| 1. |
- Persson, Anders, et al.
(författare)
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Effects of enrichment on simple aquatic food webs
- 2001
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Ingår i: The American Naturalist. ; 157:6, s. 654-669
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Tidskriftsartikel (refereegranskat)abstract
- Simple models, based on Lotka-Volterra types of interactions between predator and prey, predict that enrichment will have a destabilizing effect on
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| 2. |
- Pettersson, Håkan, et al.
(författare)
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Optically induced charge storage and current generation in InAs quantum dots
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 65:7, s. 0733041-0733044
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Tidskriftsartikel (refereegranskat)abstract
- We report on optically induced charge storage effects and current generation in self-assembled InAs quantum dots embedded in an InP matrix. Illumination with photons of energy higher than about 0.86 eV efficiently loads the dots with a maximum of about 1 hole/dot. The spectral response at lower photon energy is strongly enhanced at elevated temperatures. We present a detailed balance model for the dots and discuss the thermally assisted optical excitation processes pertinent to hole accumulation. We also show that these processes make the dots act as nanometer-scaled temperature-dependent current generators.
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| 3. |
- Lindström, B., et al.
(författare)
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A brief history of catalysis
- 2003
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Ingår i: CATTech. - 1384-6566 .- 1572-8811. ; 7:4, s. 130-138
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Tidskriftsartikel (refereegranskat)abstract
- Historical studies are usually divided into segments of time that were marked by intellectual progress or specific achievements. Some periods are clearly identified by great events or an individual accomplishment that revolutionizes the entire concept. However, in most cases the advancement from one period to another is not marked by distinct accomplishments, but rather the result of a series of advances. This paper follows this conventional style and we have divided our subject of catalysis into five distinct periods.
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| 4. |
- Lindström, B., et al.
(författare)
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Activity and characterization of Cu/Zn, Cu/Cr and Cu/Zr on gamma-alumina for methanol reforming for fuel cell vehicles
- 2002
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Ingår i: Applied Catalysis A. - 0926-860X .- 1873-3875. ; 234:02-jan, s. 111-125
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Tidskriftsartikel (refereegranskat)abstract
- The influence of catalyst properties on the activity and selectivity of hydrogen generation by methanol reforming over copper-based catalysts impregnated on gamma-alumina pellets has been investigated. In the experiments, three sets of copper-based catalysts with various compositions were tested: Cu/Zn/Al2O3, Cu/Cr/Al2O3 and Cu/Zr/Al2O3. The catalysts were characterized using temperature programmed reduction (TPR), temperature programmed oxidation (TPO), SEM-EDS, Brunauer-Emmett-Teller (BET) surface area measurement and X-ray diffraction (XRD). The copper surface area was determined by pulse chemisorption using N2O. We found a correlation between the copper surface area and catalytic activity. The activity tests were performed in a fixed bed reactor with 15 g of spherical catalyst pellets using a gas hourly space velocity (GHSV) of 25,000. The results of the activity tests indicate that the choice of promoter and the catalyst composition greatly influence the activity as well as the selectivity for CO2 formation. The highest conversions were achieved for the zinc-containing catalysts (Cu/Zn/Al2O3) for both steam reforming and the combined reforming process. Complete conversion of methanol was only obtained for the zinc-containing catalysts when running the steam reforming process. The combined reforming process generally yielded A product stream containing lower carbon monoxide concentrations compared to steam reforming at the equivalent reactor temperature for all of the catalysts tested.
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| 5. |
- Lindström, B., et al.
(författare)
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Catalytic oxidation of liquid methanol as a heat source for an automotive reformer
- 2003
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Ingår i: Chemical Engineering & Technology. - : Wiley. - 0930-7516 .- 1521-4125. ; 26:4, s. 473-478
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Tidskriftsartikel (refereegranskat)abstract
- A reactor for catalytically oxidizing liquid methanol has been developed for supplying heat to an automotive reformer. In the tests presented in this paper we show that it is possible to catalytically combust liquid methanol by dispersing the methanol and air by a nebulizer over the catalysts. In the experiments we tested several base and noble metals and found that either platinum or palladium was required at the ignition zone. The tests also showed that it was possible to achieve complete combustion when only 25% of the catalyst bed contained a noble metal.
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| 6. |
- Lindström, B., et al.
(författare)
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Combined methanol reforming for hydrogen generation over monolithic catalysts
- 2003
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Ingår i: Chemical Engineering Journal. - 1385-8947 .- 1873-3212. ; 93:1, s. 91-101
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Tidskriftsartikel (refereegranskat)abstract
- An experimental investigation on hydrogen generation from methanol using monolithic catalysts is presented in this paper. The activity and carbon dioxide selectivity for the reforming of methanol over various binary copper-based materials, Cu/Cr, Cu/Zn and Cu/Zr, have been evaluated. The methanol reforming was performed using steam reforming and combined reforming (CMR, a combination of steam reforming and partial oxidation). The CMR process was carried out at two modes of operation: near auto-thermal and at slightly exothermal conditions. The catalysts have been characterized using BET surface area measurement, X-ray diffraction (XRD), temperature programmed reduction (TPR) and scanning electron microscopy (SEM-EDS). The results show that the choice of catalytic material has a great influence on the methanol conversion and carbon dioxide selectivity of the reforming reaction. The zinc-containing catalyst showed the highest activity for the steam reforming process, whereas the copper/chromium catalyst had the highest activity for the CMR process. The copper/zirconium catalyst had the highest CO2 selectivity for all the investigated process alternatives.
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| 7. |
- Lindström, B., et al.
(författare)
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Deactivation of copper-based catalysts for fuel cell applications
- 2001
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Ingår i: Catalysis Letters. - 1011-372X .- 1572-879X. ; 74:02-jan, s. 27-30
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Tidskriftsartikel (refereegranskat)abstract
- The activity of copper catalysts for the steam reforming of methanol was investigated under deactivating conditions. The effects of adding poisonous substances which can occur in the fuel, such as sulphur and chlorine, were studied. Thermal ageing by sintering was observed while exposing the catalyst to high temperatures. The catalyst activity for steam reforming was greatly affected by the addition of low concentrations of sulphur and chlorine. Sulphur was more detrimental to the catalyst than chlorine.
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| 8. |
- Lindström, B., et al.
(författare)
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Development of a methanol fuelled reformer for fuel cell applications
- 2003
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Ingår i: Journal of Power Sources. - 0378-7753 .- 1873-2755. ; 118:02-jan, s. 71-78
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Tidskriftsartikel (refereegranskat)abstract
- A compact methanol reformer for fuel cell vehicles (FCVs) has, been developed and successfully tested. The reformer which has been constructed to serve a 5 Me fuel cell operates by combined reforming of methanol (CRM) (a combination of steam reforming and partial oxidation). The exploitable energy surplus in a fuel cell vehicle is low and therefore a combustion system for heating the reformer which utilizes a catalyst for both evaporation and oxidation of liquid methanol was developed. We were able to obtain start-up times in the region of 4-6 min depending on the oxygen-to-methanol ratio (OMR) used for the combined reforming reaction. The main drawback from decreasing the start-up time by increasing the oxygen-to-methanol ratio was that the CO concentrations in the product stream increased. The reforming reaction was performed over copper-based catalysts while the oxidation took place over a mixture of platinum and manganese-based catalysts. The catalysts were characterized using SEM-EDS, BET surface area measurement and X-ray diffraction (XRD).
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| 9. |
- Lindström, B., et al.
(författare)
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Hydrogen generation by steam reforming of methanol over copper-based catalysts for fuel cell applications
- 2001
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Ingår i: International journal of hydrogen energy. - 0360-3199 .- 1879-3487. ; 26:9, s. 923-933
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an investigation concerning the reforming of methanol over various base-metal oxide catalysts. Copper-based catalysts were effective for the steam reforming of methanol. The selectivity and conversion was studied in a flow reactor in the temperature interval 180-320 degreesC. The active materials were impregnated on gamma -alumina pellets using the wet impregnation method. The promoters used in the investigation were chromium (Cr), zinc (Zn) and zirconia (Zr). The copper content and promoter used played an important role in the catalyst's ability to selectively convert methanol at low temperatures. Catalysts with high copper contents generally gave higher conversions and selectivities for the steam reforming reaction. The use of ternary components generally increased the catalyst selectivity towards carbon dioxide. Zirconia had a positive influence on the catalytic performance at low temperatures. The possibilities for the use of reforming systems with copper-based catalysts in fuel cell applications are promising.
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| 10. |
- Lindström, B., et al.
(författare)
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Steam reforming of methanol over copper-based monoliths : the effects of zirconia doping
- 2002
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Ingår i: Journal of Power Sources. - 0378-7753 .- 1873-2755. ; 106:02-jan, s. 264-273
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, an experimental investigation concerning steam reforming of methanol over various alumina-supported monolithic copper-based catalysts is presented. The activity and carbon dioxide selectivity was studied over two sets of catalysts, one of which was doped with zirconium, with five different copper contents. The zirconium-doped catalyst were less active with respect to the hydrogen yield, however, they were at all times more selective towards carbon dioxide over the entire temperature interval. The catalysts have been characterised using Brunauer-Emmett-Teller (BET) surface area measurement and X-ray diffraction (XRD). The results show that the copper loading and modification of the active material by zirconia doping had a great influence on the methanol conversion and carbon dioxide selectivity of the steam reforming reaction.
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| 11. |
- Pettersson, Håkan, 1962-, et al.
(författare)
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Case study of an InAs quantum dot memory : Optical storing and deletion of charge
- 2001
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Ingår i: Applied Physics Letters. - New York : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 79:1, s. 78-80
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Tidskriftsartikel (refereegranskat)abstract
- We have studied self-assembled InAs quantum dots embedded in an InP matrix using photocapacitance and photocurrent spectroscopy. These dots are potentially promising for memories due to the large confinement energy for holes. In this work we have realized simple quantum dot memory by placing the dots in the space–charge region of a Schottky junction. Our measurements reveal that a maximum of about one hole can be stored per dot. We also find that illumination for an extended period deletes the stored charge. We show that these limitations do not reflect the intrinsic properties of the dots, but rather the sample structure in combination with deep traps present in the sample.
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| 12. |
- Wan, Y., et al.
(författare)
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Design, synthesis, and biological evaluation of the first selective nonpeptide AT2 receptor agonist
- 2004
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Ingår i: J Med Chem. - : American Chemical Society (ACS). - 0022-2623 .- 1520-4804. ; 47:24, s. 5995-6008
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Tidskriftsartikel (refereegranskat)abstract
- The first druglike selective angiotensin II AT(2) receptor agonist (21) with a K(i) value of 0.4 nM for the AT(2) receptor and a K(i) > 10 microM for the AT(1) receptor is reported. Compound 21, with a bioavailability of 20-30% after oral administration and a half-life estimated to 4 h in rat, induces outgrowth of neurite cells, stimulates p42/p44(mapk), enhances in vivo duodenal alkaline secretion in Sprague-Dawley rats, and lowers the mean arterial blood pressure in anesthetized, spontaneously hypertensive rats. Thus, the peptidomimetic 21 exerts a similar biological response as the endogenous peptide angiotensin II after selective activation of the AT(2) receptor. Compound 21, derived from the prototype nonselective AT(1)/AT(2) receptor agonist L-162,313 will serve as a valuable research tool, enabling studies of the function of the AT(2) receptor in more detail.
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