On the unsteady behavior of turbulence models

Periodically forced turbulence is used as a test case to evaluate the predictions of two-equation and multiple-scale turbulence models in unsteady flows. The limitations of the two-equation model are shown to originate in the basic assumption of spectral equilibrium. A multiple-scale model based on a picture of stepwise energy cascade overcomes some of these limitations, but the absence of nonlocal interactions proves to lead to poor predictions of the time variation of the dissipation rate. A new multiple-scale model that includes nonlocal interactions is proposed and shown to reproduce the main features of the frequency response correctly

Sclera solar diameter observations

Focus is given to possible variations in solar luminosity and accurate methods of monitoring it. Aside from direct bolometry, one methodology for this type of research makes use of measurements of the solar diameter and limb darkening function as indirect indicators of the solar luminosity. This approach was reviewed

Impact assessment of food policy research a stocktaking workshop: synthesis report

"This stocktaking workshop provided an opportunity for several groups with active interest in impact assessment relating to agricultural policy research to share experiences and views about what constitutes good practice in this field. The sponsoring organizations have had a long-standing concern for the relevance and effectiveness of agricultural and food policy research in general and at IFPRI in particular. That concern has been addressed in past meetings and the time seemed right for a further stocktaking. The focus of this 2004 meeting was on impact assessment experience at IFPRI. IFPRI has, since the mid-1990s, carried out a variety of activities aimed at assessing the impact of its policy research, capacity strengthening, and policy communications programs. The workshop brought together practitioners of such impact assessment work, users of such information, as well as researchers whose activities have been the subject of impact assessment. The cogency and necessity of such impact accounting work was reaffirmed in general terms. There was constructively critical commentary on the merits of particular approaches and instruments, such as narrative recordings and more quantitative methods of attempting to measure effects of research investments. The perennial issue of challenging counterfactuals was necessarily addressed, and the practicality of experimental and quasi-experimental methods considered. The need for consistency of assessment approaches between ex post studies (which have been the bulk of IFPRI's experience to date) and ex ante assessment efforts that represent an increasing share of the assessment portfolio was also discussed. There has long been a commitment to work towards a strong impact-orientation “culture” within IFPRI; the workshop concluded that, while there has been progress in working toward mainstreaming such a culture, there is still far to go, and efforts must continue in this direction." from Author's AbstractImpact assessment, Agricultural policy, Food policy Research, Capacity strengthening, Research methods,

Evidence for hard and soft substructures in thermoelectric SnSe

SnSe is a topical thermoelectric material with a low thermal conductivity which is linked to its unique crystal structure. We use low-temperature heat capacity measurements to demonstrate the presence of two characteristic vibrational energy scales in SnSe with Debye temperatures thetaD1 = 345(9) K and thetaD2 = 154(2) K. These hard and soft substructures are quantitatively linked to the strong and weak Sn-Se bonds in the crystal structure. The heat capacity model predicts the temperature evolution of the unit cell volume, confirming that this two-substructure model captures the basic thermal properties. Comparison with phonon calculations reveals that the soft substructure is associated with the low energy phonon modes that are responsible for the thermal transport. This suggests that searching for materials containing highly divergent bond distances should be a fruitful route for discovering low thermal conductivity materials.Comment: Accepted by Applied Physics Letter

Broilers with Taste - Sustainable chicken takes flight

Engelse versie van de brochure 'Pluimvee met smaak : duurzame kip krijgt vleugels', die laat zien waar kansen liggen voor de Nederlandse pluimveesector om te verduurzamen. Twee uiteenlopende concepten, de Som der Delen en de Windstreek, geven ieder op eigen wijze invulling aan duurzaamheid op het primaire bedrijf. Ze bevatten belangrijke elementen voor verduurzaming, die als geheel of in onderdelen, nu of later, in de praktijk gebracht kunnen worden. Duurzaamheid kent immers niet één, maar vele vormen, afhankelijk van de ondernemers, de markt en de omgeving

Ferromagnetism below 10 K in Mn doped BiTe

Ferromagnetism is observed below 10 K in [Bi0.75Te0.125Mn0.125]Te. This material has the BiTe structure, which is made from the stacking of two Te-Bi-Te-Bi-Te blocks and one Bi-Bi block per unit cell. Crystal structure analysis shows that Mn is localized in the Bi2 blocks, and is accompanied by an equal amount of TeBi anti-site occupancy in the Bi2Te3 blocks. These TeBi anti-site defects greatly enhance the Mn solubility. This is demonstrated by comparison of the [Bi1-xMnx]Te and [Bi1-2xTexMnx]Te series; in the former, the solubility is limited to x = 0.067, while the latter has xmax = 0.125. The magnetism in [Bi1-xMnx]Te changes little with x, while that for [Bi1-2xTexMnx]Te shows a clear variation, leading to ferromagnetism for x > 0.067. Magnetic hysteresis and the anomalous Hall Effect are observed for the ferromagnetic samples.Comment: Accepted for publication in Phys. Rev.

Equivariant differential characters and symplectic reduction

We describe equivariant differential characters (classifying equivariant circle bundles with connections), their prequantization, and reduction

Theoretical investigation of magnetic order in ReOFeAs, Re = Ce, Pr

Density functional theory (DFT) calculations are carried out on ReOFeAs, Re = Ce, Pr, the parent compounds of the high-T$_c$ superconductors ReO$_{1-x}$F$_{x}$FeAs, in order to determine the magnetic order of the ground state. It is found that the magnetic moments on the Fe sites adopt a collinear antiferromagnetic order, similar to the case of LaOFeAs. Within the generalized gradient approximation along with Coulomb onsite repulsion (GGA+U), we show that the Re magnetic moments also adopt an antiferromagnetic order for which, within the ReO layer, same spin Re sites lie along a zigzag line perpendicular to the Fe spin stripes. While within GGA the Re 4f band crosses the Fermi level, upon inclusion of onsite Coulomb interaction the 4f band splits and moves away from the Fermi level, making ReOFeAs a Mott insulator.Comment: 5 pages, 4 figure