University of Luxembourg

About: University of Luxembourg is a education organization based out in Luxembourg, Luxembourg. It is known for research contribution in the topics: Population & European union. The organization has 4744 authors who have published 22175 publications receiving 381824 citations.

Problematic video game use as an emotional coping strategy: Evidence from a sample of MMORPG gamers

Abstract: BackgroundA positive relationship between problematic gaming and escapism motivation to play video games has been well established, suggesting that problematic gaming may result from attempts to de...

The Effect of Housing on Portfolio Choice

Abstract: Economic theory predicts that home ownership should have a negative effect on risk-taking in financial portfolios. However, empirical work has not found a strong relationship between housing and portfolios. We identify two reasons for the divergence between the theory and data. First, it is critical to distinguish between home equity wealth and mortgage debt, as they have opposite-signed effects on portfolio choice. Second, it is important to isolate variation in home equity and mortgage debt that is orthogonal to unobserved determinants of portfolios. We estimate a model that permits home equity and mortgage debt to have different effects on portfolio shares. We isolate plausibly exogenous variation in home equity and mortgages by using differences across housing markets in average house prices and housing supply elasticities as instruments. Using data for 60,000 households, we find that increases in property value (holding home equity constant) reduce stockholding significantly, while increases in home equity wealth (holding property value constant) raise stockholding. Our estimates imply that the stock share of liquid wealth would rise by 1 percentage point – 6% of the mean stock share – if a household were to spend 10% less on its house, holding fixed wealth. We conclude that housing has substantial impacts on portfolio choice, as theory predicts.

Detecting offsets in GPS time series: First results from the detection of offsets in GPS experiment

Abstract: [1] The accuracy of Global Positioning System (GPS) time series is degraded by the presence of offsets. To assess the effectiveness of methods that detect and remove these offsets, we designed and managed the Detection of Offsets in GPS Experiment. We simulated time series that mimicked realistic GPS data consisting of a velocity component, offsets, white and flicker noises (1/f spectrum noises) composed in an additive model. The data set was made available to the GPS analysis community without revealing the offsets, and several groups conducted blind tests with a range of detection approaches. The results show that, at present, manual methods (where offsets are hand picked) almost always give better results than automated or semi‒automated methods (two automated methods give quite similar velocity bias as the best manual solutions). For instance, the fifth percentile range (5% to 95%) in velocity bias for automated approaches is equal to 4.2 mm/year (most commonly ±0.4 mm/yr from the truth), whereas it is equal to 1.8 mm/yr for the manual solutions (most commonly 0.2 mm/yr from the truth). The magnitude of offsets detectable by manual solutions is smaller than for automated solutions, with the smallest detectable offset for the best manual and automatic solutions equal to 5 mm and 8 mm, respectively. Assuming the simulated time series noise levels are representative of real GPS time series, robust geophysical interpretation of individual site velocities lower than 0.2–0.4 mm/yr is therefore certainly not robust, although a limit of nearer 1 mm/yr would be a more conservative choice. Further work to improve offset detection in GPS coordinates time series is required before we can routinely interpret sub‒mm/yr velocities for single GPS stations.

Optoelectronic and spectroscopic characterization of vapour-transport grown Cu2ZnSnS4 single crystals

Abstract: Single crystals of Cu2ZnSnS4 (CZTS) have been grown by iodine vapor transport with and without addition of NaI. Crystals with tin-rich copper-poor and with zinc-rich copper-poor stoichiometries were obtained. The crystals were characterized by single crystal X-ray diffraction, energy-dispersive X-ray spectroscopy, photocurrent spectroscopy and electroreflectance spectroscopy using electrolyte contacts as well as by spectroscopic ellipsometry, Raman spectroscopy and photoluminescence spectroscopy (PL)/decay. Near-resonance Raman spectra indicate that the CZTS crystals adopt the kesterite structure with near-equilibrium residual disorder. The corrected external quantum efficiency of the p-type crystals measured by photocurrent spectroscopy approaches 100% close to the bandgap energy, indicating efficient carrier collection. The bandgap of the CZTS crystals estimated from the external quantum efficiency spectrum measured using an electrolyte contact was found to be 1.64–1.68 eV. An additional sub-bandgap photocurrent response (Urbach tail) was attributed to sub bandgap defect states. The room temperature PL of the crystals was attributed to radiative recombination via tail states, with lifetimes in the nanosecond range. At high excitation intensities, the PL spectrum also showed evidence of direct band to band transitions at ∼1.6 eV with a shorter decay time. Electrolyte electroreflectance spectra and spectra of the third derivative of the optical dielectric constant in the bandgap region were fitted to two optical transitions at 1.71 and 1.81 eV suggesting a larger valence band splitting than predicted theoretically. The high values of the EER broadening parameters (192 meV) indicate residual disorder consistent with the existence of tail states.