Molecular mechanisms of inhibition of nicotinic acetylcholine receptors by tricyclic antidepressants Gumilar, Fernanda Andrea; Arias, Hugo Rubén; Spitzmaul, Guillermo Federico; Bouzat, Cecilia Beatriz In addition to their well known actions on monoamine reuptake, tricyclic antidepressants have been shown to modulate ligand-gated ion channels (LGICs). Since the muscle nicotinic acetylcholine receptor (AChR) has been the model for studying structure-function relationships of LGICs, we analyzed the action of tricyclic antidepressants on this type of AChR at both single-channel and macroscopic current levels. We also determined their effects on ACh equilibrium binding and their interactions with the different conformational states of the AChR. Antidepressants produce a significant concentration-dependent decrease in the duration of clusters of single-channels (eight fold at 20 μM). They also decrease the peak amplitude and increase the decay rate of currents elicited by rapid perfusion of ACh to outside-out patches. In equilibrium binding assays, antidepressants promote the typical high-affinity desensitized state and inhibit binding of [piperidyl-3,4-3H (N)]-(N-(1-(2-thienyl) cyclohexyl)-3,4-piperidine ([3H]TCP) to its locus in resting and desensitized AChRs. The results indicate that tricyclic antidepressants: (i) interact with resting (closed), open, and desensitized channels; (ii) do not affect significantly channel opening and closing rates; (iii) do not act as fast open-channel blockers; (iv) inhibit activation of resting channels; and (v) may increase the rate of long-lived desensitization from the open state.

Phase space structure of multi-dimensional systems by means of the mean exponential growth factor of nearby orbits Cincotta, Pablo Miguel; Giordano, Claudia Marcela; Simó, C. In this paper we deal with an alternative technique to study global dynamics in Hamiltonian systems, the mean exponential growth factor of nearby orbits (MEGNO), that proves to be efficient to investigate both regular and stochastic components of phase space. It provides a clear picture of resonance structures, location of stable and unstable periodic orbits as well as a measure of hyperbolicity in chaotic domains which coincides with that given by the Lyapunov characteristic number. Here the MEGNO is applied to a rather simple model, the 3D perturbed quartic oscillator, in order to visualize the structure of its phase space and obtain a quite clear picture of its resonance structure. Examples of application to multi-dimensional canonical maps are also included.

Geomorphologic, circulation and dynamic analysis in a meandering tidal channel, Bahía Blanca Estuary Angeles, Guillermo Raul; Perillo, Gerardo Miguel E.; Piccolo, Maria Cintia A meander of La Lista tidal channel (Bahia Blanca Estuary, Argentina) was selected in order to study the relationship between the geoforms that control the meandering channel evolution (mainly tidal flats and marshes) arid the dynamic and circulation characteristics of these channels. To achieve this goal a general survey was made in August 1999. The topographic characteristics of the channel and cross- section profiles from different sectors of the meander were compared with typical river profiles. Morphologic similarities between meander tidal channel cross-section (characterized by bidirectional flows) and meander river cross-section (characterized by unidirectional flows) were analysed. The largest velocities were measured during the ebb period (87 and 67 em S·l for U and V, respectively); during the flood period, the highest values registered were 53 and 33 em S·1 for U and V, respectively. Differences among the tidal current profiles along the meander were observed. Comparing the current velocity gradients in the different stations, the higher variations were observed during the flood period.

Gelation of beta-lactoglobulin in the presence of propylene glycol alginate: kinetics and gel properties Baeza, Rosa Isabel; Gugliotta, Luis Marcelino; Pilosof, Ana Maria Renata The role of the non-gelling polysaccharide, propyleneglycol alginate (PGA), on the dynamics of gelation and gel properties of β-lactoglobulin (β-lg) under conditions where the protein alone does not gel (6%) was analyzed. To this end, the kinetics of gelation, aggregation and denaturation of β-lg in the mixed systems (pH 7) were studied at different temperatures (64–88 °C). The presence of PGA increased thermal stability of β-lg. The rate of β-lg denaturation was decreased and the onset and peak denaturation temperatures increased by 2.2–2.4 °C. PGA promoted the formation of larger aggregates that continued to grow in time. An average aggregate diameter of approximately 300 nm is reached at the gel point in the mixed β-lg+PGA systems, irrespective of the heating temperature. Comparing the activation energies for the aggregation (193 kJ/mol), denaturation (422 kJ/mol) and formation of the primary gel structure (1/tgel) (256 kJ/mol) processes in the mixed protein–polysaccharide system, it can be concluded that the rate determining step in the formation of the primary gel structure would be the aggregation of protein. Ea values for the processes after the gel point (solid phase gelation) suggest a diffusion limited process because of the high viscosity of the solid gelling matrix. The characteristics of the mixed β-lg+PGA gels in terms of rheological and textural parameters, water loss and microstructure were studied as a function of heating temperature and time. The extent of aggregation and the type of interactions involved, prior to denaturation seem to be very important in determining the gel structure and its properties.

A model for determination of multicomponent diffusion coefficients in foods Gerla, Patricia; Rubiolo, Amelia Catalina The simultaneous diffusion of NaCl, lactic acid and water in cheese during brining, were experimentally and theoretically evaluated using multicomponent and pseudobinary mass transport models. The average concentration data of each solute in the solid at different process times were correlated with theoretical models determining the diffusion coefficients values for each solute. Applying a ternary model, main and cross diffusion coefficient values for NaCl and lactic acid showed a non-reciprocal flux interaction. The NaCl diffusion rate resulted independent of the lactic acid concentration gradient, while the lactic acid diffusion rate was increased 12 times due to NaCl concentration changes in the cheese. The results established the importance of using multicomponent mass transport models to evaluate the flux variation of solute in the global flux value.

Heat transfer in double-sided cooking of meat patties considering two-dimensional geometry and radial shrinkage Zorrilla, Susana; Singh, R. Paul A mathematical model considering a two-dimensional (2-D) cylindrical geometry, radial shrinkage, and thermal properties changing with temperature, was developed to predict temperature profiles in meat patties during double-sided cooking. The hamburger patty was assumed to be initially frozen; therefore, the approach of enthalpy formulation was used. A moving interface separating two regions when the water vaporization temperature is reached and a third type boundary condition at the patty surface considering a contact heat transfer coefficient were assumed in the radial direction. Furthermore, a third type boundary condition considering a combined heat transfer coefficient for radiation and convection and the symmetry condition in the center were assumed in the radial direction. The model was solved according to a method based on an explicit finite difference approximation and was compared with the results obtained by a one-dimensional (1-D) model. The results showed no significant difference when a cylindrical geometry or radial shrinkage was considered to predict the temperature at the geometric center of a patty under normal conditions of hamburger cooking. However, the 2-D model provides a description of temperature in regions close to the circumferential edge of the patty, which is not possible with the 1-D model.

Dynamic optimization of double-sided cooking of meat patties Zorrilla, Susana; Banga, Julio; Singh, R. Paul Optimal operating procedures for double-sided cooking of frozen hamburger patties were computed using dynamic optimization techniques. The mathematical statement was to find the optimal control (e.g., heating surface temperature) over cooking time to minimize (or maximize) the performance index J, for example minimize cooking loss, and to ensure the required lethality and safe cooking temperature. The control vector parameterization framework was applied, and stochastic algorithm was used to locate the global optimum with reasonable computation effort (Integrated Controlled Random Search for Dynamic Systems). The performance index improved when the heating temperature profile was considered as control variable and when two control elements of variable size were used (compared with the constant-temperature process or nominal case, ΔJ<3%). When the lower bound was relaxed and two control elements were used, the performance index improved significantly (ΔJ<7%). However, when the top and bottom plate temperatures were considered as two different controls, the plate temperature profiles obtained did not significantly improve the results compared with the nominal cases. When the temperature of the top and bottom plates and gap thickness were considered as control variables, and when two control elements of variable size for gap thickness were used, the performance index improved for long periods of cooking time (ΔJ<2.5%).

Effects of Salts on Crystallization Kinetics and Rheological Behavior of Concentrated α,α-Trehalose Solutions Cerdeira, Mariana; Puppo, Maria Cecilia; Martini, Silvana; Herrera, Maria Lidia The effect of addition of CaCl2 · 2H2O and MgCl2 · 6H2O on crystallization kinetics and the rheological behavior of a 70% trehalose solution was studied by polarized light microscopy and dynamic oscillatory rheometry. Salts caused a delay on nucleation with induction times for crystallization longer for Mg2+ than for Ca2+. Divalent cations were incorporated into crystals, changing the growth of certain faces preferentially, which resulted in changes in morphology. Addition of CaCl2 · 2H2O in a high salt/trehalose molar ratio dramatically increased complex modulus (G*), indicating a stronger viscoelastic behavior. A gel-like structure was formed when Ca2+ was added to trehalose solution. The behavior of Mg 2+/trehalose solutions cannot be considered viscoelastic in nature but as a fluid-like system.

Immobilized Artificial Membrane Chromatography: Quantitative Structure-Retention Relationships of Structurally Diverse Drugs Luco, Juan Maria; Salinas, Adriana Paticia; Torriero, Angel Alberto Jesus; Vázquez, Rodolfo Nieto; Raba, Julio; Marchevsky, Eduardo Jorge The Chromatographic capacity factors (log k′) for 32 structurally diverse drugs were determined by high performance liquid chromatography (HPLC) on a stationary phase composed of phospholipids, the socalled immobilized artificial membrane (IAM). In addition, quantitative structure-retention relationships (QSRR) were developed in order to explain the dependence of retention on the chemical structure of the neutral, acidic, and basic drugs considered in this study. The obtained retention data were modeled by means of multiple regression analysis (MLR) and partial least squares (PLS) techniques. The structures of the compounds under study were characterized by means of calculated physicochemical properties and several nonempirical descriptors. For the carboxylic compounds included in the analysis, the obtained results suggest that the IAM-retention is governed by hydrophobicity factors followed by electronic effects due to polarizability in second place. Further, from the analysis of the results obtained of two developed quantitative structure-permeability studies for 20 miscellaneous carboxylic compounds, it may be concluded that the balance between polarizability and hydrophobic effects is not the same toward IAM phases and biological membranes. These results suggest that the IAM phases could not be a suitable model in assessing the acid-membrane interactions. However, it is not possible to generalize this observation, and further work in this area needs to be done to obtain a full understanding of the partitioning of carboxylic compounds in biological membranes. For the non-carboxylic compounds included in the analysis, this work shows that the hydrophobic factors are of prime importance for the IAM-retention of these compounds, while the specific polar interactions, such as electron pair donor-acceptor interactions and electrostatic interactions, are also involved, but they are not dominant.

Use of Back-off Computation in Multilevel MPC Arbiza, María José; Bandoni, José Alberto; Figueroa, Jose Luis The desired operating point in Model Predictive Control is determined by a local steady-state optimization, which may be based on an economic objective.  In this paper we proposes the solution of a linear dynamic back-off problem to obtain a hierarchical scheme that ensures feasible operation in despite of disturbances.  This is performed by computing the critical disturbances and expanding the optimziation problem to ensure the existence of a control action that ensures the rejection of each perturbation.

Aqueous sodium oleate-sodium dehydrocholate mixtures at low concentration Messina, Paula Verónica; Morini, Marcela Ana; Schulz, Pablo Carlos The aqueous mixed system sodium dehydrocholate (NaDHC)-sodium oleate (NaOL) was studied by several methods to determine the influence of the hydrophobic structure of both surfactants in the mixed micellization and the formation of the mixed monolayer adsorbed at the air-water interface. The molecular area at the critical micelle concentration in pure surfactant solutions suggests that the adsorbed oleate chain was folded to allow the double bond in the middle of the molecule to remain in contact with water, and that the NaDHC molecule was situated with its plane laying parallel to the water surface, allowing the three carbonyl groups in the hydrocarbon backbone to form hydrogen bonds with water. The interaction was repulsive at the surface, and in the mixed monolayer some molecules must move away the less hydrophilic groups from water (double bond of NaOL, carbonyl groups of NaDHC). The interaction in mixed micelles was strongly attractive, showing a preferential composition roughly equimolar. The hydrolysis in mixed micelles was augmented in comparison with pure surfactants systems, which could be explained by assuming the existence of a more hydrophobic mixed micelle core. The mixed micelle degree of ionization was below that of the pure micelles, thus indicating a high surface charge density.

Expression of FcRII in chronic lymphocytic leukemia B cells. Gamberale, Romina; Geffner, Jorge Raúl; Sanjurjo, Julieta; Fernandez Calloti, Paula X.; Arrosagaray, Guillermo; Sánchez Ávalos, Julio César Américo; Giordano, Mirta Nilda We have read with interest the paper from Damle et al analyzing the surface membrane phenotype of B lymphocytes in chronic lymphocytic leukemia (B-CLL). The authors stated that the leukemic cells from all B-CLL patients evaluated (irrespective of immunoglobulin heavy chain (IgVH) gene mutational status) bear the phenotype of antigen-experienced B cells based, among other features, on the very low expression of Fcγ receptors type IIb (FcγRIIb, CD32), which is the main isoform of FcγRII in B lymphocytes.

Interaction between process design and process operability of chemical processes: An eigenvalue optimization approach Blanco, Anibal Manuel; Bandoni, Jose Alberto An increasing effort is being devoted to consider controllability issues (or in a wider sense operability issues) at the process design stage. Controllability has mainly to do with dynamics in the face of disturbances. One philosophy for the integration of design and controllability is to explicitly consider dynamic elements within the process design formulation. An outstanding feature of dynamics is stability, which is related with the spectrum (set of eigenvalues) of the dynamic system Jacobian matrix. Dynamic convergence speed may also be analyzed in terms of the eigenvalues of the matrix from a Lyapunov function related to the Jacobian of the system. It is the purpose of this contribution to formulate and solve the chemical process design problem, considering process dynamics from an eigenvalue optimization approach.

Retrofit of multiproduct batch plants through generalized disjunctive programming Montagna, Jorge Marcelo; Vecchietti, Aldo The retrofit problem for multiproduct batch plants deals with the modification of the original structure of the plant to meet new production conditions such as the introduction of new products, a new supply pattern, etc. For this problem, a disjunctive model is presented, which takes into consideration every usual alternative about the configuration of units and storage tanks. A disjunction is generated for that purpose. The selection of one of those alternatives sets up all the corresponding constraints, which are: operation time, unit size and cost, etc. Finally, the performance of this approach is analyzed through the resolution of a set of examples.

Centothecoid grasses and the evolution of panicoid spikelets Rua, Gabriel Hugo An evolutionary pathway leading to acrotonous, 2-flowered spikelets of Panicoideae has been suggested elsewhere, which involves apical reduction of many-flowered mesotonic spikelets. Current phylogenies of the grass family show a sister relationship between Panicoideae and Centothecoideae. A survey of spikelet structures occurring among centothecoid grasses shows that some representatives of this group have intermediate morphologies which are consistent with that hypothesis. Chasmanthium and Bromuniola have many-flowered spikelets with a barren proximal floret, whereas Thysanolaena, Gouldochloa and Gynerium represent a series of apical reductions leading to 2-flowered spikelets. Moreover, many-flowered spikelets with 1-3 proximal male flowers followed by several female-fertile ones occur in Puelioideae, one of the early-diverging clades of the Poaceae. This fact suggests that some "panicoid" characters may have evolved long before the radiation of the Panicoideae took place.

Predictive functional control based on fuzzy model: magnetic suspension system case study Lepetic, Marko; Skrjanc, Igor; Chiacchiarini, Hector Gerardo; Matko, Drago Fuzzy model based predictive functional controller (FPFC) is applied to the magnetic suspension system - a pilot plant for magnetic bearing. High quality control requirements are short settle time with a-periodical step response and zero steady-state error. Open loop unstable process was stabilised with linear lead compensator. The FPFC was used as a cascade controller. Due to some model uncertainties, the Takagi-Sugeno fuzzy model of stabilised system was obtained using fuzzy identification. Comparing to PID, it improved quality and robustness performance. With its computational efficiency, it proved to be ideal solution for high sampling frequency.

Lattice gas study of the kinetics of the NO-CO catalytic reaction on Pd nanoclusters Bustos Giunta, Victor Angel; Uñac, Rodolfo Omar; Zgrablich, Giorgio; Henry, Claude R. The kinetics of the NO-CO reaction on Pd nanoclusters is studied through a lattice-gas model and Monte Carlo simulation. Pd nanoclusters with three typical sizes: 2.8 nm, 6.9 nm and 15.6 nm, are considered. These nanoclusters have been epitaxially grown on MgO(100) and tested for the NO-CO reaction in previous experimental work [ref. 9-11: C. H. F. Peden, D. W. Goodman, D. S. Blair, P. J. Berlowitz, G. B. Fisher and S. H. Oh, J. Phys. Chem., 1988, 92, 1563; C. Duriez, C. R. Henry and C. Chapon, Surf. Sci., 1991, 253, 190; L. Piccolo and C. R. Henry, Appl. Surf. Sci., 2000, 162-163, 670], thus providing the motivation for the present study. According to their size, the nanoclusters present different proportions of Pd(100) and Pd(111) facets. The effects of CO and NO desorption are found to be of fundamental importance for the behavior of the system. In all cases the medium size particles are found to be the most active. At low temperature, where NO desorption can be neglected (since the activation energy for desorption of NO on Pd is about 5 kcal mol-1 greater than that for the desorption of CO), the largest particles are revealed as the less active, while at high temperature, where both NO and CO desorption take place, the smallest particles are found to be the less active. These results are in concordance with the experimentally observed behavior.

Diffusion of particles adsorbed on a triangular lattice: Pairwise and three-particle interactions Tarasenko, Alexander A.; Nieto Quintas, Felix Daniel; Jastrabík, Lubomír; Uebing, Christian In the present paper, the influence of both pairwise and three-particle interactions on the mobility of adsorbed particles diffusing on a lattice with triangular symmetry has been studied. Two different techniques has been used for describing the surface diffusion phenomenon. On one hand, explicit expressions for the chemical and jump diffusion coefficients have been calculated by using real-space renormalization group (RSRG) approach. A number of the RSRG transformations with blocks of different sizes and symmetries have been investigated. In particular, it has been shown that the precision of the method depends strongly not only on the number of sites in the RSRG blocks but also on their composition and structure. On the other hand, numerical simulations by using the Monte Carlo scheme has been used to simulate the process of particle migration. Using both methods, adsorption isotherms for different temperatures and the coverage dependencies for the thermodynamic factor and the chemical diffusion coefficient have been calculated. The behavior of the above mentioned quantities has been compared when the adparticles interact via only either pairwise or three-particle interactions. Despite the fact that both methods constitute very different approaches, the correspondence of numerical data with analytical results is surprisingly good. Therefore, it can be concluded that the RSRG method can be successfully applied for lattice gas systems to characterize the thermodynamic and kinetic properties of strongly interacting adsorbates.

Objective method for classifying air masses: an application to the analysis of the Buenos Aires' (Argentina) urban heat island intensity Bejarán, Rubén Aníbal; Camilloni, Ines Angela During recent years, numerous studies have examined the Buenos Aires urban climate, but the relationship between large-scale weather conditions and the Buenos Aires urban heat island (UHI) intensity has not been studied. The goal of this paper is to apply an objective synoptic climatological method to identify homogeneous air masses or weather types affecting Buenos Aires during winter, and to relate the results to the UHI intensity. A K-means clustering method was used to define six different air masses considering the 03:00, 09:00, 15:00 and 21:00 LT surface observations of dry bulb temperature, dew point, cloud cover, atmospheric pressure and wind direction and velocity at Ezeiza, the most rural meteorological station of the Buenos Aires metropolitan area (Fig. 1). Results show that the mean UHI intensity is at its maximum (2.8 °C) a few hours before sunrise when conditions are dominated by cold air masses associated with cold-core anticyclones, weak winds and low cloud cover. Inverse heat islands are found during the afternoon for all air masses indicating that surface processes are not dominant at that time. The relatively infrequent and warmest air mass is the only one that presents a mean negative urban-rural temperature difference (−0.1 °C) during the afternoon with the smallest diurnal cycle of the UHI intensity probably due to the prevailing high humidity and cloudy sky conditions. The paper provides an insight into the Buenos Aires urban?rural temperature difference under a variety of winter weather types and results could be useful to improve local daily temperature forecasts for the metropolitan area of Buenos Aires on the basis of the routine forecasts of weather types.

Modelling corn starch swelling in batch systems: effect of sucrose and hydrocolloids Krüger, Alejandra; Ferrero, Cristina; Zaritzky, Noemi Elisabet Hydrocolloids are used in starch-based products to improve stability and to obtain specific textural characteristics. In stirred batch systems with constant jacket temperature, xanthan gum, guar gum and sodium alginate (1% w/w) were added to corn starch (10% w/w) and sucrose (15% w/w) in aqueous systems to test their effects on granule swelling, starch gelatinization temperatures and viscoelastic behavior of the hot paste. As heating is not instantaneous, time–temperature relationships cannot be avoided. In this regard, heat penetration was faster in viscoelastic systems with lower complex dynamic modulus ðGÞ values, while pastes containing gums showed lower heat transfer rates during gelatinization. Microscopy and image analysis were applied to describe the granule swelling process in starch gelatinization. Starch granule swelling was considerably reduced by the presence of gums due to the lower heating rates and the decreased mobility of water molecules. The presence of sucrose increased starch gelatinization temperatures, measured by differential scanning calorimetry; gum addition did not show a significant influence on these temperatures. The effect of time and temperature on the starch swelling process was modelled considering, as driving force, the difference between the instantaneous mean curvature of the granule (reciprocal of the diameter) and the asymptotic curvature. Gelatinization rate constants were calculated for the different pastes and the lowest values were observed for starch pastes added with gums. Activation energies ranged from 80 ( 14) to 119 ( 3) kJ mol 1, being comparable to values reported in the literature for starch gelatinization measured by different methods.