Showing papers by "National University of Comahue published in 1992"
TL;DR: Galaxias maculatus and Odontesthes microlepidotus undertook significant habitat shifts in a small Araucanian lake during their early life history and a third movement, littoral-limnetic, is suggested through acoustic records of fish in the limnetic zone which correspond with the growth curve of littoran sampled juveniles.
Abstract: Galaxias maculatus and Odontesthes microlepidotus undertook significant habitat shifts in a small Araucanian lake during their early life history. After hatching in the littoral zone, free embryos migrate to the limnetic zone. Later, larvae return to the littoral. A third movement, littoral-limnetic, is suggested through acoustic records of fish in the limnetic zone which correspond with the growth curve of littoral sampled juveniles.
58 citations
TL;DR: The polyamines putrescine, spermidine, and spermine, are able to potentiate the toxicity of malathion in Bufo arenarum Hensel toad larvae and elevated up to 13-fold the mortality produced by this organophosphorus compound.
Abstract: The polyamines putrescine, spermidine, and spermine, are able to potentiate the toxicity of malathion in Bufo arenarum Hensel toad larvae. This action is synergistic and maximal with spermidine, which elevated up to 13-fold the mortality produced by this organophosphorus compound. Spermidine increased the degree of inhibition of acetylcholinesterase activity elicited by malathion, and impaired the recovery of this activity at the end of the treatment. Spermidine had no effect on the enzyme when applied alone. Toxic effects were also observed with the polyamines themselves when applied at concentrations similar to the intracellular levels described for rapid-growing organisms.
27 citations
TL;DR: Some aspects of the host-parasite relationships of Pomphorhynchus patagonicus (Acanthocephala) in 2 fish species from Lake Rosario were studied and the host species appears to influence attachment, size, sexual maturity, and distribution of parasites along the digestive tract.
Abstract: Some aspects of the host-parasite relationships of Pomphorhynchus patagonicus (Acanthocephala) in 2 fish species from Lake Rosario (Chubut, Argentina) were studied. The fish species Patagonina hatcheri (Atherinidae) is autochthonous, and Oncorhynchus mykiss (Salmonidae) is introduced. The host species appears to influence attachment, size, sexual maturity, and distribution of parasites along the digestive tract. In P. hatcheri, an effective major host, parasites are attached firmly to the wall of the gut, well developed, attain a greater size, and a large proportion of females is gravid with ripe eggs. In O. mykiss, an unsuccessful host, there were many unattached parasites that were small and not well developed; gravid females were rare and never had ripe eggs.
8 citations
Journal Article•
TL;DR: Metacercariae of three new species of Tylodelphys were found in the brain of Galaxias maculatus (Teleostei, Galaxiidae), at the Meliquina Lake, Neuquen Province, Argentina.
Abstract: Metacercariae of three new species of Tylodelphys (Trematoda, Diplostomatidae) were found in the brain of Galaxias maculatus (Teleostei, Galaxiidae), at the Meliquina Lake, Neuquen Province, Argentina. These metacercariae are morphologically described as Tylodelphys argentinus n. sp., Tylodelphys barilochensis n. sp. and Tylodelphys crubensis n. sp. This is the first time that a stage of genus Tylodelphys is mentioned parasitizing Galaxias maculatus. Metacercariae of T. barilochen sis n. sp. were also found in G. maculatus brain at the Perito Moreno Lake, Rio Negro Province, Argentina.
8 citations
Journal Article•
2 citations
24 Jun 1992
TL;DR: In this paper, a method to design optimal multivariable feedforward regulators for stochastic plants described by rational transfer matrices is presented, which involves spectral factorization and the solution of a polynomial matrix diophantine equation.
Abstract: A method to design optimal multivariable feedforward regulators is presented for stochastic plants described by rational transfer matrices. The plant is assumed to have an arbitrary feedback stabilizing compensator. Standard Wiener-Hopf variational argument is employed to minimize the weighted sum of inputs and outputs variances for both cases: continuous-time and discrete-time plants. The method involves spectral factorization and the solution of a polynomial matrix diophantine equation. The plant can be of non-minimum phase with delays. The solution is simple and computationally attractive. An example of feedforward on a distillation column is given to illustrate the design procedure.
2 citations
TL;DR: In this paper, a procedure for CTOD calculation under slow stable crack growth conditions is presented, which gives more accurate CTOD values than those obtained using existing standards, and can be used in tests in which the slow-stable crack growth is measured.
Abstract: A procedure for CTOD calculation under slow stable crack growth conditions is presented in this work. This procedure gives more accurate CTOD values than those obtained using existing standards, and can be used in tests in which the slow stable crack growth is measured. An analysis of the errors made, when the traditional ([I], ASTM STP 668, pp. 307-333) or the European Group of Fracture equations are used, is also made. A weighting factor on Δa is proposed for tests without crack growth measurement.
2 citations
01 Jan 1992
TL;DR: In this paper, a semi-empirical quantum chemistry model at a Hartree level of approximation was used to predict the structure of Aln clusters, and it was shown that icosahedral and cube-octahedral symmetries are almost degenerate.
Abstract: We use molecular dynamics with a semiempirical quantum chemistry model at a Hartree level of approximation to predict the structure of Aln clusters. The relative simplicity of this model allows us to relax up to few hundred atoms. We find that icosahedral and cube-octahedral symmetries are almost degenerate, but that for the cases where we performed annealing, deeper minima exist without symmetry.