Analisys of safety system pumps conditions based on their testing results

The algorithm for analyzing the conditions of emergency system pumps based on their periodical testing results is presented in the paper. The method and the algorithms are based on the presentation of the testing results in the space of the principal components. Such an approach allows representing the pump conditions in a convenient form. The parameter variation measured from the beginning of the test until the steady state conditions are achieved, i.e., the dynamic section of the curve for each parameter, is used for the analysis. Comparing the behavior curves of different technological parameters as a time function of a particular pump for different tests one can see that some sections of these curves do not change from test to test. This clearly means that these sections are not informative relative to extraction of the information concerning the defect development. These sections must be classified as some kind of “noise” and must be excluded as providing little information. On the contrary, the sections with abnormal behavior of technological parameters are more informative, and we accept these sections for further analysis. As a measure of the system uncertainty entropy H(X) is used. This new parameter is defined by the relationship H(X)=−∑i=1Npilogpi, where pi is the probability of the ith state of the system; N is the total number of the states of the system. The entropy allows describing the probabilistic variability of the measured data. The entropy has the maximum value if all the states of the system are equiprobable. We can use this feature of the entropy to choose the more informative time intervals of the dynamic behavior of the technological parameters. The smaller is the entropy, the more probable certain states of the system are. Thus, the most informative are those time sections, which have the maximum entropy value, i.e., the time sections for which the maximum variability of the measured data is observed. Using this approach, a matrix is constructed based on the time intervals with maximum entropy – the so-called matrix of informative criteria. To describe the conditions of the pump using different technological parameters measured in the course of the testing we need to normalize the values of the parameters by the root-mean-square deviations of the parameters. The normalized data are then used for the transformation of the original data matrix on the basis of the most informative criteria using statistical method known as the Karhunen–Loeve transform, which is also known as the principal components method. The approach was applied to processing the testing results of the emergency system pumps of the Kalinin NPP (Russia). Interesting results are obtained

A New Mode of Operation of Pd-NHC Systems Studied in a Catalytic Mizoroki-Heck Reaction

Metal complexes bearing N-heterocyclic carbene (NHC) ligands are typically considered the system of choice for homogeneous catalysis with well-defined molecular active species due to their stable metal-ligand framework. A detailed study involving 19 different Pd-NHC complexes with imidazolium, benzimidazolium, and triazolium ligands has been carried out in the present work and revealed a new mode of operation of metal-NHC systems. The catalytic activity of the studied Pd-NHC systems is predominantly determined by the cleavage of the metal-NHC bond, while the catalyst performance is strongly affected by the stabilization of in situ formed metal clusters. In the present study, the formation of Pd nanoparticles was observed from a broad range of metal complexes with NHC ligands under standard Mizoroki-Heck reaction conditions. A mechanistic analysis revealed two different pathways to connect Pd-NHC complexes to "cocktail"-type catalysis: (i) reductive elimination from a Pd(II) intermediate and the release of NHC-containing byproducts and (ii) dissociation of NHC ligands from Pd intermediates. Metal-NHC systems are ubiquitously applied in modern organic synthesis and catalysis, while the new mode of operation revealed in the present study guides catalyst design and opens a variety of novel opportunities. As shown by experimental studies and theoretical calculations, metal clusters and nanoparticles can be readily formed from M-NHC complexes after formation of new M-C or M-H bonds followed by C-NHC or H-NHC coupling. Thus, a combination of a classical molecular mode of operation and a novel cocktail-type mode of operation, described in the present study, may be anticipated as an intrinsic feature of M-NHC catalytic systems. © 2017 American Chemical Society

A New Mode of Operation of Pd-NHC Systems Studied in a Catalytic Mizoroki-Heck Reaction

Metal complexes bearing N-heterocyclic carbene (NHC) ligands are typically considered the system of choice for homogeneous catalysis with well-defined molecular active species due to their stable metal-ligand framework. A detailed study involving 19 different Pd-NHC complexes with imidazolium, benzimidazolium, and triazolium ligands has been carried out in the present work and revealed a new mode of operation of metal-NHC systems. The catalytic activity of the studied Pd-NHC systems is predominantly determined by the cleavage of the metal-NHC bond, while the catalyst performance is strongly affected by the stabilization of in situ formed metal clusters. In the present study, the formation of Pd nanoparticles was observed from a broad range of metal complexes with NHC ligands under standard Mizoroki-Heck reaction conditions. A mechanistic analysis revealed two different pathways to connect Pd-NHC complexes to "cocktail"-type catalysis: (i) reductive elimination from a Pd(II) intermediate and the release of NHC-containing byproducts and (ii) dissociation of NHC ligands from Pd intermediates. Metal-NHC systems are ubiquitously applied in modern organic synthesis and catalysis, while the new mode of operation revealed in the present study guides catalyst design and opens a variety of novel opportunities. As shown by experimental studies and theoretical calculations, metal clusters and nanoparticles can be readily formed from M-NHC complexes after formation of new M-C or M-H bonds followed by C-NHC or H-NHC coupling. Thus, a combination of a classical molecular mode of operation and a novel cocktail-type mode of operation, described in the present study, may be anticipated as an intrinsic feature of M-NHC catalytic systems. © 2017 American Chemical Society