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  • 2251.
    Agrell, Fredrik
    et al.
    KTH, Superseded Departments, Machine Design.
    Ångström, Hans-Erik
    KTH, Superseded Departments, Machine Design.
    Eriksson, Bengt
    Wikander, Jan
    KTH, Superseded Departments, Machine Design.
    Linderyd, Johan
    Integrated Simulation and Engine Test of Closed Loop HCCI Control by aid of Variable Valve Timings2003In: SAE transactions, ISSN 0096-736X, Vol. 112, no 3, p. 1078-1091Article in journal (Refereed)
  • 2252.
    Agrell, Fredrik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Eriksson, Bengt
    Wikander, Jan
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Linderyd, Johan
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Practical Modeling of HCCI for Combustion Timing Control and Results from Engine Test2005In: KTH Internal Combustion Engine Report MFM, Vol. 162Article, review/survey (Refereed)
  • 2253.
    Agrell, Fredrik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Ångström, Hans-Erik
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Eriksson, Bengt
    Wikander, Jan
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Linderyd, Johan
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Transient Control of HCCI Combustion by aid of Variable Valve Timing Through the use of a Engine State Corrected CA50-Controller Combined with an In-Cylinder State Estimator Estimating Lambda2005Conference paper (Refereed)
    Abstract [en]

    One of the main challenges with the Homogeneous Charge Compression Ignition, HCCI, combustion system is to control the Start Of Combustion, SOC, for varying load and external conditions. A method to achieve this on a cycle-by-cycle basis is to vary the valve timing based on a feedback signal from the SOC of previous cycles. The control can be achieved with two basic valve-timing strategies named the Overlap- and the IVC-method. The Overlap-method works by trapping of residuals while the IVC-method affects the effective compression ratio

  • 2254.
    Agrell, Fredrik
    et al.
    KTH, Superseded Departments, Machine Design.
    Ångström, Hans-Erik
    KTH, Superseded Departments, Machine Design.
    Eriksson, Bengt
    Wikander, Jan
    KTH, Superseded Departments, Machine Design.
    Linderyd, Johan
    Transient Control of HCCI Through Combined Intake and Exhaust Valve Actuation2003Conference paper (Refereed)
    Abstract [en]

    Homogeneous Charge Compression Ignition, HCCI, has the attractive feature of low particulate emission and low Nitrogen Oxides, NOx, emission combined with high efficiency. The principle is a combination of an Otto and a Diesel engine in that a premixed charge is ignited by the compression heat.

  • 2255. Agrell, H. G.
    et al.
    Boschloo, Gerrit
    Hagfeldt, Anders
    Conductivity studies of nanostructured TiO2 films permeated with electrolyte2004In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 108, no 33, p. 12388-12396Article in journal (Refereed)
    Abstract [en]

    Charge transport in nanostructured TiO2 films permeated with an electrolyte was studied, using temperature-dependent conductivity and electron accumulation measurements. Two regions for charge transport were distinguished from the relationship between conductivity and electron concentration. In the first region (similar to1-20 electrons per TiO2 particle), the effective electron mobility is dependent on the electron concentration and values between 7 x 10(-4) and 78 x 10(-4) cm(2) V-1 s(-1) were determined. The activation energy of the mobility was similar to0.3 eV. The charge transport can be described with a trapping/detrapping model that involves localized band-gap states. In the second region (> 20 electrons per TiO2 particle), the effective electron mobility is independent of electron concentration and values of similar to150 x 10(-4) cm(2) V-1 s(-1) are calculated. The activation energy of mobility is in the range of 0-0.15 eV, depending on the electrolyte. Transport of electrons in the conduction band seems to be the most applicable model.

  • 2256. Agrell, J.
    et al.
    Birgersson, H.
    Boutonnet, Magali
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Steam reforming of methanol over a Cu/ZnO/Al2O3 catalyst: a kinetic analysis and strategies for suppression of CO formation2002In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 106, no 1-2, p. 249-257Conference paper (Refereed)
    Abstract [en]

    Steam reforming of methanol (CH3OH + H2O --> CO2 + 3H(2)) was studied over a commercial Cu/ZnO/Al2O3 catalyst for production of hydrogen onboard proton exchange membrane (PEM) fuel cell vehicles. A simple power-law rate expression was fitted to experimental data in order to predict the rates Of CO2 and H-2 formation under various reaction conditions. The apparent activation energy (E-a) was estimated to be 100.9 kJ mol(-1), in good agreement with values reported in the literature. Appreciable amounts of CO by-product were formed in the reforming process at low contact times and high methanol conversions. Being a catalyst poison that deactivates the electrocatalyst at the fuel cell anode at concentrations exceeding a few ppm, special attention was paid to the pathways for CO formation and strategies for its suppression. It was found that increasing the steam-methanol ratio effectively decreases CO formation. Likewise, addition of oxygen or air to the steam-methanol mixture minimises the production of CO. By shortening the contact time and lowering the maximum temperature in the reactor, CO production can be further decreased by suppressing the reverse water-gas shift reaction.

  • 2257. Agrell, J.
    et al.
    Birgersson, H.
    Boutonnet, Magali
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Melian-Cabrera, I.
    Navarro, R. M.
    Fierro, J. L. G.
    Production of hydrogen from methanol over Cu/ZnO catalysts promoted by ZrO2 and Al2O32003In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 219, no 2, p. 389-403Article in journal (Refereed)
    Abstract [en]

    Production of H-2 from methanol by steam reforming, partial oxidation, or a combination thereof was studied over Cu/ZnO-based catalysts. The catalysts were characterized by a variety of techniques, including N2O chemisorption, X-ray photoelectron spectroscopy, X-ray diffraction, and temperature-programmed reduction/oxidation. The influence of feed composition, reaction temperature, and catalyst formulation on H-2 production rate, product distribution, and catalyst lifetime was investigated. Distinct differences between the processes were observed with respect to catalyst behavior. ZrO2-containing catalysts, especially Cu/ZnO/ZrO2/Al2O3, exhibit the best performance in the steam reforming reaction. During partial oxidation, however, a binary Cu/ZnO catalyst exhibits the lowest light-off temperature and the lowest level of CO by-product. The redox properties of the catalyst appear to play a key role in determining the pathway for H-2 production. In particular. the extent of methanol and/or H-2 combustion at differential O-2 conversion is strongly dependent on the ease of copper oxidation in the catalyst.

  • 2258. Agrell, J.
    et al.
    Boutonnet, Magali
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Fierro, J. L. G.
    Production of hydrogen from methanol over binary Cu/ZnO catalysts - Part II. Catalytic activity and reaction pathways2003In: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 253, no 1, p. 213-223Article in journal (Refereed)
    Abstract [en]

    The activity for conversion of methanol into hydrogen was investigated over binary Cu/ZnO catalysts derived from precursors prepared by two different techniques, viz. oxalates formed in microemulsion and hydroxycarbonates formed in aqueous solution. Some distinct differences in the reaction pathways were observed. During partial oxidation of methanol under a sub-stoichiometric oxygen/methanol ratio, the microemulsion materials exhibited considerably higher combustion activity in the low-temperature region than a catalyst prepared in aqueous solution. Over the former, oxygen was quickly converted by methanol combustion, after which steam reforming was initiated, producing hydrogen at the expense of water and gradually decreasing the net heat of reaction. Hence, a reaction sequence for the partial oxidation reaction over microemulsion catalysts is proposed. consisting of consecutive methanol combustion and steam reforming, followed by decomposition when all oxygen has been consumed. Over the hydroxycarbonate catalyst, the reaction ignited at a higher temperature, directly producing hydrogen by partial oxidation of methanol. When the two types of catalysts were evaluated in the steam reforming reaction, all catalysts displayed the typical S-shaped dependence of methanol conversion on temperature. However, there was a downward shift in the temperature at which methanol reached complete conversion, favouring the hydroxycarbonate, material. Hydrogen was produced selectively over all catalysts, but carbon monoxide formation was more pronounced over the microemulsion materials. The differences in catalytic behaviour are discussed in terms of catalyst morphology and the valence state of Cu in the working catalyst.

  • 2259. Agrell, J.
    et al.
    Boutonnet, Magali
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Melian-Cabrera, I.
    Fierro, J. L. G.
    Production of hydrogen from methanol over binary Cu/ZnO catalysts - Part I. Catalyst preparation and characterisation2003In: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 253, no 1, p. 201-211Article in journal (Refereed)
    Abstract [en]

    Mixed copper-zinc oxide catalysts (Cu/ZnO) were prepared by two different techniques, i.e. from hydroxycarbonate precursors formed in aqueous solution and from oxalate precursors formed in water-in-oil microemulsion. Their physicochemical properties were characterised by nitrogen adsorption-desorption, N2O chemisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and oxidation (TPO). The BET surface areas ranged from 34 to 87 m(2)/g, depending on the method of preparation. Cu surface areas between 6.6 and 22 m(2)/g were measured. It was a general observation that catalysts prepared by microemulsion technique had lower Cu dispersions than expected (3.4-5.7%), due to a proposed partial embedding of Cu in ZnO. The catalyst prepared by carbonate co-precipitation exhibited a significantly higher Cu dispersion (10.3%). In addition, this catalyst displayed better resistance to successive TPR/TPO than the microemulsion catalysts, which exhibited significant Cu crystallite growth. However, the microemulsion route provided well-mixed materials with a narrow particle size distribution and the possibility to obtain high BET surface areas (up to 87 m(2)/g) by controlling the water/surfactant ratio in the microemulsion. XPS measurements revealed the existence of Cu+ species on the surface of both types of catalysts after exposure to a O-2/CH3OH mixture. The surface composition of the hydroxycarbonate-derived sample was unaffected by reduction in hydrogen and exposure to O-2/CH3OH, while Zn-enrichment on the surface was observed in the microemulsion catalysts after reduction, indicating sintering of the Cu particles. These observations were consistent with the TPR/TPO measurements.

  • 2260. Agrell, J.
    et al.
    Germani, G.
    Järås, Sven G.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Boutonnet, Magali
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Production of hydrogen by partial oxidation of methanol over ZnO-supported palladium catalysts prepared by microemulsion technique2003In: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 242, no 2, p. 233-245Article in journal (Refereed)
    Abstract [en]

    Selective production of hydrogen by partial oxidation of methanol, using air as oxidant, was studied over a series of ZnO-supported Pd catalysts. Microemulsion-assisted synthesis and conventional impregnation techniques were used for preparation of catalysts containing Pd particles of different sizes. Catalyst characterisation included BET, XRD and TEM analyses. The influence of Pd particle size on catalytic activity and product distribution was studied by carrying out activity measurements at temperatures between 230 and 300 degreesC using a stoichiometric feed composition. All catalysts performed well with respect to methanol conversion and hydrogen yield. Both methanol conversion and hydrogen selectivity increased with increasing reaction temperature, the latter at the expense of water formation. Oxygen conversion was complete throughout the examined temperature range. These selectivity trends, with a strong dependence of hydrogen and carbon monoxide selectivities on methanol conversion and reaction temperature, support a reaction scheme consisting of consecutive methanol combustion, steam reforming and decomposition. More importantly, a correlation between Pd particle size and carbon monoxide selectivity was found. When the microemulsion catalysts are compared, carbon monoxide formation increases with increasing particle size. This was not observed over the impregnated reference catalysts, which exhibited high carbon monoxide-levels throughout the examined temperature range. Bimetallic PdZn particles were detected in spent catalysts by means of XRD and it is suggested that the catalytic activity is dependent on the formation of PdZn, the catalytic function being different from that of Pd-0.

  • 2261. Agrell, J.
    et al.
    Hasselbo, K.
    Jansson, K.
    Järås, Sven G.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Boutonnet, Magali
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Production of hydrogen by partial oxidation of methanol over Cu/ZnO catalysts prepared by microemulsion technique2001In: Applied Catalysis A: General, ISSN 0926-860X, E-ISSN 1873-3875, Vol. 211, no 2, p. 239-250Article in journal (Refereed)
    Abstract [en]

    Production of hydrogen by partial oxidation of methanol, using air as oxidant. has been studied over a series of Cu/ZnO catalysts prepared by microemulsion technique. The catalytic activity was compared to that of a reference catalyst prepared by conventional co-precipitation. The BET surface areas of the microemulsion catalysts (30-70 wt.% Cu) ranged from 22 to 36 m(2)/g and were considerably lower than that of the reference (60 m(2)/g). Nevertheless, the microemulsion catalysts were more active in the partial oxidation reaction and exhibited high hydrogen and carbon dioxide selectivities. At a molar O-2/CH3OH ratio of 0.1, hydrogen production was initiated at about 185 degreesC over the microemulsion catalysts. Over the reference, hydrogen production began at 215 degreesC under the same conditions. The catalytic activity was Found to be strongly dependent on the partial pressure of oxygen, which also plays an important role in determining the product distribution. By increasing the O-2/CH3OH ratio, the methanol conversion and carbon dioxide selectivity increase. while production of water occurs at the expense of hydrogen. By TEM and TPR, it was observed that Cu is less well-dispersed in the microemulsion catalysts than in the reference. The higher catalytic activity is not expected considering the lower number of exposed Cu sites, i.e, the turnover frequencies are substantially higher over the microemulsion catalysts. It is possible that, a strong interaction between a small part of CuO and the ZnO lattice is responsible for the higher turnover frequencies of the microemulsion catalysts, or that particular crystallographic Cu planes or surface imperfections are the active sites of the reaction.

  • 2262.
    Agrell, Johan
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Development of Methanol-Reforming Catalysts for Fuel Cell Vehicles2003Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Vehicles powered by proton exchange membrane (PEM) fuelcells are approaching commercialisation. Being inherently cleanand efficient sources of power, fuel cells constitute asustainable alternative to internal combustion engines to meetfuture low-emission legislation. The PEM fuel cell may befuelled directly by hydrogen, but other alternatives appearmore attractive at present, due to problems related to theproduction, transportation and handling of hydrogen.

    Fuelling with an alcohol fuel, such as methanol, which isoxidised directly at the anode, offers certain advantages.However, the efficiency of the direct-methanol fuel cell (DMFC)is still significantly lower than that of the conventionalhydrogen-fuelled PEM fuel cell, due to some technical problemsremaining unsolved. Hence, indirect fuelling by a reformedliquid fuel may be the most feasible option in the early stagesof the introduction of fuel cell vehicles.

    The work presented in this thesis concerns the developmentof catalysts for production of hydrogen from methanol bypartial oxidation, steam reforming or a combination thereof.The work contributes to the understanding of how thepreparation route affects catalyst morphology and howphysicochemical properties determine catalytic behaviour andreaction pathways.

    The thesis is a summary of seven papers published inscientific periodicals. The first paper (Paper I) reviews thecurrent status of catalytic hydrogen generation from methanol,focusing on the fuel cell application. Paper II investigatesthe partial oxidation of methanol over Cu/ZnO catalystsprepared in microemulsion and by a conventionalco-precipitation technique. The activity for methanolconversion in the low-temperature regime is found to besignificantly higher over the former materials and the workcontinues by determining the nature of possible Cu-ZnOinteractions in the catalysts by studying their physicochemicalproperties more thoroughly (Paper III). In Paper IV, thepathways for methanol conversion via both partial oxidation andsteam reforming are elucidated.

    In Paper V, partial oxidation of methanol is studied overPd/ZnO catalysts prepared by microemulsion technique and againcompared to conventional materials. This investigationdemonstrates that although possessing high methanol conversionactivity, palladium-based catalysts are not suitable forreforming in fuel cell applications due to the considerableamounts of carbon monoxide formed.

    In Paper VI, methanol reforming is investigated over acommercial Cu/ZnO/Al2O3 catalyst. The mechanisms for carbonmonoxide formation and strategies for its suppression arediscussed, as well as reactor design aspects. The study alsoincludes some simple kinetic modelling. Finally, Paper VIIdescribes the optimisation of catalyst composition and processconditions to reach high hydrogen production efficiency at lowoperating temperatures and with minimum carbon monoxideformation.

    Keywords:PEM fuel cells, hydrogen, methanol, reforming,(partial) oxidation, reaction pathways, carbon monoxide,catalyst, microemulsion, Cu/ZnO, Pd/ZnO, copper, redoxproperties, oxidation state

  • 2263. Agren, N. D.
    et al.
    Westermark, Mats O.
    Bartlett, M. A.
    Lindquist, T.
    First experiments on an evaporative gas turbine pilot power plant: Water circuit chemistry and humidification evaluation2002In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 124, no 1, p. 96-102Article in journal (Refereed)
    Abstract [en]

    The evaporative gas turbine (EvGT), also known as the humid air turbine (HAT) cycle, is a novel advanced gas turbine cycle that has attracted considerable interest for the last decade. This high-efficiency cycle shows the potential to be competitive with Diesel engines or combined cycles in small and intermediate scale plants for power production and/or cogeneration. A 0.6 MW natural gas-fired EvGT pilot plant has been constructed by a Swedish national research group in cooperation between universities and industry. The plant is located at the Lund Institute of Technology, Lund, Sweden. The pilot plant uses a humidification tower with metallic packing in which heated water from the flue gas economizer is brought into direct counter current contact with the pressurized air from the compressor This gives an efficient heat recovery and thereby a thermodynamically sound cycle. As the hot sections in high-temperature gas turbines are sensitive to particles and alkali compounds, water quality issues need to be carefully considered. As such, apart from evaluating the thermodynamic and part-load performance characteristics of the plant, and verifying the operation of the high-pressure humidifier, much attention is focused on the water chemistry issues associated with the recovery and reuse of condensate water from the flue gas. A water treatment system has been designed and integrated into the pilot plant. This paper presents the first water quality results from the plant. The experimental results show that the condensate contains low levels of alkali and calcium, around 2 mg/l Sigma(K,Na,Ca), probably originating from the unfiltered compressor intake, About 14 mg/l NO2- +NO3- comes from condensate absorption of flue gas NOx. Some Cu is noted, 16 mg/l, which originates from copper corrosion of the condenser tubes. After CO2 stripping, condensate filtration and a mixed bed ion exchanger the condensate is of suitable quality for reuse as humidification water The need,for large quantities of demineralized water has by manY authors been identified as a drawback for the evaporative cycle. However, by cooling the humid flue gas, the recovery, of condensed water cuts the need of water feed. A self-supporting water circuit can be achieved, with no need for any net addition of water to the system. In the pilot plant, this was achieved by cooling the flue gas to around 35degreesC.

  • 2264. Agren, N. D.
    et al.
    Westermark, Mats O. J.
    Design study of part-flow evaporative gas turbine cycles: Performance and equipment sizing - Part I: Aeroderivative core2003In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 125, no 1, p. 201-215Article in journal (Refereed)
    Abstract [en]

    The evaporative gas turbine cycle is a new high-efficiency power cycle that has reached the pilot testing stage. This paper presents calculation results of a new humidification strategy based on part flow humidification. This strategy involves using only a fraction of the compressed air for humidification. Thermodynamically, it can be shown that not all the air needs to be passed through the humidification system to attain the intrinsic good flue gas heat recovery of an EvGT cycle. The system presented also includes live steam production and superheating by heat from the hottest flue gas region. The humidifier only uses the lower temperature levels flue gas heat, where it is best suited. The analyzed system is based on data for the aeroderivative Rolls Royce Trent as a gas turbine core. Part 11 of this two-part paper presents the results based on data for the industrial gas turbine ABB GTX100. Simulation results include electric efficiency and other process datas as functions of degree of part Tow. A detailed model of the humidifier is also used and described, which produces sizing results both for column height and diameter. Full flow humidification generates an electric efficiency of 51.5% (simple cycle 41%). The efficiency increases when the humidification airflow is reduced, to reach a maximum of 52.9% when airflow to the humidification amounts to around 12% of the intake air to the compressor. At the same time, total heat exchanger area is reduced by 50% and humidifier volume by 36% compared to full flow humidification. This calls for a recommendation not to use all the compressed air for humidification.

  • 2265. Agren, N. D.
    et al.
    Westermark, Mats O. J.
    Design study of part-flow evaporative gas turbine cycles: Performance and equipment sizing - Part II: Industrial core2003In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 125, no 1, p. 216-227Article in journal (Refereed)
    Abstract [en]

    This is Part II of a two-part paper and presents calculation results of a part-flow EvGT cycle based on gas turbine data for the ABB GTX100 (modified for intercooling). The evaporative gas turbine cycle is a new high-efficiency cycle that has reached the pilot testing stage. This paper presents calculation results of a new humidification strategy based on part-flow humidification. This strategy involves using only a fraction of the compressed air for humidification. Thermodynamically, it can be shown that not all the air needs to be passed through the humidification system to attain the intrinsic good flue gas heat recovery of an EvGT cycle. The presented system also includes live steam production and superheating, by heat from the hottest flue gas region, for injection. The humidifier then only uses the lower temperature levels, where it is best suited. The analyzed system is based on data for the ABB GTX100.gas turbine in intercooled mode. Part 1 of this two-part paper presents the results based on data for the aeroderovative Rolls Royce Trent. Simulation results include electric efficiency and other process data as function of degree of part flow. A detailed model of the humidifier is used, which produces sizing results both for column height and diameter. Paper 1 includes detailed description of the modeling. For the GTXI00 system, full flow humidification generates an electric efficiency of 52.6% (simple cycle 36.2%). The efficiency is virtually unaffected if the air portion to humidification is cut to 60% of accessible compressor air (represents 48% of compressor intake). If 30% of air from the compressor after cooling bleed (24% of intake) is led to the humidifier, the efficiency is reduced to 52.2%. On the other hand is the total heat exchanger area reduced by 20% and column volume by 50%. This calls for a recommendation not to use all the compressed air for humidification. It is recommended to use 15-30% of compressor intake air. The exact economic optimum depends on local fuel prices, CO2 taxes, interest rates, etc.

  • 2266. Agren, P.
    et al.
    Andersson, K.
    Haviland, David B.
    KTH, Superseded Departments, Physics.
    Kinetic inductance and Coulomb blockade in one dimensional Josephson junction arrays2001In: Journal of Low Temperature Physics, ISSN 0022-2291, E-ISSN 1573-7357, Vol. 124, no 02-jan, p. 291-304Article in journal (Refereed)
    Abstract [en]

    One dimensional Josephson junction arrays have been fabricated and current-voltage characteristics (IVC) have been measured at cryogenic temperatures. The arrays were fabricated in a SQUID-geometry which allowed an in. situ tuning of thc Josephson energy by application of a magnetic field. The IVC of thc arrays shows a clear Coulomb blockade state. In the Coulomb blockade regime the IVC are hysteretic, The array is modeled using a Serial resistive-inductive-junction model which is able to qualitatively explain the IVC. In this model an inductance of the order of 0.1-10 mH per Junction is needed to account for the hysteresis. Kinetic inductance. stemming from the inertia of the Cooper pairs. gives the correct order of magnitude. The problem of self-heating is also discussed as an alternative explanation of the hysteresis.

  • 2267. Agren, P.
    et al.
    Johansson, J.
    Andersson, K.
    Haviland, David B.
    KTH, Superseded Departments, Physics.
    Hysteretic current-voltage characteristics and Coulomb blockade in 1D-arrays of Josephson junctions2000In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 280, no 04-jan, p. 414-415Article in journal (Refereed)
    Abstract [en]

    The IV characteristics (IVC) of 1D-arrays of small capacitance Josephson junctions with E-C similar to E-J have been measured. The IVC show Coulomb blockade of Cooper pair tunneling and exhibit a pronounced hysteresis which appears to be dual to the well-known resistively shunted junction behavior of ordinary Josephson junctions. A dual serially resistive junction model is used to qualitatively explain the measured data.

  • 2268.
    Agrenius Gustafsson, Thomas
    KTH, School of Engineering Sciences (SCI).
    A quantum chemical study of electronic circular dichroism in alanine oligopeptides2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Circular dichroism (CD) spectroscopy, exploiting the wavelength-dependentdifferential absorption of left- and right-handed circularly polarized light, isa popular method of protein characterization. Theoretically computed CDspectra from quantum mechanical computer models of peptides can widen theapplicability of the method. In this work, the usefulness of Time-DependentDensity Functional Theory (TD-DFT) with the CAM-B3LYP functional and6-31+G(d) basis set in obtaining CD spectra of model alanine α-helices 3to 15 residues long is investigated.  It is found that including 10 excitedstates per residue in the TD-DFT calculation resolves the characteristic partof the spectra sufficiently.  However, the results suffer from blueshift andimproper weakness of the 222 nm peak of the characteristic α-helix spectracorresponding to the n → π∗ transition, despite extension of the basis set to6-311++G(d,p) and use of the Polarizable Dielectric Continuum Model totreat solvent effects. In this case, these issues are limiting the usefulness ofTD-DFT for prediction of peptide CD spectra. More advanced methods totreat solvent interaction and benchmarking the performance of the functionalwith higher-level ab initio methods are suggestions for future studies.

    A introduction to electronic structure theory and the use of time-dependentperturbation theory to treat spectroscopy is also given in this work.

  • 2269.
    Agrest, Inna
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management.
    Skatt på finansiella transaktioner - En studie över hur Sverige kan komma att påverkas av skatt2013Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The idea of taxing markets have been around for decades and the goals today are the same as they were 80 years ago, to

     Harmonize existing legislation by reducing the amount of different national taxation methods,

     Stabilize markets thru decreased volatility

     Collect tax revenue

    The tax revenue will later be used to finance something that the society wants to finance.

    This thesis examines the possible effects that the financial transaction tax might have on Sweden and will present the effects that the tax might have not only inside the 11 countries in the European Union that will implement the tax from January 2014 but also on those outside, who will face higher costs even though they are not planning on implementing the tax. Sweden faces a risk with decreased pension’s funds a change in how we invest and where we invest.

  • 2270.
    Agrios, Alexander George
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry (closed 20110630). KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Cesar, I.
    Comte, P.
    Nazeeruddin, M. K.
    Grätzel, M.
    Nanostructured composite films for dye-sensitized solar cells by electrostatic layer-by-layer deposition2006In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 18, no 23, p. 5395-5397Article in journal (Refereed)
    Abstract [en]

    The possibilities for making nanocomposite semiconductor films for DSC using the ELBL method was investigated. Coated slides were cut in half vertically giving two strips that can be subjected to different treatments for comparison. The electrode was heated to 450 °C for 30 min and then Cooled to 80 °C. Scanning electron microscopy of a sintered film with 5 cycles of TiO2 nanoparticles shows that the particles are well distributed and completely cover the transparent conducting oxide substrate. Spectroscopic measurements of a dye-coated film in acetonitrile found a dye concentration within the film of 0.15 mM based on an extinction coefficient. The solar cell including a scattering layer had more than double the current of the transparent layer-only cell. It was observed that ELBL method can produce TiO2 films for DSC with high efficiencies at low thickness.

  • 2271.
    Agrogiannis, Serafim
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Applied Mechanical Engineering (KTH Södertälje).
    Agrogiannis, Christos
    KTH, School of Industrial Engineering and Management (ITM), Applied Mechanical Engineering (KTH Södertälje).
    A Critical Review and Evaluation of the Lean Concept and Corporate Social Responsibility/Sustainability: Investigating Their Interrelation and Contribution in Terms of Business Competitive Positioning2015Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
  • 2272.
    Agrén, Ola
    KTH, Superseded Departments, Electrical Systems.
    Losses and thermal analysis of a high-speed PM generator for miccroturbines2003Doctoral thesis, comprehensive summary (Other scientific)
  • 2273. Agterberg, Daniel F.
    et al.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics. University of Massachusetts, USA.
    Garaud, Julien
    KTH, School of Engineering Sciences (SCI), Theoretical Physics. University of Massachusetts, USA.
    Microscopic prediction of skyrmion lattice state in clean interface superconductors2014In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 6, p. 064509-Article in journal (Refereed)
    Abstract [en]

    When an in-plane field is applied to a clean interface superconductor, a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like phase is stabilized. This phase has a U(1)xU(1) symmetry and, in principle, this symmetry allows for flux carrying topological excitations different from Abrikosov vortices (which are the simplest defects associated with S-1 --> S-1 maps). However, in practice, largely due to electromagnetic and other intercomponent interactions, such topological excitations are very rare in superconducting systems. Here, we demonstrate that a realistic microscopic theory for interface superconductors, such as SrTiO3/LaAlO3, predicts an unconventional magnetic response where the flux-carrying objects are skyrmions, characterized by homotopy invariants of S-2 --> S-2 maps. Additionally, we show that this microscopic theory predicts that stable fractional vortices form near the boundary of these superconductors. It also predicts the appearance of type-1.5 superconductivity for some range of parameters. Central to these results is the assumption that the Rashba spin-orbit coupling is much larger than the superconducting gap.

  • 2274. Agterberg, Daniel F.
    et al.
    Garaud, Julien
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Checkerboard order in vortex cores from pair-density-wave superconductivity2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 10, article id 104512Article in journal (Refereed)
    Abstract [en]

    We consider competing pair-density-wave (PDW) and d-wave superconducting states in a magnetic field. We show that PDW order appears in the cores of d-wave vortices, driving checkerboard charge-density-wave (CDW) order in the vortex cores, which is consistent with experimental observations. Furthermore, we find an additional CDW order that appears on a ring outside the vortex cores. This CDW order varies with a period that is twice that of the checkerboard CDW and it only appears where both PDW and d-wave order coexist. The observation of this additional CDW order would provide strong evidence for PDW order in the pseudogap phase of the cuprates. We further argue that the CDW seen by nuclear magnetic resonance at high fields is due to a PDW state that emerges when a magnetic field is applied.

  • 2275.
    Aguiar Borges, Luciane
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Urban and Regional Studies.
    Education and Health in ICT-futures: Scenarios and sustainability impacts of ICT societies2015In: PROCEEDINGS OF ENVIROINFO AND ICT FOR SUSTAINABILITY 2015, Atlantis Press , 2015, p. 213-220Conference paper (Refereed)
    Abstract [en]

    This study explores the performance of the education and health sectors in relation to five ICT futures for Sweden in 2060. The accessibility, affordability, quality and efficiency of these sectors influence the creation and maintenance of essential collective values such as democracy and justice; consequently both education and health are fundamental to a sustainable society. Exploring the performance of these sectors in different futures enables the identification of barriers and undesirable developments, and encourages a debate on how ICT can be used to reinforce inclusive, and counteract unwanted, futures.

  • 2276.
    Aguiar Borges, Luciane
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Urban and Regional Studies.
    Stories of Pasts and Futures in Planning2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Societies are constantly changing, facing new challenges and possibilities generated by innovative technologies, sociospatial re-structuring and mobilities. This research approaches these challenges by exploring the role that stories about pasts, presents and futures play in planning. It sees stories as interlinked spaces of struggle over meanings, legitimacies and powers through which “our” valuable pasts and “our” desirable futures become re-constructed, framed and projected. It argues that powerful stories might consciously or unconsciously become institutionalised in policy discourses and documents, foregrounding our spatial realities and affecting our living spaces. These arguments and assumptions are investigated in relation to three cases: Regional-Pasts, SeGI-Futures and ICT-Futures. The stories about pasts, presents and futures surrounding these cases are investigated with the aim of initiating critical discussions on how stories about pasts and futures can inform, but also be sustained by, planning processes. While studies of these cases are presented in separate papers, these studies are brought together in an introductory essay and reconstructed in response to the research questions: How do regional futures become informed by the pasts? How do particular stories about the pasts become selected, framed and projected as envisioned futures? What messages are conveyed to the pasts and the presents through envisioned futures? How can stories of the past be referred and re-employed in planning to build more inclusive futures? To engage with the multidisciplinarity of these questions, they are investigated through dialogues between three main fields: heritage studies, futures studies and planning. The discussions have challenged the conventional divides between pasts, presents and futures, emphasised their plural nature and uncovered how the discursive power of stories play a significant role when interpreting pasts and envision futures in planning practices.

  • 2277.
    Aguiar Borges, Luciane
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Urban and Regional Studies.
    Using the Past to Construct Territorial Identities in Regional Planning: the Case of Mälardalen, SwedenManuscript (preprint) (Other academic)
    Abstract [en]

    This study examines how the past is used in the construction of regional identity narratives in policy discourses and documents. Despite assumptions that regional identity is based on shared culture, some authors argue that new forms of regional identity have emerged as the consequence of regions’ involvement in wider networks. Identity has been pursued as an asset to regional attractiveness and economic growth and, as such, is shaped by regional development strategies concerning particular social groups. Socially shared representations of the past through history, cultural heritage and collective memory play an important role in this process since the past is a powerful resource that may be used to construct images of places, legitimizing claims on territories. Document analysis and interviews with planners are used to analyse strategies for regional development in five counties located in the Mälardalen Region, Sweden. This study shows that regional strategies are guided by identity narratives framing regions from an exclusive outside perspective, leaving internal qualities unnoticed. The past is used to structure these narratives and construct identities that serve economic growth rather than the integration of the plural heritages of the region.

  • 2278.
    Aguiar Borges, Luciane
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Urban and Regional Studies.
    Adolphson, Marcus
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Urban and Regional Studies.
    The role of official heritage in regional spaces2016In: Urban Research and Practice, ISSN 1753-5069, E-ISSN 1753-5077Article, review/survey (Refereed)
    Abstract [en]

    Following the argument that increasing mobility has scattered consumption throughout Sweden’s regions, this study investigates how individuals’ consumption choices are influenced by official heritage. It argues that individuals’ everyday routines highlight the role played by heritage in socio-economic regional change, challenging traditional planning systems and altering individuals’ relationships with their environments, leading to new values being placed on official heritage. This argument was tested using interviews and questionnaires in Mariefred, Sweden, and demonstrates that official heritage plays multiple and contrasting roles, including the use of heritage as an attempt to reconcile opposing principles such as progress/development and tradition/conservation. 

  • 2279.
    Aguiar Borges, Luciane Aguiar
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Urban and Regional Studies.
    Humer, Alois
    University of Vienna.
    Smith, Christopher
    Europe's possible SGI futures: territorial settings and potential policy paths2015In: Services of General Interest and Territorial Cohesion: European Perspectives and National Insights / [ed] Heinz Fassmann, Daniel Rauhut, Eduarda Marques da Costa and Alois Humer, Vienna: Vienna University Press , 2015, 1, p. 123-146Chapter in book (Refereed)
  • 2280.
    Aguilar, Antonio
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    A Patient Identification System using RFID and IEEE 802.11b Wireless Networks2007Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The recent increased focus on patient safety in hospitals has yielded a flood of new technologies and tools seeking to improve the quality of patient care at the point of care. Hospitals are complex institutions by nature, and are constantly challenged to improve the quality of healthcare delivered to patients while trying to reduce the rate of medical errors and improve patient safety. Here a simple mistake such as patient misidentification, specimen misidentification, wrong medication, or wrong blood transfusion can cause the loss of a patient’s life. Misidentification of patients is a common problem that many hospitals face on the daily basis. Patient misidentification is one of the leading causes of medical errors and medical malpractice in hospitals and it has been recognised as a serious risk to patient safety.

    Recent studies have shown that an increasing number of medical errors are primarily caused by adverse drug events which are caused directly or indirectly by incorrect patient identification. In recognition of the increasing threat to patient safety, it is important for hospitals to prevent these medical errors from happening by adopting a suitable patient identification system that can improve upon current safety procedures.

    The focus of this master’s thesis is the design, implementation, and evaluation of a handheld-based patient identification system that uses radio frequency identification (RFID) and IEEE 802.11b wireless local area networks to identify patients. In this solution, each patient is given a RFID wristband which contains demographic information (patient ID number, ward number, hospital code, etc.) of the patient. A handheld device equipped with IEEE 802.11b wireless local area network connectivity and a RFID reader is then used by the medical staff to read the patient’s wristband, identify the patient, and access the relevant records of this patient.

    This work was carried out at the Department of Medical Physics and Bioengineering at the University College Hospital Galway (UCHG), Ireland and the National University of Ireland, Galway.

  • 2281.
    Aguilar, Antonio
    et al.
    Digital Enterprise Research Institute, National University of Ireland, Galway, Ireland.
    van der Putten, Wil
    Department of Medical Physics, University College Hospital Galway, Galway, Ireland .
    Maguire Jr., Gerald Q.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Positive Patient Identification using RFID and Wireless  Networks2006In: Proceedings of the HISI 11th Annual Conference and Scientific Symposium, Dublin, Ireland, Dublin, Ireland, 2006Conference paper (Refereed)
    Abstract [en]

    The increased focus on patient safety in hospitals has yielded a flood of new technologies and tools seeking to improve the quality of patient care at the point-of-care. Hospitals are complex institutions by nature, and are constantly challenged to improve the quality of healthcare delivered to patients while trying to reduce the rate of medical errors and improve patient safety. Here a simple mistake such as patient misidentification, specimen misidentification, wrong medication, or wrong blood transfusion can cause the loss of a patient's life. The focus of this paper is the implementation and evaluation of a handheld-based patient identification system that uses radio frequency identification (RFID) and 802.11b wireless networks to identify patients. In this approach, each patient is given a RFID wristband which contains demographic information (patient ID number, patient summary, hospital code) of the patient. A handheld device equipped with 802.11b wireless connectivity and a RFID reader is then used by the medical staff to read the patient's wristband and identify the patient. This work was carried out at the Department of Medical Physics and Bioengineering at the University College Hospital Galway, Ireland and in co-operation with the National University of Ireland, Galway.

  • 2282.
    Aguilar, Jorge
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Viktorsson, Morgan
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Development of an active suspension control strategy for a forestry machine with pendulum arms2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The forest industry depends on the cut to lenght method for production. The forwarder

    is one of the machines used in this process. These machines currently have

    no suspension, which leads to big problems such as lower productivity and higher

    soil damage.

    A relatively new approach to solve these problems is to use pendulum arms

    actuated by hydraulic cylinders. This solution turns out to be complex, since there

    are more actuators than variables controlled. This paper discusses several strategies

    to control such a system in order to minimize pitch and roll, while decoupling from

    vertical accelerations.

    A solution based on a nonlinear car model is suggested, and an implementation

    based on this model and using a pole placement technique is developed and compared

    in simulink with the same model with no suspension.

    Results show that this strategy is able to reduce pitch and roll considerably,

    while offering the possibility of adding a vertical displacement controller with little

    coupling between each other. The next steps towards implementation are to integrate

    the dynamics of the actuator, to consider robustness and noise interference, as well

    as the effects of discretization.

  • 2283.
    Aguilar Pérez, David
    KTH, School of Electrical Engineering (EES), Signal Processing.
    Designing schedules and Filter for cooperative localization2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In scheduled cooperative localization, devices in a network transmit pulses in a predetermined order. Every node measures inter-arrival time between received pulses to localize other nodes in the network. This thesis has looked into a few aspects of schedule based cooperative localization.First part of the thesis discusses constraints on schedule construction and algorithm to construct a schedule. An algorithm is proposed to design all possible schedules for any number of nodes.The second part of this thesis discusses designing a filter to process inter-arrival times to estimate position of all other nodes in the network. Every node runs a Kalman fi lter. Simulation results are presented for a fi lter model. Complexity of implementing the designed fi lter is discussed. A comparison is made between various ways to invert the matrix by QR decomposition. And finally, increase in fi lter complexity at every node with increase in number of nodes in network is discussed.

  • 2284.
    Aguilar, Xavier
    KTH, School of Computer Science and Communication (CSC), High Performance Computing and Visualization (HPCViz).
    Towards Scalable Performance Analysis of MPI Parallel Applications2015Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

      A considerably fraction of science discovery is nowadays relying on computer simulations. High Performance Computing  (HPC) provides scientists with the means to simulate processes ranging from climate modeling to protein folding. However, achieving good application performance and making an optimal use of HPC resources is a heroic task due to the complexity of parallel software. Therefore, performance tools  and runtime systems that help users to execute  applications in the most optimal way are of utmost importance in the landscape of HPC.  In this thesis, we explore different techniques to tackle the challenges of collecting, storing, and using  fine-grained performance data. First, we investigate the automatic use of real-time performance data in order to run applications in an optimal way. To that end, we present a prototype of an adaptive task-based runtime system that uses real-time performance data for task scheduling. This runtime system has a performance monitoring component that provides real-time access to the performance behavior of anapplication while it runs. The implementation of this monitoring component is presented and evaluated within this thesis. Secondly, we explore lossless compression approaches  for MPI monitoring. One of the main problems that  performance tools face is the huge amount of fine-grained data that can be generated from an instrumented application. Collecting fine-grained data from a program is the best method to uncover the root causes of performance bottlenecks, however, it is unfeasible with extremely parallel applications  or applications with long execution times. On the other hand, collecting coarse-grained data is scalable but  sometimes not enough to discern the root cause of a performance problem. Thus, we propose a new method for performance monitoring of MPI programs using event flow graphs. Event flow graphs  provide very low overhead in terms of execution time and  storage size, and can be used to reconstruct fine-grained trace files of application events ordered in time.

  • 2285.
    Aguilar, Xavier
    et al.
    KTH, School of Computer Science and Communication (CSC), High Performance Computing and Visualization (HPCViz).
    Fuerlinger, Karl
    Laure, Erwin
    KTH, School of Computer Science and Communication (CSC), High Performance Computing and Visualization (HPCViz).
    Automatic On-Line Detection of MPI Application Structure with Event Flow Graphs2015In: EURO-PAR 2015: PARALLEL PROCESSING, Springer Berlin/Heidelberg, 2015, p. 70-81Conference paper (Refereed)
    Abstract [en]

    The deployment of larger and larger HPC systems challenges the scalability of both applications and analysis tools. Performance analysis toolsets provide users with means to spot bottlenecks in their applications by either collecting aggregated statistics or generating loss-less time-stamped traces. While obtaining detailed trace information is the best method to examine the behavior of an application in detail, it is infeasible at extreme scales due to the huge volume of data generated. In this context, knowing the application structure, and particularly the nesting of loops in iterative applications is of great importance as it allows, among other things, to reduce the amount of data collected by focusing on important sections of the code. In this paper we demonstrate how the loop nesting structure of an MPI application can be extracted on-line from its event flow graph without the need of any explicit source code instrumentation. We show how this knowledge on the application structure can be used to compute postmortem statistics as well as to reduce the amount of redundant data collected. To that end, we present a usage scenario where this structure information is utilized on-line (while the application runs) to intelligently collect fine-grained data for only a few iterations of an application, considerably reducing the amount of data gathered.

  • 2286.
    Aguilar, Xavier
    et al.
    KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Fürlinger, K.
    Laure, Erwin
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Computer Science and Communication (CSC), Computational Science and Technology (CST).
    Online MPI trace compression using event flow graphs and wavelets2016In: Procedia Computer Science, Elsevier, 2016, p. 1497-1506Conference paper (Refereed)
    Abstract [en]

    Performance analysis of scientific parallel applications is essential to use High Performance Computing (HPC) infrastructures efficiently. Nevertheless, collecting detailed data of large-scale parallel programs and long-running applications is infeasible due to the huge amount of performance information generated. Even though there are no technological constraints in storing Terabytes of performance data, the constant flushing of such data to disk introduces a massive overhead into the application that makes the performance measurements worthless. This paper explores the use of Event flow graphs together with wavelet analysis and EZW-encoding to provide MPI event traces that are orders of magnitude smaller while preserving accurate information on timestamped events. Our mechanism compresses the performance data online while the application runs, thus, reducing the pressure put on the I/O system due to buffer flushing. As a result, we achieve lower application perturbation, reduced performance data output, and the possibility to monitor longer application runs. © The Authors. Published by Elsevier B.V.

  • 2287.
    Aguilar, Xavier
    et al.
    KTH, School of Computer Science and Communication (CSC), High Performance Computing and Visualization (HPCViz).
    Fürlinger, Karl
    Ludwig-Maximilians-Universitat (LMU).
    Laure, Erwin
    KTH, School of Computer Science and Communication (CSC), High Performance Computing and Visualization (HPCViz).
    MPI Trace Compression Using Event Flow Graphs2014Conference paper (Refereed)
    Abstract [en]

    Understanding how parallel applications behave is crucial for using high-performance computing (HPC) resources efficiently. However, the task of performance analysis is becoming increasingly difficult due to the growing complexity of scientific codes and the size of machines. Even though many tools have been developed over the past years to help in this task, current approaches either only offer an overview of the application discarding temporal information, or they generate huge trace files that are often difficult to handle.

    In this paper we propose the use of event flow graphs for monitoring MPI applications, a new and different approach that balances the low overhead of profiling tools with the abundance of information available from tracers. Event flow graphs are captured with very low overhead, require orders of magnitude less storage than standard trace files, and can still recover the full sequence of events in the application. We test this new approach with the NERSC-8/Trinity Benchmark suite and achieve compression ratios up to 119x.

  • 2288.
    Aguilar, Xavier
    et al.
    KTH, School of Computer Science and Communication (CSC), High Performance Computing and Visualization (HPCViz).
    Fürlinger, Karl
    Laure, Erwin
    KTH, School of Computer Science and Communication (CSC), High Performance Computing and Visualization (HPCViz).
    Visual MPI Performance Analysis using Event Flow Graphs2015In: Procedia Computer Science, ISSN 1877-0509, E-ISSN 1877-0509, Vol. 51, p. 1353-1362Article in journal (Refereed)
    Abstract [en]

    Event flow graphs used in the context of performance monitoring combine the scalability and low overhead of profiling methods with lossless information recording of tracing tools. In other words, they capture statistics on the performance behavior of parallel applications while pre- serving the temporal ordering of events. Event flow graphs require significantly less storage than regular event traces and can still be used to recover the full ordered sequence of events performed by the application.  In this paper we explore the usage of event flow graphs in the context of visual performance analysis. We show that graphs can be used to quickly spot performance problems, helping to better understand the behavior of an application. We demonstrate our performance analysis approach with MiniFE, a mini-application that mimics the key performance aspects of finite- element applications in High Performance Computing (HPC).

  • 2289.
    Aguilar, Xavier
    et al.
    KTH, School of Computer Science and Communication (CSC), High Performance Computing and Visualization (HPCViz).
    Laure, Erwin
    KTH, School of Computer Science and Communication (CSC), High Performance Computing and Visualization (HPCViz).
    Fürlinger, Karl
    Ludwig-Maximilians-Universität München.
    Online Performance Data Introspection with IPM2014In: Proceedings of the 15th IEEE International Conference on High Performance Computing and Communications (HPCC 2013), IEEE Computer Society, 2014, p. 728-734Conference paper (Refereed)
    Abstract [en]

    Exascale systems will be heterogeneous architectures with multiple levels of concurrency and energy constraints. In such a complex scenario, performance monitoring and runtime systems play a major role to obtain good application performance and scalability. Furthermore, online access to performance data becomes a necessity to decide how to schedule resources and orchestrate computational elements: processes, threads, tasks, etc. We present the Performance Introspection API, an extension of the IPM tool that provides online runtime access to performance data from an application while it runs. We describe its design and implementation and show its overhead on several test benchmarks. We also present a real test case using the Performance Introspection API in conjunction with processor frequency scaling to reduce power consumption.

  • 2290.
    Aguilar, Xavier
    et al.
    KTH, School of Computer Science and Communication (CSC), High Performance Computing and Visualization (HPCViz). KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Schliephake, Michael
    KTH, School of Computer Science and Communication (CSC), High Performance Computing and Visualization (HPCViz). KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Vahtras, Olav
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Gimenez, Judit
    Laure, Erwin
    KTH, School of Computer Science and Communication (CSC), High Performance Computing and Visualization (HPCViz). KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Scalability analysis of Dalton, a molecular structure program2013In: Future generations computer systems, ISSN 0167-739X, E-ISSN 1872-7115, Vol. 29, no 8, p. 2197-2204Article in journal (Refereed)
    Abstract [en]

    Dalton is a molecular electronic structure program featuring common methods of computational chemistry that are based on pure quantum mechanics (QM) as well as hybrid quantum mechanics/molecular mechanics (QM/MM). It is specialized and has a leading position in calculation of molecular properties with a large world-wide user community (over 2000 licenses issued). In this paper, we present a performance characterization and optimization of Dalton. We also propose a solution to avoid the master/worker design of Dalton to become a performance bottleneck for larger process numbers. With these improvements we obtain speedups of 4x, increasing the parallel efficiency of the code and being able to run in it in a much bigger number of cores.

  • 2291.
    Aguilar, Xavier
    et al.
    KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC.
    Schliephake, Michael
    KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC.
    Vahtras, Olav
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC.
    Gimenez, Judit
    Barcelona Supercomputing Center, Universitat Politecnica de Catalunya, Barcelona, Spain.
    Laure, Erwin
    KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC.
    Scaling Dalton, a molecular electronic structure program2011In: Seventh International Conference on e-Science, e-Science 2011, 5-8 December 2011, Stockholm, Sweden, IEEE conference proceedings, 2011, p. 256-262Conference paper (Refereed)
    Abstract [en]

    Dalton is a molecular electronic structure program featuring common methods of computational chemistry that are based on pure quantum mechanics (QM) as well as hybrid quantum mechanics/molecular mechanics (QM/MM). It is specialized and has a leading position in calculation of molecular properties with a large world-wide user community (over 2000 licenses issued). In this paper, we present a characterization and performance optimization of Dalton that increases the scalability and parallel efficiency of the application. We also propose asolution that helps to avoid the master/worker design of Daltonto become a performance bottleneck for larger process numbers and increase the parallel efficiency.

  • 2292. Aguilar-Saavedra, Juan Antonio
    et al.
    Ali, A.
    Allanach, Benjamin C.
    Arnowitt, Richard L.
    Baer, Howard A.
    Lafaye, Remi
    Univ Savoie, LAPP, CNTS IN2P3, Annecy Le Vieux, France.
    al., et
    Supersymmetry parameter analysis: SPA convention and project2006In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. C46, p. 43-60Article in journal (Refereed)
    Abstract [en]

    High-precision analyses of supersymmetry parameters aim at reconstructing the fundamental supersymmetric theory and its breaking mechanism. A well defined theoretical framework is needed when higher-order corrections are included. We propose such a scheme, Supersymmetry Parameter Analysis SPA, based on a consistent set of conventions and input parameters. A repository for computer programs is provided which connect parameters in different schemes and relate the Lagrangian parameters to physical observables at LHC and high energy e(+)e(-) linear collider experiments, i.e., masses, mixings, decay widths and production cross sections for supersymmetric particles. In addition, programs for calculating high-precision low energy observables, the density of cold dark matter (CDM) in the universe as well as the cross sections for CDM search experiments are included. The SPA scheme still requires extended efforts on both the theoretical and experimental side before data can be evaluated in the future at the level of the desired precision. We take here an initial step of testing the SPA scheme by applying the techniques involved to a specific supersymmetry reference point.

  • 2293.
    Aguilar-Sommar, Ruth S.
    et al.
    KTH.
    Poler, R.
    Integrated analysis of the production planning process using Trampolin and DGRAI as process modelling tools2006In: Production Planning and Control, ISSN 0953-7287, Vol. 17, no 1, p. 31-43Article in journal (Refereed)
    Abstract [en]

    This paper provides managers and other decision-makers with support on how to analyse business processes by presenting the use and features of Trampolin and DGRAI as complementary tools for the analysis of business processes to support enterprise integration. Two business process models were built for the production planning process in a large telecommunication company one using Trampolin and the other using DGRAI. The former offers a statistical analysis of the process showing the information required, responsible and other features of each activity along the process besides its links and sequence. The second gives a more dynamic analysis focusing on the process' decisional flow and its associated information and resources permitting to simulate and analyse the consequences of the decision-making process. A brief description of what may be analysed with each tool followed by analytical insights, and an analysis of how these tools support enterprise integration, are provided. Also the paper shows the advantages and disadvantages of each tool as well as some common and complementary characteristics found in the models.

  • 2294.
    Aguilera Costa, Joakim
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH).
    Uppgradering och identifiering av cellulosa och hemicellulosa i restströmmar från jordbruk och skogsindustri2018Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    By-products are in focus for further processing. Residues from agriculture and forest industry contain a large amount of fiber, and this work investigates the qualitative properties of residues and whether there is potential for using them in the cellulose industry.

    By-products collected were wheat straw, rapeseed straw, wheat bran, betfor, silage, branches, primary sludge, sawdust and fiber rejects. A literature study was conducted around each by-product to get a better understanding of what they consist of and how they occur.

    By extracting holocellulose from the by-products, the qualitative properties of the fibers were analyzed. For the slightest change in the shape and dimensions of fibers, a maceration method was used to extract holocellulose from the by-products.

    Methods used to analyze the qualitative properties of the by-products were viscosity, titrations and gravimetric analyzes. With these methods, mass exchanges, ash levels, mass viscosities, peracetic acid and hydrogen peroxide levels could be determined for the extracted holocellulose masses.

    To investigate whether the extracted holocellulose masses can be used in the cellulosic industry, two types of processes were tested. One was aerogel production and the other a compression mold to produce high strength biocomposites.

    It was found that the fiber rejects yielded the greatest holocellulose exchange compared to the other residues. The analyzes gave the result that sawdust had the fibers with the highest degree of polymerization while wheat bran and betfor had the fibers with the lowest degree of polymerization. The dissociation of the holocellulose mass could not be performed because the test sample had either a too high mass viscosity or a too high a proportion of hemicellulose which prevents the solvent from dissolving the fibers. Compression molding of the holocellulose mass from wheat straw was successful as it was possible to make the soft pulp a lot more rigid. Compression molding of the holocellulose masses may be an alternative for producing additive manufacturing materials (3D printing).

  • 2295. Aguilera, M.
    et al.
    Vanfretti, L.
    Gómez, Francisco José
    KTH.
    Experiences in power system multi-domain modeling and simulation with modelica & FMI: The case of gas power turbines and power systems2018In: 2018 Workshop on Modeling and Simulation of Cyber-Physical Energy Systems, MSCPES 2018 - Held as part of CPS Week, Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2018, p. 1-6, article id 8405397Conference paper (Refereed)
    Abstract [en]

    The turbine-governor models that are currently used in studies of power systems include over-simplifications of turbomachinery elements. Due to the growing need to support intermittent energy resources with other energy sources like gas turbines, more detailed models including an explicit representation of the physical dynamics are attractive. In this paper, the advantages of the Modelica language and the FMI standard are considered to carry out modeling and multi-domain simulation of gas turbines with power grids, which can be used to evaluate scenarios of power variability. The work gathers preliminary results of the potential that FMUs offer to promote the exchange of turbine models by manufacturers and to conduct multi-domain simulations in several tools.

  • 2296.
    Aguilera, Miguel
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Semantic and Physical Modeling and Simulation of Multi-Domain Energy Systems: Gas Turbines and Electrical Power Networks2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The ITEA3 OpenCPS (Open Cyber-Physical System Model-Driven CertifiedDevelopment) project focuses on interoperability between the Modelica/UnifiedModeling Language (UML)/Functional Mock-up Interface (FMI) standards, improved(co-)simulation execution speed, and verified code generation. The project aims to developa modeling and simulation framework for cyber-physical and multi-domain systems. Oneof the main use cases for the framework, is the multi-domain equation-based modelingand simulation of detailed gas turbine power plants (including the explicit equation-basedmodeling of turbomachinery dynamics) and the electrical power grid.In this work, UML class diagrams based on the Common Information Model (CIM)standard are used to describe the semantics of the electrical power grid. An extension basedon the standard ISO 15926 has been proposed to derive the multi-domain semanticsrequired by the models that integrate the electrical power grid with the detailed gas turbinedynamics.Furthermore, the multi-domain physical modeling and simulation Modelica language hasbeen employed to create the equation-based models of the use case of this project. Acomparative analysis between the Single-Domain and Multi-Domain model responses hasbeen performed both in time and frequency. The results show some interesting differencesbetween the turbine dynamics representation of the commonly used GGOV1 standardmodel and the less simplified model of a gas turbine.Finally, the models from each domain can be exchanged between two differentstakeholders by means of Functional Mock-Up Units (FMUs), defined by the FMIstandard. Promising test results were obtained with different simulation tools that supportthe standard, which demonstrates the feasibility of exchanging unambiguous multi-domainmodels with a detailed gas turbine representation. This shows the potential of the FMIstandard for manufacturers to exchange equation-based multi-domain models, while at thesame time protecting their intellectual property.

  • 2297. Aguirre, Miren
    et al.
    Johansson Salazar-Sandoval, Eric
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. SP Technical Research Institute of Sweden, Sweden.
    Johansson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Ahniyaz, Anwar
    Paulis, Maria
    Ramon Leiza, Jose
    Hybrid acrylic/CeO2 nanocomposites using hydrophilic, spherical and high aspect ratio CeO2 nanoparticles2014In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 2, no 47, p. 20280-20287Article in journal (Refereed)
    Abstract [en]

    A dispersion of CeO2 nanoparticles and nanorods stabilized with nitrilotriacetic acid (NTA) and a 4,4'-azobis(4-cyanovaleric acid) (V-501) initiator has been used to initiate the emulsion polymerization of acrylic monomers, yielding stable hybrid CeO2 nanoparticle-nanorod/polyacrylate latexes for the first time. Films cast from these hybrid latexes are transparent due to the very homogenous distribution of the polymer compatibilized CeO2. Furthermore, it has been proven that the UV-Vis absorption capacity of the hybrid latexes is enhanced with the incorporation of the nanorods.

  • 2298.
    Aguirre Quiroz, Gerardo Daniel
    KTH, School of Information and Communication Technology (ICT).
    Evaluation of the potential benefits of using Licensed Shared Access in the Americas2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Internet has become an ubiquitous service and human need. Mobile networks have been struggling with the "Mobile Data Tsunami", an increase in mobile broadband consumption due to faster networks, powerful devices and more traffic-demandingapplications, as well as a higher penetration volume. According to Cisco mobile data traffic is expected to grow to 15.9 exabytes per month by 2018, that is almost eleven times the mobile data traffic of 2013.

    Spectrum is a key factor for network deployments, since it determines the capacity of the network. Nonetheless, spectrum is a limited natural resource, i.e. a finite, non-exhaustible common resource. In order to fulfill the high performance targets of future mobile broadband (MBB) systems, a more efficient use and more effective management of spectrum resources have to be developed.

    Licensed Shared Access is a new complementary spectrum access scheme that allows for the sharing of partially used licensed spectrum from an incumbent (e.g. a government organization), by a limited number of “LSA licensees” (e.g. Mobile Network Operators). The LSA agreement follows pre-defined dynamic or static sharing conditions, that determine where, when and how to use the incumbent’s spectrum.

    The implementation of Licensed Shared Access needs the support of a very good regulatory framework and follow the harmonized spectrum pathway. Spectral harmonization, or the uniform allocation of frequency bands across entire region lowers the technology costs, making it easier for any country to consider its implementation. Once adpoted throughout the regions, economies of scale are achieved.

    Some first steps towards a new framework based on LSA have been given in Europe and North America, however to consider LSA as a real option, a complete analysis considering more markets is needed. It is crucial to consider how other regions around the world can be affected by this new approach in order to see if LSA is a viable option or not.

    The approach taken in this research covers the interrelations between technical, market and regulatory conditions in the Americas in order to present the possible value of LSA. The first part of the study deals with the analysis of the technical aspects of LSA. The following parts deal with under what conditions the evaluation is made. First, the study deals with the market conditions found in the Americas as a whole, to then deal with a more specific study of the market and regulatory conditions of selected countries in the region.

    The research showed how there are several ways LSA can bring positive value to established and emerging actors in the Americas, specially in high traffic areas, and/or indoor environments. However, and despite the advantages of LSA, the timing is not there yet. The region still has plenty of spectrum to be allocated as exclusive spectrum, which is preferred by operators. The low mobile broadband penetration in most of the region is also a factor for the low value of LSA in the time of this study.

  • 2299. Agustsson, J. S.
    et al.
    Agustsson, B. V.
    Eriksson, A. K.
    Gylfason, Kristinn B.
    KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201).
    Olafsson, S.
    Johnsen, K.
    Gudmundsson, J. T.
    Hydrogen uptake in MgO thin films grown by reactive magnetron sputtering2006Conference paper (Other academic)
    Abstract
  • 2300. Agustsson, J. S.
    et al.
    Arnalds, U. B.
    Ingason, A. S.
    Gylfason, Kristinn B.
    KTH, School of Electrical Engineering (EES), Microsystem Technology (Changed name 20121201).
    Johnsen, K.
    Olafsson, S.
    Gudmundsson, Jon Tomas
    University of Iceland, Iceland.
    Electrical resistivity and morphology of ultra thin Pt films grown by dc magnetron sputtering on SiO(2)2008In: Journal of Physics Conference Series, IOP Science , 2008, Vol. 100Conference paper (Refereed)
    Abstract [en]

    Ultra thin platinum films were grown by dc magnetron sputtering on thermally oxidized Si (100) substrates. The electrical resistance of the films was monitored in-situ during growth. The coalescence thickness was determined for various growth temperatures and found to increase from 1.3 nm for films grown at room temperature to 1.8 nm for films grown at 250 degrees C, while a continuous film was formed at a thickness of 3.9 nm at room temperature and 3.5 nm at 250 degrees C. The electrical resistivity increases with increased growth temperature, as well as the morphological grain size, and the surface roughness, measured with a scanning tunneling microscope (STM).

43444546474849 2251 - 2300 of 121339
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