Emergence of linear wave segments and predictable traits in saturated nonlinear media

We find the key behind the existence traits of asymptotic saturated nonlinear optical solitons in the emergence of linear wave segments. These traits, produced by the progressive relegation of nonlinear dynamics to wave tails, allow a direct and versatile analytical prediction of self-trapping existence conditions and simple soliton scaling laws, which we confirm experimentally in saturated-Kerr self-trapping observed in photorefractives. This approach provides the means to correctly evaluate beam tails in the saturated regime, which is instrumental in the prediction of soliton interaction forces.     

Characterization of chaotic maps using the permutation Bandt-Pompe probability distribution

By appealing to a long list of different nonlinear maps we review the characterization of time series arising from chaotic maps. The main tool for this characterization is the permutation Bandt-Pompe probability distribution function. We focus attention on both local and global characteristics of the components of this probability distribution function. We show that forbidden ordinal patterns (local quantifiers) exhibit an exponential growth for pattern-length range 3 ≤ D ≤ 8, in the case of finite time series data. Indeed, there is a minimum D _min-value such that forbidden patterns cannot appear for D < D _min. The system’s localization in an entropy-complexity plane (global quantifier) displays typical specific features associated with its dynamics’ nature. We conclude that a more “robust” distinction between deterministic and stochastic dynamics is achieved via the present time series’ treatment based on the global characteristics of the permutation Bandt-Pompe probability distribution function.     

XAS analysis of iron and palladium bonded to a polysaccharide produced anaerobically by a strain of Klebsiella oxytoca

Klebsiella oxytoca BAS‐10 ferments citrate to acetic acid and CO₂, and secretes a specific exopolysaccharide (EPS), which is able to bind different metallic species. These biomaterials may be used for different biotechnological purposes, including applications as innovative green biogenerated catalysts. In production of biogenerated Pd species, the Fe(III) as ferric citrate is added to anaerobic culture of K. oxytoca BAS‐10, in the presence of palladium species, to increase the EPS secretion and improve Pd‐EPS yield. In this process, bi‐metallic (FePd‐EPS) biomaterials were produced for the first time. The morphology of bi‐metallic EPS, and the chemical state of the two metals in the FePd‐EPS, are investigated by transmission electron microscopy, Fourier transform infra‐red spectroscopy, micro‐X‐ray fluorescence, and X‐ray absorption spectroscopy methods (XANES and EXAFS), and compared with mono‐metallic Pd‐EPS and Fe‐EPS complexes. Iron in FePd‐EPS is in the mineralized form of iron oxides/hydroxides, predominantly in the form of Fe³⁺, with a small amount of Fe²⁺ in the structure, most probably a mixture of different nano‐crystalline iron oxides and hydroxides, as in mono‐metallic Fe‐EPS. Palladium is found as Pd(0) in the form of metallic nanoparticles with face‐centred cubic structure in both bi‐metallic (FePd‐EPS) and mono‐metallic (Pd‐EPS) species. In bi‐metallic species, Pd and Fe nanoparticles agglomerate in larger clusters, but they remain spatially separated. The catalytic ability of bi‐metallic species (FePd‐EPS) in a hydrodechlorination reaction is improved in comparison with mono‐metallic Pd‐EPS.     

Drug-anaesthetic interaction in phMRI: the case of the psychotomimetic agent phencyclidine

Pharmacological magnetic resonance imaging (phMRI) provides a powerful means to map the effects of drugs on brain activity, with important applications in pharmacological research. However, phMRI studies in preclinical species are often conducted under general anaesthesia as a means to avoid head motion and to minimise the stress induced by the procedure. Under these conditions, the phMRI response to the drug of interest may be affected by interactions with the anaesthetic agent, with consequences for the interpretation of the data. Here, we have investigated the phMRI response to phencyclidine (PCP), an NMDA receptor blocker, in the halothane-anaesthetised rat for varying levels of anaesthesia and different PCP challenge doses. PCP induces psychotic-like symptoms in humans and laboratory animals and is widely applied as a pharmacological model of schizophrenia. However, PCP possesses anaesthetic properties per se, and its interactions with halothane might result in significant effects on the phMRI activation patterns. We observed two qualitatively different patterns of phMRI response. At 0.5 mg/kg iv PCP and 0.8% halothane maintenance anaesthesia, the lowest doses explored, an activation of discrete cortico-limbo-thalamic structures was observed, consistent with neuroimaging studies in humans and 2-deoxyglucose functional mapping in conscious animal models. However, higher anaesthetic concentrations or higher PCP challenge doses resulted in complete abolition of the positive response and in a widespread cortical deactivation (negative response). In the intermediate regime, we observed a dichotomic behaviour, with individual subjects showing one pattern or the other. These findings indicate a dose-dependent drug-anaesthetic interaction, with a complete reversal of the effects of PCP at higher challenge doses or HT concentrations.     

Organic film thickness influence on the bias stress instability in?sexithiophene field effect transistors

In this paper, the dynamics of bias stress phenomenon in Sexithiophene (T6) Field Effect Transistors (FETs) has been investigated. T6 FETs have been fabricated by vacuum depositing films with thickness from 10 to 130 nm on Si/SiO₂ substrates. After the T6 film structural analysis by X-ray diffraction and the FET electrical investigation focused on carrier mobility evaluation, bias stress instability parameters have been estimated and discussed in the context of existing models. By increasing the film thickness, a clear correlation between the stress parameters and the structural properties of the organic layer has been highlighted. Conversely, the mobility values as a result are found to be almost thickness independent.     

Chaotic behavior in nonlinear Hamiltonian systems and equilibrium statistical mechanics

The relation between chaotic dynamics of nonlinear Hamiltonian systems and equilibrium statistical mechanics in its canonical ensemble formulation has been investigated for two different nonlinear Hamiltonian systems. We have compared time averages obtained by means of numerical simulations of molecular dynamics type with analytically computed ensemble averages. The numerical simulation of the dynamic counterpart of the canonical ensemble is obtained by considering the behavior of a small part of a given system, described by a microcanonical ensemble, in order to have fluctuations of the energy of the subsystem. The results for the Fermi-Pasta-Ulam model (i.e., a one-dimensional anharmonic solid) show a substantial agreement between time and ensemble averages independent of the degree of stochasticity of the dynamics. On the other hand, a very different behavior is observed for a chain of weakly coupled rotators, where linear exchange effects are absent. In the high-temperature limit (weak coupling) we have a strong disagreement between time and ensemble averages for the specific heat even if the dynamics is chaotic. This behavior is related to the presence of spatially localized chaos, which prevents the complete filling of the accessible phase space of the system. Localized chaos is detected by the distribution of all the characteristic Liapunov exponents.