Range Of Parameter Variations Research Articles

Stance leg control: variation of leg parameters supports stable hopping

The spring-loaded inverted pendulum describes the planar center-of-mass dynamics of legged locomotion. This model features linear springs with constant parameters as legs. In biological systems, however, spring-like properties of limbs can change over time. Therefore, in this study, it is asked how variation of spring parameters during ground contact would affect the dynamics of the spring–mass model. Neglecting damping initially, it is found that decreasing stiffness and increasing rest length of the leg during a stance phase are required for orbitally stable hopping. With damping, stable hopping is found for a larger region of rest-length rates and stiffness rates. Here, also increasing stiffness and decreasing rest length can result in stable hopping. Within the predicted range of leg parameter variations for stable hopping, there is no need for precise parameter tuning. Since hopping gaits form a subset of the running gaits (with vanishing horizontal velocity), these results may help to improve leg design in robots and prostheses.

Electrical properties of AgSnSbSe3 under different external effects

The electrical properties of the chalcogenide AgSnSbSe3 have been investigated over a wide range of variations in external parameters, such as the temperature, the pressure, and the frequency of the electric field. It has been found that the temperature dependence of the permittivity and the dependence of the electrical resistivity on the hydrostatic pressure exhibit anomalies that are characteristic of structural phase transitions. The influence of the frequency on dielectric properties of the material has been analyzed.

RLF and TS fuzzy model identification of indoor thermal comfort based on PMV/PPD

This work presents a hybrid model to be used for effectively controlling indoor thermal comfort in a heating, ventilating and air conditioning (HVAC) system. The first modeling part is related to the building structure and its fixture. Since building models contain many nonlinearities and have large thermal inertia and high delay time, empirical calculations based on the residential load factor (RLF) is adopted to represent the model. The second part is associated with the indoor thermal comfort itself. To evaluate indoor thermal comfort situations, predicted mean vote (PMV) and predicted percentage of dissatisfaction (PPD) indicators were used. This modeling part is represented as a fuzzy PMV/PPD model which is regarded as a white-box model. This modeling is achieved using a Takagi-Sugeno (TS) fuzzy model and tuned by Gauss-Newton method for nonlinear regression (GNMNR) algorithm. The main reason for combining the two models is to obtain a proper reference signal for the HVAC system. Unlike the widely used temperature reference signal, the proposed reference signal resulting from this work is closely related to thermal sensation comfort; Temperature is one of the factors affecting the thermal comfort but is not the main measure, and therefore, it is insignificant to control thermal comfort when the temperature is used as the reference for the HVAC system. The overall proposed model is tested on a wide range of parameter variation. The corresponding results show that a good modeling capability is achieved without employing any complicated optimization procedures for structure identification with the TS model.

Ionization and stabilization of atoms in a high-intensity, low-frequency laser field

The dynamics of a model silver atom in the strong radiation field of a Ti:sapphire laser is studied in the Keldysh parameter regions γ ⩾ 1 and γ ⩽ 1. It is found that in the entire range of Keldysh parameter variations, along with ionization, the efficient excitation of Rydberg states of the atom with principal quantum numbers n = 6−14 is observed. A Rydberg wavepacket appearing in this case proved stable with respect to ionization; i.e., the atomic system in strong low-frequency electromagnetic fields becomes stable with respect to ionization. The physical reasons behind the stabilization are discussed.

Stability and coagulation of natural diamond sols in LiCl solutions

The aggregate stability of natural diamond sols in LiCl aqueous solutions in the acidic region of pH values has been investigated using flow ultramicroscopy. The range of variations in parameters of structural forces for natural diamond in these solutions has been determined. The possibility of applying the Smoluchowski theory and the Muller theory of reversible coagulation to the description of the kinetics of coagulation and the equilibrium aggregate state of polydisperse diamond sols has been discussed.

Separating foliar physiology from morphology reveals the relative roles of vertically structured transpiration factors within red maple crowns and limitations of larger scale models

A spatially explicit mechanistic model, MAESTRA, was used to separate key parameters affecting transpiration to provide insights into the most influential parameters for accurate predictions of within-crown and within-canopy transpiration. Once validated among Acer rubrum L. genotypes, model responses to different parameterization scenarios were scaled up to stand transpiration (expressed per unit leaf area) to assess how transpiration might be affected by the spatial distribution of foliage properties. For example, when physiological differences were accounted for, differences in leaf width among A. rubrum L. genotypes resulted in a 25% difference in transpiration. An in silico within-canopy sensitivity analysis was conducted over the range of genotype parameter variation observed and under different climate forcing conditions. The analysis revealed that seven of 16 leaf traits had a ≥5% impact on transpiration predictions. Under sparse foliage conditions, comparisons of the present findings with previous studies were in agreement that parameters such as the maximum Rubisco-limited rate of photosynthesis can explain ∼20% of the variability in predicted transpiration. However, the spatial analysis shows how such parameters can decrease or change in importance below the uppermost canopy layer. Alternatively, model sensitivity to leaf width and minimum stomatal conductance was continuous along a vertical canopy depth profile. Foremost, transpiration sensitivity to an observed range of morphological and physiological parameters is examined and the spatial sensitivity of transpiration model predictions to vertical variations in microclimate and foliage density is identified to reduce the uncertainty of current transpiration predictions.

Application of stability region centroids in robust PI stabilization of a class of second-order systems

In this paper we offer a tuning method for the design of stabilizing PI controllers that utilizes the stability region centroid in the controller parameter space. To this end, analytical formulas are derived to describe the stability boundaries of a class of relative-degree-one linear time invariant second-order systems, the stability region of which has a closed convex shape. The so-called centroid stable point is then calculated analytically and the resultant set of algebraic formulas are utilized to tune the controller parameters. The freedom to choose the surface density function in the calculation of centroid stable point provides the designer with the possibility to incorporate optimal or robustness requirements in the controller design process. The proposed method uses the stability regions in the controller parameter space to ensure closed-loop stability, and, while offering robust stability properties, it does not rely on predetermined information with regard to the nature or range of parameter variations and coefficient uncertainty bounds. Being situated away from the boundaries of the stability region in the controller parameter space, controllers designed based on the centroid method are both robust and non-fragile.

Robust fractional order controller for irrigation main canal pools with time-varying dynamical parameters

A new method is proposed with which to design a class of robust fractional order controllers – which we denote as FPI controllers since they can be regarded as a generalization of standard PI controllers – for the effective control of water distribution in irrigation main canal pools characterized by time-varying dynamical parameters. The closed loop behavior of the nominal plant is defined by using frequency specifications, which are combined with an optimization procedure that minimizes the IAE ( Integral of Absolute Error) – a cost related to the closed loop time response specifications – in the whole range of plant parameter variations. Interest in such robust fractional order controllers is justified by the fact that dynamical parameters of irrigation main canal pools may change drastically according to their operational regimes. Equivalent FPI, PI and PID controllers – in the sense of their exhibiting the same closed loop dynamics for the nominal plant specifications – were simulated for several working conditions, and their behaviors were compared. Additional issues, such as noise rejection or robustness to unmodelled high frequency dynamics have also been considered.

Gain Scheduled Control: Switched Polytopic System Approach

Gain Scheduled Control: Switched Polytopic System Approach

Studying the CO–CO 2 characteristics of SOFC anodes by means of patterned Ni anodes

The high potential of solid oxide fuel cells (SOFC) arises due to the high degree of efficiency and fuel flexibility. However, the elementary kinetic steps of the anodic processes taking place at the boundary of electrolyte–anode–gas are still largely unknown. Patterned Ni anodes on Y 2O 3-stabilized ZrO 2 are regarded as a promising method to determine these kinetics. In analogy to our previous study with patterned Ni anodes for the H 2–H 2O system, this study is systematically devoted to the elementary kinetics of the CO electrochemical oxidation in CO–CO 2 gas mixtures. Data analysis is backed by extensive knowledge on patterned anode stability and dynamics gained during previous studies. The electrochemical characterization is performed for a large parameter variation range ( pCO 2, pCO and T) by electrochemical impedance spectroscopy. Contrary to the characterization in H 2–H 2O atmosphere no slow relaxation processes were observed and the degradation rate is smaller. Changes in parameter dependency over the investigated parameter range indicate different reaction mechanisms as a function of gas composition. Only slightly higher polarization losses are observed for CO oxidation compared to H 2. The comparison of the results from patterned anodes to high-performance Ni/8YSZ cermet anodes employed in anode supported cells yields good agreement.

Synchronization regions of two pulse-coupled electronic piecewise linear oscillators

Stable synchronous states of different order were analytically, numerically and experimentally characterized in pulse-coupled light-controlled oscillators (LCOs). The Master-Slave (MS) configuration was studied in conditions where different time-scale parameters were tuned under varying coupling strength. Arnold tongues calculated analytically - based on the piecewise two-time-scale model for LCOs - and obtained numerically were consistent with experimental results. The analysis of the stability pattern and tongue shape for (1 : n) synchronization was based on the construction of return maps representing the Slave LCO evolution induced by the action of the Master LCO. The analysis of these maps showed that both tongue shape and stability pattern remained invariant. Considering the wide variation range of LCO parameters, the obtained results could have further applications on ethological models.

Influence des proportions volumiques air-verre sur la capacité apparente d'un modèle plan d'isolateur HT

This work is a contribution to the modelling of HV insulators and the calculation of the apparent impedance they present according to different geometrical parameters. The experimental study is devoted to a glass plan model, for two thickness and several distances between electrodes. The work showed that, for a given distance between electrodes, the thickness of the insulation affects the measured apparent impedance. The experimental study, confronted, with success, to a theoretical approach based on the analysis of the charge distribution (using the software of field calculation FEMM 4.0) allowed us to extend the range of geometrical parameters variation. A superposition method is then proposed to establish the influence degree of each dielectric (air-glass) on the apparent total capacity (impedance).

Parameter variation effects on temperature elevation in a steady-state, one-dimensional thermal model for millimeter wave exposure of one- and three-layer human tissue

The present study describes theoretical parametric analysis of the steady-state temperature elevation in one-dimensional three-layer (skin, fat and muscle) and one-layer (skin only) models due to millimeter-wave exposure. The motivation of this fundamental investigation is that some variability of warmth sensation in the human skin has been reported. An analytical solution for a bioheat equation was derived by using the Laplace transform for the one-dimensional human models. Approximate expressions were obtained to investigate the dependence of temperature elevation on different thermal and tissue thickness parameters. It was shown that the temperature elevation on the body surface decreases monotonically with the blood perfusion rate, heat conductivity and heat transfer from the body to air. Also revealed were the conditions where maximum and minimum surface temperature elevations were observed for different thermal and tissue thickness parameters. The surface temperature elevation in the three-layer model is 1.3–2.8 times greater than that in the one-layer model. The main reason for this difference is attributed to the adiabatic nature of the fat layer. By considering the variation range of thermal and tissue thickness parameters which causes the maximum and minimum temperature elevations, the dominant parameter influencing the surface temperature elevation was found to be the heat transfer coefficient between the body surface and air.

A GA-optimized Neuro-fuzzy Power System Stabilizer for Multi-machine System

The aim of this research is the design of a decentralized Power System Stabilizer (PSS) capable of performing well for a wide range of variations in system parameters and loading conditions. In addition, the designed PSS should provide effective damping of small/large disturbances and local/inter-area oscillations. The framework of the design is based on Fuzzy Logic Control (FLC). In particular, the neuro-fuzzy control rules are derived from training three classical PSSs; each is tuned using GA (Genetic Algorithms) so as to perform optimally at one operating point. The effectiveness and robustness of the designed stabilizer is investigated. The results of simulation prove that the proposed PSS offers a superior performance in comparison with the conventional stabilizer presently adopted by the industry.

Impact of total measurement uncertainty on overlay error correction

The objective of this work is to determine a guideline for defining practical overlay metrology requirements for a given design rule. Total measurement uncertainty (TMU) of overlay metrology is defined as the square root of square sum of the following items: the mean of the tool-induced shift (TIS), TIS 3-sigma, dynamic precision, and tool-to-tool matching. The TMU is dependent upon process conditions, so TMU is different by process layer. In this study, the impact of TMU on overlay error correction, which includes process and measurement noise, is investigated in terms of the stability of high-order overlay correction parameters. By evaluating the variation range of correctable parameters as a figure of merit, the corresponding TMU is determined for a given design rule. Utilizing this methodology, we determined that 2 nm of TMU value is the allowable limit for 45 nm of dynamic random access memory (DRAM) half pitch based upon simulation results. Similarly, we recommend 1 nm of TMU for 36 nm of DRAM half pitch. Our methodology is described and our simulation results are discussed.

An Experimental Technique for Characterizing Slow-Wave Characteristics of MIS-Like Transmission Lines Using Aqueous Dielectrics

This work is a study of the dielectric propagation properties of laminar substrates, which are known to support low dispersion modes with very small phase velocities. Slow modes are linked to a polarization mode supported by the insulator-semiconductor interface. The mode spectrum of metal-insulator-semiconductor lines is controlled by the substrate resistivity and the ratio of the semiconductor to insulator layer thicknesses. An experimental investigation of substrate modes normally requires the laborious fabrication of many specimens to cover a useful range of parameter variation. In this paper, we present an experimental platform that supports slow-wave propagation and allows easy adjustment of the parameters affecting the interfacial polarization mechanism.

Design and experimental investigation of a decentralized GA-optimized neuro-fuzzy power system stabilizer

The aim of this research is the design and implementation of a decentralized power system stabilizer (PSS) capable of performing well for a wide range of variations in system parameters and/or loading conditions. The framework of the design is based on Fuzzy Logic Control (FLC). In particular, the neuro-fuzzy control rules are derived from training three classical PSSs; each is tuned using GA so as to perform optimally at one operating point. The effectiveness and robustness of the designed stabilizer, after implementing it to the laboratory model, is investigated. The results of real-time implementation prove that the proposed PSS offers a superior performance in comparison with the conventional stabilizer.

Kinetics of processes and energy distribution in an electric discharge upon pumping a XeCl laser

Radiation energies and efficiencies of the XeCl laser are calculated for different pump regimes in a broad range of variations in the initial parameters [pump energy of 50 — 350 J L-1, pulse duration of 30 — 150 ns, initial concentration of HCl molecules of (0.7 — 2.5) × 1017 cm-3]. The sequence of kinetic processes during which the pump energy is converted into induced radiation and heat is determined. It is shown that when 80% — 90% of the initial HCl concentration is used per pulse, the optimal ratio between the radiation energy and the laser efficiency is provided. In these regimes, about 50% of the pump energy is spent on production of excimer molecules in the entire range of the experimental parameters and for one HCl molecule 10 ± 1.5 eV is spent.

A comprehensive parameter study of an active magnetic regenerator using a 2D numerical model

A two-dimensional numerical heat transfer model is used to investigate an active magnetic regenerator (AMR) based on parallel plates of magnetocaloric material. A large range of parameter variations are performed to study the optimal AMR. The parameters varied are the plate and channel thicknesses, cycle frequency and fluid movement. These are cast into the non-dimensional units utilization, porosity and number of transfer units (NTU). The cooling capacity vs. temperature span is mapped as a function of these parameters and each configuration is evaluated through the maximum temperature span and exergy. The results show that the optimal AMR should have a utilization in the range 0.2–1 and an NTU higher than 10 and not necessarily more than 30. It is concluded that parallel plate-based regenerators face significant challenges in terms of manufacturability. However, the benefit of parallel plate regenerators is a very low pressure drop, which is needed for high performance.

Prediction of the yield strength and shrinkage of a diamond-containing composite with a porous matrix under pressure

A theoretical model for the assessment of the yield strength of a granular composite material with a porous matrix has been developed. Parametric analysis of the model has been made; the effect of the loading type, porosity of the matrix material, and volume content of rigid inclusions on the macroscopic yield strength of the composite has been studied. An expression of the plasticity potential for a porous matrix composite, which provides a satisfactory agreement with the results of a numerical analysis of the model over the whole range of structural parameters variations, has been derived. The applicability of the developed approach to the investigation of making blanks of products from composite materials has been shown.