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Showing papers by "University of Central Florida published in 1991"


Journal ArticleDOI
TL;DR: In this article, a two-hand model is used to calculate the scaling and spectrum of the nonlinear absorption of semiconductors and wide-gap optical solids, and the bound electronic nonlinear refractive index n/sub 2/ is obtained using a Kramers-Kronig transformation.
Abstract: A two-hand model is used to calculate the scaling and spectrum of the nondegenerate nonlinear absorption. From this, the bound electronic nonlinear refractive index n/sub 2/ is obtained using a Kramers-Kronig transformation. The authors include the effects of two-photon and Raman transitions and the AC Stark shift (virtual band blocking). The theoretical calculation for n/sub 2/ shows excellent agreement with measured values for a five-order-of-magnitude variation in the modulus of n/sub 2/ in semiconductors and wide-gap optical solids. Beam distortion methods were used to measure n/sub 2/ in semiconductors. The observations result in a comprehensive theory that allows a prediction of n/sub 2/ at wavelengths beneath the band edge, given only the bandgap energy and the linear index of refraction. Some consequences for all-optical switching are discussed, and a wavelength criterion for the observation of switching is derived. >

956 citations


Journal ArticleDOI
TL;DR: In this paper, a conceptual model is proposed relating the levels of entrepreneurship, marketing activity, and marketing-related structure of a firm to the degree of perceived environmental turbulence confronting the firm.
Abstract: Entrepreneurship and marketing are approached as proactive corporate responses to an increasingly dynamic, threatening, and complex external environment. Both represent organizational orientations built around creativity, innovativeness, flexibility, and risk-taking. A conceptual model is proposed relating the levels of entrepreneurship, marketing activity, and marketing-related structure of a firm to the degree of perceived environmental turbulence confronting the firm. Results of a survey involving personal interviews with managers in 93 firms representing six industries are reported. Turbulence is found to have a significant causal impact on both the levels of entrepreneurship and the marketing orientation of the firm, but not on structural variables.

281 citations


Journal ArticleDOI
TL;DR: In this paper, a simple model based on the "constant shape approximation" is used for analyzing the propagation of laser beams within nonlinear refractive materials under most conditions, and the position of the sample with respect to the focal plane, z, is an important parameter in the fluence limiting characteristics of the output.
Abstract: We experimentally and theoretically investigate optical beam propagation in nonlinear refractive materials having a thickness greater than the depth of focus of the input beam (i.e., internal self-action). A simple model based on the "constant shape approximation" is adequate for analyzing the propagation of laser beams within such media under most conditions. In a tight focus geometry, we find that the position of the sample with respect to the focal plane, z, is an important parameter in the fluence limiting characteristics of the output. The behavior with z allows us to perform a "thick sample Z-scan" from which we can determine the sign and magnitude of the nonlinear refraction index. In CS2, we have used this method to independently measure the negative thermally induced index change and the positive Kerr nonlinearity with nanosecond and picosecond CO2 laser pulses, respectively. We have experimentally examined the limiting characteristics of thick CS2 samples that qualitatively agree with our analysis for both positive and negative nonlinear refraction. This analysis is useful in optimizing the limiting behavior of devices based on self-action.

238 citations


Journal ArticleDOI
TL;DR: In this article, a linear robust fedback control law with constant gain matrix is proposed for the trajectory following problem of a robot manipulator, which makes the resulting error system uniformly ultimately bounded.
Abstract: For the trajectory following problem of a robot manipulator, a simple linear robust fedback control law with constant gain matrix is proposed that makes the resulting error system uniformly ultimately bounded. This control law is very easy to implement by simply choosing a feedback gain according to the coefficients of a polynomial function of the tracking errors which is a bounding function for the terms in the Lagrange-Euler formulation. In the limit as the gain approaches infinity the error system becomes globally asymptotically stable. >

159 citations


Journal ArticleDOI
TL;DR: The critical importance of small business management and entrepreneurship in determining the future of the economic and social well-being of the United States is generally accepted by leading experi... as discussed by the authors.
Abstract: The critical importance of small business management and entrepreneurship in determining the future of the economic and social well-being of the United States is generally accepted by leading exper...

153 citations


Journal ArticleDOI
TL;DR: In this article, the authors determine whether the touristic experience of US students visiting the USSR affected their opinions and attitudes towards the Soviet people and their institutions and show that in general, the experience did not change their attitudes and opinions towards the USSR and the people.

133 citations


Journal ArticleDOI
TL;DR: An efficient, non-iterative polynomial time approximation algorithm which minimizes the proximal uniformity cost function and establishes correspondence over n frames and combines the qualities of the gradient and token based methos for motion correspondence is proposed.
Abstract: Given n frames taken at different time instants and m points in each frame, the problem of motion correspondence is to map a point in one frame to another point in the next frame such that no two points map onto the same point. This problem is combinatorially explosive; one needs to introduce constraints to limit the search space. We propose a proximal uniformity constraint to solve the correspondence problem. According to this constraint, most objects in the real world follow smooth paths and cover a small distance in a small time. Therefore, given a location of a point in a frame, its location in the next frame lies in the proximity of its previous location. Further, resulting trajectories are smooth and uniform and do not show abrupt changes in velocity vector over time. An efficient, non-iterative polynomial time approximation algorithm which minimizes the proximal uniformity cost function and establishes correspondence over n frames is proposed. It is argued that any method using smoothness of motion alone cannot operate correctly without assuming correct initial correspondence, the correspondence in the first two frames. Therefore, we propose the use of gradient based optical flow for establishing the initial correspondence. This way the proposed approach combines the qualities of the gradient and token based methos for motion correspondence. The algorithm is then extended to take care of restricted cases of occlusion. A metric called distortion measure for measuring the goodness of solution to this n frame correspondence problem is also proposed. The experimental results for real and synthetic sequences are presented to support our claims.

119 citations


Proceedings ArticleDOI
03 Jun 1991
TL;DR: An efficient, noniterative polynomial time approximation algorithm which minimizes the proximal uniformity cost function and establishes correspondence over n frames and is extended to take care of restricted cases of occlusion is proposed.
Abstract: A proximal uniformity constraint is proposed to solve the correspondence problem. According to this constraint, most objects in the real world follow smooth paths and cover a small distance in a small time. An efficient, noniterative polynomial time approximation algorithm which minimizes the proximal uniformity cost function and establishes correspondence over n frames is proposed. Any method using smoothness of motion alone cannot operate correctly without assuming correct initial correspondence, the correspondence in the first two frames. Therefore, the authors propose the use of gradient-based optical flow for establishing the initial correspondence. This way the proposed approach combines the qualities of the gradient- and token-based methods for motion correspondence. The algorithm is then extended to take care of restricted cases of occlusion. Experimental results for real and synthetic sequences are presented. >

97 citations


Patent
20 Dec 1991
TL;DR: In this article, a surface detection system for airport facilities is described wherein a plurality of infrared (IR) scanners as well as presence/absence detectors are located with respect to taxiways and runways of an airport complex.
Abstract: A surface detection system for airport facilities is described wherein a plurality of infrared (IR) scanners as well as presence/absence detectors are located with respect to taxiways and runways of an airport complex. These devices are arranged to perform in conjunction with local processors to generate data from aircraft and ground based vehicles available from a bar coding identification of both forms of vehicles. These data are utilized to compute alert conditions as well as to develop a real time map of the airport which may be provided at a tower installation for air traffic control utilization as well as at an aircraft flight deck during the course of ground maneuvering. Through the utilization of aircraft tail numbers as an index, a master host memory may be developed which includes flight numbers, aircraft characteristics and the like which may be employed for evolving alert conditions and the like.

89 citations


Journal ArticleDOI
TL;DR: In this article, the heat transfer characteristics in a viscoelastic fluid over a stretching sheet with frictional heating and internal heat generation or absorption were analyzed in terms of Kummer's and parabolic cylinder functions.

88 citations


Journal ArticleDOI
TL;DR: In this article, the intensity and frequency of occurrence of 30 job stressors as measured by the job stress survey (JSS) were examined in white-collar employees of a large manufacturing firm, consisting of 68 managers, 171 professional and 69 clerical personnel.
Abstract: The intensity and frequency of occurrence of 30 job stressors as measured by the job stress survey (JSS) were examined in white-collar employees of a large manufacturing firm, consisting of 68 managers, 171 professional (mostly engineers), and 69 clerical personnel. The highest levels of stress intensity were attributed to ‘lack of opportunity for advancement’ and ‘poor or inadequate supervision’. Individual stressors rated as occurring most often during the past six months were ‘frequent interruptions', ‘meeting deadlines’, and ‘dealing with crisis situations’. Factor analyses of the ratings of individual job stressors identified two job-stress factors, job pressure and lack of support, which were differentially related to age, gender, occupational level, locus of control, and job tenure and satisfaction. All three occupational groups attributed greater intensity to stressors that reflected lack of organizational support than to job pressures. Managers reported experiencing job pressures more of...

Journal ArticleDOI
TL;DR: A class of VLSI architectures for data transformation of tree-based codes is proposed, concentrating on transformation functions used for data compression and decompression, and the design approaches are applicable to any binary codes.
Abstract: A class of VLSI architectures for data transformation of tree-based codes is proposed, concentrating on transformation functions used for data compression and decompression. Two algorithms are presented: a sequential algorithm that generates the code bits serially one bit per machine cycle, and a parallel algorithm that generates the entire code bits of a symbol in one machine cycle. The algorithms use the principle of propagation of a token in a reverse binary tree constructed from the original codes. The design approaches are applicable to any binary codes, although the static Huffman code is used as an illustration. A hardware algorithm for generating adaptive Huffman codes is proposed, and a VLSI architecture for implementing the algorithm is described. The high speed of the algorithms ensures that data transformation is done on the fly, as data are being transferred from/to high-speed I/O communication devices. >

Journal ArticleDOI
TL;DR: This article found that on average first-time visitors to the Grand Canyon are willing to travel significantly greater distances than repeat visitors, and that repeat visitors are more likely to visit the canyon more frequently than first time visitors.
Abstract: This paper finds that on average first-time visitors to the Grand Canyon are willing to travel significantly greater distances than repeat visitors These findings are based upon a binary logit model of repeat visitations estimated from a recent sample of Grand Canyon visitors This model expresses the probability of repeat visitation as a function of distance travelled and visitor demographic profiles Included among the demographic characteristics are income, available leisure time, and the number of previous visits An important managerial implication of this study - not only for the Grand Canyon but also for other tourist destinations - is the value of ‘probability of revisitation’ approach in identifying subtle market fragments This opens the door to sophisticated marketing strategies that, in this case, cater to the separate needs and desires of repeat and first-time visitors to enhance revenue possibilities

Journal ArticleDOI
TL;DR: The authors used a national mail survey of chief executive officers (CEOs) of manufacturing firms to compare the performance of direct questioning, scenario, and randomized response methods for estimating the prevalence of several sensitive business practices.
Abstract: Certain business practices include legal but ethically questionable activities. Surveys intended to determine the nature and extent of such activities must employ questioning methods which mitigate the inherent threat of sensitive questions and account for social desirability effects. This study uses a national mail survey of chief executive officers (CEOs) of manufacturing firms to compare the performance of direct questioning, scenario, and randomized response methods for estimating the prevalence of several sensitive business practices. The direct questioning and scenario versions used self-reporting (individual-based) questions, as well as the CEO's perceptions of the extent to which others engage in questionable activities (other-based). In general, the estimates of the prevalence of selected questionable activities were lowest when the individual-based direct questioning was used and highest when other-based (either direct questioning or scenario) methods were used. The individual- based scenario and randomized response estimates represented intermediate estimates. Suggested guidelines for using the three methods for eliciting sensitive information are discussed.

Journal ArticleDOI
TL;DR: The effects of racism on African Americans may have deleterious consequences that necessitate their seeking counseling as mentioned in this paper, and the possible need for counselors to be proactive when working with African American clients.
Abstract: The effects of racism on African Americans may have deleterious consequences that necessitate their seeking counseling. This article addresses cultural considerations, economic factors, historical factors, and client expectations that may be salient when engaging African American clients in counseling. The article also discusses the possible need for counselors to be proactive when working with African American clients. Puede ser que los efectos del racismo en afro-americanos tenga consecuencias deletereas que hacen necesario que busquen consejeria. Este articulo habla de las consideraciones culturales, factores economicos, factores historicos y las expectativas del cliente que pueden ser destacados cuando afro-americanos estan en consejeria. Se discute tambien la posible necisidad de que los consejeros sean proactivos cuando trabajan con clientes afro-americanos.


Journal ArticleDOI
TL;DR: In this article, a nonlinear AlGaAs directional coupler using the nonresonant contribution to the intensity dependent refractive index, below half the bandgap, is reported. And this results represent the first demonstration of an ultrafast device using semiconductor waveguides, where the throughput is not limited by absorption processes.
Abstract: The observation of all-optical switching in a nonlinear AlGaAs directional coupler using the nonresonant contribution to the intensity dependent refractive index, below half the bandgap, is reported. These results represent the first demonstration of an ultrafast device using semiconductor waveguides, where the throughput is not limited by absorption processes.

Journal ArticleDOI
TL;DR: In this article, permanent laser-induced darkening in CdSxSe1−x semiconductor-doped glasses with picosecond pulses was characterized as a function of fluence, repetition rate, and pulse width.
Abstract: We have performed experiments to characterize permanent laser-induced darkening in CdSxSe1−x semiconductor-doped glasses with picosecond pulses as a function of fluence, repetition rate, and pulse width. We find that the darkening occurs by means of a nonlinear process that exhibits an anomalous dependence on pulse width. Transmission spectra show that the induced darkening is uniform over the spectral range from the absorption edge out to 820 μm. Darkening in a number of different glasses is compared. On the basis of our results we propose a mechanism that involves photoassisted trapping of electrons from the semiconductor microcrystallites into states within the glass host material.

Journal ArticleDOI
TL;DR: In this article, the quantum Hall effect is due to discontinuities in the chemical potential at certain bulk electron densities and it has been conjectured that the resulting edge states in some fractional Hall gaps can have an intricate composite structure which reflects the correlations in the incompressible bulk fluid.
Abstract: The quantum Hall effect is due to discontinuities in the chemical potential at certain bulk electron densities It has been conjectured that the resulting edge states in some fractional Hall gaps can have an intricate composite structure which reflects the correlations in the incompressible bulk fluid We present direct numerical evidence obtained from exact-diagonalization studies in favor of this conjecture We show that the states on the \ensuremath{ u}=2/3 fractional quantum Hall edge constitute a two-component system in which a \ensuremath{ u}=1/3 droplet of holes is contained within a \ensuremath{ u}=1 droplet of electrons

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the relationship between entrepreneurship and societal quality of life by examining both the functional and dysfunctional effects of entrepreneurship on seven major components of societal quality-of-life.

Journal ArticleDOI
TL;DR: In this article, the heat transfer characteristics of a second-order fluid over a continuous stretching surface with internal heat generation or absorption are analyzed, and a uniform approximation in terms of parabolic cylinder functions with a boundary layer of width is given in both the PST and PHF cases.
Abstract: The heat transfer characteristics of a second-order fluid over a continuous stretching surface with internal heat generation or absorption is analyzed. Two cases are studied, namely (i) the sheet with prescribed surface temperature (PST-case) and (ii) the sheet with prescribed wall heat flux (PHF-case). The solution and heat transfer characteristics are obtained in terms of Kummer's functions. For large values of Prandtl number a uniform approximation is given in terms of parabolic cylinder functions with a boundary layer of width\(\sqrt {{1 \mathord{\left/ {\vphantom {1 {\Pr }}} \right. \kern- ulldelimiterspace} {\Pr }}} \) in both the PST and PHF cases. It is also shown that no boundary layer type solution exists for small Prandtl number.

Journal ArticleDOI
TL;DR: In this paper, the authors identify the dominant nonlinearities in ZnSe and CdTe, due to the same processes which give rise to the effects of bound-electronic refraction and two-photon absorption, while higher order effects are due to free carrier refraction.
Abstract: Degenerate four-wave mixing experiments on ZnSe and CdTe semiconductor samples with picosecond laser pulses at wavelengths below the bandgap are described. The authors identify the dominant nonlinearities in ZnSe and CdTe. They determine these to be fast third-order nonlinearities, due to the same processes which give rise to the effects of bound-electronic refraction and two-photon absorption, while higher order effects are due to free-carrier refraction. Measurements of the absolute magnitude of the combined third order susceptibilities are described. Studies of higher order effects due to free-carrier gratings are discussed. To obtain a quantitative measurement of the carrier induced nonlinearities, an expression for the diffraction efficiency of these carrier gratings was developed, and a value for the free-carrier refractive index coefficient in ZnSe was found. By measuring the angular dependence of the grating decay, the carrier diffusion coefficient was determined as a function of carrier density. >

Journal ArticleDOI
TL;DR: In this article, the standard computed torque control law is shown to be robust with respect to unknown dynamics by judiciously choosing the feedback gains and the estimates of the nonlinear dynamics.

Proceedings Article
14 Jul 1991
TL;DR: A model is developed to analyze the time and space complexity of these three heuristic search algorithms in terms of the heuristic branching factor and solution density and presents a new algorithm, DFS*, which is a hybrid of iterative deepening and depth-first branch-and-bound, and shows that it outperforms the other three algorithms on some problems.
Abstract: We present a comparison of three well known heuristic search algorithms: best-first search (BFS), iterative-deepening (ID), and depth-first branch-and-bound (DFBB). We develop a model to analyze the time and space complexity of these three algorithms in terms of the heuristic branching factor and solution density. Our analysis identifies the types of problems on which each of the search algorithms performs better than the other two. These analytical results are validated through experiments on different problems. We also present a new algorithm, DFS*, which is a hybrid of iterative deepening and depth-first branch-and-bound, and show that it outperforms the other three algorithms on some problems.

Journal ArticleDOI
TL;DR: A pulsed GaAs laser rangefinder is analyzed and designed, and a method of threshold detection is presented and discussed, which includes receiver preamplifier transfer function and threshold detector performance.
Abstract: A pulsed GaAs laser rangefinder is analyzed and designed. Expressions for background and signal power, noise, and signal-to-noise ratio are derived. The effects of pulse rise time, receiver bandwidth, and SNR on probability of detection and range accuracy are discussed. A computer simulation is used to optimize laser power, receiver aperture, and preamplifier bandwidth. A method ofthreshold detection is presented and discussed. Experimental results include receiver preamplifier transfer function and threshold detector performance.

Journal ArticleDOI
TL;DR: A general equation is developed that describes any FM reticle of the spinning type and shows that multiple parameters can be integrated into a single reticle.
Abstract: The literature describes tracking devices that allow a single detector coupled to a spinning FM reticle to determine target location. The spinning FM reticles presented were limited to single parameter reticles of frequency vs angle, frequency vs radius, or phase. This study presents these parameters with their capabilities and limitations and shows that multiple parameters can be integrated into a single reticle. Also, a general equation is developed that describes any FM reticle of the spinning type.

Journal ArticleDOI
TL;DR: It is shown that it is possible to achieve all-optical switching, amplification, and compression of short pulses in a single device.
Abstract: A numerical study of the all-optical switching properties of solitons in an erbium-doped nonlinear fiber coupler is presented. The small gain provided by the erbium both lowers and sharpens the switching threshold, while producing pulse-compression factors of 3 to 9. As a result, we show that it is possible to achieve all-optical switching, amplification, and compression of short pulses in a single device.

Journal ArticleDOI
TL;DR: It is shown that if this network is repeatedly presented with an arbitrary list of binary input patterns, learning self-stabilizes in at most m list presentations, where m corresponds to the number of patterns of distinct size in the input list.

Journal ArticleDOI
TL;DR: In this article, the authors carried out nonlinear absorption and nonlinear refraction measurements on the pure liquid crystals 5CB and 8CB, and the liquid crystal mixture E7 using picosecond, nanosecond and millisecond pulses.
Abstract: In order to better understand the physical mechanisms responsible for the large observed optical nonlinearities of nematic liquid crystals, we have carried out nonlinear absorption and nonlinear refraction measurements on the pure liquid crystals 5CB and 8CB, and the liquid crystal mixture E7 using picosecond, nanosecond and millisecond pulses. We have used the recently developed Z-scan method1–2, a sensitive single-beam technique which allows the determination of the sign and magnitude of the nonlinear refraction and the magnitude of the nonlinear absorption for aligned samples3. We have performed these measurements on aligned samples at wavelengths of 514nm and 532nm. In addition, we have studied the temperature dependence of the nonlinear refractive indices. Possible mechanisms responsible for the observed nonlinearities are discussed.

Proceedings ArticleDOI
01 Dec 1991
TL;DR: Specific global optimization methods including simulated annealing, genetic algorithms, and Bayesian techniques are discussed in terms of their strengths and weaknesses as applied to this methodology.
Abstract: A methodology for the application of global search methods for optimizing the results of a computer simulation is presented. Specific global optimization methods including simulated annealing, genetic algorithms, and Bayesian techniques are discussed in terms of their strengths and weaknesses as applied to this methodology. In particular, the effects of simulation time, constraints, dimensionality, and computational complexity are considered as they relate to the choice of algorithms. Simulated annealing and genetic algorithms perform similarly, yet differ in many ways from the class of Bayesian algorithms. Bayesian algorithms spend additional computation time in modeling all past values of the unknown function in an effort to minimize the number of evaluations of the function. These methods would be the algorithms of choice for determining the optimal design via simulation, provided the number of design variables is less than 10 and the time required to run a single simulation is large compared with the time it takes the algorithm to determine the next point. >