Validation of SeaWiFS-derived chlorophyll for the Rio de la Plata Estuary and adjacent waters

The South Atlantic Ocean near the Río de la Plata Estuary is a highly dynamic region that encompasses four different water bodies: the Río de la Plata, the continental shelf and the Brazil and Malvinas currents. Bio-optical measurements obtained during 6–11 November 1999 provided the initial field data for validating Sea viewing Wide Field of view Sensor (SeaWiFS)-derived chlorophyll imagery for this region. The turbid waters of the Río de la Plata Estuary showed the highest variability and complexity in water optical properties, while the offshore waters of the Brazil Current had the lowest. In most cases, the estimates of chlorophyll using the SeaWiFS algorithm were higher than in situ measured values.     

Modelling the VO2 kinetic response to heavy intensity exercise in children

The purpose of this study was to apply a series of mathematical models in order to investigate the nature of the kinetic response to heavy intensity exercise with children and identify a suitable model with which to estimate parameters of the response. Sixty two children (35 male, 27 female aged 10-15 years) completed four transitions from baseline pedalling to 40% of the difference between their previously determined anaerobic threshold and peak VO2 on an electronically braked cycle ergometer. Initially three models were fitted to the averaged response profiles following the end of phase 1. and their residuals compared; 1, a single exponential with a delay term; 2, an exponential and linear term with independent delays; and 3, a double exponential with independent delays. Up to 95% of the response profiles were better fitted by either model 2 or 3 (p < 0.05), and model 3 was a statistically better fit (p < 0.05) than model 2 in 77% of cases. Residual inspection confirmed the superior fit by model 3. A fourth model which consisted of a single exponential with a delay term was fitted within the phase 2 fitting window. Estimated parameters (A1 and tau1), using model 4 were not significantly different from model 3, and model 4 was identified as the model of choice due to the wide confidence intervals in tau2 and A2 using model 3. It was concluded that the nature of the response to heavy intensity exercise in children is similar to that previously reported with adults and that the response should be modelled accordingly.     

Examination of ionic liquids and their interaction with molecules, when used as stationary phases in gas chromatography.

Stable room-temperature ionic liquids (RTILs) have been used as novel reaction solvents. They can solubilize complex polar molecules such as cyclodextrins and glycopeptides. Their wetting ability and viscosity allow them to be coated onto fused silica capillaries. Thus, 1-butyl-3-methylimidazolium hexafluorophosphate and the analogous chloride salt can be used as stationary phases for gas chromatography (GC). Using inverse GC, one can examine the nature of these ionic liquids via their interactions with a variety of compounds. The Rohrschneider-McReynolds constants were determined for both ionic liquids and a popular commercial polysiloxane stationary phase. Ionic liquid stationary phases seem to have a dual nature. They appear to act as a low-polarity stationary phase to nonpolar compounds. However, molecules with strong proton donor groups, in particular, are tenaciously retained. The nature of the anion can have a significant effect on both the solubilizing ability and the selectivity of ionic liquid stationary phases. It appears that the unusual properties of ionic liquids could make them beneficial in many areas of separation science.     

Sintering mechanisms in strontium doped lanthanum chromite

The sintering behavior of (La_0.7Sr_0.3)_xCrO₃ (0.95 x 1.05) is investigated to compare liquid phase sintering phenomena occuring in stoichiometric and non-stoichiometric compositions. Shrinkage analysis revealed marked contrast between the densification characteristics of the A-site enriched (x > 1.00) and A-site depleted (x < 1.00) materials. A-site depleted samples typically exhibited a single liquid phase sintering event at 1250 °C attributed to the melting of an exsoluted SrCrO₄ phase. A-site enriched samples indicated two rapid shrinkage events due to the melting of SrCrO₄, and a Sr_2.67(CrO₄)₂ phase with a melting temperature of 1450 °C. Sr_2.67(CrO₄)₂ was shown to evolve from a decomposition reaction between SrCrO₄ and La₂CrO₆, detected together in A-site enriched samples from 800–1000 °C. Maximum densities (93% theoretical density) were achieved for (La_0.7Sr_0.3)_xCrO₃ x = 1.00 after sintering at 1700 °C for two hours.     

Specification and verification of reactive system behaviour: The Railroad Crossing example

In this paper we present an approach to the specification and verification of reactive systems. The approach uses Timed Statecharts and Real Time Logic for the specification of temporal behaviour, and theorem proving techniques for the verification of safety and utility properties. Formal verification is achieved through the automation of semi-formal (rigorous) proofs using a theorem prover (Proofpower HOL). To illustrate the approach, we use the Railroad Crossing Problem, which has been proposed, along with a set of criteria for assessment, as a benchmark for the comparison of real-time formalisms. We conclude with our assessment of the approach against the proposed criteria.     

Electrical conductivity,self-diffusion,and volume expansion of alkali halides at the melting point

In an earlier paper, Heisenberg's uncertainty principle was invoked at the melting point T _m of crystalline solids to provide fundamental justification for Lindemann's melting law and to compute diffusion coefficients of several alkali halides. The uncertainty principle defines breakdown of Debye zone boundary (ZB) phonons as valid collective excitations when phonon energies and line widths due to anharmonicity become comparable at T _m. Upon breakdown, random, high-frequency single-particle motion or partial decoupling of crystal ions sets in. Lifetimes of these single-particle ZB motions are determined from the minimum-uncertainty product inequality by assuming that it becomes an equality at T _m for ZB phonons. The present paper addresses improved formulation of that work and extended application to ionic electrical conductivities of 18 molten alkali halides at T _m. It is shown that use of the Debye model produces an approximate lower bound to the mean free time, not the unconstrained direct estimate previouslu implied. This feature is generally reflected in results for ionic conductivities and alkali halide diffusion coefficients for which comparison experimental data were found. However, in spite of this lower-bound formulation and the simple nature of the computation, the results compare favorably with experiment. A model of random single-particle harmonic motion superimposed on the lower-frequency collective motion is proposed to account for volume expansion accompanying the partial decoupling for hard-sphere ions. Experimental comparisons for 15 alkali halides show the decoupling volume change to account largely for the total volume change of melting (in the hard-sphere approximation), yielding a closer agreement with experiment than recent calculations aimed explicitly at the total volume change.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Thermal expansion properties of 6061 Al alloy reinforced with SiC particles or short fibers

Thermal expansion measurements are reported for 6061 Al alloy and drawn composite materials reinforced with SiC particles or aligned short fibers. Samples with volume fractions of 5 and 20% SiC were measured in the drawing direction. The measurements were obtained from repeated heating and cooling cycles between room temperature and 500°C. Cumulative plastic strains were measured for the repeated thermal cycles, in association with the observation that lower expansivities generally occurred on cooling as compared with heating. Model calculations for particulate and an aligned fiber are presented for the combined elastic-plastic deformation properties of the Al/SiC composite systems. Lower expansivities and greater plastic strains are accounted for in the fiber-reinforced material.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

The dissolution and passivation of pure iron and the effect of phosphate and chromate corrosion inhibitors

The dissolution characteristics of pure iron undergoing an active-passive transition have been studied using impedance techniques, in carbonate-bicarbonate solutions at 70°C. The impedance spectra have been shown to consist of three overlapping semicircles, from which two time-constants for incremental passivation can be identified. The potential-dependence of these time-constants is related to stress corrosion cracking phenomena. The electrochemical behaviour of two stress corrosion cracking inhibitors have also been examined.