Narrow Results

A generalized optimal velocity model is analyzed, where the optimal velocity function depends not only on the headway of each car but also the headway of the immediately preceding one. The stability condition of the model is derived by considering a small perturbation around the homogeneous flow solution. The effect of the generalized optimal velocity function is also confirmed with numerical simulations, by examining the hysteresis loop in the headway-velocity phase space, and the relation between the flow and density of cars. In the model with a specific parameter choice, it is found that an intermediate state appears for the movement of cars, where the car keeps a certain velocity whether the headway is short or long. This phenomenon is different from the ordinary stop-and-go state.

La_0.5Sr_0.5MnO₃ films on (001) LaAlO₃ were prepared by RF magnetron sputtering using powder target and were studied by SQUID and XPS. The XPS results show the formation of Mn³⁺ and Mn⁴⁺, indicating the coexistence of ferromagnetic (FM) and antiferromagnetic (AFM) clusters. SQUID measurement of LSMO on LAO and Si also support an interaction between them at low temperatures, resulting in the shift of hysteresis loops. Large coercivities at low temperature can be attributed to the pinning of both FM and AFM clusters and small coercivities at high temperature to the depinning of both FM and AFM phases, resulting from the thermal motion at higher temperatures which help to overcome the energy barrier and change the magnetic alignments.

Polycrystalline single phase oxides, La_0.7-xNd_xPb_0.3)MnO₃ (0.3≤x≤0.7), have been synthesized by a standard ceramic fabrication method. A phenomenological model is proposed to describe the magnetization process, and to fit the experiment data of hysteresis loops under different composition ratio. The magnetic hysteresis behavior can be modeled by the formula of . The resulted model can satisfy the experiment data ranging from 0.005T to 5T. Explanations on the fitting coefficients of these compounds are addressed.

Based on Monte Carlo simulation, the magnetic properties of a mixed spin-1 and spin-3/2 Ising superlattice with alternate layers are studied. The effects of interlayer coupling and external magnetic field on the compensation behavior and hysteresis properties for the ferrimagnetic superlattice are investigated. The occurrence of a compensation point is found to be greatly affected by the interlayer coupling. In particular, various multiple hysteresis loops can be observed under certain system parameters. The calculated results agree well with available experimental and theoretical works.

The LaCoO₃ single crystal, 4 mm in diameter and 30 mm in length, has been grown by optical floating zone method. The magnetic measurements show that the coercivity and the remanence are 5 Oe and 1.5 × 10^-3 emu/g at 5 K, respectively. The ZFC and FC magnetic susceptibility curves overlap and the 1/χ(T) curve shows a linear variation over the interval 5 K < T < 35 K in 1000 Oe. As the temperature increases from 35 K to 90 K, the ZFC curve in 1000 Oe firstly reduces nonlinearly, and then appears as a wave crest. The χ under ZFC is higher than that under FC in the temperature range of 55~90 K. In 50 000 Oe, a slope change of 1/χ(T) at about 12 K is observed.

Angular dependence of the giant magneto impedance (GMI), hysteresis loops and magnetization curves have been investigated in amorphous wires with respect to direction and amplitude of the magnetic field in room temperature. The measurements were performed at different orientation angles of the applied magnetic field relative to the wire axis and various magnetic field strengths in moderate (0–200 Oe) and high (0–5000 Oe) ranges. The highest GMI response (500%) and magnetization (100 emu/gr) were found for angles close to the wire axis in high magnetic field range. By increasing the angle from 0°, in moderate external magnetic fields the GMI and magnetization decrease without reaching the saturation. However, in high magnetic fields (~ 5000 Oe) these parameters are nearly constant and almost saturated for all angles. In both magnetic field ranges, increasing the angle of applied field widens the impedance curves.

The dynamic response of bolted joints subjected to torsional excitation is investigated experimentally and numerically. First, the effects of the initial preload and the angular amplitude on axial force loss of the bolt were studied. Second, the change of hysteresis loops with the increasing number of loading cycles was found under a larger torsional angle. At last, a fine-meshed three-dimensional finite element model was built to simulate the bolted joint under torsional excitation, from which the hysteresis loops were obtained under varying angular amplitudes. The results of numerical analysis are in good agreement with those of experiments.

The 0.65Ba(Mg_1/3,Nb_2/3)O₃-0.35BaTiO₃ thin films was deposited on glass/aluminum substrates by using spray pyrolysis method. The effect of annealing temperature on perovskite phase and crystalline structure analysis of the BMN-BT films was performed on an X-ray diffraction (XRD). Surface morphology, roughness and particle size of the BMN-BT thin films was characterized with atomic force microscopy (AFM) and scanning electronic microscopy (SEM). Polarization hysteresis measurements was performed at different temperatures. From the P–E hysteresis loops one can observe the best temperature that led to improved properties of dielectric constant, polarization and piezoelectric coefficients were 600°C.

Investigation of the role of hydrothermal temperature on hematite nanoparticles structural, magnetic, and ferromagnetic resonance (FMR) properties was done. Ferric chloride and sodium hydroxide were used as the starting precursors. The hydrothermal temperature was varied in the range of 140–200^∘C by a step of 20^∘C. XRD, SEM, VSM, and FMR analyses were used to check the particles’ properties. The prevailing strongly phase was hematite with some small peaks related to other phases. A reduction in lattice constant and increase in the crystallite size to more than 27nm is observed. The particles’ morphology exhibited polygon particles down to spherical particles as the average particle size gets larger up to 45nm. The hysteresis loops showed unsaturated curves with rising coercivity up to 150Oe. The antiferromagnetism permeability, magnetization saturation, and dipole moment were found by Langevin fitting to the experimental hysteresis loops, where all of them have the same behavior represented by an initial drop followed by increase in their values. The FMR spectra are characterized by low intensities and low linewidths accompanied by very low blue shift in the resonance field. All samples showed Lorentzian distribution as checked by the Lorentz function. Landé $g$-factor has values very close but less than 2 due to the effect of crystal field and particle magnetic moment variations.

A simplified micromagnetic model has been proposed to calculate the hysteresis loops of nanostructured permanent magnets for various configurations, including thin films, exchange-coupled double-layer systems and bulk materials. The reversal part of the hysteresis is based on the Stoner–Wohlfarth coherent rotational model and the coercivity mechanism is due mainly to the motion of the transition region (a domain wall like magnetic moment distribution in the grain boundary). The elements of nucleation and pinning models are also incorporated.

In this paper a full-scale commercially available magnetorheological (MR) brake installed in a semi-active suspension (SAS) system is modeled and simulated. Two well-known phenomenological hysteresis models are explored: Bouc–Wen and Dahl ones. In particular, influence of their parameters on the response is evaluated and assessed. The next step is to introduce the artificial neural networks and discuss their application in the field of systems identification. Subsequently, two feedforward neural networks are created and trained to estimate parameters characterizing each of the MR damper models described. The semi-active suspension (SAS) system equipped with a MR brake is described and the detailed procedure for acquisition of the reference data used in the models validation stage is elaborated. The models outputs obtained by simulating them with the values of coefficients as identified by the networks are compared to each other as well as to the reference experimental data. Thanks to that, the comparative analysis between the suggested vibration suppression models and the full-scale MR brake is done and it is concluded which of the discussed models has a better performance. The usability of neural networks in the field of parameters estimation of the mathematical models of the real world phenomena is described as well. The novelty of the presented methodology is the application of artificial intelligence methods to estimate model parameters of a MR brake utilized in a SAS system. The results of this approach have a strong potential to be successfully implemented in the area of model-based control of semi-active vibration suppression systems.

Bi_9-xFe_5+xTi₃O₂₇ (x = 0-3) compounds of bismuth layered perovskite structure have been successfully prepared by solid-state reaction method. X-ray diffraction (XRD) studies revealed the orthorhombic crystal structure of all the compounds. Impedance spectroscopy has been studied to characterize the electrical properties of polycrystalline Bi_9-xFe_5+xTi₃O₂₇ (x = 0-3) compounds. The shape of complex impedance curves inferred the contribution of bulk and grain boundary effects on the electrical properties of the compounds. Temperature dependent magnetization measurements were made from 2 K to 300 K. Narrow hysteresis loops observed at room temperature indicate antiferromagnetic behavior of the compounds.

We have employed the Oguchi approximation (OA) to investigate the effects of a random crystal field which is active (inactive) with probability $p$$(1-p)$ for given lattice sites on the thermodynamic properties of the mixed spin-$(\frac{5}{2},\frac{1}{2})$ anisotropic Heisenberg model in the presence of an external magnetic field. By exploiting the thermal variations of the order parameters, interesting phase diagrams are produced on various planes. The phase diagrams show first- and second-order transition lines and also tricritical points. In addition to the reentrant behavior which is localized in a certain range of $p$ at very low temperature, the magnetic exponent $\beta$ calculated near the critical point exhibits interesting behaviors depending on the crystal field interaction. The hysteresis behavior of the model is also investigated and it reveals that the width of hysteresis loop decreases or increases, respectively, for negative or positive crystal field region as the probability $p$ increases.

The magnetic phase created in the Inconel alloy, which is called as PVC (permeability variation clusters) results in a eddy current test(ECT) signal distortion during the inspection of steam generator (SG) of nuclear power plant (NPP). The effects of magnetic phase on ECT signals were analyzed using the inspection of data of NPP. The hystersis loops of PVC which is extracted from retired SG tubes of Kori-1 NNP were measured. The tensile tests were performed to identify the mechanism of PVC creation. The coercivity of PVC is larger than 0.2kA/m, and hysteresis loop was appeared in the tensile tested specimen at 600 °C.

The magnetization process of the micro-wire arrays with glass covered amorphous wires (GCAWs) and NiFe/Cu composite wires (CWs) has been modeled with three hysteresis loops. In a multi-core orthogonal fluxgate sensor the micro-wire array sensing element presents a complicated magnetization process due to the operation mode that the excitation field is in the circumferential direction and the sensing field is in the axial direction. Fitting with this application, micro-wire arrays present large orthogonal fluxgate responses resulting from their anisotropy and domain structures. GCAWs have a circumferential anisotropy with a small angle to axial direction due to the core-shell domain structure. CWs present helical anisotropy with easy axis inclined to the circular direction. Correspondingly, the axial loop has been modeled with small coercivity and small susceptibility, and the circular loop has been modeled with large coercivity and large susceptibility. The axial-circular loop is based on the measured gating curves and has been simplified to linear dependence of the axial magnetization on the circular field. Based on the experimental measurement results and hypothesized models of the micro-wire arrays, an analytical model for the 2nd harmonic sensitivity of multi-core orthogonal fluxgate sensors has been established. Expressions of the 2nd harmonic output and the sensitivity derived by Fourier analysis show that the number of wires, anisotropy field, initial susceptibility and frequency are the key parameters determining the sensitivity.