Flat Topology Research Articles

Compact Topological Edge States in Flux-Dressed Graphenelike Photonic Lattices.

Flat band lattice systems promote the appearance of perfectly compact bulk states, whereas topology favors edge localization. In this work, we report the existence of compact topological edge states on flux-dressed photonic graphene ribbons. We found that robust localization is achieved through a synergy of Aharonov-Bohm caging and topological protection mechanisms. The topological nontriviality of the compact edge states is characterized through both theoretical derivations and experimental observations of an integer Zak phase obtained from the mean chiral displacement. Experiments are performed using direct laser writing of a graphene ribbon photonic lattice having 0 or π effective magnetic fluxes. Mode stability is demonstrated by the exceptional localization of the edge compact mode and its resilience to fabrication tolerances and input phase deviations. Our findings demonstrate the existence of perfectly compact topological edge states, as a concrete and promising example of synergy in between flat band physics and topology.

Malicious Node Detection Using Machine Learning and Distributed Data Storage Using Blockchain in WSNs

Abstract: Wireless Sensor Networks (WSNs) present unique opportunities for a broad spectrum of applications such as industrial automation, situation awareness, tactical surveillance for military applications, environmental monitoring, chemical or biological detection etc., Wireless Sensor Networks (WSNs) consist of hundreds of tiny nodes having the capability of sensing, computation and wireless communications. Deployed in a hostile environment, individual nodes of a wireless sensor network (WSN) could be easily compromised by the adversary due to the constraints such as limited battery lifetime, memory space and computing capability. It is critical to detect and isolate the compromised nodes in order to avoid being misled by the falsified information injected by the adversary through compromised nodes. However, it is challenging to secure the flat topology networks efficiently because of the poor scalability and high communication overhead. Since security and performance issues are a big concern in the case of wireless sensor networks, emphasis has been given to the scheme based on Weighted-Trust Evaluation (WTE). Extensive simulation is performed using MATLAB, to verify performance and efficiency of WTE by varying various parameters

Trusted Head Node for Node Behaviour Analysis for Malicious Node Detection in Wireless Sensor Networks

There has been a rise in the use of Wireless Sensor Networks (WSNs) in several fields. Depending on the malicious actions, attacks on WSN can take many forms. This research demonstrates how to leverage request and response data from each node to pinpoint the location of malicious nodes. If a node is malevolent, it will prohibit data from being sent to other nodes. They do an excellent job of pretending to be someone else. To enhance route quality, packet dropping can be used to perform a Denial of Service (DoS) assault by rejecting data packets and cutting them off from their destinations. The primary goal of this research is to expose malicious nodes within the network. To avoid being attacked by the false information fed by the adversary through compromised nodes, it is crucial to discover and isolate the nodes that have been compromised. Unfortunately, flat topology networks are difficult to keep safe because of their limited scalability and substantial communication overhead. By computing the packet drop and throughput values with valid nodes, efficient security architecture for the WSN can be proposed, allowing for the detection of malicious activity. If sensor networks are susceptible to attacks, they will be unable to fulfill their duty in a variety of event detection applications. Malicious nodes can cause unacceptable drops in event detection effectiveness and spikes in false alarm rates by producing fake readings and deceptive information. In this research, a method for identifying malicious nodes in WSNs is proposed. This research considers a Trusted Head Node (THN) for monitoring the nodes behaviour in the network to detect the malicious actions in the network. This research proposes a Trusted Head Node for Node Behaviour Analysis for Malicious Node Detection (THN-NBA-MND) in WSN. The proposed model based on node behavior analysis in frequent time intervals; detect the malicious nodes to improve the network performance in data transmission. The proposed model when contrasted with the existing model performs better in malicious node detection.

Reinforcement learning-based resilient power maximization and regulation control for large-scale wind turbines under cyber actuator attacks

Large-scale wind turbine systems (LS-WTSs) are vulnerable to cyber threats due to their flat control network topology, fragile protocols, and remote locations. To solve these security problems and improve electrical efficiency, this study aims to present a reinforcement learning (RL)-based attack-resilient coordinated pitch and torque control for LS-WTS under actuator attacks. The proposed scheme utilizes the RL technique to reduce the number of tuning parameters and computational complexity. To do this, a model-free agent-environment framework is first proposed with an aperiodic denial-of-service (ADoS) attack model to enable the RL features. Then, an RL-based resilient sliding-mode pitch and torque control scheme is proposed to optimize maximum power extraction and regulation by incorporating reward updates and adaptive learning rates for optimal control input selection under ADoS attacks with varying wind conditions. At the same time, the adaptive learning-rule-based gain fluctuations term is presented to mitigate the uncertain and disruption parameters in the control system. Finally, the effectiveness and robustness of the proposed method are verified through the evaluation of a 4.8MW benchmark and a 20MW PMSG-based LS-WTS, showing distinct advantages over conventional approaches. Theoretical insights are practically validated with experimental prototypes to confirm the resiliency of the presented method against network and physical impacts caused by cyber actuator attacks in the LS-WTS in various wind cases.

Surface modification of Polyether-ether-ketone for enhanced cell response: a chemical etching approach.

Polyether-ether-ketone (PEEK) is increasingly becoming popular in medicine because of its excellent mechanical strength, dimensional stability, and chemical resistance properties. However, PEEK being bioinert, has weak bone osseointegration properties, limiting its clinical applications. In this study, a porous PEEK structure was developed using a chemical etching method with 98wt% sulfuric acids and three post-treatments were performed to improve bone cell adhesion and proliferation. Four groups of PEEK samples were prepared for the study: Control (untreated; Group 1); Etched with sulfuric acid and washed with distilled water (Group 2); Etched with sulfuric acid and washed with acetone and distilled water (Group 3); and Etched with sulfuric acid and washed with 4wt% sodium hydroxide and distilled water (Group 4). Surface characterization of the different groups was evaluated for surface topology, porosity, roughness, and wettability using various techniques, including scanning electron microscopy, profilometer, and goniometer. Further chemical characterization was done using Energy-dispersive X-ray spectroscopy to analyze the elements on the surface of each group. Bone cell studies were conducted using cell toxicity and alkaline phosphatase activity (ALP) assays. The SEM analysis of the different groups revealed porous structures in the treatment groups, while the control group showed a flat topology. There was no statistically significant difference between the pore size within the treated groups. This was further confirmed by the roughness values measured with the profilometer. We found a statistically significant increase in the roughness from 7.22 × 10-3μm for the control group to the roughness range of 0.1µm for the treated groups (Groups 2-4). EDX analysis revealed the presence of a 0.1% weight concentration of sodium on the surface of Group 4, while sulfur weight percentage concentration was 1.1%, 0.1%, and 1.4% in groups 2, 3, and 4, respectively, indicating different surface chemistry on the surface due to different post-treatments. Cell toxicity decreased, and ALP activity increased in groups 3 and 4 over 7days compared with the control group. It is demonstrated that the surface modification of PEEK using a chemical etching method with post-processing with either acetone or sodium hydroxide provides a nano-porous structure with improved properties, leading to enhanced osteoblastic cell differentiation and osteogenic potential.

Compact and Wideband Flat Negative Group Delay Circuit Investigation

This paper introduces a dual transmission structure with bandpass (BP) negative group delay (NGD) wideband flat behavior. The flat BP-NGD topology is analytically modelled from equivalent circuit composed of transmission line (TL) and stepped-impedance resonator connected by two resistors. As proof of concept (POC), by tuning TL characteristic impedances, the influences of circuit physical variables on NGD flatness are illustrated by parametric study. The flat BP-NGD POC circuit with a size of 48.2 mm×90.8 mm (0.2λg 0.38λg) is designed, fabricated, and measured. A very good agreement is confirmed by simulation and experimentation results of 680 MHz over 290 MHz (42.6%) NGD bandwidth (BW) around 0.7 GHz NGD center frequency. Also, the flat BP-NGD BW reaches 223 MHz (31.8%) over 569 MHz to 792 MHz with ±0.05 ns group-delay fluctuation with insertion and reflection losses better than 14 dB.

Widening the Landscape of Small Molecule Activation with Gold-Aluminyl Complexes: A Systematic Study of E-H (E=O, N) Bonds, SO2 and N2 O Activation.

The electronic features of gold-aluminyl complexes have been thoroughly explored. Their similarity with Group 14 dimetallenes and other metal-aluminyl complexes suggests that their reactivity with small molecules beyond carbon dioxide could be accessed. In this work, the reactivity of the [t Bu3 PAuAl(NON)] (NON=4,5-bis(2,6 diisopropylanilido)-2,7-ditert-butyl-9,9-dimethylxanthene) complex towards water, ammonia, sulfur dioxide and nitrous oxide is computationally explored. The reaction mechanisms computed for each substrate strongly suggest that all activation processes are in principle experimentally feasible. Electronic structure analysis highlights that, in all cases, the reactivity is driven by the presence of the poorly polarized electron-sharing gold-aluminyl bond, which induces a radical-like reactivity of the complex towards all the substrates. A flat topology of the potential energy surface (PES) has been found for the reaction with N2 O, where two almost isoenergetic transition states can be located along the same reaction coordinate with different geometries, suggesting that the N2 O binding mode may not be a good indicator of the nature of N2 O activation in a cooperative bimetallic reactivity. In addition, the catalytic potentialities of these complexes have been explored in the framework of nitrous oxide reduction. The study reveals that the [t Bu3 PAuAl(NON)] complex might be an efficient catalyst towards oxidation of phosphines (and boranes) via N2 O reduction. These findings underline recurring trends in the novel chemistry of gold-aluminyl complexes and call for experimental feedbacks.

Spectroscopic evidence of flat bands in breathing kagome semiconductor Nb3I8

Kagome materials have become solid grounds to study the interplay among geometry, topology, correlation, and magnetism. Recently, niobium halide semiconductors Nb3X8 (X = Cl, Br, I) have been predicted to be two-dimensional magnets and these materials are also interesting for their breathing kagome geometry. However, experimental electronic structure studies of these promising materials are still lacking. Here, we report the spectroscopic evidence of flat and weakly dispersing bands in breathing-kagome semiconductor Nb3I8 around 500 meV binding energy, which is well supported by our first-principles calculations. These bands originate from the breathing kagome lattice of niobium atoms and have niobium d-orbital character. They are found to be sensitive to the polarization of the incident photon beam. Our study provides insight into the electronic structure and flat band topology in an exfoliable kagome semiconductor, thereby providing an important platform to understand the interaction of geometry and electron correlations in two-dimensional materials.

The structure, optical properties and photovoltaic effect in Langmuir-Schaefer films of nickel (II) bis-semiquinone complex derived from 3,6-di‑tert‑butyl‑benzoquinone annulated with a 1,3 -dithiole-2-thiocarbonyl fragment

Molecules with an extended conjugated π-electron system and a flat rigid topology have traditionally been considered as appropriate candidates for organic (semi-)conductors. With their potential for intramolecular charge transfer, these molecules can have bright prospects in optoelectronic device manufacturing. In this work we describe a novel bis-semiquinone complex of nickel and о-quinone annulated with a 1,3-dithiol-2-thiocarbonyl fragment and the peculiarities of thin-film deposition of this compound on different substrates. It is shown that a thin film can maintain the crystal structure of the original complex. A photovoltaic effect is detected in sandwich structures with an aluminum cathode. It is anticipated that further optimization of the structure of such sulfur-rich molecules will prodive solid-state ensembles with promising photovoltaic and/or photodetecting properties.

Strong interlayer coupling and stable topological flat bands in twisted bilayer photonic Moiré superlattices

The moiré superlattice of misaligned atomic bilayers paves the way for designing a new class of materials with wide tunability. In this work, we propose a photonic analog of the moiré superlattice based on dielectric resonator quasi-atoms. In sharp contrast to van der Waals materials with weak interlayer coupling, we realize the strong coupling regime in a moiré superlattice, characterized by cascades of robust flat bands at large twist-angles. Surprisingly, we find that these flat bands are characterized by a non-trivial band topology, the origin of which is the moiré pattern of the resonator arrangement. The physical manifestation of the flat band topology is a robust one-dimensional conducting channel on edge, protected by the reflection symmetry of the moiré superlattice. By explicitly breaking the underlying reflection symmetry on the boundary terminations, we show that the first-order topological edge modes naturally deform into higher-order topological corner modes. Our work pioneers the physics of topological phases in the designable platform of photonic moiré superlattices beyond the weakly coupled regime.

Magic angles and flat Chern bands in alternating-twist multilayer graphene system

Based on the effective continuum model, we study alternating-twist multilayer graphene system and emergence of magic angles and flat band topology. All the alternating-twist multilayer graphene system (from triple layers to few layers) are found to have flat bands at magic angles where the area of AA stacking equals n-fold (n is an integer) electron cyclotron area. From the pseudo-Landau-level representation, there is always an isolated Dirac band in the alternating-twist graphene system constructed by odd number of layers. Since each pair of flat bands can be perceived as the zeroth pseudo-Landau-levels in two dimensional Dirac fermions, electron in the flat band pair can feel a pseudo-magnetic field with the same magnitude but the opposite sign. Calculated Chern number for each flat band is +1 (or -1) which can be tuned by twisting in the vicinity of magic angles or by gating. The concurrent appearance of strong correlation and band topology of flat bands in the alternating-twist multilayer graphene may pave an avenue for the new understanding of superconductivity observed in triple-layered graphene, and supply a new playground for realizing (quantum) anomalous Hall effect.

Optimization and Simulation of a Dynamic Management System for Building Construction Based on Low-Power Wireless Sensor Networks

In this paper, we use a low-power wireless sensor network to conduct in-depth research and analysis on the optimization simulation of the dynamic management system of building construction and study the specific application of BIM technology in the information management of building construction sites. By analysing the classical delustering routing and combining the advantages in the delustering routing protocols, we propose a two-level Mesh wireless sensor network delustering routing protocol in terms of cluster head uniformity, energy consumption and balance, working mode, and handling of isolated nodes. The most important feature of this protocol compared to other delustering protocols is that it retains the design of flat network topology and designs three routing methods with the corresponding functions of wireless sensor networks to achieve better network performance. The supported personnel location technology and construction measures and environmental monitoring technology are introduced, the applicability of the technology in the building construction process is compared and analysed, the topology of construction measures and environmental monitoring technology is designed, and finally, the targeted development of the collection scheme for personnel, scaffolding, formwork, pits, cranes, construction hoists, and physical environment is completed. Firstly, it analyses the development status of BIM-based building construction site information management technology and application and discusses the basis of BIM technology implementation and the advantages of BIM technology application in information management. Then, this paper constructs the framework of a BIM-based building construction site information management system from three dimensions: functional, logical, and physical. To ensure the realizability and operability of the system, this paper discusses the operation mechanism of the BIM-based building construction site information management system, studies the key technology of system operation, designs the basic operation process of each application system of the system, and elaborates the organizational structure of the building construction site and the functional division of the relevant personnel.

Microstructural Evaluation of Phase Instability in Large Bandgap Metal Halide Perovskites

The optoelectronic performance of organic-inorganic halide perovskite (OIHP)-based devices has been improved in recent years. Particularly, solar cells fabricated using mixed-cations and mixed-halides have outperformed their single-cation and single-halide counterparts. Yet, a systematic evaluation of the microstructural behavior of mixed perovskites is missing despite their known composition-dependent photoinstability. Here, we explore microstructural inhomogeneity in (FAPbI3)x(MAPbBr3)1-x using advanced scanning probe microscopy techniques. Contact potential difference (CPD) maps measured by Kelvin probe force microscopy show an increased fraction of grains exhibiting a low CPD with flat topography as MAPbBr3 concentration is increased. The higher portion of low CPD contributes to asymmetric CPD distribution curves. Chemical analysis reveals these grains being rich in MA, Pb, and I. The composition-dependent phase segregation upon illumination, reflected on the emergence of a low-energy peak emission in the original photoluminescence spectra, arises from the formation of such grains with flat topology. Bias-dependent piezo-response force microscopy measurements, in these grains, further confirm vigorous ion migration and cause a hysteretic piezo-response. Our results, therefore, provide insights into the microstructural evaluation of phase segregation and ion migration in OIHPs pointing toward process optimization as a mean to further enhance their optoelectronic performance.

COMPARISON OF KUMMER LOGARITHMIC TOPOLOGIES WITH CLASSICAL TOPOLOGIES

AbstractWe compare the Kummer flat (resp., Kummer étale) cohomology with the flat (resp., étale) cohomology with coefficients in smooth commutative group schemes, finite flat group schemes, and Kato’s logarithmic multiplicative group. We are particularly interested in the case of algebraic tori in the Kummer flat topology. We also make some computations for certain special cases of the base log scheme.

Inquiring electromagnetic quantum fluctuations about the orientability of space

Orientability is an important global topological property of spacetime manifolds. It is often assumed that a test for spatial orientability requires a global journey across the whole 3-space to check for orientation-reversing paths. Since such a global expedition is not feasible, theoretical arguments that combine universality of physical experiments with local arrow of time, CP violation and CPT invariance are usually offered to support the choosing of time- and space-orientable spacetime manifolds. Another theoretical argument also offered to support this choice comes from the impossibility of having globally defined spinor fields on non-orientable spacetime manifolds. In this paper, we argue that it is possible to locally access spatial orientability of Minkowski empty spacetime through physical effects involving quantum vacuum electromagnetic fluctuations. We study the motions of a charged particle and a point electric dipole subject to these electromagnetic fluctuations in Minkowski spacetime with orientable and non-orientable spatial topologies. We derive analytic expressions for a statistical orientability indicator for both of these point-like particles in two inequivalent spatially flat topologies. For the charged particle, we show that it is possible to distinguish the orientable from the non-orientable topology by contrasting the time evolution of the orientability indicators. This result reveals that it is possible to access orientability through electromagnetic quantum vacuum fluctuations. However, the answer to the central question of the paper, namely how to locally probe the orientability of Minkowski 3-space intrinsically, comes about only in the study of the motions of an electric dipole. For this point-like particle, we find that a characteristic inversion pattern exhibited by the curves of the orientability statistical indicator is a signature of non-orientability. This result makes it clear that it is possible to locally unveil spatial non-orientability through the inversion pattern of curves of our orientability indicator for a point electric dipole under quantum vacuum electromagnetic fluctuations. Our findings might open the way to a conceivable experiment involving quantum vacuum electromagnetic fluctuations to locally probe the spatial orientability of Minkowski empty spacetime.

Flow Characteristics of Preliminary Shutdown and Startup Sequences for a Model Counter-Rotating Pump-Turbine

Pumped Hydropower Storage (PHS) is the maturest and most economically viable technology for storing energy and regulating the electrical grid on a large scale. Due to the growing amount of intermittent renewable energy sources, the necessity of maintaining grid stability increases. Most PHS facilities today require a geographical topology with large differences in elevation. The ALPHEUS H2020 EU project has the aim to develop PHS for flat geographical topologies. The present study was concerned with the initial design of a low-head model counter-rotating pump-turbine. The machine was numerically analysed during the shutdown and startup sequences using computational fluid dynamics. The rotational speed of the individual runners was decreased from the design point to stand-still and increased back to the design point, in both pump and turbine modes. As the rotational speeds were close to zero, the flow field was chaotic, and a large flow separation occurred by the blades of the runners. Rapid load variations on the runner blades and reverse flow were encountered in pump mode as the machine lost the ability to produce head. The loads were less severe in the turbine mode sequence. Frequency analyses revealed that the blade passing frequencies and their linear combinations yielded the strongest pulsations in the system.

A new approach to the patch and flat topologies on a spectral space with applications

In this article, we use quite elementary and simple ideas to rebuild and study the patch and flat topologies on the prime spectrum from a natural point of view (this new approach is based on the significant applications of the power set ring). Especially, the proof of a major result in the literature on the comparison of topologies greatly simplified and shortened. Also a new characterization for the finiteness of the minimal primes of a ring is given. Then as an application, all of the related results of Kaplansky, Anderson, Gilmer-Heinzer, Bahmanpour-Khojali-Naghipour and Naghipour on the finiteness of the minimal primes are easily deduced as special cases of this result. Another finiteness result due to Matlis is also easily obtained which states that a given ring has finitely many minimal primes if and only if no minimal prime is contained in the union of the remaining minimal primes.

Flat winding made of aluminum or copper sheet for axial flux machines

A novel flat winding topology has been proposed as an alternative to conventional windings with stranded round wires and other bar wound windings. The proposed winding is manufactured from thin conductor sheets by industrial tools such as stamping press, laser cutter, or water jet. As these tools are widely used in the production of electric machines, the flat winding topology can provide ease of manufacturing without significant modification to the production line. Besides, superior current ratings, shortened end windings, and high fill factors are other advantages of flat winding. Its performance is measured by comparison study between flat wired prototype machine and the stranded wired machines with similar ratings presented in the literature. The proposed winding is implemented on an axial flux permanent magnet machine. Analytical modeling is presented, including field modeling, voltage, torque derivations, and loss modeling. Then, experimental verification of a 1.4-kW and 26-Nm prototype with copper and aluminum flat windings is presented, and the performances of two are compared.

Intra- and inter-cluster link scheduling in CUPS-based ad hoc networks

While control and user (data) plane separation (CUPS) through clustering improves the scalability of ad hoc networks in comparison to flat topologies, it introduces additional challenges for resource scheduling when contention-free medium access is employed. This paper addresses intra- and inter-cluster link scheduling problem in multi-channel ad hoc networks employing CUPS architecture. We first describe the CUPS architecture. Then, we present a novel intra- and inter-cluster link scheduling mechanism over the CUPS architecture. We propose a link scheduling strategy that is responsive to instant communication demands and available resources as a non-linear optimization problem, which is then reduced to a linear form by eliminating non-linearities in order to simplify the problem definition and enhance optimizer performance. The results of the optimizer show that the run time cost of the optimization function drastically increases by the parameter size growth. Therefore, we propose an iterative solution to decrease the running time. The adaptation of the iterative history-based approach makes the solution feasible and ensures near-optimal satisfaction and efficiency.

Logarithmic Structures of Fontaine-Illusie. II ---Logarithmic Flat Topology

This is Part II of the author's paper Logarithmic structures of Fontaine-Illusie. We discuss log flat topology and log flat descent. We study the first log flat cohomology $H^1(X_{\log, \text{fl}}, G)$ for various sheaves of groups $G$, for example, $G=GL_n$, finite flat commutative group schemes, the log multiplicative group $M^{\text{gp}}$, etc.