Characterization of an Electron Ionization Source Trap Operating in the Presence of a Magnetic Field Through Computer Simulation

We explore the feasibility of conducting electron ionization (EI) in a radio-frequency (rf) ion source trap for mass spectrometry applications. Electrons are radially injected into a compact linear ion trap in the presence of a magnetic field used essentially to lengthen the path of the electrons in the trap. The device can either be used as a stand-alone mass spectrometer or can be coupled to a mass analyzer. The applied parallel magnetic field and the oscillating rf electric field produced by the trap give rise to a set of coupled Mathieu equations of motion. Via numerical simulations, electron trajectories are studied under varying intensities of the magnetic field in order to determine the conditions that enhance ion production. Likewise, the dynamic behavior of the ions are investigated in the proposed EI source trap and the fast Fourier transform FFT formalism is used to obtain the frequency spectrum from the numerical simulations to study the motional frequencies of the ions which include combinations of the low-frequency secular and the high-frequency micromotion with magnetron and cyclotron frequencies. The dependence of these motional frequencies on the trapping conditions is examined and particularly, the limits of applying a radial magnetic field to the EI ion trap are characterized.

Precipitation sequence during ageing in β1 phase of Cu–Al–Ni shape memory alloy

The shape memory alloys based on the ternary system Cu–Al–Ni are able to produce a memory effect at high temperatures. However, if the material undergoes an accidental overheating, a transformation process leads to progressive loss of its characteristics. In this study, the effect of ageing on the metastable β₁ (austenite) phase of a Cu–13.3 %Al–4 %Ni shape memory alloy was investigated. In addition, the effects of heating rate between 450 and 580 °C on the structural transformations of austenite after cooling to room temperature were studied. Observation by transmission electron microscopy of the structure that has undergone an isothermal ageing shows that the precipitation process depends on the maximum ageing temperature. Furthermore, calorimetric analysis shows that precipitates dissolution is possible when rapid heating between 450 and 580 °C. This behaviour is observed on the cooling diagram which shows a martensitic transformation.     

Characterization of the first mixed-valent liquid-crystalline materials. Synthesis and structural properties of new binuclear ruthenium carboxylates

Abstract

The syntheses and structural properties of new binuclear ruthenium (II, III) complexes with long chain carboxylates, of general formula Ru₂(RCO₂)₄X (R = C₈H₁₇, C₁₁H₂₃ and X = C1, RCOO), are reported. The thermodynamic behaviour of these compounds is strongly influenced by the nature of the counterion X. The chloro complexes (X = CI) are not mesomorphic whereas the carboxylato species (X = RCOO) are shown to exhibit a thermotropic columnar mesophase, thus providing the first example of a mixed-valent liquid-crystalline material.     

Application of Solid-Phase Microextraction for the Determination of Organonitrogen Pesticides in Aqueous Samples by Gas Chromatography with Nitrogen-Phosphorus Detector

A method based on solid-phase microextraction and gas chromatography nitrogen-phosphorus detector for the determination of common organonitrogen pesticides (ONPs) in aqueous samples was described. Three kinds of commercially available coated fused-silica fibres were compared: 100 µm PDMS, 85 µm PA, and 65 µm CW-DVB; 65 µm CW-DVB was the most sensitive fibre coating for the analytes' determination. The extraction time, the stirring, the content of salt, and the content of organic solvents were found to have a significant influence on extraction efficiency. The optimised conditions were 65 µm CW-DVB fibre, 40 min extraction time, with rapid stirring and concentration of NaCl was fixed at 0.25 g/mL. The linear range was 0.1-100 µg/L for most of the compounds. The limits of detection (LODs) ranged from 0.02 mg/L (for trifluralin, simazine, terbuthylazine, cyanazine, and pendimethalin) to 0.08 µg/L (for terbutryn) and RSD % of repeatability were for most of the compounds below 10%. Thus the maximum level set by the European Union for pesticides and drinking waters can be verified. The recovery of spiked water samples was compared and validated with the liquid-liquid extraction one. Environmental water samples were analysed and trifluraline was detected.     

Original ring contraction of triazine derivatives to 1,2,4-thiadiazoles

The oxidation of triazines 1 is described here. While treatment with m-CPBA or DMDO led to formation of a mixture of compounds, [TBA-OX] oxidation led exclusively to thiadiazoles 2 by ring contraction reaction.     

Computing numerically the Green’s function of the half-plane Helmholtz operator with impedance boundary conditions

In this article we compute numerically the Green’s function of the half-plane Helmholtz operator with impedance boundary conditions. A compactly perturbed half-plane Helmholtz problem is used to motivate this calculation, by treating it through integral equation techniques. These require the knowledge of the calculated Green’s function, and lead to a boundary element discretization. The Green’s function is computed using the inverse Fourier operator of its spectral transform, applying an inverse FFT for the regular part, and removing the singularities analytically. Finally, some numerical results for the Green’s function and for a benchmark resonance problem are shown.     

New organic-inorganic nanohybrids via ring opening polymerization of (di)lactones initiated by functionalized polyhedral oligomeric silsesquioxane

The synthesis of new organic-inorganic materials were investigated. Poly(ε-caprolactone) and poly(l, l-lactide) covalently end-capped by a polyhedral oligomeric silsesquioxane (POSS) moiety, leading to new nanohybrid materials, were successfully prepared by coordination-insertion ring opening polymerization (ROP) of ε-caprolactone (ε-CL) and l,l-lactide (l,l-LA) respectively. The reaction was initiated from the primary amine available on aminopropylheptakis(isobutyl)POSS nanoparticles and catalyzed by tin(II) 2-ethylhexanoate (tin octoate, Sn(oct)₂). The covalent grafting of the polyester chains onto the POSS “nanocages” was assessed by selective fractionation experiment, Fourier transform infrared spectroscopy (FTIR) and further confirmed by proton nuclear magnetic resonance (¹H NMR). The polymerization proved to be well controlled as attested by the quite narrow polydispersity indices as determined by size exclusion chromatography (SEC). Furthermore, well-defined semi-crystalline poly(ε-caprolactone)-b-polylactide block copolymer carrying such POSS nanoparticle at one end was successfully synthesized attesting for the very efficient control over the polymerization reaction.     

Interfacial interaction in EVA‐carbon nanotube and EVA‐clay nanocomposites

Proper filler‐matrix compatibility is a key factor in view of obtaining nanocomposites with well‐dispersed nanofillers displaying enhanced properties. In this respect, polymer‐filler interaction can be improved by a proper combination of matrix and nanofiller polarities. This is explored for matrices ranging from nonpolar high density poly(ethylene) to ethylene‐vinyl acetate (EVA) copolymers with varying vinyl acetate contents, in combination with several types of organoclay or carbon nanotubes. A novel in situ characterization methodology using modulated temperature differential scanning calorimetry is presented to evaluate the matrix‐filler interaction. During quasi‐isothermal crystallization of the matrix, an “excess” contribution is observed in the recorded heat capacity signal because of reversible melting and crystallization. Its magnitude considerably decreases upon addition of nanofiller in case of strong interfacial interaction, whereas the influence is moderate in case of a less interacting matrix‐filler combination. It is suggested that the “excess heat capacity” can be used to quantify the segmental mobility of polymer chains in the vicinity of the nanofiller. Hence it provides valuable information on the strength of interaction, governed by the physical and chemical nature of matrix and filler. Heating experiments subsequent to quasi‐isothermal crystallization point at a certain degree of molecular ordering, responsible for crystal nucleation in EVA copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1291–1302, 2007     

AFM study of the SIMS beam induced roughness in monocrystalline silicon in presence of initial surface or bulk defects of nanometric size

In this paper, the SIMS beam induced roughness (BIR) in monocrystalline Si in presence of initial surface or bulk defects of nanometric size is studied. We follow the development of the BIR by monitoring the increase of Si²⁺ and SiO₂⁺ signals during SIMS sputtering. The topography of the crater bottoms is measured at different steps of the evolution of the roughness using an atomic force microscope (AFM). We show that in presence of nanometric sized defects on the surface or in the bulk, the BIR develops far more rapidly than usual. It appears as soon as the crater reaches the defects and, as reported on Si free from any treatment, the same morphology evidencing waves perpendicular to the sputtering beam develops rapidly. This study of the behaviour of the BIR in presence of voluntarily introduced defects allows us to better understand the basic physical phenomena involved in its apparition.