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Flux pinning force scaling f = F p / F p , max vs. h = H a / H irr was performed on a variety of pure MgB 2 samples, including a spark plasma sintered (SPS) one and a series of samples sintered at various reaction temperatures ranging between 775 and 950 ∘ C. The SPS sample exhibits a well-developed scaling at all temperatures, and also the sintered samples prepared at 950 ∘ C; however, the obtained peak positions of the pinning force scalings are distinctly different: The SPS sample reveals dominating pinning at grain boundaries, whereas the dominating pinning for the other one is point-pinning. All other samples studied reveal an apparent non-scaling of the pinning forces. The obtained pinning parameters are discussed in the framework of the Dew–Hughes’ pinning force scaling approach.

Transition to a hydrogen-based economy requires a thorough understanding of hydrogen interaction with dislocations in metals, especially in body-centered cubic (BCC) steels. Past experimental and computational investigations regarding these interactions often demonstrate two opposing results: hydrogen-induced mobility or hydrogen-induced pinning of dislocations. Through in-situ scanning electron microscopy experiments enabled by a custom-built setup, we address here this discrepancy. Our experiments reveal hydrogen-induced dislocation motion in a BCC metal at room temperature. Interestingly, however, we also observe that the same dislocations are later pinned as well, again induced by the steady hydrogen flux. Molecular dynamics simulations of the phenomena confirm the attraction of the dislocations towards the hydrogen flux, and the pinning that follows after, upon increased hydrogen trapping at the dislocation core. Future experimental or computational studies of hydrogen thus should take into account these different regimes in order to present a full picture of hydrogen defect interactions. Hydrogen affects dislocation motion in BCC metals in different ways. Using in-situ SEM and simulations, the authors observe a two-step process: hydrogen first moves dislocations, then pins them as it builds up, explaining previously conflicting results.

This paper studies synchronization via pinning control on general complex dynamical networks, such as strongly connected networks, networks with a directed spanning tree, weakly connected networks, and directed forests. A criterion for ensuring network synchronization on strongly connected networks is given. It is found that the vertices with very small in-degrees should be pinned first. In addition, it is shown that the original condition with controllers can be reformulated such that it does not depend on the form of the chosen controllers, which implies that the vertices with very large out-degrees may be pinned. Then, a criterion for achieving synchronization on networks with a directed spanning tree, which can be composed of many strongly connected components, is derived. It is found that the strongly connected components with very few connections from other components should be controlled and the components with many connections from other components can achieve synchronization even without controls. Moreover, a simple but effective pinning algorithm for reaching synchronization on a general complex dynamical network is proposed. Finally, some simulation examples are given to verify the proposed pinning scheme. [PUBLICATION ABSTRACT]

Both the transport critical current density at the zero magnetic field and magnetic critical current density in a composite system consisting of bulk YBCO superconductor and insulating BaTiO 3 (BTO) have been studied using current–voltage ( IV ) and magnetization ( M ) as a function of magnetic field ( H ), respectively. Vortex pinning by insulating nanoparticles of BTO from the inter-granular network is investigated up to the magnetic field of 7.0 T. By analyzing magnetic critical current density the possibility of crossover from collective pinning (CP) to strong pinning (SP) and how it is affected by BTO have been explored based on the framework of Larkin–Ovchinnikov (LO) theory. Possible scenario of the strong pinning (SP) induced by insulating nanoparticles has also been studied using an exponent.

Improving the absorption of electromagnetic waves at low-frequency bands (2-8 GHz) is crucial for the increasing electromagnetic (EM) pollution brought about by the innovation of the fifth generation (5G) communication technology. However, the poor impedance matching and intrinsic attenuation of material in low-frequency bands hinders the development of low-frequency electromagnetic wave absorbing (EMWA) materials. Here we propose an interface-induced dual-pinning mechanism and establish a magnetoelectric bias interface by constructing bilayer core-shell structures of NiFe 2 O 4 (NFO)@BiFeO 3 (BFO)@polypyrrole (PPy). Such heterogeneous interface could induce distinct magnetic pinning of the magnetic moment in the ferromagnetic NFO and dielectric pinning of the dipole rotation in PPy. The establishment of the dual-pinning effect resulted in optimized impedance and enhanced attenuation at low-frequency bands, leading to better EMWA performance. The minimum reflection loss (RL min ) at thickness of 4.43 mm reaches -65.30 dB (the optimal absorption efficiency of 99.99997%), and the effective absorption bandwidth (EAB) can almost cover C-band (4.72 ~ 7.04 GHz) with low filling of 15.0 wt.%. This work proposes a mechanism to optimize low-frequency impedance matching with electromagnetic wave (EMW) loss and pave an avenue for the research of high-performance low-frequency absorbers. This paper proposes a dual-pinning mechanism induced by a magneto-electric bias interface and uses it to designs a double-layer core-shell structure, demonstrating that the mechanism improves electromagnetic wave absorption in the low-frequency bands.

In this paper, the mean-square bounded synchronization problem for a class of complex cyber-physical networks under deception attacks is investigated. The deception attack often takes place between the controller and the actuator, in which the injection of false data may cause the actuator to malfunction, while the occurrence of deception attack is always subject to Bernoulli distribution. An improved pinning impulsive control scheme is designed such that the status of all components in networks can be consistent, and the nodes with a high probability of being attacked are preferentially controlled. By means of Lyapunov method, inequality technique and mathematical induction method, it is proved that the given scheme can realize the mean-square bounded synchronization of complex networks under deception attack. Moreover, the required synchronization time is controllable and computable. Then, some sufficient conditions for mean-square bounded synchronization, error bound, and the maximum convergence time are obtained. Finally, two simulation examples demonstrate the validity of the given theoretical results.

We have studied the possibility of utilizing artificial intelligence (AI) models to optimize high-temperature superconducting (HTS) multilayer structures for applications working in a specific field and temperature range. For this, we propose a new vortex dynamics simulation method that enables unprecedented efficiency in the sampling of training data required by the AI models. The performance of several different types of AI models has been studied, including kernel ridge regression (KRR), gradient-boosted decision tree (GBDT) and neural network. From these, the GBDT based model was observed to be clearly the best fitted for the associated problem. We have demonstrated the use of GBDT for finding optimal multilayer structure at 10 K temperature under 1 T field. The GBDT model predicts that simple doped-undoped bilayer structures, where the vast majority of the film is undoped superconductor, provide the best performance under the given environment. The obtained results coincide well with our previous studies providing further validation for the use of AI in the associated problem. We generally consider the AI models as highly efficient tools for the broad-scale optimization of HTS multilayer structures and suggest them to be used as the foremost method to further push the limits of HTS films for specific applications.

Recent progress in the kinetics of grain coarsening and abnormal grain growth (AGG) is presented in this overview article. The factors affecting the kinetics of grain growth is reviewed with the emphasis on the recent findings on the solute drag and Zener pinning effects as well as the special case of duplex alloys, where the latter is discussed for the behavior of dual-phase steels during intercritical annealing. The common isothermal kinetics models for grain growth are listed, which is followed by the critical discussion on the simplifications and the commonly used methods for the determination of grain growth exponent ( n ) and activation energy ( Q ). The obtained values of n and Q for several classes of important engineering alloys such as microalloyed steels, stainless steels, magnesium alloys, aluminum alloys, titanium alloys, and high-entropy alloys are summarized with the discussion on the obtained values of kinetics parameters and their deviation from the theoretical expectations. Finally, the factors leading to AGG (such as the coarsening and dissolution of pinning particles and the crystallographic texture), the proposed mechanisms (such as the solid-state wetting and the grain boundary faceting/defaceting phenomena), and the kinetics of AGG (based on the empirical power law and the similarity of AGG to primary recrystallization in the form of secondary recrystallization) are reviewed. This overview can shed light on the understanding of grain growth and its effects.

Many traditional approaches for strengthening steels typically come at the expense of useful ductility, a dilemma known as strength-ductility trade-off. New metallurgical processing might offer the possibility of overcoming this. Here we report that austenitic 316L stainless steels additively manufactured via a laser powder-bed-fusion technique exhibit a combination of yield strength and tensile ductility that surpasses that of conventional 316L steels. High strength is attributed to solidification-enabled cellular structures, low-angle grain boundaries, and dislocations formed during manufacturing, while high uniform elongation correlates to a steady and progressive work-hardening mechanism regulated by a hierarchically heterogeneous microstructure, with length scales spanning nearly six orders of magnitude. In addition, solute segregation along cellular walls and low-angle grain boundaries can enhance dislocation pinning and promote twinning. This work demonstrates the potential of additive manufacturing to create alloys with unique microstructures and high performance for structural applications.

The main purpose of this article is to show an easier and more accurate method for analyzing high-field pinning centers. Previous methods did not allow for precise analysis and research on high-field pinning centers, they studied only the dominant pinning mechanism, and they required a maximum of pinning force ( F pmax ) to analyze pinning centers. The main advantage of this method can be used in samples without the maximum pinning force required by other methods to analyze the pinning mechanism. In addition, this method allows us to observe even small changes in the density of individual pinning centers. This method is based on analysis of critical current density values in different ranges of reduced magnetic field. The method of analysis of high-field pinning centers allows primarily to develop methods and directions for creation of high-field pinning centers. The surface pinning centers are strong pinning centers in low magnetic fields and very weak pinning centers in middle and high magnetic fields. Additionally, the analysis of pinning centers shows that dislocations, strains, substitutions in the crystal lattice, and precipitation inside the grains create strong pinning centers in high magnetic fields and very weak pinning centers in low and middle magnetic fields. Research indicates that strains, substitutions in the crystal lattice, and precipitates inside grains form pinning centers that operate in the high magnetic field range.