Análisis de la precipitación en Villa Mercedes (San Luis) periodo 1899/00-1984/85

This paper presents the results of an analysis of rainfall regime in Villa Mercedes (San Luis) from 1899/00 to 1984/85. The rainfall regime in the area is typically mensoonic, 78% of precipitation falling in spring-summer. According to PROHASKA classification the type is Normal dry. More than 50% of the years studied have received between 50 and 70 cm. per year. The highest variability (variance ratio) has been observed during autumn-winter months, 95% confidence intervals for different month rainfall show the validity of monthly averages. The annual rainfall maximum value is 3,57 times greater than the minimum one. Both annual and spring-summer rainfall trends, which have been fortnightly analyzed, are similar r=0,63 and r=0,92 respectively. This show that the annual amount increase is restricted to the wet season. Mean precipitation amount during the autumn-winter period does not reveal the presence of a real trend (r=0.36).El presente trabajo analiza el comportamiento de la precipitación en la localidad de Villa Mercedes (San Luis) a partir de 1899/00 hasta 1984/85. El régimen pluviométrico de la región es típicamente monzónico con el 78% de lluvias primavero-estivales. De acuerdo a la clasificación de PROHASKA, corresponde al tipo Normal seco. Más del 50% de los años analizados acusan valores de lluvias anuales entre 500 y 700 mm. La mayor variabilidad (coeficiente de variación) se observa en los meses de otoño e invierno. Se destaca, a través de los intervalos del 95% de confianza para precipitación de los diferentes meses, la validez de les promedios mensuales. El valor maximo de lluvia anual fue de 3,57 veces el valor mínimo. La tendencia de precipitación anual muestra similitud con la referida a precipitación del periodo primavero-estival, analizadas ambas quinquenalmente con r=0,63 y r=0,92 respectivamente, lo que significa que el incremento en los montos anuales se localiza en el período húmedo. La precipitación del período otoño-invernaI no muestra la existencia de tendencia real (r=0,36)

Prediction of extreme events in the OFC model on a small world network

We investigate the predictability of extreme events in a dissipative Olami-Feder-Christensen model on a small world topology. Due to the mechanism of self-organized criticality, it is impossible to predict the magnitude of the next event knowing previous ones, if the system has an infinite size. However, by exploiting the finite size effects, we show that probabilistic predictions of the occurrence of extreme events in the next time step are possible in a finite system. In particular, the finiteness of the system unavoidably leads to repulsive temporal correlations of extreme events. The predictability of those is higher for larger magnitudes and for larger complex network sizes. Finally, we show that our prediction analysis is also robust by remarkably reducing the accessible number of events used to construct the optimal predictor.Comment: 5 pages, 4 figure

Symmetries and Fixed Point Stability of Stochastic Differential Equations Modeling Self-Organized Criticality

A stochastic nonlinear partial differential equation is built for two different models exhibiting self-organized criticality, the Bak, Tang, and Wiesenfeld (BTW) sandpile model and the Zhang's model. The dynamic renormalization group (DRG) enables to compute the critical exponents. However, the nontrivial stable fixed point of the DRG transformation is unreachable for the original parameters of the models. We introduce an alternative regularization of the step function involved in the threshold condition, which breaks the symmetry of the BTW model. Although the symmetry properties of the two models are different, it is shown that they both belong to the same universality class. In this case the DRG procedure leads to a symmetric behavior for both models, restoring the broken symmetry, and makes accessible the nontrivial fixed point. This technique could also be applied to other problems with threshold dynamics.Comment: 19 pages, RevTex, includes 6 PostScript figures, Phys. Rev. E (March 97?

Pulse-coupled relaxation oscillators: from biological synchronization to Self-Organized Criticality

It is shown that globally-coupled oscillators with pulse interaction can synchronize under broader conditions than widely believed from a theorem of Mirollo \& Strogatz \cite{MirolloII}. This behavior is stable against frozen disorder. Beside the relevance to biology, it is argued that synchronization in relaxation oscillator models is related to Self-Organized Criticality in Stick-Slip-like models.Comment: 4 pages, RevTeX, 1 uuencoded postscript figure in separate file, accepted for publication in Phys. Rev. Lett

Curvas de crecimiento de cereales forrajeros de invierno. I. Avena (Avena sativa L.)

The trial was carried out to study dry matter yields of 6 oat (Avena sativa L.) cultivars, and the seasonal growth distribution. Green standing crop was clipped every 7 days in 90 plots arranged at random in 5 series with 3 repetitions each. The environmental conditions determined a very short growing period, principally in early cultivars. Significant differences (P < 0,05) were observed between Millauquén INTA (2,164.0 kg MS/ha) and 82/2866 Sv. and Suregrain cultivars (1,431.5 and 1,464.8 kg MS/ha, respectively). The growth equations of each cultivar was determined. The highest growth rate (28.54 kg MS/ha/day) corresponded to Millauquén INTA, and was shown at early june. Millauquén INTA, Sra. 74/76864 and Moregrain showed a better dry matter distribution than the resto during the entire growth season.El ensayo se realizó con el propósito de estudiar en forma comparativa el rendimiento de materia seca de 6 variedades cultivadas de avena (Avena sativa L.) y la distribución estacional del mismo. Se adoptó una metodología de cortes secuenciales, trabajando con 90 parcelas dispuestas en 5 series con 3 repeticiones. Las condiciones ambientales determinaron un acortamiento pronunciado de la estación de crecimiento, particularmente en los cultivares precoces. Existieron diferencias significativas (P < 0;05) entre la variedad cultivada Millauquén INTA (2.164,0 kg MS/ha) y los cultivares 82/2866 Sv. y Suregrairi (1.431,5 y 1.464,8 kg MS/ha, respectivamente). Se determinaron las ecuaciones descriptivas del crecimiento para cada cultivar. La máxima tasa de producción (28,54 kg MS/ha/día correspondió a la variedad cultivada Millauquén INTA, a comienzos de junio. Esta variedad, al igual que los cultivares Sra.74 /76864 y Moregrain, mostró una distribución más uniforme de la materia seca a través del tiempo

Transitions in non-conserving models of Self-Organized Criticality

We investigate a random--neighbours version of the two dimensional non-conserving earthquake model of Olami, Feder and Christensen [Phys. Rev. Lett. {\bf 68}, 1244 (1992)]. We show both analytically and numerically that criticality can be expected even in the presence of dissipation. As the critical level of conservation, $\alpha_c$, is approached, the cut--off of the avalanche size distribution scales as $\xi\sim(\alpha_c-\alpha)^{-3/2}$. The transition from non-SOC to SOC behaviour is controlled by the average branching ratio $\sigma$ of an avalanche, which can thus be regarded as an order parameter of the system. The relevance of the results are discussed in connection to the nearest-neighbours OFC model (in particular we analyse the relevance of synchronization in the latter).Comment: 8 pages in latex format; 5 figures available upon reques

Unified Scaling Law for Earthquakes

We show that the distribution of waiting times between earthquakes occurring in California obeys a simple unified scaling law valid from tens of seconds to tens of years, see Eq. (1) and Fig. 4. The short time clustering, commonly referred to as aftershocks, is nothing but the short time limit of the general hierarchical properties of earthquakes. There is no unique operational way of distinguishing between main shocks and aftershocks. In the unified law, the Gutenberg-Richter b-value, the exponent -1 of the Omori law for aftershocks, and the fractal dimension d_f of earthquakes appear as critical indices.Comment: 4 pages, 4 figure

Curvas de crecimiento de cereales forrajeros de invierno. III. Centeno (Secale cereale L.).

The trial was carried out to study dry matter yields of 6 rye (Secale cereale L.) cultivars, and the seasonal growth distribution. Green standing crop was clipped every 7 days in 90 plots arranged at random in 5 series with 3 repetitions each, The growth equations of each cultivar was determined. The growing period was extended until last october. Significant differences (P < 0,05) in dry matter yields were observed; highest productions were for M. Suquía, O, Enrique and Tropero cultivara. Naicó and D. Luis cultivars showed a higher dry matter distribution than the rest during the winter season.La experiencia se llevó a cabo con el objeto de estudiar comparativamente el rendimiento de materia seca de 6 cultivares de centeno (Secale cereale L.) y su distribución estacional. Se trabajó con una metodología de cortes secuenciales, utilizando 90 parcelas dispuestas en 5 series con 3 repeticiones. Se determinaron las ecuaciones descriptivas del crecimiento para cada variedad. La estación de crecimiento se extendió hasta fines de octubre. Existieron diferencias significativas (P < 0,05) en los rendimientos de, forrajimasa, sobresaliendo los cultivares Manfredi Suquía, 0011 Enrique y Tropero. Los cultivares Naicó y Don Luis brindaron, en términos porcentuales, una mayor oferta invernal de pasto

Random Neighbor Theory of the Olami-Feder-Christensen Earthquake Model

We derive the exact equations of motion for the random neighbor version of the Olami-Feder-Christensen earthquake model in the infinite-size limit. We solve them numerically, and compare with simulations of the model for large numbers of sites. We find perfect agreement. But we do not find any scaling or phase transitions, except in the conservative limit. This is in contradiction to claims by Lise & Jensen (Phys. Rev. Lett. 76, 2326 (1996)) based on approximate solutions of the same model. It indicates again that scaling in the Olami-Feder-Christensen model is only due to partial synchronization driven by spatial inhomogeneities. Finally, we point out that our method can be used also for other SOC models, and treat in detail the random neighbor version of the Feder-Feder model.Comment: 18 pages, 6 ps-figures included; minor correction in sec.

Synchronization, Diversity, and Topology of Networks of Integrate and Fire Oscillators

We study synchronization dynamics of a population of pulse-coupled oscillators. In particular, we focus our attention in the interplay between networks topological disorder and its synchronization features. Firstly, we analyze synchronization time $T$ in random networks, and find a scaling law which relates $T$ to networks connectivity. Then, we carry on comparing synchronization time for several other topological configurations, characterized by a different degree of randomness. The analysis shows that regular lattices perform better than any other disordered network. The fact can be understood by considering the variability in the number of links between two adjacent neighbors. This phenomenon is equivalent to have a non-random topology with a distribution of interactions and it can be removed by an adequate local normalization of the couplings.Comment: 6 pages, 8 figures, LaTeX 209, uses RevTe