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A system of two interacting photon modes, without constraints on the photon number, in the presence of a Kerr nonlinearity, exhibits BEC if the transfer amplitude is greater than the mode frequency. A symmetry-breaking field (SBF) can be introduced by taking into account a classical electron current. The ground state, in the limit of small nonlinearity, becomes a squeezed state, and thus the modes become entangled. The smaller is the SBF, the greater is entanglement. Superfluid-like behavior is observed in the study of entanglement growth from an initial coherent state, since in the short-time range the growth does not depend on the SBF amplitude, and on the initial state amplitude. On the other hand, the latter is the only parameter which determines entanglement in the absence of the SBF.

We apply the Dynamical Mean Field Theory to the problem of charge ordering. In this framework we solve the Holstein model for electrons interacting with classical phonons in the case of a bipartite lattice. In the normal state as well as in the Charge Density Wave (CDW) state the existence of polarons, i.e. electrons strongly coupled to local lattice deformation, is associated to the qualitative properties of the Lattice Polarization Distribution Function (LPDF). Properties of the CDW ordered state are qualitatively different in weak and strong coupling. We investigate the cross-over from weak coupling CDW behavior, characterized by a single peak LPDF in each sub-lattice centered on the sub-lattice average polarization, the strong coupling CDW regime which is characterised by a double peak non symmetric LPDF in each sub-lattice. The secondary peak is centered on the average polarization of the other sub-lattice indicating a certain amount of defects in the ordered state. This regime can be interpreted as that of a CDW phase resulting from the spatial ordering of preexisting randomly distributed polarons. The CDW critical temperature exhibits a maximum in the normal-to-polaron crossover region.

Abstract.: A system of two interacting photon modes, without constraints on the photon number, in the presence of a Kerr nonlinearity, exhibits BEC if the transfer amplitude is greater than the mode frequency. A symmetry-breaking field (SBF) can be introduced by taking into account a classical electron current. The ground state, in the limit of small nonlinearity, becomes a squeezed state, and thus the modes become entangled. The smaller is the SBF, the greater is entanglement. Superfluid-like behavior is observed in the study of entanglement growth from an initial coherent state, since in the short-time range the growth does not depend on the SBF amplitude, and on the initial state amplitude. On the other hand, the latter is the only parameter which determines entanglement in the absence of the SBF.

A system of two interacting photon modes, without constraints on the photon number, in the presence of a Kerr nonlinearity, exhibits BEC if the transfer amplitude is greater than the mode frequency. A symmetry-breaking field (SBF) can be introduced by taking into account a classical electron current. The ground state, in the limit of small nonlinearity, becomes a squeezed state, and thus the modes become entangled. The smaller is the SBF, the greater is entanglement. Superfluid-like behavior is observed in the study of entanglement growth from an initial coherent state, since in the short-time range the growth does not depend on the SBF amplitude, and on the initial state amplitude. On the other hand, the latter is the only parameter which determines entanglement in the absence of the SBF.

Abstract:  Callus induction, somatic embryogenesis and plant regeneration were obtained in six different citrus species [Citrus deliciosa Ten. (cv 'Avana'), C.limon (L.) Burm. (cv 'Berna'), C.madurensis Lour. (cv 'CNR P9'), C.medica L. (cv 'Cedro di Trabia'), C.tardiva Hort. ex Tan. (cv 'CNR P6'), C.sinensis (L.) Osb. (cv 'Ugdulena 7')] from cultures of pistil transverse thin cell layer explants [(t)TCL]. Explants were cultured on three different media: the nutrients and vitamins of Murashige and Skoog medium alone (MS) or MS supplemented with either 500 mg l–1 malt extract (MS I) or 500 mg l–1 malt extract and 13.3 μM 6-benzylaminopurine (MS II). Sucrose (146 mM) was used as the carbon source. Somatic embryos were visible 2–5 months after culture initiation. The different genotypes showed a different embryogenic frequency from stigma, style and ovary (t)TCL explants. All of the cultivars regenerated somatic embryos. Percentages of style (t)TCL explants producing somatic embryos ranged from 0% (C.deliciosa, C.madurensis, C.sinensis and C.tardiva on the three different media) to 5.2% (C.limon on MS II). Embryo formation in stigma (t)TCL explants ranged from 0% (C.madurensis on MS and MS I, C.sinensis on MS, C.deliciosa and C.tardiva on the three different media) to 42.4% (C.limon on MS II). Embryo formation in ovary (t)TCL explants ranged from 0% (C.deliciosa on MS, C.limon, C.medica, and C.sinensis on the three different media) to 9.3% (C.tardiva on MS I). After about 12 weeks somatic embryos developed into plantlets at a high frequency.

We study the fluctuations in the Malthus-Verhulst model of population dynamics in the vicinity of the instability point. We introduce a representation in terms of an-dimensional simple stochastic process, wherenis an integer related to the rate parameters of the model. We are thus able to obtain the transient behaviour for the decay from an unstable state by means of the quasi-deterministic approximation. Forn=1 and 2 we recover the well-known case of a double-well potential and the single-mode laser, respectively. We show that it is also possible to perform an analytic continuation of the results for any noninteger positiven.

We show that the problem of the decay from an unstable state can be approached by means of a systematic expansion which directly approximates the trajectories associated with the stochastic process. The first step of the expansion is a quasi-deterministic theory (QDT) which gives good results when far from the critical point and is valid only for the early times when approaching it. In the latter case the successive terms allow the description of the behavior for intermediate times and close to the steady state. The method is illustrated in the case of a symmetric double well potential and compared with the results of a direct computer simulation of the stochastic process.

Fricke-agarose gels have elicited much interest in the field of radiation dosimetry, as tissue-equivalent dosemeters. Magnetic resonance (MR) relaxation rates are measured for dose reconstruction. A major problem of Fricke-agarose gels is the diffusion of the ferric ions formed after irradiation. Knowledge of the diffusion coefficient of ferric ions may be necessary. Xylene orange, a dye that specifically chelates ferric ions, was added to the Fricke gel system to reduce ion diffusion and, as the binding gives a coloured complex, to allow optical detection of ferric ions. Diffusion of ferric ions in two dimensions and time evolution of ion concentration were evaluated. MR images were obtained at different times after irradiation. Ferric ion distribution, the corresponding images and the doses at different times after irradiation were reconstructed taking into account the calculated diffusion coefficients. Diffusion was then estimated by means of two different optical methods. The agreement obtained supports the reliability of the MRI method and of the model.