Pilar Herrero

Electrodeposition of hydroxyapatite coatings in basic conditions

Hydroxyapatite films have been grown in this work by an electrodeposition method involving both physical and chemical processes and presenting several differences with respect to other reported works. Description of the coating formation is based on the evolution of current through the sample placed as positive electrode in the basic electrolyte. The characterisation of hydroxyapatite films is of special importance since the bioactive properties related to HAP have been directly identified with its specific composition (Ca/P ratio) and crystalline structure. This characterisation has been traditionally fulfilled by the use of XRD, FTIR and SEM. Results of a further characterisation of the coatings by TEM and SFM, additional to the analysis by XRD, FTIR and SEM, are presented. Interpretation and comparison of our results with those obtained by other electrodeposition methods lead to arguments in favour of a deposition produced directly from ionic species.

Synthesizing nanocrystalline LiMn2O4 by a combustion route

Nanocrystalline samples of lithium manganese oxide with cubic spinel structure have been prepared by combustion of reaction mixtures containing Li(I) and Mn(II) nitrates that operate as oxidisers, and sucrose that acts as fuel. The samples were characterised by X-ray diffraction, transmission electron microscopy, thermal analysis, and impedance and electrochemical measurements. The effect of the fuel content on the purity and morphology of the products was analysed. The samples as prepared showed small amounts of Mn2O3 and Mn3O4 as impurities, depending on the amount of sucrose used in the synthesis. Annealing at 700 °C led to single-phase cubic spinels. In these phases, the smallest average particle size (ca. 30 nm) corresponded to the sample obtained with a hyperstoichiometric amount of fuel. This sample showed the Li1.05Mn1.95O4 composition as deduced from the thermal and electrochemical data. No variation in conductivity associated with the cubic⇔orthorhombic phase transition was observed. The electrochemical behaviour as positive electrode showed good cyclability at high current densities (reversible capacity of 73 mAh g−1 at 2.46 mA cm−2).

Direct determination of grain sizes, lattice parameters, and mismatch of porous silicon

High-resolution transmission electron microscopy and digital image processing were used to investigate in detail the structure of porous silicon (PS). It was found that PS is composed of rounded Si nanocrystals with characteristic sizes between 21 and 80 A, embedded into an amorphous matrix and with no preferential orientation. We have determined that the size distribution of the nanocrystals can be fitted to a Gaussian distribution centered at 45.89 A. Furthermore, the structure of the individual Si grains was studied, which allowed us to determine that the interplanar distance varies from 3.17 to 3.41 A, with Gaussian distribution centered at 3.24 A. Finally, the lattice parameter of the individual Si grains that compose PS was also measured, showing a Gaussian distribution centered at 5.61 A. The origin of the structure of PS is also discussed.

Conductivity relaxation parameters of some Ag+ conducting tellurite glasses containing AgI or the (AgI)0.75 (T1I)0.25 eutectic mixture

Abstract The conductivity relaxation parameters of some Ag + conducting tellurite glasses containing either AgI or the (AgI) 0.75 -(T1I) 0.25 eutectic mixture have been determined from an analysis of ac conductivity data measured in a wide temperature range. Transport properties in these materials appear as due to an Ag + ion hopping mechanism. The stretched exponential function exp-( t /τ σ ) β has been used to describe the conductivity relaxation. The relaxation parameters have been investigated as a function of the AgI rate. The results obtained are shown to be in good agreement with the predictions of the Ngai coupling model. A correlation has been also established for the glasses investigated between the stretched exponent β of conductivity relaxation function with the decoupling index R τ ( T g ), proposed by Angell, where R τ ( T g ) is the τ s /τ σ ratio of the average structural and conductivity relaxation times at the glass transition temperature T g .

Detailed analysis of leucokinin-expressing neurons and their candidate functions in the Drosophila nervous system

The distribution of leucokinin (LK) neurons in the central nervous system (CNS) of Drosophila melanogaster was described by immunolabelling many years ago. However, no detailed underlying information of the input or output connections of their neurites was then available. Here, we provide a more accurate morphological description by employing a novel LK-specific GAL4 line that recapitulates LK expression. In order to analyse the possible afferent and efferent neural candidates of LK neurons, we used this lk-GAL4 line together with other CNS-Gal4 lines, combined with antisera against various neuropeptides or neurotransmitters. We found four kinds of LK neurons in the brain. (1) The lateral horn neurons connect the antennal glomerula to the mushroom bodies. (2) The suboesophageal neurons connect the gustatory receptors to the suboesophageal ganglia and ventral nerve cord. (3) The anterior neurons innervate the corpus cardiacum of the ring gland but LK expression is surprisingly not detectable from the third instar onwards in these neurons. (4) A set of abdominal ganglion neurons connect to the dorsal median tract in larvae and send their axons to a segmental muscle 8. Thus, the methods employed in our study can be used to identify individual neuropeptidergic neurons and thereby characterize functional cues or developmental transformations in their differentiation.

Morphological, optical and electrical characterization of antireflective porous silicon coatings for solar cells

Porous silicon (PS) layers are formed on multicrystalline silicon solar cells by chemically etching the emitter of these devices. Stain etched PS provides the simultaneous formation of a selective emitter and an antireflective layer. The optical behavior of the antireflective coating over the solar spectrum is determined, resulting in very low values of the reflectance. The variation of the topography, as well as the grain size of the PS and the metallic contacts before and after PS formation, is analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Furthermore, the electrical properties of both the emitter and the front metallic contacts are investigated. Finally, the effect of rapid thermal processing in nitrogen and oxygen atmospheres on the antireflective properties of the PS is studied.

Neurosecretory identity conferred by the apterous gene: Lateral horn leucokinin neurons in Drosophila

The LIM‐HD protein Apterous has been shown to regulate expression of the FMRFamide neuropeptide in Drosophila neurons (Benveniste et al. [ 1998 ] Development 125:4757–4765). To test whether Apterous has a broader role in controlling neurosecretory identity, we analyzed the expression of several neuropeptides in apterous (ap) mutants. We show that Apterous is necessary for expression of the Leucokinin neuropeptide in a pair of brain neurons located in the lateral horn region of the protocerebrum (LHLK neurons). ap null mutants are depleted of Leucokinin in these cells, whereas hypomorphic mutants show reduced Leucokinin expression. Other Leucokinin‐containing neurons are not affected by mutations in ap gene. Co‐expression of apterous and Leucokinin is observed exclusively in the LHLK neurons, from larval stages to adulthood. Rescue assays performed in null ap mutants, by expressing Apterous protein under apGAL4 and elavGAL4 drivers, demonstrate the recovery of Leucokinin in the LHLK neurons. These results reinforce the emerging role of the LIM‐HD proteins in determining neuronal identity. They also clarify the neuroendocrine phenotype of apterous mutants. J. Comp. Neurol. 457:123–132, 2003.

Blockade of the release of the neuropeptide leucokinin to determine its possible functions in fly behavior: Chemoreception assays

Previous studies have revealed leucokinin (LK) expression in the brain and ventral ganglion of Drosophila CNS. One pair of protocerebrum neurons located in the lateral horn area (LHLK) surrounds the peduncles of the mushroom bodies while two pairs of subesophageal neurons (SELKs) project extended processes to the tritocerebrum and through a cervical connection to the ventral ganglion. There, axons of eight or nine pairs of abdominal (ABLK) neurons leave the CNS through the abdominal nerves and processes connecting each other ipsilaterally and contralaterally. The neural functions of LK remain largely unknown, especially those related to Drosophila behavior. Here, we have studied the role of LK in olfactory and gustatory perception by keeping the LK neurons electrically silent through targeted expression of inward rectifier K(+) channels. In order to examine the effects of LK failure, we first analyzed the dehydration response, comparing the leucokinin-silent individuals with their parents as a control. Our results showed significant differences that demonstrate the effectiveness of the method. We then tested the olfactory behavioral response to a set of odorants over a range of concentrations in a T-maze paradigm in which flies were allowed to choose between the odorant and solvent compartments. The feeding preference assays were carried out on microplates in which flies were allowed to choose between two colored tastes. Our results show that the blockade of LK release alters both olfactory and gustatory responses, and are therefore evidence that this neuropeptide also modulates chemosensory responses through LHLK and SELK neurons.

High-resolution transmission electron microscopic analysis of porous silicon∕silicon interface

From high-resolution transmission electron microscopy, a strong contrast was observed in the interface between porous silicon and the silicon substrate, which was associated with the presence of high stress. It was determined that stress in the porous silicon∕Si interface is caused by dislocations and that lattice matching occurs through pairs of edge-dislocations. In addition, a high density of dislocations was also observed in the neighborhood of the Si nanocrystals that compose porous silicon. From the experimental results, a mechanism for the formation of porous silicon is proposed.

Genetic differentiation among Iberian populations of the Alpine newt, Triturus alpestris

Allozyme and C-banding studies on Triturus alpestris cyreni from north and central Spain and of T. a. alpestris from west and central Europe show a distinct differentiation between the taxa. Within the Iberian subspecies a marked genetic differentiation is detected among those populations that are geographically isolated, with the exception of that from central Spain. One of the populations from northern Spain stands out as distinct on account of both cytogenetic and allozyme analyses.