Designing a Planetary-Scale IMAP Service with Conflict-free Replicated Data Types

Modern geo-replicated software serving millions of users across the globe faces the consequences of the CAP dilemma, i.e., the inevitable conflicts that arise when multiple nodes accept writes on shared state. The underlying problem is commonly known as fault-tolerant multi-leader replica- tion; actively researched in the distributed systems and database communities. As a more recent theoretical framework, Conflict-free Replicated Data Types (CRDTs) propose a solution to this problem by offering a set of always converging primitives. However, modeling non-trivial system state with CRDT primitives is a challenging and error-prone task. In this work, we propose a solution for a geo-replicated online service with fault-tolerant multi-leader replication based on CRDTs. We chose IMAP as use case due to its prevalence and simplicity. Therefore, we modeled an IMAP-CRDT and verified its correctness with the interactive theorem prover Isabelle/HOL. In order to bridge the gap between theory and practice, we implemented an open-source proto- type pluto and an IMAP benchmark for write-intensive workloads. We evaluated our prototype against the standard IMAP server Dovecot on a multi-continent public cloud. The results ex- pose the limitations of Dovecot with respect to response time performance and replication lag. Our prototype was able to leverage its conceptual advantages and outperformed Dovecot. We find that our approach is promising when facing the multitude of potential concurrency bugs in development of systems at planetary scale

Agroecology and the Struggle for Food Sovereignty in the Americas

A collaborative project of the International Institute for Environment and Development (IIED), the IUCN Commission on Environmental, Economic and Social Policy (CEESP) and the Yale School of Forestry & Environmental Studies (Yale F&ES

CORSE-81: The 1981 Conference on Remote Sensing Education

Summaries of the presentations and tutorial workshops addressing various strategies in remote sensing education are presented. Course design from different discipline perspectives, equipment requirements for image interpretation and processing, and the role of universities, private industry, and government agencies in the education process are covered

The strategic evolution of systems : principles and framework with applications to space communication networks

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. [369]-377).Complex systems in operation are constrained by legacy; in other words, the existing properties, structure, components, protocols, software, people and etc. that are inherited over time. This inheritance heavily influences the type and timing of feasible and available changes to the system, the effectiveness and desirability of their impact while accounting for uncertainty, and the future constraints imposed as a result. This thesis introduces the Strategic Evolution of Systems, a novel framework for evolving complex systems that directly addresses legacy challenges during system operation within the context of space communication networks. The framework - perspective, position, plan and pattern - is based on Mintzberg's "emergent" interpretation of strategy. This thesis also presents several unique ideas including the concept of option lock-out, or the tendency to lose access to potentially desirable regions of the architectural space when exercising a transition; an energy analogy to model static architecture value; an entropy-based formulation to evaluate the desirability, or dynamic multidimensional value, of an architecture by considering the structural and temporal space of possible transitions; and the application of the entropy-based formulation to define the overall desirability of an architecture as its position, or current situation (favorable or unfavorable) relative to accessible alternatives, in order to identify the most advantageous immediate transition. A key contribution of this thesis is a method to value legacy in a physical non-market traded system, including a demonstration of its application to a system in which benefits and costs are nonmonetary in nature.(cont.) Other important contributions include a change exposure tool, referred to as a Strategic Advantage Map, to visualize the near- and long-term impact of immediate transitions relative to legacy. Here, an architecture's position relative to the legacy system can be thought of as the region of entropy space it occupies (evaluated over time and uncertainty). The more dominating this region of position entropy is, the more desirable the architecture. For monetary-based systems, a second change exposure tool includes an "Iceberg Exposure,"which maps the exposure of net present value for each accessible transition option relative to a neutral no-gain-no-loss line, resulting in a graph resembling an iceberg. The visualization tools allow decision makers to quickly evaluate the impact (risk/opportunity) of change, based on their concept of desirability. Case studies include a historical look at the NASA Deep Space Network for insight into legacy and complex system evolution, a demonstration of the Strategic Evolution of Systems framework for a global commercial satellite communication system, and an illustration of the method extended to non-monetary systems for the deployment of communication assets to support manned exploration of Earth's moon. The satellite system case study introduces an extended market model that evaluates the attainable business segments in a global satellite communications system by integrating estimates of the global distribution of market demand, observed traffic statistics, and calculations of the resulting steady-state network performance.(cont.) This thesis will show how to use the framework and principles for evaluating a system's current position as well as how to update the evaluation as time progresses. The satellite communication case study will provide one example where the methodology enables identification of the optimal transition path over the system's operational life. It will become evident that the choice of horizon time and the use of debiasing factors can have significant influence on the results. Future study on properly identifying and constructing these variables is strongly recommended. Finally, the ideas and tools presented in this thesis may be used to compare preferred systems to suggested alternatives in order to justify expenditures or to initiate research and development programs.by Jennifer E. Manuse.Ph.D

Feature Papers of Drones - Volume II

[EN] The present book is divided into two volumes (Volume I: articles 1–23, and Volume II: articles 24–54) which compile the articles and communications submitted to the Topical Collection ”Feature Papers of Drones” during the years 2020 to 2022 describing novel or new cutting-edge designs, developments, and/or applications of unmanned vehicles (drones). Articles 24–41 are focused on drone applications, but emphasize two types: firstly, those related to agriculture and forestry (articles 24–35) where the number of applications of drones dominates all other possible applications. These articles review the latest research and future directions for precision agriculture, vegetation monitoring, change monitoring, forestry management, and forest fires. Secondly, articles 36–41 addresses the water and marine application of drones for ecological and conservation-related applications with emphasis on the monitoring of water resources and habitat monitoring. Finally, articles 42–54 looks at just a few of the huge variety of potential applications of civil drones from different points of view, including the following: the social acceptance of drone operations in urban areas or their influential factors; 3D reconstruction applications; sensor technologies to either improve the performance of existing applications or to open up new working areas; and machine and deep learning development

Conference of Remote Sensing Educators (CORSE-78)

Ways of improving the teaching of remote sensing students at colleges and universities are discussed. Formal papers and workshops on various Earth resources disciplines, image interpretation, and data processing concepts are presented. An inventory of existing remote sensing and related subject courses being given in western regional universities is included

Challenging Mobilities in and to the EU during Times of Crises

This open access book offers a cross-disciplinary view of challenging mobility issues for migrants and refugees in Europe and particularly Greece during the last decade when the economic and refugee crises coincided. It offers new analyses and data on a diverse range of topics concerning new emigrants as well as refugees and mobilities in Greece. The book covers themes which are not only related to refugee and immigrant integration and governance challenges, but also describes host attitudes, solidarity, political and protest claims in the public sphere, as well as the changing emigration environment in Greece within a European context. With contributions from the fields of philosophy, anthropology, sociology, economics, political science, geography and linguistics, this book provides a unique resource for students and scholars, but also for policy-makers and social scientists working on migration-related issues within and beyond Europe