Determination of site-specific carbon isotope ratios at natural abundance by carbon-13 nuclear magnetic resonance spectroscopy.

Site-specific natural isotope fractionation of hydrogen studied by deuterium NMR (SNIF-NMR) spectroscopy is a powerful source of information on hydrogen pathways occurring in biosyntheses in natural conditions. The potential of the carbon counterpart of this method has been investigated and compared. Three typical molecular species, ethanol, acetic acid, and vanillin, have been considered. Taking into account the requirements of quantitative 13C NMR, appropriate experimental procedures have been defined and the repeatability and reproducibility of the isotope ratio determinations have been checked in different conditions. It is shown that the carbon version of the SNIF-NMR method is capable of detecting small differences in the carbon-13 content of the ethyl fragment of ethanols from different botanical or synthetic origins. These results are in agreement with mass spectrometry determinations of the overall carbon isotope ratios. Deviations with respect to a statistical distribution of 13C have been detected in the case of acetic acid and vanillin. However, since the method is very sensitive to several kinds of systematic error, only a relative significance can be attached at present to the internal parameters directly accessible. Isotope dilution experiments have also been carried out in order to check the consistency of the results. In the present state of experimental accuracy, the 13C NMR method is of more limited potential than 2H SNIF-NMR spectroscopy. However it may provide complementary information. Moreover it is particularly efficient for detecting and quantifying adulterations that aim to mimic the overall carbon-13 content of a natural compound by adding a selectivity enriched species to a less expensive substrate from a different origin.     

Multivariable control strategy based on bifurcation analysis of an industrial gas-phase polymerization reactor

In an industrial gas-phase polyethylene reactor, the safe operating range of temperature is rather narrow. Even within this temperature range, temperature excursions must be avoided because they can result in low catalyst productivity and significant changes in product properties. If the manipulated variable for temperature control saturates (i.e., the cooling water valve position is completely open), then the reactor operates without a feedback temperature controller, leading to oscillatory behavior and limit cycles. In this work, it has been demonstrated that the saturation in the manipulated variable and the complex non-linear dynamic behavior are removed when auxiliary manipulated variables, obtained by bifurcation analysis, are used in a multivariable control strategy for the reactor temperature control. Two control structures are proposed and compared considering their impact in the reactor production and polymer melt index. In the first control structure, the designed PID controller for the reactor temperature is considered and a switching strategy with a PI controller for the auxiliary manipulated variables is included. In the second control structure, the designed PID controller for the reactor temperature is also used, however, a MPC controller for the auxiliary manipulated variables is considered. The results suggest that the use of gain-scheduling strategy in the PID temperature controller with a MPC controller for the auxiliary manipulated variables avoids the saturation of the manipulated variable and, hence, the undesired non-linear dynamic behavior, reducing the production loss and improving the product quality.     

Valve stiction estimation using global optimisation

Valve stiction is the most frequent cause of loop oscillations. Thus, detecting and quantifying this valve problem is essential to ensuring plant profitability. In this work, a novel one-stage procedure to estimate stiction parameters is proposed using a two-parameter stiction model. The optimisation problem is computed using a global optimisation algorithm. These two propositions make the stiction computation more efficient and computationally faster than the currently available method. The applicability of the proposed approach is illustrated using a large number of simulated and industrial valves. Moreover, to isolate the impact of each proposition, the novel method is compared with the currently available technique, which is based on a two-stage scheme. The results show that the global optimisation algorithm is more efficient than the direct search and genetic algorithms, as previously proposed by Jelali (2008). The two-stage procedure provides a better estimate of the apparent stiction, whereas the one-stage procedure provides a better slipjump value.     

Concentration Measurement by Proton NMR Using the ERETIC Method

The ERETIC method (Electronic REference To access In vivo Concentrations) provides a reference signal, synthesized by an electronic device, which can be used for the determination of absolute concentrations. The results presented here demonstrate the accuracy and precision of the method in the case of (1)H high resolution NMR. Five tubes were filled with D(2)O solutions of trimethylamine hydrochloride (TMA) 3.84 mM and sodium lactate at concentrations ranging from 5.25 to 54.11 mM. Results obtained with the ERETIC method were compared to those obtained by using TMA as an internal reference. The standard deviations were the same for the two methods and always lower than 1% of the mean. The accuracy (difference between true value and measured value) was slightly better for the ERETIC method than for the internal reference. No significant variation was observed when the experiments were performed over 56 h. Measurements were repeated once a month during three months. As the values obtained showed a standard deviation of only 3%, we can conclude that the ERETIC method has a good stability and only requires monthly calibration. Furthermore, it must be noted that nothing is added to the sample and that the reference signal frequency can be freely chosen to fall within a transparent region of the spectrum.     

Determination of substrate and product concentrations in lactic acid bacterial fermentations by proton NMR using the ERETIC method

A 1H NMR method is described for the determination of the concentration of a chemically diverse group of metabolites over a wide concentration range in fermentation medium. The method employs the use of the ERETIC signal, which produces a pseudo-FID acquired with the FID derived from the sample components. It is shown that this signal, once calibrated against an external standard solution, can be used to determine accurately the concentration of all components present in the medium. The method is rapid, reliable, and applicable to a wide range of biological fluids. Problems such as the invisibility of certain components in the spectrum are overcome by a simple regulation of the pH.     

Plant Chemical Defense Induced by a Seed-Eating Pollinator Mutualist

Plant-seed parasite pollination mutualisms involve a specific pollinator whose larvae develop by consuming a fraction of the host plant seeds. These mutualisms are stable only if the plant can control seed destruction by the larvae. Here, we studied the chemical response of the European globeflower Trollius europaeus to infestation by an increasing number of Chiastocheta fly larvae. We used liquid chromatographic analysis to compare the content of phenolic compounds in unparasitized and parasitized fruits collected in two natural populations of the French Alps, and mass spectrometry and nuclear magnetic resonance to elucidate the structure of adonivernith, a C-glycosyl-flavone. This compound is present in many of the organs of T. europaeus, but not found in other Trollius species. Furthermore, it is overproduced in the carpel walls of parasitized fruits, and this induced response to infestation by fly larvae is density-dependent (increases with larval number), and site-dependent (more pronounced in the high-altitude site). Mechanical damage did not induce adonivernith production. This tissue-specific and density-dependent response of T. europaeus to infestation by Chiastocheta larvae might be an efficient regulation mechanism of seed-predator mutualist population growth if it decreases survival or growth of the larvae.     

Clinician attributions associated with the diagnosis of schizophrenia in African American and non-African American patients.

The authors examined the schizophrenia diagnosis in 292 psychiatric inpatients in a largely African American community. Clinicians completed a free-response questionnaire that described their diagnostic decisions. Psychotic symptoms such as hallucinations, which were attributed to African American and non-African American patients at different rates, did not necessarily correspond to differences in diagnostic rates. Rather, symptoms not differentially attributed between groups often corresponded with higher rates of schizophrenia for African American patients. Attributions of negative symptoms showed the largest differences between African American and non-African American patients in rates of schizophrenia diagnosis; thought disorder equalized rates of the diagnosis between the 2 groups of patients. Logistic regression analyses suggested that different aggregate decision models were applied to patients of differing race. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Separating trait effects from trait-specific method effects in multitrait-multimethod models: A multiple-indicator CT-C(M-1) model.

An overview of several models of confirmatory factor analysis for analyzing multitrait-multimethod (MTMM) data and a discussion of their advantages and limitations are provided. A new class of multi-indicator MTMM models combines several strengths and avoids a number of serious shortcomings inherent in previously developed MTMM models. The new models enable researchers to specify and to test trait-specific-method effects. The trait and method concepts composing these models are explained in detail and are contrasted with those of previously developed MTMM models for multiple indicators. The definitions of the models are explained step by step, and a practical empirical application of the models to the measurement of 3 traits x 3 methods is used to demonstrate their advantages and limitations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)