
AlvarezMiranda, E., Pereira, J., Vargas, C., & Vila, M. (2022). Variabledepth local search heuristic for assembly line balancing problems. Int. J. Prod. Res., Early Access.
Abstract: Assembly lines are production flow systems wherein activities are organised around a line consisting of various workstations through which the product flows. At each station, the product is assembled through a subset of operations. The assembly line balancing problem (ALBP) consists of allocating operations between stations to maximise the system efficiency. In this study, a variabledepth local search algorithm is proposed for solving simple assembly line balancing problems (SALBPs), which are the most widely studied versions of the ALBP. Although the stateoftheart techniques for solving the SALBP consist of exact enumerationbased methods or heuristics, this paper proposes a local searchbased heuristic using variablelength sequences that allow the solution space to be efficiently explored. The proposed algorithm improves the best solution known for multiple instances reported in the literature, indicating that its efficiency is comparable to those of the stateoftheart method for solving the SALBP. Moreover, the characteristics of the instances for which the proposed procedure provides a better solution than previously reported construction procedures are investigated.



Averbakh, I., & Pereira, J. (2021). Tree optimization based heuristics and metaheuristics in network construction problems. Comput. Oper. Res., 128, 105190.
Abstract: We consider a recently introduced class of network construction problems where edges of a transportation network need to be constructed by a server (construction crew). The server has a constant construction speed which is much lower than its travel speed, so relocation times are negligible with respect to construction times. It is required to find a construction schedule that minimizes a nondecreasing function of the times when various connections of interest become operational. Most problems of this class are strongly NPhard on general networks, but are often treeefficient, that is, polynomially solvable on trees. We develop a generic local search heuristic approach and two metaheuristics (Iterated Local Search and Tabu Search) for solving treeefficient network construction problems on general networks, and explore them computationally. Results of computational experiments indicate that the methods have excellent performance.



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.



Bergmann, C., Jones, M. I., Zhao, J., Mustill, A. J., Brahm, R., Torres, P., et al. (2021). HD 76920 b pinned down: A detailed analysis of the most eccentric planetary system around an evolved star. PUBL. ASTRON. SOC. AUST., 38, e019.
Abstract: We present 63 new multisite radial velocity (RV) measurements of the K1III giant HD 76920, which was recently reported to host the most eccentric planet known to orbit an evolved star. We focused our observational efforts on the time around the predicted periastron passage and achieved nearcontinuous phase coverage of the corresponding RV peak. By combining our RV measurements from four different instruments with previously published ones, we confirm the highly eccentric nature of the system and find an even higher eccentricity of , an orbital period of 415.891(0.039)(+0.043) d, and a minimum mass of 3.13(0.43)(+0.41) MJ for the planet. The uncertainties in the orbital elements are greatly reduced, especially for the period and eccentricity. We also performed a detailed spectroscopic analysis to derive atmospheric stellar parameters, and thus the fundamental stellar parameters (M*, R*, L*) taking into account the parallax from Gaia DR2, and independently determined the stellar mass and radius using asteroseismology. Intriguingly, at periastron, the planet comes to within 2.4 stellar radii of its host star's surface. However, we find that the planet is not currently experiencing any significant orbital decay and will not be engulfed by the stellar envelope for at least another 5080 Myr. Finally, while we calculate a relatively high transit probability of 16%, we did not detect a transit in the TESS photometry.



Canessa, E., Droop, C., & Allende, H. (2012). An improved genetic algorithm for robust design in multivariate systems. Qual. Quant., 46(2), 665–678.
Abstract: In a previous article, we presented a genetic algorithm (GA), which finds solutions to problems of robust design in multivariate systems. Based on that GA, we developed a new GA that uses a new desirability function, based on the aggregation of the observed variance of the responses and the squared deviation between the mean of each response and its corresponding target value. Additionally, we also changed the crossover operator from a onepoint to a uniform one. We used three different case studies to evaluate the performance of the new GA and also to compare it with the original one. The first case study involved using data from a univariate real system, and the other two employed data obtained from multivariate process simulators. In each of the case studies, the new GA delivered good solutions, which simultaneously adjusted the mean of each response to its corresponding target value. This performance was similar to the one of the original GA. Regarding variability reduction, the new GA worked much better than the original one. In all the case studies, the new GA delivered solutions that simultaneously decreased the standard deviation of each response to almost the minimum possible value. Thus, we conclude that the new GA performs better than the original one, especially regarding variance reduction, which was the main problem exhibited by the original GA.



Carrasco, J. A., & Yanez, R. (2022). Sequential search and firm prominence. Econ. Theory, Early Access.
Abstract: We explore the role of prominence in equilibrium pricing in markets where search is sequential and random. Our model key feature is that more prominent firms are more likely to be sampled first. In contrast to orderedsearch models, we find that more prominent firms inherit larger but less elastic demands, and as such have incentives to post larger prices. However, they might post lower prices but still charge higher markups than less prominent competitors only if they are also sufficiently more efficient. Our results suggest that when search is sequential, the role of prominence depends on whether it modifies the order or just the chances with which firms are sampled.



D'Angelo, G., Di Stefano, G., Navarra, A., Nisse, N., & Suchan, K. (2015). Computing on Rings by Oblivious Robots: A Unified Approach for Different Tasks. Algorithmica, 72(4), 1055–1096.
Abstract: A set of autonomous robots have to collaborate in order to accomplish a common task in a ringtopology where neither nodes nor edges are labeled (that is, the ring is anonymous). We present a unified approach to solve three important problems: the exclusive perpetual exploration, the exclusive perpetual clearing, and the gathering problems. In the first problem, each robot aims at visiting each node infinitely often while avoiding that two robots occupy a same node (exclusivity property); in exclusive perpetual clearing (also known as graph searching), the team of robots aims at clearing the whole ring infinitely often (an edge is cleared if it is traversed by a robot or if both its endpoints are occupied); and in the gathering problem, all robots must eventually occupy the same node. We investigate these tasks in the LookComputeMove model where the robots cannot communicate but can perceive the positions of other robots. Each robot is equipped with visibility sensors and motion actuators, and it operates in asynchronous cycles. In each cycle, a robot takes a snapshot of the current global configuration (Look), then, based on the perceived configuration, takes a decision to stay idle or to move to one of its adjacent nodes (Compute), and in the latter case it eventually moves to this neighbor (Move). Moreover, robots are endowed with very weak capabilities. Namely, they are anonymous, asynchronous, oblivious, uniform (execute the same algorithm) and have no common sense of orientation. In this setting, we devise algorithms that, starting from an exclusive and rigid (i.e. aperiodic and asymmetric) configuration, solve the three above problems in anonymous ringtopologies.



Eberhardt, J., Trifonov, T., Kurster, M., Stock, S., Henning, T., Wollbold, A., et al. (2022). Dynamical Architecture of the HD 107148 Planetary System. Astron. J., 163(5), 198.
Abstract: We present an independent Doppler validation and dynamical orbital analysis of the twoplanet system HD 107148, which was recently announced in Rosenthal et al. Our detailed analyses are based on literature HIRES data and newly obtained HARPS and CARMENES radialvelocity (RV) measurements as part of our survey in search for additional planets around singleplanet systems. We perform a periodogram analysis of the available HIRES and HARPS precise RVs and stellar activity indicators. We do not find any apparent correlation between the RV measurements and the stellar activity indicators, thus linking the two strong periodicities to a moderately compact multiplanet system. We carry out orbital fitting analysis by testing various one and twoplanet orbital configurations and studying the posterior probability distribution of the fitted parameters. Our results solidify the existence of a Saturnmass planet (HD 107148b, discovered first) with a period of P (b) similar to 77.2 days and a second, eccentric (e (c) similar to 0.4), Neptunemass exoplanet (HD 107148c) with an orbital period of P (c) similar to 18.3 days. Finally, we investigate the twoplanet system's longterm stability and overall orbital dynamics with the posterior distribution of our preferred orbital configuration. Our Nbody stability simulations show that the system is longterm stable and exhibits large secular osculations in eccentricity but in no particular mean motion resonance configuration. The HD 107148 system, consisting of a solartype mainsequence star with two giant planets in a rare configuration, features a common propermotion white dwarf companion and is therefore a valuable target for understanding the formation and evolution of planetary systems.



Ritt, M., & Pereira, J. (2020). Heuristic and exact algorithms for minimumweight nonspanning arborescences. Eur. J. Oper. Res., 287(1), 61–75.
Abstract: We address the problem of finding an arborescence of minimum total edge weight rooted at a given vertex in a directed, edgeweighted graph. If the arborescence must span all vertices the problem is solvable in polynomial time, but the nonspanning version is NPhard. We propose reduction rules which determine vertices that are required or can be excluded from optimal solutions, a modification of Edmonds algorithm to construct arborescences that span a given set of selected vertices, and embed this procedure into an iterated local search for good vertex selections. Moreover, we propose a cutsetbased integer linear programming formulation, provide different linear relaxations to reduce the number of variables in the model and solve the reduced model using a branchandcut approach. We give extensive computational results showing that both the heuristic and the exact methods are effective and obtain better solutions on instances from the literature than existing approaches, often in much less time. (C) 2020 Elsevier B.V. All rights reserved.



Trifonov, T., Wollbold, A., Kurster, M., Eberhardt, J., Stock, S., Henning, T., et al. (2022). A New Third Planet and the Dynamical Architecture of the HD33142 HD 33142 Planetary System. Astron. J., 164(4), 156.
Abstract: Based on recentlytaken and archival HARPS, FEROS, and HIRES radial velocities (RVs), we present evidence for a new planet orbiting the first ascent red giant star HD 33142 (with an improved mass estimate of M1.52 +/ 0.03 Mcircle dot), already known to host two planets. We confirm the Jovianmass planets HD 33142b and c, with periods of Pb = 330.0(0.4)(+0.4) days and Pc = 810. 2(4.2)(+3.8) days and minimum dynamical masses of m(b) sin i =1.26(0.05)(+0.05) MJup and m(c) sin i = 0.89(0.05)(+0.06) MJup, respectively. Furthermore, our periodogram analysis of the precise RVs shows strong evidence for a shortperiod Doppler signal in the residuals of a twoplanet Keplerian fit, which we interpret as a third, Saturnmass planet with m(d) sin i = 0.20()(0.03)(+0.02) MJup in a closein orbit with an orbital period of Pd = 89.9(0.1)(+0.1) days. We study the dynamical behavior of the threeplanet system configuration with an Nbody integration scheme, finding it to be longterm stable with the planets alternating between low and moderate eccentricity episodes. We also perform Nbody simulations, including stellar evolution and secondorder dynamical effects such as planetstellar tides and stellar mass loss on the way to the white dwarf phase. We find that planets HD 33142b, c, and d are likely to be engulfed near the tip of the red giant branch phase due to tidal migration. These results make the HD 33142 system an essential benchmark for planet population statistics of the multipleplanet systems found around evolved stars.



Yee, S. W., Winn, J. N., Hartman, J. D., Rodriguez, J. E., Zhou, G., Quinn, S. N., et al. (2022). The TESS Grand Unified Hot Jupiter Survey. I. Ten TESS Planets. Astron. J., 164(2), 70.
Abstract: Hot Jupitersshortperiod giant planetswere the first extrasolar planets to be discovered, but many questions about their origin remain. NASA's Transiting Exoplanet Survey Satellite (TESS), an allsky search for transiting planets, presents an opportunity to address these questions by constructing a uniform sample of hot Jupiters for demographic study through new detections and unifying the work of previous groundbased transit surveys. As the first results of an effort to build this large sample of planets, we report here the discovery of 10 new hot Jupiters (TOI2193A b, TOI2207b, TOI2236b, TOI2421b, TOI2567b, TOI2570b, TOI3331b, TOI3540A b, TOI3693b, TOI4137b). All of the planets were identified as planet candidates based on periodic flux dips observed by TESS, and were subsequently confirmed using groundbased timeseries photometry, highangularresolution imaging, and highresolution spectroscopy coordinated with the TESS Followup Observing Program. The 10 newly discovered planets orbit relatively bright F and G stars (G < 12.5, T (eff) between 4800 and 6200 K). The planets' orbital periods range from 2 to 10 days, and their masses range from 0.2 to 2.2 Jupiter masses. TOI2421b is notable for being a Saturnmass planet and TOI2567b for being a “subSaturn,” with masses of 0.322 +/ 0.073 and 0.195 +/ 0.030 Jupiter masses, respectively. We also measured a detectably eccentric orbit (e = 0.17 +/ 0.05) for TOI2207b, a planet on an 8 day orbit, while placing an upper limit of e < 0.052 for TOI3693b, which has a 9 day orbital period. The 10 planets described here represent an important step toward using TESS to create a large and statistically useful sample of hot Jupiters.

