Holocene variations in Lake Titicaca water level and their implications for sociopolitical developments in the central Andes

Holocene climate in the high tropical Andes was characterized by both gradual and abrupt changes, which disrupted the hydrological cycle and impacted landscapes and societies. High-resolution paleoenvironmental records are essential to contextualize archaeological data and to evaluate the sociopolitical response of ancient societies to environmental variability. Middle-to-Late Holocene water levels in Lake Titicaca were reevaluated through a transfer function model based on measurements of organic carbon stable isotopes, combined with high-resolution profiles of other geochemical variables and paleoshoreline indicators. Our reconstruction indicates that following a prolonged low stand during the Middle Holocene (4000 to 2400 BCE), lake level rose rapidly ~15 m by 1800 BCE, and then increased another 3 to 6 m in a series of steps, attaining the highest values after ~1600 CE. The largest lake-level increases coincided with major sociopolitical changes reported by archaeologists. In particular, at the end of the Formative Period (500 CE), a major lake-level rise inundated large shoreline areas and forced populations to migrate to higher elevation, likely contributing to the emergence of the Tiwanaku culture

Holocene variations in Lake Titicaca water level and their implications for sociopolitical developments in the central Andes

Holocene climate in the high tropical Andes was characterized by both gradual and abrupt changes, which disrupted the hydrological cycle and impacted landscapes and societies. High-resolution paleoenvironmental records are essential to contextualize archaeological data and to evaluate the sociopolitical response of ancient societies to environmental variability. Middle-to-Late Holocene water levels in Lake Titicaca were reevaluated through a transfer function model based on measurements of organic carbon stable isotopes, combined with high-resolution profiles of other geochemical variables and paleoshoreline indicators. Our reconstruction indicates that following a prolonged low stand during the Middle Holocene (4000 to 2400 BCE), lake level rose rapidly ~15 m by 1800 BCE, and then increased another 3 to 6 m in a series of steps, attaining the highest values after ~1600 CE. The largest lake-level increases coincided with major sociopolitical changes reported by archaeologists. In particular, at the end of the Formative Period (500 CE), a major lake-level rise inundated large shoreline areas and forced populations to migrate to higher elevation, likely contributing to the emergence of the Tiwanaku culture

Towards more robust mobile robot navigation in dynamic structured environments

Dissertação de Mestrado Integrado em Engenharia Electrotécnica e de Computadores apresentada à Faculdade de Ciências e TecnologiaOs robôs móveis, industriais e de serviço, têm vindo a ser desenvolvidos para uma grande diversidade de aplicações e utilizações. Prevê-se que os robôs móveis se irão tornar quase omnipresentes nos locais de trabalho e nas nossas casas durante as próximas décadas. Para que um robô móvel possa navegar autonomamente, de forma segura e robusta em ambientes estruturados e dinâmicos, o robô móvel precisa de conseguir determinar a sua localização em relação a um mapa, ter a capacidade de percecionar o ambiente em seu redor e planear trajetórias para navegar entre diferentes pontos do ambiente.Neste trabalho foi feito um estudo das técnicas de navegação implementadas no Robot Operating System (ROS), mais concretamente implementadas no pacote de navegação do ROS move_base. O objetivo foi o de descobrir e resolver situações críticas que possam por em causa o bom comportamento do robô.Durante o estudo do move_base observou-se como uma configuração descuidada para o move_base dá origem a comportamentos de risco (e.g. colidir com um obstáculo). Uma afinação dos parâmetros do move_base permite a que o robô seja capaz de gerar uma trajetória mais segura e robusta.Foi descoberto que em algumas situações o move_base perde a capacidade de manter uma representação correta do mundo. Esta perda pode ser atribuída à incapacidade do move_base de utilizar certos tipos de mensagem para limpar do mapa objetos que ja não existam em cena.Estas limitações podem ser ultrapassadas fazendo a conversão dos dados do sensor para um tipo de dados que o move_base consiga usar.No final estudou-se como o move_base reage na presença de obstáculos dinâmicos, (pessoas e outros robôs). Verificou-se que o move_base tem dificuldade em interagir com estes obstáculos. As camadas sociais do ROS tentam dar resposta ao problema da interação. Os estudos realizados revelaram que as camadas sociais não uma boa resposta apresentando muitas limitações.Mobile, industrial and service robots have been developed for a wide range of applications and uses. Mobile robots are expected to become almost ubiquitous at workplaces and in our homes over the next few decades.In order for a mobile robot to be able to navigate autonomously in a secure and robust way in dynamic structured environments,the mobile robot needs to be able to determine its location in relation to a map, have the ability to perceive the surrounding environment and plan Trajectories to navigate between different points of the environment.In this work, a study of the navigation techniques implemented in the Robot Operating System (ROS) was done, more precisely the techniques implemented in the ROS navigation package move_base. The objective was to discover and solve critical situations that may jeopardize the behavior of the robot.During the study it was observed how a careless configuration for move_base gives rise to risky behaviors (e.g. colliding with an obstacle). A tuning of the move_base parameters allows the robot to be able to generate a safer and more robust trajectory.It has been found that in some situations move_base loses the ability to maintain a correct representation of the world. This loss can be attributed to move_base's inability to use certain message types to clear objects that no longer exist on the map.These limitations can be overcome by converting the sensor data to a data type that move_base can use.At the end it was studied how the move_base reacts in the presence of dynamic obstacles, (people and other robots). It has been found that move_base has difficulty interacting with these obstacles. The social layers of ROS try to address the problem of robot interaction. Studies have shown that social layers is not a good response presenting many limitations