Analysis of a finite volume element method for the Stokes problem

In this paper we propose a stabilized conforming finite volume element method for the Stokes equations. On stating the convergence of the method, optimal a priori error estimates in different norms are obtained by establishing the adequate connection between the finite volume and stabilized finite element formulations. A superconvergence result is also derived by using a postprocessing projection method. In particular, the stabilization of the continuous lowest equal order pair finite volume element discretization is achieved by enriching the velocity space with local functions that do not necessarily vanish on the element boundaries. Finally, some numerical experiments that confirm the predicted behavior of the method are provided.

Conditions pour la consolidation de la paix en Côte d'Ivoire. Rapport narratif du séminaire Abidjan, septembre 2010.

Aquesta relatoria correspon al seminari internacional “Conditions pour la consolidation de la Paix en Côte d’Ivoire” coorganitzat per l’Institut Català Internacional per la Pau, el Centre de Recherche et Action pour la Paix (CERAP), l’Université de Bouaké, i la missió del PNUD a Costa d’Ivori, que es va realitzar a Abidjan entre el 27 i el 29 de setembre de 2010. La situació al país en el moment de la realització del seminari era difícil davant la celebració d’eleccions presidencials pocs mesos després. A la relatoria es recullen diferents aspectes sociopolítics que indicaven les greus fractures a les que s’enfrontava el país, així s’analitzen les qüestions relatives a la propietat de la terra, els problemes relacionats amb la nacionalitat i ciutadania ivoriana, les possibilitats de reorganització de l’estat i la situació del jovent, majoritari a la població ivoriana. Malauradament, les dificultats prèvies a les eleccions és van agreujar amb un resultat ajustat i la proclamació dels dos candidats com a guanyadors. Aquest desafortunat escenari ha fet encara més valuosa la present relatoria.

Recrudescence induced by cyclophosphamide of chronic Trypanosoma cruzi infection in mice is influenced by the parasite strain

Reactivation of chronic chagasic patients may occur upon use of immunosuppressive drugs related to kidney or heart transplantation or when they are affected by concomitant HIV infection. This recrudescence, however, does not occur in all chagasic patients exposed to immunosuppressive agents. We therefore investigated the influence of Trypanosoma cruzi strains in the recrudescence of the parasitism in mice at the chronic phase treated with cyclophosphamide, an immunosuppressor that blocks lymphocytes DNA synthesis and therefore controls B cells response. A large variation was detected in the percentages of newly established acute phases in the groups of mice inoculated with the different strains. We suggest that reactivation of chronic T. cruzi infections is influenced by the parasite intrinsic characteristics, a phenomenon that might occur in the human disease.

N-terminal amino acid sequences of the major outer membrane proteins from a Neisseria meningitidis group B strain isolated in Brazil

The four dominant outer membrane proteins (46, 38, 33 and 28 kDa) were detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in a semi-purified preparation of vesicle membranes of a Neisseria meningitidis (N44/89, B:4:P1.15:P5.5,7) strain isolated in Brazil. The N-terminal amino acid sequence for the 46 kDa and 28 kDa proteins matched that reported by others for class 1 and 5 proteins respectively, whereas the sequence (25 amino acids) for the 38 kDa (class 3) protein was similar to class 1 meningococcal proteins. The sequence for the 33 kDa (class 4) was unique and not homologous to any known protein.

Biological comparison between three clones of Trypanosoma cruzi and the strain of origin (Bolivia) with reference to clonal evolution studies

After isolating three clones of Trypanasoma cruzi (Bolivia), we first characterized them according to parasitaemia, pleomorphism and virulence, and then histopathologically. The study's interest lies on the hypothesis that clonal evolution of T. cruzi has a major impact on biologically relevant properties of this parasite. Data obtained from the studies of parasitaemia, pleomorphism and virulence showed no differences between the groups studied. As a final point, the histopathological study shows us a muscular tissue tropism both in clones and in their mother strain (Bolivia). In this paper, we conclude that Bolivia strain and clones isolated from it, pertaining to the same major clone share similar biological properties.

Positive Torsional Strain Causes the Formation of a Four-Way Junction at Replication Forks.

Research by L. Postow, C. Ullsperger, R.W. Keller, C. Bustamante, A.V. Vologodskii, and N.R. Cozzarelli, J. Biol. Chem. 2001, 276, 2790 Condensation and commentary by Alexander Bucka and Andrzej Stasiak, Universite ´ de Lausanne, Switzerland Purpose of the Study To demonstrate that positive torsional strain generated during DNA replication can lead to reversals of replication forks and, consequently can result in the formation of four-way DNA junctions

Biological characterization of clones derived from the edmonston strain of measles virus in comparison with schwarz and CAM-70 vaccine strains

Four virus clones were derived from the Edmonston strain of measles virus by repeated plaque purification. These clones were compared with the vaccine strains Schwarz and CAM-70 in terms of biological activities including plaque formation, hemagglutination, hemolysis and replication in Vero cells and chick embryo fibroblasts (CEF). Two clones of intermediate plaque yielded mixed plaque populations on subcultivation whereas the other two, showing small and large plaque sizes, showed stable plaque phenotypes. The vaccine strains showed consistent homogeneous plaque populations. All the Edmonston clones showed agglutination of monkey erythrocytes in isotonic solution while both vaccine strains hemagglutinated only in the presence of high salt concentrations. Variation in the hemolytic activity was observed among the four clones but no hemolytic activity was detected for the vaccine virus strains. Vaccine strains replicated efficiently both in Vero cells and CEF. All four clones showed efficient replication in Vero cells but different replication profiles in CEF. Two of them replicated efficiently, one was of intermediate efficiency and the other showed no replication in CEF. Two of the clones showed characteristics similar to vaccine strains. One in terms of size and homogeneity of plaques, the other for a low hemolytic activity and both for the efficiency of propagation in CEF.

Characterization of subpopulations (clones and subclones) of the 21 SF strain of Trypanosoma cruzi after long lasting maintenance in the laboratory

Several studies have shown a clonal structure of Trypanosoma cruzi and its possible correlation with the behavioral heterogeneity of the parasite strains. In the present study, the 21 SF strain, that have been maintained in laboratory by successive passages in mice, for more than 15 years, showing a stability of biological and isoenzymic characteristics has been cloned, with the objective of establishing the characters of its clones and subclones. With the technique of isolation of a single parasite from the blood of infected mice, 5 clones and 14 subclones have been obtained. After four passages into mice, inoculum of 10(5) was obtained for each clone and subclone and inoculated into mice weighing 10 to 12 g. These were used for the study of the biological behavior of the clones: evolution of parasitemia, morphology of blood forms and host mortality. For isoenzymic characterization, the clones and subclones were analyzed for ALAT, ASAT, GPI and PGM enzymes. Results have shown that the 5 clones and the 14 subclones disclosed a biological behavior similar to the parental strain, with minor variability of the parasitemic profiles and also the same isoenzymic patterns. These results confirm the stability of the 21 SF strain and indicate a clonal homogeneity of its populations. This is compatible with the hypothesis that the T. cruzi strains represent an equilibrium of either homogenous or heterogeneous populations.

The Changing Face of the Epidemiology of Tuberculosis due to Molecular Strain Typing: A Review

About one third of the world population is infected with tubercle bacilli, causing eight million new cases of tuberculosis (TB) and three million deaths each year. After years of lack of interest in the disease, World Health Organization recently declared TB a global emergency and it is clear that there is need for more efficient national TB programs and newly defined research priorities. A more complete epidemiology of tuberculosis will lead to a better identification of index cases and to a more efficient treatment of the disease. Recently, new molecular tools became available for the identification of strains of Mycobacterium tuberculosis (M. tuberculosis), allowing a better recognition of transmission routes of defined strains. Both a standardized restriction-fragment-length-polymorphism-based methodology for epidemiological studies on a large scale and deoxyribonucleic acids (DNA) amplification-based methods that allow rapid detection of outbreaks with multidrug-resistant (MDR) strains, often characterized by high mortality rates, have been developed. This review comments on the existing methods of DNA-based recognition of M. tuberculosis strains and their peculiarities. It also summarizes literature data on the application of molecular fingerprinting for detection of outbreaks of M. tuberculosis, for identification of index cases, for study of interaction between TB and infection with the human immunodeficiency virus, for analysis of the behavior of MDR strains, for a better understanding of risk factors for transmission of TB within communities and for population-based studies of TB transmission within and between countries

Evolutionary and convergence stability for continuous phenotypes in finite populations derived from two-allele models.

The evolution of a quantitative phenotype is often envisioned as a trait substitution sequence where mutant alleles repeatedly replace resident ones. In infinite populations, the invasion fitness of a mutant in this two-allele representation of the evolutionary process is used to characterize features about long-term phenotypic evolution, such as singular points, convergence stability (established from first-order effects of selection), branching points, and evolutionary stability (established from second-order effects of selection). Here, we try to characterize long-term phenotypic evolution in finite populations from this two-allele representation of the evolutionary process. We construct a stochastic model describing evolutionary dynamics at non-rare mutant allele frequency. We then derive stability conditions based on stationary average mutant frequencies in the presence of vanishing mutation rates. We find that the second-order stability condition obtained from second-order effects of selection is identical to convergence stability. Thus, in two-allele systems in finite populations, convergence stability is enough to characterize long-term evolution under the trait substitution sequence assumption. We perform individual-based simulations to confirm our analytic results.

Characterization of a Trypanosoma rangeli Strain of Colombian Origin

A Colombian strain of Trypanosoma rangeli was characterized by analyzing its behaviour in different axenic and cellular culture, its infection rate and the histopathological lesions produced in experimental animals. Although slight inflammatory infiltrations were shown in different histopathological sections, no pseudocysts could be observed. Grace's insect medium is better than liver infusion tryptose or artificial triatomine urine supplemented with proline when studying T. rangeli metacyclogenesis, with a peak of 32% trypomastigotes. High infection rates were found in VERO and J774 cells. Because of its 100% infectivity rates and adequacy of parasitemia levels, C23 strain is a suitable model of T. rangeli biology study

Chagas' Disease and HIV Co-infection: Genotypic Characterization of the Trypanosoma cruzi Strain

In the past few years, new aspects of the immunopathology of Chagas' disease have been described in immunosuppressed patients, such as fatal central nervous system lesions related to the reactivation of the parasite. This article is the first description of the genotypic characterization, at the strain level, of Trypanosoma cruzi isolated from a patient with Chagas` disease/AIDS co-infection. The presence of four hypodense lesions was observed in the cranial compute tomographic scan. The diagnosis of AIDS was assessed by the detection of anti-HIV antibodies using enzyme-linked immunosorbent assay (ELISA) and Western blot techniques. The CD4+ lymphocyte counts were maintained under 200 cells/mm3 during one year demonstrating the severity of the state of immunosuppression. Chagas' disease was confirmed by serological and parasitological methods. Trypomastigote forms were visualized in a thick blood smear. The parasite isolated is genotypically similar to the CL strain. The paper reinforces that cerebral Chagas' disease can be considered as another potential opportunistic infection in AIDS resulting from the reactivation of a dormant T. cruzi infection acquired years earlier.

On finite unions and finite products with the D-property

We show that the product of a subparacompact C-scattered space and a Lindelöf D-space is D. In addition, we show that every regular locally D-space which is the union of a finite collection of subparacompact spaces and metacompact spaces has the D-property. Also, we extend this result from the class of locally D-spaces to the wider class of D-scattered spaces. All the results are shown in a direct way.

Species and Strain-specific Typing of Cryptosporidium Parasites in Clinical and Environmental Samples

Cryptosporidiosis has recently attracted attention as an emerging waterborne and foodborne disease as well as an opportunistic infection in HIV infected individuals. The lack of genetic information, however, has resulted in confusion in the taxonomy of Cryptosporidium parasites and in the development of molecular tools for the identification and typing of oocysts in environmental samples. Phylogenetic analysis of the small subunit ribosomal RNA (SSU rRNA) gene has shown that the genus Cryptosporidium is comprised of several distinct species. Our data show the presence of at least four species: C. parvum, C. muris, C. baileyi and C. serpentis (C. meleagridis, C. nasorum and C. felis were not studied). Within each species, there is some sequence variation. Thus, various genotypes (genotype 1, genotype 2, guinea pig genotype, monkey genotype and koala genotype, etc.) of C. parvum differ from each other in six regions of the SSU rRNA gene. Information on polymorphism in Cryptosporidium parasites has been used in the development of species and strain-specific diagnostic tools. Use of these tools in the characterization of oocysts various samples indicates that C. parvum genotype 1 is the strain responsible for most human Cryptosporidium infections. In contrast, genotype 2 is probably the major source for environmental contamination of environment, and has been found in most oysters examined from Chesapeake Bay that serve as biologic monitors of surface water. Parasites of Cryptosporidium species other than C. parvum have not been detected in HIV+ individuals, indicating that the disease in humans is caused only by C. parvum.