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1.
Alcindo A. Dos Santos Renan S. Ferrarini Jefferson L. Princival João V. Comasseto 《Tetrahedron letters》2006,47(50):8933-8935
A masked lithium homoenolate, generated by tellurium/lithium exchange, was reacted with epoxides. The lithium compound was also converted into other organometallics such as Grignard, and cuprates and the reactivity of those organometallics with epoxides was evaluated. The same building block was employed in the synthesis of (+/−)-frontalin. 相似文献
2.
Mingbao Zhang Raymond Reeves Cheng Bi Robert Dally Gaetan Ladouceur William Bullock Jefferson Chin 《Tetrahedron letters》2004,45(27):5229-5231
Three novel, optically active, 6-substituted 2-(aminomethyl)chromans were synthesized from readily available chroman 2-carboxylic acid precursors. These chroman-containing primary amines are useful building blocks for the synthesis of chroman-derived pharmaceutical agents. 相似文献
3.
P. Murzyn C. R. Pidgeon P. J. Phillips J. -P. Wells N. T. Gordon T. Ashley J. H. Jefferson T. M. Burke J. Giess M. Merrick B. N. Murdin C. D. Maxey 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):220
We have made direct pump–probe measurements of spin lifetimes in long wavelength narrow-gap semiconductors at wavelengths between 4 and 10 μm and from 4 to 300 K. In particular, we measure remarkably long spin lifetimes, τs300 ps, even at 300 K for epilayers of degenerate n-type InSb. In this material the mobility is approximately constant between 77 and 300 K, and we find that τs is approximately constant in this temperature range. In order to determine the dominant spin relaxation mechanism we have investigated the temperature dependence of τs in non-degenerate lightly n-type Hg0.78Cd0.22Te of approximately the same band gap as InSb, and find that τs varies from 356 ps at 150 K to 24 ps at 300 K. Our results, both in magnitude and temperature dependence of τs, imply that the Elliott–Yafet model dominates in these materials. 相似文献
4.
Alcides Lins Neto 《Annales Scientifiques de l'école Normale Supérieure》2002,35(2):231-266
In 1891, Poincaré started a series of three papers in which he tried to answer the following question (cf. [21-23]): “Is it possible to decide if an algebraic differential equation in two variables is algebraically integrable?” (in the sense that it has a rational first integral). More or less at the same time P. Painlevé asked the following question: “Is it possible to recognize the genus of the general solution of an algebraic differential equation in two variables which has a rational first integral?”. In this paper we give examples of one-parameter families which show that both problems have a negative answer. With some of the families we can also answer a question posed by M. Brunella in [5]. 相似文献
5.
The Jefferson Laboratory E- Collaboration 《The European Physical Journal A - Hadrons and Nuclei》2003,18(2-3):181-183
The ratio G
e
n
/G
m
n
of the electric to the magnetic form factor of the neutron has been measured by analyzing the polarization of the recoiling neutron in quasi-elastic scattering of longitudinally polarized electrons from deuterium at the Q
2 values of 0.45, 1.15, and 1.47 (GeV/c)2. The experiment has been performed in Hall C of the Thomas Jefferson National Accelerator Facility. With G
m
n
being known G
e
n
can be deduced. The preliminary results show that the lowest Q
2 points follow the Galster parametrization and that the 1.47 (GeV/c)2 point rises above this parametrization.Received: 30 September 2002, Published online: 22 October 2003PACS:
13.40.Gp Electromagnetic form factors - 14.20.Dh Protons and neutrons - 24.70. + s Polarization phenomena in reactions 相似文献
6.
7.
Increased structural complexity leads to higher activity: peptides as efficient and versatile catalysts for asymmetric aldol reactions 总被引:3,自引:0,他引:3
[reaction: see text] Peptides containing a secondary amine and a carboxylic acid in a specific orientation to each other are presented as highly efficient catalysts for asymmetric aldol reactions: (1) their activity is considerably higher compared to that of proline, and (2) the enantioselectivity of the peptidic catalysts can be changed from (R)- to (S)-selectivity by simple modifications of the secondary structure. 相似文献
8.
Designs, Codes and Cryptography - A $$\varrho $$ -saturating set of $$\text {PG}(N,q)$$ is a point set $${\mathcal {S}}$$ such that any point of $$\text {PG}(N,q)$$ lies in a subspace of dimension... 相似文献
9.
Franklin D. Hardcastle Israel E. Wachs Hellmut Eckert David A. Jefferson 《Journal of solid state chemistry》1991,90(2)
The Bi2O3---V2O5 system was examined using Raman spectroscopy and solid state 51V wideline, magic-angle spinning (MAS), and nutation NMR spectroscopy. The methods are shown to be complementary in the identification of the various phases and in the characterization of their vanadium site symmetries. Most of the compositions examined (1:1 ≤ Bi:V ≤ 60:1) are multiphasic. Depending on the Bi:V ratio, the following phases have been identified: BiVO4, Bi4V2O11, a triclinic type-II phase, a cubic type-I phase, γ-Bi2O3 doped with V(V) (sillenite), and β-Bi2O3. Detailed spectroscopic characterization reveals that vanadium is tetrahedrally coordinated in all these compounds, and that the degree of symmetry increases with increasing Bi:V ratio. At the highest Bi:V ratios, the combined interpretation of the Raman and NMR data provides strong evidence for the presence of Bi5+O4 tetrahedra. 相似文献
10.
In vivo imaging is a powerful approach to study biological processes. Beyond cellular methods, in vivo studies allow for biological stimuli (small molecules or proteins) to be studied in their native environment. This has the potential to aid in the discovery of new biology and guide the development of diagnostics and therapies for diseases. To ensure selectivity and an observable readout, the probe development field is shifting towards activity-based sensing (ABS) approaches and near-infrared (NIR) imaging modalities. This perspective will highlight recent in vivo ABS applications that utilize NIR imaging platforms. In vivo imaging is a powerful approach to study biological processes. 相似文献