3,565 research outputs found
The role of a tribofilm and wear debris in the tribological behaviour of nanocrystalline Ni–Co electrodeposits
No full textThe tribofilm and debris generated from wear tests acting as a third body can make important contributions to a tribo-system. The effect of tribofilm on sliding friction and wear depends strongly on the applied sliding conditions, and it is still lack of understanding due to insufficient experimental studies. In the present research, the electrodeposited nanocrystalline Ni–Co coatings with different cobalt content were prepared. The worn surfaces as well as the wear debris were characterised by surface analysis techniques after dry sliding tests against a stainless steel ball. The tribofilms containing iron from the counterparts were formed on the worn surface of the coatings (less than 60 at.% Co), which exhibited high coefficients of friction and wear rates. No tribofilm or iron transfer from the pin was found on the Co-rich coatings (more than 70 at.% Co) but a dramatic friction reduction of 50% and improved wear resistance were experienced. The wear debris contains a mixture of face-centred cubic (fcc) metallic phase and fcc oxidised phase, irrespective of the coating composition. The oxidised debris cannot form an efficient lubricative film to promote separation of the sliding surfaces
Time-lapse helical X-ray computed tomography (CT) data of tensile fatigue damage in GFRP
No full textThe X-ray CT data here is published with the paper -
Wang, Y.; Mikkelsen, L.P.; Pyka, G.; Withers, P.J. Time-Lapse Helical X-ray Computed Tomography (CT) Study of Tensile Fatigue Damage Formation in Composites for Wind Turbine Blades. Materials 2018, 11, 2340.
https://doi.org/10.3390/ma11112340
More information about the data and the material can be found in the paper above.
If using the data here, please cite the above paper.
Contact details for author: Ying Wang, [email protected]</p
Preparation and performance of a novel multifunctional plasma electrolytic oxidation composite coating formed on magnesium alloy
No full textPlasma electrolytic oxidation (PEO) in an alkaline phosphate electrolyte was used to produce a novel multifunctional polytetrafluoroethylene (PTFE)-containing oxide composite coatings on AM60B magnesium alloys. The composition and microstructure of the PTFE-containing PEO coatings were analyzed by X-ray photoelectron spectroscope (XPS), X-ray diffraction (XRD), and scanning electron microscope (SEM). The electrochemical corrosion behavior, tribological properties, and wetting properties of the PTFE-containing PEO composite coatings were evaluated using potentiodynamic polarization measurements, a reciprocating ball-on-disk tribometer, and a contact angle meter, respectively. Results show that the PTFE-containing PEO composite coatings exhibited superior corrosion resistance, excellent self-lubricating property, and better hydrophobic property when compared with pure PEO coatings, and will be the attractive advanced materials for a wide range of functional applications
The destiny of a person in L.P. Karsavin’s philosophy of history
No full textIn the article analyses L.P. Karsavin’s concept of a person in his philosophy of history. Opens the specificity of Karsavin’s understanding of a person in the framework of Vl. Solovyov’s All-Unity and differences from Berdyaev’s personalism. The author comes to conclusion that Karsavin’s philosophy of history has personalistic character and in it reproduced the most systematic in Russian metaphysics experience of studying and understanding forms and types of personality in history of world and Russian culture
sj-docx-1-jdr-10.1177_00220345221098334 – Supplemental material for Assembly of Ultralong Hydroxyapatite Nanowires into Enamel-like Materials
No full textSupplemental material, sj-docx-1-jdr-10.1177_00220345221098334 for Assembly of Ultralong Hydroxyapatite Nanowires into Enamel-like Materials by Q.Q. Wang, L.P. Wu, S. Zhang, Y. Tao, Y.Z. Li, Q.L. Zhou, S.L. Zheng, C.Y. Cao, Z. Zhou and Q.L. Li in Journal of Dental Research</p
Advanced GPR data processing algorithms for detection of anti-personnel landmines
No full textGround Penetrating Radar (GPR) is seen as one of several promising technologies aimed to help mine detection. GPR is sensitive to any inhomogeneity in the ground. Therefore any APM regardless of the metal content can be detected. On the other hand, all the inhomogeneities, which do not represent mines, show up as a clutter in GPR images. Moreover, it is known that reflectivity of APM is often weaker than that of stones, pieces of shrapnel and barbed wire, etc. Altogether these factors cause GPR to produce unacceptably high false alarm rate whilst it reaches the 99.6% detection rate which is prescribed by an UN resolution as a standard for humanitarian demining. The main goal of the work presented in the thesis is reduction of the false alarm rate while keeping the 99.6% detection rate intact. To reach this goal a set of data processing algorithms is developed and organized into an unsupervised target detection scheme. These algorithms are dedicated to clutter suppression and simultaneous detection of APM signatures in both GPR raw data and images resulting from them. The developed algorithms constitute together the following achievements: - An unsupervised generalized likelihood ratio test-based feature fusion framework; - A waveform based target detection/clutter suppression; - Advanced methods for construction of GPR maps The unsupervised generalized likelihood ratio test based feature fusion framework, which has been suggested in this thesis, takes as input an arbitrary amount of confidence maps corresponding to training and testing sites. The output of the framework is a list of target locations. The framework uses training data which can come from independent and non-coincident measurements with different radars and even sensors. The data from each of the sensors are processed independently to result in several detection lists. Every detection in these lists is accompanied with one or several features each represented by a scalar number. A decision level fusion is applied to reconcile the lists i.e. to associate the detections in them with the appropriate physical locations. Then the binary hypothesis testing is executed for the reconciled locations separating them on clutter and target lists. The generalized likelihood ratio test is employed to this end. The feature pre-normalization via Johnson's transform in suggested by the author to be used prior the testing. It is shown in the thesis that such approach outperforms the direct generalized likelihood ratio testing ad. hoc. based fusion techniques. The waveform based target detection/clutter suppression algorithm, which detects disc-shaped APM in heavy clutter with low false alarm rate, has been developed by the author. The algorithm detects a class of low-metal APM with a cylindrical shape (such as PMN2, M14, and NR22 etc.) using just a single reference target return. It suppresses clutter responses from friendly objects while marking the presence of targets with sharp monopulses and preserving the spatial pattern inherent to localized objects. The algorithm is insensitive to the reflectivity and physical diameter of the target and also tolerates certain volatility in the properties of the hosting soil. This algorithm is superimposed with a focusing technique to further improve the mine detectability. A number of improved projection techniques, which allow better detection of APM in focused GPR images is also developed by the author. These utilize the prior knowledge on the character of the spatial correlation properties of target images and allow detection of the burial depth of the target. The algorithms suggested in the thesis were tested on the data acquired during two separate measurement campaigns held at the special facilities for testing of mine detection systems. It has been shown, that the fused multi-feature detection that uses the algorithms reported in this thesis, significantly decreases the false alarm rate in comparison to the previously published studies for the same minefields.Electrical Engineering, Mathematics and Computer Scienc
Signal processing of FMCW Synthetic Aperture Radar data
No full textIn the field of airborne earth observation there is special attention to compact, cost effective, high resolution imaging sensors. Such sensors are foreseen to play an important role in small-scale remote sensing applications, such as the monitoring of dikes, watercourses, or highways. Furthermore, such sensors are of military interest; reconnaissance tasks could be performed with small unmanned aerial vehicles (UAVs), reducing in this way the risk for one's own troops. In order to be operated from small, even unmanned, aircrafts, such systems must consume little power and be small enough to fulfill the usually strict payload requirements. Moreover, to be of interest for the civil market, cost effectiveness is mandatory. Frequency Modulated Continuous Wave (FMCW) radar systems are generally compact and relatively cheap to purchase and to exploit. They consume little power and, due to the fact that they are continuously operating, they can transmit a modest power, which makes them very interesting for military operations. Consequently, FMCW radar technology is of interest for civil and military airborne earth observation applications, specially in combination with high resolution Synthetic Aperture Radar (SAR) techniques. The novel combination of FMCW technology and SAR techniques leads to the development of a small, lightweight and cost-effective high resolution imaging sensor. SAR techniques have been successfully applied in combination with coherent pulse radars. Also the concept of synthetic aperture with FMCW sensors has already been put forward in literature, and some experimental systems have been described. However, the practical feasibility of an airborne FMCW SAR was not evident; the experimental sensors described in literature were, in fact, radars mounted on rail supports operating in ground SAR configurations and at short distances. The FMCW radars could perform measurements in each position of the synthetic aperture and then be moved to the next one. As in conventional pulse SAR systems, the stop-and-go approximation could be used; such an approximation assumes the radar platform stationary during the transmission of the electromagnetic pulses and the reception of the corresponding echoes. For airborne FMCW radars, however, the stop-and-go approximation can be not valid anymore because the platform is actually moving while continuously transmitting. A complete model for the deramped FMCW SAR signal was missing in the literature. In addition to the particular signal aspects relative to the combination of FMCW technology and SAR techniques, the use of FMCW radars for long range high resolution applications was not evident. In practical FMCW sensors, specially when using cheap components, the presence of unwanted non-linearities in the frequency modulation severely degrades the radar performances for long distances. Again, proper processing methods to overcome such limitation due to frequency non-linearities were not available to the scientific community. Therefore, the area of FMCW SAR airborne observation and related signal processing aspects was a very novel field of research. At the International Research Centre for Telecommunications and Radar (IRCTR) of the Delft University of Technology, a project was initiated to investigate the feasibility of FMCW SAR in the field of airborne earth observation and to develop proper processing algorithms to fully exploit the capability of such sensors. Within the framework of the project, the following novelties and main results have been reached and are presented in the thesis: Non-linearities correction. The author has developed a very novel processing solution, which completely solves the problem of the presence of frequency non-linearities in FMCW SAR. It corrects for the non-linearity effects for the whole range profile at once, and it allows a perfect range focussing, independently of the looking angle. The proposed method operates directly on the deramped data and it is very computationally efficient. A complete FMCW SAR signal model. The author has proposed a detailed analytical model for the FMCW SAR signal in the two-dimensional frequency domain. Based on this model, proper algorithms have been developed which guarantee the best performance when processing FMCW SAR data. Moving Target Indication (MTI) with frequency modulated CW SAR. Two SAR MTI methods are proposed. The first is based on the frequency slope diversity in the transmitted modulation by using linear triangular FMCW SAR, while the second makes use of the Doppler filtering properties of randomized SFCW modulations. First demonstration of an X-band FMCW SAR. A flight test campaign has been organized during the last part of 2005. The results were very successful. The feasibility of an operational FMCW SAR based on cheap components has been proved under practical circumstances. Thanks to the special algorithms developed, FMCW SAR images with a measured 45 cm times 25 cm resolution (including windowing) were obtained for the first time.Electrical Engineering, Mathematics and Computer Scienc
Adaptive OFDM and CDMA Algorithms for SISO and MIMO Channels
No full textThe objective of this thesis is to study adaptive modulation algorithms for Single Input Single Output (SISO) and Multiple Input Multiple Output (MIMO) channels. The adaptive modulation technique has the advantages of flexibility, providing high transmission quality and throughput; and it can lead to a smaller volume of radio and more applications. The major contribution of the author is discussed in the following paragraphs. To the best of the authorâs knowledge, the strategy and working procedures of the adaptive modulation technique have not yet been described in the literature. We propose strategies and work procedures for adaptive modulation in this dissertation. In addition, for the first time, it is proposed that the development of adaptive modulation consists of three stages, in which the adaptivity is taken to a higher level. We assert in this thesis that adaptive modulation algorithms involve two themes, i.e., channel and modulation. We analyze two types of channels: SISO and MIMO channels. We investigate the SISO channel in time, frequency, and space domains, which is efficient for designing adaptive modulation algorithms. Further, initially we propose three approaches as solutions to problems in each of the domains, i.e., adaptive techniques (time domain), OFDM (frequency domain), and MIMO technique (space domain). These three approaches are investigated in this thesis. We study the concept, structure, and characteristics of MIMO channels. The gains of three MIMO schemes and parameters influencing these gains are generalized. What is more, we introduce a new factor, the Rician K gain, to describe the MIMO gain with respect to that of SISO channels. In addition, we work out the SNR gains of these three MIMO schemes compared with SISO channels for a large SNR range, which have not been found in literature. This is indispensable for the design of adaptive modulation algorithms for MIMO channels. With regard to modulation, we list the parameters of OFDM and CDMA modulations for adaptive OFDM and adaptive CDMA algorithms to be designed. In order to obtain direct relationships between modulation parameters and throughput, we derive two throughput formulas, an OFDM formula and a CDMA formula. We show that the traditional commonly held belief that the subcarrier bandwidth influences transmission quality is true only if the channel RDS is constant. To explain this, we define a new parameter, PFR, as the product of subcarrier bandwidth and RDS. How this parameter works and by what factors it is limited are studied in this thesis. Subsequently, we propose three successful adaptive modulation algorithms, i.e., an adaptive OFDM algorithm for SISO channels, an adaptive OFDM algorithm for MIMO channels, and an adaptive CDMA algorithm for MIMO channels. Perfect channel estimation is assumed in our work. For the adaptive OFDM algorithms, we propose three subband settings. Remarkable throughput gains are obtained from all these adaptive modulation algorithms in simulations. We put forward the new idea of employing more than one MIMO scheme in a system and adapting these schemes using our adaptive modulation algorithms. Simulation results show that extra gains can be obtained by this method. The performance gains of our algorithms are dependent on the channel situation. The influence of channel parameters on these relative gains is investigated in this work as well. We introduce an SNR boundary matrix to set processing gains and modulation levels in our adaptive CDMA algorithm for MIMO channels.Electrical Engineering, Mathematics and Computer Scienc
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