| 1. |
- Dahlman, Christian, et al.
(author)
-
Prototype effect and the persuasiveness of generalizations
- 2015
-
In: Review of Philosophy and Psychology. - : Springer Science and Business Media LLC. - 1878-5166 .- 1878-5158. ; 7:1, s. 163-180
-
Journal article (peer-reviewed)abstract
- An argument that makes use of a generalization activates the prototype for the category used in the generalization. We conducted two experiments that investigated how the activation of the prototype affects the persuasiveness of the argument. The results of the experiments suggest that the features of the prototype overshadow and partly overwrite the actual facts of the case. The case is, to some extent, judged as if it had the features of the prototype instead of the features it actually has. This prototype effect increases the persuasiveness of the argument in situations where the audience finds the judgment more warranted for the prototype than for the actual case (positive prototype effect), but decreases persuasiveness in situations where the audience finds the judgment less warranted for the prototype than for the actual case (negative prototype effect).
|
|
| 2. |
- Dahlman, Christian, et al.
(author)
-
The Effect of Imprecise Expressions in Argumentation-Theory and Experimental Results
- 2012
-
In: ARGUMENTATION 2012: International Conference on Alternative Methods of Argumentation in Law. - 9788021059481 ; , s. 15-30
-
Conference paper (peer-reviewed)abstract
- We investigate argumentation where an expression is substituted with a less precise expression. We propose that the effect that this deprecization has on the audience be called deprecization effect. When the audience agrees more with the less precise version of the argument, there is a positive deprecization effect. We conducted an experiment where the participants were presented with a court room scenario. The results of the experiment confirm the following hypothesis: If the participants find it hard to agree with the precise version of the argument and accept the use of the imprecise term, they will agree more with the imprecise version of the argument. Furthermore, we show that a person who reacts in this way to deprecization commits the fallacy of equivocation.
|
|
| 3. |
- Rieth, M., et al.
(author)
-
A brief summary of the progress on the EFDA tungsten materials program
- 2013
-
In: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 442:1-3, s. S173-S180
-
Journal article (peer-reviewed)abstract
- The long-term objective of the European Fusion Development Agreement (EFDA) fusion materials programme is to develop structural and armor materials in combination with the necessary production and fabrication technologies for reactor concepts beyond the International Thermonuclear Experimental Reactor. The programmatic roadmap is structured into four engineering research lines which comprise fabrication process development, structural material development, armor material optimization, and irradiation performance testing, which are complemented by a fundamental research programme on "Materials Science and Modeling." This paper presents the current research status of the EFDA experimental and testing investigations, and gives a detailed overview of the latest results on materials research, fabrication, joining, high heat flux testing, plasticity studies, modeling, and validation experiments.
|
|
| 4. |
- Rieth, M., et al.
(author)
-
Recent progress in research on tungsten materials for nuclear fusion applications in Europe
- 2013
-
In: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 432:1-3, s. 482-500
-
Research review (peer-reviewed)abstract
- The current magnetic confinement nuclear fusion power reactor concepts going beyond ITER are based on assumptions about the availability of materials with extreme mechanical, heat, and neutron load capacity. In Europe, the development of such structural and armour materials together with the necessary production, machining, and fabrication technologies is pursued within the EFDA long-term fusion materials programme. This paper reviews the progress of work within the programme in the area of tungsten and tungsten alloys. Results, conclusions, and future projections are summarized for each of the programme's main subtopics, which are: (1) fabrication, (2) structural W materials, (3) W armour materials, and (4) materials science and modelling. It gives a detailed overview of the latest results on materials research, fabrication processes, joining options, high heat flux testing, plasticity studies, modelling, and validation experiments.
|
|
| 5. |
|
|
| 6. |
- Wahlberg, Sverker, et al.
(author)
-
Fabrication of Nanostructured W-Y2O3 Materials by Chemical Methods
- 2012
-
In: Journal of Materials Chemistry. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 22:25, s. 12622-12628
-
Journal article (peer-reviewed)abstract
- A novel method for the fabrication of highly uniform oxide dispersion-strengthened (ODS) materials made by chemical processing is presented. The powders are fabricated by a two-step route starting with a chemical synthesis at room temperature, producing nanocrystalline yttrium doped tungsten trioxide hydrate precursor powders. Thermogravimetric analysis with evolved gas analysis revealed the presence of ammonium nitrate in the precursors. The second step is the reduction of the precursor in a hydrogen atmosphere at 600 and 800 degrees C. The reduced powders, containing W-1.2%Y2O3, showed two types of tungsten particles, cube-shaped with a size less than 250 nm and finer particles (<50 nm) of both spherical and cubic shape. The powder was consolidated by spark plasma sintering at 1100 degrees C, producing a bulk material with a relative density of 88%. Characterization of the sintered materials by high resolution scanning electron microscopy revealed a uniform microstructure with tungsten grains of less than 300 nm and nanosized oxide particles uniformly dispersed at the tungsten grain boundaries, as well as inside the tungsten grains. Experimental determination of the elastic properties was conducted by nanoindentation tests and fracture toughness was studied by radial indentation cracking.
|
|
| 7. |
- Wahlberg, Sverker, et al.
(author)
-
Nanostructured hard material composites by molecular engineering .1. Synthesis from soluble tungstate salts
- 1997
-
In: Nanostructured materials. - 0965-9773 .- 1872-9150. ; 9:1-8, s. 105-108
-
Journal article (peer-reviewed)abstract
- A key issue, in the development of very fine grades, is to produce materials with high uniformity. The aqueous chemistry of tungsten offers several possibilities for the synthesis of homogenous molecular precursors containing W and Co mixed on the atomic scale. Powders containing (NH4)(8)[H2Co2W11O40] have been prepared starting from sodium tungstate or ammonium metatungstate. Nanophase powders of W-Co and WC-Co powders were obtained after reduction at 750 degrees C under H-2 and carburisation at 1000 degrees C under H-2/CH4. Hard materials with submicron microstructures were obtained after sintering at 1410 degrees C.
|
|
| 8. |
- Wahlberg, Sverker, 1965-
(author)
-
Nanostructured Tungsten Materials by Chemical Methods
- 2011
-
Licentiate thesis (other academic/artistic)abstract
- Tungsten based-materials are used in many different technical fields, particularly in applications requiring good temperature and/or erosion resistance. Nanostructuring of tungsten alloys and composites has the potential to dramatically improve the materials’ properties, enhancing the performance in present applications or enabling totally new possibilities. Nanostructured WC-Co composites have been the focus of researchers and industries for over two decades. New methods for powder fabrication and powder consolidation have been developed. However, the fabrication of true nanograined WC-Co materials is still a challenge. Nanostructured tungsten composites for applications as plasma facing materials in fusion reactors have in recent years attracted a growing interest. This Thesis summarizes work on the development of chemical methods for the fabrication of two different types of nanostructured tungsten based materials; WC-Co materials mainly aimed at cutting tools applications and W-ODS composites with rare earth oxide particles, intended as plasma facing materials in future fusion reactors. The approach has been to prepare powders in two steps: a) synthesis of uniform powder precursors containing ions of tungsten and the doping elements by co-precipitation from aqueous solutions, and b) further processing of the precursors into W or WC based nano-composite powders. Highly homogenous W and Co containing powder precursors for WC-Co composites were prepared via two different routes. Keggin-based precursors ((NH4)8[H2Co2W11O40]) with agglomerates of sizes up to 50 μm, were made from sodium tungstate or ammonium metatungstate and cobalt acetate. The powder composition corresponded to 5.2 % Co in the final WC-Co composites. In a second approach, paratungstate-based precursors (Cox(NH4)10-2x[H2W12O42]) were prepared from ammonium paratungstate (APT) and cobalt hydroxide with different compositions corresponding to 3.7 to 9.7 % Co in WC-Co. These particles had a plate-like morphology with sides of 5-20 μm and a thickness of less than 1 μm. Both precursors were processed and sintered into highly uniform microstructures with fine scale (<1μm). The processing of paratungstate-based precursors was also further investigated. Nanostructured WC-Co powders with grains size of less than 50 nm by decreasing processing temperatures and by applying gas phase carburization. W-ODS materials were fabricated starting from ammonium paratungstate and rare earth elements (Y or La). Paratungstate-based precursors were prepared with different homogeneity and particle sizes. The degree of the chemical uniformity varied with the particle size from ca 1 to 30 μm. Tungsten trioxide hydrate-based precursors made from APT and yttrium nitrate under acidic conditions had dramatically higher homogeneity and smaller particle size. The crystallite size was decreased to a few nanometers. These precursors were further processed to composite nanopowder and sintered to a nanostructured W-1.2%Y2O3 composite with 88% relative density. In summary, APT can be converted to highly homogenous powder precursors of different compositions. The transformations are carried out in aqueous suspensions as a solvent mediated process, in which the starting material dissolves and the precursor precipitates. Powders with fine scale morphologies are obtained, e.g. plate-like particles with thickness less than 1 μm or spherical particles with size of a few nanometers. These precursors were processed further in to nano-sized composite powders and sintered to highly uniform tungsten composites with fine microstructures.
|
|
| 9. |
|
|
| 10. |
|
|
| 11. |
- Wahlberg, Sverker
(author)
-
Tungsten-Based Nanocomposites by Chemical Methods
- 2014
-
Doctoral thesis (other academic/artistic)abstract
- Tungsten based-materials find use in many different fields of engineering, particularly in applications where good temperature and/or erosion resistance is important. Nanostructuring of tungsten composites is expected to dramatically improve the materials’ properties and enhancing the performance in present applications but also enabling totally new possibilities. Nanostructured WC-Co materials have been the focus of researchers and engineers for over two decades. New fabrication methods have been developed. But, the fabrication of true nanograined WC-Co composites is still a challenge. Nanostructured tungsten-based materials for applications as plasma facing materials in fusion reactors have attracted a growing interest. This Thesis summarizes work on the development of chemical methods for the fabrication of two different types of nanostructured tungsten-based materials; WC-Co composites mainly for cutting tools applications and W-ODS materials with yttria particles, intended as plasma facing materials in fusion reactors. The approach has been to prepare powders in two steps: a) synthesis of uniform powder precursors containing ions of tungsten and cobalt or yttrium by precipitation from aqueous solutions and b) processing of the precursors into WC- or W-based nano-composite powders.Highly homogenous W- and Co- containing precursors for WC-Co composites were prepared via two different routes. Keggin-based precursors ((NH4)8[H2Co2W11O40]) were made from sodium tungstate or ammonium metatungstate and cobalt acetate. The powder composition corresponded to 5.2 % Co in the final WC-Co material. In a second approach, paratungstate-based precursors (Cox(NH4)10-2x[H2W12O42]) were prepared from ammonium paratungstate (APT) and cobalt hydroxide with different compositions corresponding to 3.7 to 9.7 % Co in WC-Co. Both precursors were processed and sintered into uniform microstructures with fine scale (<1μm). The processing of paratungstate-based precursors was also further investigated. WC-Co powders with grains size of less than 50 nm were obtained by decreasing processing temperatures and by applying gas phase carburization.W-ODS materials were fabricated starting from ammonium paratungstate and yttrium salts. Paratungstate-based precursors were prepared with different homogeneities and particle sizes. The degree of the chemical uniformity varied with the particle size from ca 1 to 30 μm. Tungsten trioxide hydrate-based precursors made from APT and yttrium salts under acidic conditions had higher uniformity and smaller particle size. The tungsten oxide crystallite size was decreased to a few nanometers. Yttrium was included either by doping or in a nanocomposite structure as yttrium oxalate. The nanocomposite precursor was found to be more reactive during hydrogen reduction, facilitating its conversion to pure W-Y2O3 nanopowder. The doped precursor were further processed to nanopowders and sintered to highly uniform W-1.2%Y2O3 composites.In summary, APT was converted to highly homogenous or uniform powder precursors ofdifferent compositions. The transformations were carried out in aqueous suspensions as a water-mediated process. These precursors were processed further in to nano-sized powders and sintered to highly uniform tungsten composites with fine microstructures.
|
|
| 12. |
- Yar, Mazher Ahmed, et al.
(author)
-
Chemically produced nanostructured ODS-lanthanum oxide-tungsten composites sintered by spark plasma
- 2011
-
In: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 408:2, s. 129-135
-
Journal article (peer-reviewed)abstract
- High purity W and W-0.9La(2)O(3) (wt.%) nanopowders were produced by a wet chemical route. The precursor was prepared by the reaction of ammonium paratungstate (APT) with lanthanum salt in aqueous solutions. High resolution electron microscopy investigations revealed that the tungstate particles were coated with oxide precipitates. The precursor powder was reduced to tungsten metal with dispersed lanthanum oxide. Powders were consolidated by spark plasma sintering (SPS) at 1300 and 1400 degrees C to suppress grain growth during sintering. The final grain size relates to the SPS conditions, i.e. temperature and heating rate, regardless of the starting powder particle size. Scanning electron microscopy revealed that oxide phases were mainly accumulated at grain boundaries while the tungsten matrix constituted of nanosized sub-grains. The transmission electron microscopy revealed that the tungsten grains consist of micron-scale grains and finer sub-grains. EDX analysis confirmed the presence of W in dispersed oxide phases with varying chemical composition, which evidenced the presence of complex oxide phases (WO-La) in the sintered metals.
|
|
| 13. |
- Yar, Mazher Ahmed, et al.
(author)
-
Micro-mechanical and high heat load testing of W-Y2O3 ODS armourmaterials fabricated by novel chemical method and SPS
-
In: Journal of nanoparticle research. - 1388-0764 .- 1572-896X.
-
Journal article (other academic/artistic)abstract
- Oxide-dispersed strengthened (ODS) - tungsten based composites can be fabricated using several methods. In this study W-Y2O3 composite powders were synthesized by an innovative chemical process yielding ultrafine to micron range grains that were subsequently compacted using spark plasma sintering (SPS). Micro-mechanical tests were conducted to investigate the elastic and fracture properties of sintered compacts with grain size from ultrafine to several microns. For the evaluation of the developed material for plasma facing armour application in the fusion reactor, high heat load tests have been performed in an electron beam test facility. Surface effects, i.e. roughening, particle erosion and crack formation in dependence of base temperature and power density, were determined for an applied number of 100 ELM like loads with a pulse duration of 1 ms. The crack paths at the surface and particularly versus the bulk material were investigated to determine the resistance of the material to the formation of cracks parallel to the surface which finally would limit the thermal transfer and lead to local overheating and probably melting. Furthermore, the thermal stability of material, i.e. the resistance to recrystallization was determined by thermal annealing up to 1800 °C and during the electron beam tests by applying heat loads that lead to a surface temperature increase of> 2000°C.
|
|
| 14. |
- Yar, Mazher Ahmed, et al.
(author)
-
Processing and Sintering of Yttrium-Doped Tungsten Oxide Nano-powders
-
In: Journal of nanoparticle research. - 1388-0764 .- 1572-896X.
-
Journal article (other academic/artistic)abstract
- Innovative chemical methods are capable of fabricating nanoscale tungsten oxide compoundsd oped with various rare-earth elements with high purity and homogeneity, which can be processed under hydrogen into nanostructured oxide-dispersed tungsten composite powders having several potential applications. However, hydrogen reduction of doped-tungsten oxide compounds is rather complex, affecting the morphology and composition of the final powder. In this study we have investigated the reduction of tungstic acid in the presence of Y and weprovide the experimental evidence that Y2O3 can be separated from Y-doped tungstic acid via hydrogen reduction to produce Y2O3-W powders. The processed powders were further consolidated by spark plasma sintering at different temperatures and holding times at 75 MPa pressure and characterized. The optimized SPS conditions suggest sintering at 1400 °C for 3 min holding time to achieve higher density composites with an optimum finer grain size (3 μm) and a hardness value up to 420 HV. Major grain growth takes place at temperatures above 1300 °C during sintering. From the density values obtained, it is recommend to apply higher pressure before 900 °C to obtain maximum density. Oxides inclusions present in the matrix were identified as Y2O3•3WO3 and Y2O3•WO3 during high resolution microscopici nvestigations.
|
|
| 15. |
- Yar, Mazher Ahmed, et al.
(author)
-
Processing and sintering of yttrium-doped tungsten oxide nanopowders to tungsten-based composites
- 2014
-
In: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 49:16, s. 5703-5713
-
Journal article (peer-reviewed)abstract
- Innovative chemical methods are capable of fabricating nanoscale tungsten oxide compounds doped with various rare-earth elements with high purity and homogeneity, which can be processed under hydrogen into nanostructured oxide-dispersed tungsten composite powders having several potential applications. However, hydrogen reduction of doped tungsten oxide compounds is rather complex, affecting the morphology and composition of the final powder. In this study, we have investigated the reduction of tungstic acid in the presence of Y and we provide the experimental evidence that Y2O3 can be separated from Y-doped tungstic acid via hydrogen reduction to produce Y2O3-W powders. The processed powders were further consolidated by spark plasma sintering at different temperatures and holding times at 75 MPa pressure and characterized. The optimized SPS conditions suggest sintering at 1400 A degrees C for 3 min holding time to achieve higher density composites with an optimum finer grain size (3 A mu m) and a hardness value up to 420 H (V). Major grain growth takes place at temperatures above 1300 A degrees C during sintering. From the density values obtained, it is recommend to apply higher pressure before 900 A degrees C to obtain maximum density. Oxides inclusions present in the matrix were identified as Y2O3 center dot 3WO(3) and Y2O3 center dot WO3 during high resolution microscopic investigations.
|
|
| 16. |
- Yar, Mazher Ahmed, et al.
(author)
-
Spark plasma sintering of tungsten-yttrium oxide composites from chemically synthesized nanopowders and microstructural characterization
- 2011
-
In: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 412:2, s. 227-232
-
Journal article (peer-reviewed)abstract
- Nano-crystalline W-1%Y2O3 (wt.%) powder was produced by a modified solution chemical reaction of ammonium paratungstate (APT) and yttrium nitrate. The precursor powder was found to consist of particles of bimodal morphology i.e. large APT-like particles up to 20 pm and rectangular yttrium containing ultrafine plates. After thermal processing tungsten crystals were evolved from W-O-Y plate like particles. spark plasma sintering (SPS) was used to consolidate the powder at 1100 and 1200 degrees C for different holding times in order to optimize the sintering conditions to yield high density but with reduced grain growth. Dispersion of yttrium oxide enhanced the sinterability of W powder with respect to lanthanum oxide. W-1%Y2O3 composites with sub-micron grain size showed improved density and mechanical properties as compared to W-La2O3 composites. Sample sintered in two steps showed improved density, due to longer holding time at lower temperature (900 degrees C) and less grain growth due to shorter holding time at higher temperature i.e. 1 min at 1100 degrees C.
|
|
| 17. |
- Zenker, Frank, et al.
(author)
-
Generalization in Legal Argumentation
- 2020
-
In: Journal of Forensic Psychology Research and Practice. - : Informa UK Limited. - 2473-2850 .- 2473-2842. ; 20:1, s. 80-99
-
Journal article (peer-reviewed)abstract
- When interpreting a natural language argument that generalizes over a contextually relevant category, audiences are likely to activate the category prototype and transfer its characteristics onto category instances. A generalized argument can thus appear more (respectively less) persuasive than one mentioning a specific category instance, provided the argument’s claim is more (less) warranted for the prototype than for the instance (positive and negative prototype effect). To investigate this effect in legal contexts using mock-scenarios, professional and lay judges at Swedish courts evaluated the persuasiveness of arguments giving a generalized or a specific description of an eyewitness. The generalized version described the witness either as an alcohol-intoxicated person or as a child, while the specific version varied both the amount of alcohol consumed (two vs. five glasses of wine) and the child’s age (four vs. 12 years). To investigate the effect of legal expertise on argument selection, moreover, law and social science students evaluate the persuasiveness of both argument versions. Though we observed statistically significant prototype effects as well as expertise effects, results were mixed and sometimes ran counter to normative expectation.
|
|
| 18. |
- Zhang, Zongyin, et al.
(author)
-
Processing of nanostructured WC-Co powder from precursor obtained by co-precipitation
- 1999
-
In: Nanostructured materials. - 0965-9773 .- 1872-9150. ; 12:1-4, s. 163-166
-
Journal article (peer-reviewed)abstract
- The paper reports the processing of a homogenous cobalt tungstate salt synthesised by co-precipitation starting from ammonium paratungstate and cobalt hydroxide. Different processing parameters such as temperatures and times of reduction and carburization and the composition of the carburization gas were studied. Powders of W and Co were obtained after the reduction of the precursor at 600 'C, 650 'C and 700 'C. The specific surface area of W-Co powders increased with decreasing reduction temperature. The carburization was carried out at 700 'C for 3 hours in different CO/CO2 - mixtures. The extent of the reaction was found to depend on the CO/CO2 - ratio. A nanophase WC-Co powder agglomerated at the micrometer scale was obtained after carburization in a 90%CO/10%CO2 gas-mixture.
|
|
