Quantum and semiclassical phase-space dynamics of a wave packet in strong fields using initial-value representations

We assess the suitability of quantum and semiclassical initial value representations, exemplified by the coupled coherent states (CCS) method and the Herman Kluk (HK) propagator, respectively, for modeling the dynamics of an electronic wave packet in a strong laser field, if this wave packet is initially bound. Using Wigner quasiprobability distributions and ensembles of classical trajectories, we identify signatures of over-the-barrier and tunnel ionization in phase space for static and time-dependent fields and the relevant sets of phase-space trajectories in order to model such features. Overall, we find good agreement with the full solution of the time-dependent Schr\"odinger equation (TDSE) for Wigner distributions constructed with both initial-value representations. Our results indicate that the HK propagator does not fully account for tunneling and over-the-barrier reflections. However, it is able to partly reproduce features associated with the wave packet crossing classically forbidden regions, although the trajectories employed in its construction always obey classical phase-space constraints. We also show that the Coupled Coherent States (CCS) method represents a fully quantum initial value representation and accurately reproduces the results of a standard TDSE solver. Furthermore, we sow that both the HK propagator and the CCS approach may be successfully employed to compute the time-dependent dipole acceleration and high-harmonic spectra. Nevertheless, the semiclassical propagator exhibits a worse agreement with the TDSE than the outcome of the CCS method, as it neither fully accounts for tunneling nor for over-the-barrier reflections. This leads to a dephasing in the time-dependent wave function which becomes more pronounced for longer times

Coupled-coherent-states approach for high-order harmonic generation

In this paper, we report a version of the coupled-coherent-states method which is able to accurately compute the high-order harmonic generation (HHG) spectrum of an electron in a laser field in one dimension by the use of trajectory-guided grids of Gaussian wave packets. It is shown that by periodic reprojection of the wave function and dynamically altering the basis set size, the method can account for a wave function which spreads out to cover a large area in phase space while still keeping computational expense low and ensuring the preservation of coherence of the wave function. The HHG spectra obtained show good agreement with those from a time-dependent Schrödinger equation solver. We show also that the part of the wave function which is responsible for HHG moves along a periodic orbit which is far from that of classical motion. Although this paper is a proof of principle and therefore focused on a simple one-dimensional system, future generalizations for the multielectron case are discussed

Numerical-Analytic Methods of Investigating Periodic Solutions

183 tr.; 20 cm

The global nutrition transition: trends, disease burdens and policy interventions

Non-communicable diseases (NCD) have increased dramatically in developed and developing countries. Unhealthy diet is one of the major factors contributing to NCD development. Recent evidence has identified deterioration in aspects of dietary quality across many world regions, including low- and middle-income countries (LMIC). Most burdens of disease attributable to poor diet can be prevented or delayed as they occur prematurely. Therefore, it is important to identify and target unhealthy dietary behaviours in order to have the greatest impact. National dietaryrelated programmes have traditionally focused on micronutrient deficiency and food security and failed to acknowledge unhealthy dietary intakes as a risk factor that contributes to the development of NCD. Inadequate intakes of healthy foods and nutrients and excess intakes of unhealthy ones are commonly observed across the world, and efforts to reduce the double burden of micronutrient deficiency and unhealthy diets should be a particular focus for LMIC. Interventions and policies targeting whole populations are likely to be the most effective and sustainable, and should be prioritized. Population-based approaches such as health information and communication campaigns, fiscal measures such as taxes on sugar-sweetened beverages, direct restrictions and mandates, reformulation and improving the nutrient profile of food products, and standards regulating marketing to children can have significant and large impacts to improve diets and reduce the incidence of NCD. There is a need for more countries to implement population-based effective approaches to improve current diets

Amorphisation and Devitrification of Al -Transition Metal - Rare Earth Alloys

Amorphisation studies by rapid solidification of Al-based alloys containing a transition metal (TM) and a rare earth element (RE) are reported. Results on primary formation of Al nanocrystals are given and discussed in relation to possible nucleation mechanisms considering the effect of various RE elements (RE = La, Cc, Nd and Sm) in Al87Ni7RE6 alloys. Ti or Zr, immiscible with RE's, are added to the ternary alloys with the aim of revealing possible phase separation in the melt. Calculations of ternary Al-Ni-Ce metastable phase equilibria are helpful in understanding the transformation sequence. Composition profiles ahead of nanocrystals are computed using the DICTRA software which correctly predicts the occurrence of composition gradients. The surface fracture of mechanically tested samples are observed in TEM to check whether crystallisation is induced by deformation