14,261 research outputs found
Functions with Prescribed Best Linear Approximations
A common problem in applied mathematics is to find a function in a Hilbert
space with prescribed best approximations from a finite number of closed vector
subspaces. In the present paper we study the question of the existence of
solutions to such problems. A finite family of subspaces is said to satisfy the
\emph{Inverse Best Approximation Property (IBAP)} if there exists a point that
admits any selection of points from these subspaces as best approximations. We
provide various characterizations of the IBAP in terms of the geometry of the
subspaces. Connections between the IBAP and the linear convergence rate of the
periodic projection algorithm for solving the underlying affine feasibility
problem are also established. The results are applied to problems in harmonic
analysis, integral equations, signal theory, and wavelet frames
Evidence of unconventional low-frequency dynamics in the normal phase of Ba(Fe1-xRhx)2As2 iron-based supercondutors
This work presents 75As NMR spin echo decay rate (1/T2) measurements in
Ba(Fe1-xRhx)2As2 superconductors, for 0.041 < x < 0.094. It is shown that 1/T2
increases upon cooling, in the normal phase, suggesting the onset of an
unconventional very low-frequency activated dynamic. The correlation times of
the fluctuations and their energy barriers are derived. The motion is favored
at large Rh content, while it is hindered by the application of a magnetic
field perpendicular to the FeAs layers. The same dynamic is observed in the
spin-lattice relaxation rate, in a quantitatively consistent manner. These
results are discussed in the light of nematic fluctuations involving domain
wall motion. The analogies with the behaviour observed in the cuprates are also
outlined
cFFR as an alternative to FFR: please do not contrast simplicity!
info:eu-repo/semantics/publishedVersio
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