The scenario of two-dimensional instabilities of the cylinder wake under EHD forcing: A linear stability analysis

We propose to study the stability properties of an air flow wake forced by a dielectric barrier discharge (DBD) actuator, which is a type of electrohydrodynamic (EHD) actuator. These actuators add momentum to the flow around a cylinder in regions close to the wall and, in our case, are symmetrically disposed near the boundary layer separation point. Since the forcing frequencies, typical of DBD, are much higher than the natural shedding frequency of the flow, we will be considering the forcing actuation as stationary. In the first part, the flow around a circular cylinder modified by EHD actuators will be experimentally studied by means of particle image velocimetry (PIV). In the second part, the EHD actuators have been numerically implemented as a boundary condition on the cylinder surface. Using this boundary condition, the computationally obtained base flow is then compared with the experimental one in order to relate the control parameters from both methodologies. After validating the obtained agreement, we study the Hopf bifurcation that appears once the flow starts the vortex shedding through experimental and computational approaches. For the base flow derived from experimentally obtained snapshots, we monitor the evolution of the velocity amplitude oscillations. As to the computationally obtained base flow, its stability is analyzed by solving a global eigenvalue problem obtained from the linearized Navier–Stokes equations. Finally, the critical parameters obtained from both approaches are compared

Важлива складова національної безпеки (Проблеми захисту науково-технічної інформації)

У статті порушується проблема забезпечення захисту інформаційних ресурсів у науково- технічній сфері. Обґрунтовується значення науково-технологічного потенціалу для економічного і соціального розвитку України. Доводиться необхідність ґрунтовної розробки відповідної нормативно-правової бази.The article is dedicated to the problem of ensuring of protection of information resources in scientific-technical sphere, significance of the scientific-technological potential for economical and social growth of Ukraine is grounded. Necessity of well-founded development of correspondent normative and legal base is proved

Drag fluctuations of a disk in a turbulent jet: Effect of turbulent scales averaging

The drag fluctuations of a disk placed on the axis of a turbulent incompressible jet are studied at $Re=70000$. Statistics and spectra have been obtained for different disk sizes. A significant spatial averaging effect is observed in the symmetrization of probability distribution function and in the low-pass filtering of spectra. These effects are associated with a redistribution of the high-frequencies energy to the low frequencies. It is shown that this redistribution is done in such a way that the rms value of the drag fluctuations increases linearly with the disk surface. These results concerning the drag fluctuations are compared and found to be consistent with fluctuations of a global kinetic energy extracted from the turbulent field in front of the disk

Synchronization and collective swimming patterns in fish ( Hemigrammus bleheri )

In this work, we address the case of red nose tetra fish Hemigrammus bleheri swimming in groups in a uniform flow, giving special attention to the basic interactions and cooperative swimming of a single pair of fish. We first bring evidence of synchronization of the two fish, where the swimming modes are dominated by ‘out-phase’ and ‘in-phase’ configurations. We show that the transition to this synchronization state is correlated with the swimming speed (i.e. the flow rate), and thus with the magnitude of the hydrodynamic pressure generated by the fish body during each swimming cycle. From a careful spatio-temporal analysis corresponding to those synchronized modes, we characterize the distances between the two individuals in a pair in the basic schooling pattern. We test the conclusions of the analysis of fish pairs with a second set of experiments using groups of three fish. By identifying the typical spatial configurations, we explain how the nearest neighbour interactions constitute the building blocks of collective fish swimming.info:eu-repo/semantics/publishe

Geographic distribution and developmental sites of Aedes albopictus (Diptera : Culicidae) during a Chikungunya epidemic event

Aedes albopictus is generally considered to have a low vectorial capacity because of its lack of host specificity. Nevertheless, it has been the sole vector of the Chikungunya virus in recent explosive epidemics on the islands of La Reunion and Mauritius. We report on investigations of the seasonal prevalence, container preferences, and geographic distribution of the species on La Reunion. Ae. albopictus showed strong ecological plasticity. In the warm wet season, small disposable containers were the principal urban breeding site, with 1939 positive containers in 750 houses. In the dry winter season, the species remained abundant throughout the island up to 800 m and was present to a maximum altitude of 1200 m. Natural containers were clearly important in this season, although productive sources were hard to find. The preferred natural developmental sites were bamboo stumps and rock holes, over 357 developmental sites observed in peri-urban and gully areas. Generalized logistic models indicated that the optimum sites contained clear water with high organic content and were situated in sites with moderate shade. Our data will provide input into the models of the epidemiology of the disease and design of vector control programs

Forced wakes far from threshold: Stuart-Landau equation applied to experimental data

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