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The slow-wave structure of a travelling-wave tube (TWT), consisting of a helix supported by a number of dielectric rods in a glass tube envelope, is modelled and theoretically analysed for the attenuation constant, phase propagation constant and interaction impedance of the structure. The expressions for these quantities are then interpreted to obtain the expressions for Pierce's velocity, loss and space-charge parameters in terms of the structure parameters.Also, the use of these expressions is demonstrated by a small-signal gain calculation for a typical satellite communication helix T~T in use. The theoretical gain is compared with the experimental gain reported elsewhere, for the same tube

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The equilibrium acidity of lactams with rings of various size and of linear N-substituted amides was measured in dimethyl sulfoxide by the spectrophotometric method. The pK values of these NH-acids thus determined varied in the range 22-27. The data are used to characterize the acidobasic equilibrium between the amide groups of the monomer, polymer and their N-anions during the anionic polymerization of lactams. The effect of acidity on the anionic copolymerization of lactams is also discussed.