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- Nathan, RP, et al.
(författare)
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Environmental dose rate heterogeneity of beta radiation and its implications for luminescence dating: Monte Carlo modelling and experimental validation
- 2003
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Ingår i: Radiation Measurements. - 1879-0925. ; 37:4-5, s. 305-313
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Tidskriftsartikel (refereegranskat)abstract
- The recent development of rapid single sand-sized grain analyses in luminescence dating has necessitated the accurate interpretation of D-e distributions to recover a representative D-e acquired since the last bleaching event. Beta heterogeneity may adversely affect the variance and symmetry of D-e distributions and it is important to characterise this effect, both to ensure that dose distributions are not misinterpreted, and that an accurate beta dose rate is employed in dating calculations. In this study, we make a first attempt providing a description of potential problems in heterogeneous environments and identify the likely size of these effects on D-e distributions. The study employs the MCNP 4C Monte Carlo electron/photon transport model, supported by an experimental validation of the code in several case studies. We find good agreement between the experimental measurements and the Monte Carlo simulations. It is concluded that the effect of beta, heterogeneity in complex environments for luminescence dating is two fold: (i) the infinite matrix dose rate is not universally applicable; its accuracy depends on the scale of the heterogeneity, and (ii) the interpretation of D-e distributions is complex and techniques which reject part of the D-e distribution may lead to inaccurate dates in some circumstances. (C) 2003 Elsevier Science Ltd. All rights reserved.
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- Shariff, S. M., et al.
(författare)
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Influence of laser glazing on properties of diffusion borided layers
- 2003
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Ingår i: ICALEO 2003 - 22nd International Congress on Applications of Laser and Electro-Optics, Congress Proceedings. ; , s. 1506-
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Konferensbidrag (refereegranskat)abstract
- Pack boriding of steels is known to possess numerous advantages over conventional techniques like carburizing and nitriding. The combination of high hardness coupled with low co-efficient of friction offered by the diffusion borided layers makes them a promising candidate for combating abrasive, adhesive and erosive wear. However, the boronizing treatment on steels is usually found to result in the formation of a porous, irregular top surface layer and often the borided layer comprises of FeB and Fe2B phases. Of the above, FeB formation is highly undesirable, as it is prone to induce cracking in the coating due to thermal expansion mismatch. While the brittle FeB layer in the boride coating can be eliminated by appropriate post heat treatment or by carefully manipulating the process parameters, porosity and structural irregularity, which play a vital role in tribological performance of the coating, continue to exist in the boride layer. The efficacy of laser post-treatment of the borided layer in overcoming the above problems has been investigated and forms the subject of this paper. A pulsed Nd: YAG laser, capable of delivering an average power of 400W, was utilized for irradiation of the borided layer. Prior to laser treatment, boronizing of En-8 steel samples was carried out by pack-boriding process using an indigenously developed boronizing mixture. The boronized layer was subjected to laser irradiation with varied laser power, under a nitrogen shroud and the laser-treated layers were extensively characterized for surface roughness, phase constitution, microstructure and hardness. Laser glazing resulted in complete densification of the irregular porous top region of the previously boronized layer. An increase in laser power was found to lead to an increase in boride layer depth with accompanying decrease in hardness and porosity. Depending on the laser power employed, distinct microstructures were noted in the treated layer and could be attributed to varying extents of dilution of the boronized layer by Fe from the substrate. Apart from analyzing the influence of laser power on the characteristics of the diffusion borided layer, tribological performance of the laser-treated layers was also evaluated and compared with that of the untreated boride layer. Results of abrasive wear tests indicated substantial improvement in tribological properties and strong dependence on the laser power employed.
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- Åkesson, Knut, 1972, et al.
(författare)
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Hybrid Computer-Human Supervision of Discrete Event Systems
- 2002
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Ingår i: proc. of 2002 IEEE International Conference on Robotics and Automation, Washington DC, MAY 11-15,, USA. ; , s. 2321-2326
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Konferensbidrag (refereegranskat)abstract
- This paper presents a framework for accommodating human intervention in a computer supervised discrete-event system. The basic mechanism for allowing such hybrid supervision by a computer and a human operator is by switching priorities between events controlled by each according to some specified schedule. To synthesize a computer supervisor under such conditions, a transformation that maps the problem to one that satisfies the model stipulations of the Supervisory Control Theory is presented. The aforementioned framework introduces a parameter that can be tuned to provide for different levels of co-operation between the human and computer supervisors. Several important properties of the resulting supervisors are presented.
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