Robust Boundary Research Articles

Topological Flatband Loop States in Fractal‐Like Photonic Lattices

AbstractNoncontractible loop states (NLSs) are a recently realized topological entity in flatband lattices, arising typically from the band touching at a point where a flat band intersects one or more dispersive bands. There exists also band touching across a plane, where one flat band overlaps another all over the Brillouin zone without crossing a dispersive band. Such isolated plane‐touching flat bands remain largely unexplored. For example, what are the topological features associated with such flatband degeneracy? Here, nontrivial NLSs and robust boundary modes in a system with such degeneracy are demonstrated. Based on a tailored photonic lattice constructed from the well‐known fractal Sierpinski gasket, the wavefunction singularities and the conditions for the existence of the NLSs are theoretically analyzed. It is shown that the NLSs can exist in both singular and nonsingular flat bands, as a direct reflection of the real‐space topology. Experimentally, directly such flatband NLSs in a laser‐written Corbino‐shaped fractal‐like lattice are observed. This work not only leads to a deep understanding of the mechanism behind the nontrivial flatband states, but also opens up new avenues to explore fundamental phenomena arising from the interplay of flatband degeneracy, fractal structures, and band topology.

Compact localized boundary states in a quasi-1D electronic diamond-necklace chain

Zero-energy modes localized at the ends of one-dimensional (1D) wires hold great potential as qubits for fault-tolerant quantum computing. However, all the candidates known to date exhibit a wave function that decays exponentially into the bulk and hybridizes with other nearby zero-modes, thus hampering their use for braiding operations. Here, we show that a quasi-1D diamond-necklace chain exhibits an unforeseen type of robust boundary state, namely compact localized zero-energy modes that do not decay into the bulk. We find that this state emerges due to the presence of a latent symmetry in the system. We experimentally realize the diamond-necklace chain in an electronic quantum simulator setup.

Robust detection of headland boundary in paddy fields from continuous RGB-D images using hybrid deep neural networks

Accurate and robust headland boundary detection in the field is crucial for formulating turning strategies for agro-machinery. The headland area is challenging to be detected because of its similar appearance to the farmland, coupled with complex field conditions such as high weed pressure and discontinuous headland edges. In this study, a machine vision-based method for headland boundary detection was proposed, which introduced depth information in addition to RGB images to improve its detection accuracy. A deep learning-based network combining convolutional neural network (CNN) and recurrent neural network (RNN) was constructed for headland semantic segmentation. An interactive attention module (IAM) was proposed to fuse complementary information in RGB-D images adaptively. A time series information processing module (TPM) composed of a set of bidirectional convolution long short-term memories (ConvLSTMs) was used to extract interrelated information from consecutive images. Image preprocessing techniques and a proposed distance-based boundary point clustering algorithm were applied to the headland segmentation mask to obtain the boundary line on the working side of the agro-machinery. Ablation study results confirmed the effectiveness of IAM and TPM in improving the headland segmentation performance. The network presented achieved excellent headland segmentation performance, with a mean intersection over union (mIoU) of up to 95.7%. The mean deviation of boundary line extraction on 256*144 resolution images was 3.57 pixels. The detection rate reached 25.8 frames per second (FPS), which could provide real-time reference lines for agro-machinery turning path planning.

PbI6 Octahedra Stabilization Strategy Based on π‐π Stacking Small Molecule Toward Highly Efficient and Stable Perovskite Solar Cells

AbstractThe unavoidable iodine loss in the perovskite layer is closely related to carrier non‐radiative and device degradation. During the post‐annealing process, the fragile PbI bond is easy to break, leading to the formation of iodine vacancies and inducing stress‐driven structure collapse. Herein, a PbI6 octahedra stabilization strategy via building robust grain boundary modification networks is developed. The introduction of conjugated structure into amides can significantly enhance their anchoring ability with PbI units, while the π–π stacking effect of benzamide enables a passivation network with polymer‐like effect. This is well evidenced by the excellent properties in eliminated iodine loss and stabilized perovskite lattice. Therefore, benzamide modification not only transform the perovskite films from n‐type to p‐type by suppressing the iodine vacancy‐doping effect, but also reduces defect density, ultimately bringing the perovskite layer longer carrier diffusion length and better charge injection efficiency. Finally, the benzamide modified devices realize both high power conversion efficiency of 24.78% and excellent operating stability. Of particular note, the module efficiency with 14 cm2 active area is over 21%.

Methodological Approach in the Simulation of the Robustness Boundaries of Tribosystems under the Conditions of Boundary Lubrication

In the presented work, a methodical approach was developed for determining rational operation modes of tribosystems, taking into account their design. This approach makes it possible in the designing stage, according to the predicted operating modes, to calculate the limits and margins of stable work in operation. The definition of the robustness of the tribosystem and the criteria for assessing the robustness are formulated based on the theory of stability of technical systems. It is shown that such a methodical approach allows for determining the modes of the rational operation of the designed structures without damaging the friction surfaces. Experimental studies have proven that not all designs of tribosystems lose stability due to the appearance of friction surface burrs. There are designs where the loss of stability occurs upon the appearance of accelerated wear. The developed criteria take into account two options for the loss of stability. An experimental verification of the modes of loss of stability of tribosystems was performed by the appearance of a burr or the beginning of accelerated wear with the calculated values of the robustness criteria. The obtained results allow us to conclude that the modeling error is within 8.3–18.7%, which is a satisfactory result in the study of friction and wear processes. Robustness criteria is based on the coefficient of friction RRf and wear rate RRI, and must be used when designing new constructions of tribosystems. Theoretical calculations of such criteria and the dependence of their change on changing the predicted operating modes will allow for justifying rational operating modes within their stability.

Robust Boundary Controller Design with Proportional Integral Observer for a Linear 1D Heat Equation*

The problem of state estimation with boundary disturbance reconstruction and output regulation for linear 1D parabolic systems with a boundary measurement and unknown constant disturbance input on the opposite boundary is addressed. As the disturbance is unmatched it cannot be directly compensated by the measurement. The problem is addressed with an approach that consists of a backstepping observer for the nominal part with an asymptotic compensation term for the disturbance reconstruction and control offset compensation. The main difference to similar studies relies in the fact that the state space does not need to be extended, leading to a reduced-order observer setup. The effectiveness of the approach is illustrated using numerical simulations.

Multi-Representation Domain Adaptation Network with Duplex Adversarial Learning for Hot-Rolling Mill Fault Diagnosis.

The multi-process manufacturing of steel rolling products requires the cooperation of complicated and variable rolling conditions. Such conditions pose challenges to the fault diagnosis of the key equipment of the rolling mill. The development of transfer learning has alleviated the problem of fault diagnosis under variable working conditions to a certain extent. However, existing diagnosis methods based on transfer learning only consider the distribution alignment from a single representation, which may only transfer part of the state knowledge and generate fuzzy decision boundaries. Therefore, this paper proposes a multi-representation domain adaptation network with duplex adversarial learning for hot rolling mill fault diagnosis. First, a multi-representation network structure is designed to extract rolling mill equipment status information from multiple perspectives. Then, the domain adversarial strategy is adopted to match the source and target domains of each pair of representations for learning domain-invariant features from multiple representation networks. In addition, the maximum classifier discrepancy adversarial algorithm is adopted to generate target features that are close to the source support, thereby forming a robust decision boundary. Finally, the average value of the predicted probabilities of the two classifiers is used as the final diagnostic result. Extensive experiments are conducted on an experimental platform of a four-high hot rolling mill to collect the fault state data of the reduction gearbox and roll bearing. The experimental results reveal that the method can effectively realize the fault diagnosis of rolling mill equipment under variable working conditions and can achieve average diagnostic rates of up to 99.15% and 99.40% on the data sets of the rolling mill gearbox and bearing, which are respectively 2.19% and 1.93% higher than the rates achieved by the most competitive method.

Robust Boundary Extension effects with different picture sets, set sizes, and presentation times

Robust Boundary Extension effects with different picture sets, set sizes, and presentation times

Demonstration of Robust Boundary Modes in Photonic Decorated Honeycomb Lattices

AbstractThe decorated honeycomb lattices (DHLs) represent a typical model that evinces nontrivial chiral spin liquid and rich topological insulating phases in condensed matter physics, yet in natural materials such lattice structures are not commonly found. Here, a photonic DHL that exhibits two singular flat bands is experimentally demonstrated, thereby observing two distinct robust boundary modes (RBMs) associated with each flat band. These RBMs rely on specially tailored open boundaries in the flatband lattice with wavefunction singularities due to band‐touching, manifesting topological noncontractible loop states that cannot be simply constructed from superposition of conventional flatband states. The robustness of such boundary modes to perturbations is also examined, corroborated by numerical simulations and theoretical analysis. This work illustrates a photonic platform exhibiting Dirac cones, singular band‐touching and multiple flat bands that may be employed to study exotic flatband phenomena and topological insulating phases in optics and beyond.

Tailoring microenvironment for enhanced electrochemical CO2 reduction on ultrathin tin oxide derived nanosheets

Electrocatalytic CO2 reduction powered by renewable electricity has been considered as a promising approach for sustainable energy storage and chemicals production. Herein, ultrathin few-layer SnO2 nanosheets exposed with (001) facets were synthesized and exhibited a rather broad potential window (0.8 V) for selective CO2 conversion to formate. Both DFT calculations and operando spectroscopic characterizations were carried out to identify key intermediate *OCHO. Systematically tailoring microenvironment in the catalyst layer of gas diffusion electrode (GDE) indicate that both flexible Nafion and solid polytetrafluoroethylene (PTFE) nanoparticles are essential to create abundant and robust triple-phase boundaries (TPB) with more active sites, where CO2 and H2O meet at nanosheet surface to output a high formate partial current density of 380 mA·cm-2 with the selectivity of 88.4%. Moreover, such novel Nafion/PTFE/SnO2 TPB porous structures above largely enhance the single-pass carbon efficiency up to 29.3% in 1 M KOH. This study implies that engineering TPB active sites is an effective approach to the design of advanced CO2 electrolyzers.

Robust modified partial internal model control for stable, unstable and integrating processes

ABSTRACT For open-loop stable processes, the internal model control (IMC) provides a simple and effective parameterisation of stabilising controllers. However, for unstable processes, it cannot be directly used for control system implementation. In this paper, a new unified approach for the IMC design is proposed for stable, unstable and integrating processes, using the modified IMC (m-IMC) structure in which an additional controller is introduced along with the basic IMC. Also, the partial IMC (PIMC) concept is utilised, wherein we write the plant as the summation of stable and unstable parts and consider only the stable part as the internal model. The combined approach is thereby referred to as modified partial IMC (m-PIMC). This paper presents a graphical method to obtain controller parameters for the proposed m-PIMC to satisfy the given gain margin () and phase margin () specifications. Further, stability boundary and robust boundary for the controller parameters are obtained which respectively give a set of all controller parameters stabilising the close loop and a set of all controller parameters ensuring robust stability. Seven different well-known standard stable, unstable and integrating process models are considered for the proposed m-PIMC design, and simulation examples are given for four selected plant models.

Cell segregation via differential collision modes between heterotypic cell populations.

In tissue development and regeneration, the establishment of sharp boundaries between heterotypic cells is essential for the differentiation of tissue functions. During the dynamic rearrangements of constituent cells that result from cell division and collective migration, the segregation boundary encounters various challenges. Several studies have suggested that cortical actomyosin structures play a crucial role in the maintenance of the boundary interface of segregated cell populations, implicating actin-mediated stresses. Examining physical cellular properties such as motility, traction, and intercellular stress, we investigated the formation and maintenance of the stable segregation between epithelial and mesenchymal cell populations devoid of heterotypic adhesions. At the contact boundary, the homotypic adhesion-mediated epithelial aggregates exerted collision-mediated compression against the surrounding mesenchymal cells. Our results demonstrated that heterotypic cell populations established a robust interfacial boundary by accumulating stress from active collisions and repulsions between two dissimilar cell types. Furthermore, the moment of the heterotypic collisions was identified by the existence of a sharp rise in maximum shear stress within the cell cluster.

Universal higher-order bulk-boundary correspondence of triple nodal points

Triple nodal points are degeneracies of energy bands in momentum space at which three Hamiltonian eigenstates coalesce at a single eigenenergy. For spinless particles, the stability of a triple nodal point requires two ingredients: rotational symmetry of order three, four, or six; combined with mirror or space-time-inversion symmetry. However, despite ample studies of their classification, robust boundary signatures of triple nodal points have until now remained elusive. In this work, we first show that pairs of triple nodal points in semimetals and metals can be characterized by Stiefel-Whitney and Euler monopole invariants, of which the first one is known to facilitate higher-order topology. Motivated by this observation, we then combine symmetry indicators for corner charges and for the Stiefel-Whitney invariant in two dimensions with the classification of triple nodal points for spinless systems in three dimensions. The result is a complete higher-order bulk-boundary correspondence, where pairs of triple nodal points are characterized by fractional jumps of the hinge charge. We present minimal models of the various species of triple nodal points carrying higher-order topology, and illustrate the derived correspondence on ${\mathrm{Sc}}_{3}\mathrm{AlC}$ which becomes a higher-order triple-point metal in applied strain. The generalization to spinful systems, in particular to the WC-type triple-point material class, is briefly outlined.

Uncertainty Quantification and Optimal Robust Design for Machining Operations

Abstract In this study, we carry out robust optimal design for the machining operations, one key process in wafer polishing in chip manufacturing, aiming to avoid the peculiar regenerative chatter and maximize the material removal rate (MRR) considering the inherent material and process uncertainty. More specifically, we characterize the cutting tool dynamics using a delay differential equation (DDE) and enlist the temporal finite element method (TFEM) to derive its approximate solution and stability index given process settings or design variables. To further quantify the inherent uncertainty, replications of TFEM under different realizations of random uncontrollable variables are performed, which however incurs extra computational burden. To eschew the deployment of such a crude Monte Carlo (MC) approach at each design setting, we integrate the stochastic TFEM with a stochastic surrogate model, stochastic kriging, in an active learning framework to sequentially approximate the stability boundary. The numerical result suggests that the nominal stability boundary attained from this method is on par with that from the crude MC, but only demands a fraction of the computational overhead. To further ensure the robustness of process stability, we adopt another surrogate, the Gaussian process, to predict the variance of the stability index at unexplored design points and identify the robust stability boundary per the conditional value at risk (CVaR) criterion. Therefrom, an optimal design in the robust stable region that maximizes the MRR can be identified.

Robust non-fragile boundary control for non-linear parabolic PDE systems with semi-Markov switching and input quantization

In this paper, the robust boundary control problem for non-linear PDE systems is discussed. Specifically, the PDE under investigation is of parabolic type with semi-Markov jumping signals subject to non-linearities and parameter uncertainties. The main goal of this paper is to devise a non-fragile boundary control law which assures the robust stabilization of the addressed system in spite of gain fluctuations and quantization in its design. In particular, to reduce the burden in the communication medium, the input signals can be quantized before transmitted to the actuator by using logarithmic quantizers. Moreover, by utilizing the Lyapunov stability theory and vector-valued Wirtinger’s inequality, a set of sufficient conditions for robust stabilization of the underlying system is established in the form of linear matrix inequalities (LMIs). Based on the obtained conditions, the existence of the desired controller is confirmed and an explicit form of the controller gains are developed. Eventually, the efficacious of the extracted theoretical results are manifested by virtue of two simulation examples.

Adaptive–adaptive robust boundary control for uncertain mechanical systems with inequality constraints

Adaptive–adaptive robust boundary control for uncertain mechanical systems with inequality constraints

Exceptional mode topological surface laser

Band topology has been studied as a design principle of realizing robust boundary modes. Here, by exploring non-Hermitian topology, we propose a three-dimensional topological laser that amplifies surface modes. The topological surface laser is protected by nontrivial topology around branchpoint singularities known as exceptional points. In contrast to two-dimensional topological lasers, the proposed three-dimensional setup can realize topological boundary modes without judicious gain at the edge or symmetry protection, which are thus robust against a broad range of disorders. We also propose a possible optical setup to experimentally realize the topological surface laser. Our results provide a general guiding principle to construct non-Hermitian topological devices in three-dimensional systems.

Robust boundary formation in a morphogen gradient via cell-cell signaling.

Establishing sharp and correctly positioned boundaries in spatial gene expression patterns is a central task in both developmental and synthetic biology. We consider situations where a global morphogen gradient provides positional information to cells but is insufficient to ensure the required boundary precision, due to different types of noise in the system. In a conceptual model, we quantitatively compare three mechanisms, which combine the global signal with local signaling between neighboring cells, to enhance the boundary formation process. These mechanisms differ with respect to the way in which they combine the signals by following either an AND, an OR, or a SUM rule. Within our model, we analyze the dynamics of the boundary formation process, and the fuzziness of the resulting boundary. Furthermore, we consider the tunability of the boundary position and its scaling with system size. We find that all three mechanisms produce less fuzzy boundaries than the purely gradient-based reference mechanism, even in the regime of high noise in the local signals relative to the noise in the global signal. Among the three mechanisms, the SUM rule produces the most accurate boundary. However, in contrast to the other two mechanisms, it requires noise to exit metastable states and rapidly reach the stable boundary pattern.

Robust boundary of stability and design of robust controller in uncertain polytopic linear systems

Abstract This paper is devoted to design of a robust controller for an uncertain continuous-time linear polytopic system. The design procedure will take place in two steps. In the first step, we calculate the robust stability boundary of a closed loop system. Then on the basis of the result obtained in this way, we select a robust controller design method that accepts the calculated stability boundary. This procedure allows better implementation of the second step of the designed robust controller. Two examples of application of the proposed method follow finally, which illustrate its effectiveness.

Exponential Stabilization of Reaction–Diffusion Systems Via Intermittent Boundary Control

Exponential stabilization is studied for reaction–diffusion systems (RDSs) with a reaction term satisfying the global Lipschitz condition by means of intermittent boundary control.First, a state-dependent intermittent boundary controller is designed when system states are available. By employing the spatial integral functional method and Poincaré’s inequality, a sufficient condition ensuring exponential stability of RDSs is presented. Then, an observer is presented to estimate the system states based on boundary output, when the information of system states is not fully accessible. An observer-based intermittent boundary controller is provided aiming to stabilize the considered RDSs based on the designed observer. Furthermore, a robust observer-based intermittent boundary controller is proposed to ensure the exponential stability for RDSs with uncertainties. Examples are given to illustrate the effectiveness of results.