143 research outputs found
Investigation of electro-optical techniques for controlling the direction of a laser beam. Part one - Beam deflector devices. Part two - Beam deflector systems Interim report
Piezoelectrically powered laser beam waveguide for electro-optical acquisition and trackin
A Combined Experimental and Theoretical Study into the Performance of Multilayer Vanadium Dioxide Nanocomposites for Energy Saving Applications
In the built environment there is a increasing issue of heat management, with buildings expending significant energy resources to maintain comfortable living temperatures. In many parts of the world, this entails the use of both heating and cooling during daylight hours depending on ambient temperatures. Due to the variation in the desired temperature control classical solutions can become counter productive in their aim of maintaining comfortable temperatures, therefore it is important to employ adaptive solutions that vary their functionality based on circumstance. In recent years vanadium dioxide (VO2) has generated a broad range of interest due to its heat-mediated structural phase transition from a semiconductor to a metal, which occurs at a critical temperature that may be tuned via doping. The phase transition of VO2 significantly modulates its optical properties, with the high temperature metallic state absorbing and reflecting considerably more infrared radiation than the lower temperature monoclinic state due to the presence of free electrons; a window coated with a VO2 film may passively vary its transmission of infrared radiation based on the ambient temperature, in doing so reducing the temperature management energy-load. Here, we present a theoretically optimised design for a thermochromic smart window film based on a multilayer stack of silica, titania and vanadium dioxide (VO2) on a glass substrate and use the simulations to guide the fabrication process. The design makes use of coherent interference within the multi-layered structure to suppress reflection of visible light and improve the reflective component of solar modulation. In doing so, we are able simultaneously improve the visible transmission and solar modulation of the film above what would be possible with a single layer film. Additionally, the use of thin film VO2 also acts to reduce the detrimental transition hysteresis typically seen in small domain sized nanoparticulate VO2 films. The multilayer structure is fabricated via spin coating of sol-gel based precursors and subsequent annealing. After which the structure is optically characterised and results are compared with simulation along with standard single layer VO2 films and other nanoparticulate based VO2 films
Magnetic properties of undoped Cu2O fine powders with magnetic impurities and/or cation vacancies
Fine powders of micron- and submicron-sized particles of undoped Cu2O
semiconductor, with three different sizes and morphologies have been
synthesized by different chemical processes. These samples include nanospheres
200 nm in diameter, octahedra of size 1 micron, and polyhedra of size 800 nm.
They exhibit a wide spectrum of magnetic properties. At low temperature, T = 5
K, the octahedron sample is diamagnetic. The nanosphere is paramagnetic. The
other two polyhedron samples synthesized in different runs by the same process
are found to show different magnetic properties. One of them exhibits weak
ferromagnetism with T_C = 455 K and saturation magnetization, M_S = 0.19 emu/g
at T = 5 K, while the other is paramagnetic. The total magnetic moment
estimated from the detected impurity concentration of Fe, Co, and Ni, is too
small to account for the observed magnetism by one to two orders of magnitude.
Calculations by the density functional theory (DFT) reveal that cation
vacancies in the Cu2O lattice are one of the possible causes of induced
magnetic moments. The results further predict that the defect-induced magnetic
moments favour a ferromagnetically coupled ground state if the local
concentration of cation vacancies, n_C, exceeds 12.5%. This offers a possible
scenario to explain the observed magnetic properties. The limitations of the
investigations in the present work, in particular in the theoretical
calculations, are discussed and possible areas for further study are suggested.Comment: 20 pages, 5 figures 2 tables, submitted to J Phys Condense Matte
Vibrational and stochastic resonances in two coupled overdamped anharmonic oscillators
We study the overdamped version of two coupled anharmonic oscillators under
the influence of both low- and high-frequency forces respectively and a
Gaussian noise term added to one of the two state variables of the system. The
dynamics of the system is first studied in the presence of both forces
separately without noise. In the presence of only one of the forces, no
resonance behaviour is observed, however, hysteresis happens there. Then the
influence of the high-frequency force in the presence of a low-frequency, i.e.
biharmonic forcing, is studied. Vibrational resonance is found to occur when
the amplitude of the high-frequency force is varied. The resonance curve
resembles a stochastic resonance-like curve. It is maximum at the value of
at which the orbit lies in one well during one half of the drive cycle of the
low-frequency force and in the other for the remaining half cycle. Vibrational
resonance is characterized using the response amplitude and mean residence
time. We show the occurrence of stochastic resonance behaviour in the
overdamped system by replacing the high-frequency force by Gaussian noise.
Similarities and differences between both types of resonance are presented.Comment: 22 pages, 13 figure
pH Landscapes in a Novel Five-Species Model of Early Dental Biofilm
Despite continued preventive efforts, dental caries remains the most common disease of man. Organic acids produced by microorganisms in dental plaque play a crucial role for the development of carious lesions. During early stages of the pathogenetic process, repeated pH drops induce changes in microbial composition and favour the establishment of an increasingly acidogenic and aciduric microflora. The complex structure of dental biofilms, allowing for a multitude of different ecological environments in close proximity, remains largely unexplored. In this study, we designed a laboratory biofilm model that mimics the bacterial community present during early acidogenic stages of the caries process. We then performed a time-resolved microscopic analysis of the extracellular pH landscape at the interface between bacterial biofilm and underlying substrate.-grown dental plaque. We employed the pH-sensitive ratiometric probe C-SNARF-4 to perform real-time microscopic analyses of the biofilm pH in response to salivary solutions containing glucose. Anaerobic glycolysis in the model biofilms created a mildly acidic environment. Decrease in pH in different areas of the biofilms varied, and distinct extracellular pH-microenvironments were conserved over several hours.-grown bacterial biofilms
All-Silicone-based distributed bragg reflectors for efficient flexible luminescent solar concentrators
Luminescent Solar Concentrators (LSCs) have drawn huge interest recently as a technology to pave the way towards the seamless integration of photovoltaics to a range of high-value industries; from architecture and sports to leisure and consumer electronics. Additional device flexibility comes with the inherent ability to attain freeform shapes, expanding the possible fabrication methods, applications and retro-fitting techniques. Unfortunately, flexible LSCs suffer from curvature induced losses which can severely reduce their efficiency, inhibiting the potential of large-scale devices. In this work, we experimentally demonstrate an all-silicone based flexible LSC and Distributed Bragg Reflector (DBR) combination diminishing curvature induced losses. The DBRs, fabricated using scalable solution-based processes, exhibit optical properties precisely engineered to partner our LSCs, as well as high uniformity, resistance to temperature and curvature. Comprehensive modelling shows that for large-scale devices (1 m2) we can essentially decouple the performance of the LSC from curvature, steering the technology towards commercial viability
Proof-of-Concept of Real-World Quantum Key Distribution with Quantum Frames
We propose and experimentally investigate a fibre-based quantum key
distribution system, which employs polarization qubits encoded into faint laser
pulses. As a novel feature, it allows sending of classical framing information
via sequences of strong laser pulses that precede the quantum data. This allows
synchronization, sender and receiver identification, and compensation of
time-varying birefringence in the communication channel. In addition, this
method also provides a platform to communicate implementation specific
information such as encoding and protocol in view of future optical quantum
networks. Furthermore, we report on our current effort to develop high-rate
error correction.Comment: 25 pages, 14 figures, 4 table
Children of Prisoners: Their Situation and Role in Long-Term Crime Prevention
Studies suggest that maintaining family ties can help reduce the likelihood of reoffending, and that while parental imprisonment can increase a child’s likelihood to offend, positive responses to the situation can aid the children’s well-being, attitude and attainment. Drawing on findings from the recently completed EU-funded COPING Project on the mental health of children of prisoners, this chapter explores the factors that aid a child’s ability to cope with parental imprisonment and the actions that different stakeholders can take to support them. It identifies some of the mental health impacts at different stages of parental imprisonment, the roles played by non-imprisoned parents/carers and by schools, and suggests options for further clarifying the factors that help and hinder children of prisoners in the short and long term
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