1,720,955 research outputs found
Ruthenium(arene){poly(pyrazolyl)borates}: Synthesis, reactivity and molecular orbital calculations
Get PDFThis thesis is concerned with the exploration of the syntheses and reactivities of a class of mixed sandwich complexes: ruthenium(η6-arene){poly(pyrazolyl)borates} and methanes. In Chapter One background to the previously explored chemistry of poly(pyrazolyl)borates as a ligand class is presented along with reports associated with ruthenium derivatives. Chapter Two details the synthesis and characterisation of a range of mixed sandwich complexes of the formula [Ru(η6-arene){HX(Pz)3}], X=B, n=l, arene = benzene [1], para-cymene [2], para-xylene [3], para-diisopropylbenzene [4], mesitylene [5], durene [6], hexamethylbenzene [7]; X = C, n=2, arene = benzene [9], para-cymene [10], para-xylene [11], mesitylene [12], The moderate reaction conditions employed not only allow the successful isolation of the previously elusive [Ru(η6 - C6H6){κ3-HB(3,5-Me2Pz)3}][PF6] [8] but also permit the formation of a range of half sandwich complexes [Ru(η6-l,4-Me2C6H4){κ2-HB(Pz)3}Cl] [13], [Ru(η6-1,3,5-Me3C6H3){κ2-HB(Pz)3}Cl] [14], [Ru(η6-C6Me6){κ2-HB(Pz)3}Cl] [15], [Ru(η6-C6H6){κ2-HC(Pz)3}Cl][PF6] [16], [Ru(η6-C6H6){κ2-HC(3,5-Me2Pz)3}Cl][PF6] [17], [Ru(η6-1,4-Me2C6H4){κ2-HC(3,5-Me2Pz)3}Cl][PF6] [18], which can be converted into the tris-chelated derivatives by treatment with NH4PF6 or AgPF6. Details of the X-ray structures of [2], [8], [10], [15] and [17] are presented. In Chapter Three compounds resulting from degradation of the mixed sandwich complexes are reported, namely [Ru(η6-C6H6{κ3-N,N,O-HB(3,5-Me2Pz)2(OEt)}][PF6] [20], [Ru(η6-1,2,4,5-Me4C6H2)(3,5-Me2PzH){κ2-HB(3,5-Me2Pz)2(OMe)}][PF6] [21] and [Ru(η6-C6H6){κ2-HN-C(Me)=(3,5-Me2PzH)}][PF6] [22]. While [20] and [22] have been comprehensively characterised [21] was only characterised through X-ray diffraction experiments. The tendency towards degradation is attributed to the large interligand repulsions between the methyl substituents on the pyrazolyl groups and the hydrogen atoms on the arene ligands. A mechanism is proposed for the speculative origin of these products. In Chapter Four when complex [1] is subjected to nucleophihc attack with Na[BH4], NaCN, KOH and Na[BD4], neutral compounds of the type [Ru(η5-C6H6Y){κ3-HB(Pz)3}], Y=H [23], CN [24], OH [25] and D [26] are formed. The dynamic NMR behaviour of these compounds is attributed to restricted rotation of the carbocycle. When nucleophiles are added to compounds bearing alkylated arenes higher rotational barriers are observed for the derived cyclohexadienyl compounds, [Ru(η5-CHD){κ3-HB(Pz)3}], CHD = [1-iPr-4MeC6H5] [27], [l-iPr-4-MeC6H4CN] [28], [l-iPr-4-MeC6H4OH] [29], [1,4-Me2C6H5] [30], [1,4-iPr2C6H5] [31], [1,3,5-Me3C6H4] [32] and [1,3,5-Me3C6H3CN] [33]. Similar observations are also made when the complexes [8]-[12] are treated with KCN and Na[BH4] to yield, [Ru(η5-CHD){κ3-HC(Pz)3}][PF6], CHD= [C6H6CN] [34], [iPr-4MeC6H4CN] [35], [1,4Me2C6H4CN] [36] and [Ru(n5-C6H7){κ3-HB(3,5-Me2Pz)3}] [37]. Details of X-ray structures of [24] and [34] are presented. Chapter Five attempts to substantiate the plausibility of restricted rotation of the cyclohexadienyl ligands being responsible for the dynamic NMR behaviour. This is carried out through Extended Huckel molecular orbital treatment of a series of ruthenium(arene)/(cyclohexadienyl){poly(pyrazolyl)borate} compounds. A variety of arenes and cyclohexadienyl ligands are subjected to rotational motion while attached to a static ruthenium {tris(pyrazolyl)borate} fragment, and their overall energies monitored. Although in general the extent of the rotational barrier increase as the number and size of the alkyl substituents increases, the actual differences within a series of mono, bis, or tris-alkylated cyclohexadienyls is very much dependent upon the positioning of the substituents on the carbocycle
Power System Stabilizer Design Using Particle Swarm Optimization
Get PDFM.E. (Power Systems and Electric Drives)Dynamic stability has challenged power system engineers since over three decades now. In the generator, the electromechanical coupling between the rotor and rest of the system causes ossillatory behaviour around the equilibrium state, following any disturbance. The use of fast acting high gain AVRs and evolution of large interconnected power systems with transfer of bulk power across weak transmission links have further aggravated the problem of low frequency oscillations. The oscillations, which are typically in the frequency range of 0.2 to 0.3 hertz, might be excited by the disturbances in the system or, in some cases, might even build up spontaneously. These oscillations limit the power transmission capability of a network and, sometimes, even cause a loss of synchronism and an eventual breakdown of the entire system.
The application of power system stabilizer can help in damping out these oscillations and improve the system stability. The traditional and till date the most popular solution to this problem is application of conventional power system stabilizer (CPSS). However, continual changes in the operating condition and network parameters result in corresponding change in system dynamics. This constantly changing nature of power system makes the design of CPSS a difficult task.
In this thesis work Particle Swarm Optimization algorithm has been used for tuning the parameters of a fixed gain power system stabilizer. The stabilizer places the troublesome system modes in an acceptable region in the complex plane and guarantees a robust performance over a wide range of operating conditions. Conventional lead/lag structure is retained but its parameters are retuned using Particle swarm optimization algorithm to obtain enhanced performance. Unlike GA and other heuristic algorithms, PSO has the flexibility to control the balance between the global and local exploration of the search space. This unique feature of PSO overcomes the premature convergence problem and enhances the search capability.EIE
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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