Showing papers by "University of Central Florida published in 1995"

Formulation for stable and efficient implementation of the rigorous coupled-wave analysis of binary gratings

Abstract: The rigorous coupled-wave analysis technique for describing the diffraction of electromagnetic waves by periodic grating structures is reviewed. Formulations for a stable and efficient numerical implementation of the analysis technique are presented for one-dimensional binary gratings for both TE and TM polarization and for the general case of conical diffraction. It is shown that by exploitation of the symmetry of the diffraction problem a very efficient formulation, with up to an order-of-magnitude improvement in the numerical efficiency, is produced. The rigorous coupled-wave analysis is shown to be inherently stable. The sources of potential numerical problems associated with underflow and overflow, inherent in digital calculations, are presented. A formulation that anticipates and preempts these instability problems is presented. The calculated diffraction efficiencies for dielectric gratings are shown to converge to the correct value with an increasing number of space harmonics over a wide range of parameters, including very deep gratings. The effect of the number of harmonics on the convergence of the diffraction efficiencies is investigated. More field harmonics are shown to be required for the convergence of gratings with larger grating periods, deeper gratings, TM polarization, and conical diffraction.

Stable implementation of the rigorous coupled-wave analysis for surface-relief gratings: enhanced transmittance matrix approach

Abstract: An enhanced, numerically stable transmittance matrix approach is developed and is applied to the implementation of the rigorous coupled-wave analysis for surface-relief and multilevel gratings. The enhanced approach is shown to produce numerically stable results for excessively deep multilevel surface-relief dielectric gratings. The nature of the numerical instability for the classic transmission matrix approach in the presence of evanescent fields is determined. The finite precision of the numerical representation on digital computers results in insufficient accuracy in numerically representing the elements produced by inverting an ill-conditioned transmission matrix. These inaccuracies will result in numerical instability in the calculations for successive field matching between the layers. The new technique that we present anticipates and preempts these potential numerical problems. In addition to the full-solution approach whereby all the reflected and the transmitted amplitudes are calculated, a simpler, more efficient formulation is proposed for cases in which only the reflected amplitudes (or the transmitted amplitudes) are required. Incorporating this enhanced approach into the implementation of the rigorous coupled-wave analysis, we obtain numerically stable and convergent results for excessively deep (50 wavelengths), 16-level, asymmetric binary gratings. Calculated results are presented for both TE and TM polarization and for conical diffraction.

Observation of two-dimensional spatial solitary waves in a quadratic medium.

Abstract: We report the first experimental demonstration of two-dimensional spatial solitary waves in second-order nonlinear optical material When an intense optical beam is focused into a phase-matchable second-order nonlinear material, the fundamental and generated second-harmonic fields are mutually trapped as a result of the strong nonlinear coupling which counteracts both diffraction and beam walkoff

Human probability matching behaviour in response to alarms of varying reliability.

Abstract: The goals of this research were to substantiate the existence of the cry-wolf effect for alarm responses, quantifying its effect on operator performance. A total of 138 undergraduate students performed two blocks of a cognitively demanding psychomotor primary task; at the same time, they were presented with alarms of varying reliabilities (25, 50 and 75% true alarms) and urgencies (green, yellow and red visual alarms presented concurrently with low-, medium- and high-urgency auditory civilian aircraft cockpit alarms). Alarm response frequencies were observed and analysed, and t-tests and repeated-measures MANOVAs were used to assess the effects of increasing alarm reliability on alarm response frequencies, speed and accuracy. The results indicate that most subjects (about 90%) do not respond to all alarms but match their response rates to the expected probability of true alarms (probability matching). About 10% of the subjects responded in the extreme, utilizing an all-or-none strategy. Implications of these results for alarm design instruction and further research are discussed.

Optimal design for antireflective tapered two-dimensional subwavelength grating structures

Abstract: Techniques for the design of continuously tapered two-dimensional (2D) subwavelength surface-relief grating structures for broadband antireflection surfaces are investigated. It has been determined that the Klopfenstein taper [ Proc. IRE44, 31 ( 1956)] produces the optimum graded-index profile with the smallest depth for any specified minimum reflectance. A technique is developed to design the equivalent tapered subwavelength surface-relief grating structure by use of 2D effective-medium theory. An optimal Klopfenstein tapered 2D subwavelength grating is designed to reduce the Fresnel reflections by 20 dB over a broad band from an air–substrate (ns = 3.0) interface. The performance is verified by use of both a 2D effective-medium-theory simulation algorithm and rigorous coupled-wave analysis. These structures are also shown to achieve this low reflectance over a wide field of view (θFOV > 110°). The pyramidal spatial profile, which has generally been assumed to produce the optimal broadband antireflection grating structure, is shown to require a significantly larger depth to achieve the same performance as a Klopfenstein-designed tapered antireflection grating structure.

Method for detecting and extracting text data using database schemas

Abstract: An Information Filtering (IF) system for retrieving relevant text data from a data base document collection is disclosed. A user can use this system to access a dynamic data stream to retrieve relevant data such as accessing e-mail or a wire-service. Alternatively, a user can use the IF system to access an data storage archive such as electronically stored patents, journals and the like. The invention includes several steps. The first step has a user reduce the information they are interested in into a tangible form such as manually writing a natural language user need statement, or alternatively imputing the statement electronically into a computer file for storage. The next step is to create a filter window having an adjustable document viewing text length, that will be used to electronically scan through the database collection of documents in order to determine a relevancy value for each scanned document. The filter can be created several ways using synonym and domain lists. Alternatively, the synonym and lists for each document can be determined by Entity-Relationship (ER) modelling to generate a search schema. After documents receive relevancy values, the user is free to view only those documents having relevancy values that exceed a preselected threshold value. Documents can be ranked from most relevant to least relevant. Feedback information from viewing the retrieved documents can be used to update the synonym/domain lists of the filtering window to enhance the relevance retrieval of subsequent documents.

Global perspectives on the ecology of human-machine systems

Abstract: Contents: Preface. J.M. Flach, The Ecology of Human-Machine Systems: A Personal History. P.A. Hancock, M.H. Chignell, On Human Factors. K.J. Vicente, A Few Implications of an Ecological Approach to Human Factors. A. Kirlik, Requirements for Psychological Models to Support Design: Toward Ecological Task Analysis. J. Rasmussen, A.M. Pejtersen, Virtual Ecology of Work. D.D. Woods, Toward a Theoretical Base for Representation Design in the Computer Medium: Ecological Perception and Aiding Human Cognition. J.M. Flach, R. Warren, Active Psychophysics: The Relation Between Mind and What Matters. W.H. Warren, Jr., Constructing an Econiche. B.S. Zaff, Designing with Affordances in Mind. M.J. Dainoff, L.S. Mark, Use of a Means-End Abstraction Hierarchy to Conceptualize the Ergonomic Design of Workplaces. R.E. Shaw, O.M. Flascher, E.E. Kadar, Dimensionless Invariants for Intentional Systems: Measuring the Fit of Vehicular Activities to Environmental Layout. G.P. Bingham, M.M. Muchisky, "Center of Mass Perception": Affordances as Dispositions by Dynamics.

Modified wurtzite structure oxide compounds as substrates for III-V nitride compound semiconductor epitaxial thin film growth

Abstract: Semiconductor light emitting and sensing devices are comprised of a lattice matching wurtzite structure oxide substrate and a III-V nitride compound semiconductor single crystal film epitaxially grown on the substrate. Single crystals of these oxides are grown and the substrates are produced. The lattice matching substrates include Lithium Aluminum Oxide (LiAlO 2 ), Lithium Gallium Oxide (LiGaO 2 ), Lithium Silicon Oxide (Li 2 SiO 3 ), Lithium Germanium Oxide (Li 2 GeO 3 ), Sodium Aluminum Oxide (NaAlO 2 ), Sodium Gallium Oxide (NaGaO 2 ), Sodium Germanium Oxide (Na 2 GeO 3 ), Sodium Silicon Oxide (Na 2 SiO 3 ), Lithium Phosphor Oxide (Li 3 PO 4 ), Lithium Arsenic Oxide (Li 3 AsO 4 ), Lithium Vanadium Oxide (Li 3 VO 4 ), Lithium Magnesium Germanium Oxide (Li 2 MgGeO 4 ), Lithium Zinc Germanium Oxide (Li 2 ZnGeO 4 ), Lithium Cadmium Germanium Oxide (Li 2 CdGeO 4 ), Lithium Magnesium Silicon Oxide (Li 2 MgSiO 4 ), Lithium Zinc Silicon Oxide (Li 2 ZnSiO 4 ), Lithium Cadmium Silicon Oxide (Li 2 CdSiO 4 ), Sodium Magnesium Germanium Oxide (Na 2 MgGeO 4 ), Sodium Zinc Germanium Oxide (Na 2 ZnGeO 4 ) and Sodium Zinc Silicon Oxide (Na 2 ZnSiO 4 ). These substrates are used to grow single crystal epitaxial films of III-V nitride compound semiconductors with the composition Al x In y Ga 1-x-y N 0≦x≦1, 0≦y≦1, and 0≦x+y≦1. The semiconductor light devices can also include mixed combinations of any two or more of the above listed compounds. Furthermore, the preferred lattice matching substrates can include all the above listed modified wurtzite structure oxide compounds and their mixed crystals with substitution of the following elements, Be, B, N, Cr, Mn, Fe, Co, Ni, Cu, In and Sb. With the exception of N which can partially replaces oxygen only, all the rest elements are able to replace partially the cations of the above mentioned wurtzite structure oxide compounds. The types of semiconductor light devices that use this invention include light emitting devices, laser diodes, optical pumped laser diodes and optical detectors such as photoluminescence sensors and photo detectors. The laser diode devices can include a lateral or vertical Fabry-Perot resonant cavity, with or without metal electrodes.

A two-handed interface for object manipulation in virtual environments

Abstract: A two-handed direct manipulation VE virtual environment interface has been developed as an intuitive manipulation metaphor for graphical objects. A new input device called ChordGloves introduces a simple technique for rapid and repeatable gesture recognition; the Chordgloves emulate a pair of 3-D mice and a keyboard. A drafting table is isomorphically mapped into the VE and provides hand support for 2-D interface techniques, as well as a reference frame for calibrating the mapping between real and virtual worlds. A cursor gravity function is used to grab vertices, edges, or faces and establish precisely aligned differential constraints between objects called anchors. The capability of subjects to translate, rotate, scale, align, and glue objects is tested with a puzzle building task. An approximation of the puzzle task is done in Adobe Illustrator to provide a performance reference. Results and informal user observations as well as topics for future work are presented.

Optical scintillations and fade statistics for a satellite-communication system

Abstract: Estimates of the scintillation index, fractional fade time, expected number of fades, and mean duration of fade time associated with a propagating Gaussian-beam wave are developed for uplink and downlink laser satellite-communication channels. Estimates for the spot size of the beam at the satellite or the ground or airborne receiver are also provided. Weak-fluctuation theory based on the log-normal model is applicable for intensity fluctuations near the optical axis of the beam provided that the zenith angle is not too large, generally not exceeding 60°. However, there is an increase in scintillations that occurs with increasing pointing error at any zenith angle, particularly for uplink channels. Large off-axis scintillations are of particular significance because they imply that small pointing errors can cause serious degradation in the communication-channel reliability. Off-axis scintillations increase more rapidly for larger-diameter beams and, in some cases, can lead to a radial saturation effect for pointing errors less than 1 µrad off the optical beam axis.

Realizing the full potential of virtual reality: human factors issues that could stand in the way

Abstract: Reviews several significant human factors issues that could stand in the way of virtual reality realizing its full potential. These issues involve maximizing human performance efficiency in virtual environments, minimizing health and safety issues, and circumventing potential social issues through proactive assessment.

Information visualization; assisting low spatial individuals with information access tasks through the use of visual mediators.

Abstract: This study investigated the use of visual mediators to facilitate information access by low spatial individuals. Based on theories of adaptive learning and field-dependence, two human-computer interfaces were developed which were intended to compensate for the inability of low spatial individuals to readily construct visual mental models of a menu system's structure. The two compensatory interfaces included: a 2D visual hierarchy and a linear structure. The information search performance of high and low spatial individuals was compared on the two compensatory interfaces and a third challenge match interface, which challenged individuals to construct a mental model of a hierarchical menu system in order to perform efficiently. The visual mediators were successful in accommodating low spatial individuals, as indicated by the lack of any significant performance differences being detected between the high and low spatial groups on the two compensatory interfaces. High spatial individuals outperformed low spat...

Local applications of the ecological approach to human-machine systems

Abstract: Contents: Preface. W. Schiff, W. Arnone, Perceiving and Driving: Where Parallel Roads Meet. S.B. Flynn, T.A. Stoffregen, Perceiving and Avoiding Rollover in Agricultural Tractors. J.M. Flach, R. Warren, Low-Altitude Flight. J. Grosz, R.T. Rysdyk, R.J. Bootsma, J.A. Mulder, J.C. van der Vaart, P.C.W. van Wieringen, Perceptual Support for Timing of the Flare in the Landing of an Aircraft. G.E. Riccio, Coordination of Postural Control and Vehicular Control: Implications for Multimodal Perception and Simulation of Self-Motion. G.J.F. Smets, Designing for Telepresence: The Delft Virtual Window System. J.P. Hansen, Representation of System Invariants by Optical Invariants in Configural Displays for Process Control. L.A. Whitaker, V.G. CuQlock-Knopp, Human Exploration and Perception in Off-Road Navigation. H.L. Pick, M.R. Heinrichs, D.R. Montello, K. Smith, C.N. Sullivan, W.B. Thompson, Topographic Map Reading. R.R. Hoffman, R.J. Pike, On the Specification of the Information Available for the Perception and Description of the Natural Terrain. G. Klein, B.W. Crandal, The Role of Mental Simulation in Problem Solving and Decision Making. M.F. Young, M.D. McNeese, A Situated Cognition Approach to Problem Solving. L.D. Segal, Designing Team Workstations: The Choregraphy of Teamwork. P.N. Kugler, G. Lintern, Risk Management and the Evolution of Instability in Large-Scale, Industrial Systems.

Hydrogen enriched natural gas as a motor fuel with variable air fuel ratio and fuel mixture ratio control

Abstract: A hydrogen and natural gas fuel mixture for internal combustion engines is provided for vehicle engines such as those used in standard production engines for automobiles, trains and lawn mowers The gaseous fuel for operating a vehicle combustion engines includes approximately 21 to 50% Hydrogen and the rest natural gas constituents such as combinations of Methane, Carbon Dioxide, Nitrogen, Ethane, Propane, Iso-Butane, N-Butane, Iso Pentane, N-Pentane, and Hexanes Plus A fuel mixture of approximately 28 to 36 percent Hydrogen and a air fuel equivalence ratio of approximately 0625 is an extreme lean burn condition that yields hydrocarbon emission levels of less than approximately 104 ppm (084 hm/hp hr) Current internal combustion engines that are in mass production can take this alternative fuel without any substantial modifications to their systems This alternative fuel is lean burning and emits emissions that are below current legal standards The novel fuel mixture can be used in internal combustion engines for automobiles, lawnmowers, and trains A control system for allowing the internal combustion engines to operate at extreme lean burn conditions is also provided for use with both a carburetor and fuel injection system For a carburetor system, a secondary demand regulator system can kick in when a throttle is wide open and will allow additional fuel to pass through the system to meet instantaneous power demands such that occur when full throttle depression is insufficient for severe grade climbing, expressway merging, passing and the like The fuel injection system can also be programed with a control algorithm that will select air fuel ratios The computer control can increase fuel with respect to air when the throttle reaches a selected point of travel The computer control can also dynamically change the hydrogen and natural gas fuel mixture ratio dynamically while the vehicle is being operated based on engine power demands and emissions

Continuous robust control design for nonlinear uncertain systems without a priori knowledge of control direction

Abstract: In this paper, a robust control scheme is proposed for a class of nonlinear systems that have not only additive nonlinear uncertainties but also unknown multiplicative signs. These signs are called control directions since they represent effectively the direction of motion under any given control. Except for the unknown control directions, the class of systems satisfy the generalized matching conditions. Nonlinear robust control is designed to identify on-line unknown control directions and to guarantee global stability of uniform ultimate boundedness without the knowledge of nonlinear dynamics except their size bounding functions. It is also shown that the proposed robust control can be made continuous through utilizing the so-called shifting laws that change smoothly and accordingly the signs of robust controls and that, no matter what time constants and gains of the shifting laws are, global stability is always ensured. The analysis and design is done using Lyapunov's direct method. >

Priority rule search technique for resource constrained project scheduling

Abstract: A Priority Rule Search Technique (PRST) heuristic computer controlled algorithm is disclosed that schedules single project, single resource and multiple project, multiple resource constrained project scheduling problems. Primary areas of utility include construction, manufacturing and research and development projects. The invention can schedule tasks/activities for large scale, multiple resource and multiple project networks that have different network and resource constraint characteristics while providing balance among different project network characteristics in order to provide an effective solution for a variety of network types. The novel PRST algorithm combines four heuristic rules (ACTM, LFT, MGRD and MACTRES) to determine a priority value for each job task/activity. The priority values are ranked to determine an optimum schedule of all job tasks and activities to complete the entire project. The invention incorporates the time (ACTM and LFT) and resource (MGRD and MACTRES) characteristics of project activities into a priority rule based search heuristic to determine an activity's priority for scheduling. The PRST scheduling invention is composed of four priority rules that are individually weighted and combined. The first two priority rules are ACTIM and Late Finish Time (LFT) heuristics. The second two priority rules allow for the allocating of limited resources to activities that cannot be scheduled concurrently. One of these priority rules designated Multiple Greatest Resource Demand (MGRD) modifies a Greatest Resource Demand heuristic to accommodate a multiple resource case. MGRD is scaled measure of the resource demanded for each activity. The second priority rule is designated Multiple ACTRESS (MACTRES) which modifies a ACTRES heuristic to accommodate the multiple resource case. MACTRES is a measure of the time and resources controlled by the activity through the network. Alternatively, the schedule of each of the job tasks/activities can be scheduled by ranking priority values based separately on MACTRES computations or MGRD calculations.

Modulation Transfer Function Measurement Using Three- and Four-bar Targets.

Abstract: Modulation-transfer-function (MTF) measurement often involves the use of three- and four-bar resolution targets. In the conversion of three- and four-bar image data to MTF, biased results can occur when we use series-expansion techniques appropriate for square-wave targets of infinite extent. For systems where the image data are digitally recorded, a convenient and accurate conversion of bar-target data to MTF can be performed using a Fourier-domain method.

Constructive learning of recurrent neural networks: limitations of recurrent cascade correlation and a simple solution

Abstract: It is often difficult to predict the optimal neural network size for a particular application. Constructive or destructive methods that add or subtract neurons, layers, connections, etc. might offer a solution to this problem. We prove that one method, recurrent cascade correlation, due to its topology, has fundamental limitations in representation and thus in its learning capabilities. It cannot represent with monotone (i.e., sigmoid) and hard-threshold activation functions certain finite state automata. We give a "preliminary" approach on how to get around these limitations by devising a simple constructive training method that adds neurons during training while still preserving the powerful fully-recurrent structure. We illustrate this approach by simulations which learn many examples of regular grammars that the recurrent cascade correlation method is unable to learn. >

Random transparency targets for modulation transfer function measurement in the visible and infrared regions

Abstract: Measurements of modulation transfer function (MTF), particularly for staring imager systems, are affected by the position of the test target with respect to the rows and columns of the detector array. We demonstrate that random transparency targets of known spatial-frequency content allow shift-invariant MTF measurement in the visible, 3- to 5-μm, and 8- to 12-μm bands. Design criteria and verification procedures for the targets are presented.

Unitary transformation and the dynamics of a three-level atom interacting with two quantized field modes

Abstract: Starting from a three-level atom coupled to two modes of radiation field, we derive a Raman-coupled Hamiltonian by a unitary transformation, evaluated perturbatively in coupling constants The Rabi oscillation frequency and the collapse and revival times of the atomic coherence are found to have strikingly different photon-intensity dependence than those found previously

Relationships among conflict management styles, levels of conflict, and reactions to work

Abstract: Relationships among (a) conflict management styles, (b) levels of conflict, (c) two general reactions to work, and (d) four types of individual outcomes experienced by employees in the United States were assessed in two studies. In Study 1, subordinates using a high-obliging style with supervisors experienced more intrapersonal conflict, supervisors using a high-integrating style with subordinates reported more intrapersonal and intragroup conflict, and low-dominating supervisors reported significantly greater intragroup conflict. In Study 2, high-integrating subordinates experienced less intrapersonal, intragroup, and intergroup conflict than low-integrating subordinates did. The results of analyses also indicated that there was a strong relationship between integrating and all six organizational outcomes. Lower job satisfaction and fewer interpersonal rewards were associated with a high-dominating style. Both integrating and compromising were positively related to interpersonal outcomes, and do...

Blue upconversion with excitation into tm ions at 780 nm in yb- and tm-codoped fluoride crystals

Abstract: Strong blue emissions have been observed in fluoride crystals, such as ${\mathrm{LiYF}}_{4}$, ${\mathrm{BaY}}_{2}$${\mathrm{F}}_{8}$, and ${\mathrm{KYF}}_{4}$, codoped with ${\mathrm{Tm}}^{3+}$ and ${\mathrm{Yb}}^{3+}$ when excited into the ${\mathrm{Tm}}^{3+}$ $^{3}$${\mathit{F}}_{4}$ state at \ensuremath{\sim}780 nm. Energy transfer from ${\mathrm{Tm}}^{3+}$ to ${\mathrm{Yb}}^{3+}$ ions followed by the transfer from ${\mathrm{Yb}}^{3+}$ to ${\mathrm{Tm}}^{3+}$ was demonstrated to be responsible for the upconversion process. A pumping scheme is proposed based on this upconversion mechanism for blue-laser applications using these materials.

Use of a Shack-Hartmann wave-front sensor to measure deviations from a Kolmogorov phase spectrum.

Abstract: Experimental results indicate that the statistics of phase measured across a telescope aperture do not always obey the power laws associated with the Kolmogorov model of atmospheric turbulence. We show that the statistical relations between a wave front and its aperture-averaged first derivative previously derived for a Kolmogorov spectrum can be easily generalized for any power law. We also show that a Shack–Hartmann sensor can be used to measure the form of the structure function of phase fluctuations, and experimental data are presented.

Turn-off switching loss model and analysis of IGBT under different switching operation modes

Abstract: Due to its high voltage and current ratings, the IGBT has become more attractive in the high voltage and high current applications than the MOSFET. However, its slow turn-off characteristics, high turn-off losses make it difficult to operate at relatively high switching frequency. Turn-off switching loss model and analysis of IGBT under the hard switching, emitter-open and mixed parallel operations were presented in this paper. Examples of full bridge DC-DC converters using IGBT and MOSFET are analyzed to show that the turn-off switching loss can be significantly reduced if soft turn-off techniques are employed when proper gate controls of IGBTs and MOSFETs are used. It can be seen that these techniques are very attractive in the full bridge type converters for high power applications. The 75 kHz, 100 Watts prototype converter was implemented to verify our theoretical analysis.

Fiber reinforced plastic ("FRP")-concrete composite structural members

Abstract: Fiber reinforced plastic FRP formed about concrete piles and columns. The FRP components generally includes an exterior shell and an interior pultruted component. The exterior shell can include multilayers of fibers wrapped in straight hoop patterns in single sheets with or without longitudinal axial fibers. Alternatively the exterior shell can include angled wrapped fibers. The interior FRP pultruted component comes in various forms such as pultruted ribs, crossed attached ribs, interior co-axial concentric cylinders and additional shapes such as ones having an H cross-shaped pattern. The FRP materials can consist of fiber and resin such as a preferred embodiment of approximately 60% glass and 40% polyester. Other fiber type materials include but are not limited to glass, carbon, Kevlar, combinations thereof, and the like. Types of resin include but are not limited to polyester, vinylester, epoxy, combinations thereof, and the like. The invention has the effect of waterproofing and insulating the exposed concrete columns and piles of infrastructure supports and protecting any steel/metal reinforcing bars and cages in the the cement cores from the effects of corrosion. The invention further increases the ductility of concrete support columns and piles without the use of additional steel reinforcing bars and cages. The invention can additionally enhance the compressive, flexural and shear strengths of concrete support columns and piles especially for infrastructures such as bridges, buildings and the like used in hurricane and seismic zone locations.