Ameliorating Effect of Chloride on Nitrite Toxicity to Freshwater Invertebrates with Different Physiology: a Comparative Study Between Amphipods and Planarians

High nitrite concentrations in freshwater ecosystems may cause toxicity to aquatic animals. These living organisms can take nitrite up from water through their chloride cells, subsequently suffering oxidation of their respiratory pigments (hemoglobin, hemocyanin). Because NO2¿ and Cl¿ ions compete for the same active transport site, elevated chloride concentrations in the aquatic environment have the potential of reducing nitrite toxicity. Although this ameliorating effect is well documented in fish, it has been largely ignored in wild freshwater invertebrates. The aim of this study was to compare the ameliorating effect of chloride on nitrite toxicity to two species of freshwater invertebrates differing in physiology: Eulimnogammarus toletanus (amphipods) and Polycelis felina (planarians). The former species presents gills (with chloride cells) and respiratory pigments, whereas in the latter species these are absent. Test animals were exposed in triplicate for 168 h to a single nitrite concentration (5 ppm NO2-N for E. toletanus and 100 ppm NO2-N for P. felina) at four different environmental chloride concentrations (27.8, 58.3, 85.3, and 108.0 ppm Cl¿). The number of dead animals and the number of affected individuals (i.e., number of dead plus inactive invertebrates) were monitored every day. LT50 (lethal time) and ET50 (effective time) were estimated for each species and each chloride concentration. LT50 and ET50 values increased with increases in the environmental chloride concentration, mainly in amphipods. Results clearly show that the ameliorating effect of chloride on nitrite toxicity was more significant in amphipods than in planarians, likely because of the absence of gills (with chloride cells) and respiratory pigments in P. felina. Additionally, this comparative study indicates that the ecological risk assessment of nitrite in freshwater ecosystems should take into account not only the most sensitive and key species in the communities, but also chloride levels in the aquatic environmen

Melting behavior of large disordered sodium clusters

The melting-like transition in disordered sodium clusters Na_N, with N=92 and 142 is studied by using a first-principles constant-energy molecular dynamics simulation method. Na_142, whose atoms are distributed in two (surface and inner) main shells with different radial distances to the center of mass of the cluster, melts in two steps: the first one, at approx. 130 K, is characterized by a high intrashell mobility of the atoms, and the second, homogeneous melting, at approx. 270 K, involves diffusive motion of all the atoms across the whole cluster volume (both intrashell and intershell displacements are allowed). On the contrary, the melting of Na_92 proceeds gradually over a very wide temperature interval, without any abrupt step visible in the thermal or structural melting indicators. The occurrence of well defined steps in the melting transition is then shown to be related to the existence of a distribution of the atoms in shells. Thereby we propose a necessary condition for a cluster to be considered rigorously amorphouslike (totally disordered), namely that there are no space regions of the cluster where the local value of the atomic density is considerably reduced. Na_92 is the only cluster from the two considered that verifies this condition, so its thermal behavior can be considered as representative of that expected for amorphous clusters. Na_142, on the other hand, has a discernible atomic shell structure and should be considered instead as just partially disordered. The thermal behavior of these two clusters is also compared to that of icosahedral (totally ordered) sodium clusters of the same sizes.Comment: LaTeX file. 7 pages with 12 picture

Kierkegaard en Polo

Se informa en este trabajo del papel del pensamiento de Kierkegaard en la filosofía de Polo. Polo acoge las descripciones kierkegaardianas de la vida estética y sus reflexiones sobre el tedio; pero percibe la insuficiencia de apelar a una raíz interior del yo, frente a su propuesta del carácter de además de la persona humana

Static critical behavior of the ferromagnetic transition in LaMnO3.14 manganite

The ferromagnetic phase transition in LaMnO3.14 is investigated by measuring the dc magnetization as a function of magnetic field and temperature. Modified Arrott plot and Kouvel Fisher analysis yield estimates for the critical exponents beta, and gama, with values between that predicted for the Heisenberg model and mean field theory. At low fields we found an anomalous small value of beta, indicating that the critical behavior is influenced by the range of magnetic fields used.Comment: Presented at ICM 2000 conference. Accepted for publication at J. Magn. Magn. Mate

Datos estructurales del valle inferior de los ríos Nalón y Narcea (Asturias)

Se describen las características estructurales de la zona comprendida entre Oviedo-Avilés y Salas (Asturias). Destaca la presencia de un conjunto de estructuras plegadas y cabalgantes hercínicas, con dirección general NE-SW. Sobre éstas inciden otras, oblicuas, que las replieguan y resultan mucho más laxas. El Mesozoico y Terciario, suavemente plegados, se disponen en las depresiones creadas por los cabalgamientos reactivados, falla cantábrica y ondulaciones resultantes del replegamiento

Crossover in the nature of the metallic phases in the perovskite-type RNiO_3

We have measured the photoemission spectra of Nd$_{1-x}$Sm$_{x}$NiO$_{3}$, where the metal-insulator transition and the N\'{e}el ordering occur at the same temperature for $x \lesssim 0.4$ and the metal-insulator transition temperature ($T_{MI}$) is higher than the N\'{e}el temperature for $x \gtrsim 0.4$. For $x \le 0.4$, the spectral intensity at the Fermi level is high in the metallic phase above $T_{MI}$ and gradually decreases with cooling in the insulating phase below $T_{MI}$ while for $x > 0.4$ it shows a pseudogap-like behavior above $T_{MI}$ and further diminishes below $T_{MI}$. The results clearly establish that there is a sharp change in the nature of the electronic correlations in the middle ($x \sim 0.4$) of the metallic phase of the $R$NiO$_3$ system.Comment: 4 pages, 4 figure, submitted to Phys. Rev.

When are dynamic and static feedback equivalent?

AbstractAn open question in Control Theory over commutative rings is: When does dynamic feedback equivalence imply (static) feedback equivalence? A second open problem is: Given a linear system Σ=(A,B), when does there exist a matrix F such that A+BF is invertible? In this paper we solve both questions, obtaining two characterizations of stable rings

Nueva técnica de sutura artroscópica transósea del manguito de los rotadores: estudio anatómico

Se ha realizado un estudio anatómico experimental sobre cadáver que ha fundamentado el desarrollo de una técnica alternativa de reparación artroscópica del manguito rotador, puramente transósea. Se han utilizado 10 hombros de cadáver fresco congelado. Mediante una guía externa diseñada específicamente para esta técnica, se han efectuado perforaciones en el troquíter con diferentes angulaciones. En cada uno de los ángulos se ha medido la distancia al nervio axilar, así como el grosor de la pastilla ósea de troquíter obtenida. El análisis de los datos ha mostrado una distribución normal de los valores, y diferencias estadísticamente significativas entre los resultados obtenidos en cada ángulo de colocación de la guía externa (p<0.001). Conclusiones: La sutura artroscópica transósea del manguito rotador, realizada mediante una guía externa a través del deltoides, es una técnica factible, que puede llevarse a cabo con márgenes de seguridad respecto a una hipotética lesión del nervio axilar.An anatomical study with ten fresh shoulder specimens was carried out in order to establish the safest angle to perform a new arthroscopic technnique for true transosseous rotator cuff repair. With an external guide designed for this study, several osseous tunnels were made through the greater tuberosity using different angles. The minimum distance from the drill to the axillary nerve was measured with each angle, as well as the thickness of the osseous bridge in the greater tuberosity. Statistically significant differences were observed between the measurements obtained with each angle of the external guide (p<0.001). From our data it is concluded that transosseous arthroscopic repair of the rotator cuff with an external guide is a feasible technique and can be performed with minimal risk for the axillary nerve

Entrenamiento combinado de electroestimulación concéntrica y pliometría frente a entrenamiento voluntario

Se analizó si el entrenamiento con electroestimulación neuromuscular (EENM) dinámica podría mejora la velocidad, la fuerza explosiva y la fuerza máxima. Se formaron 5 grupos de entrenamiento: EENM concéntrica (Ed), EENM concéntrica más pliometría (EdP), voluntario (V), voluntario con pliometría (VP) y grupo control (GC). Los grupos experimentales entrenaron el cuádriceps durante 4 semanas (16 sesiones), valorándose el tiempo de carrera en 20 m (T-20), los saltos verticales SJ y CMJ y la fuerza máxima isométrica de los extensores de la rodilla (FMI). Los protocolos de entrenamiento realizados no modificaron los tests T-20, SJ ni CMJ, pero se observaron incrementos significativos en la FMI (+30.5% entre T1 y T2 y entre T1 y T3). La EENM dinámica parece no mejorar las acciones explosivas y de velocidad, sin embargo mejora la fuerza máxima isométrica en la misma cuantía que lo hace el entrenamiento voluntario