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  • 601. Agarwal, Shilpa
    Characterisation of HZSM-5 film to study Xylene Isomerisation using FTIR/ATR spectroscopy2009Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The earlier studies carried out in the Zeolite Research group at Division of Chemical technology, showed some promising results regarding the use of FTIR/ATR technique for characterizing zeolite films. The observations indicated that the FTIR/ATR technique could be used as a characterization technique for investigating the performance as well as reaction & its kinetics occurring on active film at different temperatures and pressures. But during the experiment performed at 150oC and 828Pa for xylene isomerisation in presence of HZSM-5 film coated on ZnS crystal, some anomalies were observed within the spectral range 1300-1450 cm-1 that were not reported. In current work, zeolite ZSM-5 films were synthesized on ZnS ATR elements by an in-situ method. The films were subsequently activated by introducing Brönstedt acid sites. Xylene isomerisation reaction was successfully performed at 150oC and 828Pa on activated ZSM-5 film. The adsorption and desorption spectra obtained suggested that the bands at 1377 and 1412 cm-1 are related to methyl group of xylene and coke species. This was further confirmed by 2DCOS (Two dimensional correlation spectroscopy) treatment of the adsorption and desorption spectra. In addition tilt angle determined experimentally for p-xylene (1516 cm-1) and poly-aromatic coke (1593 cm-1) was ∼20o and ∼38o, which indicates that p-xylene adsorbs preferentially in the ZSM-5 film whereas coke adsorption is neither completely preferential nor completely random.

  • 602. Agarwal, Shilpa
    In-situ studies of thin film zeolite catalysts using FTIR/ATR spectroscopy2009Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Zeolite films have a great potential as structured catalysts, membranes and sensors in various novel technological applications. Combining zeolite membrane films with chemical reactors results in a membrane reactor which may offers better product selectivity and conversion as compared to conventional reactors. In addition, miniaturization of reactors along with the introduction of structured catalysts promises more efficient, cleaner, safer and selective operations. But till date, due to lack of sufficient knowledge in this domain, research in the field of membrane reactors as well as in microreactor technology remain relative scarce. A powerful characterization technique is needed for investigating the performance of zeolite film catalysts, one such promising technique is FTIR/ATR spectroscopy (Fourier transform infrared/ attenuated total reflection spectroscopy). In this work, zeolite ZSM-5 films were synthesized on ZnS ATR elements by an in-situ method. The films were subsequently activated by introducing Brönstedt acid sites. Xylene isomerisation reaction was successfully studied at in the temperature range 393-473K. At a constant partial pressure of p-xylene in the feed (828 Pa), the adsorption of xylene isomers was, as expected, found to be higher at lower temperatures. Furthermore the meta-/ortho-xylene ratio was observed to decrease with increasing reaction temperature. Further,during the desorption process, p- xylene and o-xylene desorbs in the order p-xylene > o-xylene, whereas m- xylene due to high diffusion limitation in the ZSM-5 film, remains constant throughout the desorption process. Besides the xylene isomers bands in IR spectra, coke was also observed and whose concentration is found to be increasing with reaction temperature and moreover it remains in the film during the desorption process. The observations indicate that the FTIR/ATR technique could be used as a characterization technique for investigating the performance as well as reaction & its kinetics occurring on active film at different temperatures and pressures.

  • 603. Age, Rickard
    ”Det var en annan gång...”: Att komponera musik till en scenisk föreställning utifrån texten och dramat2013Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
  • 604. Ageby, Pär
    Hållfasthet för limträ i belsatningsfallet drag i vinkel till fibrerna2000Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
  • 605. Agelén, Fredrik
    et al.
    Emanuelsson, Martin
    En studie av arbetsmiljö och produktivitet på Volvo Lastvagnar AB1999Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
  • 606.
    Ager, Bengt
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Human Work Science. Luleå tekniska universitet.
    Skogsarbetets humanisering och rationalisering från 1900 och framåt2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [sv]

    Rapporten belyser skogsarbetets förändring i storskogsbruket under perioden 1900 – 2013 under inflytande av rationalisering och humanisering som förändringsprocesser. Utgångsläget var ett ytterst slitsamt, riskabelt och lågbetalt säsongsarbete i kyla och snö, med bortaliggning i undermåliga kojor. I periodens början fullbordades en spontan rationalisering som inletts i slutet av 1800-talet och som bestod av att effektivare handredskap – olika typer av sågar, barkspadar och hanteringsdon - ersatte yxan som universalredskap. Organiserad rationalisering av skogsarbetet kom igång först i slutet på 30-talet. Den hämtade då sin inspiration från industrin som vid det laget hade anpassat amerikanen F W Taylors rationaliseringskoncept till den svenska arbetsmarknaden och kulturen. Arbetsstudier blev grund för effektivisering av det manuella skogsarbetet och för en rättvisare lön. Men skogsbruket kom sedan att finna egna vägar, som ledde till en världsunik teknisk och organisatorisk utveckling med början på 1950-talet och kulmen kring 1990. Under de senaste två årtiondena har rationaliseringen i skogsbruket anslutit sig till ”mainstream” i näringslivets utveckling, som styrs allt mera av dels den globaliserade marknadens mekanismer samt dels ”Lean”, ett hopkok av amerikanska och japanska organisationskoncept, och med ”outsourcing” som främsta verktyg. Under perioden 1940-2005 utvecklades produktiviteten kraftigt, med särskilt stora språng 1960-75 och 1990-2005. Efter 2005 skedde en stagnation. Humaniseringen av skogsarbetet inleddes med provinsialläkaren Hasslers larm 1907. Starten blev trög men skogsarbetarnas boende och mathållning kom att förbättras på många håll fram till 1930-talets slut. Då blev humanisering en integrerad del av den systematiska rationaliseringen, vilket innebar radikala förbättringar av det manuella skogsarbetet. När mekaniseringen tog fart under 50- och 60-talet kom människan i produktionssystemet bort ett tag, vilket ledde till omtag på humaniseringsprocessen. Ergonomin utvecklades som redskap och som vetenskap. Från slutet av 70-talet till slutet av 90-talet blev humaniseringen, stödd av flera aktörer, åter en integrerad del av rationaliseringen, nu underbyggd av det ”sociotekniska” organisationskoncept som utvecklats av engelska och norska arbetsforskare. Arbetets organisation kom i fokus. Den totala humankvaliteten kulminerade åren kring 1990. Skogsarbetet nådde då en höjdpunkt vad gäller mångsidighet, kontaktrikedom, variation, självbestämmande, ansvar och uppmärksamhet. Sedan inleddes en viss avhumanisering. Humaniseringsaktörerna försvagades eller försvann. Marknadens ”osynliga hand” tog alltmera över utvecklingen. Humankvaliteten försämrades på en rad punkter som i huvudsak kan hänföras till organisationsmiljön – färre personliga kontakter, längre arbetsresor, sämre skiftformer, kortare framförhållning och sämre kvalitet i planeringen samt sänkt relativ lönenivå. Försämringarna kompenseras delvis av att maskinernas förarmiljö och driftssäkerhet förbättrats avsevärt, men generellt har skogsarbetet förlorat i attraktivitet. Historiken summeras utförligt i kapitel 11.I kapitlet 12 om framtidens arbetsliv nationellt och i skogsbruket hävdar författaren att det behövs ett tidsanpassat humaniseringskoncept av samma dignitet som det på 60-talet lanserade sociotekniska konceptet. En skiss på ett sådant ”socioekonomiskt” koncept presenteras, inklusive en begreppsapparat som gör anspråk på att vara innovativ, samt en rad åtgärdsförslag. Därvid beaktas lärdomar från det förgångna

  • 607.
    Aghajan ghazi, Alice Lejla
    et al.
    Luleå University of Technology, Department of Health Sciences.
    Nilsson, Elin
    Luleå University of Technology, Department of Health Sciences.
    Palliativ vård på ett hospice i ett utvecklingsland – en observationsstudie2018Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Background: The aim of palliative care is to keep the quality of life by integrating a person-centered care at the end of life. Palliative care and hospice care do not focus only on symptoms and medication. Self-esteem, dignity and support were major components for the patient at the end of life. Aim: The aim of this study was to describe how palliative care is given at a hospice in a developing country. Method: The used method was a qualitative participant observation study. The participants were health care staff at a hospice, they were chosen before the study began. The observation took place three times per week for six weeks. The researcher intertwined volunteering and observing at the same time. The data was analyzed with a qualitative content analysis. Result: The study resulted in six categories: environment, nursing records, nursing care, infection control and meals. Conclusion: The conclusion was that nature and safety had a big impact on the environment. The health care staff worked as a team to fulfill their goals.

  • 608. Aghamiri, Seyed Ali
    Assessing and analyzing satisfaction level of domestic gas consumers in Tehran2007Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The quality is counted as an important and effective factor in the success and failure of any organizations and since it as a fundamental factor can be considered as the excellent and stable competition for the organizations. Therefore, all the organizations, particularly the service organizations must attempt to increase quality of their services rapidly. Moreover, service quality issues may differ from one country to another and from one industry to another one. Therefore it is definitely essential to establish services quality scales which is relevant to the country and culture where the service is offered. The present investigate is a field study research that its objective is to measure, assess and analysis services quality and satisfaction of domestic gas consumers by establishing and applying an appropriate measurement tool in Grate Tehran Gas Company (which is the largest provincial company of National Iranian gas Company). Therefore this research is conducted in Tehran (Capital of Iran) with a 1000 volume sample size in order to identify and prioritize service quality dimensions and their gaps. After collecting the data, different statistical tests including paired t-test, Friedman test, variance analysis, structural equation model (regression model), ANOVA, KMO-Bartlet test by the SPSS and Lisrel software is applied. Research results indicate that the highest perceived gap is in reliability dimension and the lowest gap is related to assurance dimension. Also the regression model exhibit that these dimensions have significant impact on gas consumer's satisfactions. At last suggestions are offered to increase the quality of services and to promote customer satisfaction and reduce identified gaps.

  • 609. Agirre Zubizarreta, Josu
    Evaluation of Tool Steels by Standing Contact Fatigue Testing2014Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Tool steels are required to show high hardness and fracture toughness, as well as good wear resistance. Furthermore, other properties such as chipping and contact fatigue resistance are also essential in order to improve the life-time of the tool. The goal of this thesis is to analyze the chipping and contact fatigue resistance of several steels and try to evaluate the correlation between these two properties.On the one hand, the performance of different ausferritic or carbide-free bainitic steels as tool steels have been studied, by taking a high-silicon steel and subjecting it to two austempering treatments, to evaluate their properties next. On the other hand, several quenched & tempered commercial tool steel have been evaluated, produced either by conventional metallurgy, powder metallurgy or electro slag remelting. The microstructure and microhardness of all the steels have been studied first, and standing contact fatigue tests have been performed next. Finally, with the obtained results, the relation between the chipping resistance and contact fatigue resistance has been evaluated.Among the commercial tool steels Calmax, Vanadis 4 Extra and Caldie show much better standing contact fatigue resistance than AISI D2. Ausferritic steels have also shown good resistance, comparable to the Calmax or, in some cases, even better. Regarding the microhardness, ausferritc steels are not as hard as the commercial tool steels, but the values are not much lower than Calmax or AISI D2 for example. Finally, Caldie, the steel with the highest standing contact fatigue resistance shows, according to the provider, the best chipping resistance.The presented work has brought some insight to the evaluation of tool steels. Standing contact fatigue tests can be used to obtain useful information and the results indicate that there might be a relation between the SCF resistance and the chipping-resistance. Moreover, it has been determined that ausferritic steels show properties similar to some commercial tool steels, and therefore, it would be possible to use them in some tool applications in the near future.

  • 610.
    Agnantiari, G.
    et al.
    National Technical University of Athens.
    Christakopoulos, Paul
    Kekos, D.
    National Technical University of Athens.
    Macris, B.J.
    National Technical University of Athens.
    A Purified α-galactosidase from aspergillus niger with enhanced kinetic characteristics1991In: Acta Biotechnologica, ISSN 0138-4988, E-ISSN 1521-3846, Vol. 11, no 5, p. 479-484Article in journal (Refereed)
    Abstract [en]

    Extracellular α-galactosidase from Aspergillus niger was purified 128-fold over the crude extract by gel filtration, ion exchange chromatography and chromatofocusing. Certain substrates and end products affected enzyme activity. Among the former p-nitrophenyl-α-galactopyranoside (PNPG) inhibited the enzyme at 1.4 mM while melibiose did not inhibit α-galactosidase at concentrations up to 50 mM. Enzymic end products such as glucose did not inhibit the enzyme at concentrations up to 100 mM while galactose exhibited a competitive inhibition with a Ki = 1.29 mM. The kinetic characteristics of the enzyme compared favourably to other microbial α-galactosidases and make it suitable for food process applications.

  • 611. Agnarsdotter, Katarina
    Aktivitet: Miljöns betydelse för lärande: sjukgymnaststuderandes upplevelser och erfarenheter av lärande under klinisk utbildning2006Conference paper (Other (popular science, discussion, etc.))
  • 612. Agnehäll, Jan
    et al.
    Rosenius, Maria
    Miljöredovisning - för vem och varför?: en fallstudie av fyra landsting i Norrland2009Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
  • 613. Agnér, Daniel
    Comparison and selection of an electronic architecture for a new type of motor breaker drive2004Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this masters thesis a new electronic architecture for control of a new type of medium voltage motor breaker drive is selected and evaluated. The new type of circuit breaker has an operating mechanism that uses algorithms that predict the zero current crossings in each phase and is able to perform an arc free interruption. A functional prototype exists that shows that the new type of medium voltage breaker system synchronized to line current and voltage is possible. The existing prototype is not ready to be manufactured due to use of exotic and high cost components in combination with a layout that does not fit a standard size printed circuit board. The main goal of the thesis work is to find a more cost effective architecture and with reduced PCB layout size. Important topics for the project are single versus multiprocessor architecture and selection of a processor to implement the main control algorithms. The goal of a cost effective architecture is achieved by re-use of circuitry from an exciting motor breaker drive in combination with the use of a new motor control DSP. A higher inter-process communication bandwidth combined with more computational demanding algorithms are reasons why an existing four DSP architecture can’t be used in this application. A new dual DSP architecture with detailed design of functionality and choice of components is presented together with an estimation of cost. Test results are also presented that shows that the new DSP is able to handle and perform the required calculations in a dual DSP architecture. Test results shows that each DSP is loaded to less then 50% during “worst case” execution of existing software. A serial bus is evaluated and decided to be used for inter processor communication. The serial bus used is proven to have the required bandwidth for this application and makes the communication between the two DSPs simple and cost effective. Finally a cost estimation shows that a dual DSP architecture can be made cost effective compared to the existing functional prototype with a component cost of less then 120 USD.

  • 614. Agnér, Linda
    et al.
    Fors, Anette
    Det måste finnas möjligheter: en studie om individuell utveckling i en kommunal förvaltning2005Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
  • 615.
    Agreste, Santa
    et al.
    Department of Mathematics and Computer Science, Physical Sciences and Earth Sciences, University of Messina.
    De Meo, Pasquale
    of Ancient and Modern Civilizations, University of Messina.
    Fiumara, Giacomo
    Department of Mathematics and Computer Science, Physical Sciences and Earth Sciences, University of Messina.
    Piccione, Giuseppe
    Department of Mathematics and Computer Science, Physical Sciences and Earth Sciences, University of Messina.
    Piccolo, Sebastiano
    Department of Management Engineering - Engineering Systems Division at the Technical University of Denmark.
    Rosaci, Domenico
    DIIES Department, University of Reggio Calabria Via Graziella.
    Sarné, Giuseppe M. L.
    DICEAM Department, University of Reggio Calabria Via Graziella.
    Vasilakos, Athanasios
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    An empirical comparison of algorithms to find communities in directed graphs and their application in Web Data Analytics2017In: IEEE Transactions on Big Data, E-ISSN 2332-7790, Vol. 3, no 3, p. 289-306Article in journal (Refereed)
    Abstract [en]

    Detecting communities in graphs is a fundamental tool to understand the structure of Web-based systems and predict their evolution. Many community detection algorithms are designed to process undirected graphs (i.e., graphs with bidirectional edges) but many graphs on the Web - e.g. microblogging Web sites, trust networks or the Web graph itself - are often directed. Few community detection algorithms deal with directed graphs but we lack their experimental comparison. In this paper we evaluated some community detection algorithms across accuracy and scalability. A first group of algorithms (Label Propagation and Infomap) are explicitly designed to manage directed graphs while a second group (e.g., WalkTrap) simply ignores edge directionality; finally, a third group of algorithms (e.g., Eigenvector) maps input graphs onto undirected ones and extracts communities from the symmetrized version of the input graph. We ran our tests on both artificial and real graphs and, on artificial graphs, WalkTrap achieved the highest accuracy, closely followed by other algorithms; Label Propagation has outstanding performance in scalability on both artificial and real graphs. The Infomap algorithm showcased the best trade-off between accuracy and computational performance and, therefore, it has to be considered as a promising tool for Web Data Analytics purposes.

  • 616. Agten, Dries
    Electronic prototyping for cardiovascular health monitoring and postural analysis2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The microgravity in space affects the human body in many different ways, leading to postflight problems such as orthostatic intolerance and postural instability. Continuous monitoring is therefore becoming increasingly important, especially when related to the cardiovascular and vestibular system. Weight scales are ideal candidates for this type of monitoring due to their low cost and ease of use. In this thesis, the electronic design and experimental verification of a weight scale capable of cardiovascular health monitoring and postural analysis is presented. Ballistocardiography (BCG) circuits use strain gauges, amplifiers and filters to measure the forces exerted by accelerating blood onto the body, while an electrocardiography (ECG) circuit records the electrical activity of the heart with an innovative two-electrode set-up integrated with the scale. These circuits can be used to assess cardiovascular health. A two-electrode electromyography (EMG) circuit to monitor the electrical activity of the lower-body muscles may also be used in this system. A center of pressure (COP) circuit is described, based on a combination of analog-to-digital and digital-to-analog conversion. The EMG and COP circuits can be used in postural analysis. Designs for each of these circuits are presented, together with the design of a dedicated power supply circuit. The BCG, ECG and EMG circuits were assembled and tested, while the COP and power supply circuits are preliminary designs that will be assembled in the future. Tests with the BCG, ECG and EMG circuits provided signals corresponding to previous measurements with standard equipment. When combined with COP and power supply circuits, the systems developed in this thesis can be used for cardiovascular health monitoring and postural analysis, which has applications in both space physiology and clinical environments.

  • 617. Agthe, Michael
    Rare Earth Oxide Nanopowder (RE = Nd, Eu, Gd, Ho, Y, Yb) by Combustion Synthesis, Sulfation and Calcination: Role of the Initial Structure2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A novel method for synthesising rare earth oxide (RE2O3) nanopowder was applied to several rare earths including Nd, Eu, Gd, Ho, Y and Yb. The process was successful in producing homogeneous, fine dispersed and deagglomerated powder particles with uniform morphology for all rare earth oxides, except neodymia. In the first process step, rare earth nitrate solutions were mixed with glycine and subsequently heated in a furnace. Glycine acted as fuel to initiate the combustion synthesis (SHS) in order to obtain nanocrystalline and weakly agglomerated particles. Powder samples were produced at three different glycine-to-nitrate ratios (G/N), involving stoichiometric ratio (G/N = 0.56) and two fuel lean ratios (0.32 and 0.25). As a consequence of low combustion temperature at fuel lean ratios were carbonate structures found and their formation was correlated to the size of the rare earth cation. Resulting cellular structures were analysed by X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The cellular structure is unsuitable to be processed to a final product. The resulting powder has a very large specific volume and is comprised of strongly agglomerated crystallites, which renders pressing and sintering of these structures difficult. Therefore an additional synthesis step was employed with the addition of ammonium sulfate and calcination for 4 h in a tube furnace at 1100°C. In order to understand the influence of the initial, cellular structure on the morphological and microstructural powder properties different sulfate concentrations were used. Samples were characterized by XRD and scanning electron microscopy (SEM). The average crystallite size increased during calcination from below 15 nm in the initial structure to 50 nm in the final product. However, the resulting particles were loosely agglomerated. A benefit of sulfate-doped rare earth compounds under heat treatment is the formation of nearly isotropic surfaces, which might be related to the promotion of surface diffusion and partial inhibition of densifying transport mechanisms such as volume diffusion.

  • 618.
    Agthe, Michael
    et al.
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Wetterskog, Erik
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Salazar-Alvarez, German
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Bergström, Lennart Magnus
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Dynamic growth modes of ordered arrays and mesocrystals during drop-casting of iron oxide nanocubes2014In: CrystEngComm, ISSN 1466-8033, E-ISSN 1466-8033, Vol. 16, no 8, p. 1443-1450Article in journal (Refereed)
    Abstract [en]

    The growth modes of self-assembled mesocrystals and ordered arrays from dispersions of iron oxide nanocubes with a mean edge length of 9.6 nm during controlled solvent removal have been investigated with a combination of visible light video microscopy, atomic force microscopy and scanning electron microscopy. Mesocrystals with translational and orientational order of sizes up to 10 μm are formed spontaneously during the final, diffusion-controlled, drop-casting stage when the liquid film is very thin and the particle concentration is high. Convection-driven deposition of ordered nanocube arrays at the edge of the drying droplet is a manifestation of the so called coffee-ring effect. Dendritic growth or fingering of rapidly growing arrays of ordered nanocubes could also be observed in a transition regime as the growth front moves from the initial three-phase contact line towards the centre of the original droplet.

  • 619. Aguilar Soto, Paola
    et al.
    Bredenberg, Karin
    Arbetsterapeuters erfarenhet av att arbeta med elever i skolan2015Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
  • 620.
    Aguilar Sánchez, Andrea
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Different fiber combinations for enhancing properties of compression molded fiber composites2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The present work involved the manufacturing and characterization of hybrid biocomposites from poly-lactic acid reinforced with cellulose derived fibers and synthetic high performing fibers, such as carbon and aramid fibers for improving the performance. The manufacturing and characterization of these composites were executed at Innventia AB in Stockholm and in the Division of Materials Science at Luleå University of Technology. A dynamic sheet former was used to obtain the pre-forms or mats. The final composite was obtained by compression molding and annealing process. The characterization of the composites was done by performing tensile test, fracture toughness test, differential scanning calorimetry, computed tomography and scanning electron microscopy. A study of the degradation of the poly-lactic acid in the composites was executed through size exclusion chromatography. Composite porosity was determined to be between 15-64%, depending on the composition. Composites containing aramid fibers showed higher values of strain at break, while composites containing carbon fibers showed higher values of tensile strength and young modulus. Synthetic fibers improved fracture toughness only when the fracture propagates in cross direction. In general, annealing process increased the degree of crystallinity of the composites. SEC results showed that samples lost around 23% and 94% of their molecular weight after compression molding and annealing process, which could have affected the mechanical behavior of the composite. Recommendations concerning the manufacturing of composites and suggestions for further experimental work are presented.

  • 621.
    Aguilar, Wilson
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Study of the Synthesis of ZSM-5 from Inexpensive Raw Materials2014Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    ZSM-5 is an aluminosilicate with high silica ratio with suitable properties for catalysis, ion exchange, adsorption and membrane applications. ZSM-5 is usually produced industrially from concentrated systems in which there is formation of an amorphous gel phase. Typical syntheses of ZSM-5 require sources of silicon and aluminium, a mineralizer and an organic molecule as so-called templating agent. The silicon and aluminum sources widely used for the synthesis are pure reagent chemicals and in particular quaternary ammonium compounds like tetrapropyl ammonium hydroxides (TPA-OH), are employed as templating agents. Unfortunately, these compounds are rather expensive. Demand for inexpensive sources of aluminosilicates for the synthesis of ZSM-5 has increased during the last two decades. Natural raw materials such as kaolin clay and diatomaceous earth (diatomite) are two potential inexpensive sources of silica and alumina. Moreover, the molecule n-butylamine (NBA) has been reported as a low-cost templating agent to replace the quaternary ammonium compounds. The aim of this work was to show for the first time that leached metakaolinite or diatomite in combination with sodium hydroxide and n-butylamine could be used as inexpensive raw materials for the synthesis of ZSM-5 without using an additional source of silica. After synthesis optimization, both sources of aluminosilicate were found to behave differently during the course of synthesis and led to slightly different products. The chemical composition of the raw materials and the products were determined using inductively coupled plasma-sector field mass spectrometry (ICP-SFMS). Crystallinity was examined by X-ray diffractometry (XRD), the morphology was studied by extreme-high-resolution scanning electron microscopy (XHR-SEM) and the specific surface area was estimated from nitrogen adsorption data by the BET method. The chemical composition of individual crystals was determined by energy dispersive spectrometry (EDS). Dealumination of the raw materials by acid leaching made it possible to reach appropriate SiO2/Al2O3 ratios and reduced the amount of impurities. The final ZSM-5 products had a SiO2/Al2O3 ratio in the range 20 – 40. The use of leached diatomite allowed reaching higher yield of ZSM-5 crystals within comparable synthesis times. However, low amounts of mordenite were formed, which was related to the high calcium content of diatomite. Another considerable advantage of diatomite over kaolin is that diatomite does not require heat treatment at high temperature to convert the kaolin to reactive metakaolin. Further characterization of the system by XHR-SEM and EDS at low voltage was carried out in order to understand the nucleation and early growth of the ZSM-5 zeolite crystals. The observations with unprecedented detail strongly suggest that nucleation and the succeeding growth occurs on the gel surface. The growth rates in the various crystallographic directions already at an early stage are such that the shape of the growing crystals resembles that of the final crystals. However, as the early growth is interface mediated, the growth rate along the gel particles is high and the gel particles will become partially embedded inside the growing crystals at an early stage. The Si and Al nutrients are probably transported along the solid/liquid interface and possibly through the liquid in the form of nanoparticles detaching from the gel. The organic template was initially contained in the liquid. However, it remains unclear at which stage the template becomes incorporated in the solid material. EDS at low voltage was also used to gain compositional information about the sodium/calcium ion exchanged products and extraneous phases when kaolin and Bolivian montmorillonite clay were used for the synthesis of zeolite A by alkali fusion. In order to evaluate the cation exchange capacity (CEC) of the synthesized zeolite, ICP-SFMS and EDS were compared. The EDS method used in this work resulted in (Na,Ca)/Al ratios in equivalent moles very close to 1.0 as expected and was therefore found more reliable than ICP-SFMS to measure cation exchange capacity for zeolite A. To summarize, the present work shows that it was possible to synthesize well-crystallized ZSM-5 zeolite from inexpensive raw materials such as leached metakaolin or leached diatomite, sodium hydroxide and n-butyl amine. Furthermore, the crystallization mechanism evidenced in this system might be more general and also apply for other concentrated systems, e.g. those using TPA as structure-directing. Finally, this work displays that EDS at low voltage can provide valuable local compositional information in the field of zeolite synthesis.

  • 622.
    Aguilar, Wilson
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering. Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Cardenas, Edgar
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering. Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering. Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Dendritic growth of NBA-ZSM-5In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093Article in journal (Other academic)
    Abstract [en]

    Crystallization of ZSM-5 zeolite from a gel using n-butylamine as structure-directing agent was studied. Extreme high-resolution transmission and scanning electron microscopy showed the presence of dendritic features that are present at the crystal surface during most of the reaction time that become smoother towards completion of the crystallization. In addition, a web that likely stems from the gel, comprised of alumina-rich nanoparticles between the dendrites at the surface of the crystals was also identified. When the gel is not in direct contact with the crystal surface, dendrites and the web are not observed, and the crystals grow faster. Thus, the alumina-rich web retards the crystal growth and cause the formation of dendritic features.

  • 623.
    Aguilar, Wilson
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Garcia, Gustavo
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Comparison between leached metakaolin and leached diatomaceous earth as raw materials for the synthesis of ZSM-52014In: SpringerPlus, E-ISSN 2193-1801, Vol. 3, no 1Article in journal (Refereed)
    Abstract [en]

    Inexpensive raw materials have been used to prepare ZSM-5 zeolites with SiO2/Al2O3 molar ratios in the range 20 - 40. Kaolin or Bolivian diatomaceous earth was used as aluminosilicate raw materials and sodium hydroxide and n-butylamine were used as mineralizing agents and template. Dealumination of the raw materials by acid leaching made it possible to reach appropriate SiO2/Al2O3 ratios and to reduce the amount of iron and other impurities. After mixing the components and aging, hydrothermal treatment was carried out and the products were recovered The results clearly show for the first time that well-crystallized ZSM-5 can be directly prepared from leached metakaolin or leached diatomaceous earth using sodium hydroxide and n-butylamine as mineralizing agents and template under appropriate synthesis conditions. A longer induction time prior to crystallization was observed for reaction mixtures prepared from leached diatomaceous earth, probably due to slower digestion of the fossilized diatom skeletons as compared with that for microporous leached metakaolin. The use of leached diatomaceous earth allowed higher yield of ZSM-5 crystals within comparable synthesis times. However, low amounts of Mordenite formed, which was related to the high calcium content of diatomaceous earth. Another considerable advantage of diatomaceous earth over kaolin is that diatomaceous earth does not require heat treatment at high temperature for metakaolinization.

  • 624.
    Aguilar-Mamani, Wilson
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Crystallization of NBA-ZSM-5 from kaolin2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    ZSM-5 is an aluminosilicate zeolite with high Si/Al ratio with suitable properties for catalysis, ion exchange, adsorption and membrane applications. The main goal of this thesis was to study the growth of ZSM-5 zeolite crystals from inexpensive natural sources of silica and alumina, as well as n-butylamine (NBA) as a low-cost structure directing agent.

    The first objective of this work was to develop pathways to synthesize ZSM-5 crystals from kaolin clay or diatomaceous earth, two inexpensive natural sources of silica and alumina (Paper I). In the case of kaolin, a heat treatment was used in order to form amorphous metakaolinite. Subsequently, dealumination of the raw materials by acid leaching made it possible to reach appropriate Si/Al ratios and to reduce the amount of impurities. Finally, leached metakaolinite or diatomaceous earth was reacted with sodium hydroxide and NBA. After synthesis optimization, both sources of aluminosilicates were found to behave differently during the course of synthesis and to lead to slightly different reaction products. The final products exhibited Si/Al ratios in the range 10-20. The use of leached diatomaceous earth allowed to reach higher yield of ZSM-5 crystals within comparable synthesis times. However, low amounts of mordenite were inevitably formed as a by-product, which was related to the high calcium content of diatomaceous earth. Therefore, the rest of the thesis focused on the kaolin system.

    In order to study the growth mechanism of ZSM-5 from leached metakaolinite, a proper methodology to gain local compositional data by energy dispersive spectroscopy (EDS) on aluminosilicates was developed (Paper II). Zeolite A was used as a model system that could be ion-exchanged with various elements. In order to evaluate the reliability of the measurements, inductively coupled plasma-sector field mass spectrometry (ICP-SFMS) and EDS were compared. The EDS method developed in this work resulted in molar ratios very close to theoretical values and was therefore found more reliable than ICP-SFMS. Therefore, the method developed for zeolite A was applied in the rest of the thesis work to study the formation and growth of ZSM-5 crystals.

    The second part of this work focused on the kaolin system in order to understand the nucleation and growth processes of the ZSM-5 crystals. This system was heterogeneous, due to the formation of a gel upon heating of the synthesis mixture. First, the internal structure of the gel was investigated (Paper III). Second, a kinetic study was performed and compared with microstructural observations (Paper IV). Finally, the mechanisms leading to Al-zoning and dendritical growth of the zeolite crystals were investigated (Paper V). The characterization of the intermediate phases during the different stages of the hydrothermal synthesis were analyzed by different analytical techniques, such as inductively coupled plasma-sector field mass spectrometry (ICP-SFMS), dynamic light scattering (DLS), extreme high resolution-scanning electron microscopy (XHR-SEM), energy dispersive spectroscopy (EDS), high resolution-transmission electron microscopy (HR-TEM), X-ray diffraction (XRD) and nitrogen gas adsorption.

    These investigations led to several important conclusions: 1) The walls of the gel were shown for the first time to be inhomogeneous and to possess a biphasic internal structure consisting of a mesoporous skeleton of aluminosilicate nanoparticles embedded in a silicate-rich soluble matrix of soft matter. 2) The kinetic study and microstructural evidences indicated that the early crystals were fully embedded inside the gel phase and that crystal growth was retarded, as the formation of the gel occurred simultaneously with the early growth of the crystals. Hence, nucleation and growth appeared to be solution mediated.  3) Finally, the Al zoning of the crystals was related to the biphasic internal structure of the gel, since the silicate-rich matrix was preferentially consumed first. 4) The dendrites present at the surface of the crystals during most of the growth process were shown to be caused by the presence of a web of nanoparticles, most likely originating from the mesoporous skeleton inside the gel.

    In the future, these findings are expected to lead to optimized synthesis pathways of catalysts with homogeneous properties and to contribute to the development of poor regions in Bolivia.

  • 625.
    Aguilar-Mamani, Wilson
    et al.
    Department of Chemistry, Faculty of Science and Technology, San Simon University, UMSS, Cochabamba.
    Akhtar, Farid
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Solution-mediated growth of NBA-ZSM-5 crystals retarded by gel entrapment2018In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 487, p. 57-64Article in journal (Refereed)
    Abstract [en]

    The synthesis of flat tablet-shaped ZSM-5 crystals from a gel using metakaolin as aluminosilicate source and n-butyl amine as structure directing agent was investigated. The evolution inside the solid phase was characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetry and mass spectrometry. A kinetic study indicated that the nucleation of the majority crystals occurred concurrently with the formation of the gel upon heating the starting liquid suspension. Microstructural evidences undeniably showed that the gel precipitated on ZSM-5 crystals and mineral impurities originating from kaolin. As a result, crystal growth was retarded by gel entrapment, as indicated by the configuration and morphology of the embedded crystals. The results presented herein are harmonized with a solution-mediated nucleation and growth mechanism. Our observations differ from the autocatalytic model that suggests that the nuclei rest inside the gel until released when the gel is consumed. Our results show instead that it is crystals that formed in an early stage before entrapment inside the gel that rest inside the gel until exposed at the gel surface. These results illustrate the limitation of the classical method used in the field to determine nucleation profiles when the crystals become trapped inside the gel.

  • 626.
    Aguilar-Mamani, Wilson
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering. Department of Chemistry, Faculty of Science and Technology, San Simon University, Cochabamba, Bolivia.
    Hedlund, Jonas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Mouzon, Johanne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Internal structure of a gel leading to NBA-ZSM-5 single crystals2018In: Journal of porous materials, ISSN 1380-2224, E-ISSN 1573-4854, Vol. 25, no 6, p. 1551-1559Article in journal (Refereed)
    Abstract [en]

    Porous gel structures are formed during the synthesis of the zeolite ZSM-5 due to the reaction between a source of aluminosilicate, sodium hydroxide, water and a structure directing agent, such as e.g. tetrapropylammonium (TPA) or n-butylamine (NBA). In the present work, the formation of the gel in a heterogeneous system leading to the crystallization of NBA-ZSM-5 zeolite from leached metakaolin was studied extensively. The solid and liquid phases obtained after separation were analyzed by inductively coupled plasma sector field mass spectrometry, dynamic light scattering, extreme high resolution-scanning electron microscopy, energy dispersive spectroscopy, high resolution-transmission electron microscopy, X-ray diffraction and nitrogen gas adsorption. The main gel phase formed after hydrothermal treatment exhibited a sponge-like structure resembling those forming in (Na, TPA)-ZSM-5-based systems. For the first time, the walls of the main gel were shown to be inhomogenous and to possess a biphasic internal structure consisting of a mesoporous skeleton of aluminosilicate nanoparticles embedded in a silicate-rich soluble matrix of soft matter. The data presented in this paper is of primary importance to understand the mechanism by which the gel is consumed and contributes to the growth process of the zeolite crystals.

  • 627.
    Aguilera, Roberto F.
    et al.
    Curtin University, Perth.
    Radetzki, Marian
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Social Sciences.
    Rewolucja £upkowa: Oewiatowe rynki gazu i ropy naftowej w warunkach transformacji2015In: Gospodarka Surowcami Mineralnymi, ISSN 0860-0953, Vol. 31, no 1, p. 5-26Article in journal (Refereed)
    Abstract [en]

    The shale gas and oil revolution has unexpectedly and forcefully begun to change the energy landscape in the United States. It is expected to spread beyond the US, with far reaching implications for the global energy map, but also for themacro-economy and politics ofmany countries. The purpose of this paper is to bring a better understanding to what prompted the revolution, to assess the production methods and associated environmental concerns, to speculate what can reasonably be expected in coming decades, and to sketch the full impact of a ripening shale revolution on the emerging economic and political policy choices for energy exporting and importing countries.We find that a large scale expansion can be expected in US shale gas and oil activities in the coming two decades. Globally, the shale leaders are likely to be countries that are already significant gas and oil producers. Setting up a policy framework to allow and promote shale development in a safe manner is a necessity for the launch of shale exploitation. The most important implication of a successful shale revolution would arguably be a downward pressure on gas and coal prices in regional markets and on the global oil price.

  • 628.
    Aguilera, Roberto F.
    et al.
    Curtin University, Perth.
    Radetzki, Marian
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Social Sciences.
    Shale gas and oil: Fundamentally changing global energy markets2013In: Oil & gas journal, ISSN 0030-1388, E-ISSN 1944-9151, Vol. 111, no 12, p. 54-61Article in journal (Refereed)
    Abstract [en]

    Shale production on a significant scale arose quite recently and is so far limited to the US with gas having a few years' lead on oil. Shale has already had a significant impact on US gas and oil output. Further sizable production increases can be expected in the US, and the shale revolution is likely to spread, with a lag, across the globe. This will result in fundamental repercussions for international energy markets. The resources in focus of our attention, comprising shale gas and coalbed methane along with tight gas and tight oil, typically lack strict definitions and they often overlap. However, they are all characterized by low permeability that yields commercially insufficient flows from vertical drilling. The shale revolution is the result of technological breakthroughs in horizontal drilling and hydraulic fracturing that have made vast dormant gas and oil resources economically exploitable

  • 629.
    Aguilera, Roberto F
    et al.
    Curtin University, Perth.
    Radetzki, Marian
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Social Sciences.
    Skifferrevolutionen: hur den kommer att transformera de globala gas- och oljemarknaderna2014In: Ekonomisk Debatt, ISSN 0345-2646, Vol. 42, no 2, p. 30-41Article in journal (Refereed)
  • 630.
    Aguilera, Roberto F.
    et al.
    Curtin University, Perth.
    Radetzki, Marian
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Social Sciences.
    The Price of Oil2015Book (Refereed)
    Abstract [en]

    Drawing on their extensive knowledge of the oil industry, Roberto F. Aguilera and Marian Radetzki provide an in-depth examination of the price of the world's most important commodity. They argue that although oil has experienced an extraordinary price increase over the past few decades, we have now reached a turning point where scarcity, uncertain supply and high prices will be replaced by abundance, undisturbed availability and suppressed price levels. They look at the potential of new global oil revolutions to bring the upward price push to an end and examine the implications of this turnaround for the world economy, as well as for politics, diplomacy, military interventions and the efforts to stabilize climate. This book will appeal to a wide readership of both academics and professionals working in the energy industry, as well as to general readers interested in the ongoing debate about oil prices

  • 631.
    Aguilera, Roberto F.
    et al.
    Curtin University, Perth.
    Radetzki, Marian
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Social Sciences.
    The shale revolution: Global gas and oil markets under transformation2014In: Mineral Economics, ISSN 2191-2203, E-ISSN 2191-2211, Vol. 26, no 3, p. 75-84Article in journal (Refereed)
    Abstract [en]

    The shale gas and oil revolution has unexpectedly and forcefully begun to change the energy landscape in the USA. It is expected to spread beyond the USA, with far reaching implications for the global energy map, but also for the macroeconomy and politics of many countries. The purpose of this paper is to bring a better understanding to what prompted the revolution, to assess the production methods and associated environmental concerns, to speculate what can reasonably be expected in coming decades, and to sketch the full impact of a ripening shale revolution on the emerging economic and political policy choices for energy exporting and importing countries. We find that a large scale expansion can be expected in US shale gas and oil activities in the coming two decades. Globally, the shale leaders are likely to be countries that are already significant gas and oil producers. Setting up a policy framework to allow and promote shale development in a safe manner is a necessity for the launch of shale exploitation. The most important implication of a successful shale revolution would arguably be a downward pressure on gas and coal prices in regional markets and on the global oil price.

  • 632.
    Aguilera, Roberto F.
    et al.
    Curtin University, Kent Street, Bentley, Perth.
    Radetzki, Marian
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Social Sciences.
    The synchronized and exceptional price performance of oil and gold: Explanations and prospects2017In: Resources policy, ISSN 0301-4207, E-ISSN 1873-7641, Vol. 54, p. 81-87Article in journal (Refereed)
    Abstract [en]

    This paper compares the global markets for gold and oil so as to explain the surprisingly high correlation of the two materials’ prices since 1970, and the exceedingly impressive rise of both price series compared with that of virtually all other primary commodities. We propose that developments in the oil market, and the resulting effects on the macroeconomy, influenced investment activity in gold, thus providing the most plausible explanation for the two commodities’ price synchronization. Our view on the extraordinary price increases of oil and gold, compared to a broad category of metals and minerals, is that oil prices rose first based on above-ground hurdles that restrained the capacity to produce, and gold prices then reacted as they were pushed up by rising safe-haven investment to store value – an attribute not shared by other metals and minerals. The paper also comments on the likely future price evolution of these important materials, arguing that oil prices will stagnate at levels observed from late 2014, or even weaken in the coming decades, but that gold prices will continue to ride relatively high – thus leading to a collapse of the oil/gold price connection.

  • 633.
    Ah Shenga, Pedro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. Luleå University of Technology.
    SAWING STRATEGIES FOR TROPICAL HARDWOOD SPECIES: Simulation studies based on industrial conditions of Mozambique2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The harvesting of Mozambique tropical hardwood species is considerable higher than the natural regrowth in the forest and the stock is decreasing drastically. Therefore, it is important to improve the material recovery when the wood is refined (i.e., in sawing and further refinement to products such as joineries, furniture etc.) to reduce the waste and to re-utilize efficiently the by-products to increase the added value. The wood processing industry is an important means to boost the industries in the rural areas and also to generate incomes for the local communities by creating jobs and business opportunities.

    The majority of the logging that can be used for sawmilling in Mozambique is exported as roundwood due to the inability of companies to meet the product standards set for export and to generate profit. The lack of capabilities of the local sawmills to generate profit, also foments the illegal logging because of the higher price of roundwood for export which contributes to increase the number of unlicensed individuals in harvesting. This threatens the law enforcement and thus the degradation of the local wood industry. An alternative to increase the profit and empower the local community could be to export more refined wood products such as sawn timber, parquet, and veneer instead of the roundwood.

    The objective of the work was to investigate alternative sawing strategies of tropical hardwood species that could increase the profitability of the Mozambique wood industry in general and at sawmill in particular. The subject was approached using a database of virtual logs and together with a sawing simulator. The thesis has two main focus areas: (1) creating the log database with the corresponding algorithms for sawing simulation, and (2) investigations of alternative sawing strategies.

    The first focus was to build the database of surface-scanned logs and develop the algorithm for the saw simulation. The results are a database of 15 logs models describing the logs outer shape in which 10 jambirre (Millettia stuhlmannii Taub.) and 5 umbila (Pterocarpus angolensis DC.), and the algorithm for the sawing simulation. The algorithm use “brute force” i.e., determines all volume yields of sawn timber from the combination of all settings of log-positioning parameters (offset, skew and rotation) and selects the maximum value of volume yield. From simulation, using three sawing patterns (cant-sawing, through-and-through sawing and square-sawing) combined with two positioning parameters (offset and rotation) it was found that the sawing pattern has great impact on volume yield and that the square-sawing gave higher yield followed by through-and-through sawing pattern.

    The second focus was on alternative sawing strategies; having in mind that the optimal volume yield is achieved by aid of computerized production systems and that these resources are not yet in use in Mozambique. Hence, the objective was to find the positioning parameters that can be set manually and improve the volume yield. The result have shown that the rotation is the most affecting parameter followed by offset and skew, and that the volume yield can decrease by between 7.7% and 12.5% from the optimal positioning when the logs are manually positioned with the knowledge about the optimal log position. In another study, using crook-up or horns-down positioning as alternative to the optimal positioning, the volume yield decreases by between 10% and 13% from the optimal positioning. By using bucked logs , the optimal volume yield increased by between 8% and 13% in relation to full lengths logs, and the volume yield of bucked logs when using crook up positioning decreases 2% in relation to optimal positioning of full length logs.

    It is concluded that there is an unexploited value potential in the wood chain which can be reached using alternative positioning and modern measurement techniques and that the grading of wood will facilitate and improve the sawing process.

  • 634.
    Ah Shenga, Pedro António
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Bomark, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    External Log Scanning for Optimizing Primary Breakdown of Tropical Hardwood Species2015Conference paper (Other academic)
    Abstract [en]

    The sawing of tropical hardwood species is a big challenge for sawmills in developing countries. In order to investigate sawing strategies and volume recovery of tropical hardwood species, a log shape database was created using a portable 3D laser scanner. The data were collected in Mozambique, where twelve Jambirre (Millettia stuhlmannii Taub.) and five Umbila (Pterocarpus angolensis DC) logs were scanned. The logs were selected among the most commercialized species and the crook was the main selection parameter. In addition, straight logs were incorporated as reference. A saw simulation Matlab algorithm that combines skew and rotation was developed. The results show that point cloud data from the 3D scanner provide detailed models of the external log geometry and accurately describe the log shapes and volumes. Preliminary results from breakdown simulation revealed that the through-and-through sawing pattern yields more than the cant saw pattern and that the increase in yield was almost the same for both species.

  • 635.
    Ah Shenga, Pedro António
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Bomark, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Simulated Breakdown of Two Tropical Hardwood Species2015In: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 11, no 4, p. 450-456Article in journal (Refereed)
    Abstract [en]

    A simulation study has been performed on a small log database of tropical hardwoods consisting of 10 Jambirre (Millettia stuhlmannii Taub.) and 5 Umbila (Pterocarpus angolensis D.C.) logs. The outer log shape was acquired by a 3D laser scanner before sawing and the heartwood content was estimated by measurement on images of the centre slabs after through-and-through sawing. Yield and value recovery using different sawing techniques and different sawing patterns, together with rotational and skew positioning errors, are presented. The results show that through-and-through sawing in the best rotation and skew positions tested improves the yield of Umbila logs by an average of 4.5 percentage points and Jambirre logs by 3.6 percentage points compared to cant sawing. It can be concluded that positioning and sawing patterns have a great influence on the yield and value recovery of these species and that log grade and species have an impact on the sawing pattern that should be used.

  • 636.
    Ah Shenga, Pedro António
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Bomark, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Simulation of Tropical Hardwood Processing: Sawing Methods, Log Positioning, and Outer Shape2015In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 10, no 4, p. 7640-7652Article in journal (Refereed)
    Abstract [en]

    To increase understanding of breakdown strategies for Mozambican timber, simulations were carried out using different sawing patterns that can be alternatives to the low degree of refinement performed for export today. For the simulations, 3D models of 10 Jambirre and 5 Umbila logs were used. The log shape was described as a point cloud and was acquired by 3D-laser scanning of real logs. Three sawing patterns (cant-sawing, through-and-through sawing, and square-sawing) were studied in combination with the log positioning variables skew and rotation. The results showed that both positioning and choice of sawing pattern had a great influence on the volume yield. The results also showed that the log grade had an impact on the sawing pattern that should be used for a high volume yield. The volume yield could be increased by 3 percentage points by choosing alternative sawing patterns for fairly straight logs and by 6 percentage points for crooked logs, compared to the worst choice of sawing pattern.

  • 637.
    Ah Shenga, Pedro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Bomark, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hagman, Olle
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    3D Phase-shift Laser Scanning of Log Shape2014In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 9, no 4, p. 7593-7605Article in journal (Refereed)
    Abstract [en]

    In this paper, a portable scanner to determine the 3D shape of logs was evaluated and compared with the measurement result of a computer tomography scanner. Focus was on the accuracy of the shape geometry representation. The objective is to find a feasible method to use for future data collection in Mozambique in order to build up a database of logs of tropical species for sawing simulations. The method chosen here was a 3D phase-shift laser scanner. Two logs, a birch log with bark and a Scots pine log without bark, were scanned, resulting in 450 cross sectional “images” of the pine log and 300 of the birch log. The areas of each point cloud cross section were calculated and compared to that of the corresponding computer tomography cross section. The average area difference between the two methods was 2.23% and 3.73%, with standard deviations of 1.54 and 0.91, for the Scots pine and birch logs, respectively. The differences in results between the two logs are discussed and had mainly to do with presence of bark and mantle surface evenness. Results show that the shape measurements derived from these methods were well correlated, which indicates the applicability of a 3D phase-shift laser scanning technology for gathering log data.

  • 638.
    Ah Shenga, Pedro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Bomark, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Log sawing positioning optimization and log bucking of tropical hardwood species to increase the volume yield2017In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 12, no 4, p. 257-262Article in journal (Refereed)
    Abstract [en]

    The sawmill industry is a very important link in the Mozambique forest products value chain, but the industry is characterized by undeveloped processing technology and high-volume export of almost unrefined logs. The low volume yield of sawn timber has been identified as a critical gap in the technological development of the industry. To improve the profitability of the industry, there is thus a need to develop methods and techniques that improve the yield. In this paper, different positioning of logs prior to sawing and the possibility of increasing the volume yield of crooked logs by bucking the logs before sawing have been studied. A computer simulation was used to study the cant-sawing and through-and-through sawing of the logs to determine the volume yield of sawn timber from the jambirre (Millettia stuhlmannii Taub.) and umbila (Pterocarpus angolensis DC.) species. The optimal position, i.e. the position of the log before sawing that gives the highest volume yield of sawn timber for a given sawing pattern when the positioning parameters, offset, skew and rotation, are considered gave a considerable higher volume yield than the horns-down position. By bucking very crooked logs and using the horns-down positioning before sawing, the volume yield can be of the same magnitude as that obtained by optimal positioning on full-length (un-bucked) logs. The bucking reduces the crook of the logs and hence increases the volume yield of sawn timber.

  • 639.
    Ah Shenga, Pedro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Bomark, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    The Effect of Log Position Accuracy on the Volume Yield in Sawmilling of Tropical Hardwood2016In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 11, no 4, p. 9560-9571Article in journal (Refereed)
    Abstract [en]

    This study investigated the effect of the positioning of the log before sawing on the volume yield of sawn timber from tropical hardwood species. Three positioning parameters were studied, the offset, skew, and rotation, combined with two sawing patterns of cant-sawing and through-and-through sawing. A database consisting of two tropical hardwood species with very different outer shapes, jambirre (Millettia stuhllmannii Taub.) and umbila (Pterocarpus angolensis DC.), was used to simulate the sawing process. The result of the simulation revealed that, according to the combined effect of offset, skew, and rotation positioning, the positioning of the log before sawing is extremely important to achieve a high volume yield of sawn timber. The positioning parameter that has the highest effect on the volume yield is the rotation, and the variation in the volume yield associated with a deviation in the positioning can reduce the volume yield of sawn timber by between 7.7% and 12.5%.

  • 640.
    Ah Shenga, Pedro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Cristovao, Luis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    A review of Mozambican wood exploitation: map of the processing chain2013In: Proceedings of the 21th International Wood Machining Semina: August 4th – 7th, Tsukuba International Congress Center, Japan, 2013, p. 293-301Conference paper (Other academic)
  • 641. Ahangeri Thornberg, Elias
    Users' perception of risk and trust in mobile payments2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Smartphones have become immensely popular in the last few years and with this popularity, new usage areas has emerged. One such area is mobile payments which allows smartphone users to pay for products with the help of their smartphones. This area has had a huge growth in different parts of the world but the growth in Sweden has been relatively low. Past studies carried out in other countries has shown that users are concerned with security related to mobile payments and that this concern affects their usage of mobile payments.The aim of this study is to examine how Swedish users perceive risk in mobile payments and determine if their perceived risk might be inhibiting the usage of mobile payments. In conjunction with examining risk, the study will also examine how well the users trust mobile payments and the companies offering mobile payments service in order to examine the relationship between the users perceived risk and trust towards mobile payments.The conclusion of this study shows that users do not perceive considerable risks with the mobile payment technology, however they are concerned about how their personal information is handled by the companies providing the mobile payment services. Trust was not seen as something that influenced the users’ perception of risk in a technological setting but played a big part in decreasing concerns that the user may have towards the companies and the way they handle their personal information.

  • 642.
    Ahdikari, Rajesh
    et al.
    Centre for Energy, Materials and Telecommunications, Institut National de la Recherche Scientifique, 1650 Boul. Lionel-Boulet, Varennes.
    Jin, Lei
    Institut National de la Recherche Scientifique Energie Varennes.
    Pardo, Fabola Navarro
    Centre for Energy, Materials and Telecommunications, Institut National de la Recherche Scientifique, Varennes.
    Benetti, Daniele
    INRS, Quebec University, Varennes, Centre for Energy, Materials and Telecommunications, Institut National de la Recherche Scientifique, Varennes.
    Otabi, Bandar Al
    Department of Electrical and Computer Engineering, McGill University, Montreal.
    Vanka, Srinivas
    Department of Electrical and Computer Engineering, McGill University, Montreal.
    Zhao, Haiguang
    Institut National de la Recherche Scientifique Energie Varennes, INRS Centre for Energy, Materials and Telecommunications, CNR-INO SENSOR Lab, Centre for Energy, Materials and Telecommunications, Institut National de la Recherche Scientifique, 1650 Boul. Lionel-Boulet, Varennes.
    Mi, Zetian
    Department of Electrical and Computer Engineering, McGill University, Montreal.
    Vomiero, Alberto
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Rosei, Frederico
    Institut National de la Recherche Scientifique Energie Varennes, Centre for Energy, Materials and Telecommunications, Institut National de la Recherche Scientifique, 1650 Boul. Lionel-Boulet, Varennes.
    High Efficiency, Pt-free Photoelectrochemical Cells for Solar Hydrogen Generation based on “Giant” Quantum Dots2016In: Nano Energy, ISSN 2211-2855, Vol. 27, p. 265-274Article in journal (Refereed)
    Abstract [en]

    Quantum dot (QD) sensitized TiO2 is considered as a highly promising photoanode material for photoelectrochemical (PEC) solar hydrogen production. However, due to its limited stability, the photoanode suffers from degradation of its long-term PEC performance. Here, we report the design and characterization of a high-efficiency and long-term stable Pt-free PEC cell. The photoanode is composed of a mesoporous TiO2 nanoparticle film sensitized with “giant” core@shell QDs for PEC solar hydrogen generation. The thick shell enhances light absorption in the visible range, increases the stability of the QDs and does not inhibit charge separation, injection and transport, needed for proper operation of the device. We prepared thin films of Cu2S nanoflakes through a simple and reproducible procedure, and used them as counter-electrodes replacing the standard Pt film, resulting in equivalent performances of the PEC cell. We obtained an unprecedented photocurrent density (~10 mA/cm2) for “giant” QDs based PEC devices (and corresponding H2 generation) and a very promising stability, indicating that the proposed cell architecture is a good candidate for long-term stable QD-based PEC solar hydrogen generation.

  • 643.
    Ahl Bollesparr, Marcus
    et al.
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences.
    Andrea John, Michelle
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences.
    Fondförvaltning: Går det fortfarande inte att generera en större riskjusterad avkastning än marknadens?2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Many Swedish households are investors, in 2018 investments in funds reached an average of 434 000 Swedish Crowns per person. The Nobel laureate Fama showed that yielding a higher risk-adjusted return than the market is not possible. Simultaneously, a great amount of actively conducted funds that pledges a higher return than the market is still launched today. Which arises a disorientation among small savers if passive or active conducted funds generate higher returns. Unlike previous studies, the range of funds were increased in this study. The purpose is to examine the returns of the funds with the performance measures Sharpe-ratio and Jensen’s Alpha. The results indicate that it is not possible to outperform a higher risk-adjusted yield than the market for the chosen time period. Overall, the passive funds had higher risk-adjusted returns compared to the active funds, which indicates that a higher fee for the funds is unjustified.

  • 644. Ahl, Martin
    et al.
    Bergman, Stefan
    Bergström, Ulf
    Eliasson, Thomas
    Ripa, Magnus
    Weihed, Pär
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Geochemical classification of plutonic rocks in central and northern Sweden2001Report (Other academic)
  • 645. Ahlberg, Anna-Karin
    et al.
    Johansson, Sofia
    Wallgren, Jenny
    Elevers attityder till läsning: en undersökning bland pojkar och flickor i skolår 6 och skolår 82007Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
  • 646. Ahlberg, Annika
    Produktutveckling av personbärande lyfttillbehör2002Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
  • 647.
    Ahlberg, Anton
    Luleå University of Technology, Department of Arts, Communication and Education, Media, audio technology and experience production and theater.
    Perceived audio quality of compressed audio in game dialogue2016Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    A game could have thousands of sound assets, to fit all of those files to a manageable storage space it is often necessary to reduce the size of the files to a more manageable size so they have to be compressed. One type of sound that often takes up a lot of disc space (because there is so much of it) is dialogue. In the popular game engine Unreal Engine 4 (UE4) the the audio is compressed to Ogg Vorbis and has as default the bit rate is set to 104 kbit/s. The goal of this paper is to see if untrained listeners find dialogue compressed in Ogg Vorbis 104 kbit/s good enough for dialogue or if they prefer higher bit rates. A game was made in UE4 that would act as a listening test. Dialogue audio was recorded with a male and a female voice-actor and was compressed in UE4 in six different bit rates. 24 untrained subjects was asked to play the game and identify the two out of six robots with the dialogue audio they thought sound the best. The results show that the subjects prefer the higher bit rates that was tested. The results was analyzed with a chi-squared test which showed that the null-hypothesis can be rejected. Only 21% of the answers were towards UE4s default bit rate of 104 kbit/s or lower. The result suggest that the subjects prefer dialogue in higher bit rates and UE4 should raise the default bit rate.

  • 648.
    Ahlberg, E.
    et al.
    Chalmers University of Technology, Department of Inorganic Chemistry.
    Forssberg, Eric
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Wang, Xianghuai
    Luleå tekniska universitet.
    The surface oxidation of pyrite in alkaline solution1990In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 20, no 6, p. 1033-1039Article in journal (Refereed)
    Abstract [en]

    The collector-less flotation of pyrite has been studied by conventional techniques and is correlated to the electrochemical behaviour of pyrite in alkaline solution (1m NaClO4, pH 11). It was concluded that the initial oxidation of pyrite produces a hydrophobic sulphur rich surface together with hydrophilic iron hydroxide species. Also upon grinding, the surface is covered by hydrophilic species and therefore no significant flotation was obtained in the absence of a collector. However, collectorless flotation was readily obtained in an iron complexing solution like EDTA. This indicates that the remaining sulphur-rich layer is responsible for the floatability of pyrite under these conditions

  • 649. Ahlberg, Emelie
    Arbetets betydelse: Om fyra ungas inställning till arbete och backpacking2011Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
  • 650. Ahlberg, Kenneth
    Pricing in industrial markets: a case study at Ovako Steel AB2005Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The aim of this thesis has been to provide a better understanding of pricing within industrial markets. Previous researchers have established that when deciding pricing strategy and ultimately the final price for a product, the marketing managers must take many factors, both internal and external, into consideration. This thesis will mainly investigate the internal factors that affect a manufacturer within industrial markets. To be able to get a better understanding of pricing within industrial markets, a case study was performed at Ovako Steel AB, a manufacturer of special engineering steel. The company operates within many markets both domestically and internationally. In many of the domestic markets, the company are market leader, both with regard to market share and price level and was therefore suitable for this study. In contradiction to previous research a finding from this study was that the investigated company actually were able to maintain a high price strategy over a longer period of time. The use of the analysis of the company’ customers and products as a tool for developing price differentiations were found to be very useful. Although the result of the analysis was not what the marketing staff had hoped for, it is a good starting point to develop a system for price differentiation. Additional finding for this study was that companies that is faced with high manufacturing costs and therefore use a high price strategy and act as price leaders in one or several markets, have to consider the use of augmented products to be able to create and maintain a high price.

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