Fibre-optic sensor technologies for humidity and moisture measurement

A review of the use of fibre-optic sensor technologies for humidity sensing is presented. The paper first provides a brief overview on the basic concept of what is meant by humidity and on conventional detection methods. This is followed by an extensive review on the various fibre-optic techniques reported for humidity sensing, covering both intrinsic and extrinsic sensor configurations

UV solar irradiance in observations and the NRLSSI and SATIRE-S models

Total solar irradiance and UV spectral solar irradiance have been monitored since 1978 through a succession of space missions. This is accompanied by the development of models aimed at replicating solar irradiance by relating the variability to solar magnetic activity. The NRLSSI and SATIRE-S models provide the most comprehensive reconstructions of total and spectral solar irradiance over the period of satellite observation currently available. There is persistent controversy between the various measurements and models in terms of the wavelength dependence of the variation over the solar cycle, with repercussions on our understanding of the influence of UV solar irradiance variability on the stratosphere. We review the measurement and modelling of UV solar irradiance variability over the period of satellite observation. The SATIRE-S reconstruction is consistent with spectral solar irradiance observations where they are reliable. It is also supported by an independent, empirical reconstruction of UV spectral solar irradiance based on UARS/SUSIM measurements from an earlier study. The weaker solar cycle variability produced by NRLSSI between 300 and 400 nm is not evident in any available record. We show that although the method employed to construct NRLSSI is principally sound, reconstructed solar cycle variability is detrimentally affected by the uncertainty in the SSI observations it draws upon in the derivation. Based on our findings, we recommend, when choosing between the two models, the use of SATIRE-S for climate studies

Application of FBG-based sensors in build environment

Fibre Bragg grating (FBG)-based optical fibre sensors have found numerous applications in various industries over nearly 20 years. This is due to their many advantageous features, which include those that are typical of fibre-optic sensors (FOSs), for example being light weight, compact, having immunity to electromagnetic fields and an ability to operate in harsh environment. In addition to that, FBG-based sensors offer intrinsic multiplexing capability and they operate using wavelength-encoded signals which are insensitive to the intensity variations that normally affect the performance of intensity-based FOSs. One particular sector that is developing an interest in the use of FBG sensing technology is the civil engineering industry, where FBG-based sensors have begun to be used as physical sensors in a variety of civil structures, many of which are built using reinforced concrete. These sensors are used as part of structural health monitoring (SHM) systems which are effective in detecting possible damage in civil structures as a result of physical loading and corrosion which can lead to deformation, crack formation, fatigue and overloading. However, such sensors are incapable of providing information pertaining to chemical attacks that cause the degradation of the concrete stmcture before physical damages have been detected or observed. Arising from this, the aim of this thesis is to address the technology gap identified through the exploration and development of a series of FBG-based sensors for structural health monitoring and required by industry. The primary objective of the work is to explore the use of polymer- coated FBGs as sensors in the cementious matrix to monitor moisture which is considered as a main agent involved in most of the chemical attacks, by transporting corrosive ions in concrete structures. The sensing concept used in this work exploits the inherent characteristics of the FBG and is based on the strain effect induced in the FBG through the swelling of the polymer coating. A direct indication of the moisture level is given by the shift of the Bragg wavelength caused by the expansion of the sensing material. The context of the work, both technical and applications- focused and the development and characterisation of the sensors are discussed extensively in this thesis. The effectiveness of the sensors developed was evaluated through a series of tests performed under various harsh conditions using a range of concrete specimens with different porosity and mix composition, designed in collaboration with civil engineers. Results of the work are reported and relevant conclusions drawn for the use of this technology in the civil engineering sector, as well as incorporating a discussion of future trends and potential wider applications

Non-commutative field theory approach to two-dimensional vortex liquid system

We investigate the non-commutative (NC) field theory approach to the vortex liquid system restricted to the lowest Landau level (LLL) approximation. NC field theory effectively takes care of the phase space reduction of the LLL physics in a $\star$-product form and introduces a new gauge invariant form of a quartic potential of the order parameter in the Ginzburg-Landau (GL) free energy. This new quartic interaction coupling term has a non-trivial equivalence relation with that obtained by Br\'ezin, Nelson and Thiaville in the usual GL framework. The consequence of the equivalence is discussed.Comment: Add vortex lattice formation, more references, and one autho

Unsupervised Fiber Bundles Registration using Weighted Measures Geometric Demons

International audienceBrain image registration aims at reducing anatomical variability across subjects to create a common space for group analysis. Multi-modal approaches intend to minimize cortex shape variations along with internal structures, such as fiber bundles. A di ficulty is that it requires a prior identi fication of these structures, which remains a challenging task in the absence of a complete reference atlas. We propose an extension of the log-Geometric Demons for jointly registering images and fi ber bundles without the need of point or ber correspondences. By representing fi ber bundles as Weighted Measures we can register subjects with di fferent numbers of fiber bundles. The ef ficacy of our algorithm is demonstrated by registering simultaneously T1 images and between 37 and 88 ber bundles depending on each of the ten subject used. We compare results with a multi-modal T1 + Fractional Anisotropy (FA) and a tensor-based registration algorithms and obtain superior performance with our approach