Aspects of linear Landau damping in discretized systems

Basic linear eigenmode spectra for electrostatic Langmuir waves and drift-kinetic slab ion temperature gradient modes are examined in a series of scenarios. Collisions are modeled via a Lenard-Bernstein collision operator which fundamentally alters the linear spectrum even for infinitesimal collisionality [Ng et al., Phys. Rev. Lett. 83, 1974 (1999)]. A comparison between different discretization schemes reveals that a Hermite representation is superior for accurately resolving the spectra compared to a finite differences scheme using an equidistant velocity grid. Additionally, it is shown analytically that any even power of velocity space hyperdiffusion also produces a Case-Van Kampen spectrum which, in the limit of zero hyperdiffusivity, matches the collisionless Landau solutions

Doppler Detection at High Instabilities of Laser Sources

The Doppler detection schemes, effective at high frequency instabilities of laser sources are of great interest for lidar performance. The stability of ≈ 10−9 is required to realize ≈ ± 1 m/s accuracy of wind speed [1,2]. Doppler detection schemes on the intermediate frequency opera ting at stabilities of order of 10−7 ÷ 10−6 are described here, based on the so-called tracking heterodyne [3,4] and the proper lidar synchronization.</jats:p

opr folia5.qxp

Abstract. The implantation in pig is superficial and non-invasive, involving phases of apposition, adhesion and attachment of conceptuses to endometrial surface epithelium. The role of integrins and ECM proteins is suggested. In the study, the expression of α5β1 integrin and FN on conceptus trophectoderm and endometrium during implantation and early pregnancy was investigated. The immunohistochemical localization of α5β1 integrin and FN was performed on formalin-fixed, paraffin-embedded tissue sections using the ABC method. The results indicate that both conceptus and uterus expressed α5β1 integrin and FN during early porcine pregnancy. The most intensive staining for α5β1 integrin and FN was found in conceptus trophectoderm and endometrial surface epithelium in all investigated periods. During placentation the immunohistochemical staining for both α5β1 integrin and FN was increased in trophectoderm and all endometrial structures. Since placenta in pigs is non-invasive, it can be suggested that both α5β1 integrin and FN participate in molecular events leading to successful implantation and placentation in species with true epitheliochorial placenta

Phase space scales of free energy dissipation in gradient-driven gyrokinetic turbulence

A reduced four-dimensional (integrated over perpendicular velocity) gyrokinetic model of slab ion temperature gradient-driven turbulence is used to study the phase-space scales of free energy dissipation in a turbulent kinetic system over a broad range of background gradients and collision frequencies. Parallel velocity is expressed in terms of Hermite polynomials, allowing for a detailed study of the scales of free energy dynamics over the four-dimensional phase space. A fully spectral code – the DNA code – that solves this system is described. Hermite free energy spectra are significantly steeper than would be expected linearly, causing collisional dissipation to peak at large scales in velocity space even for arbitrarily small collisionality. A key cause of the steep Hermite spectra is acritical balance– an equilibration of the parallel streaming time and the nonlinear correlation time – that extends to high Hermite numbern. Although dissipation always peaks at large scales in all phase space dimensions, small-scale dissipation becomes important in an integrated sense when collisionality is low enough and/or nonlinear energy transfer is strong enough. Toroidal full-gyrokinetic simulations using theGenecode are used to verify results from the reduced model. Collision frequencies typically found in present-day experiments correspond to turbulence regimes slightly favoring large-scale dissipation, while turbulence in low-collisionality systems like ITER and space and astrophysical plasmas is expected to rely increasingly on small-scale dissipation mechanisms. This work is expected to inform gyrokinetic reduced modeling efforts like Large Eddy Simulation and gyrofluid techniques.</jats:p