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We present the detailed description of the successful design and cold test of photonic band gap (PBG) resonators and traveling-wave accelerator structures. Those tests provided the essential basis for later hot test demonstration of the first PBG accelerator structure at 17.140 GHz [E. I. Smirnova, A. S. Kesar, I. Mastovsky, M. A. Shapiro, and R. J. Temkin, Phys. Rev. Lett., 95, 074801 (2005).]. The advantage of PBG resonators is that they were built to support only the main, TM₀₁-like, accelerator mode while not confining the higher-order modes (HOM) or wakefields. The design of the PBG resonators was based on a triangular lattice of rods, with a missing rod at the center. Following theoretical analysis, the rod radius divided by the rod spacing was held to a value of about 0.15 to avoid supporting HOM. For a single-cell test the PBG structure was fabricated in X-band (11 GHz) and brazed. The mode spectrum and Q factor (Q=5 000) agreed well with theory. Excellent HOM suppression was evident from the cold test. A six-cell copper PBG accelerator traveling-wave structure with reduced long-range wakefields was designed and was built by electroforming at Ku-band (17.140 GHz). The structure was tuned by etching the rods. Cold test of the structure yielded excellent agreement with the theoretical design. Successful results of the hot test of the structure demonstrating the acceleration of the electron beam were published in E. I. Smirnova, A. S. Kesar, I. Mastovsky, M. A. Shapiro, and R. J. Temkin, Phys. Rev. Lett., 95, 074801 (2005).

A comparison is made between the x-ray diffraction halos of 22 octyl alcohols and their corresponding viscosities and an unmistakable correlation found. The assumptions are that the halos indicate periodicities, that the periodicities may be interpreted as structural in the "cybotactic" groups, and that the relative diffraction intensity of the halos computed by assuming crystal structure may be used to estimate roughly the perfection of the liquid groups. It thus is shown that there is a correlation between the coefficient of viscosity and the perfection of grouping in the direction of the length of the chain molecules. This corresponds with the reasonable view that the viscosity within the liquid groups is caused by longitudinal slippage. Moreover, since the groups at any instant occupy a large fraction of the volume of the liquid, this viscosity is an important part of that measured. This interpretation accounts for the negative temperature coefficient of the viscosity, since the size of the groups decrease with temperature. The experiments and conclusions are in accord with Andrade's theory of momentary "crystallization" and with Ornstein's theory of the formation of liquid crystal groups, yet it is to be noted that these theories deal with different aspects and not the entire phenomenon.

Coercive force, retentivity, and hysteresis loop forms for evaporated films of Ni and Fe.—Films of nickel and iron, produced by evaporation at low pressure, were studied with the object of verifying the reported existence of an abrupt change of coercive force at a critical thickness, and also to discover the cause of certain peculiar hysteresis loop forms. Critical thickness was found for iron films at approximately 50 mμ, in satisfactory agreement with Sorensen. At this thickness the coercive force changes abruptly from the high value of approximately 100 for thinner films. The observations were made upon films deposited on a base of aluminum foil,.0025 cm in thickness. The foil was heated previous to and during deposit. No such critical thickness was observed in nickel. Peculiar hysteresis loops were found. Nickel films unheated have very narrow loops, with magnetic induction nearly proportional to the field up to 139 gauss, where the induction is one-third to one-half that of the metal in bulk. Films heated previous to and during deposit give a magnetic induction at 139 gauss that is approximately three times as great, or like that of metal in bulk. But the retentivity and coercive force increase five-fold and become less like those of the metal in bulk. In similarly heated films of iron, these last two magnetic properties are also much greater than with metal in bulk. The peculiarities of the films are probably caused by the nature of the crystalline state. To what extent the phenomena depend upon the presence of the aluminum base is yet to be ascertained. The present view is that the presence of gas alters the crystal growth. On the whole the experiments seem to emphasize the importance of the influence of the crystalline state upon magnetic properties.