VAPORIZATION OF ELEMENTAL MERCURY FROM MOLTEN LEAD AT LOW CONCENTRATIONS

Experiments were conducted to measure the rate of vaporization of elemental mercury from molten lead to provide a basis for estimating radiological source terms for the APT (Accelerator Production of Tritium project) lead blanket. These data also have application to other accelerator targets in which mercury may be created by proton spallation in lead. Molten pools of lead with from 0.01% to 0.10% mercury were prepared under inert conditions. Experiments were conducted which varied in duration from several hours to as long as a month to measure the mercury vaporization from the lead pools. The melt pools and gas atmospheres were controlled at 340 degrees C during the tests, above the melting temperature of lead. Parameters which were varied in the tests included the mercury concentrations, gas flow rates over the melt, circulation in the melts, gas atmosphere compositions and the addition of aluminum to the melts. The vaporization of mercury was found to scale roughly linearly with the concentration of mercury in the pool. Variations in the gas flow rates were not found to have any effect on the mass transfer, however circulation of the melt by a submerged stirrer did enhance the mercury vaporization rate. The rate of mercury vaporization under a high-purity argon atmosphere was found to exceed that for an air atmosphere by as much as a factor of from ten to 20; the causal factor in this variation was the formation of an oxide layer over the melt pool with the air atmosphere which retarded mass transfer across the melt-atmosphere interface. Aluminum was introduced into the melt to investigate its effect upon the mercury vaporization rate. No effect was observed for a case under a high-purity argon atmosphere, which suggests that there are no chemical effects of the aluminum on the vaporization kinetics. With an air atmosphere, the presence of aluminum in the melt reduced the mercury vaporization by a factor of six in comparison to the identical test but without aluminum, suggesting that aluminum in the lead/ mercury melt retards the vaporization of mercury by creating a surface oxide layer in addition to the lead-oxide layer or by changing the character of the lead-oxide layer, thereby increasing the mass transfer resistance.     

Applications of a dc constant-current source

Measuring resistance, performing a coulometric titration, measuring semiconductor breakdown voltages, operating IMPATT diodes, testing electrolytic capacitors, measuring magnetic field intensity?these represent only a few of the applications of constant-current sources. Some of the features of constant-current supplies, as well as the requirements imposed on these sources and techniques for using them in a variety of applications, are described in this article.     

Chorioallantoic membranes indicate avian exposure and biomarker responses to environmental contaminants: a laboratory study with White Leghorn chickens (Gallus domesticus)

PCB and endosulfan concentrations in the chorioallantoic membrane (CAM) of white leghorn chickens (Gallus domesticus) were evaluated as indicators of hepatic cytochrome P450 isozyme activity in hens and chicks as well as toxicant concentrations in eggs and hens. Sixteen hens were randomly divided into four groups of four and dosed with a mixture of PCB105 (2,3,3',4,4'-pentachlorobiphenyl), PCB156(2,3,3',4,4',5-hexachlorobiphenyl), PCB189 (2,3,3',4,4',5,5'-heptachlorobiphenyl), and technical grade endosulfan (3:1 ratio of alpha and beta isomers) at three different dose groups. The first 10 fertile eggs laid by each hen were collected, the even-numbered eggs incubated until hatched, and the odd numbered eggs were analyzed for test chemicals. Strong (r2), significantly positive (p value) relationships were found between total PCB mass (ng) in CAMs and both total PCB concentrations (ng/g wet wt) in adults (r2 = 0.91, p = 0.0001) and eggs (r2 = 0.87, p = 0.0001). The relationship between total PCB mass in CAMs and hepatic cytochrome p450 isozyme activity in chicks (r2 = 0.49, p = 0.0001) and hens (r2 = 0.45, p = 0.014) was also significant but not as strong. This study shows that CAMs can be used to estimate avian exposure to PCBs and resultant biological response.     

Segmentation and analysis of the human airway tree from three-dimensional X-ray CT images

The lungs exchange air with the external environment via the pulmonary airways. Computed tomography (CT) scanning can be used to obtain detailed images of the pulmonary anatomy, including the airways. These images have been used to measure airway geometry, study airway reactivity, and guide surgical interventions. Prior to these applications, airway segmentation can be used to identify the airway lumen in the CT images. Airway tree segmentation can be performed manually by an image analyst, but the complexity of the tree makes manual segmentation tedious and extremely time-consuming. We describe a fully automatic technique for segmenting the airway tree in three-dimensional (3-D) CT images of the thorax. We use grayscale morphological reconstruction to identify candidate airways on CT slices and then reconstruct a connected 3-D airway tree. After segmentation, we estimate airway branchpoints based on connectivity changes in the reconstructed tree. Compared to manual analysis on 3-mm-thick electron-beam CT images, the automatic approach has an overall airway branch detection sensitivity of approximately 73%.     

Phage typing of Salmonella enteritidis from different sources in Brazil

The occurrence of Salmonella Enteritidis (SE) phage types (PTs) in samples collected from healthy and diseased chickens, in outbreaks of human gastroenteritis related to the consumption of egg products, in samples of poultry meat, in pipped embryos of broiler chickens, in meat meal, in poultry-rearing environments, and in many foods (cheese, mayonnaise, cake, and bacon) is described for strains isolated from 1995 to 1997 in Brazil. SE strains were isolated, and the most common PT was found to be PT 4, followed by PTs 7, 21, 35, 6, 4a, 8, 30, 6a, 5a, 1, and 1b. Fourteen strains were classified as react-but-do-not-conform strains, and one strain was not typeable. The results of this study demonstrate that PT 4 has a wider distribution among the sources studied than do any other SE phage types and is the most important phage type in human salmonellosis.     

Retrieval of stratospheric aerosol size and composition information from solar infrared transmission spectra

Infrared transmission spectra were recorded by the Jet Propulsion Laboratory MkIV interferometer during flights aboard the NASA DC-8 aircraft as part of the Airborne Arctic Stratospheric Expedition II (AASE II) mission in the early months of 1992. In our research, we infer the properties of the stratospheric aerosols from these spectra. The instrument employs two different detectors, a HgCdTe photoconductor for 650-1850 cm(-1) and an InSb photodiode for 1850-5650 cm(-1), to simultaneously record the solar intensity throughout the mid-infrared. These spectra have been used to retrieve the concentrations of a large number of gases, including chlorofluorocarbons, NOy species, O3, and ozone-depleting gases. We demonstrate how the residual continua spectra, obtained after accounting for the absorbing gases, can be used to obtain information about the stratospheric aerosols. Infrared extinction spectra are calculated for a range of modeled aerosol size distributions and compositions with Mie theory and fitted to the measured residual spectra. By varying the size distribution parameters and sulfate weight percent, we obtain the microphysical properties of the aerosols that best fit the observations. The effective radius of the aerosols is found to be between 0.4 and 0.6 microm, consistent with that derived from a large number of instruments in this post-Pinatubo period. We demonstrate how different parts of the spectral range can be used to constrain the range of possible values of this size parameter and show how the broad spectral bandpass of the MkIV instrument presents a great advantage for retrieval ofboth aerosol size a nd composition over instruments with a more limited spectral range. The aerosol composition that provides the best fit to the measured spectra is a 70-75% sulfuric acid solution, in good agreement with that obtained from thermodynamic considerations.     

<Emphasis Type="Italic">K</Emphasis>-Optimal Rule Discovery

K-optimal rule discovery finds the K rules that optimize a user-specified measure of rule value with respect to a set of sample data and user-specified constraints. This approach avoids many limitations of the frequent itemset approach of association rule discovery. This paper presents a scalable algorithm applicable to a wide range of K-optimal rule discovery tasks and demonstrates its efficiency.     

Directed self-assembly of Ge nanostructures on very high index, highly anisotropic Si(hkl) surfaces

Families of very high-index planes, such as those which bifurcate spontaneously to form a hill-and-valley structure composed of opposing facets, provide natural templates for the directed growth of position-controlled self-organized nanostructures with shapes determined by the facet width ratio R. For example, deposition of a few ML of Ge on Si(173 100 373), corresponding to R(113/517) = 1.7, results in a field of 40-nm-wide Ge nanowires along [72 187] with a uniform period of 60 nm.     

Intrathoracic airway trees: segmentation and airway morphology analysis from low-dose CT scans

The segmentation of the human airway tree from volumetric computed tomography (CT) images builds an important step for many clinical applications and for physiological studies. Previously proposed algorithms suffer from one or several problems: leaking into the surrounding lung parenchyma, the need for the user to manually adjust parameters, excessive runtime. Low-dose CT scans are increasingly utilized in lung screening studies, but segmenting them with traditional airway segmentation algorithms often yields less than satisfying results. In this paper, a new airway segmentation method based on fuzzy connectivity is presented. Small adaptive regions of interest are used that follow the airway branches as they are segmented. This has several advantages. It makes it possible to detect leaks early and avoid them, the segmentation algorithm can automatically adapt to changing image parameters, and the computing time is kept within moderate values. The new method is robust in the sense that it works on various types of scans (low-dose and regular dose, normal subjects and diseased subjects) without the need for the user to manually adjust any parameters. Comparison with a commonly used region-grow segmentation algorithm shows that the newly proposed method retrieves a significantly higher count of airway branches. A method that conducts accurate cross-sectional airway measurements on airways is presented as an additional processing step. Measurements are conducted in the original gray-level volume. Validation on a phantom shows that subvoxel accuracy is achieved for all airway sizes and airway orientations.     

A new model validation tool using kernel regression and density estimation

In physiological system modelling for control or decision support, model validation is a critical element. A nonparametric approach for assessing the validity of deterministic dynamic models against empirical data is developed, based on kernel regression and kernel density estimation, yielding visual graphical assessment tools as well as numerical metrics of compatibility between the model and the data. Nonparametric regression has been suggested for assessing a parametric statistical model by constructing a confidence band for the proposed model and then checking whether the nonparametric regression curve lies within the band. However, for deterministic models, there is no confidence band that can be constructed. A reversal of roles is therefore suggested--construct a probability band for the nonparametric regression curve and check whether the proposed model lies within the band. This approach extends the utility of nonparametric regression for model assessment to deterministic models. Weighted kernel density estimation is incorporated to derive a density profile for the regression curve, creating a local graphical validation tool. In addition, the density profile is used to define and compute two numerical measures--average normalized density (AND) and relative average normalized density (RAND), representing global statistical validity measures. These tools are demonstrated using a biomedical system model for agitation-sedation and sedation management control.