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1.
When solving large complex optimization problems, the user is faced with three major problems. These are (i) the cost in human time in obtaining accurate expressions for the derivatives involved; (ii) the need to store second derivative information; and (iii), of lessening importance, the time taken to solve the problem on the computer. For many problems, a significant part of the latter can be attributed to solving Newton-like equations. In the algorithm described, the equations are solved using a conjugate direction method that only needs the Hessian at the current point when it is multiplied by a trial vector. In this paper, we present a method that finds this product using automatic differentiation while only requiring vector storage. The method takes advantage of any sparsity in the Hessian matrix and computes exact derivatives. It avoids the complexity of symbolic differentiation, the inaccuracy of numerical differentiation, the labor of finding analytic derivatives, and the need for matrix store. When far from a minimum, an accurate solution to the Newton equations is not justified, so an approximate solution is obtained by using a version of Dembo and Steihaug's truncated Newton algorithm (Ref. 1).This paper was presented at the SIAM National Meeting, Boston, Massachusetts, 1986. 相似文献
2.
Sally Dixon 《Tetrahedron》2004,60(6):1401-1416
A wide range of carbenoids (1-lithio-1-halo species), including those with α-SiR3, OEt, SPh, SO2Ph, P(O)(OEt)2, and CN substituents, insert into 5-member zirconacycles (saturated and unsaturated, mono- and bi-cyclic) to afford functionalized 6-member zirconacycles. 1-Lithio-1-haloalkenes insert to afford 6-member zirconacycles with an alkylidene substituent next to the metal. Unexpected double insertion of some carbenoids, and evidence for endocylic β-hydride transfer processes provide additional mechanistic interest. 相似文献
3.
We review the proof of a conjecture concerning the reality of the spectra of certain PT-symmetric quantum mechanical systems, obtained via a connection between the theories of ordinary differential equations and integrable models. Spectral equivalences inspired by the correspondence are also discussed. 相似文献
4.
5.
Ammar R Ball RC Banerjee S Bhat PC Bosetti P Bromberg C Canough GE Coffin T Dershem TO Dixon RL Fenker HC Ganguli SN Gensch U Girtler P Goshaw AT Grard F Gurtu A Hamilton C Henri VP Hernandez JJ Hrubec J Iori M Jones LW Kuhn D Knauss D Leedom ID Legros P Lemonne J Leutz H Liu X Malhotra PK Marraffino JM Mendez GE Miller R Naumann T Nguyen A Nowak H Pilette P Poirier J Poppleton A Raghavan R Rasner K Reucroft S Robertson WJ Roe BP Roth A Senko M Struczinski W Subramanian A Touboul MC Vonck B 《Physical review letters》1988,61(19):2185-2188
6.
M. Jonathan Fray Paul Allen Paul R. Bradley Clare E. Challenger Michael Closier Tim J. Evans Mark L. Lewis John P. Mathias Carly L. Nichols Yvonne M. Po-Ba Hayley Snow Mark H. Stefaniak Hannah V. Vuong 《Tetrahedron》2006,62(29):6869-6875
The synthesis of ten substituted aminomethylene tetrahydro-isoquinolines is described, proceeding in eight steps from 5-hydroxyisoquinoline via reductive amination of N-Boc tetrahydro-isoquinoline 5-carboxaldehyde. Likewise, reductive amination was used to prepare four substituted dihydro-isoindoles from the corresponding aldehyde. The dihydro-isoindole ring system was conveniently accessed via a 2+2+2 cycloaddition reaction. 相似文献
7.
8.
B. Brocklehurst R.S. Dixon E.M. Gardy V.J. Lopata M.J. Quinn A. Singh F.P. Sargent 《Chemical physics letters》1974,28(3):361-363
Excited state formation by ion recombination in solutions of fluorene in squalene has been studied by pulse radiolysis at the center of a large electromagnet. The products of the slower part of the ion recombination are affected by an applied magnetic field. The fluorescence yield increases by a factor of about 1.5 whereas the triplet yield decreases. 相似文献
9.
B.W. Clare P.J. Jennings J.C.L. Cornish G. Talukder C.P. Lund G.T. Hefter 《Journal of computational chemistry》1993,14(12):1423-1428
A set of simple models of hydrogenated amorphous silicon (a-Si:H) consisting of hypothetical silane molecules with diamond or similar lattices was studied by the semiempirical AM1 method. Densities of states and infrared spectra were calculated for the silane molecules and similar molecules with dangling bonds disorder, and with boron or phosphorus substitution to simulate doping. Some examples are presented, and a comparison is made with experimental properties of a-Si:H. It is proposed to use these models in a study of the Staebler–Wronski photodegradation of a-Si:H and other aspects of amorphous silicon technology. © John Wiley & Sons, Inc. 相似文献
10.
19F and (119)Sn MAS NMR spectroscopy have been used to investigate the fluoride ion conductor, BaSnF(4), a member of the MSnF(4) family of fluorite-related anionic conductors containing double layers of Sn(2+) and M(2+) cations. Two fluorine sublattices were observed by (19)F MAS NMR, which could be assigned to specific sites in the lattice. The first sublattice is due to fluorine atoms located in Ba(2+) double layers and is rigid on the MAS NMR time scale at room temperature. The second sublattice comprises the fluoride ions between the Ba(2+) and Sn(2+) layers, and the few fluorine atoms that inhabit the Sn(2+)-Sn(2+) double layers. These ions are in rapid exchange with each other, and an extremely short correlation time tau(C) for the motion of these ions of <3 x 10(-)(5) s is obtained at -100 degrees C. T(1) measurements indicate that tau(C) approaches 10(-)(8) s at room temperature. (19)F-to-(119)Sn cross-polarization (CP) experiments confirmed the assignments of the resonances, and that the fluorine atoms located next to the tin atoms are extremely mobile at room temperature (and thus do not contribute to the CP process). Two-dimensional (19)F exchange experiments showed that exchange between the rigid and mobile lattice does occur, but at a much slower rate (tau(C) approximately 10 ms at 250 degrees C). Low-temperature (19)F MAS and (19)F-to-(119)Sn CP NMR spectra demonstrate that the motion of the fluoride ions has almost completely frozen out by -150 degrees C. The results are consistent with rapid two-dimensional (anisotropic) conductivity involving the fluoride ions between the Ba and Sn layers. Conductivity in three dimensions requires hops between the ions in the BaF(2)-like layers and the mobile ions. This process does occur, but with exchange rates that are at least 6-7 orders of magnitude slower. 相似文献