A SIMPLE INTEGRAL APPROACH TO STUDY VISCOUS FREE SURFACE FLOWS

A simple strategy, based on the integration of the components of the momentum balance equation, yields a small set of nonlinear algebraic equations that models viscous flow with free surfaces. This strategy is applied to two cases already studied by numerical analysis; they are (a) slot coating and (b) forward roll-coating.

The simple models presented in this work are employed to predict the behavior of both coating devices as a function of the relevant dimensionless parameters. The results obtained show that the simple models correctly estimate the general trends given by more realistic ones based on finite element analysis. The technique applied is particularly successful when the Reynolds number is small.     

Theory of Drying

This review examines the stages of drying, with the emphasis on the constant rate period (CRP), when the pores are full of liquid. It is during the CRP that most of the shrinkage occurs and the drying stresses rise to a maximum. We examine the forces that produce shrinkage and the mechanisms responsible for transport of liquid. By analyzing the interplay of fluid flow and shrinkage of the solid network, it is possible to calculate the pressure distribution in the liquid in the pores. The tension in the liquid is found to be greatest near the drying surface, resulting in greater compressive stresses on the network in that region. This produces differential shrinkage of the solid, which is the cause of cracking during drying. The probability of fracture is related to the size of the body, the rate of evaporation, and the strength of the network. A variety of strategies for avoiding fracture during drying are discussed.     

Isotropic Constitutive Model for Sintering Particle Packings

This paper presents an isotropic model for the effective viscosities of sintering particle packings. The relationship between the macroscopic stress and deformation rate is based on the behavior of individual interparticle contacts, represented by contact viscosities, and the statistics of the packing. The contact viscosities depend on the contact area, which is the primary variable used to describe the state of the packing. A direct consequence of this choice of state variable is that the effective viscosities are identically zero for an undeformed and unsintered packing. Specific results are presented for the case of Newtonian viscous materials. The model is compared with existing models for porous Newtonian viscous materials. Experiments conducted with spherical glass powder packings show good agreement with the model. Finite-element simulations using the model have been used to study forging of a pellet.     

Ractions of SiC with H2/H2O/Ar Mixtures at 1300°C

The reactions of a sintered α-SiC with 5% H₂/H₂O/Ar at 1300°C were studied. Thermomchemical modeling indicates that three reaction regions are expected, depending on the initial water vapor or equivalently oxygen content of the gas stream. A high oxygen content ( P (O₂) > 10⁻²² atm) leads to a SiO₂ formation. This generally forms as a protective film and limits consumption of the SiC (passive oxidation). An intermediate oxygen content (10⁻²² atm > P (O₂) > 10⁻²⁶ atm) leads to SiO and CO formation. These gaseous products can lead to rapid consumption of the SiC (active oxidation). Thermogravimetric studies in this intermediate region gave reaction rates which appear to be controlled by H₂O gas-phase transport to the sample and reacted microstructures showed extensive grain-boundary attack in this region. Finally, a very low oxygen content ( P (O₂) < 10⁻²⁶ atm) is thermochemically predicted to lead to selective removal of carbon and formation of free silicon. Experimentally low weight losses and iron silicides are observed in this region. The iron silicides are attributed to reaction of free silicon and iron impurities in the system.     

Diffusion in Solids via Nuclear Track Analysis

Nuclear track analysis has been used to follow the diffusion of melted lithium hydroxide in pellets of aluminum oxide as a function of temperature and time. α particle tracks, created by thermal neutrons on an allyl diglycol carbonate monomer film, are visible under a high-power optical microscope after chemical etching in a sodium hydroxide solution. The number of tracks present at various depths within each pellet is proportional to the concentration of lithium hydroxide. Using a one-dimensional diffusion model with appropriate boundary conditions, values of the lithium hydroxide diffusion coefficient in the porous pellet have been determined. The diffusion coefficients, as well as their temperature dependency, are consistent with expectations for this type of system and it is concluded that nuclear track analysis is a viable technique for solid-state diffusion studies in appropriate materials.     

A DISTANCE MEASURE FOR CLASSIFYING ARIMA MODELS

Abstract. In a number of practical problems where clustering or choosing from a set of dynamic structures is needed, the introduction of a distance between the data is an early step in the application of multivariate statistical methods. In this paper a parametric approach is proposed in order to introduce a well-defined metric on the class of autoregressive integrated moving-average (ARIMA) invertible models as the Euclidean distance between their autoregressive expansions. Two case studies for clustering economic time series and for assessing the consistency of seasonal adjustment procedures are discussed. Finally, some related proposals are surveyed and some suggestions for further research are made.     

FISHER'S INFORMATION MATRIX FOR SEASONAL AUTOREGRESSIVE-MOVING AVERAGE MODELS

Abstract. Two procedures are described for obtaining Fisher's information matrix of a multiplicative seasonal autoregressive-moving average process. They can be useful in determining the asymptotic covariance matrix of Gaussian maximum likelihood estimators of the parameters. Components of the information matrix are expressed in the first procedure as integrals of rational functions. The second procedure makes use of the autocorrelation function of several autoregressive processes.     

Memory Fault Modeling Trends: A Case Study

In recent years, embedded memories are the fastest growing segment of system on chip. They therefore have a major impact on the overall Defect per Million (DPM). Further, the shrinking technologies and processes introduce new defects that cause previously unknown faults; such faults have to be understood and modeled in order to design appropriate test techniques that can reduce the DPM level. This paper discusses a new memory fault class, namely dynamic faults, based on industrial test results; it defines the concept of dynamic faults based on the fault primitive concept. It further shows the importance of dynamic faults for the new memory technologies and introduces a systematic way for modeling them. It concludes that current and future SRAM products need to consider testability for dynamic faults or leave substantial DPM on the table, and sets a direction for further research.     

Least squares based and gradient based iterative identification for Wiener nonlinear systems

This paper derives a least squares-based and a gradient-based iterative identification algorithms for Wiener nonlinear systems. These methods separate one bilinear cost function into two linear cost functions, estimating directly the parameters of Wiener systems without re-parameterization to generate redundant estimates. The simulation results confirm that the proposed two algorithms are valid and the least squares-based iterative algorithm has faster convergence rates than the gradient-based iterative algorithm.