Valve friction and nonlinear process model closed-loop identification

Among several process variability sources, valve friction and inadequate controller tuning are supposed to be two of the most prevalent. Friction quantification methods can be applied to the development of model-based compensators or to diagnose valves that need repair, whereas accurate process models can be used in controller retuning. This paper extends existing methods that jointly estimate the friction and process parameters, so that a nonlinear structure is adopted to represent the process model. The developed estimation algorithm is tested with three different data sources: a simulated first order plus dead time process, a hybrid setup (composed of a real valve and a simulated pH neutralization process) and from three industrial datasets corresponding to real control loops. The results demonstrate that the friction is accurately quantified, as well as ""good"" process models are estimated in several situations. Furthermore, when a nonlinear process model is considered, the proposed extension presents significant advantages: (i) greater accuracy for friction quantification and (ii) reasonable estimates of the nonlinear steady-state characteristics of the process. (C) 2010 Elsevier Ltd. All rights reserved.

Phase-Locked Loop design applied to frequency-modulated atomic force microscope

The atomic force microscope (AFM) introduced the surface investigation with true atomic resolution. In the frequency modulation technique (FM-AFM) both the amplitude and the frequency of oscillation of the micro-cantilever must be kept constant even in the presence of tip-surface interaction forces. For that reason, the proper design of the Phase-Locked Loop (PLL) used in FM-AFM is vital to system performance. Here, the mathematical model of the FM-AFM control system is derived considering high order PLL In addition a method to design stable third-order Phase-Locked Loops is presented. (C) 2010 Elsevier B.V. All rights reserved.

Route to chaos in a third-order phase-locked loop network

Phase-locked loops (PLLs) are widely used in applications related to control systems and telecommunication networks. Here we show that a single-chain master-slave network of third-order PLLs can exhibit stationary, periodic and chaotic behaviors, when the value of a single parameter is varied. Hopf, period-doubling and saddle-saddle bifurcations are found. Chaos appears in dissipative and non-dissipative conditions. Thus, chaotic behaviors with distinct dynamical features can be generated. A way of encoding binary messages using such a chaos-based communication system is suggested. (C) 2009 Elsevier B.V. All rights reserved.

Mutually connected phase-locked loop networks: dynamical models and design parameters

Distribution of timing signals is an essential factor for the development of digital systems for telecommunication networks, integrated circuits and manufacturing automation. Originally, this distribution was implemented by using the master-slave architecture with a precise master clock generator sending signals to phase-locked loops (PLL) working as slave oscillators. Nowadays, wireless networks with dynamical connectivity and the increase in size and operation frequency of the integrated circuits suggest that the distribution of clock signals could be more efficient if mutually connected architectures were used. Here, mutually connected PLL networks are studied and conditions for synchronous states existence are analytically derived, depending on individual node parameters and network connectivity, considering that the nodes are nonlinear oscillators with nonlinear coupling conditions. An expression for the network synchronisation frequency is obtained. The lock-in range and the transmission error bounds are analysed providing hints to the design of this kind of clock distribution system.

Cardiovascular Simulator Improvement: Pressure Versus Volume Loop Assessment

This article presents improvement on a physical cardiovascular simulator (PCS) system. Intraventricular pressure versus intraventricular volume (PxV) loop was obtained to evaluate performance of a pulsatile chamber mimicking the human left ventricle. PxV loop shows heart contractility and is normally used to evaluate heart performance. In many heart diseases, the stroke volume decreases because of low heart contractility. This pathological situation must be simulated by the PCS in order to evaluate the assistance provided by a ventricular assist device (VAD). The PCS system is automatically controlled by a computer and is an auxiliary tool for VAD control strategies development. This PCS system is according to a Windkessel model where lumped parameters are used for cardiovascular system analysis. Peripheral resistance, arteries compliance, and fluid inertance are simulated. The simulator has an actuator with a roller screw and brushless direct current motor, and the stroke volume is regulated by the actuator displacement. Internal pressure and volume measurements are monitored to obtain the PxV loop. Left chamber internal pressure is directly obtained by pressure transducer; however, internal volume has been obtained indirectly by using a linear variable differential transformer, which senses the diaphragm displacement. Correlations between the internal volume and diaphragm position are made. LabVIEW integrates these signals and shows the pressure versus internal volume loop. The results that have been obtained from the PCS system show PxV loops at different ventricle elastances, making possible the simulation of pathological situations. A preliminary test with a pulsatile VAD attached to PCS system was made.

Closed-loop model re-identification of processes under MPC with zone control

This work deals with a procedure for model re-identification of a process in closed loop with ail already existing commercial MPC. The controller considered here has a two-layer structure where the upper layer performs a target calculation based on a simplified steady-state optimization of the process. Here, it is proposed a methodology where a test signal is introduced in a tuning parameter of the target calculation layer. When the outputs are controlled by zones instead of at fixed set points, the approach allows the continuous operation of the process without an excessive disruption of the operating objectives as process constraints and product specifications remain satisfied during the identification test. The application of the method is illustrated through the simulation of two processes of the oil refining industry. (c) 2008 Elsevier Ltd. All rights reserved.

TFEC is a macrophage-restricted member of the microphthalmia-TFE subfamily of basic helix-loop-helix leucine zipper transcription factors

The murine homologue of the TFEC was cloned as part of an analysis of the expression of the microphthalmia-TFE (MiT) subfamily of transcription factors in macrophages. TFEC, which most likely acts as a transcriptional repressor in heterodimers with other MiT family members, was identified in cells of the mononuclear phagocyte lineage, coexpressed,vith all other known MiT subfamily members (Mitf, TFE3, TFEB), Northern blot analysis of several different cell lineages indicated that the expression of murine TFEC (mTFEC) was restricted to macrophages. A 600-bp fragment of the TATA-less putative proximal promoter of TFEC shares features with many known macrophage-specific promoters and preferentially directs luciferase expression in the RAW264.7 macrophage cell line in transient transfection assays. Five of six putative Ets motifs identified in the TFEC promoter bind the macrophage-restricted transcription factor PU,I under in vitro conditions and in transfected 3T3 fibroblasts; the minimal luciferase activity of the TFEC promoter could be induced by coexpression of PU.1 or the related transcription factor Ets-2. The functional importance of the tissue-restricted expression of TFEC and a possible role in macrophage-specific gene regulation require further investigation, but are likely to be linked to the role of the other MiT family members in this lineage.

Structure-activity relationships of omega-conotoxins MVIIA, MVIIC and 14 loop splice hybrids at N and P/Q-type calcium channels

The omega-conotoxins are a set of structurally related, four-loop, six cysteine containing peptides, that have a range of selectivities for different subtypes of the voltage-sensitive calcium channel (VSCC). To investigate the basis of the selectivity displayed by these peptides, we have studied the binding affinities of two naturally occurring omega-conotoxins, MVIIA and MVIIC and a series of 14 MVIIA/MVIIC loop hybrids using radioligand binding assays for N and P/Q-type Ca2+ channels in rat brain tissue. A selectivity profile was developed from the ratio of relative potencies at N-type VSCCs (using [I-125]GVIA radioligand binding assays) and P/Q-type VSCCs (using [I-125]MVIIC radioligand binding assays). in these peptides, loops 2 and 4 make the greatest contribution to VSCC subtype selectivity, while the effects of loops 1 and 3 are negligible. Peptides with homogenous combinations of loop 2 and 4 display clear selectivity preferences, while those with heterogeneous combinations of loops 2 and 4 are less discriminatory. H-1 NMR spectroscopy revealed that the global folds of MVIIA, MVIIC and the 14 loop hybrid peptides were similar; however, several differences in local structure were identified. Based on the binding data and the 3D structures of MVIIA, GVIA and MVIIC, we have developed a preliminary pharmacophore based on the omega-conotoxin residues most Likely to interact with the N-type VSCC. (C) 1999 Academic Press.

Er(3+) doped phosphoniobate glasses and planar waveguides: structural and optical properties

Phosphoniobate glasses with composition (mol%) (100-x) NaPO(3)-xNb(2)O(5) ( x varying from 11 to 33) were prepared and characterized by means of thermal analysis, Fourier transform infrared spectroscopy, Raman scattering and (31)P nuclear magnetic resonance. The addition of Nb(2)O(5) to the polyphosphate base glass leads to depolymerization of the metaphosphate structure. Different colors were observed and assigned as indicating the presence of Nb(4+) ions, as confirmed by electron paramagnetic resonance measurements. The color was observed to depend on the glass composition and melting temperature as well. Er(3+) containing samples were also prepared. Strong emission in the 1550 nm region was observed. The Er(3+4)I(15/2) emission quantum efficiency was observed to be 90% and the quenching concentration was observed to be 1.1 mol%( 1.45 x 10(20) ions cm(-3)). Planar waveguides were prepared by Na(+)-K(+)-Ag(+) ion exchange with Er(3+) containing samples. Optical parameters of the waveguides were measured at 632.8, 543.5 and 1550 nm by the prism coupling technique as a function of the ion exchange time and Ag(+) concentration. The optimized planar waveguides show a diffusion depth of 5.9 mu m and one propagating mode at 1550 nm.

Erbium-activated silica-zirconia planar waveguides prepared by sol-gel route

Er(3+) doped (100-x)SiO(2)-xZrO(2) planar waveguides were prepared by the sol-gel route, with x ranging from 10 up to 30 mol%. Multilayer films doped with 0.3 mol% Er(3+) ions were deposited on fused quartz substrates by the dip-coating technique. The thickness and refractive index were measured by m-line spectroscopy at different wavelengths. The fabrication protocol was optimized in order to confine one propagating mode at 1.5 mu m. Photoluminescence in the near and visible region indicated a crystalline local environment for the Er(3+) ion. (c) 2007 Elsevier B.V. All rights reserved.

The design of planar gradient coils. Part I: A winding path correction method

In this work a new approach for designing planar gradient coils is outlined for the use in an existing MRI apparatus. A technique that allows for gradient field corrections inside the diameter-sensitive volume is deliberated. These corrections are brought about by making changes to the wire paths that constitute the coil windings, and hence, is called the path correction method. The existing well-known target held method is used to gauge the performance of a typical gradient coil. The gradient coil design methodology is demonstrated for planar openable gradient coils that can be inserted into an existing MRI apparatus. The path corrected gradient coil is compared to the coil obtained using the target field method. It is shown that using a wire path correction with optimized variables, winding patterns that can deliver high magnetic gradient field strengths and large imaging regions can be obtained.

Supersonic velocimetry in a shock tube using laser enhanced ionisation and planar laser induced fluorescence

A novel flow-tagging technique is presented which was employed to measure gas velocities in the free stream of a shock tube. This method is based on the laser spectroscopic techniques of Laser-Enhanced Ionisation (LEI) and Laser-Induced Fluorescence (LIF). The flow in the shock tube is seeded with small amounts of sodium, and LEI is used to produce a substantial depletion of neutral sodium atom concentration in a well-defined region of the flow, by using two wavelength-resonance excitation and subsequent collisional ionisation. At a specific time delay, single-laser-pulse planar LIF is utilised to produce a two-dimensional (2-D) inverse image of the depleted tagged region downstream of the flow. By measuring the displacement of the tagged region, free stream velocities in a shock tube were determined. Large variations in the concentration of sodium seeded into the flow were observed and even in the presence of these large variations accurate free-stream velocity measurements were obtained. The experimentally determined value for velocity compares very well with the predicted velocity.

Measurements of neutral atom diffusion and electron-ion recombination by laser enhanced ionisation and planar laser induced fluorescence in an air-acetylene flame

The spatial and temporal evolution of a depleted atomic distribution created by laser enhanced ionisation (LEI) was employed to determine both a diffusion coefficient for sodium (Na) and an electron (e(-)) and sodium ion recombination rate coefficient in an analytical air-C2H2 flame. A depleted distribution of neutral sodium atoms was produced in a flame by ionising approximately 80% of the irradiated sodium atoms in a well defined region using a two step LEI excitation scheme. Following depletion by ionisation, planar laser induced fluorescence (PLIF) images of the depleted region recorded the diffusion and decay of the depleted Na distribution for different depletion-probe delays. From measurements of the diffused width of the distribution, an accurate diffusion coefficient D = (1.19 +/- 0.03) x 10(-3) m(2) s(-1) for Na was determined in teh burnt gases of the flame. Measurements of the integrated fluorescence intensity in the depleted region for different depletion-probe delays were related to an increase in atomic sodium concentration caused by electron-ion recombination. At high concentrations (greater than or equal to 50 mu g ml(-1)), where the electron and ion concentrations in the depleted region were assumed equal, a recombination rate coefficient of 4.2 x 10(-9) cm(3) s(-1) was calculated. (C) 1997 Elsevier Science B.V.

A methodology for current density calculations in high-frequency RF resonators

As nuclear magnetic resonance imaging and spectroscopy move inexorably toward higher field-strength magnets in search of improved signal-to-noise ratio, spectral resolution, and spatial resolution, the way in which radiofrequency (RF) probes are designed changes. At higher frequencies, resonant cavities become the favored RF ''coil'' type and may be built using streamline elements to reduce the inductance of the system. In modeling such systems, the quasi-static approach of assuming that current flows evenly in all conductor cross sections and that adjacent conductors do not affect each other becomes less reasonable. The proximity of RF conductors in resonators typically causes RF eddy currents to flow, whereby the current density in each rung is altered by the RF fields generated by nearby conductors. The proper understanding and prediction of how resonators will perform require a model of the current densities flowing in conducting sections, including all RF eddy current effects. Very few models of this type have been presented in the literature. This article presents an overview of one such model and of how it may be applied to a variety of resonators, both shielded and unshielded, circular, and elliptical, in cross section. Results are presented from a shielded head coil operating at 2 tesla. (C) 1997 John Wiley & Sons, Inc.