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71.
Franco Cristiani Francesco A. Devillanova Angelo Diaz Francesco Isaia Gaetano Verani 《Heteroatom Chemistry》1990,1(5):363-367
Using a series of N-methylated thiohydantoins as substrates, the donor properties of the sulfur atom are measured by determining the stability constants (K) of their adducts with molecular iodine. The K's have been determined by recording the UV-visible spectra of several CH2Cl2 solutions with different amounts of the reagents. The experimental data fit the 1:1 adduct model for all the compounds. The K values, compared with those previously found for the unsubstituted hydantoins and with those obtained for 5-methyl-2-thiohydantoin, show that the hydrogen-bonding interaction between the NH hydrogen and the S-bonded iodine plays an important role in determining the stability of the adduct. The K values obtained for several pentaatomic rings, all containing the thioureido group HN C() NH , are discussed on the basis of the influence of the substituents at C-4 and C-5 on the donor properties of the sulfur atom. 相似文献
72.
Silva BV Violante FA Pinto AC Santos LS 《Rapid communications in mass spectrometry : RCM》2011,25(3):423-428
Using electrospray ionization (tandem) mass spectrometry (ESI-MS(/MS)) spectrometric experiments, the Sandmeyer reaction was monitored on-line, and key intermediates were intercepted and characterized for the first time. The mechanistic information provided by on-line ESI-MS(/MS) is in accordance with Sandmeyer's proposal, and was made possible by coupling a microreactor on-line to the ESI ion source, which allowed reactions to be screened from 0.7-2.0 s, identifying and characterizing all intermediates that were formed and consumed during the reaction. 相似文献
73.
Angelo Sala Kathleen Kayganich Joseph A. Zirrolli Robert C. Murphy 《Journal of the American Society for Mass Spectrometry》1991,2(4):314-321
The sulfidopeptide leukotrienes, leukotriene E4, (LTE4,) and its N-acetyl derivative and several ω? and β-oxidized metabolites of LTE4, have been analyzed by tandem mass spectrometry. [M?H]? ions were produced by continuous flow fast atom bombardment, and collision-induced dissociation of these ions was studied by using a triple quadrupole instrument. The product ion spectra obtained were characteristic of the structure of LTE4, and mechanisms of ion formation were investigated by using deuterated compounds. β-Elimination of the peptide portion of LTE4, by loss of CO2, and ethylene amine leaves the C-l carboxyl group ionized in the most abundant fragment ion for LTE4, and all metabolites. Tandem mass spectrometry of fast atom bombardment-generated anions from ω? and β-oxidized metabolites of LTE4, produced similar ions with only a minor influence of the third carboxyl group at the omega terminus evident. Tandem mass spectrometry was used to identify unequivocally the presence of unmodified LTE4, in a high performance liquid chromatography-purified fraction of urine from a normal healthy volunteer after infusion with LTE4. 相似文献
74.
Angelo Cavallucci 《Annali di Matematica Pura ed Applicata》1969,83(1):337-362
Sunto Si prova un teorema di tracce per spazi di funzioni, definite su R
+
n
, con norme del tipo
.
Entrata in Redazione il 23 luglio 1969.
Lavoro eseguito nell'ambito dei gruppi di ricerca del Comitato Nazionale per la Matematica del C.N.R. 相似文献
75.
We investigate finite lattice approximations to the Wilson renormalization group in models of unconstrained spins. We discuss first the properties of the renormalization group transformation (RGT) that control the accuracy of this type of approximation and explain different methods and techniques to practically identify them. We also discuss how to determine the anomalous dimension of the field. We apply our considerations to a linear sigma model in two dimensions in the domain of attraction of the Ising fixed point using a Bell–Wilson RGT. We are able to identify optimal RGTs which allow accurate computations of quantities such as critical exponents, fixed-point couplings and eigenvectors with modest statistics. We finally discuss the advantages and limitations of this type of approach. 相似文献
76.
In Korchmáros et al. (2018)one-factorizations of the complete graph are constructed for with any odd prime power such that either or . The arithmetic restriction is due to the fact that the vertices of in the construction are the points of a conic in the finite plane of order . Here we work on the Euclidean plane and describe an analogous construction where the role of is taken by a regular -gon. This allows us to remove the above constraints and construct one-factorizations of for every even . 相似文献
77.
Alexander G. Ramm Alexandra B. Smirnova Angelo Favini 《Annali di Matematica Pura ed Applicata》2003,182(1):37-52
A nonlinear operator equation F(x)=0, F:H→H, in a Hilbert space is considered. Continuous Newton’s-type procedures based on a construction of a dynamical system with
the trajectory starting at some initial point x
0 and becoming asymptotically close to a solution of F(x)=0 as t→+∞ are discussed. Well-posed and ill-posed problems are investigated.
Received: June 29, 2001; in final form: February 26, 2002?Published online: February 20, 2003
This paper was finished when AGR was visiting Institute for Theoretical Physics, University of Giessen. The author thanks
DAAD for support 相似文献
78.
Comparison results of Talenti type for elliptic problems with Dirichlet boundary conditions have been widely investigated in recent decades. In this paper, we deal with Robin boundary conditions. Surprisingly, contrary to the Dirichlet case, Robin boundary conditions make the comparison sensitive to the dimension, and while the planar case seems to be completely settled, in higher dimensions some open problems are yet unsolved. © 2023 The Authors. Communications on Pure and Applied Mathematics published by Wiley Periodicals LLC. 相似文献
79.
John P. D’Angelo 《Journal of Geometric Analysis》1994,4(1):23-34
We give an explicit computation of the Bergman kernel function on the domain
相似文献
80.
We consider the constrained vector optimization problem min C f(x), g(x) ∈ ?K, where f:? n →? m and g:? n →? p are C 1,1 functions, and C ? m and K ? p are closed convex cones with nonempty interiors. Two type of solutions are important for our considerations, namely w-minimizers (weakly efficient points) and i-minimizers (isolated minimizers). We formulate and prove in terms of the Dini directional derivative second-order necessary conditions for a point x 0 to be a w-minimizer and second-order sufficient conditions for x 0 to be an i-minimizer of order two. We discuss the reversal of the sufficient conditions under suitable constraint qualifications of Kuhn-Tucker type. The obtained results improve the ones in Liu, Neittaanmäki, K?í?ek [21]. 相似文献
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