2,541 research outputs found
Numerical investigation of transitional supersonic axisymmetric wakes
No full textTransitional supersonic axisymmetric wakes are investigated by
conducting various numerical experiments. The main objective is to identify hydrodynamic instability mechanisms in the flow at M=2.46 for several Reynolds numbers, and relating these to coherent structures that are found from various visualization techniques. The premise for this approach is the assumption that flow instabilities lead to the formation of coherent structures. Three high-order accurate compressible codes were developed in cylindrical coordinates for this research: a spatial Navier-Stokes (N-S) code to conduct Direct Numerical Simulations (DNS), a linearized N-S code for linear stability investigations using axisymmetric basic states, and a temporal N-S code for performing local stability analyses. The ability of numerical simulations to deliberately exclude physical effects is exploited. This includes intentionally eliminating certain azimuthal/helical modes by employing DNS for various circumferential domain-sizes. With this approach, the impact of structures associated with certain modes on the global wake-behavior can be scrutinized. Complementary spatial and temporal calculations are carried out to investigate whether instabilities are of local or global nature. Circumstantial evidence is presented that absolutely unstable global modes within the recirculation region co-exist with convectively unstable shear-layer modes. The flow is found to be absolutely unstable with respect to modes k>0 for ReD>5,000 and with respect to the axisymmetric mode k=0 for ReD>100,000. It is concluded that azimuthal modes k=2 and k=4 are the dominant modes in the trailing wake, producing a four-lobe wake pattern. Two possible mechanisms responsible for the generation of longitudinal structures within the recirculation region are suggested
Damage detection using frequency domain ARX models and extreme value statistics
No full textThe author acknowledges Tim Johnson and Seth Gregg
and the Los Alamos Dynamic Summer School for providing
the test structure as well as helping with the set-up,
instrumentation and acquisition of data from the test
structure. Funding for the summer school was provided by
the Engineering Sciences and Application Division at Los
Alamos National Laboratory and the Department of
Energy’s Education Program Office
Application of frequency domain ARX models and extreme value statistics to impedance-based damage detection
No full textFunding for this project was provided by the Department of Energy through the internal funding program at Los Alamos National Laboratory known as Laboratory Directed Research and Development. The author acknowledges Tim Johnson and Seth Gregg and the Los Alamos Dynamic Summer School for providing the test structure as well as helping with the set-up, instrumentation and acquisition of data from the test structure. Funding for the summer school was provided by the Engineering Sciences and Application Division at Los Alamos National Laboratory and the Department of Energy’s Education Program Office
Hadron Production in Proton-Proton Collisions
No full textOnTEAM metadata: GDSID: DOC-2008-Sep-154; Attribute ID: LIBRARY-thesis_ma-2008-001; Title: [GSI Master 2008-01] Hadron Production in Proton-Proton Collisions [30.7.2008]; Author(s): Fasel, Markus; Corporate author(s): ; Publication date: 20080929; Creator: manton; Creation date: 29.09.2008 15:09:47; Change date: 30.09.2010 16:05:30; Access: Welt; Attribute type: Text.Thesis.MA; Directory path: ['GSI Publications', 'GSI as Publisher']; Attribute path: ['Infrastructure', 'Library and Documentation', 'thesis_ma', 'Added in 2008']; File name(s): ['DOC-2008-Sep-154-1.pdf']; File title(s): ['']; File access: ['GSI-intern'
Bowl Inversion of Surface-Adsorbed Sumanene
No full textBowl-shaped π-conjugated compounds offer the possibility to study curvature-dependent host–guest interactions and chemical reactivity in ideal model systems. For surface-adsorbed π bowls, however, only conformations with the bowl opening pointing away from the surface have been observed so far. Here we show for sumanene on Ag(111) that both bowl-up and bowl-down conformations can be stabilized. Analysis of the molecular layer as a function of coverage reveals an unprecedented structural phase transition involving a bowl inversion of one-third of the molecules. On the basis of scanning tunneling microscopy (STM) and complementary atomistic simulations, we develop a model that describes the observed phase transition in terms of a subtle interplay between inversion-dependent adsorption energies and intermolecular interactions. In addition, we explore the coexisting bowl-up and -down conformations with respect to host–guest binding of methane. STM reveals a clear energetic preference for methane binding to the concave face of sumanene
Extrapolating an Euler class
No full textLet R be a noetherian ring of dimension d and let n be an integer so that n≤d≤2n-3. Let (a1,..., an+1) be a unimodular row so that the ideal J=(a1,..., an) has height n. Jean Fasel has associated to this row an element [(J, ωJ)] in the Euler class group En(R), with ωJ:(R/J)n→J/J2 given by (ā1,...,ān-1,ānān+1). If R contains an infinite field F then we show that the rule of Fasel defines a homomorphism from WMSn+1(R)=Umn+1(R)/En+1(R) to En(R). The main problem is to get a well defined map on all of Umn+1(R). Similar results have been obtained by Das and Zinna [5], with a different proof. Our proof uses that every Zariski open subset of SLn+1(F) is path connected for walks made up of elementary matrices
- …
