Gate-Tunable Superconductivity

The work presented in this thesis was performed in the alternative qubits group at IBM Research Europe - Zurich. The results of three projects are presented in the following. In chapter 2 we review important concepts which are fundamental for understanding the subsequent results. Our discussion ranges from BCS theory and quasiparticle disequilibrium in superconductors to hybrid superconductor-semiconductor interfaces, templated semiconductor epitaxy and the Aharonov-Bohm effect. Chapter 3 introduces the various fabrication methods used in this work, with special focus on patterning of superconducting nanowires, indium arsenide (InAs) epitaxy in hybrid templates, and device fabrication on selective-area-grown lead telluride (PbTe) structures. In chapter 4 we investigate gated metallic superconducting nanowire switches. We explain the mechanism for triggering the transition from the superconducting to the normal state, an effect that was controversially discussed in literature and could find use in superconducting signal routers and multiplexers in the near future. Chapter 5 presents a novel method for semiconductor-superconductor hybrid device fabrication which relies on InAs epitaxy inside superconducting, CMOS compatible templates. After further optimization, this method might enable the monolithic integration of classical cryogenic CMOS control electronics into scalable quantum processors. In chapter 6 we present the first transport experiments on selective-area-grown lead telluride (PbTe) structures on InP. High electron mobility and phase coherence length, together with extreme material properties, make PbTe a promising building block for topological qubits. In chapter 7 we summarize our findings and propose future directions for all three projects

From Pinocytosis to Methuosis—Fluid Consumption as a Risk Factor for Cell Death

The volumes of a cell [cell volume (CV)] and its organelles are adjusted by osmoregulatory processes. During pinocytosis, extracellular fluid volume equivalent to its CV is incorporated within an hour and membrane area equivalent to the cell’s surface within 30 min. Since neither fluid uptake nor membrane consumption leads to swelling or shrinkage, cells must be equipped with potent volume regulatory mechanisms. Normally, cells respond to outwardly or inwardly directed osmotic gradients by a volume decrease and increase, respectively, i.e., they shrink or swell but then try to recover their CV. However, when a cell death (CD) pathway is triggered, CV persistently decreases in isotonic conditions in apoptosis and it increases in necrosis. One type of CD associated with cell swelling is due to a dysfunctional pinocytosis. Methuosis, a non-apoptotic CD phenotype, occurs when cells accumulate too much fluid by macropinocytosis. In contrast to functional pinocytosis, in methuosis, macropinosomes neither recycle nor fuse with lysosomes but with each other to form giant vacuoles, which finally cause rupture of the plasma membrane (PM). Understanding methuosis longs for the understanding of the ionic mechanisms of cell volume regulation (CVR) and vesicular volume regulation (VVR). In nascent macropinosomes, ion channels and transporters are derived from the PM. Along trafficking from the PM to the perinuclear area, the equipment of channels and transporters of the vesicle membrane changes by retrieval, addition, and recycling from and back to the PM, causing profound changes in vesicular ion concentrations, acidification, and—most importantly—shrinkage of the macropinosome, which is indispensable for its proper targeting and cargo processing. In this review, we discuss ion and water transport mechanisms with respect to CVR and VVR and with special emphasis on pinocytosis and methuosis. We describe various aspects of the complex mutual interplay between extracellular and intracellular ions and ion gradients, the PM and vesicular membrane, phosphoinositides, monomeric G proteins and their targets, as well as the submembranous cytoskeleton. Our aim is to highlight important cellular mechanisms, components, and processes that may lead to methuotic CD upon their derangement

The use of embolic signal detection in multicenter trials to evaluate antiplatelet efficacy: signal analysis and quality control mechanisms in the CARESS (Clopidogrel and Aspirin for Reduction of Emboli in Symptomatic carotid Stenosis) trial

<p><b>Background and Purpose:</b> The CARESS (Clopidogrel and Aspirin for Reduction of Emboli in Symptomatic carotid Stenosis) trial proved the effectiveness of the combination of clopidogrel and aspirin compared with aspirin alone in reducing presence and number of microembolic signals (MES) in patients with recently symptomatic carotid stenosis. The present study aimed at installing primary and secondary quality control measures in CARESS because MES evaluation relies on subjective judgment by human experts.</p> <p><b>Methods:</b> As primary quality control, centers participating in CARESS evaluated a reference digital audio tape (DAT) before the study containing both MES and artifacts. Interobserver agreement of classifying signals as MES was expressed as proportions of specific agreement of positive ratings (ps±values). For all DATs included in CARESS (n=300), online number of MES and off-line number of MES read by the central reader were compared using correlation coefficients. As secondary control, a sample of 16 of 300 DATs was cross-validated by another independent reader (post-trial validator).</p> <p><b>Results:</b> For the reference tape, the cumulative ps±value was 0.894 based on 12 of 14 observers. Two observers with very different results improved after a training procedure. Agreement between post-trial validator and central reader was ps+=0.805, indicating very good agreement. Correlation between online evaluation and off-line evaluation of DATs was very good overall (cumulative ρ=0.84; P<0.001).</p> <p><b>Conclusion:</b> Multicenter studies using MES as outcome parameter are feasible. However, primary and secondary quality control procedures are important.</p&gt

Coupled CFD-CSM Analyses of a Highly Flexible Transport Aircraft by Means of Geometrically Nonlinear Methods

The ever lasting race towards increased efficiency in the aircraft industry has resulted in excessively slender and lightweight airframes. Utilising the anisotropic characteristics of specifically tailored composites is one key driver, enabling structural concepts which were impossible a few decades ago. The results are highly flexible aircraft structures, pushing geometrically linear methods to their limits. One example of such a concept is the Boeing 787 which reaches wing tip displacements of approximately 10 % of the wing half span already during cruise flight. Thus, loads and flight dynamics analyses have to be developed which are accurate in the context of large deflections. By utilising a coupled CFD-CSM analysis in combination with a highly flexible long range jet transport model, this paper aims to establish the groundwork for a high fidelity geometrically nonlinear loads framework. In this publication, a general methodology to compute static manoeuvre cases with deflections of up to 25 % is presented. Furthermore, by computing rigid and elastic polars as well as calculating pull up and push down manoeuvres, the differences between geometrically linear and nonlinear simulations are illustrated with respect to aerodynamic parameters, cut loads, and strains

Cell Swelling Stimulates Cytosol to Membrane Transposition of ICln

ICln is a multifunctional protein that is essential for cell volume regulation. It can be found in the cytosol and is associated with the cell membrane. Besides its role in the splicing process, ICln is critically involved in the generation of ion currents activated during regulatory volume decrease after cell swelling (RVDC). If reconstituted in artificial bilayers, ICln can form ion channels with biophysical properties related to RVDC. We investigated (i) the cytosol versus cell membrane distribution of ICln in rat kidney tubules, NIH 3T3 fibroblasts, Madin-Darby canine kidney (MDCK) cells, and LLC-PK1 epithelial cells, (ii) fluorescence resonance energy transfer (FRET) in living fibroblasts between fluorescently tagged ICln and fluorochromes in the cell membrane, and (iii) possible functional consequences of an enhanced ICln presence at the cell membrane. We demonstrate that ICln distribution in rat kidneys depends on the parenchymal localization and functional state of the tubules and that cell swelling causes ICln redistribution from the cytosol to the cell membrane in NIH 3T3 fibroblasts and LLC-PK1 cells. The addition of purified ICln protein to the extracellular solution or overexpression of farnesylated ICln leads to an increased anion permeability in NIH 3T3 fibroblasts. The swelling-induced redistribution of ICln correlates to altered kinetics of RVDC in NIH 3T3 fibroblasts, LLC-PK1 cells, and MDCK cells. In these cells, RVDC develops more rapidly, and in MDCK cells the rate of swelling-induced depolarization is accelerated if cells are swollen for a second time. This coincides with an enhanced ICln association with the cell membrane