El efecto de arroyos tributarios de menor orden sobre el perifiton de un río de llanura

Confluence zones are important places to analyze discontinuities that succeed in the river continuum, when two streams of different order link up with their collector. In this work we analyzed the periphyton composition and structure in the confluence of two mountain streams, where Chocancharava river (Cuarto river) foothill reach begins, in Córdoba province. Monthly periphyton samples were taken by scraping a known surface, in three sites located in Piedras Blancas and San Bartolomé stream confluence at 550 m a.s.l. TWINSPAN classification and sample and species ordinations by means of Canonic Correspondence Analysis (CCA) were carried out. Seventy one algae species were determined. Bacillarophyceae and Chlorophyceae presented higher species richness. Dominant species were Cocconeis placentula var. euplypta and Achnanthidium minutissimum, both exhibited an annual bimodal distribution pattern, with maximal densities in autumn and spring. CCA clusters demonstrated seasonal changes in periphyton structure. Summer species were associated to higher temperature and precipitations, and winter species (were associated) to higher conductivity and pH. The tributary of minor order, San Bartolomé stream, evidenced a wider distance in the sample grouping; its flora was different in winter months, during the phase of low water levels. From the obtained results it is concluded that at the confluence sectors the composition and structure of the higher order stream is continuous with the principal river during low water levels while, during high water levels, the periphyton of both tributaries colonize the receiving river.Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) - Instituto de Limnología "Dr. Raul A. Ringuelet" (ILPLA

El efecto de arroyos tributarios de menor orden sobre el perifiton de un río de llanura

Confluence zones are important places to analyze discontinuities that succeed in the river continuum, when two streams of different order link up with their collector. In this work we analyzed the periphyton composition and structure in the confluence of two mountain streams, where Chocancharava river (Cuarto river) foothill reach begins, in Córdoba province. Monthly periphyton samples were taken by scraping a known surface, in three sites located in Piedras Blancas and San Bartolomé stream confluence at 550 m a.s.l. TWINSPAN classification and sample and species ordinations by means of Canonic Correspondence Analysis (CCA) were carried out. Seventy one algae species were determined. Bacillarophyceae and Chlorophyceae presented higher species richness. Dominant species were Cocconeis placentula var. euplypta and Achnanthidium minutissimum, both exhibited an annual bimodal distribution pattern, with maximal densities in autumn and spring. CCA clusters demonstrated seasonal changes in periphyton structure. Summer species were associated to higher temperature and precipitations, and winter species (were associated) to higher conductivity and pH. The tributary of minor order, San Bartolomé stream, evidenced a wider distance in the sample grouping; its flora was different in winter months, during the phase of low water levels. From the obtained results it is concluded that at the confluence sectors the composition and structure of the higher order stream is continuous with the principal river during low water levels while, during high water levels, the periphyton of both tributaries colonize the receiving river.Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) - Instituto de Limnología "Dr. Raul A. Ringuelet" (ILPLA

On the Nucleon Distribution Amplitude: The Heterotic Solution

We present a new nucleon distribution amplitude which amalgamates features of the Chernyak-Ogloblin-Zhitnitsky model with those of the Gari-Stefanis model. This "heterotic" solution provides the possibility to have asymptotically a small ratio \hbox{$\vert G_{M}^{n}\vert/G_{M}^{p}\le 0.1$}, while fulfilling most of the sum-rule requirements up to the third order. Using this nucleon distribution amplitude we calculate the electromagnetic and weak nucleon form factors, the transition form factor $\gamma p \Delta^{+}$ and the decay widths of the charmonium levels $^3S_{1}$, $^3P_{1}$, and $^3P_{2}$ into $p\bar p$. The agreement with the available data is remarkable in all cases.Comment: 15 pages, RUB-TPII-21/92 Preprin

La comunidad algal epilítica en hábitat de rabión en un arroyo serrano

In flowing water habitats areas of turbulent erosion, oxygenated waters and heterogeneity can be distinguished, which are called riffles. The objective of this study was to determine the composition and structure of the epilithic algal community in riffle habitat of Arroyo Achiras (Córdoba, Argentina). Two sampling sites were selected along the longitudinal gradient, one in mountainous zone (A) and another one in piedmont (B). In 2005 and 2006 epilithic samples were collected during periods of low and high waters and physico-chemical and hydraulic variables were measured. At each site algal abundance and frequency were determined. Similarity index, taxonomic richness, species diversity (Shannon) and evenness were calculated. Differences between both zones were analyzed by two-way ANOVAs. A total of 175 taxa were determined. The greatest similarity (67%) was observed between high and low water hydrological periods at site B. Ochrophyta dominated over the other algal divisions. The highest algal density was recorded at site B during the period of low water. Significant differences between sites and hydrological periods were observed in all biological parameters, except for abundance.Facultad de Ciencias Naturales y Muse

La comunidad algal epilítica en hábitat de rabión en un arroyo serrano

In flowing water habitats areas of turbulent erosion, oxygenated waters and heterogeneity can be distinguished, which are called riffles. The objective of this study was to determine the composition and structure of the epilithic algal community in riffle habitat of Arroyo Achiras (Córdoba, Argentina). Two sampling sites were selected along the longitudinal gradient, one in mountainous zone (A) and another one in piedmont (B). In 2005 and 2006 epilithic samples were collected during periods of low and high waters and physico-chemical and hydraulic variables were measured. At each site algal abundance and frequency were determined. Similarity index, taxonomic richness, species diversity (Shannon) and evenness were calculated. Differences between both zones were analyzed by two-way ANOVAs. A total of 175 taxa were determined. The greatest similarity (67%) was observed between high and low water hydrological periods at site B. Ochrophyta dominated over the other algal divisions. The highest algal density was recorded at site B during the period of low water. Significant differences between sites and hydrological periods were observed in all biological parameters, except for abundance.Facultad de Ciencias Naturales y Muse

Onychomycoses. Journal of Medical Mycology

International audienc

Soft pion theorem for hard near threshold pion production

We prove new soft pion theorem for the near threshold pion production by a hard electromagnetic probe. This theorem relates various near threshold pion production amplitudes to the nucleon distribution amplitudes. The new soft pion theorem is in a good agreement with the SLAC data for F_2^p(W,Q^2) for W^2 < 1.4 GeV^2 and 7 < Q^2 < 30.7 GeV^2.Comment: 9 pages, revised version, more general analysi

Octet-Baryon Form Factors in the Diquark Model

We present an alternative parameterization of the quark-diquark model of baryons which particularly takes care of the most recent proton electric form-factor data from the E136 experiment at SLAC. In addition to electromagnetic form factors of the nucleon, for which good agreement with data is achieved, we discuss the weak axial vector form factor of the nucleon as well as electromagnetic form factors of $\Lambda$ and $\Sigma$ hyperons. Technical advance in calculating the pertinent analytic expressions within perturbative quantum chromodynamics is gained by formulating the wave function of the quark-diquark system in a covariant way. Finally, we also comment on the influence of Sudakov corrections within the scope of the diquark model.Comment: 16 pages, WU-B 93-07, latex, uuencoded postscript files of 7 figures appended at the end of the latex fil