The concepts of subsequence and rearrangement of double sequence are used to present multidimensional analogues of the following
core questions. If x is a bounded real sequence and A is a matrix summability method, under what conditions does there exist y, a subsequence (rearrangement) of x such that each number t in the core of x is a limit point of Ay?
A phoswich radiation detector is comprised of a phosphor sandwich in which several different phosphors are viewed by a common photomultiplier. By selecting the appropriate phosphors, this system can be used to simultaneously measure multiple radiation types (alpha, beta, gamma and/or neutron) with a single detector. Differentiation between the signals from the different phosphors is accomplished using digital pulse shape discrimination techniques. This method has been shown to result in accurate discrimination with highly reliable and versatile digital systems. This system also requires minimal component count (i.e., only the detector and a computer for signal processing). A variety of detectors of this type have been built and tested including: (1) a triple phoswich system for alpha/beta/gamma swipe counting, (2) two well-type detectors for measuring low levels of low energy photons in the presence of a high energy background, (3) a large area detector for measuring beta contamination in the presence of a photon background, and (4) another large area detector for measuring low energy photons from radioactive elements such as uranium in the presence of a photon background. An annular geometry, triple phoswich system optimized for measuring alpha/beta/gamma radiation in liquid waste processing streams is currently being designed.
The problem of computing the properties of a low mass quantum particle in equilibrium in a disordered medium is considered. With the advancement of computational speed, statistical methods for sampling a complex phase space are now viable. The Feynman-Kac path integral establishes a connection between a quantum particle and classical polymer consisting of p atoms. This allows the computation of quantum mechanical equilibrium values using well known methods devised for classical systems. Here we review the application of the path integral to the computation the properties of thermalized positron and positronium and introduce some new directions of investigation.
A pulse-perturbation experiment, designed to assess the impact of top predators, resource availability, and the interaction between predators and resources, was conducted in the inquiline community found in a natural population of the pitcher plant Sarracenia purpurea. Experimental manipulations of pitchers were removal of the top predator (the filter-feeding larvae of the mosquito Wyeomia smithii), addition of resources (mealworms), and the combination of the two. Pitchers were then censused every three days for 15 days. Top-predator removal had little effect on the remaining community, in part because mosquitoes rapidly recolonized the pitchers. Resource addition resulted in large, persistent increases in both bacterial and protozoan abundances but had no effect on rotifers and mites. Therefore, “top-down” effects were relatively weak. In contrast “bottom-up” effects were strong at the lowest trophic level (bacteria) but differentially affected species at a higher trophic level that feed on bacteria. The interactions between top-down and bottom-up forces were difficult to quantify because of the rapid recolonization by mosquitoes.
Authors:P. Krey, M. Heit, H. Livingston, and K. Miller
The analyses of lake sediments from the northeastern U.S. provide depositional histories of137Cs and239+240Pu from both global fallout and fallout from the Nevada Test Site (NTS) detonations in the 1950's. These results provide an independent verification and extension of the temporal trend of the240Pu/239Pu atom ration of global fallout to earlier times. This data supports the findings of other studies of fallout in the atmospheric and marine environment.
Authors:H.L. Buckley, J.H. Burns, J.M. Kneitel, E.L. Walters, P. Munguia, and E. Miller
We examined the environmental factors associated with community structure in the inquiline communities of the purple pitcher plant (Sarracenia purpurea L.). We sampled all 141 communities in a 10- x 20-m grid and recorded their spatial relationships to determine the relative influence of environmental and spatial factors on community structure. Environmental and spatial factors contributed equally to the variance in community composition (species identity and abundance) among pitchers. The species richness of communities was influenced by both spatial and environmental variables, particularly environmental variables related to community size. In addition, our study suggests a number of hypotheses about factors influencing community structure (e.g. predation) that could be tested experimentally.
Authors:D. Miller, M. Grant, B. Erdal, R. Whipple, and H. O'Brien
Proton spallation is a relatively recent method for significant radioisotope production. A detailed discussion of the activation equation for charged-particle reactions is given, and measured values of spallation cross sections for reactions of 800-MeV protons with three target materials are reported.