Showing papers by "University of Central Florida published in 1988"

Optical limiting with semiconductors

Abstract: We present a detailed characterization of the output of passive semiconductor-based optical limiters. These devices utilize two-photon absorption along with photogenerated carrier defocusing within the material to limit the output fluence and irradiance. In addition to protecting downstream optical components, the focusing geometry combined with these nonlinearities makes the devices self-protecting. Such devices have a broad working wavelength range since both the initial two-photon absorption and the subsequent carrier refraction are slowly varying funtions of wavelength. For example, ZnSe should have a useful range of from 0.5 to 0.85 μm. In this material we have observed the onset of limiting at input powers as low as 80 W when using 10-nsec, 0.53 μm input pulses. At the same wavelength, when 30 psec pulses into a monolithic ZnSe limiter are used, limiting begins at ≃300 W or 10 nJ. We also monitored the output spatial energy distribution along with the temporal response at each position, using a 2-psec-resolution streak camera. We found that the output fluence along with the output irradiance is effectively limited below detector damage thresholds over an input range of 4 orders of magnitude. Additionally, since both two-photon absorption and the associated self-defocusing increase with decreasing band-gap energy, similar devices using narrow-gap semiconductors should have considerably lower limiting thresholds.

Coupled-Wave Analysis Of Two-Dimensional Dielectric Gratings

Abstract: Diffraction by two-dimensional surface-relief dielectric gratings are analyzed using rigorous three-dimensional vector coupled-wave approach. The method applies to arbitrary plane wave angle of incidence, wavelength, and polarization. In the resulting conical diffraction, the input TE and TM polarization are coupled and the diffracted orders are, in general, elliptically polarized. Diffraction characteristics of two-dimensional binary gratings are presented. Ultrahigh spatial-frequency gratings (grating period less light wavelength) are shown to exhibit polarization independent antireflection behavior (zero-reflectivity).

A comparison of algorithms for terminal-pair reliability

Abstract: Four algorithms for the terminal-pair-reliability problem are compared. Nelson (1970), Lin (1976), Shooman (1968), and Dotson (1979) algorithms are used in this study. It is shown that the Dotson algorithm is the fastest among the terminal-pair reliability algorithms analyzed. The Dotson algorithm is suited not only for numerical reliability, but for obtaining symbolic expression for the terminal-pair reliability with no additional effort. By modifying the Dotson algorithm the efficiency can be further improved. The modifications to this algorithm are listed and the reliability of the modified Dotson algorithm is computed. >

Vertex domination‐critical graphs

Abstract: A dominating set in a graph G is a set of vertices D such that every vertex of G is either in D or is adjacent some vertex of D. The domination number Γ(G) of G is the minimum cardinality of any dominating set. A graph is vertex domination-critical if the removal of any vertex decreases its domination number. This paper gives examples and properties of vertex domination-critical graphs, presents a method of constructing them, and poses some open questions. In the process several results for arbitrary graphs are presented.

Hybrid guided modes in uniaxial dielectric planar waveguides

Abstract: Rigorous electromagnetic methods are applied to calculate the propagation constants and the fields of the allowed guided modes in uniaxial slab waveguides for an arbitrary orientation of the optic axis. In addition to the familiar TE and TM modes, there are hybrid guided modes. These hybrid guided modes can be divided into three distinct types: homogeneous pure guided modes, inhomogeneous pure guided modes, and leaky guided modes. The conditions for the existence of these pure guided and leaky guided modes are derived. A quantitative method of classifying the hybrid modes in terms of the limiting decoupled TE and TM cases within that mode where the ordinary and extraordinary polarizations propagate independently is introduced. For each mode the propagation constant has a continuous band of allowed values as a function of optic axis orientation. Metal-indiffused positive-birefringent (lithium tantalate) and metal-in-diffused and proton-exchange negative-birefringent (lithium niobate) planar waveguides are treated for illustration. This analysis of hybrid guided modes is important, not only for the design and use of anisotropic waveguides, but also suggests a new class of waveguide devices based on material birefringence. >

Optimal Corner Detector

Abstract: A corner is defined as the junction point of two or more straight line edges Corners are special features in a image They are of great use in computing the optical flow and structure from motion In this paper, we report an optimal corner detector which uses a mathematical model for a corner An optimal gray tone corner detector is derived for a restricted case of corners, ie corners made by lines which are symmetric about a horizontal axis The resultant corner detector is described by product of sine in x and exponential in y direction in a portion of the mask and by the product of two sines in x and y directions in the remaining portion of it It is then generalized to include any corner of an arbitrary angle and orientation This results in an approximation of all corners by a total of twelve major types It is observed that all the twelve masks can actually be configured with four smaller sub-masks, and this results in a significant reduction in the computetions The computations are further reduced by using the the separability of masks Results for synthetic and real scenes are reported

Self-protecting semiconductor optical limiters.

Abstract: We present a detailed characterization of passive, picosecond optical-power-limiting devices using tightly focused beams in thick semiconductor samples. This study of limiting in ZnSe with 30-psec, 532-nm pulses shows that the resulting internal self-action (two-photon absorption plus free-carrier self-defocusing) protects the bulk material from optical damage. Simple scaling relations were determined from our results that link the limiting energy and the dynamic range to the focusing geometry and sample dimensions. These relations were used to design a monolithic optical limiter, optimized to have maximum dynamic range and minimum limiting energy. This device limits at an input energy of 10 nJ (300 W) and has a dynamic range greater than 10(4).

Global versus task-specific measures of self-efficacy.

Abstract: Two studies were conducted in order to reconcile contextualist accounts of self-efficacy with recent evidence supporting its global nature. A correlational analysis (Study 1) indicated that Tipton and Worthington’s (1984) Generalized Self-Efficacy (GSE) Scale was inversely related to Rotter’s Internal-External Locus of Control Scale and Beck’s Hopelessness Scale. In contrast, no discernible pattern of intercorrelations was obtained across six task-specific tests of self-efficacy. A single bipolar factor emerged, however, when the GSE Scale was factor analyzed with task-specific ratings of self-efficacy. Study 2 demonstrated that task-specific, but not GSE scores, were sensitive to actual performance on cognitive tasks. These results were interpreted as evidence for the hypothesis that global and task-specific measures assess relatively distinct aspects of the construct of self-efficacy.

A physics-based current-dependent base resistance mode; for advanced bipolar transistors

Abstract: A physics-based current-dependent base resistance model has been developed that includes physical mechanisms such as base-width modulation, base-conductivity modulation, phase pushout, and emitter current crowding. It describes the current-dependent characteristics of the base resistance for all injection levels. A two-dimensional device simulator, PISCES, is used to justify the underlying physics. The predictions of the model show good agreement with results of measurements and device simulations. The model has been implemented in SPICE. >

Environmental and engineering effects of Sinkholes—the processes behind the problems

Abstract: Karstic erosion of the land surface is controlled by processes occurring in the epikarstic zone—the upper portion of the limestone which is most intensely dissolved. Sinkholes developing today are generally the effects of downward movement of mantling sediment into the major karren shafts which drain the epikarstic zone deeper into the true karstic aquifer. Dissolution of the limestone itself does not cause significant changes in man's time frame. The downward erosion of mantling sediment is termed ravelling. Only in uniform sediment will an arched cavity occur. In unconsolidated sediment which is stratified, lateral tunnelling may even occur. Only the major karren can transmit sediment downward, the majority are ineffective. In mantled karst the location of surficial depressions and photo-linears does not necessarily correlate to areas of new collapse. The irregular and highly dissolved character of the epikarstic zone complicates foundation engineering. Downward drainage through this zone may be limited and cause flooding. An understanding of processes in the epikarstic zone is essential in developing on karst.

Beyond the gravity model

Abstract: Gravity theory holds that more people will travel from a particular origin to a given destination than will travel to a more distant destination of the same type and size. Distance, according to gravity theory is a deterrent to travel and empirical evidence supports such a relationship in urban settings. This relationship is, however, hypothesized not to be true for long-distance leisure travel where distance may be a utility rather than a friction to be overcome. This study examines the relationship between subjective (perceived) distance and objective (geographic) distance and tests the hypothesis that, all other things being equal, the attractiveness of tourist destinations will increase as subjective distance increases. It is concluded that tourists tend to perceive all destinations to be closer than they actually are. It is also concluded that the far-off destination has a special allure about it simply because it is far-off.

A comparioson of nonparametric unweighited and length-biased density estimation of fibres

Abstract: Two sampling procedures used to estimate the distribution of the length of textile fibres are studied . Estimators of the density function of fibre length and the asymptotic propertiesof these estimators are discussed. Simulations were undertaken to compare mean square errors of the estimators for various saniple sizes.

Common principal component subspaces in two groups

Abstract: SUMMARY One important practical application of principal component analysis is to reduce a large number of variables, say p, to a smaller number, m, by making use of the first m principal components. This technique can easily be extended to two or more groups if the subspaces spanned by the first m principal components are the same for all groups. In this paper we develop an approximate procedure for testing such a hypothesis of common subspaces when two groups are involved. The adequacy of the approximation is investigated by a simulation and the method is illustrated by a numerical example.

Older Anglophone Canadian Snowbirds in Florida: A Descriptive Profile

Abstract: This study reports on a population of Anglophone Canadian seasonal migrants to Florida. Surveys were mailed to 4,500 subscribers to Canada News, a Florida-based weekly paper, and were completed by 61% of the respondents. The descriptive profile reveals younger-old, healthy, married, home owners of moderate income who stay in Fionda for six months, but communicate regularly with their Canadian family. They utilize no social services in Florida, are satisfied with life and with their Florida health care experiences, but take various precautionary health care measures prior to leaving Canada. Their Florida visits will continue, moderated more by the exchange rate than health concerns. These data will be discussed relative to policy issues for Florida and Canada.

Relations of the parameters of the I-K distribution for irradiance fluctuations to physical parameters of the turbulence.

Abstract: By using results from perturbation techniques for weak turbulence and the asymptotic theory for strong turbulence, we develop expressions for the parameters α and ρ of the I–K distribution in terms of the Rytov variance for plane waves σ12=1.23Cn2 k7/6L11/6 and the inner scale of turbulence parameter l0. Comparisons of the resulting scintillation index to experimental data and numerical results from the solution of the fourth-moment equation for 3-D propagation show good agreement.

On unsteady hydromagnetic flows of a dusty fluid between two oscillating plates

Abstract: An initial value investigation is made of the motion of an incompressible viscous conducting fluid with embedded small spherical particles bounded by two infinite rigid non-conducting plates. The flow is generated in the fluid-particle system due to rectilinear oscillations of given frequencies superimposed on the plates in presence of an external transverse magnetic field. The operational method is used to derive exact solutions for the fluid and the particle velocities and the wall shear stress. It is shown that the effect of the dust particles on the fluid velocity depends on the time periods of the oscillating plates. When the time-periods are small, i.e., when the plates oscillate with high frequency, the fluid motion is found to be retarded by the particles. However, when the plates oscillate with larger time periods (smaller frequencies), the fluid velocity is increased by the presence of the particles at the early stage of the motion, and this effect persists until the equilibrium is reached when the particles exert their influence to resist the flow.

Criterion-related validity of self-report measures of female heterosocial functioning

Abstract: Common measures of female heterosocial functioning, the Survey of Heterosocial Interactions for Females (SHI-F) and dating frequency questions, were validated against the criterion of “male liking,” i. e., how well men like a woman. The SHI-F was unrelated to the criterion and to the other measures of heterosocial activity. The dating frequency and satisfaction questions were moderately related to the criterion. It was concluded the self-reported ability to initiate contact with men (as measured by the SHI-F) may not be related to female heterosocial functioning. Self-reported dating frequency and satisfaction appear to be a valid measure of female heterosocial functioning.

A scheme for data compression in supercomputers

Abstract: There is a growing recognition of the importance of efficient coding and data compression schemes in supercomputing centers and in networks of high-speed computing machines. Recently, there has been a considerable interest in arithmetic coding as a promising technique for reducing the cost of data storage and transmission. In this paper, we present a compression algorithm that is tailored to utilize the enormous speed and memory size of supercomputers and which utilizes an enhanced arithmetic coding scheme. The paper also presents efficient VLSI designs for the enhanced scheme. These hardware designs are suitable for inclusion in disk and communication controllers of supercomputers and would provide a practical way to effectively increase thresholds of data transfer rates and communication bandwidth.

Modulation depth characteristics of a liquid crystal television spatial light modulator.

Abstract: The performance of a commercially available liquid crystal TV display was characterized in terms of its modulation depth. Measurements of screen transmittance and modulation depth, as a function of signal level, showed that the primary limitations of the device as a spatial light modulator were due to the nature of the video scan format and the display drive electronics. The resolution of the device, as measured by the modulation transfer function, is limited more by the physical pixel spacing than by pixel crosstalk. The optical flatness of the screen was characterized interferometrically, both with and without polarizers, to show the improvement in wavefront quality obtained by replacing the original polarizers.

Magneto-thermo-elastic disturbances with thermal relaxation in a solid due to heat sources

Abstract: A study is made of the propagation of magneto-thermo-elastic disturbances with thermal relaxation in a perfectly conducting unbounded solid, due to heat sources distributed over a plane parallel to the applied magnetic field. The governing partial differential equations are solved in the Laplace transform domain by the state space approach of the modern control theory. The small-time solutions of the problem are obtained with physical significance. The solutions are found to consist of thermal wave (T-wave) and acoustic wave (A-wave). The speeds of these waves are increased due to the presence of the external magnetic field. The displacement field, the thermal field and the magnetic field experience discontinuities at each of the wave fronts. The effect of the magnetic field is to shift the position of discontinuities and to reduce their decay with distance from the source. The significant effect of the thermal relaxation is to exhibit the occurrence of some new discontinuities not encountered in the conventional theory. In the absence of the thermal relaxation and or the magnetic field, several limiting results follow as special cases of this analysis.

Community Based Aesthetics as Exhibition Catalyst and a Foundation for Community Involvement in Art Education.

Abstract: “Boats, Bait and Fishing Paraphernalia: A Local Folk Aesthetic” was an exhibit coordinated by the authors to explore potential aesthetic qualities of a range of functional objects. Members of the local fishing community worked together to identify a community based aesthetic and to curate an exhibit which would present that aesthetic to the public Attendees completed questionnaires designed to help report on the exhibition's objective: to promote community involvement and aesthetic representation. Results of a statistical analysis of questionnaire responses revealed that the exhibit attracted widespread interest and support, and that the goals of the exhibit were accomplished. Findings from the questionnaire suggest that many approaches to both the content and methodologies can be effectively used in the field of art education.

Paternal imprinting of inversion Uab1 causes homeotic transformations in Drosophila.

Abstract: Paternal transmission of the bithorax-complex (BX-C) rearrangement, inversion Uab1, causes a specific dominant gain of function phenotype in most abdominal segments. This represents a case of paternal imprinting since the mutant phenotype will occur only if inversion Uab1 is paternally transmitted. The transformations in males are toward genital arch tissue. For females the transformations are to tissue found on abdominal segment 7 (Ab7) and to structures normally restricted to the genital disc. Ninety-six percent of transformed areas appear on Ab5 and Ab6 in both sexes and on Ab7 in females, coinciding with the Abd-B domain. Four percent of the transformations occurred on Ab1 through Ab4, coinciding with the abd-A domain. The mutant phenotype can be dramatically enhanced by modifying genes such as the posterior BX-C mutant tuh-3. Expressivity is modulated by maternal effect alleles interacting with tuh-3. A region of function within inversion Uab1 appears to be programmed during spermatogenesis to function in a legacy dependent manner during embryogenesis.