Recovery of low-temperature electron-irradiated lutetium

The annealing spectrum of electron-irradiated Lu has been studied between 14 and 135 K and a tentative interpretation of the observed structure given. A comparison with other irradiated h.c.p. metals indicates that the c/a-ratio might be an important parameter for the determination of the interstitial-atom mobility.     

Molecular structures of (SiCl3)2CH2 and (SiCl3)2CCl2 as studied by electron diffraction

An electron diffraction analysis of the molecular structures of 1,1,1,3,3,3-hexachloro-1,3-disilapropane and octachloro-1,3-disilapropane has been carried out. Deviations from the staggered conformation are indicated. The data may be approximated by models with C₂ symmetry and a small tilt of the SiCl₃ groups. The main bond lengths (r_g) and bond angles obtained for (SiCl₃)₂ CH₂ are: SiCl, 202.7(4); SiC, 186.6(6); CH, 109.8(24) pm, ClSiCl, 107.9(1); SiCSi, 118.3(7)°; and for (SiCl₃)₂CCl₂: SiCl, 202.0(4); SiC, 190.2(9); CCl, 179.6(9) pm; ClSiCl, 109.5(1); SiCSi, 120.6(9); ClCCl, 110.9(16); SiCCl, 106.3(3)°.     

Optical and acoustic electron-phonon coupling in Ho and Tb dihydrides and dideuterides

We present detailed measurements of the electrical resistivity for terbium and holmium dihydrides and dideuterides. An analysis of the thermal variation, ?(T), permits to separate two contributions, one stemming from the acoustic or host metal ion vibration and a second which is related to the optical H (or D) vibrations and which is strongly isotope dependent. The thermal variations can be reasonably well represented by a Debye spectrum as concerns the acoustic phonons and by an Einstein spectrum as concerns the optical phonons. We find also that the strength of the electron-phonon coupling is much weaker for the optical phonons as compared to the acoustic ones, in agreement with recent estimates from the theory.     

Determination of some trace elements in natural and fertilised Libyan soils using INAA and ED-XRF

Samples of natural and fertilised soils were collected from Al-Gheran region, west of Tripoli, Libya. The samples were investigated by means of INAA and ED-XRF for Al, Si, K, Ca, Sc, Cr, Mn, Fe, Co, Zn, Br, Rb, Sr, Y, Zr, Nb, Cs, Ba, Hf, Ta, Pb and Th. The results indicate that the concentrations of K, Ca, Zn, Sr and Pb are 2–4 fold higher in fertilised compared to natural soil, while the concentrations of Al, Si, Cr, Mn, Fe, Co, Rb, Y, Nb, Cs, Ba Ta and Th are nearly the same in all samples. Mn and Fe values in two arable soils have been found to be 4–6 times lower than the average concentration in the earth's surface soils. This study concludes that, although the levels of some trace elements important for human health are very low in both natural and fertilised soils. Further research is needed to understand the full significance of the distribution transfer and toxicity of trace elements introduced in imported fertilisers.     

Identifiability of first order reaction systems

The question of the possibility to determine all the unknown parameters of kinetic models is considered. A simple algebraic condition for structural identifiability in first order reaction systems is given.

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