Hydrodynamic study of fine metallic powders in an original spouted bed contactor in view of chemical vapor deposition treatments

An original gas–solid contactor was developed so as to treat by chemical vapor deposition, fine (mean diameter 23 μm) and dense (bulk density 7700 kg/m3) NiCoCrAlYTa powders with large size distribution. In order to avoid the presence of a distributor in the reactive zone, a spouted bed configuration was selected, consisting in a glass cylindrical column associated through a 60° cone to an inlet tube, connected at its bottom to a grid so as to support the powders at rest. A hydrodynamic study was conducted at ambient temperature and pressure, combining pressure drop measurements and visual observations as a function of gas velocity and of the ratio H/D of the height of the bed at rest over the bed diameter. Using conventional alumina particles belonging to Geldart's group B, it was shown that this equipment is able to ensure conventional spouted bed behavior, especially for H/D ratio equal to 1. From numerous experiments conducted with the fine metallic powders of interest, it was shown that (i) conventional pressure drop curves for spouted beds are obtained for H/D ratios between 1 and 1.8, (ii) due to the large grain size distribution of particles, minimum spouted bed velocities occur in a range rather than at precise values. Visual observations reveal the presence of the spout and fountain at the minimum spouted bed velocity and for H/D equal to 1

A nonlinear Bloch model for Coulomb interaction in quantum dots

In this paper we first derive a Coulomb Hamiltonian for electron--electron interaction in quantum dots in the Heisenberg picture. Then we use this Hamiltonian to enhance a Bloch model, which happens to be nonlinear in the density matrix. The coupling with Maxwell equations when interaction with an electromagnetic field is also considered from the Cauchy problem point of view. The study is completed by numerical results and a discussion about the advisability of neglecting intra-band coherences, as is done in part of the literature.Comment: 17 pages. Journal of Mathematical Physics (2014) \`a para\^itr

Legislation and Implementation of International Environmental Law by African Countries: a Case Study of Ghana

The purpose of my thesis is to bring to the light the efforts of African countries, in this case Ghana, in implementing their environmental commitments under international law and some of the problems they face in this regard. African countries played a tremendous role in the emergence of international environmental law, after which environmental institutions and legislations have been set up for the conservation and management of natural resources. The thesis will discuss environmental issues particularly in Ghana, its obligation under various multilateral environmental conventions. The thesis will also focus on some of Ghana’s policies on the environment and its international obligations and how it adopts measures to implement them. It will also focus on some of the challenges it faces in implementation and recommend proposals for action

Off-types indicate natural outcrossing in five tropical forage legumes in Colombia

Flower colour has been used as a simple morphological marker for genetic studies in many species, including legumes. In several tropical forage legumes, grown to evaluate their environmental adaptation or for seed increase, white-flowered plants were observed when the predominant flower colour was either yellow (Chamaecrista rotundifolia) or pink, lilac or purple (Centrosema virginianum, Codariocalyx gyroides, Desmodium heterocarpon and Galactia striata). Open pollination of these 5 species took place each at one of 4 sites in Colombia. Progeny from white-flowered plants were examined for flower colour to assess the proportion of off-types. This ranged on average from 4 percent for D. heterocarpon, through 13 percent for both G. striata and Ch. rotundifolia, and 18 percent for Ce. virginianum, to 23 percent for Co. gyroides. Large differences were recorded among accessions of the same species, particularly in Ce. virginianum, where 4 of the accessions apparently produced autogamous offspring and the other 5 had high proportions of off-types, with a rate as high as 89 percent. Consequences of these results for germplasm collection, management and seed increase are discussed

Fluidized bed as a solid precursor delivery system in a chemical vapor deposition reactor

Chemical vapor deposition (CVD) using precursors that are solids at operating temperatures and pressures, presents challenges due to their relatively low vapor pressures. In addition, the sublimation rates of solid state precursors in fixed bed reactors vary with particle and bed morphology. In a recent patent application, the use of fluidized bed (FB) technology has been proposed to provide high, reliable, and reproducible flux of such precursors in CVD processes. In the present contribution, we first focus on the reactor design which must satisfy fluidization,sublimation and CVD reactor feeding constraints. Then, we report masstransport results on the sublimation of aluminium acetylacetonate, a common precursor for the CVD of alumina films. Finally, we discuss the efficiency of the precursor feeding rate, we address advantages and drawbacks of the invention and we propose design modifications in order to meet the process requirements

The Effect of Providing Peer Information on Retirement Savings Decisions

We conducted a field experiment in a 401(k) plan to measure the effect of disseminating information about peer behavior on savings. Low-saving employees received simplified plan enrollment or contribution increase forms. A randomized subset of forms stated the fraction of age-matched coworkers participating in the plan or age-matched participants contributing at least 6% of pay to the plan. We document an oppositional reaction: the presence of peer information decreased the savings of non-participants who were ineligible for 401(k) automatic enrollment, and higher observed peer savings rates also decreased savings. Discouragement from upward social comparisons seems to drive this reaction.

On the path to translation: Highlights from the 2010 Canadian Conference on Ovarian Cancer Research

Ovarian cancer continues to be the most lethal of the gynaecologic malignancies due to the lack of early detection, screening strategies and ineffective therapeutics for late-stage metastatic disease, particularly in the recurrent setting. The gathering of researchers investigating fundamental pathobiology of ovarian cancer and the clinicians who treat patients with this insidious disease is paramount to meeting the challenges we face. Since 2002, the Canadian Conference on Ovarian Cancer Research, held every two years, has served this essential purpose. The objectives of this conference have been to disseminate new information arising from the most recent ovarian cancer research and identify the most pressing challenges we still face as scientists and clinicians. This is best accomplished through direct encounters and exchanges of innovative ideas among colleagues and trainees from the realms of basic science and clinical disciplines. This meeting has and continues to successfully facilitate rapid networking and establish new collaborations from across Canada. This year, more guest speakers and participants from other countries have extended the breadth of the research on ovarian cancer that was discussed at the meeting. This report summarizes the key findings presented at the fifth biennial Canadian Conference on Ovarian Cancer Research held in Toronto, Ontario, and includes the important issues and challenges we still face in the years ahead to make a significant impact on this devastating disease