Charge conjugation from space-time inversion in QED: discrete and continuous groups

We show that the CPT groups of QED emerge naturally from the PT and P (or T) subgroups of the Lorentz group. We also find relationships between these discrete groups and continuous groups, like the connected Lorentz and Poincar\'e groups and their universal coverings.Comment: 7 page

Multiethnicity and migration at Teopancazco: investigations of a Teotihuacan neighborhood center

Published version2019-11-1

Negation, expressivism, and intentionality

Many think that expressivists have a special problem with negation. I disagree. For if there is a problem with negation, I argue, it is a problem shared by those who accept some plausible claims about the nature of intentionality. Whether there is any special problem for expressivists turns, I will argue, on whether facts about what truth-conditions beliefs have can explain facts about basic inferential relations among those beliefs. And I will suggest that the answer to this last question is, on most plausible attempts at solving the problem of intentionality, ‘no’

Los juegos de pelota en el Altiplano Central de México

The following represents a pre-press draft submitted in English and subsequently translated to Spanish.Los juegos de pelota más antiguos de Mesoamérica se encuentran en las Tierras Bajas; sin embargo, los habitantes del Altiplano Central adoptaron y construyeron canchas formales desde principios del Preclásico Medio. En periodos posteriores, el predominio de canchas varió según el sitio, los contactos regionales y las tendencias sociopolíticas más generales. Las canchas de juegos de pelota fueron particularmente numerosas en Puebla y Tlaxcala hacia finales del periodo Preclásico, y abundantes durante el Epiclásico en todo el Altiplano Central de México. Las mejores descripciones de cómo se jugó pelota en toda Mesoamérica durante los tiempos prehispánicos provienen de documentos del siglo xvi, del Altiplano; incluso el juego fue llevado a España por Cortés.Although the earliest ball-courts appear in the Mesoamerican lowlands, the inhabitants of the central highlands eagerly adopted and elaborated formal courts beginning during the Middle Preclassic period. In subsequent periods, the prevalence of ball-courts varied by site, regional contacts and broader sociopolitical forces. Courts were particularly numerous in Puebla-Tlaxcala during the later Preclassic period and throughout cent ral Mexico during the Epiclassic period. Sixteenth century documents from the Altiplano provide the best descriptions concerning how prehispanic games throughout Mesoamerica were played, even having been exported to Spain by Cortés (Figure 1)

Conceptual evaluation: epistemic

On a view implicitly endorsed by many, a concept is epistemically better than another if and because it does a better job at ‘carving at the joints', or if the property corresponding to it is ‘more natural' than the one corresponding to another. This chapter offers an argument against this seemingly plausible thought, starting from three key observations about the way we use and evaluate concepts from en epistemic perspective: that we look for concepts that play a role in explanations of things that cry out for explanation; that we evaluate not only ‘empirical' concepts, but also mathematical and perhaps moral concepts from an epistemic perspective; and that there is much more complexity to the concept/property relation than the natural thought seems to presuppose. These observations, it is argued, rule out giving a theory of conceptual evaluation that is a corollary of a metaphysical ranking of the relevant properties. conceptual ethics, explanation, naturalness, epistemic value, concept/property, semantic internalis

Causes and Consequences of the Spanish Economic Crisis: Why the Recovery is Taken so Long?

Spain is currently facing its worst crisis in the last fifty years. The crisis began as an extension of the international financial crisis, but the internal imbalances accumulated in the pre-crisis period aggravated the situation. At present their incomplete adjustment is making difficult the economic recovery. This paper describes the evolution of the economic crisis in Spain. The real estate sector and the banking sector are analysed in detail, as they played a key role in the detonation and the deepening of the crisis. The results of the main reforms carried out so far are also carefully examined. It also discusses the main factors that have delayed the economic recovery up to now (unemployment and indebtedness), and present some alternatives to define an exit strategy.Crisis, Real estate, Banking, Debt problems, Unemployment, Public debt