Interoperability in the Heterogeneous Cloud Environment: A Survey of Recent User-centric Approaches

© 2016 Copyright held by the owner/author(s). Cloud computing provides users the ability to access shared, online computing resources. However, providers often offer their own proprietary applications, interfaces, APIs and infrastructures, resulting in a heterogeneous cloud environment. This heterogeneous environment makes it difficult for users to change cloud service providers; exploring capabilities to support the automated migration from one provider to another is an active, open research area. Many standards bodies (IEEE, NIST, DMTF and SNIA), industry (middleware) and academia have been pursuing approaches to reduce the impact of vendor lock-in by investigating the cloud migration problem at the level of the VM. However, the migration downtime, decoupling VM from underlying systems and security of live channels remain open issues. This paper focuses on analysing recently proposed live, cloud migration approaches for VMs at the infrastructure level in the cloud architecture. The analysis reveals issues with flexibility, performance, and security of the approaches, including additional loads to the CPU and disk I/O drivers of the physical machine where the VM initially resides. The next steps of this research are to develop and evaluate a new approach LibZam (Libya Zamzem) that will work towards addressing the identified limitations

What sets the magnetic field strength and cycle period in solar-type stars?

Two fundamental properties of stellar magnetic fields have been determined by observations for solar-like stars with different Rossby numbers (Ro), namely, the magnetic field strength and the magnetic cycle period. The field strength exhibits two regimes: 1) for fast rotation it is independent of Ro, 2) for slow rotation it decays with Ro following a power law. For the magnetic cycle period two regimes of activity, the active and inactive branches, also have been identified. For both of them, the longer the rotation period, the longer the activity cycle. Using global dynamo simulations of solar like stars with Rossby numbers between ~0.4 and ~2, this paper explores the relevance of rotational shear layers in determining these observational properties. Our results, consistent with non-linear alpha^2-Omega dynamos, show that the total magnetic field strength is independent of the rotation period. Yet at surface levels, the origin of the magnetic field is determined by Ro. While for Ro<1 it is generated in the convection zone, for Ro>1 strong toroidal fields are generated at the tachocline and rapidly emerge towards the surface. In agreement with the observations, the magnetic cycle period increases with the rotational period. However, a bifurcation is observed for Ro~1, separating a regime where oscillatory dynamos operate mainly in the convection zone, from the regime where the tachocline has a predominant role. In the latter the cycles are believed to result from the periodic energy exchange between the dynamo and the magneto-shear instabilities developing in the tachocline and the radiative interior.Comment: 43 pages, 14 figures, accepted for publication in The Astrophysical Journa

Rheology of high-performance cement pastes: effect of calcined kaolin

The search for a quality of concrete is a major concern in Algeria especially after the 2003 earthquake (East- Algeria). So it's necessary to improve the properties of concrete using fine particles such as mineral additions as a solution. These are currently used in the concrete to develop its performance and reduce consumption of clinker. This reduction will contribute to economic and easy way to solve problems related to the environment. In this work, an experimental rheological investigation was conducted to evaluate the performances of Algerian metakaolin MK on cement pastes. The latter is obtained from calcined natural kaolin found in large amounts in eastern Algeria (Tamazert- Milia). Several rheological tests were carried out by using the stress controlled rheometer AR2000, on the fresh cement pastes incorporating 0%, 5%, 10%, 15% and 20% of MK. The effects of metakaolin on the rheological behaviour of pastes were discussed. The parameters such as shear stress, viscosity, compliance, loss and storage shear modulus were evaluated by means of rheological techniques of both flow test, oscillatory and creep dynamic tests. The study in dynamic mode allow to give information on the evolution of the paste structure related to practically interesting problems such as workability. The results obtained have shown that the metakaolin improves the flowability and exhibits viscous rheological behaviour of cement pastes compared to the elastic behaviour of control paste (0%MK). Moreover, the creep test has shown that MK exhibits a viscoelastic liquid behaviour of cement pastes compared to a viscoelastic solid behaviour of control paste. In addition, it seems that the replacement rate of 10% of MK is an optimum for better rheological behavior of cement pastes. The rheological tests give promising results that encourage the use of metakaolin as component for a high performance concrete designated for industry