Hysteresis Method Research Articles

A Novel Sliding Mode Control Technique for Indirect Current Controlled Active Power Filter

A novel sliding mode control (SMC) method for indirect current controlled three‐phase parallel active power filter is presented in this paper. There are two designed closed loops in the system: one is the DC voltage controlling loop and the other is the reference current tracking loop. The first loop with a PI regulator is used to control the DC voltage approximating to the given voltage of capacitor, and the output of PI regulator through a low‐pass filter is applied as the input of the power supply reference currents. The second loop implements the tracking of the reference currents using integral sliding mode controller, which can improve the harmonic treating performance. Compared with the direct current control technique, it is convenient to be implemented with digital signal processing system because of simpler system structure and better harmonic treating property. Simulation results verify that the generated reference currents have the same amplitude with the load currents, demonstrating the superior harmonic compensating effects with the proposed shunt active power filter compared with the hysteresis method.

Calculation of Melting Curve of Aluminum under Pressure through Molecular Dynamics Simulations

The melting curve is an important thermodynamic property in studies of solid-liquid phase transitions. It can be calculated via molecular dynamics simulations. We simulated the melting process of pure Al with three methods, the heat-until-it-melts (HUM) method, the two-phase method and the hysteresis method. The results calculated via HUM method is approximately 20% higher than experiment data while the results calculated via two-phase method and hysteresis method are in good agreement with experiment data.

A call quality performance measure for handoff algorithms

This paper proposes a new approach for performance evaluation and comparison between existing handoff algorithms taking into consideration signal levels, call dropping, and handoff cost. Using the new approach, existing handoff algorithms are then compared in terms of signal quality and number of handoffs required to achieve a desired overall signal quality. We also provide in this paper a method to estimate handoff cost and to optimize handoff sequences for retrial (where repeated call attempts are made after a call is lost) and non-retrial models based on the proposed approach. We observe that the Threshold with Hysteresis method performs better than other known methods including the one used in the GSM standard. Our results indicate that the Threshold with 4 dB Hysteresis method performs well for urban areas although with a high dropping probability, whereas the Threshold with 6 dB Hysteresis method suits for suburban areas with a low dropping probability. We find that handoff sequences obtained by existing handoff methods are less efficient than the optimal handoff sequence given in the paper by a margin of 29–45% for retrial model, and by 34–77% for non-retrial model. The paper also suggests some specific parameter values to improve the performance of currently used handoff methods based on our findings. Copyright © 2010 John Wiley & Sons, Ltd.

A new combined method in active filter design for power quality improvement in power systems

The voltage & current harmonics produced by nonlinear loads in power systems cause a reduction in power quality. In order to improve the power quality, active power filters (APFs) can be used. In this paper, a new control system for designing active filters despite nonlinear loads of electric arc furnaces (EAFs) is presented. The system is composed of three main parts: computation of reference currents, regulation of DC capacitor voltage, and production of firing pulses. In the first part, the active filter control system is presented based on the combination of the synchronous detection method and instantaneous power theory. In the second part, the DC capacitor voltage regulator is applied, producing a reference current and a proper voltage regulator is developed. For the third part of the control system, we use a PI controller to provide some conditions that follow the reference current in a complete cycle, and generate firing pulses by the hysteresis method. The proposed control system not only reduces the voltage and current harmonics in power systems but can also improve the power quality indices. The above design was implemented in the EAF system of the Mobarakeh steel complex (Isfahan, Iran). The simulation results show the effectiveness of the APFs in improving the power quality indices.

Assessments of critical flux in a pilot-scale membrane bioreactor

In this study, the influence of various parameters such as determination methods and step height and length of incremental flux on critical flux values were investigated. Experiments were carried out on a pilot-scale membrane bioreactor (MBR) treated municipal wastewater. Three of the five critical flux determination methods, such as flux linearity, 90% permeability and flux cycling conducted in this study, indicated a decline in critical flux values as the step height of incremental flux increased. However, the hysteresis method and the two-third (2/3) flux limitation method showed an increase and independence of critical flux to the step height of incremental flux, respectively. On the other hand, the step length of incremental flux had no obvious effect on critical flux values evaluated by all critical flux determination methods. Like critical flux, sustainable flux has negative relationship with the increase of step height but no influence of step length was found in this study.

Hysteretic–controlled Voltage Regulator using Integrated Circuit LM723

The analysis and testing of a dc-dc converter by means of the hysteretic control method is presented. In order to design this control method, we used the LM723 integrated circuit, mostly used for the continuous control of the voltage and current sources. Experimental results, as well as simulation results, confirm that the circuit functions well. The proposed circuit represents an alternative for designing dc-dc converter control through the hysteresis method, without using specialized integrated circuits, with low costs and high performances. Ill. 14, bibl. 11( in English; summaries in English, Russian and Lithuanian).

Fatigue testing of implantable specimens: Effect of sample size and branching on the dynamic fatigue properties of polyisobutylene-based biomaterials

In this paper we present the first results on the effect of specimen size and branching on the fatigue properties of polyisobutylene-based thermoplastic elastomers measured by the hysteresis method. It was verified that smaller specimens were inherently stronger as expected; at the same loading rate microdumbbells induced higher strain rates so they can be considered as the “worst case” scenario. Microdumbbells, which can be implanted into small animals for in vivo studies, were used for dynamic fatigue testing of linear poly(styrene-b-isobutylene-b-styrene) triblock copolymers (L_SIBS) in comparison with long-chain branched (tree-like or dendritic) versions (D_SIBS). In dynamic stress relaxation studies, D_SIBS performed better than L_SIBS. Simulated physiological conditions had negligible effect on the dynamic properties.

Cross-Layer-Based Adaptive Vertical Handoff With Predictive RSS in Heterogeneous Wireless Networks

A heterogeneous wireless network consists of various wireless networks [e.g., Worldwide Interoperability for Microwave Access (WiMAX) and Wireless Fidelity (WiFi)] and cellular communications [e.g., beyond the third generation (B3G) and the fourth generation (4G)]. Vertical handoff is an important mechanism for achieving continuous seamless transmissions in these networks. In contrast to horizontal handoff, vertical handoff considers not only the received signal strength (RSS) but also the service-class mapping between handoff-in and handoff-out networks. Most previous works have adopted the RSS-based mechanism to determine handoff thresholds, which causes a serious ping-pong effect that increases unnecessary handoff. Although integrating the RSS-based mechanism with a hysteresis method reduces the unnecessary handoff, it suffers from high dropping [i.e., high Sum of Weighted Grade of Service (SWGoS)] and low utilization. Therefore, this paper proposes a cross-layer-based adaptive vertical handoff algorithm with predictive RSS to reduce the unnecessary handoff while significantly increasing utilization and decreasing connection dropping. The proposed approach determines the optimal target network in two phases, i.e., polynomial regression RSS prediction and Markov decision process analysis. Furthermore, fast changes in bandwidth caused by vertical handoff result in inaccurate Transmission Control Protocol (TCP) congestion control and, thus, reduce the TCP goodput. The cross-layer scheme provides a TCP receiver to reply to the TCP sender with the wireless network's protocol type. By using the cross-layer information, the TCP sender can accurately predict the available bandwidth and increase the network goodput. Numerical results indicate that the proposed cross-layer-based approach outperforms the other approaches in the number of vertical handoffs and SWGoS while yielding competitive utilization. In addition, the cross-layer scheme cooperates with existing TCP algorithms to increase goodput by up to 18%.

Homogeneous nucleation and growth of melt in copper

Molecular dynamics simulations are conducted to investigate homogeneous nucleation and growth of melt in copper described by an embedded-atom method (EAM) potential. The accuracy of this EAM potential for melting is validated by the equilibrium melting point obtained with the solid-liquid coexistence method and the superheating-supercooling hysteresis method. We characterize the atomistic melting process by following the temperature and time evolution of liquid atoms. The nucleation behavior at the extreme superheating is analyzed with the mean-first-passage-time (MFPT) method, which yields the critical size, steady-state nucleation rate, and the Zeldovich factor. The value of the steady-state nucleation rate obtained from the MFPT method is consistent with the result from direct simulations. The size distribution of subcritical nuclei appears to follow a power law similar to three-dimensional percolation. The diffuse solid-liquid interface has a sigmoidal profile with a 10%-90% width of about 12 A near the critical nucleation. The critical size obtained from our simulations is in reasonable agreement with the prediction of classical nucleation theory if the finite interface width is considered. The growth of melt is coupled with nucleation and can be described qualitatively with the Johnson-Meh-Avrami law. System sizes of 10(3)-10(6) atoms are explored, and negligible size dependence is found for bulk properties and for the critical nucleation.

Border-Trap Characterization in High-$\kappa$ Strained-Si MOSFETs

In this letter, we focus on the border-trap characterization of TaN/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /Si and TaN/HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /strained-Si/Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> n-channel MOSFET devices. The equivalent oxide thickness for the gate dielectrics is 2 nm. Drain-current hysteresis method is used to characterize the border traps, and it is found that border traps are higher in the case of high-kappa films on strained- Si/Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</sub> .These results are also verified by the 1/f-noise measurements. Possible reasons for the degraded interface quality of high-kappa films on strained-Si are also proposed.

Borderless silicon nitride defect behaviour and their influences on initial data loss in single polysilicon flash memories

Pre Metal Dielectric layer characterization by capacitance versus voltage hysteresis method has revealed the larger charge amount contained in the PECVD borderless silicon nitride. Its charges, attributed to K centers, exist under two states K + and K − that can be cycled thanks to carrier injection or by direct transformation under thermal activation. Thus, this dielectric presents a memory like behaviour. Based on detailed characterization of charge exchange in this dielectric, a fast initial charge loss model is proposed in order to explain the fast charge losses observed during programming and erasing bake sequences on single polysilicon flash memories.

Solid−Liquid Interfacial Free Energy of Water: A Molecular Dynamics Simulation Study

The superheating-undercooling hysteresis method and molecular dynamics simulation [Luo et al. Phys. Rev. B 2003, 68, 134206] were applied to estimate solid-liquid interfacial free energy (γ) of model water at ambient pressure. Two models of water were selected, the TIP4P-Ew and TIP5P-Ew, which are the improved TIP4P and TIP5P model (for the use with Ewald technique), respectively. The calculated γ at 1 bar is 37 mJ/m(2) for TIP4P-Ew and 42 mJ/m(2) for TIP5P-Ew, consistent with a previous direct MD simulation (39 mJ/m(2)), as well as within the range of measured values (25-44 mJ/m(2)).

Revision of the hysteresis and excess loss computation method as a means of improving the rotational loss estimate in induction motors

The paper evaluates the impact that the relationship between purely rotational and alternating losses has on the computation of core losses in induction motors. At frequencies other than 50 Hz, the analysis is simplified if statistical loss theory is considered, as discussed in the paper. The paper outlines a practical method of computation of hysteresis and excess losses when the rotation of flux is considered and loss data for these terms at 50 Hz are available. An imposed constraint is that the quantity of experimental loss data available for the motor designer is, in general, reduced. To deal with the problem, Kochmann general relationships for 36 NO grades, covering the main spectrum of electrical steel grades at 50 Hz, have been found to be helpful. An approach is proposed to convert these relationships, so that they can be fitted into the statistical loss theory. The results are validated using FEA and bench tests. As a conclusion, the loss estimate is improved in all cases, not incurring an overestimation with respect to bench results.

Analysis and surface energy estimation of various model polymeric surfaces using contact angle hysteresis

Wetting of hydrophobic polymer surfaces commonly employed in electronic coatings and their interaction with surfactant-laden liquids and aqueous polymer solutions are analyzed using a contact angle hysteresis (CAH) approach developed by Chibowski and co-workers. In addition, a number of low surface tension acrylic monomer liquids, as well as common probe liquids are used to estimate solid surface energy of the coatings in order to facilitate a thorough analysis of surfactant effects in adhesion. Extensive literature data on contact angle hysteresis of surfactant-laden liquids on polymeric surfaces are available and are used here to estimate solid surface energy for further understanding and comparisons with the present experimental data. In certain cases, adhesion tension plots are utilized to interpret wetting of surfaces by surfactant and polymer solutions. Wetting of an ultra-hydrophobic surface with surfactant-laden liquids is also analyzed using the contact angle hysteresis method. Finally, a detailed analysis of the effect of probe liquid molecular structure on contact angle hysteresis is given using the detailed experiments of Timmons and Zisman on a hydrophobic self-assembled monolayer (SAM) surface. Hydrophobic surfaces used in the present experiments include an acetal resin [poly(oxymethylene), POM] surface, and silane, siloxane and fluoro-acrylic coatings. Model surfaces relevant to the literature data include paraffin wax, poly(methyl methacrylate) and a nano-textured surface. Based on the results, it is suggested that for practical coating applications in which surfactant-laden and acrylic formulations are considered, a preliminary evaluation and analysis of solid surface energy can be made using surfactant-laden probe liquids to tailor and ascertain the quality of the final coating.

Interaction and phase separation in the system HPMC/NaCMC/SDS

In this work, the interaction in the ternary system composed of two cellulose derivatives, anionic—sodium carboxymethylcellulose (NaCMC) and nonionic-hydroxyprophylmethylcellulose (HPMC), and anionic surfactant—sodium laurylsulfate (SDS) has been investigated by rheological measurements. Rheological measurements were performed at 20 °C using a rotational viscometer and by applying a continuous loop hysteresis method. The mass ratios of the HPMC/NaCMC in 1.0% solution were: 0.3/0.7; 0.5/0.5; 0.7/0.3, while SDS concentration increases from 0 to 2.0%. In such a system, depending on the mass ratios of the components, various interactions between HPMC–NaCMC, HPMC–SDS and NaCMC–(HPMC–SDS) takes place. The phase separation in solution was followed by turbidity and height of coacervate layer measurements. The investigations show that HPMC and NaCMC molecules interact with each other and synergistic effect on viscosity was observed. This synergistic effect disappears with SDS addition. As a result of the interactions in ternary system HPMC/NaCMC/SDS, the phase separation, i.e. coacervation occurs at particular mass ratios of the components. The coacervate formation depends on the HPMC–SDS interaction and influences turbidity and viscosity of the system.

Solid–liquid transitions of sodium chloride at high pressures

We investigate solid-liquid transitions in NaCl at high pressures using molecular dynamics simulations, including the melting curve and superheating/supercooling as well as solid-solid and liquid-liquid transitions. The first-order B1-B2 (NaCl-CsCl type) transition in solid is observed at high pressures besides continuous liquid structure transitions, which are largely analogous to the B1-B2 transition in solid. The equilibrium melting temperatures (T(m)) up to megabar pressure are obtained from the solid-liquid coexistence technique and the superheating-supercooling hysteresis method. Lindemann's vibrational and Born's mechanical instabilities are found upon melting. The Lindemann frequency is calculated from the vibrational density of states. The Lindemann parameter (fractional root-mean-squared displacement) increases with pressure and approaches a constant asymptotically, similar to the Lennard-Jones system. However, the Lindemann melting relation holds for both B1 and B2 phases to high accuracy as for the Lennard-Jonesium. The B1 and B2 NaCl solids can be superheated by 0.18T(m) and 0.24T(m), and the NaCl liquid, supercooled by 0.22T(m) and 0.32T(m), respectively, at heating or cooling rates of 1 K/s and 1 K/ps. The amount of maximum superheating or supercooling and its weak pressure dependence observed for NaCl are in accord with experiments on alkali halides and with simulations on the Lennard-Jones system and Al.

Hysteresis minor loop analysis of plastically deformed low-carbon steel

This work investigates applicability of magnetic hysteresis method for non-destructive testing of plastically deformed low-carbon steel. Recently introduced Magnetic Adaptive Testing procedure was used for evaluation of hysteresis minor loop data-sets to find the most sensitive parameter/s for indication of the material degradation stage. Inductive measurements were carried out on two identically degraded series of samples: magnetically closed window-shaped specimens, equipped with the magnetizing and the induction coils, and magnetically open strips, measured by an attached magnetizing yoke. The aim was to compare the results between these sample series in order to determine applicability and limitations of the single-yoke measurement technique. As a result, new magnetic parameters with the best sensitivity–stability ratio in a wide deformation range were introduced and proposed for utilization. Good qualitative coincidence between the measurement results on the closed and the open sample series was obtained in all range of magnetization. Several quantitative distinctions were explained and analyzed in order to improve the single-yoke technique.

Molecular dynamics simulations of melting and the glass transition of nitromethane

Molecular dynamics simulations have been used to investigate the thermodynamic melting point of the crystalline nitromethane, the melting mechanism of superheated crystalline nitromethane, and the physical properties of crystalline and glassy nitromethane. The maximum superheating and glass transition temperatures of nitromethane are calculated to be 316 and 160 K, respectively, for heating and cooling rates of 8.9 x 10(9) Ks. Using the hysteresis method [Luo et al., J. Chem. Phys. 120, 11640 (2004)] and by taking the glass transition temperature as the supercooling temperature, we calculate a value of 251.1 K for the thermodynamic melting point, which is in excellent agreement with the two-phase result [Agrawal et al., J. Chem. Phys. 119, 9617 (2003)] of 255.5 K and measured value of 244.73 K. In the melting process, the nitromethane molecules begin to rotate about their lattice positions in the crystal, followed by translational freedom of the molecules. A nucleation mechanism for the melting is illustrated by the distribution of the local translational order parameter. The critical values of the Lindemann index for the C and N atoms immediately prior to melting (the Lindemann criterion) are found to be around 0.155 at 1 atm. The intramolecular motions and molecular structure of nitromethane undergo no abrupt changes upon melting, indicating that the intramolecular degrees of freedom have little effect on the melting. The thermal expansion coefficient and bulk modulus are predicted to be about two or three times larger in crystalline nitromethane than in glassy nitromethane. The vibrational density of states is almost identical in both phases.

Biocompatibility and Fatigue Properties of Polystyrene−Polyisobutylene−Polystyrene, an Emerging Thermoplastic Elastomeric Biomaterial

This paper will discuss the biocompatibility and dynamic fatigue properties of polystyrene-b-polyisobutylene-b-polystyrene thermoplastic elastomer with 30 wt % polystyrene (SIBS30), an emerging FDA-approved biomaterial. SIBS30 is a very soft, transparent biomaterial resembling silicone rubber, with superior mechanical properties. Using the hysteresis method adopted for soft biomaterials, the dynamic fatigue properties of SIBS30 were found to be between those of polyurethane and silicone rubber, with fatigue life twice as long as that of silicone. Under single load testing (SLT, 1.25 MPa), SIBS30 displayed less than half the dynamic creep compared to silicone, both in air and in vitro (37 degrees C, simulated body fluid). Hemolysis and 30- and 180-day implantation studies revealed excellent biocompatibility of the new biomaterial. The results presented in this paper indicate that, in comparison with silicone rubber, SIBS30 has similar biocompatibility and superior dynamic fatigue properties.

Electrochemical Polarization and Stress Corrosion Cracking of Alloy 690 in 5-M Chloride Solutions at 25°C

Abstract An experimental, potential-pH diagram was constructed for the nickel-based Alloy 690 (UNS N06690) in 25°C concentrated (5 M) sodium chloride (NaCl) solution, using an electrochemical hysteresis method. The domains of immunity, general corrosion, passivation, and pitting in 5-M NaCl solutions were defined. At pH &amp;gt; 4, the passive region subdivided into areas of perfect passivation, imperfect passivation, and pitting. After anodic polarization, the surface of each specimen was carefully examined metallographically. Pitting corrosion was observed over the entire pH range investigated (0.3 to 8.52), but general corrosion predominated at lower pH values (&amp;lt;3). On the other hand, the mechanical properties, such as ultimate tensile strength (UTS), strain at fracture, and the reduction area (RA) measured by the slow strain rate test (SSRT), decreased significantly at pH &amp;lt; 3. The SSRT results are consistent with fractography and side-view observations of the tested specimens by scanning electron microscopy (SEM).