bluuebunny/crossref_metadata_2025 huggingface dataset:
Probabilistic stability analysis of a tailings dyke on presheared clayshale
Authors: El-Ramly H , Morgenstern N R , Cruden D M
Published: February 2003

Probabilistic slope stability analysis offers an efficient framework for logical, systematic incorporation of uncertainty into slope design. The slow integration of probabilistic slope analyses into practice is attributed, among other factors, to the lack of published studies illustrating the implementation and benefits of such techniques. A spreadsheet-based, probabilistic slope analysis methodology is applied to evaluate the stability of a section of the Syncrude Tailings Dyke in Fort McMurray, Canada. The dyke is approximately 44 m high and is founded on presheared clayshale. The performance of the dyke is governed by uncertainties about material properties and pore-water pressures. Starting with field and laboratory data, this study demonstrates the techniques used in quantifying the various components of parameter uncertainty, conducting a probabilistic assessment, and estimating the probability of unsatisfactory performance. The probability of unsatisfactory performance of the dyke is estimated to be 1.6 × 103. Field monitoring data indicate that the dyke performance is adequate. The study thus provides a first link between probability figures and performance. The analysis also quantifies the relative contributions of the various sources of uncertainty to the overall uncertainty in the factor of safety.Key words: probabilistic analysis, slope stability, Monte Carlo simulation, spatial variability, tailings dyke, clayshale.
Drag anchor flukesoil interaction in clays
Authors: O'Neill M P , Bransby M F , Randolph M F
Published: February 2003

Finite element analysis has been used to investigate the interaction between anchor flukes and undrained soil at failure. The behaviour of a rectangular and a wedge-shaped anchor has been investigated when the anchors are subject to combined rotational and translational loadings similar to those experienced during anchor dragging. The results have been presented in terms of a plasticity framework to produce an associated plastic failure locus for combined loading conditions. It is seen that the wedge-shaped anchor has a different shaped failure locus and displacements at failure because of its asymmetrical shape, and this will affect drag anchor behaviour. A new design method is introduced that aims to predict drag anchor embedment trajectory and holding capacity through examination of the flukesoil interaction. The yield loci and plastic potentials produced from consideration of flukesoil interaction are used in the new design method to predict drag anchor kinematics. Results from the new analysis method are compared to empirically based methods, and it is seen that there is good agreement between results, even without further calibration from physical modelling. This suggests that the approach has promise, and with further refinement of the yield loci and better approximations to the complex anchor geometry, it may develop into a useful anchor design tool that allows for both the anchor geometry and the soil conditions explicitly.Key words: drag anchor capacity, undrained clays, numerical method.
Response of flexible piles under laterally linear movement of the sliding layer in landslides
Authors: Cai Fei , Ugai Keizo
Published: February 2003

Observational results indicate that the lateral movement of the sliding layer in landslides is usually not uniform, but approximately linear. In this paper, a subgrade reaction solution for the response of flexible piles in landslides is developed where the influence of the laterally linear movement of the sliding layer on the response of flexible piles in landslides is considered. The study of case histories indicates that the calculated and measured responses of flexible piles in landslides compare well with each other. Dimensionless design charts are proposed based on the new subgrade reaction solution.Key words: piles, slope stabilization, landslides, soilpile interaction, subgrade reaction solution.
Constraint and Integer Programming in OPL
Authors: Hentenryck Pascal Van
Published: February 2003

In recent years, it has been increasingly recognized that constraint and integer programming have orthogonal and complementary strengths in stating and solving combinatorial optimization applications. In addition, their integration has become an active research topic. The optimization programming language OPL was a first attempt at integrating these technologies both at the language and at the solver levels. In particular, OPL is a modeling language integrating the rich language of constraint programming and the ability to specify search procedures at a high level of abstraction. Its implementation includes both constraint and mathematical programming solvers, as well as some cooperation schemes to make them collaborate on a given problem. The purpose of this paper is to illustrate, using OPL, the constraint-programming approach to combinatorial optimization and the complementary strengths of constraint and integer programming.
A Hybrid Exact Algorithm for the TSPTW
Authors: Focacci Filippo , Lodi Andrea , Milano Michela
Published: February 2003

The Traveling Salesman Problem with Time Windows (TSPTW) is the problem of finding a minimum-cost path visiting a set of cities exactly once, where each city must be visited within a specific time window. We propose a hybrid approach for solving the TSPTW that merges Constraint Programming propagation algorithms for the feasibility viewpoint (find a path), and Operations Research techniques for coping with the optimization perspective (find the best path). We show with extensive computational results that the synergy between Operations Research optimization techniques embedded in global constraints, and Constraint Programming constraint solving techniques, makes the resulting framework effective in the TSPTW context also if these results are compared with state-of-the-art algorithms from the literature.
Implementing Real-Time Optimization Models: A Case Application From The Motor Carrier Industry
Authors: Powell Warren B. , Marar Arun , Gelfand Jack , Bowers Steve
Published: February 2003

Online models for real-time operations planning face a host of implementation issues that do not arise in more strategic arenas. We use the seemingly simple problem of assigning drivers to loads in the truckload motor carrier industry as an instance to study the issues that arise in the process of implementing a real-time dispatch system. Although the project was moderately successful, our focus is not on documenting the benefits, but rather on summarizing the challenges that arose. The most significant theme running through the implementation hurdles we encountered was the lack of information available to the model. Computers are very good at processing vast quantities of information; humans are very good at challenging the information that is in the computer and augmenting computer-provided data with head knowledge. Our study includes a careful comparison of actual decisions with model recommendations, using a six-month database of actual transactions. This comparison is the first we have seen of its kind and provides the most rigorous evaluation of an online dispatch model that we have seen. Although the model was well used, the results demonstrate that significant improvements could have been obtained if the level of model utilization had been even higher.
Optimizing Military Airlift
Authors: Baker Steven F. , Morton David P. , Rosenthal Richard E. , Williams Laura Melody
Published: February 2003

We describe a large-scale linear programming model for optimizing strategic (intercontinental) airlift capability. The model routes cargo and passengers through a specified transportation network with a given fleet of aircraft subject to many physical and policy constraints. The time-dynamic model captures a significant number of the important aspects of an airlift system in a large-scale military deployment, including aerial refueling, tactical (intracontinental) aircraft shuttles, and constraints based on crew availability. The model is designed to provide insight into issues associated with designing and operating an airlift system. We describe analyses for the U.S. Air Force system concerning fleet modernization and concerning the allocation of resources that affect the processing capacity of airfields.
A Market-Based Approach to Optimal Resource Allocation in Integrated-Services Connection-Oriented Networks
Authors: Thomas Panagiotis , Teneketzis Demosthenis , Mackie-Mason Jeffrey K.
Published: February 2003

We present an approach to the admission control and resource allocation problem in connection-oriented networks that offer multiple services to users. users' preferences are summarized by means of their utility functions, and each user is allowed to request more than one type of service. Multiple types of resources are allocated at each link along the path of a connection. We assume that the relation between Quality of Service (QoS) and resource allocation is given, and we incorporate it as a constraint into a static optimization problem. The objective of the optimization problem is to determine the amount of and required resources for each type of service to maximize the sum of the users' utilities. We prove the existence of a solution of the optimization problem and describe a competitive market economy that implements the solution and satisfies the informational constraints imposed by the nature of the decentralized resource allocation problem. The economy consists of four different types of agents: resource providers, service providers, users, and an auctioneer that regulates the prices based on the observed aggregate excess demand. The goods that are sold are: (i) the resources at each link of the network, and (ii) services constructed from these resources and then delivered to users. We specify an iterative procedure that is used by the auctioneer to update the prices, and we show that it leads to an allocation that is arbitrarily close to a solution of the optimization problem in a finite number of iterations.
A New Interior-Point Boundary Projection Method For Solving Nonlinear Groundwater Pollution Control Problems
Authors: Mulligan Ann E. , Ahlfeld David P.
Published: February 2003

A new interior-point algorithm for solving the groundwater-pollution-control design problem is presented. The algorithm requires that the objective function is differentiable in the interior region. For minimization problems with nonlinear constraints and a concave objective function, the technique is shown to be similar to an active set gradient-projection method, where the tangent of the boundary between feasible and infeasible solutions is used to determine a search direction. In this new method, however, the search direction is translated into the interior space of the feasible region. This process allows progress to be made toward improving the objective function while remaining in the feasible space and ultimately converges to a stationary point. Although the solution technique was developed to solve a groundwater control formulation with a linear objective function and nonlinear constraints, the method has been successfully applied to an unconstrained nonconcave/nonconvex formulation and may be applicable to a wide variety of problems.
On Tightening the Relaxations of Miller-Tucker-Zemlin Formulations for Asymmetric Traveling Salesman Problems
Authors: Sherali Hanif D. , Driscoll Patrick J.
Published: February 2003

This paper is concerned with applying the Reformulation-Linearization Technique (RLT) to derive tighter relaxations for the Asymmetric Traveling Salesman Problem (ATSP) formulation that is based on the Miller-Tucker-Zemlin (MTZ) subtour elimination constraints. The MTZ constraints yield a compact representation for the Traveling Salesman Problem (TSP), and their use is particularly attractive in various routing and scheduling contexts that have an embedded ATSP structure. However, it is well recognized that these constraints yield weak relaxations, and with this motivation, Desrochers and Laporte (1991) have lifted the MTZ constraints into facets of the underlying ATSP polytope. We show that a novel application of the RLT process from a nonstandard MTZ representation of the ATSP reveals a new formulation of this problem that is compact, and yet theoretically as well as computationally dominates the lifted-MTZ formulation of Desrochers and Laporte. This approach is also extended to derive tight formulations for the Precedence Constrained Asymmetric Traveling Salesman Problem (PCATSP), based on the MTZ subtour elimination constraints. Additional classes of valid inequalities are also developed for both these versions of the ATSP, and further ideas for developing tighter representations are suggested for future investigations.
Product Cycling With Uncertain Yields: Analysis and Application to the Process Industry
Authors: Rajaram Kumar , Karmarkar Uday S.
Published: February 2003

We formulate the dynamic product-cycling problem with yield uncertainty and buffer limits to determine how much product to produce at what time to minimize total expected switching, production, inventory storage, and backorder costs. A “restricted” Lagrangian technique is used to develop a lower bound and a model-based Lagrangian heuristic. We also develop an operational heuristic and a greedy heuristic. The operational heuristic has been implemented at seven refineries at Cerestar, Europe's leading manufacturer of wheat-and corn-based starch products in the food-processing industry . This has already reduced total costs by around 5 percent or $3 million annually at these sites. Tests of the Lagrangian heuristic on data from these refineries during this period have shown the potential to further reduce total costs by at least 2 percent or about $1 million. In addition, the Lagrangian heuristic has provided an objective basis to evaluate the economic impact of several strategic decisions involving issues such as buffer expansion, variability reduction, and product selection.
A Fluid Heuristic for Minimizing Makespan in Job Shops
Authors: Dai J. G. , Weiss Gideon
Published: February 2003

We describe a simple online heuristic for scheduling job shops. We assume there is a fixed set of routes for the jobs, and many jobs, say N, on each route. The heuristic uses safety stocks and keeps the bottleneck machine busy at almost all times, while the other machines are paced by the bottleneck machine. We perform a probabilistic analysis of the heuristic, under some assumptions on the distributions of the processing times. We show that our heuristic produces makespan, which exceeds the optimal makespan by no more than clogN with a probability that exceeds 1-1/N for all N ≥ 1, where c is some constant independent of N.
Facets and Reformulations for Solving Production Planning With Changeover Costs
Authors: Magnanti Thomas L. , Sastry Trilochan
Published: February 2003

We study a scheduling problem with changeover costs and capacity constraints. The problem is NP-complete, and combinatorial algorithms for solving it have not performed well. We identify a general class of facets that subsumes as special cases some known facets from the literature. We also develop a cutting-plane-based procedure and reformulation for the problem, and we obtain optimal solutions to problem instances with up to 600 integer variables without resorting to branch-and-bound procedures.
Asymptotic Behavior of an Allocation Policy for Revenue Management
Authors: Cooper William L.
Published: February 2003

Revenue management has become an important tool in the airline, hotel, and rental car industries. We describe asymptotic properties of revenue management policies derived from the solution of a deterministic optimization problem. Our primary results state that, within a stochastic and dynamic framework, solutions arising out of a single well-known linear program can be used to generate allocation policies for which the normalized revenue converges in distribution to a constant upper bound on the optimal value. We also show similar asymptotic results for expected revenues. In addition, we describe counterintuitive behavior that can occur when allocations are updated during the booking process (updating allocations can lead to lower expected revenue). These results add to the understanding of allocation policies and help to make concrete the statement that simple policies from easy-to-solve formulations can be relatively effective, even when analyzed in the more realistic stochastic and dynamic framework.
A Statistical Test for Nested Radial Dea Models
Authors: Pastor Jesús T. , Ruiz JosÉ L. , Sirvent Inmaculada
Published: February 2003

Some problems in economics, operations research, and engineering may be approached by means of a pair of radial DEA models that are nested, i.e., that the set of constraints of one of them is included in that of the other. In this paper we have focused on analyzing the marginal role of a given variable, called candidate, with respect to the efficiency measured by means of a DEA model. First, we have defined a new efficiency contribution measure (ECM), which finally compares the efficiency scores of the two radial DEA models differing in the candidate. This can be either one input or one output. Then,based on ECM, we have also approached the problem from a statistical point of view. To be precise, we have developed a statistical test that allows us to evaluate the significance of the observed efficiency contribution of the candidate. Eventually, solving this test may provide some useful insights in order to decide the incorporation or the deletion of a variable into/from a given DEA model, on the basis of the information supplied by the data. Two procedures for progressive selection of variables were designed by sequentially applying the test: a forward selection and a backward elimination. These can be very helpful in the initial selection of variables when building a radial DEA model.
Knowing in Practice: Enacting a Collective Capability in Distributed Organizing
Authors: Orlikowski Wanda J.
Published: February 2003

In this paper, I outline a perspective on knowing in practice which highlights the essential role of human action in knowing how to get things done in complex organizational work. The perspective suggests that knowing is not a static embedded capability or stable disposition of actors, but rather an ongoing social accomplishment, constituted and reconstituted as actors engage the world in practice. In interpreting the findings of an empirical study conducted in a geographically dispersed hightech organization, I suggest that the competence to do global product development is both collective and distributed, grounded in the everyday practices of organizational members. I conclude by discussing some of the research implications of a perspective on organizational knowing in practice.
Knowledge Partitioning in the Interfirm Division of Labor: The Case of Automotive Product Development
Authors: Takeishi Akira
Published: February 2003

Drawing on an empirical study on automakers' management of supplier involvement in product development in Japan, this paper shows that when the design of a component is outsourced to a supplier, how much automakers know about the component matters for them to gain a better outcome. While the actual tasks of designing and manufacturing components could be out-sourced, automakers should retain the relevant knowledge to obtain better component design quality. The paper argues that knowledge partitioning should be distinguished from task partitioning, and provides some implications for the knowledge-based theory of the firm.

The results indicate that effective pattern of knowledge partitioning differs by the nature of component development project in terms of technological newness. For regular projects, it is more important for the automaker to have a higher level of architectural knowledge (how to coordinate various components for a vehicle) than of component-specific knowledge, which is supposed to be provided by the supplier. However, when the project involves new technology for the supplier, it is important for the automaker to have a higher level of component-specific knowledge to solve unexplored engineering problems together with the supplier. In innovative projects, effective knowledge partitioning seems to demand some overlap between an automaker and a supplier, rather than efficient and clear-cut boundaries that are optimal for regular projects. Such “fluid” nature of knowledge boundaries contingent on the project types poses a challenge for firms seeking both technological leadership and efficiency in established products.

Developing and maintaining knowledge about an outsourced component is by no means easy. When the actual design tasks are outsourced, automakers miss substantial opportunities to gain relevant knowledge through learning by doing. Also, obtained knowledge may be diffused among competitors through shared suppliers. Another problem for automakers is that component-specific knowledge is important for only limited cases (innovative projects). Even worse, component-specific knowledge has a trade off relationship with architectural knowledge.

Such an inherent dilemma of managing knowledge, however, may provide some automakers with the opportunity to achieve sustainable competitive advantage. Additional analysis shows that one automaker managed both types of knowledge better than others in a manner that deals effectively with the dilemma. Its organizational mechanisms include career development policies, extensive documentation of technological information, internal training programs, and incentive schemes. The difficulty in implementing those mechanisms in a consistent and complementary manner seems to explain why there was a significant variance among automakers in knowledge level, even when the actual tasks were carried out by a shared supplier.
Intercalation of 8-Hydroxyquinoline into Al-Smectites by Solid-Solid Reactions
Authors: Khaorapapong Nithima , Kuroda Kazuyuki , Ogawa Makoto
Published: February 2003

Tris(8-hydroxyquinoline)aluminum (III) complexes (Alq3), one of the molecules studied most widely for organic light-emitting devices, were formed in the interlayer spaces of smectites by solid-solid reactions between Al-smectites (Al-montmorillonite and Al-synthetic saponite (Sumecton)) and 8-hydroxyquinoline (8Hq) at room temperature. The intercalation of 8-hydroxyquinoline molecules into Al-smectites was demonstrated by powder XRD, FTIR, DTA, TG, TG-MS, and chemical analysis. The coordination of the ligand to the interlayer Al cations was proved by FTIR, UV-Vis, and photoluminescence spectroscopies. The luminescence intensity of Alq3-Sumecton was much greater than that of Alq3-montmorillonite, and this was ascribed to the very small amount of quenching impurities in Sumecton.
Expansion of Smectite by Hexadecyltrimethylammonium
Authors: Lee Seung Yeop , Kim Soo Jin
Published: February 2003

The adsorption of hexadecyltrimethylammonium (HDTMA) in smectite was studied by adsorption isotherms, X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Smectites that had reacted for 48 h with HDTMA cations equivalent to 0.2–3.0 times the cation exchange capacity (CEC) were converted to HDTMA-exchanged smectites with various d-spacings. Study of HDTMA-smectites by HRTEM suggests that the HDTMA adsorption results in interlayer expansion with various d-spacings and irregular wavy layer structures. We believe that HDTMA loading beyond the CEC of smectite affects the structure of clay by the additional adsorption of HDTMA-Br− via hydrophobic bonding. Surfactant orientation probably depends on the quantity of surfactant in the interlayer. Our TEM study shows that the structure of the adsorbed HDTMA layer in the interlayers of smectite depends on the charge distribution and chemical composition of smectite.
Visible Spectroscopy of Cationic Dyes in Dispersions with Reduced-Charge Montmorillonites
Authors: Bujdák Juraj , Iyi Nobuo
Published: February 2003

The aggregation behavior of one azine and three triphenylmethane cationic dyes in dispersions of reduced-charge montmorillonites (RCMs) was investigated. The extent and types of dye aggregation were monitored using visible spectroscopy. Similar relationships between dye aggregation and layer charge were observed, independent of the structure of the dye cations. High charge-density surfaces induced the formation of H-aggregates, with a face-to-face association between the dye cations that then absorb light at relatively lower wavelengths. Moderate reductions in layer charge were reflected in the lowering of the H-aggregation in favor of monomers, dimers and less densely-packed J-aggregates, absorbing light at higher wavelengths. Dye spectra in the presence of the lowest-charge RCMs resembled those of dilute dye solutions, indicating the absence of dye aggregation of any type in this case. The relationship between dye spectral changes and layer-charge densities of smectites is a general phenomenon which can potentially be used to estimate the layer charge of smectites. However, applying this method to triphenylmethane dyes, which have structurally more complicated cations, may reduce the sensitivity of the probe.
Infrared Study of Reduced and Reduced-Reoxidized Ferruginous Smectite
Authors: Fialips Claire-Isabelle , Huo Dongfang , Yan Laibin , Wu Jun , Stucki Joseph W.
Published: February 2003

Oxidation-reduction processes within natural systems greatly influence the properties of sediments, soils and clays. The objective of this experimental study was to gather new evidence for the effects of changes in redox conditions (reduction and reoxidation) on structural properties of ferruginous smectite and to understand better the mechanisms involved. The <2 µm fraction of a ferruginous smectite (sample SWa-1), which contains 17.3 wt.% of total structural Fe, was studied by infrared (IR) spectroscopy. The pure Na-saturated clay was reduced by Na dithionite for 10 to 240 min to obtain various Fe(II):(total Fe) ratios ranging from 0 to 1.0. Selected reduced samples were then reoxidized completely by bubbling O2 gas through the suspensions for up to 12 h. Infrared spectra of the initially unaltered, reduced and reduced-reoxidized samples were collected. Reduction generated changes in the three studied spectral regions (O-H stretching, M-O-H deformation, and Si-O stretching), indicating that major modifications occurred within the clay crystal beyond merely a change in Fe oxidation state. partial dehydroxylation and redistribution of Fe, and perhaps Al, cations occurred upon reduction of SWa-1, changing the structural properties of its tetrahedral and octahedral sheets. Water molecules, probably generated by dehydroxylation within the octahedral sheet upon reduction, were tightly bound to the clay surface and were possibly trapped within the clay structure. Except for dehydroxylation and the Fe oxidation state, all these modifications were largely irreversible. The tightly bound water was not completely removed upon reoxidation and the cationic rearrangements generated during reduction were not reversed: either they were preserved as in the reduced state or cations were redistributed into a different configuration from the unreduced clay.
Reductive Dissolution Kinetics of Al-Substituted Goethites
Authors: Gonzalez Estela , Ballesteros María C. , Rueda Elsa H.
Published: February 2003

Several Al-substituted goethites were synthesized by hydrolysis of Fe3+ salt solutions. The kinetics of the reductive dissolution of these goethites in dithionite-ethylenediaminetetra acetic acid (D-EDTA) was studied at pH 5.5, at 303, 323 and 333 K. The initial dissolution rate (R) per unit of surface area decreases with Al substitution. In the sample with greater Al content (G″7), the kinetic profiles of the dissolved Fe fraction vs. time gave a small positive intercept. The kinetic profile of R as a function of EDTA initial concentration shows a significant weakening in the presence of Al. The maximum is flatter and wider in Al-substituted goethite than that of pure goethite. In sample G″7, where the Al content is 11.3 mol.% the maximum is obtained when the [D]:[EDTA] initial ratio is ∼4.5 vs. 2 in un-substituted goethite. These results can be attributed to the lesser density of the more active dimeric sites, the presence of more strongly bonded Al-O-Fe with regard to Fe-O and the small value for the ≡ Al-EDTA surface species constant. Activation energy (Ea) increases with Al substitution. Its value is doubled from GO (pure goethite) to G″7 (11.3 mol.% of Al). The frequency factor (A) acts in the opposite sense to Ea, but it is not sufficient to outweigh the effect of Ea.
The Titanomagnetite to Titanomaghemite Conversion in a Weathered Basalt Profile From Southern Paraná Basin, Brazil
Authors: de Oliveira Marisa T. Garcia , Formoso Milton L. L. , da Costa Moacir Indio , Meunier Alain
Published: February 2003

This study of magnetic minerals in a weathering profile developed on plateau basalts of the subtropical southern Paraná Basin explores the evolution of titanomagnetite to titanomaghemite. Six samples studied by optical microscopy, X-ray diffraction (XRD), electron microprobe, Mössbauer spectroscopy (MS) and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) support the interpretations.

The profile studied has two major parts: an upper, porous red-clay Latosol, ∼2–8 m deep, separated by a stone line from an underlying alterite which has two different facies — its argillaceous alterite consists of a clayey matrix with a well-developed fissure system whereas the underlying boulder alterite consists of rock cores surrounded by highly-porous cortexes of Al-goethite.

Optical microscopy showed the titanomagnetite-titanomaghem ite changes in color and shape through the profile. The decrease in the lattice parameter a of the magnetic separates from the rock cores to the alterite facies was detected by XRD. Mössbauer spectroscopy identified non-stoichiometric magnetite in the rock cores and Ti-substituted maghemite in the argillaceous alterite. Chemical analysis of the titanomagnetite-titanomaghe mite grains showed that the relative proportions of TiO2 and Fe2O3 vary in the different weathering facies. By SEM and EDS we also detected the presence of minor components as Si, Al, Ca, K, Mg and Mn.

These results led to the interpretation that the titanomagnetites from the fresh Parana basalts, located in the subtropical zone of Brazil, are unstable and gradually change to titanomaghemites. The evolution of these magnetic minerals is registered in the weathering facies related to climatic changes throughout geological time.
Water Vapor Sorption Behavior of Smectite-Kaolinite Mixtures
Authors: Likos William J. , Lu Ning
Published: February 2003

An experimental program was conducted to investigate the water-vapor sorption characteristics of smectite and kaolinite mixtures. End-member smectite and kaolinite were slurry-mixed together at mass-controlled ratios corresponding to 0%, 20%, 50%, 70%, 80%, 90% and 100% smectite. Vapor desorption isotherms for the mixtures were measured at 24°C for relative humidity (RH) ranging from ∼95% to 0%.

Results show that the amount of water adsorbed by the clay mixtures at a given RH increases systematically with increasing smectite content. Derivative analysis of the sorption isotherms shows evidence of transitions between the two-, one- and zero-layer hydrate-states for the smectite-rich mixtures. The transitions become less apparent as the smectite content decreases. Monolayer coverage, specific surface area, and heat of adsorption were estimated from the isotherms using BET theory. It is shown that monolayer coverage and specific surface for the clay mixtures can be reasonably approximated by weighted averaging of the end-member clay properties. General methodologies are presented for predicting the sorption behavior (i.e. soil-water characteristics) and effective specific surface area from measurements of the end-member sorption isotherms.
Retention Mechanisms of CD on Illite
Authors: Echeverría Jesús C. , Churio Edurne , Garrido Julián J.
Published: February 2003

The adsorption of metals by clay minerals is a complex process involving different mechanisms, and is controlled by different variables which can interact. The aim of this work was to study the retention mechanisms of Cd on illite. We obtained Cd adsorption isotherms at constant pH, adsorption edges as a function of pH, adsorption isotherms at 5, 25 and 45°C (pH = 7), and response surfaces of the simultaneous effect of pH, initial concentration, ionic strength, and temperature on the retention of Cd on illite. Below pH 6, adsorption of Cd on illite is via ion exchange with H3O+ and Na+ ions which saturate the exchange sites, the exchange with Na+ being the main mechanism between pH 4.5 and 6.0. For pH values >6, the effect of ionic strength on the amount of Cd2+ retained decreased with pH, being negligible at pH 8; the proton stoichiometry was greater than for pH values <6 and an increase in the temperature favored the retention of Cd. These facts are compatible with a more specific process involving hydrolyzed species, in which Cd can associate with illite as an inner sphere complex.
Experimental Investigation of the Interaction of Clays with High-pH Solutions: A Case Study From the Callovo-Oxfordian Formation, Meuse-Haute Marne Underground Laboratory (France)
Authors: Claret Francis , Bauer Andreas , Schäfer Thorsten , Griffault Lise , Lanson Bruno
Published: February 2003

The impact of alkaline solutions (pH = 13.2) on the clay mineralogy of the Callovo-Oxfordian formation hosting the French underground laboratory for nuclear waste disposal investigation (Meuse-Haute Marne site) has been studied experimentally. Initially, each of the four samples selected as representative of the mineralogical transition in this Callovo-Oxfordian formation consists of a mixture of three main clay phases: discrete illite, discrete smectite and a randomly interstratified mixed-layered mineral (MLM) containing ∼65% of non-expandable layers. Clay separates were altered in batch reactors at 60°C using high solution:solid ratios. The mineralogy of this clay fraction and solution chemistry were monitored as a function of reaction time. In addition, the interactions between organic matter and clay particles were investigated using scanning transmission X-ray microscopy (STXM).

The clay mineralogy is little affected even though the pH is still high after 1 y reaction time. The only significant mineralogical evolution is the partial dissolution of the discrete smectite component leading to the formation of a new randomly interstratified illite-expandable MLM. Additional mineralogical transformations lead, for one sample, to the dissolution of micro-crystalline quartz and, for another sample, to the crystallization of a tobermorite-like phase. The low reactivity of clay minerals may be attributed to the presence of organic matter in the samples. In their initial state, all outer surfaces of clay particles are indeed covered with organic matter. After 1 y reaction time, STXM studies showed the basal surfaces of clay particles to be devoid of organic matter, but their edges, which are the most reactive sites, were still protected.
Benzene Displacement on Imogolite
Authors: Wilson Michael A. , Lee Garry S. H. , Taylor Renee C.
Published: February 2003

The adsorption of 13C-labeled benzene on imogolite has been studied on samples which had been evacuated and then heated to remove water below their decomposition point. After adsorption of labeled benzene, the samples were studied by nuclear magnetic resonance using non-spinning techniques. The results show that benzene can occupy more than one pore type and that water does not displace benzene from the intra-tube pores at atmospheric pressure. A further finding is that there are at least two types of adsorbed benzene in so called inter-tube pores, one of which is more rigidly held than that in intratube pores. The presence of disordered materials at the edge of pores could also play a role in altering the pore mouth thereby creating new types of pores. Moreover, where two tubes do not pack properly, space might be created where an adsorbed molecule may bind more tightly than expected in a conventional pore.
Transmission Electron Microscopy Study of Smectite Illitization During Hydrothermal Alteration of a Rhyolitic Hyaloclastite From Ponza, Italy
Authors: Bauluz Blanca , Peacor Donald R. , Ylagan Robert F.
Published: February 2003

Dioctahedral phyllosilicates from an altered rhyolitic hyaloclastite located at Ponza Island, Italy, were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The samples are from a sequence previously characterized by X-ray diffraction (XRD) methods, indicating that a complete range of illitization accompanies alteration. Backscattered electron (BSE) images, obtained from ion-milled samples, show that samples partly retain the original textures since clay minerals pseudomorph lapilli fragments and preserve vesicular texture. The lowest-grade sample studied contains obsidian clasts partially replaced by smectite. As the alteration grade increases, illitization proceeds with formation of interstratified illite-smectite (I-S), zeolites, illitic phases, feldspars and quartz. The most altered sample contains illite, mica and quartz. Lattice-fringe images show that following the formation of smectite, illitization takes place through the formation of (R=1) I-S, highly illitic I-S and illite with mica; (R=1) I-S is the only ordered interstratified I-S. The BSE and TEM images of Ponza samples show irregular cavities filled with euhedral dioctahedral clay minerals and the zeolite mordenite, providing direct evidence for neocrystallization from a fluid. Chemical compositions by analytical electron microscopy (AEM) support the sequence described. Selected area electron diffraction (SAED) patterns indicate the predominance of 1 Md polytypism both in I-S and illitic phases, and the coexistence in the more altered samples of 1Md illite and a 2-layer mica polytype (probably 2M1), without the intermediate 1M polytype generally assumed to exist in prograde sequences. Previous XRD studies indicated progressive change from cis-vacant, turbostratically stacked smectite, to interstratified cis- and trans-vacant, 1Md I-S, to trans-vacant, 1M illite, and then to 2M1 illite in Ponza Island samples. We observed a clear correlation between the chemical compositions as determined by AEM and the proportion of cis-vacant determined by XRD, suggesting that the octahedral cation distributions change in the studied samples with increasing degree of illitization.
Lepidocrocite in Hydrothermal Sediments of the Atlantis II and Thetis Deeps, Red Sea
Authors: Goldman Nurit Taitel , Koch Christian Bender , Singer Arieh
Published: February 2003

Lepidocrocite (γ-FeOOH) formation in the hydrothermal brines of the Thetis and Atlantis II Deeps in the Red Sea results in markedly different crystals (size and shape). The only foreign element associated with the crystals is Si and analyses of samples from the two deeps yielded average Si/Fe (molar) ratios of 0.03 and 0.11, respectively. The Si/Fe ratio does not affect formation of a perfect lattice along [010]. Direct observations of crystal morphology as well as X-ray diffraction patterns, Mössbauer and infrared spectra, all indicate that the Atlantis II Deep lepidocrocite is less crystalline than the Thetis Deep lepidocrocite. In one sample a poly-disperse size distribution was resolved indicating a fine-scale variation in precipitation conditions. Infrared spectroscopy suggests that the Si is adsorbed on the lepidocrocite surfaces, probably also forming polymers, as both Fe-O-Si and Si-O-Si bonds can be detected. The formation of the Atlantis II Deep lepidocrocite is due to fast oxidation of Fe2+. The blanket-like layer of lepidocrocite in Atlantis II and Thetis Deeps lepidocrocite was probably formed as a result of precipitation during an abrupt oxidation event of the brine, triggered by down-welling of a condensed oxidized brine, which originated in the northern part of the Red Sea. A difference in Si concentrations determined the different crystal properties of the lepidocrocite formed in the two deeps.
Rapid and Quantitative Measurement of Hematite and Goethite in the Chinese Loess-Paleosol Sequence by Diffuse Reflectance Spectroscopy
Authors: Ji Junfeng , Balsam William , Chen Jun , Liu Lianwen
Published: February 2003

The long, continuous deposition of dust in the Chinese loess plateau offers a unique opportunity to study the nature of Fe oxide formation in a wide range of climatic conditions. A technique to obtain quantitative estimates of the concentration of hematite and goethite in loess and paleosol samples is reported. Experiments using diffuse reflectance spectroscopy on sets of laboratory mixed and natural loess and paleosol samples show that it is possible to obtain rapid and quantitative estimates of the absolute concentration of hematite and goethite in the Chinese loess sediments. Typical loess and paleosol samples were deferrated using the CBD procedure to produce a natural matrix material to which hematite and goethite in known weight percentages were added to produce a set of calibration standards. Spectral violet, blue, green, yellow, orange, red and brightness of standards were calculated from the reflectance data and served as independent variables for a multiple linear regression analysis. The effect of changing matrix from loess to paleosol was overcome by including a variety of different loess and paleosol samples in the regression equations. The resulting calibration equations provide estimates of wt.% hematite and goethite and have correlation coefficients >0.93. The total measured hematite and goethite concentrations exhibited consistent variations with CBD extractable iron. Tests of the equations for buffering changes in matrix composition were run with samples of varying mineralogical composition (calcite, illite, etc.) and demonstrated that the equations are well buffered for changes in matrix composition from loess to paleosol.
Role of Iron Oxides in the Phosphate Adsorption Properties of Kaolinites From the Ivory Coast
Authors: Sei J. , Jumas J. C. , Olivier-Fourcade J. , Quiquampoix H. , Staunton S.
Published: February 2003

The phosphate adsorption properties of three clay samples, with kaolinite as the dominant mineral, from different deposits in the Ivory Coast have been investigated. The clays contain varying amounts of crystalline Fe oxides and kaolinite with structural Fe. All measurements were made in dilute suspension under controlled conditions of temperature, pH, ionic strength and saturating cation. Data have been fitted to Langmuir adsorption isotherms. Both P adsorption and surface area measurements have been made on samples before and after chemical removal of Fe oxides. The samples have large P adsorption capacities, which are not entirely explained by their large specific surface areas. The presence of Fe oxides makes a strong contribution to the surface area and enhances the adsorption capacities. There is little evidence that structural Fe makes a strong contribution to the enhanced P adsorption capacity.
Far Infrared Analysis of the Structural Environment of Interlayer K+, NH4+, Rb+ and Cs+ Selectively Retained by Vermiculite
Authors: Diaz M. , Huard E. , Prost R.
Published: February 2003

To get a better understanding of the mechanisms of selective retention of cations by clay minerals, we have studied the physicochemical state and the location of immobilized cations. The approach developed is based on the concomitant study of the exchange isotherms and the compensating cations/clay structure interactions, using far infrared (FIR) spectroscopy. For that, cations are used as spectroscopic probes to characterize the selective sites.

Exchanged K, Rb-, K, Cs-, K, NH4- and NH4, Cs-Llano vermiculite samples were prepared. The exchange isotherms illustrate the higher selectivity of Llano vermiculite in the following order: K+ < Rb+ < Cs+. Desorption experiments show that a 2 N MgCl2 solution can extract a small fraction of immobilized Cs+. The concomitant analyses of the exchange phenomena at microscopic (X-ray diffraction) and molecular (far and middle IR spectroscopy) levels show that: (1) only ∼65% of the interlamellar hydrated Mg2+ of Llano vermiculite is exchanged; (2) cations are randomly distributed in the interlamellar spaces; and (3) retention is strongly related to the distance between compensating cations and oxygen atoms of the ditrigonal cavity.

The low hydration energy of selectively retained cations induces strong cation/clay interactions, which give FIR absorption bands of compensating cations. The FIR absorption bands of smaller cations shift towards lower wavenumbers when the proportion of the larger cations increases, whereas the wavenumber of the larger ones is constant. This reproducible scenario shows that larger cations act as wedges and expand layers, thus increasing the distance between the smaller cations and the layers. Calculation of the distances dM-O inner and dM-O outer shows that selectively-retained cations are six-coordinated in these dehydrated systems. The decrease of the difference between dM-O outer and dM-O inner from K+ to Cs+ may explain the observed selectivity of Llano vermiculite.
Clay Mineral Changes in the Morrow Experimental Plots, University of Illinois
Authors: Velde B. , Peck T.
Published: February 2003

The clay mineralogy of soil samples from the Morrow Plot Experiment (University of Illinois, Urbana Campus) was investigated. Analysis of soil samples taken at various intervals between 1913 and 1996 indicates that there is a significant influence of cropping method on the clay minerals in the soils. Curve decomposition methods were used to identify and follow the evolution of the different clay minerals: mica, illite and two randomly mixed-layered illite-smectite phases. The most striking difference is seen for continuous corn and corn-oats-hay rotations. Little change in clay mineralogy is seen in the rotation plot while a significant loss of illitic material from different phases was noted for the continuous-corn cultivation plots. Use of NPK fertilizer since 1955 appears to restore the clay mineralogy in continuous-corn cropping compared to that of the 1913 samples. From these data it appears that the I-S minerals play the role of a K buffer, becoming K-poor when the soil cannot furnish enough K from mineral reserves of detrital phases and K-rich when the soil is able to release enough K to enter into the I-S minerals, where it is available during a growing season, for plant growth.
Two Origins of Illite at the Dexing Porphyry Cu Deposit, East China: Implications for Ore-Forming Fluid Constraint on Illite Crystallinity
Authors: Jin Zhangdong , Zhu Jinchu , Ji Junfeng , Li Fuchun , Lu Xinwei
Published: February 2003

Illite is a distinctive clay mineral formed by K alteration within hydrothermal alteration zones in porphyry Cu deposits. Based on differences in spatial distribution, Kübler index, number of swelling layers, and polytype, two kinds of illite are recognized within the Dexing porphyry Cu deposit, East China. One is a hydrothermal mineral within hydrothermally-altered granodiorite porphyry and altered tuffaceous phyllite near the contact zone with the granodiorite porphyry cupola. The hydrothermal illite is formed by illitization of plagioclase and/or micas during hydrothermal fluid-rock interaction. The considerable variation of their higher Kübler indices (0.17–1.41°Δ2θ) with swelling layer is affected by fluid/rock ratio or fluid flux. The other type of illite is a product of low-grade metamorphism within tuffaceous phyllite away from the porphyry cupola (>2 km), and has a lower Kübler index (0.06–0.13°Δ2θ), a 2M1 polytype, and no swelling layers. We suggest that, within the mineralized alteration zone, the lower the Kübler index, the stronger the degree of alteration, and the higher the copper grade. This is caused by a higher fluid/rock ratio in the middle-upper portions of the contact zone.