Van Kampen's expansion approach in an opinion formation model

We analyze a simple opinion formation model consisting of two parties, A and B, and a group I, of undecided agents. We assume that the supporters of parties A and B do not interact among them, but only interact through the group I, and that there is a nonzero probability of a spontaneous change of opinion (A->I, B->I). From the master equation, and via van Kampen's Omega-expansion approach, we have obtained the "macroscopic" evolution equation, as well as the Fokker-Planck equation governing the fluctuations around the deterministic behavior. Within the same approach, we have also obtained information about the typical relaxation behavior of small perturbations.Comment: 17 pages, 6 figures, submited to Europ.Phys.J.

Bright single-photon sources in bottom-up tailored nanowires

The ability to achieve near-unity light extraction efficiency is necessary for a truly deterministic single photon source. The most promising method to reach such high efficiencies is based on embedding single photon emitters in tapered photonic waveguides defined by top-down etching techniques. However, light extraction efficiencies in current top-down approaches are limited by fabrication imperfections and etching induced defects. The efficiency is further tempered by randomly positioned off-axis quantum emitters. Here, we present perfectly positioned single quantum dots on the axis of a tailored nanowire waveguide using bottom-up growth. In comparison to quantum dots in nanowires without waveguide, we demonstrate a 24-fold enhancement in the single photon flux, corresponding to a light extraction efficiency of 42 %. Such high efficiencies in one-dimensional nanowires are promising to transfer quantum information over large distances between remote stationary qubits using flying qubits within the same nanowire p-n junction.Comment: 19 pages, 6 figure

Patrones de distribución de la producción de forraje de Bromus catharticus Vahl. y B. parodii Covas et Itria

The objectives of this study were to estimate the growth rate, seasonal distribution of dry matter production and accumulated yield in five cultivars of Bromus catharticus Vahl. and one cultivar of B. parodii Covas et Itria. A secuential cuts methodology was used in a split plot design arranged in random blocks. At each cutting date dry matter yield was estimated. Growth rates were calculated for each mean date, accumulated seasonal yield was estimated and the seasonal distribution patterns were obtained. Growth rates and accumulated yield were analyzed by ANOVA and FLSD tests. B. parodii had lower initial growth rate and higher spring growth rate than B. catharticus. Differences in install growth rates and at the end of winter and beginning of spring were found among B. catharticus cultivars (p<0.05). Accumulated yield was similar for all cultivars (p>0.05).Los objetivos de este trabajo fueron obtener la tasa de crecimiento diaria, las curvas de distribución estacional de la producción de materia seca y la producción acumulada de cinco cultivares de cebadilla criolla y uno de cebadilla Intermedia. Se utilizó una metodología de cortes secuenciales en un diseño de parcelas divididas en bloques aleatorizados. En cada corte se determinó la producción de materia seca. Para cada fecha media se calcularon las tasas medias de crecimiento, la producción de materia seca acumulada y se elaboraron las curvas de distribución estacional. Las tasas medias, de crecimiento y la producción de materia seca acumulada se sometieron a análisis de varianza y prueba de diferencia mínima significativa (FLSD). Los resultados mostraron que la cebadilla intermedia tuvo menor crecimiento Inicial (p<0,05) y mayor crecimiento primaveral (p<0,05) que la cebadilla criolla. Dentro de cebadilla criolla se detectaron diferencias entre cultivares respecto del crecimiento inicial y el de fin de invierno - principios de primavera (p<0,05). No se encontraron diferencias en la producción acumulada de materia seca entre cultivares (5492 :1: 590 kgMS.ha) (p>0,05)

Peso de grano y vigor de plántula en centenos diploide y tetraploide

The objetives of this study were to determine the influence of seed weight and ploidy level on rye seedling vigor. Three seed weight and two ploidy levels were evaluated in blotting paper sandwich. Data were subjeted to analysis of variance and LSDs were calculated. Seedling vigor measured as green biomass, leaf blade length and seedling diameter increased with seed weight and ploidy level. Also the leaf blade length and coleoptile length increased with seed weight. Dry matter percentage decreased as the ploidy level increased.El objetivo del presente trabajo fue determinar el efecto del peso de grano y del nivel de ploidía sobre el vigor de plántula en centeno. Se establecieron tres categorías de peso de grano y se trabajó con dos niveles de ploidía. Se utilizaron germinadores tipo "sandwich". Se usó prueba de diferencia mínima significativa para comparación de medias. El vigor de plántula, medido por la producción de biomasa del sector aéreo, por el largo de la lámina de la primera hoja y por el diámetro de la plántula aumentó a medida que se incrementó el peso de grano y el nivel de ploidia. El largo del coleoptilo y el largo de la vaina de la primera hoja aumentaron a medida que se incrementó el peso de grano. El porcentaje de materia seca disminuyó con el incremento del nivel de ploidía pero no fue influenciado por el peso de grano

Exact solutions to chaotic and stochastic systems

We investigate functions that are exact solutions to chaotic dynamical systems. A generalization of these functions can produce truly random numbers. For the first time, we present solutions to random maps. This allows us to check, analytically, some recent results about the complexity of random dynamical systems. We confirm the result that a negative Lyapunov exponent does not imply predictability in random systems. We test the effectiveness of forecasting methods in distinguishing between chaotic and random time-series. Using the explicit random functions, we can give explicit analytical formulas for the output signal in some systems with stochastic resonance. We study the influence of chaos on the stochastic resonance. We show, theoretically, the existence of a new type of solitonic stochastic resonance, where the shape of the kink is crucial. Using our models we can predict specific patterns in the output signal of stochastic resonance systems.Comment: 31 pages, 18 figures (.eps). To appear in Chaos, March 200

Variabilidad en Bromus brevis Nees. (cebadilla pampeana)

The objective of this study was to evaluate the variability of B. brevis Nees. Nineteen accessions were collected at different locations of La Pampa and Buenos Aires provinces and characterized in 1992 on the basis of agronomic characters. Accessions were arranged in a randomized complete block design with 3 replications. Analysis of variance and FLSD tests were performed. High variabi-lity (p<0.01) was found for seed yield, weight of 1000 anthecium, days to flowering, plant height, flag leaf length, number of spike-Iets per panicle, and panicle lenght. Significant variability (p<0.05) was also found for dry matter yield, leaf flag width, spikelet length and number of anthecium per panicle. No variability was found for internode lenght, spikelet width, number of anthecium per spikelet, awn length, fresh matter yield, and dry matter percentage. These results showed different levels of variabilily tor the agronomic characters evaluated in B. brevis.El objetivo de este trabajo fué analizar la variabilidad existente entre 19 accesiones de cebadilla pampeana (Bromus brevis Nees.) recolectadas en diferentes localidades de las provincias de La Pampa y Buenos Aires, para caracteres agronómicos, fisiológicos y morfológicos. Durante el año 1992, se realizaron dos ensayos: en uno se determinó producción de forraje y en el otro producción de semilla, caracteres de panoja y espiguilla; se midieron en total 18 variables. Para ambos ensayos se IJSÓ un diseño en bloques aleatorizados completos con tres repeticiones, Para separación de medias se utilizó la prueba DMS protegida. Se encontraron diferencias altamente significativas (p<0,01) para producción de semilla, peso de mil antecios, periodo a panojamiento, altura de planta, largo de hoja bandera, espiguillas por panoja y largo de panoja. Las diferencias fueron significativas (p<0,05) para peso seco, ancho de hoja bandera, largo de espiguilla y numero de antecios por panoja. No se halló variabilidad para largo de entrenudo, ancho de espiguilla, numero de antecios por espiguilla, largo de arista, peso verde ni para porcentaje de materia seca. Los resultados obtenidos señalan la presencia de variabilidad para caracteres de importancia desde el punto de vista forrajero

Improving the performance of bright quantum dot single photon sources using amplitude modulation

Single epitaxially-grown semiconductor quantum dots have great potential as single photon sources for photonic quantum technologies, though in practice devices often exhibit non-ideal behavior. Here, we demonstrate that amplitude modulation can improve the performance of quantum-dot-based sources. Starting with a bright source consisting of a single quantum dot in a fiber-coupled microdisk cavity, we use synchronized amplitude modulation to temporally filter the emitted light. We observe that the single photon purity, temporal overlap between successive emission events, and indistinguishability can be greatly improved with this technique. As this method can be applied to any triggered single photon source, independent of geometry and after device fabrication, it is a flexible approach to improve the performance of solid-state systems, which often suffer from excess dephasing and multi-photon background emission