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Root exudation is a major pathway of organic carbon input into soils. It affects soil physical properties, element solubility as well as speciation, and impacts the microbial community in the rhizosphere. Root exudates contain a large number of primary and secondary plant metabolites, and the amount and composition are highly variable depending on plant species and developmental stage. Detailed information about exudate composition will allow for a better understanding of exudate-driven rhizosphere processes and their feedback loops. Although non-targeted metabolomics by high-resolution mass spectrometry is an established tool to characterize root exudate composition, the extent and depth of the information obtained depends strongly on the analytical approach applied. Here, two genotypes of Zea mays L., differing in root hair development, were used to compare six mass spectrometric approaches for the analysis of root exudates. Reversed-phase liquid chromatography and hydrophilic interaction liquid chromatography combined with time-of-flight mass spectrometry (LC-TOF-MS), as well as direct infusion Fourier-transform ion cyclotron resonance mass spectrometry (DI-FT-ICR-MS), were applied with positive and negative ionization mode. By using the same statistical workflow, the six approaches resulted in different numbers of detected molecular features, ranging from 176 to 889, with a fraction of 48 to 69% of significant features (fold change between the two genotypes of > 2 and p-value rth3). These results were in agreement with the higher total carbon and nitrogen exudation rate of the rth3-mutant as compared to the corresponding wild-type maize (WT). However, only a small fraction of features were commonly found across the different analytical approaches (20–79 features, 13–31% of the rth3-mutant up-regulated molecular formulas), highlighting the need for different mass spectrometric approaches to obtain a more comprehensive view into the composition of root exudates. In summary, 111 rth3-mutant up-regulated compounds (92 different molecular formulas) were detected with at least two different analytical approaches, while no WT up-regulated compound was found by both, LC-TOF-MS and DI-FT-ICR-MS. Zea mays L. exudate features obtained with multiple analytical approaches in our study were matched against the metabolome database of Zea mays L. (KEGG) and revealed 49 putative metabolites based on their molecular formula. Graphical Abstract

To date, several numerical models predicting the properties of TIG-arcs are available. Recently, effort has been put into testing the reliability of these models for varying process parameters by means of comparing plasma temperatures and arc voltages against measured data. However, from an engineering point of view, the goal of these models is to predict the properties of weld beads. Therefore, the heat input into and the pressure applied onto the workpiece have to be predicted. This paper deals with the comparison of measured arc pressure data and the results of an approach which couples a simplified cathode sheath model with an LTE arc model.

To date, several numerical models representing the tungsten inert gas (TIG) arc are available. However, little has been done on testing the reliability of these models for parameter values differing from the ones used in the respective papers. This paper deals with the comparison of measured arc welding data provided by E. Siewert from Linde AG and the results of the two most common arc and cathode sheath models. These models make different degrees of simplification of the actual processes in the arc, especially the cathode sheath. Different shapes of the electrodes, different welding currents and shielding gases are taken into account as well as the resolution of the numerical grid on which the calculations are carried out. The findings of this paper are used to show when a simplified approach still leads to valid results and when more sophisticated models have to be used.

In this paper, the results for keyhole welding of stainless steel 1.4301 and mild steel 1.0117 with a cathode focussed gas tungsten arc process are presented. These tests were carried out in preparation for welding the root faces of Y- or double V-groove weld preparations of thick metal plates. Welded plate thicknesses range from 6 to 10 mm for stainless steels and 6 to 12 mm for mild steels. Welding speeds are in the range of 20 to 115 cm/min at currents from 400 to 800 A. Especially for stainless steel, a big range of applicable and stable process parameters could be found. The process also works fine for mild steel even though the achievable parameter range is smaller.

This paper presents extensive investigations about the influence of He-additions to argon TIG-arc properties. Results of diagnostic methods, numerical simulations and welding trials are combined to improve the comprehension about the mode of action of gas mixtures. Additionally, selected results of the investigation with H2- and N2-additions are summarized. The investigations show that all gas additions cause an increase of the heat input into the workpiece. However, the stagnation pressure depends on the gas composition: He-additions result in a decrease of the stagnation pressure which depends on the arc length, whereas H2-and N2-additions increase the pressure. By a systematic choice of the gas mixture the weld depth and also the maximum feed speed can be influenced.