Analytische Chemie
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In this paper, members of three research teams, namely the Turfan Project of the Berlin BrandenburgAcademy of Sciences and Humanities, the Berlin-based research project on pigments in Central Asianpaper manuscripts, and the Hamburg-based project on the history and typology of Central Asian papermanuscripts, present some of the results of their cooperation. The investigated manuscripts belong tothe Berlin Turfan Collection. On the basis of different examples the contribution of scientific methods tophilological scholarship within a multidisciplinary approach is demonstrated.
Here we present the fabrication of a solid-core microstructured polymer optical fiber (mPOF) made of polycarbonate (PC), and report the first experimental demonstration of a fiber Bragg grating (FBG) written in a PC optical fiber. The PC used in this work has a glass transition temperature of 145°C. We also characterize the mPOF optically and mechanically, and further test the sensitivity of the PC FBG to strain and temperature. We demonstrate that the PC FBG can bear temperatures as high as 125°C without malfunctioning. In contrast, polymethyl methacrylate-based FBG technology is generally limited to temperatures below 90°C.
Due to the increasing utilization of silver nanoparticles in consumer related products, many studies focus on investigations regarding their toxicological potential. This includes investigations concerning uptake, distribution and excretion of the particles. So far, little attention was paid to changes of physical and chemical properties in the human body. During processes like digestion, the question arises whether they can pass this barrier in a nanoscale form. In this study we analytically monitored the changes in the size distribution of silver nanoparticles during an artificial digestion process with the help of small angle x-ray scattering (SAXS). Therefore, we synthesized polyacrylic acid stabilized ultra-small silver nanoparticles with a radius of 3 nm and a size distribution width of 18%. The artificial digestion process mimics the gastro-intestinal passage and simulates the oral, gastric and small intestinal conditions. Additionally, food components like oil, starch, glucose and skimmed milk powder are used to provide a preferably realistic environment.
In absence of any food components the low pH initiates aggregation of the particles in the stomach. However, the particles unexpectedly stabilize in a defined cluster form with a mean radius of 12 nm. By the use of the food components oil and starch we observed that the particles are dispersed again. Now we found a bimodal size distribution of primary particles and aggregates. In contrast to that, with skimmed milk powder only a slight aggregation occurs in the stomach. In the gastric tract the particle distribution is stabilized at a mean volume weighted radius of 5 nm. Hence, skimmed milk powder acts as a colloidal stabilizer. For comparison we also used silver nitrate as a control substance. Surprisingly, we observed a formation of nanoparticles already in the saliva. During the digestion process the distribution narrows and finally in the intestine it shows a stable distribution with a mean volume weighted radius of 3 nm and a small fraction of aggregates. These results indicate that the silver nanoparticles can pass the biological barriers of the digestion process in a nanoscale form but undergo a transformation in the size distribution. However, even from pure silver nitrate nanoparticle formation can be observed. This sketches a complex mechanism in which not only food components but also silver ions cause changes in nanoparticle size and aggregation.
This book is on sensors which are regularly deployed in technologies and processes related to hydrogen production, storage, distribution, and use. Not all types of sensors are equally suitable for specific hydrogen applications. The information in this book is intended to help the reader understand the basics of sensors, sensing technologies, sensor applications, and to provide guidelines for choosing the right sensors and the use of them correctly. Correct deployment of appropriate sensors demands knowledge of the sensing principle and of the physical or chemical quantities being measured. Because of the properties of hydrogen, the potential for its vastly increased use in a future low-carbon economy and possible hazards associated with its use, special attention is paid to hydrogen sensors. This book will not focus on the details of the hydrogen technologies nor on the many safety-related aspects of these technologies. Many books are already available on these topics. Instead the detection principle of hydrogen sensors and other sensor types used, in the dynamic and rapidly developing field of hydrogen technologies, are treated in detail in this book.
In the first chapter a brief overview is presented on basic hydrogen properties and particularly on those properties which are most relevant for safety and for sensing. To illustrate the extensive field of contemporary applications and the exciting possibilities for near future sensor applications, existing and emerging markets using large quantities of hydrogen are mentioned. The role of sensors as devices for monitoring and control of processes and as safety monitoring devices is outlined.
The second chapter gives an introduction to sensing technology and provides the Reader with relevant information pertaining to sensor definitions and classification, sensor metrics, and performance arameters, in addition to background information on sensor preparation technologies and techniques. While there are many books available which provide more exhaustive information on each of these topics, e.g., the level of detail provided in this chapter is sufficient to appreciate the salient features of sensing and sensing Technology which are central to hydrogen safety and monitoring of relevant applications.
Chapter 3 provides a comprehensive overview of emerging and commercially available hydrogen sensors, an explanation of their sensing principle, and important aspects of their performance. A comprehensive and up-to-date account of the theory (physical or chemical principles), design, and practical implementations of hydrogen sensors for use in hydrogen related applications is presented.
Similar information on chemical sensors for other gases, such as oxygen and trace components, which are also highly important in hydrogen technologies because of potential hazards to human health, process safety or facility performance, is provided in Chapter 4.
In Chapter 5 descriptions of physical sensors for temperature, pressure, gas flow, and fire indication, which are also germane for the safe use of hydrogen, are provided.
Standards, codes, and regulatory documents, which provide practical advice and legislative requirements regarding sensor deployment and performance, are described in Chapter 6. This chapter also makes reference to the main procedures for sensor testing in gas Standards including precise analytical methods and reference methods. The chapter concludes with a discussion on sensor selection and some installation guidelines are provided.
In Chapter 7 traditional and emerging processes and technologies involving hydrogen are described. The application of sensors in processes for the production of hydrogen, hydrogen storage, distribution, and the use of hydrogen in stationary and mobile fuel cells is discussed. Furthermore, the use of hydrogen as a coolant and chemical reagent (medium) in various processes is described. The exploitation of sensors for replacing traditional analytical instrumentation is also discussed. Finally supplementary information is provided on hydrogen properties, measuring quantities, and sensor parameters.
Hydrogen can cause unexpected material failure under consideration of stresses (external/internal) during manufacturing, processing or service of the materials. This failure is mostly based on a certain degradation of the mechanical properties. Thus, the correlation of hydrogen trapping vs. a respective microstructure is necessary for high strength steels. Thus, the scope of this work is the improvement of existing hydrogen trap models by verification of activation energies for hydrogen traps as well as the influence of the determination method. In this scope, the thermal desorption method is appropriate to distinguish between different hydrogen traps. Nevertheless, the specimen temperature has to be accounted very carefully in case of calculating the necessary trap energy.
Spatial and temporal control of thermal waves by using DMDs for interference based crack detection
(2016)
Active Thermography is a well-established non-destructive testing method and used to detect cracks, voids or material inhomogeneities. It is based on applying thermal energy to a samples’ surface whereas inner defects alter the non-stationary heat flow. Conventional excitation of a sample is hereby done spatially, either planar (e.g. using a lamp) or local (e.g. using a focused laser) and temporally, either pulsed or periodical. In this work we combine a high power laser with a Digital Micromirror Device (DMD) allowing us to merge all degrees of freedom to a spatially and temporally controlled heat source. This enables us to exploit the possibilities of coherent thermal wave shaping. Exciting periodically while controlling at the same time phase and amplitude of the illumination source induces – via absorption at the sample’s surface - a defined thermal wave propagation through a sample. That means thermal waves can be controlled almost like acoustical or optical waves. However, in contrast to optical or acoustical waves, thermal waves are highly damped due to the diffusive character of the thermal heat flow and therefore limited in penetration depth in relation to the achievable resolution. Nevertheless, the coherence length of thermal waves can be chosen in the mm-range for modulation frequencies below 10 Hz which is perfectly met by DMD technology. This approach gives us the opportunity to transfer known technologies from wave shaping techniques to thermography methods. We will present experiments on spatial and temporal wave shaping, demonstrating interference based crack detection.
The chapter describes the application of electronic noses (multigas sensors) for the quality control of spices and spice mixtures. Electronic noses were successfully applied for headspace analysis of spices. It was demonstrated in many investigations that electronic noses can contribute to the characterization of spices and spice mixtures in order to distinguish spices and spice mixtures, differentiate by origin, growth seasons,and processing,indicate adulteration from original, detect mold infestation. Electronic noses can be used as a fast screening method to provide information about the product quality. However, it needs samples and methods for reference, careful training, and complex calibration to consider influencing and disturbing effects as well as the possible limitations of the instrumentation. The correlation to classical chemical analysis methods is always advisable. Machined olfaction methods are capable to support the sensory analysis; however, they cannot yet substitute them.
We present paper-based test strips for chemical sensing with surface enhanced Raman scattering as detection method. The test strips are prepared on glass fibre paper with silver nanoparticles and a spray method with an airbrush spray setup as a low cost fabrication approach. The properties of the test strips are investigated with three classical Raman analytes rhodamine 6G, 4-aminothiophenol and adenine and optimized for a good reproducibility of the intensity measurements. All test analytes can be identified at low concentrations. For adenine, a concentration series from 10⁻⁴ M to 10⁻⁸ M is measured and the calibration data can be fitted and evaluated with a Langmuir isotherm model. The optimized test strips are applied for the identification of two antibiotics enoxacin and enrofloxacin.
Numerical measurement uncertainty determination for dimensional measurements of microparts with CT
(2016)
Up to now, the only standardized method to determine the measurement uncertainty for computed tomography (CT) is to use calibrated workpieces as specified in the Guideline VDI/VDE 2630 Part 2.1. This paper discusses a promising numerical method for uncertainty determination with help of a virtual metrological CT (VMCT). It gives an explanation of the adjustments, the input parameters and the execution of the simulation. Furthermore, it discusses the first results of uncertainty determination compared to the method of using calibrated workpieces with the aid of two example cases.
The method described here allows to determine the size of the thermal contact between two metal sheets joined by spot welding. This size is a measure for the size of the weld nugget, i.e. the zone melted during the welding process, and thus the quality of the welded joint. The method applies active thermography in transmission or reflection setup. Especially the reflection setup offers an attractive possibility for non-destructive testing when components can be accessed from one side only. The spot weld region is optically heated by laser or flash light radiation. The weld nugget provides the mechanical joint, but also constitutes a thermal bridge between the two welded sheets. The latter will be exploited in this method. The better thermal contact at the weld Nugget contrasts with the surrounding material, where the heat transfer between the two sheets is comparatively low. A major advantage of the described method is the applicability on sheets without any surface treatment. This is achieved by a proper normalization of the data, allowing for a correction of the varying surface emissivity.
Active thermography with lock-in excitation is a non-destructive testing method that is also feasible for testing of carbon fiber reinforced polymers (CFRP). For validating the method extensive investigations were done during a research project in order to advance a standardization process.
The most important parameters of optical and ultrasonic excitation thermography were investigated. For example, the appropriate selection of spectral sensitivity of the used infrared camera systems is important for recording undisturbed thermal signals. Regarding excitation,
influences of excitation power and ultrasonic frequency were studied. Furthermore, material parameters such as CFRP layup are known for strongly affecting the results of
measurement.
Over the past few decades, there has been an increased frequency and duration of cyanobacterial Harmful Algal Blooms (HABs) in freshwater systems globally. These can produce secondary metabolites called cyanotoxins, many of which are hepatotoxins, raising concerns about repeated exposure through ingestion of contaminated drinking water or food or through recreational activities such as bathing/swimming. An ultra-performance liquid chromatography tandem mass spectrometry (UPLC–MS/MS) multi-toxin method has been developed and validated for freshwater cyanotoxins; microcystins-LR, -YR, -RR, -LA, -LY and -LF, nodularin, cylindrospermopsin, anatoxin-a and the marine diatom toxin domoic acid. Separation was achieved in around 9 min and dual SPE was incorporated providing detection Limits of between 0.3 and 5.6 ng/L of original sample. Intra- and inter-day precision analysis showed relative standard deviations (RSD) of 1.2–9.6% and 1.3 –12.0% respectively. The method was applied to the analysis of aquatic samples (n = 206) from six European countries. The main class detected were the hepatotoxins; microcystin-YR (n = 22), cylindrospermopsin (n = 25), microcystin-RR (n = 17), micro-cystin-LR (n = 12), microcystin-LY (n = 1), microcystin-LF (n = 1) and nodularin (n = 5). For microcystins, the levels detected ranged from 0.001 to 1.51 mg/L, with two samples showing combined levels above the guideline set by the WHO of 1 mg/L for microcystin-LR. Several samples presented with multiple Toxins indicating the potential for synergistic effects and possibly enhanced toxicity. This is the first published pan European survey of freshwater bodies for multiple biotoxins, including two identified for the first
time; cylindrospermopsin in Ireland and nodularin in Germany, presenting further incentives for improved monitoring and development of strategies to mitigate human exposure.
Time-resolved in situ investigation of Portland cement hydration influenced by chemical admixtures
(2016)
Numerous admixtures are used in the building practice to customize the properties of the cement paste during application. The influences of admixtures on the course of cement hydration and formation of hydrate phases have to be considered. Polycarboxylate ether (PCE) based polymeric superplasticizers (SPs) are known to retard the setting of the cement paste. The extent of the retardation differs depending on the molecular structure of the SP. Additionally, the presence of a stabilizing agent (SA) in the cement paste has a retarding side effect on the setting. The initial cement hydration processes and the detailed mechanisms of the retardation influenced by PCEs, as well as their interactions with particular SAs, are insufficiently understood. Up to now, only the results of phenomenological studies were taken into account to describe this retardation process. A detailed structure analysis monitoring the change of the phase composition during the hydration was never applied. Both SP and SA affect the adsorption of the sulphate ions on the clinker particles, causing changes in the formation of ettringite during the initial hydration, and are therefore a crucial part of the setting process itself. Here, the initial hydration of cement influenced by the interaction of SP and SA was monitored in situ by synchrotron X-ray diffraction. The high time resolution of the measurements allowed a continuous detection of the hydrates formed. The hydration was followed from the starting point of water addition and for couple of hours afterwards. The hydration of the levitated cement pellets containing starch as SA was initialized by adding aqueous solutions of different commercial SPs. Changes in the ettringite formation were detected in comparison to the reference hydration of pure cement.
Online low-field NMR spectroscopy of an industrial lithiation reaction step for process control
(2016)
Online monitoring and process control requires fast and noninvasive analytical methods, which are able to monitor the concentration of reactants in multicomponent mixtures with parts-per-million resolution. Online NMR spectroscopy can meet these demands when flow probes are directly coupled to reactors, since this method features a high linearity between absolute signal area and sample concentration, which makes it an absolute analytical comparison method being independent on the matrix. Due to improved magnet design and field shimming strategies portable and robust instruments have been introduced to the market by several manufacturers during the last few years. First studies with this technology showed promising results to monitor chemical reaction in the laboratory.
Within the project CONSENS, the continuous production of high-value products in small production scale is advanced by introducing benchtop NMR spectroscopy. CONSENS is a research and innovation project on integrated control and sensing for sustainable operation of flexible intensified processes.
This poster will present the first steps of the process integration of a benchtop NMR instrument for a lithiation process and outlines further fields of activity and potential challenges. Hereby, the following issues are going to be addressed: explosion-proof housing for the spectrometer, automation of signal processing (data pretreatment, evaluation and communication to the control system), flow cells and measuring conditions. Furthermore, first online spectra of the lithiation reaction in batch mode were acquired in lab scale. The reaction was performed in a 25 mL glass reactor with thermal jackets for temperature control of the reaction mixture. The Li-HMDS was dosed stepwise by using a glass syringe. First spectra in the proton and fluorine domain were recorded online using a flowrate of 3.5 mL min–1 and a simple 5 mm polytetrafluoroethylene tube (PTFE) as a flow cell.
Online monitoring and process control requires fast and noninvasive analytical methods, which are able to monitor the concentration of reactants in multicomponent mixtures with parts-per-million resolution. Online NMR spectroscopy can meet these demands when flow probes are directly coupled to reactors, since this method features a high linearity between absolute signal area and sample concentration, which makes it an absolute analytical comparison method being independent on the matrix. Due to improved magnet design and field shimming strategies portable and robust instruments have been introduced to the market by several manufacturers during the last few years. First studies with this technology showed promising results to monitor chemical reaction in the laboratory.
Within the project CONSENS, the continuous production of high-value products in small production scale is advanced by introducing benchtop NMR spectroscopy. CONSENS is a research and innovation project on integrated control and sensing for sustainable operation of flexible intensified processes.
This poster will present the first steps of the process integration of a benchtop NMR instrument for a lithiation process and outlines further fields of activity and potential challenges. Hereby, the following issues are going to be addressed: explosion-proof housing for the spectrometer, automation of signal processing (data pretreatment, evaluation and communication to the control system), flow cells and measuring conditions. Furthermore, first online spectra of the lithiation reaction in batch mode were acquired in lab scale. The reaction was performed in a 25 mL glass reactor with thermal jackets for temperature control of the reaction mixture. The Li-HMDS was dosed stepwise by using a glass syringe. First spectra in the proton and fluorine domain were recorded online using a flowrate of 3.5 mL min–1 and a simple 5 mm polytetrafluoroethylene tube (PTFE) as a flow cell.
Quantitative Online NMR spectroscopy as a direct ratio method of analysis represents a perfect reference for calibration of further process analytical techniques, e.g., optical spectroscopic techniques. In this work we present a combined approach including Online NMR and Raman spectroscopy on a laboratory setup for development of suitable models for process monitoring. Therefore we investigated the absorption process of carbon dioxide in solutions of monoethanolamine, as well as the homogeneous catalyzed hydroformylation reaction of 1-dodecene taking place in an emulsion stabilized by a technical surfactant. The models for Raman spectroscopy were tested and approved during several days of operational studies of miniplant-scale setups for both mentioned applications.
Real Time Imaging of Deuterium in a Duplex Stainless Steel Microstructure by Time-of-Flight SIMS
(2016)
For more than one century, hydrogen assisted degradation of metallic microstructures has been identified as origin for severe technical component failures but the mechanisms behind have not yet been completely understood so far. Any in-situ observation of hydrogen transport phenomena in microstructures will provide more details for further elucidation of these degradation mechanisms. A novel experiment is presented which is designed to elucidate the permeation behaviour of deuterium in a microstructure of duplex stainless steel (DSS). A hydrogen permeation cell within a TOF-SIMS instrument enables electrochemical charging with deuterium through the inner surface of the cell made from DSS. The outer surface of the DSS permeation cell exposed to the vacuum has been imaged by TOF-SIMS vs. increasing time of charging with subsequent chemometric treatment of image data. This in-situ experiment showed evidently that deuterium is permeating much faster through the ferrite phase than through the austenite phase. Moreover, a direct proof for deuterium enrichment at the austenite-ferrite interface has been found.
The preparation and characterization of poly(ionic liquid)s (PILs) bearing a polystyrene backbone via reversible addition fragmentation chain transfer (RAFT) polymerization and their photolithographic patterning on silicon wafers is reported. The controlled radical polymerization of the styrenic ionic liquid (IL) monomers ([BVBIM]X, X = Cl− or Tf2N−) by RAFT polymerization is investigated in detail. We provide a general synthetic tool to access this class of PILs with controlled molecular weight and relatively narrow molecular weight distribution (2000 g mol−1 ≤ Mn ≤ 10 000 g mol−1 with dispersities between 1.4 and 1.3 for p([BVBIM]Cl); 2100 g mol−1 ≤ MP ≤ 14 000 g mol−1 for p([BVBIM]Tf2N)). More importantly, we provide an in-depth characterization of the PILs and demonstrate a detailed mass spectrometric analysis via matrix-assisted laser desorption ionization (MALDI) as well as – for the first time for PILs – electrospray ionization mass spectrometry (ESI-MS). Importantly, p([BVBIM]Cl) and p([DMVBIM]Tf2N) were photochemically patterned on silicon wafers. Therefore, a RAFT agent carrying a photoactive group based on ortho-quinodimethane chemistry – more precisely photoenol chemistry – was photochemically linked for subsequent controlled radical polymerization of [BVBIM]Cl and [DMVBIM]Tf2N. The successful spatially-resolved photografting is evidenced by surface-sensitive characterization methods such as X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The presented method allows for the functionalization of diverse surfaces with poly(ionic liquid)s.
Laser microprobe mass analysis (LMMS) employs local ionization by a focused laser and subsequent mass analysis. At excessive irradiation microplasmas led to undesired distortions. Thus, LMMS was discarded as promising ion source. Effective cooling under ambient conditions resulted in more controllable plasmas and development of laser induced breakdown spectroscopy (LIBS). However, little effort has been made to combine LIBS and ambient MS, since these plasmas only provide microsecond lifetimes. After these, recombination yields uncharged and newly bound species, making them inaccessible for MS. The combination of high repetition rate lasers together with growing knowledge about manipulation of charged species at atmospheric pressure allow overcoming these obstacles.
During the last years quantitative NMR spectroscopy has become a general method for solving complex problems in science and industry. The opportunity of a calibration-free quantification, related to a simple counting of the nuclear spins in the active volume of the spectrometer represents a key advantage comparing to other analytical techniques. With modern NMR systems detection limits in the lower ppm range on a molar basis are accessible in a reasonable time period, which makes it a promising method for purity assessment, as well as applications in metrological research. First experiments showed that qNMR is suitable for gas analysis with respect to components used for production of primary reference gas mixtures. For this a laboratory setup for high-pressure NMR experiments up to 20 MPa (2900 psi) in fluid and gas phase was built and tested.
In this work we show the determination of the composition of high precision mixtures, consisting of liquid and liquefied hydrocarbons commonly supplied in floating piston cylinders. Therefore an experimental setup was developed allowing sampling, as well as circulation of the mixture within a high-pressure NMR tube by using a concentric tubing assembly. Additionally, a piston-cylinder pressure cell was designed and manufactured allowing wide-range volume displacement. Mainly intended for density variation within supercritical fluid experiments, it can also function as a compression element for further increasing of gas-pressure in the system. Equipped with liquid thermostat and a motor-powered screw drive unit it is designed to operate at pressure levels up to 60 MPa (8700 psi) and temperatures up to 130 °C.
Dual orthogonal functionalities in a single material is highly desirable in many fields such as bio-imaging, sensing, coating or diagnostic and therapy. However, a precise and controlled approach to prepare two different functionalities is still a challenging task. Herein, we show the simple preparation method for the synthesis of dual-functional hybrid core/shell/shell nanoparticles consisting of a silica core with a fluorescent and a thermoresponsive polymeric layer. Silica core particles were first coated by a fluorescent layer using surface- nitiated reversible addition-fragmentation chain transfer (RAFT) polymerization. The fluorescent silica nanoparticles were then completely enclosed within a switchable protective coating made of thermoresponsive poly(N-isopropylacrylamide) via RAFT polymerization. Thermoresponsive poly(N-isopropylacrylamide) is known to change its properties according to the surroundings temperature in a reversible and controllable way (LCST behavior). The successful preparation of well-defined dual-functional hybrid core/shell/shell nanoparticles was shown by scanning electron microscopy, thermogravimetric analysis and Fourier transform infrared spectroscopy, while their fluorescence and thermoresponsive properties were confirmed by fluorescence spectroscopy and dynamic light scattering measurements, respectively.
Photo-initiated cross-linking of multifunctional acrylic esters in polymeric binders was investigated based on digital imaging using the Computer-to-Plate (CtP) technology applying laser exposure in the near-infrared (NIR). Generation of initiating radicals occurs by electron transfer from the excited state of the NIR-sensitizer to the radical generator, an onium salt. Iodonium salts derived from several borates and those with the bis(trifluoromethylsulfonyl)imide anion resulted in lithographic materials with high sensitivity. Photo-induced electron transfer plays a major function to generate initiating radicals by a sensitized mechanism but thermal events also influence sensitivity of the coating. Internal conversion was the major deactivation pathway while a certain fraction of NIR-dye fluorescence was also available. A line shape focused laser system with emission in the NIR was successfully used to bake the materials.
This article focuses on the fusion of flaw indications from multi-sensor nondestructive materials testing. Because each testing method makes use of a different physical principle, a multi-method approach has the potential of effectively differentiating actual defect indications from the many false alarms, thus enhancing detection reliability. In this study, we propose a new technique for aggregating scattered two- or three-dimensional sensory data. Using a density-based approach, the proposed method explicitly addresses localization uncertainties such as registration errors. This feature marks one of the major of advantages of this approach over pixel-based image fusion techniques. We provide guidelines on how to set all the key parameters and demonstrate the technique's robustness. Finally, we apply our fusion approach to experimental data and demonstrate its capability to locate small defects by substantially reducing false alarms under conditions where no single-sensor method is adequate.
A systematic study of annealing behavior of drawn PMMA fibers was performed. Annealing Dynamics were investigated under different environmental conditions by fiber longitudinal shrinkage monitoring. The shrinkage process was found to follow a stretched exponential decay function revealing the heterogeneous nature of the underlying molecular dynamics. The complex dependence of the fiber shrinkage on initial degree of molecular alignment in the fiber, annealing time and temperature was investigated and interpreted. Moreover, humidity was shown to have a profound effect on the annealing process, which was not recognized previously. Annealing was also shown to have considerable effect on the fiber mechanical properties associated with the relaxation of molecular alignment in the fiber. The consequences of fiber annealing for the climatic stability of certain polymer optical fiber-based sensors are discussed, emphasizing the importance of fiber controlled pre-annealing with respect to the foreseeable
operating conditions.
A fast quantitative model for the energy spectra of radiation emitted by X-ray tubes is described, handling thin as well as thick plane targets of arbitrary materials. The developed model is based on fundamental interaction cross sections, describing electron and photon transport via numerical integration of discretized distributions. While the focus lies on bremsstrahlung production, modeling of characteristic radiation is fully integrated. The model does not include any free parameters. The validity of the model is shown through comparison with measurements and Monte Carlo simulations for several combinations of target material and acceleration potential between 30 kV and 450 kV.
Synchrotron-radiation XPS analysis of ultra-thin silane films: Specifying the organic silicon
(2016)
The analysis of chemical and elemental in-depth variations in ultra-thin organic layers with thicknesses below 5 nm is very challenging. Energy- and angle-resolved XPS (ER/AR-XPS) opens up the possibility for non-destructive chemical ultra-shallow depth profiling of the outermost surface layer of ultra-thin organic films due to its exceptional surface sensitivity. For common organic materials a reliable chemical in-depth analysis with a lower limit of the XPS information depth z95 of about 1 nm can be performed. As a proof-of-principle example with relevance for industrial applications the ER/AR-XPS analysis of different organic monolayers made of amino- or benzamidosilane molecules on silicon oxide surfaces is presented. It is demonstrated how to use the Si 2p core-level region to non-destructively depth-profile the organic (silane monolayer) inorganic (SiO2/Si) interface and how to quantify Si species, ranging from elemental silicon over native silicon oxide to the silane itself. The main advantage of the applied ER/AR-XPS method is the improved specification of organic from inorganic silicon components in Si 2p core-level spectra with exceptional low uncertainties compared to conventional laboratory XPS.
We report an appropriate preparation of binary isotope calibration mixtures of the three stable isotopes of magnesium to be used in the ab initio calibration of multicollector mass spectrometers (ICPMS and TIMS). For each of the three possible combinations of binary mixtures ("24Mg" + "25Mg", "24Mg" + "26Mg", and "25Mg" + "26Mg"), three individual setups have been prepared under gravimetric control, each of them with an isotope ratio close to unity, and a total magnesium mass fraction close to 20 mg kg-1. The preparation was designed to occur via an intermediate dilution of a parent solution of a highly purified specimen of the isotopically enriched magnesium materials. For the application as calibration mixtures, a complete uncertainty budget was set up, and is presented and discussed in detail, including the aspects that went into the design of the dilution and mixing approach to minimize uncertainty. The principle parameters for the purpose of the later calibration of the mass spectrometers are the absolute masses of isotopically enriched magnesium materials in the primary calibration mixtures. For the first time relative expanded uncertainties U (k = 2) for these masses of ≤0.005% could be achieved for all mixtures.
Flexible electrochromic devices (ECDs) based on Fe(II)-metallo-supramolecular polyelectrolytes (Fe-MEPE) and vanadium oxide are studied in operando by means of x-ray absorption fine structure (XAFS) spectroscopy. The ECDs are blue-purple in the colored state at 0.0 V and become light yellow when a voltage of 1.6 V is applied. The XAFS studies at the K-edge of Fe(II) reveals that the absorption edge is shifted toward higher energies by 1.8 eV in the transparent state. Comparison of two different ECDs and different charge cycles demonstrates the reversibility and repeatability of the process. We attribute the shift to a charge transfer and a change of oxidation state of the ions from Fe2+ to Fe3+. The transition is not accompanied by a noticeable structural change of the octahedral coordination geometry as confirmed by analysis of the extended x-ray absorption fine structure (EXAFS) data. (C) 2015 Elsevier B.V. All rights reserved.
Within the scope of a DIN INS project, a flash thermography round robin test that evaluates reliability, comparability and efficiency of different testing situations is organized. The results give information about the detectability of defects e.g. by their size and depth, the evaluation method and by the materials used. Besides, the influence of equipment and parameters used by the participants on the results were analysed. All of the quantitative results as well as the feedback given by the participants will be presented in a DIN committee in order to contribute to a flash thermography standard.
The identification of different forms of dihydroergocristine (DHEC) was carried out by crystallization from different organic solvents. DHEC was identified as potential template for molecularly imprinted polymers (MIPs) for the epimeric specific analysis of ergot alkaloids (EAs) in food. DHEC was crystallized from different solvents in order to mimic the typical MIP synthesis conditions. Four new solvatomorphs of DHEC were obtained. All solvatomorphs contain a water molecule in the crystal structure, whereas three compounds contain an additional solvent molecule. Based on the conformation of DHEC a comparison with typical EA molecules was possible. The analysis showed that DHEC is a suitable template for MIPs for EAs.
Trace element concentrations in gold grains from various geological units in South Africa were measured in situ by field emission-electron probe microanalysis (FE-EPMA), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and synchrotron micro X-ray fluorescence spectroscopy (SR-µ-XRF). This study assesses the accuracy, precision and detection limits of these mostly non-destructive analytical methods using certified reference materials and discusses their application in natural sample measurement. FE-EPMA point analyses yielded reproducible and discernible concentrations for Au and trace concentrations of S, Cu, Ti, Hg, Fe and Ni, with detection limits well below the actual concentrations in the gold. LA-ICP-MS analyses required larger gold particles (> 60 µm) to avoid contamination during measurement. Elements that measured above detection limits included Ag, Cu, Ti, Fe, Pt, Pd, Mn, Cr, Ni, Sn, Hg, Pb, As and Te, which can be used for geochemical characterisation and gold fingerprinting. Although LA-ICP-MS measurements had lower detection limits, precision was lower than FE-EPMA and SR-µ-XRF. The higher variability in absolute values measured by LA-ICP-MS, possibly due to micro-inclusions, had to be critically assessed. Non-destructive point analyses of gold alloys by SR-µ-XRF revealed Ag, Fe, Cu, Ni, Pb, Ti, Sb, U, Cr, Co, As, Y and Zr in the various gold samples. Detection limits were mostly lower than those for elements measured by FE-EPMA, but higher than those for elements measured by LA-ICP-MS.
An energy-based method to determine material constants in nonlinear rheology with applications
(2016)
Many polymer-type materials show a rate-dependent and nonlinear rheological behavior. Such a response may be modeled by using a series of spring-dashpot systems. However, in order to cover different time scales the number of systems may become unreasonably large. A more appropriate treatment based on continuum mechanics will be presented herein. This approach uses representation theorems for deriving material equations and allows for a systematic increase in modeling complexity. Moreover, we propose an approach based on energy to determine thematerial parameters.This method results in a simple linear regression problemeven for highly nonlinearmaterial equations. Therefore, the inverse problem leads to a unique solution. The significance of the proposed method is that the stored and dissipated energies necessary for the procedure are measurable quantities. We apply the proposed method to a 'semi-solid' material and measure its material parameters by using a simple-shear rheometer.
A discussion is provided on the relation between non-destructive testing (NDT) and fracture mechanics. The basic tasks behind this are to guarantee the safety of a component at a potential hazard loading event, to specify inspection intervals or, alternatively, of demands on NDT for a fixed inspection regime, to plan accompanying measures for cases of temporary continued operation of structures in which cracks have been detected, and, finally, fatigue strength considerations which take into account initial defects.
Hydrophobic guest molecules like organic dyes and metalion complexes can be introduced into aqueous media via adsorption onto inorganic nanoclay host materials such as nm-sized laponite. Dispersions of these organicinorganic hybrid materials show several advantageous properties like minimum light scattering due to their small size in the nanometer regime, ease of modification, low cost, low toxicity, and long-term stability, making them perfect candidates as signaling units and optically active materials in photonics and biotechnology. In this study, we summarize first findings on the easy-to-make, but chemically and optically fairly complex behavior of nanoclay hybrids for biotechnological applications. The latter includes the preparation of nanomaterials, which are colloidally stable in buffers and in the presence of biomolecules like proteins, and methods to control their surface chemistry. For this purpose, we used two red emitting fluorophores, the small organic dye Nile Red and the rare earth complex Eu(ttfa)3(topo)2, and evaluated the interaction of the red nanoclay hybrids with two model proteins, bovine serum albumin and β-lactoglobulin. We were able to monitor the formation of the protein corona around these hybrids using absorption and luminescence spectroscopy.
Insect behavior is a common source of inspiration for roboticists and computer scientists when designing gas-sensitive mobile robots. More specifically, tracking airborne odor plumes, and localization of distant gas sources are abilities that suit practical applications such as leak localization and emission monitoring. Gas sensing with mobile robots has been mostly addressed with ground-based platforms and under simplified conditions and thus, there exist a significant gap between the outstanding insect abilities and state-of-the-art robotics systems. As a step toward practical applications, we evaluated the performance of three biologically inspired plume tracking algorithms. The evaluation is carried out not only with computer simulations, but also with real-world experiments in which, a quadrocopter-based micro Unmanned Aerial Vehicle autonomously follows a methane trail toward the emitting source. Compared to ground robots, micro UAVs bring several advantages such as their superior steering capabilities and fewer mobility restrictions in complex terrains. The experimental evaluation shows that, under certain environmental conditions, insect like behavior in gas-sensitive UAVs is feasible in real-world environments.