Tesi sul tema "Iron structures"
Segui questo link per vedere altri tipi di pubblicazioni sul tema: Iron structures.
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 saggi (tesi di laurea o di dottorato) per l'attività di ricerca sul tema "Iron structures".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi le tesi di molte aree scientifiche e compila una bibliografia corretta.
1
Tuncel, Selcan. "Synthesis Of Iron Borophosphates And Phosphates With Zeo-type Structures". Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/2/1260460/index.pdf.
Abstract (sommario):
New iron phosphate and borophosphate compounds were synthesized and characterized by single crystal/powder X-ray diffraction, infrared spectroscopy, raman spectroscopy, thermogravimetric analysis, electron microscopy and elemental analysis.
Using several compositions, Fey B(PO4)x type of compounds were attempted to be prepared by solid state reactions. The solid state reactions of boron compounds with a phosphating agent has been completed at 950oC. A new product Fe2BP3O12 is synthesized and indexed in this work which is isostructural with Cr2 BP3O12
A single crystal of iron ammonium phosphate, (NH4)3-xHxFeP3O12, was synthesized by a hydrothermal method and characterized. Its X-ray powder diffraction
pattern was indexed in orthorhombic system. The unit cell parameters were found to be as a = 7.775 (Å), b = 7.445(Å
), c = 14.331(Å
) The compound with the formula NH4FeBP2O8OH was synthesized by hydrothermal method. Its X-ray powder diffraction pattern was indexed in monoclinic system. The unit cell parameters were found to be a = 9.336, b = 8.278, c =9.642Å
, and &
#946
= 101.60o, which are good agreement with the literature values. Ferro-axinite type of compound was discovered as single crystals resembling the axinite mineral. The compound was indexed in triclinic system with the unit cell parameters of a = 7.167, b = 8.840 , c = 9.455Å
, &
#945
= 64.83o, &
#946
= 64.83o, &
#947
= 69.42o. A zeotype Fe(H2O)2BP2O8.H2O, which was obtained by hydrothermal methods before, was synthesized by a precipitation method using different initial reactant. In this case, instead of Fe+2, Fe+3 compound was used as a reactant. All the compounds have been investigated by FTIR spectroscopy and the assignments of the functional BO3, BO4 and PO4 groups have been done.
2
Cao, Jianying. "Electronic structures of iron monocarbide (FeC) and rhenium mononitride (ReN)". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ34253.pdf.
3
Mohd-Ali, B. B. "Computer mapping of grain structures in grain-oriented silicon-iron". Thesis, Bucks New University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373598.
4
Powell, Robyn. "Structures and magnetic properties of iron(III) spin-crossover compounds". Thesis, Aston University, 2017. http://publications.aston.ac.uk/37512/.
Abstract (sommario):
Transition metal fragments displaying switching behaviour are appealing materials, which may be used in a functional way in research and technology. Some molecular species containing transitionmetal ions may exhibit a crossover between states having a different magnetic moment, the magnetic interconversion between the low-spin and high-spin state in FeIII systems which can be triggered by a change in temperature, pressure or by light irradiation. The research presented in this thesis focuses on using substituted derivatives of R-salicylaldehyde 4R’-thiosemicarbazone (H2L, H2-R-thsa-R’) for generating FeIII spin crossover. The aim was to design mononuclear FeIII compounds with a view of studying their structural features and magnetic properties. The results present the full structural analysis of differently charged FeIII-bis(ligand) complexes, these include: (i) (cation+)[FeIII(L2‒)2]·x(solvent), (ii) [FeIII(HL‒)(L2‒)]·x(solvent) and(iii) [FeIII(HL‒)2](anion‒)·x(solvent). The studies discuss several influences on the structural features and the magnetic properties of the reported FeIII compounds, these include: the nature of the anionor cation associated with the FeIII complex, the degree of solvation of the complex and the variations in the ligand substituents. The magnetic studies of the (cation+)[FeIII(L2‒)2]·x(solvent) compounds have presented one high-spin compound ((CH3)2NH2[Fe(3-OEt-thsa)2]) and four low-spin compounds (Cs[Fe(3-OEt-thsa-Me)2]·CH3OH, Cs[Fe(5-Br-thsa)2], NH4[Fe(thsa)2] and NH4[Fe(5-Br-thsa)2]), of which NH4[Fe(5-Br-thsa)2] revealed a fraction of the FeIII ions convert into the high-spin state. Three [FeIII(HL‒)(L2‒)]·x(solvent) compounds have been studied, of which a rare two-step spin transition has been observed for [Fe(H-5-Cl-thsa-Me)(5-Cl-thsa-Me)]·H2O, while the isostructural compounds [Fe(Hthsa-Me)(thsa-Me)]·H2O undergoes an incomplete spin transition and [Fe(H-3-OEt-thsa-Me)(3-OEt-thsa-Me)]·H2O remains in the high-spin state. It was recognised that the steric and electronic features imposed by the R,R’-substituents may have an impact on the spin state of FeIII cations, and affect at which temperature the spin transition occurs. Furthermore, the FeIII cation of both [FeIII(HL‒)2](anion‒)·x(solvent) compounds, [Fe(H-5-Br-thsa-Et)2](NO3)·H2O and [Fe(H-4-OHthsa)2]4·(SO4)2·9H2O, were found to be in the high-spin state. Collectively, the described research has provided new insight into this family of FeIII bis(Rsalicylaldehyde4R’-thiosemicarbazone) compounds and provides a strong foundation for further studies.
5
Henderson, Richard K. "The formation and structures of iron(III) polycarboxylato species formed in aqueous solution". Thesis, University of East Anglia, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357576.
6
Olowe, A. Abiodun. "Aqueous corrosion of iron in sulphated media mechanisms, kinetics and structures /". Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37617200t.
7
Maraveas, Chrysanthos. "Fire resistance of metal framed historical structures". Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/fire-resistance-of-metal-framed-historical-structures(390efc49-7228-4ad1-a164-356213df96fb).html.
Abstract (sommario):
This thesis focuses on fire resistance of 19th century cast iron framed structures. Based on material property data obtained from a comprehensive literature review, upper and lower bound relationships of the thermal and mechanical properties of 19th century fireproof floor construction materials have been derived. Because these materials have large variability, a sensitivity analysis has been undertaken to investigate the most effective ways of representing such variability. The sensitivity analysis has indicated that the elevated mechanical properties of cast iron should be reliably quantified. The thermal expansion of cast iron can be taken as equal to that of steel as in EN1993-1-2. Variabilities in other material properties have modest effects on fire resistance of cast iron structures and can be safely modeled according the Eurocode material models for similar modern materials (using thermal properties of modern steel for cast iron, using thermal properties of modern concrete for the insulation materials of cast iron structures). In order to resolve some of the uncertainties in mechanical properties of cast iron at elevated temperatures, a total of 135 elevated temperature tests have been performed, including tension and compression tests, transient state and steady state tests, tests after cooling down and thermal expansion tests. These test results have been used to establish the elevated temperature stress-strain-temperature relationships in tension and compression. Afterwards, calculation methods are developed to calculate the bending resistance of cast iron beams and compression resistance of cast iron columns at elevated temperatures. For cast iron beams, a fibre model has been developed to calculate elevated temperature moment capacity of cast iron beams in jack arch construction, taking into consideration non-uniform temperature distributions in the cross-section. The fibre model divides the cross section into a large number of fine layers and for a given curvature and neutral axis position calculates the strain, the temperature, the stress and the force of each layer. It has been found that under historically applied load, the fire resistance of such beams can be 60 minutes or higher. The Monte Carlo simulation method has been used to take into account the variabilities of important mechanical properties of cast iron at elevated temperatures; Young’s modulus, 0.2% proof stress, ultimate strength, corresponding strain at ultimate strength and failure strain in tension and Young’s modulus, proportional limit and 0.2% proof stress in compression. This has enabled material safety factors of 1.50, 2.50, 4.50 and 5.50 to be proposed for target failure probabilities of 10-1, 10-2, 10-3 and 10-4 respectively. For cast iron columns, a finite element model, built using the commercial software ABAQUS, has been used to examine the effects of changing different design parameters (column slenderness, member imperfection, cross section imperfection, degree of axial restraint, load factor and load eccentricity) on fire resistance of cast iron columns. Validation of the finite element model was by comparison of the simulation results against six fire resistance tests, three on unprotected and three on protected cast iron columns. The results of this numerical parametric study indicate that the fire resistance of cast iron columns is generally higher than that of modern steel columns because the applied loads on cast iron columns are lower and cast iron columns have thicker sections than modern steel columns. Comparison of the numerical parametric study results with the calculation results using the steel column design method in EN1993-1-2 has found that the EN 1993-1-2 calculation results are generally on the safe side.
8
Wang, Qianen, e 王乾恩. "Electronic structures of impurity and orbital-resolved vortex core states in iron-selenide superconductors". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/206433.
Abstract (sommario):
We study the effect of a single non-magnetic impurity and vortex core states in iron-selenide superconductors by solving the Bogoliubov-de Gennes equations self-consistently based on a three-orbital model. Various pairing symmetry are considered in the calculation. The impurity-induced in-gap bound states are found only for attractive impurity scattering potential, as in the cases of doping of Co or Ni, which is characterized by the strong particle-hole asymmetry, in the nodeless d_(x^2-y^2 ) wave pairing state. This property may be used to probe the pairing symmetry of iron-selenide 122-type superconductors. The orbital-resolved vortex core states of different pairing symmetries manifest themselves as distinguishable structures due to different behavior of the quasiparticle wavefunctions. The obtained vortices are classified by the invariant subgroups of the symmetry group of the meanfield Hamiltonian in the presence of magnetic field as isotropic s- and s±-wave vortices have G_5 symmetry for each orbital, whereas d_(x^2-y^2 ) wave vortices show G(* )¦6 symmetry for d_xzand d_yz orbitals and G(* )¦5 symmetry for d_xy orbital. In the case of d_(x^2-y^2 ) wave vortices, hybridized-pairing between d_xzand d_yz orbitals gives rise to a relative phase difference in terms of winding structures of vortices between these two orbitals and d_xy orbital, which is essentially caused by a transformation of co-representation of G(* )¦5 and G(* )¦6 subgroup. Calculation of particle densities show common charging feature of vortices in the cases of s± and d_(x^2-y^2 ) wave pairing states where the electron-like vortices are observed for d_xz and d_yz orbitals while hole-like vortices for d_xyorbital. The phase difference of orbital-resolved d_(x^2-y^2 ) wave vortices and their charging effects can be verified by further experimental observations.published_or_final_version
Physics
Doctoral
Doctor of Philosophy
9
Nadler, Jason Hayes. "The hydrogen reduction of iron and chromium oxides". Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/19410.
10
Landgraf, Boris [Verfasser], e Wolfgang [Akademischer Betreuer] Hansen. "Structural, magnetic and electrical investigation of Iron-based III/V-semiconductor hybrid structures / Boris Landgraf. Betreuer: Wolfgang Hansen". Hamburg : Staats- und Universitätsbibliothek Hamburg, 2014. http://d-nb.info/1048626555/34.
11
Nguyen, Thao Ahn 1958. "Defect structures, phase relations and phase transformations of low temperature iron sulfide compounds". Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/92621.
12
Brucka, Marta Anna. "N-Heterocyclic carbene complexes of silver, rhodium and iron: structures, dynamics and catalysis". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amslaurea.unibo.it/3873/.
Abstract (sommario):
The research performed in the framework of this Master Thesis has been directly inspired by the recent work of an organometallic research group led by Professor Maria Cristina Cassani on a topic related to the structures, dynamics and catalytic activity of N-heterocyclic carbene-amide rhodium(I) complexes1. A series of [BocNHCH2CH2ImR]X (R = Me, X = I, 1a’; R = Bz, X = Br, 1b’; R = trityl, X = Cl, 1c’) amide-functionalized imidazolium salts bearing increasingly bulky N-alkyl substituents were synthetized and characterized. Subsequently, these organic precursors were employed in the synthesis of silver(I) complexes as intermediate compounds on a way to rhodium(I) complexes [Rh(NBD)X(NHC)] (NHC = 1-(2-NHBoc-ethyl)-3-R-imidazolin-2-ylidene; X = Cl, R = Me (3a’), R = Bz (3b’), R = trityl (3c’); X = I, R = Me (4a’)).
VT NMR studies of these complexes revealed a restricted rotation barriers about the metal-carbene bond. However, while the rotation barriers calculated for the complexes in which R = Me, Bz (3a’,b’ and 4a) matched the experimental values, this was not true in the trityl case 3c’, where the experimental value was very similar to that obtained for compound 3b’ and much smaller with respect to the calculated one. In addition, the energy barrier derived for 3c’ from line shape simulation showed a strong dependence on the temperature, while the barriers measured for 3a’,b’ did not show this effect. In view of these results and in order to establish the reasons for the previously found inconsistency between calculated and experimental thermodynamic data, the first objective of this master thesis was the preparation of a series of rhodium(I) complexes [Rh(NBD)X(NHC)] (NHC = 1-benzyl-3-R-imidazolin-2-ylidene; X = Cl, R = Me, Bz, trityl, tBu), containing the benzyl substituent as a chiral probe, followed by full characterization. The second objective of this work was to investigate the catalytic activity of the new rhodium compounds in the hydrosilylation of terminal alkynes for comparison purposes with the reported complexes.
Another purpose of this work was to employ the prepared N-heterocyclic ligands in the synthesis of iron(II)-NHC complexes.
13
Villalba, Pedro Javier. "Nanodiamond Based Composite Structures for Biosensing Applications". Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5144.
Abstract (sommario):
This dissertation presents the synthesis and application of nanodiamond based materials for electrochemical biosensors. In this research work, nanodiamond particles have been used to prepare doped and undoped nanocrystalline diamond films, and conducting polymer composites for enhanced biosensing. The performance of the synthetized materials towards sensing applications was evaluated against glucose amperometric biosensing. Besides, cholesterol biosensing was attempted to prove the capabilities of the platform as a generic biosensing substrate.
Biosensors have been proved to provide reliable detection and quantification of biological compounds. The detection of biological markers plays a key factor in the diagnosis of many diseases and, even more importantly, represents a major aspect in the survival rate for many patients. Among all of the biosensors types, electrochemical biosensors have demonstrated the best reliability to cost ratio. Amperometric biosensors, for example, have been used for decades as point of care sensing method to monitor different conditions such as glucose. Despite the amount the research presented, the sensitivity, selectivity, stability, low cost and robustness are always driving forces to develop new platforms for biosensor devices.
In the first phase of this dissertation, we synthesized undoped and nitrogen doped nanocrystalline diamond films. The synthetic material was thoroughly studied using different material characterization techniques and taken through a chemical functionalization process. The functionalization process produced a hydrogen rich surface suitable for enzymatic attachment. Glucose oxidase was covalently attached to the functionalized surface to form the biosensing structure. The response of the biosensor was finally recorded following voltammetry and amperometric techniques under steady state and dynamic conditions. The experimental results demonstrated that conductivity induced by the doping process enhanced the sensitivity of the sensing structure with respect to the undoped substrate. Also, the functionalization procedure showed strong bonding to avoid enzyme leaching during the measurements.
Later, in the second phase of this dissertation, the nanodiamond particles were used as filler for conducting polymer composites. The objective for developing these composite materials was to overcome the high resistivity observed for nanocrystalline films. The experimental results demonstrated that the inclusion of nanodiamond particles increased the sensitivity of the overall structure towards the quantification of glucose with respect to the nanocrystalline films and the bare polymer. Besides, the experiment showed a noticeable enhancement in the signal-to-noise ratio and the mechanical stability of the sensing platform due to the nanodiamond addition. The best structures from the previous experiments were further grafted with iron oxide nanoparticles to attempt signal amplification. Initial experiments with nanodiamond based composited showed similar current for low glucose concentrations for two different active electrochemical sensing areas. This observation indicates that more area is still available to transport signal and to enhance even further the sensing action. Oxidation of iron oxide nanoparticles after initial enzymatic decomposition of glucose has been proved to provide higher current for the same glucose concentration; thus, creating amplification effect for the signal. Finally, the toxicity of the nanomaterial synthesized during this dissertation was evaluated in mammalian cells. The advances in biosensing techniques indicate the potential application of amperometric platform for continuous implantable devices; hence, the toxicity of the materials becomes a key aspect of the platform design.
14
Medina, Ricardo A. Krawinkler Helmut. "Seismic demands for nondeteriorating frame structures and their dependence on ground motions /". Berkeley : Pacific Earthquake Engineering Research Center, 2004. http://peer.berkeley.edu/publications.
Abstract (sommario):
Originally published as first author's thesis."May 2004." "John A. Blume Earthquake Engineering Center, Dept. of Civil & Environmental Engineering, Stanford University." Includes bibliographical references.
15
Harland, Cathy. "Processing, structures and properties of nanophase rare earth - iron - boron based hard magnetic alloys". Thesis, University of Sheffield, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327729.
16
Fanello, Marta. "Later Iron Age coinage in Britain : reconstructing insular social structures and systems of value". Thesis, University of Leicester, 2016. http://hdl.handle.net/2381/37981.
Abstract (sommario):
This thesis compares numismatic and archaeological evidence from different regions of Britain in order to investigate the changes in systems of values that occurred in the late Iron Age and how these reflect transformations in endogenous social structures. Coins began to be systematically imported into Britain from Gaul during the 2nd century BC. Local gold production began in the early 1st century BC, in conjunction with the development of new settlements forms and the intensification of relations with the Roman world. The chronology of the adoption of coinage was not uniform across Britain and different regional outcomes are visible in the use of metals and imagery. Different sets of data, including coins from excavated sites, hoards, and metal detector finds are studied in order to attain a wider understanding of patterns of distribution and deposition, and to identify regional trends and variations in the character and use of coins. The thesis explores how the introduction of coins into Britain contributed to the development of diverse forms of authority, and fostered competitive processes based on local concepts of possession, status, and power. Social changes at the end of the 1st millennium BC are interpreted as a combination of the assimilation, selective reception or total rejection of continental traits, and endogenous transformations in the local systems of value.
17
Nakatani, Naoki. "Theoretical Studies of Photoproteins and Non-Heme Iron Enzymes: Electronic Structures and Reaction Processes". 京都大学 (Kyoto University), 2010. http://hdl.handle.net/2433/120885.
18
WILLIAMS, GEORGE CLAY. "STEEL CONNECTION DESIGNS BASED ON INELASTIC FINITE ELEMENT ANALYSES (GUSSET, BRACING, STRUCTURES)". Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/188168.
Abstract (sommario):
Analytical and experimental studies were made to develop design procedures for steel gusset plate connections in diagonally braced frames. Stiffness and strength models of structural fasteners based on physical tests were incorporated into inelastic finite element analyses. The modeling techniques were verified by comparing analytical and experimental results of full scale connection tests. Finite element models of bracing connections were generated to determine gusset plate force, stress, strain, and displacement distributions for a variety of connection designs including K-bracing and X-bracing. Based on these results current design procedures were scrutinized and new design procedures were proposed for predicting the tensile strength, buckling strength, and force distributions for bracing connections. Additionally, it was found that gusseted beam-to-column connections are rigid (AISC Type I) and the centroidal axes of the brace, beam, and column members do not necessarily need to intersect at a common working point.
19
Dörmbach, Karla Verfasser], Andrij Z. [Akademischer Betreuer] [Pich e Ulrich [Akademischer Betreuer] Simon. "Iron Oxide-Based Multi-Compartment Colloids with Complex Structures / Karla Dörmbach ; Andrij Pich, Ulrich Simon". Aachen : Universitätsbibliothek der RWTH Aachen, 2015. http://d-nb.info/112807611X/34.
20
Dörmbach, Karla [Verfasser], Andrij Z. [Akademischer Betreuer] Pich e Ulrich [Akademischer Betreuer] Simon. "Iron Oxide-Based Multi-Compartment Colloids with Complex Structures / Karla Dörmbach ; Andrij Pich, Ulrich Simon". Aachen : Universitätsbibliothek der RWTH Aachen, 2015. http://d-nb.info/112807611X/34.
21
Lo, David Siu-Kau. "A contribution to the computer aided design of optimized structures for the steel industry". Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/28497.
Abstract (sommario):
A practical method of incorporating realistic flexible connections including the effect of connection sizes and shear deflection in plane frame analysis is presented. The general algorithm can be easily implemented in a standard plane frame analysis program and once implemented it can be an ideal tool for production work in the steel industry. In this approach connection stiffness is programmed directly into the analysis by utilizing the connection moment-rotation equations developed by Frye and Morris but it may also be entered separately as data. Nonlinear connection analysis is carried out by the procedure outlined by Frye and Morris. Practical application of this method of analysis is demonstrated by modifying a standard plane frame analysis program to include the effect of flexible connections. The validity of the modified program, CPlane, was verified against the findings of Moncarz and Gerstle.
Using CPlane, a simple plane frame structure was analyzed under various lateral load intensities for different connection assumptions. It was found that the inclusion of connection behavior significantly altered the internal force distribution and design of the structure.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
22
Chan, Sau-han, e 陳秀嫻. "Non-heme iron(III) and gold(III) complexes with dicarboxamide ligands: synthesis, structures and anti-cancerproperties". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39557984.
23
Lui, Wing Man. "Design of cold-formed high strength stainless steel tubular columns and beam-columns /". View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202004%20LUI.
Abstract (sommario):
Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004.Includes bibliographical references (leaves 149-154). Also available in electronic version. Access restricted to campus users.
24
Chan, Sau-han. "Non-heme iron(III) and gold(III) complexes with dicarboxamide ligands synthesis, structures and anti-cancer properties /". Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/HKUTO/record/B39557984.
25
McIntosh, Monique Sandra. "Mechanisms and Factors Affecting Chromium Oxide Particle reduction in Iron-Chromium Honeycombs". Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6934.
Abstract (sommario):
In the production of iron chromium honeycombs, iron oxide and chromium oxide mixtures are reduced by hydrogen at elevated temperatures to produce a metallic alloy. The complete reduction of the iron oxide occurs prior to the reduction of the chromium oxide. The reduction of the chromium oxide particles within the iron matrix is affected by factors that include the diffusion of the reduced chromium away from the chromium oxide particle into the iron matrix, the diffusion of the gaseous reactants and products to and from the chromium oxide particles, and the porosity of the iron matrix, which changes as a result of sintering. The type of heat-treatment used, (isothermal or non-isothermal, i.e., holding at a specific temperature versus using a steadily increasing temperature) plays a vital role in how these factors will affect chromium oxide reduction.
Experimental data were used in conjunction with sintering and dissolution models to obtain an understanding of the environment in which the chromium oxide particles reduce as a function of heat-treatment. This understanding will assist in the development of more effective processing steps for the reduction of metallic honeycombs from oxide mixtures.
26
Xie, Jin, e 解錦. "Synthesis, structures and spectroscopic properties of primary and secondary phosphine complexes of iron, ruthenium and osmiumporphyrins". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B39556876.
27
Kim, Jongsun Rees Douglas C. Rees Douglas C. "Crystallographic structures and functional implications of nitrogenase molybdenum-iron proteins from Azotobacter vinelandii and Clostridium pasteurianum /". Diss., Pasadena, Calif. : California Institute of Technology, 1993. http://resolver.caltech.edu/CaltechETD:etd-09182007-093920.
28
Kpogo, Kenneth K. "X-ray crystal structures of: [Rh2(N-{2,4,6-CH3}C6H2)COCH3)4]•2NCC6H4 AND Ba1.5[Fe(C10H13N2O7)][Co(CN)6]•9H2O; two crystallographic challenges". Digital Commons @ East Tennessee State University, 2013. https://dc.etsu.edu/etd/1175.
Abstract (sommario):
The novel compound, [Rh2(N-{2,4,6-CH3}C6H2)COCH3)4] was synthesized. Crystal structures of [Rh2(N-{2,4,6-CH3}C6H2)COCH3)4]·2NCC6H5 and Ba1.5[Fe(C10H13N2O7)][Co(CN)6]·9H2O were determined employing a Rigaku Mercury375R/M CCD (XtaLAB mini) diffractometer with graphite monochromated Mo-Kα radiation. For [Rh2(N-{2,4,6-CH3}C6H2)COCH3)4]·2NCC6H5, the space group was P-421c(#114) with unit cell dimensions: a =11.0169(14)Å, c =21.499(3)Å, V = 2609.4(6)Å3. Each rhodium had approximately octahedral coordination and was bound to another rhodium atom, two nitrogens (trans to each other), two oxygens (trans to each other), and one benzonitrile nitrogen (trans to rhodium). For Ba1.5[Fe(C10H13N2O7)][Co(CN)6]·9H2O the space group was: P-1(#2) with unit cell dimensions: a=13.634Å, b=13.768Å, c=17.254Å and α=84.795°, β=87.863°, γ=78.908°, V=3164.5Å3. The iron atom (nearly octahedral) was coordinated to one chelating ligand (derived from ethylenediaminetetraacetic acid) and the nitrogen of a cyanide ligand. The carbon of the cyanide ligand was bound to cobalt (octahedral). Thus, the cyanide ligand serves as a bridge between the two metals.
29
Jiménez, Pacheco Julio. "Behavior of steel-to-concrete connections for use in repair and rehabilitation of reinforced concrete structures /". Full-text Adobe Acrobat (PDF) file, 1992. http://www.engr.utexas.edu/research/fsel/FSEL_reports/Thesis/Jimenez-Pacheco,%20Julio.pdf.
30
Dong, Chunxiao, e 董春宵. "Uni-axial behaviour of concrete-filled-steel-tubular columns with external confinement". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hdl.handle.net/10722/195975.
Abstract (sommario):
This thesis studies the uni-axial behaviour of circular double-skinned concrete-filled-steel-tubular (CFST) columns with external confinement in form of external steel rings. Particular attention is paid to the experimental behaviour of double-skinned CFST columns and theoretical model for evaluating the loadcarrying capacity of un- and ring-confined double-skinned CFST columns.
Experimental studies on circular double-skinned CFST columns with various spacing of confinement, concrete strength and hollow ratio were conducted and discussed comprehensively. The mechanical properties of double-skinned CFST columns such as elastic stiffness, elastic strength, load-carrying capacity and ductility are presented. From the result, it is found that the elastic stiffness, elastic strength, load-carrying capacity and ductility are enhanced by installing the external steel rings to the outer tube as external confinement. To verify the effectiveness of external steel rings, the Poisson’s ratios of the double-skinned CFST columns are listed and found to be similar to that of concrete so that a perfect bonding is maintained. To emphasis the excellent performance of double-skinned CFST columns with external rings under uni-axial compression, the load-carrying capacity, elastic strength and elastic stiffness are compared to those of single-skinned CFST columns and reinforced concrete columns.
To fill up the gap that no design model is provided in Eurocode 4 (EC4) for confined double-skinned CFST columns, a theoretical model based on the force equilibrium condition is proposed for evaluating the load-carrying capacity of both un- and ring-confined double-skinned CFST columns. The model takes into account the composite action between the steel tubes and core concrete. To verify the proposed model, numerous test results obtained by the author and other researchers are used for comparing the theoretical results.
According to the above theoretical model above, a parametric study is carried out to investigate the effect of various geometry and material properties on the load-carrying capacity of double-skinned CFST columns. The confining pressure is expressed in terms of geometry and material factors. A simplified design formula is proposed to facilitate the preliminary design of double-skinned CFST columns with and without external confinement.published_or_final_version
Civil Engineering
Master
Master of Philosophy
31
Biddah, Aiman Mahmoud Samy. "Evaluation of the seismic level of protection of steel moment resisting frame building structures". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0007/NQ42833.pdf.
32
Xie, Jin. "Synthesis, structures and spectroscopic properties of primary and secondary phosphine complexes of iron, ruthenium and osmium porphyrins". Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/HKUTO/record/B39556876.
33
Huo, Suguo. "Micromagnetic simulation and MFM study of micromagnetic structures in ferromagnetic materials". Thesis, University of Sheffield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287631.
34
Ibrar, Muhammad. "Microstructure of Fe-based and NiFe nanowires encapsulated by multiwalled carbon nanotube radial structures". Thesis, Queen Mary, University of London, 2018. http://qmro.qmul.ac.uk/xmlui/handle/123456789/36222.
Abstract (sommario):
The crystalline iron-based nanowires encapsulated by multiwalled carbon nanotubes have been the subject of numerous studies owing to the range of potential applications. The presence of a-Fe (bcc)/y -Fe(fcc) junctions o ers the possibility of exploitation of the exchange bias effect, an interfacial magnetic phenomenon that plays a major role in magnetocaloric cooling, spintronic and high-density magnetic storage devices. This work is concerned with the synthesis and microstructural characterization of Fe-based and NiFe nanowires encapsulated by multiwall carbon nanotube radial structures. The known attributes of these structures are well matched to the magnetocaloric application. The primary aim of this work was to determine the unknown microstructural details of the encapsulated nanowire that are of relevance to the magnetocaloric application (junction types, location and orientation relative to the nanotube axis). The secondary aim was to explore the modi cation of the synthesis route to promote desirable attributes. This is the first report of a-Fe/y -Fe sequential junctions and a-Fe/Fe3C concentric junctions in encapsulated Fe-based nanowires. The presence of a-Fe/y -Fe junctions was inferred from the observation of a-Fe nanowires terminated by a ~100 nm length y-Fe crystallites of larger diameter. The a-Fe/Fe3C junctions exhibit the Bagaryatski orientation relationship: [110 ]bcck[100 ]orth. The degree of substrate roughness was found to be a means of tailoring details of the structure and composition of the encapsulated nanowires. NiFe encapsulated nanowires were found to contain crystallites of a-NiFe, y-NiFe and Ni3Fe and the sequential junctions -NiFe/Ni3Fe and a-NiFe/y-NiFe junctions.
35
Raby, Douglas Allan. "Development of a system architecture and applications for an integrated computer software system for the analysis and design of steel structures". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0017/MQ48372.pdf.
36
Gardenghi, David Jeremiah. "Synchrotron radiation-based spectroscopic investigation of the electronic and geometric structures of iron-sulfur clusters, particles, and minerals". Diss., Montana State University, 2012. http://etd.lib.montana.edu/etd/2012/gardenghi/GardenghiD0512.pdf.
Abstract (sommario):
Iron-sulfur systems are ubiquitous in biological and geological environments. They range from molecular scale [2Fe-2S] clusters to nanometer scale particles to micrometer scale minerals. Across the length scale, each system has unique structural and functional roles with respect to its environment, such as metalloproteins or hydrothermal vents. Therefore, it is of great interest to understand the electronic and geometric structural properties that give a wide range of reactivity. The main focus of this dissertation is to investigate the possible connections among the different size scales using a primary technique, X-ray absorption spectroscopy (XAS), by gaining an understanding into the relationship between the system size and properties. X-ray absorption spectroscopy is a powerful tool to probe geometric and electronic structures across the entire length scale. In this work, extend x-ray absorption fine structure (EXAFS) analysis method was applied to determine geometric structure of the protein bound, molecular iron-sulfur cluster of HydA. It was found to contain a preformed [4Fe-4S] cluster. This method combined with Fe/S K-edge XANES analysis was applied to spore photoproduct lyase metalloprotein to structurally characterize the [4Fe-4S] cluster and its interaction with SAM. The Fe K-edge EXAFS and Fe/S K-edge XANES provide evidence for a cluster distortion upon interacting with SAM as a new EXAFS feature, indicating the presence of longer Fe-Fe distances and this provides new insights into the structure of radical SAM enzymes. At the nanometer scale, mineral and protein encapsulated particles were investigated with a possible link between molecular and micrometer scale. A reference library of FeS systems was established to describe the variation in bonding and structure. Also, a considerable amount was learned about XAS detection methods, and this was applied to the micrometer scale systems. From EXAFS and XANES analysis, the modified surface of pyrite was revealed to have an intermediate layer of Fe(I)-S phase with a metallic iron surface, and a reaction scheme was proposed. These studies of the different size iron-sulfur systems provide insights into the change in the electronic and geometric structures, and a model was proposed to describe the effects of size on the electronic and geometric structure. 'Co-authored by Sunshine C. Silver, Eric M. Shepard, Sunil G. Naik, BoiHanh Huynh, Robert K. Szilagyi, and Joan B. Broderick.'
37
Guerra, Gabriel Andrés Fonseca. "Study of the longitudinal spin Seebeck effect in hybrid structures with yttrium iron garnet and various metallic materials". Universidade Federal de Pernambuco, 2014. https://repositorio.ufpe.br/handle/123456789/12719.
Abstract (sommario):
Submitted by Daniella Sodre (daniella.sodre@ufpe.br) on 2015-04-08T12:40:55Z
No. of bitstreams: 2
DISSERTAÇÃO Gabriel Fonseca.pdf: 3837074 bytes, checksum: e2c9b20882785e374170658d648ee389 (MD5)
license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5)Made available in DSpace on 2015-04-08T12:40:55Z (GMT). No. of bitstreams: 2 DISSERTAÇÃO Gabriel Fonseca.pdf: 3837074 bytes, checksum: e2c9b20882785e374170658d648ee389 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Previous issue date: 2014-03-10
Conselho Nacional de Desenvolvimento Científi co e Tecnol ógico; Coordenação de Aperfeiçoamento de Pessoal de Ní vel Superior; Financiadora de Estudos e Projetos; Fundação de Amparo a Ciência e Tecnologia do Estado de Pernambuco.
In this master thesis we study experimentally the longitudinal spin Seebeck effect (LSSE) in bilayers made of a ferromagnetic insulator (FMI) and a metallic layer (M). We also present a theoretical model based on the spin current density ⃗ Js carried by a non-equilibrium magnon distribution, generated by a thermal gradient ∇T across the thickness of the FMI. When ⃗ Js reach the FMI/M interface it is pumped towards the M layer due to conservation of the angular momentum, so, the M layer is essential for the LSSE existence. Here the FMI consists of a Yttrium Iron Garnet (YIG) lm, grown over a Gadolinium Gallium Garnet (GGG) substrate. Different metallic materials were used as the M layer i.e. Pt and Ta that have normal behavior and Py that is a ferromagnetic metal (FMM). The experimental procedure consists of systematic measurements of the electric voltage VISHE, produced by ⃗ Js through the Inverse Spin Hall Effect (ISHE) in the normal metal or (FMM) layer. In YIG/Pt measurements were done in the temperature range from 20 to 300 K. The experimental data are tted to the proposed model for the LSSE and good agreement is obtained. The results shows that the Py and Ta can be used to detect the LSSE with the ISHE. The results of this master thesis have strong interest in the area of spin caloritronics helping to the development of the eld and to raise possibilities of new spintronic devices. ----- Nesta diserta ção e estudado experimentalmente o Efeito Seebeck de Spin Longi- tudinal (LSSE), em bicamadas formadas por um isolante ferromagn etico (FMI) e um lme metalico (M). Tamb em foi desenvolvido um modelo te orico baseado na den- sidade de corrente de spin ⃗ Js que existe quando uma distribui c~ao de m agnons fora do equil brio e gerada por um gradiente t ermico ∇T aplicado na sec ção transversal do FMI. Quando ⃗ Js chega na interface FMI/M e bombeada para a camada M satis- fazendo a conserva ção do momentum angular, assim que a camada NM e essencial para ter um LSSE. Como camada FMI foi utilizada a granada de trio e ferro (YIG) crescida num substrato de (GGG). Diferentes materiais metalicos foram utilizados como camada M, sendo Pt e Ta paramagn eticos e o Py ferromagnetico. O proced- imento experimental consiste na medi c~ao sistem atica da voltagem el etrica VISHE, que e produzida por ⃗ Js por meio do efeito Hall de spin inverso (ISHE) que ocorre na camada M. As medidas em YIG/Pt foram feitas numa faixa ampla de temperatura de 20 a 300 K. Os dados experimentais são fi tados com a teoria proposta para o LSSE encontrando-se boa concordância. Nossos resultados mostram que o Py e o Ta s~ao bons candidatos para detec ção do LSSE. Esta disserta ção e de grande interesse na area da caloritrônica de spin, ajudando no desenvolvimento deste campo e na concep ção de novos dispositivos tecnol ogicos baseados na spintrônica.
38
Linzell, Daniel Gattner. "Studies of a full-scale horizontally curved steel I-girder bridge system under self-weight". Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/18342.
39
Lodge, Julia M. "Influence of sub-MICs of B-lactam antibiotics, growth rate, and iron limitation on the surface structures of Klebsiella pneumoniae". Thesis, Aston University, 1987. http://publications.aston.ac.uk/12554/.
40
Gallegos, Mayorga Linamaría. "Contribution à la compréhension du comportement mécanique des assemblages rivetés anciens". Thesis, Brest, 2016. http://www.theses.fr/2016BRES0038/document.
Abstract (sommario):
Le patrimoine ferroviaire français comporte de nombreux ponts métalliques, principalement construits au cours de la seconde moitié du XIXème siècle. Ces ouvrages d'art sont donc en service depuis plus d’un siècle et nécessitent une politique de maintenance adaptée. En collaboration avec SNCF Réseau, cette thèse de doctorat apporte des éléments de compréhension sur le comportement mécanique des assemblages rivetés à chaud sous sollicitations monotones et cycliques. Une stratégie expérimentale a été mise en oeuvre afin d'identifier les mécanismes de ruine des assemblages rivetés. Dans un premier temps, le matériau objet de cette étude, un fer puddlé, a été extrait d'éléments provenant du pont sur l'Adour à Bayonne (1864-2013). Ce matériau a été notamment caractérisé sous chargements monotones et cycliques ; sa fragilité, son anisotropie et son comportement dispersif ont été mis en évidence et analysés. Des outils numériques ont été développés pour l’étude microscopique de cette famille de matériaux. Des éprouvettes rivetées de type détail constructif ont par la suite été conçues, fabriquées et testées sous chargements monotones et cycliques. Un scénario précis du fonctionnement et de ruine d'un assemblage mono-rivet en double recouvrement a pu être identifié. Pour cela, les influences des caractéristiques matériau, des concentrations de contraintes, du cisaillement du rivet et de l'effort de serrage ont été étudiées. Les résultats de ce travail, comparés à ceux de la littérature et aux standards de dimensionnement des structures métalliques, montrent la complémentarité d'une étude à plusieurs échelles (comportement matériau et étude locale du fonctionnement des assemblages) dans le but de comprendre et estimer le comportement des structures rivetées anciennesNumerous metallic bridges can be found in the French railway heritage. Since a majority of these structures was built during the second half of the 19th century, they have been in service for over a hundred years and need an adapted maintenance policy.These doctoral thesis, done in collaboration with SNCF Réseau, improves the understanding of the mechanical behaviour of hot riveted assemblies under monotonic and cyclic loadings. An experimental strategy was proposed and carried out in order to identify the failure mechanisms of riveted assemblies. First, the studied material, a puddled iron, was obtained from recovered elements from the bridge over the Adour river in Bayonne (1864-2013). Mechanical testing and characterisation was performed under monotonic and cyclic loadings. Puddled iron’s brittle, anisotropic and scattered behaviour was observed and analysed. In-house software applications were developed in order to study this kind of material. Additionally, hot riveted specimens (constructional details) were designed, manufactured and tested under monotonic and cyclic loadings. A precise working (and failure) scenario of the double shear mono-rivet assembly was identified. The influence of the material’s behaviour, stress concentrators, shearing of the rivet and clamping force of the rivet were studied. The results obtained during these research works, compared to the ones found in academic literature as well as construction norms for metallic structures, showed the importance and complementarity of a multi-scale approach (material behaviour and local study of assemblies) in order to understand and assess the behaviour of ancient riveted structures
41
Chao, Min. "The design and behaviour of concrete filled steel tubular beam-columns /". View thesis View thesis, 2000. http://library.uws.edu.au/adt-NUWS/public/adt-NUWS20030429.154344/index.html.
42
Bialon, Arthur [Verfasser], Ralf [Gutachter] Drautz e Jörg [Gutachter] Neugebauer. "The iron-boron system : ordered structures and point defects / Arthur Bialon ; Gutachter: Ralf Drautz, Jörg Neugebauer ; Fakultät für Physik und Astronomie". Bochum : Ruhr-Universität Bochum, 2013. http://d-nb.info/1201553490/34.
43
CABBOI, ALESSANDRO. "Automatic operational modal analysis: challenges and applications to historic structures and infrastructures". Doctoral thesis, Università degli Studi di Cagliari, 2014. http://hdl.handle.net/11584/266404.
Abstract (sommario):
The core of the work turns around the capability to automate Operational Modal Analysis methods for permanent dynamic monitoring systems. In general, the application of OMA methods requires an experienced engineer in experimental dynamics and modal analysis; in addition, a lot of time is usually spent in manual analysis, necessary to ensure the best estimation of modal parameters. Those features are in contrast with permanent dynamic monitoring, which requires algorithms in order to efficiently manage the huge amount of recorded data in short time, ensuring
an acceptable quality of results. Therefore, the use of parametric identification methods, like SSI methods, are explored and some recommendations concerning its application are provided. The identification process is combined with the automatic interpretation of stabilization diagrams based on a damping ratio check and on modal complexity inspection. Finally, a clustering method for the
identified modes and a modal tracking strategy is suggested and discussed. The whole procedure is validated with a one-month and a one-year set of "manually-identified" modal parameters. This constitutes a quite unique set of validation data in the literature. Two monitoring case studies are studied: a railway iron arch bridge (1889) and a masonry bell-tower (XII century). Within this framework, classical and new strategies to handle the huge amount of recorded and identified data are proposed and compared for structural anomaly detection. The classical strategies
are mainly based on the inspection of any irreversible frequency variation. To such purpose, it is mandatory an extensive correlation study with environmental and operational factors which affect the frequency of the vibration modes. Conversely, one of the proposed strategy aims to use alternative dynamic features that are not sensitive to environmental factors, like mode shape or
modal complexity, instead of frequency parameters in order to detect any structural anomaly. In addition, a further strategy has the goal to eliminate the environmental-induced effects on frequency without the knowledge and the measurements of such factors. The procedure is mainly based on the combination of a simple regression model with the results obtained by a Principal Component
Analysis. Furthermore, two automated Operational Modal Analysis (OMA) procedures are compared for Structural Health Monitoring (SHM) purposes: the first one is based on SSI methods, while the second one involves a non-parametric technique like the Frequency Domain Decomposition method
(FDD). In conclusion, a model updating strategy for historic structures using Ambient Vibration Test
and long term monitoring results is presented. The main goal is to integrate the information provided by a FE model with those continuously extracted by a dynamic monitoring system, basing so any detection of structural anomalies on the variation of the uncertain structural parameters.
44
Afshar, Raman Khosrow. "Iron nitrosyls derived from polypyridine ligands with carboxamide groups(s) : syntheses, structures, photolability of NO, and S-nitrosylation of thiols and papain /". Diss., Digital Dissertations Database. Restricted to UC campuses, 2005. http://uclibs.org/PID/11984.
45
Young, B. (Ben). "The behaviour and design of cold-formed channel columns". Thesis, Faculty of Engineering, 1997. http://hdl.handle.net/2123/13673.
46
Chao, Min. "The design and behaviour of concrete filled steel tubular beam-columns". Thesis, View thesis View thesis, 2000. http://handle.uws.edu.au:8081/1959.7/92.
Abstract (sommario):
Concrete filled steel tubular (CFST) columns are widely used in building and infrastructure projects throughout the world.Compared with other form of construction CFST columns offer superior structural performance and speed and ease of construction.Design procedures and recommendations provided in most of the design codes are often tedious and complex. There have been attempts to simplify the design procedure by providing a simplified expression to predict the capacity of a CFST under a general loading condition.In this thesis a rigorous analysis procedure was presented for the analysis of CFST beam-columns under general loading conditions.All the analytical results were verified by comparisons with the available test results and current ACI, AISC AND Eurocode 4 design codes. The comparisons demonstrated that the proposed numerical equations are accurate, and slightly conservative. Based on the numerical analysis, a simple and easy to follow calculation procedure was proposed for design of CFST columns under either uniaxial or biaxial bending moment and axial load.
47
Vock, Silvia. "Resolving Local Magnetization Structures by Quantitative Magnetic Force Microscopy". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-148019.
Abstract (sommario):
Zur Aufklärung der lokalen Magnetisierungs- und magnetischen Streufeldstruktur in ferromagnetischen und supraleitenden Materialien wurden magnetkraftmikroskopische (Magnetkraftmikroskopie-MFM) Untersuchungen durchgeführt und quantitativ ausgewertet. Für eine solch quantitative Auswertung muss der Einfluß der verwendeten MFM-Spitzen auf das MFM-Bild bestimmt und in geeigneter Weise subtrahiert werden. Hierzu wurden Spitzenkalibrierungsroutinen und ein Verfahren zur Entfaltung der gemessenen MFM-Daten implementiert, das auf der Wiener Dekonvolution basiert. Mit Hilfe dieser Prozedur können sowohl die räumliche Ausdehnung als auch die Größe der Streufelder direkt aus gemessenen MFM-Bildern bestimmt werden.
Gezeigt wurde diese Anwendung für die Durchmesserbestimmung von Blasendomänen in einer (Co/Pd)-Multilage und für die Bestimmung der temperaturabhängigen magnetischen Eindringtiefe in einem supraleitendem BaFe2(As0.24P0.76)2 Einkristall. Desweiteren konnte durch die Kombination von mikromagnetischen Rechnungen und der quantitativen MFM-Datenanalyse die Existenz einer dreidimensionalen Vortex-Struktur am Ende von Co48Fe52-Nanodrähten nachgewiesen
werden. Damit ist es gelungen die Tiefensensitivität der Magnetkraftmikroskopie erfolgreich in die Rekonstruktion der vermessenen Magnetisierungsstruktur einzubeziehen.
48
Rose, Michael J. "Synthesis, x-ray structures, spectroscopy, DFT electronic configuration and biological relevance of photolabile ruthenium and iron nitrosyls derived from ligands containing carboxamido-N donors /". Diss., Digital Dissertations Database. Restricted to UC campuses, 2009. http://uclibs.org/PID/11984.
49
Jagodnik, Jonathan. "Multiples mécanismes de régulation post-transcriptionnelle chez les bactéries : des structures d’ARN messager aux ARN régulateurs". Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCC111/document.
Abstract (sommario):
Chez les bactéries, la régulation de l’expression génétique est fondamentale pour permettre une adaptation optimale à l’environnement. De nombreux contrôles existent, notamment au niveau post-transcriptionnel par de nombreux ARN régulateurs (sRNA pour « small RNAs »). Ceux-ci ciblent des ARN messager (ARNm), permettant une régulation rapide de la synthèse de protéines. Le plus souvent, ces sRNAs interagissent avec leur(s) cible(s) au niveau du site de fixation du ribosome (RBS pour « ribosome binding site »), entrant dès lors en compétition avec le ribosome pour la fixation à l’ARNm et entraînant une régulation négative de l’expression des gènes cibles. Pour autant, il existe de nombreux mécanismes alternatifs de régulation par les sRNA. Nous avons ainsi pu démontrer que les deux sRNAs OmrA et OmrB, conservés au sein des entérobactéries, répriment la synthèse du récepteur FepA aux complexes fer-entérobactine en ciblant une structure de l’ARNm fepA. Cette structure en tige-boucle est située en aval du RBS de fepA, et de façon surprenante, elle contrôle positivement la synthèse de FepA via une activation de la fixation de la sous-unité 30S du ribosome à l’ARNm. Des structures similaires ont pu être prédites dans d’autres ARNm, à l’image de bamA, codant la sous-unité essentielle du complexe Bam d’adressage des protéines de membrane externe en tonneaux β. Comme pour fepA, la tige-boucle de l'ARNm bamA favorise la fixation du ribosome, suggérant que ce mécanisme de régulation pourrait être bien plus général du fait de la grande conservation de bamA au sein des bactéries à Gram négatif. De surcroît, ces résultats constituent la première illustration que les structures d'ARNm peuvent avoir un effet positif sur la traduction. Par ailleurs, deux autres sRNAs répriment également et indépendamment l’expression de fepA, à savoir SdsR et RseX. A chaque fois, le mécanisme de régulation impliqué est différent. Ainsi, SdsR s’apparie vraisemblablement à deux régions différentes de l’ARNm fepA, impliquant notamment une compétition classique avec la fixation du ribosome. La répression par RseX nécessite quant à elle la présence d’autres séquences du 5’UTR de fepA, à plus d’une centaine de nucléotides (nts) en amont du RBS. Enfin, chacun de ces sRNAs semble répondre à des stimuli différents, ce qui enrichit considérablement notre connaissance des signaux contribuant à la régulation de fepA, dont jusqu’ici seule la carence en fer était connue comme un signal de dérépression par le facteur de transcription Fur. Ce travail est une nouvelle illustration de l’immense diversité des mécanismes de régulation impliquant des ARN, dont la grande flexibilité de structure et de séquence constitue une importante source de diversité à la disposition de l’évolutionIn order to perfectly adapt to their environment, bacteria require a tight gene expression regulation. This can occur through post-transcriptional control by numerous regulatory RNAs (or small RNAs, sRNAs). These sRNAs can target mRNAs, leading to a fast regulation of protein synthesis. Most often, sRNAs base-pair with their target mRNAs at the ribosome binding site (RBS), therefore competing with the ribosome for the binding with the mRNA and repressing gene expression. However, many other regulatory mechanisms involve sRNAs. We have demonstrated that the two sRNAs OmrA and OmrB, conserved among enterobacteria, repress the synthesis of the FepA receptor for iron-enterobactin complexes through base-pairing with a secondary structure within fepA mRNA. This stem-loop structure is located downstream of fepA RBS, and most surprisingly, promotes 30S ribosomal subunit binding to fepA mRNA, therefore activating FepA synthesis. Similar stem-loop structures have been predicted in other mRNAs, such as the bamA mRNA encoding the essential subunit of the Bam outer membrane protein assembly complex. As for fepA mRNA, the stem-loop found in bamA mRNA also promotes ribosome binding, showing that this regulatory mechanism could be widespread considering the strong conservation of bamA among Gram negative bacteria. Moreover, these results challenge the commonly admitted view of mRNA secondary structures being repressors of gene expression. Two other sRNAs also repress fepA expression in an OmrA/B-independent fashion, namely SdsR and RseX. For each of these sRNAs, the regulatory mechanism involved is different. Indeed, SdsR most likely acts through two distinct binding sites, one of which leading to a classical competition with the ribosome binding. Meanwhile, RseX repression requires most of fepA 5’UTR, including sequences at about 100nt upstream of the start codon. Finally, each of these sRNAs is expressed upon diverse stimuli, considerably extending our knowledge of the signals leading to fepA regulation, for which only the Fur-dependent derepression upon iron starvation was known. This work highlights the great versatility of regulatory mechanisms involving RNAs. This illustrates how RNAs structural flexibility and sequence diversity is a key source of diversity for evolution
50
Lopez, Samuel. "Définition de nouvelles structures de circuits magnétiques de machines AC utilisant des tôles à grains orientés". Thesis, Artois, 2011. http://www.theses.fr/2011ARTO0202/document.
Abstract (sommario):
Le travail présenté porte sur la définition et le développement d’un circuit magnétique pour moteurs à haut rendement de faible et moyenne puissances. Il est réalisé avec des tôles à Grains Orientés (GO) non-segmentées. Des expérimentations réalisées en champ unidirectionnel, destinées à comparer les caractéristiques globales de la structure GO à celles obtenues sur un assemblage classique composé de tôles à grains Non-Orientés (NO), permettent de conclure quant à l’efficacité de l’association proposée en termes de pertes fer. Des investigations au niveau local, accompagnées d’une modélisation numérique, conduisent à une analyse de la répartition interne du flux magnétique dans la structure, permettant de l’optimiser. Cette technique d’assemblage est ensuite testée en champ tournant sur des moteurs statiques. Les performances obtenues, sont de nouveau comparées à celles relevées sur une maquette NO. L’étape finale consiste à tester le principe développé sur des moteurs à induction réalisés avec la configuration GO. Diverses caractéristiques sont relevées ou estimées (norme CEI) et comparées à celles de la machine NO d’origine. L’efficacité de la structure GOse traduit par une réduction notable des pertes fer, notamment statiques, conduisant à accroître sensiblement le rendement global de la machineThe work presented is focused on the design and development of a magnetic circuit for high efficiency motors of medium and small powers. It is built with non-segmented laminations of Grain Oriented (GO) steel. Experimentations on magnetic circuits excited under unidirectional magnetic field are performed. Such tests aim the comparison of the GO structure global characteristics with those of a classic one composed of Non-Oriented (NO) steel, allowing seeing the superiority of the GO structure in terms of iron losses. Local experimentations, followed by a numerical model, allow the analysis of the local distribution of the magnetic flux within the structure, leading to its optimisation. Such technique of assembly is then tested under rotational magnetic field. In that context, several experimentations are performed and its performance is compared with the one of a NO prototype. The final stage consists in testing the developed structure in induction motors built withthis GO assembly. Several characteristics are measured or estimated (IEC standard) and compared with those obtained on the initial NO motor. The GO structure efficiency leads to a remarkable reduction of the static losses, allowing the increase of the global efficiency of the motor