Gyrotron travelling wave amplifier: I. Analysis of oscillations

The operation of the gyrotron travelling wave amplifier is based on the convective cyclotron maser instability. It is found that this convective instability may become absolute (nonconvective) at a sufficiently high current level, resulting in oscillation instead of amplification. This threshold current for the transition depends sensitively on the applied magnetic field. The axial wavelength and the characteristic frequency of oscillation at the onset of absolute instability are given. It is found that momentum spread has virtually no effect on the threshold current. A small amount of resistive wall loss, however, raises the threshold current significantly. Oscillations due to partial reflection at the ends of the system are also examined. Preliminary experimental results on both types of oscillations are reported and are found to be in good agreement with the theory.     

Elastic and inelastic scattering of 18O by 16O and 18O

Angular distributions have been measured for the elastic and inelastic scattering of ¹⁸O by ¹⁶O and ¹⁸O at laboratory bombarding energies of 42 and 52 MeV. The inelastic scattering data are analyzed in terms of collective excitations using a coupled channel approach. Deformation parameters are obtained for the strongly excited states. The relationship between the strength of inelastic scattering and the amount of structure in the elastic scattering distributions is discussed.     

Visible spectra of some chloropentakis(alkylamine)-cobalt(III) complexes

All four spin-allowed transitions in the visible spectra of the complexes [Co(RNH₂)₅Cl]²⁺, R = H, Me, Et, n-Pr, and n-Bu, have been resolved and the relevant crystal field and RACAH parameters determined with a method previously described. The results appear to be consistent within the series and agree well with those reported in the literature for structurally related systems.     

Characterization of best approximations in normed linear spaces of matrices by elements of finite-dimensional linear subspaces

A general characterization theorem of best approximations in normed linear spaces is specialized to the linear space of real n × n matrices endowed with the spectral norm.     

Curvature-compensated convective transport: SMART,A new boundedness- preserving transport algorithm

The paper describes a new approach to approximating the convection term found in typical steady-state transport equations. A polynomial-based discretization scheme is constructed around a technique called ‘curvature compensation’; the resultant curvature-compensated convective transport approximation is essentially third-order accurate in regions of the solution domain where the concept of order is meaningful. In addition, in linear scalar transport problems it preserves the boundedness of solutions. Sharp changes in gradient in the dependent variable are handled particularly well. But above all, the scheme, when used in conjunction with an ADI pentadiagonal solver, is easy to implement with relatively low computational cost, representing an effective algorithm for the simulation of multi-dimensional fluid flows. Two linear test problems, for the case of transport by pure convection, are employed in order to assess the merit of the method.