Showing papers by "Rensselaer Polytechnic Institute published in 1999"

Thermodynamic determination of fragility in liquids and a fragile-to-strong liquid transition in water

Abstract: If crystallization can be avoided when a liquid is cooled, it will typically form a glass. Near the glass transition temperature the viscosity increases continuously but rapidly with cooling. As the glass forms, the molecular relaxation time increases with an Arrhenius-like (simple activated) form in some liquids, but shows highly non-Arrhenius behaviour in others. The former are said to be ‘strong’ liquids, and the latter ‘fragile’1,2. Here we show that the fragility of a liquid can be determined from purely thermodynamic data (as opposed to measurements of kinetics) near and below the melting point. We find that for most liquids the fragilities estimated this way are consistent with those obtained by previous methods and by a new method (ref. 3 and K.I., C.A.A. and C.T.M., unpublished data) at temperatures near the glass transition. But water is an exception. The thermodynamic method indicates that near its melting point it is the most fragile of all liquids studied, whereas the kinetic approach indicates that near the glass transition it is the least fragile. We propose that this discrepancy can be explained by a fragile-to-strong transition in supercooled water near 228 K, corresponding to a change in the liquid's structure at this point.

P -T paths from anatectic pelites

Abstract: A relatively simple petrogenetic grid for partial melting of pelitic rocks in the NCKFMASH system is presented based on the assumption that the only H2O available for melting is through dehydration reactions. The grid includes both discontinuous and continuous Fe-Mg reactions; contours of Fe/(Fe+Mg) for continuous reactions define P-T vectors along which continuous melting will occur. For biotite-bearing assemblages (garnet+biotite + sillimanite + K-feldspar + liquid and garnet + biotite + cordierite + K-feldspar + liquid), Fe/(Fe+Mg) contours have negative slopes and melting will occur with increasing temperature or pressure. For biotite-absent assemblages (garnet + cordierite + sillimanite + K-feldspar + liquid or garnet + cordierite + orthopyroxene + K-feldspar + liquid) Fe/(Fe + Mg) contours have flat slopes and melting will occur only with increasing pressure. The grid predicts that abundant matrix K-feldspar should only be observed if rocks are heated at P 3.8 kbar, and that generation of late biotite + sillimanite replacing garnet, cordierite, or as selvages around leu- cosomes should be common in rocks in which melt is not removed. There is also a predicted field for dehydration melting of staurolite between 5 and 12 kbar. Textures in migmatites from New Hampshire, USA, suggest that prograde dehydration melting reactions are very nearly completely reversible during cooling and crystallization in rocks in which melt is not removed. Therefore, many reaction textures in “low grade” migmatites may represent retrograde rather than prograde reactions.

Glasslike Heat Conduction in High-Mobility Crystalline Semiconductors

Abstract: The thermal conductivity of polycrystalline semiconductors with type-I clathrate hydrate crystal structure is reported. Ge clathrates (doped with Sr and/or Eu) exhibit lattice thermal conductivities typical of amorphous materials. Remarkably, this behavior occurs in spite of the well-defined crystalline structure and relatively high electron mobility ( $\ensuremath{\sim}100{\mathrm{cm}}^{2}/\mathrm{V}\mathrm{s}$). The dynamics of dopant ions and their interaction with the polyhedral cages of the structure are a likely source of the strong phonon scattering.

Motion-compensated 3-D subband coding of video

Abstract: This paper describes a video coding system based on motion-compensated three-dimensional (3-D) subband/wavelet coding (MC-3DSBC), which can overcome the limits of both 3-D SBC and MC prediction-based coding. In this new system, spatio-temporal subbands are generated by MC temporal analysis and a spatial wavelet transform, and then encoded by 3-D subband-finite state scalar quantization (3DSB-FSSQ). The rate allocation from the GOP level to each class of subbands is optimized by utilizing the structural property of MC-3DSBC that additive superposition approximately holds for both rate and distortion. The proposed video coding system is applied to several test video clips. Its performance exceeds that of both a known MPEG-1 implementation and a similar subband MC predictive coder while maintaining modest computational complexity and memory size.

Parallel and distributed association mining: a survey

Abstract: The author surveys the state of the art in parallel and distributed association-rule-mining algorithms and uncovers the field's challenges and open research problems. This survey can serve as a reference for both researchers and practitioners.

Rapid automated tracing and feature extraction from retinal fundus images using direct exploratory algorithms

Abstract: Algorithms are presented for rapid, automatic, robust, adaptive, and accurate tracing of retinal vasculature and analysis of intersections and crossovers. This method improves upon prior work in several ways: automatic adaptation from frame to frame without manual initialization/adjustment, with few tunable parameters; robust operation on image sequences exhibiting natural variability, poor and varying imaging conditions, including over/under-exposure, low contrast, and artifacts such as glare; does not require the vasculature to be connected, so it can handle partial views; and operation is efficient enough for use on unspecialized hardware, and amenable to deadline-driven computing, being able to produce a rapidly and monotonically improving sequence of usable partial results. Increased computation can be traded for superior tracing performance. Its efficiency comes from direct processing on gray-level data without any preprocessing, and from processing only a minimally necessary fraction of pixels in an exploratory manner, avoiding low-level image-wide operations such as thresholding, edge detection, and morphological processing. These properties make the algorithm suited to real-time, on-line (live) processing and is being applied to computer-assisted laser retinal surgery.

Improved Charge Transfer at Carbon Nanotube Electrodes

Abstract: The closed topology and tubular structure of carbon nanotubes make them unique among different carbon forms and provide pathways for chemical studies. A number of investigations have been carried out to find applications of nanotubes in catalysis, hydrogen storage, intercalation, etc. Since carbon-electrode-based fuel cells have been experimented with for decades, it is of importance to learn the electrodic performance of these new carbon structures. We report here results of the electrocatalytic reduction of dissolved oxygen (important H2±O2 fuel cell reaction), using microelectrodes constructed from multiwalled nanotubes. In parallel, ab initio calculations were performed for oxygen deposited on the lattice and defect sites of nanotube surfaces to determine the charge transfer during oxygen reduction and compared with similar reactions on planar graphite. The microelectrodes were constructed in the following way (see Fig. 1). Multiwalled nanotubes (10 mg) prepared by the electric arc discharge process and liquid paraffin (4 mL) were intimately mixed, placed in the narrow cylindrical slot of a Perspex holder and then packed by smooth vibration. The assembly was cured at 50 C for 30 min. From the inner side of the Perspex, contact to a copper lead was made through conducting paint. Carbon paste electrodes (based on commercially available graphite powder) were prepared similarly. Carbon nanotube electrodes were prepared earlier by similar techniques to probe bioelectrochemical reactions. The need for oxygen reduction at catalytic surfaces has been recognized in fuel cells, batteries, and many other electrodic applications. Hence, oxygen reduction at nanotube surfaces is of great interest. Electrochemical reduction of dissolved oxygen is carried out in aqueous acidic (H2SO4) and neutral media (1 M KNO3). The solution is first degassed by bubbling nitrogen gas for about 15± 30 min in order to record the background current±voltage curves. Under these conditions, no cyclic voltammetric peak in the potential range 0 to ±0.8 V were observed. The same solutions were then saturated with oxygen by bubbling oxygen gas for 15 min. The cyclic voltammetric curve showed a well-defined peak at Epc = ±0.31 V vs. SCE (saturated calomel electrode) in H2SO4 solution (pH 2) at the carbon nanotube electrodes. At the carbon paste electrodes only an ill-defined peak is seen at Epc = ±0.48 V. In the KNO3 medium (pH 6.2), the reduction of dissolved oxygen is observed at Epc = ±0.51 V at the carbon nanotube electrode. This peak is shifted at the carbon paste electrode by about 30 mV. The shift of the peaks, corresponding to the reaction on the nanotube electrodes, is a strong indication of the electrocatalysis on this electrode (see discussion below). The shift may be considered as an overpotential, which indicates a more facile reaction occurring at the nanotubes compared to other carbons. The electrochemical reduction of oxygen is a function of pH of the medium as proton participation occurs as described by Equation 1.

Venture Capitalists' Assessment of New Venture Survival

Abstract: This study investigates whether VCs' assessment policies of new venture survival are consistent with those arising from the strategy literature (using two established strategy perspectives) Strategy scholars suggest the nature of the markets, competition, and decisions made by the management team affect a new venture's survival chances The findings demonstrate that VCs' assessment policies are predominantly consistent with those proposed by strategy scholars-providing insight into why VCs consider certain criteria in their assessment of new venture survival as well as why some criteria are more important in their assessment than others Through this increased understanding of venture capitalists' decision making, entrepreneurs seeking capital may be better able to address their requests for funding to those criteria venture capitalists find most critical to the survival of a new venture Venture capitalists may use these findings to better understand their own decision making process, which, in turn, provides the opportunity to increase evaluation efficiency

The discovery and development of onium salt cationic photoinitiators

Abstract: The story of the discovery and development of onium salt photoinitiators for cationic polymerization is chronicled. The chemistry of the synthesis of these compounds is outlined, and the mechanisms of their initiation are discussed briefly. Among the most useful of these types of photoinitiators are diaryliodonium and triarylsulfonium salts, which are used widely for photoinduced cationic crosslinking reactions. From the very beginning, onium salt photoinitiated cationic polymerizations have found use in a multitude of practical applications. Specifically discussed in this article are the use of onium salts in coatings, adhesives, printing inks, release coatings, stereolithography, holographic recording, photocurable composites, and microelectronic photoresists. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4241–4254, 1999

In vivo bone response to biomechanical loading at the bone/dental-implant interface.

Abstract: Since dental implants must withstand relatively large forces and moments in function, a better understanding of in vivo bone response to loading would aid implant design. The following topics are essential in this problem. (1) Theoretical models and experimental data are available for understanding implant loading as an aid to case planning. (2) At least for several months after surgery, bone healing in gaps between implant and bone as well as in pre-existing damaged bone will determine interface structure and properties. The ongoing healing creates a complicated environment. (3) Recent studies reveal that an interfacial cement line exists between the implant surface and bone for titanium and hydroxyapatite (HA). Since cement lines in normal bone have been identified as weak interfaces, a cement line at a bone-biomaterial interface may also be a weak point. Indeed, data on interfacial shear and tensile "bond" strengths are consistent with this idea. (4) Excessive interfacial micromotion early after implantation interferes with local bone healing and predisposes to a fibrous tissue interface instead of osseointegration. (5) Large strains can damage bone. For implants that have healed in situ for several months before being loaded, data support the hypothesis that interfacial overload occurs if the strains are excessive in interfacial bone. While bone "adaptation" to loading is a long-standing concept in bone physiology, researchers may sometimes be too willing to accept this paradigm as an exclusive explanation of in vivo tissue responses during experiments, while overlooking confounding variables, alternative (non-mechanical) explanations, and the possibility that different types of bone (e.g., woven bone, Haversian bone, plexiform bone) may have different sensitivities to loading under healing vs. quiescent conditions.

Multicategory Classification by Support Vector Machines

Abstract: We examine the problem of how to discriminate between objects of three or more classes. Specifically, we investigate how two-class discrimination methods can be extended to the multiclass case. We show how the linear programming (LP) approaches based on the work of Mangasarian and quadratic programming (QP) approaches based on Vapnik‘s Support Vector Machine (SVM) can be combined to yield two new approaches to the multiclass problem. In LP multiclass discrimination, a single linear program is used to construct a piecewise-linear classification function. In our proposed multiclass SVM method, a single quadratic program is used to construct a piecewise-nonlinear classification function. Each piece of this function can take the form of a polynomial, a radial basis function, or even a neural network. For the k > 2-class problems, the SVM method as originally proposed required the construction of a two-class SVM to separate each class from the remaining classes. Similarily, k two-class linear programs can be used for the multiclass problem. We performed an empirical study of the original LP method, the proposed k LP method, the proposed single QP method and the original k QP methods. We discuss the advantages and disadvantages of each approach.

LED lamp with reflector and multicolor adjuster

Abstract: A lighting device (10) has a support that can be screwed into a standard (120) volt light socket. A ring with multiple, alternating color circumferentially spaced LEDs (19, 21, 23) is connected to the support and a reflector (31) is provided over the ring for reflecting light from the LEDs past the ring. A power supply circuit is connected to the LEDs for powering the LEDs to emit light. The light can be white if the LEDs are a combination of red, blue and green or other white-forming combinations, or the power circuit can selectively power subsets of the LEDs to produce a desired color. The same circuit can be used to vary the intensity of the light in the manner of a dimmer (18, 20, 22).

ISO-SWS observations of solid carbon dioxide in molecular clouds

Abstract: Spectra of interstellar CO2 ice absorption features at a resolving power of lambda/Delta lambda approximate to 1500-2000 are presented for 14 lines of sight. The observations were made with the Short-Wavelength Spectrometer (SWS) of the Infrared Space Observatory (ISO). Spectral coverage includes the primary stretching mode of CO2 near 4.27 mu m in all sources; the bending mode near 15.2 mu m is also detected in 12 of them. The selected sources include massive protostars (Elias 29 [in rho Oph], GL 490, GL 2136, GL 2591, GL 4176, NGC 7538 IRS 1, NCC 7538 IRS 9, S140, W3 IRS 5, and W33 A), sources associated with the Galactic Center (Sgr A*, GCS 3 I, and GCS 4), and a background star behind a quiescent dark cloud in Taurus (Elias 16); they thus probe a diverse range of environments. Column densities of interstellar CO2 ice relative to H2O ice fall in the range 10%-23%: this ratio displays remarkably little variation for such a physically diverse sample. Comparison of the observed profiles with laboratory data for CO2-bearing ice mixtures indicates that CO2 generally exists in at least two phases, one polar (H2O dominant) and one nonpolar (CO2 dominant). The observed CO2 profiles may also be reproduced when the nonpolar components are replaced with thermally annealed ices. Formation and evolutionary scenarios for CO2 and implications for grain mantle chemistry are discussed. Our results support the conclusion that thermal annealing, rather than energetic processing due to UV photons or cosmic rays, dominates the evolution of CO2-bearing ices.

Social and personal determinants of workplace aggression: Evidence for the impact of perceived injustice and the Type A Behavior Pattern

Abstract: Four hundred fifty-two employed persons rated the frequency with which they had been the victims of a wide range of aggressive actions at work. In addition, they also rated the frequency with which they themselves had aggressed against others in their workplaces. Three hypotheses were investigated: (1) covert forms of aggression, in which aggressors seek to conceal their identity from target persons, are significantly more frequent in workplaces than overt forms of aggression; (2) the greater the perceived injustice reported by employees, the greater their tendency to engage in workplace aggression; and (3) the higher individuals' scores on a measure of the Type A Behavior Pattern, the greater their reported frequency of engaging in various forms of workplace aggression, Results offered support for all three hypotheses. In addition, several demographic variables (participants' age and gender; the physical location of their workplaces) were also found to play a role in the occurrence of workplace aggression. Together, these findings were interpreted as underscoring the importance of establishing close conceptual links between research on workplace aggression andbasic research on human aggression.

Role of Granular Activated Carbon Surface Chemistry on the Adsorption of Organic Compounds. 1. Priority Pollutants

Abstract: Uptake of two synthetic organic contaminants (SOCs), trichloroethylene and trichlorobenzene, by one coal-based and one wood-based granular activated carbon (GAC), modified using liquid-phase oxidation (HNO3) and heat treatment in an inert atmosphere (N2), and by several different as-received GACs was compared. Carbons were characterized by elemental analysis, surface area and pore size distribution, water vapor adsorption, acid−base adsorption characteristics measured using the Boehm technique, and a mass titration/pH equilibration method to determine the pHpzc. The results of isotherm experiments with the surface-treated coal- and wood-based carbons indicated that carbon surface acidity played an important role on the adsorption of hydrophobic SOCs. It was found that increasing surface acidity increased the polarity of the surface and reduced adsorption of hydrophobic SOCs by GAC. However, no significant trend was evident for as-received carbons; their behavior differed significantly from surface-treated...

A genetic system yields self-cleaving inteins for bioseparations.

Abstract: A self-cleaving element for use in bioseparations has been derived from a naturally occurring, 43 kDa protein splicing element (intein) through a combination of protein engineering and random mutagenesis. A mini-intein (18 kDa) previously engineered for reduced size had compromised activity and was therefore subjected to random mutagenesis and genetic selection. In one selection a mini-intein was isolated with restored splicing activity, while in another, a mutant was isolated with enhanced, pH-sensitive C-terminal cleavage activity. The enhanced-cleavage mutant has utility in affinity fusion-based protein purification. These mutants also provide new insights into the structural and functional roles of some conserved residues in protein splicing.

Cellular automata microsimulation of bidirectional pedestrian flows

Abstract: The cellular automata (CA) microsimulation of pedestrians is a particle-hopping model in which a set of local rules prescribe the behavior of entities within local neighborhoods of cells. CA microsimulation has emerged as a tool for simulating traffic flow and modeling transportation networks. Pedestrian flow is inherently more complex than vehicular flow, and simulation models that are used for emulating vehicular traffic are not directly applicable to modeling pedestrian movements. In previous work the authors demonstrated that unidirectional pedestrian flow patterns consistent with well-established fundamental properties could be generated with CA microsimulation. This paper expands upon the previous effort and presents a CA microsimulation model and emergent fundamental flows for a bidirectional pedestrian walkway. Simulation experiments indicate that the basic model is applicable to walkways of various lengths and widths and across different directional shares of pedestrian movements.

Efficient optimistic parallel simulations using reverse computation

Abstract: In optimistic parallel simulations, state-saving techniques have traditionally been used to realize rollback. In this article, we propose reverse computation as an alternative approach, and compare its execution performance against that of state-saving. Using compiler techniques, we describe an approach to automatically generate reversible computations, and to optimize them to reap the performance benefits of reverse computation transparently. For certain fine-grain models, such as queuing network models, we show that reverse computation can yield significant improvement in execution speed coupled with significant reduction in memory utilization, as compared to traditional state-saving. On sample models using reverse computation, we observe as much as a six-fold improvement in execution speed over traditional state-saving.

Spatial and temporal regulation of gap junction connexin43 in vascular endothelial cells exposed to controlled disturbed flows in vitro

Abstract: Hemodynamic regulation of the endothelial gap junction protein connexin43 (Cx43) was studied in a model of controlled disturbed flows in vitro. Cx43 mRNA, protein expression, and intercellular communication were mapped to spatial variations in fluid forces. Hemodynamic features of atherosclerotic lesion-prone regions of the vasculature (flow separation and recirculation) were created for periods of 5, 16, and 30 h, with laminar shear stresses ranging between 0 and 13.5 dynes/cm2. Within 5 h, endothelial Cx43 mRNA expression was increased in all cells when compared with no-flow controls, with highest levels (up to 6- to 8-fold) expressed in regions of flow recirculation corresponding to high shear stress gradients. At 16 h, Cx43 mRNA expression remained elevated in regions of flow disturbance, whereas in areas of fully developed, undisturbed laminar flow, Cx43 expression returned to control levels. In all flow regions, typical punctate Cx43 immunofluorescence at cell borders was disrupted by 5 h. After 30 h of flow, disruption of gap junctions persisted in cells subjected to flow separation and recirculation, whereas regions of undisturbed flow were substantially restored to normal. These expression differences were reflected in sustained inhibition of intercellular communication (dye transfer) throughout the zone of disturbed flow (84.2 and 68.4% inhibition at 5 and 30 h, respectively); in contrast, communication was fully reestablished by 30 h in cells exposed to undisturbed flow. Up-regulation of Cx43 transcripts, sustained disorganization of Cx43 protein, and impaired communication suggest that shear stress gradients in regions of disturbed flow regulate intercellular communication through the expression and function of Cx43.

Incremental and interactive sequence mining

Abstract: The discovery of frequent sequences in temporal databases is an important data mining problem. Most current work assumes that the database is static, and a database update requires rediscovering all the patterns by scanning the entire old and new database. In this paper, we propose novel techniques for maintaining sequences in the presence of a) database updates, and b) user interaction (e.g. modifying mining parameters). This is a very challenging task, since such updates can invalidate existing sequences or introduce new ones. In both the above scenarios, we avoid re-executing the algorithm on the entire dataset, thereby reducing execution time. Experimental results confirm that our approach results in execution time improvements of up to several orders of magnitude in practice.

Two-phase modeling of deflagration-to-detonation transition in granular materials: A critical examination of modeling issues

Abstract: The two-phase mixture model developed by Baer and Nunziato (BN) to study the deflagration-to-detonation transition (DDT) in granular explosives is critically reviewed. The continuum-mixture theory foundation of the model is examined, with particular attention paid to the manner in which its constitutive functions are formulated. Connections between the mechanical and energetic phenomena occurring at the scales of the grains, and their manifestations on the continuum averaged scale, are explored. The nature and extent of approximations inherent in formulating the constitutive terms, and their domain of applicability, are clarified. Deficiencies and inconsistencies in the derivation are cited, and improvements suggested. It is emphasized that the entropy inequality constrains but does not uniquely determine the phase interaction terms. The resulting flexibility is exploited to suggest improved forms for the phase interactions. These improved forms better treat the energy associated with the dynamic compaction of the bed and the single-phase limits of the model. Companion papers of this study [Kapila et al., Phys. Fluids 9, 3885 (1997); Kapila et al., in preparation; Son et al., in preparation] examine simpler, reduced models, in which the fine scales of velocity and pressure disequilibrium between the phases allow the corresponding relaxation zones to be treated as discontinuities that need not be resolved in a numerical computation.

Computational damage mechanics for composite materials based on mathematical homogenization

Abstract: This paper is aimed at developing a non-local theory for obtaining numerical approximation to a boundary value problem describing damage phenomena in a brittle composite material. The mathematical homogenization method based on double-scale asymptotic expansion is generalized to account for damage effects in heterogeneous media. A closed-form expression relating local fields to the overall strain and damage is derived. Non-local damage theory is developed by introducing the concept of non-local phase fields (stress, strain, free energy density, damage release rate, etc.) in a manner analogous to that currently practiced in concrete [1, 2], with the only exception being that the weight functions are taken to be C0 continuous over a single phase and zero elsewhere. Numerical results of our model were found to be in good agreement with experimental data of 4-point bend test conducted on composite beam made of Blackglas™/Nextel 5-harness satin weave. Copyright © 1999 John Wiley & Sons, Ltd.

Surface modification of poly(ether sulfone) ultrafiltration membranes by low-temperature plasma-induced graft polymerization

Abstract: Low-temperature helium plasma treatment followed by grafting of N-vinyl-2-pyrrolidone (NVP) onto poly(ether sulfone) (PES) ultrafiltration (UF) membranes was used to modify commercial PES membranes. Helium plasma treatment alone and post-NVP grafting substantially increased the surface hydrophilicity compared with the unmodified virgin PES membranes. The degree of modification was adjusted by plasma treatment time and polymerization conditions (temperature, NVP concentration, and graft density). The NVP-grafted PES surfaces were characterized by Fourier transform infrared attenuated total reflection spectroscopy and electron spectroscopy for chemical analysis. Plasma treatment roughened the membrane as measured by atomic-force microscopy. Also, using a filtration protocol to simulate protein fouling and cleaning potential, the surface modified membranes were notably less susceptible to BSA fouling than the virgin PES membrane or a commercial low-protein binding PES membrane. In addition, the modified membranes were easier to clean and required little caustic to recover permeation flux. The absolute and relative permeation flux values were quite similar for the plasma-treated and NVP-grafted membranes and notably higher than the virgin membrane. The main difference being the expected long-term instability of the plasma treated as compared with the NVP-grafted membranes. These results provide a foundation for using low-temperature plasma-induced grafting on PES with a variety of other molecules, including other hydrophilic monomers besides NVP, charged or hydrophobic molecules, binding domains, and biologically active molecules such as enzymes and ribozymes. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1699–1711, 1999