The influence of the source on the resolution of a positron annihilation lifetime spectrometer

A detailed study of the prompt resolution curve of a positron annihilation lifetime spectrometer shows that the isotope used as source has great influence on its shape.     

Positron trapping and detrapping from dislocation-like defects in the pre-vacancy region in iron

The 511 keV positron annihilation lineshape was measured as a function of temperature in pure iron and in carbon doped (50 appm C) iron. After annealing at 900°C, trapping and detrapping from dislocation-like defects in the pre-vacancy region in iron was seen around 650°C. A positron-dislocation binding energy of (0.63±0.03) eV was derived for iron.     

Miniaturized EI/Q/oa TOF mass spectrometer

A miniaturized orthogonal time-of-flight mass spectrometer with an electron impact ionization ion source and a rf quadrupole ion guide has been developed. A mass resolving power of m/deltam = 5500 has been obtained in a 0.4 m instrument. The addition of helium at pressures of about 4.0 mtorr into the ion source showed collisional focusing taking place in the rf quadrupole. An automated gas chromatograph designed for air monitoring applications has been coupled to the time-of-flight mass analyzer and tested for the detection of simulants of chemical-warfare agents.     

Testing the Gumbel hypothesis by Galton's ratio

We study a generalization of a ratio of spacings introduced by Galton in 1902. The ratio proves to be an important building block in the construction of a large sample test for the hypothesis that a distribution from an extremal domain of attraction belongs to the domain of attraction of the Gumbel law.     

On the maximum likelihood estimator for the Generalized Extreme-Value distribution

The vanilla method in univariate extreme-value theory consists of fitting the three-parameter Generalized Extreme-Value (GEV) distribution to a sample of block maxima. Despite claims to the contrary, the asymptotic normality of the maximum likelihood estimator has never been established. In this paper, a formal proof is given using a general result on the maximum likelihood estimator for parametric families that are differentiable in quadratic mean but whose supports depend on the parameter. An interesting side result concerns the (lack of) differentiability in quadratic mean of the GEV family.     

On cluster kinetics and MBE growth

Based on the model of a so-called Near Surface Transition Layer (NSTL) proposed by HERMAN and ANDERSSON we discuss the possible role of clusters during MBE growth. Moreover, intentional use of small clusters instead of single atoms as beam constituents may contribute to improvements in crystal quality even at low substrate temperature and high growth rate.