Spin and Statistics and First Principles

It was shown in the early Seventies that, in Local Quantum Theory (that is the most general formulation of Quantum Field Theory, if we leave out only the unknown scenario of Quantum Gravity) the notion of Statistics can be grounded solely on the local observable quantities (without assuming neither the commutation relations nor even the existence of unobservable charged field operators); one finds that only the well known (para)statistics of Bose/Fermi type are allowed by the key principle of local commutativity of observables. In this frame it was possible to formulate and prove the Spin and Statistics Theorem purely on the basis of First Principles. In a subsequent stage it has been possible to prove the existence of a unique, canonical algebra of local field operators obeying ordinary Bose/Fermi commutation relations at spacelike separations. In this general guise the Spin - Statistics Theorem applies to Theories (on the four dimensional Minkowski space) where only massive particles with finite mass degeneracy can occur. Here we describe the underlying simple basic ideas, and briefly mention the subsequent generalisations; eventually we comment on the possible validity of the Spin - Statistics Theorem in presence of massless particles, or of violations of locality as expected in Quantum Gravity.Comment: Survey based on a talk given at the Meeting on "Theoretical and experimental aspects of the spin - statistics connection and related symmetries", Trieste, Italy - October 21-25, 200

Advanced paternal age effects in neurodevelopmental disorders?review of potential underlying mechanisms

Multiple epidemiological studies suggest a relationship between advanced paternal age (APA) at conception and adverse neurodevelopmental outcomes in offspring, particularly with regard to increased risk for autism and schizophrenia. Conclusive evidence about how age-related changes in paternal gametes, or age-independent behavioral traits affect neural development is still lacking. Recent evidence suggests that the origins of APA effects are likely to be multidimensional, involving both inherited predisposition and de novo events. Here we provide a review of the epidemiological and molecular findings to date. Focusing on the latter, we present the evidence for genetic and epigenetic mechanisms underpinning the association between late fatherhood and disorder in offspring. We also discuss the limitations of the APA literature. We propose that different hypotheses relating to the origins of the APA effects are not mutually exclusive. Instead, multiple mechanisms likely contribute, reflecting the etiological complexity of neurodevelopmental disorders

Assessment of the toxicity of ash-loaded runoff from a recently burnt eucalypt plantation

Although wildfires are identified as an important source of polycyclic aromatic hydrocarbons (PAHs) and PAHs are well-known for their pernicious properties, the toxicity of runoff from recently burnt areas has received little research attention. This knowledge gap was addressed here through laboratory assays in which four aquatic species from distinct trophic levels were exposed to different dilutions of ash-loaded runoff. The runoff was collected in a recently burnt eucalypt stand in north-central Portugal on two occasions, immediately after the wildfire and about 1 year later. The total PAH load was about four times higher at the first than second sampling occasion (1194 vs. 352 ng l-1) but even the latter value was considerably higher than those reported by prior studies on burnt areas. In addition, the two runoff samples differed noticeably in PAH composition, with a clear predominance of naphthalene in the second sample. Both runoff samples produced significant inhibitory effects on the three species representing the lower trophic levels, that is, the bacteria Vibrio fischeri, the algae Pseudokirchneriella subcapitata and the macrophyte Lemna minor. The invertebrate Daphnia magna was not significantly affected but chronic tests are needed to discard the probable propagation of toxic effects from the lower trophic levels. Surprisingly, the runoff collected 1 year after the wildfire was the most toxic to V. fischeri, P. subcapitata and L. minor. Possibly, this was due to predominance of naphthalene in this sample. Surely, however, this demonstrated that detrimental off-site effects of wildfires are not necessarily limited to the immediate post-fire situation.publishe