scholarly journals Spherical convective dynamos in the rapidly rotating asymptotic regime

2017 ◽  
Vol 813 ◽  
pp. 558-593 ◽  
Author(s):  
Julien Aubert ◽  
Thomas Gastine ◽  
Alexandre Fournier
Keyword(s):  
Large Scale ◽  
Scaling Laws ◽  
Numerical Solutions ◽  
Strong Field ◽  
Magnetic Reynolds Number ◽  
Small Scale ◽  
Asymptotic State ◽  
Asymptotic Regime ◽  
Classical Models ◽  
Definition Of

Self-sustained convective dynamos in planetary systems operate in an asymptotic regime of rapid rotation, where a balance is thought to hold between the Coriolis, pressure, buoyancy and Lorentz forces (the MAC balance). Classical numerical solutions have previously been obtained in a regime of moderate rotation where viscous and inertial forces are still significant. We define a uni-dimensional path in parameter space between classical models and asymptotic conditions from the requirements to enforce a MAC balance and to preserve the ratio between the magnetic diffusion and convective overturn times (the magnetic Reynolds number). Direct numerical simulations performed along this path show that the spatial structure of the solution at scales larger than the magnetic dissipation length is largely invariant. This enables the definition of large-eddy simulations resting on the assumption that small-scale details of the hydrodynamic turbulence are irrelevant to the determination of the large-scale asymptotic state. These simulations are shown to be in good agreement with direct simulations in the range where both are feasible, and can be computed for control parameter values far beyond the current state of the art, such as an Ekman number $E=10^{-8}$. We obtain strong-field convective dynamos approaching the MAC balance and a Taylor state to an unprecedented degree of accuracy. The physical connection between classical models and asymptotic conditions is shown to be devoid of abrupt transitions, demonstrating the asymptotic relevance of classical numerical dynamo mechanisms. The fields of the system are confirmed to follow diffusivity-free, power-based scaling laws along the path.

scholarly journals Geographical and logistical factors of sustainable development of rural tourism in the context of regional economy

2016 ◽  
pp. 9-14
Author(s):  
I. Smyrnov
Keyword(s):  
Sustainable Development ◽  
Large Scale ◽  
Regional Economy ◽  
Local Economy ◽  
Rural Tourism ◽  
Small Scale ◽  
Resource Base ◽  
Tourist Flows ◽  
Definition Of ◽  
The Impact

Rural tourism is now seen as an important direction of development of the regional economy. From the perspective of sustainable development rural tourism affects the economic, social and environmental aspects of the regional and local economy. Rural tourism is closely linked with agrotourism, eco-tourism, natural tourism and so on. Sustainable rural tourism can be realized by applying logistic, geographic and marketing approaches as components of sustainable development strategies. Logistics approach is determined by logistic potential of resource base of rural tourism and appropriate tourist flows regulation. In this context in the article the concept of tourism capacity or capacity of the resource base of rural tourism is used. The problem of the definition of tourism pressure on the resource base of rural tourism, particularly in natural landscapes is disclosed. Unlike environmental and recrealogical sciences, which stop at the capacity definition of the resource base of tourism, tourism logistics compares this figure with the existing tourist flows and accordingly determines the safe way of tourism management to ensure its sustainable nature. It was shown that these strategies boil down to two basic types – the further development of tourism in a particular area or limit such activities to conserve the resource base of tourism. Recreational (travel) load is the indicator that reflects the impact of tourism on the resource base of tourism (especially landscape complex), expressed by the number of tourists or tourists-days per area unit or per tourist site for the certain period of time (day, month, season year). There are actual, allowable (the maximum) and destructive (dangerous) types of travel load. The latter can lead recreational area or resource base of rural tourism to destruction. Thus, depending on the intensity of tourism resource base using in rural tourism it may change – according to tourist consumption. Large number of tourists affects the entire range of recreational destinations and their individual components. The most vulnerable part of the environment in this sense is vegetation, except that significant changes may occur with soil, water bodies, air and so on. The geographic dimension of the problem of rural tourism sustainable development includes the concept of zoning, ie the division of the territory, offering to develop rural tourism in several zones with different modes of travel usage – from a total ban (in protected areas) for complete freedom with transitional stages, involving various limit degrees in the development of rural tourism. Marketing approach reflects the application of the curve R. Butler to the stages of development of rural tourism destinations with the release of such steps as: research, involvement, development, consolidation, stagnation (also called “saturation”), revival or decline. Shown the models that link the stage of resource base tourist development (under “Curve Butler”), strength of tourism consumption the magnitude of such effects (eg weak (disperse) impact in large scale, strong (concentrated) impact in large scale, strong (concentrated) impact in small scale, weak (disperse) impact in small scale), dynamics of tourism development at the territory.

Conclusion

2017 ◽  
Keyword(s):  
National Identity ◽  
Geographical Distribution ◽  
Crucial Role ◽  
Large Scale ◽  
Small Scale ◽  
Modern History ◽  
Late Modernity ◽  
History Of ◽  
Definition Of

This chapter extends the book’s insights about nature, technology, and nation to the larger history of the modern period. While the modern nation loses its grip as a locus of identity and analysis, attempts to understand the operation, disruption, and collapse of continental and global infrastructures continue to mix the natural and the machinic in ways that define them both. Those vulnerabilities emphasize large-scale catastrophe; historiographically, they mask the crucial role of small-scale failures in the experience and culture of late modernity, including its definition of nature. Historical actors turned the uneven geographical distribution of small-scale failures into a marker of distinctive local natures and an element of regional and national identity. Attending to those failures helps not only situate cold-war technologies in the larger modern history of natural and machinic orders; it helps provincialize the superpowers by casting problematic “other” natures as central and primary.

scholarly journals Balanced reconnection intervals: four case studies

2008 ◽  
Vol 26 (12) ◽  
pp. 3897-3912 ◽  
Author(s):  
A. D. DeJong ◽  
A. J. Ridley ◽  
C. R. Clauer
Keyword(s):  
Case Studies ◽  
Large Scale ◽  
The Other ◽  
Small Scale ◽  
Polar Cap ◽  
Reconnection Rate ◽  
Magnetospheric Convection ◽  
The Third ◽  
New Name ◽  
Definition Of

Abstract. During steady magnetospheric convection (SMC) events the magnetosphere is active, yet there are no data signatures of a large scale reconfiguration, such as a substorm. While this definition has been used for years it fails to elucidate the true physics that is occurring within the magnetosphere, which is that the dayside merging rate and the nightside reconnection rate balance. Thus, it is suggested that these events be renamed Balanced Reconnection Intervals (BRIs). This paper investigates four diverse BRI events that support the idea that new name for these events is needed. The 3–4 February 1998 event falls well into the classic definition of an SMC set forth by Sergeev et al. (1996), while the other challenge some previous notions about SMCs. The 15 February 1998 event fails to end with a substorm expansion and concludes as the magnetospheric activity slowly quiets. The third event, 22–23 December 2000, begins with a slow build up of magnetospheric activity, thus there is no initiating substorm expansion. The last event, 17 February 1998, is more active (larger AE, AL and cross polar cap potential) than previously studied SMCs. It also has more small scale activity than the other events studied here.

scholarly journals Inverse Energy Cascade in Advanced MHD Turbulence (the RNG Method)

1993 ◽  
Vol 157 ◽  
pp. 255-261
Author(s):  
N. Kleeorin ◽  
I. Rogachevskii
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Magnetic Field Effect ◽  
Magnetic Reynolds Number ◽  
Energy Cascade ◽  
Small Scale ◽  
Magnetic Fluctuations ◽  
Mhd Turbulence ◽  
Inverse Energy Cascade ◽  
Large Scale Magnetic Field

The nonlinear (in terms of the large-scale magnetic field) effect of the modification of the magnetic force by an advanced small-scale magnetohydrodynamic (MHD) turbulence is considered. The phenomenon is due to the generation of magnetic fluctuations at the expense of hydrodynamic pulsations. It results in a decrease of the elasticity of the large-scale magnetic field.The renormalization group (RNG) method was employed for the investigation of the MHD turbulence at the large magnetic Reynolds number. It was found that the level of the magnetic fluctuations can exceed that obtained from the equipartition assumption due to the inverse energy cascade in advanced MHD turbulence.This effect can excite an instability of the large-scale magnetic field due to the energy transfer from the small-scale turbulent pulsations. This instability is an example of the inverse energy cascade in advanced MHD turbulence. It may act as a mechanism for the large-scale magnetic ropes formation in the solar convective zone and spiral galaxies.

Navier–Stokes solutions of unsteady separation induced by a vortex

2002 ◽  
Vol 465 ◽  
pp. 99-130 ◽  
Author(s):  
A. V. OBABKO ◽  
K. W. CASSEL
Keyword(s):  
Boundary Layer ◽  
Large Scale ◽  
Numerical Solutions ◽  
Stokes Equations ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Recirculation Region ◽  
Small Scale ◽  
Navier Stokes Equations ◽  
Scale Interaction

Numerical solutions of the unsteady Navier–Stokes equations are considered for the flow induced by a thick-core vortex convecting along a surface in a two-dimensional incompressible flow. The presence of the vortex induces an adverse streamwise pressure gradient along the surface that leads to the formation of a secondary recirculation region followed by a narrow eruption of near-wall fluid in solutions of the unsteady boundary-layer equations. The locally thickening boundary layer in the vicinity of the eruption provokes an interaction between the viscous boundary layer and the outer inviscid flow. Numerical solutions of the Navier–Stokes equations show that the interaction occurs on two distinct streamwise length scales depending upon which of three Reynolds-number regimes is being considered. At high Reynolds numbers, the spike leads to a small-scale interaction; at moderate Reynolds numbers, the flow experiences a large-scale interaction followed by the small-scale interaction due to the spike; at low Reynolds numbers, large-scale interaction occurs, but there is no spike or subsequent small-scale interaction. The large-scale interaction is found to play an essential role in determining the overall evolution of unsteady separation in the moderate-Reynolds-number regime; it accelerates the spike formation process and leads to formation of secondary recirculation regions, splitting of the primary recirculation region into multiple corotating eddies and ejections of near-wall vorticity. These eddies later merge prior to being lifted away from the surface and causing detachment of the thick-core vortex.

Scaling Effect on Dynamic Impact Response of Structures in Fluid Fields

2013 ◽  
Author(s):  
Zhongheng Guo ◽  
Lingyu Sun ◽  
Taikun Wang ◽  
Junmin Du ◽  
Han Li ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Dimensional Analysis ◽  
Large Scale ◽  
Scaling Laws ◽  
Scaling Law ◽  
Fluid Pressure ◽  
Structural Safety ◽  
Scale Model ◽  
Small Scale ◽  
Water Tank

At the conceptual design phase of a large-scale underwater structure, a small-scale model in a water tank is often used for the experimental verification of kinematic principles and structural safety. However, a general scaling law for structure-fluid interaction (FSI) problems has not been established. In the present paper, the scaling laws for three typical FSI problems under the water, rigid body moves at a given kinematic equation or is driven by time-dependent fluids with given initial condition, as well as elastic-plastic body moves and then deforms subject to underwater impact loads, are investigated, respectively. First, the power laws for these three types of FSI problems were derived by dimensional analysis method. Then, the laws for the first two types were verified by numerical simulation. In addition, a multipurpose small-scale water sink test device was developed for numerical model updating. For the third type of problem, the dimensional analysis is no longer suitable due to its limitation on identifying the fluid pressure and structural stress, a simulation-based procedure for dynamics evaluation of large-scale structure was provided. The results show that, for some complex FSI problems, if small-scale prototype is tested safely, it doesn’t mean the full-scale product is also safe if both their pressure and stress are the main concerns, it needs further demonstration, at least by numerical simulation.

scholarly journals Significance of the Small and Medium Enterprises (SMEs) Sector in Pakistan and Assessment of its Employment Potential

2000 ◽  
Vol 5 (1) ◽  
pp. 23-59 ◽  
Author(s):  
Shahid Amjad Chaudhry
Keyword(s):  
Health Insurance ◽  
Social Security ◽  
Old Age ◽  
Large Scale ◽  
Small And Medium Enterprises ◽  
Small Scale ◽  
Medium Enterprise ◽  
Employment Potential ◽  
Definition Of ◽  
Medium Enterprises

Definitions and Sources Definitions: In this paper it is proposed to use the definition of selfemployed, small scale (2-9 employees), medium scale (10-99 employees) and large scale (100 employees and above) to discuss the issues relating to the Small and Medium Enterprise (SME) sector in Pakistan. The national pension (regulated through the Employees Old Age Benefit Institution Legislation) and health insurance (The Provincial Social Security Institutions Legislation) is applicable to institutions with 10 or more employees and provides a natural cut off point between the small scale and medium and large scale sectors. The cut off between the medium and large scale at 100 workers is also appropriate.

scholarly journals Nonlinear Dynamo of Magnetic Fluctuations and Flux Tubes Formation in the Ionosphere of Venus

1993 ◽  
Vol 157 ◽  
pp. 481-486
Author(s):  
N. Kleeorin ◽  
I. Rogachevskii ◽  
A. Eviatar
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Magnetic Reynolds Number ◽  
Small Scale ◽  
Magnetic Fluctuations ◽  
Flux Tubes ◽  
Magnetic Flux Ropes ◽  
Flux Ropes ◽  
Induction Equation ◽  
The Magnetic Field

Magnetic field observations in the dayside ionosphere of Venus revealed the magnetic flux ropes (Russell and Elphic 1979). General properties of these small-scale magnetic field structures can be explained by the theory of magnetic fluctuations excited by random hydrodynamic flows of ionospheric plasma.A nonlinear theory of the flux tubes formation based on the Zeldovich's mechanism of amplification of the magnetic fluctuations is proposed. A nonlinear equation describing the evolution of the correlation function of the magnetic field can be derived from the induction equation, the nonlinearity being connected with the Hall effect. The large magnetic Reynolds number limit allows an asymptotic study by a modified WKB method.On the basis of this theory it is possible to explain why the flux tubes are not observed if there is a strong regular large-scale magnetic field when the ionopause is low. The theory predicts the cross section of the flux ropes in the ionosphere of Venus and the maximum value of the magnetic field inside the flux tube.

Post-Instability Behavior of Solids

1985 ◽  
Vol 9 (4) ◽  
pp. 200-209
Author(s):  
Michail Zak
Keyword(s):  
Velocity Field ◽  
Large Scale ◽  
Equations Of Motion ◽  
Small Scale ◽  
Governing Equations ◽  
Vibrational Control ◽  
Classical Models ◽  
Fractal Functions ◽  
Scale Motion ◽  
Model Reformulation

The necessity of model reformulation in elasticity results from the failure of hyperbolicity of the governing equations of motion for classical models. The reformulation is based upon the introduction of additional kinematical microstructures in the form of multivalued displacement and velocity field (or fractal functions) which arc generated by the mechanism of the instability. The small scale motions describing this microstructure interact with the original large scale motion and restore the hyperbolicity of new governing equations of motion. The applications of the reformulated models to the problem of vibrational control and impact energy absorption are discussed.

Control of Large-Scale Heat Transport by Small-Scale Mixing

2006 ◽  
Vol 36 (10) ◽  
pp. 1877-1894 ◽  
Author(s):  
Paola Cessi ◽  
W. R. Young ◽  
Jeff A. Polton
Keyword(s):  
Heat Transport ◽  
Mixed Layer ◽  
Large Scale ◽  
Scaling Laws ◽  
Mechanical Energy ◽  
Small Scale ◽  
Thermocline Depth ◽  
Leading Order ◽  
Diapycnal Diffusivity ◽  
The Mean

Abstract The equilibrium of an idealized flow driven at the surface by wind stress and rapid relaxation to nonuniform buoyancy is analyzed in terms of entropy production, mechanical energy balance, and heat transport. The flow is rapidly rotating, and dissipation is provided by bottom drag. Diabatic forcing is transmitted from the surface by isotropic diffusion of buoyancy. The domain is periodic so that zonal averaging provides a useful decomposition of the flow into mean and eddy components. The statistical equilibrium is characterized by quantities such as the lateral buoyancy flux and the thermocline depth; here, scaling laws are proposed for these quantities in terms of the external parameters. The scaling theory predicts relations between heat transport, thermocline depth, bottom drag, and diapycnal diffusivity, which are confirmed by numerical simulations. The authors find that the depth of the thermocline is independent of the diapycnal mixing to leading order, but depends on the bottom drag. This dependence arises because the mean stratification is due to a balance between the large-scale wind-driven heat transport and the heat transport due to baroclinic eddies. The eddies equilibrate at an amplitude that depends to leading order on the bottom drag. The net poleward heat transport is a residual between the mean and eddy heat transports. The size of this residual is determined by the details of the diapycnal diffusivity. If the diffusivity is uniform (as in laboratory experiments) then the heat transport is linearly proportional to the diffusivity. If a mixed layer is incorporated by greatly increasing the diffusivity in a thin surface layer then the net heat transport is dominated by the model mixed layer.

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