Projection of relativistically moving objects on a two-dimensional plane, the `train' paradox and the visibility of the Lorentz contraction

Although many papers have appeared on the theory of photographing relativistically moving objects, pioneered by the classic work of Penrose and Terrell, three problems remain outstanding. (1) There does not seem to exist a general formula which gives the projection of a relativistically moving object, applicable to any object no matter how complicated, on a two-dimensional plane in conformity with Terrell's observation. (2) No resolution seems to have been provided for the associated so-called `train' paradox. (3) No analytical demonstration seems to have been offered on how the Lorentz contraction may be actually detected on a photograph. This paper addresses all of these three problems. The analysis does not require any more than trigonometry and elementary differentiation.Comment: LaTeX, 14 pages, 6 figures, misprint correcte

Functional treatment of quantum scattering via the dynamical principle

A careful functional treatment of quantum scattering is given using Schwinger's dynamical principle which involves a functional differentiation operation applied to a generating functional written in closed form. For long range interactions, such as for the Coulomb one, it is shown that this expression may be used to obtain explicitly the asymptotic "free" modified Green function near the energy shell.Comment: 7 page

Non-noble electrocatalysts for alkaline fuel cells

The doping of solid phase precursors followed by pyrolysis or the copyrolysis of gas phase precursors has allowed us to produce catalysts with good activity toward oxygen reduction. Efforts are currently underway to better understand the reasons for the catalytic activity of the bulk doped catalysts with a view toward further improving their activity

Culture, Power and Poetry in Shiraz

Culture is a key word in contemporary Iran, especially in relation to power. Developing a practice begun in the early nineties, several national and local institutions are investing in “cultural activities” as a neutralized ground for the construction of citizens. This process intersects with poetry, which has a great power of recognition and is hegemonic well beyond the state: while on one hand poetry seems to offer expressive possibilities otherwise unavailable, on the other it is in fact an effective modality of power

Spin Correlations in e+e−e^{+}e^{-} Pair Creation by Two-Photons and Entanglement in QED

Spin correlations of $e^{+}e^{-}$ pair productions of two colliding photons are investigated and explicit expressions for their corresponding probabilities are derived and found to be \textit{energy} (speed) dependent, for initially \textit{linearly} and \textit{circularly polarized} photons, different from those obtained by simply combining the spins of the relevant particles, for initially \textit{polarized} photons. These expressions also depend on the angles of spin of $e^{+}$ (and/or of $e^{-}$), for initially {\it linearly polarized} photons, but not for {\it circularly polarized} photons, as a function of the energy. It is remarkable that these explicit results obtained from quantum field theory show a clear violation of Bell's inequality of Local Hidden Variables theories at all {\it energies} beyond that of the threshold one for particle production, in support of quantum field theory in the relativistic regime. We hope that our explicit expression will lead to experiments, of the type described in the bulk of this paper, which can monitor energy (and speed) in polarization correlation experiments.Comment: 12 pages, 4 figure

Action Principle and Algebraic Approach to Gauge Transformations in Gauge Theories

The action principle is used to derive, by an entirely algebraic approach, gauge transformations of the full vacuum-to-vacuum transition amplitude (generating functional) from the Coulomb gauge to arbitrary covariant gauges and in turn to the celebrated Fock-Schwinger (FS) gauge for the abelian (QED) gauge theory without recourse to path integrals or to commutation rules and without making use of delta functionals. The interest in the FS gauge, in particular, is that it leads to Faddeev-Popov ghosts-free non-abelian gauge theories. This method is expected to be applicable to non-abelian gauge theories including supersymmetric ones.Comment: LaTeX, 12 pages, Corrected typo