341 research outputs found
Particle orientation distribution in Y-Fe2O3magnetic tapes by Mössbauer and hysteresis loop measurements
The particle orientation in several Y-Fe2O3magnetic tapes has been quantitatively evaluated by using the data of both Mössbauer and hysteresis loop measurements performed in the three orthogonal directions. A texture function has been obtained as a development of real harmonics. The profile of the texture function gives the quality of the different magnetic tapes. A different degree of particle orientation at the surface of the tape is evidenced by means of conversion electron Mössbauer spectra
Reducing Streaking Artifacts in Quantitative Susceptibility Mapping
It is well known that reconstruction algorithms in quantitative susceptibility mapping often contain streaking artifacts. These are nondesirable objects that contaminate the image, and the possibility of removing or at least reducing them has a great practical interest. In [J. K. Choi, H. S. Park, S. Wang, Y. Wang, and J. K. Seo, SIAM J. Imaging Sci., 7 (2014), pp. 1669-1689], the cause of the artifacts is identified as propagation of singularities for a wave-type operator. In this work, we analyze such singularities using microlocal techniques and propose some strategies to reduce the artifacts.Peer reviewe
Mossbauer and magnetization studies of amorphous NdFeB compositionally modulated thin films
Several NdFeB compositionally modulated thin films are studied by using both conversion electron Mossbauer spectra and SQUID (superconducting quantum-interference-device) magnetometry. Both the hyperfine fields and the easy magnetization magnitude are not correlated with the modulation characteristic length (lambda) while the magnetization perpendicular to the thin-film plane decreases as lambda increases. The spectra were recorded at room temperature being the gamma rays perpendicular to the substrate plane. The magnetization measurements were recorded by using a SHE SQUID magnetometer in applied magnetic fields up to 5.5 T and in the temperature range between 1.8 and 30 K
Mathematical Modeling for 2D Light-Sheet Fluorescence Microscopy image reconstruction
We study an inverse problem for Light Sheet Fluorescence Microscopy (LSFM),
where the density of fluorescent molecules needs to be reconstructed. Our first
step is to present a mathematical model to describe the measurements obtained
by an optic camera during an LSFM experiment. Two meaningful stages are
considered: excitation and fluorescence. We propose a paraxial model to
describe the excitation process which is directly related with the Fermi
pencil-beam equation. For the fluorescence stage, we use the transport equation
to describe the transport of photons towards the detection camera. For the
mathematical inverse problem that we obtain after the modeling, we present a
uniqueness result, recasting the problem as the recovery of the initial
condition for the heat equation in from
measurements in a space-time curve. Additionally, we present numerical
experiments to recover the density of the fluorescent molecules by discretizing
the proposed model and facing this problem as the solution of a large and
sparse linear system. Some iterative and regularized methods are used to
achieve this objective. The results show that solving the inverse problem
achieves better reconstructions than the direct acquisition method that is
currently used
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