Emulating complex business cycles by using an electronic analogue

Long run growth of the US national economic system, for example, reveals a strong oscillatory behavior due to complex interactions of aggregates. However, modelizations of such dynamics often assume that instability is the outcome of linear and additive cycles determined by exogenous shocks. In this work, a modelization of endogenous nonlinear and inseparable cycles is retained to explain the highly complex business cycle phenomenon. Bouali’s system is built to this scope. Its numerical simulations exhibit a rich repertoire of nonlinear dynamical phenomena, but this paper introduces its electronic implementation. The robust plug and play chaotic circuit is designed to be easily realized using standard components in a rigorous, fast and inexpensive way. We find that experimental results display periodicity, bifurcations and chaos that match with high accuracy the corresponding theoretical values.     

Recurrence-based detection of the hyperchaos-chaos transition in an electronic circuit

Some complex measures based on recurrence plots give evidence about hyperchaos-chaos transitions in coupled nonlinear systems [E. G. Souza et al., "Using recurrences to characterize the hyperchaos-chaos transition," Phys. Rev. E 78, 066206 (2008)]. In this paper, these measures are combined with a significance test based on twin surrogates to identify such a transition in a fourth-order Lorenz-like system, which is able to pass from a hyperchaotic to a chaotic behavior for increasing values of a single parameter. A circuit analog of the mathematical model has been designed and implemented and the robustness of the recurrence-based method on experimental data has been tested. In both the numerical and experimental cases, the combination of the recurrence measures and the significance test allows to clearly identify the hyperchaos-chaos transition.     

Chaotic behavior in noninteger-order cellular neural networks

In this paper, a simple system showing chaotic behavior is introduced. It is based on the well-known concept of cellular neural networks (CNNs), which have already given good results in generating complex dynamics. The peculiarity of the CNN model consists in the fact that it replaces the traditional first-order cell with a noninteger-order one. The introduction of the fractional cell, with a suitable choice of the coupling parameters, leads to the onset of chaos in a simple two-cell system. A theoretical approach, based on the harmonic balance theory, has been used to investigate the existence of chaos. A circuit realization of the proposed fractional two-cell chaotic CNN is reported and the corresponding strange attractor is also shown.     

Thermodynamic characterization of the melting of a series of polyesteramides

The changes in enthalpy, entropy and volume upon melting have been determined by dilatometric and differential scanning calorimetry measurements for four polyesteramides of the type:

$\text{-[-}\text{COφCONH(CH}{}_2\text{)}{}_{\mathrm{n}}\text{}\text{NHCOφCOO(CH}{}_2\text{)}{}_{\mathrm{m}}\text{}\text{O}\text{-]-}{}_{\mathrm{x}}$

with the following values for n and m; 6-6, 12-2, 12-6 and 12-12. The changes in each state function vary quite regularly with the number of CH₂ groups/repeating unit. A comparison is made between experimental data on the entropy of fusion and theoretical predictions. There is emphasis on the influence on the thermodynamics of melting of the rigidity of the -OCO-φ-CONH- residues and, in particular, of the persistence in the molten state of many interchain hydrogen bonds.     

Spin polarization at the NiMnSb/MgO(1 0 0) interface

The half-metallic NiMnSb alloy was tested as a possible fully polarized electrode in a magnetic tunnel junction. For this purpose, epitaxial NiMnSb(0 0 1) and NiMnSb/MgO(0 0 1) systems were grown by molecular beam epitaxy. Spin-polarized photoemission experiments using the synchrotron radiation at the ESRF were performed on both the uncovered NiMnSb(0 0 1) surface and on the NiMnSb/MgO(0 0 1) interface. Starting from a NiMnSb(0 0 1) uncovered surface presenting at room temperature a 40% polarization at the Fermi level measured in the whole Brillouin zone, this polarization was observed to dramatically decrease when a MgO(0 0 1) epitaxial barrier was grown on top of it. On the other hand, the X-ray absorption experiments clearly show some oxidization of Mn after growing the MgO layer. This behavior was confirmed by testing the electronic and chemical properties of a unique atomic plane of Mn grown on a Fe buffer layer, before and after growing a MgO layer on top of it.     

Preparation of molybdenum target by centrifugal method

The molybdenum targets of 2–10 mg/cm² have been prepared on Al and Ti backings by centrifugal sedimentation. The thickness and purity of the produced targets were analysed with Rutherford back scattering measurements, scanning electron microscope and energy dispersive spectrometry. Targets were requested for pilot studies of an alternative accelerator way of ^99mTc production. Targets were tested with deuteron beam of 20 MeV energy and 10 nA intensity. They were irradiated for 10 min and showed no damage what proofed the targets suitability for irradiation with a weak beam of light projectiles.     

Liquid chromatographic methods for the quantification of catecholamines and their metabolites in several biological samples—A review

The measurement of catecholamines and their metabolites in biological samples remains a current analytical challenge, in spite of the great diversity of methodologies that have been developed throughout the years. High-performance liquid chromatography is the standard method for their separation and quantification in biological samples, either coupled with electrochemical, fluorescence, chemiluminescence or mass spectrometry detection. This review summarizes the most important physicochemical properties of catecholamines, the wide panoply of sample preparation techniques and the main issues to consider during the development of chromatographic methods. The major difficulties encountered during the optimization of these procedures are related with the high tendency of catecholamines to oxidize and the very low quantities at which they exist in biological matrices. Herein, the most important aspects that ought to be considered during collection, treatment and storage of fluid and tissue samples intended for catecholamine analysis are underlined, the chromatographic conditions are compared and the technical advantages and limitations of each detection system are discussed.