Small-Scale Finance for Water and Sanitation

The author argues that the case of lending for water and sanitation is a "classic market failure". Though it can be a productive activity for lenders and borrowers, there are a variety of factors that cause it to remain a small share of local commercial banks and micro-finance institutions' portfolios. The report outlines ways that government donors and philanthropists can be effective at spurring on this market

Direct and inverse measurement of thin films magnetostriction

Two techniques of measurements of thin film magnetostriction are compared: direct, when changes of the substrate curvature caused by the film magnetization are controlled, and inverse ("indirect"), when the modification of the magnetic anisotropy induced by the substrate deformation (usually bending) is measured. We demonstrate how both the elastic strength of the substrate and the effective magneto-mechanical coupling between the substrate deformation and magnetic anisotropy of the film depend on different conditions of bending. Equations to be used for magnetostriction value determination in typical cases are given and critical parameters for the corresponding approximations are identified.Comment: 13 pages, 10 figures, 1 table, submitted to JMM

Ossen – Le Castet

Date de l'opération : 1984 (SD) Inventeur(s) : Trémolet Cécile Au sud du village d’Ossen en Lavedan, le Castet est une motte d’éperon utilisant un relief naturel remodelé. La plate-forme sommitale présente une surface plane, tandis qu’un segment de fossé isole au sud le tertre du plateau voisin qui ne porte aucun vestige d’une basse-cour. Trois sondages ouverts sur la plate-forme ont permis d’identifier un bâtiment ruiné de plan rectangulaire (18,60 m x 9,30 m) construit en moellons liés au ..

Evaluating the Potential of Container-Based Sanitation

In the face of urbanization, alternative approaches are needed to deliver adequate and inclusive sanitation services across the full sanitation service chain. Container-based sanitation (CBS) consists of an end-to-end service—that is, one provided along the whole sanitation service chain—that collects excreta hygienically from toilets designed with sealable, removable containers and strives to ensure that the excreta is safely treated, disposed of, and reused. This report builds on four case studies (SOIL – Haiti, x-runner – Peru, Clean Team – Ghana, Sanergy – Kenya) to assess the role CBS can play in a portfolio of solutions for citywide inclusive sanitation (CWIS) services. The authors conclude that CBS approaches should be part of the CWIS portfolio of solutions, especially for poor urban populations for whom alternative on-site or sewer-based sanitation services might not be appropriate. Customer satisfaction with existing services is high and services provided by existing CBS providers are considered safe but have some areas for improvement. While the proportion of total CBS service costs covered by revenues is still small, CBS services are considered to be priced similarly to the main sanitation alternatives in their service areas. Recommendations include adopting a conducive policy and regulatory environment and exploring ways to ensure that CBS services are sustainably financed. The report also identifies areas for further analysis

Anomalous Hall effect in NiPt thin films

We study Hall effect in sputtered NixPt1-x thin films with different Ni concentrations. Temperature, magnetic field and angular dependencies are analyzed and the phase diagram of NiPt thin films is obtained. It is found that films with sub-critical Ni concentration exhibit cluster-glass behavior at low temperatures with a perpendicular magnetic anisotropy below the freezing temperature. Films with over-critical Ni concentration are ferromagnetic with parallel anisotropy. At the critical concentration the state of the film is strongly frustrated. Such films demonstrate canted magnetization with the easy axis rotating as a function of temperature. The magnetism appears via consecutive paramagnetic - cluster glass - ferromagnetic transitions, rather than a single second-order phase transition. But most remarkably, the extraordinary Hall effect changes sign at the critical concentration. We suggest that this is associated with a reconstruction of the electronic structure of the alloy at the normal metal - ferromagnet quantum phase transition.Comment: 12 pages, 17 figure

Size and polydispersity effect on the magnetization of densely packed magnetic nanoparticles

The magnetic properties of densely packed magnetic nanoparticles (MNP) assemblies are investigated from Monte Carlo simulations. The case of iron oxide nanoparticles is considered as a typical example of MNP. The main focus is put on particle size and size polydispersity influences on the magnetization curve. The particles are modeled as uniformly magnetized spheres isolated one from each other by a non magnetic layer representing the organic coating. A comparison with recent experimental results on $\gamma-$Fe$_2$O$_3$ powder samples differing by their size is given.Comment: To be published in the Journal of Applied Physics, to be found at http://jap.aip.org

First-principles calculation of magnetoelastic coefficients and magnetostriction in the spinel ferrites CoFe2O4 and NiFe2O4

We present calculations of magnetostriction constants for the spinel ferrites CoFe2O4 and NiFe2O4 using density functional theory within the GGA+U approach. Special emphasis is devoted to the influence of different possible cation distributions on the B site sublattice of the inverse spinel structure on the calculated elastic and magnetoelastic constants. We show that the resulting symmetry-lowering has only a negligible effect on the elastic constants of both systems as well as on the magnetoelastic response of NiFe2O4, whereas the magnetoelastic response of CoFe2O4 depends more strongly on the specific cation arrangement. In all cases our calculated magnetostriction constants are in good agreement with available experimental data. Our work thus paves the way for more detailed first-principles studies regarding the effect of stoichiometry and cation inversion on the magnetostrictive properties of spinel ferrites.Comment: 11 pages, 6 figure

Low rank updates in preconditioning the saddle point systems arising from data assimilation problems

The numerical solution of saddle point systems has received a lot of attention over the past few years in a wide variety of applications such as constrained optimization, computational fluid dynamics and optimal control, to name a few. In this paper, we focus on the saddle point formulation of a large-scale variational data assimilation problem, where the computations involving the constraint blocks are supposed to be much more expensive than those related to the (1, 1) block of the saddle point matrix. New low-rank limited memory preconditioners exploiting the particular structure of the problem are proposed and analysed theoretically. Numerical experiments performed within the Object-Oriented Prediction System are presented to highlight the relevance of the proposed preconditioners

Accounting for model error in strong-constraint 4DVar data assimilation

The strong constraint formulation of four-dimensional variational data assimilation (4DVar) assumes that the model used in the process perfectly describes the true dynamics of the system. However, this assumption often does not hold and the use of an erroneous model in strong constraint 4DVar can lead to a sub-optimal estimation of the initial conditions. We show how the presence of model error can be correctly accounted for in strong constraint 4D-Var by allowing for errors in both the observations and the model when considering the statistics of the innovation vector. We demonstrate that when these combined model error and observation error statistics are used in place of the standard observation error statistics in the strong constraint formulation of 4DVar, a statistically more accurate estimate of the initial state is obtained. The calculation of the combined model error and observation error statistics requires the specification of model error covariances, which in practice are often unknown. We present a method to estimate the combined statistics from innovation data that does not require explicit specification of the model error covariances. Numerical experiments using the linear advection equation and a simple nonlinear coupled model demonstrate the success of the new methods in reducing the error in the estimate of the initial state, even in the case when only the uncorrelated part of the model error is accounted for

Magnetoelectric coupling in polycrystalline FeVO4

We report coupling between magnetic and electric orders for antiferromagnetic polycrystalline FeVO4 in which magnetism-induced polarization has been recently found in noncollinear antiferromagnetic state below the second antiferromagnetic phase transition at TN2=15.7K. In this low symmetry phase space group P-1, the magnetic field dependence of electric polarization evidences a clear magnetoelectric coupling in the noncollinear spin-configured antiferromagnetic phase. The discontinuity of magnetodielectric effect observed at the vicinity of the polar to nonpolar transition evidences competition between different magnetodielectric couplings in the two different antiferromagnetic states. The existence of thermal expansion anomaly near TN2 and magnetostriction effect support magnetoelastically mediated scenario of the observed magnetoelectric effect.Comment: 4 pages, 6 figures, Phys. Rev. B 80, 172103 (2009