Transition from Townsend to glow discharge: subcritical, mixed or supercritical

The full parameter space of the transition from Townsend to glow discharge is investigated numerically in one space dimension in the classical model: with electrons and positive ions drifting in the local electric field, impact ionization by electrons ($\alpha$ process), secondary electron emission from the cathode ($\gamma$ process) and space charge effects. We also perform a systematic analytical small current expansion about the Townsend limit up to third order in the total current that fits our numerical data very well. Depending on $\gamma$ and system size pd, the transition from Townsend to glow discharge can show the textbook subcritical behavior, but for smaller values of pd, we also find supercritical or some intermediate ``mixed'' behavior. The analysis in particular lays the basis for understanding the complex spatio-temporal patterns in planar barrier discharge systems.Comment: 12 pages, 10 figures, submitted to Phys. Rev.

Implementation of a Monte Carlo method to model photon conversion for solar cells.

A physical model describing different photon conversion mechanisms is presented in the context of photovoltaic applications. To solve the resulting system of equations, a Monte Carlo ray-tracing model is implemented, which takes into account the coupling of the photon transport phenomena to the non-linear rate equations describing luminescence. It also separates the generation of rays from the two very different sources of photons involved (the sun and the luminescence centers). The Monte Carlo simulator presented in this paper is proposed as a tool to help in the evaluation of candidate materials for up- and downconversion. Some application examples are presented, exploring the range of values that the most relevant parameters describing the converter should have in order to give significant gain in photocurrent

Evaluating competing perspectives towards undeclared work: some lessons from Bulgaria

When explaining and tackling the undeclared economy in Central and Eastern Europe, participants have been conventionally viewed as rational economic actors. They engage in undeclared work when the benefits outweigh the costs. Participation is thus deterred by increasing the sanctions and/or probability of being caught. Recently, however, an alternative social actor approach has emerged which views participants as engaging in undeclared work when their norms, values and beliefs (i.e., citizen morale) do not align with the laws and regulations (i.e., state morale). Here, therefore, initiatives to develop greater symmetry between civic and state morale are pursued. To evaluate the validity and effectiveness of these competing explanations and policy approaches, 2,004 face-to-face interviews conducted in Bulgaria in late 2015 are reported. Logit marginal effects regression analysis reveals no association between participation in undeclared work and the perceived level of penalties and risk of detection, but a strong significant association with the level of asymmetry between citizen and state morale; the greater the asymmetry, the higher is the likelihood of participation in undeclared work. The paper concludes by discussing the implications for explaining and tackling undeclared work

Explaining and tackling unregistered employment : evidence from an employers’ survey

When explaining and tackling employers participating in the informal economy, they have been conventionally viewed as rational economic actors who engage when the benefits outweigh the costs, and thus their participation is deterred by increasing the sanctions and/or risks of detection. An emergent social actor approach, however, has explained employers as engaging in the informal economy when there is a lack of vertical trust (i.e., their norms, values and beliefs are not in symmetry with the laws and regulations) and horizontal trust (i.e., they believe many others are being non-compliant). The aim of this paper is to evaluate these competing perspectives by reporting a 2015 survey of 450 employers in FYR Macedonia. The finding is that although there is no association between employers using unregistered workers and the perceived level of penalties and risks of detection, there is a strong significant association with both the level of vertical and horizontal trust. Those whose beliefs do not align with the laws and regulations display a significantly greater likelihood of employing unregistered workers, as do those who perceive a larger proportion of the population to be engaged in the informal economy. The theoretical and policy implications are then discussed