Non-adiabatic Effects in the Oxidation of Alkali Metals

Non-adiabatic effects during the oxidation of alkali metal surfaces were studied. For this purpose thin film Schottky diodes based on silicon substrates were developed. The diodes were used to detect low lying electron-hole pair excitations leading to chemicurrents through the devices. The chemicurrent concept has been combined with a setup to detect highly energetic exoelectrons emitted in the cause of the reactions. In contrast to previous studies, it has been found that the chemicurrent is not simply proportional to the reaction rate. Exposure dependent chemicurrent and exoemission efficiencies have to be assumed to correctly describe the time evolution of chemicurrent and exoemission traces. Most experiments were carried for liquid nitrogen cooled samples at a temperature of 120 K. From independent photo emission experiments the reaction kinetics of the oxidation of alkali metal films in a low pressure oxygen atmosphere could be determined. The structure of the O 1s photoemission line was used to determine the chemical composition of the oxide films. For lithium and sodium substantial amounts of dissociatively adsorbed oxygen could be observed. Molecular adsorption as peroxides and superoxides is dominant for the other alkali metals. Unactivated adsorption of oxygen on fresh potassium films occurs predominantly as peroxide. The high exposure regime is dominated by diffusion of potassium atoms to the surface and the absorption of superoxide ions. Valence band photoemission (UPS) reveal the molecular adsorption which confirm the previous interpretation of the chemical shift in the O 1s XPS data. Chemicurrent and exoemission data for oxygen adsorption show that non-adiabatic effects are not restricted to the dissociation of oxygen molecules. The second charge transfer O− 2 → O2− 2 efficiently generates low lying electronic excitations which can be measured as a chemicurrent. At the same time high energy exoelectrons are emitted via Auger processes. A shift between the chemicurrent and exoemission traces are observed which is explained by the low bandwidth of the alkali metals. If the injected hole state lives sufficiently long, there is the possibility for it to be injected below the band bottom. This suppresses the resonant ionization of the adsorbate, and hence reduces the chemicurrent. The exoemission, however, is not affected. The oxidation of the surface effectively decouples the adsorbate states from the metal leading to a longer lifetime of the injected hole states. An increase of the non-adiabaticity of the adsorption is the consequence. Model calculations using a Newns-Anderson Hamiltonian were carried out to calculate non-adiabatic excitation spectra for the adsorption of an oxygen molecule on a clean K(100) surface. Parameters for the time-dependent Newns-Anderson calculation were obtained from independent DFT results. A large imbalance between excited holes and electrons is found. These results show that the effective temperature description of the spectra is not suitable for the system.In dieser Arbeit werden nicht-adiabatische Effekte bei der Oxidation von Alkalimetalloberflächen untersucht. Hierzu wurden Dünnschicht-Schottkydioden auf der Basis von Siliziumsubstrat hergestellt. Die so hergestellten Dioden dienten als Detektoren zur Messung von durch niederenergetische Elektron-Loch-Paar-Anregungen induzierte Chemoströme. Das Chemostromkonzept wurde mit einem Aufbau zur Detektion von hochangeregten Exoelektronen, die im Verlauf der Reaktion freigesetzt werden, erweitert. Im Gegensatz zu vorhergehenden Studien wurde festgestellt, dass die Chemoströme keiner einfachen Proportionalität zur Reaktionsrate folgen. Bedeckungsabhängige Chemostrom- und Exoemissionseffizienzen müssen angenommen werden um die zeitliche Entwicklung des Chemostroms und der Exoemission korrekt wiederzugeben. Die Experimente wurden größtenteils an mit flüssigem Stickstoff gekühlten Proben bei einer Temperatur von 120K vorgenommen. Durch unabhängige Photoemissionsexperimente wurde die Reaktionskinetik der Oxidation von Alkalimetallfilmen bei tiefen Temperaturen in einer Sauerstoffatmosph¨are bei niedrigem Druck bestimmt. Die Struktur der O 1s Photoemissionsline diente dazu die chemische Zusammensetzung der Oxidfilme zu bestimmen. Auf Lithiumund Natriumfilmen adsorbieren beträchtliche Anteile des angebotenen Sauerstoff dissoziativ. Bei den anderen Akalkimetallen wurde vorwiegend molekulare Adsorption als Peroxid und Superoxid gefunden. Auf unbedeckten Kaliumoberflächen wurde eine direkte Adsorption von Peroxidionen beobachtet. Bei höheren Bedeckungen wird die Reaktion durch die Diffusion von Kaliumatomen durch den Oxidfilm dominiert und durch Superoxidadsorption bestimmt. Valenzbandspektroskopie (UPS) untermauert die Interpretation der vorgestellten chemischen Verschiebung der O 1s Linie, die durch XPS-Messungen bestimmt wurde. Die Chemostrom und Exoemissionsdaten zeigen, dass die nicht-adiabatischen Effekte nicht auf die Dissoziation von Sauerstoffmolekülen beschränkt sind. Der zweite Ladungstransfer O−2 → O2−2 generiert tief liegende elektronische Anregungen, die als Chemostrom detektiert werden kännen. Gleichzeitig führen allerdings Augerprozesse zur Emission von Exoelektronen. Ein Versatz zwischen Chemostrom und Exoemission wurde beobachtet, welcher durch die niedrige Bandbreite der Alkalimetalle erklärt wird. Bei einer ausreichenden Lebensdauer des injizierten Lochzustands kann dieser unter die Bandkante des Metalls gedrückt werden, was die resonante Ionization des Adsorbats (und damit den Chemostrom) unterdrückt. Die Exoemission dagegen ist hiervon nicht betroffen. Die Oxidation der Oberfläche entkoppelt die Adsorbatzustände effektiv von denen des Metalls. Dies führt zu einer verlängerten Lebensdauer der injizierten Lochzustände, was eine erhöhte Nichtadiabatizität der Adsorption zur Folge hat. Modelrechnung wurden unter Benutzung eines Newns-Anderson Hamiltonian durchgeführt um nicht-adiabatische Anregungensspektren hervorgerufen durch die Adsorption eines Sauerstoffmoleküls auf einer K(100) Oberfläche zu beschreiben. Parameter für das zeitabhängige Newns-Anderson Model wurden aus unabhängigen Dichtefunktionalrechnungen entnommen. Ein großes Ungleichgewicht zwischen angeregten Löcher und Elektronen wurde gefunden. Diese Ergebnisse zeigen, dass eine Beschreibung durch eine effektive Temperatur für die betrachteten Systeme nicht angemessen ist

Reliability of Muscle Blood Flow and Oxygen Consumption Response from Exercise Using Near-infrared Spectroscopy

New Findings What is the central question of this study? Continuous-wave near-infrared spectroscopy, coupled with venous and arterial occlusions, offers an economical, non-invasive alternative to measuring skeletal muscle blood flow and oxygen consumption, but its reliability during exercise has not been established. What is the main finding and its importance? Continuous-wave near-infrared spectroscopy devices can reliably assess local skeletal muscle blood flow and oxygen consumption from the vastus lateralis in healthy, physically active adults. The patterns of response exhibited during exercise of varying intensity agree with other published results using similar methodologies, meriting potential applications in clinical diagnosis and therapeutic assessment. Near-infrared spectroscopy (NIRS), coupled with rapid venous and arterial occlusions, can be used for the non-invasive estimation of resting local skeletal muscle blood flow (mBF) and oxygen consumption (), respectively. However, the day-to-day reliability of mBF and responses to stressors such as incremental dynamic exercise has not been established. The aim of this study was to determine the reliability of NIRS-derived mBF and responses from incremental dynamic exercise. Measurements of mBF and were collected in the vastus lateralis of 12 healthy, physically active adults [seven men and five women; 25 (SD 6) years old] during three non-consecutive visits within 10 days. After 10 min rest, participants performed 3 min of rhythmic isotonic knee extension (one extension every 4 s) at 5, 10, 15, 20, 25 and 30% of maximal voluntary contraction (MVC), before four venous occlusions and then two arterial occlusions. The mBF and increased proportionally with intensity [from 0.55 to 7.68 ml min−1 (100 ml)−1 and from 0.05 to 1.86 ml O2 min−1 (100 g)−1, respectively] up to 25% MVC, where they began to plateau at 30% MVC. Moreover, an mBF/ muscle oxygen consumption ratio of ∼5 was consistent for all exercise stages. The intraclass correlation coefficient for mBF indicated high to very high reliability for 10–30% MVC (0.82–0.9). There was very high reliability for across all exercise stages (intraclass correlation coefficient 0.91–0.96). In conclusion, NIRS can reliably assess muscle blood flow and oxygen consumption responses to low- to moderate-intensity exercise, meriting potential applications in clinical diagnosis and therapeutic assessment

Overview on Multienzymatic Cascades for the Production of Non-canonical α-Amino Acids

SM-R thanks the University of Granada for the support provided by project PPJI2017-1 and the European Cooperation in Science and Technology (COST Action CA15133). Authors are also grateful to the Andalusian Regional Government through Endocrinology & Metabolism Group (CTS-202).The 22 genetically encoded amino acids (AAs) present in proteins (the 20 standard AAs together with selenocysteine and pyrrolysine), are commonly referred as proteinogenic AAs in the literature due to their appearance in ribosome-synthetized polypeptides. Beyond the borders of this key set of compounds, the rest of AAs are generally named imprecisely as non-proteinogenic AAs, even when they can also appear in polypeptide chains as a result of post-transductional machinery. Besides their importance as metabolites in life, many of D-α- and L-α-“non-canonical” amino acids (NcAAs) are of interest in the biotechnological and biomedical fields. They have found numerous applications in the discovery of new medicines and antibiotics, drug synthesis, cosmetic, and nutritional compounds, or in the improvement of protein and peptide pharmaceuticals. In addition to the numerous studies dealing with the asymmetric synthesis of NcAAs, many different enzymatic pathways have been reported in the literature allowing for the biosynthesis of NcAAs. Due to the huge heterogeneity of this group of molecules, this review is devoted to provide an overview on different established multienzymatic cascades for the production of non-canonical D-α- and L-α-AAs, supplying neophyte and experienced professionals in this field with different illustrative examples in the literature. Whereas the discovery of new or newly designed enzymes is of great interest, dusting off previous enzymatic methodologies by a “back and to the future” strategy might accelerate the implementation of new or improved multienzymatic cascades.University of Granada PPJI2017-1European Cooperation in Science and Technology (COST) CA15133Andalusian Regional Government through Endocrinology & Metabolism Group CTS-20

Ultrasonic Assessment of Metal Microstructures, Modelling and Validation

The uniformity of strip rolled steel and its mechanical properties are intrinsically linked to the complex microstructure along the strip length. Ultrasonic methods are sensitive to differences in grain size, grain distribution and texture. This with the intention to provide suitable tools to inline monitors the properties of hot rolled steel.In this paper, we present a comparison of results from numerical and analytical simulations of the elastic wave propagation in deterministic and stochastic models of the microstructures. Modelled microstructures are used to provide the flexibility of assessing single microstructural parameters of different steel grades and rolling conditions. The individual simulations are validated against laser ultrasonic measurements on metal sheets in thickness range of 2mm-5mm, which were independently characterized metallurgically.The correlation to parameters as texture, grain size and dual phase composition was addressed. The simulation facilitates the development of methodologies to identify quantitative values that will enable to non-destructively assess the quality of a component. Different methods are developed based on changes in attenuation and velocity. These were tested against the simulated as well as the experimental data

Intra-zero-energy Landau level crossings in bilayer graphene at high electric fields

Abstract: The highly tunable band structure of the zero-energy Landau level (zLL) of bilayer graphene makes it an ideal platform for engineering novel quantum states. However, the zero-energy Landau level at high electric fields has remained largely unexplored. Here we present magnetotransport measurements of bilayer graphene in high transverse electric fields. We observe previously undetected Landau level crossings at filling factors nu = -2, 1, and 3 at high electric fields. These crossings provide constraints for theoretical models of the zero-energy Landau level and show that the orbital, valley, and spin character of the quantum Hall states at high electric fields is very different from low electric fields. At high E, new transitions between states at nu = -2 with different orbital and spin polarization can be controlled by the gate bias, while the transitions between nu = 0 -> 1 and nu = 2 -> 3 show anomalous behavior

Validation of models for Laser Ultrasonic spectra as a function of the grain size in steel

To reduce costs of production and increase economic sustainability it is necessary to introduce quality assessment in an early stage in the manufacturing process. In an ongoing European project (Product Uniformity Control – PUC), the intention is to use ultrasonic information to assess microstructure parameters that are related to macroscale qualities such as mechanical properties. Laser induced ultrasonic technique (LUS) requires no media and can generate and detect ultrasonic information at some distance from the component. This technique is therefore addressed within this project as a solution to measure ultrasonic properties in an industrial environment.Mathematical modelling of the ultrasonic wave propagation problem has been used in order to get a deeper understanding of the physics and to identify ultrasonic properties that can be used as an indirect measurement of grain size. The use of both analytical and numerical models enabled extensive parametric studies together with investigation of ultrasonic interactions with well-defined individual microstructures.The LUS technique has previously been applied to e.g. monitor grain growth during thermomechanical processing of metals. These applications identified and used a correlation with the frequency content of the attenuation. This have been investigated as a possible indirect measurement of grain size, also in this project. The models have been used to verify the correlations and to evaluate different procedures that could be applied as an industrial solution. The suggested procedure is based on deconvolving two successive echoes and has been experimentally validated by two different LUS systems. The reference samples used in the validation were produced by changing the annealing temperature and time to obtain a variation in grain sizes. These grain sizes were then identified by EBSD and the samples were examined in terms of grain size influence on spectral attenuatio

Results of the European collaborative project “Product Uniformity Control“ to improve the inline sensing of mechanical properties and microstructure of automotive steels

A European consortium consisting of four major steel manufacturers and ten academic technology institutes has conducted a research and development project, called “Product Uniformity Control“ (PUC) in the period 2013 to 2017. This project aimed to develop and improve non-destructive (inline) measurement techniques to characterise the (uniformity of the) microstructure of steel strip products.In this project, a multitude of strip steel samples from various stages of production have been collected from the four participating steel manufacturers. The samples have been characterised in various ways, namely on their (1) non-destructive measurement parameters using different techniques suited for inline evaluation, (2) fundamental ultrasonic and electromagnetic properties (wave speed, ultrasonic attenuation, magnetisation loops, coercive field), (3) tensile properties (stress-strain curves) and (4) microstructure (by optical micrographs and EBSD images). The correlations between these different characterisations will be addressed.Besides the experimental characterisation, a strong accent has been on modelling activities: during the project, fundamental models have been developed to describe, starting from 2D and 3D microstructures, the ultrasonic and magnetic properties, which are next used as input to sensor models that predict the output of the inline measurement systems.This contribution will present the recent results of both the experimental and the modelling work, and underline their mutual importance in the interpretation of the measured data for the benefit of inline characterisation of the mechanical properties complementary to traditional destructive tensile testing

Product Uniformity Control (PUC): How 15 European research institutes contribute to improve the in-line characterisation of microstructure and mechanical properties in the manufacturing of steel strip

International audienc

In-line characterisation of microstructure and mechanical properties in the manufacturing of steel strip for the purpose of product uniformity control

International audienceThe uniformity of the microstructure of steel strip over the entire coil length and between different coils of the same grade is key to stable and consistent material behaviour in steel manufacturers’ proprietary processes, like rolling and levelling, and customers’ processes, like pressing and deep-drawing. In particular for high-strength steels, like dual phase and complex phase steels, the microstructure is very sensitive to processing variations resulting in a potentially larger spread in the mechanical properties of the product. In July 2013, a large European consortium consisting of 15 institutes started an RFCS (1) –funded project called “Product Uniformity Control” (PUC) with the primary objective to achieve enhanced and sustained product uniformity of steel strip by improved interpretation of data from inline measurement methods that aim for real-time and non-destructive characterisation of microstructure and techno-mechanical parameters. Commonly, these techniques are based on electromagnetic (EM) or ultrasonic (US) measurement principles, which are favoured because of their non-destructive and potentially contact-free nature. To improve the techniques for in-line materials characterisation, the PUC consortium takes a systematic approach to investigate the interrelations between mechanical properties -- microstructural parameters -- EM & US properties -- inline measurement thereof. The studies involve dedicated laboratory experiments, modelling of the EM and US properties of steel, modelling of inline measurement setups and statistical analysis of data from inline measurement systems. The synthesis of these activities should result in improved, model-based, calibrations and finally in a broader deployment and integration of the inline material characterisation techniques in steel manufacturing, adding value to the product and enhancing the process efficiency throughout the production chain from hot-rolling to finishing. This paper outlines the project approach, highlights interconnecting modelling and experimental research work, and demonstrates first results. Various contributions being presented at this WCNDT conference originate from the collaborative activities of this PUC project. (1). (European) Research Fund for Coal and Stee