Investigating and Modeling the Impact of Moisture on the Reliability of Mid-Power Light-Emitting Diodes

Over the past decades Light-emitting Diode (LED) devices have not only entered but occupied large segments of the general lighting market due to their flexible control features, high power conversion efficiency and exceptional long lifetime when operated at the recommended conditions. With the constant emergence of new application specific phosphor-materials niche applications are targeted. In some use cases the LEDdevice is exposed to multiple, often elevated environmental stress conditions, such as temperature and humidity. An example of such an application is horticulture lighting in vertical or greenhouse farming scenarios. However, especially the impact of moisture on the LED device as a whole is only sparsely investigated in past studies since mostly thermal and electrical stress conditions were targeted. In particular, only very few studies have been conducted on plastic-leaded chip carrier (PLCC) Mid-Power LED devices with respect to moisture. These situation is also reflected in common standards and methodologies for reliability testing and lifetime calculation. Therefore, the investigation of moisture ingress on performance of a LED and modeling this very is the main scope of this work. Over the course of this work an accelerated degradation test experiment was designed and conducted to gain further insights on the role of the combination of temperature, current and humidity on the devices degradation. This experiment included four state-of-the-art, commercially available Mid-Power LED devices recommended for the use in horticulture applications that were each subjected to 24 different temperature, humidity and current conditions. The current state of each device was measured continuously with respect to its optical, electrical and thermal characteristics. Based on the observed results it is concluded that especially moisture ingress severely impacts the devices performance by causing the encapsulant to detach from adjacent parts of the package due to shear forces introduced by hygroscopic swelling of the silicone encapsulant. Accompanying effects, such as tarnishing of the reflective lead-frame coating or accelerated dissolution admixed phosphor particles can also be reported. Regarding the modeling of the observed degradation trajectories various continuous decay functions and a segmented decay approach were investigated. Latter showed promising results especially when considering the subsequent modeling of its decay parameters according to Eyrings equation. In addition, a Gaussian Process Regression as a decay modeling approach as well as Survival Analysis as a time-to-failure approach were explored. Especially for case of non-monotonous acceleration functions both yielded an increased accuracy compared to typical physics-based modeling approaches

Goal Missed, Self Hit: Goal-Setting, Goal-Failure, and Their Affective, Motivational, and Behavioral Consequences

Setting high and specific goals is one of the best-established management tools to increase performance and motivation. However, in recent years, potential downsides of goal-setting are being discussed. One possible downside is the high risk of failing the goal. In an approach to integrate research on the consequences of goal-failure and the basic assumptions of goal-setting theory, we investigated whether failure of a high and specific goal has detrimental effects on a person’s affect, self-esteem, and motivation. In Experiment 1, 185 participants received fictitious feedback about attaining or failing an assigned high and specific goal. In Experiment 2 with 86 participants, we manipulated goal-failure through task-difficulty and we included task choice as a behavioral measure of motivation. In both experiments, participants who failed the high and specific goal showed a decrease in affect, self-esteem, and motivation compared to participants who attained that goal. Results indicate that failing a high and specific goal can be damaging for self-related factors that may be crucial for organizational long-term outcomes. We advise organizations to consider potential undesirable effects when using goal-setting interventions

The impact of assurance on compliance management systems on bank directors' decisions

Numerous corporate scandals, in conjunction with managerial misbehavior, demonstrate the need for compliance management systems (CMS) and the relevance of CMS assurance. This study investigates the impact of CMS assurance on German bank directors' perceptions and decisions, and analyzes whether the type of assurer and the level of provided assurance are relevant. For this purpose, we conducted an experiment with 105 bank directors and used ANOVA to analyze their reliance on the hypothetical company's CMS, and their decisions regarding credit granting, purchase, and recommendation of shares. We chose a 2 × 2 + 1 between‐subjects design, manipulating the assurance provider (audit firm vs. third party) and the level of assurance (limited vs. reasonable), and adding a control condition without any assurance. Our results suggest that assured CMS positively affect bank directors' perceptions and decisions, compared to CMS without assurance. Furthermore, we find that our perception measure and all three of our decision measures are strongly associated with the choice of assurance provider, but only two decision measures are associated with the assurance level. Bank directors prefer assurance provision by an audit firm, whereas the findings regarding the impact of the assurance level are inconclusive. The study's results, which confirm the decision‐usefulness of CMS assurance, are of interest for managers, in particular compliance officers, auditors, creditors, regulators, and academics

Entwicklung eines KI-Modells zur Prädiktion von Alterungseffekten an Emissionsminderungssystemen

Zur Erfüllung zukünftiger Abgasemissionsgesetzgebungen für die Individualmobilität und im Nutzfahrzeugbereich bedarf es immer besserer Konvertierungsleistungen der Abgaskatalysatoren und Filter, sowie der Abgaskonformität bei deutlich gesteigerten Laufleistungen. Die zunehmende Elektrifizierung, auch im Nutzfahrzeugbereich, erhöht die Komplexität der Abgasnachbehandlungssysteme und Betriebsstrategien und erschwert die Prädiktionsgenauigkeit von Alterungseffekten der Katalysatoren. Die sensorische Erfassung der Alterung der Katalysatoren, zur Sicherstellung von Niedrigstemissionen im gesamten Fahrbetrieb, ist ohne hochpräzise Messtechnik jedoch nicht möglich, sodass auf modelbasierte Ansätze zurückgegriffen werden muss. In diesem Beitrag wird das methodische Vorgehen zur Entwicklung einer fahrzeugunabhängigen, modellbasierten Prädiktion der Alterung von Abgasnachbehandlungssystemen dargestellt. Das Modell beruht auf dem Ansatz einer datengetriebenen KI, für deren Erstellung Messdaten einer diversen Fahrzeugflotte verwendet und analytisch aufbereitet werden

Dynamics of bubble growth during boiling at microgravity

The purpose of this investigation is to study the mechanisms of boiling heat transfer in microgravity conditions. The RUBI (Reference mUltiscale Boiling Investigation) is an experiment where the basic phenomena of boiling heat transfer processes on a heated surface are investigated on the ISS (International Space Station). The special focus is paid to the coupling of macroscopic bubble dynamics from nucleation, growth and detachment combined with the microscopic phenomena in the thin films and micro layers on the heater, underneath the boiling bubbles. The image treatment program has been developed in order to extract the bubble volume as well as the contact angle from the experimental images. The first data of the bubble growth dynamics have been obtained and analysed

Cu Electrodeposition on Nanostructured MoS₂ and WS₂ and Implications for HER Active Site Determination

Cu electrodeposition in both underpotential and overpotential regimes on nanostructured MoS₂ and WS₂ prepared by plasma-enhanced atomic layer deposition has been studied in detail. A combination of electrochemical methods, advanced characterization by X-ray absorption spectroscopy (XAS) as well as theoretical modelling were employed to reveal Cu adsorption modes on transition metal dichalcogenides (TMDs) from initial stages until bulk deposition. Since Cu UPD on TMDs has been used recently to evaluate the number of electrochemically active sites (NAS) for H₂ evolution reaction, we evaluate and discuss here the implications of the Cu electrodeposition phenomena on nanostructured MoS₂ and WS₂ gauging the general applicability of the Cu UPD method for number of HER active sites determination in TMDs. Although an apparently better correlation of HER current density with Cu UPD charge than with double layer capacitance is found, the Cu UPD method cannot be used quantitatively because of the absence of a clear H UPD phenomenon on the studied nanostructured TMDs. This is in contrast to platinum group metal catalysts where H UPD and Cu UPD sites are strongly correlated

Negative CO₂ Emissions in the Lime Production Using an Indirectly Heated Carbonate Looping Process

Lime plants are responsible for the production of raw materials that are widely used in the agriculture and the industrial sector. Lime-related products are obtained from the calcination of limestone (mainly CaCO3) at high temperature (900-1200 °C). The calcination reaction is highly endothermic, and thus a heat input, e.g. from the combustion of fuels such as coal, coke, and secondary fuels, is required. CO2 is emitted as a result of the combustion. Additional CO2 is produced due to the chemical conversion of CaCO3 into CaO during the calcination. This so-called “process CO2”, which can only be avoided through CO2 capture, represent approximately 65% of the total CO2 emissions. Overall, the total CO2 emissions per ton of burnt lime vary between 1 to 2 tCO2/tlime. In order to capture the CO2 emissions from lime plants, post-combustion technologies are to be integrated into the production process. Nonetheless, the majority of these technologies have very high energy requirements, which increase the costs of the final products and reduce the efficiency of the entire system considerably. One noteworthy post-combustion carbon capture technology is the carbonate looping process (CaL). The CaL has the potential to efficiently capture the CO2 from lime plants without considerably increasing the energy requirements of the entire process. The CO2 capture is achieved utilizing limestone as a sorbent, i.e. the raw material of the lime production facility, which makes CaL especially interesting for the application into lime plants. The sorbent binds CO2 from the kiln flue gases in a carbonator, and is regenerated with a temperature increase at a calciner. This technology has been successfully operated up to the pilot scale in Darmstadt, Germany (1 MWth), and in La Pedrera, Spain (1 MWth). For the regeneration of the sorbent in the standard CaL fuel is burnt directly in the calciner. For this, technically pure oxygen is used, which requires an air separation unit (ASU). The ASU can be avoided by indirectly heating the calciner, and thus the energy penalty is further reduced. One excellent means to achieve this is through heat pipes, which transfer heat from an external combustor into the calciner via evaporation and condensation of a fluid. This indirectly heated carbonate looping process (IHCaL) present several advantages compared to the oxy-fired CaL: reduced energy requirement, improved sorbent activity, lower sorbent attrition rates, and high purity of the captured CO2. The IHCaL has been successfully operated for 400 h at the 300 kWth facility of the Technical University of Darmstadt. Additional test campaigns in Darmstadt will be carried out during 2022 to prove the operability of the IHCaL process under lime plant conditions at the pilot scale. At the Technical University of Darmstadt, novel concepts for the integration of the IHCaL process into the lime production were developed and evaluated through process simulation. The published results consider the utilization of dried lignite as fuel for both the lime kiln and the IHCaL combustor. Nevertheless, the utilization of renewable fuels of high biogenic content, applied to these concepts has not been discussed yet. This work presents the results of the energy and mass balances of two IHCaL concepts for the lime production, utilizing high quality solid recovered fuel (SRF; LHV: 21.3 MJ/kg; 40% biogenic carbon fraction) to provide the thermal energy for the carbon capture. Furthermore, a heat recovery steam cycle is implemented in order to produce electrical power from the high temperature output flows (650 °C and 900 °) and the cooling heat from the carbonator (650 °C). For the comparison of the SRF concepts with the lignite concepts, key performance indicators are calculated, namely, net CO2 emissions—considering indirect CO2 emissions and biogenic content—, CO2 capture efficiency, avoided CO2 emissions, and specific primary energy consumption per CO2 avoided (SPECCA)

Methodik zur datenbasierten Typisierung von Quartieren anhand baulicher Strukturen

Die deutsche Gesellschaft befindet sich in einem Transformationsprozess, um der Klimakrise zu begegnen. Vor dem Hintergrund der notwendigen Dekarbonisierung der Wärmeversorgung von Gebäuden haben sich Konzepte etabliert, welche für Quartiere, d. h. mehrere Gebäude in einem räumlichen Zusammenhang, die Reduktion von Treibhausgasemissionen durch eine Erhöhung der Gebäude- und Anlageneffizienz sowie durch die Einbindung erneuerbarer Energieträger erreichen. Während auf lokaler Handlungsebene eine Vielzahl an Projekten umgesetzt wird, fehlte die empirische Basis, um die Art und Anzahl von Quartieren in Deutschland zu erfassen und die Wirkung von Quartierskonzepten in Hoch- und Szenarienrechnungen zum Klimaschutz zu integrieren. Die vorliegende Arbeit liefert eine Methodik zur Nutzung von Geobasisdaten für eine Analyse der Bebauungsstruktur und eine Einteilung dieser in geometrisch-topologisch ähnliche Gebiete mittels Clusteranalyse. Eine Vereinigung benachbarter Gebiete ähnlicher Bebauung führt im Anschluss zur Bildung von Quartieren, was schließlich eine statistische Analyse des Quartiersbestandes erlaubt. Daraus können Kenngrößen für die Beschreibung von Typvertretern für Quartiersgruppen, sogenannte Typquartiere, festgelegt werden. Die beispielhafte Anwendung der Methodik am Datensatz Berlins zeigt eine praxisgerechte Quartiersbildung sowie die Verwendbarkeit der Ergebnisse der Quartierstypisierung für vielfältige Forschungs- und Planungszwecke. Insbesondere eine Verwendung des nationalen Geodatenbestandes zur Quartierstypisierung eröffnet die Möglichkeit weiterführender Szenarioanalysen im Kontext nationaler Klimaschutzstrategien

THz Antenna-Coupled Zero-Bias Schottky Diode Detectors for Particle Accelerators

Semiconductor-based broadband room-temperature Terahertz (THz) detectors are well suitable for beam diagnosis and alignment at accelerator facilities due to easy handling, compact size, no requirement of cooling, direct detection and robustness. Zero-Bias Schottky Diode (ZBSD) based THz detectors are highly sensitive and extremely fast, enabling the detection of picosecond scale THz pulses. This contribution gives an overview of direct THz detector technologies and applications. The ZBSD detector developed by our group has undergone several tests with table-top THz sources and also characterized with the free-electron laser (FEL) at HZDR Dresden, Germany up to 5.56 THz. In order to understand the rectification mechanism at higher THz frequencies, detector modelling and optimization is essential for a given application. We show parametric analysis of a antenna-coupled ZBSD detector by using 3D electromagnetic field simulation software (CST). The results will be used for optimization and fabrication of next generation ZBSD detectors, which are planned to be commissioned at THz generating FEL accelerator facilities in near future

Carbon‐Methanol Based Adsorption Heat Pumps: Identifying Accessible Parameter Space with Carbide‐Derived Carbon Model Materials

In adsorption heat pumps, the properties of the porous adsorbent and the refrigerant determine the performance. Major parameters for this working pair are the total uptake of the adsorptive, its kinetics, and the heat transfer characteristics. In the technical application despite powdered adsorbents, thin consolidated layers of the adsorbent can be attractive and obtained by a binder‐based approach but likely result in competing material properties. Thus, for a process optimization, the accessible parameter space and interdependencies have to be known and were deduced in this work for model porous carbons (carbide‐derived carbons derived from TiC and ZrC) and methanol as well as the addition of different amounts of boron nitride, silver, and graphite as heat‐conductive agents and the use of two binders