34 research outputs found
Area-preserving dynamics of a long slender finger by curvature: a test case for the globally conserved phase ordering
A long and slender finger can serve as a simple ``test bed'' for different
phase ordering models. In this work, the globally-conserved,
interface-controlled dynamics of a long finger is investigated, analytically
and numerically, in two dimensions. An important limit is considered when the
finger dynamics are reducible to the area-preserving motion by curvature. A
free boundary problem for the finger shape is formulated. An asymptotic
perturbation theory is developed that uses the finger aspect ratio as a small
parameter. The leading-order approximation is a modification of ``the Mullins
finger" (a well-known analytic solution) which width is allowed to slowly vary
with time. This time dependence is described, in the leading order, by an
exponential law with the characteristic time proportional to the (constant)
finger area. The subleading terms of the asymptotic theory are also calculated.
Finally, the finger dynamics is investigated numerically, employing the
Ginzburg-Landau equation with a global conservation law. The theory is in a
very good agreement with the numerical solution.Comment: 8 pages, 4 figures, Latex; corrected typo
Dynamics of an Unbounded Interface Between Ordered Phases
We investigate the evolution of a single unbounded interface between ordered
phases in two-dimensional Ising ferromagnets that are endowed with
single-spin-flip zero-temperature Glauber dynamics. We examine specifically the
cases where the interface initially has either one or two corners. In both
examples, the interface evolves to a limiting self-similar form. We apply the
continuum time-dependent Ginzburg-Landau equation and a microscopic approach to
calculate the interface shape. For the single corner system, we also discuss a
correspondence between the interface and the Young tableau that represents the
partition of the integers.Comment: 9 pages, 11 figures, 2-column revtex4 format. V2: references added
and discussion section expanded slightly. Final version for PRE. V3: A few
small additional editorial change
Gamma Prime Precipitate Evolution During Aging of a Model Nickel-Based Superalloy
The microstructural stability of nickel-based superalloys is critical for maintaining alloy performance during service in gas turbine engines. In this study, the precipitate evolution in a model polycrystalline Ni-based superalloy during aging to 1000 hours has been studied via transmission electron microscopy, atom probe tomography and neutron diffraction. Variations in phase composition and precipitate morphology, size and volume fraction were observed during aging, whilst the constrained lattice misfit remained constant at approximately zero. The experimental composition of the γ matrix phase was consistent with thermodynamic equilibrium predictions, whilst significant differences were identified between the experimental and predicted results from the γʹ phase. These results have implications for the evolution of mechanical properties in service and their prediction using modeling methods.The authors wish to acknowledge Mrs. S. Rhodes, Dr. H.T. Pang, Dr. D.M. Collins, and Dr. O.M.D.M. Messé for their assistance with the experiments performed. Funding was provided by the EPSRC/Rolls-Royce Strategic Partnership under EP/M005607/1 and EP/H022309/1. The Oxford Atom Probe facility was funded by the EPSRC under EP/M022803/1. Neutron diffraction beam time was supported through the Canadian Neutron Beam Centre under Experiment number 1258
Localized 1H NMR spectroscopy of rat spinal cord in vivo
A movable, actively decoupled surface coil has been employed to obtain a localized H-1 NMR spectrum from the lumbosacral spinal cord of a live Lewis rat. A volume selective 'VOSY' normally spelled out as 'volume selective spectroscopy' spectroscopy pulse sequence that incorporates ''phase ramped'' selective RF pulses, has been used to minimize random phase jitter in the NMR signal as a result of the large frequency shifts required to locate the voxel in the center of the cord while using intense gradient pulses. Spectra from 13-mu l voxels in healthy rats and in rats inoculated with guinea pig spinal cord and complete Freund's adjuvant, resulting in experimental autoimmune encephalomyelitis, are shown