Showing papers by "Rensselaer Polytechnic Institute published in 1990"

AND/OR graph representation of assembly plans

Abstract: A compact representation of all possible assembly plans of a given product using AND/OR graphs is presented. Such a representation forms the basis for efficient planning algorithms that make possible an increase in assembly system flexibility by allowing an intelligent robot to pick a course of action according to instantaneous conditions. The AND/OR graph is equivalent to a state transition graph but requires fewer nodes and simplifies the search for feasible plans. Three applications are discussed: the preselection of the best assembly plan, the recovery from execution errors, and the opportunistic scheduling of tasks. A hypothetical error situation in the assembly of the four-part assembly is discussed to show how a bottom-up search of the AND/OR graph leads to an efficient recovery. The scheduling efficiency using this representation is compared with fixed sequence and precedence graph representations. >

NOSER: An algorithm for solving the inverse conductivity problem

Abstract: The inverse conductivity problem is the mathematical problem that must be solved in order for electrical impedance tomography systems to be able to make images. Here we show how this inverse conductivity problem is related to a number of other inverse problem. We then explain the workings of an algorithm that we have used to make images from electrical impedance data measured on the boundary of a circle in two dimensions. This algorithm is based on the method of least squares. It takes one step of a Newton's method, using a constant conductivity as an initial guess. Most of the calculations can therefore be done analytically. The resulting code is named NOSER, for Newton's One-Step Error Reconstructor. It provides a reconstruction with 496 degrees of freedom. The code does not reproduce the conductivity accurately (unless it differs very little from a constant), but it yields useful images. This is illustrated by images reconstructed from numerical and experimental data, including data from a human chest.

Two new geobarometers for garnet amphibolites, with applications to southeastern Vermont

Abstract: Two new geobarometers for the assemblage garnet + hornblende + plagioclase + quartz have been calibrated on the basis of the equilibrium 6 Anorthite + 3 Tremolite = 2 Grossular + 1 Pyrope + 3 Tschermakite + 6 Quartz and its Fe end-member equivalent. Data representing 37 natural samples that equilibrated at conditions of 2.5 to 13 kbar and 500 to 800°C were fitted to the general equation -RT In Keq= A - BT + (P - I)C by using a weighted least-squares method. Multiple correlation coefficients are high (0.98 and 0.97). Lines of constant Keqhave extremely shallow slopes in P- T space (- 2 to + 8 bars per degree), suggesting that pressures may be deduced precisely, even where temperatures are only poorly constrained. Typical analytical errors and temperature imprecisions propagate to very small errors in pressure (about ::!:500 bars). Caution is advised in applying the barometers outside the range of calibrant-mineral compositions. Application of the calibrations to samples from southeastern Vermont near the Strafford, Chester, and Athens domes documents relatively high pressure metamorphism (7 to 10 kbar) for these structures.

Environmentally Induced Positive Affect: Its Impact on Self-Efficacy, Task Performance, Negotiation, and Conflict1

Abstract: Male and female subjects performed several tasks either in the presence or absence of an environmental source of positive affect (pleasant artificial scents produced by two commercially manufactured air-fresheners). Consistent with the findings of previous research on the impact of positive affect, results indicated that several aspects of subjects' behavior were influenced by this variable. Participants exposed to pleasant scents set higher goals on a clerical coding task and were more likely to adopt an efficient strategy for performing this task than subjects not exposed to such conditions. In addition, males (but not females) reported higher self-efficacy in the presence of pleasant artificial scents than in their absence. Participants exposed to pleasant scents also set higher monetary goals and made more concessions during face-to-face negotiations with an accomplice. Finally, subjects exposed to pleasant scents reported weaker preferences for handling future conflicts with the accomplice through avoidance and competition. Analyses of covariance suggested that these differences stemmed largely from contrasting levels of positive affect among subjects in the neutral and pleasant scent conditions. Together, these results suggest that pleasant artificial scents may provide a potentially useful means for enhancing the environmental quality of work settings, and hence the performance and attitudes of persons in them.

Experimental analysis and extinction of self-injurious escape behavior.

Abstract: Three studies are presented in which environmental correlates of self-injurious behavior were systematically examined and later used as the basis for treatment. In Study 1, 7 developmentally disabled subjects were exposed to a series of conditions designed to identify factors that maintain self-injurious behavior: attention contingent on self-injurious behavior (positive reinforcement), escape from or avoidance of demands contingent on self-injurious behaviour (negative reinforcement), alone (automatic reinforcement), and play (control). Results of a multielement design showed that each subject's self-injurious behavior occurred more frequently in the demand condition, suggesting that the behavior served an avoidance or escape function. Six of the 7 subjects participated in Study 2. During educational sessions, "escape extinction" was applied as treatment for their self-injurious behavior in a multiple baseline across subjects design. Results showed noticeable reduction or elimination of self-injurious behavior for each subject and an increase in compliance with instructions in all subjects for whom compliance data were taken. The 7th subject, whose self-injurious behavior during Study 1 occurred in response to medical demands (i.e., physical examinations), participated in Study 3. Treatment was comprised of extinction, as in Study 2, plus reinforcement for tolerance of the examination procedure, and was evaluated in a multiple baseline across settings design. Results showed that the treatment was successful in eliminating self-injurious behavior and that its effects transferred across eight new therapists and three physicians. General implications for the design, interpretation, and uses of assessment studies are discussed.

The effect of S-wave arrival times on the accuracy of hypocenter estimation

Abstract: Well-constrained hypocenters (latitude, longitude, depth, and origin time) are required for nearly all studies that use earthquake data. We have examined the theoretical basis behind some of the widely accepted “rules of thumb” for obtaining accurate hypocenter estimates that pertain to the use of S phases and illustrate, in a variety of ways, why and when these “rules” are applicable. Results of experiments done for this study show that epicentral estimates (latitude and longitude) are typically far more robust with respect to data inadequacies; therefore, only examples illustrating the relationship between S phase arrival time data and focal depth and origin time estimates are presented. Most methods used to determine earthquake hypocenters are based on iterative, linearized, least-squares algorithms. Standard errors associated with hypocenter parameters are calculated assuming the data errors may be correctly described by a Gaussian distribution. We examine the influence of S -phase arrival time data on such algorithms by using the program HYPOINVERSE with synthetic datasets. Least-squares hypocenter determination algorithms have several shortcomings: solutions may be highly dependent on starting hypocenters, linearization and the assumption that data errors follow a Gaussian distribution may not be appropriate, and depth/origin time trade-offs are not readily apparent. These shortcomings can lead to biased hypocenter estimates and standard errors that do not always represent the true error. To illustrate the constraint provided by S -phase data on hypocenters determined without some of these potential problems, we also show examples of hypocenter estimates derived using a probabilistic approach that does not require linearization. We conclude that a correctly timed S phase recorded within about 1.4 focal depth9s distance from the epicenter can be a powerful constraint on focal depth. Furthermore, we demonstrate that even a single incorrectly timed S phase can result in depth estimates and associated measures of uncertainty that are significantly incorrect.

A model for garnet and plagioclase growth in pelitic schists: implications for thermobarometry and P‐T path determinations

Abstract: Numerical models of the progressive evolution of pelitic schists in the NCMnKFMASH system with the assemblage garnet + biotite + chlorite ± staurolite + plagioclase + muscovite + quartz + H2O are presented with the goal of predicting compositional changes in garnet and plagioclase along different P-T paths. The numerical models support several conclusions that should prove useful for interpreting the P-T paths of natural parageneses: (i) Garnet may grow along P-T vectors ranging from heating with decompression to cooling with compression. P-T paths deduced from garnet zoning that are inconsistent with these growth vectors are self-contradictory. (ii) There is a systematic relation between garnet and plagioclase composition and growth such that for most P-T paths, garnet growth requires plagioclase consumption. Furthermore, mass balance in a closed system requires that as plagioclase is consumed the remaining plagioclase becomes increasingly albitic. Inclusions of plagioclase in the core of garnet should be more anorthitic than those near the rim and zoned matrix plagioclase should have rims that are more albitic than the cores. Complex plagioclase textures may arise from the local variability of growth and precipitation kinetics. (iii) A decrease of Fe/(Fe + Mg) in a garnet zoning profile is a reliable indicator of increasing temperature for the assemblage modelled. However, there is no single reliable ΔP monitor and inferences about ΔP can only be made by considering plagioclase and garnet together. (iv) Consumption of garnet during the production of staurolite removes material from the outer shell of a garnet and may make recovery of peak metamorphic compositions and P-T conditions impossible. Low ‘peak’temperatures typically recorded by staurolite-bearing assemblages may reflect this phenomenon. (v) Diffusional homogenization of garnet affects the computed P-T path and results in a clockwise rotation of the computed P-T vector relative to the true P-T path.

Degenerate four-wave mixing in colloidal gold as a function of particle size

Abstract: The conjugate reflectivity of colloidal gold has been measured for four samples containing particles with mean sizes of 5, 10, 15, and 30 nm. The response times of the samples indicate a size dependence, but the conjugate signal strength was found to be only weakly dependent on particle size. Calculations of the local-field enhancement in the host matrix by the effective-medium theory indicate that the nonlinearity is inherent in the gold particles.

On the numerical evaluation of Eshelby's tensor and its application to elastoplastic fibrous composites

Abstract: A numerical evaluation of Eshelby's S tensor for an ellipsoidal inclusion imbedded in a general anisotropic matrix material is performed. The numerical scheme is valid for any degree of matrix anisotropy and for any aspect ratio of the ellipsoid, including the extreme cases of cracks and cylindrical inclusions. The influence of matrix anisotropy on the evaluation of S is tested extensively for cylindrical inclusions by considering plasticity induced anisotropy in the instantaneous properties of an elastic-plastic matrix material. The Mori-Tanaka averaging method is used to study the influence of the evaluation of S on the prediction of instantaneous effective properties of fibrous composites with elastic fibres and elastic-plastic matrix.

Gramicidin channels and pores.

Abstract: MODEL NOMENCLATURE 129 POLYMORPHISM OF GRAMICIDIN . . 133 Identification of Multiple Conformations in Solution 133 One Predominant Conformation Is Present in Membranes 137 Ion Binding Affects Gramicidin Conformations ... 139 PHYSICAL NATURE OF THE CONFORMERS 141 The Pore Is a Double Helix 1 41 The Channel Is a Helical Dimer 144 fon Binding Sites in the Pore and in the Channel 147

Countering the effects of destructive criticism: The relative efficacy of four interventions.

Abstract: Examined the effectiveness of four interventions in countering the negative impact of destructive criticism. Results agreed closely with those of the laboratory investigation: an apology and attributional information were rated as most effective by both groups. Both managers and employees viewed destructive criticism as a moderately important cause of conflict in their organizations. However, managers rated the negative impact of cristicism on motivation and working relationships as less severe than did employees

The infrared transmission spectra of four silicate glasses before and after exposure to water

Abstract: The infrared transmission spectra of four silicate glasses were investigated. By using blown glass films, 1–2 μm thick, detailed infrared transmission spectra were generated over the 4000–180 cm−1 range, both before and after the films were exposed to water. The water had little effect on the spectra of the 70SiO2–20Na2O–10Al2O3 (mol %) and Pyrex compositions, but had a large effect on the spectra of the 70SiO2–30Na2O (mol %) and Corning 015 compositions. The Si–O nonbridged stretching band at ∼950 cm−1 and a largely overlooked bending band at ∼600 cm−1 were the bands most sensitive to hydration in the 70/30 and 015 compositions. Changes were also seen in the Si–O–Si bridged stretching bands at ∼1050 cm−1 and ∼770 cm−1. The water, however, had no effect on the dominant Si–O–Si bending band at 460 cm−1. It was also discovered that the 70/30 and 015 films reacted with the atmosphere to form a carbonate layer on their surface. This carbonate accounted for the 1450 cm−1 and 230 cm−1 bands seen in their infrared transmission spectra.

Comprehension and Memory of Instruction Manual Warnings: Conspicuous Print and Pictorial Icons

Abstract: Two experiments examined the effects of increasing the noticeability of instruction manual warnings on subsequent comprehension and memory performance. Participants read one of four instruction man...

A combined octree/delaunay method for fully automatic 3‐D mesh generation

Abstract: Fully automatic three-dimensional mesh generation is a fundamental requirement for automating the numerical solution of partial differential equations. Two techniques in particular—the octree and Delaunay approaches—have been used towards this end. A method that combines both approaches to fully automatic mesh generation is presented here. The resulting algorithm provides the linear growth rate and divide-and-conquer approach of the octree method with the simplicity and optimal properties of the Delaunay triangulation.

In vivo reflectance of blood and tissue as a function of light wavelength

Abstract: The reflectance of light from in vivo tissue is described for wavelengths in the range from 420 to 940 nm, based on photon diffusion theory and on experimental results from studies of 17 subjects. The results show a minimum reflectance and a peak sensitivity to the blood pulsations in the wavelength range from 510 to 590 nm. Skin pigmentation is seen to attenuate reflectance rather than altering the character of the modulation spectra. Based on the model presented, the dependence of modulation spectra on mean blood fractional volume as well as wavelength is described theoretically and corroborated by further experimental data at 570 and 630 nm. At these latter wavelengths, the signal-to-noise ratio is calculated for the blood volume pulsation signal in the presence of physiological noise. The median for calculated ratios of reflectance modulation by blood pulsation and ratios of signal to noise between the two wavelengths are 13.1 and 7.5, respectively, for 93 sites in nine subjects. These results are seen to be consistent with the theory. >

The Prediction of Two-Phase Turbulence and Phase Distribution Phenomena Using a Reynolds Stress Model

Abstract: The void fraction distribution for turbulent bubbly air/water upflows and downflows in a pipe was analyzed using a three-dimensional two-fluid model. A τ − e (i.e., Reynolds stress) turbulence model was used for the continuous (liquid) phase. The τ − e transport equations yield all components of the Reynolds stress tensor for the liquid phase momentum equations. The effect of these stresses is to create a lateral pressure gradient that acts on the bubbles and effects their distribution. The lateral lift force on the bubbles has also been modelled. This lift force arises due to the relative motion of the bubble with respect to a nonuniform liquid velocity field. It has been observed experimentally that for upflows the bubbles concentrate near the wall while for downflows they move toward the center of the conduit. The model presented herein predicts these trends.

Technology transfer and the university

Abstract: (1992). Technology Transfer and the University. The Journal of Higher Education: Vol. 63, No. 4, pp. 476-478.

On uniform fields in heterogeneous media.

Abstract: Uniform elastic strain fields are found in two-phase fibrous media of arbitrary transverse geometry, and in two-phase media of any phase geometry. In initially stress-free fibrous solids, a single uniform field can be created by certain proportionally changing tractions derived from a uniform overall stress. In the presence of phase eigenstrains, many overall stress states can be superimposed to create uniform strain fields in fibrous media. The existence of such fields is exploited to establish a number of exact results for two-phase fibre systems. These include universal connections between phase and overall moduli, and between components of phase stress and strain fields; expressions for new transformation influence functions and concentration factors in terms of their mechanical counterparts; and also expressions for the overall stresses and strains caused by phase eigenstrains. Examples are presented for macroscopically monoclinic fibrous composites with transversely isotropic phases. In two-phase media of arbitrary phase geometry there is only a single uniform stress and strain field for each non-vanishing eigenstrain state. The existence of this field is utilized in derivation of exact connections between transformation and mechanical influence functions and concentration factors.

Performance evaluation of automated manufacturing systems using generalized stochastic Petri nets

Abstract: Generalized stochastic Petri net (GSPN) modules are used as basic building blocks to model and analyze complex manufacturing systems. This modular approach facilitates model construction and helps manage the complexity of modeling large manufacturing systems. The structural analysis ensures that the model is live and bounded, which guarantees that the equivalent Markov chain (MC) is ergodic. The temporal analysis is used to derive performance measures such as average production rates and average in process inventories. The main advantage of Petri nets (PNs) over MCs is that the number of places and transitions increases only slightly as the manufacturing system complexity increases, whereas the number of states in the MC increases exponentially. In addition, there is no need to enumerate all the possible states manually since they are automatically generated from the GSPN model. As a result, PN models can still be easily obtained for complicated interconnected systems. The straightforward application of this approach is demonstrated and reviewed for several manufacturing case studies. For serial transfer lines it is proven that this modular approach results in live and bounded GSPN models. Comparisons are made with deterministic and reduced state-space models. Examples containing as many as 9614 states are presented. >

Effects of hydrothermal alteration on the compositions of chromian spinels

Abstract: Chromite spinels in hydrothermally altered rocks from fracture-zone ultramafic rocks and from both ultramafic cumulate pods and sheeted dikes in the Josephine ophiolite, California, display a wide variety of compositions. Alteration of the spinel may not be visible in thin section. The primary composition changes accompanying hydrothermal alteration are increase in Cr/(Cr+Al) and/or Fe2+/(Fe2++Mg). In general, altered spinel grains associated with hornblende and chlorite show an increase in Cr/(Cr+Al) from core to rim. Altered spinel grains associated with serpentine show an increase in Fe2+/(Fe2++Mg) from core to rim but may not show an increase in Cr/(Cr+Al). The compositional zoning in some altered spinel grains appears to result both from reaction of clinopyroxene plus spinel to form hornblende, and from reaction of hornblende to form chlorite. These observations suggest that subsolidus hydrothermal metamorphic effects need to be considered when interpreting spinel compositions and the compositions should not be interpreted solely in terms of igneous processes. Further, the presence of highly altered spinels may be indicative of hydrothermal alteration in rocks where other evidence of such alteration is absent.

A model-fitting approach to cluster validation with application to stochastic model-based image segmentation

Abstract: A clustering scheme is used for model parameter estimation. Most of the existing clustering procedures require prior knowledge of the number of classes, which is often, as in unsupervised image segmentation, unavailable and must be estimated. This problem is known as the cluster validation problem. For unsupervised image segmentation the solution of this problem directly affects the quality of the segmentation. A model-fitting approach to the cluster validation problem based on Akaike's information criterion is proposed, and its efficacy and robustness are demonstrated through experimental results for synthetic mixture data and image data. >

Erratum to: Chemical interdiffusion of dacite and rhyolite: anhydrous measurements at 1 atm and 10 kbar, application of transition state theory, and diffusion in zoned magma chambers

Abstract: Chemical diffusivity measurements have been made on anhydrous metaluminous diffusion couples of dacite and rhyolite at 1 atm, 1200°–1400° C, and 10 kbar, 1300°–1600° C, and on anhydrous peraluminous and peralkaline dacite-rhyolite diffusion couples at 10 kbar, 1300°–1600° C. Chemical diffusivities for Si, Al, Fe, Mg, and Ca were measured in all experiments on the metaluminous diffusion couples using Boltzmann-Matano analysis, and Si diffusivities were measured on the other diffusion couples. Two 10 kbar metaluminous experiments were analyzed with the X-ray microprobe and diffusivities of Sr, Y, Zr and Nb were measured. Si diffusivity displays a weak negative correlation with SiO2 content over the range of 65%–75% SiO2. At a given SiO2 content chemical diffusivities of all non-alkali elements are usually within less than an order of magnitude of Si chemical diffusivity and are controlled by partitioning along the diffusion profile so as to maintain local equilibrium at each point along the profile. Alkali chemical diffusivities were not measured but can be estimated from the experiments to be orders of magnitude higher than non-alkali chemical diffusivities. Data were fit to Arrhenius equations for diffusivities measured at 65, 70 and 75% SiO2. At 1 atm the Arrhenius equation for non-alkalies at 70% SiO2 in the metaluminous system is: $$D_T = 72.5\exp \left( { - 82.5 kcal/RT} \right)$$ an at 10 kbar: $$D_T = 0.0673\exp \left( { - 56.5 kcal/RT} \right)$$ whereDT is the diffusivity in cm2/s,R is in calories, andT is in Kelvin. At 65 and 75% SiO2 the pre-exponential factors and activation energies are similar to the values determined at 70% SiO2. Results on the metaluminous system demonstrate that the effect of increasing pressure is to increase the diffusivity at constant temperature, by about a factor of 4 at 1300° C, less at higher temperatures. Ten kbar activation energies and pre-exponential factors for peraluminous and peralkaline systems are slightly smaller than for the metaluminous system and reflect the slightly higher diffusivities in the peraluminous and peralkaline systems consistent with their lower calculated viscosities when compared to the metaluminous system. 1-atm diffusivities can be calculated from melt viscosities using the Eyring equation to within a factor of 5, except for 75% SiO2 diffusivities which consistently display calculated diffusivities approximately an order of magnitude below measured diffusivities. Using fundamental equations of transition state theory the 1-atm chemical diffusivities of non-alkalies, and alkalies too, can be calculated from thermodynamic data and melt structure models. There are, however, discrepancies in the calculated and measured activation energies and pre-exponential factors. Application of diffusivity measurements to magma chamber processes demonstrates that diffusion is not an effective process for compositional modification and can only begin to have a significant effect on melt compositions if the dacitic and rhyolitic melts are convecting separately and separated by a thin, static zone where diffusive transport is occurring; even in this case diffusion is likely to modify alkali concentrations only, and perhaps isotopic ratios in small magma chambers, or chambers with large aspect ratios (width/height). If the dacitic melt forms enclaves which are mixed into the rhyolitic melt, then diffusion coupled with the physical mixing of enclaves has the potential to rapidly affect alkali and isotopic ratios of the rhyolite melt and dacitic enclaves. Non-alkali concentrations in both dacite enclaves and rhyolite are, however, unlikely to be significantly affected. Because of the ineffectiveness of diffusion, once a magma chamber becomes zoned in major and trace elments it will remain zoned, with the exception of alkalies and possibly isotopic ratios, unless physical mixing between the different compositions occurs.

Polymer recycling by selective dissolution

Abstract: A method for separating polymers from a physically commingled solid mixture containing a plurality of polymers comprises dissolving a first one of the polymers in a solvent at a first lower temperature to form a first preferably single phase solution and a remaining solid component. The solid component contains additional polymers which are not soluable to the solvent at the first temperature but which may be soluble at higher temperatures. The method includes subsequently heating the solvent to dissolve additional polymer from the solid component to form subsequent solutions. The polymers are then separated from their respective solution either using flash evaporation techniques when more than one polymer has been dissolved at a single temperature, or conventional techniques for extracting a polymer from a solvent in a solution.