Individual Coils Research Articles

A Model of bZIP Protein/DNA Recognition using Knob-Socket Analysis

The basic leucine zipper protein (bZIP) family binds specific DNA sequences through interactions between the individual α-helical coils and respective half-sites. Despite previous studies on target sequences and affinities of both homo- and heterodimers, the recognition and binding mechanism of bZIP dimers are not fully understood. Despite the relatively high homology between the subfamilies, dimers of bZIP coils have shown high variability in target sequences, ranging from conjoined and variably-spaced target sequences to novel and emergent sequences. To help elucidate the determinants of protein-DNA recognition, a novel Knob-Socket analysis of the packing at the protein and nucleic acid interface is able to produce an insightful model of half-site recognition specificity between a protein α-helix and the DNA double helix. The model not only characterizes the protein sequence motifs that recognize DNA bases, but uniquely is able to describe the DNA motifs that specifically pack protein residues. The bZIP coils studied include Jun, Fos, CREB, and C/EBP, through the analyses of their respective PDB files. For each half-site, the protein ɑ-helix splits recognition on both the positive and negative strands of the DNA double helix. Half of the α-helix packs into the first two nucleotides of the positive DNA strand, and the other packs into the last two nucleotides on the negative DNA strand. Along the i+4 ridge, a set of three conserved residues provides a dividing line on the protein helix between positive and negative DNA strand recognition. These three residues are also involved in a quadripartite region that specifically packs and recognizes the methyl group on a thymidine. Recognition of other bases are more complex and involve characterization of the DNA sequence motifs that pack and recognize residues on the protein α-helix.

Magnetic Force-Propelled 3D Locomotion Control for Magnetic Microrobots via Simple Modified Three-Axis Helmholtz Coil System

Magnetic microrobots are propelled by magnetic fields or magnetic field gradients generated by electromagnetic systems. Generally, 3D Helmholtz coils systems are used for microrobot propulsion, because of their low power consumption, ease of manufacture, and ease of control, for which, only three power supplies are required. Systems of this kind can only generate uniform magnetic fields, which limits their range of applications. However, generating both uniform magnetic fields and gradients typically requires more coils and power supplies, resulting in large expensive energy-intensive systems with complicated control algorithms. Although the aforementioned systems can control magnetic robots with up to 6 degrees of freedom (DOFs), most existing applications at the micro/nanoscale only require 2 rotational DOFs and 1 translational DOF. Here, we propose a new control system capable of producing 3D uniform magnetic fields with 3 DOFs and 3D gradients with 1 DOF. With this system, one pair of coils in a traditional 3D Helmholtz coil system is modified, to enable independent control of the individual coils directing a selected axis, while the configuration of the remaining two pairs of coils is unchanged. This results in a control system with low power consumption, and a simple control algorithm that can be easily applied to existing 3D Helmholtz systems, as it only requires the addition of a power supply. In combination with the developed system, we also propose a new control algorithm applicable to both permanently and temporarily magnetized microrobots, and verify this experimentally.

Alfvénic fluctuations measured by in-vessel Mirnov coils at the Wendelstein 7-X stellarator

The magnetic diagnostic system at the optimized stellarator experiment Wendelstein 7-X (W7-X) includes a total number of 125 Mirnov coils, which are mounted at the inner plasma vessel wall. A wide range of expected signal amplitudes, frequencies and mode numbers is covered to account for the complex three-dimensional geometry of W7-X. The performed amplitude and phase calibration of individual coils including all relevant data acquisition system components allows a detailed spectral and mode analysis. The damped multiple signal classification method and stochastic system identification techniques are shortly described and applied. Two observations are emphasized within this work. Firstly, independent of magnetic configuration and heating scenario (electron cyclotron resonance heating and/or neutral beam injection), broadband fluctuations around 180 kHz have been measured. The nature of these fluctuations is possibly associated with ellipticity-induced Alfvén eigenmodes in the outer regions of the plasma. The latter was inferred by studying corresponding theoretically predicted Alfvén continua calculated with the 3D-MHD continuum code CONTI. Secondly, fast collapses of plasma current and energy, which occurred during recent operational phases at W7-X, show a clear magnetic signature. Short time scale Alfvénic bursts are revealed, which are induced during these sawtooth-like collapses.

Synthesis of Amphiphilic Copolymers of Acrylic Acid and Styrene with the Desired Microstructure and Their Properties

The regularities of the controlled synthesis of amphiphilic copolymers of styrene and acrylic acid mediated by dithiobenzoate and trithiocarbonates as reversible addition fragmentation chain transfer agents in a 1,4-dioxane solution are considered. The influence of the general composition and chain microstructure on the dispersion stability and hydrodynamic sizes of polymer particles of copolymers containing from 40 to 90 mol % of acrylic acid units is studied. It is shown that in dilute aqueous media random copolymers are dispersed to individual compacted coils owing to the intrachain hydrophobic association of styrene units. The addition of two poly(acrylic acid) blocks to such a copolymer improves its dispersibility in water, and the attachment of two polystyrene blocks makes it insoluble in water because of the interchain association of polystyrene units. The synthesized copolymers possess surface activity, and when applied to a hydrophilic glass surface, they moderately hydrophobize it. In general, this synthetic approach opens up broad prospects for obtaining a wide range of new polymer macromolecules with different properties from one pair of traditional monomers.

Modeling the Resonance Shifts Due to Coupling Between HTS Coils in NMR Probes

Nuclear magnetic resonance (NMR) probes using thin-film HTS coils offer high sensitivity and are particularly suitable for small-sample applications. Typically, HTS probes are optimized for the detection of multiple nuclei and require several coils to be located within a small volume near the sample. Coupling between the coils shifts coil resonances and complicates coil trimming when tuning HTS probes. We have modeled the magnetic coupling between the coils of a 1.5-mm all-HTS NMR probe with 13C, 1H, and 2H channels. By measuring the magnetic coupling coefficients between individual coils, we solve the general coupling matrix given by KVL for six coupled resonators. Our results indicate that required trims can be accurately predicted by applying single coil trimming simulations to this magnetic coupling model. Use of the magnetic coupling model significantly improves the efficiency of tuning HTS probes.

An Inverse Calculation Study on Post-Quench Behavior of a No-Insulation REBCO Insert

This paper proposes an approach to account for a fast electromagnetic quench propagation among electromagnetically coupled no-insulation (NI) high temperature superconductor (HTS) coils. Recently, multiple groups have reported that the conventional lumped-circuit model, which has well demonstrated charging and discharging behaviors of an NI magnet, could not account for post-quench behaviors. Specifically, terminal voltages of individual pancake coils were estimated to be too high than the simulated ones. This paper proposes an approach that focuses on the post-quench simulation of an NI HTS magnet. To explain this phenomenon as a lumped circuit, a new approach was introduced. The key idea is inversely calculating key parameters of the lumped circuit that best demonstrates the non-linear post-quench behaviors. After defining the necessary assumptions, we adopted inverse-calculating methods to analyze the test results of high field NI HTS magnets. Simulation results suggest that after a quench, the index resistance changes in a different way from the previous theory, while the change in characteristic resistance is similar to conventional theory.

HTS synchronous machine critical current modelling and comparison with tests

Superconducting rotating machines generate high magnetic fields and for economic application of these machines and to ensure safe and reliable operation accurate assessment of the critical current of the superconductor is required. This paper describes a process to assess the critical current for a HTS synchronous machine with a superconducting rotor using a self-consistent numerical model. The model is used to study the critical current of first generation (1G) Bi-2223 pancake coils under self-field conditions for coil tests as well as within a machine magnetic field under full load conditions. Model results are compared against test measurements on individual HTS pancake coils as well as a double pancake coil in an operating synchronous machine at the Queensland University of Technology (QUT) test facility. Results obtain show that the self-consistent model is fast and accurate in determining the effective critical current of superconductors in such applications. Insights from the modelling assist with the design and optimisation process of the superconducting coils, selection of coil voltage sensing locations to detect the risk of quench and establish safe margins for the superconductor operating current.

Amphiphilic Copolymers of Acrylic Acid and n-Butyl Acrylate with the Predetermined Microstructure: Synthesis and Properties

Features of the synthesis of n-butyl acrylate copolymers with acrylic acid in 1,4-dioxane by free radical reversible addition-fragmentation chain transfer (RAFT) polymerization mediated by symmetric trithiocarbonates are considered. It is shown that the living mechanism of polymerization is realized in the studied systems. The chemical nature of the RAFT agent dictates different chain microstructures (random block or random) of the copolymers. The effect of chain microstructure on the properties of the copolymers containing about 90 mol % of acrylic acid units is studied by differential scanning calorimetry, contact angle measurements, turbidimetry, potentiometric titration, and dynamic light scattering. It is demonstrated that all the copolymers in the solid phase have similar properties: a single glass transition temperature close to the glass transition temperature of polyacid and a good water wettability. In dilute aqueous solutions, the properties of the copolymers are different: at the inherent pH, random copolymer macromolecules form large associates, while random block copolymers are dispersed into individual coils or micelles. All the copolymers are weaker polyacids compared with PAA; the random block copolymers are characterized by the compaction of macromolecules at small degrees of ionization. Our studies provide evidence that reversible addition-fragmentation chain transfer polymerization is an efficient tool for the targeted insertion of nonpolar units into a polyelectrolyte chain and it can be used for the fine-tuning of its properties.

Prediction of Mechanical Properties for High Strength Low Alloyed Steels in a Commercial Hot Dip Galvanizing Line without Soaking Section

The classical thermal cycle in a Hot Dip Galvanizing (HDG) line has four steps: heating, soaking, cooling, and aging. The furnace of an ArcelorMittal HDG line was revamped to increase its heating capacity. This new configuration without the soaking step led to the redefinition of the thermal cycles for all the steel grades, especially for High Strength Low Alloyed (HSLA) steels, where it was necessary to define a new control parameter based on time and temperature. This paper presents the work done to improve the control of the mechanical properties of HSLA steels in the HDG line. Four different types of numerical models (linear and polynomial regressions, artificial neural networks, and Multivariate Adaptive Regression Splines), are applied to predict the yield strength and the tensile strength of individual coils. It is concluded that the introduction of the time–temperature parameter improves the accuracy of the predictions over 10% in most of the cases. An additional improvement is obtained with the use of the process values corresponding to the sampling area instead of the coil average ones. The use of these models makes it possible, if necessary, to adjust individually the presets of the coils before processing them in the galvanizing line and reduce the scattering of the mechanical properties.

Optimized truncation to integrate multi-channel MRS data using rank-R singular value decomposition.

Multi‐channel phased receive arrays have been widely adopted for magnetic resonance imaging (MRI) and spectroscopy (MRS). An important step in the use of receive arrays for MRS is the combination of spectra collected from individual coil channels. The goal of this work was to implement an improved strategy termed OpTIMUS (i.e., optimized truncation to integrate multi‐channel MRS data using rank‐R singular value decomposition) for combining data from individual channels. OpTIMUS relies on spectral windowing coupled with a rank‐R decomposition to calculate the optimal coil channel weights. MRS data acquired from a brain spectroscopy phantom and 11 healthy volunteers were first processed using a whitening transformation to remove correlated noise. Whitened spectra were then iteratively windowed or truncated, followed by a rank‐R singular value decomposition (SVD) to empirically determine the coil channel weights. Spectra combined using the vendor‐supplied method, signal/noise2 weighting, previously reported whitened SVD (rank‐1), and OpTIMUS were evaluated using the signal‐to‐noise ratio (SNR). Significant increases in SNR ranging from 6% to 33% (P ≤ 0.05) were observed for brain MRS data combined with OpTIMUS compared with the three other combination algorithms. The assumption that a rank‐1 SVD maximizes SNR was tested empirically, and a higher rank‐R decomposition, combined with spectral windowing prior to SVD, resulted in increased SNR.

SoftCharge: Software Defined Multi-Device Wireless Charging Over Large Surfaces

This paper proposes a method for converting a large existing surface into a programmable wireless charger, capable of distributing energy efficiently at multiple locations on demand and charge different types of devices. The key innovation here is to combine magnetic resonance-based energy transfer with the so called concept of `energy hopping' across wireless inter-connected coils, where the magnetic fields are carefully shaped on the fly. The overall framework, called SoftCharge, has three components: (i) energy tiles (ETs), which are individual programmable coil units that can be attached underneath an existing table with AC mains supply only to the master tile, (ii) energy shaping algorithm executed by the master tile, that shapes the flow of energy over tiles through real-time impedance adjustment combined with selective power blocking, creating optimal energy paths to specific tiles where a device needs to be charged, and (iii) a resonance sensing architecture design and method executed in each given tile that detects the type of device to be charged and its location without any direct feedback. We build a prototype of energy tiles and provide experimental results on SoftCharge charging multiple COTS devices like mobile phones, laptops, tablets, and drones, resulting in a maximum charging rate of 23 W up-to 20 cm over a larger surface.

Reducing the measurement error of signal propagation delays using an optical reflectometer with picosecond resolution

The problems requiring high-precision measurements of signal propagation delays in optical fibers are considered. Design features of a pulsed optical reflectometer with a picosecond resolution designed for measuring propagation delays of a signal are considered. It is shown that the error of such a reflectometer includes the additive and multiplicative components. A method for determining the additive component of the optical reflectometer error based on measurements of signal delays introduced by individual optical fiber coils and the total delay introduced by series-connected coils is proposed. The requirements to the measurement conditions are formulated and the results of the error estimation of the proposed method are presented. To exclude the multiplicative component of the reflectometer error, a method for determining corrections to the reflectometer readings is proposed. The method is based on measuring the propagation delays of the signal in the coils of the optical fiber, first using reference equipment (installation for measuring the propagation delay of the signal), and then using an optical reflectometer, and then calculating the differences of the obtained measurement results. The scheme of installation for measurements of a propagation delay of signal in a coil of optical fiber is presented, the principle of operation of measuring installation is described. The results of the estimation of the error in determining the corrections to the reflectometer readings by the proposed method are presented. It is shown that the exclusion of the additive and multiplicative components of the error will reduce the error of optical reflectometers to values less than ± 100 ps.

Sensitivity analysis of different quality assurance methods for magnetic resonance imaging in radiotherapy.

Background and purposeThere are currently no standard quality assurance (QA) methods for magnetic resonance imaging (MRI) in radiotherapy (RT). This work was aimed at evaluating the ability of two QA protocols to detect common events that affect quality of MR images under RT settings.Materials and methodsThe American College of Radiology (ACR) MRI QA phantom was repeatedly scanned using a flexible coil and action limits for key image quality parameters were derived. Using an exploratory survey, issues that reduce MR image quality were identified. The most commonly occurring events were introduced as provocations to produce MR images with degraded quality. From these images, detection sensitivities of the ACR MRI QA protocol and a commercial geometric accuracy phantom were determined.ResultsMachine-specific action limits for key image quality parameters set at were comparable with the ACR acceptable values. For the geometric accuracy phantom, provocations from uncorrected gradient nonlinearity effects and a piece of metal in the bore of the scanner resulted in worst distortions of 22.2 mm and 3.4 mm, respectively. The ACR phantom was sensitive to uncorrected signal variations, electric interference and a piece of metal in the bore of the scanner but could not adequately detect individual coil element failures.ConclusionsThe ACR MRI QA phantom combined with the large field-of-view commercial geometric accuracy phantom were generally sensitive in identifying some common MR image quality issues. The two protocols when combined may provide a tool to monitor the performance of MRI systems in the radiotherapy environment.

An omnidirectional WPT platform for distributed fully implanted neural recording systems

Recent progress on human brain science requires developing advanced neural recording system to capture the activity of large neural populations accurately, across a large area of the brain, and over extended periods. Recently proposed distributed neural recording systems with numerous implanted devices require reliably energizing them wirelessly. Random distribution of these mm-sized implants and brain motion place them at different positions and orientations with respect to the power transmitter. Therefore, traditional wireless power transfer techniques fall short of reaching sufficient power for all implants simultaneously, rendering some implants nonfunctional. In this paper, a three-layer power transmitting array with three-phase coil excitation current is introduced, which is capable of producing omnidirectional and homogeneous magnetic field across the volume where the Rx coils are located. The individual coil dimensions in the array is optimized to improve the worst-case scenario in terms of homogeneity, which is further verified by the measurements using a scaled-up prototype system. The measurement results show that the minimum received voltages is improved from 0.34 V for 10-mm side-length hexagonal transmitting coil array to 0.83 V for the optimal case, i.e., 35 mm side-length hexagonal transmitting coil array.

Simulation and experimental investigation of a multi-pole multi-layer magnetorheological brake with superimposed magnetic fields

This paper presents comprehensive investigations on a new multi-pole multi-layer magnetorheological (MR) brake. This unique design features MR working gaps set between two-layer individual coils. Independent current supply was proposed to generate more flexible braking torque and lower power consumption. In this article, an exploded-view drawing of the proposed MR brake was presented, and theoretical analyses of the braking torque and temperature characteristic were conducted. Then, finite element analysis was performed to verify the effect of the magnetic field superposition. A prototype MR brake was fabricated and tested to evaluate the magnetic field superposition, preliminary dynamic behavior, temperature and the performance of individual input current. The results show that the magnetic field superposition has much influence on the braking torque, and individual current supply results in different power consumption and torque ranges. Moreover, the dynamic response performance of this brake is less affected by the slip speed. Furthermore, the maximum steady-state slip power of the proposed brake is about 160 W, and the greater the slip power is, the faster the temperature increases. The results also have verified the correctness of the structure and magnetic circuit design.

A small-molecule competitive inhibitor of phosphatidic acid binding by the AAA+ protein NSF/Sec18 blocks the SNARE-priming stage of vacuole fusion

The homeostasis of most organelles requires membrane fusion mediated by soluble N -ethylmaleimide-sensitive factor (NSF) attachment protein receptors (SNAREs). SNAREs undergo cycles of activation and deactivation as membranes move through the fusion cycle. At the top of the cycle, inactive cis-SNARE complexes on a single membrane are activated, or primed, by the hexameric ATPase associated with the diverse cellular activities (AAA+) protein, N-ethylmaleimide-sensitive factor (NSF/Sec18), and its co-chaperone α-SNAP/Sec17. Sec18-mediated ATP hydrolysis drives the mechanical disassembly of SNAREs into individual coils, permitting a new cycle of fusion. Previously, we found that Sec18 monomers are sequestered away from SNAREs by binding phosphatidic acid (PA). Sec18 is released from the membrane when PA is hydrolyzed to diacylglycerol by the PA phosphatase Pah1. Although PA can inhibit SNARE priming, it binds other proteins and thus cannot be used as a specific tool to further probe Sec18 activity. Here, we report the discovery of a small-molecule compound, we call IPA (inhibitor of priming activity), that binds Sec18 with high affinity and blocks SNARE activation. We observed that IPA blocks SNARE priming and competes for PA binding to Sec18. Molecular dynamics simulations revealed that IPA induces a more rigid NSF/Sec18 conformation, which potentially disables the flexibility required for Sec18 to bind to PA or to activate SNAREs. We also show that IPA more potently and specifically inhibits NSF/Sec18 activity than does N-ethylmaleimide, requiring the administration of only low micromolar concentrations of IPA, demonstrating that this compound could help to further elucidate SNARE-priming dynamics.

Dual-Tuned Monopole/Loop Coil Array for Concurrent RF Excitation and Reception Capability for MRI

Radiofrequency (RF) coils based on two operating frequencies, or dual-tuned (DT) coils, for magnetic resonance imaging (MRI) in parallel with MR spectroscopy (MRS) and MR spectroscopy imaging (MRSI) are used to obtain morphological and metabolic information for early diagnosis of diseases. However, this method suffers from serious problems such as the extremely low signal sensitivity of X-nuclei and the long image acquisition time required for the two measurements. In this study, a single-channel DT coil was proposed for RF excitation/reception (Tx/Rx) of hydrogen (1H) and phosphorous (31P) by using a monopole antenna and a loop coil, and it was extended to an eight-channel volume coil at 7 T. To verify the DT coil performance, we compared the single RF port of the DT coil with monopole/loop geometry to the individual coil of the 1H monopole antenna and the 31P loop coil with a cylindrical phantom. The monopole/loop coil shows no magnetic flux interaction between individual coils despite the superimposed positions owing to the single RF port. The study results demonstrated that the proposed DT monopole/loop (DTML) coil can be extended to multiple RF Tx/Rx systems and can reduce the acquisition time with a single measurement.

Optimizing acquisition and fitting conditions for 1 H MR spectroscopy investigations in global brain pathology.

To optimize acquisition and fitting conditions for nonfocal disease in terms of voxel size and use of individual coil element data. Increasing the voxel size yields a higher signal-to-noise ratio, but leads to larger linewidths and more artifacts. Several ways to improve the spectral quality for large voxels are exploited and the optimal use of individual coil signals investigated. Ten human subjects were measured at 3T using a 64-channel receive head coil with a semi-LASER localization sequence under optimized and deliberately mis-set field homogeneity. Eight different voxel sizes (8 to 99cm3 ) were probed. Spectra were fitted either as weighted sums of the individual coil elements or simultaneously without summation. Eighteen metabolites were included in the fit model that also included the lineshapes from all coil elements as reflected in water reference data. Fitting errors for creatine, myo-Inositol and glutamate are reported as representative parameters to judge optimal acquisition and evaluation conditions. Minimal Cramér-Rao lower bounds and thus optimal acquisition conditions were found for a voxel size of ~ 70cm3 for the representative upfield metabolites. Spectral quality in terms of lineshape and artifact appearance was determined to differ substantially between coil elements. Simultaneous fitting of spectra from individual coil elements instead of traditional fitting of a weighted sum spectrum reduced Cramer-Rao lower bounds by up to 17% for large voxel sizes. The optimal voxel size for best precision in determined metabolite content is surprisingly large. Such an acquisition condition is most relevant for detection of low-concentration metabolites, like NAD+ or phenylalanine, but also for longitudinal studies where very small alterations in metabolite content are targeted. In addition, simultaneous fitting of single channel spectra enforcing lineshape and coil sensitivity information proved to be superior to traditional signal combination with subsequent fitting.

PARAMETRIC ANALYSIS AND STRAY FIELDS OF TOROIDAL SUPERCONDUCTING MAGNETIC ENERGY STORAGE

Purpose. To carry out a parametric analysis of superconducting toroidal magnetic systems with a discrete winding, establishing the possibility of using an idealized model in the form of a toroidal current surface and an approximate method for determining the level of fields of scattering of a real magnetic system. Methodology. The calculation of the distribution of the magnetic flux density in the winding, the field of scattering and energy of the storage’s field was carried out using asymptotic methods for solution of the problems of electrodynamics in systems with massive curvilinear conductors with current. An iterative calculation procedure was used to determine the dimensionless characteristics. Results. The dimensionless characteristics of a toroidal magnetic system with a winding in the form of individual superconducting coils of circular shape are calculated. The results are obtained depending on the value of the storage's energy capacity for various values of the relative radial size of the torus. For a toroidal superconducting storage device with energy capacity of 450 MJ, enough to perform the function of damping irregular oscillations of power transmitted over the transmission line, magnetic fields of scattering are calculated for different numbers of coils and torus section sizes. Originality. Based on a comparison of the values of dimensionless characteristics calculated for a system with individual coils, and for an idealized mathematical model of a continuous current surface, it was established that the relative deviation of the dimensionless characteristics does not exceed 10 %. In contrast to the idealized model, the magnetic field of a toroidal system composed of individual coils spreads beyond the toroidal surface and decreases the faster, the smaller the relative radial sectional size of the torus, the greater the number of coils used and the closer they are to each other. Practical value. The results obtained for dimensionless characteristics allow to conclude that the idealized model can be used at the first stage of the development of a superconducting inductive storage. The estimation of the field of scattering can be made on the basis of a simple model of unidirectional current filaments.

Experimental validation of an inductive probe for narrow gap measurement based on numerical modelling

Experimental validation of numeric results for an inductive probe shows that narrow gaps between two plates can be measured with accuracy suitable for laser beam welding. A two-coil inductive probe for measurement of the gap was built based on finite element modelling results. The individual coils were calibrated using a complex response method, and results from the physical coils closely match the numerical results regarding distance to gap and lift-off above the plate. The measurement of a realistic gap shows results that can be used in industrial applications for position, plate height and height alignment.