On a Statistical Approach to Phase Synchronization in Some Map-Based Neural Chaotic Spiking–Bursting Models

Radiophysics and Quantum Electronics - Under coupling, a large group of chaotic spiking–bursting oscillating neurons can undergo neuronal regularization. This aspect has been studied in...     

Strain-induced modification of magnetic structure and new magnetic phases in rare-earth epitaxial films

Rare earths exhibit complex magnetic phase diagrams resulting from the competition between various contributions to the magnetic energy: exchange, anisotropy and magnetostriction. The epitaxy of a rare-earth film on a substrate induces (i) a clamping to the substrate and (ii) pseudomorphic strains. Both these effects are shown to lead to modifications of the magnetic properties in (0 0 1)Dy, (0 0 1)Tb and (1 1 0)Eu films. In Dy and Tb films, spectacular variations of the Curie temperature have been evidenced. Additionally, Tb films exhibit a new large wavelength magnetic modulation. In Eu films, one of the helical magnetic domains disappears at low temperature whereas the propagation vectors of the other helices are tilted. The link between structural and magnetic properties is underlined via magnetoelastic models. Moreover, molecular beam epitaxy permits the growth of Sm in a metastable dhcp phase. The magnetic structure of dhcp Sm has been elucidated for the first time. In this review, neutron scattering is shown to be a powerful technique to reveal the magnetic structures of rare-earth films.     

Training effect in an exchange bias system: the role of interfacial domain walls

Polarized neutron reflectivity (PNR) is used to obtain the magnetic depth profile of an antiferromagnetically coupled ferrimagnetic/ferrimagnetic bilayer, Gd40Fe60/Tb12Fe88. This system shows a transition from positive to negative exchange bias field H(E) as the cooling field H(cf) is increased from small to large positive value. It also exhibits training behavior upon field cycling which affects H(E) and the coercive field H(C). From the PNR measurements at room temperature and at 15 K, we confirm that the magnetic configuration inside the TbFe layer is frozen when the sample is cooled in various H(cf). The thickness and pitch of the magnetic twist inside the TbFe layer depend on H(cf) and give rise to the observed differences in the bias field. Irreversible reorganization of the TbFe magnetization at the interface occurs upon GdFe magnetization reversal and is found to explain the training effect as well as the overall reduction in coercivity.     

Effect of Pr-Ca substitution on the transport and magnetic behavior of LaMnO3 perovskite

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO₃ perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La_1−2x Pr _x Ca _x )MnO₃ (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T _c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.     

Automated DBS Extraction Prior to Hilic/RP LC–MS/MS Target Screening of Drugs

This article describes a rapid LC–MS/MS target screening method based on an automated extraction of 5 μL dried blood spots (DBS), two 5 min chromatographic runs on orthogonal phase columns (RP and Hilic) and a data dependent acquisition (DDA) of product ions spectra for the reliable identification of the detected compounds. The extraction step was performed in 2 min by using the LC autosampler itself in 96-well plates. This procedure was evaluated using 22 model compounds frequently encountered in forensic investigations, i.e., cocaine, benzodiazepines, amphetamines, opioids, antidepressants and antipsychotics. These investigations showed that even if the extraction step was reduced to a minimum, the extraction recoveries were satisfactory (median value of 40 %) and allowed for the detection of the model compounds in their therapeutic ranges, with the exception of morphine. Moreover, the use of two different chromatographic columns broadened the number of screening targets to those that behaved poorly under RP conditions, such as amphetamines or glucuronides, while keeping chromatographic gradients very short. This procedure was applied to 34 authentic post-mortem cases. It allowed the detection of 89 % of the compounds that were quantified in the routine procedures and the formal identification of 77 % of the compounds using their product ions spectra. These results were considered more than satisfactory compared to routine screening alone (GC–MS and LC-DAD, 55 % compound identification). The method described in this article is therefore a powerful approach for a fast, reliable and efficient target screening of drugs in forensic and clinical investigations.     

Separation of iota-, kappa and lambda-carrageenans by capillary electrophoresis

The present study reports a novel method for the separation of the high-molecular-weight anionic polysaccharides, iota, kappa, and lambda carrageenans, in capillary electrophoresis (CE). Carrageenan samples are first derivatised with 9-aminopyrene-1,4,6-trisulfonic acid (APTS), separated in an ammonium acetate background electrolyte (BGE) and detected with laser-induced fluorescence (LIF). The effects of changes of instrumental parameters (temperature, injection mode, field strength) and the composition of the BGE (concentration and pH) are reported, and are explained in terms of the physical chemistry of the BGE and the biopolymers. Optimal separation conditions for kappa, iota, and lambda carrageenans, including an APTS internal standard, were found in a polyvinyl alcohol coated capillary with an ammonium acetate BGE of low concentration (25 mM) and moderate pH (8.0). This BGE gave the best reproducibility in tests on iota/kappa mixtures, with relative standard deviations (RSDs) in migration times and normalised peak areas (relative to the APTS internal standard) of less than 0.1% and 1%, respectively. Using this BGE at 50 degrees C and a voltage of 30 kV, all three carrageenan subtypes were separated in a run time of 3 min.     

Composition-controlled exchange bias training effect in FeCr/IrMn bilayers

For FeCr/IrMn bilayers, the exchange bias training effect and the magnetization reversal mechanism are correlated to each other and depend on the composition of the ferromagnetic layer. For high Fe contents, the asymmetric magnetization reversal is observed. During the training effect, both exchange field and coercivity decrease monotonically, suggesting a type I training effect. For low Fe contents, the domain wall depinning takes place for the two hysteresis loop branches. Only exchange field diminution happens in the training effect. The coercivity almost does not change in the process, corresponding to a type II training effect. It is suggested that the motion of antiferromagnetic spins is modified by the magnetization reversal mechanism in the ferromagnetic layer.