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41.
Bashore CG Vetelino MG Wirtz MC Brooks PR Frost HN McDermott RE Whritenour DC Ragan JA Rutherford JL Makowski TW Brenek SJ Coe JW 《Organic letters》2006,8(26):5947-5950
[Structure: see text] The development of a concise enantioselective synthesis of nicotinic alkaloid 1 is presented. The route features the synthesis and use of a "stable" aliphatic triflate 21 in an alkylation step to generate Heck precursor 24 and an enantioselective cyclization to establish a compound with the key [3.2.1]-bicyclic core, 29. 相似文献
42.
A method of determining asymptotic expansions for weakly couplednonlinearly perturbed systems of harmonic oscillators with slowlyvarying frequencies is presented. In an example with two oscillators,each one experiences a separate resonance passage that producesa first-order amplitude change. Simultaneously, second-orderadjustments occur to both oscillators. The determination isachieved by carrying the calculations to third order. 相似文献
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Abstract This paper is devoted to investigate extinction and nonextinction conditions of the extended Beverton–Holt equation (BHE) for dynamics of populations in Ecology when potential discontinuities at sampling points are included in the model. The proposed model is described by means of four sequences of parameters. Two of them are the intrinsic growth rate and the carrying capacity sequences which are included in the basic BHE model. The other two ones, namely, the harvesting (i.e., the hunting or fishing quota) and the internal consumption (which can include positive and negative migrations in the considered population habitat) sequences are included to parameterize the model discontinuities. Such discontinuities are related to impulses in the corresponding continuous‐time logistic equation. The obtained results establish how the harvesting quota and/or the internal consumption has to be fixed to guarantee the population nonextinction or, eventually, its extinction. Finally, some controllability results related to the search of a carrying capacity sequence such that the solution of the proposed impulsive BHE tracks a reference one are obtained. 相似文献
45.
One way of estimating a function from indirect, noisy measurements is to regularise an inverse of its Fourier transformation, using properties of the adjoint of the transform that degraded the function in the first place. It is known that when the function is smooth, this approach can perform well and produce estimators that have optimal convergence rates. When the function is unsmooth, in particular when it suffers jump discontinuities, an analogue of this approach is to invert the wavelet transform and use thresholding to decide whether wavelet terms should be included or excluded in the final approximation. We evaluate the performance of this approach by applying it to a large class of Abel-type transforms, and show that the smoothness of the target function and the smoothness of the transform interact in a particularly subtle way to determine the overall convergence rate. The most serious difficulties arise when the target function has a jump discontinuity at the origin; this has a considerably greater, and deleterious, impact on performance than a discontinuity elsewhere. In the absence of a discontinuity at the origin, the rate of convergence is determined principally by an inequality between the smoothness of the function and the smoothness of the transform. 相似文献
46.
Stevenson S Phillips JP Reid JE Olmstead MM Rath SP Balch AL 《Chemical communications (Cambridge, England)》2004,(24):2814-2815
The X-ray crystal structure of Gd(3)N@C(80).Ni(II)(OEP).1.5(benzene) shows that the Gd(3)N unit within the I(h) C(80) cage is pyramidal, whereas Sc(3)N@C(80), Sc(3)N@C(78), Sc(3)N@C(68), Lu(3)N@C(80) and Sc(2)ErN@C(80) have planar M(3)N units. 相似文献
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48.
WANG Yue BI Xiao-Jun CUI Shu-Wang DING Lin-Kai DAN Zeng-Luo-Bu DING Xiao-Hong FAN Chao FENG Cun-Feng FENG Zhao-Yang FENG Zhen-Yong GAO Xiao-Yu GENG Qing-Xi GUO Hong-Wei HE Hui-Hai HE Mao HU Hai-Bing HU Hong-Bo HUANG Qing JIA Huan-Yu LA Ba-Ci-Ren LE Gui-Ming LI Ai-Feng LI Jin-Yu LOU Yu-Qing LU Hong LU Sui-Ling MENG Xian-Ru MU Jun REN Jing-Ru TAN You-Heng WANG Bo WANG Hui WANG Yong-Gang WU Han-Rong XUE Liang YANG Xian-Chu YE Zong-Hai YU Guang-Ce YUAN Ai-Fang ZHANG Hui-Min ZHANG Ji-Long ZHANG Nai-Jian ZHANG Xue-Yao ZHANG Yong ZHANG Yi ZHA Xi-Sang-Zhu ZHOU Xun-Xiu YUAN Qiang 《中国物理C(英文版)》2008,32(11)
Using the data taken from Tibet Ⅱ High Density (HD) Array (1997 February--1999 September) and Tibet-Ⅲ array (1999 November--2005 November), our previous northern sky survey for TeV γ-ray point sources has now been updated by a factor of 2.8 improved statistics. From 0.0° to 60.0° in declination (Dec) range, no new TeV γ-ray point sources with sufficiently high significance were identified while the well-known Crab Nebula and Mrk421 remain to be the brightest TeV T-ray sources within the field of view of the Tibet air shower array. Based on the currently available data and at the 90% confidence level (C.L.), the flux upper limits for different power law index assumption are re-derived, which are approximately improved by 1.7 times as compared with our previous reported limits. 相似文献
49.
A Schur-type decomposition for Hamiltonian matrices is given that relies on unitary symplectic similarity transformations. These transformations preserve the Hamiltonian structure and are numerically stable, making them ideal for analysis and computation. Using this decomposition and a special singular-value decomposition for unitary symplectic matrices, a canonical reduction of the algebraic Riccati equation is obtained which sheds light on the sensitivity of the nonnegative definite solution. After presenting some real decompositions for real Hamiltonian matrices, we look into the possibility of an orthogonal symplectic version of the QR algorithm suitable for Hamiltonian matrices. A finite-step initial reduction to a Hessenberg-type canonical form is presented. However, no extension of the Francis implicit-shift technique was found, and reasons for the difficulty are given. 相似文献
50.