Design and performance of an aerodynamic molecular beam and beam detection system

Design and performance of aerodynamic molecular beam syste

Durch Sprachförderung zum fachlichen Erfolg?

Im Rahmen des interdisziplinären Forschungsprojekts FaSaF wird der Einfluss einer evidenzbasierten Sprachförderung auf die Deutsch- und Mathematikfachleistung von Schülerinnen und Schülern untersucht. In diesem Zusammenhang werden zwei verschiedene Sprachförderkonzepte in der schulischen Praxis mit N=256 Schülerinnen und Schülern erprobt und bezüglich ihrer Effekte auf fachspezifische Leistungszuwächse wissenschaftlich untersucht. Aus mathematikdidaktischer Perspektive steht dabei vor allem der Einfluss der beiden Sprachförderkonzepte auf die Entwicklung der Modellierungskompetenz im Fokus der Forschungsarbeiten

Explosions of water clusters in intense laser fields

Energetic, highly-charged oxygen ions, $O^{q+}$ ($q\leq 6$), are copiously produced upon laser field-induced disassembly of highly-charged water clusters, $(H_2O)_n$ and $(D_2O)_n$, $n\sim$ 60, that are formed by seeding high-pressure helium or argon with water vapor. $Ar_n$ clusters (n$\sim$40000) formed under similar experimental conditions are found undergo disassembly in the Coulomb explosion regime, with the energies of $Ar^{q+}$ ions showing a $q^2$ dependence. Water clusters, which are argued to be considerably smaller in size, should also disassemble in the same regime, but the energies of fragment O$^{q+}$ ions are found to depend linearly on $q$ which, according to prevailing wisdom, ought to be a signature of hydrodynamic expansion that is expected of much larger clusters. The implication of these observations on our understanding of the two cluster explosion regimes, Coulomb explosion and hydrodynamic expansion, is discussed. Our results indicate that charge state dependences of ion energy do not constitute an unambiguous experimental signature of cluster explosion regime.Comment: Submitted to Phys. Rev.

An Experimental Technique for Determining Cycle-Resolved Pre-Combustion in-Cylinder Composition and its Application Towards the Understanding of Diesel Engine Emissions during Transient Operation.

This study introduces an experimental technique to quantify cycle-resolved values of pre-combustion in-cylinder compositions during transient engine operation. The work is motivated by increased particulate and NOX emissions during transient engine operation, which contribute significantly to overall cumulative diesel emissions. The study is divided into three major tasks: technique development, validation, and application to demonstrate its capability to provide new insight into transient engine behavior. One cylinder of a 6.0L V-8 diesel engine is instrumented to obtain cycle-resolved masses of three in-cylinder pre-combustion constituents: fuel, air, and stoichiometric combustion products. Fuel is determined through use of an instrumented fuel injector and cylinder pressure. The mass of air is determined through calculation of the air/fuel ratio of each cycle from measurements of CO2 concentrations in the exhaust and in the cylinder. Stoichiometric combustion product mass is quantified through the pre-combustion in-cylinder measurement of CO2. Validation of the technique is accomplished by first determining that the methodology does not significantly alter combustion. Error and sensitivity analysis confirm that the technique provides accurate results. The masses of fuel, air, and stoichiometric combustion products are known to ±0.74%, ±2.82%, and ±3.93%, respectively, with a 95th percentile confidence interval. The technique provides data on a cycle-by-cycle basis, a resolution that is unattainable with traditional test cell hardware. This allows insight into engine behavior that was previously impossible, especially during transient operation. Engine data is taken in three separate investigations: steady-state conditions, constant-speed load sweeps, and realistic in-vehicle engine behavior during an FTP 75 driving schedule. Cycle-resolved NO emissions and fast particulate measurements are also made to characterize transient emissions. During the first few cycles of intense accelerations, excessive levels of over-fueling occur, resulting in cycles with equivalence ratios as high as 1.4. These cycles cause extremely high particulate emissions. High levels of NO emissions occur 3-4 cycles into strong accelerations and are attributed to intensely-premixed combustion with high levels of in-cylinder oxygen. In summary, this study demonstrates that tighter cycle-resolved control of fuel injection and EGR systems, including internal residual, are necessary prerequisites for realizing the full potential of low-emissions transient engine operation strategies.Ph.D.Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/58436/1/jhagena_1.pd

Selenium-Containing Glycosides and Glycosyl Phosphates as Precursors of Glycosyl Epoxides: New Approaches to the Synthesis of (5-Fluoro) and (5-Cyano) Glycosides.

ABSTRACT Enzyme-catalyzed transformations of carbohydrates proceed through different transition states, which may be studied by altering the electron density at various positions of the carbohydrate ring. By placing fluorine near a developing partial charge of a donor substrate, the reaction may be inhibited due to destabilization of the transition state. The pKa of an acceptor alcohol is also lowered by fluorine, possibly affecting its nucleophilicity. Epoxide fluoridolysis has been previously used in our lab to synthesize (5-F) GlcNAc glycosides and glycosyl phosphates. This methodology involves a two-step process of oxidation of a phenylselenide to a selenoxide and thermal elimination with DHP. This thesis extends this fluoridolysis methodology to (5-F) isoLacNAc and (5-F) LacNAc glycosides and also investigates fluorination in the GalNAc series. Results from attempts at fluorination of the GalNAc glycosides have resulted in a premature epoxide opening hypothesis. This hypothesis was derived from differences in fluorination of glycosyl epoxides containing different neighboring protecting groups. In the pursuit of the (iso)LacNAc glycosides, selenium-containing monosaccharide acceptor substrates were unsuccessful in glycoside formation. In contrast, glycosylation of non-selenium containing monosaccharide acceptor substrates were successful in glycoside formation and were converted to selenium-containing disaccharides after glycosylation. The resulting selenium-containing disaccharides were then transformed into their corresponding epoxides and eventually into (5-F) isoLacNAc and (5-F) LacNAc glycosides. In addition to studying fluorinated glycosides, formation of a new stable C-C bond has been investigated. This new transformation would increase functionality on the carbohydrate ring by installing a CN group at C-5. The CN group was installed using a Lewis acid activator and TMS-CN in cyanosilylation of glycosyl epoxides. This new method allows for subsequent reduction of the CN functional group to an amine, which could then be transformed into a probe of carbohydrate metabolizing enzymes.Ph.D.ChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/58513/1/tconser_1.pd

Brennpunkt Afghanistan

Versuch einer historischen, geopolitischen, geostrategischen, militärpolitischen Erklärung des Afghanistan-Krieges. Argumente zur Sinnlosigkeit einer militärischen Problemlösung und zum Übergang zu einer politischen Regelung.:Autorenbeiträge: Hermann Hagena, Afghanistan: ein sinnloser Krieg? Arne C. Seifert, Den Krieg in Afghanistan beenden und sofort zu einer politischen Lösung übergehen. Redaktioneller Anhang: Übersichten, Karten; Bild- und Kartennachweise; Über die Autoren; Aktuelle Afghanistan-Dokumente und -Publikationen (Auswahl)