Uncoupling thermal problems of terminal storage of spent nuclear fuel assemblies in bedded salt

Spent nuclear fuel assemblies stored in bedded salt can be modeled with a large array of dimensioned decay heat sources (spent fuel assemblies) in an extended thermal conducting media. Although a finite-difference or finite-element representation of the total storage facility could be established, regions of the repository should be analyzed separately since a model of the total repository would require formidable digital computing capacity. This paper explains the basis for thermally analyzing the total storage facility with separate models for the stored fuel assembly package and the salt medium. In addition, the effect of fuel assembly packaging on the maximum fuel temperature, the related problems of fuel handling prior to storage, and uncoupling of the effects of mine ventilation and conduction in the salt medium are discussed.     

THE RESIDENTIAL SEGREGATION OF AMERICAN INDIANS IN METROPOLITAN AREAS OF MICHIGAN

American Indian or Native American residential segregation is viewed within the general framework of ecological theory. According to theorists of human ecology, variation in segregation between groups relates directly to measurable differences on social and economic variables. This study uses 1980 census tract data and the index of dissimilarity to measure the extent of residential segregation in Michigan's 12 Standard Metropolitan Statistical Areas. Correlation coefficients were computed to assess whether a strong relationship exists between the residential segregation of American Indians and the spatial distribution of housing value and rent. The findings revealed that Indian-white residential segregation is lower than black-white segregation and that American Indians are more segregated from blacks than from whites. The segregated distribution pattern of American Indians is not strongly related to the cost of housing.     

Relating Requirements and Architectures: A Study of Data-Grids

The requirements and architecture of any complex software system are highly interdependent. We have studied the relationship between these two concerns in several data-Grid systems. Data-Grids are characterized by an infrastructure that focuses on the coordinated management of, and access to distributed data resources. We survey current data-Grid projects to demonstrate that a set of general requirements for data-Grid systems can be identified. Architectural styles are a way of highlighting design and engineering similarities between software systems. We consider the styles that are exhibited by current data-Grids and use a lightweight methodology to analyze how these styles support general requirements. Our conclusions provide guidelines to assist the data-Grid developer in making informed architectural choices.     

Film as <Emphasis Type="Italic">Explicador</Emphasis> for Hypertext

A few ideas from film theory, most notably Eisenstein's concept of montage, can improve students' understanding of hypertexts and lessen their resistance to open-ended, nonlinear narratives. These structural characteristics, so frustrating to many new readers of hypertext, can also be found in popular and experimental films. In particular, Godfrey Reggio's (1983) documentary Koyaanisqatsi provides a good starting point for merging hypertext and film theory. Koyaanisqatsi not only broke new ground for documentary film; its structure also resembles Landow's model for an axial hypertext. At the same time, techniques pioneered by Landow, Joyce, Guyer, and others involved in creating and critiquing hypertext can be used to examine film. Having students look closely at Koyaanisqatsi's composition allows them to become amateur cinematographers, who now possess software for breaking a film down and examining its composition, montage, transitions, subliminal messages, and motifs – a process that may then be applied to hypertext.     

Finite element modelling of nanostructured piezoelectric resonators (NAPIERs)

A new modification to the traditional piezoelectric thin film bulk acoustic wave resonator (FBAR) and solidly mounted acoustic wave resonator (SMR) is proven to significantly improve their performances. The proposed design involves the surface micro/nano structuring of planar piezoelectric thin films to realize an array of a large number of rod-like structures. In contrast to the plate-like thickness extensional resonance in traditional FBAR and SMR devices, the rod-like structures can be excited in their length extensional resonance, yielding a higher electromechanical coupling factor and effectively eliminating the spurious resonances from lateral modes of vibration. The designs have been investigated by two and three-dimensional finite element analyses and one-dimensional transmissionline modelling. The results show that significant increases in the electromechanical coupling factor of ca. 40% can be achieved by using the rod-like length extensional resonances as compared with the plate-like thickness extensional resonances in traditional devices. Simulations show that rod width-to-thickness aspect ratios of less than 0.5 could result in an electromechanical coupling factor (k2eff) of over 10% for a zinc oxide device, compared with approximately 7% for a conventional design.     

Effectiveness of SiGe Buffer Layers in Reducing Dark Currents of Ge-on-Si Photodetectors

The effectiveness of thin SiGe buffer layers in terminating threading dislocations and reducing photodiode dark current for Ge epitaxially grown on Si (001) has been investigated. The structural morphology of the films was studied by atomic force microscopy and transmission electron microscopy. The dark current of Ge on Si photodiodes can be reduced by over an order of magnitude by incorporating two different composition SiGe buffer layers. The origin of dark current and the effectiveness of thermal annealing the SiGe layers were also studied     

Control of Fano resonances and phase of a multi-terminal Aharanov-Bohm ring with three embedded quantum dots

We study a four-terminal AB-ring with three embedded quantum dots in one arm. A tight-binding model is employed to analytically obtain the transmission through the system. Results show that the magnitude and sharpness of the resonance phase-jumps diminish as a function of the degree of coupling to the extra terminals. The Fano resonance zeros become complex with a non-zero coupling matrix element to the extra terminals. The zeros can be returned to the real energy axis by increasing the flux for values of the coupling less than a critical value. A simple analytical model of the Fano resonances shows naturally how the phase transition across the resonance peak will soften and diminish in the case where the transmission zero energy is no longer real, but complex.