Stability Domain Research Articles

Asymmetric Manipulation of Perpendicular Exchange Bias and Programmable Spin Logical Cells by Spin-Orbit Torque in a Ferromagnet/Antiferromagnet System.

Antiferromagnets are competitive candidates for the next generation of spintronic devices owing to their superiority in small-scale and low-power-consumption devices. The electrical manipulation of the magnetization and exchange bias (EB) driven by spin-orbit torque (SOT) in ferromagnetic (FM)/antiferromagnetic (AFM) systems has become focused in spintronics. Here, the realization of a large perpendicular EB field in Co/IrMn and the effective manipulation of the magnetic moments of the magnetic Co layer and EB field by SOT in Pt/Co/IrMn system is reported. During the SOT-driven switching process, an asymmetrically manipulated state is observed. Current pulses with the same amplitude but opposite directions induce different magnetization states. Magneto-optical Kerr measurements reveal that this is due to the coexistence of stable and metastable antiferromagnetic domains in the AFM. Exploiting the asymmetric properties of these FM/AFM structures, five spin logic gates, namely AND, OR, NOR, NAND, and NOT, are realized in a single cell via SOT. This study provides an insight into the special ability of SOT on AFMs and also paves an avenue to construct the logic-in-memory and neuromorphic computing cells based on the AFM spintronic system.

Vector multipole solitons of fractional-order coupled saturable nonlinear Schrödinger equation

Three kinds of vector multipole solitons of fractional coupled saturable nonlinear Schrödinger equation are reported, including fractional dipole-dipole, dipole-tripole and tripole-dipole vector soliton solutions. Firstly, their existence domains, which are modulated by potential function parameters, are constructed in a certain interval. Secondly, the stable regions of three kinds of vector multipole solitons, which are modulated by the soliton power of each component, are found. The properties of solitons are explored through these existence and stability domains. Finally, the stability of three kinds of fractional vector multipole solitons is verified by the numerical evolution. Compared with the integer-order results, there are differences in the existence and stable regions of soliton solutions, and the Lévy index affects the existence and stability of vector multipole solitons.

Efficient approximation of stochastic turning process based on power spectral density

Turning is one of the most important material removal processes in manufacturing, where the proper understanding of the process is crucial for the quality of the final product. In this study, the stochastic cutting force is utilized to enhance the existing 1-degree-of-freedom turning model. A stochastic model is adopted to address the stochastic resonance phenomenon occurring near stability boundaries. Additionally, a novel simplified stochastic model is introduced with additive noise only. The comparison of the two models reveals that, with the recommended noise intensity of 0.1 to 1%, there is no significant difference in the stability charts and mean square characteristics between the two models. As a result, the time-consuming numerical methods can be bypassed, as the simplified model offers a computationally more efficient analytical approach to compute variance based on power spectral density (PSD). By combining techniques such as D-separation to determine stability boundaries and the PSD-based variance calculation, it only takes a minute instead of hours to construct a heatmap using the introduced simplified stochastic turning model that clearly outlines dangerous stochastic resonance regions inside the stable domain.

Stable Operation Domain Analysis of Back-to-Back Converter Based Flexible Multi-State Switches Considering PLL Dynamics

Flexible multi-state switches (FMSSs), also called soft open point (SOP), are regarded as the core devices in flexible interconnected distribution network. However, due to their more complex control structure and nonlinear characteristics, there is a tight and complex coupling relationship between the transmission power limit and stability of two (or more) converter sides, which brings difficulties to the planning and power flow dispatching control of flexible interconnected distribution networks. In this paper, taking the back-to-back converter based FMSS (BTBC-FMSS) as the research object, the dynamic equivalent circuit connected to the distribution network is constructed, and the transmission active and reactive power expression of the converter on both sides considering PLL dynamics is deduced. The variation rules of transmission power limits on both sides of the device with various structures and control parameters are summarized. Furthermore, the stable operation domain of the BTBC-FMSS is constructed, and the effective measures to improve the transmission power stability of the device are given according to the analysis of the stable operation domain. Finally, a simulation model is built in Matlab/Simulink to verify the effectiveness of the analysis results.

Non-linear three-mode coupling of gravity modes in rotating slowly pulsating B stars

Context. Slowly pulsating B (SPB) stars display multi-periodic variability in the gravito-inertial mode regime with indications of non-linear resonances between modes. Several have undergone asteroseismic modeling in the past few years to infer their internal properties, but only in a linear setting. These stars rotate fast, so that rotation is typically included in the modeling by means of the traditional approximation of rotation (TAR). Aims. We aim to extend the set of tools available for asteroseismology, by describing time-independent (stationary) resonant non-linear coupling among three gravito-inertial modes within the TAR. Such coupling offers the opportunity to use mode amplitude ratios in the asteroseismic modeling process, instead of only relying on frequencies of linear eigenmodes, as has been done so far. Methods. Following observational detections, we derive expressions for the resonant stationary non-linear coupling between three gravito-inertial modes in rotating stars. We assess selection rules and stability domains for stationary solutions. We also predict non-linear frequencies and amplitude ratio observables that can be compared with their observed counterparts. Results. The non-linear frequency shifts of stationary couplings are negligible compared to typical frequency errors derived from observations. The theoretically predicted amplitude ratios of combination frequencies match with some of their observational counterparts in the SPB targets. Other, unexplained observed ratios could be linked to other saturation mechanisms, to interactions between different modes, or to different opacity gradients in the driving zone. Conclusions. For the purpose of asteroseismic modeling, our non-linear mode coupling formalism can explain some of the stationary amplitude ratios of observed resonant mode couplings in single SPB stars monitored during 4 years by the Kepler space telescope.

Fractional-Order Modeling and Nonlinear Dynamic Analysis of Forward Converter

To accurately investigate the nonlinear dynamic characteristics of a forward converter, a fractional-order state-space averaged model of a forward converter in continuous conduction mode (CCM) is established based on the fractional calculus theory. And nonlinear dynamical bifurcation maps which use PI controller parameters and a reference current as bifurcation parameters are obtained. The nonlinear dynamic behavior is analyzed and compared with that of an integral-order forward converter. The results show that under certain operating conditions, the fractional-order forward converter exhibits bifurcations characterized by low-frequency oscillations and period-doubling as certain circuit and control parameters change. Under the same circuit conditions, there is a difference in the stable parameter region between the fractional and integral-order models of the forward converter. The stable zone of the fractional-order forward converter is larger than that of the integral-order one. Therefore, the circuit struggles to enter states of bifurcation and chaos. The stability domain for low-frequency oscillations and period-doubling bifurcations can be accurately predicted by using a small signal model and a predictive correction model of the fractional-order forward converter, respectively. Finally, by performing circuit simulations and hardware-in-the-loop experiments, the rationality and correctness of the theoretical analysis are verified.

Revisiting the thermodynamic properties of the ZrCr2 Laves phases by combined approach using experimental and simulation methods

A comprehensive study of ZrCr2 Laves phases is important for both fundamental research and technological applications. The ZrCr2 compound is a typical precipitate observed in Zr-based alloys including the newly developed Cr-coated Zr cladding known as Accident Tolerant Fuel cladding. The brittle behavior of the Laves phases and the low melting point at the interface zone between the precipitates and the Zr matrix are considered as governing the thermomechanical behaviors of these newly developed nuclear fuel claddings for normal operating conditions but more dramatically in case of Loss Of Coolant Accident (LOCA) conditions. The aim of the present study is to investigate the various ZrCr2 Laves polymorphs and their thermodynamic features particularly where conflicts exist in the literature. Based on diffraction experiments of annealed samples, it has been established that the transformation from the C14 high-temperature form to the C15 low-temperature form is of displacive nature without the C36 polymorph forming as an intermediate phase. The stable and metastable domains of C14 and C15 and their thermodynamic properties have been determined. The specific heat of both C14 and C15 types was measured over a wide range of temperatures from 2 to 1063 K by coupling relaxation calorimetry and DSC. The experimental data were fitted using a modified Einstein model. The room temperature entropies of the C14 and C15 phases were evaluated. The enthalpy of formation was measured for the first time using drop solution calorimetry in liquid Al at 1173 K in a Tian–Calvet calorimeter. The experimental value is in good agreement with Density Functional Theory (DFT) calculations. Finally, all these new results are discussed regarding the abundant literature on the ZrCr2 Laves phases.

Hot deformation characteristics and processing map analysis of Al-Zn/stainless steel particles-based composite

The hot deformation behavior of Al-Zn/martensitic stainless steel particles-based composite (Al-Zn/6 %SSp), was examined in this study. The composite was tested using isothermal compression at 200–350 °C/0.01–10 s−1 and a global strain of 0.5. From the results, it was noticed that the composite’s flow stress increased with strain rate increase and drop in temperature. The constitutive equation from the hot-worked composites resulted in an estimated activation energy of 226.27 kJ/mol, which was 58 % more than that for the self-diffusion of aluminum alloy (142 kJ/mol). These findings suggest dynamic recrystallization (DRX) as the dominant deformation mechanism, as confirmed from the microstructures of the hot worked samples mostly at high temperatures and strain rates. Work hardening was predicted to dominate the deformation process by the stress exponent (n) value of 10.36 (which exceeded 5), but this was inconsistent with the microstructural observations. Comparing the linear fitting of calculated flow stress data with the estimated flow stress yielded a correlation coefficient (R2) of approximately 0.97. This observation demonstrates an effective relationship involving the calculated stress with the computed stress value for the composite material that was fabricated. Based on the processing map analysis, the instability regime occurs at 200270 °C/0.01–10 s−1. The stable domain established was at 280–340◦C/0.01–10 s−1 which is most suitable for achieving the best microstructural conditions for enhanced service performance.

Mathieu–Hill Equation Stability Analysis for Trapped Ions: Anharmonic Corrections for Nonlinear Electrodynamic Traps

The stability properties of the Hill equation are discussed, especially those of the Mathieu equation that characterize ion motion in electrodynamic traps. The solutions of the Mathieu-Hill equation for a trapped ion are characterized by employing the Floquet theory and Hill’s method solution, which yields an infinite system of linear and homogeneous equations whose coefficients are recursively determined. Stability is discussed for parameters a and q that are real. Characteristic curves are introduced naturally by the Sturm–Liouville problem for the well-known even and odd Mathieu equations cem(z,q) and sem(z,q). In the case of a Paul trap, the stable solution corresponds to a superposition of harmonic motions. The maximum amplitude of stable oscillations for ideal conditions (taken into consideration) is derived. We illustrate the stability diagram for a combined (Paul and Penning) trap and represent the frontiers of the stability domains for both axial and radial motion, where the former is described by the canonical Mathieu equation. Anharmonic corrections for nonlinear Paul traps are discussed within the frame of perturbation theory, while the frontiers of the modified stability domains are determined as a function of the chosen perturbation parameter and we demonstrate they are shifted towards negative values of the a parameter. The applications of the results include but are not restricted to 2D and 3D ion traps used for different applications such as mass spectrometry (including nanoparticles), high resolution atomic spectroscopy and quantum engineering applications, among which we mention optical atomic clocks and quantum frequency metrology.

Design of a water-soluble transmembrane receptor kinase with intact molecular function by QTY code

Membrane proteins are critical to biological processes and central to life sciences and modern medicine. However, membrane proteins are notoriously challenging to study, mainly owing to difficulties dictated by their highly hydrophobic nature. Previously, we reported QTY code, which is a simple method for designing water-soluble membrane proteins. Here, we apply QTY code to a transmembrane receptor, histidine kinase CpxA, to render it completely water-soluble. The designed CpxAQTY exhibits expected biophysical properties and highly preserved native molecular function, including the activities of (i) autokinase, (ii) phosphotransferase, (iii) phosphatase, and (iv) signaling receptor, involving a water-solubilized transmembrane domain. We probe the principles underlying the balance of structural stability and activity in the water-solubilized transmembrane domain. Computational approaches suggest that an extensive and dynamic hydrogen-bond network introduced by QTY code and its flexibility may play an important role. Our successful functional preservation further substantiates the robustness and comprehensiveness of QTY code.

Quasi-"In Situ" Analysis of the Reactive Liquid-Solid Interface during Magnesium Corrosion Using Cryo-Atom Probe Tomography.

The early stages of corrosion occurring at liquid-solid interfaces control the evolution of the material's degradation process, yet due to their transient state, their analysis remains a formidable challenge. Here corrosion tests are performed on a MgCa alloy, a candidate material for biodegradable implants using pure water as a model system. The corrosion reaction is suspended by plunge freezing into liquid nitrogen. The evolution of the early-stage corrosion process on the nanoscale by correlating cryo-atom probe tomography (APT) with transmission-electron microscopy (TEM) and spectroscopy, is studied. The outward growth of Mg hydroxide Mg(OH)2 and the inward growth of an intermediate corrosion layer consisting of hydrloxides of different compositions, mostly monohydroxide Mg(OH) instead of the expected MgO layer, are observed. In addition, Ca partitions to these newly formed hydroxides and oxides. Density-functional theory calculations suggest a domain of stability for this previously experimental unreported Mg(OH) phase. This new approach and these new findings advance the understanding of the early stages of magnesium corrosion, and in general reactions and processes at liquid-solid interfaces, which can further facilitate the development of corrosion-resistant materials or better control of the biodegradation rate of future implants.

Complexity analysis of technology spillover supply chain with dual business objectives

ABSTRACT Based on the existence of technology spillover effect of manufacturers, considering the manufacturer's commercial goals of profit and market share, a dynamic price game model of technology spillover supply chain with dual commercial goals is established. Based on game theory and nonlinear dynamics theory, the equilibrium point and local stability of the system are analyzed. In addition, the effects of price adjustment rate, balance coefficient of business objectives, and technology spillover on model complexity, the change of manufacturer price and profit were analyzed through numerical simulation. The results show that the price adjustment rate, the balance coefficient of business objectives, and the technology spillover have an impact on the stability and complexity of the manufacturer's price competition model. Rationally controlling the price adjustment rate, and enhancing technological spillovers are beneficial to the healthy development of manufacturers and the healthy competition among manufacturers, maintaining the stability of product market prices, and effectively avoiding market chaos. Moreover, when considering market share, manufacturers can expand the system stability domain.

Stability analysis of hydropower unit operation conditions considering hydro-turbine nonlinearity

Abstract This paper aims to study the law that the stability of hydropower systems changes with the system operating point and clarify the impact of hydro-turbine nonlinearity and hydraulic nonlinearity on the system stability. Firstly, the piecewise linearized model of the hydro-turbine regulation system (HTRS) at various operating points is established. Then, the HTRS stability domain is calculated and analyzed under various working heads and guide vane openings, and the impact of head variation on system stability is researched from the perspectives of discharge and power. Finally, the stability of various operating conditions under ideal hydro-turbine conditions and rated hydraulic parameter conditions are and compared to clarify the role of the water system and turbine nonlinearity on the stability. The results show that hydro-turbine nonlinearity helps to improve the system stability of the overall operating conditions, but the stability of the HTRS is relatively weak during high-load and low-head operations. Moreover, the hydro-turbine nonlinearity plays a dominant role in the process of stability changing with the operating head. This paper provides a comprehensive analysis of the system stability at different operating points, which can help guide the control optimization of hydropower systems.

Reliability and Validity of the Turkish Version of the Comprehensive Lower Limb Amputee Socket Survey

Purpose: The aim of this study was to translate the Comprehensive Lower Limb Amputee Socket Survey (CLASS) into Turkish and examine its reliability and validity in lower limb amputees. Material and Methods: This cross-sectional study included 97 lower limb amputees. Cronbach's alpha coefficient was used to evaluate internal consistency, and intraclass correlation coefficient was used to evaluate test-retest reliability. The retest of the CLASS was applied one week later. The satisfaction with the prosthesis subscale of the Trinity Amputation and Prosthesis Experience Scale (TAPES) was used to assess convergent validity. Results: The mean age of the participants was 46.78±15.04 years and 71.1 % were male. Internal consistency was found to be high for all domains of the Turkish CLASS (Cronbach's alpha ranged from 0.81 to 0.90). Test-retest reliability was found to be high (intraclass correlation coefficient ranged from 0.82-0.95). A significant relationship was found between all domains of the CLASS and TAPES prosthesis satisfaction subscale (r=0.553 for stability domain, r=0.509 for suspension domain, r=0.482 for comfort domain, r= 0.444 for appearance domain, p

Axion domain walls, small instantons, and non-invertible symmetry breaking

Non-invertible global symmetry often predicts degeneracy in axion potentials and carries important information about the global form of the gauge group. When these symmetries are spontaneously broken they can lead to the formation of stable axion domain wall networks which support topological degrees of freedom on their worldvolume. Such non-invertible symmetries can be broken by embedding into appropriate larger UV gauge groups where small instanton contributions lift the vacuum degeneracy, and provide a possible solution to the domain wall problem. We explain these ideas in simple illustrative examples and then apply them to the Standard Model, whose gauge algebra and matter content are consistent with several possible global structures. Each possible global structure leads to different selection rules on the axion couplings, and various UV completions of the Standard Model lead to more specific relations. As a proof of principle, we also present an example of a UV embedding of the Standard Model which can solve the axion domain wall problem. The formation and annihilation of the long-lived axion domain walls can lead to observables, such as gravitational wave signals. Observing such signals, in combination with the axion coupling measurements, can provide valuable insight into the global structure of the Standard Model, as well as its UV completion.

Variation in structural motifs within SARS-related coronavirus spike proteins.

SARS-CoV-2 is the third known coronavirus (CoV) that has crossed the animal-human barrier in the last two decades. However, little structural information exists related to the close genetic species within the SARS-related coronaviruses. Here, we present three novel SARS-related CoV spike protein structures solved by single particle cryo-electron microscopy analysis derived from bat (bat SL-CoV WIV1) and civet (cCoV-SZ3, cCoV-007) hosts. We report complex glycan trees that decorate the glycoproteins and density for water molecules which facilitated modeling of the water molecule coordination networks within structurally important regions. We note structural conservation of the fatty acid binding pocket and presence of a linoleic acid molecule which are associated with stabilization of the receptor binding domains in the "down" conformation. Additionally, the N-terminal biliverdin binding pocket is occupied by a density in all the structures. Finally, we analyzed structural differences in a loop of the receptor binding motif between coronaviruses known to infect humans and the animal coronaviruses described in this study, which regulate binding to the human angiotensin converting enzyme 2 receptor. This study offers a structural framework to evaluate the close relatives of SARS-CoV-2, the ability to inform pandemic prevention, and aid in the development of pan-neutralizing treatments.

Domain wall magnetic tunnel junction-based artificial synapses and neurons for all-spin neuromorphic hardware

We report a breakthrough in the hardware implementation of energy-efficient all-spin synapse and neuron devices for highly scalable integrated neuromorphic circuits. Our work demonstrates the successful execution of all-spin synapse and activation function generator using domain wall-magnetic tunnel junctions. By harnessing the synergistic effects of spin-orbit torque and interfacial Dzyaloshinskii-Moriya interaction in selectively etched spin-orbit coupling layers, we achieve a programmable multi-state synaptic device with high reliability. Our first-principles calculations confirm that the reduced atomic distance between 5d and 3d atoms enhances Dzyaloshinskii-Moriya interaction, leading to stable domain wall pinning. Our experimental results, supported by visualizing energy landscapes and theoretical simulations, validate the proposed mechanism. Furthermore, we demonstrate a spin-neuron with a sigmoidal activation function, enabling high operation frequency up to 20 MHz and low energy consumption of 508 fJ/operation. A neuron circuit design with a compact sigmoidal cell area and low power consumption is also presented, along with corroborated experimental implementation. Our findings highlight the great potential of domain wall-magnetic tunnel junctions in the development of all-spin neuromorphic computing hardware, offering exciting possibilities for energy-efficient and scalable neural network architectures.

MILD combustion stabilization issues through the analysis of hysteresis behaviors: The case of new energy carriers

MILD combustion processes are renewed to reveal a strong resilience to extinction phenomena and/or instabilities, whereas the oxidation process is stabilized trough ignition phenomena. Under MILD conditions, igni-diffusive and/or perfectly mixed kernels, forming during the mixing process between hot products and fresh reactants, are so much diluted and pre-heated to escape classical feed-back flammable flames stabilization mechanisms, while ignition and extinction events merge in a unique condition through “anhysteretic” behaviors. So far, considering methane as reference fuel, it has been largely demonstrated the mentioned “anhysteretic” condition is very conservative and defines a sub-domain of MILD combustion processes, following Cavaliere and de Joannon's definition. Furthermore, the coincidence of ignition and extinction phenomena can occur also preserving hysteresis phenomena. In turns, this condition strongly enlarges the stabilization domain of MILD combustion processes, starting from the upper branch of the hysteresis behaviors to the real extinction, with characteristic unstable loci to consider as further/last opportunity to promote stable operative conditions through the formation of local thermo-kinetic conditions in the combustion chamber during hot products/fresh reactants mixing process (injection configuration/burner design), or by forced ignition events. The hysteresis behaviors of renewable/alternative fuels, relevant within the decarbonization policies of several energy sectors, are thoroughly discussed under MILD conditions through numerical studies in model reactors in order to shed light on common and/or different features, and outline practical rules towards the definition of stable MILD combustion domains. Results show that, as MILD combustion is a chemical kinetics-driven processes, stability issues have to be discussed in relation to fuel nature, albeit with common behavior can be derived. The coincidence between extinction/ignition phenomena is reached for extremely diluted conditions, already ascribable to MILD combustion conditions, thus defining a small sub-domain of the process. This condition can be reached through “hysteretic” or “anhysteretic” behaviors.

Enhancement of phase transition temperature through hydrogen bond modification in molecular ferroelectrics

Molecular ferroelectrics are attracting great interest due to their light weight, mechanical flexibility, low cost, ease of processing and environmental friendliness. These advantages make molecular ferroelectrics viable alternatives or supplements to inorganic ceramics and polymer ferroelectrics. It is expected that molecular ferroelectrics with good performance can be fabricated, which in turns calls for effective chemical design strategies in crystal engineering. To achieve so, we propose a hydrogen bond modification method by introducing the hydroxyl group, and successfully boost the phase transition temperature (Tc) by at least 336 K. As a result, the molecular ferroelectric 1-hydroxy-3-adamantanammonium tetrafluoroborate [(HaaOH)BF4] can maintain ferroelectricity until 528 K, a Tc value much larger than that of BTO (390 K). Meanwhile, micro-domain patterns, in stable state for 2 years, can be directly written on the film of (HaaOH)BF4. In this respect, hydrogen bond modification is a feasible and effective strategy for designing molecular ferroelectrics with high Tc and stable ferroelectric domains. Such an organic molecule with varied modification sites and the precise crystal engineering can provide an efficient route to enrich high-Tc ferroelectrics with various physical properties.

Percolation transition and bimodal density distribution in hydrogen fluoride.

Hydrogen-bond networks in associating fluids can be extremely robust and characterize the topological properties of the liquid phase, as in the case of water, over its whole domain of stability and beyond. Here, we report on molecular dynamics simulations of hydrogen fluoride (HF), one of the strongest hydrogen-bonding molecules. HF has more limited connectivity than water but can still create long, dynamic chains, setting it apart from most other small molecular liquids. Our simulation results provide robust evidence of a second-order percolation transition of HF's hydrogen bond network occurring below the critical point. This behavior is remarkable as it underlines the presence of two different cohesive mechanisms in liquid HF, one at low temperatures characterized by a spanning network of long, entangled hydrogen-bonded polymers, as opposed to short oligomers bound by the dispersion interaction above the percolation threshold. This second-order phase transition underlines the presence of marked structural heterogeneity in the fluid, which we found in the form of two liquid populations with distinct local densities.