Carlos Garcia

A dorsal root ganglia cell line derived from trisomy 16 fetal mice, a model for Down syndrome

We have established two immortalized cell lines from dorsal root ganglia of normal (G4b) and trisomy 16 mice (GT1), a model for Down syndrome. By immunohistochemistry, both cell lines exhibit neuronal traits and lack glial markers. GTl cells exhibited greater [3H]choline uptake than G4b cells. K+ and nicotine-mediated acetylcholine release was greater in GT1 cells. Basal intracellular Ca2+ concentration ([Ca2+]i) was significantly lower in GTl cells. More GTl cells responded to neurotransmitters with a transient [Ca2+]i increase compared to G4b cells, but both cell types showed similar amplitudes of [Ca2+]i responses. The results show that both cell lines retain neuronal characteristics and respond to specific neurotransmitter stimuli. Altered GT1 cell responses could be related to neuronal pathophysiology in Downs syndrome.

Distinct protein kinases regulate SNAP-25 expression in chromaffin cells

The contribution of distinct Ca2+‐sensitive protein kinases to the regulation of the expression of the synaptosomal‐associated protein SNAP‐25 was examined in bovine chromaffin cells. Prolonged incubation with high K+ (38 mM) or 1,1‐dimethyl‐4‐phenyl‐piperazinium (DMPP), a nicotinic receptor agonist, significantly increased SNAP‐25 protein and mRNA expression, as assessed by immunoblotting and semi‐quantitative RT‐PCR analysis. Both stimuli preferentially enhanced mRNA coding for the SNAP‐25a isoform. Increase of SNAP‐25 expression induced by K+ or DMPP was inhibited over 70% by KN‐62 and KN‐93, two Ca2+/calmodulin‐dependent protein kinase (CaMK) inhibitors, whereas the inactive analogue KN‐92 only reduced the expression by 34%. The three compounds also inhibited the high K+‐elicited [Ca2+]i signal by 40%, suggesting that the effect of KN‐62 and KN‐93 was a combination of CaMK/ Ca2+ influx inhibitory actions. Incubation of the cells with mitogen‐activated protein kinase (MAPK) inhibitors PD98059 and U0126 reduced protein expression elicited by high K+ by 50%, but did not modify the response to DMPP. Interestingly, although protein kinase A (PKA) inhibition by H‐89 did not affect the high K+ or DMPP‐induced SNAP‐25 expression, basal protein levels were significantly modified upon activation or inhibition of this pathway. Basal expression of SNAP‐25 was also modified by the protein kinase C (PKC) activator, phorbol 12‐myristate 13‐acetate, but not by Gö6976, a PKC‐α inhibitor, suggesting that the Ca2+‐insensitive PKC‐ϵ isoform control basal expression of SNAP‐25 in these cells. Taken together, these results provide the first evidence that diverse protein kinases might converge in the induction of SNAP‐25 expression in chromaffin cells. The preferential contribution of one or another kinase would depend on the physiological or experimental conditions.

Structural and Magnetic Characterization of Half-Metallic Co 2 MnAl Heusler Alloy

Magnetic and structural characterization of full Heusler Co2MnAl alloys prepared by rapid quenching from pure elements was studied. This technique allows a fast production of relatively a large amount of Heusler alloys without the necessity of further thermal treatment. The Heusler alloys have been prepared by the melt-spinning method in the form of ribbons with homogeneous chemical composition (Co = 46.1%, Mn = 29.4%, and Al = 24.5%). The X-ray diffraction shows a single-phase B2 crystalline structure with lattice parameter α = 5.671 Å. Magnetic measurements reveal an anisotropic character of the Co2MnAl ribbon with easy magnetization axis well defined in parallel direction with respect to the ribbon plane. Curie temperature was estimated from magnetization measurement to be 710 K.

Exchange bias in (FeNi/IrMn)n multilayer films evaluated by static and dynamic techniques

Exchange bias properties of [FeNi/IrMn]n multilayer films with variable thickness of the ferromagnetic layers and different repetitions n were determined by using static and dynamic measurement techniques. The static magnetic properties were revealed through magnetometry measurements at room temperature following major hysteresis loops and first-order reversal curves protocols. Room temperature x-band ferromagnetic resonance (FMR) and vector network analyser (VNA)-FMR experiments were used to determine dynamically the exchange anisotropy in the FeNi/IrMn multilayers. From the static measurements the exchange anisotropy was determined while dynamic measurements allowed the determination of additional parameters including anisotropy field, saturation magnetization and rotatable anisotropy. The differences between the values of the exchange biased obtained from each technique are discussed.

Magnetic entropy change plateau in a geometrically frustrated layered system: FeCrAs-like iron-pnictide structure as a magnetocaloric prototype

Monte Carlo modeling suggests that the magnetothermal features of the Fe2P-structured FeCrAs-like compound offer a promising route for the design of magnetocaloric materials. The prototype structure is modeled as antiferromagnetically coupled layered Heisenberg systems mimicking the distorted Kagome/triangular stacked architecture of FeCrAs iron-pnictide. The magnetic entropy change ΔSm(T) presents a plateau-like behavior which can be tailored by tuning either the JCr-Fe/JCr-Cr exchange energy ratio or the magnetic field. The plateau is defined by cooperative spin ordering within a ferrimagnetic region which exists between two critical temperatures separating at the lower bound (Tac) a canted antiferromagnetic phase and at the upper bound (Tdc) the thermally disordered phase. The refrigerant capacity and adiabatic change of temperature are A(H)(Tdc - Tac) and A(H)Tp/Cm respectively, with Tac < Tp < Tdc, A(H) an increasing positive function of the field defining the height of the plateau and Cm the magnetic specific heat, whose critical behavior is related to the T(a,d)(c) values.

Uncertainty assessment of standard tests of bituminous mixtures

Characterization of any material requires the existence of test methods to quantify with the greatest reliability properties in the scope of the analysis. In the body of EN standards of asphalt mixtures, there is a section where the precision values shows repeatability and reproducibility of the test method. Test methods variability is usually based on interlaboratory exercises. However this section is not always completed, or the detailed data come from limited experiences or that do not correspond exactly to the method described in the standard. Information provided about the accuracy of the method should be considered very relevant. This study is based on a work developed by Aleas (Group of Spanish Laboratories Associated to Asefma), a set of organizations specialized in the production and characterization of asphalt mixtures. Its aim is to evaluate the accuracy described in the test method “EN 12697-12 water sensitivity of bituminous mixtures”, according to Method A, through a round robin test. In this EN standard, paragraph regarding accuracy indicates that the precision data have not been established, and there is a reference regarding similar indirect tensile tests. In this paper it is estimated the precision of the test for two types of bituminous mixtures: BBTM type B and AC, through a round robin test which involved 15 laboratories. Final results are compared with those of the reference published in the EN standard. This study has also used to calculate an overall estimate of its uncertainty using a methodology developed within the working group ALEAS.

Carbon Nanotubes for Assessing the Structural Integrity of Composite Bonded Joints with Film Adhesives

This work analyses the capability of the application of self-sensing film adhesives for assessing the structural integrity of typical aeronautical bonded joints without altering its mechanical behavior. Tests have been carried out on carbon fiber reinforced polymer composites (CFRP) although the method has been also validated on aluminum substrates, showing that different types of strain and damage are detected depending on the characteristics of the joined materials. In both cases, the structural health monitoring of the bonded joints has been achieved. The developed technologies are based on the addition of carbon nanotubes (CNT) to the film adhesives in order to provide electrical conductivity to the different interfaces. The high conductivity and relative large aspect ratio of CNT result in percolation thresholds around 0.1% weight of carbon nanotubes in the adhesive. The CNT network formed in the adhesive offers significant potential to develop sensing for damage detection and health monitoring using direct-current measurements. Loads applied over the nanodoped adhesives produce damage (i.e. cracks, delaminations,…) appearance and/or damage progression in the material, that modifies the integrity of carbon networks and increases the electrical resistivity of the adhesive. Two different methods have been developed to deposit CNTs on film adhesives: innovative inkjet printing methods and mask methods. In both cases the CNTs used were stabilized in water solution to use a solvent that did not damage the behavior of the adhesive. Then, the CNT solution was incorporated in the nanoreinforcement with controlled geometries over the films, providing local and controlled sensitivity to the bonded joints and giving information of the location of the damages, their characteristics and their propagations in an accurate way. doi: 10.12783/SHM2015/270

Thermal Annealing Influence on Magnetic and Structural Properties of Cu56Ga28Mn16 Microwires

We report on the crystalline structure, morphology and thermomagnetic properties of glass-coated magnetic microwires with Cu 56 Ga 28 Mn 16 composition, as well as the thermal annealing influence on its magneto-structural properties. As-cast CuMnGa microwires exhibit a majority cubic B2 phase, and upon annealing at temperatures up to 573 K a new hexagonal phase appears coexisting with the cubic B2 major phase. Thermal annealing treatments also shift the Curie temperature about 150 K with respect to the one for the as-cast microwire. Furthermore, the signature of a structural phase transition is observed for the microwire annealed at 523 K