Experimental study of liquid-vapor mass transfer in non-reacting and reacting droplet chains

[EN] The dynamics of liquid-vapor mass transfer largely determines the performance of internal and gas turbine spray combustors. The key mechanisms however typically take place on small spatial scales of less than 100 μm which have been difficult to measure. The present work thus aims at the development and application of an experimental technique for the characterization of droplet evaporation with high spatial resolution. Single chains of monodisperse acetone droplets with diameters of 125 and 225 μm are injected into a channel with a cross-section of 60x60 mm² and quartz glass side walls for optical access. The droplet chains are surrounded by a laminar air flow with velocity and temperature of about 0.1 m/s and 300 K, respectively. The distribution of acetone vapor around the droplets is measured using planar laser-induced fluorescence (PLIF) excited by the 4th harmonic of a Nd:YAG laser at 266 nm. The measurements are performed in thin transversal sections between the droplets in order to avoid signal corruption by halation effects that occur when the laser directly hits the droplets as reported in previous studies. In addition, the spatial resolution of the PLIF setup was enhanced by using proper sheetforming and imaging optics. The resulting in-plane resolution and out-plane-resolution (i.e. thickness of the laser sheet) are both determined to about 20 μm, which thus allows an accurate characterization of the small-scale vapor distribution near the droplets. Using a separate calibration measurement, quantitative acetone concentrations are obtained for non-reacting conditions. As a complementary technique, the droplet evaporation is measured using shadowgraphy droplet sizing. Both non-reacting and reacting droplet chains are studied. The results for the non-reacting cases show that the droplet chains are surrounded by a column of nearly-saturated acetone vapor with a concentration maximum at the centerline. For increasing radial distances, the vapor concentration decays quickly with a half width of 0.5 mm and reaches almost zero for r>1 mm. It is further seen that the width of the vapor column increases with streamwise distance. For the experiment with a reacting droplet chain, which is continuously ignited by a heating wire at the channel inlet, a cylindrical reaction zone around the chain with a radius of about 1.5 mm is observed. The shadowgraphy measurements show that the rate of droplet evaporation is significantly enhanced for the reacting conditions. This is attributed to the high rate of heat transfer from the flame to the droplets and the resulting enhanced acetone mass transfer to the sink at the reaction zone.The contribution of Tobias Biesner to the design and setup of the experiment is appreciated. Financial support from the DLR project R2F is gratefully acknowledged.Stöhr, M.; Werner, S.; Meier, W. (2017). Experimental study of liquid-vapor mass transfer in non-reacting and reacting droplet chains. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 738-745. https://doi.org/10.4995/ILASS2017.2017.4767OCS73874

Regulation of chondrocyte differentiation by posterior Hox genes

Hox-Gene spielen bei der Gliedmaßenentwicklung eine entscheidende Rolle, da sie durch ihre überlappenden Expressionsdomänen die Identität der einzelnen Knochen definieren. Für die Bildung von Ulna und Radius sind Hoxa11 und Hoxd11 essentiell, wie die erhebliche Reduktion dieser Knochen in Hoxa11-/-;Hoxd11-/--Mausmutanten beweist (Boulet und Capecchi, 2004; Davis et al., 1995). Neben dem Einfluss von Hox-Genen auf die Identität der Gliedmaßenelemente wurden in Hoxa11-/-;Hoxd11-/--Embryonen Hinweise auf eine Funktion der Hox-Gene während der Chondrozytendifferenzierung gefunden (Boulet und Capecchi, 2004). Der Einfluss von Hoxa11 und Hoxd11 auf die Chondrozytendifferenzierung sollte im Rahmen dieser Arbeit mit Hilfe der Vorderextremitäten von Hoxa11-/-;Hoxd11-/--Mausmutanten im Detail analysiert werden. Da nach Mendel die Wahrscheinlichkeit in einem Wurf einen Hoxa11-/-;Hoxd11-/--Embryo zu bekommen nur 6,25% beträgt, wurden zusätzlich die Vorderextremitäten von Mäusen mit der dominanten Ulnaless-Mutation untersucht, die in einem Wurf 50% Ulnaless-Embryonen erzeugen. Die Ulnaless-Mäuse dienten als Modell der Hoxa11-/-;Hoxd11-/--Mutation, da im Zeugopod dieser Mäuse die Funktion von Hoxa11 und Hoxd11 durch ektopische Expression posteriorer Hox-Gene reprimiert ist und sie deshalb einen ähnlichen Phänotyp der Vordergliedmaßen wie Hoxa11-/-;Hoxd11-/--Mutanten besitzen. Der Vergleich der Chondrozytendifferenzierung in den Vordergliedmaßen von Hoxa11-/-;Hoxd11-/-- und Ulnaless-Mutanten ergab, dass nur die Ulna der Ulnaless-Embryonen durch die ektopische Expression von Hoxd12 und Hoxd13 beeinflusst ist und somit als Modell der Hoxa11-/-;Hoxd11-/--Mutation dienen kann. Beide Mauslinien weisen im Zeugopod am Tag E14.5 und E16.5 sowohl auf morphologischer als auch molekularer Ebene eine Inhibition der Chondrozytendifferenzierung auf. Es wurden hauptsächlich Chondrozyten eines frühen Differenzierungsstadiums in Ulna und Radius der Mutanten detektiert. In späteren Embryonalstadien wurden jedoch auch kolumnare und hypertrophe Chondrozyten im Zeugopod der Mutanten nachgewiesen, so dass man insgesamt von einer erheblich verzögerten, hypertrophen Differenzierung der Chondrozyten sprechen muss. Weiterhin wurde eine veränderte Lokalisation der kolumnaren und hypertrophen Chondrozyten in den Gliedmaßen der Hoxa11-/-;Hoxd11-/-- und Ulnaless-Mutanten beobachtet, die ein Indiz für die Funktion von Hoxa11 und Hoxd11 in der Anordnung der Chondrozyten in der Wachstumsfuge ist. Hoxa11 und Hoxd11 sind demnach notwendig, um eine exakte, zeitliche und räumliche Abfolge der Chondrozytendifferenzierung in Ulna und Radius zu ermöglichen. Obwohl die Chondrozytendifferenzierung in der Ulna von Ulnaless-Gliedmaßen mit der Differenzierung der Chondrozyten in Ulna und Radius von Hoxa11-/-;Hoxd11-/--Extremitäten vergleichbar ist, so wurden doch auch Unterschiede zwischen den Vordergliedmaßen dieser beiden Mauslinien gefunden. Durch die Analyse von postnatalen Ulnaless-Vorderextremitäten wurde offensichtlich, dass in Ulnaless-Mutanten nur das Olecranon vorhanden ist. Demnach sind Hoxa11 und Hoxd11 auch für die Bildung der distalen Ulna verantwortlich. Durch die molekulare Analyse der Vorderextremitäten beider Mauslinien wurde Shox2 als potentielles Zielgen von Hoxa11 und Hoxd11 detektiert. Ob diese posterioren Hox-Gene Shox2 aktivieren können und dadurch die hypertrophe Differenzierung der Chondrozyten induziert wird, soll in weiteren Experimenten durch Analyse des Shox2-Promotors und durch Überexpression von Shox2 in Ulnaless-Gliedmaßen geklärt werden. Des Weiteren wurde eine Analyse des Ihh-Promotors durchgeführt, um zu verstehen, wie Ihh während der Chondrozytendifferenzierung reguliert wird. Es wurden konservierte Bereiche im genomischen 5’Bereich von Ihh nachgewiesen und auf Enhancer-Aktivität in vitro und in vivo getestet. In vivo konnte keine Enhancer-Aktivität der untersuchten, genomischen Sequenzen ermittelt werden. Vermutlich sind längere Fragmente oder weiter entfernte Sequenzen notwendig, um die Expression von Ihh in den Gliedmaßen zu regulieren. In vitro wurde dagegen das T1-Fragment als Ihh-Enhancer identifiziert. Als Aktivatoren der Ihh-Expression wurden die Homöobox-Transkriptionsfaktoren SHOX und SHOX2 detektiert. Eine Repression erfolgte in vitro durch BMP2 sowie mit HOXA9, Hoxa11 und Hoxd11. Als weiterer, putativer Aktivator von Ihh wurde MMP3 in einem Hefe-Ein-Hybrid System identifiziert. Zur Bestätigung der Regulation der Ihh-Expression durch MMP3 sind elektrophoretische Mobilitätstests oder Luciferase-Assays notwendig. Insgesamt konnten durch diese Promotor-Analyse neue Regulatoren von Ihh und somit der hypertrophen Differenzierung der Chondrozyten ermittelt werden.Hox genes are major regulators of limb development. They are defining the identity of specific limb elements by their overlapping expression patterns. Hoxa11 and Hoxd11 are essential factors for the formation of ulna and radius, which was shown by the severe reduction in size of these bones in Hoxa11-/-;Hoxd11-/- double mutant mice (Boulet und Capecchi, 2004; Davis et al., 1995). Beside the function of Hox genes in specifying the elements of the limbs, it was indicated in Hoxa11-/-;Hoxd11-/- mice that Hox genes also play a role in chondrocyte differentiation (Boulet und Capecchi, 2004). In this study, the impact of Hoxa11 und Hoxd11 on chondrocyte differentiation was investigated by analyzing the forelimbs of Hoxa11-/-;Hoxd11-/- mice. The likelihood to get Hoxa11-/-;Hoxd11-/- double mutant embryos is 6,25%. Therefore, the forelimbs of mice with the dominant Ulnaless mutation were analyzed in addition. Because of the dominance of this mutation, the frequency to get a mutant Ulnaless embryo is around 50%. The Ulnaless mice serve as model for the Hoxa11-/-;Hoxd11-/- mutation, because in these mice the complete Hoxd cluster is inverted, which causes the repression of the Hoxa11 and Hoxd11 function. That’s why, the Ulnaless forelimbs show the same phenotype as Hoxa11-/-;Hoxd11-/- forelimbs. The comparison of chondrocyte differentiation in forelimbs of Hoxa11-/-;Hoxd11-/- and Ulnaless mice demonstrated that only the ulna of Ulnaless embryos is influenced by the ectopic expression of Hoxd12 and Hoxd13. Therefore, only the ulna of Ulnaless mutants can be used as a model for the Hoxa11-/-;Hoxd11-/- mutation. Furthermore, the inhibition of chondrocyte differentiation was shown at E14.5 and E16.5 in the zeugopod of both mouse strains on the morphological and molecular level. At these stages, chondrocytes of an early differentiation step were detected in ulna and radius of Hoxa11-/-;Hoxd11-/- and Ulnaless forelimbs, whereas at later stages, columnar and hypertrophic chondrocytes could be seen in the zeugopod of the mutants. In conclusion, chondrocyte differentiation in the zeugopod of Hoxa11-/-;Hoxd11-/- and Ulnaless mice is severely delayed. Additionally, the change in the localization of columnar and hypertrophic chondrocytes in the forelimbs of Hoxa11-/-;Hoxd11-/- and Ulnaless mice showed that Hoxa11 and Hoxd11 also have a function in aligning the chondrocytes in the growth plate. In summary, Hoxa11 and Hoxd11 are necessary to allow the correct temporal and spatial organization of chondrocyte differentiation in ulna and radius. Although chondrocyte differentiation in the ulna of Ulnaless forelimbs is comparable to the differentiation in ulna and radius of Hoxa11-/-;Hoxd11-/- limbs, some differences were observed between the forelimbs of the two mouse strains. The analysis of Ulnaless forelimbs at postnatal stages demonstrated the exclusive presence of the olecranon process in Ulnaless forelimbs. Thus, Hoxa11 and Hoxd11 are responsible for the formation of the distal ulna. The molecular analysis of the forelimbs of both mutant mouse strains indicated that Shox2 is a target of Hoxa11 and Hoxd11. To confirm this, further analysis of the Shox2 promoter or overexpression of Shox2 in the forelimbs of Ulnaless mice could be done to see if a rescue of the chondrocyte differentiation defect occurs. Besides, the promoter of Ihh was analyzed to get a better understanding of the regulation of Ihh during chondrocyte differentiation. Conserved elements of the genomic upstream region of Ihh were identified and examined in vitro and in vivo for enhancer activity. In vivo, no enhancer activity could be detected with either fragment. Presumably, longer fragments or more distant sequences are needed to drive the expression of Ihh in the limbs. But in vitro the T1 fragment was identified as an enhancer of Ihh. Furthermore, SHOX and SHOX2 were proved to act as activators of this Ihh enhancer. In contrast, BMP2 as well as the homeobox proteins HOXA9, Hoxa11 and Hoxd11 repressed the enhancer activity. As another transcriptional activator of Ihh expression, MMP3 was found in a yeast one hybrid assay. To confirm this regulation of Ihh expression by MMP3, gel shifts or luciferase assays are useful. In summary, this study identified novel regulators of Ihh and of chondrocyte hypertrophy

Constraining two climate field reconstruction methodologies over the North Atlantic realm using pseudo-proxy experiments

This study presents pseudo-proxy experiments to quantify the reconstruction skill of two climate field reconstruction methodologies for a marine proxy network subject to age uncertainties. The BARCAST methodology (Bayesian Algorithm for Reconstructing Climate Anomalies in Space and Time) is tested for sea surface temperature (SST) reconstruction for the first time over the northern North Atlantic region, and compared with a classic analogue reconstruction methodology. The reconstruction experiments are performed at annual and decadal resolution. We implement chronological uncertainties inherent to marine proxies as a novelty, using a simulated age-model ensemble covering the past millennium. Our experiments comprise different scenarios for the input data network, with the noise levels added to the target variable extending from ideal to realistic. Results show that both methodologies are able to reconstruct the Summer mean SST skillfully when the proxy network is considered absolutely dated, but the skill of the analogue method is superior to BARCAST. Only the analogue method provides skillful correlations with the true target variable in the case of a realistic noisy and age-uncertain proxy network. The spatiotemporal properties of the input target data are partly contrasting with the BARCAST model formulations, resulting in an inferior reconstruction ensemble that is similar to a white-noise stochastic process in time. The analogue method is also successful in reconstructing decadal temperatures, while BARCAST fails. The results contribute to constraining uncertainties in CFR for ocean dynamics which are highly important for climate across the globe

Constraining two climate field reconstruction methodologies over the North Atlantic realm using pseudo-proxy experiments

This study presents pseudo-proxy experiments to quantify the reconstruction skill of two climate field reconstruction methodologies for a marine proxy network subject to age uncertainties. The BARCAST methodology (Bayesian Algorithm for Reconstructing Climate Anomalies in Space and Time) is tested for sea surface temperature (SST) reconstruction for the first time over the northern North Atlantic region, and compared with a classic analogue reconstruction methodology. The reconstruction experiments are performed at annual and decadal resolution. We implement chronological uncertainties inherent to marine proxies as a novelty, using a simulated age-model ensemble covering the past millennium. Our experiments comprise different scenarios for the input data network, with the noise levels added to the target variable extending from ideal to realistic. Results show that both methodologies are able to reconstruct the Summer mean SST skillfully when the proxy network is considered absolutely dated, but the skill of the analogue method is superior to BARCAST. Only the analogue method provides skillful correlations with the true target variable in the case of a realistic noisy and age-uncertain proxy network. The spatiotemporal properties of the input target data are partly contrasting with the BARCAST model formulations, resulting in an inferior reconstruction ensemble that is similar to a white-noise stochastic process in time. The analogue method is also successful in reconstructing decadal temperatures, while BARCAST fails. The results contribute to constraining uncertainties in CFR for ocean dynamics which are highly important for climate across the globe

Constraining two climate field reconstruction methodologies over the North Atlantic realm using pseudo-proxy experiments

This study presents pseudo-proxy experiments to quantify the reconstruction skill of two climate field reconstruction methodologies for a marine proxy network subject to age uncertainties. The BARCAST methodology (Bayesian Algorithm for Reconstructing Climate Anomalies in Space and Time) is tested for sea surface temperature (SST) reconstruction for the first time over the northern North Atlantic region, and compared with a classic analogue reconstruction methodology. The reconstruction experiments are performed at annual and decadal resolution. We implement chronological uncertainties inherent to marine proxies as a novelty, using a simulated age-model ensemble covering the past millennium. Our experiments comprise different scenarios for the input data network, with the noise levels added to the target variable extending from ideal to realistic. Results show that both methodologies are able to reconstruct the Summer mean SST skillfully when the proxy network is considered absolutely dated, but the skill of the analogue method is superior to BARCAST. Only the analogue method provides skillful correlations with the true target variable in the case of a realistic noisy and age-uncertain proxy network. The spatiotemporal properties of the input target data are partly contrasting with the BARCAST model formulations, resulting in an inferior reconstruction ensemble that is similar to a white-noise stochastic process in time. The analogue method is also successful in reconstructing decadal temperatures, while BARCAST fails. The results contribute to constraining uncertainties in CFR for ocean dynamics which are highly important for climate across the globe

Constraining two climate field reconstruction methodologies over the North Atlantic realm using pseudo-proxy experiments

This study presents pseudo-proxy experiments to quantify the reconstruction skill of two climate field reconstruction methodologies for a marine proxy network subject to age uncertainties. The BARCAST methodology (Bayesian Algorithm for Reconstructing Climate Anomalies in Space and Time) is tested for sea surface temperature (SST) reconstruction for the first time over the northern North Atlantic region, and compared with a classic analogue reconstruction methodology. The reconstruction experiments are performed at annual and decadal resolution. We implement chronological uncertainties inherent to marine proxies as a novelty, using a simulated age-model ensemble covering the past millennium. Our experiments comprise different scenarios for the input data network, with the noise levels added to the target variable extending from ideal to realistic. Results show that both methodologies are able to reconstruct the Summer mean SST skillfully when the proxy network is considered absolutely dated, but the skill of the analogue method is superior to BARCAST. Only the analogue method provides skillful correlations with the true target variable in the case of a realistic noisy and age-uncertain proxy network. The spatiotemporal properties of the input target data are partly contrasting with the BARCAST model formulations, resulting in an inferior reconstruction ensemble that is similar to a white-noise stochastic process in time. The analogue method is also successful in reconstructing decadal temperatures, while BARCAST fails. The results contribute to constraining uncertainties in CFR for ocean dynamics which are highly important for climate across the globe

Constraining two climate field reconstruction methodologies over the North Atlantic realm using pseudo-proxy experiments

This study presents pseudo-proxy experiments to quantify the reconstruction skill of two climate field reconstruction methodologies for a marine proxy network subject to age uncertainties. The BARCAST methodology (Bayesian Algorithm for Reconstructing Climate Anomalies in Space and Time) is tested for sea surface temperature (SST) reconstruction for the first time over the northern North Atlantic region, and compared with a classic analogue reconstruction methodology. The reconstruction experiments are performed at annual and decadal resolution. We implement chronological uncertainties inherent to marine proxies as a novelty, using a simulated age-model ensemble covering the past millennium. Our experiments comprise different scenarios for the input data network, with the noise levels added to the target variable extending from ideal to realistic. Results show that both methodologies are able to reconstruct the Summer mean SST skillfully when the proxy network is considered absolutely dated, but the skill of the analogue method is superior to BARCAST. Only the analogue method provides skillful correlations with the true target variable in the case of a realistic noisy and age-uncertain proxy network. The spatiotemporal properties of the input target data are partly contrasting with the BARCAST model formulations, resulting in an inferior reconstruction ensemble that is similar to a white-noise stochastic process in time. The analogue method is also successful in reconstructing decadal temperatures, while BARCAST fails. The results contribute to constraining uncertainties in CFR for ocean dynamics which are highly important for climate across the globe

Kontroverse : Anmerkungen zu Wolfgang J. Steinle: "Der Beitrag kleinerer und mittlerer Unternehmen zur Beschäftigungsentwicklung" in MittAB, Heft 2, 1984

Die Autoren begründen in diesem Beitrag ihre Kritik an dem in Heft 2/1984 der "Mitteilungn aus der Arbeitsmarkt- und Berufsforschung" veröffentlichten Aufsatz von W. J. Steinle. Die Kritik bezieht sich vor allem auf das analytisch-methodische Vorgehen des Verfassers. (IAB)Mittelbetrieb, Kleinbetrieb, Beschäftigungseffekte - Kritik

CCBR-Driven Business Process Evolution

Process-aware information systems (PAIS) allow coordinating the execution of business processes by providing the right tasks to the right people at the right time. In order to support a broad spectrum of business processes, PAIS must be flexible at run-time. Ad-hoc deviations from the predefined process schema as well as the quick adaptation of the process schema itself due to changes of the underlying business processes must be supported. This paper presents an integrated approach combining the concepts and methods provided by the process management systems ADEPT and CBRFlow. Integrating these two systems enables ad-hoc modifications of single process instances, the memorization of these modifications using conversational case-based reasoning, and their reuse in similar future situations. In addition, potential process type changes can be derived from cases when similar ad-hoc modifications at the process instance level occur frequently