Lead aerosols in the atmosphere: increasing concentrations

The concentrations of atmospheric lead around San Diego, California, have been determined and their geographic and seasonal variations are explained. The lead aerosol concentration at San Diego is increasing at a rate of 5 percent per year. The isotopic composition of lead aerosols is similar to that of the lead additives isolated from gasoline, which are the largest contributors to atmospheric lead pollution.     

Self-arrangement of molybdenum particles into cubes

An unusual distribution of particle sizes has been observed following the formation of molybdenum particles by argon ion sputtering. Many of the molybdenum particles produced by sputtering at the threshold pressure for particle formation in the vapor appear to be single crystalline cubes. There are two prominent peaks in the edge length distribution of the cubes, one centered at 4.8 nanometers with a halfwidth of approximately 1.3 nanometers and the other at 17.5 nanometers. The peak for the larger cubes is approximately square and has a total width of 7.0 nanometers. Evidence is presented that the larger cubes are formed by a 3 by 3 by 3 self-arrangement of the smaller cubes, which contain approximately 7000 atoms. Self-arrangement in inorganic structures is normally only observed when the building blocks are atoms, molecules, or clusters of less than 100 atoms.     

Effect of Wheat Bran Fiber and Bran Particle Size on Fat and Fiber Digestibility and Gastrointestinal Tract Measurements in the Rat

The effect of wheat bran (AACC hard red) and bran particle size on fat and fiber digestibility and gastrointestinal tract measurements were investigated with diets containing 5.7–10.7% dietary fiber. Fifty‐six male weanling Sprague‐Dawley rats were randomly assigned to four diets containing 5% cellulose (C5); 10.5% cellulose (C10); 21.5% coarse (2 mm) wheat bran (CB); or 22.2% fine (0.5 mm) wheat bran (FB) in a sixweek study. Dietary fiber digestibilities were significantly different (P < 0.05) among treatment diets (CB > FB > C5 > C10) but there was no effect in fat digestibility among treatments. High‐fiber diets fed to rats resulted in significantly greater wet and dry fecal weights than low‐fiber diets. Bran diets resulted in significantly higher fecal moisture than cellulose diets. Cecum lengths increased significantly with bran diets compared with cellulose diets. The CB diet resulted in significantly higher stomach weights than with cellulose diets. Stomachs were heavier and cecal lengths were greater with bran diets than with cellulose diets; however, a high‐cellulose diet resulted in increased colon weight. Except for higher fiber digestibility of coarse bran, bran particle size had no significant effects. Healthful effects of wheat bran may be associated with gastrointestinal morphology and function. Fecal bulking and decreased intestinal transit time can prevent constipation and may dilute or reduce absorption of toxic or carcinogenic metabolites, thus improving gastrointestinal health and lowering the risk of tumor development and cancer.