Synchronization of Low Reynolds Number Plane Couette Turbulence

We demonstrate that a separation of the velocity field in large and small scales according to a streamwise Fourier decomposition identifies subspaces with stable Lyapunov exponents and allows the dynamics to exhibit properties of an inertial manifold, such as the synchronization of the small scales in simulations sharing the same large scales or equivalently the decay of all small scale flow states to the state uniquely determined from the large scale flow. This behaviour occurs for deviations with streamwise wavelength smaller than 130 wall units which was shown in earlier studies to correspond to the streamwise spectral peak of the cross-flow velocity components of the top Lyapunov vector of the turbulent flow

Reduction of Hf via Hf/Zr Substitution in Mechanically Alloyed (Hf,Ti)CoSb Half-Heusler Solid Solutions

Abstract (Hf,Zr,Ti)Co(Sb,Sn) Solid solutions were prepared by mechanical-alloying followed by hot-press method as an attempt to reduce Hf concentration and therefore the material’s cost without negatively affecting the thermoelectric performance. To this end, two different methods were applied: (a) Hf substitution with its lighter and cheaper homologue Zr; and (b) fine tuning of carrier concentration by the substitution of Sb with Sn. The isoelectronic substitution of Hf with Zr was investigated in Hf0.6-xZrxTi0.4CoSb0.8Sn0.2 solid solutions and resulted in lower power factors and ZTs. However, the low thermal conductivity of Hf0.4Zr0.2Ti0.4CoSb0.8Sn0.2 contributed in achieving a relatively good ZT~0.67 at 970 K. The effect of charge carrier concentration was investigated by preparing Hf0.4Zr0.2Ti0.4CoSb1-ySny (y = 0.15–0.25) compounds. Hf0.4Zr0.2Ti0.4CoSb0.83Sn0.17 composition prepared by six hours milling reached the highest ZT of 0.77 at 960 K.publishedVersio

Distributed Artificial Intelligence Solution for D2D Communication in 5G Networks

Device to Device (D2D) Communication is one of the technology components of the evolving 5G architecture, as it promises improvements in energy efficiency, spectral efficiency, overall system capacity, and higher data rates. The above noted improvements in network performance spearheaded a vast amount of research in D2D, which have identified significant challenges that need to be addressed before realizing their full potential in emerging 5G Networks. Towards this end, this paper proposes the use of a distributed intelligent approach to control the generation of D2D networks. More precisely, the proposed approach uses Belief-Desire-Intention (BDI) intelligent agents with extended capabilities (BDIx) to manage each D2D node independently and autonomously, without the help of the Base Station. The paper includes detailed algorithmic description for the decision of transmission mode, which maximizes the data rate, minimizes the power consumptions, while taking into consideration the computational load. Simulations show the applicability of BDI agents in jointly solving D2D challenges.Comment: 10 pages,9 figure

Fluctuation covariance-based study of roll-streak dynamics in Poiseuille flow turbulence

The roll-streak (R-S) is fundamentally involved in the dynamics of wall-turbulence and, despite its central role, the physical mechanism responsible for its formation and maintenance remains controversial. In this work we investigate the dynamics maintaining the R-S in turbulent Poiseuille flow at $Re=1650$. Spanwise collocation is used to remove spanwise displacement of the streaks and associated flow components, which isolates the streamwise-mean flow R-S component and the second-order statistics of the streamwise-varying fluctuations that are collocated with the R-S. This streamwise-mean/fluctuation partition of the dynamics facilitates exploiting insights gained from the analytic characterization of turbulence in restricted nonlinear dynamics and its closely associated second-order statistical state dynamics (SSD) analogue, referred to as S3T. Symmetry of the statistics about the streak centerline permits separation of the fluctuations to sinuous and varicose components. The Reynolds stress forcing induced by the sinuous and varicose components to the R-S is shown to reinforce low- and high-speed streaks respectively. This targeted reinforcement of streaks by the Reynolds stresses occurs continuously as the fluctuation field is strained by the streamwise-mean streak and not intermittently as would be associated with streak-breakdown events. The Reynolds stresses maintaining the streamwise-mean roll can be attributed primarily to the dominant POD modes of the fluctuations, which were identified as the time average structure of optimal perturbations on the streak. These results are consistent with a universal process of streak instability in turbulent shear flow arising from torques generated by straining turbulent fluctuations, which was identified using the S3T SSD.Comment: 23 pages, 17 figures, submitted for publication to the Journal of Fluid Mechanic

From Lewis Carroll’s “Alice in Wonderland” to “Alice on social media”: Approaches of fantasy as a real experience in Cyberspace

In the present study, we implement the theory of Hermeneutics in order to understand the element of reality in the virtual world experience. We attempted to formulate cases on the user experiences and interpret them, as described in existing research and reflected on social media. Our focus topic consists of the use of imagination and its contribution to the construction of identity, behavior and relationships in the virtual environment of social media. We also make references to the elements of irrationality and time, two variables that are likely to affect the way users perceive reality. The online methodological tools and programs Concept-mapping and Social Network Visualiser were used in order to collect and capture the mentioned and further related concepts as well. The results of the study include possible conceptual correlations in social media, for which we argue that their virtuality depends on the actions of the user, and individual conclusions about the function of the imagination, which we consider to be an integral part of conception, implementation and quality of reality