Validity of dietary data in young populations and implications of measurement errors

Abstract: A high number of relationships between dietary intakes and health outcomes has been suggested and investigated during the last decades (Ezzati & Riboli, 2012; Vargas & Thompson, 2012; Alinia et al., 2009; Howarth et al., 2005; Kushi, 1992). Diet is of special interest as it is a modifiable risk factor. However, to date little is known with certainty on the complex relations between diet and specific diseases as respective research requires accurate, quantitative information on dietary intakes. Hence, the description of dietary intakes is one of the main tasks of dietary monitoring surveys and epidemiological studies. Assessment of dietary intakes is challenging due to changes in diet during life as well as due to the day-to-day variation that characterizes dietary intakes in general. In addition, the estimation of long-term consumption frequencies and amounts is difficult for most people as it relies on long-term memory and the capability of correct averaging. Strictly spoken, dietary intakes cannot be measured without error and will presumably never be. Researchers investigating associations between diet and specific diseases or distributions of dietary intakes need to account for various measurement errors to avoid drawing erroneous conclusions. The nature and magnitude of measurement errors in dietary data depend on the study population under investigation as well as on the assessment instrument. To date, there are only few recommendations available for measuring dietary intakes among children. As young children do not have the cognitive ability to report their dietary intakes themselves, usually parents are asked to proxy-report their child's intakes. This means that additional problems emerge from meals that are not under parents' control like e.g. school meals leading to unintentional misreporting. Little is known about the validity of proxy-reported dietary data, potential determinants of misreporting and additional sources of measurement errors in young populations yet. Therefore, this thesis aimed to investigate the extent and effects of measurement errors when assessing and modeling dietary data in young children. Special emphasis was put on differential measurement errors resulting from misreporting where different methods to counteract attenuation or distortion of risk estimates were encountered and evaluated. In summary, differences in the determinants of misreporting were found for proxy-reported dietary data compared to those previously reported for self-reported data where the problem of misreporting seemed to be even more severe in case of proxy-reports. Misreporting strongly affected effect estimates of associations between diet and overweight/obesity. Results strongly depended on the chosen statistical model where even reversed signs were observed when accounting or not-accounting for reporting errors. These findings suggest that studies on diet-disease associations based on proxy-reported dietary data are problematic as there is still no formal way to handle differential measurement errors caused by misreporting. In the absence of objective validation data, the true effects remain unknown. A large number of associations reported so far in epidemiological studies may be biased due to the application of models relying on the assumption of non-differential measurement errors only

Advances and challenges of ammonia delivery by urea-water sprays in SCR systems

Over the past decades, selective catalytic reduction (SCR) using aqueous urea sprays as ammonia precursor has become the prevalent technique for NO$_{X}$ emission control in mobile applications. Preparation of ammonia from urea water sprays still represents a challenge in aftertreatment engineering as complex interactions of multi-phase physics and chemical reactions have to be handled. Increasingly stringent emission legislations and the ongoing development of fuel-efficient engines and close-coupled aftertreatment systems raise high demands to SCR systems. Due to highly transient conditions and short mixing lengths, incomplete spray evaporation can result in liquid/wall contact and formation of solid urea deposits lowering ammonia selectivity and homogeneity. This article reviews the ongoing development of SCR systems with focus on the efficient evaporation and decomposition of the injected spray for a homogeneous ammonia distribution in front of the SCR catalyst. Critical aspects of spray evaporation and impingement, liquid film and deposit formation are pointed out and potentials for system optimization are discussed

Thermodynamics and reaction mechanism of urea decomposition

Selective catalytic reduction (SCR) for automotive applications depends on ammonia production from a urea-water solution by thermolysis and hydrolysis. In this process, undesired liquid and solid by-products are formed in the exhaust pipe. The formation and decomposition of these by-products have been studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Based on a previously published reaction mechanism by Brack et al. [1], a new reaction scheme is proposed that emphasizes the role of thermodynamic equilibrium of the reactants in liquid and solid phases [2]. The observed phenomenon of liquefaction and re-solidification of biuret in the temperature range 193–230 °C can be explained by formation of a eutectic mixture with urea. According to DSC data, the direct decomposition of urea to ammonia and isocyanic acid can be ruled out. The dominant route is a self-polymerisation of urea to biuret and triuret. Biuret and triuret decomposition are dominated by thermodynamic equilibria with gaseous isocyanic acid. For this, thermodynamic data of triuret have been refined. The apparent melting point of biuret at 193 °C is explained by the formation of a eutectic mixture within the urea-biuret-triuret-cyanuric acid ensemble. Furthermore, DSC data shows that cyanuric acid sublimates without decomposition at temperatures above 300 °C. Numerical simulations of the TGA and DSC experiments are performed by a multi-phase tank reactor model (DETCHEMMPTR [3]). The new reaction mechanism describes well the main features (decomposition steps and calorimetry) and dependencies (on heating rate and surface area) of the decompositions of urea, biuret, triuret and cyanuric acid. [1] W. Brack, B. Heine, F. Birkhold, M. Kruse, G. Schoch, S. Tischer and O. Deutschmann, “Kinetic modeling of urea decomposition based on systematic thermogravimetric analyses of urea and its most important by-products”, CES 106, 1–8 (2014). [2] S. Tischer, M. Börnhorst, J. Amsler, G. Schoch and O. Deutschmann, “Thermodynamics and reaction mechanism of urea decomposition”, PCCP, in press, DOI: 10.1039/C9CP01529A (2019). [3] www.detchem.co

Spatially Resolved Measurements of HNCO Hydrolysis over SCR Catalysts

In order to understand deposit formation during urea selective catalytic reduction (SCR) resulting from isocyanic acid (HNCO) formation, the present study investigates the potential of HNCO hydrolysis by spatially resolved gas phase concentration profiles along a single catalyst channel of commercial Cu-zeolite and V-based SCR catalysts. The spatially resolved profiles, obtained in a special hot gas test rig via capillary technique, provide information on reaction rates of HNCO hydrolysis, NH$_3$ adsorption and NO conversion, hereby revealing a better performance of the standard V-based catalyst regarding the HNCO hydrolysis, which is attributed to the TiO$_2$ support

Thermodynamics and reaction mechanism of urea decomposition

The selective catalytic reduction technique for automotive applications depends on ammonia production from a urea-water solution by thermolysis and hydrolysis. In this process, undesired liquid and solid by-products are formed in the exhaust pipe. The formation and decomposition of these by-products have been studied by thermogravimetric analysis and differential scanning calorimetry. A new reaction scheme is proposed that emphasizes the role of thermodynamic equilibrium of the reactants in liquid and solid phases. Thermodynamic data for triuret have been refined. The observed phenomenon of liquefaction and re-solidification of biuret in the temperature range 193–230 °C is explained by formation of a eutectic mixture with urea

NaWuReT Colloquium: From PhD Student to Assistant Professor – Early Career Chemical Engineers in Academia

The Nachwuchs Reaktionstechnik (NaWuReT) are early-career scientists from the ProcessNet Division Reaction Engineering. In autumn 2021, they organized an online colloquium with international early-career scientists from the chemical engineering community. Five guests were invited to give a scientific talk and provide insights into their career paths. The guests gave advice and emphasized the main challenges and opportunities during their early careers. Crucial points are networking, guidance, mentoring, as well as funding acquisition and the personal work-life balance

Iron as recyclable energy carrier: Feasibility study and kinetic analysis of iron oxide reduction

Carbon-free and sustainable energy storage solutions are required to mitigate climate change. One possible solution, especially for stationary applications, could be the storage of energy in metal fuels. Energy can be stored through reduction of the oxide with green hydrogen and be released by combustion. In this work a feasibility study for iron as possible metal fuel considering the complete energy cycle is conducted. On the basis of equilibrium calculations it could be shown that the power-to-power efficiency of the iron/iron oxide cycle is 27 %. As technology development requires a more detailed description of both the reduction and the oxidation, a first outlook is given on the kinetic analysis of the reduction of iron oxides with hydrogen. Thermogravimetric experiments using Fe$_2$O$_3$, Fe$_3$O$_4$ and FeO indicate a three-step process for the reduction. The maximum reduction rate can be achieved with a hydrogen content of 25 %. Based on the experimental results a reaction mechanism and accompanied kinetic data were developed for description of Fe$_2$O$_3$ reduction with H$_2$ under varying experimental conditions

Usual energy and macronutrient intakes in 2-9-year-old European children

OBJECTIVE: Valid estimates of population intakes are essential for monitoring trends as well as for nutritional interventions, but such data are rare in young children. In particular, the problem of misreporting in dietary data is usually not accounted for. Therefore, this study aims to provide accurate estimates of intake distributions in European children. DESIGN: Cross-sectional setting-based multi-centre study. SUBJECTS: A total of 9560 children aged 2-9 years from eight European countries with at least one 24-h dietary recall (24-HDR). METHODS: The 24-HDRs were classified in three reporting groups based on age- and sex-specific Goldberg cutoffs (underreports, plausible reports, overreports). Only plausible reports were considered in the final analysis (N=8611 children). The National Cancer Institute (NCI)-Method was applied to estimate population distributions of usual intakes correcting for the variance inflation in short-term dietary data. RESULTS: The prevalence of underreporting (9.5%) was higher compared with overreporting (3.4%). Exclusion of misreports resulted in a shift of the energy and absolute macronutrient intake distributions to the right, and further led to the exclusion of extreme values, that is, mean values and lower percentiles increased, whereas upper percentiles decreased. The distributions of relative macronutrient intakes (% energy intake from fat/carbohydrates/proteins) remained almost unchanged when excluding misreports. Application of the NCI-Method resulted in markedly narrower intake distributions compared with estimates based on single 24-HDRs. Mean percentages of usual energy intake from fat, carbohydrates and proteins were 32.2, 52.1 and 15.7%, respectively, suggesting the majority of European children are complying with common macronutrient intake recommendations. In contrast, total water intake (mean: 1216.7 ml per day) lay below the recommended value for >90% of the children. CONCLUSION: This study provides recent estimates of intake distributions of European children correcting for misreporting as well as for the daily variation in dietary data. These data may help to assess the adequacy of young children's diets in Europe