Phantom reflexes: Muscle contractions at a frequency not physically present in the input stimuli Manjarrez, Elías; Balenzuela, Pablo; García Ojalvo, Jordi; Vásquez, E.E.; Martínez, Lourdes; Flores, A.; Mirasso, Claudio R. In the motor system, the periodic stimulation of one Ia-afferent input produces reflex muscle contractions at the input frequency. However, we observed that when two Ia monosynaptic reflex-afferent inputs are involved the periodic muscle contractions may occur at a frequency physically not present in the afferent inputs even when these inputs are sub-threshold. How can the muscles respond with such phantom reflex contractions at a frequency physically absent in the sub-threshold Ia-afferent input stimuli? Here we provide an explanation for this phenomenon in the cat spinal cord, that we termed "ghost motor response". We recorded monosynaptic reflexes in the L7 ventral root, intracellular potentials in the motoneurons, and the associated muscular contractions elicited by stimulation of the lateral and medial gastrocnemius nerves. By stimulating with periodic pulses of sub-threshold intensities and distinct frequencies of 2 and 3 Hz the lateral and medial gastrocnemius nerves, respectively, we observed monosynaptic responses and phantom reflex muscle contractions occurring at the fundamental frequency (1 Hz), which was absent in the input stimuli. Thus we observed a reflex ghost motor response at a frequency not physically present in the inputs. We additionally studied the inharmonic case for sub-threshold stimuli and observed muscular contractions occurring at much lower frequencies, which were also conspicuously absent in the inputs. This is the first experimental evidence of a phantom reflex response in the nervous system. The observed behavior was modeled by numerical simulations of a pool of neurons subjected to two different input pulses.

CDW theoretical description of the single ionization of argon by positron and electron impact Otranto, Sebastián; Olson, Ronald E. In this work, we consider the single ionization of Ar by 200 eV positron and electron impact. The quantum mechanical continuum distorted wave (CDW) model is used in the one-active electron approximation. Parametrizations of Hartree-Fock potentials by Garvey et al. are used to represent the interaction of the light particles with the Ar + ion. The post collisional interaction (PCI) between the emitted electron and the receding projectile is naturally considered by the present model. Comparison with recent experimental data for very asymmetric geometries is made. The role of the PCI is studied by analyzing the differences in the angular distributions for positron and electron impact predicted by the CDW model and the first Born approximation.

Evolution of the properties of PtGe/Al2O3 reforming catalysts with Ge content Mariscal, Rafael; García Fierro, José Luis; Yori, Juan Carlos; Parera, Jose; Grau, Javier Mario The effect of the Pt/Ge atomic ratio on the catalytic activity of PtGe/Al2O3 catalysts used in n-heptane reforming was studied. The samples were prepared by the coimpregnation method on chlorinated alumina. The platinum content was 0.5 wt.%, and Ge-loading was varied to obtain Pt/Ge atomic ratios of 0.3, 0.7, 1.4, 2.1 and 3.5. Pt/Al2O3 and Ge/Al2O3 catalysts were also prepared as references. Characterization was carried out by temperature-programmed reduction (TPR), temperature-programmed desorption of ammonia (NH3-TPD), Fourier transform IR spectroscopy (FTIR) with CO as the probe molecule, X-ray photoelectron spectroscopy (XPS), cyclohexane (CH) dehydrogenation, and n-heptane reforming. The preparation method followed in this work revealed a decrease in the metallic activity of Pt due to the presence of Ge. The Ge2+ and Ge4+ species, after reduction at 500 °C, were detected on the surface of PtGe catalysts. The increase in the Ge content led to a decrease in hydrogenolysis activity and the formation of aromatics; an increase in the formation of isomers and cycloparaffins, and a reduction in the production of gas and in deactivation by coke, thereby improving catalyst stability. The results show that the maximum isoparaffin yield of all catalysts tested was obtained for a Ge-loading of 0.27 wt.% (Pt/Ge atomic ratio = 0.7). These changes in the performance of the PtGe catalysts may be attributed to the modifications occurring in the metallic and in the acid function of Pt/Al2O3 due to the introduction of Ge. The metallic catalytic activity of Pt is modified by the geometrical effect (dilution of Pt ensembles) and changes in the electronic properties of platinum. Ge addition produces a weakening of Pt/Al2O3 acid strength and an increase in the acid sites total density by the presence of Ge oxides.

2-Dimension from the topological viewpoint Barmak, Jonathan Ariel; Minian, Elias Gabriel In this paper we study the 2-dimension of a finite poset from the topological point of view. We use homotopy theory of finite topological spaces and the concept of a  beat point to improve the classical results on 2-dimension, giving a more complete answer to the problem of all possible 2-dimensions of  an n-point poset.

New antitumoral acetogenin “guanacone type” derivatives: isolation and bioactivity. Molecular dynamics simulation of diacetyl-guanacone Barrachina, Isabel; Royo, Inmaculada; Baldoni, Hector Armando; Chahboune, Nadia; Suvire, Fernando Daniel; DePedro, Nuria; Zafra Polo, M. Carmen; Bermejo, Almudena; El Aouad, Noureddine; Cabedo, Nuria; Saez, Jairo; Tormo, José R.; Enriz, Ricardo Daniel; Cortes, Diego We describe herein the isolation and semisynthesis of four acetogenin derivatives (1–4) as well as their ability to inhibit the mitochondrial respiratory chain and several tumor cell lines. In addition, four nanoseconds (ns) of MD simulation of compound 4, in a fully hydrated POPC bilayer, is reported.

Modelado de la extracción con hexano de molido de soja pretratado enzimáticamente; Modelling the hexane extraction of soya enzymatically pretreated grits Grasso, Florencia Verónica; Maroto, Beatriz Graciela; Camusso, Celso Clemente; Zaritzky, Noemi Elisabet En este trabajo se estudia la influencia de las variables de proceso que pueden tener efecto sobre el rendimiento de la extracción con hexano a partir de soja molida pretratada enzimáticamente. Se propone a partir de los resultados experimentales, un modelo matemático para el cálculo del rendimiento de la extracción. Los tests estadísticos utilizados para obtener este modelo demostraron que el rendimiento en aceite no depende del pH de la incubación enzimática mientras que si depende tanto de la temperatura como del tiempo de ataque enzimático sobre el molido de soja. El modelo ajustó satisfactoriamente los datos experimentales.; In this work, the influence of the variables which can affect oil extraction from soybean enzymatically pretreated grit using hexane, were studied. From the experimental results, a mathematical model for calculating the extraction yield was proposed. The statistical tests used to obtain this model showed that the yield does not depend on the enzymatic incubation pH but on the temperature and time of enzymatic treatment and on the interaction between time and temperature. The proposed model fit the experimental data well.

Evaluación de disfunción endotelial en pacientes con diabetes tipo 2; Dysfunction endothelial evaluation in type 2 diabetes patients Velarde, María Susana; Prado, María Mercedes; Carrizo, Teresita del Rosariio; Abregu, Adela Victoria; Sanchez, Sara Serafina del V. El objetivo de este trabajo fue estudiar moléculas involucradas en la activación endotelial, tales como la molécula de adhesión sE-Selectina (sE-S) y el péptido vasoconstrictor Endotelina-1 (ET-1) en individuos diabéticos tipo 2 y su asociación con otros factores de riesgo cardiovascular. Se estudiaron 62 pacientes diabéticos que se compararon con un grupo control. Las concentraciones de sE-S y ET-1 fueron significativamente mayores en los diabéticos que en los controles (sE-S: 90,6±26,2 ng/mL vs. 49,5±9,2 ng/mL, p<0,00001; ET-1: 11,3±3,7 vs. 7,7±0,5 pg/mL, p<0,001, respectivamente). Estas moléculas, en pacientes con índice de masa corporal (IMC) normal y aumentado, mostraron diferencias significativas (sE-S: 75,5±22,4 vs. 97,1±32,9 ng/mL, p< 0,05; ET-1: 8,4±2,4 vs. 14,1±4,9 pg/mL, p=0,001, respectivamente). No se encontraron diferencias entre individuos diabéticos normo e hipertensos, no fumadores y fumadores, ni normo e hipercolesterolémicos. El 81% de la población estudiada presentó un pobre control glucémico (HA1c>7%), siendo significativamente mayores los niveles de ET-1 en este grupo (p<0,01) no así para sE-S (p=0,74). Los resultados obtenidos muestran que los pacientes diabéticos presentan activación endotelial reflejada en los niveles elevados de sE-S y ET-1. El IMC aumentado y el pobre control glucémico incrementan la disfunción endotelial en estos pacientes.; The object of this work was to study molecules involved in endothelial activation, such as E-selectin (sE-S) and the vasoconstrictor peptide Endothelin-1 (ET-1) in Type 2 diabetes patients, and their relation with other cardiovascular risk factors. Sixty-two patients with diabetes were compared with matched controls. sE-S and ET-1 concentrations in diabetes patients were significantly elevated compared with controls (sE-S: 90.6±26.2 ng/mL vs 49.5±9.2 ng/mL, p<0.00001; ET-1: 11.3±3.7 vs 7.7±0.5 pg/mL, p<0.001, respectively). sE-S and ET-1 levels in diabetes patients with normal and increased body mass index showed significant differences (sE-S: 75.5±22.4 vs. 97.1±32.9 ng/mL, p<0.05; ET-1: 8.4±2.4 vs. 14.1±4.9 pg/mL, p=0.001 respectively). There were no significant differences in none of the molecules values between patients with or without hypertension, smokers or non-smokers, neither in diabetes patients with or without hypercholesterolemia. Eighty-one percent of the population with diabetes presented a poor glycemic control (HA1c>7%) and in these patients, ET-1 plasma levels were significantly increased (p<0.01), but not sE-S (p=0.74). These results show that obesity and a poor glycemic control increase the endothelial dysfunction in type 2 diabetes patients.

Time dependence of isotopic temperatures Barrañón, Armando; Dorso, Claudio Oscar; López, Jorge A. In this study the double isotope yield ratio thermometer, commonly used in heavy ion reactions, is put to the test in molecular dynamics simulations for a variety of nuclear reactions and energies. Comparing results to other estimates of the temperature and to experimental measurements, it is determined that the double isotope yield temperature indeed reflects the hot and dense phase of the reaction. Correlations between the double isotope yield temperature, the system size, beam energies, and collision times were investigated. © 2007 Elsevier B.V. All rights reserved.

Crop rotation and tillage systems as a proactive strategy in the control of peanut fungal soilborne diseases Vargas Gil, Silvina; Meriles, Jose Manuel; Haro Juarez, Ricardo Javier; Casini, Cristiano; March, Guillermo Juan Soil management practices can affect the population dynamics of soil microbial communities. Cultural practices can be adequately combined to benefit natural populations of microorganisms that may have a role in biological control (actinomycetes, Trichoderma spp., and Gliocladium spp.), thus contributing to the management of peanut fungal soilborne diseases in a sustainable manner within ecological boundaries. During six agricultural cycles, rhizosphere soil samples were taken from a field subjected to crop rotation (soybean, peanut, and maize), peanut being under two tillage systems (no till, reduced tillage) with the aim of quantifying populations of soil microorganisms. The incidence of diseases caused by soilborne fungi in peanut was determined at harvest. The highest amount of actinomycetes, Trichoderma spp., and Gliocladium spp. were recorded when maize was the preceding crop. Regarding tillage systems, the populations of the three groups of microorganisms were higher in peanut under no tillage than under reduced tillage. Under these conditions, the lowest incidence of peanut blight (Sclerotinia minor) and root rot (strains of Fusarium solani) was observed, suggesting a possible natural control of peanut soilborne pathogens. The quantification of actinomycetes, Trichoderma spp., and Gliocladium spp. was used as a tool to explore the impacts of different management systems on microbial groups that may be involved in the biological control of soilborne diseases, with the aim of combining those practices that improve native populations of possible beneficial microorganisms. This manipulation can provide sustainable management strategies in the control of soilborne diseases, avoiding the use of artificial inoculations of microorganisms, and reducing agrochemical application.

Comparative studies of loblolly pine biodegradation and enzyme production by Argentinean white rot fungi focused on biopulping processes Levin, Laura Noemí; Villalba, Laura; Da Re, Cristina Verónica; Forchiassin, Flavia; Papinutti, Víctor Leandro The ability of eight white rot fungi: Coriolopsis rigida, Coriolus versicolor var. antarcticus, Peniophora sp., Phanerochaete sordida, Pycnoporus sanguineus, Steccherinum sp., Trametes elegans and Trametes villosa to selectively delignify loblolly pine (Pinus taeda) chips was studied. They were selected among 34 basidiomycetes from Argentina because of their capacity to decolorize Poly R-478 and Azure B. Fungal pretreatment caused changes in wood chemical composition as well as in physical structure. The present study allowed the identification of a new strain, potentially a candidate for use in softwoods biopulping processes. Results showed that P. sanguineus was able to reduce lignin content in 11% in 14 days of treatment, but also that P. taeda wood suffered notable structural changes of lignin and hemicelluloses during the treatment, as revealed from 13C CP-MAS NMR spectra. An increase of 15% in porosity of decayed wood confirmed physical changes due to fungal attack.

In silico study of the wettabilitty effects on gas cluster growth by solute diffusion in correlated porous media Rodríguez, C.M.; Felipe, Carlos; Vidales, Ana Maria; Domínguez, Armando; Kornhauser, Isaac; Rojas, Fernando Simulations of bubble growth in porous media are carried out with a 2D numerical automaton built on a set of hypotheses derived from experimental observations at pore scale. Various types of 2D numerical networks are used as models of porous media with the aim to study the outcome of the combined effects of the wettabilitty (homogeneous and mixed) and the spatial correlation among the porous network entities on the evolution of a gas cluster growing by solute diffusion into it. The porous networks are constructed by using a variation of the dual site bond model (DSBM) framework. For the same pore-size distribution, the DSBM can provide simulated porous media of different topological structures. Under these scenarios, numerical simulations concerning the growth pattern and the growth rate of a single gas cluster are performed.

Use of vegetation chemical signals for digging orientation in the subterranean rodent Ctenomys talarum (Rodentia: Ctenomyidae) Schleich, Cristian; Zenuto, Roxana Rita Sensory modalities involved in the localization and selection of food represent critical information for understanding the foraging behavior of subterranean rodents. The objective of this study was to determine if a subterranean rodent that forages on aboveground plant parts, Ctenomys talarum, is able to detect the presence of odorous chemicals released by the plants into the soil to guide its excavation, as has been shown for subterranean species that forage on roots and bulbs. Individuals were introduced into an artificial Y‐maze, whose arms were filled with sandy soil in which plants either had or had not been growing (control). Digging activity exhibited in each soil type was recorded. The following plant species, present in the natural habitat of C. talarum, were used: Panicum racemosum (three different concentrations), Cortadeira sp., Margiricarpus pignatus, Ambrosia sp. and Raphanus sativus. The individuals allocated more time to excavation in the soil in which vegetation had been growing in comparison with the control for the five analysed plant species, except in the case of P. racemosum at its lowest concentration. The number of individuals that completed excavation in the tube‐containing soil in which plants had been growing was significantly higher than in the tube‐containing soil in which no plants had been growing, with the exception of P. racemosum at its lowest concentration and R. sativus. The results of the present study suggest that C. talarum have the ability to use olfaction to orient their digging while foraging even though members of this species consume mainly aboveground plant parts.

Magneto-optic imaging: Normal and parallel field components of in-plane magnetized samples Ferrari, Hernan Javier; Bekeris, Victoria Isabel; Thibeault, M.; Johansen, T. H. Magneto-optical (MO) imaging has become a powerful tool for determining magnetic properties of materials by detecting the stray magnetic fields. The technique consists in measuring the Faraday rotation, θF, in the light polarization plane when light travels through a transparent sensitive garnet (ferrite garnet film, FGF) placed in close contact to the sample. For in-plane magnetized samples, the MO image is not trivially related to the sample magnetization, and to contribute to this understanding we have imaged commercial audio tapes in which computer-generated functions were recorded. We present MO images of periodically in-plane magnetized tapes with square, sawtooth, triangular and sinusoidal waveforms, for which we analytically calculate the perpendicular and parallel stray magnetic field components generated by the tape. As a first approach we correlate the measured light intensity with the perpendicular magnetic field component at the FGF, and we show that it can be approximated to the gradient of the sample magnetization. A more detailed calculation, taking into account the effect of both field components in the Faraday rotation, is presented and satisfactorily compared with the obtained MO images. The presence of magnetic domains in the garnet is shown to be related to the change in sign of the parallel component of the stray magnetic field, which can be approximated to the second derivative of the sample magnetization. © 2007 Elsevier B.V. All rights reserved.

Sur quelques nouveaux Phytocoris Fallén, 1814 provenant de l'Argentine et du Chili. I. (Heteroptera: Miridae) Carpintero, Diego Leonardo; Cherot, Fréderic 12 espèces nouvelles du genre Phytocoris FALLÉN, 1814 sont décrites d'Argentine et du Chili, à savoir: P. albiventris n. sp., P. chaquensis n. sp., P. comechingon n. sp., P. eylesi n. sp., P. neuquinus n. sp., P. patagoniensis n. sp., P. pehuenche n. sp., P. picunche n. sp., P. puelche n. sp., P. quichua n. sp., P. quilmes n. sp., P. rionegrensis n. sp. Autant que faire ce peut, l'habitus, ainsi que les structures génitales des deux sexes sont figurés.

Use of 13Ca chemical-shifts in protein structure determination Vila, Jorge Alberto; Ripoll, Daniel R.; Scheraga, Harold A. A physics-based method aimed at determining protein structures by using NOE-derived distances together with observed and computed 13C chemical shifts is proposed. The approach makes use of 13Cα chemical shifts, computed at the density functional level of theory, to obtain torsional constraints for all backbone and side-chain torsional angles without making a priori use of the occupancy of any region of the Ramachandran map by the amino acid residues. The torsional constraints are not fixed but are changed dynamically in each step of the procedure, following an iterative self-consistent approach intended to identify a set of conformations for which the computed 13Cα chemical shifts match the experimental ones. A test is carried out on a 76-amino acid, all-α-helical protein; namely, the Bacillus subtilis acyl carrier protein. It is shown that, starting from randomly generated conformations, the final protein models are more accurate than an existing NMR-derived structure model of this protein, in terms of both the agreement between predicted and observed 13Cα chemical shifts and some stereochemical quality indicators, and of similar accuracy as one of the protein models solved at a high level of resolution. The results provide evidence that this methodology can be used not only for structure determination but also for additional protein structure refinement of NMR-derived models deposited in the Protein Data Bank.

Ghost resonance in a pool of heterogeneous neurons Balenzuela, Pablo; Garcia Ojalvo, Jordi; Manjarrez, Elías; Martínez, Lourdes; Mirasso, Claudio R. We numerically study the subharmonic response of a heterogeneous pool of neurons to a pair of independent inputs. The neurons are stimulated with periodic pulse trains of frequencies f1 = 2 Hz and f2 = 3 Hz, and with inharmonic pulses whose frequencies f1 and f2 are equally shifted an amount Δ f. When both inputs are subthreshold, we find that the neurons respond at a frequency equal to f2 - f1 in the harmonic situation (Δ f = 0), that increases linearly with Δ f in the inharmonic case. Thus the neurons detect a frequency not present in the input; this effect is termed "ghost resonance". When one of the inputs is slightly suprathreshold the ghost resonance persists, but responses related with the frequency of the suprathreshold input also emerge. This behavior must be taken into account in experimental studies of signal integration and coincidence detection by neuronal pools.

Diets of three species of andean carnivores in high-altitude deserts of Argentina Walker, Rebecca Susana; Novaro, Andres Jose; Perovic, Pablo Gastón; Palacios, Rocio; Donadio, Emiliano; Lucherini, Mauro; Pia, Monica Valeria; López, María Soledad We present the 1st data on the diet of the Andean mountain cat (Leopardus jacobitus), and the 1st on the colocolo (Leopardus colocolo) and the culpeo (Lycalopex culpaeus) in high-altitude deserts of northern Argentina, based on fecal analysis. Feces of Andean mountain cats and colocolos were distinguished by DNA analysis. The Andean mountain cat (n= 57) was the most specialized, relying heavily on southern mountain vizcachas (Lagidium viscacia). The colocolo (n = 504) also was specialized, consuming mostly cricetine rodents and tuco-tucos (Ctenomys). The culpeo (n= 399) was a generalist, consuming all prey items that the cats used, and a greater variety of invertebrates. Short-tailed chinchillas (Chinchilla chinchilla) were found in 3 culpeo feces, indicating that this rodent, considered extinct in Argentina, is still present in the wild. Both southern mountain vizcachas and tuco-tucos have a patchy distribution, indicating that very large areas may be required to support populations of the cats that depend on these prey species.

Groundwater chemical pollution risk: Assessment through a soil attenuation index Heredia, Olga Susana; Fernandez Cirelli, Alicia Aquifer vulnerability is frequently estimated through methodologies that don't consider most physical and chemical soil parameters. A soil attenuation index is proposed to estimate groundwater chemical pollution risk, that takes into account organic carbon content, pH, cation exchange capacity, clay content, phreatic depth and landscape position. The attenuation index is constructed by a methodology similar to that developed for water quality index. P, Mn and Zn concentrations in groundwater from selected places were used to validate the proposed index. © 2007 Springer-Verlag.

A quantitative method for zoning of protected areas and its spatial ecological implications Sabatini, Maria del Carmen; Verdiell, Adriana Beatriz; Rodríguez Iglesias, Ricardo Manuel; Vidal, Marta Cecilia Zoning is a key prescriptive tool for administration and management of protected areas. However, the lack of zoning is common for most protected areas in developing countries and, as a consequence, many protected areas are not effective in achieving the goals for which they were created. In this work, we introduce a quantitative method to expeditiously zone protected areas and we evaluate its ecological implications on hypothetical zoning cases. A real-world application is reported for the Talampaya National Park, a UNESCO World Heritage Site located in Argentina. Our method is a modification of the zoning forest model developed by Bos [Bos, J., 1993. Zoning in forest management: a quadratic assignment problem solved by simulated annealing. Journal of Environmental Management 37, 127-145.]. Main innovations involve a quadratic function of distance between land units, non-reciprocal weights for adjacent land uses (mathematically represented by a non-symmetric matrix), and the possibility of imposing a connectivity constraint. Due to its intrinsic spatial dimension, the zoning problem belongs to the NP-hard class, i.e. a solution can only be obtained in non-polynomial time [Nemhausser, G., Wolsey, L., 1988. Integer and Combinatorial Optimization. John Wiley, New York.]. For that purpose, we applied a simulated annealing heuristic implemented as a FORTRAN language routine. Our innovations were effective in achieving zoning designs more compatible with biological diversity protection. The quadratic distance term facilitated the delineation of core zones for elements of significance; the connectivity constraint minimized fragmentation; non-reciprocal land use weightings contributed to better representing management decisions, and influenced mainly the edge and shape of zones. This quantitative method can assist the zoning process within protected areas by offering many zonation scheme alternatives with minimum cost, time and effort. This ability provides a new tool to improve zoning within protected areas in developing countries.

Anti-beta1-adrenergic receptor autoantibodies in patients with chronic Chagas heart disease Labovsky, Vivian; Smulski, Cristian Roberto; Gomez, Karina Andrea; Levy, Gabriela Vanesa; Levin, Mariano Jorge Chronic Chagas heart disease (cChHD), a chronic manifestation of the Trypanosoma cruzi infection, is characterized by high antibody levels against the C-terminal region of the ribosomal P proteins (i.e. peptide R13, EEEDDDMGFGLFD) which bears similarity with the second extracellular loop of beta1-adrenergic receptor (beta1-AR, peptide H26R HWWRAESDEARRCYNDPKCCDFVTNR). Because it has not been demonstrated clearly that IgGs from cChHD patients bind to native human beta1-AR, the aim of this study was to investigate further the physical interaction between cChHD IgGs and the human beta1-AR. Immunofluorescence assays demonstrated the binding of these antibodies to the receptor expressed on stably transfected cells, together with a beta1-AR agonist-like effect. In addition, immunoadsorption of the serum samples from cChHD patients with a commercially available matrix, containing peptides representing the first and the second extracellular loop of the beta1-AR, completely abolished reactivity against the H26R peptide and the physiological response to the receptor. The follow-up of this specificity after in vitro immunoadsorption procedures suggests that this treatment might be used to diminish significantly the serum levels of anti-beta1-AR antibodies in patients with Chagas heart disease.