Showing papers by "Rensselaer Polytechnic Institute published in 1976"
TL;DR: In this paper, a new process was described for preparing dense polycrystalline hydroxylapatite, which has close theoretical density and is free of fine pores and second phases.
Abstract: A new process is described for preparing dense, polycrystalline hydroxylapatite. This material has close to theoretical density and is free of fine pores and second phases. The best material has an average compressive strength of 917 MN m−2 (133×103 psi), and polished samples have an average tensile strength of 196 MN m−2 (28.4×103 psi). The material is highly translucent, and the degree of translucence depends upon processing conditions. The relationship between processing variables and microstructure, strength, and translucence is described. This dense hydroxylapatite has good promise for bone implants and dental applications.
803 citations
TL;DR: The average evaporation heat-transfer coefficient for the interline region of an adsorption controlled wetting film in which the disjoining pressure is approximated by P d =− A δ −3 can be represented bykh=hid[1−O5(η−1+η −2)]hid is the ideal liquid-vapor interfacial heat transfer coefficient and η is a function of the physical properties of the system.
424 citations
TL;DR: In this article, the axial growth rate of a freely growing dendrite can be expressed asV =βGΔθn, wheren and β are the exponent and prefactor derived from each theory, G is a lumped material parameter, and Δθ is the supercooling.
Abstract: Steady-state theories of dendritic solidification are reviewed, and three nonisothermal theories, expressed as simple power laws, are chosen for experimental verification. Specifically, the axial growth rate,V, of a freely growing dendrite can be expressed asV =βGΔθn, wheren andβ are the exponent and prefactor derived from each theory,G is a lumped material parameter, andΔθ is the supercooling. Succinonitrile, a low entropy-of-fusion plastic crystal, was prepared in several states of purity as the test system, and dendritic growth was studied both in the usual manner in long tubes, and in a novel apparatus in which the conditions for “free” dendritic growth were attained. Kinetic measurements show that only when “free” growth conditions obtain are the data reconcilable with current theory in the form discussed above. In particular, we show thatn = 2.6, in agreement with the theories of Nash and Glicksman and that of Trivedi; however, the prefactorsβ of those theories do not agree with the value determined for succinonitrile, which is the only substance for whichG is known accurately. Tip radius measurements, taken over a relatively narrow range of supercooling, when combined with the growth rate data prove that the Peclet number-supercooling relationship derived for each of the three nonisothermal steady-state theoriesall agree with experiment. This curious agreement, along with the inability to “decompose” the Peclet numbers into acceptable velocity-supercooling and tip radius-supercooling relationships is explained on the basis of the limitations imposed by the steady-state assumption itself. Directions for future theoretical and experimental investigation are discussed in the light of the findings presented.
330 citations
TL;DR: Results indicate that there is significantly more glucose metabolized via this pathway in brains of hypoxic rats than in the controls.
Abstract: —Tyrosine hydroxylase (TH), dopa decarboxylase (DDC), glutamic acid decarboxylase (GAD), choline acetyltransferase (CAT), and acetylcholinesterase (AChE) were measured in 18–55 areas of brain from humans post mortem. Individuals meeting sudden and unexpected death (22), patients dying in hospital with non–neurological illness (6), Parkinson's disease (12), Huntington's chorea (8), terminal coma (6) or head injury (2) were included in the series. The absolute values obtained compared favourably with some previous human studies where high values for these enzymes were obtained, as well as with monkey and baboon data. The regional distributions of the enzymes were also comparable to those previously reported in human and animal studies. A number of important points with regard to human tissue seemed to emerge from the study. The mode of death was not a factor in enzyme levels in non–neurological and non-coma cases. Post mortem delay did not seem to be a major factor either even though a substantial decline in GAD, TH and DDC could be demonstrated in rats left several hours between sacrifice and removal of the brain for assay. Age had a highly significant effect in certain areas of brain. The decline typically followed a curvilinear pattern (activity = A/age + B with the sharpest drops being in the younger age groups). DDC seemed to be the enzyme most severely affected by age but all the enzymes showed declines in certain brain areas, while in other areas there was no significant decline. All the enzymes were very depressed by coma from illness except AChE. TH and DDC in the brain stem were, however, not affected in the head injury cases. The Parkinsonian cases showed a sharply decreased TH activity in the substantia nigra, caudate and putamen. There were decreases in GAD in the globus pallidus (GP) and substantia nigra with marginal decreases in the neostriatum. CAT levels in the extrapyramidal nuclei were normal. In Huntington's chorea there was a substantial decrease in GAD in all the extrapyramidal structures. There was a patchy loss of CAT in the neostriatum and locus coeruleus.
310 citations
TL;DR: In this article, the wavelength dependence of interstellar linear polarization [p(λ) was investigated using the usual Serkowski relation with three parameters: p max, λ max, and K. Optical and infrared measurements were obtained simultaneously in eight photometric passbands between U and K, giving a coherent data set for a total of 105 reddened stars.
Abstract: New observations of the wavelength dependence of interstellar linear polarization [p(λ)] made to investigate the influence of the environment on the effective size distribution of the aligned polarizing particles are presented. Optical and infrared measurements were obtained simultaneously in eight photometric passbands between U and K, giving a coherent data set for a total of 105 reddened stars. The p(λ) data were modeled using the usual Serkowski relation with three parameters: p max , λ max , and K
249 citations
TL;DR: From previous work it was postulated that joint lubrication is accomplished first by fluid exudation into the joint space, and second by imbibition of the expelled fluid back into the cartilage toward the trailing edge of the contact area caused by the "elastic" recovery of the tissue.
Abstract: The permeability of bovine articular cartilage was measured in an apparatus designed to permit this measurement while the fluid pressure gradient across the cartilage and the axial compressive strain applied to the cartilage were varied independently. For all of the pressure gradients tested the permeability of the cartilage decreased as the compressive strain increased. From previous work, it was postulated that joint lubrication is accomplished first by fluid exudation into the joint space. both at the leading edge of the moving contact area and between portions of the opposing cartilaginous surfaces, and second by imbibition of the expelled fluid back into the cartilage toward the trailing edge of the contact area caused by the "elastic" recovery of the tissue. The present work extends this model to include the condition that the permeability of cartilage is dependent on the extent to which it is deformed.
242 citations
TL;DR: This paper formulates the nurse-scheduling problem as one of selecting a configuration of nurse schedules that minimize an objective function that balances the trade-off between staffing coverage and schedule preferences of individual nurses, subject to certain feasibility constraints on the nurse schedules.
Abstract: This paper formulates the nurse-scheduling problem as one of selecting a configuration of nurse schedules that minimize an objective function that balances the trade-off between staffing coverage and schedule preferences of individual nurses, subject to certain feasibility constraints on the nurse schedules. The problem is solved by a cyclic coordinate descent algorithm. We present results pertaining to a six-month application to a particular hospital unit and draw comparisons between the algorithm and hospital-generated schedules.
239 citations
TL;DR: The microtextural symmetry of dry human cortical bone was found to be consistent with hexagonal symmetry, based on microstructural observations as well as on the ultrasonic velocity measurements at 5 MHz and at room temperature using a pulse transmission method.
237 citations
Book•
01 Dec 1976TL;DR: In this article, the impact response of engineering surfaces is considered and a zero-impact wear model is proposed to quantify the impact of impact on a given surface, based on elastic contact solutions.
Abstract: 1. Considerations of Friction and Wear. 2. Methods of Impact Stress Analysis. 3. Impact Response of Engineering Surfaces. 4. Erosion by Solid Particles: Ductile and Brittle Theories. 5. General Aspects of Solid Particle Erosion. 6. Experimental Background of Percussive Impact Wear. 7. The Zero Impact Wear Model. 8. Measurable Impact Wear Theory. 9. Impact Wear in the Plastic Stress Range. 10. Impact Wear Through Flexible Media. 11. Liquid Erosion. Appendices: 1. Computer Programs in APL Programming Language. 2. Elastic Contact Solutions. 3. Hardness Tests. 4. Surface Texture. Author Index. Subject Index.
200 citations
TL;DR: An algorithm to compute the expected shortest travel time between two nodes in the network when the travel time on each link has a given independent discrete probability distribution is presented.
TL;DR: In this paper, the interfingering relationships of specific evaporitic facies having clear and recognizable physical characteristics are presented, such as sub-aerial deposits of nodular calcium sulphate formed displacively within clastic sediments, all of which are reworked sediments and are mixed in varying degrees with other clastic materials (subaerial, supratidal, and intertidal to deep basinal deposits).
Abstract: In Sicily, Messinian evaporitic sedimentary deposits are developed under a wide variety of hypersaline conditions and in environments ranging from continental margin (subaerial), to basin-margin supratidal, to intertidal, to subtidal and out into the hypersaline basin proper. The actual water depth at the time of deposition is indeterminate; however, relative terms such as ‘wave base’ and ‘photic zone’ are utilized. The inter-fingering relationships of specific evaporitic facies having clear and recognizable physical characteristics are presented. These include sub-aerial deposits of nodular calcium sulphate formed displacively within clastic sediments; gypsiferous rudites, arenites and arenitic marls, all of which are reworked sediments and are mixed in varying degrees with other clastic materials (subaerial, supratidal, and intertidal to deep basinal deposits). Laminated calcium sulphate alternating with very thin carbonate interlaminae and having two different aspects; one being even and continuous and the other of a wavy, irregular appearance (subtidal, intertidal, and supratidal deposits). Nodular calcium sulphate beds, usually associated with wavy, irregular laminated beds (supratidal, sabkha deposits); very coarsely crystalline gypsum beds (selenite), associated with more even, laminated beds (subaqueous, intertidal to subtidal deposits); wavy anastomozing gypsum beds, composed of very fine, often broken crystals (subaqueous, current-swept deposits); halite having hopper and chevron structures (supratidal to intertidal); and halite, potash salts, etc. having continuous laminated structure (subaqueous, possibly basinal).
Evidence for diagenetic changes is observed in the calcium sulphate deposits which apparently formed by tectonic stress and also by migrating hypersaline waters. These observations suggest that the common, massive form of alabastrine gypsum (or anhydrite, in the subsurface) may not always be ascribed to original depositional features, to syndiagenesis or to early diagenesis but may be the result of late diagenesis.
TL;DR: A strain of Alcaligenes, isolated from soil and grown in nutrient broth in the presence of arsenite, possessed the ability to oxidize arsenite to arsenate, and response of the arsenite-oxidizing enzyme system to respiratory inhibitors suggested that electrons resulting from arsenite oxidation by an oxido-reductase with a bound flavin are transferred via cy tochrome c and cytochrome oxidase to oxygen.
Abstract: A strain of Alcaligenes, isolated from soil and grown in nutrient broth in the presence of arsenite, possessed the ability to oxidize arsenite to arsenate. Washed cell suspensions consumed one-half mol of oxygen/mol of arsenite and produced arsenate. The optimum pH for arsenite oxidation was 7.0. The Km for arsenite was 1.5 × 10-4 M and Vmax was 6.7 μl of oxygen/min. The arsenite-oxidizing enzyme system was induced by growth in arsenite. Response of the arsenite-oxidizing enzyme system to respiratory inhibitors suggested that electrons resulting from arsenite oxidation by an oxido-reductase with a bound flavin are transferred via cytochrome c and cytochrome oxidase to oxygen. The presence of the cytochromes in crude extract was confirmed by spectral measurements.
TL;DR: In this paper, a displaced Maxwellian approximation for the electron distribution function was used to calculate the hot electron microwave conductivity of the wide bandgap semiconductors GaN, SiC and Diamond.
Abstract: Hot electron microwave conductivity of the wide bandgap semiconductors GaN, SiC and Diamond has been calculated using displaced Maxwellian approximation for the electron distribution function. The effects of both the energy and momentum relaxation times due to scattering by acoustical, optical intervalley phonons and by ionized impurities are included in the derivations. Numerical results for the microwave conductivity and the change in dielectric constant as a function of frequency and bias electric field are presented. It is found that significant change in the conductivity and dielectric constant contribution for a fixed bias field occurs at very high frequencies on the order of 10 12 Hz, which is well beyond the range of current microwave device interest.
TL;DR: The basic equations relating the five independent second-order elastic stiffness constants (fourth-rank tensor) to the ultrasonic wave speeds in a hexagonal medium are derived, with special emphasis on determining the microtextural symmetry of human cortical bone.
TL;DR: In this paper, the conservation equations for one-dimensional two-phase flow are derived from first principles and the effects of the radial distributions of velocities, enthalpies, and void fraction are taken into account through the use of correlation coefficients.
TL;DR: Data support the existence of a new species of actin, called F-ATP-actin monomer, which has the same physical properties and the same bound nucleotide as G-Actin, but digestion characteristics like F-actsin.
TL;DR: The performance of short constraint length convolutional codes in conjunction with binary phase-shift keyed (BPSK) modulation and Viterbi maximum likelihood decoding on the classical Rician fading channel is examined in detail and fairly general upper bounds on bit error probability performance in the presence of fading are obtained.
Abstract: The performance of short constraint length convolutional codes in conjunction with binary phase-shift keyed (BPSK) modulation and Viterbi maximum likelihood decoding on the classical Rician fading channel is examined in detail. Primary interest is in the bit error probability performance as a function of E_{b}/N_{0} parameterized by the fading channel parameters. Fairly general upper bounds on bit error probability performance in the presence of fading are obtained and compared with simulation results in the two extremes of zero channel memory and infinite channel memory. The efficacy of simple block interleaving in combating the memory of the channel is thoroughly explored. Results include the effects of fading on tracking loop performance and the subsequent impact on overall coded system performance. The approach is analytical where possible; otherwise resort is made to digital computer simulation.
TL;DR: Data suggest that the fungal AHH activity is due to a cytochrome P -450, which is NADPH dependent and exhibits a pH optimum near 7.8 and inhibition by CO, SKF 525-A, and metyrapone, but cyanide shows no inhibitory effect.
TL;DR: It is found that during normal function of healthy articular cartilage the consolidation effects will dominate the movement of interstitial fluid, and in degenerative cartilage, as characterized by increasing the surface porosity and permeability and a decrease in tissue stiffness, Darcy's law becomes comparable to those of consolidation.
TL;DR: In this paper, a liquid transition-metal theory is applied to the Ni-P alloys and the heat capacity results support the use of that theory and also show that a "sinking band" model is appropriate for this system.
TL;DR: In this article, a multidimensional "goal programming" model is developed to aid resource allocation decisions in the U.S. Coast Guard's Marine Environmental Protection (MEP) program, which is then extended to a model of "goal interval programming" (GIP) type where exact values for the indicated goals, as in ordinary goal programming, are replaced by ranges.
TL;DR: In this paper, the breakdown voltage of abrupt cylindrical and spherical junctions has been obtained, using suitable approximations for the electric field in the depletion layer, using a single curve for each situation.
Abstract: Analytical solutions for the breakdown voltage of abrupt cylindrical and spherical junctions have been obtained, using suitable approximations for the electric field in the depletion layer. These solutions are shown to be within ±1% of exact computer solutions for doping densities of less thant 10 16 cm −1 . By normalization to the parallel plane case, these solutions have been presented in a form which allows the computation of the breakdown voltage of both cylindrical and spherical junctions using a single curve for each situation.
TL;DR: Findings suggest that this "quinoidal" type ESR transient functions as the physiological donor to the oxidized reaction center chlorophyll, P-680+.
TL;DR: In this paper, the effects of lift and Brownian motion in basic parallel flows are considered in order to determine the importance and the consequences of these effects, and the relation of the Brownians motion model involving momentum balance to the diffusive model of particle motions is studied.
Abstract: Constitutive relations for the lift force on the particulate phase and the effect of Brownian motion are presented. These constitutive relations are derived subject to three new principles of constitutive equations. The effects of lift and Brownian motion in basic parallel flows are considered in order to determine the importance and the consequences of these effects. The relation of the Brownian motion model involving momentum balance to the diffusive model of particle motions is studied. Dimensional and scaling arguments are given.
TL;DR: The equations of motion for each phase and the total mixture were derived from the extended Hamilton's Principle, where the Rayleigh dissipative resistance is considered as a generalized body force field, as well as Biot's consolidation equations for the liquid transport due to the dilatation of the solid phase.
TL;DR: In this article, a (k + 1)-parameter version of the k-dimensional multivariate exponential distribution (MVE) of Marshall and Olkin is investigated and a simple estimator (INT) is derived as the first iterate in solving the likelihood equations iteratively.
Abstract: Parameter estimation for a (k + 1)-parameter version of the k-dimensional multivariate exponential distribution (MVE) of Marshall and Olkin is investigated. Although not absolutely continuous with respect to Lebesgue measure, a density with respect to a dominating measure is specified, enabling derivation of a likelihood function and likelihood equations. In general, the likelihood equations, not solvable explicitly, have a unique root which is the maximum likelihood estimator (MLE). A simple estimator (INT) is derived as the first iterate in solving the likelihood equations iteratively. The resulting sequence of estimators converges to the MLE for sufficiently large samples. These results can be extended to the more general (2 k − 1)-parameter MVE.
TL;DR: The detrimental effect on search times of larger code sizes is interpreted as a camouflage of the color contour of the target's class by the multiple color boundaries in the heterogeneous background.
Abstract: Twenty observers searched for three–digit numbers on displays ranging in density from 10 to 50 items coded in one through ten colors. Search times increased linearly with density and showed a curvi...
TL;DR: In this article, the authors extended the theory of Mamuro and Hattori to beds of less than the maximum spoutable height and presented a new model that gives predictions for the fluid flow pattern, minimum spouting velocity and spouting pressure drop.
Abstract: This study extends the theory of Mamuro and Hattori to beds of less than the maximum spoutable height. The new model gives predictions for the fluid flow pattern, minimum spouting velocity and spouting pressure drop which are in agreement both with experimental data on beds spouted with air and water (obtained in this study) and with literature data.
A correlation for Hm in water spouted beds of spherical glass particles is also presented.
On fait, dans l'etude presente, une extension de la theorie de Mamuro et Hattori a des lits de hauteur moindre que la hauteur maximale a laquelle on peut gicler. Le nouveau modele prevoit le type d'ecoulement fluide, la vitesse minimale de giclement et la chute de pression de la giclee; cs previsions concordent a la fois avec les donnees publiees et avec les resultats experimentaux (obtenus dans l'etude presente) sur les lits gicles avec de l'air et de l'eau.
On prescente egalement une correlation relative a Mm dans les lits formes de particules de verre spheriques et gicles avec de l'eau.