2,113 research outputs found
Hydrogen Dissociation and Diffusion on Ni and Ti -doped Mg(0001) Surfaces
It is well known, both theoretically and experimentally, that alloying
MgH with transition elements can significantly improve the thermodynamic
and kinetic properties for H desorption, as well as the H intake by Mg
bulk. Here we present a density functional theory investigation of hydrogen
dissociation and surface diffusion over Ni-doped surface, and compare the
findings to previously investigated Ti-doped Mg(0001) and pure Mg(0001)
surfaces. Our results show that the energy barrier for hydrogen dissociation on
the pure Mg(0001) surface is high, while it is small/null when Ni/Ti are added
to the surface as dopants. We find that the binding energy of the two H atoms
near the dissociation site is high on Ti, effectively impeding diffusion away
from the Ti site. By contrast, we find that on Ni the energy barrier for
diffusion is much reduced. Therefore, although both Ti and Ni promote H
dissociation, only Ni appears to be a good catalyst for Mg hydrogenation,
allowing diffusion away from the catalytic sites. Experimental results
corroborate these theoretical findings, i.e. faster hydrogenation of the Ni
doped Mg sample as opposed to the reference Mg or Ti doped Mg.Comment: 17 pages, 15 figures, to appear in Journal of Chemical Physic
FeO Content of Earth’s Liquid Core
The standard model of Earth’s core evolution has the bulk composition set at formation, with slow
cooling beneath a solid mantle providing power for geomagnetic field generation. However, controversy
surrounding the incorporation of oxygen, a critical light element, and the rapid cooling rates needed to
maintain the early dynamo have called this model into question. The predicted cooling rates imply early
core temperatures that far exceed estimates of the lower mantle solidus, suggesting that early core evolution
was governed by interaction with a molten lower mantle. Here we develop ab initio techniques to compute
the chemical potentials of arbitrary solutes in solution and use them to calculate oxygen partitioning
between liquid Fe-O metal and silicate melts at the pressure-temperature (P-T) conditions expected for the
early core-mantle system. Our distribution coefficients are compatible with those obtained by extrapolating
experimental data at lower P-T values and reveal that oxygen strongly partitions into metal at core
conditions via an exothermic reaction. Our results suggest that the bulk of Earth’s core was undersaturated
in oxygen compared to the FeO content of the magma ocean during the latter stages of its formation,
implying the early creation of a stably stratified oxygen-enriched layer below the core-mantle boundary
(CMB). FeO partitioning is accompanied by heat release due to the exothermic reaction. If the reaction
occurred at the CMB, this heat sink could have significantly reduced the heat flow driving the core
convection and magnetic field generation
Structure of nanoparticles embedded in micellar polycrystals
We investigate by scattering techniques the structure of water-based soft
composite materials comprising a crystal made of Pluronic block-copolymer
micelles arranged in a face-centered cubic lattice and a small amount (at most
2% by volume) of silica nanoparticles, of size comparable to that of the
micelles. The copolymer is thermosensitive: it is hydrophilic and fully
dissolved in water at low temperature (T ~ 0{\deg}C), and self-assembles into
micelles at room temperature, where the block-copolymer is amphiphilic. We use
contrast matching small-angle neuron scattering experiments to probe
independently the structure of the nanoparticles and that of the polymer. We
find that the nanoparticles do not perturb the crystalline order. In addition,
a structure peak is measured for the silica nanoparticles dispersed in the
polycrystalline samples. This implies that the samples are spatially
heterogeneous and comprise, without macroscopic phase separation, silica-poor
and silica-rich regions. We show that the nanoparticle concentration in the
silica-rich regions is about tenfold the average concentration. These regions
are grain boundaries between crystallites, where nanoparticles concentrate, as
shown by static light scattering and by light microscopy imaging of the
samples. We show that the temperature rate at which the sample is prepared
strongly influence the segregation of the nanoparticles in the
grain-boundaries.Comment: accepted for publication in Langmui
The Dynamics of the Innovation System for Functional Foods in South Brazil
 This study aims at identifying the dynamics of the innovation system for functional foods (FF) in Rio Grande do Sul, Brazil. Functional food is any healthy food claimed to have a health-promoting or disease-preventing property beyond the basic function of supplying nutrients. Health has been named as the most significant trend and innovation driver in the global food and drinks market. Brazil is one of the leading countries in food production and consumption, and the market for functional foods have been growing 10% per year, three times more than the market for conventional foods. Although this food category is considered mature in some developed markets (such as in Japan, in the Nordic countries and in the U.S), it is still unknown for many consumers, especially those located in developing countries. On the other hand, functional foods has been attracting the attention of multinationals and local food industries, since innovation can significantly impact on their competitive advantages. Therefore, in this study, first we are going to investigate consumers’ motivations, attitudes and intention to buy functional foods, since the market demands a better understanding of this trend. A survey with 450 consumers was conducted and provided quantitative insights. Secondly, we identified the availability of functional food products in the local retail market, through observation techniques. Our aim was to confront consumers’ needs with local food companies’ market supply. In a further stage, we are going to analyse the functioning of this innovation system, describing the agents involved in this context and their relations through in-depth interviews with local representatives (stakeholders). Innovation system is here understood as the set of distinct institutions which jointly and individually contribute to the development and diffusion of new technologies and which provides the framework within which governments form and implement policies to influence the innovation process. As such "it is a system of interconnected institutions to create, store and transfer the knowledge, skills and artefacts which define new technologies." (Metcalfe, 1995). Hence, we are investigating issues such as: Are local food companies ready to innovate in such a competitive and dynamic scenario? How can this system respond to consumers’ demands? Are there conditions for an innovative food network in South Brazil? Our contributions help to shed light into these questions. Preliminary results indicate that the innovation system for functional foods in Rio Grande do Sul is incipient, but it is developing fast. Stronger governance and co-ordination strategies are needed. There are few local functional food products in the market, but those are attractive to consumers and indicate promising opportunities. The survey shows that interviewed consumers presented positive attitudes towards functional foods and enough purchasing power to buy it. Nutritionists and other health professionals have high credibility and could help inform consumers about the benefits of particular categories of functional foods. Food industry itself is not regarded as the most trustworthy source. Finally, this study shows that the understanding of Brazilian consumers is fundamental to help food companies define their strategies. To map the most accepted categories of functional foods is also important, aiming to avoid the "tentative and error" approach
Structural properties and enthalpy of formation of magnesium hydride from quantum Monte Carlo calculations
We have used diffusion Monte Carlo (DMC) calculations to study the structural
properties of magnesium hydride (MgH), including the pressure-volume
equation of state, the cohesive energy and the enthalpy of formation from
magnesium bulk and hydrogen gas. The calculations employ pseudopotentials and
B-spline basis sets to expand the single particle orbitals used to construct
the trial wavefunctions. Extensive tests on system size, time step, and other
sources of errors, performed on periodically repeated systems of up to 1050
atoms, show that all these errors together can be reduced to below 10 meV per
formula unit. We find excellent agreement with the experiments for the
equilibrium volume of both the Mg and the MgH crystals. The cohesive energy
of the Mg crystal is found to be 1.51(1) eV, and agrees perfectly with the
experimental value of 1.51 eV. The enthalpy of formation of MgH from Mg
bulk and H gas is found to be eV/formula unit, or kJ/mole, which is off the experimental one of kJ/mole only by 6
kJ/mole. This shows that DMC can almost achieve chemical accuracy (1 kcal/mole)
on this system. Density functional theory errors are shown to be much larger,
and depend strongly on the functional employed.Comment: 11 pages, 7 figures, to appear in Physical Review
A public dataset of 24-H multi-levels psycho-physiological responses in young healthy adults
Wearable devices now make it possible to record large quantities of physiological data, which can be used to obtain a clearer view of a person’s health status and behavior. However, to the best of our knowledge, there are no open datasets in the literature that provide psycho-physiological data. The Multilevel Monitoring of Activity and Sleep in Healthy people (MMASH) dataset presented in this paper provides 24 h of continuous psycho-physiological data, that is, inter-beat intervals data, heart rate data, wrist accelerometry data, sleep quality index, physical activity (i.e., number of steps per second), psychological characteristics (e.g., anxiety status, stressful events, and emotion declaration), and sleep hormone levels for 22 participants. The MMASH dataset will enable the investigation of possible relationships between the physical and psychological characteristics of people in daily life. Data were validated through different analyses that showed their compatibility with the literature
Eigenvalue repulsions in the quasinormal spectra of the Kerr-Newman black hole
We study the gravito-electromagnetic perturbations of the Kerr-Newman (KN)
black hole metric and identify the two photon sphere and near-horizon
families of quasinormal modes (QNMs) of the KN black hole, computing the
frequency spectra (for all the KN parameter space) of the modes with the
slowest decay rate. We uncover a novel phenomenon for QNMs that is unique to
the KN system, namely eigenvalue repulsion between QNM families. Such a feature
is common in solid state physics where \eg it is responsible for energy
bands/gaps in the spectra of electrons moving in certain Schr\"odinger
potentials. Exploiting the enhanced symmetries of the near-horizon limit of the
near-extremal KN geometry we also develop a matching asymptotic expansion that
allows us to solve the perturbation problem using separation of variables and
provides an excellent approximation to the KN QNM spectra near extremality. The
KN QNM spectra here derived are required not only to account for the
gravitational emission in astrophysical environments, such as the ones probed
by LIGO, Virgo and LISA, but also allow to extract observational implications
on several new physics scenarios, such as mini-charged dark-matter or certain
modified theories of gravity, degenerate with the KN solution at the scales of
binary mergers.Comment: 9 pages, 2 figure
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