Descripción: New organophosphorus insecticides of dialkylsulphoximines derived with activity upon acetylcholinesterase were synthesized. The obtained compounds were characterized by NMR and IR, and anticholinesterase activity and toxicity was measured. A simulation through computer was done in order to establish the relationship between structure and activity.

Descripción: A recently reported symmetry breaking of density profiles of fluid argon confined by two parallel solid walls of carbon dioxide is studied. The calculations are performed in the framework of a nonlocal density functional theory. It is shown that the existence of such asymmetrical solutions is restricted to a special choice for the adsorption potential, where the attraction of the solid-fluid interaction is reduced by the introduction of a hard-wall repulsion. The behavior as a function of the slit's width is also discussed. All the results are placed in the context of the current knowledge on this matter. © 2008 American Institute of Physics.

Descripción: A simple model that employs a periodic, planar array of parallel cylinders representing the nanotubes is presented. Using this method, the existence of several phase transitions in the film is demonstrated. These include both two-dimensional (2D) transitions and quasi-1D transitions.

Descripción: The horizontal averaging of global positioning system radio occultation retrievals produces an amplitude attenuation and phase shift in any plane gravity wave, which may lead to significant discrepancies with respect to the original values. In addition, wavelengths cannot be straightforwardly inferred due to the observational characteristics. If the waves produce small departures from spherical symmetry in the background atmosphere and under the assumption that the refractivity kernel may be represented by a delta function, an analytical expression may be derived in order to find how the retrieved amplitudes become weakened (against the original ones). In Particular, we study the range of waves that may be detected and the consequent reduction in variance calculation, which is found to be around 19%. A larger discrepancy was obtained when comparing an occultation variance with the one computed from a numerical simulation of that case. Wave amplitudes can be better resolved when the fronts are nearly horizontal or when the angle between the occultation line of sight and the horizontal component of the wave vector approaches π/2. Short horizontal scale waves have a high probability of becoming attenuated or of not being detected at all. We then find geometrical relations in terms of the relative orientation between waves and sounding, so, as to appropriately interpret wavelengths extracted from the acquired data. Only inertio-gravity waves, which exhibit nearly horizontal fronts, will show small differences between detected and original vertical wavelengths. Last, we analyze the retrieval effect on wave phase and find a shift between original and detected wave that generally is nonzero and approaches π /4 for the largest horizontal wavelengths. Copyright 2008 by the American Geophysical Union.

Descripción: We investigate the ideal and incompressible magnetohydrodynamic (MHD) equations in three space dimensions for the development of potentially singular structures. The methodology consists in implementing the fourfold symmetries of the Taylor-Green vortex generalized to MHD, leading to substantial computer time and memory savings at a given resolution; we also use a regridding method that allows for lower-resolution runs at early times, with no loss of spectral accuracy. One magnetic configuration is examined at an equivalent resolution of 61443 points and three different configurations on grids of 40963 points. At the highest resolution, two different current and vorticity sheet systems are found to collide, producing two successive accelerations in the development of small scales. At the latest time, a convergence of magnetic field lines to the location of maximum current is probably leading locally to a strong bending and directional variability of such lines. A novel analytical method, based on sharp analysis inequalities, is used to assess the validity of the finite-time singularity scenario. This method allows one to rule out spurious singularities by evaluating the rate at which the logarithmic decrement of the analyticity-strip method goes to zero. The result is that the finite-time singularity scenario cannot be ruled out, and the singularity time could be somewhere between t=2.33 and t=2.70. More robust conclusions will require higher resolution runs and grid-point interpolation measurements of maximum current and vorticity. © 2013 American Physical Society.

Descripción: We have studied the hydration and diffusion of the hydroxyl radical O H0 in water using classical molecular dynamics. We report the atomic radial distribution functions, hydrogen-bond distributions, angular distribution functions, and lifetimes of the hydration structures. The most frequent hydration structure in the O H0 has one water molecule bound to the O H0 oxygen (57% of the time), and one water molecule bound to the O H0 hydrogen (88% of the time). In the hydrogen bonds between the O H0 and the water that surrounds it the O H0 acts mainly as proton donor. These hydrogen bonds take place in a low percentage, indicating little adaptability of the molecule to the structure of the solvent. All hydration structures of the O H0 have shorter lifetimes than those corresponding to the hydration structures of the water molecule. The value of the diffusion coefficient of the O H0 obtained from the simulation was 7.1× 10-9 m2 s-1, which is higher than those of the water and the O H-. © 2005 American Institute of Physics.

Descripción: Fil:Mocskos, E. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: Calcium signals participate in a large variety of physiological processes. In many instances, they involve calcium entry through inositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs), which are usually organized in clusters. Recent high-resolution optical experiments by Smith & Parker have provided new information on Ca2+ release from clustered IP3Rs. In the present paper, we use the model recently introduced by Solovey & Ponce Dawson to determine how the distribution of the number of IP3Rs that become open during a localized release event may change by the presence of Ca2+ buffers, substances that react with Ca2+, altering its concentration and transport properties. We then discuss how buffer properties could be extracted from the observation of local signals. © 2010 The Royal Society.

Descripción: A citywide control program of Aedes aegypti (L.) (Diptera: Culicidae) mainly based on the use of larvicides reduced infestations but failed to achieve the desired target levels in Clorinda, northeastern Argentina, over 5 yr of interventions. To understand the underlying causes of persistent infestations and to develop new control tactics adapted to the local context, we conducted two pupal surveys in a large neighborhood with ≈2,500 houses and recorded several variables for every container inspected in fall and spring 2007. In total, 4,076 lots and 4,267 containers were inspected over both surveys, and 8,391 Ae. aegypti pupae were collected. Large tanks used for potable water storage were the most abundant and the most productive type of container, accounting for 6584% of all the pupae collected. Therefore, large tanks were key containers and candidates for improved targeted interventions. Multivariate analysis showed that containers located in the yard, at low sun exposure, unlidded, filled with rain water, and holding polluted water were all more likely to be infested by larvae or pupae. When only infested containers were considered, productivity of pupae was most closely associated with large tanks and rain water. A stochastic simulation model was developed to calculate the expected correlations between pupal and Stegomyia indices according to the characteristics of the distribution of larvae and pupae per container and the spatial scale at which the indices were computed. The correlation between pupal and Stegomyia indices is expected to increase as infestation levels decline. © 2009 Entomological Society of America.

Descripción: This paper evaluates a present climate simulation over southern South America performed with the Meteorological Research Institute/Japanese Meteorological Agency (MRI/JMA) high resolution global model. Main patterns of low and upper-level atmospheric circulation were analysed in a 25-year simulation as well as climate means, interannual variability, trends and bias of temperature and precipitation. The model is able to reproduce the main atmospheric circulation patterns and mean surface variables, although some deficiencies were found such as an overestimation of temperature over central Argentina in most of seasons, an overestimation of austral winter precipitation over northeastern and central Argentina, an underestimation of precipitation in all the seasons over southeast of Brazil, an underestimation of the amplitude of the annual cycle temperature in some regions and an overestimation of the amplitude of the annual cycle of precipitation over mountainous areas. Model interannual variability was also assessed. In general, temperature variability is overestimated, whereas precipitation is underestimated. The spatial structure of the year-to-year variability of precipitation is correctly simulated by the model, although some patterns were misplaced. Most of regions present a cold seasonal bias reaching values of - 2 °C in some regions. It was found that precipitation biases are between 3 and - 1 mm day-1. In some regions and seasons observed and simulated temperature trends coincide, as in austral summer or spring, where the model and the observations show positive trends in most of regions. However, there is no agreement between observed and simulated precipitation trends in almost all the regions and seasons. © 2012 Royal Meteorological Society.

Descripción: We study a cost function for the aggregate behavior of all the agents involved in the minority game (MG) or the bar attendance model (BAM). The cost function allows us to define a deterministic, synchronous dynamic that yields results that have the main relevant features than those of the probabilistic, sequential dynamics used for the MG or the BAM. We define a temperature through a Langevin approach in terms of the fluctuations of the average attendance. We prove that the cost function is an extensive quantity that can play the role of an internal energy of the many-agent system while the temperature so defined is an intensive parameter. We compare the results of the thermal perturbation to the deterministic dynamics and prove that they agree with those obtained with the MG or BAM in the limit of very low temperature. © 2002 The American Physical Society.

Descripción: Multilevel resistance states in silver-manganite interfaces are studied both experimentally and through a realistic model that includes as a main ingredient the oxygen vacancies diffusion under applied electric fields. The switching threshold and amplitude studied through hysteresis switching loops are found to depend critically on the initial state. The associated vacancy profiles further unveil the prominent role of the effective electric field acting at the interfaces. While experimental results validate main assumptions of the model, the simulations allow to disentangle the microscopic mechanisms behind the resistive switching in metal-transition metal oxide interfaces. © 2010 American Institute of Physics.

Descripción: We present results from two 15363 direct numerical simulations of rotating turbulence where both energy and helicity are injected into the flow by an external forcing. The dual cascade of energy and helicity toward smaller scales observed in isotropic and homogeneous turbulence is broken in the presence of rotation, with the development of an inverse cascade of energy now coexisting with direct cascades of energy and helicity. In the direct cascade range, the flux of helicity dominates over that of energy at low Rossby number. These cascades have several consequences for the statistics of the flow. The evolution of global quantities and of the energy and helicity spectra is studied, and comparisons with simulations at different Reynolds and Rossby numbers at lower resolution are done to identify scaling laws. © 2010 American Institute of Physics.

Descripción: We present 3D, gasdynamic simulations of jet/cloud collisions, with the purpose of modelling the HH 270/110 system. From the models, we obtain predictions of Hα and H2 1-0 s(1) emission line maps, which qualitatively reproduce some of the main features of the corresponding observations of HH 110. We find that the model that better reproduces the observed structures corresponds to a jet that was deflected at the surface of the cloud ∼ 1000 yr ago, but is now boring a tunnel directly into the cloud. This model removes the apparent contradiction between the jet/cloud collision model and the lack of detection of molecular emission in the crossing region of the HH 270 and HH 110 axes.

Descripción: An atomistic model for Cu electrodeposition under nonequilibrium conditions is presented. Cu electrodeposition takes place with a height-dependent deposition rate that accounts for fluctuations in the local [formula presented] ions concentration at the interface, followed by surface diffusion. This model leads to an unstable interface with the development of protrusions and grooves. Subsequently the model is extended to account for the presence of organic additives, which compete with [formula presented] for adsorption at protrusions, leading to a stable interface with scaling exponents consistent with those of the Edwards-Wilkinson equation. The model reproduces the interface evolution experimentally observed for Cu electrodeposition in the absence and in the presence of organic additives. © 2002 The American Physical Society.

Descripción: We study the intermittency properties of the energy and helicity cascades in two 15363 direct numerical simulations of helical rotating turbulence. Symmetric and antisymmetric velocity increments are examinedas well as probability density functions of the velocity field and of the helicity density. It is found that the direct cascade of energy to small scales is scale invariant and nonintermittentwhereas the direct cascade of helicity is highly intermittent. Furthermorethe study of structure functions of different orders allows us to identify a recovery of isotropy of strong events at very small scales in the flow. Finallywe observe the juxtaposition in space of strong laminar and persistent helical columns next to time-varying vortex tanglesthe former being associated with the self-similarity of energy and the latter with the intermittency of helicity. © 2010 American Institute of Physics.

Descripción: Zero-range processes with jump rates that decrease with the number of particles per site can exhibit a condensation transition, where a positive fraction of all particles condenses on a single site when the total density exceeds a critical value. We consider rates which decay as a power law or a stretched exponential to a non-zero limiting value, and study the onset of condensation at the critical density. We establish a law of large numbers for the excess mass fraction in the maximum, as well as distributional limits for the fluctuations of the maximum and the fluctuations in the bulk. © 2013 Elsevier B.V. All rights reserved.

Descripción: Background: Coupled biological oscillators can tick with the same period. How this collective period is established is a key question in understanding biological clocks. We explore this question in the segmentation clock, a population of coupled cellular oscillators in the vertebrate embryo that sets the rhythm of somitogenesis, the morphological segmentation of the body axis. The oscillating cells of the zebrafish segmentation clock are thought to possess noisy autonomous periods, which are synchronized by intercellular coupling through the Delta-Notch pathway. Here we ask whether Delta-Notch coupling additionally influences the collective period of the segmentation clock. Results: Using multiple-embryo time-lapse microscopy, we show that disruption of Delta-Notch intercellular coupling increases the period of zebrafish somitogenesis. Embryonic segment length and the spatial wavelength of oscillating gene expression also increase correspondingly, indicating an increase in the segmentation clock's period. Using a theory based on phase oscillators in which the collective period self-organizes because of time delays in coupling, we estimate the cell-autonomous period, the coupling strength, and the coupling delay from our data. Further supporting the role of coupling delays in the clock, we predict and experimentally confirm an instability resulting from decreased coupling delay time. Conclusions: Synchronization of cells by Delta-Notch coupling regulates the collective period of the segmentation clock. Our identification of the first segmentation clock period mutants is a critical step toward a molecular understanding of temporal control in this system. We propose that collective control of period via delayed coupling may be a general feature of biological clocks. © 2010 Elsevier Ltd. All rights reserved.