An improved error bound for a finite element approximation of a model for phase separation of a multi-component alloy

Using the approach of Rulla (1996 SIAM J. Numer. Anal. 33, 68-87)for analysing the time discretization error and assuming moreregularity on the initial data, we improve on the error boundderived by Barrett and Blowey (1996 IMA J. Numer. Anal. 16,257-287) for a fully practical piecewise linear finite elementapproximation with a backward Euler time discretization of amodel for phase separation of a multi-component alloy.     

Medium-resolution autonomous in situ gamma detection system for marine and coastal waters

We are developing a medium-resolution autonomous in situ gamma detection system for marine and coastal waters. The system is designed to extract and preconcentrate isotopes of interest from natural waters prior to detection in order to eliminate signal attenuation of the gamma rays traveling through water and lower the overall background from the presence of naturally occurring radioactive isotopes (⁴⁰K and U–Th series radionuclides). Filtration is used to preconcentrate target isotopes residing on suspended particles, while chemosorption is employed to preferentially extract truly dissolved components from the water column. Used filter and chemosorbent media will be counted autonomously using two LaBr₃ detectors in a near 4-π configuration around the samples. A compact digital pulse processing system, developed in-house and capable of running in coincidence mode, is used to process the signal from the detectors to a small on-board computer. The entire system is extremely compact (9″ dia. × 30″ len.) and platform independent, but designed for initial deployment on a research buoy. A variety of commercial and in-house nano-porous chemosorbents have been selected, procured or produced, and these and filter and detector components have been tested.     

Finite element approximation of a model for phase separation of a multi-component alloy with a concentration-dependent mobility matrix

We consider a model for phase separation of a multi-componentalloy with a concentration-dependent mobility matrix and logarithmicfree energy. In particular we prove that there exists a uniquesolution for sufficiently smooth initial data. Further, we provean error bound for a fully practical piecewise linear finiteelement approximation in one and two space dimensions. Finallynumerical experiments with three components in one space dimensionare presented.     

Gamma-ray signatures for state-of-health analysis and monitoring of widely-arrayed radiation portal monitor systems

Pacific Northwest National Laboratory (PNNL) has deployed a large array of radiation portal monitors for the Department of Homeland Security and U.S. Customs and Border Protection. These portal monitors scan incoming vehicles crossing the U.S. border and shipping containers leaving international ports for radioactive material via gamma-ray and neutron detection. Data produced and captured by these systems are recorded for every vehicle related to radiation signature, sensor/system status, local background, as well as a host of other variables. Within the Radiation Portal Monitor Project at PNNL, state-of-health observation and analysis for the whole RPM array using these data to determine functionality and performance is ongoing. Advanced state-of-health analysis and monitoring algorithms are being developed. Preparations are underway to incorporate the more difficult state-of-health monitoring of the mobile RPM and Advanced Spectroscopic Portals.