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排序方式: 共有578条查询结果,搜索用时 15 毫秒
101.
Dr. Mauricio Rodríguez-Mayorga Dr. Eloy Ramos-Cordoba Prof. Xabier Lopez Prof. Miquel Solà Prof. Jesus M. Ugalde Dr. Eduard Matito 《ChemistryOpen》2019,8(4):411-417
We analyze the Coulomb hole of Ne from highly-accurate CISD wave functions obtained from optimized even-tempered basis sets. Using a two-fold extrapolation procedure we obtain highly accurate results that recover 97 % of the correlation energy. We confirm the existence of a shoulder in the short-range region of the Coulomb hole of the Ne atom, which is due to an internal reorganization of the K-shell caused by electron correlation of the core electrons. The feature is very sensitive to the quality of the basis set in the core region and it is not exclusive to Ne, being also present in most of second-row atoms, thus confirming that it is due to K-shell correlation effects. 相似文献
102.
Acelas Mauricio Kouznetsov Vladimir V. Romero Bohórquez Arnold R. 《Molecular diversity》2019,23(1):183-193
A novel and highly efficient synthetic approach for the expedite construction of new octahydroacridine-isoxazole- and octahydroacridine-1,2,3-triazole-based molecular hybrids is first reported. Rapid access to the octahydroacridine core was achieved in a highly diastereoselective fashion via cationic Povarov reaction of N-propargyl anilines and citronella essential oil (Cymbopogon nardus). The subsequent 1,3-dipolar and Cu (I) catalyzed alkyne-azide cycloaddition reaction of the terminal alkyne fragment with the corresponding oxime or azide affords the desired 3,5-isoxazoles and 1,2,3-triazoles, respectively, as interesting molecular hybrid models for pharmacological studies.
相似文献103.
Ersan Altun Vasco Heredia Ertan Pamuklar Mauricio Zapparoli Richard C. Semelka 《Magnetic resonance imaging》2009,27(9):1198-1207
Purpose
To determine the feasibility of post-gadolinium three-dimensional gradient-echo (3D-GE) sequence for the evaluation of the pulmonary arterial vasculature in patients with suspected pulmonary embolism (PE) and in patients with a variety of other disease processes.Materials and Methods
Twenty-six consecutive patients (18 females, 8 males; mean age±S.D., 46.6±21.1 years) who underwent chest magnetic resonance imaging (MRI) including post-gadolinium 3D-GE sequence for the evaluation of PE (Group A, n=13) and a variety of other disease processes (Group B, n=13) were included in the study. Post-gadolinium 3D-GE MR sequences were retrospectively, independently and blindly evaluated by two reviewers for the image quality of pulmonary arterial vasculature, and findings of PE and other disease processes. Clinical and imaging follow-up data for all patients were obtained. Interobserver agreement was calculated by kappa statistics.Results
All central and lobar pulmonary arteries, 71.4–89.6% of segmental arteries and 46.7–52.7% of subsegmental arterial units in both groups were visualized with sufficient diagnostic image quality on post-gadolinium 3D-GE sequences. PE involving lobar and segmental arteries was diagnosed in two patients in each group. Other disease processes including pneumonia, lung nodules, superior vena cava stenosis, lung metastases, chronic lymphocytic leukemia and aortic aneurysm were detected in 10 of 26 patients. There was good to excellent interobserver agreement (0.73 to 1.00) for all findings.Conclusion
Post-gadolinium 3D-GE sequence may be an alternative technique for the visualization of central, lobar and segmental arteries, and may diagnose PE and other pathologies involving the chest in different patient populations. 相似文献104.
Mariano Anabitarte Mauricio Bellini 《The European Physical Journal C - Particles and Fields》2009,60(2):297-301
We revisit an extension of the well-known formalism for gauge-invariant scalar metric fluctuations to study the spectra for
both the inflaton and gauge-invariant (scalar) metric fluctuations in the framework of a single-field inflationary model,
in which the quasi-exponential expansion is driven by an inflaton which is minimally coupled to gravity. The proposal here
examined is valid also for fluctuations with large amplitudes, but for cosmological scales, where vector and tensor perturbations
can be neglected and the fluid is irrotacional. 相似文献
105.
Model studies towards the total synthesis of syringolides using a rhodium-catalyzed intramolecular C-H insertion reaction as the key step are described. A highly stereospecific synthesis of spirolactones is achieved employing this methodology. 相似文献
106.
John Hurtado Alvaro Muñoz-Castro Raúl Quijada René Rojas Mauricio Valderrama 《Journal of organometallic chemistry》2009,694(16):2636-223
Reactions of 2,6-bis(bromomethyl)pyridine with 3,5-dimethylpyrazole and 1H-indazole yield the terdentate ligands 2,6-bis(3,5-dimethylpyrazol-1-ylmethyl)pyridine (5) and 2,6-bis(indazol-2-ylmethyl)pyridine (6). The molecular structure of the new compound 6 was determined by single-crystal X-ray diffraction. These ligands react with the CrCl3(THF)3 complex in THF to form neutral complexes of general formula [CrCl3{2,6-bis(azolylmethyl)pyridine-N,N,N}] (7, 8) which are isolated in high yields as stable green solids and characterized by means of elemental analysis, magnetic moments, IR, and mass spectroscopy. Theoretical calculations predict that the thermodynamically preferred structure of the complexes is the fac configuration. After reaction with methylaluminoxane (MAO) the chromium(III) complexes are active in the polymerization of ethylene. 相似文献
107.
Ronsein GE de Oliveira MC de Medeiros MH Di Mascio P 《Journal of the American Society for Mass Spectrometry》2009,20(2):188-197
The fragmentation mechanisms of singlet oxygen [O(2) ((1)Delta(g))]-derived oxidation products of tryptophan (W) were analyzed using collision-induced dissociation coupled with (18)O-isotopic labeling experiments and accurate mass measurements. The five identified oxidized products, namely two isomeric alcohols (trans and cis WOH), two isomeric hydroperoxides (trans and cis WOOH), and N-formylkynurenine (FMK), were shown to share some common fragment ions and losses of small neutral molecules. Conversely, each oxidation product has its own fragmentation mechanism and intermediates, which were confirmed by (18)O-labeling studies. Isomeric WOH lost mainly H(2)O + CO, while WOOH showed preferential elimination of C(2)H(5)NO(3) by two distinct mechanisms. Differences in the spatial arrangement of the two isomeric WOHs led to differences in the intensities of the fragment ions. The same behavior was also found for trans and cis WOOH. FMK was shown to dissociate by a diverse range of mechanisms, with the loss of ammonia the most favored route. MS/MS analyses, (18)O-labeling, and H(2)(18)O experiments demonstrated the ability of FMK to exchange its oxygen atoms with water. Moreover, this approach also revealed that the carbonyl group has more pronounced oxygen exchange ability compared with the formyl group. The understanding of fragmentation mechanisms involved in O(2) ((1)Delta(g))-mediated oxidation of W provides a useful step toward the structural characterization of oxidized peptides and proteins. 相似文献
108.
109.
Alexandre Salles da Cunha Nelson Maculan Mauricio G.C. Resende 《Discrete Applied Mathematics》2009,157(6):1198-1217
Given an undirected graph G with penalties associated with its vertices and costs associated with its edges, a Prize Collecting Steiner (PCS) tree is either an isolated vertex of G or else any tree of G, be it spanning or not. The weight of a PCS tree equals the sum of the costs for its edges plus the sum of the penalties for the vertices of G not spanned by the PCS tree. Accordingly, the Prize Collecting Steiner Problem in Graphs (PCSPG) is to find a PCS tree with the lowest weight. In this paper, after reformulating and re-interpreting a given PCSPG formulation, we use a Lagrangian Non Delayed Relax and Cut (NDRC) algorithm to generate primal and dual bounds to the problem. The algorithm is capable of adequately dealing with the exponentially many candidate inequalities to dualize. It incorporates ingredients such as a new PCSPG reduction test, an effective Lagrangian heuristic and a modification in the NDRC framework that allows duality gaps to be further reduced. The Lagrangian heuristic suggested here dominates their PCSPG counterparts in the literature. The NDRC PCSPG lower bounds, most of the time, nearly matched the corresponding Linear Programming relaxation bounds. 相似文献
110.
Alexandre X. Martins Mauricio C. de Souza Marcone J. F. Souza Túlio A. M. Toffolo 《Journal of Heuristics》2009,15(2):133-151
We propose a GRASP using an hybrid heuristic-subproblem optimization approach for the Multi-Level Capacitated Minimum Spanning
Tree (MLCMST) problem. The motivation behind such approach is that to evaluate moves rearranging the configuration of a subset
of nodes may require to solve a smaller-sized MLCMST instance. We thus use heuristic rules to define, in both the construction
and the local search phases, subproblems which are in turn solved exactly by employing an integer programming model. We report
numerical results obtained on benchmark instances from the literature, showing the approach to be competitive in terms of
solution quality. The proposed GRASP have in fact improved the best known upper bounds for almost all of the considered instances. 相似文献