The values for energy imparted at CT in pediatric patients were generally lower than in adults. The smaller mass of children, however, caused the corresponding effective doses to be higher than those in adults undergoing similar CT examinations.

A knowledge of the permittivity and loss tangent of snow and ice is essential in studying both radar echoes from snow-covered terrain and the attenuation of microwave energy through snowstorms. To provide this information, a program was carried out at the National Research Council of Canada to measure the permittivity and loss tangent of ice and snow, and also to determine the reflection coefficients of snow-covered surfaces, at a wavelength of 3.2 centimeters. As a result of these investigations values have been obtained for the permittivity and loss tangent of snow of varying density, temperature, and water content. Theoretical values of the reflection coefficients of snow-covered surfaces, calculated from these data, are compared with the values obtained from the direct measurement of reflections from natural snow surfaces.

Expectorationof large, branching, bronchial casts, termed plastic bronchitis, is an uncommon condition in children. Asthma or allergy often is the cause of cast production, but in some instances no etiology is found. Five children produced large, obstructing bronchial casts that either were expectorated or were extracted at bronchoscopy. Four of the children had asthma or allergies and the fifth had congenital tricuspid atresia and chronic pericardial and pleural effusions.

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