2,716 research outputs found
Dynamic Procedure for Filtered Gyrokinetic Simulations
Large Eddy Simulations (LES) of gyrokinetic plasma turbulence are
investigated as interesting candidates to decrease the computational cost. A
dynamic procedure is implemented in the GENE code, allowing for dynamic
optimization of the free parameters of the LES models (setting the amplitudes
of dissipative terms). Employing such LES methods, one recovers the free energy
and heat flux spectra obtained from highly resolved Direct Numerical
Simulations (DNS). Systematic comparisons are performed for different values of
the temperature gradient and magnetic shear, parameters which are of prime
importance in Ion Temperature Gradient (ITG) driven turbulence. Moreover, the
degree of anisotropy of the problem, that can vary with parameters, can be
adapted dynamically by the method that shows Gyrokinetic Large Eddy Simulation
(GyroLES) to be a serious candidate to reduce numerical cost of gyrokinetic
solvers.Comment: 10 pages, 10 figures, submitted to Physics of Plasma
Continuous control of ionization wave chaos by spatially derived feedback signals
In the positive column of a neon glow discharge, two different types of
ionization waves occur simultaneously. The low-dimensional chaos arising from
the nonlinear interaction between the two waves is controlled by a continuous
feedback technique. The control strategy is derived from the time-delayed
autosynchronization method. Two spatially displaced points of observation are
used to obtain the control information, using the propagation characteristics
of the chaotic wave.Comment: Elsevier-Tex-File, 8 pages, 6 figures, submitted to PL
Period 2 regulates neural stem/progenitor cell proliferation in the adult hippocampus
BACKGROUND: Newborn granule neurons are generated from proliferating neural stem/progenitor cells and integrated into mature synaptic networks in the adult dentate gyrus of the hippocampus. Since light/dark variations of the mitotic index and DNA synthesis occur in many tissues, we wanted to unravel the role of the clock-controlled Period2 gene (mPer2) in timing cell cycle kinetics and neurogenesis in the adult DG. RESULTS: In contrast to the suprachiasmatic nucleus, we observed a non-rhythmic constitutive expression of mPER2 in the dentate gyrus. We provide evidence that mPER2 is expressed in proliferating neural stem/progenitor cells (NPCs) and persists in early post-mitotic and mature newborn neurons from the adult DG. In vitro and in vivo analysis of a mouse line mutant in the mPer2 gene (Per2Brdm1), revealed a higher density of dividing NPCs together with an increased number of immature newborn neurons populating the DG. However, we showed that the lack of mPer2 does not change the total amount of mature adult-generated hippocampal neurons, because of a compensatory increase in neuronal cell death. CONCLUSION: Taken together, these data demonstrated a functional link between the constitutive expression of mPER2 and the intrinsic control of neural stem/progenitor cells proliferation, cell death and neurogenesis in the dentate gyrus of adult mice
Wiggly Relativistic Strings
We derive the equations of motion for general strings, i.e. strings with
arbitrary relation between tension and energy per unit length
. The renormalization of and that results from
averaging out small scale wiggles on the string is obtained in the general case
to lowest order in the amount of wiggliness. For Nambu-Goto strings we find
deviations from the equation of state in
higher orders. Finally we argue that wiggliness may radically modify the gauge
cosmic string scenario.Comment: 10 pages, LaTeX, UFIFT-HEP-92-1
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