One-count memory circuit prevents machine mode interaction

One-count memory logic circuit used with electromechanical counter-printer machines operates in either count or print mode. The circuit advances the counter when the machine is in the count mode and provides storage for the count pulse when the machine is in the print mode

A Spherical Plasma Dynamo Experiment

We propose a plasma experiment to be used to investigate fundamental properties of astrophysical dynamos. The highly conducting, fast-flowing plasma will allow experimenters to explore systems with magnetic Reynolds numbers an order of magnitude larger than those accessible with liquid-metal experiments. The plasma is confined using a ring-cusp strategy and subject to a toroidal differentially rotating outer boundary condition. As proof of principle, we present magnetohydrodynamic simulations of the proposed experiment. When a von K\'arm\'an-type boundary condition is specified, and the magnetic Reynolds number is large enough, dynamo action is observed. At different values of the magnetic Prandtl and Reynolds numbers the simulations demonstrate either laminar or turbulent dynamo action

Optimized boundary driven flows for dynamos in a sphere

We perform numerical optimization of the axisymmetric flows in a sphere to minimize the critical magnetic Reynolds number Rm_cr required for dynamo onset. The optimization is done for the class of laminar incompressible flows of von Karman type satisfying the steady-state Navier-Stokes equation. Such flows are determined by equatorially antisymmetric profiles of driving azimuthal (toroidal) velocity specified at the spherical boundary. The model is relevant to the Madison plasma dynamo experiment (MPDX), whose spherical boundary is capable of differential driving of plasma in the azimuthal direction. We show that the dynamo onset in this system depends strongly on details of the driving velocity profile and the fluid Reynolds number Re. It is found that the overall lowest Rm_cr~200 is achieved at Re~240 for the flow, which is hydrodynamically marginally stable. We also show that the optimized flows can sustain dynamos only in the range Rm_cr<Rm<Rm_cr2, where Rm_cr2 is the second critical magnetic Reynolds number, above which the dynamo is quenched. Samples of the optimized flows and the corresponding dynamo fields are presented

Identification of vortexes obstructing the dynamo mechanism in laboratory experiments

The magnetohydrodynamic dynamo effect explains the generation of self-sustained magnetic fields in electrically conducting flows, especially in geo- and astrophysical environments. Yet the details of this mechanism are still unknown, e.g., how and to which extent the geometry, the fluid topology, the forcing mechanism and the turbulence can have a negative effect on this process. We report on numerical simulations carried out in spherical geometry, analyzing the predicted velocity flow with the so-called Singular Value Decomposition, a powerful technique that allows us to precisely identify vortexes in the flow which would be difficult to characterize with conventional spectral methods. We then quantify the contribution of these vortexes to the growth rate of the magnetic energy in the system. We identify an axisymmetric vortex, whose rotational direction changes periodically in time, and whose dynamics are decoupled from those of the large scale background flow, is detrimental for the dynamo effect. A comparison with experiments is carried out, showing that similar dynamics were observed in cylindrical geometry. These previously unexpected eddies, which impede the dynamo effect, offer an explanation for the experimental difficulties in attaining a dynamo in spherical geometry.Comment: 25 pages, 12 figures, submitted to Physics of Fluid

Soliton self-modulation of the turbulence amplitude and plasma rotation

The space-uniform amplitude envelope of the Ion Temperature Gradient driven turbulence is unstable to small perturbations and evolves to nonuniform, soliton-like modulated profiles. The induced poloidal asymmetry of the transport fluxes can generate spontaneous poloidal spin-up of the tokamak plasma.Comment: Latex file, 66 pages, 24 postscript figures included. New section on rotation five new figures, comparison with magnetic pumping dampin

Community Leader Participation in the Extension Programme Decision-Making Process

This research studied participation levels of community leaders in the extension programme decision-making process, as perceived by extension staff. The objectives were to determine (1) if the perceived particpation levels differed by tasks associated with two different types of programme decisions, (2) if the perceived participation levels varied by tasks associated with different steps of the decision-making process, and (3) how the perceived participation levels relate to extension staffs attitudes toward community leader participation, for each type of programme decision. This research found the following: (1) Contrary to expectation, the perceived participation levels of community leaders did not differ for both 'more technical' and 'less technical' programme decisions: (2) The perceived participation levels varied by the different decision-making steps,. Community leaders were perceived to participate least at the choice of alternatives and the plan of action steps of decision making. (3) Only for 'less technical' programme decisions were attitudes of extension staff positively related to perceived community leader participation levels

Measurements of the magnetic field induced by a turbulent flow of liquid metal

Initial results from the Madison Dynamo Experiment provide details of the inductive response of a turbulent flow of liquid sodium to an applied magnetic field. The magnetic field structure is reconstructed from both internal and external measurements. A mean toroidal magnetic field is induced by the flow when an axial field is applied, thereby demonstrating the omega effect. Poloidal magnetic flux is expelled from the fluid by the poloidal flow. Small-scale magnetic field structures are generated by turbulence in the flow. The resulting magnetic power spectrum exhibits a power-law scaling consistent with the equipartition of the magnetic field with a turbulent velocity field. The magnetic power spectrum has an apparent knee at the resistive dissipation scale. Large-scale eddies in the flow cause significant changes to the instantaneous flow profile resulting in intermittent bursts of non-axisymmetric magnetic fields, demonstrating that the transition to a dynamo is not smooth for a turbulent flow.Comment: 9 pages, 11 figures, invited talk by C. B. Forest at 2005 APS DPP meeting, resubmitted to Physics of Plasma

UNDERSTANDING PROXIMITIES: THE CONTRIBUTION OF THE DESIGN-CENTRED APPROACH TO INNOVATION

accessible en ligne à l'adresse : http://www.cjrs-rcsr.org/V33/3/6-33-3-FOREST-SERRATE.pdfInternational audienceThe spatial character of innovative activities was initially explained with reference to externalities that prompt activities to group together. Although the spatial character of innovative activities can be observed empirically (Madiès and Prager, 2008), it is no longer analysed uniquely in terms of physical proximity. By examining the modalities governing the externalities diffusion, a growing number of researches have shown that geographical proximity is only profitable when it is associated with other types of proximity: relational, organised, institutional or cognitive (RERU, 1993; Pecqueur and Zimmerman, 2004; Boschma, 2005). Although most researchers accept that there are several types of proximity, questions remain about the relations between them and about the modalities of these relations. The present research used the design process, which is the central process of the innovation process (Kline and Rosenberg, 1986), to study the relations between the different types of proximity involved in all innovative processes. Data on the actors involved in the various stages of the design process were compiled via a quantitative survey of 800 firms in the Rhône-Alpes Region of France. As well as highlighting differences in the types of actors involved in the successive stages of the design process, our study allowed us to examine how the different types of proximity coexist and interrelate within the design process. In addition to confirming the validity of the proposition that "geographical proximity will be mobilised in different ways and to different extents according to the stages in the collaboration process" (Rallet and Torre, 2006), our approach is interesting for two other reasons. First, it shows that Rallet and Torre's proposition is also valid for other types of proximity. Second, it allows the mobilisation modalities of several different types of proximity to be investigated simultaneously, thereby breaking with existing dynamic approaches, which usually only consider the mobilisation of one form of proximity.La spatialisation des activités innovantes a initialement été justifiée par l'existence des externalités attachées à l'agglomération des activités. Si le caractère spatialisé des activités innovantes semble une réalité empiriquement observable (Madiès et Prager, 2008), l'analyse s'est depuis affranchie d'une lecture standard de l'espace. Intégrant les modalités CJRS (Online)/ RCSR (en ligne) ISSN : 1925-2218 Vol. 33 (3): 63-76 64 de diffusion des externalités, les travaux de recherche en sont venus à souligner que la proximité géographique n'est profitable qu'associée à d'autres formes de proximité : relationnelle, organisationnelle, institutionnelle ou cognitive (RERU, 1993; Pecqueur and Zimmerman, 2004; Boschma, 2005). Si l'existence d'une pluralité de proximité semble être largement admise, reste ouverte la question de comprendre comment ces différentes formes de proximité s'articulent et selon quelles modalités. La présente communication propose de s'intéresser au processus de conception en tant qu'espace de structuration de l'innovation pour comprendre l'enchevêtrement des différentes formes de proximité impliquées dans tout processus dynamique et innovant. Nous montrerons, partant des résultats d'une étude quantitative menée auprès de 800 entreprises de la région Rhône-Alpes, qu'en considérant l'innovation à partir de son processus central, à savoir le processus de conception, il est certes possible de mettre en avant une mobilisation des acteurs externes différenciée selon l'étape du processus de conception considérée mais aussi de voir comment les différentes formes de proximité coexistent et s'articulent au sein du processus de conception. Ce résultat mérite d'être considéré à sa juste valeur car d'une part s'il confirme la thèse selon laquelle " la proximité géographique va être mobilisée selon des manières et des hauteurs différentes en fonction des étapes du processus de collaboration " (Rallet et Torre, 2006) il révèle que cette thèse est valable pour les différentes formes de proximité, d'autre part il permet de considérer la mobilisation différenciée des différentes formes de proximité de manière simultanée ce qui rompt avec les approches dynamiques existantes habituellement centrée sur l'étude de la mobilisation d'une unique forme de proximité

Numerical simulation of laminar plasma dynamos in a cylindrical von K\'arm\'an flow

The results of a numerical study of the magnetic dynamo effect in cylindrical von K\'arm\'an plasma flow are presented with parameters relevant to the Madison Plasma Couette Experiment. This experiment is designed to investigate a broad class of phenomena in flowing plasmas. In a plasma, the magnetic Prandtl number Pm can be of order unity (i.e., the fluid Reynolds number Re is comparable to the magnetic Reynolds number Rm). This is in contrast to liquid metal experiments, where Pm is small (so, Re>>Rm) and the flows are always turbulent. We explore dynamo action through simulations using the extended magnetohydrodynamic NIMROD code for an isothermal and compressible plasma model.We also study two-fluid effects in simulations by including the Hall term in Ohm's law. We find that the counter-rotating von K\'arm\'an flow results in sustained dynamo action and the self-generation of magnetic field when the magnetic Reynolds number exceeds a critical value. For the plasma parameters of the experiment, this field saturates at an amplitude corresponding to a new stable equilibrium (a laminar dynamo). We show that compressibility in the plasma results in an increase of the critical magnetic Reynolds number, while inclusion of the Hall term in Ohm's law changes the amplitude of the saturated dynamo field but not the critical value for the onset of dynamo action.Comment: Published in Physics of Plasmas, http://link.aip.org/link/?PHP/18/03211