Monotonic Change Research Articles

Size effects of elastic properties for auxetic cellular structures: bending energy-based method

Auxetic cellular structures have attracted growing attention due to their distinctive mechanical properties including increased stiffness, energy absorption capacity and high strength-to-weight ratio. In this paper, the size effects of elastic properties for a double-arrowed auxetic honeycomb (DAAH) has been investigated. With the microscopic size of DAAH taken into account, analytical models predicting the in-plane effective Young’s modulus and Poisson’s ratio have been established by adopting a bending energy-based method (BEM) and a strain-based expansion homogenization method (HM), respectively. Further, an integrated experimental and simulation approach has been conducted to validate the analytical models. The comparison shows that the bending energy-based method can reveal the size effects of elastic properties for DAAH with an acceptable accuracy. Further, a variety of analytical results have been presented to investigate the size effects. It is shown that with the increase of scale factor, the predicted elastic properties prove to feature a monotonic change and then tend to a convergence. Finally, the influence of volume fraction on the size effects has been discussed. It is believed that this work can greatly expand the engineering application of auxetic structures with stable mechanical properties in various scales.

Simulation of the SiGe use effi-ciency for the production of high-voltage thyristors

Power semiconductor devices often subjected to appreciable terrestrial atmospheric neutron flows. For the improvement of their radiation hardness, the use of silicon doped with Ge (SiGe) was proposed. The stability of last is much higher in comparison with convenient type silicon. Earlier received results confirmed effectiveness of isovalent doping of silicon with germanium at radiation tests of low power (current approx. 100 mA) discrete devices. Power thyristors Т122-25 are used for the transformation and regulation of AC and DC current up to 25А, frequency up to 500 Гц in the circuits with voltage 100 – 1600V (1-16 class). In the data sheets directly indicated that these devices are not suitable for operating in the conditions of ionizing radiation. Therefore, the main practically important mission of the article was the confirmation the technological efficiency of SiGe use, or, in other words, possibility of radiation hard material use for high voltage power devices technology. The purpose of the present work was the modeling of the experimental findings for the informed choice of Ge concentration for manufacturing of high voltage thyristors Т122. The data concern the workable general-purpose power thyristors Т122 type yield, manufactured in accordance with the identical technology, based on CZ-Si и CZ-Si. At SiGe implementation in the technology of power semiconductors was observed no monotonic change of the thyristors gain share for devices of high (10, 11, 12) ranges (classes), the value of pulse recurring voltage in off-state is 1000, 1100 and 1200 V. Simulation of the experimental results was performed in MathCAD. The concentration of Ge, suitable for the manufacture of high-voltage thyristors, is in the range 2 ·1019 - 1·1020 cm-3, i.e. in the linear region of dependence. Previously, the authors have experimentally shown the possibility and mechanism of increasing the radiation resistance of SiGe with a concentration of Ge 5·1019 cm-3. It is allowed to admit the possibility of reaching the radiation resistance of high-voltage power discrete thyristors when tested with γ-quanta in the dose range up to ≅ 3·106 mSv.

Pan-Arctic seasonal cycles and long-term trends of aerosol properties from 10 observatories

Abstract. Even though the Arctic is remote, aerosol properties observed there are strongly influenced by anthropogenic emissions from outside the Arctic. This is particularly true for the so-called Arctic haze season (January through April). In summer (June through September), when atmospheric transport patterns change, and precipitation is more frequent, local Arctic sources, i.e., natural sources of aerosols and precursors, play an important role. Over the last few decades, significant reductions in anthropogenic emissions have taken place. At the same time a large body of literature shows evidence that the Arctic is undergoing fundamental environmental changes due to climate forcing, leading to enhanced emissions by natural processes that may impact aerosol properties. In this study, we analyze 9 aerosol chemical species and 4 particle optical properties from 10 Arctic observatories (Alert, Kevo, Pallas, Summit, Thule, Tiksi, Barrow/Utqiaġvik, Villum, and Gruvebadet and Zeppelin Observatory – both at Ny-Ålesund Research Station) to understand changes in anthropogenic and natural aerosol contributions. Variables include equivalent black carbon, particulate sulfate, nitrate, ammonium, methanesulfonic acid, sodium, iron, calcium and potassium, as well as scattering and absorption coefficients, single scattering albedo and scattering Ångström exponent. First, annual cycles are investigated, which despite anthropogenic emission reductions still show the Arctic haze phenomenon. Second, long-term trends are studied using the Mann–Kendall Theil–Sen slope method. We find in total 41 significant trends over full station records, i.e., spanning more than a decade, compared to 26 significant decadal trends. The majority of significantly declining trends is from anthropogenic tracers and occurred during the haze period, driven by emission changes between 1990 and 2000. For the summer period, no uniform picture of trends has emerged. Twenty-six percent of trends, i.e., 19 out of 73, are significant, and of those 5 are positive and 14 are negative. Negative trends include not only anthropogenic tracers such as equivalent black carbon at Kevo, but also natural indicators such as methanesulfonic acid and non-sea-salt calcium at Alert. Positive trends are observed for sulfate at Gruvebadet. No clear evidence of a significant change in the natural aerosol contribution can be observed yet. However, testing the sensitivity of the Mann–Kendall Theil–Sen method, we find that monotonic changes of around 5 % yr−1 in an aerosol property are needed to detect a significant trend within one decade. This highlights that long-term efforts well beyond a decade are needed to capture smaller changes. It is particularly important to understand the ongoing natural changes in the Arctic, where interannual variability can be high, such as with forest fire emissions and their influence on the aerosol population. To investigate the climate-change-induced influence on the aerosol population and the resulting climate feedback, long-term observations of tracers more specific to natural sources are needed, as well as of particle microphysical properties such as size distributions, which can be used to identify changes in particle populations which are not well captured by mass-oriented methods such as bulk chemical composition.

Transient chirality inversion during racemization of a helical cobalt(III) complex.

SignificanceWe first observed a transient chirality inversion on a simple unimolecular platform during the racemization of a chiral helical complex [LCo3A6]3+, i.e., the helicity changed from P-rich (right-handed) to M-rich (left-handed), which then racemized to a P/M equimolar mixture in spite of the absence of a reagent that could induce the M helix. This transient chirality inversion was observed only in the forward reaction, whereas the reverse reaction showed a simple monotonic change with an induction time. Consequently, the M helicity appeared only in the forward reaction. These forward and reverse reactions constitute a hysteretic cycle. Compounds showing such unique time responses would be useful for developing time-programmable switchable materials that can control the physical/chemical properties in a time-dependent manner.

Visualizing molecular weights differences in supramolecular polymers

Issues of molecular weight determination have been central to the development of supramolecular polymer chemistry. Whereas relationships between concentration and optical features are established for well-behaved absorptive and emissive species, for most supramolecular polymeric systems no simple correlation exists between optical performance and number-average molecular weight (Mn). As such, the Mn of supramolecular polymers have to be inferred from various measurements. Herein, we report an anion-responsive supramolecular polymer [M1·Zn(OTf)2]n that exhibits monotonic changes in the fluorescence color as a function of Mn Based on theoretical estimates, the calculated average degree of polymerization (DPcal) increases from 16.9 to 84.5 as the monomer concentration increases from 0.08 mM to 2.00 mM. Meanwhile, the fluorescent colors of M1 + Zn(OTf)2 solutions were found to pass from green to yellow and to orange, corresponding to a red shift in the maximum emission band (λmax ). Therefore, a relationship between DPcal and λmax could be established. Additionally, the anion-responsive nature of the present system meant that the extent of supramolecular polymerization could be regulated by introducing anions, with the resulting change in Mn being readily monitored via changes in the fluorescent emission features.

Modelling the influence of interphase and magnetostatic interaction on the magnetic characteristics of core/shell nanoparticles

In this work, we present the results of a theoretical study of the dependence of the hysteresis characteristics of core/shell nanoparticles on their size, interphase exchange and interparticle magnetic interactions. By modelling the influence of the size effect on the saturation magnetisation Ms, the remanent magnetisation Mrs and the coercive field Hc of nanoparticles (Fe/Fe3O4andCo/Au), in which there is a difference in the magnetostatic interaction between the core and shell of the systems, we show that an increase in the size of the nanoparticles leads to an increase in Ms and Mrs,and non-monotonic (Co/Au) and monotonic (Fe/Fe3O4) changes in Hc. The increased hysteresis characteristics of the nanoparticles are due to both a decrease in the proportion in the superparamagnetic state and the peculiarities of the reversal of magnetisation. The interphase exchange interaction, regardless of its sign, leads to an increase in the coercive force and remanent saturation magnetisation of Fe/Fe3O4 nanoparticles, and has only very weak effects on the hysteresis characteristics of Co/Au nanoparticles. It was found that an increase in the interparticle magnetic interaction (volume concentration) of core/shell nanoparticles, and consequently their chaotisation, leads to a decrease in the coercive force and remanent saturation magnetisation. Moreover, an increase in the size of the nanoparticles leads to a higher rate of decrease in the hysteresis characteristics. A calculation of the blocking temperature TB for the core/shell nanoparticles shows that it is determined not only by their volume but also by the size dependence of the critical fields of the phase magnetisation reversal. With an increase in the interfacial exchange interaction constant Ain, the blocking temperature of the Fe/Fe3O4 nanoparticles quickly reaches saturation, while for Co/Au nanoparticles, TB is practically independent of Ain. The magnetic interaction between nanoparticles leads to chaos in the distribution of their magnetic moments, and hence to an increase in the blocking temperature. The results obtained here are in good agreement with experimental data.

MODELLING OF SEGMENTS OF ONE-DIMENSIONAL CONTOURS ACCORDING TO THE SPECIFIED CONDITIONS

The formation of one-dimensional contours on the basis on the given conditions is one of the most popular geometric modeling problems. The problem is solved by variative discrete geometric modeling, which assumes the formation of intermediate points for the initial set of condensation points. The discrete model of the curve consists of a point sets, given geometric characteristics and a condensation algorithm.
 A discretely presented curve (DPC) is formed by a condensation of the initial point set of an arbitrary configuration in areas on which it is possible to ensure a monotonic change in the values of its characteristics. Monotone plots are joined at special points. Every three consecutive points of the duodenum define an adjacent plane. Four adjacent planes passing through two consecutive points limit the tetrahedron. The chain of consecutive tetrahedrons defined on all segments is the region of the location of the smooth curve of the constant stroke line interpolating the initial point sets. The torsion on the sections of the DPC is estimated by the value of the ratio of the angle between adjacent adjacent planes to the length of the corresponding chord of the accompanying broken line. The point of thickening is assigned inside the tetrahedron of the DPC. As a result of successive condensations, we obtain a continuous bypass of a constant stroke, at each point of which there is a single position of the main trihedron. The point of condensation is assigned in such a way that the values of the torsion in the duodenum points change monotonically. This ensures that the torsion values are regular at the points of the bypass.
 The imposition of additional conditions on the DPC formed requires the definition of the corresponding region of a possible solution within the DPC arrangement tetrahedron.

Controlling thermal cycling effect in phase separated manganites with high temperature thermal treatments

Several phase separated manganites present a peculiar effect each time they go through a phase transition within the range characterized by phase separation. The effect is known as the thermal cycling effect (TCE) and is characterized by monotonous changes in the relative content of the coexisting phases.In this work, we analyze a way to control the effects induced by TCE, performing thermal treatments at high temperature. Our results revealed a complex interplay between the dynamic and static characteristics of the phase separated state, which can be analyzed in terms of three simple parameters. One related to the static properties, another to the dynamic properties and a last one that acts as a link between both features.

Coal gangue image segmentation method based on edge detection theory of star algorithm

ABSTRACT Aiming at the difficult problem of coal gangue image segmentation in complex backgrounds, this paper proposes an image segmentation method based on the edge detection theory of the star algorithm. The pixel matrix is extracted one by one in the X and Y directions of the coal gangue image, and the central pixel of the matrix satisfying the monotonic change condition is assigned as 0. They are mapped to single-value images with equal size in turn, to realize the detection of coal and gangue edges in the images. The response strategy of adjusting matrix length n and assignment factor β in real-time by using the feedback result of the illuminance meter in changing illumination environment is given. Combining the edge detection method of the star algorithm with the morphological method, the fine segmentation of the coal gangue image is completed. The segmentation results are based on the segmentation results obtained by the AI algorithm, and the error rates of the pixel area and centroid coordinates of coal gangue are within 0.29%. This study provides a novel, precise and efficient solution to the problem of image edge detection and segmentation in complex backgrounds.

THE EXPRESS REGISTRATION OF THERMAL CONDUCTIVITY ANOMALIES OF SOLIDS

Investigation of the thermophysical characteristics of materials at low temperatures (T ≤ ,  is the Debye temperature) makes it possible to obtain information on the interaction of quasiparticles and is in demand in the applied plan. For the indicated temperatures, a method of express registration (ER) of anomalies in the thermal conductivity of solids (k), which is a variation of the classical method of uniaxial stationary heat flux (USHF), but which, unlike the prototype, does not require taking into account heat losses (HL). A feature of the ER method is the measurement of the temperature dependence of the difference δΤ = T1−T2 between the ends of the sample under conditions of simultaneous monotonicity of the change in Т of the sample and all HL. In this case, the measured scaled thermal conductivity Ҝ(Q/Ψ)/δΤ (Ψ is a monotonic scale factor in T) correlates with the real kQ/δΤ. For the interval 300…77 K, one of the variants of the ER method was tested, in which a step-by-step movement of the sample in a column of gaseous nitrogen above the surface of liquid N2 in a Dewar vessel was used. In the case of a monotonic change in the distance from the sample to the liquid, the formed configuration of isotherms ensures the monotonicity of the change in T of the sample and, at the same time, the monotonicity of the HL along the channels of thermal conductivity and radiation. The possibilities of the ER method are illustrated by examples of determining the temperatures and signs of anomalies in the thermal conductivity coefficients of high-temperature superconductors (HTSC) in the pseudogap state (PGS) and a high-entropy alloy Аl0.5CoCuCrNiFе, which is promising for use in the cryogenic temperature range. The method made it possible for the first time to discover the staging of the temperature evolution of the thermal conductivity of YBa2Cu3O7-x and Bi1.6(Pb0.4)Sr2Ca2Cu3O10+х in the PGS and to determine the temperatures and signs of the anomalies. The data obtained convincingly confirmed the results of probing the PGS of HTSCs by the method of polarized neutron scattering carried out with the participation of a number of EU research institutes. Also, for the first time, an extended thermal conductivity anomaly of a high-entropy Аl0.5CoCuCrNiFе alloy in the range of ~ 220…170 K was discovered, which is probably a consequence of changes in the configuration of the Fermi surface.

Physical-mechanical properties of synthesized layers of Ti-Ni-Nb-based surface alloys, formed on the surface of TiNi alloy

The physical-mechanical properties (microhardness, Young's modulus, plasticity characteristic, shape recovery ratio) of the synthesized layers of Ti-Ni-Nb-based surface alloys of ~2 μm thickness, formed on the surface of TiNi alloy by the additive thin-film electron beam method were investigated by the instrumented indentation. It was found that the change in physical-mechanical properties in the synthesized surface alloys based on Ti-Ni-Nb is due to their layered structure. In particular, it is due to the thickness of the sublayers, their phase composition, and the structural states of the phases (nanocrystalline and amorphous). It was established that high strength and elastic-plastic parameters of the outer layer and a monotonic change in the physical-mechanical properties from the surface to TiNi substrate are provided in the surface Ti-Ni-Nb alloy with a lower volume fraction of the amorphous phase in the synthesized layers. It was found that the multilayer structure of the surface Ti-Ni-Nb alloy and the monotonically change in the physical-mechanical properties to the substrate ensure high mechanical compatibility of the synthesized layers of surface alloys with the TiNi substrate. Keywords: nickel titanium alloy, additive thin-film electron-beam synthesis, surface alloy, structure, physical-mechanical properties.

Физико-механические свойства синтезированных слоев поверхностных сплавов на основе Ti-Ni-Nb, сформированных на поверхности сплава TiNi

The physical-mechanical properties (microhardness, Young’s modulus, plasticity characteristic, shape recovery ratio) of the synthesized layers of Ti-Ni-Nb-based surface alloys of ~2 μm thickness, formed on the surface of NiTi alloy by the additive thin-film electron beam method were investigated by the instrumented indentation. It was found that the change in physical-mechanical properties in the synthesized surface alloys based on Ti-Ni-Nb is due to their layered structure. In particular, it is due to the thickness of the sublayers, their phase composition, and the structural states of the phases (nanocrystalline and amorphous). It was established that high strength and elastic-plastic parameters of the outer layer and a monotonic change in the physical-mechanical properties from the surface to TiNi substrate are provided in the surface Ti-Ni-Nb alloy with a lower volume fraction of the amorphous phase in the synthesized layers. It was found that the multilayer structure of the surface Ti-Ni-Nb alloy and the monotonically change in the physical-mechanical properties to the substrate ensure high mechanical compatibility of the synthesized layers of surface alloys with the TiNi substrate.

Design, Implementation, and Optimization of Sliding Mode Controller for Automatic Voltage Regulator System

Academic studies on the Automatic Voltage Regulator (AVR) have focused on a linear mathematical model which lacks protective features. More accurate model of the AVR system includes protective features as described in IEEE standards. The AVR models without protective features, namely limiters, result in less accurate control performance since the outputs of real controllers are always bounded. In the present study, the controller outputs are limited between -0.9pu and 1.0pu, and the upper bound of exciter output is limited by 3.1pu with the direction of IEEE standards. The effect of limiters on the controller performance is investigated. Two controllers with a novel sliding surface function are proposed based on a mathematical model of the AVR (SMC3) and its approximate reduced-order model (SMC2). The proposed controllers having only two parameters are optimized with improved particle swarm optimization (PSO) algorithm. After optimization, the robustness of the controllers is compared with the results of various operating conditions identical to the previous studies. Nominal time constants of the AVR constituents are perturbed from -50% to 50%, and ±10% output disturbance is applied to the output. Although controller outputs and exciter output are limited, the overshoot is measured less than 0.1% at no-load conditions. The robustness of the controllers against parameter uncertainties is measured with an average overshoot at the output. Another superiority among the reported results in the literature is obtained from the proposed controllers, where the minimum average overshoots are measured. In addition, when ±10% load is applied to the output of the AVR, the proposed controllers generate accurate control inputs that reject the load disturbance successfully. Furthermore, the proposed controllers keep the output within the ±5% band if there is a monotonic change at the output. All the results show that the proposed controllers with the improved PSO have drawn the best performance from the perspective of time-domain specifications in comparison with the recently reported controllers.

Increasing in productivity of ball-rolling mills by using over-threaded roll grooving

The calculation methods of the productivity of ball-rolling mills is given and the effect of design and technological factors on the productivity of ball-rolling mills is considered. It is established that the most effective factors in improving of the productivity of ball-rolling mills is increase in the roll-in and rotational speed of rolls, which are limited by the quality of the rolled balls, mainly due to the quality of the ball-rolling rolls, determined by the quality of grooving (shape of groove) of the roll s, the accuracy of their manufacture and adjustment. The use of over-threated low-energy monotonous grooving of ball-rolling rolls having smooth monotonous change in the pitch of screw groove allows to create rolls with smooth ball forming mode, which reduces the load during rolling and improves the quality of balls while increasing the durability of the rolls. At the same time, these advantages allow to increase the rolling speed. The use of such roll grooving is currently the most efective way to increase the productivity of ball-rolling mills.

Inventory policies for monotonic change in the purchase price

Inventory policies for monotonic change in the purchase price

Study of Thermal Stress Fluctuations at the Die-Attach Solder Interface Using the Finite Element Method

Solder joints in electronic packages are frequently exposed to thermal cycling in both real-life applications and accelerated thermal cycling tests. Cyclic temperature leads the solder joints to be subjected to cyclic mechanical loading and often accelerates the cracking failure of the solder joints. The cause of stress generated in thermal cycling is usually attributed to the coefficients of thermal expansion (CTE) mismatch of the assembly materials. In a die-attach structure consisting of multiple layers of materials, the effect of their CTE mismatch on the thermal stress at a critical location can be very complex. In this study, we investigated the influence of different materials in a die-attach structure on the stress at the chip–solder interface with the finite element method. The die-attach structure included a SiC chip, a SAC solder layer and a DBC substrate. Three models covering different modeling scopes (i.e., model I, chip–solder layer; model II, chip–solder layer and copper layer; and model III, chip–solder layer and DBC substrate) were developed. The 25–150 °C cyclic temperature loading was applied to the die-attach structure, and the change of stress at the chip–solder interface was calculated. The results of model I showed that the chip–solder CTE mismatch, as the only stress source, led to a periodic and monotonic stress change in the temperature cycling. Compared to the stress curve of model I, an extra stress recovery peak appeared in both model II and model III during the ramp-up of temperature. It was demonstrated that the CTE mismatch between the solder and copper layer (or DBC substrate) not only affected the maximum stress at the chip–solder interface, but also caused the stress recovery peak. Thus, the combined effect of assembly materials in the die-attach structure should be considered when exploring the joint thermal stresses.

4-Dialkylamino-2,5-dihydroimidazol-1-oxyls with Functional Groups at the Position 2 and at the Exocyclic Nitrogen: The pH-Sensitive Spin Labels.

Local acidity and electrostatic interactions are associated both with catalytic properties and the adsorption activity of various materials, and with the vital functions of biomolecules. The observation of acid–base equilibria in stable free radicals using EPR spectroscopy represents a convenient method for monitoring pH changes and the investigation of surface electrostatics, the advantages of which are especially evident in opaque and turbid samples and in porous materials such as xerogels. Imidazoline nitroxides are the most commonly used pH-sensitive spin probes and labels due to the high sensitivity of the parameters of the EPR spectra to pH changes, their small size, and their well-developed chemistry. In this work, several new derivatives of 4-(N,N-dialkylamino)-2,5-dihydrioimidazol-1-oxyl, with functional groups suitable for specific binding, were synthesized. The dependence of the parameters of their EPR spectra on pH was studied. Several showed a pKa close to 7.4, following the pH changes in a normal physiological range, and some demonstrated a monotonous change of the hyperfine coupling constant by 0.14 mT upon pH variation by four units.

Physical properties of liquid oxygen under ultrahigh magnetic fields

We studied the acoustic properties of liquid oxygen up to 90 T by means of ultrasound measurements. We observed a monotonic decrease of the sound velocity and an asymptotic increase of the sound attenuation when applying magnetic fields. The unusual attenuation, twenty times as large as the zero-field value, suggests strong fluctuations of the local molecular arrangement. We assume that the observed fluctuations are related to a liquid-liquid transition or crossover, from a small-magnetization to a large-magnetization liquid, which is characterized by a local-structure rearrangement. To investigate higher-field properties of liquid oxygen, we performed single-turn-coil experiments up to 180 T by means of the acoustic, dilatometric, magnetic, and optical techniques. We observed only monotonic changes of these properties, reflecting the absence of the proposed liquid-liquid transition in our experimental conditions.

Quantification of Fracture Roughness by Change Probabilities and Hurst Exponents

The objective of the current study is to utilize an innovative method called “change probabilities” for describing fracture roughness. In order to detect and visualize anisotropy of rock joint surfaces, the roughness of one-dimensional profiles taken in different directions is quantified. The central quantifiers, change probabilities, are based on counting monotonic changes in discretizations of a profile. These probabilities, which usually vary with the scale, can be reinterpreted as scale-dependent Hurst exponents. For a large class of Gaussian stochastic processes, change probabilities are shown to be directly related to the classical Hurst exponent, which generalizes a relationship known for fractional Brownian motion. While related to this classical roughness measure, the proposed method is more generally applicable, therefore increasing the flexibility of modeling and investigating surface profiles. In particular, it allows a quick and efficient visualization and detection of roughness anisotropy and scale dependence of roughness.

Singular magnetic dilution behavior in a quasicrystal approximant

We report the effect of magnetic dilution on the physical properties of $({\mathrm{Gd}}_{1\ensuremath{-}x}{\mathrm{Y}}_{x}){\mathrm{Cd}}_{6}$ approximant crystals (ACs), close siblings of their corresponding quasicrystal (QC). Compared to the pure system ${\mathrm{GdCd}}_{6}$, we observe remarkable changes in the thermodynamic and magnetic bulk properties near and below the static-ordering temperatures from diluting the magnetic Gd atoms with nonmagnetic Y atoms by only 1--3% $(x=0.01--0.03)$. On the other hand, the corresponding QC system exhibits a monotonic change in its spin-glass behavior upon the magnetic dilution. We discuss the origin of the magnetic-dilution behavior in the present AC system in terms of possible magnetic frustration and short-range magnetic correlation that can be linked to its peculiar structure.