In this article, the fundamental suitability of the open-source hypervisor Xen for safety-critical real-time application is analyzed. In the field of avionics, satisfying criteria such as safety ...criticality and real-time capability are mandatory and pose one of the greatest challenges when developing systems and functions that are to be qualified for the installation in passenger aircraft. System architectures that additionally aspire adaptive behavior in terms of self-configuration and reconfiguration complicate these challenges even more. Spatial and temporal partitioning is a fundamental requirement for the implementation of safety-critical systems but is of static behavior in current avionic standards such as A653. Implementing a fully functional partitioning that is able to reconfigure during runtime would be a great leap forward in the field of adaptive avionics. The open-source hypervisor Xen offers features to dynamically create and manage virtual machines that natively come with architecture-related segregation. In order to determine the feasibility of Xen in the field of safety-critical real-time application, its spatial and temporal partitioning capabilities and occurring latencies are analyzed in this article. The analysis is based on specifically designed benchmarks that measure the accuracy of periodic task execution with different system load levels featuring various Xen schedulers and guest operating system kernels. The overall results for the spatial partitioning and real-time capabilities turn out to be promising but remain with minor interferences, varying based on the setup benchmarking configuration. The temporal partitioning enforced by Xen remains with clearly identified and fixable issues before a deterministic function execution in hard real time is reached.
This work is focused on the effect of pouring temperature on the thermal-microstructural response of an eutectic spheroidal graphite cast iron (SGCI). To this end, experiments as well as numerical ...simulations were carried out. Solidification tests in a wedge-like part were cast at two different pouring temperatures. Five specific locations exhibiting distinct cooling rates along the sample were chosen for temperature measurements and metallographic analysis to obtain the number and size of graphite nodules at the end of the process. The numerical simulations were performed using a multinodular-based model. Reasonably good numerical-experimental agreements were obtained for both the cooling curves and the graphite nodule counts.
The effect of heating rate on the formation and decomposition of austenite was investigated on cold-rolled low carbon steel. Experiments were performed at two heating rates, 150 °C/s and 1500 °C/s, ...respectively. The microstructures were characterized by means of scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). Experimental evidence of nucleation of austenite in α/θ, as well as in α/α boundaries is analyzed from the thermodynamic point of view. The increase in the heating rates from 150 °C/s to 1500 °C/s has an impact on the morphology of austenite in the intercritical range. The effect of heating rate on the austenite formation mechanism is analyzed combining thermodynamic calculations and experimental data. The results provide indirect evidence of a transition in the mechanism of austenite formation, from carbon diffusion control to interface control mode. The resulting microstructure after the application of ultrafast heating rates is complex and consists of a mixture of ferrite with different morphologies, undissolved cementite, martensite, and retained austenite.
The Ni-based superalloy René 41 has sparked recent interest for applications in next-generation aircraft engines due to its high-temperature strength that is superior to all similar grades. These ...desirable properties are achieved by careful control of the microstructure evolution during thermomechanical processing, and this is commonly informed by simulations. In particular, the grain boundary carbides M
6
C and M
23
C
6
play an essential role in controlling the grain size and strength of the final product. Therefore, a solid understanding of the thermodynamic stability and thermokinetic evolution of these carbides is essential. However, thermokinetic simulations using existing thermodynamic databases have been demonstrated to have discrepancies between thermodynamic stabilities and experimental observations. Here, we collected a new experimental time–temperature–precipitation diagram. In conjunction with improved crystallographic descriptions, these experimental results are used to modify a CALPHAD database for M
6
C and M
23
C
6
. The modified database correctly identifies temperature regions with rapid carbide precipitation kinetics. Further, kinetic simulations and strengthening models successfully predict the hardness increase due to γ′ precipitation. The modified database has been applied to Udimet 700, Waspaloy, and Haynes 282, demonstrating improved results. These updates will facilitate more accurate simulations of the microstructure evolution during thermomechanical processing of advanced Ni-based superalloys for aerospace and other applications.
Cast and wrought Ni‐based superalloys are materials of choice for harsh high‐temperature environments of aircraft engines and gas turbines. Their compositional complexity requires sophisticated ...thermo‐mechanical processing. A typical microstructure consists of a polycrystalline γ‐matrix, strengthening Ni3(Al,Ti) γ′ precipitates, carbides (MC, M6C, and M23C6), borides (M2B, M3B2, and M5B3), and other inclusions. Microalloying additions of B, C, and Zr commonly improve high‐temperature strength and creep resistance, although excessive additions are detrimental. Grain boundary (GB) segregation may improve cohesion and displace embrittling impurities. Finely dispersed carbides and borides are desired to control grain size via GB pinning. However, excessive decoration of GBs may lead to failure during processing and in‐service. Hence, a systematic review on the roles of B, C, and Zr in cast and wrought Ni‐based superalloys is required. The current state of knowledge on GB segregation and precipitation is reviewed. Experimental and modeling results are compared across various processing steps. The impact of GB precipitation on mechanical properties is most well researched. Co‐precipitation in proximity to GBs interacting with local microstructure evolution and mechanical properties remains less explored. Addressing these gaps in knowledge allows a more complete understanding of processing–microstructure–properties relationships in advanced cast and wrought Ni‐based superalloys.
Microalloying additions of B, C, and Zr in cast and wrought Ni‐based superalloys are reviewed. Grain boundary segregation improves cohesion and strength. Excessive additions promote (co‐)precipitation of borides, carbides, and other inclusions, which benefit or deteriorate mechanical properties during processing. A more complete understanding of the microstructure–mechanical properties relationship requires detailed knowledge of interfaces in proximity to grain boundaries.
Tourismus und Reisen stellen fur viele Menschen bedeutsame Bestandteile ihres Lebens dar. Dies gilt sowohl fur Urlaubsreisen als auch fur geschaftliche Reisen und die daran geknupften Erlebnisse und ...Verpflichtungen. Der Tourismusnachfrage steht eine breite Palette touristischer Anbieter gegenuber, die vielfaltige Produkte und Services unternehmerisch am Markt platzieren. Das Buch bietet eine umfangreiche Einfuhrung in diese unterschiedlichen Facetten des Tourismus. Auf Basis des Systems Tourismus und dessen historischer Entwicklung werden die Grundlagen der touristischen Nachfrage und die Besonderheiten des Tourismusmanagements erortert. Ebenso werden die touristischen Angebotselemente von Verkehrstragern uber die Hotellerie, Reiseveranstalter und -buros bis hin zu Destinationen vorgestellt. Kapitel zur Tourismuspolitik und Tourismuskritik sowie zum touristischen Informations- und Geschaftsreisemanagement vervollstandigen das Buch. Die umfassende Einfuhrung wendet sich an Studierende, Praktiker und alle am Tourismus Interessierten.
The A2M3O12 class of materials are mostly known for their negative thermal expansion properties, however, little research has been conducted in regards to their electrochemical properties. The ...A2M3O12 structure consists of rigid polyhedra, featuring large structural voids which may be sufficiently large to reversibly host Li-, Na- and K-ions with minimal strain being induced during insertion/extraction. In the present work, members of the Al2W3−xMoxO12 (0 ≤ x ≤ 3) family were synthesised, and characterised structurally and electrochemically. The Al2W3−xMoxO12 solid solutions adopt a monoclinic P21/a space-group symmetry which transforms to the orthorhombic Pnca space-group symmetry between the compositions Al2W2MoO12 and Al2W2.5Mo0.5O12. The W and Mo cations appear to be randomly distributed on the 6 or 2 independent crystallographic sites in the monoclinic or orthorhombic symmetries, respectively. Discharge against Li yields a relatively high first discharge capacity of 883 mA h g−1 for Al2Mo3O12 with a reversible capacity of 136 mA h g−1 by the 100th cycle which seems to be relatively insensitve to the applied currents used here. The capacities decrease with increasing W content to 654 mA h g−1 for Al2W3O12 in the first and 96 mA h g−1 in the 100th discharge cycle. X-ray absorption spectroscopy and ex situ synchrotron X-ray diffraction data were used to describe the change in oxidation state of Mo and the structural evolution upon discharge and indicate the formation of an amorphous or nanocrystalline phase(s) upon lithiation. Na- and K-half-cells achieved reversible discharge capacities below 28 mA h g−1 while typically introducing less change in the structure. This work illustrates the influence of composition and structure on the electrochemical performance in this family of compounds.
The aim of the present work is to study the microstructure evolution of a cold‐rolled low carbon steel alloyed with Cr, Mn, Mo, and Nb during continuous heating. The formation of austenite and its ...further transformation is examined by means of peak annealing experiments at three different heating rates, followed by quenching. The effect of carbide‐forming alloying elements in the kinetics of austenite formation and decomposition is discussed with the aim of DICTRA calculations. Electron Probe Micro Analysis allows the detection of small compositional fluctuations within the microstructure, which are responsible for local changes in the mechanism of austenite formation. It is experimentally demonstrated that the temperature dependence of the austenite fraction is relatively insensitive to the heating rate. It is suggested that carbide‐forming alloying elements slow down the kinetics of austenite formation.
During continuous heating of low carbon steel, the formation of austenite might be accomplished either under carbon diffusion or interface controlled (massive) mechanism. The transition of one to another mechanism depends on local equilibrium conditions at the γ/α interface. In the present study, the effect of small variations in the chemical composition is evaluated in order to calculate the local transition temperature (defined as Am), and discussed in the light of the observed microstructure.
Sc2(WO4)3, prepared by solid state synthesis and constructed as an electrode, is discharged to different states in half-cell batteries, versus a Na negative electrode. The structural evolution of the ...Na-containing electrodes is studied with synchrotron powder X-ray diffraction (PXRD) revealing an increase in microstrain and a gradual amorphization taking place with increasing Na content in the electrode. This indicates that a conversion reaction takes place in the electrochemical cell. X-ray absorption spectroscopy (XAS) at the tungsten L3 absorption edge shows a reduction in the tungsten oxidation state. Variable temperature (VT) PXRD shows that the Sc2(WO4)3 electrode remains relatively stable at higher temperatures, while the Na-containing samples undergo a number of phase transitions and/or turn amorphous above ∼400 °C. Although, Sc2(WO4)3 is a negative thermal expansion (NTE) material only a subtle change of the thermal expansion is found below 400 °C for the Na-containing electrodes. This work shows the complexity in employing an electrochemical cell to produce Na-containing Sc2(WO4)3 and the subsequent phase transitions.
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