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101.
Lainton JA Allen MC Burton M Cameron S Edwards TR Harden G Hogg R Leung W Miller S Morrish JJ Rooke SM Wendt B 《Journal of combinatorial chemistry》2003,5(4):400-407
Efficient and general procedures have been developed for the solution-phase preparation of substituted morpholine derivatives, and a library has been produced around generic structure 1. This library was designed with proprietary modeling software for use as a general screening library. The 30 R1 reagents were phenols, and the 275 R2 reagents were taken from five different reagent classes, giving a variety of product classes in the final library of 8250 potential products. All of the library members were generated from a common intermediate, mesylate (5), which was synthesized efficiently, in bulk, in three steps from N-benzylethanolamine (2). High-throughput chemistry using robotics was carried out to produce the 7907 library members, which were individually characterized by reversed-phase LC/MS analysis. 相似文献
102.
Let be a surface, and let be a holomorphic curve in representing a primitive homology class. We count the number of curves of geometric genus with nodes passing through generic points in in the linear system for any and satisfying .
When , this coincides with the enumerative problem studied by Yau and Zaslow who obtained a conjectural generating function for the numbers. Recently, Göttsche has generalized their conjecture to arbitrary in terms of quasi-modular forms. We prove these formulas using Gromov-Witten invariants for families, a degeneration argument, and an obstruction bundle computation. Our methods also apply to blown up at 9 points where we show that the ordinary Gromov-Witten invariants of genus constrained to points are also given in terms of quasi-modular forms. 相似文献
103.
104.
An experimental investigation has been performed to determine the effects of different arrangements of obstacles on the
cooling of simulated electronic package. The considered simulated electronic package consisted of a channel formed by two
parallel plates. The bottom plate is attached with five identical electrically heated square obstacles, which are perpendicular
to the mean airflow and arranged with different side-to-side distances. The experimental results show that the conventional
equi-spaced arrangement might not be the optimum option and should be avoided. A better thermal performance could be obtained
when the side-to-side distances between the obstacles followed a geometric series. For example, at Re=800, the highest temperature
of the optimum arrangement could be reduced by 12% compare to the equi-spaced arrangement and the maximum temperature difference
among the five obstacles is lower than that of equi-spaced arrangement by 32.1%.
Received on 17 December 1999 相似文献
105.
Sze-Kar Leung 《Tetrahedron letters》2005,46(15):2709-2712
Cyclopropanations of an 8-oxabicyclo[3.2.1]octene substrate using diazocarbonyl compounds provided exo, exo-cyclopropanated products as the sole or major diastereomeric oxatricyclic products. Reductive cleavage of a meso-oxatricyclic ketone by samarium iodide resulted in desymmetrization without concomitant oxygen bridge cleavage. 相似文献
106.
C.W. Tan Y.C. Chan Bernard N.W. Leung John Tsun Alex C.K. So 《Optics and Lasers in Engineering》2005,43(2):374
For the packaging of a pump laser in butterfly package, the most crucial assembly step is the fiber-to-laser diode coupling and attachment. The use of laser welding as the joining method offers several advantages if compared with the adhesive joints: strong joining strength, short process time and less contamination. This paper reports on laser welding process characteristics; weld strength and its fracture mode. The penetration depth and melt area of laser spot welds were found to be complicated functions of laser pulse energy, intensity, and beam diameter. Effects of pulse width, input power and size of the focal spot on the rate of energy input to the workpieces and consequently, the weld strength were reported. The weld strength was found to be dependent on the overlapping area between the two joining materials. Surface roughness, Ra, has influence on the fraction of energy absorbed, A, and therefore, affecting the penetration depth. Thermal analysis was carried out on the laser-welded joints and its heat-affected zone (HAZ) induced by various power densities was examined. These data are important in order to optimize and utilize the laser welding process as an effective manufacturing tool for fabrication of reliable pump laser. 相似文献
107.
Björn Schwarz Issic K. C. Leung Nils Buchholtz Gabriele Kaiser Gloria Stillman Jill Brown Colleen Vale 《ZDM》2008,40(5):791-811
In this paper, qualitative results of a case study about the professional knowledge in the area of argumentation and proof of future teachers from universities in three countries are described. Based on results of open questionnaires, data about the competencies these future teachers have in the areas of mathematical knowledge and knowledge of mathematics pedagogy are presented. The study shows that the majority of the future teachers at the participating universities situated in Germany, Hong Kong and Australia, were not able to execute formal proofs, requiring only lower secondary mathematical content, in an adequate and mathematically correct way. In contrast, in all samples there was evidence of at least average competencies of pedagogical content reflection about formal and pre-formal proving in mathematics teaching. However, it appears that possessing a mathematical background as mandated for teaching and having a high affinity with proving in mathematics teaching at the lower secondary level are not a sufficient preparation for teaching proof. 相似文献
108.
A high-performance liquid chromatographic method has been developed for the determination of vitamin U in tablets and capsules. Threonine was employed as the internal standard through the assay. The o-phthalaldehyde derivatives were prepared and then chromatographed isocratically on a reversed-phase C18 column. The optimum reaction time for both vitamin U and threonine at pH 10.5 is 5 min. Vitamin U and its major degradation product in the dosage forms, viz., methionine sulphoxide, were separated and quantified with a relative standard deviation of about 1%, using a fluorescence detector with excitation and emission wavelengths at 340 and 450 nm respectively. A linear relationship has been established between the peak area ratio of vitamin U/threonine and the concentration of vitamin U over the range of 2.5-50 micrograms/ml. 相似文献
109.
Toby Cubitt Aram W. Harrow Debbie Leung Ashley Montanaro Andreas Winter 《Communications in Mathematical Physics》2008,284(1):281-290
Complementing recent progress on the additivity conjecture of quantum information theory, showing that the minimum output
p-Rényi entropies of channels are not generally additive for p > 1, we demonstrate here by a careful random selection argument that also at p = 0, and consequently for sufficiently small p, there exist counterexamples.
An explicit construction of two channels from 4 to 3 dimensions is given, which have non-multiplicative minimum output rank;
for this pair of channels, numerics strongly suggest that the p-Rényi entropy is non-additive for all p ≲ 0.11. We conjecture however that violations of additivity exist for all p < 1. 相似文献
110.
We are interested in the problem of scheduling orders for different product types in a facility with a number of machines
in parallel. Each order asks for certain amounts of various different product types which can be produced concurrently. Each
product type can be produced on a subset of the machines. Two extreme cases of machine environments are of interest. In the
first case, each product type can be produced on one and only one machine which is dedicated to that product type. In the
second case, all machines are identical and flexible; each product type can be produced by any one of the machines. Moreover,
when a machine in this case switches over from one product type to another, no setup is required. Each order has a release
date and a weight. Preemptions are not allowed. The objective is minimizing the total weighted completion time of the orders.
Even when all orders are available at time 0, both types of machine environments have been shown to be NP-hard for any fixed
number (≥2) of machines. This paper focuses on the design and analysis of approximation algorithms for these two machine environments.
We also present empirical comparisons of the various algorithms. The conclusions from the empirical analyses provide insights
into the trade-offs with regard to solution quality, speed, and memory space.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users.
This research is supported by the National Science Foundation through grants DMI-0300156 and DMI-0245603. 相似文献