Influence of AISI D2 Workpiece Roughness on Heat Partition and Plasma Channel Radius in the WEDM Process

As an important advanced machining process, in Wire Electrical Discharge Machining (WEDM) certain fundamental issues remain need to be studied in-depth, such as the effect of part surface roughness on heat transfer mechanisms. In the WEDM process, roughing cut wire goes into the workpiece to do the first shaping and in trim cut the wire sweeps on the outer surface to improve the surface roughness. In both of these two cases, the generation of sparks depends on the passing surface roughness. Therefore, with AISI D2 material and brass wire, this paper presents a study of the influence of part surface roughness on heat partition and the radius of the plasma channel in the WEDM process. Through extensive single discharge experiments, it is shown that the removal capacity per discharge can increase if the discharge occurs on a smoother surface. A Finite Element thermal model was then used for inverse fitting of the values of heat partition and radius of the plasma channel. These parameters completely define the characteristics of the heat conduction problem. The results indicate a strong correlation between an increase in heat partition ratio and a decrease in part surface roughness. The values of plasma channel radius show an increase in this value when discharging on rougher surfaces. It means that with the increasing of plasma channel radius, the heat source goes into the workpiece more dispersed. In the case of rougher surface, although the there is more area that affected by the heat source, finally the temperature of most area cannot reach to the melting point and it causes the smaller crater radius and volume, while the metal removal rate decreases. These results contribute towards a more complete understanding of the influence of surface roughness to the spark occurring.This research was funded by the Spanish Ministry of Economy and Competitiveness and the European Regional Development Fund (ERDF) operation program for funding the project “Scientific models and machine-tool advanced sensing techniques for efficient machining of precision components of Low-Pressure Turbines” (DPI2017-82239-P)

Influence of magnetic ordering on structural instabilities in insulating perovskites

We propose a general model, based on Anderson superexchange and the pseudo Jahn-Teller effect, to explain why ferroelectric and octahedral tilting distortions are favored by ferromagnetic ordering when compared to antiferromagnetic tilting distortions in ABX3 (A = alkali, alkaline-earth ion, f-filling rare earth; B = magnetic transition-metal ion; X = O2−, F−) perovskite crystals. Ab initio calculations are used to check the model under a wide range of pressures for oxides and fluorides, with the latter displaying an enhancement of the ferroelectric distortion when pressure is increased.The support by the Spanish Ministerio de Ciencia y Tecnología under Project FIS2009-07083 and computational time in both the Altamira Supercomputing node and Calderon HPC cluster in Universidad de Cantabria is acknowledged. We would like to thank J. Junquera and M.T. Barriuso for valuable discussions

An Original Tribometer to Analyze the Behavior of Abrasive Grains in the Grinding Process

Manufacturing of grinding wheels is continuously adapting to new industrial requirements. New abrasives and new wheel configurations, together with wheel wear control allow for grinding process optimization. However, the wear behavior of the new abrasive materials is not usually studied from a scientific point of view due to the difficulty to control and monitor all the variables affecting the tribochemical wear mechanisms. In this work, an original design of pin-on-disk tribometer is developed in a CNC (Computer Numerical Control) grinding machine. An Alumina grinding wheel with special characteristics is employed and two types of abrasive are compared: White Fused Alumina (WFA) and Sol-Gel Alumina (SG). The implemented tribometer reaches sliding speeds of between 20 and 30 m/s and real contact pressures up to 190 MPa. The results show that the wear behavior of the abrasive grains is strongly influenced by their crystallographic structure and the tribometer appears to be a very good tool for characterizing the wear mechanisms of grinding wheels, depending on the abrasive grains.The authors gratefully acknowledge the funding support received from the Spanish Ministry of Economy and Competitiveness and the FEDER operation program for funding the project "Scientific models and machine-tool advanced sensing techniques for efficient machining of precision components of Low Pressure Turbines" (DPI2017-82239-P). Funding support was also received from the contracting call for the training of research staff in UPV/EHU 2016, of Vice-rectorate of research to develop this project

Benchmark study for the application of density functional theory to the prediction of octahedral tilting in perovskites

The results of a systematic study of octahedral tilting in oxo- and fluoroperovskites by density functional theory (DFT) calculations are presented and discussed. Eleven perovskites displaying different structural, magnetic, and metallic properties have been studied by means of nine exchange-correlation functionals, ranging from the basic local density approximation to more advanced hybrid functionals, in order to determine the accuracy of these methods for the prediction of octahedral rotation angles. Octahedral tilting has attracted much attention lately due to the possibility of using them to trigger improper ferroelectricity and new families of multiferroic materials. We show that all DFT methods tend to overestimate the octahedral rotation angles by approximately 20 %, with this quantity being only slightly corrected by hybrids, including, at least, 25% of the Hartree?Fock exchange. We propose a correction to the prediction of these angles based on quantum fluctuations and the anharmonic nature of the energy surface around the minimum but find that it is only important for very small rotation angles appearing in systems like SrTiO3.We acknowledge economic support from the Spanish Ministerio de Ciencia y Tecnolog´ıa under Project No. FIS2012-30996 and the Science Foundation Ireland (SFI) Research Frontiers Programme (Reference No. 10/RFP/MTR2868

Tunneling splitting of Jahn-Teller ions in oxides

The magnitude of tunneling splitting, 3?, that governs decoherence in quantum systems under symmetric potentials, is frequently unknown. Using first-principles calculations, we have obtained 3? for a number of E?e Jahn-Teller impurities in solids. Calculated values span 6 orders of magnitude on passing from KCl?Ag2+ to MgO?Cu2+. Values associated with Cu2+- and Ag2+-doped MgO are 2 orders of magnitude larger than those previously assumed and consistent with the existence of a dynamic Jahn-Teller effect. The origin and enhancement with pressure of these high 3? values is discussed in detail.The support by the Spanish Ministerio de Ciencia y Tecnología under Projects FIS2006-02261 and FIS2009- 07083 is acknowledged

Internal electric fields and color shift in Cr3+-based gemstones

Seeking to better understand the origin of the different colors of emerald and ruby, both ab initio periodic and cluster calculations have been carried out. The calculations reproduce the interatomic distances measured for pure Be3Si6Al2O18 and Al2O3 as well as the Cr3+?O2? distances in emerald and ruby. The mean Cr3+?O2? distance for Be3Si6Al2O18:Cr3+ and Al2O3:Cr3+ is found to be practically equal to 1.97 Å, in agreement with recent experimental values. The present calculations confirm that the variations of optical properties due to Cr3+ impurities along the series of ionic oxides can be understood merely through the CrO69? unit but subject to the electric field due to the rest of the lattice ions. As a salient feature it is proved that changes in electronic density and covalency due to the internal field are not the cause of the color shift. Therefore, the red color of ruby is not due to the polarization of the electronic cloud around chromium as a result of the C3 local symmetry. The present study also demonstrates that the variation of the ligand field splitting parameter, 10Dq, induced by the internal electric field comes mainly from the contributions of first shells of ions around the CrO69? unit. As a consequence, 10Dq in emerald is not influenced by the internal field, as the contribution from Be2+ first neighbors is practically compensated by that of Si4+ second neighbors. In contrast, in ruby the t2g levels are shifted by the internal field 0.24 eV more than the eg ones, so explaining the color shift in this gemstone in comparison with emerald. This result is shown to arise partially from the asymmetric form of the internal electrostatic potential along the C3 axis in Al2O3.Support from the Spanish Ministerio de Ciencia y Tecnología under Project No. FIS2009-07083 is acknowledge

Innovative in vivo and in vitro bioassays for the establishment of toxicity thresholds of pollutants in sediment quality assessment using polychaetes and their immune cells.

Sediment toxicity testing has become a crucial component for assessing the risks posed by contaminated sediments and for the development of sediment quality assessment strategies. Commonly used organisms for bioassays with estuarine sediments include amphipods, Arenicola marina polychaetes and echinoids. Among the latter, the Sea Urchin Embryo test (SET) is the most widely used. However, one relevant limitation of this bioassay is the unavailability of gametes all year-round, particularly outside the natural spawning seasons. Consequently, the establishment of an appropriate and complementary model organism for a continuous assessment of sediment quality is recommended. A reliable assessment of the hazards resulting from pollutants in sediments or pore water, can be achieved with ecologically relevant species of sediment such as the polychaete Hediste diversicolor, which is widespread in estuaries and has the capacity to accumulate pollutants. The aim of this work was to develop reliable in vivo and in vitro bioassays with H. diversicolor and its coelomocytes (immune cells) to determine the toxicity thresholds of different contaminants bounded to sediments or resuspended into water. Polychaetes were exposed to sublethal concentrations of CuCl2 (in vivo) and a non-invasive method for collection of polychaetes coelomocytes was applied for the in vitro bioassay, exposing cells to a series of CuCl2 and AgNPs concentrations. Same reference toxicants were used to expose Paracentrotus lividus following the SET (ICES N 51; Beiras et al., 2012) and obtained toxicity thresholds were compared between the two species. In vivo exposure of polychaetes to high concentrations of Cu produced weight loss and histopathological alterations. After in vitro approaches, a significant decrease in coelomocytes viability was recorded for both toxicants, in a monotonic dose-response curve, at very short-exposure times (2h). The toxicity thresholds obtained with polychaetes were in line with the ones obtained with the SET, concluding that their sensitivity is similar. In conclusion, in vivo and in vitro bioassays developed with H. diversicolor are accurate toxicity screenings of pollutants that could be bounded to sediments or dissolved in the pore water, and may complement the SET outside the spawning period of the echinoderms. The bioassays herein developed could be applied not only to establish the toxicity thresholds of individual compounds or mixtures, but also to assess the toxicity of field collected sediments.The authors thank Basque Government (Grant to Consolidated Research Groups; IT1302-19, IT1213-19) and Spanish Ministry of Economy and Competitiveness (SEAdimenTOX project, CTM 2017-87766-R)

Reproductive Parameters in the Critically Endangered Blue-Throated Macaw: Limits to the Recovery of a Parrot under Intensive Management

Rediscovered in the wild twenty years ago, the breeding biology of wild Blue-throated Macaws remains largely unexplored, yet is essential to its effective conservation and recovery. Here, we analyse reproductive parameters in an intensively managed wild population of Blue-throated Macaws, providing the first data on the breeding biology of this critically endangered species. During the six-year study period, 2007–2012, the number of active breeding pairs either remained constant or decreased, depending on the site, and no new breeding pairs were discovered despite extensive searching. We documented nesting attempts in natural cavities in dead palms or live hardwoods, and artificial nest boxes. Egg-laying was concentrated during the end of dry season and the beginning of the wet season, August through December. Hatching failure was the greatest cause of egg losses. Half of the breeding attempts of Blue-throated Macaws produced at least one fledging, on average two, after a 85 days nestling period. An average of 4.3 nestlings per year fledged from all known wild nests combined. Each pair lost roughly 65% of its initial reproductive investment at each nesting attempt. In most successful nesting attempts of individualized pairs, a new nesting attempt was not detected the following year. All monitored breeding pairs showed high nest site fidelity, reusing hardwood-tree cavities and nest boxes. Our findings will aid conservation efforts by refining current actions and prompting new approaches towards the conservation and recovery of the Blue-throated Macaw.Fil: Berkunsky, Igor. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto Multidisciplinario de Ecosistemas y Desarrollo Sustentable; Argentina. The World Parrot Trust; Bolivia. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Daniele, Gonzalo. The World Parrot Trust; BoliviaFil: Kacoliris, Federico Pablo. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto Multidisciplinario de Ecosistemas y Desarrollo Sustentable; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Zoología de Vertebrados; Argentina. The World Parrot Trust; Bolivia. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Diaz Luque, José Antonio. The World Parrot Trust; BoliviaFil: Silva Frías, Carmen Paz. The World Parrot Trust; Bolivia. Universidad Austral de Chile; ChileFil: Aramburu, Rosana Mariel. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Zoología de Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gilardi, James D.. The World Parrot Trust; Estados Unido

Impurities bound to vacancies in insulators: electronic relaxation and physical properties of the Cr 3 + − V M model center in K M F 3 ( M = Mg, Zn)

This work is aimed at gaining a better insight into the influence of a close vacancy, V, on the properties of impurities in insulating materials. To achieve this goal the Cr3+−VM model center formed in KMF3 (M = Mg, Zn) fluoroperovskites has been explored in detail by means of ab initio calculations on clusters involving up to 87 ions. It is shown that the presence of the M2+ vacancy, VM, induces a significant structural relaxation on the CrF3−6 cubic complex which cannot be fully understood assuming that ions were rigid spheres that could not be polarized. Thus, although VM forces all the ligands to move away, the Cr3+−F− distance corresponding to the furthest ligand, Ffar, is found to be slightly higher than that for the closer equatorial ions. This unexpected fact is shown to be due to the electronic relaxation also induced by VM on the CrF3−6 complex, causing a charge of 0.2e to be transferred from the closest ligand to VM, Fnext, mainly to Ffar, and, to a lesser extent, to any equatorial ligand. This transfer of charge is mainly accomplished through orbitals lying in planes containing the C4 axis. In spite of these changes due to the vacancy, the 4A2g→4T2g optical transition is found to be weakly altered, a fact that concurs with available experimental data and whose origin is discussed. In contrast, electron paramagnetic resonance parameters such as gyromagnetic or superhyperfine tensors, which do depend on the electronic density around a point of the CrF3−6 complex, are shown to be particularly sensitive to the electronic relaxation induced by VM. In particular, the present study explains that the dominant component of the superhyperfine tensor for the Fnext ligand is clearly higher than that for Ffar, in agreement with experimental data. The relevance of the present results for understanding the electronic properties of other systems involving vacancies is also discussed. Some results on the Cr3+−Li+ center formed in KMgF3 are also discussed for comparison.The support by the Spanish Ministerio de Ciencia y Tecnología under Project FIS2009-07083 is acknowledge