19 research outputs found

    The Fast Regulation of Photosynthesis in Diatoms: an inquiry into the physiological and physical origins of non-photochemical chlorophyll fluorescence quenching.

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    Diatoms are renowned for their robust ability to perform NPQ (Non-Photochemical Quenching of chlorophyll fluorescence) as a dissipative response to heightened light stress on photosystem II, plausibly explaining their dominance over other algal groups in turbulent light environs. Their NPQ mechanism has been principally attributed to a xanthophyll cycle involving the lumenal pH regulated reversible de-epoxidation of diadinoxanthin. The principal goal of this dissertation is to reveal the physiological and physical origins and consequences of the NPQ response in diatoms during short-term transitions to excessive irradiation. The investigation involves diatom species from different originating light environs to highlight the diversity of diatom NPQ and to facilitate the detection of core mechanisms common among the diatoms as a group. A chiefly spectroscopic approach was used to investigate NPQ in diatom cells. Prime methodologies include: the real time monitoring of PSII excitation and de-excitation pathways via PAM fluorometry and pigment interconversion via transient absorbance measurements, the collection of cryogenic absorbance spectra to measure pigment energy levels, and the collection of cryogenic fluorescence spectra and room temperature picosecond time resolved fluorescence decay spectra to study excitation energy transfer and dissipation. Chemical inhibitors that target the trans-thylakoid pH gradient, the enzyme responsible for diadinoxanthin de-epoxidation, and photosynthetic electron flow were additionally used to experimentally manipulate the NPQ response. Multifaceted analyses of the NPQ responses from two previously un-photosynthetically characterised species, Nitzschia curvilineata and Navicula sp., were used to identify an excitation pressure relief ‘strategy’ for each species. Three key areas of NPQ were examined: (i) the NPQ activation/deactivation processes, (ii) how NPQ affects the collection, dissipation, and usage of absorbed light energy, and (iii) the interdependence of NPQ and photosynthetic electron flow. It was found that Nitzschia cells regulate excitation pressure via performing a high amplitude, reversible antenna based quenching which is dependent on the de-epoxidation of diadinoxanthin. In Navicula cells excitation pressure could be effectively regulated solely within the PSII reaction centre, whilst antenna based, diadinoxanthin de-epoxidation dependent quenching was implicated to be used as a supplemental, long-lasting source of excitation energy dissipation. These strategies for excitation balance were discussed in the context of resource partitioning under these species’ originating light climates. A more detailed investigation of the NPQ response in Nitzschia was used to develop a comprehensive model describing the mechanism for antenna centred non-photochemical quenching in this species. The experimental evidence was strongly supportive of a mechanism whereby: an acidic lumen triggers the diadinoxanthin de-epoxidation and protonation mediated aggregation of light harvesting complexes leading to the formation of quencher chlorophyll a-chlorophyll a dimers with short-lived excited states; quenching relaxes when a rise in lumen pH triggers the dispersal of light harvesting complex aggregates via deprotonation events and the input of diadinoxanthin. This model may also be applicable for describing antenna based NPQ in other diatom species

    Does Cleistanthin A modulate proton currents of human neutrophils in the presence of ATP?

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    Cleistanthus collinus is a poisonous plant, the leaves of which are consumed for suicide in many parts of southern India. Exact mechanism of toxicity remains unclear. Previously, two toxic principles present in this plant namely, Cleistanthin A and Cleistanthin C were tested for proton channel blockade in human neutrophils. While neither compound blocked proton channels, the impression was that Cleistanthin A may actually enhance proton currents, though the increase was not statistically significant. Since ATP was not present in the pipette in the earlier experiments, we hypothesized that in the presence of ATP, Cleistanthin A may enhance proton currents significantly. This data is important because it will help us establish this effect as the mechanism of toxicity leading to respiratory arrest in cases of Cleistanthus collinus poisoning. AIM : To study the effect of Cleistanthin A on voltage gated proton channels of human neutrophils, with ATP included in the patch pipette. OBJECTIVES : 1. To record proton currents in freshly isolated human neutrophils using Patch clamp technique. 2. To compare the percentage of proton currents remaining after the addition of the test (Cleistanthin A) and control solutions (ethanol), as compared to the currents recorded before the addition, while ATP was included in the patch pipette. METHODS : • Isolation of fresh human neutrophils. • Isolation of Cleistanthin A. • Recording proton currents in isolated neutrophils by Patch Clamp technique. • Analysis of the percentage of proton currents remaining after the addition of the test and control solutions in comparison to currents recorded before addition. RESULTS: When the proton currents recorded at different voltage-clamp levels, after the addition of either Cleistanthin A (test) or ethanol (control), were expressed as percentages of the pre-intervention currents at the same voltages, there was no statistically significant difference in the percentage current remaining after intervention in both groups. CONCLUSION: The results indicate that even in the presence of ATP, Cleistanthin A does not show any significant effect on voltage gated proton channels of human neutrophils

    Traction axial flux motor-generator for hybrid electric bus application

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    Tato dizertační práce se zabývá návrhem původního motor-generátoru s axiálním tokem a buzením permanetními magnety, zkonstruovaným specificky pro hybridní elektrický autobus. Návrhové zadání pro tento stroj přineslo požadavky, které vedly k této unikátní topologii tak, aby byl dosažen výkon, účinnost a rozměry stroje. Tato partikulární topologie motor-generátoru s axiálním tokem je výsledkem literární rešerše, kterou následoval výběr koncepce stroje s představeným návrhem jako výsledkem těchto procesů. Přístup k návrhu stroje s axiálním tokem sledoval „multi-fyzikální“ koncepci, která pracuje s návrhem elektromagnetickým, tepelným, mechanickým, včetně návrhu řízení, v jedné iteraci. Tím je v konečném návrhu zajištěna rovnováha mezi těmito inženýrskými disciplínami. Pro samotný návrh stroje byla vyvinuta sada výpočtových a analytických nástrojů, které byly podloženy metodou konečných prvků tak, aby samotný návrh stroje byl přesnější a spolehlivější. Modelování somtného elektrického stroje a celého pohonu poskytlo představu o výkonnosti a účinnosti celého subsytému v rozmanitých operačních podmínkách. Rovněž poukázal na optimizační potenciál pro návrh řízení subsystému ve smyslu maximalizace účinnosti celého pohonu. Bylo postaveno několik prototypů tohoto stroje, které prošly intensivním testováním jak na úrovni sybsytému, tak systému. Samotné výsledky testů jsou diskutovány a porovnány s analytickými výpočty parametrů stroje. Poznatky získané z prvního prototypu stroje pak sloužily k představení možností, jak zjednodušit výrobu a montáž stroje v příští generaci. Tato práce zaznamenává jednotlivé kroky během všech fází vývoje elektrického stroje s axiálním tokem, počínaje výběrem konceptu stroje, konče sumarizací zkušeností získaných z první generace prototypu tohoto stroje.This thesis deals with a design of a novel Axial-Flux Permanent Magnet Motor-Generator for a hybrid electric bus application. Thus, the design specification represents a set of requirements, which leads toward a concept of a unique topology meeting performance, efficiency and dimensional targets. The particular topology of the Axial-Flux Permanent Magnet Motor-Generator discussed in this work is an outcome of deep literature survey, followed by the concept selection stage with the layout of the machine as an outcome of this processes. The design approach behind this so-called Spoke Axial-Flux Machine follows an idea of multiphysics iterations, including electromagnetic, thermal, mechanical and controls design. Such a process behind the eventually proposed design ensured a right balance in between all of these engineering disciplines. A set of bespoke design and analysis tools was developed for that reason, and was backed up by extensive use of Finite-Element Analysis and Computational Fluid Dynamics. Therefore, the actual machine design gained higher level of confidence and fidelity. Modelling of the machine and its drive provided understanding of performance and efficiency of the whole subsystem at various operational conditions. Moreover, it has illustrated an optimization potential for the controls design, so that efficiency of the machine and power electronics might be maximized. Several prototypes of this machine have been built and passed through extensive testing both on the subsystem and system level. Actual test results are discussed, and compared to analytical predictions in terms of the machine's parameters. As a lesson learned from the first prototype of this machine, a set of redesign proposals aiming for simplification of manufacturing and assembly processes, are introduced. This work records steps behind all phases of development of the Axial Flux Machine from a basic idea as an outcome of concept selection stage, up to testing and wrap-up of experience gained from the first generation of the machine.

    Chemical Bionics - a novel design approach using ion sensitive field effect transistors

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    In the late 1980s Carver Mead introduced Neuromorphic engineering in which various aspects of the neural systems of the body were modelled using VLSI1 circuits. As a result most bio-inspired systems to date concentrate on modelling the electrical behaviour of neural systems such as the eyes, ears and brain. The reality is however that biological systems rely on chemical as well as electrical principles in order to function. This thesis introduces chemical bionics in which the chemically-dependent physiology of specific cells in the body is implemented for the development of novel bio-inspired therapeutic devices. The glucose dependent pancreatic beta cell is shown to be one such cell, that is designed and fabricated to form the first silicon metabolic cell. By replicating the bursting behaviour of biological beta cells, which respond to changes in blood glucose, a bio-inspired prosthetic for glucose homeostasis of Type I diabetes is demonstrated. To compliment this, research to further develop the Ion Sensitive Field Effect Transistor (ISFET) on unmodified CMOS is also presented for use as a monolithic sensor for chemical bionic systems. Problems arising by using the native passivation of CMOS as a sensing surface are described and methods of compensation are presented. A model for the operation of the device in weak inversion is also proposed for exploitation of its physical primitives to make novel monolithic solutions. Functional implementations in various technologies is also detailed to allow future implementations chemical bionic circuits. Finally the ISFET integrate and fire neuron, which is the first of its kind, is presented to be used as a chemical based building block for many existing neuromorphic circuits. As an example of this a chemical imager is described for spatio-temporal monitoring of chemical species and an acid base discriminator for monitoring changes in concentration around a fixed threshold is also proposed

    Changes in energy uxes during NPQ in LHCII and PSII-LHCII

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    PhD ThesisThe non-photochemical quenching of excess energy (NPQ) is a fast molecular adaptation of photosynthetic organisms to variations of sunlight intensities. In plants, the energy-dependent quenching (qE) is the main NPQ component, which promptly protects the thylakoid membrane components by dissipating the excess energy absorbed. While the trigger of this physiological process is known to be thylakoid DpH, the site in the membrane, the structural changes involved and the nature of the quencher pigment are still a subject of debate. In this thesis, I addressed these gaps in our knowledge of qE. The results presented here show that neither minor light harvesting antenna complexes nor reaction cores are sites of qE, which instead takes place entirely in major LHCII trimers. The nature of the change from a light-harvesting to a dissipative state in LHCII and its dependence on the binding of xanthophyll-cycle carotenoids was investigated. Zeaxanthin was found to exert no e ect on the quenching dynamics of single LHCII trimers, disproving its role as a quencher. However, it controls the kinetics of the transition to the quenched state by favouring LHCII aggregation. To determine the nature of the quencher species, transient absorption spectroscopy was applied to isolated LHCII. A mechanism was identi ed whereby chlorophylls donate energy to a carotenoid species, likely a lutein, leading to quick energy dissipation. Overall, this work reveals the self-regulatory nature of photosynthetic light harvesting, showing that in principle only trimeric LHCII and the proton gradient are su cient to enable qE in vivo. The protein PsbS and zeaxanthin exert an allosteric regulation of the process, that, by tuning the degree of antennae sensitivity to the amplitude of the proton gradient, assures a ne control of light harvestin

    Advanced Technologies in Hydropower Flow Systems

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    Hydropower is an essential part of the renewable energy sector. High efficiency, immediate availability, and safe operation of hydroelectric power plants are the three key issues in recent developments in the hydropower sector. This book brings together the latest achievements addressing these key factors. In addition, one contribution deals with the alternative harvesting of hydro energy from pivoted cylinders by generating flow-induced vibrations, which are unwanted phenomena in classical pump–turbine units

    Field-Effect Sensors

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    This Special Issue focuses on fundamental and applied research on different types of field-effect chemical sensors and biosensors. The topics include device concepts for field-effect sensors, their modeling, and theory as well as fabrication strategies. Field-effect sensors for biomedical analysis, food control, environmental monitoring, and the recording of neuronal and cell-based signals are discussed, among other factors

    Genome mutation and physiology of Synechocystis sp. PCC 6803 wild types and pH-sensitive Photosystem II mutants

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    The model cyanobacterium Synechocystis sp. PCC 6803 is widely used in studies of photosynthesis, environmental sensing, and stress-response. Its capacity for straightforward genetic engineering and the early publication of its genome sequence meant that substrains of this organism have been dispersed widely among laboratories, particularly for the purposes of investigating the function of the water-splitting enzyme of photosynthesis, Photosystem II (PS II). Recently, advances in genome sequencing technology have revealed genomic divergence among these substrains, with a largely unknown level of resultant phenotypic variation. In this study, the capacity for Synechocystis sp. PCC 6803 wild types to undergo genomic change was analysed by assembly of the genome sequence of the ‘GT-O1’ and ‘GT-O2’ substrains in use at the University of Otago. In the GT-O1 substrain, a possible instance of active genome transposition processes involving a Tc1/mariner-type transposase-encoding gene was observed, and in the GT-O2 substrain a mutation detected in chlH was associated with a reduction in chlorophyll biosynthesis. It is suggested that long-term culture conditions induce genomic changes with major functional consequences in some wild-type substrains, in spite of theoretically ideal laboratory growth conditions. However, phenotypic analysis suggested that the GT-O1 substrain is comparable to other substrains of Synechocystis sp. PCC 6803 held overseas. The capacity for genome mutation in response to gene deletions affecting PS II was also analysed. Some strains carrying mutations in the extrinsic proteins or domains of PS II display an enigmatic pH 7.5-sensitive phenotype, but pH 7.5-growth of a ∆PsbO:∆PsbU strain could be rescued by genome mutations that apparently affect PS II-independent cellular processes. Assembly of the genome of a pH-insensitive ∆PsbO:∆PsbU pseudorevertant identified a mutation in pmgA that appears to affect carbon uptake, and accordingly CO2 enrichment rescued growth of some pH-sensitive PS II mutants, including the ∆PsbO:∆PsbU strain. To further investigate the effect of external pH on the membrane-embedded PS II complex, analysis of a pH-sensitive strain lacking PsbV and carrying a mutation in Loop E of the PS II core antenna CP47 protein revealed that mutations in the vicinity of the redox-active tyrosine YD appear to alter PS II redox equilibria. In a CP47 E364Q:∆PsbV mutant, the stability of YD+QA- charge pairs in PS II and possibly the capacity of YD to maintain charge equilibrium with the PS II oxygen-evolving complex was altered, likely contributing to pH-sensitivity. This suggests that pH affects PS II directly and indirectly, due to a complex interplay of pH effects on electron transport, carbon uptake, pH homeostasis, and PS II redox equilibria

    Development, design and optimization of a novel Endcap DIRC for PANDA

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    PANDA, ein Experiment an der zukünftigen FAIR Anlage in Darmstadt, strebt die Spektroskopie von Hadronen mit hoher Präzision und Statistik an. Dazu wird die gluonenreiche Proton-Antiproton Annihilation im Bereich von 1.5 GeV/c bis 15 GeV/c genutzt. Eine möglichst vollständige Abdeckung des Raumwinkels mit allen Detektoren ist eine Grundvoraussetzung um dieses Ziel zu erreichen. Gegenstand dieser Dissertation ist das Systemdesign eines neuartigen DIRC Cherenkov Detektortyps zur Identifikation geladener Hadronen im Bereich der vorderen Endkappe des PANDA Target-Spektrometers. Ein besonderes Merkmal dieses Detektors ist die kompakte, planare Bauweise welche im Akzeptanzbereich (theta < 22°) weniger als 5 cm Platz in Strahlrichtung und ca. 20 cm am äußeren Rand benötigt, wo einzelphotonenabbildende Kameras platziert sind. Nach der Definition von Systemanforderungen wurde das System in logische Komponenten zerlegt. Für jede Komponente wurden mögliche Hardware- und Designoptionen identifiziert, analysiert und hinsichtlich ihrer Konformität mit den Systemanforderungen sowie ihrem Einfluss auf die Leistungsfähigkeit bewertet. Das optische System und Sensor-Layout wurden optimiert um einen Kompromiss zwischen Komplexität und Auflösung zu erlangen. Dieser Ansatz führte zu einem hochgradig modularen Detektordesign. Die resultierende Systemdefinition umfasst die Spezifikation des optischen Systems, der Sensoren und der Ausleseelektronik. Weiter wurde ein Konzept zur Implementierung eines Musterrekonstruktionsalgorithmus zur Online Analyse vorgeschlagen. Das neuartige Konzept erforderte die Entwicklung von speziellen Algorithmen zur Teilchenidentifikation, welche die effiziente Analyse der gemessenen zeitkorrelierten Photonenmuster ermöglichen. Diese Algorithmen wurden mit Signalen getestet, welche mit zeit-basierten Monte Carlo Simulationen generiert wurden um die Zeitcharakteristik der quasikontinuierlichen Interaktion bei der höchsten an PANDA erwarteten Rate nachzubilden. Die daraus folgende Schätzung der Detektoreffizienz ergibt eine Pi/K–Separation von bis zu 4sigma bei einem Impuls von 4 GeV/c.PANDA, an experiment at the upcoming FAIR facility in Germany, aims at hadron spectroscopy with high precision and rate by exploiting gluon-rich proton-antiproton collisions at momenta from 1.5 GeV/c to 15 GeV/c. Almost 4pi coverage by all detector components is a prerequisite to realize this goal. The objective of this thesis is the system design of a novel type of DIRC Cherenkov detector for particle identification at the forward endcap of the PANDA target spectrometer. A key feature of this detector is its compact, planar design which occupies less than 5 cm in beam direction at the acceptance region (theta < 22°) and about 20 cm at the outer rim where single-photon imaging cameras are located. After the definition of system requirements, the system has been dissected into individual logical components. For each component, possible hardware and design options have been identified, analyzed and evaluated for compliance with the requirements and their impact on the system performance. The optical system and sensor layout have been optimized to compromise complexity and performance, leading to a highly modular detector setup. The resulting definition of the design comprises the specification of the optical setup, the photosensor and the front-end electronics. Further, a concept for the implementation of the pattern reconstruction algorithm for online reconstruction has been proposed. The novel concept also required the development of dedicated particle identification algorithms which permit the efficient analysis of the measured time-correlated photon patterns. These algorithms have been tested with signals generated by means of time-based Monte Carlo simulations which resemble the time characteristics of the quasi-continuous interaction at the highest rate expected at PANDA. The resulting performance estimations predict a Pi/K–separation up to 4sigma at 4 GeV/c
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