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Controversies on the origin of life
International Microbiology , 2005,
Abstract: different viewpoints, many with deep philosophical and historical roots, have shaped the scientific study of the origin of life. some of these argue that primeval life was based on simple anaerobic microorganisms able to use a wide inventory of abiotic organic materials (i.e. a heterotrophic origin), whereas others invoke a more sophisticated organization, one that thrived on simple inorganic molecules (i.e. an autotrophic origin). while many scientists assume that life started as a self-replicative molecule, the first gene, a primitive self-catalytic metabolic network has also been proposed as a starting point. even the emergence of the cell itself is a contentious issue: did boundaries and compartments appear early or late during life's origin? starting with a recent definition of life, based on concepts of autonomy and open-ended evolution, it is proposed here that, firstly, organic molecules self-organized in a primordial metabolism located inside protocells. the flow of matter and energy across those early molecular systems allowed the generation of more ordered states, forming the cradle of the first genetic records. thus, the origin of life was a process initiated within ecologically interconnected autonomous compartments that evolved into cells with hereditary and true darwinian evolutionary capabilities. in other words, the individual existence of life preceded its historical-collective dimension.
Acedia y depresión. Aportes para una reconstrucción histórica
Rubén Peretó Rivas
E? : Revista de Humanidades Médicas & Estudios Sociales de la Ciencia y la Tecnología , 2011,
Abstract: Las numerosas historias de la depresión que se han escrito en las últimas décadas dedican, a mi juicio, pocas páginas al estudio de un importante antecedente de esta patología que tuvo lugar en ámbitos religiosos cerrados propios de los primeros siglos del cristianismo y, más adelante, durante la Edad Media. Me refiero al fenómeno espiritual denominado acedia y que fue objeto de estudio de notables personajes de esas épocas. Las manifestaciones de este fenómeno se asimilarán a las de la melancolía durante la modernidad y centrará la atención no solo de médicos sino también de literatos.El objeto de este artículo es delinear algunos elementos fundamentales de la acedia y sus estrechas relaciones con lo que hoy denominamos depresión, a través de una aproximación que tenga en cuenta principalmente los escritos de los autores cristianos patrísticos y medievales y sus proyecciones en la época moderna.
Food resources sustaining the fish fauna in a section of the upper S?o Francisco River in Três Marias, MG, Brazil
Alvim, M. C. C.;Peret, A. C.;
Brazilian Journal of Biology , 2004, DOI: 10.1590/S1519-69842004000200003
Abstract: with the purpose of determining the principal food resources responsible for maintaining the fishery yield in a section of the s?o francisco river, 6 sampling of the fish fauna were made downstream from the três marias dam, from september 1996 to july 1997. a total of 1,127 individuals of 35 species were captured, using gillnets with mesh sizes varying from 3 to 16 cm. the stomach contents of 33 species were examined in order to determine their diets. five trophic guilds were established, in the following order of importance: ilyophagous, herbivorous, piscivorous, terrestrial invertebrates feeders, and aquatic invertebrates feeders. the resources sustaining the fish fauna were mainly of allochthonous origin. the ichthyonenosis appears to be mainly dependent on the detritus chain. the ciliary forest and seasonal flooding pulses are the main suppliers of food for the fish fauna.
Stability of crack propagation during bending tests on brittle materials
Peret, C. M.;Rodrigues, J. A.;
Ceramica , 2008, DOI: 10.1590/S0366-69132008000300018
Abstract: applications of ceramic materials usually involve thermal stresses that can reduce their lifetime considerably. one of the most relevant mechanical properties for evaluating thermal shock damage resistance is the energy of fracture. in order to obtain this property, a stable crack growth regimen must be achieved throughout the test. in this paper, three-point bending tests are analyzed to determine how machine stiffness influences load point displacement rates. understanding the differences between recorded and adjusted displacement rates is important in determining the stability of crack growth. this statement is corroborated by experimental data on sintered high-alumina, low-cement refractory castables.
Fibras metálicas e sua influência no comportamento mecanico de concretos refratários durante a secagem
Peret, C. M.;Pandolfelli, V. C.;
Ceramica , 2005, DOI: 10.1590/S0366-69132005000100002
Abstract: the addition of fibers to refractory castables can improve their dry-out behavior by two main mechanisms: permeability increase or mechanical reinforcement. steel fibers present a great potential as reinforcement, because their tensile strength and modulus of elasticity are maintained even at high temperatures. in this work, the mechanical behavior and the resistance to spalling on the drying of a refractory castable containing short and long steel fibers (from 2 to 25 mm long) were evaluated, and compared to the behavior of the same castable with polyaramid (par) fibers. the steel fibers improved the work-of-fracture but were not efficient in avoiding damage upon drying. their volume, about one thousand times that of the polymeric fibers, results in a lower number of fibers per unit volume of the castable. therefore, localized stress fields in the matrix cannot have full benefit from the reinforcement provided by these fibers. the results attested the need of taking into account the magnitude of the expected stress fields in order to define the size and shape of the reinforcement particles that will lead to an optimum performance.
Diet, reproduction and population structure of the introduced Amazonian fish Cichla piquiti (Perciformes: Cichlidae) in the Cachoeira Dourada reservoir (Paranaíba River, central Brazil)
Ferraz Luiz,Tatiane; Roquetti Velludo,Marcela; Carvalho Peret,Alberto; Rodrigues Filho,Jorge Luiz; Moldenhauer Peret,André;
Revista de Biología Tropical , 2011,
Abstract: the blue peacock bass (cichla piquiti), native to the tocantins-araguaia river basin of the amazon system, was introduced into the basin of the paranaíba river, paraná river system. cachoeira dourada reservoir is one of a series of dams on the paranaíba river in central brazil, where this fish has become established. a study of its feeding spectrum, combined with information about its reproductive characteristics and population structure, would enable the current state of this species in the reservoir to be assessed and might provide useful data for the management of other species native to this habitat. this study showed that the peacock bass has no predators or natural competitors in the reservoir and that reproduces continuously, with high reproductive rates, and has a smaller median length at first maturity (l50) than other species of cichla. its successful establishment in habitats strongly affected by human activity should cause changes in the whole structure of the local fish communities. nonetheless, in this reservoir, there appears to be some sharing of the functions of this species with native carnivorous fish, a situation that may be sustained by the presence of a wide variety of foraging fish. rev. biol. trop. 59 (2): 727-741. epub 2011 june 01.
Metabolic Networks of Sodalis glossinidius: A Systems Biology Approach to Reductive Evolution
Eugeni Belda, Francisco J. Silva, Juli Peretó, Andrés Moya
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0030652
Abstract: Background Genome reduction is a common evolutionary process affecting bacterial lineages that establish symbiotic or pathogenic associations with eukaryotic hosts. Such associations yield highly reduced genomes with greatly streamlined metabolic abilities shaped by the type of ecological association with the host. Sodalis glossinidius, the secondary endosymbiont of tsetse flies, represents one of the few complete genomes available of a bacterium at the initial stages of this process. In the present study, genome reduction is studied from a systems biology perspective through the reconstruction and functional analysis of genome-scale metabolic networks of S. glossinidius. Results The functional profile of ancestral and extant metabolic networks sheds light on the evolutionary events underlying transition to a host-dependent lifestyle. Meanwhile, reductive evolution simulations on the extant metabolic network can predict possible future evolution of S. glossinidius in the context of genome reduction. Finally, knockout simulations in different metabolic systems reveal a gradual decrease in network robustness to different mutational events for bacterial endosymbionts at different stages of the symbiotic association. Conclusions Stoichiometric analysis reveals few gene inactivation events whose effects on the functionality of S. glossinidius metabolic systems are drastic enough to account for the ecological transition from a free-living to host-dependent lifestyle. The decrease in network robustness across different metabolic systems may be associated with the progressive integration in the more stable environment provided by the insect host. Finally, reductive evolution simulations reveal the strong influence that external conditions exert on the evolvability of metabolic systems.
Alimenta??o de peixes (osteichthyes, characiformes) em duas lagoas de uma planície de inunda??o brasileira da bacia do rio paraná
Mar?al-Simabuku,Mara Adriana; CarvAlho Peret,Alberto;
Interciencia , 2002,
Abstract: feeding of common species such as cyphochacax modestus, c. nagelii, prochilodus scrofa, leporinus lacustris and hoplias malabaricus was studied in two different environments of the mogi-gua?u river floodplain: an oxbow lake seasonally flooded and an artificial lake with permanent connection with the main channel. the diets were studied through one river flood cycle, from september 1997 to october 1998, when no large flooding occured. for interespecific comparisons, previous data from leporinus aff. friderici and schizodon nasutus species has been included. differences in relation to food activity were observed among the species, in the wet and dry seasons, and according to the environments. from stomach content analises, c. modestus, c. nagelii and p. scrofa were considered as iliophagous species, l. lacustris as omnivorous with herbivorous tendency, while l. aff. friderici was predominantly omnivorous; s. nasutus was considered as an herbivorous species and h. malabaricus piscivorous. high values of food overlap (>0,60) were verified in both wet and dry seasons.
Structure of the phytoplankton community in the Cachoeira Dourada reservoir (GO/MG), Brazil
Teixeira de Oliveira, M.;Rocha, O.;Peret, AC.;
Brazilian Journal of Biology , 2011, DOI: 10.1590/S1519-69842011000400003
Abstract: the limnological features and the phytoplankton community of the cachoeira dourada reservoir were analyzed in december 2006, may 2007 and november 2007. temporal changes in the taxonomic composition, density, diversity and dominance of species were analyzed in relation to climatic factors and the physical and chemical characteristics of the water. a positive correlation was found between some of the physical and chemical variables and the phytoplankton community. according to the cca, variables such as the extent of the euphotic zone, temperature, ph, nitrogen and phosphorus concentrations directly affected the phytoplankton dynamics. organisms belonging to the class cyanophyceae were the most representative in all the sampling periods, comprising the functional groups k, s1, m and h. hydrodynamics and seasonal fluctuations of environmental factors were the driving forces determining the composition and abundance of the algal assemblages. despite the prevalence of cyanobacteria, the reservoir is still oligotrophic. the absence of blooms and the relatively low population abundances indicated that the quality of the reservoir's water still lies within the limits required for its multiples uses.
Oxygen demand during mineralization of aquatic macrophytes from an oxbow lake
Bianchini Jr., I.;Cunha-Santino, MB.;Peret, AM.;
Brazilian Journal of Biology , 2008, DOI: 10.1590/S1519-69842008000100009
Abstract: this study presents a kinetic model of oxygen consumption during aerobic decomposition of detritus from seven species of aquatic macrophytes: cabomba furcata, cyperus giganteus, egeria najas, eichhornia azurea, salvinia auriculata, oxycaryum cubense and utricularia breviscapa. the aquatic macrophytes were collected from óleo lagoon situated in the mogi-gua?u river floodplain (sp, brazil). mineralization experiments were performed using the closed bottles method. incubations made with lake water and macrophytes detritus (500 ml and 200 mg.l-1 (dm), respectively) were maintained during 45 to 80 days at 20 °c under aerobic conditions and darkness. carbon content of leachates from aquatic macrophytes detritus and dissolved oxygen concentrations were analyzed. from the results we concluded that: i) the decomposition constants differ among macrophytes; these differences being dependent primarily on molecular and elemental composition of detritus and ii) in the short term, most of the oxygen demand seems to depend upon the demineralization of the dissolved carbon fraction.
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