Mixed memory, (non) Hurst effect, and maximum entropy of rainfall in the tropical Andes

Diverse linear and nonlinear statistical parameters of rainfall under aggregation in time and the kind of temporal memory are investigated. Data sets from the Andes of Colombia at different resolutions (15 min and 1-h), and record lengths (21 months and 8-40 years) are used. A mixture of two timescales is found in the autocorrelation and autoinformation functions, with short-term memory holding for time lags less than 15-30 min, and long-term memory onwards. Consistently, rainfall variance exhibits different temporal scaling regimes separated at 15-30 min and 24 h. Tests for the Hurst effect evidence the frailty of the R/S approach in discerning the kind of memory in high resolution rainfall, whereas rigorous statistical tests for short-memory processes do reject the existence of the Hurst effect.Rainfall information entropy grows as a power law of aggregation time, S(T) ∼ T^β with 〈β〉 = 0.51, up to a timescale, T_MaxEnt (70-202 h), at which entropy saturates, with β = 0 onwards. Maximum entropy is reached through a dynamic Generalized Pareto distribution, consistently with the maximum information-entropy principle for heavy-tailed random variables, and with its asymptotically infinitely divisible property. The dynamics towards the limit distribution is quantified. Tsallis q-entropies also exhibit power laws with T, such that S_q(T) ∼ T^β(q), with β(q) ? 0 for q ? 0, and β(q) ? 0.5 for q ? 1. No clear patterns are found in the geographic distribution within and among the statistical parameters studied, confirming the strong variability of tropical Andean rainfall.     

On the dissolution time of a class of binary systems

To test the various theories of the dissolution time of binary systems, we have performed a series of numerical experiments. The present simulations represent a number of binaries subject to perturbations by passing field stars. Various masses and velocities of the field stars were used to exhibit their effects on the dissolution time. Because of simplicity, the pair considered consisted of a primary of one solar mass plus a secondary of negligible mass.The computations gave, among other things, the evolution in time of the energies and excentricities of the secondary components. We found from these results the need to redefine the concept of time of dissolution to represent more realistically the rate of loss of secondary components. The dissolution times found from the present computations do not agree with any of the existing theories, neither in the general behavior nor in actual numerical values. The times of dissolution found in the present calculations are between a factor of two and a factor of fifteen longer than predicted by existing theories.     

TimeBliography: A Dynamic and Online Bibliography on Temporal GIS

This article introduces an online bibliography on temporal GIS, a research area in which different scientific fields and researchers have provided substantial results and literature over the past few years. We first define the scientific domain of temporal GIS, its origin and recent evolution, and the context of this bibliography. Then, the components and functionalities of the web‐based application that support the online bibliography are described. The bibliography, entitled TimeBliography, is accessible on the Web at http://spaceandtime.wsiabato.info .     

Perihelion precession in binary systems: higher order corrections

Higher order corrections (up to n-th order) are obtained for the perihelion precession in binary systems like OJ287 using the Schwarzschild metric and complex integration. The corrections are performed considering the third root of the motion equation and developing the expansion in terms of \(r_{s}/ (a(1-e^{2}) )\).The results are compared with other expansions that appear in the literature giving corrections to second and third order. Finally, we simulate the shape of relativistic orbits for binary systems with different masses.     

Detection of long-term trends in monthly hydro-climatic series of Colombia through Empirical Mode Decomposition

We test for the existence of long-term trends in 25- to 50-year long series of monthly rainfall, average river discharges, and minimum air temperatures in Colombia. The Empirical Mode Decomposition method is used as a mathematical filter to decompose a given time series into a finite number of intrinsic mode functions, assuming the coexistence of different frequency oscillatory modes in the series, and that the residual captures the likely existing long-term trends. The Mann-Kendall test for autocorrelated data is used to assess the statistical significance of the identified trends, and the Sen test is used to quantify their magnitudes. Results show that 62 % of river discharge series exhibit significant decreasing trends between 0.01-1.92 m ³ s ^?1 per year, which are highly consistent downstream albeit with different ratios between the trend magnitudes and mean discharges. Most minimum temperature series (87 %) exhibit increasing trends (0.01-0.08 °Cyr ^?1). Results for precipitation series are inconclusive owing to the mixing between increasing trends (41 %, between 0.1-7.0 mm yr ^?1) and decreasing trends (44 %, between 0.1-7.4 mm yr ^?1), with no clear-cut geographical pattern, except for the increasing trend identified along the Pacific region, consistent with the increasing trend identified in the strength of the Chocó low-level wind jet off the Pacific coast of Colombia, an important moisture source of continental precipitation. Our results contribute to discerning between signals of climate change and climate variability in tropical South America.     

Distant components in double and multiple stars

Summary A discussion is presented of the IDS, LDS, and Gliese's catalogues, inasmuch as they are relevant to the multiplicity of field stars and the distribution of separations of the companions in binaries and triples. The effect of dissociation of binaries with time is exhibited for a ‘quasi-unbiased’ sample of 106 nearby binaries taken from Gliese's catalogue. There are no binaries as old or older than the Sun with separations larger than 4000 AU, while binaries younger than the Sun may have separations as large as 180000 AU. The rate of this disruption seems too large to be produced by field stars; probably molecular clouds and spiral arms are the most effective agents. It appears that the size of the inner commet cloud cannot be much larger than 2000–4000 AU.     

On the reproducibility of run-away stars formed in collapsing clusters

To test the stability of the trajectories of run-away stars we present the results of a comparative study of 26 star clusters involving very strong encounters. Each one of these clusters was computed with different time steps, different techniques of integration and on different machines. We confirmed that, in general, the values of the energies, velocities and positions for the individual stars are not reproducible from run to run. We found, however, that in all the cases that have been tested, the run-away star preserved its energy, velocity and position from one run to another. It was also found that escapers are more reproducible than stars with negative energy.Part of this work was done at the Department of Aerospace Engineering and Engineering Mechanics of the University of Texas at Austin during a summer stay of C.A.     

Survey of antibodies to Mycoplasma agalactiae and Mycoplasma mycoides subsp. mycoides (large colony type) in dromedaries (Camelus dromedarius) in close contact with an infected goat population

Given recent evidence of a possible role of camelids in the epidemiology of diseases caused by mycoplasma species in other ruminants, we examined the prevalence of the mycoplasmas most commonly responsible for contagious agalactia (CA) in small ruminants among the dromedaries (Camelus dromedarius) of Lanzarote. On this island, one of the most arid regions of Spain in which CA is considered endemic, dromedaries and infected small ruminants such as goats and sheep, live in close contact. Specific IgG antibodies against Mycoplasma agalactiae and Mycoplasma mycoides subsp. mycoides (large colony biotype) were determined using two indirect enzyme immunoassays in 28% of the island's dromedary population. None of the serum samples tested were found to have antibodies against the two mycoplasma species, suggesting that the camels are not potential carriers of the main causative agents of CA.