bluuebunny/crossref_metadata_2025 huggingface dataset:
Discrete Time Noncollocated Control of Flexible Mechanical Systems Using Time Delay
Authors: Kang M. S. , Yang B.
Published: March 2008

This paper studies discrete time noncollocated control of flexible mechanical systems. A sampled data system with one sensor and one actuator is formulated. Specific time delay is introduced in the feedback loop to eliminate the destabilizing effect of noncollocation of the sensor and actuator. A stability criterion that explicitly relates the closed-loop stability to the sampling frequency, time delay, and sensor and actuator locations, is derived. Based on the criterion, particular noncollocated controllers are designed for a simply supported beam. A sensitivity analysis yields a robust control condition in terms of the sampling frequency, system parameter uncertainties, and inherent delays. In addition, the relationship between frequency folding in data sampling and spill-over instability is discussed.
Efficient Dynamic Simulation of Multiple Chain Robotic Mechanisms
Authors: Lilly K. W. , Orin D. E.
Published: March 2008

An efficient O(mN) algorithm for the dynamic simulation of simple closed-chain robotic mechanisms is presented in this paper, where m is the number of chains, and N is the number of links for each chain. A wide range of contact conditions between each of the chains and the support surface or common body, load, or object may be simulated so that the algorithm is applicable to multilegged vehicles, multiple manipulators, and dexterous hands. The algorithm is based on the computation of the operational space inertia matrix (6 × 6) for each chain as seen by the common body, load, or object. Computation of the open-chain dynamics for each chain is also required, and the most efficient algorithm known is used for this purpose. The total computation required is tabulated in terms of the number of scalar operations needed. Efficient spatial transformations form the basis for these computations. Parallel implementation of the dynamics calculations for each chain and the common body results in an O(N) + O(log2m) algorithm.
Predictive Controller and Estimator for NASA Deep Space Network Antennas
Authors: Gawronski W.
Published: March 2008

This paper presents a modified output prediction procedure, and a new controller design based on the predictive control law. Also, a predictive estimator is developed for implementing the controller. The predictive controller was designed and simulated for tracking control of the NASA Deep Space Network 70-m antenna. Simulation results show significant improvement in tracking performance compared to the linear quadratic controller and estimator presently in use.
An Application of Extended Kalman Filtering to Heat Exchanger Models
Authors: Jonsson G. , Palsson O. P.
Published: March 2008

This paper shows how an extended Kalman filter can be applied to the parameter estimation in continuous time heat exchanger models. The model is based on lumping of the heat exchanger. It is on state space form where the temperature in each section is a model state. By letting the model parameters be functions of the massflows and the temperatures one obtains a model that is capable of accurately describing the dynamics of the heat exchanger for all relevant working conditions. Since the parameters are functions of temperature, the model is nonlinear in the states and an extended Kalman filter is applied to the state estimation. Empirical relations of the heat transfer coefficients are incorporated in the model parameters in order to cope with the massflow and temperature dependence. Some of the parameters in the empirical relations are also estimated, thereby adjusting the formulas to the specific heat exchanger.
Laser Surface Height and Orientation Measurement System
Authors: Lin Psang Dain , Chen Yu Lung
Published: March 2008

This paper describes a new optical measurement system that measures the surface height and orientation changes. Homogeneous transformation matrices are used to derive the sensor reading equations. In order to investigate the system’s accuracy, each sensor reading is broken down into two parts. One part concentrates on ideal configuration, while the other examines system errors. A calibration method is provided so that the effects of the latter can be eliminated. The implementation of an actual measurement system is presented and the results show that the performance of this measurement system is excellent.
The Suction Dynamics of Positive Displacement Axial Piston Pumps
Authors: Harris R. M. , Edge K. A. , Tilley D. G.
Published: March 2008

The suction dynamics of axial piston pumps become more critical if the pump is to be used at high speeds. In order to prevent air-release and cavitation from occurring within the pump it is necessary to pressurise the pump inlet. As the speed of a pump is increased, higher boost pressures are required, due to the extra losses incurred through the suction line and portplate at the higher flowrates. However, the lack of data regarding axial piston pump behavior at high speeds creates problems for the system designer in selecting suitable boost conditions and for the pump designer in selecting the portplate configuration that is required to reduce fluid-borne-noise levels. This paper discusses the suction performance of piston pumps, and presents experimental and simulation results exploring the behavior of a high-speed axial-piston pump. Different air-release and cavitation models that are suitable for simulation studies are investigated.
A Geometric Representation of Root Sensitivity
Authors: Kurfess T. R. , Nagurka M. L.
Published: March 2008

In this paper, we present a geometric method for representing the classical root sensitivity function of linear time-invariant dynamic systems. The method employs specialized eigenvalue plots that expand the information presented in the root locus plot in a manner that permits determination by inspection of both the real and imaginary components of the root sensitivity function. We observe relationships between root sensitivity and eigenvalue geometry that do not appear to be reported in the literature and hold important implications for control system design and analysis.
Force and Motion Control of a Constrained Flexible Robot Arm
Authors: Hu F. L. , Ulsoy A. G.
Published: March 2008

The results of a study on the combined joint motion control, vibration control, and force control of a constrained rigid-flexible robot arm for both regulation and tracking are presented. A nonlinear modified Corless-Leitmann controller is proposed for control of the flexible motion using only joint actuators. Experimental studies, which demonstrate the effectiveness of the proposed method, are described.
An Algorithm for the Generation of an Optimum CMM Inspection Path
Authors: Lu E. , Ni J. , Wu S. M.
Published: March 2008

An algorithm for generating an optimum CMM inspection path is developed to improve the throughput of CMMs. In this algorithm, a modified 3-D ray tracing technique is applied to an octree database of a CMM configuration space to detect obstacles between any two target points. After an obstacle is detected, collision-free silhouette contour vertices of the object are generated, from a selection criterion, as potential points of a vertex path. As the ray advances, a sequential-decision-making technique is used to derive the suboptimum vertex path from possible collision-free vertex paths. After the suboptimum vertex path is generated, a selection strategy is employed to ensure a correct edge path sequence for deriving an optimum edge point path. A 3-D simulation shows that the proposed global algorithm eliminates the dynamically undesirable characteristics of octree based algorithms and saves searching time in congested work spaces by finding paths around colliding objects. Actual measurement of a test part indicates that the proposed method can reduce the inspection time to less than half as compared to the interactive graphic method.
Dynamic Modeling and Adaptive Control of the Gas Metal Arc Welding Process
Authors: Song Jae-Bok , Hardt David E.
Published: March 2008

Control of the welding process is a very important step in welding automation. Since the welding process is complex and highly nonlinear, it is very difficult to accurately model the process for real-time control. In this research, a discrete-time transfer function matrix model for gas metal arc welding process is proposed. This empirical model takes the common dynamics for each output and inherent process and measurement delays into account. Although this linearized model is valid only around the operating point of interest, the adaptation mechanism employed in the control system render this model useful over a wide operating range. Since welding is inherently a nonlinear and multi-input, multi-output process, a multivariable adaptive control system is used for high performance. The process outputs considered are weld bead width and depth, and the process inputs are chosen as the travel speed of the torch and the heat input. A one-step-ahead (or deadbeat) adaptive control algorithm combined with a recursive least-squares methods for on-line parameter estimation is implemented in order to achieve the desired weld bead geometries. Control weighting factors are used to maintain the stability and reduce excessive control effort. Some guidelines for the control design are also suggested. Command following and disturbance rejection properties of the adaptive control system for both SISO and MIMO cases are investigated by simulation and experiment. Although a truly independent control of the outputs is difficult to implement because of a strong output coupling inherent in the process, a control system for simultaneous control of bead width and depth was successfully implemented.
Dynamic Modeling of Gas Springs
Authors: Kornhauser A. A.
Published: March 2008

Linear dynamic modeling of gas springs is important for basic design of free piston Stirling engines. The conventional gas spring model, a dashpot in parallel with an ideal spring, gives poor prediction of gas spring performance. The anelastic model presented here consists of two parallel springs, one of which is in series with a dashpot. With proper selection of spring and damping constants, it gives improved prediction of gas spring dynamics.
Damage-Mitigating Control of Mechanical Systems: Part II—Formulation of an Optimal Policy and Simulation
Authors: Ray Asok , Wu Min-Kuang , Carpino Marc , Lorenzo Carl F.
Published: March 2008

The objective of damage-mitigating control introduced in the first part of this two-part paper is to achieve high performance without overstraining the mechanical structures. The major benefit is an increase in the functional life of critical plant components along with enhanced safety, operational reliability, and availability. Specifically, a methodology for modeling fatigue damage has been developed as an augmentation to control and diagnostics of complex dynamic processes such as advanced aircraft, spacecraft, and power plants. In this paper which is the second part, an optimal control policy is formulated via nonlinear programming under specified constraints of the damage rate and accumulated damage. The results of simulation experiments for upthrust transient operations of a reusable rocket engine are presented to demonstrate efficacy of the damage-mitigating control concept.
Robust Adaptive Controllers for Interconnected Mechanical Systems: Influence of Types of Interconnections on Time-Invariant and Time-Varying Systems
Authors: Singh Sunil K. , Shi Lin
Published: March 2008

We investigate robust adaptive controller designs for interconnected systems when no exact knowledge about the structure of the nonlinear interconnections between various subsystems is available. In this study, we concentrate on several different types of systems. We deal with both linear time-invariant (LTI) and linear time-varying (LTV) systems with nonlinear interconnections. For LTI systems, we examine the following types of interconnections: • interconnections that are bounded by first order polynomials in state space; • slowly time varying interconnections; • interconnections bounded by higher-order polynomials in state-space together with input channel interconnections. For LTV systems we deal with interconnections bounded by first-order polynomials in state space. We show that the nature of the nonlinear interactions influences the adaptation laws. We use the direct method of Lyapunov for the design of adaptive controllers for tracking in such systems. We investigate issues such as stability, transient performance and steady-state errors, and derive quantitative estimates and analytical bounds for various different adaptive controllers. For time-varying systems, we analyze the effect of the time variations of parameters and interactions and propose a modified adaptive control scheme with better performance. Simulation results are presented to validate our conclusions. We also investigate these results experimentally on a two-link robot manipulator. Experimental results validate theoretical conclusions and demonstrate the usefulness of such robust adaptive controllers for high-speed motions in uncertain systems.
Electro-Rheological Fluids: A Systematic Approach to Classifying Modes of Operation
Authors: Stanway R. , Sproston J. L.
Published: March 2008

In this paper, the authors describe a systematic procedure for classifying the modes of operation of ER fluids. The classification is achieved by treating an ER device as a generalized modulator and examining the different variables which can be assigned to the input, output, and control ports. This leads to a matrix, each of whose blocks corresponds to a mode of operation. It is shown how examination of these blocks leads to classification of existing applications and a systematic means of broadening.
Optimal Nonlinear Estimation of Linear Stochastic Systems
Authors: Hopkins M. A. , VanLandingham H. F.
Published: March 2008

This paper presents a new nonlinear method of simultaneous parameter and state estimation called pseudo-linear identification (PLID), for stochastic linear time-invariant discrete-time systems. No assumptions are required about pole or zero locations; nor about relative degree, except that the system transfer function must be strictly proper. Under standard gaussian assumptions, for completely controllable and observable systems, it is proved that PLID is the minimum mean-square-error estimator of the states and model parameters, conditioned on the input and output measurements. It is also proved, given persistent excitation, that the parameter estimates converge a.e. to the true parameter values. All results have been extended to the multiple-input, multiple-output case, but the single-input, single-output case is presented here to simplify notation.
A New Look at PID-Controller Tuning
Authors: Pessen David W.
Published: March 2008

The well-known Ziegler-Nichols method for tuning controllers has been used for 50 years. Since it is still popular, the time is ripe for a reappraisal. It is shown that the Ziegler-Nichols settings for PID-controllers have been misapplied by being used indiscriminately with different PID-controller configurations. Computer simulation made on 15 representative processes indicates how these settings should be modified to obtain good response for load step changes. The results are presented in three different forms, for different controller configurations.
Controlling Chaos: The Example of an Impact Oscillator
Authors: Kalagnanam Jayant R.
Published: March 2008

The OGY algorithm (Ott et al., 1990) allows the conversion of a chaotic attractor to any one of a large number of periodic orbits by making small time-dependent perturbations of an available system parameter. We have applied this method to impact oscillators and stabilized its chaotic attractor on period-1 and period-2 orbits using small time-dependent pertubations of the driving frequency. We also demonstrate the ability to switch the chaotic system between the period-1 and period-2 orbits at will by controlled time-dependent perturbations. However, before the system settles on the stabilized orbit, it exhibits a long chaotic transient. We demonstrate how the exponential sensitivity of a chaotic system to small perturbations can be exploited to control the duration of this chaotic transient.
Optimal Feed-Forward Digital Tracking Controller Design
Authors: Tsao Tsu-Chin
Published: March 2008

This paper presents an approach for optimal digital feed-forward tracking controller design. The tracking problem is formulated as a model matching problem, in which the distance between a specified tracking reference model and the achievable tracking performance by feedforward compensation is minimized. Desired input/output characteristics, finite length preview action, tracking of specific classes of constrained signals, time domain reference signal velocity or acceleration bound, and frequency domain weighting are conveniently incorporated in the proposed controller design and their roles in tracking performance are discussed. The tracking error bound is also explicitly expressed in terms of the controller design parameters. An l1 norm optimal tracking controller is proposed as a solution to the mechanical tolerance control problem. A motion control example illustrates the design approach and several aspects of the resulting optimal feedforward controller, including the optimality of the zero phase error tracking controller.
Design of Controller for Linear Mechanical Descriptor Systems
Authors: Yu Tie-Jun , Mu¨ller P. C.
Published: March 2008

Mechanical descriptor systems, i.e., constrained mechanical systems, have many applications in practice. This paper studies the control of mechanical descriptor systems. First, a class of the state feedback controllers assigning the finite poles of mechanical descriptor systems at any desired locations is presented. Second, based on the degrees of freedom of pole-assignment controller, an optimization method for designing the controller that assigns the finite poles of closed-loop mechanical descriptor system and simultaneously minimizes a quadratic performance index is proposed. The necessary condition for the pole-assignment controller to be optimal is derived and the corresponding algorithms are discussed. An example is given to illustrate the validity of method in this paper.
Frequency Domain Design for Maximizing the Allowable Size of a Step Disturbance in Linear Uncertain Systems
Authors: Jayasuriya Suhada , Sobhani Massoud
Published: March 2008

A design methodology is developed for a linear, uncertain, SISO system for maximizing the size of a step disturbance in the presence of hard time domain constraints on system states, control input, output and the bandwidth. It is assumed that the system dynamics can be represented by a combination of structured uncertainty in the low frequencies and unstructured uncertainty in the high frequencies. The design procedure is based on mapping the time domain constraints into an equivalent set of frequency domain constraints which are then used to determine an allowed design region for the nominal loop transfer function in the plane of amplitude-phase. Once such a region is found, classical loop shaping determines a suitable nominal loop transfer function. The pole-zero structure of the compensator is a natural consequence of loop shaping and is not preconceived. An illustrative example demonstrates the trade-off between controller bandwidth, or the cost of feedback, and the tolerable size of step disturbance.
Rule-Based Guidance for Highway Driving in the Presence of Uncertainty
Authors: Niehaus Axel , Stengel Robert F.
Published: March 2008

The principal objective of this research is to study the feasibility of a real-time, rule-based guidance system for an automobile on a limited-access highway. The inputs to the system are parameters describing the traffic situation, road geometry, vehicle state, and a driver selected goal. The output of the system consists of guidance parameters that command control logic governing the throttle, steering angle, and brakes. During our past research, a dynamic expert system accomplished this guidance task under the assumption that all inputs were available deterministically, i.e., without error. This paper investigates the types and effects of uncertainties encountered in a more realistic environment, and it proposes a stochastic methodology to extend the expert system to handle information that is known only in a probabilistic way.
Detection and Suppression of Drilling Chatter
Authors: Tarng Y. S. , Li T. C.
Published: March 2008

The paper presents a simple but effective method to detect and suppress chatter in drilling operations. Unlike conventional approaches, complex cutting dynamics in drilling operations do not need to model and analyze in this new approach. Chatter is detected when a large thrust force or torque variation is observed. Then, a simple spindle speed change method using the chatter frequency to guide the modification of spindle speed for suppression of chatter is applied. It is shown, by experimental results, that chatter in drilling can be effectively suppressed by using this method.
A System Dynamics Model of Fire-Tube Shell Boiler
Authors: Huang B. J. , Ko P. Y.
Published: March 2008

A system dynamics model of fire-tube shell boiler was developed. The derivation of the dynamics model started with a nonlinear time-variant dynamic modeling based on the transport phenomena in the fire-tube boiler. A linear time-invariant perturbed model around steady-state operating points was then derived. The identifiable parameters τmw, τwa, K, β, and τd were identified by using field test data and least-squares estimation method; the coefficients C’s were, meanwhile, directly predicted by using the small-perturbation relations. Empirical correlations of the identifiable parameters were further derived to account for the variation of parameters with operating conditions. The present perturbed model is thus semi-empirical and can describe the dynamic behaviour of fire-tube boilers over a wide range of operating conditions. The predictions of dynamic responses using the present model were shown to agree very well with the test results.
An Optimal Estimation Method for Nonlinear Models of Mechanical Systems
Authors: van de Molengraft M. J. G. , Veldpaus F. E. , Kok J. J.
Published: March 2008

This paper presents an optimal estimation method for nonlinear mechanical systems. The a priori knowledge of the system in the form of a nonlinear model structure is taken as a starting point. The method determines estimates of the parameters and estimates of the positions, velocities, accelerations, and inputs of the system. The optimal estimation method is applied to an experimental mechanical system. The unknown parameters in this system relate to inertia, friction and elastic deformation. It is shown that the optimal estimation method on the basis of a relatively simple model structure can lead to a useful description of the system.
A Simplified Dynamic Model of the Space Shuttle Main Engine
Authors: Duyar Ahmet , Eldem Vasfi , Merrill Walter , Guo Ten-Huei
Published: March 2008

This paper presents a simplified model of the space shuttle main engine (SSME) dynamics valid within the range of operation of the engine. This model is obtained by linking the linearized point models obtained at 25 different operating points of the SSME. The simplified model was developed for use with a model-based diagnostic scheme for failure detection and diagnostics studies, as well as control design purposes. This simplified model was tested by designing an input signal which covers the whole range of operating points considered and then comparing the responses of linked model and the nonlinear simulation. The comparison indicated good agreement between these responses.
On the Optimization of Robotic Manipulator Trajectories With Bounded Joint Actuators or Joint Kinetic Loads Considered as Control Variables
Authors: Bessonnet G. , Lallemand J. P.
Published: March 2008

A general approach to the dynamics of robotic manipulators is developed in order to select an array of joint actuators and joint kinetic loads to be dealt with as control variables to carry out optimization of manipulator trajectories. Optimization is performed along free paths between work stations. The selected joint forces or torques are submitted to bounds and are optimized together with the travel time by minimizing a mixed performance index.
Robust Stability of Plants With Mixed Uncertainties and Quantitative Feedback Theory
Authors: Jayasuriya Suhada , Zhao Yongdong
Published: March 2008

Quantitative Feedback Theory (QFT) has often been criticized for lack of a rigorous mathematical theory to support its claims. Yet it is known to be a very effective design methodology. In this paper, we re-examine QFT and state several results that confirm the validity of this highly effective framework proposed by Horowitz. Also provided are some additional insights into the QFT methodology that may not be immediately apparent. We consider three important fundamental questions: (i) whether or not a QFT design is robustly stable, (ii) does a robust stabilizer exist, and (iii) does a controller assuring robust QFT performance exist. The first two are obvious precursors for synthesizing controllers for performance robustness. We give necessary and sufficient conditions that unambiguously resolve the question of robust stability under mixed uncertainty, thereby, confirming that a properly executed QFT design is automatically robustly stable. Also given is a sufficiency condition for a robust stabilizer to exist which is derived from the well known Nevanlinna-Pick theory in classical analysis. Finally, we give a sufficiency theorem for the existence of a QFT controller and deduce that when the uncertain plant set is minimum phase with no unstructured uncertainty there always exists a controller satisfying robust performance specifications in the sense of QFT.
Disturbance Rejection Through an External Model for Nonminimum Phase Systems
Authors: Yang Wei-Chi , Tomizuka Masayoshi
Published: March 2008

This paper considers the use of an external model for the cancellation of disturbances in a nonminimum phase system where disturbances can be regarded as the output of a stable (in the sense of Lyapunov) autonomous system. It is assumed that the parameters in the nonminimum phase system are unknown, but the orders of the numerator and denominator polynomials, and the delay steps are known. External model method is a kind of adaptive feedforward controller that the control input is the function of estimated external disturbance. In order to cancel the effect of disturbances, we use two consecutive recursive parameter identification algorithms to estimate external disturbances. The stability of the closed-loop system is proved.
Bovicin HC5, a Lantibiotic Produced by
Streptococcus bovis
HC5, Catalyzes the Efflux of Intracellular Potassium but Not ATP
Authors: Mantovani Hilário C. , Russell James B.
Published: March 2008

Bovicin HC5, a broad-spectrum lantibiotic produced by
Streptococcus bovis
HC5, catalyzed the efflux of intracellular potassium from
Streptococcus bovis
JB1, a sensitive strain. The level of ATP also decreased, but this decline appeared to be caused by the activity of the F
1
F
0
ATPase rather than efflux per se.
Comparison of the Efficacies of Oral β-Lactams in Selection of
Haemophilus influenzae
Transformants with Mutated
ftsI
Genes
Authors: Takahata Sho , Kato Yoshihisa , Sanbongi Yumiko , Maebashi Kazunori , Ida Takashi
Published: March 2008

Horizontal transfer of the mutated
ftsI
gene from β-lactamase-nonproducing ampicillin-resistant (BLNAR)
Haemophilus influenzae
to a susceptible strain was examined in vitro under selection with nine oral β-lactams (ampicillin, amoxicillin, cefprozil, cefuroxime, cefpodoxime, cefdinir, cefcapene, cefditoren, and tebipenem). Compared to the penicillins and the carbapenem, the cephalosporins showed a wide selection window for the genetic transfer.
Chlamydia pneumoniae
Growth Inhibition in Cells by the Steroid Receptor Antagonist RU486 (Mifepristone)
Authors: Yamaguchi Hiroyuki , Kamiya Shigeru , Uruma Tomonori , Osaki Takako , Taguchi Haruhiko , Hanawa Tomoko , Fukuda Minoru , Kawakami Hayato , Goto Hajime , Friedman Herman , Yamamoto Yoshimasa
Published: March 2008

Since steroids are powerful anti-inflammatory agents and increase susceptibility to a variety of infections, including
Chlamydia
(
Chlamydophila
)
pneumoniae
respiratory tract infections, the effect of the steroid receptor antagonist RU486 (mifepristone) on
C. pneumoniae
growth in epithelial HEp-2 cells was examined. Treatment of HEp-2 cells with RU486 significantly inhibited the growth of
C. pneumoniae
in a dose-dependent manner. Electron microscopic studies also revealed that the treatment of infected cells with RU486 resulted in a marked destruction of infecting organisms. The addition of the host cell protein synthesis inhibitor cycloheximide to the infected cells did not alter the inhibition of
C. pneumoniae
growth by RU486. Pretreatment of
C. pneumoniae
organisms with RU486 before addition to culture also did not result in any modulation of bacterial growth in the cells. However, the binding of RU486 to
C. pneumoniae
organisms in cells at 24 h after infection was demonstrated by immune electron microscopy with anti-RU486 antibody. Incubation of cells with anti-RU486 antibody completely diminished the inhibition of
C. pneumoniae
growth by RU486. These results indicate that RU486 may directly bind to the bacteria within cells and cause the destruction of
C. pneumoniae
. This novel mode of regulation of
C. pneumoniae
growth in cells by RU486 might provide a new approach to understanding complicated aspects of
C. pneumoniae
infection.
Role for Nitric Oxide in Hookworm-Associated Immune Suppression
Authors: Dondji Blaise , Bungiro Richard D. , Harrison Lisa M. , Vermeire Jon J. , Bifulco Carlo , McMahon-Pratt Diane , Cappello Michael
Published: March 2008

Hookworm infection is a major cause of anemia and malnutrition in resource-poor countries. Human and animal studies suggest that infection with these intestinal nematodes is associated with impaired cellular immunity, characterized by reduced lymphocyte proliferation in response to both parasite and heterologous antigens. We report here data from studies aimed at defining mechanisms through which hookworms modulate the host cellular immune response. Splenocytes and mesenteric lymph node (MLN) cells from hamsters infected withAncylostoma ceylanicumshowed minimal proliferation in response to mitogen at days 20 and 30 postinfection (p.i.), with partial recovery noted at day 70 p.i. The proliferative capacity of enriched splenocyte T-cell preparations from infected animals following stimulation with hookworm antigens was partially restored in the presence of antigen-presenting cells from uninfected hamsters. Analysis by fluorescence-activated cell sorting revealed that hookworm infection is associated with reduced percentages of both CD4+and surface immunoglobulin G-positive lymphocytes in the spleen and MLN cells. Splenocytes from infected hamsters also secreted more nitric oxide (NO) in culture than did those from naïve animals. Inhibition of NO secretion was associated with partial restoration of the proliferative capacity of splenocytes from infected animals in response to concanavalin A, suggesting a role for NO in mediating this effect. Together, these data demonstrate that hookworm infection is associated with impaired function of antigen-presenting cells and depletion of important lymphocyte subpopulations and also suggests a role for NO in parasite-induced immunosuppression.
Entamoeba histolytica
Encodes Unique Formins, a Subset of Which Regulates DNA Content and Cell Division
Authors: Majumder Shubhra , Lohia Anuradha
Published: March 2008

The formin family of proteins mediates dynamic changes in actin assembly in eukaryotes, and therefore it is important to understand the function of these proteins in
Entamoeba histolytica
, where actin forms the major cytoskeletal network. In this study we have identified the formin homologs encoded in the
E. histolytica
genome based on sequence analysis. Using multiple tools, we have analyzed the primary sequences of the eight
E. histolytica
formins and discovered three subsets: (i)
E. histolytica
formin-1 to -3 (Ehformin-1 to -3), (ii) Ehformin-4, and (iii) Ehformin-5 to -8. Two of these subsets (Ehformin-1 to -3 and Ehformin-4) showed significant sequence differences from their closest homologs, while Ehformin-5 to -8 were unique among all known formins. Since Ehformin-1 to -3 showed important sequence differences from Diaphanous-related formins (DRFs), we have studied the functions of Ehformin-1 and -2 in
E. histolytica
transformants. Like other DRFs, Ehformin-1 and -2 associated with F-actin in response to serum factors, in pseudopodia, in pinocytic and phagocytic vesicles, and at cell division sites. Ehformin-1 and -2 also localized with the microtubular assembly in the nucleus, indicating their involvement in genome segregation. While increased expression of Ehformin-1 and -2 did not affect phagocytosis or motility, it clearly showed an increase in the number of binucleated cells, the number of nuclei in multinucleated cells, and the average DNA content of each nucleus, suggesting that these proteins regulate both mitosis and cytokinesis in
E. histolytica
.
Tuberculous Granulomas Are Hypoxic in Guinea Pigs, Rabbits, and Nonhuman Primates
Authors: Via Laura E. , Lin P. Ling , Ray Sonja M. , Carrillo Jose , Allen Shannon Sedberry , Eum Seok Yong , Taylor Kimberly , Klein Edwin , Manjunatha Ujjini , Gonzales Jacqueline , Lee Eun Gae , Park Seung Kyu , Raleigh James A. , Cho Sang Nae , McMurray David N. , Flynn JoAnne L. , Barry Clifton E.
Published: March 2008

Understanding the physical characteristics of the local microenvironment in which
Mycobacterium tuberculosis
resides is an important goal that may allow the targeting of metabolic processes to shorten drug regimens. Pimonidazole hydrochloride (Hypoxyprobe) is an imaging agent that is bioreductively activated only under hypoxic conditions in mammalian tissue. We employed this probe to evaluate the oxygen tension in tuberculous granulomas in four animal models of disease: mouse, guinea pig, rabbit, and nonhuman primate. Following infusion of pimonidazole into animals with established infections, lung tissues from the guinea pig, rabbit, and nonhuman primate showed discrete areas of pimonidazole adduct formation surrounding necrotic and caseous regions of pulmonary granulomas by immunohistochemical staining. This labeling could be substantially reduced by housing the animal under an atmosphere of 95% O
2
. Direct measurement of tissue oxygen partial pressure by surgical insertion of a fiber optic oxygen probe into granulomas in the lungs of living infected rabbits demonstrated that even small (3-mm) pulmonary lesions were severely hypoxic (1.6 ± 0.7 mm Hg). Finally, metronidazole, which has potent bactericidal activity in vitro only under low-oxygen culture conditions, was highly effective at reducing total-lung bacterial burdens in infected rabbits. Thus, three independent lines of evidence support the hypothesis that hypoxic microenvironments are an important feature of some lesions in these animal models of tuberculosis.
T Cells Help To Amplify Inflammatory Responses Induced bySalmonella entericaSerotype Typhimurium in the Intestinal Mucosa
Authors: Godinez Ivan , Haneda Takeshi , Raffatellu Manuela , George Michael D. , Paixão Tatiane A. , Rolán Hortensia G. , Santos Renato L. , Dandekar Satya , Tsolis Renée M. , Bäumler Andreas J.
Published: March 2008

Salmonella entericaserotype Typhimurium causes an acute inflammatory reaction in the ceca of streptomycin-pretreated mice. We determined global changes in gene expression elicited by serotype Typhimurium in the cecal mucosa. The gene expression profile was dominated by T-cell-derived cytokines and genes whose expression is known to be induced by these cytokines. Markedly increased mRNA levels of genes encoding gamma interferon (IFN-γ), interleukin-22 (IL-22), and IL-17 were detected by quantitative real-time PCR. Furthermore, the mRNA levels of genes whose expression is induced by IFN-γ, IL-22, or IL-17, including genes encoding macrophage inflammatory protein 2 (MIP-2), inducible nitric oxide synthase (Nos2), lipocalin-2 (Lcn2), MIP-1α, MIP-1β, and keratinocyte-derived cytokine (KC), were also markedly increased. To assess the importance of T cells in orchestrating this proinflammatory gene expression profile, we depleted T cells by using a monoclonal antibody prior to investigating cecal inflammation caused by serotype Typhimurium in streptomycin-pretreated mice. Depletion of CD3+T cells resulted in a dramatic reduction in gross pathology, a significantly reduced recruitment of neutrophils, and a marked reduction in mRNA levels ofIfn-γ,Il-22, Il-17, Nos2, Lcn2, andKc. Our results suggest that T cells play an important role in amplifying inflammatory responses induced by serotype Typhimurium in the cecal mucosa.
Guides d’activité physique pour les Canadiens : stratégies de diffusion des messages, attentes réalistes pour le changement et évaluationCet 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: Brawley Lawrence R. , Latimer Amy E.
Published: March 2008

Les directives relatives à la pratique de l’activité physique proposent des comportements types qui diminuent le risque de morbidité et de mortalité si on y adhère. En fait, les directives indiquent le quoi faire, mais ni le pourquoi ni le comment. Par conséquent, pour favoriser la pratique de l’activité physique, les messages issus des directives ne devraient pas seulement donner la quantité d’activité physique à faire et pourquoi, mais aussi comment le faire. Les guides d’activité physique canadiens sont une mise en application de ces directives. Dans cet article, nous présentons un bref aperçu des défis créés par la publication de ces guides et nous relevons les aspects pratiques et les observations empiriques à prendre en compte dans le futur pour élaborer et diffuser des messages congruents. Nous nous inspirons des succès passés pour bien communiquer les directives relatives aux objectifs de la pratique de l’activité physique et nous nous référons à la littérature scientifique récente en matière de promotion pour faire des recommandations. Pour motiver les gens à atteindre les objectifs véhiculés dans les directives, il faut formuler des messages à caractère informatif, incitatif et convaincant. On devrait diffuser ces messages auprès du public au moyen d’une campagne de promotion en plusieurs étapes, soigneusement planifiée et soumise à une évaluation rigoureuse.
Lignes directrices sur l’activité physique à l’intention des enfants et des jeunesCet 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: Janssen Ian
Published: March 2008

The aim of this review is to provide a scientific update on evidence related to the biological and psycho-social health benefits of physical activity in school-aged children and youth. To accomplish this aim, the first part of the paper reviews existing physical activity guidelines for school-aged children and youth, with an emphasis placed on how Canada’s guidelines compare and contrast with those of other countries and organizations. The paper then provides an overview of physical activity levels of Canadian children and youth, which indicates that few Canadian youngsters meet current physical activity recommendations. The next section of the paper summarizes the literature that informs how much physical activity is required to promote health and well-being in children and youth. The paper then provides suggestions on modifications that could be made to Canada’s physical activity guidelines for children and youth. Specifically, consideration should be given to setting both minimal (≥60 min/d) and optimal (up to several hours per day) physical activity targets. The final section identifies future research needs. In this section, a need is noted for comprehensive dose–response studies of physical activity and health in the paediatric age group
Limitations des données sur l’activité physique du Canada : répercussions sur les tendances de la surveillanceCet 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: Katzmarzyk Peter T. , Tremblay Mark S.
Published: March 2008

Le faible niveau de pratique de l’activité physique chez les Canadiennes et les Canadiens constitue une préoccupation majeure de santé publique. Bien entendu, il est important de saisir les pratiques et les tendances actuelles. Des irrégularités concernant le monitorage, l’analyse et l’établissement du bilan créent de la confusion auprès des chercheurs, des décideurs et du public en général. Cette étude se propose de consolider les observations antérieures, de faire une évaluation critique des méthodes d’observation et d’analyse de la pratique de l’activité physique et de présenter des résultats couramment utilisées au Canada. Nous proposons une approche afin d’interpréter de façon juste et valable les observations et nous recommandons des stratégies de surveillance.
Lignes directrices éclairées par des données probantes sur l’activité physique à l’intention des Canadiens adultesCet 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: Warburton Darren E.R. , Katzmarzyk Peter T. , Rhodes Ryan E. , Shephard Roy J.
Published: March 2008

Cet article fait le tour des dernières études scientifiques sur les fondements biologiques et psychosociaux du Guide d’activité physique canadien pour une vie active saine et porte une attention particulière à l’effet de l’activité physique sur la santé des adultes âgés de 20 à 55 ans. Nous exposons brièvement les directives provenant d’un peu partout dans le monde en matière d’activité physique à l’intention des adultes et nous les comparons aux directives canadiennes. Nous présentons l’épidémiologie descriptive de l’activité physique et de l’inactivité physique et nous analysons l’importance de la relation entre l’activité physique et certaines répercussions sur la santé en mettant l’accent sur les quantités minimale et optimale requises à cette fin. En conclusion, nous mentionnons des pistes de recherche particulières. En bref, les directives canadiennes et la plupart des directives issues des autres pays recommandent la pratique d’activité physique d’intensité modérée presque tous les jours de la semaine. L’activité physique diminue fort probablement le risque de souffrir de plus de 25 conditions chroniques, notamment la maladie coronarienne, l’accident cérébrovasculaire, l’hypertension, le cancer du sein, le cancer du côlon, le diabète de type 2 et l’ostéoporose. D’après les études recensées, si la population canadienne entière adhérait aux recommandations du Guide, on éviterait environ un tiers des décès associés à la maladie coronarienne, un quart des décès associés à l’accident cérébrovasculaire et à l’ostéoporose, un cinquième des décès associés au cancer du côlon, à l’hypertension et au diabète de type 2 et un septième des décès associés au cancer du sein. Il semble aussi que la prévention du gain de poids et le maintien de la perte de poids exigent de plus gros efforts que ne l’indiquent les recommandations actuelles.
Lignes directrices et guides sur l’activité physique à l’intention des Canadiens : les faits et l’avenir
Authors: Tremblay Mark S. , Shephard Roy J. , Brawley Lawrence R. , Cameron Christine , Craig Cora Lynn , Duggan Mary , Esliger Dale W. , Hearst William , Hicks Audrey , Janssen Ian , Katzmarzyk Peter T. , Latimer Amy E. , Ginis Kathleen A. Martin , McGuire Ashlee , Paterson Donald H. , Sharratt Michael , Spence John C. , Timmons Brian , Warburton Darren , Young T. Kue , Zehr Lori
Published: March 2008

This article summarizes the main findings from the papers included in this journal supplement. It consolidates the evidence currently available to inform and advance the development of physical activity guidelines for Canadians, and it highlights the specific needs of various population subgroups. The challenges of translating guideline information into effective and persuasive physical activity messages, of campaigns to disseminate messages and of related evaluations are underlined. Recommendations on how to proceed are based on the evidence base provided by this series of papers; the immediate next steps mandated by this initiative are outlined and priorities for future research are indicated.
DIELECTRIC AND FERROELECTRIC BEHAVIORS OF NOVELPbTiO3/NiFe2O4THIN FILMS PREPARED BY SOL–GEL METHOD
Authors: DONG YANLING , WANG XIN , CHAI XIAOYAN , WENG WENJIAN , HAN GAORONG , DU PIYI
Published: March 2008

Ferroelectric/ferromagnetic (ME) biphase composite thin films with the type of (1–x) PbTiO3( PT )–x NiFe2O4(NFO) (x = 1–9) were successfully formed in situ by sol–gel process. The dielectric and ferroelectric behaviors of the composite thin films were investigated. The asymmetrical hysteresis loops of the composite arise from the leak current due to low resistivity of NFO. The stronger stress in the thin films due to the strong conjunction between PT and the substrate contributes to the increase (decrease) of the coercive force (the remanent polarization) with increasing the content of PT. The ME composites exhibit slight percolation effect. The high dielectric constant near the percolation threshold is attributed to the "micro-capacitors" in the composite thin films.