1,721,422 research outputs found
Diagonal material matrices for arbitrary simplicial meshes for solving poisson problems with one unknown per element
No full textWe present a technique to construct diagonal material matrices for arbitrary triangular and tetrahedral meshes and arbitrary scalar material parameters. The recipe is based on a novel dual complex called folded Voronoï diagram. The proposed matrices are tailored to enable the use of a complementary-dual formulation for Poisson problems featuring one unknown per element
12 Aerobic Oxidative Intermolecular Cross-Coupling and Heck Reactions
No full textTransition-metal-promoted oxidative cross-coupling reactions involving two different carbon–hydrogen bonds for the construction of a new carbon–carbon ó bond are very at- tractive synthetic processes, since the preactivation of the reactants by, for example, hal- ogenation or metalation, is not necessary.[1–10] As a consequence, new carbon–carbon ó bonds may be constructed adopting effective atom- and step-economical strategies, and avoiding the generation of stoichiometric amounts of potentially toxic waste.
An oxidative cross coupling, as the name suggests, requires an oxidant acting as a hy- drogen acceptor in the step that formally closes the catalytic cycle (vide infra). Among all the possible oxidants, molecular oxygen is the most ecologically and economically desir- able reagent,[11–14] given its availability and the generation of water as the only byproduct. The adjective “aerobic” is employed in this chapter to refer to transformations in which molecular oxygen acts as a stoichiometric oxidant, regardless of whether it is applied in the form of air or as pure gaseous dioxygen (O2). A substoichiometric amount of a different oxidizing agent may also be present that acts as an oxidation catalyst, i.e. by performing the required oxidation and then in turn being regenerated with the concomitant reduc- tion of dioxygen.
In the following sections, the preeminent results on intermolecular aerobic oxidative Heck coupling reactions are discussed, in which alkenyl-substituted (het)arenes 1 are ob- tained by the transition-metal-mediated activation of a (hetero)aromatic and an sp2 olefin- ic C—H bond (Scheme 1).[10] The related aerobic oxidative intermolecular (het)arylation and alkynylation reactions of (het)arenes to give bi(het)aryls 2 and alkynyl(het)arenes 3 is also discussed.
These transformations fit the requirements of “green” chemistry, and it is expected that their use in synthesis will increase in the future until they are considered a standard tool-of-the-trade of organic chemists
Earth Fault During RFX Initial Operations
No full textRFX, the largest RFP machine, has air-core poloidal windings. A tree-shaped earthing geometry has been adopted for all the machine components, to avoid electrical loops. Nevertheless, during the first operation phase a number of accidental contacts occurred, which caused loops currents high enough to distort plasma equilibrium. These loops could be detected by means of RGM, a system designed to perform fast winding protection, but able to detect accidental earth currents as well. After careful analyses of the signals, these earth faults were always located and removed. The use of a compass resulted particularly useful in the occasion of a number of these faults, the others were detected by means of Rogowski coil probes
Coupled thermal-hydraulic/electromagnetic analysis and interpretation of the test results of the ITER TFPRO2 OST1 conductor
No full textSynthesis of 3-Aryl Substituted Triimidazotriazines via Regioselective Direct Arylation
No full textA general and convenient selective direct arylation of the 3-position of triimidazo[1,2-a:1’,2’-c:1’’,2’’-e][1,3,5]triazine (1) with (hetero)aryl halides in DMA was successfully achieved in the presence of K2CO3 as the base and a catalyst precursor consisting of Pd(OAc)2 and P(2-furyl)3. Electron-poor and -rich (hetero)aryl moieties, including the strongly deactivated and sterically encumbered 2,4,6-trimethoxyphenyl unit, are well tolerated in the electrophilic partner. The data obtained in this synthetic study support a reaction mechanism involving an electrophilic attack of an arylpalladium-(II) halide species onto the triazine ring
Design, Construction and Operation of the Fast Protection System of the Windings of RFX
No full textThe protection of the Windings of RFX against fast electric faults relies on an original dedicated Fast Protection System able to operate within 1 ms. The first ring of the protection chain is the fault protection system of the winding, named RGM, that consists of: about hundred highly reliable voltage and current probes, all electric signal lines and an analog-digital device where signals are processed and logic alarms are generated. RGM is an original machine that required a careful design and manufacturing work. After a long test and adjustment phase it now operates properly. It has already operated against some earth faults which, due to low level of earth current, were not dangerous for the machine but very hard to detect
Numerical Investigation on Induced Current Distribution and AC Losses in a Prototype Cable for the European DEMO TF Coils
No full textA new geometrical model has been implemented in the THELMA code, aiming at permitting the study of multistage, forced-flow cable-in-conduit conductors with rectangular cross-section, like that proposed for the toroidal field (TF) magnets of the future fusion reactor DEMO. This model gives verisimilar strand trajectories which should enable the adoption of a more detailed interstrand electrical contact model. This paper shows the results of the first application of these new code features to a set of contact resistance and ac loss experiments carried out by Twente University on a DEMO TF prototype conductor. The results of this analysis present some unforeseen aspects that need further work to be fully understood, to improve and validate the model
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