bluuebunny/crossref_metadata_2025 huggingface dataset:
Computation in a Single Neuron: Hodgkin and Huxley Revisited
Authors: Arcas Blaise Agüera y , Fairhall Adrienne L. , Bialek William
Published: July 2003

A spiking neuron “computes” by transforming a complex dynamical input into a train of action potentials, or spikes. The computation performed by the neuron can be formulated as dimensional reduction, or feature detection, followed by a nonlinear decision function over the low-dimensional space. Generalizations of the reverse correlation technique with white noise input provide a numerical strategy for extracting the relevant low-dimensional features from experimental data, and information theory can be used to evaluate the quality of the low-dimensional approximation. We apply these methods to analyze the simplest biophysically realistic model neuron, the Hodgkin-Huxley (HH) model, using this system to illustrate the general methodological issues. We focus on the features in the stimulus that trigger a spike, explicitly eliminating the effects of interactions between spikes. One can approximate this triggering “feature space” as a two-dimensional linear subspace in the high-dimensional space of input histories, capturing in this way a substantial fraction of the mutual information between inputs and spike time. We find that an even better approximation, however, is to describe the relevant subspace as two dimensional but curved; in this way, we can capture 90% of the mutual information even at high time resolution. Our analysis provides a new understanding of the computational properties of the HH model. While it is common to approximate neural behavior as “integrate and fire,” the HH model is not an integrator nor is it well described by a single threshold.
Learning the Nonlinearity of Neurons from Natural Visual Stimuli
Authors: Kayser Christoph , Körding Konrad P. , König Peter
Published: July 2003

Learning in neural networks is usually applied to parameters related to linear kernels and keeps the nonlinearity of the model fixed. Thus, for successful models, properties and parameters of the nonlinearity have to be specified using a priori knowledge, which often is missing. Here, we investigate adapting the nonlinearity simultaneously with the linear kernel. We use natural visual stimuli for training a simple model of the visual system. Many of the neurons converge to an energy detector matching existing models of complex cells. The overall distribution of the parameter describing the nonlinearity well matches recent physiological results. Controls with randomly shuffled natural stimuli and pink noise demonstrate that the match of simulation and experimental results depends on the higher-order statistical properties of natural stimuli.
Neural Representation of Probabilistic Information
Authors: Barber M. J. , Clark J. W. , Anderson C. H.
Published: July 2003

It has been proposed that populations of neurons process information in terms of probability density functions (PDFs) of analog variables. Such analog variables range, for example, from target luminance and depth on the sensory interface to eye position and joint angles on the motor output side. The requirement that analog variables must be processed leads inevitably to a probabilistic description, while the limited precision and lifetime of the neuronal processing units lead naturally to a population representation of information. We show how a time-dependent probability densityρ(x; t) over variable x, residing in a specified function space of dimension D, may be decoded from the neuronal activities in a population as a linear combination of certain decoding functions φi(x), with coefficients given by the N firing rates ai(t) (generally with D ≪ N). We show how the neuronal encoding process may be described by projecting a set of complementary encoding functions [Formula: see text]i(x) on the probability density ρ(x; t), and passing the result through a rectifying nonlinear activation function. We show how both encoders [Formula: see text]i (x) and decoders φi(x) may be determined by minimizing cost functions that quantify the inaccuracy of the representation. Expressing a given computation in terms of manipulation and transformation of probabilities, we show how this representation leads to a neural circuit that can carry out the required computation within a consistent Bayesian framework, with the synaptic weights being explicitly generated in terms of encoders, decoders, conditional probabilities, and priors.
Learning the Gestalt Rule of Collinearity from Object Motion
Authors: Prodöhl Carsten , Würtz Rolf P. , von der Malsburg Christoph
Published: July 2003

The Gestalt principle of collinearity (and curvilinearity) is widely regarded as being mediated by the long-range connection structure in primary visual cortex. We review the neurophysiological and psychophysical literature to argue that these connections are developed from visual experience after birth, relying on coherent object motion. We then present a neural network model that learns these connections in an unsupervised Hebbian fashion with input from real camera sequences. The model uses spatiotemporal retinal filtering, which is very sensitive to changes in the visual input. We show that it is crucial for successful learning to use the correlation of the transient responses instead of the sustained ones. As a consequence, learning works best with video sequences of moving objects. The model addresses a special case of the fundamental question of what represents the necessary a priori knowledge the brain is equipped with at birth so that the self-organized process of structuring by experience can be successful.
Time Felt, Time Understood
Authors:   Fraser
Published: July 2003

The experience of time's passage is intimately familiar, the idea of time is strangely elusive. Mature, healthy humans find it is easy to act consistently with the notions of tomorrow, yesterday and today.Yet, explaining what is meant by future, past, and present, without assuming prior familiarity with time, seems impossible. The asymmetry between the obviousness of the experience of time, and the unobviousness of the idea of time, has been a source of perplexity to reflective thought for at least fourteen centuries. This essay sees the sources of that asymmetry in the evolutionary structuring of the cognitive capacities of the human brain. It draws attention to certain conflicts rooted in the differences between those cognitive capacities- copresent in the mind- and notes the importance of the humanities in the management of the conflicts.
Father Time, Speed, and the Temporality of Posters Around 1900
Authors: Iskin Ruth
Published: July 2003

The essay proposes that advertising posters around 1900 construct a popular-culture iconography of a modern temporality associated with new technologies. In addition, it proposes, posters themselves embody a new temporality as a medium. The essay analyses how posters portray time by focusing on several images, some of which depict an updated allegorical figure of Father Time in order to advertise a racing automobile or precision watch.The essay also addresses the temporality of posters as a medium by investigating their conditions of viewing and the role of their advertising function. The discussion of the media specificity of posters, their cultural context, and a detailed analysis of their imagery, concludes that posters both elicit a certain kind of temporal viewing and portray a conflictual transition between old and new temporalities.
Degrees of Separation in the Phaedo
Authors: Pakaluk Michael
Published: July 2003

It can be shown that, if we assume 'substance dualism', or the real distinctness of the soul from the body, then the standard objections to the Cyclical Argument in the Phaedo fail. So charity would presumably require that we take substance dualism to be presupposed by that argument. To do so would not beg any question, since substance dualism is a significantly weaker thesis than the immortality of the soul. Moreover, there is good textual evidence in favor of this presumption. A closer look at the immediately preceding passage, viz. "Socrates' Defense", reveals an argument for a real distinction between soul and body, not unlike Descartes' famous argument, based on the identification of an activity in which the soul can in principle engage on its own, without assistance from the body. The argumentative project of the Phaedo, on this reading, becomes: given that the soul is really distinct, show that it is immortal. And Plato aims to do this in two stages. The three initial arguments are meant to establish merely the minimal claim that the continued existence of the soul across cycles of reincarnation is the most plausible view to take, given substance dualism; and it is left to the Final Argument to argue for something that we might regard as immortality, that is, the imperishability of the soul, come what may.
Zeno on the Unity of Philosophy
Authors: Mansfeld Jaap
Published: July 2003

The formula 'the elements of logos' in the Zeno quotation by Epictetus at Arrian, Diss. 4.8.12 need not, pace e.g. von Arnim, pertain to the parts of speech, but more probably means the elements i.e. primary theorems of philosophical theory, or doctrine. Theory moreover should become internalized to the soul and 'lived': philosophy is also the so-called 'art of life'. These theorems are to be distinguished but should reciprocally entail each other. Philosophy according to Zeno is both tripartite and one, and tripartite especially in that its parts (and subparts) cannot be transferred simultaneously: of necessity these have to taught and learned one after the other.
Are Birds the Primary Selective Force Leading to Evolution of Mimicry and Aposematism in Butterflies? An Opposing Point of View
Authors: Kassarov Luka
Published: July 2003

Birds are universally considered to be the primary selective force leading to the evolution of mimicry in butterflies and the evolution of aposematic coloration. This concept does not take into account the visual capabilities of birds. In this paper it is argued that the aerial hawker insectivorous birds, which are the primary predators of butterflies, are not able to differentiate the separate elements in the color patterns of flying butterflies. They cannot distinguish details in color of the markings or their shape, size, and distribution. As a consequence, birds cannot serve as a selective force for evolution of mimicry and aposematic coloration in these insects. Many aspects of vision, and especially vision in birds, on which my conclusions are based are discussed in detail. The different morphological and behavioral characteristics of butterflies, especially their flight characteristics, correlate with their profitability as a source of energy and nutrients. The flight pattern of the butterfly is the first stimulus that the bird sees, not the color pattern. It is this characteristic flight pattern, not the bright aposematic coloration pattern, that birds are able to recognize and then learn rapidly to associate visually with the profitability of the prey. The characteristic flight behavior signals to the bird whether the prey is energetically profitable or not, thus whether to attack or ignore a potential prey. The ability to distinguish prey types by flight pattern allows the bird to conserve energy and maximize its feeding efficiency.
Behavioural Responses by Red-backed Salamanders to Conspecific and Heterospecific Cues
Authors: Sullivan Aaron , Rohr Jason , Madison Dale
Published: July 2003

Chemical cues released from injured prey are thought to indicate the proximity of a predator or predation event, and therefore, an area of elevated predation risk. Prey often avoid chemical cues released from injured heterospecifics, but there is little evidence to determine whether this is due to homologous cues among phylogenetically related species, or avoidance of injured syntopic species that experience predation from the same predators. The purpose of this study was to examine the response of terrestrial red-backed salamanders (Plethodon cinereus) to chemical cues from non-injured and injured members of their prey guild that vary in their relatedness to P.cinereus. In the laboratory, P.cinereus avoided chemical cues from injured conspecifics, injured and non-injured slimy salamanders (P.glutinosus), and injured confamilial dusky salamanders (Desmognathus ochrophaeus). Red-backed salamanders did not avoid rinses from non-injured conspecifics and dusky salamanders, or cues from injured and non-injured earthworms (Lumbricus sp.), a more distantly related prey guild member. These results cannot be fully explained by either phylogenetic relatedness (among plethodontid salamanders) or prey guild membership alone. We suggest that a combination of these factors, and perhaps others, likely influenced the evolution of heterospecific alarm cue avoidance in the red-backed salamander.
Identity and Daily Space in Two Municipalities in Mexico City
Authors: D. Miguel Angel Aguilar
Published: July 2003

To analyze how different characteristics of daily space can construct an urban social identity, the author carried out an exploratory study in two Mexico City municipalities, one of them founded 35 years ago and the other 15 years ago. To obtain information on the use of the space, significant sites, and the value placed on social life, the author surveyed 100 people and observed socially relevant places. The presentation and analysis of the results explore different meanings of the information obtained on the formation of an urban social identity. In both places, local physical space was unimportant to the formation of identity traits. Results also showed the relevance of how value is placed, that is, the social meanings attributed to space. It is argued that the most important referent in the formation of an urban social identity is a generic notion of the urban against which the settlement is compared.
Appropriation and Interpersonal Relationships
Authors: Moser Gabriel , Ratiu Eugénia , fleury-Bahi Ghozlane
Published: July 2003

Based on the results of three field research studies in Paris, this article outlines the way in which the individual constructs a cognitive and behavioral relationship with the environment at three different levels: housing, the residential neighborhood, and the city as a whole. Identity and environmental identification generating social cohesion and satisfaction is, according to the City-Identity-Sustainability model, an important condition for ecological behavior to occur. The appropriation or nonappropriation of a particular environmental context is analyzed in light of the differentiation of the relation to the dwelling, the immediate neighborhood, and the city and described in terms of modalities of interpersonal relationships, affective investment, satisfaction, and self-expression through residential history and place identity. The characteristics of modern urban life (mobility, transitional situations, and the denaturalization of the urban context) contribute to alter the individual’s relations to dwelling as well as to the immediate and enlarged urban context.
Values, Gender, and Concern about Potentially Dangerous Wildlife
Authors: Zinn Harry C. , Pierce Cynthia L.
Published: July 2003

In this study, the authors investigated wildlife value orientations, gender, and concern about risks posed by a large, potentially dangerous predator—the mountain lion. A survey (58% response rate) was used to collect data from a random sample of adult residents ( N = 2,469) in Colorado metropolitan areas. Both gender and parental role predicted concern about being attacked. Women expressed greater concern than men, and participants with children living at home expressed greater concern than participants without children at home. Participants with utilitarian values were more likely than those with protectionist ones to accept destroying a lion in a residential area, and men were more likely than women to accept destroying it. Additional research is needed to understand why women perceived more risk from a mountain lion but were less willing to accept destroying it, as well as to understand the relationships among gender, parental role, and environmental risk concern.
Emerging High-Growth Firms and Economic Development Policy
Authors: Buss Terry F.
Published: July 2003

Emerging high-growth firms create the lion’s share of jobs in the United States. Even though these firms are economically important, policy researchers have not studied them to a great extent. This focus section tries to stimulate interest in the issue by reporting results of cutting-edge exploratory research on emerging high-growth firms and public policy. Authors, in turn, explore contributions of Chinese and Indian immigrant entrepreneurs in high-tech Silicon Valley industries, recipients of Small Business Innovation Research awards, connections between home-based businesses and e-commerce, and the Clinton administration’s New Markets Initiative.
Silicon Valley’s New Immigrant High-Growth Entrepreneurs
Authors: Saxenian AnnaLee
Published: July 2003

This article examines the economic contributions of skilled Asian immigrants in Silicon Valley—both directly, as entrepreneurs, and indirectly, as facilitators of trade with and investment in their countries of origin. Skilled immigrants account for one third of the region’s engineering workforce and are increasingly visible as entrepreneurs and investors. Two thirds of the region’s foreign-born engineers were from Asia. Chinese and Indian immigrants in turn accounted for 74% of the total Asian-born engineering workforce. In 1998, Chinese and Indian engineers were senior executives at one quarter of Silicon Valley’s technology businesses. These immigrant-run companies collectively accounted for more than $26.8 billion in sales and 58,282 jobs. The region’s most successful immigrant entrepreneurs rely heavily on ethnic resources while integrating into the mainstream technology economy. The challenge for policy makers will be to recognize these mutually beneficial connections between immigration, investment, trade, and economic development.
Home-Based Firms, E-Commerce, and High-Technology Small Firms: Are they Related?
Authors: Phillips Bruce D.
Published: July 2003

This article demonstrates the importance of home-based businesses to the U.S. economy. These firms produced 10% of all receipts of the small-business sector in 1996, and their numbers have grown rapidly. This article examines what kinds of businesses are being run out of the home but concentrates on the subset that may be called truly entrepreneurial: the firms that gross at least $1 million and have employees working in the home. Different sections of this article contrast the characteristics of firms run out of the home with the motivations and backgrounds of their owners. The influence of the Internet on these entrepreneurial firms is also explored, as well as regulations that may be preventing a faster expansion of home-based activities.
The Economic Impact of Educational Institutions: Issues and Methodology
Authors: Blackwell Melanie , Cobb Steven , Weinberg David
Published: July 2003

This article provides a framework for conducting economic analysis for educational institutions. Such institutions, because they affect future output and income through human capital formation, have effects beyond the usual form of economic impact. To date, we are aware of no published impact studies that have adequately dealt with this issue, and most have not effectively handled the traditional sources of impact as arise through the import substitution phenomenon (the impact from increased local source spending in the area caused by the institution’s presence.) This study demonstrates an approach to handling all three sources of impact (export, import substitution, and human capital) and provides a description of the data sources needed to conduct such a study. In addition, the authors include a case study of Xavier University’s impact to demonstrate the viability of their proposed methodology.
Finite Element Modeling of MFC/AFC Actuators and Performance of MFC
Authors: Azzouz M. Salim , Mei Chuh , Bevan Jeffrey S. , Ro Jeng Jong
Published: July 2003

The anisoparametric three-node MIN6 shallow shell element is extended for modeling Macro-Fiber Composite/Active Fiber Composites (MFCTM/AFC) actuators for active vibration and acoustic control of curved and flat panels. The recently developed MFCTM/AFC actuators exhibit enhanced performance, they are anisotropic and highly conformable as compared to the traditional monolithic isotropic piezoceramic actuators. The extended MIN6 shell element includes embedded or surface bonded MFCTM/AFC laminae. The fully coupled electrical-structural formulation is general and it is able to handle arbitrary doubly curved laminated composite and isotropic shell structures. A square and a triangular cantilever isotropic plates are modeled using the MIN6 elements to demonstrate the anisotropic actuation of a surface bonded MFCTM actuator for coupled bending and twisting plate motions. Steady state modal bending and twisting amplitudes of the cantilever square and triangular plates with MFCTM actuator are compared with the plate’s steady state modal amplitudes with traditional PZT 5A actuator for different angle orientations. Frequency Response Functions (FRF) for the square plate with MFCTM and PZT 5A actuators are also obtained and their actuation performance is compared. The actuation performance of the MFCTM at different locations is also investigated.
Ring Type Uni/Bimorph Piezoelectric Actuators
Authors: Dong Shuxiang , Bouchilloux Philippe , Du Xiao-Hong , Uchino Kenji
Published: July 2003

This paper presents a ring type piezoelectric actuator that combines a ring-shaped piezoelectric component with a thin metal disc. In this actuator, the ring-shaped piezoelectric ceramic produces a radial contraction or expansion, and results in a large flexural displacement of the center of the metal disc. When the PZT ring under the metal disc contracts, the unbounded portion at the center of the disc is permitted to bend with a larger curve in positive (upper) direction. Both experimental results and FEM analysis support the new concept and confirm that the ring type uni/bimorph (ring-morph) configuration has a larger displacement output than that of conventional disc type uni/bimorph actuators with comparable dimensions.
Vibration Control of a CD-ROM Feeding System Using Electro-Rheological Mounts
Authors: Lim Soo-Cheol , Park Jong-Sung , Choi Seung-Bok , Park Young-Pil
Published: July 2003

This paper presents vibration control of a CD-ROM (compact disc-read only memory) drive feeding system using an electro-rheological (ER) fluid mount. An appropriate size of the ER mount, which is adaptable to existing CD-ROM drive feeding system, is designed and manufactured on the basis of Bingham characteristics of an ER fluid. After verifying that damping force of the ER mount can be tuned by the intensity of electric field, the ER mount is installed to the drive feeding system. The governing equation of motion is then derived, and a skyhook controller is designed to effectively control unwanted vibration caused from external excitation. The controller is incorporated with the hardware-in-the-loop simulation (HILS) methodology, and vibration control performances are evaluated in both frequency and time domains.
Feasibility to Control Launch Vehicle Internal Acoustics Using Piezoelectric Actuators
Authors: Niezrecki Christopher , Cudney Harley H.
Published: July 2003

Future launchvehicle payload fairings will be manufactured from advanced lightweight composite materials. The loss of distributed mass causes a significant increase in the internal acoustic environment, causing a severe threat to the payload. Using piezoelectric (PZT) actuators to control the fairing vibration and the internal acoustic environment has been proposed. To help determine the acoustic control authority of piezoelectric actuators mounted on a rocket fairing, the internal acoustic response created by the actuators needs to be determined. In this work the internal acoustic response of a closed simply-supported (SS) cylinder actuated by PZT actuators is determined using an impedance model for the actuator and boundary element analysis. The experimentally validated model is used to extrapolate results for a SS cylinder that emulates a Minotaur payload fairing. The internal cylinder acoustic levels are investigated for PZT actuation between 35 and 400 Hz. Significant reductions in the structural response due to increased damping do not equate to similar reductions in the acoustic sound pressure levels (SPLs) for the cylinder. The sound levels at the acoustic resonant frequencies are essentially unaffected by the significant increase in structural damping while the acoustic levels at the structural resonant frequencies are mildly reduced. The interior acoustic response of the cylinder is dominated by the acoustic modes and therefore significant reductions in the overall interior acoustic levels will not be achieved if only the structural resonances are controlled. As the actuation frequency is reduced, the number of actuators required to generate acoustic levels commensurate to that found in the fairing increases to impractical values. Below approximately 100 Hz, the current demands reach levels that are extremely difficult to achieve with a practical system. The results of this work imply that PZT actuators do not have the authority to control the payload fairing internal acoustics below 100 Hz.
Finite Element Modeling and Active Control of an Inflated Torus Using Piezoelectric Devices
Authors: Lewis Jackson A. , Inman Daniel J.
Published: July 2003

Satellite antenna design requirements are driving the satellite size to dimensions that cannot be launched into space using current technology. In order to reduce the launch size and mass of satellites, inflatable structures, also known as gossamer structures, are being considered. Inflatable space-based structures are susceptible to vibration disturbance due to their low stiffness and damping. This paper discusses the structural dynamics and vibration suppression via piezoelectric actuators of an inflatable torus.

A commercial finite element package, ANSYS, is used to model the inflated torus. The effect of torus aspect ratio and inflation pressure on the vibratory response of the structure is investigated. The interaction with the torus of the surface-mounted piezoelectric patches, made of PVDF, is modeled using Euler-Bernoulli beam theory. A state space representation is created of the model in modal space and modal truncation is performed. Traditional control tools are used to suppress vibration in the structure. First observer-based full state feedback is used, then direct output velocity feedback is explored.
State-Switched Absorber for Vibration Control of Point-Excited Beams
Authors: Cunefare Kenneth A.
Published: July 2003

A system that has the capability to make instantaneous changes in its mass, stiffness, or damping may be termed a state-switchable dynamical system. Such a system will display different dynamical responses dependent upon its current state. State-switchable stiffness may be practically obtained through the control of the termination impedance of piezoelectric stiffness elements. If such a switchable stiffness element is incorporated as part of the spring element of a vibration absorber, the change in stiffness causes a change in the resonance frequencies of the system, thereby instantaneously ‘retuning’ the state-switched absorber to a new frequency. In between state switches, the operation of such a device is passive, being fundamentally a passive vibration absorber. This concept has improved performance over classical passive vibration absorbers or dampers, particularly for disturbances with multiple spectral components. This paper considers the application of such a device for the purpose of vibration control on beams subjected to harmonic point-force excitation.
Piezoceramic Hysteresis in the Adaptive Structural Vibration Control Problem
Authors: Lee Soon-Hong , Ozer M. Bulent , Royston Thomas J.
Published: July 2003

Structural vibration control via passive electrical shunting and active (hybrid) actuation of a piezoceramic wafer bonded onto the surface of a simply supported beam is investigated with emphasis on modeling and understanding the effect of piezoceramic nonlinearity on system performance. A nonlinear rate-independent hysteresis model, the Ishlinskii hysteresis (IM) model, is experimentally identified for the PZT wafer by itself and then integrated into the coupled dynamic equations of the overall system consisting of the beam and electrically shunted PZT wafer. Experimental studies of the system validate the theoretical model. This model is then used to investigate the impact of PZT hysteresis on its vibration control performance in passive and hybrid scenarios that have been optimized based on a linear system assumption. A multi-term describing function representation of the IM hysteresis model is formulated to aid in computational studies.
The Effect of Uniaxial Cyclic Deformation on the Evolution of Phase Transformation Fronts in Pseudoelastic NiTi Wire
Authors: Iadicola Mark A. , Shaw John A.
Published: July 2003

Experiments are presented of the response of pseudoelastic NiTi wires subjected to displacement controlled cycles. A custom-built thermo-mechanical testing apparatus is used to control the background temperature field of the wire specimen while allowing the evolution of transformation fronts to be tracked by full-field infrared imaging. Two experiments under similar end-displacement histories, but at temperatures approximately 8°C apart, are shown to give remarkably different cyclic responses. The mechanical response for the lower temperature experiment continued to soften but retained its shape through 43 partial transformation cycles, and the pattern of transformation fronts seemed to reach a steady state. The response for the higher temperature experiment showed a change in shape of the mechanical response and distinct changes in transformation front patterns over 31 partial transformation cycles.
Command Shaping Nonlinear Inputs Using Basis Functions
Authors: Agostini Michael J. , Parker Gordon G.
Published: July 2003

Manufacturing operations exist which require robotic repositioning of flexible payloads. Product quality or throughput can be adversely affected if payload vibration is not controlled. Using command shaped inputs can prevent excitation of payload dynamics, however, most of the literature has focused on linear, single input systems. General robotic repositioning typically involves simultaneous motion of multiple degrees of freedom resulting in the payload excitation function being a nonlinear combination of the robot input states. Under these conditions, removal of the individual input’s frequency content in the vicinity of the payload’s resonances does not guarantee that the nonlinear combination of the inputs will be free of detrimental frequency content. Presented in this paper is a method for trajectory design of point-to-point flexible payload maneuvers with multiple inputs nonlinearly driving payload dynamics. Simulation and experimental results are provided for the coordinated maneuver of a flexible beam. Using this trajectory generation approach, the residual oscillation is reduced by a factor of 20 as compared to the worst case maneuver, without a reduction in total maneuver time.
Comparison of Active Constrained Layer Damping by Using Extension and Shear Mode Piezoceramic Actuators
Authors: Batra R. C. , Geng T. S.
Published: July 2003

We analyze, numerically by the finite element method, three-dimensional electromechanical deformations of a thick laminated plate with layers made of aluminum, a viscoelastic material and a piezoceramic (PZT). Two arrangements of layers are considered. In one case a central PZT layer is surrounded on both sides by viscoelastic layers and aluminum layers are on the outside surfaces. The PZT is poled in the longitudinal direction and an electric field is applied to it in the transverse direction. Thus shearing deformations of the PZT layer dominate over its extensional deformations. In the second arrangement, the aluminum layer is in the middle and the PZT layers are on the outside. The poling direction and the electric field are along the thickness of the PZT layer. Extensional deformations of the PZT layer are significantly more than its shearing deformations. The problem formulation incorporates geometric nonlinearities and the constitutive relation for the PZT includes quadratic terms in the electric field. For each set up of the layers, the system is excited at its first natural frequency. The enhancement in damping induced by the actuation of the PZT layers is ascertained, and the optimum thicknesses of the viscoelastic layers and the PZT layers for maximum damping are determined. The effect of nonlinear terms in the constitutive relation for the PZT is ascertained. The problem of exciting the laminated plate simultaneously at the first and the second frequencies and annulling these has been scrutinized. It is found that the energy of electric deformations of the PZT material is more for the shear mode actuators than that for the extension mode actuators.
Mass Transfer Induced Hydraulic Actuation in Ionic Polymer-Metal Composites
Authors: Shahinpoor Mohsen , Kim Kwang J.
Published: July 2003

Discussed is the phenomenon of mass transfer-induced hydraulic actuation in ionic polymer-metal composites (IPMCs) strips with chemically plated surface electrodes. A new category of actuators as “mass transfer induced hydraulic actuators (MTIHAs)” is thus defined. Such mass transport of ions and water is across the thickness of the strip and ends up near the permeable metal electrodes. The imposition of an electric field causes the mobile hydrated cations that are conjugated to the polymeric network anions to undergo electrophoretic dynamic migration that can result in local deformation of the material. Such an electrophoretic behavior of the hydrated cations in IPMC causes the water to flow across the strip and partially leak out of the cathode side of the permeable electroded boundary. These leakages are undesirable because they lower the actuation performance. The IPMC is a good example of such MTIHAs. The advantage of MTIHAs is their potential to generate substantially high force densities if the leakage can be minimized or eliminated. Based upon this MTIHA concept, a certain manufacturing technique was developed to minimize the leakage and increase the force density of the conventional IPMCs by almost a factor of two (100% improvement in force). This phenomenon and the associated experimental results are presented in this paper.
Modeling a Piezothermoelastic Laminated Plate-Membrane
Authors: Rogers James W. , Agnes Gregory S.
Published: July 2003

Analysis of laminated piezopolymer actuated circular membranes is presented. The nonlinear equations of motion governing a continuous circular laminate of arbitrary thermal, electrical and mechanical properties are developed. Assuming axisymmetry, a closed-form asymptotic solution is developed using a combination of perturbation techniques. These governing equations are applied to a model laminate of Kapton and PVDF materials where static and dynamic results are discussed.
Comparison of Damping Augmentation Mechanisms with Position and Velocity Feedback in Active Constrained Layer Treatments
Authors: Gandhi Farhan , Munsky Brian
Published: July 2003

In active constrained layer damping treatments there are two distinct physical mechanisms that contribute to vibration damping - increased passive damping due to increased shear in the viscoelastic material (VEM) layer, and damping due to transmission of active forces to the host structure. The present study demonstrates that the first mechanism is dominant when proportional feedback is used while the second mechanism is dominant when derivative feedback is used. In the case of proportional feedback, the shear in the VEM increases considerably so that the passive damping is significantly larger than that obtained for the zero-voltage case, but the active action is actually detrimental. In the case of velocity feedback, the shear strain levels in the VEM are virtually unchanged, and all of the damping augmentation is due to the active action. It is also seen that if position feedback is used, moderate values of VEM shear modulus that provide optimal passive damping, are best. On the other hand, if velocity feedback is used, high values of VEM shear modulus that allow best transmission of active forces from the active piezoelectric layer to the host structure, provide maximum augmentation in damping, with the maximum total damping depending on the feedback gain used.
Investigation of Thunder™ Actuators as Underwater Propulsors
Authors: Balakrishnan Sivakumar , Niezrecki Christopher
Published: July 2003

Piezoelectric actuators have been used for active vibration control, noise suppression, health monitoring, etc. The large appeal in using smart material actuators stems from their high mechanical energy density. A relatively new actuator Thin Layer Composite Unimorph Ferroelectric Driver and Sensor (THUNDER) has overcome the displacement hurdles that have plagued traditional piezoelectric based actuators. It is capable of providing a displacement of the order of 0.5 cm. This allows the actuator to be used in some underwater applications, such as propulsion. To date the electrical power consumption and electro-mechanical efficiency of these actuators has not been quantified; specifically, applied as underwater propulsors. Some of the challenges in obtaining this information stems from the actuator’s nontraditional actuating architecture, high voltage requirements, and its electrical nonlinearity. This work experimentally determines the mechanical displacement and the electrical power consumption of the THUNDER actuators used as underwater propulsors. An estimate of a lower bound of the thrust that can be generated by the clamshell actuator is obtained. It is found that the actuator has a peak flow rate of approximately 1500 cm3/s and can generate a peak thrust greater than approximately 4.5 N. This preliminary analysis neglected the pressure forces acting on the actuator and therefore, the actual thrust is not computed. It is found that the average electrical power consumed by two THUNDER actuators placed in a clamshell configuration operating at 14 Hz is approximately 8 W, which is significantly less than that consumed by other autonomous underwater vehicles. The displacement response and the current draw of the actuators are determined to be nonlinear. The result of this work indicates that the use of THUNDER actuators has great potential to create an underwater propulsor that has low power consumption, can operate at great depths, and eliminates the need for seals, bearings and a propeller.
A Computational Model for Sound Field Absorption by Acoustic Arrays
Authors: Banks H. T. , Cole D. G. , Furati K. M. , Ito K. , Pinter G. A.
Published: July 2003

In this paper we discuss the sound absorption property of arrays of micro-acoustic actuators at a control surface. We use the wave equation over the half plane for the velocity potential with a boundary dissipation by a proportional pressure feedback law along the half plane boundary. The feedback gain over the array is described by a distributed shape function. We develop a computational method based on the Fourier transform and employ it for analyzing and evaluating the decay rate of acoustic energy. Specifically, we carry out computations for a diffusive random initial field and report on our resulting numerical findings.
Nonlinear Frequency Spectrum Analysis of Vibration System with ER Damper
Authors: Chen Suhuan , Yang Guang
Published: July 2003

The Electro-rheological (ER) fluid is a new kind of smart material which has been applied to various engineering problems. Using the viscous and bilinear hysteretic damping model, this paper discusses the nonlinear frequency spectrum by iterative perturbation method for nonlinear vibration system with ER damper. Iterative perturbation is based on the matrix perturbation. The initial frequencies are found by subspace iteration. The subsequent frequency spectrum of nonlinear states, which is based upon the tangent stiffness of the structure, is calculated by the iterative perturbation method. A numerical example is given to illustrate the method presented by this paper.
Electromechanical Modeling and Characterization of Ionic Polymer Benders
Authors: Newbury Kenneth M. , Leo Donald J.
Published: July 2003

This paper presents a coupled, electromechanical model of a Nafion-based ionic polymer transducer used in the cantilevered bender configuration. A comparison of simulatedandexperimental responses for a 0.2 mm 5.0 mm 17 mm actuator validates both the form of the model and the empirically determined model parameters. In one of the experiments used for parameter identification, the short circuit current is found to be proportional to the induced actuator velocity, with the constant of proportionality on the order of 104A/(m/s). This dynamic model differs from those presented by other researchers in that it is able to represent the transducer as either a sensor or as an actuator. Also presented is an assessment of the polymer actuators’ ability to perform mechanical work. The results of a series of force versus deflection experiments are outlined, and energy densities are calculated to facilitate comparison with other actuator technologies. The maximum blockedforce with a 1.25 V step input was 1.6 mN (with a 17 mm actuator), andthe maximum free deflection with a 1.25 V step input was 1.8 mm (with a 22 mm actuator). The energy densities ranged from 1.1 to 12.8 mJ/kg and3.4E-06 to 4.0E-05 mJ/mm3 with an input range of 0.75–1.25 V.
A Model for the Analysis of Beams with Embedded Piezoelectric Layers
Authors: Wang Q. , Quek S. T.
Published: July 2003

This paper provides a basic mechanics model for the flexural analysis of beams with embedded piezoelectric layers. The Euler model for a long and thin beam is employed and two different ways of connecting the electrodes on the surfaces of the piezoelectric layers, namely, closed circuit (Case I) and open circuit (Case II) are considered. The distribution of the piezoelectric potential in the longitudinal direction is derived by including Maxwell equation in the formulation and assuming a half-cosine distribution for the potential in the thickness direction of the piezoelectric layer for Case I. The validity of this assumption is investigated first theoretically and then numerically by FEM for a pure piezoelectric beam subjected to uniform moment. A semi-analytical analysis is carried out for Case II where an electric potential function is assumed. The resonant frequencies of the structure for the models presented are first validated by the FEM software, ABAQUS, for simply-supported and propped cantilever boundary conditions. Based on the results of vibration analysis, it is shown that the dynamic characteristics of the entire structure can be significantly affected by piezoelectric effects, especially for the open circuit case. More importantly, the mode shapes of the electric potential in the piezoelectric layer are different for Cases I and II. For the closed circuit case, the potential shape function is related to the transverse displacement, or more accurately the curvature of the beam. For the open circuit case, the potentials at the boundaries in the longitudinal direction are directly related to the slope of the deflection of the beam. Hence, the commonly adopted assumption of uniform electric potential needs to be carefully re-examined.
Chinese Cultural Influences on Parental Caregiving Obligations Toward Children With Disabilities
Authors: Holroyd Eleanor E.
Published: July 2003

The author draws on the personal and public dilemmas that result when Chinese families care for children with disabilities. She employed an ethnographic approach to interview 15 Hong Kong Chinese families caring for children aged 5 to 16 with disabilities. Twelve of these families included sons with disabilities. The following themes emerged: disruptions to natural order, public opinions on what constitutes personhood and ordered bodies, and the establishment of moral reputations linked to shame and blame and the gendered division of parenting. The author highlights the centrality of parenthood in Chinese society as the acceptance of responsibility and its cyclic enactment, and emphasizes how the care of children with handicaps strains and violates the Chinese culturally expected order of parental obligations.
Remyelination within the CNS: Do Schwann Cells Pave the Way for Oligodendrocytes?
Authors: Jasmin Luc , Ohara Peter T.
Published: July 2003

Schwann cells that have myelinated the CNS can be replaced by myelinating oligodendrocytes. It is unclear, however, why oligodendrocyte remyelination would occur for axons that are already myelinated. The Schwann cells might signal their own replacement by oligodendrocytes, but more probably a third player, the reactive astrocyte, is essential to this phenomenon. We propose that as long as reactive astrocytes do not form fibrous gliosis, they are beneficial to oligodendrocyte remyelination. Unknown is whether reactive astrocytes induce oligodendrocyte progenitor (NG2 immunopositive cells) cells to differentiate, a phenomenon that is absent in multiple sclerosis. So what role do Schwann cells play in CNS remyelination? They appear to serve to protect central axons and might coincidentally prevent reactive astrocytes from laying down scar tissue that impedes oligodendrocyte remyelination.
Retinal Waves: Implications for Synaptic Learning Rules during Development
Authors: Butts Daniel A.
Published: July 2003

Neural activity is often required for the final stages of synaptic refinement during brain development. It is thought that learning rulesacting at the individual synapse level, which specify how pre and postsynaptic activity lead to changes in synaptic efficacy, underlie such activity-dependent development. How such rules might function in vivo can be addressed in the retinogeniculate system because the input activity from the retina and its importance in development are both known. In fact, detailed studies of retinal waves have revealed their complex spatiotemporal properties, providing insights into the mechanisms that use such activity to guide development. First of all, the information useful for development is contained in the retinal waves and can be quantified, placing constraints on synaptic learning rules that use this information. Furthermore, knowing the distribution of activity over the entire set of inputs makes it possible to address a necessary component of developmental refinement: rules governing competition between synaptic inputs. In this way, the detailed knowledge of retinal input and lateral geniculate nucleus development provides a unique opportunity to relate the rules of synaptic plasticity directly to their role in development.
Interleukin-6 (IL-6): A Possible Neuromodulator Induced by Neuronal Activity
Authors: Jüttler Eric , Tarabin Victoria , Schwaninger Markus
Published: July 2003

IL-6 and its receptor(s) are found in the CNS in health and disease. Cellular sources are glial cells and neurons. Glial production of IL-6 has intensively been studied, but comparatively little is known about the induction of IL-6 in neurons. Emerging evidence suggests that IL-6 possesses neurotrophic properties. Recent data show that neuronal IL-6 expression is induced by excitatory amino acids or membrane depolarization. This implicates that IL-6 is produced not only under pathological conditions but may play a critical role as a physiological neuromodulator that is induced by neuronal activity and regulates brain functions. In the following article, the authors review the current data on IL-6 expression in neurons, with special reference to the induction of IL-6 by neuronal activity. They discuss its direct and indirect effects as a neuromodulator and speculate about the possible function of IL-6 as a physiological regulatory molecule and as a neuroprotective agent in brain pathology.