Electromagnetic and Gravitational Waves on a de Sitter background

One of the longstanding problems of modern gravitational physics is the detection of gravitational waves, for which the standard theoretical analysis relies upon the split of the space-time metric into a background metric plus perturbation. However, as is well known, the background need not be Minkowskian in several cases of physical interest. Thus, we here investigate in more detail what happens if the background space-time has a non-vanishing Riemann curvature. In the case in which the de Donder gauge is imposed, its preservation under infinitesimal space-time diffeomorphisms is guaranteed if and only if the associated covector is ruled by a second-order hyperbolic operator. Moreover, since in this case the Ricci term of the wave equation has opposite sign with respect to the wave equation of Maxwell theory in the Lorenz gauge, it is possible to relate the solutions of the two problems. We solve completely the homogeneous vector wave equation of Maxwell theory in the Lorenz gauge when a de Sitter space-time is considered. The decoupling technique, analytic formulae and plots are original and have been first presented, in the literature, by Bini, Esposito and the author in Gen. Rel. Grav. 42, 51-61 (2010). Moreover, we solve explicitly the Einstein equations for metric perturbations on a de Sitter background. In fact, by using the Regge-Wheeler gauge, the coupled system of differential equations, to first-order in the metric perturbation, has been here solved in terms of the Heun general functions.Comment: 86 pages, 37 figures, Ph.D. thesis of the autho

Modelling Rainfall-induced Shallow Landslides at Different Scales Using SLIP - Part I

AbstractSLIP (Shallow Landslides Instability Prediction) is a mathematical model developed to foresee the triggering of rainfall-induced shallow landslides (soil slips) and the unstable condition of slopes affected by these phenomena. This physically-based model gives the factor of safety in function of the principal variables influencing the trigger of soil slips: rainfall, geometry, soil state, mechanical and hydraulic characteristics of soil. The specific characteristics of SLIP allowed to use the same means to model the phenomenon from the scale of the representative elementary volume (i.e. flume laboratory tests) to the medium and large scale (regional and national level). This paper (Part I), that is companion of another one published in this Conference (Part II), contains a brief description of the model and focuses on the approach followed in the application of the SLIP model at laboratory scale

A model for triggering mechanisms of shallow landslides

Abstract. Rainfall-induced shallow landslides, also called "soil slips", are becoming ever more frequent all over the world and are receiving a rising interest in consequence of the heavy damage they produce. At the University of Parma, a simplified physically based model has been recently set up for the evaluation of the safety factor of slopes which are potentially at risk of a soil slip. This model, based on the limit equilibrium method applied to an infinite slope, takes into account some simplified hypotheses on the water down-flow and defines a direct correlation between the safety factor of the slope and the rainfall depth. In this paper, this model is explained in detail and is used in a back analysis process to verify its capability to foresee the triggering instant of rainfall-induced shallow landslides for some recent case studies in the Emilia Romagna Apennines (Northern Italy). The results of the analyses and of the model implementation are finally shown

Phylogeography of the Neotropical Fish Genus Rhoadsia (Teleostei: Characidae) in Ecuador

Western Ecuador is considered a biodiversity hotspot. Nevertheless, studies of population genetic structure and variation are rare, especially in aquatic species. The genus Rhoadsia is an endemic freshwater fish in this region with two recognized species, Rhoadsia minor and R. altipinna. Little is known about the evolutionary relationships of their populations, and due to morphological similarities, their validity as distinct species has been questioned. The present study uses a phylogeographic approach to examine the evolutionary history of the genus and the validity of the two described species. Furthermore, I investigated the possible geographical origin of the genus based on patterns of genetic diversity and genetic distance from two sister genera. I also estimated potential zoogeographic breaches based on patterns of genetic divergence that could reflect points of genetic divergence between populations of other freshwater fishes. I used several molecular markers with different rates of evolution: cytochrome oxidase I (COI) and cytochrome b (Cyt-b) from the mitochondrial genome (mtDNA) and 12 microsatellite loci from the nuclear genome (nDNA). Sampling was conducted in drainages across Western Ecuador and an effort was made to sample at different elevations (from 30 to 1260 m above sea level), given the known patterns of morphological divergence associated with elevation. The phylogenetic tree resolved with the mtDNA data confirmed the presence of two species exhibiting genetic introgression at the border between the species ranges (Northern Guayas). A Bayesian-based analysis of the microsatellite data revealed the existence of ten populations of Rhoadsia divided into three main groups (I, II, and III). Group I coincided with the distribution of R. minor while group II and III seemed to represent geographic subgroups of R. altipinna. Patterns of genetic divergence and diversity were used to suggest potential evolutionarily significant units within both species for conservation efforts. The most likely geographical origin of the genus appeared to be in the Guayas drainage. However, this result is a hypothesis and should be examined more carefully in the future using other approaches. Two major zoogeographic breaches were identified: the first one was between the two largest drainages (Esmeraldas and Guayas) and the second one was located farther south cutting through the Jubones drainage and isolating the central Guayas and drainages just south from the southernmost drainages of western Ecuador. Future research should include biological and ecological data to reinforce the validity of the species. I also suggest looking for signals of adaptive divergence between species or between populations from contrasting habitats like low and high elevations. This study provides a baseline for future studies examining biogeographic relationships of freshwater species in Western Ecuador

Investigating the Granulometric Distribution of Fluvial Sediments through the Hybrid Technique: Case Study of the Baganza River (Italy)

Sediment characterization is a key parameter to understand the geomorphological attributes of a catchment (i.e., assessing the variability of the sediment transport capacity and surface roughness of a hydraulic channel). This assessment can be performed in several ways, for instance, through numerous sampling techniques (i.e., pebble count and zig-zag methods). Sediment sampling using manual sieving inside a laboratory is a hectic process as it requires ample time and physical effort, particularly when the scale of interest is at the catchment level. In order to find the granulometric distribution of some sections of the Baganza streambed (northern Italy), in order to carry out analysis at the catchment scale, a hybrid technique (a combination of the conventional and photogrammetric method) is introduced. Different grain size distribution curves (GSDs) obtained from the image processing technique using Digital Gravelometer software and traditional sediment sieve analysis (sieve-by-weight method) were compared. Sediment sampling was limited to sections of the streambed that were visible during lower flows in the dry summer season. Sediment samples including fine soil fraction, were collected up to a depth of 30 cm, although the exposed areas behaved as gravels and cobble bars. The adopted hybrid technique approach for the characterization of fluvial sediments is desirable in order to accommodate the full range of particle sizes inside the riverbed. Digital photography was performed at ten different cross sections, along the longitudinal profile of the 30 km long reach of the Baganza River, to examine the sediment distribution, grading, and representative particle sizes (D10, D50, D90) at each of the respective cross sections. A comparison of the photogrammetric method and traditional sieve analysis revealed strong agreement in coarser segments of the grain size distributions, but it was deficient in the finer part (<2 mm) due to the shielding effect produced by bigger particles. However, the adopted hybrid technique appears to be quite efficient and promising in determining the GSD by reducing the costs and the sediment sample collection time in the field

Predicting landslide susceptibility and risks using GIS-based machine learning simulations, case of upper Nyabarongo catchment

Sustainable landslide mitigation requires appropriate approaches to predict susceptible zones. This study compared the performance of Logistic Model Tree (LMT), Random Forest (RF) and Naïve-Bayes Tree (NBT) in predicting landslide susceptibility for the upper Nyabarongo catchment (Rwanda). 196 past landslides were mapped using field investigations. Thus, the inventory map was split into training and testing datasets. Fifteen predisposing factors were analysed and information gain (IG) technique was used to analyse the correlation between factors and observed landslides. Therefore, the area under receiver operating characteristic (AUROC) with other statistical estimators including accuracy, precision, and root mean square error (RMSE) were employed to compare the models. The AUC values were 78.7%, 80.9% and 82.4% for RF, LMT and NBT models, respectively. Additionally, the NBT produced the highest accuracy and precision values (0.799 and 0.745, respectively). Regarding RMSE values, the NBT model achieved an optimized prediction than RF and LMT models (0.301; 0.428 and 0.364, respectively). The results of the current study may inform further studies and appropriate landslide risk reduction and mitigation measures. They can also be instrumental for policy and decision making in regards with natural risk management

TVFS: Topology Voltage Frequency Scaling for Reliable Embedded ConvNets

This brief introduces Topology Voltage Frequency Scaling (TVFS), a performance management technique for embedded Convolutional Neural Networks (ConvNets) deployed on low-power CPUs. Using TVFS, pre-trained ConvNets can be efficiently processed over a continuous stream of data, enabling reliable and predictable multi-inference tasks under latency constraints. Experimental results, collected from an image classification task built with MobileNet-v1 and ported into an ARM Cortex-A15 core, reveal TVFS holds fast and continuous inference (from few runs, up to 2000), ensuring a limited accuracy loss (from 0.9% to 3.1%), and better thermal profiles (average temperature 16.4 °C below the on-chip critical threshold)

Solution of Maxwell's equations on a de Sitter background

The Maxwell equations for the electromagnetic potential, supplemented by the Lorenz gauge condition, are decoupled and solved exactly in de Sitter space-time studied in static spherical coordinates. There is no source besides the background. One component of the vector field is expressed, in its radial part, through the solution of a fourth-order ordinary differential equation obeying given initial conditions. The other components of the vector field are then found by acting with lower-order differential operators on the solution of the fourth-order equation (while the transverse part is decoupled and solved exactly from the beginning). The whole four-vector potential is eventually expressed through hypergeometric functions and spherical harmonics. Its radial part is plotted for given choices of initial conditions. We have thus completely succeeded in solving the homogeneous vector wave equation for Maxwell theory in the Lorenz gauge when a de Sitter spacetime is considered, which is relevant both for inflationary cosmology and gravitational wave theory. The decoupling technique and analytic formulae and plots are completely original. This is an important step towards solving exactly the tensor wave equation in de Sitter space-time, which has important applications to the theory of gravitational waves about curved backgrounds.Comment: 11 pages, 5 figures, Latex. The presentation has been improved, and the title has been change

Advances in Shallow Landslide Hydrology and Triggering Mechanisms: A Multidisciplinary Approach

The vadose zone of steep slopes is often affected by rainfallinduced shallow landslides, which can cause widespread direct and indirect damage to the terrain and infrastructures, as well as urban and rural developments. These phenomena are determined by hydrological or subsurface flow processes and also mechanical (stress equilibrium) processes. Some models attempt to link dynamics of hydrologic behavior with the mechanical state of a hillslope and the onset of failure. However, the hydrological dynamics leading to shallow landslide initiation, the hydraulic properties at the slope scale, and the role of hysteretic effects as well as the soil nonequilibrium processes in slope stability assessment are still not completely understood and require further investigation. Furthermore, these open questions are generally treated separately by geologists, hydrologists, agronomists, and geotechnical engineers, whereas a multidisciplinary approach is a key factor in the study of these phenomena occurring in the vadose zone