Role of the E2g phonon in the superconductivity of MgB2: a Raman scattering study

Temperature dependent Raman scattering studies in polycrystalline MgB2(10<T<300 K)reveal that the E2g phonon does not experience any self energy renormalization effect across the superconducting critical temperature Tc ~ 40 K. In contrast, most of the current theoretical models rely on the role of the E2g phonon in the electron-phonon coupling mechanism of superconductivity in MgB2. According to these models, a hardening of 12% is expected below Tc at the Gamma point of the Brillouim zone. In the presence of our results, those models must be reviewed. The analysis of the temperature dependence of the E2g phonon frequency yields to a isobaric Gruneisen parameter of -1.2< gama(E2g)< 0.2, smaller than the value of 3.9 obtained from isothermal Raman experiments under pressure. It is suggested that this apparent disagreement can be explained in terms of pressure induced changes of the topology of the Fermi surface. Finally we notice that the phonon linewidth presents the expected two-phonon anharmonic decay as a function of T and no anomalous temperature dependence of the linewidth is observed near Tc.Comment: Published in Solid State Comm. 125, 499 (2003

A century of trends in adult human height

Being taller is associated with enhanced longevity, and higher education and earnings. We reanalysed 1472 population-based studies, with measurement of height on more than 18.6 million participants to estimate mean height for people born between 1896 and 1996 in 200 countries. The largest gain in adult height over the past century has occurred in South Korean women and Iranian men, who became 20.2 cm (95% credible interval 17.5-22.7) and 16.5 cm (13.3-19.7) taller, respectively. In contrast, there was little change in adult height in some sub-Saharan African countries and in South Asia over the century of analysis. The tallest people over these 100 years are men born in the Netherlands in the last quarter of 20th century, whose average heights surpassed 182.5 cm, and the shortest were women born in Guatemala in 1896 (140.3 cm; 135.8-144.8). The height differential between the tallest and shortest populations was 19-20 cm a century ago, and has remained the same for women and increased for men a century later despite substantial changes in the ranking of countries