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排序方式: 共有286条查询结果,搜索用时 312 毫秒
31.
Quentin Michaudel Guillaume Journot Alicia Regueiro‐Ren Animesh Goswami Zhiwei Guo Thomas P. Tully Lufeng Zou Raghunath O. Ramabhadran Kendall N. Houk Phil S. Baran 《Angewandte Chemie (International ed. in English)》2014,53(45):12091-12096
Physicochemical properties constitute a key factor for the success of a drug candidate. Whereas many strategies to improve the physicochemical properties of small heterocycle‐type leads exist, complex hydrocarbon skeletons are more challenging to derivatize because of the absence of functional groups. A variety of C H oxidation methods have been explored on the betulin skeleton to improve the solubility of this very bioactive, yet poorly water‐soluble, natural product. Capitalizing on the innate reactivity of the molecule, as well as the few molecular handles present on the core, allowed oxidations at different positions across the pentacyclic structure. Enzymatic oxidations afforded several orthogonal oxidations to chemical methods. Solubility measurements showed an enhancement for many of the synthesized compounds. 相似文献
32.
In this survey we attempt to give a unified presentation of a variety of results on the lifting of valid inequalities, as
well as a standard procedure combining mixed integer rounding with lifting for the development of strong valid inequalities
for knapsack and single node flow sets. Our hope is that the latter can be used in practice to generate cutting planes for
mixed integer programs.
The survey contains essentially two parts. In the first we present lifting in a very general way, emphasizing superadditive
lifting which allows one to lift simultaneously different sets of variables. In the second, our procedure for generating strong
valid inequalities consists of reduction to a knapsack set with a single continuous variable, construction of a mixed integer
rounding inequality, and superadditive lifting. It is applied to several generalizations of the 0–1 single node flow set.
This paper appeared in 4OR, 1, 173–208 (2003).
The first author is supported by the FNRS as a chercheur qualifié. This paper presents research results of the Belgian Program on Interuniversity Poles of Attraction
initiated by the Belgian State, Prime Minister’s Office, Science Policy Programming. The scientific responsibility is assumed
by the authors. 相似文献
33.
The reflection coefficient for a bounded ultrasonic beam incident on a liquid-solid-liquid system (LSL) is studied. Systematic measurements were carried out to investigate the variations of the amplitude of the reflection modulus ∣RLSL∣ with incident angle and parameter Fd (frequency-thickness of the plate). The experimental plots confirm the theoretical works of Claeys et al1 and Bogy and Gracewski2. It is shown that the attenuation of the media has a great influence on the variations of this coefficient as has been already mentioned in the literature, for liquid-solid configurations. 相似文献
34.
P. Quentin I. Brissaud R. de Swiniarski 《Zeitschrift für Physik A Hadrons and Nuclei》1980,298(1):37-40
By computing self consistently the nuclear density of238U with the Skyrme SIII effective force, the hexadecapole deformation parameter has been found to vary considerably in the nuclear surface. This suggests an explanation for some discrepancies observed betweenβ 4 parameters estimated from different inelastic scattering experiments. 相似文献
35.
Macocco K Grimal Q Naili S Soize C 《The Journal of the Acoustical Society of America》2006,119(2):729-740
The axial transmission technique can measure the longitudinal wave velocity of an immersed solid. An elementary model of the technique is developed with a set of source and receivers placed in a semi-infinite fluid coupled at a plane interface with a semi-infinite solid. The acoustic fluid is homogeneous. The solid is homogeneous, isotropic, and linearly elastic. The work is focused on the prediction of the measured velocity (apparent velocity) when the solid is considered to have random material properties. The probability density functions of the random variables modeling each mechanical parameter of the solid are derived following the maximum entropy principle. Specific attention is paid to the modeling of Poisson's ratio so that the second-order moments of the velocities remain finite. The stochastic solver is based on a Monte Carlo numerical simulation and uses an exact semianalytic expression of the acoustic response derived with the Cagniard-de Hoop method. Results are presented for a solid with the material properties of cortical bone. The estimated mean values and confidence regions of the apparent velocity are presented for various dispersion levels of the random parameters. A sensibility analysis with respect to the source and receivers locations is presented. 相似文献
36.
We revisit Kolchin's results on definability of differential Galois groups of strongly normal extensions, in the case where the field of constants is not necessarily algebraically closed. In certain classes of differential topological fields, which encompasses ordered or p‐valued differential fields, we find a partial Galois correspondence and we show one cannot expect more in general. In the class of ordered differential fields, using elimination of imaginaries in , we establish a relative Galois correspondence for relatively definable subgroups of the group of differential order automorphisms. 相似文献
37.
38.
Quentin Brouette 《Mathematical Logic Quarterly》2013,59(3):247-254
We use the model completeness and axiomatisation of the theory of closed ordered differential fields to give a differential version of Dubois, Krivine and Risler's nullstellensatz and Stengle's positivstellensatz for ordered fields. 相似文献
39.
Quentin Dherbassy Srimanta Manna Fabien J. T. Talbot Watcharapon Prasitwatcharakorn Gregory J. P. Perry David J. Procter 《Chemical science》2020,11(42):11380
The copper-catalyzed functionalization of enyne derivatives has recently emerged as a powerful approach in contemporary synthesis. Enynes are versatile and readily accessible substrates that can undergo a variety of reactions to yield densely functionalized, enantioenriched products. In this perspective, we review copper-catalyzed transformations of enynes, such as boro- and hydrofunctionalizations, copper-mediated radical difunctionalizations, and cyclizations. Particular attention is given to the regiodivergent functionalization of 1,3-enynes, and the current mechanistic understanding of such processes.The copper-catalyzed functionalization of enynes is a powerful approach to yield densely functionalized products. This review covers various transformations, such as boro- and hydrofunctionalizations, copper-mediated radical difunctionalizations, and cyclizations. 相似文献
40.
Transition Metal Free Cycloamination of Prenyl Carbamates and Ureas Promoted by Aryldiazonium Salts 下载免费PDF全文
Roman Abrams Dr. Quentin Lefebvre Prof. Jonathan Clayden 《Angewandte Chemie (International ed. in English)》2018,57(41):13587-13591
Upon treatment with aryldiazonium salts, prenyl carbamates and ureas undergo redox‐neutral azocycloamination. In general, N‐aryl O‐prenyl carbamates cyclize in a photocatalytic reaction with visible light and an organic dye. With electron‐deficient diazonium salts, electronic matching with an electron‐rich N‐aryl substituent results in a reaction proceeding in the ground state, without either light or photocatalyst. Cyclic voltammetry suggests that this radical reaction is initiated by hydrogen‐atom abstraction mediated by an aryl radical, followed by a radical addition cascade and proton‐coupled hole propagation. The reaction proceeds at room temperature in short reaction times, and a range of functional groups is tolerated. 相似文献