Periodic orbits for a class of galactic potentials

In this work, applying general results from averaging theory, we find periodic orbits for a class of Hamiltonian systems H whose potential models the motion of elliptic galaxies.     

Evolution of hard gluons in a medium with q^(t)∼tn and the thermalization problem

We study the energy distribution of hard gluons traversing a dense quark-gluon plasma by comparing various transverse momentum broadening rates , using a probabilistic perturbative approach. These results were applied to address the thermalization problem in heavy ion collisions. Within the weak coupling model, thermalization follows a “bottom-up” process: early-formed high-energy partons emit low-energy gluons, leading to their equilibrium formation, creating a thermal bath that facilitates equilibrium in the high-energy sector. Under this scenario, we model the time dependencies of $$ as a power-law $$, and assess the impact of $$ on the distribution of hard gluons passing through the medium.     

A methodology for structural analysis and optimization of riser connection joints

In riser structural systems, the region where the riser is connected to the platform is critical due to the development of high stress levels. To reduce the stress concentration in this region, bend stiffeners and stress joints are used in order to provide a gradual stiffness transition between the riser and the platform. The present paper presents an optimization design approach for bend stiffeners and stress joints, using a slender beam procedure for the connection joint analysis and an evolution strategies multi-objective optimization algorithm. This approach produces similar results when compared to a finite element analysis of the complete riser, but with significant reduction of computational costs. Numerical examples are presented, showing the efficiency and robustness of the suggested methodology.     

Forward modeling of GPS multipath for near-surface reflectometry and positioning applications

Multipath is detrimental for both GPS positioning and timing applications. However, the benefits of GPS multipath for reflectometry have become increasingly clear for soil moisture, snow depth, and vegetation growth monitoring. Most multipath forward models focus on the code modulation, adopting arbitrary values for the reflection power, phase, and delay, or they calculate the reflection delay based on a given geometry and keep reflection power empirically defined. Here, a fully polarimetric forward model is presented, accounting for right- and left-handed circularly polarized components of the GPS broadcast signal and of the antenna and surface responses as well. Starting from the fundamental direct and reflected voltages, we have defined the interferometric and error voltages, which are of more interest in reflectometry and positioning applications. We examined the effect of varying coherence on signal-to-noise ratio, carrier phase, and code pseudorange observables. The main features of the forward model are subsequently illustrated as they relate to the broadcast signal, reflector height, random surface roughness, surface material, antenna pattern, and antenna orientation. We demonstrated how the antenna orientation—upright, tipped, or upside-down—involves a number of trade-offs regarding the neglect of the antenna gain pattern, the minimization of CDMA self-interference, and the maximization of the number of satellites visible. The forward model was also used to understand the multipath signature in GPS positioning applications. For example, we have shown how geodetic GPS antennas offer little impediment for the intake of near-grazing reflections off natural surfaces, in contrast to off metal, because of the lack of diversity with respect to the direct signal—small interferometric delay and Doppler, same sense of polarization, and similar direction of arrival.     

Experimental verification of effective anisotropic crack theories in variable crack aspect ratio medium

Physical modelling of cracked/fractured media using downscaled laboratory experiments has been used with great success as a useful alternative for understanding the effect of anisotropy in the hydrocarbon reservoir characterization and in the crustal and mantle seismology. The main goal of this work was to experimentally verify the predictions of effective elastic parameters in anisotropic cracked media by Hudson and Eshelby–Cheng's effective medium models. For this purpose, we carried out ultrasonic measurements on synthetic anisotropic samples with low crack densities and different aspect ratios. Twelve samples were prepared with two different crack densities, 5% and 8%. Three samples for each crack density presented cracks with only one crack aspect ratio, whereas other three samples for each crack density presented cracks with three different aspect ratios in their composition. It results in samples with aspect ratio values varying from 0.13 to 0.26. All the cracked samples were simulated by penny‐shaped rubber inclusions in a homogeneous isotropic matrix made with epoxy resin. Moreover, an isotropic sample for reference was constructed with epoxy resin only. Regarding velocity predictions performed by the theoretical models, Eshelby–Cheng shows a better fit when compared with the experimental results for samples with single and mix crack aspect ratio (for both crack densities). From velocity values, our comparisons were also performed in terms of the ε, γ, and δ parameters (Thomsen parameters). The results show that Eshelby–Cheng effective medium model fits better with the measurements of ε and γ parameters for crack samples with only one type of crack aspect ratio.     

Damage assessment of the 2015 Mw 8.3 Illapel earthquake in the North-Central Chile

Natural Hazards - Destructive megathrust earthquakes, such as the 2015 Mw 8.3 Illapel event, frequently affect Chile. In this study, we assess the damage of the 2015 Illapel Earthquake in the...     

A review of the geodynamic constraints on the development and evolution of geothermal systems in the Central Andean Volcanic Zone (18–28°Lat.S)

ABSTRACT

Geothermal exploration in the Central Andean Volcanic Zone (CAVZ) focuses on heat capacities of known geothermal systems, yet the role of faults, veins, fractures and folds on the evolution and migration of fluids is far from complete. Here, we present a compilation of He and Sr isotope data and newly generated structural maps to examine if particular tectonic configurations are associated with fluids migrating from different crustal levels. Accordingly, we defined three tectono-geothermal environments (T1–T3) depicting specific structural arrangements and spatial relation with geothermal and volcanic manifestations. T1 is dominated by left-lateral strike-slip NW-striking faults, and geothermal and volcanic manifestations occur along the traces of these structures. T2 is dominated by N-striking thrust faults and parallel fault-propagated folds, cut and displaced by NW-striking faults. Here, geothermal manifestations occur at fault intersections and at fold hinges. T3 is defined by left-lateral/normal NW-striking faults, with geothermal and volcanic manifestations lying along fault traces. Each tectono-geothermal environment yields distinctive isotope ratios and geothermal reservoir temperatures. T1 shows high helium and low strontium ratios, and temperatures between 220° and 310°C. T3 shows low helium and high strontium ratios and temperatures between 260° and 320°C. T2 isotope ratios fall between T1 and T3, with lowest (130°-250°C) reservoir temperatures. We argue that these particular isotope signatures are due to a structural control on reservoir location and orientation. The orientation of the fracture mesh genetically associated with each tectono-geothermal environment is a first-order control on the migration pathway of fluids. Our model shows that T1 allows fluxing of deeper fluids, T2 promotes storage and favors longer residence times and T3 enhances subvertical fluid migration. Results here help to explain the evolution of geothermal systems in a wider context, including fault systems and Sr and He isotope variations, thus providing a framework for geothermal exploration in the CAVZ.     

Adaptive POD model reduction for solute transport in heterogeneous porous media

We study the applicability of a model order reduction technique to the solution of transport of passive scalars in homogeneous and heterogeneous porous media. Transport dynamics are modeled through the advection-dispersion equation (ADE) and we employ Proper Orthogonal Decomposition (POD) as a strategy to reduce the computational burden associated with the numerical solution of the ADE. Our application of POD relies on solving the governing ADE for selected times, termed snapshots. The latter are then employed to achieve the desired model order reduction. We introduce a new technique, termed Snapshot Splitting Technique (SST), which allows enriching the dimension of the POD subspace and damping the temporal increase of the modeling error. Coupling SST with a modeling strategy based on alternating over diverse time scales the solution of the full numerical transport model to its reduced counterpart allows extending the benefit of POD over a prolonged temporal window so that the salient features of the process can be captured at a reduced computational cost. The selection of the time scales across which the solution of the full and reduced model are alternated is linked to the Péclet number (P e), representing the interplay between advective and dispersive processes taking place in the system. Thus, the method is adaptive in space and time across the heterogenous structure of the domain through the combined use of POD and SST and by way of alternating the solution of the full and reduced models. We find that the width of the time scale within which the POD-based reduced model solution provides accurate results tends to increase with decreasing P e. This suggests that the effects of local-scale dispersive processes facilitate the POD method to capture the salient features of the system dynamics embedded in the selected snapshots. Since the dimension of the reduced model is much lower than that of the full numerical model, the methodology we propose enables one to accurately simulate transport at a markedly reduced computational cost.     

Human-made disasters and economic impact for a developing economy: evidence from Brazil

Natural Hazards - This article analyzes the short-term economic impacts of the collapse of the ‘Fundão’ mining tailings dam, located in the Brazilian state of Minas Gerais. This...