Journal Staff

Sju forskare vid Linköpings universitet ventilerar olika sidor av samhällsundervisningens problematik och möjligheter, såsom hur samhällsundervisningens villkor ständigt förändras och konsekvenserna av detta, vilken roll teknikhistoria bör ha i grundskolan, hur gymnasieskolans nya kursplan i historia har påverkat läromedlen, innehållet i sponsrade läromedel, betydelsen av religionsundervisning i särskolan, hur staten främjar utbildning i samband med ett jubileum samt vikten av internationellt utbyte.

Nonlinear Model Predictive Control for Combined Cycle Power Plants

This master thesis project serves to investigate the possibilities of Nonlinear Model Predictive Control (NMPC) using the example of enthalpy control of the BENSON HRSG (heat recovery steam generator) of a combined cycle power plant (CCPP). The general idea of NMPC is to solve an optimization problem, to nd the next control action, and this optimization problem is based on a model of the system. The models used in the controller implementation are Modelica-based, and the system is described by algebraic dierential equations (DAEs). The controller was implemented in the Python interface of JModelica.org (Modelica-based modeling tool, supporting the Modelica extension Optimica for optimization), together with an extended Kalman lter (EKF) for state estimation. The control algorithm was only evaluated for a setup where the controller model is very similar to the model representing the real process; both models are simplied representations of the real process

Availability Estimations for Utilities in the Process Industry

An important performance measure of a plant is the plant-availability. The higher availability the better, since a high availability implies a possibility for a large production volume and thereby an increased profit for the company. One way of increasing the plant-availability is by eliminating, or minimizing the effect of disturbances. The cause of a disturbance can be personnel, material or equipment, where material includes both raw materials and utilities. The aim of this work is to increase the plant-availability by decreasing the effects of plant-wide disturbances caused by utilities. The first step is to determine the set of utilities that can be present at an industrial site, what disturbances these utilities can suffer, and how frequent and safety-critical these disturbances are. A later step will be to determine the effects on the plant-availability, and ways to decrease or eliminate these effects

A General Method for Handling Disturbances on Utilities in the Process Industry

Utilities, such as steam or cooling water, have shown to play an important role within the process industry, since a malfunctioning utility is a plant-wide disturbance that can lead to large revenue losses due to reduced production quantities. This work focuses on identifying disturbances on utilities that give economical consequences. Measures of utility availability and area availability are introduced and used for estimating the ratio of disturbances on utilities. A generic method for handling disturbances on utilities is presented, which could be applied using site models of different level of detail. Some modeling approaches for modeling a site are described and the framework of the general method is demonstrated with a case study example at Perstorp AB, Sweden

Barns svarsmönster på semantiska ordflödesuppgifter – kan analyser utifrån ordflödesstrategier och prototypteori avslöja något om barnens mentala lexikon?

I uppsatsen analyseras barns svarsmönster på semantiska ordflödesuppgifter. Uppgiftstypen går ut på att producera så många ord som möjligt inom en given kategori under en minut. Analyserna bygger på data från 63 barn med typisk språkutveckling. 32 av barnen gick i förskoleklass och 31 av barnen gick i årskurs två vid tiden för datainsamlingen. I den första frågeställningen analyseras svarsorden utifrån prototypteorin; har barn som inkluderar kategorins mest prototypa svarsord under uppgiftens inledningsskede ett stort totalt antal svarsord? Resultaten visar att det inte finns något samband mellan många svarsord och tidig produktion av kategorins mest prototypa ord. Svarsorden analyseras också utifrån två strategier som är betydelsefulla för goda resultat på ordflödesuppgifter. Att svarsorden brukar produceras i ett antal tidsmässiga ”spurtar” och att orden inom samma spurt ofta hör till samma subkategori avslöjar de två ordflödesstrategierna – klustring och växling. Klustring innebär produktion av efterföljande ord som hör till samma subkategori/kluster. Klustringen sammanfaller med spurtarna. Växling innebär förmåga att växla mellan olika kluster. Klustringen tros spegla semantiska förmågor och växlingen antas återspegla exekutiva funktioner. I föreliggande uppsats utreds i vilken utsträckning klustring (och därmed semantiska förmågor) respektive växling (och därmed exekutiva funktioner) påverkar prestationen på semantiska ordflödesuppgifter. Flera tidigare studier har konstaterat att ordflödesuppgifter påverkas mer av exekutiva funktioner och mindre av semantiska förmågor. I föreliggande studie har en rad olika mått på både klustrings- och växlingsförmågan använts och jämförts mot varandra. Resultaten påvisar ett samband mellan växlingsmåtten och det totala antalet svarsord. Ett av fem klustringsmått påvisar ett minst lika starkt samband med det totala antalet svarsord, medan övriga klustringmått förefaller influera ordflödesuppgiften i mindre utsträckning. För att kunna avgöra klustringens respektive växlingens relativa bidrag till det totala antalet svarsord måste framtida studier fastställa vilket som är det mest rättvisande klustringsmåttet och vilket som är det mest rättvisande växlingsmåttet och jämföra dem mot varandra

The Nonpenetrating Telescopic Sham Needle May Blind Patients with Different Characteristics and Experiences When Treated by Several Therapists

Background. Little is known which factors influence the blinding in acupuncture studies. Aim. To investigate if blinding varied between patients with different characteristics receiving verum or sham acupuncture. Methods. We randomised cancer patients to verum (n = 109) or sham acupuncture (n = 106) with a nonpenetrating telescopic sham needle for nausea. Level of blinding was compared between different sub-groups of patients using Bang's blinding index (BI) ranged −1 to 1 (−1 = all state the opposite treatment, 1 = all identify treatment). Results. Most patients in the verum (74 of 95; 78%, BI 0.72) and the sham (68 of 95; 72%, BI −0.60). acupuncture group believed they had received verum acupuncture. The probability for a patient to believe he/she received verum acupuncture was related to the received needling type (P = .003) and to the patient's belief in received treatment effects (P = .008). Hospital (P = .425), therapist (P = .434), previous acupuncture experience (P = .578), occurrence of nausea (P = .157), gender (P = .760), and age (P = .357) did not affect blinding. Conclusions. Blinding was successfully achieved irrespective of age, gender, acupuncture experience, treatment effect, or in which hospital or by which therapist the patient received treatment. Patients with higher belief in the effect of the treatment were more likely to believe they had received verum acupuncture

Characterization of fuel segregation in a fluidized bed by magnetic particle tracking

A Magnetic Particle Tracking (MPT) system is used to experimentally characterize the vertical distribution of fuel particles in a fluidized bed. The measurements are carried out in a fluid-dynamically down-scaled cold unit resembling a 1×1 m2 boiler operating at 850 °C. The MPT system yields spatial and temporal information of the tracer particle with accuracies in the order of 10-3 m and 10-3 s, respectively. The MPT system is used to study how fuel segregation is influenced by physical properties of the fuel (sizes and densities representing different fuel types) and operational conditions, such as fluidization velocity, bed height and pressure drop across the gas distributor. For the range of fluidization velocities investigated, the results show two fuel segregation regimes: 1) a low-velocity mixing-regime, for which the presence of fuel particles at the dense bed surface and splash zone decreases strongly with increased fluidization velocity, and 2) a high-velocity mixing-regime where the presence of fuel at the bed surface and the splash zone increases with fluidization velocity, but with a weaker dependence than in the low-velocity regime. The fluidization velocity separating the two regimes depends on bed height and fuel properties

Reducing revenue loss due to disturbances in utilities using buffer tanks - A case study at Perstorp

Utilities, such as steam and cooling water, are often shared by several production areas at an industrial site. In order to minimize the loss of revenue due to disturbances in the supply of utilities, the optimal supply of utilities to different areas has to be determined. It is not evident how utility resources should be divided, as both buffer tank levels, the connections between areas, and the profitability of different products must be considered. This paper presents a case study at Perstorp, the objectives of which were to identify the utilities causing the greatest revenue losses at the site, and suggest strategies for reducing this loss using an on/off modeling approach including buffer tanks between areas

Modeling Axial Mixing of Fuel Particles in the Dense Region of a Fluidized Bed

A semiempirical model for the axial mixing of fuel particles in the dense region of a fluidized bed is presented and validated against experimental magnetic particle tracking in a fluid-dynamically downscaled fluidized bed (K\uf6hler et al. Powder Technol., 2017, 316, 492-499) that resembles hot, large-scale conditions. The model divides the bottom region into three mixing zones: a rising bubble wake solid zone, a zone with sinking emulsion solids, and the splash zone above the dense bed. In the emulsion zone, which is crucial for the mixing, the axial motion of the fuel particle is shown to be satisfactorily described by a force balance that applies experimental values from the literature and an apparent emulsion viscosity of Newtonian character. In contrast, the values derived from the literature for key model parameters related to the bubble wake zone (such as the upward velocity of the tracer), which are derived from measurements carried out under cold laboratory-scale conditions, are known to underestimate systematically the measurements relevant to hot large-scale conditions. When applying values measured in a fluid-dynamically downscaled fluidized bed (K\uf6hler et al. Powder Technol., 2017, 316, 492-499), the modeled axial mixing of fuel tracers shows good agreement with the experimental data.\ua0\ua9 2020 American Chemical Society

Movement pattern of the Exeter femoral stem: A radiostereometric analysis of 22 primary hip arthroplasties followed for 5 years

Background The design of the Exeter stem may facilitate distal migration, but radiostereometric analysis (RSA) studies have been limited to 2 years of follow-up. Patients and methods We followed migration of the Exeter femoral stems in 22 primary hip arthroplasties for 5 years with RSA. Results All stems migrated distally and the median migration at 2 years was 1.34 mm, while at 5 years it was 1.77 mm. 7 stems migrated above accuracy between 3 and 5 years. (RSA) evaluation of the cement mantle could be performed in 14 cases, and in 5 slight migration was found. Most of the stems rotated towards retroversion and the median rotation at 2 years was 1.2°, while at 5 years it was 1.6°. We found 1 patient with impending clinical failure but no deviation in the RSA migration pattern, and 1 patient with unstable migration pattern but no clinical symptoms. Interpretation We found a greater distal migration of the Exeter stem for longer periods of time than seen with other types of cemented implants