186,837 research outputs found
Peţirea primejdiosă : novelă
No full textPeţirea primejdiosă : novelă / de Ferdinand Stolle. - In: Noua bibliotecă română, p. 51-83
[heading right side:] Gedicht von Ferdinand Stolle WK
No full textf. 1v Beginn eines Liedfragments in E-Dur, mit dem Text "Die Sonn' ist schön und still geschieden" von Ferdinand Stolle. Eine andere Vertonung dieses Gedichtes unter D-KA, WK Mus.Ms. 42Wilhelm Kalliwoda [ermittelt]Diplomatischer Titel: [heading right side:] Gedicht von Ferdinand Stolle WK:Text: Ferdinand StolleQuelle: Autograph manuscriptProvenienz: Nachlass KalliwodaBesetzungshinweis: V, p
[heading:] Lied von Ferd: Stolle [right side:] WK
No full textWilhelm Kalliwoda [ermittelt]Diplomatischer Titel: [heading:] Lied von Ferd: Stolle [right side:] WK:Text: Ferdinand StolleQuelle: Autograph manuscriptProvenienz: Nachlass KalliwodaBesetzungshinweis: V, p
Intramolecular Diels-Alder reactions of pyrimidines, a synthetic and computational study
No full textThis thesis deals with an investigation on the ringtransformation reactions of 2and 5-(ω-alkynyl)pyrimidine derivatives, which undergo upon heating an intramolecular Diels-Alder reaction and subsequently a spontaneous retro Diels- Alder reaction. To get a better insight into the applicability and the mechanistic aspects of these conversions synthetical organic experiments were carried out and computational chemistry methods were used to explain the obtained results.In Chapter 1 a historical overview, a classification of the Diels-Alder reactions and a general introduction on computational chemistry is given, because the latter is a relatively unknown field within the organic chemistry. Finally the scope of this thesis is given.In Chapter 2 the synthesis and ringtransformations of 2-(2- trimethylsilylethynylphenyl-X)pyrimidines (X= O, S, NAc, CH 2 , CO, NH) are described. In case of X= O, S, NAc, CH 2 and CO this yields new tricyclic annelated heteroaromatic systems. Because the reaction rate of these compounds (t 1/2 : CO < NAc < O < CH2 < S << NH) is not as was expectated, a computational study towards the reactivity of some specific analogs was performed in Chapter 3.From semi-empirical calculations (MNDO) it appeared that the heat of activation of the intramolecular Diels-Alder reactions is not the rate determining factor. Therefore the origin of the differences in reactivity has to be found in the sterical (e.g. conformational) properties of the molecules. To investigate a methodology was developed in which the reactivity of a conformation is coupled to the probability of the molecule to be in that conformation. By means of a "Rigid Rotor" approximation a large number of conformations can be generated and their energies calculated (Molecular Mechanics). Then it is possible to determine the probability of the molecule to be in each generated conformation by means of the "Bolzmann" distribution equation. As a measure for the reactivity of a conformation the distance between the diene and dienophile was taken. From the combination of reactivity and probability of the conformations it could be concluded that the reactivity of the molecules under study is determined by the probability of the molecules to be in a conformation which is able to undergo an intramolecular Diels-Alder reaction.By means of this methodology and the previously mentioned semi- empirical calculations the enhanced reactivity of α,α-dicyano-2-(pent-4-yn-l-yl)pyrimidine as compared to its α,α-dihydro analog was investigated (Chapter 4). Starting with the crystal structures of 5- p -nitrophenyl-2-(pent-4-yn-l-yl)pyrimidine and 2-(1,1-dicyanopent-4-yn-l-yl)-5-nitropyrimidine the heats of activation and the probability-reactivity relationships were determined. Analysis of these data revealed that the enhanced reactivity by introduction of the two cyano groups is caused by: i) a decrease of the heat of activation, due to the electron withdrawing capacity of the cyano groups, ii) a rotamer effect, iii) the so called "Thorpe-Ingold"/ gem -dialkyl effect.Chapter 5 deals with an investigation towards the reactivity and selectivity of 2en 5-(ω-alkynyl)pyrimidines. In the synthetic part it appears that 2-(prop-2-ynyloxycarbonyl)pyrimidine gives a Diels-Alder reaction under the applied reaction conditions (nitrobenzene, 210 °C), whereas the isomeric 5-(prop-2-ynyl- oxycarbonyl)pyrimidine does not react. Likewise, it appeared that 5 -phenyl-2- (2(1-prop-2-ynyl)pyrrolidinyl)pyrimidine does react, wherease its aromatic analog 5-phenyl-2-(2-(1-prop -2-ynyl)pyrryl) pyrimidine does not. On the other hand, the aromatic 2-(2-prop-2ynyloxyphenyl)pyrimidines do react under relatively mild conditions. It was determined that the observed differences in reactivities could not be explained by the differences in the heats of activation. By application of the previous mentioned computational technics, it appeared that the differences in reactivity between often closely related molecules were determined by the (im)possibilities of the molecules to be in conformations in which the diene and dienophile can react.In Chapter 6 the synthesis of 5-propynyloxycycloalkanepyrimidine derivatives is presented and their reactivity and selectivity in intramolecular Diels-Alder reactions. Upon introduction a methyl, ethyl or phenyl substituent alfa according to the pyrimidine moiety the reactivity of the molecules under study increase 4 - 10 times. The selectivity of the retro Diels-Alder reaction appears to be determined mainly by the size of the cycloalkane ring: cyclohexane ring, cycloheptane ring or no ring at all. In case of the last two the expulsion of HCN is favoured, whereas in the first case mainly the expulsion of -X-CH 2 CN is observed. Besides, the ringtransformation of 2-phenyl-S-propynyloxy-5,6,7,8-tetrahydroquinazoline and the two 5- H -S-R-2phenyl-S-propynyloxy-6,7,8,9-tetrahydrocyclohepta- [b]pyrimidines yielded two hitherto unknown ringsystems: 4-phenyl-2 H -6,7,8,8a-tetrahydrofuro[4,3,2- de ]quinoline and 2 H -1,6,7,8,9,9a-hexahydro-4-phenyl-9a-R-5- aza-1-oxo-benz[c,d]azulenes.From computations towards the differences in selectivity and the reactivity of the 5-propynyloxycycloalkanepyrimidine derivatives, as presented in Chapter 7, it appeared that both properties were determined by differences in the heats of activation. Determination of the energies and dipole moments of the transition states of the different reaction pathways revealed that the ratio of the product formation was determined by the polarity of the transiton states as represented by their dipole moments in combination with the polarity of the reaction medium. Also the reactivity of the compounds under study appeared to depend on the polarity of the transition state of the initial Diels-Alder reaction. The differences in dipole moments of the different TS's are ascribed to the geometry of the molecules in the TS's. Furthermore, a comparison of the heats of activation of the initial Diels-Alder reaction and the subsequent retro Diels-Alder reaction showed that the first one is the rate determining step
Analysis of Chromatic Aberration Effects in Triple-Junction Solar Cells Using Advanced Distributed Models
No full textThe consideration of real operating conditions for the design and optimization of a multijunction solar cell receiver-concentrator assembly is indispensable. Such a requirement involves the need for suitable modeling and simulation tools in order to complement the experimental work and circumvent its well-known burdens and restrictions. Three-dimensional distributed models have been demonstrated in the past to be a powerful choice for the analysis of distributed phenomena in single- and dual-junction solar cells, as well as for the design of strategies to minimize the solar cell losses when operating under high concentrations. In this paper, we present the application of these models for the analysis of triple-junction solar cells under real operating conditions. The impact of different chromatic aberration profiles on the short-circuit current of triple-junction solar cells is analyzed in detail using the developed distributed model. Current spreading conditions the impact of a given chromatic aberration profile on the solar cell I-V curve. The focus is put on determining the role of current spreading in the connection between photocurrent profile, subcell voltage and current, and semiconductor layers sheet resistance
Shifting inequalities? Patterns of exclusion and inclusion in emerging forms of political participation
No full textPrevious research has found a steady increase in the number of people involved in emerging forms of civic engagements such as Internet campaigns, protests, political consumerism, and alternative lifestyle communities. Verba et al. (1995) have established that various forms of political participation in the United States follow a pattern of structural inequality, based on income, education, gender and civic skills. The growing popularity of emerging action repertoires forces us to re-evaluate the claims of this literature. Do these patterns of inequality persist for the emerging action repertoires across advanced industrialized democracies, or are they becoming even stronger, as Theda Skocpol (2003, 2004) argues? The results of this cross-national analysis with longitudinal comparisons suggest that gender inequalities in emerging political action repertoires have substantially declined since the 1970s, whereas other forms of inequality have persisted. However, contrary to the more pessimistic claims about a "participation paradox", there is no evidence that inequality based on socio-economic status has substantially increased since the 1970s. --
Meister Stolle nach der Jenaer Handschrift.
No full text"Text nach J[enaer] Handschrift": p. 73-91.Vita.Inaug.-Diss.--Leipzig.Mode of access: Internet
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Beproeving van gaffel verbindingen voor ronde buisprofielen
No full textCivil Engineering and GeosciencesStructural Engineerin
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