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Electron spin resonance linewidths of Fe3+ in single crystal MgO were examined at 9 GHz for crystals having iron concentrations of 2300 ppm and 4300 ppm over the temperature range 293 to 4.2 K. For the + 1/2 ? -1/2 transition the linewidth remains constant from 293 to about 15 K, below which line broadening occurs. From 15 to 4.2 K the linewidth increases steadily without any change in the g value of the line. At 4.2 K the width of the line is about 3.7 times larger than at 77 K for each concentration. The lineshapes are Lorentzian over the whole temperature range examined and the data suggested that the effects observed below 15 K were due to non-secular line broadening mechanisms (the “10/3” effect) originally proposed by Anderson and Weiss.

Line broadening has been observed at 9 GHz in the ESR absorption spectrum of Cr3+ in MgO in the liquid helium temperature range, for a range of Cr3+ concentrations from 800 7400 ppm. The broadened linewidths at 4.2 K are about two times larger than those at 77 K and depend on polar angle. The lineshapes are Gaussian, in contrast to the Lorentzian lineshape between 293 and 77 K. The broadening is interpreted by the combined effects of strain, due to the charge misfit of Cr3+ and the host cation, and temperature which causes both exchange striction and departure from the cubic symmetry to a lower symmetry. Analysis of the linewidth data gives ?D=(5.25±0.40)×10-4 cm-1 and confirms that the total linewidth, ?Ht, is given by ?Ht=?H0+?(2?D/gß) cos ?H? where ?H0 is the linewidth independent of concentration, temperature and polar angle, ?H.

Electron spin resonance linewidths of Co2+ in single-crystal MgO at 9 GHz were examined experimentally and theoretically for a range of Co2+ concentration from 310 to 9900 ppm. In contrast to the behaviour expected from dipolar broadening, the experimental peak-to-peak linewidth for the octed hyperfine lines were about twelve to fifty times less than the calculated dipolar linewidths according to temperature and concentrations. The peak-to-peak linewidths as determined experimentally increase from 0.8 mT at 310 ppm Co2+ to 4.0 mT at 9900 ppm Co2+ at a polar angle ?H= O° and at 20 K. Peak-to-peak linewidths independent of polar angle but strongly dependent on temperature and slightly dependent on concentrations were observed. The ratio of moments M41/4/M21/2derived from the experimental data lay between 1.35 to 1.44 and the lineshapes were markedly Lorentzian in the range of temperature measured. The data suggest that Co2+ entered the lattice substitutionally, occupying magnesium sites, that the linewidths were determined, after exchange energy, over the whole concentration range examined and that the exchange energy whose values lay between 6 and 77 GHz, varied linearly with concentration.

The dielectric properties of titanium doped magnesium oxide (Ti/MgO) and gadolinium doped magnesium oxide (Gd/MgO) single crystals have been measured at room temperature over the frequency range 500 Hz to 50 kHz. For both the crystals, the dielectric constant?' is found to be independent of frequency and the ac conductivity Re{sae} agrees well with the relation Re{sae}?On,O being the angular frequency with n=0.84±0.05 for Ti/MgO andn=0.81±0.03 for Gd/MgO. The data fits well with the relation???On-1(n<1),?? being the dielectric loss factor. An explanation may be found on the basis of the hopping phenomenon.

Electron spin resonance linewidths of Cr3+ in single crystal MgO at 9 GHz and 35 GHz were examined experimentally and theoretically for a range of Cr3+ concentrations. In contrast to the behaviour expected from dipolar broadening the experimental peak-to-peak linewidth for the 1/2 to-1/2 transition, which had a value of about 0.5 mT at 293 K, was independent of both polar angle and concentration over the range from 800 p.p.m. Cr to 15 100 p.p.m. Cr. The calculated dipolar linewidths exceeded those observed by factors of over one hundred; the ratio of momentsM41/2/M21/2 derived from the experimental data lay between 1.33 and 1.39 and the lineshapes were markedly Lorentzian. The data suggested that Cr3+ entered the lattice substitutionally, occupying magnesium sites, that the linewidths were determined by exchange narrowing over the whole concentration range examined and that the exchange energy, whose values lay between 4 GHz and 100 GHz, varied linearly with concentration.

A regional seminar on the application of remote sensing techniques to coastal zone management and environmental monitoring was held in Dhaka, Bangladesh, from 18 to 26 November 1986. The seminar was jointly organized by the UNDP/ESCAP Regional Remote Sensing Programme and the Bangladesh Space Research and Remote Sensing Organization (SPARRSO). The purpose of the seminar was to exchange information and experience in the application of remote sensing techniques to coastal zone management and environmental monitoring. Results of the pilot studies carried out in Bangladesh, India and China on coastal zone monitoring and environmental impact assessment were presented. Experience was shared among the participating countries to evolve a common regional perspective for wider application of the results of such pilot studies. The programme included presentations on the pilot projects by the principal investigators. These were followed by discussions and presentations on similar activities in the region by the participants. Participants from the countries of the ESCAP region, developed countries and international organizations attended the seminar. They presented updated developmental and operational activities in the field of remote sensing application to coastal zone management and environmental monitoring. The latest activities and operations in the field of remote sensing applications were presented in the seminar.

The dielectric properties of titanium-doped magnesium oxide (Ti/MgO) and nickel-doped magnesium oxide (Ni/MgO) single crystals have been measured in the range of temperature from 300 to 450 K at the microwave frequency of 9.31 GHz. For both crystals the dielectric properties are found similar. From the conductivity data, the activation energy in the measured temperature region has been estimated to be 0.15 eV. The values of the temperature dependence (e'-1)-1(e'+2)-1 (?e'/?T)p have been calculated. The data confirms the Bosmann and Havinga postulate that, for materials in which the dielectric constant;e' is less than 20 the temperature dependence should be positive.