2,969 research outputs found

    Development of visible-light-driven photocatalysts for the degradation of organic pollutants and the disinfection of microorganisms

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    In this research, several visible-light driven photocatalysts were developed and their photocatalytic activities were evaluated in the removal of organic pollutants. Wastewater containing pathogen carriers such as total coliforms, and E. coli was tested for disinfection using the synthesized visible-light photocatalysts. Graphitic carbon nitride (GCN or g-C3N4), a visible-light driven photocatalyst, was synthesized from different precursors. Also, different composites of GCN such GCN/Ag2CrO4, and GCN/ZnO-Cu were synthesized. The purpose of these GCN composites is to enhance the photocatalytic activity of the GCN. Several characterization techniques were used to understand the physicochemical properties of the photocatalysts. The initial photocatalytic experiments, detailed in Chapter 3, were on degrading 4-CP under a royal blue LED (450 nm) using precursor-derived GCNs and GCN composites. The results show that the GCN/0.3Ag2CrO4 performed well with over 95% degradation of 4-CP. The second set of photocatalytic experiments, detailed in Chapter 4, were on investigating the degradation of 2,4-D and MCPP, BSA protein, SARS-CoV-2 (Covid-19) spike protein, cATP, and total coliforms/E. coli using the best performing GCN/0.3Ag2CrO4 in the first photocatalytic experiments and royal blue LED. Over 85% of 2,4-D and MCPP were simultaneously degraded, 77.5% of Covid-19 spike protein was achieved, and over one log reduction of cATP, total coliforms/E. coli was achieved in wastewater treatment. In Chapter 5 (third set of experiments), new sets of photocatalysts were synthesized. GCN/0.1ZnO-Cu3% performed best with over 65% of 4-CP degradation under royal blue LED. A complete 5.5 log reduction of coliforms-containing wastewater primary influent was achieved with the same photocatalyst. In Chapter 6, the best-performing GCN/ZnO-Cu nanocomposite in observed in chapter 5 was coated on a polyvinyl chloride (PVC) substrate and the performance was evaluated under a 5000K LED (400 – 700 nm). The result shows a 2-log reduction of the coliform-containing wastewater treatment on the self-disinfecting coated surface. To the best of our knowledge, this is the first research to investigate the comprehensive use and practical application of self-disinfecting coated surfaces under commercial and industrial light (5000K LED) irradiation. All our results demonstrate that compositing GCN with metals can degrade pollutants and disinfect wastewater under visible light irradiation

    New Porous Nanomaterials For Battery and Supercapacitor

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    Lithium-Sulfur batteries have a high energy storage capacity while their sulfur cathode suffers large volume change, polysulfides dissolution and shuttle effect, and capacity fading during long-term cycling. To help lock sulfur and mitigate these problems, we introduced halloysite, a natural clay material with a nanotube format, to disperse and confine sulfur nanoparticles as well as to suppress the dissolution and migration of polysulfides. Halloysite was made conductive by covering it with a glucose-derived carbon skin. Sulfur nanoparticles were then trapped in both the lumen and outside surface of individual nanotubes with a loading dosage up to 80 %. In this new halloysite/sulfur composites cathode, the hollow nanostructure of halloysite provides space to allow dimension changes of encapsulated sulfur nanoparticles during repeated lithiation while limiting their size up to the diameter of nanotube lumen (i.e., 25 nm or less). The stacked halloysite clusters further create many nanoscale voids to divide the sulfur-electrolyte interface into isolated domains and increase the migration tortuosity in electrolytes to suppress the dissolution and shuttle effect of polysulfides. These features together contribute to improved cycling stability, retaining nearly ~84% of the starting capacity over 250 cycles, though the diffusion of lithium ions going in and out of nanotubes show some differences. In project 2, we worked on the anode development for LIBs. Silicon-rich (e.g., \u3e30 wt.%) anodes are desired to leverage the current capacity of lithium-ion batteries (LIBs) towards commercial cell performance requirements in critical markets, such as the transportation sector. A new type of nanofiber-in-microfiber silicon/carbon composite electrode was prepared and tested as a potential silicon-rich anode candidate. A co-axial electrospinning setup was used to produce a unique hybrid composite fiber configuration, in which silicon nanoparticles were suspended in a polymer solution to serve as the middle stream while the sheath stream was comprised of another polymer solution. Polyvinyl alcohol (PVA) was chosen as the silicon dispersion fluid because of its limited viscosity increase even at a very high solid allowance, which after carbonization held those nanoparticles together as short, branched nanofibers. Polyacrylonitrile (PAN) sheath fluid helped wrap the formed short, silicon-rich nanofiber bundles to form a nonwoven, ductile microfiber mat. After being carbonized into composite anodes, the silicon-rich nanofibers were used to host the majority of lithium ions while their thin carbon skin, originating from carbonized PVA, promotes conductivity and charge transfer. The nanofibrous morphology and the mesoscale space in between help accommodate the notorious volume expansion issues in silicon anodes during lithiation/delithiation processes. The outside PAN-derived microfibers provide structural support for the encapsulated silicon-rich nanofibers and simultaneously serve as the three-dimensional current collector. The new composite anodes were confirmed on their unique fibrous configuration and improved electrochemical performance. With 40 wt% Si, such silicon-rich, nanofiber-in-microfiber anodes achieve ~900 mAhg-1 reversible capacity and ~90% capacity retention over 250 cycles by effectively balancing challenges on silicon-rich fibrous anode and electrode pulverization. Beside battery research, we also worked on supercapacitors with high power density in project 3. Despite the great benefits plastics have brought to our modern lives, a large volume of plastic wastes increasingly threatens our environment and human health. Through a hydrothermal carbonization and crystallization process involving nitric acid and ethanol, drinking bottles made of polyethylene terephthalate were successfully converted into carbon quantum dots (CQDs) and thin carbon sheets simultaneously, with the former well dispersed and intercalated in the latter as a ball-sheet carbon structure (BSCs). The formed unique, connected, and conductive carbon network allows rapid transport of ions and electrons besides their large surface area and numerous ion hosting sites. The electrodes made of such a plastic ball-sheet carbon structure (PBSCs) therefore exhibit pseudocapacitance behavior with the specific capacity reaching 237 F/g at the charge rate of 1 A/g. Superior cycling stability on the energy storage was also found. Our method offers a new avenue to upcycle some plastic wastes as valuable energy storage systems, to help boost the recycling of plastic waste, and move forwards to the sustainable deployment of various clean energy resources

    Accurate quantum transport modelling and epitaxial structure design of high-speed and high-power In0.53Ga0.47As/AlAs double-barrier resonant tunnelling diodes for 300-GHz oscillator sources

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    Terahertz (THz) wave technology is envisioned as an appealing and conceivable solution in the context of several potential high-impact applications, including sixth generation (6G) and beyond consumer-oriented ultra-broadband multi-gigabit wireless data-links, as well as highresolution imaging, radar, and spectroscopy apparatuses employable in biomedicine, industrial processes, security/defence, and material science. Despite the technological challenges posed by the THz gap, recent scientific advancements suggest the practical viability of THz systems. However, the development of transmitters (Tx) and receivers (Rx) based on compact semiconductor devices operating at THz frequencies is urgently demanded to meet the performance requirements calling from emerging THz applications. Although several are the promising candidates, including high-speed III-V transistors and photo-diodes, resonant tunnelling diode (RTD) technology offers a compact and high performance option in many practical scenarios. However, the main weakness of the technology is currently represented by the low output power capability of RTD THz Tx, which is mainly caused by the underdeveloped and non-optimal device, as well as circuit, design implementation approaches. Indeed, indium phosphide (InP) RTD devices can nowadays deliver only up to around 1 mW of radio-frequency (RF) power at around 300 GHz. In the context of THz wireless data-links, this severely impacts the Tx performance, limiting communication distance and data transfer capabilities which, at the current time, are of the order of few tens of gigabit per second below around 1 m. However, recent research studies suggest that several milliwatt of output power are required to achieve bit-rate capabilities of several tens of gigabits per second and beyond, and to reach several metres of communication distance in common operating conditions. Currently, the shortterm target is set to 5−10 mW of output power at around 300 GHz carrier waves, which would allow bit-rates in excess of 100 Gb/s, as well as wireless communications well above 5 m distance, in first-stage short-range scenarios. In order to reach it, maximisation of the RTD highfrequency RF power capability is of utmost importance. Despite that, reliable epitaxial structure design approaches, as well as accurate physical-based numerical simulation tools, aimed at RF power maximisation in the 300 GHz-band are lacking at the current time. This work aims at proposing practical solutions to address the aforementioned issues. First, a physical-based simulation methodology was developed to accurately and reliably simulate the static current-voltage (IV ) characteristic of indium gallium arsenide/aluminium arsenide (In-GaAs/AlAs) double-barrier RTD devices. The approach relies on the non-equilibrium Green’s function (NEGF) formalism implemented in Silvaco Atlas technology computer-aided design (TCAD) simulation package, requires low computational budget, and allows to correctly model In0.53Ga0.47As/AlAs RTD devices, which are pseudomorphically-grown on lattice-matched to InP substrates, and are commonly employed in oscillators working at around 300 GHz. By selecting the appropriate physical models, and by retrieving the correct materials parameters, together with a suitable discretisation of the associated heterostructure spatial domain through finite-elements, it is shown, by comparing simulation data with experimental results, that the developed numerical approach can reliably compute several quantities of interest that characterise the DC IV curve negative differential resistance (NDR) region, including peak current, peak voltage, and voltage swing, all of which are key parameters in RTD oscillator design. The demonstrated simulation approach was then used to study the impact of epitaxial structure design parameters, including those characterising the double-barrier quantum well, as well as emitter and collector regions, on the electrical properties of the RTD device. In particular, a comprehensive simulation analysis was conducted, and the retrieved output trends discussed based on the heterostructure band diagram, transmission coefficient energy spectrum, charge distribution, and DC current-density voltage (JV) curve. General design guidelines aimed at enhancing the RTD device maximum RF power gain capability are then deduced and discussed. To validate the proposed epitaxial design approach, an In0.53Ga0.47As/AlAs double-barrier RTD epitaxial structure providing several milliwatt of RF power was designed by employing the developed simulation methodology, and experimentally-investigated through the microfabrication of RTD devices and subsequent high-frequency characterisation up to 110 GHz. The analysis, which included fabrication optimisation, reveals an expected RF power performance of up to around 5 mW and 10 mW at 300 GHz for 25 μm2 and 49 μm2-large RTD devices, respectively, which is up to five times higher compared to the current state-of-the-art. Finally, in order to prove the practical employability of the proposed RTDs in oscillator circuits realised employing low-cost photo-lithography, both coplanar waveguide and microstrip inductive stubs are designed through a full three-dimensional electromagnetic simulation analysis. In summary, this work makes and important contribution to the rapidly evolving field of THz RTD technology, and demonstrates the practical feasibility of 300-GHz high-power RTD devices realisation, which will underpin the future development of Tx systems capable of the power levels required in the forthcoming THz applications

    Beam scanning by liquid-crystal biasing in a modified SIW structure

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    A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

    Rational development of stabilized cyclic disulfide redox probes and bioreductive prodrugs to target dithiol oxidoreductases

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    Countless biological processes allow cells to develop, survive, and proliferate. Among these, tightly balanced regulatory enzymatic pathways that can respond rapidly to external impacts maintain dynamic physiological homeostasis. More specifically, redox homeostasis broadly affects cellular metabolism and proliferation, with major contributions by thiol/disulfide oxidoreductase systems, in particular, the Thioredoxin Reductase Thioredoxin (TrxR/Trx) and the Glutathione Reductase-Glutathione-Glutaredoxin (GR/GSH/Grx) systems. These cascades drive vital cellular functions in many ways through signaling, regulating other proteins' activity by redox switches, and by stoichiometric reductant transfers in metabolism and antioxidant systems. Increasing evidence argues that there is a persistent alteration of the redox environment in certain pathological states, such as cancer, that heavily involve the Trx system: upregulation and/or overactivity of the Trx system may support or drive cancer progression, making both TrxR and Trx promising targets for anti-cancer drug development. Understanding the biochemical mechanisms and connections between certain redox cascades requires research tools that interact with them. The state-of-the-art genetic tools are mostly ratiometric reporters that measure reduced:oxidized ratios of selected redox pairs or the general thiol pool. However, the precise cellular roles of the central oxidoreductase systems, including TrxR and Trx, remain inaccessible due to the lack of probes to selectively measure turnover by either of these proteins. However, such probes would allow measuring their effective reductive activity apart from expression levels in native systems, including in cells, animals, or patient samples. They are also of high interest to identify chemical inhibitors for TrxR/Trx in cells and to validate their potential use as anti-cancer agents (to date, there is no selective cellular Trx inhibitor, and most known TrxR inhibitors were not comprehensively evaluated considering selectivity and potential off-targets). However, small molecule redox imaging tools are underdeveloped: their protein specificity, spectral properties, and applicability remain poorly precedented. This work aimed to address this opportunity gap and develop novel, small molecule diagnostic and therapeutic tools to selectively target the Trx system based on a modular trigger cargo design: artificial cyclic disulfide substrates (trigger) for oxidoreductases are tethered to molecular agents (cargo) such that the cargo’s activity is masked and is re-established only through reduction by a target protein. The rational design of these novel reduction sensors to target the cell's strongest disulfide-reducing enzymes was driven by the following principles: (i) cyclic disulfide triggers with stabilized ring systems were used to gain low reduction potentials that should resist reduction except by the strongest cellular reductases, such as Trx; and (ii) the cyclic topology also offers the potential for kinetic reversibility that should select for dithiol-type redox proteins over the cellular monothiol background. Creating imaging agents based on such two-component designs to selectively measure redox protein activity in native cells required to combine the correct trigger reducibility, probe activation kinetics, and imaging modalities and to consider the overall molecular architecture. The major prior art in this field has applied cyclic 5-membered disulfides (1,2 dithiolanes) as substrates for TrxR in a similar way to create such tools. However, this motif was described elsewhere as thermodynamically instable and was due to widely used for dynamic covalent cascade reactions. By comparing a novel 1,2 dithiolane-based probe to the state-of-the-art probes, including commercial TrxR sensors, by screening a conclusive assay panel of cellular TrxR modulations, I clarified that 1,2 dithiolanes are not selective substrates for TrxR in biological settings (Nat Commun 2022). Instead, aiming for more stable ring systems and thus more robust redox probes, during this work, I developed bicyclic 6 membered disulfides (piperidine fused 1,2 dithianes) with remarkably low reduction potentials. I showed that molecular probes using them as reduction sensors can be mostly processed by thioredoxins while being stable against reduction by GSH. The thermodynamically stabilized decalin like topology of the cis-annelated 1,2 dithianes requires particularly strong reductants to be cleaved. They also select for dithiol type redox proteins, like Trx, based on kinetic reversibility and offer fast cyclization due to the preorganization by annelation (JACS 2021). This work further expanded the system’s modularity with structural cores based on piperazine-fused 1,2 dithianes with the two amines allowing independent derivatization. Diagnostic tools using them as reduction sensors proved equally robust but with highly improved activation kinetics and were thus cellularly activated. Cellular studies evolved that they are substrates for both Trxs and their protein cousins Grxs, so measuring the cellular dithiol protein pool rather than solely Trx activity (preprint 2023). Finally, a trigger based on a slightly adapted reduction sensor, a desymmetrized 1,2 thiaselenane, was designed for selective reduction by TrxR’s selenol/thiol active site, then combined with a precipitating large Stokes’ shift fluorophore and a solubilizing group, to evolve the first selective probe RX1 to measure cellular TrxR activity, which even allowed high throughput inhibitor screening (Chem 2022). The central principle of this work was further advanced to therapeutic prodrugs based on the duocarmycin cargo (CBI) with tunable potency (JACS Au 2022) that can be used to create off-to-on therapeutic prodrugs. Such CBI prodrugs employing stabilized 1,2 dichalcogenide triggers proved to be cytotoxins that depend on Trx system activity in cells. They could further be exploited for cell-line dependent reductase activity profiling by screening their redox activation indices, the reduction-dependent part of total prodrug activation, in 177 cell lines. Beyond that, these prodrugs were well-tolerated in animals and showed anti-cancer efficacy in vivo in two distinct mouse tumor models (preprint 2022). Taken together, I introduced unique monothiol-resistant reducible motifs to target the cellular Trx system with chemocompatible units for each for TrxR and Trx/Grx, where the cyclic nature of the dichalcogenides avoids activation by GSH. By using them with distinct molecular cargos, I developed novel selective fluorescent reporter probes; and introduced a new class of bioreductive therapeutic constructs based on a common modular design. These were either applied to selectively measure cellular reductase activity or to deliver cytotoxic anti cancer agents in vivo. Ongoing work aims to differentiate between the two major redox effector proteins Trx and Grx, requiring additional layers of selectivity that may be addressed by tuned molecular recognition. The flexible use of various molecular cargos allows harnessing the same cellular redox machinery by either probes or prodrugs. This allows predictive conclusions from diagnostics to be directly translated into therapy and offers great potential for future adaptation to other enzyme classes and therapeutic venues.Die zelluläre Redox-Homöostase hängt von Thiol/Disulfid-Oxidoreduktasen ab, die den Stoffwechsel, die Proliferation und die antioxidative Antwort von Zellen beeinflussen. Die wichtigsten Netzwerke sind die Thioredoxin Reduktase-Thioredoxin (TrxR/Trx) und Glutathion Reduktase-Glutathion-Glutaredoxin (GR/GSH/Grx) Systeme, die über Redox-Schalter in Substratproteinen lebenswichtige zelluläre Funktionen steuern und so an der Redox-Regulation und -Signalübertragung beteiligt sind. Persistente Veränderungen des Redoxmilieus in pathologischen Zuständen, wie z. B. bei Krebs, sind in hohem Maße mit dem Trx-System verbunden. Eine Hochregulierung und/oder Überaktivität des Trx-Systems, die bei vielen Krebsarten auftreten, unterstützt zudem das Fortschreiten des Krebswachstums, was TrxR/Trx zu vielversprechenden Zielproteinen für die Entwicklung neuer Krebsmedikamente macht. Um die biochemischen Prozesse dahinter zu erforschen, sind spezielle Techniken zur Visualisierung und Messung enzymatischer Aktivität nötig. Die hierzu geeigneten, meist genetischen Sensoren messen ratiometrisch das Verhältnis reduzierter/oxidierter Spezies in zellulärem Umfeld oder spezifisch ausgewählte Redoxpaare. Die weitere Erforschung der exakten Funktion von TrxR/Trx und deren Substrate ist jedoch durch mangelnde Nachweismethoden limitiert. Diese sind außerdem zur Validierung chemischer Hemmstoffe für TrxR/Trx in Zellen und deren potenziellen Verwendung als Krebsmittel von großem Interesse. Bislang gibt es keinen selektiven zellulären Trx-Inhibitor und potenzielle Off-Target-Effekte der bekannten TrxR-Inhibitoren wurden nicht abschließend bewertet. Ziel dieser Arbeit ist die Entwicklung niedermolekularer, diagnostischer und therapeutischer Werkzeuge, die selektiv auf das Trx-System abzielen und auf einem modularen Trigger-Cargo Design basieren. Hierzu werden zyklische Disulfid-Substrate (Trigger) für Oxidoreduktasen so mit molekularen Wirkstoffen (Cargo) verknüpft, dass dabei die Wirkstoffaktivität maskiert, und erst nach Reduktion durch ein Zielprotein wiederhergestellt wird. Diese neuartigen, synthetischen Reduktionssensoren basieren auf den folgenden Grundprinzipien: (i) Zyklische Disulfide sind thermodynamisch stabilisiert und können nur durch die stärksten Reduktasen gespalten werden; und (ii) die zyklische Topologie ermöglicht die kinetische Reversibilität der zwei Thiol-Disulfid-Austauschreaktionen, die eine erste Reaktion mit Monothiolen, wie z. B. GSH, sofort umkehrt und so eine vollständige Reduktion verhindert. Die meisten früheren Arbeiten auf diesem Gebiet verwendeten ein zyklisches, fünfgliedriges Disulfid (1,2 Dithiolan) als Substrat für TrxR. Das gleiche Strukturmotiv wurde jedoch an anderer Stelle als thermodynamisch instabil beschrieben und aufgrund dieser Eigenschaft explizit für dynamische Kaskadenreaktionen verwendet. Deshalb vergleicht diese Arbeit zu Beginn einen neuen 1,2 Dithiolan basierten fluorogenen Indikator mit bestehenden, z. T. kommerziellen, Redox Sonden für TrxR in einer Reihe von Zellkultur-Experimenten unter Modulation der zellulären TrxR Aktivität und stellt so einen Widerspruch in der Literatur klar: 1,2 Dithiolane eignen sich nicht als selektive Substrate für TrxR, da sie labil sowohl gegen die Reduktion durch andere Redoxproteine, als auch gegen den Monothiol Hintergrund in Zellen sind (Nat. Commun. 2022). Als alternatives Strukturmotiv wird in dieser Arbeit ein bizyklisches sechsgliedriges Disulfid (anneliertes 1,2 Dithian) etabliert. Durch sein niedriges Reduktionspotenzial, also seine hohe Resistenz gegen Reduktion, werden molekulare Sonden basierend auf diesem 1,2 Dithian als Reduktionssensor fast ausschließlich von Trx aktiviert, nicht aber von TrxR oder GSH (JACS 2021). Dieses Kernmotiv bestimmt dabei die Reduzierbarkeit, und damit die Enzymspezifität, durch seine zyklische Natur und die Annelierung, auch unter Verwendung unterschiedlicher Farb-/Wirkstoffe. Auf dieser Grundlage konnte die molekulare Struktur durch einen weiteren Modifikationspunkt für die flexible Verwendung weiterer funktioneller Einheiten ergänzt werden. Obwohl zelluläre Studien ergaben, dass diese neuartigen 1,2 Dithian Einheiten in Zellen sowohl Trx als auch das strukturell verwandte Grx adressieren, sind die daraus resultierenden diagnostischen Moleküle wertvoll, um den katalytischen Umsatz zellulärer Dithiol-Reduktasen, der sogenannten Trx Superfamilie, selektiv anzuzeigen (Preprint 2023). Begünstigt durch das modulare Moleküldesign stellt diese Arbeit zudem das erste Reportersystem RX1 zum selektiven Nachweis der TrxR-Aktivität in Zellen vor. Es basiert auf der Verwendung eines zyklischen, unsymmetrischen Selenenylsulfid-Sensors (1,2 Thiaselenan), der selektiv von dem einzigartigen Selenolat der TrxR angegriffen wird, und dadurch letztlich nur von TrxR reduziert werden kann. RX1 eignete sich zudem für eine Hochdurchsatz-Validierung bestehender TrxR Inhibitoren und unterstreicht dadurch den kommerziellen Nutzen derartiger Diagnostika (Chem 2022). Das zentrale Trigger-Cargo Konzept dieser Arbeit wurde für therapeutische Zwecke weiterentwickelt und nutzt dabei den einzigartigen Wirkmechanismus der Duocarmycin-Naturstoffklasse (CBI) (JACS Au 2022) zur Entwicklung reduktiv aktivierbarer Therapeutika. CBI Prodrugs basierend auf stabilisierten Redox-Schaltern (1,2 Dithiane für Trx; 1,2 Thiaselenan für TrxR) reagierten signifikant auf TrxR-Modulation in Zellen. Sie wurden darüber hinaus durch das Referenzieren ihrer Aktivität gegenüber nicht-reduzierbaren Kontrollmoleküle für die Erstellung zelllinienabhängiger Profile der Reduktaseaktivität in 177 Zelllinien genutzt. Schließlich waren diese neuen Krebsmittel im Tiermodell gut verträglich und zeigten in zwei verschiedenen Mausmodellen eine krebshemmende Wirkung (Preprint 2022b). Zusammenfassend präsentiert diese Dissertation monothiol-resistente reduzierbare Trigger-Einheiten für das zelluläre Trx-System zur Entwicklung neuartiger, selektiver Reporter-Sonden, sowie eine neue Klasse reduktiv aktivierbarer Krebsmittel auf Basis eines adaptierbaren Trigger-Cargo Designs. Diese fanden entweder zur selektiven Messung zellulärer Proteinaktivität oder zum Einsatz als Antikrebsmittel Verwendung. Es wurden chemokompatible Motive sowohl für TrxR als auch für Trx/Grx identifiziert, wobei deren zyklische Natur eine Aktivierung durch GSH verhindert. Eine weitere Differenzierung zwischen den beiden Redox-Proteinen Trx und Grx und anderen Proteinen der Trx-Superfamilie erfordert eine zusätzliche Ebene der Selektierung, z. B. durch molekulare Erkennung, und ist Gegenstand laufender Arbeiten. Die flexible Verwendung verschiedener molekularer Wirkstoffe ermöglicht dabei die „Pipeline-Entwicklung“ von Diagnostika und Therapeutika, die von der zellulären Redox-Maschinerie analog umgesetzt werden, und dadurch Schlussfolgerungen aus der Diagnostik direkt auf eine Therapie übertragbar machen. Dies birgt großes Potenzial für künftige Entwicklungen bei einer potenziellen Übertragung des modularen Konzepts auf andere Enzymklassen und therapeutische Einsatzgebiete

    Analog Photonics Computing for Information Processing, Inference and Optimisation

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    This review presents an overview of the current state-of-the-art in photonics computing, which leverages photons, photons coupled with matter, and optics-related technologies for effective and efficient computational purposes. It covers the history and development of photonics computing and modern analogue computing platforms and architectures, focusing on optimization tasks and neural network implementations. The authors examine special-purpose optimizers, mathematical descriptions of photonics optimizers, and their various interconnections. Disparate applications are discussed, including direct encoding, logistics, finance, phase retrieval, machine learning, neural networks, probabilistic graphical models, and image processing, among many others. The main directions of technological advancement and associated challenges in photonics computing are explored, along with an assessment of its efficiency. Finally, the paper discusses prospects and the field of optical quantum computing, providing insights into the potential applications of this technology.Comment: Invited submission by Journal of Advanced Quantum Technologies; accepted version 5/06/202

    Reducción de la Decoherencia Cuántica en Fotónica Integrada

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    Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de Materiales. Fecha de Lectura: 24-03-2023La fotónica cuántica integrada es un elemento indispensable para para la miniaturización, estabilización y escalabilidad de las tecnologías cuánticas. El desarrollo de circuitos fotónicos integrados para aplicación en tecnologías cuánticas ayudará a traspasar el cuello de botella hacia niveles superiores de disponibilidad tecnológica y comercialización. La decoherencia cuántica supone uno de los retos técnicos a nivel fundamental con mayor relevancia para la realización de este desarrollo. En este contexto, el objetivo de este proyecto ha sido el de proporcionar herramientas teóricas para orientar la conceptualización y el diseño de los bloques fundamentales de los circuitos cuánticos integrados con vistas a la reducción de la decoherencia cuántica en estos sistemas. Los resultados obtenidos en forma de modelos teóricos, métodos numéricos de simulación y esquemas de optimización facilitan estas herramientas a través una serie de nuevos instrumentos matemáticos que sirven tanto para la caracterización de la decoherencia en diferentes componentes como para guías de diseño para su reducción: Expresiones analíticas que relacionan directamente los parámetros de diseño de estructuras fotónicas con el grado de decoherencia de la plataforma; Modelos para la simulación numérica de emisores cuánticos integrados en estructuras fotónicas que conectan la variación de los parámetros del diseño con el impacto en las figuras de mérito que caracterizan la decoherencia; Esquemas de optimización basados en métodos de Machine Learning para estructuras de fotónica cuántica integrada que ofrecen una reducción sin precedentes en términos de consumo de recursos computacionales; Interpretaciones físicas de las soluciones de los modelos desarrollados que contribuyen al avance del conocimiento del comportamiento de componentes de circuito en diferentes condiciones. El aparato matemático desarrollado ha sido evaluado a través de su aplicación en diferentes casos prácticos validando su fiabilidad y demostrando resultados prometedores: Identificación de los valores de los parámetros de diseño necesarios para la maximización de la indistinguibilidad y la eficiencia de extracción en emisores cuánticos acoplados a guías de onda dependiendo de las características del emisor, estimando incrementos en la indistinguibilidad de hasta un 30% para diseños optimizados; Optimización del diseño de una cavidad óptica para integración en chip de emisores cuánticos que garantiza valores de indistinguibilidad y eficiencia de extracción cercanos a la unidad con emisores fuertemente disipativos a temperatura ambiente; Relajación de los requisitos técnicos generales para cavidades ópticas a partir de una nueva plataforma propuesta basada en la integración de clústeres de emisores cuánticos acoplados que garantiza indistinguibilidad perfecta con emisores fuertemente disipativos a temperatura ambiente para las configuraciones óptimas. Esperamos que los resultados obtenidos en esta disertación contribuyan al avance del conocimiento para el desarrollo de la fotónica cuántica integrada y sirvan de hoja de ruta para la realización de nuevas demostraciones experimentales que incrementen su impacto en el estado del arte de las tecnologías cuántica

    Topology, Correlation, and Information in Designer Quantum Systems

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    This thesis discusses the use of subgap and boundary modes for quantum engineering of novel phases, devices and response characteristics. It is comprised of four separate topics: quantum magnetism in Yu-Shiba-Rusinov chains, single-atom Josephson diodes, readout ofMajorana qubits, and surface photogalvanic response inWeyl semimetals. Chains of magnetic adatoms on superconductors have been discussed as promising systems for realizingMajorana end states. Here,we showthat dilute Yu-Shiba-Rusinov (YSR) chains are also a versatile platform for quantum magnetism and correlated electron dynamics, with widely adjustable spin values and couplings. Focusing on subgap excitations, we derive an extended t − J model for dilute quantum YSR chains and use it to study the phase diagram as well as tunneling spectra. We explore the implications of quantum magnetism for the formation of a topological superconducting phase, contrasting it to existing models assuming classical spin textures. Current-biased Josephson junctions exhibit hysteretic transitions between dissipative and superconducting states as characterized by switching and retrapping currents. Here, we develop a theory for diode-like effects in the switching and retrapping currents ofweakly-damped Josephson junctions. We find that while the diode-like behavior of switching currents is rooted in asymmetric current-phase relations, nonreciprocal retrapping currents originate in asymmetric quasiparticle currents. These different origins also imply distinctly different symmetry requirements. We illustrate our results by a microscopic model for junctions involving YSR subgap states. Our theory provides significant guidance in identifying the microscopic origin of nonreciprocities in Josephson junctions. Schemes for topological quantum computation withMajorana bound states rely heavily on the ability to measure products ofMajorana operators projectively. Here,weemployMarkovian quantum measurement theory, including the readout device, to analyze such measurements. Specifically, we focus on the readout of Majorana qubits via continuous charge sensing of a tunnel-coupled quantum dot by a quantum point contact. We show that projective measurements of Majorana products can be implemented by continuous charge sensing under quite general circumstances. Essential requirements are that a combined local parity ˆπ, involving the quantum dot charge along with the Majorana product of interest, be conserved, and that the two eigenspaces of the combined parity ˆπ generate distinguishable measurement signals. The photogalvanic effect requires the intrinsic symmetry of the medium to be sufficiently low, which strongly limits candidate materials for this effect.We explore how inWeyl semimetals the photogalvanic effect can be enabled and controlled by design of Fermi arc states at the material surface. Specifically, we provide a theory of ballistic photogalvanic current in a Weyl semimetal slab. We show that the confinement-induced response is tightly linked to the configuration of Fermi-arc surface states, thus inheriting the same directionality and sensitivity to boundary conditions. In principle this enables the control of the photogalvanic response through manipulation at the surface only

    Microscopy of spin hydrodynamics and cooperative light scattering in atomic Hubbard systems

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    Wechselwirkungen zwischen quantenmechanischen Teilchen können zu kollektiven Phänomenen führen, deren Eigenschaften sich vom Verhalten einzelner Teilchen stark unterscheiden. Während solche Quanteneffekte im Allgemeinen schwierig zu beobachten sind, haben sich ultrakalte, in optischen Gittern gefangene atomare Gase als vielseitige experimentelle Plattform zur Erforschung der Quantenvielteilchenphysik erwiesen. In dieser Arbeit setzten wir ein Gitterplatz- und Einzelatom-aufgelöstes Quantengasmikroskop für bosonische Rb-87 Atome ein, um Vielteilchensysteme im und außerhalb des Gleichgewichts zu untersuchen. Zunächst betrachteten wir den quantenmechanischen Phasenübergang zwischen dem suprafluiden und dem Mott-isolierenden Zustand im Bose-Hubbard-Modell, das nativ durch kalte Atome in optischen Gittern realisiert wird, und zeigten, dass sich die Brane-Parität eignet, um nichtlokale Ordnung im konventionell als ungeordnet erachteten zweidimensionalen Mott-Isolator zu identifizieren. Mithilfe eines mikroskopischen Ansatzes zur Realisierung einstellbarer Gittergeometrien und programmierbarer Einheitszellen implementierten wir Quadrats-, Dreiecks-, Kagome- und Lieb-Gitter und beobachteten die Skalierung des Phasenübergangspunkts mit der mittleren Koordinationszahl des Gitters. In einem eindimensionalen Gitter untersuchten wir zudem den Hochtemperatur-Spintransport im Heisenberg-Modell, das durch Superaustausch in der Mott-isolierenden Phase eines zwei-Spezies Bose-Hubbard-Modells realisiert wurde. Durch Betrachten der Relaxationsdynamik eines als Domänenwand präparierten Anfangszustandes fanden wir eine superdiffusive Raum-Zeit-Skalierung mit einem anomalen dynamischen Exponenten von 3/2. Anschließend untersuchten wir die theoretisch vorhergesagten mikroskopischen Voraussetzungen für Superdiffusion, indem wir reguläre Diffusion im nicht-integrablen, zweidimensionalen Heisenberg-Modell und ballistischen Transport für SU(2)-Symmetrie-gebrochene magnetisierte Anfangszustände nachwiesen. Weiterhin maßen wir die Zählstatistik der durch die Domänenwand transportierten Spins; die sich daraus ergebende schiefe Verteilung deutete auf einen nichtlinearen zugrundeliegenden Transportprozess hin, der an die dynamische Kardar-Parisi-Zhang Universalitätsklasse erinnert. Mittels Mott-Isolatoren im Limit tiefer Gitter konnten wir darüber hinaus die durch Photonen vermittelten Wechselwirkungen in einem Spinsystem untersuchen, das aus zwei über einen geschlossenen optischen Übergang gekoppelten Zuständen besteht. Durch spektroskopische Untersuchung der Reflexion und Transmission konnten wir die direkte Anregung einer subradianten Eigenmode und kohärente Spiegelung beobachten, was auf die Realisierung einer effizienten, im freien Raum operierenden, paraxialen Licht-Materie-Schnittstelle hindeutet.The interplay of quantum particles can give rise to collective phenomena whose characteristics are distinct from the behavior of individual particles. While quantum effects are generally challenging to observe, ultracold atomic gases trapped in optical lattices have emerged as a versatile experimental platform to study quantum many-body physics. In this thesis, we employed a site– and single-atom–resolved quantum gas microscope of bosonic Rb-87 atoms to explore many-body systems in and out of equilibrium. We first considered the ground-state quantum phase transition between the superfluid and Mott-insulating state in the Bose–Hubbard model, natively realized by cold atoms in optical lattices, for which we found brane parity to be suitable for detecting nonlocal order in the conventionally unordered two-dimensional Mott insulator. Using a microscopic approach to realizing tunable lattice geometries and programmable unit cells, we implemented square, triangular, kagome and Lieb lattices, and observed the mean-field scaling of the phase transition point with average coordination number. In a one-dimensional lattice, we furthermore studied high-temperature spin transport in the Heisenberg model, realized by superexchange in the Mott-insulating phase of a two-species Bose–Hubbard model. By tracking the relaxation dynamics of an initial domain-wall state, we found superdiffusive space–time scaling with an anomalous dynamical exponent of 3/2. We then probed the predicted microscopic requirements for superdiffusion, verifying regular diffusion for the integrability-broken two-dimensional Heisenberg model and ballistic transport for SU(2)-symmetry–broken net magnetized initial states. Subsequently, we measured the full counting statistics of spins transported across the domain wall; the resulting skewed distribution implied a nonlinear underlying transport process, reminiscent of the Kardar–Parisi–Zhang dynamical universality class. Moving to Mott insulators in the deep-lattice limit, we could moreover study photon-mediated interactions on a subwavelength-spaced, array-ordered spin system consisting of states coupled by a closed optical transition. By spectroscopically probing the reflectance and transmittance, we demonstrated the direct excitation of a subradiant eigenmode and observed specular reflection, indicating the realization of an efficient free-space paraxial light–matter interface

    Solar Concentrators and Solar-pumped Lasers

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    Innovative substitutions for Fresnel lenses concentrators by Elliptical shaped Fresnel lens (ESFL) and parabolic concentrators by ring array concentrator (RAC) models are presented, as well as, advances of solar-pumped lasers of Ce:Nd:YAG operation during a clean and clouded weather. The design of the ESFL and RAC were modelled into Zemax® non-sequential ray-tracing soft-ware from well-defined mathematical equations. Most of the key parameters were analysed and the resulting outputs were compared and documented in publications. The design parameters for solar-pumped lasers were optimized using Zemax®, and then the LAS-CAD™ laser cavity system software was used to further optimize the laser resonator parameters. A solar laser prototype was built with an active medium of Ce:Nd:YAG and tested using a heliostat-parabolic mirror system at both NOVA University of Lisbon and Procédés, Matériaux et Énergie Solaire - Centre National de la Recherche Scientifique (PROMES-CNRS) in Odeillo-Font Romeu, France. The ESFL offers a 4.58 W/mm2 increase in solar flux concentration compared to a Fresnel lens, which only achieves 2.66 W/mm2 at the same size and focal distance. A 3.14 m2 RAC with a focal length of 300 mm can capture over 18 W/m2. The first recorded Ce:Nd:YAG solar laser operating with a small collection area of 0.293 m2 at the NOVA facility, produced a multimode output power of 11.2 W, resulting in a solar-to-laser power conversion efficiency of 3.37%, with a minimum threshold pump power of 66 W. The MSSF parabolic mirror from PROMES-CNRS achieved a lower threshold pump power of 32.4 W using a smaller col-lection area of 0.075 m2, and during cloudy weather, a threshold pump power was further reduced to 29.2 W. Furthermore, cloud interference improved the solar-to-laser conversion efficiency to 6.32%, nearly tripling the 2.32% efficiency on a clear sky, while the solar laser conversion efficiency of 21.47 W/m2 was nearly twice the value of 12.62 W/m2 on a clear sky. The research efforts performed during this work are explained. Experimental results are dis-cussed, and future suggestions are proposed.Inovações para substituições de concentradores de lentes de Fresnel por lentes de Fresnel elípticas (ESFL) e concentradores parabólicos por modelos de concentradores de matriz de anéis (RAC) são apresentados, bem como avanços de lasers solares de Ce:Nd:YAG operando no limiar mais baixo e durante o clima nublado. O projeto do ESFL e do RAC foi modelado incorporando as equações recém-deduzidas no software de rastreamento de raios não sequencial Zemax®. A maioria dos principais parâ-metros foi analisada e as saídas resultantes foram comparadas e documentadas em publicações. Em relação aos lasers solares bombeados, todos os parâmetros de projeto foram otimizados e adaptados no Zemax® e o software de sistema de cavidade a laser LASCAD™ foi usado para otimizar os parâmetros do ressonador a laser. O protótipo de laser solar com o meio ativo de Ce:Nd:YAG foi construído e testado na instalação helióstato-parabólica na Universidade Nova de Lisboa e no forno solar de tamanho médio (MSSF) no Procédés, Matériaux et Énergie Solaire - Centre National de la Recherche Scientifique (PROMES-CNRS) em Odeillo-Font Romeu, França. O ESFL oferece um aumento de 4,58 W/mm2 na concentração de fluxo solar em comparação com uma lente de Fresnel, que alcança apenas 2,66 W/mm2 no mesmo tamanho e distância focal. Um RAC de 3,14 m2 com uma distância focal de 300 mm pode capturar mais de 18 W/m2. O primeiro laser solar Ce:Nd:YAG registrado, operando com uma pequena área de coleta de 0,293 m2 na instalação da NOVA, produziu uma potência de saída multimodo de 11,2 W, resultando em uma eficiência de con-versão de energia solar para laser de 3,37%, com uma potência mínima de bombeamento de 66 W. O espelho parabólico MSSF do PROMES-CNRS alcançou uma potência de bombeamento de limiar mais baixa de 32,4 W usando uma área de coleta de 0,075 m2 e, durante o tempo nublado, uma potência de bombeamento de limiar de 29,2 W foi registada. Além disso, a interferência das nuvens melhorou a eficiência de conversão de energia solar para laser em 6,32%, quase triplicando a eficiência de 2,32% em um céu claro, enquanto a eficiência de conversão de energia do laser solar de 21,47 W/m2 foi quase o dobro do valor de 12,62 W/m2 em um céu claro
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