Convergence and frequency-domain analysis of a discrete first-order model reference adaptive controller

SUMMARY We study the convergence properties of a direct model reference adaptive control system by applying techniques from numerical analysis. In particular, a first-order discrete system coupled to a minimal control synthesis algorithm discretized by the one-step one-stage zero-order-hold sampling is studied. This results in a strongly non-linear dynamic system owing to the adaptive mechanism where stability at steady state, i.e. at the operating point, equates to successful control. This paper focuses on the convergence analysis of the overall dynamical system for understanding accuracy, stability and performance at steadystate. The local stability of the steady state solution is considered by linearizing the system in the neighbourhood of an operating point when the input is a step function. This analysis allows us to specify two gain space domains which define the region of local stability. Moreover, both the accuracy and the frequency-domain analyses give insight into the range of adaptive control weightings that results in optimal performance of the minimal control synthesis algorithm and also highlights a possible approach to a priori selection of the time step and adaptive weighting values. The effectiveness of the proposed analysis is further demonstrated by simulations and experiments on a first-order plant. Copyright # 2006 John Wiley & Sons, Ltd

Quasi-periodicity and multi-scale resonators for the reduction of seismic vibrations in fluid-solid systems

This paper presents a mathematical model for an industry-inspired problem of vibration isolation applied to elastic fluid-filled containers. A fundamental problem of suppression of vibrations within a finite-width frequency interval for a multi-scale fluid-solid system has been solved. We have developed a systematic approach employing full fluid-solid interaction and dispersion analysis, which can be applied to finite and periodic multi-scale systems. The analytical findings are accompanied by numerical simulations, including frequency response analyses and transient regime computations

COMPARISON OF RENALGUARD SYSTEM, CONTINUOUS VENOVENOUS HEMOFILTRATION AND HYDRATION IN HIGH-RISK PATIENTS FOR CONTRAST-INDUCED NEPHROPATHY

Contrast-induced nephropathy (CIN) is a relatively frequent complication of percutaneous coronary and peripheral artery interventions and is associated with significant in-hospital and long term morbidity and mortality. We aim to compare the impact on major events of RenalGuard system (RG), continuous veno-venous Hemofiltration (CVVH) and hydration (Hy) with sodium bicarbonate plus N-acetylcysteine in patients with severe renal failure

Hybrid simulations of a multi-span rc viaduct with plain bars and sliding bearings

This paper deals with the seismic response assessment of an old reinforced concrete viaduct and the effectiveness of friction-based retrofitting systems. Emphasis was laid on an old bridge, not properly designed to resist seismic action, consisting of 12 portal piers that support a 13-span bay deck for each independent roadway. On the basis of an OpenSEES finite element frame pier model, calibrated in a previous experimental campaign with cyclic displacement on three 1:4 scale frame piers, a more complex experimental activity using hybrid simulation has been devised. The aim of the simulation was twofold: (i) to increase knowledge of non-linear behavior of reinforced concrete frame piers with plain steel rebars and detailing dating from the late 1950s; and (ii) to study the effectiveness of sliding bearings for seismic response mitigation. Hence, to explore the performance of the as built bridge layout and also of the viaduct retrofitted with friction-based devices, at both serviceability and ultimate limit state conditions, hybrid simulation tests were carried out. In particular, two frame piers were experimentally controlled with eight-actuator channels in the as built case while two frame piers and eight sliding bearings were controlled with 18-actuator channels in the isolated case. The remaining frame piers were part of numerical substructures and were updated offline to accurately track damage evolution

Renalguard, hemofiltration and hydration in prevention of contrast induced nephropathy in patients with severe chronic kidney disease undergoing percutaneous vascular interventions

Contrast-induced nephropathy (CIN) is a frequent complication of percutaneous coronary and peripheral artery interventions and is associated with significant in-hospital and long-term morbidity and mortality. We aim to compare the impact on major events of RenalGuard system(RG), continuous veno-venous Hemofiltration (CVVH) and hydration (Hy) with sodium bicarbonate plus N-acetylcysteine in patients with severe renal failure

The crystal structure of mineral fibres. 2. Amosite and fibrous anthophyllite

This study reports for the first time crystal-structure data for amosite and fibrous anthophyllite. The chemical composition of the two fibre species was determined from EMPA. Crystal structures were refined using powder-diffraction data, using both laboratory sources and synchrotron radiation. Results were compared with the available literature data for the non-fibrous varieties grunerite and anthophyllite, respectively. The calculated site-occupancies for all samples are in agreement with the chemical compositions calculated from EMPA. The existing structure models of grunerite and orthorhombic anthophyllite also applies to the corresponding fibrous varieties amosite and fibrous anthophyllite, respectively. In amosite, both Fe2+ and Fe3+ atoms are found at the sites M(1), M(2) and M(3) and Fe2+ ions is the only atomic species found at site M(4). Mg is disordered over the C sites with a preference for site M(2). Minor Ca and Na have been assigned to the A site. In fibrous anthophyllite, Mg is the only atomic species found at the M1, M2 and M3 sites. Fe2+, Mg (and minor Mn) have been assigned to the M4 site, whereas minor Ca has been assigned to the A site. In both structures, the environment at the M(4) site in amosite and M4 site in fibrous anthophyllite is highly distorted. This work can be considered a basis for studies aimed at understanding the potential toxicity/ pathogenicity of these mineral fibres

Fire performance of blind-bolted connections to concrete filled tubular columns in tension

This paper describes an advanced numerical model to predict the fire behaviour of blind-bolts in the tension area of endplate connections between I-beams and concrete filled tubular (CFT) columns. It is the continuation of a previous research on the thermal response of connections, considering the tension load of a moment-resisting connection. Due to the absence of experiments and data on blind-bolts fire performance the aim was to provide a model for their study. The effect of two main variables was researched, the concrete infill of the columns and the anchored extension of the blind-bolt. The fire resis- tance rating (FRR), the failure mode and the force–displacement–temperature curve at high temperatures were discussed. Results proved that concrete inside the column enhanced the connections response at elevated temperatures in terms of FRR and stiffness. On the other hand, the use of anchored blind-bolts compared with normal blind-bolts provided stiffer connections, but the FRR improvement depended on the plate thickness and steel bolt properties. Finally, the use of fire resistant steel bolts as a method to enhance the fire response was assessed, observing the benefits to these connections when the shank of the blind-bolt governs the failure

A strategy to characterize the LISA-Pathfinder cold gas thruster system

The cold gas micro-propulsion system that will be used during the LISA-Pathfinder mission will be one of the most important component used to ensure the "free-fall" of the enclosed test masses. In this paper we present a possible strategy to characterize the effective direction and amplitude gain of each of the 6 thrusters of this system

The LISA pathfinder mission

ISA Pathfinder (LPF), the second of the European Space Agency's Small Missions for Advanced Research in Technology (SMART), is a dedicated technology validation mission for future spaceborne gravitational wave detectors, such as the proposed eLISA mission. LISA Pathfinder, and its scientific payload - the LISA Technology Package - will test, in flight, the critical technologies required for low frequency gravitational wave detection: it will put two test masses in a near-perfect gravitational free-fall and control and measure their motion with unprecedented accuracy. This is achieved through technology comprising inertial sensors, high precision laser metrology, drag-free control and an ultra-precise micro-Newton propulsion system. LISA Pathfinder is due to be launched in mid-2015, with first results on the performance of the system being available 6 months thereafter. The paper introduces the LISA Pathfinder mission, followed by an explanation of the physical principles of measurement concept and associated hardware. We then provide a detailed discussion of the LISA Technology Package, including both the inertial sensor and interferometric readout. As we approach the launch of the LISA Pathfinder, the focus of the development is shifting towards the science operations and data analysis - this is described in the final section of the paper