Simultaneous Determination of Key Osmoregulants in Halophytes Using HPLC–ELSD

Osmoregulants are the substances produced by plants that assist in tolerating environmental stresses. Three commonly analysed osomoregulants include mannitol, betaine and proline. A simple, sensitive and rapid HPLC–ELSD method has been developed for the simultaneous analysis of these common osmoregulants in plant extracts. Osmoregulants were extracted using 80 % ethanol and separated on an NH₂ column using 0.1 % formic acid and acetonitrile as the mobile phase. Retention time repeatability was 0.85, 1.50, and 0.93 % for mannitol, betaine and proline, respectively. The limit of detection (μmol) was 1.43 × 10^?4, 7.81 × 10^?5 and 1.08 × 10^?4 for mannitol, betaine and proline, respectively. The developed method was applied to three different plant extracts, Stylosanthes guianensis, Atriplex cinerea and Rhagodia baccata. A second method using a C18 column with 0.1 % heptafluorobutyric acid and acetonitrile as the mobile phase proved to be a useful complementary method for verifying tentative peak identifications.     

Simultaneous quantitative analysis of polyphenolic compounds in human plasma by liquid chromatography tandem mass spectrometry

A diet rich in polyphenolic compounds has recognized health benefits, and as such is routinely monitored as part of dietary intervention studies. A method for the simultaneous determination of 36 phenolic compounds, including phenolic acids and flavonoids, using liquid chromatography and tandem mass spectrometry is described here. The target analytes were quantified based on their specific mass spectral fragments using a selected reaction monitoring approach. A C18 column with embedded aromatic functionality ensured separation of all phenolic compounds studied which included several pairs of isomers. Sample preparation involved the use of β‐glucuronidase to release the phenolic compounds from their conjugated forms. The intra‐day and inter‐day precision and accuracy was less than 7% for all phenolic compounds studied. Recoveries, where plasma was spiked with three different concentrations of the analytes, ranged from 95–115%. The limits of detection and quantification were 0.23–3.89 and 1.15–7.79 nM, respectively. The method was successfully applied to real samples and the range reported for each phenolic compound, with the exception of hydroferulic acid, nordihydroguaiaretic acid, methylgallate, and m‐coumaric acid, was at least an order of magnitude higher than the limit of quantification for the method.     

An accurate and efficient method for the incompressible Navier–Stokes equations using the projection method as a preconditioner

The projection method is a widely used fractional-step algorithm for solving the incompressible Navier–Stokes equations. Despite numerous improvements to the methodology, however, imposing physical boundary conditions with projection-based fluid solvers remains difficult, and obtaining high-order accuracy may not be possible for some choices of boundary conditions. In this work, we present an unsplit, linearly-implicit discretization of the incompressible Navier–Stokes equations on a staggered grid along with an efficient solution method for the resulting system of linear equations. Since our scheme is not a fractional-step algorithm, it is straightforward to specify general physical boundary conditions accurately; however, this capability comes at the price of having to solve the time-dependent incompressible Stokes equations at each timestep. To solve this linear system efficiently, we employ a Krylov subspace method preconditioned by the projection method. In our implementation, the subdomain solvers required by the projection preconditioner employ the conjugate gradient method with geometric multigrid preconditioning. The accuracy of the scheme is demonstrated for several problems, including forced and unforced analytic test cases and lid-driven cavity flows. These tests consider a variety of physical boundary conditions with Reynolds numbers ranging from 1 to 30000. The effectiveness of the projection preconditioner is compared to an alternative preconditioning strategy based on an approximation to the Schur complement for the time-dependent incompressible Stokes operator. The projection method is found to be a more efficient preconditioner in most cases considered in the present work.     

Ion dynamics and sublattice melting in the superionic conductor PbF2

The F¹⁹ relaxation rates in PbF₂ exhibit anamolous changes as the temperature is increased into the superionic phase. These changes confirm the concept of a continuous melting of the fluorine sublattice and show that the fluorine motion in the superionic phase is highly correlated.     

Development of some hypersonic benchmark flows using CFD and experiment

Abstract. This paper presents a set of test cases in high speed aerodynamics that describe our perceived relationship between experiment and computation. Computational fluid dynamics, with sensible interpretation, can guide experimental design, so that wind tunnel studies can focus better on fundamental ‘benchmark’ studies. Likewise experimental data may be used as feed back to evaluate codes and to improve their physical modelling. Here we present several test cases, developed in our laboratory, that we regard as basic ‘building blocks’ for high speed aerodynamics. These include: design for boundary-layer/pressure-gradient interaction; cavity flows; shock-wave/boundary-layer interactions; techniques for a graduated and controlled study of three-dimensional separated flows. Received 10 October 2001/ Accepted 19 November 2002 Published online 4 February 2003 Correspondence to: R. Hillier (r.hillier@ic.ac.uk) An abridged version of this paper was presented at the 23rd Int. Symposium on Shock Waves at Fort Worth, Texas, from July 22 to 27, 2001     

Modeling the anisotropic finite-deformation viscoelastic behavior of soft fiber-reinforced composites

This paper presents constitutive models for the anisotropic, finite-deformation viscoelastic behavior of soft fiber-reinforced composites. An essential assumption of the models is that both the fiber reinforcements and matrix can exhibit distinct time-dependent behavior. As such, the constitutive formulation attributes a different viscous stretch measure and free energy density to the matrix and fiber phases. Separate flow rules are specified for the matrix and the individual fiber families. The flow rules for the fiber families then are combined to give an anisotropic flow rule for the fiber phase. This is in contrast to many current inelastic models for soft fiber-reinforced composites which specify evolution equations directly at the composite level. The approach presented here allows key model parameters of the composite to be related to the properties of the matrix and fiber constituents and to the fiber arrangement. An efficient algorithm is developed for the implementation of the constitutive models in a finite-element framework, and examples are presented examining the effects of the viscoelastic behavior of the matrix and fiber phases on the time-dependent response of the composite.     

Rotational and vibrational temperature measurements using CARS in a hypervelocity shock layer flow and comparisons with CFD calculations

Broadband single pulse coherent anti-Stokes Raman scattering (CARS) experiments employing a folded-box phase-matching geometry in a pulsed hypervelocity blunt body flow are presented. Rovibrational spectra of molecular nitrogen, produced in the freestream and within the shock layer at moderately high enthalpy (8.4 MJ/kg), are examined. Difficulties peculiar to the application of a single pulse optical technique to a high enthalpy pulsed flow facility are discussed and measurements of flow temperatures are presented. Theoretically calculated values for temperatures based upon algorithms used to determine freestream and shock layer conditions agree well with experimental measurements using the CARS technique. The measurements indicate that thermal non-equilibrium conditions exist within the freestream, and that near thermal equilibrium exists at the point of measurement within the shock layer. The comparison between the experiment and theory in the shock layer is improved by using the measured freestream temperatures as input to the shock layer computations.     

Simultaneous determination of antioxidants, preservatives and sweeteners permitted as additives in food by mixed micellar electrokinetic chromatography.

A micellar electrokinetic chromatography method was developed to simultaneously analyse commonly used food additives. The additive mixture, comprising propyl gallate, octyl gallate, dodecyl gallate, butylated hydroxyanisole, butylated hydroxytoluene, tertiary butylhydroquinone, p-hydroxybenzoic acid methyl ester, p-hydroxybenzoic acid ethyl ester, benzoic acid, sorbic acid, saccharin, aspartame and acesulfame-K, was not resolved using single surfactant micellar systems consisting of sodium dodecyl sulfate (SDS), sodium cholate (SC) or sodium deoxycholate (SDC). The separation of these additives using mixed micellar systems, involving SDS/SC, SDS/SDC and SC/SDC, was investigated. Organic solvents were added to the mixed micellar phases to optimise the separation. The mixture was successfully separated using a 20 mM borate buffer with 35 mM SC, 15 mM SDS and 10% methanol added at pH 9.3. Additives in cola beverages and low-joule jam were investigated and quantified using this method.