COLLECTIVE EFFECTS IN THE DESORPTION PROCESS INDUCED BY Hn+ CLUSTERS NEAR THE BOHR'S VELOCITY

The emission yield of the positive ions Cs+ and H+ from CsI bombarded by 600 keV Hn+ clusters, has been correlated with the energy deposited by these particles. Above the BOHR'S velocity, vo, the concept of equipartition between close and distant collisions could apply while below vo, collective effects are still observed (distant collisions). The same power relationship between the emission yield and an "efficent" mean stopping power for the cluster is pointed out within the whole investigated velocity range

Participation as an end versus a means : understanding a recurring dilemma in urban upgrading

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 2007.Some pages folded.Includes bibliographical references (p. 163-182).Since the 1920s, participatory approaches to urban upgrading in developing nations have demonstrated that involving the urban poor in the physical, social, and economic development of their settlements could improve their living conditions. These housing policies and projects have since been central to urban poverty reduction. Yet, while participatory upgrading is still used on a limited scale, it has failed to become a mainstream component of urban development. This dissertation analyzes some reasons for that failure by investigating the trajectory of an urban poverty reduction program that had much potential for success in Cambodia, but whose results yet surprisingly fell short of expectations. It connects the results to a critical analysis of international experience with policies and programs for urban poverty reduction. It explores the issue in two steps: First it analyzes the historical evolution of the policies and practices of urban poverty reduction in developing nations. This highlights the apparently weak link between lessons from experience, international policy recommendations, and the programs actually implemented by governments. Second, it presents a narrative analysis of how a participatory urban poverty reduction policy originated, was implemented, and evolved in Phnom Penh from 1996 to 2004. That story provides a micro-level understanding of the shape and constraints of the evolution of policies and practices, complementing the macro-historical analysis. The findings illustrate that three main issues have prevented international and local agencies from promoting urban development assistance, using lessons learned from concrete experience over time, and thus kept them from adopting a more continuous use of proven practices.(cont.) First, a conflict of frames between agencies over the meaning of development as human-centered versus growth-led, and of the meaning of participation as an end of development vs. a means to implement centrally-decided projects at a low-cost. Second, the lack of consideration for local institutions and politics in helping them understand why and how new approaches could be absorbed, or instead resisted. And third, an apparently lack of consistency in policy directions over time, with the abandonment of proven participatory practices, and the adoption of single-sided market-based approaches to development, when history had shown that both were needed together.by Pierre Fallavier.Ph.D

Developpement des techniques d'analyse par faisceaux d'ions acceleres elementaires (PIXE PIGE) et structurales (HSF-SIMS): - applications a l'analyse des sols sans traitement prealable

BIASPas de résum

Utilisation d'ions lithium pour l'analyse des surfaces et des couches minces

Dans la tendance actuelle à utiliser des ions plus lourds que les particules α en rétrodiffusion élastique (domaine d'énergie de l'ordre du MeV), l'emploi d'ions lithium apparaît constituer une amélioration notable des caractéristiques essentielles de la méthode. Ceci est particulièrement vrai en ce qui concerne la résolution en profondeur, avec le maintien de la résolution des détecteurs, pour ce type d'ions. Nous présentons ici, en même temps qu'une étude comparative des performances analytiques des ions Li et d'autres particules, quelques applications en montrant l'intérêt dans l'étude des surfaces et des couches minces. Parmi les applications les plus caractéristiques, citons, pour des échantillons épais, l'étude simultanée de la composition des couches d'oxydation anodique formées à la surface d'aluminium et du comportement de l'impureté majeure du bain de formation. Dans les études de couches minces, outre la détermination précise de la stoechiométrie des couches diélectriques AlN, SiO, Al2O3, des effets d'implantation pourront être étudiés, comme l'oxygène dans les couches SiO

Laser annealing of silicon on sapphire

Silicon-implanted silicon-on-sapphire wafers have been annealed by 50-ns pulses from a Q-switched Nd : YAG laser. The samples have been analyzed by channeling and by omega-scan x-ray double diffraction. After irradiation with pulses of a fluence of about 5 J cm^–2 the crystalline quality of the silicon layer is found to be better than in the as-grown state

Intense emission of cluster anions from gold targets under impact of keV/u gold clusters

CAS, BIASPas de résum

Very large gold and silver sputtering yields induced by keV to MeV energy Aun_n clusters (n = 1-13)

CAS, BIA