Packaging and integration technologies for future high-frequency power supplies

This paper reviews data from the International Technology Roadmap for Semiconductors to establish where dc-dc converters are headed in the first decade of the new millennium. It focuses on the high performance computing (high current, fast response, high power density) and portable/handheld (low profile) sectors. Magnetics and power device packaging technologies needed to allow power supplies to move to operating frequencies in the 1-10 MHz region are discussed. It introduces the concept of magnetic components fully embedded (windings and core) in PCB and silicon offering low profile and low losses at high frequency. It also reviews developments in wirebond-free power packaging such as flip-chip assembly that offer low profile, reduced parasitics and increased thermal performance. Finally, consideration is given to the changes in the power electronics industry that may need to be addressed to enable these new technologies to play a strategic role.     

In vitro assessment of a collagen sponge for engineering urothelial grafts

OBJECTIVE: To investigate the deposition of urinary crystals and the growth characteristics of urothelial cells on a collagen sponge, as a preliminary step in engineering urothelial autologous grafts. MATERIALS AND METHODS: Collagen sponges were exposed to a continuous flow of urine at pH 5.3 and 6.3 for 1 week. The sponges were examined microscopically for crystal deposition and analysed for their calcium content. Two cell lines, RT112, derived from a well-differentiated transitional cell carcinoma, and UROtsa, an immortalized urothelial cell line, were seeded on the collagen sponges. Cells were cultured for 6, 12 and 21 days. The pattern of growth was analysed by histology and immunostaining with a pan-cytokeratin antibody. Growth was assayed to quantify cell proliferation on the sponges. RESULTS: No crystals were evident on any of the collagen sponges. Calcium deposition was negligible at pH 5.3. Although calcium levels were measurable at pH 6.3, the levels were very low. Both cell lines attached and grew in a stratified manner on the collagen sponge, RT112 forming a layer 6-8 cells thick, and UROtsa a layer 4-6 cells thick; cell proliferation was maximal at 5-10 days. The sponge remained easy to handle after 3 weeks in culture. CONCLUSION: These findings show that collagen sponges support the growth and stratification of urothelial cells, and indicate that the collagen sponge is a suitable substrate for developing urothelial autologous grafts.     

The design and evaluation of online help for Unix EMACS: capturingthe user in menu design

The card-sort technique and cluster analysis were used for determining an effective organization for a help menu in Unix EMACS. Similarity data were gathered for with a card-sorting task using EMACS commands, and a hierarchical cluster analysis of the data was performed. The results indicate that differences among novices, intermediates, and experts appear with computer-based concepts such as windows and buffers, but that the sorts are more similar than they are different. It is argued that cluster analysis may aid designers in determining a functional organization, but that in the domain of this study, this organization may not help users bridge the mapping from real world tasks to computer tasks     

Epitaxial growth and piezoelectric properties of A1N,GaN, and GaAs on sapphire or spinel

Heteroepitaxial films of the III-V compounds, A1N, GaN and GaAs have been grown on insulating substrates by reactions involving Group III metal-organic compounds and Group V hydrides. The films were examined with respect to crystallography, surface topography, uniformity, residual strain, and electrical and acoustic properties with emphasis on those orientations which are of particular interest to surface acoustic wave (SAW) device applications. Aluminum nitride films up to 10 μm in thickness were grown on 1″ diameter sapphire substrates with a 5% to 10% thickness variation. The films, though characterized as single crystal by x-ray means, exhibited a grain-like structure and considerable surface faceting. The residual strain in the films depends on the crystallographic direction and increases substantially with film thickness. These films exhibit useful surface acoustic properties. Epitaxial GaN films are more easily prepared than A1N films but by contrast are semiconducting unless “doped” with Zn or Li during the growth process. Films of this material are similar crystallographically to A1N and preliminary results show that they exhibit piezoelectric properties. The lack of published data on the acoustic properties of GaN films is probably due to the difficulty in compensating the films to provide insulating layers in device structures. Preliminary results obtained on GaAs epitaxial layers are discussed briefly because of the semiconducting properties of this material. Research jointly sponsored by the Air Force Materials Laboratory, Wright-Patterson Air Force Base, under Contract F33615-70-C-1536     

Survival of salmonella transformed to express green fluorescent protein on Italian parsley as affected by processing and storage

To study the effect of processing and storage parameters on the survival of Salmonella on fresh Italian parsley, parsley bunches were dipped for 3 or 15 min in suspensions that were preequilibrated to 5, 25, or 35 degrees C and inoculated with Salmonella transformed to express enhanced green fluorescent protein. Loosely attached and/or associated, strongly attached and/or associated, and internalized and/or entrapped Salmonella cells were enumerated over 0, 1, and 7 days of storage at 25 degrees C and over 0, 1, 7, 14, and 30 days of storage at 4 degrees C using surface-plating procedures. Leaf sections obtained from samples after 0, 1, and 7 days of storage were examined using confocal scanning laser microscopy. Temperature of the dip suspension had little effect on the attachment and survival of Salmonella cells on parsley. Regardless of the temperature or duration of dip, Salmonella was internalized. Immersion for longer times resulted in higher numbers of attached and internalized cells. Microscopic observations supported these results and revealed Salmonella cells near the stomata and within cracks in the cuticle. Storage temperature had the greatest impact on the survival of Salmonella cells on parsley. When stored at 25 degrees C, parsley had a shelf life of 7 days, and Salmonella populations significantly increased over the 7 days of storage. For parsley stored at 4 degrees C, numbers of Salmonella cells decreased over days 0, 1, and 7. After 7 days of storage, there were no viable internalized Salmonella cells detected. Storage temperature represents an important control point for the safety of fresh parsley.     

Optimization of photosynthetic hydrogen yield from platinized photosystem I complexes using response surface methodology

Light-dependent hydrogen production by platinized Photosystem I isolated from the cyanobacterium Thermosynechococcus elongatus BP-1 was optimized using response surface methodology (RSM). The process parameters studied included temperature, light intensity and wavelength, and platinum salt concentration. Application of RSM generated a model that agrees well with the data for H₂ yield (R² = 0.99 and p < 0.001). Significant effects on the total H₂ yield were seen when the platinum salt concentration and temperature were varied during platinization. However, light intensity during platinization had a minimal effect on the total H₂ yield within the region studied. The values of the parameters used during the platinization that optimized the production of H₂ were light intensity of 240 μE m⁻² s⁻¹, platinum salt concentration of 636 μM and temperature of 31 °C. A subsequent validation experiment at the predicted conditions for optimal process yield gave the maximum H₂ yield measured in the study, which was 8.02 μmol H₂ per mg chlorophyll.