
Bandi, M. M., Concha, A., Wood, R., & Mahadevan, L. (2013). A pendulum in a flowing soap film. Phys. Fluids, 25(4), 6 pp.
Abstract: We consider the dynamics of a pendulum made of a rigid ring attached to an elastic filament immersed in a flowing soap film. The system shows an oscillatory instability whose onset is a function of the flow speed, length of the supporting string, the ring mass, and ring radius. We characterize this system and show that there are different regimes where the frequency is dependent or independent of the pendulum length depending on the relative magnitude of the addedmass. Although the system is an infinitedimensional, we can explain many of our results in terms of a one degreeoffreedom system corresponding to a forced pendulum. Indeed, using the vorticity measured via particle imaging velocimetry allows us to make the model quantitative, and a comparison with our experimental results shows we can capture the basic phenomenology of this system. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4800057]



Barra, F., Lund, F., Mujica, N., & Rica, S. (2012). Shear modulus of an elastic solid under external pressure as a function of temperature: The case of helium. Phys. Rev. B, 85(6), 6 pp.
Abstract: The energy of a dislocation loop in a continuum elastic solid under pressure is considered within the framework of classical mechanics. For a circular loop, this is a function with a maximum at pressures that are well within reach of experimental conditions for solid helium, suggesting, in this case, that dislocation loops can be generated by a pressureassisted thermally activated process. It is also pointed out that pinned dislocation segments can alter the shear response of solid helium by an amount consistent with current measurements, without any unpinning.



Barrera, J., & Fontbona, J. (2010). The Limiting MoveToFront SearchCost In Law Of Large Numbers Asymptotic Regimes. Ann. Appl. Probab., 20(2), 722–752.
Abstract: We explicitly compute the limiting transient distribution of the searchcost in the movetofront Markov chain when the number of objects tends to infinity, for general families of deterministic or random request rates. Our techniques are based on a “law of large numbers for random partitions,” a scaling limit that allows us to exactly compute limiting expectation of empirical functionals of the request probabilities of objects. In particular, we show that the limiting searchcost can be split at an explicit deterministic threshold into one random variable in equilibrium, and a second one related to the initial ordering of the list. Our results ensure the stability of the limiting searchcost under general perturbations of the request probabilities. We provide the description of the limiting transient behavior in several examples where only the stationary regime is known, and discuss the range of validity of our scaling limit.



Barrera, J., & Ycart, B. (2014). Bounds for left and right window cutoffs. ALEALatin Am. J. Probab. Math. Stat., 11(2), 445–458.
Abstract: The location and width of the time window in which a sequence of processes converges to equilibrum are given under conditions of exponential convergence. The location depends on the side: the leftwindow and rightwindow cutoffs may have different locations. Bounds on the distance to equilibrium are given for both sides. Examples prove that the bounds are tight.



Barrera, J., Bertoncini, O., & Fernandez, R. (2009). Abrupt Convergence and Escape Behavior for Birth and Death Chains. J. Stat. Phys., 137(4), 595–623.
Abstract: We link two phenomena concerning the asymptotical behavior of stochastic processes: (i) abrupt convergence or cutoff phenomenon, and (ii) the escape behavior usually associated to exit from metastability. The former is characterized by convergence at asymptotically deterministic times, while the convergence times for the latter are exponentially distributed. We compare and study both phenomena for discretetime birthanddeath chains on a"currency sign with drift towards zero. In particular, this includes energydriven evolutions with energy functions in the form of a single well. Under suitable drift hypotheses, we show that there is both an abrupt convergence towards zero and escape behavior in the other direction. Furthermore, as the evolutions are reversible, the law of the final escape trajectory coincides with the time reverse of the law of cutoff paths. Thus, for evolutions defined by onedimensional energy wells with sufficiently steep walls, cutoff and escape behavior are related by time inversion.



Barrera, J., Cancela, H., & Moreno, E. (2015). Topological optimization of reliable networks under dependent failures. Oper. Res. Lett., 43(2), 132–136.
Abstract: We address the design problem of a reliable network. Previous work assumes that link failures are independent. We discuss the impact of dropping this assumption. We show that under a commoncause failure model, dependencies between failures can affect the optimal design. We also provide an integerprogramming formulation to solve this problem. Furthermore, we discuss how the dependence between the links that participate in the solution and those that do not can be handled. Other dependency models are discussed as well. (C) 2014 Elsevier B.V. All rights reserved.



Barrera, J., HomemDeMello, T., Moreno, E., Pagnoncelli, B. K., & Canessa, G. (2016). Chanceconstrained problems and rare events: an importance sampling approach. Math. Program., 157(1), 153–189.
Abstract: We study chanceconstrained problems in which the constraints involve the probability of a rare event. We discuss the relevance of such problems and show that the existing samplingbased algorithms cannot be applied directly in this case, since they require an impractical number of samples to yield reasonable solutions. We argue that importance sampling (IS) techniques, combined with a Sample Average Approximation (SAA) approach, can be effectively used in such situations, provided that variance can be reduced uniformly with respect to the decision variables. We give sufficient conditions to obtain such uniform variance reduction, and prove asymptotic convergence of the combined SAAIS approach. As it often happens with IS techniques, the practical performance of the proposed approach relies on exploiting the structure of the problem under study; in our case, we work with a telecommunications problem with Bernoulli input distributions, and show how variance can be reduced uniformly over a suitable approximation of the feasibility set by choosing proper parameters for the IS distributions. Although some of the results are specific to this problem, we are able to draw general insights that can be useful for other classes of problems. We present numerical results to illustrate our findings.



Barrera, J., Moreno, E., & Varas K., S. (2018). A decomposition algorithm for computing income taxes with passthrough entities and its application to the Chilean case. Ann. Oper. Res., to appear.
Abstract: Income tax systems with “passthrough” entities transfer a firm's incomes to the sharehold ers, which are taxed individually. In 2014, a Chilean tax reform introduced this type of entity and changed to an accrual basis that distributes incomes (but not losses) to shareholders. A crucial step for the Chilean taxation authority is to compute the final income of each individual, given the complex network of corporations and companies, usually including cycles between them. In this paper, we show the mathematical conceptualization and the solution to the problem, proving that there is only one way to distribute incomes to taxpayers. Using the theory of absorbing Markov chains, we define a mathematical model for computing the taxable incomes of each taxpayer, and we propose a decomposition algorithm for this problem. This allows us to compute the solution accurately and with the efficient use of computational resources. Finally, we present some characteristics of the Chilean taxpayers' network and computational results of the algorithm using this network.



Barria, A. M., Lardies, M. A., Beckerman, A. P., & Bacigalupe, L. D. (2014). Latitude or biogeographic breaks? Determinants of phenotypic (co)variation in fitnessrelated traits in Betaeus truncatus along the Chilean coast. Mar. Biol., 161(1), 111–118.
Abstract: Ectothermal organisms distributed along environmental gradients in a wide geographical distribution display extensive phenotypic variation. This is particularly pervasive along latitudinal clines, which are linked to gradual changes in environmental factors. Widespread species may also be distributed among biogeographic breaks, which in contrast to smooth clines, often show abrupt changes in phenotypic traits. In species with widespread latitudinal distribution that also encompass important biogeographical breaks, it is not clear which of those factors prevails on shaping the phenotypic variation or if some traits are particularly more sensitive to one or the other. To evaluate this, we measured 4 fitnessrelated traits in 6 populations of the intertidal snapping shrimp Betaeus truncatus, as its distribution along Chile expands over 40A degrees in latitude and three major biogeographical provinces. Here, we statistically evaluated the role of both, latitude and biogeographic breaks, on mean population values of fitnessrelated traits but also on the variances and covariances (i.e., Pmatrix) between them. Overall, our results (1) indicate that latitude is more important than breaks in shaping the phenotypic variation of most of these fitnessrelated traits, (2) show that the differences in the variancecovariance relationship among traits between the extremes of the gradient arises from gradual increases in variance and rather sharp changes in covariance at midlatitudes and (3) show that at present, it is difficult to unambiguously determine whether natural selection or plasticity is responsible for the observed pattern in means, variances and covariances and only further work might disentangle these possibilities.



BarrientosDiaz, L., Gidekel, M., & GutierrezMoraga, A. (2008). Characterization of rhizospheric bacteria isolated from Deschampsia antarctica Desv. World J. Microbiol. Biotechnol., 24(10), 2289–2296.
Abstract: Deschampsia antarctica Desv. is the only gramineae capable of colonizing the Antarctic due to the region's extreme climate and soil environment. In the present research, bacteria colonizing the rhizospheric soil of D. antarctica were isolated and characterized. The soil studies showed that D. antarctica possesses a wide spectrum of psychrotolerant bacteria with extensive and varied antibiotic resistance, as well as heavy metal tolerance. The bacterial strains isolated from the rhizosphere of D. antarctica also produced a diverse pattern of enzymes. Based on the strain identification with partial characterization of the 16S rRNA gene, the majority of the isolates correspond to different Pseudomonas species, and species of the genus Flavobacterium sp. and Arthrobacter sp. The isolated strains collected from this research constitute a unique collection for future, more detailed taxonomic analysis and physiological characterization, contributing to the search for potential biotechnological uses. These findings and others have great potential for developing new biotechnological products from Antarctic microorganisms.



Becker, F., Kosowski, A., Matamala, M., Nisse, N., Rapaport, I., Suchan, K., et al. (2015). Allowing each node to communicate only once in a distributed system: shared whiteboard models. Distrib. Comput., 28(3), 189–200.
Abstract: In this paper we study distributed algorithms on massive graphs where links represent a particular relationship between nodes (for instance, nodes may represent phone numbers and links may indicate telephone calls). Since such graphs are massive they need to be processed in a distributed way. When computing graphtheoretic properties, nodes become natural units for distributed computation. Links do not necessarily represent communication channels between the computing units and therefore do not restrict the communication flow. Our goal is to model and analyze the computational power of such distributed systems where one computing unit is assigned to each node. Communication takes place on a whiteboard where each node is allowed to write at most one message. Every node can read the contents of the whiteboard and, when activated, can write one small message based on its local knowledge. When the protocol terminates its output is computed from the final contents of the whiteboard. We describe four synchronization models for accessing the whiteboard. We show that message size and synchronization power constitute two orthogonal hierarchies for these systems. We exhibit problems that separate these models, i.e., that can be solved in one model but not in a weaker one, even with increased message size. These problems are related to maximal independent set and connectivity. We also exhibit problems that require a given message size independently of the synchronization model.



Benitez, S., Duarte, C., Opitz, T., Lagos, N. A., Pulgar, J. M., Vargas, C. A., et al. (2017). Intertidal pool fish Girella laevifrons (Kyphosidae) shown strong physiological homeostasis but shy personality: The cost of living in hypercapnic habitats. Mar. Pollut. Bull., 118(12), 57–63.
Abstract: Tide pools habitats are naturally exposed to a high degree of environmental variability. The consequences of living in these extreme habitats are not well established. In particular, little it is known about of the effects of hypercanic seawater (i.e. high pCO(2) levels) on marine vertebrates such as intertidal pool fish. The aim of this study was to evaluate the effects of increased pCO(2) on the physiology and behavior in juveniles of the intertidal pool fish Girella laevifrons. Two nominal pCO(2) concentrations (400 and 1600 patm) were used. We found that exposure to hypercapnic conditions did not affect oxygen consumption and absorption efficiency. However, the lateralization and boldness behavior was significantly disrupted in high pCO(2) conditions. In general, a predatorrisk cost of boldness is assumed, thus the increased occurrence of shy personality in juvenile fishes may result in a change in the balance of this biological interaction, with significant ecological consequences. (C) 2017 Elsevier Ltd. All rights reserved.



Berkovits, N., & Chandia, O. (2014). Simplified pure spinor b ghost in a curved heterotic superstring background. J. High Energy Phys., (6), 12 pp.
Abstract: Using the RNSlike fermionic vector variables introduced in arXiv:1305.0693, the pure spinor b ghost in a curved heterotic superstring background is easily constructed. This construction simplifies and completes the b ghost construction in a curved background of arXiv:1311.7012.



Besaury, L., Ouddane, B., Pavissich, J. P., DubrulleBrunaud, C., Gonzalez, B., & Quillet, L. (2012). Impact of copper on the abundance and diversity of sulfatereducing prokaryotes in two chilean marine sediments. Mar. Pollut. Bull., 64(10), 2135–2145.
Abstract: We studied the abundance and diversity of the sulfatereducing prokaryotes (SRPs) in two 30cm marine chilean sediment cores, one with a longterm exposure to coppermining residues, the other being a nonexposed reference sediment. The abundance of SRPs was quantified by qPCR of the dissimilatory sulfite reductase gene betasubunit (dsrB) and showed that SRPs are sensitive to high copper concentrations, as the mean number of SRPs all along the contaminated sediment was two orders of magnitude lower than in the reference sediment. SRP diversity was analyzed by using the dsrBsequencesbased PCRDGGE method and constructing gene libraries for dsrBsequences. Surprisingly, the diversity was comparable in both sediments, with dsrB sequences belonging to Desulfobacteraceae, Syntrophobacteraceae, and Desulfobulbaceae, SRP families previously described in marine sediments, and to a deep branching dsrAB lineage. The hypothesis of the presence of horizontal transfer of copper resistance genes in the microbial population of the polluted sediment is discussed. (C) 2012 Elsevier Ltd. All rights reserved.



Besson, S., & Dumais, J. (2014). Stochasticity in the symmetric division of plant cells: when the exceptions are the rule. Front. Plant Sci., 5, 4 pp.



Bitran, E., Rivera, P., & Villena, M. J. (2014). Water management problems in the Copiapo Basin, Chile: markets, severe scarcity and the regulator. Water Policy, 16(5), 844–863.
Abstract: This research focuses on the determination of the factors that led to the failure of water management in the Copiapo Basin in Chile. Interestingly, the existence of full private ownership and free tradability of water rights has not prevented the overexploitation of groundwater resources. In the paper, firstly, water regulation and the role of the regulator in Chile are briefly discussed. Secondly, the evolution of water resources in the Copiapo region is characterized and analyzed, and the granting of water use rights in the basin in the last 30 years is concisely described. Thirdly, we examine and analyze prices and quantities traded in the water market of the Copiapo region. We will argue that this crisis is a consequence first of failure in regulatory implementation and second of an extremely rigid regulatory framework that leaves limited room for adjustment to changing conditions, especially regarding the emergence of new information concerning water availability. We believe this investigation is not only relevant for this case in particular, but also for other regions and countries where water markets are in place.



Bitran, G., & Mondschein, S. (2015). Why individualized contact policies are critical in the mass affluent market. Acad.Rev. Latinoam. Adm., 28(2), 251–272.
Abstract: Purpose – The purpose of this paper is to study the optimal contact policies for customers that belong to the mass affluent market. Design/methodology/approach – The authors formulate a stochastic dynamic programming model to determine the optimal frequency of contacts in order to maximize the expected return of the company. Findings – The authors show that personalized marketing strategies provide a competitive advantage to companies that contact their customers directly through, for example, phone calls or meetings. The authors show that a threshold policy is only optimal for customers with increasing sensitivity to contact. In all other cases, optimal policies might have a less intuitive structure. The authors also study the importance of the size of the customer database and determine the optimal maximum recency when maintenance costs are present. Practical implications – Contact policies should be tailored for each company/industry individually, due to their sensitivity to customers' purchasing behavior.



Bottcher, L., WoolleyMeza, O., Goles, E., Helbing, D., & Herrmann, H. J. (2016). Connectivity disruption sparks explosive epidemic spreading. Phys. Rev. E, 93(4), 8 pp.
Abstract: We investigate the spread of an infection or other malfunction of cascading nature when a system component can recover only if it remains reachable from a functioning central component. We consider the susceptibleinfectedsusceptible model, typical of mathematical epidemiology, on a network. Infection spreads from infected to healthy nodes, with the addition that infected nodes can only recover when they remain connected to a predefined central node, through a path that contains only healthy nodes. In this system, clusters of infected nodes will absorb their noninfected interior because no path exists between the central node and encapsulated nodes. This gives rise to the simultaneous infection of multiple nodes. Interestingly, the system converges to only one of two stationary states: either the whole population is healthy or it becomes completely infected. This simultaneous cluster infection can give rise to discontinuous jumps of different sizes in the number of failed nodes. Larger jumps emerge at lower infection rates. The network topology has an important effect on the nature of the transition: we observed hysteresis for networks with dominating local interactions. Our model shows how local spread can abruptly turn uncontrollable when it disrupts connectivity at a larger spatial scale.



Braun, S., Asenjo, F. A., & Mahajan, S. M. (2014). Comment on “SpinGradientDriven Light Amplification in a Quantum Plasma” Reply. Phys. Rev. Lett., 112(12), 1 pp.



Brems, A., Caceres, G., Dewil, R., Baeyens, J., & Pitie, E. (2013). Heat transfer to the riserwall of a circulating fluidised bed (CFB). Energy, 50, 493–500.
Abstract: The circulating fluidized bed is of increasing importance for gassolid and gascatalytic reactions, for drying, and recently its use in solar energy capture and storage has been advocated. In all applications, the supply or withdrawal of heat is a major issue, and the heat transfer coefficient from the gassolid suspension to the heat transfer surface needs to be determined as design parameter. The present paper investigates the heat transfer coefficient for different operating gas velocity and solids circulation flux, whilst covering the different hydrodynamic solid flow regimes of dilute, coreannulus or dense mode. Measured values of the walltobed heat transfer coefficients are compared with empirical predictions of both Molodstof and Muzyka, and Golriz and Grace. The application of a packet renewal mechanism at the wall is also investigated, and introducing the predicted solid contact time at the wall provides a very fair estimate of the heat transfer coefficient. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.

