Distribution by Scientific Domains

Selected Abstracts

The Independence of the Bank Of England: an Update

Stephen Hall
In this article, Stephen Hall and Brian Henry reconsider the arguments for further coordination of fiscal and monetary policy in the UK. The recent inflation-unemployment performance in the UK has been good, but it appears mainly the result of beneficial developments in the world economy. Further improvement in the policy-making framework in the UK is called for. Many of the present drawbacks could be dealt with by treating fiscal policy on a par with monetary policy. There are arguments that further cooperation is not needed but these are unpersuasive. They recommend the setting up of an independent committee charged with reviewing fiscal decisions, and coordinating these with monetary decisions by the MPC. [source]

Prudence and Pragmatism in the Fiscal Stance

Simon Proce
In this article, Simon Price argues that the government is pursuing a remarkably conservative fiscal policy. Not only has demand management been left almost entirely to the MPC, but since 1997 spending has been held down while the overall tax burden has been raised. Consequently, the relative size of the national debt is declining at a rapid rate. There are rules that are intended to govern debt policy, but they are based on less sound principles than the government argues, and may be inconsistent. Oddly, despite the emphasis on these rules, the government has announced a path for spending that makes it clear that it is in fact planning not to follow them. The government may be planning to reduce the national debt at an excessive rate. This may make sense in the short run, but is more problematic in the medium to long term. This is not to say fiscal policy should be immediately relaxed; the current low levels of private sector saving may well justify a temporarily tight fiscal stance. [source]


The transparency and openness of the monetary policy-making process at the Bank of England has provided very detailed information on both the decisions of individual members of the Monetary Policy Committee (MPC) and the information on which they are based. In this paper, we consider this decision-making process in the context of a model in which inflation forecast targeting is used, but there is heterogeneity among the members of the committee. We find that rational partisan theory can explain spatial voting behavior under forecast uncertainty about the output gap. Internally generated forecasts of output and market-generated expectations of medium-term inflation provide the best description of discrete changes in interest rates, in combination with uncertainty in the macroeconomic environment. There is also a role for developments in asset, housing and labor markets. Further, spatial voting patterns clearly differentiate between internally and externally apzpointed members of the MPC. The results have important implications for committee design and the conduct of monetary policy. [source]

Multiple primary cancer: an increasing health problem.

Strategies for prevention in cancer survivors
LÓPEZ M.L., LANA A., DÍAZ S., FOLGUERAS M.V., SANCHEZ L., COMENDADOR M.A., BELYAKOVA E., RODRÍGUEZ J.M. & CUETO A. (2009) European Journal of Cancer Care Multiple primary cancer: an increasing health problem. Strategies for prevention in cancer survivors This study was set to look for associations between the sites of the first and subsequent tumours in patients with multiple primary cancer (MPC) diagnosed from 1975 to 2002 in the reference hospital of a Spanish northern region, and propose prevention strategies. Patient and tumour variables were measured. Crude and standardized incidence rates per 100 000 inhabitants were obtained, and the association between MPC incidence and time was analysed by means of lineal regression. Relative risks were calculated to analyse associations between tumour sites. A total of 2737 MPC cases were registered (male/female ratio = 2). The percentage of MPC with respect to the total cancer increased from 1.78% in the 1975,1979 period to 7.08% in the 2000,2002 period (R2 = 0.92; P = 0.003). Great increase of incidence by time was found (R2 = 0.90; P = 0.004). Breast, prostate and bladder cancers increase risk of second tumour in female genital organs [RR 4.78 (3.84,5.93)], urinary system [RR 3.69 (2.89,4.69)] and male genital organs [RR 3.76 (2.84,4.69)] respectively. The MPC incidence is increasing. Interventions for MPC prevention, according to the European Code against Cancer, should be implemented early after the first cancer principally if patients suffer breast, bladder, prostate, larynx and colon cancers. [source]

From doves to hawks: A spatial analysis of voting in the Monetary Policy Committee of the Bank of England

This article examines the making of monetary policy in the United Kingdom between 1997 and 2008 by analysing voting behaviour in the Bank of England's Monetary Policy Committee (MPC). It provides a new set of measures for the monetary policy preferences of individual MPC members by estimating a Bayesian item response model. The article demonstrates the usefulness of these measures by comparing the ideal points of outgoing MPC members with their successors and by looking at changes over time in the median ideal point on the MPC. The analysis indicates that the British Government has been able to move the position of the median voter on the MPC through its appointments to the Committee. This highlights the importance of central bank appointments for monetary policy. [source]

Metastatic pulmonary calcification in a dialysis patient: Case report and a review

Christoph H. EGGERT
Abstract A 19-year-old male presented with chest pain and dyspnea. He was anephric following nephrectomy for focal segmental glomerulosclerosis, had a subsequent failed transplant, and had been dialysis dependent for 3 years. Workup revealed hyperparathyroidism and an abnormal chest X-ray and computed tomography scan, significant for massive extra-skeletal pulmonary calcification. A markedly abnormal Technitium99 methylene diphosphonate (Tc99m-MDP) bone scan confirmed the clinical suspicion of metastatic pulmonary calcification. Metastatic pulmonary calcification (MPC) is common, occurring in 60% to 80% of dialysis patients on autopsy and bone scan series. It may lead to impaired oxygenation and restrictive lung disease. Typically, the calcium crystal is whitlockite rather than hydroxyapatite, which occurs in vascular calcification. Four major predisposing factors may contribute to MPC in dialysis patients. First, chronic acidosis leaches calcium from bone. Second, intermittent alkalosis favors deposition of calcium salts. Third, hyperparathyroidism tends to cause bone resorption and intracellular hypercalcemia. Finally, low glomerular filtration rate can cause hyperphosphatemia and an elevated calcium-phosphorus product. There may be other factors. Some authors suggest that the incidence of MPC in recent years may be lower due to improved dialysis techniques. The diagnosis is confirmed by biopsy, but can be suspected by typical findings on a Tc99m-MDP bone scan. Therapy is limited to ensuring adequate dialysis, correcting calcium-phosphorus product, and hyperparathyroidism; discontinuing vitamin D analogues may help. Conflicting reports show that transplantation may either improve or worsen the situation. MPC should be considered in dialysis patients who have characteristic abnormal chest radiography and/or pulmonary symptoms. [source]

Plant-wide control of a hybrid process

C. de Prada
Abstract This paper deals with the model predictive control (MPC) of an industrial hybrid process where continuous and batch units operate jointly: the crystallization section of a sugar factory. The paper describes a plant-wide predictive controller that takes into account, both, continuous objectives and manipulated variables, as well as those related to the discrete operation and logic of the batch units. The MPC is formulated with time events, so that a more efficient NLP optimization technique, instead of MINLP, could be applied. Adaptation is provided by model updating and error estimation. Results of the controller operation in an industrial simulator are provided. Copyright © 2007 John Wiley & Sons, Ltd. [source]

An online active set strategy to overcome the limitations of explicit MPC

H. J. Ferreau
Abstract Nearly all algorithms for linear model predictive control (MPC) either rely on the solution of convex quadratic programs (QPs) in real time, or on an explicit precalculation of this solution for all possible problem instances. In this paper, we present an online active set strategy for the fast solution of parametric QPs arising in MPC. This strategy exploits solution information of the previous QP under the assumption that the active set does not change much from one QP to the next. Furthermore, we present a modification where the CPU time is limited in order to make it suitable for strict real-time applications. Its performance is demonstrated with a challenging test example comprising 240 variables and 1191 inequalities, which depends on 57 parameters and is prohibitive for explicit MPC approaches. In this example, our strategy allows CPU times of well below 100 ms per QP and was about one order of magnitude faster than a standard active set QP solver. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Circadian phase entrainment via nonlinear model predictive control

N. Bagheri
Abstract A nonlinear model predictive control algorithm is developed to investigate the phase-resetting properties of robust nonlinear biological oscillators; in particular, those of the circadian rhythm. This pacemaker is an autonomous biochemical oscillator with a free-running period close to 24 h. Research in chronobiology indicates that light stimuli may delay or advance the phase of the oscillator, allowing it to synchronize physiological processes and entrain to the environment. In this paper, a closed-loop optimal phase tracking control algorithm is developed and applied to a mammalian circadian model. The integration of MPC-based light pulses, coupled with environmental light:dark cycles, allows the circadian system to recover phase differences within 1.5 days,a fraction of the natural open-loop simulated mammalian recovery time. Accelerated phase entrainment may alleviate disorders caused by circadian rhythms that are out of phase with the environment, and improve performance. Copyright © 2007 John Wiley & Sons, Ltd. [source]

A hybrid model predictive control approach to the direct torque control problem of induction motors

Georgios Papafotiou
Abstract Direct torque control (DTC) is a state-of-the-art control methodology for electric motor drives which features favourable control performance and implementation properties. In DTC, the core of the control system is the inverter switching table, and any efforts to enhance the system's performance aim at improving its design. This issue is addressed in this paper, where we propose a new design procedure for the DTC problem. The DTC drive, comprising a two- or three-level dc-link inverter driving a three-phase induction motor, is modelled in the hybrid mixed logical dynamical (MLD) framework, and a constrained finite-time optimal control problem is set up and solved over a receding horizon using model predictive control (MPC). Simulation results are provided and compared to the current industrial standard demonstrating the potential for notable performance improvements. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Predictive control of parabolic PDEs with state and control constraints

Stevan Dubljevic
Abstract This work focuses on predictive control of linear parabolic partial differential equations (PDEs) with state and control constraints. Initially, the PDE is written as an infinite-dimensional system in an appropriate Hilbert space. Next, modal decomposition techniques are used to derive a finite-dimensional system that captures the dominant dynamics of the infinite-dimensional system, and express the infinite-dimensional state constraints in terms of the finite-dimensional system state constraints. A number of model predictive control (MPC) formulations, designed on the basis of different finite-dimensional approximations, are then presented and compared. The closed-loop stability properties of the infinite-dimensional system under the low order MPC controller designs are analysed, and sufficient conditions that guarantee stabilization and state constraint satisfaction for the infinite-dimensional system under the reduced order MPC formulations are derived. Other formulations are also presented which differ in the way the evolution of the fast eigenmodes is accounted for in the performance objective and state constraints. The impact of these differences on the ability of the predictive controller to enforce closed-loop stability and state constraints satisfaction in the infinite-dimensional system is analysed. Finally, the MPC formulations are applied through simulations to the problem of stabilizing the spatially-uniform unstable steady-state of a linear parabolic PDE subject to state and control constraints. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Explicit robust model predictive control using recursive closed-loop prediction

Danlei Chu
Abstract In this paper, we develop an algorithm to compute robust MPC explicit solutions for constrained MIMO systems with internal uncertainties and external disturbances. Our approach is based on a recursive closed-loop prediction strategy to realize a finite horizon robust MPC regulator, which has the feature that only one-step state prediction is sufficient to realize robust MPC with an arbitrary prediction horizon. The paper defines a set of recursive sub-optimization problems as multiple-parametric sub-quadratic programming (mp-SQP), and shows that the optimal solution to the mp-SQP problem is piecewise affine functions of states, associated with piece objectives and state critical regions. Asymptotic closed-loop stability can be guaranteed by a terminal weighting and a terminal feedback gain; also by introducing two tuning variables, the algorithm is capable of adjusting the trade-off between system performance and robustness. The state admissible set, which is not easily derived from physical vision, is constructed by two methods: a piecewise linear norm of signals, and polyhedral Voronoi sets. Finally, two simulation examples demonstrate that the algorithm is efficient, feasible and flexible, and can be applied to both slow and fast industrial MIMO systems. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Model predictive control for constrained systems with uncertain state-delays

Xiao-Bing Hu
Abstract This paper presents a model predictive control (MPC) algorithm for a class of constrained linear systems with uncertain state-delays. Based on a novel artificial Lyapunov function, a new stabilizing condition dependent of the upper bound of uncertain state-delays is presented in an LMI (linear matrix inequality) form. The proposed MPC algorithm is developed by following the fashion of stability-enforced scheme. The new algorithm is then extended to linear time varying (LTV) systems with multiple uncertain state-delays. Numerical examples illustrate the effectiveness of the new algorithm. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Discontinuous feedbacks, discontinuous optimal controls, and continuous-time model predictive control

Fernando A. C. C. Fontes
Abstract It is known that there is a class of nonlinear systems that cannot be stabilized by a continuous time-invariant feedback. This class includes systems with interest in practice, such as nonholonomic systems, frequently appearing in robotics and other areas. Yet, most continuous-time model predictive control (MPC) frameworks had to assume continuity of the resulting feedback law, being unable to address an important class of nonlinear systems. It is also known that the open-loop optimal control problems that are solved in MPC algorithms may not have, in general, a continuous solution. Again, most continuous-time MPC frameworks had to artificially assume continuity of the optimal controls or, alternatively, impose some demanding assumptions on the data of the optimal control problem to achieve the desired continuity. In this work we analyse the reasons why traditional MPC approaches had to impose the continuity assumptions, the difficulties in relaxing these assumptions, and how the concept of ,sampling feedbacks' combines naturally with MPC to overcome these difficulties. A continuous-time MPC framework using a strictly positive inter-sampling time is argued to be appropriate to use with discontinuous optimal controls and discontinuous feedbacks. The essential features for the stability of such MPC framework are reviewed. Copyright © 2003 John Wiley & Sons, Ltd. [source]

To go or not to go: Migration of human mesenchymal progenitor cells stimulated by isoforms of PDGF

Jörg Fiedler
Abstract The recruitment of mesenchymal progenitor cells (MPCs) and their subsequent differentiation to osteoblasts is mandatory for bone development, remodeling, and repair. To study the possible involvement of platelet-derived growth factor (PDGF) isoforms, primary human MPCs and osteogenic differentiated progenitor cells (dOB) were examined for chemotaxic response to homodimeric human platelet-derived growth factor AA, -BB, and heterodimeric PDGF-AB. The role of PDGF receptors was addressed by preincubation with PDGF receptor alpha and beta chain specific antibodies. Migration of MPCs, dOB, and primary osteoblasts (OB) was stimulated by the addition of rhPDGF-AA, rhPDGF-BB, and rhPDGF-AB. The effect was highest in MPCs and for rhPDGF-BB, and declining with osteogenic differentiation. Preincubation with the receptor alpha specific antibody decreased the CI to borderline values while pretreatment with the receptor beta specific antibody led to a complete loss of chemotactic response to PDGF isoforms. In control experiments, basal migration values and rhBMP-2 as well as rxBMP-4 induced chemotaxis of MPC were not influenced by the addition of receptor alpha or beta antibodies. Interestingly, without preincubation the parallel exposure of MPC to rhTGF-,1 instantaneously leads to a selective loss of migratory stimulation by rhPDGF-AA. The chemotactic effect of PDGF isoforms for primary human MPCs and the influence of osteogenic differentiation suggest a functional role for recruitment of MPCs during bone development and remodeling. Moreover, these observations may be useful for novel approaches towards guided tissue regeneration or tissue engineering of bone. © 2004 Wiley-Liss, Inc. [source]

Muscle precursor cells isolated from aged rats exhibit an increased tumor necrosis factor-, response

AGING CELL, Issue 1 2009
Simon J. Lees
Summary Improving muscle precursor cell (MPC, muscle-specific stem cells) function during aging has been implicated as a key therapeutic target for improving age-related skeletal muscle loss. MPC dysfunction during aging can be attributed to both the aging MPC population and the changing environment in skeletal muscle. Previous reports have identified elevated levels of tumor necrosis factor-, (TNF-,) in aging, both circulating and locally in skeletal muscle. The purpose of the present study was to determine if age-related differences exist between TNF-,-induced nuclear factor-kappa B (NF-,B) activation and expression of apoptotic gene targets. MPCs isolated from 32-month-old animals exhibited an increased NF-,B activation in response to 1, 5, and 20 ng mL,1 TNF-,, compared to MPCs isolated from 3-month-old animals. No age differences were observed in the rapid canonical signaling events leading to NF-,B activation or in the increase in mRNA levels for TNF receptor 1, TNF receptor 2, TNF receptor-associated factor 2 (TRAF2), or Fas (CD95) observed after 2 h of TNF-, stimulation. Interestingly, mRNA levels for TRAF2 and the cell death-inducing receptor, Fas (CD95), were persistently upregulated in response to 24 h TNF-, treatment in MPCs isolated from 32-month-old animals, compared to 3-month-old animals. Our data indicate that age-related differences may exist in the regulatory mechanisms responsible for NF-,B inactivation, which may have an effect on TNF-,-induced apoptotic signaling. These findings improve our understanding of the interaction between aged MPCs and the changing environment associated with age, which is critical for the development of potential clinical interventions aimed at improving MPC function with age. [source]

A re-examination of the excess smoothness puzzle when consumers estimate the income process

Anurag N. Banerjee
Abstract The excess smoothness puzzle is explored using a simple version of the permanent income hypothesis. The new feature is that consumers do not know the observed data-generating process for income. Instead they estimate the income process every period using the past income data and update their income forecasts as new data arrive. Two scenarios are examined: first, where the income has a linear deterministic trend and second, where the income has a constant trend. There is a misspecification bias in the estimate of the marginal propensity to consume (MPC). This bias is of second-order importance in the first scenario while it is of first-order importance in the second. We conclude that the second scenario, which may be relevant for less developed countries, may offer a potential solution to the excess smoothness puzzle. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Model predictive control with learning-type set-point: Application to artificial pancreatic ,-cell

AICHE JOURNAL, Issue 6 2010
Youqing Wang
Abstract A novel combination of model predictive control (MPC) and iterative learning control (ILC), referred to learning-type MPC (L-MPC), is proposed for closed-loop control in an artificial pancreatic ,-cell. The main motivation for L-MPC is the repetitive nature of glucose-meal-insulin dynamics over a 24-h period. L-MPC learns from an individual's lifestyle, inducing the control performance to improve from day to day. The proposed method is first tested on the Adult Average subject presented in the UVa/Padova diabetes simulator. After 20 days, the blood glucose concentrations can be kept within 68,145 mg/dl when the meals are repetitive. L-MPC can produce superior control performance compared with that achieved under MPC. In addition, L-MPC is robust to random variations in meal sizes within ±75% of the nominal value or meal timings within ±60 min. Furthermore, the robustness of L-MPC to subject variability is validated on Adults 1,10 in the UVa/Padova simulator. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source]

Safe-steering of batch process systems

AICHE JOURNAL, Issue 11 2009
Siam Aumi
Abstract This work considers the problem of controlling batch processes to achieve a desired final product quality subject to input constraints and faults in the control actuators. Specifically, faults are considered that cannot be handled via robust control approaches, and preclude the ability to reach the desired end-point, necessitating fault-rectification. A safe-steering framework is developed to address the problem of determining how to utilize the functioning inputs during fault rectification to ensure that after fault-rectification, the desired product properties can be reached upon batch termination. To this end, first a novel reverse-time reachability region (we define the reverse time reachability region as the set of states from where the desired end point can be reached by batch termination) based MPC is formulated that reduces online computations, as well as provides a useful tool for handling faults. Next, a safe-steering framework is developed that utilizes the reverse-time reachability region based MPC in steering the state trajectory during fault rectification to enable (upon fault recovery) the achieving of the desired end point properties by batch termination. The proposed controller and safe-steering framework are illustrated using a fed-batch process example. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Outsiders at the Bank of England's MPC

monetary policy committees; Bank of England; outsiders; recession aversion The monetary policy committee (MPC) of the Bank of England consists of five internal and four external members. We study the voting record and show that outsiders dissent more often than insiders and tend to prefer lower rates, especially during economic downturns. Moreover, dissents by outsiders help forecast future interest rate changes, in contrast to dissents by insiders. A model in which outsiders in contrast to insiders are "recession averse" and more uncertain regarding the appropriate level of interest rates replicates the observed voting pattern well. [source]

Factorized approach to nonlinear MPC using a radial basis function model

AICHE JOURNAL, Issue 2 2001
Sharad Bhartiya
A new computationally efficient approach for nonlinear model predictive control (NMPC) presented here uses the factorability of radial basis function (RBF) process models in a traditional model predictive control (MPC) framework. The key to the approach is to formulate the RBF process model that can make nonlinear predictions across a p-step horizon without using future unknown process measurements. The RBF model avoids error propagation from use of model predictions us input in a recursive or iterative manner. The resulting NMPC formulation using the RBF model provides analytic expressions for the gradient and Hessian of the controller's objective function in terms of RBF network parameters. Solution of the NMPC optimization problem is simplifed significantly by factorization of the RBF model output into terms containing only known and unknown parts of the process. [source]

Evaluation of lignans and free and linked hydroxy-tyrosol and tyrosol in extra virgin olive oil after hydrolysis processes

Nadia Mulinacci
Abstract We describe chemical hydrolytic procedures to evaluate the total amount of tyrosol and hydroxy-tyrosol free and/or linked to secoiridoidic molecules (acid hydrolysis). At the same time a rapid determination of the lignans in complex minor polar compound (MPC) extracts is proposed (alkaline hydrolysis). High-performance liquid chromatography/diode array detection (HPLC/DAD) and HPLC/MS were applied as reference methods to evaluate the quantitative results from the hydrolysis experiments. The optimized acid hydrolysis procedures were first applied to an oleuropein standard and then to MPC fractions extracted from several commercial extra virgin olive oils. The results confirm the applicability of the method, consisting in the acid hydrolysis of complex mixtures of secoiridoidic derivatives, to determine the antioxidant potential in terms of MPC. These data can contribute to forecasting the potential ageing resistance of an extra virgin olive oil in terms of antioxidant potency. Finally, alkaline hydrolysis allows confirmation and easy determination of the amount of lignans, especially in those MPC fractions which are particularly complex. Copyright © 2006 Society of Chemical Industry [source]

Influence of perfusion on high-intensity focused ultrasound prostate ablation: A first-pass MRI study,

Marlène Wiart
Abstract Our aim was to evaluate the influence of regional prostate blood flow (rPBF) on high-intensity focused ultrasound (HIFU) treatment outcome. A total of 48 patients with clinically localized prostate cancer were examined by dynamic contrast-enhanced (DCE)-MRI prior to HIFU therapy. A prostate-specific antigen (PSA) nadir threshold of 0.2 ng/ml was used to define the populations of responders and nonresponders. A dedicated tracer kinetic model, namely "monoexponential plus constant" (MPC) deconvolution, was implemented to provide quantitative estimates of rPBF. The results were compared with those obtained by semiquantitative (steepest slope, mean gradient) and quantitative (Fermi deconvolution) approaches. Of the four methods studied, quantitative rPBF obtained by MPC deconvolution proved the most sensitive to the perfusion changes encountered in this study. Furthermore, blood-flow values obtained with MPC deconvolution in the prostate and muscle (12 ± 8 and 5 ± 3 ml/min/100 g, respectively) were in good agreement with literature data. The mean pretreatment rPBF obtained with MPC deconvolution was significantly higher in nonresponders compared to responders (16 ± 9 vs. 10 ± 6 ml/min/100 g), suggesting a correlation between baseline perfusion and treatment outcome. The present work describes and validates the use of dynamic MRI to estimate rPBF in patients, which in the future may help to refine the conduct of HIFU therapy. Magn Reson Med 58:119,127, 2007. © 2007 Wiley-Liss, Inc. [source]

Constructive model predictive control for constrained nonlinear systems

De-Feng He
Abstract This paper develops a new model predictive control (MPC) design for stabilization of continuous-time nonlinear systems subject to state and input constraints. The key idea is to construct an analytic form of the controller with some undetermined parameters and to calculate the parameters by minimizing online a performance index. By using the method of control Lyapunov functions (CLFs), we construct an appropriate variation on Sontag's formula, with one degree of freedom reflecting ,decay rate' of CLFs. Moreover, the constructed univariate control law is used to characterize the terminal region that guarantees the feasibility of the optimal control problem. Provided that the initial feasibility of the optimization problem is satisfied, the stability of the control scheme can be guaranteed. An example is given to illustrate the application of the constructive MPC design. Copyright © 2008 John Wiley & Sons, Ltd. [source]

On fusion of PCA and a physical model-based predictive control strategy for efficient load-cycling operation of a thermal power plant

Girijesh Prasad
Abstract Controlling a thermal power plant optimally during load-cycling operation is a very challenging control problem. The control complexity is enhanced further by the possibility of simultaneous occurrence of sensor malfunctions and a plethora of system disturbances. This paper proposes and evaluates the effectiveness of a sensor validation and reconstruction approach using principal component analysis (PCA) in conjunction with a physical plant model. For optimal control under severe operating conditions in the presence of possible sensor malfunctions, a predictive control strategy is devised by appropriate fusion of the PCA-based sensor validation and reconstruction approach and a constrained model predictive control (MPC) technique. As a case study, the control strategy is applied for thermal power plant control in the presence of a single sensor malfunction. In particular, it is applied to investigate the effectiveness and relative advantage of applying rate constraints on main steam temperature and heat-exchanger tube-wall temperature, so that faster load cycling operation is achieved without causing excessive thermal stresses in heat-exchanger tubes. In order to account for unstable and non-minimum phase boiler,turbine dynamics, the MPC technique applied is an infinite horizon non-linear physical model-based state-space MPC strategy, which guarantees asymptotic stability and feasibility in the presence of output and state constraints. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Figures of merit of magneto-optic spatial light modulators with magnetophotonic crystals

K. Takahashi
Abstract This paper presents the simulated and measured results of two types of one dimensional magnetophotonic crystals (1-D MPC) with single cavity and dual cavity respectively for applcation to thin film type magneto-optic spatial light modulators (MOSLMs). The use of MPC is expected to be effective for thin film type MOSLM, because the apparent Faraday rotation is largely enhanced due to light localization in magnetic defect layer of MPC with a large number of periodic dielectric layers. The complex chracteristics of MPCs are discussed in this paper , Faraday rotation ,F, transmittance T, and figure of merit F = T sin(2,F). It is key point of finding optimal structure of MPC for application of MOSLM to use F, because the T decreased with increase of k, while Faraday rotation ,F increased, indicating that the enhancement of light modulation rate could be achieved by optimizing the figure of merit F defined by F , T ·sin2,F. The maximum F = 13.7 was obtained in dual cavity MPC, while F = 12.5 was obtained in single cavity MPC. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Design of a slim optical image stabilization actuator for mobile phone cameras

Hsing-Cheng Yu
Abstract Mechanical optical image stabilization actuator (OISA) will quickly become a standard feature in a high resolution mobile phone camera (MPC) and the quantity of MPC will exceed that of digital still cameras in several years. Whenever jitter arises from shaky hands or environment in taking photos, optical images projected upon an image sensor blur. Designing a slim OISA in MPC is an effective solution that addresses image quality. Therefore, this work presents a slim OISA utilized in MPC to compensate jitter form camera shake in taking photos. Two proportional-integral-derivative controllers based on transfer functions for dual axes of the slim OISA system in MPC obtained from system identification have been designed. The settling time of dual axes are less than 0.03 sec. Furthermore, a thrust ball bearing in this study has reduced the friction force between the movable and the stationary parts, so as to minimize the driving current to be less than 5 mA. Hence, the slim OISA has satisfied low power consumption requirement, and is also possible to reduce dimension in the MPC application. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

A combined ion source for fast switching between electrospray and matrix-assisted laser desorption/ionization in Fourier transform ion cyclotron resonance mass spectrometry

Gökhan Baykut
A new ion source has been developed for Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) that enables quick changes between matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) modes. When operating as an ESI source, the sample solution is sprayed through an angled nebulizer. The generated ions pass through a glass capillary followed by a skimmer and three sequential hexapole ion guides. Ions can be accumulated in the third hexapole (storage hexapole) before they are injected into the ICR trap. The second hexapole is mounted on a movable platform which also carries the MALDI sample plate. During the switch from ESI to MALDI, this platform moves the second hexapole out of the hexapole series and locates a MALDI sample plate with 384 sample positions into the area directly in front of the storage hexapole. The storage hexapole is in a medium pressure chamber (MPC) which has windows both for the incoming laser beam and for the observation optics, as well as a gas tube for pulsing collision gas into the chamber. During the MALDI operation the focused laser beam enters the MPC, passes between the hexapole rods and irradiates a MALDI sample on the target plate. The sample molecules are desorbed/ionized into the storage hexapole and simultaneously cooled by collisions with the pulsed gas. Ions desorbed from multiple laser shots can be accumulated in this hexapole before they are transferred to the ICR trap. With the combined ion source a computer-controlled switch between MALDI and ESI modes is possible in less than a minute, depending on the position of the MALDI target on the 384-spot plate. Immediate acquisition of mass spectra is possible after mode switching without the need for tuning or re-calibration. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Enhanced Performance Assessment of Subspace Model-Based Predictive Controller with Parameters Tuning

Qiang Zhang
Abstract This study focuses on performance assessment of model predictive control. An MPC-achievable benchmark for the unconstrained case is proposed based on closed-loop subspace identification. Two performance measures can be constructed to evaluate the potential benefit to update the new identified model. Potential benefit by tuning the parameter can be found from trade-off curves. Effect of constraints imposed on process variables can be evaluated by the installed controller benchmark. The MPC-achievable benchmark for the constrained case can be estimated via closed-loop simulation provided that constraints are known. Simulation of an industrial example was done using the proposed method. Cette étude porte sur l'évaluation de la performance du contrôle prédictif par modèles (MPC). On propose un banc d'essai adapté au MPC pour le cas non contraint en se basant sur l'identification de sous-espaces en boucle fermée. Deux mesures de performance sont élaborées pour évaluer l'avantage potentiel de mettre à jour le nouveau modèle identifié. L'avantage potentiel par réglage du paramètre peut s'obtenir à partir des courbes de compromis. L'effet des contraintes imposé sur les variables de procédé peut être évalué par le banc d'essai de contrôleur installé. Le banc d'essai adapté au MPC pour le cas contraint peut être estimé par la simulation en boucle fermée dans la mesure où les contraintes sont connues. On a réalisé la simulation d'un exemple industriel à l'aide de la méthode proposée. [source]

Perturbation signal design for neural network based identification of multivariable nonlinear systems

Pankaj S. Kulkarni
Abstract The paper focuses on issues in experimental design for identification of nonlinear multivariable systems. Perturbation signal design is analyzed for a hybrid model structure consisting of linear and neural network structures. Input signals, designed to minimize the effects of nonlinearities during the linear model identification for the multivariable case, have been proposed and its properties have been theoretically established. The superiority of the proposed perturbation signal and the hybrid model has been demonstrated through extensive cross validations. The utility of the obtained models for control has also been proved through a case study involving MPC of a nonlinear multivariable neutralization plant. On traite dans cet article de la problématique des plans expérimentaux pour la détermination des systèmes multivariés non linéaires. La conception des signaux de perturbation est analysée pour un modèle de structure hybride composée de structures à réseaux linéaires et neuronaux. Des signaux d'entrée, con,us pour minimiser les effets des non-linéarités lors de la détermination du modèle linéaire pour le cas multivarié, sont proposés et leurs propriétés sont établies de manière théorique. La supériorité du signal de perturbation et du modèle hybride proposés est démontrée par des validations croisées poussées. L'utilité des modèles obtenus pour le contr,le est également prouvée par une étude de cas faisant intervenir le MPC d'une installation de neutralisation multivariée non linéaires. [source]