted in a gain in the amplitude of the fundamental harmonic of the output voltage for the three-phase inverter operation mode compared to the SPWM method. The appropriate precision of the frequency control step was also obtained, and the test results confirmed the functionality of the converter.

Assessment of the impact of climate risks on agriculture in the context of global warming

Understanding the possible climate risks and potential economic losses of agribusiness in different regions is becoming a determining factor in the strategic planning of agricultural activities in the context of global warming. The purpose of this work was to assess the climate risks for agriculture in Russia. The study was conducted using techniques and tools of multivariate correlation analysis. The authors investigated the influence of deviations of the average monthly amounts of temperatures and precipitation from the average long-term values on the deviation of grain yields, using a set of data for 17 regions of the Central Federal district of Russia for the period of 2000-2019. The results showed that a smooth change in the parameters of heat and precipitation does not significantly affect the yield of grain crops. At the same time, increasing annual temperature variability and precipitation significantly reduce yields. An increase in the frequency of extreme events causes a growth in the probability of environmental and economic damage and the magnitude of climate risks. The maximum level of climate risk requires an appropriate adjustment of the agribusiness development strategy and the creation of an institution in society of fair compensation for damage caused by global warming factors.

The Szymkowiak’s over-expanded cycle in the rocker engine with the variable compression ratio – kinematics

The article discusses the innovative concept of the over-expanded thermodynamic cycle, the author of which is the Polish engineer-designer Mirosław Szymkowiak. This cycle is realized on the basis of a new and innovative, previously unknown design, of a piston-crankshaft linkage mechanism with the aid of an additional element known as a rocker arm. Additionally, the proposed mechanism allows for a smooth change of the compression/expansion ratio of the engine during its operation. In the beginning, the earlier conceptions of the rocker engine developed by Szymkowiak were presented, and then the main construction assumptions and kinematic calculations were described. It was confirmed, that the developed linkage has big potential in improving the engine's thermal efficiency by approximately 12% relative. Additionally, it significantly reduces the exhaust gas pressure, when the exhaust valve is opened, therefore, contributes to the reduction of the noise emitted by the engine.

Analysis of physical condition of children 7-8 years old

Differentiation and individualization of school physical education allows one to take into account the features of each child, its existing experience and level of achievements, interests and inclinations. To organize a differentiated approach during a teacher of physical culture, operational information on the physical state of students of a particular class is required. The purpose of the work is to analyze the physical condition of children 7-8 years for planning physical activity during exercises. Methods of research: analysis of scientific and methodological literature; Pedagogical observation and experiment; testing; Methods of mathematical statistics. Organization of research. The research was conducted on the basis of School No. 66 of the Dnipro. 125 children 7-8 years have participated in the study. The processing of test results was carried out using the KIFZOS Computer Program. Research results. The age of 7-8 years is the most calm period in the development of children, during which there is a smooth change in the structures and functions of the organism. However, despite the slowdown in growth rates, the length of the body in girls and the boys increases more intense than body weight. The body proportions are changing, the volume of the chest increases, that is, there is a "pulling" of the body. A clear difference between boys and girls in anthropometric indicators almost not observed. The general assessment of the level of health of children under the method of G. L. Apanasenko allowed to distribute examined schoolchildren to 3 groups by levels of somatic health. Most children belonged to the group "Patients". Among boys, low level of physical fitness is observed more in children for 8 years - 63.0% (7 years - 33.3%). High levels are not fixed. Among girls, low levels of physical fitness had 29.4% - 7 years, 14.3% - 8 years. High levels were observed in 7.1% of girls 8 years. Conclusions. Thus, an individual assessment of the physical state of school-age children allows you to determine the means and methods of development of motor qualities, taking into account sensitive periods and age-sexual characteristics of students. The obtained data indicate a low level of physical condition of children, which determines the use of a differentiated approach in planning physical activity. Prospects for further research. We plan to develop exercises for increasing the level of physical status of schoolchildren who can be used when working on-line.

The rate of environmental change as an important driver across scales in ecology

Global change has been predominantly studied from the prism of ‘how much’ rather than ‘how fast’ change occurs. The paradigm underlying the former assumes that a smooth change in an environmental driver can force a regime shift between alternative states (Bifurcation-tipping). This presupposes that environmental conditions change at a rate which allows the ecological entity to track them and thus reach equilibrium. However, current rates of environmental change are often too fast for this paradigm to apply, necessitating a shift in approach to improve predictions on the impacts of rapid environmental change. The theory of rate-induced tipping (Rate-tipping) demonstrates how rates of environmental change can cause tipping phenomena even in the absence of alternative states. We illustrate how Rate-tipping can apply to a range of ecological scenarios and explore the literature for properties which increase the sensitivity to rates of change. Further, we discuss how targeted empirical studies can investigate the ecological and evolutionary mechanisms through which rate-induced phenomena can propagate across levels of organisation. Finally, we argue for the inclusion of Rate-tipping in the study of global change as the first step towards the theoretical synthesis necessary to account for multiple stressors impacting ecological entities simultaneously.

Profile of a new extended range-of-vision IOL: a laboratory study

Purpose To evaluate the surface profile of a new-generation extended range-of-vision intraocular lens (IOL) and to compare it with that obtained for a monofocal IOL based on the same platform. Methods Prospective, experimental, laboratory study comparing the surface profile of the DFT015 (AcrySof IQ Vivity; Alcon Laboratories, Inc.), a new-generation presbyopia-correcting IOL, with the profile of the SN60WF (AcrySof IQ; Alcon Laboratories, Inc.), an aspheric monofocal IOL based on the same platform. Raw profiles were obtained using contact profilometry. The best-fit form was then subtracted from each raw profile to highlight potential differences. Results No significant differences were appreciated in raw profiles. On the contrary, after form removal, the new extended range-of-vision IOL showed a peculiar profile characterized by the presence of two altitudinal symmetrical changes in the order of 1 µm, localized in the central portion of the optic. Conclusions The new-generation extended range-of-vision IOL evaluated showed a smooth change of its surface compared to the same platform monofocal IOL. The altitudinal changes blended in the central design of the new presbyopia-correcting IOL, although micrometric, might play a crucial role in creating a continuous focal range while minimizing visual disturbances.

Aging of the OT4-VT23, VT6-VT23, VT19-VT23 Titanium Welded Pairs

The structure, the phase composition and microhardness over the section of welded joints aged at 500 and 550 °C have been studied by means of structural and microdurometric analyzes. The welded joints of OT4-VT23, VT6-VT23 and VT19-VT23 titanium alloys pairs were obtained by the argon-arc welding with a nonconsumable tungsten electrode. It has been established that the aging at 500 °C for 8 hours promotes the decomposition of metastable phases (b, a”) which formed after welding in the welded joint of VT19-VT23 titanium alloys pair. The decomposition process leads to strengthening of the main zones of the welded joint (except for the parent metal of VT23 alloy) and provides a favorable smooth change of microhardness in the joint during the transition from one alloy to another. The aging at 500 and 550 °C during 8 hours of the welded joints of OT4-VT23, VT6-VT23 titanium alloys pairs also led to the development of the decomposition of metastable phases (b, a”, a’) in the weld and heat affected zones of the alloys being joined, but did not provide the required monotonic change in microhardness over the cross section of the joint.

DFT-Based Approach Enables Deliberate Tuning of Alloy Nanostructures Plasmonic Properties

<div>Using DFT we calculated band structures and dielectric functions of multiple binary alloy systems. The obtained data enabled us to elucidate the interconnection between alloy composition, fundamental properties such as band structure and their optical properties. The analysis provides the explanation for the smooth change of optical properties in the UV/VIS range and reveals the appearance of strong optical losses in the IR range due to interband transitions. Since they are present in all alloys but not in pure metals we identify such transitions as an emergent property of alloying. To predict plasmonic properties of different alloy nanostructures we performed electrodynamics simulations based on calculated and experimental dielectric functions. The results showed that that calculations based on the standardly used PBE functional in some cases drastically deviate from experiment-based results, and the calculations with an equally efficient GLLB-SC functional are superior. <br></div>

DFT-Based Approach Enables Deliberate Tuning of Alloy Nanostructures Plasmonic Properties

<div>Using DFT we calculated band structures and dielectric functions of multiple binary alloy systems. The obtained data enabled us to elucidate the interconnection between alloy composition, fundamental properties such as band structure and their optical properties. The analysis provides the explanation for the smooth change of optical properties in the UV/VIS range and reveals the appearance of strong optical losses in the IR range due to interband transitions. Since they are present in all alloys but not in pure metals we identify such transitions as an emergent property of alloying. To predict plasmonic properties of different alloy nanostructures we performed electrodynamics simulations based on calculated and experimental dielectric functions. The results showed that that calculations based on the standardly used PBE functional in some cases drastically deviate from experiment-based results, and the calculations with an equally efficient GLLB-SC functional are superior. <br></div>