Showing papers by "University of Delaware published in 2006"

Spatial Diversity in Radars—Models and Detection Performance

Abstract: Inspired by recent advances in multiple-input multiple-output (MIMO) communications, this proposal introduces the statistical MIMO radar concept To the authors' knowledge, this is the first time that the statistical MIMO is being proposed for radar The fundamental difference between statistical MIMO and other radar array systems is that the latter seek to maximize the coherent processing gain, while statistical MIMO radar capitalizes on the diversity of target scattering to improve radar performance Coherent processing is made possible by highly correlated signals at the receiver array, whereas in statistical MIMO radar, the signals received by the array elements are uncorrelated Radar targets generally consist of many small elemental scatterers that are fused by the radar waveform and the processing at the receiver, to result in echoes with fluctuating amplitude and phase It is well known that in conventional radar, slow fluctuations of the target radar cross section (RCS) result in target fades that degrade radar performance By spacing the antenna elements at the transmitter and at the receiver such that the target angular spread is manifested, the MIMO radar can exploit the spatial diversity of target scatterers opening the way to a variety of new techniques that can improve radar performance This paper focuses on the application of the target spatial diversity to improve detection performance The optimal detector in the Neyman–Pearson sense is developed and analyzed for the statistical MIMO radar It is shown that the optimal detector consists of noncoherent processing of the receiver sensors' outputs and that for cases of practical interest, detection performance is superior to that obtained through coherent processing An optimal detector invariant to the signal and noise levels is also developed and analyzed In this case as well, statistical MIMO radar provides great improvements over other types of array radars

The Determinants of Corporate Board Size and Composition: An Empirical Analysis

Abstract: Many theories have been proposed to explain how corporate boards are structured. This paper groups these theories into three hypotheses and tests them empirically. We utilize a unique panel dataset that tracks corporate board development from the time of a firm's IPO through 10 years later. The data indicate that: (i) board size and independence increase as firms grow in size and diversify over time; (ii) board size - but not board independence - reflects a trade-off between the firm-specific benefits of monitoring and the costs of such monitoring; and (iii) board independence is negatively related to the manager's influence and positively related to constraints on such influence. These results are consistent with the view that economic considerations - in particular, the specific nature of the firm's competitive environment and managerial team - help explain cross-sectional variation in corporate board size and composition. Nonetheless, much of the variation in board structures remains unexplained even when all three hypotheses are combined, suggesting that idiosyncratic factors affect many individual boards' characteristics.

Intergroup Threat and Outgroup Attitudes: A Meta-Analytic Review

Abstract: This article examines the relationship between intergroup threat and negative outgroup attitudes. We first qualitatively review the intergroup threat literature, describing the shift from competing theories toward more integrated approaches, such as the integrated threat theory (ITT; W. G. Stephan & Stephan, 2000). The types of threats discussed include: realistic threat, symbolic threat, intergroup anxiety, negative stereotypes, group esteem threat, and distinctiveness threat. We then conducted a quantitative meta-analysis examining the relationships between various intergroup threats and outgroup attitudes. The meta-analysis, involving 95 samples, revealed that 5 different threat types had a positive relationship with negative outgroup attitudes. Additionally, outgroup status moderated some of these relationships. Implications and future directions are considered.

Electron acceleration from contracting magnetic islands during reconnection

Abstract: Electrons gain kinetic energy by reflecting from the ends of the contracting 'magnetic islands' that form as reconnection proceeds. The repetitive interaction of electrons with many islands allows large numbers to be efficiently accelerated to high energy. A long-standing problem in the study of space and astrophysical plasmas is to explain the production of energetic electrons as magnetic fields ‘reconnect’ and release energy. In the Earth's magnetosphere, electron energies reach hundreds of thousands of electron volts (refs 1–3), whereas the typical electron energies associated with large-scale reconnection-driven flows are just a few electron volts. Recent observations further suggest that these energetic particles are produced in the region where the magnetic field reconnects4. In solar flares, upwards of 50 per cent of the energy released can appear as energetic electrons5,6. Here we show that electrons gain kinetic energy by reflecting from the ends of the contracting ‘magnetic islands’ that form as reconnection proceeds. The mechanism is analogous to the increase of energy of a ball reflecting between two converging walls—the ball gains energy with each bounce. The repetitive interaction of electrons with many islands allows large numbers to be efficiently accelerated to high energy. The back pressure of the energetic electrons throttles reconnection so that the electron energy gain is a large fraction of the released magnetic energy. The resultant energy spectra of electrons take the form of power laws with spectral indices that match the magnetospheric observations.

When supervisors feel supported: Relationships with subordinates' perceived supervisor support, perceived organizational support, and performance.

Abstract: The authors surveyed full-time retail employees and their supervisors to investigate relationships of supervisors' perceived organizational support (POS) with subordinates' perceptions of support from their supervisors (perceived supervisor support [PSS]), POS, and in-role and extra-role performance. The authors found that supervisors' POS was positively related to their subordinates' perceptions of supervisor support. Subordinates' PSS, in turn, was positively associated with their POS, in-role performance, and extra-role performance. Beyond these bivariate relationships, subordinates' perceptions of support from the supervisor mediated positive relationships of the supervisors' POS with the subordinates' POS and performance. These findings suggest that supervisors who feel supported by the organization reciprocate with more supportive treatment for subordinates.

A Comparison of Bifactor and Second-Order Models of Quality of Life.

Abstract: Bifactor and second-order factor models are two alternative approaches for representing general constructs comprised of several highly related domains. Bifactor and second-order models were compared using a quality of life data set (N = 403). The bifactor model identified three, rather than the hypothesized four, domain specific factors beyond the general factor. The bifactor model fit the data significantly better than the second-order model. The bifactor model allowed for easier interpretation of the relationship between the domain specific factors and external variables, over and above the general factor. Contrary to the literature, sufficient power existed to distinguish between bifactor and corresponding second-order models in one actual and one simulated example, given reasonable sample sizes. Advantages of bifactor models over second-order models are discussed.

Size dependency of nanocrystalline TiO2 on its optical property and photocatalytic reactivity exemplified by 2-chlorophenol

Abstract: Anatase TiO2 nanocrystallines (17–29 nm) were successfully synthesized by the metal–organic chemical vapor deposition method (MOCVD). Moderate manipulation of system parameters of MOCVD can control the particle size. The electro-optical and photocatalytic properties of the synthesized TiO2 nanoparticles were studied along with several commercially available ultra-fine TiO2 particles (e.g., 3.8–5.7 nm). The band gap of the TiO2 crystallines was determined using the transformed diffuse reflectance technique according to the Kubelka–Munk theory. Results showed that the band gap of TiO2 monotonically decreased from 3.239 to 3.173 eV when the particle size decreased from 29 to 17 nm and then increased from 3.173 to 3.289 eV as the particle size decreased from 17 to 3.8 nm. The results of band gap change as a function of particle size agreed well with what was predicted by the Brus’ equation, i.e., the effective mass model (EMM). However, results of the photocatalytic oxidation of 2-chlorophenol (2-CP), showed that the smaller the particle size, the faster the degradation rate. This is attributed in part to the combined effect of band gap change relative to the spectrum of the light source and the specific surface area (or particle size) of the photocatalysts. The change of band gap due to particle size represents only a small optical absorption window with respect to the total spectrum of the light source, i.e., from 380 to 400 nm versus >280 nm. Consequently, the gain in optical property of the larger particles was severely compromised by their decrease in specific surface area. Our results clearly indicated the importance of specific surface area in controlling the photocatalytic reactivity of photocatalysts. Results also showed that the secondary particle size grew with time due mainly to particle aggregation. The photocatalytic rate constants decreased exponentially with increase in primary particle size. Primary particle size alone is able to predict the photocatalytic rate as it is closely related to the electro-optical properties of photocatalysts.

Adaptation to ER stress is mediated by differential stabilities of pro-survival and pro-apoptotic mRNAs and proteins.

Abstract: The accumulation of unfolded proteins in the endoplasmic reticulum (ER) activates a signaling cascade known as the unfolded protein response (UPR). Although activation of the UPR is well described, there is little sense of how the response, which initiates both apoptotic and adaptive pathways, can selectively allow for adaptation. Here we describe the reconstitution of an adaptive ER stress response in a cell culture system. Monitoring the activation and maintenance of representative UPR gene expression pathways that facilitate either adaptation or apoptosis, we demonstrate that mild ER stress activates all UPR sensors. However, survival is favored during mild stress as a consequence of the intrinsic instabilities of mRNAs and proteins that promote apoptosis compared to those that facilitate protein folding and adaptation. As a consequence, the expression of apoptotic proteins is short-lived as cells adapt to stress. We provide evidence that the selective persistence of ER chaperone expression is also applicable to at least one instance of genetic ER stress. This work provides new insight into how a stress response pathway can be structured to allow cells to avert death as they adapt. It underscores the contribution of posttranscriptional and posttranslational mechanisms in influencing this outcome.

Biomechanical factors associated with tibial stress fracture in female runners.

Abstract: MILNER, C. E., R. FERBER, C. D. POLLARD, J. HAMILL, and I. S. DAVIS. Biomechanical Factors Associated with Tibial Stress Fracture in Female Runners. Med. Sci. Sports Exerc., Vol. 38, No. 2, pp. 323–328, 2006. Purpose: Tibial stress fractures (TSF) are among the most serious running injuries, typically requiring 6–8 wk for recovery. This cross-sectional study was conducted to determine whether differences in structure and running mechanics exist between trained distance runners with a history of prior TSF and those who have never sustained a fracture. Methods: Female runners with a rearfoot strike pattern, aged between 18 and 45 yr and running at least 32 kmIwk j1 , were recruited for this study. Participants in the study were 20 subjects with a history of TSF and 20 ageand mileage-matched control subjects with no previous lower extremity bony injuries. Kinematic and kinetic data were collected during overground running at 3.7 mIs j1 using a six-camera motion capture system, force platform, and accelerometer. Variables of interest were vertical impact peak, instantaneous and average vertical loading rates, instantaneous and average loading rates during braking, knee flexion excursion, ankle and knee stiffness, and peak tibial shock. Tibial varum was measured in standing. Tibial area moment of inertia was calculated from tibial x-ray studies for a subset of runners. Results: The TSF group had significantly greater instantaneous and average vertical loading rates and tibial shock than the control group. The magnitude of tibial shock predicted group membership successfully in 70% of cases. Conclusion: These data indicate that a history of TSF in runners is associated with

Optical properties of deep glacial ice at the South Pole

Abstract: We have remotely mapped optical scattering and absorption in glacial ice at the South Pole for wavelengths between 313 and 560 nm and depths between 1100 and 2350 m. We used pulsed and continuous light sources embedded with the AMANDA neutrino telescope, an array of more than six hundred photomultiplier tubes buried deep in the ice. At depths greater than 1300 m, both the scattering coefficient and absorptivity follow vertical variations in concentration of dust impurities, which are seen in ice cores from other Antarctic sites and which track climatological changes. The scattering coefficient varies by a factor of seven, and absorptivity (for wavelengths less than ∼450 nm) varies by a factor of three in the depth range between 1300 and 2300 m, where four dust peaks due to stadials in the late Pleistocene have been identified. In our absorption data, we also identify a broad peak due to the Last Glacial Maximum around 1300 m. In the scattering data, this peak is partially masked by scattering on residual air bubbles, whose contribution dominates the scattering coefficient in shallower ice but vanishes at ∼1350 m where all bubbles have converted to nonscattering air hydrates. The wavelength dependence of scattering by dust is described by a power law with exponent -0.90 ± 0.03, independent of depth. The wavelength dependence of absorptivity in the studied wavelength range is described by the sum of two components: a power law due to absorption by dust, with exponent -1.08 ± 0.01 and a normalization proportional to dust concentration that varies with depth; and a rising exponential due to intrinsic ice absorption which dominates at wavelengths greater than ∼500 nm. Copyright 2006 by the American Geophysical Union.

The versatile epsilon-proteobacteria: key players in sulphidic habitats.

Abstract: The epsilon-proteobacteria have recently been recognized as globally ubiquitous in modern marine and terrestrial ecosystems, and have had a significant role in biogeochemical and geological processes throughout Earth's history. To place this newly expanded group, which consists mainly of uncultured representatives, in an evolutionary context, we present an overview of the taxonomic classification for the class, review ecological and metabolic data in key sulphidic habitats and consider the ecological and geological potential of the epsilon-proteobacteria in modern and ancient systems. These integrated perspectives provide a framework for future culture- and genomic-based studies.

Number Sense Growth in Kindergarten: A Longitudinal Investigation of Children at Risk for Mathematics Difficulties

Abstract: Number sense development of 411 middle- and low-income kindergartners (mean age 5.8 years) was examined over 4 time points while controlling for gender, age, and reading skill. Although low-income children performed significantly worse than middle-income children at the end of kindergarten on all tasks, both groups progressed at about the same rate. An exception was story problems, on which the low-income group achieved at a slower rate; both income groups made comparable progress when the same problems were presented nonverbally with visual referents. Holding other predictors constant, there were small but reliable gender effects favoring boys on overall number sense performance as well as on nonverbal calculation. Using growth mixture modeling, 3 classes of growth trajectories in number sense emerged.

Concurrent multipath transfer using SCTP multihoming over independent end-to-end paths

Abstract: Concurrent multipath transfer (CMT) uses the Stream Control Transmission Protocol's (SCTP) multihoming feature to distribute data across multiple end-to-end paths in a multihomed SCTP association. We identify three negative side-effects of reordering introduced by CMT that must be managed before efficient parallel transfer can be achieved: (1) unnecessary fast retransmissions by a sender; (2) overly conservative congestion window (cwnd) growth at a sender; and (3) increased ack traffic due to fewer delayed acks by a receiver. We propose three algorithms which augment and/or modify current SCTP to counter these side-effects. Presented with several choices as to where a sender should direct retransmissions of lost data, we propose five retransmission policies for CMT. We demonstrate spurious retransmissions in CMT with all five policies and propose changes to CMT to allow the different policies. CMT is evaluated against AppStripe, which is an idealized application that stripes data over multiple paths using multiple SCTP associations. The different CMT retransmission policies are then evaluated with varied constrained receive buffer sizes. In this foundation work, we operate under the strong assumption that the bottleneck queues on the end-to-end paths used in CMT are independent.

Social Identities and Commitments at Work: Toward an Integrative Model.

Abstract: Although social identities and work-related commitment are important aspects of employee attachment, distinctions between and relations among the two have not been clearly articulated. In this conceptual piece, we propose that identity and commitment are distinguishable in terms of their essential meaning, foci of attachment, mindsets, volitionality, and behavioral implications. We further suggest that situated and deep structure social identities are differentially antecedent to exchange-based and value-based commitments, and that commitment mediates, at least partially, the effects of identities on motivation and work behavior. Finally, we consider the implications of multiple identities for employees in different kinds of collectives (nested and cross-cutting). Copyright © 2006 John Wiley & Sons, Ltd.

Direct and interaction effects of top management team and board compositions on R&D investment strategy

Abstract: This paper examines why firms differ in levels of R&D investment intensity by developing and testing a theory of direct and interaction effects of top management team and board outsider composition on R&D intensity. The theory is tested in a longitudinal sample of technology-intensive firms that completed an initial public offering. The results indicate that both top management team composition and board composition have direct and additive effects on R&D investment intensity. Also, monitoring by outsider directors does not constitute a universally effective governance mechanism with regard to a firm's R&D investment strategy. Firms opt for lower levels of R&D investment intensity when their outsider-rich board interacts with a team of managers who have high levels of (1) firm tenure, (2) shared team-specific experience, or (3) functional heterogeneity. When a firm's competitiveness relies on sustained R&D investments, it is important to note these interaction effects and make adjustments to promote a healthy dialogue between managers and the board. Adjustments could be made to the management team composition (e.g., initiating management turnover to reduce firm tenure) or to the bundle of governance mechanisms (e.g., partially substituting board monitoring with other mechanisms). Copyright © 2006 John Wiley & Sons, Ltd.

On the role of continuum-driven eruptions in the evolution of very massive stars and Population III stars

Abstract: We suggest that the mass lost during the evolution of very massive stars may be dominated by optically thick, continuum-driven outbursts or explosions, instead of by steady line-driven winds. In order for a massive star to become a Wolf-Rayet star, it must shed its hydrogen envelope, but new estimates of the effects of clumping in winds from O-type stars indicate that line driving is vastly insufficient. We discuss massive stars above roughly 40-50 M☉, which do not become red supergiants and for which the best alternative is mass loss during brief eruptions of luminous blue variables (LBVs). Our clearest example of this phenomenon is the 19th century outburst of η Carinae, when the star shed 12-20 M☉ or more in less than a decade. Other examples are circumstellar nebulae of LBVs and LBV candidates, extragalactic η Car analogs (the so-called supernova impostors), and massive shells around supernovae and gamma-ray bursters. We do not yet fully understand what triggers LBV outbursts or what supplies their energy, but they occur nonetheless, and they present a fundamental mystery in stellar astrophysics. Since line opacity from metals becomes too saturated, the extreme mass loss probably arises from a continuum-driven wind or a hydrodynamic explosion, both of which are insensitive to metallicity. As such, eruptive mass loss could have played a pivotal role in the evolution and ultimate fate of massive metal-poor stars in the early universe. If they occur in these Population III stars, such eruptions would also profoundly affect the chemical yield and types of remnants from early supernovae and hypernovae thought to be the origin of long gamma-ray bursts.

How Presentation Flaws Affect Perceived Site Quality, Trust, and Intention to Purchase from an Online Store

Abstract: Although there has been a great deal of research on impression formation, little application of that research has been made to electronic commerce. A research model was constructed that hypothesized errors, poor style, and incompleteness to be inversely related to the users' level of perceived quality of an online store. Further, this perceived quality of the online store's Web site would be directly related to users' trust in the store and, ultimately, to users' intentions to purchase from the store. An experimental study with 272 undergraduate and graduate student volunteers supported all the hypotheses. In addition, it was found that the relationship between the factors and perceived quality was mediated by the perception of the flaws. The perception of flaws rather than the actual flaws influenced users' perception of quality. Supplemental analysis also seemed to indicate a pattern of diminishing effects with each subsequent flaw.

A Multi-Theoretical Model of Knowledge Transfer in Organizations: Determinants of Knowledge Contribution and Knowledge Reuse*

Abstract: Knowledge has become one of the most important sources of competitive advantage for firms in many industries, particularly those in which firms provide knowledge services to their clients. Many knowledge intensive firms have spent enormous amounts of time and money trying to find ways to better manage their knowledge resources. Effective leveraging of knowledge resources through the transfer and reuse of existing knowledge is an important aspect of most knowledge management systems. In this study we argue that the effectiveness of intrafirm knowledge transfer based on the reuse of existing knowledge depends on two key factors: (1) the willingness of individuals to contribute their knowledge to the system; and (2) the rate at which individuals access and reuse knowledge within the system. Here we use social exchange theory to develop a model of the factors that will impact the frequency with which individuals contribute their knowledge to the system. Additionally, we use expectancy theory to develop a model of the factors that lead to knowledge reuse. Results of hypothesis tests using data collected from a multinational services firm support our multi-theoretical model, and suggest ways in which the model might be refined. We discuss the implications of these findings for further theory building and for managers engaged in the development and improvement of knowledge management systems.

Halftone visual cryptography

Abstract: Visual cryptography encodes a secret binary image (SI) into n shares of random binary patterns. If the shares are xeroxed onto transparencies, the secret image can be visually decoded by superimposing a qualified subset of transparencies, but no secret information can be obtained from the superposition of a forbidden subset. The binary patterns of the n shares, however, have no visual meaning and hinder the objectives of visual cryptography. Extended visual cryptography was proposed recently to construct meaningful binary images as shares using hypergraph colourings, but the visual quality is poor. In this paper, a novel technique named halftone visual cryptography is proposed to achieve visual cryptography via halftoning. Based on the blue-noise dithering principles, the proposed method utilizes the void and cluster algorithm to encode a secret binary image into n halftone shares (images) carrying significant visual information. The simulation shows that the visual quality of the obtained halftone shares are observably better than that attained by any available visual cryptography method known to date.

Simulating Radiating and Magnetized Flows in Multiple Dimensions with ZEUS-MP

Abstract: This paper describes ZEUS-MP, a multi-physics, massively parallel, message-passing implementation of the ZEUS code. ZEUS-MP differs significantly from the thoroughly documented ZEUS-2D code, the completely undocumented (in peer-reviewed literature) ZEUS-3D code, and a marginally documented “version 1” of ZEUS-MP first distributed publicly in 1999. ZEUS-MP offers an MHD algorithm which is better suited for multidimensional flows than the ZEUS-2D module by virtue of modifications to the Method of Characteristics scheme first suggested by Hawley & Stone (1995). This MHD module is shown to compare quite favorably to the TVD scheme described by Ryu et al. (1998). ZEUS-MP is the first publicly-available ZEUS code to allow the advection of multiple chemical (or nuclear) species. Radiation hydrodynamic simulations are enabled via an implicit flux-limited radiation diffusion (FLD) module. The hydrodynamic, MHD, and FLD modules may be used, singly or in concert, in one, two, or three space dimensions. Additionally, so-called “1.5-D” and “2.5-D” grids, in which the “half-D” denotes a symmetry axis along which a constant but non-zero value of velocity or magnetic field is evolved, are supported. Self gravity may be included either through the assumption of a GM/r potential or a solution of Poisson’s equation using one of three linear solver packages (conjugategradient, multigrid, and FFT) provided for that purpose. Point-mass potentials are also supported. Because ZEUS-MP is designed for large simulations on parallel computing platforms, considerable attention is paid to the parallel performance characteristics of each module in the code. Strong-scaling tests involving pure hydrodynamics (with and without self-gravity), MHD, and RHD are performed in which large problems (256 3 zones) are distributed among as many as 1024 processors of an IBM SP3. Parallel efficiency is a strong function of the amount of communication required between processors in a given algorithm, but all modules are shown to scale well on up to 1024 processors for the chosen fixed problem size. Subject headings: hydrodynamics – methods:numerical – methods:parallel – MHD – radiative transfer

Intentional modulation of emotional responding to unpleasant pictures: An ERP study

Abstract: Intentionally altering responses to unpleasant stimuli affects physiological and hemodynamic activity associated with emotional and cognitive processing. In the present experiment, we measured the late-positive potential (LPP) of the visually evoked event-related brain potential to examine the effects of intentional emotion modulation on electrophysiological correlates of emotional and cognitive processing. Seventeen participants received instructions to view, suppress, and enhance emotional responses to unpleasant stimuli. Results revealed significantly decreased electrophysiological activity during suppression of emotional responses beginning around 250 ms poststimulus and lasting several hundred milliseconds. These data suggest that ERPs are sensitive to emotion modulation/regulation processes. Descriptors: Late-positive potential, LPP, Unpleasant pictures, Emotion modulation/regulation, Attention Researchers have begun to examine the effects of instructions to alter responding to emotional stimuli on physiological and neural indices of emotional and cognitive processing (cf. Ochsner &

Polymer crystallization-driven, periodic patterning on carbon nanotubes

Abstract: We report herein a unique means to periodically pattern polymeric materials on individual carbon nanotubes (CNTs) using a controlled polymer crystallization method. One-dimensional (1D) CNTs were periodically decorated with polymer lamellar crystals, resulting in nano-hybrid shish-kebab (NHSK) structures. The periodicity of the polymer lamellae varies from 20 to 150 nm. The kebabs are approximately 5-10 nm thick (along CNT direction) with a lateral size of approximately 20 nm to micrometers, which can be readily controlled by varying crystallization conditions. Both polyethylene and Nylon 66 were successfully decorated on single-walled carbon nanotubes (SWNTs), multiwalled carbon nanotubes (MWNTs), as well as vapor grown carbon nanofibers (CNFs). The formation mechanism was attributed to "size-dependent soft epitaxy". Because NHSK formation conditions depend on CNT structures, it further provides a unique opportunity for CNT separation. The reported method opens a gateway to periodically patterning polymers and different functional groups on individual CNTs in an ordered and controlled manner, an attractive research field that is yet to be explored.

qualitative-methods-in-inverse-scattering-theory

Abstract: A major problem in the use of ultrasound or microwaves for purposes of nondestructive testing or medical imaging is the computational complexity of solving the inverse scattering problem that arises in such applications. This is due to the fact that in order to achieve satisfactory resolution and sufficient penetration of the wave into the material it is often necessary to use frequencies in the resonance region. In this case the inverse scattering problem is not only improperly posed but also nonlinear and even in the case of two dimensions the time needed to solve such problems can be prohibitive. To date the time consuming nature of the problem has mainly been dealt with by the introduction of various innovative schemes that avoid the use of volume integral equations and instead rely on finite difference or finite element methods (cf. [5], [8]). However, for large scale problems (for example those involving imaging of the human body) the problem of computational complexity remains a serious problem for any practitioner. In this paper we would like to propose a different approach to this problem that, although still in its infancy, has the promise of providing rapid solutions to a number of inverse scattering problems of practical significance.

Flapping flight for biomimetic robotic insects: part I-system modeling

Abstract: This paper presents the mathematical modeling of flapping flight inch-size micro aerial vehicles (MAVs), namely micromechanical flying insects (MFIs). The target robotic insects are electromechanical devices propelled by a pair of independent flapping wings to achieve sustained autonomous flight, thereby mimicking real insects. In this paper, we describe the system dynamic models which include several elements that are substantially different from those present in fixed or rotary wing MAVs. These models include the wing-thorax dynamics, the flapping flight aerodynamics at a low Reynolds number regime, the body dynamics, and the biomimetic sensory system consisting of ocelli, halteres, magnetic compass, and optical flow sensors. The mathematical models are developed based on biological principles, analytical models, and experimental data. They are presented in the Virtual Insect Flight Simulator (VIFS) and are integrated together to give a realistic simulation for MFI and insect flight. VIFS is a software tool intended for modeling flapping flight mechanisms and for testing and evaluating the performance of different flight control algorithms

Automating Arm Movement Training Following Severe Stroke: Functional Exercises With Quantitative Feedback in a Gravity-Reduced Environment

Abstract: An important goal in rehabilitation engineering is to develop technology that allows individuals with severe motor impairment to practice arm movement without continuous supervision from a rehabilitation therapist. This paper describes the development of such a system, called Therapy WREX or ("T-WREX"). The system consists of an orthosis that assists in arm movement across a large workspace, a grip sensor that detects hand grip pressure, and software that simulates functional activities. The arm orthosis is an instrumented, adult-sized version of the Wilmington Robotic Exoskeleton (WREX), which is a five degrees-of-freedom mechanism that passively counterbalances the weight of the arm using elastic bands. After providing a detailed design description of T-WREX, this paper describes two pilot studies of the system's capabilities. The first study demonstrated that individuals with chronic stroke whose arm function is compromised in a normal gravity environment can perform reaching and drawing movements while using T-WREX. The second study demonstrated that exercising the affected arm of five people with chronic stroke with T-WREX over an eight week period improved unassisted movement ability (mean change in Fugl-Meyer score was 5 points plusmn2 SD; mean change in range of motion of reaching was 10%, p<0.001). These results demonstrate the feasibility of automating upper-extremity rehabilitation therapy for people with severe stroke using passive gravity assistance, a grip sensor, and simple virtual reality software