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IoT-Plattformen stellen ein zentrales Element für die Vernetzung von physischen Objekten und die Bereitstellung deren Daten für digitale Zwillinge dar. Der Markt für solche Plattformen ist in den vergangenen Jahren stark gewachsen. Bei inzwischen über 600 Anbietern ist die Wahl der „richtigen“ Plattform für das eigene Unternehmen keine triviale Aufgabe mehr. Dieser Beitrag soll Unternehmen im Auswahlprozess unterstützen, indem gängige Funktionen von IoT-Plattformen und Kriterien für die Auswahl von IoT-Plattformen aufgezeigt werden.
Fans stärken Marken
(2016)
Eine repräsentative Studie mit 2.400 deutschen Arbeitnehmern zeigt, dass Mitarbeiter seltener krank werden, wenn sie sich an ihr Unternehmen gebunden fühlen. Die Studie offenbart auch, dass die Intensität des Commitment maßgeblich von fünf Einflussfaktoren abhängt. Die Kenntnis dieser Faktoren ermöglicht es Personalmanagern, Mitarbeiter gezielter an das Unternehmen zu binden, um so den Krankenstand positiv zu beeinflussen.
To this date, it is difficult to find high-level statistics on YouTube that paint a fair picture of the platform in its entirety. This study attempts to provide an overall characterization of YouTube, based on a random sample of channel and video data, by showing how video provision and consumption evolved over the course of the past 10 years. It demonstrates stark contrasts between video genres in terms of channels, uploads and views, and that a vast majority of on average 85% of all views goes to a small minority of 3% of all channels. The analytical results give evidence that older channels have a significantly higher probability to garner a large viewership, but also show that there has always been a small chance for young channels to become successful quickly, depending on whether they choose their genre wisely.
The free convection in a vertical gap is generalized to realize new analytical solutions of the Boussinesq-equations. The steady and time-dependent solutions for the temperature and velocity distribution are discussed in detail depending on the mass flux in vertical direction. The range of existence for flows with and without back flow is obtained. The transient behaviour of the solutions during the time-dependent development displays interesting physical behaviour.
Flows in nature and technology are often associated with specific structures and pattern. This paper deals with the development and behaviour of such flow pattern. Flow structures are important for the mass, momentum and energy transport. The behaviour of different flow pattern is used by engineers to obtain an efficient mass and energy consumption. Mechanical power is transmitted via the momentum of rotating machine parts. Therefore the physical and mathematical knowledge of these basic concepts is important. Theoretical and experimental investigations of principle experiments are described in the following. We start with the classical problem of the flow between two concentric cylinders where the inner cylinder rotates. Periodic instabilities occur which are called Taylor vortices. The analogy between the cylindrical gap flow, the heat transfer in a horizontal fluid layer exposed to the gravity field and the boundary layer flow along concave boundaries concerning their stability behaviour is addressed. The vortex breakdown phenomenon in a cylinder with rotating cover is also described. A generalization to spherical sectors leads then to investigations with different boundary conditions. The spherical gap flow exhibits interesting phenomena concerning the nonlinear character of the Navier-Stokes equations. Multiple solutions in the nonlinear regime give rise to different routes during the laminar-turbulent transition. The interaction of two rotating spheres results in flow structures with separation and stagnation lines. Experimental results are confirmed by numerical simulations.
Shapes and structures of vortex breakdown phenomena in rotating fluids are visualized. We investigate the flow in a cylindrical container and in a cone between two spherical surfaces. The primary swirling flow is induced by the rotating upper disk in the cylindrical case and by the lower boundary in the spherical case. The upper surface can be fixed with a no slip condition or can be a stress-free surface. Depending on these boundary conditions and on the Reynolds number novel structures of recirculation zones are realized. Experiments are done to visualize the topological structure of the flow and to determine their existence range as function of the geometry and rotation rate. A comparison between the experimental and theoretical approach shows a good agreement in respect to the topological structures of the flows.
Rotating flow systems are often used to study stability phenomena and structure developments. The closed spherical gap problem is generalized into an open flow system by superimposing a mass flux in meridional direction. The basic solutions at low Reynolds numbers are described by analytical methods. The nonlinear supercritical solutions are simulated numerically and realized in experiments. Novel steady and time-dependent modes of flows are obtained. The extensive results concern the stability behaviour, non-uniqueness of supercritical solutions, symmetry behaviour and transitions between steady and time-dependent solutions. The experimental investigations concern the visualization of the various instabilities and the quatitative description of the flow structures including the laminar-turbulent transition. A comparison between theoretical and experimental results shows good agreement within the limit of rotational symmetric solutions from the theory.
Jürgen Zierep passed away on July 29, 2021, at the age of 92. To him, science and education was not only a profession, but an affair of the heart. His impressive contributions in fluid mechanics comprise about 200 scientific publications in the fields of gas dynamics, similarity laws, flow instabilities, flows with energy transfer, and non-Newtonian fluids. In addition, he wrote eleven textbooks with great dedication. Those books by the “scientist who loves to teach” are nowadays available in different languages and regularly appear in new editions.
Electrolyte-gated thin-film transistors (EGTs) with indium oxide channel, and expected lifetime of three months, enable low-voltage operation (~1 V) in the field of printed electronics (PEs). The channel width of our printed EGTs is varied between 200 and 1000 μm, whereas a channel length between 10 and 100 μm is used. Due to the lack of uniform performance p-type metal oxide semiconductors, n-type EGTs and passive elements are used to design circuits. For logic gates, transistor-resistor logic has been employed so far, but depletion and enhancement-mode EGTs in a transistor-transistor logic boost the circuit performance in terms of delay and signal swing. In this article, the threshold voltage of the EGT, which determines the operation mode, is tuned through sizing of the EGTs channel geometry. The feasibility of both transistor operation modes is demonstrated for logic gates and ring oscillators. An inverter operating at a supply voltage of 1 V shows a maximum gain of 9.6 and a propagation delay time of 0.7 ms, which represents an improvement of ~ 2x for the gain and oscillation frequency, in comparison with the resistor-transistor logic design. Moreover, the power consumption is reduced by 6x.
Oxide semiconductors have the potential to increase the performance of inkjet printed microelectronic devices such as field-effect transistors (FETs), due to their high electron mobilities. Typical metal oxides are n-type semiconductors, while p-type oxides, although realizable, exhibit lower carriermobilities. Therefore, the circuit design based on oxide semiconductors is mostly in n-type logic only. Here we present an inkjet printed pn-diode based on p- and n-type oxide semiconductors.Copper oxide or nickel oxide is used as p-typesemiconductor whereas n-typesemiconductor is realized with indium oxide. Themeasurements show that the pn-diodes operate in the voltage window typical for printed electronics and the emission coefficient is 1.505 and 2.199 for the copper oxide based and nickel oxidebased pn-diode, respectively.Furthermore, a pn-diode model is developed and integrable into a circuit simulator.
In the domain of printed electronics (PE), field-effect transistors (FETs) with an oxide semiconductor channel are very promising. In particular, the use of high gate-capacitance of the composite solid polymer electrolytes (CSPEs) as a gate-insulator ensures extremely low voltage requirements. Besides high gate capacitance, such CSPEs are proven to be easily printable, stable in air over wide temperature ranges, and possess high ion conductivity. These CSPEs can be sensitive to moisture, especially for high surface-to-volume ratio printed thin films. In this paper, we provide a comprehensive experimental study on the effect of humidity on CSPE-gated single transistors. At the circuit level, the performance of ring oscillators (ROs) has been compared for various humidity conditions. The experimental results of the electrolyte-gated FETs (EGFETs) demonstrate rather comparable currents between 30%-90% humidity levels. However, the shifted transistor parameters lead to a significant performance change of the RO frequency behavior. The study in this paper shows the need of an impermeable encapsulation for the CSPE-gated FETs to ensure identical performance at all humidity conditions.
Printed electrolyte-gated oxide electronics is an emerging electronic technology in the low voltage regime (≤1 V). Whereas in the past mainly dielectrics have been used for gating the transistors, many recent approaches employ the advantages of solution processable, solid polymer electrolytes, or ion gels that provide high gate capacitances produced by a Helmholtz double layer, allowing for low-voltage operation. Herein, with special focus on work performed at KIT recent advances in building electronic circuits based on indium oxide, n-type electrolyte-gated field-effect transistors (EGFETs) are reviewed. When integrated into ring oscillator circuits a digital performance ranging from 250 Hz at 1 V up to 1 kHz is achieved. Sequential circuits such as memory cells are also demonstrated. More complex circuits are feasible but remain challenging also because of the high variability of the printed devices. However, the device inherent variability can be even exploited in security circuits such as physically unclonable functions (PUFs), which output a reliable and unique, device specific, digital response signal. As an overall advantage of the technology all the presented circuits can operate at very low supply voltages (0.6 V), which is crucial for low-power printed electronics applications.
Nonlinearity can give rise to intermodulation distortions in surface acoustic wave (SAW) devices operating at high input power levels. To understand such undesired effects, a finite element method (FEM) simulation model in combination with a perturbation theory is applied to find out the role of different materials and higher order nonlinear tensor data for the nonlinearities in such acoustic devices. At high power, the SAW devices containing metal, piezoelectric substrate, and temperature compensating (TC) layers are subject to complicated geometrical, material, and other nonlinearities. In this paper, third-order nonlinearities in TC-SAW devices are investigated. The materials used are LiNbO 3 -rot128YX as the substrate and copper electrodes covered with a SiO 2 film as the TC layer. An effective nonlinearity constant for a given system is determined by comparison of nonlinear P-matrix simulations to third-order intermodulation measurements of test filters in a first step. By employing these constants from different systems, i.e., different metallization ratios, in nonlinear periodic P-matrix simulations, a direct comparison to nonlinear periodic FEM-simulations yields scaling factors for the materials used. Thus, the contribution of the different materials to the nonlinear behavior of TC-SAW devices is obtained and the role of metal electrodes, substrate, and TC film are discussed in detail.
Design of next-generation cdma using orthogonal complementary codes and offset stacked spreading
(2007)
This article presents an innovative code-division multiple access system architecture that is based on orthogonal complementary spreading codes and time-frequency domain spreading. The architecture has several advantages compared to conventional CDMA systems. Specifically, it offers multiple-access-interference-free operation in AWGN channels, reduces co-channel interference significantly, and has the potential for higher capacity and spectral efficiency than conventional CDMA systems. This is accomplished by using an "offset stacked" spreading modulation technique followed by quadrature amplitude modulation, which optimizes performance in a fading environment. This new spreading modulation scheme also simplifies the rate matching algorithms relevant for multimedia services and IP-based applications.
Der Entwurf von Strukturen zum reflexionsarmen Einbetten von Halbleiterbauteilen in Mikrostreifenleitungsschaltungen gestaltet sich mit steigender Frequenz kritischer. Deshalb wird ein Verfahren vorgestellt, das es ermöglicht, das Streuverhalten solcher Strukturen unter Anwendung der dreidimensionalen Finite-Differenzen-Methode auf die Maxwellschen Gleichungen numerisch zu berechnen. Hierauf aufbauend wurde das Programmpaket F3D entwickelt. Das Streuverhalten einer Verbindung zweier GaAs-Chips durch eine dielektrische Wand wird in Abhängigkeit von Geometrieparametern diskutiert. Außerdem werden Ersatzschaltbilder unterschiedlicher Komplexität für CAD-Anwendungen vorgestellt. Diese ermöglichen zudem eine rechenzeiteffektive Optimierung dieser Struktur, die somit Filteraufgaben übernehmen kann. Dies wird am Beispiel eines Tiefpasses gezeigt.
It is demonstrated that microwave structures incorporating dielectric resonators (DR) are accurately characterised by means of a 3-dimensional finite-difference CAD package. All major assumptions made so far have been dropped, offering the possibility of a rigorous analysis of the embedding of dielectric resonators into microwave structures. In particular, a finite thickness for the microstrip conductor has been taken into account. The coupling of the DR to a microstrip placed in a metallic housing has been theoretically and experimentally investigated. Theoretical and experimental results are in good agreement and give new insight into DR coupling to microstrip circuits.
The embedding of microwave devices is treated by applying the finite-difference method to three-dimensional shielded structures. A program package was developed to evaluate electromagnetic fields inside arbitrary transmission-line connecting structures and to compute the scattering matrix. The air bridge, the transition through a wall, and the bond wire are examined as interconnecting structures. Detailed results are given and discussed regarding the fundamental behavior of embedding.
The advantages of the coupled-mode (COM) formalism and the transmission-matrix approach are combined in order to create exact and computationally efficient analysis and synthesis tools for the design of coupled surface acoustic wave resonator filters. The models for the filter components, in particular gratings, interdigital transducers (IDTs) and multistrip couplers (MSCs), are based on the COM approach that delivers closed-form expressions. To determine the pertinent COM parameters, the COM differential equations are solved and the solution is compared with analytically derived expressions from the transmission-matrix approach and the Green's function method. The most important second-order effects, such as energy storage, propagation loss, and mechanical and electrical loading, are fully taken into account. As an example, a two-pole, acoustically coupled resonator filter at 914.5 MHz on AT quartz is investigated. Excellent agreement between theory and measurement is found.
Wood juice, a liquid produced during wood processing, is a harmful waste that requires utilization. To achieve a circular economy, biowastes should be recycled, reducing fossil carbon usage. Therefore, the objective of this work was to examine the potential of wood juice as a feedstock for bioplastic synthesis by Bacillus sp. G8_19. Polyhydroxyalkanoate (PHA) syntheses using wood juice from Douglas fir trees and that from a mixture of spruce/fir trees were compared. It was found that the PHA content was higher after using wood juice from spruce/fir trees than that from Douglas fir trees (18.0% vs 6.1% of cell dry mass). Gas chromatography analysis showed that, with both wood juices, Bacillus sp. G8_19 accumulated poly(3-hydroxybutyrate-co-3-hydroxyvalerate). The content of 3-hydroxyvalerate (3HV) monomers was higher when spruce/fir wood juice was used (10.7% vs 1.9%). The C/N ratio did not have a statistically significant effect on the copolymer content in biomass, but it did significantly influence the 3HV content. The proposed concept may serve as an approach to wood waste valorization via production of biodegradable materials.
We present a novel scheme for Slotted ALOHA random access systems that combines physical-layer network coding (PLNC) with multiuser detection (MUD). The PLNC and MUD are applied jointly at the physical layer to be able to extract any linear combination of messages experiencing a collision within a slot. The set of combinations extracted from a whole frame is then processed by the receiver to recover the original packets. A simple precoding stage at the transmitting terminals allows the receiver to further decrease the packet loss rate. We present results for the decoding at the physical layer as well as several performance measures at frame level, namely, throughput, packet loss rate, and energy efficiency. The results we present are promising and suggest that a cross-layer approach leveraging on the joint use of PLNC and MUD can significantly improve the performance of random access systems in the presence of slow fading.
The current methods used to assess the energy performance of ventilation devices do not consider all the aspects necessary for a comprehensive evaluation of decentralised ventilation concepts and can only be partially adapted to their needs. In order to improve the energy evaluation and to ensure the comparability of different systems, a calorimetric method was developed and implemented in test facilities for the evaluation of two decentralised devices: one equipped with a recuperative counter flow heat exchanger and one with a regenerative heat exchanger. This method, based on direct measurements of the heating load in an insulated test room, includes the effect of the electrical consumption of the fans on the energy performance of the ventilation devices. The calorimetric evaluation method was extended to a seasonal evaluation on the basis of a heating-degree-day method implemented for a warm, a cool and a moderate location in Europe: Athens, Strasbourg and Copenhagen. All the results are above 50% efficiency for both devices, even in Athens where the use of heat recovery ventilation is not usual.
Ozon-Querempfindlichkeit bei der Immissionsmessung von schwebstaubakkumuliertem Benzo[a]pyren
(2002)
Für die Beschreibung der Belastung der Luft mit polycyclischen aromatischen Kohlenwasserstoffen (PAK) wird vorwiegend die Konzentration eines Vertreters, das auf Schwebstaub akkumulierte Benzo[a]pyren (BaP), analysiert. Hierbei stellt Benzo[a]pyren die Leit komponen te für die Stoffklasse der PAK dar. Auf europäischer Ebene ist vorgesehen, für diesen Luftinhaltsstoff einen Grenzwert als Jahresmittelwert festzulegen. Deshalb wird bei bei der Normungsbehörde CEN zurzeit eine Europäische Norm für diesen Stoff erarbeitet. Aus der Literatur ist bekannt, dass für Benzo[a]pyren eine Querempfindlichkeit gegen Ozon und NO2 besteht. Im Zuge der Neuentwicklung eines Probenahmekopfs (PNK) für PAK-Immissionsmessungen, der durch den Einsatz eines Ozon- Scrubbers eine ozonfreie Immissionsmessung der Benzo[a]pyren-Konzentration ermög licht, wurde in dieser Arbeit die prinzipielle Einsetzbarkeit dieses Probe nahmekopfs geprüft. Zu diesem Zweck wurden Voruntersuchungen und Feldversuche durchgeführt, mit dem Ziel, Kenntnisse über die Ozon-Querempfindlichkeit zu erhalten. Um die Ozon-Querempfindlichkeit bei der Benzo[a]pyren-Bestimmung zu studieren, wurde Ozon in den Ansaugbereich der Probenahme dosiert. Als Ergebnis der Untersuchungen kann festgehalten werden, dass für die Benzo[a]pyren-Immissionsmessung eine deutliche Ozon-Querempfindlichkeit besteht, die unter Einsatz des neuen Ozon- Scrubbers vermieden werden kann.
This paper presents an overview of the coding aspects of a GNSS receiver. Coding allows detection and correction of channel-induced errors at the receiver, here the focus is on the mitigation of threats from malicious interferences. Although the effects of interference at different stages of GNSS baseband processing has been deeply analyzed in the literature, little attention was devoted to its impact on the navigation message decoding stage. Theis paper provides an introduction to the various coding schemes employed by current GNSS signals, discussing their performance in the presence of noise in terms of block-error rate. Additionally, the benefits of soft-decoding schemes for navigation message decoding are highlighted when jamming interferences are present. The proposed scheme requires estimating the noise plus interference power, yielding to enhanced decoding performances under severe jamming conditions. Finally, cryptographic schemes as a means of providing anti-spoofing for geosecurity location-based services, and their potential vulnerability are discussed, with particular emphasis on the dependence on the dependence of the scheme on successful navigation message decoding
Member Lens
(2013)
Im Rahmen des Kontinentalen Tiefbohrprogramms der Bundesrepublik Deutschland (KTB) wurde im September 1987 in der Oberpfalz bei Windischeschenbach mit der Vorbohrung begonnen, die im Frühjahr des letzten Jahres bei einer Tiefe von 4000m erfolgreich abgeschlossen wurde. Mit der in diesem Jahr beginnenden Hauptbohrung will man 10 bis 12km tief in das Erdinnere vorstoßen. Nicht nur anhand von Gesteins- und Flüssigkeitsproben, sondern auch mit Hilfe von Meßsonden werden umfangreiche geophysikalische Daten gewonnen. Der Aufsatz beschreibt, wie die magnetische Suszeptibilität von Gesteinen bis ca. 300°C Umgebungstemperatur und einem Druck von 2kbar gemessen wird und die Daten über ein 14km langes Bohrlochkabel von der Sonde zum Steuerrechner übertragen werden.
Aqueous lithium–oxygen batteries are promising candidates for electric energy storage. In this paper we present and discuss a multiphase continuum model of an aqueous lithium–oxygen single cell including reactions and transport in a porous gas diffusion electrode (GDE). The model is parameterized using in-house half-cell experiments and available literature data on aqueous electrolytes. We validate our transport model with cyclic voltammetry and electrochemical impedance spectroscopy measurements over a wide range of temperatures (25, 40, 55 °C) and electrolyte concentrations (0.1–2 M). We observe very good agreement between simulations and measurements during oxygen reduction conditions. A sensitivity analysis of the validated model demonstrates the influence of the porous structure on GDE performance and gives directions for the future development of electrodes.
The structure of the separation bubble that appears in the secondary meridional flow between two coaxially rotating spheres at low and finite Reynolds number (Re) is considered. The low Re analytical study was motivated by recognizing some errors in the analytical work on this problem by Arunachalam and Majhi (1987, Q. Jl Mech. Appl. Math., 40, 47) whilst the finite Re experimental study was motivated by the desire to observe the separation bubble in the laboratory. Though the finite Re experiments were performed in a confined apparatus, they exhibit the qualitative features of the low Re theoretical predictions for the axisymmetric separation bubble that encloses two toroidal vortices symmetrically disposed above and below the mid‐plane of sphere separation, but strong effects of confinement are apparent. The flows observed include (i) a wall‐attached bubble symmetric about the mid‐plane at low Re, (ii) symmetric free‐standing bubbles at moderate Re, and (iii) an asymmetric bubble with flow separating from one sphere and attaching to the support shaft between the spheres at sufficiently high Re.
In this work the adsorption of CO2 and CH4 on a series of isoreticular microporous metal–organic frameworks based on 2-substituted imidazolate-4-amide-5-imidates, IFP-1–IFP-6 (IFP = Imidazolate Framework Potsdam), is studied firstly by pure gas adsorption at 273 K. All experimental isotherms can be nicely described by using the Tòth isotherm model and show the preferred adsorption of CO2 over CH4. At low pressures the Tòth isotherm equation exhibits a Henry region, wherefore Henry's law constants for CO2 and CH4 uptake could be determined and ideal selectivity αCO2/CH4 has been calculated. Secondly, selectivities were calculated from mixture data by using nearly equimolar binary mixtures of both gases by a volumetric–chromatographic method to examine the IFPs. Results showed the reliability of the selectivity calculation. Values of αCO2/CH4 around 7.5 for IFP-5 indicate that this material shows much better selectivities than IFP-1, IFP-2, IFP-3, IFP-4 and IFP-6 with slightly lower selectivity αCO2/CH4 = 4–6. The preferred adsorption of CO2 over CH4 especially of IFP-5 and IFP-4 makes these materials suitable for gas separation application.
On the Fundamental and Practical Aspects of Modeling Complex Electrochemical Kinetics and Transport
(2018)
Numerous technologies, such as batteries and fuel cells, depend on electrochemical kinetics. In some cases, the responsible electrochemistry and charged-species transport is complex. However, to date, there are essentially no general-purpose modeling capabilities that facilitate the incorporation of thermodynamic, kinetic, and transport complexities into the simulation of electrochemical processes. A vast majority of the modeling literature uses only a few (often only one) global charge-transfer reactions, with the rates expressed using Butler–Volmer approximations. The objective of the present paper is to identify common aspects of electrochemistry, seeking a foundational basis for designing and implementing software with general applicability across a wide range of materials sets and applications. The development of new technologies should be accelerated and improved by enabling the incorporation of electrochemical complexity (e.g., multi-step, elementary charge-transfer reactions and as well as supporting ionic and electronic transport) into the analysis and interpretation of scientific results. The spirit of the approach is analogous to the role that Chemkin has played in homogeneous chemistry modeling, especially combustion. The Cantera software, which already has some electrochemistry capabilities, forms the foundation for future capabilities expansion.
The technique of laser ultrasonics perfectly meets the need for noncontact, noninvasive, nondestructive mechanical probing of nanometer- to millimeter-size samples. However, this technique is limited to the excitation of low-amplitude strains, below the threshold for optical damage of the sample. In the context of strain engineering of materials, alternative optical techniques enabling the excitation of high-amplitude strains in a nondestructive optical regime are needed. We introduce here a nondestructive method for laser-shock wave generation based on additive superposition of multiple laser-excited strain waves. This technique enables strain generation up to mechanical failure of a sample at pump laser fluences below optical ablation or melting thresholds. We demonstrate the ability to generate nonlinear surface acoustic waves (SAWs) in Nb-SrTiO3 substrates, with associated strains in the percent range and pressures up to 3 GPa at 1 kHz repetition rate and close to 10 GPa for several hundred shocks. This study paves the way for the investigation of a host of high-strain SAW-induced phenomena, including phase transitions in conventional and quantum materials, plasticity and a myriad of material failure modes, chemistry and other effects in bulk samples, thin layers, and two-dimensional materials.
Private households constitute a considerable share of Europe's electricity consumption. The current electricity distribution system treats them as effectively passive individual units. In the future, however, users of the electricity grid will be involved more actively in the grid operation and can become part of intelligent networked collaborations. They can then contribute the demand and supply flexibility that they dispose of and, as a result, help to better integrate renewable energy in-feed into the distribution grids.
Experimental and theoretical investigations of the time of equalization of the concentration of an impurity in a rectangular flow‐type chamber have been carried out. It has been shown that the process of equalization of the concentration with time is exponential in character. The characteristic equalization time has been computed using the theory of turbulent diffusion. Theoretical results describe experimental regularities with an accuracy of about 10%. The value of the coefficient of turbulent diffusion for different configurations of flows in the chamber has been obtained from a comparison of experimental and calculated results.
The Humboldt Portal has been designed and implemented as part of an ongoing research project to develop an information system on the Internet to share the documents and rare books of Alexander von Humboldt, a 19th century German scientist and explorer, who viewed the natural world holistically and described the harmony of nature among the diversity of the physical world. Even after more than two centuries he is admired for his ability to see the natural world and human nature in the context of a complex network of relationships. The design and implementation of the Humboldt Portal are also oriented to support further research on Humboldt’s intellectual perspective.
Although all of Humboldt's works can be found on the internet as digitized documents, the complexity and internal inter-connectivity of his vision of nature cannot be adequately represented only by digitized papers or scanned documents in digital libraries.
As a consequence a specific portal of the Humboldt's documents was developed, which extends the standards of digital libraries and offers a technical approach for the adequate presentation of highly interconnected data.
Due to the continuous scientific and literary research, new insights and requirements for the digital presentation of Humboldt documents are constantly emerging, so that this article only provides a summary of the concepts realized at now. Consequently, the design and implementation of the Humboldt Portal is both: a consequence of a continuing research project and oriented to support more research on Humboldt´s intellectual holistic perspective, which was an anticipation to the System Approach of the last Century.
The Humboldt digital library (HDL) represents an innovative system to access the works and legacy of Alexander von Humboldt in a digital form on the Internet (www.avhumboldt.net). It contributes to the key question about how to present interconnected data in an appropriate form using information technologies. The HDL has been created as a dynamic digital library with the capability of connecting multilingual and multimedia data from diverse online archives. Humboldt’s volumes have become available, but beyond that any relevant information related to the observations of Humboldt, even outside the works can become immediately accessible. This makes it possible to recognize natural changes and compare Humboldt’s descriptions with recent situations. The technology we have developed addresses the issues of sustainability and makes it possible to detect changes in the environment since the time of Humboldt’s observations.
Automatic Identification of Travel Locations in Rare Books - Object Oriented Information Management
(2017)
The digital content of the Internet is growing exponentially and mass digitization of printed media opens access to literature, in particular the genre of travel literature from the 18th and 19th century, which consists of diaries or travel books describing routes, observations or inspirations. The identification of described locations in the digital text is a long-standing challenge which requires information technology to supply dynamic links to sources by new forms of interaction and synthesis between humanistic texts and scientific observations.
Using object oriented information technology, a prototype of a software tool is developed which makes it possible to automatically identify geographic locations and travel routes mentioned in rare books. The information objects contain properties such as names and classification codes for populated places, streams, mountains and regions. Together, with the latitudes and longitudes of every single location, it is possible to geo-reference this information in order that all processed and filtered datasets can be displayed by a map application. This method has already been used in the Humboldt Digital Library to present Alexander von Humboldt’s maps and was tested in a case study to prove the correctness and reliability of the automatic identification of locations based on the work of Alexander von Humboldt and Johann Wolfgang von Goethe.
The results reveal numerous errors due to misspellings, change of location names, equality of terms and location names. But on the other hand it becomes very clear that results of the automatic object detection and recognition can be improved by error-free and comprehensive sources. As a result an increase in quality and usability of the service can be expected, accompanied by more options to detect unknown locations in the descriptions of rare books.
In the 19th century Alexander von Humboldt explored the nature and was conceived a new vision of nature that still influences the way we understand the new world. Humboldt believed in the importance of accurate measurements and precise description of observations. His vision of nature included not only facts but also emotions.
Nowadays smart solutions will be developed by using computer technology, which will influence our relationship to nature, our handling of the complexity and diversity of nature itself and the technological influences on the society. Could we avoid a new form of “Colonialism”, when a network of super computers will create a smarter world?
To do justice to the legacy of Alexander von Humboldt, a 19th century German scientist and explorer an information and knowledge management system is required to preserve the author’s original intent and promote an awareness of all his relevant works. Although all of Humboldt's works can be found on the internet as digitized papers, the complexity and internal interconnectivity of the writings is not very transparent. Humboldt's concepts of interaction cannot be adequately represented only by digitized papers or scanned documents.
The Humboldt Portal is an attempt to create a new generation of digital libraries, providing a new form of interaction and synthesis between humanistic texts and scientific observation. The digital version of his documents supplies dynamic links to sources, maps, images, graphs and relevant texts in accordance with his visions, because “everything is interconnectedness”.
In rural low voltage grid networks, the use of battery in the households with a grid connected Photovoltaic (PV) system is a popular solution to shave the peak PV feed-in to the grid. For a single electricity price scenario, the existing forecast based control approaches together with a decision based control layer uses weather and load forecast data for the on–off schedule of the battery operation. These approaches do bring cost benefit from the battery usage. In this paper, the focus is to develop a Model Predictive Control (MPC) to maximize the use of the battery and shave the peaks in the PV feed-in and the load demand. The solution of the MPC allows to keep the PV feed-in and the grid consumption profile as low and as smooth as possible. The paper presents the mathematical formulation of the optimal control problem along with the cost benefit analysis . The MPC implementation scheme in the laboratory and experiment results have also been presented. The results show that the MPC is able to track the deviation in the weather forecast and operate the battery by solving the optimal control problem to handle this deviation.
Die Analyse von Engpässen im Güterverkehr ist eine wichtige Voraussetzung, um zukünftige Heraus-forderungen der Infrastrukturplanung und Logistik bewältigen zu können. Im Rahmen des EU-Projekts Code24 sollen Strategien für die Behandlung zukünftiger Herausforderungen im Schienengüterverkehr im wichtigsten europäischen Güterverkehrskorridor Rotterdam-Genua entwickelt werden. Hierfür sind Infor-mationen über Zugzahlen und die Kapazitätsauslastung auf einzelnen Streckenabschnitten eine wichtige Voraussetzung.
Interpreting seismic data requires the characterization of a number of key elements such as the position of faults and main reflections, presence of structural bodies, and clustering of areas exhibiting a similar amplitude versus angle response. Manual interpretation of geophysical data is often a difficult and time-consuming task, complicated by lack of resolution and presence of noise. In recent years, approaches based on convolutional neural networks have shown remarkable results in automating certain interpretative tasks. However, these state-of-the-art systems usually need to be trained in a supervised manner, and they suffer from a generalization problem. Hence, it is highly challenging to train a model that can yield accurate results on new real data obtained with different acquisition, processing, and geology than the data used for training. In this work, we introduce a novel method that combines generative neural networks with a segmentation task in order to decrease the gap between annotated training data and uninterpreted target data. We validate our approach on two applications: the detection of diffraction events and the picking of faults. We show that when transitioning from synthetic training data to real validation data, our workflow yields superior results compared to its counterpart without the generative network.
The high frequency (HF) catheter ablation is the gold standard for the therapy of many cardiac tachyarrhythmias, such as atrioventricular node re-entry tachycardia (AVNRT), atrioventricular re-entry tachycardia (AVRT) or atrial flutter (AFL). The aim of the study was to simulate the HF ablation of AVNRT, AVRT, AFL and its heat propagation in reference to the supplied power with different electrode material and electrode size. The modeling and simulation were performed with the thermal and electromagnetic simulation software CST® (Computer Simulation Technology, Darmstadt). The modeling and simulation were carried out using ablation catheters with 4 mm tip electrode and 8 mm tip electrode with different electrode materials. Both electrode types were made of platinum and gold respectively. For the measurement of the heat propagation in the heart tissue, the catheters were integrated in the Offenburg heart rhythm model. The HF ablation procedures were performed with the 4 mm platinum tip electrode, with an application duration of 45 seconds and a power output of 40 watts. The HF ablation of the atrioventricular node slow pathway produced a maximum temperature of 66.33 °C. The Kent bundle HF ablation in the left atrium achieved a maximum temperature of 67.14 °C. The HF ablation of the right atrial isthmus resulted 65.96 °C. The 8 mm distal platinum tip electrode and a power output of 60 watts reached 72.85 °C. The 8 mm distal gold tip electrode and a power output of 60 watt reached 64.66 °C, due to the improved thermal conductivity of gold. Virtual heart and ablation electrode models allow the static and dynamic simulation of HF ablation with different electrode material and electrode size. The 3D simulation of the temperature profile may be used to optimize the AVNRT, AVRT and AFL HF ablation.
We present a planar chromatographic separation method for the compounds caffeine, artemisinin, and equol, separated on high-performance thin-layer chromatography (HPTLC) silica gel plates. As solvents for separation, methyl t-butyl ether and cyclohexane (1:1, V/V) have been used for equol, cyclohexane and ethyl acetate (7:3, V/V) for artemisinin, and ethyl acetate and acetone (7:3, V/V) for caffeine. After separation, the plate was scanned with a very specific time of flight-direct analysis in real time-mass spectrometry (TOF-DART-MS) system using the (M + 1)+ signals of equol, artemisinin, and caffeine. The (M + 1) peak of artemisinin at 283.13 m/z is clearly detectable, which is the proof that DART-MS is applicable for the quantitative determination of rather instable molecules. The planar set-up of DART source, HPTLC plate and detector inlet in a line showed higher sensitivities compared to desorption at an angle. The optimal detector voltage increases with the molar mass of the analyte, thus an individual determination of optimal detector voltage setting for the different analyte is recommended to achieve the best possible measurement conditions. In conclusion, DART-MS detection in combination with an HPTLC separation allows very specific quantification of all three compounds.
Background: R-wave synchronised atrial pacing is an effective temporary pacing
therapy in infants with postoperative junctional ectopic tachycardia. In the technique
currently used, adverse short or long intervals between atrial pacing and ventricular
sensing (AP–VS) may be observed during routine clinical practice.
Objectives: The aim of the study was to analyse outcomes of R-wave synchronised
atrial pacing and the relationship between maximum tracking rates and AP–VS
intervals.
Methods: Calculated AP–VS intervals were compared with those predicted by experienced
pediatric cardiologist.
Results: A maximum tracking rate (MTR) set 10 bpm higher than the heart rate (HR)
may result in undesirable short AP–VS intervals (minimum 83 ms). A MTR set 20 bpm
above the HR is the hemodynamically better choice (minimum 96 ms). Effects of either
setting on the AP–VS interval could not be predicted by experienced observers. In our
newly proposed technique the AP–VS interval approaches 95 ms for HR > 210 bpm
and 130 ms for HR < 130 bpm. The progression is linear and decreases strictly
(− 0.4 ms/bpm) between the two extreme levels.
Conclusions: Adjusting the AP–VS interval in the currently used technique is complex
and may imply unfavorable pacemaker settings. A new pacemaker design is advisable
to allow direct control of the AP–VS interval.
Printed electronics (PE) circuits have several advantages over silicon counterparts for the applications where mechanical flexibility, extremely low-cost, large area, and custom fabrication are required. The custom (personalized) fabrication is a key feature of this technology, enabling customization per application, even in small quantities due to low-cost printing compared with lithography. However, the personalized and on-demand fabrication, the non-standard circuit design, and the limited number of printing layers with larger geometries compared with traditional silicon chip manufacturing open doors for new and unique reverse engineering (RE) schemes for this technology. In this paper, we present a robust RE methodology based on supervised machine learning, starting from image acquisition all the way to netlist extraction. The results show that the proposed RE methodology can reverse engineer the PE circuits with very limited manual effort and is robust against non-standard circuit design, customized layouts, and high variations resulting from the inherent properties of PE manufacturing processes.
Printed electronics (PE) is a fast-growing field with promising applications in wearables, smart sensors, and smart cards, since it provides mechanical flexibility, and low-cost, on-demand, and customizable fabrication. To secure the operation of these applications, true random number generators (TRNGs) are required to generate unpredictable bits for cryptographic functions and padding. However, since the additive fabrication process of the PE circuits results in high intrinsic variations due to the random dispersion of the printed inks on the substrate, constructing a printed TRNG is challenging. In this article, we exploit the additive customizable fabrication feature of inkjet printing to design a TRNG based on electrolyte-gated field-effect transistors (EGFETs). We also propose a printed resistor tuning flow for the TRNG circuit to mitigate the overall process variation of the TRNG so that the generated bits are mostly based on the random noise in the circuit, providing a true random behavior. The simulation results show that the overall process variation of the TRNGs is mitigated by 110 times, and the generated bitstream of the tuned TRNGs passes the National Institute of Standards and Technology - Statistical Test Suite. For the proof of concept, the proposed TRNG circuit was fabricated and tuned. The characterization results of the tuned TRNGs prove that the TRNGs generate random bitstreams at the supply voltage of down to 0.5 V. Hence, the proposed TRNG design is suitable to secure low-power applications in this domain.
Printed electronics (PE) enables disruptive applications in wearables, smart sensors, and healthcare since it provides mechanical flexibility, low cost, and on-demand fabrication. The progress in PE raises trust issues in the supply chain and vulnerability to reverse engineering (RE) attacks. Recently, RE attacks on PE circuits have been successfully performed, pointing out the need for countermeasures against RE, such as camouflaging. In this article, we propose a printed camouflaged logic cell that can be inserted into PE circuits to thwart RE. The proposed cell is based on three components achieved by changing the fabrication process that exploits the additive manufacturing feature of PE. These components are optically look-alike, while their electrical behaviors are different, functioning as a transistor, short, and open. The properties of the proposed cell and standard PE cells are compared in terms of voltage swing, delay, power consumption, and area. Moreover, the proposed camouflaged cell is fabricated and characterized to prove its functionality. Furthermore, numerous camouflaged components are fabricated, and their (in)distinguishability is assessed to validate their optical similarities based on the recent RE attacks on PE. The results show that the proposed cell is a promising candidate to be utilized in camouflaging PE circuits with negligible overhead.
Advances in printed electronics (PE) enables new applications, particularly in ultra-low-cost domains. However, achieving high-throughput printing processes and manufacturing yield is one of the major challenges in the large-scale integration of PE technology. In this article, we present a programmable printed circuit based on an efficient printed lookup table (pLUT) to address these challenges by combining the advantages of the high-throughput advanced printing and maskless point-of-use final configuration printing. We propose a novel pLUT design which is more efficient in PE realization compared to existing LUT designs. The proposed pLUT design is simulated, fabricated, and programmed as different logic functions with inkjet printed conductive ink to prove that it can realize digital circuit functionality with the use of programmability features. The measurements show that the fabricated LUT design is operable at 1 V.
Energy efficiency and hygrothermal performance of hemp clay walls for Moroccan residential buildings
(2023)
Hemp-based building envelopes have gained significant popularity in developed countries, and now the trend of constructing houses with hemp-clay blocks is spreading to developing countries like Morocco. Investigating the hygrothermal behavior of such structures under actual climate conditions is essential for advancing and promoting this sustainable practice. This paper presents an in-depth experimental characterization of a commercial hemp-clay brick that has been exposed to the outdoor environment for four years, in addition to field measurements on a building scale demonstration prototype. Additionally, the study simulates 17 representative cities to assess the hygrothermal performance and energy-saving potential in each of Morocco's six existing climate zones, using the EnergyPlus engine. The experimental campaign's findings demonstrate excellent indoor air temperature and relative humidity regulation within the hemp-clay wall building, leading to satisfactory levels of thermal comfort within hemp-clay wall buildings. This is attributed to the material's good thermal conductivity and excellent moisture buffering capacity (found to be 0.31 W/mK and 2.25 g/m2%RH), respectively). The energy simulation findings also point to significant energy savings, with cooling and heating energy reductions ranging from 27.7% to 47.5% and 33.7% to 79.8%, respectively, as compared to traditional Moroccan buildings.
Economic growth is usually driven by improvements in productivity, economic efficiency, trade and innovation. Increasing efficiency means to produce larger output using the same amount of factors for production such as raw materials, labour, and capital. However, regardless of the driver, growth is often investment-hungry and it is not rare to find an economy with potential for growth but lacking locally available investment. In this scenario, Foreign Direct Investment (FDI) can fill the gap between investment needed to promote economic growth and locally available investments.
This review provides an overview on the production and analysis techniques of antioxidative peptides from food proteins. Regarding the production of antioxidative peptides, interlinked factors must be considered. Depending on the protein substrate, different peptidases or peptidase systems containing multiple enzymes as well as a specific production process must be chosen. The antioxidative peptides might be produced in a batch process including multiple pre- and post-treatments, besides the hydrolyses with peptidases itself. As an alternative, the potential of continuous production systems is discussed in this review. Furthermore, robust analyses tools are needed to gain control of the process and final product properties. With no standardized methodology available for antioxidative peptide evaluation, pros and cons of various strategies for peptide separation and antioxidative measurement are discussed in this review. Therefore, this review provides a roadmap for antioxidative peptide generation from various sources for research and development as well as for potential industrial use.
Properties of higher-order surface acoustic wave modes in Al(1-x)Sc(x)N / sapphire structures
(2021)
In this work, surface acoustic wave (SAW) modes and their dependence on propagation directions in epitaxial Al0.68Sc0.32N(0001) films on Al2O3(0001) substrates were studied using numerical and experimental methods. In order to find optimal propagation directions for higher-order SAW modes, phase velocity dispersion branches of Al0.68Sc0.32N on Al2O3 with Pt mass loading were computed for the propagation directions <11-20> and <1-100> with respect to the substrate. Experimental investigations of phase velocities and electromechanical coupling were performed for comparison with the numerical results. Simulations carried out with the finite element method (FEM) and with a Green function approach allowed identification of each wave type, including Rayleigh, Sezawa and shear horizontal wave modes. For the propagation direction <1-100>, significantly increased wave guidance of the Sezawa mode compared to other directions was observed, resulting in enhanced electromechanical coupling (k2eff = 1.6 %) and phase velocity (vphase = 6 km/s). We demonstrated, that selecting wave propagation in <1-100> with high mass density electrodes results in increased electromechanical coupling without significant reduction in phase velocities for the Sezawa wave mode. An improved combination of metallization, Sc concentration x, and SAW propagation direction is suggested which exhibits both high electromechanical coupling (k2eff > 6 %) and high velocity (vphase = 5.5 km/s) for the Sezawa mode.
Cellular phone antennas are generally designed to have radiation patterns that are as omnidirectional as possible. Omnidirectional antennas allow a phone’s radio to work well for many orientations of the phone with respect to the cellular base station. Recent studies, however, are generating uncertainty about the health effects of prolonged exposure to electromagnetic (EM) radiation from cellular phones. In this paper, an antenna array is designed primarily to minimize users’ exposure to EM radiation. The antenna comprises a beamforming 4 by 3 array of microstrip patch antennas that is controlled by an accelerometer-only inertial navigation system. The proposed design reduces radiated power directed toward the user to below 10% of the total in the worst case.
Printed electronics can benefit from the deployment of electrolytesas gate insulators,which enables a high gate capacitance per unit area (1–10 μFcm−2) due to the formation of electrical double layers (EDLs). Consequently, electrolyte-gated field-effect transistors (EGFETs) attain high-charge carrier densities already in the subvoltage regime, allowing for low-voltage operation of circuits and systems. This article presents a systematic study of lumped terminal capacitances of printed electrolyte-gated transistors under various dc bias conditions. We perform voltage-dependent impedancemeasurements and separate extrinsic components from the lumped terminal capacitance.
The proposed Meyer-like capacitance model, which also accounts for the nonquasi-static (NQS) effect, agrees well with experimental data. Finally, to verify the model, we implement it in Verilog-A and simulate the transient response of an inverter and a ring oscillator circuit. Simulation results are in good agreement with the measurement data of fabricated devices.
Electrolyte-gated, printed field-effect transistors exhibit high charge carrier densities in the channel and thus high on-currents at low operating voltages, allowing for the low-power operation of such devices. This behavior is due to the high area-specific capacitance of the device, in which the electrolyte takes the role of the dielectric layer of classical architectures. In this paper, we investigate intrinsic double-layer capacitances of ink-jet printed electrolyte-gated inorganic field-effect transistors in both in-plane and top-gate architectures by means of voltage-dependent impedance spectroscopy. By comparison with deembedding structures, we separate the intrinsic properties of the double-layer capacitance at the transistor channel from parasitic effects and deduce accurate estimates for the double-layer capacitance based on an equivalent circuit fitting. Based on these results, we have performed simulations of the electrolyte cutoff frequency as a function of electrolyte and gate resistances, showing that the top-gate architecture has the potential to reach the kilohertz regime with proper optimization of materials and printing process. Our findings additionally enable accurate modeling of the frequency-dependent capacitance of electrolyte/ion gel-gated devices as required in the small-signal analysis in the circuit simulation.
Rectifiersare vital electronic circuits for signal and power conversion in various smart sensor applications. The ability to process low input voltage levels, for example, from vibrational energy harvesters is a major challenge with existing passive rectifiers in printed electronics, stemming mainly from the built-in potential of the diode's p-njunction. To address this problem, in this work, we design, fabricate, and characterize an inkjet-printed full-wave rectifier using diode-connected electrolyte-gated thin-film transistors (EGTs). Using both experimental and simulation approaches, we investigate how the rectifier can benefit from the near-zero threshold voltage of transistors, which can be enabled by proper channel geometry setting in EGT technology. The presented circuit can be operated at 1-V input voltage, featuring a remarkably small voltage loss of 140 mV and a cutoff frequency of ~300 Hz. Below the cutoff frequency, more than 2.6-μW dc power is obtained over the load resistances ranging from 5 to 20 kQ. Furthermore, experiments show that the circuit can work with an input amplitude down to 500 mV. This feature makes the presented design highly suitable for a variety of energy-harvesting applications.
An analytical and numerical study of the wobbling dynamics of friction disks is presented. Of particular interest is the excitation mechanism taking into account two contrarian effects both originating in dry friction: the circulatory terms describing the energy input due to the sliding contacts and the friction induced damping which stabilizes the system. Balance of these terms determines the instability domain in the parameter space. It is shown that there is a slip threshold so that, if the slip is under this limit, the system remains stable. If the slip is larger than this limit, then the criterion of stability is determined by the relation between the friction coefficient and the internal damping. The limit cycle appearing in the unstable domain is also investigated. It is shown that the limit cycle can be described as a kind of a regular reverse precession of the wobbling disc. Its amplitude is limited by the geometric nonlinearity and partial contact loss. Analytic results are compared with numeric simulations.
In the present paper, the influence of locally varying microstructures in case of an AlSi12 cast aluminium alloy is investigated by means of extracting the test pieces from different removal positions and low cycle fatigue tests. The temperature-dependent damage mechanisms, the material specific defect types, sizes and their influence on the fatigue properties of two AlSi7 and AlSi12 cast aluminium alloys are studied. An extreme value statistics methodology is applied to predict maximum defect sizes expected in a critical surface volume from two-dimensional metallographic micrographs. A damage map for the AlSi12 cast aluminium alloy is presented explaining the influence of the temperature- and load-dependent damage mechanisms on the observed isothermal and thermomechanical lifetime behavior.
Detailed material investigations of the fatigue behavior of two cast aluminium alloys used in combustion engines are presented. The network of intermetallic phases of both aluminium alloys is characterized by means of detailed energy dispersive X-ray spectroscopy. In order to investigate the temperature-dependent fatigue behavior of the materials, tensile, low cycle and thermomechanical fatigue tests are performed over a wide temperature and loading range. The influence of the temperature dependence on the experimental results is discussed.
In this work, the influence of superimposed high cycle fatigue on the LCF/HCF and TMF/HCF lifetime is investigated for two cast aluminium alloys of the types AlSi7 and AlSi12. The replica technique is used to examine the short crack growth behavior under pure LCF and LCF/HCF loading. The observed short crack growth evolution explains the observed lifetime reduction with increasing HCF amplitudes.
In this paper fatigue crack closure under in-phase and out-of-phase thermomechanical fatigue (TMF) loading is studied using a temperature dependent strip yield model. It is shown that fatigue crack closure is strongly influenced by the phase relation between mechanical loading and temperature, if the temperature difference goes along with a temperature dependence of the yield stress. In order to demonstrate the effect of the temperature dependent yield stress, the influence of in-phase and out-of-phase TMF loading is studied for a polycrystalline nickel-base superalloy. By using a mechanism based lifetime model, implications for fatigue lives are demonstrated.
A crack opening stress equation for in-phase and out-of-phase thermomechanical fatigue loading
(2016)
In this paper, a crack opening stress equation for in-phase and out-of-phase thermomechanical fatigue (TMF) loading is proposed. The equation is derived from systematic calculations of the crack opening stress with a temperature dependent strip yield model for both plane stress and plane strain, different load ratios and different ratios of the temperature dependent yield stress in compression and tension. Using a load ratio scaled by the ratio of the yield stress in compression and tension, the equation accounts for the effect of the temperature dependent yield stress and the constraint on the crack opening stress. Based on the scaling relation established in this paper, Newman's crack opening stress equation for isothermal loading is enabled to predict the crack opening stress under TMF loading.
This paper treats the interaction between acoustic modes and light (Brillouin scattering) in a single mode optical fibre. Different observed spectra of the Brillouin backscattering in several fibres have been already reported. In order to have a clear idea of the process, we made a simulation to be able to `draw' the theoretical Brillouin spectrum of an optical fibre and to identify the origin of the observed backscattered lines.
First, the model and the computation method used in our simulation are described. Second, the experimentally observed spectra of two real fibres are compared with their computed spectra. Real spectra and simulated spectra are in good agreement.
Our work provides an interesting tool to investigate the changes in the Brillouin spectrum when the input parameters (characteristics of an optical fibre) vary. This should give useful indications to people working on systems which use Brillouin backscattering.
Digitalisierung ist heute allgegenwärtig. Wo im Privaten bereitwillig neue digitale Tools, Apps und Funktionen genutzt werden, tun sich Unternehmen in der Umsetzung von Digitalisierungsprojekten oft schwer. Dieser Beitrag beleuchtet die Motive für Digitalisierungsvorhaben, ihre Hürden sowie die Auswirkung auf die Arbeitsbelastung von Mitarbeitenden und versucht in der Verknüpfung mit den Grundprinzipien des Kontinuierlichen Verbesserungsprozesses, Handlungsempfehlungen für eine erfolgreiche Umsetzung dieser abzuleiten.
In this work the nonlinear behavior of layered surface acoustic wave (SAW) resonators is studied with the help of finite element (FE) computations. The full calculations depend strongly on the availability of accurate tensor data. While there are accurate material data for linear computations, the complete sets of higher-order material constants, needed for nonlinear simulations, are still not available for relevant materials. To overcome this problem, scaling factors were used for each available nonlinear tensor. The approach here considers piezoelectricity, dielectricity, electrostriction, and elasticity constants up to the fourth order. These factors act as a phenomenological estimate for incomplete tensor data. Since no set of fourth-order material constants for LiTaO3 is available, an isotropic approximation for the fourth-order elastic constants was applied. As a result, it was found that the fourth-order elastic tensor is dominated by one-fourth order Lamé constant. With the help of the FE model, derived in two different, but equivalent ways, we investigate the nonlinear behavior of a SAW resonator with a layered material stack. The focus was set to third-order nonlinearity. Accordingly, the modeling approach is validated using measurements of third-order effects in test resonators. In addition, the acoustic field distribution is analyzed.
Bislang gibt es keine Güterstraßenbahnsysteme, die im urbanen Warentransport im Realbetrieb eingesetzt werden. Bestehende Konzepte sind auf einzelne Branchen, ausgewählte Transportgüter oder einzelne Verlader ausgerichtet. Untersuchungen zu Güterstraßenbahnprojekten konzentrieren sich auf individuelle Kunden (zum Beispiel "CarGo Tram" Dresden). Für die Realisierung einer Güterstraßenbahn im urbanen Raum wäre zu klären, welche Anforderungen potenzielle Nutzer haben und wie diese Anforderungen in ein logistisches Konzept integriert werden können. In einer multiplen Fallstudie werden drei Unternehmen aus verschiedenen Branchen analysiert. Aufgrund heterogener Anforderungen wird ein modulares Logistikkonzept vorgeschlagen. Der Beitrag entstand im Rahmen des Projektes "LogIKTram: Logistikkonzept und IKT-Plattform für stadtbahnbasierten Gütertransport".
The instability of ultra-thin films of an electrolyte bordering a dielectric gas in an external tangential electric field is scrutinized. The solid wall is assumed to be either a conducting or charged dielectric surface. The problem has a steady one-dimensional solution. The theoretical results for a plug-like velocity profile are successfully compared with available experimental data. The linear stability of the steady-state flow is investigated analytically and numerically. Asymptotic long-wave expansion has a triple-zero singularity for a dielectric wall and a quadruple-zero singularity for a conducting wall, and four (for a conducting wall) or three (for a charged dielectric wall) different eigenfunctions. For infinitely small wave numbers, these eigenfunctions have a clear physical meaning: perturbations of the film thickness, of the surface charge, of the bulk conductivity, and of the bulk charge. The numerical analysis provides an important result: the appearance of a strong short-wave instability. At increasing Debye numbers, the short-wave instability region becomes isolated and eventually disappears. For infinitely large Weber numbers, the long-wave instability disappears, while the short-wave instability persists. The linear stability analysis is complemented by a nonlinear direct numerical simulation. The perturbations evolve into coherent structures; for a relatively small external electric field, these are large-amplitude surface solitary pulses, while for a sufficiently strong electric field, these are short-wave inner coherent structures, which do not disturb the surface.
Diese Arbeit beschäftigt sich mit der Biomechanik der Halswirbelsäule (HWS) beim Umgang mit dem Smartphone. Die Kräfte, die auf Wirbelkörper, Wirbelgelenke, Bandscheiben, Muskeln und Bänder wirken, werden mit steigendem Flexionswinkel der HWS größer. Die Beschwerden hingegen, welche der Smartphone-Nacken hervorruft, sind meist akut und mit regelmäßiger Bewegung und der Stärkung der Nackenmuskulatur gut zu behandeln. Eine Therapie ist somit auch zur Vorbeugung geeignet. Doch die Langzeitauswirkungen sind nicht außer Acht zu lassen, denn durch die steigenden Nutzungsmöglichkeiten der Smartphones steigt auch der durchschnittliche tägliche Gebrauch stärker an. So wird vor allem die tägliche Bildschirmzeit bei Jugendlichen immer länger. Das aktuell noch akute Krankheitsbild des Smartphone-Nackens, das nur selten einen chronischen Verlauf nimmt und Langzeitschäden verursacht, könnte sich durch fehlende oder zu späte Maßnahmen zu einem größeren chronischen Krankheitsbild entwickeln.
Oxide semiconductors are highly promising candidates for the most awaited, next-generation electronics, namely, printed electronics. As a fabrication route for the solution-processed/printed oxide semiconductors, photonic curing is becoming increasingly popular, as compared to the conventional thermal curing method; the former offers numerous advantages over the latter, such as low process temperatures and short exposure time and thereby, high throughput compatibility. Here, using dissimilar photonic curing concepts (UV–visible light and UV-laser), we demonstrate facile fabrication of high performance In2O3 field-effect transistors (FETs). Beside the processing related issues (temperature, time etc.), the other known limitation of oxide electronics is the lack of high performance p-type semiconductors, which can be bypassed using unipolar logics from high mobility n-type semiconductors alone. Interestingly, here we have found that our chosen distinct photonic curing methods can offer a large variation in threshold voltage, when they are fabricated from the same precursor ink. Consequently, both depletion and enhancement-mode devices have been achieved which can be used as the pull-up and pull-down transistors in unipolar inverters. The present device fabrication recipe demonstrates fast processing of low operation voltage, high performance FETs with large threshold voltage tunability.
Surface treatment intensity monitoring is still an open and challenging nondestructive testing problem. For the estimation of residual stress with ultrasonic measurements, local linear and nonlinear elastic constants are needed as input. In this paper, nonlinear elastic-wave interactions (also called wave mixing or scattering) — namely, the generation of secondary ultrasonic waves in a nonlinear medium — are considered as a prospective means for near-surface nonlinear elastic parameter evaluation. The allowed interactions between bulk and surface waves, as well as the dependence of the scattering efficiency on the frequency and angle between source waves, were investigated through an analytical model, then compared with FEM simulations and experimental results. Finally, possible future steps for the development of the applied methods for the determination of near-surface higher-order elastic constants are discussed. In addition, several problem-relevant data processing procedures are presented.
This work compares the performance of Bluetooth Mesh implementations on real chipsets against the ideal implementation of the specification. Measurements are taken in experimental settings and reveal non-idealities in the underlying Bluetooth Low Energy specification in real chipsets and in the implementation of Mesh, which introduces an unruly transmission as well as reception behavior. These effects lead to an impact on transmission rate, reception rate, latency, as well as a more significant impact on the average power consumption.
We revisit the quantitative analysis of the ultrafast magnetoacoustic experiment in a freestanding nickel thin film by Kim and Bigot [J.-W. Kim and J.-Y. Bigot, Phys. Rev. B 95, 144422 (2017)] by applying our recently proposed approach of magnetic and acoustic eigenmode decomposition. We show that the application of our modeling to the analysis of time-resolved reflectivity measurements allows for the determination of amplitudes and lifetimes of standing perpendicular acoustic phonon resonances with unprecedented accuracy. The acoustic damping is found to scale as ∝ω2 for frequencies up to 80 GHz, and the peak amplitudes reach 10−3. The experimentally measured magnetization dynamics for different orientations of an external magnetic field agrees well with numerical solutions of magnetoelastically driven magnon harmonic oscillators. Symmetry-based selection rules for magnon-phonon interactions predicted by our modeling approach allow for the unambiguous discrimination between spatially uniform and nonuniform modes, as confirmed by comparing the resonantly enhanced magnetoelastic dynamics simultaneously measured on opposite sides of the film. Moreover, the separation of timescales for (early) rising and (late) decreasing precession amplitudes provide access to magnetic (Gilbert) and acoustic damping parameters in a single measurement.
Micro gas turbines (MGTs) are regarded as combined heat and power (CHP) units which offer high fuel utilization and low emissions. They are applied in decentralized energy neration.
To facilitate the planning process of energy systems, namely in the context of the increasing application of optimization techniques, there is a need for easy-to-parametrize component models with sufficient accuracy which allow a fast computation. In this paper, a model is proposed where the non-linear part load characteristics of the MGT are linearized by means of physical insight of the working principles of turbomachinery. Further, it is shown that the model can be parametrized by the data usually available in spec sheets. With this model a uniform description of MGTs from several manufacturers
covering an electrical power range from 30kW to 333kW can be obtained. The MGT model was
implemented by means of Modelica/Dymola. The resulting MGT system model, comprising further heat exchangers and hydraulic components, was validated using the experimental data of a 65kW MGT from a trigeneration energy system.
Polygeneration systems are a key technology for the reduction of primary energy usage and emissions. High costs, lack of flexibility and effort for parameterization hinder the wide usage of modeling tools during their conceptual design. This paper describes how planning tools can be structured for the conceptual design phase where only little information is available to the planner. A library concept was developed using the principles of object-oriented modeling to address the flexibility issue. With respect to cost and expandability, the open-source modeling language Modelica was chosen. Furthermore, easy-to-parameterize component models were developed. In addition to the improved library concept and novel component models, an easy-to-adapt control concept is proposed. The component models were validated and the applicability of the library was demonstrated by means of an example. It was shown that the data usually obtained from spec sheets are sufficient to parameterize the models. In addition to this, the control concept was approved.
Many commonly well-performing convolutional neural network models have shown to be susceptible to input data perturbations, indicating a low model robustness. To reveal model weaknesses, adversarial attacks are specifically optimized to generate small, barely perceivable image perturbations that flip the model prediction. Robustness against attacks can be gained by using adversarial examples during training, which in most cases reduces the measurable model attackability. Unfortunately, this technique can lead to robust overfitting, which results in non-robust models. In this paper, we analyze adversarially trained, robust models in the context of a specific network operation, the downsampling layer, and provide evidence that robust models have learned to downsample more accurately and suffer significantly less from downsampling artifacts, aka. aliasing, than baseline models. In the case of robust overfitting, we observe a strong increase in aliasing and propose a novel early stopping approach based on the measurement of aliasing.
Numerous 2,5-dimethoxy-N-benzylphenethylamines (NBOMe), carrying a variety of lipophilic substituents at the 4-position, are potent agonists at 5-hydroxytryptamine (5HT2A ) receptors and show hallucinogenic effects. The present study investigated the metabolism of 25D-NBOMe, 25E-NBOMe, and 25N-NBOMe using the microsomal model of pooled human liver microsomes (pHLM) and the microbial model of the fungi Cunninghamella elegans (C. elegans). Identification of metabolites was performed using liquid chromatography-high resolution-tandem mass spectrometry (LC-HR-MS/MS) with a quadrupole time-of-flight (QqToF) instrument. In total, 36 25D-NBOMe phase I metabolites, 26 25E-NBOMe phase I metabolites and 24 25N-NBOMe phase I metabolites were detected and identified in pHLM. Furthermore, 14 metabolites of 25D-NBOMe, 11 25E-NBOMe metabolites, and nine 25N-NBOMe metabolites could be found in C. elegans. The main biotransformation steps observed were oxidative deamination, oxidative N-dealkylation also in combination with hydroxylation, oxidative O-demethylation possibly combined with hydroxylation, oxidation of secondary alcohols, mono- and dihydroxylation, oxidation of primary alcohols, and carboxylation of primary alcohols. Additionally, oxidative di-O-demethylation for 25E-NBOMe and reduction of the aromatic nitro group and N-acetylation of the primary aromatic amine for 25N-NBOMe took place. The resulting 25N-NBOMe metabolites were unique for NBOMe compounds. For all NBOMes investigated, the corresponding 2,5-dimethoxyphenethylamine (2C-X) metabolite was detected. This study reports for the first time 25X-NBOMe N-oxide metabolites and hydroxylamine metabolites, which were identified for 25D-NBOMe and 25N-NBOMe and all three investigated NBOMes, respectively. C. elegans was capable of generating all main biotransformation steps observed in pHLM and might therefore be an interesting model for further studies of new psychoactive substances (NPS) metabolism.
Tryptamines can occur naturally in plants, mushrooms, microbes, and amphibians. Synthetic tryptamines are sold as new psychoactive substances (NPS) because of their hallucinogenic effects. When it comes to NPS, metabolism studies are of crucial importance, due to the lack of pharmacological and toxicological data. Different approaches can be taken to study in vitro and in vivo metabolism of xenobiotica. The zygomycete fungus Cunninghamella elegans (C. elegans) can be used as a microbial model for the study of drug metabolism. The current study investigated the biotransformation of four naturally occurring and synthetic tryptamines [N,N‐Dimethyltryptamine (DMT), 4‐hydroxy‐N‐methyl‐N‐ethyltryptamine (4‐HO‐MET), N,N‐di allyl‐5‐methoxy tryptamine (5‐MeO‐DALT) and 5‐methoxy‐N‐methyl‐N‐isoporpoyltryptamine (5‐MeO‐MiPT)] in C. elegans after incubation for 72 hours. Metabolites were identified using liquid chromatography–high resolution–tandem mass spectrometry (LC–HR–MS/MS) with a quadrupole time‐of‐flight (QqTOF) instrument. Results were compared to already published data on these substances. C. elegans was capable of producing all major biotransformation steps: hydroxylation, N‐oxide formation, carboxylation, deamination, and demethylation. On average 63% of phase I metabolites found in the literature could also be detected in C. elegans. Additionally, metabolites specific for C. elegans were identified. Therefore, C. elegans is a suitable complementary model to other in vitro or in vivo methods to study the metabolism of naturally occurring or synthetic tryptamines.
Synergieprognosen spielen bei der Begründung von Unternehmensübernahmen regelmäßig eine wichtige Rolle. Da diese Prognosen unsicher sind, bedürfen sie einer fundierten Beurteilung, was wiederum eine offene Diskussion innerhalb von Vorstand und Aufsichtsrat voraussetzt. Solche Diskussionen sind jedoch keine Selbstverständlichkeit, da Gruppen dazu neigen, problematische Entscheidungsaspekte nicht angemessen zu würdigen. Mit dem Tornado-Diagramm wird ein Instrument vorgestellt, das diesem Effekt entgegenwirkt und die Entscheider dazu motiviert, auch ungünstige Synergieprognosen zu diskutieren. Auf diese Weise kann die Übernahmeentscheidung auf eine bessere Informationsgrundlage gestellt werden.
Zielvereinbarungen sollen SMART formuliert werden, um die Leistungsbereitschaft von Mitarbeitern optimal zu fördern - so wird es zumindest in der praxisorientierten betriebswirtschaftlichen Literatur propagiert. Ob Zielvereinbarungen, die spezifisch, messbar, erreichbar, relevant für das Unternehmen und zeitlich terminiert sind, wirklich eine höhere Leistungsbereitschaft zur Folge haben, wird im Folgenden auf Basis einer empirischen Untersuchung überprüft.
Die Rolle des Aufsichtsrats wird zunehmend als eine strategische charakterisiert, ohne dies jedoch näher zu erläutern. Die aktuelle Diskussion zeigt, dass daraus Unschärfen in der Abgrenzung zur Rolle des Vorstands resultieren. In dem Beitrag wird die Rolle des Aufsichtsrats im Rahmen strategischer Entscheidungen präzisiert.
Lithium-oxygen cells with organic electrolyte suffer high overpotentials during charge, indicating asymmetric charge/discharge reaction mechanisms. We present a multi-physics dynamic modeling and simulation study of the Li/O2 cell cycling behavior. We present three different multi-step mechanisms of the 2 Li + O2 ⇄ Li2O2 cell reaction, (A) a reversible 5-step mechanism, (B) a partially irreversible 6-step mechanism, and (C) a partially irreversible 8-step mechanism that includes reactions of a redox mediator. Model predictions are compared to experimental galvanostatic cycling data of Swagelok cells without and with 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) as redox mediator. All mechanisms are able to predict the discharge behavior in good agreement to the experimental results. The experimentally observed high charge overpotentials as well as their reduction by using a redox mediator can be qualitatively reproduced with the irreversible reaction mechanisms. However, the particular shape of the experimental charge curve with continuously increasing charge overpotential cannot be reproduced with the present mechanisms.
Lithium–oxygen cells with nonaqueous electrolyte show high overpotentials during charge, indicating asymmetric charge/discharge reaction mechanisms. We present a kinetic modeling and simulation study of the lithium–oxygen cell cycling behavior. The model includes a multistep reaction mechanism of the cell reaction (2Li + O2 ⇄ Li2O2) forming lithium peroxide by precipitation, coupled to a 1D porous-electrode transport model. We apply the model to study the asymmetric discharge/charge characteristics and analyze the influence of a redox mediator dissolved homogeneously in the liquid electrolyte. Model predictions are compared to experimental galvanostatic cycling data of cells without and with 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO) as redox mediator. The predicted discharge behavior shows good agreement with the experimental results. A spatiotemporal analysis of species concentrations reveals inhomogeneous distributions of dissolved oxygen and reaction products within the cathode during discharge. The experimentally observed charge overpotentials as well as their reduction by using a redox mediator can be qualitatively reproduced with a partially irreversible reaction mechanism. However, the proposed models fail to reproduce the particular shape of the experimental charge curve with continuously increasing charge overpotential, which implies that part of the reaction mechanism is still open for investigation in future work.
Seven cell design concepts for aqueous (alkaline) lithium–oxygen batteries are investigated using a multi-physics continuum model for predicting cell behavior and performance in terms of the specific energy and specific power. Two different silver-based cathode designs (a gas diffusion electrode and a flooded cathode) and three different separator designs (a porous separator, a stirred separator chamber, and a redox-flow separator) are compared. Cathode and separator thicknesses are varied over a wide range (50 μm–20 mm) in order to identify optimum configurations. All designs show a considerable capacity-rate effect due to spatiotemporally inhomogeneous precipitation of solid discharge product LiOH·H2O. In addition, a cell design with flooded cathode and redox-flow separator including oxygen uptake within the external tank is suggested. For this design, the model predicts specific power up to 33 W/kg and specific energy up to 570 Wh/kg (gravimetric values of discharged cell including all cell components and catholyte except housing and piping).
Electrochemical impedance spectroscopy (EIS) is a widely-used diagnostic technique to characterize electrochemical processes. It is based on the dynamic analysis of two electrical observables, that is, current and voltage. Electrochemical cells with gaseous reactants or products (e.g., fuel cells, metal/air cells, electrolyzers) offer an additional observable, that is, the gas pressure. The dynamic coupling of current and/or voltage with gas pressure gives rise to a number of additional impedance definitions, for which we use the term electrochemical pressure impedance. It also gives rise to different experimental probing approaches. In this article we present a model-based study of electrochemical pressure impedance spectroscopy (EPIS). Possible quantifications and realizations of EPIS are discussed. The study of generic cell geometries consisting of gas reservoir, diffusion layer(s) and electrochemically active layer(s) reveals distinct spiral-shaped features in the Nyquist plot. Using the example of a sodium/oxygen (Na/O2) cell, the dynamic spatiotemporal behavior of the state variables is quantified and interpreted. Results are compared to first experimental EPIS measurements by Hartmann et al. [J. Phys. Chem. C118, 1461, 2014]. A sensitivity analysis highlights the properties of EPIS with respect to geometric, transport, and kinetic parameters. We demonstrate that EPIS is sensitive to transport parameters that are not well-accessible with standard EIS.
We report improved separation of the highly toxic contact herbicides paraquat, diquat, difenzoquat, mepiquat, and chloromequat by HPTLC. Quantification was based on a new derivatization reaction using sodium tetraphenylborate. Measurements were in the wavelength range from 440 to 480 nm or from 440 to 590 nm. An LED emitting very intense light at 365 nm was used for excitation. The quantification limits of paraquat and diquat in water, using improved solid-phase extraction, was in the low ng L −1 range. The linear range covered more than two orders of magnitude. Recovery was investigated for all the compounds, and was insufficient, ranging from 11 to 92%, but the method is inexpensive, rapid, and works reliably.