Periodic Pulsed Controllability with Applications to NMR

In this thesis we study a class of problems that require simultaneously controlling a large number of dynamical systems, with varying system dynamics, using the same control signal. We call such problems ensemble control problems, as the goal is to simultaneously steer the entire ensemble of systems. These problems are motivated by many physical systems and we will be particularly interested in the manipulation of nuclear spins in Nuclear Magnetic Resonance (NMR) experiments. System dispersion arise from imprecise magnets for controls, or from disruptive intermolecular interactions. In all cases, the aim is to attenuate the aspects fo the dynamics that correspond to noise or errors, while perserving the aspects that contain the quantities of interest. In liquid NMR experiments this could correspond to preserving Larmor frequency in the presence of inhomogeneities of the strength of the applied radio frequency (RF) field. In solid state NMR, reducing or eliminating orientation dependent magnetic fields is of key concern, so that a precise spectrum can be observed. We approach the problem from the standpoint of mathematical control theory in which the challenge is to simultaneously steer a continuum of systems between points of interest with the same control signal. At the heart of this problem is finding ways for the nonlinearity of the system to be used to our advantage, so that while all members of the ensemble will be driven with the same controls, their final orientations can be orchestrated to arbitrary precision. This thesis develops the methods necessary for two such ensemble control problems arising in NMR, RF (control) amplitude inhomogeneity and systems with periodic drifts that exhibit dispersions in their amplitude and phase. In both cases, robust controls will rely on the non-commutativity of the system's dynamics enabling the generation of alternative and more robust control elements.Engineering and Applied Science

Theory for Nonlinear Spectroscopy of Vibrational Polaritons

Molecular polaritons have gained considerable attention due to their potential to control nanoscale molecular processes by harnessing electromagnetic coherence. Although recent experiments with liquid-phase vibrational polaritons have shown great promise for exploiting these effects, significant challenges remain in interpreting their spectroscopic signatures. In this letter, we develop a quantum-mechanical theory of pump-probe spectroscopy for this class of polaritons based on the quantum Langevin equations and the input-output theory. Comparison with recent experimental data shows good agreement upon consideration of the various vibrational anharmonicities that modulate the signals. Finally, a simple and intuitive interpretation of the data based on an effective mode-coupling theory is provided. Our work provides a solid theoretical framework to elucidate nonlinear optical properties of molecular polaritons as well as to analyze further multidimensional spectroscopy experiments on these systems

Revealing Hidden Vibration Polariton Interactions by 2D IR Spectroscopy

We report the first experimental two-dimensional infrared (2D IR) spectra of novel molecular photonic excitations - vibrational-polaritons. The application of advanced 2D IR spectroscopy onto novel vibrational-polariton challenges and advances our understanding in both fields. From spectroscopy aspect, 2D IR spectra of polaritons differ drastically from free uncoupled molecules; from vibrational-polariton aspects, 2D IR uniquely resolves hybrid light-matter polariton excitations and unexpected dark states in a state-selective manner and revealed hidden interactions between them. Moreover, 2D IR signals highlight the role of vibrational anharmonicities in generating non-linear signals. To further advance our knowledge on 2D IR of vibrational polaritons, we develop a new quantum-mechanical model incorporating the effects of both nuclear and electrical anharmonicities on vibrational-polaritons and their 2D IR signals. This work reveals polariton physics that is difficult or impossible to probe with traditional linear spectroscopy and lays the foundation for investigating new non-linear optics and chemistry of molecular vibrational-polaritons

Divergent effects of acute and repeated quetiapine treatment on dopamine neuron activity in normal vs. chronic mild stress induced hypodopaminergic states

Abstract Clinical evidence supports the use of second-generation dopamine D2 receptor antagonists (D2RAs) as adjunctive therapy or in some cases monotherapy in patients with depression. However, the mechanism for the clinical antidepressant effect of D2RAs remains unclear. Specifically, given accumulating evidence for decreased ventral tegmental area (VTA) dopamine system function in depression, an antidepressant effect of a medication that is expected to further reduce dopamine system activity seems paradoxical. In the present paper we used electrophysiological single unit recordings of identified VTA dopamine neurons to characterize the impact of acute and repeated administration of the D2RA quetiapine at antidepressant doses in non-stressed rats and those exposed to the chronic mild stress (CMS) rodent depression model, the latter modeling the hypodopaminergic state observed in patients with depression. We found that acute quetiapine increased dopamine neuron population activity in non-stressed rats, but not in CMS-exposed rats. Conversely, repeated quetiapine increased VTA dopamine neuron population activity to normal levels in CMS-exposed rats, but had no persisting effects in non-stressed rats. These data suggest that D2RAs may exert their antidepressant actions via differential effects on the dopamine system in a normal vs. hypoactive state. This explanation is supported by prior studies showing that D2RAs differentially impact the dopamine system in animal models of schizophrenia and normal rats; the present results extend this phenomenon to an animal model of depression. These data highlight the importance of studying medications in the context of animal models of psychiatric disorders as well as normal conditions

Chemical differentiation in regions of high-mass star formation I. CS, dust and N2H^+ in southern sources

Aims. Our goals are to compare the CS, N2H+ and dust distributions in a representative sample of high-mass star forming dense cores and to determine the physical and chemical properties of these cores. Methods. We compare the results of CS(5-4) and 1.2 mm continuum mapping of twelve dense cores from the southern hemisphere presented in this work, in combination with our previous N2H+(1-0) and CS(2-1) data. We use numerical modeling of molecular excitation to estimate physical parameters of the cores. Results. Most of the maps have several emission peaks (clumps). We derive basic physical parameters of the clumps and estimate CS and N2H+ abundances. Masses calculated from LVG densities are higher than CS virial masses and masses derived from continuum data, implying small-scale clumpiness of the cores. For most of the objects, the CS and continuum peaks are close to the IRAS point source positions. The CS(5-4) intensities correlate with continuum fluxes per beam in all cases, but only in five cases with the N2H+(1-0) intensities. The study of spatial variations of molecular integrated intensity ratios to continuum fluxes reveals that I(N2H+)/F{1.2} ratios drop towards the CS peaks for most of the sources, which can be due to a N2H+ abundance decrease. For CS(5-4), the I(CS)/F{1.2} ratios show no clear trends with distance from the CS peaks, while for CS(2-1) such ratios drop towards these peaks. Possible explanations of these results are considered. The analysis of normalized velocity differences between CS and N2H+ lines has not revealed indications of systematic motions towards CS peaks.Comment: 13 pages, 5 figures, accepted by Astronomy and Astrophysic