Correct Topology Research Articles

Correction of topological errors in automated traces of neurites.

Our understanding of synaptic connectivity in the brain relies on the ability to accurately trace sparsely labeled neurons from 3D optical microscopy stacks of images. A variety of automated algorithms and software tools have been developed for this task. These algorithms can capture the general layout of neurites with high fidelity, but the resulting traces often contain topological errors such as broken and incorrectly merged branches. Even a small number of isolated topological errors can drastically alter the connectivity, and therefore, their detection and correction are paramount for connectomics studies. Here, we describe an automated trace proofreading approach that utilizes machine learning to correct trace topology. Multiple stacks of neuron images were traced by two users to create a labeled dataset and assess the baseline of inter-user variability. All traces were then disconnected at branch points and a deep neural network was trained to detect the correct way of reconnecting the branches. Custom morphological features were generated for each cluster of branch points, in a way that is dependent on a merging scenario but invariant to translations, rotations, and reflections of the cluster in the imaging plane. The features and image volume centered at the branch point were used for training a neural network that concatenates these input streams and outputs the confidence measure for different branch merging scenarios. The designed method significantly reduces the number of topological errors in automated traces and comes close to the accuracy achieved by expert users which is the gold standard in the field.

Comparison of thyristor and insulated-gate bipolar transistor -based power supply topologies in industrial water electrolysis applications

The demand for green hydrogen is growing as the increasing production of pure hydrogen can no longer be based on fossil hydrocarbons. As water electrolysis would move from niche to a significant consumer of emission-free electricity, the efficiency of electrolytic gas production, lifetime of water electrolysis systems, and balance in the electricity grid become essential. The operational and investment costs of an industrial-scale alkaline water electrolyzer with four practical rectifier topologies are investigated. The results show thyristor-based rectifiers provide poor quality for the AC and DC sides, which leads to nonoptimal specific energy consumption (SEC) of the water electrolyzer and a notable reactive power component. Transistor-based topologies may offer up to 4.5% lower SEC of the electrolyzer than the conventional 6-pulse thyristor bridge. The reactive power results in additional costs in either investments in compensation equipment or regular allowance costs. An additional DC/DC converter can be installed to improve the power quality for the electrolyzer, but the second conversion stage adds to the system complexity and cost without eliminating reactive power. A modular single-stage rectifier based on insulated-gate bipolar transistor (IGBT) bridges is suggested as an alternative to provide improved power quality for both the electrolyzer and the electricity grid.

Models and Methods for Discovery of Local Area Network Topology with Incomplete Data

A lot of network management tasks require a description of the logical and physical computer network topology. Obtaining such a description in an automatic way is complicated due to the possibility of incompleteness and incorrectness of the initial data on the network structure. This article provides a study on the properties of incomplete initial data on network device connectivity on the link layer. Methods for generalized handling of the heterogeneous input data on the link layer are included. We describe models and methods for deriving a missing part of the data, as well as the condition in which it is possible to get a single correct network topology description. The article includes algorithms for building a link layer topology description from incomplete data when this data is possible to fulfill up to the required level. Also, we provide methods for detecting and resolving an ambiguity in the data and methods for improving incorrect initial data. The tests and evaluations provided in the article demonstrate the applicability and effectiveness of the build methods for discovering various heterogeneous real-life networks. Additionally, we show the advantages of the provided methods over the previous analogs: our methods are able to derive up to 99% data on link layer connectivity in polynomial time; able to provide a correct solution from an ambiguous data.

Models and methods for local area network topology discovery with incomplete data

A lot of network management tasks require a description of the logical and physical computer network topology. Obtaining such a description in an automatic way is complicated due to the possibility of incompleteness and incorrectness of the initial data on the network structure. This article provides a study on the properties of incomplete initial data on network device connectivity on the link layer. Methods for generalized handling of the heterogeneous input data on the link layer are included. We describe models and methods for deriving a missing part of the data, as well as the condition in which it is possible to get a single correct network topology description. The article includes algorithms for building a link layer topology description from incomplete data when this data is possible to fulfill up to the required level. Also, we provide methods for detecting and resolving an ambiguity in the data and methods for improving incorrect initial data. Tests and evaluations provided in the article demonstrate the applicability and effectiveness of the build methods for discovering various heterogeneous real-life networks. Additionally, we show advantages of the provided methods over the previous analogs: our methods are able to derive up to 99\% data on link layer connectivity in polynomial time; able to provide a correct solution from an ambiguous data.

Hybrid Modular Multilevel Rectifier: A New High-Efficient High-Performance Rectifier Topology for HVDC Power Delivery

This letter presents a novel three-phase rectifier topology, namely hybrid modular multilevel rectifier (HMMR) for medium or high voltage ac-dc power conversion applications. Compared with modular multilevel converter (MMC), up to 50% of the IGBTs and submodules (SMs) including capacitors can be replaced by simple high-efficient high-voltage line-frequency diode stacks. HMMR can keep the key benefits of MMC, such as modularity, reliability, and excellent harmonic performance, while significantly reducing the power losses, costs, and volume. Unlike the thyristor-based line-commutated converter (LCC) rectifier, HMMR can operate under different grid conditions and can even provide reactive power support, making it a strong candidate of rectifier unit for point-to-point MV and HV power delivery. The feasibility of proposed converter is verified by the simulation as well as experimental results.

Design Optimization and Electro-Thermal Modeling of an Off-Board Charging System for Electric Bus Applications

This paper proposes a co-design optimization procedure of a high-power off-board charger for electric vehicle (EV) applications. The primary purpose is to design a 175 kW SiC DC-charging system with high power density to achieve high efficiency at a wide operating range. For the active part of the DC off-board charger, a three-phase active front end (AFE) rectifier topology is considered in the design optimization and the modelling. The design methodology focuses on the optimal design of the passive filters, accurate electro-thermal modelling of the converter, inductor design, capacitor selection, loss and geometric modelling of the passive filters and control system design. The design optimization of the high-power charging system is performed in MATLAB Simulink using a closed-loop dynamic electro-thermal simulation of the off-board charger. The switching frequency, loss and temperature-dependent efficiency of the charger is investigated in parallel. Through this proposed technique, efficiency greater than 96% is achieved at a switching frequency of 40 kHz, along with a smaller size and lower weight of the system. Moreover, it operates with a current total harmonic distortion (THDi) below 3% and a power factor (PF) above 99% at rated power condition.

Self-Adaptive Rectenna with High Efficiency over a Wide Dynamic Range for RF Energy Harvesting Applications

This paper presents a novel simple adaptive and efficient rectenna with automatic power distribution to achieve high radio frequency-direct current (RF-DC) power conversion efficiency (PCE) over a wide range of RF input power. This design employs two rectifier paths operating at low and high-power levels, respectively. Automatic power distribution method exploits the power-dependent input impedance of the rectifier and routes the RF input power into the assigned path according to the input power level. A distinctive enhancement in the rectifier dynamic range is achieved when dividing the high path power equally into two or more parallel diode cells, which helps the high path to camouflage the diode breakdown voltage in case of high input power level. The proposed adaptive design applies two different rectifier topologies, one by using shunt diode topology and the other by using voltage doubler topology at 2.45 GHz. Simulated PCE of this work is kept above 50% over a range of 25.1 dBm from -5.7 to 19.4 dBm of RF input power using shunt diode topology and over a range of 30 dBm from -6.3 to 23.7 dBm of RF input power using voltage doubler topology.

High-Voltage Stations for Electric Vehicle Fast-Charging: Trends, Standards, Charging Modes and Comparison of Unity Power-Factor Rectifiers

Emission of greenhouse gases and scarcity of fossil fuels have put the focus of the scientific community, industry and society on the electric vehicle (EV). In order to reduce CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> emissions, cutting-edge policies and regulations are being imposed worldwide, where the use of EVs is being encouraged. In the best of scenarios reaching 245 million EVs by 2030 is expected. Extensive use of EV-s requires the installation of a wide grid of charging stations and it is very important to stablish the best charging power topology in terms of efficiency and impact in the grid. This paper presents a review of the most relevant issues in EV charging station power topologies. This review includes the impact of the battery technology, currently existing standards and proposals for power converters in the charging stations. In this review process, some disadvantages of current chargers have been identified, such as poor efficiency and power factor. To solve these limitations, five unidirectional three-phase rectifier topologies have been proposed for fast EV charging stations that enhance the current situation of chargers. Simulation results show that all the proposed topologies improve the power factor issue without penalizing efficiency. The topologies with the best overall performance are the Vienna 6-switch and the Vienna T-type rectifier. These two converters achieve high efficiency and power factor, and they allow a better distribution of losses among semiconductors, which significantly increase the life-cycle of the semiconductor devices and the reliability of the converter.

Convergence of maximum likelihood supertree reconstruction

&lt;abstract&gt;&lt;p&gt;Supertree methods are tree reconstruction techniques that combine several smaller gene trees (possibly on different sets of species) to build a larger species tree. The question of interest is whether the reconstructed supertree converges to the true species tree as the number of gene trees increases (that is, the consistency of supertree methods). In this paper, we are particularly interested in the convergence rate of the maximum likelihood supertree. Previous studies on the maximum likelihood supertree approach often formulate the question of interest as a discrete problem and focus on reconstructing the correct topology of the species tree. Aiming to reconstruct both the topology and the branch lengths of the species tree, we propose an analytic approach for analyzing the convergence of the maximum likelihood supertree method. Specifically, we consider each tree as one point of a metric space and prove that the distance between the maximum likelihood supertree and the species tree converges to zero at a polynomial rate under some mild conditions. We further verify these conditions for the popular exponential error model of gene trees.&lt;/p&gt;&lt;/abstract&gt;

Gene Tree Estimation Error with Ultraconserved Elements: An Empirical Study on Pseudapis Bees.

Summarizing individual gene trees to species phylogenies using two-step coalescent methods is now a standard strategy in the field of phylogenomics. However, practical implementations of summary methods suffer from gene tree estimation error, which is caused by various biological and analytical factors. Greatly understudied is the choice of gene tree inference method and downstream effects on species tree estimation for empirical data sets. To better understand the impact of this method choice on gene and species tree accuracy, we compare gene trees estimated through four widely used programs under different model-selection criteria: PhyloBayes, MrBayes, IQ-Tree, and RAxML. We study their performance in the phylogenomic framework of $>$800 ultraconserved elements from the bee subfamily Nomiinae (Halictidae). Our taxon sampling focuses on the genus Pseudapis, a distinct lineage with diverse morphological features, but contentious morphology-based taxonomic classifications and no molecular phylogenetic guidance. We approximate topological accuracy of gene trees by assessing their ability to recover two uncontroversial, monophyletic groups, and compare branch lengths of individual trees using the stemminess metric (the relative length of internal branches). We further examine different strategies of removing uninformative loci and the collapsing of weakly supported nodes into polytomies. We then summarize gene trees with ASTRAL and compare resulting species phylogenies, including comparisons to concatenation-based estimates. Gene trees obtained with the reversible jump model search in MrBayes were most concordant on average and all Bayesian methods yielded gene trees with better stemminess values. The only gene tree estimation approach whose ASTRAL summary trees consistently produced the most likely correct topology, however, was IQ-Tree with automated model designation (ModelFinder program). We discuss these findings and provide practical advice on gene tree estimation for summary methods. Lastly, we establish the first phylogeny-informed classification for Pseudapis s. l. and map the distribution of distinct morphological features of the group. [ASTRAL; Bees; concordance; gene tree estimation error; IQ-Tree; MrBayes, Nomiinae; PhyloBayes; RAxML; phylogenomics; stemminess].

Target-capture phylogenomics provide insights on gene and species tree discordances in Old World treefrogs (Anura: Rhacophoridae).

Genome-scale data have greatly facilitated the resolution of recalcitrant nodes that Sanger-based datasets have been unable to resolve. However, phylogenomic studies continue to use traditional methods such as bootstrapping to estimate branch support; and high bootstrap values are still interpreted as providing strong support for the correct topology. Furthermore, relatively little attention has been given to assessing discordances between gene and species trees, and the underlying processes that produce phylogenetic conflict. We generated novel genomic datasets to characterize and determine the causes of discordance in Old World treefrogs (Family: Rhacophoridae)-a group that is fraught with conflicting and poorly supported topologies among major clades. Additionally, a suite of data filtering strategies and analytical methods were applied to assess their impact on phylogenetic inference. We showed that incomplete lineage sorting was detected at all nodes that exhibited high levels of discordance. Those nodes were also associated with extremely short internal branches. We also clearly demonstrate that bootstrap values do not reflect uncertainty or confidence for the correct topology and, hence, should not be used as a measure of branch support in phylogenomic datasets. Overall, we showed that phylogenetic discordances in Old World treefrogs resulted from incomplete lineage sorting and that species tree inference can be improved using a multi-faceted, total-evidence approach, which uses the most amount of data and considers results from different analytical methods and datasets.

An interface-enriched generalized finite element method for level set-based topology optimization

During design optimization, a smooth description of the geometry is important, especially for problems that are sensitive to the way interfaces are resolved, e.g., wave propagation or fluid-structure interaction. A level set description of the boundary, when combined with an enriched finite element formulation, offers a smoother description of the design than traditional density-based methods. However, existing enriched methods have drawbacks, including ill-conditioning and difficulties in prescribing essential boundary conditions. In this work, we introduce a new enriched topology optimization methodology that overcomes the aforementioned drawbacks; boundaries are resolved accurately by means of the Interface-enriched Generalized Finite Element Method (IGFEM), coupled to a level set function constructed by radial basis functions. The enriched method used in this new approach to topology optimization has the same level of accuracy in the analysis as the standard finite element method with matching meshes, but without the need for remeshing. We derive the analytical sensitivities and we discuss the behavior of the optimization process in detail. We establish that IGFEM-based level set topology optimization generates correct topologies for well-known compliance minimization problems.

Unbalance characteristics of fundamental and harmonic currents of three‐phase electric vehicle battery chargers

Three-phase electric vehicle (EV) battery chargers are expected to not impact the unbalance of distribution networks; moreover, using active power factor correction topologies they are expected to behave like resistive loads not affecting the system harmonic distortion. In this study, unexpected unbalance characteristics of fundamental and harmonic currents of three-phase EV battery chargers are analysed by means of experimental tests performed on two EV cars of different technology. In order to quantify unbalance and harmonic distortion, proper comprehensive indices, in part developed in this study with specific reference to currents, are utilised. The unbalanced current absorbed even under ideal voltage balanced supply conditions by one of the two EV tested is shown and quantified constituting a real-life case study of endogenous unbalance. Then, the influence of voltage unbalance supply conditions on fundamental and harmonic currents is evaluated by means of a proposed testing procedure, obtaining case studies of exogenous unbalance. The experimental results obtained for the two EVs should be extended to a larger set of cars; anyway, they show the need, before moving forward to full grid EV connection, for utilities and for designers to improve the current standard certification process and the control performances of three-phase battery chargers.

A W-Band 2 × 2 Rectenna Array With On-Chip CMOS Switching Rectifier and On-PCB Tapered Slot Antenna for Wireless Power Transfer

This article presents a W-band rectenna unit that incorporates a novel CMOS switching rectifier and a print tapered slot antenna. The operation principle of the switching rectifier is analyzed. The proposed rectifier topology shows improved reliability, and it utilizes the body-diode effect (BDE) to improve power conversion efficiency (PCE). Besides, a high-gain W-band antipodal linearly tapered slot antenna is implemented on PCB to improve the overall efficiency. In order to demonstrate the utility of the proposed rectenna unit for large-scale rectenna array, a 1 × 2 (parallel) and 2 × 2 (series-parallel) rectenna arrays in 40-nm bulk CMOS technology and PCB process have been implemented. The switching rectifier achieves a peak PCE of 45.8% at 94GHz with improved reliability. Occupying only 0.0756 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the overall PCEs of the rectenna unit and the 2 × 2 rectenna array are 25% and 23%, delivering 5.6and 20-mW output dc power, respectively, at 90-mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> incident power density. The proposed rectifier and rectenna array achieve the highest PCE among recently reported W-band rectifiers and rectenna arrays with different technologies.

Structured layer surface segmentation for retina OCT using fully convolutional regression networks.

Optical coherence tomography(OCT) is a noninvasive imaging modality with micrometer resolution which has been widely used for scanning the retina. Retinal layers are important biomarkers for many diseases. Accurate automated algorithms for segmenting smooth continuous layer surfaces with correct hierarchy(topology) are important for automated retinal thickness and surface shape analysis. State-of-the-art methods typically use a two step process. Firstly, a trained classifier is used to label each pixel into either background and layers or boundaries and non-boundaries. Secondly, the desired smooth surfaces with the correct topology are extracted by graph methods(e.g., graph cut). Data driven methods like deep networks have shown great ability for the pixel classification step, but to date have not been able to extract structured smooth continuous surfaces with topological constraints in the second step. In this paper, we combine these two steps into a unified deep learning framework by directly modeling the distribution of the surface positions. Smooth, continuous, and topologically correct surfaces are obtained in a single feed forward operation. The proposed method was evaluated on two publicly available data sets of healthy controls and subjects with either multiple sclerosis or diabetic macular edema, and is shown to achieve state-of-the art performance with sub-pixel accuracy.

Bridgeless PFC Topology Simplification and Design for Performance Benchmarking

Compared with conventional power factor correction topologies, although dual-converter cell-based bridgeless topologies usually have higher efficiency, most of them suffer from high component counts. Thus, this article proposes general topology simplification methods for these topologies. Besides, several selected converter cells are exemplified to show the specific topology simplification processes, and the performance of the resultant simplified topologies is reviewed. Meanwhile, based on the same design specifications, in order to provide an unbiased quantitative topology comparison in terms of power loss, cost, and volume, this article introduces a consistent component database-based design procedure with electrical, thermal, and cost models. As case studies, the conventional and two selected bridgeless buck–boost-type topologies are compared by following the design procedure. The comparison results are analyzed to provide a reference for topology selection. Three prototypes are built and tested to verify the theoretical analysis.

Creation of a network model on the basis of a universal sequence of construction works

Introduction. Building information modeling is the main direction of development of automated design and control systems. An important component of information modeling is the transfer of data into construction management systems. The most complicated issue is the problem of creating the correct graph topology relevant to the process sequence and construction management experience. The development of automated progress schedule compilation system based on the use of a universal sequence developed earlier is examined. Materials and methods. As a result of the analysis of the progress schedule compilation process, the topology creation algorithm is divided into several stages. At the first stage, a text description of the information model is given, which is then converted into a list of building or structure elements. The list of elements should be transformed into the work item list and then supplemented with work items not reflected in the list of elements. This is a separate complex task, which is not examined in this study, and is the direction of further research by the authors. At the next stage, the work items in the list are assigned codes that define the location of the scope of works in time and space. Results. An algorithm for converting the work item list into a coherent work schedule, the topology of which takes into account the spatial location of the work area and the sequence of interrelated processes over time, has been developed. The sequence of works is determined by a preliminarily designed universal list. The list of requirements for the information produced by BIM models is developed. Splitting the algorithm into stages allows for manual correction of the work item list and the properties of work items, if necessary. Conclusions. The developed method allows for automation of the processes of creating construction plans based on the list of building elements and universal work sequence. At any implementation stage, the work item list may be interactively changed and supplemented. In the future, it is necessary to form a set of parameters for structural elements that will allow automating the choice of technological processes.

4-kW 3-phase rectifier with high efficiency and wide operational range via 3-mode SVPWM

There are 6 modes in the full working state of a traditional 3-phase rectifier, and each mode is necessary for power factor correcting and for realizing the corresponding DC-link voltage. It is obvious that too many modes in the full working state increase the switch stresses, which results in high switching loss and increased economic cost. Reducing the number of working modes is a feasible solution to solve this problem. By improving the m-mode controllability in inverters, a 3-mode control strategy is derived for the traditional 3-phase rectifier to enhance its operational features. Note that the proposed control strategy can maintain a high-power factor above 0.99 and have higher efficiency when compared with the traditional control strategy. Finally, a lab-prototype with a load varying from 800 W to 4 kW is conducted to validate the feasibility of the proposed control strategy. Experimental results show that all of the tested cases have a 0.99 power factor and that highest efficiency of 96.7%. The results also reveal that the proposed strategy is superior to the traditional one in laboratory conditions. In addition, the proposed method is generalized and can be extended to other rectifier topologies.

Single-Phase Bridgeless PFC Topology Derivation and Performance Benchmarking

This article introduces two general ways to derive single-phase bridgeless power factor correction (PFC) topologies and then, 15 accessible bridgeless topologies are derived based on the configuration of different basic types of dc–dc converter cells. Although the majority of the topologies have been previously proposed, other possible research points are reviewed. Besides, a consistent component sizing procedure with electric, thermal, and cost models is applied to conduct the performance benchmarking of these PFC topologies in terms of power loss, volume, and cost. Three boost-type PFC topologies are chosen as examples to demonstrate the procedure and the corresponding benchmarking results with both theoretical analyses and experimental verification. Finally, mission profiles of one specific application are introduced to show the material cost payback period of adopting one modified bridgeless boost topology instead of conventional one in different scenarios.

Effect of electronic correlations on the spectral and magnetic properties of ZrZn2

We present results of a theoretical study of a prototypical weak ferromagnet ZrZn$_2$. We use the density-functional theory (DFT)+dynamical mean-field theory (DMFT) method to study the electronic and local magnetic properties. The obtained DFT+DMFT electronic self-energies are Fermi-liquid like, indicating a small effective mass enhancement of the Zr $4d$ states $m^*/m\sim 1.1 - 1.3$ accompanied by partly formed local moments within the electronic states of $t_{2g}$ symmetry. The effect of electronic interaction is shown to be essential for determining the correct topology of some of the Fermi surface sheets. To study in detail the pressure dependence of the Curie temperature $T_{\rm C}$ and corresponding pressure-induced quantum phase transition, we consider an effective single-band model, constructed using the Zr $4d$ contribution to the total density of states. The model is studied within static and dynamic mean-field theory, as well as spin-fermion approach. We show that the spin-fermion approach yields the temperature dependence of susceptibility at ambient pressure and the pressure dependence $T_{\rm C}(p)$, including the first-order quantum phase transition at $p\approx 1.7$~GPa, comparable well with the experimental data.