Comparison of chlorine and chloramine in the release of mercury from dental amalgam

The purpose of this project was to compare the ability of chlorine (HOCl/OCl⁻) and monochloramine (NH₂Cl) to mobilize mercury from dental amalgam. Two types of amalgam were used in this investigation: laboratory-prepared amalgam and samples obtained from dental-unit wastewater. For disinfectant exposure simulations, 0.5 g of either the laboratory-generated or clinically obtained amalgam waste was added to 250 mL amber bottles. The amalgam samples were agitated by end-over-end rotation at 30 rpm in the presence of 1 mg/L chlorine, 10 mg/L chlorine, 1 mg/L monochloramine, 10 mg/L monochloramine, or deionized water for intervals of 0 h, 2 h, 4 h, 8 h, and 24 h for the clinically obtained amalgam waste samples and 4 h and 24 h for the laboratory-prepared samples. Chlorine and monochloramine concentrations were measured with a spectrophotometer. Samples were filtered through a 0.45 µm membrane filter and analyzed for mercury with USEPA standard method 245.7. When the two sample types were combined, the mean mercury level in the 1 mg/L chlorine group was 0.020 mg/L (n = 25, SD = 0.008). The 10 mg/L chlorine group had a mean mercury concentration of 0.59 mg/L (n = 25, SD = 1.06). The 1 mg/L chloramine group had a mean mercury level of 0.023 mg/L (n = 25, SD = 0.010). The 10 mg/L chloramine group had a mean mercury level of 0.024 mg/L (n = 25, SD = 0.011). Independent samples t-tests showed that there was a significant difference between the natural log mercury measurements of 10 mg/L chlorine compared to those of 1 mg/L and 10 mg/L chloramine. Changing from chlorine to chloramine disinfection at water treatment plants would not be expected to produce substantial increases in dissolved mercury levels in dental-unit wastewater.     

Determination of Energy Levels in AgBr Emulsion Crystals from Optical Measurements

The width of the forbidden energy gap and the position of the top of the valence band cannot be determined as precisely for AgBr at room temperature as for many ionic crystals. Some choices for these parameters, which are necessarily arbitrary, are given here to provide good agreement with the variety of optical and photographic measurements made with small AgBr crystals. Changes of the energy levels with temperature, iodide incorporation, and the presence of surfaces were measured. Surface states located at lattice ions are too shallow to act as electron traps or to be detected in our optical absorption experiments. Luminescence of pure AgBr was investigated at 77°K. The luminescence centre is at an electron trap which is 0.75 eV below the bottom of the conduction band. This centre, which is stable when formed by exposures at 77°K, is the same as the unstable latent image centre at room temperature investigated by Webb and is thought to be a single electron trapped at two silver ions. The stable latent image centre at 300°K has an electron trap depth of 1.20 eV. which is precisely the Fermi level in bulk silver.     

Asymptotics of evanescence

Abstract

The wave from an isotropic point source in two and three dimensions is separated into its homogeneous (H) and evanescent (E) parts, with respect to a distinguished direction z, and the far field r θ evaluated asymptotically as a function of polar angle θ. Only in the ‘forward needle’ θ = 0 (three dimensions) and the transverse directions θ = π/2 (two and three dimensions) is the E wave of comparable strength to the H wave. Uniform asymptotic approximations (in terms of Bessel functions and Fresnel integrals) accurately interpolate between these directions of significant evanescence and all other angles (where the amplitude of E relative to H decays as 1/r¹/²). The forward needle in three dimensions is analogous to glory scattering.     

Validation of mid-infrared spectrometry in milk for predicting body energy status in Holstein-Friesian cows

Cow energy balance is known to be associated with cow health and fertility; therefore, routine access to data on energy balance can be useful in both management and breeding decisions to improve cow performance. The objective of this study was to determine if individual cow milk mid-infrared spectra (MIR) could be useful to predict cow energy balance across contrasting production systems. Direct energy balance was calculated as the differential between energy intake and energy output in milk and maintenance (maintenance was predicted using body weight). Body energy content was calculated from (change in) body weight and body condition score. Following editing, 2,992 morning, 2,742 midday, and 2,989 evening milk MIR records from 564 lactations on 337 Scottish cows, managed in a confinement system on 1 of 2 diets, were available. An additional 844 morning and 820 evening milk spectral records from 338 lactations on 244 Irish cows offered a predominantly grazed grass diet were also available. Equations were developed to predict body energy status using the milk spectral data and milk yield as predictor variables. Several different approaches were used to test the robustness of the equations calibrated in one data set and validated in another. The analyses clearly showed that the variation in the validation data set must be represented in the calibration data set. The accuracy (i.e., square root of the coefficient of multiple determinations) of predicting, from MIR, direct energy balance, body energy content, and energy intake was 0.47 to 0.69, 0.51 to 0.56, and 0.76 to 0.80, respectively. This highlights the ability of milk MIR to predict body energy balance, energy content, and energy intake with reasonable accuracy. Very high accuracy, however, was not expected, given the likely random errors in the calculation of these energy status traits using field data.     

X-ray diffraction from intact tau aggregates in human brain tissue

We describe an instrument to record x-ray diffraction patterns from diseased regions of human brain tissue by combining an in-line visible light fluorescence microscope with an x-ray diffraction microprobe. We use thiazine red fluorescence to specifically label and detect the filamentous tau protein pathology associated with Pick's disease, as several labs have done previously. We demonstrate that thiazine red-enhanced regions within the tissue show periodic structure in x-ray diffraction that is not observed in healthy tissue. One observed periodicity (4.2 ?) is characteristic of cross-beta sheet structure, consistent with previous results from powder diffraction studies performed on purified, dried tau protein.     

Racial/ethnic differences in the criterion-related validity of cognitive ability tests: A qualitative and quantitative review.

The correlation between cognitive ability test scores and performance was separately meta-analyzed for Asian, Black, Hispanic, and White racial/ethnic subgroups. Compared to the average White observed correlation ( = .33, N = 903,779), average correlations were lower for Black samples ( = .24, N = 112,194) and Hispanic samples ( = .30, N = 51,205) and approximately equal for Asian samples ( = .33, N = 80,705). Despite some moderating effects (e.g., type of performance criterion, decade of data collection, job complexity), validity favored White over Black and Hispanic test takers in almost all conditions that included a sizable number of studies. Black–White validity comparisons were possible both across and within the 3 broad domains that use cognitive ability tests for high-stakes selection and placement: civilian employment, educational admissions, and the military. The trend of lower Black validity was repeated in each domain; however, average Black–White validity differences were largest in military studies and smallest in educational and employment studies. Further investigation of the reasons for these validity differences is warranted. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Enhanced Electron Mobility Due to Dopant‐Defect Pairing in Conductive ZnMgO

The increase of the band gap in Zn_1‐xMg_xO alloys with added Mg facilitates tunable control of the conduction band alignment and the Fermi‐level position in oxide‐heterostructures. However, the maximal conductivity achievable by doping decreases considerably at higher Mg compositions, which limits practical application as a wide‐gap transparent conductive oxide. In this work, first‐principles calculations and material synthesis and characterization are combined to show that the leading cause of the conductivity decrease is the increased formation of acceptor‐like compensating intrinsic defects, such as zinc vacancies (V_Zn), which reduce the free electron concentration and decrease the mobility through ionized impurity scattering. Following the expectation that non‐equilibrium deposition techniques should create a more random distribution of oppositely charged dopants and defects compared to the thermodynamic limit, the paring between dopant Ga_Zn and intrinsic defects V_Zn is studied as a means to reduce the ionized impurity scattering. Indeed, the post‐deposition annealing of Ga‐doped Zn_0.7Mg_0.3O films grown by pulsed laser deposition increases the mobility by 50% resulting in a conductivity as high as σ = 475 S cm^‐1.