Bulk and microscopic properties of copolymer networks in mixed aqueous solvents

Amphiphilic films and hydrogels have been prepared from ethanol/water solutions containing a hydrocarbon-grafted water-soluble cellulose ether. These materials are characterized by dispersed hydrophobic microdomains which form spontaneously in the solvent due to the inherent incompatibility of the side chains with water. At low applied shear stress, the microdomains behave as temporary linkages of finite lifetimes, imparting viscoelastic properties to the networks. The molecular weight between microdomains was found to be independent of the volume fraction of polymer in the gel, and the number of linkages per backbone ranges from 22.8 ± 1.3 to 26.2 ± 1.5 over the frequency range 30–50 rad/s. The behavior of the solutions and gels was characterized using fluorescence and dynamic rheological measurements. It was demonstrated that the microdomains are capable of sequestering water-insoluble solutes. © 1992 John Wiley & Sons, Inc.     

The possible role of intermediate NH species in oscillations of the NO+H2 reaction on noble metal surfaces

A comparative study of the thermodynamic properties of adsorbed NH_n species (n = 0, 1, 2, 3) on transition metal surfaces is performed by using the semi-empirical method of interacting bonds. The principal difference between single crystal surfaces exhibiting oscillatory behavior in the NO+H₂ reaction, and those surfaces which do not show such a behavior is that the combination reaction of NH species can easily proceed in the former case, whereas it is substantially endothermic on the latter surfaces.A trigger-like route for the oscillatory behavior is considered where the combination reaction of NH species operates as a temporary reaction pathway. This pathway practically does not contribute to the N₂ formation until the nitrogen coverage reaches some critical value, which ensures a sufficiently close distance between adjacent NH particles. The trigger pathway starts upon reaching that stage initiating the surface wave propagation, and stops immediately when the wave propagation is completed. The surface becomes then nearly clean and ready for the next oscillatory cycle. In this way, the feedback mechanism and the critical point of the regular wave initiation can be understood without any further assumptions. An alternative key reaction is also considered.     

The dynamics of random interfaces in phase transitions

A review is given of recent developments involving the dynamics of random interfaces formed in the evolution of metastable and unstable systems. Topics which are discussed include interface growth and nonequilibrium dynamical scaling. The possibility of there being dynamical universality classes in first-order phase transitions is also discussed. There are a large number of systems of experimental interest which include binary alloys, binary fluids, and polymer mixtures. Other systems studied by computer simulation include the kinetic Ising, Potts, andZ _N models.Work supported by NSF grant No. DMR-8013700.     

Linear restrictions and two step least squares with applications

In this paper we consider the full rank regression model with arbitrary covariance matrix: Y = Xß + ε. It is shown that the effect of restricting the information Y to T = A′Y may be analyzed through an associatedi regression problem which is amenable to solution by two step least squares. The results are applied to the important case of missing observations, where some classical results are rederived.     

The asymptotic validity of invariant procedures for the repeated measures model and multivariate linear model

Fairly general sufficient conditions are given to guarantee that invariant tests about means in the multivariate linear model and the repeated measures model have the correct asymptotic size when the normal assumption under which the tests are derived is relaxed. These conditions are the same as Huber's condition which guarantees asymptotic validity of the size of the F-test for the univariate linear model.     

THE ECONOMICS OF TIMBER SUPPLY: AN ANALYTICAL SYNTHESIS OF MODELING APPROACHES

The joint supply of timber and other services from forest environments plays a central role in most forest land debates. This paper defines a general conceptual model of timber supply that provides the context for discussing both individual harvest choice and aggregate supply models. While the structure and breadth of these models has developed considerably over the last twenty years, unresolved issues remain. Supply formulations that account for the quality and vintage distribution of forest capital will be necessary for improving medium- and long-run forecasts. This will be especially important for examining the potential impacts of structural changes in forest production and timber markets. In addition, consistent aggregation of individual owners to total supply will be required to address changing forest land ownership patterns.     

归一化偏差本体反射特征的研究

使图像获得不受光照和几何条件影响的颜色特性描述是实现颜色恒常性的关系，利用双色反射模型和有限维线性模型，提取归一化偏差体反射特征。被实验证明是实现颜色恒常性的一个重要途径，本文详细阐述了归一化偏差本体反射特征的特性，其计算方法，应用的前提条件，以及应用限制，并在实际图像处理中，考虑到了这些影响的因素。     

中立型线性控制系统的最优控制

本文将就形如　的中立型线性控制系统进行深入讨论，给出此类系统的最优控制的最大值原理，并举例说明这一重要结论在经济管理系统中的应用。