11 |
Effects of nickel and manganese on the embrittlement of low-copper pressure vessel steelsZelenty, Jennifer Evelyn January 2016 (has links)
Solute clustering is known to play a significant role in the embrittlement of reactor pressure vessel (RPV) steels. When precipitates form they impede the movement of dislocations, causing an increase in hardness and a shift in the ductile-brittle transition temperature. Over time this can cause the steel to become brittle and more susceptible to fracture. Thus, understanding precipitate formation is of great importance to the nuclear industry. The first part of this thesis aims to isolate and better understand the thermal aging component of embrittlement in low copper, model RPV steels. Currently, relatively little is known about the effects of Ni and Mn in a low copper environment. Therefore, it is of interest to determine if Ni and Mn form precipitates under these conditions. To this end, hardness measurements and atom probe tomography were utilized to link the mechanical properties to the microstructure. After 11,690 hours of thermal aging a statistically significant decrease in hardening was observed. Consistent with hardness measurements, no precipitates were present within the matrix of the thermally aged RPV steels. The local chemistry method was then applied to investigate the very early stages of solute clustering. Association was found to be statistically significant in both the thermally aged and as-received model RPV steels. Therefore, no apparent trends regarding the changes in solute association between the as-received and thermally aged RPV steels were identified. Small, non-random clusters were observed at heterogeneous nucleation sites, such as carbide/matrix interfaces and grain boundaries, within the thermally aged material. The clusters found at the carbide/matrix interfaces were all rich in Mn and approximately 90-150 atoms in size. The clusters located along the observed low-angle grain boundary, however, were significantly larger (on the order of hundreds of atoms) and rich in Ni. Lastly, copper-rich precipitates (CRPs) and Mn- and Ni-rich precipitates (MNPs) were observed within the cementite phase of a high copper and low copper RPV steel, respectively, following long term thermal aging. APT was used to characterize these precipitates and obtain more detailed chemical information. The presence of such precipitates indicates that a range of precipitation can take place within the cementite phase of thermally aged RPV steels. The second part of this thesis aims to investigate the effects of ion irradiation on the microstructure of low copper RPV steels via APT. These steels were ion irradiated with 6.4 MeV Fe<sup>3+</sup> ions with a dose rate of 1.5 x 10<sup>-4</sup> dpa/s at 290°C. MNPs were observed in all five of the RPV steels analyzed. These precipitates were found to have nucleated within the matrix as well as at dislocations and grain boundaries. Using the maximum separation method these MNPs were extracted and characterized. Precipitate composition, size, volume fraction, and number density were determined for each of the five samples. Lastly, several grain boundaries were characterized. Several emerging trends were observed within the samples: Ni content within the precipitates did not vary significantly once a threshold between 30-50% was reached; bulk Mn content appeared to dictate Si and Mn content within the precipitates; and samples low in bulk Ni content were characterized by a higher number density of smaller precipitates. Additionally, by regressing precipitate volume fraction against the interaction of Ni and Mn, a linear relationship was found to be statistically significant.
|
12 |
Visual contributions to spatial perception during a remote navigation taskEshelman-Haynes, Candace Lee 28 July 2009 (has links)
No description available.
|
13 |
Search for displaced leptons in the e-mu final state at the CMS experimentLiu, Bingxuan January 2016 (has links)
No description available.
|
14 |
STED nanoscopy of the living brain / STED-Mikroskopie des intakten GehirnsBerning, Sebastian 13 December 2011 (has links)
No description available.
|
15 |
Einzelmolekülstudien auf Nanoskalen: STED Fluoreszenzfluktuationsspektroskopie / Single molecule studies at the nanoscale: STED Fluorescence Fluctuation Spectroscopy in subdiffraction focal volumesRingemann, Christian 20 November 2008 (has links)
No description available.
|
16 |
3D STED Microscopy with Pulsed and Continuous Wave Lasers / 3D STED Mikroskopie mit gepulsten und DauerstrichlasernHarke, Benjamin 02 April 2008 (has links)
No description available.
|
17 |
A Dedicated Endstation for Waveguide-based X-Ray Imaging / Ein dediziertes Instrument für Röntgenbildgebung mit WellenleiternKalbfleisch, Sebastian 17 April 2012 (has links)
Röntgenmikroskopie ist in den vergangenen
Jahren zu einer leistungsfähigen und vielseitigen bildgebenden
Methode in vielen Bereiche der Wissenschaft geworden, mit der opake
Medien bei hoher räumlicher Auflösung untersucht werden können. Es
bleibt jedoch eine Herausforderung, geeignete Röntgenlinsen
herzustellen, wie z.B. Frsenlesche Zonenplatten oder refraktive
Linsen. In einem alternativen Ansatz linsenloser Abbildung wird die
Probe mit kohärenter Röntgenstrahlung beleuchtet. Die
Probeninformation wird dann aus dem aufgenommenen Streubild durch
numerische, iterative Algorithmen rekonstruiert. In dieser Arbeit
wird zunächst die Grundlage von linsenloser holographischer
Abbildung mit Röntgenwellenleitern erläutert und zu einem Konzept
der Röntgeninterferometrie mit Wellenleitern erweitert. Die
spezifische Instrumentierung, die erforderlich war für
Demonstrationsexperimente mit Röntgenwellenleitern zur
holographischen Abbildung, wird erklärt und die erzielten
Ergebnisse präsentiert. Basierend auf diesen Ergebnissen der
Demonstrationsexperimente wurde ein Instrument zur holographischen
Abbildung mit Röntgenwellenleitern entwickelt und aufgebaut. Die
Spezifikationen und Eigenschaften des Kirckpatrick-Beaz
Spiegelsystems und anderen mechanischen und optischen Komponenten
werden beschrieben und experimentell charakterisiert, zusammen mit
dem Steuerungssystem und verschiedenen verfügbaren Detektoren.
Erste Ergebnisse belegen die hohe Abbildungsqualität des
vorgestellten Instruments.
|
18 |
Možnosti vnějšího dochlazování tlakové nádoby při havárii s roztavením aktivní zóny / Possibilities of the external cooling of a pressure vessel in case of the accident with active zone meltingHanuš, Jan January 2014 (has links)
The accident at the Fukushima Daiichi nuclear power plant has shown us that there may be situations where the applied technology will not be able to successfully cool the reactor core. These situations may occur when more elements such as supply of energy to power the pumps and diesel generators are destroyed for example by tsunami or earthquake, or other not expected natural disasters. The inability of the residual heat removal leads to the melting of core, relocation to the bottom of reactor pressure vessel (RPV) and failure of RPV. Result of this accident may be containment failure and leakage of fission products into the environment. One way to prevent this scenario may be a passive system called IVR (In-Vessel Retention) by using external cooling of RPV that retains melted core in. This system counts with flooding of RPV´s shaft by water. After natural circulation of water provides the heat transfers from the wall of RPV. The applicability of IVR for VVER 1000 reactors is still in the course of research. However it´s already clear that the submersion of RPV shaft by water will not sufficient. Other elements as suitable insulation and RPV coating which provides a more intensive heat transfer from the walls of RPV will be needed.
|
19 |
Development and Implementation of a Flight Test Program for a Geometrically Scaled Joined Wing SensorCraft Remotely Piloted VehicleAarons, Tyler David 20 January 2012 (has links)
The development and implementation of a flight test program for an unmanned aircraft is a multidisciplinary challenge. This thesis presents the development and implementation of a rigorous test program for the flight test of a Geometrically Scaled Joined Wing SensorCraft Remotely Piloted Vehicle from concept through successful flight test. The design methodology utilized in the development of the test program is presented, along with the extensive formal review process required for the approval of the test plan by the Air Force Research Laboratory. The design, development and calibration of a custom instrumentation package is also presented along with the setup, procedure and results from all testing. Results are presented for a wind tunnel test for air data boom calibration, propulsion system static thrust testing, a bifilar pendulum test for experimental calculation of mass moments of inertia, a static structural loading test for structural design validation, a full taxi test and a successful first flight. / Master of Science
|
20 |
Dielektrische Wellenleitergitter in Resonanz / Theorie, Charakterisierung und Anwendung / All-dielectric Resonant Waveguide Gratings / Theory, Characterization and ApplicationSelle, André 19 November 2008 (has links)
No description available.
|
Page generated in 0.0138 seconds