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We show that confinement in small volumes affects the interplay of exchange and dipolar interactions and the magnetic phases of hard and soft spherical core-shell nanoparticles. Large variations in the magnetization of thin shells may occur due to the core dipolar field gradient within the shell. The reversal field is tunable by the trends imposed by the dipolar and core-shell interface exchange energies. We show, for instance, that the reversal field of a ${\mathrm{CoFe}}_{2}{\mathrm{O}}_{4}$(30 nm)@${\mathrm{MnFe}}_{2}{\mathrm{O}}_{4}$(6 nm) particle ranges from 15.5 kOe for antiferromagnetic coupling down to 2.5 kOe for ferromagnetic coupling.

We report a theoretical study of the impact of finite size on the magnetocaloric effect (MCE) of thin Ho films. For strong external field strengths, the adiabatic temperature change ΔTad is comparable to the value found in bulk Ho, reaching about 12 K for an external field strength change ΔH = 50 kOe. For thicknesses below the helix period, there is a large enhancement. In this thickness range, the helical state does not form, leading to a giant MCE reaching ΔT/ΔH = 6.5 K/T for ΔH = 2 kOe.

The differential phase scintillations between two neighbouring frequencies on the side of the oxygen absorption peak have been measured. The −8/3 slope of the asymptotes to the measured spectra at the lowest and highest scintillation frequencies and the spectral ratio between these asymptotes are in good agreement with the theoretical model proposed.

Results are presented of the determination of the atmospheric refractive index structure parameter C2n, deduced from amplitude scintillation measurements made on a 36-GHz radio link and also from refractivity measurements using a turbulence probe. These measurements were made in a town environment (central London) and covered a range of atmospheric conditions. The two methods of measurement give good agreement, particularly in convective conditions, and provide further experimental evidence of the applicability of Tatar-ski's wave propagation theory in a turbulent medium to millimeter wavelengths.

Simultaneous rainfall measurements at 36 GHz and 55 GHz on a common 4.1 km path show, under the conditions of these experiments, that the attenuation due to rainfall lies between the attenuation values predicted by the lognormal and the Best rain drop size distributions.

To investigate the effect of atmospheric turbulence on microwave communication links, temperature and water vapor pressure have been measured and radio refractivity has been computed, during different meteorological conditions, in the atmospheric boundary layer of an urban site. The cospectra between temperature (T) and water vapor pressure (e) have been found to be either negative over the whole range of frequencies, or the low-frequency end of the cospectrum is of opposite sign relative to higher frequency end. In both cases cospectra follow a−5/3 law in the inertial subrange, in agreement with the theoretical predictions. The coherence spectra clearly show that the temperature and humidity fluctuations are highly coherent within the inertial subrange under both convective and stable conditions. The relative contribution ofC ,C eT andC to the real refractive index structure parameterC is examined and discussed.

This paper discusses the relationship between the rain-induced attenuation of two vertically polarised line-of-sight mm-wave links at 36GHz and 55GHz. The links share a 4.1km common path across central London and have fading margins of 20dB and 23dB resepctively. Details of the system are given elsewhere {1}. The advantage of a dual frequency measurement is that, since both links share the same propagation path, the attenuation at both frequencies is due to the same volume of rainfall. Thus the rainfall rate is not required and the error introduced by its measurement is eliminated. This technique is also a sensitive indicator of the actual raindrop size.

The probability distributions of the amplitude scintillations on 36 GHz and 55 GHz millimetre wave links along a 4.1 km path across central London have been obtained. These show that the log-normal distribution applies for the case of 36 GHz, but for 55 GHz, on the side of the oxygen absorption peak, the distribution departs significantly from log-normal.

Scintillation measurements made on a 55 GHz millimetre wave link along a 4.1 km path across Central London are described. Observations are reported which can be explained by the theoretical work of Ott and Thompson for amplitude scintillations in an absorption region.