Correct Topology Research Articles

A Flexible Architecture for Extracting Metro Tunnel Cross Sections from Terrestrial Laser Scanning Point Clouds

This paper presents a novel framework to extract metro tunnel cross sections (profiles) from Terrestrial Laser Scanning point clouds. The entire framework consists of two steps: tunnel central axis extraction and cross section determination. In tunnel central extraction, we propose a slice-based method to obtain an initial central axis, which is further divided into linear and nonlinear circular segments by an enhanced Random Sample Consensus (RANSAC) tunnel axis segmentation algorithm. This algorithm transforms the problem of hybrid linear and nonlinear segment extraction into a sole segmentation of linear elements defined at the tangent space rather than raw data space, significantly simplifying the tunnel axis segmentation. The extracted axis segments are then provided as input to the step of the cross section determination which generates the coarse cross-sectional points by intersecting a series of straight lines that rotate orthogonally around the tunnel axis with their local fitted quadric surface, i.e., cylindrical surface. These generated profile points are further refined and densified via solving a constrained nonlinear least squares problem. Our experiments on Nanjing metro tunnel show that the cross sectional fitting error is only 1.69 mm. Compared with the designed radius of the metro tunnel, the RMSE (Root Mean Square Error) of extracted cross sections’ radii only keeps 1.60 mm. We also test our algorithm on another metro tunnel in Shanghai, and the results show that the RMSE of radii only keeps 4.60 mm which is superior to a state-of-the-art method of 6.00 mm. Apart from the accurate geometry, our approach can maintain the correct topology among cross sections, thereby guaranteeing the production of geometric tunnel model without crack defects. Moreover, we prove that our algorithm is insensitive to the missing data and point density.

A 900/1800 MHz dual‐band high‐efficiency rectenna

AbstractThis article presents a high‐efficiency dual‐band rectenna, for RF energy harvesting in GSM bands (900‐1800 MHz). The rectifier used is a dual‐diode rectifier topology based on a Delon voltage doubler. To ensure, the highest efficiency as possible, source‐pull simulations are used to determine the optimal diodes input impedance. The antenna is a spiral planar structure, where two slots ring resonators have been added to expand bandwidth at low frequencies without increasing its initial size. It is associated with a broadband balun to transform its impedance into the desired 50‐Ω rectifier input impedance. The antenna and balun are sized for broadband operation to cover the main wireless communication bands. Measurement results show high RF‐DC conversion efficiencies of 28% and 20% at 890 MHz and 1780 MHz, respectively, for a low RF input power of −20 dBm and with a 10 kΩ DC load. Efficiency reaches 43.5% with a dual‐tone signal at −20 dBm.

Three-Phase ZVR Topology and Modulation Strategy for Transformerless PV System

Leakage current reduction is crucial for operating transformerlss photovoltaic (PV) systems. In this letter, a new three-phase topology and modulation strategy is proposed. It is derived from the single-phase zero-voltage state rectifier topology, but the operation mechanism is quite different. Therefore, a new modulation strategy based on the Boolean logic function is proposed to achieve the constant common-mode voltage, so as to eliminate the leakage current. Finally, the experimental tests are carried out to verify the feasibility and effectiveness of the proposed solution.

Development of dipole magnet power supply for BEPC-II energy upgrading project

In order to make BEPC-II to run at a higher energy, the Institute of High Energy Physics undertook an upgrading project. One of the important factors limiting the energy boost is the power and performance of the dipole magnet power supplies; therefore, these four magnet power supplies are developed for the BEPC-II upgrading. The power supplies adopt topologies of thyristor rectifiers to realize a high-power output. In the control unit of each power supply, a digital current closed loop is adopted, and the key components in the feedback loop are thermostatically controlled. In order to improve the performances of the power supplies, analog voltage regulators are added to the inner control loops. These four power supplies have been tested and have already been officially used in BEPC-II, and their powers have reached the requirements of the upgrading. The test results of the current stability are described and shown in this paper, which testifies that the stabilities meet the design parameters. A digital control is applied to each SCR rectifier control. The performances of the power supplies are improved by the combination of digital current control loops and the analog voltage control loops, which makes the performances of the dipole magnet power supplies meet the requirements of the upgrading project.

Principle and control strategy of pulse width modulation rectifier for hydraulic power generation system

According to the characteristics of the hydraulic power generation system (HPGS), HPGS can be directly fed into a DC nano grid through using an uncontrolled rectifier. However, determined only by the DC voltage, the motor speed of the HPGS is a constant rather than an optimal speed, whose curve is unknown yet during the whole power generation process. In order to realize the control of the HPGS's motor speed and reduce the armature current harmonics, a pulse width modulation (PWM) rectifier topology is introduced to replace the uncontrolled rectifier. First, the principle of the PWM rectifier is studied. Second, a control structure of this PWM rectifier is established, including a current decoupling control in the inner loop and a speed feedback control in the outer loop. After this, a maximum efficiency converting control strategy is adopted. Based on the above, the simulation model of the PWM rectifier which was fed into DC nano grid was established and a series of experiments were carried out. The experimental results show that the armature current waveform is sine wave and its rectification is flexible. Furthermore, the maximum efficiency converting control strategy is realized with HPGS's always working at the optimal speed curve.

Fully Convolutional Boundary Regression for Retina OCT Segmentation.

A major goal of analyzing retinal optical coherence tomography (OCT) images is retinal layer segmentation. Accurate automated algorithms for segmenting smooth continuous layer surfaces, with correct hierarchy (topology) are desired for monitoring disease progression. State-of-the-art methods use a trained classifier to label each pixel into background, layer, or surface pixels. The final step of extracting the desired smooth surfaces with correct topology are mostly performed by graph methods (e.g. shortest path, graph cut). However, manually building a graph with varying constraints by retinal region and pathology and solving the minimization with specialized algorithms will degrade the flexibility and time efficiency of the whole framework. In this paper, we directly model the distribution of surface positions using a deep network with a fully differentiable soft argmax to obtain smooth, continuous surfaces in a single feed forward operation. A special topology module is used in the deep network both in the training and testing stages to guarantee the surface topology. An extra deep network output branch is also used for predicting lesion and layers in a pixel-wise labeling scheme. The proposed method was evaluated on two publicly available data sets of healthy controls, subjects with multiple sclerosis, and diabetic macular edema; it achieves state-of-the art sub-pixel results.

Developing focal construct technology for in vivo diagnosis of osteoporosis

Osteoporosis is a prevalent bone disease around the world, characterised by low bone mineral density and increased fracture risk. Currently, the gold standard for identifying osteoporosis and increased fracture risk is through quantification of bone mineral density (BMD), using dual energy X-ray absorption (DEXA). However, the use of BMD to diagnose osteoporosis is not without limitation and arguably the risk of osteoporotic fracture should be determined collectively by bone mass, architecture and physicochemistry of the mineral composite building blocks. Rather than depending exclusively on the ‘mass’ of bone, our previous research investigated predicting the risk of fracture using ‘bone quality’. The work highlighted that the material properties of OP tissue differ significantly to that of ‘normal’ bone and for the first time reported the clinical value of new biomarkers (obtained from X-ray scatter signatures) for fracture risk prediction. Thus, in order to improve fracture prediction models, diagnostic tools need to be developed which not only measure bone mineral density, but also bone quality.This pilot study builds on our previous work and aims to develop a new technology, Focal Construct Technology (FCT), which is hoped can measure XRD signatures in vivo. Our previous work was performed entirely with interrogating probes applied in transmission mode. This has some disadvantages that would be overcome were reflection mode employed. This study involves the creation of unique, high impact data with the potential to form the basis of a new generation of medical diagnostic instrumentation. A systematic series of conventional reflection mode ex vivo experiments were performed in which bone specimens were examined through increasing thicknesses of overlaying muscle/fat/skin. Further, we applied FCT to these geometries. This had not previously been attempted and required some initial modelling to ensure correct topologies of the hollow beams. The results from this study suggest it may be possible to obtain the parameters in vivo with the same precision as those obtained within the laboratory when using FCT.

Resonant Converter with Voltage-Doubler Rectifier or Full-Bridge Rectifier for Wide-Output Voltage and High-Power Applications

This paper presents a resonant converter with the benefits of wide output voltage, wide soft switching characteristics for power devices and high circuit efficiency. Since the series resonant circuit is adopted on the primary side, the power switches are turned on under zero voltage switching and power diodes on the secondary side can be turned off under zero current switching. To overcome the drawback of narrow voltage operation range in the conventional resonant converter, full-bridge rectifier and voltage-doubler rectifier topologies are employed on the secondary side for low-voltage output and high-voltage output applications. Therefore, the voltage rating of power devices on the secondary side is clamped at output voltage, rather than two times output voltage, in the center-tapped rectifier circuit. Synchronous power switches are used on the secondary side to further reduce the conduction losses so that the circuit efficiency can be further improved. To verify the theoretical analysis and circuit performance, a laboratory prototype with 1 kW rated power was built and tested.

ATP-dependent force generation and membrane scission by ESCRT-III and Vps4.

The endosomal sorting complexes required for transport (ESCRTs) catalyze reverse-topology scission from the inner face of membrane necks in HIV budding, multivesicular endosome biogenesis, cytokinesis, and other pathways. We encapsulated ESCRT-III subunits Snf7, Vps24, and Vps2 and the AAA+ ATPase (adenosine triphosphatase) Vps4 in giant vesicles from which membrane nanotubes reflecting the correct topology of scission could be pulled. Upon ATP release by photo-uncaging, this system generated forces within the nanotubes that led to membrane scission in a manner dependent upon Vps4 catalytic activity and Vps4 coupling to the ESCRT-III proteins. Imaging of scission revealed Snf7 and Vps4 puncta within nanotubes whose presence followed ATP release, correlated with force generation and nanotube constriction, and preceded scission. These observations directly verify long-standing predictions that ATP-hydrolyzing assemblies of ESCRT-III and Vps4 sever membranes.

Design of an efficiency‐enhanced Greinacher rectifier operating in the GSM 1800 band by using rat‐race coupler for RF energy harvesting applications

Radio frequency energy harvesting (RFEH) circuits can convert the power of communication signals from radio frequencies (RF) in the environment into direct current and voltage (DC power). In this study, the Greinacher full-wave rectifier circuit topology was combined with a 180° hybrid ring (rat-race) coupler which was a passive RF/microwave circuit. Thus, higher RF-DC conversion efficiency was obtained. First, using the Greinacher rectifier topology, RFEH circuit operating at the center frequency of 1850 MHz was designed. Then, at this frequency, designing of the rat-race coupler having 1000 MHz bandwidth was made. The S-parameter measurements and simulation data of the designed coupler circuit were compared. Finally, the high efficiency rectifier circuit where these two circuits were used together was designed. The proposed rectifier circuit was constructed on 70 × 70 × 1.6 mm3 FR4 substrate material with a permittivity of 4.3 (εr = 4.3). The power conversion efficiency (PCE) of the rectifier circuit, which had 125 MHz bandwidth at the center frequency of 1850 MHz and was developed with rat-race coupler, was calculated as 71% at 4.7 dBm input power. In addition, with this study, at −15 dBm input power, which was a relatively low power level, 40% PCE value was obtained.

Accurate Operating Analysis of Boundary Mode Totem-Pole Boost PFC Converter Considering the Reverse Recovery of mosfet

The boundary conduction mode (BCM) totem-pole boost power factor correction (PFC) topology is becoming popular in high-efficiency and high power density applications because of its advantages of fewer devices and low conduction losses. The ideal design methodology for the BCM boost converter ignores the reverse recovery of mosfet s’ body diode and the resonance between the inductance and output junction capacitances of switches. However, as the switching frequency increases, these two factors affect the peak value of the inductance current and the switching frequency significantly, which are critical parameters for the boost PFC inductor design. In order to calculate the practical peak current and switching frequency range accurately, this letter proposes an analytical reverse recovery model of the body diode and presents accurate switching cycle operating modes. Either the predicted inductance peak current or the switching frequency range matches the measured result on a 600-W totem-pole boost PFC prototype.

SiC + Si three‐phase 48 V electric vehicle battery charger employing current‐SVPWM controlled SWISS AC/DC and variable‐DC‐bus DC/DC converters

Wide-bandgap (WBG) devices such as SiC and GaN switches are regarded as next-generation power semiconductors, due to their superior performance over conventional Si devices, for instance, a low switching loss and high thermal conductivity. Its bottleneck, however, is the high cost, which is critical for renewable energy and automotive industries. This study adopts SWISS AC/DC rectifier topology for the three-phase 380-480 VAC along with an isolated DC/DC converter, indicating such topology can maximise the advantages of Si (low conduction loss) and SiC (high switching loss), altogether thereby yielding the high performance and low cost. A novel space-vector pulse width modulation (SVPWM) was proposed to control such a current-source power factor correction, where only two SiC devices were adopted for the DC-bus voltage control. The closed-loop control of the grid current is realised for the unity power factor. Such topology further allows the DC-bus voltage to be varied with the output voltage, thereby minimising the system loss. A final prototype was built to charge a 48 V battery at 11 kW. Experimental results validated the effectiveness of such battery charger design.

Research on Three-Phase Cascade PWM Rectifier

For the application of high voltage and high power, a three-phase six-module cascade rectifier topology is proposed for high voltage and high power conditions, And analyze this topology from the working principle and control strategy. In order to achieve unity power factor, a control strategy based on carrier phase shift method for reactive power and voltage closed-loop control is proposed. Then the simulation model was built by MATLAB/Simulink. By analyzing the simulation results in detail and by changing the load, the correctness and stability of the proposed control strategy are further verified, it can effectively reduce the harmonics, improve power quality, and achieve unity power factor input and regulated output.

Identification of molecular determinants that govern distinct STIM2 activation dynamics.

The endoplasmic reticulum (ER) Ca2+ sensors stromal interaction molecule 1 (STIM1) and STIM2, which connect ER Ca2+ depletion with extracellular Ca2+ influx, are crucial for the maintenance of Ca2+ homeostasis in mammalian cells. Despite the recent progress in unraveling the role of STIM2 in Ca2+ signaling, the mechanistic underpinnings of its activation remain underexplored. We use an engineering approach to direct ER-resident STIMs to the plasma membrane (PM) while maintaining their correct membrane topology, as well as Förster resonance energy transfer (FRET) sensors that enabled in cellulo real-time monitoring of STIM activities. This allowed us to determine the calcium affinities of STIM1 and STIM2 both in cellulo and in situ, explaining the current discrepancies in the literature. We also identified the key structural determinants, especially the corresponding G residue in STIM1, which define the distinct activation dynamics of STIM2. The chimeric E470G mutation could switch STIM2 from a slow and weak Orai channel activator into a fast and potent one like STIM1 and vice versa. The systemic dissection of STIM2 activation by protein engineering sets the stage for the elucidation of the regulation and function of STIM2-mediated signaling in mammals.

Novel High-Efficiency High Voltage Gain Topologies for AC–DC Conversion With Power Factor Correction for Elevator Systems

Novel power factor corrected ac–dc rectifier topologies suitable for induction motor drive based elevator application are proposed. These converters make use of coupled inductor for power conversion and are capable of providing high voltage gain at low duty cycle and high efficiency. The current flowing through the coupled inductor is controlled through a feedback control loop to achieve unity power factor. The total harmonic distortion (THD) value of the current is observed to be approximately 4.8%, which is within the limits prescribed by various standards. With the use of coupled inductor, the voltage stress of the switches operating at high frequency is reduced, which reduces switching losses. The loss comparison with the conventional converters shows a reduction of at least 22% of losses. The proposed scheme also results in reduction of the variable frequency drive's dc-link capacitance value as an ultracapacitor bank is interfaced with the dc link through a bidirectional converter for improving efficiency and providing transient power requirements. This also helps in increasing the reliability and dynamic response of the system. The settling time for a step change in voltage reference is observed to be reduced by nearly 50%. Proposed topologies and schemes are validated through MATLAB/Simulink simulations and experiments.

Specialized chaperones required

Protein Folding Although some proteins can reach a properly folded state without assistance, many require help to adopt the correct topology and avoid kinetic trapping in nonnative states. Chaperones encapsulate guest proteins and use adenosine triphosphate (ATP)–driven conformational changes to help them fold, but not all chaperones work for all substrates. Balchin et al. compared the folding pathway of the cytoskeleton protein actin with its proper chaperone, TRiC, to the incorrect folding that occurs with the bacterial chaperone GroEL. TRiC functions by stabilizing an extended form of actin with the proper secondary structure and topology. ATP binding and hydrolysis drives release of this partially folded intermediate into the chaperone where it can successfully fold. GroEL fails to bind the intermediate properly and thus is not able to successfully fold actin, even after ATP binding and hydrolysis. Cell 174 , 1507 (2018).

Simulation for accelerator dynamic power supply based on current-source PWM rectifier

The booster power supply of high-energy photon source is dynamic power supply, and the output is 2-Hz bias sine wave. Current-source rectifier (CSR) topology can achieve the 2-Hz current directly. In order to get the output current and good power factor of the power grid, the algorithm of “indirect current control” is applied. This method needs to measure the voltage of three phases and calculates several certain parameters of the circuit. The control strategy based on the “indirect current control” of the CSR is built in the Simulink simulation environment. Parameters and algorithms are described in detail, and the control block diagram and simulation model are given. The control strategy can output the right current and make a good power factor in the side of grid. The CSR topology, as a good choice of power supply of accelerator, has a well-researched prospect.

Disrupted chimera ordering of magnetization within FeCl2 layers

As a follow-up to a recent report about chimera ordering in Monte Carlo simulations of a three-dimensional Ising spin model (Singh R. et al., EPL, 95 (2011) 10004), further simulations are performed to ascertain the validity and the applicability of the initial results. In the initial work only nearest-neighbour interactions were considered within a cubic lattice of spins, having ferromagnetic interaction between spins within the same plane and anti-ferromagnetic interaction between spins in adjacent planes. This model was proposed as a prototype for certain layered magnetic systems, such as FeCl2. In the present work two main deficiencies in the initial work are addressed. First, use is made of parallel tempering to explore whether or not the reported chimera ordering could be a simulation artefact. This step is important because it is well known that, at lower temperatures, Monte Carlo simulations can often become trapped in local minima of the energy landscape. Furthermore, in the case of frustrated systems, such as the one that was considered, the energy landscape is well known to be complicated, typically containing many local minima. Second, the initial model of a cubic lattice of spins is extended to the face-centred cubic structure for FeCl2. Our extended model, consisting of the frustrated 3-dimensional face-centred cubic lattice of Ising spins, has the correct coupling topology and known exchange interactions for FeCl2. We find that the chimera ordering is robust to the parallel tempering and that it is influenced by the boundary conditions and the number of layers in the fcc lattice. In general one can expect to find small disruptions in the chimera ordering of the magnetization within different layers.

Innovative Filter Topology for Power Grid Protection from Switching Ripple Harmonics Produced by Matrix Converter

This article presents an innovative CLCR filter topology for protecting power grid from switching ripple harmonics produced by AC drives based on a direct matrix converter. The filter as an intermediate link between the power grid and the matrix drive is an essential part. Choosing the correct filter topology and filter components value would reduce filter weight, size and cost. This is especially important for high-power matrix matric converter-based AC drives. Depending on the composition of the harmonics generated by the matrix converter and the frequency response of the filters, the traditional LCR filter is supplemented with a small capacity capacitor. This changed the filter frequency response and increased the filter attenuation rate at the frequency range of switching ripple harmonics generated by the matrix converter. The effectiveness of the innovative CLCR topology has been demonstrated through simulations using MATLAB and MATLAB/Simulink and experimental results on a laboratory prototype.

Coordinated MPPT and DPC Strategies for PMSG based Grid Connected Wind Energy Conversion System

This paper presents a novel control strategy employing the maximum power point tracking (MPPT) and direct power control strategy (DPC) for permanent magnet synchronous generator (PMSG) based wind energy conversion system (WECS). The WECS adopts medium voltage source converter with AC-DC-AC configuration. The 10 MW wind farm is implemented in this paper which consists of 2 MW PMSG’s wind systems. The PMSG’s of the wind farm is connected to the DC collection grid through a DC/DC rectifier topology. The DC collection system is connected to the AC grid using single DC/AC inverter thus providing simple control technique which controls the number of PMSG generators. The output power fluctuations are compensated using direct torque control based maximum power point controller and direct power control. The DC link voltage and the active power injected to AC grid is controlled using grid side controller and the maximum power is extracted using the machine side controller of the wind turbine. Pitch angle control strategy is also used in order to reduce the turbine speed during high wind speed condition. The proposed controller provides aneffective solution for grid integration and constant power flow from the generator system to thegrid system. Simulation results are presented and analyzed the performance of the control strategies implemented in the system.