34,717 research outputs found
Improving the Knowledge on Seismogenic Sources in the Lower Tagus Valley for Seismic Hazard Purposes
The Lower Tagus Valley, that includes the metropolitan area of Lisbon, has been struck by several earthquakes which produced significant material damage and loss of lives. Their exact location remains unknown. Our goal is to shed some light into the seismogenic sources in the area using seismic reflection and geological data. In areas with no seismic coverage, potential-field data interpretation was carried out. Seismicity was overlaid to the potential seismogenic structures and high-resolution data was acquired in order to confirm which structures have been active into the Quaternary. Three major fault-zones affecting the Neogene were identified: V. F. Xira, Samora-Alcochete and Pinhal Novo. For the first fault, strong evidences suggest it is active. The other two fault-zones and other structures previously unknown can be correlated with several epicentres. Empirical relationships between maximum moment magnitude and fault area indicate that MW > 6.5 earthquakes can be expected for the larger structures
Debye temperature of disordered bcc-Fe-Cr alloys
Debye temperature, TD, of Fe100-xCrx disordered alloys with 0<x<99.9 was
determined from the temperature dependence of the centre shift of 57Fe
Mossbauer spectra recorded in the temperature range of 80-300K. Its
compositional dependence shows an interesting non-monotonous behaviour. For
0<x<~45 as well as for ~75<x<~95 the Debye temperature is enhanced relative to
its value of a metallic iron, and at x=~3 there is a local maximum having a
relative height of ~12% compared to a pure iron. For ~45~95
the Debye temperature is smaller than the one for the metallic iron, with a
local minimum at x=~55 at which the relative decrease of TD amounts to ~12%.
The first maximum coincides quite well with that found for the spin-waves
stiffness coefficient, D0, while the pretty steep decrease observed for x>~95
which is indicative of a decoupling of the probe Fe atoms from the underlying
chromium matrix is likely related to the spin-density waves which constitute
the magnetic structure of chromium in that interval of composition. The
harmonic force constant calculated from the Debye temperature of the least
Fe-concentrated alloy (x>99.9) amounts to only 23% of the one characteristic of
a pure chromium.Comment: 15 pages, 7 figures, 26 reference
Knowledge Acquisition by Networks of Interacting Agents in the Presence of Observation Errors
In this work we investigate knowledge acquisition as performed by multiple
agents interacting as they infer, under the presence of observation errors,
respective models of a complex system. We focus the specific case in which, at
each time step, each agent takes into account its current observation as well
as the average of the models of its neighbors. The agents are connected by a
network of interaction of Erd\H{o}s-Renyi or Barabasi-Albert type. First we
investigate situations in which one of the agents has a different probability
of observation error (higher or lower). It is shown that the influence of this
special agent over the quality of the models inferred by the rest of the
network can be substantial, varying linearly with the respective degree of the
agent with different estimation error. In case the degree of this agent is
taken as a respective fitness parameter, the effect of the different estimation
error is even more pronounced, becoming superlinear. To complement our
analysis, we provide the analytical solution of the overall behavior of the
system. We also investigate the knowledge acquisition dynamic when the agents
are grouped into communities. We verify that the inclusion of edges between
agents (within a community) having higher probability of observation error
promotes the loss of quality in the estimation of the agents in the other
communities.Comment: 10 pages, 7 figures. A working manuscrip
Otimização de procedimentos de coleta de N2O e CH4 do solo na Amazônia Oriental para validação de metódo para medição por cromatografia gasosa (GC).
Objetivou-se otimizar o método de armazenamento e transporte de coleta dos gases - N2O; CH4 - para melhor integridade das amostras visando dados analíticos de medições químicas por cromatografia gasosa de melhor qualidade. Os frascos foram pesados e o vácuo extremamente controlado para estabilização do peso dois tipos de septos para selagem dos frascos de borossilicato, septos de borracha siliconizada cinza de tubos vacutainer® e septos de borracha siliconizada convencional vermelha de tubos vacutainer®. O septo de borracha siliconizada cinza apresentou melhores resultados na retenção de vácuo nos frascos. E indica-se a sua reutilização em no máximo duas coletas para coleta de N2O e CH4 do solo coletados sob o método da câmara estática
The tetrazolium test for soybean seeds.
History. Principles of the test. Equipment and supplies. Seed evaluation. Diagnosis of the causes of soybean seed deterioration. Identification of levels of viability. Class 1 (very high vigor). Class 2 (high vigor). Class 3 (medium vigor). Class 4 (low vigor). Class 5 (very low vigor). Class 6 (non-viable). Class 7 (non-viable). Class 8 (dead seed). Recording and interpreting the results. Precision and accuracy of results. Advantages and limitations of the test. When the test should be applied.bitstream/item/67888/1/Documentos-115.pd
Insights into the room temperature magnetism of ZnO/Co3O4 mixtures
The origin of room temperature (RT) ferromagneticlike behavior in ZnO-based
diluted magnetic semiconductors is still an unclear topic. The present work
concentrates on the appearance of RT magnetic moments in just mixed ZnO/Co3O4
mixtures without thermal treatment. In this study, it is shown that the
magnetism seems to be related to surface reduction of the Co3O4 nanoparticles,
in which, an antiferromagnetic Co3O4 nanoparticle (core) is surrounded by a
CoO-like shell. This singular superficial magnetism has also been found in
other mixtures with semiconductors such as TiO2 and insulators such as Al2O3
Learning about knowledge: A complex network approach
This article describes an approach to modeling knowledge acquisition in terms
of walks along complex networks. Each subset of knowledge is represented as a
node, and relations between such knowledge are expressed as edges. Two types of
edges are considered, corresponding to free and conditional transitions. The
latter case implies that a node can only be reached after visiting previously a
set of nodes (the required conditions). The process of knowledge acquisition
can then be simulated by considering the number of nodes visited as a single
agent moves along the network, starting from its lowest layer. It is shown that
hierarchical networks, i.e. networks composed of successive interconnected
layers, arise naturally as a consequence of compositions of the prerequisite
relationships between the nodes. In order to avoid deadlocks, i.e. unreachable
nodes, the subnetwork in each layer is assumed to be a connected component.
Several configurations of such hierarchical knowledge networks are simulated
and the performance of the moving agent quantified in terms of the percentage
of visited nodes after each movement. The Barab\'asi-Albert and random models
are considered for the layer and interconnecting subnetworks. Although all
subnetworks in each realization have the same number of nodes, several
interconnectivities, defined by the average node degree of the interconnection
networks, have been considered. Two visiting strategies are investigated:
random choice among the existing edges and preferential choice to so far
untracked edges. A series of interesting results are obtained, including the
identification of a series of plateaux of knowledge stagnation in the case of
the preferential movements strategy in presence of conditional edges.Comment: 18 pages, 19 figure
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