Characterization and Diffusion Kinetics of Silicon on AISI D2 Steel

This paper presents the simultaneous influence of two different activators (NH4Cl and NaF) on the kinetic evolution during siliconising of steel. The AISI D2 tool steel surface was coated by pack siliconising through the growing of silicon on the surface. Pack siliconising was accomplished by employing a mixture of powders of Si 12 wt% + NH4Cl 0.5 wt% + NaF 0.5 wt% + Al2O3 at 923, 1073 and 1223 K for 1 to 5 h, respectively. The thermodynamics of the different chemical reactions were calculated for the forecast of the coating growth mechanisms of pack siliconising. The microstructure and the precipitation evolution of the silicides were analysed by Energy Dispersive X-ray Spectroscopy line scan (EDS-line scan), X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The ranges of the silicide layers thickness resulted between 19 and 337 μm depending on the employed processing parameters. The maximum hardness related to the siliconising parameters for fabricating the different thickness of the intermetallics on the surface of the AISI D2 tool steel and the ranges of the microhardness of the substrate after siliconising is between 750 and 800 HV. The growth of the FeSi, Fe2Si and FeSi2 on the sub-layer is a function of the treatment temperature and time, their growth behavior was used for revealing the kinetics during the process. The results showed that the diffusion coefficient (k) was enhanced by increasing the treatment temperature. Activation energy (Q) resulted 138 KJmol . The crystal growth rate resistance (k) are from 1.141 × 10 - 8 to 1.078×10-6m2s .</p

The natural axis of transmitter receptor distribution in the human cerebral cortex

Transmitter receptors constitute a key component of the molecular machinery for intercellular communication in the brain. Recent efforts have mapped the density of diverse transmitter receptors across the human cerebral cortex with an unprecedented level of detail. Here, we distill these observations into key organizational principles. We demonstrate that receptor densities form a natural axis in the human cerebral cortex, reflecting decreases in differentiation at the level of laminar organization and a sensory-to-association axis at the functional level. Along this natural axis, key organizational principles are discerned: progressive molecular diversity (increase of the diversity of receptor density); excitation/inhibition (increase of the ratio of excitatory-to-inhibitory receptor density); and mirrored, orderly changes of the density of ionotropic and metabotropic receptors. The uncovered natural axis formed by the distribution of receptors aligns with the axis that is formed by other dimensions of cortical organization, such as the myelo- and cytoarchitectonic levels. Therefore, the uncovered natural axis constitutes a unifying organizational feature linking multiple dimensions of the cerebral cortex, thus bringing order to the heterogeneity of cortical organization

Mechanical behaviour of additively manufactured lunar regolith simulant components

Additive manufacturing and its related techniques have frequently been put forward as a promising candidate for planetary in-situ manufacturing, from building life-sustaining habitats on the Moon to fabricating various replacements parts, aiming to support future extra-terrestrial human activity. This paper investigates the mechanical behaviour of lunar regolith simulant material components, which is a potential future space engineering material, manufactured by a laser-based powder bed fusion additive manufacturing system. The influence of laser energy input during processing was associated with the evolution of component porosity, measured via optical and scanning electron microscopy in combination with gas expansion pycnometry. The compressive strength performance and Vickers microhardness of the components were analysed and related back to the processing history and resultant microstructure of the lunar regolith simulant build material. Fabricated structures exhibited a relative porosity of 44 – 49% and densities ranging from 1.76 – 2.3 g cm-3 , with a maximum compressive strength of 4.2 ± 0.1 MPa and elastic modulus of 287.3 ± 6.6 MPa, the former is comparable to a typical masonry clay brick (3.5 MPa). The 2 AM parts also had an average hardness value of 657 ± 14 HV0.05/15, better than borosilicate glass (580 HV). This study has shed significant insight into realizing the potential of a laser-based powder bed fusion AM process to deliver functional engineering assets via in-situ and abundant material sources that can be potentially used for future engineering applications in aerospace and astronautics

The fluorescence explorer (FLEX) mission:imaging spectroscopy in very high spectral resolution

The FLuorescence EXplorer (FLEX) mission was selected in 2015, by the European Space Agency, as the 8th ESA Earth Explorer, to be launched in 2025. The key scientific objective of the mission is the quantitative mapping of actual photosynthetic activity of terrestrial ecosystems, at a global scale and with a spatial resolution adequate to resolve land processes associated to vegetation dynamics. To accomplish such objective, the FLEX satellite carries the Fluorescence Imaging Spectrometer (FLORIS). FLEX will fly in tandem with Copernicus Sentinel-3 (same orbit at 815 km, 27 days repeat cycle). Together with FLORIS, the OLCI and SLSTR instruments on Sentinel-3 provide all the necessary information to retrieve the emitted vegetation fluorescence, including compensation for atmospheric effects and the derivation of the additional biophysical information needed to map the spatial and temporal dynamics of vegetation photosynthesis from such global measurements

The impact of 3D printing process parameters on the dielectric properties of high permittivity composites

Fused filament fabrication (FFF) is a well-known and greatly accessible additive manufacturing technology, that has found great use in the prototyping and manufacture of radiofrequency componentry, by using a range of composite thermoplastic materials that possess superior properties, when compared to standard materials for 3D printing. However, due to their nature and synthesis, they are often a great challenge to print successfully which in turn affects their microwave properties. Hence, determining the optimum printing strategy and settings is important to advance this area. The manufacturing study presented in this paper shows the impact of the main process parameters: printing speed, hatch spacing, layer height and material infill, during 3D printing on the relative permittivity (εr), and loss tangent (tanδ) of the resultant additively manufactured test samples. A combination of process parameters arising from this study, allowed successful 3D printing of test samples, that marked a relative permittivity of 9.06 ± 0.09 and dielectric loss of 0.032 ± 0.003