Multi-step Transition Research Articles

Multiple Heterointerfaces and Heterostructure Engineering in MXene@Co-P-S Hybrids Promote High-Performance Sodium-Ion Half/Full Batteries.

In this paper, heterogeneous cobalt phosphosulfide (Co4S3/Co2P) nanocrystals anchoring on few-layered MXene nanosheets (MXene@Co4S3/Co2P) were prepared by in situ growth and the subsequent high-temperature phosphorization/sulfidation processes. Thanks to the synergistic effect and the abundant phase interfaces of Co4S3, Co2P, and MXene, the electron transfer and Na+ diffusion processes were greatly accelerated. Meanwhile, the high electrical conductivity of MXene nanosheets and the heterogeneous structure of Co4S3/Co2P effectively avoided the MXene restacking and the agglomeration of phosphosulfide particles, thus mitigating volumetric expansion during charging and discharging. The results show that the MXene@Co4S3/Co2P heterostructure presents good rate capability (251.08 mAh g-1 at 1 A g-1) and excellent cycling stability (198.69 mAh g-1 after 407 cycles at 5 A g-1). Finally, the storage mechanism of Na+ in the heterostructure and the multistep phase transition reaction were determined by ex situ X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS) analyses. This study provides a new perspective on the formation of metal phosphosulfide and MXene hybrids with multiple heterointerfaces as well as demonstrates MXene@Co4S3/Co2P composites as the promising anode material in sodium-ion batteries.

Lithium storage behaviour of AgNbO3 perovskite: Understanding electrochemical activation and charge storage mechanisms

In this study, a model AgNbO3 perovskite is prepared via polyacrylamide synthesis technique, and the underlying unique Li+storage mechanism is studied. This structure is projected to provide low Li+ storage capacity due to all occupied crystallographic sites. It delivered a specific capacity of 17 mAh.g−1 at 0.1A.g−1 within the potential range of 1.2–3.0 V vs. Li+/Li. However, at lower potentials, the material undergoes activation for Li+ storage by a multistep structural transition that included in-situ Ag-exsolution from the A-site of the lattice and an electrochemically induced crystalline-to-amorphous transition. At low potential the materials delivers high specific capacity (226 mAh.g−1 at 0.1 A.g−1 in 0.01–3 V vs. Li+/Li potential range) due to the contribution of improved Nb-redox activity and nanoscale Ag-Li (de)alloying mechanisms that were comprehensively examined utilizing advanced characterization tools. In addition, good capacity retention of 72 mAh.g−1 at high current density of 2A.g−1 and an excellent cyclic stability with coulombic efficiencies above 99.9 % are obtained for 2500 cycles at 1 A.g−1 underlining the performance and the stability of AgNbO3. This study introduces an alternative approach for tailoring electrode material using an electrochemically driven in-situ activation process. It also serves as a paradigm for the use of exsolved materials as negative electrodes in fast-charging batteries, paving the way for a better understanding of charge storage mechanisms in perovskites.

Transition Propagation Graph Neural Networks for Temporal Networks.

Researchers of temporal networks (e.g., social networks and transaction networks) have been interested in mining dynamic patterns of nodes from their diverse interactions. Inspired by recently powerful graph mining methods like skip-gram models and graph neural networks (GNNs), existing approaches focus on generating temporal node embeddings sequentially with nodes' sequential interactions. However, the sequential modeling of previous approaches cannot handles the transition structure between nodes' neighbors with limited memorization capacity. In detail, an effective method for the transition structures is required to both model nodes' personalized patterns adaptively and capture node dynamics accordingly. In this article, we propose a method, namely t ransition p ropagation g raph n eural n etworks (TIP-GNN), to tackle the challenges of encoding nodes' transition structures. The proposed TIP-GNN focuses on the bilevel graph structure in temporal networks: besides the explicit interaction graph, a node's sequential interactions can also be constructed as a transition graph. Based on the bilevel graph, TIP-GNN further encodes transition structures by multistep transition propagation and distills information from neighborhoods by a bilevel graph convolution. Experimental results over various temporal networks reveal the efficiency of our TIP-GNN, with at most 7.2% improvements of accuracy on temporal link prediction. Extensive ablation studies further verify the effectiveness and limitations of the transition propagation module. Our code is available at https://github.com/doujiang-zheng/TIP-GNN.

Phase transitions and gravitational waves in a model of ℤ3 scalar dark matter

Theories with more than one scalar field often exhibit phase transitions producing potentially detectable gravitational wave (GW) signal. In this work we study the semi-annihilating ℤ3 dark matter model, whose dark sector comprises an inert doublet and a complex singlet, and assess its prospects in future GW detectors. Without imposing limits from requirement of providing a viable dark matter candidate, i.e. taking into account only other experimental and theoretical constraints, we find that the first order phase transition in this model can be strong enough to lead to a detectable signal. However, direct detection and the dark matter thermal relic density constraint calculated with the state-of-the-art method including the impact of early kinetic decoupling, very strongly limit the parameter space of the model explaining all of dark matter and providing observable GW peak amplitude. Extending the analysis to underabundant dark matter thus reveals region with detectable GWs from a single-step or multi-step phase transition.

Unraveling potential phase transition mechanism of NBT-based systems: From an interesting view to survey ferroelectric loops

As for assessing strain performances of Na0.5Bi0.5TiO3-based systems, the driving field level is a critical parameter. Currently, both current density and strain rate evaluation methods have been utilized to characterize the driving field. However, we find that some discrepancies indeed exist between these two evaluation methods, especially for the highly ergodic condition. By means of the typical ferroelectric theory, the initial analysis for discrepant current density and strain rate loops reveals that the relaxor-ferroelectric transition is likely to be a multi-step transition process. Dynamic dielectric loss/permittivity evolution further confirms the speculation and suggests that partial transition steps may be consisted of successive transition events. Ferroelectric and dielectric loops not only provide a fantastic view to unravel the multi-step relaxor-ferroelectric transition process, but also guides to regulate the strain appraisal system.

Minimal Inert Doublet benchmark for dark matter and the baryon asymmetry

In this article we discuss a minimal extension of the Inert Doublet Model (IDM) with an effective CP-violating D=6 operator, involving the inert Higgs and weak gauge bosons, that can lift it to a fully realistic setup for creating the baryon asymmetry of the Universe (BAU). Avoiding the need to stick to an explicit completion, we investigate the potential of such an operator to give rise to the measured BAU during a multi-step electroweak phase transition (EWPhT) while sustaining a viable DM candidate in agreement with the measured relic abundance. We find that the explored extension of the IDM can account quantitatively for both DM and for baryogenesis and has quite unique virtues, as we will argue. It can thus serve as a benchmark for a minimal realistic extension of the SM that solves some of its shortcomings and could represent the low energy limit of a larger set of viable completions.After discussing the impact of a further class of operators that open the possibility for a larger mass splitting (enhancing the EWPhT) while generating the full relic abundance also for heavy inert-Higgs DM, we ultimately provide a quantitative evaluation of the induced lepton electric dipole moments in the minimal benchmark for the BAU. These arise here at the two-loop level and are therefore less problematic compared to the ones that emerge when inducing CP violation via an operator involving the SM-like Higgs.

An interactive feature selection method based on multi-step state transition algorithm for high-dimensional data

Feature selection (FS) has been extensively employed in classification tasks to reduce data dimensionality and enhance prediction performance effectively. Recently, hybrid filter-wrapper methods have exhibited promising results in FS problems by leveraging both advantages. However, the inadequate integration of the filter method into the wrapper method leads to the hybrid algorithms exhibiting poor efficiency in classification as datasets grow in complexity. In this paper, an interactive feature selection framework based on state transition algorithm (STA) is proposed to address high-dimensional FS problems. In this framework, prior knowledge of the features is formed via the mutual information-based filter method. The STA is a powerful search engine that traverses the feature space in the wrapper stage. Moreover, an external trainer with prior knowledge will guide the exploration direction of STA in a simple but efficient way to accelerate the search process. And a self-adaptive mechanism is proposed to adjust the prior knowledge during the search process. Specifically, the external trainer establishes the interactive loop, while the self-adaptive mechanism aims to feed feature information back to the loop. In addition, the search process is prevented from being trapped in local optima by employing a multi-step STA, which allows for continuous transformations of the solution in probability. Finally, the proposed FS method is applied to various public classification datasets. The experimental results demonstrate that the proposed method is a highly competitive FS method, outperforming several state-of-the-art algorithms in generating an optimal subset of features.

Efficiency of charge transfer in changing the dissociation dynamics of OD+ transients formed after the photo-fragmentation of D2O.

We present an investigation of the relaxation dynamics of deuterated water molecules after direct photo-double ionization at 61eV. We focus on the very rare D+ + O+ + D reaction channel in which the sequential fragmentation mechanisms were found to dominate the dynamics. Aided by theory, the state-selective formation and breakup of the transient OD+(a1Δ, b1Σ+) is traced, and the most likely dissociation path-OD+: a1Δ or b1Σ+ → A 3Π → X 3Σ- → B 3Σ--involving a combination of spin-orbit and non-adiabatic charge transfer transitions is determined. The multi-step transition probability of this complex transition sequence in the intermediate fragment ion is directly evaluated as a function of the energy of the transient OD+ above its lowest dissociation limit from the measured ratio of the D+ + O+ + D and competing D+ + D+ + O sequential fragmentation channels, which are measured simultaneously. Our coupled-channel time-dependent dynamics calculations reproduce the general trends of these multi-state relative transition rates toward the three-body fragmentation channels.

Preliminary characterization and thermal evaluation of a direct contact cascaded immiscible inorganic salt/high-density polyethylene as moderate temperature heat storage material

The present work assesses the direct contact cascaded immiscible phase change material (PCM) for solar heat storage systems (SHSS) in water heating applications. The direct contact cascaded immiscible PCM uses ternary salt mixture (TSM) and high-density polyethylene (HDPE). Improvement on phase behavior and thermal properties are obtained for the direct contact cascaded immiscible TSM/HDPE. The plasticity effect of HDPE leads to a stable phase transition of the mixture with the lowest supercooling degree by 0.9 °C. The initial thermal decomposition temperature for TSM and HDPE is above 400 °C, which is suitable for moderate temperature operation of SHSS. The immiscibility between TSM and HDPE leads to a multistep phase transition between 110.2 and 139.6 °C. The phase behavior during the liquid-solid transition demonstrates the lowest temperature gradient of 13.9 °C, implying a steady phase transition. It allows the stored heat can be released effectively without causing significant volume expansion of the TSM. Moreover, the enthalpy of fusion for TSM/HDPE is increased, making it favorable as solar thermal energy for water heating applications in SHSS.

Electroweak baryogenesis between broken phases in multi-step phase transition

Possibility of electroweak baryogenesis (EWBG) via multi-step phase transition (PT) is considered. We investigate the EWBG between SU(2) broken phases in the second step PT of the two-step PT. The produced baryon number asymmetry is evaluated using a prototypical model with a SU(2) charged CP-odd scalar field. We show that the second step PTs where the sphaleron rate is possible to be un-suppressed before the PTs, which can reproduce the sufficient baryon number asymmetry. Our studies can be adapted to models with extra SU(2) scalar fields. We discuss specific models suitable for our scenario.

Suppression of multistep phase transitions of O3-type cathode for sodium-ion batteries

O3-type layered oxide cathodes have been widely investigated due to their high reversible capacities and sufficient Na+ reservoirs. However, such materials usually suffer from complex multistep phase transitions along with drastic volume changes, leading to the unsatisfied cycle performance. Herein, we report a Mg/Ti co-doped O3-type NaNi0.5Mn0.5O2, which can effectively suppress the complex multistep phase transition and realize a solid-solution reaction within a wide voltage range. It is confirmed that, the Mg/Ti co-doping is beneficial to enhance the structural stability and integrity by absorbing micro-strain and distortions. Thus, the as obtained sample delivers an outstanding cyclic performance (82.3% after 200 cycles at 1 C) in the voltage range of 2.0–4.0 V, and a high discharge capacity of 86.6 mAh/g after 100 cycles within the wide voltage range (2.0–4.5 V), which outperform the existing literatures. This co-doping strategy offers new insights into high performance O3-type cathode for sodium ion batteries.

Theoretical approach to the one-step versus two-step spin transitions in Hofmann-like FeII SCO metal-organic frameworks

Guest molecules in the 3D Hofmann-type FeII spin-crossover (SCO) metal-organic frameworks modulate the magnetic properties of the host, modifying the spin state, transition temperature, width of the hysteresis loop and are responsible for the occurrence of a single-step or multistep spin transition. In this work we explore the guest-dependent SCO properties of the Hofmann-like FeII SCO clathrates with formula {Fe(bpb)[Pt(CN)4]}⋅2G. We use a computational strategy based on DFT periodic calculations on the whole system, CASSCF/NEVPT2 calculations on single metal fragments and plots of the reduced density gradients to identify and quantify the dominant effects governing the occurrence of one-step or two-step spin transitions in these systems. Our results inform about the strength of the ligand field around Fe sites, the relative stability of the different spin states, the amplitude and nature of the host-guest and guest-guest interactions, and the role of the vibronic effects on the SCO properties of Hofmann-type FeII clathrates.

Heterogeneous Nucleation in Finite-Size Adaptive Dynamical Networks

Phase transitions in equilibrium and nonequilibrium systems play a major role in the natural sciences. In dynamical networks, phase transitions organize qualitative changes in the collective behavior of coupled dynamical units. Adaptive dynamical networks feature a connectivity structure that changes over time, coevolving with the nodes' dynamical state. In this Letter, we show the emergence of two distinct first-order nonequilibrium phase transitions in a finite-size adaptive network of heterogeneous phase oscillators. Depending on the nature of defects in the internal frequency distribution, we observe either an abrupt single-step transition to full synchronization or a more gradual multistep transition. This observation has a striking resemblance to heterogeneous nucleation. We develop a mean-field approach to study the interplay between adaptivity and nodal heterogeneity and describe the dynamics of multicluster states and their role in determining the character of the phase transition. Our work provides a theoretical framework for studying the interplay between adaptivity and nodal heterogeneity.

Thermal stress influence on the long-term performance of fast-charging paraffin-based thermal storage

• Fast-charging cycle leads to a higher thermal stress and hysteresis losses. • 10,000 cycle assessment reveals the deterioration on thermal performances. • The storage efficiency decreases 12.7% after 10,000 fast charging cycles. • Isothermal phase transition provides a better power rate and duration. The present study evaluates the impact of charging speeds on the long-term performance of paraffin-based thermal energy storage (TES) up to 10,000 actual thermal cycles. Paraffin and form-stable phase change material (FSPCM) is used as the reference materials. The FSPCM is made of paraffin (80 wt%) and high-density polyethylene (HDPE, 20 wt%). The thermal cycling treatment is applied to the samples using slow (1 °C/min), normal (5 °C/min) and fast-charging cycles (10 °C/min). Performance assessment is conducted using an active thermal storage model. According to the assessment, thermal stress and hysteresis effect occur severely after 10,000 fast-charging cycles. It disrupts the heat transfer process, reducing the power and charging rate. Scanning electron microscope (SEM) shows the void formation for paraffin which correspond to a lower efficiency (62.5%) than FSPCM (66.6%). The presence of HDPE reduces the impact of the fast-charging effect on paraffin. The SEM micrograph for FSPCM indicates that a chemi-crystallization leads to phase-separation between paraffin and HDPE. It helps to maintain the charging and discharging duration after 10,000 fast-charging cycles. Furthermore, the decrement of melting enthalpy of FSPCM (5.5%) is much lower than paraffin (12.7%). Hence, FPSCM maintains the storage capacity after 10,000 fast-charging cycles at a sufficient level. The multi-step transition and power curve during the charging/discharging cycle are discussed in detail within the article. Further improvement can be taken to minimize the performance degradation of fast-charging paraffin-based TES by compositing paraffin to withstand thermal stress or modifying the system operation after a certain fast-charging cycle.

Simultaneous Realization of Good Piezoelectric and Strain Temperature Stability via the Synergic Contribution from Multilayer Design and Rare Earth Doping

AbstractNiobate‐based lead‐free piezoceramics have attracted wide attention due to their excellent piezoelectric properties. Although the temperature sensitivity of piezoelectricity or strain in one sample has been solved to a certain extent, how to simultaneously improve the temperature stability of both in one sample is still an issue. Herein, by constructing multilayer composite ceramics and doping Ho element, both improved piezoelectric and strain temperature stability (the variations are below 3% under 30–100 °C) are achieved, showing great property advantage compared with previous reports. Different from the compositionally graded composite ceramic design, the Ho doping can not only increase orthorhombic‐tetragonal phase transition temperature (TO‐T) and then create the condition for the formation of successive phase transition, but also stabilize the oriented domain state. Therefore, the excellent temperature stability of both piezoelectricity and strain can be attributed to the multistep phase transition induced by the multilayer design, the fine regulation of TO‐T interval by the optimization of lamination combination, and the stabilized polarization induced by Ho doping. The new strategy for solving both piezoelectric and strain temperature sensitivity can further promote the commercial application of potassium sodium niobate‐based lead‐free piezoelectric ceramics.

Dual-Band Dual-Polarization Horn Antenna Array Based on Orthomode Transducers With High Isolation for Satellite Communication

A dual-band dual-polarization horn antenna array is proposed for Ku-band satellite communication (SATCOM) in this article. A miniaturized orthomode transducer (OMT) using the mutually perpendicular multistep waveguide transition and coupled transition to transmit TE10 mode and TE01 mode, respectively, is integrated into the radiation element. The high isolation characteristic of horizontal polarization in the transmitting band (Tx) and vertical polarization in the receiving band (Rx) desired for SATCOM is realized. Moreover, the sinusoid-tapered horn antenna and the radiating cross-shaped cavity are employed as the shared-aperture element to radiate orthogonal waves simultaneously, having the potential of wide bandwidth, low sidelobes, and high radiation efficiency. With the facility of the 3-D metal printing technology, a horn antenna array consisting of the proposed 4 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times4$ </tex-math></inline-formula> radiation elements and feeding networks is demonstrated and fabricated. The gains up to 26.48 and 26.51 dBi with radiation efficiencies of around 94% and 90% are obtained at Tx- and Rx-bands, respectively. Benefitted from the advantages of compact size, high gain, and high efficiency, the proposed horn antenna array is suitable to tackle the high-throughput demand in Ku-band SATCOM systems.

The electrochemical properties of bismuth-antimony-tin alloy anodes for magnesium ion batteries

Magnesium ion batteries (MIBs) have attracted wide attention due to their high theoretical specific capacity and abundance of Mg resources. However, the kinetics of magnesiation/demagnesiation is slow due to the formation of passive film in the interface between electrolyte and anode if pure Mg is directly employed as anode material. The development of alloy-type anodes is one of the promising strategies to address this issue. In this work, the electrochemical properties of bismuth-antimony-tin (Bi–Sb–Sn) alloy anodes for MIBs have been studied. Bi–Sb–Sn alloys with varied compositions have been synthesized using the mechanical alloying method. The Mg storage mechanism of Bi–Sb–Sn anodes has been clarified and the demagnesiation activity of Mg3Sb2 is improved by Sn substitution for Mg to form SbSn phase. Additionally, the electrochemical behavior of Bi–Sb–Sn anodes shows the formed multi-phase structure and the multi-step phase transition process are beneficial to the transport kinetics of Mg ions and the cycling stability and rate performance of anodes. Specifically, the Bi10Sb10Sn80 anode can deliver high capacity as 417 mAh g−1 at a current density of 500 mA g−1 and 517 mAh g−1 at a current density of 20 mA g−1, respectively.

Hierarchical Symbol Transition Entropy: A Novel Feature Extractor for Machinery Health Monitoring

This article develops a novel collaborative health monitoring framework based on hierarchical symbol transition entropy (HSTE) and 2-D-extreme learning machine (2-D-ELM) without fusion. In the proposed framework, a novel metric called symbol transition entropy (STE) is first presented to evaluate the dynamical complexity of time series through multistep transition and the joint probability distribution of the symbol state and its transition state. Compared with the existing entropy algorithms, STE has better robustness and captures more detailed dynamical changes. Subsequently, a new feature representation method called HSTE is proposed by combining STE with the hierarchical analysis. The two-order tensor features can be constructed for multichannel data by stacking HSTE values extracted from each single-channel data. Finally, 2-D-ELM is incorporated to identify the extracted two-order tensor features without vectorization. The feasibility of the proposed schemes is verified through simulation and experimental studies, and the final results confirm that the developed schemes have better performance than the existing entropy-based collaborative fault diagnosis methods.

Possibility of a multi-step electroweak phase transition in the two-Higgs doublet models

Abstract We discuss whether a multi-step electroweak phase transition (EWPT) occurs in two-Higgs doublet models (2HDMs). The EWPT is related to interesting phenomena such as baryogenesis and the ensuing gravitational wave. We examine parameter regions in CP-conserving 2HDMs and find certain areas where multi-step EWPTs occur. The parameter search shows the multi-step EWPT prefers the scalar potential with the approximate Z2 symmetry and a mass hierarchy between the neutral CP-odd and CP-even extra scalar bosons mA &amp;lt; mH. By contrast, the multi-step EWPT whose first step is strongly first order favors a mass hierarchy mA &amp;gt; mH. In addition, we compute the Higgs trilinear coupling in the parameter region where multi-step EWPTs occur, which can be observed at future colliders. We also discuss a multi-peaked gravitational wave from a multi-step EWPT. Subject index B53, B59

Rational design of hairpin RNA excited states reveals multi-step transitions

RNA excited states represent a class of high-energy-level and thus low-populated conformational states of RNAs that are sequestered within the free energy landscape until being activated by cellular cues. In recent years, there has been growing interest in structural and functional studies of these transient states, but the rational design of excited states remains unexplored. Here we developed a method to design small hairpin RNAs with predefined excited states that exchange with ground states through base pair reshuffling, and verified these transient states by combining NMR relaxation dispersion technique and imino chemical shift prediction. Using van’t Hoff analysis and accelerated molecular dynamics simulations, a mechanism of multi-step sequential transition has been revealed. The efforts made in this study will expand the scope of RNA rational design, and also contribute towards improved predictions of RNA secondary structure.