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Poster presented at Science Week 2014 - Bioversity International HQ, Rome (Italy), 24-27 Feb 201

Stagnation and Infall of Dense Clumps in the Stellar Wind of tau Scorpii

Observations of the B0.2V star tau Scorpii have revealed unusual stellar wind characteristics: red-shifted absorption in the far-ultraviolet O VI resonance doublet up to +250 km/s, and extremely hard X-ray emission implying gas at temperatures in excess of 10^7 K. We describe a phenomenological model to explain these properties. We assume the wind of tau Sco consists of two components: ambient gas in which denser clumps are embedded. The clumps are optically thick in the UV resonance lines primarily responsible for accelerating the ambient wind. The reduced acceleration causes the clumps to slow and even infall, all the while being confined by the ram pressure of the outflowing ambient wind. We calculate detailed trajectories of the clumps in the ambient stellar wind, accounting for a line radiation driving force and the momentum deposited by the ambient wind in the form of drag. We show these clumps will fall back towards the star with velocities of several hundred km/sec for a broad range of initial conditions. The infalling clumps produce X-ray emitting plasmas with temperatures in excess of (1-6)x10^7 K in bow shocks at their leading edge. The infalling material explains the peculiar red-shifted absorption wings seen in the O VI doublet. The required mass loss in clumps is 3% - 30% ofthe total mass loss rate. The model developed here can be generally applied to line-driven outflows with clumps or density irregularities. (Abstract Abridged)Comment: To appear in the ApJ (1 May 2000). 24 pages, including 6 embedded figure

Circumstellar grain extinction properties of recently discovered post AGB stars

The circumstellar grains of two hot evolved post asymptotic giant branch (post AGB) stars, HD 89353 and HD 213985 were examined. From ultraviolet spectra, energy balance of the flux, and Kurucz models, the extinction around 2175 A was derived. With visual spectra, an attempt was made to detect 6614 A diffuse band absorption arising from the circumstellar grains so that we could examine the relationship of these features to the infrared features. For both stars, we did not detect any diffuse band absorption at 6614 A, implying the carrier of this diffuse band is not the carrier of the unidentified infrared features not of the 2175 A bump. The linear ultraviolet extinction of the carbon-rich star HD 89353 was determined to continue across the 2175 A region with no sign of the bump; for HD 213985 it was found to be the reverse: a strong, wide bump in the mid-ultraviolet. The 213985 bump was found to be positioned at 2340 A, longward of its usual position in the interstellar medium. Since HD 213985 was determined to have excess carbon, the bump probably arises from a carbonaceous grain. Thus, in view of the ultraviolet and infrared properties of the two post AGB stars, ubiquitous interstellar infrared emission features do not seem to be associated with the 2175 A bump. Instead, the infrared features seem related to the linear ultraviolet extinction component: hydrocarbon grains of radius less than 300 A are present with the linear HD 89353 extinction; amorphous anhydrous carbonaceous grains of radius less than 50 A might cause the shifted ultraviolet extinction bump of HD 213985

Case Study #8-7 of the Program: ''Food Policy For Developing Countries: The Role Of Government In The Global Food System''

13 pp.©Cornell University, Ithaca, New York. All rights reserved. This case study may be reproduced for educational purposes without express permission but must include acknowledgment to Cornell University. No commercial use is permitted without permission.Soil salinity is one of the critical factors responsible for the ongoing land degradation in the irrigated lowlands of Central Asia, including in the lower reaches of the Amudarya Delta. This land degradation hinders sustainable development and presents a major challenge for the area's rural population, whose livelihood security depends on irrigated agriculture. The factors causing soil salinity are multifaceted and interlinked; recent studies and interventions confirm that no one action alone will deliver a sustainable solution. Recommendations for alleviating soil salinity should take into account the complex interactions and can be formulated only once the interlinked factors causing soil salinity are understood. In the past, little attention was paid to creeping land degradation, which has resulted from soil salinization and waterlogging across huge agricultural and even nonagricultural areas. This case study focuses on the vicious circle of soil salinization: agriculture's consumption of large amounts of water contributes to shallow groundwater, leading to recurring soil salinity, which in turn demands more water for leaching (flushing the salts out of the rooting zone). The situation is exacerbated when water is not available in sufficient amounts in time and in space. The seemingly stable present water flows in the major water source (the Amudarya River) since the major drought in 2000–01 is caused by increased glacier melting in upstream countries. This water supply in turn diverts attention from the strong need for improved irrigation and cropping practices. Efforts aimed at reducing the amounts of irrigation water use face the problem of the devilish vicious circle, which has not only technical but also financial and political dimensions. Your assignment is to present policy options for managing soil salinity in a more sustainable way. Focus on incentives and instruments to solve the artificial water shortage problem.Cornell University Division of Nutritional Science

The photometric evolution of dissolving star clusters I: First predictions

We calculated the broad-band photometric evolution of unresolved star clusters, including the preferential loss of low-mass stars due to mass segregation. The stellar mass function of a cluster evolves due to three effects: (a) the evolution of massive stars; (b) early tidal effects reduce the mass function independently of the stellar mass; (c) after mass segregation has completed, tidal effects preferentially remove the lowest-mass stars from the cluster. Results: (1) During the first ~40% of the lifetime of a cluster the cluster simply gets fainter due to the loss of stars by tidal effects. (2) Between ~40 and ~80% of its lifetime the cluster gets bluer due to the loss of low-mass stars. This will result in an underestimate of the age of clusters if standard cluster evolution models are used (0.15 -- 0.5 dex). (3) After ~80% of the total lifetime of a cluster it will rapidly get redder. This is because stars at the low-mass end of the main sequence, which are preferentially lost, are bluer than the AGB stars that dominate the light at long wavelengths, resulting in an age overestimate. (4) Clusters with mass segregation and the preferential loss of low-mass stars evolve along almost the same tracks in colour-colour diagrams as clusters without mass segregation. Therefore it will be difficult to distinguish this effect from that due to the cluster age for unresolved clusters, unless the total lifetime of the clusters can be estimated. (5) The changes in the colour evolution of unresolved clusters due to the preferential loss of low-mass stars will affect the determination of the SFHs. (6) The preferential loss of low-mass stars might explain the presence of old (~13 Gyr) clusters in NGC 4365 which are photometrically disguised as intermediate-age clusters (2 - 5 Gyr). [Abridged]Comment: accepted for publication in A&

Hot Die Forming - Flat (HDF-F^Al):An innovative hot forming technology for extreme lightweight in aluminum sheet alloys

Aluminum is an ideal material for light transport applications. Despite the obvious advantages in weight ratio and corrosion resistance, high strength aluminum alloys have limited formability compared to traditional steels at room temperature conditions. A solution is to combine mechanical loading with thermal component i.e. deformation at elevated temperature. Currently super plastic forming and Quick Plastic Forming (QPF) is used to enhance the formability of Aluminum alloys. However, the cycle time for super plastic forming as well as for QPF is too high for mass production. An innovative and novel forming method called Hot Die Forming (HDF) has been developed to achieve high strains in high strength aluminum alloys (maximum 700 [MPa]) by heating them to Solution Heat Temperature (SHT), while keeping the cycle time suitable for large scale production. To study the feasibility and optimize the process parameters, a digital platform has been developed for simulations of HDF process. The simulation process has been automated, the user can provide tool geometries and input parameters to check the feasibility of HDF process or to optimize the parameters and die shape