7,638 research outputs found
Long-wavelength limit of gyrokinetics in a turbulent tokamak and its intrinsic ambipolarity
Recently, the electrostatic gyrokinetic Hamiltonian and change of coordinates
have been computed to order in general magnetic geometry. Here
is the gyrokinetic expansion parameter, the gyroradius over the
macroscopic scale length. Starting from these results, the long-wavelength
limit of the gyrokinetic Fokker-Planck and quasineutrality equations is taken
for tokamak geometry. Employing the set of equations derived in the present
article, it is possible to calculate the long-wavelength components of the
distribution functions and of the poloidal electric field to order
. These higher-order pieces contain both neoclassical and turbulent
contributions, and constitute one of the necessary ingredients (the other is
given by the short-wavelength components up to second order) that will
eventually enter a complete model for the radial transport of toroidal angular
momentum in a tokamak in the low flow ordering. Finally, we provide an explicit
and detailed proof that the system consisting of second-order gyrokinetic
Fokker-Planck and quasineutrality equations leaves the long-wavelength radial
electric field undetermined; that is, the turbulent tokamak is intrinsically
ambipolar.Comment: 70 pages. Typos in equations (63), (90), (91), (92) and (129)
correcte
Electronic scanning pressure measuring system and transducer package
An electronic scanning pressure system that includes a plurality of pressure transducers is examined. A means obtains an electrical signal indicative of a pressure measurement from each of the plurality of pressure transducers. A multiplexing means is connected for selectivity supplying inputs from the plurality of pressure transducers to the signal obtaining means. A data bus connects the plurality of pressure transducers to the multiplexing means. A latch circuit is connected to supply control inputs to the multiplexing means. An address bus is connected to supply an address signal of a selected one of the plurality of pressure transducers to the latch circuit. In operation, each of the pressure transducers is successively scanned by the multiplexing means in response to address signals supplied on the address bus to the latch circuit
Stellarator bootstrap current and plasma flow velocity at low collisionality
The bootstrap current and flow velocity of a low-collisionality stellarator
plasma are calculated. As far as possible, the analysis is carried out in a
uniform way across all low-collisionality regimes in general stellarator
geometry, assuming only that the confinement is good enough that the plasma is
approximately in local thermodynamic equilibrium. It is found that conventional
expressions for the ion flow speed and bootstrap current in the
low-collisionality limit are accurate only in the -collisionality regime
and need to be modified in the -regime. The correction due to
finite collisionality is also discussed and is found to scale as
Conditions for up-down asymmetry in the core of tokamak equilibria
A local magnetic equilibrium solution is sought around the magnetic axis in
order to identify the key parameters defining the magnetic-surface's up-down
asymmetry in the core of tokamak plasmas. The asymmetry is found to be
determined essentially by the ratio of the toroidal current density flowing on
axis to the fraction of the external field's odd perturbation that manages to
propagate from the plasma boundary into the core. The predictions are tested
and illustrated first with an analytical Solovev equilibrium and then using
experimentally relevant numerical equilibria. Hollow current-density
distributions, and hence reverse magnetic shear, are seen to be crucial to
bring into the core asymmetry values that are usually found only near the
plasma edge.Comment: 6 pages, 2 figures, submitted for publicatio
Symmetry breaking in MAST plasma turbulence due to toroidal flow shear
The flow shear associated with the differential toroidal rotation of tokamak
plasmas breaks an underlying symmetry of the turbulent fluctuations imposed by
the up-down symmetry of the magnetic equilibrium. Using experimental
Beam-Emission-Spectroscopy (BES) measurements and gyrokinetic simulations, this
symmetry breaking in ion-scale turbulence in MAST is shown to manifest itself
as a tilt of the spatial correlation function and a finite skew in the
distribution of the fluctuating density field. The tilt is a statistical
expression of the "shearing" of the turbulent structures by the mean flow. The
skewness of the distribution is related to the emergence of long-lived density
structures in sheared, near-marginal plasma turbulence. The extent to which
these effects are pronounced is argued (with the aid of the simulations) to
depend on the distance from the nonlinear stability threshold. Away from the
threshold, the symmetry is effectively restored
A Practical Environment to Apply Model-Driven Web Engineering
The application of a model-driven paradigm in the development of Web Systems has yielded very good research
results. Several research groups are defining metamodels, transformations, and tools which offer a suitable environment,
known as model-driven Web engineering (MDWE). However, there are very few practical experiences in real
Web system developments using real development teams. This chapter presents a practical environment of MDWE
based on the use of NDT (navigational development techniques) and Java Web systems, and it provides a practical
evaluation of its application within a real project: specialized Diraya.Ministerio de Educación y Ciencia TIN2007-67843-C06-03Ministerio de Educación y Ciencia TIN2007-30391-
Quadratic cavity soliton optical frequency combs
We theoretically investigate the formation of frequency combs in a dispersive second-harmonic generation cavity system, and predict the existence of quadratic cavity solitons in the absence of a temporal walk-off
A Practical Example for Model-Driven Web Requirements
The number of approaches for Web environments has grown very fast
in the last years: HDM, OOHDM, and WSDM were among the first, and now a
large number can be found in the literature. With the definition of MDA (Model-
Driven Architecture) and the acceptance of MDE (Model-Driven Engineering)
techniques in this environment, some groups are working in the use of metamodels
and transformations to make their approaches more powerful. UWE (UMLBased
Web Engineering) or OOWS (Object-Oriented Web Solutions) are only
some examples. However, there are few real experiences with Web Engineering in
the enterprise environment, and very few real applications of metamodels and
MDE techniques. In this chapter the practical experience of a Web Engineering
approach, NDT, in a big project developed in Andalusia is presented. Besides, it
shows the usability of metamodels in real environments
The ROCK inhibitor Fasudil prevents chronic restraint stress-induced depressive-like behaviors and dendritic spine loss in rat hippocampus
Indexación: Web of Science; Scopus.Background: Dendritic arbor simplification and dendritic spine loss in the hippocampus, a limbic structure implicated in mood disorders, are assumed to contribute to symptoms of depression. These morphological changes imply modifications in dendritic cytoskeleton. Rho GTPases are regulators of actin dynamics through their effector Rho kinase. We have reported that chronic stress promotes depressive-like behaviors in rats along with dendritic spine loss in apical dendrites of hippocampal pyramidal neurons, changes associated with Rho kinase activation. The present study proposes that the Rho kinase inhibitor Fasudil may prevent the stress-induced behavior and dendritic spine loss. Methods: Adult male Sprague-Dawley rats were injected with saline or Fasudil (i.p., 10 mg/kg) starting 4 days prior to and maintained during the restraint stress procedure (2.5 h/d for 14 days). Nonstressed control animals were injected with saline or Fasudil for 18 days. At 24 hours after treatment, forced swimming test, Golgi-staining, and immuno-western blot were performed. Results: Fasudil prevented stress-induced immobility observed in the forced swimming test. On the other hand, Fasudiltreated control animals showed behavioral patterns similar to those of saline-treated controls. Furthermore, we observed that stress induced an increase in the phosphorylation of MYPT1 in the hippocampus, an exclusive target of Rho kinase. This change was accompanied by dendritic spine loss of apical dendrites of pyramidal hippocampal neurons. Interestingly, increased pMYPT1 levels and spine loss were both prevented by Fasudil administration. Conclusion: Our findings suggest that Fasudil may prevent the development of abnormal behavior and spine loss induced by chronic stress by blocking Rho kinase activity.https://academic.oup.com/ijnp/article/20/4/336/263217
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