Assessment of Existing and Prospective World Economic and Food Trends

This report is part of a broad study addressed to an assessment of the world food situation undertaken at IIASA. The central objectives of the study are to: evaluate the nature and dimensions of the world food situation; identify the underlying factors; investigate alternative courses of policy action at the national, regional, and global level that may alleviate existing and emerging food problems in years ahead; and develop models suitable for quantifying intra- and intercountry and global food interdependencies based on strategic variables and probable policy alternatives. Pursuing these objectives the study divides into the following interrelated and integrated components: (I) Assessment of Existing and Prospective World Economic and Food Trends; (II) Evaluation of Physical, Economic and Institutional Factors Affecting the Food and Agriculture Economy; (III) Tracing Linkages Between the World Food Economy and Energy, Water, Chemicals, Climate and Environment and Constraints Imposed by them on (IV) Definition and Measurement of Food and Nutrition Deficiencies; (V) Development of Sets of National and International Policy Strategies for Meeting Food and Nutrition Goals; This report provides a current assessment of the dimensions of the general problem as background for country modeling efforts underway in the Food and Agriculture project at IIASA

National and International Food Policies and Options that Impact on World Trade and Aid

This report includes firstly a discussion of food goals, instruments and performance indicators in a general policy classification scheme. Then the main policy goals and instruments affecting agriculture and food trade on a country and commodity basis are noted. In the final two sections major international trade and aid policies and options are summarized and evaluated

Spin-orbit induced backflow in neutron matter with auxiliary field diffusion Monte Carlo

The energy per particle of zero-temperature neutron matter is investigated, with particular emphasis on the role of the $\vec L\cdot\vec S$ interaction. An analysis of the importance of explicit spin--orbit correlations in the description of the system is carried out by the auxiliary field diffusion Monte Carlo method. The improved nodal structure of the guiding function, constructed by explicitly considering these correlations, lowers the energy. The proposed spin--backflow orbitals can conveniently be used also in Green's Function Monte Carlo calculations of light nuclei.Comment: 4 pages, 1 figur

Raman spectroscopies in shock-compressed materials

Spontaneous Raman spectroscopy, stimulated Raman scattering and coherent anti-Stokes Raman scattering have been used to measure temperatures and changes in molecular vibrational frequencies for detonating and shocked materials. Inverse Raman and Raman induced Kerr effect spectroscopies have been suggested as diagnostic probes for determining and phenomenology of shock-induced chemical reactions. The practicality, advantages, and disadvantages of using Raman scattering techniques as diagnostic probes of microscopic phenomenology through and immediately behind the shock front of shock-compressed molecular systems are discussed

Growing Correlation Length on Cooling Below the Onset of Caging in a Simulated Glass-Forming Liquid

We present a calculation of a fourth-order, time-dependent density correlation function that measures higher-order spatiotemporall correlations of the density of a liquid. From molecular dynamics simulations of a glass-forming Lennard-Jones liquid, we find that the characteristic length scale of this function has a maximum as a function of time which increases steadily beyond the characteristic length of the static pair correlation function $g(r)$ in the temperature range approaching the mode coupling temperature from above

Large eddy simulation of a turbulent non-premixed propane-air reacting flame in a cylindrical combustor

Large Eddy Simulation (LES) is applied to investigate the turbulent non-premixed combustion flow, including species concentrations and temperature, in a cylindrical combustor. Gaseous propane (C3H8) is injected through a circular nozzle which is attached at the centre of the combustor inlet. Preheated air with a temperature of 773 K is supplied through the annulus surrounding of this fuel nozzle. In LES a spatial filtering is applied to the governing equations to separate the flow field into large-scale and small-scale eddies. The large-scale eddies which carry most of the turbulent energy are resolved explicitly, while the unresolved small-scale eddies are modelled using the Smagorinsky model with Cs = 0.1 as well as dynamically calibrated Cs. The filtered values of the species mass fraction, temperature and density, which are the functions of the mixture fraction (conserved scalar), are determined by integration over a beta probability density function (β-PDF). The computational results are compared with those of the experimental investigation conducted by Nishida and Mukohara. According to this experiment, the overall equivalence ratio of 0.6, which is calculated from the ratio of the air flow rate supplied to the combustion chamber to that of the stoichiometric reaction, is kept constant so that the turbulent combustion at the fuel nozzle exit starts under the fuel-rich conditions

Neutron matter at zero temperature with auxiliary field diffusion Monte Carlo

The recently developed auxiliary field diffusion Monte Carlo method is applied to compute the equation of state and the compressibility of neutron matter. By combining diffusion Monte Carlo for the spatial degrees of freedom and auxiliary field Monte Carlo to separate the spin-isospin operators, quantum Monte Carlo can be used to simulate the ground state of many nucleon systems (A\alt 100). We use a path constraint to control the fermion sign problem. We have made simulations for realistic interactions, which include tensor and spin--orbit two--body potentials as well as three-nucleon forces. The Argonne $v_8'$ and $v_6'$ two nucleon potentials plus the Urbana or Illinois three-nucleon potentials have been used in our calculations. We compare with fermion hypernetted chain results. We report results of a Periodic Box--FHNC calculation, which is also used to estimate the finite size corrections to our quantum Monte Carlo simulations. Our AFDMC results for $v_6$ models of pure neutron matter are in reasonably good agreement with equivalent Correlated Basis Function (CBF) calculations, providing energies per particle which are slightly lower than the CBF ones. However, the inclusion of the spin--orbit force leads to quite different results particularly at relatively high densities. The resulting equation of state from AFDMC calculations is harder than the one from previous Fermi hypernetted chain studies commonly used to determine the neutron star structure.Comment: 15 pages, 15 tables and 5 figure

An NMR-based nanostructure switch for quantum logic

We propose a nanostructure switch based on nuclear magnetic resonance (NMR) which offers reliable quantum gate operation, an essential ingredient for building a quantum computer. The nuclear resonance is controlled by the magic number transitions of a few-electron quantum dot in an external magnetic field.Comment: 4 pages, 2 separate PostScript figures. Minor changes included. One reference adde

Dynamic Front Transitions and Spiral-Vortex Nucleation

This is a study of front dynamics in reaction diffusion systems near Nonequilibrium Ising-Bloch bifurcations. We find that the relation between front velocity and perturbative factors, such as external fields and curvature, is typically multivalued. This unusual form allows small perturbations to induce dynamic transitions between counter-propagating fronts and nucleate spiral vortices. We use these findings to propose explanations for a few numerical and experimental observations including spiral breakup driven by advective fields, and spot splitting

Cosmic distance-duality as probe of exotic physics and acceleration

In cosmology, distances based on standard candles (e.g. supernovae) and standard rulers (e.g. baryon oscillations) agree as long as three conditions are met: (1) photon number is conserved, (2) gravity is described by a metric theory with (3) photons travelling on unique null geodesics. This is the content of distance-duality (the reciprocity relation) which can be violated by exotic physics. Here we analyse the implications of the latest cosmological data sets for distance-duality. While broadly in agreement and confirming acceleration we find a 2-sigma violation caused by excess brightening of SN-Ia at z > 0.5, perhaps due to lensing magnification bias. This brightening has been interpreted as evidence for a late-time transition in the dark energy but because it is not seen in the d_A data we argue against such an interpretation. Our results do, however, rule out significant SN-Ia evolution and extinction: the "replenishing" grey-dust model with no cosmic acceleration is excluded at more than 4-sigma despite this being the best-fit to SN-Ia data alone, thereby illustrating the power of distance-duality even with current data sets.Comment: 6 pages, 4 colour figures. Version accepted as a Rapid Communication in PR