Ensambles de arqueas y bacterias en la Zona de Mínimo Oxígeno del ecosistema de surgencia de Chile central determinados mediante biomarcadores orgánicos

Indexación: Web of Science; Scielo.Organic biomarkers were used to investigate the influence of seasonal changes in oxygenation and water chemistry on the distribution of archaea and bacteria in the water column and surface sediments of the continental shelf off central Chile (ca. 36°S), an area influenced by seasonal upwelling and the development of an oxygen minimum zone. We were interested in establishing if occurrence of archaea and bacteria responds to oxygenation and water chemistry for which we analyzed archaeal isoprenoid (i) and bacterial branched (br) glycerol dialkyl glycerol tetraethers (GDGTs). Our results combined with molecular data from a year round observational program at the same sampling site and depths indicatives the occurrence and dominance of the marine pelagic group Thaumarchaeota. Changes in the distribution of iGDGTs might be explained by (i) the presence of archaeal populations in sub-oxic waters, phylogenetically different from those in surface water, (ii) changes in the relative contribution of Euryarchaeota with depth, and (iii) a relationship between Thaumarchaeota and environmental factors other than temperature. Branched GDGTs were more abundant in the upper, oxic layer during the non-upwelling season, may be a result of higher river runoff, whereas their diversity was higher within sub-oxic waters. Our results indicate a vertical segregation of iGDGTs and brGDGTs, with predominance of archaeal biomarkers during the low productivity season.Se utilizaron biomarcadores orgánicos en para investigar la influencia de cambios estacionales en los niveles de oxigenación y la química del agua sobre la distribución de arqueas y bacterias en la columna de agua y los sedimentos superficiales de la plataforma continental frente a Chile central, un área influenciada por surgencia estacional asociada al desarrollo de una zona de mínimo oxígeno. Nuestro interés es establecer si la ocurrencia de arquea y bacteria responde a la oxigenación y química del agua para lo cual analizamos gliceroles dialquil gliceroles tetra-éteres (GDGTs) isoprenoides arqueanos (i) y ramificados bacterianos (r). Nuestros resultados, combinados con datos moleculares de observaciones durante un año en el mismo lugar y profundidades del sitio de estudio indican la presencia y dominancia del grupo arqueano marino- pelágico Thaumarchaeota. Los cambios observados en la distribución de iGDGTs podrían explicarse por (i) la presencia de poblaciones de arqueas marinas en la capa de agua sub-óxica, filogenéticamente diferentes a las de aguas superficiales, (ii) cambio en la contribución relativa de Euryarchaeota con profundidad, y (iii) una relación entre Thaumarchaeota y factores ambientales distintos a la temperatura. Los GDGTs ramificados fueron más abundantes en la capa óxica superior durante el periodo de no-surgencia, tal vez influenciado por la alta descarga de ríos, mientras que su diversidad fue más alta en el agua sub-óxica. Nuestros resultados indican una segregación vertical de los GDGTs isoprenoides y ramificados, con el predominio de biomarcadores arqueanos durante el periodo de baja productividad.http://ref.scielo.org/vq5y7

NONLINEAR MODELS WITH REPEATED MEASURES FOR ANALYZING DISEASE PROGRESS IN PLANT EPIDEMIOLOGY

Nonlinear models are commonly used in plant disease epidemiology to model temporal changes in the proportion of diseased plants (disease index). Most of the times they are fit using linearizing transformations or nonlinear least squares. These approaches assume that the disease index has a normal distribution, that they are independent and that they have constant variance. None of these assumptions can be justified in disease indices. In this paper we apply different strategies to model the progress of papaya ring spot virus in papaya. Using the logistic model we compare different strategies using the SAS® System. Marginal (population average) and subjectspecific interpretations of the models are discussed

Archaeal and bacterial assemblages in the Oxygen Minimum Zone of the upwelling ecosystem off Central Chile as determined by organic biomarkers

Organic biomarkers were used to investigate the infl uence of seasonal changes in oxygenation and water chemistry on the distribution of archaea and bacteria in the water column and surface sediments of the continental shelf off central Chile (ca. 36°S), an area infl uenced by seasonal upwelling and the development of an oxygen minimum zone. We were interested in establishing if occurrence of archaea and bacteria responds to oxygenation and water chemistry for which we analyzed archaeal isoprenoid (i) and bacterial branched (br) glycerol dialkyl glycerol tetraethers (GDGTs). Our results combined with molecular data from a year round observational program at the same sampling site and depths indicatives the occurrence and dominance of the marine pelagic group Thaumarchaeota. Changes in the distribution of iGDGTs might be explained by (i) the presence of archaeal populations in sub-oxic waters, phylogenetically different from those in surface water, (ii) changes in the relative contribution of Euryarchaeota with depth, and (iii) a relationship between Thaumarchaeota and environmental factors other than temperature. Branched GDGTs were more abundant in the upper, oxic layer during the non-upwelling season, may be a result of higher river runoff, whereas their diversity was higher within sub-oxic waters. Our results indicate a vertical segregation of iGDGTs and brGDGTs, with predominance of archaeal biomarkers during the low productivity season. KEYWORDS: Glycerol dialkyl glycerol tetraethers (GDGTs); archaea; bacteria; oxygen minimum zone; upwelling; Chil

Universal Magnetic-Field-Driven Metal-Insulator-Metal Transformations in Graphite and Bismuth

Applied magnetic field induces metal - insulator and re-entrant insulator-metal transitions in both graphite and rhombohedral bismuth. The corresponding transition boundaries plotted on the magnetic field - temperature (B - T) plane nearly coincide for these semimetals and can be best described by power laws T ~ (B - B_c)^k, where B_c is a critical field at T = 0 and k = 0.45 +/- 0.05. We show that insulator-metal-insulator (I-M-I) transformations take place in the Landau level quantization regime and illustrate how the IMT in quasi-3D graphite transforms into a cascade of I-M-I transitions, related to the quantum Hall effect in quasi-2D graphite samples. We discuss the possible coupling of superconducting and excitonic correlations with the observed phenomena, as well as the signatures of quantum phase transitions associated with the M-I and I-M transformations.Comment: 23 pages including 14 figure

The onset of dissipation in high-temperature superconductors: magnetic hysteresis and field dependence

Recently, we showed that the self-field transport critical current, Ic(sf), of a superconducting wire can be defined in a more fundamental way than the conventional (and arbitrary) electric field criterion, Ec = 1 microV/cm. We defined Ic(sf) as the threshold current, Ic,B, at which the perpendicular component of the local magnetic flux density, measured at any point on the surface of a high-temperature superconducting tape, abruptly crosses over from a non-linear to a linear dependence with increasing transport current. This effect results from the current distribution across the tape width progressively transitioning from non-uniform to uniform. The completion of this progressive transition was found to be singular. It coincides with the first discernible onset of dissipation and immediately precedes the formation of a measureable electric field. Here, we show that the same Ic,B definition of critical currents applies in the presence of an external applied magnetic field. In all experimental data presented here Ic,B is found to be significantly (10-30%) lower than Ic,E determined by the common electric field criterion of Ec = 1 microV/cm, and Ec to be up to 50 times lower at Ic,B than at Ic,E.Comment: 14 pages, 10 figure