Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

Although global food demand is expected to increase 60% by 2050 compared with 2005/2007, the rise will be much greater in sub-Saharan Africa (SSA). Indeed, SSA is the region at greatest food security risk because by 2050 its population will increase 2.5-fold and demand for cereals approximately triple, whereas current levels of cereal consumption already depend on substantial imports. At issue is whether SSA can meet this vast increase in cereal demand without greater reliance on cereal imports or major expansion of agricultural area and associated biodiversity loss and greenhouse gas emissions. Recent studies indicate that the global increase in food demand by 2050 can be met through closing the gap between current farm yield and yield potential on existing cropland. Here, however, we estimate it will not be feasible to meet future SSA cereal demand on existing production area by yield gap closure alone. Our agronomically robust yield gap analysis for 10 countries in SSA using location-specific data and a spatial upscaling approach reveals that, in addition to yield gap closure, other more complex and uncertain components of intensification are also needed, i.e., increasing cropping intensity (the number of crops grown per 12 mo on the same field) and sustainable expansion of irrigated production area. If intensification is not successful and massive cropland land expansion is to be avoided, SSA will depend much more on imports of cereals than it does today.

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Can sub-Saharan Africa feed itself?

With the presentation of a theory of liquid alloys, we have now assembled all the necessary tools for the ab initio construction of an alloy phase diagram.

Alloy Phase Diagrams

An ultrafine-grained (UFG) surface layer was produced on Zr–1%Nb alloy using severe plastic deformation process induced by ultrasonic impact peening (UIP). XRD analysis and TEM observations allow establishing the links between the microstructure formed at different extents of the effective strain ē and superficial microhardness and corrosion resistance. In the topmost surface layer about 10 μm thick, average grain size diminishes down to approx. 100 nm after the UIP process for 4 min ( ē  ≈ 0.86). The mechanism of the grain subdivision is discussed on the basis of TEM observations of microstructure in surface layer at different strain extents with taking into account the dynamic recrystallization process facilitated by deformation induced heating. XRD analysis reveals high compressive residual stresses and strong basal texture. Two features of the surface layer formed after the UIP process, viz. UFG structure and strong basal texture, are considered to play the major roles in essential increase in microhardness (from 1 to 2.35 GPa) and corrosion resistance of the Zr-1%Nb alloy in saline solution. Decreased surface roughness and large compressive residual stresses also promote higher corrosion resistance.

Ultrafine-grained textured surface layer on Zr–1%Nb alloy produced by ultrasonic impact peening for enhanced corrosion resistance

Effect of heat treatment on the crystallographic orientation evolution in a near-α titanium alloy Ti60

Microstructural and textural developments during Zircaloy-4 fuel tube fabrication

Annealing of cold worked two-phase Zr-2.5 Nb—Associated microstructural developments

Cloud customers require highly reliable and performant leased datacenter infrastructure to deliver quality service for their users. It is thus critical for cloud providers to quickly detect and mitigate infrastructure faults. While much is known about managing faults that arise in the datacenter physical infrastructure (i.e., network and server equipment), comparatively little has been published regarding management of the logical overlay networks frequently employed to provide strong isolation in multi-tenant datacenters. We present a first look into the nuances of monitoring these "virtualized" networks through the lens of a large cloud provider. We describe challenges to building cloud-based fault monitoring systems, and use the output of a production system to illuminate how virtualization impacts multi-tenant datacenter fault management. We show that interactions between the virtualization, tenant software, and lower layers of the network fabric both simplify and complicate different aspects of fault detection and diagnosis efforts.

R. K. Tewari

Papers

Microstructural and textural developments during Zircaloy-4 fuel tube fabrication

Annealing of cold worked two-phase Zr-2.5 Nb—Associated microstructural developments

Cloud Datacenter SDN Monitoring: Experiences and Challenges

Development of Nb-1%Zr-0.1%C alloy as structural components for high temperature reactors

Coarsening of second phase in a two-phase Zr-2.5Nb: On the role of phase boundaries