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The bulk photovoltaic effect (BPVE) offers an interesting approach to generate a steady photocurrent in a single-phase material under homogeneous illumination, and it has been extensively investigated in ferroelectrics exhibiting spontaneous polarization that breaks inversion symmetry. Flexoelectricity breaks inversion symmetry via a strain gradient in the otherwise nonpolar materials, enabling manipulation of ferroelectric order without an electric field. Combining these two effects, we demonstrate active mechanical control of BPVE in suspended 2-dimensional CuInP2S6(CIPS) that is ferroelectric yet sensitive to electric field, which enables practical photodetection with an order of magnitude enhancement in performance. The suspended CIPS exhibits a 20-fold increase in photocurrent, which can be continuously modulated by either mechanical force or light polarization. The flexoelectrically engineered photodetection device, activated by air pressure and without any optimization, possesses a responsivity of 2.45 × 10–2A/W and a detectivity of 1.73 × 1011jones, which are superior to those of ferroelectric-based photodetection and comparable to those of the commercial Si photodiode.

Balancing the strength, ductility and Elastic modulus of β-Ti alloys is still a great challenge for medical implantation, extremely limiting its further applications. Herein, we prepared a fine-grain β-type Ti–24Nb–4Zr-2.5Mn alloy with high performance by adding CaB6deoxidizer via mechanical alloying and spark plasma sintering. The effects of CaB6addition on the microstructure and mechanical properties were systematically investigated, and the results show that adding a trace amount of CaB6will form in-situ nano-sized CaTiO3particles and micro-sized (Ti,Nb)B2solid solution whiskers, which can significantly refine the grain size and inhibit the grain boundary movement and dislocation motion, thus improving the comprehensive mechanical properties of Ti–24Nb–4Zr-2.5Mn alloys. With a trace addition of 0.1 wt% CaB6, the Ti–24Nb–4Zr-2.5Mn alloy exhibits an excellent combination of high strength of ∼971 MPa, good ductility of ∼17.8% and low elastic modulus of ∼79.1 GPa. This work may provide a new methodology to prepare high-performance biomedical Ti alloys.

This study investigates the effects of laser shock peening (LSP) on the microstructural evolution and surface hardening of MAR-M247 nickel-based alloy. Experimental and numerical simulation methods are employed to analyze the influence of pulse power density and spot size. The results demonstrate that LSP significantly enhances surface hardness and yield strength. As the pulse power density increases, the magnitude and depth of plastic deformation increase. Higher power densities can implant deeper and greater compressive residual stress (CRS), but the corresponding tensile residual stress (TRS) also increases. Reducing both power density and spot size decreases the amount of plastic deformation of the surface. However, decreasing the spot size results in a decrease in the depth of the CRS. On the other side, based on the analysis of the microstructure, during the process of LSP, many dislocations accumulate in the γ matrix and evolve into subgrain boundaries, resulting in grain refinement. Additionally, LSP induces the precipitation of nanoscale carbides. This study tries to establish the influence law and action mechanism between LSP process-material property-microscopic evolution, which provides theoretical and applied data support for engineering applications.

• S-N curves of TC17 titanium alloy electron beam welded joint undergo a transition from a single linear decline at RT to a bilinear decline at 400 ℃. • By utilizing the Chapetti model curve to modify the K–T diagram, the lower threshold stress amplitude is introduced, enabling the determination of a safe size for welded pores at 400 ℃, which is calculated to be 11.3 μm. • The Gumbel probability distribution function is employed to assess the maximum size of welded pores. • Based on dislocation interactions, the formation mechanism of the FGA consisting of discontinuous nanograins with high-density dislocations is elucidated. Welded structures in aero-engines commonly operate in high-temperature environments, making them susceptible to reduced fatigue life and premature failure due to welding defects within the structure. Thus, the gigacycle fatigue behaviors of titanium alloy welded joints at both room temperature (RT) and 400 °C were investigated, aiming to uncover the mechanism behind the formation of fine granular area (FGA) surrounding welded pores. The research findings demonstrate that the S-N curves of TC17 titanium alloy electron beam welded joint undergo a transition from a single linear decline at RT to a bilinear decline at 400 °C. However, the fatigue failure mode remains unaffected by temperatures, and crack initiation is attributed to welded pores. By utilizing the Chapetti model curve to modify the Kitagawa–Takahashi (K–T) diagram, the lower threshold stress amplitude is introduced, enabling the determination of a safe size for welded pores at 400 °C, which is calculated to be 11.3 µm. Additionally, the Gumbel probability distribution function is employed to assess the maximum size of welded pores. Finally, based on dislocation interactions, the formation mechanism of the FGA consisting of discontinuous nanograins with high-density dislocations is elucidated. [Display omitted] [ABSTRACT FROM AUTHOR]

Dielectric capacitors are employed extensively due to their exceptional performance, including a rapid charge–discharge speed and superior power density. However, their practical implementation is hindered by constraints in energy-storage density (ESD), efficiency (ESE), and thermal stability. To achieve domain engineering and improved relaxor behavior in 0.67BiFeO3-0.33BaTiO3-based Pb-free ceramics, the concerns have been addressed here by employing a synergistic high-entropy strategy involving the design of the composition of Sr(Mg1/6Zn1/6Ta1/3Nb1/3)O3with B-site multielement coexistence and high configuration entropy. Remarkably, in (0.67-x)BiFeO3-0.33BaTiO3-xSr(Mg1/6Zn1/6Ta1/3Nb1/3)O3ceramics with x= 0.08, a good ESE (η) of 75% and a recoverable ESD (Wrec) of 2.4 J/cm3at 190 kV/cm were attained together with an ultrahigh hardness of ∼7.2 GPa. The high-entropy strategy, which is tailored by an increase in configuration entropy, can be attributed to the superior mechanical and ES properties. It also explains the enhanced random field and relaxation behavior, the structural coexistence of ferroelectric rhombohedral (R3c) and nonpolar pseudocubic (Pm-3m) symmetries, the decreased domain size, and evenly distributed polar nanoregions (PNRs). Moreover, improved thermal stability and outstanding frequency stability are also obtained. By boosting the configuration entropy, BiFeO3–BaTiO3materials dramatically improved their complete energy storage performance. This suggests that designing high-performance dielectrics with high entropy can be a convenient yet effective technique, leading to the development of advanced capacitors.

Purpose: The purpose of this paper is to determine the ultra-high cycle fatigue behavior and ultra-slow crack propagation behavior of selective laser melting (SLM) AlSi7Mg alloy under as-built conditions. Design/methodology/approach: Constant amplitude and two-step variable amplitude fatigue tests were carried out using ultrasonic fatigue equipment. The fracture surface of the failure specimen was quantitatively analyzed by scanning electron microscope (SEM). Findings: The results show that the competition of surface and interior crack initiation modes leads to a duplex S–N curve. Both manufacturing defects (such as the lack of fusion) and inclusions can act as initially fatal fatigue microcracks, and the fatigue sensitivity level decreases with the location, size and type of the maximum defects. Originality/value: The research results play a certain role in understanding the ultra-high cycle fatigue behavior of additive manufacturing aluminum alloys. It can provide reference for improving the process parameters of SLM technology.

High entropy alloys （HEAs） have excellent properties because they can form simple solid solution (SS) phases, including body-centered cubic (BCC) phase, face-centered cubic (FCC) phase, or FCC + BCC phase, so phase prediction is the first step in alloy design. In current research, machine learning (ML) approach had been widely used to guide the discovery and design of materials. The prediction of HEAs phase structure based on machine learning (ML) is a hot topic. In this work, five ML algorithms were utilized to predict HEAs for SS and amorphous (AM) phases based on 399 collected data sets, including 120 BCC alloys, 87 FCC alloys, 82 BCC + FCC alloys and 110 a.m. alloys. To enhance the model's accuracy, grid search and K-fold cross validation were used to optimize performance. Valence electron concentration (VEC) and ΔHmixexhibit high importance in prediction in compared to other parameters. The results show that the random forest can effectively distinguish BCC phase, FCC phase, mixed solid solution phase (FCC + BCC) and AM, with an accuracy is 0.87. After that, the CoCrFeNiAlx (x = 0, 0.5, 1) system alloys were characterized by XRD and SEM-EDS. The experimental results validated that the phase structure of CoCrFeNiAlx alloys changed from FCC to BCC + FCC and BCC with the increase of Al content, which is consistent with the ML prediction.

The event-triggered sliding mode control (ETSMC) for high-speed train (HST) is addressed under the energy-limited deception attacks (DA), where the multibody, transmission delay and network bandwidth of HST are considered in unity. Firstly, the error equation of HST with transmission delays is built with the time-varying running resistance. Then, the sliding mode surface (SMS) function is constructed, and the event-triggered mechanism is established to balance the transmission frequency and HST stability. Next, under the energy-limited DA, sufficient conditions are deduced and converted into linear matrix inequalities (LMIs). An ETSMC scheme is established to guarantee the reachability condition of SMS within a finite time. Finally, an example from Japan Shinkansen HST is conducted to verify the effectiveness of the proposed ETSMC.

Accelerating the redox conversion of lithium polysulfides (LiPSs) with electrocatalysts has been regarded as an effective avenue to surmount the shuttle effect and realize high-performance lithium–sulfur (Li–S) batteries. However, the complicated reaction process, especially the real-time evolution of sulfur-containing species and electrocatalysts under working conditions, has brought great difficulties in the explicit understanding of reaction mechanism of Li–S batteries, thereby severely hampering the design of highly efficient electrocatalysts. Therefore, a crucial prerequisite for correctly identifying the reaction mechanism is an in-depth analysis of the dynamic evolution of reaction intermediates and their structure-performance relationships. In this review, we comprehensively summarized the most recent progress in the dynamic behaviors of LiPSs and electrocatalysts of Li–S batteries under working conditions in conjunction with closely related in-situ/operandocharacterizations to recognize the realtime evolution of phase, composition, and atomic/electronic structure, thereby unraveling the corresponding catalytic mechanism. In addition, the major challenges and unexplored issues of catalytic conversion of LiPSs were summarized and discussed, aiming to provide perspectives into the development of highly efficient electrocatalysts in Li–S chemistry. Based on this review, we believe that reasonable regulation of reconstruction behaviors can achieve satisfactory electrocatalysts with high catalytic activity, accelerating the development of green energy.

Electrocardiogram (ECG) feature extraction is an important step in applying machine learning for biomedical processing tasks. In deep learning studies centered on ECG data, established methods mainly rely on labeled data to automatically extract signal features. However, obtaining high-quality labeled records from open-source datasets is challenging, whereas many unlabeled data remain underused. Unsupervised pre-training methods have shown significant efficacy in using unlabeled datasets. Therefore, using unsupervised pre-training paradigms for ECG feature extraction could improve overall performance. This article presents an unsupervised pre-training framework based on a masked autoencoder (MAE) for extracting ECG signal features. An encoder-decoder framework is proposed to recover artificially masked ECGs. During the reconstruction process, the framework learns features from masked samples. Benefiting from the utilization of large-scale datasets, the framework enables learning generalized features and has a high performance for a wide range of deep learning tasks. In particular, the framework achieves an accuracy of 95.6% on the MITDB dataset for the ECG arrhythmia classification task and 98.8% on the ECGIDDB dataset for the human identification task. Evaluation using multiple downstream tasks and comparisons with the state-of-the-art confirm the validity of our proposed approach.

Electrochromic materials change color or opacity when subjected to electrical stimuli, often through reversible chemical reactions or phase transitions. Their optical switch capabilities make them promising for applications like smart windows and glasses, thus garnering widespread attention in recent years. Van der Waals layered ferroelectric α-In2Se3, known for its rich polymorphs, is a promising candidate for exploring physical property modulation via phase transformations. However, the discovery of electrochromism in In2Se3has been impeded by similar optical constants among its polymorphs. Herein, we report the experimental observation of reversible electrochromism in α-In2Se3thin flakes accompanied by ferroelectric polarization switching. Microscopic structural characterizations reveal that the color change stems from a crystalline-to-amorphous phase transition. An improved Kramer-Kronig analysis was employed to quantify the change in optical constants of the flake. A disordered polarization switching model, inherent to the crystal symmetry of α-In2Se3, was proposed to explain the electrically driven amorphization. This work delivers distinct insight into the unique electrochromic behavior and unveils opportunities of relevant applications for the van der Waals layered ferroelectric.

In this paper, the distributed cooperative control of virtual coupling high-speed trains (HSTs) subject to full-state constraints, actuator limitations, dynamical uncertainties and environmental disturbances is investigated. Targeting at the full-state constraints in cooperative operation of HSTs, a distributed nonlinear state-dependent function (DNSDF) is first proposed to convert the state-constrained problem of the leader-following consensus control to the boundedness problem of DNSDF. Then, the distributed control law of each train is designed by combining the command filtering backstepping method and the adaptive neural network approximation technique. Meanwhile, combined with the DNSDF, a novel auxiliary dynamical system (ADS) is designed to compensate for the adverse effects of actuator input saturation, and thus ensure the closed-loop stability of the HSTs system when the state constraints and the input saturation are considered simultaneously. By utilizing the Lyapunov theory, the convergence of the proposed controller is analyzed. Finally, the feasibility and effectiveness of the proposed control scheme are verified by simulations. Note to Practitioners—This work was motivated by the problem of cooperative control for virtual coupling HSTs with different initial states, actuator input saturation, full-state constraints, etc. The proposed approach addresses the train position and speed constraints by applying DNSDF, which can ensure train coordinated operation with relative braking distance and further reduce the tracking interval between trains. Specifically, the upper bound of the train position constraint varies with the real-time position of the preceding train and the relative speed of the adjacent trains, rather than a constant value. More importantly, an ADS is designed based on the DNSDF, which guarantees the stability of the controller when the input saturation and state constraints exist simultaneously, and avoids the chattering phenomenon of the train control input. The simulation results show that the trains can operate cooperatively at any initial speed within the speed limitations. In future, we will focus on the cooperative control of HSTs with communication delay, and the energy saving optimization cooperative control of HSTs.

Heavy haul train manipulation is extremely challenging due to cyclic pneumatic brake application and safe operation demand. To reduce the driving difficulties and enhance transportation efficiency, this article proposes a trajectory optimization method to conduct optimal speed profile with pneumatic brake application regimes. The discontinuous characteristics and safe guidelines of cyclic pneumatic brake application are fully included in trajectory optimal model to find out optimal brake regimes without stopping release, which ensures transportation efficiency to the largest extent. Integer variables and convex relaxation are introduced in optimal model construction process to linearize time-accumulated constraints of cyclic pneumatic brake application and regularize the nonconvex relationship between operation time and speed. With the aforementioned deduction and matrix construction, the trajectory optimization problem can be constructed as mixed integer programming model with quadratic constraints (QCMIP) and solved by mature solvers. Finally, simulation experiments with commercial freight line data are carried out to verify the effectiveness of the proposed optimal method. Comparisons with the piecewise affine (PWA) linearization method and dynamic programming (DP) method verify the superior performance of the proposed optimal method.

Cyber-security is widely regarded as the main factor affecting the cooperation efficiency of multiple high-speed trains (MHSTs). In this work, based on the proposed weighted train-to-train (T2T) communication network, a consensus tracking scheme for MHSTs subject to malicious deception attacks is proposed, which is a data-driven control approach. Firstly, a deception attack model along with a T2T communication protocol incorporating weight factors is introduced, and followed by the presented distributed model free adaptive control (MFAC) scheme for MHSTs. Additionally, in the extended research, a novel priority-based attack strategy is investigated, and a compensation algorithm to counter deception attacks is also established for the first time. Finally, Simulink and StarSim hardware-in-loop (HIL) semi-physical platforms are employed to validate the findings presented in this study.

Generally, high-strength metallic materials with large ductility are of technological importance in various engineering fields, including aerospace, fuel efficiency, and emission reduction. This work developed a new type of steel with exceptional yield strength (1.5∼2.0 GPa) and high total elongation (11∼26%) through a simple three-step process involving cold-rolling, warm-rolling and annealing treatments. Microstructural analysis revealed that the steel is composed of nano platelets made up of austenite and martensite. These platelets aggregate within elongated prior austenite grains, forming hierarchical lamellar structures. The study thoroughly investigated the anisotropic mechanical properties of the steel, particularly its strength and yield point behavior in rolling and transverse directions. The primary sources of strength were mainly originated from nano lamellae and high density of dislocations, while the anisotropic strengthening and yield point behavior was attributed to the textures and lamellar boundaries. With increasing warm-rolling reduction, the anisotropy level of dislocation strengthening gradually decreases, while the anisotropy level of boundary strengthening significantly increases. The discrepancy in yield point behavior along the rolling and transverse directions is ascribed to the differing number of boundaries per unit area of cross-section perpendicular to the tensile direction and the shear stress required for dislocation slip. This study provides a deep insight into understanding the anisotropy of strengthening and yield point behavior in nanolamellar steel so as to contribute to its future applications in engineering structural components.

In this paper, the speed and position tracking problem of high-speed trains is investigated in the presence of actuator faults. A multi-agent system model is constructed, where each vehicle of the train is regarded as a controllable agent. A distributed adaptive controller is then proposed for healthy train system based on terminal sliding mode control. Further, a distributed adaptive fault-tolerant controller (DAFC) is designed for high-speed trains considering actuator faults, and an auxiliary system is introduced to cope with the influence of input saturation. To the best of our knowledge, it is the first time that the distributed fault-tolerant control is considered in a multi-agent system model, which can better utilize the residual power of each vehicle when actuator faults occur. The stability of the closed-loop control system is analyzed through Lyapunov theory, and it is proven that the speed and position tracking errors of all vehicles are cooperative convergence. The simulation results are presented to demonstrate the effectiveness of the proposed DAFC. Compared with the existing method, the proposed DAFC reduces the average speed and position control errors by 54.3$\%$ and 55$\%$, respectively.

• The SMEs of NiTi SMAs underwent a GS engineering are studied by phase field simulation. • The reorientation modulus during OWSME is increased by GS engineering. • The transformation temperature window during SATWSME is widened by GS engineering. • The effects of GS and introduced stress gradient can be superimposed or competing. • The optimal GS engineering schemes with tunable SMEs are revealed. The inelastic deformations of shape memory alloys (SMAs) always show poor controllability due to the avalanche-like martensite transformation, and the effective control for the deformation of precision devices has been not yet mature. In this work, the phase field method was used to investigate the shape memory effects (SMEs) of NiTi SMAs undergoing grain size (GS) engineering, to obtain tunable one-way and stress-assisted two-way SMEs (OWSME and SATWSME). The OWSME and SATWSME of the systems with various gradient-nanograin structures and bimodal grain structure, as well as that with geometric gradients were simulated. The simulated results indicate that due to the GS dependences of martensite transformation and reorientation, the occurrence and expansion of martensite reorientation, martensite transformation and its reverse can be efficaciously controlled via the GS engineering. When combining the GS engineering and geometric gradient design, since the effects of GS and stress gradient can be superimposed or competing, and the responses of martensite reorientation, martensite transformation and its reverse to this are different, the OWSME and SATWSME of the geometrically graded systems with various nanograin structures can exhibit different improvements in controllability. In short, the reorientation hardening modulus during OWSME is increased and the transformation temperature window during SATWSME is widened by GS engineering, indicating the improved controllability of SMEs. The optimal GS engineering schemes revealed in this work provide the basic reference and guidance for designing tunable SMEs and producing NiTi-based driving devices catering to desired functional performance in various engineering fields. [ABSTRACT FROM AUTHOR]

A new filler metal was developed to join the new generation weathering steel Q690qNH. Microstructural evolutions and the associated mechanical behavior of weldments were comparatively studied in hot rolled and tempered thick Q690qNH plates with initial microstructure of lath bainite and granular bainite respectively. Phase transformations in the HAZ promote the work hardening capacity of the weld jointed tempered Q690qNH (Q690T) plate and enable the joints to exhibit a different mechanical response upon the tensile loading in comparison to the weld jointed hot rolled Q690qNH (Q690R) plate. Prior austenite reconstruction was carried out to understand the crack nucleation behavior in HAZ. The plastic incompatibility between martensitic-austenitic (M-A) and bainitic ferrite leads to the nucleation of plastic micro-voids from the prior austenite grain boundary or M-A boundary. The fracture of Q690R joint is caused by coalescing micro-voids in HAZ with a strength reduction of 10%–14% that caused by the welding process. The continuous yielding behavior regarding the retained austinite in HAZ results in a competition of the plastic deformation in each subzone of the Q690T joint, of which the catastrophic fracture is dominated by the initial microstructure comprising the ferrite and the granular bainite.

Coupling effects of fretting wear and cyclic stress could result in significant fatigue strength degradation, thus potentially causing unanticipated catastrophic fractures. The underlying mechanism of microstructural evolutions caused by fretting wear is ambiguous, which obstructs the understanding of fretting fatigue issues, and is unable to guarantee the reliability of structures for long-term operation. Here, fretting wear studies were performed to understand the microstructural evolution and oxidation behavior of an α/β titanium alloy up to 108cycles. Contact surface degradation is mainly caused by surface oxidation and the generation of wear debris during fretting wear within the slip zone. The grain size in the topmost nanostructured layer could be refined to ∼40 nm. The grain refinement process involves the initial grain rotation, the formation of low angle grain boundary (LAGB; 2°–5°), the in-situincrements of the misorientation angle, and the final subdivision, which have been unraveled to feature the evolution in dislocation morphologies from slip lines to tangles and arrays. The formation of hetero microstructures regarding the nonequilibrium high angle grain boundary (HAGB) and dislocation arrays gives rise to more oxygen diffusion pathways in the topmost nanostructured layer, thus resulting in the formation of cracking interface to separate the oxidation zone and the adjoining nanostructured domain driven by tribological fatigue stress. Eventually, it facilitates surface degradation and the formation of catastrophic fractures.

This article considers the speed tracking control problem for high-speed train systems (HSTs) under the condition of passing through neutral sections in the presence of parametric uncertainties. Noticing the prominent feature of HSTs operation, i.e., the spatial repetitiveness, a novel spatial iterative learning control (ILC) scheme is proposed. First, the motion dynamic model of HSTs is constructed with the aid of temporal-spatial conversion. Meanwhile, input saturation constraint is introduced to address the limitation of system power supply capability and the loss of traction/braking force in neutral section. Then, the ILC law and the associated parametric updating law are devised to address the system uncertainties and realize the adaptive tracking control simultaneously. The stability of the closed-loop system and the convergence of the tracking errors are confirmed based on a space-weighted Lyapunov–Krasovskii-like composite energy function (CEF). Finally, numerical simulations are performed to illustrate the effectiveness of the proposed control scheme.

This paper studies the distributed data-driven event-triggered model free adaptive iterative learning control (ETMFAILC) of multiple high-speed trains (MHSTs) under iteration-varying topologies, which breaks away from the dependence on the train dynamics. Firstly, the nonlinear MHSTs with unknown dynamics are converted into a linear model. Then, combining the proposed event-based triggering condition and the linear model, the ETMFAILC scheme under the fixed topology is designed. Next, theoretical analysis proves the bounded input bounded output (BIBO) stability of MHSTs. Finally, the study is extended to the switching topologies and the validity of the ETMFAILC is verified by a numerical example.

Gaseous thallium (Tl) pollution events, primarily caused by non-ferrous mineral refineries and fossil fuel combustion, have increased over the past few decades. To prevent gaseous Tl distribution from flue gas, MnO2/CeO2@HKUST-1 (MCH) was synthesized and found to achieve a gaseous Tl(I) removal level of up to 90% at 423 K, a weight hourly space velocity (WHSV) of 2000 h–1/mL with an Mn dose of 10%, maintained over 10 h. The best Mn/Ce ratio was found to be 9:1. To further investigate surface kinetic behavior, four commonly used kinetic models were applied, including the Eley–Rideal (ER) model, Langmuir–Hinshelwood (LH) model, Mars–van Krevelen (MVK) model, and pseudo-first-order (PFO) model. While the ER and LH models had the slightest deviation, the MVK model was the most reliable. The CatMAP software was also used to match the simulation deviation. This work demonstrated the Tl removal mechanism and provided insights into the accuracy of kinetic models on minor-radius heavy metal. Thus, this research may help promote the design of reactors, heavy metal removal rates, and flue gas purification technology selection.

Purpose: The purpose of this paper is to determine (1) the relationship between microstructure and fatigue cracking behavior and (2) effect of rolling on the process of crack initiation and propagation in FeCrAl alloys. Design/methodology/approach: The qualitative and quantitative fracture studies were performed using scanning electron microscopy and the non-contact optical measurement system (IFMG5). Findings: The results show that the formation of facets, rough facets and parallel stripes in the crack initiation and early crack propagation zones are closely related to the sensitivity of crack behavior to the microstructure of the material. Besides, the rolling process has a significant influence on the small crack initiation and propagation behavior. Quantitative analysis demonstrates that the size of the stress intensity factor and plastic zone size in the rough zone is associated with the rolling process. Originality/value: The findings of this study have the potential to enhance the understanding of the microstructural crack formation mechanisms in FeCrAl alloys and shed light on the impact of rolling on the long-term and ultra-long fatigue behavior of these alloys. This new knowledge is vital for improving manufacturing processes and ensuring the safety and reliability of FeCrAl alloys used in nuclear industry applications.

Eco-driving for trains has traditionally focused on minimizing mechanical energy consumption at wheels, while completely ignoring traction chain losses that are rather significant. This article presents a computationally efficient approach to minimize the total electrical energy consumption from traction substations (TS). After a nonlinear and non-convex program is formulated in time domain, a nonlinear and non-convex program is formulated in space domain to overcome the drawbacks of the model in time domain. By convex modeling steps, the non-convex program in space domain is reformulated as a convex program that can be efficiently solved. To further reduce computational effort, a real-time iteration sequential quadratic programming (SQP) algorithm is proposed to solve the convex program in a model predictive control framework. Numerical results indicate that the proposed SQP method yields a near-optimal solution with high computational efficiency. Compared to a traditional mechanical energy consumption model, a TS-to-traction energy efficiency can be improved.

NiTi shape memory alloy (SMA) has been suggested as an environmentally friendly solid-state refrigerant that is expected to replace the traditional vapor compression technology. However, its various refrigeration indicators still need to be further explored and enhanced. Nanocrystalline NiTi SMA has significant advantages in terms of elastocaloric effect (eCE) and cyclic stability compared with traditional coarse-grained NiTi SMA. In this work, the influence of aspect ratio (L/W, where Land Ware the gauge length and width of the samples, respectively) on the eCE and its cyclic stability of nanocrystalline NiTi SMA was investigated experimentally. The in-situcyclic tensile tests were performed to observe the axial strain field and temperature field on the surface of the specimens with different aspect ratios. Some microscopic observations were also carried out to clarify the internal mechanism. The experimental results show that as the aspect ratio decreases, the adiabatic temperature change ΔTad(elasocaloric cooling capacity) of the nanocrystalline NiTi SMA gradually decreases, while the coefficient of the performance of material (COPmat) increases, and the cyclic stability of eCE was enhanced. However, the dependence of eCE and its cyclic stability on the aspect ratio is gradually weakened when L/W > 4. The eCE and its cyclic stability of nanocrystalline NiTi SMA are not related to the dislocation slipping but rather attributed to the cyclically accumulated residual martensite. This work can provide valuable reference for designing efficient and reliable nanocrystalline NiTi SMA based solid-state refrigeration devices.

Graphical Abstract:

Pervasive mechanical force in nature and human activities is closely related to intriguing physics and widespread applications. However, describing stress distribution timely and precisely in three dimensions to avoid “groping in the dark” is still a formidable challenge, especially for nonplanar structures. Herein, we realize three-dimensional (3D) stress imaging for sharp arbitrary targets via advanced 3D printing, owing to the use of fluoride nanocrystal(NC)-based ink. Notably, a fascinating mechano-luminescence (ML) is observed for the homogeneously dispersed NaLuF4:Tb3+NCs (∼25 nm) with rationally designed deep traps (at 0.88 and 1.02 eV) via incorporating Cs+ions and using X-ray irradiation. Carriers captured in the corresponding traps are steadily released under mechanical stimulations, which enables a ratio metric luminescence intensity based on the applied force. As a result, a significant mechano-optical conversion and superior optical waveguide of the corresponding transparent printed targets demonstrate stress in 3D with a high spatial and temporal resolution based on stereovision. These results highlight the optical function of the 3D-printed fluoride NCs, which cast light into the black boxes of stress described in space, benefiting us in understanding the ubiquitous force relevant to most natural and engineering processes.

The newly discovered nickelate superconductors so far only exist in epitaxial thin films synthesized by a topotactic reaction with metal hydrides1. This method changes the nickelates from the perovskite to an infinite-layer structure by deintercalation of apical oxygens1–3. Such a chemical reaction may introduce hydrogen (H), influencing the physical properties of the end materials4–9. Unfortunately, H is insensitive to most characterization techniques and is difficult to detect because of its light weight. Here, in optimally Sr doped Nd0.8Sr0.2NiO2H epitaxial films, secondary-ion mass spectroscopy shows abundant H existing in the form of Nd0.8Sr0.2NiO2Hx(x≅ 0.2–0.5). Zero resistivity is found within a very narrow H-doping window of 0.22 ≤ x≤ 0.28, showing unequivocally the critical role of H in superconductivity. Resonant inelastic X-ray scattering demonstrates the existence of itinerant interstitial s(IIS) orbitals originating from apical oxygen deintercalation. Density functional theory calculations show that electronegative H–occupies the apical oxygen sites annihilating IIS orbitals, reducing the IIS–Ni 3dorbital hybridization. This leads the electronic structure of H-doped Nd0.8Sr0.2NiO2Hxto be more two-dimensional-like, which might be relevant for the observed superconductivity. We highlight that H is an important ingredient for superconductivity in epitaxial infinite-layer nickelates.

Magnetically actuated miniature machines can perform multimodal locomotion and programmable deformations. However, they are either solid magnetic elastomers with limited morphological adaptability or liquid material systems with low mechanical strength. Here, we report magnetoactive phase transitional matter (MPTM) composed of magnetic neodymium-iron-boron microparticles embedded in liquid metal. MPTMs can reversibly switch between solid and liquid phase by heating with alternating magnetic field or through ambient cooling. In this way, they uniquely combine high mechanical strength (strength, 21.2 MPa; stiffness, 1.98 GPa), high load capacity (able to bear 30 kg), and fast locomotion speed (>1.5 m/s) in the solid phase with excellent morphological adaptability (elongation, splitting, and merging) in the liquid phase. We demonstrate the unique capabilities of MPTMs by showing their dynamic shape reconfigurability by realizing smart soldering machines and universal screws for smart assembly and machines for foreign body removal and drug delivery in a model stomach.

The Carbon Neutralization is a grand strategy to deal with global climate change. As a major energy consumer, urban rail transit (URT) system should contribute corresponding solutions. This paper proposes an energy-efficient train control and schedule integrated optimization method under DC traction power supply system (TPSS) with reversible substation (RSS). The dynamic coupling mechanism between the train movement process and the RSS working mode is analyzed and modeled. Aiming to minimize the total RSS energy consumption for the train traveling over multi-interstation with a given total trip time, the train trajectory and schedule optimization problem is integrated in the same level, and is formulated as a multi-phase optimal control problem (MOCP) to be solved by a pseudo-spectral method (PSM). As a supplement, a customized dynamic programming (DP) method for the problem is introduced to verify the validity of the proposed solution framework. Simulation results under the models of the RSS energy together with conventional rectifier substation energy and vehicle mechanical energy are presented and compared, indicating that the proposed methodology has great energy saving performance for the new-type DC railway system.

With weak interlayer interactions and unique physical properties, bismuth oxyselenide (Bi2O2Se) has become a rising star as a novel quasi-2D material, possessing high symmetry, adjustable electronic structure, ultra-high electron mobility, persistent quantum oscillations, unique defects, strong spin-orbital coupling, natural oxide layers, excellent stability, and marvelous optoelectronic performance. These characteristics will help to break through existing technical barriers for applications such as field-effect transistors and photodetectors. Its unique crystal structure and suitable lattice parameters allow it to grow on lattice-matched (SrTiO3and LaAlO3) and unmatched (mica and SiO2) substrates, establishing a link between traditional epitaxy and emerging van der Waals epitaxy. This review aims to provide an overview of this promising semiconductor from a fundamental structure, physics, and physical properties perspective. We especially pay attention to the correlation of electronic structure to various physical properties and material performance. We also identify current problems and challenges regarding the fundamental properties of this material.

The interior defect-induced crack initiation mechanism and early growth behavior of Ti6Al4V alloy fabricated by laser powder bed fusion (LPBF) has been investigated in very high cycle fatigue (VHCF) regime. P–S–Ncurves under 10% and 90% failure probabilities are obtained in VHCF regime. The cracks inside the early stages of fine granular area (FGA) formation are driven by the maximum shear stress and propagate as Mode II + III mixed cracks. It can be found that the FGA region is composed of many discontinuous nanograins for Ti6Al4V alloys manufactured by LPBF, which are responsible for grain refinement. Grain refinement is associated with dislocation movement within the martensite laths. Dislocation pileup and rearrangement in martensitic laths form dislocation cells, which further develop into nanograins and low angle boundaries. Besides, both the fatigue loading process and the LPBF process form their respective microvoids, which merge and aggregate with each other, thus accelerating the microcrack extension.