Dissertations / Theses on the topic 'Neutral clusters'
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Bieske, Evan John, and n/a. "The Electronic Spectroscopy of Neutral and Ionic Clusters." Griffith University. School of Science, 1989. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20051109.112502.
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This thesis is concerned with weakly bound neutral and ionic clusters. Spectra of the region near the S1fS0 electronic origin of four neutral van der Waals molecules - aniline-argon, phenol-argon, chlorobenzene-argon and fluorobenzene-argon - were obtained using resonance enhanced multiphoton ionization (REMPI). These spectra indicate that Fermi resonances between van der Waals stretching and bending motions are important in these molecules. Effective Hamiltonians are constructed that describe well the low frequency vibrations. In order to better discuss the low frequency van der Waals motions of aromatics bound to one and two rare gas atoms a simple model for the vibrations is developed. The model enables expression of van der Waals frequencies in terms of fundamental molecular properties and enables facile comparison of effective force constants in a variety of van der Waals molecules. The model is successfully employed to explain van der Waals vibrational structure associated with the origin region of aniline-(argon)2 using van der Waals potential parameters derived from the aniline-(argon)1 spectrum. REMPI and emission spectra of larger clusters of aniline and argon are also reported and discussed. Using atom-atom potentials, equilibrium structures for aniline-(argon)n (n=l, 2, 3) are calculated. The calculations prove useful in the analysis of the spectra.The BfX transitions of the cation complexes fluorobenzene+-argon and chlorobenzene+-argon have been investigated. The cations were prepared by resonance enhanced multiphoton ionization of the neutral van der Waals molecules. A time delayed tunable dye laser was then used to dissociate the cations, loss of an argon atom being the dominant process. When the second laser was tuned to a cation resonance the dissociation cross section increased markedly, allowing characterization of BfX transition. The resulting spectra are presented and discussed.
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Bieske, Evan John. "The Electronic Spectroscopy of Neutral and Ionic Clusters." Thesis, Griffith University, 1989. http://hdl.handle.net/10072/367202.
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This thesis is concerned with weakly bound neutral and ionic clusters. Spectra of the region near the S1fS0 electronic origin of four neutral van der Waals molecules - aniline-argon, phenol-argon, chlorobenzene-argon and fluorobenzene-argon - were obtained using resonance enhanced multiphoton ionization (REMPI). These spectra indicate that Fermi resonances between van der Waals stretching and bending motions are important in these molecules. Effective Hamiltonians are constructed that describe well the low frequency vibrations. In order to better discuss the low frequency van der Waals motions of aromatics bound to one and two rare gas atoms a simple model for the vibrations is developed. The model enables expression of van der Waals frequencies in terms of fundamental molecular properties and enables facile comparison of effective force constants in a variety of van der Waals molecules. The model is successfully employed to explain van der Waals vibrational structure associated with the origin region of aniline-(argon)2 using van der Waals potential parameters derived from the aniline-(argon)1 spectrum. REMPI and emission spectra of larger clusters of aniline and argon are also reported and discussed. Using atom-atom potentials, equilibrium structures for aniline-(argon)n (n=l, 2, 3) are calculated. The calculations prove useful in the analysis of the spectra.The BfX transitions of the cation complexes fluorobenzene+-argon and chlorobenzene+-argon have been investigated. The cations were prepared by resonance enhanced multiphoton ionization of the neutral van der Waals molecules. A time delayed tunable dye laser was then used to dissociate the cations, loss of an argon atom being the dominant process. When the second laser was tuned to a cation resonance the dissociation cross section increased markedly, allowing characterization of BfX transition. The resulting spectra are presented and discussed.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Science
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Cui, Zhen. "Mechanistic studies of neutral and synthetic metallo-sulfur clusters." Thesis, University of East Anglia, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251443.
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Pedersen, David B. "The reactivity of gas-phase neutral transition-metal clusters, reactions of W clusters with cyclopropane and Ta clusters with alkanes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape7/PQDD_0007/NQ38324.pdf.
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Falconer, Travis M. Glish Gary L. "Ion capture in helium droplets formation of cold ion-neutral clusters /." Chapel Hill, N.C. : University of North Carolina at Chapel Hill, 2008. http://dc.lib.unc.edu/u?/etd,1949.
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Thesis (Ph. D.)--University of North Carolina at Chapel Hill, 2008.Title from electronic title page (viewed Dec. 11, 2008). "... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Chemistry." Discipline: Chemistry; Department/School: Chemistry.
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Bergersen, Henrik. "Free Neutral Clusters and Liquids Studied by Electron Spectroscopy and Lineshape Modeling." Doctoral thesis, Uppsala University, Department of Physics and Materials Science, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8652.
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The electronic and geometrical structure of free neutral clusters and liquids have been studied using synchrotron-radiation based photoelectron and Auger electron spectroscopy in combination with lineshape modeling. A novel experimental setup has been developed for studies of liquids, based on the liquid microjet technique. Theoretical lineshapes have been computed using both classical (molecular dynamics) and quantum mechanical (mainly density functional theory) methods.
Clusters are finite ensembles of atoms or molecules, ranging in size from a few to several thousand atoms. Apart from being fundamentally interesting, clusters are also promising as building blocks for nano-technology. In this thesis results are presented for rare-gas and molecular clusters, ranging from weakly van-deer-Waals bonded to hydrogen bonded. It is shown that the combination of core-level photoelectron spectroscopy (XPS) and lineshape modeling can be used to estimate the sizes of clusters. A model for treating the effect of inter-molecular nuclear relaxation upon ionization is proposed. The structure of single-component molecular clusters are investigated by molecular dynamics simulations, validated against XPS data. Finally, the radial structure of a two-component molecular cluster is investigated by XPS.
Liquids have been studied for centuries, but still many questions remain regarding the microscopic properties. With the recent development of the liquid microjet technique, new insight into the atomic structure can be obtained. In this thesis we study aqueous solutions using photoelectron and Auger electron spectroscopy (AES). We investigate the structure of surface active molecules by XPS, study the Auger decay after core-level ionization in aqueous potassium chloride (KCl), and follow the changes in molecular structure of glycine as a function of pH.
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Nagaya, Kiyonobu. "EXAFS-PEPICO Synchronous Measurements for the Size-Selective Structure Analysis of Neutral Free Clusters." 京都大学 (Kyoto University), 2003. http://hdl.handle.net/2433/148358.
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Kaur, Baljeet. "Theoretical Investigation of the structures and stability of gas phase neutral and cationic TixOy clusters." VCU Scholars Compass, 2010. http://scholarscompass.vcu.edu/etd/83.
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Theoretical investigation of the structure and stability of neutral and cationic TixOy cluster series (where y =2x-1, 2x, 2x+1) have been performed. The lowest lying structures for the neutral clusters are usually found in the singlet state. Generally, in bulk and in the case of the neutral TixOy clusters, the 2x cluster series is relatively more abundant than the 2x-1 and the 2x+1 cluster series. But in the case of cationic TixOy clusters, the 2x-1 series is more abundant. To understand the origin of the stability of the TixO2x-1+ clusters, we use density functional theory within the NRLMOL set of codes. Different analyzing factors such as ionization potential, TiO2 removal energy, oxygen removal energy, binding energy per atom and HOMO-LUMO gap have been used to examine the relative stability of TixO2x-1+ clusters. After analyzing the above criteria, we find that the ionization potential and HOMO-LUMO gap are more reliable, as the low ionization potential of the 2x-1 series generally implies low HOMO-LUMO gap and suggests that the 2x-1 cluster series more likely prefer to remain as cations. To further confirm this, we examine the density of states of Ti3O5 and Ti3O6 which show a larger HOMO- HOMO-1 gap in case of Ti3O5, indicating that the cluster would like to lose an electron for enhancing electronic stability.
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Vidal-García, A., S. Charlot, G. Bruzual, and I. Hubeny. "Modelling ultraviolet-line diagnostics of stars, the ionized and the neutral interstellar medium in star-forming galaxies." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/625298.
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We combine state-of-the-art models for the production of stellar radiation and its transfer through the interstellar medium (ISM) to investigate ultraviolet-line diagnostics of stars, the ionized and the neutral ISM in star-forming galaxies. We start by assessing the reliability of our stellar population synthesis modelling by fitting absorption-line indices in the ISM-free ultraviolet spectra of 10 Large Magellanic Cloud clusters. In doing so, we find that neglecting stochastic sampling of the stellar initial mass function in these young (similar to 10-100 Myr), low-mass clusters affects negligibly ultraviolet-based age and metallicity estimates but can lead to significant overestimates of stellar mass. Then, we proceed and develop a simple approach, based on an idealized description of the main features of the ISM, to compute in a physically consistent way the combined influence of nebular emission and interstellar absorption on ultraviolet spectra of star-forming galaxies. Our model accounts for the transfer of radiation through the ionized interiors and outer neutral envelopes of short-lived stellar birth clouds, as well as for radiative transfer through a diffuse intercloud medium. We use this approach to explore the entangled signatures of stars, the ionized and the neutral ISM in ultraviolet spectra of star-forming galaxies. We find that, aside from a few notable exceptions, most standard ultraviolet indices defined in the spectra of ISM-free stellar populations are prone to significant contamination by the ISM, which increases with metallicity. We also identify several nebular-emission and interstellar-absorption features, which stand out as particularly clean tracers of the different phases of the ISM.
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Al-Mubarak, Ala'a Sami Khalaf. "IR laser induced photodissociation of neutral cluster." Thesis, University of Sussex, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.682732.
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Begin, Steve. "A search for fast pulsars in globular clusters." Thesis, Link to full text, 2006. http://hdl.handle.net/2429/69.
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Sowrey, Frank Edward. "Electronic and magnetic coupling in triangular metal clusters." Thesis, University of East Anglia, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338298.
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Teyssier, Cécile. "Spectrométrie de masse COINTOF : Conception et d'un analyseur à temps de vol et développement de la méthode d'analyse." Phd thesis, Université Claude Bernard - Lyon I, 2012. http://tel.archives-ouvertes.fr/tel-00744850.
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Le Dispositif d'Irradiation d'Agrégats Moléculaires (DIAM) est conçu pour l'étude de mécanismes de dissociation résultant de l'interaction de nanosystèmes moléculaires avec des protons de 20-150 keV. Une technique originale de spectrométrie de masse appelée COINTOF (Correlated Ion and Neutral Time Of Flight) permet la mesure corrélée du temps de vol des fragments neutres et chargés issus de la dissociation d'un système moléculaire sélectionné en masse. Une stratégie de traitement des signaux a été développée afin de pouvoir distinguer des fragments proches en temps (< 1ns). Les données collectées sont structurées dans le logiciel ROOT® pour l'analyse statistique des corrélations. Le fonctionnement de la technique COINTOF est illustré par des expériences de dissociation induite par collision d'agrégats d'eau protonés sur une cible gazeuse. La méthodologie d'analyse des données est exposée à travers l'étude du canal de dissociation du trimère d'eau protoné produisant l'ion chargé H3O+ et deux molécules d'eau. La distribution de la différence de temps de vol entre les deux fragments neutres est mesurée, mettant en évidence une énergie libérée de quelques eV. En parallèle, un second spectromètre de masse à temps de vol adapté à l'évolution du dispositif a été développé. Il associe un temps de vol linéaire et un temps de vol orthogonal et intègre un détecteur à position (ligne à retard). Des simulations ont démontré les potentialités du nouvel analyseur. Enfin, des travaux ont été menés au laboratoire R.-J. A. Lévesque (Université de Montréal) portant sur les capacités d'imagerie de détecteurs à position multi-pixel de la collaboration MPX-ATLAS.
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Smith, J. A. "A new perspective on the photodissociation of rare gas cluster ions : the detection of neutral fragments." Thesis, University of Sussex, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358250.
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Fahlquist, Henrik. "Transition Metal Hydride Complexes and Hydrogenated Gallium Clusters : Synthesis and Structural Properties." Doctoral thesis, Stockholms universitet, Institutionen för material- och miljökemi (MMK), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-89760.
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Synthesis and structural characterisation of metal hydrides in two important systems are presented. The first system presented is low valent cobalt and nickel complex hydrides with the compositions BaMg5Co2H10, RbMg5CoNiH10, SrMg2CoH7and Sr4Mg4Co3H19 featuring nickel with oxidation state of 0 and cobalt with oxidation state +I and -I. The second system presented is polyanionic gallium complex hydrides with the compositions RbGaH2, RbxK(1−x)GaH2 (0.5≤x≤1), CsxRb(8−x)Ga5H15 (0≤x≤8) and Cs10Ga9H25 featuring novel hydrogenous polyanionic gallium hydride clusters mimicking common hydrocarbons. The syntheses of the compounds were performed at elevated temperatures and at moderate hydrogen pressures (50-100 bar). The structural investigations were mainly done by X-ray powder diffraction (XRPD) and neutron powder diffraction (NPD). The metal-hydrogen bond was investigated by vibrational spectroscopy using Fourier Transform IR-spectroscopy (FTIR) and Inelastic Neutron Scattering (INS).By subtle changes in the compositions of the hydrides it was possible to induce major changes in band gaps, oxidation states and structures.At the time for the doctoral defence the following papers were unpublished and had a status as follows: Paper 1: Manuscript; Paper 2: Accepted; Paper 5: Manuscript
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Bircher, Roland. "Studies of single-molecule magnets and spin clusters by inelastic neutron scattering and magnetic measurements /." Bern : [s.l.], 2005. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.
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Siglow, Klaus. "Hochauflösende UV-Spektroskopie von neutralen und ionischen Molekülen und Clustern Rydbergzustände und Starkeffekt /." [S.l. : s.n.], 2000. http://deposit.ddb.de/cgi-bin/dokserv?idn=962036382.
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Kobayashi, Fumiharu. "Systematic investigation of dineutron correlation in light neutron-rich nuclei." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188479.
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Dunn, Aaron Yehudah. "Radiation damage accumulation and associated mechanical hardening in thin films and bulk materials." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/54959.
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The overall purpose of this dissertation is to develop a multi-scale framework that can simulate radiation defect accumulation across a broad range of time and length scales in metals.
In order to accurately describe defect accumulation in heterogeneous microstructures and under complex irradiation conditions, simulation methods are needed that can explicitly account for the effect of non-homogeneous microstructures on damage accumulation. In this dissertation, an advanced simulation tool called spatially resolved stochastic cluster dynamics (SRSCD) is developed for this purpose. The proposed approach relies on solving spatially resolved coupled rate equations of standard cluster dynamics methods in a kinetic Monte Carlo scheme. Large-scale simulations of radiation damage in polycrystalline materials are enabled through several improvements made to this method, including a pseudo-adaptive meshing scheme for cascade implantation and implementation of this method in a synchronous parallel kinetic Monte Carlo framework. The performance of the SRSCD framework developed in this dissertation is assessed by comparison to other simulation methods such as cluster dynamics and object kinetic Monte Carlo and experimental results including helium desorption from thin films and defect accumulation in neutron-irradiated bulk iron. The computational scaling of the parallel framework is also investigated for several test cases of irradiation conditions. SRSCD is next used to investigate radiation damage in three main types of microstructures, using α-iron as a test material: iron thin films, coarse-grained bulk iron, and nanocrystalline iron. SRSCD is used to investigate the mechanisms involved with defect accumulation in irradiated materials, such as effective diffusivity of helium in thin films and the effect of grain boundary sink strength on defect accumulation in nano-grained metals, and to predict defect populations in irradiated materials for comparison with experiments. Particular emphasis is placed on the role of microstructural features such as free surfaces and grain boundaries in influencing damage accumulation. Finally, the methodology developed in this dissertation is applied in the context of multiscale modeling and experimental design. To complete the multi-scale transition between defect-level behavior and macroscopic material property changes caused by irradiation, the relationship between mechanical loading and radiation damage is investigated. The impact of radiation damage on hardening of irradiated materials is investigated by using the results of SRSCD as inputs into polycrystalline crystal plasticity simulations. This is carried out in bulk iron by fitting hardening models to experimental data from neutron irradiation of iron and then used to predict hardening under irradiation conditions beyond what has already been accomplished in experimental studies. In addition, SRSCD is used to demonstrate the temperature shift required to achieve equivalent damage accumulation in irradiation conditions with significantly differing dose rates, such as in the case of using ion irradiation to simulate damage from neutron irradiation. In this dissertation, the development of SRSCD and its application in a multi-scale framework to predict macroscopic material property changes in metals represents a significant improvement over the state of the art due to improved simulations of defect accumulation and direct upscaling of results into polycrystalline plasticity models. The tools and understanding of defect behavior developed here will allow predictive modeling of metal degradation in reactor-relevant damage environments, including the defected microstructure and macroscopic material property changes due to irradiation.
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Morita, Hiroyuki. "Gamow-Teller transitions in the light N = Z odd-odd nuclei:Proton-neutron correlation and SU(4) symmetry with clusters." Kyoto University, 2019. http://hdl.handle.net/2433/242608.
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Martinet, Guillaume. "Fragmentation d'agrégats de carbone neutres formés par collision atomique à haute vitesse." Phd thesis, Université Paris Sud - Paris XI, 2004. http://tel.archives-ouvertes.fr/tel-00008105.
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Bogdanov, Slavko, Craig O. Heinke, Feryal Özel, and Tolga Güver. "NEUTRON STAR MASS–RADIUS CONSTRAINTS OF THE QUIESCENT LOW-MASS X-RAY BINARIES X7 AND X5 IN THE GLOBULAR CLUSTER 47 TUC." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622762.
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We present Chandra/ACIS-S subarray observations of the quiescent neutron star (NS) low-mass X-ray binaries X7 and X5 in the globular cluster 47 Tuc. The large reduction in photon pile-up compared to previous deep exposures enables a substantial improvement in the spectroscopic determination of the NS radius and mass of these NSs. Modeling the thermal emission from the NS surface with a non-magnetized hydrogen atmosphere and accounting for numerous sources of uncertainties, we obtain for the NS in X7 a radius of R = 11.1(-0.7)(+0.8) km for an assumed stellar mass of M = 1.4 M-circle dot (68% confidence level). We argue, based on astrophysical grounds, that the presence of a He atmosphere is unlikely for this source. Due to the excision of data affected by eclipses and variable absorption, the quiescent low-mass X-ray binary X5 provides less stringent constraints, leading to a radius of R = 9.6(-1.1)(+0.9) km, assuming a hydrogen atmosphere and a mass of M. =. 1.4 Me. When combined with all existing spectroscopic radius measurements from other quiescent low-mass X-ray binaries and Type I X-ray bursts, these measurements strongly favor radii in the 9.9-11.2 km range for a similar to 1.5 M-circle dot NS and point to a dense matter equation of state that is somewhat softer than the nucleonic ones that are consistent with laboratory experiments at low densities.
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Do-Thi, Nga. "Etude théorique de la fragmentation des petits agrégats neutres de carbone Cn et des hydrocarbures CnH." Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00651020.
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Ce travail de thèse porte sur l'étude théorique de la fragmentation de petits agrégats carbonés et d'hydrocarbures neutres par le modèle statistique Micarocanonical Metropolis Monte Carlo (MMMC). Ce modèle décrit, à contrainte d'énergie fixée, l'espace des phases associé à tous les degrés de liberté accessibles au système (partitions des masses, mouvements de translation et de rotation, spin et moment angulaire des fragments, etc.). Les ingrédients de base du modèle (énergies de dissociation, géométries, fréquences de vibration etc.) doivent être obtenus par un calcul ab initio. Ils ont été calculés à l'aide de la théorie de la fonctionnelle de la densité (DFT) au niveau de calcul B3LYP/6-311+G(3df). Les probabilités obtenues des voies de fragmentation en fonction de l'énergie d'excitation, ont été comparées aux données expérimentales obtenues auprès du Tandem. Des faisceaux de haute vitesse (projectile de Cn+ à v = 2.6 u.a. et de CnH+ à v = 4.5 u.a.) entraient en interaction avec les noyaux d'hélium. Tous les rapports de branchement des voies de fragmentation des Cn (n ≤ 9) et des CnH (n ≤ 4) résultant de capture électroniques ont été mesurés. La distribution d'énergie d'excitation de l'agrégat parent a du être ajustée pour que les mesures expérimentales soient reproduites d'une façon optimale, à l'aide de deux algorithmes : Non-Negative Least Squares et backtracing Bayesien. La comparaison des probabilités théoriques et expérimentales montre un bon accord global. Les deux algorithmes de minimisation ont convergé vers des distributions d'énergie déposée présentant des pics. Ces pics pourraient être la signature d'états moléculaires spécifiques jouant un rôle dans la fragmentation du cluster.
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Buridon, Victor. "Application de la spectrométrie de masse COINTOF à l'étude de la dissociation de petits agrégats d'eau protonés par collision sur un atome d'argon : développement d'une cible de nano-gouttes de gaz rare." Phd thesis, Université Claude Bernard - Lyon I, 2013. http://tel.archives-ouvertes.fr/tel-00994146.
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L'étude de l'irradiation dans le système moléculaire à l'échelle du nanomètre est un domaine d'investigation innovant des sciences des radiations. Le Dispositif d'Irradiation d'Agrégats Moléculaires (DIAM) est conçu en vue les conséquences de l'irradiation dans des petits systèmes moléculaires modèles comme les agrégats d'eau protonés. L'irradiation provoque la fragmentation en plusieurs fragments neutres ou chargés. La technique de spectrométrie de masse COINTOF (Correlated Ion and Neutral Time of Flight) permet la détection corrélées des fragments neutres et chargés issus de la dissociation d'un système moléculaire préalablement sélectionné en masse et en vitesse. Les données collectées sont traitées et structurées pour permettre l'analyse statistique des corrélations sur un grand nombre d'événements de fragmentation. Parallèlement à l'identification des canaux de fragmentation, la technique COINTOF permet la mesure de leur rapport de branchement et de leur section efficace. La méthode est présentée pour la dissociation induite par collision sur un atome d'argon, d'agrégats d'eau protonés H+(H2O)n:[2;7], accélérés à 8keV. L'efficacité de détection, information déterminante pour la production de données quantitatives, est mesurée à partir des données et étudiée en fonction de la distribution l'amplitude des signaux de détection. Enfin, un nouveau système de cible constituée de nanogouttes de gaz rares a été développé
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Nadel-Turonski, Pawel. "Experimental Studies of Neutron Emission Induced by Heavy-Ion Scattering." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3570.
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Bernigaud, Virgile. "Etude de la fragmentation de molécules d'intérêt biologique isolées et nano-solvatées induite par collision avec des ions multichargés et des particules neutres." Caen, 2009. http://www.theses.fr/2009CAEN2078.
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Cette thèse est une étude de la fragmentation en phase gazeuse de molécules d’intérêt biologique soumises à des collisions avec des ions multichargés de basse énergie (énergie cinétique de quelques keV) et des atomes alcalins ou de gaz rare. L’objectif est d’étudier les processus physique qui conduisent à la dissociation de ces systèmes soumis à une excitation électronique intense. Afin de mettre en évidence les propriétés intrinsèques de certaines biomolécules (porphyrines et acides aminés), des expériences sur des systèmes isolés ont été effectuées. Les résultats obtenus rendent compte de la grande stabilité des porphyrines lors de l’arrachement ou de l’attachement d’électrons. La dépendance des voies de fragmentation induite par les ions multichargés en fonction de l’isomérie de l’alanine a été démontrée. Dans un second temps, la prise en compte d’un environnement modèle autour des biomolécules à mis en évidence l’apparition ou la modification des voies de dissociation provoquée par la présence d’autres molécules biologiques (agrégats de bases nucléiques) ou de molécules de solvant (eau, méthanol, acétonitrile) autour de la biomolécule étudiée. Enfin dans le but de poursuivre ces études avec des systèmes de plus grande taille, un nouveau dispositif expérimental, développé durant la thèse et basé sur une source electrospray et un quadripôle de sélection en masse, est présenté. Les tests réalisés avec ce dispositif et les améliorations proposées permettent d’envisager, à l’avenir, des études sur la dynamique de fragmentation de grands systèmes biomoléculaires chargés et hydratés provoquée par des ions multichargés de basse énergieThis thesis concerns a gas phase study of the fragmentation of biomolecular systems induced by slow collisions with multiply charged ions (in the keV-region), alkali atoms and rare gases. The main objective was to study the physical processes involved in the dissociation of highly electronically excited systems. In order to elucidate the intrinsic properties of certain biomolecules (porphyrins and amino acids) we have performed experiments in the gas phase with isolated systems. The obtained results demonstrate the high stability of porphyrins after electron removal and attachment. Furthermore, a dependence of the fragmentation pattern produced by multiply charged ions on the isomeric structure of the alanine molecule has been shown. In a second part of the thesis, a strong influence of the environment of the biomolecule on the fragmentation channels, their modification and their new opening, has been clearly proven. This phenomenon occurs in the presence of other surrounding biomolecules (clusters of nucleobases) as well as for molecules of a solvent (molecules of water, methanol and acetonitrile) in which the biomolecule is embedded. In order to extend these studies to larger systems, a new experimental set-up, based on an electro-spray ion source combined with a quadrupole mass filter has been developed. Due to the successful tests and proposed improvements of the device future experiments will become available concerning the fragmentation of large charged and solvated biomolecular systems induced by collision processes
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Gebretsadik, Adane Samuel Gebretsadik. "INTERPLAY BETWEEN CHEMICAL AND MAGNETIC DISORDER IN SELECTED ALLOYS CLOSE TO A FERROMAGNETIC QUANTUM PHASE TRANSITION." Kent State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=kent1527609152939816.
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Silva, Francisco Wilton de Freitas. "DFA e an?lise de agrupamento aplicadas a perfis de porosidade neutr?nico em po?os de petr?leo." Universidade Federal do Rio Grande do Norte, 2009. http://repositorio.ufrn.br:8080/jspui/handle/123456789/18534.
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Previous issue date: 2009-05-22?Peng was the first to work with the Technical DFA (Detrended Fluctuation Analysis), a tool capable of detecting auto-long-range correlation in time series with non-stationary. In this study, the technique of DFA is used to obtain the Hurst exponent (H) profile of the electric neutron porosity of the 52 oil wells in Namorado Field, located in the Campos Basin -Brazil. The purpose is to know if the Hurst exponent can be used to characterize spatial distribution of wells. Thus, we verify that the wells that have close values of H are spatially close together. In this work we used the method of hierarchical clustering and non-hierarchical clustering method (the k-mean method). Then compare the two methods to see which of the two provides the best result. From this, was the parameter ? (index neighborhood) which checks whether a data set generated by the k- average method, or at random, so in fact spatial patterns. High values of ? indicate that the data are aggregated, while low values of ? indicate that the data are scattered (no spatial correlation). Using the Monte Carlo method showed that combined data show a random distribution of ? below the empirical value. So the empirical evidence of H obtained from 52 wells are grouped geographically. By passing the data of standard curves with the results obtained by the k-mean, confirming that it is effective to correlate well in spatial distribution
Peng foi o primeiro a trabalhar com a T?cnica DFA (Detrended Fluctuation Analysis), uma ferramenta capaz de detectar auto-correla??o de longo alcance em s?ries temporais com n?o-estacionaridade. Nesse trabalho, a t?cnica de DFA ? utilizada para obter o expoente de Hurst (H) do perfil el?trico de Porosidade Neutr?nica dos 52 po?os petrol?feros Campo de Namorado, situado na Bacia de Campos ? RJ. A finalidade ? saber se o expoente de Hurst pode ou n?o ser usado para se caracterizar uma distribui??o espacial dos po?os. Assim, queremos verificar se os po?os que apresentam valores pr?ximos de H est?o espacialmente pr?ximos entre si. Neste trabalho foi utilizado o m?todo de agrupamento hier?rquico e o m?todo de agrupamento n?o hier?rquico (m?todo do k-m?dia). Em seguida comparamos os dois m?todos para ver qual dos dois fornece o melhor resultado. A partir disso, foi criado o par?metro (?ndice de vizinhan?a) o qual verifica se um conjunto de dados gerados pelo m?todo km?dia, ou de forma aleat?ria, forma de fato padr?es espaciais. Altos valores de indicam que os dados est?o agregados, enquanto que baixos valores de indicam que os dados est?o espalhados (sem correla??o espacial). Com aux?lio do m?todo de Monte Carlo observou-se que dados agrupados aleatoriamente apresentam uma distribui??o de inferior ao valor emp?rico. Portanto os dados emp?ricos de H obtidos dos 52 po?os est?o agrupados espacialmente. Ao cruzar os dados das curvas de n?vel com os resultados obtidos pelo k-m?dia, confirmam que este ? eficaz para correlacionar po?os em distribui??o espacial
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Ganchenkova, Maria, Vladimir A. Borodin, Andreas Ulbricht, Jürgen Böhmert, Roman Voskoboinikov, and Eberhard Altstadt. "Mikrostrukurelle Mechanismen der Strahlenversprödung." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-28422.
Full textAbstract:
Gegenstand des Vorhabens im Rahmen der WTZ mit Russland ist die Versprödung des Reaktordruckbehälters infolge der Strahlenbelastung mit schnellen Neutronen im kernnahen Bereich. Um den Einfluss von bestrahlungsinduzierten Gitterdefekten auf die mechanischen Eigenschaften zu ermitteln, wurden analytische Berechnungen zum Einfluss von Hindernissen auf die Beweglichkeit von Versetzungen und damit auf die Ausbildung einer plastischen Zone an der Rissspitze durchgeführt. Es wird demonstriert, dass sich die an der Rissspitze entstehenden Versetzungen an dem Hindernis (bestrahlungsinduzierte Punktdefekte) aufstauen. In Abhängigkeit der Rissbelastung KI und der Entfernung des Hindernisses von der Rissspitze werden die Versetzungsdichte und das durch den Versetzungsstau verursachte Spannungsfeld berechnet. Mit Hilfe von Experimenten zur Neutronenkleinwinkelstreuung (SANS - small angle neutron scattering) an verschiedenen WWER-Stählen und Modelllegierungen wurden Größenverteilungen und die Volumenanteile der strahleninduzierten Defekte für verschiedene Bestrahlungszustände (Fluenzen, Bestrahlungstemperaturen) ermittelt. Es wurde gezeigt, dass sich die strahleninduzierte Werkstoffschädigung durch Wärmebehandlung weitgehend wieder ausheilen lässt. Nach der thermischen Ausheilung ist der Werkstoff bei erneuter Bestrahlung weniger anfällig für strahleninduzierte Defekte. Die Ergebnisse der SANS-Untersuchungen wurden mit der Änderung der mechanischen Eigenschaften (Härte, Streckgrenze und Sprödbruchübergangstemperatur) korreliert. Mit der kinetischen Gitter-Monte-Carlo-Methode wurden numerische Sensitivitätsstudien zum Einfluss des Cu-Gehalts auf die Stabilität von Defekt-Clustern durchgeführt. Die Berechnungen zeigen, dass die Anwesenheit von Cu-Atomen zur Bildung von langlebigen Defekten führt. Dabei werden Leerstellen in Cu/Leerstellen-Cluster eingefangen. Leerstellen in reinem Eisen sind bei Bestrahlungstemperaturen von 270 °C dagegen nicht stabil, die Lebensdauer liegt zwischen 0.01 s und 1 s. Die kritische Cu-Konzentration, ab welcher stabile Defekte entstehen, beträgt ca. 0.1 Masseprozent.
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Ganchenkova, Maria, Vladimir A. Borodin, Andreas Ulbricht, Jürgen Böhmert, Roman Voskoboinikov, and Eberhard Altstadt. "Mikrostrukurelle Mechanismen der Strahlenversprödung." Forschungszentrum Rossendorf, 2006. https://hzdr.qucosa.de/id/qucosa%3A21669.
Full textAbstract:
Gegenstand des Vorhabens im Rahmen der WTZ mit Russland ist die Versprödung des Reaktordruckbehälters infolge der Strahlenbelastung mit schnellen Neutronen im kernnahen Bereich. Um den Einfluss von bestrahlungsinduzierten Gitterdefekten auf die mechanischen Eigenschaften zu ermitteln, wurden analytische Berechnungen zum Einfluss von Hindernissen auf die Beweglichkeit von Versetzungen und damit auf die Ausbildung einer plastischen Zone an der Rissspitze durchgeführt. Es wird demonstriert, dass sich die an der Rissspitze entstehenden Versetzungen an dem Hindernis (bestrahlungsinduzierte Punktdefekte) aufstauen. In Abhängigkeit der Rissbelastung KI und der Entfernung des Hindernisses von der Rissspitze werden die Versetzungsdichte und das durch den Versetzungsstau verursachte Spannungsfeld berechnet. Mit Hilfe von Experimenten zur Neutronenkleinwinkelstreuung (SANS - small angle neutron scattering) an verschiedenen WWER-Stählen und Modelllegierungen wurden Größenverteilungen und die Volumenanteile der strahleninduzierten Defekte für verschiedene Bestrahlungszustände (Fluenzen, Bestrahlungstemperaturen) ermittelt. Es wurde gezeigt, dass sich die strahleninduzierte Werkstoffschädigung durch Wärmebehandlung weitgehend wieder ausheilen lässt. Nach der thermischen Ausheilung ist der Werkstoff bei erneuter Bestrahlung weniger anfällig für strahleninduzierte Defekte. Die Ergebnisse der SANS-Untersuchungen wurden mit der Änderung der mechanischen Eigenschaften (Härte, Streckgrenze und Sprödbruchübergangstemperatur) korreliert. Mit der kinetischen Gitter-Monte-Carlo-Methode wurden numerische Sensitivitätsstudien zum Einfluss des Cu-Gehalts auf die Stabilität von Defekt-Clustern durchgeführt. Die Berechnungen zeigen, dass die Anwesenheit von Cu-Atomen zur Bildung von langlebigen Defekten führt. Dabei werden Leerstellen in Cu/Leerstellen-Cluster eingefangen. Leerstellen in reinem Eisen sind bei Bestrahlungstemperaturen von 270 °C dagegen nicht stabil, die Lebensdauer liegt zwischen 0.01 s und 1 s. Die kritische Cu-Konzentration, ab welcher stabile Defekte entstehen, beträgt ca. 0.1 Masseprozent.
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Bernigaud, Virgile. "Étude de la fragmentation de molécules d'intérêt biologique isolées et nano-solvatées induite par collision avec des ions multichargés et des particules neutres." Phd thesis, Université de Caen, 2009. http://tel.archives-ouvertes.fr/tel-00461627.
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Cette thèse est une étude de la fragmentation en phase gazeuse de molécules d'intérêt biologique soumises à des collisions avec des ions multichargés de basse énergie (énergie cinétique de quelques keV) et des atomes alcalins ou de gaz rare. L'objectif est d'étudier les processus physique qui conduisent à la dissociation de ces systèmes soumis à une excitation électronique intense. Afin de mettre en évidence lespropriétés intrinsèques de certaines biomolécules (porphyrines et acides aminés), des expériences sur des systèmes isolés ont été effectuées. Les résultats obtenus rendent compte de la grande stabilité des porphyrines lors de l'arrachement ou de l'attachement d'électrons. La dépendance des voies de fragmentation induite par les ions multichargés en fonction de l'isomérie de l'alanine a été démontrée. Dans un second temps, la prise en compte d'un environnement modèle autour des biomolécules à mis en évidence l'apparition ou la modification des voies de dissociation provoquée par la présence d'autres molécules biologiques (agrégats de bases nucléiques) ou de molécules de solvant (eau, méthanol, acétonitrile) autour de la biomolécule étudiée. Enfin dans le but de poursuivre ces études avec des systèmes de plus grande taille, un nouveau dispositif expérimental, développé durant la thèse et basé sur une source electrospray et un quadripôle de sélection en masse, est présenté. Les tests réalisés avec ce dispositif et les améliorations proposées permettent d'envisager, à l'avenir, des études sur la dynamique de fragmentation de grands systèmes biomoléculaires chargés et hydratés provoquée par des ions multichargés de basse énergie.
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Chandezon, Frédéric. "Étude expérimentale de la stabilité d'agrégats de sodium multichargés produits par collision d'agrégats neutres avec des ions." Université Joseph Fourier (Grenoble ; 1971-2015), 1994. http://www.theses.fr/1994GRE10201.
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Le but de cette these est d'etudier la stabilite d'un agregat de sodium vis-a-vis d'un exces de charge positive. Dans un premier temps, nous avons procede a la construction de l'experience. La source utilisee pour la formation des agregats est du type thermalisation gazeuse. Avec cette source, nous avons obtenu des agregats froids de quelques atomes jusqu'a environ un millier. Le spectrometre de masse a temps de vol construit pour l'experience utilise un systeme d'acceleration a deux etages type wiley-mclaren, mais avec une focalisation amelioree. Une resolution en masse superieure a 2000 est obtenue vers la masse 1100 uma, et les agregats de sodium monocharges ayant jusqu'a 700 atomes peuvent etre separes. Dans un deuxieme temps, nous avons etudie la production et la stabilite d'agregats de sodium multicharges. L'ionisation sequentielle d'agregats neutres par une impulsion laser permet d'obtenir des agregats multicharges chauds, c'est-a-dire evaporant des atomes. La charge maximale des agregats est limitee par l'energie des photons. L'interaction d'agregats neutres avec des ions montre la coexistence de deux processus d'ionisation: la capture a distance d'electrons par le champ coulombien de l'ion et l'emission statistique d'electrons suite a l'excitation electronique de l'agregat quand un ion le traverse. Lorsque la charge de l'ion augmente, le premier processus devient predominant. Ceci implique une diminution de la temperature des agregats multicharges obtenus qui se traduit experimentalement par une diminution de la taille critique. En conclusion, l'interaction d'agregats neutres avec des ions permet de produire des agregats multicharges, de charge, de taille et de temperature variables. Elle apparait comme une methode de choix pour l'etude de la fragmentation lorsque ces edifices sont instables
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Harman-Clarke, Adam. "Contraintes Topologiques et Ordre dans les Systèmes Modèle pour le Magnétisme Frustré." Thesis, Lyon, École normale supérieure, 2011. http://www.theses.fr/2011ENSL0659.
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Dans cette thèse, l’étude de plusieurs modèles de systèmes magnétiques frustrés a été couverte. Leur racine commune est le modèle de la glace de spin, qui se transforme en modèle de la glace sur réseau kagome (kagome ice) et réseau en damier (square ice) à deux dimensions, et la chaîne d’Ising à une dimension. Ces modèles ont été particulièrement étudiés dans le contexte de transitions de phases avec un ordre magnétique induit par les contraintes du système : en effet, selon la perturbation envisagée, les contraintes topologiques sous-jacentes peuvent provoquer une transition de Kasteleyn dans le kagome ice, ou une transition de type vitreuse dans la square ice, due à l’émergence d’un ordre ferromagnétique dans une chaîne d’Ising induit seulement par des effets de taille fini. Dans tous les cas, une étude détaillée par simulations numériques de type Monte Carlo ont été comparées à des résultats théoriques pour déterminer les propriétés de ces transitions. Les contraintes topologiques du kagome ice ont requis le développement d’un algorithme de vers permettant aux simulations de ne pas quitter l’ensemble des états fondamentaux. Une revue poussée de la thermodynamique et de la réponse de la diffraction de neutrons sur kagome ice sous un champ magnétique planaire arbitraire, nous ont amené à une compréhension plus profonde de la transition de Kasteleyn, et à un modèle numérique capable de prédire les figures de diffraction de neutrons de matériau de kagome ice dans n’importe quelles conditions expérimentales. Sous certaines conditions, ce modèle a révélé des propriétés thermodynamiques quantifiées et devrait fournir un terreau fertile pour de futurs travaux sur les conséquences des contraintes et transitions de phases topologiques. Une étude combinée du square ice et de la chaîne d’Ising a mise en lumière l’apparition d’un ordre sur réseau potentiellement découplé de l’ordre ferromagnétique sous-jacent, et particulièrement pertinent pour les réseaux magnétiques artificiels obtenus par lithographieIn this thesis a series of model frustrated magnets have been investigated. Their common parent is the spin ice model, which is transformed into the kagome ice and square ice models in two-dimensions, and an Ising spin chain model in one-dimension. These models have been examined with particular interest in the spin ordering transitions induced by constraints on the system: a topological constraint leads, under appropriate conditions, to the Kasteleyn transition in kagome ice and a lattice freezing transition is observed in square ice which is due to a ferromagnetic ordering transition in an Ising chain induced solely by finite size effects. In all cases detailed Monte Carlo computational simulations have been carried out and compared with theoretical expressions to determine the characteristics of these transitions. In order to correctly simulate the kagome ice model a loop update algorithm has been developed which is compatible with the topological constraints in the system and permits the simulation to remain strictly on the groundstate manifold within the appropriate topological sector of the phase space. A thorough survey of the thermodynamic and neutron scattering response of the kagome ice model influenced by an arbitrary in-plane field has led to a deeper understanding of the Kasteleyn transition, and a computational model that can predict neutron scattering patterns for kagome ice materials under any experimental conditions. This model has also been shown to exhibit quantised thermodynamic properties under appropriate conditions and should provide a fertile testing ground for future work on the consequences of topological constraints and topological phase transitions. A combined investigation into the square ice and Ising chain models has revealed ordering behaviour within the lattice that may be decoupled from underlying ferro- magnetic ordering and is particularly relevant to magnetic nanoarrays
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Mayer, Charlotte. "Nouveaux matériaux magnétocaloriques à base de terres rares pour la réfrigération magnétique." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2011. http://tel.archives-ouvertes.fr/tel-00649399.
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Les travaux présentés dans ce manuscrit portent sur la synthèse et la caractérisation de nouveaux matériaux magnétocaloriques à basse de terres rares pour la réfrigération magnétique. Le premier chapitre constitue une introduction aux notions d'effet magnétocalorique et de réfrigération magnétique et dresse un état de l'art des matériaux magnétocaloriques existants. Dans le but d'obtenir des matériaux à forte capacité de réfrigération (RC) et d'identifier des stratégies d'amélioration de ce critère de performance, deux voies de recherche ont été explorées : l'élargissement de la transition magnétique et l'effet de l'élément de transition M et de l'élément p (X) dans les verres métalliques Gd60M30X10 (M = Mn, Fe, Co, Ni, Cu et X = Al, Ga, In) d'une part, et la synthèse de nouveaux siliciures ternaires dans les systèmes R-M-Si (R = Nd, Gd, Tb et M = Co, Ni) à fort potentiel magnétocalorique, d'autre part. Le second chapitre de cette thèse présente les propriétés magnétiques des rubans amorphes à base de gadolinium synthétisés par la technique de melt-spinning, dans lesquels le désordre structural induit un très fort élargissement de la transition magnétique (vis-à-vis de celle du gadolinium par exemple). Il montre dans un premier temps, la faible influence de l'élément p (X) sur les propriétés magnétiques des rubans Gd60Mn30X10 (X = Al, Ga, In). Une seconde partie présente la très forte influence de l'élément de transition M, tant sur la nature de la transition magnétique que sur les propriétés magnétocaloriques des verres métalliques Gd60M30In10 (M = Mn, Fe, Co, Ni, Cu), avec en particulier une température de Curie variant entre 86 (M = Ni) et 220 K (M = Fe) et l'existence d'un phénomène de type cluster-glass en dessous de 35 K lorsque M = Mn. Le chapitre trois de cette thèse se décline en trois parties. La première décrit les conditions de synthèse parfois délicates, notamment dans le choix des températures de recuit, des siliciures R5MSi2, Gd5Si3 et du composé à domaine d'existence Gd3Co2,5 ± xSi1,5 ± y. L'utilisation de la méthode Rietveld pour l'affinement des diffractogrammes de rayons X sur poudre et monocristaux et neutrons a permis de montrer que les composés R5MSi2 adoptent une structure de type Cr5B3 avec la particularité de l'occupation mixte du site 8h par Co et Si à 50 %/50 % et que Gd3Co2,5 ± xSi1,5 ± y adopte une structure de type Er3Ge4 avec des sites mixtes Co/Si en positions 4a et 4c. La seconde partie présente les propriétés magnétiques et magnétocaloriques du siliciure Gd5CoSi2. Ce composé subit une transition ferromagnétique à la température de Curie de 169 K qui s'accompagne d'une variation d'entropie magnétique calculée par l'application de la relation de Maxwell, de -4,7 et 8,7 J kg-1 K-1 pour des variations de champ magnétique respectives de 2 et 5 T. Le troisième volet de ce chapitre décrit les propriétés magnétiques de Nd5CoSi2 et Nd5NiSi2 qui présentent une transition ferromagnétique respectivement à 55 et 44 K. Il décrit également l'affinement de la structure ferromagnétique cantée de Nd5CoSi2 obtenue par des mesures de diffraction neutronique. Il ressort de ces travaux que l'évaluation des matériaux magnétocaloriques par le seul critère de capacité de réfrigération ne mène pas vers les matériaux les plus adaptés à l'application. Il faudrait cibler plus spécifiquement, pour chaque type de cycle de réfrigération envisagé, des critères pragmatiques tels qu'une fenêtre de température d'utilisation autour de la température de Curie ou une valeur de chaleur spécifique optimale afin de mieux guider la recherche de nouveaux matériaux magnétocaloriques.
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Chiat, Lim Chong, and 林仲杰. "Studying Neutral Gold Clusters by the Brownian-type and Metadynamics Molecular Dynamics Simulations." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/b66xk6.
Full textAbstract:
碩士國立中央大學
物理學系
106
The parametrized density functional tight-binding (DFTB) theory is used to calculate the force field of a neutral gold cluster and it is then combined with the Brownian-type molecular dynamics (MD) algorithm [S. K. Lai, W. D. Lin, K. L. Wu, W. H. Li, and K. C. Lee, J. Chem. Phys. 121, 1487 (2004)] to perform simulation studies for this system within the Nosé-Hoover thermostat scheme. We analyze the simulation data for four selected Au clusters which were prepared at T=300 K, and deduce from their thermally evolved behaviors the (a) fluxional character, (b) chiral behavior, and (c) traits of the bi- to tridimensional transition. In all of these MD simulations studies, the initial input position coordinates of ions in these clusters were the lowest energy configurations which we obtained separately from an optimization algorithm [T.W. Yen, T.L. Lim, T.L. Yoon and S.K. Lai, Comput. Phys. Commun. 220, 143 (2017)] where the individual cluster’s energy function employed is within the same DFTB theory. Using these same initial structures, we carried out also independent metadynamics MD (MMD) simulations at 300 K and generated biased trajectories for two of these selected clusters in a collective-variable space instead of the conventional configurational space in terms of the position coordinates of ions. The MMD simulations serve to explore the temporal change of Au clusters in the collective-variable space. It is hoped that an analysis of clusters whose energy functions are calculated in the DFTB theory in the latter and the comparison of simulation results with similar MMD simulations conducted with an empirical potential whose potential parameters are determined from bulk solid-state data would shed light on the subtlety and importance of s-d hybridization which is known to play an important role in both the electronic and structural properties of Au clusters. In this work, we delve into the effects of this covalent-like behavior of these selected clusters, examining them in parallel the features (a)-(c) mentioned above in Brownian-type MD and MMD simulations.
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Mancera-Rodríguez, Luis Alberto [Verfasser]. "Vibrational anharmonicity in small neutral gold and silver clusters / vorgelegt von Luis Alberto Mancera-Rodríguez." 2010. http://d-nb.info/1010587129/34.
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Tsou, Chih-Chin, and 鄒智欽. "Nitrosylation of Biomimetic [4Fe4S] Clusters and Interconversion among Neutral/Anionic Roussin’s Red Ester and Dinitrosyl Iron Complexes." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/36000483925587423151.
Full textAbstract:
碩士國立清華大學
化學系
95
The formation mechanisms of DNIC produced by nitosylation of the biomimetic ferredoxin [Fe4S4(SR)4]2- and [4Fe-4S] cluster precursor[Fe4(SR)10]2– (R = Et, Ph) was exhibited. After isolating [Fe4S3(NO)7]– (2) from nitosylation of [Fe4S4(SR)4]2-, the dinitrosyl or mononitrosyl iron cores of complex 2 degraded to DNICs [(RS)2Fe(NO)2]– (5) or reduced to [Fe4S3(NO)7]2– via nucleophilic attack of [SR]– (R = Ph, Et), respectively. Complexes [Fe4S4(NO)4]– (3) (g = 1.624 at 4 K) and [Fe4S3(NO)7]2– (g = 2.020 at 250 K), intermediate and byproduct of [Fe4S4(SR)4]2- degradation, suggested the variety of EPR spectra for modification of [4Fe-4S] clusters with NO in biological system. Nitrosylation of the [4Fe-4S] cluster precursors [Fe4(SR)10]2- (R = SPh, SEt) led to the formation of the MNICs [(RS)3Fe(NO)]– (7), then DNICs [(RS)2Fe(NO)2]– (5) and RRE [Fe(μ-SR)(NO)2]2 (8) were also demonstrated in further nitrosylation. Interestingly, reaction of [Fe4(SPh)10]2– and [NO2]– only resulted in the formation of [(PhS)3Fe(NO)]– (7-Ph). In this work, anionic RRE syn/anti-[Fe(μ-SEt)(NO)2]2– (9) and [Fe(μ-SEt)(NO)2]2 (8-Et) was synthesized, and the oxidation state of iron cores were about +0.87 and +1.0, respectively, characterized by X-ray Fe K-edge and L-edge absorption spectra. The different nucleophile ([SEt]– vs [(EtS)2Fe(NO)2]– vs [(PhS)2Fe(NO)2]–) functions to control the reaction pathways (bridged-thiolate cleavage vs reduction vs no reaction) upon reaction of [Fe(μ-SR)(NO)2]2 (8) and nucleophiles. It was confirmed [(EtS)2Fe(NO)2]– (5-Et) and [Fe(μ-SEt)(NO)2]2– (9) can be oxidized to form complex 8 by NO, and supported the probable factor that [Fe(μ-SR)(NO)2]2 was major product in the nitrosylation of FNR. Importantely, [Fe(μ-SEt)(NO)2]2– (9) and d9-DNIC (proposed reduced form of [(RS)2Fe(NO)2]–) have very similar synthetic method and EPR spectra.
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"Ab initio studies on the size dependence effects of solvation structures and intracluster reaction of neutral Na(H2O)n and cationic Na+(CH3OH)n clusters." 2004. http://library.cuhk.edu.hk/record=b5896181.
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Wong Shu Yan.On t.p. "n" is subscript.
Thesis submitted in: January 2003.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2004.
Includes bibliographical references (leaves 112-115).
Abstracts in English and Chinese.
TITLE PAGE --- p.i
THESIS EXAMINATION COMMITTEE --- p.ii
ABSTRACT (ENGLISH) --- p.iii
(CHINESE) --- p.v
ACKNOWLEDGEMENTS --- p.vii
TABLE OF CONTENTS --- p.viii
LIST OF FIGURES --- p.xi
LIST OF TABLES --- p.xiii
Chapter CHAPTER ONE --- Introduction
Chapter 1.1 --- Introduction --- p.1
Chapter 1.2 --- Solvation of clusters --- p.2
Chapter 1.3 --- Reaction of a sodium atom with water --- p.3
Chapter 1.4 --- Reaction of a sodium cation with methanol --- p.8
Chapter 1.5 --- Computational Method --- p.12
Chapter 1.5.1 --- Born-Oppenheimer (BO) Approximation --- p.12
Chapter 1.5.2 --- Self-Consistent Fields (SCF) ´ؤ Hartree-Fock (HF) --- p.14
Chapter 1.5.2.1 --- Moller-Plesset (MP) Perturbation Theory --- p.15
Chapter 1.5.2.2 --- Ab Initio Molecular Orbital (MO) Calculation --- p.16
Chapter 1.5.2.3 --- Basis Set Superposition Errors --- p.17
Chapter 1.5.3 --- Density Functional Theory (DFT) --- p.18
Chapter 1.5.3.1 --- Generalized-Gradient Approximation (GGA) --- p.20
Chapter 1.5.3.2 --- Plane-wave Basis Set --- p.21
Chapter 1.5.3.3 --- Pseudopotential Approximation --- p.21
Chapter 1.5.3.4 --- Ab Initio Molecular Dynamics (MD) Calculation --- p.23
Chapter CHAPTER TWO --- Reaction Mechanism of the Hydrogen Elimination Reaction of Na(H20)n clusters for n = 1 - 6
Chapter 2.1 --- Introduction --- p.25
Chapter 2.2 --- Computation details --- p.26
Chapter 2.3 --- Optimized Structure of Na(H20)n and H.. .Na0H(H20)n-1 --- p.27
Chapter 2.3.1 --- Solvation structures with n = 1-3 --- p.27
Chapter 2.3.2 --- Solvation structures with n= 4-6 --- p.34
Chapter 2.3.3 --- Relative energy of isomers --- p.40
Chapter 2.3.4 --- Energy barrier of hydrogen elimination reaction --- p.42
Chapter 2.3.5 --- Natural population analysis --- p.42
Chapter 2.4 --- "Reaction energy for hydrogen loss in Na(H20)n, n = 1 -6" --- p.46
Chapter 2.5 --- Ionization potential energy --- p.47
Chapter 2.6 --- Summary --- p.50
Chapter CHAPTER THREE --- Reaction Mechanism of the Ether Elimination Reaction of Na+(CH3OH)n cluster ions
Chapter 3.1 --- Introduction --- p.52
Chapter 3.2 --- Computational details --- p.53
Chapter 3.3 --- Optimized Structure for Na+(CH3OH)n (n = 1) --- p.55
Chapter 3.4 --- Optimized Structure forNa+(CH3OH)n (n = 2-5) --- p.59
Chapter 3.4.1 --- Na+(CH3OH)2 --- p.59
Chapter 3.4.2 --- Na+(CH3OH)3 --- p.67
Chapter 3.4.3 --- Na+(CH3OH)n(n = 4 and 5) --- p.75
Chapter 3.5 --- Mechanism of ether elimination reaction --- p.79
Chapter 3.6 --- Ab initio molecular dynamics study on Na+(CH3OH)n (n =6 and 8) --- p.85
Chapter 3.6.1 --- Solvation dynamics for Na+(CH3OH)6 --- p.85
Chapter 3.6.1.1 --- Dynamical structural for Na+(CH3OH)6 --- p.86
Chapter 3.6.1.2 --- "Optimized Structures for Na+(CH3OH)n, n =6" --- p.95
Chapter 3.6.2 --- Solvation dynamics for Na+(CH3OH)8 --- p.98
Chapter 3.6.2.1 --- Dynamical structural for Na+(CH3OH)8 --- p.99
Chapter 3.6.2.2 --- "Optimized Structures for Na+(CH3OH)n, n =8" --- p.106
Chapter 3.7 --- Summary --- p.109
REFERENCES --- p.112
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Shingles, Luke Jeremy. "Neutron-Capture Nucleosynthesis and the Chemical Evolution of Globular Clusters." Phd thesis, 2015. http://hdl.handle.net/1885/16507.
Full textAbstract:
Elements heavier than iron are almost entirely produced in stars through neutron captures
and radioactive decays. Of these heavy elements, roughly half are produced by the slow
neutron-capture process (s-process), which takes place under extended exposure to low
neutron densities. Most of the s-process production occurs in stars with initial masses
between roughly 0.8 and 8 M , which evolve through the Asymptotic Giant Branch (AGB)
phase.
This thesis explores several topics related to AGB stars and the s-process, with a focus on
comparing theoretical models to observations in the literature on planetary nebulae, post-
AGB stars, and globular cluster stars. A recurring theme is the uncertainty of 13C-pocket
formation, which is crucial for building accurate models of s-process nucleosynthesis.
We first investigated whether neutron-capture reactions in AGB stars are the cause of
the low sulphur abundances in planetary nebulae and post-AGB stars relative to the
interstellar medium. Accounting for uncertainties in the size of the partial mixing zone
that forms 13C pockets and the rates of neutron-capture and neutron-producing reactions,
our models failed to reproduce the observed levels of sulphur destruction. From this, we
concluded that AGB nucleosynthesis is not the cause of the sulphur anomaly. We also
discovered a new method to constrain the extent of the partial mixing zone using neon
abundances in planetary nebulae.
We next aimed to discover the stellar sites of the s-process enrichment in globular clusters
that have inter- and intra-cluster variation, with the examples of M4 (relative to M5) and
M22, respectively. Using a new chemical evolution code developed by the candidate, we
tested models with stellar yields from rotating massive stars and AGB stars. We compared
our model predictions for the production of s-process elements with abundances from
s-poor and s-rich populations. We found that rotating massive stars alone do not explain
the pattern of abundance variations in either cluster, and that a contribution from AGB
stars with 13C pockets is required. We derived a minimum enrichment timescale from
our best-fitting chemical evolution models and, although the value depends on the
assumptions made about the formation of 13C pockets, our estimate of 240–360 Myr for
M22 is consistent with the upper limit of 300 Myr inferred by isochrone fitting.
Lastly, there is accumulating evidence that some stars (e.g., in ! Centauri) have been born
with helium mass fractions as high as 40%. This motivated us to explore the impact of
helium-rich abundances on the evolution and nucleosynthesis of intermediate-mass (3–6
M ) AGB models. We found that the stellar yields of s-process elements are substantially
lower in He-rich models, largely as a result of less intershell material being mixed into the
envelope. We also found evidence that high He abundances could restrict the s-process
production by 13C pockets to stars with lower initial masses.
40
Bang, Woosuk. "Cluster fusion experiments on the Texas Petawatt Laser." 2012. http://hdl.handle.net/2152/22132.
Full textAbstract:
Interactions between an intense laser pulse and cluster targets are investigated using the recent experimental results of the cluster fusion experiments on the Texas Petawatt Laser (TPW). We achieved about 2x10⁷ DD fusion neutrons per shot on the TPW by optimizing the laser and gas jet parameters. A few different types of cluster targets were used on the TPW including deuterium clusters, deuterated methane clusters, deuterium cluster + helium-3 mixture, and deuterated methane cluster + helium-3 mixture. We designed our own neutron detectors and proton detectors for the measurements of the fusion yields. The calibration method of neutron detectors is described in detail. Through the yield measurements of the 2.45 MeV neutrons from the DD fusion reactions and 14.7 MeV protons from the D-³He fusion reactions in the deuterium-helium-3 mixture target, we successfully measured the ion temperature of the fusion plasma at the time of the fusion reactions.text
41
Liao, Jian-Hong, and 廖健宏. "A Size Effect in Self-Assembly Process: Halide-Encapsulated Silver(I) Clusters Stabilized by Dichalcogenophosphinate Ligands;X-ray and Neutron Diffraction Studies of Copper Hydride Clusters." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/esknb6.
Full textAbstract:
博士國立東華大學
化學系
106
Chapter 1: A Size Effect in Self-Assembly Process: Halide-Encapsulated Silver(I) Clusters Stabilized by Dichalcogenophosphinate Ligands: We synthesized a serious of the following new compounds, [Ag8(μ8-X){E2P(CH2CH2Ph)2}6](PF6) (E = S, X = F (1), Cl (2), Br (3); E = Se, X = F (5), Cl (6), Br (7)), and the first example of cuboctahedron Ag12. skeleton, [Ag12(μ12-I)(μ3-I)4{E2P(CH2CH2Ph)2}6](I) E = S (4), Se (8), with a μ12-iodide in the center by experimental and theoretical investigations. Chapter 2: X-ray and Neutron Diffraction Studies of Copper Hydride Clusters: Locate the number and the location of hydride atoms by single-crystal X-ray and neutron diffraction in five copper hydride clusters, [Cu20(H)11{S2P(OiPr)2}9] (9), [Cu32(H)20{S2P(OiPr)2}12] (10), [Cu20(H)11{Se2P(OiPr)2}9] (11), [Cu36(H)21{S2P(OiPr)2}12]PF6 (12), and [Cu36(D)19Cl2{S2P(OiBu)2}12]PF6 (13).
42
Siglow, Klaus [Verfasser]. "Hochauflösende UV-Spektroskopie von neutralen und ionischen Molekülen und Clustern : Rydbergzustände und Starkeffekt / Klaus Siglow." 2000. http://d-nb.info/962036382/34.
Full text
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Sigurdsson, Steinn. "Dynamics of neutron stars and binaries in globular clusters or, Ménages à trois: revitalizing burnt out degenerates through partner swapping." Thesis, 1992. https://thesis.library.caltech.edu/6638/1/Sigurdsson_s_1992.pdf.
Full textAbstract:
Interaction cross-sections and collision cross-sections for a set of hard multi-mass binary-single star interactions are calculated in order to estimate three-body collision cross-sections in galactic globular clusters. The cross-sections are calculated by direct integration of binary-single star encounters, using Monte Carlo sampling to average over the three-body phase space. A number of mass-ratios physically relevant to the globular cluster environment are used. Differential energy transfer rates due to three-body interactions are calculated. Parametric
approximations for the various cross-sections calculated are found.
The results of the cross-sections are used to evaluate various formation scenarios for the pulsars PSR2127+11C (M15C) and PSR1744-24A (TER5A). In addition the contribution of the globular cluster system to the galactic birthrate of PSR1913+16 type systems is estimated.
The dynamics and interactions of a test binary population in a number of globular cluster models are calculated in a static background. The cluster method used are isotropic multi-mass King models of varying concentration and density.
The model developed is generalisable to an arbitrary cluster distribution function, including one evolving in time. Relative probabilities of different encounters are
found for binaries on arbitrary trajectories in the various cluster models. The actual interaction rates of the test population are calculated by direct integration, using Monte Carlo sampling to average over the initial binary parameters. The number of neutron stars expected to be recycled in different concentration clusters is estimated with a particular view to understanding the pulsar population observed in clusters 47Tuc and M15.
Estimates are also made of the binary density profile of the different concentration class clusters, and the final distribution in binary parameters. The production rate of "blue stragglers" and the interaction rate of (sub)giants and white dwarfs in the various clusters are also estimated.
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Custódio, Tiago Emanuel Anjo de Oliveira. "Low Density Warm Stellar Matter with Light Clusters and Hyperclusters, Hyperons and Delta Isobars." Master's thesis, 2021. http://hdl.handle.net/10316/97914.
Full textAbstract:
Dissertação de Mestrado em Física apresentada à Faculdade de Ciências e TecnologiaThe abundance of light nuclei, hyperons and $\Delta$ isobars that are produced in stellar environments such as supernova or binary neutron star mergers, is calculated within both Nonlinear and Density-Dependent relativistic mean-field models in low-density matter. Five purely nucleonic light nuclei ($ ^2 $H, $ ^3 $H, $ ^3 $He, $ ^4 $He, $ ^6 $He) are considered, together with three light hypernuclei ($^{3}_{\Lambda}\text{H}$, $^{4}_{\Lambda}\text{H}$, $^{4}_{\Lambda}\text{He}$). We show that the presence of hyperons and $\Delta$s shifts the dissolution of clusters to larger densities, and increases the amount of clusters. This effect is larger the smaller the charge fraction, and the higher the temperature. The abundance of hyperons and $\Delta$s is also affected by the cluster formation: neutral and positively charged hyperons and $\Delta$s suffer a reduction, and the negatively charged ones an increase. We also observe that the dissolution of the less-abundant clusters occurs at larger densities due to smaller Pauli-blocking effects. Overall, hypernuclei set in at temperatures above 25 MeV, and depending on the temperature and chemical composition, they may be more abundant than $^4$He, or even more abundant than other heavier clusters. It is also seen that for some values of the couplings of the $\Delta$s, the nucleon effective mass becomes zero at too low densities, preventing the corresponding EoS of reaching the maximum mass star, therefore not being adequate to describe neutron stars.
A abundância de agregados leves, hiperões e partículas $\Delta$ produzidas em ambientes estelares tais como supernovas e colisões de duas estrelas de neutrões é calculada a baixas densidades no âmbito de modelos relativistas de campo médio não lineares e com acoplamentos dependentes da densidade. Em relação aos agregados leves, consideraram-se cinco agregados puramente nucleónicos e três hiperagregados. Verifica-se que a introdução de hiperões e partículas $\Delta$ empurra a dissolução dos agregados leves para densidades mais altas, aumentando também a sua abundância. Este efeito é tanto maior quanto menor for a fração de carga do sistema e quanto maior a temperatura. Por outro lado, as abundâncias de hiperões e partículas $\Delta$ são também afetadas pela presença de agregados leves no sistema, fazendo com que os hiperões e $\Delta$s de carga positiva ou neutra diminuam de quantidade, enquanto que os de carga negativa aumentam. Também se observa que a dissolução dos agregados menos abundantes ocorre a densidades mais elevadas fruto da redução dos efeitos de Pauli-blocking. De um modo geral, os hiperagregados apenas se formam a temperaturas superiores a 25 MeV, sendo que dependendo da temperatura e composiçao química do sistema, podem chegar a ser mais abundantes que o $ ^4 $He ou mesmo mais abundantes que outros agregados mais pesados. Também se verifica que para alguns valores dos acoplamentos das partículas $\Delta$ aos mesões, a massa efetiva do nucleão torna-se zero a baixas densidades, impedindo a equação de estado correspondente de atingir a estrela de massa máxima. Quando tal acontece, a equação de estado correspondente a esses acoplamentos não serve para descrever estrelas de neutrões.
Outro - Bolsa de Investigação Licenciado, duração 14 meses, no âmbito do projeto POCI-01-0145-FEDER-029912.