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## Analysis of the Dispersion of the Helical Slow_Wave System with Dielectric Supports

The effect of dielectric supports on the slowing factor and dispersion of the helical line in TWT is considered. A method for the calculation of the slowing down in the helical line with the complicated configuration of the dielectric supports is proposed. A procedure for the experimental study of dispersion in the helical slow_wave system is presented. The calculated results are compared with the experimental data.

IVEC was originally created in 2000 by merging the U.S. Power Tubes Conferences and the European Space Agency TWTA Workshops. Now a fully international conference, IVEC is held every other year in the U.S., and in Europe and Asia alternately every fourth year. After the successful and enjoyable meeting in Paris, France in May, IVEC 2014 will return to its beautiful U.S. location in the city of Monterey.

The Seventeenth International Vacuum Electronics Conference (IVEC 2016) helded on 19-21 April 2016 in Monterey, California. With technical co-sponsorship from the IEEE Electron Devices Society (EDS), the conference provide a forum for scientists and engineers from around the globe to present the latest developments in vacuum electronics technology at frequencies ranging from the UHF to THz frequency bands.

IVEC was originally created in 2000 by merging the U.S. Power Tubes Conferences and the European Space Agency TWTA Workshops. Now a fully international conference, IVEC is held every other year in the U.S., and in Europe and Asia alternately every fourth year. After the successful and enjoyable meeting in Beijing, China in May, IVEC 2016 will return to its beautiful U.S. location in the city of Monterey.

The interaction of short single-component vector solitons in the frame of the coupled third–order nonlinear Schrodinger equations taking into account third–order linear dispersion, self–stepping, self–stimulated Ramanscattering, cross–stepping and cross–stimulated Raman-scattering terms is considered. Conditions of reflection and propagation of the solitons through each other and also the condition of oscillator interaction (vector breather) are obtained.

A TWT model formed by a meta-magnetic plate and a metal screen is offered and analyzed. The dispersion equation of the model in the presence of a homogeneous electron beam filling the space between the plate and the screen is derived and solved. The coupling and depression coefficients are calculated by the method of differentiation the dispersion equation. The calculated characteristics are compared with the TWT models on a dielectric plate and an “impedance” comb.

A study of waveguide structures with magnetic walls that were based on mushroom-shaped metamaterials has been carried out. We used Ansoft HFSS to simulate waveguide filters with a forbidden frequency band. The results obtained showed that a magnetic wall made of periodic various sized unit cells can provide several forbidden frequency bands instead of only one in case of single sized elements. We also demonstrated that it is possible to control rejection bands of frequency-selective surfaces by varying the permeability of ferrite coating of the metamaterial.

The 18th International Vacuum Electronics Conference (IVEC 2017) helded on 24-26 April 2017 in London, UK. With technical co-sponsorship from the IEEE Electron Devices Society (EDS), the conference provide a forum for scientists and engineers from around the globe to present the latest developments in vacuum electronics technology at frequencies ranging from the UHF to THz frequency bands. IVEC was originally created in 2000 by merging the U.S. Power Tubes Conferences and the European Space Agency TWTA Workshops. Now a fully international conference, IVEC is held every other year in the U.S., and in Europe and Asia alternately every fourth year.

Propagation of the short vector envelope solitons in a inhomogeneous medium with linear potential in coupled third–order nonlinear Shrodinger equations frame is considered. Explicit vector soliton solution is obtained. The explicit solution for the solitons trajectories is studied. In particular cases this solitons solution can be reduced as to the short scalar soliton solution on linear inhomogeneity profile, as to well – known Chen soliton solution.

Let k be a field of characteristic zero, let G be a connected reductive algebraic group over k and let g be its Lie algebra. Let k(G), respectively, k(g), be the field of k- rational functions on G, respectively, g. The conjugation action of G on itself induces the adjoint action of G on g. We investigate the question whether or not the field extensions k(G)/k(G)^G and k(g)/k(g)^G are purely transcendental. We show that the answer is the same for k(G)/k(G)^G and k(g)/k(g)^G, and reduce the problem to the case where G is simple. For simple groups we show that the answer is positive if G is split of type A_n or C_n, and negative for groups of other types, except possibly G_2. A key ingredient in the proof of the negative result is a recent formula for the unramified Brauer group of a homogeneous space with connected stabilizers. As a byproduct of our investigation we give an affirmative answer to a question of Grothendieck about the existence of a rational section of the categorical quotient morphism for the conjugating action of G on itself.

Let G be a connected semisimple algebraic group over an algebraically closed field k. In 1965 Steinberg proved that if G is simply connected, then in G there exists a closed irreducible cross-section of the set of closures of regular conjugacy classes. We prove that in arbitrary G such a cross-section exists if and only if the universal covering isogeny Ĝ → G is bijective; this answers Grothendieck's question cited in the epigraph. In particular, for char k = 0, the converse to Steinberg's theorem holds. The existence of a cross-section in G implies, at least for char k = 0, that the algebra k[G]G of class functions on G is generated by rk G elements. We describe, for arbitrary G, a minimal generating set of k[G]G and that of the representation ring of G and answer two Grothendieck's questions on constructing generating sets of k[G]G. We prove the existence of a rational (i.e., local) section of the quotient morphism for arbitrary G and the existence of a rational cross-section in G (for char k = 0, this has been proved earlier); this answers the other question cited in the epigraph. We also prove that the existence of a rational section is equivalent to the existence of a rational W-equivariant map T- - - >G/T where T is a maximal torus of G and W the Weyl group.