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81.
82.
Perera SC Tsoi G Wenger LE Brock SL 《Journal of the American Chemical Society》2003,125(46):13960-13961
The reaction of Mn2(CO)10 with P(SiMe3)3 in coordinating solvents at T >/= 220 degrees C yields low polydispersity, highly crystalline MnP nanoparticles for the first time. The effect of dimensional limiting has resulted in the stabilization of a ferromagnetic ground state at low temperatures, rather than the metamagnetic state observed in bulk (microcrystalline) MnP. The synthetic methodology reported here is demonstrated to be general for a number of different metals and phosphine sources. 相似文献
83.
Lowell Abrams Donniell E. Fishking Silvia Valdes-Leon 《Linear and Multilinear Algebra》2000,47(2):129-136
Let B denote either of two varieties of order n Pascal matrix, i.e., one whose entries are the binomial coefficients. Let BR denote the reflection of B about its main antidiagonal. The matrix B is always invertible modulo n; our main result asserts that B-1 ≡ BR mod n if and only if n is prime. In the course of motivating this result we encounter and highlight some of the difficulties with the matrix exponential under modular arithmetic. We then use our main result to extend the "Fibonacci diagonal" property of Pascal matrices. 相似文献
84.
Shasha Li Sean A. Newmister Andrew N. Lowell Jiachen Zi Callie R. Chappell Fengan Yu Robert M. Hohlman Jimmy Orjala Robert M. Williams David H. Sherman 《Angewandte Chemie (International ed. in English)》2020,59(21):8166-8172
Stereospecific polycyclic core formation of hapalindoles and fischerindoles is controlled by Stig cyclases through a three‐step cascade involving Cope rearrangement, 6‐exo‐trig cyclization, and a final electrophilic aromatic substitution. Reported here is a comprehensive study of all currently annotated Stig cyclases, revealing that these proteins can assemble into heteromeric complexes, induced by Ca2+, to cooperatively control the stereochemistry of hapalindole natural products. 相似文献
85.
Dr. Shasha Li Dr. Sean A. Newmister Dr. Andrew N. Lowell Dr. Jiachen Zi Callie R. Chappell Dr. Fengan Yu Robert M. Hohlman Prof. Jimmy Orjala Prof. Robert M. Williams Prof. David H. Sherman 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(21):8243-8249
Stereospecific polycyclic core formation of hapalindoles and fischerindoles is controlled by Stig cyclases through a three-step cascade involving Cope rearrangement, 6-exo-trig cyclization, and a final electrophilic aromatic substitution. Reported here is a comprehensive study of all currently annotated Stig cyclases, revealing that these proteins can assemble into heteromeric complexes, induced by Ca2+, to cooperatively control the stereochemistry of hapalindole natural products. 相似文献
86.
Lowell Abrams 《Israel Journal of Mathematics》2000,117(1):335-352
The Poincaré duality of classical cohomology and the extension of this duality to quantum cohomology endows these rings with
the structure of a Frobenius algebra. Any such algebra possesses a canonical “characteristic element;” in the classical case
this is the Euler class, and in the quantum case this is a deformation of the classical Euler class which we call the “quantum
Euler class.” We prove that the characteristic element of a Frobenius algebraA is a unit if and only ifA is semisimple, and then apply this result to the cases of the quantum cohomology of the finite complex Grassmannians, and
to the quantum cohomology of hypersurfaces. In addition we show that, in the case of the Grassmannians, the [quantum] Euler
class equals, as [quantum] cohomology element and up to sign, the determinant of the Hessian of the [quantum] Landau-Ginzbug
potential. 相似文献
87.
A graph G is packable by the graph F if its edges can be partitioned into copies of F. If deleting the edges of any F-packable subgraph from G leaves an F-packable graph, then G is randomly F-packable. If G is F-packable but not randomly F-packable then G is F-forbidden. The minimal F-forbidden graphs provide a characterization of randomly F-packable graphs. We show that for each ρ-connected ρ-regular graph F with ρ > 1, there is a set
(F) of minimal F-forbidden graphs of a simple form, such that any other minimal F-forbidden graph can be obtained from a graph in
(F) by a process of identifying vertices and removing copies of F. When F is a connected strongly edge-transitive graph having more than one edge (such as a cycle or hypercube), there is only one graph in
(F). 相似文献
88.
89.
Andrew N. Lowell 《Tetrahedron》2010,66(30):5573-5582
Syntheses of an isocoumarin subunit suitable for the completion of purpuromycin are outlined. Specifically, work targeting an orthogonally protected isocoumarin (eventually 12% yield over 12 steps) and an improved synthesis of a symmetrically protected isocoumarin (18% over 10 steps) are described. A new modification for selective catechol protection as mediated by potassium bicarbonate is also presented along with insights into oxidative and reductive functionalization of isocoumarins. 相似文献
90.
We present and discuss an efficient, high‐order numerical solution method for solving the Boltzmann equation for low‐speed dilute gas flows. The method's major ingredient is a new Monte Carlo technique for evaluating the weak form of the collision integral necessary for the discontinuous Galerkin formulation used here. The Monte Carlo technique extends the variance reduction ideas first presented in Baker and Hadjiconstantinou (Phys. Fluids 2005; 17 , art. no. 051703) and makes evaluation of the weak form of the collision integral not only tractable but also very efficient. The variance reduction, achieved by evaluating only the deviation from equilibrium, results in very low statistical uncertainty and the ability to capture arbitrarily small deviations from equilibrium (e.g. low‐flow speed) at a computational cost that is independent of the magnitude of this deviation. As a result, for low‐signal flows the proposed method holds a significant computational advantage compared with traditional particle methods such as direct simulation Monte Carlo (DSMC). Copyright © 2008 John Wiley & Sons, Ltd. 相似文献