Bioaccessibility of arsenic(V) bound to ferrihydrite using a simulated gastrointestinal system

The risk posed from incidental ingestion to humans of arsenic-contaminated soil may depend on sorption of arsenate (As(V)) to oxide surfaces in soil. Arsenate sorbed to ferrihydrite, a model soil mineral, was used to simulate possible effects on ingestion of soil contaminated with As-(V) sorbed to Fe oxide surfaces. Arsenate sorbed to ferrihydrite was placed in a simulated gastrointestinal tract (in vitro) to ascertain the bioaccessibility of As(V) and changes in As(V) surface speciation caused by the gastrointestinal system. The speciation of As was determined using extended X-ray absorption fine structure (EXAFS) analysis and X-ray absorption near-edge spectroscopy (XANES). The As(V) adsorption maximum was found to be 93 mmol kg(-1). The bioaccessible As(V) ranged from 0 to 5%, and surface speciation was determined to be binuclear bidentate with no changes in speciation observed post in vitro. Arsenate concentration in the intestine was not constant and varied from 0.001 to 0.53 mM for the 177 mmol kg(-1) As(V) treated sample. These results suggest that the bioaccessibility of As(V) is related to the As(V) concentration, the As(V) adsorption maximum, and that multiple measurements of dissolved As(V) in the intestinal phase may be needed to calculate the bioaccessibility of As(V) adsorbed to ferrihydrite.     

The Omni-family of all-purpose access methods: a simple and effective way to make similarity search more efficient

Similarity search operations require executing expensive algorithms, and although broadly useful in many new applications, they rely on specific structures not yet supported by commercial DBMS. In this paper we discuss the new Omni-technique, which allows to build a variety of dynamic Metric Access Methods based on a number of selected objects from the dataset, used as global reference objects. We call them as the Omni-family of metric access methods. This technique enables building similarity search operations on top of existing structures, significantly improving their performance, regarding the number of disk access and distance calculations. Additionally, our methods scale up well, exhibiting sub-linear behavior with growing database size.     

Long-Term Behavior of Fixated Flue Gas Desulfurization Material Grout in Mine Drainage Environments

In this research, we examine the long-term ( ～ 4 years) behavior of fixated flue gas desulfurization (FGD) material grout following placement within the Roberts–Dawson underground coal mine. Surface water and groundwater samples were collected to examine the impact of grouting on water quality, and core samples were obtained to assess the geochemical stability of the grout material. Surface water samples collected from the main seep at the Roberts–Dawson mine indicated that 4 years after grout placement the long-term fluxes of acidity, iron, sulfur, and calcium were slightly elevated compared to pregrout conditions. The long-term discharge of these constituents was likely due to continued dissolution of grout material (for Ca and S) as well as changes in flow paths and subsequent solubilization of metal salts accumulated within the mine voids (for acidity, Fe, Al, and S). Although the fluxes of these elements were elevated, no measurable deleterious impact was observed for the underlying groundwater or adjacent surface water reservoir. Groundwater samples collected from monitoring wells installed within the grout material indicated that acid mine drainage waters were neutralized by the grout material. Mineralogical analyses demonstrated minimal penetration of mine drainage water into the high strength fixated FGD material grout, and little weathering of the material was observed. These data indicate that the high strength fixated FGD material grout injected into the Roberts–Dawson mine was geochemically stable and could locally neutralize mine drainage waters. However, more complete grouting and more extensive mine flooding is likely needed in order to bring about significant improvements in seep water quality.     

Dense La0.9Sr0.1Ga0.8Mg0.2O2.85 electrolyte for IT-SOFC's: Sintering study and electrochemical characterization

This paper presents the sintering behaviour of a La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85 coral-like microstructure powder. This is prepared by a successive freeze-drying and self-ignition process followed by calcination at 1200 °C during 1 h. This synthesis method gives great uniformity of the powder and allows shaping into compacts without requiring a grinding step. The grain size distribution (between 0.5 and 4 μm) favours a good sintering behaviour: open porosity disappear at 1400 °C and relative densities over 99% can be achieved after 6 h at 1450 °C. The same powder can also be sintered into a thin disc of ∼100 μm thickness. The characterization of the dense material by impedance spectroscopy shows that the activation energies below and above 600 °C are 1.0 eV and 0.7 eV, respectively. The conductivity at 800 °C is ∼0.11 S cm⁻¹. Special attention is devoted to the temperature range between 200 °C and 400 °C, where the intragrain and intergrain contributions can be distinguished. The analysis of the parameters describing the intragrain constant phase element in the equivalent circuit suggests that, above 325 °C, the system evolves from a distribution of relaxation time to only one relaxation time. The analysis of the data by the complexes permittivity show that ionic oxide conduction mechanism would occur in two steps. In the first, an oxygen vacancy would be released and, in the second, the migration of the ionic oxide would take place in the material.     

Inhibited Cr(VI) reduction by aqueous Fe(II) under hyperalkaline conditions

This study investigated Cr(VI) reduction by dissolved Fe(II) in hyperalkaline pH conditions as found in fluid wastes associated with the U.S. nuclear weapons program. The results show that Cr(VI) reduction by Fe(II) at alkaline pH solutions proceeds very quickly. The amount of Cr(VI) removed from solution and the amount reduced increases with Fe(II):Cr(VI) ratio. However, the Cr(VI) reduction under alkaline pH condition is nonstoichiometric, probably due to Fe(II) precipitation and mixed iron(III)-chromium-(III) (oxy)hydroxides blocking Fe(II) surface sites, as well as removing Fe(II) from solution through O2 oxidation. After Cr(VI) was reduced to Cr(III), it precipitated out as mixed Fe(x)Cr1-xO3(solids) and various Fe(III) precipitates with an overall Cr:Fe ratio of 1:3; all Cr remaining in the solution phase was unreduced Cr(VI). EXAFS data showed that Cr-O and Cr-Cr distances in the precipitates equal to 1.98 and 3.01 A, respectively, consistent with the spinel-type structure as chromite.     

Description of integrated competency examination: tools to assess the chiropractic curriculum effectiveness and students' competency levels

Los Angeles College of Chiropractic (LACC) has developed a variety of methods to monitor the effectiveness of its competency based/problem-centered curriculum. The College introduced two Integrative Competency Examination courses (ICE I and ICE II) to assess the chiropractic program's effectiveness and students' competency levels. The ICE courses are pass/fail examinations that use a multistation, objective structured clinical examination (OSCE) format that involves standardized patients along with cognitive assessment of basic science information as methods of evaluation. ICE I requires students to perform psychomotor skills and interpret clinical data; ICE II requires students to perform at a higher level. They are directed to select, perform and interpret clinical data appropriately and correlate this data with relevant basic science information. Through these two levels of evaluation, the educational program, the individual courses and the competency level of each student are assessed. This paper describes the format, content and evaluation tools used in the ICE courses as well as the potential benefits of the courses.     

Sonolytic desorption of mercury from aluminum oxide: effects of pH, chloride, and organic matter

The effects of pH, Cl-, and humic acid (HA) on sonolytic desorption of Hg(II) from aluminum oxide were examined. Results showed that Hg(II) desorption was achieved by lowering the pH from 7.0 to 4.0. Ultrasound enhanced Hg(II) release at short times compared to both hydrodynamic mixing and that expected on the basis of the pH-dependent Hg(II) adsorption curve. However, prolonged sonication led to decreases in Hg(II) desorption due to occlusion by aluminum hydroxide precipitation induced by ultrasound. The presence of Cl- greatly improved Hg(II) desorption at pH 4.0 due to the formation of stable nonadsorbing HgCl2(0) complexes at low pH, reducing free Hg(II) ion in solution. However, Cl- did not affect Hg(ll) desorption at pH 8.0, where Hg(OH)2(0) is the dominant Hg species rather than HgCl2(0). Hg(ll) desorption from HA-laden Al2O3 was dominated by HA. The greater the desorption of HA, the greater the desorption of Hg(II). Ultrasound enhanced the initial Hg(II) release by facilitating HA desorption. However, decreases in Hg(II) desorption were observed over longer sonication times due to the sonochemically induced reassociation of desorbed HA back onto Al2O3. Information obtained in this study provides insight into understanding sonolytic release of Hg from Hg-contaminated particles and sediments.     

AC vs. DC electrophoretic deposition of hydroxyapatite on titanium

In this study, electrophoretic deposition (EPD) of hydroxyapatite (HA) powder on titanium plate was performed using butanol as solvent under direct current (DC) and alternating current (AC) fields. The zeta potential of the suspensions was measured to define their stability and the charge on the particles. Coating thickness was varied by adjusting the voltage and time of deposition. Surface morphology and cross section thickness were studied using scanning electron microscopy and image analysis software. Surface crack density was calculated from the micrographs. The results showed that the samples of similar thickness have higher grain density when coated using AC as compared to DC EPD. This facile but novel test proves the capability of AC-EPD to attain denser and uniform HA coatings from non-aqueous medium.     

Fast indexing and visualization of metric data sets usingslim-trees

Many recent database applications need to deal with similarity queries. For such applications, it is important to measure the similarity between two objects using the distance between them. Focusing on this problem, this paper proposes the slim-tree, a new dynamic tree for organizing metric data sets in pages of fixed size. The slim-tree uses the triangle inequality to prune the distance calculations that are needed to answer similarity queries over objects in metric spaces. The proposed insertion algorithm uses new policies to select the nodes where incoming objects are stored. When a node overflows, the slim-tree uses a minimal spanning tree to help with the splitting. The new insertion algorithm leads to a tree with high storage utilization and improved query performance. The slim-tree is a metric access method that tackles the problem of overlaps between nodes in metric spaces and that allows one to minimize the overlap. The proposed "fat-factor" is a way to quantify whether a given tree can be improved and also to compare two trees. We show how to use the fat-factor to achieve accurate estimates of the search performance and also how to improve the performance of a metric tree through the proposed "slim-down" algorithm. This paper also presents a new tool in the slim-tree's arsenal of resources, aimed at visualizing it. Visualization is a powerful tool for interactive data mining and for the visual tracking of the behavior of a tree under updates. Finally, we present a formula to estimate the number of disk accesses in range queries. Results from experiments with real and synthetic data sets show that the new slim-tree algorithms lead to performance improvements. These results show that the slim-tree outperforms the M-tree by up to 200% for range queries. For insertion and splitting, the minimal-spanning-tree-based algorithm achieves up to 40 times faster insertions. We observed improvements of up to 40% in range queries after applying the slim-down algorithm