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  • 251.
    Alvi, Sajid
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Akhtar, Farid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    High temperature tribology of CuMoTaWV high entropy alloy2019In: Wear of Materials, 2019, Vol. 426-427, p. 412-419Conference paper (Refereed)
    Abstract [en]

    An equiatomic high entropy alloy (HEA) CuMoTaWV was designed for room temperature to high temperature wear applications using spark plasma sintering of elemental powder mixture at 1400 °C. The sintered solid solution showed uniform distribution of elements in a BCC high entropy alloy phase along with V rich solid solution phase with an average hardness of 600 Hv and 900 Hv, respectively. Room temperature (RT) dry sliding wear tests, against alloy steel (700–880 Hv) for 200 m sliding distance at 5 N normal load, showed negligible wear of 5 × 10−7 mm/N m and a coefficient of friction (COF) of 0.5. Sliding wear characterization of sintered CuMoTaWV alloy against Si3N4 (1550 Hv) counter body from RT to 600 °C showed an increasing average COF of 0.45–0.67 from RT to 400 °C and then reducing to 0.54 at 600 °C. The wear rate was found to be lower at RT (4 × 10−3 mm3/N m) and 400 °C (5 × 10−3 mm3/N m), and slightly higher at 200 °C (2.3 × 10−2 mm3/N m) and 600 °C (4.5 × 10−2 mm3/N m). The CuMoTaWV alloy showed wear mechanisms specific to the test temperatures. The wear of CuMoTaWV alloy was governed by adhesive wear at RT and 200 °C and oxidative wear at 400 °C and 600 °C. The analyses of wear surfaces showed that the low wear rate at RT was due to the high hardness of the HEA, presence of V rich zones and formation of W and Ta tribofilm. At 400 °C, the formation of CuO tribolayer reduced the wear and hindered oxidation of wear track. At 600 °C, the wear rate increased due to oxidation of Cu, Ta and W. Moreover, the formation of lubricating elongated magneli phase V2O5 in V rich regions of CuMoTaWV alloy reduced the COF to 0.54.

  • 252.
    Alvi, Sajid
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Akhtar, Farid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    High temperature tribology of polymer derived ceramic composite coatings2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 15105Article in journal (Refereed)
    Abstract [en]

    Polymer derived ceramic (PDC) composite coatings were deposited on AISI 304 substrates using siloxane based preceramic polymer polymethlysilsquioxane (PMS) and ZrSi2 as active filler or Ag as passive filler. The tribological performance of the composite coatings was evaluated at room temperature and moderately high temperatures (150 °C, 200 °C, 300 °C and 400 °C). The composite coatings showed low coefficient of friction (COF), µ, from 0.08 to 0.2 for SiOC-ZrSi2 composite coatings, and from 0.02 to 0.3 for SiOC-Ag composite coatings, at room temperature with increasing normal load from 1 to 5 N. High temperature tribology tests showed high COF values from 0.4 to 1 but low wear for SiOC-ZrSi2 coating, and low COF from 0.2 to 0.3 for SiOC-Ag coatings at lower temperature ranges. Low load friction tests at room temperature showed negligible wear in SiOC-ZrSi2 coatings, suggesting good wear resistant and lubricating properties due to formation of t-ZrO2 and carbon. Low COF and high amount of wear was observed in SiOC-Ag composite coatings at room temperature due to high ductility of Ag and smearing of wear debris in the wear track. The coatings and wear tracks were characterized to evaluate the lubrication and wear behavior.

  • 253.
    Alzghoul, Ahmad
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Improving availability of industrial products through data stream mining2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Products of high quality are of great interest for industrial companies. The quality of a product can be considered in terms of production cost, operating cost, safety and product availability, for example. Product availability is a function of maintainability and reliability. Monitoring prevents unplanned stops, thus increasing product availability by decreasing needed maintenance. Through monitoring, failures can be detected and/or avoided. Detecting failures eliminates extra costs such as costs associated with machinery damage and dissatisfied customers, and time is saved since stops can be scheduled, instead of having unplanned stops. Product monitoring can be done through searching the data generated from sensors installed on products.Nowadays, the data can be collected at high rates as part of a data stream. Therefore, data stream management systems (DSMS) and data stream mining (DSM) are being used to control, manage and search the data stream. This work investigated how the availability of industrial products can be increased through the use of DSM and DSMS technologies.A review of the data stream mining algorithms and their applications in monitoring was conducted. Based on the review, a new data stream classification method, i.e. Grid-based classifier was proposed, tested and validated. Also, a fault detection system based on DSM and DSMS technologies was proposed. The proposed fault detection system was tested using data collected from Hägglunds Drives AB (HDAB) hydraulic motors. Thereafter, a data stream predictor was integrated into the proposed fault detection system to detect failures earlier, thus gaining more time for response actions. The modified fault detection system was tested and showed good performance. The results showed that the proposed fault detection system, which is based on DSM and DSMS technologies, achieved good performance (with classification accuracy around 95%) in detecting failures on time. Detecting failures on time prevents unplanned stops and may improve the maintainability of the industrial systems and, thus, their availability.

  • 254.
    Alzghoul, Ahmad
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Mining data streams to increase ‎industrial product availability2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Improving product quality is always of industrial interest. Product availability, a function of product maintainability and reliability, is an example of a measurement that can be used to evaluate product quality. Product availability and cost are two units which are especially important to manage in the context of the manufacturing industry, especially where industry is interested in selling or buying offers with increased service content. Industry in general uses different strategies for increasing equipment availability; these include: corrective (immediate or delayed) and preventive strategies. Preventive strategies may be further subdivided into scheduled and predictive (condition-based) maintenance strategies. In turn, predictive maintenance may also be subdivided into scheduled inspection and continuously monitored. The predictive approach can be achieved by early fault detection. Fault detection and diagnosis methods can be classified into three categories: data-driven, analytically based, and knowledge-based methods. In this thesis, the focus is mainly on fault detection and on data-driven models.Furthermore, industry is generating an ever-increasing amount of data, which may eventually become impractical to store and search, and when the data rate is increasing, eventually impossible to store. The ever-increasing amount of data has prompted both industry and researchers to find systems and tools which can control the data on the fly, as close to real-time as possible, without the need to store the data itself. Approaches and tools such as Data Stream Mining (DSM) and Data Stream Management Systems (DSMS) become important. For the work reported in this thesis, DSMS and DSM have been used to control, manage and search data streams, with the purpose of supporting increased availability of industrial products.Bosch Rexroth Mellansel AB (formerly Hägglunds Drives AB) has been the industrial partner company during the course of the work reported in this thesis. Related data collection concerning the functionality of the BRMAB hydraulic system has been performed in collaboration with other researchers in Computer Aided Design at Luleå University of Technology.The research reported in this thesis started with a review of data stream mining algorithms and their applications in monitoring. Based on the review, a data stream classification method, i.e. Grid-based classifier, was proposed, tested and validated (Paper A). Also, a fault detection system based on DSM and DSMS was proposed and tested, as reported in Paper A. Thereafter, a data stream predictor was integrated into the proposed fault detection system to detect failures earlier, thus demonstrating how data stream prediction can be used to gain more time for proactive response actions by industry (Paper B). Further development included an automatic update method which allows the proposed fault detection system to be able to overcome the problem of concept drift (Paper E). The proposed and modified fault detection systems were tested and verified using data collected in collaboration with Bosch Rexroth Mellansel AB (BRMAB). The requirements for the proposed fault detection system and how it can be used in product development and design of the support system were also discussed (Paper C). In addition, the performance of a knowledge-based method and a data- driven method for detecting failures in high-volume data streams from industrial equipment have been compared (Paper D). It was found that both methods were able to detect all faults without any false alert. Finally, the possible implications of using cloud services for supporting industrial availability are discussed in Paper F. Further discussions regarding the research process and the relations between the appended papers can be found in Chapter 2, Figure 4 and in Chapter 5, Figure 21.The results showed that the proposed and modified fault detection systems achieved good performance in detecting and predicting failures on time (see Paper A and Paper B). In Paper C, it is shown how data stream management systems may be used to increase product availability awareness. Also, both the data-driven method and the knowledgebased method were suitable for searching data streams (see Paper D). Paper E shows how the challenge of concept drift, i.e. the situation in which the statistical properties of a data stream change over time, was turned to an advantage, since the authors were able to develop a method to automatically update the safe operation limits of the one-class data-driven models.In general, detecting faults and failures on time prevents unplanned stops and may improve both maintainability and reliability of industrial systems and, thus, their availability (since availability is a function of maintainability and reliability). By the results, this thesis demonstrates how DSM and DSMS technologies can be used to increase product availability and thereby increase product quality in terms of availability.

  • 255. Alzghoul, Ahmad
    et al.
    Backe, Björn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Löfstrand, Magnus
    Uppsala universitet.
    Byström, Arne
    Uppsala University, Department of Information Technology, Division of Computing Science.
    Liljedahl, Bengt
    Bosch Rexroth Mellansel AB.
    Comparing a knowledge-based and a data-driven method in querying data streams for system fault detection: A hydraulic drive system application2014In: Computers in industry (Print), ISSN 0166-3615, E-ISSN 1872-6194, Vol. 65, no 8, p. 1126-1135Article in journal (Refereed)
    Abstract [en]

    The field of fault detection and diagnosis has been the subject of considerable interest in industry. Fault detection may increase the availability of products, thereby improving their quality. Fault detection and diagnosis methods can be classified in three categories: data-driven, analytically based, and knowledge-based methods. In this work, we investigated the ability and the performance of applying two fault detection methods to query data streams produced from hydraulic drive systems. A knowledge-based method was compared to a data-driven method. A fault detection system based on a data stream management system (DSMS) was developed in order to test and compare the two methods using data from real hydraulic drive systems. The knowledge-based method was based on causal models (fault trees), and principal component analysis (PCA) was used to build the data-driven model. The performance of the methods in terms of accuracy and speed, was examined using normal and physically simulated fault data. The results show that both methods generate queries fast enough to query the data streams online, with a similar level of fault detection accuracy. The industrial applications of both methods include monitoring of individual industrial mechanical systems as well as fleets of such systems. One can conclude that both methods may be used to increase industrial system availability

  • 256.
    Alzghoul, Ahmad
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Löfstrand, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Increasing availability of industrial systems through data stream mining2011In: Computers & industrial engineering, ISSN 0360-8352, E-ISSN 1879-0550, Vol. 60, no 2, p. 195-205Article in journal (Refereed)
    Abstract [en]

    Improving industrial product reliability, maintainability and thus availability is a challenging task for many industrial companies. In industry, there is a growing need to process data in real time, since the generated data volume exceeds the available storage capacity. This paper consists of a review of data stream mining and data stream management systems aimed at improving product availability. Further, a newly developed and validated grid-based classifier method is presented and compared to one-class support vector machine (OCSVM) and a polygon-based classifier.The results showed that, using 10% of the total data set to train the algorithm, all three methods achieved good (>95% correct) overall classification accuracy. In addition, all three methods can be applied on both offline and online data.The speed of the resultant function from the OCSVM method was, not surprisingly, higher than the other two methods, but in industrial applications the OCSVMs' comparatively long time needed for training is a possible challenge. The main advantage of the grid-based classification method is that it allows for calculation of the probability (%) that a data point belongs to a specific class, and the method can be easily modified to be incremental.The high classification accuracy can be utilized to detect the failures at an early stage, thereby increasing the reliability and thus the availability of the product (since availability is a function of maintainability and reliability). In addition, the consequences of equipment failures in terms of time and cost can be mitigated.

  • 257.
    Alzghoul, Ahmad
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Löfstrand, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Backe, Björn
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Data stream forecasting for system fault prediction2012In: Computers & industrial engineering, ISSN 0360-8352, E-ISSN 1879-0550, Vol. 62, no 4, p. 972-978Article in journal (Refereed)
    Abstract [en]

    Competition among today’s industrial companies is very high. Therefore, system availability plays an important role and is a critical point for most companies. Detecting failures at an early stage or foreseeing them before they occur is crucial for machinery availability. Data analysis is the most common method for machine health condition monitoring. In this paper we propose a fault-detection system based on data stream prediction, data stream mining, and data stream management system (DSMS). Companies that are able to predict and avoid the occurrence of failures have an advantage over their competitors. The literature has shown that data prediction can also reduce the consumption of communication resources in distributed data stream processing.In this paper different data-stream-based linear regression prediction methods have been tested and compared within a newly developed fault detection system. Based on the fault detection system, three DSM algorithms outputs are compared to each other and to real data. The three applied and evaluated data stream mining algorithms were: Grid-based classifier, polygon-based method, and one-class support vector machines (OCSVM).The results showed that the linear regression method generally achieved good performance in predicting short-term data. (The best achieved performance was with a Mean Absolute Error (MAE) around 0.4, representing prediction accuracy of 87.5%). Not surprisingly, results showed that the classification accuracy was reduced when using the predicted data. However, the fault-detection system was able to attain an acceptable performance of around 89% classification accuracy when using predicted data.

  • 258.
    Alzghoul, Ahmad
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Löfstrand, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Karlsson, Lennart
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Karlberg, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Data stream mining for increased functional product availability awareness2011In: Functional Thinking for Value Creation: Proceedings of the 3rd CIRP International Conference on Industrial Product Service Systems, Technische Universität Braunschweig, Braunschweig, Germany, May 5th - 6th, 2011 / [ed] Jürgen Hesselbach; Christoph Herrmann, Berlin: Encyclopedia of Global Archaeology/Springer Verlag, 2011, p. 237-241Conference paper (Refereed)
    Abstract [en]

    Functional Products (FP) and Product Service Systems (PSS) may be seen as integrated systems comprising hardware and support services. For such offerings, availability is key. Little research has been done on integrating Data Stream Management Systems (DSMS) for monitoring (parts of) a FP to improve system availability. This paper introduces an approach for how data stream mining may be applied to monitor hardware being part of a Functional Product. The result shows that DSMS have the potential to significantly support continuous availability awareness of industrial systems, especially important when the supplier is to supply a function with certain availability.

  • 259.
    Amer, Eynas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Pulsed laser ablation studied using digital holographic interferometry2008Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Pulsed digital holographic interferometry has been used to investigate the plume and the shock wave generated in the ablation process of a Q-switched Nd-YAG (lambda= 1064 nm and pulse duration = 12 ns) laser pulse on a polycrystalline Boron Nitride (PCBN) target under atmospheric air pressure. A special set-up based on using two synchronised wavelengths from the same laser for simultaneous processing and measurement has been used. Digital holograms were recorded for different time delays using collimated laser light (lambda= 532 nm) passed through the volume along the target. Numerical data of the integrated refractive index field were calculated and presented as phase maps showing the propagation of the shock wave and the plume generated by the process. Radon inversion has been used to estimate the 3D refractive index fields measured from the projections assuming rotational symmetry. Verification of the point explosion model has been done. The amount of released energy i.e. the part of the incident energy of the laser pulse that is eventually converted to a shock wave has been estimated. Shock wave front densities have been calculated from the reconstructed refractive index fields using the Gladstone-Dale equation. A comparison of the shock front density calculated from the reconstructed data and that calculated using the point explosion model at different time delays has been done. The comparison shows quite good agreement between the model and the experimental data. Finally the reconstructed refractive index field has been used to estimate the electron number density distribution within the laser induced plasma. The results show that pulsed digital holographic interferometry is a promising technique to study laser ablation processes. Different materials and laser parameters like wavelength, focusing, number of pulses can be studied in combinations with other techniques.

  • 260.
    Amer, Eynas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Pulsed laser ablation studied using digital holography2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Pulsed digital holographic interferometry has been used to study the plume and the shock wave generated in the laser ablation process on different targets under atmospheric air pressure. A pulsed Nd-YAG laser system (pulse duration 12 ns) has been used both for ablating the material (wavelength 1064 nm) and for measurement (wavelength 532 nm). Digital holograms were recorded for different time delays using collimated laser light passed through the volume along the target. Numerical data of the integrated refractive index field were calculated and presented as phase maps. The Radon inversion has been used to estimate the 3D refractive index fields measured from the projections assuming rotational symmetry. Intensity maps have been calculated from the recorded digital holograms and used to calculate the attenuation of the probing laser beam by the ablated plume. Qualitative and quantitative information have been extracted from both the phase map and the intensity map to help describing the laser ablation process. Also 3D information about the induced plume has been obtained by numerical reconstruction of the digital holograms at different planes along the plume. The amount of released energy due to laser impact on a PCBM target has been estimated using the point explosion model. The released energy is normalized by the incident laser pulse energy and the energy conversion efficiency between the laser pulse and the target has been calculated and it seems to be constant around 80 %. The 3D refractive index fields have been used to calculate the shock wave front density and the electron number density distribution within the induced plasma. The electron number densities are found to be in the order of 1018 cm-3 and decay at a rate of 3x1015 electrons/cm3ns. The effect of the laser spot diameter on the shock wave generated in the ablation process of a Zn target has been studied. The induced shock wave has an ellipsoidal shape that approaches a sphere for decreasing spot diameter. A model was developed that approaches the density distribution that facilitates the derivation of the particle velocity field. The method provides quantitative results that are discussed; in particular a comparison with the point explosion theory. The effect of the physical properties of the target on the laser ablation process has been studied. The comparison of the laser ablation of Zn and Ti shows that different laser ablation mechanisms are observed for the same laser settings and surrounding gas. At a laser fluence of 5 J/cm2, phase explosion appears to be the ablation mechanism in case of Zn, while for Ti normal vaporisation seems to be the dominant mechanism. The results show that pulsed digital holographic interferometry is a promising technique to give a physical picture and increase the understanding of the laser ablation process in a time resolved manner.

  • 261.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Edenharder, Stefan
    Institut für Technische Optik, Universität Stuttgart.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Stimulated Raman scattering detection for chemically specific time-resolved imaging of gases2016In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 24, no 9, p. 9984-9993Article in journal (Refereed)
    Abstract [en]

    stimulated Raman scattering (SRS) imaging technique based on spatial modulation of the pump beam has been used to study gases. The SRS gain signal was separated from the Stokes beam background in the spatial frequency domain. The SRS signal shows linear behaviour with the gas pressure at a range from 1.0 to 8.0 bars. The signal is linearly proportional to the pump beam intensity while it is enhanced with increasing the Stokes beam intensity to a certain limit than it saturates. Further, the chemical specificity of the technique has been investigated. Two sharp peaks with line width at half maximum of about 0.30 nm have been obtained at Stokes beam wavelengths of 629.93 nm and 634.05 nm corresponding to the methane and ethylene gases, respectively. The results show that SRS imaging is a promising technique to provide chemical specificity as well as spatial and temporal information of gaseous species

  • 262.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Edenharder, Stefan
    Institut für Technische Optik, Universität Stuttgart.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Stimulated Raman scattering holography for time-resolved imaging of methane gas2016In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 55, no 13, p. 3429-3434Article in journal (Refereed)
    Abstract [en]

    In this paper, pulsed digital holographic detection is coupled to the stimulated Raman scattering (SRS) process for imaging gases. A Q-switched Nd-YAG laser (532 nm) has been used to pump methane gas (CH4) at pressures up to 12 bars. The frequency-tripled (355 nm) beam from the same laser was used to pump an optical parametric oscillator (OPO). The Stokes beam (from the OPO) has been tuned to 629.93 nm so that the frequency difference between the pump (532 nm) and the Stokes beams fits a Raman active vibrational mode of the methane molecule (2922 cm(-1)). The pump beam has been spatially modulated with fringes produced in a Michelson interferometer. The pump and the Stokes beams were overlapped in time, space, and polarization on the gas molecules, resulting in a stimulated Raman gain of the Stokes beam and a corresponding loss of the pump beam through the SRS process. The resulting gain of the Stokes beam has been detected using pulsed digital holography by blending it with a reference beam on the detector. Two holograms of the Stokes beam, without and with the pump beam fringes present, were recorded. Intensity maps calculated from the recorded digital holograms showed amplification of the Stokes beam at the position of overlap with the pump beam fringes and the gas molecules. The gain of the Stokes beam has been separated from the background in the Fourier domain. A gain of about 4.5% at a pump beam average intensity of 4 MW/cm(2) and a Stokes beam intensity of 0.16 MW/cm(2) have been recorded at a gas pressure of 12 bars. The gain decreased linearly with decreasing gas pressure. The results show that SRS holography is a promising technique to pinpoint a specific species and record its spatial and temporal distribution

  • 263.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Sjödahl, Mikael
    Impact of an extended source in laser ablation using pulsed digital holographic interferometry and modelling2009In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 255, no 21, p. 8917-8925Article in journal (Refereed)
    Abstract [en]

    Pulsed digital holographic interferometry has been used to study the effect of the laser spot diameter on the shock wave generated in the ablation process of an Nd:YAG laser pulse on a Zn target under atmospheric pressure. For different laser spot diameters and time delays, the propagation of the expanding vapour and of the shock wave were recorded by intensity maps calculated using the recorded digital holograms. From the latter phase maps, the refractive index and the density field can be derived. A model was developed that approaches the density distribution, in particular the ellipsoidal expansion characteristics. The induced shock wave has an ellipsoid shape that approaches a sphere for decreasing spot diameter. The ellipsoidal shock waves have almost the same centre offset towards the laser beam and the same aspect ratio for different time steps. The model facilitates the derivation of the particle velocity field. The method provides valuable quantitative results that are discussed, in particular in comparison with the simpler point source explosion theory.

  • 264.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Shaer, M. El
    Department of Engineering Physics and Mathematics, Faculty of Engineering, Zagazig University.
    Comparison of the laser ablation process on Zn and Ti using pulsed digital holographic interferometry2010In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 256, no 14, p. 4633-4641Article in journal (Refereed)
    Abstract [en]

    Pulsed digital holographic interferometry has been used to compare the laser ablation process of a Q-switched Nd-YAG laser pulse (wavelength 1064 nm, pulse duration 12 ns) on two different metals (Zn and Ti) under atmospheric air pressure. Digital holograms were recorded for different time delays using collimated laser light (532 nm) passed through the volume along the target. Numerical data of the integrated refractive index field were calculated and presented as phase maps. Intensity maps were calculated from the recorded digital holograms and are used to calculate the attenuation of the probing laser beam by the ablated plume. The different structures of the plume, namely streaks normal to the surface for Zn in contrast to absorbing regions for Ti, indicates that different mechanisms of laser ablation could happen for different metals for the same laser settings and surrounding gas. At a laser fluence of 5 J/cm2, phase explosion appears to be the ablation mechanism in case of Zn, while for Ti normal vaporisation seems to be the dominant mechanism.

  • 265.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Ramser, Kerstin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Measurement of selective species concentration using spectroscopic holography2018In: Speckle 2018: VII International Conference on Speckle Metrology / [ed] M. Kujawińska ; L. R. Jaroszewicz, SPIE - International Society for Optical Engineering, 2018, Vol. 10834, article id 108340PConference paper (Refereed)
    Abstract [en]

    Spectroscopic holography refers to techniques in which the detected hologram contains information about specific species in the medium under study. In general, at least two lasers are required with wavelengths chosen carefully to fit the interaction process utilized. In this process, energy from the shorter wavelength laser beam is transferred to the longer wavelength coherently through the process of stimulated emission. Two interaction mechanisms are considered; Stimulated Laser Induced Fluorescence (LIF) and Stimulated Raman Scattering (SRS), which both are species specific with the ability of coherent interaction. In this paper, the fundamental properties of spectroscopic holography is presented and demonstrated with a few idealized experiments. These validation experiments are performed in a gas chamber in which different gases may be blended and the gas pressure changed between 1-12 bars. In addition, two examples of applications are presented. In the first set of experiments, LIF holography is used to image light absorption and laser heating in a dye simultaneously. The second set of experiments is performed in a ow of methane gas. It is demonstrated that the combination of holographic phase measurements and SRS gain images may be used for calibration. This calibration may further be used to measure absolute concentration in a burning flame.

  • 266.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Laser-ablation-induced refractive index fields studied using pulsed digital holographic interferometry2009In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 47, no 7-8, p. 793-799Article in journal (Refereed)
    Abstract [en]

    Pulsed digital holographic interferometry has been used to investigate the plume and the shock wave generated in the ablation process of a Q-switched Nd-YAG (λ=1064 nm and pulse duration=12 ns) laser pulse on a polycrystalline boron nitride (PCBN) target under atmospheric air pressure. A special setup based on two synchronised wavelengths from the same laser for simultaneous processing and measurement has been used. Digital holograms were recorded for different time delays using collimated laser light (λ=532 nm) passed through the volume along the target. Numerical data of the integrated refractive index field were calculated and presented as phase maps showing the propagation of the shock wave and the plume generated by the process. Radon inversion has been used to estimate the 3D refractive index fields measured from the projections assuming rotational symmetry. The shock wave density has been calculated using the point explosion model and the shock wave condition equation and its behaviour with time at different power densities ranging from 1.4 to 9.1 GW/cm2 is presented. Shock front densities have been calculated from the reconstructed refractive index fields using the Gladstone-Dale equation. A comparison of the shock front density calculated from the reconstructed data and that calculated using the point explosion model at different time delays has been done. The comparison shows quite good agreement between the model and the experimental data. Finally the reconstructed refractive index field has been used to estimate the electron number density distribution within the laser-induced plasma. The electron number density behaviour with distance from the target at different power densities and its behaviour with time are shown. The electron number densities are found to be in the order of 1018 cm-3 and decay at a rate of 3×1015 electrons/cm3 ns.

  • 267.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Pulsed laser ablation studied using digital holographic interferometry2009In: Svenska mekanikdagarna: Södertälje 2009, Stockholm: Svenska nationalkommittén för mekanik , 2009, p. 87-Conference paper (Other academic)
  • 268.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Shock wave generation in laser ablation studied using pulsed digital holographic interferometry2008In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 41, no 21Article in journal (Refereed)
    Abstract [en]

    Pulsed digital holographic interferometry has been used to study the shock wave induced by a Q-switched Nd-YAG laser (λ = 1064 nm and pulse duration 12 ns) on a polycrystalline boron nitride (PCBN) ceramic target under atmospheric air pressure. A special setup based on using two synchronized wavelengths from the same laser for processing and measurement simultaneously has been introduced. Collimated laser light (λ = 532 nm) passed through the volume along the target and digital holograms were recorded for different time delays after processing starts. Numerical data of the integrated refractive index field were calculated and presented as phase maps showing the propagation of the shock wave generated by the process. The location of the induced shock wave front was observed for different focusing and time delays. The amount of released energy, i.e. the part of the incident energy of the laser pulse that is eventually converted to a shock wave has been estimated using the point explosion model. The released energy is normalized by the incident laser pulse energy and the energy conversion efficiency between the laser pulse and PCBN target has been calculated at different power densities. The results show that the energy conversion efficiency seems to be constant around 80% at high power densities.

  • 269.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Single-shot polarization digital holography for recording stimulated Raman scattering signal for time-resolved measurement of gaseous species2017In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 56, no 36, p. 10016-10023Article in journal (Refereed)
    Abstract [en]

    The stimulated Raman scattering (SRS) process is sensitive to the relation between the polarization direction of the two laser beams (the pump and the Stokes) that generate it. In this paper, we made use of the polarization sensitivity of the SRS process and used polarization-resolved pulsed digital holography to record the signal from one single-shot hologram. The pump beam polarization was kept vertical, while the Stokes beam polarization was 45 deg. The two polarization components of the Stokes beam were recorded in a single hologram by blending the Stokes beam with two reference beams with orthogonal polarization on the detector. The two components of the Stokes beam were separated in the Fourier domain, and the corresponding intensity maps were calculated. The vertically polarized component of the Stokes beam was amplified due to the SRS process, while the horizontal component experienced no gain. The difference between the vertically and horizontally polarized intensity maps, respectively, was calculated and Fourier transformed to separate the gain signal in the spatial frequency domain. The method was demonstrated on methane (CH4) gas at a pressure of 12 bars. Results show that SRS polarization holography is a promising technique for recording the SRS signal from one single-shot hologram for time-resolved monitoring of specific species. 

  • 270.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Stimulated laser induced fluorescence holography for imaging fluorescent species2013In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 311, p. 124-128Article in journal (Refereed)
    Abstract [en]

    In this paper pulsed digital holographic detection is coupled to the stimulated laser induced fluorescence (LIF) effect for imaging fluorescent species. A frequency tripled Q-switched Nd-YAG laser (wavelength 355 nm, pulse duration 12 ns) has been used to pump Coumarin 153 dye solved in ethanol. Simultaneously a frequency doubled pulse (532 nm) from the same laser is used to probe the solvent resulting in a gain through stimulated emission. The resulting gain of the probe beam is recorded using digital holography by blending it with a reference beam on the detector. Intensity maps were calculated from the recorded digital holograms and used to calculate the gain of the probe beam due to stimulated fluorescence emission which is coupled to the concentration of the dye. The results show that the amplification of the probe beam (532 nm) due to stimulated LIF emission is seen in the intensity maps. The gain is about 40% at a dye concentration of 0.32 g/L and decreases to be about 20% at a dye concentration of 0.04 g/L for a probe beam energy density of 0.1 mJ/cm2. Spectroscopic measurements have been carried out to confirm the holographic results. The results show that stimulated LIF holography is a promising technique for quantitative imaging of fluorescent species.

  • 271.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Stimulated Raman scattering imaging for studying specific species2015In: SPECKLE 2015: VI International Conference on Speckle Metrology : 24-26 August 2015, Guanajuato, México / [ed] Fernando Mendoza Santoyo, Washington: SPIE - International Society for Optical Engineering, 2015, article id 96600VConference paper (Refereed)
    Abstract [en]

    The stimulated Raman scattering (SRS) signal in diffuse light has been recorded using an optical imaging technique based on spatial modulation. A frequency doubled Q-switched Nd-YAG laser (wavelength 532 nm) has been used to pump a polymethyl methacrylate (PMMA) cylinder. The frequency tripled (355 nm) beam from the same laser is used to pump an optical parametric oscillator (OPO). The Stokes beam (from the OPO) has been tuned to 631.27 nm so that the frequency difference between the pump and the Stokes beams fits a Raman active vibrational mode of the PMMA molecule (2956 cm-1). The two laser beams were overlapped in time and space on a PMMA cylinder resulting in a gain of the Stokes beam through the SRS process of about 4.0 %. For separating the SRS signal, the pump beam was spatially modulated with fringes produced in a Michelson interferometer. The gain of the Stokes beam due to SRS was separated from the Stokes beam background in the Fourier domain. The intensity image has been calculated from an inverse Fourier transform of the separated gain signal. The intensity image shows a gain of the Stokes beam at the area of overlap between the pump beam fringes and the Stokes beam compared to the undisturbed surrounding. The results show that spatial modulation of the pump beam is a promising method to separate the weak SRS signal from the Stokes beam background. This technique can be applied to pin-point specific species and record its spatial and temporal distribution

  • 272.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Stimulated Raman scattering signals recorded by the use of an optical imaging technique2015In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 54, no 20, p. 6377-6385Article in journal (Refereed)
    Abstract [en]

    In this paper, stimulated Raman scattering (SRS) signals have been recorded by an optical imaging technique that is based on spatial modulation. A frequency doubled Q-switched Nd:YAG laser (532 nm) was used to pump a polymethyl methacrylate (PMMA) target. The frequency tripled (355 nm) beam from the same laser was used to pump an optical parametric oscillator (OPO). The Stokes beam (from the OPO) was tuned to 631.27 nm so that the frequency difference between the pump and the Stokes beams fit the Raman active vibrational mode of the PMMA molecule (2956 cm(-1)). The pump beam has been spatially modulated with fringes produced in a Michelson interferometer. The pump and the Stokes beams were overlapped on the target resulting in a gain of the Stokes beam of roughly 2.5% and a corresponding loss of the pump beam through the SRS process. To demodulate the SRS signal, two images of the Stokes beam without and with the pump beam fringes present were recorded. The difference between these two images was calculated and Fourier transformed. Then, the gain of the Stokes beam was separated from the background in the Fourier domain. The results show that spatial modulation of the pump beam is a promising method to separate the weak SRS signal from the background.

  • 273.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    UV laser interaction with a fluorescent dye solution studied using pulsed digital holography2013In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, no 21, p. 25316-25323Article in journal (Refereed)
    Abstract [en]

    A frequency tripled Q-switched Nd-YAG laser (wavelength 355 nm, pulse duration 12 ns) has been used to pump Coumarin 153 dye solved in ethanol. Simultaneously, a frequency doubled pulse (532 nm) from the same laser is used to probe the solvent perpendicularly resulting in a gain through stimulated laser induced fluorescence (LIF) emission. The resulting gain of the probe beam is recorded using digital holography by blending it with a reference beam on the detector. Two digital holograms without and with the pump beam were recorded. Intensity maps were calculated from the recorded digital holograms and used to calculate the gain of the probe beam due to the stimulated LIF. In addition numerical data of the local temperature rise was calculated from the corresponding phase maps using Radon inversion. It was concluded that about 15% of the pump beam energy is transferred to the dye solution as heat while the rest is consumed in the radiative process. The results show that pulsed digital holography is a promising technique for quantitative study of fluorescent species

  • 274.
    Amer, Eynas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Stenvall, Jonas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Stimulated LIF studied using pulsed digital holography and modelling2013In: Optical Measurement Systems for Industrial Inspection VIII / [ed] Peter H. Lehmann; Wolfgang Osten; Armando Albertazzi, SPIE - International Society for Optical Engineering, 2013Conference paper (Refereed)
    Abstract [en]

    A frequency tripled Q-switched Nd-YAG laser (wavelength 355 nm, pulse duration 12 ns) has been used to pump Coumarin 153 dye solved in ethanol. The laser induced fluorescence (LIF) spectrum has been recorded using a spectrometer at different dye concentrations. The frequency doubled 532 nm beam from the same laser is used as a probe beam to pass through the excited volume of the dye. Because of stimulated emission an increase of the probe (532 nm) beam energy is recorded and a reduction of the spontaneous fluorescence spectrum intensity is observed. A model was developed that approaches the trend of the gain as a function of the probe beam energy at low dye concentrations (less than 0.08 g/L). The stimulated LIF is further recorded using digital holography. Digital holograms were recorded for different dye concentrations using collimated laser light (532 nm) passed through the dye volume. Two holograms without and with the UV laser beam were recorded. Intensity maps were calculated from the recorded digital holograms and are used to calculate the gain of the green laser beam due to the stimulated fluorescence emission which is coupled to the dye concentration. The gain of the coherent 532 nm beam is seen in the intensity maps and its value is about 40% for a dye concentration of 0.32 g/L and decreases with the decrease of the dye concentration. The results show that pulsed digital holography can be coupled to the stimulated LIF effect for imaging fluorescent species

  • 275.
    Ameur, Yacin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Near-boundary asymptotics for correlation kernels2013In: Journal of Geometric Analysis, ISSN 1050-6926, E-ISSN 1559-002X, Vol. 23, no 1, p. 73-95Article in journal (Refereed)
    Abstract [en]

    We discuss asymptotic formulas for the correlation kernel corresponding to a (more or less) general potential Q in the plane. If Kn is such a kernel, there is a known asymptotic formula Kn(z, z)=nΔQ(z)+B1(z)+n-1B2(z)+⋯ valid for z in the interior of a certain compact set known as the "droplet" corresponding to Q (on which ΔQ>0). On the other hand, if z is in the exterior of the droplet, Kn(z, z) converges to zero exponentially in n. Results of this type are useful in random matrix theory and conformal field theory; they have recently been used to prove the Gaussian field convergence in the interior of the droplet for fluctuations of eigenvalues of random normal matrices. To be able to extend such results beyond the interior, it becomes necessary to have a certain uniformity of estimates as z approaches the boundary either from the interior or from the exterior. Such estimates have to our knowledge hitherto not been known on a rigorous level. This note intends to fill this gap. We will consider applications in later publications. Our treatment of the (interior) asymptotics relies in an essential way on previous work due to Berman, Berndtsson, and Sjöstrand (Ark. Mat. 46, 2008), and Berman (Indiana Univ. Math. J. 58, 2009). We hope that this note can to some extent be regarded as a contribution to that work.

  • 276.
    Ameur, Yacin
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Hedenmalm, Håkan
    Royal Institute of Technology, Department of Mathematics.
    Makarov, Nikolai
    CALTECH, Department of Mathematics, Pasadena.
    Fluctuations of eigenvalues of random normal matrices2011In: Duke mathematical journal, ISSN 0012-7094, E-ISSN 1547-7398, Vol. 159, no 1, p. 31-81Article in journal (Refereed)
    Abstract [en]

    In this article, we consider a fairly general potential in the plane and the corresponding Boltzmann-Gibbs distribution of eigenvalues of random normal matrices. As the order of the matrices tends to infinity, the eigenvalues condensate on a certain compact subset of the plane-the "droplet." We prove that fluctuations of linear statistics of eigenvalues of random normal matrices converge on compact subsets of the interior of the droplet to a Gaussian field, and we discuss various ramifications of this result.

  • 277.
    Amin, Sidra
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. National Centre of Excellence in Analytical Chemistry, University of Sindh, Jamshoro, Pakistan.Department of Chemistry, Shaheed Benazir Bhutto University, Shaheed Benazirabad, Pakistan.
    Tahira, Aneela
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Solangi, Amber
    National Centre of Excellence in Analytical Chemistry, University of Sindh, Jamshoro, Pakistan.
    Beni, Valerio
    RISE Acreo, Research Institute of Sweden, Norrköping, Sweden.
    Morante, J.R
    Catalonia Institute for Energy Research (IREC), Barcelona, Spain.
    Liu, Xianjie
    Department of Physics, Chemistry and Biology, Surface Physics and Chemistry, Linköping University, Faculty of Science & Engineering, Sweden.
    Falhman, Mats
    Department of Physics, Chemistry and Biology, Surface Physics and Chemistry, Linköping University, Faculty of Science & Engineering, Sweden.
    Mazzaro, Raffaello
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ibupoto, Zafar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Institute of Chemistry, University of Sindh, Jamshoro, Pakistan.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    A practical non-enzymatic urea sensor based on NiCo2O4 nanoneedles2019In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 9, no 25, p. 14443-14451Article in journal (Refereed)
    Abstract [en]

    We propose a new facile electrochemical sensing platform for determination of urea, based on a glassy carbon electrode (GCE) modified with nickel cobalt oxide (NiCo2O4) nanoneedles. These nanoneedles are used for the first time for highly sensitive determination of urea with the lowest detection limit (1 μM) ever reported for the non-enzymatic approach. The nanoneedles were grown through a simple and low-temperature aqueous chemical method. We characterized the structural and morphological properties of the NiCo2O4 nanoneedles by TEM, SEM, XPS and XRD. The bimetallic nickel cobalt oxide exhibits nanoneedle morphology, which results from the self-assembly of nanoparticles. The NiCo2O4 nanoneedles are exclusively composed of Ni, Co, and O and exhibit a cubic crystalline phase. Cyclic voltammetry was used to study the enhanced electrochemical properties of a NiCo2O4 nanoneedle-modified GCE by overcoming the typical poor conductivity of bare NiO and Co3O4. The GCE-modified electrode is highly sensitive towards urea, with a linear response (R2 = 0.99) over the concentration range 0.01–5 mM and with a detection limit of 1.0 μM. The proposed non-enzymatic urea sensor is highly selective even in the presence of common interferents such as glucose, uric acid, and ascorbic acid. This new urea sensor has good viability for urea analysis in urine samples and can represent a significant advancement in the field, owing to the simple and cost-effective fabrication of electrodes, which can be used as a promising analytical tool for urea estimation.

  • 278.
    Amin, Sidra
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. National Centre of Excellence in Analytical Chemistry, University of Sindh, Jamshoro, Pakistan. Department of Chemistry, Shaheed Benazir Bhutto University, Shaheed Benazirabad, Pakistan.
    Tahira, Aneela
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Solangi, Amber
    National Centre of Excellence in Analytical Chemistry, University of Sindh, Jamshoro, Pakistan.
    Mazzaro, Raffaello
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Ibupoto, Zafar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science. Department of Chemistry, Shaheed Benazir Bhutto University, Shaheed Benazirabad, Pakistan.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    A sensitive enzyme-free lactic acid sensor based on NiO nanoparticles for practical applications2019In: Analytical Methods, ISSN 1759-9660, E-ISSN 1759-9679, Vol. 11, p. 3578-3583Article in journal (Refereed)
    Abstract [en]

    A facile and efficient electrochemical sensing platform has been successfully exploited for the first time for the determination of lactic acid using a nickel oxide (NiO) nanoparticle-modified glassy carbon electrode (GCE). Nickel oxide nanoparticles were prepared by a chemical growth method using different quantities of arginine as a soft template. The structural and morphological properties of NiO nanoparticles were characterized by Raman spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Cyclic voltammetry (CV) was used to study the electrochemical properties of various samples. The modified electrode is highly sensitive and presents a linear response over a wide range (0.005–5 mM) of lactic acid concentrations in 0.1 M NaOH. The detection limit for the sensor was found to be 5.7 μM, and it exhibits good stability. Furthermore, the sensor shows excellent selectivity in the presence of common interfering species. The lactic acid sensor showed good viability for lactic acid analysis in real samples (milk, yogurt and red wine) and demonstrated significant advancement in sensor technology for practical applications.

  • 279.
    Amiri, Kaveh
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    An experimental investigation of flow in a Kaplan runner: steady-state and transient2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Water turbines are since some years widely used for grid stabilization purposes according to their exceptional load variation capability which gives them the ability to compensate grid fluctuations initiated by the customer’s consumption or intermittent electricity production systems such as wind and solar power. Different renewable power generation technologies can be combined in mini-grids to electrify isolated villages and extend existing grid networks. In these occasions, small hydro units are also a good option to reduce the overall variability of supply to low levels and provide low‑cost, local electrification solutions. Hence, initially designed hydropower turbines for steady operation at on-design operating condition experience many off-design, start/stop and load variations during their life time according to the nowadays on-demand energy market and introduction of intermittent power generation systems to the electricity market.Start/stop and load variations can be harsh for the turbines due to the time dependent forces exerted on different parts of the turbines, especially rotating parts. Off-design performance of hydropower systems may also result in unfavorable and harmful periodic forces on the rotating parts. Therefore, investigations are required to study these working conditions and consider them in design of new hydropower plants and refurbished turbines. This was the motivation for the experimental investigation of a Kaplan turbine during on-design, off-design and transient operations with focus on the turbine’s rotor. The test case was a 1:3.1 scaled model of Porjus U9; a Kaplan turbine. The first paper deals with pressure measurements on the runner blades of the model under steady state operating conditions to find and quantify the sources of pressure fluctuations exerted on the runner at different operating points. The goal was to investigate the turbine’s performance at the best efficiency point with concentration on the performance of the water supply system and compare it to operations at high load and part load for a constant blades angle. The model results are compared with prototype measurements to corroborate the findings. The second paper presents the model investigations during load acceptance and load rejection. The model was investigated with pressure measurement on the stationary and rotating parts of the turbine under different load variations between part load, high load and best efficiency point. The third paper focuses on velocity measurements in the runner blade channels and at the runner outlet under on-design and off-design operating conditions. The velocity measurements are performed with a laser Doppler anemometry (LDA) system. The results of the model investigations along two propeller curves are presented to investigate the runner blade angle effects on the turbine’s performance.

  • 280.
    Amiri, Kaveh
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Experimental investigation of a Kaplan runner under steady-state and transient operations2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Hydropower is a key part in electricity production nowadays. Hydropower electricity production rose to 3579.5 TWh in 2013, ranked as the second source of electricity production in the world after fossil fuels. It is the principle source of renewable electricity production, producing 16.2% of the electricity in 2013, accounting for 78% of the renewable electricity production in the world. Specifically in Sweden, hydropower is the main source of electricity production producing 47.5% of the required electricity. Nuclear, biomass, and wind placed in the following positions in the ranking in 2013 with 38.4%, 6.5%, and 4.3%, respectively.Besides meeting electricity demand with an environmental-friendly method, hydropower has a unique and important role which is grid regulation: balancing electricity production and consumption. Gas turbines and hydraulic turbines called “Primary reserves” are the only electricity production systems that can be used for fast regulations due to their short start-up time from 1 to 60 s. The obvious environmental problems, air pollution, and costs associated with gas turbines make hydropower a prime alternative whenever applicable. In Sweden, the share of fossil fuels in electricity production is small; 2.8% in 2012 with an average annual growth of -0.7% in the period 2002-2012. Hence, hydropower is practically the only available source used to regulate the grid fluctuations resulting from deregulated market and fast growth of intermittent power generation systems, i.e., solar and wind energy. Hydraulic turbines are subject to frequent off-design and transient operations because of their grid regulation responsibility. Such operating conditions decrease turbine’s efficiency and affect its lifetime significantly. Off-design and transient operation of hydraulic turbines may induce unpredicted pressure fluctuations on the stationary and rotating parts of the turbine. Special attention should be dedicated to the effects of such phenomena on the runner blades because of their importance on the efficiency of the turbine, and their vulnerability to the pressure fluctuations.This thesis presents an experimental investigation on the effects of off-design and transient operation of an axial hydraulic turbine on velocity fields and pressure fluctuations exerted on the runner and the draft tube of a turbine. The investigation was performed on a 1:3.1 scaled model of a Kaplan turbine known as Porjus U9. The main objective was to investigate the effect of operating point on pressure and velocity fluctuations in the runner and the draft tube. Another objective was to study the effect of transient operation on pressure fluctuations exerted on the runner and the draft tube, to investigate the formation and mitigation process of a rotating vortex rope (RVR) within the draft tube. Finally, the effect of the swirl leaving the runner and the draft tube bend on the performance of the turbine was investigated. The study involves pressure measurements on the runner blades and draft tube walls of the turbine, laser Doppler anemometry (LDA) measurements within and after the runner, and particle image velocimetry (PIV) measurements within the draft tube.The pressure and LDA results acquired during steady state operation of the turbine showed different sources of fluctuations on the runner at different operating points resulting in symmetric and asymmetric fluctuating forces on the runner. The pressure measurements during transient operating conditions exhibited pressure fluctuations exerted on the runner during load variations and elucidated some aspects of formation and mitigation process of RVR within the draft tube. The PIV measurements performed after the draft tube bend of the turbine focuses on the physical phenomena resulting in flow asymmetry after the draft tube bend of hydraulic turbines affecting their efficiency.

  • 281.
    Amiri, Kaveh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Mulu, Berhanu
    Vattenfall Research and Development, Älvkarleby.
    Experimental investigation of the hydraulic loads on the runner of a Kaplan turbine model and the corresponding prototype2015In: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 53, no 4, p. 452-465Article in journal (Refereed)
    Abstract [en]

    This paper reports on unsteady pressure measurements on the runner blades of a Kaplan turbine model as well as torque and radial load bearing measurements on the corresponding prototype at several operating points to investigate the sources of periodic loads exerted on the runner when operating at the best efficiency point and off design. Pressure measurements on the model runner blades indicated that the spiral casing delivers a poorly conditioned flow to the guide vanes close to the lip-entrance junction, resulting in flow separation on the guide vanes. The asymmetric flow delivered to the runner induces large oscillations with respect to the guide vane passing frequency, runner frequency and its harmonics to the runner blades. The torque measurements on the prototype also revealed an asymmetric flow at the distributor outlet. The bearing radial load measurements performed on the prototype support the torque measurement results. The asymmetric hydraulic loads on the runner result in shaft wobbling, and the oscillatory forces exerted on the blades are transferred to the main shaft and bearings. Another source of oscillating forces exerted on the runner blades is the rotating vortex rope (RVR) formation that occurs at part-load operation of the turbine and induces pressure fluctuations at two sub-synchronous frequencies to the runner.Keywords: Bearing load; blade pressure measurement; flow-induced vibration; Kaplan turbine; prototype measurement; spiral casingperformance

  • 282.
    Amiri, Kaveh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Mulu, Berhanu
    Vattenfall Research & Development.
    Raisee, Mehrdad
    Mechanical Engineering Department, University of Tehran.
    Experimental study of fluid structure interaction in a Kaplan turbine runner blade2013Conference paper (Refereed)
  • 283.
    Amiri, Kaveh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Raisee, M.
    School of Mechanical Engineering, University of Tehran.
    Effects of flow unsteadiness on the wall shear stress2012In: 26th IAHR Symposium on Hydraulic Machinery and Systems: 19–23 August 2012, Beijing, China, IOP Publishing Ltd , 2012, p. 62033-Conference paper (Refereed)
    Abstract [en]

    Measurements were performed on pulsating fully turbulent flows in a pipe test rig with a diameter of 100 mm. Sinusoidal oscillatory flow at different frequencies was superimposed on a mean flow of averaged Reynolds number Re=20000 based on the pipe diameter. The measurements have been performed at different forcing frequencies (0.001 < ω+ < 0.08) covering all the oscillatory regimes; quasi-steady, relaxation, quasi laminar and high frequency. The amplitude of the flow oscillation was small enough to allow a linear response in the measurements, i.e., all flow parameters showed an oscillatory behavior at the frequency of the flow. The amplitude of the oscillatory flow was about 10% of the mean velocity in all cases. The results include mean and phase averaged values of different parameters. The centerline velocity was measured by a 2D LDA system. Hot film and constant temperature anemometry system was used to determine the wall shear stress. Bulk velocity and pressure gradient along the pipe were also acquired. The results showed a good agreement with the previous analytical, experimental and numerical results available in the literature.

  • 284.
    Amiri, Kaveh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Mulu, Berhanu
    Vattenfall Research and Development, Älvkarleby.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Experimental Investigation of the Interblade Flow in a Kaplan Runner at Several Operating Points Using Laser Doppler Anemometry2016In: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 138, no 2, article id 21106Article in journal (Refereed)
    Abstract [en]

    This paper presents laser Doppler anemometry (LDA) measurements within the runner blade channels and at the runner outlet of a Kaplan turbine model. The model was investigated at six operating points located on two propeller curves of the turbine to study the flow condition during on-cam and off-cam operations. Main and secondary flows within and after the runner were analyzed, and the effects of the hub and tip clearances on the velocity fields within and after the runner were evaluated. Operation of the turbine at flow rates that are lower than the designed rate for the corresponding propeller curve resulted in vortex breakdown and the formation of a rotating vortex rope (RVR). The RVR formation produced an asymmetrical velocity distribution within and after the runner. The results demonstrated the occurrence of an oscillating flow with the same frequency as the vortex rope within the blade channels located upstream of the RVR. This results in an asymmetric flow through the runner and oscillating forces on the runner blades. The measured velocities indicated that the geometrical asymmetries in the runner manufacturing process resulted in various flow asymmetries at the measured sections. The asymmetries were up to 3% within the runner and 7% at the runner outlet

  • 285.
    Amiri, Kaveh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Mulu, Berhanu
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Raisee, Mehrdad
    School of Mechanical Engineering, University of Tehran, Mechanical Engineering Department, University of Tehran.
    Effects of load variation on a Kaplan turbine runner2016In: International Journal of Fluid Machinery and Systems, ISSN 1882-9554, E-ISSN 1882-9554, Vol. 9, no 2, p. 182-193Article in journal (Refereed)
    Abstract [en]

    Introduction of intermittent electricity production systems like wind and solar power to electricity market together with the deregulation of electricity markets resulted in numerous start/stops, load variations and off-design operation of water turbines. Hydraulic turbines suffer from the varying loads exerted on their stationary and rotating parts during load variations they are not designed for such operating conditions. Investigations on part load operation of single regulated turbines, i.e., Francis and propeller, proved the formation of a rotating vortex rope (RVR) in the draft tube. The RVR induces pressure pulsations in the axial and rotating direction called plunging and rotating modes, respectively. This results in oscillating forces with two different frequencies on the runner blades, bearings and other rotating parts of the turbine. This study investigates the effect of transient operations on the pressure fluctuations exerted on the runner and mechanism of the RVR formation/mitigation. Draft tube and runner blades of the Porjus U9 model, a Kaplan turbine, were equipped with pressure sensors for this purpose. The model was run in off-cam mode during different load variations. The results showed that the transients between the best efficiency point and the high load occurs in a smooth way. However, during transitions to the part load a RVR forms in the draft tube which induces high level of fluctuations with two frequencies on the runner; plunging and rotating mode. Formation of the RVR during the load rejections coincides with sudden pressure change on the runner while its mitigation occurs in a smooth way.

  • 286.
    Amiri, Kaveh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Mulu, Berhanu G.
    Vattenfall Research and Development, Älvkarleby.
    Raisee, Mehrdad
    Mechanical Engineering Department, University of Tehran.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Effects of upstream flow conditions on runner pressure fluctuations2017In: Journal of Applied Fluid Mechanics, ISSN 1735-3572, E-ISSN 1735-3645, Vol. 10, no 4, p. 1045-1059Article in journal (Refereed)
    Abstract [en]

    The rotor-stator interaction and the corresponding pressure fluctuations represent one of the sources of pressure and load fluctuations on the rotating parts of rotating machineries. The high-Reynolds flow is subject to rotation in the comparably large vaneless space of axial turbines, causing wake interaction and wake dissipation in this region. This increases the level of flow complexity in this region. This study examined the effect of the flow condition entering the spiral casing on the flow condition within the distributor and the runner and the physical source of pressure fluctuations exerted on the runner of a Kaplan turbine model. Simulations were performed within the water supply system, including the upstream tank, penstock, and the Francis turbines, the level of entering the spiral casing; the results were compared with laser Doppler anemometry (LDA) results. The results were considered as the inlet boundary condition for simulation of the turbine model from the spiral inlet to the draft tube outlet to investigate the flow condition within the distributor and the runner. The CFD simulations showed that the water supply system induces inhomogeneity to the velocity distribution at the spiral inlet. However, the flow condition does not affect the pressure fluctuations exerted on the runner blades due to the rotor-stator interactions. Moreover, the dominant frequencies exerted on the runner blades were accurately approximated although the amplitudes of the fluctuations were underestimated.

  • 287.
    Amiri, Kaveh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Mulu, Berhanu
    Raisee, Mehrdad
    School of Mechanical Engineering, University of Tehran, Mechanical Engineering Department, University of Tehran.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Experimental study on flow asymmetry after the draft tube bend of a Kaplan turbine2016In: Advances and Applications in Fluid Mechanics, ISSN 0973-4686, Vol. 19, no 2, p. 441-472Article in journal (Refereed)
    Abstract [en]

    Flow condition in a Kaplan turbine draft tube is investigated using laser Doppler anemometry (LDA) and particle image velocimetry(PIV). The investigated draft tube is composed of a cone followed by an elbow and a straight diffuser. The three velocity components were measured after the elbow at two different locations across the straight diffuser to quantify the flow asymmetry as well as the secondary flows formed in this region. The velocity profiles at the draft tube inlet are measured using a 2D LDA system allowing estimation of the draft tube inlet swirl. The results are presented at three operating points of the turbine. The flow condition after the draft tube bend was shown to be highly dependent on the vortex structures within the straight draft tube; namely Dean vortices and the swirl leaving the runner. At operating points with high flow rates and low swirl, Dean vortices dominate the upstream swirl; a symmetric but inhomogeneous flow resembling flow after a pipe bend forms within the straight diffuser. At part load operating points with high swirl and low flow rate, the flow after the bend is dominated by the upstream swirl resulting in asymmetric flow after the draft tube bend. The flow asymmetry is shown to be a 2nd order function of the swirl-to-Dean ratio.

  • 288.
    Amiri, Kaveh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Mulu, Berhanu
    Vattenfall Research & Development.
    Raisee, Mehrdad
    School of Mechanical Engineering, University of Tehran, Mechanical Engineering Department, University of Tehran.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Load variation effects on the pressure fluctuations exerted on a Kaplan turbine runner2014In: 27th IAHR Symposium on Hydraulic Machinery and Systems, IAHR 2014: Montreal, Canada, 22- 26 September 2014 / [ed] A-M Giroux, IOP Publishing Ltd , 2014, article id 32005Conference paper (Refereed)
    Abstract [en]

    Introduction of intermittent electricity production systems like wind power and solar systems to electricity market together with the consumption-based electricity production resulted in numerous start/stops, load variations and off-design operation of water turbines. The hydropower systems suffer from the varying loads exerted on the stationary and rotating parts of the turbines during load variations which they are not designed for. On the other hand, investigations on part load operation of single regulated turbines, i.e., Francis and propeller, proved the formation of rotating vortex rope (RVR) in the draft tube. The RVR induces oscillating flow both in plunging and rotating modes which results in oscillating force with two different frequencies on the runner blades, bearings and other rotating parts of the turbine. The purpose of this study is to investigate the effect of transient operations on the pressure fluctuations on the runner and mechanism of the RVR formation/mitigation. Draft tube and runner blades of the Porjus U9 model, a Kaplan turbine, were equipped with pressure sensors. The model was run in off-cam mode during different load variation conditions to check the runner performance under unsteady condition. The results showed that the transients between the best efficiency point and the high load happens in a smooth way while transitions to/from the part load, where rotating vortex rope (RVR) forms in the draft tube induces high level of fluctuations with two frequencies on the runner; plunging and rotating mode of the RVR.

  • 289.
    Amiri, Kaveh
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Mulu, Berhanu
    Vattenfall Research and Development, Älvkarleby.
    Raisee, Mehrdad
    School of Mechanical Engineering, University of Tehran, Mechanical Engineering Department, University of Tehran.
    Cervantes, Michel
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Unsteady pressure measurements on the runner of a Kaplan turbine during load acceptance and load rejection2016In: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 54, no 1, p. 56-73Article in journal (Refereed)
    Abstract [en]

    The paper addresses unsteady pressure measurements on the blades and stationary parts of a Kaplan turbine model (Porjus U9) during load variation. The turbine was studied in various load acceptance and load rejection scenarios in off-cam mode to investigate the effect of the transients on the turbine performance. The formation and mitigation processes for the rotating vortex ropes and their effects on the forces exerted on the runner were also investigated. The results show a smooth transition during load variations between high load and the best efficiency point, at which no rotating vortex ropes form in the draft tube. However, load variation to part load resulted in a draft tube surge and the formation of a rotating vortex rope with two fluctuating components: rotating and plunging. The rotating vortex ropes began to form at the end of the draft tube cone during the closure of the guide vanes and travelled upstream with further guide vane closure. The plunging mode induced flow oscillation throughout the entire turbine conduit, whereas the rotating mode resulted in local pressure fluctuations. The rotating vortex ropes induced wide-band pressure fluctuations on the suction side of the runner close to the hub section. The formation of the rotating vortex ropes near the runner resulted in a sudden change in the pressure exerted on the suction side of the blades, whereas the rotating vortex rope mitigation process proceeded in a smooth manner.

  • 290.
    Amundsdotter, Eva
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Andersson, Susanne
    Stockholms Universitet.
    Developing innovative organisations: using action-orientated gender research2012In: Promoting innovation: Policies, Practices and Procedures, Stockholm: Vinnova , 2012, p. 310-327Chapter in book (Refereed)
    Abstract [en]

    Lack of gender awareness affects not only the conditions under which people work, itis also an obstacle to organisations’ ability to produce, develop and organise for innovation.This article presents an approach called action-orientated gender research, amerger of two theoretical perspectives: a) the doing-gender perspective, with its understandingof gender as formed in on-going relational activities and b) learning theorywithin the action research tradition, which focuses on reflection, learning and especiallyreflective learning for transformation. Gender theory and learning theory are combinedinto joint learning processes in networks of participants from different organisationswithin innovation systems. This makes it possible to uncover taken-for-grantedassumptions and gendered power relations which constrain the development of newinnovative possibilities in organisations.This article will present basic theoretical characteristic of the action-orientatedgender research approach, plus examples of how we have worked with this approachin a network of middle managers. Moreover, we will elaborate on the important considerationswe have discovered for organising transformative learning aimed at developinggender-aware, innovative organisations. The empirical material in the articlecomes from two meetings. One in which co-research was conducted with two managersworking in the same organisation. The other meeting took place one month laterwhen all the managers in the Gender network were present. During this second meeting,observations from the earlier co-research were presented and discussed using theconcentric circle method.

  • 291.
    Amundsdotter, Eva
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Gunnarsson, Ewa
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Human Work Science.
    Westerberg, Mats
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    GAAL: a model for practical equality work in an engineering environment2013Conference paper (Other academic)
  • 292.
    Ananías, Rubén A.
    et al.
    Department of Wood Engineering, University of Bío-Bío, Concepción.
    Sepúlveda-Villarroel, Victor
    Departamento de Ingenieria en Maderas, Universidad del Bio Bio, Avenida Collao 1202, Casilla 5-C-CP: 4081112, Concepción.
    Perez-Peña, Natalia
    Departamento de Ingenieria en Maderas, Universidad del Bio Bio, Avenida Collao 1202, Casilla 5-C-CP: 4081112, Concepción.
    Leandro-Zuñiga, Laura
    Instituto Costarricense de la Madera, San Pedro, San José.
    Salvo-Sepúlveda, Linette
    Departamento de Ingenieria en Maderas, Universidad del Bio Bio, Avenida Collao 1202, Casilla 5-C-CP: 4081112, Concepción.
    Salinas-Lira, Carlos
    Departamento de Ingenieria en Maderas, Universidad del Bio Bio, Avenida Collao 1202, Casilla 5-C-CP: 4081112, Concepción.
    Cloutier, Alain
    Society of Wood Science & Technology Member, Centre de Recherche sur le Bois, Université Laval, Québec.
    Elustondo, Diego
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Collapse of Eucalyptus nitens Wood after Drying Depending on the Radial Location Within the Stem2014In: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 32, no 14, p. 1699-1705Article in journal (Refereed)
    Abstract [en]

    Collapse is almost certain to occur in the industrial drying of Eucalyptus nitens, and as such this prevents the lumber manufacturing industry in Chile from producing commercial solid wood products from this species. This problem is still unsolved, and different studies to reduce collapse are currently underway. In this exploratory study, shrinkage and collapse after drying of Eucalyptus nitens was measured for boards cut from different radial locations within the stem (core, transition and outer wood from pith to bark) and having different annual ring orientation (flat-sawn and quarter-sawn). Even though exploratory, the results appear to confirm that pieces that were cut from the center of the trees were less susceptible to collapse than the pieces cut from the transition zone between the center and the periphery. On average, collapse in transition wood was approximately 50% higher than the collapse observed in wood cut from the central zone of the trees.

  • 293.
    Andersen, O.
    et al.
    Centre for Electronic Materials, University of Manchester.
    Dobaczewski, L.
    Centre for Electronic Materials, University of Manchester.
    Peaker, A.R.
    Centre for Electronic Materials, University of Manchester.
    Nielsen, K. Bonde
    Institute of Physics and Astronomy, University of Aarhus.
    Hourahine, B.
    Department of Physics, University of Exeter.
    Jones, R.
    Department of Physics, University of Exeter.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Piezospectroscopic analysis of the hydrogen-carbon complexes in silicon2001In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 308, p. 139-142Article in journal (Refereed)
    Abstract [en]

    We have observed the donor (Ec-0.22 eV) and acceptor (Ec-0.16 eV) levels related to hydrogen-carbon complexes in silicon. The donor level is only detected at low temperatures after proton implantation. This hydrogen-carbon complex irreversibly reconfigures at temperatures above 225 K to a configuration characterized by the acceptor level, which is stable up to room temperature. The same acceptor level is also observed after atomic hydrogen diffusion. We have used Laplace transform deep level transient spectroscopy (DLTS) to show the influence of uniaxial stress on the electron emission process and the effect of the stress-induced alignment for the acceptor state. The pattern of the Laplace DLTS peak splittings indicate a trigonal symmetry of the defect. First principles calculations were carried out on the hydrogen-carbon defects with a view of determining their electrical levels and stress response for comparison with the experimental results.

  • 294.
    Andersen, O.
    et al.
    Centre for Electronic Materials, University of Manchester.
    Peaker, A.R.
    Centre for Electronic Materials, University of Manchester.
    Dobaczewski, L.
    Centre for Electronic Materials, University of Manchester.
    Nielsen, K. Bonde
    Institute of Physics and Astronomy, University of Aarhus.
    Hourahine, B.
    School of Physics, University of Exeter.
    Jones, R.
    School of Physics, University of Exeter.
    Briddon, P.R.
    Department of Physics, University of Newcastle.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Electrical activity of carbon-hydrogen centers in Si2002In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 66, no 23, p. 235205-1Article in journal (Refereed)
    Abstract [en]

    The electrical activity of Cs-H defects in Si has been investigated in a combined modeling and experimental study. High-resolution Laplace capacitance spectroscopy with the uniaxial stress technique has been used to measure the stress-energy tensor and the results are compared with theoretical modeling. At low temperatures, implanted H is trapped as a negative-U center with a donor level in the upper half of the gap. However, at higher temperatures, H migrates closer to the carbon impurity and the donor level falls, crossing the gap. At the same time, an acceptor level is introduced into the upper gap making the defect a positive-U center.

  • 295.
    Anderson, Jan-Olof
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Westerlund, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Analysis of the heat demand in batch kilns2012Conference paper (Other academic)
    Abstract [en]

    During the production of lumber more than half of the entering timber to the sawmill becomes biomass. About 12 %wt of the entering timber is combusted to supply heat for the sawmill. Major part of the heat is supply the kilns. Due to the high evacuation losses the energy efficiency in a traditional drying kiln is only 13 %. This makes the lumber drying to a low and ineffective process in an energy point of view.Forced drying technologies are a compromise between high lumber quality, low lead time and decreased energy use. Often is the quality and lead time prioritised. This paper advises an appropriate method to simulate the energy efficiency when drying lumber in a batch kiln. To ensure real life drying conditions, with sufficient quality and lead time the initial conditions were made from simulated drying schemes, from simulation program called Torksim. By combine thermodynamics and psychrometric relationship, the energy streams and losses during the drying scheme were established. The program can be used to compare several drying conditions and clarify the magnitude of losses. Different types of technologies affecting the kiln energy efficiency and to compare drying conditions to each other. For instance heat exchanger, heat pumps, condense walls, absorption system etc.The used drying conditions are suitable for north European lumber and climate, but the initial conditions can be changed for analyses of other types of drying conditions. The program is a usable tool to analyses different types of technologies effect on the kiln energy efficiency and to compare drying conditions and different drying scheme to each other.

  • 296.
    Andersons, J.
    et al.
    University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Estimation of the tensile strength of an oriented flax fiber-reinforced polymer composite2011In: Composites. Part A, Applied science and manufacturing, ISSN 1359-835X, E-ISSN 1878-5840, Vol. 42, no 9, p. 1229-1235Article in journal (Refereed)
    Abstract [en]

    Unidirectional orientation of natural fibers in a polymer composite ensures the highest efficiency of reinforcement. Flax fiber reinforcement is discontinuous due to limited fiber length and heterogeneous due to the presence of elementary fibers and their bundles. In order to assess the upper limit of tensile strength of such slightly misoriented, nominally UD natural fiber composite, a statistical strength model of continuous UD fiber reinforced composites is applied. It is found that the experimental strength of UD flax composites, produced from rovings or manually aligned fibers, approaches the theoretical limit only at relatively low fiber volume fraction ca. 0.2, being markedly below it at higher fiber content.

  • 297.
    Andersons, J.
    et al.
    University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hojo, M.
    Ochiai, S.
    Kyoto University.
    Fibre fragment distribution in a single-fibre composite tension test2001In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 32, no 4, p. 323-332Article in journal (Refereed)
    Abstract [en]

    Single fibre fragmentation tests are performed for brittle fibres with Weibull strength distribution and different surface treatments. The fragmentation process is modelled and closed-form expressions for break spacing distribution are obtained. The model accounts for the effect of finite fibre length on the initial fragmentation as well as for break interaction on the advanced fragmentation stage. It is assumed that the exclusion zone due to fibre-matrix interface failure and stress recovery in the fibre is linearly dependent on the applied load. This assumption is validated experimentally. The derived theoretical average fragment length dependence on applied load is used to determine the fibre strength distribution parameters and the effective interfacial shear stress for carbon/epoxy single fibre composites with different fibre surface treatment and for glass/vinylester single fibre composite. Fragment length distribution is predicted for several load levels. Predictions are in good agreement with experimental data

  • 298.
    Andersons, J.
    et al.
    University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hojo, M.
    Mesoscopic Materials Research Center, Kyoto University.
    Ochiai, S.
    Mesoscopic Materials Research Center, Kyoto University.
    Glass fibre strength distribution determined by common experimental methods2002In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 62, no 1, p. 131-145Article in journal (Refereed)
    Abstract [en]

    The tensile strength of brittle fibres is routinely described by the Weibull distribution. The parameters of the distribution can be obtained from tests on single fibres and fibre bundles or from model composite tests. However, there is growing evidence that the distribution parameters obtained by different experimental techniques differ systematically. In order to investigate the possible causes of such discrepancies, single-fibre tension, fibre bundle, and single-fibre fragmentation tests are employed in this study to obtain strength distribution of commercial E-glass fibres. The results reveal parameter dependence on the approach used to extract the distribution parameters from experimental data. Particularly, in the case of single-fibre tension tests, the shape parameter obtained from average fibre strength vs. length data is larger than that obtained at a fixed gauge length. It is assumed that the apparent fibre strength scatter is caused by both the inherent flaw structure along a fibre and by the fibre-to-fibre strength variability within a batch, due to slightly differing processing and handling history of the fibres. Fibre fragmentation test results are used to derive the Weibull distribution parameters applicable to the fibre batch. The strength distribution obtained is compared with strength data for the single fibres, and reasonably good agreement is observed.

  • 299.
    Andersons, J.
    et al.
    Institute of Polymer Mechanics, University of Latvia.
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Sparnins, Edgars
    Institute of Polymer Mechanics, University of Latvia.
    Weichert, D.
    Institute of General Mechanics, RWTH-Aachen University.
    Modeling the effect of reinforcement discontinuity on the tensile strength of UD flax fiber composites2011In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 46, no 15, p. 5104-5110Article in journal (Refereed)
    Abstract [en]

    To exploit the potential of natural fibers as reinforcement of polymer matrix composites, aligned bast fiber composite materials are being produced and studied. Bast fiber reinforcement is discontinuous due to the limited length of natural fibers, which needs to be reflected in predictive models of mechanical properties of composites. The strength in tension in the fiber direction of an aligned flax fiber-reinforced composite is modeled assuming that a cluster of adjacent fiber discontinuities is the origin of fracture. A probabilistic model of tensile strength, developed for UD composites containing a microdefect, is applied. It follows from the theoretical analysis that the experimental tensile strength as a function the fiber volume fraction can be described with acceptable accuracy assuming the presence of a cluster of ca. 4 × 4 elementary fiber discontinuities

  • 300.
    Andersons, J.
    et al.
    University of Latvia.
    Sparnins, Edgars
    Joffe, Roberts
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Prediction of crack onset strain in composite laminates at mixed mode cracking2009In: 5th International EEIGM/AMASE/FORGEMAT Conference on Advanced Materials Research, Bristol: IOP Publishing Ltd , 2009, Vol. 5Conference paper (Refereed)
    Abstract [en]

    Failure process of continuous fiber reinforced composite laminates in tension usually starts with appearance of intralaminar cracks. In composite laminates with complex lay-ups and/or under combined loading, intralaminar cracks may develop in plies with different reinforcement directions. A necessary part of mixed mode cracking models is the criterion of failure. For propagation-controlled fracture it is usually formulated in terms of energy release rates and their critical values of the particular composite material. Intralaminar fracture toughness of unidirectionally reinforced glass/epoxy composite was experimentally determined at several mode I and mode II ratios. It is found that the crack propagation criterion, linear in terms of the energy release rates, reasonably well approximates the test results. The determined mixed mode cracking criterion was applied to predict intralaminar crack onset in cross-ply glass/epoxy composite under tensile loading. The predicted crack onset strain values agree with test results at small off-axes angles of the cracking ply (on-axis and 15° off-axis loading), but underestimate crack onset at larger reinforcement angles with respect to the loading direction. The discrepancy is likely to be caused by the deviation of linearity in laminate response before cracking onset in these laminates, related to non-linear shear characteristics of unidirectional plies. The applicability of strength-based fracture criterion for initiation-controlled cracking is discussed.

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