From Davydov solitons to decoherence-free subspaces: self-consistent propagation of coherent-product states

The self-consistent propagation of generalized $D_{1}$ [coherent-product] states and of a class of gaussian density matrix generalizations is examined, at both zero and finite-temperature, for arbitrary interactions between the localized lattice (electronic or vibronic) excitations and the phonon modes. It is shown that in all legitimate cases, the evolution of $D_{1}$ states reduces to the disentangled evolution of the component $D_{2}$ states. The self-consistency conditions for the latter amount to conditions for decoherence-free propagation, which complement the $D_{2}$ Davydov soliton equations in such a way as to lift the nonlinearity of the evolution for the on-site degrees of freedom. Although it cannot support Davydov solitons, the coherent-product ansatz does provide a wide class of exact density-matrix solutions for the joint evolution of the lattice and phonon bath in compatible systems. Included are solutions for initial states given as a product of a [largely arbitrary] lattice state and a thermal equilibrium state of the phonons. It is also shown that external pumping can produce self-consistent Frohlich-like effects. A few sample cases of coherent, albeit not solitonic, propagation are briefly discussed.Comment: revtex3, latex2e; 22 pages, no figs.; to appear in Phys.Rev.E (Nov.2001

Cutting efficiency evaluation of Quantec Series 2000 orifice openers with computed tomography (CT)

Introduction: Orifice openers or orifice shapers are used to shape the coronal part of the root canals during endodontic treatment. Objectives: The aim of this work was to analyse the cutting efficiency of Quantec Series 2000 system orifice shapers by means of computerised tomography (CT). Materials and methods: Mandibular molars were selected, preoperative CT was performed and the cross-sections and surface area of the root canals were measured. Following access opening and preparation of the coronal part of the canals with Quantec Series 2000 orifice shapers, a further CT was obtained of all the teeth, the previous measurements were repeated and the two sets of measurements were compared. Results: Although the canals suffered modifications due to the action of the instruments, they remained centred and retained their original morphology; the changes were greater in the most coronal part of the canals. Conclusions: the orifice shapers of the system under study kept the canals centred on their original position, so they do not present great aggressiveness during endodontic treatment; the canals that were initially the widest were those that showed the greatest modification; the CT system employed in the study showed itself to be an effective, noninvasive system for studying the changes that had taken place inside the root canals

The mediterranean biotypes of Tylenchulus semipenetrans in Spanish citrus orchards

Les capacités de reproduction de quatorze populations du nématode des citrus (#Tylenchulus semipenetrans$) collectées dans la principale zone de citriculture de l'Espagne ont été comparées sur oranger amer et citrange Carrizo. Toutes les populations ont été identifiées comme appartenant au biotype méditerranéen. La capacité de reproduction varie considérablement en fonction des populations. Le pouvoir infestant et le taux de reproduction des populations collectées dans la rhizosphère des porte-greffes citranges Troyer ou Carrizo sont plus élevés (P supérieur ou égal à 0,05) que ceux des populations collectées sur oranger amer. (Résumé d'auteur