Evaluation of VIDAS Salmonella (SLM) easy Salmonella method for the detection of Salmonella in a variety of foods: collaborative study

The VIDAS Salmonella (SLM) Easy Salmonella method is a specific enzyme-linked fluorescent immunoassay performed in the automated VIDAS instrument. The VIDAS Easy Salmonella method is a simple 2-step enrichment procedure, using pre-enrichment followed by selective enrichment in a newly formulated broth, SX2 broth. This new method was compared in a multilaboratory collaborative study to the U.S. Food and Drug Administration's Bacteriological Analytical Manual, Chapter 5 method for five food matrixes (liquid egg, vanilla ice cream, spinach, raw shrimp, and peanut butter) and the U.S. Department of Agriculture's Microbiology Laboratory Guidebook 4.04 method for deli turkey. Each food type was artificially contaminated with Salmonella at three inoculation levels. A total of 15 laboratories representing government, academia, and industry, throughout the United States, participated. In this study, 1583 samples were analyzed, of which 792 were paired replicates and 791 were unpaired replicates. Of the 792 paired replicates, 285 were positive by both the VIDAS and reference methods. Of the 791 unpaired replicates, 341 were positive by the VIDAS method and 325 were positive by the cultural reference method. A Chi-square analysis of each of the six food types was performed at the three inoculation levels tested. For all foods evaluated, the VIDAS Easy SLM method demonstrated results comparable to those of the reference methods for the detection of Salmonella.     

Palladium(II) complexes of readily functionalized bidentate 2-pyridyl-1,2,3-triazole "click" ligands: a synthetic, structural, spectroscopic, and computational study

The Cu(I)-catalyzed 1,3-cycloaddition of organic azides with terminal alkynes, the CuAAC "click" reaction is currently receiving considerable attention as a mild, modular method for the generation of functionalized ligand scaffolds. Herein we show that mild one-pot "click" methods can be used to readily and rapidly synthesize a family of functionalized bidentate 2-pyridyl-1,2,3-triazole ligands, containing electrochemically, photochemically, and biologically active functional groups in good to excellent yields (47-94%). The new ligands have been fully characterized by elemental analysis, HR-ESI-MS, IR, (1)H and (13)C NMR and in three cases by X-ray crystallography. Furthermore we have demonstrated that this family of functionalized "click" ligands readily form bis-bidentate Pd(II) complexes. Solution studies, X-ray crystallography, and density functional theory (DFT) calculations indicate that the Pd(II) complexes formed with the 2-(1-R-1H-1,2,3-triazol-4-yl)pyridine series of ligands are more stable than those formed with the [4-R-1H-1,2,3-triazol-1-yl)methyl]pyridine "click" ligands.     

Investigation of the thermal decomposition and flammability of PEEK and its carbon and glass-fibre composites

Conventional thermally durable materials such as metals are being replaced with heat resistant engineering polymers and their composites in applications where burn-through resistance and structural integrity after exposure to fire are required. Poly aryl ether ether ketone (PEEK) is one such engineering polymer. Little work has been published with regards to the flammability of PEEK and its filled composites. The current study aims to assess the flammability and fire behaviour of PEEK and its composites using thermogravimetric analysis, pyrolysis combustion flow calorimetry, limiting oxygen index, a vertical flame resistance test, and fire (cone) calorimetry.     

A comparison of theory and experiment for high density,high temperature germanium spectra

This paper compares results from theoretical predictions to experimental emission data from germanium obtained on the HELEN laser at AWE. The aim of the comparison was to test opacity predictions of highly stripped, medium Z elements, a regime which has received relatively little attention due the difficulty of achieving conditions near LTE at high temperatures. The data show emission from the 2p–3d and 2s–3p transitions from a layer of germanium buried in plastic and heated by the HELEN CPA beam. Predictions of spectra constructed using data generated by the grasp2K atomic structure code coupled to Saha–Boltzman population dynamics were compared to the experimental emission. It was found that the grasp2K calculations match the position of all the features in the experiment well, but non-LTE effects in the experiment make it unreasonable to expect a match to line strengths. Two opacity codes, CASSANDRA and DAVROS, were benchmarked against the grasp2K simulations. It was shown that the major difference in the two opacity codes is due to different approaches to calculating total ion energies. For this reason the DAVROS line positions are significantly more accurate than those of CASSANDRA.     

Centrifugal waves on a flexible chain

A chain is attached at one end to a rigid rotating hub. Centrifugal force induces a nonuniform tension in the chain, which therefore supports transverse vibrations. Solution of the appropriate wave equation shows that the natural frequencies depend only on the rotational speed and the length of the chain relative to the hub diameter. Experiments demonstrating the existence of these vibrations show that an initial impulsive disturbance reoccurs as an “echo” in which all the eigenmodes reinforce each other. This echo occurs even though the eigenfrequencies are not harmonically related. The explanation of the echo is found in the (almost) linear relation between eigenfrequency and mode number.     

Principal Bundles and the Dixmier Douady Class

A systematic consideration of the problem of the reduction and “lifting” of the structure group of a principal bundle is made and a variety of techniques in each case are explored and related to one another. We apply these to the study of the Dixmier-Douady class in various contexts including string structures, bundles and other examples motivated by considerations from quantum field theory. Received: 26 February 1997 / Accepted: 5 August 1997     

Geochemical profile of Chautauqua Lake sediments

Neutron activation analysis techniques were used to study sediments from Chautauqua Lake. The concentrations of Eu, Na, Mn, K, Br, As, Ga, La, Hf, Cs, Tb, Sc, Fe, Ta, Sb were determined and compared with similar data for the bedrock and soils surrounding the lake. The lake sediments are found to be enriched in Na, Mn, Br, As, Hf, Tb, Ta, and Sb relative to the surrounding source beds. High pairwise linear correlation coefficients (R～0.9) were found between the concentrations of antimony, cesium, and scandium. For many elements a relationship was indicated between their concentrations and the clay fraction of the sediment, possibly due to the higher cation exchange potential of the clay minerals.     

Azo compounds for free radical crosslinking of polysiloxane stationary phases

There has been much effort spent in recent years developing the technology for free radical crosslinking of polysiloxane polymers to prepare capillary columns coated with thermally stable and nonextractable stationary phases. Organic peroxides have been used extensively as the free radical initiators for the in situ polymerization of the stationary phases. However, these peroxides adversely affect the phase polarity and column activity. Seven azo compounds were studied for crosslinking efficiency. Azo compounds can be used as free radical initiators to prepare nonextractable stationary phases without the adverse effects caused by peroxides.     

Pressure‐Dependent Polymorphism and Band‐Gap Tuning of Methylammonium Lead Iodide Perovskite

We report the pressure‐induced crystallographic transitions and optical behavior of MAPbI₃ (MA=methylammonium) using in situ synchrotron X‐ray diffraction and laser‐excited photoluminescence spectroscopy, supported by density functional theory (DFT) calculations using the hybrid functional B3PW91 with spin‐orbit coupling. The tetragonal polymorph determined at ambient pressure transforms to a ReO₃‐type cubic phase at 0.3 GPa. Upon continuous compression to 2.7 GPa this cubic polymorph converts into a putative orthorhombic structure. Beyond 4.7 GPa it separates into crystalline and amorphous fractions. During decompression, this phase‐mixed material undergoes distinct restoration pathways depending on the peak pressure. In situ pressure photoluminescence investigation suggests a reduction in band gap with increasing pressure up to ≈0.3 GPa and then an increase in band gap up to a pressure of 2.7 GPa, in excellent agreement with our DFT calculation prediction.