Solidification Morphology Analysis of SLM of Cu Powder

The solidification morphology analysis of fine Cu powder melted by a raster scanned energy beam from a focused Nd:YAG laser is presented here. The powder was processed inside of sealed chamber where it was subjected to a high vacuum cycle. The laser fusion process consisted raster scanning a narrow rectangular pattern with a high density of scanning lines, the chamber was purged with inert gas during the process. Up to a 3.3 mm/s laser travel speed and maximum laser power level of 240 W were used to melt a 2 mm thick bed of loose powder. The resulting solidified ingots were separated into categories based on their shape integrity. Metallographic analysis by means of optical microscopy and scanning electron microscopy was performed on the cross section and longitudinal section of the ingots with homogeneous surface and complete shape integrity. Characterization revealed an elongated columnar grain structure with a grain orientation along the direction of the laser travel direction, some degree of porosity was observed too in some of the specimens. It was observed that grains diameter ranged from 10 to 100 µm and contained a two phase eutectic microstructure of copper and it oxides. Oxygen content was accounted from a 5.5 up to 8.1 atomic percent, a small percentage of chlorine was present, too. A 2 to 8 percent variation in the Vickers microhardness values were found between the different specimens when measured along the longitudinal section. These HV values corresponded to approximate 20-25% cold rolled oxygen free copper (80-90 HV). The ingots thus produced suggest that a multilayer structure from Cu powder could be build by the SLM process having sufficiently adequate compositional, microstructure and mechanical properties for functional applications.Mechanical Engineerin

Mechanical Behavior of SLS Components in Relation to the Build Orientation During the Sintering Process as Measured by ESPI

Selective Laser Sintering (SLS) allows producing real parts from CAD data from materials with different characteristics compared to the final model, presenting dissimilar mechanical properties between the prototype and the product. The purpose of this work is to correlate the mechanical behavior of beam-type specimens produced by SLS with build orientation angle used as a process parameter, also attempting to demonstrate how this parameter affects the accuracy of the Empirical Similitude Method (ESM). ESM presents itself as a valuable tool when creating scale models with SLS, specifically in the framework of evolutionary product design. More specifically, the Young modulus variation of test specimens of well-known dimensions and material (DuraformTM PA2 ), will be characterized by loading them within the elastic range. The resulting elastic deformations will be measured using the technique of Electronic Speckle Pattern Interferometry (ESPI) for small deformations in an out-of-plane configuration, contrasting these results with the elastic theory of deformations. As a main result, it was found that there exists a linear correlation between the build angle and the elastic modulus of the parts. Secondly, it was demonstrated empirically that the ESM predicts better the mechanical response of the part than TSM. Moreover, a 30% error reduction can be achieved within the ESM when using the build orientation angle as a process parameter.Mechanical Engineerin

Effect of habitat subdivision on the population dynamics of herbivorous and predatory insects in central Chile

ABSTRACT Habitat subdivision may facilitate the persistence at low densities of both predator and prey populations. But habitat subdivision may also allow herbivores to escape from predators and therefore reach higher local densities. The outcome will depend on the dispersal behaviour of organisms. The effect of habitat subdivision on populations of aphidophagous coccinellids Eriopis connexa and Hippodamia variegata and their prey Brevicoryne brassicae was evaluated in crops of Brassica o/eraceae. In particular, the following responses were analysed: a) density/plant of herbivorous and predatory insects, b) colonisation of herbivorous and predatory insects, c) movement between plant patches and residence time of predators, d) in situ recruitment of predators, and e) final weight of plants. Nine continuous and subdivided plots of B. oleracea were set up following a 3 x 3 completely randomised block design. The three treatments were: a) continuous, b) subdivided plus weeds, and c) subdivided plus cloth barriers. Density per plant of herbivorous and predatory insects was lower in subdivided plus barriers habitats. Colonisation by herbivores and predators was more rapid in continuous or subdivided plus weeds habitats. Residence time and in situ recruitment of predators was greater in continuous habitats. Plant weight was greater in subdivided than continuous habitats. Therefore, habitat subdivision, particularly when patches were more isolated, negatively affected the population densities of both herbivorous and predatory insects. This is likely due to lesser colonisation and in situ recruitment, and greater emigration of insects in those subdivided habitats. Key words: Brevicoryne brassicae, Eriopis connexa, Hippodamia variegata, spatial subdivision, predator-prey relationships. RESUMEN La subdivision del hábitat puede facilitar la persistencia a bajas densidades de herbfvoros y sus depredadores. Pero la subdivision del hábitat puede tambien permitir que Ios herbfvoros escapen de sus depredadores, alcanzando altas densidades a nivel local. El resultado dependera de la conducta de dispersion de Ios organismos involucrados. En este trabajo se evaluo el efecto de la subdivision del habitat sobre las dinamicas poblacionales de Ios coccinelidos Eriopis connexa e Hippodamia variegata y de su presa, el áfido Brevicoryne brassicae asociados a Brassica o/eraceae. En particular se analizaron !as siguientes respuestas: a) densidad/planta de insectos herbfvoros y depredadores, b) colonizacion de insectos herbfvoros y depredadores, c) movimiento entre parches de plantas y tiempo de residencia de depredadores, d) reclutamiento in situ de Ios depredadores, y e) peso final de !as plantas. Se implementaron nueve habitats continuos y subdivididos siguiendo un disefio de bloques al azar de 3 x 3. Los tres tratamientos fueron: a) continuo, b) subdividido más malezas y c) subdividido más barreras de tela. La densidad/planta de insectos herbfvoros y depredadores fue menor en Ios habitats subdivididos más barreras. La colonizacion por herbfvoros y depredadores fue más rapida en habitats continuos o subdivididos más malezas. El tiempo de residencia y el reclutamiento in situ de Ios depredadores fue mayor en habitats continuos. El peso final de !as plantas fue mayor en hábitats subdivididos. La subdivision del habitat, particularmente cuando Ios parches de plantas están más aislados, afecta negativamente !as densidades poblacionales de insectos herbfvoros y depredadores. Esto se deberfa a la menor colonizacion, menor reclutamiento in situ y mayor emigracion de insectos en aquellos habitats más subdivididos. Palabras clave: Brevicoryne brassicae, Eriopis connexa, Hippodamia variegata, subdivision del habitat, relacion depredador-presa

The Involvement of Urinary Kallikrein in the Renal Escape from the Sodium Retaining Effect of Mineralocorticoids

It is well known that the normal kidney escapes the sodium retaining effect of mineralocorticoids. However, the mechanism that mediates this escape is not understood. The possible role of kallikrein in this escape phenomenon was investigated by placing seven dogs in metabolic cages and giving them a constant sodium diet. After they had been on this diet three days, urine was collected for two 24-hour periods. DOCA (25 mg/day) was then given intramuscularly for five days. Urine was collected daily during this DOCA period and for two additional 24- hour periods. Urine volume, sodium, potassium, protein, and kallikrein excretion were then measured. Urinary kallikrein increased from 251.9 ± 34.8 (mean ± SE) in the second day of the control period to 639.8 ± 110.1 IJ-g/day (P \u3c .01) by the third day of treatment. It remained elevated two days after DOCA was discontinued. Sodium excretion decreased significantly on the first day of DOCA treatment, returning to the previous values thereafter. Urine protein excretion remained constant. The enhanced urinary kallikrein during the escape suggests that the kallikrein system could be involved in the regulation of sodium metabolism by acting as a natriuretic factor, or perhaps by regulating the renal blood flow

One-Step Hydrothermal Synthesis of Cu2ZnSnS4 Nanoparticles as an Efficient Visible Light Photocatalyst for the Degradation of Congo Red Azo Dye

A hydrothermal method was successfully employed to synthesize kesterite Cu2ZnSnS4 (CZTS) nanoparticles. X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and optical ultraviolet-visible (UV-vis) spectroscopy were used for characterization of structural, chemical, morphological, and optical properties. XRD results confirmed that a nanocrystalline CZTS phase corresponding to the kesterite structure was formed. Raman analysis confirmed the existence of single pure phase CZTS. XPS results revealed the oxidation states as Cu+, Zn2+, Sn4+, and S2−. FESEM and TEM micrograph images revealed the presence of nanoparticles with average sizes between 7 nm to 60 nm. The synthesized CZTS nanoparticles bandgap was found to be 1.5 eV which is optimal for solar photocatalytic degradation applications. The properties as a semiconductor material were evaluated through the Mott–Schottky analysis. The photocatalytic activity of CZTS has been investigated through photodegradation of Congo red azo dye solution under solar simulation light irradiation, proving to be an excellent photo-catalyst for CR where 90.2% degradation could be achieved in just 60 min. Furthermore, the prepared CZTS was reusable and can be repeatedly used to remove Congo red dye from aqueous solutions.Partial funding for open access charge: Universidad de Málag

Mechanisms affecting population density in fragmented habitat

We conducted a factorial simulation experiment to analyze the relative importance of movement pattern, boundary-crossing probability, and mortality in habitat and matrix on population density, and its dependency on habitat fragmentation, as well as inter-patch distance. We also examined how the initial response of a species to a fragmentation event may affect our observations of population density in post-fragmentation experiments. We found that the boundary-crossing probability from habitat to matrix, which partly determines the emigration rate, is the most important determinant for population density within habitat patches. The probability of crossing a boundary from matrix to habitat had a weaker, but positive, effect on population density. Movement behavior in habitat had a stronger effect on population density than movement behavior in matrix. Habitat fragmentation and inter-patch distance may have a positive or negative effect on population density. The direction of both effects depends on two factors. First, when the boundary-crossing probability from habitat to matrix is high, population density may decline with increasing habitat fragmentation. Conversely, for species with a high matrix-to-habitat boundary-crossing probability, population density may increase with increasing habitat fragmentation. Second, the initial distribution of individuals across the landscape: we found that habitat fragmentation and inter-patch distance were positively correlated with population density when individuals were distributed across matrix and habitat at the beginning of our simulation experiments. The direction of these relationships changed to negative when individuals were initially distributed across habitat only. Our findings imply that the speed of the initial response of organisms to habitat fragmentation events may determine the direction of observed relationships between habitat fragmentation and population density. The time scale of post-fragmentation studies must, therefore, be adjusted to match the pace of post-fragmentation movement responses

Analysis of Local and Global Aromaticity in Si3C5 and Si4C8 Clusters. Aromatic Species Containing Planar Tetracoordinate Carbon

The minimum energy structures of the Si3C5 and Si4C8 clusters are planar and contain planar tetracoordinate carbons (ptCs). These species have been classified, qualitatively, as global (π) and local (σ) aromatics according to the adaptive natural density partitioning (AdNDP) method, which is an orbital localization method. This work evaluates these species’ aromaticity, focusing on confirming and quantifying their global and local aromatic character. For this purpose, we use an orbital localization method based on the partitioning of the molecular space according to the topology of the electronic localization function (LOC-ELF). In addition, the magnetically induced current density is analyzed. The LOC-ELF-based analysis coincides with the AdNDP study (double aromaticity, global, and local). Moreover, the current density analysis detects global and local ring currents. The strength of the global and local current circuit is significant, involving 4n + 2 π- and σ-electrons, respectively. The latter implicates the Si-ptC-Si fragment, which would be related to the 3c-2e σ-bond detected by the orbital localization methods in this fragment.Fil: Torres Vega, Juan J.. Universidad Nacional Mayor de San Marcos; PerúFil: Alcoba, Diego Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Oña, Ofelia Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Vasquez Espinal, A.. Universidad Andrés Bello; ChileFil: Baez Grez, R.. Universidad Andrés Bello; ChileFil: Lain, Luis. Universidad del País Vasco; EspañaFil: Torre, Alicia. Universidad del País Vasco; EspañaFil: García, Victor Raúl. Universidad Nacional Mayor de San Marcos; Perú. Universidad Andrés Bello; ChileFil: Tiznado, William. Universidad Andrés Bello; Chil