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861.
A synthesis of bicyclo[3.3.1]non-1-ene and of a 10:1 mixture of bicyclo[4.2.1]non-1(8)-ene and bicyclo[4.2.1]non-1(2)-ene by gas-phase pyrolysis of the corresponding bridgehead acetates and chlorides is reported. 相似文献
862.
Bishop S Azuma RE Buchmann L Chen AA Chatterjee ML D'Auria JM Engel S Gigliotti D Greife U Hernanz M Hunter D Hussein A Hutcheon D Jewett C José J King J Kubono S Laird AM Lamey M Lewis R Liu W Michimasa S Olin A Ottewell D Parker PD Rogers JG Strieder F Wrede C 《Physical review letters》2003,90(16):162501
The 21Na(p,gamma)22Mg reaction is expected to play an important role in the nucleosynthesis of 22Na in oxygen-neon novae. The decay of 22Na leads to the emission of a characteristic 1.275 MeV gamma-ray line. This report provides the first direct measurement of the rate of this reaction using a radioactive 21Na beam, and discusses its astrophysical implications. The energy of the important state was measured to be E(c.m.)=205.7+/-0.5 keV with a resonance strength omegagamma=1.03+/-0.16(stat)+/-0.14(sys) meV. 相似文献
863.
864.
865.
Let be field, and let A and B be n × n matrices with elements in . Suppose that A is completely reducible and that B is symmetric. If the principal minors of A determined by the 1- and 2-circuits of the graph of B and by the chordless circuits of the graph of A are equal to the corresponding principal minors of B, then A is diagonally similar to B; and conversely. 相似文献
866.
Some speculations on a causal model that could provide a common conceptual foundation for relativity, gravitation, and quantum mechanics are presented. The present approach is a unification of three theories, the first being the repulsive theory of gravitational forces first proposed by Lesage in the eighteenth century. Lesage attempted to explain gravitational forces from the principle of conservation of momentum of some hypothetical particles, which we shall call gravitons. These gravitons, whose density is assumed homogenous, are constantly colliding with objects. The gravitational force is caused by a shielding effect of bodies when they are near each other. One also can make a clear physical distinction between an accelerating and a nonaccelerating object from this viewpoint. The second of these theories is the Brownian motion theory of quantum mechanics or stochastic mechanics, which treats the nondeterministic nature of quantum mechanics as being due to a Brownian motion of all objects. This Brownian motion being caused by the statistical variation in the graviton flux. The above two theories are unified in this article with the causal theory of special relativity. Within the present context, the time dilations (and other effects) of relativity are explained by assuming that the rate of a clock is a function of the total number or intensity of gravitons and the average frequency or energy of the gravitons that the clock receives. Two clocks having some relative velocity in the same intensity gravitational field would then have a different rate because the average frequency of the gravitons would be different for each clock owing to the Doppler effect. That is, they would essentially be in different fields considering both the frequency and intensity. The special theory would then be the special case of the general theory where the intensity is constant but the average frequency varies. In all the previous it is necessary to assume a particular model of the creation of the universe, namely the Big Bang theory. This assumption gives us the existence of a preferred reference frame, the frame in which the Big Bang explosion was at rest. The above concepts of graviton distribution and real time dilations become meaningful by assuming the Big Bang theory along with this preferred frame. An experimental test is proposed. 相似文献
867.
P. Steiner R. Zimmermann F. Reinert Th. Engel S. Hüfner 《Zeitschrift für Physik B Condensed Matter》1995,99(4):479-490
3s- and 3p-core level excitations for a large number of 3d-transition metal oxides, with a formal 3d occupation from 3d0 to 3d10, have been measured by electron energy loss spectroscopy in reflection geometry (REELS) with primary energies 200 eV≤E 0≤1600 eV. Their intensities decrease systematically with the formal 3d-count, classifying them as transitions to empty 3d-states. The structure of the 3s excitations is analysed in detail and is compared to the 3s-XPS photoemission spectra of the samples. This 3s-REELS structure and its change with the 3d occupation can be explained by the assumption that the excitation arises mainly from a 3s23dn→3s13dn+1 quadrupole transition. 相似文献
868.
869.
Marta Horecha Volodymyr Senkovskyy Konrad Schneider Anton Kiriy Manfred Stamm 《Colloid and polymer science》2011,289(5-6):603-612
Poly(N-isopropylacrylamide) (PNIPAM)-based microgels covered with hydrophobic but water-permeable shell were used for modification of a hydrophilic substrate with the aim to provide a ??contraphilic?? wetting behaviour, namely, to make the surface more hydrophobic in water environment (polar medium) than in dry state in air (non-polar medium). Bottom-up approach has been applied for a stepwise preparation of a structured two-component surface. Loosely packed microgels self-organised into quasiperiodic arrays were chemically grafted to the hydrophilic, functionalised substrate. Afterwards, a surface-initiated polymerisation of isoprene was performed selectively from microgels making them hydrophobic. The surface was found to be water-sensitive, as observed by in situ AFM measurements. The surface fraction of the hydrophobic component increased from 13% in the dry state up to 25% in water due to swelling of the microgels. However, small contraphilic effect was recorded by water contact angle measurements because of a moderate lateral swelling of the core-shell microgels and due to a fast swelling of the microgels already upon the measurements. 相似文献
870.
The possibility to perform a stimulated Raman adiabatic passage process in molecules on the ultrafast time scale is investigated theoretically. Motivated by recent experiments, the mid R:B<--mid R:X electronic transitions in molecular iodine are studied as a prototype example with the goal to selectively induce a population transfer employing two intense and time-delayed ultrashort laser pulses and different coupling schemes. For the purpose of interpretation, the coupled multilevel vibronic problem is reduced to a quasi-three-level system by averaging over the vibrational degree of freedom. It is shown that the vibrational dynamics becomes essential at high field intensities. Considering a 2-dimensional parameter space (intensity and delay time of the femtosecond laser pulses), a strong-field control landscape is constructed. 相似文献