GAS-PRESSURE BONDING OF ZIRCALOY-CLAD FLAT-PLATE URANIUM DIOXIDE FUEL ELEMENTS

A solid-state bonding technique involving the use of gas pressure at elevated temperatures was investigated for the preparation of compartmented Zircaloy-clad flat-plate uranium dioxide fuel elements. These investigations involved development of methods for the surface preparation and assembly of fuel- element components for bonding, determination of optimum bonding parameters, development of barrier coatings for uranium dioxide to prevent reaction with Zircaloy, and extensive testing and evaluation of the bonded fuel elements. During the course of this work, the process was continually modified and refined in an effort to improve the quality of the bonded element and decrease the cost of fabrication. The surface-preparation studies indicated that satisfactory bonding could be obtained consistently with both machined and belt-abraded components. Belt abrasion is more economical and was used as the standard technique in the development phases of the program. Initially the elements were assembled into a stainless steel or Ti-Namel envelope which was evacuated and sealed prior to bonding. Later studies showed that the quality of bonded elements could be improved and process costs decreased by edge welding the Zircaloy components to form a gastight assembly that was then bonded without use of a protective envelope. Further cost reductions were incorporated into the process by the use of piece Zircaloy components to form the picture frame. Optimum bending with a minimum core-to-cladding reaction was achieved by pressure bonding at 1500 to 1550 deg F for 4 hr using a helium gas pressure of 10,000 psi. A postbonding heat treatment for 5 min at 1850 deg F in a salt bath promoted additional grain growth at the bond interface during the alpha-to-beta transformation. Barrier layers of graphite. chronaium, iron. molybdenum, nickel, niobium, palladium, and various oxides were investigated to prevent reaction between the UO/sub 2/ core and Zircaloy cladding. Graphite, in the form of a sprayed and buffed coating, and chromium were found to be relatively effective barriers. The graphite coating was easy to apply and less expensive than a chromium electroplate. (auth

Microbial contamination of laboratory constructed removable orthodontic appliances

OBJECTIVES: This study aims to determine whether laboratory constructed removable orthodontic appliances are free from microbial contamination prior to clinical use and to evaluate the dental hospital cross-infection procedures to ensure that patient-derived contamination does not enter the construction process, thereby propagating a cycle of cross-contamination.MATERIALS AND METHODS: The construction process of removable orthodontic appliances from three individuals was evaluated at every stage, from impression to final delivery of the appliance using molecular microbiological techniques. The bacterial profiles at each stage of appliance construction were obtained using denaturing gradient gel electrophoresis, along with the bacterial profiles of the three participants' saliva. This enabled the bacterial profiles found at each stage of construction to be compared directly with the saliva of the person for whom the appliance was being constructed. Bacteria were identified at each stage using 16S rDNA PCR amplification and sequence phylogeny.RESULTS: There was no evidence of bacterial cross-contamination from patients to the laboratory. The current process of disinfection of impression appears to be adequate. Contamination was found on the final removable appliances (0.97 × 10(2)-1.52 × 10(3) cfu ml(-1)), and this contamination occurred from within the laboratory itself.CONCLUSIONS: Every effort is made to reduce potential cross-infection to patients and dental professionals. Newly constructed removable appliances were shown not to be free from contamination with bacteria prior to clinical use, but this contamination is environmental. Further studies would be required to determine the level of risk this poses to patients.CLINICAL SIGNIFICANCE: Dental professionals have a duty of care to minimise or eradicate potential risks of cross-infection to patients and other members of the team. To date, much less attention has been paid to contamination from the orthodontic laboratory, so contamination and infection risks are unknown.</p

Geotechnical Site Characterization of Sandy Beach Sediments from Satellite-Based Synthetic Aperture Radar Imagery

The potential use of synthetic aperture radar (SAR) imagery for estimating moisture contents at sandy beaches is discussed. These systems are considered all-weather satellites, can provide data during storm events, and allow for the monitoring of sandy beaches during adverse conditions. SAR images are composed of the backscatter coefficient, which is a representation of the returned energy. It is impacted by radar properties (wavelength of the transmitted signal, incidence angle, and polarization) and terrain characteristics (dielectric properties, surface roughness, and feature orientation). Typical trends in backscatter, moisture content, surface roughness, and roughness category are presented for a case study from the sandy Atlantic beach in Duck, North Carolina, and potential models how to address these factors in a data analysis framework are discussed. Moisture contents here ranged from 3.7% to 23%, backscatter coefficient ranged from -20.5 dB to -13.3 dB, and standard deviation of the surface height variation (or RMS height) ranged from 0.101 to 0.491 cm. Preliminary results indicate that SAR images are a feasible option for the derivation of moisture content data, especially for images collected at intermediary incidence angles (-30 degrees-46 degrees)

Geotechnical Investigation of Exposed Intertidal Flats at the Great Bay Estuary Using Sediment Sampling and Satellite-Based Synthetic Aperture Radar

Abstract Estuarine intertidal flats are exposed to a wide range of changing environmental conditions, but despite many years of field studies, little is known about their geotechnical characteristics. This study investigates (1) the variability of sediment grain size distributions, water contents, and Atterberg limits of three distinct exposed tidal flats; and (2) the potential pathways for remote characterization of those sites. Sediment samples were collected from three flats in the Great Bay Estuary located in the Gulf of Maine at the border of New Hampshire and Maine, United States: two sites composed of primarily fine-grained soils (Adams Point and Woody) and one composed of predominately coarse-grained soils (Mast Cove). Additionally, high-resolution X-band synthetic aperture radar (SAR) images were collected concurrently to field measurements from various satellites and over different incidence angles. In each image, the footprint area corresponding to the three exposed tidal flats was extracted, and statistical properties of the backscatter intensity histograms for each region were computed and compared. Moisture contents, fines contents, and grain size distributions varied between the three sites, with the USCS classifications ranging from elastic silts (Woody) and low-plasticity silts (Adams Point) with high water contents (83.2%–172.7%) and fines contents (83.4%–99.5%) to silty sand and well-graded sands with gravels (Mast Cove) with lower water contents (17.7%–48.3%) and fines contents (4.8%–44.3%). Across the sites, the statistical properties of the SAR backscatter exhibited distinct trends regarding mean backscatter, entropy, and uniformity in relation to the Unified Soil Classification Scheme (USCS) classification and fines content. These trends were consistent across all images collected. A potential sediment classification scheme to derive the USCS classification from the X-band SAR imagery is suggested utilizing the mean, entropy, and uniformity of the backscatter coefficient

Assessment of moisture content in sandy beach environments from multispectral satellite imagery

A framework for estimating moisture content from satellite-based multispectral imagery of sandy beaches was tested under various site conditions and sensors. It utilizes the reflectance of dry soil and an empirical factor c relating reflectance and moisture content for a specific sediment. Here, c was derived two ways: first, from in situ measurements of moisture content and average NIR image reflectance; and second, from laboratory-based measurements of moisture content and spectrometer reflectance. The proposed method was tested at four sandy beaches: Duck, North Carolina; and Cannon Beach, Ocean Cape, and Point Carrew, Yakutat, Alaska. Both measured and estimated moisture content profiles were impacted by site geomorphology. For profiles with uniform slopes, moisture contents ranged from 3.0% to 8.0% (zone 1) and from 8.0% to 23.0% (zone 2). Compared to field measurements, the moisture contents estimated using c calibrated from in situ and laboratory data resulted in percent error of 3.6%-44.7% and 2.7%-58.6%, respectively. The highest percent error occurred at the transition from zone 1 to zone 2. Generally, moisture contents were overestimated in zone 1 and underestimated in zone 2, but followed the expected trends based on field measurements. When estimated moisture contents in zone 1 exceeded 10%, surface roughness, debris, geomorphology, and weather conditions were considered