bluuebunny/crossref_metadata_2025 huggingface dataset:
Experiment and Comparison of Robust Linear and Sliding Mode Controllers for Regulation of a Magnetic Bearing System
Authors: Emadzadeh Amir A. , Lorentz Thomas D. , Tsao Tsu-Chin
Published: February 2011

Based on a reduced order state-space model of an MBC 500 magnetic bearing system with fixed shaft (i.e. non rotating), two different observer-based digital controllers are designed to regulate the shaft. One is a robust linear pole-placement controller, and the other is a sliding mode controller. Each controller’s performance is mathematically analyzed. Using a more representative higher order model of the fixed shaft, the controllers are numerically simulated to ensure stable operation. Then, the controllers are digitally implemented on an MBC 500 benchmark. Controller performance is compared by introducing un-modeled dynamics — in particular, continuous rotation of the shaft. Regulation performance is examined over a range of different rotation rates.
A Rule-Based Strategy for a Series/Parallel Hybrid Electric Vehicle: An Approach Based on Dynamic Programming
Authors: Bianchi Domenico , Rolando Luciano , Serrao Lorenzo , Onori Simona , Rizzoni Giorgio , Al-Khayat Nazar , Hsieh Tung-Ming , Kang Pengju
Published: February 2011

Dynamic programming (DP) provides the optimal global solution to the energy management problem for hybrid electric vehicles (HEVs), but needs complete a-priori knowledge of the driving cycle and has high computational requirements. This article presents a possible methodology to extract rules from the dynamic programming solution to design an implementable rule-based strategy. The case study considered is a series/parallel HEV, in which a clutch allows to switch from one configuration to another. The strategy works according to a two layer policy: the supervisory controller, which decides the powertrain configuration (either series or parallel), and the energy management, which decides the power split. The process of deriving the rules from the optimal solution is described. Then, the performance of the resulting rule-based strategy is studied and compared with the solution given by the dynamic programming, which functions as a benchmark.
A High Fidelity Lumped-Parameter Engine Model for Powertrain Control Design and Validation
Authors: Follen K. , Canova M. , Midlam-Mohler S. , Guezennec Y. , Rizzoni G. , Lee B. , Matthews G.
Published: February 2011

The paper presents a lumped-parameter modeling approach for the characterization of internal combustion engine systems dynamics, suitable for the design, analysis and calibration of powertrain control. Through an analysis of the deficiencies of traditional filling and emptying, crank angle resolved models, a novel approach is presented to calibrate the distributed effects of charge heating, backflow, and wave propagation dynamics within the context of a zero-dimensional (lumped) model. The resulting model is capable of predicting the cycle averaged values of volumetric efficiency and torque, as well as the crank angle resolved values of cylinder pressure and indicated torque in steady state and transient conditions within accuracy comparable to a 1D gas dynamic model, while maintaining a significantly reduced computational effort. The approach is applied to a 4-cylinder spark ignition engine with dual independent variable valve timing, and validated using simulation and experimental data. Validation results allow for an evaluation of the model’s high accuracy and low computation effort.
Dynamic Modeling and Stability Analysis of Water-Cooled Centrifugal Chillers
Authors: Li Pengfei , Li Yaoyu , Seem John E.
Published: February 2011

This paper presents a study on the dynamics of a water-cooled centrifugal chiller from two aspects: dynamic simulation modeling and stability analysis. First, the transient model is developed in Modelica with Dymola and the TLK/IfT Library (TIL). The centrifugal compressor is modeled in detail based on the turbomachinery theory. The chiller capacity control is achieved by the combination of variable inlet guide vane (VIGV) and variable speed drive (VSD). The shell-and-tube heat exchangers are discretized based on the finite volume method with convenient and numerically efficient two-phase property evaluations. A thermal expansion valve (TXV) is used to regulate the mass flow rate. These models are interconnected to form a centrifugal chiller system. Second, the stability of the chiller is studied based on Lyapunov analysis. The centrifugal chiller is effectively a “closed-loop” concatenation of the centrifugal compressor, condenser, expansion device and evaporator because the refrigerant flow stays within the closed path of the chiller system. The inherent unstable aspect of the compressor dynamics (e.g. surge) becomes more intrigued because the input and output flow are correlated, as compared to the typical “open-loop” centrifugal compressor applications such as compressed air systems or turbochargers. The Lyapunov stability analysis presented herein constructs partial foundation for future nonlinear control design for the centrifugal chiller systems.
Model Predictive Control of an Electroporation Process
Authors: Ge Peinan , Yi Jingang , Li Jianbo , Lin Hao
Published: February 2011

Electroporation is an elegant means to deliver molecules into the cellular cytoplasm, while simultaneously maintaining cell viability and functionality. Despite extensive research, however, electroporation methods still fall short of the desired efficiency and reliability. We present a model predictive control (MPC) design for enabling highly efficient and reliable electroporation processes. Instead of using one single electrical pulse in current practice, we consider a controlled multi-pulse electroporation based on an MPC framework. The most attractive properties of using MPC design of multi-pulse electroporation are the fast computation of optimal control solutions and the real-time tunability of the electrical field density during the process. We demonstrate the controlled electroporation process through simulation examples.
Computational Studies of Controlled Nanoparticle Agglomerations for MRI-Guided Nanorobotic Drug-Delivery Systems
Authors: Vartholomeos Panagiotis , Aylak Suleyman S. , Mavroidis Constantinos
Published: February 2011

Magnetic Resonance Imaging (MRI) guided nanorobotic systems that could perform diagnostic, curative and reconstructive treatments in the human body at the cellular and sub-cellular level in a controllable manner have recently been proposed. The concept of a MRI-guided nanorobotic system is based on the use of a MRI scanner to induce the required external driving forces to guide magnetic nanocapsules to a specific target. However, the maximum magnetic gradient specifications of existing clinical MRI systems are not capable of driving superparamagnetic nanocapsules against the blood flow and therefore these MRIs do not allow for navigation. The present paper proposes a way to overcome this critical drawback through the formation of micron size agglomerations where their size can be regulated by external magnetic stimuli. This approach is investigated through modeling of the physics that govern the self-assembly of the nanoparticles. Additionally a computational tool has been developed that incorporates the derived models and performs simulation, visualization and post-processing analysis. Preliminary simulation results demonstrate that external magnetic field causes aggregation of nanoparticles while they flow in the vessel. This is a promising result — in accordance with similar experimental results — and encourages further investigation on the nanoparticle based self-assembly structures for use in nanorobotic drug delivery.
Vehicle Sideslip Angle Estimation Using Two Single-Antenna GPS Receivers
Authors: Yoon Jong-Hwa , Peng Huei
Published: February 2011

Knowing vehicle sideslip angle accurately is critical for active safety systems such as Electronic Stability Control (ESC). Vehicle sideslip angle can be measured through optical speed sensors, or dual-antenna GPS. These measurement systems are costly (∼$5k to $100k), which prohibits wide adoption of such systems. This paper demonstrates that the vehicle sideslip angle can be estimated in real-time by using two low-cost single-antenna GPS receivers. Fast sampled signals from an Inertial Measurement Unit (IMU) compensate for the slow update rate of the GPS receivers through an Extended Kalman Filter (EKF). Bias errors of the IMU measurements are estimated through an EKF to improve the sideslip estimation accuracy. A key challenge of the proposed method lies in the synchronization of the two GPS receivers, which is achieved through an extrapolated update method. Analysis reveals that the estimation accuracy of the proposed method relies mainly on vehicle yaw rate and longitudinal velocity. Experimental results confirm the feasibility of the proposed method.
Model Predictive Control (MPC) Based Combined Wheel Torque and Steering Control Using a Simplified Tire Model
Authors: Adireddy Ganesh , Shim Taehyun , Rhode Douglas , Asgari Jahan
Published: February 2011

Wheel torque control and active front steer are effective means of improving vehicle handling and stability. In this paper, a vehicle chassis control system that controls both wheel torques at each wheel and front steer has been developed using model predictive control in order to enhance vehicle yaw motion and ability to track the desired trajectory. A simplified nonlinear tire model that is computationally efficient and easy to implement in the control algorithms and an 8 degree of freedom (DOF) vehicle model are used in the controller. The performance of this controller is compared to that based on well known Magic Formula tire model. The effectiveness and limitations of the proposed controller are discussed through simulation.
Modeling, Simulation, and Control of Active Pneumatic Suspension System
Authors: Wang Jia , Kelkar A. G.
Published: February 2011

This paper presents analytical modeling, system identification, and controller design for a “pneumatic-only” vibration isolation system. There exist extensive literature on traditional suspension designs but the literature on purely pneumatic suspension devices is very sparse. This paper presents an extensive modeling and experimental work for characterizing dynamical behavior of the system. The experimental data was used to derive approximate but simple low-order dynamic models using system identification techniques. A solenoid operated orifice mechanism is used to control the flow of air mass between air spring and accumulator. The design of accumulated air spring with controlled orifice constitutes a Continuously Variable Natural Frequency and Damping (CVNFD) device introduced in previous work by the second author. The paper also presents a robust control analysis and design for disturbance rejection problem. The results show promising trends for potential use of such simple and inexpensive system in various vibration isolation applications.
Fault-Tolerant Control of Electric Ground Vehicles With Independently-Actuated Wheels
Authors: Wang Rongrong , Wang Junmin
Published: February 2011

This paper presents a fault-tolerant control method for four-wheel independently driven (4WID) electric vehicles. 4WID electric vehicle is one of the promising architectures for electric vehicles in the future. While such a vehicle architecture greatly increases the flexibility for vehicle control, it also demands more on system reliability, safety, and fault tolerance due to the increased number of actuators and subsystems. An active fault tolerant control approach for 4WID electric vehicle is developed to accommodate the fault of in-wheel motor and motor driver pairs. Based on an in-wheel motor/motor driver fault detection mechanism, a control-allocation based vehicle control system is designed to accommodate the in-wheel motor/motor driver fault by automatically allocating the control effort among other healthy wheels. Simulations using a high-fidelity CarSim® full-vehicle model show the effectiveness of the proposed fault-tolerant control approach.
An Intelligent Sensing Network of Distributed Swarming Agents for Perimeter Detection and Surveillance
Authors: Fricke Gregory K. , Zhang Guoxian , Caccavale Adam , Li Walter , Garg Devendra P.
Published: February 2011

Perimeter detection and surveillance by a distributed swarm of autonomous agents offers a solution in multiple cases where human safety or environmental protection is of concern. An algorithmic method is developed for detection and surveillance of one or more dynamic perimeters via distributed control under local-area sensing and communication. Local graphs among neighbors are formed based on proximity, at which point communication among graph members becomes possible. Hardware-in-the-loop mixed-simulation experiments validate the method utilizing iRobot Create® ground robots and a NaturalPoint OptiTrack vision system.
A Multi-Level Modularized System Architecture for Mobile Robotics
Authors: Basso Brandon , Kehoe Benjamin , Hedrick J. Karl
Published: February 2011

This paper describes a modular system architecture for mobile robotics. It presents the view of an individual robot as a collection of many small pieces of hardware and software grouped into functional subsystems. A set of robots can then join together to form a larger system. The goal of this work is to describe a software design philosophy and architecture that is flexible yet robust enough to meet the challenges of the mobile robotics domain. The guiding design principle is bottom-to-top modularization, from individual algorithms, to software executables, to functional groupings of executables. These functional groupings are presented as canonical subsystems for collaborative robotics, applicable to a wide range of robotics systems. A multi-agent multi-user UAV application is presented as a case study and proof of the generality of the design philosophy.
On Sensitivity of Capacitive Microresonators Near Three Half Natural Frequency
Authors: Caruntu Dumitru I. , Knecht Martin
Published: February 2011

This paper deals with sensitivity of electrostatically actuated micro resonator sensors near three half natural frequency. Mass deposition changes resonance frequencies of structures. Resonator sensitivity, defined as a fraction of change in frequency per unit deposited mass, can be found for microcantilever sensors electrostatically actuated to include fringe and Casimir effects. These actuation forces produce nonlinear parametric oscillations. Constant thickness mass deposition on all four lateral surfaces of the cantilever of rectangular cross-section was assumed. The Euler-Bernoulli theory was used under the assumption that the beams are slender. Mass deposition on the free end surface of the cantilever was neglected. The deposition thickness was considered uniform and very small compared to any beam dimension. The deposited mass had no contribution to the stiffness, only to the mass. Analytical expression of the sensitivity of electrostatically actuated uniform microcantilever resonators sensor near natural frequency can be determined.
Design and Evaluation of Statically Balanced Compliant Mechanisms for Haptic Interfaces
Authors: Leishman Levi C. , Ricks Daniel J. , Colton Mark B.
Published: February 2011

Compliant mechanisms have the potential to increase the performance of haptic interfaces by reducing the friction and inertia felt by the user. The net result is that the user feels the dynamic forces of the virtual environment, without feeling the dynamics of the haptic interface. This “transparency” typically comes at a cost — compliant mechanisms exhibit a return-to-zero behavior that must be compensated in software. This paper presents a step toward improving the situation by using statically balanced compliant mechanisms (SBCMs), which are compliant devices that do not exhibit the return-to-zero behavior typical with most compliant mechanisms. The design and construction of a prototype haptic device based on SBCMs is presented, along with its mathematical model derived using the pseudo-rigid body model (PRBM) approach. Experimental results indicate that SBCMs effectively eliminate the return-to-zero behavior and are a feasible design element in haptic interfaces.
Prototype Medical Exoskeleton for Paraplegic Mobility: First Experimental Results
Authors: Strausser Katherine A. , Swift Tim A. , Zoss Adam B. , Kazerooni H.
Published: February 2011

Spinal cord injuries leave thousands of patients confined to wheelchairs, resulting in a life of severely limited mobility. This condition also subjects them to the risk of secondary injuries. Because exoskeletons are externally driven machines in which the actuation is coupled to the person’s joints, they offer an ideal method to help paraplegics walk. The exoskeleton presented here is a mobile, battery powered device that uses hydraulically actuated hip and knee joints in the sagittal plane to move a patient’s joints. The control strategy mimics standard human walking using foot sensors to determine the walking state. This activates position control of the joints to follow standard walking trajectories based on clinical gait analysis data. Initial patient testing of the device showed that the exoskeleton enabled one incomplete paraplegic to significantly improve his gait function and three complete paraplegic patients to walk.
Target Estimate PDF-Based Optimal Path Planning Algorithm With Application to UAV Systems
Authors: Wood Jared G. , Kehoe Benjamin , Hedrick J. Karl
Published: February 2011

Companies are starting to explore investing in UAV systems that come with standard autopilot trackers. There is a need for general cooperative local path planning algorithms that function with these types of systems. We have recently finished a project in which algorithms for autonomously searching for, detecting, and tracking ground targets was developed for a fixed-wing UAV with a visual spectrum gimballed camera. A set of scenarios are identified in which finite horizon path optimization results in a non-optimal ineffective path. For each of these scenarios, an appropriate path optimization problem is defined to replace finite horizon optimization. An algorithm is presented that determines which path optimization should be performed given a UAV state and target estimate probability distribution. The algorithm was implemented and thoroughly tested in flight experiments. The experimental work was successful and gave insight into what is required for a path planning algorithm to robustly work with standard waypoint tracking UAV systems. This paper presents the algorithm that was developed, theory supporting the algorithm, and experimental results.
Artificial Immune System for Heterogeneous Mobile Robotic Systems
Authors: Raza Ali , Fernandez Benito R.
Published: February 2011

Artificial immune system draws its inspiration from the biological immune functions mainly those of humans. Recently, newer definitions of biological immune system have appeared and gained significance because of their strong immunological roots e.g. danger theory. This raises the need to look into earlier work on immuno-inspired robotics. Especially, older approach of idiotypic-network must be compared with the newer approach of danger-theory. Authors in this research have successfully applied both the definitions on heterogeneous mobile robotic systems. Idiotypic connections between antibodies have been used as a tool to navigate robots as well as to establish inter-robot communication in an immune network approach. Similarly, co-stimulatory signal concentrations have been used to contextualize the environment, in a danger theory approach, to initiate and regulate the immuno responses. Immune metaphors have been translated into relevant computational models and simulated in search and rescue operation in an obstacle filled arena.
Cathode Pressure Modeling of the Buckeye Bullet II 540 kW Hydrogen Fuel Cell System
Authors: Hillstrom Edward , Canova Marcello , Guezennec Yann , Rizzoni Giorgio
Published: February 2011

This paper applies a well published control level model for fuel cell system dynamics to the unique fuel cell system of the world’s fastest fuel cell vehicle, the Buckeye Bullet 2. The goal is to develop a system model to predict the pressure dynamics of the cathode system so the cathode can be operated at maximum allowable pressure to provide maximum performance. The details of how the model must be modified to fit the unique fuel cell system are provided. The results of the initial implementation show several shortcomings when the published model is implemented. The largest problems are found to be with how the model treats the liquid product water that is generated. For this reason, modifications are implemented to attempt to improve the correlation between the model and collected data. The results show partial improvements in 3 areas of performance, indicating that more accurate dynamic models are needed to fully characterize the phenomena. Further model development and testing are planned based on the initial results.
An Internal Model-Based Tracking Control for a Class of Uncertain Linear Time-Varying Systems
Authors: Zhang Zhen , Sun Zongxuan , Ye Peiqing
Published: February 2011

In this paper, we extend previous results for a novel internal model-based tracking control with a class of known LTV plant models driven by LTI exosystems to uncertain LTI plant models driven by LTV exosystems. The augmented time-varying system to be stabilized becomes uncertain. Moreover, the time-varying fashion under consideration renders the augmented uncertain system linear parameter-varying (LPV). By means of an output-feedback gain-scheduling design, the augmented uncertain LTV system is stabilized. Simulation results illustrate the proposed design method.
Sustainable Acrobot Walking Based on the Swing Phase Exponentially Stable Tracking
Authors: Anderle Milan , Cˇelikovsky´ Sergej
Published: February 2011

The Acrobot is the simplest walking like underactuated system which at the same time comprises all typical difficulties of the underactuated walking. In particular, efficient algorithms for the Acrobot walking may be generalized to more general walking like configurations through their special decomposition. The main contribution of this paper is to design the algorithm how to compute a cyclic walking like trajectory which is crucial to have the hybrid exponentially stable multi step tracking of this trajectory later on. Notice, that such a design is not an easy task as the walking trajectory initial conditions are changed along the single step into different end conditions and these should be subsequently mapped by the impact map into the same initial condition for the second step. For this sake we use the special partial linearized coordinates to demonstrate their advantage for the design of the cyclic walking trajectory. Such a trajectory is then used to demonstrate the sustainable walking based on the swing phase exponentially stable tracking via computer simulations.
Active Roll Control for Rollover Prevention of Heavy Articulated Vehicles With Multiple-Rollover-Index Minimization
Authors: Huang Hsun-Hsuan , Yedavalli Rama K.
Published: February 2011

This paper presents the application of a nominal control design algorithm for rollover prevention of heavy articulated vehicles with active anti-roll bar control. This proposed methodology is based on an extension of Linear Quadratic Regulator (LQR) control for ‘state derivative induced (control coupled) output regulation’ problems. For heavy articulated vehicles with multiple axles, a performance index with Multiple Rollover Indices (MRI) is proposed. The proposed methodology allows us to compare the usefulness of various control configurations (i.e. actuators at different axles of the vehicle) based on the interaction of this control configuration with vehicle dynamics. Application of this methodology to a specific heavy articulated vehicle with tractor semi-trailer shows that a single active anti-roll bar system at the trailer unit gives better performance than multiple-axle actuators at tractor and trailer together with the double lane change maneuver as the external disturbance.
Robust Nonlinear Control Design for a Hypersonic Aircraft Using Sum–of–Squares Method
Authors: Ataei-Esfahani Armin , Wang Qian
Published: February 2011

In recent years, Sum–Of–Squares (SOS) method has attracted increasing interest as a new approach for stability analysis and controller design of nonlinear dynamic systems. This paper utilizes SOS method to design a robust nonlinear controller for longitudinal dynamics of a hypersonic aircraft model. Specifically, the searching of the nonlinear robust controller is reformulated as a robust SOS/robust LMI problem, and then solved via a stochastic iterative algorithm. As the simulation results show, the designed controller is capable of stabilizing the aircraft and following pilot commands in presence of parametric uncertainties in the aircraft model.
Distributed Cyclic Motion Control of Multiple UAVs for Wildfire Monitoring
Authors: Sharma Balaji R. , Venkata Narasimha Koushik S. , Ramakrishnan Subramanian , Kumar Manish
Published: February 2011

This work focuses on the use of a swarm of unmanned aerial vehicles (UAVs) for fire front monitoring applications. Typically, fire monitoring relies on satellite imagery or manned aircraft missions for tracking fire spread. However, both methods have limitations in terms of accuracy and safety. In this paper the authors establish a framework for cooperative, persistent tracking of a dynamic perimeter using a swarm of UAVs with an emphasis on improved accuracy and reduced delays in the tracking process. The objective is to implement a coordinated, cyclic movement of the UAVs around the evolving fire perimeter thereby facilitating efficient tracking even with a limited number of agents. An expanding closed-curve model is introduced in order to represent a growing fire and the perimeter tracking process is demonstrated using numerical simulations. The control framework comprises of two aspects: (1) radial tracking of the perimeter by each UAV based on the fire boundary it perceives within its field of view, and (2) coordinated cyclic movement of the UAVs around the growing perimeter based on artificial potential functions that govern inter-UAV dynamics. Control vectors incorporating both the aspects are implemented in this study. It is demonstrated by means of simulation results that, interestingly, the multi-agent system of UAVs converges to stable configurations under both static and dynamic perimeter tracking scenarios. Additionally, the accuracy of perimeter tracking and spatial distribution while in cyclic pursuit is investigated. The article concludes with a discussion of directions of further research.
Smooth Motion Control of the Adaptive Cruise Control System With Linear Quadratic Control With Variable Weights
Authors: Kim Sanggyum , Tomizuka Masayoshi , Cheng Kuo-Hsiang
Published: February 2011

A virtual lead vehicle scheme is introduced to make the switching between the speed control algorithm and the distance control algorithm unnecessary. This method is shown to provide a good reaction for when a lead vehicle cuts in or out. A linear quadratic controller with variable weights is suggested to control the virtual lead vehicle. This scheme shows improved performance in terms of passenger comfort and fuel efficiency of the host vehicle.
Iterative Learning Control With Optimal Feedback and Feedforward Control
Authors: Yu Shuwen , Tomizuka Masayoshi
Published: February 2011

Iterative learning control (ILC) is a feedforward control strategy used to improve the performance of a system that executes the same task repeatedly, but is incapable of compensating for non-repetitive disturbances. Thus a well-designed feedback controller needs to be used in combination with ILC. A robustness filter called the Q-filter is essential for the ILC system stability. The price to pay, however, is that the Q-filter makes it impossible for ILC to achieve perfect tracking of the repetitive reference or perfect cancellation of repetitive disturbances. To reduce error, it is effective to apply a pre-design feedforward control input in addition to ILC. In this paper, a simple P-type ILC is combined with an optimal feedback-feedforward control inspired by classic predictive control, so as to take advantages of each control strategy. It will be shown that the choice of the injection point of the learned ILC effort is crucial for a tradeoff between stability and performance. Therefore, the stability and performance analysis based on different injection points is studied. A systematic approach to the combined control scheme is also proposed. The combined control scheme is attractive due to its simplicity and promising performance. The effectiveness of the combined control scheme is verified by simulation results with a wafer scanner system.
Microelectrothermal Bridge Circuits for Thermal Conductivity Measurement of Metallic and Semiconducting Nanowires
Authors: Stojanovic Nenad , Berg Jordan M. , Maithripala D. H. S. , Holtz Mark
Published: February 2011

We develop a method for direct measurement of thermal conductivity of nanowires, consisting of a microelectrothermal test device and a complementary parameter estimation algorithm. Simulations of a simplified version of the problem show how differential measurements can address the problem of parasitic heat loss, and examine several different parameter estimation schemes. As reported elsewhere, measurements have been performed on aluminum nanowire arrays, with excellent results. Several design modifications are required to accommodate semiconducting samples. A device design for silicon nanowire arrays is presented. A simulation study suggests that these devices will also perform extremely well.
Life Extending Minimum-Time Path Planning for a Hexapod Robot
Authors: Wu Xin , Li Yaoyu , Consi Thomas R.
Published: February 2011

This paper presents a life extending minimum-time path planning algorithm for legged robots, with application for a six-legged walking robot (hexapod). The leg joint fatigue life can be extended by reducing the constraint on the dynamic radial force. The dynamic model of the hexapod is built with the Newton Euler Formula. In the normal condition, the minimum-time path planning algorithm is developed through the bisecting-plane (BP) algorithm with the constraints of maximum joint angular velocity and acceleration. According to the fatigue life model for ball bearing, its fatigue life increases while the dynamic radial force on the bearing decreases. The minimum-time path planning algorithm is thus revised by reinforcing the constraint of maximum radial force based on the expectation of life extension. A symmetric hexapod with 18 degree-of-freedom is used for simulation study. As a simplified treatment, the magnitudes of dynamic radial force on proximal joints at the pair of supporting legs are set identical to achieve similar degradation rates on each joint bearing and obtain the dynamic radial force on each joint. The simulation results validate the effectiveness of the proposed idea. This scheme can extend the operating life of robot (joint bearing fatigue life) by modifying the joint path only without affecting the primary task specifications.
State Estimation for Kinematic Model Over Lossy Network
Authors: Jeon Soo
Published: February 2011

The major benefit of the kinematic Kalman filter (KKF), i.e., the state estimation based on kinematic model is that it is immune to parameter variations and unknown disturbances regardless of the operating conditions. In carrying out complex motion tasks such as the coordinated manipulation among multiple machines, some of the motion variables measured by sensors may only be available through the communication layer, which requires to formulate the optimal state estimator subject to lossy network. In contrast to standard dynamic systems, the kinematic model used in the KKF relies on sensory data not only for the output but also for the process input. This paper studies how the packet dropout occurring from the input sensor as well as the output sensor affects the performance of the KKF. When the output sensory data are delivered through the lossy network, it has been shown that the mean error covariance of the KKF is bounded for any non-zero packet arrival rate. On the other hand, if the input sensory data are subject to lossy network, the Bernoulli dropout model results in an unbounded mean error covariance. More practical strategy is to adopt the previous input estimate in case the current packet is dropped. For each case of packet dropout models, the stochastic characteristics of the mean error covariance are analyzed and compared. Simulation results are presented to illustrate the analytical results and to compare the performance of the time varying (optimal) filter gain with that of the static (sub-optimal) filter gain.
Self-Optimizing Robust Control of Wind Power Generation With Doubly-Fed Induction Generator
Authors: Chen Quan , Li Yaoyu , Yang Zhongzhou , Seem John E. , Creaby Justin
Published: February 2011

This study presents a self-optimizing robust control scheme for maximizing the power generation for a variable speed wind turbine with DFIG. The control system consists of two control loops. The outer loop is an Extremum Seeking Control (ESC) based generator torque regulation via the rotor power feedback. The ESC can search for the optimal generator torque to maximize the rotor power under variation of the power map. The inner loop is electrical control using PWM converters via vector control schemes. An ℋ∞ controller is synthesized for maximizing the conversion from the rotor power to grid power, with performance weight defined with the spectrum of the rotor power obtained by the ESC. Also, the controller is designed to be robust against the variations of some parameters for the DFIG system. The proposed control strategy is validated via simulation study based on the synergy of several software packages including the TurbSim and FAST developed by NREL, Simulink and SimPowerSystems.
Characterization of Lateral Flagella of Selenomonas ruminantium
Authors: Haya Shohei , Tokumaru Yuya , Abe Naoki , Kaneko Jun , Aizawa Shin-ichi
Published: February 2011

Selenomonas ruminantium
produces a tuft of flagella near the midpoint of the cell body and swims by rotating the cell body along the cell's long axis. The flagellum is composed of a single kind of flagellin, which is heavily glycosylated. The hook length of
S. ruminantium
is almost double that of
Salmonella
.
Deletion or Overexpression of Mitochondrial NAD
+
Carriers in
Saccharomyces cerevisiae
Alters Cellular NAD and ATP Contents and Affects Mitochondrial Metabolism and the Rate of Glycolysis
Authors: Agrimi Gennaro , Brambilla Luca , Frascotti Gianni , Pisano Isabella , Porro Danilo , Vai Marina , Palmieri Luigi
Published: February 2011

The modification of enzyme cofactor concentrations can be used as a method for both studying and engineering metabolism. We varied
Saccharomyces cerevisiae
mitochondrial NAD levels by altering expression of its specific mitochondrial carriers. Changes in mitochondrial NAD levels affected the overall cellular concentration of this coenzyme and the cellular metabolism. In batch culture, a strain with a severe NAD depletion in mitochondria succeeded in growing, albeit at a low rate, on fully respiratory media. Although the strain increased the efficiency of its oxidative phosphorylation, the ATP concentration was low. Under the same growth conditions, a strain with a mitochondrial NAD concentration higher than that of the wild type similarly displayed a low cellular ATP level, but its growth rate was not affected. In chemostat cultures, when cellular metabolism was fully respiratory, both mutants showed low biomass yields, indicative of impaired energetic efficiency. The two mutants increased their glycolytic fluxes, and as a consequence, the Crabtree effect was triggered at lower dilution rates. Strikingly, the mutants switched from a fully respiratory metabolism to a respirofermentative one at the same specific glucose flux as that of the wild type. This result seems to indicate that the specific glucose uptake rate and/or glycolytic flux should be considered one of the most important independent variables for establishing the long-term Crabtree effect. In cells growing under oxidative conditions, bioenergetic efficiency was affected by both low and high mitochondrial NAD availability, which suggests the existence of a critical mitochondrial NAD concentration in order to achieve optimal mitochondrial functionality.
Cholate-Stimulated Biofilm Formation by Lactococcus lactis Cells
Authors: Zaidi Arsalan Haseeb , Bakkes Patrick J. , Krom Bastiaan P. , van der Mei Henny C. , Driessen Arnold J. M.
Published: February 2011

Bile acid resistance by
Lactococcus lactis
depends on the ABC-type multidrug transporter LmrCD. Upon deletion of the
lmrCD
genes, cells can reacquire bile acid resistance upon prolonged exposure to cholate, yielding the Δ
lmrCD
r
strain. The resistance mechanism in this strain is non-transporter based. Instead, cells show a high tendency to flocculate, suggesting cell surface alterations. Contact angle measurements demonstrate that the Δ
lmrCD
r
cells are equipped with an increased cell surface hydrophilicity compared to those of the parental and wild-type strains, while the surface hydrophilicity is reduced in the presence of cholate. Δ
lmrCD
r
cells are poor in biofilm formation on a hydrophobic polystyrene surface, but in the presence of subinhibitory concentrations of cholate, biofilm formation is strongly stimulated. Biofilm cells show an enhanced extracellular polymeric substance production and are highly resistant to bile acids. These data suggest that non-transporter-based cholate resistance in
L. lactis
is due to alterations in the cell surface that stimulate cells to form resistant biofilms.
Continuous Control of the Flow in Biochemical Pathways through 5′ Untranslated Region Sequence Modifications in mRNA Expressed from the Broad-Host-Range Promoter
Pm
Authors: Lale Rahmi , Berg Laila , Stüttgen Friederike , Netzer Roman , Stafsnes Marit , Brautaset Trygve , Vee Aune Trond Erik , Valla Svein
Published: February 2011

The inducible
Pm
promoter integrated into broad-host-range plasmid RK2 replicons can be fine-tuned continuously between the uninduced and maximally induced levels by varying the inducer concentrations. To lower the uninduced background level while still maintaining the inducibility for applications in, for example, metabolic engineering and synthetic (systems) biology, we report here the use of mutations in the
Pm
DNA region corresponding to the 5′ untranslated region of mRNA (UTR). Five UTR variants obtained by doped oligonucleotide mutagenesis and selection, apparently reducing the efficiency of translation, were all found to display strongly reduced uninduced expression of three different reporter genes (encoding β-lactamase, luciferase, and phosphoglucomutase) in
Escherichia coli
. The ratio between induced and uninduced expression remained the same or higher compared to cells containing a corresponding plasmid with the wild-type UTR. Interestingly, the UTR variants also displayed similar effects on expression when substituted for the native UTR in another and constitutive promoter,
P1
(

P
antitet

), indicating a broad application potential of these UTR variants. Two of the selected variants were used to control the production of the C
50
carotenoid sarcinaxanthin in an engineered strain of
E. coli
that produces the precursor lycopene. Sarcinaxanthin is produced in this particular strain by expressing three
Micrococcus luteus
derived genes from the promoter
Pm
. The results indicated that UTR variants can be used to eliminate sarcinaxanthin production under uninduced conditions, whereas cells containing the corresponding plasmid with a wild-type UTR produced ca. 25% of the level observed under induced conditions.
Reduction of Escherichia coli O157:H7 Shedding in Cattle by Addition of Chitosan Microparticles to Feed
Authors: Jeong Kwang Cheol , Kang Min Young , Kang Jihun , Baumler David J. , Kaspar Charles W.
Published: February 2011

Enterohemorrhagic
Escherichia coli
O157:H7 (EHEC) is a significant human pathogen that resides in healthy cattle. It is thought that a reduction in the prevalence and numbers of EHEC in cattle will reduce the load of EHEC entering the food chain. To this end, an intervention strategy involving the addition of chitosan microparticles (CM) to feed in order to reduce the carriage of this pathogen in cattle was evaluated. Experiments with individual Holstein calves and a crossover study found that the addition of CM to feed decreased
E. coli
O157:H7 shedding. In the crossover study, CM resulted in statistically significant reductions in the numbers recovered from rectal swab samples (
P
< 0.05) and the duration of shedding (
P
< 0.05). The effects of feeding CM to calves differed, indicating that the optimal levels of CM may differ between animals or that other factors are involved in the interaction between CM and
E. coli
O157:H7.
In vitro
studies demonstrated that
E. coli
O157:H7 binds to CM, suggesting that the reduction in shedding may result at least in part from the binding of positively charged CM to negatively charged
E. coli
cells. Additional studies are needed to determine the impact of CM feeding on animal production, but the results from this study indicate that supplementing feed with CM reduces the shedding of
E. coli
O157:H7 in cattle.
Improvement of the Efficacy of Linear Undecapeptides against Plant-Pathogenic Bacteria by Incorporation of
d
-Amino Acids
Authors: Güell Imma , Cabrefiga Jordi , Badosa Esther , Ferre Rafael , Talleda Montserrat , Bardají Eduard , Planas Marta , Feliu Lidia , Montesinos Emilio
Published: February 2011

A set of 31 undecapeptides, incorporating 1 to 11
d
-amino acids and derived from the antimicrobial peptide BP100 (KKLFKKILKYL-NH
2
), was designed and synthesized. This set was evaluated for inhibition of growth of the plant-pathogenic bacteria
Erwinia amylovora
,
Pseudomonas syringae
pv. syringae, and
Xanthomonas axonopodis
pv. vesicatoria, hemolysis, and protease degradation. Two derivatives were as active as BP100, and 10 peptides displayed improved activity, with the all-
d
isomer being the most active. Twenty-six peptides were less hemolytic than BP100, and all peptides were more stable against protease degradation. Plant extracts inhibited the activity of BP100 as well as that of the
d
-isomers. Ten derivatives incorporating one
d
-amino acid each were tested in an infectivity inhibition assay with the three plant-pathogenic bacteria by using detached pear and pepper leaves and pear fruits. All 10 peptides studied were active against
E. amylovora
, 6 displayed activity against
P. syringae
pv. syringae, and 2 displayed activity against
X. axonopodis
pv. vesicatoria. Peptides BP143 (KKL
F
KKILKYL-NH
2
) and BP145 (K
K
LFKKILKYL-NH
2
), containing one
d
-amino acid at positions 4 and 2 (underlined), respectively, were evaluated in whole-plant assays for the control of bacterial blight of pepper and pear and fire blight of pear. Peptide BP143 was as effective as streptomycin in the three pathosystems, was more effective than BP100 against bacterial blight of pepper and pear, and equally effective against fire blight of pear.
Lack of Correlation between Turnover of Low-Molecular-Weight Dissolved Organic Carbon and Differences in Microbial Community Composition or Growth across a Soil pH Gradient
Authors: Rousk Johannes , Brookes Philip C. , Glanville Helen C. , Jones David L.
Published: February 2011

We studied how soil pH (pHs 4 to 8) influenced the mineralization of low-molecular-weight (LMW)-dissolved organic carbon (DOC) compounds, and how this compared with differences in microbial community structure. The mineralization of LMW-DOC compounds was not systematically connected to differences in soil pH, consistent with soil respiration. In contrast, the microbial community compositions differed dramatically. This suggests that microbial community composition data will be of limited use in improving the predictive power of soil C models.
Protein Kinase B Gene Homologue
pkbR1
Performs One of Its Roles at First Finger Stage of Dictyostelium
Authors: Ochiai Hiroshi , Takeda Kosuke , Fukuzawa Masashi , Kato Atsushi , Takiya Shigeharu , Ohmachi Tetsuo
Published: February 2011

Dictyostelium discoideum
has protein kinases AKT/PKBA and PKBR1 that belong to the AGC family of kinases. The protein kinase B-related kinase (PKBR1) has been studied with emphasis on its role in chemotaxis, but its roles in late development remained obscure. The
pkbR1
null mutant stays in the first finger stage for about 16 h or longer. Only a few aggregates continue to the migrating slug stage; however, the slugs immediately go back probably to the previous first finger stage and stay there for approximately 37 h. Finally, the mutant fingers diversify into various multicellular bodies. The expression of the
pkbR1
finger protein probably is required for development to the slug stage and to express
ecmB
, which is first observed in migrating slugs. The mutant also showed no
ST-lacZ
expression, which is of the earliest step in differentiation to one of the stalk cell subtypes. The
pkbR1
null mutant forms a small number of aberrant fruiting bodies, but in the presence of 10% of wild-type amoebae the mutant preferentially forms viable spores, driving the wild type to form nonviable stalk cells. These results suggest that the mutant has defects in a system that changes the physiological dynamics in the prestalk cell region of a finger. We suggest that the arrest of its development is due to the loss of the second wave of expression of a protein kinase A catalytic subunit gene (
pkaC
) only in the prestalk region of the
pkbR1
null mutant.
Role of Four Calcium Transport Proteins, Encoded bynca-1,nca-2,nca-3, andcax, in Maintaining Intracellular Calcium Levels in Neurospora crassa
Authors: Bowman Barry J. , Abreu Stephen , Margolles-Clark Emilio , Draskovic Marija , Bowman Emma Jean
Published: February 2011

We have examined the distribution of calcium inNeurospora crassaand investigated the role of four predicted calcium transport proteins. The results of cell fractionation experiments showed 4% of cellular calcium in mitochondria, approximately 11% in a dense vacuolar fraction, 40% in an insoluble form that copurifies with microsomes, and 40% in a high-speed supernatant, presumably from large vacuoles that had broken. Strains lacking NCA-1, a SERCA-type Ca2+-ATPase, or NCA-3, a PMC-type Ca2+-ATPase, had no obvious defects in growth or distribution of calcium. A strain lacking NCA-2, which is also a PMC-type Ca2+-ATPase, grew slowly in normal medium and was unable to grow in high concentrations of calcium tolerated by the wild type. Furthermore, when grown in normal concentrations of calcium (0.68 mM), this strain accumulated 4- to 10-fold more calcium than other strains, elevated in all cell fractions. The data suggest that NCA-2 functions in the plasma membrane to pump calcium out of the cell. In this way, it resembles the PMC-type enzymes of animal cells, not the Pmc1p enzyme inSaccharomyces cerevisiaethat resides in the vacuole. Strains lacking thecaxgene, which encodes a Ca2+/H+exchange protein in vacuolar membranes, accumulate very little calcium in the dense vacuolar fraction but have normal levels of calcium in other fractions. Thecaxknockout strain has no other observable phenotypes. These data suggest that “the vacuole” is heterogeneous and that the dense vacuolar fraction contains an organelle that is dependent upon the CAX transporter for accumulation of calcium, while other components of the vacuolar system have multiple calcium transporters.