1,724,938 research outputs found
Turbulent skin-friction drag reduction by travelling waves induced by spanwise Lorentz force
No full textThe streamwise and spanwise travelling waves induced by spanwise Lorentz force are studied for skin-friction drag reduction in a turbulent channel. The streamwise travelling wave by spanwise Lorentz force on drag reduction is compared to the with the spanwise wall motion. The drag reduction map shows a drag reduction region and a drag increase region, depending on a time scale . For spanwise travelling wave, a large drag reduction appears at large oscillation frequencies and small spanwise wave numbers, while all stationary wave cases give a drag increase. When the wave travels at an oblique angle to the streamwise mean flow, the optimal drag reduction appears in backward travelling wave case. Generally, the backward streamwise travelling wave is found to be most efficient in drag reduction among all oblique travelling waves. Spanwise oscillation, forward streamwise travelling, spanwise travelling and backward streamwise travelling wave cases share a similar drag reduction mechanism: first, the spanwise motion directly breaks the near wall quasi-streamwise vortices structure array \cite{Jeong_etal1997}, which results in the shortening of streamwise streaks; second, the spanwise velocity layer maintains the asymmetry of the positive and negative quasi-streamwise vortices, which leads to a sustained drag reduction
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variable-power scheduling for perpetual target coverage in energy harvesting wireless sensor networks
No full textWe study perpetual target coverage with an energy harvesting wireless sensor network (WSN) assuming that each sensor can modulate its sensing range by dynamically varying its operating power, e.g., radar sensors. In this variable-power scheduling scenario, we first consider the maximum network lifetime problem for battery-powered WSNs. The solution to this problem allows us to decide if a given energy harvesting WSN is capable of perpetual operation satisfying energy neutrality. Then, we formulate the energy efficient perpetual target coverage problem and prove its NP completeness. A polynomial algorithm is proposed, and its effectiveness is validated through extensive numerical simulations
Theoretical Investigation of the Circularly Polarized Luminescence of a Chiral Boron Dipyrromethene (BODIPY) Dye
Full text linkOver the last decade, molecules capable of emitting circularly polarized light have attracted growing attention for potential technological and biological applications. The efficiency of such devices depend on multiple parameters, in particular the magnitude and wavelength of the peak of emitted light, and also on the dissymmetry factor for chiral applications. In light of these considerations, molecular systems with tunable optical properties, preferably in the visible spectral region, are particularly appealing. This is the case of boron dipyrromethene (BODIPY) dyes, which exhibit large molecular absorption coefficients, have high fluorescence yields, are very stable, both thermally and photochemically, and can be easily functionalized. The latter property has been extensively exploited in the literature to produce chromophores with a wide range of optical properties. Nevertheless, only a few chiral BODIPYs have been synthetized and investigated so far. Using a recently reported axially chiral BODIPY derivative where an axially chiral BINOL unit has been attached to the chromophore unit, we present a comprehensive computational protocol to predict and interpret the one-photon absorption and emission spectra, together with their chiroptical counterparts. From the physico-chemical properties of this molecule, it will be possible to understand the origin of the circularly polarized luminescence better, thus helping to fine-tune the properties of interest. The sensitivity of such processes require accurate results, which can be achieved through a proper account of the vibrational structure in optical spectra. Methodologies to compute vibrationally-resolved electronic spectra can now be applied on relatively large chromophores, such as BODIPYs, but require more extensive computational protocols. For this reason, particular attention is paid in the description of the different steps of the protocol, and the potential pitfalls. Finally, we show how, by means of appropriate tools and approaches, data from intermediate steps of the simulation of the final spectra can be used to obtain further insights into the properties of the molecular system under investigation and the origin of the visible bands
Investigation and development of an advanced virtual coordinate measuring machine
Full text linkThis thesis was submitted for the degree of Doctor of Philosophy and was awarded by Brunel UniversityDimensional measurement plays a critical role in product development and quality control. With the continuously increasing demand for tighter tolerances and more complex workpiece shapes in the industry, dimensional metrology often becomes the bottleneck of taking the quality and performance of manufacturing to the next level. As one kind of the most useful and powerful measuring instruments, coordinate measuring machines (CMMs) are widely employed in manufacturing industries. Since the accuracy and efficiency of a CMM have a vital impact on the product quality, productivity and manufacturing cost, the evaluation and improvement of CMM performance have always been important research topics since the invention of CMM.
A novel Advanced Virtual Coordinate Measuring Machine (AVCMM) is proposed against such a background. The proposed AVCMM is a software package that provides an integrated virtual environment, in which user can plan inspection strategy for a given task, carry out virtual measurement, and evaluate the uncertainty associated with the measurement result, all without the need of using a physical machine. The obtained estimate of uncertainty can serve as a rapid feedback for user to optimize the inspection plan in the AVCMM before actual measurement, or as an evaluation of the result of a performed measurement. Without involving a physical CMM in the inspection planning or evaluation of uncertainty, the AVCMM can greatly reduce the time and cost needed for such processes. Furthermore, as the package offers vivid 3D visual representation of the virtual environment and supports operations similar to a physical CMM, it does not only allow the user to easily plan and optimise the inspection strategy, but also provide a cost-effective, risk-free solution for training CMM operators.
A modular, multitier architecture has been adopted to develop the AVCMM system, which incorporates a number of functional components covering CMM and workpiece modelling, error simulation, inspection simulation, feature calculation, uncertainty evaluation and 3D representation. A new engine for detecting collision/contact has been developed and utilized, which is suitable for the virtual environment of simulated CMM inspections. A novel approach has been established to calculate errors required for the error simulation, where the data are obtained from FEA simulations in addition to conventional experimental method. Monte Carlo method has been adopted for uncertainty evaluation and has been implemented with multiple options available to meet different requirements.
A prototype of the proposed AVCMM system has been developed in this research. Its validity, usability and performance have been verified and evaluated through a set of experiments. The principles for utilising the AVCMM in practical use have also been established and demonstrated.
The results have indicated that the proposed AVCMM system has great potentials to improve the functionalities and overall performance of CMMs.ORSAS and the School of Engineering and Design of Brunel University
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Three dimensions of biodiversity: New perspectives and methods
No full textAlthough the knowledge and understanding of biodiversity is rapidly increasing, very little of the total biodiversity is currently considered in applied conservation actions. In this sense, it is crucial to integrate independent fields of biodiversity models and perspectives with conservation issues, in particular, the views that address the links between biodiversity, ecosystem services and human well-being, species interaction, and focal charismatic species. This study overcomes the lack of framework necessary for this integration, and proposes three perspectives and approaches to assess biodiversity. The first perspective is biodiversity potential. It considers the correlation between renewable resources in local ecosystems and biodiversity potential, in terms of the possibility of maintaining a high degree of biodiversity. The energy cost is evaluated using both static and dynamic methods, based on the measure of the emergy of local renewable resources and of the total emergy throughput needed by components in ecosystem food webs, respectively, also highlighting the link between biodiversity and ecosystem services, species interactions via energy transfer respectively. The second perspective considers the contribution of biodiversity to human well-being, such as domestication. In this approach, we assess the contribution of biodiversity to humans by calculating the emergy of non-renewable resources required to domesticate animals or plants into agricultural products. The third perspective highlights the significance of local focal charismatic species to global biodiversity conservation. Taking rare species as an example, the emergy required to maintain rare species per unit area is used as a quantitative indicator of the role of local rare species in maintaining global biodiversity. By measuring biodiversity from these three perspectives (potential, contribution and significance) simultaneously, biodiversity conservation strategies are addressed for different regions. Taking China as a case study, it shows that the provinces featuring high potential, low contribution and low significance can moderately increase biodiversity development. The provinces with high significance to global biodiversity should strengthen conservation to halt biodiversity loss. The areas exhibiting overexploitation of biodiversity should in turn restrict biodiversity exploitation. The general approaches proposed in this study could be applied to different cases, situations and species, promoting the integration to biodiversity conservation actions at different scales. © 2021 The Author(s
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Development of novel design methodology for product mass customization based on human attributes and cognitive behaviours
No full textThis thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The competition in the global market is accelerating rapidly because of less technological gap, matured manufacturing level, and various changing customer needs. Increasingly customers choose products in terms of experience desires, psychological desires and whether the products can reflect their values, in addition to the main product functions. Moreover, there are a large number of small and medium sized manufacturing companies in the developing countries. OEM (Original Equipment Manufacturer) and simple mass production cannot generate good value for these manufacture companies, and they have been seeking new opportunities to create higher value for their products/services and satisfy different needs of customers.
Mass customization is one of the main business forms in the future, which can best meet the needs of individual customer, especially psychological needs. The key to mass customization is to provide enough modules to meet individual needs with a limited cost increase. The problem has been how to identify the real user needs and individual differences.
The purpose of this research is to develop a sound design methodology based upon the current product design theories and practices for future product innovation and sustainable growth of small and medium sized manufacturing enterprises. The research focuses on the user-product cognitive behaviours and the relationship between human attributes and product features. Orthogonal experiment, eye tracking technology and artificial neural network have been successfully applied in this research.
The research has developed a user needs hierarchy model and added value hierarchy model, and a robust theoretical basis to predict and evaluate (individual) user needs for product design.
The research has further made the following contributions:
1) The relationship between human attributes and product features has been established, which can help designers understand the differences of various customer groups;
2) The different effects of various influence factors on people’s cognition and preference choice based on vision have been analysed and discussed;
3) A new method to identify, cluster, and combine common needs and personalized needs in early design stage for mass customization has been developed;
4) The research results can be reused in the future design of the same or similar kind of products
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