Дисертації: "Nuclear properties"

1

Amore, Paolo. "Modifications of the nucleon properties in the nuclear medium." W&M ScholarWorks, 2000. https://scholarworks.wm.edu/etd/1539623982.

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In this thesis we consider the possible modifications of the properties of the nucleon inside a nucleus. This problem is studied by applying the Wigner-Seitz approximation to different effective field theory models of the nucleon based on the underlying symmetries of QCD. The Wigner-Seitz approximation reduces the complex many-body problem to an effective one-body problem. By following this approach we calculate the static properties of the nucleon in the nuclear medium in both the Skyrme and the chiral quark soliton models. We also use the same chiral quark-soliton model to calculate the modification of the quark distribution functions measured in deep inelastic electron scattering when a nucleon is inside the nucleus.

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2

Macadangdang, Joan Karla. "Nuclear and Cytoskeletal Prestress Govern the Anisotropic Mechanical Properties of the Nucleus." Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/23310.

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Physical forces in the cellular microenvironment play an important role in governing cell function. Forces transmitted through the cell cause distinct deformation of the nucleus, and possibly play a role in force-mediated gene expression. The work presented in this thesis drew upon innovative strategies employing simultaneous atomic force and laser-scanning confocal microscopy, as well as parallel optical stretching experiments, to gain unique insights into the response of eukaryotic cell nuclei to external force. Non-destructive approaches confirmed the existence of a clear anisotropy in nuclear mechanical properties, and showed that the nucleus' mechanical response to extracellular forces is differentially governed by both nuclear and cytoskeletal prestress: nuclear prestress regulates shape and anisotropic deformation, whereas cytoskeletal prestress modulates the magnitude and degree of deformation. Importantly, the anisotropic mechanical response was conserved among diverse differentiated cell types from multiple species, suggesting that nuclear mechanical anisotropy plays an important role in cell function.

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3

Burnett, Mark Michael Stoddard Elizabeth P. "Single-particle properties of nuclear matter at finite temperature." Diss., UMK access, 2007.

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Thesis (M.S.)--Dept. of Physics. University of Missouri--Kansas City, 2007.
"A thesis in physics." Typescript. Advisor: Elizabeth P. Stoddard. Vita. Title from "catalog record" of the print edition Description based on contents viewed Dec. 18, 2007. Includes bibliographical references (leaf 23). Online version of the print edition.

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4

Marchetti, Mara. "Elastic properties characterization of nuclear fuels under extreme conditions." Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTS053/document.

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Ce travail de recherche vise à étudier les propriétés élastiques par microscopie acoustique du combustible nucléaire dans trois situations particulières: combustible en utilisation normale en réacteur nucléaire, combustible stocké après la période d’irradiation et combustible en conditions extrêmes suite à un accident nucléaire. Les mesures réalisées sur les échantillons irradiés ont conduit à plusieurs résultats majeurs: validation d’une loi corrélant la vitesse des ondes de Rayleigh à la densité du dioxyde d’uranium irradié ou frais; détermination de la porosité dans le combustible irradié; évaluation du gonflement de la matrice en fonction du taux de combustion dans la gamme 0-100 GWdt-1M; développement d'un modèle empirique capable de prévoir la variation de module de Young en fonction du taux de combustion en prenant même en compte la teneur en dopants (Gd2O3, CeO2) ; quantification de l’évolution du module de Young du combustible suite à l'endommagement en stockage ; premières mesures sur du corium. Enfin, grâce au lien entre les propriétés thermiques et élastiques, différentes propriétés thermiques de l'UO2 ont été calculées en mesurant la vitesse de l'onde de surface de Rayleigh seule
The focus of the present thesis is the determination of the elastic properties of nuclear fuel using high frequency acoustic microscopy. The nuclear fuel is considered under three different conditions: during its normal life in reactor, after its discharge and disposal in interim or long-term storage and subsequently to its severe degradation caused by a nuclear accident. Measurements performed on irradiated fuels allowed to validate a law between the density of fresh and irradiated fuel and the Rayleigh wave velocity; the determination of the irradiated fuel porosity and matrix swelling in the broad burnup range 0-100 GWdt-1M; the development of an empirical model capable of predicting the evolution of Young's modulus versus burnup correcting also for the additives content (Gd2O3, CeO2); Young's modulus evolution due to alpha-decay damage as in-storage condition; first corium measurements. Moreover, several UO2 thermal parameters were calculated only by means of the Rayleigh wave velocity thanks to the link between thermal and elastic properties

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5

Chan, Chii Jou. "Non-canonical aspects in cell and nuclear mechanics." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708974.

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6

Maphossa, Alexandre M. "A nuclear magnetic resonance investigation of Archis hypogaea L. (groundnut)." Thesis, University of Kent, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309779.

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7

Moore, Alexander Patrick. "Computational properties of uranium-zirconium." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50339.

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The metallic binary-alloy fuel Uranium-Zirconium is important for use in the new generation of advanced fast reactors. Uranium-Zirconium goes through a phase transition at higher temperatures to a (gamma) Body Centered Cubic (BCC) phase. The BCC high temperature phase is particularly important since it corresponds to the temperature range in which the fast reactors will operate. A semi-empirical Modified Embedded Atom Method (MEAM) potential is presented for Uranium-Zirconium. This is the first interatomic potential created for the U-Zr system. The bulk physical properties of the Uranium-Zirconium binary alloy were reproduced using Molecular Dynamics (MD) and Monte Carlo (MC) simulations with the MEAM potential. The simulation of bulk metallic alloy separation and ordering phenomena on the atomic scale using iterative MD and MC simulations with interatomic potentials has never been done before. These simulations will help the fundamental understanding of complex phenomena in the metallic fuels. This is a large step in making a computationally acceptable fuel performance code, able to replicate and predict fuel behavior.

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8

Mastropas, Ekaterina V. "Some properties of meson excited states from lattice QCD." W&M ScholarWorks, 2015. https://scholarworks.wm.edu/etd/1539624001.

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The work presented here is devoted to the calculations of the decay constants of the pion and its excited states. All calculations were carried out in the framework of lattice quantum chromodynamics, a well-established formalism of strong interactions enabling the ab initio solution of the theory. After a short introduction and review of the fundamental approaches and methods commonly used in lattice QCD, I provide a detail description of the numerical simulations which were performed at three values of the pion mass between 400 and 700 MeV, using an anisotropic clover fermion action with three flavors of quarks. The results obtained indicate that the decay constant of the first excitation, and more notably of the second, is suppressed with respect to that of the ground-state pion, but that the suppression shows little dependence on the quark mass. The second part of this thesis is focused on applications of the methods of perturbation theory to lattice QCD. Here, I give some motivation, and describe the main techniques of perturbative calculations on the lattice, emphasizing its distinctions from the continuum counterpart. I then employ the same anisotropic clover action that was used in numerical study for derivation of lattice Feynman rules which might be used for the calculations of the renormalization parameters helping to connect bare lattice results with real physics.

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9

Karaman, Turker. "Prediction Of Multiphase Flow Properties From Nuclear Magnetic Resonance Imaging." Phd thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12610382/index.pdf.

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In this study a hybrid Pore Network (PN) model that simulates two-phase (water-oil) drainage and imbibition mechanisms is developed. The developed model produces Nuclear Magnetic Resonance (NMR) T2 relaxation times using correlations available in the literature. The developed PN was calibrated using experimental relative permeability data obtained for Berea Sandstone, Kuzey Marmara Limestone, Yenikö
y Dolostone and Dolomitic Limestone core plugs. Pore network body and throat parameters were obtained from serial computerized tomography scans and thin section images. It was observed that pore body and throat sizes were not statistically correlated. It was also observed that the developed PN model can be used to model different displacement mechanisms. By using the synthetic data obtained from PN model, an Artificial Neural Network (ANN) model was developed and tested. It has been observed that the developed ANN tool can be used to estimate oil &ndash
water relative permeability data very well (with less than 0.05 mean square error) given a T2 signal. It was finally concluded that the developed tools can be used to obtain multiphase flow functions directly from an NMR well log such as Combinable Magnetic Resonance (CMR).

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10

Tseggai, Mehreteab. "Synthesis, Nuclear Structure, and Magnetic Properties of some Perovskite Oxides." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4826.

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11

Murovhi, Phathutshedzo. "Low temperature thermal properties of HTR nuclear fuel composite graphite." Diss., University of Pretoria, 2013. http://hdl.handle.net/2263/33156.

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Graphite and graphite composite materials are of great importance in various applications; however, they have been widely used in nuclear applications. Primarily in nuclear applications such, as a moderator where its primary aim is to stop the fast neutrons to thermal neutron. The composite graphite (HTR-10) has potential applications as a moderator and other applications including in aerospace field. Structurally the composite shows stable hexagonal form of graphite and no traces of the unstable Rhombohedral patterns. Thermal conductivity indicates the same trends observed and known for nuclear graded graphite. The composite was made as a mixture of 64 wt% of natural graphite, 16 wt% of synthetic graphite binded together by 20 wt% of phenolic resin. The resinated graphite powder was uni-axially pressed by 19.5 MPa to form a disc shaped specimen. The disc was then cut and annealed to 1800 °C. The composite was further cut into two directions (parallel and perpendicular) to the pressing direction. For characterization the samples were cut into 2.5 x 2.5 x 10 mm3. There were exposed to proton irradiation for 3 and 4.5 hrs respectively and characterized both structurally and thermally. Through the study what we have observed was that as the composite is exposed to proton irradiation there is an improvement structurally. Thus, the D peak in the Raman spectroscopy has decreased substantially with the irradiated samples. XRD has indicated that there is no un-stable Rhombohedral phase pattern in both the pristine and the irradiated samples. However this was further confirmed with that thermal conductivity is also increasing with irradiation exposure. This is anomalous to irradiated graphite in which defects are supposedly induced. Looking into the electrical resistivity we have noted that pristine samples have higher resistivity as compared to the irradiated samples. Seebeck coefficient indicates that there is some form of structural perfection and the samples have a phonon drag dip at the known graphite temperature of 35 K. This has shown us there are no impurities induced by irradiation of the samples.
Dissertation (MSc)--University of Pretoria, 2013.
gm2014
Physics
Unrestricted

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12

Li, Kang-Wen K. "Remote determination of radioactive molten glass properties." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/13055.

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13

Wolf, Matthew Dearing. "Structural optimization and properties of clusters." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/30928.

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14

Adam, Ahmad Yahia. "Theoretical Prediction of Nuclear Magnetic Shielding Constants of Acetonitrile." Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/76769.

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Gauge invariant shielding constants calculations of ?H, ?C, and ??N were calculated for acetonitrile in the gas and liquid phases. Dierent basis sets as well as dierent ab initio and DFT methods were tested to select a time-ecient level of theory with reasonable accuracy. The eect of nuclear motion on the shielding constants was also explored. To investigate solvent eects on the shielding constants of acetonitrile, dierent clusters were extracted from molecular dynamics simulations. Convergence to the experimental values varied for the dierent clusters. The geometry of the central molecule in a cluster played an important factor in reaching convergence.
Master of Science

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15

Balboa, lópez Hector. "Simulation of thermomechanical properties of U-PuO2 nuclear fuel under irradiation." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX108/document.

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L’objectif de cette thèse a été d’utiliser une approche numérique pour étudier l’impact des dommages d'irradiation sur la microstructure du combustible nucléaire composé d'un mélange d’oxyde de plutonium et d’uranium (MOX). Cette approche, réalisée à l'échelle atomique, repose sur l'utilisation de potentiels empiriques développés dans la littérature pour l'oxyde mixte $(U,Pu)O_2$ dans l’approximation des interactions d’ions rigides.Une première étape a été une analyse critique des propriétés structurales, thermodynamiques et mécaniques prédites par 5 potentiels de la littérature. Les calculs de dynamique moléculaire ont été réalisés à l'aide du code LAMMPS, sur l'ensemble de la gamme de composition de $UO_2$ à $PuO_2$ et à des températures comprises entre 300 K et le point de fusion. Nous montrons que les potentiels les plus satisfaisants sont ceux développés par Cooper et Potashnikov. Ces deux potentiels reproduisent correctement la stabilité thermodynamique des phases ainsi que l'évolution en température des paramètres de maille et de la chaleur spécifique. Cependant le comportement mécanique des oxydes est différent selon le potentiel choisi. Tout d'abord, on note que les constantes élastiques et le facteur d'anisotropie obtenus par le potentiel Cooper sont plus fidèles aux recommandations de la littérature. Ensuite, nous montons que la propagation d'une fracture induit une transformation de phase en pointe de fissure avec le potentiel de Cooper alors qu'une fissuration fragile est observée avec le potentiel Potashnikov.Une seconde étape a été l'étude des dommages d'irradiation dans les oxydes mixtes en se limitant à l'utilisation des deux potentiels de Cooper et de Potashnikov. Des calculs de dynamique moléculaire de cascades de déplacement ont été réalisés à différentes énergies, température et compositions en plutonium. Ensuite, afin d'évaluer les dommages d'irradiation sur des temps plus longs que ceux accessibles en dynamique moléculaire, la méthode d’accumulation de défauts a été utilisée. Pour les deux potentiels, l’évolution des dommages primaires avec l’augmentation de la dose suit globalement les mêmes étapes que celles trouvées précédemment dans $UO_2$. Tout d’abord, les défauts ponctuels sont créés. Par la suite, ils se regroupent et forment de petites boucles de Frank, qui après se transforment en dislocations parfaites. Cependant, la cinétique de la recombinaison de défauts ponctuels est significativement plus lente avec le potentiel de Cooper ce qui conduit à la création de petites régions désordonnées pour les cascades d'énergie élevée. L’effet de la teneur en plutonium est analysé. Nous montrons en particulier que la densité de dislocations crée diminue lorsque la teneur en plutonium augmente.Bien que la dynamique moléculaire a été décrite comme un microscope moléculaire en raison de sa capacité à décrire avec précision des systèmes atomiques, elle présente un inconvénient majeur, celui lié aux temps de l’ordre de la femto-seconde nécessaires pour résoudre les vibrations atomiques. Cela limite le temps total de simulation approximativement quelques nanosecondes. Afin de stimuler les processus, tels que la diffusion de cations, un autre outil de calcul est nécessaire. Les techniques de Monte Carlo (KMC) atomiques peuvent simuler de plus longtemps que la dynamique moléculaire . Cependant, pour que KMC fonctionne avec précision, il est nécessaire de connaître a priori tous les mécanismes de transition entre les états possibles. Pour cette raison, la method de Monte Carlo cinétique adaptative (aKMC) est choisie pour surmonter ces limitations. Cette méthode détermine les états de transition disponibles pendant la simulation. De cette manière, elle entraîne le système dans des états imprévus via des mécanismes complexes. La puissance de cet outil s'est révélée efficace pour découvrir la recombinaison de cations sur de plus longues périodes de temps que la DM
The objective of this doctoral research is to use a numerical approach to study the impact of irradiation damage on the microstructure of the mixed uranium-plutonium oxide fuel (MOX). This numerical approach comprises mainly the use of Molecular Dynamics (MD) using empirical potential. Several empirical potentials for $(U,Pu)O_2$ can be found in the literature. The results of these potentials can exhibit significant differences. For this reason an extensive assessment of the main empirical potential found in the literature had to be performed.Five empirical interatomic potentials were assessed in the approximation of rigid ions and pair interactions for the $(U_{1-y},Pu_y)O_2$ solid solution. Simulations were carried out on the structural, thermodynamics and mechanical properties over the full range of plutonium composition, meaning from pure $UO_2$ to pure $PuO_2$ and for temperatures ranging from 300 K up to the melting point. The best results are obtained by potentials referred as Cooper and Potashnikov. The first one reproduces more accurately recommendations for the thermodynamics and mechanical properties exhibiting ductile-like behaviour during crack propagation, whereas the second one gives brittle behaviour at low temperature.From our results from the empirical potentials assessment, we can move to the radiation damage using only two potentials (Cooper and Potashnikov). In order to know the main source of defect during irradiation, MD displacement cascades were simulated. This revealed the damage created due to varying projectile energies. In addition, the Frenkel pair accumulation method was chosen to investigate the dose effect. This method circumvents the highly computing time demanding accumulation of displacement cascade by directly creating their final states, i.e. mainly point defects. Overall, results obtained with both potentials show the same trend. However, kinetics of point defect recombination are significantly slower with Cooper potential implying creation of small disordered region with high energy displacement cascades. The evolution of the primary damage with increasing dose follows the same steps as those found previously in pure $UO_2$. First, point defects are created. Subsequently, they cluster and form small Frank loops, which in turn transform and grow into unfaulted loops. We demonstrate also that increasing temperatures accelerate the production of dislocations shifting their creation to lower doses. The effect of the plutonium content is also evidenced, especially with Cooper potential. It shows that the dislocation density decreases when the plutonium content increases.Although, MD has been described as a molecular microscope due to its ability to discribe accuratily systems of atoms, it has a large drawback that is the short time steps of the order of femto-seconds needed to resolve the atomic vibrations. This limits the time typically few microsecond. In order to invetigate processess, such as, cation diffusion and rare-event annihilation of defects after cascaces, another computational tool is required. Atomistic or object kinetic Monte Carlo (KMC) techniques can run for longer timescales than MD. However, for KMC to work accurately, all of the possible inter-state transition mechanisms and their associated rates need to be known a priori. For this reason, the adaptive kinetic Monte Carlo (AKMC) is chosen to overcome these limitations. This method determines the available transition states during simulation. In this way, it takes the system into unforeseen states via complex mechanisms. The power and range of this tool proved to be efficient to discover cation Frenkel pair recombination over a longer periods of time than MD

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16

Chen, Shuo. "A Study on Properties of Novel Metallic Foam for Nuclear Applications." Thesis, North Carolina State University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10110535.

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Developing new multifunctional materials in recent years for nuclear systems has become increasingly critical owing to the high demand on better shielding in extreme environments. The purpose of this research was to design, manufacture, and evaluate the feasibility of utilizing novel light weight close-cell composite metallic foam (CMF) and open-cell Al foam with fillers as radiation shields at nuclear facilities to attenuate the background of ionization radiations to a minimum level for creating a safer workplace, meeting regulatory requirements and maintaining high quality performance.

Steel-steel composite metal foams (S-S CMFs) and Aluminum-steel composite metal foams (Al-S CMFs) with various sphere sizes and matrix materials were manufactured and investigated for nuclear and radiation environments applications. 316L stainless steel, highspeed T15 steel and aluminum materials were used as the matrix material together with 2, 4 and 5.2 mm steel hollow spheres to manufacture various types of composite metal foams (CMFs). High-speed T15 steel is selected due to its high tungsten and vanadium concentration (both high-Z elements) to further improve the shielding efficiency of CMFs. This new type of S-S CMF is called High-Z steel-steel composite metal foam (HZ S-S CMF). Open-cell Al foams with fillers were obtained by infiltrating original empty pores with variety of hydrogen-rich compounds: petroleum wax, borated polyethylene, water, and borated water.

All the foams were investigated for their radiation shielding efficiency in terms of X ray, gamma ray and neutron. X-ray transmission measurements were carried out on a highresolution microcomputed tomography (microCT) system. Gamma-emitting sources: 3.0mCi ⁶⁰Co, 1.8mCi ¹³⁷Cs , 13.5mCi ¹²⁴Am, and 5.0mCi ¹³³Ba were used for gamma-ray attenuation analysis. The evaluations of neutron transmission measurements were conducted at the Neutron Powder Diffractometer beam facility at North Carolina State University. The experimental results were verified theoretically through XCOM and Monte Carlo Z-particle Transport Code (MCNP).

A mechanical investigation was performed by the means of quasi-static compressive testing. Thermal characterizations were carried out through effective thermal conductivity and thermal expansion analyses in terms of high temperature guarded-comparativelongitudinal heat flow technique and thermomechanical analyzer (TMA), respectively. The experimental results were compared with analytical results obtained from respectively Brailsford and Major’s model and modified Turner’s model for verification. Flame test was performed in accordance with United States Nuclear Regulatory Commission (USNRC) standard. CMF sample and a 304L stainless steel control sample were subjected to a fully engulfing fire with an average flame temperature of 800°C for a period of 30 minutes. Finite Element Analysis was conducted to secure the credibility of the experimental results.

This research indicates the potential of utilizing the lightweight close-cell CMFs and open-cell Al foam with fillers as shielding material replacing current heavy structures with additional advantage of high-energy absorption and excellent thermal characteristics.

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17

Bestembayeva, A. "Biophysical properties of the transport barrier in the nuclear pore complex." Thesis, University College London (University of London), 2016. http://discovery.ucl.ac.uk/1474430/.

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The Nuclear Pore Complex (NPC) is a large protein structure found in eukaryotic cells, perforating the nuclear envelope. It mediates bidirectional selective transport between the nucleus and the cytoplasm. The NPC contains a permeability barrier consisting of unstructured nuclear pore proteins. The structure of the permeability barrier is not well defined. As a consequence, various models have been proposed for its structure and functionality. Typically, these models consider the unstructured nuclear pore proteins as weakly or strongly interacting polymers: In the first case nuclear pore proteins protrude from the pore creating an entropic barrier; in the second case they may form a meshwork occupying the central channel, resembling a hydrogel. In this thesis, I measure the nanomechanical properties of this barrier in intact NPCs, and compare them to the properties expected for entropic brushes and gel-like materials. To this end, I carried out nanometre-scale force spectroscopy measurements using Atomic Force Microscopy (AFM). Prior to the measurements the pores were treated with reagents that activated the transport process, thus flushing out the pores to ensure that I was probing the barrier itself instead of cargo stuck in transit. I carried out Laser Scanning Confocal Microscopy experiments to verify this procedure, as well as to measure transport properties of the pores in isolated nuclei. For comparison, I also measure nanomechanical properties of artificial polymer brushes, and set the first steps towards creating protein-coated solid-state nanopores as a reductionist model system for the NPC. My results indicate that the proteins in the NPC form a condensed network, more closely resembling a hydrogel than a brush dominated by entropic interactions.

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18

Xu, Jie. "The low temperature synthesis, characterization and properties of ferroelectrics." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/26239.

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19

Lax, Derek Michael. "Memory efficient indexing algorithm for physical properties in OpenMC." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/97862.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 55-56).
OpenMC is an open source Monte Carlo code designed at MIT with a focus on parallel scalability for large nuclear reactor simulations. The target problem for OpenMC is a full core high-fidelity multi-physics coupled simulation. This encompasses not only nuclear physics, but also material science and thermohydraulics. One of the challenges associated with this problem is efficient data management, as the memory required for tallies alone can easily enter the Terabyte range. This thesis presents an efficient system for data storage which allows for physical properties of materials to be indexed without any constraints on the geometry. To demonstrate its functionality, a sample depletion calculation with 4 isotopes is completed on the BEAVRS benchmark geometry. Additionally, a temperature distribution assembly layout is presented.
by Derek Michael Lax.
S.M.

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20

Sacramento, Santana Hesdras Henrique. "Improving mechanical properties and microstructure development of fiber reinforced ceramic nuclear fuel." Doctoral thesis, Universitat Politècnica de València, 2014. http://hdl.handle.net/10251/37199.

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At the present work the UO2 fuel production process was extensively studied and analyzed. The objectives of such investigation were to understand and analyze the influence of different additives and the variation of the production process steps on the microstructure and consequently in the mechanical strength of the nuclear fuel pellet. Moreover, an improvement of the qualitative characteristics of the ceramic fuel pellets was also aimed. For this purpose UO2 pellets without additives, the so-called standard pellets, pellets containing as additive for example AZB (Azodicarbonamid), black U3O8 (Oxidized uranium pellet scrap - OS), green U3O8 (Oxidized uranium powder - OP), keratin fibers (a non conventional additive) were produced. The introduction of these additives to the UO2 powder mixture prior or after the granulation production step and in different concentrations produced several microstructure configurations. As it would not be possible to analyze all of them here so during the investigation pre-tests some of them were separated to be studied in more detail. Pellets with AZB added after the granulation presented larger grains and larger pores than those with AZB added before granulation, also porosity free grains and a granulate structure instead of a homogeneous one. Pellets with OS present fine porosity distributed all over the pellet matrix with some porosity clusters whereas pellets containing OP show in its matrix porosity agglomerated in form of hooks. As for the grain size, a more uniform grain size distribution can be observed in pellets OS than in pellets with OP. The variations in the amount of keratin fibers added, sintering dwell time and green density resulted indeed in different microstructures. Nevertheless, some common characteristics among them were observed such as the presence of elongated pores, porosity clusters and larger grains located at the pellets borders while the smaller ones were concentrated more in the central part of the pellet. This distribution of grains was identified as bi-modal structure. The mentioned microstructure aspects certainly influence on the mechanical properties of the fuel pellet. However, the sintering parameters, the green and final pellet density and the pellet dimensions also have an influence on the mechanical characteristics of the pellets. For studying the influence of all these parameters on the pellet mechanical properties four testing procedures were utilized the so-called squirrel-cage where the mechanical resistance of the not sintered pellets against mechanical shocks was tested, the diametrical compression test (Brazilian Test) where the strength of sintered and not sintered pellets was studied, the Vickers indentation technique and the creep test where the pellet plasticity respectively at room and at elevated temperatures was analyzed. The squirrel-cage results showed that the pellets with keratin fibers were much more mechanically resistant than those pellets without it, which means that the keratin fibers acted, prior sintering, as a powder binder increasing the cohesion among the powder granules proportionating the green pellets higher mechanical resistance against impacts. The Brazilian test evaluated the influence of the pellet length to the pellet diameter (L/D ratio), the influence of different additives mixed to the UO2 powder and the different pellet production processes. The L/D influence analysis showed that if one fixes the pellet diameter and increase the pellet length the Weibull modulus (here a measure of the pellet lot reliability) will also increase. By comparing pellets with OS, OP and 0.3% keratin fibers it was observed that pellets with OS presented the highest volume of pores smaller than 10 mm while pellets with OP and keratin presented the highest volume of pores larger than 20 mm. It seems that this relevant characteristic favored to the highest Weibull strength value for pellets with OS. In the indentation test standard pellets, pellets with OS and pellets with keratin fibers were tested. The results showed that the calculated hardness for the standard pellets is slightly lower when compared to the values obtained by the pellets with keratin fibers. Also the pellets containing OS when compared to the keratin fibers pellets have in most of the cases a lower hardness. The calculated fracture toughness and fracture surface energy values show also a better mechanical behavior for the keratin fibre pellets than in the standard pellets. Standard pellets, pellets with 30%OP, which had the smallest grain size, pellets with keratin fibers, having the bi-modal structure and pellets with chromium oxide, which had the largest grain size, were tested in the creep furnace. The results showed that all pellets with additives presented a better creep behavior than the standard pellets. Among the pellets prepared with additives the comparison clearly showed that under lower stresses pellets with smaller grains have a better creep rate. By increasing the applied stresses we observe an improvement of the creep rate of the pellets with chromium oxide and keratin fibre even slightly overcoming the pellets with 30%OP at the highest applied stress.
Sacramento Santana, HH. (2014). Improving mechanical properties and microstructure development of fiber reinforced ceramic nuclear fuel [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/37199
TESIS

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21

Holmboe, Michael. "The Bentonite Barrier : Microstructural properties and the influence of γ-radiation". Doctoral thesis, KTH, Kärnkemi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-34048.

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22

Ng, Shao-Chin Cindy. "Cosmological models with quintessence : dynamical properties and observational constraints." Title page, table of contents and abstract only, 2001. http://web4.library.adelaide.edu.au/theses/09PH/09phn5758.pdf.

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Bibliography: leaves 100-106. Studies different models of "quintessence", in particular, a quintessence arising from an ultra-light pseudo Nambu-Goldstone boson. Overviews dynamical properties for these models using phase-space analyses to study attractor and tracker solutions. Studies high-redshift type Ia supernovae constraints on these models. Studies the impact of a simple phenomenological model for supernovae luminosity evolution on the PNGB models and the potentials of a future supernovae data set to discriminate the PNGB models over the other quintessence models. Studies gravitational lensing statistics of high luminosity quasars upon the quintessence models.

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23

Cook, Laurel A. (Laurel Anne). "Scattering properties of polyacrylamide gels and their relation to protein electrophoretic migration." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/28107.

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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1994, and Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Physics, 1994.
Includes bibliographical references (leaves 98-103).
by Laurel A. Cook.
B.S.
M.S.

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24

He, Dian. "Studies of PPI dendrimers -- structures, properties, and potential applications." Huntington, WV : [Marshall University Libraries], 2002. http://www.marshall.edu/etd/descript.asp?ref=165.

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25

Uh, Jinsoo. "Nuclear magnetic resonance imaging and analysis for determination of porous media properties." Texas A&M University, 2005. http://hdl.handle.net/1969.1/4899.

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Advanced nuclear magnetic resonance (NMR) imaging methodologies have been developed to determine porous media properties associated with fluid flow processes. This dissertation presents the development of NMR experimental and analysis methodologies, called NMR probes, particularly for determination of porosity, permeability, and pore-size distributions of porous media while the developed methodologies can be used for other properties. The NMR relaxation distribution can provide various information about porous systems having NMR active nuclei. The determination of the distribution from NMR relaxation data is an ill-posed inverse problem that requires special care, but conventionally the problem has been solved by ad-hoc methods. We have developed a new method based on sound statistical theory that suitably implements smoothness and equality/inequality constraints. This method is used for determination of porosity distributions. A Carr-Purcell-Meiboom-Gill (CPMG) NMR experiment is designed to measure spatially resolved NMR relaxation data. The determined relaxation distribution provides the estimate of intrinsic magnetization which, in turn, is scaled to porosity. A pulsed-field-gradient stimulated-echo (PFGSTE) NMR velocity imaging experiment is designed to measure the superficial average velocity at each volume element. This experiment measures velocity number distributions as opposed to the average phase shift, which is conventionally measured, to suitably quantify the velocities within heterogeneous porous media. The permeability distributions are determined by solving the inverse problem formulated in terms of flow models and the velocity data. We present new experimental designs associated with flow conditions to enhance the accuracy of the estimates. Efforts have been put forth to further improve the accuracy by introducing and evaluating global optimization methods. The NMR relaxation distribution can be scaled to a pore-size distribution once the surface relaxivity is known. We have developed a new method, which avoids limitations on the range of time for which data may be used, to determine surface relaxivity by the PFGSTE NMR diffusion experiment.

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26

Brown, Richard Matthew. "Coherent transfer between electron and nuclear spin qubits and their decoherence properties." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:21e043b7-3b72-44d7-8095-74308a6827dd.

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Conventional computing faces a huge technical challenge as traditional transistors will soon reach their size limitations. This will halt progress in reaching faster processing speeds and to overcome this problem, require an entirely new approach. Quantum computing (QC) is a natural solution oﬀering a route to miniaturisation by, for example, storing information in electron or nuclear spin states, whilst harnessing the power of quantum physics to perform certain calculations exponentially faster than its classical counterpart. However, QCs face many diﬃculties, such as, protecting the quantum-bit (qubit) from the environment and its irreversible loss through the process of decoherence. Hybrid systems provide a route to harnessing the beneﬁts of multiple degrees of freedom through the coherent transfer of quantum information between them. In this thesis I show coherent qubit transfer between electron and nuclear spin states in a ¹⁵N@C₆₀ molecular system (comprising a nitrogen atom encapsulated in a carbon cage) and a solid state system, using phosphorous donors in silicon (Si:P). The propagation uses a series of resonant mi- crowave and radiofrequency pulses and is shown with a two-way ﬁdelity of around 90% for an arbitrary qubit state. The transfer allows quantum information to be held in the nuclear spin for up to 3 orders of magnitude longer than in the electron spin, producing a ¹⁵N@C₆₀ and Si:P ‘quantum memory’ of up to 130 ms and 1.75 s, respectively. I show electron and nuclear spin relaxation (T₁), in both systems, is dominated by a two-phonon process resonant with an excited state, with a constant electron/nuclear T₁ ratio. The thesis further investigates the decoherence and relaxation properties of metal atoms encapsulated in a carbon cage, termed metallofullerenes, discovering that exceptionally long electron spin decoherence times are possible, such that these can be considered a viable QC candidate.

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27

Alonso, Edgar Andre Ramirez. "The properties of the circum-nuclear obscuring region in powerful radio galaxies." Thesis, University of Sheffield, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.566693.

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Rhodococcus has been used in bioremediation because of its low eco- toxicity, high tolerance to harsh environments, and ability to be cultivated in mixed microbial consortia with certain contaminants as its nutrients. Excretion of extracellular polymeric substances (EPS) allows Rhodococcus to trap and to effectively degrade contaminants. Mycolic acid (MA) which covers the cell wall provides Rhodococcus with a hydrophobic cell surface to contact hydrocarbon contaminant droplets. This work concerns the influence of the conformational change in MA and rhodococcal EPS on their mechanical properties. Neutron reflection revealed that when the solution pH increases, a hydration layer is generated between the bound (hydrophobic) MA (LB _MA) and the silicon substrate, whereas the intermolecular repulsion unfolds the extractable (hydrophilic) MA (LS_MA), and allows water to fill in the formerly folded space. Force spectroscopy using a polystyrene colloidal probe showed that the strength of the adhesion force between a hydrophobic particle and MA is affected by the conformation of MA. The existence of a hydration layer in the MA enhances cell adhesion. Classical DLVO theory indicated that the electrostatic force dominates the long range (a distance larger than the Debye length) interactions between a polystyrene (hydrophobic) particle and MA, whereas the van der Waals force has a negligible influence. EPS generated at the early exponential phase (E EPS) and the late stationary phase (S EPS) of Rhodococcus manifested different physiochemical and mechanical properties. Force spectroscopy using Rhodococcus as a bacterial cell probe suggested that S EPS possess a higher differential capacitance than E EPS do for cells to store charges and energy. The nonspecific binding sites to silicon (an abundant material in the sediments of groundwater) are not evenly distributed; they exist mainly in S EPS close to the cell surface, but rarely in E EPS. Therefore, S EPS have a stronger adhesion to the silicon surface than E EPS do. Contraction and stretch of the EPS chains affect the strength of the adhesion force to a silicon surface. S EPS possess a better resilience against compression than E EPS do, thus retaining water in both S EPS and the inner E EPS. 4

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28

Sarma, Ashapurna. "Circadian Timing of Curcumin Efficacy and Nuclear Transport Properties of Cancer Cells." Bowling Green State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1447971823.

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29

Fager, Fredrick, and Serg Chanouian. "Nuclear Waste Canister : Evaluating the mechanical properties of cassette steel after casting." Thesis, KTH, Materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209803.

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Företaget Svensk Kärnbränslehantering AB (SKB) håller på att utveckla en slutförvaringskapsel som kommer innehålla avfall från den svenska kärnkraften. Det är dock fortfarande en process under utveckling och därför undersöks olika typer av metoder och kapselmaterial för att kunna tillverka en hållbar och säker kapsel. Kapseln består av ett hölje av kopparrör med svetsad botten och lock och en insats med stållock. Insatsen är en cylindrisk konstruktion av segjärn och innehåller en svetsad stålkassett för att skapa utrymmen till det använda kärnbränslet. Insatsen innehåller bland annat stålrör som under tillverkning får utstå en gjutprocess med segjärn och erhåller efter det icke homogena egenskaper. Målet med undersökningen är hur stor påverkan gjutningen har på stålets kemiska sammansättning samt mikrostrukturer. Det som orsakar de inhomogena egenskaperna är främst värmebehandlingen som driver diffusionen av kol från gjutjärnet till stålet, som då ger ett hårdare men sprödare material. Med hjälp av experiment och simuleringar upptäcks hur mycket kol som diffunderar in i stålet samt ändringar i den kemiska sammansättningen i de påverkade zonerna. Identifiering av fasomvandlingar, diffusion och ändringar i mikrostrukturer är stora faktorer som i sin tur ändrar de mekaniska egenskaperna i stålet.
The Swedish Nuclear Fuel and Waste Management Company (SKB) have developed a final storage canister that will contain waste from the Swedish nuclear power plants. However, it is still in a development phase and therefore different types of methods and canister materials are investigated to produce the most durable and safe canister. The canister is made of a copper tube with a welded bottom and lid with an insert. The insert is a cylindrical construction of nodular cast iron that contains a welded steel cassette, to make space for the spent fuel, and a steel lid. The steel tubes showed inhomogeneous properties after being exposed to a casting around them. The aim of this investigation is to clarify the impact of casting on the chemical composition of the steel as well as the microstructure. The cause to the inhomogeneous properties were the diffusion of carbon from the cast iron to the steel, which then produced a harder and more brittle material. Experiments and simulations were used to see the carbon diffusion into the steel as well as what happens with the chemical composition in the affected zones. Identification of phase changes, diffusion and microstructures contributed to changes of mechanical properties in the steel.

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30

Shahin, Mohammad S. M. Massachusetts Institute of Technology. "Irradiation effects on mechanical and physical properties of SS304L-nanotube composites." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/129112.

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Анотація:

Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, September, 2020
Cataloged from the official PDF of thesis.
Includes bibliographical references (pages 44-47).
For decades nuclear power has been a reliable and affordable source of base-load power[1] with relatively small amounts of CO2 emissions.[2] The levelized cost of electricity generated by nuclear power plants is dominated by the capital cost of the structural components,[3] therefore extending the operating lifetime of these plants is of high economic and environmental interests. However, degradation of mechanical behavior of structural materials due to radiation damage is a key limiting factor to service lifetime. The development of advanced materials can potentially improve material performance under irradiation and increase their design lifetime. Traditional alloy design always sacrifices one property for another, such as strength for ductility, or creep strength for radiation resistance.
However, a new approach promises to break this property dependency, allowing for obtaining the best properties potentially without sacrificing others.[3-5] This work aims to study the effects of introducing a variety of NanoTubes (NTs) within the metal matrix of austenitic Stainless SS (SS) type 304L on the radiation resistance of the composites. Rapid non- and semi- destructive methods are used to quantify these effects and study the correlation between them. SS and SS Metal Matrix Composites (MMCs) were synthesized by powder metallurgy and Spark Plasma Sintering (SPS) to densify bulk samples approaching the theoretical density. The synthesized materials were then irradiated by accelerated heavy charged particles to mimic the damage caused by neutron irradiation in a nuclear reactor over a longer period of time.
Finally, the mechanical and physical properties of the irradiated SS as well as the MMCs were characterized and compared to the non-irradiated samples to study the effects of incorporating the NTs, and to test the hypothesis that the metal-nanotube interfaces serve as recombination sites for defects. The experimental examination of the new materials is necessary to assess their potential for future developments in reactor designs, which would allow improvements to overcome current limitations in service lifetime and hence improve the economy of nuclear power. The results show that the dispersion of NTs within the SS304L mostly caused a slight decrease in thermal diffusivity and an increase in hardness. The results also indicate that incorporating NTs did not break the correlation of property changes after irradiation that was observed in the control (NT-free) sample.
In addition, all the SS matrices showed a potential inherent recovery in at least one of the measured properties when irradiated beyond 1 dpa (up to 10 dpa), which suggest the occurrence of onset of defect clustering between 1 and 10 dpa when the SS matrix is irradiated with Ni ions at room temperature.
by Mohammad Shahin.
S.M.
S.M. Massachusetts Institute of Technology, Department of Nuclear Science and Engineering

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31

Joyce, Malcolm John. "Magnetic properties and Coriolis splitting of the superdeformed Â¹â¹Â³Hg nucleus." Thesis, University of Liverpool, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359027.

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32

Hussin, Rosli Bin. "Nuclear magnetic resonance studies of some germanate and phosphate based glasses." Thesis, University of Warwick, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310014.

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33

Magampa, Philemon Podile. "Properties of graphitic composites." Thesis, University of Pretoria, 2013. http://hdl.handle.net/2263/40244.

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The Pebble Bed Modular Reactor (PBMR) is a high temperature graphite-moderated nuclear reactor that uses helium as a coolant. The triple coated (TRISO) particles contain enriched uranium oxide fuel which is coated with layers of various forms of pyrolytic carbon and silicon carbide. The TRISO particles are further embedded in the matrix of spherical graphite pebbles. The graphite matrix is a composite moulded from a compound containing natural flake graphite (64 wt.%), synthetic graphite (16 wt.%) and a phenolic resin binder (20 wt.%) heated to 1800 °C in inert atmosphere. The graphitic composite provides structural integrity, encasement and act as a moderator material. In this work, low density model graphite composites similar to those used in nuclear applications as encasement material in fuel pebbles were made by uniaxial cold compression moulding. The graphitic composites contained various ratios of natural flake graphite and synthetic graphite at fixed phenolic novolac resin binder content of 20 wt.% (green state). The fabrication process employed entails mixing the graphite powders, followed by addition of methanol phenolic resin solution to the graphite powder mix, drying, grinding, milling and sieving; and finally compression moulding in a stainless steel die at 13 MPa using a hydraulic press. The green moulded disc specimens were then carbonized at 900 °C in nitrogen atmosphere to remove volatiles followed by annealing at 1800 °C in helium atmosphere. The annealing step diminishes structural defects and result in densification of the composites. The microstructure of fabricated graphitic composites was characterized using various techniques. Particle Size Distributions determined using Laser diffraction showed that the inclusion of the binder leads to agglomeration. The composite powders had larger mean particle sizes than the raw graphite powders showing the binding effect of the novolac phenolic resin. X-ray diffraction studies showed that the graphitic composites had a hexagonal crystal structure after annealing. Raman spectroscopy revealed the presence of the structurally disordered phase derived from the resin carbon (indicated by the pronounced D-band in the Raman spectra). XRD and Raman observations were consistent with literature and gave results supporting existing knowledge base. Optical microscopy revealed a flake-like microstructure for composites containing natural graphite and needle-coke like particles for composites containing mainly synthetic graphite. Optical microscopy confirmed that the effect of the manufacturing route employed here was to align the particles in the direction perpendicular to the compression moulding direction. As a result, the graphitic composites exhibited anisotropic property behavior. The bulk density of the composites increased with the increase in the natural graphite content due to compactability of natural flakes in the manufacturing route. Thermogravimetric analysis studies on the composites showed that they were stable in air to 650 °C. Composites containing mainly synthetic graphite were thermally more stable in air compared to their natural graphite counterparts. The linear coefficients of thermal expansion of the composites were measured using thermomechanical analysis (20-600 °C). In the moulding direction, the average CTE (αP) values were in the range (5-9) × 10-6 K-1 and increased with increment in the natural graphite content in the composite. In the direction perpendicular to moulding direction, the average CTE (αN) values were in the range (1.7-2.1) × 10-6 K-1 showing that the expansion was similar or constant in this direction. Therefore an anisotropic expansion ratio, i.e. αP:αN, of about 3 was observed in the composites. This anisotropy is attributable to the alignment of the filler particles in the manufacturing route. The thermal conductivity of the annealed composites were measured in the pressing direction from 100 to 1000 °C and the values ranged from 19 to 30 W m-1 K-1. Anisotropy was also observed as far as strength was concerned. A composite containing 64:16:20 wt.% ratio had the best mechanical properties, high thermal conductivity and slightly high expansion coefficient. This work demonstrates the complimentary properties of the graphite fillers in the composites. It also reports for the first time, data on the effect of variation of the filler graphites on microstructure and properties of model low density compression moulded graphitic composites.
Thesis (PhD)--University of Pretoria, 2013.
gm2014
Chemistry
unrestricted

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34

Tolós, Rigueiro Laura. "The properties of antikaons in hot and dense matter." Doctoral thesis, Universitat de Barcelona, 2003. http://hdl.handle.net/10803/1585.

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Understanding the behavior of matter under extreme conditions of density and temperature, such as those found in neutron stars or in heavy-ion collisions, requires a good knowledge on the modification of the properties of hadrons in the nuclear medium. In particular, the in-medium effects on antikaons have received much attention over the last years, especially after the speculation of the possible existence of an antikaon condensed phase in neutron stars and the analysis of the experimental data coming from the programs developed at SIS-GSI, SPS-CERN and RHIC-BNL.

The purpose of this thesis is to present a self-consistent calculation of the antikaon properties in dense and hot matter in order to explore the typical conditions found in heavy-ion collisions at GSI, studying the possible implications that the inclusion of the in-medium effects at finite temperature on the antikaon optical potential would have on the K-/ K+ ratio.

Solving the Bethe-Goldstone equation for G-matrix, we obtain the K- optical potential from the K- N effective interaction in nuclear matter at T=0 taking, as a bare meson-baryon interaction, the meson-exchange potential of the Julich group. The momentum dependence and the effect of higher partial waves of the K- N effective interaction, beyond the L=0 component, are studied using this microscopic and self-consistent calculation.

Afterwards, the model is extended by incorporating finite temperature effects in order to adapt our calculations to the experimental conditions in heavy-ion collisions. In the rank of densities studied, the finite temperature K- optical potential shows a smooth behavior if we compare it to the T=0 outcome.

Finally, our model is applied to the study of the ratio between K- and K+ produced at GSI with T around 70 MeV in the framework of thermal models. Different approaches for the K- self-energy are taken into account so as to analyze the effects on the determination of this ratio.

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35

Marchais, Edouard. "Infrared properties of scalar field theories." Thesis, University of Sussex, 2013. http://sro.sussex.ac.uk/id/eprint/45244/.

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Phase transitions and critical phenomena are of central importance in quantum field theory and statistical physics. We investigate the low energy properties of O(N) symmetric scalar field theories using functional renormalisation group methods for all N. This modern formulation of Wilson's renormalisation group allows a continuous interpolation between short and long distance physics without resorting to a weak coupling expansion. To leading order in the derivative expansion, we study the phase transition and the approach to convexity in the deep infrared limit. In the limit of infinite N, the fluctuations of the Goldstone modes dominate allowing for a complete analytical discussion of the effective potential. For finite N, the radial fluctuations become important and we resort to systematic series expansions. In both cases a systematic and thorough analysis of the diverse fixed point solutions is carried out. This leads to a comprehensive picture of the scaling potential for a large number of universality classes. We also study the dependence of our results on the regularisation scheme. Finally, we establish that the infrared completion of the effective potential in the broken phase is driven by a fixed point that leads to the flattening of the non-convex part of the potential.

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36

Lovett, Phyllis Maria. "An experiment to simulate the heat transfer properties of a dry, horizontal spent nuclear fuel assembly." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/17294.

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Анотація:

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1991.
Science hard copy bound in 1 v.
Includes bibliographical references (leaves 163-165).
by Phyllis Maria Lovett.
M.S.

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37

Collins, Steven Jeremiah. "Estimating warhead design properties from multiple resonances in physical cryptographic warhead verification." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/119045.

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Анотація:

Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2018.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 55-57).
Further progress towards complete nuclear disarmament hinges upon the development of technologies that can reliably verify the authenticity of nuclear weapons without revealing classified information about their design. One recently developed approach makes use of isotope-specific nuclear resonance fluorescence (NRF) measurements to verify a candidate warhead's isotopic and geometric characteristics. To conceal sensitive design information, the NRF signal from the warhead is not directly measured, but is first convolved with that of an encrypting foil containing relevant warhead isotopes in quantities unknown to inspectors. The measured NRF spectrum from the candidate warhead is then compared with that of a trusted template warhead to confirm or deny the authenticity of the candidate warhead. This work examines the information security of this protocol by evaluating the accuracy with which an inspector can estimate warhead properties from multiple NRF peaks. A mathematical model of the measured NRF spectrum is developed, and measurement spectra are simulated for a collection of simple, representative warheads. A least squares estimator for the areal density of each resonant isotope in the warhead is calculated. It is shown that for a single measurement with a 2.6 MeV bremsstrahlung beam, the areal densities of the fissile isotopes U-235 and Pu-239 are virtually always estimated with less than 100% error. By adjusting the beam endpoint energy to 2.16 MeV, the error on the plutonium estimators is shown to increase substantially. The effect of isotopic enrichment on the quality of inference is demonstrated by varying the grade of plutonium in the warhead from 6% Pu-240 to 18% Pu-240 by mass.
by Steven Jeremiah Collins.
S.M.

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38

Lam, Stephen Tsz Tang. "Accelerated atomistic prediction of structure, dynamics and material properties in molten salts." Thesis, Massachusetts Institute of Technology, 2020. https://hdl.handle.net/1721.1/129108.

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Анотація:

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, September, 2020
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 122-142).
Various advanced nuclear reactors including fluoride high-temperature salt-cooled reactors (FHRs), molten salt reactors (MSRs) and fusion devices have proposed to use molten salt coolants. However, there remain many uncertainties in the chemistry, dynamics and physicochemical properties of many salts, especially over the course of reactor operation, where impurities are introduced, and compositional and thermodynamic changes occur. Density functional theory (DFT) and ab initio molecular dynamics (AIMD) were used for property, structure and chemistry predictions for a variety of salts including LiF, KF, NaF, BeF2, LiCl, KCl, NaCl, prototypical Flibe (66.6%LiF-33.3%BeF2), and Flinak (46.5%LiF-11.5NaF-42%KF). Predictions include thermophysical and transport properties such as bulk density, thermal expansion coefficient, bulk modulus, and diffusivity, which were compared to available experimental data.
DFT consistently overpredicted bulk density by about 7%, while all other properties generally agreed with experiments within experimental and numerical uncertainties. Local structure was found to be well predicted where pair distribution functions showed similar first peak distances (+ 0.1 A) and first shell coordination numbers (+ 0.4 on average), indicating accurate simulation of chemical structures and atomic distances. Diffusivity was also generally well predicted within experimental uncertainty (+20%). Validated DFT and AIMD methods were applied to study tritium in prototypical salts since it is an important corrosive and diffusive impurity found in salt reactors. It was found that tritium species diffusivity depended on its speciation (TF vs. T2), which was related to chemical structures formed in Flibe and Flinak salts. Further, predictions allowed comparison with and interpretation of past contradictory experimental results found in the literature.
Lastly, robust neural network interatomic potentials (NNIPs) were developed for LiF and Flibe. The LiF NNIP accurately reproduced DFT calculations for pair interactions, solid LiF and liquid molten salt. The Flibe NNIP was developed for molten salt at the reactor operating temperature of 973K and was found to reproduce local structures calculated from DFT and showed good stability and accuracy during extended MD simulation. Ab initio methods and NNIPs can play a major role in advanced reactor development. Combined with experiments, these methods can greatly improve fundamental understanding and accelerate materials discovery, design and selection.
by Stephen Tsz Tang Lam.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Nuclear Science and Engineering

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39

Fan, Yue Ph D. Massachusetts Institute of Technology. "Atomistic simulation of defect structure evolution and mechanical properties at long time scales." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82865.

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Анотація:

Thesis (Ph. D.)--Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 127-146).
This thesis is a computational and theoretical investigation of the response of materials' mechanical properties to a wide range of environmental conditions, with a particular focus on the coupled effects of strain rate and temperature. The thesis provides original contributions to the fundamental understanding of how the materials mechanical properties change, as manifested by defect structure evolution, with temperature and strain rate conditions, as well as to the development of methodology used for enabling the investigation of dislocation-defect interactions over a much wider range of time scales than of reach to traditional techniques. This thesis advanced the capabilities of a recently developed activation-relaxation based atomistic method to enhance the accuracy of kinetic predictions, and to enable the investigation of dislocation-defect interactions dynamically at long time scales. We took the Autonomous Basin Climbing (ABC) method as a starting point, and incorporated the ability to sample multiple transition pathways associated with a given state. This new feature addresses the problem of overestimating the system evolution time due to the one-dimensional nature of the original ABC algorithm. The ABC method was further implemented in a dynamic framework, which makes it possible for the first time to directly simulate the dislocation-obstacle interactions at very low strain rates. This approach allows for a new way to connect the atomistic results to models at the meso-scale for simulating the plasticity of metals. We analytically derived how the applied strain rate couples with the thermal activation process, based on the framework of transition state theory informed by the atomistic approach described above. We demonstrated the coupling effect is a common mechanism behind many important phenomena, and provide three examples from the atomic level on the dislocation mobility and dislocation interactions with radiation induced defects. (i) A well-known universal flow stress upturn behavior in metals has been examined. We provide a simple physically based model to predict the flow stress at various strain rates, without invoking any assumed mechanisms or fitting parameters as in the traditional constitutional models. (ii) We implemented this new model in (i) to investigate the dislocation-obstacle interactions. The approach enabled us to map the interaction between an edge dislocation and a self interstitial atom (SIA) cluster in Zr in a two-parameter space consisting of temperature and strain rate. This approach allows the direct atomistic simulation of dislocation-obstacle interactions at experimental time scale, namely at low strain rates, which cannot be reached by traditional atomistic techniques. The dislocation is found to absorb the SIA cluster and climb at low strain rates and high temperatures, while it passes through the SIA cluster at high strain rates and low temperatures. The predicted mechanism map is able to reconcile the seeming controversy between previous experimental and computational findings. (iii) A dislocation-void interaction in bcc Fe at prescribed strain rate is also investigated. We demonstrated that different applied strain rates can affect the interaction mechanism and the defect microstructure, and eventually lead to a negative strain rate sensitivity (nSRS) of yield strength below a critical strain rate. This finding at the unit process level supplements the previous explanations of the nSRS with higher level constitutive relations. Beyond the specific cases analyzed in metals in this thesis, the insights gained on the coupling between strain rate and thermal activation can be used to explain the dependence on strain rate and temperature in other important classes of materials (e.g. colloids, cement) and phenomena (e.g. corrosion, creep).
by Yue Fan.
Ph.D.

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40

Zhang, Hantao S. M. Massachusetts Institute of Technology. "Computational investigation of the thermal conductivities and phonon properties of strontium cobalt oxides." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/123356.

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This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Thesis: S.M., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2019
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 87-91).
The thermal conductivities of electrochemically tuned strontium cobalt oxides (SCO) are significantly different among the perovskite SrCoO3 (P-SCO), the brownmillerite SrCoO2.5 (BM-SCO) and the hydrogenated HSrCoO2.5 (H-SCO)1. The underlying mechanism causing this large difference is still unclear. And phonon properties in SCO have not been investigated thoroughly or have some contradictive predictions. In this work, we have calculated the thermal conductivities in P-SCO and BM-SCO by applying molecular and lattice dynamics, and successfully reconstructed the large difference of the thermal conductivities, consistent with measurements. Furthermore, several phonon properties including heat capacities, group velocities, lifetimes and mean free paths have been calculated, and the key roles of local atomic environment and crystal symmetry in determining the thermal conductivities have been identified. We have also analyzed the impact of interfaces, isotropic strains and defects on thermal conductivities, predicted the neutron scattering intensity in P-SCO, and tested the accuracy and performance of molecular dynamics based on deep learning. Additionally, even though the calculations about the phonon properties in H-SCO are not complete, it still offers some inspirations about its thermal conductivity. The thorough investigations about the phonon properties and the mechanisms determining the thermal conductivities in SCO may benefit future research about tunable thermal conductivities in complex oxides.
by Hantao Zhang.
S.M.
S.M. Massachusetts Institute of Technology, Department of Nuclear Science and Engineering

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41

Rios, Huguet Arnau. "Thermodynamical Properties of Nuclear Matter from a newline Self-Consistent Green's Function Approach." Doctoral thesis, Universitat de Barcelona, 2007. http://hdl.handle.net/10803/1588.

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The main contribution of this thesis concerns the application of the Luttinger-Ward formalism to the study of the thermodynamical properties of nuclear matter. This formalism is devoted to compute the different thermodynamical potentials from the Green's functions and therefore offers a consistent theoretical framework within which the microscopic as well as the macroscopic properties of nuclear matter can be treated at the same level.

In this thesis, the Luttinger-Ward formalism has been applied to nuclear matter within two different approximations. The Hartree-Fock approximation leads to unrealistic results, but it is very useful to check the validity of the formalism in the mean-field case. Within the ladder approximation, the application of the Luttinger-Ward formalism leads to analytical results for the thermodynamical potentials in terms of the microscopical properties of the system. Therefore, using the Self-Consistent Green's Function scheme, which offers a realistic description of nuclear systems at the microscopical level, one obtains a set of microscopical properties (spectral functions, NN interaction in the medium, etc) which can be used directly in the calculation of the thermodynamical observables of dense matter.

In particular, in this thesis special attention has been paid to the computation of the entropy of a system of correlated nucleons within the dynamical quasi-particle approximation. From this quantity, the free energy as well as other thermodynamical potentials of the system have been computed, leading to a full characterization of nuclear matter at the macroscopic level. In addition, the thermodynamical consistency of the approach has been shown by means of the microscopic and macroscopic chemical potentials. Finally, the liquid-gas phase transition of nuclear matter has been studied at a qualitative level.
La principal contribució d'aquesta tesi ha estat l'aplicació del formalisme de Luttinger-Ward a l'estudi de les propietats termodinàmiques de la matèria nuclear. Aquest formalisme permet obtenir els diferents potencials termodinàmics a partir de les funcions de Green i constitueix doncs un marc teòric consistent en què les propietats microscòpiques i macroscòpiques de la matèria nuclear poden ser tractades al mateix nivell.

En aquesta tesi, el formalisme de Luttinger-Ward s'ha aplicat a la matèria nuclear per a dues aproximacions diferents. En l'aproximació de Hartree-Fock, els resultats obtinguts són poc realistes, però permeten comprovar la validesa del formalisme en el cas del camp mig. En l'aproximació d'escala, l'aplicació del funcional de Luttinger-Ward dóna resultats analítics per als potencials termodinàmics a partir de les propietats microscòpiques del sistema. D'aquesta manera, mitjançant l'esquema de Funcions de Green Autoconsistents, que ofereix una descripció realista del sistema nuclear a nivell microscòpic, obtenim una sèrie de propietats microscòpiques (funcions espectrals, interacció NN en el medi nuclear, etc) que poden ser utilitzades directament en el càlcul dels observables termodinàmics de la matèria densa.

En particular, en aquesta tesi hem fet èmfasi en el càlcul de l'entropia d'un sistema de nucleons correlacionats en l'aproximació de quasi-partícula dinàmica. A partir d'aquesta quantitat, s'han obtingut l'energia lliure i altres potencials termodinàmics del sistema, fet que ens permet caracteritzar-lo a nivell macroscòpic. A més, s'ha demostrat la consistència termodinàmica de l'aproximació a partir de càlculs del potencial químic macroscòpic i microscòpic. Finalment, s'ha estudiat de manera qualitativa la transició líquid-gas de la matèria nuclear.
RESUMEN:

La principal contribución de esta tesis concierne la aplicación del formalismo de Luttinger-Ward al estudio de las propiedades termodinámicas de la materia nuclear. Este formalismo permite obtener los diferentes potenciales termodinámicos a partir de las funciones de Green y constituye por lo tanto un marco teórico consistente en el que las propiedades microscópicas y macroscópicas de la materia nuclear pueden ser tratadas al mismo nivel.

En esta tesis, el formalismo de Luttinger-Ward se ha aplicado a la materia nuclear para dos aproximaciones distintas. En la aproximación de Hartree-Fock, los resultados obtenidos son poco realistas, pero permiten comprobar la validez del formalismo en el caso del campo medio. En la aproximación de escalera, la aplicación del funcional de Luttinger-Ward da lugar a resultados analíticos para los potenciales termodinámicos a partir de las propiedades microscópicas del sistema. De este modo, mediante el esquema de Funciones de Green Autoconsistentes, que ofrece a una descripción realista del sistema nuclear a nivel microscópico, obtenemos una serie de propiedades microscópicas (funciones espectrales, interacción NN en el medio nuclear, etc) que pueden ser usadas directamente en el cálculo de los observables termodinámicos de la materia densa.

En particular, en esta tesis se ha prestado especial atención al cálculo de la entropía de un sistema de nucleones correlacionados en la aproximación de quasi-partícula dinámica. A partir de esta cantidad, se ha obtenido la energía libre, así como otros potenciales termodinámicos del sistema, lo que nos permite caracterizarlo a nivel macroscópico. Así mismo, se ha demostrado la consistencia termodinámica de la aproximación a partir de los cálculos del potencial químico macroscópico y microscópico. Finalmente, se ha estudiado de forma cualitativa la transición líquido-gas de la materia nuclear.

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42

Papachristodoulou, Maria. "A study of the ligand-binding properties of hepatocyte nuclear factor 4Î± (HNF4Î±)." Thesis, University of Surrey, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429895.

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43

Scivetti, I. "Quantum Nuclear Effects in the Structural and Vibrational Properties of Molecules and Crystals." Thesis, Queen's University Belfast, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501404.

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44

Hinoki, Tatsuya. "Investigation of Mechanical Properties and Microstructure of SiC/SiC Composites for Nuclear Application." Kyoto University, 2001. http://hdl.handle.net/2433/150496.

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Kyoto University (京都大学)
0048
新制・課程博士
博士(エネルギー科学)
甲第9050号
エネ博第37号
新制||エネ||10(附属図書館)
UT51-2001-F380
京都大学大学院エネルギー科学研究科エネルギー応用科学専攻
(主査)教授香山晃, 教授塩津正博, 教授木村晃彦
学位規則第4条第1項該当

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45

Studer, Dominik [Verfasser]. "Probing atomic and nuclear structure properties of promethium by laser spectroscopy / Dominik Studer." Mainz : Universitätsbibliothek Mainz, 2020. http://d-nb.info/1212691989/34.

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46

Ecay, Lionel. "Concrete transfer properties evolution and nuclear containment vessel tightness assessment during an accident." Thesis, Pau, 2018. http://www.theses.fr/2018PAUU3022/document.

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L’accident de Fukushima a démontré qu’aujourd’hui encore, malgré les progrès déjà réalisésdans le domaine de la sûreté nucléaire, une interruption prolongée du circuit de refroidissement primaire du réacteur (plusieurs semaines ici) était possible. La France s’est par conséquent vue contrainte de réévaluer le niveau de sûreté de ses centrales. Plus spécifiquement, le cas le plus défavorable qu’EDF considérait jusqu’alors, qui consistait en un arrêt total du système de refroidissement primaire de 24h, a été réévalué à deux semaines. Ce changement d’échelle temporelle a introduit des problématiques de fluage, d’évolution hygrométrique du béton ainsi que de flux de vapeur – celle-ci transportant les radionucléides – jusque-là laissées de côté. De ces considérations est né le projet ANR/RSNR MACENA (MAîtrise du Confinement d’une ENceinte en Accident), qui vise à évaluer le confinement d’une enceinte soumise à une température de 180°C et à une pression de 5 bar pendant deux semaines. Ce travail s’inscrit dans la lignée de celui entamé par Khaddour [2014] dans le but de parvenir à une meilleure prédiction des propriétés de transport des milieux poreux en se basant uniquement sur une caractérisation indirecte, la distribution des tailles de pore obtenue grâce à la technique de porosimétrie par intrusion de mercure. Si l’aptitude du modèle initial à estimer correctement les perméabilités intrinsèques a été confirmée sur des matériaux représentant une large gamme de perméabilités, il n’était pas, en l’état, capable de prédire les perméabilités relatives au gaz et au liquide. C’est pourquoi une approche dite redistributive a été développée, laquelle a montré de bons résultats sur diverses PSD. Enfin, un nouveau modèle a été développé pour essayer de s’affranchir de cette approche tout en améliorant la capacité à déterminer les perméabilités relatives. Bien qu’efficace sur des PSD monomodales, étroites ou larges, il a montré ses limites sur une PSD réelle bimodale. En parallèle, une étude de faisabilité a exhibé la possibilité de suivre un front de saturation à l’intérieur d’un matériau poreux, ce qui permettrait à terme de valider l’inclusion d’autres phénomènes dans le modèle, liés notamment à la pression de perçage
The Fukushima catastrophe that struck Japan in 2011 demonstrated that despite significant progress in the field of nuclear safety a prolonged reactor primary cooling circuit breakdown was possible (several weeks in this specific case). With 4 nuclear power plants located on its shoreline, France therefore needed to reassess the safety level of its facilities. More specifically, the worst case scenario considered up until that point by EdF — which consisted in a 24h breakdown of the primary cooling system — was revised up to two weeks. This time-scale shift induced creep, drying and vapour flow problems previously left aside. Thus came to be the ANR/RSNR MACENA (MAîtrise du Confinement d’une ENceinte en Accident) project, which aims at bettering the tightness assessment of a nuclear containment vessel submitted to a temperature of 180°C and to a pressure of 5 bar for two weeks. This work falls in line with that initiated by Khaddour [2014], who set out to better predict porous materials’ transport properties based solely on an indirect characterisation of their topology, namely Pore Size Distribution (PSD) which is obtained via an experimental technique called Mercury Intrusion Porosimetry (MIP). The initial model’s ability to correctly estimate intrinsic permeabilities was confirmed on several different materials whose intrinsic permeabilities span several orders of magnitude. However, it was not fit to accurately account for gas and liquid relative permeabilities. This led to the introduction of a so-called redistributive approach, which yielded better results on various PSD and corresponding experimental datasets. Finally, a new model was developed to try and avoid said approach while bettering relative permeability predictions. Although it behaved well with monomodal pore size distributions, be they wide or narrow, it fell short when applied to a real bimodal PSD. In parallel, an experimental feasibility study demonstrated the possibility of tracking a saturation front within a porous material, which should ultimately allow for the implementation of several other phenomena into the model, linked among others to breakthrough capillary pressure

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47

Dogo, Harun. "Point defect properties in iron chromium alloys." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2006. http://library.nps.navy.mil/uhtbin/hyperion/06Sep%5FDogo.pdf.

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Thesis (M.S. in Applied Physics)--Naval Postgraduate School, September 2006.
Thesis Advisor(s): Craig Smith, Xavier Maruyama. "September 2006." Includes bibliographical references (p. 57-59). Also available in print.

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48

Darawsheh, Mohanad D. "Spin crossover supramolecular coordination compounds: design, synthesis and properties." Doctoral thesis, Universitat de Barcelona, 2016. http://hdl.handle.net/10803/400859.

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The results obtained in this thesis demonstrate the importance of supramolecular chemistry for the design of potential new SCO clusters. Starting from synthesizing the suitable ligands with suitable functional groups, novel host-guest systems could be obtained where the guest play a major role in tuning the physical properties of the guest. Two bis-pyrazolylpyridine lignads, H2L4 and H2L6 were designed and prepared to achieve the assembly of transition metal ions in a triple-stranded helicate fashion where the central cavity can encapsulate different counterions depending on the size of this cavity. The N-H groups found in these ligands which usually directed toward the internal cavity help in the encapsulation of hydrogen acceptor anions. 13 iron-based compounds have been crystallized and studied adding significantly to the helical SCO compounds in the literature. The crystal structure for all the compounds were resolved, which allowed for an extensive study of supramolecular interactions and the influence of these interactions on the magnetic properties of the compounds. The first part of the thesis deals with spin-crossover dinuclear triple-stranded helicates compounds with encapsulated halide ions using H2L4. Six of such helicates with different encapsulated halide or counter ions were synthesized: Cl⊂[Fe2(H2L4)3]Cl(PF6)2·5.7CH3OH (1) Br⊂[Fe2(H2L4)3]Br(PF6)2·4CH3OH (2) Cl⊂[Fe2(H2L4)3]Cl(PF6)2·3CH3OH·1H2O (1a) Br⊂[Fe2(H2L4)3]Br(PF6)2·1CH3OH·1H2O (2a) Cl⊂[Fe2(H2L4)3](I3)3·3(Et2O) (3) Br⊂[Fe2(H2L4)3](I3)3·3(Et2O) (4) These isostructural compounds consist of triple-stranded helicates that encapsulate halide ion inside their cavity. The main difference is the kind of outer counterions and lattice solvents which affect dramatically the magnetic properties of these compounds as a result of changing the supramolecular interactions. Changing the halide ion from chloride to bromide in 1 and 2, respectively, shift the spin transition by 30 K. The SCO occur here from [HS-LS] to [HS-HS] upon heating. Compounds 1a and 2a are the water solvate helicates that produced from single-crystal to single-crystal exchange by exposing the crystals to the ambient water. This exchange leads to important changes; the {X⊂ [Fe2(H2L4)3]}3+ helicate are now symmetric and the two Fe centers are crystallographically identical. This change in the solvent affects dramatically the SCO behavior of the helicates. Two-step SCO from [LS-LS] à [HS- LS]à [HS-HS] states was observed in the bulk magnetic studies. Compounds 3 and 4 consists of {X⊂ [Fe2(H2L4)3]}3+ triple-stranded helicates similar to the one seen in previous helicates where the counter ions are now three triodide (I3-) linear ions occupying the outer space formed between the helical strands and the solvent is ether. In these complexes the iron centers remain in the HS state through all the temperatures. The change of the solvents used in the reaction yielded different supramolecular compounds using the same ligands H2L4. Dimerized mononuclear helicates {X⊂[Fe(H2L4)3]2}3+ was prepared where a halide ion is encapsulated inside the cavity formed by the intercalating dimers. Five dimerized triple-stranded helicates are presented in this thesis: Cl⊂[Fe(H2L4)3]2(OH)(PF6)2·H2O (5). Cl⊂[Fe(H2L4)3]2(FeCl4)3·2C3H6O·4C7H8 (6). Br⊂[Fe(H2L4)3]2(OH)(PF6)2·H2O (7). I⊂[Fe(H2L4)3]2(PF6)2.23(I)0.21(I3)0.56·2CH3OH (8) I⊂[Fe(H2L4)3]2(I)2(I3)0.6(OH)0.4·0.6H2O·2CH3OH·2C3H6O (9) In every mononuclear helicate, one pyrazolyl-pyridine side of each ligand is not coordinated to any metal ion. The SCO behavior of the dimer is also affected by the nature of the halide ions which make hydrogen bonding with the N-H groups of the pyrazole rings. Using the ligand H2L6, the encapsulation of [M(III)(ox)3]3- (M = Fe and Cr; ox = oxalate) metal complexes inside the helical cavity of [Fe2(H2L6)3]4+ was achieved. Two of such triple-stranded helicates are presented in this thesis: Fe(C2O4)3⊂[Fe2(H2L6)3](BF4)·4CH3OH·3.7H2O (10). Cr(C2O4)3⊂[Fe2(H2L6)3](BF4)·1.4CH3OH·6H2O (11). The Fe(II) ions of the helicate exhibit SCO behavior and LIESST effect in the case of the encapsulated chromium oxalate complex. Interestingly, the guest [Cr(III)(ox)3]3- exhibits SIM-like behavior at low temperatures. This is the first example where a host- guest system exhibits both LIESST effect and SIM behavior.
Dos ligandos bis-pyrazolylpyridine, H2L4 y H2L6 fueron diseñados y preparados para sintetizar ensamblajes con iones de metales de transición en forma de helicatos de cadena triple donde la cavidad central puede encapsular diferentes contraiones en función del tamaño de esta cavidad. 13 compuestos a base de hierro se han cristalizado y estudiado, con la adición de manera significativa de compuestos helicoidales con SCO de la literatura. La estructura cristalina de todos los compuestos fueron resueltas, lo que permitió un amplio estudio de las interacciones supramoleculares y la influencia de estas interacciones sobre las propiedades magnéticas de los compuestos. La primera parte de la tesis trata de compuestos helicoidales dinucleares de cadena triple presentando transición de espín con iones haluro encapsulados utilizando H2L4. Estos compuestos isoestructurales consisten en helicatos de cadena triple que encapsulan iones haluro dentro de su cavidad. La principal diferencia es el tipo de contraiones exteriores y disolventes de cristalización que afectan dramáticamente las propiedades magnéticas de estos compuestos, como resultado de cambiar las interacciones supramoleculares. El cambio del ión haluro, de cloruro a bromuro, da un cambio de la transición de espín de unos 30 K. En los complejos metanólicos, la SCO se producen por calentamiento, a partir de [HS-LS] a [HS-HS], donde los estados de espín mixtos se consigue gracias a diferente distorsión alrededor de los iones metálicos, como resultado de diferentes enlaces de hidrógeno supramolecular cerca de los dos. Los helicatos con agua se producen a partir de una transformación cristal-cristal, mediante la exposición de los cristales a agua a temperatura ambiente. Este cambio en el disolvente afecta dramáticamente el comportamiento del SCO. Dos pasos en el SCO ([LS-LS] à [HS-LS] à [HS-HS]) se observarón en los estudios magnéticos. El cambio de los aniones a triyoduro (I3-) estabilizan el estado HS en todas las temperaturas medidas. El cambio en los disolventes utilizados en la reacción produjo diferentes compuestos supramoleculares utilizando el mismo ligando H2L4. Diferente helicatos mononucleares dimerizados {X⊂[Fe(H2L4)3]2}3+ fueron preparado donde se encapsula un ion haluro dentro de la cavidad formada por los dímeros intercalantes. En cada helicato mononuclear, un lado pirazolilo-piridina de cada ligando no se coordina a ningun ion metálico. El comportamiento de SCO del dímero también se ve afectada por la naturaleza de los iones haluro que forman con los enlaces de hidrógeno con los grupos N-H de los anillos de pirazol. Utilizando el ligando H2L6, se logró la encapsulación de complejos metálios de tipo [M(III)(ox)3]3- (M = Fe y Cr; ox = oxalato) dentro de la cavidad helicoidal [Fe2(H2L6)3]4+. Los iones Fe (II) del helicato exhiben SCO y efecto LIESST en el caso del complejo de cromo oxalato encapsulado. Curiosamente, el invitado [Cr(III)(ox)3]3- presenta un comportamiento de SIM a bajas temperaturas. Este es el primer ejemplo en el que un sistema hospedador-huésped exhibe tanto efecto LIESST y comportamiento SIM.

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49

Tzou, Der-Lii M. "Solid state 13C NMR studies of the Morphology and orientational order of polymer fibers." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/30276.

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50

Youssef, Mostafa Youssef Mahmoud. "Probing water properties and cationic exchange in calcium-silicate-hydrate : an atomistic modeling study." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62710.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2010.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Two problems related to the assessment of the performance of cementitious materials in the nuclear fuel cycle are investigated by means of atomistic simulations. The first is the structural and dynamic nature of water confined in the nano-pores of the highly disordered calcium-silicate-hydrate (C-S-H) which is the major binding phase of cement. The microscopic structure and dynamics of water confined in C-S-H have important implications on describing the cohesion and mechanical behavior of cement from its setting to its aging; nevertheless they have not been fully elucidated prior to this thesis. The second problem is the encapsulation of strontium-90, an important radionuclide, in C-S-H and its crystalline analogue tobermorite 9 A by means of cationic exchange with calcium. We showed that the nature of the interaction between the confined water and C-SH is hydrophilic. The interlayer calcium ions and the disorder in the silicate chains act synergistically to achieve this hydrophilic interaction. The water molecules ultra-confined in this hydrophilic and disordered interlayer space adopt a unique multi-range structure: at short range they are tetrahedrally coordinated but with distortions, at intermediate range they exhibit a structure similar to that of dense fluids and supercooled phases, and at ranges up to 10 A spatial correlations persist through dipole-dipole interactions that are enhanced by the directionality of the hydrogen bonds formed between the confined water and the defective silicate chains. This confined water exhibits a three-stage dynamics evidenced in the mean square displacement (MSD) results, with a clear cage stage characteristic of glassy dynamics similar to that of supercooled liquids and glass forming materials. The glassy dynamics is induced primarily because of the attractive interactions of water molecules with the calcium silicate walls, serving to constrain the motion of the water molecules at the interface, as if with an effective temperature lower than the actual simulation temperature. At intermediate time scales that correspond to the p-relaxation of glassy materials, the non-Gaussian parameter indicates a significant heterogeneity in the translational dynamics of the confined water, also consistent with the cage stage identified in the MSD of the water molecules. Strontium was shown to favor energetically substituting calcium in the interlayer sites in C-S-H and tobermorite 9 A with the trend more pronounced in the latter. The silicate chains in both cementitious waste forms were not affected by strontium substitution within our molecular dynamics simulation. Finally, we observed degradation in the mechanical properties in the strontium-containing cementitious waste form. The degradation increases with the increase of strontium concentration, but overall this degradation is not limiting for the use of C-S-H or tobermorite 9 A as candidates in immobilizing radioactive strontium.
by Mostafa Youssef Mahmoud Youssef.
S.M.

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