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991.
992.
Claudio C. Silveira Samuel R. Mendes Lucas Wolf Guilherme M. Martins 《Tetrahedron letters》2010,51(15):2014-3697
Anhydrous CeCl3 was successfully used as a catalyst for the synthesis of several 3-sulfenyl indoles in good to excellent yields through the reaction of indole with N-(alkylthio) and N-(arylthio)phthalimides in DMF. 相似文献
993.
Kaloudi-Chantzea A Karakostas N Raptopoulou CP Psycharis V Saridakis E Griebel J Hermann R Pistolis G 《Journal of the American Chemical Society》2010,132(46):16327-16329
The two sp(3) hybridized fluorine atoms of a Bodipy dye have been synthetically replaced with the linear donor ligand 4-ethynylpyridine (-C≡C-Py) to form a rigid and highly symmetrical 109.5° building block in which the fluorophore subunit is vertically aligned to the plane formed by the -C≡C-Py donors. Upon reaction of the above tecton with a 90° organoplatinum acceptor unit, an intensely fluorescent rhomboid cavitand was manifested in solution. In contrast to the vast majority of coordination-driven self-assembled chromophoric systems, the present one fully conserves the excellent photophysical properties of the parent Bodipy dye. These unique features of the present metallosupramolecular entity constitute a fascinating metal-to-ligand self-assembled prototype for building compact and intensely luminescent materials with host-guest capabilities. 相似文献
994.
Gaseous WS2Cl2 and WS2Br2 are formed by the reaction of solid WS2 with chlorine resp. bromine at temperatures of about 1000 K. This could be shown by mass spectrometric measurements. The heats of formation and entropies of WS2Cl2 and WS2Br2 have been determined by means of mass spectrometry (MS) and quantum chemical calculations (QC). WS2I2 could not be detected by experimental methods. This is in line with the quantum chemically determined equilibrium constant of the formation reaction. The following values are given:, ΔfH0298(WS2Cl2) = –230.8 kJ · mol–1 (MS), ΔfH0298(WS2Cl2) = –235.0 kJ · mol–1 (QC),, S0298(WS2Cl2) = 370.7 J · K–1 · mol–1 (QC) and, cp0T(WS2Cl2) = 103.78 + 7.07 × 10–3 T – 0.93 × 105 T–2 – 3.25 × 10–6 T2 (298.15 K < T < 1000 K) (QC). ΔfH0298(WS2Br2) = –141.9 kJ · mol–1 (MS), ΔfH0298(WS2Br2) = –131.5 kJ · mol–1 (QC),, S0298(WS2Br2) = 393.9 J · K–1 · mol–1 (QC) and, cp0T(WS2Br2) = 104.84 + 5.32 × 10–3 T – 0.75 × 105 T–2 – 2.45 × 10–6 T2 (298.15 K < T < 1000 K) (QC). ΔfH0298(WS2I2) = –18.0 kJ · mol–1 (QC), S0298(WS2I2) = 409.9 J · K–1 · mol–1 (QC) and, cp0T(WS2I2) = 105.17 + 4.77 × 10–3 T – 0.67 × 105 T–2 – 2.19 × 10–6 T2 (298.15 K < T < 1000 K) (QC). These molecules have the expected C2v‐symmetry. 相似文献
995.
996.
Scott MS Lucas AC Luckhurst CA Prodger JC Dixon DJ 《Organic & biomolecular chemistry》2006,4(7):1313-1327
The enantioselective synthesis of acyclic pyrrole, indole and other N-carbazole carbinols via ligand-mediated addition of lithium carbazolates to aldehydes, together with studies into their catalytic enantioselective synthesis using substoichiometric base and ligand, are reported. The subsequent exploitation of the resulting stereocentre as a controlling element in 1,3-syn- and anti-selective reduction of beta-ketones and elaboration to homoallylic alcohols is also described. 相似文献
997.
Theoretical investigations of the new Cokriging method for variable-fidelity surrogate modeling 总被引:1,自引:0,他引:1
Cokriging is a variable-fidelity surrogate modeling technique which emulates a target process based on the spatial correlation of sampled data of different levels of fidelity. In this work, we address two theoretical questions associated with the so-called new Cokriging method for variable-fidelity modeling:
相似文献
- (1)A mandatory requirement for the well-posedness of the Cokriging emulator is the positive definiteness of the associated Cokriging correlation matrix. Spatial correlations are usually modeled by positive definite correlation kernels, which are guaranteed to yield positive definite correlation matrices for mutually distinct sample points. However, in applications, low-fidelity information is often available at high-fidelity sample points and the Cokriging predictor may benefit from the additional information provided by such an inclusive sampling. We investigate the positive definiteness of the Cokriging covariance matrix in both of the aforementioned cases and derive sufficient conditions for the well-posedness of the Cokriging predictor.
- (2)The approximation quality of the Cokriging predictor is highly dependent on a number of model- and hyper-parameters. These parameters are determined by the method of maximum likelihood estimation. For standard Kriging, closed-form optima of the model parameters along hyper-parameter profile lines are known. Yet, these do not readily transfer to the setting of Cokriging, since additional parameters arise, which exhibit a mutual dependence. In previous work, this obstacle was tackled via a numerical optimization. Here, we derive closed-form optima for all Cokriging model parameters along hyper-parameter profile lines. The findings are illustrated by numerical experiments.
998.
Lucas Dahinden 《Abhandlungen aus dem Mathematischen Seminar der Universit?t Hamburg》2018,88(1):87-96
The classical Bott–Samelson theorem states that if on a Riemannian manifold all geodesics issuing from a certain point return to this point, then the universal cover of the manifold has the cohomology ring of a compact rank one symmetric space. This result on geodesic flows has been generalized to Reeb flows and partially to positive Legendrian isotopies by Frauenfelder–Labrousse–Schlenk. We prove the full theorem for positive Legendrian isotopies. 相似文献
999.
In this article we include discrete dividends in the stock price model and solve the corresponding generalized portfolio optimization problem. For this, we develop a new discrete dividend model that allows for the possibility of early announcement and ensures that the drop of the stock price at the ex-dividend date equals the dividend. The resulting portfolio problem can be solved explicitly for both the wealth and the trading strategy. We find that the resulting optimal portfolio process differs from the Merton strategy. 相似文献
1000.
Josephs RD Krska R MacDonald S Wilson P Pettersson H 《Analytical and bioanalytical chemistry》2004,378(5):1182-1189
Several previous interlaboratory studies in the field of mycotoxin analysis have revealed considerable problems, apparent as high between-laboratory standard deviations, or rather non-comparable and non-traceable results. A major reason is lack of proper calibrants for external calibration. Public awareness of substances that mimic or interfere with the activity of natural hormones (endocrine disrupters) has led to increased interest in mycotoxins with estrogenic potential, e.g. zearalenone (ZON). During a large-scale standard measurement and testing (SMT) project of the European Commission (EC) dealing with the preparation and certification of reference materials for determination of the mycotoxin ZON in maize, a ZON calibrant in acetonitrile was prepared and intensively checked for purity, homogeneity, and stability. Preparation of the material, study of its homogeneity and stability, and characterisation of the calibrant on the basis of its preparation, with discussion of the results obtained, are described in this paper. The certified value of 9.95 µg mL–1 for ZON in acetonitrile and its corresponding expanded uncertainty of ±0.30 µg mL–1 were calculated in compliance with the Guide to the Expression of Uncertainty in Measurement (GUM). 相似文献