Showing papers by "Lehigh University published in 1993"

Log-domain filtering: an approach to current-mode filtering

Abstract: A novel approach to filter design, based on Adams' [1] ‘log-domain’ filters, is proposed that yields a truly current-mode circuit realisation. Adams' idea, which was introduced in a limited context, is generalised to permit a complete distortionless synthesis procedure, which results in circuit implementations readily realisable using complementary bipolar processes. It is shown that, by introducing an exponential map on the state-space description of the desired linear system, a log-domain filter can be fully realised with transistors configured in current mirror-type groupings, current sources and capacitors. Owing to the mapping, the state variables are intrinsically related to current, and not voltage, in the resulting circuits, a fact that emphasises the current-mode nature of the design. A general biquadratic filter section is designed, and, following discussion of cascading sections, a seventh-order Chebychev lowpass filter is designed. All designed circuits are shown to be tunable over a two-decade range in frequency while their characteristics are accurately preserved, even for biquad sections whose f0Q product is greater than fT/10. The Chebychev filter is shown in simulation to possess nearly 60 dB dynamic range relative to 0.9% THD, with a cutoff frequency of nearly 5 MHz, using transistor models from AT&T's CBIC-R 300 MHz complementary bipolar process.

Inequality decomposition analysis and the Gini coefficient revisited

Abstract: The Gini coefficient has long been thought unsuitable for inequality decomposition analysis because of a troublesome and little-understood residual term that occurs when subgroup income ranges overlap after the between-groups and within-groups contributions to inequality have been separated out. In this paper, graphical analysis is used to provide a solid understanding of the residual term as a subarea of the Lorenz diagram. Implications for inequality decomposition analysis are considered. Copyright 1993 by Royal Economic Society.

Parent training for Attention Deficit Hyperactivity Disorder: Its impact on parent functioning

Abstract: This study examined changes in parent functioning resulting from parental participation in a behavioral parent training (PT) program specifically designed for school-aged children with attention-deficit hyperactivity disorder (ADHD). Relative to wait list controls, subjects who completed the nine-session PT program showed significant posttreatment gains in both child and parent functioning, which were maintained 2 months after treatment. In particular, there were PT-induced reductions in parenting stress and increases in parenting self-esteem, which accompanied parent-reported improvements in the overall severity of their child's ADHD symptoms. In addition to their statistical importance, these findings are discussed in terms of their clinical significance, utilizing methods developed by Jacobson and Truax (1991).

Representational content in humans and machines

Abstract: This article focuses on the problem of representational content. Accounting for representational content is the central issue in contemporary naturalism: it is the major remaining task facing a naturalistic conception of the world. Representational content is also the central barrier to contemporary cognitive science and artificial intelligence: it is not possible to understand representation in animals nor to construct machines with genuine representation given current (lack of) understanding of what representation is. An elaborated critique is offered to current approaches to representation, arguing that the basic underlying approach is, at root, logically incoherent, and, thus, that standard approaches are doomed to failure. An alternative model of representation— interactivism is presented that avoids or solves the problems facing standard approaches. Interactivism is framed by a version of functionalism, and a naturalization of that functionalism completes an outline of a naturalization of r...

Mechanical behavior of alumina-silicon carbide «Nanocomposites»

Abstract: The fracture behavior of Al2O3 containing 5 vol% 0.15μm SiC particles was investigated using indentation techniques. A significant increase in strength was achieved by the addition of SiC particles to the base Al2O3. Specifically, the strength increased from 560 MPa for Al2O3 to 760 MPa for the composite samples (average values for unindented hotpressed bars tested in four-point bending). After annealing for 2 h at 1300°C, the average strength of the composite samples increased to about 1000 MPa. Toughness was estimated using indentation-strength data. While there was a slight increase in toughness, the increase was not sufficient to account for the increase in the unindented strength on SiC particle addition. It is suggested that the observed strengthening and apparent toughening were due to a machining-induced compressive surface stress.

Redistribution effect and unequal income tax treatment

Abstract: Decomposing the post-tax Gini coefficient across groups of pre-tax equals reveals the separate contributions to the redistributive effect of an income tax of (1) the effective schedule (the vertical effect), (2) the unequal treatment of equals arising from departures from this effective schedule (the horizontal effect), and (3) the reranking of unequals as a result of such departures (the reranking effect). The methodology is applied to U.K. microdata. Throughout the period 1978-91, reranking understates the (negative) contribution to redistributive effect of unequal tax treatment by about one third and is far outweighed by the vertical effect. Copyright 1994 by Royal Economic Society.

Chaotic digital encoding: an approach to secure communication

Abstract: A method for using chaos in the digital domain for secure communications is proposed. The method uses a nonlinear digital filter with finite precision (8 bits) in conjunction with its inverse filter to implement an encoder and a decoder, respectively. The nature of the encoder is such that it behaves in a quasi-chaotic fashion (since chaotic behavior requires infinite precision), both with zero and nonzero input sequences. The determination of its quasi-chaotic behavior is based on QC-properties defined in the paper, which are proposed as a test for finite state digital filters. At the very least, these properties suggest that the encoder possessing them will be of value in secure communications applications. Variations on the encoding scheme are suggested that allow the potential for a wide range of applications, ranging from cost-effective real-time systems to high security systems incorporating one or more "keys." Simulation results as well as a mathematical analysis are used to promote an understanding of the performance of the nonlinear encoder/decoder. >

Control of particle size in dispersion polymerization of methyl methacrylate

Abstract: Poly(methyl methacrylate) (PMMA) particles ranging in diameter from 2 to 10 μm were prepared by dispersion polymerization. The effects of various polymerization parameters on the size and monodispersity were systematically investigated. The particle size was found to increase with increasing polymerization temperature, concentration and decomposition rate of the initiator, and solvency of the dispersion medium. It also increased with increasing concentration and molecular weight of the polymeric stabilizer, poly(vinyl pyrrolidone) (PVP). As the monomer concentration was increased from 5 to 20 wt %, a minimum was found in the particle size at a monomer concentration of 10 wt %. A costabilizer was found to be necessary for preparing monodisperse particles at stabilizer concentrations below 2 wt %. A recycling experiment showed that the consumption of PVP was quite small in each cycle and the residual materials in this system could be reused readily. © 1993 John Wiley & Sons, Inc.

Synchronous anatexis, metamorphism, and rapid denudation at Nanga Parbat (Pakistan Himalaya)

Abstract: The Nanga Parbat-Haramosh massif of the western Himalaya is a north-trending half-window of Indian crust that provides spectacular exposures of Precambrian basement gneisses that have been overprinted by Himalayan metamorphism. We report here petrologic data and U/Pb dates on zircon and monazite which document that Nanga Parbat gneisses underwent a Pliocene-Pleistocene episode of high-grade metamorphism and anatexis during an interval in which the Nanga Parbat massif was undergoing rapid denudation at mean rates of ∼5 mm/yr. We speculate that by initiating decompression melting, this denudation may be at least partly responsible for the anatexis and high-grade metamorphism.

Teacher use of descriptive analysis data to implement interventions to decrease students' problem behaviors.

Abstract: We conducted two field studies using a behavioral consultation approach to reduce children's problem behaviors in public school settings. The first study consisted of a descriptive analysis in which the students and their teachers were observed during naturally occurring classroom activities. The results of the descriptive analysis provided hypotheses regarding the operant function of the students' problem behaviors. The hypotheses were tested in the second experiment directly through a modified experimental analysis and indirectly through an evaluation of the treatment effects. The interventions were designed to disrupt the inappropriate response-reinforcer relation by discontinuing contingent reinforcement (i.e., extinction), providing the reinforcer contingent on appropriate play behaviors, and teaching the students verbal skills functionally equivalent to the inappropriate response. The classroom teachers were trained to implement the interventions and conduct the experimental analyses during classroom activities in which the problem behaviors occurred most frequently. The interventions were effective in decreasing the students' problem behaviors while concurrently increasing their appropriate verbal skills.

Engineering Applications of Electrorheological Materials

Abstract: This article provides a summary of the current state of electrorheological (ER) material applications research and development. The use of ER materials in a variety of intelligent material systems is covered. A description of basic material configurations used in controllable system components, as well as a discussion of controllable devices such as antivibration mounts, clutches, and dampers, is presented. More recent developments in the area of ER material adaptive structures are then reviewed. Concepts underlying such structures are presented, and models that have been developed to simulate the response of such structures are summarized. Throughout the ar ticle, an attempt is made to identify current and future key areas of research and development in ER material applications technology.

Review : Material Aspects of Electrorheological Systems

Abstract: This paper provides a summary of the current state of electrorheological (ER) material research and development. In particular, a description of the electrorheological effect, a defini tion of obse...

Political Similarity and American Foreign Trade Patterns

Abstract: International economic flows have become an increasingly prominent component of both international relations and domestic politics over the last two decades Even though politically motivated governments have played a growing role in shaping these transactions, empirical studies have largely ignored the political determinants of international trade patterns This study addresses that important gap in our understanding of the international political economy with particular reference to United States trade We theorize that two aspects of the relations between nations should predict enhanced trade levels: similarity in political system and similarity in foreign policy orientation We test this proposition for US exports to 76 importing nations over an 18-year period in a pooled time- series design that controls for known influences on trade flows Our results suggest that these two political factors have a substantial and predictable impact on US export patterns We consider some possible criticisms of

High image-density particle image velocimetry using laser scanning techniques

Abstract: Laser scanning, corresponding to time-dependent deflections of laser beam across a field of interest, can provide relatively high illumination intensity of small particles, thereby allowing implementation of high image-density particle image velocimetry (PIV). Scanning techniques employing a rotating (multi-faceted) mirror, an oscillating mirror, and an acousto-optic deflector are addressed. Issues of illumination intensity and exposure, rate of scan of the laser beam, and retrace time of the scanning beam are assessed. Representative classes of unsteady separated flows investigated with laser-scanning PIV are described.

Peer Tutoring Effects on the Classroom Performance of Children with Attention Deficit Hyperactivity Disorder.

Abstract: Classwide peer tutoring procedures involve instructional procedures (e.g., provision of frequent, immediate feedback) that are known to be successful for children with Attention Deficit Hyperactivi...

Regulation of microtubule dynamic instability

Abstract: Characterization of microtubule assembly in vivo and in vitro has raised questions of how cells regulate dynamic instability. While dynamic instability is an intrinsic property of the tubulin molecule, factors are required to increase the plus-end elongation rate and increase the frequencies of both catastrophe and rescue to achieve cellular tubulin turnover rates. It is likely that the activities of the transition frequency regulators are themselves regulated during the cell cycle, but the mechanisms of regulation are not known. As we identify the proteins which alter microtubule assembly, new classes of MAPs will emerge. An understanding of how these proteins function may provide further insight into how cells organize the different arrays of microtubules used for such processes as vesicle transport, polarized organization of organelles, and chromosome movement.

Flaw-tolerance and crack-resistance properties of alumina-aluminum titanate composites with tailored microstructures

Abstract: The microstructures of alumina-aluminum titanate (A-AT) composites have been tailored with the intent of altering their crack-resistance (R- or T-curve) behavior and resulting flaw tolerance. Specifically, two microstructural parameters which influence grain-localized crack bridging, viz., (1) internal residual stresses and (2) microstructural coarseness, have been investigated. Particulate aluminum titanate was added to alumina to induce intense internal residual stresses from extreme thermal intense internal residual stresses from extreme thermal expansion mismatch. It was found that A-AT composites with uniformly distributed 20-30 vol% aluminum titanate (duplex) showed significantly improved flaw tolerance over single-phase alumina. Coarsening of the duplex microstructure via grain growth scaling was relatively ineffective in improving the flaw tolerance further. Onset of spontaneous microcracking precluded further exploitation of this scaling approach. Therefore, an alternative approach to coarsening was developed, in which a uniform distribution of large alumina grains was incorporated within a fine-grain A-AT matrix (duplex-bimodal), via a powder processing route. The duplex-bimodal composites yielded excellent flaw tolerance with steady-state toughness of [approximately]8 MPa [center dot] m[sup 1/2]. A qualitative model for microstructure development in these duplex-bimodal composites is presented.

Anger and Gender: Theory, Research, and Implications

Abstract: The idea that women and men differ significantly in the experience and expression of anger continues to be a popular one in the psychological and counseling literature, even though there is little empirical support for it. In this article the author examines theoretical perspectives on female and male anger and provides a review of studies that have explored anger as a function of gender. Implications for research and practice are discussed.

Polar fluctuations and first-order Raman scattering in highly polarizable KTaO3 crystals with off-center Li and Nb ions.

Abstract: Relatively low concentrations of randomly substituted off-center ions are known to induce ferroelectric order in highly polarizable crystals. In the case of potassium tantalate (KTaO[sub 3]) doped with lithium or niobium, the results of first-order Raman scattering from two hard phonon modes (TO[sub 2] and TO[sub 3]) show that polar microregions are formed at relatively high temperatures. At lower temperatures, and above a certain critical dopant concentration, the Raman results are consistent with the occurrence of a structural phase transition. These results can be reasonably explained by using a random-molecular-field theory that takes into account the indirect dipolar interactions mediated by the soft lattice. This approach accounts for the characteristic asymmetry of the TO[sub 2] Raman scattering detected at high temperatures and for the subsequent increase in the integrated scattering intensity with decreasing temperature. An analysis of the Raman results provides a means for determining the size of the polar microregions formed in the highly polarizable KTaO[sub 3] lattice. The good agreement obtained between the theoretical and experimental results provides support to the physical concepts embodied in the present theoretical approach to describing the onset of order in these systems.

Control of vortices on a delta wing by leading-edge injection

Abstract: This experimental investigation addresses the control of flow past a half-delta wing at high angle of attack. Application of steady blowing, steady suction, or alternate suction-blowing in the tangential direction along the leading edge of the wing can retard substantially the onset of vortex breakdown and stall. The most effective period of the alternate suction-blowing is on the order of one convective time scale of the flow past the wing. As a result of this type of control, the vortex structure in the crossflow plane is modified from a fully stalled condition to a highly coherent leading-edge vortex. This transformation to a restabilized vortex is represented by instantaneous velocity fields, streamline patterns, and vorticity contours

Paleomagnetically derived folding rates, southern Pyrenees, Spain

Abstract: Well-dated syntectonic unconformities with the Spanish Pyrenees allow characterization of sedimentation and deformation within an orogenic foreland. The Spanish Pyrenees are composed of a south-vergent thrust belt and foreland basin in which folds developed both parallel and perpendicular to tectonic transport. Unconformity geometries and magnetostratigraphic data from synorogenic strata provide a precise temporal framework for the quantitative analysis of the Mediano anticline, the largest of the transverse folds. Folding began in the early Eocene and ended by ∼42 Ma at which time an anticline 20 km long and ∼5 km in wavelength had been produced. Angular and progressive unconformities within syntectonic sedimentary units preserve the history of fold development. Fold growth resulted from west-ward salt movement driven by prograding sediments and was characterized by 2-3 m.y. intervals of slow continuous limb tilting, 2.2°-4.2°/m.y., preserved as progressive unconformities within syntectonic strata. Because the emplacement of the Cotiella-Montsec thrust sheet was episodic, intervals of slow fold growth were punctuated by intervals lasting