83,737 research outputs found
Mathematical models of some nematic and cholesteric liquid crystal devices
No full textThis thesis describes the mathematical modelling and analysis of liquid crystal systems when an electric field is applied. This analysis is performed for Nematic, Twisted nematic, and Super-twisted nematic cells and for Polymer Gels. The mathematical techniques employed are: linear and non-linear stability analysis; perturbation theory; and the method of matched asymptotic expansions. For conventional nematic systems analytic expressions are obtained which describe the distortion of the liquid crystal and the coupled electric field at low, intermediate, and high applied voltages. Aspects of the dynamics are considered for both strong and weak anchoring and also with the inclusion of a coupled flow. It is shown that certain weakly anchored nematic systems admit travelling wave solutions. This is particularly relevant to the relaxation of polymer gels. For these systems a model is proposed which treats the polymer matrix as comprising thin orientated fibrils which act as weak anchoring sites distributed throughout the liquid crystal. The model is shown to correctly predict many of the experimentally observed properties of polymer gels. Specifically it predicts the enhanced critical voltage for such systems and also indicates that they saturate at a voltage proportionately close to the critical voltage. The model predicts that the decay of a polymer gel from a highly distorted state occurs via a travelling wave. This in turn implies that the decay constant will depend linearly on the width of the cell containing the gel
Open access self-archiving: An author study
No full textThis, our second author international, cross-disciplinary study on open access had 1296 respondents. Its focus was on self-archiving. Almost half (49%) of the respondent population have self-archived at least one article during the last three years. Use of institutional repositories for this purpose has doubled and usage has increased by almost 60% for subject-based repositories. Self-archiving activity is greatest amongst those who publish the largest number of papers. There is still a substantial proportion of authors unaware of the possibility of providing open access to their work by self-archiving. Of the authors who have not yet self-archived any articles, 71% remain unaware of the option. With 49% of the author population having self-archived in some way, this means that 36% of the total author population (71% of the remaining 51%), has not yet been appraised of this way of providing open access. Authors have frequently expressed reluctance to self-archive because of the perceived time required and possible technical difficulties in carrying out this activity, yet findings here show that only 20% of authors found some degree of difficulty with the first act of depositing an article in a repository, and that this dropped to 9% for subsequent deposits. Another author worry is about infringing agreed copyright agreements with publishers, yet only 10% of authors currently know of the SHERPA/RoMEO list of publisher permissions policies with respect to self-archiving, where clear guidance as to what a publisher permits is provided. Where it is not known if permission is required, however, authors are not seeking it and are self-archiving without it. Communicating their results to peers remains the primary reason for scholars publishing their work; in other words,
researchers publish to have an impact on their field. The vast majority of authors (81%) would willingly comply with a mandate from their employer or research funder to deposit copies of their articles in an institutional or subject-based repository. A further 13% would comply reluctantly; 5% would not comply with such a mandate
Aircraft classification for efficient modelling of environmental noise impact of aviation
No full textWith the environmental externalities of civil aviation under unprecedented scrutiny, and with the projected significant increase in air traffic demand over the next few decades, fleet-level studies are required to assess the potential benefit of novel aircraft technologies and operational procedures for minimising environmental impact of aviation. Using a statistical classification process, the UK commercial aircraft fleet is reduced to four representative-in-class aircraft onthe basis of aircraft physical characteristics, and aircraft noise and engine exhaust emissions. These four representative aircraft, that appropriately capture the noise and emissions characteristics for each category within the UK commercial fleet, are also selected to be used as baseline cases for the high-level assessment of the environmental benefit of novel aircraft technologies. For the particular case of aviation noise, the modelling tools are highly sensitiveto the number of aircraft types in the flight schedule. A reduction of about 80% in computational time with relatively minor decrease in accuracy (between -4% and +5%) is observed when the whole aircraft fleet is replaced with the four representative-in-class aircraft for computing noise contours. Therefore, the statistical classification and selection of representative-in-class aircraft presented in this paper is a valid approach for the rapid and accurate computation of a large number of exploratory cases to assess aviation noise reduction strategies
Evaluation of environmentally optimal descent and take-off slopes for existing and novel aircraft
No full textDescent and takeoff slopes of civil aircraft influence the associated noise and emissions impact around airports. Steep take-off and approach procedures are expected to reduce the noise footprint around airports whereas they could offer local air quality benefits as well. This paper appraises the optimal descent and take-off slopes in terms of noise and emissions for existing civil aircraft, as well as fora future blended wing-body (BWB) concept aircraft. The effect of the interdependencies between noise and emissions is demonstrated, whereas estimated Noise-Power-Distance (NPD) curves for the steep operations are presented. It is shown that a common optimum slope for both environmental concerns is unlikely to occur and that generally, noise benefits come to the expense of increased fuel consumption. However, it is also highlighted that new, more flexible ways of expressing the noise and emissions interdependencies may be required in order to determine optimum slopes more realistically
Investigation into the turbulence statistics of installed jets using hot-wire anemometry
No full textThis work presents a detailed study of theturbulence flow statistics of a jet mounted with its axisparallel to a rigid flat plate. Hot-wire constant tem-perature anemometry has been used to measure thesingle-point and two-point statistics of the axial velocitycomponent at several locations within the jet flow field.Results show that the jet mean flow near the plate sur-face is subjected to a local acceleration and redirectiondue to a Coand ̆a-type effect. The propagation of theseeffects downstream of the plate trailing edge are stronglydependent on the plate position. Regarding the velocityfluctuations, the mean turbulence intensity levels areseen to decrease as the radial distance between the jetand surface decreases. Analysis of the single-point powerspectral density data on the shear layer close to the plateshows that the reduction in magnitude of the low fre-quency content of the energy spectrum is responsiblefor the decrease in turbulence intensity. Additionally,the characteristic time and length-scales computed fromtwo-point measurements reduce as the plate is mountedcloser to the jet centre-line. The axial eddy convectionvelocity is seen to increase in the region of high turbulentkinetic energy in the shear layer adjacent to the surface.Empirical models for turbulence characteristic scalesand eddy convection velocity are presented. These find-ings suggest that both the amplitude and distributionof the jet mixing noise sources are affected when closelyinstalled next to a surface. This paper is a continuationof a recent investigation on the turbulence statistics ofisolated jets presented in Proen ̧ca et al. (2019
Data for: Aircraft classification for efficient modelling of environmental noise impact of aviation
No full textAircraft database used in this research, with the associated noise and engine exhaust emission data.</span
Effects of a hovering unmanned aerial vehicle on urban soundscapes perception
No full textSeveral industry leaders and governmental agencies are currently investigating the use of Unmanned Aerial Vehicles (UAVs), or ‘drones’ as commonly known, for an ever-growing number of applications from blue light services to parcel delivery. For the specific case of the delivery sector, drones can alleviate road space usage and also lead to reductions in CO
2 and air pollution emissions, compared to traditional diesel-powered vehicles. However, due to their unconventional acoustic characteristics and operational manoeuvres, it is uncertain how communities will respond to drone operations. Noise has been suggested as a major barrier to public acceptance of drone operations in urban areas. In this paper, a series of audio-visual scenarios were created to investigate the effects of drone noise on the reported loudness, annoyance and pleasantness of seven different types of urban soundscapes. In soundscapes highly impacted by road traffic noise, the presence of drone noise lead to small changes in the perceived loudness, annoyance and pleasantness. In soundscapes with reduced road traffic noise, the participants reported a significantly higher perceived loudness and annoyance and a lower pleasantness with the presence of the same drone noise. For instance, the reported annoyance increased from 2.3 ± 0.8 (without drone noise) to 6.8 ± 0.3 (with drone noise), in an 11-point scale (0-not at all, 10-extremely). Based on these results, the concentration of drone operations along flight paths through busy roads might aid in the mitigation of the overall community noise impact caused by drones.
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Noise assessment of aircraft with distributed electric propulsion using a new noise estimation framework
No full textFuture aircraft are envisioned to have significantly smaller noise footprint and emissions impact in order to satisfy the ambitious long-term aircraft noise and emissions goals set by several organisations worldwide, for example ACARE and NASA. Distributed electric propulsion (DEP) is anticipated as one of the most suitable and efficient options for powering these aircraft. DEP is the dispersion of thrust among multiple propulsors that are driven electrically rather than mechanically. This paper presents preliminary noise estimations for a civil aircraft that uses various DEP architectures (e.g. different number of electric propulsors, powered by either batteries or gas turbine engines), obtained through a new noise estimation framework that estimates noise variations arising from technological and/or operational changes with respect to a baseline scenario, where the noise levels are known. The aim of the paper is therefore twofold; investigate the possible noise benefits of DEP aircraft, whilst on the other hand demonstrate the core methodology and capabilities of our framework for estimating the noise impact of future aircraft concepts. This preliminary study indicates the framework’s potential in correctly capturing trends
Author Self-Citation in the Turkish Otorhinolaryngology Literature
No full textObjective:To evaluate the prevalence and other characteristics of author self-citations in six Turkey-originated general otorhinolaryngology (ORL) journals of Turkish ORL literature.Methods:A total of 970 articles published in six Turkey-originated general ORL journals (ENT Updates, Journal of Ear Nose Throat and Head Neck Surgery, KBB-Forum, Praxis of Otorhinolaryngology, The Turkish Journal of Ear Nose and Throat, and Turkish Archives of Otorhinolaryngology) in 2016-2020 were analyzed for author self-citations. The association between author self-citations and journal types, study types, study topics, country of origin, and compatibility with the topic were also evaluated.Results:There were 265 author self-citations (0.273 per article) which corresponded to 1.36% of all citations. There was no significant difference between the journal types, study topics, and origin of the studies in terms of mean self-citation values per study, whereas case reports had significantly lower self-citations than review and original investigations. There were three citations (1.1%) that were irrelevant to the study topic.Conclusion:To the best of our knowledge, this is the first study that investigated the practice of author self-citation in Turkish ORL literature. Author self-citation rate in the Turkish-originated general ORL journals was found remarkably lower than the medical literature, whereas the self-citations were found compatible with the study topic to a very large extent. Members of the scientific community including authors, readers, and journal editors should be cautious regarding the unethical practices of self-citations
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