Considering Human Aspects on Strategies for Designing and Managing Distributed Human Computation

A human computation system can be viewed as a distributed system in which the processors are humans, called workers. Such systems harness the cognitive power of a group of workers connected to the Internet to execute relatively simple tasks, whose solutions, once grouped, solve a problem that systems equipped with only machines could not solve satisfactorily. Examples of such systems are Amazon Mechanical Turk and the Zooniverse platform. A human computation application comprises a group of tasks, each of them can be performed by one worker. Tasks might have dependencies among each other. In this study, we propose a theoretical framework to analyze such type of application from a distributed systems point of view. Our framework is established on three dimensions that represent different perspectives in which human computation applications can be approached: quality-of-service requirements, design and management strategies, and human aspects. By using this framework, we review human computation in the perspective of programmers seeking to improve the design of human computation applications and managers seeking to increase the effectiveness of human computation infrastructures in running such applications. In doing so, besides integrating and organizing what has been done in this direction, we also put into perspective the fact that the human aspects of the workers in such systems introduce new challenges in terms of, for example, task assignment, dependency management, and fault prevention and tolerance. We discuss how they are related to distributed systems and other areas of knowledge.Comment: 3 figures, 1 tabl

Nonextensive statistical mechanics - Applications to nuclear and high energy physics

A variety of phenomena in nuclear and high energy physics seemingly do not satisfy the basic hypothesis for possible stationary states to be of the type covered by Boltzmann-Gibbs (BG) statistical mechanics. More specifically, the system appears to relax, along time, on macroscopic states which violate the ergodic assumption. Some of these phenomena appear to follow, instead, the prescriptions of nonextensive statistical mechanics. In the same manner that the BG formalism is based on the entropy $S_{BG}=-k \sum_i p_i \ln p_i$, the nonextensive one is based on the form $S_q=k(1-\sum_ip_i^q)/(q-1)$ (with $S_1=S_{BG}$). Typically, the systems following the rules derived from the former exhibit an {\it exponential} relaxation with time toward a stationary state characterized by an {\it exponential} dependence on the energy ({\it thermal equilibrium}), whereas those following the rules derived from the latter are characterized by (asymptotic) {\it power-laws} (both the typical time dependences, and the energy distribution at the stationary state). A brief review of this theory is given here, as well as of some of its applications, such as electron-positron annihilation producing hadronic jets, collisions involving heavy nuclei, the solar neutrino problem, anomalous diffusion of a quark in a quark-gluon plasma, and flux of cosmic rays on Earth. In addition to these points, very recent developments generalizing nonextensive statistical mechanics itself are mentioned.Comment: 23 pages including 5 figures. To appear in the Proceedings of the Xth International Workshop on Multiparticle Production - Correlations and Fluctuations in QCD (8-15 June 2002, Crete), ed. N. Antoniou (World Scientific, Singapore, 2003). It includes a reply to the criticism expressed in R. Luzzi, A.R. Vasconcellos and J.G. Ramos, Science 298, 1171 (2002

Input Selection for Dimensionless Shear Rates in Herschel-Bulkley and Power-Law Models

Master's thesis in Petroleum EngineeringHerschel-Bulkley and Power-Law models are mathematical expressions widely used to describe the pseudoplastic nature of drilling muds. Despite their popularity, these models carry an intrinsic limitation because the consistency index is a function of the flow behavior index. Some works have proposed the use of dimensionless shear rates to overcome this issue. However, this solution requires two inputs, which are taken from the experimental data set. The bigger the number of experimental points is, the bigger the number of input combinations becomes. Moreover, the selection of such points is not a self-evident task and relies heavily on one’s experience.This thesis presents: first, a methodology from which two objective approaches for selection of inputs were derived; second, a MATLAB code that enables curve-fitting of rheological data and some hydraulic calculations. These techniques were meant to balance computation time and goodness of fit. Non-linear regression, which is the best solution in terms of goodness of fit, was taken as a benchmark and was compared to the two proposed approaches. Rheological characterization and hydraulic calculations were performed for different recipes of oil-based mud (OBM) and polyanionic cellulose (PAC) solution. For the fluid modeled by Power-Law model, hydraulic predictions had an error of 3% at most, whereas the computing time was only about 5% of the non-linear’s in the worst case. For the fluid modeled by Herschel-Bulkley model and flow rates greater than approximately 600 l/min, these values were, respectively, 5% and 1%. Therefore, the proposed approaches are extremely faster than a non-linear regression at a relatively low cost in terms of accuracy loss. Moreover, it was shown how the use of a single iteration can increase the goodness of fit in the dimensionless shear rate approach and how error propagation theory can be applied to the dimensionless Power-Law model.Finally, the methodology and the MATLAB code contributed to a SPE Conference Paper that explored the impact of Power-Law model parameters on frictional pressure loss uncertainty

Constructing fail-controlled nodes for distributed systems: a software approach

PhD ThesisDesigning and implementing distributed systems which continue to provide specified services in the presence of processing site and communication failures is a difficult task. To facilitate their development, distributed systems have been built assuming that their underlying hardware components are Jail-controlled, i.e. present a well defined failure mode. However, if conventional hardware cannot provide the assumed failure mode, there is a need to build processing sites or nodes, and communication infra-structure that present the fail-controlled behaviour assumed. Coupling a number of redundant processors within a replicated node is a well known way of constructing fail-controlled nodes. Computation is replicated and executed simultaneously at each processor, and by employing suitable validation techniques to the outputs generated by processors (e.g. majority voting, comparison), outputs from faulty processors can be prevented from appearing at the application level. One way of constructing replicated nodes is by introducing hardwired mechanisms to couple replicated processors with specialised validation hardware circuits. Processors are tightly synchronised at the clock cycle level, and have their outputs validated by a reliable validation hardware. Another approach is to use software mechanisms to perform synchronisation of processors and validation of the outputs. The main advantage of hardware based nodes is the minimum performance overhead incurred. However, the introduction of special circuits may increase the complexity of the design tremendously. Further, every new microprocessor architecture requires considerable redesign overhead. Software based nodes do not present these problems, on the other hand, they introduce much bigger performance overheads to the system. In this thesis we investigate alternative ways of constructing efficient fail-controlled, software based replicated nodes. In particular, we present much more efficient order protocols, which are necessary for the implementation of these nodes. Our protocols, unlike others published to date, do not require processors' physical clocks to be explicitly synchronised. The main contribution of this thesis is the precise definition of the semantics of a software based Jail-silent node, along with its efficient design, implementation and performance evaluation.The Brazilian National Research Council (CNPq/Brasil)

G\"odel-type Spacetimes in Induced Matter Gravity Theory

A five-dimensional (5D) generalized G\"odel-type manifolds are examined in the light of the equivalence problem techniques, as formulated by Cartan. The necessary and sufficient conditions for local homogeneity of these 5D manifolds are derived. The local equivalence of these homogeneous Riemannian manifolds is studied. It is found that they are characterized by three essential parameters $k$, $m^2$ and $\omega$: identical triads $(k, m^2, \omega)$ correspond to locally equivalent 5D manifolds. An irreducible set of isometrically nonequivalent 5D locally homogeneous Riemannian generalized G\"odel-type metrics are exhibited. A classification of these manifolds based on the essential parameters is presented, and the Killing vector fields as well as the corresponding Lie algebra of each class are determined. It is shown that the generalized G\"odel-type 5D manifolds admit maximal group of isometry $G_r$ with $r=7$, $r=9$ or $r=15$ depending on the essential parameters $k$, $m^2$ and $\omega$. The breakdown of causality in all these classes of homogeneous G\"odel-type manifolds are also examined. It is found that in three out of the six irreducible classes the causality can be violated. The unique generalized G\"odel-type solution of the induced matter (IM) field equations is found. The question as to whether the induced matter version of general relativity is an effective therapy for these type of causal anomalies of general relativity is also discussed in connection with a recent article by Romero, Tavakol and Zalaletdinov.Comment: 19 pages, Latex, no figures. To Appear in J.Math.Phys.(1999

A mesma pressão, diferentes reações : serviços ecossistêmicos realizados por morcegos sob risco no Brasil

Dissertação (mestrado)—Universidade de Brasília, Instituto de Ciências Biológicas, Departamento de Ecologia, 2019.Atividades humanas afetam os sistemas da Terra de forma indiscriminada e a perda da biodiversidade tem sido uma consequência ubíquia. Com a perda de espécies, interações ecológicas antes estabelecidas, são enfraquecidas ou perdidas e funções ecossistêmicas são alteradas ou extintas. Os morcegos são um grupo diversificado de mamíferos e desempenham papéis importantes em ecossistemas tropicais. Os papéis funcionais de morcegos têm sido associados a provisão de serviços ecossistêmicos. Sua diversidade está atualmente sendo ameaçada pela perda de habitat e o Brasil tem um longo histórico de conversão de áreas naturalmente vegetadas em terras agrícolas. Pouco se sabe sobre como a perda de habitat afetou a diversidade funcional dos morcegos. Aplicamos modelos de distribuição de espécies (SDMs) para avaliar a distribuição da diversidade funcional de morcegos brasileiros entre os biomas. Usamos informações sobre preferências alimentares e tamanho do corpo para atribuir as espécies a grupos funcionais provedores de serviços ecossistêmicos. Os impactos do desmatamento foram avaliados para o Brasil e cada região biogeográfica. As regiões diferiram em seus valores de provisão potencial e no histórico de conversão e dinâmica do uso da terra. Isso levou a diferentes perdas proporcionais entre os grupos de morcegos, sem um padrão geral aparente. Os impactos negativos foram mais fortes nas espécies maiores. Nossos resultados junto com informações publicadas sobre a resposta funcional de morcegos à fragmentação destacam o possível estado dos serviços ecossistêmicos prestados pelos morcegos nas regiões biogeográficas brasileiras. Há ainda muito a ser investigado sobre a conservação da diversidade funcional de morcegos e, diante o contexto, há uma urgência de estudos adicionais para compreensão adequada do papel efetivo de morcegos na prestação de serviços ecossistêmicos no Brasil. Somente então, planos de manejo que visem a conservação e a maximização das contribuições desse grupo poderão ser desenvolvidos.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).Human activities have affected Earth's systems in an indiscriminate away and biodiversity loss has been the ubiquitous consequence. Along with the loss of species, ecological interactions once established are weakened or lost and ecosystem functions are changed or extinguished. Bats are a diverse group of mammals and are known to play significant roles in tropical ecosystems. The functional roles of bats have been associated with provision of ecosystems services. Bat diversity is currently being threatened by habitat loss and Brazil has a long history of converting naturally vegetated areas to farmland. Little is known about how habitat loss has affected bat functional diversity. Here we use species distribution models (SDMs) to assess the distribution of the functional diversity of Brazilian bats amongst Brazilian biogeographical regions. We used information on food preferences and body size to assigned species to guilds and functional groups. Habitat conversion impacts on providing guilds and groups were assessed for each Brazilian biome. Each region differed on their potential provision values and on history of land use conversion. This led to different proportional losses between bat groups, with no apparent general pattern. Negative impacts were strongest on larger species. Our results together with published information on bat's functional response to fragmentation highlight the possible current state of the ecosystems services provided by bats in Brazil’s biogeographical regions. We provide recommendations for the safeguarding of bat functional diversity and highlight the urgency of further studies to adequately understand the underlying role of bats in providing ecosystem services in Brazil. Only then, effective management plans involving bats and the delivery of ecosystem services can be developed