Topological Effects Research Articles

Engineering the thin film characteristics for optimal performance of superconducting kinetic inductance amplifiers using a rigorous modelling technique.

Background: Kinetic Inductance Travelling Wave Parametric Amplifiers (KITWPAs) are a variant of superconducting amplifier that can potentially achieve high gain with quantum-limited noise performance over broad bandwidth, which is important for many ultra-sensitive experiments. In this paper, we present a novel modelling technique that can better capture the electromagnetic behaviour of a KITWPA without the translation symmetry assumption, allowing us to flexibly explore the use of more complex transmission line structures and better predict their performance. Methods: In order to design a KITWPA with optimal performance, we investigate the use of different superconducting thin film materials, and compare their pros and cons in forming a high-gain low-loss medium feasible for amplification. We establish that if the film thickness can be controlled precisely, the material used has less impact on the performance of the device, as long as it is topologically defect-free and operating within its superconducting regime. With this insight, we propose the use of Titanium Nitride (TiN) film for our KITWPA as its critical temperature can be easily altered to suit our applications. We further investigate the topological effect of different commonly used superconducting transmission line structures with the TiN film, including the effect of various non-conducting materials required to form the amplifier. Results: Both of these comprehensive studies led us to two configurations of the KITWPA: 1) A low-loss 100 nm thick TiN coplanar waveguide amplifier, and 2) A compact 50 nm TiN inverted microstrip amplifier. We utilise the novel modelling technique described in the first part of the paper to explore and investigate the optimal design and operational setup required to achieve high gain with the broadest bandwidth for both KITWPAs, including the effect of loss. Conclusions: Finally, we conclude the paper with the actual layout and the predicted gain-bandwidth product of our KITWPAs.

Dual-Responsive Supramolecular Chiral Assemblies from Amphiphilic Dendronized Tetraphenylethylenes.

Supramolecular assembly of amphiphilic molecules in aqueous solutions to form stimuli-responsive entities is attractive for developing intelligent supramolecular materials for bioapplications. Here we report on the supramolecular chiral assembly of amphiphilic dendronized tetraphenylethylenes (TPEs) in aqueous solutions. Hydrophobic TPE moieties were connected to the hydrophilic three-fold dendritic oligoethylene glycols (OEGs) through a tripeptide proline-hydroxyproline-glycol (POG) to afford the characteristic topological structural effects of dendritic OEGs and the peptide linker. Both ethoxyl- and methoxyl-terminated dendritic OEGs were used to modulate the overall hydrophilicity of the dendronized TPEs. Their supramolecular aggregates exhibited thermoresponsive behavior that originated from the dehydration and collapse of the dendritic OEGs, and their cloud point temperatures (Tcps) were tailored by solution pH conditions. Furthermore, aggregation-induced fluorescent emission (AIE) from TPE moieties was used as an indicator to follow the assembly, which was reversibly tuned by temperature variation at different pH conditions. Supramolecular assemblies from these dendronized amphiphiles exhibited enhanced supramolecular chirality, which was dominated mainly by the interaction balance between TPE with dendritic OEG and TPE with POG moieties and was modulated through different solvation by changing solution temperature or pH conditions. More interestingly, ethoxyl-terminated dendritic OEG provided a much stronger shielding effect than its methoxyl-terminated counterpart to prevent amino groups within the peptide from protonation, even in strong acidic conditions, resulting in different responsive behavior to the solution temperature and pH conditions for these supramolecular aggregates.

Tuning of Single Mixed (Helical) Dislocations in Core-Shell van der Waals Nanowires.

Linear defects (dislocations) not only govern the mechanical properties of crystalline solids but they can also produce distinct electronic, thermal, and topological effects. Accessing this functionality requires control over the placement and geometry of single dislocations embedded in a small host volume to maximize emerging effects. Here we identify a synthetic route for rational dislocation placement and tuning in van der Waals nanowires, where the layered crystal limits the possible defect configurations and the nanowire architecture puts single dislocations in close proximity to the entire host volume. While homogeneous layered nanowires host single screw dislocations, the synthesis of radial nanowire heterostructures (here exemplified by GeS-Ge1-xSnxS monochalcogenide core-shell nanowires) transforms the defect into a mixed (helical) dislocation whose edge/screw ratio is tunable via the core-shell lattice mismatch. The ability to design nanomaterials with control over individual mixed dislocations paves the way for identifying the functional properties of dislocations and harnessing them in technology.

Thermochemistry of hybrid materials.

This paper is based on a lecture Navrotsky gave honouring the memory of Paul McMillan. It summarizes our recent findings in the thermodynamics of hybrid materials including metal organic frameworks (MOFs), polymer-derived ceramics (PDCs) and ionic organic-inorganic compounds. This work describes the main structure types and their corresponding thermodynamic stability, obtained from calorimetric measurements in our laboratory. The effects of linker substituent and framework topology on the thermodynamic stability of isostructural zeolitic imidazolate frameworks and other MOFs are discussed. The paper documents the effects of interdomain interaction and bonding speciation on the thermodynamic stability of various PDC compositions, including SiC, SiOC and SiCN systems. The paper further describes effects of different cations on the thermodynamic stability of selected ionic organic-inorganic compounds. Similarities and differences among these materials are emphasized. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 2)'.

The exceptional point of PT-symmetry metasurface: Topological phase studies and highly sensitive refractive index sensing applications

Exceptional points (EPs) are critical phase points in non-Hermitian systems, exhibiting fantastic physical phenomena and plenty of applications, such as unidirectional reflectionless and ultrahigh-sensitive detection of perturbations. Here, a non-Hermitian metasurface based on multilayers split-ring resonators (SRRs) is proposed with specific EP effects. By changing the angle of the SRRs and adjusting the geometric parameters of the metasurface, EPs are generated with topologically protected 2π-phase accumulation. A unique EP effect can be achieved in the THz region, and high-performance sensing of environment refractive index can be realized around the EP position. Therefore, this work demonstrates an EP-based sensing enhancement at non-Hermitian systems compared to Hermitian ones and paves the way for the design of high-performance THz sensors based on topological polaritonic effects.

Giant Atomic Swirl in Graphene Bilayers with Biaxial Heterostrain.

The study of moiré engineering started with the advent of van der Waals heterostructures in which stacking two-dimensional layers with different lattice constants leads to a moiré pattern controlling their electronic properties. The field entered a new era when it wasfound that adjusting the twist between two graphene layers led to strongly-correlated-electron physics and topological effects associated with atomic relaxation. Twist is now used routinely to adjust the properties of two-dimensional materials. Here, weinvestigate a new type of moiré superlattice in bilayer graphene when one layer is biaxially strained with respect to the other - so-called biaxial heterostrain. Scanning tunneling microscopy measurements uncover spiraling electronic states associated with a novel symmetry-breaking atomic reconstruction at small biaxial heterostrain. Atomistic calculations using experimental parameters as inputs reveal that a giant atomic swirl forms around regions of aligned stacking to reduce the mechanical energy of the bilayer. Tight-binding calculations performed on the relaxed structure show that the observed electronic states decorate spiraling domain wall solitons as required by topology. This study establishes biaxial heterostrain as an important parameter to be harnessed for the next step of moiré engineering in van der Waalsmultilayers. This article is protected by copyright. All rights reserved.

Topological effects of cosmic string on radial eigenvalue solution with Mie-type potential

Topological effects of cosmic string on radial eigenvalue solution with Mie-type potential

Rolling contact fatigue performance of M50 steel: A combined experimental and analytical approach to determine life

This article presents an experimental and analytical investigation into the rolling contact fatigue (RCF) performance of AISI M50 bearing steel across a range of Hertzian contact pressures (Ph=2.6GPa to 3.4GPa). RCF experiments were conducted using a ball-on-rod test rig at three contact pressures to experimentally establish the relationship between contact pressure (contact stress) and the RCF life of M50. Simultaneously, a previously developed continuum damage mechanics finite element (CDM-FE) model, employing the Fatemi-Socie critical plane approach as the failure criteria, was utilized to provide analytical predictions of RCF life. The CDM-FE model’s damage rate equation was calibrated using open literature AISI M50 bearing steel torsion stress life (SN) data. The CDM-FE model incorporated Voronoi tessellations to represent the material microstructure and capture the material topological effect on fatigue scatter. RCF simulations were conducted at seven contact pressures ranging from 1.0 GPa to 3.4 GPa in 0.4 GPa increments. Similar to the experimental results, the analytical RCF life data set yielded a relationship between contact pressure and simulation life for M50. Good corroboration is observed between the contact pressure – life relationships from the experimental and analytical RCF life data sets. This is significant as it supports the use of a hybrid approach combining experimental tools (e.g. torsion fatigue and ball-on-rod) and a CDM-FE computational model to efficiently assess the RCF performance of bearing materials.

Review and comparison of turbulent convective heat transfer in state-of-the-art 3D truss periodic cellular structures

To promote the development and application of periodic cellular structures (PCSs), this paper reviews and systematically compares the heat transfer and pressure drop of state-of-the-art 3D truss PCSs. Relative merits among these PCSs in the turbulent regime are clarified which have been fuzzy in the open literature. The topological and orientation effects on the thermo-fluids of the PCSs are also investigated. Twelve PCSs with the same height and porosity, separately in two different orientations, are evaluated by numerical simulations. These PCSs include the cubic lattice (CL), the body-centered cubic lattice (BCCL), the face-centered cubic lattice (FCCL), octet lattice (OL), circular pyramid lattice (CPL), rectangular pyramidal lattice (RPL), tetrakaidecahedron lattice (TL), X-lattice (XL), shifted X-lattice (SXL), circular tetrahedral lattice (CTL), rectangular tetrahedral lattice (RTL), and Kagome lattice (KL). It is found that the entry and exit effects on heat transfer and pressure drop are limited within the first four unit cells and the last unit cell, respectively. For a given Reynolds number within the range of 2692–11087, the SXL in orientation A (SXL-OA in abbreviation) exhibits the best overall heat transfer; and the SXL-OA also has the best endwall heat transfer. In addition, the OL-OA, XL-OA and SXL-OA show the best heat transfer on the PCS core. In terms of pressure drop for a given Reynolds number, the RTL-OA and RTL-OB exhibits the highest and the lowest pressure drop, respectively. For a given pumping power, the OL exhibits the best overall heat transfer. Thermo-fluidic mechanisms are also explored with representative PCSs. For the given porosity and range of Reynolds number, correlations for overall heat transfer, local heat transfer and pressure drop are presented, which are beneficial for engineers to quickly evaluate and compare the PCSs made of different materials. The systematic comparison in the turbulent regime extends the comparison in the laminar regime in the open literature, which is expected to promote reasonable development and application of PCSs in heat exchangers and thermal management systems. Applications of PCSs in different scenarios and future work are also commented.

Existence and synchronization of coupled stochastic infinite-dimensional systems via aperiodically intermittent control

This paper analyzes a class of stochastic coupled systems with time-varying delays in infinite dimensions. The existence and uniqueness as a prerequisite to ensure synchronization of the solution is analyzed, based on the idea of the contraction mapping principle, graph theory, and mild Itô's formula. Next, the p-th moment exponential synchronization (PMES) of infinite-dimensional systems is realised using the discrete control strategy, namely, aperiodically intermittent control (AIC). By combining graph theory with the Lyapunov method, several criteria for synchronizing infinite-dimensional systems are obtained using the mild Itô's formula. These criteria show the effects of control parameters, topology, and time delays on PMES. Finally, the theoretical results are applied to a class of neural networks with reaction-diffusion, and some numerical simulations are also given.

Effects of zeolite framework topology on Cu(I) oxidation and Cu(II) reduction kinetics of NOx selective catalytic reduction with NH3

Effects of zeolite framework topology on Cu(I) oxidation and Cu(II) reduction kinetics of NOx selective catalytic reduction with NH3

The Effect of the Domain Topology on the Number of Positive Solutions for Fractional p-laplacian Equation with Critical Growth

The Effect of the Domain Topology on the Number of Positive Solutions for Fractional p-laplacian Equation with Critical Growth

Giant anomalous Hall and Nernst conductivities in cubic Fe3Pt and Ni3In

The topological anomalous Hall effect and the anomalous Nernst effect are of great interest for the development of spintronic devices for energy-efficient data storage and energy harvesting. Using first-principles calculations, we have studied the anomalous Hall conductivity (AHC) and anomalous Nernst conductivity (ANC) of six ferromagnetic compounds Co3Al, Fe3Ge, Fe3Pt, Ni3Ga, Ni3In, and Rh3Cr belonging to the cubic Cu3Au structure. A large AHC of 1973 S cm−1 is obtained for Fe3Pt. Parallel to the large AHC, a giant ANC of −5.41 A mK−1 and −4.18 A mK−1 is observed for Ni3In and Co3Al, respectively. Finally, we found that AHC and ANC can be adjusted by switching the magnetization direction.

Spatial organisation of the mesoscale connectome: A feature influencing synchrony and metastability of network dynamics.

Significant research has investigated synchronisation in brain networks, but the bulk of this work has explored the contribution of brain networks at the macroscale. Here we explore the effects of changing network topology on functional dynamics in spatially constrained random networks representing mesoscale neocortex. We use the Kuramoto model to simulate network dynamics and explore synchronisation and critical dynamics of the system as a function of topology in randomly generated networks with a distance-related wiring probability and no preferential attachment term. We show networks which predominantly make short-distance connections smooth out the critical coupling point and show much greater metastability, resulting in a wider range of coupling strengths demonstrating critical dynamics and metastability. We show the emergence of cluster synchronisation in these geometrically-constrained networks with functional organisation occurring along structural connections that minimise the participation coefficient of the cluster. We show that these cohorts of internally synchronised nodes also behave en masse as weakly coupled nodes and show intra-cluster desynchronisation and resynchronisation events related to inter-cluster interaction. While cluster synchronisation appears crucial to healthy brain function, it may also be pathological if it leads to unbreakable local synchronisation which may happen at extreme topologies, with implications for epilepsy research, wider brain function and other domains such as social networks.

Rational Design and Cellular Synthesis of Proteins with Unconventional Chemical Topology

Comprehensive SummaryChemical topology refers to the three‐dimensional arrangement (i.e., connectivity and spatial relationship) of a molecule's constituent atoms and bonds. The molecular mechanism for translation defines the linear configuration of all nascent proteins. Nontrivial protein topology arises only upon post‐translational processing events and often imparts functional benefits such as enhanced stability, making topology a unique dimension for protein engineering. Utilizing the assembly‐reaction synergy, our group has developed several methods for the effective and convenient cellular synthesis of a variety of topological proteins, such as lasso proteins, protein rotaxanes, and protein catenanes. The work opens the access to new protein classes and paves the road toward illustrating the topological effects on structure‐function relationship of proteins, which lays solid foundation for exploring topological proteins’ practical application.What is the most favorite and original chemistry developed in your research group?Cellular synthesis of artificial topological proteins using genetically programmed post‐translational cascade events.How do you get into this specific field?I was trained as a polymer chemist and always dream of accomplishing full control over macromolecules’ length, sequence, stereochemistry, and topology. I got to learn about how nature uses polymer chemistry during my postdoc study at Caltech and was amazed by the delicate cellular machinery for making biopolymers. However, the rigorous template polymerization mechanism also defines the linear configuration of DNA, RNA, and protein. Inspired by my experience in supramolecular chemistry and genetically encoded click chemistry, I proposed the use of “assembly‐reaction” synergy to make nonlinear proteins. By pre‐programming information regarding assembly and reaction into the precursor protein's gene, the nascent linear protein knows what to do and undergoes a series of cascade events to transform into various chemical topologies. I enjoy this interdisciplinary approach in tackling a long‐standing challenge.How do you supervise your students?Recognize that students are different. Start from a small project and finish it. Be rigorous on science, but flexible on routines. Give them sufficient freedom to explore, yet not too much to get lost. Open to debate and cultivate critical thinking. Always ready to help. Try to be a role model by acts, not words.What is the most important personality for scientific research?Curiosity, courage, persistence, and optimism.What are your hobbies?Reading and hiking.If you have anything else to tell our readers, please feel free to do so.There is no real boundary between scientific disciplines. They are often set by our training and mindsets. It often requires tremendous efforts to break such boundaries in order to advance science.

Finite element optimization of Pratt trusses using trial and error

Steel production is considered one of the most material and energy-consuming industries, and using less energy is considered vital to promote environmental sustainability. Steel is used as the main building material in the construction of factories, hangars, and workshops in the form of trusses. A truss system is a set of structural elements connected at pin joints, with different types, shapes, and weights. Optimizing truss systems for max strength and minimum weight is a sustainable approach to reducing steel production and promoting environmental sustainability. In this paper 27 Pratt trusses were optimized by trial and error using finite element analysis (FEM) to predict the optimum topology for various cross-sections. Correlations between the span length, cross-sectional area, and height of the trusses were developed to conclude the ideal topology of the Pratt truss that gives minimum compression and tension stresses. The effect of topology on the reaction forces was also addressed. Results showed that the optimum horizontal span length between joints ranged between 3.4 and 3.6 m for minimal compressive stresses and minimum horizontal and vertical reaction forces at supports, and from 3.0 to 3.6 m for minimal tensile stresses.

Simultaneous Suppression of Cross-Band Scattering and Coupling Between Closely Spaced Dual-Band Dual-Polarized Antennas

When two antennas working in different frequency bands are placed in proximity, they suffer from strong cross-band interactions that degrade their radiation performance and reduce the isolation between them. This paper presents holistic methods to simultaneously suppress cross-band scattering and coupling. Specifically, we develop a systematic solution to suppress the scattering of low-band (LB) antennas to high-band (HB) radiation as well as the scattering of HB antennas to LB radiation using three new techniques. This leads to much reduced cross-band coupling between the LB and HB antennas. The proposed methods are applied to a “1 LB + 1 HB” dual-band array configuration with only one LB cross-dipole and one HB cross-dipole placed side-by-side to exclude the effects of the array topology. The robustness of the proposed methods is comprehensively verified for different scenarios by simulations and experiments. Furthermore, the methods are evaluated in a “1 LB + 4 HB” array configuration. In addition to effectively suppressing cross-band scattering and coupling, the proposed methods also demonstrated a significant reduction in in-band coupling between adjacent HB antennas.

Damping of coronal oscillations in self-consistent 3D radiative magnetohydrodynamics simulations of the solar atmosphere

Context. Oscillations are abundant in the solar corona. Coronal loop oscillations are typically studied using highly idealised models of magnetic flux tubes. In order to improve our understanding of coronal oscillations, it is necessary to consider the effect of a realistic magnetic field topology and the density structuring. Aims. We analyse the damping of coronal oscillations using a self-consistent 3D radiation-magnetohydrodynamics simulation of the solar atmosphere spanning from the convection zone into the corona, the associated oscillation dissipation and heating, and finally, the physical processes that cause the damping and dissipation. The simulated corona that forms in this model does not depend on any prior assumptions about the shape of the coronal loops. Methods. We analysed the evolution of a bundle of magnetic loops by tracing the magnetic field. Results. We find that the bundle of magnetic loops shows damped transverse oscillations in response to perturbations in two separate instances, with oscillation periods of 177 s and 191 s, velocity amplitudes of 10 km s−1 and 16 km s−1, and damping times of 176 s and 198 s. The coronal oscillations lead to the development of velocity shear in the simulated corona, which results in the formation of vortices seen in the velocity field that are caused by the Kelvin-Helmholtz instability. This contributes to the damping and dissipation of the transverse oscillations. Conclusions. The oscillation parameters and evolution we observed are in line with the values that are typically seen in observations of coronal loop oscillations. The dynamic evolution of the coronal loop bundle suggests that the models of monolithic and static coronal loops with constant lengths might need to be re-evaluated by relaxing the assumption of highly idealised wave guides.

Effects of noise on the critical points of Turing instability in complex ecosystems.

Noise is ubiquitous in natural and artificial systems. In a noisy environment, the interactions among nodes may fluctuate randomly, leading to more complicated interactions. In this paper we focus on the effects of noise and network topology on the Turing pattern of ecological networks with activator-inhibitor structure, which may be interpreted as prey-predator interactions. Based on the stability theory of stochastic differential equations, a sufficient condition for the uniform state is derived. The analytical results indicate that noise is beneficial for the uniform state. When the ratio between the diffusion coefficients of the predator and prey increases, the ecosystems can exhibit a transition from a uniform stable state to a Turing pattern, while when the ratio decreases, the ecosystems transit from a Turing pattern to a uniform stable state. There are two crucial critical points in Turing patterns, forward and backward. We find that both forward and backward critical points increase as the noise intensity increases. This means that noise favors a stable homogeneous state compared to a state with a heterogeneous pattern, which is consistent with the analytical results. In addition, noise can weaken the hysteresis phenomenon and even eliminate it in some cases. Furthermore, we report that network topology plays an important role in modulating the uniform state of ecosystems, such as the size of prey-predator systems, the network connectivity, and the strength of interaction.

Evaluation of the Topology Space of DNA-Encoded Libraries.

DNA-encoded libraries (DELs) are widely used in the discovery of drug candidates, and understanding their design principles is critical for accessing better libraries. Most DELs are combinatorial in nature and are synthesized by assembling sets of building blocks in specific topologies. In this study, different aspects of library topology were explored and their effect on DEL properties and chemical diversity was analyzed. We introduce a descriptor for DEL topological assignment (DELTA) and use it to examine the landscape of possible DEL topologies and their coverage in the literature. A generative topographic mapping analysis revealed that the impact of library topology on chemical space coverage is secondary to building block selection. Furthermore, it became apparent that the descriptor used to analyze chemical space dictates how structures cluster, with the effects of topology being apparent when using three-dimensional descriptors but not with common two-dimensional descriptors. This outcome points to potential challenges of attempts to predict DEL productivity based on chemical space analyses alone. While topology is rather inconsequential for defining the chemical space of encoded compounds, it greatly affects possible interactions with target proteins as illustrated in docking studies using NAD/NADP binding proteins as model receptors.