| 21. |
- Andersson, Marlene
(författare)
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Mechanisms of native and artificial spinning of spider silk
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Spider silk is tougher than all other known natural and man-made fibers, and represents an environmentally friendly material that could potentially be used for many different purposes, ranging from biomaterials to construction materials. However, for large-scale production of silk, methods to produce artificial silk fibers must be developed. In this thesis, the molecular mechanisms of silk spinning were studied with the aim of developing a biomimetic method for production of artificial spider silk fibers. Major ampullate glands of spiders were studied using light and transmission electron microscopy. Three different epithelial cell types were identified in the tail and sac, two of which produce spider silk proteins (spidroins) that make up the silk and one of which produces carbonic anhydrase that maintains a pH gradient along the gland. The pH gradient was determined to go from pH 7.6 in the tail to pH 5.7 halfway along the duct. Silkworm silk glands were also shown to contain several different epithelial cell types and it was determined that carbonic anhydrase maintains a pH gradient from 8.2 to 6.2 along the gland. Spidroins consist of a repetitive region with alternating poly-alanine blocks and glycine-rich repeats, flanked by highly conserved globular domains, the N-terminal (NT) and C-terminal (CT) domain. Recombinant versions of NT and CT were studied under the conditions found in the major ampullate gland, and were shown to regulate fiber formation by responding to pH in coordinated but opposite ways, following a lock and trigger mechanism. While NT gets more stable and dimerizes as pH is lowered, and thereby interconnects the spidroins into large networks (lock), CT is destabilized, unfolds and turns into β-sheet amyloid-like fibrils in response to low pH and high pCO2, which may nucleate further β-sheet formation of the repetitive region (trigger). Based on the knowledge generated on native silk spinning, a biomimetic method to spin artificial spider silk fibers was developed. A chimeric recombinant spidroin was designed by combining a highly soluble NT and CT with a short repetitive region. The extremely soluble spidroin could be concentrated to unprecedented levels, and formed tough, kilometer-long fibers upon spinning into a low pH aqueous buffer.
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| 22. |
- Asp, Elina
(författare)
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Drift-Type Waves in Rotating Tokamak Plasma
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The concept of energy production through the fusion of two light nuclei has been studied since the 1950’s. One of the major problems that fusion scientists have encountered is the confinement of the hot ionised gas, i.e. the plasma, in which the fusion process takes place. The most common way to contain the plasma is by using at magnetic field configuration, in which the plasma takes a doughnut-like shape. Experimental devices of this kind are referred to as tokamaks. For the fusion process to proceed at an adequate rate, the temperature of the plasma must exceed 100,000,000C. Such a high temperature forces the plasma out of thermodynamical equilibrium which plasma tries to regain by exciting a number of turbulent processes. After successfully quenching the lager scale magnetohydrodynamic turbulence that may instantly disrupt the plasma, a smaller scale turbulence revealed itself. As this smaller scale turbulence behaved contrary to the common theory at the time, it was referred to as anomalous. This kind of turbulence does not directly threaten existents of the plasma, but it allows for a leakage of heat and particles which inhibits the fusion reactions. It is thus essential to understand the origin of anomalous turbulence, the transport it generates and most importantly, how to reduce it. Today it is believed that anomalous transport is due to drift-type waves driven by temperature and density inhomogeneities and the theoretical treatment of these waves is the topic of this thesis.The first part of the thesis contains a rigorous analytical two-fluid treatment of drift waves driven solely by density inhomogeneities. Effects of the toroidal magnetic field configuration, the Landau resonance, a peaked diamagnetic frequency and a sheared rotation of the plasma have been taken into account. These effects either stabilise or destabilise the drift waves and to determine the net result on the drift waves requires careful analysis. To this end, dispersion relations have been obtained in various limits to determine when to expect the different effects to be dominant. The main result of this part is that with a large enough rotational shear, the drift waves will be quenched.In the second part we focus on temperature effects and thus treat reactive drift waves, specifically ion temperature gradient and trapped electron modes. In fusion plasmas the α-particles, created as a by-product of the fusion process, transfer the better part of their energy to the electrons and hence the electron temperature is expected to exceed the ion temperature. In most experiments until today, the ion temperature is greater than the electron temperature and this have been proven to improve the plasma confinement. To predict the performance of future fusion plasmas, where the fusion process is ongoing, a comprehensive study of hot-electron plasmas and external heating effects have been carried out. Especially the stiffness (heat flux vs. inverse temperature length scale) of the plasma has been examined. This work was performed by simulations done with the JETTO code utilising the Weiland model. The outcome of these simulations shows that the plasma response to strong heating is very stiff and that the plasma energy confinement time seems to vary little in the hot-electron mode.
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| 23. |
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| 24. |
- Bakhshi Valojerdi, Zeinab, 1986-
(författare)
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Persistent Fault-Tolerant Storage at the Fog Layer
- 2021
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Clouds are powerful computer centers that provide computing and storage facilities that can be remotely accessed. The flexibility and cost-efficiency offered by clouds have made them very popular for business and web applications. The use of clouds is now being extended to safety-critical applications such as factories. However, cloud services do not provide time predictability which creates a hassle for such time-sensitive applications. Moreover, delays in the data communication between clouds and the devices the clouds control are unpredictable. Therefore, to increase predictability an intermediate layer between devices and the cloud is introduced. This layer, the Fog layer, aims to provide computational resources closer to the edge of the network. However, the fog computing paradigm relies on resource-constrained nodes, creating new potential challenges in resource management, scalability, and reliability. Solutions such as lightweight virtualization technologies can be leveraged for solving the dichotomy between performance and reliability in fog computing. In this context, container-based virtualization is a key technology providing lightweight virtualization for cloud computing that can be applied in fog computing as well. Such container-based technologies provide fault tolerance mechanisms that improve the reliability and availability of application execution. By the study of a robotic use-case, we have realized that persistent data storage for stateful applications at the fog layer is particularly important. In addition, we identified the need to enhance the current container orchestration solution to fit fog applications executing in container-based architectures. In this thesis, we identify open challenges in achieving dependable fog platforms. Among these, we focus particularly on scalable, lightweight virtualization, auto-recovery, and re-integration solutions after failures in fog applications and nodes. We implement a testbed to deploy our use-case on a container-based fog platform and investigate the fulfillment of key dependability requirements. We enhance the architecture and identify the lack of persistent storage for stateful applications as an important impediment for the execution of control applications. We propose a solution for persistent fault-tolerant storage at the fog layer, which dissociates storage from applications to reduce application load and separates the concern of distributed storage. Our solution includes a replicated data structure supported by a consensus protocol that ensures distributed data consistency and fault tolerance in case of node failures. Finally, we use the UPPAAL verification tool to model and verify the fault tolerance and consistency of our solution.
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| 25. |
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| 26. |
- Barrera Diaz, Carlos Alberto, 1987-, et al.
(författare)
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Availability Analysis of Reconfigurable Manufacturing System Using Simulation-Based Multi-Objective Optimization
- 2022
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Ingår i: SPS2022. - Amsterdam; Berlin; Washington, DC : IOS Press. - 9781643682686 - 9781643682693 ; , s. 369-379
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Konferensbidrag (refereegranskat)abstract
- Nowadays, manufacturing companies face an increasing number of challenges that can cause unpredictable market changes. These challenges are derived from a fiercely competitive market. These challenges create unforeseen variations and uncertainties, including new regional requirements or regulations, new technologies and materials, new market segments, increasing demand for new product features, etc. To cope with the challenges above, companies must reinvent themselves and design manufacturing systems that seek to produce quality products while responding to the changes faced. These capabilities are encompassed in Reconfigurable Manufacturing Systems (RMS), capable of dealing with uncertainties quickly and economically. The availability of RMS is a crucial factor in establishing the production capacity of a system that considers all events that could interrupt the planned production. The impact of the availability in RMS is influenced by the configuration of the systems, including the number of resources used. This paper presents a case study in which a simulation-based multi-objective optimization (SMO) method is used to find machines’ optimal task allocation and assignment to workstations under different scenarios of availability. It has been shown that considering the availability of the machines affects the optimal configuration, including the number of resources needed, such as machines and buffers. This study demonstrates the importance of the availability consideration during the design of RMS.
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| 27. |
- Benedicks, Michael, et al.
(författare)
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Kneading sequences for double standard maps
- 2009
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Ingår i: Fundamenta Mathematicae. - : Institute of Mathematics, Polish Academy of Sciences. - 0016-2736 .- 1730-6329. ; 206, s. 61-75
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the symbolic dynamics for the double standard maps of the circle onto itself, given by f(a,b) (x) = 2x + a + (b/pi) sin(2 pi x) (mod 1), where b = 1 and a is a real parameter, 0 <= a < 1
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| 28. |
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| 29. |
- Björnsson, Marcus A., et al.
(författare)
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A two-compartment effect site model describes the bispectral index after different rates of propofol infusion
- 2010
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Ingår i: Journal of Pharmacokinetics and Pharmacodynamics. - : Springer Science and Business Media LLC. - 1567-567X .- 1573-8744. ; 37:3, s. 243-255
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Tidskriftsartikel (refereegranskat)abstract
- Different estimates of the rate constant for the effect site distribution (k(e0)) of propofol, depending on the rate and duration of administration, have been reported. This analysis aimed at finding a more general pharmacodynamic model that could be used when the rate of administration is changed during the treatment. In a cross-over study, 21 healthy volunteers were randomised to receive a 1 min infusion of 2 mg/kg of propofol at one occasion, and a 1 min infusion of 2 mg/kg of propofol immediately followed by a 29 min infusion of 12 mg kg(-1) h(-1) of propofol at another occasion. Arterial plasma concentrations of propofol were collected up to 4 h after dosing, and BIS was collected before start of infusion and until the subjects were fully awake. The population pharmacokinetic-pharmacodynamic analysis was performed using NONMEM VI. A four-compartment PK model with time-dependent elimination and distribution described the arterial propofol concentrations, and was used as input to the pharmacodynamic model. A standard effect compartment model could not accurately describe the delay in the effects of propofol for both regimens, whereas a two-compartment effect site model significantly improved the predictions. The two-compartment effect site model included a central and a peripheral effect site compartment, possibly representing a distribution within the brain, where the decrease in BIS was linked to the central effect site compartment concentrations through a sigmoidal E-max model.
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| 30. |
- Blennow, Katarina, et al.
(författare)
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A Comparison of Refugee Education Policy and Practice in England and Sweden: Participatory Parity in Schooling and Moves Towards Ordinariness
- 2018
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Konferensbidrag (refereegranskat)abstract
- There are more child refugees in Europe than at any point since the end of the Second World War (Save the Children 2016). This is affecting both communities on the move and communities where uprooted people are resettling. A humanitarian problem on this scale demands a socially just response. For young refugees, education is a fundamental means of integrating into their new context and the act of going to school is a facilitating factor in their resumption of an everyday existence after periods of traumatic upheaval.This paper’s focus is a case study of how schools work with newly arrived children in England (historically both focus and locus for immigrants) and Sweden (to whom large numbers of immigrants are a new phenomenon). Understanding the positioning of the newly arrived within national educational policy discourses illuminates the values underpinning political decision making in these two differing European contexts (Ball 1998, 124). Policies and practices in these contexts which lead to, or obstruct, new arrivals living an everyday life and participating in education are examined through the two theoretical concepts: ‘participatory parity’ (Fraser 2003) and ‘resumption of an ordinary life’ (Kohli 2014) as we explore each state’s policy response.
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