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In March 2019, German-speaking scientists and scholars calling themselves Scientists for Future, published a statement in support of the youth protesters in Germany, Austria, and Switzerland (Fridays for Future, Klimastreik/Climate Strike), verifying the scientific evidence that the youth protestors refer to. In this article, they provide the full text of the statement, including the list of supporting facts (in both English and German) as well as an analysis of the results and impacts of the statement. Furthermore, they reflect on the challenges for scientists and scholars who feel a dual responsibility: on the one hand, to remain independent and politically neutral, and, on the other hand, to inform and warn societies of the dangers that lie ahead.
Outdoor performance analyses of photovoltaic modules can be advantageous compared to indoor investigations, as they take into account the influences of natural test conditions on the modules. However, such outdoor performance assessments usually suffer from poor accuracies due to undefined test conditions for the modules. This paper reports on a comprehensive concept for improved outdoor analysis which results in performance data with indoor laboratory precision. The approach delivers current-voltage characteristics for even more test conditions than required by the standard IEC 61853-1. Hence, curves of modules’ electrical parameters above irradiance can be deduced for any temperatures. The concept allows precise determination of temperature coefficients for user-defined irradiances taking into account outdoor effects like light-soaking or light-induced degradation. The calibration and measurement uncertainty of the presented outdoor analysis method is evaluated quantitatively. For the measurements an advanced outdoor set-up was used.
Effiziente Lüftungssysteme zur Sicherstellung guter Luftqualität sind für energieeffiziente Gebäude essentiell. Ein Hemmnis für den Einsatz stellen insbesondere in der Sanierung die nach wie vor hohen Kosten dar. In mehreren Projekten [Schiantarelli 2015] [Sibille et al. 2013] wurde bisher versucht, vereinfachte Systeme zu entwickeln [Sibille, Pfluger 2016] [Huber 2013]. In diesem Forschungsprojekt wurde die Idee einer technisch einfachen und möglichst kanalfreien Belüftungsmöglichkeit mithilfe von aktiven Überströmern untersucht. Dabei wird die Zuluft nur zentral in der Mischzone der Wohnung (Flur, offenes Wohnzimmer) eingebracht. Die Abluft wird konventionell erfasst. Dadurch kann auf ein Zuluftkanalnetz verzichtet werden. Der aktive Überströmer ist dabei in die Zwischenwand bzw. im Türsturz des Anforderungsraumes (z.B. Schlafzimmer) eingebaut. Er besteht aus einem Axiallüfter mit einem Durchmesser von 120 mm, der (bei geschlossener Tür) die Luft aus der Mischzone in das angrenzende Schlafzimmer fördert.
In this study, an experimental apparatus is used to excite four U-tube-shaped liquid pistons connected in series, and to study their behaviour. Some of the gas spaces are heated to induce piston oscillations; in others, gas expansion is utilised to produce a refrigeration effect. It was discovered that the liquid piston surface would become unstable and turbulent at relatively low gas charge pressures (2 bar–3 bar). Cylindrical polyethylene floats were employed at each piston surface in order to reduce the area of the free surface of each piston and allow experiments to be conducted over a wide range of operating conditions. Experiments were carried out using gas charge pressures in the range of 1 bar–6 bar. The resulting liquid piston oscillations were measured and analysed to assess the impact of any developing piston instability. Evidence of a liquid piston acceleration limit, likely resulting from the Rayleigh-Taylor instability phenomenon, is consistently observed during the experiments. The use of submerged polyethylene piston floats is found to increase the surface stability and enable maximum accelerations of 25 ms−2 to 30 ms−2.
Ziel des Projektes ist es, ein Verfahren für elektrische Vorort-Leistungsanalysen von Photovoltaik (PV)-Anlagen zu entwickeln. Dazu werden die elektrischen Parameter von PV-Strings lokal und global mit Hilfe eines neuen Feldlaboransatzes mit Indoor-Laborgenauigkeit vermessen. Das neue Messverfahren ist normgerecht und wird helfen, die Standardisierung von Feldmessungen weiterzuentwickeln. Im Projekt werden bekannte Messmethoden der Photovoltaik, (IR-Thermografie, I-U-String-Messung, digitale Datenverarbeitung mittels Selbstreferenzierung) zu einem innovativen Gesamtkonzept synthetisch zusammengeführt. Die Entwicklung des Messverfahrens wird an speziell gealterten PV-Anlagen marktbestimmender Technologien (c-Si-, CdTe-, CIGS-Muster-PV-Anlagen) vorangetrieben. So wird das Verfahren auf Erkennung spezifischer Degradationsszenarien und marginaler quantitativer Parameterveränderungen trainiert und geschärft
In this work we investigate students’ thinking about and difficulties with incompressible, steady pipe flow. There is substantial evidence that students have difficulty applying and prioritizing the two basic principles of mass conservation (i.e., the continuity equation) and energy conservation (i.e., Bernoulli’s equation). When distracted by questions which involve gravity students based their answers on ill-supported assumptions about local pressures. The predominant arguments use a simplified Bernoulli equation, descriptive arguments or analogies to single-particle motion. Based on these results, an instructional intervention is developed that seems to address the observed difficulties.
This thesis investigates the measurement and prediction of machinery noise in timber-frame buildings. To quantify the structure-borne sound power input from multi-point sources, simplified approaches were assessed that reduce the required data for out-of-plane force excitation. This identified approaches that give estimates within ±5 dB from 20 Hz to 2000 Hz. To investigative the importance of out-of-plane moment excitation, inverse methods were used to determine the power input; these were affected by noise but processing was used to overcome this shortcoming. A series of experimental investigations were carried out on a timber-frame structure undergoing mechanical point excitation. The driving-point mobility showed orthotropic plate characteristics at low frequencies, ribbed-plate characteristics in a narrow frequency band and infinite plate characteristics in mid- and high-frequency ranges. The moment mobility above or in-between studs was similar to infinite beam or plate theory with interpolation between these theories where necessary. The experimental work indicated the potential to use Statistical Energy Analysis (SEA) to predict sound transmission. The first experimental finding was that above the mass-spring-mass resonance frequency, the vibrational response of the wall leaves was uncorrelated. The second was a significant decrease in vibration across the wall from the excitation point, with structural intensity showing a decrease in net power flow across successive timber studs. The third was that tongue and groove connections between chipboard sheets significantly reduce the vibration transmission above 500 Hz. This led to different SEA models being used to model a timber-frame wall undergoing mechanical point excitation. A 41-subsystem model was found to be necessary to reproduce the measured vibration levels on both leaves within 10 dB. As there is a significant decrease in vibration with distance in the mid- and high-frequency range, the region close to the excitation point is particularly important and the SEA model has better accuracy in this region. An alternative engineering approach to the prediction of machinery noise in timber-frame buildings was introduced and validated that used measured transmission functions between the injected power and the spatial-average sound pressure level in a receiving room. A field survey and case studies indicate this is a feasible and practical approach.
We describe an investigation of the heterogeneity in conceptual understanding of first-year
engineering students by using the force concept inventory (FCI) as a diagnostic tool. The
average FCI pre- and posttest results depend significantly on the type of school graduation.
Even interactive teaching methods that have proven to be more effective in learning outcome
cannot dissolve this heterogeneity within the first year of university study.
In the project, domestic ventilation concepts with PushPull-Fans were investigated. These ventilation units are characterized by a periodically changing supply and exhaust air operation. To ensure balanced operation, these ventilation units are always used in pairs, with one unit being in the exhaust air mode and the other in supply air mode. Measurements were made in a research apartment. The results were used to validate a CFD simulation model for transient studies. A room-by-room layout with two units in one room and a cross-room ventilation layout with two connected units in two rooms were analysed. The age of air was used as the evaluation parameter. With the room-by-room ventilation layout a lower age of air in the bedroom compared to the cross-room layout was obtained. However, in the room-by-room layout, the air flow through the larger living room with connected corridor was poorer in the rear area. With the cross-room layout, the flow through the rooms was more uniform. With the cross-room layout, the average age of air in the apartment could be slightly reduced compared to the room-by-room layout.