Growth rate distribution and intermittency in kinematic turbulent dynamos : which moment predicts the dynamo onset?

We consider the generation of magnetic field by a turbulent flow. For the linear induction equation (i.e. the kinematic dynamo problem), we show that the statistical moments of the magnetic field display multiscaling and in particular moments of different order turn unstable for different values of the control parameter. On a canonical example, we map the problem onto the calculation of the injected power by a time correlated fluctuating force acting on a Brownian particle. We are then able to calculate analytically the growth rate of the moments of the magnetic field and explain the origin of this intermittency. We finally show that the onset for the nonlinear problem is predicted by the linear onset of the moment of order 0 + (i.e. the logarithm of the magnetic field

On the edge of an inverse cascade

We demonstrate that systems with a parameter-controlled inverse cascade can exhibit critical behavior for which at the critical value of the control parameter the inverse cascade stops. In the vicinity of such a critical point standard phenomenological estimates for the energy balance will fail since the energy flux towards large length scales becomes zero. We demonstrate these concepts using the computationally tractable model of two-dimensional magneto-hydrodynamics in a periodic box. In the absence of any external magnetic forcing the system reduces to hydrodynamic fluid turbulence with an inverse energy cascade. In the presence of strong magnetic forcing the system behaves as 2D magneto-hydrodynamic turbulence with forward energy cascade. As the amplitude of the magnetic forcing is varied a critical value is met for which the energy flux towards the large scales becomes zero. Close to this point the energy flux scales as a power law with the departure from the critical point and the normalized amplitude of the fluctuations diverges. Similar behavior is observed for the flux of the square vector potential for which no inverse flux is observed for weak magnetic forcing, while a finite inverse flux is observed for magnetic forcing above the critical point. We conjecture that this behavior is generic for systems of variable inverse cascade

Surface gravity waves propagating in a rotating frame: the Ekman-Stokes instability

We report on an instability arising when surface gravity waves propagate in a rotating frame. The Stokes drift associated to the uniform wave field, together with global rotation, drives a mean flow in the form of a horizontally invariant Ekman-Stokes spiral. We show that the latter can be subject to an instability that triggers the appearance of an additional horizontally-structured cellular flow. We determine the instability threshold numerically, in terms of the Rossby number Ro associated to the Stokes drift of the waves and the Ekman number E. We confirm the numerical results through asymptotic expansions at both large and low Ekman number. At large E the instability reduces to that of a standard Ekman spiral driven by the wave-induced surface stress instead of a wind stress, while at low E the Stokes-drift profile crucially determines the shape of the unstable mode. In both limits the instability threshold asymptotes to an Ekman-number-independent critical Rossby number, which in both cases also corresponds to a critical Reynolds number associated to the Lagrangian base-flow velocity profile. Parameter values typical of ocean swell fall into the low-E unstable regime: the corresponding "anti-Stokes" flows are unstable, with possible consequences for particle dispersion and mixing

A Handbook on Protein-Ligand Docking Tool: AutoDock 4

This tutorial aricle DOES NOT HAVE A ABSTRACT.If mandatory, it can be added on in the later stage

Onset of three-dimensionality in rapidly rotating turbulent flows

Turbulent flows driven by a vertically invariant body force were proven to become exactly two-dimensional above a critical rotation rate, using upper bound theory. This transition in dimensionality of a turbulent flow has key consequences for the energy dissipation rate. However, its location in parameter space is not provided by the bounding procedure. To determine this precise threshold between exactly 2D and partially 3D flows, we perform a linear stability analysis over a fully turbulent 2D base state. This requires integrating numerically a quasi-2D set of equations over thousands of turnover times, to accurately average the growth rate of the 3D perturbations over the statistics of the turbulent 2Dbase flow. We leverage the capabilities of modern GPUs to achieve this task, which allows us to investigate the parameter space up to Re = 10^5. At Reynolds numbers typical of 3D DNS and laboratory experiments, Re in [10^2, 5x10^3], the turbulent 2D flow becomes unstable to 3D motion through a centrifugal-type instability. However, at even higher Reynolds number another instability takes over. A candidate mechanism for the latter instability is the parametric excitation of inertial waves by the modulated 2D flow, a phenomenon that we illustrate with an oscillatory 2D Kolmogorov flow

Antimicrobial activity and phytochemicals of Solanum trilobatum Linn.

In this study, aqueous methanol and n-butanol extracts of aerial parts of Solanum trilobatum L. (Solanaceae) were tested for antimicrobial activity by disc diffusion method. From the results, it was found that extracts from leaves, flowers, stem and fruits revealed antimicrobial activity against Gram (+) and Gram (-) bacteria. Maximal antibacterial activity was seen against Klebsiella with aqueous extract whereas methanol extract of stem showed maximal activity against Staphylococcus aureus. TheMinimum Inhibitory Concentration (MIC) exhibited by S. trilobatum aqueous extracts against tested organisms ranged between 0.06-0.5 mg/ml. Presence of tannins, saponins, flavanoides, phenoliccompounds, cardiac glycosides and carbohydrates indicates S. trilobatum, is one of the potential medicinal plant for therapeutic use

Dynamo saturation down to vanishing viscosity: strong-field and inertial scaling regimes

We present analytical examples of fluid dynamos that saturate through the action of the Coriolis and inertial terms of the Navier-Stokes equation. The flow is driven by a body force and is subject to global rotation and uniform sweeping velocity. The model can be studied down to arbitrarily low viscosity and naturally leads to the strong-field scaling regime for the magnetic energy produced above threshold: the magnetic energy is proportional to the global rotation rate and independent of the viscosity. Depending on the relative orientations of global rotation and large-scale sweeping, the dynamo bifurcation is either supercritical or subcritical. In the supercritical case, the magnetic energy follows the scaling-law for supercritical strong-field dynamos predicted on dimensional grounds by Petrelis & Fauve (2001). In the subcritical case, the system jumps to a finite-amplitude dynamo branch. The magnetic energy obeys a magneto-geostrophic scaling-law (Roberts & Soward 1972), with a turbulent Elsasser number of the order of unity, where the magnetic diffusivity of the standard Elsasser number appears to be replaced by an eddy diffusivity. In the absence of global rotation, the dynamo bifurcation is subcritical and the saturated magnetic energy obeys the equipartition scaling regime. We consider both the vicinity of the dynamo threshold and the limit of large distance from threshold to put these various scaling behaviors on firm analytical ground

ANTIBACTERIAL AND ANTIFUNGAL ACTIVITY OF STREPTOMYCES SP. VITDDK3 ISOLATED FROM ENNORE COAST, TAMIL NADU, INDIA

Actinobacteria isolated from soil samples collected at the Ennore saltern, Tamil Nadu was screened for antibacterial and antifungal activity against common clinical pathogens. The isolate VITDDK3 exhibited more promising antagonistic activity against Escherichia coli, Pseudomonas aeruginosa, Aspergillus flavus and Aspergillus fumigatus. Presence of LL-Diaminopimelic acid and glycine assigned the isolate VITDDK3 to the genus Streptomyces. Further 16S rRNA partial gene sequence was carried out to confirm the chemotaxonomic results. BLAST analysis showed that the strain VITDDK3 possessed 98% similarity with Streptomyces sp. A254Ydz-ZZ but phylogenetic analysis revealed that its closest neighbour was Streptomyces tricolor HBUM175176. The rRNA secondary structure and the restriction sites of VITDDK3 were predicted using Genebee and NEBCutter online softwares respectivel