Analytic equilibrium of "straight tokamak" plasma bounded by a magnetic separatrix

Theoretical and experimental considerations suggest that axisymmetric perturbations that are resonant at the X-point(s) of a magnetic divertor separatrix may play a role in the understanding of Edge Localized Modes in tokamak experiments and their active control via so-called vertical kicks. With this motivation in mind, the first step in the development of an analytical model for resistive axisymmetric X-point modes is presented, i.e., finding an adequate, but at the same time relatively simple analytical magnetohydrodynamic equilibrium for a plasma column with a noncircular cross section bound by a magnetic separatrix. An early example is Gajewski's equilibrium solution [R. Gajewski, Phys. Fluids 15, 70 (1972)], which, however, has the shortcoming that infinite external currents placed at an infinite distance from the X-points produce the elliptical elongation of the plasma column. In this article, Gajewski's solution is extended to the case where external currents are located at a finite distance from the boundary of the plasma current density and the latter is distributed uniformly over a domain bound by a nearly elliptical magnetic flux surface

Analytic equilibrium of elongated plasmas bounded by a magnetic separatrix and the problem of resistive axisymmetric X-point modes

Theoretical and experimental considerations suggest that axisymmetric perturbations that are resonant at the X-point(s) of a magnetic divertor separatrix may play a role for the understanding of ELMs in tokamaks and their active control via so-called vertical kicks. The first step in the development of an analytic model for resistive axisymmetric X-point modes is presented, i.e., finding an adequate and relatively simple analytic MHD equilibrium for a plasma column with noncircular cross section bounded by a magnetic separatrix

Factors controlling the groundwater transport of U, Th, Ra, and Rn

A model for the groundwater transport of naturally occurring U, Th, Ra, and Rn nuclides in the ^(238)U and ^(232)Th decay series is discussed. The model developed here takes into account transport by advection and the physico-chemical processes of weathering, decay, α-recoil, and sorption at the water-rock interface. It describes the evolution along a flowline of the activities of the ^(238)U and ^(232)Th decay series nuclides in groundwater. Simple sets of relationships governing the activities of the various species in solution are derived, and these can be used both to calculate effective retardation factors and to interpret groundwater data. For the activities of each nuclide, a general solution to the transport equation has been obtained, which shows that the activities reach a constant value after a distance ϰ_i, characteristic of each nuclide. Where ϰ_i is much longer than the aquifer length, (for ^(238)U, ^(234)U, and ^(232)Th), the activities grow linearly with distance. Where ϰ_i is short compared to the aquifer length, (for ^(234)Th, ^(230)Th, ^(228)Th, ^(228)Ra, and ^(224)Ra), the activities rapidly reach a constant or quasi-constant activity value. For ^(226)Ra and ^(222)Rn, the limiting activity is reached after 1 km. High δ ^(234)U values (proportional to the ratio ^(ɛ234)Th/^(W238)U) can be obtained through high recoil fraction and/or low weathering rates. The activity ratios ^(230)Th/^(232)Th, ^(228)Ra/^(226)Ra and ^(224)Ra/^(226)Ra have been considered in the cases where either weathering or recoil is the predominant process of input from the mineral grain. Typical values for weathering rates and recoil fractions for a sandy aquifer indicate that recoil is the dominant process for Th isotopic ratios in the water. Measured data for Ra isotope activity ratios indicate that recoil is the process generally controlling the Ra isotopic composition in water. Higher isotopic ratios can be explained by different desorption kinetics of Ra. However, the model does not provide an explanation for ^(228)Ra/^(226)Ra and ^(224)Ra/^(226)Ra activity ratios less than unity. From the model, the highest ^(222)Rn emanation equals 2_ɛ. This is in agreement with the hypothesis that ^(222)Rn activity can be used as a first approximation for input by recoil (Krishnaswamiet al 1982). However, high ^(222)Rn emanation cannot be explained by production from the surface layer as formulated in the model. Other possibilities involve models including surface precipitation, where the surface layer is not in steady-state

Resonant Axisymmetric Modes

Axisymmetric modes in shaped tokamak plasmas are normally associated with vertical displacement events. However, not enough attention has been given to the fact that these modes can be resonant in two different ways. Firstly, for a plasma bounded by a divertor separatrix, a generic n=0 ideal-MHD perturbation, ξ, is singular at the divertor X- point(s), where Beq · ∇ξ = 0, with Beq the equilibrium magnetic field. As a consequence, n=0 perturbations can give rise to current sheets localized along the divertor separatrix. Secondly, a feedback-stabilized n=0 mode tends to acquire an Alfv ́enic oscillation frequency. As a result, a resonant interaction with energetic particle orbits can lead to a new type of fast ion instability

Metastatic melanoma cells with BRAF G469A mutation: nab‑paclitaxel better than vemurafenib?

Purpose BRAF G469A is a missense mutation within exon 11 of the BRAF gene resulting in a constitutively activated enzyme frequently associated with MAP kinase cascade signaling activation. No evidence currently exists about its role in determining sensitivity/resistance to BRAF inhibitors, utilized in the treatment of patients carrying BRAF V600 mutations, and to chemotherapy. The newly established metastatic melanoma (MM) cell line MO-1 was characterized for its sensitivity to vemurafenib and nabpaclitaxel, both already utilized for the treatment of MM. Methods All analyses were carried out by comparing results with those found in MM cells wild type for BRAF or mutated in V600. In addition, cellular effectors were investigated by ELISA kits, western blotting and flow cytometry. Results The exposure to vemurafenib inhibited MO-1 cell proliferation at concentrations similar to those obtained in vemurafenib-resistant melanoma models, and an explanation of this sensitivity is the strong activation of Erk1/2 . and the low expression of MITF. Nab-paclitaxel strongly reduced proliferation of MO-1 cells perhaps for the very low expression level of PMEL17, transcriptionally regulated by MITF and negatively involved in determining sensitivity to taxanes. Conclusions Thus, the mutation BRAF G469A in MM might be related to a weak effectiveness of therapy with BRAF inhibitors and a promising therapeutic approach may be with nab-paclitaxel