
Slepneva, S., O'Shaughnessy, B., Vladimirov, A. G., Rica, S., Viktorov, E. A., & Huyet, G. (2019). Convective NozakiBekki holes in a long cavity OCT laser. Opt. Express, 27(11), 16395–16404.
Abstract: We show, both experimentally and theoretically, that the loss of coherence of a long cavity optical coherence tomography (OCT) laser can be described as a transition from laminar to turbulent flows. We demonstrate that in this strongly dissipative system, the transition happens either via an absolute or a convective instability depending on the laser parameters. In the latter case, the transition occurs via formation of localised structures in the laminar regime, which trigger the formation of growing and drifting puffs of turbulence. Experimentally, we demonstrate that these turbulent bursts arc seeded by appearance of NozakiBekki holes, characterised by the zero field amplitude and pi phase jumps. Our experimental results are supported with numerical simulations based on the delay differential equations model. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement



Hernandez, R., & Venegas, O. (2019). Distortion Theorems Associated with Schwarzian Derivative for Harmonic Mappings. Complex Anal. Oper. Theory, 13(4), 1783–1793.
Abstract: Let f be a complexvalued harmonic mapping defined in the unit disc D. The theorems of Chuaqui and Osgood (J Lond Math Soc 2:289298, 1993), which assert that the bounds of the size of the hyperbolic norm of the Schwarzian derivative for an analytic function f imply certain bounds for distortion and growth of f, are extended to the harmonic case.



Asenjo, F. A., & Moya, P. S. (2019). The contribution of magnetic monopoles to the ponderomotive force. J. Phys. AMath. Theor., 52(25), 13 pp.
Abstract: When magnetic monopoles are assumed to exist in plasma dynamics, the propagation of electromagnetic waves is modified as Maxwell equations acquire a symmetrical structure due to the existence of electric and magnetic charge and current densities. This work presents a theoretical exploration on how far we can push the limits of a plasma theory under the presence of magnetic monopoles. In particular, we study the modification of ponderomotive forces in a plasma composed by electric and magnetic charges. We show that the general ponderomotive force on this plasma depends nontrivially on the magnetic monopoles, through the slow temporal and spatial variations of the electromagnetic field amplitudes. The magnetic charges introduce corrections even if the plasma is unmagnetized. Also, it is shown that the magnetic monopoles also experience a ponderomotive force due to the electrons. This force is in the direction of propagation of the electromagnetic waves.



Fullenkamp, K., Montane, M., Caceres, G., & ArayaLetelier, G. (2019). Review and selection of EPCM as TES materials for building applications. Int. J. Sustain. Energy, 38(6), 561–582.
Abstract: In order to improve the thermal efficiency of building thermal energy storage (TES) systems, the feasibility of using encapsulated phase change materials (EPCMs) as heat storage media is analysed in this work. Specifically, the finite element method is used to perform thermal behaviour analyses of several EPCMs. These analyses include technical and economic assessments in order to identify the best combination of PCM and shell material, using as main parameters: thermal energy storage, heat transfer rate, materials cost, among others. The results show that EPCMs composed by Na2SO4 center dot 6H(2)O as PCM and covered by stainless steel highlight as TES materials.



Matus, O., Barrera, J., Moreno, E., & Rubino, G. (2019). On the MarshallOlkin Copula Model for Network Reliability Under Dependent Failures. IEEE Trans. Reliab., 68(2), 451–461.
Abstract: The MarshallOlkin (MO) copulamodel has emerged as the standard tool for capturing dependence between components in failure analysis in reliability. In this model, shocks arise at exponential random times, that affect one or several components inducing a natural correlation in the failure process. However, because the number of parameter of the model grows exponentially with the number of components, MO suffers of the “curse of dimensionality.” MO models are usually intended to be applied to design a network before its construction; therefore, it is natural to assume that only partial information about failure behavior can be gathered, mostly from similar existing networks. To construct such an MO model, we propose an optimization approach to define the shock's parameters in the MO copula, in order to match marginal failures probabilities and correlations between these failures. To deal with the exponential number of parameters of this problem, we use a columngeneration technique. We also discuss additional criteria that can be incorporated to obtain a suitable model. Our computational experiments show that the resulting MO model produces a close estimation of the network reliability, especially when the correlation between component failures is significant.



Santana, L. E., & Canepa, G. H. (2019). Are they bots? Social media automation during Chile's 2017 presidential campaign. Cuad. Info, (44), 61–77.
Abstract: This research sought for automated strategies of creation or diffusion of electoral propaganda in social media during Chile's 2017 presidential campaign. We collected and analyzed almost 2 million tweets that utilized election hashtags or were linked to one of the candidates or their campaigns; we also collected and analyzed 2,927 official Facebook posts of the candidates and 453,668 comments. While on Facebook the behavior was relatively normal, we discovered that on Twitter there were digital brigades who act autonomously in astroturfing campaigning during the first round of the election.



During, G., Josserand, C., Krstulovic, G., & Rica, S. (2019). Strong turbulence for vibrating plates: Emergence of a Kolmogorov spectrum. Phys. Rev. Fluids, 4(6), 12 pp.
Abstract: In fluid turbulence, energy is transferred from one scale to another by an energy cascade that depends only on the energydissipation rate. It leads by dimensional arguments to the Kolmogorov 1941 (K41) spectrum. Here we show that the normal modes of vibrations in elastic plates also manifest an energy cascade with the same K41 spectrum in the fully nonlinear regime. In particular, we observe different patterns in the elastic deformations such as folds, developable cones, and even more complex stretching structures, in analogy with spots, swirls, vortices, and other structures in hydrodynamic turbulence. We show that the energy cascade is dominated by the kinetic contribution and that the stretching energy is at thermodynamical equilibrium. We characterize this energy cascade, the validity of the constant energydissipation rate over the scales. Finally, we discuss the role of intermittency using the correlation functions that exhibit anomalous exponents.



Canfora, F., Gomberoff, A., Oh, S. H., Rojas, F., & SalgadoRebolledo, P. (2019). Meronic EinsteinYangMills black hole in 5D and gravitational spin from isospin effect. J. High Energy Phys., (6), 32 pp.
Abstract: We construct an analytic black hole solution in SU(2) EinsteinYangMills theory in five dimensions supporting a Meron field. The gauge field is proportional to a pure gauge and has a nontrivial topological charge. The wouldbe singularity at the Meron core gets shielded from the exterior by the black hole horizon. The metric has only one integration constant, namely, its ADM mass, which is shown to be finite once an appropriate boundary term is added to the action. The thermodynamics is also worked out, and a firstorder phase transition, similar to the one occurring in the ReissnerNordstrom case is identified. We also show that the solution produces a spin from isospin effect, i.e., even though the theory is constructed out of bosons only, the combined system of a scalar field and this background may become fermionic. More specifically, we study scalar excitations in this purely bosonic background and find that the system describes fermionic degrees of freedom at spatial infinity. Finally, for the asymptotically AdS(5) case, we study its consequences in the context of the AdS/CFT correspondence.



Fuenzalida, C., JerezHanckes, C., & McClarren, R. G. (2019). Uncertainty Quantification For Multigroup Diffusion Equations Using Sparse Tensor Approximations. SIAM J. Sci. Comput., 41(3), B545–B575.
Abstract: We develop a novel method to compute first and second order statistical moments of the neutron kinetic density inside a nuclear system by solving the energydependent neutron diffusion equation. Randomness comes from the lack of precise knowledge of external sources as well as of the interaction parameters, known as cross sections. Thus, the density is itself a random variable. As Monte Carlo simulations entail intense computational work, we are interested in deterministic approaches to quantify uncertainties. By assuming as given the first and second statistical moments of the excitation terms, a sparse tensor finite element approximation of the first two statistical moments of the dependent variables for each energy group can be efficiently computed in one run. Numerical experiments provided validate our derived convergence rates and point to further research avenues.



Valle, M. A., Ruz, G. A., & Rica, S. (2019). Market basket analysis by solving the inverse Ising problem: Discovering pairwise interaction strengths among products. Physica A, 524, 36–44.
Abstract: Large datasets containing the purchasing information of thousands of consumers are difficult to analyze because the possible number of different combinations of products is huge. Thus, market baskets analysis to obtain useful information and find interesting pattern of buying behavior could be a daunting task. Based on the maximum entropy principle, we build a probabilistic model that explains the probability of occurrence of market baskets which is equivalent to Ising models. This type of model allows us to understand and to explore the functional interactions among products that make up the market offer. Additionally, the parameters of the model inferred using Boltzmann learning, allow us to suggest that the buying behavior is very similar to the spinglass physical system. Moreover, we show that the resulting parameters of the model could be useful to describe the hierarchical structure of the system which leads to interesting information about the different market baskets. (C) 2019 Elsevier B.V. All rights reserved.



Villena, M. J., & Contreras, M. (2019). Global And Local Advertising Strategies: A Dynamic MultiMarket Optimal Control Model. J. Ind. Manag. Optim., 15(3), 1017–1048.
Abstract: Differential games have been widely used to model advertising strategies of companies. Nevertheless, most of these studies have concentrated on the dynamics and market structure of the problem, neglecting their multimarket dimension. Since nowadays competition typically operates on multiproduct contexts and usually in geographically separated markets, the optimal advertising strategies must take into consideration the different levels of disaggregation, especially, for example, in retail multiproduct and multistore competition contexts. In this paper, we look into the decisionmaking process of a multimarket company that has to decide where, when and how much money to invest in advertising. For this purpose, we develop a model that keeps the dynamic and oligopolistic nature of the traditional advertising game introducing the multimarket dimension of today's economies, while differentiating global (i.e. national TV) from local advertising strategies (i.e. a price discount promotion in a particular store). It is important to note, however, that even though this problem is real for most multimarket companies, it has not been addressed in the differential games literature. On the more technical side, we steer away from the traditional aggregated dynamics of advertising games in two aspects. Firstly, we can model different markets at once, obtaining a global instead of a local optimum, and secondly, since we are incorporating a variable that is common to markets, the resulting equations systems for every market are now coupled. In other words, one's decision in one market does not only affect one's competition in that particular market; it also affects one's decisions and one's competitors in all markets.



Carrera, P., Campo, R., Mendez, R., Di Bella, G., Campos, J. L., MosqueraCorral, A., et al. (2019). Does the feeding strategy enhance the aerobic granular sludge stability treating saline effluents? Chemosphere, 226, 865–873.
Abstract: The development and stability of aerobic granular sludge (AGS) was studied in two Sequencing Batch Reactors (SBRs) treating fish canning wastewater. R1 cycle comprised a fully aerobic reaction phase, while R2 cycle included a plugflow anaerobic feeding/reaction followed by an aerobic reaction phase. The performance of the AGS reactors was compared treating the same effluents with variable salt concentrations (4.9713.45 g NaCl/L) and organic loading rates (OLR, 1.806.65 kg CODs/(m(3).d)). Granulation process was faster in R2 (day 34) than in R1 (day 90), however the granular biomass formed in the fully aerobic configuration was more stable to the variable feeding composition. Thus, in R1 solid retention times (SRT), up to 15.2 days, longer than in R2, up to 5.8 days, were achieved. These long SRT5 values helped the retention of nitrifying organisms and provoked the increase of the nitrogen removal efficiency to 80% in R1 while it was approximately of 40% in R2. However, the presence of an anaerobic feeding/reaction phase increased the organic matter removal efficiency in R2 (8090%) which was higher than in R1 with a fully aerobic phase (7585%). Furthermore, in R2 glycogenaccumulating organisms (GAOs) dominated inside the granules instead of phosphorousaccumulating organisms (PADS), suggesting that GAOs resist better the stressful conditions of a variable and highsaline influent. In terms of AGS properties an anaerobic feeding/reaction phase is not beneficial, however it enables the production of a better quality effluent. (C) 2019 Elsevier Ltd. All rights reserved.



SilvaOelker, G., JerezHanckes, C., & Fay, R. (2019). Hightemperature tungstenhafnia optimized selective thermal emitters for thermophotovoltaic applications. J. Quant. Spectrosc. Radiat. Transf., 231, 61–68.
Abstract: Tungstenhafnia (WHfO2) selective thermal emitters with high hemispherical emittance for thermophotovoltaic (TPV) applications are explored through numerical simulations. Two structures were analyzed: a planar multilayer stack and a grating. In both cases, through suitable design choices high thermal emittance with low directional sensitivity can be obtained. The designs are obtained by optimization of the structures using a genetic algorithm and a suitable cost function, along with simulations of the structures' emittance by using rigorous coupled wave analysis. Calculations show that these optimized structures possess high hemispherical thermal emittance for the wavelength range that matches the optical response of GaSb photovoltaic cells. For each structure, both the output power from the TPV cell and the conversion efficiency are studied as a function of emitter temperature and physical understanding of the optimized structures is developed. (C) 2019 Elsevier Ltd. All rights reserved.



Harrison, R., & Lagunoff, R. (2019). Tipping points and businessasusual in a global commons. J. Econ. Behav. Organ., 163, 386–408.
Abstract: This paper analyzes a dynamic strategic model of resource extraction from a global commons. Countries derive benefits from both direct extraction and aggregate conservation of an open access resource. Each period, a country's output depends both on its resource usage and on the global stock of the resource stored within the ecosystem. Leading examples are ocean fisheries, habitat preservation, forestry, and land carbon biomass. The production coefficients on these inputs vary across countries and evolve stochastically over time. A Businessasusual (BAU) equilibrium characterizes each country's resource usage in the absence of an effective international agreement. Under nonconcave resource dynamics, depletion of the resource in a BAU equilibrium may reach a tipping point below which the stock spirals downward toward a steady state of marginal sustainability. Under the assumptions of the model, the tipping points emerge endogenously. If the number of extractors exceeds some fixed, finite bound, the commons always tips regardless of the initial stock. We find that countries will accelerate their rates of extraction the closer they are to reaching the lowend steady state. By contrast, in the socially efficient plan the commons never tips if the initial stock is large. (C) 2019 Elsevier B.V. All rights reserved.



Campos, J. L., Dumais, J., Pavissich, J. P., Franchi, O., Crutchik, D., Belmonte, M., et al. (2019). Predicting Accumulation of Intermediate Compounds in Nitrification and Autotrophic Denitrification Processes: A Chemical Approach. Biomed Res. Int., 2019, 9 pp.
Abstract: Nitrification and sulfurbased autotrophic denitrification processes can be used to remove ammonia from wastewater in an economical way. However, under certain operational conditions, these processes accumulate intermediate compounds, such as elemental sulphur, nitrite, and nitrous oxide, that are noxious for the environment. In order to predict the generation of these compounds, an analysis based on the Gibbs free energy of the possible reactions and on the oxidative capacity of the bulk liquid was done on case study systems. Results indicate that the Gibbs free energy is not a useful parameter to predict the generation of intermediate products in nitrification and autotrophic denitrification processes. Nevertheless, we show that the specific productions of nitrous oxide during nitrification, and of elemental sulphur and nitrite during autotrophic denitrification, are well related to the oxidative capacity of the bulk liquid.



Elorrieta, F., Eyheramendy, S., & Palma, W. (2019). Discretetime autoregressive model for unequally spaced timeseries observations. Astron. Astrophys., 627, 11 pp.
Abstract: Most timeseries models assume that the data come from observations that are equally spaced in time. However, this assumption does not hold in many diverse scientific fields, such as astronomy, finance, and climatology, among others. There are some techniques that fit unequally spaced time series, such as the continuoustime autoregressive moving average (CARMA) processes. These models are defined as the solution of a stochastic differential equation. It is not uncommon in astronomical time series, that the time gaps between observations are large. Therefore, an alternative suitable approach to modeling astronomical time series with large gaps between observations should be based on the solution of a difference equation of a discrete process. In this work we propose a novel model to fit irregular time series called the complex irregular autoregressive (CIAR) model that is represented directly as a discretetime process. We show that the model is weakly stationary and that it can be represented as a statespace system, allowing efficient maximum likelihood estimation based on the Kalman recursions. Furthermore, we show via Monte Carlo simulations that the finite sample performance of the parameter estimation is accurate. The proposed methodology is applied to light curves from periodic variable stars, illustrating how the model can be implemented to detect poor adjustment of the harmonic model. This can occur when the period has not been accurately estimated or when the variable stars are multiperiodic. Last, we show how the CIAR model, through its state space representation, allows unobserved measurements to be forecast.



AlvarezMiranda, E., & Pereira, J. (2019). On the complexity of assembly line balancing problems. Comput. Oper. Res., 108, 182–186.
Abstract: Assembly line balancing is a family of combinatorial optimization problems that has been widely studied in the literature due to its simplicity and industrial applicability. Most line balancing problems are NPhard as they subsume the bin packing problem as a special case. Nevertheless, it is common in the line balancing literature to cite [A. Gutjahr and G. Nemhauser, An algorithm for the line balancing problem, Management Science 11 (1964) 308315] in order to assess the computational complexity of the problem. Such an assessment is not correct since the work of Gutjahr and Nemhauser predates the concept of NPhardness. This work points at over 50 publications since 1995 with the aforesaid error. (C) 2019 Elsevier Ltd. All rights reserved.



Carrera, P., MosqueraCorral, A., Mendez, R., Campos, J. L., & del Rio, A. V. (2019). Pulsed aeration enhances aerobic granular biomass properties. Biochem. Eng. J., 149, 7 pp.
Abstract: The reduced footprint of Aerobic Granular Sludge (AGS) systems constitutes a good alternative to conventional treatments, despite their associated drawbacks (long startup periods and high aeration requirements for granules formation and integrity). This study presents a pulsed aeration regime as a strategy to overcome these problems. Two AGS sequencing batch reactors (SBRs) were operated treating lowstrength wastewater (190 mg COD/L) with pulses of 1 s ON/2 s OFF (R1) and continuous aeration (R2). Initially, different superficial gas velocities (SGV) of 3.6 cm/s (R1) and 1.2 cm/s (R2) were imposed for the same airflow (448 L/cycle). The granulation process was completed in 38 days for R1 whereas it took 48 days for R2. Denser and smaller granules were formed with pulsed regime and phosphate accumulating organisms were developed faster. The removal efficiencies were practically the same in both SBRs, being of 85% for COD, 95% for phosphorus and 30% for nitrogen. After granules formation the airflow in both reactors was reduced. For a SGV of 1.2 cm/s both systems behaved similarly. The minimum SGV required to maintain a uniform mixture of the biomass inside the reactor was 1.2 (R1) and 0.5 cm/s (R2), meaning less air consumption in the pulsed system (149 L/cycle) compared to the continuous one (179 L/min). Therefore, pulsed aeration successfully reduced granulation periods and aeration requirements in AGS systems.



OsorioValenzuela, L., Pereira, J., Quezada, F., & Vasquez, O. C. (2019). Minimizing the number of machines with limited workload capacity for scheduling jobs with interval constraints. Appl. Math. Model., 74, 512–527.
Abstract: In this paper, we consider a parallel machine scheduling problem in which machines have a limited workload capacity and jobs have deadlines and release dates. The problem is motivated by the operation of energy storage management systems for microgrids under emergency conditions and generalizes some problems that have already been studied in the literature for their theoretical value. In this work, we propose heuristic and exact algorithms to solve the problem. The heuristics are adaptations of classical bin packing heuristics in which additional conditions on the feasibility of a solution are imposed, whereas the exact method is a branchandprice approach. The results show that the branchandprice approach is able to optimally solve random instances with up to 250 jobs within a time limit of one hour, while the heuristic procedures provide near optimal solution within reduced running times. Finally, we also provide additional complexity results for a special case of the problem. (C) 2019 Elsevier Inc. All rights reserved.



Hiptmair, R., JerezHanckes, C., & UrzúaTorres, C. (2020). Optimal Operator Preconditioning For Galerkin Boundary Element Methods On 3D Screens. SIAM J. Num. Anal., 58(1), 834–857.
Abstract: We consider firstkind weakly singular and hypersingular boundary integral operators for the Laplacian on screens in $\mathbb{R}^{3}$ and their Galerkin discretization by means of loworder piecewise polynomial boundary elements. For the resulting linear systems of equations we propose novel Calderóntype preconditioners based on (i) new boundary integral operators, which provide the exact inverses of the weakly singular and hypersingular operators on flat disks, and (ii) stable duality pairings relying on dual meshes. On screens obtained as images of the unit disk under biLipschitz transformations, this approach achieves condition numbers uniformly bounded in the meshwidth even on locally refined meshes. Comprehensive numerical tests also confirm its excellent preasymptotic performance.

