44 research outputs found
Neue Formen der Zusammenarbeit - Die Kooperation in den digitalen und globalen Arbeitsräumen der IT-Branche
No full textIm Fokus der Forschungsarbeit steht die Frage danach, welche Formen die Zusammenarbeit in globalen Projekten annimmt, wenn diese auf der Basis moderner Informations- und Kommunikationstechnologien stattfindet. IT Tools wie Wikis, Chats und Collaboration Software als Basis standortübergreifender Projekte verändern die Arbeit. Es wird deutlich, dass die Tätigkeiten auf Arbeitsebene, der Aufbau sozialer Beziehungen zwischen den Kooperationspartnern und das Teilen von Wissen andere Formen annehmen. Welche das sind, ist immer auch ein Ergebnis des sozialen Kontextes in den verschiedenen Projekten. Aus diesem Grund sind sie immer auch Gegenstand von sozialen Aushandlungsprozessen. Die Untersuchung findet anhand von Fallanalysen eines globalen Softwareunternehmens und eines Open Source Projektes statt
Identifying collaboration dynamics of bipartite author-topic networks with the influences of interest changes
No full textKnowing driving factors and understanding researcher behaviors from the dynamics of collaborations over time offer some insights, i.e. help funding agencies in designing research grant policies. We present longitudinal network analysis on the observed collaborations through co-authorship over 15 years. Since co-authors possibly influence researchers to have interest changes, by focusing on researchers who could become the influencer, we propose a stochastic actor-oriented model of bipartite (two-mode) author-topic networks from article metadata. Information of scientific fields or topics of article contents, which could represent the interests of researchers, are often unavailable in the metadata. Topic absence issue differentiates this work with other studies on collaboration dynamics from article metadata of title-abstract and author properties. Therefore, our works also include procedures to extract and map clustered keywords as topic substitution of research interests. Then, the next step is to generate panel-waves of co-author networks and bipartite author-topic networks for the longitudinal analysis. The proposed model is used to find the driving factors of co-authoring collaboration with the focus on researcher behaviors in interest changes. This paper investigates the dynamics in an academic social network setting using selected metadata of publicly-available crawled articles in interrelated domains of "natural language processing" and "information extraction". Based on the evidence of network evolution, researchers have a conformed tendency to co-author behaviors in publishing articles and exploring topics. Our results indicate the processes of selection and influence in forming co-author ties contribute some levels of social pressure to researchers. Our findings also discussed on how the co-author pressure accelerates the changes of interests and behaviors of the researchers.</p
Modeling Legal Requirements
No full textS.418-433Ever increasing complexity is one of the key challenges for software-intensive systems. All phases of the system engineering lifecycle are affected; thus, appropriate methods, techniques, and tools must be provided to manage this increasing complexity. Another challenge arises from the fact that requirements are traditionally documented in natural language. This is especially true for legal artifacts such as laws or standards, since organizations are required to consider these kinds of legal requirements when bringing products to the market. Applying model-based engineering approaches is one possibility to address these problems, but methodical uncertainties caused by a lack of method support have so far prevented their widespread use in early project phases. This paper addresses these uncertainties by introducing a systematic approach for modeling legal artifacts such as laws or standards. The method is assessed in the context of emission legislation in the automotive domain.27Nr.
Discrete Multitone Modulation for Maximizing Transmission Rate in Step-Index Plastic Optical Fibres
No full textThe use of standard 1-mm core-diameter step-index plastic optical fiber (SI-POF) has so far been mainly limited to distances of up to 100 m and bit-rates in the order of 100 Mbit/s. By use of digital signal processing, transmission performance of such optical links can be improved. Among the different technical solutions proposed, a promising one is based on the use of discrete multitone (DMT) modulation, directly applied to intensity-modulated, direct detection (IM/DD) SI-POF links. This paper presents an overview of DMT over SI-POF and demonstrates how DMT can be used to improve transmission rate in such IM/DD systems. The achievable capacity of an SI-POF channel is first analyzed theoretically and then validated by experimental results. Additionally, first experimental demonstrations of a real-time DMT over SI-POF system are presented and discusse
Synthesis and electrochemical characterization of thiophenes with pendant fluorescent terpyridine
No full textA novel series of thiophenes with terpyridine pendant groups were synthesized by Steglich esterification in the presence of DCC/DMAP and the synthesized monomers were electrochemically polymerized onto microelectrodes using glassy carbon and carbon fiber as active electrode materials. Each pendant group has aliphatic spacers with different chain lengths affecting the movement of the terpyridine groups. The synthesized thiophene derivatives were characterized by electrochemical and spectroscopic methods. The electrochemical impedance spectroscopic measurements of polythiophene-terpyridine (PTh-Terpy) derivatives were given comparatively. The fluorescence properties of the compounds were observed; all compounds were fluorescent, with higher fluorescence intensity for the shorter chain length, and slightly reduced fluorescence relative to that of the free terpyridine fluorophore. Morphological characterization was achieved via scanning electron microscopy
Synthesis, electrochemistry and fluorescence behavior of thiophene derivatives decorated with coumarin, pyrene and naphthalene moieties
No full textA novel series of functionalized thiophenes incorporating coumarin, pyrene and naphthalene pendants were synthesized by Steglich esterification in the presence of DCC/DMAP (dicyclohexylcarbodiimide/N,N-dimethylaminopyridine) and the synthesized monomers were electrochemically deposited onto glassy carbon and carbon fiber micro electrodes as active electrode materials. The synthesized thiophene derivatives were characterized by 1H NMR, 13C NMR, FTIR, cyclic voltammetry, electrochemical impedance spectroscopy and electronic absorption as well as fluorescence spectroscopy. An electrochemical impedance study was performed on the surface modified electrodes. Variation of capacitance values was explained according to the different fluorophore groups attached to the thiophene as well as the different substrates. The fluorescence properties of the three compounds in dimethylsulfoxide were measured, with varying effects of the thiophene moiety on the fluorescence emission. The morphology of the monomers was monitored using SEM
Stereoselektive Synthesen von quartären alpha-Aminosäuren unter Verwendung von Chemo- und Biokatalysatoren
No full textAim of this Ph.D.-thesis was the synthesis of alpha,alpha-dialkyl amino acids of type 4 via novel synthetic approaches applying a catalytic key step for the enantioselective construction (or resolution) of the quaternary stereogenic center. To reach this aim, three different synthetic concepts based on three different catalytic key steps, namely addition to a sp2-hybridised carbon, desymmetrisation and kinetic resolution, were examined intensively. Modern methods of organocatalysis and biocatalysis were applied in these key steps. Steglich rearrangement was chosen as an example of an organocatalytic addition to a sp2-hybridised carbon. Enantioselective Steglich rearrangement of acyl groups such as acetyl allows acces to beta-hydroxy alpha,alpha-dialkyl amino acids of type 16. The key step is catalysed most effectively by applying chiral cyclic isothioureas (“Birman-type catalyst”) such as (S)-tetramisole ((S)-59) or (R)-benzotetramisole ((R)-60a), which showed superior enantioselectivities when compared to planar chiral aminopyridine catalysts (“Fu-type catalysts”) such as (S)-49a or (S)-49d. It was shown that a combination of an enantioselective organocatalytic Steglich rearrangement and subsequent diastereoselective reduction using sodium borohydride and N-Boc-proline as reducing agent is a suitable and practical synthetic route towards all stereoisomers of (enantiomerically enriched) alpha-methyl threonine (16a). Furthermore, stereoselctive induction is possible at both stages, thus offering the potential for obtaining a high “overall” enantiomeric excess. As an example of desymmetrisation for the construction of quaternary stereogenic centers, PLE-catalysed hydrolysis of malonates was chosen, since no suitable enzyme for the ammonolysis of malonates could be identified. Even though this method was literature known in general, further examinations were needed for the optimisation of this biocatalytic key step. Application of an optimised reaction media (consisting of buffer - isopropanol, 7:3) allowed access to the desired key intermediate 79b with a high enantiomeric excess of 95% ee. Monoester 79b was converted into desired (S)-2,5-dimethyl norleucine ((S)-14b) as a representative of the product class of alpha-methylated aliphatic amino acids 14. A satisfactory overall yield of 37% related to malonate 28b was obtained for this amino acid (S)-14b. In addition, the inversion of the stereogenic center of malonate monoester is well known; hence the synthesis of both enantiomers is principally possible by this method. However, the synthesis of beta-hydroxy alpha,alpha-dialkyl amino acids of type 16 as well as the synthesis of alpha-methylated phenylalanines of type 20 by this synthetic route turned out to be insufficient. In contrast, the enantioselective synthesis of alpha-methylated substituted phenylalanines of type 20 was possible by kinetic resolution of a racemic azo compound rac-32a as a key step. The lipase CAL-B was identified as a suitable enzyme for the kinetic resolution of azo compound rac-32a. An enantioselectivity of the resolution step of E=24 was achieved when using CAL-B as a biocatalyst in the optimised solvent mixture consisting of MTBE and buffer. The enantiomerically enriched product 31a of this key step was converted into alpha,O-dimethyl tyrosine (20a) as a representative of the product class of alpha-methylated phenylalanines 20. Altogether three new synthetic strategies towards enantiomerically enriched alpha,alpha-dialkyl amino acids of type 4 were investigated. Each strategy is based on a catalytic enantioselective key step. All three desired sub-classes, beta-hydroxy alpha,alpha-dialkyl amino acids 16, alpha-methylated aliphatic amino acids 14 and alpha-methylated substituted phenylalanines 20 are available by the application of one of these strategies. As none of these novel synthetic strategies is general (allowing access to all subclasses of alpha,alpha-dialkyl amino acids 4), each strategy can be called “tailor made” for a specific subclass. Access to all stereoisomers of the desired products is possible, starting from easily available substrates and applying readily commercial available catalysts. The criterion of high conversion, yields and selectivities was met in most cases. However, further improvements with respect to e. g. yield and selectivity are needed in the future to increase the applicability of the new strategies. Since methods to improve the catalysts (either by synthesis of novel thioureas or by enzyme-engineering of the applied enzymes) are readily known, there is potential to achieve these improvements in the future. As all synthetic approaches meet the criterion of few and easy to handle synthetic steps, they represent a good basis for further investigations towards the development of highly effective synthesis of alpha,alpha-dialkyl amino acids 4.Ziel dieser Doktorarbeit war die Synthese von alpha,alpha-Dialkylaminosäuren 4 über neuartige Synthesewege, welche einen katalytischen Schlüsselschritt für den enantioselektiven Aufbau (oder die Racematspaltung) eines quartären Kohlenstoffzentrums verwenden. Um dieses Ziel zu erreichen, wurden drei verschiedene synthetische Konzepte intensiv untersucht. Diese Konzepte basieren auf drei verschiedene katalytische Schlüsselschritte - Addition an ein sp2-hybridisiertes Kohlenstoffatom, Desymmetrisierung und kinetische Racematspaltung. Moderne Methoden der Organo- und Biokatalyse sollten hierfür in den Schlüsselschritten angewendet werden. Die Steglich-Umlagerung wurde als ein Beispiel für eine organokatalytische Addition an ein sp2-hybridisiertes Kohlenstoffatom ausgewählt. Enantioselektive Steglich-Umlagerungen von Acylgruppen können dazu verwendet werden beta-Hydroxy-alpha,alpha-dialkylaminosäuren vom Typ 16 zu synthetisieren. Im Rahmen dieser Arbeit wurde gefunden, dass dieser Schlüsselschritt am effektivsten durch Verwendung chiraler cyclischer Isothioharnstoffe (Birman-Katalysatoren) bewerkstelligt wird. Diese Isothioharnstoffe erbrachten bessere Enantioselektivitäten, verglichen mit planar chiralen Aminopyridinderrivaten („Fu-Katalysatoren“) . Es wurde gezeigt, dass die Kombination einer enantioselektiven organokatalytischen Steglich-Umlagerung und nachfolgender diastereoselektiven Reduktion unter Verwendung von Natriumborhydrid und N-Boc-Prolin als Reduktionsmittel eine sinnvolle und praktische Syntheseroute zur Synthese aller Stereoisomere von (enantiomerenangereicherten) alpha-Methlythreonin (16a) darstellt. Außerdem ist eine stereoselektive Induktion auf beiden Stufen möglich, so dass ein hoher „Gesamtenantiomerenüberschuss“ resultiert. Als Beispiel für eine Desymmetrisierung zum Aufbau des quartären Stereozentrums einer alpha,alpha-Dialkylaminosäure 4 wurde die PLE-katalysierte Hydrolyse von Malonaten 28 gewählt. Die Anwendung eines optimierten Reaktionsmediums erlaubte den Zugang zum gewünschten Schlüsselintermediat (R)-79b mit einem hohen Enantiomerenüberschuss von 95% ee. Der Monoester (R)-79b wurde in die gewünschte Zielverbindung (S)-2,5-Dimethylnorleucin ((S)-14b), einem Repräsentanten der Produktklasse der alpha-methylierten aliphatischen Aminosäuren 14, umgesetzt. Für diese Aminosäure (S)-14b wurde eine zufriedenstellende Gesamtausbeute von 37%, bezogen auf das Malonat 28b, erhalten. Die Synthese von beta-Hydroxy-alpha,alpha-dialkylaminosäuren vom Typ 16 über diese Syntheseroute erwies sich jedoch als unbefriedigend, genauso wie die Synthese von alpha-methylierten Phenylalaninen vom Typ 20. Im Gegensatz dazu ist die enantioselektive Synthese von alpha-methylierten substituierten Phenylalaninen vom Typ 20 unter Verwendung einer kinetischen Racematspaltung der racemischen Azoverbindung rac-32a als Schlüsselschritt möglich. Die Lipase CAL-B wurde als ein nützlicher Biokatalysator für diese kinetische Racematspaltung identifiziert. Eine Enantioselektivität von E=24 wird erreicht, wenn CAL-B im optimierten Solvensgemisch aus Puffer und MTBE verwendet wird. Das enantiomerenangereicherte Produkt 31a dieses Schlüsselschrittes wurde zu alpha,O-Dimethyltyrosin (20a), einem Vertreter der Produktklasse der alpha-methylierten Phenylalanine 20, umgesetzt. Insgesamt wurden drei neue Synthesestrategien für enantiomerenangereicherte alpha,alpha-Dialkylaminosäuren vom Typ 4 untersucht. Dabei basiert jede Strategie auf einem katalytischen enantioselektiven Schlüsselschritt. Alle drei gewünschten Unterklassen, beta-Hydroxy-alpha,alpha-dialkylaminosäuren 16, alpha-methylierte aliphatische Aminosäuren 14 und alpha-methylierte substituierte Phenylalanine 20, sind nun über eine dieser Strategien verfügbar. Da keine dieser neuartigen Synthesestrategien allgemein ist (Zugang zu allen Unterklassen von alpha,alpha-Dialkylaminosäuren 4), kann man jede Strategie „maßgeschneidert“ für eine spezifische Produktklasse nennen. Dabei ist der Zugang zu allen Stereoisomeren möglich, ausgehend von einfach erhaltbaren Substraten unter Verwendung von kommerziell erhältlichen Katalysatoren. Das Kriterium hoher Umsätze, Ausbeuten und Selektivitäten wurde meist erfüllt. Trotz alledem werden weitere Verbesserungen im Hinblick auf beispielsweise Ausbeuten und Selektivitäten nötig sein, um die Anwendbarkeit der neuen Strategien zu verbessern. Nachdem Methoden zur Verbesserung der verwendeten Katalysatoren bekannt sind (Synthese neuer Thioharnstoffe bzw. Mutation der verwendeten Enzyme), sollten weitere Verbesserungen erreichbar sein. Da alle Syntheserouten das Kriterium weniger und leicht handhabbarer Syntheseschritte erfüllen, stellen diese eine aussichtsreiche Basis für weitere Forschungsvorhaben mit dem Ziel der Entwicklung hocheffizienter Synthesen von alpha,alpha-Dialkylaminosäuren 4 dar
Heavy-fermion superconductivity: Experimental status report
No full textNew observations are reported for the heavy-fermion superconductors CeCu 2Si 2, UBe 13 and UPt 3. These results are discussed with respect to the following issues: (i) the competition between different cooperative phenomena in CeCu 2Si 2; (ii) the question whether the whole Fermi surface contributes to the superconducting transition in the three compounds; (iii) the nature of the superconducting order parameter. Taking into account more published data for these systems, the author can delineate the present status of the field: CeCu 2Si 2 behaves as a singlet superconductor with possibly anisotropic Cooper pairing. UPt 3 appears to possess an anisotropic order parameter, either of the singlet or triplet type. No definite conclusions can yet be drawn for UBe 13, mainly because its superconducting properties are severely modified by field and temperature dependences of the normal-state parameters
