Structure and energetics of ammonia clusters (NH3)n (n=3-20) investigated using a rigid-polarizable model derived from ab initio calculations

An analytical model has been developed to describe the interaction between rigid ammonia molecules including the explicit description of induction. The parameters of the model potential were chosen by fitting high quality ab initio data obtained using second-order Moller-Plesset (MP2) perturbation theory and extended basis sets. The description of polarization effects is introduced by using a noniterative form of the "charge on spring model", the latter accounting for more than 95% of the dipole induction energy and of the increased molecular dipole. Putative global minima for (NH3)(n) (n = 3-20) have been optimized using this new model, the structure and energetics of the clusters with n = 3-5 being found in good agreement with previous ab initio results including electronic correlation. Results for larger species have been compared with previous structural studies where only nonpolarizable models were employed. Our model predicts larger binding energies for any cluster size than previous analytical surfaces, the results often suggesting a reorganization of the relative energy ranking and a different structure for the global minimum

Fruit set and development of tomato grown in greenhouse : application of variable doses of plant growth regulators.

Las hormonas vegetales son capaces de controlar el desarrollo reproductivo, desde la diferenciación floral hasta los últimos estadios del desarrollo de los frutos. En particular, la etapa de fructificación y desarrollo depende del contenido endógeno de estas sustancias, y es posible manipular la iniciación del desarrollo del fruto por aplicación externa de hormonas. Previamente se evaluó el proceso de fructificación y desarrollo en el cultivo de tomate en invernadero en respuesta a la aplicación de b-NOA y AG3 en dosis fijas: se observó sensibilidad diferencial dependiendo del genotipo y tipo de regulador. El objetivo de este trabajo fue establecer dosis y momento óptimo para la aplicación de b-NOA y AG3 como formas de mejorar la fructificación y el desarrollo de frutos partenocárpicos. Como factores se consideraron tipo de regulador -b-NOA y AG3- en dosis y momentos de aplicación variables. Empleando ovarios no polinizados como sistema experimental fue posible concluir que la aplicación de 40 ppm de b-NOA a 7 días post antesis ofrece las mayores ventajas desde el punto de vista del rendimiento y menor impacto fisiológico, sin alterar el período de desarrollo de los frutos.Vegetable hormones are capable of controlling the reproductive development, from the flower differentiation until the last stages in the fruit development. In particular, the fruit set and development stage depends on the endogenous content of this substance, being possible to manipulate the beginning of the fruit development by external application of hormones. We have previously evaluated the fruit set and development process in tomato cultivation in greenhouse in response to the application of b-NOA and GA3 in fixed doses. Differential sensitivity was observed depending on the genotype and regulator type. The purpose of this work is to establish the optimum dose and moment for the application of b-NOA and GA3 as ways to improve the fruit set and development of parthenocarpic fruits. Regulator types b-NOA and GA3 in variable doses and application moments were considered as factors. Using unpollinated ovaries as an experimental system, it was possible to conclude that the application of 40 ppm of b-NOA at 7 days post antesis would offer the best advantages from a performance point of view and a lower physiologic impact, not altering the period of fruit development.Fil: Agüero, Marta S..Fil: Barral, Gabriela.Fil: Miguelisse, Nancy E..Fil: Castillo, Oscar E.

Quantifying entropy production in active fluctuations of the hair-cell bundle from time irreversibility and uncertainty relations

We introduce lower bounds for the rate of entropy production of an active stochastic process by quantifying the irreversibility of stochastic traces obtained from mesoscopic degrees of freedom. Our measures of irreversibility reveal signatures of time's arrow and provide bounds for entropy production even in the case of active fluctuations that have no drift. We apply these irreversibility measures to experimental recordings of spontaneous hair-bundle oscillations in mechanosensory hair cells from the ear of the bullfrog. By analyzing the fluctuations of only the tip position of hair bundles, we reveal irreversibility in active oscillations and estimate an associated rate of entropy production of at least similar to 3k (B)/s, on average. Applying thermodynamic uncertainty relations, we predict that measuring both the tip position of the hair bundle and the mechano-electrical transduction current that enters the hair cell leads to tighter lower bounds for the rate of entropy production, up to similar to 10(3) k (B)/s in the oscillatory regime

Fruit set and development of tomato grown in greenhouse : effect of plant growth regulators

El proceso de fructificación y desarrollo en tomate puede ser inducido naturalmente por polinización o partenocarpia y artificialmente por aplicación de reguladores; esta respuesta es variable según tipo y dosis de hormona, momento de aplicación y cultivar involucrado. El objetivo de este trabajo fue evaluar la capacidad de auxinas y giberelinas para inducir el desarrollo partenocárpico en genotipos de crecimiento indeterminado. Como factores se consideraron tipo de regulador -AG3 y β-NOA- en dosis fija, momento de aplicación -0, 5, 12, 19, 26 dpa- y genotipo -Rutgers, Fortaleza F1 y Colt 45-. Las mejores respuestas a nivel de porcentaje de fructificación y peso fresco se obtuvieron con β-NOA en comparación con AG3. Considerando todos los factores analizados, solamente la aplicación de β-NOA a 5 dpa permitió alcanzar porcentajes de fructificación y tamaño final de frutos similares a los obtenidos por autopolinización. El período de sensibilidad y el tamaño final de los frutos presentaron interacción con las variables genotipo, momento de aplicación y tipo de regulador. Se observó además que AG3 provocó un escaso desarrollo placentario y ausencia de óvulos mientras que β-NOA indujo un desarrollo de placentas y óvulos similar al de los frutos obtenidos por autopolinización.The process of fruit set and development in tomato can be naturally induced by pollination or parthenocarpy and artificiall y by hormonal application; this response is variable according to type and dose of the hormone, moment of application and cultivar involved. The purpose of this work was to evaluate the capacity of auxins and gibberellins to induce the parthenocarpic development in genotypes of undetermined growth. The considered factors were type of regulator -AG3 and β-NOAin set dose, moment of application -0, 5, 12, 19, 26 dpa-, and genotype -Rutgers, Fortaleza F1 and Colt 45-. The best responses regarding percentage of fructification and fresh weight are obtained with β-NOA in comparison with AG3. Considering all the analyzed factors, only the application of β-NOA to 5 dpa allowed to obtain the percentages of fruit set and final size of fruits similar to the ones obtained by autopollination. The period of sensitivity and the final size of fruits presented interaction with the genotype variables, moment of application and type of regulator. It was also observed that AG3 caused a scarce placental development and ovule absence while β-NOA induced a placenta and ovule development similar to the one in fruits obtained by autopollination.Fil: Castillo, Oscar E..Fil: Barral, Gabriela.Fil: Rodríguez, Gustavo.Fil: Miguelisse, Nancy E..Fil: Agüero, Marta S.

Gamma rays from microquasars Cygnus X-1 and Cygnus X-3

Gamma-ray observations of microquasars at high and very-high energies can provide valuable information of the acceleration processes inside the jets, the jet-environment interaction and the disk-jet coupling. Two high-mass microquasars have been deeply studied to shed light on these aspects: Cygnus X-1 and Cygnus X-3. Both systems display the canonical hard and soft X-ray spectral states of black hole transients, where the radiation is dominated by non-thermal emission from the corona and jets and by thermal emission from the disk, respectively. Here, we report on the detection of Cygnus X-1 above 60 MeV using 7.5 yr of Pass8 Fermi-LAT data, correlated with the hard X-ray state. A hint of orbital flux modulation was also found, as the source is only detected in phases around the compact object superior conjunction. We conclude that the high-energy gamma-ray emission from Cygnus X-1 is most likely associated with jets and its detection allow us to constrain the production site. Moreover, we include in the discussion the final results of a MAGIC long-term campaign on Cygnus X-1 that reaches almost 100 hr of observations at different X-ray states. On the other hand, during summer 2016, Cygnus X-3 underwent a flaring activity period in radio and high-energy gamma rays, similar to the one that led to its detection in the high-energy regime in 2009. MAGIC performed comprehensive follow-up observations for a total of about 70 hr. We discuss our results in a multi-wavelength context.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC 2017), Bexco, Busan, Korea (arXiv:1708.05153

Lognormal scale invariant random measures

In this article, we consider the continuous analog of the celebrated Mandelbrot star equation with lognormal weights. Mandelbrot introduced this equation to characterize the law of multiplicative cascades. We show existence and uniqueness of measures satisfying the aforementioned continuous equation; these measures fall under the scope of the Gaussian multiplicative chaos theory developed by J.P. Kahane in 1985 (or possibly extensions of this theory). As a by product, we also obtain an explicit characterization of the covariance structure of these measures. We also prove that qualitative properties such as long-range independence or isotropy can be read off the equation.Comment: 31 pages; Probability Theory and Related Fields (2012) electronic versio