Wavelet entropy and fractional Brownian motion time series

We study the functional link between the Hurst parameter and the Normalized Total Wavelet Entropy when analyzing fractional Brownian motion (fBm) time series--these series are synthetically generated. Both quantifiers are mainly used to identify fractional Brownian motion processes (Fractals 12 (2004) 223). The aim of this work is understand the differences in the information obtained from them, if any.Comment: 10 pages, 2 figures, submitted to Physica A for considering its publicatio

Wavelet entropy of stochastic processes

We compare two different definitions for the wavelet entropy associated to stochastic processes. The first one, the Normalized Total Wavelet Entropy (NTWS) family [Phys. Rev. E 57 (1998) 932; J. Neuroscience Method 105 (2001) 65; Physica A (2005) in press] and a second introduced by Tavares and Lucena [Physica A 357 (2005)~71]. In order to understand their advantages and disadvantages, exact results obtained for fractional Gaussian noise (-1<alpha< 1) and the fractional Brownian motion (1 < alpha < 3) are assessed. We find out that NTWS family performs better as a characterization method for these stochastic processes.Comment: 12 pages, 4 figures, submitted to Physica

Neutral‐based processes overrule niche‐based processes in shaping tropical montane orchid communities across spatial scales

Tropical montane forests (TMF) are characterised by high endemism, species richness and turnover across elevations. A key question is how niche-based processes, via adaptation of species to local environmental conditions, and neutral-based processes from dispersal limitation shape community composition at different spatial scales across human-modified landscapes. We expect that (1) communities are highly distinct even within the same habitat type and (2) niche-based processes play the main role in compositional turnover. To address these expectations, we investigated the compositional turnover of orchids, one of the most prominent floristic elements of TMFs. We sampled orchids in 332 plots spanning over 270 km in the eastern Colombian Andes. Plots ranged between elevations of 1160–3750 m. We used two different spatial extents (whole gradient and two elevational bands), two grains of analysis for the first expectation (regional and local) and two spatial grains for the second expectation (broad and fine scales based on Moran's Eigenvector Maps [MEMs]). We found 331 orchid species in 171 (51%) plots. We found a strong pattern of high compositional turnover across scales (>72% of total beta diversity is given by species turnover), with 87.5% of the total species pool occurring in fewer than five plots, supporting our first expectation. Contrary to our second expectation, we found that community composition is mainly driven by geographical distance, while the relative influence of elevation, environmental variables and their combined fractions were negligible across habitats and spatial scales, rejecting niche-based processes. Synthesis. High compositional turnover, even across habitats with the highest degree of human intervention, suggests that both forest-dwelling and open-habitat species do not easily disperse across habitats. Species dispersal is the major force of orchid community turnover and might be strongly dependent upon macroevolutionary processes and species life-history traits over multiple scales. Dispersal limitation also draws attention to the importance of preserving habitat connectivity to halt biodiversity losses

Nuevos modelos de predicción del incremento en volumen para bosques mezclados del Estado de Durango, México

Thirty models were evaluated to predict the timber yield in 28 Permanent Silvicultural Research Plots (SPIS), in the Ejido Pueblo, Durango, Mexico. The most predominant plant association is the corresponding to mixed stands of Pinus and Pinus-Quercus, besides the vegetation associated to these forests. The models in their logarithmic form incorporate 10 competition indexes (IC) independent of the distance, 3 indexes of density (ID), besides the variable age and height at the average level of the stand. The new mathematical models relate in an indirect way the effect of the competition and the density in the growth of trees present in the stand. According to the variance analyses and the hypothesis tests, it was found that the best IC incorporated in a mathematical model for the prediction of the increment in volume was the competition index of area basal density (IABN), the competition index of diameter quadratic density (IDCN), the competition index of area basal total density (IABTN) and the competition index of maximum total height (IHMAX). The best models present a high level of accuracy with Prob &gt; |t| = 0.0001 and values average of 0.99 in R2. The best models presented average values of R2 = 0.99 and a highly significant level of accuracy (Pr &gt; |t| = 0.0001).Fueron evaluados 30 modelos para predecir el incremento maderable en 28 Sitios Permanentes de Investigación Silvícola (SPIS), ubicados en el Ejido Pueblo Nuevo del Estado de Durango, México. La asociación vegetal más predominante es la correspondiente a rodales mezclados de Pinus y Pinus-Quercus, además de la vegetación asociada a estos bosques. Los modelos en su forma logarítmica incorporan 10 índices de competencia (IC) independientes de la distancia, 3 índices de densidad (ID), además de las variables edad y altura a nivel promedio del rodal. Los nuevos modelos matemáticos relacionan de una manera indirecta el efecto de la competencia y la densidad en el crecimiento de los arboles presentes en el rodal. De acuerdo con los análisis de varianza y las pruebas de hipótesis realizadas, se encontró que los mejores IC incorporados en un modelo matemático para la predicción del incremento en volumen, fueron el índice de competencia de área basal densidad (IABN), índice de competencia de diámetro cuadrático densidad (IDCN), índice de competencia de área basal total densidad (IABTN) y el índice de competencia de altura total máxima (IHMAX). Los mejores modelos presentan un alto nivel de exactitud con Prob > |t| = 0,0001 y valores promedio de 0,99 en R2

On the equivalence between Implicit Regularization and Constrained Differential Renormalization

Constrained Differential Renormalization (CDR) and the constrained version of Implicit Regularization (IR) are two regularization independent techniques that do not rely on dimensional continuation of the space-time. These two methods which have rather distinct basis have been successfully applied to several calculations which show that they can be trusted as practical, symmetry invariant frameworks (gauge and supersymmetry included) in perturbative computations even beyond one-loop order. In this paper, we show the equivalence between these two methods at one-loop order. We show that the configuration space rules of CDR can be mapped into the momentum space procedures of Implicit Regularization, the major principle behind this equivalence being the extension of the properties of regular distributions to the regularized ones.Comment: 16 page

Role of Ambiguities and Gauge Invariance in the Calculation of the Radiatively Induced Chern-Simons Shift in Extended Q.E.D.

We investigate the possibility of Lorentz and CPT violations in the photon sector, of the Chern-Simons form, be induced by radiative corrections arising from the Lorentz and CPT non-invariant fermionic sector of an extended version of QED. By analyzing the modified vacuum polarization tensor, three contributions are considered: two of them can be identified with well known amplitudes; the (identical) QED vacuum polarization tensor and the (closely related) $AVV$ triangular amplitude. These amplitudes are evaluated in their most general form (to include in our discussion automatically the question of ambiguities) on the point of view of a strategy to manipulate and calculate divergent amplitudes that can avoid the explicit calculation of divergent integrals. Rather than this only general properties are used in intermediary steps. With this treatment, the results obtained by others authors can be easily recovered and we show that, if we choose to impose U(1) gauge invariance maintenance in the pure QED calculated amplitudes, to be consistent with the renormalizability, the induced Chern-Simons term assumes a nonvanishing ambiguities free value. However if, in addition, we choose to get an answer consistent with renormalizability by anomaly cancellation of the Standard Model a vanishing value can be obtained, in accordance with what was previously conjectured by other authors.Comment: 15 pages, LaTe

Comparing Implicit, Differential, Dimensional and BPHZ Renormalisation

We compare a momentum space implicit regularisation (IR) framework with other renormalisation methods which may be applied to dimension specific theories, namely Differential Renormalisation (DfR) and the BPHZ formalism. In particular, we define what is meant by minimal subtraction in IR in connection with DfR and dimensional renormalisation (DR) .We illustrate with the calculation of the gluon self energy a procedure by which a constrained version of IR automatically ensures gauge invariance at one loop level and handles infrared divergences in a straightforward fashion. Moreover, using the $\phi^4_4$ theory setting sun diagram as an example and comparing explicitly with the BPHZ framework, we show that IR directly displays the finite part of the amplitudes. We then construct a parametrization for the ambiguity in separating the infinite and finite parts whose parameter serves as renormalisation group scale for the Callan-Symanzik equation. Finally we argue that constrained IR, constrained DfR and dimensional reduction are equivalent within one loop order.Comment: 21 pages, 2 figures, late

Review: Strategies for enteric methane mitigation in cattle fed tropical forages

Methane (CH4) is a greenhouse gas (GHG) produced and released by eructation to the atmosphere in large volumes by ruminants. Enteric CH4 contributes significantly to global GHG emissions arising from animal agriculture. It has been contended that tropical grasses produce higher emissions of enteric CH4 than temperate grasses, when they are fed to ruminants. A number of experiments have been performed in respiration chambers and head-boxes to assess the enteric CH4 mitigation potential of foliage and pods of tropical plants, as well as nitrates (NO3−) and vegetable oils in practical rations for cattle. On the basis of individual determinations of enteric CH4 carried out in respiration chambers, the average CH4 yield for cattle fed low-quality tropical grasses (>70% ration DM) was 17.0 g CH4/kg DM intake. Results showed that when foliage and ground pods of tropical trees and shrubs were incorporated in cattle rations, methane yield (g CH4/kg DM intake) was decreased by 10% to 25%, depending on plant species and level of intake of the ration. Incorporation of nitrates and vegetable oils in the ration decreased enteric CH4 yield by ∼6% to ∼20%, respectively. Condensed tannins, saponins and starch contained in foliages, pods and seeds of tropical trees and shrubs, as well as nitrates and vegetable oils, can be fed to cattle to mitigate enteric CH4 emissions under smallholder conditions. Strategies for enteric CH4 mitigation in cattle grazing low-quality tropical forages can effectively increase productivity while decreasing enteric CH4 emissions in absolute terms and per unit of product (e.g. meat, milk), thus reducing the contribution of ruminants to GHG emissions and therefore to climate change