Structural and lattice-energy analyses of the different low-temperature phases of ferrocene Fe(C5H5)2: Relation between the molecular packings

X-Ray analysis of the metastable triclinic phase of ferrocene has been carried out at 130 K, from a single crystal cooled through the transition temperature (164 K). The molecular packing is close to a face centred one; however the numerous reflections breaking this symmetry give evidence for a P1 or P1̄ superstructure which appears to be disordered. Calculations of lattice energy performed at 130 K and 15 K show that the triclinic phase of ferrocene has two possible molecular packings, quite energetically similar, of face-centred or P1̄ symmetry. Thus, when the triclinic phase is obtained by cooling a crystal from room temperature, its structure is constituted by a mixture of both packings whose ratio depends on the thermal history. On the other hand, the molecular coordinates and the configuration of ferrocene (D_5h) in the stable ordered orthorhombic phase have been determined by minimizing the lattice energy. The mechanism of the order-disorder phase transition at 250 K (orthorhombic monoclinic), as also the existence below 164 K of another ordered packing, the triclinic one, are discussed in terms of ring libration.     

Dynamic and convective results for a developing laminar unsteady flow

Dynamic and thermal results for developing laminar pulsed flows in a duct are presented. They have been investigated by means of a finite difference model. This flow is described in terms of an unsteady pulsed flow superimposed on a steady incompressible one with the following main assumptions: a sinusoidal modulation for the pulsation and a uniform wall temperature. Results emphasize the importance of this entry region, where four simultaneous developments occur: steady—dynamic and thermal—and unsteady—dynamic and thermal.     

New fluorinated thermoplastic elastomers. I. The synthesis and thermal characteristics of α,ω‐dihydrosilane hybrid fluorinated polysiloxane precursors

The synthesis of new α,ω‐dihydrosilane hybrid fluorinated polysiloxanes is described via the polycondensation between a diallyl perfluorinated compound and tetramethyldisiloxane. Control over the size of the oligomers is possible when the reaction is performed in two steps. The length of the polysiloxane chains influences the glass‐transition temperature and the thermal stability of the fluorinated oligomers: the higher the length is, the higher the glass‐transition temperature and the thermal stability are. The synthesized compounds have been characterized with ¹H, ¹⁹F, and ²⁹Si NMR spectroscopy. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4485–4492, 2002     

Characterization and comparison of Cm(III) and Eu(III) complexed with 2,6-di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine using EXAFS, TRFLS, and quantum-chemical methods

The complexation of Cm(III) and Eu(III) with 2,6-di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine (n-C3H7-BTP) in nonaqueous organic solution is studied with extended X-ray absorption spectroscopy. Bond lengths are the same in both complexes. Quantum-chemical calculations performed at different levels support this finding. On the other hand, the Cm.(n-C3H7-BTP)3 complex is formed at much lower ligand-to-metal concentration ratio than the Eu.(n-C3H7-BTP)3 complex, as shown by time-resolved laser-induced fluorescence spectroscopy. This is in good agreement with n-C3H7-BTP's high selectivity for trivalent actinides over lanthanides in liquid-liquid extraction.     

Comparison between Gibbs free energy minimization and mass action law for a multitemperature plasma with application to nitrogen

This paper gives all the necessary physical equations to determine the composition and the thermodynamic properties in a multitemperature plasma utilizing two different methods: the first method is based on Gibbs free energy minimization and the second is based on the resolution of the mass action law. The lowering terms of the ionization potential and thermodynamic properties are given for a multitemperature plasma using the Debye-Hückel approximation. Numerical application is made to a nitrogen plasma.     

Determination of persistent organohalogenated pollutants in human hair reference material (BCR 397): an interlaboratory study

A human powdered hair material (BCR 397) was tested for its content in persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and polybrominated diphenyl ethers (PBDEs). Using different methods, three laboratories (two from Canada and one from Belgium) analysed a powdered hair sample to evaluate some methodologies and to obtain consensus values for selected POPs. Measured values for all PCB congeners and p,p-DDE were within a relative standard deviation (RSD) of 15%. These first results contribute to the accuracy and precision for POPs quantification in hair and render test results more comparable among different laboratories.     

Evaluation of nanopores as candidates for electronic analyte detection

In an effort to increase throughput and decrease the cost of electrophoretic separation of DNA and proteins, various groups are developing highly parallel, miniaturized separation devices based on capillaries etched into silicon, glass or plastic substrates. To date, these miniaturized devices have relied on optical detectors, thus placing a lower limit on instrument size, and complicating the incorporation of an entire DNA analyzer instrument on a chip. To address this limitation, we are evaluating nanopores as candidate Coulter counters for purely electronic detection of analytes in miniaturized electrophoresis and similar separation devices. To establish feasibility of this detection scheme, we have investigated the detection sensitivity of a nanopore sensor through experiments with the alpha-hemolysin (alpha-HL) ion channel, and through a Monte Carlo (MC) model of polymer capture rate with a cylindrical nanopore under an applied voltage. Experimental and model results are extrapolated to predict the capture rate of synthetic pores operating at higher voltages than presently achievable with protein pores.