85 research outputs found
A novel double-hybrid learning method for modal frequency-based damage assessment of bridge structures under different environmental variation patterns
Monitoring of modal frequencies under an unsupervised learning framework is a practical strategy for damage assessment of civil structures, especially bridges. However, the key challenge is related to high sensitivity of modal frequencies to environmental and/or operational changes that may lead to economic and safety losses. The other challenge pertains to different environmental and/or operational variation patterns in modal frequencies due to differences in structural types, materials, and applications, measurement periods in terms of short and/or long monitoring programs, geographical locations of structures, weather conditions, and influences of single or multiple environmental and/or operational factors, which may cause barriers to employing stateof-the-art unsupervised learning approaches. To cope with these issues, this paper proposes a novel double-hybrid learning technique in an unsupervised manner. It contains two stages of data partitioning and anomaly detection, both of which comprise two hybrid algorithms. For the first stage, an improved hybrid clustering method based on a coupling of shared nearest neighbor searching and density peaks clustering is proposed to prepare local information for anomaly detection with the focus on mitigating environmental and/or operational effects. For the second stage, this paper proposes an innovative non-parametric hybrid anomaly detector based on local outlier factor. In both stages, the number of nearest neighbors is the key hyperparameter that is automatically determined by leveraging a self-adaptive neighbor searching algorithm. Modal frequencies of two full-scale bridges are utilized to validate the proposed technique with several comparisons. Results indicate that this technique is able to successfully eliminate different environmental and/or operational variations and correctly detect damage
Synchronously diagnosed eosinophilic granuloma and Hodgkin's disease in a 12-year-old boy: a case report
Relationships between plasma measures of oxidative stress and metabolic control in NIDDM
Scheme dependence of NLO corrections to exclusive processes
We apply the so-called conformal subtraction scheme to predict perturbatively
exclusive processes beyond leading order. Taking into account evolution
effects, we study the scheme dependence for the photon-to-pion transition form
factor and the electromagnetic pion form factor at next-to-leading order for
different pion distribution amplitudes. Relying on the conformally covariant
operator product expansion and using the known higher order results for
polarized deep inelastic scattering, we are able to predict perturbative
corrections to the hard-scattering amplitude of the photon-to-pion transition
form factor beyond next-to-leading order in the conformal scheme restricted to
the conformal limit of the theory.Comment: RevTeX, 25 pages, 2 figures, 5 tables, minor changes, to be published
in Phys. Rev.
Complete next-to-leading order perturbative QCD prediction for the pion electromagnetic form factor
We present the results of a complete leading-twist next-to-leading order
(NLO) QCD analysis of the spacelike pion electromagnetic form factor at large
momentum transfer Q. We have studied their dependence on the form of the pion
distribution amplitude. For a given distribution amplitude, we have examined
the sensitivity of the predictions to the choice of the renormalization and
factorization scales. Theoretical uncertainty of the LO results related to the
renormalization scale ambiguity has been significantly reduced by including the
NLO corrections. Adopting the criteria according to which a NLO prediction is
considered reliable if, both, the ratio of the NLO to LO contributions and the
strong coupling constant are reasonably small, we find that reliable
perturbative predictions for the pion electromagnetic form factor with all
distribution amplitudes considered can already be made at a momentum transfer
Q<10 GeV, with corrections to the LO results being typically of the order of ~
20%. To check our predictions and to discriminate between the distribution
amplitudes, it is necessary to obtain experimental data extending to higher
values of Q.Comment: 39 pages, RevTex, 17 figures included; revised version (an error in
the analytical expression for T_H corrected, numerical results correspondigly
modified; presentation of the results modified to some extent and some points
discussed in more detail after referees reports
Next-to-next-to-leading order prediction for the photon-to-pion transition form factor
We evaluate the next-to-next-to-leading order corrections to the
hard-scattering amplitude of the photon-to-pion transition form factor. Our
approach is based on the predictive power of the conformal operator product
expansion, which is valid for a vanishing -function in the so-called
conformal scheme. The Wilson--coefficients appearing in the non-forward
kinematics are then entirely determined from those of the polarized
deep-inelastic scattering known to next-to-next-to-leading accuracy. We propose
different schemes to include explicitly also the conformal symmetry breaking
term proportional to the -function, and discuss numerical predictions
calculated in different kinematical regions. It is demonstrated that the
photon-to-pion transition form factor can provide a fundamental testing ground
for our QCD understanding of exclusive reactions.Comment: 62 pages LaTeX, 2 figures, 9 tables; typos corrected, some references
added, to appear in Phys. Rev.
The Evolution of the Pion Distribution Amplitude in Next-to-Leading Order
The evolution of the pion distribution amplitude in next-to-leading order is
studied for a fixed and a running coupling constant. In both cases, the
evolution provides a logarithmic modification in the endpoint region. Assuming
a simple parameterization of the distribution amplitude at a scale of , it is shown numerically that these effects are large enough at
that they have to be taken into account in the
next-to-leading-order analysis for exclusive processes. Alternatively, by
introducing a new distribution amplitude that evolves more smoothly, this
logarithmic modification can be included in the hard-scattering part of the
considered process.Comment: 17 pages LaTeX + 3 uuencoded and compressed postscript figure
Different strategies of secondary phase incorporation into metallic sheets by friction stir processing in developing surface composites
Health monitoring of large‐scale civil structures: An approach based on data partitioning and classical multidimensional scaling
A major challenge in structural health monitoring (SHM) is the efficient handling of big data, namely of high‐dimensional datasets, when damage detection under environmental variability is being assessed. To address this issue, a novel data‐driven approach to early damage detection is proposed here. The approach is based on an efficient partitioning of the dataset, gathering the sensor recordings, and on classical multidimensional scaling (CMDS). The partitioning procedure aims at moving towards a low‐dimensional feature space; the CMDS algorithm is instead exploited to set the coordinates in the mentioned low‐dimensional space, and define damage indices through norms of the said coordinates. The proposed approach is shown to efficiently and robustly address the challenges linked to high‐dimensional datasets and environmental variability. Results related to two large‐scale test cases are reported: the ASCE structure, and the Z24 bridge. A high sensitivity to damage and a limited (if any) number of false alarms and false detections are reported, testifying the efficacy of the proposed data‐driven approach
- …