Table of contents

The theory for acoustic gravity modons is generalized. As a result, the equations governing the whole internal gravity wave branch are deduced. The threshold velocity is also found.

In the theory of nonlinear surface waves, a particular case has been found where the basic equations reduce considerably. Thus, it turns out that they can be rewritten in the form of a system that contains only purely time-dependent variables.

Neutrino fields obeying the dominant energy condition can be of embedding class one only if they are pure radiation fields of Petrov type N.

A Monte Carlo simulation of the rare decay b → sγ at the Z⁰ peak is presented. The calculation makes use of the peculiar features of the DELPHI detector at LEP, such as the Ring Imaging CHerenkov (RICH) and the microvertex detector. The sensitivity to B → K*γ, B → K**γ and B_s → ϕγ decays is good, between 20% and 30%, for a background rejection of the order of 10⁻⁵.

The high-spin structure of ^202,204Po was studied using the ^196,198Pt(¹²C, 6n) and ²⁰⁴Pb(α, 4n) reactions at a beam energy of 100 and 52-54 MeV, respectively. In-beam conversion electron and γ-ray spectroscopy measurements including γγ(t) coincidence, γ(t) and angular distributions were performed. The level scheme of ²⁰²Po was extended to spin 21 h and the excitation energy 5.5 MeV while levels in ²⁰⁴Po were observed at 5.9 MeV with a spin of 20 h. The previously observed isomeres in ²⁰²Po and ²⁰⁴Po were confirmed and in addition to these a J^π = 13⁻ level with the half-life 9(3) ns was observed in ²⁰⁴Po at 3387.3 keV. The expected configuration of this state is πh_9/2² ⊗ vf_5/2^-1i_13/2^-1. A shell-model description of the observed excited states is given.

The shape fluctuation energy from the cubic polynomial in J for the g-band spectra of even-even nuclei is used to study the constancy of the level structure of the nuclei related to the F-spin multiplets arising in the Interacting Boson Model (IBM). The shape phase transition from the SU(3) to SU(5) or O(6) character of the 2₁⁺ state as a function of the total boson number N_B and the N_pN_n product is illustrated for the A = 120-200 region. The relevance of the isotonic and isotopic multiplets in specified regions is supported. A comparison is made with the phenomenological IBM.

The characteristics of a commercial 1523 nm He-Ne laser have been studied. The modes of this internal mirror laser show elliptical or circular polarizations. A modified two-mode (polarization) method stabilizes the mode frequencies within 10 MHz and the total output intensity within 1%. This makes the laser an excellent source for coherent communication research.

Spectra of highly ionized Kr and Mo, emitted from the JET tokamak plasmas, have been recorded in the region 30-355 Å. Detailed analysis of the n = 3, Δn = 0 transitions in Kr XXIV-XXVI and Mo XXX-XXXII has resulted in a number of new spectral classifications. Some isoelectronic regularities for Al-like and Mg-like ions are discussed.

Recent measurements of the transition probabilities of ns²¹S₀-nsnp³P₁⁰ (Δn = 0, ΔS = 1) transitions in ions with two electrons outside a closed shell [isoelectronic sequences Be I (n = 2), Mg I (n = 3), Zn I (n = 4), Cd I and Sm I (n = 5)] are reviewed and compared with theoretical results. Ranges of ionic charges are identified for which better data are needed.

The one-dimensional motion of a Langmuir soliton passing by the region of a density barrier is considered. It is found that the soliton is accelerated due to the plasma inhomogeneity. The accelerated soliton radiates two pulses of ion-sound waves propagated in opposite directions away from the barrier. The spatial distribution of the perturbed density in the ion-sound waves is investigated and the energy loss of the soliton, as a result of the emission, is estimated.

The dispersion relation for low-frequency plasma oscillations in the lower part of the ionosphere has been deduced by taking the temperature dependence of the electron-neutral collision frequency into account. It is shown that the threshold values for short wavelength instabilities can be significantly reduced when the collision frequency increases with temperature.

The nonlinear evolution of convective cells in low-β plasmas is considered. The formation of vortex chains from local disturbances of the plasma density and current is analysed. The stability properties of such vortex structures are studied by means of the Lyapunov method. Applications of the present theoretical results to observations of rayed auroral forms are discussed.

A variational approach is outlined for the deduction of impurity confinement scaling laws. Given the forms of the diffusive and convective components to the impurity particle flux, we present a variational principle for the impurity confinement time in terms of the diffusion time scale and the convection parameter, which is a non-dimensional measure of the size of the convective flux relative to the diffusive flux. These results are very general and apply irrespective of whether the transport fluxes are of theoretical or empirical origin. The impurity confinement time scales exponentially with the convection parameter in cases of practical interest.

A Keating model calculation of phonon dispersion in CdGeAs₂ with two bond stretching force constants between nearest neighbours and two bond bending force constants between second nearest neighbours is presented. The four parameters have been determined from a least mean square fit to our Raman data. In this study one emphasizes the relationship which connects zone centre modes in CdGeAs₂ and phonons at Γ, X and W points of the Brillouin zone in the associated zincblende materials: GaAs and InAs, on the one hand, and the binary analog Ga_0.5In_0.5As, on the other hand. One shows that the optical modes in CdGeAs₂ can be classified as GaAs-like, InAs-like and mixed GaAs/InAs-like.

Our measurement system is far from being static. It is continually evolving in response to the ever more sophisticated demands of our civilisation. The accuracy of measurement depends on the state of science and technology and consequently there are trends that are well beyond the capabilities of the individual metrologist. It is therefore rewarding to look from time to time at the fascination of our measurement system as a whole. The general developments in metrology will be reviewed, from early times through our present system towards that of the next century.

The realisation of the SI second according to its definition necessitates an arrangement between different physical effects. The compromises that have been made for the PTB's primary clocks are outlined. The performances and the uncertainty of the standards are discussed.

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A new planar thin film design of multijunction thermocouples on a silicon chip containing a window with a SiO₂-membrane for low heat conductance underneath of the thermocouples is described. It is used as the sensor for the temperature difference in a multijunction thermal converter for ac-dc transfer of electrical quantities like voltage, current and power via Joule heat in a thin film resistor. By coating the heater with an optically absorbing layer it is used as a highly sensitive radiometer transferring absorbed energy to Joule heat in the resistor. The design can easily be optimized for all different frequency applications. It offers the possibility of the mass production of transfer standards at highest level of accuracy.

The design and operation of large Josephson series arrays as a precise potentiometer or voltage standard are described. The reproducibility of the voltage measurement at room temperature is mainly determined by the systems the output voltage of which is to be calibrated and may reach a few parts in 10¹⁰.

On 1st January 1990 the International Temperature Scale of 1990 (ITS-90) will come into force. This brief article describes the new scale and gives the differences between temperatures measured on ITS-90 and those measured on the current international scale, the International Practical Temperature Scale of 1968 (IPTS-68).

The Swedish National Testing Institute (SP) in Borås is this country's leading impartial authority on technical assessment and calibration. The Institute, within a broad field of activity, contains laboratories for nine of the thirteen primary standards of measurement maintained at the national level, and coordinated by the Swedish Metrology Organisation. This presentation exemplified the research activity in metrology at SP by focusing on recent developments in the national measurement standards.