Regulation of photosynthesis under dynamic light conditions in Chlamydomonas reinhardtii : Impact on hydrogen production

The development of renewable biofuels to ensure sustainable energy supply is one of the biggest global challenges of modern society. Hydrogen has great potential to become the fuel of the future, since it provides energy without CO2 emission. The green alga Chlamydomonas reinhardtii possesses hydrogenase enzymes and is able to photoproduce hydrogen under specific conditons. Hydrogenases, together with flavodiiron proteins (FDPs), PROTON GRADIENT-REGULATION 5 (PGR5), and PGR5-LIKE PHOTOSYNTHETIC PHENOTYPE 1 (PGRL1), represent key players of alternative electron transport (AET) in C. reinhardtii. Photosynthetic organisms have evolved AET routes such as these to adjust the photosynthetic apparatus under dynamic environmental conditions, like changing carbon supply or fluctuating light (FL) intensity. The interplay of all of these AET routes was the subject of my doctoral research, which was performed in order to understand AET regulation and to identify possible bottlenecks towards commercially profitable hydrogen production by C. reinhardtii. In the first part of my thesis, I demonstrated that all three proteins; FDPs, PGR5, and PGRL1, contribute to the photoprotection of C. reinhardtii under FL. FDPs form a rapid electron sink downstream of PSI and are absolutely crucial for survival under FL conditions. PGR5 operates on a slower time-scale than FDPs and is the next important protein to act under FL stress. A lack of PGR5 inhibits cell growth, even under mild FL conditions. It is possible that PGR5 acts as a redox-dependent regulator of photosynthesis. The importance of PGRL1 on the growth performance is only observed under severe FL conditions, despite the importance of PGRL1-mediated cylic electron transport during high light transients. In the second section of my thesis, I studied the role of FDPs in H2-photoproduction during the transition to anaerobiosis. Anoxic culture conditions are necessary to enable the function of oxygen-sensitive hydrogenases. Here, it is shown that FDPs may accelerate the transition of C. reinhardtii cells to anaerobiosis during S-deprivation. Furthermore, application of a magnesium (Mg)-deprivation protocol resulted in prolonged H2 production and improved cell viability. High accumulation levels of FDPs during the H2 production phase suggested a contribution of these proteins to the maintenance of anoxia when Mg-deprivation is employed to induce H2 production.Siirretty Doriast

Second Variations of the Causal Action for Regularized Dirac Sea Configurations

The theory of causal fermion systems provides a new mathematical framework which allows for a unified description of contemporary fundamental physics. One essential ingredient of this framework is the so-called causal action which is a certain functional of a measure defined on a specific subset of the bounded linear operators on a Hilbert space. For a given measure, this functional can be regarded as a quantifier of the weighted causal relation of all operators within the support of the measure. Moreover, the functional is subject to the causal action principle which aims at minimizing the causal action by varying the measure and in this way makes the measure a dynamical variable. All of this, as well as further fundamental objects of the theory which are relevant to this thesis, are introduced and explained in Chapter 1. Within these structures and based on certain foundational conceptions, one can now model concrete physical systems, which are always understood as a combination of some spacetime manifold together with the fermionic particle content existing therein. The foundational conception underlying the modelling is to regard fermions as the fundamental building blocks of nature and to conceive the vacuum, according to Dirac’s interpretation, as the presence of all negative-energy solutions of the Dirac equation in the respective spacetime. To get into the framework of the theory of causal fermion systems, one chooses the above-mentioned Hilbert space as these negative-energy solutions and simultaneously forgets about all the other geometrical and topological structures of spacetime. In order to take into account a possibly existing, though yet not observed, non-trivial microstructure of spacetime which leads to a modified high-energy behaviour of the Dirac solutions, the elements of the Hilbert space are equipped with a so-called regularization. As will be explained in further detail in Chapter 2, it is this regularization which in the modelling of a physical system within the structures provided by the theory of causal fermion systems plays the role of the measure and is thus dynamically determined through the causal action principle. Embedded in this setting, the present thesis is concerned with the derivation and analysis of the multipole expansion of second variations of the above-mentioned causal action which are caused by variations of the regularization of the so-called regularized kernel of the fermionic projector. The thesis is divided into three major parts: In Part I: Basics we lay the foundations by first introducing and discussing the fundamental mathematical structures of the theory of causal fermion systems and subsequently explaining in detail how concrete physical systems can be realized within this abstract setting and what exactly the underlying foundational conceptions are. Part II: Developments is devoted to the derivation of the multipole expansion of second variations of the regularized causal action. More specifically, in Chapter 3 we derive second variations of the regularized causal action for a homogeneous regularized kernel of the fermionic projector having vector-scalar structure which results in Theorem 3.4.3. Starting from this result, the multipole expansion of the second variation of the regularized causal action is derived and simplified through several steps in Chapter 4, ultimately leading to Theorem 4.3.1 which expresses the multipole moments of the second variation of the regularized causal action in terms of integral operators. In Part III: Applications we then analyze the second variation of the regularized causal action for special regularizations. More concretely, in Chapter 5 we consider an anisotropic generalization of the so-called iε-regularization which is extensively studied in the literature and demonstrate in Theorem 5.2.5 that Lorentz boosts of the velocity vector of this regularization leave the regularized causal action invariant. Additionally, we prove that anisotropically iε-regularized kernels of the fermionic projector lead to a non-vanishing second-order variation of the local particle density compared with the symmetric situation. Finally, in Chapter 6 we outline a procedure which, under certain simplifying assumptions, ultimately allows to demonstrate invertibility of the lowest-order multipole moment of the second variation of the regularized causal action. A generalization of this approach to higher multipole moments is part of a novel mechanism of baryogenesis within the theory of causal fermion systems

Elimination of the flavodiiron electron sink facilitates long-term H2 photoproduction in green algae

The development of renewable and sustainable biofuels to cover the future energy demand is one of the most challenging issues of our time. Biohydrogen, produced by photosynthetic microorganisms, has the potential to become a green biofuel and energy carrier for the future sustainable world, since it provides energy without CO2 emission. The recent development of two alternative protocols to induce hydrogen photoproduction in green algae enables the function of the O2-sensitive [FeFe]-hydrogenases, located at the acceptor side of photosystem I, to produce H2 for several days. These protocols prevent carbon fixation and redirect electrons toward H2 production. In the present work, we employed these protocols to a knockout Chlamydomonas reinhardtii mutant lacking flavodiiron proteins (FDPs), thus removing another possible electron competitor with H2 production.The deletion of the FDP electron sink resulted in the enhancement of H2 photoproduction relative to wild-type C. reinhardtii. Additionally, the lack of FDPs leads to a more effective obstruction of carbon fixation even under elongated light pulses.We demonstrated that the rather simple adjustment of cultivation conditions together with genetic manipulation of alternative electron pathways of photosynthesis results in efficient re-routing of electrons toward H2 photoproduction. Furthermore, the introduction of a short recovery phase by regular switching from H2 photoproduction to biomass accumulation phase allows to maintain cell fitness and use photosynthetic cells as long-term H2-producing biocatalysts

"When you either rush or take it slow" - En fallstudie av medias inverkan på NATO:s intervenerande i Bosnien & Hercegovina och Kosovo

Denna uppsats ämnar till att via en fallstudie av Bosnienkriget och konflikten i Kosovo påvisa en skillnad i NATO:s benägenhet att intervenera med media som den påverkande faktorn. För denna studie har det applicerats delar av två olika teorier, vilket är cnn-effekten och chain-ganging & buck-passing. Resultatet påvisade att när medias rapporter ger en uppmålning av en snabbt utvecklande process sker ett ansvarstagande. När media istället målar upp konflikten som långsamt utvecklande läggs ansvaret på en andra aktörer. Det som tidigare ämnades att vara en teoriutveckling av nämnda teorier, landade i skapandet av en ny teori kallat ‘’Rush or Slow’’ - teorin

Communicative Access Measures for Stroke

Reducing communication barriers to ensure promotion of patients’ rights to have information presented in a way that it can be understood and the right to participate fully in decision-making is consistent with policies in the USA, Canada, UK and Australia. For example, the Joint Commission (the organization responsible for hospital accreditation in the US) now includes communicative access and health literacy within its standards

A mechanism of baryogenesis for causal fermion systems

It is shown that the theory of causal fermion systems gives rise to a novel mechanism of baryogenesis. This mechanism is worked out computationally in globally hyperbolic spacetimes in a way which enables the quantitative study in concrete cosmological situations

A new approach for sustained and efficient H2 photoproduction by Chlamydomonas reinhardtii

Sustained H2 photoproduction is demonstrated in green algae under a train of strong white light pulses interrupted by longer dark phases. The devised protocol relies on the presence of the [FeFe]-hydrogenase in algal chloroplasts, which is activated within a few seconds after the establishment of anaerobiosis. H2 photoproduction proceeds for up to 3 days with the maximum rate occurring in the first 6 hours

Semantic variant primary progressive aphasia: Practical recommendations for treatment from 20 years of behavioural research

People with semantic variant primary progressive aphasia (svPPA) present with a char-acteristic progressive breakdown of semantic knowledge. There are currently no pharmacological interventions to cure or slow svPPA, but promising behavioural approaches are increasingly reported. This article offers an overview of the last two decades of research into interventions to support language in people with svPPA including recommendations for clinical practice and future research based on the best available evidence. We offer a lay summary in English, Spanish and French for education and dissemination purposes. This paper discusses the implications of right-versus left-predominant atrophy in svPPA, which naming therapies offer the best outcomes and how to capitalise on preserved long-term memory systems. Current knowledge regarding the maintenance and generalisation of language therapy gains is described in detail along with the development of compensatory approaches and educational and support group programmes. It is concluded that there is evidence to support an integrative framework of treatment and care as best practice for svPPA. Such an approach should combine rehabilitation interventions addressing the language impairment, compensatory approaches to support activities of daily living and provision of education and support within the context of dementia