bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Formation and Propagation of Macroscopic Martensitic Front in Shape Memory Alloy Wire
Authors: Ziółkowski A.
Published: July 2003

In the present paper we investigate the conditions under which the formation of a martensitic phase transformation front in a shape memory alloy (SMA) sample is possible at a macroscopic level. The phenomenon is a result of the interplay between thermal and mechanical effects. Specifically, it is shown that the shape memory materials exhibiting negligible or weak transformation hardening are prone to macroscopic transformation front formation. However, the constitutive law that regulates internal hysteresis loops formation is responsible for the internal structure of the propagating front. The phase transformation kinetics is dependent, among others, on the crystalline state of the sample (monocrystalline versus polycrystalline), its chemical composition and thermo-mechanical treatment. The present investigations are based on numerical simulations performed for a NiTi wire with the aid of finite element method. Thermo-mechanical coupling effects are taken into account during numerical simulation experiments.
On the Circuit Model of Piezoceramics
Authors: Park Chul H.
Published: July 2003

The proper equivalent interface circuit of a piezoelectric material below ultrasonic frequency range is developed and analyzed incorporating a voltage source and a capacitor theoretically and experimentally. The emphasis is placed on the physical connection between a capacitor and a voltage source. The first model considered is of a capacitor connected in series with a voltage source. The second model consists of a capacitor connected in parallel with a voltage source. This paper presents the analyses of these two different circuit models for a piezoceramic by discussing the electric impedance and phase angle of a piezoceramic theoretically and experimentally and determines the best-fit model of a PZT to use for structural vibration applications.
Behaviors and Performance Evaluation of a Lightweight Piezo-Composite Curved Actuator
Authors: Goo Nam Seo , Kim Cheol , Kwon Young-Doo , Yoon Kwang Joon
Published: July 2003

The present study investigates the behavior and performance of the recently proposed LIPCA actuator. As such, a reliable finite element program that can predict the behavior of piezoelectric structures is developed based on fully-coupled formulations for piezo electric materials and three-dimensional eight-node incompatible elements. After verifying the proposed code, the actuation displacements of a LIPCA actuator are calculated and compared with experimental results, which were foundto be in goodagreement. Finally, a method for modeling the screw-fixed end condition used in the experimental apparatus is investigated along with effects of the curvature on the actuation displacement and fundamental frequency.
Energy Dissipation Analysis of Piezoceramic Semi-Active Vibration Control
Authors: Corr Lawrence R. , Clark William W.
Published: July 2003

In this paper, the performances of two novel low frequency piezoceramic shunt techniques for structural damping are compared to the traditional passive resonant shunt circuit technique. The first novel technique is a semi-active variable stiffness technique in which bonded piezoceramic actuators are switched from the short circuit to open circuit states. This technique changes the stiffness of the structure for two quarters of its vibration period, thus dissipating energy. The second novel technique is a semi-active pulse switching technique in which a resistor-inductor shunt circuit is periodically connected to the bonded piezoceramic actuators. This technique applies charges to the piezoceramic actuators in a manner similar to the well-known Direct Velocity Feedback control technique. The energy dissipated from the structure depends on the magnitude of the applied charge. A description of energy dissipation mechanisms is shown for each switching method and for the traditional passive resonant shunt technique applied to a simple single degree of freedom system.
Piezoelectric Hydraulic Pump System Dynamic Model
Authors: Oates William S. , Lynch Christopher S.
Published: July 2003

A system dynamic model was developed for use in the design of piezohydraulic pumps. The model was implemented in MATLAB to predict the electrical/mechanical/fluid coupled behavior of the piezoelectric pump system. Model results were used in a performance assessment of a pumping system that was comprised of a stack actuator driven pump, accumulator, power supply, four-way valve, and hydraulic actuator. The model provided reasonable predictions of performance. Rate effects at higher voltage and frequency reduced pressure and flow rate performance. The heat generation of the piezoelectric stack actuator, flow resistance of the check valves, and compressibility of the fluid contributed to bandwidth limitations.
A Plate Electrostrictive Finite Element - Part I: Modeling and Variational Formulations
Authors: Pablo F. , Osmont D. , Ohayon R.
Published: July 2003

Piezoelectric plates have been widely used for the vibration reduction and noise control of structures. Due to power forces considerations, electrostrictive patches present a growing interest. It is thus the purpose of the present research to contribute to modeling aspects of thin structures integrating such actuators. Many three-dimensional finite element models have then been elaborated to simulate these structures behavior but no two-dimensional models have been presented up to now. The aim of this article is thus to set out the elaboration of a thin plate electrostrictive finite element for PMN-PT type ceramics used as actuators. This element is developed for dynamic purposes and thus takes into account phenomena induced by applying to the patch a cycling electric field. The finite element formulation is based on electromechanical constitutive equations derived in a previous paper, mechanical and electrical considerations and direct a priori plate assumptions. The electrostrictive finite element is here derived using techniques inspired from a piezoelectric finite element. This method has the particular property of reducing the initial electromechanical problem to a purely mechanical problem based on a modified elastic constitutive law. The electrical unknowns are then explicitly derived from the mechanical displacements. This method considerably simplifies the resolution of the problem since classical finite elements for laminated plates can be used to model the electrostrictive plate with a modified constitutive law. This paper is focused on the plate modeling and corresponding variational formulations.
Finite Element Modeling of Shape Memory Alloy Composite Actuators: Theory and Experiment
Authors: Ghomshei M. M. , Khajepour A. , Tabandeh N. , Behdinan K.
Published: July 2003

The present paper proposes a non-linear finite element model for the time response of a novel shape memory alloy (SMA) actuator. The actuator has a plane beam configuration composed of a matrix material with SMA sheets or wires embedded in and/or bonded to the matrix part. The finite element model can be used to analyze both active and passive (with or without heating activation) responses of this kind of actuators. Due to large shear stresses and deformations, the model is developed based on a higher order shear deformation beam theory together with the von-Karman strain field. A one-dimensional constitutive equation with non-constant material functions together with sinusoidal phase transformation kinetics is used for the thermo-mechanical behavior of the SMA actuator. The constitutive and phase transformation kinetic equations make distinction between the stress-induced and temperature-induced martensite fractions. To evaluate the model, the fabrication of a prototype SMA composite actuator for conducting experiments is briefly described and the experimental work performed on the prototype actuator is presented. The test results are compared with the finite element numerical results. A good agreement between the finite element and experimental results corroborate the nonlinear finite element modeling approach.
Simultaneous Active Damping and Health Monitoring of Aircraft Panels
Authors: Inman Daniel J. , Ahmadian Mehdi , Claus Richard O.
Published: July 2003

The concept of using the same hardware to perform both structural health monitoring and control simultaneously is explored. Aircraft panels often require damping treatments in order to reduce fatigue. At the same time, manufacturers are starting to use health monitoring as a basis for maintenance. Here, an example of doing simultaneous health monitoring and control on a sample plate is presented as experimental evidence that both functions can be performed with the same set of hardware. In this case, smart materials, a piezoceramic patch (PZT) and a fiber optic sensor, are used as the common hardware.
Modal Sensor for Axial Propagating Waves in an Infinite In-Vacuo Pipe
Authors: Variyart W. , Brennan M. J.
Published: July 2003

In an infinite in-vacuo pipe, the radial vibration can be decomposed into an infinite number of circumferential modes. For each mode, there is a right-going and a left-going propagating axial wave. In this paper, a sensor to detect either one of these waves is described. The wave chosen belongs to the first circumferential (n 1/4 2) mode of vibration, and the sensor consists of two PVDF (polyvinylidene fluoride) elements shaped in the form of sine and cosine functions. Two elements are required because the orientation of the wave at some arbitrary point on the pipe is generally unknown. The relationship between the charge generated on the element to the combination of axial and circumferential bending strains, is established for the case of in-extensional deformation. It is found that a practical sensor is sensitive to higher order modes as well as the n 1/4 2 mode, and this cross-sensitivity is dependent upon the width of the modal sensor. It is shown that the cross-sensitivity is small provided that the width of the modal sensor is less than one third of the wavelength of the propagating wave at the ring frequency. Experimental results are presented to validate the sensor sensitivity equation.
Active Structural Acoustic Control of a Launch Vehicle Fairing Using Monolithic Piezoceramic Actuators
Authors: Lane Steven A. , Griffin Steven , Leo Don
Published: July 2003

This study investigated the feasibility of using active structural acoustic control with monolithic piezoceramic actuators to reduce the low frequency noise transmission through rocket fairings during launch. Closed-loop simulation results are presented using a fully coupled structural acoustic model of a lightly damped composite fairing structure with integrated piezoceramic actuators. Constraints were placed on controller mass and maximum allowable actuator voltage in order to provide a baseline of reasonable expected performance. Realistic disturbance levels were used in the simulations, and two disturbance cases were considered with significantly different spectral characteristics. Simulations were conducted to compare the effects of actuator thickness, covered surface area, and maximum actuator voltage on controller performance and energy requirements. Linear Quadratic Regulator control laws were computed assuming full-state feedback using three design approaches. The results provide significant insight into the noise transmission problem and to the physical dynamics of the control approach. The best-case reduction in the spatially averaged interior acoustic response was determined to be approximately 2.5 dB over the 0-300 Hz bandwidth.
Overview of Modern Lithography Techniques and a MEMS-Based Approach to High Throughput Rate Electron Beam Lithography
Authors: Chase J. Geoffrey , Smith Bram W.
Published: July 2003

The ever-increasing drive to fabricate Integrated Circuits (ICs) with smaller feature sizes is stretching the capabilities of today’s optical lithography methods. Current research is focused on alternative lithographic techniques to create new platforms that more easily scale to sub-50 nm feature size and beyond. This paper presents an overview of alternative lithography technologies being investigated, analyzes them, and determines critical tradeoffs with respect to necessary production throughput rates. An alternative approach for sub-50 nm lithography that utilizes recent developments in smart materials and Micro-Electro-Mechanical Systems (MEMS) is then presented as a result of this analysis. Specifically, MEMS fabricated arrays of electron beam emitters offer the resolution and scalability of Multi-column Electron Beam Lithography (MEBL), while overcoming limitations in production rate, and optical complexity. The critical tradeoffs between significant variables are developed to determine the feasibility and define the design space of the approach presented. A highly parallel, multi-column EBL system with a production rate from 10-60 wafers/h at 50 nm resolution is shown to be feasible with near-term evolution in technology. This solution exploits converging technologies and represents a new leverage point where the application of MEMS technology creates significant innovation and new opportunities.
Effective Electroelastic Properties of a Piezocomposite with Viscoelastic and Dielectric Relaxing Matrix
Authors: Jiang B. , Batra R. C.
Published: July 2003

We use the correspondence principle of linear viscoelasticity and the Mori-Tanaka averaging method to determine the effective electroviscoelastic moduli of a piezocomposite made of piezoceramic (PZT) inclusions and a viscoelastic matrix whose dielectric constants also vary with time t. For elliptic cylindrical PZT inclusions, closed form expressions for the electroviscoelastic moduli are derived. It is found that for the 1-3 piezocomposite, the relaxation of the dielectric constants of the matrix affects only the dielectric moduli and the shear components of the piezoelectric and the viscoelastic moduli of the piezocomposite. However, the viscoelasticity of the matrix influences every effective electroelastic modulus of the piezocomposite. The relaxation times of any two effective moduli are different, and the piezocomposite is an orthotropic material. For time-harmonic loading of the piezocomposite studied, only frequencies in the range of 10 2- 102 Hz strongly influence the effective storage and the effective loss moduli. Whereas thin PZT ribbons provide the most mechanical strength to the piezocomposite, they give the least piezoelectric effect.
Actuator Power Reduction Using L-C Oscillator Circuits
Authors: Sirohi Jayant , Chopra Inderjit
Published: July 2003

Piezoelectric actuators are widely used in smart structural systems to actively control vibration and noise, and to enhance performance. Because of the highly capacitive nature of these actuators, special power amplifiers, capable of delivering large currents, are required to drive these systems. The large currents result in excessive heat generation, and are a cause of concern in designing rotating actuation systems with sliprings for power transmission. In this paper, a means of reducing the current drawn from the power amplifier is investigated. This is accomplished by incorporating the actuator in a tuned L-C oscillator circuit. Non-ideal circuit performance is addressed, along with theoretical limits to possible power savings and practical difficulties in achieving them. The practical limitation of the size of a physical inductor needed for this purpose is recognized and the use of an active pseudo-inductor is investigated. This pseudo-inductor is connected in parallel with a commercially available power amplifier and reduction in current drawn from the amplifier is demonstrated.
Experimental Aeroelastic Response of Piezoelectric and Aileron Controlled 3D Wing
Authors: Suleman Afzal , Crawford Curran , Costa Antonio P.
Published: July 2003

This paper presents the results of wind tunnel testing performed on a three-dimensional adaptive wing structure. The focus of this study was to test the aeroelastic response and control of a wing built with adaptive stressed skins. The aeroelastic performance of the wing using traditional aerodynamic control surface methods is compared to the results obtained using piezoelectric actuators bonded to the skins of the wing. Smaller piezoelectric sensors also bonded to the wing are used to provide feedback for the control law. Results are presented for the system identification, free stream vibration and buffeting tests performed in the wind tunnel.
Effect of Feedback Control on the Power Consumption of Induced-Strain Actuators
Authors: Chandrasekaran Sriram , Lindner Douglas K. , Leo Donald J.
Published: July 2003

In this paper we study the closed loop power flow characteristics between a controlled piezoelectric actuator and a current controlled drive amplifier for two different structural control laws. We determine the real and reactive power flow through the structure and actuator into the amplifier when the structure is excited with a sinusoidal disturbance force under both control laws. The dependence of the real and reactive components of the power on the material properties of the actuator, structure and the configuration of the controller is presented. These real and reactive power estimates are useful for sizing the drive amplifier for the actuator.
Design and Construction of a Piezoelectric Point Actuated Active Aperture Antenna
Authors: Angelino Marc R. , Washington Gregory N.
Published: July 2003

In this research, an antenna’s far field radiation pattern is controlled by controlling the shape of a sub reflector in a Cassegrain antenna system. The antenna is actuated using multiple point actuators in contact with the reflector surface. A lead sarcomata titan ate (PZT) stack coupled with a friction-based compliant mechanism gives the point actuators used in this design an advantage over similar studies using PZT bimorph or PAD actuators. The main advantage stems from the fact that the displacement can be maintained without the continuous application of voltage. An electromechanical model is used to describe the motion of the stack, and the friction based compliant mechanism is modeled similar to power screw-type actuators. A combined finite element-electromagnetic analysis code is used to determine the desired shape of the reflector and the corresponding actuator displacements. The final shape of the reflector is verified using stereo photogrammetry.
A General Magneto-Elastic Model of Terfenol-D Particle Actuated Composite Materials
Authors: Armstrong William D.
Published: July 2003

A new theory is presented of the nonlinear multi-axial magneto-elastic behavior of magnetostrictive particle actuated composite materials. The analysis assumes a uniform external magnetic field is operating on a large number of well-distributed, crystallographically and shape parallel ellipsoidal magnetostrictive particles encased in an elastic, nonmagnetic composite matrix. Comparisons between experimental and model magnetostriction results show that the model is able to provide a quantitatively correct dependence on particulate volume fraction and longitudinal stress and quantitatively accurate magnetostriction curves for both homogenous Terfenol-D rod and magnetically ordered Terfenol-D particulate actuated epoxy matrix composites over experimentally applied field ranges.
An Experimental Setup for Measuring Unstable Thermo-Mechanical Behavior of Shape Memory Alloy Wire
Authors: Iadicola Mark A. , Shaw John A.
Published: July 2003

An experimental arrangement is demonstrated that overcomes some difficulties in thermo-mechanical testing of thin Shape Memory Alloy (SMA) wires under uniaxial tension. It is now well known that stress-induced transformations in some SMAs under uniaxial loading can lead to mechanical instabilities and propagating phase transformation fronts. Critical parameters, such as nucleation barriers are difficult to measure by conventional testing techniques and are often masked by unavoidable stress concentrations at grips. In addition, simultaneous full field measurements of localized deformation and temperature fields are difficult to obtain for different ambient conditions. The current scheme uses a temperature-controlled conduction block and a non-uniform temperature field induced by thermoelectric modules to uncover the underlying thermo-mechanical response of the wire. The approach also allows access for optical and infrared imaging of the specimen deformation and temperature fields.
Magneto-Rheological Fluid Dampers for Control of Bridges
Authors: Gordaninejad F. , Saiidi M. , Hansen B. C. , Ericksen E. O. , Chang F -K
Published: July 2003

Magneto-rheological fluid (MRF) dampers are utilized to control vibration of a scaled, two-span bridge. In this work, the focus is on a combination of passive and semi-active damping capabilities of a bridge structure. Theoretical and experimental studies are performed to evaluate the effectiveness of MRF dampers. In addition, steel and graphite/epoxy-concrete (G/E-C) columns are utilized in the scaled bridge to increase passive structural damping. Finite element and experimental studies are conducted to assess the performance of each column. Strains in the columns are determined under different input motions and electric power input to MRF dampers. The results demonstrate that MRF dampers can significantly improve the response of the scaled model bridge. It is also shown that, although stiffer, the steel column develops much higher strains compared to those of G/E-C column.
Noncontact Electron Gun Actuation of a Piezoelectric Polymer Thin Film Bimorph Structure
Authors: Martin Jeffrey W. , Main John A.
Published: July 2003

Noncontact electron gun actuation of a bimorphmirror structure composed of two polyvinylidene fluoride layers is demonstrated. The electric field is applied to the piezoelectric structure by controlling the potential of a nickel-copper electrode on one side of the bimorph mirror and subjecting the opposite, bare side of the bimorph to an electron flux. The electrode also serves as the reflecting surface of the thin film mirror structure. Significant characteristics of this actuation approach are demonstrated, including the ability to address discrete areas of the continuous mirror without affecting the global mirror shape and the persistence of the shape changes after the electron beam is turned off.
Strain and Current Responses During Electron Flux Excitation of Piezoelectric Ceramics
Authors: Hadinata Philip C. , Main John A.
Published: July 2003

The electric field induced strain in piezoelectric materials subjected to an electron flux is examined in this paper. An analysis using quantum mechanics indicates that stable and controllable strains with very low current draw should be achievable over a range of positive and negative control potentials. The model also predicts instability in the internal electric field at larger negative potentials.

The model was evaluated by observing the strain output of PZT5h plates subjected to an electron flux on one face and voltage inputs from a single electrode on the opposite face. The strain response and current flow were measured as a function of electrode potential and electron energy. All of the significant predictions of the model were verified by the experimental results. Further experiments were performed to examine the time response of the strain induced in the plate. It was found that the location and potential of the electron collector dramatically influences the dynamic response of the system.
Use of FEA Derived Impedances to Design Active Structures
Authors: Littlefield Andrew G. , Fairweather James A. , Craig Kevin C.
Published: July 2003

Previously, the impedance method has been applied to simple structures by determining the modal response using closed-form methods. The present work uses finite element analysis (FEA) to generate the host structure’s mechanical impedances from eigenvectors. Two-dimensional structures are studied, though the method should be extendable to any structure that can be modeled by FEA. The equations to recover the impedances and structure’s response from an FEA normal mode analysis are developed. The method is then experimentally verified for plates with different boundary conditions, material types, and actuator orientations. The method is found to accurately predict the plate’s response.
A Modified Electro-Mechanical Impedance Model of Piezoelectric Actuator-Sensors for Debonding Detection of Composite Patches
Authors: Xu Y. G. , Liu G. R.
Published: July 2003

A modified electro-mechanical impedance model of piezoelectric actuator-sensors is presented in this study. The presented model treats the bonding layer between a piezoelectric patch and a host structure as a spring-mass-damper system in the coupled electro-mechanical analysis. The effect of bonding layers on the dynamic interaction between piezoelectric actuator-sensors and host structures is thus taken into account. The model is then used for debonding detection of composite patches. A debonding model is accordingly developed. The debonding model uses infinitesimal-length springs to model the joint between a composite patch and its base structure. The spring stiffness varies with the joint rigidity and directly influences the structural mechanical impedance as well as the piezoelectric electric admittance. A numerical example is provided to reveal the effect of bonding layers and demonstrate the feasibility of the proposed detection method.
Phenomenological Modeling and Numerical Simulation of Shape Memory Alloys: A Thermo-Plastic-Phase Transformation Coupled Model
Authors: Savi Marcelo A. , Paiva Alberto , Baeta-Neves Alessandro P. , Pacheco Pedro M. C. L.
Published: July 2003

The thermomechanical behavior of shape memory alloys (SMAs) may be modeled either by microscopic or macroscopic point of view. Shape memory, pseudoelasticity and thermal expansion are phenomena related to the SMA behavior. Constitutive models consider phenomenological aspects of these phenomena. The present contribution considers a one-dimensional constitutive model with internal constraint to describe SMA behavior including the effect of plastic strains. The proposed theory contemplates four phases: three variants of martensite and an austenitic phase. Different material parameters for austenitic and martensitic phases are considered. Thermal expansion phenomenon and plastic effects are also contemplated. Hardening effect is represented by a combination of kinematic and isotropic behaviors. A plastic-phase transformation coupling is incorporated into the model. A numerical procedure is developed and numerical results show that the proposed model is capable to capture the general thermomechanical behavior of shape memory alloys.
Full-Stroke Static and Dynamic Analysis of High-Power Piezoelectric Actuators
Authors: Pomirleanu Radu , Giurgiutiu Victor
Published: July 2003

A method for characterizing smart materials actuators in full-stroke static and low frequency dynamic regimes is presented. At first, static and dynamic linear models of the piezoelectric actuator response under electro-mechanical excitation are discussed. Then, a thorough static and dynamic experimental characterization on a typical large-stroke piezoelectric actuator is performed. The measurements indicated a strong dependence of the actuator stiffness and piezoelectric properties on the electromechanical loading. The comparison of the model with the measured behavior is performed and the material coefficients are tuned to locally match the observed nonlinear behavior. The comparison also allows the identification of key parameters of the induced-strain actuator model. These parameters are necessary for design optimization towards maximum mechanical energy output and minimum electrical power input. The paper provides useful basic data for the design of actuation systems incorporating active materials actuators.
FE Analysis of Piezo-Laminate Composites Under Thermal Loads
Authors: Bansal A. , Ramaswamy A.
Published: July 2003

A shear flexible 4-noded finite element formulation, having five mechanical degrees of freedom per node, is presented for modeling the dynamic as well as the static thermal response of laminated composites containing distributed piezoelectric layers. This element has been developed to have one electrical degree of freedom per piezoelectric layer. The mass, stiffness and thermo-electro-mechanical coupling effects on the actuator and sensor layers have been considered. Numerical studies have been conducted to investigate both the sensory and active responses on piezoelectric composite beam and plate structures. It is concluded that both the thermal and pyroelectric effects are important and need to be considered in the precision distributed control of intelligent structures.
Quasi-Static Heat Transfer in an Experimental Device with a Radial Electro-Structured Fluid Clutch
Authors: Oravsky Vladimir
Published: July 2003

In the paper an experimental device with upper half of a radial electro-structured fluid (ESF) clutch with vertical axis (consisting of a lower stationary disc and upper rotating disc) is examined for constant speed of rotation. The narrow gap between the discs is filled with a viscous liquid, so electro-structural effect is not taken into consideration. Frictional tangential forces in the fluid generate heat which is transferred through the fluid and rotating disc (by conduction) into surrounding air (by convection). A steady state model of heat transfer for the system in question in nondimensional form is built up and solved. Several novelties in approach and solution relative to existing ones are adopted and realized (described in detail in 5 appendices).

Analysis of influence of the system parameters upon results of solution is given. For some particular cases theoretical results are compared with experimental ones by means of tables and diagrams and very good agreement is pointed out.
Development of a Shape-Memory-Alloy Actuated Biomimetic Hydrofoil
Authors: Rediniotis O. K. , Wilson L. N. , Lagoudas D. C. , Khan M. M.
Published: July 2003

The development and testing of a biomimetic active hydrofoil that utilizes Shape-Memory-Alloy (SMA) actuator technology is presented. This work is the second stage in the development of a vehicle that has a skeletal structure similar to that of aquatic animals and SMA actuators for muscles. The current work describes the development and testing of a six-segment demonstration vehicle and the control schemes used. Each SMA actuation element consists of a thin wire that joins together two adjacent vertebrae segments of the hydrofoil skeleton and induces relative movement of one with respect to the other. Controlled heating and cooling of the wire sets generates bi-directional rotation of the vertebrae, which in turn causes a change in the shape of the hydrofoil. Each SMA wire is embedded in an elastic water channel that facilitatesfast active SMA cooling via forced water circulation. This hydrofoil was able to deform to several shapes mimicking aquatic animal swimming, with controlled oscillation frequencies of up to 1 Hz, with 1/2 Hz oscillation producing the largest body motion amplitudes.
Effect of Electrode Morphology on the Behaviour of Electrorheological Fluids in Torsional Flow
Authors: Abu-Jdayil Basim , Brunn Peter O.
Published: July 2003

In this study, we report experiments on experimental and commercial electrorheological (ER)-fluids in torsional flow. A torsional flow device (clutch) suitable for ER-fluids was designed and constructed. The flow curves measured with this device were compared with flow curves from a conventional rotational viscometer (a concentric-cylinders system). The agreement between the two devices was encouraging. To study the influence of inhomogeneous flow conditions besides the influence of the inhomogeneity of the electric field on the behaviour of an ER-fluid in a clutch mechanism, a set of smooth plates and three further sets of plates with different surface finishes were used in this investigation. Relative to the smooth plates, an increase in the relative ER-effect resulted from both ER-fluids used, when the oblique plates were used in an AC-and DC-field. This improvement in ER-effect seems to be tied to the increase in local field strength at the thick rim of the oblique plate. The addition of metal sheets to the smooth plates of the clutch provided a small increase in ER-effect under AC conditions. But in DC-field, the increase in ER-effect relative to that for smooth plates was rather pronounced, but so was the increase in electric current.
Multi-Modal Vibration Control Using Adaptive Positive Position Feedback
Authors: Rew Keun-Ho , Han Jae-Hung , Lee In
Published: July 2003

An adaptive controller, Adaptive Positive Position Feedback (APPF) is proposed for the multi-modal vibration control of frequency varying structures. Spillover phenomena and real-time system identification have been obviously difficult obstacles for the multi-modal adaptive vibration control. To overcome these problems, a fast and powerful algorithm is proposed to identify the frequencies of time-varying structures. Variable PPF controllers are adjusted with estimated natural frequencies at every time step. A composite plate with a bonded piezoelectric sensor and an actuator was prepared as an experimental model, and the natural frequencies of the model are changed by attaching masses. The experimental results show that natural frequencies are estimated quite accurately and that the vibration of controlled modes is significantly reduced. No significant performance reduction has been observed with respect to approximately 10% frequency changes of the corresponding modes. On the contrary, the performance of the conventional LQG controller is significantly degraded due to frequency variations.
Distribution of Active and Passive Constraining Sections for Hybrid Constrained Layer Damping Treatments
Authors: Liu Yanning , Wang K. W.
Published: July 2003

This paper investigates the effect of the distribution of the active and passive constraining materials on the damping performance of an active–passive hybrid constrained layer (HCL) treatment. Earlier studies have demonstrated that the HCL can provide higher open-loop and closed-loop damping than an active constrained layer (ACL) system when a stiffer passive material is integrated into the cover sheet and the coverage ratio of the active-to-passive materials is appropriately designed. The objective of this research is to advance the state of the art in HCL system studies by investigating the effect of multiple active and passive constraining section distributions and the effect of host structure strain fields (mode shapes) on the treatment performance. Using a simple supported beam as an example, these effects are examined and quantified. The findings provide deeper insight toward HCL operations and will be useful in forming guidelines for HCL designs.
Older Women’s Response to Residential Relocation: Description of Transition Styles
Authors: Rossen Eileen K. , Knafl Kathleen A.
Published: July 2003

Older women relocating to institutional facilities are at risk for negative outcomes such as poorer health, decreased self-esteem, increased sense of social isolation and loneliness, loss of social support, and depression. However, little is known about relocation to congregate living facilities (CLF), the relocation transition process, or factors that contribute to outcomes. The perspectives of 31 women on their relocation experiences to CLF were elicited using a naturalistic approach. The Schumacher & Meleis nursing model of transitions was used to focus the study. Three distinct relocation transition styles emerged: Full Integration (45%), Partial Integration (42%), and Minimal Integration (13%). By understanding the characteristics and risk factors of relocation, unhealthy outcomes can be minimized and healthy outcomes promoted.
Caring for Patients Under Medicaid Mandatory Managed Care: Perspectives of Primary Care Physicians
Authors: Chaudry Rosemary V. , Brandon William P. , Thompson Carolyn R. , Clayton R. Stephen , Schoeps Nancy B.
Published: July 2003

The purpose of the study was to describe the experiences of primary care physicians caring for Medicaid recipients in a demonstration mandatory health maintenance organization (HMO) managed care program. The authors collected data through semistructured individual or focus group interviews with 14 physicians and through interviews with the chief executive officers of the three HMOs participating in the demonstration program. Interview questions, developed initially from a review of the literature, addressed physicians’ experiences as primary care providers for Medicaid recipients under traditional fee-for-service and under managed care arrangements through the demonstration program. Four themes emerged: providers’ hassles and burdens, the complex needs of Medicaid patients, improved access to care under managed care, and individual providers’ disconnect from the processes of health policy implementation and program evaluation.
Images of Recovery: A Photo-Elicitation Study on the Hospital Ward
Authors: Radley Alan , Taylor Diane
Published: July 2003

The authors attempted to discover the part the physical setting of the ward plays in patients’ recovery by asking patients to take photographs of their ward, its spaces and objects, and then interviewing them about these images in hospital and subsequently in their homes. Photography allowed the patients to identify and capture aspects of the setting that they found salient and provided the photo-elicitation material for the interviews. Based on these data, the authors present (a) a critical discussion of the use of photography as method and its implications for qualitative analysis, (b) an overview of the kinds of image taken with respect to the ward and the course of patients’ recovery, and (c) a theoretical analysis, employing Walter Benjamin’s use of the concept of mimesis, that understands recovery as a bodily act in response to the shock to the senses that hospitalization and surgery produce.
Redefining Parental Identity: Caregiving and Schizophrenia
Authors: Milliken P. Jane , Northcott Herbert C.
Published: July 2003

When parents try to assume responsibility for an ill adult-child with schizophrenia, the law, mental health practitioners, and often the ill person reject their right to do so. Consequently, these parents regard themselves as disenfranchised, i.e., lacking the rights required to care properly for their loved ones. Redefining Parental Identity, a grounded theory of caregiving and schizophrenia, traces changes in a parent’s identity and caregiving during the erratic course of the child’s mental illness. Participants were a purposive sample of 29 parent caregivers from 19 families in British Columbia, Canada, caring for 20 adult children. This understanding of their experience will be helpful to parents of people with schizophrenia, professional practitioners, and those involved in mental health care reform.
Consent in Oral History Interviews: Unique Challenges
Authors: Boschma Geertje , Yonge Olive , Mychajlunow Lorraine
Published: July 2003

The literature on oral history methods has increased over the past decade. Yet, the issues in gaining consent warrant specific attention. The process of gaining consent in oral history interviews has unique features and varies from accepted procedures in qualitative research. The authors discuss the legalities and ethics of oral history interviews and provide examples regarding the consent process from an oral history project that they conducted. The researchers conclude that despite its complexity, presenting the transcribed interview to the interviewee contributes in an important way to the ethical integrity of the interview process.
Reconsidering Reflexivity: Introducing the Case for Intellectual Entrepreneurship
Authors: Cutcliffe John R.
Published: July 2003

In this article, the author reconsiders reflexivity and attempts to examine some unresolved issues by drawing particular attention to the relationship between reflexivity and certain related phenomena/processes: the researcher’s a priori knowledge, values, beliefs; empathy within qualitative research; the presence and influence of the researcher’s tacit knowledge, and May’s “magic” in method. Given the limitations of some reflexive activity identified in this article, the author introduces the case for greater intellectual entrepreneurship within the context of qualitative research. He suggests that excessive emphasis on reflexive activity might inhibit intellectual entrepreneurship. Wherein intellectual entrepreneurship implies a conscious and deliberate attempt on the part of academics to explore the world of ideas boldly; to take more risks in theory development and to move away from being timid researchers.
Brain Imaging Studies of the Functional Organization of Human Olfaction
Authors: Savic Ivanka
Published: July 2003

It is believed that sensory functions are organized in a hierarchical and parallel manner. The sense of smell differs in several aspects from other senses: odors can immediately elicit emotional evocations, they are remembered after a long time, and they are difficult to label. This raises the question of whether odorous stimuli may be processed differently from the other sensory stimuli. New data from brain imaging studies suggest that this is not the case and that the specific characteristics of the sense of smell can be attributed to the engagement of limbic structures at an early stage in the signal processing.
Mechanisms of Hypoxic Neurodegeneration in the Developing Brain
Authors: Johnston Michael V. , Nakajima Wako , Hagberg Henrik
Published: July 2003

Asphyxia and other insults to the developing brain are responsible for several human neurodevelopmental disorders. The pattern of neonatal brain injury differs from that seen in the adult nervous system, and there are wide differences in regional vulnerability. Recent evidence suggests that two events that contribute to this pattern of selective vulnerability are developmental changes in excitatory glutamate-containing neurotransmitter circuits and the propensity for immature neurons to die by apoptosis rather than necrosis. Developmental up-regulation of NMDA receptors with enhanced function and increased expression of caspase-3 at critical periods in development are linked to these mechanisms. Although these molecular changes enhance the developing brain's capacity for plasticity by helping to prune redundant synapses and neurons, they can become “Achilles heels” in the face of a brain energy crisis.
Molecular Adaptations for Survival during Anoxia: Lessons from Lower Vertebrates
Authors: Bickler Philip E. , Donohoec Paul H. , Buck Leslie T.
Published: July 2003

Anoxia-tolerant neurons from several species of animals may offer unparalleled opportunities to identify strategies that might be employed to enhance the hypoxia or ischemia tolerance of vulnerable neurons. In this review, the authors describe how the response of hypoxia-tolerant neurons to limited oxygen supply involves a suite of mechanisms that reduce energy expenditure in concert with decreased energy availability. This response avoids energy depletion, excitotoxic neuronal death, and apoptosis. Suppression of ion channel functions, particularly those of the ionotropic glutamate receptors, is a response common in hypoxia-tolerant neurons. The depression of excitability thereby achieved is essential given that the fundamental response to oxygen lack in anoxia-tolerant cells is a throttling down of metabolism to “pilot-light” levels. Many different types of processes have been found to down-regulate ion channel function. These include phosphorylation control, interactions with intracellular and extracellular ions, removal of active receptors from the neurolemma, and the direct sensing of oxygen by Na+ and K+ channels. Changes in [Ca2+]i may initiate a protective down-regulation of many different pumps or channels. Transcriptional events leading to differential and/or decreased expression of receptors, proteins, and their subunits are probably very important but little studied.
Ion Regulation in the Brain: Implications for Pathophysiology
Authors: Somjen George G.
Published: July 2003

Ions in the brain are regulated independently from plasma levels by active transport across choroid plexus epithelium and cerebral capillary endothelium, assisted by astrocytes. In “resting” brain tissue, extracellular potassium ([K+]o) is lower and [H+]o is higher (i.e., pHo is lower) than elsewhere in the body. This difference probably helps to maintain the stability of cerebral function because both high [K+]o and low [H+]o enhance neuron excitability. Decrease in osmolarity enhances synaptic transmission and neuronal excitability whereas increased osmolarity has the opposite effect. Iso-osmotic low Na+ concentration also enhances voltage-dependent Ca2+ currents and synaptic transmission. Hypertonicity is the main cause of diabetic coma. In normally functioning brain tissue, the fluctuations in ion levels are limited, but intense neuronal excitation causes [K+]o to rise and [Na+]o, [Ca2+]o to fall. When excessive excitation, defective inhibition, energy failure, mechanical trauma, or blood-brain barrier defects drive ion levels beyond normal limits, positive feedback can develop as abnormal ion distributions influence neuron function, which in turn aggravates ion maldistribution. Computer simulation confirmed that elevation of [K+]o can lead to such a vicious circle and ignite seizures, spreading depression (SD), or hypoxic SD-like depolarization (anoxic depolarization).
Patient Self-Assessment of Walking Ability and Fracture Risk in Older Australian Adults
Authors: Bliuc Dana , Tran Thach , Alarkawi Dunia , Chen Weiwen , Alajlouni Dima A. , Blyth Fiona , March Lyn , Blank Robert D. , Center Jacqueline R.
Published: January 2024

Importance

The relationship between self-reported walking limitation, a proxy of muscle function, and fracture risk has not been investigated.

Objective

To examine the association between a self-reported walking limitation of 1000 m or less and 5-year risk of fracture.

Design, Setting, and Participants

This prospective cohort study compared individuals with various degrees of walking ability limitation at 1000 m (a little limitation and a lot of limitation) and those without limitation (no limitation) accounting for age, falls, prior fractures, and weight. Participants from the ongoing population-based Sax Institute 45 and Up Study were followed from recruitment (2005-2008) for 5 years (2010-2013). Data analysis was conducted from July 2020 to September 2023.

Exposure

Self-reported walking limitation.

Main Outcomes and Measures

Incident fracture and site-specific fractures (hip, vertebral, and nonhip nonvertebral [NHNV] fractures).

Results

Among the 266 912 participants enrolled in the 45 and Up Study, 238 969 were included, with 126 015 (53%) women (mean [SD] age, 63 [11] years) and 112 954 (47%) men (mean [SD] age, 61 [11] years). Approximately 20% reported a degree of limitation in walking 1000 m or less at baseline (39 324 women [24%]; 23 191 men [21%]). During a mean (SD) follow-up of 4.1 (0.8) years, 7190 women and 4267 men experienced an incident fracture. Compared with participants who reported no walking limitations, a little limitation and a lot of limitation were associated with higher risk of fracture (a little limitation among women: hazard ratio [HR], 1.32; 95% CI, 1.23-1.41; a little limitation among men: HR, 1.46; 95% CI, 1.34-1.60; a lot of limitation among women: HR, 1.60; 95% CI, 1.49-1.71; a lot of limitation among men: HR, 2.03; 95% CI, 1.86-2.22). Approximately 60% of fractures were attributable to walking limitation. The association was significant for hip, vertebral, and NHNV fracture and ranged between a 21% increase to a greater than 219% increase.

Conclusions and Relevance

In this cohort study of 238 969 participants, self-reported walking limitations were associated with increased risk of fracture. These findings suggest that walking ability should be sought by clinicians to identify high-risk candidates for further assessment.