Descripción: We discuss the evolution of the fluctuations in a symmetric φ c-exponential potential which provides a power-law expansion during inflation using both the gauge-invariant field Φ and the Sasaki-Mukhanov field.

Descripción: We discuss a semiclassical treatment to inflationary models from Kaluza-Klein theory without the cylinder condition. We conclude that the evolution of the early universe could be described by a geodesic trajectory of a cosmological 5D metric here proposed, so that the effective 4D FRW background metric should be a hypersurface on a constant fifth dimension. © 2003 Elsevier B.V. All rights reserved.

Descripción: Fil:Marenssi, S.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: The relationships between landscapes features evolution and soil genesis and distribution are studied. The area is located in southern Entre Rios province (33o00'-33o45'S and 58o30'-59o17'W). The Parana River Delta, has a complex genetic evolution, due to river processes, marine ingressions and aeolian actions. These processes resulted in an unstable landscape, that imprinted its particular features in soils. Nine geomorphic units were recognized: 1) Gualeguay river alluvial plain and terraces, 2) Arroyo Ñancay aluvial plain and terrazes, 3) Minor streams aluvial plains, 4) Gualeguay river delta, 5) Deltaic plain, 6) Beach ridges, 7) Old lagoon and tidal plain, 8) Loessic plain and 9) Dunes. Soils are mainly Entisols, Inceptisols and Mollisols, and a spatial trend is recognized in the Delta Region. Soil evolution is controlled by a) an active morphodynamic, b) soil landscape features that resulted in a dominant aquic regime of soils and c) Late Quaternary climatic fluctuations that resulted in sea level variations. Finally, soil development, soil features and distribution and soil drainage are studied in relation with landscape main features and evolution. © 2004 Asociación Geológica Argentina.

Descripción: The evolution of the turbulent properties in the solar wind, during the travel of the parcels of fluid from the Sun to the outer heliosphere still has several unanswered questions. In this work, we will present results of an study on the dynamical evolution of turbulent magnetic fluctuations in the inner heliosphere. We focused on the anisotropy of the turbulence integral scale, measured parallel and perpendicular to the direction of the local mean magnetic field, and study its evolution according to the aging of the plasma parcels observed at different heliodistances. As diagnostic tool we employed single-spacecraft correlation functions computed with observations collected by Helios 1 & 2 probes over nearly one solar cycle. Our results are consistent with driving modes with wave-vectors parallel to the direction of the local mean magnetic field near the Sun, and a progressive spectral transfer of energy to modes with perpendicular wave-vectors. Advances made in this direction, as those presented here, will contribute to our understanding of the magnetohydrodynamical turbulence and Alfvénic-wave activity for this system, and will provide a quantitative input for models of charged solar and galactic energetic particles propagation and diffusion throughout the inner heliosphere. © 2012 International Astronomical Union.

Descripción: We study in this paper the time evolution of the spreading process of a small drop in contact with a flat dry surface, using asymptotic techniques. We reduced the problem by solving a quasisteady self-similar macroscopic problem and matched with the precursor region solution, where the van der Waals forces are important. A final nonlinear third-order ordinary differential equation has been solved numerically using shooting methods based on the fourth-order Runge-Kutta techniques. We obtained how the capillary number changes when the drop size decreases with time. The evolution process then diverges slightly from that obtained using the spherical cap approximation. The influence of gravity is also considered for both hanging and sitting drops. © 1998 The American Physical Society.

Descripción: We study the emergence and evolution of AR NOAA 10314, observed on the solar disk during March 13-19, 2003. This extremely complex AR is of particular interest due to its unusual magnetic flux distribution and the clear rotation of the polarities of a d-spot within the AR. Using SOHO/MDI magnetograms we follow the evolution of the photospheric magnetic flux to infer the morphology of the structure that originates the AR. We determine the tilt angle variation for the d-spot and find a counter-clockwise rotation corresponding to a positive writhed flux tube. We compute the magnetic helicity injection and the total accumulated helicity in the AR and find a correlation with the observed rotation. © 2012 International Astronomical Union.

Descripción: We study the effects of the environment at zero temperature on tunneling in an open system described by a static double-well potential. We show that the evolution of the system in an initial Schrödinger cat state, can be summarized in terms of three main physical phenomena, namely decoherence, quantum tunneling and noise-induced activation. Using large-scale numerical simulations, we obtain a detailed picture of the main stages of the evolution and of the relevant dynamical processes. © 2007 IOP Publishing Ltd.

Descripción: Argentine operational rawinsonde records spanning a 30-year period (1968-1997) were used to study the climatology of the tropopause from the subtropics to the southern mid-latitudes, approximately along the 60°W meridian. The thermal tropopause annual cycle as well as its variability was analyzed at three sites: Resistencia (RES), Ezeiza (EZE), and Comodoro Rivadavia (CRD). Single and double tropopause observations were studied, given the comparatively frequent occurrence of double tropopause events at all three sites. The tropopause behavior at RES and CRD is distinct, whereas at EZE it shows a winter evolution similar to the one at CRD and a summer evolution closer to the one at RES, in agreement with the annual evolution of the subtropical jet. The tropopause evolution is discussed under the light of the dynamic climatology of southern South America. In the presence of double tropopause events and in terms of potential temperature, it should be noted that the upper tropopause temperature is close to the 380 K isentropic, i.e. the tropical tropopause layer. Moreover, the lower tropopause and single tropopause events are fairly close together, i.e. coincident with the lowermost stratosphere. Considering previous research and results from the present analysis, a definition of Extratropical Tropopause Layer (ExTL) is introduced in this work. It is proposed that the lowermost stratosphere should be regarded as the ExTL. Copyright © 2006 Royal Meteorological Society.

Descripción: Recent studies have shown the value of complementing standard taxonomy with genetic analyses to reveal cryptic diversity and to aid in the understanding of patterns of evolution. We surveyed variation in the COI mitochondrial gene in members of the three genera of centropagid copepods from the inland waters in Argentina. In general, we found a close association between molecular and morphological systematics in this group. Similar to findings for marine calanoids, genetic distances within Boeckella species were modest (< 4%), while distances among morphospecies were much larger (> 11%). Parabroteas is currently monotypic, although we detected cryptic genetic diversity, with two lineages showing 5.5% divergence. In contrast, Karukinka was not a valid genus, apparently representing an interesting and atavistic offshoot of B. poppei, a result reinforcing the value of considering both morphological and molecular evidence. Moreover, we used combined genetic and morphological information, analysed with maximum likelihood methods, to evaluate the common assumption that evolution tends to proceed via the loss of structures in crustaceans. Although analysis of other taxa and character types is required to evaluate fully the reduction hypothesis, our results suggest that structures may be gained readily as well as lost. © 2007 The Linnean Society of London.

Descripción: Background. The rapid evolution of genital morphology is a fascinating feature that accompanies many speciation events. However, the underlying patterns and explanatory processes remain to be settled. In this work we investigate the patterns of intraspecific variation and interspecific divergence in male genitalic morphology (size and shape) in the cactophilic sibling species Drosophila buzzatii and D. koepferae. Genital morphology in interspecific hybrids was examined and compared to the corresponding parental lines. Results. Despite of being siblings, D. buzzatii and D. koepferae showed contrasting patterns of genital morphological variation. Though genitalic size and shape variation have a significant genetic component in both species, shape varied across host cacti only in D. buzzatii. Such plastic expression of genital shape is the first evidence of the effect of rearing substrate on genitalic morphology in Drosophila. Hybrid genital morphology was not intermediate between parental species and the morphological resemblance to parental strains was cross-dependent. Conclusion. Our results suggest the evolution of different developmental networks after interspecific divergence and the existence of a complex genetic architecture, involving genetic factors with major effects affecting genital morphology. © 2007 Soto et al; licensee BioMed Central Ltd.

Descripción: In the present work, we have used the papillomavirus E7 oncoprotein to pursue structure-function and evolutionary studies that take into account intrinsic disorder and the conformational diversity of globular domains. The intrinsically disordered (E7N) and globular (E7C) domains of E7 show similar degrees of conservation and co-evolution. We found that E7N can be described in terms of conserved and coevolving linear motifs separated by variable linkers, while sequence evolution of E7C is compatible with the known homodimeric structure yet suggests other activities for the domain. Within E7N, inter-residue relationships such as residue co-evolution and restricted intermotif distances map functional coupling and co-occurrence of linear motifs that evolve in a coordinate manner. Within E7C, additional cysteine residues proximal to the zinc-binding site may allow redox regulation of E7 function. Moreover, we describe a conserved binding site for disordered domains on the surface of E7C and suggest a putative target linear motif. Both homodimerization and peptide binding activities of E7C are also present in the distantly related host PHD domains, showing that these two proteins share not only structural homology but also functional similarities, and strengthening the view that they evolved from a common ancestor. Finally, we integrate the multiple activities and conformations of E7 into a hierarchy of structure-function relationships. © 2012 Chemes et al.

Descripción: The proopiomelanocortin gene (POMC) encodes several bioactive peptides, including adrenocorticotropin hormone, α-, β-, and γ-melanocyte-stimulating hormone, and the opioid peptide β-endorphin, which play key roles in vertebrate physiology. In the human, mouse, and chicken genomes, there is only one POMC gene. By searching public genome projects, we have found that Tetraodon (Tetraodon nigroviridis), Fugu (Takifugu rubripes), and zebrafish (Danio rerio) possess two POMC genes, which we called POMCα and POMCβ, and we present phylogenetic and mapping evidence that these paralogue genes originated in the whole-genome duplication specific to the teleost lineage over 300 MYA. In addition, we present evidence for two types of subfunction partitioning between the paralogues. First, in situ hybridization experiments indicate that the expression domains of the ancestral POMC gene have been subfunctionalized in Tetraodon, with POMCα expressed in the nucleus lateralis tuberis of the hypothalamus, as well as in the rostral pars distalis and pars intermedia (PI) of the pituitary, whereas POMCβ is expressed in the preoptic area of the brain and weakly in the pituitary PI. Second, POMCβ genes have a β-endorphin segment that lacks the consensus opioid signal and seems to be under neutral evolution in tetraodontids, whereas POMCα genes possess well-conserved peptide regions. Thus, POMC paralogues have experienced subfunctionalization of both expression and peptide domains during teleost evolution. The study of regulatory regions of fish POMC genes might shed light on the mechanisms of enhancer partitioning between duplicate genes, as well as the roles of POMC-derived peptides in fish physiology.

Descripción: The 15 species in the weevil genus Galapaganus Lanteri 1992 (Entiminae: Curculionidae: Coleoptera) are distributed on coastal Peril and Ecuador and include 10 flightless species endemic to the Galapagos islands. These beetles thus provide a promising system through which to investigate the patterns and processes of evolution on Darwin's archipelago. Sequences of the mtDNA locus encoding cytochrome oxidase subunit I (COI) were obtained from samples of seven species occurring in different ecological zones of the oldest south-eastern islands: San Cristobal, Espanola and Floreana, and the central island Santa Cruz. The single most parsimonious tree obtained shows two well-supported clades that correspond to the species groups previously defined by morphological characters. Based on a mtDNA clock calibrated for arthropods, the initial speciation separating the oldest species, G. galapagoensis (Linell) on the oldest island, San Cristobal, from the remaining species in the Galapagos occurred about 7.2 Ma. This estimate exceeds geological ages of the extant emerged islands, although it agrees well with molecular dating of endemic Galapagos iguanas, geckos and lizards. An apparent explanation for the disagreement between geological and molecular time-frames is that about 7 Ma there were emerged islands which subsequently disappeared under ocean waters. This hypothesis has gained support from the recent findings of 11 -Myr-old submarine seamounts (sunken islands), south-east of the present location of the archipelago. Some species within the darwini group may have differentiated on the extant islands, 1-5 Ma.

Descripción: The purpose of the paper is to analyze the geomorphology and hydrodynamic of the coastal area, to model the evolution of the coastal cohesive cliffs and the handing dune barrier system along southern Buenos Aires coast. The morphology and evolution of coastal transverse profile are used as geoindicator of erosional susceptibility for planning and manage the coastal communities' development. The vulnerability to erosion increases from dune coasts, to stabilized dunes, cliffs covered with ramps, cliffs with ramps, cliffs with mixed ramps, inactive cliffs and active cliffs. Human intervention such as afforestation, urbanization, mining and interruption of the littoral drift by Quequen harbor groins, have altered the eolian and marine sand supply in the area, modifying the coastal profile configuration, trending to the disappearance of sand ramps.

Descripción: Drosophila serido Vilela & Sene is a polytypic and cactophilic species with broad geographic distribution in Brazil. The morphology of the aedeagi of eight natural populations of D. serido was analyzed. Based on features of their aedeagi, populations of D. serido were discriminated with an efficiency of nearly 75%. The analysis using the Mantel test suggests that the morphological divergence of D. serido is correlated with the geographic distance among populations. There is no single cause to explain the observed pattern; therefore, the results were discussed considering the three main hypotheses to explain the aedeagus evolution: lock and key, pleiotropy and sexual selection. Alternatively, the aedeagus variability of D. serido might be related to environmental causes, such as temperature and/or host cacti.

Descripción: With the purpose of modeling the process of mountain building, we investigate the evolution of the ridge produced by the convergent motion of a system consisting of two layers of liquids that differ in density and viscosity to simulate the crust and the upper mantle that form a lithospheric plate. We assume that the motion is driven by basal traction. Assuming isostasy, we derive a nonlinear differential equation for the evolution of the thickness of the crust. We solve this equation numerically to obtain the profile of the range. We find an approximate self-similar solution that describes reasonably well the process and predicts simple scaling laws for the height and width of the range as well as the shape of the transversal profile. We compare the theoretical results with the profiles of real mountain belts and find an excellent agreement. © 2010 American Institute of Physics.

Descripción: With the aim of describing the mountain building process, we have previously applied the lubrication approximation to obtain the evolution equations of the problem of two stacked layers of viscous fluids with different densities and different viscosities. The lubrication approximation is a perturbation method where the small parameter is the aspect ratio (thickness/lenght) of the current. This approximation is widely used to study the slow flow of one layer of a viscous fluid, but it is not well known under which conditions it can be applied in more general settings. Here we analyze in detail the assumptions needed to apply the lubrication theory to study the flow of two stacked viscous fluid layers. We employ the same perturbation method and we found that, besides the usual conditions (low Reynolds number and gentle slope), we must require that the viscosity and density ratios are of the order of unity. These requirements determine the range of validity of the equations of our model of the mountain building.

Descripción: The haploid DNA content of Aeshna confusa (2n = 27, n = 13 + XO, male). A. bonariensis (2n = 26, n = 12 + neo-XY, male) and A. cornigera planaltica (2n = 16, n = 7 + neo-XY, male) has been determined (2.16 ± 0.16 pg, 1.81 ± 0.17 pg, and 2.08 ± 0.08 pg, respectively). Despite the differences in chromosome size and number, differences in DNA content between species are not significant. The karyotypic analysis of Aeshna species leads to the conclusion that fusions between autosomes or autosome and the sex chromosome, are the only chromosome rearrangement that occurred during evolution. In the species here studied, fusions have taken place with a minimal loss of DNA; however, other species of the genus show important differences in genome size, which cannot only be justified by fusion events.