Functional Fe–Pd nanomaterials synthesized by template-assisted methods

In this work, we highlight our recent progress in the synthesis and characterization of functional nanomaterials based on Fe–Pd ferromagnetic alloys by means of template-assisted deposition techniques employing highly ordered nanoporous alumina membranes, such as ordered arrays of nanowires and antidots thin films. Special attention is paid on their basic magnetic properties, such as coercivity, remanence and magnetic anisotropy, and their dependence on the microstructure and morphological parameters of the ordered arrays.     

Random replicators with high-order interactions

We use tools of the equilibrium statistical mechanics of disordered systems to study analytically the statistical properties of an ecosystem composed of N species interacting via random mutual interactions, as well as via deterministic self-interactions of order p>/=2. We show that the main effect of increasing the order of the interactions among the species is to make the system less competitive, in the sense that the fraction of extinct species is greatly reduced. In addition, we find that for p>2 there is a threshold value which gives a lower bound to the concentration of the surviving species, preventing then the existence of rare species and, consequently, increasing the robustness of the ecosystem to external perturbations.     

Bursting as a source for predictability in biological neural network activity

The role of bursting as a unit of neural information has received considerable support in the recent years. Experimental evidence shows that in many different neural systems, e.g. visual cortex or hippocampus, bursting is essential for coding and processing. We have recently demonstrated (Menendez de la Prida et al., 1996) the spontaneous presence of bursts in in vitro hippocampal slices from newborn animals, providing a good system to investigate bursting dynamics in physiological conditions. Here we analyze the interspike intervals (ISIs) of five intracellularly recorded cells from immature hippocampal networks. First, we test the time series against Poisson processes, typical of pure random behavior, using the Kolmogorov-Smirnov test. Only 2/5 records strongly deviate from Poisson process. Nonlinear diction tests are then applied to compare original series with its Gaussian-scaled random phase surrogates and signs of short time predictability are observed (1/5). This predictability is originated by the intrinsic structure of bursts, in an otherwise purely random process, and can be removed completely by eliminating the bursts from the original time series. Here we introduce this method of eliminating bursts to get insight into the nonlinear dynamics of firing. Also the interburst intervals are indistinguishable from pure noise. The analysis of unstable periodicities within the bursts in the original ISIs shows that signs of nonlinearities can be statistically differentiated from their surrogate realizations (Pierson-Moss method). We discuss the computational implication of these results.     

FePd melt-spun ribbons and nanowires: Fabrication and magneto-structural properties

Fe-30%Pd alloys in ribbon and nanowire geometry have been prepared. Ribbon samples were produced by the melt-spinning technique in the Ar environment. FePd nanowires, having about 35 nm in diameter, 105 nm inter-nanowires distance and around 4 μm in length, were synthesized into nanoporous anodic alumina membranes as templates. Energy dispersive X-ray microanalysis of ribbons shows an average atomic composition of Fe (73.2%) and Pd (26.8%). The X-ray diffraction at RT analysis was performed on both surfaces, free and wheel side, of the melt-spun ribbon. It shows the coexistence of two phases: fct and bct FePd, but with differences between both surfaces consisting the existence of Fe oxides (Fe₂O₃ and Fe₃O₄) and a textured 200 reflection in the free side. Heating and cooling thermomagnetic curves exhibit a reversible behaviour from RT to 720 K, but around 770 K a clear irreversible transformation takes place.     

Magnetoimpedance effect in Nanoperm alloys

The influence of isothermal annealing (1 h at 600 °C in Ar atmosphere) on the soft magnetic properties and magnetoimpedance (MI) effect has been studied in ribbons of the following Nanoperm alloys: Fe₉₁Zr₇B₂, Fe₈₈Zr₈B₄, Fe₈₇Zr₆B₆Cu₁ and Fe₈₀Zr₁₀B₁₀. A maximum MI ratio of about 27% was measured for the nanocrystalline alloy Fe₈₇Zr₆B₆Cu₁ at a driving frequency of 0.2 MHz. The thermal annealing led to magnetic softening for this alloy, while a hardening is observed for the Fe₈₀Zr₁₀B₁₀ alloy.     

Maturation of auditory temporal integration and inhibition assessed with event-related potentials (ERPs)

Background

We examined development of auditory temporal integration and inhibition by assessing electrophysiological responses to tone pairs separated by interstimulus intervals (ISIs) of 25, 50, 100, 200, 400, and 800 ms in 28 children aged 7 to 9 years, and 15 adults.

Results

In adults a distinct neural response was elicited to tones presented at ISIs of 25 ms or longer, whereas in children this was only seen in response to tones presented at ISIs above 100 ms. In adults, late N1 amplitude was larger for the second tone of the tone pair when separated by ISIs as short as 100 ms, consistent with the perceptual integration of successive stimuli within the temporal window of integration. In contrast, children showed enhanced negativity only when tone pairs were separated by ISIs of 200 ms. In children, the amplitude of the P1 component was attenuated at ISIs below 200 ms, consistent with a refractory process.

Conclusions

These results indicate that adults integrate sequential auditory information into smaller temporal segments than children. These results suggest that there are marked maturational changes from childhood to adulthood in the perceptual processes underpinning the grouping of incoming auditory sensory information, and that electrophysiological measures provide a sensitive, non-invasive method allowing further examination of these changes.     

Electrolyte influence on the anodic synthesis of TiO2 nanotube arrays

We report on the structural and morphological features of self-aligned titanium oxide nanotube arrays grown by electrochemical anodization in different electrolytes comprising aqueous acidic media or organic neutral media, and at several potentiostatic voltages ranging between 12 and 60 V. The results show an improvement in the self-alignment of the nanotube arrays and an increase of about 10,000% in the nanotubes length obtained by anodization performed with NH₄F in ethylene glycol electrolyte, respect to the case obtained employing the aqueous electrolytes.     

Fast domain wall dynamics in amorphous glass-coated microwires

Here we report on the domain wall dynamics in amorphous glass-coated FeCuNbSiB microwires measured in the temperature range from 77 up to 400 K. At low temperatures below 200 K, the domain wall velocity is proportional to the applied magnetic field. At temperatures above 200 K, two regions have been found: one with low domain wall mobility at low fields and another one with high domain wall mobility at high fields. The different regions of the domain wall dynamics are treated in terms of the change of the domain wall configuration from transversal to vortex one. Moreover, non-linear regime is shown at low fields at the temperature 373 K as a result of the domain wall interaction with the local defects.     

Ionic transport across tailored nanoporous anodic alumina membranes

Monodispersed silica particles with bimodal size distribution were successfully prepared through adding an ethanol (EtOH) solution containing tetraethylorthosilicate (TEOS) dropwise into an ammonia EtOH solution at a constant low rate. The effects of the reaction parameters such as ammonia/ethanol ratio, feeding rate of TEOS solution, reaction temperature, and time on the size and size distribution of the as-obtained particles were investigated. Based on these phenomena, a modified LaMer model of nucleation and growth mechanism was proposed to reasonably explain the formation of the as-obtained silica particles with bimodal size distribution. The as-prepared monodispersed silica particles with bimodal size distribution can be directly fabricated into binary colloidal crystals with small particles surrounding large particles by evaporation-induced cooperative self-assembly. This suggests that the method reported here provides a straightforward and effective route to the in situ fabrication of novel binary colloidal crystals and their replicated patterns in one reaction system.