Three garnet compositions for bubble domain memories

The choice of magnetic garnet compositions for bubble memories is always a compromise dictated by the material requirements generated by the specifications on the memories. The three compositions reported, Y_2.62Sm_o.38Fe_3.85Ga_1.15O₁₂, Gd_2.lLu_O.9Fe_4.4Al_0.6O₁₂, and Y_l.92Sm_0.1Ca_0.98Fe_4.02Ge_0.98O₁₂, represent three examples of such a compromise. The first composition is excellent for use in circuits operating at 100 KH_z over a temperature range of -20° to 80°C. The second has a mobility up to 5000 cm/sec/0e and is capable of very high speed operation at the sacrifice of stability toward temperature. The third exhibits excellent stability toward temperature and has operated at 1 MHz but is compositionally more complex. Melt compositions for film growth and a summary of magnetic properties are presented for the three compositions. Factors to be weighed in composition selection for bubble domain memories are discussed.     

Infra-red striagraph topography for imaging defects in semiconductor crystals

A very simple method for imaging the shape of the growth interface in InP crystals using infra-red sensitive film has been developed. Images of large samples (several square inches) are obtained which show high resolution (better than 25 microns) and high sensitivity. A variety of other imperfections are revealed. Free carrier concentration changes are displayed with high spatial resolution. The method should be a useful tool in guiding improvements in bulk crystal growth. The use of a CCD camera for imaging imperfections, for example, residual processing damage, was explored and found to be potentially useful for rapid screening of the quality of production wafers of these materials.     

Making reuse cost-effective

Until reuse is better understood, significant reductions in the cost of building large systems will not be possible. This assertion is based primarily on the belief that the defining characteristic of good reuse is not the reuse of software per se, but the reuse of human problem solving. Analytical approaches for making good reuse investments are suggested in terms of increasing a quality-of-investment measure, Q, which is simply the ratio of reuse benefits to reuse investments. The first strategy for increasing Q is to increase the level of consumer reuse. The second technique for increasing Q is to reduce the average cost of reusing work products by making them easy and inexpensive to reuse. The third strategy is to reduce investment costs. Reuse strategies, and reuse and parameterizations, are discussed     

Correlation of the thermal expansion coefficients of rare earth and transition metal oxides and fluorides

The product of the average linear thermal expansion coefficient (α_?) times melting point in °C (M_p) tends to be $\text{α}{}_{\mathrm{?}}\text{M}{}_{\mathrm{p}}\text{? 0.020}$ for the oxides of the 4f-rare earths and the comparable fluorides that have the tysonite structure. Correlation of rutile-like structures are based on deviations from α_?M_p = 0.027 caused by the cations moving the anions into sites with planar symmetry. The deviation tends to be proportional to the average cation to nearest neighbor anion distance. Additional effects are also discussed.     

The growth of low dislocation densityp-lnP single crystals

High qualityp-type InP is critical for devices ranging from high power injection lasers to space-based solar cells. The growth of 50 mm diameter, low defect density,p-type, Zn:InP substrates has been achieved for the first time at doping levels below 10¹⁸ cm⁻³. The 600 gram 〈111〉 B-seeded crystals were grown by the vertical dynamic gradient freeze technique. Dislocation densities are more than an order of magnitude below those achieved in comparable LEC-growth material. These range from 300 cm⁻² at the seed end to 1200 cm⁻² in the 50 mm diameter portion of the crystal. Single crystals were grown with carrier concentrations ranging from 1–5 × 10¹⁷ cm⁻³ as determined by Hall measurements. Hole mobilities as high as 100 cm² volt⁻¹ sec⁻¹ were achieved. The in-corporation of the zinc dopant follows normal freezing and a distribution coefficient of 0.67 ± .09 was determined. Infrared transmission imaging shows a lower level of stria-tion contrast relative to that observed for sulfur doped InP.     

Perfection of quartz and its connection to crystal growth

The perfection of cultured quartz and its connection to growth processes is reviewed. The principal macroscopic imperfection, ;creative flawing', is shown to be the hydrothermal crystal growth analog of dendritic growth and can be eliminated by the proper choice of growth direction and manipulation of conditions to minimize the effects of diffusion. Acoustic loss (1/Q) is proportional to the infrared absorption at the OH stretch frequency and is most likely due to a small (a few hundred molecules) number of aggregates of H(2)O, although lesser quantities of OH, which charge-compensate Al(+3) and Fe(+3) at Si(+4) sites, are also present. Techniques for preparing cultured quartz with Q equivalent to the best natural quartz are now routine. Radiation hardness is discussed in terms of impurity content. Impurity-decorated dislocations are shown to be the most probable cause of latent etch channels. Dislocations propagate from the seed but may be initiated by particulate inclusions and/or lattice parameter mismatch between the growth and the seed. Dislocation-free material can be grown by seed selection and procedures that eliminate inclusions.     

Lattice parameters and thermal expansion coefficients of thorium tetrafluoride (monoclinic)

The lattice parameters of ThF₄ were measured at four temperatures between 25° and 83°C. The unit cell volume contraction upon heating was confirmed. No phase transition was found between ?105° and 400°C. Other crystallographic data are given.     

Digital Infrastructures and Urban Governance

Abstract

The urban built environment is underpinned by an increasingly complex digital infrastructure, which is posing a variety of unpredictable and unprecedented challenges for urban governance. The paper discusses how the new “hard” digital infrastructures such as broadband are accompanied by the need to understand the governance of public sector information; and in turn how this relates to the emergence of smart city strategies. The paper is illustrated using empirical examples drawn from Australian digital infrastructure development, with reference to the international landscape of “smart city” developments. It argues that there is a significant mismatch between the often small scale, bounded capabilities of municipal government, and the operational expertise and scope of technology firms.