14,871 research outputs found
Simulation of various damage scenarios using finite element modelling for structural health monitoring systems
© 2017 Taylor & Francis Group, London. Structural Health Monitoring (SHM) is a developing technology for asset management of structures including bridge assets. A crucial benefit of SHM is its ability to monitor the health status of structures using continuous measurements. As a key in SHM, the application of damage detection algorithms to assess the condition of a structure using vibration measurements can be enhanced by providing structural information under various damaged scenarios, which can be obtained from updated numerical models that realistically represent the in-situ structure. However, the dynamic characteristics of a structure are sensitive to uncertainties of various parameters, including material properties and boundary conditions, which require updating in the Finite Element (FE) model to ensure that the model replicates the actual structure. This study focuses on the development of an FE model for the accurate simulation of a jack arch replica structure of the Sydney Harbour Bridge. An experimental jack arch replica is produced to simulate various damage scenarios for laboratory testing. A matching FE model of the jack arch replica is generated and updated using Genetic Algorithm (GA) based on experimental measurements. Damage is simulated in the updated model and the results are validated using the experimental test results. The successful simulation of damage using updated FE models enables the generation of a large number of damage cases that can be trained into an SHM system to improve its damage detection capabilities
Anion and Cation-yield Spectroscopy of Core-excited SF6
We report an extensive study on total and partial-ion-yield spectroscopy around both the S 2p and F 1s thresholds in SF6. All positive and negative single-ion channels have been measured. Below the F 1s threshold we detect a large variation in relative intensity of the resonant structures according to the specific channel monitored, indicating selective fragmentation. Above threshold, at variance with previous cases described by us, we detect high-intensity structures related to shape resonances not only in the cation channels but also for the anions. We discuss the applicability and limits of a model we have developed for the analysis of shape resonances in anion yields as a function of molecular size
Investigation of Non-Stable Processes in Close Binary Ry Scuti
We present results of reanalysis of old electrophotometric data of early type
close binary system RY Scuti obtained at the Abastumani Astrophysical
Observatory, Georgia, during 1972-1990 years and at the Maidanak Observatory,
Uzbekistan, during 1979-1991 years. It is revealed non-stable processes in RY
Sct from period to period, from month to month and from year to year. This
variation consists from the hundredths up to the tenths of a magnitude.
Furthermore, periodical changes in the system's light are displayed near the
first maximum on timescales of a few years. That is of great interest with
regard to some similar variations seen in luminous blue variable (LBV) stars.
This also could be closely related to the question of why RY Sct ejected its
nebula.Comment: 11 pages, 6 figures, 2 table
Superconductivity at the Border of Electron Localization and Itinerancy
The superconducting state of iron pnictides and chalcogenides exists at the
border of antiferromagnetic order. Consequently, these materials could provide
clues about the relationship between magnetism and unconventional
superconductivity. One explanation, motivated by the so-called bad-metal
behaviour of these materials, proposes that magnetism and superconductivity
develop out of quasi-localized magnetic moments which are generated by strong
electron-electron correlations. Another suggests that these phenomena are the
result of weakly interacting electron states that lie on nested Fermi surfaces.
Here we address the issue by comparing the newly discovered alkaline iron
selenide superconductors, which exhibit no Fermi-surface nesting, to their iron
pnictide counterparts. We show that the strong-coupling approach leads to
similar pairing amplitudes in these materials, despite their different Fermi
surfaces. We also find that the pairing amplitudes are largest at the boundary
between electronic localization and itinerancy, suggesting that new
superconductors might be found in materials with similar characteristics.Comment: Version of the published manuscript prior to final journal-editting.
Main text (23 pages, 4 figures) + Supplementary Information (14 pages, 7
figures, 3 tables). Calculation on the single-layer FeSe is added.
Enhancement of the pairing amplitude in the vicinity of the Mott transition
is highlighted. Published version is at
http://www.nature.com/ncomms/2013/131115/ncomms3783/full/ncomms3783.htm
Effects of urban living environments on mental health in adults
Urban-living individuals are exposed to many environmental factors that may combine and interact to influence mental health. While individual factors of an urban environment have been investigated in isolation, no attempt has been made to model how complex, real-life exposure to living in the city relates to brain and mental health, and how this is moderated by genetic factors. Using the data of 156,075 participants from the UK Biobank, we carried out sparse canonical correlation analyses to investigate the relationships between urban environments and psychiatric symptoms. We found an environmental profile of social deprivation, air pollution, street network and urban land-use density that was positively correlated with an affective symptom group (r = 0.22, P perm < 0.001), mediated by brain volume differences consistent with reward processing, and moderated by genes enriched for stress response, including CRHR1, explaining 2.01% of the variance in brain volume differences. Protective factors such as greenness and generous destination accessibility were negatively correlated with an anxiety symptom group (r = 0.10, P perm < 0.001), mediated by brain regions necessary for emotion regulation and moderated by EXD3, explaining 1.65% of the variance. The third urban environmental profile was correlated with an emotional instability symptom group (r = 0.03, P perm < 0.001). Our findings suggest that different environmental profiles of urban living may influence specific psychiatric symptom groups through distinct neurobiological pathways
Nanoscale Origins of the Damage Tolerance of the High-Entropy Alloy CrMnFeCoNi
Damage-tolerance can be an elusive characteristic of structural materials
requiring both high strength and ductility, properties that are often mutually
exclusive. High-entropy alloys are of interest in this regard. Specifically,
the single-phase CrMnFeCoNi alloy displays tensile strength levels of ~1 GPa,
excellent ductility (~60-70%) and exceptional fracture toughness (KJIc > 200
MPa/m). Here, through the use of in-situ straining in an aberration-corrected
transmission electron microscope, we report on the salient atomistic to
micro-scale mechanisms underlying the origin of these properties. We identify a
synergy of multiple deformation mechanisms, rarely achieved in metallic alloys,
which generates high strength, work hardening and ductility, including the easy
motion of Shockley partials, their interactions to form stacking-fault
parallelepipeds, and arrest at planar-slip bands of undissociated dislocations.
We further show that crack propagation is impeded by twinned, nano-scale
bridges that form between the near-tip crack faces and delay fracture by
shielding the crack tip.Comment: 6 figures, 4 figure
Kinetic frustration and the nature of the magnetic and paramagnetic states in iron pnictides and iron chalcogenides
The iron pnictide and chalcogenide compounds are a subject of intensive
investigations due to their high temperature superconductivity.\cite{a-LaFeAsO}
They all share the same structure, but there is significant variation in their
physical properties, such as magnetic ordered moments, effective masses,
superconducting gaps and T. Many theoretical techniques have been applied
to individual compounds but no consistent description of the trends is
available \cite{np-review}. We carry out a comparative theoretical study of a
large number of iron-based compounds in both their magnetic and paramagnetic
states. We show that the nature of both states is well described by our method
and the trends in all the calculated physical properties such as the ordered
moments, effective masses and Fermi surfaces are in good agreement with
experiments across the compounds. The variation of these properties can be
traced to variations in the key structural parameters, rather than changes in
the screening of the Coulomb interactions. Our results provide a natural
explanation of the strongly Fermi surface dependent superconducting gaps
observed in experiments\cite{Ding}. We propose a specific optimization of the
crystal structure to look for higher T superconductors.Comment: 5 pages, 3 figures with a 5-page supplementary materia
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