Measurements of Solid Spheres Bouncing Off Flat Plates

Recent years have seen a substantial increase of interest in the flows of granular materials whose rheology is dominated by the physical contact between particles and between particles and the containing walls. Considerable advances in the theoretical understanding of rapid granular material flows have been made by the application of the statistical methods of molecular gas dynamics (e.g., Jenkins and Savage (1983), Lun et al. (1984)) and by the use of computers simulations of these flows (e.g., Campbell and Brennen (1985), Walton (1984)). Experimental studies aimed at measurements of the fundamental rheology properties are much less numerous and are understandably limited by the great difficulties involved in trying to measure velocity profiles, solid fraction profiles, and fluctuating velocities within a flowing granular material. Nevertheless, it has become clear that one of the most severe problems encountered when trying to compare experimental data with the theoretical models is the uncertainty in the material properties governing particle/particle or particle/wall collisions. Many of the theoretical models and computer simulations assume a constant coefficient of restitution (and, in some cases, a coefficient of friction). The purpose of the present project was to provide some documentation for particle/wall collisions by means of a set of relatively simple experiments in which solid spheres of various diameters and materials were bounced off plates of various thickness and material. The objective was to provide the kind of information on individual particle/wall collisions needed for the theoretical rheological models and computer simulations of granular material flows: in particular, to help resolve some of the issues associated with the boundary condition at a solid wall. For discussion of the complex issues associated with dynamic elastic or inelastic impact, reference is made to Goldsmith (1960) and the recent text by Johnson (1985)

Random Displacement Modulus and Damping Determination

Modulus and damping values were determined for both undisturbed and remolded silty sand specimens by cyclic triaxial methods utilizing both sinusoidal and random displacement stroke control. Remolded specimens were prepared at 3 different dry unit weights using a preparation technique that gave the same formation factor as the undisturbed specimen. Results indicated that the random displacement method tends to produce results which are similar to those obtained by the sinusoidal procedure at shearing strain levels less than 10-1 %. At shearing strain levels greater than 10-1 % the random displacement method gives lower modulus and higher damping ratio values when compared to the sinusoidal procedure. In addition, stress history effects as demonstrated by the location of the cycle in the record being analyzed were observed not to be important over the sample unit weights investigated

Coastal Bluff Retreat at Big Lagoon, California

Big Lagoon, located 30 miles north of Eureka, California is formed behind a bay barrier built across the mouth of a drowned river valley. To the south of the bay the beach follows rising wave cut slightly cemented sand and gravel sea cliffs and terminates at the south end of Agate Beach. The retreat of these sea cliffs and its effect on property development along the top of the cliff is the focus of the paper. Measurements of bluff retreat in this area have been documented extensively from November 1941 to March 1986 through ground surveys and air photos. Review of the data indicates that the retreat rate is not constant along the cliff but has either been decreasing or remaining the same over the last 45 years. Using information on the rate of retreat, a method is developed to predict the cliff erosion in the future

The Occurrence and Distribution of Heterandria formosa (Teleostei, Poeciliidae) in Lowndes County, Georgia

Heretofore in the literature, Heterandria formosa had not been reported from Lowndes County, Georgia. Based on a survey of Lowndes County; we discovered eight localities from the southeast­ern portion of the county that collectively produced 30 specimens of H. formosa. The southeastern portion of the county is primarily flatwoods with numerous wetlands and low gradient streams compared to the remainder of the county, which is typified by a more upland habitat with greater relief and greater stream gradients. It is postulated that the greater stream gradients inhibited the migration of H. formosa into the southwestern and northern portions of the county

Response of Non-Saturated Soil to Cyclic Loading

The response of partially saturated and dry sand materials under cyclic loading is controlled by the compressibility of the pore fluid. For dry sand the limiting axial and volumetric strain occurs within 5 to 15 cycles of load application and is a function of the number of cycles of cyclic stress, relative density, and effective consolidation pressure. In addition the axial strain is shown to be independent of the consolidation stress ratio for loose sand and decreases with increasing consolidation stress ratio for dense sand under a constant cyclic stress

Une bibliothèque de recherche face à l'édition électronique

Le développement des collections de périodiques a toujours constitué une composante majeure des politiques d'acquisition des bibliothèques de recherche. Aujourd'hui, les voilà confrontées simultanément, et de manière aiguë, à une difficulté certes récurrente : l'augmentation ininterrompue du coût des abonnements, et à une nouveauté radicale encore très difficile à maîtriser et qui engendre plutôt des surcoûts : la mise sur le marché de documents numérisés, principalement des périodiques. Organe d'un établissement pionnier en matière d'utilisation des réseaux informatiques pour la diffusion des résultats de la recherche, la bibliothèque du CERN a depuis plusieurs années déjà intégré cette nouvelle donne dans sa politique d'acquisition