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41.
42.
Cheng-Hsia Angeline Lee 《Tetrahedron letters》2006,47(5):809-812
A highly enantioselective one-pot synthesis of linear homoallylic alcohols with terminal ester functionality has been achieved. The reactions were controlled by ordered addition of reagents and catalysts, ensuring complete consumption of aldehyde. The synthetic utility of this strategy has been demonstrated in a short synthesis of a low boiling point intermediate for grahamimycin A. 相似文献
43.
Mariappan PeriasamyN. KishoreBabu Keela Natarajan Jayakumar 《Tetrahedron letters》2003,44(50):8939-8941
The reactions of arylacetic acid esters with tertiary arylamines in the presence of TiCl4 give α-arylated products in 65-90% yields, as well as 10-20% yields of the corresponding benzidines. 相似文献
44.
针对传统的DEA模型在评估过程中并未考虑决策者对相关指标权重的偏好,将最优最差方法(BWM)嵌入到传统DEA模型中,基于决策者偏好排序的判断矩阵,构建一种含有偏好的DEA-BWM评价方法。首先在保持传统DEA方法的优势基础上,构建了CCR-BWM评价模型对各DMU进行评价。同时考虑为了便于各决策单元在统一权重基础上相互比较,构建了CSW-BWM公共权重模型。另外考虑决策单元自评和互评,构建了NCE-BWM中立型交叉效率。然后采用min-max方法分别将上述三种多目标评价模型转换为单目标线性规划进行求解。最后,选择一组算例对三种模型的有效性与合理性进行验证。 相似文献
45.
The computation ofL
1 smoothing splines on large data sets is often desirable, but computationally infeasible. A locally weighted, LAD smoothing spline based smoother is suggested, and preliminary results will be discussed. Specifically, one can seek smoothing splines in the spacesW
m
(D), with [0, 1]
n
D. We assume data of the formy
i
=f(t
i
)+
i
,i=1,..., N with {t
i
}
i=1
N
D, the
i
are errors withE(
i
)=0, andf is assumed to be inW
m
. An LAD smoothing spline is the solution,s
, of the following optimization problem
相似文献
46.
We propose an algorithm for the computation ofL
1 (LAD) smoothing splines in the spacesW
M
(D), with
. We assume one is given data of the formy
i
=(f(t
i
) +
i
, i=1,...,N with {itti}
i=1
N D
, the
i
are errors withE(
i
)=0, andf is assumed to be inW
M
. The LAD smoothing spline, for fixed smoothing parameter0, is defined as the solution,s
, of the optimization problem
(1/N)
i=1
N
¦y
i
–g(t
i
¦+J
M
(g), whereJ
M
(g) is the seminorm consisting of the sum of the squaredL
2 norms of theMth partial derivatives ofg. Such an LAD smoothing spline,s
, would be expected to give robust smoothed estimates off in situations where the
i
are from a distribution with heavy tails. The solution to such a problem is a thin plate spline of known form. An algorithm for computings
is given which is based on considering a sequence of quadratic programming problems whose structure is guided by the optimality conditions for the above convex minimization problem, and which are solved readily, if a good initial point is available. The data driven selection of the smoothing parameter is achieved by minimizing aCV() score of the form
.The combined LAD-CV smoothing spline algorithm is a continuation scheme in 0 taken on the above SQPs parametrized in, with the optimal smoothing parameter taken to be that value of at which theCV() score first begins to increase. The feasibility of constructing the LAD-CV smoothing spline is illustrated by an application to a problem in environment data interpretation. 相似文献
47.
Odin C 《Magnetic resonance in chemistry : MRC》2004,42(4):381-388
A variable-temperature high-resolution 13C and 87Rb solid-state NMR study of powder rubidium hydrogencarbonate, RbHCO3, is presented for the first time. At ambient temperature, RbHCO3 is formed by centrosymmetric dimers linked by hydrogen bonds, but almost no information is available on this compound concerning proton disorder and the low-temperature phase. However, potassium hydrogencarbonate, KHCO3, which has an isomorphic structure for the high temperature phase, was well studied: it undergoes a non-ferroic, non-ferroelectric phase transition at Tc = 318 K between two monoclinic structures. The protons are disordered in an asymmetric double-well potential in the low-temperature phase, and the double-well potential becomes symmetric in the high-temperature phase. By comparison with recent solid-state NMR experimental results on KHCO3, we show that RbHCO3 undergoes a phase transition at Tc approximately 245 K, and give evidence that the proton dynamic disorder in both compounds is very similar. 相似文献
48.
自行研制了电子碰撞离子化的飞行时间型质量分析器(TOFMS),用于物质的化学分析。用研制的TOFMS测量了Ar离子化的飞行时间谱和离子的部分电离截面积比与碰撞电子能量的依赖关系,将它与Stepshan等人的实验结果进行了比较。 相似文献
49.
50.
A continuous flow, microwave-assisted, parallel-capillary microreactor has been developed. Libraries of drug candidates were prepared on the milligram scale with this reactor by injecting plugs of reagents from separate syringes into common reaction capillaries, thereby producing discrete compounds in excellent yield and purity. Microwave irradiation provides the necessary energy that existing room-temperature microreactor technology lacks for higher activation barrier transformations, producing the required amounts of desired compounds in minutes or less. 相似文献
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