Showing papers by "Rensselaer Polytechnic Institute published in 1984"
TL;DR: This review is aimed at unifying the understanding of cartilage viscoelastic properties in compression, in particular the role of compression-dependent permeability in controlling interstitial fluid flow and its contribution to the observed vis coelastic effects.
1,000 citations
TL;DR: In this paper, the authors examined the solubility and dissolution kinetics of apatite in felsic melts at 850°-1500°C and showed that at 6 wt% H2O, the diffusion energy of P reaches an activation energy (E) of 143.6 ± 2.8 kcal-mol−1 and frequency factor (D0) of 2.23+2.88−1.
761 citations
TL;DR: An octree-based fully automatic three-dimensional mesh generator is presented, capable of meshing non-manifold models of arbitrary geometric complexity through the explicit tracking and enforcement of geometric compatibility and geometric similarity at each step of the meshing process.
Abstract: An octree-based fully automatic three-dimensional mesh generator is presented. The mesh generator is capable of meshing non-manifold models of arbitrary geometric complexity through the explicit tracking and enforcement of geometric compatibility and geometric similarity at each step of the meshing process. The resulting procedure demonstrates a linear growth rate with respect to the number of elements and can be easily integrated with any geometric modeller through a set of geometric operators.
700 citations
TL;DR: The cost of a number of sequential coding search algorithms is analyzed in a systematic manner and it is found that algorithms that utilize sorting are much more expensive to use than those that do not; metric-first searching regimes are less efficient than breadth-first or depth-first regimes.
Abstract: The cost of a number of sequential coding search algorithms is analyzed in a systematic manner. These algorithms search code trees, and find use in data compression, error correction, and maximum likelihood sequence estimation. The cost function is made up of the size of and number of accesses to storage. It is found that algorithms that utilize sorting are much more expensive to use than those that do not; metric-first searching regimes are less efficient than breadth-first or depth-first regimes. Cost functions are evaluated using experimental data obtained from data compression and error correction studies.
623 citations
TL;DR: Analytical solutions have been obtained for the internal deformation and fluid-flow fields and the externally observable creep, stress relaxation, and constant strain-rate behaviors which occur during the unconfined compression of a cylindrical specimen of a fluid-filled, porous, elastic solid, such as articular cartilage, between smooth, impermeable plates.
Abstract: Analytical solutions have been obtained for the internal deformation and fluid-flow fields and the externally observable creep, stress relaxation, and constant strain-rate behaviors which occur during the unconfined compression of a cylindrical specimen of a fluid-filled, porous, elastic solid, such as articular cartilage, between smooth, impermeable plates. Instantaneously, the "biphasic" continuum deforms without change in volume and behaves like an incompressible elastic solid of the same shear modulus. Radial fluid flow then allows the internal fluid pressure to equilibrate with the external environment. The equilibrium response is controlled by the Young's modulus and Poisson's ratio of the solid matrix.
559 citations
TL;DR: In this article, explicit formulas for a doubly coprime fractional representation of the transfer function of a lumped LTI system are given in terms of a stabilizable and detectable state-space realization of the transferred function.
Abstract: Explicit formulas for a doubly coprime fractional representation of the transfer function of a lumped LTI system are given in terms of a stabilizable and detectable state-space realization of the transfer function. These formulas allow existing computational algorithms to be utilized for the purpose of computing doubly coprime factorizations. Several additional implications of this result are briefly discussed, as are some immediate extensions and future research directions.
460 citations
TL;DR: In this article, a growth equation for free dendrites growing in a liquid alloy was developed by coupling their diffusion fields for a parabolic tip and by applying a stability criterion.
454 citations
01 Jan 1984
TL;DR: Here the pyramid will be viewed primarily as a computational tool, however, interesting similarities will be noted between pyramid processing and processing within the human visual system.
Abstract: Many basic image operations may be performed efficiently within pyramid structures. Pyramid algorithms can generate sets of low-and band-pass filtered images at a fraction of the cost of the FFT. Local image properties such as texture statistics can be estimated with equal efficiency within Gaussianlike windows of many sizes. Pyramids support fast “coarse-fine” search strategies. Pyramids also provide a neural-like image representation which is robust, compact and appropriate for a variety of higher level tasks including motion analysis. Through “linking,” pyramids may be used to isolate and represent image segments of arbitrary size and shape. Here the pyramid will be viewed primarily as a computational tool. However, interesting similarities will be noted between pyramid processing and processing within the human visual system.
452 citations
TL;DR: It is demonstrated that similar performance can be expected for a wide range of memoryless sources and that the worst case performance is observed to be less than 0.3 bits/sample from the rate-distortion bound.
Abstract: The performance of optimum quantizers subject to an entropy constraint is studied for a wide class of memoryless sources. For a general distortion criterion, necessary conditions are developed for optimality and a recursive algorithm is described for obtaining the optimum quantizer. Under a mean-square error criterion, the performance of entropy encoded uniform quantization of memoryless Gaussian sources is well-known to be within 0.255 bits/sample of the rate-distortion bound at relatively high rates. Despite claims to the contrary, it is demonstrated that similar performance can be expected for a wide range of memoryless sources. Indeed, for the cases considered, the worst case performance is observed to be less than 0.3 bits/sample from the rate-distortion bound, and in most cases this disparity is less at Iow rates.
380 citations
01 Jan 1984
296 citations
TL;DR: Synthese et distribution de HCN: obtention de nitriles ou de liants oligomeres, role possible des composes cyano comme agents de condensation.
TL;DR: Since then gradient theories have been used to analyze phase transitions, spinodal decomposition, and other physical phenomena and obtained several important results concerning the interfacial energy between phases.
Abstract: : VAN DER WAALS, in his classic paper, gave arguments in support of a compressible fluid whose free energy at constant temperature depends not only on the density, but also on the density gradient. CAHN & HILLIARD, apparently unaware of VAN DER WAALS' paper, rederived VAN DER WAALS' theory and, using this theory, obtained several important results concerning the interfacial energy between phases. Since then gradient theories have been used to analyze phase transitions, spinodal decomposition, and other physical phenomena.
TL;DR: An algorithm known as generalized projections, which can be used to handle the restoration-from-magnitude (RFM) as well as other nonconvex constraints, is described and its properties are discussed.
Abstract: The method of projections onto convex sets can be used to solve many problems in image restoration, e.g., restoration from phase, spectral extrapolation, and signal recovery in computer-aided tomography. However, image-restoration problems involving nonconvex constraints cannot be handled by the method of projection onto convex sets in a fashion that ensures convergence. The restoration-from-magnitude (RFM) problem is such a case. To handle the RFM as well as other nonconvex constraints, we describe an algorithm known as generalized projections and discuss its properties. When sets are nonconvex, it is possible for the algorithm to exhibit pathological behavior that is never manifest in convex projections. We introduce an error criterion called the summed-distance error (SDE) and show under what circumstances the SDE is a monotonically decreasing function of the number of iterations. Near-optimum performance of the algorithm is achieved by relaxation parameters. Comparisons with other RFM methods are furnished for synthetic imagery.
TL;DR: In this paper, the multi-particle diffusion problem (MDP) is treated by an embedding technique, where growing and shrinking domains are represented by point sources or sinks, and a novel formulation is developed based on the concept of an interaction matrix, the elements of which are Ewald sums.
TL;DR: In this article, the authors used the multi-particle diffusion solution to determine the collective behavior of a system of dispersed second phase particles undergoing Ostwald ripening and found that the collective behaviour of the coarsening ensemble was highly dependent on the initial distribution.
TL;DR: Conventional and high-resolution imaging in the TEM demonstrated direct chemical bonding between bone and hydroxylapatite, and the bone at the ceramic surface was the same as normal bone away from the interface.
Abstract: The bone-hydroxylapatite interface has been examined directly in the transmission electron microscope (TEM). The bone-hydroxylapatite interface was characterized by using several electron microscopy techniques, including bright and dark field imaging, electron diffraction, high-resolution imaging, and energy dispersive analysis in the scanning-transmission electron microscope (STEM EDS). Mechanical grinding followed by argon-ion milling produced interface regions of unstained and undecalcified rat bone and hydroxylapatite that were transparent to electrons. Thus the exact location of the interface could be established and the bone at the interface studied. Conventional and high-resolution imaging in the TEM demonstrated direct chemical bonding between bone and hydroxylapatite. The bone at the ceramic surface was the same as normal bone away from the interface.
01 Jan 1984
TL;DR: The field of mesophases is subdivided into six different phases: liquid crystals, plastic crystals, condis crystals and the corresponding LC, PC, and CD glasses as discussed by the authors, which are the traditional phases with positional and orientational disorder, respectively.
Abstract: The field of mesophases is subdivided into six different phases: liquid crystals, plastic crystals, condis crystals and the corresponding LC, PC, and CD glasses. Liquid and plastic crystals are the traditional phases with positional and orientational disorder, respectively. Condis crystals are conformationally disordered. On hand of tables of thermodynamic transition parameters of small and large molecules it is shown that the orientational order in liquid crystals is only a few per cent of the total possible, while the positional order in plastic crystals is virtually complete. Condis crystals have a wide variety of different degrees of conformational disorder. The glass transitions of all mesophases are similar in type. Macromolecules in the liquid crystalline state produce high orientation on deformation. Plastic crystals consist always of small molecules. Condis crystals may under proper conditions anneal to extended chain crystals.
TL;DR: In this article, it has been observed that accessory minerals in continental rocks may contain a substantial fraction of the whole-rock complement of trace elements and geochemically important isotopes.
TL;DR: It was concluded that increments in opioid activity increase rats' avidity for ethanol and naloxone reduced intakes of both fluids.
TL;DR: The analysis of Cox and Brenner as mentioned in this paper for the particle motion in a nonporous duct is extended to include the effect of the wall porosity, and particle trajectories and concentrations profiles are calculated for a plane Poiseuille flow with one porous wall.
TL;DR: In this paper, a numerical study of the dynamic response of end-bearing piles embedded in a number of idealized soil deposits and subjected to vertically propagating harmonic S-waves is presented.
TL;DR: It is shown by numerical examples that the simplest form of this approximation yields nearly optimal (asymptotic) performance for the problem of locally optimum detection.
Abstract: The Middleton Class A narrow-band non-Gaussian noise model [9]-[12] is examined. It is shown that this noise model (which is known to fit closely a variety of non-Gaussian noises) can itself be closely approximated by a computationally much simpler noise model. It is then shown by numerical examples that, for the problem of locally optimum detection, the simplest form of this approximation yields nearly optimal (asymptotic) performance. The performance of other simple suboptimal threshold detectors in Class A noise is also examined. Finally, a useful relationship between the Class A model and the e-mixture model is developed.
TL;DR: In this paper, a fast algorithm for solving the multiparticle diffusion problem (MDP) is described, permitting simulation of coarsening dynamics by cyclic time-stepping and updating the diffusion solution for large random particle arrays.
Abstract: Phase coarsening, also termed Ostwald ripening, is generally thought to be a slow, diffusion-controlled process which occurs subsequent to phase separation under extremely small under- or over-saturation levels. The theory due to Lifshitz, Slyozov, and Wagner (LSW), which predicts the coarsening kinetics and the particle distribution function, are applicable todilute systems only, in which particle-particle interactions are unimportant. Most liquid phase sintered systems, however, have large enough volume fractions of the dispersed phase to violate the essential assumptions of LSW theory. Recent progress will be described on simulating Ostwald ripening in randomly dispersed, high volume fraction systems. A fast algorithm for solving the multiparticle diffusion problem (MDP) will be described, permitting simulation of coarsening dynamics by cyclic time-stepping and updating the diffusion solution for large random particle arrays. The rate constants, controlling the growth of the average particle, and the particle distribution functions were obtained by numerical simulations up to a volume fraction of 0.55. A new statistical mean field theory has now been developed which reproduces the MDP simulation data accurately, and finally makes clear how the linear mean-field approximations employed by LSW theory must be modified to describe real systems. The predictions of the mean field are found to compare favorably with experimental measurements made over a wide range of volume fraction solid of the kinetics of Ostwald ripening in liquid phase sintered Fe-Cu alloys. The new theory provides a comprehensive approach to understanding microstructural coarsening in liquid phase sintered systems.
TL;DR: Slit-lamp photographs from four human subjects, aged 11, 19, 29, and 45 were reanalyzed using computer-based digitization and curve-fitting methods in order to obtain more complete information on internal lens curvature changes during accommodation.
TL;DR: The argument that adaptation occurs to optimize properties requires additional clarification since haversian bone appears to have inferior mechanical properties to plexiform bone, which in older or more mature animals converts by internal remodeling into multiple concentric lamellar units, secondary osteons, forming haversia bone.
Abstract: Cortical bone can be modeled as a complex hierarchical composite interrelating both structure and material properties on four levels of structural organization: molecular, ultrastructural, microscopic, and macroscopic. In young animals, the microstructural systems are long parallel lamellar units, plexiform bone, which in older or more mature animals converts by internal remodeling into multiple concentric lamellar units, secondary osteons, forming haversian bone. Ultrasonic wave propagation measurements performed on both plexiform and haversian bone clearly show a definitive relationship with microstructure; haversian bone can be described as a transversely symmetric material whereas plexiform bone appears to be orthotropic in nature. The anisotropy of the elastic constants are found to reflect the tissue symmetry; moreover, plexiform bone is stiffer and more rigid in all directions than is haversian bone. Similar experiments were performed on osteoporotic and osteopetrotic bone. While the results for osteoporotic bone are understandable in terms of the increased porosity, the results for the osteopetrotic bone are anomalous with respect to its density. Since Wolff, the remodeling of bone has been interpreted as a way of altering the mechanical properties to suit some need. For haversian remodeling from plexiform bone, the argument that adaptation occurs to optimize properties requires additional clarification since haversian bone appears to have inferior mechanical properties to plexiform bone.
TL;DR: In this paper, the authors analyzed polytetrafluoroethylenes of different crystallinity between 220 and 700 K by differential scanning calorimetry, and the measured heat capacity data were combined with all literature data into a recommended set of thermodynamic properties for the crystalline polymer.
Abstract: Polytetrafluoroethylenes of different crystallinity were analyzed between 220 and 700 K by differential scanning calorimetry. A new computer coupling of the standard DSC is described. The measured heat capacity data were combined with all literature data into a recommended set of thermodynamic properties for the crystalline polymer and a preliminary set for the amorphous polymer (heat capacity, enthalpy, entropy, and Gibbs energy; range 0–700 K). The crystal heat capacities have been linked to the vibrational spectrum with a θ3 of 54 K, and θ1 of 250 K, and a full set of group vibrations. Cv to Cp conversion was possible with a Nernst–Lindemann constant of A = 1.6 × 10−3 mol K/J. The glass transition was identified as a broad transition between 160 and 240 K with a ΔCp of 9.4 J/K mol. The room-temperature transitions at 292 and 303 K have a combined heat of transition of 850 J/mol and an entropy of transition of 2.90 J/K mol. The equilibrium melting temperature is 605 K with transition enthalpy and entropy of 4.10 kj/mol and 6.78 J/K mol, respectively. The high-temperature crystal from is shown to be a condis crystal (conformationally disordered), and for the samples discussed, the crystallinity model holds.
TL;DR: An algorithm is designed and applied which interpolates/extrapolates the missing Fourier domain information by POCS and reconstructs an image by DFM and a simulated human thorax cross section is restored and reconstructed.
Abstract: We consider the problem of reconstructing CAT imagery by the direct Fourier method (DFM) when not all view data are available. To restore the missing information we use the method of projections onto convex sets (POCS). POCS is a recursive image restoration technique that finds a solution consistent with the measured data and a priori known constraints in both the space and Fourier domain. Because DFM reconstruction is a frequency-domain technique it is ideally matched to POCS restoration when, for one reason or another, we are forced to generate an image from a less than complete set of view data. We design and apply an algorithm (PRDF) which interpolates/extrapolates the missing Fourier domain information by POCS and reconstructs an image by DFM. A simulated human thorax cross section is restored and reconstructed. The restorations using POCS are compared with the Gerchberg-Papoulis extrapolation method and shown to be superior. Applications of PRDF to other types of medical imaging modalities are discussed.
TL;DR: In this article, the authors prove the existence of traveling wave solutions connecting liquid and vapor phases in a van der Waals fluid with the main constitutive assumptions that the fluid be an elastic fluid possessing a higher order correction given by Korteweg's theory of capillarity and the fluid is a conductor of heat with large specific heat at constant volume.
TL;DR: In this paper, the sintering atmosphere role in stabilizing detrimental residual pore structures was examined on alloys containing 93, 95, or 97 wt pct W with Ni:Fe ratios of 7:3.
Abstract: Residual porosity has a strong negative effect on the ductility of tungsten-nickel-iron heavy metals. This investigation examines the sintering atmosphere role in stabilizing detrimental residual pore structures. Two types of experiments are reported on alloys containing 93, 95, or 97 wt pct W with Ni:Fe ratios of 7:3. The negative effect of prolonged sintering is attributed to pore coarsening involving trapped gas in the pores. Calculated pore growth rates for hydrogen filled pores suggest that pore coarsening involves both ripening and coalescence driven by tungsten grain growth. The effect of the sintering atmosphere is analyzed for final stage pore elimination. It is demonstrated that a change in sintering atmosphere from hydrogen to argon midway through the sintering cycle can aid pore degassing and increase the sintered ductility and strength.
TL;DR: Results show that hydroxylapatite implanted subcutaneously in rats and dogs produces little or no inflammatory response and is compatible with tissue irrespective of the shape of the implant.