4,000 research outputs found
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
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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 -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
COVID-19 Related Mobility Reduction: Heterogenous Effects on Sleep and Physical Activity Rhythms
Mobility restrictions imposed to suppress coronavirus transmission can alter
physical activity (PA) and sleep patterns. Characterization of response
heterogeneity and their underlying reasons may assist in tailoring customized
interventions. We obtained wearable data covering baseline, incremental
movement restriction and lockdown periods from 1824 city-dwelling, working
adults aged 21 to 40 years, incorporating 206,381 nights of sleep and 334,038
days of PA. Four distinct rest activity rhythms (RARs) were identified using
k-means clustering of participants' temporally distributed step counts.
Hierarchical clustering of the proportion of time spent in each of these RAR
revealed 4 groups who expressed different mixtures of RAR profiles before and
during the lockdown. Substantial but asymmetric delays in bedtime and waketime
resulted in a 24 min increase in weekday sleep duration with no loss in sleep
efficiency. Resting heart rate declined 2 bpm. PA dropped an average of 38%. 4
groups with different compositions of RAR profiles were found. Three were
better able to maintain PA and weekday/weekend differentiation during lockdown.
The least active group comprising 51 percent of the sample, were younger and
predominantly singles. Habitually less active already, this group showed the
greatest reduction in PA during lockdown with little weekday/weekend
differences. Among different mobility restrictions, removal of habitual social
cues by lockdown had the largest effect on PA and sleep. Sleep and resting
heart rate unexpectedly improved. RAR evaluation uncovered heterogeneity of
responses to lockdown and can identify characteristics of persons at risk of
decline in health and wellbeing.Comment: 30 pages, 3 main figures, 3 tables, 4 supplementary figure
Teachers as writers: a systematic review
This paper is a critical literature review of empirical work from 1990-2015 on teachers as writers. It interrogates the evidence on teachers’ attitudes to writing, their sense of themselves as writers and the potential impact of teacher writing on pedagogy or student outcomes in writing. The methodology was carried out in four stages. Firstly, educational databases keyword searches located 438 papers. Secondly, initial screening identified 159 for further scrutiny, 43 of which were found to specifically address teachers’ writing identities and practices. Thirdly, these sources were screened further using inclusion/exclusion criteria. Fourthly, the 22 papers judged to satisfy the criteria were subject to in-depth analysis and synthesis. The findings reveal that the evidence base in relation to teachers as writers is not strong, particularly with regard to the impact of teachers’ writing on student outcomes. The review indicates that teachers have narrow conceptions of what counts as writing and being a writer and that multiple tensions exist, relating to low self-confidence, negative writing histories, and the challenge of composing and enacting teacher and writer positions in school. However, initial training and professional development programmes do appear to afford opportunities for reformulation of attitudes and sense of self as writer
Joint T1 and Brain Fiber Log-Demons Registration Using Currents to Model Geometry
International audienceWe present an extension of the diffeomorphic Geometric Demons algorithm which combines the iconic registration with geometric constraints. Our algorithm works in the log-domain space, so that one can efficiently compute the deformation field of the geometry. We represent the shape of objects of interest in the space of currents which is sensitive to both location and geometric structure of objects. Currents provides a distance between geometric structures that can be defined without specifying explicit point-to-point correspondences. We demonstrate this framework by registering simultaneously T1 images and 65 fiber bundles consistently extracted in 12 subjects and compare it against non-linear T1, tensor, and multi-modal T1+ Fractional Anisotropy (FA) registration algorithms. Results show the superiority of the Log-domain Geometric Demons over their purely iconic counterparts
Effect of the GaAsP shell on optical properties of self-catalyzed GaAs nanowires grown on silicon
We realize growth of self-catalyzed core-shell GaAs/GaAsP nanowires (NWs) on
Si substrates using molecular-beam epitaxy. Transmission electron microscopy
(TEM) of single GaAs/GaAsP NWs confirms their high crystal quality and shows
domination of the zinc-blende phase. This is further confirmed in optics of
single NWs, studied using cw and time-resolved photoluminescence (PL). A
detailed comparison with uncapped GaAs NWs emphasizes the effect of the GaAsP
capping in suppressing the non-radiative surface states: significant PL
enhancement in the core-shell structures exceeding 2000 times at 10K is
observed; in uncapped NWs PL is quenched at 60K whereas single core-shell
GaAs/GaAsP NWs exhibit bright emission even at room temperature. From analysis
of the PL temperature dependence in both types of NW we are able to determine
the main carrier escape mechanisms leading to the PL quench
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Automatic procedure for realistic 3D finite element modelling of human brain for bioelectromagnetic computations
Realistic computer modelling of biological objects requires building of very accurate and realistic computer models based on geometric and material data, type, and accuracy of numerical analyses. This paper presents some of the automatic tools and algorithms that were used to build accurate and realistic 3D finite element (FE) model of whole-brain. These models were used to solve the forward problem in magnetic field tomography (MFT) based on Magnetoencephalography (MEG). The forward problem involves modelling and computation of magnetic fields produced by human brain during cognitive processing. The geometric parameters of the model were obtained from accurate Magnetic Resonance Imaging (MRI) data and the material properties – from those obtained from Diffusion Tensor MRI (DTMRI). The 3D FE models of the brain built using this approach has been shown to be very accurate in terms of both geometric and material properties. The model is stored on the computer in Computer-Aided Parametrical Design (CAD) format. This allows the model to be used in a wide a range of methods of analysis, such as finite element method (FEM), Boundary Element Method (BEM), Monte-Carlo Simulations, etc. The generic model building approach presented here could be used for accurate and realistic modelling of human brain and many other biological objects
Flux-Line Lattice Structures in Untwinned YBa2Cu3O
A small angle neutron scattering study of the flux-line lattice in a large
single crystal of untwinned YBa2Cu3O is presented. In fields parallel to the
c-axis, diffraction spots are observed corresponding to four orientations of a
hexagonal lattice, distorted by the a-b anisotropy. A value for the anisotropy,
the penetration depth ratio, of 1.18(2) was obtained. The high quality of the
data is such that second order diffraction is observed, indicating a well
ordered FLL. With the field at 33 degrees to c a field dependent re-orientation
of the lattice is observed around 3T.Comment: 4 pages, 4 figure
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