A reverse transition route from inertial to elasticity-dominated turbulence in viscoelastic Taylor–Couette flow

A high-order transition route from inertial to elasticity-dominated turbulence (EDT) in Taylor–Couette flows of polymeric solutions has been discovered via direct numerical simulations. This novel two-step transition route is realized by enhancing the extensional viscosity and hoop stresses of the polymeric solution via increasing the maximum chain extension at a fixed polymer concentration. Specifically, in the first step inertial turbulence is stabilized to a laminar flow much like the modulated wavy vortex flow. The second step destabilizes this laminar flow state to EDT, i.e. a spatially smooth and temporally random flow with a $-3.5$ scaling law of the energy spectrum reminiscent of elastic turbulence. The flow states involved are distinctly different to those observed in the reverse transition route from inertial turbulence via a relaminarization of the flow to elasto-inertial turbulence in parallel shear flows, underscoring the importance of polymer-induced hoop stresses in realizing EDT that are absent in parallel shear flows.

ACTIVE AND PASSIVE WORK OF THE TRACTOR IN THE COMPOSITION OF TILLAGE UNITS

Purpose of the study. Improving the efficiency of using a tractor as part of a tillage machine through scientific and technical substantiation of energy conservation. This goal is achieved by increasing the active (useful) and reducing the passive (not useful) work of the tractor. Research methods. The method of partial accelerations based on the reverse transition from the vector sum in the space of forces acting on the tractor to the vector sum in the space of accelerations is the basis for assessing the traction-energy and dynamic parameters of tractors in the composition of tillage machines. The results of the study. The unevenness of the movement significantly affects the decrease in the active work of the tillage unit and, accordingly, the increase in the passive work. A dependence is proposed for determining the additional energy consumption for oscillatory movements with an uneven movement of the tractor unit. It is proved that the additional energy consumption during the unstable movement of the tillage unit on the rut is 2-3 % (passive work) of the total energy consumption. The method of partial accelerations, which is based on the reverse transition from the vector sum in the space of forces acting on the tractor, to the vector sum in the space of accelerations, is the basis for assessing the traction-energy and dynamic parameters of tractors in the composition of tillage machines. On the basis of this method, the methodology for assessing the traction-energy and dynamic indicators of the tractor when performing the technological process without the use of dynamometric means has been substantiated. The modernized measuring and registration complex, developed with the participation of the authors of the article at the Kharkiv National Automobile and Highway University, P. Vasilenko Kharkiv National Technical University of Agriculture and the Kharkiv branch of L. Pogorilyy UkrNDIPVT in the direction of software for assessing the resistance of aggregated machines, traction efficiency of the tractor, longitudinal acceleration of the unit. The use of this complex when testing tractors is aimed at implementing the methodology of L. Pogorilyy UkrNDIPVT with the definition of traction indicators of tractors and standards of the Code 2 of the Organization for Economic Cooperation and Development (OECD). Conclusions. The article contains a theoretical generalization and a new solution to the scientific problem of increasing the efficiency of a tractor as part of a tillage unit, based on a decrease in additional energy costs (passive work). The research results made it possible to formulate the main theoretical and scientific-practical conclusions. The scientific value of the study lies in clarifying the dependence of the tractor operation as part of the tillage machine in the direction of reducing the useless (passive) work on turns at the headland and on a turn on the rut. It has been proven that in order to ensure maximum operation of this unit, it must be operated with increased traction force and reduced travel speed. The dynamic model of the tractor as part of the tillage unit has been improved. The practical value of the study lies in the standard developed on the basis of the partial acceleration method for assessing the traction properties of the tractor SOU 71.2-37-046043080-017: 2015, which is recommended by the Ministry of Agrarian Policy and Food of Ukraine for use in testing and modernizing tractors.

Effect of electric hysteresis on fatigue behavior in antiferroelectric bulk ceramics under bipolar loading

Antiferroelectric ceramics are exploited for applications in high energy-density capacitors due to their reversible electric-field-induced phase transitions. The difference in the fields between the forward and reverse transition is termed...

LAYERED IN2SE3 ON SI (111) SURFACE WITH HYSTERESIS OF THE TEMPERATURE DEPENDENCE OF RESISTANCE

In this work, the methods of controlled growth of two-dimensional In2Se3 on a Si (111) substrate were studied by reflection high-energy electron diffraction (RHEED). According to experimental data, the deposition rate reduction increases the size of two-dimensional In2Se3 islands. The temperature dependence of the film resistance was measured by the two-contact technique. At temperature decrease near T = 140 K, an abrupt decrease in resistance by a factor of ~ 1000 was found. The reverse transition occurs near T = 180 K. At T = 20–40 K the second hysteresis occurring without the film resistance jump was found.

Silicon Microcantilever Sensors to Detect the Reversible Conformational Change of a Molecular Switch, Spiropyan

The high sensitivity of silicon microcantilever sensors has expanded their use in areas ranging from gas sensing to bio-medical applications. Photochromic molecules also represent promising candidates for a large variety of sensing applications. In this work, the operating principles of these two sensing methods are combined in order to detect the reversible conformational change of a molecular switch, spiropyran. Thus, arrays of silicon microcantilever sensors were functionalized with spiropyran on the gold covered side and used as test microcantilevers. The microcantilever deflection response was observed, in five sequential cycles, as the transition from the spiropyran (SP) (CLOSED) to the merocyanine (MC) (OPEN) state and vice-versa when induced by UV and white light LED sources, respectively, proving the reversibility capabilities of this type of sensor. The microcantilever deflection direction was observed to be in one direction when changing to the MC state and in the opposite direction when changing back to the SP state. A tensile stress was induced in the microcantilever when the SP to MC transition took place, while a compressive stress was observed for the reverse transition. These different type of stresses are believed to be related to the spatial conformational changes induced in the photochromic molecule upon photo-isomerisation.

Observation of the shock-induced β-Sn to b.c.t.-Sn transition using time-resolved X-ray diffraction

Time-resolved X-ray diffraction measurements have been carried out on dynamically compressed Sn up to a maximum pressure of ∼13 GPa at the European Synchrotron Radiation Facility. The phase transition from β-Sn to body-centered tetragonal (b.c.t.) Sn has been observed using synchrotron X-ray diffraction for the first time undergoing shock compression and release. Following maximum compression, the sample releases to lower pressures for several nanoseconds until the reverse transition occurs. The data are in good agreement with previous shock boundaries that indicate that the β-Sn phase is stable ∼2 GPa higher than the static boundary upon compression and the b.c.t.-Sn phase is stable ∼1 GPa lower upon release. The transition to the high-pressure phase reveals a loss of texture in the X-ray diffraction data from the `quasi' single-crystal β-Sn structure to a more powder-like Debye–Scherrer ring.

Влияние времени нарастания напряжения на переходные процессы при токовой перегрузке в стабилизированных ВТСП-проводах второго поколения

The effect of spontaneous reverse transition of the stable HTSC tape from the normal to the resistive state with rapid input voltage and current overload at alternating current is detected. For the first time it is established that during the occurrence of this effect and at the thickness of the stabilizer above 13 µm, the main heat releases occur in the copper stabilizer and are effectively discharged into the refrigerant, which significantly reduces the heating of the HTSC layer. In this case, the resistance of the secondary resistive state decreases and the time of its existence increases. These data make it possible to use the detected effect to increase the time of current limitation and reliability of HTSC current limiters.

The Art of Coercion: Repressions and Repressiveness in Putin’s Russia

While repressions are seen to be a backbone of authoritarian rule, there is a lack of case studies of repressions and repressive policies in different kinds of authoritarian regimes and their interaction with other mechanisms of authoritarian sustainability. As Russia has demonstrated a transition from ‘soft’ electoral authoritarianism to its more ‘hard’ version during Putin’s third term in office, the role of repressions has increased. What are their scope and functions in Russia during this reverse transition? This article offers an analysis of the causes, types and mechanisms of repressions, and presents various ways of measuring their scale as well as the sources and means of their legitimation within the framework of an electoral regime. It shows that the regime prefers to demonstrate its high repressiveness—its willingness and propensity to repress—but in a limited number of cases; it also describes the role of repressive populism, namely presenting repressions as a necessary response to multiplying threats, as well as the scope and function of counter-elite repressions. The latter are seen as no less important than political repressions in the regime’s reverse transition, and as the main leverage of redistribution of power and institutional rearrangement in its course.

A phase transition caught in mid-course: independent and concomitant analyses of the monoclinic and triclinic structures of ( n Bu4N)[Co(orotate)2(bipy)]·3H2O

The preparation and characterization of the n Bu4N+ salts of two bis-orotate(2−) complexes of cobalt, namely bis(tetra-n-butylammonium) diaquabis(2,4-dioxo-1,2,3,4-tetrahydropyrimidin-1-ide-6-carboxylato-κ2 N 1,O 6)cobalt(II) 1.8-hydrate, (C16H36N)2[Co(C5H2N2O4)2(H2O)2]·1.8H2O, (1), and tetra-n-butylammonium (2,2′-bipyridine-κ2 N,N′)bis(2,4-dioxo-1,2,3,4-tetrahydropyrimidin-1-ide-6-carboxylato-κ2 N 1,O 6)cobalt(III) trihydrate, (C16H36N)[Co(C5H2N2O4)2(C10H8N2)]·3H2O, (2), are reported. The CoIII complex, (2), which is monoclinic at room temperature, presents a conservative single-crystal-to-single-crystal phase transition below 200 K, producing a triclinic twin. The transition, which involves a conformational change in one of the n Bu groups of the cation, is reversible and can be cycled. Both end phases have been characterized structurally and the system was also characterized structurally in a two-phase intermediate state, using single-crystal diffraction techniques, with both the monoclinic and triclinic phases present. Thermal analysis allows a rough estimate of the small energy content, viz. 0.25 kJ mol−1, for both the monoclinic-to-triclinic transformation and the reverse transition, in agreement with the nature of the structural changes involving only the n Bu4N+ cation.