Commuting Polynomial Operations of Distributive Lattices

We describe which pairs of distributive lattice polynomial operations commute.     

Stable isotopic analysis of pyrogenic organic matter in soils by liquid chromatography–isotope‐ratio mass spectrometry of benzene polycarboxylic acids

Pyrogenic organic matter (PyOM), the incomplete combustion product of organic materials, is considered stable in soils and represents a potentially important terrestrial sink for atmospheric carbon dioxide. One well‐established method of measuring PyOM in the environment is as benzene polycarboxylic acids (BPCAs), a compound‐specific method, which allows both qualitative and quantitative estimation of PyOM. Until now, stable isotope measurement of PyOM carbon involved measurement of the trimethylsilyl (TMS) or methyl (Me) polycarboxylic acid derivatives by gas chromatography–combustion–isotope ratio mass spectrometry (GC‐C‐IRMS). However, BPCA derivatives can contain as much as 150% derivative carbon, necessitating post‐analysis correction for the accurate measurement of δ¹³ C values, leading to increased measurement error. Here, we describe a method for δ¹³ C isotope ratio measurement and quantification of BPCAs from soil‐derived PyOM, based on ion‐exchange chromatography (IEC‐IRMS). The reproducibility of the δ¹³ C measurement of individual BPCAs by IEC‐IRMS was better than 0.35‰ (1σ). The δ¹³ C‐BPCA analysis of PyOM in soils, including at natural and artificially enriched ¹³ C‐abundance, produced accurate and precise δ¹³ C measurements. Analysis of samples that differed in δ¹³ C by as much as 900‰ revealed carryover of <1‰ between samples. The weighted sum of individual δ¹³ C‐BPCA measurements was correlated with previous isotopic measurements of whole PyOM, providing complementary information for bulk isotopic measurements. We discuss potential applications of δ¹³ C‐BPCA measurements, including the study of turnover rates of PyOM in soils and the partitioning of PyOM sources based on photosynthetic pathways. Copyright © 2011 John Wiley & Sons, Ltd.     

Meeting Report: SSRL School on Synchrotron X-ray Scattering Techniques in Materials and Environmental Sciences: Theory and Application

Modern synchrotron-based X-ray scattering (SR-XRS) techniques offer the ability to probe nano- and atomic-scale structures, interfaces, and order/disorder relationships that govern the properties of advanced technological and environmental materials. Important materials studied at the Stanford Synchrotron Radiation Laboratory (SSRL) include thin films and interfaces, nanoparticles, amorphous materials, solutions, polymers, and bacteriogenic minerals. Good planning and a working knowledge of beam lines and techniques are required to successfully conduct SR-XRS measurements. This second annual School at SSRL on Synchrotron X-ray Scattering Techniques in Materials and Environmental Sciences, held at the Stanford Linear Accelerator Center (SLAC) on May 15–17, 2007, provided a practical users' guide to planning and conducting scattering measurements at SSRL beam lines, with an emphasis on information that cannot be found in textbooks. More than 45 researchers, mostly graduate students and postdocs, participated in this crosscutting workshop. Attendees represented a variety of fields including material sciences, applied physics, environmental sciences, and chemistry.     

Trace Determination of Domoic Acid in Sea Water and Phytoplankton by High-Performance Liquid Chromatography of the Fluorenylmethoxycarbonyl (FMOC) Derivative

Abstract

A method is presented for the trace determination of domoic acid, a neurotoxic amino acid responsible for cases of Amnesic Shellfish Poisoning resulting from the consumption of contaminated shellfish. The method involves pre-column derivatization with 9-fluorenylmethylchloroformate to form the FMOC derivative followed by reversed-phase HPLC with fluorescence detection. The detection limit for domoic acid in seawater and aqueous extracts is 15pg/mL (50 pM) using gradient elution, a 20μL injection volume, and a 2.1mm I.D. microbore column. Use of dihydrokainic acid as an internal standard improved quantitation. The method was applied to the detection of domoic acid in seawater, in phytoplankton cultures (Nitzschia pungens forma multiseries), and in natural mixed phytoplankton assemblages in estuarine waters.     

Solid-state 91Zr NMR spectroscopy studies of zirconocene olefin polymerization catalyst precursors

(91)Zr (I = 5/2) solid-state NMR (SSNMR) spectra of the zirconocene compounds, Cp(2)ZrCl(2), Cp*(2)ZrCl(2) (1), Cp(2)ZrBr(2) (2), (Me(3)SiC(5)H(4))(2)ZrBr(2) (3), O(Me(2)SiC(5)H(4))(2)ZrBr(2) (4), (1,3-C(5)H(3))(SiMe(2)OSiMe(2))(2)(1,3-C(5)H(3))ZrBr(2) (5), Ind(2)ZrCl(2) (6), Cp(2)ZrMeCl (7), Cp(2)ZrMe(2) (8), and [Cp(2)ZrMe][MeB(C(6)F(5))(3)] (9) have been acquired. Static (91)Zr SSNMR spectra have been acquired for all complexes at magnetic fields of 9.4 and 21.1 T. Cp(2)ZrCl(2) and complexes 1 to 5 possess relatively narrow central transition powder patterns which allows for magic-angle spinning (MAS) (91)Zr solid-state NMR spectra to be acquired at a moderate field strength of 9.4 T. Complexes 6 to 9 possess ultrawideline central transition SSNMR spectra necessitating piece-wise acquisition techniques. From the static and MAS (91)Zr SSNMR spectra, it is possible to measure (91)Zr electric field gradient (EFG) and chemical shift (CS) tensor parameters, as well as the Euler angles which describe their relative orientation. Basis sets and methods for the accurate quantum chemical calculation of (91)Zr EFG and CS tensors have been identified. The origin of the observed EFG and CS tensor parameters are further investigated by visualization of the EFG and CS tensor orientations within the molecular frames. Correlations between the observed and calculated NMR tensor parameters and molecular symmetry and structure are made. All of these observations suggest that (91)Zr SSNMR spectroscopy can be utilized to probe the molecular structure of a variety of homogeneous and heterogeneous olefin polymerization catalysts.     

Modeling and Simulation of Multiple Cracking in Textile Reinforced Concrete Tension Specimen using Fracture Mechanics Approaches

This paper concerns with the finite element simulation of textile reinforced concrete (TRC) behavior under tension loading by using discrete cracking concept and fracture mechanics approaches. 3D Finite-Element models are formulated on the meso-scale by simulating all the heterogeneous structural components, the matrix, the fibers, and the fracture mechanisms in both fiber-matrix interface, and the discrete cracks of the matrix. The presented numerical simulation in this study allows for better understanding of the stress distribution and the interaction between all damage mechanisms and the corresponding energy dissipations. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)