bluuebunny/crossref_metadata_2025_split huggingface dataset:
Extending an Algebraic Modeling Language to Support Constraint Programming
Authors: Fourer Robert , Gay David M. 
Published: February 2003

Although algebraic modeling languages are widely used in linear and nonlinear programming applications, their use for combinatorial or discrete optimization has largely been limited to developing integer linear programming models for solution by branch-and-bound procedures. Yet much of a modeling language's underlying structure for expressing integer programs is equally useful for describing more general combinatorial optimization constructs. Constraint programming solvers offer an alternative approach to solving combinatorial optimization problems, in which natural combinatorial constructs are addressed directly within the solution procedure. Hence the growing popularity of constraint programming motivates a variety of extensions to algebraic modeling languages for the purpose of describing combinatorial problems and conveying them to solvers. We examine some of these language extensions along with the significant changes in solver interface design that they require. In particular, we describe how several useful combinatorial features have been added to the AMPL modeling language and how AMPL's general-purpose solver interface has been adapted accordingly. As an illustration of a solver connection, we provide examples from an AMPL driver for ILOG Solver.
The Access-Control Problem on Capacitated FIFO Networks With Unique O-D Paths is Hard
Authors: Erera Alan L. , Daganzo Carlos F. , Lovell David J. 
Published: February 2003

This paper is concerned with the performance of multicommodity capacitated networks in a deterministic but time-dependent environment. For a given time-dependent origin-destination table, this paper asks if it is easy to find a way of regulating the input flows into the network to avoid queues from growing internally, i.e., to avoid capacity violations. Problems of this type are conventionally approached in the traffic/transportation field with variational methods such as control theory (if time is continuous) and with mathematical programming (if time is discrete). However, these approaches can only be expected to work well ifthe set off easible solutions is convex. Unfortunately, it is found in this paper that this is not the case. It is shown that continuous-time versions of the problem satisfying the smoothness conditions of control theory can have a finite but very large number off easible solutions. The same happens for the discrete time case. These difficulties arise even with the simplest versions of the problem (with unique origin-destination paths, perfect information, and deterministic travel times). The paper also shows that the continuous-time feasibility problem is NP-hard, and that if we restrict our attention to (practical) problems whose data can be described with a finite number ofbits (e.g., in discrete time), then the problem is NP-complete. These results are established by showing that the problem instances of interest can be related to the Directed Hamiltonian Path problem by a polynomial transformation.
Knowledge as a Contingency Variable: Do the Characteristics of Knowledge Predict Organization Structure?
Authors: Birkinshaw Julian , Nobel Robert , Ridderstråle Jonas 
Published: February 2003

This paper examines the validity of knowledge as a contingency variable. Building on recent advances in thinking about the dimensions of knowledge assets (Winter 1987, Zander and Kogut 1995), we argue that such dimensions might have an important influence on organization structure. More specifically, we focus on two dimensions of knowledge—observability and system embeddedness—and their influence over the level of unit autonomy and interunit integration in an international network of R&D units. Statistical analysis of questionnaire responses from 110 R&D unit managers show strong association between the dimensions of knowledge and organization structure. It also indicates partial support for the “fit” hypothesis in contingency theory.The paper makes two important contributions to the knowledge management literature. First, we find support for the contingency logic, suggesting that effective organization design has to take into account the underlying characteristics of the firm's knowledge base. Second, we shed light on a relatively neglected dimension of knowledge that we call system embeddedness. This is the extent to which knowledge is a function of the social and physical system in which it exists. In the statistical analysis it emerges as a strong predictor of organization structure. Moreover, it also appears to be conceptually distinct from the tacit-articulate dimension that is normally emphasized. This allows us to speculate on four generic forms that a firm's knowledge might take, that we label integrated, isolated, opaque, and transparent. These are discussed using examples from the data.
Islands of Shared Knowledge: Specialization and Mutual Understanding in Problem-Solving Teams
Authors: Postrel Steven 
Published: February 2003

Where should the boundaries of knowledge between economic actors be located in order to maximize the efficiency of their interactions? In particular, what circumstances determine whether it makes sense for adjacent stages in the value chain to invest in the development of common understanding, and when does it make sense for them to operate in mutual ignorance? To address these questions, it is necessary to construct a kind of production function which takes different forms of knowledge—specialist capability and trans-specialist understanding—as inputs and relates them to problem-solving output. Using a simple model of product design as a template, it is possible to derive such a production function. One can then use its properties in conjunction with plausible assumptions about the cost of acquiring different kinds of knowledge to develop general principles that explain when efficiency requires costly learning across specialties and when it is better to allow specialties to operate in mutual ignorance of one another's domains. The derived production function, contrary to some intuition and previous literature, implies that specialist capability can substitute for knowledge shared across specialties. This result in turn implies that the nature of learning costs, rather than the shape of knowledge benefits, plays the predominant role in determining when mutual ignorance is a good idea. The analysis also helps resolve the following paradox: The economy depends for its efficiency upon a drastic separation of knowledge across individuals and organizational units, yet studies of product development find that greater knowledge commonality is associated with better firm performance. An implication of the substitutability of specialized and trans-specialty knowledge is that situations where learning across specialties is desirable seem relatively rare in the economy as a whole. These situations are disproportionately common, however, in those areas where important managerial activity takes place. A key role of management is to attend to the strategic, operational, and governance needs of these “islands of shared knowledge in a sea of mutual ignorance.”
Coexistence of Two Polytypic Groups in Cronstedtite From Lostwithiel, England
Authors: Kogure Toshihiro , Hybler Jiří , Yoshida Hideto 
Published: February 2003

AbstractCronstedtite from Lostwithiel, Cornwall, England, in which two polytypic groups (A and C) are present within the same crystal, has been investigated using various techniques to reveal the distribution of the two groups and the relationship between polytypic structure and chemical composition. X-ray precession photographs from cleaved fragments of pyramidal crystals revealed the variable proportions of the two groups from the top to the base. Near the top, the crystal consists entirely of group C, with 1Tas the dominant polytype. Near the base, both groups A and C are present. Back-scattered electron images from cross-sections parallel to the pyramidal axis showed mosaic contrast near the base, suggesting that two compositionally-different domains of several tens of microns in size are present, whereas the contrast was uniform near the top. Electron microprobe chemical analysis indicated the compositions(Fe2.312+Fe0.693+)(Si1.31Fe0.693+)O5(OH)4and(Fe2.162+Fe0.843+)(Si1.16Fe0.843+)O5(OH)4. Electron back-scattered patterns (EBSPs) confirmed that the domain with Si-rich composition belongs to group C and that with Si-poor composition to group A. This is the first evidence that specific chemical compositions are related to the polytypic structures in cronstedtite. Transmission electron microscopy revealed that intergrowth of groups A and C at the monolayer level is also present as stacking disorder in both domains near the base, whereas such intergrowth was not observed in the region near the top.
Crystallization of Layered Double Hydroxides by Ultrasound and the Effect of Crystal Quality on Their Surface Properties
Authors: Seida Yoshimi , Nakano Yoshio , Nakamura Yasuo 
Published: February 2003

AbstractThe ultrasound technique was applied to the synthesis of layered double hydroxides. The use of ultrasound in the synthesis of these compounds was studied in terms of its effect on their crystal qualities and surface properties. The crystal qualities of the compounds synthesized with ultrasound were compared with those of compounds synthesized without ultrasound to elucidate the effect of the ultrasound on the synthesis. The effect of crystal quality (crystallite size) on the adsorption behavior of humic substances was examined. The compounds synthesized under ultrasonic conditions showed a larger crystallite size and a larger adsorption capacity for humic substances than those synthesized without ultrasonic treatment. The degree of adsorption correlated well with crystal quality.
Hydraulic Performance of Untreated and Polymer-Treated Bentonite in Inorganic Landfill Leachates
Authors: Ashmawy Alaa K. , El-Hajji Darwish , Sotelo Nestor , Muhammad Naim 
Published: February 2003

AbstractShort- and long-term exposure to inorganic solutions can cause significant degradation of the hydraulic properties of bentonite clay used in geosynthetic clay liners (GCLs). In particular, the increase in hydraulic conductivity due to cation exchange when Na-montmorillonite is subjected to leachates rich in Ca and Mg has caused problems in incinerator ash landfill liners located in wet environments, where large quantities of leachates are generated. Experimental results are presented to evaluate the immediate change in hydraulic conductivity of seven types of GCL clays upon permeation with leachate generated from three ash landfills. The composition of the ash, which is a by-product of the incineration of municipal solid waste (MSW), in turn influences the composition of the resulting leachate. Falling head permeability tests were performed on flexible-wall permeameter specimens, with back-pressure saturation. Chemical analysis shows that the three leachate products contain high, medium, and low concentration Ca and Mg cations. The clay component of GCL materials tested in this study consists of regular and polymer-treated bentonite. Polymer treatment is believed to render the clay non-reactive to many organic and inorganic chemicals. The results of this study indicate that: (1) polymer treatment is generally more beneficial if the clay is first saturated with water and not directly with the leachate; (2) high swell potential of the bentonite is more advantageous than polymer treatment, especially when low hydraulic conductivity is required in the short term and if the clay is pre-hydrated. Experiment setup and special specimen preparation procedures are also discussed.
Micro-Structure and Hydraulic Conductivity of Simulated Sand-Bentonite Mixtures
Authors: Abichou Tarek , Benson Craig H. , Edil Tuncer B. 
Published: February 2003

AbstractThis paper describes the relationship between the micro-structure and hydraulic conductivity of simulated sand-bentonite mixtures (SSBMs) prepared with powdered and granular bentonite. Glass beads were used to simulate sand grains because of their superior optical properties. The micro-structure of SSBMs was observed using optical micrography and scanning electron microscopy. For mixtures prepared with powdered bentonite, the indications are that bentonite coats the particles. As the bentonite content increases, the thickness of bentonite coating increases and reduces the area available for flow. For mixtures containing granular bentonite, the dry bentonite granules occupy the space between the particles and then swell to fill the void space. As the bentonite content increases, the number of granules increases, leading to more void spaces being filled with bentonite. At higher bentonite content (>8%), flow paths devoid of bentonite are unlikely, and the hydraulic conductivity appears to be controlled by the hydraulic conductivity of bentonite. The changes in micro-structure that were observed are consistent with the decrease in hydraulic conductivity that occurs with increasing bentonite content. However, the relationship between hydraulic conductivity and bentonite content differs depending on whether a mixture contains powdered or granular bentonite.
Early Stages of Volcanic Tuff Alteration in Hydrothermal Experiments: Formation of Mixed-Layer Illite-Smectite
Authors: de la Fuente Sandra , Cuadros Javier , Linares José 
Published: February 2003

AbstractVolcanic tuff from the Cabo de Gata region in Almería, southeastern Spain, was altered under hydrothermal conditions at different temperatures (60 to 180°C), reaction times (60 to 360 days), and reacting solutions (deionized water and NaCl and KCl solutions with Na/K ratios from 0.01 to 100, and a total salt concentration of 0.1 to 1 M).X-ray diffraction (XRD) patterns of the reacted samples revealed a very weak, broad peak at ∼13 Å that migrated to 17 Å upon glycolation. Comparison between simulated (NEWMOD) and experimental XRD patterns indicated that the neoformed phase is a random mixed-layer illite-smectite (I-S) with 75% expandable layers. Fourier transform infrared (FTIR) spectroscopy showed that I-S formation was most extensive for high pH (8–9) solutions, corresponding to dilute solutions and, especially, to deionized water. Analytical electron microscopy (AEM) analyses of isolated I-S particles showed that most of them are smectite-rich I-S regardless of the experimental conditions, in agreement with XRD results. The I-S particles had a wide range of octahedral Mg contents. The pH and Na, K, Ca and Mg concentrations in the final solutions suggested cation (including H+) exchange as a major process in the alteration experiments. Analysis of aqueous activity diagrams (log aK/aHvs. log aSiO2) showed that some solution compositions are consistent and some are inconsistent with I-S formation. These results, combined with complementary electron microscopy analyses (de la Fuente et al., 2000a), are interpreted to be due to direct transformation of the glass into I-S in a process controlled by glass composition.
Origin of Allophane and Retardation of Pebble Weathering in Quaternary Marine Terrace Deposits
Authors: Jeong Gi Young , Bae Jin Han , Cheong Chang Sik 
Published: February 2003

AbstractQuaternary marine terrace deposits consisting of gravels interbedded with thin sandy gravel layers have been subjected to subaerial weathering. Restricted to the sandy gravel layers, allophane gel either replaced bytownite sands to form a pseudomorph or coated the pebbles. The allophane has an average Al/Si atomic ratio of 1.5 with 45% H2O. The sandy gravels were originally rich in bytownite (av. An86) sands derived from underlying Tertiary basaltic lapilli tuff. The highly soluble and aluminous bytownite favored the formation of allophane. In the sandy gravel layers, pebbles coated with allophane gel were almost fresh whereas those in the gravel layers were highly weathered to form halloysite-rich clays. Allophane gels acted as a somewhat impermeable geochemical barrier impeding a mineral-water reaction in the bytownite-rich sandy gravel layers and thus significantly retarding pebble weathering, while prolonged weathering in the gravel layers resulted in the severe decomposition of pebbles. Bytownite protected the pebbles against weathering, implying that minor soluble minerals might be one of the factors in the natural variation of the weathering rates of rocks and sediments.
The Nature of Soil Kaolins From Indonesia and Western Australia
Authors: Hart Robert D. , Gilkes Robert J. , Siradz Syamsul , Singh Balwant 
Published: February 2003

AbstractPurified soil kaolins from Indonesia and Western Australia were characterized using analytical TEM, XRD, TGA and chemical analysis. The Indonesian kaolins, formed from tuff, consist of a mixture of tubular kaolin crystals with relatively low Fe concentrations and platy kaolin crystals with higher Fe concentrations. Western Australian kaolins also contained tubular and platy crystals but showed no systematic relationship of crystal morphology with Fe content. The coherently scattering domain (CSD) size of the Indonesian samples (5–6 nm for 001,i.e. caxis dimension) is remarkably consistent and is approximately half of the value for the Western Australian kaolins (9.7–13.4 nm), and both are much smaller sizes than values for the reference kaolins (15.6–27.8 nm). Coherently scattering domain sizes derived from the Scherrer equation are approximately twice the values obtained from the Bertaut-Warren-Averbach Fourier method but the results show the same pattern of variation. For the Indonesian, Western Australian and reference kaolins, the N2-BET surface area ranges 59–88, 44–56 and 5–28 m2/g; the dehydroxylation temperatures range 486–499, 484–496 and 520–544°C, the mean cation exchange capacities (CEC) are 9.4, 5.0 and 3.5 meq 100 g−1and the surface densities of charge range 0.10–0.14, 0.08–0.10 and 0.04–0.12 C/m2. The properties of the Western Australian kaolins and Indonesian kaolins differ substantially, but kaolins within each group have similar properties. These results suggest that soil kaolin properties may be characteristic of a particular pedoenvironment and that a systematic study of kaolins in different pedoenvironments is required.
Thermal Evolution of Fluorine From Smectite and Kaolinite
Authors: Chipera Steve J. , Bish David L. 
Published: February 2003

AbstractThe fluoride ion is crystal chemically very similar to the hydroxyl ion, substituting for hydroxyl in many minerals in which hydrogen bonding is not important. Fluoride substitutions are particularly common in 2:1 layer silicates, such as micas, illites and smectites. The brick and tile industries, which use naturally occurring clays as their primary raw materials, have devoted considerable effort to understanding fluorine evolution during firing of the raw materials due to increasingly stringent fluorine emission regulations. In order to understand fluorine evolution from ceramic raw materials, we have studied a number of phyllosilicate materials used in making bricks. X-ray powder diffraction and fluorine analyses were combined with heating experiments and thermogravimetric analysis to evaluate the chemical and structural changes taking place on heating. Fluorine remained in 2:1 layer silicates to higher temperatures than did hydroxyl, but it behaved identically to hydroxyl in the kaolinite studied. In all cases, fluorine evolution coincided with structural breakdown of the clay host. These results show that fluorine evolution will consistently occur during firing of clay raw materials, and the problems of fluorine emission cannot be readily solved by simple variations of firing temperatures or times.
High-Temperature X-Ray Diffraction, Differential Thermal Analysis and Thermogravimetry of the Kaolinite-Dimethylsulfoxide Intercalation Complex
Authors: Franco F. , Ruiz Cruz M. D. 
Published: February 2003

AbstractThe intercalation complex of a kaolinite from Cornwall, UK, with dimethylsulfoxide (DMSO) was studied by high-temperature X-ray diffraction (HTXRD), differential thermal analysis (DTA) and thermogravimetry (TG). The X-ray pattern obtained at room temperature indicated that intercalation of DMSO into kaolinite caused an increase of the basal spacing of kaolinite from 7.14 to 11.19 Å. Heating between 25 and 300°C caused the removal of the DMSO, which occurred over several stages. In a first stage (25–125°C), an expansion (from 11.19 to 11.28 Å) followed by a contraction (from 11.28 to 11.19 Å) is observed, at the same time as the intensity of the basal reflection decreased and was replaced by a broad band extending from ~11 to ~7 Å. In a second stage (125–200°C), the loss of DMSO did not lead to changes in the HTXRD patterns; and finally, in a third stage, the loss of DMSO caused an important increase in intensity and sharpening of the basal reflections of the kaolinite. These stages were also shown by the DTA-TG curves for the complex. The TG curve indicated that the loss of ~15% of the intercalated DMSO occurs below 150°C, and caused the disruption of the structure. The remaining molecules, forming stronger bonds with the kaolinite surfaces, were lost between 150 and 300°C.
Weathering of Chlorite: II. Reactions and Products in Microsystems Controlled by Solution Avenues
Authors: Aspandiar Mehrooz F. , Eggleton Richard A. 
Published: February 2003

AbstractWeathering of chlorite adjacent to macro- and micro-passages (fissures) in regolith units has been studied to determine the alteration mechanisms and products and compare them to those that prevail at a distance from the open passages. The micro-fissures in the saprolith units evolve as a function of weathering with an increase in micro-fissure density and their infilling with ferriargillans corresponding to an increase in weathering intensity. In the saprock and saprolite units, goethite-rich bands with surrounding reddish haloes invade the chlorite adjoining the micro-fissures. In the reddish haloes surrounding the goethite bands and fissures, the phyllosilicates alter to an intimate mixture of goethite, kaolinite, feroxyhyte and halloysite with the possible nanoscale presence of other fine-grained iron aluminosilicates such as hisingerite and smectite. In the fine saprolite, the weathering products after original chlorite adjoining the micro-fissures bearing ferriargillans, alter directly to ferriargillan products — kaolinite and goethite. The lack of orientation of the products with the parent phyllosilicates indicates the operation of a dissolution-precipitat ion mechanism which is in contrast to the topotactic alteration mechanism functioning at a distance within the phyllosilicate grain assemblage. The differences in alteration mechanisms and products of chlorite weathering in different microsites suggest the rate of weathering of chlorite can differ in microsites within individual regolith units. The presence of fine-grained metastable products in the form of feroxyhyte and halloysite adjoining the fissures suggests an Ostwald Step Rule sequence during alteration of phyllosilicates with rapid oxidation of Fe and the presence of Si in the microsite considered the main factor favoring fine-grained metastable products.