bluuebunny/crossref_metadata_2025 huggingface dataset:
Lagrangian Bond Graphs for Solid Continuum Dynamics Modeling
Authors: Fahrenthold E. P. , Wargo J. D.
Published: March 2008

The limitations of existing continuum bond graph modeling techniques have effectively precluded their use in large order problems, where nonrepetitive graph structures and causal patterns are normally present. As a result, despite extensive publication of bond graph models for continuous systems simulations, bond graph methods have not offered a viable alternative to finite element analysis for the vast majority of practical problems. However, a new modeling approach combining Lagrangian (mass fixed) bond graphs with a selected finite element discretization scheme allows for direct simulation of a wide range of large order solid continuum dynamics problems. With appropriate modifications, including the use of Eulerian (space fixed) bond graphs, the method may be extended to include fluid dynamics modeling.
On the Stability of PD Control for a Two-Link Rigid-Flexible Manipulator
Authors: Yigit Ahmet S.
Published: March 2008

Controller design for a rigid-flexible two-link manipulator is considered. Robustness of independent joint PD control is investigated. It has been shown that the stability of independent joint PD control does not depend explicitly on the system parameters. No discretization or linearization of the equations of motion is required to assure the stability. Simulation studies also show that independent joint PD control gives reasonably good results for the flexible system, and is robust to parameter uncertainties.
Compressible-Flow Modeling With Pseudo Bond Graphs
Authors: Tan Jinglu , Stelson Kim A. , Janni Kevin A.
Published: March 2008

A finite lump pseudo bond graph scheme for isothermal and isentropic pipe flows of ideal gas is developed on the basis of the governing differential equations and an assumption of staggered spatial profiles for the variables. Element constitutive relationships are formally derived. A new CONVECTANCE element is defined to model convective acceleration. The bond graph is simple and convenient to use.
Quantitative Robust Control of Temperature and Humidity in Hot-and-Dry Climates
Authors: Attia A. E. , Rezeka S. F.
Published: March 2008

In dry and hot weather, both temperature and humidity control should be adopted in buildings, industrial plants, and passenger cars. Because of the unsatisfactory performance of the available classical control system, a quantitative servo-controller is synthesized in this paper. The proposed feedback controller is constructed by a state observer related to the plant and utilizing the measured room temperature and humidity as an input. The robustness properties of such a system to model error are discussed. The feasibility of both the synthesized and the conventional control systems are investigated in the presence of uncertainty in both the room internal loads and the outside load. The introduced controller is found capable of adjusting the room temperature and humidity at the design values for all time.
An Approach to Motion and Force Control of Coordinated Robot Arms in the Presence of Joint Flexibility
Authors: Hu Yan-Ru , Goldenberg Andrew A.
Published: March 2008

A system consisting of several flexible joint robot arms is studied in this paper. The paper addresses the motion and force control problem of such systems. A coordinating controller, consisting of a motion controller, contact force controller, and internal force controller, is designed to distribute the load between the coordinated flexible joint robot arms, and control the motion of the object, the internal force and contact force between the object and the environment, as well generate the desired joint elastic force. The system stability is analyzed based on Lyapunov stability theory. It is shown that with the proposed controller the motion and force control variables can be regulated to track asymptotically their desired trajectories. Simulation results are given to illustrate the performance of the proposed controller.
Normal Forms, Averaging and Resonance Control of Flexible Structures
Authors: Pinsky Mark A. , Essary Bill
Published: March 2008

In this paper, we address a novel averaging method for analysis and control of high dimensional, stiff nonlinear differential equations governing the dynamics of a variety of flexible structures. The method yields significant reduction of the initial equations by the averaging of high oscillatory elastic distortions over slow rigid-body motions which can be given in either analytical or numerical form. The averaging allows the stiff property to be overcome. In the averaging equations only exceptional resonance nonlinear terms persist which actually control the plant’s stability. A stabilization problem is addressed for an averaging nonlinear plant and the error involved in such an approximation is estimated. A nonlinear stabilizing control is then evaluated in terms of the averaging normal form and the resonance feedback is shown to be an efficient design procedure.
Damage-Mitigating Control of Mechanical Systems: Part I—Conceptual Development and Model Formulation
Authors: Ray Asok , Wu Min-Kuang , Carpino Marc , Lorenzo Carl F.
Published: March 2008

A major goal in the control of complex mechanical systems such as advanced aircraft, spacecraft, and power plants is to achieve high performance with increased reliability, availability, component durability, and maintainability. The current state-of-the-art of control systems synthesis focuses on improving performance and diagnostic capabilities under constraints that often do not adequately represent the dynamic properties of the materials. The reason is that the traditional design is based upon the assumption of conventional materials with invariant characteristics. In view of high performance requirements and availability of improved materials, the lack of appropriate knowledge about the properties of these materials will lead to either less than achievable performance due to overly conservative design, or over-straining of the structure leading to unexpected failures and drastic reduction of the service life. The key idea of the research reported in this paper is that a significant improvement in service life can be achieved by a small reduction in the system dynamic performance. This requires augmentation of the current system-theoretic techniques for synthesis of decision and control laws with governing equations and inequality constraints that would model the properties of the materials for the purpose of damage representation and failure prognosis. The major challenge in this research is to characterize the damage generation process in a continuous-time setting, and then utilize this information for synthesizing algorithms of robust control, diagnostics, and risk assessment in complex mechanical systems. Damage mitigation for control of mechanical systems is reported in the two-part paper. The concept of damage mitigation is introduced and a continuous-time model of fatigue damage dynamics is formulated in this paper which is the first part. The second part which is a companion paper presents the synthesis of the open-loop control policy and the results of simulation experiments for transient operations of a reusable rocket engine.
A Quantitative Performance Index for Observer-Based Monitoring Systems
Authors: Huh Kunsoo , Stein Jeffrey L.
Published: March 2008

Model-based monitoring systems based on state observer theory are attractive for machine monitoring because practical, inexpensive, and reliable sensors can be located remote to the signal(s) of interest. Then, a model of the machine plus an estimation algorithm are utilized to convert the output of the remote sensors to signals representing the desired local behavior. While this type of monitoring system has shown much promise in the laboratory, it has not been widely accepted by industry because, in practice, these systems often have poor performance with respect to accuracy, bandwidth, reliability (false alarms), and robustness. In this paper, the limitations of the deterministic state observer are investigated quantitatively from the machine monitoring viewpoint. The limitations in the transient and steady-state observer performance are quantified based on the estimation error bounds, and from these error bounds, performance indices are selected. Then, based on the relationships between the indices, a main index is determined in order to represent the overall observer performance. The index is the condition number of the observer eigenvectors in L2 norm. It is shown that observers with small condition numbers are guaranteed to have small error bounds. This index can be utilized as a quality condition for any linear observer regardless of how it is designed as well as form the basis for an observer design methodology for high performance observer-based monitoring systems.
A Robust Method to Determine the Coordinates of a Wave Source for 3-D Position Sensing
Authors: Figueroa Fernando , Mahajan Ajay
Published: March 2008

This work addresses a method for location of a wave source by observing the wave as it reaches various observation points (receivers), or conversely, this is also a method for location of a receiver at an observation point, by probing with waves generated at various sources. The terms observing and probing imply measurement of time-of-flight (TOF) between a source (transmitter) and a receiver. Practical implications of this work include development and improvement of systems that triangulate the position of a point of interest based on TOF measurements to observation points. Typical applications to benefit from this work include 3-D digitization devices based in ultrasonic, laser, or infrared wave energy. This paper proposes a formulation for location of a wave source (receiver) using a minimum of five receivers (transmitters). It will also be shown that the proposed formulation defines a system that is inherently self-installing and self-calibrating. Also, conditions are developed to geometrically locate the observation points such that a solution to the problem is feasible, and last, a method to define an optimum geometric configuration of the observation points is provided. The case of an ultrasonic 3-D location system mounted on an autonomous vehicle is used as an example.
Estimation of Steady-State Optimal Filter Gain From Nonoptimal Kalman Filter Residuals
Authors: Chen Chung-Wen , Huang Jen-Kuang
Published: March 2008

This paper proposes a new algorithm to estimate the optimal steady-state Kalman filter gain of a linear, discrete-time, time-invariant stochastic system from nonoptimal Kalman filter residuals. The system matrices are known, but the covariances of the white process and measurement noises are unknown. The algorithm first derives a moving average (MA) model which relates the optimal and nonoptimal residuals. The MA model is then approximated by inverting a long autoregressive (AR) model. From the MA parameters the Kalman filter gain is calculated. The estimated gain in general is suboptimal due to the approximations involved in the method and a finite number of data. However, the numerical example shows that the estimated gain could be near optimal.
A Digital Segmented Repetitive Control Algorithm
Authors: Hu Jwusheng , Tomizuka Masayoshi
Published: March 2008

This paper presents the structure and analysis of the segmented discrete-time repetitive controller. The repetitive controller is designed to reject periodic disturbance and/or track periodic reference signal with known period. Resulted from the Internal Model Principle, the repetitive control law is applied to the entire control path. However, when crucial segments within a control path are of concern, the segmented repetitive control law, which applies control actions only to those segments, can be utilized to save the memory space. It is shown that such a segmented repetitive control system is stable if the original nonsegmented one is stable.
A Global Approach to Vehicle Control: Coordination of Four Wheel Steering and Wheel Torques
Authors: Yu Ssu-Hsin , Moskwa John J.
Published: March 2008

Currently, advanced control systems implemented on production ground vehicles have the goal of promoting maneuverability and stability. With proper coordination of steering and braking action, these goals may be achieved even when road conditions are severe. This paper considers the effect of steering and wheel torques on the dynamics of vehicular systems. Through the input-output linearization technique, the advantages of four-wheel steering (4WS) system and independent torques control are clear from a mathematical point of view. A sliding mode controller is also designed to modify driver’s steering and braking commands to enhance maneuverability and safety. Simulation results show the maneuverability and safety are improved. Although the controller design is based on a four-wheel steering vehicle, the algorithm can also be applied to vehicles of different configurations with slight changes.
Robust Observer-Based Control of Large Flexible Structures
Authors: Lin Chun-Liang , Chen Bor-Sen
Published: March 2008

This paper considers robust stabilization of the spillover phenomenon of large flexible structures. New frequency domain robustness measures for a large flexible structure system controlled by an observer-based compensator is derived via a state-space framework. In the present approach, control and observation spillover are viewed as parametric perturbations, and the total spillover (combination of control and observation spillover) is treated as the unmodeled dynamics. A robust observer-based output feedback control law, obtained by solving two algebraic Riccati equations, is provided. Finally, a simply supported beam example is included to illustrate the application.
Perfect Parallel Parking Via Pontryagin’s Principle
Authors: Patten William Neff , Wu Hsien-Cheng , Cai Wei
Published: March 2008

Parallel parking of an automobile can be a frustrating exercise for the driver. A simple, on vehicle control augmentation design for parallel parking is described in the paper. Using a steering control model, parking is cast as an optimal control problem. The minimization of a path length objective function, which was constrained by the bounds on the steering control angle, provided the setting for the problem definition. Pontryagin’s maximum principal was employed to discover a family of optimal trajectories that guaranteed perfect parallel parking. A bang-bang controller logic was shown to result. The design was experimentally tested using a light duty truck outfitted with a drive-by-wire capability.
The Emergence of Multiple Equilibria in Electromechanical Systems
Authors: Hemati Neyram
Published: March 2008

The dynamic characteristics of brushless dc machines are considered. It is demonstrated that due to the inherent nonlinear dynamics of these systems, multiple steady-state solutions can exist. The presence of multiple equilibrium solutions is in turn used to provide an explanation for the loss of stability associated with a locally stable operating state. Numerical simulations are used to help verify the presence of multiple equilibria and their effect on the stability of the systems under investigation. Finally, an example is presented which demonstrates that the presence of multiple equilibria can lead to chaotic behavior in bldcm systems with variable reluctance.
Simulation and Field Testing of Tracked Vehicle Suspension Dynamics
Authors: Sankar S. , Dhir A. , Shankhla V. S.
Published: March 2008

A nonlinear, in-plane ride dynamic simulation model of a typical off-road tracked vehicle is developed assuming constant forward vehicle speed and nondeformable terrain surface. The ride model includes nonlinear suspension characteristics, wheel/track-terrain interactions, and dynamic track loads. An equivalent damper and continuous radial spring formulation is employed to model wheel/track-terrain interactions, whereas dynamic track loads are modeled in view of track belt stretching and initial track tension. Typical simulation results are presented for a conventional armoured personnel carrier traversing discrete half round obstacles, and a random course, and are validated against field measurements. The predicted ride responses exhibit generally good agreement with field test data.
Estimation of Dynamic Fuel Parameters in Automotive Engines
Authors: Moskwa J. J.
Published: March 2008

Many automotive engine models exist for the development of control algorithms. These models should include the important lags and delays which can affect the response of the overall controlled system. One of the most important, and most difficult parts of the engine to estimate is the fuel delivery model, from when the demand for fuel is calculated to intake valve closing. This paper describes procedures for estimating the parameters of a fuel delivery model, and provides experimental results using these techniques.
A Frequency Domain Analysis of Learning Control
Authors: Goh C. J.
Published: March 2008

The convergence of learning control is traditionally analyzed in the time domain. This is because a finite planning horizon is often assumed and the analysis in time domain can be extended to time-varying and nonlinear systems. For linear time-invariant (LTI) systems with infinite planning horizon, however, we show that simple frequency domain techniques can be used to quickly derive several interesting results not amenable to time-domain analysis, such as predicting the rate of convergence or the design of optimum learning control law. We explain a paradox arising from applying the finite time convergence criterion to the infinite time learning control problem, and propose the use of current error feedback for controlling possibly unstable systems.
Application of Repetitive Control to a Peristaltic Pump
Authors: Hillerstro¨m Gunnar , Sternby Jan
Published: March 2008

The aim of this paper is to study angular velocity control of a rotating axis, a peristaltic pump where the disturbance is associated with certain angular positions. The use of constant sampling rate then implies varying disturbance period. A discrete repetitive control scheme based on a reduced order disturbance model tuned to the setpoint of the angular velocity is shown to reject the modeled disturbance with asymptotically zero error. With axis angle synchronization of sampling, the plant model is time-varying but it gives a static discrete disturbance model independent of the angular velocity. If the deviation from the nominal working point is not too large this is to prefer while it gives faster convergence.
Neural-Network Based Learning Control of Flexible Mechanism With Application to a Single-Link Flexible Arm
Authors: Takahashi Kazuhiko , Yamada Ichiro
Published: March 2008

This paper shows the effectiveness of a neural-network controller for controlling a flexible mechanism such as a flexible robot arm. An adaptive-type direct neural controller is formulated using state-space representation of the dynamics of the target system. The characteristics of the controller are experimentally investigated by using it to control the tip angular position of a single-link flexible arm.
A Self-Tuning Fuzzy Controller With Switching Control Modes
Authors: Batur C. , Kasparian V. S.
Published: March 2008

A fuzzy controller that adjusts its structure in relation to changes in system or disturbance dynamics is proposed. The controller output membership functions are tuned for optimum performance. The tuning is implemented by a control supervisor that makes its decisions depending on the reliability of the current process model. If the model is reliable, the prediction error is used to tune the controller, otherwise, the tuning is realized by a measure of past performance. To prove the feasibility of the controller, the proposed technique is applied to the speed control of a DC motor.
Model-Matching Controller Design With Input-Output Data—A Numerical Approach for Redundantly Actuated Systems
Authors: Chan Jenq-Tzong H.
Published: March 2008

A numerical technique for control system synthesis based on input-output data is presented. The method is applicable when the system is open-loop stable and redundantly actuated. The major merits of the method are as follows. First, the closed-loop system equation may be arbitrarily assigned. Second, explicit knowledge of an open-loop system model is not needed for controller synthesis. Third, the stability of the synthesized system may be verified during the synthesis process; hence, the workability of the controller is ensured.
Feedback Design of a Canonical Multivariable System With Application to Shape Control in Sendzimir Mills
Authors: Ringwood J. V. , Owens D. H. , Grimble M. J.
Published: March 2008

The shape control problem, for a Sendzimir Cold Rolling Mill, is multivariable. The plant transfer function matrix, however, has the special form: G(s) = g(s)Gm, where g(s) is a scalar transfer function and Gm a square matrix of constant gains. The control philosophy presented exploits this structure by diagonalising the system using an eigenvector/eigenvalue decomposition resulting in a scalar frequency response design problem. An important consideration in shape control systems is the robustness of the design due to the wide range of materials rolled, reflected in changes in the elements of Gm. Therefore, a development is included which represents the robustness of the design, with respect to errors in Gm, in terms of a set of strict inequalities.
Fast Pipeline Models for Simulation of Hydraulic Systems
Authors: Krus Petter , Weddfelt Kenneth , Palmberg Jan-Ove
Published: March 2008

In most cases it is justified to regard pipelines as lumped capacitances when hydraulic systems are simulated. In some cases, however, when the system is widely distributed the wave propagation effects in lines may become important and there exists very good models today to simulate these effects. The price to be paid is that of a much larger computational effort. In this paper, a numerically highly efficient model is presented which is just slightly more demanding than a model to represent a pure capacitance, yet it captures all the essential characteristics of a line, the finite wave propagation speed and the distributed frequency dependent friction. The model only calculates state variables at the ends of a line and not in any internal nodes as most models do. Despite this, the model gives good results both in the time and frequency domain which compared to more elaborate models. If for some reason internal state variables are wanted they can be obtained by representing a line with several line elements. The model is integrated in the library of the HOPSAN simulation package and has been used successfully for simulation of oil hydraulic systems as well as the human cardiovascular system.
A High Precision Synchronizing Control System for Biaxial Positioning Tables
Authors: Shahruz S. M. , Pradeep A. K.
Published: March 2008

In this paper, a control system is designed that synchronizes the motions of biaxial positioning tables. The control system consists of nonlinear feedback laws of the displacements and the velocities of the table along its axes. It is proved that in the absence of parametric uncertainty and disturbances, the designed control system generates desired contours, for instance, contours with sharp corners, such as a heart-shaped contour (cardioid), on the workpiece, with zero error in finite time. Simulation results show that the designed control system compensates for the effects of parametric uncertainty and disturbances to the system.
Robust Adaptive and Repetitive Digital Tracking Control and Application to a Hydraulic Servo for Noncircular Machining
Authors: Tsao Tsu-Chin , Tomizuka Masayoshi
Published: March 2008

This paper presents the development of robust digital tracking control algorithms and their real-time implementation on an electrohydraulic servo-actuator for tool positioning in noncircular machining. Robust adaptive feedforward controller for tracking arbitrary signals and robust repetitive controller for tracking periodic signals against disturbances and unmodeled dynamics have been developed. Experimental results are presented to illustrate the control system synthesis procedures and tracking performance.
Multi-Rate Analysis and Design of Visual Feedback Digital Servo-Control System
Authors: Nemani Mahadevamurty , Tsao Tsu-Chin , Hutchinson Seth
Published: March 2008

This paper addresses the analysis and design of digital motion control system with machine vision as a feedback measurement in the servo loop. The camera vision is modeled as a discrete time-delayed sensor. A multirate formulation is proposed based on the fact that vision update rate is slower than the digital servo-control update rate and is analyzed through the lifting technique which converts the periodic time varying multirate system to a time invariant one. Some interesting properties of this specific multirate system are found and are utilized in control system design. An l-1 norm optimal control problem is formulated to minimize the maximum time domain error, which has direct connection to camera field of view and mechanical tolerance. A numerical example is given to demonstrate the presented methods.
Dynamic Analysis of Flexible Bodies Using Extended Bond Graphs
Authors: Yen Chiaming , Masada Glenn Y.
Published: March 2008

An Extended Bond Graph (EBG) formulation is described for analyzing the dynamics of a flexible multibody system. This work extends the EBG method, which was originally developed for systems with small spatial motion, to rigid and flexible multibody systems exhibiting large overall motions. The development uses modular models for the elements so that complex system models can be derived by coupling these modules. The EBG formulation for moving reference frames is used to derive models of one-link and two-link flexible manipulator systems. This approach has several advantages over the Lagrangian and Newtonian methods, such as its ability to solve the forward and inverse dynamic problems using the same bond graph. Finally, the EBG formulations for cantilever beams and for multi-rigid body dynamic systems are shown to be special cases of the general EGBs for flexible bodies.
Implementation of Uniform Damping Control by the Block-Independent Control Method
Authors: Berg J. L. , Norris M. A.
Published: March 2008

The use of block-independent control is investigated for active damping of a flexible structure. The control gains are designed to approximate Uniform Damping Control, in which the target modal decay rates are equivalent. Modal estimation is performed using a Kalman filter. Reaction wheels are used to apply control torques and are found to possess significant dynamics in the controller frequency bandwidth. To reduce the effect of the actuator dynamics, the reaction wheels are targeted to control blocks of modes within the controller bandwidth, thereby providing approximate block-independent control. Analytical and experimental results indicate that the effect of modal coupling is small for low-to-medium authority block-independent control.
Inhibition of Hepatitis C Virus (HCV) RNA Polymerase by DNA Aptamers: Mechanism of Inhibition of In Vitro RNA Synthesis and Effect on HCV-Infected Cells
Authors: Bellecave Pantxika , Cazenave Christian , Rumi Julie , Staedel Cathy , Cosnefroy Ophélie , Andreola Marie-Line , Ventura Michel , Tarrago-Litvak Laura , Astier-Gin Thérèse
Published: March 2008

We describe here the further characterization of two DNA aptamers that specifically bind to hepatitis C virus (HCV) RNA polymerase (NS5B) and inhibit its polymerase activity in vitro. Although they were obtained from the same selection procedure and contain an 11-nucleotide consensus sequence, our results indicate that aptamers 27v and 127v use different mechanisms to inhibit HCV polymerase. While aptamer 27v was able to compete with the RNA template for binding to the enzyme and blocked both the initiation and the elongation of RNA synthesis, aptamer 127v competed poorly and exclusively inhibited initiation and postinitiation events. These results illustrate the power of the selective evolution of ligands by exponential enrichment in vitro selection procedure approach to select specific short DNA aptamers able to inhibit HCV NS5B by different mechanisms. We also determined that, in addition to an in vitro inhibitory effect on RNA synthesis, aptamer 27v was able to interfere with the multiplication of HCV JFH1 in Huh7 cells. The efficient cellular entry of these short DNAs and the inhibitory effect observed on human cells infected with HCV indicate that aptamers are useful tools for the study of HCV RNA synthesis, and their use should become a very attractive and alternative approach to therapy for HCV infection.
Multiclonal Outbreak of
Klebsiella pneumoniae
Producing Extended-Spectrum β-Lactamase CTX-M-2 and Novel Variant CTX-M-59 in a Neonatal Intensive Care Unit in Brazil
Authors: de Oliveira Garcia Doroti , Doi Yohei , Szabo Dora , Adams-Haduch Jennifer M. , Vaz Tânia M. I. , Leite Daniela , Padoveze Maria Clara , Freire Maristela P. , Silveira Fernanda P. , Paterson David L.
Published: March 2008

An outbreak of cephalosporin-resistant
Klebsiella pneumoniae
occurred in a neonatal intensive care unit in São Paulo, Brazil. Of the 10 pulsotypes identified during the outbreak and follow-up periods, nine produced CTX-M-2 or its new variant CTX-M-59 and one produced SHV-5.
bla
CTX-M-2
/
59
genes were located on closely related plasmids that were transferable.
Trypanosoma cruziInduces Regulatory Dendritic Cells In Vitro
Authors: Poncini Carolina Verónica , Soto Catalina Dirney Alba , Batalla Estela , Solana Maria Elisa , González Cappa Stella Maris
Published: March 2008

A main feature of acute infection withTrypanosoma cruziis the presence of immunological disorders. A previous study demonstrated that acute infection with the virulent RA strain downregulates the expression of major histocompatibility complex class II (MHC-II) on antigen-presenting cells and impairs the T-cell stimulatory capacity of splenic dendritic cells (DC). In the present work, we assessed the ability of trypomastigotes (Tp) to modulate the differentiation stage and functionality of bone marrow-derived DC in vitro. We observed that the Tp stage ofT. cruzifailed to activate DC, which preserved their low expression of MHC-II and costimulatory molecules, as well as their endocytic activity. We also show that Tp induced transforming growth factor β (TGF-β) secretion by DC and enhanced the gap between interleukin-10 (IL-10) and IL-12p70 production, showing a higher IL-10/IL-12p70 ratio upon lipopolysaccharide (LPS) treatment. In addition, we observed that Tp prevented DC full activation induced by LPS, thereby downregulating their MHC-II surface expression and inhibiting their capacity to stimulate lymphocyte proliferation. In vitro IL-10 neutralization during the differentiation process of DC with Tp+LPS showed a reversion of their inhibitory effect during mixed lymphocyte reaction. In contrast, only simultaneous neutralization of IL-10 and TGF-β, after DC differentiation, was involved in the partial restitution of lymphocyte proliferation. Since both TGF-β and IL-10 are immunosuppressive cytokines essential in the modulation of the immune response and important in the induction of tolerance, our results suggest for the first time that Tp are responsible for the generation of regulatory DC in vitro.
A Cluster of Four Surface Antigen Genes Specifically Expressed in Bradyzoites,SAG2CDXY, Plays an Important Role inToxoplasma gondiiPersistence
Authors: Saeij Jeroen P. J. , Arrizabalaga Gustavo , Boothroyd John C.
Published: March 2008

Toxoplasma gondiiis one of the most successful protozoan parasites of warm-blooded animals. Stage-specific expression of its surface molecules is thought to be key to its ability to establish chronic infection in immunocompetent animals. The rapidly dividing tachyzoite stage displays a different subset of family of surface antigen 1 (SAG1)-related sequences (SRSs) from that displayed by the encysted bradyzoite stage. It is possible that this switch is necessary to protect the bradyzoites against an immune response raised against the tachyzoite stage. Alternatively, it might be that bradyzoite SRSs evolved to facilitate invasion of different cell types, such as those found in the brain, where cysts develop, or the small intestine, where bradyzoites must enter after oral infection. Here we studied the function of a cluster of four tandem genes, encoding bradyzoite SRSs called SAG2C, -D, -X, and -Y. Using bioluminescence imaging of mice infected with parasites expressing firefly luciferase (FLUC) driven by theSAG2Dpromoter, we show stage conversion for the first time in living animals. A truncated version of theSAG2Dpromoter (SAG2Dmin) gave efficient expression of FLUC in both tachyzoites and bradyzoites, indicating that the bradyzoite specificity of the completeSAG2Dpromoter is likely due to an element(s) that normally suppresses expression in tachyzoites. Comparing mice infected with the wild type or a mutant where theSAG2CDXYcluster of genes has been deleted (ΔSAG2CDXY), we demonstrate that whereas ΔSAG2CDXYparasites are less capable of maintaining a chronic infection in the brain, they do not show a defect in oral infectivity.
Heterogeneity in the Polarity of Nra Regulatory Effects on Streptococcal Pilus Gene Transcription and Virulence
Authors: Luo Feng , Lizano Sergio , Bessen Debra E.
Published: March 2008

Transcription of several key virulence factors of
Streptococcus pyogenes
is under the control of Mga and Nra/RofA. In an M serotype 49 (M49) strain, Nra is a negative regulator of pilus gene transcription; also, Nra represses
mga
expression, leading to downregulation of the M protein surface fibril and secreted cysteine protease SpeB. In this report, the role of Nra in the virulence of an M53 classical skin strain was investigated. In contrast to the case for the M49 strain, Nra functions as a positive regulator of pilus gene transcription in the M53 strain, and inactivation of
nra
leads to loss of virulence in a humanized mouse model of superficial skin infection. Furthermore, Nra has no measurable effect on
mga
transcription in the M53 strain; this finding is further supported by a lack of detectable Nra effects on M protein- and SpeB-dependent phenotypes. Whereas MsmR is reported to activate
nra
and pilus gene transcription in the M49 strain, in the M53 strain it acts as a repressor of these genes. In both strains, MsmR and Nra form a feed-forward loop network motif for pilus gene transcription, but their effects have opposite signs. The findings demonstrate key strain-specific differences in the transcriptional circuitry governing virulence gene expression in
S. pyogenes
and its impact on pathogenesis.
Vibrio parahaemolyticusInhibition of Rho Family GTPase Activation Requires a Functional Chromosome I Type III Secretion System
Authors: Casselli Timothy , Lynch Tarah , Southward Carolyn M. , Jones Bryan W. , DeVinney Rebekah
Published: March 2008

Vibrio parahaemolyticusis a leading cause of seafood-borne gastroenteritis; however, its virulence mechanisms are not well understood. The identification of type III secreted proteins has provided candidate virulence factors whose functions are still being elucidated. Genotypic strain variability contributes a level of complexity to understanding the role of different virulence factors. The ability ofV. parahaemolyticusto inhibit Rho family GTPases and cause cytoskeletal disruption was examined with HeLa cells. After HeLa cells were infected, intracellular Rho activation was inhibited in response to external stimuli. In vitro activation of Rho, Rac, and Cdc42 isolated from infected HeLa cell lysates was also inhibited, indicating that the bacteria were specifically targeting GTPase activation. The inhibition of Rho family GTPase activation was retained for clinical and environmental isolates ofV. parahaemolyticusand was dependent on a functional chromosome I type III secretion system (CI-T3SS). GTPase inhibition was independent of hemolytic toxin genotype and the chromasome II (CII)-T3SS. Rho inhibition was accompanied by a shift in the total actin pool to its monomeric form. These phenotypes were abrogated in a mutant strain lacking the CI-T3S effector Vp1686, suggesting that the inhibiting actin polymerization may be a downstream effect of Vp1686-dependent GTPase inhibition. Although Vp1686 has been previously characterized as a potential virulence factor in macrophages, our findings reveal an effect on cultured HeLa cells. The ability to inhibit Rho family GTPases independently of the CII-T3SS and the hemolytic toxins may provide insight into the mechanisms of virulence used by strains lacking these virulence factors.
Both CD4
+
and CD8
+
T Cells Respond to Antigens Fused to Anthrax Lethal Toxin
Authors: Shaw Christine A. , Starnbach Michael N.
Published: March 2008

The lethal toxin produced by
Bacillus anthracis
is a bipartite toxin in which the first protein, protective antigen (PA), transports the second protein, lethal factor, across the host cell membrane. We have previously shown that CD8
+
T-cell epitopes fused to a nontoxic derivative of lethal factor (LFn) are delivered into the host cell cytosol in a PA-dependent manner. Delivery of these antigens targets them to the intracellular major histocompatibility complex (MHC) class I processing and presentation pathway and leads to the stimulation of antigen-specific CD8
+
T cells in vivo. In this report, we describe the generation and characterization of LFn fusion proteins that include not only a CD8
+
T-cell epitope but also a CD4
+
T-cell epitope. We first show that these fusion proteins induce antigen-specific CD4
+
T-cell responses following incubation with dendritic cells in vitro or injection into mice. Stimulation of CD4
+
T cells by LFn fusion proteins does not require PA but is enhanced by PA in vitro. We also show that a single LFn fusion protein and PA can deliver antigen to both the MHC class II and the MHC class I pathways, resulting in the simultaneous induction of antigen-specific CD4
+
T cells and antigen-specific CD8
+
T cells in the same mouse. These results suggest that this toxin delivery system is capable of stimulating protective immune responses where effective immunization requires stimulation of both classes of T cells.
Facteurs dont il faut tenir compte dans la création d’un guide d’activité physique pour les Canadiens qui ont un handicap physiqueCet article est tiré d’un supplément intituléAdvancing physical activity measurement and guidelines in Canada: a scientific review and evidence-based foundation for the future of Canadian physical activity guidelines(Favoriser les lignes directrices et la mesure de l’activité physique au Canada: examen scientifique et justification selon les données probantes pour l’avenir des lignes directrices de l’activité physique canadienne) publié parPhysiologie appliquée, nutrition et métabolismeet laRevue canadienne de santé publique. On peut aussi mentionner Appl. Physiol. Nutr. Metab. 32 (Suppl. 2F) ou Can. J. Public Health 98 (Suppl. 2).
Authors: Martin Ginis Kathleen A. , Hicks Audrey L.
Published: March 2008

This paper provides a brief overview of the epidemiological data regarding Canadians with physical disabilities, with a particular emphasis on health status. A literature review is then presented, focusing on activity levels and the physiological and health-related quality of life benefits of activity for people with four different physical disabilities (arthritis, fibromyalgia, spinal cord injury, and multiple sclerosis). The unique physical activity barriers faced by people with physical disabilities are discussed. The paper concludes with recommendations for the development of a physical activity guide for Canadians with physical disabilities.
L’activité physique chez les Autochtones au CanadaCet article est tiré d’un supplément intituléAdvancing physical activity measurement and guidelines in Canada: a scientific review and evidence-based foundation for the future of Canadian physical activity guidelines(Favoriser les lignes directrices et la mesure de l’activité physique au Canada: examen scientifique et justification selon les données probantes pour l’avenir des lignes directrices de l’activité physique canadienne) publié parPhysiologie appliquée, nutrition et métabolismeet laRevue canadienne de santé publique. On peut aussi mentionner Appl. Physiol. Nutr. Metab. 32 (Suppl. 2F) ou Can. J. Public Health 98 (Suppl. 2).
Authors: Young T. Kue , Katzmarzyk Peter T.
Published: March 2008

Cet article présente un bilan des pratiques de l’activité physique, des facteurs et des conséquences de même que des effets de plusieurs interventions menées pour accroître la pratique de l’activité physique chez les Aborigènes du Canada et des États-Unis. Peu d’études nationales ont été menées à propos de la pratique de l’activité physique chez les peuples aborigènes. Les données les plus récentes proviennent de l’Enquête régionale longitudinale sur la santé des Premières Nations (2002–2003) : 21 % des adultes (hommes, 27 %, femmes, 15 %) font en une journée au moins 30 min d’activité physique d’intensité modérée à vigoureuse, et ce, 4 jours ou plus par semaine. Cet article indique les défis particuliers auxquels les Aborigènes sont confrontés et souligne le besoin pour cette population de s’approprier le savoir collectif à propos de la quantité d’activité physique à pratiquer et des modalités à suivre pour la promotion et le maintien de la santé. En ce moment, des individus travaillent à adapter le guide d’activité physique aux Premières Nations, aux Inuits et aux Métis. Les prochaines études devraient porter sur les niveaux, minimal et optimal, de pratique de l’activité physique chez ces populations afin qu’elles en retirent les bienfaits au plan de la santé.
Le mouvement secondaire, l’activité intégrée aux habitudes de vie et le sommeil : les nouvelles frontières de l’évaluation de l’activité physiqueCet article est tiré d’un supplément intitulé Advancing physical activity measurement and guidelines in Canada: a scientific review and evidence-based foundation for the future of Canadian physical activity guidelines (Favoriser les lignes directrices et la mesure de l’activité physique au Canada: examen scientifique et justification selon les données probantes pour l’avenir des lignes directrices de l’activité physique canadienne) publié par Physiologie appliquée, nutrition et métabolisme et la Revue canadienne de santé publique. On peut aussi mentionner Appl. Physiol. Nutr. Metab. 32 (Suppl. 2F) ou Can. J. Public Health 98 (Suppl. 2).
Authors: Tremblay Mark S. , Esliger Dale W. , Tremblay Angelo , Colley Rachel
Published: March 2008

Les messages de santé publique en matière d’activité physique au Canada ont mis traditionnellement l’accent sur la prescription d’exercices physiques utiles, principalement pratiqués durant les périodes de loisir (LTPA). Même si les LTPA contribuent à la dépense énergétique totale (TEE), une grande partie des activités faites durant la journée sont négligées à moins de porter une attention à l’énergie dépensée en plus des activités utiles. Cet article analyse l’impact des activités physiques dites accessoires (ne constituant pas de l’exercice physique en soi ou n’étant pas utiles) et des activités physiques intégrées dans le mode de vie (les tâches journalières et la marche concomitante) sur la TEE et les indicateurs de santé. Comme les mouvements accessoires s’accomplissent de façon intermittente dans le quotidien, cette forme de dépense d’énergie devrait diminuer face à la généralisation de la mécanisation et de l’automatisation des tâches. Cet article analyse aussi la relation entre l’inactivité physique, y compris le sommeil, et l’activité physique, la TEE et les répercussions sur la santé. On y trouve également des propositions visant à la prescription d’activité physique plus détaillée incluant toutes les composantes de la TEE. Le monitorage objectif des activités physiques selon les périodes de la journée constitue le meilleur moyen d’évaluer et d’analyser les mouvements humains durant toute la journée.
DIELECTRIC BEHAVIOR OF NOVEL ACETYLENE BLACK–PVDF/BaTiO3TRI-PHASE COMPOSITE FILM
Authors: CHEN QIAN , JIN LU , WENG WENJIAN , HAN GAORONG , DU PIYI
Published: March 2008

A novel three-phase film with conductive acetylene black (AB) and ferroelectric phase ( BaTiO3) introduced intoβ-polyvinylidene fluoride (β-PVDF) was prepared by using dip-coating method. The high dielectric constant of 650 can be obtained in the AB–PVDF/ BaTiO3composite film when AB content approached the percolation threshold (3.3 vol%), which is 40 times more than that of (PVDF + BaTiO3) matrix. The dielectric constant of the composite film is almost independent of frequency.
ENHANCEMENT OF GIANT MAGENTO-IMPEDANCE EFFECT USING LC RESONANCE
Authors: WU Z. M. , ZHAO Z. J. , LIU L. P. , LIN H. , CHENG J. K. , YANG J. X. , YANG X. L.
Published: March 2008

In this study, resonance enhancement of giant magneto-impedance (GMI) effect in Fe -based Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 glass-coated microwires was investigated. A new method was adopted by sputtering a copper layer in the outside of the Fe -based glass-coated wire. A capacitance forms between the ferromagnetic core and outer copper layer, where the glass insulator works as a dielectric layer. Therefore, the composite wire forms an LC resonance circuit (which consists of an inductor, represented by the letter L, and a capacitor, presented by the letter C) itself, resulting in an increase of GMI ratio from 250% to 330%. Meanwhile, the influence of resonance frequency on the GMI effect was discussed.
BIOMIMETIC DEPOSITION OF APATITE ON SURFACE CHEMICALLY MODIFIED POROUS NiTi SHAPEMEMORY ALLOY
Authors: WU S. L. , LIU X. M. , CHUNG C. Y. , CHU PAUL K. , CHAN Y. L. , YEUNG K. W. K. , CHU C. L.
Published: March 2008

Porous NiTi shape memory alloy (SMA) with 48% porosity and an average pore size of 50–800 μm was synthesized by capsule-free hot isostatic pressing (CF-HIP). To enhance the surface bioactivity, the porous NiTi SMA was subjected to H 2 O 2 and subsequent NaOH treatment. Scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analyses revealed that a porous sodium titanate ( Na 2 TiO 3) film had formed on the surface of the porous NiTi SMA. An apatite layer was deposited on this film after immersion in simulated body fluid at 37°C, while no apatite could be found on the surface of the untreated porous NiTi SMA. The formation of the apatite layer infers that the bioactivity of the porous NiTi SMA may be enhanced by surface chemical treatment, which is favorable for its application as bone implants.
LASER DICING OF SILICON WAFER
Authors: TANG Y. , FUH J. Y. H. , LOH H. T. , WONG Y. S. , LIM Y. K.
Published: March 2008

The effect of various laser processing parameters on the kerf width and cut quality of Si wafer as well as encapsulated Si wafer is investigated. The parameters are then optimized to minimize the heat affect zone and obtain the best possible cut quality. It has been found that oxygen is the most suitable assist gas for laser dicing and that the highest gas pressure may not produce the best cut quality. The effect of laser repetition rate, pump energy, feed rate, and number of passes are also studied. Under optimized parameters, the cut quality of Si wafer using laser dicing is found to be comparable to diamond saw dicing.