Single Loop Research Articles

Biot-Savart routines with minimal floating point error

A set of routines to compute the magnetic vector potential and magnetic field of two types of current carriers is presented. The (infinitely thin) current carrier types are a straight wire segment and a circular wire loop. The routines are highly accurate and exhibit the correct asymptotic behavior far away from and close to the current carrier. A suitable global set of test points is introduced and the methods presented in this work are tested against results obtained using arbitrary-precision arithmetic on all test points. The results are accurate to approximately 16 decimal digits of precision when computed using 64 bit floating point arithmetic. There are a few exceptions where accuracy drops to 13 digits. These primitive current carrier types can be used to assemble more complex arrangements, such as a current along a polygon (by means of defining straight wire segments from point to point along the polygon) and a multi-winding coil with circular cross-section. Reference data is provided along with the code for benchmarks with other implementations. Program summaryProgram Title: Biot-Savart Routines with Minimal Floating Point ErrorCPC Library link to program files:https://doi.org/10.17632/zcwk7zzt9y.1Developer's repository link:https://github.com/jonathanschilling/abscabLicensing provisions: Apache-2.0Programming language: C, Python, Java, FortranSupplementary material: Reference output data for all methods described in this article.Nature of problem: A common task in computational physics is to compute the magnetic field and magnetic vector potential originating from current-carrying wire arrangements. These current carriers are often approximated for computational simplicity as infinitely thin filaments following the center lines of the real current carrier. Computational methods are thus needed to compute the magnetic field and the magnetic vector potential of a single straight wire segment or a single circular wire loop as basis for modeling more complex current carrier arrangements by superposition of the current carrier primitives. A current carrier path specified by (x,y,z) coordinates can be modeled as a set of straight wire segments from point to point along the polygon describing the current carrier geometry. Closed circular wire loops are also commonly used as a proxy for a physical coil with helical windings.Solution method: Analytical expressions are derived in this work to accurately compute the magnetic field and the magnetic vector potential of a straight wire segment and a circular wire loop. The expressions consist of several special cases, which are automatically switched between depending on the location of the evaluation location in the coordinate system of the current carrier primitive. This approach guarantees that always the most accurate formulation available for a given evaluation location is used, including explicit use of simplifications in certain special cases for speed and accuracy.Additional comments including restrictions and unusual features: For most test cases, the full relative accuracy of the floating point arithmetic chosen for implementation is retained throughout the computations (16 digits of precision in the IEEE-754 binary64 implementation). There are a few exceptions where accuracy drops by up to 3 digits of precision (in the binary64 case). The provided implementations have not been optimized for speed.

Computational analysis of multichannel magnetothermal neural stimulation using magnetic resonator array.

Heating nanoparticles with a magnetic field could facilitate selective remote control of neural activity in deep tissue. However, current magnetothermal stimulation approaches are limited to single-channel stimulation. Here, we investigated various designs for multichannel magnetothermal stimulation based on an array of resonant coils that are driven by a single loop coil. Using a tuning capacitor that allows resonant coils to resonate at the operating frequency, each coil's ON and OFF resonance can be controlled, enabling us to select stimulation channels. We found that smaller inner diameters of resonant coils produce more localized magnetic fields while larger coils produce magnetic fields over a longer distance. The constructed multichannel resonant coil arrays can provide a high enough magnetic field intensity to raise the temperature of nanoparticles by 8°C when we apply 35.2W into the loop coil that is spaced 1mm from the target neurons. This multichannel stimulation using a simple resonant circuit approach would be useful for clinical applications of magnetothermal neural stimulation.

Removal of a leadless pacemaker using a 2.5cc syringe and silk thread during surgical treatment of infective endocarditis

Removal of a leadless pacemaker using a 2.5cc syringe and silk thread during surgical treatment of infective endocarditis

Percolation and dissolution of Borromean networks.

Inspired by experiments on topologically linked DNA networks, we consider the connectivity of Borromean networks, in which no two rings share a pairwise-link, but groups of three rings form inseparable triplets. Specifically, we focus on square lattices at which each node is embedded a loop which forms a Borromean link with pairs of its nearest neighbors. By mapping the Borromean link network onto a lattice representation, we investigate the percolation threshold of these networks (the fraction of occupied nodes required for a giant component), as well as the dissolution properties: the spectrum of topological links that would be released if the network were dissolved to varying degrees. We find that the percolation threshold of the Borromean square lattice occurs when approximately 60.75% of nodes are occupied, slightly higher than the 59.27% typical of a square lattice. Compared to the dissolution of Hopf-linked networks, a dissolved Borromean network will yield more isolated loops, and fewer isolated triplets per single loop. Our simulation results may be used to predict experiments from Borromean structures produced by synthetic chemistry.

Single Loop Voltage Control Strategy Based on Model Predictive Control for NPC-UPS

UPS can provide stable electrical energy for sensitive loads when severe grid disturbance happens. A neutral point clamped (NPC) three-level voltage source converter is used as the circuit topology for UPS. In this study, the discrete mathematical model of UPS is derived and a single voltage loop control strategy based on model predictive control is presented. The proposed method has a simple control structure and a fast response speed and omits the current inner loop and modulator. Furthermore, it can achieve ac voltage control and the balance of dc-side voltages. A three-level UPS simulation model is set up in PSCAD, and the efficacy of the proposed method is verified by means of simulation results under various types of loads.

DNA folding by protamine from loops to stacks.

In sperm, DNA undergoes a dramatic reorganization to a semi-crystalline state. This incredible compaction is the work of positively charged protamine proteins which bend and loop negatively charged DNA into a series of toroids. Interestingly, other positively charged molecules such as spermine or cations such as cobalt (+3) have been shown to form these toroid structures in vitro, indicating that the physics that drives this process is likely to be electrostatic. Still, the exact mechanism and the states in the folding pathway are unknown. We have previously shown that multiple protamine molecules “bind and bend” the DNA into a loop. But, what happens after loop formation? To answer this question, we measured folding by protamine in vitro on DNA molecules (length = 600-3000 bp) that are known to form several loops. Using atomic force microscopy (AFM), we were able to identify several intermediate folded structures: molecules with a single loop (a loop), molecules with two or more loops that were connected at a single location like a flower (flowers), and molecules with two or more loops stacked on top of one another (stacks). Using a tethered particle motion (TPM) assay we measured real-time folding of the DNA into these structures. At low protamine concentrations (0.1 µM), we observed many, long-lived, discrete folded states indicative of protamine bending, but at higher concentrations (>0.1 µM) these states appeared as a single, initial folding event. We hypothesize that this single, initial folding event is protamine bending the DNA all along its length, causing multiple loops. These loops then collapse into a stack. More work is necessary to determine how these stacks eventually form toroids. This work is important for spermiogenesis and DNA condensation, but also may useful in DNA nanoengineering.

Study on the load loss characteristics of a space nuclear power system with multi Brayton loops

Space nuclear power system (SNPS) is very attractive for the future civil and military space demands. SNPS with multi Brayton loops (SNPS-MBL) can achieve high-power output for space applications. The accident characteristics is the key to safe and efficient operation of SNPS-MBL. In this study, the dynamic model of the SNPS-MBL was established, the characteristics of SNPS with dual Brayton loops (SNPS-DBL) after single or dual Brayton loop (BL) load loss were studied. The results indicated that load loss was a serious accident. The positive torque on the turbine shaft after load loss increased the rotational speed rapidly to maximum value at 69.15 krpm exceeded the upper limit. Countermeasures should be taken after load loss. There was a coupling effect between the two BLs after load loss of single BL. load loss of the accident BL increased speed rapidly to 69.15 krpm, and decreased the BL power generation to 0 kW. The increase of inventory in normal operation BL increased power generation. Total power generation of SNPS-DBL decreased from rated value 150.8–81.8 kW. Furthermore, the influence of BL number on the safety of SNPS-MBL under accidents was analyzed. The results showed that increase of BL number improved the safety of SNPS-MBL in case of one BL load loss. The maximum speed of accident BL was not related to the number of BL. This study provides a reference for the design and operation of SNPS-MBL.

Transanal recto-anal anastomosis for treatment of rectal atresia: a review of 4 cases

IntroductionRectal atresia is a rare subtype of anorectal malformations in which the patients are born with a normal anal canal but have complete atresia located few centimeters proximal to the dentate line. We present the transanal end-to-end rectoanal anastomosis as a surgical technique for the management of these patients, highlight the outcomes, and emphasize on some clinical tips.MethodsFour patients were diagnosed as having rectal atresia on clinical and radiological basis. All of them underwent single loop low sigmoid colostomy in the first 24 h. After 6 months, transanal end-to-end rectoanal anastomosis was performed followed by closure of the stoma 3 months later.ResultsThe 2 cases that are older than 3 years demonstrated normal continence and are clean between bowel movements, while the other two showed good anal tone and passing stools between 1–3 times daily, being dry in between.ConclusionTransanal recto-anal anastomosis allows a safer route of anatomical reconstruction of the anorectum, therefore avoiding the potential complications associated with the other more invasive approaches.

Mechanical properties and strengthening mechanism of Ni/Al nanolaminates: Role of dislocation strengthening and constraint in soft layers

This work focuses on the mechanical properties and strengthening mechanism of Ni/Al nanolaminates, where dislocation strengthening and constraint dominate in the soft Al nanolayers. Nanoindentation and micropillar compression experiments highlight a constrained plasticity of Al nanolayers, which endows Ni/Al nanolaminates with a strain hardened behavior. Plasticity of Ni/Al nanolaminate begins with yielding of Al, and the Al yield strength depends on the individual layer thickness. Based on an inverse methodology, the Al yield strength as a function of Al grain size is determined. The results evidence a significant strengthening in the Al nanolayers. Specially, when Al layer thickness decreases from ≈110 nm to ≈16 nm, its yield strength is increased for ≈68 %, from ≈0.69 GPa to ≈1.16 GPa. The strengthening rule follows a confined layer slip model that is developed based on confining of single dislocation loops in nanolayers. Both the dislocation strengthening and the constraint effects in the Al layers contribute to a more sensitivity of Ni/Al strength with the variation of Al layer thickness, instead of Ni layer thickness. The work may forward the fundamental understanding in the strengthening mechanism and mechanical behavior of metallic nanolaminates with large elastoplastic mismatch.

Ship specific optimization of pre-duct energy saving devices using reduced order models

Hydrodynamic energy saving devices (ESD) have been widely explored as an effective alternative to improve energy efficiency of vessels by reducing losses across propellers, especially in the presence of strong interactions between hull and propellers. In this work, we propose a computational optimization framework for the design of pre-duct ESD for a specific hull form. For optimization of duct geometries, the framework is based on computational fluid dynamic (CFD) approach for prediction of hull resistance as well as propeller performance under changes in the design of pre-swirl duct geometrical parameters. We have implemented two improvements in the numerical procedure to speed up simulations; enabling the affordable computational design of the duct. First, an overset grid approach is used to realize a change in duct geometries on a background solution of flows over the hull and propeller only. This accelerates the convergence of RANS simulations for a specific design. For every single optimization loop, the propulsive energy efficiency was calculated using proper-orthogonal decomposition (POD) based reduced-order model for the hull, propeller, and duct. Using the POD interpolation technique it is possible to predict the resistance of hull and duct as well as propeller thrust at a particular design parameter using offline flow solutions pre-computed with a sample of design parameters. The accelerated CFD approach has been applied for design of pre-swirl duct on the Japan Bulk Carrier hull using the surrogate-based optimization approach. The performance of the propeller at the optimal design of the duct is simulated with CFD and compared with an earlier proposed duct design. The optimization framework demonstrates the potential of the approach for future applications for the design of ESDs for specific hulls, especially in retrofitting ships.

Adaptive shoot-through duty ratio control methodology of stand-alone quasi Z-source inverter

This paper presents an adaptive shoot-through duty ratio control methodology for a stand-alone three-phase quasi-Z-source inverter (qZSI). In practice, variable active and reactive load powers must be met by a qZSI-based stand-alone system. In this context, existing shoot-through control schemes for qZSI adjust the capacitor voltage or DC-link voltage at a fixed reference value. This causes extra voltage stresses on switches, high distortions, and an operating range reduction of the power inverter under variable load demands. On the contrary, the proposed shoot-through control scheme adjusts the shoot-through duty ratio adaptively based on load voltage feedback to improve performances. In this logic, the controllable shoot-through duty ratio facilitates various improved features in comparison to conventional schemes under load power variations. These features include reduced voltage stress across the switches, reduced distortions, and an extended operating range. The suggested proportional-integral (PI)-based scheme has a single control loop with a single measured quantity, i.e., sensing of load voltage only. The proposed concept has been verified via both simulation and experimental studies.

A software framework for virtual testing of a production control system

Production planning poses major challenges due to high product diversity, high fluctuations in demand and strong dynamic fluctuations in delivery quantities and times. This makes automation of production planning increasingly necessary to enable optimized sequence planning based on current production data. Production control systems (PRS) offer the possibility of automatic corrective actions in the event of deviations from the specified target dates. Production, PRS and data acquisition are considered as a single control loop and are the subject of various development and research topics. However, automatic interventions in planning and control can lead to serious disruptions if there are errors in the software of the PRS. Therefore, testing and validation of PRS is a crucial factor in development, but is hardly possible in real production environments due to the availability of physical manufacturing facilities and the associated risks. Therefore, in the scope of the paper, a concept for a software framework is proposed to provide a test environment for a PRS. A virtual production environment, which can be combined with the PRS and parameterized in form of a discrete-event simulation, offers the possibility to test the PRS. It is also possible to couple the simulation with a reference calculation to show the behavior of the production environment. The entire framework is designed to enable the identification of critical machines and times as well as, in further steps, the detection of software errors in the PRS.

A Chopper-Stabilized Amplifier With a Relaxed Fill-In Technique and 22.6-pA Input Current

In chopper amplifiers, the interaction between the input signal and the chopper clock can cause intermodulation distortion (IMD). This is mainly due to finite amplifier bandwidth, which causes signal-dependent output spikes at the chopping transitions. Such chopper-induced IMD can be mitigated by the fill-in technique, which involves ping-ponging between the outputs of two identical OTAs chopped in quadrature, thus generating a spike-free output. In this work, a relaxed implementation is proposed in which the output of a fill-in OTA is only briefly used to avoid the spikes of a chopped main OTA. As a result, the fill-in OTA does not need to be chopped, and so it can be duty-cycled to save power. Furthermore, the chopper ripple caused by the main OTA can now be suppressed by a single low-noise ripple-reduction loop, rather than the two AZ loops required in a previous ping-pong implementation of the fill-in technique. Compared to the latter, the proposed amplifier achieves similar IMD performance (-125.7dB), a 25× lower input current (22.6pA) and a flat noise floor (12 nV/Hz).

An Ultra-Low-Voltage Single-Crystal Oscillator-Timer (XO-Timer) Delivering 16-MHz and 32.258-kHz Clocks for Sub-0.5-V Energy-Harvesting BLE Radios in 28-nm CMOS

This paper reports an ultra-low-voltage (ULV) single-crystal oscillator-timer (XO-Timer) for sub-0.5 V Bluetooth low-energy (BLE) radios that aims for self-powering by harvesting the ambient energies. Specifically, we tailor an on-chip micropower manager (lPM) to customize the voltage and current budgets for each sub-function of the XO-Timer. Such lPM shows a high power efficiency by introducing a 3-stage cascaded structure and a single voltage-regulation loop; they together uphold the performance of the XO-Timer amid supply-voltage and temperature variations. The core amplifier of the XO-Timer is ULV-enabled, and is reconfigurable (i.e., 1-stage and 3-stage gm) to balance between the power budget and performance under the high-performance mode (HPM) and low-power mode (LPM). Fabricated in 28-nm CMOS, the XO-Timer in HPM generates a 16-MHz clock with a power of 24.3 lW, and a phase noise of.133.8 dBc/Hz at 1-kHz offset, resulting in a Figure-of-Merit (FoM1) of.236 dBc/Hz. In the LPM, the XO-Timer delivers a 32.258-kHz clock while consuming 11.4 lW. The sleep-timer FoM2 is 14.8 lW and the Allan deviation is 35.1 ppb, achieving the lowest supply voltage (0.25 V) not only for a dual-mode XO-Timer but also for a MHz-range XO.

Control Loop Stability Criterion and Interaction Law Analysis for Grid-Connected Inverter in Weak Grid

The study of stability criterion and interaction analysis for grid-connected inverter under weak grid is of great value. Different from traditional impedance stability criterion, this paper proposes control loop stability criterion for grid-connected inverter from the perspective of controller bandwidth overlap. Firstly, the system d-q overall small-signal model G0 considering phase-locked loop (PLL) of grid-connected inverter under weak grid is given and split into three multiplied independent parts: grid impedance, phase-locked loop and current controller. Then using the equivalent loop ratio expression obtained by combining PLL and grid impedance together and then divided by the current controller, the control loop stability criterion is proposed. The proposed stability criterion can not only maintain the independence of each single loop, but also can analyze the overall system stability. So, further analysis of the interaction law among the three parts under this control loop stability criterion is carried out by deducing the expression of the bandwidth ratio n of the PLL and current controller. And it is found that under the weak grid, the interaction between the links will be generated when the bandwidth ratio is greater than the threshold of n. This phenomenon can be represented by the overlapping area of amplitude-frequency curves in the bode diagram for G0. And the weaker the grid or the closer the bandwidth of PLL is to current controller, the larger the overlapping area of amplitude-frequency curves, and the more likely it is to lead the closed-loop gain to infinity. Furthermore, when the bandwidth of the current controller is fixed, the threshold of n varies in the regions of less than 1 as well as more than 1 with the change of the grid strength. Therefore, the system can remain stable no matter what the bandwidth ratio of the phase-locked loop to the current controller is greater or less than 1. Accuracy of the proposed control loop stability criterion and interaction analysis is verified through simulation and experimental results.

Wire Osteosynthesis in the Treatment of Mandible Fractures in Low Resource Settings: A Force Study.

Cadaveric investigation. Rigid internal fixation (RIF) using plates and screws is often not feasible in low and middle-income countries due to limited resources. Interosseous wiring to achieve semi-rigid fixation is often used, but lacks biomechanical force data. Herein we aim to quantitatively compare interosseous wiring to RIF. Cadaveric mandibles were fractured at the parasymphysis and angle. Fixation was achieved using interosseous wiring in both single wire loop and figure-of-eight formations, as well as plate and screw fixation (n = 5 for each fixation type at each fracture site). A force gauge was used to measure the number of Newtons (N) required to achieve diastasis and complete failure at the fixation site. For angle fractures, the mean force required for initial diastasis was 4.1, 5.9, and 10.9N for single wire, figure-of-eight wiring, and plating respectively (P < .001). Complete failure was achieved with 152.9, 168.9, and 237.6N of force for the three methods, respectively (P < .001). Complete failure was achieved for parasymphyseal fractures with 197.7, 263.0, and 262.8N of force for single wire, figure-of-eight wiring, and plating respectively (P = .002). Forces to achieve initial diastasis for parasymphyseal fractures were not statistically significant among the three fixation methods (P = .29). Figure-of-eight interosseous wiring resists comparable forces across mandibular fractures compared to the gold standard of plating. In resource-limited settings when plates and screws are not available, this technique can be considered to achieve semi-rigid fixation of mandibular fractures.

Phase Noise Modeling and Experimental Demonstration of Single and Dual-Loop Direct Modulation Optoelectronic Oscillator

A single and dual loop direct modulation Opto-Electronic Oscillator (DMOEO) phase noise model for generation of low phase noise signal operating in Radio Frequency (RF) and microwave frequency range is proposed and experimentally demonstrated. The distribute feedback (DFB) laser diode is used in the proposed design to perform the RF to optical conversion by exploiting its non-linear transfer function characteristics, in contrast to external modulator in conventional OEO designs. We presented the theoretical phase noise model for single and multi-loop DMOEO deign with all possible noise contributions. Also, simulation scenarios have been demonstrated to show the impact of different noise source on the overall phase noise performance of the OEO. A single and dual loop DMOEO with phase noise of −112 dBc/Hz and −110 dBc/Hz at 10 kHz offset from 2.4 GHz carrier respectively is designed and the side mode suppression better than 50 dB is achieved for the generated signal with 11 dBm output power.

Optimized Drainage of Pancreatic-Digestive Anastomosis in Patients with Pancreatoduodenal Resection

Summary The study compared early post-surgical complications between two groups of patients with pancreatoduodenal resection for pancreatic head carcinoma: patients with pancreatic-gastric anastomosis with mixed drainage and controls with pancreatic jejunal anastomosis with external drainage. The present study was a cohort study. The patient group was selected prospectively, and the control group – retrospectively. Patients were randomized by sex, age, primary tumor location, pancreatic parenchyma density, clinical symptoms, tumor–node–metastasis (TNM), and grade (G). We used the IBM SPSS Statistics software with the following tests: Fisher’s exact test, Pearson’s chi-squared test, Mann–Whitney U test. The optimized reconstruction approach with mixed drainage reduced early complications: early mortality - by 2.5%, overall morbidity - by 7.5%; pancreatic-digestive anastomosis insufficiency - by 2.5%; intra-abdominal bleeding - by 2.5%; intra-abdominal infection - by 2.5%; gastroparesis - by 5.0%; wound infection - by 2.5%; biliary leakage -by 2.5%. There were no cases of clinically significant pancreatic fistula. The control group was associated with an average of 9-fold higher relative risk of early complications. The passage was restored between the 4th and 7th day. Patients had a shorter average hospital stay (11 days) compared to controls (22 days). Digestive anastomoses reconstruction on a single loop and mixed intraluminal drainage through a modified nasogastric tube led to a 7-fold reduction in early post-surgical complications and a 2-fold shorter hospital stay.

Single-Loop Control for Single-Phase Dual-Boost Grid-Tied Inverter With Half Cycle Modulation and Feedforward Virtual-Vectors MPC

In this letter, a simplified single current loop control scheme for single-phase dual-boost inverter has been developed, combining half cycle modulation and virtual-vector (VV) based model predictive control (MPC). As the control reference can be slipped and allocated into two side boost, only a unified grid current reference is relied on in this proposed control method. Furthermore, with the concept of feedforward control, the global optimal solution space in MPC can be compressed, taking the duty ratio as boundary for the precompacted solution space. Thereby, the improved MPC can select the optimal VV in a smaller and closer subspace. Consequently, much finer control effect can be obtained. Experimental tests are provided to validate the proposed solution and its merits.

Experimental implementation of low-cost and robust sensorless control based on SOGI-FLL estimator for electric vehicles

Sensorless control techniques of electric motor dedicated to electric vehicles (EVs) offer low-cost and high operating performance. In this paper, a low-cost and robust speed-sensorless control scheme based on a second-order generalized integrator-frequency-locked loop method (SOGI-FLL) is proposed with only one current sensor. The SOGI-FLL is introduced to estimate accurately the motor angular speed from a measured current signal. While the scalar control technique, based on a single loop speed regulation, is used to determine the &lt;em&gt;‎&lt;/em&gt;control signals. According to the proposed control scheme, the overall system will be very effective in terms of low-cost control and easy practical implementation, which have a great impact on electric vehicle applications. dSPACE micro labox platform is used to implement the proposed control scheme to drive an induction motor. The obtained results confirm the effectiveness and high performance of the proposed control to properly estimate the angular speed and drive the induction motor.