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791.
The present paper investigates properties of the solutions obtained with the equivalent sources method in scattering problems with the aim of identifying suitable monopole arrangements. Simple geometry scatterers--parallelepipeds with different aspect ratios--are considered and easy-to-implement source supports are tested: linear, circular, elliptical, and a "double linear" one. It was found that the supports providing best solutions differ according to the body geometry and the incidence angle of the impinging wave. Moreover, in the situations in which the other supports fail, it is shown that the double linear one provides satisfactory solutions with a minimum number of monopoles. Rules that furnish appropriate numbers of sources to use as well as their positioning are given for the different cases. A simple procedure based on these rules is proposed for scatterers with a more complex geometry, guaranteeing, still with a low number of monopoles, solutions with satisfactory accuracy. 相似文献
792.
Charge Effects in PCP Pincer Complexes of NiII bearing Phosphinite and Imidazol(i)ophosphine Coordinating Jaws: From Synthesis to Catalysis through Bonding Analysis
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Dr. Boris Vabre Dr. Yves Canac Dr. Christine Lepetit Dr. Carine Duhayon Prof. Remi Chauvin Prof. Davit Zargarian 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(48):17403-17414
This contribution reports on a new family of NiII pincer complexes featuring phosphinite and functional imidazolyl arms. The proligands RPIMCHOPR′ react at room temperature with NiII precursors to give the corresponding complexes [(RPIMCOPR′)NiBr], where RPIMCOPR=κP,κC,κP‐{2‐(R′2PO),6‐(R2PC3H2N2)C6H3}, R=iPr, R′=iPr ( 3 b , 84 %) or Ph ( 3 c , 45 %). Selective N‐methylation of the imidazole imine moiety in 3 b by MeOTf (OTf=OSO2CF3) gave the corresponding imidazoliophosphine [(iPrPIMIOCOPiPr)NiBr][OTf], 4 b , in 89 % yield (iPrPIMIOCOPiPr=κP,κC,κP‐{2‐(iPr2PO),6‐(iPr2PC4H5N2)C6H3}). Treating 4 b with NaOEt led to the NHC derivative [(NHCCOPiPr)NiBr], 5 b , in 47 % yield (NHCCOPiPr=κP,κC,κC‐{2‐(iPr2PO),6‐(C4H5N2)C6H3)}). The bromo derivatives 3–5 were then treated with AgOTf in acetonitrile to give the corresponding cationic species [(RPIMCOPR)Ni(MeCN)][OTf] [R=Ph, 6 a (89 %) or iPr, 6 b (90 %)], [(RPIMIOCOPR)Ni(MeCN)][OTf]2 [R=Ph, 7 a (79 %) or iPr, 7 b (88 %)], and [(NHCCOPR)Ni(MeCN)][OTf] [R=Ph, 8 a (85 %) or iPr, 8 b (84 %)]. All new complexes have been characterized by NMR and IR spectroscopy, whereas 3 b , 3 c , 5 b , 6 b , and 8 a were also subjected to X‐ray diffraction studies. The acetonitrile adducts 6 – 8 were further studied by using various theoretical analysis tools. In the presence of excess nitrile and amine, the cationic acetonitrile adducts 6 – 8 catalyze hydroamination of nitriles to give unsymmetrical amidines with catalytic turnover numbers of up to 95. 相似文献
793.
Dr. Marc Comet Dr. Geoffrey Vidick Fabien Schnell Yves Suma Bernard Baps Dr. Denis Spitzer 《Angewandte Chemie (International ed. in English)》2015,54(15):4458-4462
Metal sulfates (Ba, Bi, Ca, Cu, Mg, Mn, Na, Zn, Zr) were used as oxidizers in reactive compositions with Al nanopowder. These new kinds of nanothermites have outstandingly high reaction heats (4–6 kJ g?1) compared to conventional Al/metal oxides (1.5–4.8 kJ g?1) and also have good combustion velocities (200–840 m s?1 vs 100–2500 m s?1). These compositions are extremely insensitive to friction making their preparation and handling easy and safe. The sulfate hydration water increases the reaction heats and has a significant effect on the sensitivity to impact and to electrostatic discharge. The reaction of Al with water is easier to initiate than the one with sulfate which leads to two possible decomposition modes for samples exposed to an open flame. The pyrotechnical properties observed with sulfates have also been found for other sulfur oxygenates (SO32?, S2O32?, S2O82?) which opens up new horizons in the domain of metastable interstitial composites. 相似文献
794.
Covalent Functionalization of HiPco Single‐Walled Carbon Nanotubes: Differences in the Oxidizing Action of H2SO4 and HNO3 during a Soft Oxidation Process
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Dr. Xavier Devaux Dr. Brigitte Vigolo Dr. Edward McRae Dr. Fabrice Valsaque Naoual Allali Dr. Victor Mamane Prof. Yves Fort Prof. Alexander V. Soldatov Dr. Manuel Dossot Dr. Svetlana Yu. Tsareva 《Chemphyschem》2015,16(12):2692-2701
The results of a study on the evolution of HiPco single‐walled carbon nanotubes during the oxidizing action of H2SO4 and HNO3 are presented. The process conditions used have been chosen so as to avoid any significant damage to the nanotube structure. The type and level of functionalization, the location of the grafted functions on the surface of the nanotube and the changes in morphological characteristics of the samples were examined by using a wide and complementary range of analytical techniques. We propose an explanation for the differences in the oxidizing action of sulfuric and nitric acids. The combined results allow us to suggest possible reaction mechanisms that occur on the surface of the nanotube. 相似文献
795.
Dipl. Chem. Yannick Baeten Dr. Eduard Fron Dr. Christian Ruzié Prof. Dr. Yves Henri Geerts Prof. Dr. Mark Van Der Auweraer 《Chemphyschem》2015,16(18):3992-3996
Phthalocyanines (Pcs) have attracted a lot of interest as small molecules for organic electronics. However, some excited‐state properties of metal‐free phthalocyanines, as for example, the dynamics of the transition between the nondegenerate Qx and Qy states in a metal‐free phthalocyanine, have not been fully established. This effect results in a blue‐shifted shoulder with low intensity in the Pc fluorescence spectrum. This shoulder was suggested to be related to emission from the more energetic Qy state. By using ultrafast femtosecond transient absorption, we have found a clear equilibrium between the Qx and Qy state of metal‐free phthalocyanines in solution. 相似文献
796.
Tylleman B Vande Velde CM Balandier JY Stas S Sergeyev S Geerts YH 《Organic letters》2011,13(19):5208-5211
The regiospecific total synthesis and characterization of anti-isomers of 2,8-dialkylanthradithiophenes are described. The "anti" structure of the ADT derivatives is demonstrated by (13)C NMR as well as single crystal X-ray diffraction. 相似文献
797.
The retention mechanism of a series of peptides on a single-wall carbon nanotube (SWCNT) stationary phase inside an HPLC column was investigated over a wide range of mobile phase compositions. While the similar size C18 column exhibited an efficiency of 11.5 μm, the SWCNT column increased the efficiency, i.e. 7.10 μm at a flow rate of 0.8 mL/min, and significantly affected the separation quality of the peptides. The values of enthalpy (ΔH) and entropy (ΔS(*)) of transfer of the peptides from the mobile to the SWCNT stationary phase were determined. The method studied each factor, i.e. ACN fraction x in the ACN/water mixture and column temperature. The changes in retention factor, ΔH and ΔS(*) as a function of the ACN fraction in the mobile phase were examined. These variations are explained using the organization of ACN in clusters in the ACN/water mixture and on the steric and electronic forces implied in the retention process. The information obtained in this work makes this SWCNT stationary phase useful for peptide research and demonstrated the role of ACN to improve the separation quality. 相似文献
798.
Endre Boros Yves Crama Peter L. Hammer Toshihide Ibaraki Alexander Kogan Kazuhisa Makino 《Annals of Operations Research》2011,188(1):33-61
Learning from examples is a frequently arising challenge, with a large number of algorithms proposed in the classification,
data mining and machine learning literature. The evaluation of the quality of such algorithms is frequently carried out ex post, on an experimental basis: their performance is measured either by cross validation on benchmark data sets, or by clinical
trials. Few of these approaches evaluate the learning process ex ante, on its own merits. In this paper, we discuss a property of rule-based classifiers which we call “justifiability”, and which
focuses on the type of information extracted from the given training set in order to classify new observations. We investigate
some interesting mathematical properties of justifiable classifiers. In particular, we establish the existence of justifiable
classifiers, and we show that several well-known learning approaches, such as decision trees or nearest neighbor based methods,
automatically provide justifiable classifiers. We also identify maximal subsets of observations which must be classified in
the same way by every justifiable classifiers. Finally, we illustrate by a numerical example that using classifiers based
on “most justifiable” rules does not seem to lead to overfitting, even though it involves an element of optimization. 相似文献
799.
Mohamed Ayman Boujelben Yves De Smet Ahmed Frikha Habib Chabchoub 《International Journal of Approximate Reasoning》2011,52(8):1171-1194
We consider ranking problems where the actions are evaluated on a set of ordinal criteria. The evaluation of each alternative with respect to each criterion may be imperfect and is provided by one or several experts. We model each imperfect evaluation as a basic belief assignment (BBA). In order to rank the BBAs characterizing the performances of the actions according to each criterion, a new concept called RBBD and based on the comparison of these BBAs to ideal or nadir BBAs is proposed. This is performed using belief distances that measure the dissimilarity of each BBA to the ideal or nadir BBAs. A model inspired by Xu et al.’s method is also proposed and illustrated by a pedagogical example. 相似文献
800.
Manganese (Mn)-enhanced magnetic resonance imaging (MEMRI) is an emerging technique for visualizing neuronal pathways and mapping brain activity modulation in animal models. Spatial and intensity normalizations of MEMRI images acquired from different subjects are crucial steps as they can influence the results of groupwise analysis. However, no commonly accepted procedure has yet emerged. Here, a normalization method is proposed that performs both spatial and intensity normalizations in a single iterative process without the arbitrary choice of a reference image. Spatial and intensity normalizations benefit from this iterative process. On one hand, spatial normalization increases the accuracy of region of interest (ROI) positioning for intensity normalization. On the other hand, improving the intensity normalization of the different MEMRI images leads to a better-averaged target on which the images are spatially registered. After automatic fast brain segmentation and optimization of the normalization process, this algorithm revealed the presence of Mn up to the posterior entorhinal cortex in a tract-tracing experiment on rat olfactory pathways. Quantitative comparison of registration algorithms showed that a rigid model with anisotropic scaling is the best deformation model for intersubject registration of three-dimensional MEMRI images. Furthermore, intensity normalization errors may occur if the ROI chosen for intensity normalization intersects regions where Mn concentration differs between experimental groups. Our study suggests that cross-comparing Mn-injected animals against a Mn-free group may provide a control to avoid bias introduced by intensity normalization quality. It is essential to optimize spatial and intensity normalization as the detectability of local between-group variations in Mn concentration is directly tied to normalization quality. 相似文献