A model for delineating the relative importance of particle size, particle shape, and porosity, (and their interactions), in explaining the variability of hydraulic conductivity of a granular porous medium is developed and tested. Three types of porous media are considered in this work: spherical glass beads; granular sand; and irregularly shaped, shredded glass particles. A reliable method for quantifying the three‐dimensional shape and packing of large samples of irregular particles based on their angle of repose is presented. The results of column experiments indicate that in the size range examined (i.e., 149 μm to 2380 μm), the single most important predictor of hydraulic conductivity is seen to be particle size, explaining 69% of the variability. Porous media comprising irregular particles exhibit lower hydraulic conductivity only for the larger (707 to 841 μm) particles. For the smaller (149 to 177 μm) particles, particle shape has no observable influence on hydraulic conductivity. The results of the regression analysis reveal the importance of the interaction between particle size and porosity, indicating that similar pore configurations for a given type of particle are not achieved at different sizes. This empirical model seems to provide better estimates of the hydraulic conductivity of granular porous media comprising irregular particles than selected models based solely on grain size, including Hazen, Kozeny‐Carman, and more recently Alyamani and Sen.

An ion‐exchange model originally developed for pure oxides prepared in the laboratory is extended to study of ion exchange and surface charge on a naturally occurring montmorillonite clay. The range of surface charges (−2.0 × 10−6 to 0 mol/m2) measured for montmorillonite with various electrolyte solutions and clay pretreatments is within the range of those measured for a wide variety of oxides prepared in the laboratory (−6.0 × 10−6 to 1.0 × 10−7 mol/m2), including MnO2‐IC1, MnO2‐IC12, MnO2‐IC22, titanium dioxide, ferric oxide, and aluminum oxide. In addition, fitted parameter values for lateral interaction constants and equilibrium constants for the acid sites that characterize ion exchange on montmorillonite are on the same order of magnitude as those obtained for pure oxides. Surface charge of montmorillonite in sodium nitrate solution is measured to be approximately 15 to 25% greater than that measured between a pH of 4 and 9 in calcium chloride solution. This difference is attributed to the greater charge on the calcium (2+) ion; thus, its stronger electrostatic attraction to the acid hydroxyl site. An order of magnitude change in solids concentration (Cp) can lead to a difference in measured net surface charge density of the same oxide sample of several orders of magnitude. This difference increases at higher pH, indicating the importance of reporting the corresponding Cp at which experiments are conducted.

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We describe a training program to teach applied behavior analysis (ABA) knowledge competencies to paraprofessional staff (N = 47) at a habilitation services agency for adults with developmental disabilities. Before and following training, staff completed assessment of knowledge tests for three content areas: basic le arning principles, instructional strategies, and prompting and prompt-fading methods. Training was implemented in a group format that included a standardized curriculum, didactic presentation, case illustration, and directed discussion. Average tests scores (percent correct) for the three ABA knowledge competencies increased from pretraining to posttraining. Practical considerations relative to large-scale staff training are discussed.

There is little information about the sleep patterns of adults who have mental retardation and are supported in the community. In the present study, direct-care staff recorded sleep behaviors of 59 adults residing in 16 suburban group homes. Based on direct observation and measurement procedures, the adults averaged 7.9 hours of sleep each evening and had low incidence of sleep problems. Sleep duration was not influenced by age, gender, degree of mental retardation, or psychiatric status. Adults taking antidepressant medication (SSRI) had fewer hours of sleep. We discuss implications of these findings and factors contributing to healthy sleep hygiene among community-living adults with mental retardation.