Results of two field experiments showed that selective removal of omnivorous mosquito larvae (Aedes triseriatus (Say)) functioning as top predators in the food web of a temperate, tree hole ecosystem resulted rapidly in increased abundance of flagellate and then ciliate populations. Flagellate density increased from <1 per ml to >103 per ml within 4 days of omnivore removal, followed shortly thereafter by an increase in ciliate density from <1 per ml to >102 per ml, after which flagellate density declined, and flagellate and ciliate densities stabilized. Rod-shaped bacteria increased slightly in density after removal of larval mosquitoes, then declined as protist density increased. Cocciform bacteria did not vary in density with these changes, thus the trophic cascade dampened at the remotest trophic level. Concomitant with the increase in protist densities, some bacteria formed elongated filaments >10 μm in length, likely an anti-predation, morphological response stimulated by suddenly intensified grazing as protozoan density rose. Results suggest that feeding by omnivorous mosquito larvae exhibited strong top-down effects on flagellate and ciliate populations, depressing them to below their equilibrium densities and nearly to extinction in tree hole ecosystems.
A recently-developed quadrupole mass spectrometer system specifically designed for thermal analysis studies, has been linked
to a thermobalance and a simultaneous TG-DTA unit, for evolved gas analysis. The performance and applicability of the system
is illustrated by examples from four fields of study
Authors:M. Brown, E. Antunes, B. Glass, M. Lebete and R. Walker
Differential scanning calorimetry was used to examine the thermal behaviour of mixtures of the drug prochlorperazine with
standard excipients, to assess potential interactions, and of mixtures with cyclodextrins, to investigate inclusion complexation
which could increase the photostability of the drug. For most of the excipients (magnesium stearate, stearic acid, Explotab®, Ac-Di-Sol®, Encompress® and Ludipress®, lactose and Starch 1500) disappearance or broadening of the melting endotherm of the drug indicated interactions. Lubritab® was the only 'inert' excipient tested. Mixtures of prochlorperazine and the cyclodextrins gave incomplete inclusion complexation
as shown by only partial disappearance of the melting endotherm of the drug.
Authors:P. Warwick, N. Evans, A. Hall, G. Walker and E. Steigleder
Conditional stability constants have been determined for U(IV) and U(VI) Boom Clay humic acid (BCHA) and Aldrich humic acid
(AHA) complexes, under anaerobic and carbonate free conditions. The constants are needed for nuclear waste repository performance
assessment purposes. The U(IV) constants were obtained by developing an approach based on the solubility product of amorphous
U(OH)4. The U(VI) constants were obtained by applying the Schubert ion-exchange approach.
Authors:K. Inn, B. Coursey, E. Eisenhower, M. Walker, H. Heaton and K. Duvall
Over the past ten years, the National Institute of Standards and Technology has, through its Office of Radiation Measurement, developed a national program for Secondary Laboratories. These Secondary Laboratories provide the necessary calibrations and quality assurance testing to support and affirm the caliber of the measurements in the areas they serve. The areas that are in the program include State Radiation Protection, Personnel Dosimetry, Survey Instrument Calibration, High-Level Dosimetry, Radiation Therapy, Bioassay, Survey Instrument Testing, Ionizing Radiation, Environmental Radioactivity, Radioactivity Standards, and Radon.
Authors:R. L. Brodzinski, R. A. Craig, S. D. Fink, W. K. Hensley, N. O. Holt, M. A. Knopf, E. A. Lepel, O. D. Mullen, S. R. Salaymeh, T. J. Samuel, J. E. Smart, M. R. Tinker and D. D. Walker
An online monitor has been designed, built, and tested that is capable of measuring the residual transuranic concentrations in processed high-level wastes with a detection limit of 370 Bq/ml (10 nCi/ml) in less than six hours. The monitor measures the (α,n) neutrons in the presence of gamma-ray fields up to 1 Sv/h (100 R/h). The optimum design was determined by Monte Carlo modeling and then tempered with practical engineering and cost considerations. A multiplicity counter is used in data acquisition to reject the large fraction of coincident and highly variable cosmic-ray-engendered background events and results in an S/N ratio ~1.
Authors:L. Tandon, E. Hastings, J. Banar, J. Barnes, D. Beddingfield, D. Decker, J. Dyke, D. Farr, J. FitzPatrick, D. Gallimore, S. Garner, R. Gritzo, T. Hahn, G. Havrilla, B. Johnson, K. Kuhn, S. LaMont, D. Langner, C. Lewis, V. Majidi, P. Martinez, R. McCabe, S. Mecklenburg, D. Mercer, S. Meyers, V. Montoya, B. Patterson, R. Pereyra, D. Porterfield, J. Poths, D. Rademacher, C. Ruggiero, D. Schwartz, M. Scott, K. Spencer, R. Steiner, R. Villarreal, H. Volz, L. Walker, A. Wong and C. Worley
The goal of nuclear forensics is to establish an unambiguous link between illicitly trafficked nuclear material and its origin.
The Los Alamos National Laboratory (LANL) Nuclear Materials Signatures Program has implemented a graded “conduct of operations”
type analysis flow path approach for determining the key nuclear, chemical, and physical signatures needed to identify the
manufacturing process, intended use, and origin of interdicted nuclear material. This analysis flow path includes both destructive
and non-destructive characterization techniques and has been exercized against different nuclear materials from LANL’s special
nuclear materials archive. Results obtained from the case study will be presented to highlight analytical techniques that
offer the critical attribution information.