Topological Transformation Research Articles

Topotactic Transition: A Promising Opportunity for Creating New Oxides

AbstractTopotactic transition is a structural phase change in a matrix crystal lattice mediated by the ordered loss/gain and rearrangement of atoms, leading to unusual coordination environments and metal atoms with rare valent states. As early as in 1990s, low temperature hydride reduction is utilized to realize the topotactic transition. Since then, topological transformations are developed via multiple approaches. Especially, the recent discovery of the Ni‐based superconductivity in infinite‐layer nickelates has greatly boosted the topotactic transition mean to synthesizing new oxides for exploring exotic functional properties. In this review, a detailed and generalized introduction is provided to oxygen‐related topotactic transition. The main body of the review includes four parts: the structure‐facilitated effects, the mechanism of the topotactic transition, some examples of topotactic transition methods adopted in different metal oxides (V, Mn, Fe, Co, Ni) and the related applications. This study is to provide timely and thorough strategies to successfully realize topotactic transitions for researchers who are eager to create new oxide phases or new oxide materials with desired functions.

In-situ constructed ultrathin hydrotalcite derivative supported PtIn catalyst for isobutane direct dehydrogenation

The stable and ultrathin hydrotalcite nanosheets with thickness of ca. 1.0 nm have been built on the surface of Al2O3 by sharing Al element and using layer growth inhibitor formamide. Based on the topological transformation characteristics of hydrotalcite and the structural memory effect of calcined product, the supported PtIn bimetallic catalyst was achieved by stepwise incipient wetness impregnation method followed by calcination and reduction, and evaluated in isobutane direct dehydrogenation (IDH) to isobutene. The derived ultrathin bimetallic catalyst possesses excellent IDH activity under extreme conditions, in which the isobutane conversion and isobutene selectivity can remain above 63% and 92% respectively, and the turnover frequency is as high as 13.45 s−1. The excellent activity can be attributed to the formation of ultrathin hydrotalcite precursor, which can greatly enhance the specific surface area, interaction among metal components, surface acidity of weak- and medium-acid sites and surface In3+/In0 ratio, and further effectively inhibit carbon deposition and improve dispersion and stability of active Pt species in the corresponding derivative.

A strong bimetal-support interaction in ethanol steam reforming

The metal-support interaction (MSI) in heterogeneous catalysts plays a crucial role in reforming reaction to produce renewable hydrogen, but conventional objects are limited to single metal and support. Herein, we report a type of RhNi/TiO2 catalysts with tunable RhNi-TiO2 strong bimetal-support interaction (SBMSI) derived from structure topological transformation of RhNiTi-layered double hydroxides (RhNiTi-LDHs) precursors. The resulting 0.5RhNi/TiO2 catalyst (with 0.5 wt.% Rh) exhibits extraordinary catalytic performance toward ethanol steam reforming (ESR) reaction with a H2 yield of 61.7%, a H2 production rate of 12.2 L h−1 gcat−1 and a high operational stability (300 h), which is preponderant to the state-of-the-art catalysts. By virtue of synergistic catalysis of multifunctional interface structure (Rh-Niδ−-Ov-Ti3+; Ov denotes oxygen vacancy), the generation of formate intermediate (the rate-determining step in ESR reaction) from steam reforming of CO and CHx is significantly promoted on 0.5RhNi/TiO2 catalyst, accounting for its ultra-high H2 production.

In situ switchable local resonance in elastic metamaterials through bistable topological transformation

We report a topology-transformable resonator with two distinct stable states, one kinematically determinate and endowed with nearly rigid-body motion at low-frequencies, and the other accompanied by a floppy pseudo zero-energy mode capable of showing low-frequency local resonance. Through a combination of numerical simulations and experiments, we unveil the role of contact-induced topological transformation, a phenomenon that empowers the resonator with negative dynamic effective mass. We demonstrate that the bistable resonator can be embedded into elastic metamaterials to enable in situ switch of local resonance, allowing on-demand augmentation and attenuation of elastic wave propagation within a prescribed regime of frequency.

Experimental study of the topological flow transformations in an aerial vortex bioreactor with a floating washer.

Research into the flow structure in an aerial vortex bioreactor is relevant for developing the methods for growing cell cultures. Determining the optimal cultivation condition for a certain process is especially important in the case when such parameters of the medium as density and viscosity significantly change with the culture growth in the bioreactor. The research of the flow dynamic was carried out in an 8.5 L universal aerial vortex bioreactor, with a washer freely floating on its surface and stabilizing the motion of the working fluid. The regularities of the vortex motion of the culture medium have been determined by Particle Image Velocimetry depending on its volume and the intensity of rotation of the activator, generating vortex motion in the air. The observed vortex structure and its dynamics at increasing flow swirl intensity are established to coincide with the structure of a confined vortex flow in a cylindrical container with no washer for both single and two-fluid configurations. This novel methodology of the flow optimization shows that an ascending swirling jet forms in the vicinity of the bioreactor axis, and a bubble-like vortex breakdown forms in the axial region. This article is protected by copyright. All rights reserved.

Observation of hybrid magnetic skyrmion bubbles in Fe3Sn2 nanodisks

It has been widely established that there exist two types of magnetic bubbles. Here, the authors present the theory and experiment of a novel three-dimensional bubble state, referred to as the type-III bubble, which is composed of N\'eel-twisted skyrmions with topological charge $Q$ = -1 in the near-surface layers and type-II bubbles with $Q$ = 0 in the interior layers. Furthermore, the authors demonstrate a method for creating the type-III bubble and the topological magnetic transformation among the three types of bubbles.

Some remarks on Swampland conjectures, fluxes and K-theory in IIB toroidal compactifications

In this note, we present a scenario in which the existence of dS vacua is jeopardized by topological transitions between non-BPS branes and fluxes in type IIB toroidal compactifications. We focus our study on a six-dimensional torus compactification modded out by an orientifold three-plane. In particular, we consider the presence of non-BPS five branes, which allows the construction of apparent stable dS vacua. Since moduli stabilization requires the presence of NS–NS fluxes, we also describe the minimal required conditions to avoid the appearance of Freed–Witten anomalies. Cancellation of these anomalies implies a topological transformation between non-BPS states and fluxes with the same discrete K-theory charge. After the transition, we observe that the scalar potential undergoes major changes, implying that the dS vacua are unstable. We discuss a scenario in which, even if the discrete K-theory charge is globally canceled, the above transitions could still be relevant, allowing the existence of short-lived dS minima. We briefly comment on how these implications seem to be in concordance with the Refined de Sitter and Trans-Planckian Censorship Conjectures.

Structure-dependent room-temperature hydrogen sensing of Nb2O5 nanorods prepared by topological transformation process

The development of reliable low-power-consumption hydrogen gas sensors is of great significance for the accurate detection of hydrogen leakage in the hydrogen-related industries. Nb2O5 nanomaterials have exhibited great potential for building highly selective hydrogen sensors owing to its outstanding hydrogen catalytic capability, but still suffer from relatively low hydrogen sensitivity at room temperature. Herein, the orthorhombic and hexagonal Nb2O5 nanorods with different defect states are prepared through a combined topological transformation process. The Nb2O5 nanorods with polycrystalline orthorhombic structures exhibit much higher room-temperature hydrogen response comparing with the single-crystalline hexagonal Nb2O5 nanorods. Moreover, both phases of the Nb2O5 nanorods exhibit certain amounts of oxygen vacancies, as well as the interstitial Nb4+ and related oxygen defects. The elimination of the Nb4+ and related oxygen defects can significantly enhance the surface reactivity of the Nb2O5 nanorods and improve the sensor response of the chemiresistor devices. The sensor based on the defect-modified orthorhombic Nb2O5 nanorods shows sensitive and highly selective room-temperature hydrogen sensing performance with the detection limit of 160 ppm. The structure-dependent hydrogen sensing behavior of the Nb2O5 nanorods can be attributed to the redox reaction between hydrogen and pre-adsorbed oxygens, which can be promoted by the superior gas adsorption and pathway effect of the orthorhombic Nb2O5 lattice.

Ultrafast reversible self-assembly of living tangled matter.

Tangled active filaments are ubiquitous in nature, from chromosomal DNA and cilia carpets to root networks and worm collectives. How activity and elasticity facilitate collective topological transformations in living tangled matter is not well understood. We studied California blackworms (Lumbriculus variegatus), which slowly form tangles in minutes but can untangle in milliseconds. Combining ultrasound imaging, theoretical analysis, and simulations, we developed and validated a mechanistic model that explains how the kinematics of individual active filaments determines their emergent collective topological dynamics. The model reveals that resonantly alternating helical waves enable both tangle formation and ultrafast untangling. By identifying generic dynamical principles of topological self-transformations, our results can provide guidance for designing classes of topologically tunable active materials.

Facile synthesis of calabash-shaped and twin-tail tadpole-shaped copolymers via photothermal-induced topological transformation

Rational design of architecture-transformable polymers with dynamic covalent bonds allows to form multiple ring-bearing analogues and gain insight into topology-tunable physicochemical properties. To reveal unique properties originating from size-asymmetric twincycles and ring-linear conjugates, twin-tail tadpole-shaped (TTP) and calabash-shaped bicyclic (CLB) copolymers comprising poly(ε-caprolactone) (PCL, A) and polystyrene (PSt, B) segments are synthesized. Controlled polymerization and radical trap-assisted atom transfer radical coupling are combined to synthesize a multisite telechelic ABA. By virtue of UV-induced intramolecular anthracene dimerization and selective thermolysis of in-chain alkoxyamine and anthracene dimer linkers of the macrocycle, versatile topological transformations from linear copolymer to TTP, CLB and ring/tail-reversal TTP are achieved. Owing to distinct chain architectures, three types of analogues can exhibit some differences in hydrodynamic volume, crystallization, diffusion coefficient and aggregation behavior, revealing pronounced topology effect. This study affords a promising method to construct stimuli-labile ring-bearing architectures to reveal topology-dependent properties.

β-Ni(OH)2/NiFe2O4 heterostructure composite derived from layered double hydroxides precursor for ethanol oxidation electrocatalysis

We reported facile fabrication of a novel β-Ni(OH)2/NiFe2O4 heterostructure composite by KOH alkaline etching three-component NiFeAl-layered double hydroxides (NiFeAl-LDHs) precursor for ethanol oxidation electrocatalysis. Detailed investigation of evolution progress from NiFeAl-LDHs precursor to β-Ni(OH)2/NiFe2O4 demonstrated that growth of such composite structure underwent partial dealumination and spontaneous lattice rearrangement of NiFeAl-LDHs to form α-Ni(OH)2/NiFeAl-LDHs compound, followed by deep dealumination and topological transformation to produce β-Ni(OH)2/NiFe2O4. Compared to NiFeAl-LDHs precursor, β-Ni(OH)2/NiFe2O4 heterostructure prepared in 15 M KOH alkaline had enhanced activity (approximately 10 times) for ethanol electrocatalysis, smaller electron transfer resistance of 1.33 Ω, and increased long-term stability. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and in situ Raman spectroscopy were further performed to explore reaction mechanism and transformation process of β-Ni(OH)2/NiFe2O4 in ethanol electrocatalysis, which verified that the process of electron donating and electron receiving between NiFe2O4 and β-Ni(OH)2 realized more electron transfer and greatly improved the fuel utilization.

Synergistic Catalysis at the Ni/ZrO2–x Interface toward Low-Temperature CO2 Methanation

The CO2 methanation reaction, which achieves the carbon cycle and gains value-added chemicals, has attracted much attention, but the design and exploitation of highly active catalysts remain a big challenge. Herein, zirconium dioxide-supported Ni catalysts toward low-temperature CO2 methanation are obtained via structural topological transformation of NiZrAl-layered double hydroxide (LDH) precursors, which have the feature of an interfacial structure (Ni-O-Zr3+-Vö) between Ni nanoparticles and ZrO2-x support (0 < x < 1). The optimized catalyst (Ni/ZrO2-x-S2) exhibits exceptional CO2 conversion (∼72%) at a temperature as low as 230 °C with a ∼100% selectivity to CH4, without obvious catalyst deactivation within a 110 h reaction at a high gas hourly space velocity of 30,000 mL·g-1·h-1. Markedly, the space-time yield of CH4 reaches up to ∼0.17 ·gcat-1·h-1, which is superior to previously reported Ni catalysts evaluated under similar reaction conditions. Both in situ/operando investigations (diffuse reflectance infrared Fourier transform spectroscopy and X-ray absorption fine structure) and catalytic evaluations substantiate the interfacial synergistic catalysis at the Ni/ZrO2-x interface: the Zr3+-Vö facilitates the activation adsorption of CO2, while the H2 molecule experiences dissociation at the metallic Ni sites. This work demonstrates that the metal-support interface effect plays a key role in improving the catalytic behavior toward CO2 methanation, which can be extended to other high-performance heterogeneous catalysts toward structure-sensitive systems.

Ensuring SDN Resilience under the Influence of Cyber Attacks: Combining Methods of Topological Transformation of Stochastic Networks, Markov Processes, and Neural Networks

The article proposes an approach to ensuring the functioning of Software-Defined Networks (SDN) in cyber attack conditions based on the analytical modeling of cyber attacks using the method of topological transformation of stochastic networks. Unlike other well-known approaches, the proposed approach combines the SDN resilience assessment based on analytical modeling and the SDN state monitoring based on a neural network. The mathematical foundations of this assessment are considered, which make it possible to calculate the resilience indicators of SDN using analytical expressions. As the main indicator, it is proposed to use the correct operation coefficient for the resilience of SDN. The approach under consideration involves the development of verbal models of cyber attacks, followed by the construction of their analytical models. In order to build analytical models of cyber attacks, the method of topological transformation of stochastic networks (TTSN) is used. To obtain initial data in the simulation, the SDN simulation bench was justified and deployed in the EVE-NG (Emulated Virtual Environment Next Generation) virtual environment. The result of the simulation is the time distribution function and the average time for the cyber attack implementation. These results are then used to evaluate the SDN resilience indicators, which are found by using the Markov processes theory. In order to ensure the resilience of the SDN functioning, the article substantiates an algorithm for monitoring the state of controllers and their automatic restructuring, built on the basis of a neural network. When one is choosing a neural network, a comparative evaluation of the convolutional neural network and the LSTM neural network is carried out. The experimental results of analytical modeling and simulation are presented and their comparative evaluation is carried out, which showed that the proposed approach has a sufficiently high accuracy, completeness of the obtained solutions and it took a short time to obtain the result.

Synthesis of Bandgap-tunable Transition Metal Sulfides through Gas-phase Cation Exchange-induced Topological Transformation.

Oriented synthesis of transition metal sulfides (TMSs) with controlled compositions and crystal structures has long been promising for electronic devices and energy applications. Liquid-phase cation exchange (LCE) is a well-studied route by varying the compositions. However, achieving crystal structure selectivity is still a great challenge. Here, we demonstrate gas-phase cation exchange (GCE), which can induce a specific topological transformation (TT), for the synthesis of versatile TMSs with identified cubic or hexagonal crystal structures. The parallel six-sided subunit (PSS), a new descriptor, is defined to describe the substitution of cations and the transition of the anion sublattice. Under this principle, the band gap of targeted TMSs can be tailored. Using the photocatalytic hydrogen evolution as an example, the optimal hydrogen evolution rate of a zinc-cadmium sulfide (ZCS4) is determined to be 11.59 mmol h-1 g-1 , showing a 36.2-fold improvement over CdS.

Synthesis of Bandgap‐tunable Transition Metal Sulfides through Gas‐phase Cation Exchange‐induced Topological Transformation

AbstractOriented synthesis of transition metal sulfides (TMSs) with controlled compositions and crystal structures has long been promising for electronic devices and energy applications. Liquid‐phase cation exchange (LCE) is a well‐studied route by varying the compositions. However, achieving crystal structure selectivity is still a great challenge. Here, we demonstrate gas‐phase cation exchange (GCE), which can induce a specific topological transformation (TT), for the synthesis of versatile TMSs with identified cubic or hexagonal crystal structures. The parallel six‐sided subunit (PSS), a new descriptor, is defined to describe the substitution of cations and the transition of the anion sublattice. Under this principle, the band gap of targeted TMSs can be tailored. Using the photocatalytic hydrogen evolution as an example, the optimal hydrogen evolution rate of a zinc‐cadmium sulfide (ZCS4) is determined to be 11.59 mmol h−1 g−1, showing a 36.2‐fold improvement over CdS.

Phase Field Simulation of the effect of Aging Precipitates on Grain Growth in Aluminum Alloys

Aluminum alloy skin for automobile is the focus of development, application and research of aluminum alloy for automobile. At present, the problems such as aging stability, formability, concavity resistance and bake hardening of anti-baking paint need to be solved urgently. The aging precipitates of baking varnish have the effect of pinning grain boundaries and refining grains. In this study, the topological transformation law of polycrystalline evolution during normal grain growth was analyzed by continuous phase field model, and the influence of different size, morphology and volume fraction of precipitated phase particles on polycrystalline growth were simulated. By verifying the Zener relationship between the particle size of the precipitate and the limit radius of the grain, an exponential function relationship different from the growth law of the ideal spherical particle pinned polycrystals was obtained. This research has an important scientific guiding role in the aging modification design of automobile skin and in improving the service life of aluminum alloy sheets.

Distributed Consensus Kalman Filter Design with Dual Energy-Saving Strategy: Event-Triggered Schedule and Topological Transformation.

In the distributed information fusion of wireless sensor networks (WSNs), the filtering accuracy is commonly negatively correlated with energy consumption. Therefore, a class of distributed consensus Kalman filters was designed to balance the contradiction between them in this paper. Firstly, an event-triggered schedule was designed based on historical data within a timeliness window. Furthermore, considering the relationship between energy consumption and communication distance, a topological transformation schedule with energy-saving is proposed. The energy-saving distributed consensus Kalman filter with a dual event-driven (or event-triggered) strategy is proposed by combining the above two schedules. The sufficient condition of stability for the filter is given by the second Lyapunov stability theory. Finally, the effectiveness of the proposed filter was verified by a simulation.

Superconductivity in an Orbital‐Reoriented SnAs Square Lattice: A Case Study of Li0.6Sn2As2 and NaSnAs

AbstractSearching for functional square lattices in layered superconductor systems offers an explicit clue to modify the electron behavior and find exotic properties. The trigonal SnAs3 structural units in SnAs‐based systems are relatively conformable to distortion, which provides the possibility to achieve structurally topological transformation and higher superconducting transition temperatures. In the present work, the functional As square lattice was realized and activated in Li0.6Sn2As2 and NaSnAs through a topotactic structural transformation of trigonal SnAs3 to square SnAs4 under pressure, resulting in a record‐high Tc among all synthesized SnAs‐based compounds. Meanwhile, the conductive channel transfers from the out‐of‐plane pz orbital to the in‐plane px+py orbitals, facilitating electron hopping within the square 2D lattice and boosting the superconductivity. The reorientation of p‐orbital following a directed local structure transformation provides an effective strategy to modify layered superconducting systems.

Superconductivity in an Orbital-Reoriented SnAs Square Lattice: A Case Study of Li0.6 Sn2 As2 and NaSnAs.

Searching for functional square lattices in layered superconductor systems offers an explicit clue to modify the electron behavior and find exotic properties. The trigonal SnAs3 structural units in SnAs-based systems are relatively conformable to distortion, which provides the possibility to achieve structurally topological transformation and higher superconducting transition temperatures. In the present work, the functional As square lattice was realized and activated in Li0.6 Sn2 As2 and NaSnAs through a topotactic structural transformation of trigonal SnAs3 to square SnAs4 under pressure, resulting in a record-high Tc among all synthesized SnAs-based compounds. Meanwhile, the conductive channel transfers from the out-of-plane pz orbital to the in-plane px +py orbitals, facilitating electron hopping within the square 2D lattice and boosting the superconductivity. The reorientation of p-orbital following a directed local structure transformation provides an effective strategy to modify layered superconducting systems.

Topological transformation and free-space transport of photonic hopfions

Structured light fields embody strong spatial variations of polarization, phase, and amplitude. Understanding, characterization, and exploitation of such fields can be achieved through their topological properties. Three-dimensional (3D) topological solitons, such as hopfions, are 3D localized continuous field configurations with nontrivial particle-like structures that exhibit a host of important topologically protected properties. Here, we propose and demonstrate photonic counterparts of hopfions with exact characteristics of Hopf fibration, Hopf index, and Hopf mapping from real-space vector beams to homotopic hyperspheres representing polarization states. We experimentally generate photonic hopfions with on-demand high-order Hopf indices and independently controlled topological textures, including Néel-, Bloch-, and antiskyrmionic types. We also demonstrate a robust free-space transport of photonic hopfions, thus showing the potential of hopfions for developing optical topological informatics and communications.