1,235 research outputs found
Determining key research areas for healthier diets and sustainable food systems in Viet Nam
Vietnamese food systems are undergoing rapid transformation, with important implications for human and environmental health and economic development. Poverty has decreased, and diet quality and undernutrition have improved significantly since the end of the Doi Moi reform period (1986-1993) as a result of Viet Nam opening its economy and increasing its regional and global trade. Yet poor diet quality is still contributing the triple burden of malnutrition, with 25 percent stunting among children under age 5, 26 percent and 29 percent of women and children, respectively, anemic, and 21 percent of adults overweight. Agricultural production systems have shifted from predominantly diverse smallholder systems to larger more commercialized and specialized systems, especially for crops, while the ‘meatification’ of the Vietnamese diet is generating serious trade-offs between improved nutrition and sustainability of the Vietnamese food systems. The food processing industry has developed rapidly, together with food imports, resulting in new and processed food products penetrating the food retail outlets, trending towards an increase in the Westernized consumption patterns that are shifting nutrition-related problems towards overweight and obesity and, with it, an increase of non-communicable disease-related health risks. While regulatory policies exist across the food system, these are not systematically implemented, making food safety a major concern for consumers and policy makers alike. Where data exists, it is not easy to aggregate with data from across food system dimensions, making it difficult for Viet Nam to make an informed analysis of current and potential food system trade-offs. In our research, we reviewed existing literature and data, and applied a food systems framework to develop an initial food systems profile for Viet Nam and to identify a comprehensive set a of research questions to fill current data gaps identified through the review. Insights on these would provide the comprehensive evidence needed to inform policy makers on how to develop new food systems policies for Viet Nam, and further refine and improve existing policies to achieve better quality diets and more sustainable food systems in Viet Nam. Based on these, we then engaged with stakeholders to develop research priorities in the Viet Nam context and identified 25 priority research questions. This paper aims to stimulate such reflections by clearly outlining key areas for research, government policy, and development programs on priority investment to build the evidence base around inclusive food systems interventions that aim to result in healthier diets and more sustainable food systems for Viet Nam
Neural noise distorts perceived motion: the special case of the freezing illusion and the Pavard and Berthoz effect
When a slowly moving pattern is presented on a monitor which itself is moved, the pattern appears to freeze on the screen (Mesland and Wertheim in Vis Res 36(20):3325–3328, 1996) even if we move our head with the monitor, as with a head mounted display (Pavard and Berthoz in Perception 6:529–540, 1977). We present a simple model of these phenomena, which states that the perceived relative velocity between two stimuli (the pattern and the moving monitor) is proportional to the difference between the perceived velocities of these stimuli in space, minus a noise factor. The latter reflects the intrinsic noise in the neural signals that encode retinal image velocities. With noise levels derived from the literature the model fits empirical data well and also predicts strong distortions of visually perceived motion during vestibular stimulation, thus explaining both illusions as resulting from the same mechanism
Crystal Field Splitting and Charge Flow in the Buckled-Dimer Reconstruction of Si(100)—2× 1
The effect of the 2×1 reconstruction on the core-electron binding energies of the outermost Si(100) layers has been determined using high-resolution photoemission data. A previously unobserved 190-meV crystal-field splitting is resolved for the up-atoms of the asymmetric surface dimers, whose average core-level shift is -400 meV. The signal from the down-atoms is clearly identified and has a shift of +220 meV. These new findings indicate a charge flow of ∼0.05e from the subsurface to the surface layers, with a substantially larger difference of ∼0.34e between the up-atoms and down-atoms in the dimer
Thermal and Surface Core-Electron Binding-Energy Shifts in Metals
High-resolution photoemission spectra from the shallow core levels of alkali metals and of In have been obtained between 78 K and room temperature. The data yield values for the alkali-metal surface-atom core-level shift and show thermal shifts of comparable size for bulk and surface. The positive surface shifts are due to the spill-out of conduction-electron charge, which is responsible for the surface dipole layer. The surface shifts are in good agreement with values obtained from a Born-Haber cycle expressed in terms of surface energies. The thermal shifts are proportional to the lattice expansion, and arise from both initial-state and final-state effects. As the lattice expands, the Fermi level decreases, decreasing the core-electron binding energy. At the same time, the expansion of the conduction-electron charge increases rs, thereby decreasing the potential at the core level and increasing the binding energy. The expansion also decreases the relaxation energy, further increasing the core-electron binding energy. In the alkali metals, the combined potential- and relaxation-energy terms dominate the Fermi-level term, making the shifts positive. In divalent metals the three terms tend to cancel, while in trivalent metals it is the Fermi-level term that dominates, making the shifts negative
Metallic behaviour of carrier-polarized C molecular layers: Experiment and Theory
Although C is a molecular crystal with a bandgap E of ~2.5 eV, we
show that E is strongly affected by injected charge. In sharp contrast to
the Coulomb blockade typical of quantum dots, E is {\it reduced} by the
Coulomb effects. The conductance of a thin C layer sandwiched between
metal (Al, Ag, Au, Mg and Pt) contacts is investigated. Excellent Ohmic
conductance is observed for Al electrodes protected with ultra-thin LiF layers.
First-principles calculations, Hubbard models etc., show that the energy gap of
C is dramatically reduced when electrons hop from C to
C.Comment: 4 PRL style pages, 2 figures. email: [email protected]
Many-body aspects of positron annihilation in the electron gas
We investigate positron annihilation in electron liquid as a case study for
many-body theory, in particular the optimized Fermi Hypernetted Chain (FHNC-EL)
method. We examine several approximation schemes and show that one has to go up
to the most sophisticated implementation of the theory available at the moment
in order to get annihilation rates that agree reasonably well with experimental
data. Even though there is basically just one number to look at, the
electron-positron pair distribution function at zero distance, it is exactly
this number that dictates how the full pair distribution behaves: In most
cases, it falls off monotonously towards unity as the distance increases. Cases
where the electron-positron pair distribution exhibits a dip are precursors to
the formation of bound electron--positron pairs. The formation of
electron-positron pairs is indicated by a divergence of the FHNC-EL equations,
from this we can estimate the density regime where positrons must be localized.
This occurs in our calculations in the range 9.4 <= r_s <=10, where r_s is the
dimensionless density parameter of the electron liquid.Comment: To appear in Phys. Rev. B (2003
The Structure of the Vortex Liquid at the Surface of a Layered Superconductor
A density-functional approach is used to calculate the inhomogeneous vortex
density distribution in the flux liquid phase at the planar surface of a
layered superconductor, where the external magnetic field is perpendicular to
the superconducting layers and parallel to the surface. The interactions with
image vortices are treated within a mean field approximation as a functional of
the vortex density. Near the freezing transition strong vortex density
fluctuations are found to persist far into the bulk liquid. We also calculate
the height of the Bean-Livingston surface barrier.Comment: 8 pages, RevTeX, 2 figure
Self Consistent Molecular Field Theory for Packing in Classical Liquids
Building on a quasi-chemical formulation of solution theory, this paper
proposes a self consistent molecular field theory for packing problems in
classical liquids, and tests the theoretical predictions for the excess
chemical potential of the hard sphere fluid. Results are given for the self
consistent molecular fields obtained, and for the probabilities of occupancy of
a molecular observation volume. For this system, the excess chemical potential
predicted is as accurate as the most accurate prior theories, particularly the
scaled particle (Percus-Yevick compressibility) theory. It is argued that the
present approach is particularly simple, and should provide a basis for a
molecular-scale description of more complex solutions.Comment: 6 pages and 5 figure
Phase separation in mixtures of colloids and long ideal polymer coils
Colloidal suspensions with free polymer coils which are larger than the
colloidal particles are considered. The polymer-colloid interaction is modeled
by an extension of the Asakura-Oosawa model. Phase separation occurs into
dilute and dense fluid phases of colloidal particles when polymer is added. The
critical density of this transition tends to zero as the size of the polymer
coils diverges.Comment: 5 pages, 3 figure
Effective Magnetic Hamiltonian and Ginzburg Criterion for Fluids
We develop further the approach of Hubbard and Schofield (Phys.Lett., A40
(1972) 245), which maps the fluid Hamiltonian onto a magnetic one. We show that
all coefficients of the resulting effective Landau-Ginzburg-Wilson (LGW)
Hamiltonian may be expressed in terms of the compressibility of a reference
fluid containing only repulsive interactions, and its density derivatives; we
calculate the first few coefficients in the case of the hard-core reference
fluid. From this LGW-Hamiltonian we deduce approximate mean-field relations
between critical parameters and test them on data for Lennard-Jones,
square-well and hard-core-Yukawa fluids. We estimate the Ginzburg criterion for
these fluids.Comment: 4 pages, LaTeX, To appear in Phys.Rev.
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