222 research outputs found
Wave packet dynamics in triplet states of Na2 attached to helium nanodroplets
The dynamics of vibrational wave packets excited in Na2 dimers in the triplet
ground and excited states is investigated by means of helium nanodroplet
isolation (HENDI) combined with femtosecond pump-probe spectroscopy. Different
pathways in the employed resonant multi-photon ionization scheme are
identified. Within the precision of the method, the wave packet dynamics
appears to be unperturbed by the helium droplet environment
Atom-molecule collisions in an optically trapped gas
Cold inelastic collisions between confined cesium (Cs) atoms and Cs
molecules are investigated inside a CO laser dipole trap. Inelastic
atom-molecule collisions can be observed and measured with a rate coefficient
of cm s, mainly independent of the
molecular ro-vibrational state populated. Lifetimes of purely atomic and
molecular samples are essentially limited by rest gas collisions. The pure
molecular trap lifetime ranges 0,3-1 s, four times smaller than the atomic one,
as is also observed in a pure magnetic trap. We give an estimation of the
inelastic molecule-molecule collision rate to be cm
s
Development of a Coupling Model for Fluid-Structure Interaction using the Mesh-free Finite Element Method and the Lattice Boltzmann Method
In the presented thesis work, the meshfree method with distance fields was coupled with the lattice Boltzmann method to obtain solutions of fluid-structure interaction problems. The thesis work involved development and implementation of numerical algorithms, data structure, and software. Numerical and computational properties of the coupling algorithm combining the meshfree method with distance fields and the lattice Boltzmann method were investigated. Convergence and accuracy of the methodology was validated by analytical solutions.
The research was focused on fluid-structure interaction solutions in complex, mesh-resistant domains as both the lattice Boltzmann method and the meshfree method with distance fields are particularly adept in these situations. Furthermore, the fluid solution provided by the lattice Boltzmann method is massively scalable, allowing extensive use of cutting edge parallel computing resources to accelerate this phase of the solution process. The meshfree method with distance fields allows for exact satisfaction of boundary conditions making it possible to exactly capture the effects of the fluid field on the solid structure
The excitation function for Li+HF-->LiF+H at collision energies below 80 meV
We have measured the dependence of the relative integral cross section of the
reaction Li+HF-->LiF+H on the collision energy using crossed molecular beams.
By varying the intersection angle of the beams from 37{\deg} to 90{\deg} we
covered the energy range 25 meV < E_tr < 131 meV. We observe a monotonous rise
of the cross section with decreasing energy over the entire energy range
indicating that a possible translational energy threshold to the reaction is
significantly smaller than 25 meV. The steep rise is quantitatively recovered
by a Langevin-type excitation function based on a vanishing threshold and a
mean interaction potential energy ~R^-2.5 where R is the distance between the
reactants. To date all threshold energies deduced from ab-initio potentials and
zero-point vibrational energies are at variance with our results, however, our
findings support recent quantum scattering calculations that predict
significant product formation at collision energies far below these theoretical
thresholds.Comment: 8 pages, 7 figure
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