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81.
Oxime directed aromatic C-H bond activation and oxidative coupling to alkenes is reported using a cationic Rh(III) catalyst. Significantly, the method can be used to oxidatively couple unactivated, aliphatic alkenes. 相似文献
82.
Gianetti TL Tomson NC Arnold J Bergman RG 《Journal of the American Chemical Society》2011,133(38):14904-14907
The discovery of a Nb(III)-mediated catalytic hydrogenation of internal alkynes to (Z)-alkenes that proceeds through an unprecedented mechanism is reported. The mechanistic proposal involves initial reduction of the alkyne by the Nb(III) complex (BDI)Nb(N(t)Bu)(CO)(2) to provide a Nb(V) metallacyclopropene, itself capable of σ-bond metathesis reactivity with H(2). The resulting alkenyl hydride species then undergoes reductive elimination to provide the (Z)-alkene product and regenerate a metal complex in the Nb(III) oxidation state. Support for the proposed mechanism is derived from (i) the dependence of the product selectivity on the relative concentrations of CO and H(2), (ii) the isolation of complexes closely related to those proposed to be part of the catalytic cycle, (iii) H/D crossover experiments, and (iv) DFT studies of multiple possible reaction pathways. 相似文献
83.
Wang ZJ Brown CJ Bergman RG Raymond KN Toste FD 《Journal of the American Chemical Society》2011,133(19):7358-7360
Gold(I)-phosphine complexes are readily encapsulated by a tetrahedral supramolecular host (Ga(4)L(6)). We have investigated the catalytic activity of the resulting complexes for the intramolecular hydroalkoxylation of allenes. The catalytic activity of Me(3)PAuBr was increased 8-fold by encapsulation, as determined by initial rate kinetics, and we observed up to 67 catalytic turnovers by Me(3)PAu(+) encapsulated in Ga(4)L(6). 相似文献
84.
Leonid I. Manevitch Mercedes Mane Lawrence A. Bergman 《International Journal of Non》2011,46(1):247-252
We present a novel type of an energy trap providing targeted energy transfer in a system of weakly coupled pendulums. Our approach is based on the analogy we revealed between the behavior of two weakly coupled classical parametric pendulums (in linear approximation) and the nonadiabatic Landau-Zener tunneling in a two-state quantum system. This analogy leads us to the prediction of an efficient irreversible transfer of vibration energy from one subsystem to another, when the eigenfrequency of at least one of them changes in time, so that the coupled subsystems pass through an internal resonance. The existence of such a phenomenon is not restricted to coupled pendulums, but is inherent to a wide class of both linear and nonlinear parametric oscillatory systems. This opens up the possibility of designing new types of energy traps and absorbers for the dynamic protection of various mechanical systems. 相似文献
85.
A time-domain nonlinear system identification method based on multiscale dynamic partitions 总被引:1,自引:0,他引:1
Young S. Lee Stylianos Tsakirtzis Alexander F. Vakakis Lawrence A. Bergman D. Michael McFarland 《Meccanica》2011,46(4):625-649
Based on a theoretical foundation for empirical mode decomposition, which dictates the correspondence between the analytical
and empirical slow-flow analyses, we develop a time-domain nonlinear system identification (NSI) technique. This NSI method
is based on multiscale dynamic partitions and direct analysis of measured time series, and makes no presumptions regarding
the type and strength of the system nonlinearity. Hence, the method is expected to be applicable to broad classes of applications
involving time-variant/time-invariant, linear/nonlinear, and smooth/non-smooth dynamical systems. The method leads to nonparametric
reduced order models of simple form; i.e., in the form of coupled or uncoupled oscillators with time-varying or time-invariant coefficients forced by nonhomogeneous
terms representing nonlinear modal interactions. Key to our method is a slow/fast partition of transient dynamics which leads
to the identification of the basic fast frequencies of the dynamics, and the subsequent development of slow-flow models governing
the essential dynamics of the system. We provide examples of application of the NSI method by analyzing strongly nonlinear
modal interactions in two dynamical systems with essentially nonlinear attachments. 相似文献
86.
D. R. Bergman 《Waves in Random and Complex Media》2005,15(4):417-435
Paraxial ray tracing has gained popularity in seismology and underwater acoustics for modelling the propagation of sound when the medium is stationary and time independent. In this article differential geometry is used to derive a generalized paraxial ray-tracing procedure valid for any fluid media described by a local sound speed and velocity depending arbitrarily on position and time. Geodesic deviation is used to model acoustic beam deformation, and the sectional curvature along a ray to determine convergence and divergence zones in space. The resulting paraxial equations presented here are the most general that can be derived for the acoustic field and apply to any environment including those with time dependence and fluid motion. Applied to layered media the geodesic deviation equation is solved exactly. Some illustrative examples are included. 相似文献
87.
88.
We discuss the notion of spin squeezing considering two mutually exclusive classes of spin-s states, namely, oriented and non-oriented states. Our analysis shows that the oriented states are not squeezed while non-oriented
states exhibit squeezing. We also present a new scheme for construction of spin-s states using 2s spinors oriented along different axes. Taking the case of s=1, we show that the ‘non-oriented’ nature and hence squeezing arise from the intrinsic quantum correlations that exist among
the spinors in the coupled state. 相似文献
89.
A direct-current glow discharge is used to excite flowing mixtures of NO/He and NO/N2. A strongly vibration-vibration pumped vibrational population distribution over the states NO(X 2Π, υ = 1) to NO(X2Π, υ = 15) is measured by infrared emission spectroscopy. Measured population distributions are consistent with results calculated from earlier measurements of V-V and V-T,R rates. 相似文献
90.
R. N. Bergman R. E. Kalaba K. Spingarn 《Journal of Optimization Theory and Applications》1976,20(1):47-63
A glucose tolerance test was performed on dogs by injecting glucose intravenously and measuring the plasma glucose and insulin concentrations versus time. Various analytical and computational techniques were utilized to fit the data to a minimal model and to estimate the parameters of the blood glucose regulation process. A relatively good fit was obtained in spite of the rather simple model.Animal experiments were funded by the National Institute of Health Grant No. AM-17236 awarded to Dr. R. N. Bergman at U.S.C. 相似文献