[en] Dislocation dynamics in Ni₃Al intermetallic single crystals has been studied by mechanical spectroscopy between 300 and 700 K. It has been found that in the anomaly domain of the flow stress, which is characteristic of this material, the mechanical loss of predeformed specimens is strongly dependent on strain amplitude, predeformation level, annealing temperature and time. The results can be interpreted as a combination of two phenomena which simultaneously occur as temperature is increased from 300 K to about 500 K: exhaustion of the mobile dislocation segments (superkinks) and pinning of the screw dislocation segments via cross-slip from the (111) onto the (010) planes

[en] Full text: Titanium and titanium-based alloys are excellent materials for a number of engineering applications because of their high strength, lightweight, good corrosion resistance, non magnetic characteristic and biocompatibility. The current processing steps are usually costly, and there is a growing demand for net-shape solutions for manufacturing parts of increasing complexity. Powder injection moulding is becoming a competitive alternative, thanks to the advances in production of good quality base-powders, binders and sintering facilities. Titanium hydride powders, have the attractiveness of being less reactive than fine titanium powders, easier to handle, and cheaper. This paper summarizes recent advances on PIM of titanium and titanium alloys from TiH2 powders, including shape-memory NiTi alloys. (author)

[en] In order to make a significant step forward in the low energy γ-ray astronomy, a telescope with high sensitivity and fine angular resolution with imaging capability down to a few tenths of a degree is required. The coded aperture mask used together with a position sensitive detector make possible the achievement of these capabilities. Laboratory tests of the position sensitive sodium iodide detection system and the expected performance of the coded imaging mask derived from simulations are presented

[en] A hard X-ray (30-190 keV) observation of A0535+26 in outburst was performed during a balloon flight on October 4, 1980. Detailed spectral analysis shows that the average photon spectrum of A0535+26 can be well fitted by a Wein law with kT = 7.68 + or - 0.035 keV. This spectral law is in good agreement with theoretical model spectra of X-ray pulsars. The energy spectra over 51 phase bins are also well fitted by a Wein law with a kT variable with pulse phase from 7.3 to about 8.5 keV. Apart from this spectral variability, photon spectra averaged over a pulse period strongly suggest that chaotic spectral variability is also present. A simple geometrical model for the X-ray emission and modulation with pulse phase from A0535+26 is presented. This model gives good qualitative agreement with the present observations. 29 references

[en] The transient X-ray pulsar A0535 + 26 was observed on Oct. 4, 1980 during a high level intensity outburst with a balloon-borne hard X-ray detector. High statistical quality source spectra were determined up to 100 keV. Both blackbody and Wien laws fit well the data. Pulse phase spectroscopy shows variation of temperature index between 7.5 and 8.5 keV in the off source spectra and between 7.4 and 10.5 keV in the off pulse spectra. The time-averaged luminosity above 30 keV is about 8 x 10 to the 36th erg/s. 11 references

[en] The X-ray source A0535+26 is well established as a recurrent transient. During its activity it shows long period pulsations (Papprox.=104 sec) with a relevant and variable rate of decrease of the pulse period. On the basis of its peak luminosity and pulsation features, the source has been suggested (see e.g. Elsner and Lamb, 1976) as an accreting neutron star in a binary system. In September-October 1980 the source showed a very high level outburst. Oda and the Hakucho Team (1980) gave a flux level in the 1-12 keV energy range of about 1 Crab on October 2nd, and 2 Crab on October 7th. We observed the source in the hard X-ray energy range on October 5th. Thanks to high signal from A0535+26 the observation resulted to be very effective to study its time variability and energy spectrum. (orig.)

[en] It is known that the counting rate of both Na I and Cs I hard X-ray detectors can have intense enhancements of brief (< 1 s) duration, which appear like very short cosmic gamma-ray bursts but probably are due to phosphorescence in the detector itself. Unfortunately, this problem is not limited to short bursts. We present here three much longer (up to 80 s) pseudo-gamma-ray bursts observed during a transatlantic balloon flight. We conclude that detections of gamma-ray bursts (and probably also of hard X-ray source flares) based only on a rate increase by a single scintillator should always be confirmed by at least one other instrument. (orig.)

[en] A long observation of the recurrent transient X-ray pulsar A0535+26 was performed when the source was near the maximum of its high intensity level outburst occurred on October 1980. A light curve quite different from those observed in previous outbursts is found. The time averaged pulsed spectrum is well fitted both by a blackbody (kT = 9.0 +- 0.1 keV) and a Wien law (kT = 9.1 +- 0.1 keV). Spectral variability with pulse phase has also been observed. (Auth.)

No abstract available

[en] In the present work, the effect of small doses of neutron irradiation on mechanical behaviour is correlated with changes found in the internal friction spectrum of their alloys after irradiation. As the mechanisms contributing to this spectrum have been previously investigated, these results are applied to evaluate microstructural changes due to neutron irradiation. (Author)