A grid refinement and coarsening scheme has been developed for tetrahedral and triangular grid-based calculations in message-passing environments. The element adaption scheme is based on an edge bisection of elements marked for refinement by an appropriate error indicator. Hash-table/linked-list data structures are used to store nodal and element formation. The grid along inter-processor boundaries is refined and coarsened consistently with the update of these data structures via MPI calls. The parallel adaption scheme has been applied to the solution of a transient, three-dimensional, nonlinear, groundwater flow problem. Timings indicate efficiency of the grid refinement process relative to the flow solver calculations.

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In biomineralized tissue, Nature often uses a single crystal system to form tools with widely varied form and functionality. To accomplish this, organisms have developed methods to deterministically modify and control crystal habit, commonly creating shapes with lower symmetry than is possessed by the pure crystal. In this paper we use atomic force microscopy to investigate the effect of chiral amino acids on calcite growth. We show that the atomic steps and resultant macroscopic shape exhibit a lower symmetry that reflects the chirality of the amino acid. We use this result to constrain the possible stereospecific binding sites. We argue that the change in morphology is not due to the incorporation of the amino acid, but rather that it acts like a surfactant changing the energetics of the interface. These results suggest that the conventional paradigm for understanding the geometrical and chemical aspects of biomineralization in terms of stereochemical recognition should be expanded to capture the energetic controls that determine the mechanisms of mineral modification by biomolecules.

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Statistical agencies seek to disseminate useful data while keeping low the risk of statistical confidentiality disclosure. Recognizing that reidentification of data is generally inadequate to protect its confidentiality against attack by a data snooper, agencies restrict the data they release for general use. Typically, these restricted data procedures have involved transformation or masking of the original, collected data through such devices as adding noise, topcoding, data swapping, and recoding. Recently, proposals have been put forth for the release of synthetic data, simulated from models constructed from the original data. This paper gives a framework for the comparison of masking and synthetic data as two approaches to disclosure limitation. Particular attention is paid to data utility and disclosure risk. Examples of instantiation of masking and of synthetic data construction are provided to illustrate the concepts. Particular attention is paid to data swapping. Insights drawn from the Bayesian paxadigm are provided.

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This article is about the Chopping effect observed at cathodic arc initiation. It is argued that current chopping at the rising edge is similar to the current chopping effect that is well-known for the arc current approaching current-zero.

Environmental and health issues coupled with increasingly stringent nitrogen oxide (NOx) emission standards indicates a need for the development of alternative low-cost technologies for the removal of NOx from gas streams. Biological NOx conversion offers promise as a novel treatment method. Thermophilic denitrifying bacteria indigenous to composts and soils are capable of converting NOx to environmentally benign nitrogen via a dissimilatory reductive pathway. The present study compares the performance of three bioreactor packing materials (compost, perlite, and biofoam) for the removal of nitric oxide (NO) from a simulated wet-scrubbed combustion gas. Although all three materials performed well (>85% NO removal) at residence times of 70-80 seconds, the compost performed better than the other materials at shorter residence times (13-44 seconds). The perlite and biofoam materials, however, both offer long-term thermal stability and lower pressure drop compared with compost. The feasibility of biological NOx conversion processes will depend on the combined factors of NOx removal ability and pressure drop. The results presented here suggest that the compost, perlite and biofoam systems, subject to further optimization, offer potential for the biological removal of NOx from gas streams.

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Development of an assessment framework and indicators can be used to evaluate effectiveness of wetland restoration. Example of these include index of biotic integrity and the hydrogeomorphic method. Both approaches provide qualitative ranks. We propose a new method based on the EPA wetland research program. Similar to other methods, indexes are compared to reference communities; however, the comparisons are quantitative. In this paper we discuss the results of our framework using the Pen Branch riparian wetland system as an example.

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An array of fast electric-field-change sensors has been operated in New Mexico, Texas, Florida, and Nebraska during 1998--2000 to improve identification of lightning processes responsible for VHF and optical signals detected by the FORTE satellite. Differential time of arrival methods are used to provide gee-locations of events from multi-station observations. A comparison of two dimensional location from the steric array and the National Lightning Detection Network operated by Global Atmospherics, Inc. is presented. Also, the time differences of multiple paths of the lightning signals to a station due to ionospheric reflection can be used to determine the altitude of a temporally narrow event. We present altitude determination of Compact Intracloud Discharges observed by the steric array and compare with the Kennedy Space Center Lightning Detection and Ranging (LDAR) system in Florida.

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Many techniques have been developed and applied in the US and other countries for the control of the special nuclear materials (SNM) plutonium and uranium, but no standard methods exist for the determination of neptunium in bulk containers. Such methods are needed because the U.S. Department of Energy requires all Government-owned {sup 237}Np be treated as if it were SNM and the International Atomic Energy Agency is considering how to monitor this material. We present the results of the measurements of several samples of neptunium metal with a variety of techniques. Analysis of passive gamma-ray spectra uniquely identifies the material, provides isotopic ratios for contaminants, such as {sup 243}Am, and may provide information about the shielding, mass, and time since processing. Active neutron interrogation, using the delayed neutron technique in a package monitor, provides useful data even if the neptunium is shielded. The tomographic gamma scanner yields a map of the distribution of the neptunium and shielding in a container. Active photon interrogation with pulses from a 10-MeV linac produces delayed neutrons between pulses, even when the container is heavily shielded. Data from one or more of these techniques can be used to identify the material and estimate a mass …

Aqueous processing is necessary for the removal of impurities from {sup 238}Pu dioxide ({sup 238}PuO{sub 2}) fuel due to unacceptable levels of {sup 234}U and other non-actinide impurities in the scrap fuel. Impurities at levels above General Purpose Heat Source (GPHS) fuel specifications may impair the performance.of the heat sources. Efforts at Los Alamos have focused on developing the bench scale methodology for the aqueous process steps which includes comminution, dissolution, ion exchange, precipitation, and calcination. Recently, work has been performed to qualify the bench scale methodology, to show that the developed process produces pure {sup 238}PuO{sub 2} meeting GPHS fuel specifications. In addition, this work has enabled us to determine how waste volumes may be minimized during full-scale processing. Results of process qualification for the bench scale aqueous recovery operation and waste minimization efforts are presented.