Las Escorias y Tierras Cocidas de la Pampa Zárate, Marcelo Arístides; Schultz, Peter Los enigmáticos fragmentos vítreos asociados a otros parecidos ladrillos que se encuentran en los sedimentos de la cercanos a Mar del Plata se deben al impacto de ocurrido hace 3,3 millones de años

Embryonal mass and hormone-associated effects of pregnancy inducing a differential growth of four murine tumors Bustuoabad, Oscar David; di Gianni, Pedro D.; Franco, Marcela; Kordon, Edith Claudia; Vanzulli, Silvia I.; Meiss, Roberto P.; Grion, Lorena C.; Diaz, Graciela Susana; Nosetto, Sergio H.; Hockl, Pablo Francisco; Lombardi, María Gabriela; Pasqualini, Christiane Dosne; Ruggiero, Raul Alejandro A differential effect of pregnancy on the growth of subcutaneous implants of four murine tumors has been observed. Two tumors lacking receptors for progesterone and estrogen [methylcholanthrene-induced fibrosarcoma (MC-C) and spontaneous lymphoid leukemia (LB)] exhibited slow kinetics throughout the course of pregnancy, although inhibition was stronger beyond day 10. On the other hand, one of two tumors bearing receptors for progesterone and estrogen [medroxyprogesterone (MPA)-induced mammary adenocarcinoma (C7HI)] exhibited three phases: up to days 8-10 of gestation the tumor grew faster than in virgins, between days 8-10 and 15 it reached a plateau, and beyond day 15 a sharp reduction in tumor mass was observed. The other tumor [mouse mammary tumor virus (MMTV)-induced mammary carcinoma(T2280)] behaved as a typical pregnancy-dependent tumor (i.e., it grew in pregnant but not in virgin mice, regressed soon after delivery, and reassumed its growth at the middle of a second round of pregnancy). Neither MPA nor estrogen affected MC-C and LB tumor growth. On the other hand, MPA-treated mice enhanced C7HI tumor and reciprocally C7HI tumor-bearing mice treated with estrogen strongly inhibited tumor growth. As for T2280, neither MPA nor estrogen alone could promote tumor growth and, in consequence, no tumor developed. However, when MPA plus estrogen was administered in a schedule simulating the successive appearance of these hormones in pregnancy, T2280 grew even faster than in pregnant mice. When the four tumors were implanted in mice bearing grafts of embryonal tissues (teratomas), all of them were inhibited. This antitumor effect was similar to that observed in pregnancy when tumors unresponsive to progesterone and estrogen were tested. On the other hand, with tumors bearing progesterone and estrogen receptors, differences in tumor growth were detected in pregnant and teratoma-bearing mice. This suggested the existence during pregnancy of two factors potentially acting on tumor growth. First, a progesterone and estrogen-mediated hormonal component, which would exert either inhibitory or stimulatory effects only evidenced with tumors bearing hormonal receptors. Secondly, an antitumor effect proportional to the growing embryonal mass, inhibiting all tumors independently of their origin or hormone responsiveness. This antitumor effect could be attributed to a beat-resistant serum factor (1,000-1,200 Da molecular weight) presumably associated with the pathway of the arachidonic acid metabolism. The interplay between the hormonal component and the serum factor associated with embryonal mass could account for some of the largely heterogeneous and otherwise unexplained effects of pregnancy on tumor growth reported in the literature and illustrated by the four tumors studied here.

Linear Viscoelastic Relaxation Modulus of Polydisperse Poly(dimethylsiloxane) Melts Containing Unentangled Chains Deiber, Julio Alcides; Peirotti, Marta Beatriz; Villar, Marcelo Armando; Ressia, Jorge Aníbal; Valles, Enrique Marcelo This work analyzes the relationship between the shear relaxation modulus of entangled, linear and flexible homopolymer blends and its molecular weight distribution (MWD) when a fraction of the sample contains chains with molecular weight M lower than the effective critical molecular weight between entanglements Mceff. This effective critical parameter is defined in terms of the critical molecular weight between entanglements Mc of the bulk polymer that forms the physical network and the effective mass fraction Wceff of the unentangled chains. In the terminal zone of the linear viscoelastic response, the double reptation mixing rule for blended entangled chains and a modified law for the relaxation time of chains in a polydisperse matrix are considered, where the effect of chains with MMceff. This mechanism is independent from the MWD. The unentangled chains with M

Un ejercicio de historia regional comparada. Coacción y mercado de trabajo. Tucumán y Mendoza en el horizonte latinoamericano (segunda mitad del siglo XIX Campi, Daniel Enrique A.; Jorba, Rodolfo Richard El artículo plantea un enfoque comparativo de los procesos de constitución de los mercados laborales en Tucumán y Mendoza en las décadas finales del siglo XIX. El análisis se enmarca en el debate que sobre el peonaje por deudas y –en general sobre las diversas modalidades del trabajo coactivo– se dio en la historiografía latinoamericana, que se complementa con un repaso de las diversas interpretaciones que la cuestión deparó en la historiografía rioplatense y en la historiografía tucumana. En el tratamiento del problema se pone énfasis en las prácticas –en las iniciativas del Estado provincial, de los tomadores de mano de obra asalariada, de los trabajadores–, para concluir proponiendo una hipótesis sobre las razones de la extinción del sistema coactivo. En la misma se contemplan diversas variables, entre las cuales se destacan las estrategias de resistencia de los trabajadores y la aparición en el escenario de un nuevo y decisivo actor, el Estado nacional.

Two new phoxocephalids (Crustacea: Amphipoda: Phoxocephalidae) from the south-west Atlantic Alonso, Gloria Maria A new genus and species, Parafoxiphalus longicarpus, and a new species, Metharpinia protuberantis belonging to the family Phoxocephalidae, are described from the Argentine Sea. Both taxa were collected from sandy substrata in the intertidal and subtidal regions. Parafoxiphalus longicarpus is related to Foxiphalus Barnard, 1979 and they share many characters, most of them in plesiomorphic condition. Metharpinia protuberantis is an intermediate species between Metharpinia Schellenberg, 1931 and Microphoxus Barnard, 1960, and its assignation to the first genus is discussed.

Andean Cenozoic foreland basins: a review Gonzalez Bonorino, Gustavo; Kraemer, P.; Re, G. Interaction between the South American craton and the oceanic Nazca Plate throughout the Cenozoic gave rise to the Andean orogen and a related assemblage of retroarc foreland basins. This review partly summarizes abundant existing data on the sedimentary and tectonic evolution of Andean Cenozoic foreland basins and intends to serve as a geographic and geologic framework for the detailed papers in this special issue. Several of these papers were presented orally at a special Andean session held during the 14th Congreso Geológico Argentino, Salta, Argentina, on September 1999.

Characterization of static bifurcations in the frequency domain Itovich, Griselda Rut; Moiola, Jorge Luis In this paper two-dimensional systems with static bifurcations are considered. An analysis of the bifurcation behavior is proposed using a frequency domain approach. The analyzed bifurcations are known as elementary since they are the building blocks to understand other more complex singularities.

Chaos prediction and bifurcation analysis in control engineering Alonso, Diego; Calandrini, Guillermo Luis; Berns, Daniel Walther; Paolini, Eduardo Emilio; Moiola, Jorge Luis In this paper, two different methods to compute the period-doubling route to chaos (or Feigenbaum chaos) in nonlinear systems are presented. The first one is a semi-analytical procedure, based on a symbolic calculation of an approximate monodromy matrix. The second one takes advantage of software packages for continuation of periodic solutions. Both procedures are used to analyze Chua´s circuit. The second method is also applied to the Rössler system and one of the chaotic systems of Sprott. In all three cases, several period-doubling bifurcation points in the parameter space are detected, allowing to compute a sequence of values supposedly converging to Feigenbaum´s constant. This "experimental´´ computer verification agrees with experiments performed by other researchers in real systems. This material has been used in final projects in a graduate course in dynamical systems.

A PCR-based method for the screening of bacterial strains with antifungal activity in suppressive soybean rhizosphere. Giacomodonato, Mónica Nancy; Pettinari, María Julia; Souto, Guadalupe; Mendez, Beatriz Silvia; López, Nancy Irene Selection and evaluation of microbial strains for their antifungal activity in natural environments is time- and energy-consuming. We have adapted a PCR-based method to avoid these inconveniences. Soils that are naturally suppressive to plant disease were chosen as a source of antibiotic-producing bacteria. The screening was performed by means of PCR amplification using degenerate primers corresponding to peptide synthetase genes. Amplification fragments were obtained using template DNA from the rhizosphere of three different soybean fields. In order to assay their potential utility in pathogen control, several Bacillus strains were analysed for their in vitro antifungal activity by testing growth inhibition of Sclerotinia sclerotiorum. Four Bacillus sp. isolates gave a positive amplification signal, and three of them had an inhibitory effect on S. sclerotiorum growth, whereas two strains that failed to give an amplification signal did not inhibit fungal growth. These results show that PCR-based techniques could be useful to assess the presence of strains with potential use as biocontrol agents.

Aspectos sedimentarios y palinología de la Formación Agua Colorada (Carbonífero Superior) en quebrada El Arbolito, departamento Tinogasta, Catamarca, Argentina; Sedimentary aspects and palynology of Agua Colorada Formation (Upper Paleozoic) in El Arbolito creek, Tinogasta Department, Catamarca, Argentina Vergel, Maria del Milagro; Lech, Roberto Ricardo Se analiza desde el punto de vista sedimentológico una sucesión estratigráfica asignada a la Formación Agua Colorada aflorante en quebrada El Arbolito, al sur de Tinogasta, Catamarca. El paleoambiente sedimentario se interpreta como pertenecientea depósitos de origen fluvial. Del tramo superior de la sucesión se recuperó una asociación microflorística compuesta principalmente por granos de polen monosacados (Cannanoropollis janakii, C. densus, Plicaripollenires gondwanensis, P. malabarensis, Potonieisporires spp. Circumplicatipolis plicatii Caheniasaccites ovatus). En menor proporción ocurren esporas triletes (Punctarisporites gretensis P. glaber, Calamospora hartungiana, C. smileyana, Apiculiretusispora variornata, Apiculatasporites caperatus, Apiculatisporis rallus, Horriditriletes uruguaiensis and Cristarisporites inconstans) y aunque escasos, granos de polen bisacados y bisacados estriados (Alisporites sp., Limitisporites rectus, Protohaploxipinus bharadwajii and P. amplus). Los datos palinológicos y estratigráficos sugieren una antigüedad Carbonífera Tardía (Westfaliano Superior-Stefaniano) para la sucesión analizada.; A stratigraphic sequence of the Agua Colorada Formation in El Arbolito creek, at south of Tinogasta, Catamarca, is analyzed. The paleoenvironment is interpreted us fluvial deposits. The presence of a palynological assemblage recovered from the upper part of the sequence is documented. Monosaccate pollen grains are the more common components (Cannanoropollis janakii, C. densus, Plicaripollenires gondwanensis, P. malabarensis, Potonieisporires spp. Circumplicatipolis plicatii Caheniasaccites ovatus). The spores are less frecuent (Punctarisporites gretensis P. glaber, Calamospora hartungiana, C. smileyana, Apiculiretusispora variornata, Apiculatasporites caperatus, Apiculatisporis rallus, Horriditriletes uruguaiensis and Cristarisporites inconstans), whereas bisaccate and bisaccate striate pollen.grains are al so represented although in scarce amount, e.g. Alisporires sp., Limitisporites rectus, Protohaploxypinus bltaradwajii and P. amplus. Palynological and stratigraphic data suggest a Late Carboniferous age (Upper Westphalian-Stephanian).

Nonperturbative effective-field theory for two-leg antiferromagnetic spin ladders Cabra, Daniel Carlos; Dobry, Ariel Oscar; Rossini, Gerardo Luis We study the long wavelength limit of a spin- 2 Heisenberg antiferromagnetic two-leg ladder, treating the interchain coupling in a nonperturbative way. We perform a mean field analysis and then include the fluctuations in an exact way. This allows for a discussion of the phase diagram of the system and provides an effective-field theory for the low-energy excitations. The coset fermionic Lagrangian obtained corresponds toa perturbed SU(4)  / U(1) conformal field theory CFT . This effective theory is naturally embedded in a SU(2) x Z_2 CFT, where perturbations are easily identified in terms of conformal operators in the two sectors.Crossed and zigzag ladders are also discussed using the same approach.

Alteraciones ultraestructurales en la mucosa del colon de ratas tratadas con nifurtimox; Ultrastructural alterations in colonic mucosa of nifurtimox treated rats Montalto, Maria; Rodriguez de Castro, Carmen; Diaz, Edith Graciela; Castro, Jose Alberto El nifurtimox (Nfx) es un fármaco empleado en el tratamiento del Mal de Chagas agudo que ha evidenciado en su uso clínico y en estudios experimentales efectos colaterales tóxicos que comprometen su empleo. Estos efectos fueron correlacionados con la nitrorreducción del Nfx a radical nitroanión y la generación de aniones superóxido a través de un ciclo redox. El objetivo de este trabajo fue verificar si después de la administración oral de Nfx (100 mgžkg-1) a ratas macho Sprague Dawley se observan alteraciones ultraestructurales en el colon. Los resultados mostraron que 24 h después de administrar el Nfx se observan alteraciones consistentes en una dilatación moderada del retículo endoplásmico y en una dilatación intensa del complejo de Golgi en las células epiteliales colónicas. El Nfx está presente en el tejido colónico 1 y 3 h después de su administración oral, en concentraciones de 9.7 ± 2.9 y 7.0 ± 1.7 nmolžg -1 respectivamente. Los estudios de actividad nitrorreductásica del Nfx, espectrofotómetricos y por HPLC, en fracciones subcelulares, permiten establecer su presencia en la fracción microsomal, con valores de 0.72 ± 0.29 y 0.26 ± 0.04 nmol Nfxžmin‑1žmg-1 proteína, pero no en el citosol. Los resultados muestran una correlación entre la localización del daño observado y la fracción celular donde ocurre la nitrorreducción. El daño intenso del complejo de Golgi producido por el Nfx sugiere potenciales alteraciones en las funciones de síntesis y/o almacenamiento de productos de secreción de la mucosa colónica.; Nifurtimox (Nfx) is a chemotherapeutic agent used in the treatment of acute Chagas’ disease. Clinical and experimental studies with this nitroheterocyclic compound evidenced serious undesirable side effects. These were correlated with Nfx nitroreduction to a nitroanion radical followed by superoxide anion generation through a redox cycling process. The aim of this study was to verify whether the oral administration of Nfx to Sprague Dawley male rats (100 mgžkg-1, po) produced any observable ultrastructural alteration in the cells of the colonic mucosa. Results showed that 24 h after Nfx administration there were observable alterations in this type of cells. They essentially consisted of moderate dilatation of their endoplasmic reticulum and intense dilatation of their Golgi complex. Already 1 and 3 h after Nfx administration, the original compound reached a concentration of 9.7 ± 2.9 and 7.0 ± 1.7 nmolžg-1 respectively in the colonic tissue. Studies on Nfx nitroreductase activity of colonic mucosa as determined spectrophotometrically and by HPLC methods showed that the microsomal fraction (from 0.72 ± 0.29 to 0.26 ± 0.04 nmol Nfxžmin-1žmg-1 protein) but not the cytosol had the ability to nitroreduce Nfx. The results obtained show a correlation between the ultrastructural localization of injury and that of nitroreductase activity. The intense deleterious effects of Nfx in the Golgi apparatus suggest the potential occurrence of alterations in the synthesis/storage of secretory products of the colonic mucosa.

El Grupo Los Menucos: redefinición estratigráfica del Triásico superior del Macizo Nordpatagónico; Los Menucos Group. Stratigraphic redefinition of the Upper Triassic f rom the Northpatagonian Massif Labudia, Carlos Horacio; Bjerg, Ernesto Alfredo El Grupo Los Menucos incluye ignimbritas dacíticas y riolíticas ,lavas y tobas riolíticas, conglomerados yareniscas. El Grupo está compuesto por dos entidades: Formación Vera y Sierra Colorada; la primera de ellas (la más antigua) se integra con areniscas fosilíferas y flujos piroclásticos dacíticos; la segunda (la más moderna) comprende principalmente rocas riolíticas. En años recientes se avanzó en forma significativa en el conocimiento Iitoestratigráfico de estas unidades, lo cual permite su redefinición de acuerdo con el Código Argentino de Estratigrafía.; Los Menucos Group includes Upper Tria ssic ignimbrites dacites, conglomerates, sandstones a nd pyroclastic acidic rocks (rhyolites). This group is composed by the Vera Formation (tbe lower unit) and the Sierra Colorada Formation (the upper unit); the form er includes fosi liferous sa nd stone and pyroclastic dacitic flux es, and the second one is mainly composed by rhyolitic rocks. In recent years, there has been a significant prog ress of knowledge of these lithoestratigraphical units, which favored their redefinitions according with the Argentine Stratigraphic Code.

Quistes de dinoflagelados del Cenozóico de la Cuenca del Colorado, Argentina; Cenozoic dinoflagellate cytests from the Colorado basin, Argentina Guerstein, Gladys Raquel; Junciel, Gabriela Cenozoic sediments from the well Cx-l of offshore Colorado Basin were studied. The dinoflagellate cysts assemblages are diverse and well preserved praviding stratigraphic control for the section. Selected dinoflagellate cyst last occurrences or abundance events suggest seven age intervals: Maastrichtian, Paleocene, Late Eocene to Early Oligocene, Late Oligocene to Early Miocene, Mid Miocene, Late Miocene and Late Miocene to Early Pliocene. These results are compared with previous studies, carried out by other authors exhibiting a consistent succession of events throughout the basin. Qualitative and quantitative dinoflagellate cyst data allow the recognition of apparent sea level changes. Sediments ranging frorn Maastrichtian to Selandian in age show a gradual rise in sea leve!. These assemblages bear both gonyaulacacean and peridiniacean dinoflagellate cysts suggesting open marine conditions with a marked fall in sea level at the top of this interval. Sediments interpreted as Late Eocene to Early Oligocene in age were deposited in a more open marine environment. At the Early Oligocene/Late Oligocene boundary a second low see level episode occurred.Throughout the Late Oligocene to Early Miocene and Mid to Late Miocene intervals high dinocyst abundances and the presence of oceanic species suggest a sea level highstand. Upwards the dominance of terrestrially derived palynomorphs as well as the scarcity of dinoflagellate cysts indicate nearshore depositional environments at the end of the Miocene-Early Pliocene

Microscopic dynamics of small fragmenting systems Dorso, Claudio Oscar We calculate the Caloric Curve of fragmenting drops of Lennard Jones particles, defined as the temperature of the system at fragmentation time. We show how to calculate the time of fragment formation, and the temperature at this time. We explore the role played by the collective motion. The competition between the collective radial, ordered, motion and the intrisic, chaotic, motion is analyzed using the Maximum Local Lyapunov Exponent.

Lyapunov exponent, generalized entropies and fractal dimensions Dorso, Claudio Oscar; Bonasera, A. We calculate the maximal Lyapunov exponent, the generalized entropies, the asymptotic distance between nearby trajectories and the fractal dimensions for a finite two-dimensional system at different initial excitation energies. We show that these quantities have a maximum at about the same excitation energy. The presence of this maximum indicates the transition from a chaotic regime to a more regular one. In the chaotic regime the system is composed mainly of a liquid drop while the regular one corresponds to almost freely flowing particles and small clusters. At the transitional excitation energy the fractal dimensions are similar to those estimated from the Fisher model for a liquid-gas phase transition at the critical point.

Household solid waste sampling for Mar del Plata City, Argentina Menna, Máximo; Jacob, Susana; Plaza, Gloria del Carmen; Divelz, Horacio; Cid, Juan Carlos; Pacheco, Osvaldo This work arices from and adrement between Universidad National de Mar del Plata (UNMDP) and the Municipality of Partido de General Pueyrredon, Buenos Aires, Province, ARgentina. A sampling was designed taking, as the starting point, data from a population and housing census (INDEC, 1991) for the evaluation of home solid waste in Mar del Plata city. The sample type in study concient of stratification with replacement, according to social - economic - cultural variables. Waste was classified in origen in six fraction: paper/cardboard, glass, organic, plastic, metal and other. Waste weightings were obtaining dayling, according to housing, stratun and fraction components. Data obtained during the for seasons in 1997 are shown in the present work, from wich de percentajes of ich waste type and the results of statistical calculations for the organic fraction and for the total of the housing solid waste were obtained.

Biorremediación en suelos contaminados con hidrocarburos Plaza, Gloria del Carmen; Otero Cabada, M.; Torres, N.; Velásquez, M.; Corbalán, E.; Rodríguez, T. Se estudia la bioremediación de suelos contaminados con el interés de disminuir el efecto contaminante de hidrocarburos a niveles no tóxicos. Los ensayos a escala laboratorio, desarrollados en condiciones de temperatura, aireación y humedad controlada permiten evaluar alternativas de utilización de nutrientes, inoculación de bacterias y/o aprovechamiento de la microflora natural del suelo. Los resultados muestran la activación de la microflora natural por la utilización de nutrientes en proporción adecuada, obteniéndose remociones de hidrocaburo de 70 % en 55 días de proceso. Asimismo, se analiza la efectividad del proceso de bioremediación cuando se utiliza suelo recuperado. Así, la utilización de suelo virgen puede limitarse al mínimo evitando desmontes innecesarios para su provisión.

Bacillariophyceae de los canales de drenaje de Corfo (Río Colorado, Buenos Aires, Argentina) Vouilloud, Amelia Alejandra Beatriz; Leonardi, Patricia Ines Bacillariophyceae from the channels of CORFO (Colorado River, Buenos Aires. Argentina). This work is a contribution to the knowledge of the diatomaceous flora from the drainage channels of brackish water of CORFO (Colorado River), located in the southern area of the province of Buenos Aires, Argentina. Ninety species were identified; seven of them belong to the order Centrales and the remaining eighty-three to the order Pennales. Cylindrotheca gracilis (Brébisson) Grunow and Nitzschia agnita Hustedt are new records for Argentina, while Hyalodiscus Ientiginosus John, Navicula circumtexta Meister, Plagiotropis lepidoptera (Pfitzer) Cleve, Nitzschia desertorum Hustedt, N. heuflen'ana Grunow, N. rautenbachiae Cholnoky, and N. reverse W. Smith are new records for Buenos Aires. This study includes a table showing the presence/absence of the identified taxa, as well as a description of the species which are either new or rare for Argentina and the province of Buenos Aires, or interesting because of their morphology and/or taxonomy.; Esta es una contribucién al conocimiento de la flora diatomolégica de Ios canales de drenaje de agua salobre de CORFO (Rio Colorado), al sur de la provincia de Buenos Aires, Argentina. Se iden- tificaron noventa especies, siete pertenecientes al orden Centrales y ochenta y tres al orden Pennales. Se cita Cylindrotheca gracilis (Brébisson) Grunow por primera vez para la Argentina, mientras que Hyalodiscus lentiginosus John, Navicula circumtexta Meister, Plagiotropis Iepidoptera (Pfitzer) Cleve, Nitzschia desertorum Hustedt, N. intermedia Hantzsch, N. rautenbachiae Cholnoky y N. reverse W. Smith son nuevas citas para la provincia de Buenos Aires. Se describen especies nuevas o raras para Argentina y la provincia de Buenos Aires y [es que por su morfologia y/o taxonomia resuitan de interés.

On the effect of chaotic orbits on dynamical friction Cora, Sofia Alejandra; Vergne, Maria Marcela; Muzzio, Juan Carlos Chaotic orbits suffer significant changes as a result of small perturbations. One can thus wonder whether the dynamical friction suffered by a satellite on a regular orbit, and interacting with the stars of a galaxy, will be different if the bulk of the stars of the galaxy are in regular or chaotic orbits. In order to check that idea, we investigated the orbital decay (caused by dynamical friction) of a rigid satellite moving within a larger stellar system (a galaxy) whose potential is nonintegrable. We performed numerical experiments using two kinds of triaxial galaxy models: (1) the triaxial generalization of Dehnen´s spherical mass model (Dehnen; Merritt & Fridman); (2) a modified Satoh model (Satoh; Carpintero, Muzzio, & Wachlin). The percentages of chaotic orbits present in these models were increased by perturbing them. In the first case, a central compact object (black hole) was introduced; in the second case, the perturbation was produced by allowing the galaxy to move on a circular orbit in a logarithmic potential. The equations of motion were integrated with a non-self-consistent code. Our results show that the presence of chaotic orbits does not affect significantly the orbital decay of the satellite.