A New Approach to Model Confined Suspensions Flows in Complex Networks: Application to Blood Flow

The modeling of blood flows confined in micro-channels or micro-capillary beds depends on the interactions between the cell-phase, plasma and the complex geometry of the network. In the case of capillaries or channels having a high aspect ratio (their longitudinal size is much larger than their transverse one), this modeling is much simplified from the use of a continuous description of fluid viscosity as previously proposed in the literature. Phase separation or plasma skimming effect is a supplementary mechanism responsible for the relative distribution of the red blood cell’s volume density in each branch of a given bifur- cation. Different models have already been proposed to connect this effect to the various hydrodynamics and geometrical parameters at each bifurcation. We discuss the advantages and drawbacks of these models and compare them to an alternative approach for modeling phase distribution in complex channels networks. The main novelty of this new formulation is to show that albeit all the previous approaches seek for a local origin of the phase segre- gation phenomenon, it can arise from a global non-local and nonlinear structuration of the flow inside the network. This new approach describes how elementary conservation laws are sufficient principles (rather than the complex arametric models previously proposed) to provide non local phase separation. Spatial variations of the hematocrit field thus result from the topological complexity of the network as well as nonlinearities arising from solving a new free boundary problem associated with the flux and mass conservation. This network model approach could apply to model blood flow distribution either on artificial micro-models, micro-fluidic networks, or realistic reconstruction of biological micro-vascular networks

Contingent Valuation in Community-Based Project Planning: The Case of Lake Bamendjim Fishery Restocking in Cameroon

The study examined the usefulness and relevance of the contingent valuation method (CVM) in community-based (CB) project planning and implementation. To elicit willingness to pay (WTP) values for the restocking of Lake Bamendjim with Tilapia nilotica and Heterotis niloticus fish species, the study used pre-tested questionnaires interviewer-administered to 1,000 randomly selected households in the Bambalang Region of Cameroon.The datawere elicitedwith the conventional referendumdesign and analysed using a referendum model. Empirical findings indicated that about 85% of the sampled households were willing to pay about CFAF1,054 (US$2.1) for the restocking project. This amount was found to be significantly related to the starting price used in the referendum design, household income, the gender of the respondent, the age of the respondent, household poverty status, and previous participation of a household in a community development project.The findings prompted the following recommendations. Firstly, in order to reduce community burden due to cash constraints, it is advisable for the mean estimate obtained for the scheme to be split into four instalments over a year. Secondly, since the success of the scheme largely depends on the governing roles of the scheme, it is further advisable for the community to allowthemanagement of the scheme to be handled by the elderly community members. Finally, it will be important during the financing of the scheme, to levy wealthier household heads an amount sufficient to subsidize poorer household heads who cannot afford to pay the threshold price.

The Distributional Impact of Healthcare Financing in Nigeria: A Case Study of Enugu State

The deregulation of healthcare financing and supply in Nigeria has shifted the healthcare system towards competitive market ideals. Households' decision to utilize healthcare is identical with healthcare financing. This financing arrangement has potentials for income redistribution in a society with already high levels of inequality in resource redistribution. This study attempts to examine the extent to which this system of healthcare financing leads to catastrophic expenditures, defined as a threshold percentage of a household's income, and the extend of impoverishment arising from healthcare spending. It also uses the Aronson, Johnson, and Lambert (1994) decomposition framework to analyze redistributive effects in terms of vertical and horizontal inequities, as well as re-ranking effect. The study finds that healthcare spending engenders high incidence of catastrophic spending and impoverishment in the population. It also finds that healthcare spending is pro-rich in its redistributive effect, with significant vertical and horizontal inequities as well as reranking inherent in the system. The paper suggests policy reforms that separate healthcare utilization from healthcare financing if the poor are to have access to healthcare services.Redistributive effects, Healthcare financing, Catastrophic financing, Impoverishing effects, Equity, Nigeria

Estimating the willingness to pay for community healthcare insurance in rural Nigeria

Health care financing in Nigeria is dominated by private out-of-pocket payment that is not affordable to the poor. This has greatly reduced access to quality health care for the predominantly rural poor. Insurance schemes as options for increasing access to health care services have not received considerable attention in Nigeria. In this regard, a community health prepayment scheme is proposed, and the Contingent Valuation Method is used to investigate the willingness of rural households to pay for this scheme. Contributing through agricultural commodities produced statistically higher estimates than through direct cash. Also, by incorporating uncertainty in responses using the Random Valuation Model, higher contribution amounts were obtained. This provides an option for its use in healthcare contingent valuation studies where respondents are uncertain about their true responses. The groups that are willing to pay lesser amounts into the scheme as compared with their counterparts are women, the less educated, and the less wealthy households.Health care financing, Prepayment scheme, contingent valuation, willingness to pay, dichotomous choice, uncertainy, random valuation, stochastic payment card

Cartografia automàtica de la fertilitat dels sòls del terme de El Poal (Lleida)

L'objectiu genèric del treball és, basant-se en l'existència d'un Sistema d'Informació de Sòls (SIS), arribar a millorar la utilització dels adobs com a factor de la producció agrària. Es tracta d'un treball per a: — Posar a punt una metodologia per a arribar a una aplicació d'un Banc de Dades de Sòls, concretament per a crear uns arxius en els quals hom conservi la informació referent al contingut en elements nodridors dels sòls, a nivell de parcel•la. —Elaborar mapes de fertilitat com a reflex de l'estat de la fertilització d'una àrea geogràfica concreta en un moment donat. —Proposar recomanacions d'adobatge que tinguin en compte els nivells de fertilitat del sòl i les extraccions dels diferents conreus. — Possibilitar les comparacions automàtiques dels nivells de fertilitat d'una mateixa zona al llarg del temps, per a facilitar la contrastació dels plans d'adobatge proposats. — Estudiar estratègies de fertilització mitjançant simulació.The generic objective of the work, based on the existence of the Soil Information System (SIS), is to succeed in the better use of fertilizers as a factor of agricultural production. It is a work to: —Prepare a methodology in order to be able to use a SOIL DATA BANK, specifically to create a file in which the information about the contents and nutritive elements of the soils is kept for each piece of ground. — Prepare maps of fertility reflecting the fertility level of a given geographical area at a given time. —Propose means of fertilising wich take into account the fertility level of the soil and the different mineral apportation of the plants grown there. — Make automatic comparisons of the fertility levels of the same zone through different years in order contrast the fertilizing plans wich are proposed. Study strategies of fertilizing through experiments.El objetivo genérico del trabajo es, basándose en la existencia de un Sistema de Información de Suelos (SIS), mejorar la utilización de los abonos como factor de la producción agraria. Se trata de un trabajo para: —Puesta a punto de una metodología para aplicar un Banco de Datos de Suelos, concretamente para crear archivos en los que se conserve la información referente al contenido en elementos nutritivos de los suelos, a nivel de parcela. —Elaborar mapas de fertilidad como reflejo del estado de la fertilización de una área geográfica concreta en un momento dado. —Proponer recomendaciones de abonado que tengan en cuenta los niveles de fertilidad del suelo y las extracciones de los diferentes cultivos. —Posibilitar las comparaciones automáticas de los niveles de fertilidad de una misma zona a lo largo del tiempo para facilitar el contraste de los planes de abonado propuestos. —Estudiar estrategias de fertilización mediante simulación

From cerebral blood flow modeling to vascular units map in primate cortex

The amazing topological and geometrical complexity of micro-vascular networks in the brain, and in other organs, has challenged many researchers for decades. Since the brain's vascular system is structured by a highly reticulated pial surface network which plunges down into a set of penetrating vessels, it is tempting to attribute a vascular unit to each penetrating arteriole. Recent experimental analysis have led to a breakthrough on the properties of the blood supply in the brain. Penetrating arterioles have been identified as the bottleneck of brain perfusion. Furthermore, it has also been realized that targeted clots of penetrating arterioles are not compensated by active changes in the diameter of their neighbor arteries. This observation suggests passive compensatory mechanisms resulting from the couplings between arteriolar territories consistent with other recent observations of active blood flow reorganization via collateral vessels (inter-arterial connections). A systematic investigation of the three-dimensional extent of compensation is not possible with experimental measurements but in silico simulations permit a systematic investigation of the spatial distribution of the brain perfusion

Brain Tumor Vascular Network Segmentation from Micro-Tomography

Micro-tomography produces high resolution images of bio- logical structures such as vascular networks. In this paper, we present a new approach for segmenting vascular network into pathological and normal regions from considering their micro-vessel 3D structure only. We define and use a condi- tional random field for segmenting the output of a watershed algorithm. The tumoral and normal classes are thus character- ized by their respective distribution of watershed region size interpreted as local vascular territories

Vascular network segmentation: an unsupervised approach

Micro-tomography produces high resolution images of biological structures such as vascular networks. In this paper, we present a new approach for segmenting vascular network into pathological and normal regions from considering their micro-vessel 3D structure only. We consider a partition of the volume obtained by a watershed algorithm based on the distance from the nearest vessel. Each territory is characterized by its volume and the local vascular density. The volume and density maps are first regularized by minimizing the total variation. Then, a new approach is proposed to segment the volume from the two previous restored images based on hypothesis testing. Results are presented on 3D micro-tomographic images of the brain micro-vascular network

From homogeneous to fractal normal and tumorous microvascular networks in the brain

We studied normal and tumorous three-dimensional (3D) microvascular networks in primate and rat brain. Tissues were prepared following a new preparation technique intended for high-resolution synchrotron tomography of microvascular networks. The resulting 3D images with a spatial resolution of less than the minimum capillary diameter permit a complete description of the entire vascular network for volumes as large as tens of cubic millimeters. The structural properties of the vascular networks were investigated by several multiscale methods such as fractal and power- spectrum analysis. These investigations gave a new coherent picture of normal and pathological complex vascular structures. They showed that normal cortical vascular networks have scale- invariant fractal properties on a small scale from 1.4 lm up to 40 to 65 lm. Above this threshold, vascular networks can be considered as homogeneous. Tumor vascular networks show similar characteristics, but the validity range of the fractal regime extend to much larger spatial dimensions. These 3D results shed new light on previous two dimensional analyses giving for the first time a direct measurement of vascular modules associated with vessel-tissue surface exchange

Blood pressure distribution in microvascular networks

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.Blood rheology is complex and nonlinear. The effective viscosity variations are important due to red blood cells packing inside capillaries, the socalled FåhræusLindquist effect, whilst concomitantly phase segregation appears in bifurcations. We have performed direct numerical simulations of different nonlinear rheological models of the blood on realistic threedimensional microvascular networks. These simulations point out two significant results. First, various rheological models lead to very similar pressure distributions over the whole range of physiologically relevant hematocrits. Secondly, different models for phase segregation lead to very distinct hematocrit distributions in the microvascular network. Moreover, for all the investigated rheological models, the hematocrit distribution very weakly affects the pressure distribution, when prescribing uniform pressure boundary conditions.The research was supported by GDR n° 2760 Biomécanique des fluides et des transferts Interaction fluide/structure biologique, the ASUPS A03 and A05 of Paul Sabatier University, Toulouse, France and the ANR project ANR06BLAN023801