Showing papers by "Lehigh University published in 1991"

Use of Hammerstein Models in Identification of Nonlinear Systems

Abstract: The utility of the Hammerstein model, which is composed of a static nonlinear element in series with a linear dynamic part, was investigated to represent the dynamics of nonlinear chemical processes. Different methods to identify the parameters of Hammerstein models were tested. The methods were applied to the identification of simulated distillation columns and to an experimental heat exchanger process. The results show that the dynamics of such processes can be better represented by Hammerstein-type models than by linear models.

External Reinforcement of Concrete Beams Using Fiber Reinforced Plastics

Abstract: A series of 16 under-reinforced beams was tested to study the effectiveness of external strengthening using fiber reinforced plastic (FRP) plates. Plates of glass, carbon and aramid fibers were bonded to the tension side of the beams using a 2-part epoxy. An interative analytical method was developed to predict the stiffness and maximum strength in bending of the plated beam. Increases in stiffness (over the working load range) from 17 to 99 percent and increases in strength (ultimate) from 40 to 97% were achieved for the beams with FRP plates. Predicted and acutal load-deflection curves showed fairly good agreement, although generally the theoretical curves were stiffer. Experimental failure did not occur in the maximum moment region on many of the beams, despite attempts at end anchorages to postpone local shear failure. The ulltimate loads of the beams that did fail in the maximum region were within about 5% of predicted values.

Determination of Degree of Substitution of Formyl Groups in Polyaldehyde Dextran by the Hydroxylamine Hydrochloride Method

Abstract: Colorimetric or potentiometric titration of the aldehyde residues in polyaldehyde dextran by the hydroxylamine hydrochloride/sodium hydroxide method has been found to be a convenient and accurate method to determine formyl content. Nitrogen combustion analyses on the isolated oximes confirmed the titrametric results.

Linking descriptive and experimental analyses in the treatment of bizarre speech.

Abstract: Descriptive and experimental methods were used to analyze the environmental determinants of an adult's bizarre speech. A descriptive analysis of behavior under natural conditions indicated that bizarre vocalizations occurred most often in the presence of task-related demands and in the absence of adult attention. Further, bizarre speech occurring during tasks was followed frequently by the cessation of task demands by staff or the subject's voluntary disengagement from task-related activities; bizarre speech observed during noninteractional periods (i.e., in the absence of adult attention) was frequently followed by staff attention. The escape and attention hypotheses were tested under analogue conditions. Results of the experimental analysis supported only the attention hypothesis; that is, bizarre speech appeared to function as an attention-producing behavior. The functional analysis data were used to select two different yet functionally equivalent treatments. The first treatment provided the subject with noncontingent scheduled attention. The second intervention taught the subject social language skills in the form of initiation and expansion statements. Both interventions were effective in suppressing maladapted speech. Advantages of linking descriptive and experimental analyses are discussed.

On the dynamics of near-wall turbulence

Abstract: A model of the dynamic physical processes that occur in the near-wall region of a turbulent flow at high Reynolds numbers is described The hairpin vortex is postulated to be the basic flow structure of the turbulent boundary layer It is argued that the central features of the near-wall flow can be explained in terms of how asymmetric hairpin vortices interact with the background shear flow, with each other, and with the surface layer near the wall The physical process that leads to the regeneration of new hairpin vortices near the surface is described, as well as the processes of evolution of such vortices to larger-scale motions farther from the surface The model is supported by recent important developments in the theory of unsteady surface-layer separation and a number of `kernel' experiments which serve to elucidate the basic fluid mechanics phenomena believed to be relevant to the turbulent boundary layer Explanations for the kinematical behaviour observed in direct numerical simulations of low Reynolds number boundary-layer and channel flows are given An important aspect of the model is that it has been formulated to be consistent with accepted rational mechanics concepts that are known to provide a proper mathematical description of high Reynolds number flow

Mediated and convergent lexical priming in language production: a comment on Levelt et al. (1991).

Abstract: Levelt et al. (1991) argued that modular semantic and phonological stage theories of lexical access in language production are to be preferred over interactive spreading-activation theories (e.g., Dell, 1986). As evidence, they show no mediated semantic-phonological priming during picture naming: Retrieval of sheep primes goat, but the activation of goat is not transmitted to its phonological relative, goal. This research reconciles this result with spreading-activation theories and shows how the absence of mediated priming coexists with the convergent priming necessary to account for mixed semantic-phonological speech errors. The analysis leads to the proposal that the language-production system may best be characterized as globally modular but locally interactive.

Stability of Earth Slopes

Abstract: The failure of a mass of soil in a downward and outward movement of a slope is called a slide or slope failure. Slides occur in almost every conceivable manner, slowly or suddenly, and with or without any apparent provocation. They are usually caused by excavation, by undercutting the foot of an existing slope, by a gradual disintegration of the structure of the soil, by an increase of the pore water pressure in a few exceptionally permeable layers, or by a shock that liquefies the soil.

A generalization of the Berlekamp-Massey algorithm for multisequence shift-register synthesis with applications to decoding cyclic codes

Abstract: A generalization of the Berlekamp-Massey algorithm is presented for synthesizing minimum length linear feedback shift registers for generating prescribed multiple sequences. A more general problem is first considered, that of finding the smallest initial set of linearly dependent columns in a matrix over an arbitrary field, which includes the multisequence problem as a special case. A simple iterative algorithm, the fundamental iterative algorithm (FIA), is presented for solving this problem. The generalized algorithm is then derived through a refinement of the FIA. Application of this generalized algorithm to decoding cyclic codes up to the Hartmann-Tzeng (HT) bound and Roos bound making use of multiple syndrome sequences is considered. Conditions for guaranteeing that the connection polynomial of the shortest linear feedback shift register obtained by the algorithm will be the error-locator polynomial are determined with respect to decoding up to the HT bound and special cases of the Roos bound. >

A Raman and ultraviolet diffuse reflectance spectroscopic investigation of alumina-supported molybdenum oxide

Abstract: Summary A thorough calorimetric investigation of graphite-supported iridium particle chemistry was conducted. A careful determination of the particle size distribution assisted in the interpretation. The stoichiometry of oxygen, carbon monoxide, and hydrogen was determined: CO/Ir, = 0.50, O/h, = 1.0, H/h, = 1.0. The differential heats of adsorption of these molecules on the iridium surface was found to be very similar to those reported for alumina-supported iridium particles, suggesting support effects are minimal. Differential rate data were made available for the first time. It is clear that this basic information regarding adsorption stoichiometries, rates, and heats will be useful in future studies of the surface composition of multimetallic supported catalysts that contain iridium. The calorimeter allowed a study of the interaction between hydrogen and oxygen on an iridium surface. The rate, heat, stoichiometry, and sequence of steps that occur when differential hydrogen reduction of a preoxidized surface is carried out were all studied. It was found that the heat of reaction and the rate of reaction between dosed hydrogen and adsorbed oxygen progressively decreased. The measured integral heat, however, agreed with a simple thermodynamic model. The results of this study suggests that differential calorimeters can be valuable tools for providing information of the type required for detailed kinetic modeling of reactions taking place on catalyst surfaces. They also suggest that this type of calorimetry can provide detailed insight into the mechanism of surface reaction, an area of intense research at the present time.

Linear and nonlinear optical measurements of the Lorentz local field.

Abstract: We have studied the resonant optical response of a dense atomic potassium vapor under conditions such that the response is strongly influenced by local-field effects. Our experimental results are in good agreement with the predictions of theory. We have also discovered a collision-induced shift of the potassium resonance lines given by \ensuremath{\Delta}${\mathrm{\ensuremath{\omega}}}_{\mathrm{c}\mathrm{o}\mathrm{l}=}$\ensuremath{\beta}N, where \ensuremath{\beta}=-5.0\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}8}$ ${\mathrm{sec}}^{\mathrm{\ensuremath{-}}1}$ ${\mathrm{cm}}^{3}$ for the 4 $^{2}$${\mathit{S}}_{1/2}$\ensuremath{\leftrightarrows}4 $^{2}$${\mathit{P}}_{1/2}$ transition and where \ensuremath{\beta}=-3.0\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}8}$ ${\mathrm{sec}}^{\mathrm{\ensuremath{-}}1}$ ${\mathrm{cm}}^{3}$ for the 4 $^{2}$${\mathit{S}}_{1/2}$\ensuremath{\leftrightarrows}4 $^{2}$${\mathit{S}}_{1/2}$\ensuremath{\leftrightarrows}4 $^{2}$${\mathit{P}}_{3/2}$ transition.

Vortex-induced boundary-layer separation. Part 1. The unsteady limit problem Re [rightward arrow] [infty infinity]

Abstract: The unsteady boundary-layer flow produced by a two-dimensional vortex in motion above an infinite plane wall in an otherwise stagnant fluid is considered in the limit of infinite Reynolds number. This study is part of a continuing investigation into the nature of the physical processes that occur near the surface in transitional and fully turbulent boundary layers. The adverse pressure gradient due to the vortex leads to the development of a zone of recirculation in the viscous flow near the surface, and the boundary-layer flow then focuses rapidly toward an eruption along a band which is very narrow in the stream wise direction. The evolution of the unsteady boundary layer is posed in Lagrangian coordinates and computed using an efficient, factored ADI numerical method. The boundary-layer solution is found to develop a separation singularity and to evolve toward a terminal stage which is generic in two-dimensional unsteady flows. The computed results are compared with the results of asymptotic theory of two-dimensional boundary-layer separation and the agreement is found to be excellent.

Acute versus chronic grief: the case of pregnancy loss.

Abstract: Conceptual and measurement problems in identifying those at risk of chronic grief are reviewed, and results are presented of a longitudinal study of people who have experienced pregnancy loss. Coping resources, particularly prior mental health and social support, were the best predictors of low scores on subscales of the Perinatal Grief Scale that indicate chronic grief reactions. Results also offer some evidence of delayed grief responses, especially among men and those who experienced early losses.

A special theory of crack propagation

Abstract: The Griffith concept [1, 2] of imperfection instability in a solid was the first step toward predicting the fracture strength of solids. The basic idea behind his theory is that a crack will begin to propagate if the elastic energy released by its growth is greater than the energy required to create the fractured surfaces. As a model, Griffith considered the problem of a crack of length 2a in a plate under tension σ as in Figure 1.1(a).

Interfacial phenomena controlling particle morphology of composite latexes

Abstract: A thermodynamic analysis and a mathematical model were derived to describe the free energy changes corresponding to various possible morphologies in composite latex particles. Seeded batch emulsion polymerization was carried out at 70°C using as seed monodisperse polystyrene latex particles having different surface polarity. The surface polarity was estimated by contact angle measurement at the latex “film”/water interface for octane as the probe liquid. Methyl methacrylate and ethyl methacrylate were polymerized in a second stage seeded emulsion polymerization using polystyrene particles as seed in the presence of a nonionic stabilizer, nonyphenol polyethylene oxide (Igepal Co-990). Two types of initiators, potassium persulfate (K2S2O8) and azobisiobutyronitrile (AIBN), were used to change the interfacial tension between the second stage polymer (in monomer) and water interface. The values of the interfacial tension of polymer solutions in the second stage monomer vs. the aqueous phase, measured by drop-weight–volume method under conditions similar to those prevailing during the polymerization, correlated well with the determined particle surface polarity and the observed TEM particle morphology. The results showed that, rather than the polymer bulk hydrophilicity, the surface particle polarity is the controlling parameter in deciding which phase is inside or outside in the composite particle. The variation of the polymer phase interfacial tension with polymer concentration was also estimated. Based on experimentally measured interfacial tensions, composite particle configurations were predicted. The predicted morphologies showed good agreement with the observed particle morphologies of the composite latexes.

The crack problem in bonded nonhomogeneous materials

Abstract: The plane elasticity problem for two bonded half planes containing a crack perpendicular to the interface was considered. The effect of very steep variations in the material properties near the diffusion plane on the singular behavior of the stresses and stress intensity factors were studied. The two materials were thus, assumed to have the shear moduli mu(o) and mu(o) exp (Beta x), x=0 being the diffusion plane. Of particular interest was the examination of the nature of stress singularity near a crack tip terminating at the interface where the shear modulus has a discontinuous derivative. The results show that, unlike the crack problem in piecewise homogeneous materials for which the singularity is of the form r/alpha, 0 less than alpha less than 1, in this problem the stresses have a standard square-root singularity regardless of the location of the crack tip. The nonhomogeneity constant Beta has, however, considerable influence on the stress intensity factors.

Vortex-induced boundary-layer separation. part 2. unsteady interacting boundary-layer theory

Abstract: The unsteady boundary layer induced by the motion of a rectilinear vortex above an infinite plane wall is calculated using interacting boundary-layer methods. The boundary-layer solution is computed in Lagrangian variables since it is possible to compute the flow evolution accurately in this formulation even when an eruption starts to evolve. Results are obtained over a range of Reynolds numbers, Re. For the limit problem Re - infinity (studied in Part 1), a singularity develops in the non-interacting boundary-layer solution at finite time. The present results show that the interacting boundary-layer calculations also terminate in a singularity at a time which is earlier than in the limit problem and which decreases with decreasing Reynolds number. The computed results are compared with the length-and timescales predicted by recent asymptotic theories and are found to be in excellent agreement. See also previous abstract.

Remarkable Spreading Behavior of Molybdena on Silica Catalysts. An In Situ EXAFS-Raman Study.

Abstract: In contrast to the frequently reported lack of interaction between hexavalent molybdenum and SiO2 and the tendency of silica-supported MoO3 to coalescence, it has been found that on dehydration small molybdenum oxide clusters spread over a silica support. A combined Raman spectroscopy-X-ray absorption study shows a significantly altered structure of the molybdenum oxide phase after dehydration. In EXAFS the total Mo-Mo coordination number drops from 3.27 to 0.20 after anin situ thermal treatment at 673 K. The increase of the peak in the XANES region (Is -→ 4d) indicates that the coordination sphere of the molybdenum atoms strongly alters after dehydration. The Raman spectra reflect the change of the structure through a shift of the position of the terminal Mo=O bond from 944 to 986 cm−1 and the disappearance of the bridged Mo-O-Mo vibration at 880 cm−1. It is concluded that dehydration produces almost isolated molybdenum sites in this highly dispersed sample. Water ligands stabilize the oligomeric clusters under ambient conditions; the removal of water causes spreading of these clusters.

Monitoring cell concentration and activity by multiple excitation fluorometry.

Abstract: Four key cellular metabolic fluorophores--tryptophan, pyridoxine, NAD(P)H, and riboflavin--were monitored on-line by a multiple excitation fluorometric system (MEFS) and a modified SLM 8000C scanning spectrofluorometer in three model yeast fermentation systems--bakers' yeast growing on glucose, Candida utilis growing on ethanol, and Saccharomyces cerevisiae RTY110/pRB58 growing on glucose. The measured fluorescence signals were compared with cell concentration, protein concentration, and cellular activity. The results indicate that the behavior and fluorescence intensity of various fluorophores differ in the various fermentation systems. Tryptophan fluorescence is the best signal for the monitoring of cell concentration in bakers' yeast and C. utilis fermentations. Pyridoxine fluoresce is the best signal for the monitoring of cell concentration in the S. cerevisiae RTY110/pRB58 fermentation. In bakers' yeast fermentations the pyridoxine fluorescence signal can be used to monitor cellular activity. The NAD(P)H fluorescence signal is a good indicator of cellular activity in the C. utilis fermentation. For this fermentation NAD(P)H fluorescence can be used to control ethanol feeding in a fed-batch process.

Charge motion in ferroelectric thin films

Abstract: Switching of the direction of polarization in ferroelectric thin films can be used as a mechanism for space-efficient memory storage in microcircuits. The fields required for adequate switching rates are of the order of 5 × 105 volts/cm. At these high fields, there are several potential mechanisms for the motion of charged species in the film with a resulting degradation of properties. The defect chemistry and charge transport mechanisms in perovskite-based systems are reviewed, and their pertinence for the development of stable, reliable memory elements is discussed.

The effects of gestational age and gender on grief after pregnancy loss.

Abstract: The roles of gestational age and gender in grief reactions following loss of pregnancy were explored. Parents with losses later in pregnancy reported more intense grief than did those whose losses were earlier. Women expressed higher levels of grief than did men six to eight weeks after the loss; however, this difference had decreased by one and two years after the loss.