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The Next Generation of Magnetoresistive Devices
No full textMagnetometers have existed in some form for almost 200 years and play a critical role in our technological environment. New applications are continually developed as the resolution capabilities of these devices increases. State-of-the-art magnetometers such as superconducting quantum interference devices (SQUIDs) can have an excellent magnetic field resolution but are encumbered by the need for cryogenic liquid He cooling, heavy magnetic shielding, and extensive ancillary equipment and software which makes their operation expensive and outside of the reach of all but the most capital intensive institutions. It is therefore of scientific and technological interest to develop inexpensive and simple magnetometers which can also provide the fine field resolution necessary for many of the most challenging applications.One such magnetometry technique which to date remains relatively unexplored but may hold significant promise derives from a phenomenon known as extraordinary magnetoresistance (EMR). This effect occurs in hybrid systems of high mobility semiconductors interfaced with a second, higher conductivity material. The flow of current through the devices is heavily altered by a magnetic field, as a Lorentz force at the interface causes the charge carriers to deflect and travel through the higher resistance semiconductor, leading to large changes in the device resistance. Recent developments in both materials science and computational numerical simulations present an opportunity to improve the performance of EMR devices to the point where they are competitive with established high-performance magnetometers.In this thesis I detail the development of fabrication processes for producing EMR devices from InSb thin films, InAs quantum wells, and graphene encapsulated with hBN. While these processes have existed broadly for decades, they are novel in our research group and required extensive development before yielding usable devices. InSb and InAs samples were tested in magnetic fields up to 2 T and characterized, yielding insights about the intrinsic transport properties which were buttressed by analytical calculations and numerical simulations. In particular I show how the intrinsic magnetoresistance in InSb can be explained by the presence of multiple carrier bands and how the properties of the bands change upon thermal degradation of the material. EMR devices fabricated from these materials were also tested. I show how annealing can improve the contact resistivity by two orders of magnitude and results in an increase of the magnetoresistance from 870% to over 65,000%.Secondly, I also demonstrate how a synergistic relationship can be formed between numerical simulations and experimental data. Finite element analysis (FEA) simulations were used to predict the performance of EMR devices and showed good agreement to experimental data. The simulations could also be used to explain deviations between the experimental data and the expected behavior. In particular, I show how the behavior of one of our devices can be explained by inhomogenous material properties as a result of the diffusion of gold into our structure. Electron diffraction spectroscopy measurements later supported this interpretation. The simulations were also used to study the effect of the sensor boundary on performance, a parameter which to-date had remained unexplored. The simulations predicted that increases in the maximum sensitivity and the presence of a zero-field sensitivity could be obtained if material was removed from key areas of the device. Experimental devices were realized with these geometries with behavior that matched the predictions from simulations in most cases. I found that the model deviates from experiments for the cases where the intrinsic magnetoresistance of the material is large and the EMR effect is weak and propose a method for including intrinsic magnetoresistance into the FEA simulations. The predictive power of the simulations was tested with topology optimized designs which in theory should show magnetoresistances on the order of 1011%. However, while experimental devices made with these designs did not match the simulations they did show promising results with regards to the minimum field resolution suggesting that further tuning of the algorithm could yield significant results. Finally, I extended the FEA simulations into the realm of semiconductor nanowires where we show that more accurate estimations of the transport properties can be made with the help of numerical simulations
Advanced Nanosystems for Multidirectional Inhibition of Glioblastoma Growth and Recurrence
No full textGlioblastoma (GBM) is one of the most common malignant primary tumors in the central nervous system (CNS), characterized by high incidence, extremely easy metastasis and recurrence, and high mortality rate. Currently, the main treatment method for GBM is surgery, assisting with radiotherapy and chemotherapy. However, the prognosis of patients with GBM is still poor and the recurrence rate is high. Abundant evidence has demonstrated the existence of GBM stem cells (GSCs) could be the root cause of tumor formation, growth, metastasis, and recurrence since they have excellent self-renewal ability, rapid proliferation rate, and resistance to radiotherapy and chemotherapy. In addition, the existence of the blood-brain barrier (BBB) blocks most small molecules and almost all macromolecules, resulting in the low delivery efficiency of chemotherapy drugs. Meanwhile, the lack of targeting property of free drugs induces low efficiency of GBM cell and GSC elimination. In recent decades, the development of biocompatible nano-delivery systems has brought new ideas for the treatment of GBM. In this work, in order to improve GBM prognosis, we developed two novel nano-delivery systems to efficiently cross BBB and combat GSCs:(1) In the first nanoplatform, we constructed multifunctional magnetic therapeutic nanoparticles (MTNPs), which are coated with [Des-arg9]bradykinin (BK) to transiently open the BBB (BK@MTNPs). This NP contains the magnetite (Fe3O4) NPs, cysteine, crizotinib (CZT), and anti-PDL1 antibody (aPDL1). BK@MTNPs were demonstrated to induce DNA damage, activate the transcription of tumor suppressor gene-PTEN, inhibit GSC function, promote intratumoral infiltration of cytotoxic T lymphocytes (CTLs), and increase M1 type macrophages. Based on the in vivo and in vitro results, we identified that BK@MTNPs have a synergistic tumoricidal effect in modulating the tumor microenvironment (TME), boosting immune response, and inhibiting GBM recurrence.(2) In the second work, we proposed a nanoplatform that is coated with an engineered T cell membrane to target GBM and kill GSCs by local photothermal therapy (PTT). The human primary T cells were genetically engineered to express chimeric antigen receptor (CAR) on the surface— against CD133 and epidermal growth factor receptor (EGFR), which contribute to targeting both GSCs and GBM cells. Then the engineering T cell membrane (CM) was extracted and coated onto aggregation-induced emission (AIE) nanoparticles (CM@AIE NPs). The T-cell-mimic CM shell endows CM@AIE NPs to cross the BBB naturally by triggering an intracellular signaling cascade to modulate the opening of tight junctions (TJs). The dual-target molecules provide CM@AIE NPs with excellent in vivo accumulation in the tumor region that allows the generated photothermal effect to completely inhibit the tumorigenesis and recurrence under 980 nm laser irradiation
UV-assisted punching for fabrication of biocompatible microgel shapes for applications in drug delivery
No full textwide range of micro-and nano- carriers entrapping active pharmaceutical ingredients to improve their delivery are described today. Amongst these, hydrogel based carriers are of particular interest for the delivery of biomacromolecules, as they provide a water-rich environment in addition to a protective polymeric matrix for these compounds. The use of replication based top-down microfabrication techniques to precisely configure the shape and size of these micro- and nanocarriers is becoming increasingly popular. This is due to the high degree of control offered by these techniques as opposed to the more established bottom-up techniques which mainly produce polydisperse spherical carriers. Recent studies have successfully demonstrated that carrier shape and size play a significant role in carrier flow, bioadhesion, internalization and interaction with biological membranes. Thus, this work explored the microfabrication of shape-specific hydrogel based carriers for oral and intravenous drug delivery.UV-assisted punching was developed as a novel two-step microfabrication technique that allows for the fabrication of biocompatible poly(ethylene glycol)-based hydrogel micro-carriers termed as “microgel shapes”. UV-assisted punching is a facile, temperature ambient and solventless method that allows for the fabrication of individual microgel shapes by mechanical punching with a robust thermoplastic stamp. Furthermore, it allows for a process integrated incorporation of biomacromolecules. In the current work, microgel shapes targeted towards oral drug delivery were initially fabricated in circular, elliptical, square and rod-like geometries with a carrier length/diameter of 100 μm and a height of 25 μm. For each of the geometries, successful incorporation of a fluorescently labelled model biomacromolecule was demonstrated by fluorescence microscopy. In vitro release studies were performed to quantify the macromolecular content and the release profile associated with the produced microgel shapes. After establishment of UV-assisted punching as a fabrication method, process optimizations with use of alternate materials for thermoplastic stamps were performed. A versatile use of different thermoplastic stamps in UV-assisted punching for microgel shape fabrication was demonstrated.Furthermore, an evaluation of thermoplastic stamps in native, degassed and plasma activated conditions was conducted to assess its correlation on stamp wetting and microgel shape yield.Finally, a step-wise downscaling of microgel shape size for all the aforementioned geometries was carried out to obtain carriers with a length/diameter of 8 μm and a height of 2 μm relevant for intravenous applications. Biocompatibility of the developed carriers was demonstrated through hemocompatibility and cell viability assays. Moreover, successful process integrated loading of the microgel shapes with model enzyme and the retention of its activity post-loading to obtain microreactors was demonstrated. Overall, microgel shapes in various geometries with lengths/diameters ranging from 100 – 8 μm and a heights ranging from 25 – 2 μm were successfully fabricated by UV-assisted punching. Furthermore, a process integrated loading of biomacromolecules was demonstrated
New perspectives on Eastern Baltic cod movement patterns from historical and contemporary tagging data
No full textKnowledge of the movement patterns and area utilisation of commercially important fish stocks is critical to management. The Eastern Baltic cod Gadus morhua, one of the most commercially and ecologically important stocks in the Baltic Sea, is currently one of the most severely impacted fish stocks in Europe. During the last 2 decades, this stock has experienced drastic decreases in population size, distributional range, individual growth and body condition, all of which may have affected the movements between different areas of the Baltic Sea. In this study, we investigated the seasonal movement patterns of Eastern Baltic cod by re-analysing historical tagging data collected by the countries surrounding the Baltic Sea (1955-1988) and compared historical patterns with contemporary data from a recent international tagging experiment (2016-2019). Our re-analyses of historical data showed the presence of different movement behaviours, i.e. resident or seasonally migratory, with larger distances moved by cod released in the northern and central Baltic areas compared to cod released in the southern Baltic areas. Furthermore, trends from the recent tagging experiment indicate a persistent resident strategy in the southern Baltic area. These findings present additional information on general movement patterns and area utilisation of Eastern Baltic cod that could inform future management actions and aid stock recovery
3D structuring of sustainable carbon electrodes for energy storage
No full textAs the world is moving towards decarbonization, electric vehicles and other clean energy technologies offer a path towards a sustainable future. Sustainable electrochemical energy storage (EES) devices such as supercapacitors (SC) and batteries will be essential to the transition to net-zero emissions. However, these devices today use electrode materials comprising mined minerals and other materials manufactured from petroleum or coal products, both of which are non-sustainable approaches. One way of improving the sustainability of an EES device is to develop sustainable carbon electrodes. Carbon, the fourth most abundant element in nature, plays a unique and dominant role in ecosystems and the economy and is already an integral part of most EES devices. State-of-the-art preparation of carbon-based electrodes for SC relies on conventional slurry-based electrode fabrication that utilizes inactive materials such as current collectors, insulating binders, and conductive agents. Furthermore, this type of fabrication often requires multiple processing steps such as coating, drying, calendaring, and punching and also possesses limitations in the electrode geometries or dimensions, which restrict the overall performance of the devices. To lower the production costs, environmental impact, and use of inert materials, while improving the energy storage efficiency, this dissertation focused on fabricating 3D structured, free-standing, sustainable electrodes from renewable resources such as biomass precursors. Green and naturally abundant polysaccharide-based biopolymers were used as the substrate or skeleton to develop 3D structured free-standing biomass-derived carbon aerogel (BCA) energy storage materials. The main goal of the dissertation was to fabricate advanced, free-standing, 3D structured BCA electrode architectures with low tortuosity and tailored macro-, meso- and microstructure using single or multiple materials by utilizing the versatility and ability of 3D printing to control the geometry in all three dimensions. For this, three different fabrication strategies involving 3D printing for patterning the BCA were developed. Furthermore, a novel strategy for mineralization of hydrogels was proposed and optimized, allowing to significantly enhance the micro-, meso- and nanoporosity of the BCA electrodes. Efforts were also directed towards understanding the structure-property relationship, including the interfacial molecular structure, morphology, chemical composition, surface area, porosity, and pore-size distribution of the as-developed, multi-scale architectured, free-standing BCAs in comparison with state-of-the-art slurry-based electrodes. Electrochemical experiments revealed that the free-standing, BCA-based electrodes reported in this dissertation delivered an outstanding specific capacitance (322 F g–1 (Paper II), 547.7 F g_carbonizedbiomass-1 (Paper III), 2819.7 F g_carbonizedbiomass –1 (Paper IV) and 331 F g–1 (Paper V)) in comparison with those of other free-standing BCA (285 F g–1) and most powder-based activated carbons (usually < 250 F g–1). Furthermore, all the electrodes exhibited an outstanding rate capability and extremely high cyclic stability with high capacitance retention (>100%), confirming their superior energy storage performance compared with commercially available activated carbons and biomass-derived analogues fabricated using slurry-based techniques.Architecting the geometry of porous BCA electrodes at multiple length scales using 3D printing not only substantially reduced the number of steps associated with conventional electrode fabrication but also improved the electrochemical performance owing to the enhanced surface area within the same footprint. Furthermore, it can eliminate the requirement of additional high-weight inactive materials (binders and conductive agents) and high-cost current collectors, thus making the fabrication cost-effective and less energy-consuming. The multi-scale approach of designing biomass-derived, 3D structured, free-standing carbon electrodes reported in this dissertation may open up for substantial performance-enhancing capabilities for various EES devices such as SC, batteries, flow batteries, and fuel cells, paving the way for truly sustainable energy storage
Examining fish movement in terms of advection or diffusion: a case study of northeastern Atlantic cod
No full textAdvection (directional movement) and diffusion (dispersed movement) were applied for the first time to describe movement patterns in Atlantic cod in the North Sea and Baltic Sea between 1955 and 2020. The advection-diffusion approach provided more detailed estimates of movement that corresponded to previously observed patterns using different analytical techniques. Spatial patterns were evident with greater movement distances in cod from the North Sea and eastern Baltic Sea compared to the western Baltic and Kattegat-Skagerrak. Furthermore, comparative case studies on different ecotypes in the western and eastern Baltic suggested that inshore cod were more resident compared to offshore cod. This preliminary study highlights the usefulness of the advection-diffusion method to describe movements in fish populations, and can be further expanded by incorporating information on environment and mortality and providing information to spatially explicit population models
In-situ studies of CO<sub>2</sub> hydrogenation catalysts
No full textThis thesis summarizes and discusses the work conducted throughout this Ph.D. project and consist of a total of eight chapters followed by ten appendices containing relevant information and graphs that did not find suitable for the main manuscript, such as programs and testing of associated, however, less relevant materials.This thesis opens with a general introduction to catalysis and the terms and topics within. Hereafter is general terms and associated classification of activity and deactivation presented, followed by a talk in about how to design and create a new catalyst and the various levels at which research is taking place. Hereafter a brief discussion regarding CO2 utilization and how it can play a role in and aid in facilitating the green transition. Lastly, suggested mechanistic pathways of CO2 hydrogenation from the literature is presented.Hereafter the importance of catalytic testing is discussed. The whole design process of a new set-up is laid out and discussed. This discussion is accompanied with the design phase and processing of a catalytic reactor used extensively throughout this thesis.Hereafter is the theory behind all the analytic techniques used throughout the dissertation explained and the principles behind is briefly discussed. These techniques include X-ray powder diffraction, nitrogen physisorption, chemisorption, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy.Hereafter there is an in-depth explanation regarding the Fourier transform infrared spectroscopy (FTIR) and the functional principles with a Michelson interferometer and interferograms. Followed by a presentation of an experimental method called modulation excitation phase sensitive detection (ME-PSD) performed with a diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) apparatus. Hereafter is the application procedure and effects shown by an exemplified study of ZrO2. Hereafter is the DRIFTS technique called steady-state isotopic transient kinetic analysis (SSITKA) explained and discussed. This is all followed up by a discussion of the set-up and the programming and control hereof.The first case study regarded the synthesis of cheap and durable nano MgO support that supported Ni and Ru. In this chapter it is shown that, by the simple precipitation of MgC2O4 and calcination to obtain MgO. When impregnating with Ni or Ru, it is shown that the catalysts is capable perform excellent in methanation of CO2 and is comparable with top-of-the-shelf reported literature results.In the second study case a stereotypical Ni/Al2O3 catalyst is studied, and how different calcination and reduction temperatures affects the acidity, selectivity, and stability. It is shown that there is a significant difference, and this is caused by the metal-support interactions and reactions, herein differentiation of nanoparticles and their size and a hard-to-reduce Ni-Al2O3 spinel phase. It is furthermore shown that the activity and selectivity of the catalysts undergoes the same reaction mechanism, and the optimal Ni-particle size is between 5-10 nm.In the third study case, a prolonged investigation in the dynamic and novel Mn-based heterogenous catalysts as the active metal for CO2 hydrogenation. In this work, a broad range of Mn prepared on the most common metal oxide supports have been evaluated for catalytic activity. In this, it has been shown that Mn supported on ZrO2, MgO, and MgAl2O4 does all work very well in the reverse water gas shift reaction. These three catalysts were furthermore promoted with different alkali metals (Li, Na, K, Cs, and Rb). Mn/ZrO2 did show a high activity and selectivity by itself, however, when promoted with alkali metals it had a remarkably high increase in terms of activity. Therefore, it was selected to perform an in-depth analysis of Mn/ZrO2. An in-situ XRD study of the catalyst did show, that the Mn did occupy an oxidation state of 2+ at catalytic relevant conditions, however, as Mn was well dispersed only around 1/3 of the Mn-loading were XRD active. Lastly, there was a comprehensive DRIFTS study that showed, that the Mn/ZrO2 catalyst does undergo the carbonate mechanism, and when promoted with K, there is a parallel reaction. This parallel reaction is the so-called carbonate catalyzed reaction mechanism and does explain the increase in activity.Lastly, the dissertation finishes with a summary and perspectives of future endeavors
Metagenomic insights into phenanthrene biodegradation in electrical field governed biofilms for groundwater bioremediation
No full textElectrical fields (EFs)-assisted in-situ bioremediation of petroleum-contaminated groundwater, such as polycyclic aromatic hydrocarbons, has drawn increasing attention. However, the long-term stability, the EFs influence, and metabolic pathways are still poorly understood, hindering the further development of robust technology design. Herein, a series of EFs was applied to the phenanthrene-contaminated groundwater, and the corresponding system performance was investigated. The highest removal capacity of phenanthrene (phe) (7.63 g/(m3·d)) was achieved with EF_0.8 V biofilm at a hydrolytic retention time of 0.5 d. All the biofilms with four EFs exhibited a high removal efficiency of phe over 80% during a 100-d continuous-flow operation. Intermediates analysis revealed the main pathways of phe degradation: phthalate and salicylate via hydroxylation, methylation, carboxylation, and ring cleavage steps. Synergistic effects between phe-degraders (Dechloromonas), fermentative bacteria (Delftia), and electroactive microorganisms (Geobacter) were the main contributors to the complete phe mineralization. Genes encoding various proteins of methyl-accepting (mcp), response regulator (cheABDRY), and type IV pilus (pilABCMQV) were dominant, revealing the importance of cell motility and extracellular electron transfer. Metagenomics analysis unveiled phe-degrading genes, including ring reduction enzymes (bamBCDE), carboxylase of aromatics (ubiD), and methyltransferase protein (ubiE, pcm). These findings offered a molecular understanding of refractory organics’ decompositions in EFs-governed biotechnology