Hamiltonian for a particle in a magnetic field on a curved surface in orthogonal curvilinear coordinates

The Schr\"odinger Hamiltonian of a spin zero particle as well as the Pauli Hamiltonian with spin-orbit coupling included of a spin one-half particle in electromagnetic fields that are confined to a curved surface embedded in a three-dimensional space spanned by a general Orthogonal Curvilinear Coordinate (OCC) are constructed. A new approach, based on the physical argument that upon squeezing the particle to the surface by a potential, then it is the physical gauge-covariant kinematical momentum operator (velocity operator) transverse to the surface that should be dropped from the Hamiltonian(s). In both cases,the resulting Hermitian gauge-invariant Hamiltonian on the surface is free from any reference to the component of the vector potential transverse to the surface, and the approach is completely gauge-independent. In particular, for the Pauli Hamiltonian these results are obtained exactly without any further assumptions or approximations. Explicit covariant plug-and-play formulae for the Schr\"odinger Hamiltonians on the surfaces of a cylinder, a sphere and a torus are derived.Comment: 7 pages, 1 figure, references adde

Hermitian spin-orbit Hamiltonians on a surface in orthogonal curvilinear coordinates: a new practical approach

The Hermitian Hamiltonian of a spin one-half particle with spin-orbit coupling (SOC) confined to a surface that is embedded in a three-dimensional space spanned by a general Orthogonal Curvilinear Coordinate (OCC) is constructed. A gauge field formalism, where the SOC is expressed as a non-Abelian $SU(2)$ gauge field is used. A new practical approach, based on the physical argument that upon confining the particle to the surface by a potential, then it is the physical Hermitian momentum operator transverse to the surface, rather than just the derivative with respect to the transverse coordinate that should be dropped from the Hamiltonian.Doing so, it is shown that the Hermitian Hamiltonian for SOC is obtained with the geometric potential and the geometric kinetic energy terms emerging naturally. The geometric potential is shown to represent a coupling between the transverse component of the gauge field and the mean curvature of the surface that replaces the coupling between the transverse momentum and the gauge field. The most general Hermitian Hamiltonian with linear SOC on a general surface embedded in any 3D OCC system is reported. Explicit plug-and-play formulae for this Hamiltonian on the surfaces of a cylinder, a sphere and a torus are given. The formalism is applied to the Rashba SOC in three dimensions (3D RSOC) and the explicit expressions for the surface Hamiltonians on these three geometries are worked out.Comment: 8 pages, 1 figur

Mode of infection and spread of <i>Vibrio anguillarum</i> in turbot <i>Scophthalmus maximus</i> larvae after oral challenge through life feed

The infection route of the marine fish pathogen Vibrio anguillarum was studied after oral challenge of the juvenile turbot Scophthalmus maximus L. through a life feed. Artemia nauplii were incubated in a suspension of V. anguillarum cells, and subsequently fed twice to the fish. All challenged fish died within 4d after the first challenge, while no mortality occurred in the non-challenged controls. The results of an immunohistochemical examination of the sectioned fish samples clearly demonstrated that V. anguillarum cells were ingested by the Artemia and that the latter were ingested by the fish. Bacteria were released from the Artemia mainly in the anterior part of the intestine. Most challenged fish started to show disease signs 24h after the second challenge and died 2d later. A histopathological analysis of moribund fish showed the development of septicaemia. Moreover, the sequential sampling, allowed the reconstruction of the infection route after oral challenge. Our results show that V. anguillarum was transported through the intestinal epithelium by endocytosis, after which the bacterium was released in the lamina propria. From there the bacterium was transported by the blood to the different organs, eventually leading the septicaemia and mortality

L'exploitation des algues rouges Gelidium dans la région d’El-Jadida : aspects socio-économiques et perspectives

L’algue rouge Gelidium forme le long de la côte atlantique marocaine des champs relativement importants. La majeure partie des algues récoltée et fournie à l’industrie de transformation provient de la zone maritime d’El Jadida-Jorf Lasfar. L’évaluation de l’évolution de la production d’algues rouges Gelidium sesquipedale dans 16 stations de la région d’El-Jadida a été entreprise dans le but d’élucider sa variation spatio-temporelle durant deux années d’étude 2011 et 2012. Les résultats montrent une variation de la production entre les différentes stations durant les deux années d’étude. Les productions enregistrées en 2011 dans les deux stations Sidi Abed (3086 tonnes d’algues humides) et Moulay Abdellah (5276 tonnes d’algues humides) sont les plus importantes, par contre la station de Sidi Bouzid a reconnu une substitution de l’espèce étudiée par l’Halopithys incurvus. En 2012, la production enregistrée dans la station de Sidi Abed reste aux alentours de 3281 tonnes d’algues humides. Cependant, celle enregistrée dans Moulay Abdelleah a trop diminué (2632 tonnes d’algues humides). L’effort de pêche pratiqué dans les stations de la zone étudiée signifie le nombre de jours de la collecte des algues pendant seulement les campagnes autorisées pour la collecte des algues marines. Les  résultats obtenus montrent qu’il y a une corrélation entre l’évolution de la production (tonnes) et l’effort de pêche. Ceci signifié que l’effort pratiqué pour la collecte de G. sesquipedale influence négativement les champsd’algues présents dans la zone d’étude. La classe d'âge comprise entre 19–35 ans représente la part la plus importante des enquêtés, suivieensuite par la classe 35–51 et la classe des moins de 18 ans. Cela traduit le potentiel humain important dans la communauté qui intervient dans la collecte des algues rouges. La classe active est dominante. Enfin, on note qu’il y a une surexploitation des champs d’algues naturels par braconnage ou par le non respect des quantités déterminées par quota nationale.Mots-clés : algue rouge, Gelidium sesquipedale, production, exploitation, effort de pêche, surexploitation