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  • Public defence: 2024-02-21 09:00 FB53, Stockholm
    Hannukainen, Julia D.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Anomaly and Topology: On the axial anomaly, domain wall dynamics, and local topological markers in quantum matter2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Chiral anomalies and topological phases of matter form the basis of the research presented in this dissertation. The chiral anomaly is considered both in the context of magnetic Weyl semimetals and in the context of non-Hermitian Dirac actions. Topological phases of matter play a role in this work through the research on Weyl semimetals and in the formulation of local topological markers.

    The simplest example of magnetic Weyl semimetals consist of two Weyl cones separated in momentum space by a magnetisation vector which acts as an axial gauge field. We describe the emergence of axial electromagnetic fields by considering a magnetic field driven domain wall in this magnetisation. The parallel axial magnetic and axial electric fields give rise to the axial anomaly, and in turn to the chiral magnetic effect; a nonequilibrium current located at the domain wall. The chiral magnetic effect is a source of electromagnetic radiation, and a measurement of this radiation would provide evidence of the existence of the axial anomaly.

    Electronic manipulation of domain walls is a central objective in spintronics. We describe how the axial anomaly, in terms of external electromagnetic fields, acts as a torque on the domain wall, and allows for electric control of the equilibrium configuration of the domain wall. We show how the axial anomaly is used to flip the chirality of the domain wall by tuning the electric field. Measuring the change in domain wall chirality constitutes a signal of the axial anomaly. We also describe how the Fermi arc boundary states of the Weyl semimetal at the domain wall result in an effective hard axis anisotropy which allows for large domain wall velocities irrespective of the intrinsic anisotropy of the material.

    Our interest in non-Hermitian chiral anomalies stems from the existence of topological phases of matter in non-Hermitian models. We evaluate the chiral anomaly for a non-Hermitian Dirac theory with massless fermions with complex Fermi velocities coupled to non-Hermitian axial and vector gauge fields. The anomaly is compared with the corresponding anomaly of a Hermitianised and an anti-Hermitianised action derived from the non-Hermitian action. We find that the non-Hermitian anomaly does not correspond to the combined anomalous terms derived from the Hermitianised and anti-Hermitianised theory, as would be expected classically, resulting in new anomalous terms in the conservation laws for the chiral current.

    Local topological markers are real space expressions of topological invariants evaluated by local expectation values and are important for characterising topology in noncrystalline structures. We derive analytic expressions for local topological markers for strong topological phases of matter in odd dimensions, by generalising the formulation of the even dimensional local Chern marker. This is not a straightforward task since the topological invariants in odd dimensions are basis dependent. Our solution is to express the invariants in terms of a family of parameter dependent projectors interpolating between a trivial state and the topological state of interest. The odd dimensional invariant is therefore expressed as a Chern character integrated over the combined space of the odd dimensional Brillouin zone and the one dimensional parameter space. As a result, we provide an easy-to-use chiral marker for symmetry classes with a chiral constraint, and a Chern-Simons marker for symmetry classes with either time reversal symmetry (in three dimensions) or particle hole symmetry (in one dimension). These markers are readily extended to interacting systems by considering the topological equivalence between a gapped one-particle density matrix of the interacting state and a projector corresponding to a free fermion state.

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    kappa
  • Public defence: 2024-02-21 09:30 FA31, Albanova University Center, Stockholm
    Deng, Yucheng
    KTH, School of Engineering Sciences (SCI), Physics.
    Experimental Study on Steam Explosions in Chemical Solutions and Seawater2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Steam explosions may be encountered in severe accidents of light water reactors (LWRs), which are thermal detonations caused by rapid and intense vaporization of the coolant upon its direct contact with the core melt (corium). Motivated by the interest in understanding and mitigation of severe accident progression, many studies have been conducted to investigate the steam explosion phenomena during severe accidents. However, most of the previous studies did not consider the effect of chemical additives in the coolant of nuclear power plants, such as additions of H3BO3, NaOH and Na3PO4 for water chemistry control, and direct utilization of seawater (NaCl additive) under an extreme condition like the Fukushima accident. The present thesis work is motivated to fill the knowledge gap concerning the impacts of chemical additives (H3BO3, NaOH, Na3PO4, and NaCl) on steam explosions.  

    The primary objective of the present research is to obtain characteristics of steam explosions in seawater and chemical solutions of H3BO3/NaOH/Na3PO4 with prototypical concentrations. To achieve this goal, a series of experiments have been carried out in the MISTEE experimental platform at KTH, involving single droplet and multiple droplets falling into a variety of coolant pool filled with seawater or chemical solutions of H3BO3/NaOH/Na3PO4 additives. The thesis work consists of four parts as follows.

    The first part is a description of the experimental methodology developed in the present study. Two experimental facilities, dubbed MISTEE-CE and MISTEE-SEA of respective mechanical plug and aerodynamic levitation for melt delivery, were designed on the MISTEE platform. Both setups were equipped with high-speed cameras for visualization, a pressure sensor for dynamic pressure measurement, and a fragment catcher for debris collection. A double-crucible design was employed to enable induction heating while avoiding melt contamination. The aerodynamic levitation system was implemented in MISTEE-SEA to reduce the disturbance of the mechanical plug. All chemical solutions were prepared in the laboratory with degassed deionized water. Tin (Sn) was chosen as the melt material due to benign properties suitable for safe handling in the laboratory.

    The second part is the presentation of visual observations and parameters selected to characterize steam explosions. The visualization includes the phenomena of droplet-coolant interactions and steam explosion occurrences. A molten single droplet falling into the coolant pool with deionized water or chemical solution might experience one of the three typical phenomena: deformation without fragmentation, minor fragmentation, or spontaneous steam explosion. In contrast, a multi-droplet test might involve merging and multiple explosions of droplets, resulting in a more complex set of phenomena. The quench depth and the lateral deformation ratio were defined and used to analyze the dynamic process of a single droplet in the coolant, while the peak pressure was employed to compare steam explosion energetics. In addition, the size distribution of debris particles was scrutinized.

    The third part is a summary and highlights of the experimental study on single-droplet steam explosion in different chemical solutions, using 1g of melt sample. The results revealed that the H3BO3 additive had little impact on steam explosion when the H3BO3 concentration was lower than 1.2 wt.%, but the risk of steam explosion in 3.2 wt.% H3BO3 solution was higher. The addition of NaOH and Na3PO4 to an H3BO3 solution significantly offset the influence on steam explosion. This suggests that the presence of PO43- and H+ ions play a significant role in spontaneous steam explosions. Additionally, seawater enhanced the occurrence of spontaneous steam explosions, with a clear correlation between increasing salinity and a higher likelihood of steam explosion. Compared to deionized water, chemical solutions (including seawater) caused more pronounced deformation in molten droplets at equivalent depths prior to direct contact of melt with coolant. Furthermore, the peak pressures of steam explosions in chemical solutions had the potential to reach notably higher values than those in deionized water. The chemical solutions except for the one of 1.2 wt.% H3BO3 tended to produce higher fractions of finer debris particles. 

    The fourth part is about the experimental results of an investigation on steam explosion involving multiple droplets falling into deionized water and chemical solutions, using 5 g and 20 g of melt samples, respectively. It was found that under identical test conditions, the peak pressure of steam explosion increased with melt sample mass, resulting in a noticeably higher fraction of fine debris particles in the case of 20 g melt sample. The steam explosion location was concentrated within a shallower range when using chemical solutions instead of deionized water. In contrast to single-droplet experiments, the influence of the chemical solutions on the steam explosion was diminishing in the tests with multiple droplets.

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    PhD thesis-web
  • Public defence: 2024-02-21 10:00 F3, Stockholm
    Chien, Tzu-En
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Process Technology.
    Near-ambient pressure velocity map imaging2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Catalytic reactions on solid surfaces have been studied under Ultra-high vacuum (UHV) conditions for decades. These studies provide crucial information for catalytic reactions, such as surface structures, adsorption sites, and reaction mechanisms. However, industrial catalysis operates under high gas pressure to increase the reaction rate, so the knowledge we learn from the previous UHV studies may not be able to directly transfer to the industry. This difference is referred to as the “pressure gap”, and it represents the difficulties that scientists encounter when attempting to investigate and comprehend catalytic reactions at high pressure. To address this issue, in situ/operando techniques and instruments have been developed to study reactions at pressures closer to real-world applications.The present thesis aims to showcase the new instrument, Near-Ambient Pressure Velocity Map Imaging (NAP-VMI), and its applications to molecular spectroscopy and surface science at near-ambient pressures. This instrument features a velocity map imaging (VMI) setup with redesigned ion optics and uses differential pumping to achieve a working pressure of 10−3 mabr. It allows time-resolved measurements at microsecond time scales using the pump-probe technique with a pulsed molecular beam and a pulsed laser. The performance is validated using N2O photodissociation and N2 surface scattering. CO oxidation on Pd(110) and Pd(100) surfaces is studied at elevated oxygen pressure (1×10−5 mbar) where the surfaces reconstruct.The results show the suppression of CO2 production in oxygen rich environments for both surfaces. The difference in kinetics and dynamics behavior between the two surfaces also suggests that surface structures and adsorption sites are important in the reaction mechanisms. These findings highlight the importance of surface structure in catalytic reactions and pave the way for more effective catalysts to be designed by tailoring surface properties and reaction conditions.

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  • Public defence: 2024-02-22 10:00 https://kth-se.zoom.us/j/61765490226, Stockholm
    Latupeirissa, Adrian Benigno
    KTH, School of Electrical Engineering and Computer Science (EECS), Human Centered Technology, Media Technology and Interaction Design, MID.
    From Motion Pictures to Robotic Features: Adopting film sound design practices to foster sonic expression in social robotics through interactive sonification2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This dissertation investigates the role of sound design in social robotics, drawing inspiration from robot depictions in science-fiction films. It addresses the limitations of robots’ movements and expressive behavior by integrating principles from film sound design, seeking to improve human-robot interaction through expressive gestures and non-verbal sounds.

    The compiled works are structured into two parts. The first part focuses on perceptual studies, exploring how people perceive non-verbal sounds displayed by a Pepper robot related to its movement. These studies highlighted preferences for more refined sound models, subtle sounds that blend with ambient sounds, and sound characteristics matching the robot’s visual attributes. This part also resulted in a programming interface connecting the Pepper robot with sound production tools.

    The second part focuses on a structured analysis of robot sounds in films, revealing three narrative themes related to robot sounds in films with implications for social robotics. The first theme involves sounds associated with the physical attributes of robots, encompassing sub-themes of sound linked to robot size, exposed mechanisms, build quality, and anthropomorphic traits. The second theme delves into sounds accentuating robots’ internal workings, with sub-themes related to learning and decision-making processes. Lastly, the third theme revolves around sounds utilized in robots’ interactions with other characters within the film scenes.

    Based on these works, the dissertation discusses sound design recommendations for social robotics inspired by practices in film sound design. These recommendations encompass selecting the appropriate sound materials and sonic characteristics such as pitch and timbre, employing movement sound for effective communication and emotional expression, and integrating narrative and context into the interaction.

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    Kappa
  • Public defence: 2024-02-23 09:00 https://kth-se.zoom.us/j/66088467200, Stockholm
    Luis, Israel
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Walking efficiently with smart springs2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Numerous assistive exoskeletons have been developed in recent years to assist walking in individuals with and without motor disorders. A standard metric to measure the efficacy of assistance is the change in the metabolic energy cost between unassisted and assisted conditions. Various experimental methods, such as human-in-the-loop optimization, have been developed to find the optimal exoskeleton control to minimize metabolic energy. Such an approach is powerful yet time- and resource-intensive. In this regard, computational methods might complement state-of-the-art experimental approaches. Developing accurate models of the musculoskeletal system and neuromuscular commands could accelerate the development of exoskeletons and improve our understanding of human-exoskeleton interaction. The aims of the thesis were to model and simulate muscle-tendon mechanics and energetics of walking across speeds in unassisted conditions and with the support of ideal exoskeleton assistance with two modes of assistance: motor-based and spring-based actuators. 

    The first three studies examined multiple musculoskeletal models, calibration methods of the muscle-tendon architecture, performance criteria for solving the muscle redundancy, and metabolic energy models to accurately estimate muscle excitations, fiber lengths, and metabolic energy cost compared to available experimental data. The musculoskeletal model proposed by Rajagopal et al. with calibrated muscle passive fiber-length curves and personalized Achilles and patellar tendon stiffness provided good agreement with muscle excitations and fiber lengths obtained from electromyographic signal and ultrasound imaging, respectively. Also, among multiple metabolic energy models in the literature, the model proposed by Bhargava et al. best estimated the average metabolic rates of the whole body compared to experimental measurements computed from spiroergometry. With the best estimations of muscle-tendon mechanics and energetics, the relative cost of the stance phase was predicted to increase significantly with walking speeds, and the metabolic cost of ankle plantarflexors was the highest among muscle groups and increased with walking speeds. The fourth study examined the optimal assistance to reduce muscle activations using motor-based and spring-based assistance of ankle plantarflexor, knee extensor, hip flexor, and hip abductor muscle groups. The largest reduction of muscle activation compared to unassisted conditions was obtained with hip flexor assistance with both actuation systems at high walking speeds. The reduction of metabolic rates compared to unassisted conditions was greater with walking speed with motor-based ankle plantarflexor assistance. In contrast, assisting this muscle group with spring-based actuation resulted in lower metabolic cost compared to unassisted conditions as walking speed increased. Interestingly, the decrease in muscle activations did not necessarily imply a reduction of metabolic energy cost compared to unassisted conditions, for instance with spring-based hip flexor and abductor assistance at some walking speeds. Metabolic energy rates during specific periods of the gait cycle were larger than in unassisted conditions due to increased muscle positive work, which is associated with high metabolic cost. 

    The computational methods in the thesis might inspire future studies in the field. The software to calibrate muscle-tendon parameters, such as tendon compliance based on electromyography and muscle passive force-length curves based on ultrasound imaging, and to simulate exoskeleton assistance, are available in public repositories and can be adapted to integrate more experimental observations and simulate other motions than walking. Future studies will validate the predicted muscle-tendon mechanics with exoskeleton assistance.

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  • Public defence: 2024-02-23 10:00 FA31, Albanova Universitetscentrum, Roslagstullsbacken 21, Stockholm
    Ohlin, Hanna Ohlin
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Nanofabrication processes for high-aspect ratio X-ray zone plates2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The field of nanofabrication is vast, and there are many methods available to facilitate the fabrication of different types of structures. Nanostructured materials make up critical infrastructure in fields like medical technology, energy storage and production, computer science and more. These can come in many different shapes, including particles, crystallites, patterned structures and more. 

    A common material for nanostructures of more deterministic natures is silicon. Processing silicon can be done in many ways, and within nanofabrication, methods are sorted as either top-down or bottom-up. Each term describes the process of reaching the desired size of the structure by either breaking down a bulk (top-down) or building up from smaller particles (bottom-up). Through combining different methods of nanofabrication, advanced nanostructures for complicated applications can be made.

    One area where such nanostructures are needed is X-ray imaging. Nanostructures make up the optical components responsible for the focusing of the light. For this purpose, there are many options available. One is zone plates, which are circular gratings with radially decreasing features that through diffraction focus the X-rays to a spot. The resolution of a zone plate is determined by the size of the outermost zone. As X-ray imaging is a technique commonly used for imaging of very small samples, such as viruses, cells, particles, or crystals, a zone plate needs to offer the possibility to resolve small features. This leads to the outermost zone of the zone plate needing to be very small, preferably on the nanoscale. For efficiency, a high aspect ratio is desirable. To achieve this, precise nanofabrication is key, and the processes for fabricating these devices are many, complex, and depend on good control and optimization to get the best results.

    The purpose of this thesis is to investigate and improve these methods for the fabrication of zone plate nanostructures for X-ray imaging purposes. Among these are electron beam lithography, electroplating, lift-off methods and metal-assisted chemical etching - MACE. 

    An optimized and controlled electroplating process was evaluated for filling of direct-written zone plate structures in CSAR62, an e-beam lithography resist, with gold in a miniaturized sulphite-based bath. This bottom-up approach yielded free-standing zone plates on silicon nitrate membranes with a height between 400 and 450 nm and an outermost feature size of 40 nm, which constitutes an aspect ratio of 1:10. 

    MACE is a promising process for the fabrication of zone plate nanostructures and has the capability to achieve high aspect ratios. It has, however proven to be complex in nature and difficult to control fully. In this thesis, the MACE process is explored further in regard to how to facilitate the fabrication of these kinds of structures. This includes the single-layer lift-off process for MACE, which was optimized and evaluated to raise the yield of usable samples for etching. It was found that despite the tiny process window available, cyclic processing was crucial to the success of the method. Furthermore, starting materials were evaluated in regards to N and P-type silicon, and the resulting etched structures were studied. Lastly, an investigation into a lift-off-free process was conducted, where the more conventional evaporation to lift-off method was replaced by an electroplated bi-layer catalyst. This was then etched in vapour phase and subsequently evaluated. The aspect ratio from initial image tests was approximated to 1:50. 

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  • Public defence: 2024-02-23 10:00 F3, Stockholm
    Atoufi, Zhaleh
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.
    Development and Tailoring of Low‐Density Cellulose‐Based Structures for Water Treatment2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The challenges posed by our limited clean water sources and the well-known global waterpollution demand more efficient water purification technologies. Additionally, the increasingenvironmental awareness has inspired a shift towards eco-friendly and renewable materials andtechnologies. This thesis is focused on developing effective adsorbent materials from renewableresources to eliminate organic solvents, dyes, and metal ions from water. Cellulose, the most abundantbiopolymer in nature, is the main component used to develop new materials in the present study. Itsdistinctive physical and colloidal properties, in the form of nanocellulose, along with tunable surfacechemistry, play key roles in enhancing the effectiveness of the developed materials.

    The primary focus of the first part of the thesis was to develop a molecular layer-by-layermodification technique to customize the surface functionality of cellulose aerogels in a uniform andcontrolled manner. Through the sequential deposition of diamine and triacid monomers, exceedinglythin polyamide coatings were formed on the cellulose aerogels, altering the surface properties fromhydrophilic to hydrophobic. This transformation made them well-suited structures for oil-waterseparation.

    Following this, a biohybrid aerogel was developed based on cellulose nanofibrils (CNFs) andamyloid nanofibrils (ANFs), the latter derived by heat treatment of β-lactoglobulin proteins. The pHtunablesurface charge of the aerogel, controlled by the amphiphilicity of the protein, allowed for theadsorption of both cationic and anionic contaminants by adjusting the pH of the solutions.Furthermore, the aerogels exhibited remarkable selectivity for lead (II) ions and they could also beregenerated and reused after each adsorption cycle without a significant loss of their adsorptioncapacity. This was to a large extent possible due to the excellent wet stability of these aerogels, whichwas achieved by crosslinking the CNFs during freezing and ice templating, eliminating the need forfreeze-drying. However, a solvent exchange to acetone after melting was still necessary to reduce theinfluence of the capillary forces during drying to avoid the collapse of the aerogels. In a consecutivestudy, the foaming characteristics of the heat-treated β-lactoglobulin system were exploited to createhighly stable Pickering foams with the aid of using CNFs as stabilizers and to physically lock thesystem through a controlled pH reduction. Interestingly, these Pickering foams could be directlyoven-dried without collapsing, yielding low-density foams. Furthermore, it was demonstrated that thefoams can be chemically crosslinked by incorporating chemical crosslinkers in the formulation or bypre-functionalizing the CNFs with dialdehydes. This crosslinking naturally also provided wet stabilityto the oven-dried foams.

    Finally, an innovative and environmentally friendly method was introduced to increase the charge of cellulose fibers by radical polymerization of acrylic acid from the fibers, enabling the preparationof fibers with an exceptionally high charge of 6.7 mmol/g. The introduction of these charged groupssignificantly enhanced the interaction of the fibers with methylene blue as a model dye and lead (II),Copper (II), and Zinc (II) ions as model metal ions, showing the huge potential of these fibers asbuilding blocks for a wide range of adsorbent applications. Overall, this thesis demonstrates thedevelopment and characterization of several bio-based adsorbents for water remediation.

  • Public defence: 2024-02-23 14:00 Kollegiesalen, Stockholm
    Xavier, Donnatella
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics.
    Uncertainty quantification for time varying quantities in turbulent flows2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Quantification of uncertainty in results is crucial in both experiments and simulations of turbulence, yet this practice is notably underutilized. This thesis project delves into statistical tools within the framework of uncertainty quantification to systematically quantify uncertainties that occur in the time varying quantities of turbulence. Two main categories of variance estimators for quantifying time averaging uncertainties in turbulent flow time series are examined in detail – the batch-means based methods and autoregressive model-based methods. The batch size is critical to estimation of uncertainty by the batch methods. We discuss reasons for biased estimates and provide guidance on the selection of batch sizes for the non-overlapping, overlapping and batch means-batch correlations estimators, to obtain consistent estimates of uncertainty when dealing with turbulence time samples. The autoregressive model (ARM)-based estimator was found to be more efficient than the batch methods, in terms of computational efficiency and sample requirements. A novel insight into the operating principle of the ARM, enabled fast quantification of uncertainty with few samples and with batch means series. The extension of univariate autoregressive processes to model entire 2D space-time fields of turbulence, through vector autoregression has been discussed and its potential as a turbulent inflow boundary condition has been illustrated. A crucial flow case that questioned the reliability of Computational Fluid Dynamics (CFD), namely flow through Food and Drug Administration benchmark nozzle device was also simulated in this doctoral thesis project, with a well-defined turbulent inflow boundary condition. Novel insights on the flow physics due to geometrical effects were obtained through statistical analysis, anisotropy invariant maps and proper orthogonal decomposition. These insights provide answers to many open questions in this domain. This work provides analyses and methods to increase the reliability of simulations, expanding the scope of CFD to applications where safety and precision are paramount.

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  • Public defence: 2024-03-01 09:00 FA32, Albanova, Stockholm
    Roos, August K.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Superconducting kinetic inductance devices for nanoscale force sensing2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis, we present a force sensor for atomic force microscopy based on cavity optomechanical principles. We explain the function, design, fabrication and characterisation of the force sensor. The mechanical part of the force sensor consists of a cantilever with a very fine tip. Near the cantilever's base is an LC circuit with resonance frequency in the range 4-5 GHz. The inductor consists of a superconducting meandering nanowire that changes its inductance when strained. Thus, the mechanical movement of the cantilever can be detected by measuring how the resonance frequency of the LC circuit changes. The mechanical movement gives rise to sidebands in the microwave spectrum. One detection method is based on the circuit being driven by two microwave tones while the cantilever is actuated near its mechanical resonance by a piezoelectric shaker mounted near the sensor. The amplitude of the measured signal depends on the phase difference between the motion of the cantilever and the microwave tones.

    Key steps in the fabrication include release of the cantilever by etching away the substrate from both the front and back sides, and deposition of a tip on the free end of the cantilever. Fabrication is done over an entire semiconductor wafer and exhibits high yield. The optomechanical coupling strength g0 was measured in the order of a few Hertz at temperatures of a few millikelvin. However, an accurate calibration of the coupling constant relating mechanical movement of the cantilever to the shift of resonance frequency of the LC circuit was not possible due the presence of a non-thermal fluctuating force. We also present how the microwave losses in the LC circuit vary in the range 1.7-6 K. Our circuits exhibit higher losses than expected from thermal-equilibrium quasiparticles, which we attribute to the circuit dielectric. Quasiparticle losses set an upper limit on the quality factor that our circuits can achieve regardless of topology. In addition, the LC circuit exhibits a nonlinear relationship between current and kinetic inductance that enables parametric amplification of the mechanical sidebands. Thus, the presented force sensor integrates the force transducer (cantilever), the detector (LC circuit) and a parametric signal amplifier (via the nonlinearity of the LC circuit) in one and the same component.

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    kappa
  • Public defence: 2024-03-01 14:00 F3, Stockholm
    Li, Sichao
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science.
    Electro-Interfacial Composition Control by Ionic Liquid Technology: Nanostructure, Self-Assembly, and Friction2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Given the potential of ionic liquids (ILs) for batteries, supercapacitors and advanced lubricants, it is crucial to understand how electric fields affect the interfacial behaviour in IL-solvent systems and the intricate relationship between nanostructure and tribotronic properties. This thesis investigates the structural and compositional changes of ILs with different solvents at electrified interfaces.

    The four papers constituting this thesis can be broadly divided into two studies. The first study outlines the electro-interfacial behaviour of various monocationic (MILs) and dicationic ILs (DILs) dispersed in propylene carbonate. Combining electrochemical quartz crystal microbalance, neutron reflectivity (EC-NR), and atomic force microscopy, a voltage-induced interphase transition from a self-assembled cation bilayer to a conventional electrical double-layer structure has been revealed in bis(oxalato)borate anion MILs. This interphase transition has not been observed in DILs, attributed to the dual charge centres reducing the segregation between polar and apolar domains of dications for self-assembly interaction. 

    The second study explores three MILs sharing the same phosphonium cation with varying orthoborate-based anions dissolved in 2-ethylhexyl laurate (2-EHL). EC-NR measurements reveal a solvent-rich interfacial corona layer and the subtlety of anion architecture in tuning electro-interfacial properties. Meanwhile, EC-NR has been used as a complementary probe to elucidate the nano-scale structural and compositional changes in the boundary films of IL/2-EHL systems with varying potentials, providing a direct link between the molecular controllability and macroscopic tribotronic performance studies.

    This thesis contributes to the fundamental understanding of electro-interfacial behaviour and controllability of IL-solvent systems and offers valuable molecular insights for deploying these novel ILs as additives in advanced tribological and electrochemical contexts.

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    Summary
  • Public defence: 2024-03-04 09:00 F3, Stockholm
    Vickerfält, Amanda
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Process. Swerim AB.
    A study of an autogenous slag for steel production with consideration of possible vanadium extraction2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The thesis discusses the use of the autogenous slag that forms from the residual oxides present in hydrogen reduced iron (H-DRI) pellets during melting. The studies are motivated by a better understanding of how H-DRI affect the steelmaking operations. A possible optimization of the steelmaking process is to recover the vanadium that is contained in the iron ore raw material. Therefore, understanding the role of vanadium during melting of H-DRI is given an extra focus. 

     

    Taking advantage of the autogenous slag by utilizing its dephosphorization power to a maximum, or using it to extract vanadium, could make an important contribution to the process economics. To assist the developments in these directions, the phosphorus and vanadium partitions between slag and metal (LP and LV) as well as the phase relationship of the autogenous slag were investigated. The partitions were studied by melting H-DRI with reduction degrees between 91 and 99% in closed systems at 1873 K. The obtained LP and LV were in the ranges 8-26 and 501-1994, respectively. The LV values increased with decreased reduction degrees. The values for LP increased with decreasing reduction degrees until a 97% degree of reduction. Further lowered reduction degrees correlated with decreased LP values. The lowest phosphorus levels encountered in the iron (130 ppm) were obtained after melting of H-DRI with degrees of reduction between 94 and 98%. This indicates that the autogenous slag has a potential to make a significant contribution to the phosphorus refining. 

     

    To find out about the phase relationship in the autogenous slag at 1873 K, small (5 g) samples of synthetic slag were equilibrated with 1 g iron in closed systems. Composition-wise, these slags corresponded to the autogenous slags from H-DRI with 98.4-99.7% reduction degrees. Preservation of the high temperature phase relationship required fast cooling; therefore, the samples were quenched in oil. This was also the reason for using small samples. Spinel, magnesiowüstite and liquid phase were identified as the stable phases at 1873 K. The spinel and magnesiowüstite phases were high in V, while the liquid contained almost no V. Increased FeO-contents (decreased degrees of reduction) correlated with a decreased amount of spinel, an increased amount of magnesiowüsite, as well as a decreased content of V in both phases.

     

    To increase the understanding about the phases in the autogenous slag, a sub-system containing MgO and V2O3 was investigated under conditions relevant to H-DRI melting, namely temperatures between 1661-1873 K and pO2 values between 1.75×10-11 and 1.75×10-10 atm. The phase boundaries for the three stable phases MgO-halite, spinel and V2O3-corundum were established. The oxygen potential and the temperature had limited impacts on the phase boundaries for the spinel and V2O3-corundum phases, while the maximum solubility of V2O3 in MgO-halite was affected to a somewhat larger extent. As earlier research has shown that an acid slag could be suitable for V extraction, the pseudo-ternary phase diagram between Al2O3, SiO2 and V2O3 at 1873 K and pO2=3.4×10-11-3.4×10-9 atm was also investigated. 5 different phases were identified, namely mullite, Al2O3-corundum, V2O3-corundum, cristobalite, and a liquid phase. The most significant effect of the oxygen potential was on the invariant point representing double Al2O3 and V2O3 saturation of the liquid. The multivalent nature of vanadium is suggested as the reason for the slight impact of the oxygen potential on the phase diagrams.

     

    To understand how the autogenous slag forms from the residual oxides, individual pellets with 90 and 99% reduction degrees were studied during heating to either 1773 or 1873 K. It was observed that the autogenous slag forms before iron melts. The slag likely forms as FeO melts and dissolves the other remaining oxides. Thereby, vanadium is transferred to the autogenous slag. Before iron melts, the movement of the autogenous slag is restricted to the pellet’s pore network. Thereafter, when iron melts, the slag starts to coalesce as well as to floatate.

     

    As the autogenous slag may contain solid phases, the effect of the fraction of solid phase on the slags foamability was finally investigated. This was done by measuring the maximum foaming heights of slags containing Al2O3, CaO, FeO and SiO2, reminiscent in their compositions to the autogenous slag. The slag compositions were chosen so that the fraction of precipitated magnesiowüstite phase was the main variable. It was found that some amount of solid phase (1.6 vol%) increased the foaming height by approximately 7%, while ≥8.7 vol% more than halved the foaming height.

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  • Public defence: 2024-03-05 09:00 Nils Ringertz, Solna
    Buchmann, Sebastian
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Protein Science, Nano Biotechnology. AIMES - Center for the Advancement of Integrated Medical and Engineering Sciences at KI and KTH/ 3 Department of Neuroscience, Karolinska Institutet, Stockholm, Sweden.
    Organic Electronics and Microphysiological Systems to Interface, Monitor, and Model Biology2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Biological processes in the human body are regulated through complex and precise arrangements of cell structures and their interactions. In vivo models serve as the most accurate choice for biological studies to understand these processes. However, they are costly, time-consuming, and raise ethical issues. Microphysiological systems have been developed to create advanced in vitro models that mimic in vivo-like microenvironments. They are often combined with integrated sensing technologies to perform real-time measurements to gain additional information. However, conventional sensing electrodes, made of inorganic materials such as gold or platinum, differ fundamentally from biological materials. Organic bioelectronic devices made from conjugated polymers are promising alternatives for biological sensing applications and aim to improve the interconnection between abiotic electronics and biotic materials. The widespread use of these devices is partly hindered by the limited availability of materials and low-cost fabrication methods. In this thesis, we provide new tools and materials that facilitate the use of organic bioelectronic devices for in vitro sensing applications. We developed a method to pattern the conducting polymer poly(3,4‑ethylenedioxythiophene) polystyrene sulfonate and to fabricate organic microelectronic devices using wax printing, filtering, and tape transfer. The method is low-cost, time-effective, and compatible with in vitro cell culture models. To achieve higher resolution, we further developed a patterning method using femtosecond laser ablation to fabricate organic electronic devices such as complementary inverters or biosensors. The method is maskless and independent of the type of conjugated polymer. Besides fabrication processes, we introduced a newly synthesized material, the semiconducting conjugated polymer p(g42T‑T)‑8%OH. This polymer contains hydroxylated side chains that enable surface modifications, allowing control of cell adhesion. Using the new femtosecond laser-based patterning method, we could fabricate p(g42T‑T)‑8%OH‑based organic electrochemical transistors to monitor cell barrier formations in vitro. Microphysological systems are further dependent on precise compartmentalization to study cellular interaction. We used femtosecond laser 3D printing to develop a co-culture neurite guidance platform to control placement and interactions between different types of brain cells. In summary, the thesis provides new tools to facilitate the fabrication of organic electronic devices and microphysiological systems. This increases their accessibility and widespread use to interface, monitor, and model biological systems. 

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  • Public defence: 2024-03-06 10:00 https://kth-se.zoom.us/j/62065064122, Stockholm
    Zojaji, Sahba
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Embodying Politeness in Persuasive Humanoid Agents for Small Group Scenarios2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In both physical and virtual environments, small group interactions significantly shape our social experiences. Understanding and replicating situated group interactions with virtual agents or physical robots pose possibilities and challenges. Central to these challenges lies the critical aspect of politeness, which serves as a fundamental cornerstone in shaping our social interactions. This PhD thesis investigates the profound significance of politeness strategies in shaping social interactions within small free-standing conversational groups in physical and virtual environments with humanoid artificial agents. It particularly focuses on their adaptability to virtual characters or Embodied Conversational Agents (ECAs) and Human-Robot Interaction (HRI). The thesis explores the impact of these strategies on persuasiveness, adherence to social norms, and the formation of positive perceptions during interactions between participants and virtual agents or humanoid robots while joining a group of artificial humanoid agents. It involves a series of user studies with an experimental setup, which entails presenting participants with dilemmas in either a virtual or physical environment. Participants should decide between expending more effort to comply with the agent’s request or opting for a least-effort alternative to join a group while ignoring the request. Additionally, the setup evaluates participant responses to various politeness strategies expressed by virtual agents or robots when extending invitations to join a small, free-standing group. The research contributes by defining behaviors aligned with politeness strategies, revealing participant adherence to social norms even in situations requiring more effortful choices, and pinpointing optimal behaviors based on criteria such as persuasiveness, politeness, and social adherence. Ultimately, the findings provide insights into the indispensable role of politeness strategies in Human-Agent Interaction to gently influence the decisions of humans while maintaining positive relations with them. These insights pave the way for designing more effective and socially acceptable behaviors for virtual agents and robots across diverse domains.

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  • Public defence: 2024-03-06 13:00 Sal C, Stockholm
    Roy, Debaditya
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Software and Computer systems, SCS.
    Towards Trustworthy Machine Learning For Human Activity Recognition2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Human Activity Recognition presents a multifaceted challenge, encompassing the complexity of human activities, the diversity of sensors used, and the imperative to safeguard user data privacy. Recent advancements in machine learning, deep learning, and sensor technology have opened up new possibilities for human activity recognition. Wearable sensor-based human activity recognition involves collecting time-series data from various sensors, capturing intricate aspects of human activities. The focus of the above activity recognition problem is classifying human activities from the time-series data. Hence, this time-series classification problem demands efficient utilization of temporal properties. Moreover, while accurate prediction is crucial in human activity recognition, the reliability of predictions often goes unnoticed. Ensuring that predictions are reliable involves addressing two issues: calibrating miscalibrated predictions that fail to accurately represent the true likelihood of the data and addressing the challenges around uncertain predictions. Modern deep learning models, used extensively in human activity recognition, often struggle with the above issues. In addition to reliability concerns, machine learning algorithms employed in Human Activity Recognition are also plagued by privacy issues stemming from the utilization of sensitive activity data during model training. While existing techniques such as federated learning can provide some degree of privacy protection in these scenarios, they tend to adhere to a uniform concept of privacy and lack quantifiable privacy metrics that can be effectively conveyed to users and customized to cater to their individual privacy preferences. Hence, in the thesis, we identify the challenges around the effective use of temporal data, reliability, and privacy issues of machine learning models used for wearable sensor-based human activity recognition. To tackle these challenges, we put forth novel solutions, striving to enhance the overall performance and trustworthiness of machine learning models employed in human activity recognition.

    Firstly, to improve classification performance, we propose a new temporal ensembling framework that uses data temporality effectively. The framework accommodates various window sizes for time-series data and trains an ensemble of deep-learning models based on that. It enhances classification accuracy and preserves temporal information.

    Secondly, we address reliability through calibration and uncertainty estimation. The aforementioned temporal ensembling framework is used for calibration and uncertainty estimation. It provides well-calibrated predictions for human activity recognition and detects out-of-distribution activities, an important task of uncertainty estimation. Furthermore, we apply these methods to real-world scenarios, enhancing the reliability of human activity recognition models.

    Thirdly, to address the privacy concern, we introduce a differentially private framework for time-series human activity recognition, quantifying privacy. Additionally, we develop a collaborative federated learning framework, allowing users to define their privacy preferences, advancing privacy preservation in human activity recognition.

    These contributions address major challenges and promote improved classification, reliability, and privacy preservation in human activity recognition. It helps us to move towards trustworthy machine learning in human activity recognition, facilitating their usage in realistic and practical scenarios.

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  • Public defence: 2024-03-06 13:00 Ka-Sal B, Stockholm
    Tavana, Morteza
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Communication Systems, CoS.
    RF Energy Harvesting for Zero-Energy Devices and Reconfigurable Intelligent Surfaces2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The growth of Internet of Things (IoT) networks has made battery replacement in IoT devices increasingly challenging. This issue is particularly pronounced in scenarios with a large number of IoT devices, in locations where IoT devices are difficult to access, or when frequent replacement is necessary. The risk of losing or forgetting some IoT devices also exists, leading to a risk of hazardous chemical leakage and e-waste in nature. Radio Frequency(RF) wireless power transfer (WPT) offers an alternative solution for powering these devices. Moreover, it has been observed that the receivers absorb less than one-millionth of the transmitter energy while surrounding objects absorb the remainder. This situation opens up the possibility of leveraging existing wireless infrastructures, such as base stations (BSs), to charge IoT devices. In this thesis, we focus on analyzing the feasibility and limitations of battery-less operation of IoT devices using RF WPT technology, along with energy harvesting (EH) from existing wireless communication infrastructure. We explore both indoor and outdoor scenarios for powering IoT devices. Initially, we consider an outdoor environment where an IoT device periodically harvests energy from existing BSs and transmits a data packet related to sensor measurement. We analyze the coverage range of energy harvesting from a BS for powering IoT devices, which shows a tradeoff between the coverage range and the rate of sensor measurements. Additionally, we compare the operational domain in terms of the range and measurement rate for WPT and battery-powered technologies. Furthermore, we consider the coverage probability for a multi-site scenario, which is the likelihood that a randomly allocated IoT device harvests enough power to enable its operation. We derive an expression for this probability at a random location in terms of harvesting sufficient power for IoT device operation at a given measurement rate. Next, we consider the remote powering of IoT devices inside an aircraft. Wired sensors add weight and maintenance costs to the aircraft. Although replacing data cables with wireless communication reduces costs and simplifies deployment, providing power cables for the sensors remains challenging. We assume fixed locations for IoT devices inside an aircraft. The goal is to minimize the number of WPT transmitters for a given cabin geometry and IoT device duty cycles. We address WPT system design under channel uncertainties through robust optimization. Following this, we turn our attention to energy harvesting at a reconfigurable intelligent surface (RIS). The potential benefits of using RIS compared to traditional relays when it comes to improving wireless coverage have been debated in previous works, under the assumption that both technologies have a wired power supply. The comparison would be entirely different if the RIS can become self-sustaining, which is not possible for relays. Therefore, we explore energy harvesting for RIS, proposing an algorithm for phase adjustment to maximize energy harvesting from RF sources based on power measurements. Lastly, we explore the charging of zero-energy devices (ZEDs) via a RIS. Mitigating the path loss in WPT requires large antenna arrays, which leads to increased hardware complexity, as it demands an RF chain per antenna element. Alternatively, RIS offers high beamforming gain with simpler hardware. Therefore, we consider RIS-assisted RF charging of ZEDs. We develop dynamic algorithms for battery-aware and queue-aware scenarios, adjusting RIS phases and transmission power to meet the requirements.

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  • Public defence: 2024-03-07 16:00 https://kth-se.zoom.us/j/64013906066, Stockholm
    Cabrera Arteaga, Javier
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Software and Computer systems, SCS.
    Software Diversification for WebAssembly2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    WebAssembly, now the fourth ocially recognized web language, enables web browsers to port native applications to the Web. Furthermore, WebAssembly has evolved into an essential element for backend scenarios such as cloud and edge computing. Therefore, WebAssembly finds use in a plethora of applications, including but not limited to, web browsers, blockchain, and cloud computing. Despite the emphasis on security since its design and specification, WebAssembly remains susceptible to various forms of attacks, including memory corruption and side-channels. Furthermore, WebAssembly has been manipulated to disseminate malware, particularly in cases of browser cryptojacking. 

    Web page resources, including those containing WebAssembly binaries, are predominantly served from centralized data centers in the modern digital landscape. In conjunction with browser clients, thousands of edge devices operate millions of identical WebAssembly instantiations every second. This phenomenon creates a highly predictable ecosystem, wherein potential attackers can anticipate behavior either in browsers or backend nodes. Such predictability escalates the potential impact of vulnerabilities within these ecosystems, paving the way for high-impact side-channel and memory attacks. For instance, a flaw in a web browser, triggered by a defective WebAssembly program, holds the potential to aect millions of users. 

    This work aims to harden the security within the WebAssembly ecosystem through the introduction of Software Diversification methods and tools. Software Diversification is a strategy designed to augment the costs of exploiting vulnerabilities by making software less predictable. The predictability within ecosystems can be diminished by automatically generating dierent, yet functionally equivalent, program variants. These variants strengthen observable properties that are typically used to launch attacks, and in many instances, can eliminate such vulnerabilities. 

    This work introduces three tools: CROW, MEWE as compiler-based approaches, and WASM-MUTATE as a binary-based approach. Each tool has been specifically designed to tackle a unique facet of Software Diversification. We present empirical evidence demonstrating the potential application of our Software Diversification methods to WebAssembly programs in two distinct ways: Oensive and Defensive Software Diversification. Our research into Oensive Software Diversification in WebAssembly unveils potential paths for enhancing the detection of WebAssembly malware. On the other hand, our experiments in Defensive Software Diversification show that WebAssembly programs can be hardened against side-channel attacks, specifically the Spectre attack. 

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  • Public defence: 2024-03-08 13:00 F3, Stockholm
    Das, Sandipan
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Information Science and Engineering.
    State estimation with auto-calibrated sensor setup2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Localization and mapping is one of the key aspects of driving autonomously in unstructured environments. Often such vehicles are equipped with multiple sensor modalities to create a 360o sensing coverage and add redundancy to handle sensor dropout scenarios. As the vehicles operate in underground mining and dense urban environments the Global navigation satellite system (GNSS) is often unreliable. Hence, to create a robust localization system different sensor modalities like camera, lidar and IMU are used along with a GNSS solution. The system must handle sensor dropouts and work in real-time (~15 Hz), so that there is enough computation budget left for other tasks like planning and control. Additionally, precise localization is also needed to map the environment, which may be later used for re-localization of the autonomous vehicles as well. Finally, for all of these to work seamlessly, accurate calibration of the sensors is of utmost importance.

    In this PhD thesis, first, a robust system for state estimation that fuses measurements from multiple lidars and inertial sensors with GNSS data is presented. State estimation was performed in real-time, which produced robust motion estimates in a global frame by fusing lidar and IMU signals with GNSS components using a factor graph framework. The proposed method handled signal loss with a novel synchronization and fusion mechanism. To validate the approach extensive tests were carried out on data collected using Scania test vehicles (5 sequences for a total of ~ 7 Km). An average improvement of 61% in relative translation and 42% rotational error compared to a state-of-the-art estimator fusing a single lidar/inertial sensor pair is reported.  

    Since precise calibration is needed for the localization and mapping tasks, in this thesis, methods for real-time calibration of the sensor setup is proposed. First, a method is proposed to calibrate sensors with non-overlapping field-of-view. The calibration quality is verified by mapping known features in the environment. Nevertheless, the verification process was not real-time and no observability analysis was performed which could give us an indicator of the analytical traceability of the trajectory required for motion-based online calibration. Hence, a new method is proposed where calibration and verification were performed in real-time by matching estimated sensor poses in real-time with observability analysis. Both of these methods relied on estimating the sensor poses using the state estimator developed in our earlier works. However, state estimators have inherent drifts and they are computationally intensive as well. Thus, another novel method is developed where the sensors could be calibrated in real-time without the need for any state estimation. 

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  • Public defence: 2024-03-11 15:00 F3, Stockholm
    Taghavian, Liam Hamed
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Externally positive systems: Analysis and control based on combinatorial polynomials2024Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Monotonic tracking is required in many control systems, including those that cannot tolerate any overshoots and undershoots in their closed-loop responses. Classical examples are found in vehicle cruise control and liquid tank level control. In the former, an overshoot happens when the speed of the vehicle goes beyond the set value violating the safety measures, and in the latter an overshoot is considered as filling up the tank with an excessive amount of liquid which leads to a waste of resources. Controllers that eliminate overshoots are undeniably more desirable in these examples. In fact, the same requirement is in place for many more engineering applications, including biological systems, robotics and process control, indicating widespread benefits of controllers which can guarantee monotonicity in the system response. Formally, linear systems that exhibit monotonically increasing step responses are called externally positive. Designing controllers that render the closed-loop system externally positive requires a thorough understanding of this property in linear systems. In this thesis, we leverage combinatorial polynomials and their properties to study external positivity in both discrete-time and continuous-time linear systems modelled by transfer functions or impulse responses. Several conditions are provided that are either necessary, sucientor both necessary and sufficient for a linear system to be externally positive. These conditions are then used to synthesize controllers that ensure external positivity in closed-loop systems and hence, eliminate both overshoots and undershoots in the system response. In particular, we provide synthesis techniques based on convex optimization that ensure stability, robustness and offset-free monotonic tracking in the closed-loop system and improve its decay rate and sensitivity. We compare the results with the state-of-the-art in the literature and demonstrate the efficacy of the proposed controller synthesis methods through several numerical examples.

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  • Public defence: 2024-03-12 13:00 Sal F3, Stockholm
    Al Ghafri, Aziza
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Accounting, finance, economics and organization (AFEO).
    "I Wanna Be Free": On the Challenges and Coping Strategies of Women Entrepreneurs in Sweden2024Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Women's entrepreneurship is often presented as important for creating economic prosperity at the national level and is said to offer freedom, independence, and emancipation for women. The purpose of this study is to explore the conditions of women entrepreneurs who have different backgrounds in Sweden. To achieve this purpose, this study focuses on the challenges women entrepreneurs perceive and the coping strategies they employ to navigate these challenges. The study adopts an intersectional gender perspective, grounded in research on entrepreneurship, gender, and ethnicity. It draws on qualitative data collected through semi-structured interviews with women entrepreneurs in Sweden who have different backgrounds. The findings show that the challenges experienced by the women entrepreneurs included lack of support, being belittled, being excluded, having to work harder and be strong and having to adapt. The analysis discusses that these challenges can be understood as a result of gendered perceptions of entrepreneurship and processes of Othering. Ethnicity and race also play a role in shaping these conditions. The interviewed women deal with the conditions through four strategies: the assimilation strategy; the positive strategy, the ambiguity strategy, and the change strategy. The coping strategies are discussed in relation to empowerment and emancipation. From a theoretical perspective, this study contributes to developing concepts and conceptual relationships to capture how gender, ethnicity, and race impact women's conditions as entrepreneurs. 

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  • Public defence: 2024-03-15 10:00 Inghesalen, Solna
    Höjer, Pontus
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Gene Technology. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Exploring human variations by droplet barcoding2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Biological variations are being explored at ever-increasing rates through the rapid advancement of analytical techniques. Techniques like massively parallel sequencing empower scientists to accurately differentiate individuals’ genetic compositions, cellular functionalities, and healthy tissue from diseased. The knowledge gained from these techniques brings us ever closer to grasping the complexities of life, contributing to human development. Still, to fully elucidate biological variations in different samples requires novel sensitive and high- throughput techniques, capable of placing everything in its correct context. One such technique gaining promise is droplet barcoding. 

    Droplet barcoding leverages emulsion droplets to segregate samples into their functional components, coupled with barcodes that can group tagged molecules following sequencing. This technique constitutes a versatile tool for studying biological variations in both the phenotype and genotype. This thesis leverages droplet barcoding to explore variations relating to human biology. 

    Droplet barcoding was used to study phenotype variations, looking at protein compositions in single extracellular vesicles (Paper I) and single cells (Paper II). Paper I studies extracellular vesicles which are naturally released from cells. They carry heterogeneous protein signatures that can inform about their cellular origin. Tens of thousands of extracellular vesicles were profiled, including approximately 25,000 from lung cancer patients. From these protein profiles, extracellular vesicles could be grouped into putative subtypes. Paper II presents a novel method for studying single cells which was used to characterize blood-derived immune cells. The method enabled the identification of most major immune cell lineages. 

    Haplotype-resolved genetic variations were analyzed using a linked read sequencing method based on droplet barcoding. Linked-read sequencing conserves long-range information from short-read sequencing by co- barcoding subsections of long DNA fragments. Paper III presents an open-source pipeline (BLR) for whole genome haplotyping using linked reads. BLR generates accurate and continuous haplotypes, outperforming PacBio HiFi-based diploid assembly. We further show that integration with low-coverage long-read data can improve phasing accuracy in tandem repeats. With 10X Genomics linked reads, BLR generated more continuous haplotypes compared to other workflows. Paper IV applies linked read sequencing to reveal the haplotype complexities of cancer genomes. In two patients with colorectal cancer, we identified several large-scale aberrations impacting cancer-related genes. Additionally, several short somatic variants were found to impact nearly all oncogenic networks identified by TCGA. Demonstrating the importance of haplotype-resolved analysis for cancer genomics, one patient exhibited two nonsense mutations on separate haplotypes in the well-known colorectal cancer gene APC. 

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