Novel ionization reagent for the measurement of gas-phase ammonia and amines using a stand-alone atmospheric pressure gas chromatography (APGC) source.

RationaleContaminants present in ambient air or in sampling lines can interfere with the target analysis through overlapping peaks or causing a high background. This study presents a positive outcome from the unexpected presence of N-methyl-2-pyrrolidone, released from a PALL HEPA filter, in the analysis of atmospherically relevant gas-phase amines using chemical ionization mass spectrometry.MethodsGas-phase measurements were performed using a triple quadrupole mass spectrometer equipped with a modified atmospheric pressure gas chromatography (APGC) source which allows sampling of the headspace above pure amine standards. Gas-phase N-methyl-2-pyrrolidone (NMP) emitted from a PALL HEPA filter located in the inlet stream served as the ionizing agent.ResultsThis study demonstrates that some alkylamines efficiently form a [NMP + amine+H]+ cluster with NMP upon chemical ionization at atmospheric pressure. The extent of cluster formation depends largely on the proton affinity of the amine compared with that of NMP. Aromatic amines (aniline, pyridine) and diamines (putrescine) were shown not to form cluster ions with NMP.ConclusionsThe use of NMP as an ionizing agent with stand-alone APGC provided high sensitivity for ammonia and the smaller amines. The main advantages, in addition to sensitivity, are direct sampling into the APGC source and avoiding uptake on sampling lines which can be a significant problem with ammonia and amines

Turing Instability in a Boundary-fed System

The formation of localized structures in the chlorine dioxide-idodine-malonic acid (CDIMA) reaction-diffusion system is investigated numerically using a realistic model of this system. We analyze the one-dimensional patterns formed along the gradients imposed by boundary feeds, and study their linear stability to symmetry-breaking perturbations (Turing instability) in the plane transverse to these gradients. We establish that an often-invoked simple local linear analysis which neglects longitudinal diffusion is inappropriate for predicting the linear stability of these patterns. Using a fully nonuniform analysis, we investigate the structure of the patterns formed along the gradients and their stability to transverse Turing pattern formation as a function of the values of two control parameters: the malonic acid feed concentration and the size of the reactor in the dimension along the gradients. The results from this investigation are compared with existing experiments.Comment: 41 pages, 18 figures, to be published in Physical Review

Amplitude equations near pattern forming instabilities for strongly driven ferromagnets

A transversally driven isotropic ferromagnet being under the influence of a static external and an uniaxial internal anisotropy field is studied. We consider the dissipative Landau-Lifshitz equation as the fundamental equation of motion and treat it in $1+1$~dimensions. The stability of the spatially homogeneous magnetizations against inhomogeneous perturbations is analyzed. Subsequently the dynamics above threshold is described via amplitude equations and the dependence of their coefficients on the physical parameters of the system is determined explicitly. We find soft- and hard-mode instabilities, transitions between sub- and supercritical behaviour, various bifurcations of higher codimension, and present a series of explicit bifurcation diagrams. The analysis of the codimension-2 point where the soft- and hard-mode instabilities coincide leads to a system of two coupled Ginzburg-Landau equations.Comment: LATeX, 25 pages, submitted to Z.Phys.B figures available via [email protected] in /pub/publications/frank/zpb_95 (postscript, plain or gziped

Transition in incompressible boundary layers with two-dimensional excrescences

An experimental investigation of the transition process in boundary layers subjected to forward- or aft-facing two-dimensional step excrescences is described. The objective of the work was to characterize the variation of transition Reynolds numbers with measurable roughness and boundary layer parameters, with the specific goal of specifying new tolerance criteria for laminar flow airfoils, alongside a fundamental investigation of linear boundary layer stability mechanisms. Results from an ongoing program of increasing complexity on effects of pressure gradient on excrescence-induced transition are presented. Preliminary N-factor calculations are used to determine the effects of boundary layer stability and attempt to isolate the effect of the disturbance due to the excrescence

Transitions/relaxations in polyester adhesive/PET system

The correlations between the transitions and the dielectric relaxation processes of the oriented poly(ethylene terephthalate) (PET) pre-impregnated of the polyester thermoplastic adhesive have been investigated by differential scanning calorimetry (DSC) and dynamic dielectric spectroscopy (DDS). The thermoplastic polyester adhesive and the oriented PET films have been studied as reference samples. This study evidences that the adhesive chain segments is responsible for the physical structure evolution in the PET-oriented film. The transitions and dielectric relaxation modes’ evolutions in the glass transition region appear characteristic of the interphase between adhesive and PET film, which is discussed in terms of molecular mobility. The storage at room temperature of the adhesive tape involves the heterogeneity of the physical structure, characterized by glass transition dissociation. Thus, the correlation between the transitions and the dielectric relaxation processes evidences a segregation of the amorphous phases. Therefore, the physical structure and the properties of the material have been linked to the chemical characteristics

Phase Dynamics of Nearly Stationary Patterns in Activator-Inhibitor Systems

The slow dynamics of nearly stationary patterns in a FitzHugh-Nagumo model are studied using a phase dynamics approach. A Cross-Newell phase equation describing slow and weak modulations of periodic stationary solutions is derived. The derivation applies to the bistable, excitable, and the Turing unstable regimes. In the bistable case stability thresholds are obtained for the Eckhaus and the zigzag instabilities and for the transition to traveling waves. Neutral stability curves demonstrate the destabilization of stationary planar patterns at low wavenumbers to zigzag and traveling modes. Numerical solutions of the model system support the theoretical findings

The Effect of Acoustic Forcing on Instabilities and Breakdown in Swept-Wing Flow over a Backward-Facing Step

Instability interaction and breakdown were experimentally investigated in the flow over a swept backward-facing step. Acoustic forcing was used to excite the Tollmien-Schlichting (TS) instability and to acquire phase-locked results. The phase-averaged results illustrate the complex nature of the interaction between the TS and stationary cross flow instabilities. The weak stationary cross flow disturbance causes a distortion of the TS wavefront. The breakdown process is characterized by large positive and negative spikes in velocity. The positive spikes occur near the same time and location as the positive part of the TS wave. Higher-order spectral analysis was used to further investigate the nonlinear interactions between the TS instability and the traveling cross flow disturbances. The results reveal that a likely cause for the generation of the spikes corresponds to nonlinear interactions between the TS, traveling cross flow, and stationary cross flow disturbances. The spikes begin at low amplitudes of the unsteady and steady disturbances (2-4% U (sub e) (i.e. boundary layer edge velocity)) but can achieve very large amplitudes (20-30 percent U (sub e) (i.e. boundary layer edge velocity)) that initiate an early, though highly intermittent, breakdown to turbulence

Implementation of stability-based transition model by means of transport equations

A natural laminar-turbulent transition model compatible with Computation Fluid Dynamics is presented. This model accounts for longitudinal transition mechanisms (i.e. Tollmien-Schlichting induced transition) thanks to systematic stability computation on similar boundary profiles from Mach zero to four both on adiabatic and isothermal wall. The model embeds as well the so-called “C1-criterion” for transverse transition mechanisms (i.e. cross-flow waves induced transition). The transition model is written under transport equations formalism and has been implemented in the solver elsA (ONERA-Airbus-Safran property). Validations are performed on three dimensional configurations and comparisons are shown against a database method for natural transition modeling and experiments

Sucrose diffusion in aqueous solution.

The diffusion of sugar in aqueous solution is important both in nature and in technological applications, yet measurements of diffusion coefficients at low water content are scarce. We report directly measured sucrose diffusion coefficients in aqueous solution. Our technique utilises a Raman isotope tracer method to monitor the diffusion of non-deuterated and deuterated sucrose across a boundary between the two aqueous solutions. At a water activity of 0.4 (equivalent to 90 wt% sucrose) at room temperature, the diffusion coefficient of sucrose was determined to be approximately four orders of magnitude smaller than that of water in the same material. Using literature viscosity data, we show that, although inappropriate for the prediction of water diffusion, the Stokes-Einstein equation works well for predicting sucrose diffusion under the conditions studied. As well as providing information of importance to the fundamental understanding of diffusion in binary solutions, these data have technological, pharmaceutical and medical implications, for example in cryopreservation. Moreover, in the atmosphere, slow organic diffusion may have important implications for aerosol growth, chemistry and evaporation, where processes may be limited by the inability of a molecule to diffuse between the bulk and the surface of a particle