Easter Island’s Collapse : A Tale of a Population Race

The Easter Island tragedy has become an allegory for ecological catastrophe and a warning for the future. In the economic literature the collapse is usually attributed to irrational or myopic behaviors in the context of a fragile ecosystem. In this paper we propose an alternative story involving non-cooperative bargaining between clans to share the crop. Each clan’s bargaining power depends on its threat level when fighting a war. The biggest group has the highest probability of winning. A clan’s fertility is determined ex ante by each group. In the quest for greater bargaining power, each clan’s optimal size depends on that of the other clan, and a population race follows. This race may exhaust the natural resources and lead to the ultimate collapse of the society. In addition to well-known natural factors, the likelihood of a collapse turns out to be greater when the cost of war is low, the probability of succeeding in war is highly responsive to the number of fighters, and the marginal return to labor is not too low. We analyze whether these factors can account for the difference between Easter and Tikopia Islands. The paper also makes a methodological contribution in that it is the first fertility model to include strategic complementarities between groups’ fertility decisionsFertility, War, Bargaining Power, Collapse, Natural Resources

Easter Island’s collapse: A tale of a population race

We study different extended formulations for the set (formule) in order to tackle the feasibility problem for the set (formule). Here the goal is not to find an improved polyhedral relaxation of conv(X+), but rather to reformulate in such a way that the new variables introduced provide good branching directions, and in certain circumstances permit one to deduce rapidly that the instance is infeasible. For the case that A has one row a we analyze the reformulations in more detail. In particular, we determine the integer width of the extended formulations in the direction of the last coordinate, and derive a lower bound on the Frobenius number of a. We also suggest how a decomposition of the vector a can be obtained that will provide a useful extended formulation. Our theoretical results are accompanied by a small computational study.fertility, war, bargaining power, collapse, natural resources.

Analysis of resonances in grand design spiral galaxies

We have searched for corotations (CR) in three Southern grand design spiral galaxies: NGC 1365, NGC 1566 and NGC 2997. We have also introduced a method of quantifying errors in the phase diagram used to detect CR. We established the m=2 pattern CR at 12.1 kpc, 9.4 kpc and 7 kpc, for NGC 1365, NGC 1566 and NGC 2997, respectively. By using published rotation curves, we could determine spiral pattern angular speeds of 25.0 km/sec/kpc, 12.2 km/sec/kpc and 17.6 km/sec/kpc, respectively. A three armed component has been detected in NGC 2997, with the CR placed at 8.7 kpc with a pattern angular speed Omega_{CR_3}=12.7 km/sec/kpc. An m=1 component was detected in NGC 1566. We warily locate the CR at 7.1 kpc, with a pattern angular speed Omega_{CR} approx. 16.6 km/sec/kpc. This pattern does not present ILR. Ages have been determined by studying the radial density profile of the m=2 Fourier components in g (newly formed stars) and i (perturbing SDW supported by the disk of old stars), aided by the global aspect of the real spiral pattern in comparison with numerical simulations. The pattern is approx. 1200 Myr old in NGC 1365, approx. 800 Myr old in NGC 1566 and younger than 80 Myr in NGC 2997.Comment: 49 pages, 24 figures, 2 tables. Accepted for publication in ApJ Large figures can be find at http://www.inaoep.mx/~puerari/resonance

Análise de viabilidade do uso de biogás nas frotas de caminhões de coleta de lixo urbano no Rio de Janeiro

iv Resumo da Monografia apresentada à Escola de Química como parte dos requisitos necessários para obtenção do grau de Engenheiro Químico ANÁLISE DE VIABILIDADE DO USO DE BIOGÁS NAS FROTAS DE CAMINHÕES DE COLETA DE LIXO URBANO NO RIO DE JANEIRO Filipe Dottori de Oliveira Fevereiro, 2022 Orientadora: Profa. Clarice Campelo de Melo Ferraz, D.Sc. A busca por combustíveis renováveis tem aumentado cada vez mais ao redor do mundo, sobretudo devido a crescente preocupação trazida pela crise climática. Em particular, a substituição de combustíveis fósseis, devido ao seu elevado potencial poluidor, é de grande interesse. A produção de resíduos sólidos é outro fator de preocupação, que contribui para propagar os problemas climáticos devido a produção de gases do efeito estufa. Nesse contexto, o biogás e o biometano se apresentam como uma fonte de estudo de grande interesse, por se apresentarem como possível solução para ambos os problemas. O presente estudo teve como objetivo determinar o potencial de se produzir biometano no munícipio do Rio de Janeiro, para a substituição do combustível diesel utilizado pelos caminhões de coleta de lixo, utilizando os resíduos sólidos como fonte de matéria prima. Os resultados obtidos demonstram a viabilidade técnica do projeto, observando que o potencial de produção de tais combustíveis é suficiente para atender a demanda necessária para a operação atual na cidade. Além disso, foi proposto um modelo de financiamento para o projeto para analisar sua viabilidade econômica O modelo proposto inclui alguns aspectos técnicos baseados em outras operações similares no estado e no país. Desse modo, o projeto criado demonstrou ter potencial para reduzir os problemas ambientais associados a operação atual, além de oferecer vantagem financeira, reduzindo os gastos dispendidos com a mesma

Reparo automático de programas usando corretude relativa

O reparo automático de programas consiste em identificar e consertar falhas em um código até que o mesmo passe a se adequar a uma especificação fornecida. Tal especificação é geralmente feita através de uma suíte de testes. Neste caso, um código é considerado absolutamente correto se passa em todos os testes. Ferramentas atuais nesse ramo fazem uso de técnicas como a programação genética, que se baseia em princípios da computação evolutiva, para construir programas corretos a partir de incorretos. Tais ferramentas são capazes de realizar consertos em diversos casos, mas têm sua utilidade limitada por se basearem em uma noção muito simples de corretude, onde programas são considerados apenas absolutamente corretos ou absolutamente incorretos, sem se levar em conta programas intermediários. Essa dificuldade aparece frequentemente em casos com múltiplas falhas. O presente trabalho propõe expandir o escopo de algumas das ferramentas existentes através de uma teoria de corretude relativa, na qual é possível determinar quais programas podem ser considerados estritamente mais corretos que outros. O uso dessa teoria permite a criação de um paradigma novo de reparo de programas focado em aprimoramentos graduais. O trabalho também relata estudos de caso que visam verificar que, com esse novo paradigma, há a possibilidade de consertar programas que não eram reparáveis pelos métodos originais

Capture of field stars by globular clusters in dense bulge regions

The recent detection of a double Red Giant Branch in the optical color-magnitude diagram (CMD) of the bulge globular cluster HP1 (Ortolani et al. 1997), a more populated metal-poor steep one corresponding to the cluster itself, and another metal-rich curved, led us to explore in the present Letter the possibility of capture of field stars by a globular cluster orbiting in dense bulge regions over several gigayears. Analytical arguments, as well as N-body calculations for a cluster model of 10^5 solar masses in a bulge-like environment, suggest that a significant fraction of cluster stars may consist of captures. Metal-poor globular clusters in the inner bulge, like HP1, contrasting at least in Delta [Fe/H] = 1.0 dex with respect to the surrounding metal-rich stars, are ideal probes to further test the capture scenario. In turn, if this scenario is confirmed, the double RGB of HP1 could provide direct estimates of blanketing amounts, which is fundamental for the photometric calibration of metal-rich stellar populations.Comment: 6 pages, 2 included figures, aas2pp4,sty Latex style. To be published in Astrophysical Journal Letter

Morphologies and ages of star cluster pairs and multiplets in the Small Magellanic Cloud

An isophotal atlas of 75 star cluster pairs and multiplets in the Small Magellanic Cloud is presented, comprising 176 objects. They are concentrated in the SMC main body. The isophotal contours were made from Digitized Sky Survey images and showed relevant structural features possibly related to interactions in about 25% of the sample. Previous N-body simulations indicate that such shapes could be due to tidal tails, bridges or common envelopes. The diameter ratio between the members of a pair is preferentially in the range 1 - 2, with a peak at 1. The projected separation is in the range ~ 3 - 22 pc with a pronounced peak at ~ 13 pc. For 91 objects it was possible to derive ages from Colour-Magnitude Diagrams using the OGLE-II photometric survey. The cluster multiplets in general occur in OB stellar associations and/or HII region complexes. This indicates a common origin and suggests that multiplets coalesce into pairs or single clusters in a short time scale. Pairs in the SMC appear to be mostly coeval and consequently captures are a rare phenomenon. We find evidence that star cluster pairs and multiplets may have had an important role in the dynamical history of clusters presently seen as large single objects

Ages and Metallicities of Star Clusters and Surrounding Fields in the Outer Disk of the Large Magellanic Cloud

We present Washington system C,T_1 CMDs of 13 star clusters and their surrounding fields which lie in the outer parts of the LMC disk. Ages are determined by means of the magnitude difference between the giant branch clump and the turnoff, while metallicities are derived from the location of the giant and subgiant branches as compared to fiducial star clusters. We find that in most cases the stellar population of each star cluster is quite similar to that of the field where it is embedded. Three particular fields present remarkable properties: (i) The so far unique cluster ESO121-SC03 at ~9 Gyr has a surrounding field which shares the same properties. (ii) The field surrounding the far eastern intermediate age cluster OHSC37 is noteworthy in the sense that we do not detect any evidence of LMC stars. (iii) The fields of SL388 and SL509 present CMDs with a secondary clump ~0.45 mag fainter than the dominant intermediate age clump, suggesting a stellar population component located behind the LMC disk at a distance comparable to that of the SMC. The mean metallicity derived for the intermediate age outer disk clusters is =-0.7 and for their surrounding fields =-0.6. These values are significantly lower than found by Olszewski et al. (1991, AJ, 101, 515) for a sample of clusters of similar age, but are in good agreement with several recent studies. A few clusters stand out in the age--metallicity relation in the sense that they are intermediate age clusters at relatively low metallicity ([Fe/H]~-1).Comment: LaTeX, to be published in July, 1998 Astronomical Journa

NGC 1912 and NGC 1907 : a close encounter between open clusters?

The possible physical relation between the closely projected open clusters NGC 1912 (M 38) and NGC 1907 is investigated. Previous studies suggested a physical pair based on similar distances, and the present study explores in more detail the possible interaction. Spatial velocities are derived from available radial velocities and proper motions, and the past orbital motions of the clusters are retrieved in a Galactic potential model. Detailed N-body simulations of their approach suggest that the clusters were born in different regions of the Galaxy and presently experience a fly-by