Rotating light, OAM paradox and relativistic complex scalar field

Recent studies show that the angular momentum, both spin and orbital, of rotating light beams possesses counter-intuitive characteristics. We present a new approach to the question of orbital angular momentum of light based on the complex massless scalar field representation of light. The covariant equation for the scalar field is treated in rotating system using the general relativistic framework. First we show the equivalence of the U(1) gauge current for the scalar field with the Poynting vector continuity equation for paraxial light, and then apply the formalism to the calculation of the orbital angular momentum of rotating light beams. If the difference between the co-, contra-, and physical quantities is properly accounted for there does not result any paradox in the orbital angular momentum of rotating light. An artificial analogue of the paradoxical situation could be constructed but it is wrong within the present formalism. It is shown that the orbital angular momentum of rotating beam comprising of modes with opposite azimuthal indices corresponds to that of rigid rotation. A short review on the electromagnetism in noninertial systems is presented to motivate a fully covariant Maxwell field approach in rotating system to address the rotating light phenomenon.Comment: No figure

On the relation of Thomas rotation and angular velocity of reference frames

In the extensive literature dealing with the relativistic phenomenon of Thomas rotation several methods have been developed for calculating the Thomas rotation angle of a gyroscope along a circular world line. One of the most appealing concepts, introduced in \cite{rindler}, is to consider a rotating reference frame co-moving with the gyroscope, and relate the precession of the gyroscope to the angular velocity of the reference frame. A recent paper \cite{herrera}, however, applies this principle to three different co-moving rotating reference frames and arrives at three different Thomas rotation angles. The reason for this apparent paradox is that the principle of \cite{rindler} is used for a situation to which it does not apply. In this paper we rigorously examine the theoretical background and limitations of applicability of the principle of \cite{rindler}. Along the way we also establish some general properties of {\it rotating reference frames}, which may be of independent interest.Comment: 14 pages, 2 figure

Les obstacles à la réalisation du cycle vital des poissons

Les pressions physiques et chimiques d'origine naturelle ou artificielles s'exerçant sur les cours d'eau limitent le développement d'un nombre important d'espèces particulièrement parmi les migrateurs amphibiotiques. Les différents types d'atteinte au milieu aquatique entraînant la raréfaction de ces espèces maintenant protégées au titre de la loi sur la protection de la nature sont illustrées par quelques exemples. Le déroulement du cycle vital des diverses espèces de poissons comprend plusieurs phases : reproduction et développement embryonnaire, développement juvénile, développement adulte et plusieurs fonctions (reproduction, alimentation, repos) généralement situées en des sites différenciés. L'accomplissement du cycle complet est tributaire de l'adéquation de l'environnement aux besoins des espèces au cours de ces différentes phases (habitat et qualité des eaux) et des possibilités de circulation entre les sites correspondantes