Dynamic partitioning for concurrent waveform relaxation-based circuit simulation

A new dynamic circuit partitioning algorithm for the waveform relaxation method is presented. Such an algorithm dynamically changes the partitioning as the simulation proceeds through the simulation interval. The proposed algorithm is suitable for implementation on a multicomputer. Experimental results show that the algorithm decreases the runtimes for circuits where good static partitioning is difficult to find. This is true both in the ideal case, i.e., when communication overhead for the repartitioning is not included and the load is distributed as evenly as possible among the processors, and in the real-world case, when all the partitioning overhead and load imbalance are included in actual measured run times

Mediabilder av elevers litteracitet. En diskursteoretisk analys av texter publicerade i Dagens Nyheter och Aftonbladet år 2014

Sammanfattning: I föreliggande uppsats genomförs en analys av tidningsartiklar om elevers litteracitet, som har publicerats i Aftonbladet och Dagens Nyheter under år 014. Uppsatsens teoretiska ramverk utgår från Laclau och Mouffes (008) diskursteori och för att konkretisera mitt tillvägagångssätt har Sahlins (1999) diskursanalytiska metod använts. Även forskning kring medias makt och kring elevers litteracitet har inkluderats i uppsatsen för att synliggöra hur media, genom påverkan på exempelvis medborgarnas verklighetsuppfattning och den politiska dagordningen, påverkar skolan samt för att placera resultaten i en vidare litteracitetskontext. Uppsatsen syftar, utifrån ovanstående bakgrund, till att synliggöra och kritiskt granska vilken bild som artikuleras diskursivt av de svenska elevernas litteracitet i de valda tidningarna. Följande frågor kommer att besvaras: Hur artikuleras den svenska mediedebatten kring elevers litteracitet i tidningarna Aftonbladet och Dagens Nyheter år 014? Hur förhåller sig dessa diskurser till det aktuella forskningsläget gällande vilka litteracitetsförmågor som ska premieras i den svenska skolan? Vilka likheter och skillnader finns mellan de diskurser som artikuleras i de båda tidningarna? Texterna i Aftonbladet polemiserar mot den litteraturpolitiska och skolpolitiska diskursen under alliansregerings styre. Istället förespråkas ökad tillgänglighet av litteratur, ekonomiska bidrag för läsfrämjande och minskad segregation för att på så sätt förbättra elevernas litteracitet. De polemiserar även mot hur PISA-debatten är artikulerad, eftersom viktiga frågor utelämnas. En god litteracitetsförmåga är någonting som alla ska uppnå, men vad denna förmåga innehåller lämnas i majoriteten av texterna outtalat. Skribenterna i Dagens Nyheter intervjuar många forskare inom litteracitetsområdet och det framgår att metoder för att uppnå en god litteracitet exempelvis kan vara användandet av lässtrategier eller högläsning. Om litteracitetsförmågan utvecklas kan exempelvis ordförrådet, skrivförmågan och den empatiska förmågan utvecklas. Flera av texterna utgår från ett bristperspektiv där det framgår vad eleverna saknar eftersom de inte kan läsa tryckta, traditionella böcker. II av II

Synthesis gas generation by chemical-looping reforming in a continuously operating laboratory reactor

Chemical-looping reforming is a technology that can be used for partial oxidation and steam reforming of hydrocarbon fuels. This paper describes continuous chemical-looping reforming of natural gas in a laboratory reactor consisting of two interconnected fluidized beds. Particles composed of 60 wt% NiO and 40 wt% MgAl2O4 are used as bed material, oxygen carrier and reformer catalyst. There is a continuous circulation of particles between the reactors. In the fuel reactor, the particles are reduced by the fuel, which in turn is partially oxidized to H-2, CO, CO2 and H2O. In the air reactor the reduced oxygen h of reforming were recorded. Formation of solid carbon was noticed for some cases. Adding 25 vol% steam to the natural gas reduced or eliminated the carbon formation

Chemical-Looping Combustion and Chemical-Looping Reforming in a Circulating Fluidized-Bed Reactor Using Ni-Based Oxygen Carriers

Three oxygen carriers for chemical-looping combustion and chemical-looping reforming have been investigated in a small circulating fluidized-bed reactor. N2AM1400 was produced by freeze granulation with MgAl2O4 as a support material and had a NiO content of 20%. Ni18-αAl was produced by impregnation onto α-Al2O3 and had a NiO content of 18%. Ni21-γAl was produced by impregnation onto γ-Al2O3 and had a NiO content of 21%. Over 160 h of operation has been recorded. The conversion of natural gas into products was 96−100% depending on oxygen carrier and experimental conditions. For chemical-looping combustion, N2AM1400 and Ni21-γAl provided poor selectivity toward CO2 and H2O while Ni18-αAl initially showed very high selectivity, which declined as a function of time. For chemical-looping reforming, operating the reactor at the desired process parameters, which was a fuel reactor temperature of 950 °C and an air factor of 0.30, was possible with all of the tested oxygen-carrier materials. When only natural gas was used as fuel, there was significant formation of solid carbon in the fuel reactor for Ni18-αAl and Ni21-γAl. Adding 30% steam or CO2 to the fuel removed or decreased the carbon formation. During the course of the experiments, N2AM1400 and Ni18-αAl retained their physical and chemical structure, while Ni21-γAl displayed a significant reduction in porosity but remained highly reactive

Combined oxides as oxygen-carrier material for chemical-looping with oxygen uncoupling

Oxygen-carrier materials for chemical-looping with oxygen uncoupling (CLOU) must be capable of taking up and releasing gas-phase O2 at conditions relevant for generation of heat and power. In principle, the capability of a certain material to do so is determined by its thermodynamic properties. This paper provides an overview of the possibility to design feasible oxygen carrier materials from combined oxides, i.e. oxides with crystal structures that include several different cations. Relevant literature is reviewed and the thermodynamic properties and key characteristics of a few selected combined oxide systems are calculated and compared to experimental data. The general challenges and opportunities of the combined oxide concept are discussed. The focus is on materials with manganese as one of its components and the following families of compounds and solid solutions have been considered: (MnyFe1-y)Ox, (MnySi1-y)Ox, CaMnO3-δ,(NiyMn1-y)Ox, (MnyCu1-y)Ox and (MnyMg1-y)Ox. In addition to showing promise from a thermodynamic point of view, reactivity data from experimental investigations suggests that the rate of O2 release can be high for all systems. Thus these combined oxides could also be very suitable for practical application

Waste products from the steel industry with NiO as additive as oxygen carrier for chemical-looping combustion

Fe2O3-containing waste materials from the steel industry are proposed as oxygen carrier for chemical-looping combustion. Three such materials, red iron oxide, brown iron oxide and iron oxide scales, have been examined by oxidation and reduction experiments in a batch fluidized-bed reactor at temperatures between 800 and 950°C. NiO-based particles have been used as additive, in order to examine if it is possible to utilize the catalytic properties of metallic Ni to facilitate decomposition of hydrocarbons into more reactive combustion intermediates such as CO and H2. The experiments indicated modest reactivity between the waste materials and CH4, which was used as reducing gas. Adding small amounts of NiO-based particles to the sample increased the yield of CO2 in a standard experiment, typically by a factor of 1.5-3.5. The fraction of unconverted fuel typically was reduced by 70-90%. The conversion of CH4 to CO2 was 94% at best, corresponding to a combustion efficiency of 96%. This was achieved using a bed mass corresponding to 57 kg oxygen carrier per MW fuel, of which only 5 wt% was NiO-based synthetic particles. The different materials fared differently well during the experiments. Red iron oxide was fairly stable, while brown iron oxide was soft and subject to considerable erosion. Iron oxide scales experienced increased reactivity and porosity as function of the numbers of reduction cycles

Combined Cu/Mn Oxides as an Oxygen Carrier in Chemical Looping with Oxygen Uncoupling (CLOU)

This study investigates the O2 uncoupling properties of five different oxygen carrier particles, consisting of combined oxides of CuO and Mn3O4. The oxygen carriers were produced by freeze granulation followed by calcination at 950 °C for 6 h. Particles with 5, 10, 20, 31, and 61 wt % CuO were examined in both an inert (pure N2) atmosphere and in the presence of solid fuel (wood char) at 750 °C. At this relatively low temperature during fluidization with N2, the samples were capable of releasing gas-phase O2 in concentrations up to 1%. During reduction with wood char in 15 g of oxygen carriers, some materials could release gaseous O2 equal to 1.4% of their total mass. When the crushing strength and attrition index were measured with a customized jet cup, the mechanical stability of these samples was compared. These measurements showed that, in general, samples with a higher CuO content were more mechanically stable. On the basis of XRD analysis of the oxygen carriers, the major phase transitions were Mn2O3 ↔ Mn3O4 and combined spinel (Cu,Mn)3O4 ↔ CuMnO2. These transitions both provide a considerable amount of O2. It is concluded that the Cu–Mn–O system has considerable potential to be used as a oxygen carrier in chemical-looping applications at lower temperatures, perhaps interesting for biofuel combustion

Chemical Looping Combustion and Chemical Looping with Oxygen Uncoupling Experiments in a Batch Reactor Using Spray-Dried CaMn1–xMxO3−δ (M = Ti, Fe, Mg) Particles as Oxygen Carriers

Chemical looping combustion and chemical looping with oxygen uncoupling (CLOU) with oxygen carrier particles consisting of CaMn1-xMxO3-delta (M = Ti, Fe, Mg) has been studied by consecutive oxidation and reduction experiments in a fluidized-bed batch reactor. The examined particles were produced by spray drying, and all did show a significant release of gas-phase oxygen to the inert atmosphere at 900 and 1000 degrees C. All particles also provided very high reactivity with syngas and methane. Some of the examined particles showed unfavorable fluidization characteristics, i.e., they formed dust during operation or showed agglomeration or defluidization tendencies. The crushing strength of the particles that formed dust was typically <1.2 N. The desired perovskite structure was detected in all samples by X-ray diffractometry. The materials that included iron and titanium had these elements incorporated in the perovskite structure, substituting manganese. When magnesium had been included, it was not incorporated into the crystal structure; instead, it was present as a separate phase of MgO. In addition to a perovskite phase, most samples also contained small amounts of marokite (CaMn2O4). Particles doped with MgO calcined at 1300 degrees C showed good fluidization behavior, as well as particularly high reactivity with fuel

Using chemical-looping with oxygen uncoupling (CLOU) for combustion of six different solid fuels

AbstractChemical-looping with oxygen uncoupling (CLOU) is a novel method to burn solid fuels in gas-phase oxygen without the need for an energy intensive air separation unit. This paper presents batch laboratory fluidized bed CLOU tests where six different solid fuels are used with a Cu-based oxygen carrier. The results show that CLOU results in a factor 3 to 15 faster fuel conversions than conversional chemical-looping combustion

Combined Oxides of Iron, Manganese and Silica as Oxygen Carriers for Chemical-Looping Combustion

Spray-dried particles with the chemical compositions of Fe0.66Mn1.33SiO3 and FeMnSiO3 have been examined as oxygen carrier materials for chemical-looping combustion. The performance of the materials was examined in oxygen release experiments and during fuel operation with natural gas and syngas. The experiments were carried out in a fluidized-bed chemical-looping reactor system designed for a thermal power of 300 W. The reactor system includes an air reactor and a fuel reactor, as well as loop seals and means for circulation of the oxygen carrier particles. Both materials were able to release gas phase oxygen in inert atmosphere at temperatures between 800-950°C, and with approximately equal oxygen concentrations. Fe0.66Mn1.33SiO3 provided higher conversion of natural gas as compared to FeMnSiO3 and the fuel conversion increased with temperature for both materials. During natural gas operation with Fe0.66Mn1.33SiO3 the conversion reached 100% at around 950°C with a fuel reactor inventory of 235 kg/MW. The fuel conversion was improved when the solids inventory was increased; this improvement could especially be observed for FeMnSiO3 as the fuel conversion was lower for this material. Fe0.66Mn1.33SiO3 provided higher fuel conversion than FeMnSiO3 also when syngas was used as fuel. The fuel conversion increased with temperature for both materials and full conversion was reached above 800°C with a fuel reactor inventory of 225 kg/MW for Fe0.66Mn1.33SiO3, while FeMnSiO3 was incapable of providing full conversion. A rather large elutriation of fines and a significant change in particle size distribution could be observed during operation for both materials. Both materials could work as oxygen carrier for chemical-looping with oxygen uncoupling. Fe0.66Mn1.33SiO3 would be preferred as it has higher conversion of both syngas and natural gas, but the attrition behavior of the material would need to be further investigated