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971.
Yamada CM Dellinger DJ Caruthers MH 《Journal of the American Chemical Society》2006,128(15):5251-5261
Phosphonoformate oligodeoxyribonucleotides were prepared via a solid phase synthesis strategy. The first step in the preparation of appropriate synthons was condensation of bis(N,N-diisopropylamino)phosphine and diphenylmethylsilylethyl chloroformate in the presence of sodium metal to yield formic acid, [bis(N,N-diisopropylamino)phosphino]-beta-(diphenylmethylsilylethyl) ester. The product of this reaction was then condensed with appropriately protected 2'-deoxynucleosides using 4,5-dicyanoimidazole to yield the 3'-O-phosphinoamidite reactive monomers. The exocyclic amines of cytosine, adenine, and guanine were protected with 9-fluorenylmethyloxycarbonyl, and oligodeoxyribonucleotides were synthesized on controlled pore glass using the hydroquinone-O,O'-diacetic acid linker. Synthons were sequentially added to this support using tetrazole as an activator, oxidized to phosphonoformate, and the transient 5'-protecting group was removed with acid. Following total synthesis of an oligomer, protecting groups were removed with TEMED.HF and products purified by HPLC. These analogues were resistant to nucleases, formed duplexes with complementary RNA (A-form), and, as chimeric oligomers containing phosphate at selected sites, stimulated RNase H1 activity. 相似文献
972.
The infrared spectra of the (H(2)O)n-SO(2) complexes trapped in argon matrices have been investigated using Fourier transform infrared spectroscopy. In addition to the 1:1 and 2:1 complexes, the first spectroscopic evidence for the 3:1 complex has been obtained from the spectra of the SO stretching and the OH stretching modes. The observed frequency shifts in the bonded OH stretching region indicate that the hydrogen bonds of the 2:1 and 3:1 complexes are strengthened compared to that of the 1:1 complex, which suggests the cyclic structure of the complexes. 相似文献
973.
Futaba DN Hata K Namai T Yamada T Mizuno K Hayamizu Y Yumura M Iijima S 《The journal of physical chemistry. B》2006,110(15):8035-8038
We propose a statistical and macroscopic analysis to estimate the catalyst activity of water-assisted growth (super-growth) of single-walled nanotubes (SWNT) and to characterize SWNT forests. The catalyst activity was estimated to be 84% (+/-6%), the highest ever reported. The SWNT forest was found to be a very sparse material where SWNTs represent only 3.6% of the total volume. This structural sparseness is believed to play a critical role in achieving highly efficient growth. 相似文献
974.
[STRUCTURE: SEE TEXT] On treating readily prepared benzyl 2,3,3-trifluoroacrylate with various Grignard reagents, e.g., aryl-, alkyl-, or alkenylmagnesium halide, in the presence of a catalytic amount of copper(I) salt in THF at -78 degrees C for 1 h, the corresponding alpha,beta-difluoroacrylates were obtained in 54-98% yields with high Z-selectivity. 相似文献
975.
For a given boundary Γ in Rn consisting of arcs and vertices, with two or more arcs meeting at each vertex, we treat the problem of estimating the area
density of a soap film-like surface Σ spanning Γ. Σ is assumed locally to minimize area, or more generally, to be strongly
stationary for area with respect to Γ. We introduce a notion of total curvature (Γ) for such graphs, or nets, Γ. We show that 2π times the area density of Σ at any point is less than or equal to (Γ). For n=3, these density estimates imply, for example, that if (Γ)≤3.649π, then the only possible singularities of a piecewise smooth (M,0,δ)-minimizing set Σ are curves, along which three smooth sheets of Σ meet with equal angles of 120°.
Second author supported in part by NSF grant 00-71862. 相似文献
976.
The preparation of new thalidomide derivatives 4-methyl-(3S,4R)-3a and 4-phenyl-(3S,4S)-3b starting from pyroglutamic acids (2R,3R)-7a and (2R,3S)-7b, possessing an inappropriate stereochemistry, was successfully realized due to stereochemically complete epimerization at the alpha-stereogenic center upon formation of the corresponding N-phthaloyl anhydrides 9a,b. The demonstrated conformational stability of these new thalidomide derivatives provides solid experimental evidence for practical feasibility of the approach described here to overcome the inherent problem of configurational instability of thalidomide by introducing an alkyl or aryl group in the C4 position. [reaction: see text]. 相似文献
977.
An experimental study on the Reynolds stress tensor was conducted in the three-dimensional flow in the plane turbulent wall jet induced by an isolated streamwise vortex generated by the half-delta wing mounted on the wall. Oscillation of the angle of attack of the wing induced a periodic perturbation in the strength of the streamwise vortex. Analysis by triple velocity decomposition and phase averaging shows that the oscillation induces periodic variations in the strength, radius, and position of the streamwise vortex center. The effect of periodic perturbation manifests itself in the magnitude of the Reynolds stress components
and
Simulations prove that the periodic variations in the strength, radius, and position of the vortex center can generate an apparent shear stress, denoted herein as
相似文献
978.
979.
Omid Bozorg Haddad Mahsa Mirmomeni Mahboubeh Zarezadeh Mehrizi Miguel A. Mariño 《Computational Optimization and Applications》2010,47(1):97-128
Effective project management requires the development of a realistic plan and a clear communication of the plan from the beginning
to the end of the project. The critical path method (CPM) of scheduling is the fundamental tool used to develop and interconnect
project plans. Ensuring the integrity and transparency of those schedules is paramount for project success. The complex and
discrete nature of the solution domain for such problems causes failing of traditional and gradient-based methods in finding
the optimal or even feasible solution in some cases. The difficulties encountered in scheduling construction projects with
resource constraints are highlighted by means of a simplified bridge construction problem and a basic masonry construction
problem. The honey-bee mating optimization (HBMO) algorithm has been previously adopted to solve mathematical and engineering
problems and has proven to be efficient for searching optimal solutions in large-problem domains. This paper presents the
HBMO algorithm for scheduling projects with both constrained and unconstrained resources. Results show that the HBMO algorithm
is applicable to projects with or without resource constraints. Furthermore, results obtained are promising and compare well
with those of well-known heuristic approaches and gradient-based methods. 相似文献
980.
Takahiro Nakanishi Tatsuo Aono Masatoshi Yamada Masashi Kusakabe 《Journal of Radioanalytical and Nuclear Chemistry》2010,283(3):831-838
Five survey cruises were carried out from 2004 to 2007 to determine 137Cs concentrations in the water columns off Rokkasho Village, Aomori Prefecture, Japan, where the spent nuclear fuel reprocessing
plant of Japan Nuclear Fuel Ltd has been undergoing test operation since March 2006. Seawater samples were collected with
a large volume in situ filtration and concentration system at different depths in the water column. 137Cs in particulate form could not be detected in the survey area. Dissolved 137Cs showed temporal variation, especially in the surface water. Based on the results, it was concluded that no observable 137Cs contamination was present in the investigated area. The distribution of 137Cs concentrations was influenced by the mixing between the Tsugaru and Oyashio Currents. 相似文献