3,349 research outputs found
A technique for making clean holes in metallic piping and components
Testing was conducted to develop a technique of providing clean holes in process piping or in a metal surface accessible from one side only without disassembling the system. The method was performed on sample pieces of piping and worked successfully with no contaminants being found on the inside of the pipe. The materials tested were Inconel 600, 304 stainless steel, Hastelloy X, and ASTM-A53 black steel. The technique was developed such that it could be done in the field with hand-held power tools and a portable tungsten inert gas welding machine
Performance and evaluation of two liquid-metal pumps for sodium-potassium service
Performance tests on liquid metal pumps for sodium potassium loop
Coherent optical transfer of Feshbach molecules to a lower vibrational state
Using the technique of stimulated Raman adiabatic passage (STIRAP) we have
coherently transferred ultracold 87Rb2 Feshbach molecules into a more deeply
bound vibrational quantum level. Our measurements indicate a high transfer
efficiency of up to 87%. As the molecules are held in an optical lattice with
not more than a single molecule per lattice site, inelastic collisions between
the molecules are suppressed and we observe long molecular lifetimes of about 1
s. Using STIRAP we have created quantum superpositions of the two molecular
states and tested their coherence interferometrically. These results represent
an important step towards Bose-Einstein condensation (BEC) of molecules in the
vibrational ground state.Comment: 4 pages, 5 figure
Cruising through molecular bound state manifolds with radio frequency
The emerging field of ultracold molecules with their rich internal structure
is currently attracting a lot of interest. Various methods have been developed
to produce ultracold molecules in pre-set quantum states. For future
experiments it will be important to efficiently transfer these molecules from
their initial quantum state to other quantum states of interest. Optical Raman
schemes are excellent tools for transfer, but can be involved in terms of
equipment, laser stabilization and finding the right transitions. Here we
demonstrate a very general and simple way for transfer of molecules from one
quantum state to a neighboring quantum state with better than 99% efficiency.
The scheme is based on Zeeman tuning the molecular state to avoided level
crossings where radio-frequency transitions can then be carried out. By
repeating this process at different crossings, molecules can be successively
transported through a large manifold of quantum states. As an important
spin-off of our experiments, we demonstrate a high-precision spectroscopy
method for investigating level crossings.Comment: 5 pages, 5 figures, submitted for publicatio
Atomistic studies of transformation pathways and energetics in plutonium
One of the most challenging problems in understanding the structural phase
transformations in Pu is to determine the energetically favored, continuous
atomic pathways from one crystal symmetry to another. This problem involves
enumerating candidate pathways and studying their energetics to garner insight
into instabilities and energy barriers. The purpose of this work is to
investigate the energetics of two transformation pathways for the delta to
alpha' transformation in Pu that were recently proposed [Lookman et al., Phys.
Rev. Lett. 100:145504, 2008] on the basis of symmetry. These pathways require
the presence of either an intermediate hexagonal closed-packed (hcp) structure
or a simple hexagonal (sh) structure. A subgroup of the parent fcc and the
intermediate hexagonal structure, which has trigonal symmetry, facilitates the
transformation to the intermediate hcp or sh structure. Phonons then break the
translational symmetry from the intermediate hcp or sh structure to the final
monoclinic symmetry of the alpha' structure. We perform simulations using the
modified embedded atom method (MEAM) for Pu to investigate these candidate
pathways. Our main conclusion is that the path via hcp is energetically favored
and the volume change for both pathways essentially occurs in the second step
of the transformation, i.e. from the intermediate sh or hcp to the monoclinic
structure. Our work also highlights the deficiency of the current
state-of-the-art MEAM potential in capturing the anisotropy associated with the
lower symmetry monoclinic structure.Comment: 12 pages, 5 figures, accepted for publication in Philos. Ma
Repulsively bound atom pairs: Overview, Simulations and Links
We review the basic physics of repulsively bound atom pairs in an optical
lattice, which were recently observed in the laboratory, including the theory
and the experimental implementation. We also briefly discuss related many-body
numerical simulations, in which time-dependent Density Matrix Renormalisation
Group (DMRG) methods are used to model the many-body physics of a collection of
interacting pairs, and give a comparison of the single-particle quasimomentum
distribution measured in the experiment and results from these simulations. We
then give a short discussion of how these repulsively bound pairs relate to
bound states in some other physical systems.Comment: 7 pages, 3 figures, Proceedings of ICAP-2006 (Innsbruck
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