Advective-diffusive gaseous transport in porous media: the molecular diffusion regime

1993 Spring.Includes bibliographical references.Traditional mathematical models for advective-diffusive transport in porous media fail to represent important physical processes when fluid density depends on composition. Such is the case for gas mixtures comprised of species with differing molecular masses, such as found in the vadose zone near chlorinated hydrocarbon sources. To address problems of this nature, a more general advection-diffusion (A-D) model is presented, which is valid for porous media with permeabilities exceeding 10-10 cm2 (where Klinkenberg and Knudsen effects are negligible). The new mathematical model is derived by thermodynamic means, based on identifying the meaning of Darcy's advective reference velocity in terms of a weighted average of species drift velocities~ The resulting model has no additional parameters, and introduces no additional complexity or nonlinearity when compared to the traditional A-D model most commonly used in hydrology and environmental science. Because the form of traditional A-D models is retained, the new formulations fit readily into existing numerical simulators for the solution of subsurface transport problems. The new model is equivalent to the Dusty-Gas Model of Mason et al. (1967) for cases where the molecular diffusion regime prevails and pressure, temperature, and forced diffusion are negligible. Further support of the model is provided by hydrodynamic analysis, accounting for the diffusive-slip flux identified by Kramers and Kistemaker (1943). The new model is analytically compared to two existing A-D models, one from the hydrology literature, where Darcy's law is assumed to yield a mass-average velocity, and one from the chemical engineering literature, where Darcy's law is assumed to yield a mole-average velocity. Significant differences are shown to exist between the three transport models. The new model is shown to match closely with the experimental data of Evans et al. (1961a), while the existing A-D models are shown to fail in this regard

Tangible user interfaces and social interaction in children with autism

Tangible User Interfaces (TUIs) offer the potential for new modes of social interaction for children with Autism Spectrum Conditions (ASC). Familiar objects that are embedded with digital technology may help children with autism understand the actions of others by providing feedback that is logical and predictable. Objects that move, playback sound or create sound – thus repeating programmed effects – offer an exciting way for children to investigate objects and their effects. This thesis presents three studies of children with autism interacting with objects augmented with digital technology. Study one looked at Topobo, a construction toy augmented with kinetic memory. Children played with Topobo in groups of three of either Typically Developing (TD) or ASC children. The children were given a construction task, and were also allowed to play with the construction sets with no task. Topobo in the task condition showed an overall significant effect for more onlooker, cooperative, parallel, and less solitary behaviour. For ASC children significantly less solitary and more parallel behaviour was recorded than other play states. In study two, an Augmented Knights Castle (AKC) playset was presented to children with ASC. The task condition was extended to allow children to configure the playset with sound. A significant effect in a small sample was found for configuration of the AKC, leading to less solitary behaviour, and more cooperative behaviour. Compared to non-digital play, the AKC showed reduction of solitary behaviour because of augmentation. Qualitative analysis showed further differences in learning phase, user content, behaviour oriented to other children, and system responsiveness. Tangible musical blocks (‘d-touch’) in study three focused on the task. TD and ASC children were presented with a guided/non-guided task in pairs, to isolate effects of augmentation. Significant effects were found for an increase in cooperative symbolic play in the guided condition, and more solitary functional play was found in the unguided condition. Qualitative analysis highlighted differences in understanding blocks and block representation, exploratory and expressive play, understanding of shared space and understanding of the system. These studies suggest that the structure of the task conducted with TUIs may be an important factor for children’s use. When the task is undefined, play tends to lose structure and the benefits of TUIs decline. Tangible technology needs to be used in an appropriately structured manner with close coupling (the distance between digital housing and digital effect), and works best when objects are presented in familiar form

Measurement of snowpack properties using active FM-CW microwave systems

1982 Summer.Includes bibliographical references.This paper reports on the use of an FM-CW active microwave system, in a research mode, to remotely sense water equivalence and liquid water content of snowpacks. A three-component "electrical path length" dielectric mixture model is described which accounts for the microwave system response as a function of operating frequency, snow density and depth (water equivalence), and liquid water content. This physically based model is compared to currently accepted, semi-empirical mixture models and the limited data that exists. The "electrical path length" model compares favorably and has a distinctly simpler form than other models, making it workable for the specific problem addressed. It is concluded that by collecting data in two frequency ranges (just below the relaxation frequency of water), the depth of ice, the depth of liquid water, and thus the water equivalence of dry or wet snowpacks could be determined. Liquid water content determinations, made on a real-time basis, could then serve as invaluable melt-rate indexes for remote sites. Recommendations are given for the design configuration of an operational system, which could be incorporated into hydrometeorological data acquisition platforms such as SNOTEL

A Physiological Role for Amyloid Beta Protein: Enhancement of Learning and Memory

Amyloid beta protein (A[beta]) is well recognized as having a significant role in the pathogenesis of Alzheimer's disease (AD). The reason for the presence of A[beta] and its physiological role in non-disease states is not clear. In these studies, low doses of A[beta] enhanced memory retention in two memory tasks and enhanced acetylcholine production in the hippocampus _in vivo_. We then tested whether endogenous A[beta] has a role in learning and memory in young, cognitively intact mice by blocking endogenous A[beta] in healthy 2-month-old CD-1 mice. Blocking A[beta] with antibody to A[beta] or DFFVG (which blocks A[beta] binding) or decreasing A[beta] expression with an antisense directed at the A[beta] precursor APP all resulted in impaired learning in T-maze foot-shock avoidance. Finally, A[beta]1-42 facilitated induction and maintenance of long term potentiation in hippocampal slices, whereas antibodies to A[beta] inhibited hippocampal LTP. These results indicate that in normal healthy young animals the presence of A[beta] is important for learning and memory

Variances: A Canary in the Coal Mine for Zoning Reform?

There is perhaps no area of land use law where practice departs more from legal doctrine than the realm of zoning variances. According to the legal doctrine, variances are to be granted sparingly, providing a “safety valve” that alleviates unique hardships encountered by a property owner. In practice, variances are granted at high rates—often around ninety percent of applications are approved—and, in some jurisdictions, in high volumes. In such cases, variances effectively serve as a rezoning, enabling jurisdictions to permit otherwise prohibited uses and allow growth and development to occur without addressing needed zoning reforms. By allowing neighbors the opportunity to weigh in on the smallest of changes, with little attention to the relevant legal doctrine, they also create significant uncertainty, delay, and cost for property owners. This problem is particularly acute in the City of Boston, where the city grants thousands of variances each year. In this symposium contribution, we share the results of an empirical study of variance decisions in Boston. We compare Boston to three neighboring jurisdictions: Cambridge, Brookline, and Somerville. We find that variances in Boston are, consistent with prior studies elsewhere, granted at a very high rate. Looking at the substance of these decisions, we find that little attention is given to the legal requirements for a variance. Instead, decisions are shaped by a desire to help individual applicants, a willingness to permit development consistent with the neighborhood, and the policy preferences of board members. This study suggests a number of lessons for reformers. Variance decisions shed light on particularly onerous elements of local zoning, revealing targets for reform. The process itself highlights how local residents understand zoning and their expectations regarding their own role in land use decision-making. In jurisdictions that rely heavily on variances to permit new development, reformers will need to grapple with how they might substitute the voice residents currently exercise through the variance process

High Q-factor Sapphire Whispering Gallery Mode Microwave Resonator at Single Photon Energies and milli-Kelvin Temperatures

The microwave properties of a crystalline sapphire dielectric whispering gallery mode resonator have been measured at very low excitation strength (E/hf=1) and low temperatures (T = 30 mK). The measurements were sensitive enough to observe saturation due to a highly detuned electron spin resonance, which limited the loss tangent of the material to about 2e-8 measured at 13.868 and 13.259 GHz. Small power dependent frequency shifts were also measured which correspond to an added magnetic susceptibility of order 1e-9. This work shows that quantum limited microwave resonators with Q-factors > 1e8 are possible with the implementation of a sapphire whispering gallery mode system