Experimental Study of Adaptation and Postural Control after Sleep Deprivation

This thesis investigates the influence of sleep deprivation on the human's postural control and conceptions of adaptation. Seventeen subjects were investigated with posturography after 24 h and 36 h of sleep deprivation, and a control posturography trial was performed either one week before or one week after the sleep deprivation trials. Stabilizing torques and forces were recorded by a force platform and the body sway was recorded by a 3D ultrasonic positioning system. Stimulation according to a pseudo random binary sequence (PRBS) was applied using two vibrators attached to the calf muscles of the subjects. Posturographic tests were performed with eyes open and eyes closed. Subspace based modeling was used to assess postural control after sleep deprivation. Also, quantitative variance and correlation analysis were applied to the recorded data. The results of the investigation showed that it is possible to identify MIMO models with stimulus as input signal and torques and body sway as output signals. When body sway is characterized by the variance of the position data, statistical evidence was found for an increase of body sway after 24 hours of sleep deprivation. Also, sleep deprivation impairs postural adaptation

Christianity and Judaism under Islam in Medieval Iraq: Da'ûd al-Muqammas and Sa'd b. Mansûr Ibn Kammûna

In the present paper two attitudes towards Christianity among Jews in Medieval Iraq are discussed, viz. Da'ûd al-Muqammas (second half of the 9th century) and Sa'd b. Mansûr Ibn Kammûna (second half of the 13th century). Da'ûd al-Muqammas was writing in a period when Christianity may have been an attractive alternative for intellectual Jews. His major work still available, 'Ishrûn Maqâla, "Twenty chapters", is an anti-Christian tract demonstrating the continuing validity of Judaism. Addressing a Gentile readership in his Tanqîh al-abhâth li'l-milal al-thalâth, "The examination of the inquiries into the three faiths", Sa'd b. Mansûr Ibn Kammûna upholds the validity of Judaism and Christianity against the claims of Islam in a period when Islam had been reduced to the same status as Judaism and Christianity in the early Mongol rule of Iraq

Nonequilibrium Green's functions and atom-surface dynamics: Simple views from a simple model system

We employ Non-equilibrium Green's functions (NEGF) to describe the real-time dynamics of an adsorbate-surface model system exposed to ultrafast laser pulses. For a finite number of electronic orbitals, the system is solved exactly and within different levels of approximation. Specifically i) the full exact quantum mechanical solution for electron and nuclear degrees of freedom is used to benchmark ii) the Ehrenfest approximation (EA) for the nuclei, with the electron dynamics still treated exactly. Then, using the EA, electronic correlations are treated with NEGF within iii) 2nd Born and with iv) a recently introduced hybrid scheme, which mixes 2nd Born self-energies with non-perturbative, local exchange-correlation potentials of Density Functional Theory (DFT). Finally, the effect of a semi-infinite substrate is considered: we observe that a macroscopic number of de-excitation channels can hinder desorption. While very preliminary in character and based on a simple and rather specific model system, our results clearly illustrate the large potential of NEGF to investigate atomic desorption, and more generally, the non equilibrium dynamics of material surfaces subject to ultrafast laser fields.Comment: 10 pages, 5 figure

Long-range excitations in time-dependent density functional theory

Adiabatic time-dependent density functional theory fails for excitations of a heteroatomic molecule composed of two open-shell fragments at large separation. Strong frequency-dependence of the exchange-correlation kernel is necessary for both local and charge-transfer excitations. The root of this is static correlation created by the step in the exact Kohn-Sham ground-state potential between the two fragments. An approximate non-empirical kernel is derived for excited molecular dissociation curves at large separation. Our result is also relevant for the usual local and semi-local approximations for the ground-state potential, as static correlation there arises from the coalescence of the highest occupied and lowest unoccupied orbital energies as the molecule dissociates.Comment: 7 pages, 2 figure

Classical Nuclear Motion in Quantum Transport

An ab initio quantum-classical mixed scheme for the time evolution of electrode-device-electrode systems is introduced to study nuclear dynamics in quantum transport. Two model systems are discussed to illustrate the method. Our results provide the first example of current-induced molecular desorption as obtained from a full time-dependent approach and suggest the use of ac biases as a way to tailor electromigration. They also show the importance of non-adiabatic effects for ultrafast phenomena in nanodevices.Comment: 5 pages, 3 figure

Lanczos-adapted time evolution for open boundary quantum transport

We increase the efficiency of a recently proposed time integration scheme for time dependent quantum transport by using the Lanczos method for time evolution. We illustrate our modified scheme in terms of a simple one dimensional model. Our results show that the Lanczos-adapted scheme gives a large increase in numerical efficiency, and is an advantageous route for numerical time integration in ab-initio treatment of open boundary quantum transport phenomena.Comment: 11 pages, 1 figur

Theory of Auger core-valence-valence processes in simple metals. II. Dynamical and surface effects on Auger line shapes

ABSTRACT: Auger CVV spectra of simple metals are generally believed to be well described by one-electronlike theories in the bulk which account for matrix elements and, in some cases, also static core-hole screening effects. We present here detailed calculations on Li, Be, Na, Mg, and Al using selfconsistent bulk wave functions and proper matrix elements. The resulting spectra differ markedly from experiment and peak at too low energies. To explain this discrepancy we investigate effects of the surface and dynamical effects of the sudden disappearance of the core hole in the final state. To study core-hole effects we solve Mahan —Nozieres —De Dominicis (MND) model numerically over the entire band. The core-hole potential and other parameters in the MND model are determined by self-consistent calculations of the core-hole impurity. The results are compared with simpler approximations based on the final-state rule due to von Barth and Grossmann. To study surface and mean-free-path effects we perform slab calculations for Al but use a simpler infinite-barrier model in the remaining cases. The model reproduces the slab spectra for Al with very good accuracy. .In all cases investigated either the effects of the surface or the effects of the core hole give important modifications and a much improved agreement with experiment