Showing papers by "Lehigh University published in 1985"

On the solution of integral equations with strong ly singular kernels

Abstract: In this paper some useful formulas are developed to evaluate integrals having a singularity of the form (t-x) sup-m, m or = 1 Interpreting the integrals with strong singularities in Hadamard sense, the results are used to obtain approximate solutions of singular integral equations A mixed boundary value problem from the theory of elasticity is considered as an example Particularly for integral equations where the kernel contains, in addition to the dominant term (t,x) sup-m, terms which become unbounded at the end points, the present technique appears to be extremely effective to obtain rapidly converging numerical results

The Crack Problem for Bonded Nonhomogeneous Materials Under Antiplane Shear Loading

Abstract: The singular nature of the crack tip stress field in a nonhomogeneous medium having a shear modulus with a discontinuous derivative was investigated. The problem is considered for the simplest possible loading and geometry, namely the antiplane shear loading of two bonded half spaces in which the crack is perpendicular to the interface. It is shown that the square-root singularity of the crack tip stress field is unaffected by the discontinuity in the derivative of the shear modulus. The problem is solved for a finite crack and extensive results are given for the stress intensity factors.

The chemistry and biochemistry of C-nucleosides and C-arylglycosides.

Abstract: Publisher Summary This chapter reviews recent advances in the chemistry and biochemistry of C-nucleosides, the literature concerning C-arylglycoside (i.e., nonnitrogen heterocyclic C-nucleoside) antibiotics, and recent significant advances in the synthesis of C-nucleosides and C-glycosides. It also discusses biological test data and data that are relevant to structure–activity relationships. Modification of readily available natural C-nucleosides is an attractive route to new C-nucleoside analogs and derivatives, because one starting material often possesses much of the desired functionality and chiral properties. The chapter illustrates this approach with examples. The most frequently used strategy for C-nucleoside synthesis involves the construction of a heterocyclic aglycone from the C-1 substituent of a functionalized sugar intermediate.

Singular Value Decomposition for Constrained Dynamical Systems

Abstract: On montre que la methode de decomposition des valeurs singulieres est utile dans le probleme de reduction des equations de mouvement pour une classe de systemes dynamiques contraints, a leur dimension minimale

Dynamics of flexible bodies in tree topology - A computer oriented approach

Abstract: An approach suited for automatic generation of the equations of motion for large mechanical systems (i.e., large space structures, mechanisms, robots, etc.) is presented. The system topology is restricted to a tree configuration. The tree is defined as an arbitrary set of rigid and flexible bodies connected by hinges characterizing relative translations and rotations of two adjoining bodies. The equations of motion are derived via Kane's method. The resulting equation set is of minimum dimension. Dynamical equations are imbedded in a computer program called TREETOPS. Extensive control simulation capability is built in the TREETOPS program. The simulation is driven by an interactive set-up program resulting in an easy to use analysis tool.

Swelling of Hot-Pressed A12O3

Abstract: Fully dense aluminas, prepared by hot-pressing, were found to swell during annealing at 1600°C in air, but not during annealing in a reducing atmosphere (po2= 10-7 Pa). The reaction followed the relation p - po = -K log t, where po and p are the initial and final densities, respectively, t is the time, and AT is a constant. The rate of swelling was enhanced by MgO solute. The reduction in density resulted from the nucleation and growth of grain-boundary pores. Pore formation was attributed to the reaction of carbon and sulfur impurities at the boundaries with oxygen, which had diffused down the grain boundaries from the ambient, to form CO/CO2 and SO2 gas at high pressures. Preliminary results indicate that this reaction can be avoided by preannealing powders in flowing oxygen prior to hot-pressing. The consequences of internal gas-forming reactions to other processes such as high-temperature creep and sintering are also discussed.

Flow along a channel with a time-dependent indentation in one wall: the generation of vorticity waves

Abstract: We describe flow-visualization experiments and theory on the two-dimensional unsteady flow of an incompressible fluid in a channel with a time-dependent indentation in one wall. There is steady Poiseuille flow far upstream, and the indentation moves in and out sinusoidally, its retracted position being flush with the wall. The governing parameters are Reynolds number Re, Strouhal number (frequency parameter) St and amplitude parameter e (the maximum fraction of the channel width occupied by the indentation); most of the experiments were performed with e ≈ 0.4. For St ≤ 0.005 the flow is quasi-steady throughout the observed range of Re (360 0.005 a propagating train of waves appears, during every cycle, in the core flow downstream of the indentation, and closed eddies form in the separated flow regions on the walls beneath their crests and above their troughs. Later in the cycle, a second, corotating eddy develops upstream of the first in the same separated-flow region (‘eddy doubling’), and, later still, three-dimensional disturbances appear, before being swept away downstream to leave undisturbed parallel flow at the end of the cycle. The longitudinal positions of the wave crests and troughs and of the vortex cores are measured as functions of time for many values of the parameters; they vary with St but not with Re. Our inviscid, long-wavelength, small-amplitude theory predicts the formation of a wavetrain during each cycle, in which the displacement of a core-flow streamline satisfies the linearized Kortewegde Vries equation downstream of the indentation. The waves owe their existence to the non-zero vorticity gradient in the oncoming flow. Eddy formation and doubling are not described by the theory. The predicted positions of the wave crests and troughs agree well with experiment for the larger values of St used (up to 0.077), but less well for small values. Analysis of the viscous boundary layers indicates that the inviscid theory is self-consistent for sufficiently small time, the time of validity increasing as St increases (for fixed e).

Adolescents' theories about the development of their relationships with parents.

Abstract: Using a retrospective method, we assessed late adolescents' developmental theories about their affective relationships with their parents. Subjects used drawings and questionnaire ratings to portray their relationships with parents at five points between infancy and the present. From infancy to their current age, adolescents portrayed their relationships in two major ways. They perceived themselves as gaining in responsibility, dominance, independence, and similarity from infancy to the present, whereas they portrayed their parents as experiencing a decline on these dimensions. For variables indicating closeness and love, however, there was a striking discontinuity in these linear trends: Although adolescents perceived linear trends from infancy to adolescence, they depicted their current relationships as involving a great deal more love and closeness. They also portrayed their relationships with mothers and fathers somewhat differently. More responsibility was felt towards the mothers and they were portrayed as especially friendly, but subjects felt more similar to their fathers, whom they perceived as dominant. We interpreted the results as indicating that late adolescents constructed theories of the affective components of their relationships with their parents to serve the needs of separation while maintaining a close affective tie to the parents.

How Parents Label Objects for Young Children: The Role of Input in the Acquisition of Category Hierarchies.

Abstract: CALLANAN, MAUREEN A. How Parents Label Objects for Young Children: The Role of Input in the Acquisition of Category Hierarchies. CHILD DEVELOPMENT, 1985, 56, 508-523. Young children readily learn categories at the basic level, but they have difficulty organizing categories into hierarchies. Parents may influence this acquisition through the information they provide about categories at different levels. Adults use basic level terms in naming objects for children. They also may "anchor" children at the basic level by not using superordinate or subordinate terms for an object unless it is also labeled with a basic level tenn. However, these labeling patterns could be accounted for by a confounding of familiarity with category level. Basic level terms are the most familiar to children, and parents may use them for that reason, rather than to provide information about levels. 2 studies were conducted in which mothers taught concepts to their 2-4-year-old children with pictures that varied in familiarity. The anchoring effect was partially replicated. When teaching superordinates, mothers used basic ostension more than superordinate ostension, regardless of the familiarity of the basic level names for the pictures. However, there was no such anchoring effect when subordinate categories were taught. Further, mothers' teaching of superordinate categories contrasted with their teaching of basic and subordinate categories in other ways: superordinate terms were used often with groups of objects rather than single objects, and explicit statements of inclusion occurred only when superordinate categories were being taught. The results suggest that children must learn basic and subordinate categories through ostensive labeling, but that they are given extra infonnation that may help them to learn superordinate categories.

Polymerization of styrene miniemulsions

Abstract: Polymerization of styrene miniemulsions, prepared using a mixed emulsifier system comprising sodium lauryl sulfate and cetyl alcohol, was carried out using both water-soluble (potassium persulfate) and oil-soluble [2,2′-azobis-(2-methyl butyronitrile)] initiators. The effects of variation of initiator concentration, polymerization temperature, and added inhibitor on the kinetics and particle-size distributions were investigated to obtain more quantitative evidence concerning the locus of polymerization in miniemulsion systems. Experimental results for the kinetics and particle-size distributions clearly showed that monomer droplets became the main source of polymer particle formation. This was attributed to the fact that stable emulsions with droplet diameters in the range of 0.05 to 0.15 μm were produced using this mixed-emulsifier system. In this size range, droplet initiation could effectively compete with other mechanisms due to their large surface area. Their size was indeed similar to the corresponding latex particle size obtained after polymerization.

Grain‐Growth Kinetics for Alumina in the Absence of a Liquid Phase

Abstract: The kinetics of grain growth in fully dense Al2O3 with and without MgO solute additions were measured for high-purity samples containing no liquid phases. The MgO was found to suppress the grain-boundary migration rate by a factor of 50. Compensating lattice defects are suggested to play a role in grain-growth inhibition. Implications of these results to the sintering of Al2O3 are discussed.

Solubility of BaO in BaTiO3

Abstract: The solubility and mode of incorporation for BaO in BaTiO3 were studied by X-ray powder diffraction, scanning and transmission electron microscopy, electron probe microanalysis, and equilibrium electrical conductivity measurements. The presence of barium orthotitanate, Ba2TiO4, as a second phase for samples containing >0.1 mol% excess BaO was confirmed by direct microscopic examination. There was no evidence to support the incorporation of excess BaO into BaTiO3 by a Ruddlesden-Popper type of superlattice ordering mechanism. Measurement of the equilibrium electrical conductivity showed no detectable shift in the conductivity profile resulting from excess BaO, thus setting an upper limit of 100 ppm for the solubility of BaO in BaTiO3.

Hydrogen-acceptor pairs in silicon: Pairing effect on the hydrogen vibrational frequency.

Abstract: We calculate the electronic structures of the hydrogen-boron and hydrogen-aluminum pairs in silicon which are believed to form when the corresponding shallow acceptor activity is neutralized by hydrogen. In particular, computed infrared vibrational frequencies are reported for the first time and compared with recent experimental measurements. Both theory and experiment reveal an interesting reduction in the vibrational frequency for hydrogen in the H-B pair with respect to the isolated monohydride. This we analyze in terms of two- and three-body interactions involving the hydrogen, the acceptor impurity, and the nearby silicon atoms.

Applications of Self-Management to Individuals with Severe Handicaps: A Review:

Abstract: Self-management procedures involve an individual in implementing strategies which may enhance his or her behavior change. These strategies may be applied as antecedents or consequences to the targe...

Solid‐state fermentation of sweet sorghum to ethanol

Abstract: Solid-state fermentation of chopped sweet sorghum particles to ethanol was studied in static flasks using an ethanol tolerant yeast strain. The influence of various process parameters, such as temperature, yeast cell concentration, and moisture content, on the rate and extent of ethanol fermentation was investigated. Optimal values of these parameters were found to be 35 degrees C, 7 x 10(8) cells/g raw sorghum, and 70% moisture level, respectively.

Experimental observations on the nucleation and growth of δ′ (Al3Li) in dilute Al-Li alloys

Abstract: The influence of nucleation temperature and pre-aging thermal history on δ′ (Al3Li) precipitate distributions was studied in a binary Al-8.2 at. pct Li alloy. The distribution of δ′ in the microstructure is found to be homogeneous and insensitive to variations in pre-aging thermal history when nucleation occurs at large undercoolings (ΔT > 90 °C). When nucleation occurs at low undercoolings (90 °C > gDT > 40 °C), nucleation is homogeneous but the precipitate number density is influenced by preaging thermal history. At very small undercoolings (ΔT < 40 °C) nucleation next to dislocations is favored unless large numbers of excess vacancies are present, in which case homogeneous nucleation can be more prevalent than nucleation next to dislocations. The early stages of δ′ growth are seen to be consistent with bulk diffusion control. Enhanced growth rates are observed when the material contains a higher concentration of excess vacancies. The retention of this enhanced growth for long periods of time suggests that vacancies can be trapped within the structure for long times despite their mobility. Morphological instabilities are found to develop during δ′ particle growth. These instabilities occur at very small particle sizes and cause the normally spherical particles to tend toward a dendritic morphology.

Biological removal of pyritic sulfur from coal by the thermophilic organism Sulfolobus acidocaldarius.

Abstract: More than 90% of initial pyritic sulfur was removed from bituminous coal samples (containing 2.1% pyritic sulfur) using the thermophilic organism Sulfolobus acidocaldarius. Microbial desulfurization rate was improved nearly ten fold by adjusting the N/P and N/Mg ratios in the nutrient medium. Environmental conditions were optimized. The optimal values of temperature and pH were 70 degrees C and 1.5, respectively. The influence of certain process variables (such as coal pulp density, particle size, and initial cell number density) on the rate of pyritic sulfur removal were determined. A pulp density of 20%, particle size of D (p) < 48 microm, and an initial cell number density of 10(12) cells/g pyrite in coal were found to be optimal. The carbon dioxide enriched air did not improve the rate of pyritic sulfur removal compared to pure air at 10% pulp density of coal samples containing 2.1% pyritic sulfur. The kinetics of microbial leaching of pyritic sulfur from coal was investigated. The rate of leaching was found to be first order with respect to pyritic sulfur concentration in the reaction medium.

Solid-state fermentation of sweet sorghum to ethanol in a rotary-drum fermentor

Abstract: Sugar compounds present in chopped solid-sweet sorghum particles were fermented to ethanol in a rotary-drum fermentor (RDF) using an ethanol tolerant yeast strain. The influence of rotational speed of the RDF on the rate of ethanol fermentation was investigated and compared with static-flask experiments. The rate of ethanol formation decreased with increasing rotational speed. The maximum rate and extent of ethanol formation were ca. 3.1 g EtOH/L h (based on expressed juice volume) and ca. 9.6 g EtOH/100 g mash, respectively, at 1 rpm rotational speed.

Lithographic plates and production process therefor

Abstract: Lithographic plate, and method for making same, comprises a plate substrate with a selectively ink-receptive coating in the image area of the plate, rendered ink receptive by heat conversion of an initially water-soluble polymer coating of specifically defined polymer classes.

Viscous flow induced by counter‐rotating vortices

Abstract: The nature of the viscous boundary‐layer flow induced near a wall, caused by a pair of counter‐rotating vortices above the wall, is investigated. Solutions for the unsteady flow that develops near the wall are obtained numerically for a variety of cases. The vortices are taken to be of equal strength with cores located at equal distances from the wall; depending upon the assumed sense of rotation, the vortices either move toward the wall or recede from it, creating a region of either inflow or outflow near the wall, respectively. The calculated results show that the adverse pressure gradient near the wall induced by the vortex motion gives rise to explosively growing regions of recirculating flow near the wall. The possible relevance of these results to Gortler vortex instability and turbulent flow near walls is discussed.

Optically detected magnetic resonance study of SiC:Ti.

Abstract: We describe optically detected magnetic resonance (ODMR) experiments carried out on the green luminescence band in 4H, 6H, and 15R polytypes of SiC:Ti. It is found that the luminescence is due to radiative transitions from excited spin triplet (S=1) to ground singlet (S=0) states. Unusually large isotope shifts in the zero-field splittings demonstrate that the light-emitting centers involve a single Ti and six equivalent neighboring silicon atoms. Spectral dependence studies of the ODMR signals allow us to discuss the microscopic nature of the inequivalent lattice sites for the Ti atom as well as to correctly assign the zero-phonon line and the accompanying characteristic phonons associated with each Ti site. We interpret our results in terms of the model proposed by Patrick and Choyke of Ti substituting on the silicon sublattice, the excitonic triplet state being formed from an electron tightly bound in a normally unoccupied ${d}_{e}$ orbital of the Ti atom plus a Coulombically bound hole. The ODMR spectra are extremely sensitive to subtle (second- and third-nearest-neighbor) differences between the inequivalent lattice sites. This, plus a sizable Franck-Condon shift observed in the luminescence and the unusual isotope effects, are interpreted as possible evidence for vibronic properties of the bound hole, implying intermediate to strong localization for it also.