Дисертації: "SRFT"

1

Smith, Gemma Ann. "Regulation of SRF activity." Thesis, University College London (University of London), 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404483.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

2

Matsushima, Aki. "Transverse laser cooling of SrF." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/17839.

Повний текст джерела

Анотація:

This thesis discusses an experiment, which has demonstrated transverse laser cooling of a pulsed supersonic beam of strontium monofluoride (SrF) molecules. Producing ultracold molecules is important because they could advance many fields including many-body physics, quantum chemistry and precision measurements to explore fundamental forces in nature. Direct laser cooling of molecules is a new and promising way to produce molecules with temperatures in the sub-millikelvin range. In the experiment, SrF molecules produced from a pulsed supersonic source were cooled in the transverse direction using light from just two lasers. The molecular beam brightness was increased by about 20%. I discuss the detailed experimental setup, laser system and data analysis. I also present several theoretical models, which give insight into the cooling experiment. Finally, I discuss improvements to this experiment, which should enable higher yields of ultracold molecules to be produced.

Стилі APA, Harvard, Vancouver, ISO та ін.

3

Vennekate, Hannes. "Emittance Compensation for SRF Photoinjectors." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-229164.

Повний текст джерела

Анотація:

The advantages of contemporary particle injectors are high bunch charges and good beam quality in the case of normal conducting RF guns and increased repetition rates in the one of DC injectors. The technological edge of the concept of superconducting radio frequency injectors is to combine the strengths of both these sides. As many future accelerator concepts, such as energy recovery linacs, high power free electron lasers and certain collider designs, demand particle sources with high bunch charges and high repetition rates combined, applying the superconductivity of the accelerator modules to the injector itself is the next logical step. However, emittance compensation — the cornerstone for high beam quality — in case of a superconducting injector is much more challenging than in the normal conducting one. The use of simple electromagnets generating a solenoid field around the gun’s resonator interferes with its superconducting state. Hence, it requires novel and sophisticated techniques to maintain the high energy gain inside the gun cavity, while at the same time alleviating the detrimental fast transverse emittance growth of the bunch. In the case of the ELBE accelerator at the Helmholtz-Zentrum Dresden-Rossendorf, a superconducting electron accelerator provides beam for several independent beamlines in continuous wave mode. The applications include IR to THz free electron lasers, neutron and positron generation, to Thompson backscattering with an inhouse TW laser, and hence, call for a flexible CW injector. Therefore, the development of a 3.5 cell superconducting electron gun was initiated in 1997. The focus of this thesis lies on three approaches of transverse emittance compensation for this photoinjector: RF focusing, the installation of a superconducting solenoid close to the cavity’s exit, and the introduction of a transverse electrical mode of the RF field in the resonator. All three methods are described in theory, examined by numerical simulation, and experimentally reviewed in the particular case of the ELBE SRF Gun II at HZDR and a copy of its niobium resonator at Thomas Jefferson National Laboratory, Newport News, VA, USA.

Стилі APA, Harvard, Vancouver, ISO та ін.

4

Zaromytidou, Alexia Ileana. "Molecular study of SRF-cofactor interactions." Thesis, University College London (University of London), 2008. http://discovery.ucl.ac.uk/1445165/.

Повний текст джерела

Анотація:

Serum Response Factor regulates a large array of genes involved in diverse processes including cell proliferation, muscle differentiation and development, and cytoskeletal processes such as cell migration and adhesion. The specificity and versatility of the SRF responses is achieved by combinatorial interactions with accessory factors. SRF binds to the CC(A/T)2A(A/T)3GG CArG box consensus sequence within the promoters of its target genes and acts as a docking platform for diverse signal regulated and cell- type specific cofactors to elicit their distinct responses. In fibroblasts two pathways signal through SRF in a mutually exclusive manner. MAP kinase signalling results in transcriptional activation of a subset of SRF target genes, via the interaction of SRF with members of the TCF family of Ets domain proteins. In contrast Rho-signalling induced changes in actin dynamics result in the association of SRF with members of the Myocardin-related family of SRF cofactors (MAL/MRTF-A/MKL1 and MAL16/MRTF-B/MKL2). The results described in this thesis characterise the molecular mechanism of MAL-SRF complex formation. MAL binds SRF as a dimer via a seven-residue core sequence within the MAL B1 region. Residues in the neighbouring Q-box enhance MAL-SRF complex formation, although these do not contact SRF directly. The MAL-SRF interaction displays the properties of a Rho-regulated cofactor. MAL competes with TCF for SRF binding due to the interaction of both cofactors with the same hydrophobic groove and pocket on SRF. In contrast to TCF, MAL-SRF complex formation depends on the intact N-terminus of the SRF DNA-binding domain. Mutations in the SRF al-helix that reduce DNA bending also impair complex formation with MAL. These mutations however do not affect DNA distortion in the MAL-SRF complex. Efficient MAL-SRF complex formation requires that SRF be bound to its cognate DNA and that MAL directly contacts DNA on either side of the CArG box. My results support a model in which each MAL monomer adds a p-strand consisting of the core B1 sequence, to the p-sheet of the SRF DNA-binding domain in a similar way to TCF, while also making direct DNA contacts in the ternary complex facilitated by SRF- induced DNA distortion. My analysis of complex formation between MAL and SRF demonstrates that members of the MRTF and TCF families of SRF cofactors interact with SRF using related but distinct mechanisms, thus providing a molecular rationale for their mutually exclusive transcriptional responses and the specificity of signalling to SRF.

Стилі APA, Harvard, Vancouver, ISO та ін.

5

Valente-Feliciano, Anne-Marie. "Development of SRF monolayer/multilayer thin film materials to increase the performance of SRF accelerating structures beyond bulk Nb." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112254/document.

Повний текст джерела

Анотація:

La réduction du cout de construction et d’exploitation des futurs accélérateurs d particules, a grande et petite échelles, dépend du développement de nouveaux matériaux pour les surfaces actives des structures supraconductrices en radiofréquence (SRF). Les propriétés SRF sont essentiellement un phénomène de surface vu que la profondeur de pénétration (profondeur de pénétration de London, λ) des micro-ondes (RF) est typiquement de l’ordre de 20 à 400 nm en fonction du matériau. Lorsque les procédés de préparation de surface sont optimises, la limite fondamentale du champ RF que les surfaces SRF peuvent supporter est le champ RF maximum, Hc₁, au-delà duquel le flux magnétique commence à pénétrer la surface du supraconducteur. Le matériau le plus utilise pour des applications SRF est le niobium (Nb) massif, avec un champ Hc₁ de l’ordre de 170 mT, qui permet d’atteindre un champ accélérateur de moins de 50 MV/m. Les meilleures perspectives d’amélioration des performances des cavités SRF sont liées à des matériaux et méthodes de production produisant la surface SRF critique de façon contrôlée. Dans cette optique, deux avenues sont explorées pour utiliser des couches minces pour augmenter les performances des structures SRF au-delà du Nb massif, en monocouche ou en structures multicouches Supraconducteur-Isolant-Supraconducteur (SIS) : La première approche est d’utiliser une couche de Nb déposée sur du cuivre (Nb/Cu) à la place du Nb massif. La technologie Nb/Cu a démontré, au cours des années, être une alternative viable pour les cavités SRF. Toutefois, les techniques de dépôt communément utilisées, principalement la pulvérisation magnétron, n’ont jusqu’à présent pas permis de produire des surfaces SRF adaptées aux performances requises. Le récent développement de techniques de dépôt par condensation énergétiques, produisant des flux d’ions énergétiques de façon contrôlée (telles que des sources d’ions ECR sous ultravide) ouvrent la voie au développement de films SRF de grand qualité. La corrélation entre les conditions de croissance, l’énergie des ions incidents, la structure et les performances RF des films produits est étudiée. Des films Nb avec des propriétés proches du Nb massif sont ainsi produits. La deuxième approche est basée sur un concept qui propose qu’une structure multicouche SIS déposée sur une surface de Nb peut atteindre des performances supérieures à celles du Nb massif. Bien que les matériaux supraconducteurs à haute Tc aient un champ Hc₁ inférieur à celui du Nb, des couches minces de tels matériaux d’une épaisseur (d) inférieure à la profondeur de pénétration voient une augmentation de leur champ parallèle Hc₁ résultant au retardement de la pénétration du flux magnétique. Cette surcouche peut ainsi permettre l’écrantage magnétique de la surface de Nb qui est donc maintenue dans l’état de Meissner à des champs RF bien plus importants que pour le Nb massif. La croissance et performance de structures multicouches SIS basées sur des films de NbTiN, pour le supraconducteur, et de l’AlN, pour le diélectrique, sont étudiées. Les résultats de cette étude montrent la faisabilité de cette approche et le potentiel qui en découle pour l’amélioration des performances SRF au-delà du Nb massif
The minimization of cost and energy consumption of future particle accelerators, both large and small, depends upon the development of new materials for the active surfaces of superconducting RF (SRF) accelerating structures. SRF properties are inherently a surface phenomenon as the RF only penetrates the London penetration depth λ, typically between 20 and 400 nm depending on the material. When other technological processes are optimized, the fundamental limit to the maximum supportable RF field amplitude is understood to be the field at which the magnetic flux first penetrates into the surface, Hc₁. Niobium, the material most exploited for SRF accelerator applications, has Hc₁~170 mT, which yields a maximum accelerating gradient of less than 50 MV/m. The greatest potential for dramatic new performance capabilities lies with methods and materials which deliberately produce the sub-micron-thick critical surface layer in a controlled way. In this context, two avenues are pursued for the use of SRF thin films as single layer superconductor or multilayer Superconductor-Insulator-Superconductor structures: Niobium on copper (Nb/Cu) technology for superconducting cavities has proven over the years to be a viable alternative to bulk niobium. However the deposition techniques used for cavities, mainly magnetron sputtering, have not yielded, so far, SRF surfaces suitable for high field performance. High quality films can be grown using methods of energetic condensation, such as Electron Cyclotron Resonance (ECR) Nb ion source in UHV which produce higher flux of ions with controllable incident angle and kinetic energy. The relationship between growth conditions, film microstructure and RF performance is studied. Nb films with unprecedented “bulk-like” properties are produced. The second approach is based on the proposition that a Superconductor/Insulator/Superconductor (S-I-S) multilayer film structure deposited on an Nb surface can achieve performance in excess of that of bulk Nb. Although, many higher-Tc superconducting compounds have Hc₁ lower than niobium, thin films of such compounds with a thickness (d) less than the penetration depth can exhibit an increase of the parallel Hc₁ thus delaying vortex entry. This overlayer provides magnetic screening of the underlying Nb which can then remain in the Meissner state at fields much higher than in bulk Nb. A proof of concept is developed based on NbTiN and AlN thin films. The growth of NbTiN and AlN films is studied and NbTiN-based multilayer structures deposited on Nb surfaces are characterized. The results from this work provide insight for the pursuit of major reductions in both capital and operating costs associated with future particle accelerators across the spectrum from low footprint compact machines to energy frontier facilities

Стилі APA, Harvard, Vancouver, ISO та ін.

6

Kolb, Philipp Ulrich. "The TRIUMF nine-cell SRF cavity for ARIEL." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/57725.

Повний текст джерела

Анотація:

Modern physics research relies on particle accelerators and available beam time is a very limited resource. The ARIEL eLINAC will strengthen the rare isotope program at TRIUMF by providing an alternative way to create rare isotope beams (RIB). A possible way to add additional use to this machine is to create a return beam line and use the beam to excite a free electron laser (FEL). The remaining beam can be used to drive fields in the SRF cavities to reduce the required RF power. One limitation of these energy recovery LINACs (ERL) is beam-break up. Higher order modes (HOM), especially dipole modes, have a negative influence on the beam which can lead to beam loss. The design of the SRF cavity has to accommodate this to make sure a beam current of up to 10mA can be used for both RIB production and ERL operation. This thesis will go through the design process of the ARIEL 1.3 GHz nine-cell cavity. The design relies on simulations to calculate the fields inside the cavity and with it the shunt impedance of HOMs. The investigations showed that resistive beam line absorbers can be used to reduce the shunt impedance of HOMs sufficiently without interfering with the accelerating mode. The performance of the absorber material has been verified in dedicated low temperature measurements, while the HOM field distribution has been measured via beadpulling on a copper model of the cavity. These measurements showed good agreement with the simulations. The power dissipation in the SRF cavities is of vital importance. The cryogenic system is a signicant part of the capital investment for the accelerator and sets the power budget for each cavity to around 10 W. This corresponds to a Q₀ value of 1 x 10¹⁰ at an operational temperature of 2 K. The gradient goal is 10 MV/m to reach the design energy of 50 MeV with five cavities. Both Q₀ and Eacc specifications have been met in the first two cavities that are installed in cryomodules. Two more cavities have been built and are in their qualification phase.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

Стилі APA, Harvard, Vancouver, ISO та ін.

7

Guettler, Sebastian. "Regulation of the SRF cofactor MAL by actin." Thesis, University College London (University of London), 2007. http://discovery.ucl.ac.uk/1445537/.

Повний текст джерела

Анотація:

Serum Response Factor (SRF) is controlled by actin dynamics at many of its target genes: Rho-induced depletion of G-actin is sensed by MAL, a member of the myocardin family of SRF coactivators. MAL binds G-actin via its N-terminus, the "RPEL domain", containing three RPEL motifs. MAL rapidly circulates between nucleus and cytoplasm in resting NIH3T3 fibroblasts. It accumulates in the nucleus and activates SRF upon serum stimulation, which alters interactions between G-actin and the RPEL domain. In contrast, myocardin (MC) itself is constitutively nuclear and active when expressed in fibroblasts, suggesting that it is not controlled through Rho. This thesis addresses the mode and functions of actin binding by myocardin-family proteins. Actin binding targets MAL for efficient CRM1-mediated nuclear export. Nuclear accumulation of MAL is not sufficient for activation of SRF-mediated transcription unless an inhibitory MAL-actin interaction in the nucleus is released. Actin therefore fulfils a dual role in MAL regulation by controlling MAL localisation as well as activity. The MAL RPEL domain is sufficient to confer actin-regulated nucleocytoplasmic trafficking and binds multiple actin molecules, efficiently sequestering them from polymerisation. Actin-binding toxins directly interfere with the MAL-actin complex. The RPEL motif represents an actin-binding unit: affinities of MAL RPEL motifs 1 and 2 for actin are relatively high while RPEL3 binds actin weakly. RPEL motifs cooperate to regulate MAL. The regulatory contribution of an RPEL3-actin interaction depends on actin binding by the RPEL 1-2 unit, differences in which account for differential regulation of MAL and MC, which binds actin weakly. A model of MAL regulation by differential actin occupancy of multiple RPEL motifs is proposed. Crystal structures of MAL RPEL motifs 1 and 2 bound to G-actin were obtained. RPEL motifs maintain hydrophobic interactions with a hydrophobic cleft at the subdomain 1-3 interface of actin and a "platform" on subdomain 3, both at the "base" of the actin molecule in its conventional view (Kabsch et al., 1990). The RPEL motif also establishes critical polar interactions with actin. Conservation of the RPEL motif reflects actin binding. The structures rationalise RPEL-actin affinities and competition of actin-binding toxins and profilin with MAL. A crystal structure of the MAL RPEL domain bound to three actin molecules revealed an additional actin-binding site within the RPEL 1-2 linker and actin-actin contacts in the RPEL domain-actin complex.

Стилі APA, Harvard, Vancouver, ISO та ін.

8

Xiao, Binping. "Surface Impedance of Superconducting Radio Frequency (SRF) Materials." W&M ScholarWorks, 2012. https://scholarworks.wm.edu/etd/1539623605.

Повний текст джерела

Анотація:

Superconducting radio frequency (SRF) technology is widely adopted in particle accelerators. There remain many open questions, however, in developing a systematic understanding of the fundamental behavior of SRF materials, including niobium treated in different ways and various other bulk/thin film materials that are fabricated with different methods under assorted conditions. A facility that can measure the SRF properties of small samples in a range of 2∼40 K temperature is needed in order to fully answer these questions. The Jefferson Lab surface impedance characterization (SIC) system has been designed to attempt to meet this requirement. It consists of a sapphire-loaded cylindrical Nb TE011 cavity at 7.4 GHz with a 50 mm diameter flat sample placed on a non-contacting end plate and uses a calorimetric technique to measure the radio frequency (RF) induced heat on the sample. Driving the resonance to a known field on this surface enables one to derive the surface resistance of a relatively small localized area. TE011 mode identification has been done at room temperature and 4 K, and has been compared with Microwave StudioRTM and SuperFish simulation results. RF loss mechanisms in the SIC system are under investigation. A VCO phase lock loop system has been used in both CW and pulsed mode. Two calorimeters, with stainless steel and Cu as the thermal path material for high precision and high power versions, respectively, have been designed and commissioned for the SIC system to provide low temperature control and measurement. A power compensation method has been developed to measure the RF induced power on the sample. Simulation and experimental results show that with these two calorimeters, the whole thermal range of interest for SRF materials has been covered, The power measurement error in the interested power range is within 1.2% and 2.7% for the high precision and high power versions, respectively. Temperature distributions on the sample surface for both versions have been simulated and the accuracy of sample temperature measurements have been analysed. Both versions have the ability to accept bulk superconductors and thin film superconducting samples with a variety of substrate materials such as Al, A12O3, Cu, MgO, Nb and Si. Tests with polycrystalline and large grain bulk Nb samples have been done at impedance, least-squares fittings have been done using SuperFit2.0, a code developed by G. Ciovati and the author.;Microstructure analyses and SRF measurements of large scale epitaxial MgB2 films have been reported. MgB2 films on 5 cm dia. sapphire disks were fabricated by a Hybrid Physical Chemical Vapor Deposition (HPCVD) technique. The electron-beam backscattering diffraction (EBSD) results suggest that the film is a single crystal complying with a MgB2(0001)//A1 2O3(0001) epitaxial relationship. The SRF properties of different film thicknesses (200 nm and 350 nm) were evaluated using SIC system under different temperatures and applied fields at 7.4 GHz. A surface resistance of 9+/-2 muO has been observed at 2.2 K.;Based on BCS theory with moving Cooper pairs, the electron states distribution at 0K and the probability of electron occupation with finite temperature have been derived and applied to anomalous skin effect theory to obtain the surface impedance of a superconductor with moving Cooper pairs. We present the numerical results for Nb.

Стилі APA, Harvard, Vancouver, ISO та ін.

9

Gualdrini, F. "Mechanisms of transcriptional regulation by SRF co-factors." Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1460723/.

Повний текст джерела

Анотація:

Serum response factor (SRF) controls gene activation in response to changes in actin dynamics and mitogen-activated protein kinases. SRF has low intrinsic transcriptional activity and requires the recruitment of one of two families of co-activators: the MRTFs (myocardin-related transcription factors) and the TCFs (ternary complex factors). MRTFs are actin-binding proteins. Disruption of the actin-MRTF interaction is sufficient to induce MRTF nuclear accumulation and transcriptional activation. The TCF family are specifically activated by MAPK signalling. This thesis aims to elucidate how the SRF transcription network is controlled. The work presented encompasses two projects focused on each of the co-activator families. The regulation of MRTF shuttling from the cytoplasm to the nucleus is relatively well understood while its regulation once in the nucleus is still uncharacterized. The work demonstrates that nuclear MRTF activities are influenced by nuclear actin. Nuclear actin interferes with MRTF-DNA binding and target gene activation. In the presence of G-actin, nuclear MRTF can associate with target loci and recruit Pol II that, although traverses the gene body, does not generate stable mRNA. This inhibited state is accompanied by hypo-phosphorylation of the Pol II CTD. Dissociation of MRTF-actin interaction is required to re-establish Pol II phosphorylation and mRNA accumulation. The Erk-TCF signalling pathway was used to investigate how chromatin signatures are established in response to cues. Fibroblasts lacking all three TCFs, or reconstituted with mutant derivatives of the Elk-1 TCF were generated. Following Erk activation, chromatin immunoprecipitation and RNA-sequencing techniques, were employed to study the role of the TCFs in chromatin changes and transcriptional activation. It was possible to show that signal-induced chromatin changes occur in absence of transcription, and the specific chromatin signature requires Elk-1 DNA binding and phosphorylation. In addition analysis of the H3K27me3 mark demonstrated that Elk-1 activation is required to maintain a permissive chromatin landscape.

Стилі APA, Harvard, Vancouver, ISO та ін.

10

Fortier-Topping, Hugo. "Conception d'une chambre de combustion pour la microturbine à gaz SRGT-2." Mémoire, Université de Sherbrooke, 2014. http://hdl.handle.net/11143/5417.

Повний текст джерела

Анотація:

Dans un contexte mondial où les ressources énergétiques commencent à se faire rares, beaucoup de recherches se font sur l’amélioration de l’efficacité thermique et de la densité de puissance des sources d’énergie existantes. Ainsi, un projet de développement d’une microturbine à gaz avec une architecture de nouveau genre permettant d’augmenter la densité de puissance tout en réduisant les coûts a vu le jour. La recherche proposée dans le présent document se concentre sur la conception et la caractérisation d’une chambre de combustion et d’un banc d’essai pour la turbine SRGT-2. Une chambre de combustion à écoulement inverse est conçue et caractérisée expérimentalement. Un modèle 0D de la chambre est tout d’abord fait. Par la suite, une optimisation numérique est faite jusqu’à l’atteinte des objectifs de conception. Finalement, la chambre de combustion est testée durant 30 secondes avec de l’hydrogène comme carburant. Une température de sortie de la chambre de combustion de 1000 K a été maintenue avec une efficacité de combustion de plus de 85%. Le banc d’essai conçu pour le projet de recherche utilise un démarreur électropneumatique permettant d’accélérer le prototype jusqu’à 102 000 RPM. Le module fluide est la partie du banc d’essai qui contient les différentes parties de la turbine SRGT-2 comme le rotor, les stators et la chambre de combustion. Le module est instrumenté dans le but d’obtenir une caractérisation complète de la turbine. Sa configuration modulaire permet aussi de caractériser chacune des composantes individuellement en changeant certaines sections.

Стилі APA, Harvard, Vancouver, ISO та ін.

11

Jones, F. W. "Evidence for dissociable learning processes from the SRT task." Thesis, University of Cambridge, 2001. http://create.canterbury.ac.uk/11341/.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

12

Greaney, Peter. "Regulation of cell survival by caspase-mediated SRF cleavage." Thesis, University of Nottingham, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.403410.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

13

Gustafsson, Helena, and Anna Nilsson. "Avskaffandet av revisionsplikten : en studie av SRF och Skatteverket." Thesis, Högskolan i Borås, Institutionen Handels- och IT-högskolan, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:hb:diva-19773.

Повний текст джерела

Анотація:

Bakgrund och problem: Idag förs det en diskussion om avskaffandet avrevisionsplikten. Den 7 september 2006 bestämde regeringen att reglerna om revision försmå bolag skulle ses över och granskas genom en utredning. Idag (2009) är företagenskyldiga att använda sig av en revisor där hon/han kontrollerar styrelsens och denverkställande direktörens förvaltning. Avskaffandet av revisionsplikten skulle innebäraatt 96 procent av Sveriges företag skulle slippa plikten att ha en revisor. Ett avskaffandekommer att beröra olika parter exempelvis företag, revisorer, redovisningskonsulter,Skatteverket, kunder, leverantörer etc.Problemet idag för de två aktörer som vi har valt att undersöka i den här uppsatsen, SRFoch Skatteverket är bland annat att skattefelet ökar och att det blir en negativ konsekvensför Skatteverket. För SRF kan arbetsuppgifterna öka och de anser att små företagarnaskulle gynnas av avskaffandet av revisionsplikten.Genom avskaffandet finns det en oro över att kvaliteten i redovisningen kommer attförsämras då företagen inte längre är skyldiga att använda sig av en revisor och får väljavilka tjänster de behöver och vill använda i företaget.Syfte: Med uppsatsen vill vi få en förståelse för hur SRF och Skatteverket påverkas avavskaffandet av revisionsplikten.Metod: Vi har använt oss av en kvalitativ metod i uppsatsen och har intervjuat tvårespondenter, en från vardera verksamhet. Respondenterna som vi har intervjuat har varitinformationsrika inom området vilket enligt oss har medfört en god validitet till studien.Genom intervjuerna har vi fått en förståelse för hur de olika aktörerna ser på förändringenoch hur de kommer att påverkas.Resultat och slutsatser: Resultatet från studien är att SRF kommer att påverkas merpositivt än Skatteverket som det ser ut. SRF kommer att få en ökad möjlighet att erbjudasina tjänster till följd av avskaffandet av revisionsplikten då företagen kan behövaaffärsrådgivning. För Skatteverket är det mer osäkert. Skattefelet kan komma att ökagenom avskaffandet av revisionsplikten då medvetna fel kan förekomma mer än idageftersom företagen själva får välja vilka tjänster de vill ha och inte längre är tvingade tilldem. Om revisionsplikten avskaffas bör en kontroll upprättas för de små företagen för attupprätthålla kvaliteten i redovisningen och för att inte öka skattefelen för Skatteverket.Det här innebär även en fördel och mer tjänster för SRF.

Стилі APA, Harvard, Vancouver, ISO та ін.

14

Faltová, Karolína. "Název práce: Je srst bobra evropského (Castor fiber) vhodným indikátor intoxikace rizikovými prvky?" Master's thesis, Česká zemědělská univerzita v Praze, 2016. http://www.nusl.cz/ntk/nusl-260339.

Повний текст джерела

Анотація:

This thesis deals with the burden of European beaver (Castor fiber) populations with risk elements in three areas of the Czech Republic and one area in Slovakia. There were investigated concentrations of heavy metals (Cd, Zn, Fe, Cu, Pb and As) in the kidneys, livers, lungs, hearts, muscles and fur of 19 found dead beaver individuals. Furthermore, their food was analysed to determine the contamination of their areas of origin and discover, which organ reflects the observed concentrations of Cd the best. The main aim of the study was to determine whether the analysis of hair could be used as a non-invasive method to reflect the concentrations of heavy metals in beaver populations in future. The results were conclusive only for As, whose concentrations in the hair was the second highest and correlated with the content of As in the lungs, which contained the highest concentrations of arsenic. Cadmium in the fur showed a reverse structure compared to the content of Cd in kidney and liver. There were found significant differences in the contamination with heavy metals between beaver populations and their environments. Analysis of the fur is not proved for most of the elements and it is necessary to investigate further non-invasive methods to determine the load of toxic elements on beaver populations.

Стилі APA, Harvard, Vancouver, ISO та ін.

15

Schmidt, Larisa. "Synthese und Charakterisierung von nano-SrF2 und -YbF3 für Anwendungen in der Dentalmedizin." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2015. http://dx.doi.org/10.18452/17272.

Повний текст джерела

Анотація:

Das Ziel der Promotionsarbeit ist es optisch transparente, nanoskalige Strontiumfluorid- und Ytterbiumfluorid-Sole hoher Konzentration für mögliche Anwendung in der Dentalmedizin zu synthetisieren. Über die fluorolytische Sol-Gel-Synthese ist es gelungen nanoskalige MFn-Sole (M=Sr, Yb) erfolgreich herzustellen. Die Umsetzung der Metallpräkursoren mit alkoholischer HF-Lösung im organischen Lösungsmittel führt zu transparenten, niedrig viskosen Solen. Mittels DLS, XRD und TEM wurden die Sole hinsichtlich ihrer Partikelgröße und ihres Alterungsverhaltens untersucht. Mittels WAXS-Messungen wurde das Alterungsverhalten der SrF2-Sole analysiert. Mit Hilfe der XRD und 19F-MAS-NMR-Spektroskopie wurde eine fluorhaltige, kristalline Spezies als Intermediat in der fluorolytischen Sol-Gel-Synthese des SrF2 nachgewiesen. DLS-Untersuchungen an Ytterbium-Solen zeigen eine Bildung von Partikeln im unteren Nanometerbereich sowie eine konzentrationsabhängige Partikelgrößenverteilung der Solpartikel. Die erhaltenen Xerogele sind röntgenamorph. Zudem konnten neue Yb(III)-Komplexe isoliert und strukturanalytisch charakterisiert werden. Die vorliegende Arbeit zeigt eine Möglichkeit, wie Kompositmaterialien auf Basis von nano-MFn (M=Sr, Yb) hergestellt werden können. Ausgehend von transparenten Solen konnten transparente Komposite mit einem großen Anteil an anorganischen Komponenten synthetisiert werden. Des Weiteren wurde die fluorolytische Sol-Gel-Synthese auf die Synthese von Nanopartikeln im System SrF2-YbF3 übertragen. Die Untersuchungen mittels DLS und TEM zeigen die Bildung von monodispersen Partikeln mit Partikelgrößen im unteren Nanometerbereich. Die nichtstöchiometrischen Phasen Sr1-xYbxF2+x sind durch einen weiten Homogenitätsbereich (bis ca. 50 mol-% Yb) charakterisiert und zeigen Anwendungspotential auf den Gebieten der Medizin, Zahnmedizin und Optik.
The focus of this thesis is the synthesis and characterization of nanoscopic metal fluorides for dental applications. Nanoscopic metal fluorides MFn (M = Sr, Yb) have been successfully synthesized via the fluorolytic sol-gel synthesis. The reaction of the metal precursors with alcoholic HF solution in organic solvents yields in transparent sols of high concentrations and low viscosity. DLS, TEM and XRD confirmed the formation of sol particles in the lower nm range and were used to characterize the particles as well as the aging behavior of the sols. Mechanistic insights were gained by following the reaction progress. A fluorine-containing crystalline species was detected by XRD and solid state 19F MAS NMR spectroscopy indicating the formation of an intermediate phase during the fluorolysis reaction. The investigation by DLS and TEM revealed the existence of ytterbium fluoride sol particles with diameter of approximately 5 nm. Additionally, DLS studies show a concentration dependency on particle size. XRD revealed total amorphousness of the product. In addition, new ytterbium(III) complexes were isolated and structurally characterized by X-ray analysis. Furthermore, the fluorolytic sol-gel synthesis has been modified for the preparation of transparent nanocomposite bulk materials. Large amounts of nanoscopic metal fluorides MFn (M=Sr, Yb) can be embedded in the organic polymer matrix commonly used in dentistry without facing loss of visual optical transparency. A new approach to prepare nanoparticles in SrF2-YbF3 systems via the fluorolytic sol-gel synthesis is presented. The investigations by DLS and TEM revealed the presence of monodisperse solid particles with sizes in the lower nm range. The Sr1-xYbxF2+x nonstoichiometric fluorite phases are characterized by a wide range of homogeneity (up to approx. 50 mol % Yb) and show promise of a wide range of applicability in the areas of medicine, dentistry and optics.

Стилі APA, Harvard, Vancouver, ISO та ін.

16

Parlakian, Ara. "Rôle du facteur de transcription SRF dans le système cardiovasculaire." Paris 7, 2004. http://www.theses.fr/2004PA077137.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

17

Tian, Hui. "Surface study of niobium for superconducting radio frequency (SRF) accelerators." W&M ScholarWorks, 2008. https://scholarworks.wm.edu/etd/1539623534.

Повний текст джерела

Анотація:

Niobium rf superconductivity is a near-surface phenomenon because of the shallow rf penetration depth. Accordingly, the performance of Nb SRF accelerator cavities is strongly impacted by the topmost few nanometers interior surface, especially as impacted by the final surface conditioning treatments.;Surface topography impacts performance through local loss of superconductivit caused by intrusion of the rf magnetic field, which is enhanced at sharp protrusions. "Sharpness" comprises both vertical and lateral aspects, requiring development a new characterization approach beyond the familiar roughness measurements (Ra, Rz), which view only the vertical component. Stylus profilomety and atomic force microscopy traces view surface topography from mm size to near atomic dimensions. Power spectral density analysis combines data across this whole dimensional scale, so that the effect of preparation variables on topography has been studied systematically for the first time.;Surface chemistry impacts performance through the presence of a complex surface oxide structure and the response of the surface to post-treatments, notably low temperature baking (e.g., 125??C, 24 hrs). Previous XPS studies consistently found that the surface chiefly comprises a few nm of Nb2O5 on top of Nb metal, with small amount of Nb suboxides near the interface. Efforts to unambiguously discern the variation of composition with depth in the surface region by angle-resolved XPS have been confounded by the effect of surface roughness. The problem was avoided here by, for the first time, using a synchrotron source to vary x-ray photon energy at fixed take-off angle, obtaining a range of sample depths in a fixed column of material spanning the oxide layer thickness. One result is that variation of etching practice chiefly affects the thickness of the top Nb2O5 layer, but the sub-oxide accommodation zone at the interface remains substantially constant. A second is that low temperature baking in vacuum results in significant thinning and reduction of the oxide layer, which is completely recovered on subsequent air exposure without loss of the SRF performance improvement.;The effect of the most commonly employed treatment-BCP on polycrystalline niobium sheet over a range of realistic solution flow rates has been examined through multiple surface characterization techniques. The surface exhibits micron-scale roughness, whose extent does not change with treatment conditions. The outermost surface consists of a few-nm thick layer of Nb2O5, whose thickness increases with solution flow rate to a maximum of 1.3∼1.4 times that resulting from static solution.;Electropolishing is believed to be an effective technique to treat niobium cavity surfaces for achieving reproducibly high performance SRF cavities. However the operation condition is basically optimized through practical processing. By using improved electrochemical techniques, the temperature, flow rate and HF concentration dependence of each potential were indentified. The first use of electrochemical impedance spectroscopy (EIS) on this system was reported. EIS results are consistent with the compact salt film mechanism for niobium electropolishing in hydrofluoric sulfuric acid electrolyte and do not supports either the porous salt film or the absorbate-acceptor mechanism.

Стилі APA, Harvard, Vancouver, ISO та ін.

18

Völker, Jens. "Development of a compact test facility for SRF Photoelectron injectors." Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19322.

Повний текст джерела

Анотація:

SHF Photoelektroneninjektoren sind eine vielversprechende Elektronquelle für hochbrillante Teichenbeschleuniger mit hohem mittlerem Strom und kurzen Teilchenpulsen, wie FELs und ERLs. Für das ERL Projekt bERLinPro wurde einer unabhängige Testanlage GunLab entwickelt um die Leistungsfähigkeit der Injektoren und die Strahlparameter zu überprüfen. Darüber hinaus können neue Komponenten zur Strahldiagnose getestet werden. Die Hauptaufgabe von GunLab ist die Beschreibung des vollständigen sechsdimensionalen Phasenraums der Elektronen in Abhängigkeit aller Injektorparameter. Die Anlage besteht aus einer kompakten Diagnosestrahlführungan dem SHF Photoelektroneninjektoren und einem Kathodenlasersystem. Im Rahmen dieser Arbeit wurden analytische und numerische Studien zu den SHF Photoelektroneninjektoren durchgeführt, um zu erwartende Strahlparameter zu detektieren und die Anforderungen an die Strahldiagnose festzulegen. Darüber hinaus wurden verschiedene Emittanzbeiträge der einzelnen Injektorkomponenten untersucht. Diesbezüglich wurde das Magnetfeld des aktuellen Solenoiden kartiert und auf Asymmetrien getestet, die ebenfalls zu Emittanzvergrößerungen beitragen können. Eine der wesentlichen Komponenten der Diagnosestrahlführung ist das (transversale) Phasenraummesssystem, für das eine besondere Magnetgeometrie entwickelt wurde. Weitere Diagnose Komponenten sind ein optimierter Spektrometerdipol und eine transversal ablenkende Kavität, durch die sich zusammen mit zwei Quadrupolmagneten die Scheibenemittanz bestimmen lässt. Für GunLab wurden unterschiedliche optische Messsysteme entwickelt und optimiert. Der herausforderndste Aufbau ist dabei das Strahl-Halo Messsystem. Es ermöglicht die Beobachtung der transversalen Ladungsverteilung über einen Dynamikbereich von bis zu 6 Größenordnungen. Die Leistungsfähigkeit und die Auflösung aller Messsysteme und Messroutinen wurden bestimmt, um die Visualisierung des kompletten Phasenraums durch GunLab sicher zu stellen.
SRF photoelectron injectors are promising electron sources for high brightness accelerators with high average current and short pulse duration like FELs and ERLs. For the ERL project bERLinPro an independent test facility called GunLab was developed and set up to optimize the operation performance of SRF photoinjectors and the electron beam parameters. Furthermore, GunLab allows to investigate the operation of different kinds of photocathodes in the environment of an SRF accelerator and to study new beam diagnostic concepts. Of outmost importance is the characterization of the full six dimensional phase space as a function of all injector parameters. GunLab consists of the compact diagnostic beam line, connected to the SRF photoinjetor module, and a drive laser. In the context of this thesis, analytical and numerical investigations of the SRF photoinjector were performed to estimate beam parameter ranges and to determine the diagnostics requirements. Furthermore, various emittance contributors of the injector were determined. Thereby the magnetic field of the final designed solenoid was measured to determine field asymmetries, which are one major source of emittance growth. One of the central diagnostic components of the beamline is the (horizontal) phase space scanner system. For this purpose, a dedicated air-coil magnet design was developed. Additional diagnostic components include an optimized spectrometer system, a transverse deflecting cavity (TCav) and two quadrupole magnets, to determine longitudinal and sliced emittance. For GunLab different optical measurement systems were developed and optimized, the most challenging setup is a beam halo measurement system. This device is able to observe the transverse charge density with a dynamic range of up to 6 orders of magnitude. The performance and the resolution of all measurement systems and routines for GunLab were determined to ensure the visualization of the electron beam phase space.

Стилі APA, Harvard, Vancouver, ISO та ін.

19

Recari, Ansa Javier. "Gasification of biomass and solid recovered fuels (SRFs) for the synthesis of liquid fuels." Doctoral thesis, Universitat Rovira i Virgili, 2017. http://hdl.handle.net/10803/450856.

Повний текст джерела

Анотація:

La gasificació és una tecnologia prometedora per l’aprofitament energètic de biomassa i residus, ja que permet convertir els combustibles sòlids en un gas de síntesi (syngas) amb diverses aplicacions. No obstant això, algunes limitacions encara impedeixen la completa implementació d’aquesta tecnologia a escala industrial, en particular per a la producció de combustibles líquids a partir del procés Fischer-Tropsch (FT). Els principals inconvenients estan relacionats amb la qualitat del syngas, per exemple una baixa relació H2/CO i la presència d’impureses (tar i contaminants menors), i depenen de la naturalesa del material i de les condicions d’operació del procés de gasificació. Aquesta tesi es centra en la millora de la qualitat del syngas de gasificació de biomassa i combustibles sòlids recuperats (CSRs) per a la producció de combustibles líquids. El treball es divideix en dos parts principals. La primera part consisteix en estudis experimentals de gasificació de biomassa i CSRs en un reactor de llit fluïditzat a escala de laboratori per tal d’analitzar la influència de les condicions d’operació (temperatura, agents de gasificació, etc.) en el rendiment del procés i la composició del gas. Ja que els CSRs contenen més quantitats de precursors de contaminants que la biomassa, es va desenvolupar un mètode per tal de determinar la concentració de HCl, H2S, HCN i NH3 en el syngas mitjançant la potenciometria d’ió-selectiu. També, es proposa l’aplicació d’un pretractament tèrmic (torrefacció) als materials de gasificació com un mètode per tal de millorar les propietats dels materials i disminuir l’emissió de contaminants en el syngas. Per últim, la segona part d’aquest treball consisteix en un estudi tecno-econòmic per estimar els costos d’inversió i d’operació de plantes de combustibles líquids FT a partir de la gasificació de biomassa i residus, partint dels resultats obtinguts experimentalment.
La gasificación es una tecnología prometedora para el aprovechamiento energético de biomasa y residuos ya que permite convertir los combustibles sólidos en un gas de síntesis (syngas) con múltiples aplicaciones. Sin embargo, ciertas limitaciones todavía impiden la completa implementación de esta tecnología a escala industrial, en particular para la producción de combustibles líquidos a partir del proceso Fischer Tropsch (FT). Los principales inconvenientes están relacionados con la calidad del syngas, por ejemplo una baja relación H2/CO y la presencia de impurezas (tar y contaminantes menores), y dependen de la naturaleza del material y de las condiciones de operación del proceso de gasificación. Esta tesis se centra en la mejora de la calidad del syngas de gasificación de biomasa y combustibles sólidos recuperados (CSRs) para la producción de combustibles líquidos. El trabajo se divide en dos partes principales. La primera parte consiste en estudios experimentales de gasificación de biomasa y CSRs en un reactor de lecho fluidizado a escala de laboratorio para evaluar la influencia de las condiciones de operación (temperatura, materiales de lecho, agentes de gasificación, etc.) en el rendimiento del proceso y la composición del gas. Debido a que los CSRs contienen mayores cantidades de precursores de contaminantes que la biomasa, se ha desarrollado un método para determinar la concentración de HCl, H2S, HCN y NH3 en el syngas mediante potenciometría de ion selectivo. Además, se propone la aplicación de un pretratamiento térmico (torrefacción) a los materiales de gasificación como un método para mejorar las propiedades de los materiales y disminuir la emisión de contaminantes en el syngas. Por último, la segunda parte consiste en un estudio tecno-económico para estimar los costes de inversión y de operación de plantas de combustibles líquidos FT a partir de la gasificación de biomasa y residuos, partiendo de los resultados obtenidos experimentalmente.
Gasification is a promising technology for energy exploitation of biomass and waste, converting carbonaceous fuels into a synthesis gas (syngas) with multiple applications. However, technical obstacles hinder the full implementation of this technology at industrial scale, particularly for the production of liquid fuels through Fischer-Tropsch (FT) synthesis. Those challenges are mainly related to the syngas quality, such as a low H2/CO ratio and the presence of impurities (tar and minor contaminants), strongly influenced by the nature of the feedstock and the operating conditions of the gasification process. This thesis focuses on the improvement of the syngas quality from gasification of biomass and solid recovered fuels (SRFs) aiming to produce liquid fuels. The present work is divided in two main blocks. The first block corresponds to biomass and SRFs gasification experiments in a lab-scale fluidized bed reactor in order to study the influence of key operating conditions (temperature, bed materials, gasification agents, etc.) on the gasification performance and gas composition. Since SRF materials contain higher amounts of contaminants precursors than biomass, a method to assess the concentration of HCl, H2S, HCN and NH3 in the syngas by means of ion-selective potentiometry was developed. The application of a thermal pretreatment (torrefaction) to the gasification feedstocks is proposed as a way to upgrade the feedstock properties and abate the release of contaminants in the syngas. The second part of this work consists in a techno-economic analysis that estimates capital and production costs of FT liquid fuel plants based on biomass and waste gasification, using as input the experimental results.

Стилі APA, Harvard, Vancouver, ISO та ін.

20

Vézina, Gabriel. "Aérodynamique d'une turbomachine à architecture concentrique de type SRGT (Supersonic RIM-ROTOR gaz turbine)." Mémoire, Université de Sherbrooke, 2014. http://hdl.handle.net/11143/5419.

Повний текст джерела

Анотація:

Le groupe de recherche CAMUS de l'Université de Sherbrooke a conceptualisé et breveté en 2011 une nouvelle architecture de turbine à gaz nommé SRGT (Supersonic Rim-Rotor Gas Turbine). Aucune démonstration expérimentale n’a encore permis d’évaluer ses performances. Ce projet de maitrise consiste donc à l’analyse de la dynamique des gaz d’une turbomachine de type SRGT afin d’évaluer la possibilité de générer de la puissance nette positive en régime permanent. L’objectif de ce projet de recherche est de concevoir les composantes aérodynamiques d’une turbine à gaz SRGT en mode supersonique et de caractériser l’écoulement sur toute la plage d’opération du moteur. Ainsi, on pourra évaluer le potentiel de cette technologie et la pertinence de continuer le développement vers un produit futur. L’évaluation des performances aérodynamiques des composantes du moteur a été effectuée selon un modèle analytique 1D généralisé des écoulements compressibles et selon l’analyse des triangles des vitesses. Des simulations numériques par la méthode de la mécanique des fluides numérique (CFD) ont permis de valider le modèle analytique du moteur. Le point d’opération du moteur (vitesse du moteur de 125 000 rpm, débit massique d’air de 130 g/s, rapport de pression du compresseur de 2.75 et température maximum à l’entrée de la turbine de 1000 K) a été sélectionné afin de produire une puissance nette de plus de 1 kW. Un prototype a été fabriqué et mis en fonction sur un banc de test développé spécialement pour le moteur. L’expérimentation a démontré que le compresseur peut fournir un rapport de pression de plus de 1.35 à 100 krpm pour un débit massique d’air supérieur à 50 g/s. La carte de performance du compresseur a été obtenue expérimentalement ainsi que ses limites d’opérations (limite de blocage et de pompage) pour des vitesses jusqu’à 90 krpm. Des tests d’allumage ont démontré que le moteur avait un gain de puissance de plus de 1 kW durant sa phase d’accélération, bien que la puissance nette du moteur reste négative. La caractérisation de la turbine n’a pas pu révéler si sa conception était adéquate en mode supersonique. L’expérimentation du prototype n’a pas permis de valider si le moteur peut produire une puissance nette positive en régime permanent.

Стилі APA, Harvard, Vancouver, ISO та ін.

21

Wilde, Stuart. "Development of superconducting thin films for use in SRF cavity applications." Thesis, Loughborough University, 2017. https://dspace.lboro.ac.uk/2134/34659.

Повний текст джерела

Анотація:

Superconducting thin films are a possible alternative to bulk niobium for superconducting radio frequency cavity applications. Thin film cavities have produced larger Q0 than bulk niobium at low accelerating voltages [1], are less susceptible to external magnetic fields and therefore require less magnetic shielding than bulk niobium cavities [2] and can benefit from substrates which conduct heat more effectively than bulk niobium [3]. The major drawback for current thin film cavity technology is the large Q slope which is observed above accelerating gradients of 6 7 MV/m. The mechanism for the Q slope is not yet fully understood. Theories have been suggested but are not accepted by everyone within the scientific community [2, 4, 5, 6, 7]. It is assumed that a better understanding of the physical properties of superconducting films is required before the origins of the sharp Q slope can be elucidated. This study has been conducted to better understand the physical properties of superconducting thin films deposited by the magnetron sputtering process. In particular, superconducting niobium films have been deposited by high power impulse magnetron sputtering (HiPIMS) and tested by a wide range of analytical techniques as a function of the substrate temperature and applied bias during deposition. Analytical techniques which have been used include x-ray diffraction crystallography, Rutherford backscattering spectroscopy, scanning electron microscopy, residual resistance ratio, DC magnetometry and RF surface resistance measurements. Results showed that the application of an applied bias during deposition resulted in increased energy of bombarding ions and enhanced rates of surface diffusion and defect annihilation within the microstructure of a growing niobium film. However, large numbers of random complex defects formed once the energy of bombarding ions becomes too large. The systematic approach that was described to investigate the changing morphological and DC superconducting properties of deposited films, as a function of the applied bias, allowed the identification of which process conditions produce the fewest random complex defects. The same systematic investigations could be applied to any HiPIMS deposition facility to provide similar results. An important observation during the study is that the initial substrate conditions have a large influence on the properties of a deposited niobium film. Niobium films deposited onto polycrystalline copper substrate that was pre-annealed at 700 ˚C prior to deposition displayed more stable magnetic flux pinning, larger RRR and an enhanced resistance to the onset of flux penetration, than was observed for films deposited with a wide range of process conditions onto as received copper substrate. Superconductors other than niobium have been successfully deposited by HiPIMS and tested. Niobium titanium nitride thin films displayed a superconducting transition temperature up to 16.7 K, with a normal state resistivity as small as 45±7 μΩcm. The findings suggest that similar niobium titanium nitride thin films could produce smaller RF surface resistance than bulk niobium cavities at 4.2 K.

Стилі APA, Harvard, Vancouver, ISO та ін.

22

Zhao, Liang. "Surface polishing of niobium for superconducting radio frequency (SRF) cavity application." W&M ScholarWorks, 2015. https://scholarworks.wm.edu/etd/1563899057.

Повний текст джерела

Анотація:

Niobium cavities are important components in modern particle accelerators based on superconducting radio frequency (SRF) technology. The interior of SRF cavities are cleaned and polished in order to produce high accelerating field and low power dissipation on the cavity wall. Current polishing methods, buffered chemical polishing (BCP) and electropolishing (EP), have their advantages and limitations. We seek to improve current methods and explore laser polishing (LP) as a greener alternative of chemical methods. The topography and removal rate of BCP at different conditions (duration, temperature, sample orientation, flow rate) was studied with optical microscopy, scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). Differential etching on different crystal orientations is the main contributor to fine grain niobium BCP topography, with gas evolution playing a secondary role. The surface of single crystal and bi-crystal niobium is smooth even after heavy BCP. The topography of fine grain niobium depends on total removal. The removal rate increases with temperature and surface acid flow rate within the rage of 0~20 °C, with chemical reaction being the possible dominate rate control mechanism. Surface flow helps to regulate temperature and avoid gas accumulation on the surface. The effect of surface flow rate on niobium EP was studied with optical microscopy, atomic force microscopy (AFM), and power spectral density (PSD) analysis. Within the range of 0~3.7 cm/s, no significant difference was found on the removal rate and the macro roughness. Possible improvement on the micro roughness with increased surface flow rate was observed. The effect of fluence and pulse accumulation on niobium topography during LP was studied with optical microscopy, SEM, AFM, and PSD analysis. Polishing on micro scale was achieved within fluence range of 0.57~0.90 J/cm 2, with pulse accumulation adjusted accordingly. Larger area treatment was proved possible by overlapping laser tracks at proper ratio. Comparison of topography and PSD indicates that LP smooths the surface in a way similar to EP. The optimized LP parameters were applied to different types of niobium surfaces representing different stages in cavity fabrication. LP reduces the sharpness on rough surfaces effectively, while doing no harm to smooth surfaces. Secondary ion mass spectrometer (SIMS) analysis showed that LP reduces the oxide layer slightly and no contamination occurred from LP. EBSD showed no significant change on crystal structure after LP.

Стилі APA, Harvard, Vancouver, ISO та ін.

23

Juntong, Nawin. "Investigation of optimised electromagnetic fields in SRF cavities for the ILC." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/investigation-of-optimised-electromagnetic-fields-in-srf-cavities-for-the-ilc(d0ddfc7c-c72e-4c68-810a-8cecacb20407).html.

Повний текст джерела

Анотація:

The International Linear Collider (ILC) project aims at colliding electrons and positrons at an initial centre of mass energy of 500 GeV with high luminosity, and thus will allow scientists to probe new energy regimes. A general consensus within the accelerator physics and particle physics community has been made to utilise superconducting technology rather than normal conducting technology. A superconducting radio frequency (SRF) cavity will be used to accelerate bunches of particles to the design energy before delivering them to an interaction point. The major financial cost of the ILC lies in the area of the main linacs. These linacs consist of nine-cell cavities and are based on the TESLA design. An option being considered to reduce the overall footprint and project cost is to enhance the cavity gradient. This research concerns itself with my new cavity design with a view to reaching higher gradients. This design is focussed on minimising the surface electromagnetic fields and maximising the bandwidth of the accelerating mode. This new shape, which is referred to as the New Low Surface Field (NLSF) design, bears a similarity to the current Ichiro and Reentrant designs. A design of a complete nine-cell cavity, including power couplers and higher order mode damping couplers is presented. An equivalent circuit model theory is applied to represent the radio frequency (rf) mode properties of the cavity for both the fundamental accelerating mode and higher order modes. This represents an almost complete design, including HOM damping, for a unique high gradient superconducting cavity.

Стилі APA, Harvard, Vancouver, ISO та ін.

24

Papaefthymiou, Aikaterini. "Role of the Srf transcription factor in adult muscle stem cells." Thesis, Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCB120/document.

Повний текст джерела

Анотація:

Le muscle squelettique adulte est un tissu avec une grande plasticité étant donné qu’il adapte sa taille suite à la surcharge fonctionnelle et il régénère suite à une lésion. La base de cette plasticité est la myofibre et les cellules souches associées, les cellules satellites (CS). Suite aux stimuli, les CS sortent de la quiescence, elles s’activent, proliférent, s’engagent dans la voie myogénique et fusionnent entre elles ou bien avec la fibre pre-éxistante. Une partie des CS retourne à la quiescence afin de maintenir le « pool » de progéniteurs. Ce projet a pour objectif de mieux caractériser des voies de signalisation responsables des adaptations des CS au cours de la régénération et le l’hypertrophie compensatoire. Srf est un facteur de transcription, particulièrement exprimé dans les muscles. Les gènes cibles de Srf sont des gènes qui participent à la régulation de la prolifération cellulaire et des gènes codant des protéines sarcomériques du muscle ou bien des gènes ayant un rôle dans l’adhésion cellulaire, la migration et l’organisation du cytosquelette. Il a été montré que la perte de fonction de Srf dans la lignée de cellules musculaire C2C12 inhibe leur prolifération et leur différenciation et que Srf contrôle l’expression de MyoD qui est un gène de détermination myogénique. Aucune donnée n’est disponible à ce jour concernant la fonction de Srf dans les CS in vivo. Nous avons généré des souris dépourvues de Srf spécifiquement dans les CS adultes. Les CS ont été recruitées par l’hypertrophie et la régénération musculaire. En parallèle des études ex vivo ont été menées afin de préciser si les phénotypes observés sont cellule-autonomes et afin de disséquer les mécanismes sous-jacents. Nous montrons que la perte de Srf dans les CS affecte fortement les processus de régénération et d’hypertrophie suggérant un rôle de Srf dans le contrôle du destin cellulaire de CS. Nos études montrent que la perte le Srf dans les SC n’affecte pas leur prolifération et leur engagement dans la différenciation myogénique. Par contre, leur motilité et leur capacité de fusion sont fortement réduites. Afin d’identifier les effecteurs de Srf impliqués dans la motilité et le défaut de fusion des CS mutantes, nous avons réalisé des études transcriptomiques et identifié le set de gènes dont l’expression est altérée par la perte de Srf dans des conditions de prolifération et de différenciation. L’analyse des fonctions altérées nous a indiqué que la voie de signalisation du cytosquelette d’actine était perturbée. En effet les CS dépourvues de Srf expriment moins d’actine et présentent une organisation du cytosquelette d’actine perturbée. Des expériences de sauvetage utilisant un modèle de souris permettant la surexpression inductible d’actine alpha dans les CS dépourvues de Srf ont montré que la surexpression d’actine chez les mutants Srf était suffisante pour rétablir partiellement l’organisation du cytosquelette et améliorer les capacités de fusion des CS. De manière intéressante, seule la fusion hétérotypique (entre une cellule contrôle et une cellule mutante), et pas la fusion homotypique (entre deux cellules mutantes), est rétablie par l’expression de l’actine. In vivo, le rétablissement de la fusion hétérotypique restaure la croissance hypertrophique des muscles alors que l’altération de la régénération chez les mutants Srf n’est que faiblement améliorée par la surexpression de l’actine. Cette étude nous a permis d’avoir une vision d’ensemble et mécanistique de la contribution du facteur de transcription Srf dans la biologie des CS et de mettre en évidence l’importance structurale du maintien du cytosquelette d’actine pour la fusion des cellules musculaires
The adult skeletal muscle is a high plastic tissue as it adapts its size upon overload and it is capable of regeneration upon muscle lesion. The skeletal muscle is composed of a specialized syncytium, the myofiber, which is the functional unit of the muscle and a small population of myogenic progenitors, residing adjacent to the myofibers, termed as satellite cells (SCs). SCs are the muscle-specific stem cells which endow the skeletal muscle with its remarkable capacity to repair and to maintain homeostasis during muscle turnover. In resting adult muscles, SCs are quiescent but they activate upon exposure to stimuli. The activated SCs (myoblasts) proliferate extensively and subsequently differentiate and fuse between them or pre-existing myofibers, a series of cellular events called myogenesis. In parallel to the myogenesis, a reserve population of SCs escapes the myogenic program and self-renews to replenish the SC pool. The current project aims to further characterize the signalling pathways involved in SC functions during muscle regeneration and compensatory hypertrophy (CH). Srf is a muscle-enriched transcription factor with Srf-target genes implicated in cell proliferation, differentiation (sarcomeric proteins), adhesion, migration and cellular cytoskeleton. Studies in C2C12 mouse myogenic cell line showed that Srf loss prevent the myoblast proliferation and differentiation by down-regulating the expression of the myogenic determinant MyoD gene. We used a genetic murine model for adult SC-specific Srf-loss in order to conduct in vivo and ex vivo studies for the Srf role in SCs. Compensatory hypertrophy and regeneration are the two means by which SCs were recruited. We show that loss of Srf in SCs affects the regeneration process and the CH suggesting the Srf role in the SC fate. Srf-depleted SCs display probably no defect in their proliferation and differentiation but reduced capacity in motility and fusion. Transcriptomic analysis revealed altered actin cytoskeleton and signalling. Srf-depleted SCs show reduced actin expression and altered actin cytoskeleton. Rescue of actin expression in Srf-depleted SCs partially restored the cytoskeleton organization and the fusion process. Interestingly by actin overexpression only the heterotypic/asymmetric fusion was established but not the homotypic/symmetric fusion. Therefore actin overexpression restored the hypertrophic growth in the CH (in vivo model of heterotypic fusion) but failed to do so in the regeneration (in vivo model of homotypic fusion). This study contributed to the in vivo investigation of the Srf mechanistic role in adult SCs and underlined the importance of actin cytoskeleton maintenance in the fusion of myogenic cells

Стилі APA, Harvard, Vancouver, ISO та ін.

25

Blais, Mélody. "Apprentissage procédural moteur et mémoire procédurale dans le trouble développemental de la coordination : études comportementales, en électroencéphalographie et en imagerie par résonance magnétique." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30061/document.

Повний текст джерела

Анотація:

Le Trouble Développemental de la Coordination (TDC) se caractérise par une altération des habiletés motrices. Si le déficit du contrôle moteur est univoque, les études testant un déficit d'apprentissage procédural moteur restent peu nombreuses et aboutissent à des résultats divergents. L'objectif principal de ce travail est de mettre en évidence les conditions dans lesquelles les enfants présentant un TDC manifestent ou non un déficit d'apprentissage procédural et de la mémoire procédurale. Quatre études ont été menées pour comparer l'apprentissage procédural moteur d'enfants présentant un TDC et d'enfants contrôles. Nous avons testé des tâches comportementales d'apprentissage variées telles que l'apprentissage d'une nouvelle coordination bimanuelle, l'apprentissage de séquences perceptivo-motrices et l'apprentissage de séquences motrices rythmiques dans différentes conditions. Nous avons investigué les corrélats cérébraux fonctionnels et structurels associés, en utilisant l'électroencéphalographie ou l'imagerie par résonance magnétique. Les résultats indiquent des différences comportementales et cérébrales lors de tâches d'apprentissage, révélées par des variables spécifiques. De plus, certaines conditions expérimentales ont amélioré l'apprentissage procédural et la mémoire procédurale des enfants présentant un TDC. Ces résultats amènent à penser que les conditions favorisant l'apprentissage et la mémoire procédurale des enfants présentant un TDC pourraient contribuer à une meilleure prise en charge
Developmental Coordination Disorder (DCD) is characterized by impaired motor skills. While the motor control deficit is unambiguous, studies testing motor procedural learning are few and lead to contradictory results. The main objective of this work is to understand the conditions under which children with DCD demonstrate a procedural learning and procedural memory deficits. Four studies were conducted to compare the motor procedural learning of children with and without DCD. We tested various learning behavioural tasks such as learning a new bimanual coordination, learning perceptual-motor sequences and learning rhythmic motor sequences in different conditions. We investigated the associated functional and structural brain correlates, using electroencephalography and magnetic resonance imaging. The results indicate some behavioural and brain differences during learning tasks, revealed by specific variables. In addition, some experimental conditions have improved the procedural learning and procedural memory of children with DCD. These results suggest that conditions in which procedural learning and memory of children with DCD are improved could contribute to better therapeutic interventions

Стилі APA, Harvard, Vancouver, ISO та ін.

26

Grüner, T. "A functional RNAi screen for regulators of the serum response factor (SRF)." Thesis, University College London (University of London), 2009. http://discovery.ucl.ac.uk/19000/.

Повний текст джерела

Анотація:

Serum response factor (SRF) controls transcription of numerous immediate early and muscle-specific genes by its association with diverse co-activators. Amongst the SRF binding regulators are the TCF family proteins, including Elk1, SAP1 and SAP2 and the myocardin-related transcription factor (MRTF) family proteins including MAL and MAL16. Both types of transcriptional coactivators form a complex with SRF, which binds to serum response elements (SREs) upon serum activation by different upstream signal transduction pathways. While SRF activation by TCFs occur through the MAP kinase pathway, MRTFs regulate SRF specifically through the RhoA pathway. MAL, a G-actin binding protein, continuously shuttles between cytoplasm and nucleus in many unstimulated cells and appears cytoplasmic. Upon RhoA-induced actin polymerization, MAL nuclear export is blocked due to disruption of the MAL-actin interaction. MAL accumulates in the nucleus where it binds to SRF, which results in target gene expression. Although many of the pathway components are already known, it is probable that there are still uncharacterized factors that regulate SRF. Therefore this thesis addresses the identification of new regulators of SRF that are specifically dependent on the RhoA pathway. Since the interaction of MAL with SRF and actin represents an evolutionarily conserved regulatory mechanism between Drosophila and human and the Drosophila genome lacks much of the genetic redundancy observed in human, a genome-wide RNA interference (RNAi) screen in cultured Drosophila cells was performed to identify key regulators of SRF. Using RNAi, 295 proteins in Drosophila cells were identified, of which 50 were further validated in human cells. Amongst the final confirmed hits, eukaryotic elongation translation factor (eEF1A) was a promising regulator for RhoA induced SRF activation. eEF1A2 was shown to interact with MAL and depletion of eEF1A2 in unstimulated cells led to nuclear accumulation of MAL, suggesting its role as a MAL regulator. Potential roles of the remaining hits confirmed in the rescreen are also discussed in this thesis.

Стилі APA, Harvard, Vancouver, ISO та ін.

27

Lu, Pengnan. "Optimization of an SRF Gun for High Bunch Charge Applications at ELBE." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-223386.

Повний текст джерела

Анотація:

As a cutting-edge technology for photoinjectors, SRF guns are expected to provide CW electron beams with high bunch charge and low emittance, which is critical to the development of future FELs, ERLs and 4th/5th generation light sources. However, existing research has not explored the full potential of SRF guns as predicted by theory. Currently, the research activities at ELBE focus on solving technological challenges of a 3.5 cell SRF gun as well as applying it to high-bunch-charge experiments. This thesis aims to optimize the ELBE SRF gun and the relevant beam transport for future high-bunch-charge applications at pELBE, nELBE, TELBE and CBS experimental stations. Chapter 1 describes the demands of these applications on the SRF gun in detail. Chapter 2 outlines the development of a simulation tool based on ASTRA and Elegant, followed by the optimized gun parameters and the beam transport for the four experimental stations. Chapter 3 introduces beam diagnostic methods and data processing applied in this thesis. Chapter 4 presents results of experiments, including the pulse length measurement of the UV laser for generating electrons from the photcathode, the commissioning of ELBE SRF Gun II, a verification experiment on the LSC effect conducted at PITZ and a beam transport experiment with the bunch charge of 200 pC. Simulation results have determined the effect of each SRF gun parameter on the beam quality and have provided optimized settings according to the requirements in Chapter 1. Experimentally, the LSC effect was confirmed at PITZ, in agreement with simulations which indicated that LSC significantly influences beam quality. The performance of ELBE SRF Gun II was improved and a beam with a bunch charge of 200 pC and an emittance of 7.7 μm from ELBE SRF Gun II has been transported through ELBE without visible beam loss. The development of the simulation tool and beam diagnostics will serve further research at ELBE. Results of both simulations and experiments enrich the understanding of the existing SRF gun as well as the ELBE beamline and will guide continuing improvements. Already, ELBE SRF Gun II can deliver twice the bunch charge and lower emittance compared to the thermionic injector routinely used for ELBE. Ongoing modifications and development of the gun-cavity and photocathodes are expected to provide still further improvements. Progress on high-bunch-charge experiments at ELBE can be expected by applying the SRF gun.

Стилі APA, Harvard, Vancouver, ISO та ін.

28

Cunha, Gina Michelle Mac?do da. "Altera??es nas concentra??es das SRAT, conte?do de GSH e atividade da CAT em pacientes com esquistossomose aguda." Universidade Federal do Rio Grande do Norte, 2008. http://repositorio.ufrn.br:8080/jspui/handle/123456789/13435.

Повний текст джерела

Анотація:

Made available in DSpace on 2014-12-17T14:16:21Z (GMT). No. of bitstreams: 1 GinaMMC.pdf: 1174181 bytes, checksum: 37699ea266658587623a87a8fcd376f3 (MD5) Previous issue date: 2008-01-30
Schistosomiasis is an ancient disease caused by helminth Schistosoma mansoni and is a public health problem in Brazil. The granulomatous lesion, typical of the disease, associates itself with increase in the oxidative damage through the generation of free radicals. The aim of this work was to evaluate the occurrence of changes in parameters oxidant / antioxidant that are part of the human defense system, and observe whether they would cause oxidative stress in subjects with schistosomiasis. Moreover, correlating with some biochemical and hematological parameters. Two groups were selected for study, consisting of individuals of both sexes, aged between 16 and 30 years. A control group, formed by individuals without schistosomiasis (n = 30) and a test group, formed by individuals with schistosomiasis (n = 30). The evaluation of lipid peroxidation in plasma was performed by determination of malondialdehyde and antioxidant defense by the quantification of reduced glutathione and catalase activity. For the parameters that assess oxidative stress, the results showed a decrease in the content of reduced glutathione and no change in the activity of catalase, with an increase in the value of malondialdehyde. Therefore, the data found suggest the occurrence of oxidative stress in subjects with schistosomiasis. Of the parameters that assess hepatic function, only levels of aspartate aminotransferase have been high, while there was a decrease of bilirubine. There was a significant change in the lipid profile (p <0.5), however with regard to the renal function of patients, there was a decrease in creatinine. The assessment hematological, made through hemogram and the quantification of hemoglobin, shows increase of eosinophils individuals in the group test, which can be related to the presence of the parasite. The amendments suggest the involvement of oxidative stress in the pathophysiology of this disease
A esquistossomose ? uma doen?a milenar causada pelo helminto Schistosoma mansoni e constitui um problema de sa?de p?blica no Brasil. A les?o granulomatosa, t?pica da doen?a, est? associada com o aumento do dano oxidativo atrav?s da gera??o de radicais livres. O objetivo deste trabalho foi avaliar a ocorr?ncia de altera??es nos par?metros oxidante/antioxidante que fazem parte do sistema de defesa do organismo, e observar se os mesmos provocariam estresse oxidativo em indiv?duos com esquistossomose. Al?m disso, correlacionando com alguns par?metros bioqu?micos e hematol?gicos. Foram selecionados dois grupos de estudo, constitu?dos de indiv?duos de ambos os sexos, com faixa et?ria compreendida entre 16 e 30 anos. Um grupo controle, formado por indiv?duos sem esquistossomose (n=30) e um grupo teste, formado por indiv?duos com esquistossomose (n=30). A avalia??o da peroxida??o lip?dica no plasma foi realizada por meio da determina??o do malondialde?do e a defesa antioxidante pela dosagem da glutationa reduzida e determina??o da atividade da catalase. Em rela??o aos par?metros que avaliam o estresse oxidativo, os resultados demonstraram uma diminui??o do conte?do de glutationa reduzida e nenhuma altera??o na atividade da catalase, com um aumento nos valores de malondialde?do. Portanto, os dados encontrados sugerem a ocorr?ncia do estresse oxidativo nos indiv?duos com esquistossomose. Dos par?metros que avaliam a fun??o hep?tica, apenas os n?veis de aspartato amino transferase mostraram-se elevados, enquanto ocorreu uma diminui??o da bilirrubina. N?o houve uma altera??o significativa no perfil lip?dico (p<0.5), entretanto com rela??o ? fun??o renal dos pacientes, houve uma diminui??o da creatinina. A avalia??o hematol?gica, realizada atrav?s do hemograma completo e a dosagem da hemoglobina, mostra eosinofilia nos indiv?duos do grupo teste, que pode estar relacionada com a presen?a do parasita. As altera??es apresentadas sugerem a participa??o do estresse oxidativo na fisiopatologia da referida doen?a

Стилі APA, Harvard, Vancouver, ISO та ін.

29

Tomáš, Petr. "Návrh a realizace senzorického systému pro mobilní robot s využitím frameworku ROS." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231374.

Повний текст джерела

Анотація:

The essence of this master thesis is design and implementation of sensor system based on robotic framework which is called ROS (Robot Operating System). The main task is to perform detailed analysis and test of capabilities of the framework with final implementation on specific robot application (sensor system) with following evaluation of applicability of the system in mobile robotics. As parallel aim is to create detailed general and practical guide for beginners with ROS which they are also beginners in Linux based operating systems.

Стилі APA, Harvard, Vancouver, ISO та ін.

30

Bezerra, Claudiane dos Santos. "Estudo estrutural e óptico do CaF2, SrF2 e LiCaAlF6 produzidos pelo método hidrotermal assistido por micro-ondas." Universidade Federal de Sergipe, 2016. https://ri.ufs.br/handle/riufs/5266.

Повний текст джерела

Анотація:

Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
In this work, CaF2, SrF2 and LiCaAlF6 pure and doped with rare earths were produced by microwave-assisted hydrothermal synthesis, which is a promising method to produce nanostructured powders in a simple, low cost and fast way. The samples were produced with or without using chelating agent and synthesized at low temperature, under pressure and a short time period. The crystalline phases of the samples were identified by X-ray diffraction (XRD) and the morphology of the particles was determined by scanning electron microscopy (SEM). The particles present similar morphology to CaF2 and SrF2 samples produced with and without using chelating agent. While the LiCaAlF6 samples presented a different morphology when produced with EDTA. The study of the chemical composition of CaF2 was performed by X-ray Photoelectron Spectroscopy (XPS) and the results indicated the presence of reasonable amounts of hydroxyl groups and oxygen ions in the samples produced with chelating agent. Optical study was conducted by emission and excitation spectra to understand the band structure and to determine the band gap of the materials. The emission spectrum showed that the CaF2 and SrF2 presents an intrinsic luminescence with an band at approximately 300 nm associated with the exciton emission. The fundamental absorption associated to the band gap was estimated at 11.7 eV for CaF2, 10.9 eV for SrF2 and 12.1 eV for LiCaAlF6. The emission and excitation spectra were measured in the Toroidal Grating Monochromator (TGM) beamline of the Brazilian Synchrotron Light Laboratory (LNLS) and the results shown evidences that the formation energy of the exciton and band gap energy are smaller than the ones for the single crystal.
Neste trabalho, CaF2, SrF2 e LiCaAlF6 puros e dopados com terras raras foram produzidos pelo método hidrotermal assistido por micro-ondas, o qual é um método promissor para produzir pós nanoestruturados de uma forma simples, com baixo custo e rápida. As amostras foram produzidas com e sem agente quelante e sintetizadas em baixa temperatura, sob pressão e curto período de tempo. As fases cristalinas das amostras foram identificadas por Difração de Raios X (DRX) e a morfologia das partículas determinada por microscopia eletrônica de varredura (MEV). As partículas apresentaram morfologias semelhantes para as amostras de CaF2 e SrF2 produzidas com e sem o uso do agente quelante. Enquanto que as amostras de LiCaAlF6 apresentaram uma morfologia diferente ao adicionar agente quelante. O estudo da composição química do CaF2 foi realizado por espectroscopia de fotoelétrons excitados por raios X (XPS) e os resultados indicaram a presença de uma quantidade razoável de grupos OH e íons de oxigênio na amostra produzida com agente quelante. Os estudos ópticos foram conduzidos por meio dos espectros de emissão e excitação para compreender a estrutura de bandas e determinar o band gap dos materiais. Os espectros de emissão mostraram que o CaF2 e o SrF2 apresentam luminescência intrínseca com uma banda em aproximadamente 300 nm associada a emissão do éxciton. A absorção fundamental associada ao band gap foi estimada em 11,7 eV para o CaF2, 10,9 eV para o SrF2 e 12,1 para o LiCaAlF6. Os espectros de emissão e excitação foram realizados na linha de luz TGM do Laboratório Nacional de Luz Sincrotron (LNLS) e os resultados mostraram evidências de que a energia de formação do éxciton e a energia do band gap são menores do que para o monocristal.

Стилі APA, Harvard, Vancouver, ISO та ін.

31

Li, Shijie. "Mechanistic analysis of SRF and the myocardin family of coactivators during muscle development." Access to abstract only; dissertation is embargoed until after 12/20/2006, 2005. http://www4.utsouthwestern.edu/library/ETD/etdDetails.cfm?etdID=132.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

32

Kim, Hyun Sung. "Experimental and Numerical Analysis of Hydroformed Tubular Materials for Superconducting Radio Frequency (SRF) Cavities." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1462533811.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

33

Al-Sayegh, Mohamed. "The role of SRF coactivators MRTF-A and MRTF-B in adipogenesis in vitro." Thesis, St George's, University of London, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.589960.

Повний текст джерела

Анотація:

This thesis comprises the work undertaken to investigate the role of the family of myocardin- related transcription factors, MRTF-A and MRTF-B, at regulating adipogenesis using the well- established in vitro model of 3T3-LI preadipocyte cells. Serum response factor (SRF) is an essential transcription factor that activates the expression of early immediate genes via recruitment of the family ternary complex factors or the transcription of cytoskeleton and muscle-specific genes via MRTF-A and MRTF-B recruitment. It has been shown that SRF depletion is sufficient to promote adipocyte differentiation in the absence of adipogenic stimuli though the mechanisms responsible for this are unknown. The work presented in this thesis shows that MRTF activity is abrogated at the onset of adipogenesis by two mechanisms: relocation of MRTF protiens to the cytoplasm and downregulation of both MRTF-A and MRTF- B protein and mRNA expression levels. These results suggest that inhibition of MRTF activity might be a pre-requisite for adipogenesis to proceed. In agreement with this, depletion of MRTF- A and MRTF-B protein levels via lentiviral mediated RNA interference was shown to promote adipogenesis in the absence of adipogenic cues where overexpression of a dominant positive MRTF-A form inhibited adipocyte differentiation. Several potential endogenous MRTF target genes that could mediate the effects of MR TFs on adipogenesis were identified using a combination of genome-wide RNA expression analysis of MRTF-depleted cells, quantitative PCR and chromatin immunoprecipitation assays. •

Стилі APA, Harvard, Vancouver, ISO та ін.

34

Penkava, Josef [Verfasser], and Thomas [Akademischer Betreuer] Gudermann. "Charakterisierung von Myoferlin als neues MKL/SRF-abhängiges Zielgen / Josef Penkava ; Betreuer: Thomas Gudermann." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2019. http://d-nb.info/1202011926/34.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

35

Stoll, Christian Philipp [Verfasser]. "Beam dynamical behaviour of the MESA SRF structures under recirculating operation / Christian Philipp Stoll." Mainz : Universitätsbibliothek der Johannes Gutenberg-Universität Mainz, 2020. http://d-nb.info/1224896653/34.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

36

Roach, Wiliam Michael. "Superconducting Thin Films for SRF Cavity Applications: A Route to Higher Field Gradient Linacs." W&M ScholarWorks, 2014. https://scholarworks.wm.edu/etd/1539623638.

Повний текст джерела

Анотація:

Many linear accelerator (linac) applications rely on the use of superconducting radio frequency (SRF) cavities. In order to overcome the current field gradient limits imposed by the use of bulk niobium, a model involving the deposition of alternating superconducting-insulating-superconducting (SIS) thin films onto the interior surface of SRF cavities has been proposed. Since SRF performance is a surface phenomenon, the critical surface of these cavities is less than 1 micron thick, thus enabling the use of thin films. Before such approach can successfully be implemented fundamental studies correlating the microstructure and superconducting properties of thin films are needed. to this end the effect of grain boundary density and interfacial strain in thin films has been explored. Thin films with a smaller grain boundary density were found to have better superconducting properties than films with a larger grain boundary density. Interfacial strain due to a lattice mismatch between the film and substrate lead to two regions in films, one strained region near the interface and one relaxed region away from the interface. The presence of two regions in the film resulted in two types of superconducting behavior. Niobium films were deposited onto copper surfaces to help understand why previous attempts of implementing niobium coated copper cavities in order to exploit the better thermal properties of copper had varying degrees of success. It was found that an increased growth temperature produced niobium films with larger grains and correspondingly better superconducting properties. Proof of principle multilayer samples were prepared to test the SIS model. For the first time, multilayers were produced that were capable of shielding an underlying niobium film from vortex penetration beyond the lower critical field of bulk niobium. This result provides evidence supporting the feasibility of the SIS model.

Стилі APA, Harvard, Vancouver, ISO та ін.

37

Neumann, Axel. "Compensating microphonics in SRF cavities to ensure beam stability for future free-electron-lasers." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2008. http://dx.doi.org/10.18452/15848.

Повний текст джерела

Анотація:

Laser-initiierte Freie Elektronen Laser (FEL) und Energy Recovery Linearbeschleuniger (ERL) erfordern höchste Stabilität der beschleunigten Elektronenpakete. Die zeitliche Streuung der Elektronenpakete und die mittlere Energieabweichung in den Undulatoren sollten in der Grössenordnung von Femtosekunden bzw. im Promille Bereich liegen. Das erfordert eine Regelung der Hochfrequenz (HF) Beschleunigungsfelder in den supraleitenden Hohlraumresonatoren bis zu 0.02° Phasen- und 1e-4 Amplitudengenauigkeit. Die TESLA Resonatoren des 2.3 GeV Linearbeschleunigers des geplanten BESSY-FEL sollen im Dauerstrichbetrieb bei geringer Strahllast betrieben werden. Die HF Resonanzbreite ist folglich sehr schmalbandig und liegt im Bereich von 10 Hertz. Um die erreichbare Feldstabilität zu erfassen, wurden die Resonatoren einem umfangreichen Messprogramm in der HoBiCaT Testanlage unterzogen. Eine Charakterisierung der vollständigen Resonatoreinheit hinsichtlich der mechanischen Verstimmung durch Mikrophonie, statische -und dynamische Lorentzkraftverstimmung, ihrer mechanischen Eigenschaften und HF-System Rauschen erbrachte wichtige Daten, um die zu erwartende Feld -und somit Strahlstabilität im Linac zu simulieren. Die gemessene Mikrophonie betrug 1-5 Hz rms, ist somit eine dominante Fehlergröße und wirkt sich limitierend auf die Strahlstabilität im Linac aus. Um sie zu minimieren, wurden aktive Dämpfungsmethoden entwickelt. Dazu wurden unterschiedliche mechanische Abstimmungssysteme mit integrierten Piezoelementen getestet. Ein adaptiver, vorauskompensierender Regelungsalgorithmus wurde entwickelt, welcher die gemessene Transferfunktion der Abstimmvorrichtung beinhaltet. Damit wurde eine Kompensierung der Mikrophonie um einem Faktor von zwei bis sieben erreicht. Die Einbeziehung dieser Regelung in die Linacsimulationen zeigte, dass diese einen wichtigen Beitrag zur Erreichbarkeit der benötigten Strahlstabilität für zukünftige FELs und ERLs darstellt.
In seeded High-Gain-Harmonic-Generation free electron lasers or energy recovery linear accelerators the requirements for the bunch-to-bunch timing and energy jitter of the beam are in the femtosecond and per mill regime. This implies the ability to control the cavity radio-frequency (RF) field to an accuracy of 0.02° in phase and up to 1e-4 in amplitude. For the planned BESSY-FEL it is envisaged to operate 144 superconducting 1.3 GHz cavities of the 2.3 GeV driver linac in continuous wave mode and at a low beam current. The cavity resonance comprises a very narrow bandwidth of the order of tens of Hertz. Such cavities have been characterized under accelerator like conditions in the HoBiCaT test facility. It was possible to measure the error sources affecting the field stability in continuous wave (CW) operation. Microphonics, the main error source for a mechanical detuning of the cavities, lead to an average fluctuation of the cavity resonance of 1-5 Hz rms. Furthermore, the static and dynamic Lorentz force detuning and the helium pressure dependance of the cavity resonance have been measured. Single cavity RF control and linac bunch-to-bunch longitudinal phase space modeling containing the measured properties showed, that it is advisable to find means to minimize the microphonics detuning by mechanical tuning. Thus, several fast tuning systems have been tested for CW operation. These tuners consist of a motor driven lever for slow and coarse tuning and a piezo that is integrated into the tuner support for fast and fine tuning. Regarding the analysis of the detuning spectrum an adaptive feedforward method based on the least-mean-square filter algorithm has been developed for fast cavity tuning. A detuning compensation between a factor of two and up to a factor of seven has been achieved. Modeling the complete system including the fast tuning scheme, showed that the requirements of the BESSY-FEL are attainable.

Стилі APA, Harvard, Vancouver, ISO та ін.

38

Panofski, Eva. "Beam Dynamics and Limits for High Brightness, High Average Current Superconducting Radiofrequency (SRF) Photoinjectors." Doctoral thesis, Humboldt-Universität zu Berlin, 2019. http://dx.doi.org/10.18452/19962.

Повний текст джерела

Анотація:

Zukünftige Beschleunigerprojekte und Nutzerexperimente erfordern für ihren Betrieb einen hochbrillanten Elektronenstrahl mit hohem mittlerem Strom. Eine Elektronenquelle mit dem Potential die Anforderungen erfüllen, ist ein supraleitender Hochfrequenz (SHF) Photoinjektor im Dauerstrichbetrieb. Die Strahldynamik eines solchen Photoinjektor Systems bestimmt die maximal zu erreichende Strahlbrillanz und wird ihrerseits von den Design und Betriebsparametern des Photoinjektors beeinflusst. Ziel ist immer die entscheidenden Design- und Betriebsparameter der Elektronenquelle hinsichtlich einer maximalen Strahlbrillanz zu wählen. Diese Aufgabe verlangt ein detailliertes Verständnis der Strahldynamik-Prozesse. Ferner ist es notwendig, eine Optimierung des Photoinjektors als Ganzes, mit dem Ziel einer maximalen Strahlqualität bei hohem mittlerem Strom, vorzunehmen. Dieses ermöglicht auch, die physikalischen Grenzen eines gegebenen Designs zu ermitteln und im Betrieb vollständig auszunutzen. Diese Doktorarbeit befasst sich mit der Strahldynamik in einem SHF Photoinjektor, unter Berücksichtigung interner Raumladungseffekte. Die Erkenntnisse zur Strahldynamik werden für die Entwicklung eines Optimierungsprogramms verwendet, um die Leistung des Injektors hinsichtlich der Strahlbrillanz zu verbessern. Die entwickelte Methode basiert auf Pareto-Optimierung mehrerer Zielfunktionen, unter Verwendung eines generischen Algorithmus. Das zentrale Ergebnis dieser Arbeit umfasst ein universelles Optimierungsprogramm, das für Photoinjektoren unabhängig von ihrem Design und Anwendungsgebiet genutzt werden kann. Für den Betrieb mit hoher Strahlbrillanz ist es möglich aus den erhaltenen Pareto-optimalen Lösungen einen stabilen Satz an Einstellwerten für den Photoinjektor zu extrahieren. Durch die allgemeine Optimierungsstrategie lässt sich das entwickelte Programm auch für andere Beschleunigerabschnitte, oder die Optimierung einer ganzen Anlage mit erweiterter Zielsetzung anpassen.
An increasing number of future accelerator projects, light sources and user experiments require high brightness, high average current electron beams for operation. Superconducting radio-frequency (SRF) photoinjectors running in continuous-wave (cw) mode hold the potential to serve as an electron source that generates electron beams of high brightness. Different operation and design parameters of the SRF photoinjector impact the beam dynamics and, thus, the beam brightness. Therefore, an in-depth understanding of the beam dynamics processes in an SRF photoinjector and the dependency of the beam dynamics on the photoinjector set parameters is crucial. A high brightness beam operation requires a global optimization of the SRF photoinjector that allows to find suitable photoinjector settings and to figure out and extend the physical performance limits of the investigated injector design. The dissertation at hand offers a detailed analysis of the beam dynamics in an SRF photoinjector regarding internal space charge effects. Furthermore, the impact of the photoinjector elements on the electron beam is discussed. The lessons learned from this theoretical view are implemented in the development of an optimization tool to achieve a high brightness performance. A universal multi-objective optimization program based on a generic algorithm was developed to extract stable, optimum gun parameter from Pareto-optimum solutions. This universal tool is able to optimize and find the physical performance limit of any (S)RF photoinjector independent from the individual application of the electron source (energy recovery linac, free electron laser, ultra-fast electron diffraction). This thesis thereby verifies and complements existing theoretical considerations regarding photoinjector-beam interactions. The global optimization strategy can be introduced to variable optimization objectives as well as it can be extended to an optimization of further parts of the accelerator facility.

Стилі APA, Harvard, Vancouver, ISO та ін.

39

Möller, K., A. Arnold, P. Lu, P. Murcek, J. Teichert, H. Vennekate, and R. Xiang. "Emittance minimization at the ELBE superconducting electron gun." Forschungszentrum Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-146950.

Повний текст джерела

Анотація:

The transverse emittance is one of the most important quantities which characterize the quality of an electron source. For high quality experiments low beam emittance is required. By means of theoretical considerations and simulation calculations we have studied how the emittance of the Rossendorf superconducting radio-frequency photoelectron source (SRF gun) can be minimized. It turned out that neither a solenoid magnet nor the effect of space charge forces is needed to create a pronounced emittance minimum. The minimum appears by just adjusting the starting phase of the electron bunch with respect to the RF phase of the gun in a suitable way. Investigation of various correlations between the properties of the beam particles led to an explanation on how the minimum comes about. It is shown that the basic mechanism of minimization is the fact that the longitudinal properties of the particles (energy) are strongly influenced by the starting phase. Due to the coupling of the longitudinal and transverse degrees of freedom by the relativistic equation of motion the transverse degrees of freedom and thereby the emittance can be strongly influenced by the starting phase as well. The results obtained in this study will be applied to minimize the emittance in the commissioning phase of the SRF gun.

Стилі APA, Harvard, Vancouver, ISO та ін.

40

Senanayake, Pubudu Seewali. "Two-Colour Excitation of Impurity Trapped Excitons in Wide Bandgap Insulators." Thesis, University of Canterbury. Department of Physics and Astronomy, 2013. http://hdl.handle.net/10092/8710.

Повний текст джерела

Анотація:

Impurity trapped excitons (ITEs) occurring in divalent ytterbium doped calcium and strontium fluoride crystals have been investigated by exploiting the radically different radiative decay rates of the lowest exciton state and higher excited states, utilizing a novel two-colour transient photoluminescence enhancement experiment. The ITE energy levels have been directly measured with the observation of sharp transitions occurring from the changes of states of the localized hole and broad bands associated with changes of state of the delocalized electrons. The dynamic behaviour under excitation by time delayed ultra-violet (UV) and infrared (IR) pulses has been observed allowing for the identification of excitation and decay pathways between the ITE states. The position and transition intensities of the sharp lines within the IR excitation spectrum have been successfully matched using a semi-empirical effective Hamiltonian crystal field model. In CaCaF₂:Yb²⁺ the lines occurring at 249 and 1145 cm⁻¹ were matched with the crystal field parameter B4 = 800 cm⁻¹ and the exchange parameter G3(fs) = 5900 cm⁻¹. In SrCaF₂:Yb²⁺ these lines were observed at 178 and 1284 cm⁻¹ and matched with B4 = 600 cm⁻¹ and G3(fs) = 7278 cm⁻¹. Local heating and direct absorption by intra-excitonic transitions are found to be the causes of the broad band observed in the spectrum and have been deconvolved by studying the dynamic behaviour of the monitored emission at different IR excitation frequencies. Through this modeling, higher lying ITE states have been identified occurring at 785 cm⁻¹ in SrCaF₂:Yb²⁺ and in between 740 - 820 cm⁻¹ in CaCaF₂:Yb²⁺. The dynamic model developed successfully simulates the temporal behaviour of the emission under IR excitation under a variety of parameters including IR fluence, excitation frequency, sample temperature and UV - IR pulse delay. Examination of the SrCaF₂:Yb²⁺ dynamic behaviour over a time scale of 100 ms shows UV driven trap population at a rate of approximately 3% per pulse, which are liberated and recycled to the Yb²⁺ ground state by the IR pulse. The two-colour technique is applied to MgCaF₂:Yb²⁺, a candidate for possible ITE emission. Temperature dependent emission spectra obtained under UV excitation indicates the possibility of an ITE state, independently populated from the 5d level of the Yb²⁺. Typical 5d emission is also observed from this system. Under IR excitation, liberation of shallow traps and possible local heating is observed. No ITE emission is conclusively found with IR probing.

Стилі APA, Harvard, Vancouver, ISO та ін.

41

Weißbach, Julia [Verfasser]. "The role of WH2-containing proteins in regulating Actin-MRTF-SRF-mediated transcription / Julia Weißbach." Halle, 2017. http://d-nb.info/1150704489/34.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

42

Yu, Wai Man C. Y. O. L. "Targeting the Myocardin-related transcription factor/serum response factor (MRTF/SRF) pathway in conjunctival fibrosis." Thesis, University College London (University of London), 2017. http://discovery.ucl.ac.uk/1559574/.

Повний текст джерела

Анотація:

Glaucoma is the leading cause of irreversible blindness and its prevalence is estimated to reach 79.6 million people by 2020. Wound contraction and scarring are the principal causes of blockage of aqueous flow at the drainage site in glaucoma filtration surgery. The cytotoxic antimetabolites, mitomycin-C and 5-fluorouracil, are widely used but have potentially blinding complications. There is thus a large unmet need for alternative agents with more targeted physiological effects and less cytotoxicity. The myocardin-related transcription factor/serum response factor (MRTF/SRF) pathway is a master regulator of cytoskeletal gene expression and thus represents a promising therapeutic target to prevent fibrosis. The MRTF/SRF pathway in human conjunctival fibroblasts responds to actin dynamics but as human conjunctival fibroblasts have constitutively high MRTF-A and MRTF-B nuclear concentrations, they show a relatively small response to serum stimulation and actin binding drugs, such as latrunculin B and cytochalasin D. The localisation of MRTF-A and MRTF-B is also conserved across species in mouse and rabbit conjunctival fibroblasts. As the MRTF/SRF pathway is a master regulator of many key cytoskeletal genes in fibrosis, we next studied the effects of downregulating the MRTF/SRF pathway in human conjunctival fibroblasts using three-dimensional in vitro collagen contraction assays. MRTF-A and MRTF-B siRNA silencing significantly decreased collagen matrix contraction, the cell protrusive activity, matrix degradation, and the expression of key matrix metalloproteinase genes. Liposome-peptide-siRNA nanoparticles also represent an efficient and safe siRNA delivery system for MRTF silencing in conjunctival fibrosis. We further compared the contractility of fibrotic and non-fibrotic human conjunctival fibroblasts from glaucoma patients with and without previous glaucoma surgery, respectively. Fibrotic human conjunctival fibroblasts were significantly more contractile than non-fibrotic human conjunctival fibroblasts, and the increased contractility was linked to the upregulation of alpha smooth muscle actin, a marker of myofibroblast differentiation. We finally validated in vivo the effects of inhibiting the MRTF/SRF pathway in conjunctival fibrosis using a rabbit model of experimental glaucoma filtration surgery. We have identified a new MRTF/SRF pathway inhibitor CCG-222740, which was more potent in the fibroblast-mediated collagen contraction assay, less cytotoxic, and a more potent inhibitor of alpha smooth muscle actin expression than inhibitor CCG-203971. Local delivery of CCG-222740 and CCG-203971 in a rabbit model of conjunctival fibrosis significantly increased the long-term success of the surgery and decreased scar tissue formation histologically. Unlike mitomycin-C, neither CCG-222740 nor CCG- 203971 caused any epithelial toxicity or systemic side effects with very low drug levels measured in the aqueous, vitreous and serum. In conclusion, our in vitro and in vivo results support that inhibiting the MRTF/SRF pathway represents a potential new therapeutic target to prevent conjunctival fibrosis in glaucoma and other contractile scarring conditions in the eye.

Стилі APA, Harvard, Vancouver, ISO та ін.

43

SOULEZ, MARIELLE. "Role des boites carg et de la proteine srf au cours de la differenciation myogenique." Paris 7, 1996. http://www.theses.fr/1996PA077137.

Повний текст джерела

Анотація:

Les sequences carg, de consensus cc(a/t)#6gg, sont presentes dans les regions regulatrices de genes de specificite differente des genes repondant precocement aux facteurs de croissance et des genes musculaires et sont impliquees dans l'activite specifique de ceux-ci. Le double jeu des sequences carg constitue un modele d'etude des mecanismes de regulation transcriptionnelle. L'activation transcriptionnelle en reponse a la stimulation par le serum a ete tres bien etudiee dans le cas du proto-oncogene c-fos. Celle-ci depend d'une sequence active en cis appelee sre (serum response element) qui comprend en son centre une boite carg et d'un facteur actif en trans, la proteine srf (serum response factor) qui se fixe au sre sous forme de dimere. Nous avons etudie ex vivo le mode d'action des boites carg dans l'activation transcriptionnelle specifique du muscle et l'implication de la proteine srf au cours de la differenciation myogenique. Les resultats marquants de ce travail sont les suivants: des multimeres de la boite hca1 (boite carg proximale du gene d'-actine cardiaque) sont capables de conferer a un promoteur minimum limite a une boite tata une forte activation transcriptionnelle specifiquement dans les cellules musculaires. Aucune combinaison specifique de sequences d'adn fixant d'autres facteurs transcriptionnels n'est donc requise pour cette activation. Les boites carg exercent leur role activateur tres tot lors de la differenciation myogenique. Cet evenement fut etudie lors de la conversion des cellules fibroblastiques c3h10t1/2 en cellules myogeniques apres traitement par un agent demethylant, la 5-azacytidine. La fixation de la proteine srf sur les boites carg de genes musculaires est impliquee dans leur activation transcriptionnelle. La proteine srf est necessaire a la proliferation des myoblastes, a la differenciation des myoblastes en myotubes plurinuclees et a l'expression de la proteine myod

Стилі APA, Harvard, Vancouver, ISO та ін.

44

Huet, Alexis. "Interaction du facteur de transcription SRF avec l' ADN : études spectroscopiques des mécanismes de reconnaissance." Paris 7, 2005. http://www.theses.fr/2005PA077099.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

45

Keckert, Sebastian [Verfasser], and Jens [Gutachter] Knobloch. "Characterization of Nb3Sn and multilayer thin films for SRF applications / Sebastian Keckert ; Gutachter: Jens Knobloch." Siegen : Universitätsbibliothek der Universität Siegen, 2019. http://d-nb.info/1211819957/34.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

46

Vennekate, Hannes [Verfasser], Jochen [Akademischer Betreuer] Teichert, Ulrich [Gutachter] Schramm, and Arno [Gutachter] Straessner. "Emittance Compensation for SRF Photoinjectors / Hannes Vennekate ; Gutachter: Ulrich Schramm, Arno Straessner ; Betreuer: Jochen Teichert." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://d-nb.info/1140735241/34.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

47

Beringer, Douglas. "Thin Film Approaches to The Srf Cavity Problem: Fabrication and Characterization of Superconducting Thin Films." W&M ScholarWorks, 2016. https://scholarworks.wm.edu/etd/1499449840.

Повний текст джерела

Анотація:

Superconducting Radio Frequency (SRF) cavities are responsible for the acceleration of charged particles to relativistic velocities in most modern linear accelerators, such as those employed at high-energy research facilities like Thomas Jefferson National Laboratory’s CEBAF and the LHC at CERN. Recognizing SRF as primarily a surface phenomenon enables the possibility of applying thin films to the interior surface of SRF cavities, opening a formidable tool chest of opportunities by combining and designing materials that offer greater benefit. Thus, while improvements in radio frequency cavity design and refinements in cavity processing techniques have improved accelerator performance and efficiency – 1.5 GHz bulk niobium SRF cavities have achieved accelerating gradients in excess of 35 MV/m – there exist fundamental material bounds in bulk superconductors limiting the maximally sustained accelerating field gradient (approximately 45 MV/m for Niobium) where inevitable thermodynamic breakdown occurs. With state of the art niobium based cavity design fast approaching these theoretical limits, novel material innovations must be sought in order to realize next generation SRF cavities. One proposed method to improve SRF performance is to utilize thin film superconducting-insulating-superconducting (SIS) multilayer structures to effectively magnetically screen a bulk superconducting layer such that it can operate at higher field gradients before suffering critically detrimental SRF losses. This dissertation focuses on the production and characterization of thin film superconductors for such SIS layers for radio-frequency applications.

Стилі APA, Harvard, Vancouver, ISO та ін.

48

Collard, Laura. "Rôle du facteur de transcription Srf au cours de l’atrophie du muscle squelettique et dans les cellules satellites." Thesis, Paris 5, 2013. http://www.theses.fr/2013PA05T068/document.

Повний текст джерела

Анотація:

Le muscle squelettique adulte est un tissu possédant la capacité fondamentale d’adapter sa taille à la demande fonctionnelle : il peut s’atrophier ou s’hypertrophier en réponse à une variation de la charge mécanique qui lui est appliquée. A l’heure actuelle, les facteurs impliqués dans la plasticité musculaire demeurent méconnus. D’une part, grâce à différents modèles d’atrophie musculaire, nous démontrons que le facteur de transcription Srf joue le rôle de médiateur de la mécano-transduction par la voie actine/Mrtfs/Srf. L’arrêt de l’activité mécanique provoque une accumulation nucléaire d’actine monomérique, une délocalisation de Mrtf-A, coactivateur de Srf, et une diminution de l’activité de Srf, se traduisant notamment par une baisse de la transcription Srf-dépendante. Les gènes cibles de Srf comptant un grand nombre de protéines sarcomériques, telles que l’α-actine squelettique, la réduction de leur expression pourrait participer à l’atrophie musculaire. De plus, nos travaux suggèrent que la diminution de l’activité de Srf pourrait influencer l’organisation du réseau mitochondrial et le flux autophagique par des mécanismes qui restent à élucider. D’autre part, en tirant parti d’un modèle d’invalidation conditionnelle et inductible de Srf dans les cellules satellites, nous montrons que le phénomène d’hypertrophie compensatoire requiert l’expression de Srf par les cellules satellites. L’absence de Srf n’altère ni la prolifération ni l’entrée en différenciation des myoblastes, néanmoins elle provoque un défaut de fusion des myoblastes aux fibres au cours de l’hypertrophie induite par surcharge. Ainsi, nos travaux démontrent que Srf est un acteur majeur de la plasticité musculaire, à la fois en tant que médiateur de la mécano-transduction par la voie actine/Mrtfs/Srf et par son implication dans la fusion des cellules satellites aux fibres musculaires, nécessaire à l’hypertrophie compensatoire
Adult skeletal muscle is able to adapt its size to functional demand. It can undergo atrophy or hypertrophy according to mechanical load. To date, the molecules that mediate muscle plasticity remain unclear.Using different models inducing muscle atrophy, we show that the transcription factor Srf is a mediator of mechanotransduction through the actin/Mrtfs/Srf pathway. Mechanical load abolition leads to G-actin nuclear accumulation, delocalization of Mrtf-A, an Srf coactivator, and Srf activity downregulation. This results in a decrease in Srf-dependent transcription. Many Srf target genes encode sarcomeric proteins such as α-skeletal actin, thus a downregulation of Srf-dependent transcription could participate to muscle atrophy. In addition, our results suggest that Srf activity decrease could affect mitochondrial network organization and autophagic flux in a way that remains to be determined. Besides, using a satellite cell-specific conditional and inducible Srf knockout, we show that overload hypertrophy requires Srf expression by satellite cells. Myoblasts proliferation and early differentiation are not altered by Srf loss. However, mutant myoblasts are unable to fuse with myofibers during overload hypertrophy. Altogether, our results demonstrate that Srf is an important player in skeletal muscle plasticity: it is a mediator of mechanotransduction via the actin/Mrtfs/Srf pathway and its expression by satellite cells is required for myoblasts to fuse with myofibers during overload hypertrophy

Стилі APA, Harvard, Vancouver, ISO та ін.

49

Swinarski, Marie. "PCP-driven cardiac remodeling couples changes in actomyosin tension with myocyte differentiation." Doctoral thesis, Humboldt-Universität zu Berlin, Lebenswissenschaftliche Fakultät, 2017. http://dx.doi.org/10.18452/17775.

Повний текст джерела

Анотація:

Im Zuge der frühen embryonalen Herzentwicklung entstehen ausgehend von einem einfachen Herzschlauch zwei deutlich voneinander getrennte Herzkammern. Die Kardiomyozyten des Atriums und Ventrikels weisen spezifische Eigenschaften auf, die sich morphologisch wie auch funktionell auf das Herz auswirken. Veränderungen in der Gewebsarchitektur werden hauptsächlich durch Zellinterkalation und kollektive Zellmigration erreicht. Viele Studien zeigen, dass der Wnt/PCP-Signalweg eine essentielle Rolle in der Regulation dieser Bewegungen einnimmt. Die Daten dieser Studie belegen, dass die nicht-kanonischen Liganden Wnt11 und Wnt5b sowie die Kernkomponenten des PCP Signalweges Fzd7, Vangl2, Dvl2 und Pk1 an der Steuerung der Reorganisation der Kardiomyozyten während der Kammerbildung beteiligt sind, was Einfluss auf die Architektur des frühen Myokardiums nimmt. Effektoren des PCP Signalweges umfassen das Zytoskelett sowie Adhäsions- und Migrationsprozesse. In dieser Studie wird gezeigt, dass die Komponenten dieses Signalweges im Myokardium hauptsächlich Prozesse der Actomyosin Modulation regulieren und damit unter anderem die Morphologie der Kardiomyozyten beeinflussen. Zusätzlich ist die frühe Kardiogenese durch eine Relokalisierung der phosphorylierten Form der Myosin Regulatory Light Chain (MRLC) vom Kern zur Membran gekennzeichnet. Hier wird gezeigt, dass die Phosphorylierung von MRLC sowie die Relokalisation von den Kernkomponenten des PCP Signalweges kontrolliert werden sowie dass es im Verlauf der frühen Herzentwicklung u.a. durch die Relokalisierung von pMRLC zu Änderungen in der Gewebespannung kommt, welche sich auf die nukleäre Spannung auswirken und damit Veränderungen in der Genregulation hervorrufen. Diese Veränderungen werden hauptsächlich durch Effekte auf die Lokalisation und Aktivität des Serum Response Factors (SRF) vermittelt, welche in diesem Kontext durch die PCP Kernkomponente Pk1 reguliert sind.
Formation of a complex multiple-chambered heart from the simple linear heart tube does not only require orchestrated morphogenesis of the myocardium, but also cardiac muscle differentiation and changes in intercellular electrical coupling. To date, the processes that lead to the formation of a functional syncytium are incompletely understood. One of the major pathways controlling multiple aspects of organogenesis and tissue morphogenesis is the planar cell polarity (PCP) pathway. Changes in tissue architecture are controlled by cell intercalation and collective cell migration. It is widely accepted that Wnt/PCP signaling plays a crucial role in guiding these cellular processes. This study provides evidence that morphogenesis of the heart is controlled by the non-canonical ligands Wnt11 and Wnt5b and the PCP core components Fzd7, Vangl2, Dvl2, and Pk1 through regulation of cell rearrangements during embryonic cardiac remodeling. Downstream effectors of the PCP pathway target adhesion processes, cytoskeleton, and migration. Here, it is revealed that PCP signaling in the heart affects cardiomyocyte morphology and actomyosin organization. Specifically, changes in the subcellular localization of the phosphorylated non-muscle myosin II regulatory light chain (pMRLC) at LHT stage are targeted by the PCP pathway core components. Furthermore, actomyosin relocalization concurs with changes in nuclear tension and SRF signal transduction within the myocardium. This study unravels a novel function of the PCP core component Pk1 in regulation of SRF translocation and target gene expression that is critical to cardiac maturation. Taken together, this study provides evidence that the PCP pathway is a major regulator of cardiac remodeling and organ maturation by modulating mechanosensitive SRF signal transduction involved in muscle differentiation.

Стилі APA, Harvard, Vancouver, ISO та ін.

50

Gilbert, Kristen Nicole. "Psychometrically Equivalent Bisyllabic Words for Speech Reception Threshold Testing in Mongolian." Diss., CLICK HERE for online access, 2009. http://contentdm.lib.byu.edu/ETD/image/etd2877.pdf.

Повний текст джерела

Стилі APA, Harvard, Vancouver, ISO та ін.

Дисертації з теми "SRFT"

Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями