Specific Topology Research Articles

Generalized Kanzaki force field of extended defects in crystals with applications to the modeling of edge dislocations

The Kanzaki forces and their associated multipolar moments are standard ways of representing point defects in an atomistically informed way in the continuum. In this article, the Kanzaki force approach is extended to other crystalline defects. The article shows how the resulting Kanzaki force fields are to be computed for any general extended defect by first computing the relaxed defect's structure and then defining an affine mapping between the said defect structure and the original perfect lattice. This methodology can be employed to compute the Kanzaki force field of any mass-conserving defect, including dislocations, grain and twin boundaries, or cracks. Particular focus is then placed on straight edge dislocation in face-centered cubic (fcc) and body-centered cubic (bcc) pure metals, which are studied along different crystallographic directions. The particular characteristics of these force fields are discussed, drawing a distinction between the slip Kanzaki force field associated with the Volterra disregistry that characterizes the dislocation, and the core Kanzaki force field associated with the specific topology of the dislocation's core. The resulting force fields can be employed to create elastic models of the dislocation that, unlike other regularization procedures, offer a geometrically true representation of the core and the elastic fields in its environs, capturing all three-dimensional effects associated with the core.

Hydrogen Abstraction from the C15 Position of the Cholesterol Skeleton

Cholesterol (Ch) is an integral part of cell membrane, where it is prone to oxidation. In humans, oxidation of Ch is commonly linked to various pathologies like Alzheimer's disease, atherosclerosis, and even cancer, which proceed via mechanisms involving enzymatic and free radical pathways. The latter begin with hydrogen abstraction (HA) from Ch by a reactive free radical. It has been established that the most efficient HA from Ch occurs at C7, although HA from C4 by peroxyl radicals has recently been observed. Conversely, HA from Ch positions other than the thermodynamically preferred C7 or C4 has never been reported. We have designed a Ch derivative where a benzophenone moiety is linked to C7 by a covalent bond. This mirrors a specific orientation of Ch within a confined environment. Product analysis and time-resolved spectroscopic studies reveal an unprecedented HA from C15, which is a thermodynamically unfavorable position. This indicates that a specific topology of reactants is crucial for the reactivity of Ch. The relative orientation of the reactants can also be relevant in biological membranes, where Ch, polyunsaturated fatty acids, and numerous oxidizing species are confined in highly restricted and anisotropic environments.

Enhancing distributed functional monitoring with quantum protocols

In distributed functional monitoring (DFM), N players located at different sites; each observes a stream of items and communicates with one coordinator, whose goal is to compute a function of the union of the streams. In threshold monitoring, a special case of DFM, the coordinator wants to know whether $$f(v(t)) > T$$, where v(t) is a binary vector that represents the state of the stream as an average of local states at the sites. In this paper, we enhance the classical geometric monitoring (GM) method with quantum communication and entanglement. The proposed quantum geometric monitoring (QGM) protocol can be further specialized by defining specific network topologies. In QGM-Flat, the coordinator is connected to all N players. When N becomes too large, the performance of QGM-Flat deteriorates. For a scalable implementation, we propose to organize the players in a tree structure, with the QGM-Tree protocol. We have implemented both QGM-Flat and QGM-Tree with SimulaQron, a novel Python library for the development and simulation of quantum networking applications. We analyze the proposed quantum protocols, showing that they outperform their classical counterparts in terms of reduced communication cost, while showing the same accuracy.

Placement and Chaining for Run-Time IoT Service Deployment in Edge-Cloud

This paper investigates an efficient placement and chaining of Virtual Network Functions (VNFs) to provide cloud based IoT services with minimal resource usage cost. We take into account bandwidth capacity and link delay of network connection between clouds where VNFs are allocated and underlying IoT networks where sensors and IoT gateways are deployed. Regarding the constantly changing network dynamics, input traffic of service components is considered at the lower granularity level of messages based on the communication between each VNF and corresponding sensors via IoT gateways. From the algorithm perspective, the specific topology of multiple edge clouds is leveraged to improve the solution. In this paper, we present an NFV-based high-level architecture for a system that enables the deployment of IoT services across multiple edges and clouds. We formulate the VNF placement problem using a non-convex Integer Programming model. Taking into account different IoT topologies, we devise two algorithms for small- and large-scale networks to find the near optimal solution: i) a customized Markov approximation with two techniques, i.e., multi-start and batching, and a node ranking-based heuristic. Simulation and experimental results show that the proposed solution improves the cost up to 21% compared to state-of-the-art schemes.

A steady-state electrical model of a microbial fuel cell through multiple-cycle polarization curves

The use of Microbial Fuel Cells as power sources in rural or remote locations can solve issues related with power availability and wastewater cleaning. Furthermore, the application of such technology in wireless smart sensors applied to wastewater treatment plants can also help in water quality monitoring, increasing the process autonomy and reliability. A trustworthy power source needs to have a predictable and repeatable behavior, which cannot be achieved without adequate models and supporting hardware for energy regulation and storage. The work herein described proposes a steady-state model, represented by an electric circuit made of passive components. This model was first applied to a specific 28 mL air-cathode Microbial Fuel Cells working with artificial wastewater and using graphite brush anodes. Afterwards, the model was further validated by applying it to a larger reactor and to other bibliographic records. The goal of the study is to propose a method for finding a Microbial Fuel Cell model to be used with maximum power point tracking research, guaranteeing the best-case scenario for Microbial Fuel Cell operation as a power source. The reactors used in this study were analyzed by relating time and voltage development, both in colonization and in polarization studies. A mathematical relationship model was developed and proposed allowing to separate MFC's behavior, concerning energy production, in to meaningful components. From the experimental data the method was used to obtain a two-component circuit model that describes the power behavior of this specific Microbial Fuel Cell topology. The same method can be used to described other MFC.

Anisotropic nature of thermal conductivity in graphene spirals revealed by molecular dynamics simulations

Spiral nanostructures with many potential applications in next-generation high-tech industries can show outstanding mechanical, electrical and thermal properties thanks to their special topologies. In this study, we report a detailed analysis of heat transport in graphene spiral nanostructures. The non-equilibrium molecular dynamics simulation is used to investigate the thermal conductivity of the spirals in both axial (symmetric) and radial (asymmetric) directions for different geometries. The results reveal that with increasing widths of the graphene spirals, effective thermal conductivity (kA) in the axial direction and the thermal conductivity (k) in the radial direction increase. But with increasing the lengths of the graphene spirals (number of turns), only the axial thermal conductivity increases. Furthermore, the axial tensile strain and the addition of an extra layer to form a double-layer spiral structure have positive effects on increasing the thermal conductivity in the axial direction. Moreover, the results show that the thermal conductivity in radially inward and outward directions differ from each other arising from asymmetricity between the two radial directions where the heat flux prefers the inward direction.

Adsorption of triclosan, trichlorophenol and phenol by high-silica zeolites: Adsorption efficiencies and mechanisms

High-silica zeolites can be used for adsorption of organic compounds (OCs) from water. The adsorption efficacy could vary with the properties of OCs, as well as the porous and surface features of high-silica zeolites. In this study, the adsorption of triclosan, trichlorophenol (TCP) and phenol by ten high-silica zeolites were investigated. The plateaus of adsorption isotherms were observed in the adsorption of triclosan. The maximum adsorption capacity of triclosan could be related to the surface area and volume of micropores. The adsorption of TCP by FAU zeolites gave an S-shaped isotherm due to the possible lateral interactions of TCP molecules in the specific pore topology of FAU zeolites. The adsorption of phenol by high-silica zeolites had no adsorption plateau. Zeolites with channel structures, e.g. MFI zeolites, possess closely fitted pores for phenol, which slightly promoted its adsorption efficacy. The active adsorption sites of zeolites, i.e. Brønsted acid sites (BAS) and Lewis acid sites (LAS) failed to promote phenol adsorption. Phenol adsorption was favoured by carbon-based adsorbents with aromatic rings and functional groups, e.g. carboxyl and carbonyl, while the lack of active adsorption sites limited the phenol adsorption by high-silica zeolites, especially at the low concentration range.

A Rhombic Dodecahedron Topology for Human-Centric Banking Big Data

Banks are collecting an unprecedentedly large amount of data about their customers from difference sources, considering their cyber, physical, social activities. The focus of this paper is to study the problem of information sharing and lower the communication overhead among different nodes for a specific data mining approach in distributed big data architectures. This problem can be abstracted as how to efficiently search under a specific cluster node topology. This paper proposes a new design rule for topologies including: 1) low coordination number; 2) high packing density; and 3) having a 3-D structure. According to this rule, a rhombic dodecahedron topology is proposed. A distributed banking big data mining framework based on the proposed topology is implemented. The experiments based on multioptimization benchmark functions show the excellent searching ability of the proposed topology; and a banking customer feature reduction prototype has been implemented to showcase the practicality of the data mining framework.

Simultaneous Shape and Topology Optimization of Planar Linkage Mechanisms Based on the Spring-Connected Rigid Block Model

Abstract Using the topology optimization can be an effective means of synthesizing planar rigid-body linkage mechanisms to generate desired motion, as it does not require a baseline mechanism for a specific topology. While most earlier studies were mainly concerned with the formulation and implementation of topology optimization-based synthesis in a fixed grid, this study aims to realize the simultaneous shape and topology optimization of planar linkage mechanisms using a low-resolution spring-connected rigid block model. Here, we demonstrate the effectiveness of simultaneous optimization over a higher-resolution fixed-grid rigid block-based topology optimization process. When shape optimization to change the block shapes is combined with topology optimization to synthesize the mechanism, the use of low-resolution discretized models improves the computation efficiency considerably and helps to yield compact mechanisms with less complexity, making them more amenable to fabrication. After verifying the effectiveness of the simultaneous shape and topology optimization process with several benchmark problems, we apply the method to synthesize a mechanism which guides a planar version of a human's gait trajectory.

Modeling and Detectability of Full Open Gate Defects in FinFET Technology

FinFET technology is an attractive candidate for high-performance and power-efficient application and is currently used for several electronic products. FinFET technology incorporates new technologies in the manufacturing processes that may generate new defect topologies which need to be considered during test generation. This paper analyzes the electrical behavior of full open gate defects, i.e., a transistor gate with infinite resistance. It is shown that classical models, called single open (SO) and interconnect open (IO), that have been proposed in the past for CMOS technology are not sufficient in FinFET technology. The modern FinFET-based logic cells using multifin and multifinger design techniques give rise to new specific defect topologies called “subset full open gate defect.” The static and dynamic electrical behaviors of the two new topologies, subset SO (SOsub) and subset IO (IOsub), are analyzed, and the detectability of the defect in the context of Boolean testing and delay testing is derived. The detectability is analyzed taking into account process variation, temperature, and power supply control.

Robust Faulted Line Identification in Power Distribution Networks via Hybrid State Estimator

Distribution networks with high penetration of distributed generation yield complicated and uncertain power flow, which makes most existing faulted line identification methods not adaptable for industrial applications. Driven by this motivation, a novel single-phase-to-ground (SPTG) faulted line identification method is proposed based on hybrid state estimator (HSE). The first step of the method is to present an HSE for power distribution networks using power flow measurements mixed phasor measurement units. Then, an SPTG fault on a power line is treated as an event that suddenly increases one virtual bus in the monitored network, so as to form the extended bus admittance matrix and augmented HSE based on the specific network topology. In this way, the faulted line identification could be obtained by computing parallel estimated results transversally. Robustness and effectiveness of the proposed HSE and the HSE-based SPTG faulted line identification method are validated by means of a cyber-physical system (a cosimulation platform), where two typical three-phase power distribution networks are considered to simulate with its hybrid measurement system.

Time-Delay Origins of Fundamental Tradeoffs Between Risk of Large Fluctuations and Network Connectivity

For the class of noisy time-delay linear consensus networks, we obtain explicit formulas for risk of large fluctuations of a scalar observable as a function of Laplacian eigenspectrum. It is shown that there is an intrinsic tradeoff between risk and effective resistance of the underlying coupling graph of the network. The main implication is that increasing network connectivity, increases the risk of large fluctuations. For vector-valued observables, we obtain computationally tractable lower and upper bounds for joint risk measures. Then, we study behavior of risk measures for networks with specific graph topologies and show how risk scales with the network size.

Magnetic field configurational study on a helicon-based plasma source for future neutral beam systems

A helicon-based plasma source is under development and exploration at CEA-IRFM to produce an efficient and dense magnetized plasma column. The final objective of this development is the extraction and acceleration of a blade-like negative ion beam in view of future neutral beam injector systems for fusion reactors. The extraction of a negative ion beam from a magnetized plasma column requires a specific topology of the magnetic confinement, which significantly impacts the plasma parameters and wave propagation along the column. The magnetic confinement under investigation is based on water-cooled internal coils implemented under vacuum along the source (column) axis; these coils are supplied with a high DC current (∼1000 A), providing the axial magnetic field (B// ∼ 10 mT). Different diagnostics developed in academic laboratories, such as 3D B-dot probes, optical emission spectroscopy and Langmuir probes, have been used for plasma characterization. The paper reports the experimental results obtained under different operating conditions of this particular magnetic confinement.

A comparative study of cascade H-bridge multilevel voltage source inverter and parallel inductor multilevel current source inverter

This paper presents the analysis study between multilevel inverters that are often classified into multilevel voltage source and multilevel current source inverters. For multilevel voltage source inverter (MVSI), the specific topology studied for this work is the Cascaded H-Bridge MVSI. Whereas, the multilevel current source inverter (MCSI) is based on Paralleled Inductor Configuration MCSI. For this study, the analysis between these converters are done with respect to the number of components, the advantages and disadvantages of each converters during performing inverter operation. In term of output voltage and current quality, the percentage of the Total Harmonic Distortion (THD) are measured and compared for both topologies. MATLAB/Simulink software has been used in this research to design and simulate in order to study the performances of both inverters.

Composite DC Power Flow Controller

The utilization of a dc power flow controller in multiterminal HVDC (MTDC) can increase the control dimension of dc power flow, by which both the active power distribution capability and coordination control performance can be enhanced in MTDC. In this article, a novel concept of “composite dc power flow controller (CDCPFC)” has been proposed, and the general construction principles of technical frame have been given for function description. A specific CDCPFC topology has been implemented, which is featured with a straightforward dc-dc power conversion path via a transformerless structure. The operation principle, circuit characteristics, and control strategy of the proposed CDCPFC are analyzed in detail. Both simulation and experimental results proved that the proposed topology could realize power flow control function of two individual lines under various conditions with a good application prospect.

Black phosphorene exhibiting negative thermal expansion and negative linear compressibility

Positive expansion on heating, and positive contraction on hydrostatic compression are our general understanding. Actually, the abnormal negative thermal expansion (NTE) or negative linear compressibility (NLC) behavior is permissible, but exists in very few materials. Interestingly, we find that the NTE and NLC behaviors can coexist in the low-dimensional black phosphorene using first-principles calculations. In the temperature-field, the volume-NTE of black phosphorene can be exhibited below about 200 K, while the axial-NTE exists in the whole studied temperature range. In the hydrostatic pressure-field, the NLC behavior can occur along a zigzag direction or armchair direction in different pressure ranges. The phonon abnormality in black phosphorene is detected. It is found that acoustic phonons, especially the lowest-frequency TAz mode, play a very important role. The re-entrant honeycomb network in black phosphorene, as the specific topology, will facilitate the occurrence of NTE and NLC behaviors. This work can provide some foundations and clues for exploring the abnormal properties in other 2D materials.

Performance Evaluation of Wireless Sensor Network MAC protocols with Early Sleep problem

Energy efficiency and increased throughput are the two major goals in the design of MAC protocols in wireless sensor networks (WSNs). The traditional sensor-MAC (S-MAC) and timeout-MAC (T-MAC) protocols have been proposed to achieve these dual desirable goals by proper scheduling of duty cycles. Although these protocols have been proved to excel the performance when compared with their predecessor protocols for MANETs, the idea of duty cycling, if not tuned carefully may not work well in some linear chain topologies. We, in this paper investigated the 'early sleep' problem in specific topologies which results in undesirable extended latency in packets delivery. In this paper, we evaluated the performance of T-MAC protocol with early sleep problem. As a solution to this problem, this work also proposes a disable extended timeout MAC (DETMAC) protocol that helps the forwarding nodes towards the sink node to adaptively re-schedule their sleep/wakeup timing. It is shown through simulation results that our proposed DETMAC protocol outperforms in the terms of throughput and energy efficiency when compared to T-MAC and its variants.

Energy management and power quality enhancement in grid‐tied single‐phase PV system using modified PUC converter

Pack U-Cell (PUC) multi-level inverter is an attractive topology which widely investigated in the past few years for renewable energy conversion systems. This study introduces a modified five-level packed Unit-cell converter (MPUC5) for single-phase double stage grid-tied photovoltaic (PV) system with unity power factor. The proposed system operates as a single-phase active power filter able to compensate reactive power generated by non-linear loads connected to the point of common coupling, feeds the non-linear load by the generated PV power, and injects the extra power into the grid. The MPUC5 inverter has a special topology with two DC-link capacitors and six switches. One DC-link of the inverter is connected to the PV arrays through DC/DC Cuk converter to draw the maximum power. Therefore, finite-control-set model predictive control (FCS-MPC) for such configuration appears as a promising alternative for this inverter to work properly. Where the proposed FCS-MPC algorithm is designed to ensure a high grid current quality, taking into consideration the issue of the capacitor voltages balancing and the switching frequency minimisation. Both simulation results and experimental validation through real-time hardware in the loop system prove the validity and feasibility of the proposed control scheme, regarding PV power management and quality enhancement.

A Novel Transverse Flux Permanent Magnet Generator for Small-Scale Direct Drive Wind Turbine Application: Design and Analysis

This study focuses on a special topology of Transvers Flux Permanent Magnet Generator which benefits from low PM cost due to using cheap Ferrite PMs. In this structure, only one PM per phase is used where leads to easy manufacturing process. In spite of the above mentioned advantages of the topology, there are some disadvantages such as unbalanced voltage, high demagnetisation risk of the PM, and high cogging torque. Aiming to solve these problems while maintaining the advantages of the topology, a new structure is proposed. The stator of this structure contains two series connected coils which eliminates all the even order harmonics and balances the voltage waveform. This trick reduces the armature reaction as well as demagnetisation of the PMs, significantly. Additionally, the rotor teeth of the proposed structure are skewed where leads to a noticeable reduction in cogging torque. The output results of the proposed structure are compared with the original one in terms of harmonic components, cogging torque profile, and PM demagnetisation.

Ultrasonic-Assisted Linker Exchange (USALE): A Novel Post-Synthesis Method for Controlling the Functionality, Porosity, and Morphology of MOFs.

The introduction of organic ligands into metal-organic frameworks (MOFs) with a specific topology and that cannot be attained by direct synthesis is a big challenge. To meet this challenge, different ligand exchange/incorporation methods have been employed. Here, a new method, called ultrasonic-assisted linker exchange (USALE), has been developed to overcome the above-mentioned problems. USALE is a novel method for ligand exchange based on the use of ultrasonic waves. The temperature and pressure caused by the USALE method in microscopic zones are so intense that the linker exchange process is much faster than with other methods. In addition to saving time during synthesis, the use of the USALE method leads to a higher surface area and pore volume compared with other methods such as solvent-assisted linker exchange (SALE). In this way, improved gas adsorption capacity has been achieved for daughter frameworks synthesized by the USALE method. By using the USALE method, we have transformed a nonporous and easy-to-synthesize TMU framework ([Zn(OBA)(BPDB)0.5]n⋅2DMF (TMU-4), in which H2OBA=4,4'-oxybis(benzoic acid) and BPDB=1,4-di(4-pyridyl)-2,3-diaza-1,3-butadiene) into another porous framework ([Zn(OBA)(H2DPT)0.5]n⋅DMF (TMU-34), in which H2DPT=3,6-di(4-pyridyl)-1,4-dihydro-1,2,4,5-tetrazine) that otherwise requires a relatively long time to synthesize. In addition to reducing the synthesis time for TMU-34 (in comparison with both direct sonochemical synthesis and the indirect SALE method), the data obtained revealed that the daughter TMU-34 framework synthesized by the USALE method has a higher surface area and accessible pore volume than TMU-34 frameworks synthesized by SALE and direct methods. The application of SALE-TMU-34 and USALE-TMU-34 in a catalytic Henry condensation reaction and Congo Red adsorption experiments showed that the higher porosity of USALE-TMU-34 leads to a higher turn-over frequency and saturation capacity compared with SALE-TMU-34.