1. |
- Överstam, Henrik, 1975-
(author)
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The interdependence of plastic behaviour and final properties of steel wire, analysed by the finite element method
- 2004
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Doctoral thesis (other academic/artistic)abstract
- The finite element method (FEM) has been used in order to study the interdependence of plastic behaviour and final properties in steel wire. Three processes metal forming have been studied: billet forging, wire rod rolling, and cold drawing. The forging study focuses on the possibilities to eliminate voids, pores and pipes by altering the bite ratio in open die forging. Forging is used in wire manufacturing when dealing with materials that are difficult or impossible to roll, e.g. tool steels like high-speed steels, and powder metallurgically manufactured materials like tungsten-molybdenum filament wire. The elimination of inner defects by forging were successfully simulated by the FEM. The rolling study focuses on the problems due of the extreme finish rolling velocities in modern wire rod mills and modern technologies such as thermo-mechanical rolling and sizing. A design for a high-speed laboratory mill for studies of material behaviour at extreme strain rates was made. With a combination of two-high stands and three-roll units is it possible to obtain a smoother temperature distribution in the bar cross section. Two studies of the cold drawing process were made. The first describes the distribution of the plastic deformation due to the die geometry. It was found that the influence of the die angle on the amount of inhomogeneous deformation decreases with increasing area reduction. The frictional behaviour was also studied. The second study describes how the bearing geometry affects the residual stress-state in the wire. It was found that a small taper could change the residual stress state in the surface immensely. This was shown with FE simulations and verified by X-ray diffraction measurements. The results in this paper gives a tool for control of the residual stress-state in the wire. This gives a possibility to increase e.g. the fatigue strength in the final product.
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2. |
- A Atlasov, Kirill, et al.
(author)
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1D photonic band formation and photon localization in finite-size photonic-crystal waveguides
- 2010
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Ingår i: OPTICS EXPRESS. - 1094-4087. ; 18:1, s. 117-122
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Tidskriftsartikel (refereegranskat)abstract
- A transition from discrete optical modes to 1D photonic bands is experimentally observed and numerically studied in planar photonic-crystal (PhC) L-N microcavities of length N. For increasing N the confined modes progressively acquire a well-defined momentum, eventually reconstructing the band dispersion of the corresponding waveguide. Furthermore, photon localization due to disorder is observed experimentally in the membrane PhCs using spatially resolved photoluminescence spectroscopy. Implications on single-photon sources and transfer lines based on quasi-1D PhC structures are discussed.
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3. |
- A Herrera, I, et al.
(författare)
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Comparing a multi-linear (STEP) and systemic (FRAM) method for accident analysis
- 2010
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Ingår i: RELIABILITY ENGINEERING and SYSTEM SAFETY. - London, UK : Elsevier Science B.V., Amsterdam.. - 0951-8320. ; 95:12, s. 1269-1275, s. 19-26
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Tidskriftsartikel (refereegranskat)abstract
- Accident models and analysis methods affect what accident investigators look for, which contributory factors are found, and which recommendations are issued. This paper contrasts the Sequentially Timed Events Plotting (STEP) method and the Functional Resonance Analysis Method (FRAM) for accident analysis and modelling. The main issue addressed in this paper is the comparison of the established multi-linear method STEP with the new systemic method FRAM and which new insights the latter provides for accident analysis in comparison to the former established multi-linear method. Since STEP and FRAM are based on a different understandings of the nature of accidents, the comparison of the methods focuses on what we can learn from both methods, how, when, and why to apply them. The main finding is that STEP helps to illustrate what happened, involving which actors at what time, whereas FRAM illustrates the dynamic interactions within socio-technical systems and lets the analyst understand the how and why by describing non-linear dependencies, performance conditions, variability, and their resonance across functions.
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4. |
- Aalberg, L, et al.
(författare)
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Development of a harmonised method for the profiling of amphetamines : II. Stability of impurities in organic solvents
- 2005
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Ingår i: Forensic Science International. - : Elsevier. - 0379-0738 .- 1872-6283. ; 149:03-Feb, s. 231-241
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Tidskriftsartikel (refereegranskat)abstract
- The present study focused on the stability of 22 amphetamine impurities dissolved in six organic solvents: isooctane, toluene, ethanol, dichloromethane, ethyl acetate, and diethyl ether. The aim was to find the most inert, and thereby most suitable, solvent for amphetamine profiling. Mixtures of the impurities were prepared in the different solvents, and changes in the concentrations of the individual compounds over-time were monitored by gas chromatographic analysis after 0, 4, 12, 24, 48, and 96 h. Isooctane and toluene provided the most inert conditions, although, a few of the impurities were insufficiently stable in these two solvents. The present experiments were performed as a part of the development of a harmonised method for profiling of amphetamine. The results can be used to support the choice of organic solvents for sample preparation. They also provide information about the stability of the impurities that are found in profiles of illicit amphetamine. This is essential due to the fact, that unstable compounds can have a negative influence on the comparison of profiles.
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5. |
- Aarao, J, et al.
(författare)
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Numerical implementation of the EDEM for modified Helmholtz BVPs on annular domains
- 2011
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Ingår i: JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS. - : Elsevier Science B.V., Amsterdam.. - 0377-0427. ; 235:5, s. 1342-1353
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Tidskriftsartikel (refereegranskat)abstract
- In a recent paper by the current authors a new methodology called the Extended-Domain-Eigenfunction-Method (EDEM) was proposed for solving elliptic boundary value problems on annular-like domains. In this paper we present and investigate one possible numerical algorithm to implement the EDEM. This algorithm is used to solve modified Helmholtz BVPs on annular-like domains. Two examples of annular-like domains are studied. The results and performance are compared with those of the well-known boundary element method (BEM). The high accuracy of the EDEM solutions and the superior efficiency of the EDEM over the BEM, make EDEM an excellent alternate candidate to use in the animation industry, where speed is a predominant requirement, and by the scientific community where accuracy is the paramount objective.
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6. |
- Aarao, J, et al.
(författare)
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The extended-domain-eigenfunction method for solving elliptic boundary value problems with annular domains
- 2010
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Ingår i: JOURNAL OF PHYSICS A-MATHEMATICAL AND THEORETICAL. - : Iop. - 1751-8113 .- 1751-8121. ; 43:18, s. 185202-
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Tidskriftsartikel (refereegranskat)abstract
- Standard analytical solutions to elliptic boundary value problems on asymmetric domains are rarely, if ever, obtainable. In this paper, we propose a solution technique wherein we embed the original domain into one with simple boundaries where the classical eigenfunction solution approach can be used. The solution in the larger domain, when restricted to the original domain, is then the solution of the original boundary value problem. We call this the extended-domain-eigenfunction method. To illustrate the methods strength and scope, we apply it to Laplaces equation on an annular-like domain.
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7. |
- Aarnio, Harri, et al.
(författare)
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Spontaneous Charge Transfer and Dipole Formation at the Interface Between P3HT and PCBM
- 2011
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Ingår i: Advanced Energy Materials. - : Wiley-VCH Verlag Berlin. - 1614-6832 .- 1614-6840. ; 1:5, s. 792-797
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Tidskriftsartikel (refereegranskat)abstract
- In the pursuit of developing new materials for more efficient bulk-heterojunction solar cells, the blend poly (3-hexylthiophene):[ 6,6]-phenyl-C(61)-butyric acid methyl ester (P3HT:PCBM) serves as an important model system. The success of the P3HT: PCBM blend comes from efficient charge generation and transport with low recombination. There is not, however, a good microscopic picture of what causes these, hindering the development of new material systems. In this report UV photoelectron spectroscopy measurements on both regiorandom-(rra) and regioregular-(rr) P3HT are presented, and the results are interpreted using the Integer Charge Transfer model. The results suggest that spontaneous charge transfer from P3HT to PCBM occurs after heat treatment of P3HT: PCBM blends. The resulting formation of an interfacial dipole creates an extra barrier at the interface explaining the reduced (non-)geminate recombination with increased charge generation in heat treated rr-P3HT: PCBM blends. Extensive photoinduced absorption measurements using both above-and below-bandgap excitation light are presented, in good agreement with the suggested dipole formation.
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8. |
- Aasmundtveit, K.E., et al.
(författare)
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Structural anisotropy of poly(alkylthiophene) films
- 2000
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 33:8, s. 3120-3127
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Tidskriftsartikel (refereegranskat)abstract
- The structural anisotropy of various poly(alkylthiophene) films have been studied by X-ray diffraction, using both conventional methods and synchrotron radiation at grazing incidence. Solution-cast films orient with the side chains preferably normal to the film surface, whereas spin-cast films of nonstereoregular material orient with both the main and the side chains in the film plane. For thick (10-50 µm) solution-cast films, the degree of orientation depends strongly on the solvent used for casting, and on the stereoregularity of the polymer, films of stereoregular materials being more oriented than those of nonregular materials. The most oriented nonregular films are those cast from mixtures of chloroform and tetrahydrofuran. Thin (50-500 nm) solution-cast films are more oriented than the thicker ones, and the effects of different stereoregularity or different casting solvents are small. For spin-cast films, the degree of orientation is independent of substrate and solvent. Spin-cast films of stereoregular material have two different phases: One with the side chains normal to the substrate, and another where they are parallel to the substrate. The diffraction peaks of spin-cast poly(octylthiophene) narrow considerably upon heating.
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9. |
- Aasmundtveit, K.E., et al.
(författare)
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Structural aspects of electrochemical doping and dedoping of poly(3,4-ethylenedioxythiophene)
- 2000
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Ingår i: Synthetic metals. - 0379-6779 .- 1879-3290. ; 113:1, s. 93-97
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemical dedoping and redoping of p-toluene sulfonate doped poly(3,4-ethylenedioxythiophene) (PEDOT) has been studied with in situ grazing incidence diffraction with water used as an electrolyte. The diffraction peak positions and integrated intensities do not change significantly during doping and dedoping, while the peak widths increase upon dedoping and decrease upon doping. This implies that the lattice parameters and the relative positions of the polymer chains and the p-toluene sulfonate ions remain unchanged, the redox processes being carried out by the motion of smaller ions between the polymer and the electrolyte, and that the structural order decreases upon dedoping and increases upon doping in a reversible manner.
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10. |
- Aasmundtveit, K.E., et al.
(författare)
-
Structural ordering in phenyl-substituted polythiophenes
- 2000
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 33:15, s. 5481-5489
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Tidskriftsartikel (refereegranskat)abstract
- Various substituted poly(phenylthiophene)s have been studied by X-ray diffraction. They are semicrystalline, with very different degrees of crystallinity. Those with para-substituted phenyl groups have a low degree of crystallinity, whereas those with ortho-substituted phenyl groups are more crystalline. The most crystalline materials in this study have two equally long substituents on the phenyl ring, one at the ortho position and the other at the ortho or meta position on the opposite side of the phenyl ring. Poly(3-(2,5-dioctylphenyl)thiophene) (PDOPT) was most thoroughly studied, and a structural model is proposed. The structure of PDOPT is quite different from previously studied substituted polythiophenes in that the octyl side chains are directed normal to the thiophene planes. In this way, the conjugated polymer chains are kept separated from each other. Solution-cast and spin-cast PDOPT films are anisotropic, with the octyl side chains oriented normal to the film surface in both cases. This is contrary to the situation for poly(3-alkylthiophene)s, where solution-cast and spin-cast films orient in different ways.
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