Showing papers by "Rensselaer Polytechnic Institute published in 1986"

Subband coding of images

Abstract: Subband coding has become quite popular for the source encoding of speech. This paper presents a simple yet efficient extension of this concept to the source coding of images. We specify the constraints for a set of two-dimensional quadrature mirror filters (QMF's) for a particular frequency-domain partition, and show that these constraints are satisfied by a separable combination of one-dimensional QMF's. Bits are then optimally allocated among the subbands to minimize the mean-squared error for DPCM coding of the subbands. Also, an adaptive technique is developed to allocate the bits within each subband by means of a local variance mask. Optimum quantization is employed with quantizers matched to the Laplacian distribution. Subband coded images are presented along with their signal-to-noise ratios (SNR's). The SNR performance of the subband coder is compared to that of the adaptive discrete cosine transform (DCT), vector quantization, and differential vector quantization for bit rates of 0.67, 1.0, and 2.0 bits per pixel for 256 × 256 monochrome images. The adaptive subband coder has the best SNR performance.

Efficient algorithms for finding minimum spanning trees in undirected and directed graphs

Abstract: Recently, Fredman and Tarjan invented a new, especially efficient form of heap (priority queue). Their data structure, theFibonacci heap (or F-heap) supports arbitrary deletion inO(logn) amortized time and other heap operations inO(1) amortized time. In this paper we use F-heaps to obtain fast algorithms for finding minimum spanning trees in undirected and directed graphs. For an undirected graph containingn vertices andm edges, our minimum spanning tree algorithm runs inO(m logβ (m, n)) time, improved fromO(mβ(m, n)) time, whereβ(m, n)=min {i|log(i) n ≦m/n}. Our minimum spanning tree algorithm for directed graphs runs inO(n logn + m) time, improved fromO(n log n +m log log log(m/n+2) n). Both algorithms can be extended to allow a degree constraint at one vertex.

Distinguishability of Conductivities by Electric Current Computed Tomography

Abstract: We give criteria for the distinguishability of two different conductivity distributions inside a body by electric current computed tomography (ECCT) systems with a specified precision. It is shown in a special case how these criteria can be used to determine the measurement precision needed to distinguish between two different conductivity distributions. It is also shown how to select the patterns of current to apply to the body in order to best distinguish given conductivity distributions with an ECCT system of finite precision.

Calibrations of phase abundance, composition, and particle size distribution for olivine-orthopyroxene mixtures from reflectance spectra

Abstract: An analytical method for quantifying the characteristics (phase abundances, phase composition, and grain size) of an olivine-orthopyroxene mixture from reflectance spectra is described. The spectral parameters related to reflectance, wavelength position, and albedo are investigated; the absorption bands for the olivine-orthopyroxene mixture is also studied. Primary calibrations useful for the determination of the olivine-orthopyroxene mixture characteristics are examined.

Monazite solubility and dissolution kinetics: implications for the thorium and light rare earth chemistry of felsic magmas

Abstract: A series of monazite dissolution experiments was conducted in a hydrous (1–6 wt%) granitic melt at 8 kbar over the temperature range 1,000–1,400° C A polished cube of monazite was immersed in a natural obsidian melt and allowed to partially dissolve Electron microprobe traverses perpendicular to the crystal-melt interface revealed concentration gradients in the LREEs and P Diffusivities of the LREEs and P were calculated from these profiles, yielding the following Arrhenius relations for the LREEs: D=023 exp(−601 kcal mol−1/RT) at 6% water D=230×107 exp(−1221 kcal mol−1/RT) at 1% water These results demonstrate the importance of dissolved water on REE diffusion Phosphorus diffusivities are nearly identical to those of the rare-earths, suggesting that P diffusion charge-compensates REE diffusion The concentration of LREEs required for monazite saturation in these melts is given by the level of dissolved LREEs at the crystal-melt interface These values also show a dependence on dissolved water, with LREEsat=60 ppm at 6% H2O when extrapolated down to 700° C, and LREEsat=30 ppm at 1% H2O Calculated dissolution rates based on the above parameters indicate that minute ( 2% H2O), whereas larger (> 50 μm) crystals will likely be residual over the duration of an anatectic event The low solubility of monazite in this melt suggests that the LREE depletion observed in some felsic differentiation suites may be the result of monazite crystallization Limited experimental and geochemical/petrologic evidence indicates that compositional changes in the melt accompanying differentiation decrease the solubility of monazite drastically Kinetic and chemical constraints may also lead to localized monazite saturation and inclusion in major phases or even other accessories Variations in the REE composition of monazite from different parageneses probably reflects the REE pattern of the parent melt, and may be due to gradational differences in the stability of individual or subgroup REE-complexes as a function of melt composition Particularly important in this regard seems to be the lime+alkali/alumina balance of the melt and its volatile content

Thrombin-induced increase in albumin permeability across the endothelium.

Abstract: We studied the effect of thrombin on albumin permeability across the endothelial monolayer in vitro. Bovine pulmonary artery endothelial cells were grown on micropore membranes. Morphologic analysis confirmed the presence of a confluent monolayer with interendothelial junctions. Albumin permeability was measured by the clearance of 125I-albumin across the endothelial monolayer. The control 125I-albumin clearance was 0.273 +/- 0.02 microliter/min. The native enzyme, alpha-thrombin (10(-6) to 10(-10) M), added to the luminal side of the endothelium produced concentration-dependent increases in albumin clearance (maximum clearance of 0.586 +/- 0.08 microliter/min at 10(-6) M). Gamma (gamma) thrombin (10(-6) M and 10(-8) M), which lacks the fibrinogen recognition site, also produced a concentration-dependent increase in albumin clearance similar to that observed with alpha-thrombin. Moreover, the two proteolytically inactive forms of the native enzyme, i-Pr2 P-alpha-thrombin and D-Phe-Pro-Arg-CH2-alpha-thrombin, increased the 125I-albumin clearance (0.610 +/- 0.09 microliter/min and 0.609 +/- 0.02 microliter/min for i-Pr2 P-alpha-thrombin and D-Phe-Pro-Arg-CH2-alpha-thrombin at 10(-6) M, respectively). Since the modified forms of thrombin lack the fibrinogen recognition and active serine protease sites, the results indicate that neither site is required for increased albumin permeability. The increase in albumin clearance with alpha-thrombin was not secondary to endothelial cell lysis because lactate dehydrogenase concentration in the medium following thrombin was not significantly different from baseline values. There was also no morphological evidence of cell lysis. Moreover, the increase in 125I-albumin clearance induced by alpha-thrombin was reversible by washing thrombin from the endothelium. The basis for the increased albumin permeability following the addition of alpha-thrombin appears to be a reversible change in endothelial cell shape with formation of intercellular gaps.

Identification of image and blur parameters for the restoration of noncausal blurs

Abstract: An optimal statistical parameter estimation technique is presented for the identification of unknown image and blur model parameters. The development leads to an autoregressive moving average (ARMA) model identification problem, where the image model coefficients define the AR part, and the blur parameters define the MA part. Conditional maximum-likelihood estimates of the unknown parameters are derived both in the absence and in the presence of observation noise. The proposed algorithms constitute a generalization of previous work on blur identification in that they are able to locate the zero loci of the blurred image spectrum on the entire z 1 - z 2 plane. Simulation results, as well as photographically blurred images processed with the proposed algorithms, are shown as examples.

Interaction of Flows with the Crystal-Melt Interface

Abstract: The coupling between a crystal-melt interface and fluid flow is investigated. The solidification boundary conditions at the crystal-melt interface are described. The influences of morphological and double-diffusive instabilities during directional solidification on the interface are studied. The experiments by Glicksman and Mickalonis (1982) and Fang et al. (1985) which examine the relationship between the hydrodynamic state of the phase melt and phase-change interface are analyzed. The Rayleigh-Benard problem, and the effect of crystal-melt interaction on the Rayleigh number are examined. Various applications for melt-flow interactions with solid-liquid interface to engineering and welding are discussed.

Thrombin-induced chemotaxis and aggregation of neutrophils

Abstract: Thrombin-induced neutrophil chemotaxis and aggregation were studied using cells isolated from either human or sheep blood. Sheep neutrophils (10(8) cells/ml) exhibited maximum chemotactic migration towards 10(-8)M human alpha-thrombin, 10(-8)M gamma-thrombin (which lacks the fibrinogen site), and 10(-12)MD-Phe-Pro-Arg-CH2-alpha-thrombin (catalytically inactive thrombin). Chemotactic responses of the same magnitude were obtained with human neutrophils (10(8) cells/ml). The chemotactic responses to thrombin were comparable to those obtained with diluted (1:200 v/v) zymosan activated serum (ZAS) and 10(-11)M FMLP. Premixing of the thrombin forms with hirudin in 1:1 stoichiometric amounts abolished the chemotaxis but not chemokinesis Aggregatory responses of human and sheep neutrophils were comparable for ZAS, alpha-thrombin, and gamma-thrombin. The responses of both human and sheep neutrophils to D-Phe-Pro-Arg-CH2-alpha-thrombin were attenuated, indicating that the proteolytic site may be involved in the aggregatory response. The results suggest that thrombin-induced neutrophil chemotaxis and aggregation are mediated by different mechanisms, since chemotaxis is a catalytically independent response whereas aggregation is an active site independent response.

Corrective Control of Power System Flows by Line and Bus-Bar Switching

Abstract: A fast algorithm is developed for automatic selection and ranking all possible circuits for corrective control by network switching to relieve system overloads. The non-iterative DC approximate model for a power system is used to generate linear sensitivity factors. These factors are calculated using relevant elements of the sparse bus impedance matrix and branch reactances. Special treatment of substation circuit breakers makes it possible to use bus-bar splitting for corrective action. The method was tested on two systems. Test results show the reliability and effectiveness of the method in selecting lines and circuit breakers for corrective overload control.

Sub-band coding of images

Abstract: This paper presents an extension of sub-band coding to two-dimensions with particular application to images. We employ a 16 band decomposition using a tree structure of separable quadrature mirror filters and decimators. The sub-bands are encoded using DPCM with bits allocated to approximately minimize the mean-square error. A block-adaptive variant is also presented. A limited SNR comparison shows adaptive sub-band coding to outperform the adaptive discrete cosine transform and two types of vector quantizers.

Finite Deformation of Soft Tissue: Analysis of a Mixture Model in Uni-Axial Compression

Abstract: The dynamic finite deformational behavior of a biphasic model for soft hydrated tissue is examined. In the case of uni-axial confined compression the displacement and stress fields are derived for steady-state permeation, creep, and stress-relaxation. It is shown how to use the results of this analysis to obtain the constitutive relations, as well as the associated material parameters, from the corresponding experiments. It is also shown that the solutions from the theory go much farther, giving a detailed account of the deformation and interaction of the fluid and solid phases in the tissue.

Continuous hybridoma growth and monoclonal antibody production in hollow fiber reactors–separators

Abstract: Growth of a hybridoma culture, along with production of monoclonal antibody, was demonstrated over extended periods in polysulfone hollow fiber membrane modules. The molecular weight cutoffs of the membranes were 70,000, 50,000, and 100,000 daltons. The hybridoma cell line, designated 65/26, produced IgG (2b/kappa) directed at mouse thymus cell surface antigen, TL.1. Cell growth occurred in the shell space of the reactor, using supplemented RPMI 1640 (20% fetal bovine serum) supplied from a separate reservoir vessel through the hollow fiber lumen. The reservoir contained 125 mL media, which was changed every 4 days. Concentrations of immunoglobulin were determined by an enzyme immunoassay (using protein A and alkaline phosphatase-labeled antibody conjugate). For the 10K, 50K, and 100K hollow fiber membrane modules, the maximum IgG concentrations detected in the 2.5-mL shell space were 47.5-80, 510, and 740 mug/mL, respectively. In the 125-mL reservoir for the 100K hollow fiber membrane module, the IgG concentration was measured at 260 mug/mL These values compare with an IgG concentration of 1 mug/mL when grown in a standard tissue culture flask and 3.2-7.6 mug/mL when grown in 100 ml media in a spinner flask. In addition, 10K and 50K hollow fiber membrane modules were run in a mode that decreased the fetal bovine serum supplement with time. Differences between these systems suggest that it is possible to obtain high IgG accumulation rates, both during and after the exponential growth phase of the hybridoma population.

Multiple Model Adaptive Control Procedure for Blood Pressure Control

Abstract: Multiple model adaptive control procedures have been considered for a computer-based feedback system which regulates the infusion rate of a drug (nitroprusside) in order to maintain desired blood pressure. Because the transfer function parameters are different for each patient, and furthermore are time variant, such an algorithm is desirable for maintaining both steady-state and transient specifications. To this effect, computer simulation has shown that multiple model adaptive control procedures might be successfully applied to the control of blood pressure despite the uncertainty in the delays, time constant, and gains. Additional efforts concerned with the actual demonstration of these concepts on dogs have further supported the role of adaptive control for blood pressure regulation.

Implementation of adaptive array algorithms

Abstract: Some new, efficient, and numerically stable algorithms for the recursive solution of matrix problems arising in optimal beam-forming and direction finding are described and analyzed. The matrix problems considered are systems of linear equations and spectral decomposition. While recursive solution procedures based on the matrix inversion lemma may be unstable, ours are stable. Furthermore, these algorithms are extremely fast.

Neurulation and the cortical tractor model for epithelial folding.

Abstract: We present here a new model for epithelial morphogenesis, which we call the ‘cortical tractor model’. This model assumes that the motile activities of epithelial cells are similar to those of mesenchymal cells, with the added constraint that the cells in an epithelial sheet remain attached at their apical circumference. In particular, we assert that there is a time-averaged motion of cortical cytoplasm which flows from the basal and lateral surfaces to the apical region. This cortical flow carries with it membrane and adhesive structures that are inserted basally and resorbed apically. Thus the apical seal that characterizes epithelial sheets is a dynamic structure: it is continuously created by the cortical flow which piles up components near where they are recycled in the apical region. By use of mechanical analyses and computer simulations we demonstrate that the cortical tractor motion can reproduce a variety of epithelial motions, including columnarization (placode formation), imagination and rolling. It also provides a mechanism for driving active cell rearrangements within an epithelial sheet, while maintaining the integrity of the apical seal. Active repacking of epithelial cells appears to drive a number of morphogenetic processes. Neurulation in amphibians provides an example of a process in which all four of the above morphogenetic movements appear to play a role. Here we reexamine the process of neurulation in amphibians in light of the cortical tractor model, and find that it provides an integrated view of this important morphogenetic process.

Synthesis of decentralized process control structures using the concept of block relative gain

Abstract: The concept of block relative gain (BRG) is introduced to define a measure of interaction for decentralized control structures. This new theoretical development generalizes the original Bristol's relative gain array (RGA) to block pairing of inputs and outputs that are not necessarily single-input single-output pairings. Various properties of BRG are rigorously derived and formulated in a mathematical framework suited to analysis and synthesis. Based on these important properties, a methodology is developed for the systematic generation and selective screening of alternative decentralized control structures. Subsequently, a controller design procedure for the most promising decentralized structures is given. A boiler furnace and a system of heat-integrated reactors are used to illustrate the significance and the utility of the proposed method for industrial processes.

Shock waves and phase changes in a large-heat-capacity fluid emerging from a tube

Abstract: The emergence of a shockwave from the open end of a shock tube is studied, with special emphasis on test fluids of high molar heat capacity, i.e. retrograde fluids. A variety of wavelike vapour-liquid phase changes are observed in such fluids, including the liquefaction shock, mixture-evaporation shock, condensation waves associated with shock splitting and liquid-evaporation waves (these phenomena have analogues in the polymorphic phase changes of solids; only the first two are treated in this paper). The open end of the shock-tube test section discharges into an observation chamber where photographs of the emerging flow are taken. Calculations were performed with the Benedict-Webb-Rubin, van der Waals and other equations of state. Numerical (finite-difference) predictions of the flow were made for single-phase and two-phase flows: solutions were tested against the experimental shock diffraction and vortex data of Skews. The phase-change properties of the test fluid can be quantified by the ‘retrogradicity’ r(T), measuring the difference in slope between the P, T isentrope and the vapour-pressure curve, and the ‘kink’ k(T), measuring the difference between the single-phase and mixture sound speeds. Mixture-evaporation (i.e. rarefaction) shocks appear to have a sonic-sonic or double Chapman-Jouguet structure and show agreement with amplitude predictions based on k(T). Liquefaction shocks are found to show a reproducible transition from regular, smooth shock fronts to irregular, chaotic shock fronts with increasing shock Mach number. This transition can be correlated with published stability limits.

Molecular segregation and nucleation of poly(ethylene oxide) crystallized from the melt. I. Calorimetric study

Abstract: Thermal analysis is used to elucidate the fusion of fractions of poly(ethylene oxide) of from 3500 to 5000000 molecular weight. In addition, the equilibrium and nonequilibrium phase diagrams of binary mixtures of these fractions have been studied. Complete segregation from high-molecular-weight polymer is possible up to at leat 20000 molecular weight. This segregation is not governed by the melting/crystallization equilibrium, but rather by molecular nucleation. Over a broader crystallization temperature range three regions can be identified. At low crystallization temperature, solid solutions result, at higher temperature one finds an intermediate type of crystallization, and ultimately one reaches complete, eutectic segregation. This work will be followed by analysis of the kinetics of crystallization.

ZrO2‐Transformation‐Toughened Glass‐Ceramics Prepared by the Sol‐Gel Process from Metal Alkoxides

Abstract: Glasses of composition 3ZrO/sub 2/.2SiO/sub 2/ were prepared by the sol-gel process from metal alkoxides. Tetragonal ZrO/sub 2/ was precipitated by appropriate heat treatment at 1000/sup 0/ to 1200/sup 0/C. The fracture toughness of these glass-ceramics increased with increasing crystallite size of the tetragonal ZrO/sub 2/, reaching approx. = 5.0 Mn/M/sup 32/ at a size of approx. = 40 Nm. The higher fracture toughness was attributed to tetragonal ..-->.. monoclinic ZrO/sub 2/ transformation toughening.