Current Loop Model Research Articles

Compton effect in terms of spintronic

Compton effect with spin effect is studied. Although the incoming wave has been taken into account in the current loop model the final result is the same as before. Namely, the total angular momentum in z-direction before the collision will be equal to the total angular momentum after the collision. Let us take the z-component of the spin of the incident light as, (1, 0, −1) and the spin of the electron as, (½, −½). Applying the conservation of the z-component of the total angular momentum gives access to spin-flips. We find that the probability of spin-flip is 40%. We believe that this analysis will be helpful for deepening in the spintronic event better.

Conformational sampling and structure prediction of multiple interacting loops in soluble and β-barrel membrane proteins using multi-loop distance-guided chain-growth Monte Carlo method.

Loops in proteins are often involved in biochemical functions. Their irregularity and flexibility make experimental structure determination and computational modeling challenging. Most current loop modeling methods focus on modeling single loops. In protein structure prediction, multiple loops often need to be modeled simultaneously. As interactions among loops in spatial proximity can be rather complex, sampling the conformations of multiple interacting loops is a challenging task. In this study, we report a new method called multi-loop Distance-guided Sequential chain-Growth Monte Carlo (M-DiSGro) for prediction of the conformations of multiple interacting loops in proteins. Our method achieves an average RMSD of 1.93 Å for lowest energy conformations of 36 pairs of interacting protein loops with the total length ranging from 12 to 24 residues. We further constructed a data set containing proteins with 2, 3 and 4 interacting loops. For the most challenging target proteins with four loops, the average RMSD of the lowest energy conformations is 2.35 Å. Our method is also tested for predicting multiple loops in β-barrel membrane proteins. For outer-membrane protein G, the lowest energy conformation has a RMSD of 2.62 Å for the three extracellular interacting loops with a total length of 34 residues (12, 12 and 10 residues in each loop). The software is freely available at: tanto.bioe.uic.edu/m-DiSGro. jinfeng@stat.fsu.edu or jliang@uic.edu Supplementary data are available at Bioinformatics online.

Tilted loop currents in cuprate superconductors

The paper briefly surveys theoretical models for the polar Kerr effect (PKE) and time-reversal symmetry breaking in the pseudogap phase of cuprate superconductors. By elimination, the most promising candidate is the tilted loop-current model, obtained from the Simon–Varma model by tilting one triangular loop up and another one down toward the apical oxygens. The model is consistent with the PKE, spin-polarized neutron scattering, and optical anisotropy measurements. Spontaneous currents in this model flow between the in-plane and apical oxygens in such a manner that each oxygen belongs to one current loop. This loop-current pattern is similar to the spin order in the magnetoelectric antiferromagnet Cr2O3, where the PKE is observed experimentally. By analogy, it should be possible to train the PKE sign in the cuprates magnetoelectrically. Several experiments are proposed to confirm the loop-current order: the magnetic-field-induced polarity, the nonlinear anomalous Hall effect, and the second-harmonic generation.

Quantum spin Hall effect in a three-orbital tight-binding Hamiltonian

We consider the quantum spin hall (QSH) state in a three-orbital model, with a certain spin loop current order which is induced by spin-dependent interactions. This type of order is motivated by the loop current model, which was proposed long ago to describe the pseudogap phase of cuprates. It is shown that this model has nontrivial Chern parity by directly counting the zeros of the Pfaffian of the time reversal operator. By connecting to the second Chern number, we explicitly show the property of singularities of the wave-functions, and also their dependance on the gauge choices. Also it is shown that the Berry phase of the QSH state can be mapped to a non-Abelian instanton.

Connection stiffness and dynamical docking process of flux pinned spacecraft modules

This paper describes a novel kind of potential flux pinned docking system that consists of guidance navigation and control system, the traditional extrusion type propulsion system, and a flux pinned docking interface. Because of characteristics of passive stability of flux pinning, the docking control strategy of flux pinned docking system only needs a series of sequential control rather than necessary active feedback control, as well as avoidance of hazardous collision accident. The flux pinned force between YBaCuO (YBCO) high temperature superconductor bulk and permanent magnet is able to be given vent based on the identical current loop model and improved image dipole model, which can be validated experimentally. Thus, the connection stiffness between two flux pinned spacecraft modules can be calculated based on Hooke's law. This connection stiffness matrix at the equilibrium position has the positive definite performance, which can validate the passively stable connection of two flux pinned spacecraft modules theoretically. Furthermore, the relative orbital dynamical equation of two flux pinned spacecraft modules can be established based on Clohessy-Wiltshire's equations and improved image dipole model. The dynamical docking process between two flux pinned spacecraft modules can be obtained by way of numerical simulation, which suggests the feasibility of flux pinned docking system.

Proposed Chiral Texture of the Magnetic Moments of Unit-Cell Loop Currents in the Pseudogap Phase of Cuprate Superconductors

We propose a novel chiral order parameter to explain the unusual polar Kerr effect in underdoped cuprates. It is based on the loop-current model by Varma, which is characterized by the in-plane anapole moment N and exhibits the magnetoelectric effect. We propose a helical structure where the vector N(n) in the layer n is twisted by the angle π/2 relative to N(n-1), thus breaking inversion symmetry. We show that coupling between magnetoelectric terms in the neighboring layers for this structure produces optical gyrotropy, which results in circular dichroism and the polar Kerr effect.

Field‐aligned current loop model on formation of sporadic metal layers

This paper proposes a new mechanism for the formation of the sporadic layers by metallic ions as well as metallic atoms in the lower thermosphere and upper mesosphere. The mechanism is based on sporadic occurrence of an electric current loop consisting of the magnetic field‐aligned current (FAC) and horizontal Pedersen current in the ionosphere connected with the FAC. The essential point of the present mechanism is the existence of the horizontal electric field convergence at the foot of the upward FAC region in the current loop, where the positive ions including the metallic ions may converge by the horizontal Pedersen flow. The accumulated metallic ions are reacted to the clustered metallic ions, which are transferred to the metallic atoms through the dissociative recombination with electrons. The density profile of the sporadic layer for metallic ions has been obtained in the analytical form by solving the continuity equation. The density profile of the sporadic layer for metallic atoms has been obtained also in the analytical form by assuming that 100% of the loss of the metallic ions is converted to metallic atoms. The simulation based on the present mechanism has been examined with respect to three species of metallic components: sodium, iron, and calcium. The sporadic sodium layer (SSL) derived from the present model is compared with the SSL observed by the sodium lidar installed at the European Incoherent Scatter radar site in Tromsø (69.6°N, 19.2°E), Norway, and reasonable agreement has been attained with respect to the density profile of the SSL.

CNC Servo System Base on PMSM

The paper study object is the CNC servo system, and it presented three closed-loops control strategy based on PMSM. Through dynamic mathematical model of current loop, rotational speed loop and position loop were established and simplified. The closed-loop regulator was designed. The system was corrected by the controller. The simulation, tuning and calculation of the closed-loop were carried in MATLAB/SIMULINK. The results indicated that the system design was correct, and the desired effect of control was achieved.

LORENTZ SELF-FORCE OF AN ELLIPSE CURRENT LOOP MODEL

In this work, the Lorentz self-force of an ellipse current loop model is derived. We are motivated by the fact that it has been reported in the literature that coronal mass ejection morphology can resemble an ellipse in the field of view of coronagraph images. Deriving the Lorentz self-force using an ellipse geometry has the advantage of being able to be solved analytically, as opposed to other more complex geometries. The derived ellipse model is compared with the local curvature approximation, where the Lorentz self-force at the ellipse major/minor axis is compared with the Lorentz self-force of a torus with curvature equal to the local curvature at the ellipses major/minor axis. It is found that the local curvature approximation is valid for moderate values of eccentricity.

Modeling and analysis of current harmonic distortion from grid connected PV inverters under different operating conditions

Due to the fast growth of photovoltaic (PV) installations, concerns are rising about the harmonic distortion generated from PV inverters. High current total harmonic distortion (THD) occurs when PV inverters operate under light load conditions due to low solar insolation. A general model modified from the conventional control structure diagram is introduced to analyze the harmonic formation process. Causes of the current harmonics are summarized and its relationship with output power levels is analyzed. The field measurement for current harmonics is carried out at the Commonwealth Scientific and Industrial Research Organisation (CSIRO) microgrid to validate the analysis results. In particular for two-stage inverter, unlike previous papers that assume the DC-link voltage is constant, the DC-link voltage ripple is identified as the source of a series of odd harmonics. A mew periodic time-varying model is proposed by including the DC-link voltage ripple into the conventional current control loop model. This model is able to simulate the characteristics of the harmonic components and show their dependence on the DC-link voltage ripple.

Random Coordinate Descent with Spinor-matrices and Geometric Filters for Efficient Loop Closure.

Protein loop closure constitutes a critical step in loop and protein modeling whereby geometrically feasible loops must be found between two given anchor residues. Here, a new analytic/iterative algorithm denoted random coordinate descent (RCD) to perform protein loop closure is described. The algorithm solves loop closure through minimization as in cyclic coordinate descent but selects bonds for optimization randomly, updates loop conformations by spinor-matrices, performs loop closure in both chain directions, and uses a set of geometric filters to yield efficient conformational sampling. Geometric filters allow one to detect clashes and constrain dihedral angles on the fly. The RCD algorithm is at least comparable to state of the art loop closure algorithms due to an excellent balance between efficiency and intrinsic sampling capability. Furthermore, its efficiency allows one to improve conformational sampling by increasing the sampling number without much penalty. Overall, RCD turns out to be accurate, fast, robust, and applicable over a wide range of loop lengths. Because of the versatility of RCD, it is a solid alternative for integration with current loop modeling strategies.

Lateral Force and Lateral Connection Stiffness of Flux Pinned Docking Interface

Another novel flux pinned docking interface consisting of an YBCO high temperature superconductor bulk and two electromagnets is designed in order to improve the connection stiffness of this docking interface and the detailed control strategy of the docking process is introduced. Using this novel docking interface, two spacecraft modules appear with a noncontacting connection status through intervehicle interaction, but with the characteristics of passive stability. The identical current loop model is proposed based on the Ampere current loop hypothesis to treat the magnetic field of the cylindrical permanent magnet that may be installed in the flux pinned docking interface, and the improved image dipole model is adopted with the intention of analyzing the flux pinned lateral force of the novel docking interface theoretically. Additionally, the experiment data of the flux pinned lateral force between a YBCO high temperature superconductor bulk and a cylindrical NdFeB permanent magnet is collected. The theoretical calculation and experimental data both show an initial decrease then increase with the increase of lateral displacement. Moreover, the theoretical analysis compared to the corresponding experimental data indicates that the improved image dipole model is an effective approach. Furthermore, the flux pinned lateral connection stiffness is obtained based on Hooke’s law, showing that this stiffness initially decreases then increases as the lateral displacement that is larger than zero increases.

DC Link Active Power Filter for Three-Phase Diode Rectifier

In this paper, a dc link active power filter (APF) for three-phase diode rectifier is proposed. The proposed dc link APF, which is composed of two series-connected bidirectional boost converters, intends to eliminate the input current harmonics. It is paralleled at the dc link of the diode rectifier and is coupled to the ac input with three line-frequency switches. Compared with the full power processed power factor correction (PFC) solution, the dc link APF is partially power processed in that it only compensates for the harmonic current component at the dc link. Thus, it features with lower power processing. Moreover, it exhibits better total harmonic distortion of the ac line current when compared with the traditional ac side shunt APF. Voltage and current loop models are developed for average current control, and the selection of the current loop bandwidth is presented. Switching stresses of the ac APF, the dc link APF, and the six-switch PFC are also calculated and analyzed. Experimental and simulation results demonstrate the effectiveness of this dc link APF.

Conceptual design of a novel insertion device using bulk superconducting magnet

An undulator or a wiggler with a strong magnetic field will play an important role in future synchrotron light sources, free electron lasers, and linear colliders. We proposed the bulk high critical temperature superconductor staggered array undulator (Bulk HTSC SAU) in order to generate a strong periodic field. The Bulk HTSC SAU consists of stacked bulk high-Tc superconductors (HTSs) and a solenoid magnet which is used to magnetize the bulk HTSs. A periodic magnetic field was produced and controlled using a prototype of the Bulk HTSC SAU using 11 pairs of REBaCuO bulk HTSs at 77K. The expected performance at low temperatures around 20K is calculated using a loop current model.

The Zero-Crossing Distortion and One Cycle Control in Single-phase PFC

Input current distortion in the vicinity of input voltage zero crossing of Boost single-phase active power factor corrected rectifier in high line frequency is studied based on one cycle control method in this paper. The current loop model and input admittance model of active power correction based on one cycle control is particularly analyzed. The results point out that its equivalent power stage of current loop is a 1st order system, and that its input admittance is the pure resistive around low frequency domain and the capacitive characteristics above 1 kHz. From about the frequency 1 kHz, then, the input line current phase leads input voltage. However, it is does not matter in aero ac power system with 400Hz or 360~800Hz line frequency in the future, and it is suitable for applications as front converter in aero power supply system.

Protein loop modeling by using fragment assembly and analytical loop closure.

Protein loops are often involved in important biological functions such as molecular recognition, signal transduction, or enzymatic action. The three dimensional structures of loops can provide essential information for understanding molecular mechanisms behind protein functions. In this article, we develop a novel method for protein loop modeling, where the loop conformations are generated by fragment assembly and analytical loop closure. The fragment assembly method reduces the conformational space drastically, and the analytical loop closure method finds the geometrically consistent loop conformations efficiently. We also derive an analytic formula for the gradient of any analytical function of dihedral angles in the space of closed loops. The gradient can be used to optimize various restraints derived from experiments or databases, for example restraints for preferential interactions between specific residues or for preferred backbone angles. We demonstrate that the current loop modeling method outperforms previous methods that employ residue-based torsion angle maps or different loop closure strategies when tested on two sets of loop targets of lengths ranging from 4 to 12.

PHOTON IN THE FRAME OF THE CURRENT LOOP MODEL

We show that the electron–positron annihilation process ending with the creation of two gamma photons (with right- and left-hand circular helicity) can be explained in terms of the current loop model. We first show that both electron and positron (which are spin 1/2 particles) carry an intrinsic flux quantum of ±Φ0/2 even in the absence of an external magnetic field. By using the conservation of the magnetic flux quanta for collisions, we then argue that photon also carries a magnetic flux quantum of ±Φ0 = ±(hc/e) with itself along the propagation direction, where the (+) sign corresponds to the right-hand helicity and (-) one to the left-hand one.

Molecular Mechanism of Cell-autonomous Circadian Gene Expression ofPeriod2, a Crucial Regulator of the Mammalian Circadian Clock

Although circadian transcription of Period2 (Per2) is fundamental for the generation of circadian rhythm, the molecular mechanism remains unclear. Here we report that cell-autonomous circadian transcription of Per2 is driven by two transcriptional elements, one for rhythm generation and the other for phase control. The former contains the E-box-like sequence (CACGTT) that is sufficient and indispensable to drive oscillation, and indeed circadian transcription factors site-specifically bind to it. Furthermore, the nature of this atypical E-box is different from that of the classical circadian E-box. The current feedback loop model is based mainly on Period1. Our results provide not only compelling evidence in support of this model but also an explanation for a general basic mechanism to produce various patterns in the phase and amplitude of cell-autonomous circadian gene expression.

Normal-state bubbles and lamellae in type-I superconductors

We report an extensive study of the formation of normal-state domains in type-I superconductors. Domain patterns are first considered theoretically. The magnetic interaction between domains is described in the framework of the ``current-loop'' model: the intermediate state is modeled by a set of loops of screening current encircling the domains and interacting as in the free space. This system is shown to be formally equivalent to a set of uniformly magnetized domains. An extension of the current-loop model is proposed to take into account the constraint of the magnetic shielding by the superconducting regions. We determine the free energy of a hexagonal array of cylindrical domains (bubbles) and of a lattice of infinitely long and parallel stripes. The equilibrium values of both the volume fraction of the normal phase and the domain size are calculated as functions of the magnetic field. A bubble-to-stripe transition is predicted to occur for a volume fraction of the normal phase about 0.3. Experimentally, normal-state domains are studied with the high-resolution magneto-optical imaging technique. The observed patterns consist in coexisting bubbles and disordered labyrinthine lamellae structures. We show evidence of the contribution of pinning on the position of domain interfaces. The average width of the lamellae is then analyzed as a function of the applied magnetic field and found to increase in good agreement with the predictions. In contrast, the average diameter of bubbles remains constant: it is almost independent of the magnetic interaction between domains. A very good agreement, over three decades of the magnetic Bond number, is found with the equilibrium diameter of an isolated bubble. The proposed constrained current-loop model is shown to provide significantly more accurate predictions than the current-loop model, in particular for small magnetic Bond numbers. Additionally, increasing the volume fraction of the normal phase results in a bubble-to-lamella transition, as predicted theoretically.

B209 三角形ループ電流モデルを用いた励磁電流の可視化と励磁コイルの概念設計

A triangular loop current model visualizes exciting currents giving the desired magnetic field distribution by means of inverse problems. Combining a set of three line currents as a triangular loop represents magnetic field sources holding the conservation of currents, as well as magnetic fluxes. For designing exciting coils, at first, the region for the coils is filled with the current elements. Second, the desired magnetic field distribution represented as an input vector derives a system of equations from the relation between the magnetic field distribution and currents. Third, solving this ill-posed linear system determines the intensity of current in each of the elements. Finally, the current vector visualization performs designing exciting coils. The applications in homogeneous and concentrated magnetic field generation are presented.