Compositional analysis of American southwestern ceramics by neutron activation analysis

Mercury, a known neurotoxin, has been implicated in the etiology and pathogenesis of such disease states as Alzheimer's and Parkinson's diseases. There is concern that the exposure to mercury vapor released from dental amalgam restorations is a potential health hazard. Measurement of mercury concentrations in blood or urine may be useful in diagnosis of mercury poisoning and in assessing the extent of exposure. This study describes the optimization of pre-neutron activation analysis procedures such as sampling, selection of irradiation and counting vials and acid digestion in order to minimize mercury loss via volatilization and/or permeation through containers. Therefore, the determination of mercury can be complicated by these potential losses. In the optimized procedure 20 mL of urine was spiked with three different concentrations of mercury, digested with concentrated nitric acid, and placed in polypropylene vials for irradiation and counting. Analysis was performed by subtracting the Se-75 photopeak contribution to the 279 keV Hg-203 photopeak and applying the method of standard additions. Urinary mercury concentrations in normal human subjects were determined to be of the order of 10 ng/mL.     

Propagating belief functions in qualitative Markov trees

This article is concerned with the computational aspects of combining evidence within the theory of belief functions. It shows that by taking advantage of logical or categorical relations among the questions we consider, we can sometimes avoid the computational complexity associated with brute-force application of Dempster's rule.The mathematical setting for this article is the lattice of partitions of a fixed overall frame of discernment. Different questions are represented by different partitions of this frame, and the categorical relations among these questions are represented by relations of qualitative conditional independence or dependence among the partitions. Qualitative conditional independence is a categorical rather than a probabilistic concept, but it is analogous to conditional independence for random variables.We show that efficient implementation of Dempster's rule is possible if the questions or partitions for which we have evidence are arranged in a qualitative Markov tree—a tree in which separations indicate relations of qualitative conditional independence. In this case, Dempster's rule can be implemented by propagating belief functions through the tree.     

Raman measurements of the superionic conductor KAg4I5

Raman measurements of the superionic conductor KAg₄I₅ are reported between 77K and 296K and compared to similar data of RbAg₄I₅. The mode frequencies for the two materials are very similar and a mode at 22.7 cm^?1 abruptly and reversibly disappears at the transition temperature, T_c=137 K, as is observed in RbAg₄I₅, at 121 K.     

Symmetry of the top of the valence band in MoS2

It is shown that the previously reported EPR parameters for various acceptors in MoS₂ are characteristic of p_z symmetry for the top of the valence band and not of d_z² symmetry as was previously believed.     

Infrared Line Strengths and Pressure Broadening Coefficients in the ν12 Vibrational Band of Hydrazine Measured by Infrared Tunable Diode Laser Spectroscopy

Infrared line positions, linestrengths, and pressure-broadening coefficients are required to determine absolute trace gas concentrations from high-resolution absorption spectra. We have measured these values for the infrared absorption lines in the ν₁₂ band (antisymmetric wag) of hydrazine between 965.4 and 965.7 cm⁻¹ using a high-resolution tunable diode laser system with 0.0006 cm⁻¹ spectral resolution and an 18-m path length multiple pass absorption cell. A continuous flow of hydrazine diluted to 100-500 parts per million in nitrogen at pressures between 0.1 and 50 Torr was used to prevent decomposition in the sampling cell. The total integrated linestrength from 965.477 to 965.663 cm⁻¹ is (2.20±0.14)×10⁻²⁰ cm² molecule⁻¹ cm⁻¹. The strongest line in this region at 965.5557 cm⁻¹ has a strength of 2.8×10⁻²¹ cm² molecule⁻¹ cm⁻¹. The only isolated line in this region, at 965.4905 cm⁻¹, has a broadening coefficient by nitrogen of 0.11±0.01 cm⁻¹ atm⁻¹ at 295 K. These results are compared to the qualitative high resolution spectra determined by other researchers using FTIR spectroscopy, and have been used to construct a HITRAN-format line list that can be used both to spectroscopically distinguish hydrazine from other components and to determine its concentration in a complex gas phase mixture.     

Micro-HPLC/TLC/FTIR

Identification problems often encountered in high performance liquid chromatography (HPLC)/Fourier transform infrared spectrometry (FTIR) can be circumvented through the use of a thin-layer chromatographic (TLC) plate as deposition and infra-red sampling medium. The combination of complementary separation modes is shown to demonstrate increased resolution of the components of complex mixtures. In this particular work, the effluent from a reversed-phase microcolumn is continuously deposited on a TLC plate with alumina stationary phase. The solute remains on the plate as a continuous record of the HPLC separation, which is then analyzed by diffuse reflectance FTIR. When the HPLC separation is inadequate for full separation of the components, the immobilized HPLC chromatogram serves as a starting point for subsequent TLC separation. A number of FTIR reconstructed chromatograms and spectra which are derived from the TLC plate aid in the interpretation.