1,546 research outputs found
Aided diagnosis of structural pathologies with an expert system
Sustainability and safety are social demands for long-life buildings. Suitable inspection and maintenance tasks on structural elements are needed for keeping buildings safely in service. Any malfunction that causes structural damage could be called pathology by analogy between structural engineering and medicine. Even the easiest evaluation tasks require expensive training periods that may be shortened with a suitable tool. This work presents an expert system (called Doctor House or DH) for diagnosing pathologies of structural elements in buildings. DH differs from other expert systems when it deals with uncertainty in a far easier but still useful way and it is capable of aiding during the initial survey 'in situ', when damage should be detected at a glance. DH is a powerful tool that represents complex knowledge gathered from bibliography and experts. Knowledge codification and uncertainty treatment are the main achievements presented. Finally, DH was tested and validated during real surveys.Peer ReviewedPostprint (author's final draft
Continuous-time random walks with reset events: Historical background and new perspectives
In this paper, we consider a stochastic process that may experience random
reset events which relocate the system to its starting position. We focus our
attention on a one-dimensional, monotonic continuous-time random walk with a
constant drift: the process moves in a fixed direction between the reset
events, either by the effect of the random jumps, or by the action of a
deterministic bias. However, the orientation of its motion is randomly
determined after each restart. As a result of these alternating dynamics,
interesting properties do emerge. General formulas for the propagator as well
as for two extreme statistics, the survival probability and the mean
first-passage time, are also derived. The rigor of these analytical results is
verified by numerical estimations, for particular but illuminating examples.Comment: 11 pages, 5 figure
Structural phase transitions in the Ag2Nb4O11 – Na2Nb4O11 solid solution
The phase transitions between various structural modifications of the natrotantite-structured system
xAg2Nb4O11 – (1-x)Na2Nb4O11 have been investigated and a phase diagram constructed as a function
of temperature and composition. This shows three separate phase transition types: (1) paraelectric –
ferroelectric, (2) rhombohedral – monoclinic and (3) a phase transition within the ferroelectric
rhombohedral zone between space groups R3c and R3. The parent structure for the entire series has
space group R-3c. Compositions with x > 0.75 are rhombohedral at all temperatures whereas
compositions with x < 0.75 are all monoclinic at room temperature and below. At x = 0.75,
rhombohedral and monoclinic phases coexist with the phase boundary below room temperature being
virtually temperature-independent. The ferroelectric phase boundary extends into the monoclinic
phase field. No evidence was found for the R3–R3c phase boundary extending into the monoclinic
phase field and it is concluded that a triple point is formed
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