Energy Level Alignment in Organic-Organic Heterojunctions: The TTF-TCNQ Interface

The energy level alignment of the two organic materials forming the TTF-TCNQ interface is analyzed by means of a local orbital DFT calculation, including an appropriate correction for the transport energy gaps associated with both materials. These energy gaps are determined by a combination of some experimental data and the results of our calculations for the difference between the TTF_{HOMO} and the TCNQ_{LUMO} levels. We find that the interface is metallic, as predicted by recent experiments, due to the overlap (and charge transfer) between the Density of States corresponding to these two levels, indicating that the main mechanism controlling the TTF-TCNQ energy level alignment is the charge transfer between the two materials. We find an induced interface dipole of 0.7 eV in good agreement with the experimental evidence. We have also analyzed the electronic properties of the TTF-TCNQ interface as a function of an external bias voltage \Delta, between the TCNQ and TTF crystals, finding a transition between metallic and insulator behavior for \Delta~0.5 eV

Quasinormal frequencies of asymptotically flat two-dimensional black holes

We discuss whether the minimally coupled massless Klein-Gordon and Dirac fields have well defined quasinormal modes in single horizon, asymptotically flat two-dimensional black holes. To get the result we solve the equations of motion in the massless limit and we also calculate the effective potentials of Schrodinger type equations. Furthermore we calculate exactly the quasinormal frequencies of the Dirac field propagating in the two-dimensional uncharged Witten black hole. We compare our results on its quasinormal frequencies with other already published.Comment: 12 pages. Accepted for publication in Gen. Rel. and Gra

Semiconductor cavity QED: Bandgap induced by vacuum fluctuations

We consider theoretically a semiconductor nanostructure embedded in one-dimensional microcavity and study the modification of its electron energy spectrum by the vacuum fluctuations of the electromagnetic field. To solve the problem, a non-perturbative diagrammatic approach based on the Green's function formalism is developed. It is shown that the interaction of the system with the vacuum fluctuations of the optical cavity opens gaps within the valence band of the semiconductor. The approach is verified for the case of large photon occupation numbers, proving the validity of the model by comparing to previous studies of the semiconductor system excited by a classical electromagnetic field. The developed theory is of general character and allows for unification of quantum and classical descriptions of the strong light-matter interaction in semiconductor structures

Virtuts de la paideia atlètica

El tema principal d'aquest article és la dimensió esportiva de la pedagogia grega. El nostre propòsit és mostrar la rellevància de l'educació física i la gimnàstica en l'itinerari formatiu que seguiren els grecs, aquell procés que coneixem amb el nom de paideia. En aquest sentit, hem destacat que els grecs van saber trobar un equilibri entre els valors intel·lectuals i els valors corporals, harmonia ben expressada en la coneguda màxima del poeta llatí Juvenal: mens sana in corpore sano. Cal dir que aquest sistema es trobava en perfecta consonància amb el caràcter agonístic de la societat grega i amb el valuós ideal de la kalokagathia. Però també hem volgut indicar l'evolució que experimentarà aquest model formatiu, uns canvis que acabaran convertint aquesta educació en marcadament intel·lectual i racional.Virtues of athletic paideia. The main topic of this article is the sporting dimension of Greek pedagogy. Our aim is to show the importance of physical education and gymnastics in the educational path followed by the Greeks, a process that goes by the name of paideia. In this respect, we have underscored the fact the Greeks were able to find a balance between intellectual values and bodily values, a harmony succinctly expressed in the well-known maxim of the Roman poet Juvenal: mens sana in corpore sano. It should be said that this system was perfectly consistent with the agonistic nature of Greek society and with the valuable ideal of kalokagathia. In addition, our intention is to indicate the evolution that this educational model underwent and the changes that turned it into one that is markedly intellectual and rational

Inner and outer star forming regions over the disks of spiral galaxies. I. Sample characterization

Context. The knowledge of abundance distributions is central to understanding the formation and evolution of galaxies. Most of the relations employed for the derivation of gas abundances have so far been derived from observations of outer disk HII regions, despite the known differences between inner and outer regions. Aims. Using integral field spectroscopy (IFS) observations we aim to perform a systematic study and comparison of two inner and outer HII regions samples. The spatial resolution of the IFS, the number of objects and the homogeneity and coherence of the observations allow a complete characterization of the main observational properties and differences of the regions. Methods. We analyzed a sample of 725 inner HII regions and a sample of 671 outer HII regions, all of them detected and extracted from the observations of a sample of 263 nearby, isolated, spiral galaxies observed by the CALIFA survey. Results. We find that inner HII regions show smaller equivalent widths, greater extinction and luminosities, along with greater values of [NII]{\lambda}6583/H{\alpha} and [OII]{\lambda}3727/[OIII]{\lambda}5007 emission-line ratios, indicating higher metallicites and lower ionization parameters. Inner regions have also redder colors and higher photometric and ionizing masses, although Mion/Mphot is slighty higher for the outer regions. Conclusions. This work shows important observational differences between inner and outer HII regions in star forming galaxies not previously studied in detail. These differences indicate that inner regions have more evolved stellar populations and are in a later evolution state with respect to outer regions, which goes in line with the inside-out galaxy formation paradigm.Comment: 16 page