Impact of extreme electrical fields on charge density distributions in Al3Sc alloy

Indexación: Web of Science.In this study, the authors investigated how extreme electrical fields affect charge distribution of metallic surfaces and bond character at the moment of evaporation. The surface structure and neighborhood chemistry were also studied as a function of various field evaporation pathways. Density functional theory (DFT) was used to model the surface bonding and charge distribution and then correlate the DFT results with experimental results by comparing the calculated evaporation fields with atom probe tomography measurements. The evaporation fields of different surface neighborhood chemistries in L1(2)-Al3Sc were calculated, with the Sc atoms occupying the corners of a cubic unit cell and the Al atoms occupying the face centers. Al-Al surface atoms are found via DFT to be more likely to evaporate as dimers because of the Al-Al shared charge density. In contrast, Al-Sc evaporates as single ions due to the increased density localized around the Sc atom. This difference in evaporation behavior correlates with the resistance to degradation under extreme fields. This work allows better interpretation of the atom probe data by clarifying the relationship between different evaporation events and the role of surface and subsurface chemistry. (C) 2016 Author(s).http://avs.scitation.org/doi/10.1116/1.496483

Modeling field evaporation degradation of metallic surfaces by first principles calculations: A case study for Al, Au, Ag, and Pd

Indexación: Scopus.Under the effects of an extreme electric field, the atoms on a metallic surface evaporate by breaking their bonds with the surface. In this work, we present the effects of a high electric field, by the use of computational simulations, for different metallic surface chemistries: Al, Au, Ag, and Pd. To model this bond breaking procedrure (i.e. field evaporation), we use density functional theory through the Quantum-Espresso (QE) simulation package, which incorporates the electric fields by adding a saw-like funcion into the Hamiltonian. This approach, known as dipole correction, was applied to all simulations as is implemented in the QE package. In this work, we calculate the evaporation field (Fe ) for all metallic species, which corresponds to the mean field at which atoms can break their bonds from the surface and evaporate. This result is compared with experimantal data from Atom Probe Tomography (APT) and computational data from prior simulations. © Published under licence by IOP Publishing Ltd.This work was supported by the Proyecto FONDECYT Iniciación 11130501. JP Also acknowledges partial support from Proyecto FONDECYT Regular 1140514 and Proyecto UAB-775. CL acknowledges support from Proyecto FONDECYT Iniciación 11150279, Proyecto PAI-79140025, and Proyecto DI-1350-16/R.https://iopscience.iop.org/article/10.1088/1742-6596/1043/1/01203

Dynamic resource management in SDN-based virtualized networks

Network virtualization allows for an abstraction between user and physical resources by letting a given physical infrastructure to be shared by multiple service providers. However, network virtualization presents some challenges, such as, efficient resource management, fast provisioning and scalability. By separating a network's control logic from the underlying routers and switches, software defined networking (SDN) promises an unprecedented simplification in network programmability, management and innovation by service providers, and hence, its control model presents itself as a candidate solution to the challenges in network virtualization. In this paper, we use the SDN control plane to efficiently manage resources in virtualized networks by dynamically adjusting the virtual network (VN) to substrate network (SN) mappings based on network status. We extend an SDN controller to monitor the resource utilisation of VNs, as well as the average loading of SN links and switches, and use this information to proactively add or remove flow rules from the switches. Simulations show that, compared with three state-of-art approaches, our proposal improves the VN acceptance ratio by about 40% and reduces VN resource costs by over 10%

PC4CAST: A tool for DSN load forecasting and capacity planning

Effectively planning the use and evolution of the Deep Space Network (DSN) is a complex problem involving many parameters. The tool that models many of these complexities, yet requires simple structured inputs and provides concise easy-to-understand metrics to aid in the planning process is discussed. The tool, PC4CAST, is used for both load forecasting (predicting how well planned that DSN resources meet expected demand) and as a decision support tool in the capacity-planning process (determining the relative benefits of capacity expansion options). It is now in use in the TDA Planning Office, has been used in numerous studies, and is also being used by the JPL Multimission Operations System Office (MOSO) as an integral part of Resource Allocation Team activities. Experience using the tool has helped to identify additional requirements that will further improve the planning process, which can be met by future PC4CAST versions

Single-particle transfer and nuclear supersymmetry

Transfer reactions constitute a stringent test for nuclear supersymmetry, a theory that simultaneously describes neighboring nuclei with bosonic and fermionic character. We construct and analytically evaluate one-nucleon transfer matrix elements between supersymmetric partners with the U( 6/4) case as an example, and stress the need for a careful treatment of bosonic and fermionic operators in the construction of mixed tensor operators.CONACyT 32416-E 32397-EPAGA-UNAM IN106400DGICYT PB98-111

Mechanisms and functions of intestinal vascular specialization.

The intestinal vasculature has been studied for the last 100 years, and its essential role in absorbing and distributing ingested nutrients is well known. Recently, fascinating new insights into the organization, molecular mechanisms, and functions of intestinal vessels have emerged. These include maintenance of intestinal epithelial cell function, coping with microbiota-induced inflammatory pressure, recruiting gut-specific immune cells, and crosstalk with other organs. Intestinal function is also regulated at the systemic and cellular levels, such that the postprandial hyperemic response can direct up to 30% of systemic blood to gut vessels, while micron-sized endothelial cell fenestrations are necessary for nutrient uptake. In this review, we will highlight past discoveries made about intestinal vasculature in the context of new findings of molecular mechanisms underpinning gut function. Such comprehensive understanding of the system will pave the way to breakthroughs in nutrient uptake optimization, drug delivery efficiency, and treatment of human diseases

Influence of turbidity and clouds on satellite total ozone data over Madrid (Spain)

This article focuses on the comparison of the total ozone column data from three satellite instruments; Total Ozone Mapping Spectrometers (TOMS) on board the Earth Probe (EP), Ozone Monitoring Instrument (OMI) on board AURA and Global Ozone Monitoring Experiment (GOME) on board ERS/2, with ground-based measurement recorded by a well calibrated Brewer spectrophotometer located in Madrid during the period 1996–2008. A cluster classification based on solar radiation (global, direct and diffuse), cloudiness and aerosol index allow selecting hazy, cloudy, very cloudy and clear days. Thus, the differences between Brewer and satellite total ozone data for each cluster have been analyzed. The accuracy of EP-TOMS total ozone data is affected by moderate cloudiness, showing a mean absolute bias error (MABE) of 2.0%. In addition, the turbidity also has a significant influence on EP-TOMS total ozone data with a MABE ~1.6%. Those data are in contrast with clear days with MABE ~1.2%. The total ozone data derived from the OMI instrument show clear bias at clear and hazy days with small uncertainties (~0.8%). Finally, the total ozone observations obtained with the GOME instrument show a very smooth dependence with respect to clouds and turbidity, showing a robust retrieval algorithm over these conditions.Manuel Ant´on thanks Ministerio de Ciencia e Innovaci´on and Fondo Social Europeo for the award of a postdoctoral grant (Juan de la Cierva). This work was partially supported by Ministerio de Ciencia e Innovacion under project CGL2008-05939-C03-02/CLI

Are Audiologists Directly Referring Children with Hearing Loss to Early Intervention?

This article describes the ways that pediatric audiologists are directing infants into Early Intervention, and the related barriers and facilitators. Over one hundred pediatric audiologists responded to an online survey including questions on how audiologists provide direct and indirect referrals to Early Intervention for those infants that are diagnosed with hearing loss. Most respondents agreed that audiologists are the best person to provide this referral, but many audiologists did not make the direct referral. Barriers to direct referral included time constraints and resistance from parents. Opportunities identified to improve referral included online referral systems and national guidelines for what qualifies a child with hearing loss for Early Intervention