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.

An Environment for Modeling and Managing the Process Design Process Gonnet, Silvio Miguel; Mannarino, Gabriela; Leone, Horacio Pascual; Henning, Gabriela Patricia A three-layer object based environment architecture (Client, Application Server and Server) to support the modeling and management of the process design process is presented. It guides the design process and explicitly maintains the evolution of the design knowledge as a consequence of each design decision that is adopted during a particular design project. The Client encapsulates the interface of the designer to the design environment. The Application Server is responsible for managing the designer requirements by resorting to the Server data. It manages the definition of generic design tasks and the administration of the scenarios that are generated when a particular design process is carried out. Design tasks are defined according to the Coordinates language syntax. Basically, a design process is viewed as a set of tasks that are linked by temporal relationships and/or a set of resources they share. Generic design tasks can be instantiated and used in a specific design project. The Server contains the data that are created, used or modified by the Application Server.

Analysis of dielectric properties of cytosine in aqueous solution Manzur, Maria Eugenia; Romano, Élida; Vallejo, S.; Wesler, S.; Suvire, Fernando Daniel; Enriz, Ricardo Daniel; Molina, María A. A. The dipole moment of cytosine in dilute aqueous solutions was experimentally determined through permitivity, refraction index and density measurements in order to study the solvent effect on the behaviour of cytosine under the action of a low frequency electric field. Buckingham's equation was used, and μexp = 7.99 D was obtained. A theoretical study was also undertaken which considered cytosine in isolation and in two association models of the solute with four and six molecules of water respectively. The data for the dipole moment as well as an estimation of the hydration energies were obtained from models evaluated at three theoretical levels: Semiempirical calculations (in particular the AM1 method), ab initio calculations at the RHF/6-31+G* level of theory and density functional theory (B3LYP/6-31+G*) for the inclusion of electronic correlation. Although the six water molecule model bonded by hydrogen bonds was shown to be the more stable one, the results of μexp confirm that both intermolecular association models are compatible.

Geometría óptima de canales viales urbanos en zona árida Papparelli, Alberto Hermes; Kurban, Alejandra Silvia; Cunsulo, Mario Esteban; Montilla González, Eduardo Alejandro Se estudian las relaciones dimensionales de los Canales Viales Urbanos (CVU) de la ciudad de San Juan, en función de la incidencia de la radiación solar global en invierno y verano, analizando los ángulos de visión al cielo. Se analiza un muestreo de Canales Viales Urbanos de la ciudad de San Juan, en los que se efectúan relevamientos de sus elementos constitutivos y se registran mediciones de radiación solar global, temperatura y humedad en invierno y verano. Analizando el comportamiento a la radiación en las dos direcciones cardinales típicas del trazado urbano: este-oeste y nortesur, se obtienen los Angulos Libres de Enmascaramiento Edilicio y los Angulos Netos de Visión al Cielo que consideran la obstrucción que producen la edificación y la arboleda urbana a la radiación solar respectivamente. Correlacionadas las gráficas de ambas estaciones se definen los ángulos de visión al cielo óptimos, obteniéndose los CVU que presentan los mejores comportamientos a la radiación solar, como un aporte al potencial bioclimático urbano.; The dimensional relationship of the Urban Lane Channel (ULCH) of the San Juan city, are studied. Those studies are made in relation to the incidence of the global solar radiation during winter and summer, analyzing the angles of sky vision. 112 ULCH are analyzed as an example of the urban space of the city of San Juan. In those examples, the measurement of the constitutive elements as well as the measurements of the global solar radiation, temperature and humidity are done, both during winter and summer. The angles of free mask and the net angles of sky view, considering the obstruction both of the buildings and public forest are obtained, analyzing the behavior of the solar radiation and differentiating them according to the two typical cardinal direction of the urban plan: east-west and north-south. In this way urban profiles are obtained presenting the best behavior with respect to the solar radiation , as a contribution to the urban bioclimatic potential.

Effect of Bacillus cereus Exocellular Factors on Human Intestinal Epithelial Cells Minnaard, Jessica; Humen, Martin Andres; Perez, Pablo Fernando To gain insight on the biological effects of the exocellular factors produced by Bacillus cereus, culture filtrate supernatants of different strains were coincubated with differentiated Caco-2 cells. Exocellular factors were able to detach enterocyte-like cells from the substratum after 1 h of incubation. In addition, microvilli effacing and dramatic changes on the cellular surface of enterocytes were found after incubation periods as short as 20 min. Since cell detachment was not inhibited by fetal calf serum, thiol activated cholesterol-binding cytolysin, cereolysin O, does not seem to be involved. Also, translocation of phosphatidylserine from the inner to the outer leaflets of the plasma membrane was demonstrated by using fluorescein isothiocyanate (FITC)-Annexin V. In contrast to the high capability of detaching Caco-2 cells shown by all the strains under study, the mitochondrial dehydrogenase activity was lowered by culture filtrate supernatants in a strain-dependent manner. For strain M2, the decrease in dehydrogenase activity was already evident after 30 min of incubation. Production of biologically active factors depends on the growth phase, and maximal activity was found in late exponential-early stationary phases. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of concentrated exocellular factors showed a very complex scenery supporting the multifactorial character of the biological activity of B. cereus.

C and Sr isotopic evolution of carbonate sequences in NW Argentina: Implications for a probable Precambrian-Cambrian transition Sial, A. N.; Ferreira, V. P.; Toselli, Alejandro Jose; Aceñolaza, Florencio Gilberto; Pimentel, M. M.; Parada, Marcela Alejandra; Alonso, Ricardo Narciso Upper Precambrian-Lower Cambrian sequences in the Tucuman, Salta and Jujuy provinces, NW Argentina, comprise sandstone, slate, conglomerate and black limestone (Las Tienditas/Volcan Fms.) with abundant Vendian/Tommotian trace fossils in the clastic facies rocks. The Precordillera basin, San Juan province, represents a continuous carbonate sequence belonging to the Lower to Middle Cambrian La Laja Fm. The Pie-de-Palo Range, Pampean Range, characterized by carbonates intercalated with greenschist/amphibolite facies metaclastic rocks, forms a part of the Precordillera basement. The δ13C values in carbonates of the Las Tienditas Fm. show a gradual decrease from the base (+3.4 ‰PDB) to the top with a minimum of -1.6‰ observed at ∼15m from the top, the latter having a higher clay content. Carbonates in a 700m thick section within La Laja Fm. is marked by a slightly positive δ13C values at the base (marly) with a negative anomaly (-2.0‰) at ∼20 m above, followed by a small positive anomaly (+0.5‰) ∼100 m from the base. All the values above this point are around -0.5‰ with a negative anomaly (-2.0‰) recorded at ∼240m above the base. Seawater 87Sr/86Sr values define a non-monotonic increase (0.70870 - 0.71082) through the carbonates in Las Tienditas Fm. while the La Laja Fm carbonates vary from 0.70926 to 0.71030, with higher values at the base. C and Sr isotopes, thus suggest that the Las Tienditas carbonates record the Precambrian-Cambrian transition (∼15m from the top of studied section). The same is also evident at ∼30 m from the base of the La Laja Fm. The narrow range of δ13C variation (-1.4 to + 1.3‰) and 87Sr/86Sr in the 0.709-0.710 range for the Caucete Group carbonates of the Pie-de-Palo Range, although unequivocally, appear to be in consonance with a Vendian to Tommotian age, reinforced by the presence of the trace fossils Didymaulichnus and Gordia.

Relationship of different ovarian stimulation response with vascular endothelial growth factor and degree of granulosa cell apoptosis. Quintana, R; Kopcow, L.; Marconi, G.; Sueldo, C.; Diradourian, M.; Barañao, Rosa Ines The aim of this study was to evaluate the concentration of vascular endothelial growth factor (VEGF) in follicular fluid and in granulosa cell cultures in relation to the degree of apoptosis in granulosa cells from patients with different types of ovarian response to controlled ovarian hyperstimulation. We studied 30 women who underwent controlled ovarian hyperstimulation and oocyte retrieval. Group A comprised patients with 1-4 follicles (n = 10), group B patients with 5-14 follicles (n = 10) and group C patients with >15 follicles (n = 10).

Absorption Kinetics of Sulfur Dioxide in Flint Corn during Steeping Haros, C. M.; Aguerre, Roberto Jorge; Suarez, C. A mathematical model was proposed to simulate simultaneous sulfur dioxide absorption and reaction during corn steeping. The parameters of the model, the diffusion coefficient and the reaction rate constant, were determined. The reaction rate of sulfur dioxide in corn grain followed first-order kinetics, with rate constants in the range 1.49×10-7to 9.78×10-7s-1for steeping temperatures from 25 to 55 °C. The Arrhenius activation energy for sulfur dioxide loss was 60.5 kJ/mol. The fitting of the mathematical model to the absorption curves determined the diffusion coefficient of sulfur dioxide in corn kernels. These varied from 1.17×10-11to 5.18×10-11m2/s for the temperature range 25-55 °C. Temperature-dependent diffusion coefficients was shown to obey the Arrhenius equation with an activation energy of 39.8 kJ/mol.

A quasilinearization approach for parameter identification in nonlinear abstract Cauchy problems Morin, Pedro; Spies, Ruben Daniel A quasilinearization approach to parameter identification in nonlinear abstract Cauchy problems in which the parameter appears in the nonlinear term, is presented. This approach has two main advantages over the classical one: it is much more intuitive and the derivation of the algorithm is done without need of the sensitivity equations on which classical quasilinearization is based. Sufficient conditions for the convergence of the algorithm are derived in terms of the regularity of the solutions with respect to the parameters. A comparison with the standard approach is presented and an application is included in which the nonphysical parameters in a mathematical model for shape memory alloys are estimated.