Mass Measurement Techniques Research Articles

Photometric Determination of Leaf Input into Tropical Streams

ABSTRACT Four methods often used in preparing leaves for studies on the fate of leaves falling into mid-latitude streams were analyzed in a tropical rainforest stream. Both t h e techniques and plant species affected processing rates for four species of tropical wet forest riparian plants. More leaf area remained for fresh leaf disks than for dried leaf disks. Photometric rather than the usual dry leaf mass measurement techniques were used because, 1) leaves do not have to be dried before they are used, 2) artificially dried leaves do not simulate natural conditions, especially in humid tropical forests, 3) leaves can be measured photometrically and replaced in streams without damaging tissue, 4)photometric methods are commonly used in terrestrial studies on leaf damage and these methods should be equally adaptable to aquatic systems, and 5) the correlation between leaf area loss and dry mass loss for terrestrial studies has been shown to be high; therefore, dry mass data from studies on aquatic leaf decomposition studies are expected to be similar to photometrically-derived leaf area data.

Heavy-Ion Reactions as a Technique for Direct Mass Measurements of UnknownZ>NNuclei

The reactions $^{40}\mathrm{Ca}(^{12}\mathrm{C},t)^{49}\mathrm{Mn}$ and $^{40}\mathrm{Ca}$($^{12}\mathrm{C}$, $^{3}\mathrm{He}$)$^{49}\mathrm{Cr}$ have been observed with ground-state cross sections of the order of 1 \ensuremath{\mu}b/sr. The results for $^{49}\mathrm{Mn}$ are consistent with its predicted mass excess of -37.72 \ifmmode\pm\else\textpm\fi{} 0.08 MeV.

In-Flight Mass Measurement of Small Fragments and Projectiles

Penetration and cratering studies at hypervelocities make use, primarily, of light gas guns and explosive devices to accelerate projectiles for the impact study. The highest velocities achievable to date with other than micron-sized projectiles are obtained from explosive accelerators (shaped charge) or modified light gas guns incorporating a third stage. Such devices produce one or more randomly shaped particles of undetermined mass; and meaningful impact studies at very high velocities require a method of accurate measurement of the mass of a small fragment after acceleration but before impact. An experimental technique for mass measurement, which is simple in concept and operation, has been developed and demonstrated. A high-speed flash X-ray system is used to photograph the projectile or projectiles in flight. A theoretical treatment utilizing the X-ray mass absorption coefficient of the projectile material, and the linearity of the film density as a function of the logarithm of the exposure, is used to demonstrate that the density change over a finite area of the film is directly proportional to the mass in the path of the X-ray beam. The measurement is independent of ``blurring'' due to the finite exposure time and tumbling of the projectile. Analysis of the exposed film can be conducted in a few minutes and requires only the measurement of average density at five or six positions on the film. Independent measurements of the masses of all projectiles in the field of view are possible. The demonstrated accuracy of the technique is better than ±5 percent.