Tesi sul tema "Isotope shift"

At present several groups are analysing quasar absorption spectra to search for variation of the fine structure constant, alpha, across space and time. These studies compare the wavelengths of several transitions observed in the absorption clouds with those seen in the laboratory, and interpret anomalies as variation in alpha. One group has already presented evidence that alpha may have been smaller at an early epoch. Other groups using different telescopes see no variation. These studies use the ???many-multiplet??? method, which relies on the utilisation of many transitions in many ions to enhance the size of the effects and remove sources of systematic error. While this method offers an order-of-magnitude improvement in sensitivity over the previously used alkali-doublet method, the alpha-dependence (relativistic shift) of every transition used in the analysis must be calculated ab initio. In this thesis we present a method for the precise calculation of relativistic shifts, based on an energy calculation involving combination of the configuration interaction method and many-body perturbation theory. The many-multiplet method also introduces a potential systematic error: if the relative isotope abundances of the absorbers differ from terrestrial abundances then there can be spurious shifts in the measured wavelengths, which may be incorrectly interpreted as variation of alpha. A ???conspiracy??? of several isotopic abundances may provide an alternative explanation for the observed spectral anomalies. To account for these systematic errors we need accurate values of the isotope shift. We calculate these shifts using the finite-field method to reduce the problem to that of an energy calculation, which in turn is done using the same method used for the relativistic shift. We present the results of our calculations for a variety of atoms and ions seen in quasar absorption spectra. The results of this research should allow astrophysicists to measure isotope abundances in the absorbers directly. This can provide a test for models of nuclear reactions in stars and supernovae, and of the chemical evolution of the Universe. Our calculations can also be used in conjunction with measurements to extract changes in nuclear charge radii between isotopes.

We perform high precision measurements of an isotope shift between the two stable isotopes of helium. We use laser excitation of the 2^3 S_1-2^3 P_0 transition at 1083 nm in a metastable beam of 3He and 4He atoms. A newly developed tunable laser frequency selector along with our previous electro-optic frequency modulation technique provides extremely reliable, adaptable, and precise frequency and intensity control. The intensity control contributes negligibly to overall experimental uncertainty by stabilizing the intensity of the required sideband and eliminating the unwanted frequencies generated during the modulation of 1083 nm laser carrier frequency. The selection technique uses a MEMS based fiber switch and several temperature stabilized narrow band (~3 GHz) fiber gratings. A fiber based optical circulator and an inline fiber amplifier provide the desired isolation and the net gain for the selected frequency. Also rapid (~2 sec.) alternating measurements of the 2^3 S_1-2^3 P_0 interval for both species of helium is achieved with a custom fiber laser for simultaneous optical pumping. A servo-controlled retro-reflected laser beam eliminates residual Doppler effects during the isotope shift measurement. An improved detection design and software control makes negligible subtle potential biases in the data collection. With these advances, combined with new internal and external consistency checks, we are able to obtain results consistent with the best previous measurements, but with substantially improved precision. Our measurement of the 2^3 S_1-2^3 P_0 isotope shift between 3He and 4He is 31 097 535.2 (5) kHz. The most recent theoretic calculation combined with this measurement yields a new determination for nuclear size differences between 3He and 4He: ∆r_c=0.292 6 (1)_exp (8)_th (52)_exp fm, with a precision of less than a part in 〖10〗^4 coming from the experimental uncertainty (first parenthesis), and a part in 〖10〗^3 coming from theory. This value is consistent with electron scattering measurement, but a factor of 10 more precise. It is inconsistent (4 sigma) with a recent isotope shift measurement on another helium transition (2^1 S_0-2^3 S_1). Comparisons with ongoing muonic helium measurements may provide clues to the origin of what is currently called the proton puzzle: electronic and muonic measurements of the proton size do not agree. In the future, the experimental improvements described here can be used for higher precision tests of atomic theory and quantum electrodynamics, as well as an important atomic physics source of the fine structure constant.

Quand les effets de la masse finie du noyau et de la distribution de charge spatiale sont pris en compte dans l’Hamiltonien décrivant un système atomique, les isotopes d’un élément, caractérisés par le même nombre de protons mais un nombre différent de neutrons, ont des niveaux d’énergie électronique différents. Le déplacement entre les niveaux d’énergie (pour un même état quantique) de deux isotopes différents est appelé le déplacement isotopique de niveau. De manière générale, on peut distinguer les déplacements isotopiques de champ (field shift) et les déplacements isotopiques de masse (mass shift). Pour les systèmes à plus d’un électron, le specific mass shift (SMS) apparaît. Grâce à sa faible pondération, le paramètre SMS peut être traité comme une perturbation de l’Hamiltonien ;son estimation fait appel aux intégrales de Vinti [5].

Dans un contexte relativiste, les programmes grasp2K [2] et mcdf-gme [1] permettent de résoudre les équations de Dirac-Fock associées à un état multiconfigurationnel et d’en fournir l’énergie ainsi que la représentation numérique des orbitales monoélectroniques. Nous avons créé et introduit dans le programme mcdf-gme une sous-routine capable d’estimer les paramètres de masse et de champ à partir des fonctions d’onde multiconfigurationnelles. Pour le programme GRASP2K, un module indépendant à été créé.

Par ailleurs, un opérateur plus complet impliquant des corrections en αZ, a été dérivé par Shabaev [4] et, de manière indépendante, par Palmer [3]. Nous avons déduit la forme tensorielle de cet opérateur et avons également implémenté dans les programmes cités ci-dessus le calcul de ses éléments de matrice.

Grâce à ces outils nous avons pu étudier la détérioration de l’opérateur d’énergie cinétique pour estimer le normal mass shift et travailler divers systèmes comme le lithium neutre et sa séquence isoélectronique. Par la suite nous avons également travaillé sur les séquences isoélectroniques du bore, du béryllium, du carbone et de l’azote. Enfin, certains effets isotopiques ont été étudiés pour plusieurs transitions dans le baryum neutre.

Bibliographie

[1] J. P. Desclaux. A relativistic multiconfiguration Dirac-Fock package. In E. Clementi, editor, Methods and Techniques in Computational Chemistry - vol. A :Small Systems of METTEC, page 253. STEF, Cagliari, 1993.

[2] P. Jönsson, X. He, C. Froese Fischer and I. P. Grant. The GRASP2K relativistic atomic structure package. Comput. Phys. Commun. 177 :597–622, 2007.

[3] C. W. P. Palmer. Reformulation of the theory of the mass shift. J. Phys. B :At. Mol. Phys. 20 :5987–5996, 1987.

[4] V. M. Shabaev and A. N. Artemyev. Relativistic nuclear recoil corrections to the energy levels of multicharged ions. J. Phys. B :At. Mol. Phys. 27 :1307–1314, 1994.

[5] J. P. Vinti. Isotope shift in magnesium. Phys. Rev. 56 :1120–1132, 1939.
Doctorat en Sciences de l'ingénieur
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Green sea turtles in Bermuda are overgrazing the seagrasses on which later life stages are thought to specialize. I hypothesized that larger green turtles in Bermuda would display individual diet specializations during seagrass scarcity. Stable isotope methods were used to determine the diet composition of green sea turtles from the Bermuda Platform as a function of size class and in turtles captured in successive years. Individual turtles had a wide range of diets, however, the variation in diets was driven by differences among size class rather than within the size classes of larger turtles, indicating that green turtles undergo a dietary ontogenetic shift during their residency on the Bermuda Platform and no clear specialization of diets among late-stage individuals. The apparent lack of dietary specialization of larger turtles indicates that older turtles are not diversifying their diets in response to the drastic reductions in seagrass in Bermuda.

Cette thèse est consacrée à l'étude des effets isotopiques dans les atomes neutres et ions négatifs. En particulier, nous ciblons notre recherche sur le calcul ab initio des déplacements isotopiques (DI) sur les électroaffinités des éléments des blocs p des deuxième et troisième périodes (B à F et Al à Cl). Ces derniers sont les systèmes les plus susceptibles d'être l'objet d'études expérimentales de haute précision.

Le premier chapitre se concentre sur une étude didactique du problème atomique et des effets isotopiques. Nous concluons par une description détaillée des motivations de notre thèse.

Le second chapitre présente le modèle Hartree-Fock (HF) et son extension multi-configurationelle (MCHF). Nous y énonçons le théorème de Brillouin et sa généralisation à un ansatz MCHF. Pour ce faire, nous formulons de manière originale le principe d'invariance d'une fonction d'onde CAS (Complete Active Set) par rapport aux rotations d'états d'orbitales. De cette formulation, nous caractérisons la famille des solutions CAS n'interagissant pas avec une fonction d'état de configuration (CSF) particulière et démontrons sa multiplicité. Finalement, nous appliquons notre technique d'analyse à l'étude de modèles concrets et prédisons l'apparition de minima locaux correspondant à chacune de ces solutions GBT. Introduisant le concept de quasi-symétrie de la fonctionnelle d'énergie, nous expliquons l'origine de fortes perturbations du "coeur" atomique dans des modèles particuliers.

Les troisième et quatrième chapitres fournissent les outils méthodologiques de base utilisés dans la deuxième partie de notre thèse qui présente des résultats quantitatifs originaux.

Le cinquième chapitre traite des DI et structures hyperfines des termes les plus bas de S, S-, Cl, Cl-, Si et Si-.

Dans le sixième chapitre, nous rapportons un profond désaccord entre théorie et expérience au sujet de la structure hyperfine de transitions de l'azote dans le infrarouge lointain. Nous montrons que les simulations basées sur nos valeurs de constantes isotopiques sont compatibles avec les spectres enregistrés moyennant une réassignation des raies faibles à des signaux de "cross-overs". Sur cette base, nous déduisons un nouvel ensemble de constantes hyperfines pour les états considérés, en bon accord avec nos valeurs théoriques, en nous basant uniquement sur les données expérimentales.

Le septième chapitre est une étude globale des configurations de plus basse énergie du C et C- (i.e. tous les états liés de ce dernier). Par une étude détaillée de nos incertitudes, nous obtenons des estimations très fiables et de grande précision pour un ensemble de propriétés. En particulier, nous présentons les valeurs de structure fine et hyperfine du C-, ainsi que les probabilités de transitions intra-configurationelles fournissant une base solide pour l'étude spectroscopique de ce système.

Dans le huitième chapitre, nous étudions la périodicité du déplacement spécifique de masse sur l'électroaffinité dans le Tableau Périodique des Eléments. Nous avançons les contributions dominantes qui interviennent dans cette grandeur et analysons les principales limitations des techniques de calcul actuelles dans ce contexte.

Nous présentons nos conclusions générales et les perspectives de notre travail dans le neuvième chapitre.

Doctorat en Sciences
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Fish can have complex life histories and use multiple habitats and resources throughout their life span. Consequently, their life histories are often poorly understood. The Atlantic Tarpon, Megalops atlanticus, is a large, typically migratory, elopomorph fish that is both ecologically and economically important. Atlantic Tarpon are under threat due to regional exploitation, loss of natal and juvenile habitat, poor water management, and offshore impacts. In addition, little is known about its lifelong habitat and resource use. In Chapter 1, I used stable isotope analysis of eye lens δ13C and δ15N values to explore patterns in trophic history and habitat use of 16 Atlantic Tarpon from West-Central Florida and Louisiana. The stable isotope chronologies showed 100% use of backcountry habitats during the early life history and an ontogenetic habitat shift to coastal waters at approximately 10 years of age and 140 cm total length. During the coastal phase Atlantic Tarpon displayed among-individual variability and within-individual consistency in basal resource use. In Chapter 2, mark-recapture data from a multi-year genetic tagging program were used to investigate survival and growth rates, ontogenetic habitat use, and migration of juvenile Atlantic Tarpon in Florida. The study found that juvenile Atlantic Tarpon take approximately 10 years to reach the length associated with maturity, and appear to have a high survival rate (~80%), possibly due to effective use of habitats with reduced competition and predation. Atlantic Tarpon underwent several ontogenetic habitat shifts throughout the juvenile phase. In addition, juvenile Atlantic Tarpon did not migrate long distances but instead showed fidelity to systems wherein only short movements were needed to shift habitat types. This work serves to fill critical gaps in our knowledge of Atlantic Tarpon life history and may aid in better management and conservation of the species.

The first aim of this thesis is to perform relativistic calculation of atomic and ionic polarizabilities and two-photon decay rates. Hydrogenic systems are treated by the Lagrange-mesh method. The extension to alkali-like systems is realized by means of a semiempirical-core-potential approach combined with the Lagrange-mesh method. The studied systems are partitioned into frozen-core electrons and an active valence electron. The core orbitals are defined by a Dirac-Hartree-Fock (DHF) calculation using the GRASP2K package. The valence electron is described by a Dirac-like Hamiltonian involving a core-polarization potential to simulate the core-valence electron correlation. Polarizabilities appear in a large number of fields and applications, namely in cold atoms physics, metrology and chemical physics. Two-photon transitions are part of a priori highly unlikely processes and are therefore called forbidden radiative processes. Experimental situations report decays from metastable excited states through these channels. Long lifetimes were measured for highly charged Be-like ions in recent storage-ring experiments, but their interpretation is problematic. The study of the competition between forbidden (one-photon beyond the dipole approximation, or multi-photon) and unexpected (hyperfine-induced or induced by external magnetic fields) radiative processes is all obviously relevant. The second aim of this thesis is to perform relativistic ab initio calculations of electronic isotope-shift (IS) factors by using the multiconfiguration DHF (MCDHF) method implemented in the RIS3/GRASP2K and RATIP program packages. Using the MCDHF method, two different approaches are adopted for the computation of electronic IS factors for a set of transitions between low-lying levels of neutral systems. The first one is based on the estimate of the expectation values of the one- and two-body nuclear recoil Hamiltonian for a given isotope, including relativistic corrections derived by Shabaev, combined with the calculation of the total electron densities at the origin. In the second approach, the relevant electronic factors are extracted from the calculated transition shifts for given triads of isotopes. These electronic quantities together with observed ISs between different pairs of isotopes provide the changes in mean-square charge radii of the atomic nuclei. Within this computational approach for the estimation of the mass- and field-shift factors, different models for electron correlation are explored in a systematic way to determine a reliable computational strategy, and to estimate theoretical error bars of the IS factors.
Doctorat en Sciences de l'ingénieur et technologie
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L’objectif de cette thèse est l'étude par spectroscopie laser colinéaire à haute résolution de la structure nucléaire des isotopes d’étain riches en neutrons, vers de la fermeture de couche N=82 et au-delà. Les structures hyperfines et les déplacements isotopiques le long de ¹⁰⁸⁻¹³⁴Sn ont été mesurés en utilisant l’expérience COLLAPS à ISOLDE au CERN. Deux expériences indépendantes, utilisant des propriétés de transitions complémentaires l’une à 452 et l’autre à 286 nanomètres, ont étudiées les états 5p6s ¹P₁ et 5p6s ³P₁ dans l'atome neutre. L'état singlet fournit une sensibilité élevée au moment quadrupolaire tandis que le triplet facilite une grande séparation magnétique. A partir d'une analyse auto-cohérente des deux ensembles de données, les spins nucléaires, les moments électromagnétiques et les rayons de charge ont été extraits. Les propriétés des isomères à vie longue des noyaux ¹¹³Sn, ¹²³Sn, ¹²⁸Sn ainsi que l'état fondamental de ¹³³Sn et ¹³⁴Sn ont été évalués pour la première fois. Les moments quadrupolaires des états 11/2⁻, déterminés avec une plus grande précision que les études précédentes, suivent une tendance presque linéaire. Un coude à N=82 dans la courbe des rayons a été observé pour la première fois. Des calculs de champ moyen fournissent une description précise des rayons et relient en outre la tendance globale aux corrélations provenant des fluctuations des moments quadrupolaires
The aim of this thesis is the study of nuclear structure properties of the neutron-rich Sn isotopes towards the N=82 shell closure and beyond by high-resolution collinear laser spectroscopy. The hyperfine structures and isotope shifts along ¹⁰⁸⁻¹³⁴Sn were measured using the COLLAPS instrumentation at ISOLDE, CERN. Two independent experiments using transitions with complementary properties, respectively at 452 and 286 nanometres studied the 5p6s ¹P₁ and the 5p6s ³P₁ states in the neutral atom. The singlet state provided high sensitivity to quadrupole moments while the triplet facilitated a large magnetic splitting. From a self-consistent analysis of the two data sets, nuclear spins, electromagnetic moments and charge radii have been extracted. The properties of the long-lived isomers in ¹¹³Sn, ¹²³Sn, ¹²⁸Sn and the ground state of ¹³³Sn and ¹³⁴Sn have been assessed for the first time. The quadrupole moments of the 11/2⁻ states, determined with much higher precision than in previous studies, have been found to follow a nearly linear trend. A "kink" in the radii trend at N=82 was observed for the first time. Beyond mean-field calculations provide an accurate description of the radii and further relate the overall trend to correlations stemming from the fluctuations of the quadrupole moments

Ostracods are a diverse group of arthropod crustaceans with a geological record from the Ordovician. Their radiation from marine to non-marine environments is a key step in the evolution of the group. The nature and chronology of this transition is examined, and proxies for non-marine environments determined. The Mississippian of the Midland Valley of Scotland contains a wide range of marine to non-marine ostracods, macrofauna and sediments that make it an ideal study area. This study documents the evidence for early Mississippian freshwater ostracods, 20 million years older than previously recorded. Twentyfive ostracod species from the orders Myodocopida, Palaeocopida and Podocopida are described, four of which are new species. Macrofossils are used to interpret the environmental tolerance of the ostracods. Important brackish to freshwater macrofauna are the bivalves Carbonicola, Curvirimula and Naiadites, the vermiform microconchid “Spirorbis”, conchostracans and fish. Eurytopic ostracods are species of Cavellina, palaeocopes and Shemonaella siveteri n. sp. Key brackish to freshwater ostracods are species of Geisina arcuata, and Paraparchites circularis n. sp. Freshwater ostracods are species of Carbonita. Non-marine sediments contain three new types of algal palynomorph, Botryococcus sp., and arthropod fragments. The algal palynomorphs are interpreted as freshwater. Brackish to freshwater habitats identified include estuaries, lakes, temporary pools and swamps. A protocol for the examination of diagenetic alteration of ostracods and macrofossils is proposed, which is essential prior to any isotope analysis. Diagenetically altered ostracods may be mistaken as pristine specimens, without a study of the carapace ultrastructure. This is assessed by comparing Carboniferous and Recent specimens. The Carboniferous ostracods have undergone seven diagenetic stages: 1. neomorphic calcite; 2. dissolution and pitting; 3. euhedral pyrite; 4. ferroan calcite; 5. ferroan dolomite; 6. iron oxide; 7. sphalerite and barite. The carbon and oxygen stable isotope data from the ostracods reflect these stages of diagenesis.

The N=88 nuclei lie in a transitional region of the nuclear chart. Collective structure and nuclear deformation for this region is commonly occurring. Previously, some of the nuclei having 88 neutrons have been well studied, e.g., 148Nd, 150Sm, 152Gd, 154Dy; however, 156Er has not. To be able to understand the nuclei in this region one needs to extract all the systematics of these deformed nuclei and the relations between them. The structure of 156Er is the main focus in this thesis and the work seeks understanding of the N=88 nuclei and systematics among them. To accomplish this task, 156Tm to 156Er beta decay was studied. Many new levels and gamma transitions have been added to the existing scheme. The significance for detailed decay scheme studies far from stability is also discussed.

Introduced species can become invasive and cause catastrophic alterations to the system they invade. Both zebra mussels (Dreissena polymorpha) and quagga mussels (Dreissena bugensis) have caused significant ecosystem alterations wherever they have invaded. These Dreissena species have caused changes in water quality and biodiversity and have disrupted energy pathways which can have cascading effects on other trophic levels. Recently quagga mussels invaded Lake Powell, a reservoir located in the southwestern USA, creating the possibility of a trophic cascade that could alter energy flow in the reservoir and change the trophic niche structure of the fishes in the lake. However, due to Lake Powell’s large size, dynamic nature, and complex hydrological structure, the effects of quagga mussels on fish species is uncertain. To determine impacts of quagga mussels on Lake Powell fishes, we quantified trophic niches of five species of sport fish over three years (2017-2019) using stable isotopes of nitrogen, δ15N, and carbon, δ13C. We test the following hypothesis: quagga mussels will cause a shift in trophic niche in more pelagic fishes such that pelagic fishes decrease in trophic position and shift toward use of more littoral energy. In addition, we compare the trophic niche of these species with a previous study on the trophic niche of fish in Lake Powell prior to full colonization of the lake by quagga mussels (2014-2015). In general, fish in the southern region of the lake exhibited a trend of decreasing δ15N suggesting decreasing trophic position and an enrichment of δ13C indicating a littoral energy shift in some species. Fish in the northern region of the lake exhibited a slight increase in trophic position and a shift towards pelagic energy across the same time period. These shifts support the hypothesis with pelagic fish experiencing a trophic niche shift, in the direction predicted, but only in the southern region of Lake Powell. Additionally, this shift is not exclusive to pelagic fish, but happened in all five species. Sediment laden input from the Colorado River may offset the impact of quagga mussels in the northern region of the lake resulting in observed regional differences.

A espectrometria de absorção atômica (AAS) é consolidada como uma técnica robusta, cujas aplicações estendem-se a diversos analitos e matrizes. Sua limitação encontra-se na região do UV distante (~ 190 nm), por isso ela permaneceu exclusiva à determinação de metais durante vários anos: não-metais geralmente absorvem na região de UV de vácuo. Com o advento da AAS de alta resolução com fonte contínua, houve a implementação de uma terceira dimensão (comprimento de onda) nas análises: a visualização da região espectral da linha analítica. Esta nova característica permitiu um maior número de informações espectrais, principalmente em relação às bandas estruturadas de moléculas diatômicas, o que resultou na determinação de absorção molecular (HR CS MAS). Destarte, o objetivo deste trabalho foi a elaboração de novos procedimentos analíticos para determinação de não-metais por HR CS MAS, especificadamente Br, Cl e S, com atomizador de forno de grafite. O bromo foi avaliado via CaBr em componentes plásticos de amostras eletrônicas, extraído por extração Soxhlet com tolueno, e obteve limites de detecção (LD) e quantificação (LQ) de 4,3 e 14 ng de Br, respectivamente, com Pd como modificador químico. Duas matrizes foram estudadas para a quantificação de enxofre via CS: carvão e diesel. O carvão foi injetado em HR CS MAS como uma suspensão com Triton X-100 0,04 % m v-1, e (NH4)2SO4 foi empregado como padrão de enxofre. Os LD e LQ obtidos para o método foram 0,01 e 0,05 % m m-1, respectivamente. Para o diesel, dois métodos foram estudados: (i) emulsão alcoólica com etanol 50 % v v-1, a qual apresentou LD de 0,12 g kg-1 e LQ de 0,40 g kg-1, adequados para determinação de altos teores de S em diesel; e (ii) injeção direta de diesel no sistema de HR CS MAS, cujos LD e LQ foram 3 e 9 mg kg-1, respectivamente. Ambos empregaram nanopartículas de Pd como modificador químico, das quais a análise direta de diesel obteve melhores resultados. Finalmente, um novo conceito foi investigado em HR CS MAS: o deslocamento isotópico em moléculas diatômicas. Os estados vibracionais e rotacionais presentes na transição eletrônica observada em HR CS MAS confere esta propriedade. As moléculas de AlCl e CaBr, cujos isótopos de interesse foram 35Cl e 37Cl, e 79Br e 81Br, respectivamente, foram estudadas. Os deslocamentos isotópicos observados foram de 15,6 pm para AlCl e 41,6 pm para CaBr nos comprimentos de onda selecionados, suficientes para implementação de calibração por diluição isotópica, a qual apresentou LDs de 2,5 e 64 ng, respectivamente. Amostras de água natural e mineral foram empregadas para o Cl, enquanto o Br foi determinado em amostras de PVC e folhas de tomate, as quais foram introduzidas diretamente como sólidos. A diluição isotópica corrigiu adequadamente as interferências espectrais acarretadas pelas matrizes de ambos os analitos.
Atomic Absorption Spectrometry (AAS) is a robust analytical technique whose applications extend to many different analytes and matrices. Its limitation lies on the far UV region (~ 190 nm) and therefore it remained exclusive for metal determination as non-metals typically absorb within the vacuum-UV region. With the invention of the High-Resolution Continuum Source AAS (HR CS AAS), the AAS analysis has been upgraded and a new dimension (wavelength) was added: the visualization of the analytical lines vicinity. This new feature allowed improved spectral information, mainly related to the structured bands of diatomic molecules, giving rise to the HR CS Molecular Absorption Spectrometry (MAS). The goal of this thesis was the evaluation of new analytical procedures for non-metals determination by HR CS MAS, specifically Br, Cl, and S, using graphite furnace as the atomizer. Bromine in plastic electronic components was evaluated as CaBr after Soxhlet extraction with toluene. This method had limits of detection (LD) and quantification (LQ) of 4.3 and 14 -ng, respectively, using Pd as chemical modifier. Sulfur determination via CS molecule employed two distinct matrices: coal and diesel. Coal samples were prepared as a slurry with Triton X-100 0.04% m v1 for injection in the HR CS MAS and the external calibration employed was (NH4)2SO4as sulfur standard. The method LD and LQ were 0.01% m m1 and 0.05% m m1, respectively. Two methods were studied for diesel samples: (i) alcoholic emulsion with ethanol 50% v v1, with an LD of 0.12 g kg1 and an LQ of 0.40 g kg1, suitable for sulfur high concentration determination in diesel; and (ii) direct diesel injection in the HR CS MAS system, whose LD and LQ were 3 mg kg-1and 9 mg kg-1, respectively. Both methods employed Pd nanoparticles as chemical modifier, with better results for direct diesel analysis. Ultimately, a new concept was investigated in HR CS MAS: the isotopic shift of diatomic molecules. An absorption profile consisted of multiple peaks was due to vibrational and rotational energy couplings within the electronic transition observed by HR CS MAS, which provided the isotopic shift. This effect was detected on AlCl and CaBr molecules, whose target isotopes were, respectively, 35Cl &37Cl and 79Br &81Br. The observed isotopic shifts were 15.6 pm (AlCl) and 41.6 pm (CaBr) at the selected wavelengths, appropriate for isotopic dilution calibration, which featured LDs of 2.5 ng and 64 ng, respectively. Natural and mineral water samples were evaluated for Cl determination; and Br was found in PVC and tomato leaves samples, both introduced as solid samples in HR CS GFMAS. Isotopic dilution adequately corrected the spectral interferences derived from the matrices of both analytes.

L’interprétation théorique des résultats expérimentaux repose sur des calculs "a priori" menés au moyen d'un programme Dirac-Foch multiconfigurationnel auquel s'ajoutent d'autres calculs par méthode de Racah dans le formalisme de Judd pour la structure hyperfine

The conservation of marine ecosystem structure and functioning is a priority target within the context of the environmental management. This is especially important in oligotrophic systems such as the Balearic Sea, where food availability is a limiting factor. For such a target is fundamental to know the array of predator-prey interactions as a basis to understand the food web trophodynamics. In this Thesis, the trophic structure of the pelagic and benthic habitats off the Balearic Islands and the feeding ecology of three taxonomic groups (cephalopods, elasmobranchs and mesopelagic fishes) playing a key role in marine ecosystems, were investigated A relatively large food web (89 species) encompassing both the pelagic and the benthic habitats were analysed. The food webs extended up to 4 trophic levels in both habitats, and most species occupied intermediate trophic levels. A high partitioning rate of trophic resources was found, which might be related to the reduction of competition for food. The energy link between the pelagic and benthic communities (benthopelagic coupling; BPC) was stronger on the shelf break, where higher hydrodinamism mix the water column and associated nutrients, than on the slope. The geographical variability of oceanographic drivers (i.e. eddies, currents) influenced the strength of the BPC. Regarding species trophic interactions, stomach contents provided evidence of mesopelagic prey coupling pelagic and benthic habitats, especially down the shelf break. Rays from the shelf consumed mainly decapod crustaceans and teleosts, whereas sharks from the slope fed primarily upon mesopelagic prey (i.e myctophids, euphausiids). Sharks and rays variation in diet was driven by species specific ontogenetic stages and habitat use. The diet of the two squid Loligo vulgaris and L. forbesii, examined for the first time in the Mediterranean, showed their highly piscivorous habits. Their prey composition revealed a lack of diet overlap as a result of their bathymetric segregation. Both squids showed shifts in diet related to size and their reproduction period. The squid L. vulgaris feed on small benthic prey until they reach a size threshold and feed on benthopelagic fish thereafter. Seasonal changes in diet in both squid species, likely related to reproduction, might help improving their individual body condition. During this period, L. vulgaris increased the consumption of highly nutritive polychaetes, whereas the adults of L. forbesii carried out movements to deeper waters to feed on lipid-rich mesopelagic prey. Mesopelagic prey are important food resources for demersal species in the Balearic Sea and, as a result of their nycthemeral movements, they have important implications for the transport of mass and energy through the water column. The trophodynamics of this group revealed that food sources (δ13C) varied little over the spatial scales sampled (location and depth) but showed high seasonality, reflecting intra-annual changes in the species composition of the phytoplankton community. By contrast, spatio-temporal variations of mesopelagic trophic interactions (δ15N) were minimal. Important niche segregation was observed between the non-migratory stomiiforms and some of the extensive migratory myctophids. Finally, the comparative analysis of the trophic ecology of deep-sea cephalopods and elasmobranchs showed that they displayed different feeding strategies with a clear resource partitioning between and within taxa. Segregation of the isotopic space indicated a contrasting food source gradient (δ13C) stretching from pelagic (squids and cuttlefishes) to nektobenthic (octopuses and elasmobranchs) sources. However, deep-sea sharks off the Balearic Islands frequently preyed on mesopelagic species, as did squids and cuttlefishes. Cephalopods, in turn, constituted an important food resource for deep-sea sharks. Squid and shark species identified as benthopelagic feeders, play a key role in the transport of energy from midwater regions to the benthic community.

Doutoramento em Bioquímica
The work presented in this Thesis investigates the dynamics and molecular interactions of p22HBP and the p22HBP-tetrapyrrole complex. Specifically, the key residues involved when a tetrapyrrole binds to p22HBP were sought. Previous molecular modelling studies identified three possible charged residues R56, K64 and K177 as possibly being important in tetrapyrrole binding via electrostatic interactions with the propionate groups of the tetrapyrrole. A number of variants of murine p22HBP were therefore prepared and fluorescence quenching and NMR used to verify the integrity of the variants and their interaction with tetrapyrrole. The same molecular modelling studies identified a mobile loop Y171-R180 in p22HBP that decreased in mobility on tetrapyrrole binding, therefore to confirm this mobility change dynamics studies based on NMR relaxation experiments were carried out. Finally in order to obtain a non heme-binding form of human p22HBP a chimeric p22HBP was designed and constructed. This construct, and the resulting protein, will be important for future siRNA knockdown studies where rescue or recovery of function experiments are required to prove the knockdown results. Chapter one discusses the current state of the art in terms of the biological, structural and functional aspects of p22HBP. The main objectives of the Thesis are also introduced here. Chapter two presents a detailed description of the different expression vectors (pNJ2 and pet28-a) and procedures used for overexpression and purification of murine p22HBP and its variants and human p22HBP. All expression and purification systems used gave good yields and allowed isotopic labeling to be carried out. The fluorescence quenching results for tetrapyrrole binding to murine p22HBP and variants are presented in chapter three along with the dissociation constants that were found to be in the nanomolar range for wild type murine and human p22HBP. The same studies were performed for murine p22HBP variants, with hydrophobic and polar changes being introduced at R56, K64 and K177. The dissociation constants were found to double in some cases but no significant changes in the strength of hemin-protein interactions were observed. The tetrapyrrole interaction with p22HBP was also followed by NMR spectroscopy, where chemical shift mapping was used to identify binding pocket location. All the variants and wild type human p22HBP were found to bind at the same location. Chapter 4 contains the data from 2D and 3D experiments carried out on 15N/13C labelled human p22HBP that was used to obtain backbone assignments. Comparison with wild type murine p22HBP assignments, PPIX titrations and theoretical calculations based on chemical shifts (Talos+) allowed 82% of the backbone resonances to be assigned. The results from the relaxation experiments used to probe the dynamics of the mobile loop in p22HBP on binding to tetrapyrrole are presented in chapter 5. The overall protein was found to tumble isotropically in the free and bound forms however the results to probe mobility changes in the 171-180 loop on tetrapyrrole binding proved inconclusive as only residue could be assigned and this did not seem to become significantly less mobile. The final chapter describes the design and construction of a chimeric p22HBP. For these purpose, the alfa1-helix sequence of human p22HBP in the phHBP1 plasmid was replaced by its homologous sequence in hSOUL, a non heme-binding protein with identical 3D structure. The results however indicated that either the incorrect sequence was introduced into the plasmid or the purification procedure was inadequate.
O trabalho apresentado nesta Tese focou-se na dinâmica e nas interações moleculares da p22HBP e do complexo p22HBP-tetrapirrol, nomeadamente nos resíduos chave envolvidos nesta interação. Estudos prévios de modelação molecular identificaram três possíveis resíduos chave R56, K64 e K177 como sendo importantes na interação com os tetrapirróis, através de interações eletrostáticas com os grupos propionato do tetrapirrol. Foram desenhados e construídos variantes da p22HBP murina e foram desenvolvidos estudos de extinção de fluorescência e RMN para avaliar a integridade dos variantes e a sua interação com os tetrapirróis. Os mesmos estudos de modelação molecular identificaram ainda uma zona flexível (Y171-R180) na p22HBP que diminui a mobilidade com a interação do tetrapirrol. Para confirmar esta alteração de mobilidade, foram realizados estudos de dinâmica, baseados em RMN. Por fim, com o intuito de obter uma versão não funcional da p22HBP humana, foi planeada e construída uma versão quimérica da p22HBP humana. No futuro, esta nova versão da p22HBP quimérica, será importante para os estudos de knockdown envolvendo siRNA. O capítulo um introduz uma revisão dos aspetos biológicos da p22HBP nomeadamente os estudos estruturais e as possíveis funções que foram identificadas. Os principais objetivos da tese são também apresentados neste capítulo. No capítulo dois é apresentada uma descrição detalhada dos diferentes vectores de sobreexpressão (pNJ2 e pet28-a) e dos métodos de sobreexpressão e purificação da p22HBP murina e respectivos variantes, bem como da p22HBP humana. Todos os sistemas de sobreexpressão e purificação utilizados obtiveram bons rendimentos e permitiram a marcação isotópica das proteínas. No capítulo 3 são apresentados os resultados de extinção de fluorescência para a interação da p22HBP murina e humana com hemina através das constantes de dissociação determinadas na ordem dos nanomolar. Os mesmos estudos foram realizados para os variantes da p22HBP murina, com alterações hidrofóbicas e de polaridade nos resíduos R56, K64 e K177. Em alguns casos, as constantes de dissociação determinadas são mais elevadas, embora não se tenham verificado alterações significativas na força da interação proteína-hemo. As interações tetrapirrólicas com a p22HBP foram também estudadas por espectroscopia de RMN, onde foram mapeadas as diferenças nos desvios químicos para identificar a localização da zona de interação. A localização da zona de interação dos variantes da p22HBP e a p2HBP humana mantém-se igual à p22HBP murina. No capítulo 4 encontram-se os resultados das experiências 2D e 3D realizadas na p22HBP humana, isotopicamente marcada com 15N/13C, para identificar as ressonâncias da cadeia principal. 82% dos sistemas de spin da cadeia principal foram identificados através da comparação com a p22HBP murina, das titulações com PPIX e de cálculos teóricos baseados nos desvios químicos (Talos+). No capítulo 5 são apresentados os resultados das experiências de relaxação, usados para comprovarem a dinâmica do loop na p22HBP aquando da interação com o tetrapirrol. A proteína no seu todo move-se de uma forma isotrópica na forma livre e ligada. No entanto os resultados para comprovar as alterações de mobilidade no loop 171-180 na presença de hemo, foram inconclusivos uma vez que só a um resíduo foi atribuído um sistema de spin, e não foi indicativo da perda significativa de mobilidade. O último capítulo descreve o planeamento e a construção da p22HBP quimérica. Para tal, a sequência que codifica a hélix alfa 1 da p22HBP humana, no plasmídeo phHBP1, foi substituída pela sequência homóloga da SOUL humana, uma proteína com uma estrutura 3D semelhante mas não liga ao hemo. Os resultados no entanto demonstraram que ou a sequência não foi introduzida corretamente no plasmídeo ou o sistema de purificação não foi adequado.

Thesis (M. Sc.)--York University, 2001. Graduate Programme in Physics and Astronomy.
Typescript. Includes bibliographical references (leaves 119-126). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ66411.

碩士
國立清華大學
物理系
102
We have precisely measured the hyperfine intervals and isotope shift of D1 lines of atomic lithium 6,7Li in a collimated atomic beam. The spectroscopy laser, an external-cavity diode laser (ECDL) with wavelength 670.9 nm, which is locked to a Fabry-Perot cavity by Pound-Drever-Hall technique, scans the spectrums by changing the cavity length. The reference laser is locked to molecular iodine transition. The laser-induced fluorescence signal is detected by photomultiplier, and the beat frequency between spectroscopy laser and reference laser is recorded. The results of 6,7Li for 2S1/2 hyperfine interval are 228.198 (12) MHz and 803.495(8) MHz. For 2P1/2 hyperfine interval, they are 26.108(9) MHz and 91.873(5) MHz. The isotope shift is 10533.800(15) MHz. Our results resolve the discrepancies between former measurements, and are consistent with most theoretical calculations.

Resonant ionization laser ion sources are applied worldwide to increase purity and intensity of rare isotopes at radioactive ion beam facilities. Especially for heavy elements the laser wavelengths required for efficient resonant laser ionization are not only element dependent, but also vary to small degrees from isotope to isotope. Since the first operation of an actinide target at ISAC-TRIUMF in 2008, the demand for neutron-rich isotopes far away from stability has steadily increased. Those isotopes often have very low production rates so that often only a few ions per second are released. In order to study isotope shifts and hyperfine structure of silver, actinium and astatine, in-source resonant ionization spectroscopy in combination with radioactive decay detection has been applied. Despite the Doppler limited resolution, it has the advantage that it is ultra-sensitive and the atomic spectrum for the nuclear ground and isomeric states can be investigated individually. An isobaric separation has been demonstrated for 115-119Ag, where the hyperfine structure of one state showed a splitting of 22 GHz to 38 GHz while for the other state only a single peak spectrum can be resolved. For astatine and actinium, the main interest is to measure and study the optical isotope shift, which is for the first excitation step for neutron-rich isotopes in the order of IS_FES≈±3.7GHz/u for both elements, as these observables give insight into nuclear moments and shape. In addition, also the isotope shift of the second excitation step for astatine has been measured to IS_SES,At≈-1.7GHz/u. Laser spectroscopy on astatine has mainly been performed on the neutron-deficient isotopes 199,205At due to high count rates and low isobaric contamination. With the results obtained it is possible to extrapolate the required wavelength for ionizing and delivering the isotopes 221-225At which are of interest to e.g. electric dipole moment studies.
October 2017

Thesis (M.S.)--University of Wisconsin--Madison, 2003.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 37-44).

Hu Hong Bing.
"May 2004."
"13" in title is superscript.
Thesis (Ph.D.)--Chinese University of Hong Kong, 2004.
Includes bibliographical references.
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Mode of access: World Wide Web.
Abstracts in English and Chinese.

The green turtle, Chelonia mydas, is a circumglobal species that exhibits several important developmental or ontogenetic shifts throughout its life history. The first major shift occurs when juvenile turtles migrate from pelagic habitat, where they forage as omnivores, to coastal neritic habitat, where they become primarily herbivores, foraging on algae and seagrass. Anecdotal evidence and gut-content analyses suggest that juvenile green turtles in south Texas bays, such as the lower Laguna Madre and Aransas Bay, undergo an additional ontogenetic shift during this important life history stage. Evidence from stable isotope analysis (SIA) of scute tissues of green turtles from Texas' lower Laguna Madre and Aransas Bay supports an intermediate stage between this species' shift from pelagic waters to seagrass beds in neritic waters; this additional shift comprises an initial recruitment of post-pelagic juveniles to jetty habitat located on the channel passes Gulf-ward of adjacent bays before subsequently recruiting to seagrass beds in these bays. Examination of stable carbon ([delta]¹³C) and nitrogen ([delta]¹⁵N) isotopes in microlayers of scute tissue from several size classes of green turtles from the lower Laguna Madre and Aransas Bay was used to confirm the occurrence of two ontogenetic shifts. Smaller green turtles (< 35 cm SCL) exhibited more depleted [delta]¹³C signatures and more enriched [delta]¹⁵N signatures, consistent with jetty habitat, compared to those of larger counterparts (> 45 cm SCL) that displayed enriched [delta]¹³C signatures and depleted ¹⁵N signatures, consistent with seagrass habitat. Changes in the isotopic composition between these size classes indicate distinct shifts in diet. Post-pelagic juveniles first recruit to jetty habitat and forage primarily on algae, before subsequently shifting to seagrass beds and foraging primarily on seagrass. These findings indicate the use of a characteristic sequence of distinct habitats by multiple life history stages of green turtles in Texas bays, a conclusion with broad management implications for this endangered species.

Upwelling, atmospheric nitrogen (N2) fixation by cyanobacteria, and freshwater inputs from the Mississippi River system have been shown to stimulate new production by alleviating nitrogen (N) limitation in the northern Gulf of Mexico (GoM). Stable carbon (delta13C) and nitrogen (delta15N) isotopes were used to investigate whether these sources are utilized differentially by coastal and marine pelagic food webs. Particulate organic matter (POM), Trichodesmium, and zooplankton were collected from the Mississippi River plume and Loop Current (LC) which were detected using remote sensing data. Stable isotope values were used to separate coastal and marine water masses and environmental data (salinity, nutrient and pigment concentrations) allowed me to relate variability to the degree of freshwater influence. Published food web data from these two environments were then assessed to establish whether isotopic baseline shifts observed in our data occur at an ecosystem level. Isotope values of the POM and zooplankton were found to be significantly different between coastal and marine water masses. This was not the case for Trichodesmium whose isotope values were not significantly different between the two water masses. We found that marine water masses (sal > 35) exhibited silicate concentrations, cyanobacterial pigments and DIN: P that suggest an increased abundance of diazotrophs. In contrast, coastal water masses (sal < 35) exhibited increased diatom pigments and molar C:N indicating terrestrial sources fuel phytoplankton production. When published food web data were compared, we found producer and consumer delta15N values were enriched in the coastal compared to the marine environments. This work suggests that differences in delta15N values within my data set and published data reflect a shift in the use of biologically available N where higher trophic levels are sustained by diazotrophic activity in marine environments versus those supported by terrestrial sources in coastal ones. Food webs that have been constructed without considering Trichodesmium as a significant source of organic matter in the GoM should be reconsidered. By re-evaluating published data, this research gives insight into the early life ecology of larval fishes and works to help answer questions about the structure and function of pelagic food webs.

Effective population management of green sea turtles (Chelonia mydas) necessitates understanding the temporal variation in foraging grounds used in ontogenetic stages, and the effect that the assimilated diet within those habitats has on nutritional gain, growth and eventual reproductive output. Texas coastal waters provide foraging grounds critical to meeting the nutritional needs of green turtles during early life history. To characterize temporal shifts in foraging strategy stomach contents combined with stable carbon (delta13C) and nitrogen (delta15N) isotopes of scute tissue were examined across size classes of stranded juvenile green turtles from the middle and lower Texas coast during 2007-2010. Findings from dietary analysis generally corroborated those from stable isotopes in scute samples. Results indicate green sea turtles exhibit multiple shifts in diet and habitat along the Texas coast. Although isotope values in the tissues of some <25 cm SCL turtles signified recent recruitment to jetty habitat, most in this size class exhibited depleted delta13C and enriched delta15N values indicative of oceanic life. Reinforcing oceanic occupancy from stable isotope results was forage material dominated by oceanic items such as Sargassum spp., Scyphozoa spp., and plastic debris. Diet analysis of 25-34.9 cm SCL turtles implied regional differences existed in macroalgae and seagrass consumption. Enriched delta13C and delta15N values in newest scute suggest most turtles inhabited the jetty environment, where macroalgae is the most available forage. A definitive shift by >35 cm SCL turtles to inshore seagrass habitat was revealed by a diet of seagrasses and tissue enriched in delta13C and depleted in delta15N. This is the first study to integrate stomach contents of several green turtle size classes with tissue analysis of stable isotopes. The combination of these techniques provided an assessment of the effectiveness of stable isotope analyses in documenting diet and habitat shifts. Stomach content examination determined the most recent diet consumed within the habitat occupied, whereas stable isotope analysis provided a time-integrated synopsis of diet and habitat shifts. Findings indicate integration of stomach content and stable isotope analysis is highly effective for characterizing habitat use and foraging strategy of ontogenetic-stage green sea turtles.