4,993 research outputs found
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 , the
nonextensive one is based on the form (with
). 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
, and : identical triads 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
with , or depending on the essential parameters ,
and . 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
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