0000000000535018
AUTHOR
Michael Braun
Geometric versus numerical optimal control of a dissipative spin-12particle
We analyze the saturation of a nuclear magnetic resonance (NMR) signal using optimal magnetic fields. We consider both the problems of minimizing the duration of the control and its energy for a fixed duration. We solve the optimal control problems by using geometric methods and a purely numerical approach, the grape algorithm, the two methods being based on the application of the Pontryagin maximum principle. A very good agreement is obtained between the two results. The optimal solutions for the energy-minimization problem are finally implemented experimentally with available NMR techniques.
Simultaneous time-optimal control of the inversion of two spin-12particles
We analyze the simultaneous time-optimal control of two-spin systems. The two noncoupled spins, which differ in the value of their chemical offsets, are controlled by the same magnetic fields. Using an appropriate rotating frame, we restrict the study to the case of opposite shifts. We then show that the optimal solution of the inversion problem in a rotating frame is composed of a pulse sequence of maximum intensity and is similar to the optimal solution for inverting only one spin by using a nonresonant control field in the laboratory frame. An example is implemented experimentally using nuclear magnetic resonance techniques.
Optimizing the nickel boride layer thickness in a spectroelectrochemical ATR-FTIR thin-film flow cell applied in glycerol oxidation
Abstract The influence of the drop-casted nickel boride catalyst loading on glassy carbon electrodes was investigated in a spectroelectrochemical ATR-FTIR thin-film flow cell applied in alkaline glycerol electrooxidation. The continuously operated radial flow cell consisted of a borehole electrode positioned 50 µm above an internal reflection element enabling operando FTIR spectroscopy. It is identified as a suitable tool for facile and reproducible screening of electrocatalysts under well-defined conditions, additionally providing access to the selectivities in complex reaction networks such as glycerol oxidation. The fast product identification by ATR-IR spectroscopy was validated by the …
Singular Extremals for the Time-Optimal Control of Dissipative Spin 1/2 Particles
We consider the time-optimal control by magnetic fields of a spin 1/2 particle in a dissipative environment. This system is used as an illustrative example to show the role of singular extremals in the control of quantum systems. We analyze a simple case where the control law is explicitly determined. We experimentally implement the optimal control using techniques of nuclear magnetic resonance. To our knowledge, this is the first experimental demonstration of singular extremals in quantum systems with bounded control amplitudes.
¿Más allá de la literatura? Narradores muertos en la literatura contemporánea
Der tote Erzähler, der eine Geschichte erzählt, die seine eigene ist, gehört ins Genre der Jenseitserzählung. Doch diese Gattungstheorie liefert nur einen Teil der Erklärung für dieses merkwürdige, ja paradoxe Phänomen, das Vladimir Nabokov einmal so formuliert hat: ?The ?I? of the book cannot die in the book?. Der Beitrag untersucht, welche Rolle der Tod des Erzählers für sein unzuverlässiges Erzählen spielt, und zwar an den unterschiedlichen Beispielen von Patrick Roths Novelle Johnny Shines oder Die Wiedererweckung der Toten (1993) und von Daniel Kehlmanns Erzählung Der fernste Ort (2001). Das Jenseits, so zeigt sich, verschiebt die Grenze der Wahrnehmung des Erzählers ins Surreale und i…