A tandem-based compact dual-energy gamma generator.

A dual-energy tandem-type gamma generator has been developed at E. O. Lawrence Berkeley National Laboratory and Sandia National Laboratories. The tandem accelerator geometry allows higher energy nuclear reactions to be reached, thereby allowing more flexible generation of MeV-energy gammas for active interrogation applications. Both positively charged ions and atoms of hydrogen are created from negative ions via a gas stripper. In this paper, we show first results of the working tandem-based gamma generator and that a gas stripper can be utilized in a compact source design. Preliminary results of monoenergetic gamma production are shown.

Predator size and the suitability of a common prey.

Although a predator's mass should influence the suitability of its prey, this subject has received little direct attention. We studied the capture and processing of an abundant syrphid fly Toxomerus marginatus (c. 4 mg) by 0.6- to 40-mg juvenile crab spiders Misumena vatia (Thomisidae) to determine how profitability, relative profitability (profitability/predator mass), overall gain in mass, and relative gain in mass differed with predator mass, and whether foraging changed concurrently. In multi-prey experiments, the smallest successful spiders (0.6-3.0 mg) extracted less mass from flies, and did so more slowly, than large spiders. This gain was proportionately similar to that of 10- to 40-mg spiders with access to many Toxomerus. However, many small spiders failed to capture flies. When we gave spiders only a single Toxomerus, the smallest ones again extracted mass more slowly than the large ones and increased in mass less than the large ones, but increased in mass proportionately more than large ones. Relative gain in mass from a single prey decreased with increasing spider mass. Spiders larger than 10 mg all extracted similar amounts of mass from a single Toxomerus at similar rates, but varied in time spent between captures. Thus, Toxomerus changes with spider mass from a large, hard-to-capture bonanza to a small, easy-to-capture item of low per capita value. However, Toxomerus is common enough that large spiders can capture it en masse, thereby compensating for its decline in per capita value.

DNA and total protamine masses in individual sperm from fertile mammalian subjects.

The total amount of phosphorus and sulfur inside the nuclei of individual bull, stallion, hamster, human, and mouse sperm from fertile subjects has been measured using Particle Induced X-ray Emission (PIXE). Using the sulfur masses, we determined the total protamine (protamine 1 plus protamine 2) mass within the sperm nuclei of each species. Using the phosphorus masses, we determined the DNA mass present within the sperm nuclei of each species. The results reveal that although the relative proportion of protamine 1 to protamine 2 varies among the species examined, the total protamine mass to DNA mass ratio is similar in bull, stallion, hamster, and mouse sperm nuclei. In contrast, mature human sperm nuclei were found to contain significantly less protamine. This observation is consistent with other studies, which suggest that as much as 15% of the DNA in human sperm remain packaged by histones. Using the data obtained for bull sperm, the length of DNA that could be covered by each protamine 1 molecule in bull sperm has been estimated. Making the assumption that the size of the protamine 1 binding site on DNA is similar in the sperm of these species, the length of DNA covered by a single protamine 2 molecule also has been estimated.

Resource partitioning in bumble bees: the role of behavioral factors.

Small Bombus ternarius workers for age most frequently on the distal parts of goldenrod flower clusters when large B. terricola workers are present. This shift results from B. ternarius avoiding B. terricola. In this way B. ternarius can exploit, without conflict, resources whose availability changes constantly because of fluctuating numbers of larger consumers.