Mass spectrometric analysis of nanoparticle formation in premixed low-pressure flames

Die vorliegende Arbeit umfasst Untersuchungen zu Bildung und Wachstum von Eisenoxid- und Wolf-ramoxid-Nanopartikeln in einem vorgemischten Niederdruckflammenreaktor bei Zugabe von Eisenpenta¬carbonyl (Fe(CO)5) beziehungsweise Wolframhexafluorid (WF6) als Prekursor. In Niederdruckflammen können die Partikelbildungsprozesse mithilfe von Molekularstrahl-Probenahmetechniken und laseroptischen Messverfahren im Detail untersucht werden. Mit diesem Untersuchungssystem konnte der bestehende Reaktionsmechanismus zur Synthese von Eisenoxid-Nanopartikeln aus Flammen ergänzt und validiert werden. Hinsichtlich eines Reaktionsmechanismus für die Synthese von Wolframoxid-Nanopartikeln aus Flammen wurden wichtige Intermediate identifiziert und deren Konzentrationsprofile ermittelt, wodurch die Erstellung eines Mechanismus ermöglicht wurde. Es wurde festgestellt, dass sich die Zerfallskinetik der beiden Prekursoren erheblich unterscheidet. Wäh-rend Fe(CO)5 bereits vor der Flammenfront aufgrund der lokalen Temperatur zerfällt und zur intermediären Bildung von Eisen-Clustern führt, reagiert WF6 mit dem in der Flamme gebildeten Wasser. Für Eisenoxid wurden die Zerfallsprodukte des Prekursors und die Wachstumsspezies des Reaktions-mechanismus über Flugzeitmassenspektrometrie (TOF-MS) erstmal in der Niederdruckflamme nachge-wiesen. Messungen mit Partikelmassenspektrometrie (PMS) konnten zeigen, dass ein monotones Parti-kelwachstum vorliegt. Abweichungen von diesem Wachstum, wie sie in der Vergangenheit beobachtet wurden, konnten auf durch Auftriebseffekte verursachte Artefakte zurückgeführt werden. Die Synthese von Wolframoxid-Nanopartikeln wurde erstmals umfassend mit Inline-Messungen unter-sucht. Es konnten sowohl stöchiometrische als auch unterstöchiometrische WOx-Cluster als wesentliche Intermediate des Wachstumsprozesses identifiziert werden. Es liegt ein schrittweises Wachstum vor, bei dem größere WO3-Cluster auf Kosten kleinerer Cluster wachsen. Die mit PMS und Quarzmikrowaage (QCM) detektierbaren Spezies wachsen anschließend aus den größeren Clustern. Erstmals konnte die Größenverteilung geladener Nanopartikel mit einer Quarzmikrowaage ermittelt werden, wobei sich wie erwartet eine massebasierte Größenverteilung einstellt, anstelle der anzahlbasierten Größenverteilung aus den Messungen mit einem PMS und Faraday-Detektoren. Aufgrund der höheren Messzeit und der schlechteren Nachweisbarkeit kleiner Partikel bei Verwendung einer QCM im Vergleich mit klassischen PMS-Messungen erweist sich diese Methode nicht als vorteilhaft. Die Kombination von QCM- und PMS-Messungen liefert wichtige Zusatzinformationen. Es konnte nachgewiesen werden, dass die Aufladung der Partikel auf Kollisionen mit geladenen Flammenionen beruht, der Einfluss von thermischer Aufladung der Partikel kann bei den vorliegenden Prozessbedingungen der Par¬tikelsynthese vernachlässigt werden. Der Anteil geladener Partikel konnte dabei aus den Massendepositionsraten auf einer Mikrowaage auf der Achse des Molekularstrahls mit und ohne angelegte Ablenkspannung bestimmt werden. Das Verhältnis von positiv zu negativ geladenen Partikeln wurde aus den PMS-Signalen berechnet. Das Vorliegen von unterstöchiometrischem Wolframoxid konnte schon während der Synthese in Form von Clustern mit einem fehlenden Sauerstoffatom gezeigt werden, dieser Zusammenhang zwischen nachweis¬baren Intermediaten und Eigenschaften der resultierenden Nanopartikel stellt einen weiteren Schritt auf dem Weg zur detaillierten Beschreibung der Synthese metalloxidischer Nanopartikel in Flammen dar.In this thesis, the combustion synthesis of nanoscale iron-oxide and tungsten-oxide particles from the precursors iron pentacarbonyl (Fe(CO)5) and tungsten hexafluoride (WF6) is investigated in a low-pressure flat flame. Low-pressure flat flames allow a detailed investigation of the particle formation and growth mechanism. The reactor is equipped with molecular-beam sampling of post-flame gases at varia-ble height above burner (HAB) and can as well be studied by laser-optical in situ methods. On the one hand, the established reaction mechanism for the flame synthesis of iron oxide nanoparticles was com-pleted and validated. On the other hand, main intermediate tungsten species were identified aiming towards a reaction mechanism for tungsten oxide nanoparticles. While Fe(CO)5 decomposed rapidly in the preheating zone of the flame giving rise to iron clusters before reaching the flame front, WF6 reacts with water produced in the flame in the flame front. Regarding the synthesis of iron oxide the decomposition products of the precursor and the main intermediates of the particle growth mechanism have been studied for the first time in a low pressure flame using time-of-flight mass spectrometry (TOF-MS). As the burner has been shifted from a horizontal configuration to a configuration where the flame burns from bottom to top towards the sampling nozzle, buoyancy effects on the flow pattern could be avoided. This led to the observation of a monotonous particle growth measured by particle mass spectrometry (PMS) and a quartz crystal microbalance (QCM). This result indicates that previous measurements with horizontally-arranged flames have partially been affected by buoyancy leading to an erroneous determination of particle growth rates at large distances from the burner. Inline measurements of import intermediates of the growth of WOx nanoparticles were performed for the first time. Stoichiometric as well as sub-stoichiometric clusters of tungsten oxide were identified as main intermediates of the subsequent WOx particle formation process. With increasing HAB, (WO3)n clusters with increasing cluster size appear in the burnt gases at the expense of the concentration of W1 species. Small clusters appear at larger HAB compared to W1 species, followed by larger clusters at even larger HABs. Within this work, the particle-size distribution of charged nanoparticles was measured for the first time using a QCM as the detector instead of a Faraday cup. As a QCM measures deposited mass rather than the number of charges, the particle-size distribution is mass related. The mass related distribution can be converted to the standard number-based PMS distribution using Hatch-Choate equations for log-normally distributed particle sizes. Compared to the classical PMS measurements, the use of a QCM to measure deflected nanoparticles leads to longer measurement times and reduced sensitivity for smaller particles, which makes this method less suitable for detailed studies of particle growth in the initial phase. Complementing PMS measurements with QCM measurements on the axis of the molecular beam offers the possibility to measure the fraction of charged nanoparticles in the molecular beam. By using this approach, collisions of particles with flame ions could be identified as the main charging mechanism of the metal-oxide nanoparticles for our conditions. The absolute amount of charged nanoparticles was evaluated by comparing the mass deposition rate on the axis with and without applying a deflection voltage. The relative amount of positively and negatively charged nanoparticles was calculated from the PMS signal. The formation of sub-stoichiometric tungsten-oxide particles that is observed under oxygen-deficient flame conditions was studied for the first time also in the early phase based on oxygen-deficient clusters detected via TOF-MS. Linking product properties with measureable intermediates is another key step towards the detailed description of the synthesis of metal-oxide nanoparticles

Clofibrate treatment in pigs: Effects on parameters critical with respect to peroxisome proliferator-induced hepatocarcinogenesis in rodents

BACKGROUND: In rodents treatment with fibrates causes hepatocarcinogenesis, probably as a result of oxidative stress and an impaired balance between apoptosis and cell proliferation in the liver. There is some debate whether fibrates could also induce liver cancer in species not responsive to peroxisome proliferation. In this study the effect of clofibrate treatment on peroxisome proliferation, production of oxidative stress, gene expression of pro- and anti-apoptotic genes and proto-oncogenes was investigated in the liver of pigs, a non-proliferating species. RESULTS: Pigs treated with clofibrate had heavier livers (+16%), higher peroxisome counts (+61%), higher mRNA concentration of acyl-CoA oxidase (+66%), a higher activity of catalase (+41%) but lower concentrations of hydrogen peroxide (-32%) in the liver than control pigs (P < 0.05); concentrations of lipid peroxidation products (thiobarbituric acid-reactive substances, conjugated dienes) and total and reduced glutathione in the liver did not differ between both groups. Clofibrate treated pigs also had higher hepatic mRNA concentrations of bax and the proto-oncogenes c-myc and c-jun and a lower mRNA concentration of bcl-X(L )than control pigs (P < 0.05). CONCLUSION: The data of this study show that clofibrate treatment induces moderate peroxisome proliferation but does not cause oxidative stress in the liver of pigs. Gene expression analysis indicates that clofibrate treatment did not inhibit but rather stimulated apoptosis in the liver of these animals. It is also shown that clofibrate increases the expression of the proto-oncogenes c-myc and c-jun in the liver, an event which could be critical with respect to carcinogenesis. As the extent of peroxisome proliferation by clofibrate was similar to that observed in humans, the pig can be regarded as a useful model for investigating the effects of peroxisome proliferators on liver function and hepatocarcinogenesis

Workers' Participation in Europe: Challenges facing the European policy of the European Parliament and the European Commission for 2014 and subsequent years

- The economic and financial crisis has raised questions about the meaning and purpose of corporate governance. After the manifest failure of the economic-liberal "shareholder value" model, a new model of "good corporate governance" deserves a closer look. How can this be optimally backed up and embedded in European company law, as well as in the European Directives on employee involvement? - In 18 of the 28 EU Member States, employee participation in top-level management is provided for by law. In 12 EU Member States and in Norway, these practices are widespread. Workers' participation at company board level is a core component of European company law, and information and consultation are basic rights in a social Europe. - European policy must pay attention to protecting, strengthening and further developing workers' rights in the interest of enhancing Europe in the eyes of its citizens and for the sake of its economy. There should be no loopholes that make it possible to circumvent workers' participation

Mitbestimmung in Europa: Anforderungen an die Politik des Europäischen Parlaments und der EU-Kommission für 2014 und Folgejahre

- Die Finanz- und Wirtschaftskrise hat Fragen uber Sinn und Ziel von Unternehmensführung aufgeworfen. Nach dem offensichtlichen Scheitern des liberalen Shareholder Value Modells geht es um ein neues Leitbild "guter Unternehmensfuhrung". Wie kann dieses Leitbild optimal im europäischen Gesellschaftsrecht sowie in den Europäischen Richtlinien zur Arbeitnehmerbeteiligung begleitet und verankert werden? - In 18 der 28 EU-Mitgliedsstaaten gibt es gesetzliche Moglichkeiten zur Arbeitnehmerbeteiligung an der Unternehmensspitze. In 12 EU-Staaten und in Norwegen ist sie weit verbreitet. Mitbestimmung ist ein Kernbestandteil des europäischen Gesellschaftsrechts und Unterrichtung und Anhorung sind Grundrechte eines sozialen Europas. - Europaische Politik muss sich im Interesse eines attraktiven Europas fur seine Bürgerinnen und Bürger sowie fur seine Wirtschaft um Schutz, Stärkung und Weiterentwicklung von Arbeitnehmerrechten kümmern. Schlupflöcher zur Umgehung von Mitbestimmung darf es nicht geben

People’s reactions to decisions by human vs. algorithmic decision-makers: the role of explanations and type of selection tests

Research suggests that people prefer human over algorithmic decision-makers at work. Most of these studies, however, use hypothetical scenarios and it is unclear whether such results replicate in more realistic contexts. We conducted two between-subjects studies (N=270; N=183) in which the decision-maker (human vs. algorithmic, Study 1 and 2), explanations regarding the decision- process (yes vs. no, Study 1 and 2), and the type of selection test (requiring human vs. mechanical skills for evaluation, Study 2) were manipulated. While Study 1 was based on a hypothetical scenario, participants in pre-registered Study 2 volunteered to participate in a qualifying session for an attractively remunerated product test, thus competing for real incentives. In both studies, participants in the human condition reported higher levels of trust and acceptance. Providing explanations also positively influenced trust, acceptance, and perceived transparency in Study 1, while it did not exert any effect in Study 2. Type of the selection test affected fairness ratings, with higher ratings for tests requiring human vs. mechanical skills for evaluation. Results show that algorithmic decision-making in personnel selection can negatively impact trust and acceptance both in studies with hypothetical scenarios as well as studies with real incentives

People’s reactions to decisions by human vs. algorithmic decision-makers: the role of explanations and type of selection tests

Research suggests that people prefer human over algorithmic decision-makers at work. Most of these studies, however, use hypothetical scenarios and it is unclear whether such results replicate in more realistic contexts. We conducted two between-subjects studies (N=270; N=183) in which the decision-maker (human vs. algorithmic, Study 1 and 2), explanations regarding the decision- process (yes vs. no, Study 1 and 2), and the type of selection test (requiring human vs. mechanical skills for evaluation, Study 2) were manipulated. While Study 1 was based on a hypothetical scenario, participants in pre-registered Study 2 volunteered to participate in a qualifying session for an attractively remunerated product test, thus competing for real incentives. In both studies, participants in the human condition reported higher levels of trust and acceptance. Providing explanations also positively influenced trust, acceptance, and perceived transparency in Study 1, while it did not exert any effect in Study 2. Type of the selection test affected fairness ratings, with higher ratings for tests requiring human vs. mechanical skills for evaluation. Results show that algorithmic decision-making in personnel selection can negatively impact trust and acceptance both in studies with hypothetical scenarios as well as studies with real incentives

Three-Dimensional Biomechanical Analysis of Rearfoot and Forefoot Running

Background: In the running community, a forefoot strike (FFS) pattern is increasingly preferred compared with a rearfoot strike (RFS) pattern. However, it has not been fully understood which strike pattern may better reduce adverse joint forces within the different joints of the lower extremity. Purpose: To analyze the 3-dimensional (3D) stress pattern in the ankle, knee, and hip joint in runners with either a FFS or RFS pattern. Study Design: Descriptive laboratory study. Methods: In 22 runners (11 habitual rearfoot strikers, 11 habitual forefoot strikers), RFS and FFS patterns were compared at 3.0 m/s (6.7 mph) on a treadmill with integrated force plates and a 3D motion capture analysis system. This combined analysis allowed characterization of the 3D biomechanical forces differentiated for the ankle, knee, and hip joint. The maximum peak force (MPF) and maximum loading rate (LR) were determined in their 3 ordinal components: vertical, anterior-posterior (AP), and medial-lateral (ML). Results: For both strike patterns, the vertical components of the MPF and LR were significantly greater than their AP or ML components. In the vertical axis, FFS was generally associated with a greater MPF but significantly lower LR in all 3 joints. The AP components of MPF and LR were significantly lower for FFS in the knee joint but significantly greater in the ankle and hip joints. The ML components of MPF and LR tended to be greater for FFS but mostly did not reach a level of significance. Conclusion: FFS and RFS were associated with different 3D stress patterns in the ankle, knee, and hip joint, although there was no global advantage of one strike pattern over the other. The multimodal individual assessment for the different anatomic regions demonstrated that FFS seems favorable for patients with unstable knee joints in the AP axis and RFS may be recommended for runners with unstable ankle joints. Clinical Relevance: Different strike patterns show different 3D stress in joints of the lower extremity. Due to either rehabilitation after injuries or training in running sports, rearfoot or forefoot running should be preferred to prevent further damage or injuries caused by inadequate biomechanical load. Runners with a history of knee joint injuries may benefit from FFS whereas RFS may be favorable for runners with a history of ankle joint injuries

Time-resolved optical shadowgraphy of solid hydrogen jets as a testbed to benchmark particle-in-cell simulations

Particle-in-cell (PIC) simulations are a superior tool to model kinetics-dominated plasmas in relativistic and ultrarelativistic laser-solid interactions (dimensionless vectorpotential $a_0 > 1$). The transition from relativistic to subrelativistic laser intensities ($a_0 \lesssim 1$), where correlated and collisional plasma physics become relevant, is reaching the limits of available modeling capabilities. This calls for theoretical and experimental benchmarks and the establishment of standardized testbeds. In this work, we develop such a suitable testbed to experimentally benchmark PIC simulations using a laser-irradiated micron-sized cryogenic hydrogen-jet target. Time-resolved optical shadowgraphy of the expanding plasma density, complemented by hydrodynamics and ray-tracing simulations, is used to determine the bulk-electron temperature evolution after laser irradiation. As a showcase, a study of isochoric heating of solid hydrogen induced by laser pulses with a dimensionless vectorpotential of $a_0 \approx 1$ is presented. The comparison of the bulk-electron temperature of the experiment with systematic scans of PIC simulations demostrates that, due to an interplay of vacuum heating and resonance heating of electrons, the initial surface-density gradient of the target is decisive to reach quantitative agreement at \SI{1}{\ps} after the interaction. The showcase demostrates the readiness of the testbed for controlled parameter scans at all laser intensities of $a_0 \lesssim 1$

Efficient laser-driven proton acceleration from cylindrical and planar cryogenic hydrogen jets.

We report on recent experimental results deploying a continuous cryogenic hydrogen jet as a debris-free, renewable laser-driven source of pure proton beams generated at the 150 TW ultrashort pulse laser Draco. Efficient proton acceleration reaching cut-off energies of up to 20 MeV with particle numbers exceeding 109 particles per MeV per steradian is demonstrated, showing for the first time that the acceleration performance is comparable to solid foil targets with thicknesses in the micrometer range. Two different target geometries are presented and their proton beam deliverance characterized: cylindrical (∅ 5 μm) and planar (20 μm × 2 μm). In both cases typical Target Normal Sheath Acceleration emission patterns with exponential proton energy spectra are detected. Significantly higher proton numbers in laser-forward direction are observed when deploying the planar jet as compared to the cylindrical jet case. This is confirmed by two-dimensional Particle-in-Cell (2D3V PIC) simulations, which demonstrate that the planar jet proves favorable as its geometry leads to more optimized acceleration conditions