Showing papers by "Universidade Federal de Minas Gerais published in 1998"

Biodiversity Hotspots and Major Tropical Wilderness Areas: Approaches to Setting Conservation Priorities

Abstract: The accelerating and potentially catastrophic loss of biotic diversity is unlike other environmental threats because it is irreversible. Given the rapid loss of biodiversity and limited resources available to address environmental issues, we must set priorities for our efforts to conserve biological resources. Because biodiversity is by no means evenly distributed, some areas are far richer than others in overall diversity and endemism. Furthermore, many of the richest areas also happen to be under the most severe threat. Over the next few decades, focusing conservation efforts on areas with the greatest concentrations of biodiversity and the highest likelihood of losing significant portions of that biodiversity will achieve maximum impact for conservation investment. By focusing on these high-priority areas we are not suggesting that other less diverse, less threatened areas should be written off, only that the high-biodiversity areas receive priority attention. Of the three different priority setting approaches we have used, we will discuss two in some detail: biodiversity hotspots and major tropical wilderness areas. A third approach, megadiversity countries, represents a country-based method intended mainly to better market biodiversity conservation in the world’s top 17 countries for species diversity and endemism (Mittermeier et al. 1997). All three of these approaches are based on five fundamental premises:

Regulation and Function of T-Cell-Mediated Immunity during Toxoplasma gondii Infection

Abstract: The intracellular protozoan Toxoplasma gondii is a widespread opportunistic parasite of humans and animals. Normally, T. gondii establishes itself within brain and skeletal muscle tissues, persisting for the life of the host. Initiating and sustaining strong T-cell-mediated immunity is crucial in preventing the emergence of T. gondii as a serious pathogen. The parasite induces high levels of gamma interferon (IFN-γ) during initial infection as a result of early T-cell as well as natural killer (NK) cell activation. Induction of interleukin-12 by macrophages is a major mechanism driving early IFN-γ synthesis. The latter cytokine, in addition to promoting the differentiation of Th1 effectors, is important in macrophage activation and acquisition of microbicidal functions, such as nitric oxide release. During chronic infection, parasite-specific T lymphocytes release high levels of IFN-γ, which is required to prevent cyst reactivation. T-cell-mediated cytolytic activity against infected cells, while easily demonstrable, plays a secondary role to inflammatory cytokine production. While part of the clinical manifestations of toxoplasmosis results from direct tissue destruction by the parasite, inflammatory cytokine-mediated immunopathologic changes may also contribute to disease progression.

Germ Cell Genotype Controls Cell Cycle during Spermatogenesis in the Rat

Abstract: Spermatogenesis is one of the most productive self-renewing systems in the body: on the order of 10(7) spermatozoa are produced daily per gram of testis tissue. In each mammalian species, the time required for completion of the process is unique and unalterable. Because the process is supported by somatic Sertoli cells, it has generally been thought that cell-cell interaction between germ and Sertoli cells controls the duration of cell cycles and cellular organization. We have used the newly developed technique of spermatogonial transplantation to examine which cell type(s) determines the rate at which germ cells proceed through spermatogenesis. Rat germ cells were transplanted into a mouse testis, and the mouse was killed 12.9-13 days after administration of a single dose of [3H]thymidine. The most advanced rat cell type labeled was the pachytene spermatocyte at stages VI-VIII of the spermatogenic cycle. In animals given only rat cells, some endogenous spermatogenesis of the mouse recovered. The most advanced labeled mouse cell types in recipients killed 12.9-13 days after administration of a single dose of [3H]thymidine were meiotic cells or young spermatids, which is consistent with a spermatogenic cycle length comparable to the 8.6 days reported for the mouse. The same results were obtained if a mixture of rat and mouse cells were transplanted. There existed two separate timing regimens for germ cell development in the recipient mouse testis; one of rat and one of mouse duration. Rat germ cells that were supported by mouse Sertoli cells always differentiated with cell cycle timing characteristic of the rat and generated the spermatogenic structural pattern of the rat, demonstrating that the cell differentiation process of spermatogenesis is regulated by germ cells alone.

Transfer of angular spectrum and image formation in spontaneous parametric down-conversion

Abstract: We show that the two-photon state generated in the process of spontaneous parametric down-conversion in a thin crystal carries information about the angular spectrum of the pump beam. This information transfer allows one to control the transverse correlation properties of the down-converted fields by manipulating the pump field, with consequences for a broad class of experiments. The effect is demonstrated theoretically and experimentally, in connection with the formation of fourth-order images by the down-converted beams.

Global patterns in local number of insect galling species

Abstract: . We evaluate a three-part hypothesis explaining why gall-inducing insect species richness is so high in scleromorphic vegetation: (1) persistence of low nutrient status scleromorphic leaves facilitates the galling habit in warm temperate latitudes; (2) favourable colonization sites for gallers result from reduced hygrothermal stress, high phenolics in the outer cortex of the gall, and reduced carnivore and fungal attack in the gall; and (3) in more mesic sites, mortality is high due to carnivore attack and invasion of galls by fungi. Over 280 samples of local species of galling herbivorous insects from fourteen countries on all continents except Antarctica revealed a strong pattern of highest richness in warm temperate latitudes, or their altitudinal equivalents. The peak of galling species richness on the latitudinal gradient from the equator into the Arctic was between 25 to 38° N or S. Galling species were particularly diverse in sclerophyllous vegetation, which commonly had greater than twelve species per local sample. In mesic, non-sclerophyllous vegetation types the number of galling species was lower with twelve or fewer species present. Many sites in sclerophyllous vegetation supported between thirteen and forty-six galling species locally, including campina islands in Amazonia, cerrado savanna in central Brazil, the Sonoran Desert in Arizona and Mexico, shrubland in Israel, fynbos in South Africa and coastal scleromorphic vegetation in Australia. At the same latitude, or its elevational equivalent, galling species richness was significantly higher in relatively xeric sites when compared to riparian or otherwise mesic habitats, even when scleromorphic vegetation dominated the mesic sites. The results were consistent with the hypothesis and extend to a more general level the patterns and predictions on the biogeography of gall-inducing insects.

Probing the genetic population structure of Trypanosoma cruzi with polymorphic microsatellites

Abstract: We describe here the identification of eight polymorphic microsatellite loci with (CA)n repeats in the Trypanosoma cruzi genome based on the affinity capture of fragments using biotinylated (CA)12 attached to streptavidin-coated magnetic beads. The presence of two peaks in PCR amplification products from individual clones confirmed that T. cruzi is diploid. Hardy–Weinberg and linkage disequilibrium analyses suggested that sexual reproduction is rare or absent and that the population structure is clonal. Several strains, especially those isolated from nonhuman sources, showed more than two alleles in many loci demonstrating that they were multiclonal. The phylogenetic analysis of T. cruzi based on microsatellites revealed a great genetic distance among strains, although the strain dispersion profile in the Wagner network was in general agreement with the species dimorphism found by PCR amplification of the divergent region of the rRNA 24Sα gene.

Microevolution of a standard strain of Cryptococcus neoformans resulting in differences in virulence and other phenotypes

Abstract: Cryptococcus neoformans is a major fungal pathogen for patients with debilitated immune systems. However, no information is available on the stability of virulence or of phenotypes associated with virulence for C. neoformans laboratory strains. A serendipitous observation in our laboratory that one isolate of C. neoformans ATCC 24067 (strain 52D) became attenuated after continuous in vitro culture prompted us to perform a comparative study of nine strain 24067 isolates obtained from six different research laboratories. Each isolate was characterized by DNA typing, virulence for mice, proteinase production, extracellular protein synthesis, melanin synthesis, carbon assimilation pattern, antifungal drug susceptibility, colony morphology, growth rate, agglutination titers, phagocytosis by murine macrophages, capsule size, and capsular polysaccharide structure. All isolates had similar DNA typing patterns consistent with their assignment to the same strain, although minor chromosome size polymorphisms were observed in the electrophoretic karyotypes of two isolates. Several isolates had major differences in phenotypes that may be associated with virulence, including growth rate, capsule size, proteinase production, and melanization. These findings imply that C. neoformans is able to undergo rapid changes in vitro, probably as a result of adaptation to laboratory conditions, and suggest the need for careful attention to storage and maintenance conditions. In summary, our results indicate that C. neoformans (i) can become attenuated by in vitro culture and (ii) is capable of microevolution in vitro with the emergence of variants exhibiting new genotypic and phenotypic characteristics.

Quantum Dynamical Manifestation of Chaotic Behavior in the Process of Entanglement

Abstract: Manifestation of chaotic behavior is found in an intrinsically quantum property. The entanglement process, quantitatively expressed in terms of the reduced density linear entropy, is studied for the $N$-atom Jaynes-Cummings model. For a given energy, initial conditions are prepared as minimum uncertainty wave packets centered at regular and chaotic regions of the classical phase space. We find for short times a faster increase in decoherence for the chaotic initial conditions as compared to regular ones, which have oscillatory increase.

Logging and Tropical Forest Conservation

Abstract: The international community has experimented with a range of strategies to conserve biodiversity and curb tropical deforestation. But new logging investments in primary tropical forests, including those made in the name of "sustainability," are likely to do more harm than good. Conservationists should instead focus on more investments in protected areas and creative ways to prevent the spread of logging in these rapidly-declining ecosystems.

Neoproterozoic oceanic remnants in eastern Brazil: Further evidence and refutation of an exclusively ensialic evolution for the Araçuaí–West Congo orogen

Abstract: The Aracuai (eastern Brazil) and West Congo (southwestern Africa) belts are counterparts of the same Neoproterozoic orogen located between the Sao Francisco and Congo cratons. The Macaubas Group represents a major passive margin sequence and is a key unit for interpreting the evolution of that orogen. The Salinas Formation is the distal rock assemblage of the Macaubas Group and consists of a deep-sea sand-mud sequence, and a volcanic-sedimentary unit called the Ribeirao da Folha facies. The latter includes metamorphosed volcanic-exhalative sediments associated with ocean-floor basalts (amphibolites). The magmatic protoliths of these amphibolites crystallized at about 816 ± 72 Ma (Sm-Nd whole-rock isochron, ϵ Nd(t) =+3.8 ± 0.2). Regional metamorphism reached the amphibolite facies at about 630 Ma (Rb-Sr whole-rock isochron), when slabs of ultramafic rocks were tectonically emplaced over the Ribeirao da Folha facies. We consider this volcanic-sedimentary facies and the coeval slabs of ultramafic rocks to be remnants of a branch of the Adamastor-Brazilide ocean. The extensive occurrence of syntectonic to late tectonic calc-alkalic granitoids along the internal domain of the Aracuai belt implies that a reasonably large amount of ocean crust was consumed, via an east-dipping subduction zone, during formation of the Aracuai–West Congo orogen.

Intracellular Signal Triggered by Cholera Toxin in Saccharomyces boulardii and Saccharomyces cerevisiae

Abstract: As is the case for Saccharomyces boulardii, Saccharomyces cerevisiae W303 protects Fisher rats against cholera toxin (CT). The addition of glucose or dinitrophenol to cells of S. boulardii grown on a nonfermentable carbon source activated trehalase in a manner similar to that observed for S. cerevisiae. The addition of CT to the same cells also resulted in trehalase activation. Experiments performed separately on the A and B subunits of CT showed that both are necessary for activation. Similarly, the addition of CT but not of its separate subunits led to a cyclic AMP (cAMP) signal in both S. boulardii and S. cerevisiae. These data suggest that trehalase stimulation by CT probably occurred through the cAMP-mediated protein phosphorylation cascade. The requirement of CT subunit B for both the cAMP signal and trehalase activation indicates the presence of a specific receptor on the yeasts able to bind to the toxin, a situation similar to that observed for mammalian cells. This hypothesis was reinforced by experiments with 125I-labeled CT showing specific binding of the toxin to yeast cells. The adhesion of CT to a receptor on the yeast surface through the B subunit and internalization of the A subunit (necessary for the cAMP signal and trehalase activation) could be one more mechanism explaining protection against the toxin observed for rats treated with yeasts.

Maps of epidemiological rates: a Bayesian approach

Abstract: This article presents statistical methods recently developed for the analysis of maps of disease rates when the geographic units have small populations at risk. They adopt the Bayesian approach and use intensive computational methods for estimating risk in each area. The objective of the methods is to separate the variability of rates due to differences between regions from the background risk due to pure random fluctuation. Risk estimates have a total mean quadratic error smaller than usual estimates. We apply these new methods to estimate infant mortality risk in the municipalities of the State of Minas Gerais in 1994.

Multivoicedness and univocality in classroom discourse: an example from theory of matter

Abstract: The analyses of talk amongst students in three episodes, video recorded from a teaching sequence on the particle model for Brazilian students (age 14‐15) is presented. The analysis has two dimensions: the discoursive dimension is an attempt to understand how meanings are constructed in the classroom as a result of discoursive interactions; the conceptual dimension comprises the description of the patterns of evolution of ideas of matter based on the notion of a conceptual profile of matter, in which conceptual and historical features of the atom concept are profiled with pupils’ and adolescents’ ideas on atomism. From the students talk we can hear the interaction among different ‘voices’, representing different zones of a conceptual profile of matter. In this interaction, the students resort to both ‘authoritative’ and ‘internally persuasive’ discourses. The analysis emphasizes the role of these two types of discourse and of epistemological and ontological obstacles in the construction of scientific meani...

Development of Germ Cell Transplants in Mice

Abstract: Development of spermatogonial transplants was studied by using 5- to 6-wk-old histocompatible mice as cell donors and sterile (W-locus) mice as recipients. Groups of animals transplanted with germ cell suspensions were killed at 10 min, 9 h, 24 h, 1 wk, 1 mo, 2 mo, and 3 mo along with age-matched "start" and "end" W-locus controls. Weight of testes increased significantly at 24 h through 3 mo after germ cell transplantation, suggesting that the infused cells quickly stimulated organ function. Small clones of young spermatocytes were evident at 1 mo and sperm at 2 mo. The percentage of tubular profiles containing active spermatogenesis originating from spermatogonia increased with time (0.8% at 1 mo, 8.9% at 2 mo, and 28.2% at 3 mo). Most transplanted germ cells were eliminated from the seminiferous epithelium through phagocytosis by Sertoli cells that occurred primarily before 1 wk, although some pachytene cells were able to proceed through meiosis by 1 wk. A variety of abnormal features are described that characterize developing spermatogenesis in the transplanted testis. Spermatogenesis improved quantitatively and qualitatively with time although released sperm were frequently engulfed by intratubular macrophages and Sertoli cells. A quantitative analysis of spermatogenesis from transplanted germ cells will serve as a basis for improving spermatogonial transplant efficiency.

The Pre-Main-Sequence Eclipsing Binary TY Coronae Australis: Precise Stellar Dimensions and Tests of Evolutionary Models

Abstract: We analyze new photometric data for the Herbig Be eclipsing binary TY CrA, which securely reveal the secondary eclipse, ~0.03 mag deep in y. From the light-curve solution and our previous spectroscopic data, absolute dimensions of the primary and secondary stars are derived. The masses are found to be M1 = 3.16 ± 0.02 M☉ and M2 = 1.64 ± 0.01 M☉, the radii are R1 = 1.80 ± 0.10 R☉ and R2 = 2.08 ± 0.14 R☉, the luminosities are L1 = 67 ± 12 L☉ and L2 = 2.4 ± 0.8 L☉, and the effective temperatures are T1 = 12,000 ± 500 K and T2 = 4900 ± 400 K. Here the uncertainties represent high-confidence limits, not standard deviations. The secondary star is a pre–main-sequence star located at the base of the Hayashi tracks. As such, it is the least evolved star with a dynamically measured mass. Given higher effective temperatures for the primary (e.g., 12,500 K), the solar-composition 1.64 M☉ evolutionary tracks of Swenson et al., Claret, and D'Antona & Mazzitelli are all consistent with the properties of the TY CrA secondary and suggest an age of order 3 Myr. The radius and projected rotational velocity of the secondary star are consistent with synchronous rotation. The primary star is located near the zero-age main sequence, which, for solar compositions, is consistent with an age of 3 Myr. However, the primary star is not well represented by any of the 3.16 M☉ evolutionary models, which predict somewhat higher effective temperatures than observed.

Critical behavior of the spin- 3 2 Blume-Capel model in two dimensions

Abstract: The phase diagram of the spin-3/2 Blume-Capel model in two dimensions is explored by conventional finite-size scaling, conformal invariance and Monte Carlo simulations. The model in its $\tau$-continuum Hamiltonian version is also considered and compared with others spin-3/2 quantum chains. Our results indicate that differently from the standard spin-1 Blume-Capel model there is no multicritical point along the order-disorder transition line. This is in qualitative agreement with mean field prediction but in disagreement with previous approximate renormalization group calculations. We also presented new results for the spin-1 Blume-Capel model.

Query performance for tightly coupled distributed digital libraries

Abstract: We consider a digital library distributed in a tightly coupled environment. The library is indexed by inverted files and the vector space model is used as ranking strategy. Using a simple analytical model coupled with a small simulator, we study how query performance is affected by the index organization, the network speed, and the disks transfer rate. Our results, which are based on the Tipster/Trec3 collection, indicate that a global index organization might outperform a local index organization.

Activity budget of Geoffroy's marmoset (Callithrix geoffroyi) in an Atlantic forest in southeastern Brazil

Abstract: This report describes the activity budget of a group of Callithrix geoffroyi in a patch of Atlantic forest on the Brazilian coast, between February 1993 and January 1994, using the scan sampling methods. On average, the group rested for 29% of the daylight hours, fed for 21%, moved for 20%, and foraging and gouging occupied 14% and 13% of this period, respectively. A greater proportion of time was spent resting during the wet seasons (32.1%) than the dry seasons (17.8%), but the reverse observed for time spent foraging (9.7% and 20.6% of the group's daylight hours during wet and dry seasons, respectively). The time allocated to feeding was greater in the first hours of the day. Gum consumption showed two peaks, a larger one in the early morning and a minor one in the afternoon. Animal prey foraging occurred throughout the day, but was more intense during the hottest hours. The increase in foraging and decrease in resting during the dry season was related to a decrease in the availability of insects.

On the non-equivalence of observables in phase-space reconstructions from recorded time series

Abstract: In practical problems of phase-space reconstruction, it is usually the case that the reconstruction is much easier using a particular recorded scalar variable. This seems to contradict the general belief that all variables of a dynamical system are equivalent in phase-space reconstruction problems. This paper will argue that, in many cases, the choice of a particular scalar time series from which to reconstruct the original dynamics could be critical. It is argued that different dynamical variables do not provide the same level of information (observability) of the underlying dynamics and, as a consequence, the quality of a global reconstruction critically depends on the recorded variable. Examples in which the choice of observables is critical are discussed and the level of information contained in a given variable is quantified in the case where the original system is known. A clear example of such a situation arises in the R ¨ ossler system for which the performance of a global vector field reconstruction technique is investigated using time series of variables x, y or z, taken one at a time.

Cataract formation after posterior chamber phakic intraocular lens implantation

Abstract: Posterior chamber phakic intraocular lens (PCP IOL) implantation is an emerging refractive procedure. We report a case of cataract formation 6 months after uneventful implantation of a Staar PCP IOL to correct high myopia. Visual recovery was achieved after explantation of the phakic IOL and phacoemulsification with implantation of a foldable IOL through the same unenlarged self-sealing corneal incision.

Community participation and control of endemic diseases in Brazil: problems and possibilities

Abstract: Community participation (CP) is considered one of the most important elements for the control of endemic diseases in poor countries, particularly for prevention and epidemiological surveillance. Mainly affecting the poorest segments of the population, endemic diseases are costly and require specific government action aimed at efficient, egalitarian, universal health system, where CP acts in a guardian, monitoring capacity and entails other specific tasks. Despite its rationality, CP has not been encouraged in countries like Brazil, due to the highly centralized nature of political power and activity. Several examples and situations of CP in Brazilian endemic diseases are described and discussed in the article. CP for endemic disease control should be seen as an ongoing social process, a profound social exercise, and a great challenge for the country as a whole and the new Unified Health System now being implemented in Brazil.

Pleistocene Bats from Cave Deposits in Bahia, Brazil

Abstract: Twenty-seven taxa of bats from late Pleistocene fossils originated from five caves in Bahia, Brazil. In one cave, humeri of Mormoops megalophylla were dated radiometrically to 20,060 ± 290 years ago. In another cave, a cranium of Desmodus rotundus was found adhering to the underside of a coprolite of a sloth ( Nothrotherium ) that had a radiometric age of 12,200 ± 120 radiocarbon years ago. Among taxa represented by the fossils were one extinct species ( Desmodus draculae ), the first South American fossil records for Mimon bennettii, Furipterus horrens , and Tadarida brasiliensis , and the first Brazilian fossil records for M. megalophylla, Phyllostomus discolor, Diphylla ecaudata , and Nyctinomops macrotis . All caves but one occur within the semiarid Caatinga biome today. However, fossil occurrences of several species ( M. megalophylla, M. bennettii , and Eptesicus fuscus ), which today select moister habitats or humid caves, suggest that conditions in the area during part of the late Pleistocene were wetter than at present.

Sliding mode algorithm for training multilayer artificial neural networks

Abstract: On-line learning algorithms for artificial neural networks (ANNs) are expected to adapt network parameters in order to face new control situations. A new on-line learning algorithm, based on sliding mode control (SMC) is presented. The results show that ANN inherits some of the advantages of SMC: high speed of learning and robustness.

The yeast genus Starmerella gen. nov. and Starmerella bombicola sp. nov., the teleomorph of Candida bombicola (Spencer, Gorin & Tullock) Meyer & Yarrow

Abstract: Seven strains of a heterothallic haploid yeast species were isolated from flowers of Calystegia sepium (hedge bindweed, Convolvulaceae) and associated sap beetles of the genus Conotelus. Conjugation was observed between some of the isolates and the type strain of Candida bombicola, resulting in evanescent asci with one ascospore with a convoluted surface. The sequences of the D1/D2 variable domain of the large subunit of the rDNAs of three strains differed by only one or two bases from that of the type strain. The new genus Starmerella, with the single species Starmerella bombicola. is proposed to accommodate the teleomorph of C. bombicola. The designated isotype is strain UWO(PS)97–1181(h-; CBS 84511).