NMR studies of the configuration of the isomeric 2,3-dimethyloxetanes

The ¹H and ¹³C NMR spectra of cis- and trans-2,3-dimethyloxetane have been re-examined and the published NMR assignments shown to be in error.     

A coupled non-linear hyperbolic-sobolev system

Summary A boundary-initial value problem for a quasilinear hyperbolic system in one space variable is coupled to a boundary-initial value problem for a quasilinear equation of Sobolev type in two space variables of the form Mu_t(x, t)+L(t) u (x, t)=f(x, t, u(x, t)) where M and L(t) are second order elliptic spacial operators. The coupling occurs through one of the boundary conditions for the hyperbolic system and the source term in the equation of Sobolev type. Such a coupling can arise in the consideration of oil flowing in a fissured medium and out of that medium via a pipe. Barenblatt, Zheltov, and Kochina[2] have modeled flow in a fissured medium via a special case of the above equation. A local existence and uniqueness theorem is demonstrated. The proof involves the method of characteristics, some applications of results of R. Showalter and the contraction mapping theorem. Entrata in Redazione il 28 luglio 1976.     

X-ray photoelectron spectroscopy study of disordering in Gd2(Ti1-xZrx)2O7 pyrochlores

The dramatic increases in ionic conductivity in Gd2(Ti1-xZrx)2O7 solid solution are related to disordering on the cation and anion lattices. Disordering in Gd2(Ti1-xZrx)2O7 was characterized using x-ray photoelectron spectroscopy (XPS). As Zr substitutes for Ti in Gd2Ti2O7 to form Gd2(Ti1-xZrx)2O7 (0.25 < x < or =0.75), the corresponding O 1s XPS spectrum merges into a single symmetric peak. This confirms that the cation antisite disorder occurs simultaneously with anion disorder. Furthermore, the O 1s XPS spectrum of Gd2Zr2O7 experimentally suggests the formation of a split vacancy.     

Prototyping disposable electrophoresis microchips with electrochemical detection using rapid marker masking and laminar flow etching

Two novel methods are described for the fabrication of components for microchip capillary electrophoresis with electrochemical detection (microchip CEEC) on glass substrates. First, rapid marker masking is introduced as a completely nonphotolithographic method of patterning and fabricating integrated thin-film metal electrodes onto a glass substrate. The process involves applying the pattern directly onto the metal layer with a permanent marker that masks the ensuing chemical etch. The method is characterized, and the performance of the resulting electrode is evaluated using catecholamines. The response compares well with photolithographically defined electrodes and exhibits detection limits of 648 nM and 1.02 microM for dopamine and catechol, respectively. Second, laminar flow etching is introduced as a partially nonphotolithographic method of replicating channel networks onto glass substrates. The replication process involves applying a poly(dimethylsiloxane) (PDMS) mold of the channel network onto a slide coated with a sacrificial metal layer and then pulling solutions of metal etchants through the channels to transfer the pattern onto the sacrificial layer. The method is tested, and prototype channel networks are shown. These methods serve to overcome the time and cost involved in fabricating glass-based microchips, thereby making the goal of a disposable high performance lab-on-a-chip more attainable.     

Formation of halide reactant ions and effects of excess reagent chemical on the ionization of TNT in ion mobility spectrometry

The efficiency of chloride reactant ion formation, when chlorinated hydrocarbon reagent chemicals were added to the ionization region of an ion mobility spectrometer, corresponded to the electron attachment rate constant of the chemical. The chemicals investigated here included chloromethane, dichlormethane, trichloromethane, tetrachloromethane and chlorobenzene, with tetrachloromethane producing the greatest amount of chloride reactant ions for the amount of chemical added. Reagent chemicals with smaller electron attachment rate constants required the addition of more chemical to reach functional reactant ion levels. The excess neutral reagent molecules clustered to the chloride reactant ions and reduced the effectiveness of abstracting a proton from 2,4,6-trinitrotoluene (TNT). The effect of clustering was different for each chemical. Tetrachloromethane, which had the least exothermic clustering reaction, had the most effective production of the (TNT-H)(-) product ion per mole of reagent chemical. Bromide and iodide ions were also investigated as potential reactant ions. Bromide was found to effectively produce the proton abstracted (TNT-H)(-) ion. Iodide, however, was not a strong enough base to form (TNT-H)(-) from TNT. There was no apparent transfer of an electron to TNT by chloride, bromide or iodide.     

Nanoscale manipulation of pyrochlore: new nanocomposite ionic conductors

The ionic conductivity of isometric pyrochlore, ideally A2B2O (7), is extremely sensitive to disordering of A- and B-site cations and oxygen anion vacancies. We report the first use of ion beam irradiation-induced disordering in Gd 2Ti 2O (7) to produce a strain-free, buried, disordered defect-fluorite layer approximately 12 nm thick within an ordered pyrochlore matrix. This approach provides a new means of creating nanoscale, mixed ionic-electronic conductors in pyrochlore ceramics, such as those required for solid-state electrochemical cells.     

Desorption electrospray ionization–mass spectrometric analysis of low vapor pressure chemical particulates collected from a surface

The collection of a low vapor pressure chemical simulant triethyl phosphate sorbed onto silica gel (TEP/SG) from a surface with subsequent analysis of the TEP/SG particulates using desorption electrospray ionization–mass spectrometry (DESI–MS) is described. Collection of TEP/SG particulates on a surface was accomplished using a sticky screen sampler composed of a stainless steel screen coated with partially polymerized polydimethylsiloxane (PDMS). DESI–MS analysis of TEP/SG particulates containing different percentages of TEP sorbed onto silica gel enabled the generation of response curves for the TEP ions m/z 155 and m/z 127. Using the response curves the calculation of the mass of TEP in a 25 wt% sample of TEP/SG was calculated, results show that the calculated mass of TEP was 14% different from the actual mass of TEP in the sample using the m/z 127 TEP ion response curve. Detection limits for the TEP vapor and TEP/SG particulates were calculated to be 4 μg and 6 particles, respectively.     

Simulation of multiphase flows in porous media

The ability to numerically simulate single phase and multiphase flow of fluids in porous media is extremely important in developing an understanding of the complex phenomena governing the flow. The flow is complicated by the presence of heterogeneities in the reservoir and by phenomena such as diffusion, dispersion, and viscous fingering. These effects must be modeled by terms in coupled systems of nonlinear partial differential equations which form the basis of the simulator. The simulator must be able to handle both single and multiphase flows and the transition regimes between the two. A discussion of some of the aspects of modeling dispersion and viscous fingering is presented along with directions for future work.The partial differential equation models are convection-dominated and contain important local effects. An operator-splitting technique is used to address these different effects accurately. Convection is treated by time stepping along the characteristics of the associated pure convection problem, and diffusion is modeled via a Galerkin method for single phase flow and a Petrov-Galerkin technique for multiphase regimes. ELLAM (Eulerian-Lagrangian Localized Adjoint Methods) are discussed to effectively treat the advection-dominated processes. Accurate approximations of the fluid velocities needed in the Eulerian-Lagrangian time-stepping procedure are obtained by mixed finite element methods. Adaptive local grid refinement techniques are then indicated to resolve important local phenomena around wells and large heterogeneities or to resolve the moving internal boundary layers which often govern the mass transfer between phases.