bluuebunny/crossref_metadata_2025 huggingface dataset:
An Instant Center Approach to the Conceptual Design of Compliant Mechanisms
Authors: Kim Charles J. , Kota Sridhar , Moon Yong-Mo
Published: April 2009

The conceptual design of compliant mechanisms is generally performed using one of two methods: topology optimization or the Pseudo-Rigid-Body Model. In this paper, we present a conceptual design methodology which utilizes a building block approach. The concept of the instant center is developed for compliant mechanisms and is used to characterize the building blocks. The building block characterization is used in guiding the problem decomposition. The compliant four-bar building block is presented as a base mechanism for the conceptual design. The geometric advantage is used as a quantitative measure to guide the designer in determining the shape of the building block. An example problem demonstrates the methodology’s capacity to obtain viable conceptual designs in a straightforward manner. Resulting mechanisms satisfy initial kinematic requirements and are ready for further refinement using size and geometry optimization.
High Precision Compliant Parallel Robot With an Optimized Large Workspace
Authors: Raatz Annika , Wrege Jan , Soetebier Sven , Hesselbach Ju¨rgen
Published: April 2009

In this paper a macro parallel robot is presented in which conventional bearings are replaced by pseudo-elastic flexure hinges. The robot consists of a spatial parallel structure with three translational degrees of freedom and is driven by three linear direct drives. The structure has been optimized with respect to workspace and transmission ratio. Additionally, in simulations with the FEM tool ANSYS different geometrical arrangements and combinations of flexure hinges have been investigated with respect to the dynamic behavior of the compliant mechanism. Due to the symmetrical character of the structure and the optimized design of the combined flexure hinges the structure is very stiff. The experimental measured repeatability of the compliant robot is below 0.3 μm.
Closed-Loop Tape Springs as Fully Compliant Mechanisms: Preliminary Investigations
Authors: Vehar Christine , Kota Sridhar , Dennis Robert
Published: April 2009

The paper introduces tape springs as elements of fully compliant mechanisms. The localized folds of tape springs serve as compact revolute joints, with a very small radius and large range of motion, and the unfolded straight segments serve as links. By exploiting a tape spring’s ability to function as both links and joints, we present a new method of realizing fully compliant mechanisms with further simplification in their construction. Tape springs, typically found in carpenter tape rules, are thin-walled strips having constant thickness, zero longitudinal curvature, and a constant transverse curvature. The paper presents a closed-loop tape spring mechanism. By representing its folds as idealized revolute joints and its variable length links as sliding joints connecting rigid links, we present a modified Gruebler’s equation to determine its kinematic and idle degrees of freedom. To realize practical utility of tape spring mechanisms, we propose a simple actuation scheme incorporating shape memory alloy (SMA) wire actuators and successfully demonstrate its performance with a proof-of-concept prototype. The paper also presents potential applications for actuated tape spring mechanisms including a large displacement translational mechanism, planar positioning mechanisms, bi-stable, multi-stable, and variable stiffness mechanisms.
A Parallel 5 DOF Positioner for Semi-Spherical Workspaces
Authors: Maurin Benjamin , Bayle Bernard , Gangloff Jacques , de Mathelin Michel , Piccin Olivier
Published: April 2009

In this paper, a new five-degree-of-freedom parallel manipulator is described and modeled. This structure has been specially designed for medical applications that require in the same time mobility, compactness and accuracy around a functional point. The purpose of this robotic device is to help practitioners to perform accurate needle insertions while preserving them from harmful intra-operative X-ray imaging devices. The system is built from revolute joints, among which only five joints are actuated to convey the required five degrees of freedom to its moving platform. A numerical simulation of the workspace and a physical prototype are presented.
Active Suspension Control via Redundant Actuation
Authors: Freeman Robert A.
Published: April 2009

The use of redundant actuation in the design and control of active automotive suspension systems is described. Redundantly actuated systems consist of more active force / torque inputs than degrees-of-freedom and allow for active control of the effective stiffness of the system to the environment without a change in the equilibrium position. A frontal plane half-car, double A-arm, independent suspension model is investigated. Results show that five actuators, with one connecting the two suspensions, is required for full stiffness and motion control. Due to the dependence of this approach on correct stiffness modeling a previously developed stiffness model is reviewed. The validity of this model is illustrated through some simple yet sufficient examples.
Geometric Constructions for Determining the Screw Reciprocal to Five Lines
Authors: Collins Curtis L.
Published: April 2009

Screws reciprocal to five lines appear in the inverse Jacobian and statics equations of many serial and parallel robots. By closely examining the geometry of systems of five lines, a set of geometric procedures for computing reciprocal screws is derived. The methodology is based on the fact that one screw in a cylindroid reciprocal to four lines is reciprocal to a fifth independent line. The constructions are easy to implement and provide geometric insight into reciprocal screws and singularities.
3D Path Planning and Real-Time Simulation for Robot Manipulators With Applications to Aerospace Manufacturing
Authors: Lambert Jason Michel , Mantegh Iraj , Perron Claude
Published: April 2009

This paper presents a practical scheme for path and trajectory generation with applications in real-time simulation of robotic systems. The path planning is solved as a series of local obstacle avoidance problems which produce via points in the 3D Cartesian space as well as the normal vector to the obstacle surface at each via point. This vector is later utilized for trajectory generation. An intermediate orientation representation is used to guarantee continuity at the angular acceleration level for real-time simulation and control purposes. The proposed method is implemented in a real-time simulation environment for testing and final application. The real-time data generation allows hardware-in-the loop simulation, which is crucial in many aerospace applications.
Design of a Gravity-Balanced Assistive Device for Sit-to-Stand Tasks
Authors: Fattah Abbas , Agrawal Sunil K. , Fitzgibbons John
Published: April 2009

The joint torques in hip, knee and ankle are computed using inverse dynamic model during standing up for a paraplegic patient. The joint torque comprises the dynamical torque due to the inertia forces, and a passive torque due to the muscles and gravitational torque. It has been observed that the contribution to the joint torques by the gravitational torque is dominant. On the basis of this result, a gravity balanced assistive device is proposed for the elderly and impaired people such as spinal cord injury and paraplegic patients. This passive device uses a hybrid method to identify the center of mass of the system using auxiliary parallelograms first. Next appropriate springs are connected to the device to vanish the total potential energy of the system due to the gravity during standing up. A prototype with the underlying principles is currently being fabricated at the University of Delaware.
Linkage Mechanisms With Cam Integrated Joints for Controlled Harmonic Content of the Output Motion: Theory and Application
Authors: Yuan L. , Rastegar J.
Published: April 2009

In a recent study, the authors presented a systematic method for the modification of the output motion of linkage mechanisms with closed-loop chains using cams positioned at one or more of the mechanism joints. In this paper, the method is applied to the design of a linkage mechanism with an integrated cam mechanism for the purpose of eliminating the high harmonic component of the output link motion. The mechanism may be synthesized using well-developed linkage mechanism synthesis techniques for the intended application. Based on this method, a cam mechanism is synthesized for a prescribed output link motion while limiting the output motion to a simple harmonic motion with the frequency of its constant input velocity. The mechanism is constructed and tested. In mechanisms with relatively rigid links, the primary source of high harmonics in the output motion is the nonlinearity of the kinematics of their closed-loop chains. With the present method, a selected range or ranges of high harmonic motions generated due to such nonlinearities may be eliminated by integrating appropriately designed cams. By eliminating the high harmonic component of the output motion of a mechanism, the potential vibrational excitation that the mechanism can impart on the overall system, including its own structure, is greatly reduced. The resulting system should therefore be capable of operating at higher speeds and with increased precision.
Design and Control of Path-Following Compliant Mechanisms
Authors: Swan Colby C. , Rahmatalla Salam F.
Published: April 2009

A control algorithm to manipulate the input actuation forces on hinge-free compliant mechanism models synthesized utilizing continuum topology optimization formulations is implemented and successfully tested in this work, such that the mechanisms follow their specified trajectories and nearby trajectories with high degree of accuracy even when confronted with different resistance forces. The validity of the proposed formulations is tested and demonstrated on number of practical problems involving finite deformation.
Sparse Monolithic Compliant Mechanisms Using Continuum Structural Topology Optimization
Authors: Rahmatalla Salam , Swan Colby C.
Published: April 2009

A formulation for design of continuous, hinge-free compliant mechanisms is developed and examined within a continuum structural topology optimization framework. The proposed formulation involves solving two nested optimization problems. In the inner problem the arrangement of a constrained amount of structural material is optimized to maximize the mechanism’s mutual potential energy in response to a force loading at the input port while working against artificial springs on the input and output ports. As the relative stiffness of the artificial springs increases, the material continuity of the mechanism also increases to the point where de facto “hinge” regions are eliminated. In the outer problem, one solves for an appropriate amount of structural material that yields the desired compliance characteristics of the mechanism when working against the workpiece resistance. Different aspects of the proposed formulation are demonstrated on a number of examples and discussed.
Non-Invasive Laser Based Measurement of the Helicoidal Motion of a Vibratory Platform With Three Leaf-Spring Legs
Authors: Silversides Richard W. , Dai Jian S. , Althoefer Kaspar A. , Seneviratne Lakmal
Published: April 2009

A vibratory platform is a crucial part of automated assembly and has a similar structure to many parallel mechanisms. To investigate the platform, it is necessary to measure the helicoidal motion produced. This paper develops a new way of measuring the helicoidal motion by using reflective projection and by developing an analytical relationship between the measured vectors. A further relationship is developed between the cross sectional area of the laser light, the displacement of the platform and the output voltage from a photodiode. The study leads to a novel development of a non-invasive laser based measuring device. The paper further develops a dynamic calibration method, leading to calibration methods for both angular and linear displacements. The method is then confirmed by measurement to an accuracy of 20μm.
Line Based Collision Detection of Cylindrical Rigid Bodies
Authors: Ketchel John S. , Larochelle Pierre M.
Published: April 2009

This paper presents a novel methodology for detecting collisions of cylindrically shaped rigid bodies moving in three dimensions. This algorithm uses line geometry and dual number algebra to exploit the geometry of cylindrical objects to facilitate the detection of collisions. First, the rigid bodies are modelled with infinite cylinders and a necessary condition for collision is evaluated. If the necessary condition is not satisfied then the two bodies do not collide. If the necessary condition is satisfied then a collision between the bodies may occur and we proceed to the next stage of the algorithm. In the second stage the bodies are modelled with finite cylinders and a definitive necessary and sufficient collision detection algorithm is employed. The result is a straight-forward and efficient means of detecting collisions of cylindrically shaped bodies moving in three dimensions. This methodology has applications in spatial mechanism design, robot motion planning, and workspace analyses of parallel kinematic machines such as Stewart-Gough platforms. A case study examining a spatial 4C mechanism for self collisions is included.
An Algorithm for Efficient Self-Reconfiguration of Chain-Type Unit-Modular Robots
Authors: Nelson Carl A. , Cipra Raymond J.
Published: April 2009

The problem of self-reconfiguration of modular robots is discussed, and an algorithm for efficient parallel self-reconfiguration is presented. While much of the previous work has been focused on the lattice-type modular robots, this paper addresses the self-reconfiguration of chain-type robots. Relatively little attention has heretofore been given to this sub-problem, and of the existing work, none incorporates the kinematic limitations of real-life robots into the reconfiguration algorithm itself. The method presented here is based on understanding a robot’s physical “composition” using a graph-theoretic robot representation, and it sheds new light on self-reconfiguration of chain-type modular robots by incorporating elements of the robot kinematics as part of the criteria in choosing reconfiguration steps.
Dynamic Balancing of Multi-Degree-of-Freedom Parallel Mechanisms With Multiple Legs
Authors: Wu Yangnian , Gosselin Cle´ment M.
Published: April 2009

This paper systematically presents an effective algorithm for the dynamic balancing of multi-degree-of-freedom parallel mechanisms with multiple legs and the dynamic equivalence between point masses and arbitrary moving platforms. The mass and inertia of the moving platform are replaced by point masses located at the points of attachment of the legs to the platform and the mechanisms are balanced by considering each of the legs independently. The validity and feasibility of this algorithm is first verified both theoretically and using numerical simulations in ADAMS. Two, three and four point masses are respectively discussed for different cases. Finally, some reactionless planar and spatial multi-degree-of-freedom parallel mechanisms synthesized based on this algorithm are given.
Workspace Delineation of Cable-Actuated Parallel Manipulators
Authors: Stump Ethan , Kumar Vijay
Published: April 2009

While there is extensive literature available on parallel manipulators in general, there has been much less attention given to cable-driven parallel manipulators. In this paper, we address the problem of analyzing the reachable workspace using the tools of semi-definite programming. We build on earlier work [1, 2] done using similar techniques by deriving limiting conditions that allow us to compute analytic expressions for the boundary of the reachable workspace. We illustrate this computation for a planar parallel manipulator with four actuators.
Optimal Synthesis of Compliant Mechanisms Using Subdivision and Commercial FEA
Authors: Hull Patrick V. , Canfield Stephen
Published: April 2009

The field of distributed-compliance mechanisms has seen significant work in developing suitable topology optimization tools for their design. These optimal design tools have grown out of the techniques of structural optimization. This paper will build on the previous work in topology optimization and compliant mechanism design by proposing an alternative design space parameterization through control points and adding another step to the process, that of subdivision. The control points assist a specific design to be represented as a solid model during the optimization process. The process of subdivision creates an additional number of control points that help smooth the surface (for example a C2 continuous surface depending on the method of subdivision chosen) creating a manufacturable design free of traditional numerical instabilities. Note that these additional control points do not add to the number of design parameters. This alternative parameterization and description as a solid model effectively and completely separates the design variables from the analysis variables during the optimization procedure. The motivation behind this work is to avoid several of the numerical instabilities that occur in topology optimization and to create an automated design tool from task definition to functional prototype created on a CNC or rapid-prototype machine. This paper will describe the complaint mechanism design process including subdivision and will demonstrate the procedure on several common examples.
Maximizing Walking Step Length for a Near Omni-Directional Hexapod Robot
Authors: Schmiedeler James P. , Bradley Nathan J. , Kennedy Brett
Published: April 2009

A foot path planning algorithm is presented for a robot with six limbs symmetrically located on the faces of its hexagonal body, enabling it to walk at a constant height with an alternating tripod gait. The symmetry results in near omni-directional locomotion capability, so the algorithm is formulated for walking in any direction and at any height. The approach is to determine the maximum length foot path through each limb’s workspace and then modify those foot paths based upon static stability analysis. The stability analysis is conducted in two phases to ensure stability without excessively reducing step length. Compared to an optimization approach, the algorithm yields foot paths within 9.1% of the maximal foot paths for all directions and heights. Unlike the optimization approach, the developed algorithm is computationally efficient enough to be implemented in realtime.
A Contact-Aided Compliant Mechanical Cycle-Doubler: Preliminary Analysis and Testing
Authors: Mankame Nilesh D. , Ananthasuresh G. K.
Published: April 2009

The performance of a contact-aided compliant mechanism that functions as a cycle doubler is studied in this paper via nonlinear finite element simulations. The topology of this mechanism was obtained from a systematic synthesis procedure and is reported elsewhere. Although the design was obtained for a quasi-static specification, the kinematic characteristics of the design suggest its ability to function adequately at low to moderate frequencies. The scalability of the design and its single-piece construction enable fabrication using different materials at various length scales. Therefore, it is possible to choose a scale and material combination that yields the frequency doubling action for various input frequencies. Explicit dynamic nonlinear finite element simulations are used to verify the functionality of the design at two different length scales: macro (device footprint of 289 sq. cm) corresponding to an input frequency of 20 Hz and meso (device footprint of a square of 14.3 sq. cm) corresponding to an input frequency of 1 kHz. Experiments on a macro scale prototype are used to validate the FE simulations for low frequencies.
Kinematic Registration Using Line Geometry
Authors: Eberharter Johannes K. , Ravani Bahram
Published: April 2009

This paper uses line geometry to find an elegant solution to the kinematic registration problem involving reconstruction of a spatial displacement from data on three homologous points at two finitely separated positions of a rigid body. The bisecting linear line complex of two position theory in kinematics is used in combination with recent results from computational line geometry to present an elegant computational geometric method for the solution of this old problem. The results have applications in robotics, manufacturing, and biomedical imaging. The paper considers when minimal, over-determined, and perturbed sets of point data are given.
Intelligent Mechanisms
Authors: Chew Meng-Sang , Longman Richard W. , Phan Minh Q.
Published: April 2009

An intelligent mechanism is a traditional mechanism that incorporates within it, elements of intelligence both at the design stage. Thepurpose is to increase the operational envelop of the original meachanism so that it can now exhibit some from of learning, adapting, or responding to changes in the environment or new operating conditions. Since mechanisms are usually designed for repetitive motions, the application of intelligence that makes specific use of repetitive characteristics will markedly improve the functionality of the mechanisms. This is particularly true if the mechanisms have been incorporated with such intelligence at the early stages of design. This article develops the concept of an intelligent mechanism through the application of Iterative Learning Control and Repetitive Control methodologies to several traditional mechanisms. These range from the simple slider-crank and four-bar linkage to timing belts.
Kinematic Calibration for Redundantly Actuated Parallel Mechanisms: Theory and Application for 2-DOF Mechanism
Authors: Jeong Jay il , Kang Dongsoo , Kim Jongwon
Published: April 2009

We present a new kinematic calibration algorithm for redundantly actuated parallel mechanisms. The calibration algorithm for a non-redundant case does not apply for a redundantly actuated parallel mechanism, because the angle error of the actuating joint varies with position and the geometrical constraint fails to be consistent. Such change of joint angle error comes from constraint torque variation with each kinematic pose. To calibrate a redundant parallel mechanism, one therefore has to consider constraint torque equilibrium and the relationship of constraint torque to torsional deflection, in addition to geometric constraint. In this paper, we develop the calibration algorithm for a redundantly actuated parallel mechanism using these three relationships, and formulate cost functions for an optimization algorithm. As a case study, we executed the calibration of a 2-degree of freedom (DOF) parallel mechanism with three actuators using the developed algorithm. Coordinate values of tool plate were measured using a laser ball bar and the actual kinematic parameters were identified with a new cost function of the optimization algorithm. Experimental results showed that the accuracy of the tool plate improved by 82% after kinematic calibration in a redundant actuation case.
Design of a Mobile Platform for Overhead Detectors for Vehicles on the Highway
Authors: Duane Jacob S. , Palen Joe A. , Eke Fidelis O. , Cheng Harry H.
Published: April 2009

The California Department of Transportation, like many such departments in the United States, is working on developing a new family of electronic sensing devices for the purpose of monitoring certain characteristics of road vehicles as they move along the highway. The devices currently under development are to be located overhead individual highway traffic lanes, from where they can have a clear “view” of ground vehicles. In order to deploy these devices, there is a need to develop the capability to safely and efficiently mount them above highway traffic lanes, using existing overhead bridges and sign structures as support structures. This paper presents a technical study of a universal support platform for these devices. The study discusses such issues as mobility, reliability, and resistance to environmental and other hazards. Results of tests conducted on a prototype are also presented.
Design of Harmonic Motion Generating RSSR Four Bar Mechanisms for High Speed Application
Authors: Farhang Kambiz , Ghatti Vinay , Cabradilla Jorge M.
Published: April 2009

Consideration of a mechanism for high-speed application inevitably poses certain kinematic design requirements that can be cast as a function generation synthesis problem involving the entire motion cycle of the mechanism. This paper addresses such application of RSSR four bar mechanisms for high-speed application. It employs a perturbational kinematic analysis of the mechanism to obtain approximate equations relating the follower and input angular displacements. The follower angular motion is derived, approximately, as a linear combination of two simple harmonic functions, in terms of the first and second harmonics of the crank angle. Albeit the exact mathematical description relating the input and output links exists it is not conductive to a kinematic design for dynamic performance. In contrast the approximate equations derived in this paper enable function generation of RSSR four bar mechanisms in which the higher harmonics of the input link are minimized. This utility of the approximate equations are demonstrated through several mechanism design examples.
Derivation of Friction Torque-Speed Relation Due to Viscoelastic Contact in a Two-Disk Brake
Authors: Farhang Kambiz , Lim Aik-Liang
Published: April 2009

Using a nonlinear model of a two disk brake system, coupled equations of motion are found for their frictional interaction. The mathematical formulation relates the tribological events at micron-scale and the macroscopic scale vibration response of a two-disk brake system. This is accomplished by a visco-elastic account of interaction at the micron scale, its statistical quantification through the approximate analytical representation of the statistical expectation of contact force and the introduction of the contact force into the macro-scale dynamics of the two-disk system. Steady-state analysis of the system establishes the relation between friction torque and speed and supports observed behavior of many mechanical systems with friction. It is shown that, as a result of coupling of the macro-system’s dynamics and contact, there are combinations of parameters at the micro-and macro-scale that yield negative slope in friction torque/sliding speed relation, a well known source of dynamic instability. This results in an effective negative damping that tends to decrease with decrease in the normal load and/or increase in structural damping of the system.
A Vibration Model of a Suspension-Tire System
Authors: Mohamad Naser , Farhang Kambiz
Published: April 2009

A two-dimensional suspension-Tire system is modeled to investigate the dynamic interaction between the suspension and the tire of an automotive system. A double A-arm suspension system is used in the model. Lagrange equation for a constrained set of generalized coordinates is employed to derive a lumped-mass model of the system. The effects of friction and mechanical characteristics of the tire-road interface in both lateral and vertical directions is modeled and utilized in the system’s dynamics using the Magic Formula for tire. The utilization of Lagrange equation along with the Magic Formula provided a means of prediction of the system’s dynamic response to different initial sprung mass load conditions and the alteration and optimization of the suspension system geometry to achieve minimum sprung mass and tire vibration. The model is used to illustrate tire slip angle variation as a result of induced vibration due to a step load along the vertical and lateral direction. Albeit the response is a damped nonlinear vibration response, the system shows relatively large variation in slip angle in the transient regime of the system response.
Eliminating Structural Error in Real-Time Adjustable Four-Bar Path Generators Using Iterative Learning Control
Authors: Chen Hong-Jen , Longman Richard W. , Chew Meng-Sang
Published: April 2009

Fundamental concepts of Iterative Learning Control (ILC) are applied to path generating problems in mechanisms. As an illustration to such class of problems, an adjustable four-bar linkage is used. The coupler point of a four-bar traces a coupler curve that will in general deviate from the desired coupler path. Except at the precision points, the coupler curve will exhibit some structural error, which is the deviation from the specified curve. The structural error will repeat itself every cycle at exactly the same points over the range of interest. Since ILC is a methodology that was developed to handle similar repetitive errors in control systems, it is believed that it will be well served to apply it to this class of problems. Results show that ILC can be simple to implement, and it is found to be very well suited for such path generation problems.
Control Modes for a Three-Dimensional Galloping Machine
Authors: Waldron Kenneth J. , Kallem Vinutha
Published: April 2009

A set of relationships are developed to estimate the effects of control inputs on different axes of a galloping machine. It is demonstrated that control must be approached on a stride cycle basis to avoid serious cross-coupling between degrees of freedom. It is also demonstrated that a somewhat different approach to the Raibert controller is necessary for galloping. The relationships developed are primarily useful to estimate sensitivities to different control approaches, and thereby develop useful design information. Their use is illustrated by calculating sensitivities for our KOLT galloping vehicle.
Case Study of Energy Flow in Cyclic Systems: Walking Machine
Authors: Mukherjee S. , Sangwan V. , Taneja A.
Published: April 2009

A self-excited biped walking mechanism consisting of two legs that are connected in a series at the hip joint through a servomotor is studied as a cyclic system with collisions. A torque proportional to angle between the shank and the vertical is seen to sustain a gait. Each leg has a thigh and a shank connected at a passive knee joint that has a knee stopper restricting the forward motion like the human knee. A mathematical model for the dynamics of the system including the impact equations is used to analyse the stability of the system through examination of phase plane plots. Phase plane plots along with energy flow during the cycle show the nature of the system.
Screw System Analysis of Parallel Mechanisms and Applications to Constraint and Mobility Study
Authors: Dai Jian S. , Huang Zhen , Lipkin Harvey
Published: April 2009

The Kutzbach-Gru¨bler mobility criterion calculates the degrees-of-freedom of a general mechanism. However, the criterion can break down for mechanisms with special geometries, and in particular, the class of so-called overconstrained mechanisms. The problem is that the criterion treats all constraints as active, even redundant constraints, which do not affect the mechanism degrees-of-freedom. This paper examines the screw systems of a parallel mechanism to identify the redundant constraints. The screw system characteristics and relationships are then investigated for physical properties. Then a new approach to mobility analysis is proposed based on screw system decompositions. A new version of the mobility criterion is presented to eliminate the redundant constraints and correctly predict the platform degrees-of-freedom. Several examples of overconstrained mechanisms from the literature illustrate the results.
Shape Optimization of a Compliant Mechanism for an Actively Conformable Rotor Airfoil
Authors: Nissly Andrew , Anusonti-Inthra Phuriwat , Frecker Mary , Gandhi Farhan
Published: April 2009

In the present study, the optimal shape of a limited amount of passive material in a compliant mechanism of predetermined topology was determined. The simple compliant mechanism with a small number of actuators can be packaged in the long, narrow space of the rotor airfoil cross-section. The compliant mechanism is designed for maximum rotation angle under actuation loads, and minimum deflection under aerodynamic loads. Rotation angle (RA) and Strain Energy (SE), are used as measures of the deflections created by the actuation and aerodynamic loads, respectively. The design objectives are achieved by maximizing a multi-criteria objective function that represents a ratio of the RA to SE. Shape optimization of the compliant mechanism is conducted and the results indicate that the optimal compliant mechanism consists of a passive substructure with uniform cross section. The optimal geometry of the compliant mechanism is also determined in a parametric study (optimal ratio of the length to height of 0.3), and this structure can produce rotation angle of 13 Deg/m. when the actuators provide 1% actuation strain. The deflection due to aerodynamic loads is extremely small. The performance of the mechanism is examined further with variations in material and actuator properties. Additional results include an analysis of a compliant mechanism structure based on a modified topology, which is introduced to reduce numbers of actuators.
Modeling and Design of an Optically Powered Microactuator for a Microfluidic Dispenser
Authors: Deshpande Mandar , Saggere Laxman
Published: April 2009

This paper presents the modeling and design of an optically powered piezolectric microactuator for application in actuating and dispensing small amounts of fluid from a novel microfluidic device. This work is motivated by an ongoing project towards the development of a novel retinal prosthesis that requires such a device. The microactuator treated in this paper comprises of a solar cell integrated with a piezoelectric microactuator consisting of an active piezoelectric layer and a passive silicon layer. An integrated model combining various components of the dispenser is derived and optimal dimensions of the microactuator are obtained so that the microfluidic dispenser meets the estimated application performance requirements.
Neural Mechanisms of a Genome-Wide Supported Psychosis Variant
Authors: Esslinger Christine , Walter Henrik , Kirsch Peter , Erk Susanne , Schnell Knut , Arnold Claudia , Haddad Leila , Mier Daniela , Opitz von Boberfeld Carola , Raab Kyeon , Witt Stephanie H. , Rietschel Marcella , Cichon Sven , Meyer-Lindenberg Andreas
Published: April 2009

A genetic polymorphism associated with schizophrenia conveys a risk for abnormal connectivity between brain regions.
Evidence for a Superglass State in Solid
4
He
Authors: Hunt B. , Pratt E. , Gadagkar V. , Yamashita M. , Balatsky A. V. , Davis J. C.
Published: April 2009

Glasslike Supersolid

Recent experiments with solid helium confined to the ring of a torsional oscillator at extremely low temperatures have been interpreted in terms of an exotic supersolid phase—a crystalline solid that somehow flows like a superfluid. However, behavioral differences between samples have raised many questions (see the Perspective by

Saunders

).

Hunt
et al.

(p.
632
) present a comprehensive study of the relaxation dynamics of the torsional oscillator system as a function of time and temperature. The data provides evidence for a “supersolid glass,” where glassy behavior of crystal dislocations and superfluidity can coexist. In a separate theoretical study,
Anderson
(p.
631
) argues that supersolidity ought to be a ground state for all bose solids, but that defects in the sample may mask the supersolid signature.
A Yeast Hybrid Provides Insight into the Evolution of Gene Expression Regulation
Authors: Tirosh Itay , Reikhav Sharon , Levy Avraham A. , Barkai Naama
Published: April 2009

Gene Expression in Hybrids

A large proportion of genes differ in their expression patterns between closely related species, and this divergence is believed to be an important driver of phenotypic evolution. However, little is known about the genetic basis of this divergence.

Tirosh
et al.

(p.
659
) use allele-specific expression profiling of two yeast species and their hybrid to identify which genes diverged in expression owing to changes in their genomic loci (cis) and which genes diverged owing to changes in their regulators (trans). The data can be used to explain the distinct gene expression pattern observed in the hybrid.
Burst Spiking of a Single Cortical Neuron Modifies Global Brain State
Authors: Li Cheng-yu T. , Poo Mu-ming , Dan Yang
Published: April 2009

Single-Cell Brain Switching

Different behavioral states of an animal are characterized by distinct patterns of global brain activity. For example, slow-wave sleep is associated with membrane potential transitions in cortical neurons and high-amplitude, low-frequency local field potential and electroencephalogram signals. In contrast, during rapid—eye-movement sleep and wakefulness, low-amplitude, high-frequency cortical activity dominates with neuronal membrane potentials fluctuating around a depolarized level.

Li
et al.

(p.
643
) asked whether action potentials in a single neuron can change global network activity. In a series of in vivo single-cell stimulation experiments, using intracellular stimulation via a whole-cell patch pipette, a brief episode of intracellular stimulation switched brain states.
A Cytidine Deaminase Edits C to U in Transfer RNAs in Archaea
Authors: Randau Lennart , Stanley Bradford J. , Kohlway Andrew , Mechta Sarah , Xiong Yong , Söll Dieter
Published: April 2009

Edited Information Flow

RNA is generally a faithful mirror of the information encoded in DNA. However, posttranscriptional RNA editing is a widespread phenomenon that can result in a translated protein differing from its gene code. A class of deaminase enzymes related to human APOBEC (apolipoprotein B editing complex protein) edit adenosines in eukaryotes.

Randau
et al.

(p.
657
) have discovered an addition to this enzyme family in prokaryotes that edits cytosine to uridine at the highly conserved and structurally critical position 8 in the majority of transfer RNAs of the hyperthermophilic archaebacterium
Methanopyrus kandleri
.
A Glassy State of Supersolid Helium
Authors: Saunders John
Published: April 2009

Disorder and defects appear to play an important role in the formation of a supersolid from helium-4 atoms.
Science in the White House
Authors: Holdren John P.
Published: April 2009

The U.S. President's science advisor—officially, the Assistant to the President for Science and Technology (S&T)—has the daunting task of providing accurate and timely input to the president, the vice president, and their senior advisors on the full range of S&T topics that bear on the policy challenges facing the nation, from economic recovery to national security to environmental sustainability. Besides these “S&T for policy” responsibilities, moreover, “policy for S&T” must be attended to: helping craft the S&T budgets for the executive-branch departments and agencies that support much of the country's R&D; partnering with the Domestic Policy Council and the Department of Education in efforts to strengthen science, technology, engineering, and mathematics (STEM) education; enhancing the capabilities and diversity of the science and engineering workforce; ensuring coordination and cooperation among the numerous governmental S&T initiatives that involve multiple agencies; advancing appropriate forms of international S&T cooperation; promoting openness, transparency, and scientific integrity in the conduct of the nation's S&T business; and more.
Complicated Supercomplexes
Authors: Livingston David M.
Published: April 2009

Molecular details of how proteins interact to repair DNA breaks reveal complexities that underlie their tumor-suppressive effects in different cancers.
As Swine Flu Circles Globe, Scientists Grapple With Basic Questions
Authors: Cohen Jon , Enserink Martin
Published: April 2009

Shortly after the Centers for Disease Control and Prevention rang the alarm about two cases of swine flu in southern California, scientists and health officials around the world went on alert, concerned that this never-before-seen virus could lead to a killer pandemic. But some say the world hasn't done nearly enough over the past 10 years to prepare for a pandemic.
Hundreds Gather for Rally to Defend Animal Research
Authors: Miller Greg
Published: April 2009

Last week marked what some hope will be a turning point in the clash of wills between proponents of biomedical research and animal-rights extremists. On 22 April, hundreds of people turned out for a pro-research rally at the University of California, Los Angeles.
‘Protein’ in 80-Million-Year-Old Fossil Bolsters Controversial
T. rex
Claim
Authors: Service Robert F.
Published: April 2009

A controversial finding that protein fragments can be recovered from dinosaur fossils has been replicated for the first time. On page
626
of this week's issue of
Science
, the same team reports finding an even larger number of protein fragments from an 80-million-year-old fossil from a duck-billed dinosaur, or hadrosaur, known as
Brachylophosaurus canadensis
.
On the Origin of The Immune System
Authors: Travis John
Published: April 2009

Did the immune system evolve to keep out harmful organisms, or is it like a bouncer at a nightclub, trained to allow the right microbes in and kick the less desirable ones out? In the fifth essay in
Science
's series in honor of the
Year of Darwin
, John Travis explores the evolution of the immune system.
Defying Skeptics, Richard Scheller Thinks Genentech Will Thrive
Authors: Miller Greg
Published: April 2009

Finally allowed to speak publicly, Richard Scheller, Genentech's new executive vice president for research and early development, spoke with
Science
last week about what the merger with Roche will (and mostly won't) mean for research at Genentech.
Corn-Based Ethanol Flunks Key Test
Authors: Charles Dan
Published: April 2009

In setting state rules for low-carbon fuels, California officials have calculated that corn ethanol is worse than gasoline.
Clinical Features That Affect Indirect-Hemagglutination-Assay Responses to
Burkholderia pseudomallei
Authors: Harris Patrick N. A. , Ketheesan Natkunam , Owens Leigh , Norton Robert E.
Published: April 2009

Melioidosis, a disease endemic to northern Australia and Southeast Asia, is caused by the soil saprophyte
Burkholderia pseudomallei
. The indirect hemagglutination assay (IHA) is the most frequently used serological test to help confirm exposure to the causative organism. However, despite culture-confirmed disease, patients often have a negative IHA result at presentation and occasionally fail to seroconvert in serial testing. We retrospectively examined results for all patients with culture-confirmed melioidosis from our laboratory between January 1996 and August 2008. One hundred forty patients had a recorded IHA titer at presentation, 71 of which were positive at a titer of 1:40 or greater. Fifty-three patients went on to have subsequent IHAs 1 month or more after presentation. The relationships between IHA responses and clinical features were examined. The presence of bacteremia was significantly associated with a negative IHA at presentation. The coexistence of diabetes was associated with the presence of a positive IHA at presentation. In total, 14 patients (26%) demonstrated persistently negative IHA titers upon serial testing. No clinical factors were found to be significantly associated with this phenomenon. Supplementary testing using melioidosis-specific immunoglobulin G by EIA demonstrated different effects, with only Aboriginal or Torres Straits Islander ethnicity being significantly associated with a positive EIA at presentation. Reasons for these findings are examined, and directions for future research are discussed.
Towards a New Reference Test for Surra in Camels
Authors: Tran Thao , Claes Filip , Verloo Didier , De Greve Henri , Büscher Philippe
Published: April 2009

Current serological diagnosis of
Trypanosoma evansi
infection in camels is based on the native variable antigen type RoTat 1.2. The goal of this study was to develop a novel serological diagnostic test based on a nonvariable protein and freed from the use of rats or mice for its production. An enzyme-linked immunosorbent assay using a recombinant extracellular domain of invariant surface glycoprotein 75 (ELISA/rISG75) was developed and tested on a collection of 184 camel sera. The results were compared to those obtained from three established antibody detection tests based on variable surface glycoprotein RoTat 1.2: an ELISA for
T. evansi
(ELISA/
T. evansi
), a card agglutination test for trypanosomiasis (CATT/
T. evansi
), and an immune trypanolysis (TL) assay. The ELISA/rISG75 and the ELISA/
T. evansi
showed a sensitivity of 94.6% (95% confidence interval [CI], 87.8 to 98.2%, at 19% positivity cutoff value) and 98.9% (95% CI, 94.1 to 99.8, at 12% positivity cutoff value), respectively. The ELISA/rISG75 had 100% specificity (CI, 95.9 to 100%), while the ELISA/
T. evansi
showed 98.9% specificity (CI, 95.9 to 100%). The ELISA/rISG75 demonstrated an almost perfect agreement with the TL assay, the CATT/
T. evansi
, and the ELISA/
T. evansi
, with kappa scores of at least 0.94. The ELISA/rISG75, having a performance comparable to that of the gold standard (the TL assay) and being independent of antigenic variation, may become a new reference test for surra in camels. It opens avenues for the diagnosis of
T. evansi
infections in other hosts as well as for the development of a pan-
Trypanozoon
test for detection of
Trypanosoma brucei brucei
,
T. b. gambiense
,
T. b. rhodesiense
,
T. evansi
, and
T. equiperdum
.
Epidemic of Postsurgical Infections Caused by
Mycobacterium massiliense
Authors: Duarte Rafael Silva , Lourenço Maria Cristina Silva , Fonseca Leila de Souza , Leão Sylvia Cardoso , Amorim Efigenia de Lourdes T. , Rocha Ingrid L. L. , Coelho Fabrice Santana , Viana-Niero Cristina , Gomes Karen Machado , da Silva Marlei Gomes , de Oliveira Lorena Nádia Suely , Pitombo Marcos Bettini , Ferreira Rosa M. C. , de Oliveira Garcia Márcio Henrique , de Oliveira Gisele Pinto , Lupi Otilia , Vilaça Bruno Rios , Serradas Lúcia Rodrigues , Chebabo Alberto , Marques Elizabeth Andrade , Teixeira Lúcia Martins , Dalcolmo Margareth , Senna Simone Gonçalves , Sampaio Jorge Luiz Mello
Published: April 2009

An epidemic of infections after video-assisted surgery (1,051 possible cases) caused by rapidly growing mycobacteria (RGM) and involving 63 hospitals in the state of Rio de Janeiro, Brazil, occurred between August 2006 and July 2007. One hundred ninety-seven cases were confirmed by positive acid-fast staining and/or culture techniques. Thirty-eight hospitals had cases confirmed by mycobacterial culture, with a total of 148 available isolates recovered from 146 patients. Most (
n
= 144; 97.2%) isolates presented a PRA-
hsp65
restriction pattern suggestive of
Mycobacterium bolletii
or
Mycobacterium massiliense
. Seventy-four of these isolates were further identified by
hsp65
or
rpoB
partial sequencing, confirming the species identification as
M. massiliense
. Epidemic isolates showed susceptibility to amikacin (MIC at which 90% of the tested isolates are inhibited [MIC
90
], 8 μg/ml) and clarithromycin (MIC
90
, 0.25 μg/ml) but resistance to ciprofloxacin (MIC
90
, ≥32 μg/ml), cefoxitin (MIC
90
, 128 μg/ml), and doxycycline (MIC
90
, ≥64 μg/ml). Representative epidemic
M. massiliense
isolates that were randomly selected, including at least one isolate from each hospital where confirmed cases were detected, belonged to a single clone, as indicated by the analysis of pulsed-field gel electrophoresis (PFGE) patterns. They also had the same PFGE pattern as that previously observed in two outbreaks that occurred in other Brazilian cities; we designated this clone BRA100. All five BRA100
M. massiliense
isolates tested presented consistent tolerance to 2% glutaraldehyde. This is the largest epidemic of postsurgical infections caused by RGM reported in the literature to date in Brazil.