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Pour réaliser les conditions des réactions de fusion thermonucléaire dans le tokamak ITER, des moyens additionnels de chauffage sont requis. L'une des principales méthodes pour chauffer les ions du plasma de coeur sera l'injection de neutres D0 énergétiques. Le neutraliseur est l'étape de l'injecteur de neutres d'ITER où le faisceau de deutérium prend ses propriétés en termes de taux de neutres D0 et de direction de propagation. L'interaction entre le faisceau à 1MeV et le gaz D2 neutralisant (~0.1Pa) crée un plasma secondaire. Les phénomènes physiques en jeu sont présentés à travers l'analyse des résultats du code OBI-2. OBI-2 est un code PIC-MCC (Particle In Cell Monte Carlo Collision) en géométrie cylindrique (2D3V) développé au LPGP qui permet de suivre la propagation du faisceau et les particules du plasma le long du neutraliseur.L'injection de lithium comme cible neutralisante a été étudiée et comparée au deutérium. Une étude paramétrique sur le neutraliseur basé sur le lithium a été réalisée dans la mesure où la longueur et/ou la densité de Li injectée peuvent être modifiées. Le profil de densité de Li a été estimé par le code Monte-Carlo 3D MC-OLIJET développé au LPGP. Le profil résultatnt a été implémenté en entrée du code PIC-MCC. Les résultats montrent la faisabilité du neutraliseur basé sur le lithium, gardant la convergence correcte du faisceau et avec de meilleures performances en termes de durée de vie des cryompompes avant régénération, de neutralisation du faisceau, d'effet de rétrodiffusion des ions positifs. / To achieve thermonuclear fusion reactions in the ITER tokamak, additional heating is required. One of the main method to heat the core plasma ions will be the injection of energetic D0 neutrals. The neutralizer is the stage of the Neutral Beam Injector of ITER where the deuterium beam gets its properties in terms of neutral rate D0 and direction of propagation. The interaction between the 1MeV beam and the D2 neutralizing gas (~0.1Pa) creates a secondary plasma. These physical phenomena involved are presented through the analysis of the OBI-2 code results. OBI-2 is a PIC-MCC (Particle In Cell Monte-Carlo Collision) code in cylindrical geometry (2D3V) developed in the LPGP which allows to follow beam propagation and plasma particles along the neutralizer.The injection of lithium neutralizing target has been investigated and compared to deuterium one. Parametric study of the Li based neutralizer has been performed since the length and/or density of Li injected can be modified. The Li density profile has been estimated through the Monte-Carlo 3D code MC-OLIJET developed in the LPGP. The resulted profile has been implemented as an imput of the PIC-MCC code. Results show the feasibility of a lithium based neutralizer, keeping correct beam focusing and with better performance in terms of cryompump lifetime before regeneration, beam neutralization, positive ion backstreaming effect.

Previous research has established that the majority of nominally anhydrous minerals (NAMs) in Earth’s mantle can incorporate water in the form of structurally bound hydrogen and, correspondingly, the mantle is thought to contain a substantial volume of water. Water has been shown to play a key role in the geodynamics of the Earth’s interior and quantifying the amount, and distribution, of water in the mantle is an important step in understanding many deep-Earth processes. One of the parameters highly sensitive to the incorporation of water in the mantle is electrical conductivity, as hydrogen is highly mobile and acts as the dominant charge-carrying species. In theory, this relationship can be used in conjunction with geophysical techniques that measure mantle-scale electrical conductivity to ‘map-out’ the deep Earth’s water content – but accurate interpretation of such data requires full understanding of hydrogen mobility in NAMs under extreme conditions, which remains poorly constrained. The aim of this project is to contribute to the reconciliation of geophysical observations with laboratory measurements of electrical conductivity, by considering hydrogen-deuterium exchange in single crystals. In a novel experimental design, hydrogen in crystals synthesised under mantle conditions (such that the hydrogen defects present correspond to the conditions being studied) exchanges with deuterium from a liquid source under controlled (mantle) pressure and temperature conditions for a specified time period. This results in hydrogen-deuterium exchange profiles that can be characterised by SIMS and subsequently fitted to Fick’s law to calculate hydrogen diffusion coefficients – which in turn can be related to electrical conductivity through the Nernst-Einstein equation. Analysis of the experimental results underlines the complexity of the influence of hydrogen on electrical conductivity in NAMs, and emphasises the need for careful consideration when interpreting and applying the results of diffusion studies. Ultimately, the data obtained in this study provides a useful contribution to understanding hydrogen diffusion in mantle minerals, but the non-trivial nature of both the experimental and analytical aspects mean that the method cannot easily be applied to other mantle phases.

Stream food webs are supported by carbon produced within the stream (autochthonous) and from terrestrial environments (allochthonous). Allochthonous carbon (C) inputs are assumed to be the dominant C source supporting food webs within small streams, but few direct estimates of resource use in small streams have been made, especially in boreal streams. The objective of this study was to determine the relative dependence on allochthonous and autochthonous C by consumers in relation to C pools within streams with high terrestrial inputs. Furthermore, this study aimed to investigate if the relative resource use of allochthonous and autochthonous C by consumers differed among seasons (summer and fall), between streams of different sizes, and locations within the catchment. To estimate consumer resource use, δ2H signatures for organic C sources were compared to those of six key consumers in five streams of varying catchment sizes in northern Sweden. Macroinvertebrate biomass was quantified to calculate a taxa-specific biomass-weighted allochthony, and compared with the mass of different C pools potentially available for consumers. The biomass-weighted mean allochthony for all samplings ranged between 43.5-61.5%; there was thus high autochthonous support despite low algal density and high terrestrial C pools within the streams. No significant trend in allochthony was observed over season (linear regression, p-value >0.05). Allochthony differed by invertebrate taxa and was not related to stream size or location in catchment. These results suggest that autochthonous C is far more important for consumers in boreal streams than previously recognized.

This dissertation presents extensive structural studies of gas-phase peptide fragment ions, with a specific focus on b₂⁺ ions. Fragment ion structures can provide important insights into peptide fragmentation mechanisms. Based on the structures formed, information about the preference of competing b ion formation pathways can be obtained. b₂⁺ ion structures are of interest because of their large relative abundances in MS/MS spectra, which are difficult to predict. Prior to this work, only a few b₂⁺ ion structures were determined; these systems featured only aliphatic residues and all formed oxazolones. The work presented herein examines the influence of basic, acidic, and backbone-attached sidechains on peptide fragmentation mechanisms, as revealed by the resulting b₂⁺ fragment ion structure(s) formed. Specifically, the structures of several histidine, aspartic acid, and proline-containing b₂⁺ ions are determined by using action IRMPD spectroscopy, fragment ion HDX, and DFT calculations. The structures of a series of histidine analogue-containing b₂⁺ ions reveal that the location and availability of the pi-nitrogen is essential for diketopiperazine formation. The histidine sidechain bulk or strain interferes with the complete trans-cis isomerization required for diketopiperazine formation, so the oxazolone structure is also present. Xxx- Pro b₂⁺ ions favor oxazolone formation with aliphatic N-terminal residues. HP favors the diketopiperazine, combining the histidine effect and the proline cis conformation propensity. For Xxx-Asp b₂⁺ ions, aspartic acid significantly influences b₂⁺ ion structure only with an N-terminal histidine or lysine; both HD and KD form a mixture of oxazolone, anhydride, and diketopiperazine structures, presenting the first spectroscopic evidence for the anhydride b₂⁺ion structure. The HA and AH b₂⁺ ions feature the same structures, but HP and PH do not, showing that residue position matters. Additionally, while relative intensities and HDX rates featured some fluctuation, peptide precursor composition differences did not alter the mixture of b₂⁺ ion structures formed for a given b₂⁺ ion. To complement existing gas-phase structural methods, the utility of a new technique, QCID-HDX-IRMPD, was applied to m/z 552.28 from YAGFL-OH. Both the standard b₅⁺ fragment ion and an isobaric non-C-terminal water loss ion are present. Without separation of these isomers, MS/MS spectral interpretation would be complicated.

The human society of today has a significantly negative impact on the environment and needs to change its way of living towards a more sustainable path if to continue to live on a healthy planet. One path is believed to be an increased usage of naturally degradable and renewable raw materials and, therefore, attention has been focused on the highly abundant biopolymer cellulose. However, a large drawback with cellulose-based materials is the significant change of their mechanical properties when in contact with water. Despite more than a century of research, the extensively investigated interaction between water and cellulose still possesses many unsettled questions, and if the answer to those were known, cellulose-based materials could be more efficiently utilized. It is well understood that one interaction between cellulose and water is through hydrogen bonds, established between water and the hydroxyl groups of the cellulose. Due to the very similar properties of the hydroxyl groups in water and the hydroxyl groups of the cellulose, the specific interaction-induced effect on the hydroxyl groups at a cellulose surface is difficult to investigate.  Therefore, a method based on 2H MAS NMR spectroscopy has been developed and validated in this work. Due to the verified ability of the methodology to provide site-selective information regarding the molecular dynamics of the cellulose deuteroxyl groups (i.e. deuterium-exchanged hydroxyl groups), it was shown by investigating 1H-2H exchanged cellulose samples that only two of the three accessible hydroxyl groups (on the surface of cellulose fibrils) exchange with water. This finding was also verified by FT-IR spectroscopy, and together with MD simulations we could establish that it is O(2)H and O(6)H hydroxyl groups (of the constituting glucose units) that exchange with water. From the MD simulations additional conclusion could be drawn regarding the molecular interactions required for hydrogen exchange; an exchanging hydroxyl group needs to donate its hydrogen in a hydrogen bond to water. Exchange kinetics of thin cellulose films were investigated by monitoring two different exchange processes with FT-IR spectroscopy. Specific information about the two exchanging hydroxyl/deuteroxyl groups was then extracted by deconvoluting the changing intensities of the recorded IR spectra. It was recognized that the exchange of the hydroxyl groups were well described by a two-region model, which was assessed to correspond to two fibrillary surfaces differentiated by their respective positions in the fibril aggregate. From the detailed deconvolution it was also possible to estimate the fraction of these two surfaces, which indicated that the average aggregate of cotton cellulose is built up by three to four fibrils.                       2H MAS NMR spectroscopy was used to examine different states of water in cellulose samples, hydrated at different relative humidities of heavy water. The results showed that there exist two states of water adsorbed onto the cellulose, differentiated by distinct different mobilities. These two states of water are well separated and had negligible exchange on the time scale of the experiments. It was suggested that they are located at the internal and external surfaces of the fibril aggregates. By letting cellulose nanofibrils undergo an epoxidation reaction with a mono epoxide some indicative results regarding how to protect the cellulose material from the negative impact of water were presented. The protecting effect of the epoxidation were examined by mechanically testing and NMR spectroscopy. It was proposed that by changing the dominant interaction between the fibril aggregates from hydrophilic hydrogen bonds to hydrophobic π-interactions the sensitivity to moisture was much reduced. The results also indicated that the relative reduction in moisture sensitivity was largest for the samples with highest moisture content. / <p>QC 20161229</p>

Graphene, a one-atom-thick sheet of carbon atoms, is impermeable to all atoms and molecules; the same can be expected for other 2D crystals like hexagonal boron nitride (hBN). In this work we show that monolayers of graphene and hBN are highly permeable to thermal protons. As a reference, we show that monolayers of molybdenum disulphide as well as bilayers of graphene and tetralayers of hBN are not. Moreover, we show that water plays a crucial role in the transport mechanism. Because of the zero point energy of vibration in the oxygen-hydrogen bonds in water, protons face energy barriers smaller than previously predicted by theory. The effect, revealed by substituting hydrogen for deuterium, also shows that protons and deuterons transport at different rates across the membranes; establishing them as membranes with subatomic selectivity. Beyond the purely scientific implications, our results establish monolayers of graphene and hBN as a promising new class of proton conducting materials with potential applications in fuel cells, hydrogen purification and isotope enrichment technologies.

Since the discovery that diazomethane, CH2N2, can effect the cyclopropanation of alkenes under palladium catalysis in the 1960s, this reaction has been used to great effect in synthesis. However, the necessity of preparing and handling diazomethane, a toxic and explosive reagent, is unappealing. The substitution of diazomethane for a commercially-available and thermally-stable silylated congener, namely trimethylsilyldiazomethane (TMSDAM), has been investigated. Under optimised conditions, designed to promote protodesilylation, use of this reagent affords the same products as would be obtained with the more hazardous diazomethane, with no trace of the corresponding silylated cyclopropanes. NMR spectroscopy has revealed that the protodesilylating agent employed in the reaction, tetrabutylammonium bifluoride (n-Bu4N+ HF2 -, TBABF), reacts cleanly with TMSDAM to generate diazomethane. Under catalytic conditions, the consumption of the desilylated diazo reagent by palladium is sufficiently rapid to prevent the accumulation of this hazardous reagent in solution. Spectroscopic titration studies also revealed a “hidden” mode of TBABF catalysis, whereby adventitious water drives the regeneration of the bifluoride salt. This observation was exploited by the development of an EtOH-driven reaction variant in which catalytic amounts (20 mol%) of TBABF could be employed. The ability to effect the in situ generation of diazomethane has allowed for mechanistic studies into the course of the cyclopropanation reaction to be undertaken. These reveal a partitioning in the consumption of nascent diazomethane between the desired cyclopropanation reaction and a side reaction. The product of the side reaction was identified as cyclopropane (C3H6), the product of formal methylene cyclotrimerisation, by employing EtOD in TBABF-catalysed deuterodesilylative cyclopropanation. The partitioning between the two pathways is dependent on the nature of the substrate, with efficient cyclopropanation dominating with electrondeficient alkenes. For an electronically-varied range of styrenes, the relative rate of productive diazomethane consumption correlates well with the energy of the frontier molecular orbitals (as determined by DFT calculations). These results are consistent with an initial, substrate-dependent partitioning of the palladium pre-catalyst between species able to effect alkene cyclopropanation, and those (likely higher-order) species which promote only the cyclotrimerisation of diazomethane.

Actin's ability to engage in a wide range of physiological functions requires that it be subject to complex spatial and temporal regulation. This regulation is achieved internally through monomer-monomer contacts and externally through interactions with actin binding proteins. The first part of my thesis focused on better understanding the role of inter-monomeric ionic interactions proposed between subdomains 2 and 3 of opposing monomers in F-actin stabilization. I studied several yeast actin mutants: A167R to disrupt a proposed ionic attraction with R39, A167E to mimic a proposed ionic attraction in muscle actin, and D275R to disrupt a proposed ionic attraction with R39. I investigated the effects of mutations in vivo, effects on filament polymerization characteristics and appearance in vitro, as well as interaction of the mutants with the filament severing protein cofilin. While both in vivo and in vitro data demonstrated the importance of the R39-D275 interaction for yeast actin and the interaction of the filament with cofilin, disruption of this interaction alone did not cause filament fragmentation. Conversely, results with A167 do demonstrate the in vivo and in vitro importance of another potential R39 ionic interaction for filament stabilization. In the second part of my work I used amide proton hydrogen/deuterium (HD) exchange detected by mass spectrometry as a tool to gain structural insight into yeast and muscle actin and profilin isoform differences and the actin-profilin interaction. The yeast and muscle actin HD analysis showed greater exchange for yeast G-actin compared to muscle actin in the barbed end pivot region and areas in subdomains 1 and 2, and for F-actin in monomer-monomer contact areas. These results suggest greater flexibility of the yeast actin monomer and filament compared to muscle actin. For yeast-muscle hybrid G-actins, the muscle-like and yeast-like parts of the molecule generally showed exchange characteristics resembling their parent actins. There were a few exceptions to this rule, however: a peptide on top of subdomain 2 and the pivot region between subdomains 1 and 3. These exhibited muscle actin-like exchange characteristics even though the areas were yeast-like, suggesting that there is crosstalk between subdomains 1 and 2 and the large and small domains. Hybrid F-actin data showing greater exchange compared to both yeast and muscle actins are consistent with mismatched yeast-muscle actin interfaces resulting in decreased stability of the hybrid filament contacts. Actin-profilin HD exchange results demonstrated a possible differential interaction of specific profilin isoforms with specific actin isoforms. While profilin binding mostly caused a decreased exchange for yeast actin peptides, it caused an increase in exchange for muscle actin peptides. Many of the changes observed were in peptides that line or contact the nucleotide cleft, consistent with profilin's ability to alter the kinetics of nucleotide exchange.

R.E. Hillger, M.W.P. Strandberg. / II. HDS. / "October 5, 1950." / Includes bibliography. / Army Signal Corps Contract DA36-039 sc-100 Project no. 8-102B-0. Dept. of the Army Project 3-99-10-022.