Symmetric Cycle Research Articles

Symmetric Cell Study of Ferri/Ferrocyanide Stability As a Flow Battery Active Material

The attraction of aqueous organic redox flow batteries (AORFBs) lies in the potential for low mass-production cost and long lifetime of the organic reactants. To reach a cell potential greater than 1.0 V, several AORFBs have employed the ferri/ferrocyanide redox couple as a positive electrolyte (posolyte) in an alkaline full cell. Recent works [1,2] have reported significant amounts of capacity fade of this redox couple at high pH, attributed to an apparent chemical decomposition associated with cyanide ligand dissociation and subsequent irreversible hydroxylation of the iron complex. An in-depth analysis of the chemical and electrochemical stability of ferri/ferrocyanide is performed utilizing a volumetrically unbalanced, compositionally-symmetric cell method [3]. The dependence on pH of the apparent interaction of carbonaceous electrodes with active species will be reported, and keys to suppressing electrolyte degradation will be discussed. The accuracy of electrochemical techniques (e.g. high-precision coulometry) and chemical characterization (e.g. NMR, UV-vis) to understand ferri/ferrocyanide degradation will also be compared. Collectively, these results will highlight opportunities for improving energy storage systems. [1] J. Luo, A. Sam, B. Hu, C. DeBruler, X. Wei, W. Wang, and T.L. Liu, “Unraveling pH dependent cycling stability of ferricyanide/ferrocyanide in redox flow batteries”, Nano Energy 42, 215 (2017). [2] J. Luo, B. Hu, C. Debruler, Y. Bi, Y. Zhao, B. Yuan, M. Hu, W. Wu, and T.L. Liu, “Unprecedented Capacity and Stability of Ammonium Ferrocyanide Catholyte in pH Neutral Aqueous Redox Flow Batteries”, Joule, in press (2018). [3] M-A. Goulet, M.J. Aziz, “Flow Battery Molecular Reactant Stability Determined by Symmetric Cell Cycling Methods”, Journal of the Electrochemical Society 165, A1466 (2018).

Derivation of Motor Mean Phase Currents in PMSM Drives Operating with Low Switching-to-Fundamental Frequency Ratio

Abstract Pulse width modulation (PWM) of inverter output voltage causes the waveforms of motor phase currents to consist of distinctive ripples. In order to provide suitable feedback for the motor current controllers, the mean value must be extracted from the currents’ waveforms in every PWM cycle. A common solution to derive the mean phase currents is to sample their value at the midpoint of a symmetrical PWM cycle. Using an assumption of linear current changes in steady PWM subintervals, this midpoint sample corresponds to the mean current in the PWM cycle. This way no hardware filtering or high-rate current sampling is required. Nevertheless, the assumption of linear current changes has been recently reported as over simplistic in permanent magnet synchronous motor (PMSM) drives operating with low switching-to-fundamental frequency ratio (SFFR). This, in turn, causes substantial errors in the representation of the mean phase currents by the midpoint sample. This paper proposes a solution for deriving mean phase currents in low SFFR PMSM drives, which does not rely on the linear current change assumption. The method is based on sampling the currents at the start point of a PWM cycle and correcting the sampled value using a model-based formula that reproduces the current waveforms. Effectiveness of the method is verified by simulation for an exemplary setup of high-speed PMSM drive. The results show that the proposed method decreases the error of determining the mean phase currents approximately 10 times when compared to the classical midpoint sampling technique.

Sulfonated poly(ether ether ketone) membrane for quinone-based organic flow batteries

Over the past few years, organic flow batteries have gained immense attention owing to their potential for large-scale energy storage applications and modifiable properties. Organic redox couples usually involve only one type of counter-ion for ion exchange membranes, and hence provide opportunities to use low-cost membranes in organic flow batteries. In this study, we prepared a sulfonated poly (ether ether ketone) (sPEEK) membrane for application in acidic flow batteries of 1,2-dihydroxybenzene-3,5-disulfonic acid/anthraquinone-2-sulfonic acid. The proton conductivity of the prepared sPEEK membrane was 50% lower than that of Nafion-212 membrane. However, the Coulombic efficiency of the sPEEK cell was similar to that of Nafion cell, and the voltage efficiency was 0.99%–2.66% higher than that of Nafion cell at different current densities. The cell using the sPEEK membrane also exhibited long-term stability, retaining 96.93% reversible capacity after 100 charge/discharge cycles at the current density of 100 mA cm−2. The results of symmetric cell cycling indicated that the decay of reversible capacity in this organic flow battery system was mainly due to the instability of organic compounds in the positive electrolyte, which was also confirmed by the self-discharge measurements of the sPEEK cell. These results demonstrate that the sPEEK membrane is highly suitable for organic flow batteries. These results will be helpful for realizing cost-effective energy storage systems.

The Improved Hatch Cover Construction for Universal Open Box-type Wagon from the Strength and Durability Point of View

Dynamic load of the improved hatch cover construction for universal open-box type wagon is researched, taking in to account the worse loading scheme - impact of 150 kg cargo from height of 3000 mm. In the case of improved hatch cover construction, dynamic load character reduction up to 50% can be reached, compare to conventional one. Hatch cover model of proposed construction for strength calculation was created. Strength calculation is done by finite-elements method in Cosmos Works software. Calculation of hatch cower durability, considering symmetrical and asymmetrical load cycle are carried out. In the proposed construction, areas with maximum equivalent stresses caused by usual operational load are defined. Results of conducted research can be useful for projection of new wagon generation with improved technical, economical and operational parameters.

Poly(ionic liquid) iongel membranes for all solid-state rechargeable sodium battery

Sodium-ion is seen as one of the most promising alternative technologies to the current lithium-ion batteries. Sodium is cheap and widely available in comparison to lithium, however new electrode and polymer electrolyte materials need to be found to improve the performance and security of sodium batteries. In this work, we show a new iongel electrolyte with excellent properties for an all solid-state rechargeable sodium batteries. This iongel membrane is based on the poly(dimethyldiallylammonium) polyDADMA-TFSI poly(ionic liquid), N-Propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (C3mpyrFSI) and sodium bis (fluorosulfonyl)imide (NaFSI) the salt. PolyDADMA-TFSI can incorporate up to 50 wt% of C3mpyrFSI ionic liquid content in a self-standing membrane with high ionic conductivity. The increasing the NaFSI concentration in this electrolyte was beneficial for the sodium transference number but detrimental for the ionic conductivity of the membranes. The addition of alumina nanoparticles further improved the membrane mechanical robustness without affecting significantly the ionic conductivity. The iongel membranes presented a wide electrochemical window of 5 V thereby supporting sodium electrochemistry as demonstrated by excellent symmetric sodium cell cycling at 70 ᵒC for 60 cycles. Finally, the electrochemical performance of the optimum composition iongel was evaluated in sodium all solid-state battery using a sodium metal anode and NaFePO4 as the cathode material. The cells show good capacity retention with high coulombic efficiency (>97%) at C rates between C/20 and C/5 achieving 110 mAhg−1 at C/20.

Water as an Effective Additive for High-Energy-Density Na Metal Batteries? Studies in a Superconcentrated Ionic Liquid Electrolyte.

The effect of water on the properties of superconcentrated sodium salt solutions in ionic liquids (ILs) was investigated to design electrolytes for sodium battery applications with water as an additive. Water was added to a 50 mol % solution of NaFSI [FSI=bis(fluorosulfonyl)imide] in the ionic liquid N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (C3 mpyrFSI). Although the thermal properties (e.g., glass transition temperature) showed little dependence on the water content, the viscosity and, in particular, the ionic conductivity were strongly affected. The Na|Na symmetrical cell cycling performance was strongly dependent on the applied current density as well as on the water content. At higher current densities (1.0 mA cm-2 ) the polarization profiles showed a water dependence, suggesting that water was actively involved in the formation of an improved solid electrolyte interface layer (SEI) for high-water-content samples (1000-5000 ppm), resulting in improved long-term cycling stability. The initial impedance of cells cycled at 1.0 mA cm-2 (measured after 20 cycles) was elevated after water addition, and large polarizations occured for the "wet" samples. However, with further cycling the wet cells began to exhibit lower polarization and improved stability compared to the "dry" sample. The Na|NaFePO4 cell cycling performance was also demonstrated with minimal effect on the cell capacity, further highlighting the negligible activity of water in these electrolyte systems. In fact, reduced cell polarization and a more clearly defined charge profile were evident after water addition. The work shown here suggests that water may be used as a convenient and inexpensive additive for superconcentrated sodium IL electrolytes for improved device performance.

Driven-dissipative dynamics of atomic ensembles in a resonant cavity: Nonequilibrium phase diagram and periodically modulated superradiance

We study the dynamics of two ensembles of atoms (or equivalently, atomic clocks) coupled to a bad cavity and pumped incoherently by a Raman laser. Our main result is the nonequilibrium phase diagram for this experimental setup in terms of two parameters - detuning between the clocks and the repump rate. There are three main phases - trivial steady state (Phase I), where all atoms are maximally pumped, nontrivial steady state corresponding to monochromatic superradiance (Phase II), and amplitude-modulated superradiance (Phase III). Phases I and II are fixed points of the mean-field dynamics, while in most of Phase III stable attractors are limit cycles. Equations of motion possess an axial symmetry and a $\mathbb{Z}_{2}$ symmetry with respect to the interchange of the two clocks. Either one or both of these symmetries are spontaneously broken in various phases. The trivial steady state loses stability via a supercritical Hopf bifurcation bringing about a $\mathbb{Z}_{2}$-symmetric limit cycle. The nontrivial steady state goes through a subcritical Hopf bifurcation responsible for coexistence of monochromatic and amplitude-modulated superradiance. Using Floquet analysis, we show that the $\mathbb{Z}_{2}$-symmetric limit cycle eventually becomes unstable and gives rise to two $\mathbb{Z}_{2}$-asymmetric limit cycles via a supercritical pitchfork bifurcation. Each of the above attractors has its own unique fingerprint in the power spectrum of the light radiated from the cavity. In particular, limit cycles in Phase III emit frequency combs - series of equidistant peaks, where the symmetry of the frequency comb reflects the symmetry of the underlying limit cycle. For typical experimental parameters, the spacing between the peaks is several orders of magnitude smaller than the monochromatic superradiance frequency, making the lasing frequency highly tunable.

Surprising Enhancement in the Ion Transport Properties and Sodium Metal Cycling in a Water Tolerant Ionic Liquid Electrolyte

Present energy demand is hard to sustain due to increasing energy consumption. Thus new energy storage and supply technologies are required which are reliable, safe, inexpensive and show high energy and power densities. Among various battery chemistries, Na based batteries have been identified as potential efficient stationary energy storage technologies. Electrolytes are an integral component of a sodium battery spatially ionic liquid based electrolytes have attracted great interest1. The use of additives during electrolyte preparation is often carried out to achieve better transport performance, tune the composition of the solid electrolyte interphase, SEI, and alter other characteristics1–3. Recently, electrolyte additives for Na batteries is an emerging area for researchers3 The effect of water on the properties of sodium salt solutions of ionic liquids (ILs) was investigated in order to design electrolytes for sodium battery applications using water as an additive. Water amounts ranging from 100 to 10000 ppm were added to a superconcentrated NaFSI salt (50 mol%) solution in the ionic liquid N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (C3mpyrFSI)4. While the thermal properties (glass transition temperature) are little dependent on the water content, the viscosity and, in particular the ionic conductivity (fig1a), are strongly affected. Whereas addition of the NaFSI salt to the IL significantly increases viscosity with a concommitant decrease in conductivity, adding water up to 10000 ppm (0.99 wt%) remarkably restores the values close to those of the neat ionic liquid (i.e., reversing the detrimental effect of Na salt addition on conductivity). Na|Na symmetrical cell cycling performance is strongly dependent on the applied current density as well as on the water content (fig1b). At higher current densities (1.0 mAcm-2) the polarisation profiles show a water dependence suggesting that water is being actively involved in the formation of a solid electrolyte interphase (SEI) for high water content samples (1000 – 5000 ppm). The work shown here suggests that water may be a convenient and inexpensive additive in high concentrated ionic liquid electrolytes for sodium which can improve device performance. Reference: Armand, M., Endres, F., MacFarlane, D. R., Ohno, H. & Scrosati, B. Ionic-liquid materials for the electrochemical challenges of the future. Nat. Mater. 8, 621–9 (2009).Yan, Y. et al. Roles of Additives in the Trihexyl(tetradecyl) Phosphonium Chloride Ionic Liquid Electrolyte for Primary Mg-Air Cells. J. Electrochem. Soc. 161, A974–A980 (2014).Komaba, S. et al. Fluorinated ethylene carbonate as electrolyte additive for rechargeable Na batteries. ACS Appl. Mater. Interfaces 3, 4165–4168 (2011).Forsyth, M. et al. Novel Na+ Ion Diffusion Mechanism in Mixed Organic-Inorganic Ionic Liquid Electrolyte Leading to High Na+ Transference Number and Stable, High Rate Electrochemical Cycling of Sodium Cells. J. Phys. Chem. C 120, 4276–4286 (2016). Figure 1

All Organic Interface Layer Formed from Vinylene Carbonate and Stable Plating of Lithium Metal

Prevailing demand for lithium-ion batteries with higher energy density draws more researcher's attentions on the use of lithium metal as the anode material. An order of magnitude higher specific capacity and much lower reduction potential of lithium metal compared to graphite makes lithium metal suitable anode for the next-generation lithium-sulfur and lithium-air batteries. However, nonuniform plating or dendrite formation of lithium metal is a major issue for shorting batteries. Stable interface between lithium metal and electrolyte is the key to the uniform growth of lithium. Vinylene carbonate (VC) is a widely used additive in commercial electrolyte for lithium-ion batteries, and the effect of VC on stabilizing lithium metal has been reported. VC is proposed to polymerize on lithium surface to form flexible thin coating layer, which regulates the lithium-ion flux at the interface and put a mechanical pressure on the growing lithium dendrite. The interface layer is composed of multiple decomposition products from organic solvents and fluorinated salt and extremely complex to analyze. Here we propose a gel electrolyte composed of vinylene carbonate and lithium iodide (LiI) to form polymer coating layer on the lithium surface. FTIR, NMR, and GC-FID analysis confirm polymerization of vinylene carbonate is triggered by lithium iodide through decarboxylation and forms poly(vinylene catbonate). Because iodide is electrochemically irreducible anion, no decomposition occurs on the lithium surface and simplifies the interface composition. Without the formation of inorganic compounds in VC-LiI gel electrolyte, Li//Li symmetric cell cycles for 1000 hours at 1 mA cm-2 and 1 mAh cm-2, with a practical electrolyte thickness of 25 μm (separator free). Coulombic efficiency of lithium plating/stripping in VC-LiI gel electrolyte is 98.6%, which is significantly higher than conventional carbonate-based electrolyte. Cross-sectional SEM image of cycled lithium metal reveals dense polymer coating and dendrite free morphology. Therefore, the simple all-organic interface, differing from conventional heterogeneous inorganic/organic mixture, can stabilize the lithium surface. We present a new perspective on the design of electrolyte and lithium interface.

Probing the Interactions and Dynamics in an Ionic Liquid – Organic Solvent Hybrid Electrolyte System for Potential Application in Li-S Batteries

The depletion of fossil fuel and strict environmental regulation on carbon footprints has prompted a greater reliability on sustainable energy sources. Batteries represent an important energy storage option due to their wide range of applicability and portability, however, for certain applications such as transportation, a higher energy density battery is required. Beyond the conventional Li-ion battery system, current research is focusing on next-generation cost effective devices. Amongst them, the Li-S battery technology is very promising due to its high theoretical capacity and energy density [1]. However, the chemistry involved in the Li-S battery is a complex process with multiple consecutive electrochemical reactions. Despite having many advantages, its application is still limited by several issues, e.g., the dissolution and diffusion of intermediate polysulphides, unstable plating and stripping of Li metal, both resulting in rapid capacity fading [2]. Previously, we reported the application of a novel electrolyte system composed of N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide, C3mpyrFSI, ionic liquid (IL) and 1,2 dimethoxyethane (DME) in the presence of varying saturated lithium bis(fluorosulfonyl)imide, LiFSI which predominantly suppressed the polysulphide dissolution and diffusion while showing improved lithium plating and stripping behavior [3]. In order to expand our understanding on the role of DME and the lithium salt concentration; in this work, we have considered a similar ionic liquid based electrolyte system but at a constant concentration of LiFSI salt. The ionic interactions among different species of the electrolyte system have been extensively studied by nuclear magnetic resonance (NMR) spectroscopy using 1D chemical shift, PFG-NMR and Heteronuclear Overhauser Effect SpectroscopY (HOESY) measurements. We found that, when increasing the DME concentration in the system, a strong association of Li+ cation with the DME occurs due to the electronegative oxygen atoms present in the DME molecules which leads to strong coordination. This leads to a change of the chemical shift of 7Li nuclei due to them being increasingly de-shielded. Interestingly, we found that the diffusivity of both Li+ and DME species are very similar, which also confirms that a Li-DME complex is present with FSI anion associated in the next coordination sphere to counterbalance the positively charged Li complex. MD simulations are underway to better elucidate the molecular shell structure of the system. We have also carried out electrochemical characterizations of these hybrid electrolytes to determine their potential applicability in a lithium sulphur battery. It was apparent using cyclic voltammogram (CV) performed in a three electrode set-up, that an increasing amount of DME increases the ionic conductivity but decreases the lithium plating-stripping efficiency. A coin-cell study of Li/Li symmetrical cycling showed an excellent plating-stripping behaviour for 70%IL-30%DME composition. We have carried out a full cell cycling against sulphur cathode and the optimised electrolyte composition obtained a promising first discharge capacity of 1100mAh/g. Additionally, we have investigated the sulphur speciation in the presence of this ionic liquid in a three-electrode system where platinum mesh has been used as working electrode coupled with in-situ UV-vis spectroscopy. Finally, a time dependent bulk electrolysis study revealed the plausible intermediates formed during the charge-discharge cycle of sulphur redox reaction. From these studies it appears that the composition of this novel hybrid electrolyte system can be tuned to provide a system with improved transport, electrochemical and sulphur speciation properties which lend themselves to a higher performance, next generation lithium sulphur battery technology.

The features of behavior of the Lyapunov's exponents from the symmetry of thermodynamic potential described by lifshitz invariant

The influence of the thermodynamic potential ( n ) symmetry on the behavior of the Lyapunov exponents is investigated. The calculation of the system of second-order differential equations was performed by a multi-step variable-order BDF method. The Lyapunov coefficients were calculated using Python software using Skipy, JiTCODE libraries. It is established that for values of n ≥ 5, the dynamics of the incommensurate superstructure is determined by the spatial change in the amplitude of the order parameter (the first integral of the motion of the incommensurate superstructure). For n < 5, the dynamics of a incommensurate superstructure is determined by the spatial change of the phase of the order parameter and its perturbation. It is shown that the dynamics of the superstructure is not affected by the ferroelectric or ferroelastic nature of the incommensurate superstructure. In order to obtain a detailed picture of the dynamics of the incommensurate superstructure, phase portraits were investigated in the coordinates R , R `, and φ at different values of the anisotropic interaction of the superstructure and the initial phase values of the order parameter φ 0 . It is established that the dynamics of this system is determined by the cascades of transition to chaos and areas of self-organization of the superstructure. It is shown that at the final stage of the transition to chaos, the system is characterized by the emergence of a chaotic attractor, which has a more complex phase portrait structure. The projection of such an attractor consists of two symmetrical parts with respect to the axis of the abscissa. The movement of a typical trajectory of a chaotic attractor can be divided into two phases. In the first phase of the trajectory, chaotic movements are made along the turns of the upper (lower) part of the attractor from time to time, passing to the boundary of the localization region where the stability of the upper (lower) symmetric boundary cycles is lost. At an unpredictable time, the trajectory moves from the upper (lower) part of the attractor to its upper (lower) part. This process is repeated infinitely many times. Thus, the transition to chaos has features characteristic of the Feigenbaum scenario (infinite cascade of bifurcations of doubling cycles), and for mixing (unpredictable mixing between the upper and lower parts of the emerging chaotic attractor). The self-organization process can be associated with the localization of a wave vector of incommensurate superstructure at a commensurate higher order value. It is shown that the distortion of the order parameter phase at the edge of the crystal can be related to boundary conditions in the first approximation. According to the authors, such cascading transitions to chaos are related to the modes of existence of a incommensurate superstructure. The emergence of chaos in the third stage is caused by the transition of a incommensurate superstructure to its stochastic mode of existence. In a stochastic mode of existence of a incommensurate superstructure, a chaotic, possibly incommensurate phase arises, which is a prototype of this chaotic state. It should be noted that the initial conditions (boundary conditions) stabilize the system, thereby leading to the removal of the degeneracy of the system, and the transition of a incommensurate superstructure to a state characterized by the existence of long-period proportional phases. Key words: incommensurate superstructures, phase portraits, Lyapunov’s exponents.

Accelerated Life Test and FEM Simulation-Based Fatigue Analysis of an Aluminum Alloy Push Rod

The accelerated life test based on the spectrum of fatigue loads was used both in numerical simulation and bench tests of the push rod. The symmetrical cycling of the push rod was presented as the positive pulsating load spectrum corresponding to the stress spectrum of the critical node in the finite element model. As FEM analysis demonstrates, the fatigue crack initiation would occur at the edge of the first-position pin hole with maximum stress and minimum fatigue life. Bench test results show that the fatigue crack initiation and fatigue life of the push rod are in good agreement with FEM data.

Disordered Oscillations in a Neural Network of Three Oscillators with a Delayed Broadcast Connection

A model of neural association of three pulsed neurons with a delayed broadcast connection is considered. It is assumed that the parameters of the problem are chosen near the critical point of stability loss by the homogeneous equilibrium state of the system. Because of the broadcast connection the equation corresponding to one of the oscillators can be detached in the system. The two remaining impulse neurons interact with each other and, in addition, there is a periodic external action, determined by the broadcast neuron. Under these conditions, the normal form of this system is constructed for the values of parameters close to the critical ones on a stable invariant integral manifold. This normal form is reduced to a four-dimensional system with two variables responsible for the oscillation amplitudes, and the other two, defined as the difference between the phase variables of these oscillators with the phase variable of the broadcast oscillator. The obtained normal form has an invariant manifold on which the amplitude and phase variables of the oscillators coincide. The dynamics of the problem on this manifold is described. An important result was obtained on the basis of numerical analysis of the normal form. It turned out that periodic and chaotic oscillatory solutions can occur when the coupling between the oscillators is weakened. Moreover, a cascade of bifurcations associated with the same type of phase rearrangements was discovered, where a self-symmetric stable cycle alternately loses symmetry with the appearance of two symmetrical cycles. A cascade of bifurcations of doubling occurs with each of these cycles with the appearance of symmetric chaotic regimes. With further reduction of the coupling parameter, these symmetric chaotic regimes are combined into a self-symmetric one, which is then rebuilt into a self-symmetric cycle of a more complex form compared to the cycle obtained at the previous step. Then the whole process is repeated. Lyapunov exponents were calculated to study chaotic attractors of the system.

Bandwidth-efficient network monitoring algorithms based on segment routing

We study the bandwidth-efficient network monitoring algorithms using segment routing on topologies that can be modelled as a symmetric directed graph. Aiming at directly minimizing the cycle cover length, four new two-phase algorithms, A, B, C and D, are proposed. Algorithm A is a simple extension of an existing algorithm. Algorithm B utilizes the notion of symmetric cycles. Algorithm C enhances B by adopting a new path metric. Algorithm D further improves C with a parallel and sequential cycle construction process. Since two-phase algorithms require a dedicated monitoring topology, the four two-phase algorithms are then enhanced to function without monitoring topology. Although the cycle cover length found is slightly increased, we argue that the cost saving in removing monitoring topology is far more significant.

Scenario to chaos and multistability in a modified Coullet system: effects of broken symmetry

Recently, the study of nonlinear systems with multiple attractors has drained the attention of researchers worldwide owing to its fundamental and technological relevance. In this work, we consider a modified Coullet system with a cubic polynomial nonlinearity in the form $$ \varphi_{m} \left( x \right) = x - mx^{2} - x^{3} $$ where $$ m $$ is a control parameter. The new system bridges the gap between chaotic systems with symmetry and those without symmetry. In fact for $$ m = 0 $$ , the system displays a perfect symmetry which is reflected on the location of equilibria, the type of attractors, and the shape of basins of attraction as well. In this special case, multistability involves a pair of mutually symmetric periodic or chaotic attractors, a pair of chaotic attractors with a pair of limit cycles, two pairs of limit cycles with a pair of chaotic attractors, and so on. For $$ m \ne 0 $$ , the system is non symmetric and more complex nonlinear phenomena are observed such as parallel bifurcation branches, coexisting multiple asymmetric attractors, and hysteresis. For instance, the coexistence of a stable fixed point with a limit cycle, two different non symmetric limit cycles or chaotic attractors, three or four different non symmetric periodic and chaotic attractors are reported when monitoring the system parameters and initial conditions as well. Basins of attraction with non-trivial basin boundaries structures are computed to visualize the magnetization of the state space in the presence of multiple attractors. Experimental results based on a suitable electronic implementation of the proposed jerk system are included.

Dependence of the limit endurance of specimens with notches from the depth of hardened surface layer

It is shown that, growth of the layer with compressive residual stresses at advanced surface plastic deformation of smooth samples leads to an increase in the endurance limit of the notched specimens due to an increase in the compressive residual stresses in their dangerous section. The study was conducted on the specimens with outer diameterDequal to 10 and 25 mm and on a 25 mm specimen with inner diameterd= 15 mm which were subjected to air shot blasting and roll-in. Residual stresses in smooth specimens were determined by the mechanical method. Circular incisions (R= 0.3 and 0.5 mm) were applied on hardened smooth samples with a shaped cutter. Residual stresses in notched specimens were determined by a numerical method calculating the redistribution of the residual stresses upon the incision. As the diameter of the samples increases with the same strengthening surface treatment,the depth of the layer with the compressive residual stresses increases due to an increase in the rigidity of the samples. The effect of surface hardening on the endurance limit of notched specimens was evaluated according to the criterion of the average integral residual stresses, which takes into account both the magnitude and completeness of the residual stresses. This criterion was calculated from the depth of the non-propagating fatigue crack that occurs in the surface layer in the dangerous section of the specimen during the fatigue test at the limit endurance. Fatigue tests are carried out in symmetrical cycle, the test base being 3 × 106cycles of loading. Estimation of the increment of the limit endurance of surface-hardened cylindrical specimens with semicircular notches gave the results acceptable for practice. The use of the proposed method can significantly reduce long-term and expensive fatigue tests.

Improved estimation of iron losses for non-sinusoidal voltages

PurposeThe electrical machines connected to modern electric power grids are non-sinusoidal excited, and their augmented losses, including iron losses, limit their working characteristics. This paper aims to propose a prediction method for iron losses in non-oriented grains (NO) FeSi sheets under non-sinusoidal voltage, involving an inverse classical Preisach hysteresis model and the time-integration of each loss component.Design/methodology/approachThe magnetic history management in inverse Preisach model is optimized and a numerical Everett function is identified from measured symmetrical hysteresis cycles. The experimental data for sinusoidal waveforms obtained by a single sheet tester were also used to identify the parameters involved in Bertotti’ losses separation method. The non-sinusoidal magnetic induction waveform, corresponding to a measured voltage in an industrial electrical grid, was the input for Preisach model, the output magnetic field being accurately computed. The hysteresis, classical and excess losses are calculated by time-integration and the total losses are compared with those obtained for sinusoidal excitation.FindingsThe proposed method allows to estimate the iron losses for non-sinusoidal magnetic induction, using carefully identified parameters of FeSi NO sheets, using experimental data from sinusoidal regimes.Originality/valueThe method accuracy is assured by using a numerical Everett function, a variable Preisach grid step (adapted for the high non-linearity of FeSi sheets) and high-order fitting polynomials for the microscopic parameters involved in the excess loss estimation. The procedure allows a better design of magnetic cores and an improved estimation of the electric machine derating for non-sinusoidal voltages.

System-level modeling of nonlinear hysteretic piezoelectric actuators in quasi-static operations

Abstract This paper aims at providing a simple yet efficient model for predicting the strain-voltage relationship in piezoelectric actuators subjected to high driving conditions, and featuring hysteretic response under such excitation. The originality of the model lies in proposing a high-level, system approach for modeling hysterestic response, using a butterfly-shaped electromechanical coupling term between the voltage and strain derivatives. The model is based on function reversal, and can be applied to many hysteresis types as the function can be properly chosen. Furthermore, the model requires few parameters and works both in unipolar and symmetric cycles, while being able to handle minor loops as well. Experimental results made on an unipolar piezoelectric actuator show good agreement with theoretical predictions. As a general hysteresis model, the proposed model can besides be applied to other domains, such as in magnetism, magnetic actuation or hydraulics.

Stability of Organic Reactants for Aqueous Flow Batteries

The transition to non-emitting renewable energy requires cost-effective arbitrage on several timescales to balance the disparity between peak demand and the electricity supplied from intermittent renewables. Among the technologies available for grid scale energy storage, flow batteries have recently gained considerable interest for longer duration timescales because their energy and power costs are decoupled. With the aim of minimizing these energy costs, many researchers have shifted toward designing electrolytes with synthetic redox active organic molecules made from inexpensive and earth abundant materials. Within this trend, it has become evident that the calendar life, rather than the cycle life, of the organic compound is a limiting factor for the viability of many chemistries. We present here some examples connecting flow battery capacity fade to electrolyte stability. An in-depth analysis on the chemical stability and decomposition of one particular molecule, 2,6-dihydroxyanthraquinone, is presented and compared with other mechanisms of capacity fade observed for similar molecules. In most cases, symmetric cell cycling is used to assess the capacity fade and stability of single electrolytes and these results are linked to decomposition of electrolytes stored at elevated temperatures in both reduced and oxidized form.

Sulfide Based Solid Electrolyte for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have the potential to deliver higher energy at lower cost compared to state-of-the-art Li-ion batteries. Greatest obstacles for deployment of Li-S batteries lie in polysulfide dissolution/shuttle and high Electrolyte/sulfur ratio required for stable long term cycling. In all-solid-state Li-S batteries (ASSLiS), S conversion undergoes the solid-state route therefore excludes the problems of polysulfide dissolution and high E/S ratio. Sulfide-based solid electrolytes are most suitable for ASSLiS and excellent performance of S cathode has been demonstrated.1 Due to the insulating nature of S particles, short diffusion length is needed to realize high S utilization. Liquid phase synthesis of sulfide-based solid electrolyte has advantages of easy preparation of nanosized particle, great flexibility and tunability, better scalability, and thus is desired for sulfur electrode preparation. It was found in our study the crystalline Li7P3S11 forms through a two-step reaction: 1) formation of solid Li3PS4∙ACN and amorphous ‘Li2S∙P2S5’ phases in the liquid phase; 2) solid-state conversion of the two phases.2 The other significant obstacle of ASSLiS is lack of solid state electrolytes that support stable Li metal cycling at relevant current density and cycling depth. We developed a sulfide-based solid electrolyte that has extremely high ionic conductivity of 4.7 mS/cm and kinetically stable, low-impedance interface (< 10 Ω cm2) with Li metal anode. Long term Li/Li symmetric cell cycling was achieved at 0.5 mA/cm2. In addition, the material remains stable in structure and ionic conductivity within two hours exposure in the dry room environment. In this talk, we present our progress on the sulfide-based solid electrolytes for ASSLiS. References H. Nagata, Y. Chikusa. Journal of Power Sources 264 (2014) 206-210Y. Wang, D. Lu, Z Deng, J Xiao, J. Zhang and J. Liu. Chemistry of Materials 30 (3):990-997. doi:10.1021/acs.chemmater.7b04842