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A three-step classification framework to handle complex data distribution for radar UAV detection
Get PDFUnmanned aerial vehicles (UAVs) have been used in a wide range of applications and become an increasingly important radar target. To better model radar data and to tackle the curse of dimensionality, a three-step classification framework is proposed for UAV detection. First we propose to utilize the greedy subspace clustering to handle potential outliers and the complex sample distribution of radar data. Parameters of the resulting multi-Gaussian model, especially the covariance matrices, could not be reliably estimated due to insufficient training samples and the high dimensionality. Thus, in the second step, a multi-Gaussian subspace reliability analysis is proposed to handle the unreliable feature dimensions of these covariance matrices. To address the challenges of classifying samples using the complex multi-Gaussian model and to fuse the distances of a sample to different clusters at different dimensionalities, a subspace-fusion scheme is proposed in the third step. The proposed approach is validated on a large benchmark dataset, which significantly outperforms the state-of-the-art approaches
Experimental data on Helically Coiled Oscillating Heat Pipe (HCOHP) design and thermal performance
Get PDFExperimental and derived data from three Helically Coiled Oscillating Heat Pipes (HCOHPs) charged with ethanol, methanol and deionized water working fluids respectively are presented. The data was obtained from prototypes of the HCOHPs fabricated out of copper and tested under laboratory conditions. The primary data presented covers the HCOHP aspects, charging of the working fluid and temperature measurements from Omega K-type Thermocouples installed on the evaporators, condensers, adiabatic sections, and on the cylindrical copper vessel integrated with it. The derived data covers the HCOHPs performances and thermal contact resistance experienced during laboratory testing. The data on the aspects and charging of the working fluid provides useful information for the validation of design parameters of other heat pipes. The measured temperature data and the derived performance data can used to validate the performance of heat pipes in other studies and to depict performance profiles in standard text and reference books. The nature of the data presented as a whole would be useful for comparative analysis involving heat pipes and other passive heat transfer devices
Good teachers: visions of values and virtues in university student metaphors
Get PDFGood teachers in university education embody combinations of continuity and change. In the first part here, university teaching is considered in Western philosophies and educational discourse to suggest teacher characteristics and meta-functions, but this article proposes wider internationalised dialogues within humanities which crucially take student views into account. In the second part, we analyse a database of 863 metaphors about teachers given by 439 university students in Malaysia, adopting a socio-cultural approach based on cognitive linguistics. This elicited metaphor analysis explores student views of “good” teachers expressed in such metaphors as “a good teacher is a burning candle” or “a piece of chalk”. Our analysis of metaphor entailments reveals meta-functions and virtues of good teachers which though absent in some official discourses, cohere with the educational philosophy of part one: they include cognitive, social/cultural, affective, moral/spiritual and aesthetic meta-functions. These emphasise the purposes of what teachers “do” and the character of what teachers “are”, as models for what students “do” and what they “become”. This gives challenging insights for teachers (and students) to self-cultivate virtues if these participant visions are taken seriously for learner-centred approaches to humanities in new balances of continuity and change
Stable and robust design of active disturbance-rejection current controller for permanent magnet machines in transportation systems
Get PDFActive disturbance-rejection control (ADRC) as a current control (CC) method for ac drive systems has been recently shown to have significant strengths. Its robustness to system uncertainties and its high disturbance-rejection capability render it an attractive control scheme for various mobile applications. Until now, however, all the known tuning methods available in literature are based on a number of assumptions that may lead to the degraded drive performance and even to the loss of stability. This article, thus, provides a rigorous analysis and proposes a new CC design method based on the ADRC technique. The design derives a generic closed-loop transfer function considering system delays and the dynamics of the extended state observer. Based on this analysis, a tuning method able to guarantee a set performance to avoid unstable operation is thus proposed. The effects of model uncertainties on the current loop system stability and robustness are also analyzed and reported. A tuning criterion to enhance system robustness and to improve its dynamic performance is developed and validated experimentally on a case study system
Synthesis of graphene: potential carbon precursors and approaches
Get PDFGraphene is an advanced carbon functional material with inherent unique properties that make it suitable for a wide range of applications. It can be synthesized through either the top–down approach involving delamination of graphitic materials or the bottom–up approach involving graphene assembly from smaller building units. Common top–down approaches are exfoliation and reduction while bottom–up approaches include chemical vapour deposition, epitaxial growth, and pyrolysis. A range of materials have been successfully used as precursors in various synthesis methods to derive graphene. This review analyses and discusses the suitability of conventional, plant- and animal-derived, chemical, and fossil precursors for graphene synthesis. Together with its associated technical feasibility and economic and environmental impacts, the quality of resultant graphene is critically assessed and discussed. After evaluating the parameters mentioned above, the most appropriate synthesis method for each precursor is identified. While graphite is currently the most common precursor for graphene synthesis, several other precursors have the potential to synthesize graphene of comparable, if not better, quality and yield. Thus, this review provides an overview and insights into identifying the potential of various carbon precursors for large-scale and commercial production of fit-for-purpose graphene for specific applications
Asymptotic solutions of the Helmholtz equation: generalised Friedlander-Keller ray expansions of fractional order
Get PDFApplications of a WKBJ-type `ray ansatz' to obtain asymptotic solutions of the Helmholtz equation in the high{frequency limit are now standard, and underpin the construction of `geometrical optics' ray diagrams in many electromagnetic, acoustic and elastic reflection, transmission and other scattering problems. These applications were subsequently extended by Keller to include other types of rays - called `diffracted' rays - to provide an accessible and impressively accurate theory which is relevant in wide-ranging sets of circumstances. Friedlander and Keller then introduced a modified ray ansatz to extend yet further the scope of ray theory and its applicability to certain other classes of diffraction problems (tangential ray incidence upon an obstructing boundary, for instance), and did so by the inclusion of an extra term proportional to a power of the wavenumber within the exponent of the initial ansatz. Our purpose here is to generalise this further still by the inclusion of several such terms, ordered in a natural sequence in terms of strategically-chosen fractional powers of the large wavenumber, and to derive a systematic sequence of boundary value problems for the coefficient phase functions that arise within this generalised exponent, as well as one for the leading-order amplitude occurring as a pre-exponential factor. One particular choice of fractional power is considered in detail, and waves with specified radially-symmetric or planar wavefronts are then analysed, along with a boundary value problem typifying two-dimensional radiation whereby arbitrary phase and amplitude variations are specified on a prescribed boundary curve. This theory is then applied to the scattering of plane and cylindrical waves at curved boundaries with small-scale perturbations to their underlying profile
Kinetic study of the pyrolysis of microalgae under nitrogen and CO2 atmosphere
Get PDFIn this study, three primary components of algae (lipid, carbohydrate and protein) and one microalgae (spirulina) were pyrolyzed using a thermogravimetric analyser (TGA) under nitrogen and CO2 atmosphere at four heating rates. It was found that protein decomposed first, followed by carbohydrate and then lipid. The kinetic study revealed that the lowest activation energy for the initiation of the pyrolysis of ovalbumin (protein) is ∼70 kJ/mol. Oil droplet showed higher activation energy of 266.5 kJ/mol during its pyrolysis in the CO2 atmosphere, which suggests that algal lipid is more difficult to decompose in the CO2 atmosphere. However, for the pyrolysis of cellulose (carbohydrate), the activation energy (∼310 kJ/mol) is similar under two different gas atmospheres tested. This study showed that CO2 atmosphere favors the pyrolysis of algae with high protein content and low lipid content, since the existence of CO2 promotes the cracking of VOCs (volatile organic compounds) as well as the reaction between VOCs and CO2
The geology of Tianshui‐Qin'an area of the western Loess Plateau and the chemical characteristics of its Neolithic pottery
Get PDFThe difference in the chemical compositions between Neolithic pottery from the eastern and western ends of the northern Chinese Loess Plateau has been known for some time and a number of possible explanations have been proposed. However, a full understanding of the difference is yet to be achieved. Based on recent geological studies of the Tianshui-Qin’an area on the western Loess Plateau, the present study establishes a logical connection between the chemical characteristics of Neolithic pottery from the western Loess Plateau and the primary sediments available in the area. Moreover, this study reveals that the chemical compositions of clay used for fine wares and coarse wares at Dadiwan also bear some clear differences. Based on these findings, the paper discusses possible clay selection methods by potters in the Neolithic western Loess Plateau to make their different wares based on the locales where suitable raw materials are available. The paper demonstrates that the raw materials available for pottery making on the eastern and western Loess Plateau differ significantly and this explains the marked difference in ceramic composition between the two locations
Automated classification metrics for energy modelling of residential buildings in the UK with open algorithms
Get PDFEstimating residential building energy use across large spatial extents is vital for identifying and testing effective strategies to reduce carbon emissions and improve urban sustainability. This task is underpinned by the availability of accurate models of building stock from which appropriate parameters may be extracted. For example, the form of a building, such as whether it is detached, semi-detached, terraced etc and its shape may be used as part of a typology for defining its likely energy use. When these details are combined with information on building construction materials or glazing ratio, it can be used to infer the heat transfer characteristics of different properties. However, these data are not readily available for energy modelling or urban simulation. Although this is not a problem when the geographic scope corresponds to a small area and can be hand-collected, such manual approaches cannot be easily applied at the city or national scale. In this paper, we demonstrate an approach that can automatically extract this information at the city scale using off-the-shelf products supplied by a National Mapping Agency. We present two novel techniques to create this knowledge directly from input geometry. The first technique is used to identify built form based upon the physical relationships between buildings. The second technique is used to determine a more refined internal/external wall measurement and ratio. The second technique has greater metric accuracy and can also be used to address problems identified in extracting the built form. A case study is presented for the City of Nottingham in the United Kingdom using two data products provided by the Ordnance Survey of Great Britain (OSGB): MasterMap and AddressBase. This is followed by a discussion of a new categorisation approach for housing form for urban energy assessment
Spatio-temporal pattern of land degradation from 1990 to 2015 in Mongolia
Get PDFLand degradation is an important environmental problem facing the world. "Land Degradation Neutrality" is one of the core indicators in the 15th goal of the "United Nations Sustainable Development Goals" for 2030. Mongolia is an important country for global land degradation. The increasingly serious land degradation has caused a direct impact on the ecosystem of the entire Mongolian plateau. We analyzed the patterns of land degradation and restoration during 1990-2010 and 2010-2015 and determined the driving forces behind the variations, by using fine resolution land cover data for the first time in Mongolia. The results showed that the spatial distribution of newly increased land degradation and restoration have a strong transitional nature. For the past 25 years, the trend of land change in Mongolia was dominated by land degradation. However, land degradation was accompanied by ongoing restoration of some land areas, and the capacity for land restoration has been gradually improved. This study discovers a series of typical land degradation and restoration regions and provides an interpretation of the driving forces in these areas. The joint effects of natural and socioeconomic factors have been found to result in land degradation and restoration in different regions
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