The design of Flow Injection manifolds to give the best detection limits for methods involving on-line chemical derivatisation Part 2. The spectrophotometric determination of chloride

The optimisation of a flow injection manifold for the spectrophotometric determination of chloride is described. Factors contributing to the baseline noise due to refractive index and reagent absorption effects are removed by a combination of design features. Firstly, a double-line manifold is used; secondly, pulse-dampers and a packed bed reactor are incorporated into the flow lines and thirdly a delay coil is introduced to resolve the valve switching peaks from the determinand peaks. The appropriate conditions for obtaining the maximum sensitivity are found from an off-line experiment and the guidelines established on the basis of the well-stirred tank model for dispersion applied to the design of the operating parameters of flow rate ratio and volume injected. Good agreement between the predicted and experimentally determined values were obtained. The resulting manifold gave a linear calibration from the detection limit (4.5-8.0 ppb) to 2.00 ppm

Elimination of Double Peaks in the Iodimetric Flow Injection Visible Spectrophotometric Determination of Sulphite Using a Single-Channel Manifold

A flow injection method of determining sulphite with amperometric monitoring of iodine using a single-channel manifold in which iodine is formed in the reverse flow injection (rFI) manner and reacts with sulphite dispersing in the normal flow injection (nFI) manner has been adapted for use with visible spectrophotometry. The carrier stream consists of an alkaline solution containing iodate and an excess of iodide: injections of acid and then of acidified sulphite are made. The decrease in the iodine signal (measured at 352 nm) in the presence of sulphite is proportional to the sulphite concentration in the injectate. The alkalinity of the carrier stream was adjusted to reduce the signal widths and to prevent the appearance of double peaks. A rectilinear decrease in signal size (down to ca. 10% of the signal size in the absence of sulphite) was obtained in the range 1 x 10-s_7 x 10-4 M sulphite using a single-channel manifold consisting of 3 m of 0.8 mm bore transmission tubing with a flow-rate of 5 ml min-1 and an injection volume of 15 rd, when the carrier stream was 6.7 x 1 Q-6 Min iodate, 6.7 x 10-2 Min iodide and 3.5 x 1 Q-3 Min sodium hydroxide, and the sample solution was 0.1 M in hydrochloric acid

Shapes of Normal and Reverse Flow Injection Signals: On-Line Formation of Iodine from Iodate, Iodide, and Hydrogen Ion

Signal shapes for the on-line formation of iodine from iodate, iodide and hydrogen ion in a single-channel manifold using large-volume slug and large-volume time-based injections have been determined using visible spectrophotometry. These large injection volume studies were made first as a means of understanding the shapes of normal and reverse flow injection signals obtained at more conventional injection volumes (10--100 µI). The signal shapes at large injection volumes were determined for the six possible combinations of the reagents in the two solutions serving as carrier stream and injectate so that one solution contained two reagents and the other solution one or two reagents. Each combination of reagents represents two complementary systems in which the roles of each solution as carrier stream and injectate are reversed. At these large injection volumes each signal consisted of two independent peaks caused by dispersion at the front and rear boundaries of the injected bolus. The signals obtained for the time-based injections for complementary systems were identical in shape and height except that the front peak of one system was identical with the rear peak of its complementary system and vice versa. Clearly, at such large injection volumes the terms normal flow injection (nFI) and reverse flow injection (rFI) have no real meaning, the shape of each independent peak being determined by the composition and relative positions of the two solutions forming the boundary at which the peak is formed. For slug injections, similar shapes were observed but the peak heights were affected markedly by the greater dispersion at the rear boundary which travels further than the front boundary. This comparison of the signals obtained with slug and time-based injections, despite different flow-rates being used for the two modes of injection, clearly shows the effect of the unequal dispersion at the two boundaries in the slug injection method. Examination of the signals obtained with time-based injection, however, clearly indicates that the solution compositions, and their relative positions in the flow stream, also affect the shapes and relative heights of the front and rear peaks. The shapes of all these signals are illustrated. The effect of reducing the slug injection volume stepwise from 2 ml to 100 µI was studied for the 103-J- \u3c H+ and H+ \u3c 103-1- systems(\u3c denotes the direction of the boundary shape). This indicated that the shapes and heights of the single peaks observed in the rFI and nFI formation of iodine carried out at the more conventional lower injection volumes are determined by dispersion at the rear and front boundaries of the bolus, respectively. Hence, as the two peaks observed in a large-volume injection merged as the injection volume was decreased, the major peak predominated and became the observed signal. The use of a much smaller injection volume was necessary in rFI than in nFI in order to obtain a single peak

Shapes of Flow Injection Signals: Effect of Refractive Index on Spectrophotometric Signals Obtained for On-Line Formation of Bromine from Bromate, Bromide, and Hydrogen Ion in a Single-Channel Manifold Using Large-Volume Time-Based Injections

The shapes of the spectrophotometric signals obtained with a single-channel manifold for large-volume (4 ml) time-based injections for the six possible combinations of the reagents bromate, bromide and nitric acid in the injectate and carrier stream, by which bromine can be formed on-line, have been determined. The injectate and carrier stream were 5.25 x 10-4 M in bromate, 0.030 M in bromide and 1 M in nitric acid when these reagents were present. The signals consisted of two separate peaks caused by formation of bromine at the front and rear boundaries of the injected bolus. When both injectate and carrier stream were 1 M in nitric acid (i.e., for the reagent combination H+Br03- - H+Br-)the two peaks were of equal height, and the signal was. virtually the same whichever solution was used as the injectate. In reagent combinations where only one solution contained nitric acid the peaks were different in size, the smaller peak being that produced by the boundary in which the acidic solution was flowing behind the other solution. This difference in size between the front and rear peaks was shown to be caused by refractive index effects. When the refractive indices of the two solutions were matched either by increasing the potassium bromide concentration or by making the non-acidic solution 7% in sodium nitrate, the peaks became equal in size. When the potassium bromide concentration was increased there was an appreciable increase in peak size (about 4-fold): the changes in the amount of bromine formed must be due to kinetic or equilibrium effects. This increase in size did not occur when sodium nitrate was used to balance the refractive indices

Heterocyst placement strategies to maximize growth of cyanobacterial filaments

Under conditions of limited fixed-nitrogen, some filamentous cyanobacteria develop a regular pattern of heterocyst cells that fix nitrogen for the remaining vegetative cells. We examine three different heterocyst placement strategies by quantitatively modelling filament growth while varying both external fixed-nitrogen and leakage from the filament. We find that there is an optimum heterocyst frequency which maximizes the growth rate of the filament; the optimum frequency decreases as the external fixed-nitrogen concentration increases but increases as the leakage increases. In the presence of leakage, filaments implementing a local heterocyst placement strategy grow significantly faster than filaments implementing random heterocyst placement strategies. With no extracellular fixed-nitrogen, consistent with recent experimental studies of Anabaena sp. PCC 7120, the modelled heterocyst spacing distribution using our local heterocyst placement strategy is qualitatively similar to experimentally observed patterns. As external fixed-nitrogen is increased, the spacing distribution for our local placement strategy retains the same shape while the average spacing between heterocysts continuously increases.Comment: This is an author-created, un-copyedited version of an article accepted for publication in Physical Biology. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The definitive publisher-authenticated version will be available onlin

Elemental abundances and minimum mass of heavy elements in the envelope of HD 189733b

Oxygen (O) and carbon (C) have been inferred recently to be subsolar in abundance from spectra of the atmosphere of the transiting hot Jupiter HD 189733b. Yet, the mass and radius of the planet coupled with structure models indicate a strongly supersolar abundance of heavy elements in the interior of this object. Here we explore the discrepancy between the large amount of heavy elements suspected in the planet's interior and the paucity of volatiles measured in its atmosphere. We describe the formation sequence of the icy planetesimals formed beyond the snow line of the protoplanetary disk and calculate the composition of ices ultimately accreted in the envelope of HD 189733b on its migration pathway. This allows us to reproduce the observed volatile abundances by adjusting the mass of ices vaporized in the envelope. The predicted elemental mixing ratios should be 0.15--0.3 times solar in the envelope of HD 189733b if they are fitted to the recent O and C determinations. However, our fit to the minimum mass of heavy elements predicted by internal structure models gives elemental abundances that are 1.2--2.4 times oversolar in the envelope of HD189733b. We propose that the most likely cause of this discrepancy is irradiation from the central star leading to development of a radiative zone in the planet's outer envelope which would induce gravitational settling of elements. Hence, all strongly irradiated extrasolar planets should present subsolar abundances of volatiles. We finally predict that the abundances of nitrogen (N), sulfur (S) and phosphorus (P) are of $\sim$ $2.8 \times 10^{-5}$, $5.3 \times 10^{-6}$ and $1.8 \times 10^{-7}$ relative to H$_2$, respectively in the atmosphere of HD 189733b.Comment: Accepted for publication in Astronomy & Astrophysic

Making the user more efficient: Design for sustainable behaviour

User behaviour is a significant determinant of a product’s environmental impact; while engineering advances permit increased efficiency of product operation, the user’s decisions and habits ultimately have a major effect on the energy or other resources used by the product. There is thus a need to change users’ behaviour. A range of design techniques developed in diverse contexts suggest opportunities for engineers, designers and other stakeholders working in the field of sustainable innovation to affect users’ behaviour at the point of interaction with the product or system, in effect ‘making the user more efficient’. Approaches to changing users’ behaviour from a number of fields are reviewed and discussed, including: strategic design of affordances and behaviour-shaping constraints to control or affect energyor other resource-using interactions; the use of different kinds of feedback and persuasive technology techniques to encourage or guide users to reduce their environmental impact; and context-based systems which use feedback to adjust their behaviour to run at optimum efficiency and reduce the opportunity for user-affected inefficiency. Example implementations in the sustainable engineering and ecodesign field are suggested and discussed