24,969 research outputs found
Optimum matchings in weighted bipartite graphs
Given an integer weighted bipartite graph we consider the problems of finding all the edges that occur in
some minimum weight matching of maximum cardinality and enumerating all the
minimum weight perfect matchings. Moreover, we construct a subgraph of
which depends on an -optimal solution of the dual linear program
associated to the assignment problem on that allows us to reduced
this problems to their unweighed variants on . For instance, when
has a perfect matching and we have an -optimal solution of the dual
linear program associated to the assignment problem on , we solve the
problem of finding all the edges that occur in some minimum weight perfect
matching in linear time on the number of edges. Therefore, starting from
scratch we get an algorithm that solves this problem in time
, where , , and .Comment: 11 page
Earthen construction: structural vulnerabilities and retrofit solutions for seismic actions
Earthen structures present very appealing characteristics regarding a more sustainable practice with the
preservation of our natural resources. However, when subjected to earthquake ground motions, this type of
construction may present a deficient performance, which may cause significant human losses and important
structural damage. The seismic response of earthen structures is typically characterized by fragile failures. There
are several examples of recent earthquakes that affected earthen buildings in a severe way, evidencing the
vulnerability of this type of construction, like the El Salvador earthquake, in 2001, the Bam, Iran earthquake, in
2003, the Pisco, Peru earthquake, in 2007 and the Maule, Chile earthquake, in 2010.
The construction of earth structures on earthquake-prone areas must be carefully studied and should include
seismic reinforcement solutions in order to improve their seismic performance.
In this paper, the performance of earthen structures in recent earthquakes will be examined, analyzing failure
modes inherent to these particular construction materials and associated construction techniques. Also, seismic
reinforcement approaches and techniques will be presented in a comprehensive manner. Examples of tests conducted for the assessment of retrofitting solutions efficiency will be presented, and the results obtained will be discussed
Synchronisation effects on the behavioural performance and information dynamics of a simulated minimally cognitive robotic agent
Oscillatory activity is ubiquitous in nervous systems, with solid evidence that synchronisation mechanisms underpin cognitive processes. Nevertheless, its informational content and relationship with behaviour are still to be fully understood. In addition, cognitive systems cannot be properly appreciated without taking into account brain–body– environment interactions. In this paper, we developed a model based on the Kuramoto Model of coupled phase oscillators to explore the role of neural synchronisation in the performance of a simulated robotic agent in two different minimally cognitive tasks. We show that there is a statistically significant difference in performance and evolvability depending on the synchronisation regime of the network. In both tasks, a combination of information flow and dynamical analyses show that networks with a definite, but not too strong, propensity for synchronisation are more able to reconfigure, to organise themselves functionally and to adapt to different behavioural conditions. The results highlight the asymmetry of information flow and its behavioural correspondence. Importantly, it also shows that neural synchronisation dynamics, when suitably flexible and reconfigurable, can generate minimally cognitive embodied behaviour
Work functions of self-assembled monolayers on metal surfaces
Using first-principles calculations we show that the work function of noble
metals can be decreased or increased by up to 2 eV upon the adsorption of
self-assembled monolayers of organic molecules. We identify the contributions
to these changes for several (fluorinated) thiolate molecules adsorbed on
Ag(111), Au(111) and Pt(111) surfaces. The work function of the clean metal
surfaces increases in this order, but adsorption of the monolayers reverses the
order completely. Bonds between the thiolate molecules and the metal surfaces
generate an interface dipole, whose size is a function of the metal, but it is
relatively independent of the molecules. The molecular and bond dipoles can
then be added to determine the overall work function.Comment: 5 pages, 2 figure
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