Bidirectional Field Research Articles

In situ scanning electron microscopy study of strains of ionic electroactive polymer actuators

We have developed a technique to determine the bending strain of ionic electroactive polymer actuators without the use of the macroscopic bending geometry. In situ comparisons of the scanning electron microscope micrographs from a bending ionic electroactive polymer actuator, using a digital image correction methodology, identify its bi-directional deformation field. The developed technique allows verification of the factual axial and thickness strains of any notional layer of the actuator, including the outer surfaces of the electrodes. Thus, calculation of the bending and thickness strains of the ionic electroactive polymer laminate becomes possible. Moreover, the technique allows the determination of the position of the neutral layer of bending that is an important requirement for the calculation of the second area and bending moments of the beam. The four examples presented demonstrate the potential variations of the bending schemes, in cases where the neutral layer is at the centroid and shifted away from the centroid.

Investigation of magnetic field effect on pulsatile blood flow through the atherosclerotic right coronary artery

In the present work, flow characteristics of blood flow in the atherosclerotic right coronary artery in the presence of bi-directional magnetic field are investigated with numerical methods. The right coronary artery is one of two blood vessels that branch from the aorta and carry oxygen-rich blood to the heart muscle. Blockage of any branch of the coronary arteries causes death of a portion of the heart. A mathematical modelling is applied to analyse the pulsatile blood flow. Transient Navier-Stokes equations in 2D idealised arterial models of a bending artery coupled with Maxwell's equations for obtaining effect of magnetic field are discretised using the finite-volume method and solved by SIMPLE algorithm in curvilinear coordinate. The magnetic field is applied in both x and y directions. The amount of wall shear stress on the surface of atherosclerotic plaque is obtained for various times, and different states of magnetic field. Therefore, it is observed that how magnetic field modifies the flow patterns and decreases the destructive effects of atherosclerotic plaque.

The Heart as a Bi-directional Scalar Field Antenna

The Heart as a Bi-directional Scalar Field Antenna

Dynamic loss analysis for 4.5 MJ SMES

Dynamic or transient loss inside the proposed sector toroidal coil cryostat has been evaluated for the indigenous development of 4.5 MJ/1 MW superconducting magnetic energy storage (SMES) at VEC Centre, Kolkata. The frequent charging/discharging mode of operation in SMES coil results in dynamic loss that needs to be addressed for safe and reliable operation of the coil. The dynamic losses are derived considering local bi-directional magnetic field variation on the conductor for constant voltage output across the SMES coil through DC link. This loss will eventually determine the stability of Rutherford type cable inside the bath cooled cryostat. The result of dynamic loss analysis and subsequent additional cryogen load on plant is presented here.

Paper] High Efficiency Retransmission Control for Bidirectional Field Pick-up Unit Systems

Paper] High Efficiency Retransmission Control for Bidirectional Field Pick-up Unit Systems

SIFT flow for large-displacement object tracking.

Traditional tracking methods place an emphasis on how to cope with the variations in target appearance effectively. However, when the motion displacement of the target between image frames becomes larger, these methods may be unstable. This paper presents a novel (to our knowledge) visual object tracking method. In this method, we first introduce scale-invariant feature transform (SIFT) flow into the tracking problem and develop a real-time motion prediction method to capture large displacement between consecutive image frames. Then we use belief propagation (BP) to convert the problem of finding maximum a posteriori probability (MAP) to globally minimizing an energy function to get the best matching pairs of points for producing good candidate regions of the target. And last, the refined point trajectories are obtained according to the bidirectional flow field consistency estimation and covariance region descriptor matching, which can update model states efficiently so as to achieve enhanced robustness for visual tracking. Compared with the state-of-art tracking methods, the experimental results demonstrate that the proposed algorithm shows favorable performance when the object undergoes large motion displacement between image frames.

Bidirectional Repeating Long Pulse Magnet System for Magnetic Refrigerator

A bidirectional repeating long pulse magnet system for room temperature magnetic refrigerator has been designed in Wuhan National High Magnetic Field Center. By using ac power capacitor bank and anti-parallel thyristors, a bidirectional magnetic field is generated and the classical crowbar is removed for maximizing the utilization of energy. For the sake of long pulse width and repeating pulse application, a special rapid cooling magnet with large inductance of 87 mH and internal cooling channels is designed. It has a 60 mm bore and 16 layers, with 7 internal cooling channels built by annular sticks between layers. Finally, the proposed bidirectional repeating long pulse magnet system with bidirectional magnetic field of + 6.2 T/ -3.8 T and pulse width of 193 ms has been successfully achieved. The design and implementation of the proposed repeating pulsed magnet system will be presented in detail in the paper.

Wave energy fluxes and multidecadal shoreline changes in two coastal embayments in Denmark

Spatial patterns of multidecadal shoreline changes in two microtidal, low-energetic embayments of southern Zealand, Denmark, were investigated by using the directional distribution of wave energy fluxes. The sites include a barrier island system attached to moraine bluffs, and a recurved spit adjacent to a cliff coast. The barrier island system is characterized by cross-shore translation and by an alignment of the barrier alongshore alternating directions of barrier-spit progradation in a bidirectional wave field. The recurved spit adjacent to the cliff coast experienced shoreline rotation through proximal erosion and distal lateral accretion in a unidirectional wave climate. The multidecadal shoreline changes were coupled to a slope-based morphological coastal classification. All erosive shores occurred within a narrow range of onshore and offshore coastal slopes. The alongshore variability of directional distributions of wave energy fluxes furthermore outlined potential sediment sources and sinks for the evolution of the barrier island system and for the evolution of the recurved spit.

Topology of Blood Transport in the Human Left Ventricle by Novel Processing of Doppler Echocardiography

Novel processing of Doppler-echocardiography data was used to study blood transport in the left ventricle (LV) of six patients with dilated cardiomyopathy and six healthy volunteers. Bi-directional velocity field maps in the apical long axis of the LV were reconstructed from color-Doppler echocardiography. Resulting velocity field data were used to perform trajectory-based computation of Lagrangian coherent structures (LCS). LCS were shown to reveal the boundaries of blood injected and ejected from the heart over multiple beats. This enabled qualitative and quantitative assessments of blood transport patterns and residence times in the LV. Quantitative assessments of stasis in the LV are reported, as well as characterization of LV vortex formations from E-wave and A-wave filling.

Uni- and Bidirectional Flux Variation Loci Method for Analytical Prediction of Iron Losses in Doubly-Salient Field-Excited Switched-Flux Machines

Field-Excited Flux-Switching machines are doubly-salient machines with complex flux-density waveforms in the core. Hence, prediction of iron losses is difficult. In this article, we propose a method to determine flux loci in iron parts in an analytical manner, accounting for bidirectional field in back-irons of stator and rotor. The analytical model for flux-density prediction in the core at no-load was first validated with 2D FE simulations. Then measured iron losses on a prototype machine were used to calibrate an iron loss model. It was shown that in FE-SF machines rotor iron losses are not negligible and represent 28% of total iron losses. This model could be advantageously used in a design optimization procedure.

A Novel Dual-Permanent-Magnet-Excited Machine for Low-Speed Large-Torque Applications

This paper proposes a novel dual-permanent-magnet-excited (DPME) machine, in which two sets of permanent magnets (PMs) are employed, one on stator and the other on rotor. Bi-directional field modulation effect (BFME) is artfully engaged to guarantee the effective coupling between the magnetic field excited by the armature windings and those excited by the two sets of PMs. Machine configuration and its operating fundaments are elaborated. Finite element analysis demonstrates that the proposed DPME machine can offer much higher torque capability than its existing counterparts, which allows it a strong competitor for low-speed large-torque applications.

Bi-Directional Giant Magneto Impedance Sensor

A thin film giant magneto impedance (GMI) based on magnetic field sensor has been developed using electrodeposited Ni-Fe permalloy. Chemical composition, surface morphology, and magnetic properties of Ni-Fe permalloy were char-acterized as a function of plateup parameters, and process conditions were established to deposit a Ni-Fe thin film with a high permeability (~1000) and a low coercivity (0.6 Oersted). Conventional GMI sensors are uni-directional and are several millimeters long. In this work, a spiral-shaped sensor using electroplated Ni-Fe permalloy to detect bi-directional magnetic field is reported. Excellent bi-directional magnetic field sensing has been demonstrated using the 1 mm2 compact double-spiral structure.

Helical solutions of the bidirectional vortex in a cylindrical cyclone: Beltramian and Trkalian motions

In this work, two families of helical motions are investigated as prospective candidates for describing the bidirectional vortex field in a right-cylindrical chamber. These basic solutions are relevant to cyclone separators and to idealized representations of vortex-fired liquid and hybrid rocket engines in which bidirectional vortex motion is established. To begin, the bulk fluid motion is taken to be isentropic along streamlines, with no concern for reactions, heat transfer, viscosity, compressibility or unsteadiness. Then using the Bragg–Hawthorne equation for steady, inviscid, axisymmetric motion, two families of Euler solutions are derived. Among the characteristics of the newly developed solutions one may note the axial dependence of the swirl velocity, the Trkalian and Beltramian types of the helical motions, the sensitivity of the solutions to the outlet radius, the alternate locations of the mantle, and the increased axial and radial velocity magnitudes, including the rate of mass transfer across the mantle, for which explicit approximations are obtained. Our results are compared to an existing, complex lamellar model of the bidirectional vortex in which the swirl velocity reduces to a free vortex. In this vein, we find the strictly Beltramian flows to share virtually identical pressure variations and radial pressure gradients with those associated with the complex lamellar motion. Furthermore, both families warrant an asymptotic treatment to overcome their endpoint limitations caused by their omission of viscous stresses. From a broader perspective, the work delineates a logical framework through which self-similar, axisymmetric solutions to bidirectional and multidirectional vortex motions may be pursued. It also illustrates the manner through which different formulations may be arrived at depending on the types of wall boundary conditions. For example, both the slip condition at the sidewall and the inlet flow pattern at the headwall may be enforced or relaxed.

Construction of orthogonal synchronized bi-directional field to enhance heating efficiency of magnetic nanoparticles

Magnetic hyperthermia using magnetic nanoparticles (MNPs) has attracted considerable attention as one of the promising tumor therapy. The study has been developed under single magnetic field. Recently, we found that the immobile MNP may generate more heat under two synchronous ac magnetic fields than traditional single and circular polarized fields based on model simulation result. According to this finding we constructed an orthogonal synchronized bi-directional field (OSB field). The system contained two LC resonant inverters (L: inductor, C: capacitor) and both vertical and transverse ac magnetic fields were generated by two Helmholtz coils. To reduce the interference, the axis directional of two coils were arranged orthogonally. The experiments showed that the heating ability of aggregated MNPs is greatly enhanced under this newly designed OSB field without increasing the strength of magnetic field. The OSB field system provides a promising way for future clinical hyperthermia.

TU‐A‐BRA‐06: EPID Operation in a Bi‐Directional MRI‐Linac System: A Monte Carlo Study

Purpose: To examine via Monte Carlo simulation the dosimetric operation of an EPID inside a bi‐directional MRI‐Linac system. The proposed system is a 1 T MRI which supports both perpendicular (transverse) and inline (longitudinal) 6 MV MRIgRT. Methods: BEAMnrc Monte Carlo simulations were used to model a Varian 6 MV linac. Phase space files were produced below the MLCs and were inputs to Geant4 Monte Carlo simulations. These consist of transporting the radiation beam through a phantom and then on to a detailed model of a Varian EPID. The Geant4 simulations take place inside magnetic field maps matched to Finite Element Modeling of the MRI‐Linac system (COMSOL). Hence the EPID operation is simulated in the same conditions as a real MRI‐linac system. Various EPID SSD's were simulated in both inline and perpendicular field MRI‐linac systems. Dose to the EPID layers were taken for each field and compared with zero magnetic field. Results: The inclusion of the magnetic fringe field had little impact in the inline direction, however in the perpendicular direction the electron‐return effect (ERE) caused secondary electrons to return to the phosphor scoring level. This induced a lateral blur and overdosing of the images that was related directly to the SSD or strength of the fringe field in the transverse direction (5% at 0.25 T, 10% at 1 T). Including 1 cm of water material below the phosphor layer significantly reduced the ERE and improved the dose image quality. Conclusion: Novel Monte Carlo simulations of the operation of an EPID working inside a bidirectional field MRI‐linac have been performed. The main effect which induced an image or dose artifact was the ERE in the perpendicular field arrangement. This can however be almost eliminated by the use of an exit side bolus on the EPID.

Optical transmission modulation by disk-shaped ferromagnetic particles

Lithographically defined iron-nickel disks 1 micron in diameter and 60 nm in thickness with a spin-vortex ground state are used to achieve magnetic field-driven light modulation by passing the light through an aqueous solution of magnetic disks with controlled orientations. We demonstrate a significant improvement of the accessible modulation frequency over 60 Hz with a single modulating magnetic field of up to 1 kHz with alternating (ac) bi-directional field.

Fundamental Rules to Construct Highly Integrated Organic Nanowires as Nanodevices

Recent advances in inorganic nanowires techniques have led to more efficient and reliable electronic nanodevices as bipolar transistors, field effect transistors, junctions, logic-gate structures and applications from barcodes to LEDs. Otherwise, a true organic nanowire (ONW) device has not been realized. In this paper we describe few rules that will be useful to construct ONWs as well as the influence of mettalic contacts. Based on an equilibrium technique, we present electronic transport simulation for a well-known one-dimensional polymer prototype attached with donor/acceptor groups. Our results are consistent with: (i) asymmetric electronic transport (Charge Accumulation/Depletion-Voltage) curve for the ONW with and without the presence of contacts; (ii) for donor-polyacetylene-acceptor we find out assymetric nonresonance tunneling type conduction in the I–V curve; (iii) the aluminum atoms show to be a good candidate as mettalic contact when bonded with Sulfur atoms provoking rectification for lower values when compared with the system without Aluminum; (iv) For forward and reverse bias the resonance takes place suggesting in operational limit working as non-symetric bi-directional molecular field effect transistor (FET).

A Bidirectional Light Field ‐ Hologram Transform

Abstract In this paper, we propose a novel framework to represent visual information. Extending the notion of conventional image‐based rendering, our framework makes joint use of both light fields and holograms as complementary representations. We demonstrate how light fields can be transformed into holograms, and vice versa. By exploiting the advantages of either representation, our proposed dual representation and processing pipeline is able to overcome the limitations inherent to light fields and holograms alone. We show various examples from synthetic and real light fields to digital holograms demonstrating advantages of either representation, such as speckle‐free images, ghosting‐free images, aliasing‐free recording, natural light recording, aperture‐dependent effects and real‐time rendering which can all be achieved using the same framework. Capturing holograms under white light illumination is one promising application for future work.

Structure of the neuronal interactions underlying human contour integration

Contour integration is believed to be an important step in human image processing and object recognition, and has been shown to be performed very efficiently by the visual system. However, its neuronal mechanisms are still not well understood. Most contour integration models propose lateral connections between distant orientation columns of similar orientation preference for establishing a so-called 'association field', which links colinearily aligned edge elements into a single contour. However, these models differ both in their dynamics and structure. In some models, afferent input from visual stimuli and lateral input are summed up, in other models these quantities are multiplied. In addition, one finds different assumptions on the range, geometry, and symmetry of the lateral connectivity. It is often assumed that long-range horizontal interactions in V1 serve as the neuronal substrate for the association field. Probabilistic models require unidirectional lateral interactions, linking orientation columns in only one direction, in order to get optimal contour detection performance. In contrast, experimental findings in monkeys rather suggest isotropic connections, spreading symmetrically into all directions from an orientation column. In order to analyze the range and symmetry of lateral interactions underlying contour integration in the human brain, we compared simulations of multiplicative and additive model dynamics with psychophysical contour detection data. For these investigations we used stimuli generated from association fields with different geometries. As expected, models detect contours exceedingly well when using the same association field for contour generation and contour detection. However, analyzing the correlations between human behavior and model prediction on a trial-by-trial basis showed that human behavior is reproduced best, when using the same association field for all contour geometries. Furthermore it turned out that a bidirectional association field reaching only to the nearest neighboring edge elements can not explain the correlations found among the responses of different subjects, while a single unidirectional association field can do so. However, when assuming connections up to the next to-nearest-neighbor elements, a bidirectional association field also explains the correlations between human subjects. The stimuli were designed such that the distance between two neighboring elements lies within the range of long-range connections found in V1. Hence our results allow two possible conclusions: If contour integration relies on horizontal interactions of the spatial range like in V1, a so far unknown unidirectional linking mechanism between neuronal columns is required. If such a unidirectional mechanism does not exist, our results suggest that contour integration is based on interactions on a larger spatial scale as found in higher cortical areas.

Non-linear springing excitation due to a bidirectional wave field

Significant springing vibrations in ships have recently been measured in a large ocean-going bulk carrier. So far calculations using various linear and non-linear hydrodynamic procedures have not been able to predict the measured responses. In the present paper it is shown that the springing response depends strongly on second-order (sum frequency) terms involving cross-coupling terms from the combined wind- and swell-driven wave system. The calculations are based on the second-order strip theory formulation and thus no three-dimensional effects are accounted for. The agreement with measured springing responses is found to be greatly improved when these second-order cross-coupling terms are included.