Innovative private micro-hydro power development in Rwanda

Under the “Private Sector Participation in Micro-Hydro Development Project in Rwanda”, four newly registered Rwandan companies are each constructing a micro-hydro electricity plant (100–500 kW) and building a low-voltage distribution grid. These companies financed their plants through their own equity and debt with support from the PSP Hydro project. This support comprised a subsidy of 30–50% of investment costs, technical and business development assistance, project monitoring and financial controlling. The experiences gained so far have important implications for similar future micro-hydro energy sector development projects and this paper puts forward three key messages: (i) institutional arrangements rather than technical quality determine the success of such projects; (ii) truly sustainable rural electrification through micro-hydro development demands a high level of local participation at all levels and throughout all project phases, not just after plant commissioning; and (iii) real impact and sustainability can be obtained through close collaboration of local private and financial sector firms requiring only limited external funds. In short, micro-hydro projects can and will be taken up by local investors as a business if the conditions are right. Applying these messages could result in an accelerated uptake of viable micro-hydro activities in Rwanda, and in the opinion of the authors elsewhere too.     

Testing degenerate polynomials

Two methods to test whether a given polynomial has two distinct roots whose quotient is a root of unity are discussed.     

Plasma Sprayed Dense MgO-Y2O3 Nanocomposite Coatings Using Sol-Gel Combustion Synthesized Powder

MgO-Y₂O₃ nanostructured composite powder (volume ratio of 50:50) was synthesized by a sol-gel combustion process which generated crystal sizes in the 10-20 nm range. The MgO-Y₂O₃ nanopowder was plasma sprayed using a conventional, DC arc plasma spray system. X-ray diffraction analysis shows that the as-sprayed MgO-Y₂O₃ coating is composed of cubic MgO and Y₂O₃ phases and has ~95% density. Microstructure characterization by SEM reveals that the as-sprayed coating has fine grain sizes of 100-300 nm as a result of rapid solidification. The hardness of the coating, 7.5 ± 0.6 GPa, is higher than that of coarse-grained, dense MgO, and Y₂O₃ ceramics. This approach demonstrates the potential of plasma spray processes for making thick, dense MgO-Y₂O₃ nanocomposite performs for applications as durable, infrared windows.     

Multiphase poroelastic modeling in semi-space for deformable reservoirs

Field observations suggest that while pressure depletion is a local process that occurs dominantly in reservoirs being exploited, it triggers a redistribution of effective stress in a more extensive domain that involves not just the adjacent strata, but the entire overburden and surrounding rocks out to considerable distances. In an infinite or semi-infinite domain, a petroleum reservoir can be simulated as a displacement discontinuity, permitting use of an efficient displacement discontinuity boundary element method to calculate surrounding stress and displacement changes. A 3D poroelastic finite element method is used to account for the local reservoir model. By coupling the displacement discontinuity and finite element models, a 3D poroelastic reservoir in an infinite or semi-infinite domain is simulated. The numerical model has been verified and numerical examples are given. Results show that the relative deformation properties of surrounding strata have significant effects on pressure drawdown and reservoir deformation during production, and thus should be taken into account.     

Numerical analysis of the stress distribution in single-lap shear tests under elastic assumption—Application to the optimisation of the mechanical behaviour

The single lap joint is the most used test in order to analyse the behaviour of an adhesive in an assembly as on one hand, the manufacturing of such specimens is quite easy, and on the other hand they require only a classic tensile testing machine. However, such specimens are associated with complex loading of the adhesive, i.e. non-uniform shear stress along the overlap length, quite large peel stress at the two ends of the overlap and significant edge effects associated with geometrical and material parameters. In addition, the stress concentrations can contribute to fracture initiation in the adhesive joints and thus can lead to an incorrect analysis of the adhesive behaviour. Therefore, understanding the stress distribution in an adhesive joint can lead to improvements in adhesively bonded assemblies. The first part of this paper presents the influence of edge effects on the stress concentrations in single lap joints under elastic assumption of the material and using a pressure-dependent elastic limit of the adhesive. In the second part, some usual geometries, proposed in the literature about stress limitation, are compared with respect to the maximum load transmitted by single lap joint. The last part presents some geometries, which significantly limit the influence of edge effects and are more appropriate for analysing the behaviour of the adhesive.     

Approximation algorithms for shop scheduling problems with minsum objective: A correction

We present a correction to the paper, “Approximation algorithms for shop scheduling problems with minsum objective” (Journal of Scheduling 2002; 5:287–305) by Queyranne and Sviridenko. This correction provides a correct derivation of its 2eρ approximation result. Wenhua Li and Jinjiang Yuan: Project supported by NNSFC (Grant 10371112) and NSFHN (Grant 0411011200). Maurice Queyranne: Supported by research grants from NSERC, the Natural Sciences and Engineering Research Council of Canada.     

Computational methods for database repair by signed formulae*

We introduce a simple and practical method for repairing inconsistent databases. Given a possibly inconsistent database, the idea is to properly represent the underlying problem, i.e., to describe the possible ways of restoring its consistency. We do so by what we call signed formulae, and show how the ‘signed theory’ that is obtained can be used by a variety of off-the-shelf computational models in order to compute the corresponding solutions, i.e., consistent repairs of the database. *This paper is a revised and extended version of [9].     

Pulsed Laser Deposition of Zr1-xCexO2 and Ce1-xLaxO2-x/2 for Buffer Layers and Insulating Barrier in Oxide Heterostructures

We have studied the pulsed laser deposition (PLD) of Zr_1-xCexO₂ and Ce_1-xLa_xO₂-x/2 initially to grow buffer layers for perovskite films deposited on Si, LaAlO₃, SrTiO₃ and MgO and then to produce tunneling barriers for cuprate or manganite heterostructures. On (1 0 0) Si, the deposition of Zr_1-xCexO₂ (x = 0.12) produces a smooth epitaxial layer (R _RMS = 0.25/1m²), which allows the further deposition of high quality YBa₂Cu₃O₇ (Tc 88 K) and La_0.7Sr_0.3MnO₃ films. On the other hand, the use of Ce_1-xLa_xO_2-x/2 (0 x 0.4) makes it possible to match the YBa₂Cu₃O₇ and La_0.7Sr_0.3MnO₃ layers to various substrates. The buffer layers are epitaxially grown with a 45° rotation of the in-plane axes with respect to those of the substrate, and the smoothness is high (R _RMS = 0.25/1m²). In the case of an ultra-thin barrier (2.5 nm) of Ce_1-xLa_xO_2-x/2 sandwiched in a La_0.7Sr_0.3MnO₃, the out-of-plane mismatch of 2 induces distortions at the interface steps, which propagate into the topmost La_0.7Sr_0.3MnO₃ layer. This is in contrast to the case of SrTiO₃ barriers where an ideal crystal continuity in the growth direction is observed.     

Atomic snapshots using lattice agreement

Summary Thesnapshot object is an important tool for constructing wait-free asynchronous algorithms. We relate the snapshot object to thelattice agreement decision problem. It is shown that any algorithm for solving lattice agreement can be transformed into an implementation of a snapshot object. The overhead cost of this transformation is only a linear number of read and write operations on atomic single-writer multi-reader registers. The transformation uses an unbounded amount of shared memory. We present a deterministic algorithm for lattice agreement that usedO (log² n) operations on 2-processorTest & Set registers, plusO (n) operations on atomic single-writer multi-reader registers. The shared objects are used by the algorithm in adynamic mode, that is, the identity of the processors that access each of the shared objects is determined dynamically during the execution of the algorithm. By a randomized implementation of 2-processorsTest & Set registers from atomic registers, this algorithm implies a randomized algorthm for lattice agreement that uses an expected number ofO (n) operations on (dynamic) atomic single-writer multi-reader registers. Combined with our transformation this yields implementations of atomic snapshots with the same complexity.Cambridge Research Laboratory, Digital Equipment Corporation Hagit Attiya received the B.Sc. degreeiin Mathematics and Computer Science from the Hebrew University of Jerusalem, in 1981, the M.Sc. and Ph.D. degrees in Computer Science from the Hebrew University of Jerusalem, in 1983 and 1987, respectively. She is presently a senior lecturer at the departtment of Computer Science at the Technion, Israel Institute of Technology. Prior to this, she has been a post-doctoral research associate at the Laboratory for Computer Science at M.I.T. Her general research interests are distributed computation and theoretical computer science. More specific interests include fault-tolerance, timing-based and asynchronous algorithms. Maurice Herlihy received the A.B. degree in Mathematics from Harvard University, and the M.S. and the Ph.D. degrees in Computer Science from M.I.T. From 1984 to 1989 he was a faculty member in the Computer Science Department at Carnegie Mellon University in Pittsburgh, PA. In 1989 he joined the research staff at the Digital Equipment Corporation's Cambridge Research Laboratory in Cambridge MA. Since 1994, he has been on the faculty at the Computer Science Department at Brown University. Dr. Herlihy's research interests encompass practical and theoretical aspects of distributed and concurrent computation. Ophir achman received a B.A. in computer science from the Technion, Haifa, Israel in 1989 and M.Sc. in computer science from the Technion, Haifa, Israel, in 1992. He is now studying for a D.Sc. in computer science at the Technion. His currentarea of research is distributed computing, and in particular, asynchronous shared memory systems.This work appeared in preliminary form in proceedings ofthe 6th International Workshop on Distributed Algorithms [12]. This research was partially supported by grant No. 92-0233 from the United States-Israel Binational Science Foundation (BSF), Jerusalem, Technion V.P.R. funds — B. and G. Greenberg Research Fund (Ottawa), and the fund for the promotion of research in the TechnionPart of the work of this author was performed while visiting DEC Cambridge Research Laboratory