The inverse problem of determining the filtration function and permeability reduction in flow of water with particles in porous media

The original publication can be found at www.springerlink.comDeep bed filtration of particle suspensions in porous media occurs during water injection into oil reservoirs, drilling fluid invasion of reservoir production zones, fines migration in oil fields, industrial filtering, bacteria, viruses or contaminants transport in groundwater etc. The basic features of the process are particle capture by the porous medium and consequent permeability reduction. Models for deep bed filtration contain two quantities that represent rock and fluid properties: the filtration function, which is the fraction of particles captured per unit particle path length, and formation damage function, which is the ratio between reduced and initial permeabilities. These quantities cannot be measured directly in the laboratory or in the field; therefore, they must be calculated indirectly by solving inverse problems. The practical petroleum and environmental engineering purpose is to predict injectivity loss and particle penetration depth around wells. Reliable prediction requires precise knowledge of these two coefficients. In this work we determine these quantities from pressure drop and effluent concentration histories measured in one-dimensional laboratory experiments. The recovery method consists of optimizing deviation functionals in appropriate subdomains; if necessary, a Tikhonov regularization term is added to the functional. The filtration function is recovered by optimizing a non-linear functional with box constraints; this functional involves the effluent concentration history. The permeability reduction is recovered likewise, taking into account the filtration function already found, and the functional involves the pressure drop history. In both cases, the functionals are derived from least square formulations of the deviation between experimental data and quantities predicted by the model.Alvarez, A. C., Hime, G., Marchesin, D., Bedrikovetski, P

Objectives Cluster solution of block tridiagonal systems

In order to exploit the capacities of cluster computing in relatively small numerical problems, we compare the performance of parallel algorithms for the solution of block tridiagonal linear systems, one based on cyclic reduction and the other on the divide and conquer paradigm

Indications for eye removal over a 13-year period at an ophthalmology referral center in São Paulo, Brazil

Purpose: To analyze the indications and types of eye removal at Latin America's highest-volume ophthalmic reference center in Sao Paulo, Brazil. Methods: A retrospective analysis was conducted of surgical pathological reports in the electronic database of the Ophthalmology Department of the Universidade Federal de Sao Paulo Hospital of patients who underwent eye-removal procedures between January 2000 and December 2012. Results: A total of 412 cases met the inclusion criteria for this study. The most common indications for eye removal were ocular melanoma and retinoblastoma, representing 35.4% and 31.1% of the total cases, respectively. Other frequent indications included endophthalmitis (6.3%), nonspecific inflammation (4.1%), squamous cell carcinoma (3.6%), panophthalmitis (3.4%), and phthisis bulbi (1.2%). The remaining indications accounted for 14.8% of all cases, with each accounting for <1% of the total cases. Enucleation was the most common eye-removal procedure seen in our study. Conclusions: The two most common indications for eye removal were ocular melanoma and retinoblastoma. Alternative treatment options are effective in limiting the need for eye removal but are constrained by our public center's socioeconomic context.Univ Cidade Sao Paulo, Fac Med, Sao Paulo, SP, BrazilUniv Montreal, Dept Ophthalmol, Montreal, PQ, CanadaUniv Fed Sao Paulo, Dept Pathol, Sao Paulo, SP, BrazilUniv Fed Sao Paulo, Ocular Oncol Serv, Dept Ophthalmol & Visual Sci, Sao Paulo, SP, BrazilMcGill Univ, Henry C Witelson Ocular Pathol Lab, Montreal, PQ, CanadaUniv Fed Sao Paulo, Dept Pathol, Sao Paulo, SP, BrazilUniv Fed Sao Paulo, Ocular Oncol Serv, Dept Ophthalmol & Visual Sci, Sao Paulo, SP, BrazilWeb of Scienc