Evidence for non-axial shapes in81, 82, 83Kr

Excitations up to I=12 have been found in⁸²Kr during an (α, 2n) in-beam experiment. Several levels are interpreted as due to (g9/2)² neutron excitations. A comparison with g9/2 neutron bands in^{81, 83}Kr and with cranked shell model calculations indicates non-axial deformation in connection with a rotation-aligned band starting with an 8⁺ level. Non-collective excitations, 8⁺ (and 6⁺), have been interpreted as deformation-aligned two-neutron states.     

Comparative studies of methylmercury determination in biological and environmental samples

Some parameters affecting the accuracy of various approaches to methylmercury (MeHg) determination in biological and environmental samples were studied. Different isolation techniques (ion-exchange, extraction, volatilization, distillation) and final measurement via cold vapour atomic absorption spectroscopy (CV AA) or gas chromatography (GC) were compared. Results obtained by the various isolation techniques are comparable for almost all biological and environmental samples, except for soils and some sediments, where disagreement between the results obtained by GC and CV AA was found. In order to resolve these problems, a new separation technique based on distillation of MeHg from the sample followed either by CV AA or GC was developed. The new method results in very good recovery and reproducibility (95 ± 2%) for all samples examined (fish, mussel, shrimp, blood, hair, algae, sediment, etc.), is specific for MeHg and provides for its differentiation from other species by an indirect CV AA determination. Gas-chromatographic measurement of the isolated MeHg using different packings and conditioning of the columns is also discussed. The distillation method with GC detection is advantageous in producing cleaner chromatograms and in prolonging the life-time of the packing and the intervals between reconditioning.     

Speckle photography by birefringent plates

This paper describes a birefringent system with which it is possible to record three laterally shifted speckle images of an object, on a photographic plate. The recording is made with only two exposures. The exposure times and relative positions of the images are adjusted automatically by the birefringent plates.     

Testing of a mathematical model for viscoelastic behaviour of poly-α-olefins using polyisobutene

The analytical model proposed for poly-α-olefins has been tested on polyisobutene. Relaxation modulus E(t) and distribution of relaxation times have been predicted from dynamic experiments and agree with literature data.     

Measurements of axial displacements undergone by a diffusing object in speckle photography

The speckles of the image plane of an object are both radially shifted and decorrelated when the object is axially translated through an amount ?. We demonstrate that this radial shift, which is related to the position of the pupil of the optical system, disappears when the pupil lies in the back focal plane of the imaging lens. However, if the irradiance of the image plane is twice recorded on a photographic plate which is laterally shifted through ζ_H between the exposures, the minimum value of the contrast of the Fourier fringes exhibited by the plate after processing, gives the value of ? if ? is less than a particular value, ?_M which will be defined. Also we propose a new speckle measurement method in which the fringes are automatically removed when ? is greater than ?_M. We record the image of the object illuminated in convergent light through an amplitude diffuser placed in the Fourier plane of the object. The mean speckle speckle size of the diffuser is equal to the mean size of the speckles generated by the object in its Fourier plane.     

JESS, A joint expert speciation system-I. Raison d'être

JESS is a new computer package for modelling chemical systems in solution and performing numerical analyses on associated experimental data. It was developed to solve problems requiring specialist knowledge of chemical speciation. It currently comprises over 150 programs, 1200 subroutines and 120,000 lines of Fortran code. The main reasons for the development of JESS, and the principles which underpin it, are described. Subsequent papers detail the major facilities which JESS now provides.