Urban growth and environmental degradation: The case of Cairo, Egypt

The immense growth of cities, especially in developing countries, is resulting in the urbanization of both poverty and environmental degradation to a greater degree than ever before. This paper examines the processes of growth and degradation in the Greater Cairo Metropolitan Region (GCMR), currently the world’s tenth largest mega-city. It reviews the region’s growth and selected environmental issues as well as impacts of current efforts on managing the region. The assertion of this paper is that current management policies and bodies lack a comprehensive view of urban governance for the region, which does not bode well for the future environmental and economic sustainability of the region.     

Iterative interference cancellation for high spectral efficiencysatellite communications

The problem of efficient utilization of the frequency spectrum for satellite systems is investigated; one which results as a consequence of highly crowding adjacent channels. An analytical characterization of the resulting interference channel is introduced and then exploited for interference cancellation. Two classes of cancelers are investigated. The first approach does not benefit from the forward error control (FEC) coding information which limits the performance gain. This motivates the second approach where a joint implementation of interference cancellation and decoding is developed using soft-input-soft-output (SISO) modules along with the iterative structure. It is shown that iterative interference cancellation techniques can achieve significant gains compared with the single-user matched filter receiver     

Ionoluminescence decay measured with single ions

A new ion beam analysis-based, single ion technique called the time to first photon has been developed to measure the decay of the luminescence signal of phosphors. Such measurements are currently needed to study luminescence decay mechanisms following high-density excitations and to identify strongly luminescent phosphor coatings with short lifetimes for ion photon emission microscopy (IPEM). The samples for this technique consist of thin phosphor layers placed or coated on the surface of PIN diodes. Single ions from an accelerator strike this sample and simultaneously create ion beam induced luminescence (IBIL) from the phosphor that is measured by a single-photon-detector, and an ion beam induced charge collection (IBICC) signal in the PIN diode. In this case, the IBICC signal provides the start pulse and the IBIL signal the stop pulse to a time to amplitude converter. It is straightforward to show that this approach also measures a signal proportional to activity versus time with an accuracy of 5% as long as the number of detected photons per ion is less than 0.1, which usually requires the use of absorbers for the IBIL detector or electronic discrimination for the IBIL signals. Details of the new analysis are given together with examples of luminescence decay measurements of several ceramic phosphors being considered to coat IPEM samples. IPEM is currently being developed at Sandia National Laboratory (SNL), the University of North Texas in Denton, and the Universities and INFN of Padova and Torino.     

Electroplating of nickel-cadmium alloys from alkaline solutions

The electroplating of Ni-Cd alloy coatings was carried out from alkaline baths (pH 10). For comparison, electroplating of the parent metals, Ni and Cd, was performed individually under the same conditions. The cathodic current efficiency for codeposition was high and decreased with increasing current density. The codeposition process is an anomalous type of plating with Cd being the preferentially deposited metal. The Ni content in the deposits increased with increasing current density. This increase in Ni content improves the corrosion resistance and microhardness of the deposits. X-ray diffraction analysis showed that the deposits consist of a mixture of Ni, β, γ, γ¹ phases.     

An analytical model for high electron mobility transistors

In this paper we present a new model for HEMT's which is based on a single analytical function that describes the electron concentrations in the two dimensional electron gas and in the AlGaAs layer. Besides accounting for the AlGaAs conduction, the model includes the effect of mobility degradation, channel length modulation in the saturation region and the series resistances R_S and R_D. The model results in closed form expressions for the current, transconductance, output conductance and gate capacitance. Finally, the theoretical predictions of the model are compared with the experimental data and shown to be in good agreement over a wide range of bias conditions     

Electrical properties of tri-n-butyl tin acrylate-methylmethacrylate copolymers

The copolymerization of tri-n-butyl tin acrylate (TBTA) with methylmethacrylate (MMA) has been investigated in dioxane. The composition of these copolymers was determined quantitatively by ¹H nuclear magnetic resonance (NMR) spectroscopy. The tin contents were estimated by gravimetric as well as thermogravimetric techniques (TGA). The reactivity ratio of such copolymers was estimated by application of the Kelen-Tudos method. The dielectric properties of the copolymers have been studied over a frequency range of 100–50 kHz at different temperatures from 20 to 70°C. The electrical conductivity for such copolymers was also measured. The results are interpreted in terms of the tin content of the copolymers.     

Synthesis and structural characterization of new defect pyrochlore type AxLnySb2O6+z antimoniates (0<x, y, z<1; A = Rb, Cs, Tl; Ln = Eu, Gd, and Y) prepared by coprecipitation

New cubic defect pyrochlore type A_xLn_ySb₂O_6+z antimoniates (0<x,y,z<1; A=Rb, Cs, Tl; Ln=Eu, Gd, and Y) (space group Fd3m) were prepared by calcination in air at 650 °C of compositions obtained by a coprecipitation method. Their crystal structures were refined by the Rietveld procedure and further confirmed by X-ray absorption spectroscopy (EXAFS) experiments. Refinements of the X-ray powder diffraction data show a partial and statistical occupation of the 8b site by alkaline or thallous ions and oxygen and lead to values close to 0.33 for the only refinable positional x parameter of the 48f oxygenated site.     

Manganese Distribution between FeO‐MnO‐SiO2–CaO–MgO‐Al2O3 Slags and Molten Iron

Pretreatment of high manganese hot metal is suggested to produce hot metal suitable for further processing to steel in conventional LD converter and rich manganese slags satisfy the requirements for the production of silicomanganese alloys. Manganese distribution between slag and iron represents the efficiency of manganese oxidation from hot metal. The present study has been done to investigate the effect of temperature, slag basicity and composition of oxidizer mixture on the distribution coefficient of manganese between slag and iron. Ferrous oxide activity was determined in molten synthetic slag mixtures of FeO‐MnO‐SiO₂–CaO–MgO‐Al₂O₃. The investigated slags had chemical compositions similar to either oxidizer mixture or slags expected to result from the treatment of high manganese hot metal. The technique used to measure the ferrous oxide activity in the investigated slag systems was the well established one of gas‐slag‐metal equilibration in which molten slags contained in armco iron crucibles are exposed to a flowing gas mixture with a known oxygen potential until equilibrium has been attained. After equilibration, the final chemical analysis of the slags gave compositions having a particular ferrous oxide activity corresponding to the oxygen potential of the gas mixture. The determined values of ferrous oxide activity were used to calculate the equilibrium distribution of manganese between slag and iron. Higher manganese distribution between slag and iron was found to be obtained by using oxidizer containing high active iron oxide under acidic slag and relatively low temperature of about 1350°C.