Gregory von Winckel

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This work is concerned with the structure of bilinear minimization problems arising in recovering subsampled and modulated images in parallel magnetic resonance imaging. By considering a physically reasonable simplified model exhibiting the same fundamental mathematical difficulties, it is shown that such problems suffer from poor gradient scaling and(More)
The Cartesian parallel magnetic imaging problem is formulated variationally using a high-order penalty for coil sensitivities and a total variation like penalty for the reconstructed image. Then the optimality system is derived and numerically discretized. The objective function used is non-convex, but it possesses a bilinear structure that allows the(More)
We present a fast and efficient spectral method for computing the eigenvalues and eigenfunctions for a one-dimensional piecewise smooth potential as is the case of epitaxially grown semiconductor heterostructures. Many physical devices such as quantum well infrared photo-detectors and quantum cascade lasers rely upon transitions between bound and(More)
Terahertz detection capability of an n-type heterojunction interfacial work function internal photoemission (HEIWIP) detector is demonstrated. Threshold frequency, f0, of 3.2 THz (93 lm) was obtained by using n-type GaAs emitter doped to 1 · 10 cm 3 and Al0.04Ga0.96As single barrier structure. The detector shows a broad spectral response from 30 to 3.2 THz(More)
HEterojunction Interfacial Workfunction Internal Photoemission (HEIWIP) detectors using AlGaAs as both the emitter and the barrier material with different Al fractions for the two layers are demonstrated. The extension of the HEIWIP concept to wavelengths longer than 110 lm in the GaAs/AlGaAs system requires the use of AlGaAs as the emitter material to(More)
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