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Preliminary comparison of the burst data to the model parameters obtained from the gap distributions were performed for K=2. Definite statements concerning the validity of the model be made only after the comparison for several values of K has been performed. Product codes were investigated and theoretical performance equations were derived.

Experimental results for the distributions of the Markov channel model were derived for the VHF channel. The bursty nature of the channel was confirmed by the abundance of gaps of length zero. The conditional gap distributions again indicate that a renewal model does not fit the data. Preliminary comparison of the burst data to the model parameters obtained from the gap distributions was performed for K=1 (solid bursts). Additional investigation of these data is in progress. Interleaving is a proven useful technique for bursty channels. To test the effectiveness of interleaving we have calculated P sub e (m,n) statistics for files number 712T002, number 712T103, number 712T104 and number 712T105, for n = 31 and n = 63. The results indicate that the interleaving degree has to be in the order of 500 for the interleaved codes to be effective. (Author)

The paper discusses an experimental unit which incorporates error correcting coding into digital data communication systems for increased reliability. A short, random correcting block code is used in this unit. The code is taken from the class of Euclidean geometry codes which can be decoded by simple majority logic. The unit is complete with an encoder whixh encodes a block of information digits into a codeword before transmission, a decoder which determines from each codeword the information digits it contains, and an error generator which simulates a noisy channel. For demonstration purposes teletype machines will be used as the data source and the destination of this unit. (Author)

The report shows that Projective Geometry codes are orthogonalizable in less than or equal to 3 steps. Thus, this class of codes is majority-logic decodable in no more than 3 steps. The improved decoding algorithm reduces the decoding complexity of Projective Geometry codes enormously in most cases. This should make Projective Geometry codes very attractive for practical use on error-control systems. (Author)

The paper gives a survey of recent advances in majority-logic decoding for linear block codes. General majority-logic decoding algorithms are reviewed. The decoding schemes for product codes and the finite geometry codes are discussed. An improved decoding algorithm for the finite geometry codes is described. The improved decoding algorithm greatly reduces the decoding complexity of the codes. It should make the finite geometry codes very attractive in practical use on error-control systems. (Author)

An improved decoding algorithm for Euclidean Geometry codes is presented. It is shown that this class of codes can be orthogonalized in less than or equal to 3 steps. That is, it requires no more than 3 steps of majority logic in decoding these codes. This results greatly reduces the decoding complexity without reducing the error-correcting capabilities of the codes. The proposed decoding algorithm is a general one. In fact, it is applicable for all codes that are constructed from finite geometries. The application to Projective Geometry codes will be presented in a separate report. (Author)

A theory was developed describing the magnitude and wavelength dependence of the resonance radiation emitted as the result of thermal excitation. The predictions of the theory are compared with the results of measurements at a temperature of 788K as obtained in a cell capable of operating up to 1050K. The absorption coefficients and total absorption for the cesium resonance lines at 8944, 8521, 4593 and 4555 A for cesium is argon at pressures near atmospheric have been measured over a wide range of cesium densities and found to scale as the product of the cesium and argon densities. These results are consistent with broadening as the result of binary collisions between cesium and argon atoms. Our theory of resonance fluorescence for optically thick systems is found to give good agreement with experiments in which mercury was illuminated with a resonance line source. The dominant loss mechanism at moderate and high densities is diffusion to the window. Significant discrepancies remain between the theory and our measurements in cesium using a white light source. (Author), See also report dated 25 Jul 69, AD-691 470.

The resonance radiation emitted by thermally excited cesium vapor was observed at a temperature of 800K and cesium densities between 3.7 and 37 x 10 to the 16th power atoms/cc. The spectral distribution of the radiation shows the line reversal effects expected for a finite rate of production of excited atoms. Measurements of the magnitude and wavelength dependence of the specular reflection of light in the vicinity of the resonance line have been extended to cesium densities near 6 x 10 to the 17th power atom/cc and support the Taylor-Langmuir formula for the equilibrium cesium vapor pressure rather than the recent results of Volyak, Vinogradev and Anisemov. The theoretical studies of the backscattering of resonance radiation have been extended to include the effects of the non-radiative transport of excited resonance atoms to boundaries, such as the windows of the experimental cell. The theory was also extended to include illumination by narrow line sources, such as the resonance line source used in the studies of mercury vapor by Hansen and Webb. (Author), See also Yearly rept. for Jul 67-Jun 68, AD-674 120.

Measurements of the magnitude and wavelength dependence of the specular reflection of light in the vicinity of the cesium resonance lines from a cesium-sapphire interface verify the Taylor-Langmuir formula for the vapor pressure of cesium in the temperature range from 500 to 600K. This result eliminates the Cs density as a source of systematic error in our previous measurements of the self-broadening of the Cs resonance lines at 8521 and 8944A. Measurements have been made of the total amount of diffusely scattered resonance radiation for pure Cs and for Cs-nitrogen mixtures at Cs densities between 10 to the 14th power and 10 to the 16th power atom/cu cm. A preliminary analysis of this data shows that the method is capable of yielding quenching cross sections at high alkali vapor densities. Some features of the results, such as the apparent quenching caused by pure Cs, are not yet understood. (Author), See also AD-657 864.

An experimental study of the self-broadening of cesium resonance lines was made using measurements of the transmission of white light through a cell filled with Cs. Discrepancies between previous results were resolved in favor of the older results of Gregory. It was found that recent investigators have not taken proper account of the transmission characteristics of the monochromator used in the measurements. The understanding of the role of the monochromator makes available an additional technique for the measurement of cesium and other metal vapors in power conversion devices. The results of exploratory measurements of the scattering of resonance radiation are discussed. (Author)