JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact

As one increases the concentration of a colloidal suspension, the system exhibits a dramatic increase in viscosity. Beyond a certain concentration, the system is said to be a colloidal glass; structurally, the system resembles a liquid, yet motions within the suspension are slow enough that it can be considered essentially frozen. For several decades, colloids have served as a valuable model system for understanding the glass transition in molecular systems. The spatial and temporal scales involved allow these systems to be studied by a wide variety of experimental techniques. The focus of this review is the current state of understanding of the colloidal glass transition, with an emphasis on experimental observations. A brief introduction is given to important experimental techniques used to study the glass transition in colloids. We describe features of colloidal systems near and in glassy states, including increases in viscosity and relaxation times, dynamical heterogeneity and ageing, among others. We also compare and contrast the glass transition in colloids to that in molecular liquids. Other glassy systems are briefly discussed, as well as recently developed synthesis techniques that will keep these systems rich with interesting physics for years to come.

February 1999This is a preprint of a paper intended for publication in a journal or proceedings. Since changes may be made before publication, this preprint is made available with the understanding that it will not be cited or reproduced without the permission of the author. PREPRINTThis paper was prepared for submittal to the DISCLAIMER This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. 1999-01- Charles K. WestbrookLawrence Livermore National Laboratory ABSTRACT This paper proposes a structure for the diesel combustion process based on a combination of previously published and new results. Processes are analyzed with proven chemical kinetic models and validated with data from production-like direct injection diesel engines. The analysis provides new insight into the ignition and particulate formation processes, which combined with laser diagnostics, delineates the twostage nature of combustion in diesel engines. Data are presented to quantify events occurring during the ignition and initial combustion processes that form soot precursors.A framework is also proposed for understanding the heat release and emission formation processes.

We use confocal microscopy to directly observe 3D translational and rotational diffusion of tetrahedral clusters, which serve as tracers in colloidal supercooled fluids. We find that as the colloidal glass transition is approached, translational and rotational diffusion decouple from each other: Rotational diffusion remains inversely proportional to the growing viscosity whereas translational diffusion does not, decreasing by a much lesser extent. We quantify the rotational motion with two distinct methods, finding agreement between these methods, in contrast with recent simulation results. The decoupling coincides with the emergence of non-Gaussian displacement distributions for translation whereas rotational displacement distributions remain Gaussian. Ultimately, our work demonstrates that as the glass transition is approached, the sample can no longer be approximated as a continuum fluid when considering diffusion. R apidly cooling a glass-forming liquid fundamentally changes the nature of fluid transport at a molecular scale (1-7). For a tracer in a continuum fluid, the translational and rotational diffusion coefficients D T and D R , respectively, depend on temperature T and viscosity η as D ∝ T/η. Therefore, the ratio D T /D R is a constant that is independent of both T and η. However, this relationship breaks down in the deeply supercooled regime near the glass transition, according to experiments with molecular glass formers and also molecular dynamics simulations (1)(2)(3)(8)(9)(10)(11)(12)(13)(14).Experiments with glass-forming materials find that rotational diffusion remains strongly coupled with viscosity, where D R ∝ η −1 , whereas translational diffusion decouples, developing a fractional dependence on η where D T ∝ η −ξ with ξ < 1 (2, 8, 15). Near the glass transition, D T can be enhanced by two orders of magnitude over what would be calculated from the material's viscosity. The rotational diffusion coefficients from these experiments are inferred from measurements related to molecular rotations, and are evaluated using the "Debye model" due to an inability to directly observe molecular rearrangements in a material's bulk (3, 8-10, 16, 17). This experimental limitation has inspired computational studies where diffusion can be calculated using the Debye model and also a complementary method, the "Einstein formulation," which is more directly related to the trajectories of the diffusing objects. These simulations studied pure systems of water (9), ortho-terphenyl (10), and hard dumbbell particles (11). Intriguingly, the simulations found that decoupling depends qualitatively on the analysis method: They find rotational motion is enhanced over translational motion when quantified with the Einstein formulation, with the opposite being true in the Debye formulation. The results from these simulations raise the need for a critical reexamination of our current understanding of the relationship between translational and rotational diffusion, and only through direct observation can these differences be add...

Purpose -The purpose of this paper is to identify variables that intervene in the relationship between shopping center image and frequency of visits to that shopping center. Variables investigated as intervening are desires, intentions, and positive anticipated emotions. Design/methodology/approach -The method uses a two wave mail survey. One wave gathers intentions and variables antecedent to intentions while a second wave gathers behavioral data. Findings -Findings suggest that desire (i.e. motivation), intention, and positive anticipated emotions intervene between shopping center image and frequency of shopping center visits. Positive anticipated emotions are not emotions felt while shopping but are the expected emotional consequences of achieving a goal, in this case visiting a shopping center. Visiting a shopping center might be a goal in itself or it could be the means to goal attainment (e.g. shopping to get a product). Research limitations/implications -A limitation of the study is that results are aggregated across types of shopping centers and across respondent classifications. Practical implications -Results provide evidence that desire, intention, and positive anticipated emotions intervene between shopping center image and frequency of visits to the shopping center. Implications for shopping center managers are guidance for allocating resources towards increasing desire, intention, and positive anticipated emotions. Originality/value -The value of this study is investigation of the process by which shopping center image impacts the frequency of visits to a shopping center. Focusing on this process should allow shopping center managers to more efficiently allocate resources. The value of this study is offering resource allocation guidance to shopping center managers.