Cubic Defects: Comparing the Eight-State-System with its Two-Level-Approximation

Substitutional defects in a cubic symmetry (such as a lithium defect in a KCl host crystal) can be modeled appropriately by an eight-state-system. Usually this tunneling degree of freedom is approximated by a two-level-system. We investigate the observable differences between the two models in three contexts. First we show that the two models predict different relations between the temperature dependence of specific heat and static susceptibility. Second we demonstrate that in the presence of external forces (pressure and electric field) the eight-state-system shows features that cannot be understood within the framework of the two-level-approximation. In this context we propose an experiment for measuring the parameter for tunneling along the face diagonal. Finally we discuss the differences between the models appearing for strongly coupled pairs. Geometric selection rules and particular forms of asymmetry lead to clear differences between the two models.Comment: 19 pages, Latex, submitted to J. of Phys., some small supplement

A model for ripple instabilities in granular media

We extend the model of surface granular flow proposed in \cite{bcre} to account for the effect of an external `wind', which acts as to dislodge particles from the static bed, such that a stationary state of flowing grains is reached. We discuss in detail how this mechanism can be described in a phenomenological way, and show that a flat bed is linearly unstable against ripple formation in a certain region of parameter space. We focus in particular on the (realistic) case where the migration velocity of the instability is much smaller than the grains' velocity. In this limit, the full dispersion relation can be established. We find that the critical wave vector is of the order of the saltation length. We provide an intuitive interpretation of the instability.Comment: 11 pages, latex, 2 encapsulated postscript figure

Rotating wave approximation: systematic expansion and application to coupled spin pairs

We propose a new treatment of the dynamics of a periodically time-dependent Liouvillian by mapping it onto a time-independent problem and give a systematic expansion for its effective Liouvillian. In the case of a two-level system, the lowest order contribution is equivalent to the well-known rotating wave approximation. We extend the formalism to a pair of coupled two-level systems. For this pair, we find two Rabi frequencies and we can give parameter regimes where the leading order of the expansion is suppressed and higher orders become important. These results might help to investigate the interaction of tunneling systems in mixed crystals by providing a tool for the analysis of echo experiments.Comment: 15 pages, Latex, submitted to European Physical Journal

Labor markets in a globalizing world: trends, challenges and opportunities

Profound changes in the nature and structure of employment have been propelled by the combined effect from technology and international trade. Technological obsolescence and the global slicing up of the value chain often jeopardize the economic future of the most vulnerable groups of workers. At the geographical level, the economic decay of lagging-behind regions has fueled the political polarization, fertilizing the ground for political opportunistic narratives. Despite their omnipresent effects, the precise labor market implications from technology and trade remain largely elusive due to contradictory evidence and methodological challenges. Against this background, the current thesis provides new insight which stimulates the academic and social debate.First, the systematic synthesis of the literature documents that both technology and trade impose economically meaningful effects. Nevertheless, the analysis reveals that the effect is conditional on the characteristics of the workers, the spatial unit ofanalysis or the period under consideration. Second, using the Dutch labor market, it is shown that automation and the trade jointly polarize the employment growth, both at the national and the regional level. Furthermore, the analysis establishes that the incidence of employment polarization and skills mismatch is intertwined, while their economic effects differ in more disaggregated demographic groups, such as young and senior workers.From a policy perspective, the current thesis stresses the instrumental role of life-long learning to prevent the technological obsolescence and indicates work-related practices to incentivize workers to develop their skills portfolio. Such whole-of-society approaches will safeguard job security and enable the modern societies to be more prosperous, inclusive and democratic;necessary conditions to face the current and future challenges

Islands and destination image: the case of Ios

This study was conducted to identify the image of Ios as a tourist destination as perceived by the visitors, in order to contribute to the formation of an effective marketing plan. The strengths and weaknesses of the image of Ios were measured and presented, accompanied with a number of recommendations. The findings revealed that Ios has a very strong destination image as a party island, with the majority of the visitors being international young students coming to enjoy the relaxing atmosphere and the party mood of the island. As a result, Ios needs to strengthen its image compared to other islands or destinations which offer the same product, by promoting its competitive advantages, such as; the nightlife, the relatively low prices, the relaxing atmosphere and the friendliness of the locals

The role of visual media in religious tourists' destination image, choice, and on-site experience: the case of Tinos, Greece

Although visual media are known to influence the image people have of tourism destinations worldwide, only a few studies have examined their role in the context of religious tourism. This study explores the role TV news and documentaries play in religious tourists’ destination image, choice and on-site experience. Ethnographic research (31 participant observations and 38 in-depth interviews) was conducted in two organized coach trips to the sacred island of Tinos, Greece. The findings suggest that broadcasted images of the holy icon, the leading politicians, and the performing religious crowd shape the image of Tinos and influence visitation patterns. Additionally, the visual projection of religious tourists’ offerings appears to condition peoples’ on-site experience. The theoretical and practical implications of the study are also discussed